We present first experimental results of the successful transfer of our monolithic integrated double-stack multi quantum well laser-modulator approach from the traditional InGaAsP/InP to the more promising InGaAlAs/InP material system. In continuous wave operation at room temperature, the devices achieved threshold currents of <21 mA, fiber coupled optical power levels up to 570 μW and static extinction ratios in the range of 15 dB/V. The measured small-signal modulation bandwidth of about 10 GHz is capacitance limited due to a conservative device layout.

Future DVD-systems require optical pickup units with high bandwidth and high sensitivity in the red and blue spectral range. OEICs (OptoElectronic Integrated Circuits) use monolithically integrated photodetectors in order to avoid the bond pad capacitances between photodiode and amplifier and to increase the bandwidth compared to discrete or two-chip optical receivers. For this reason, OEICs are a good approach for future DVD-applications. We introduce a solution that integrates a PIN photodiode and a transimpedance amplifier in a 0.6μm BiCMOS process. The innovative transimpedance amplifier consists of two branches connected via a common current source in order to achieve differential outputs and to double the transimpedance without increasing the offset voltage. The amplifier is optimized for high bandwidth. The measured results show a -3dB cut-off frequency of 500MHz and a differential transimpedance of 76kΩ. This is 2.2 times the bandwidth and 1.3 times the transimpedance compared to the results presented in the literature. Measurements also show that the OEIC is appropriate for fiber receiver applications at 1.25Gb/s with a record sensitivity of -27.7dBm.

In this work the fabrication of integrated polymer waveguide components (waveguides, S-bends, splitters) by means of several approaches is reported. Fabrication of one type of waveguide involves laser-assisted micro-patterning of small grooves in (Polymethylmethacrylat) PMMA substrates which are subsequently filled with index-matched materials. Another type of waveguide is realized by local physical modification of PMMA in a laser direct writing process. The transmission characteristics of the waveguide were studied at the optical communication wavelengths of 1520-1620 nm. Fabrication of filled waveguides with oil as waveguide medium yielded low loss of 2.6 dB/cm and single-mode behavior for 10 μm wide grooves. Filling of 20 μm grooves with PMMA/MMA/dye mixture and subsequent polymerization yielded multi-mode waveguides with higher loss of 5.9 dB/cm. The laser direct writing (Nd:YAG, 266 nm) of waveguides showed loss of 6.3 dB/cm and multi-mode behavior indicating a need for further process optimization. Two Y-splitters fabricated by laser patterning and filling with branch radii of 10 mm and 25 mm showed device loss of 16 dB and 19 dB for a 25 mm device length. These results are compared to the performance of reference Y-splitters fabricated by UV-lithography, where parametric studies of the device geometry revealed the best branch radius of 20 mm.

The expansion of high capacity optical transmission techniques into price-sensitive areas such as datacom and access networks requires a major reduction in the cost of optical components. Polymer waveguides are attractive because they are very simple to process and are promising for low-cost devices. Deep UV-induced modification of the dielectric properties of polymers is a useful technique for low cost realization of integrated optical circuits for telecommunication und sensor applications. The technique presented here has several advantages with respect to common methods because only a single polymer layer is used, which serves as the substrate and waveguide as well and no further etching or development step is required. The integration of the waveguide circuits in a polymer microoptical bench offers the possibility of combining the devices with semiconductor based optical circuits and also achieve easy fiber-chip coupling. In this work, preliminary results of Y-junctions, directional couplers, multimode interference (MMI) couplers will be given.

Symmetric buried channel waveguides fabricated on silicon substrates by the organic-inorganic hybrid sol-gel process are reported. The buffer/cladding layer material is composed of methyl-modified silanes and presents high network flexibility and low refractive index, at low cost. Film thickness above 10 mm is possible without cracks, even after thermally baking the films at 150°C, and the refractive index is 1.468 at 632.8 nm. The influence of the methylsiloxane species on the material absorption loss was investigated, in particular at 1.55 mm. For channel waveguide core definition, a photopatternable layer was polymerised by 248 nm laser radiation through an amplitude mask, and the unexposed material was simply removed by an organic solvent. The transmission spectrum of the waveguides is presented and reveals an acceptable loss level of 0.3dB/cm at 1300 nm, but larger loss in the 1550 nm region. The procedure developed is compatible with optoelectronic integration in silicon.

In future airplanes optical data networks are expected to be state of the art. The advantages of optical technology compared to wire-based systems are higher data rates, smaller sensitivity against electromagnetic interference (EMI) and less weight. Today avionics full duplex switched ethernet (AFDX) is realised on duplex copper wires connecting two switches. An optical version of AFDX could be realised on a simplex fibre, using a two-wavelength transmission over one fibre. This would require a wavelength selective coupler, allowing a bi-directional data transmission with two wavelengths. In this work a simple WDM module is introduced, based on the principle of a micro-optical bench made of a polymer with hybrid integration of lenses and filters and allowing both multiplexing as well as de-multiplexing of wavelengths 850 nm and 1310 nm. Two different designs have been realised, one with ball lenses and one with GRIN lenses, both using edge filters for wavelength separation. The fabrication and optical performance of such couplers is described and discussed.

Transient and steady-state measurements of photo-induced birefringence variations in single domain and periodically poled lithium niobate (LN) crystals containing different non-photorefractive impurities are presented. The birefringence change is induced by a 532-nm laser beam in the intensity range 0-500 W/cm², and is probed by 632.8- and 1523-nm beams. Data were taken at 25 and 50°C. We find that HfO₂ doping is very effective in reducing the photorefraction. This is interesting also because it is known that Hafnium-doped LN crystals can be periodically-poled during growth. The analysis of the rise and decay of the induced birefringence shows that doping considerably increases both the photoconductivity and the dark conductivity of the LN crystals.

MicroRaman spectroscopy has been used for the surface characterization of lithium niobate (LiNbO₃) crystals. 3" wafers with different Li/Nb ratio, i.e., conventional congruent (CLN) and quasi-stoichiometric LiNbO₃ have been analyzed. A correlation between the width of the 150cm^-1 and 870cm^-1 line and the crystal composition has been found. A narrowing of the linewidths for quasi-stoichiometric crystals has been observed, showing an ordered structure, if compared with CLN. The 870cm^-1 line has been used to study the surface quality of 3" Z-cut CLN crystals after the wafering process. The presence of a surface structural disorder up to 30micron has been found. Various etching methods have been employed in order to minimize both the thickness of the damaged layer and the degree of damage during the wafer slicing and polishing processes. A reliable surface stress release method has been found for optical surface finishing of LiNbO₃ substrates

This paper reports the development and modelling of the reverse-proton-exchange process for the realization of high quality optical waveguides in MgO doped stoichiometric lithium tantalate, a promising nonlinear material due to its low coercive field and high damage threshold. Reverse-proton-exchange gives rise to a buried refractive index-profile providing significant advantages in terms of attenuation, insertion losses and overlap of the fields interacting through the nonlinear susceptibility. By characterizing several samples fabricated under different experimental conditions, we identified a fabrication procedure which is simpler than the conventional one used for lithium niobate: the annealing and reverse-exchange processes are indeed performed at the same temperature so that the diffusion of hydrogen ions towards the substrate during the reverse-exchange occurs in the same conditions as during the annealing. This results in very simple empirical laws relating the fabrication to the optical parameters. By such a modeling we defined fabrication parameters giving rise to a single-mode waveguide at l=1.55mm with good fiber mode-matching and high efficiency when used as a nonlinear device for telecom applications.

