This PDF file contains the front matter associated with SPIE Proceedings Volume 11775

We’ve come a long way since 1609, from spectacle lenses to mirrors in space, from twitching frog legs to the Event Horizon Telescope observing a black hole. But far more is possible. On the ground, a new generation of optical telescopes is under construction, up to 39 m in diameter. Adaptive optics compensates for the turbulent atmosphere, but could work far better with an orbiting reference beacon in space. Bright chemiluminescent emission lines in the upper atmosphere interfere with observations, but could be blocked by fiber optic filters. Energy-resolving photon counting detectors promise far greater sensitivity. New ways of making mirrors offer far better resolution for space X-ray telescopes. Coronagraphs can suppress starlight enough to reveal exoplanets in direct imaging, or starshades can cast star shadows on telescopes to do the same thing. New generations of far IR detectors with large cryogenic telescopes in space can reveal the cool and cold universe. Radio telescopes on the quiet far side of the Moon can overcome the limits of the ionosphere and intense local interference to see events in the early universe as it heated up again after the Big Bang expansion cooled everything. Neutrino telescopes can see stars being shredded by black holes, and gravitational wave detectors see merging neutron stars and black holes. Atom wave gravimeters can measure the internal structure of planets and asteroids, and sample return missions are already bring back distant bits of the solar system. What will happen next? I don’t know but it will be glorious.

Terahertz photonics and optoelectronics

We report ultrahigh bandwidth applications of Kerr microcombs to optical neural networks and to optical data transmission, at data rates from 44 Terabits/s (Tb/s) to approaching 100 Tb/s. Convolutional neural networks (CNNs) are a powerful category of artificial neural networks that can extract the hierarchical features of raw data to greatly reduce the network complexity and enhance the accuracy for machine learning tasks such as computer vision, speech recognition, playing board games and medical diagnosis [1-7]. Optical neural networks can dramatically accelerate the computing speed to overcome the inherent bandwidth bottleneck of electronics. We use a new and powerful class of micro-comb called soliton crystals that exhibit robust operation and stable generation as well as a high intrinsic efficiency with an extremely low spacing of 48.9 GHz. We demonstrate a universal optical vector convolutional accelerator operating at 11 Tera-OPS/s (TOPS) on 250,000 pixel images for 10 kernels simultaneously — enough for facial image recognition. We use the same hardware to sequentially form a deep optical CNN with ten output neurons, achieving successful recognition of full 10 digits with 900 pixel handwritten digit images. We also report world record high data transmission over standard optical fiber from a single optical source, at 44.2 Terabits/s over the C-band, with a spectral efficiency of 10.4 bits/s/Hz, with a coherent data modulation format of 64 QAM. We achieve error free transmission across 75 km of standard optical fiber in the lab and over a field trial with a metropolitan optical fiber network. Our work demonstrates the ability of optical soliton crystal micro-combs to exceed other approaches in performance for the most demanding practical optical communications applications.

Silicon photonic waveguides patterned at the subwavelength level behave as metamaterials whose optical properties, including refractive index, dispersion and anisotropy can be tuned by judiciously designing the subwavelength geometry. Over the past years, the added design freedom afforded by these structures has enabled a wide variety of novel high performance devices, ranging from high efficiency fibre-to-chip couplers, to on-chip polarization and mode management, and ultra-broadband waveguide couplers covering several optical communication bands. In this invited keynote talk we will revisit the physical foundations of these structures, explore some of the latest advances in the field with applications in both telecommunications and sensing, and discuss some of the outstanding challenges to move these structures from research labs to large-scale commercialisation.

The monolithic integration of active materials providing optical gain and optical non-linearities is instrumental to increase the functionality of integrated photonic circuits. A double layer integration scheme has been experimentally demonstrated, exhibiting transition losses between the two materials of less than 0.2 dB. Furthermore, a single layer integration scheme is proposed, which decreases the number of process steps, reducing fabrication cost, and also decreasing the sensitivity to fabrication tolerances. In this paper, we will overview our recent developments on the monolithic integration of both, Al2O3 and TiO2 onto the passive Si3N4 and Al2O3 platforms for the development of on-chip amplifiers and lasers.

Silicon photonics has been largely developed as a platform to address the future challenges in several applications including datacom, sensing or optical communications, among others. However, the properties of silicon itself is not enough to overcome all limitations in terms of speed, power consumption and scalability. New strategies have then been encouraged based on the hybrid integration of new materials in the silicon photonics platform. In this paper, we will introduce the recent advances in the hybrid integration of doped crystalline-oxides on silicon and silicon nitride waveguides. Especially, Yttria-stabilized zirconia (YSZ) with a lattice parameter compatible with the silicon lattice has been considered because it exhibits promising linear and nonlinear optical properties: low propagation loss, no two photon absorption (TPA) due to its large bandgap energy, a large transparency window from the ultraviolet to the mid-infrared and a good Kerr effect. Furthermore, YSZ can be doped with many dopants to develop active photonic devices with strong second- and third-order nonlinearities and light emission. We have recently demonstrated propagation loss in YSZ waveguides as low as 2dB/cm at a wavelength of 1380 nm, a nonlinear refractive index (Kerr effect) comparable with the SiN coefficient and light amplification in Er3+ doped YSZ on SiN waveguides. The recent results are very promising to pave the way for the development of low cost and low power consumption devices.