The paper presents a short review of the theoretical basics of modeling techniques in integrated optics, essentially mode solving and field propagation, and some of the underlying numerical approaches in short. To meet the requirements of an effective design process of a potentially complex waveguide circuitry different levels of abstraction are used preferably. Thus, the application of tools adequate for the individual problem and the confirmation of results is of special importance. If the waveguide device is to be regarded as a real multi-physics microsystem-as in the case of the simple thermo-optical switch-the use of parametric models is a prevalent procedure to speed up the design process. For different applications, ranging from sensor devices to standard telecom components, specific requirements of the design and the use of standard and individual design tools are discussed.

Uniform, nonuniform and adaptive mesh refinement FDTD approaches to solving 3D Maxwell's equations are compared and contrasted. Specific applications of such schemes to optical memory, nanophotonics and plasmonics problems will be illustrated.

Rigorous modal solutions of tapered spot-size converters, using buried core and deep-etched structures, through semiconductor fabrication techniques, are presented. Results for devices where both the primary and the mode forming secondary waveguides are operating close to their modal cutoff are presented, by using a full-vectorial finite elementbased modal solution and a full-vectorial beam propagation approach, also based on the finite element method. Mode beating in the tapered section, the expansion of the spot-size and the consequent enhancement of the coupling to an optical fiber are also reported. Numerically simulated results indicate that, overall, a narrow far-field profile with a higher coupling efficiency, along with a better relaxation of the fabrication tolerances for the SSC designs presented here, can be achieved.

Although much research has been done on fiber-optic gyroscopes (FOG), these sensors often show bias errors, i.e. the offset rotation rate varies with temperature and other environmental parameters. A low coherence light source is used to avoid undesirable interferences between error signals. Nevertheless in the standard FOG design it is possible that unintentionally optical paths match which may cause bias errors. The parasitic interferences may originate from reflections and polarization cross-coupling, whether intended or not. A new simulation tool for modeling interferometric fiber optic sensors with inclusion of polarization and coherence effects is presented. It allows for the first time to model the FOG signal quantitatively considering temperature dependence, light source parameters and all perturbations and interferences between them with the corresponding degree of coherence. An analysis of the gyroscope design is made which leads to a localization of a bias error source which has not been described yet. This problem may occur in every FOG with an integrated optics circuit (IOC) and a Lyot depolarizer. Reflection paths from the IOC match phase differences gained in the depolarizer and lead to temperature dependent bias errors. Guidelines for an optimum design avoiding the perturbing interferences are given.

In this paper we propse various applications of guided wave optics to quantum optics experiments. An immediate application concerns entangled photon sources. Long term objectives will be mulitparticle (n>2) and multiport configurations, needed for quantum error-correction. We show how guided wave optics, incorporating both integrated optics and fiber optics, could provide a realistic means of constructing experiments and devices.

Scientific and technological issues and considerations regarding the integration of miniaturized microphotonic devices, circuits and systems in micron, submicron, and quantum scale, are presented. First, we examine the issues regarding the miniaturization of photonic devices including the size effect, proximity effect, energy confinement effect, microcavity effect, optical and quantum interference effect, high field effect, nonlinear effect, noise effect, quantum optical effect, and chaotic effect. Secondly, we examine the issues regarding the interconnection including the optical alignment, minimizing the interconnection losses, and maintaining optical modes. Thirdly, we address the issues regarding the two-dimensional or three-dimensional integration either in a hybrid format or in a monolithic format between active devices and passive devices of varying functions. We find that the concept of optical printed circuit board (O-PCB) that we propose is highly attractive as a platform for micro/nano/quantum-scale photonic integration. We examine the technological issues to be addressed in the process of fabrication, characterization, and packaging for actual implementation of the miniaturization, interconnection and integration. Devices that we have used for our study include: mode conversion schemes, micro-ring and micro-racetrack resonator devices, multimode interference devices, lasers, vertical cavity surface emitting microlasers, and their arrays. Future prospects are also discussed.

The dynamic characteristics of an ultra-long semiconductor optical amplifier (UL-SOA) with a length of 4 mm are investigated experimentally. An optically clocked technique is applied for suppressing the patterning effects in an SOA and for exploiting effectively the fast intra-band effects. The gain dynamic in the UL-SOAs is here stabilised by a sinusoidal optical clock signal which is additionally injected into the device, bit interleaved with a PRBS data signal. The optimal operation condition of the novel scheme concerning power levels of the RZ data signal and clock signal are analysed in detail at 40 Gbit/s. We use the ultra-fast nonlinearities in the UL-SOAs for regenerating of a 40 Gbit/s data signal in amplitude, time and pulse shape. The 40 GHz recovered clock signal in the optically clocked 3R regenerator is generated by a self-pulsating three section DFB laser. An excellent regenerative performance even for strong degraded data signals is demonstrated.

It is desirable for data networks to have low transmission latency. This may be achieved by exploiting the short packet lengths and the high bandwidths that can be achieved using multi-wavelength operation. Semiconductor optical amplifiers (SOAs) have been demonstrated as building blocks for optical switches and have also been shown to be well suited to the fast switching required for optical packet switching [1]. We have realised an InP based add-drop multiplexer (ADM) integrated on a single 850 μm x 850 μm chip. The bit error penalty performance has previously been shown to be below 1.2 dB for each of the operating paths through the device: add, drop and through modes at 2.5 Gbit/s data rates. Further, low penalty operation has previously been demonstrated experimentally with 4 simultaneous wavelengths [2]. It is known that the dynamic range of an SOA can limit the number of wavelengths supported and that the pattern sensitivity in SOAs increases their operating penalty [3]. We investigate the multi-wavelength operation of our ADM device and show that a power penalty of less than 0.8 dB is maintained over a 20 dB input power dynamic range. We also show a -3 dB optical bandwidth of 30 nm suitable for multi-wavelength operation of cascaded ADMs. Finally we present experimental results to show that the pattern dependent operating penalty of the ADM is reduced as the number of wavelengths of asynchronous data is increased. This result may be exploited in our proposed optical data network to produce an improved optical penalty.

The advantage of hybrid organic-inorganic sol-gel as a simple, low-cost method for the fabrication of optoelectronic integration is described. High performance integrated optics using mulit-layer photo-patternable hybrid sol-gel on high-index InP compound semiconductor is achieved. An MMI based 1x12 beam splitter with low polarization sensitivity and high uniformity is demonstrated. The development of EO and NLO active sol-gels are described and the fabrication of active waveguides are presented. The chromophore doped active sol-gels demonstrate high stability which makes them attractive material for integrated optoelectronics. The results show the great potential of the hybrid sol-gel for heterogeneous integration with semiconductor lasers and optoelectronic components.

The hybrid sol-gel process is recognized to be an alternative route for production of low cost silica-based integrated optic devices, since it allows the elaboration of ridge waveguides without recourse to high cost processing, like ion etching. However, the high absorption of these materials in the NIR region (1300 and 1550 nm) has limited so far their use. The main objective of this article is to describe the major factors that lead to high losses in the final material and to give solutions to overcome this drawback. The choice of hybrid precursors and the influence of the experimental conditions of gel preparation are of paramount importance. Appropriate synthesis conditions allow a significant decrease of the gel losses (to 0,5 dB/cm) while keeping good wetability and UV-patternability. Each step of the waveguides elaboration was studied separately (UV-irradiation, etching, overcladding, storage) regarding the losses of the material. Post-baking of the waveguides is a way to significantly decrease the losses at 1550 nm. Under appropriate conditions, the losses measured in the waveguides can be kept below 1 dB/cm.

Ion exchange on glass substrates has proved to be an efficient low cost and high performance technology to realise integrated optic devices. Among structures developed thanks to this technology, those presenting both surface and buried waveguides are of great interest. In this paper, we first describe a fabrication process of selectively buried ion exchange waveguides. Its principle is based on a two step ion exchange process. First a surface waveguide is realised by a thermal exchange of Ag\+-Na\+. Then a mask is deposited on the back side of the optical wafer perpendicularly to the axis of the waveguide. Finally a second step assisted by an external electric field is performed. Then we report the performances of this method through the measurement of the burying depth evolution. When the mask is wide enough, the burying depth varies from 2 μm above the middle of the mask to 12 μm in the unmasked region. The transition is 3 mm long and therefore avoid any excess losses. For this structure, no deformation of the fundamental mode has been observed. Finally, the first results of use of these selectively buried waveguides to realize Bragg filters with a surface grating is presented through a comparison of measured reflexion spectra.

UV sensitivity of B-Ge codoped cores in PECVD silica waveguides has been investigated. Photoinduced refractive index changes have been introduced by KrF excimer laser irradiation at 248 nm, without any presensitization method. The effects of B codoping of Ge doped silica have been examined. It has been shown that B addition mildly increases glass network disorder, by broadening the O bridging angle distribution as from FTIR measurements, but on the other hand it does not produce point defects which may contribute to the absorption band at 5eV already generated by the presence of Ge doping. The fabricated channel waveguides show low optical loss even without high temperature annealing. Strong Bragg gratings imprinted into these waveguides confirm that in non thermally annealed Ge doped PECVD silica glass, where a small absorption band still exist at 5eV, B codoping supplies sufficient photosensitivity amplification to make hydrogen loading unnecessary.

Er³⁺ / Yb³⁺ co-doped phosphate glass and Er³⁺ : ZBLALiP fluoride glass microsphere lasers have been studied under pumping by a fiber taper at 1480 nm. Whispering Gallery Mode laser spectra were analyzed for different sphere diameters. Red-shift effect on the wavelengths of both fluorescence and laser spectra is experimentally observed when the pump power is increased, originating from thermal effects. We showed coupling effect between microspherical laser and an external cavity made by a metallic mirror. We observed line shift to lower wavelengths due to optical feedback effect.

The spatio-temporal dynamics of whispering gallery modes in microdisk lasers is studied by time-domain computer simulations based on full vectorial Maxwell-Bloch equations. In particular, we focus on the spatial interaction of the optical mode with the inversion density of the active material. The electromagnetic field evolution described by the Maxwell curl equations are solved with a full three-dimensional finite-difference in time-domain algorithm with uniaxial perfectly matching layer boundary conditions. The nonlinear active material is modelled via optical Bloch equations that are transformed to real value differential equations which can be computed efficiently and highly accurately. Our computer simulations give insight into the internal interrelated carrier-light-field dynamics of microdisk lasers and reveal fundamental aspects of the progression of degenerated modes in nonlinear active material through spatial hole burning.

We realized an InGaAs/InP pin-diode photodiode in monomode waveguide configuration. Measuring the photocurrent spectra as a function of the applied reverse bias voltage under illumination of the pin-diode with TE polarized light (1510-1580 nm), we observe one dominant peak, whose position shifts linearly with increasing wavelength towards higher reverse bias voltages. By comparing the peak position with the energies, calculated for the different interband transitions in the InGaAs quantum well and taking into account the polarization dependence, we assign this peak to the optical transition between the heavy-hole energy level and the second electron energy level in the quantum well. By operating the pin-diode in an resistor biased Self-Electrooptic Effect Device configuration we clearly observe bistability at a wavelength of 1550nm. The possible operation of this device as smart waveguide photoreceiver with flip-flop functionality is demonstrated.

Optical interconnects are, nowadays, considered a promising alternative to electrical ones and monolithic integration in Si is the only choice when high volumes, low fabrication costs and reduced spaces are needed. We fabricated an electro-optic Si-based modulator working at 1.5 um using a Bipolar Mode Field-Effect transistor integrated within a Si rib waveguide. The principle of operation is the light absorption by a plasma of free carrier that can be opportunely moved inside or outside the device optical channel by properly changing the bias. The optical channel of the modulator is embodied within its vertical electrical channel. The devices were fabricated using epitaxial Si wafers and standard clean room processing. The optical characterization in static conditions shows a modulation depth, defined as M=(P_Off-P_On)/P_Off , of ~ 90 %. It was measured at 1.48 um using a laser diode source coupled with the modulator through a silica optical fiber. The dynamic electrical characterization provides an electrical switching time of ≈10 ns. A modulation depth of 72 % is observed at 100kHz electrical modulation frequency.

The evolution of the optical beam profile along a high-power tapered semiconductor amplifier has been demonstrated by using a rigorous finite element-based and full-vectorial modal solution, coupled with the beam propagation approach. Numerically simulated results indicate that many higher order modes are generated and propagate along the tapered structure and their interference with the fundamental mode causes variations of the optical beam, both along the transverse and the axial directions, which significantly modify the output beam quality. Key words: Semiconductor Optical Amplifiers, Numerical Analysis, Finite element method, Beam propagation method.

A waveguide switch structure with three input and two output ports is designed in SiGe/Si material for the operation around 1.55 μm in wavelength. Strained Si_0.96Ge_0.04 layer with a thickness of 2.5 μm is used as the waveguide core layer. Single mode ridge waveguide of 10 μm wide and 1µm deep is formed by plasma etching. The switching functi^aa on is realized by total internal reflection. Two separate electrodes are used to control the refractive index change in the intersection region through carrier injection. The switch device can also work as splitter, modulator, or add-drop multiplexer, etc. around wavelength of 1.55 μm. An extinction ratio of about 20 dB is achieved for the modulation state from the two side input ports and about 10dB for the central input port.

The relation of optical properties including propagation loss of rf magnetron sputtered ZnO thin films on corning glass substrates with structural properties of the films has been studied. The film was deposited in sputtering gas oxygen : argon ratio of 80 : 20 without substrate heating, and annealed at 380 degree Celsius in air for different times. The structural properties of the films were studied by X-ray diffraction and atomic force microscopy and the waveguiding properties were studied by prism-coupling using a He-Ne laser. A significant improvement of crystalline orientation of the film on annealing was observed. The initial decrease in the estimated value of the extraordinary refractive index of the film with annealing was attributed to the observed lattice contraction. On further annealing, the indices were found to increase slightly. The values of packing density of the films for different annealing times were estimated from the refractive indices, taking into consideration the effect of variation of lattice constant. The packing density was found to initially increase with annealing, and thereafter became constant on further annealing. The propagation loss was found to decrease by more than an order, to a value of 3 dB/cm on annealing for one hour, and this was attributed to the observed decrease in stress, increase in packing density and improved crystalline orientation of the film.

The characterization and optimization of optical microring resonator-based optical filters on deeply etched GaInAsP-Inp waveguides, using the finite element-based beam propagation approach is presented here. Design issues for directional coupler- and multimode interference coupler-based devices, such as field evolution, optical power, phase, fabrication tolerance and wavelength dependence have been investigated.

Because of their compact size, ring resonators can be a cost effective solution for many Dense Wavelength Division Multiplexing (DWDM) components, as well as many low cost applications such as part of optical sensor circuits, or low cost optical signal processing. Modulators, filters, add-drop multiplexers, and switches are all components that can be realised with a ring resonator. Their potentially large Free Spectral Range (FSR), finesse, and quality factor, together with the potential for low cost fabrication, make them a viable alternative to many current DWDM devices. However, for such devices to be commercially viable, they need to be insensitive to the polarisation state of the input signal. The results obtained herein show that a single input/output optical racetrack resonator has been fabricated so that the minima in the resonance spectra align to better than 1pm. The rings also exhibit relatively low loss with measured Q-factors of approximately 90,000 and finesse values of 12.

We present a two dimensional analytical method for studying the effect of gratings on microdisk dielectric resonators. Our model based on a Coupled Mode Theory (CMT) needs the normalization of the Whispering Gallery Mode (WGM). In the past, few normalizations have been proposed, all of them assume the mode to be bound which is not true as WGMs are leaky modes. In this paper, we propose a new normalization with no approximation. Then we apply the CMT in order to compute the resonance wavelength of the perturbated structure. This theory has been checked against 2D FDTD and shows accurate results with very little computation time.

We demonstrated conversion of optical signals from 1550nm band to the 1300nm band in silicon waveguides. The conversion is based on parametric Stokes to anti-Stokes coupling using the Raman susceptibility of silicon. Achieving high conversion efficiency requires phase matching in the waveguides as well as means to reduce waveguide losses including the free carrier loss due to two photon absorption.

Photorefractive bright solitons have been generated in undoped lithium niobate crystals for the first time. Such solitons have been formed applying a strong static bias field: consequently to this strong bias, the photorefractive screening effect can exceed the photovoltaic one, giving rise to a beam selfocusing and bright solitons. Due to the slow response time of the lithium niobate, both in soliton formation and relaxation, the solitonic channel remains memorized for long time after the writing procedure is switched off. According to this procedure, channel as well as conical waveguides can be created.

A novel approach for realization of all-optical pulse reshaping in an integrated microring resonator is proposed. The concept presented in this study is based on four-wave mixing in a passive GaAs/AlGaAs microring resonator side coupled to a bus waveguide, taking into account all higher order non-linear effects such as self-phase modulation (SPM), cross-phase modulation (XPM), pump depletion and two-photon absorption (TPA), the latter being the dominant process here. We also include in the description changes in absorption and refractive indexes induced by free-carriers generated by TPA. This scheme is investigated for its regenerative characteristics using an optical pump modulation scheme. The application of the modulation bit stream in the pump wave leads in a conjugate wave power being proportional to the square of the pump power, resulting in a corresponding extinction ratio improvement. Because of the strong TPA, enhanced by the resonance effect, the converted signal power saturates as pump power increases, providing noise suppression at high power levels. A detailed study of the static and dynamic reshaping characteristics of the wavelength converter has been carried out. Its performance, evaluated by extinction ratio (ER) and Q factor calculations, showed satisfactory regenerative properties up to 10Gb/s.

We compare the predictions of three inverse Fourier transform (IFT) Maker fringe techniques that we have developed over the last 2 years to measure uniquely and accurately the second-order nonlinearity spatial profile of thin films. These techniques involve clamping two wafers with unknown nonlinearity profiles together to form a sandwich structure and measuring its Maker fringe (MF) spectrum. As a result of interference between the two nonlinear films, these spectra contain information on both the magnitude and phase of the FT of the two unknown profiles. These FT magnitude and phase can be processed numerically and the full FT is inverted to recover the profiles. In the first method the samples are different, in the second one they are identical, and in the third technique one of the two wafers has a known profile. The latter methods are advantageous because they require a single MF measurement, and consequently, their algorithms are simpler, and data processing is much faster. We present experimental evidence using thermally poled silica samples showing that when all three techniques are applied to the same sample, they yield very similar profiles, which gives credence to all three techniques.

A set of samples co-doped with Er and Ag were prepared with a combined sol-gel and ion-exchange route. This multistep process sytnthesizes samples in which the silver atoms are dispersed in the matrix and/or aggregated in Ag multimers or nanoclusters. The samples exhibit a different photo-luminescence response depending on the sensitizing effect due to silver atoms. The spectroscopic properties were correlated with the structural properties investigated by extended x-ray absorption fine structure (EXAFS) spectroscopy and x-ray diffraction. The Er³⁺ excitation via energy transfer, obtained in a wide range of wavelengths, has been clearly related to the presence in the sample of Ag multimers.

The spectral properties of Er³⁺-doped As₂S₃ and Ge₃₃As₁₂Se₅₅ chalcogenide glasses are presented and discussed. Bulk samples and thin films have been studied. Bulk samples have been obtained by melt-quenching. Thin films have been obtained by RF sputtering. Sputtering targets have been fabricated from home-made cut and polished doped bulk samples and from commercial undoped targets with erbium pieces on the surface. The film morphology has been analysed by AFM and a column-like structure has been observed for the Ge₃₃As₁₂Se₅₅ films. The presence of Er³⁺ ions in As₂S₃ and Ge₃₃As₁₂Se₅₅ films has been confirmed by PL emission at 1.55 µm. A PL lifetime of 4 ms has been measured in Er-doped As₂S₃ films. Single mode waveguides have been fabricated by wet etching in Ge₃₃As₁₂Se₅₅ films.

In this work we report on spectroscopic properties of Er³⁺-doped and Er³⁺/Ce³⁺-codoped tungsten-tellurite glasses of molar composition 45 TeO₂: 39 WO₃: 15 Na₂O: 1 Er₂O₃ and 43 TeO₂: 39 WO₃: 15 Na₂O: 1 Er₂O₃: 2 CeO₂, respectively. Vibrational properties were investigated by Raman spectroscopy. The measured absorption spectra were analyzed by McCumber theory, in order to obtain radiative transition rates and stimulated emission cross sections. The study of de-excitation dynamics of the ⁴I_11/2 and ⁴I_13/2 Er³⁺ states upon pulsed excitation at 532 nm shows that Ce³⁺ codoping is highly effective in favoring the population feeding of the ⁴I_13/2 Er³⁺ level.

Infrared chalcogenide glasses are studied with respect to their non linear optical properties. These glasses are sulfur or selenide glasses synthesized in the binary or ternary systems of the Ge-As-S-Se family and are transparent from the end of the visible region to wavelengths above 10 μm depending on the composition. The non linear optical characteristics are firstly determined through a spatially resolved Mach Zender interferometer with the help of a Nd-YAG laser at 1064 nm. Non linearities three order of magnitude above the non linearity of silica glass are achieved. Then, the non linear imaging technique has been used to characterize the glasses at the telecommunication wavelength of 1.55μm. This one shot technique has allow us to obtain values for the non linear refractive index n2 as high as 14 10-18 m2/W. The non linear absorption at 1.55 μm has also been evaluated and is below 1 cm/GW for all the glasses. These third order non linear optical properties make these glasses suitable candidates for integrated ultra fast all optical devices. On the basis of the GeSe4 vitreous composition, an optical fiber, single mode at 1.55 μm, is achieved.

We numerically analyze the selfocusing process of laser pulses propagating inside a photorefractive BSO crystal, simulating the carrier dynamics inside the material. We demonstrate that the soliton regime cannot be reached because of the delay of the photorefractive response in comparison to the excitation. As a consequence only relatively long pulses can efficiently excite the photorefractive nonlinearity, which is able to partially confine the pulse. The confined part has the typical polarization dynamics of a soliton in an optically active media, while the initial part just diffracts following a polarization dynamics which evolves towards the linear regime.

In this paper we describe a novel approach to the fabrication of optical waveguides by focused low-repetition-rate femtosecond laser pulses. This approach overcomes the main limitation of the technique, i.e. the strong asymmetry of the waveguide profile. By using an astigmatic beam and suitably controlling both beam waist and focal position in tangential and sagittal planes, it is possible to shape the focal volume in such a way as to obtain waveguides with a circular transverse profile and of the desired size. This technique is applied to the fabrication of active waveguides in Er:Yb-doped glass substrates. The waveguides are single-mode at 1.5 mm, exhibit propagation losses of about 0.25 dB/cm and an internal gain of 1.4 dB at 1534 nm.

A polarization independent optical waveguide structure suited for operation in the third communication window has been developed and optimized towards minimized dependence on deviations in the processing parameters and very low processing complexity. The tolerance analysis and optimization have been based on the thin film parameters of the widely applied silicon oxynitride technology. The silicon oxynitride layers have typically a material birefringence (nTMnTE) between 1-2 x 10^-3 and can be deposited within a uniformity and reproducibility of 1% in thickness (d), 5x10^-4 in refractive index (n) and 100 nm in channel width (w). The optimized waveguide structure meets the criterion of a channel birefringence (Δn_eff,TM-TE) within 5x10^-5 taking the processing tolerance into account. Moreover, it was found that the channel birefringence is thickness independent (within the 10^-5 criterion) over a range of up to 200 nm (δΔn_eff,TM-TE ,/ δd = 0). Furthermore, the optimized waveguide is fulfilling the remaining demands of the application aimed at, such as monomodality, low fiber to chip coupling loss (< 0.5 dB/facet) and low loss bends with a radius down to 600 nm. This waveguiding structure has been applied for the realization of a passband flattened add-drop multiplexing device (or interleaver) with 0.4 nm free spectral range and 0.03 nm TE-TM shift. Based on this shift, a polarization dependence of 3 x 10^-5 was calculated for the optical waveguides.

Recently there has been a strong trend to fabricate smaller photonic devices. In the literature, the problem of coupling optical fibres with thin semiconductor waveguides has not been solved sufficiently well to obtain both high coupling efficiency and good fabrication tolerances. This paper discusses a new approach, the Dual Grating-Assisted Directional Coupling (DGADC), which can result in a robust and very efficient device, with relaxed fabrication tolerances. Theoretical investigation of the coupler is presented. Coupling efficiency and device length are determined as functions of layer thicknesses and refractive indices, grating periods, depths and duty ratios, and finally wavelength. Fabrication of the coupler is also given, as well as preliminary experimental results.

Periodic luminescent patterns based on active color centers have been efficiently created in Lithium Fluoride (LiF) crystals and films by Extreme Ultra-Violet (EUV) light and soft x-rays from a laser-plasma source by masking the incoming radiation. Strong visible photoluminescence at room temperature has been measured from colored geometric microstructures, produced with high spatial resolution on large areas in short exposure times. Accurate spectrophotometric measurements allow estimating a significant increase in the real part of the refractive index, locally induced by the formation of high concentrations of stable primary and aggregate electronic defects at the surface of the LiF irradiated crystal, in a very thin layer, whose depth has been evaluated around 50 nm. On the basis of a semi-classical dipole-electromagnetic field interaction model, the contribution of different kinds of point defects to the overall refractive index change has been quantified. Promising opportunities in the fabrication of passive and active devices for integrated optics, such as gratings and distributed lasers, are offered by the use of this kind of radiation.

Glass waveguide devices fabricated by ion exchange have evolved to the point where conventional assumptions of waveguide symmetry and mutual independence are no longer valid. The modeling of ion-exchanged waveguide devices is far more complicated compared to, e.g., silica on Si waveguide devices. For example, during field-assisted ion exchange processes, the nonhomogeneity of ionic conductivity in the vicinity of the waveguide results in a time-dependent perturbation of the electric field. Previous studies have shown that the depth and vertical symmetry of buried waveguides are affected by the field perturbation. In this work, we describe an advanced modeling tool for guided-wave devices based on ion-exchanged glass waveguides. The effect of field perturbation, due not only to the conductivity profile, but also to the proximity of adjacent waveguides or partial masking during a field-assisted burial are accounted for. A semivectorial finite difference method is then employed to determine the modal properties of the waveguide structures.

In this paper the ring core doped Dy³⁺ions fibre is presented. In the first part of this report because of inner stimulation possibility, the analyse of light transfer between inner cladding and ring-core in ring-core optical fibre is presented. The second part presents drawing method and parameters of doped Dy³⁺ ions ring core optical fibre.

A simple Monte Carlo model is used to simulate excess noise characteristics of a range of Al_0.6Ga_0.4As - GaAs single heterojunction APDs in which the heterojunction is located at varying positions within the avalanche region. Excess noise is shown to depend critically upon the length of Al_0.6Ga_0.4As layer. The present results suggest that to achieve the lowest noise the Al_0.6Ga_0.4As layer must be sufficiently long to allow primary electrons to heat up and able to ionize as soon as they cross into the GaAs, but not so long as to allow significant hole ionization in the Al_0.6Ga_0.4As layer, which leads to noisy feedback processes. The excess noise characteristics of a range of Al_xGa_1-xAs - GaAs (x = 0.3, 0.45 and 0.6) single heterojunction APDs are measured experimentally. The excess noise is shown to increase with x, which is explained in terms of an increase in the hole ionization coefficient leading to increased noisy feedback chains.

Nowadays, imagers based on CMOS active pixel sensors (APS) have performances that are competitive with those based on charge-coupled devices (CCD). CMOS imagers offer advantages in on-chip functionalities, system power reduction, cost and miniaturisation. The FAst MOS Imager (FAMOSI) project consists in reproducing the streak camera functionality with a CMOS imager. In this paper, we present the second version of FAMOSI which makes up for the drawbacks of the first one. FAMOSI 2 has a new architecture of pixel which implements an electronic shutter and analogue accumulation capabilities. With this kind of pixel and the new architecture for controlling the integration, FAMOSI 2 can work in the low power repetitive synchroscan mode. The prototype has been fabricated in the AMS 0.35μm CMOS process. The chip is composed of 64 columns per 64 rows of pixels. The pixels have a size of 20μm per 20μm and a fill factor of 47%. The simulation shows that a conversion gain of 3.4μV/e- is obtained with a dynamic range of 1.2V, a time resolution of 400ps and a light pulse repetitive rate of 300kHz.

The development and application of a three-dimensional finite-difference time-domain (FDTD) model for a traveling-wave heterojunction phototransistor (TW-HPT) are presented. The model is enhanced using effective permittivity schemes at the dielectric interfaces and special techniques for the treatment of very thin material sheets. The 3D full-wave electgromagnetic model allows the numerical calculation of the output photocurrent, electrical characteristic impedance, light absorption, microwave losses as well as microwave and optical dispersion. Run in a fast, parallel processing, machine the simulation herein allowed (for the first time, to the best of the authors' knowledge) the simultaneous investigation of the optical and microwave characteristics of the traveling-wave structure. This is in contrast to the approach followed by other researchers in the past, as well as by popular simulation packages, based on which results only for the microwave property can be obtained. Snapshots of the field propagation inside the device provide valuable insight into its passive behavior and clearly demonstrate the device's velocity mismatch between the optical signal and the photogenerated electrical pulse. Numerical results for the effective refractive indices of the optical and electrical wave quantify the difference in the velocities of the two waves.

This paper considers the application of the Generalized Telegrapher’s Equations (GTE) to the electromagnetic modelling and designing of integrated electro-optical devices. This approach allows to eliminate the restrictions introduced by others models, as: weakly guiding condition and isotropic unperturbed medium and to value the modulator time response for a generic modulating signal. The presence of small dielectric perturbations and the large difference between the optical and modulating signal frequencies are the hypotheses considered in deriving the model. The analysis has been applied to a GaAs phase modulator in order to validate the equations and to evidence the effects of the induced anisotropy on the time-domain response. The model can be extended to the analysis of multimode dielectric waveguides, such as independent polarization and directional coupler modulator.

We present a theoretical study of a double microcavity resonators system with absorption or gain. The output intensity and the power intensity inside the microresonator are derived. Some interesting features and their possible application are discussed. The results may be useful for modulator, amplifier, laser and sensor.

A new wafer-scale replication process for fabricating buried ridge waveguides for telecom/datacom applications using an uv-curable sol-gel material is proposed. Spin coating of the core material on the replication mould is used to form the waveguide cores with a smooth thin layer. The spin parameters allow an accurate control of the thickness and homogeneity. The bottom-cladding is uv-cast between a substrate and the mould, which is covered by the spun core layer. The ridge waveguide cores are demoulded and buried under a top cladding. This process allows the stacking of several layers of waveguides on top of each other to form two-dimensional waveguide arrays. A specially adapted SUSS mask aligner is used to control the cladding thickness between individual waveguide layers and to align them. A waveguide loss comparable to lithographically fabricated waveguides has been achieved.

All optical architectures for Wavelet Packet Division Multiplexing (WPDM) are presented, that can be used in multiple access networks to increase the number of simultaneous users. Wavelet waveform coding spreads data signals both in time and frequency domains, with a large capacity improvement with respect to standard Optical-Code Division Multiple Access (O-CDMA) systems. In addition, the orthogonal property of the wavelet atoms ensures low InterSymbol Interference (ISI) and Multiple Access Interference (MAI) noises. To exploit the large bandwidth capacity of optical fibres, the Optical-Electrical-Optical (O-E-O) conversion is completely avoided, and we designed an all optical system that realizes the WPDM fully in the optical domain. A single Planar Lightwave Circuit (PLC) device multiplies/demultiplies N different users and a diffractive or an integrated optical device performs the waveform coding/decoding. The Wavelet Packet (WP) encoder/decoder is realized as a tree of lattice-form delay-line filters, and can be integrated on a single device along with the optical waveform modulator, resulting in a compact planar optical system. In addition, we show that different choices of WP encoders/decoders are possible to further enhance the system performances.

In the last decade, the processing of the waveguide structures on various substrates under mild conditions has been an appealing aim. The lithographic patterning of organic-inorganic hybrid materials processed by means of sol-gel technology allows the production of waveguides and other optical components. We describe the synthesis of a new, photo-patternable, organically modified material with an improved ageing stability. Synthesis step does not involve widely used zirconia precursors, but it retains the same possibility of altering the refractive index by tailoring of the material composition. Refractive index values varied from 1.4700 to 1.5100. Measured birefringence values meet the requirements of most integrated planar optic applications. The synthesized material is compatible with silicon, glass and plastic substrates. Material was analyzed using ²⁹Si NMR techniques. The processed slab waveguides were characterized by using the prism coupling technique at various wavelengths. The attenuation in the waveguide was determined by the cut-back method, and it was found to be less than 0.5dB/cm at the wavelength of 830 nm. The morphology of the microstructures was measured by using the interferometer equipment. Slab waveguides rms values were in order of only 2 nm.

A generalized m-line spectroscopy method enables evaluation of the parameters (the refractive index, n and the thickness, W) of sub-guiding films deposited on a planar waveguide. A sub-guiding film (not reaching the guiding effect) when deposited on the existing planar waveguide influences the present guiding system and affects its guiding properties. In the method a laser beam is coupling via a prism to the sample and a light distribution decoupled by the same prism is studied. Complementary to the beam spot reflected geometrically from the prism base the light distribution takes a form of discrete lines, m-modes. This image is observed but only for some discrete values of the coupling angles. The refractive index, n and thickness, W of the waveguide are then calculated by numerical evaluation of the dispersion equation with a set of the coupling angles. From the previous and actual coupling angles the thin film parameters can be evaluated. In the paper an application of the generalized m-line spectroscopy method to biological samples is presented. Some initial measurements reveal an effect of the presence of the films on the coupling angles of the structure. The presence of glucose has been revealed in secretions of patients suffering from diabetes. Testing of glucose presence with the proposed method is performed with a trace amount of the patient secretion alike in medical preliminary tests.

In this talk, we propose a novel tunable optical add/drop multiplexer (OADM), based on Asymmetric Bragg Coupler (ABC) and the liquid crystal as the active layer material. The asymmetric Bragg coupler is made of OG series polymer ridged waveguide. The liquid crystal is filled to cover the waveguide structure, which sandwiches between upper and bottom electrodes. When the external voltage applied, the index of liquid crystal changes to adjust effective index of coupler and inherently tunes the transmission spectrum of the device precisely. The transmission bandwidth is about 32.5GHz, and the tunable range is about 250GHz centered at 1.55nm.

We report on systematic growth and characterization of low-loss germanosilicate layers for use in optical waveguides. Plasma enhanced chemical vapor deposition (PECVD) technique was used to grow the films using silane, germane and nitrous oxide as precursor gases. Chemical composition was monitored by Fourier transform infrared (FTIR) spectroscopy. N-H bond concentration of the films decreased from 0.43x10²² cm^-3 down to below 0.06x10²² cm^-3, by a factor of seven as the GeH4 flow rate increased from 0 to 70 sccm. A simultaneous decrease of O-H related bonds was also observed by a factor of 10 in the same germane flow range. The measured TE rate increased from 5 to 50 sccm, respectively. In contrast, the propagation loss values for TE polarization at λ=632.8 nm were found to increase from are 0.20 ± 0.02 to 6.46 ± 0.04 dB/cm as the germane flow rate increased from 5 to 50 sccm, respectively. In contrast, the propagation loss values for TE polarization at λ=1550 nm were found to decrease from 0.32 ± 0.03 down to 0.14 ± 0.06 dB/cm for the same samples leading to the lowest values reported so far in the literature, eliminating the need for high temperature annealing as is usually done for these materials to be used in waveguide devices.

There is a clear need for low cost, high performance and large-scale production of photonic chips. Network development requires more interconnecting components. A flexible and low-cost process using good quality material is necessary. The sol-gel process is a chemical method to fabricate glasses at ambient pressure and moderate temperature. The resulting material properties can be tuned depending on the precursors used. Hybrid materials, mixing organic and inorganic parts, offer the advantages of polymer-like materials and glasses. We have developed sol-gel-processed integrated optical circuits using hybrid materials. We report on the development of active devices based on the thermo-optic effect. Thermo-optic coefficients as high as -2.10^-4/°K have been measured in our materials. This enables the design of compact devices with low power consumption. Our goal is to utilise the thermo-optic effect in the development of integrated optical switches. The kHz response time of such switches makes them unsuitable for modulation applications, but they can be used for network protection, reconfiguration purposes in routing and multiplexing applications such as Code Division Multiplexing. New designs, based on multimode interference couplers (MMIC), have also been created. In this work we first describe the synthesis of the hybrid materials as well as the fabrication processes. Using the measured properties of the materials developed, we can simulate the optical and thermal properties of the target devices. The simulation results have been exploited to model and optimise a range of switch designs, including MMI-based 1xN switches. Finally, we report on the full characterisation of the different structures and devices created in terms of fabrication quality and optical and thermal response.

In this paper a novel configuration of optical modulator is presented. It combines the effect of fast electron-hole plasma injection obtained with a SiGe HBT together with the usage of a distributed Bragg reflector. Numerical simulations performed on a non-optimized device shows that the presence of the SiGe HBT enhances significantly the performances obtained with a similar device realized with and all-silicon pin diode. Switching speed higher than 1 GHZ have been numerically simulated.

In this paper we present a simulation strategy for the accurate prediction of the functionality of an InP based optoelectronic modulator. The device is composed of an InP/InGaAsP p-i-n diode embedded in a rib waveguide and a Mach-Zehnder interferometer. Finite Element Analysis for both semiconductor and optical equations solution is exploited. The presented numerical results, indicating a reverse bias voltage of 5.5 V for a 180° phase shift in a 2 mm-long device, are confirmed by measured data. Transient simulation predicts that this structure is suitable for 40 Gbit/s operation.

The chalcogenide glasses possess interesting optical properties such as a good transmission in the nIR-mIR wavelength region, high linear and non-linear refractive index and photosensitivity, which allows holographic patterns writing. Moreover, their low-phonon energy makes them good candidates for optical amplification. In order to design an integrated circuit on chalcogenide glasses, the pulsed laser deposition (PLD) technique is a suitable method for deposition of glass with complex composition. Amorphous Ge-Ga-Sb-S films (pure and dysprosium doped) were prepared by PLD using different energy of the laser beam pulses. Compositional, morphological and structural characteristics of the films were studied by MEB-EDS, atomic force, scanning electron microscopy, X-ray diffraction and Raman spectroscopy analyses. The photo-luminescence of Dy doped Ge-Ga-Sb-S films was investigated. The emission band centered at 1340 nm corresponding to ⁶F_11/2, ⁶H_9/2-⁶H_15/2 electron transitions of Dy³⁺ ions was identified in luminescence spectra of dysprosium doped thin films. A study of the optical properties and the effects of exposure and thermal annealing below the glass transition temperature on the optical parameters of thin films from the Ge-Ga-Sb-S system will be presented.

The influence of surface irradiation of GaAs with a KrF excimer laser on the magnitude of a quantum well (QW) intermixing effect has been investigated in GaAs/AlGaAs QW heterostructures. The irradiation was carried out in an atmospheric environment with laser pulses of fluence between 60 and 90 mJ/cm². Following the irradiation, the samples were annealed in a rapid thermal annealing furnace at temperatures ranging from 850 to 925°C. Compared with non-irradiated samples, a strong suppression of the bandgap shift has been observed in all laser irradiated samples. The suppression increased from 5 to 22 nm for samples irradiated with 88 mJ/cm² pulses and annealed at 850 and 900°C, respectively. This increased thermal stability of excimer laser irradiated samples indicates the potential for developing a process for selective area bandgap engineering of large area GaAs/AlGaAs QW wafers.

Optical communications networks require integrated photonic components with negligible polarization dependence, which typically means that the waveguides must feature very low birefringence. Recent studies have shown that waveguides with low birefringence can be obtained, e.g., by using silica on Si waveguides and by buried ion-exchanged glass waveguides. However, many integrated photonic circuits consist of waveguides with varying widths. Therefore, low birefringence is consequently required for waveguides having different widths. This is a difficult task for most waveguide fabrication technologies. In this paper we present theoretical and experimental results on waveguide birefringence for buried silver ion-exchanged glass waveguides. We show that the waveguide birefringence is on the order of 10-6 for waveguide mask opening widths ranging from 2 to 9 μm. The measured values are in good agreement with the values calculated with our modeling software for ion-exchanged glass waveguides. This unique feature of ion-exchanged waveguides may be of significant importance in a wide variety of integrated photonic circuits requiring polarization independent operation.

Optical add/drop multiplexers (OADM) based on asymmetric y-branches and tilted gratings can be easily fabricated using ion exchange techniques and photosensitive glasses. These devices offer excellent operating characteristics. However, optimum OADM performance depends critically on the angle of the tilted grating. In this paper, results from fabrication and modeling are compared for the ion exchange process using four different angles of the tilted grating. The transmission spectra for the fabricated and simulated OADMs show an excellent agreement.

Recent results obtained for SiO₂-HfO₂: Er³⁺ and SiO₂-TiO₂: Er³⁺-Yb³⁺ waveguides are presented. (100-x)SiO₂-xHfO₂ (x = 10, 20, 30, 40 mol) planar waveguides, doped with 0.01 and 0.3 mol % Er³⁺ ions were prepared by sol-gel route, using dip-coating deposition on v-SiO₂ substrates. The waveguides were characterized by m-line, Raman and photoluminescence spectroscopy. The spectral shape of the band assigned to the ⁴I_13/2->⁴I_15/2 transition does not change practically with the hafnium and erbium content. The ⁴I_13/2 level decay curves present a single-exponential profile, with a lifetime between 5.5 and 7.1 ms, for the 0.3 mol% doped samples, and between 8.5 and 6.6 ms for the 0.01 mol% doped samples. The SiO₂-TiO₂: Er³⁺-Yb³⁺ waveguides were prepared by rf-sputtering technique. All waveguides were single-mode at 1550 nm. The losses, for the TE0 mode, were evaluated at 632.8 and 1300 nm and an attenuation coefficient equal or lower than 0.2 dB/cm was measured both at 632.8 nm and 1300 nm. The emission of ⁴I_13/2->⁴I_15/2 of Er³⁺ ion transition was observed upon excitation in the TE0 mode at 981 and 514.5 nm. Back energy transfer from Er³⁺ to Yb³⁺ was demonstrated by measurement of Yb³⁺ emission upon Er³⁺ excitation at 514.5 nm. Photoluminescence excitation spectroscopy was used to obtain information about the effective excitation efficiency of Er³⁺ ions by co-doping with Yb³⁺ ions.

The luminescence of rare earth ions Re³⁺ = Pr³⁺, Er³⁺, and Tm³ in PZG fluoride glass (36PbF₂-24ZnF₂-35GaF₃-5YF₃-2AlF₃ in mol%) doped with ReCl₃ was investigated. This study was initiated in the perspective of realizing by vapor phase deposition (PVD) rare earth activated fluoride glass channel waveguides acting as integrated optical amplifiers, ReCl₃ being more volatile than the fluoride counterpart. The results were compared to the spectroscopic properties of ReF₃-doped PZG glasses. For phonon-sensitive radiative transitions, the lifetime was prolonged at low ReCl₃ concentration because of phonon energy and/or electron coupling are reduced. For Pr³⁺, the doping with PrCl₃ increases the lifetime by 50% in respect to PrF₃ doping. These results suggest that the chlorine ions remain in the coordination sphere of the rare earth ions in the ReCl₃-doped glass after melting. The luminescence decay of Er³⁺: ⁴I_13/2 level in ErCl₃-doped channel waveguides is also discussed.

In this paper the optical characterization of a novel, metal-oxide-silicon (MOS) capacitor-based, high speed, silicon optical modulator is presented. By using a capacitor based rather than the conventional p-i-n junction based architecture to modulate the free carrier density inside the waveguide, we show the realization of a fast, 2.5-GHz, optical modulator.

The design and characterization of very compact passive devices based on Silicon On Insulator (SOI) are investigated. Our devices have been realised on 8 inch wafer at CEA LETI using microelectronics technology for the demonstration of an optical clock distribution. We have studied strip waveguide of 0.3μm width and 0.38 μm in height, Y junctions, MMI splitters and two kinds of microbends with constant or progressive radius of curvature.

There have been many papers reporting visible luminescence and light emission at 1.54 micron, at room temperature, from porous silicon (Psi) and from Erbium doped Psi, respectively. These results have stimulated a great deal of excitement, because they suggest the possibility of a silicon based optoelectronics technology. In this paper, in order to generate radiation at 1.54 micron in Psi, a diffferent approach based on Raman scattering is presented. This approach has important advantages: no special impurities are required, so samples realisation is simple and chip; moreover enhancement of Raman scattering and nonlinear effects in nanostructured porous silicon could be experienced. Finally preliminary experimental results of Raman emission in porous silicon at 1.54 micron are reported.