We review our recent progress on graphene integrated photonics for next generation optical communications. We present the design principles of graphene photodetectors and optical modulators as well as recent results on Si and SiN photonic platforms. We show optical modulators at communication wavelengths with electro-optical bandwidth up to 30GHz and operation at 50Gb/s on-off keying (OOK). We report on very recent progress about graphene photodetectors with ultra-high bandwidth (>67GHz) based on the photo-thermo-electric (PTE) effect. The last is of particular interest as it enables a zero dark-current direct conversion of the optical signal into a voltage which can be amplified by a voltage pre-amplifier rather than a transimpedance amplifier (TIA). This is a potential breakthrough in scaling the bandwidth of photoreceiver towards increasing bandwidths, as the TIA imposes strict trade-offs between gain and bandwidth. With the proposed device we show direct detection of optical signals exceeding 100Gb/s in a voltage detection scheme without dark current bias.

Silicon photonics is recognized as one of the most promising platforms for on-chip optical interconnects. In order to further enhance the on-chip optical-interconnect link capacity, silicon photonic devices for advanced multiplexing technologies have been widely investigated, including wavelength-division-multiplexing (WDM), mode-divisionmultiplexing (MDM), as well as the hybrid multiplexing. This paper gives a review for our recent progresses in the development of silicon-based on-chip wavelength/mode-division-multiplexers.

We discuss our recent work on mode division multiplexing (MDM) silicon devices for on-chip optical interconnects. First, we demonstrate a 4-channel MDM device based on directional couplers. The crosstalk values are below -13.3 dB at 1550 nm for the TE0, TM0, and TM1 channels. The TE1 channel experiences the largest crosstalk at 1553 nm of -6.5 dB and the highest loss of 2.6 dB. Four channels of 40Gb/s signals in the form of 20-Gbaud quadrature phase shift keying (QPSK) are multiplexed through MDM to test the device The 160-Gb/s data is transmitted through a multi-mode waveguide and then de-multiplexed for bit-error ratio (BER) measurement. By using multiple-input multiple-output (MIMO) digital processing, error free operation is achieved. Second, to further increase the capacity, we design and implement an 11-channel MDM device by employing subwavelength grating (SWG) couplers. The main limiting factor in the number of MDM channels is the susceptibility of the effective waveguide refractive index to the width variation due to the fabrication errors, and the index curves of for the multi-mode bus waveguide and the single mode access waveguide are of different slopes. Through index engineering by duty cycle optimization of the SWG access waveguide, the index curves of the two different waveguides can be matched and thus the phase matching condition in the MDM process is maintained with the similar fabrication errors imposed on the two waveguides. The crosstalk values of such a SWG based 11-channel MDM device remain lower than -7 dB for all channels, and the loss is below 13.7 dB for the worst channel. We then use 30-Gbaud 16-quadrature amplitude-phase modulation (QAM) signals to test the device, and the BERs are below the 7% feedforward error correction threshold after MIMO processing. A total transmission capacity of 1.23 Tb/s on a single wavelength is achieved.

Integrated silicon nanophotonics has progressed a lot over past decades with great promises for many surging applications in optoelectronics, information and communication technologies, sensing or health monitoring. Enabling low-cost, dense integration, and compatibility with modern semiconductor nanofabrication processes, silicon nanophotonics deliver compact and high-performance devices on single chips. A variety of nanophotonic functionalities, both passive and active, are nowadays available on semiconductor substrates, leveraging the maturity of open-access silicon foundries and epitaxial germanium integration. It encompasses essential functions such as light generation and amplification, fast electro-optical modulation, and reliable conversion of optical into electrical signals. Germaniumbased optical photodetectors are main building blocks within the library of integrated silicon nanophotonics, with performances that are nowadays on par with their III-V-based counterparts. Germanium photodetectors integrated at the end of waveguides are attractive for next-generation on-chip interconnections, because of their compactness, bandwidth and speed, energy consumption and cost. In this work, we present our latest advances on silicon-germanium p-i-n waveguide-integrated photodetectors based on lateral silicon-germanium-silicon heterojunctions. Our hetero-structured photodetectors were fabricated on top of 200-mm silicon-on-insulator substrates using industrial-scale fabrication processes compatible with complementary metal-oxide-semiconductor technology. Silicon-germanium p-i-n photodetectors operated under low bias voltages exhibited low dark-currents (~100 nA), cut-off frequencies beyond 50 GHz, and photo-responsivities of about 1.2 A/W. Photodetector sensitivities of -14 dBm and -11 dBm were achieved for communication data rates of 10 Gbps and 25 Gbps, respectively. P-i-n photodetectors with lateral heterojunction operated in an avalanche regime offered an additional degree of freedom to improve device performances. High-speed and low-noise characteristics were obtained in our p-i-n photodetectors upon avalanche operation, with a gain-bandwidth product of 210 GHz and a low carrier impact ionization ratio of about 0.25. The measured sensitivity of avalancheoperated devices was -11 dBm for 40 Gbps signal detection. As demonstrated in the reported achievements, heterostructured p-i-n photodetectors are thus suitable communication devices in future intra-data center links or high-speed optical interconnects.

The large mode size mismatch between standard single-mode optical fibers and silicon-on-insulator (SOI) waveguides poses a significant challenge to efficiently couple light from the optical fiber to the chip, and vice versa. Surface grating couplers are often used for this purpose, however, their operational bandwidth is limited to a few tens of nanometers, as a consequence of the wavelength-dependent radiation angle. This constraint seriously hampers the use of surface grating couplers for next-generation passive optical networks (PONs), in which the wavelengths used for the upstream and downstream channels are separated more than 150 nm. In this work, we present a dual-band grating coupler for 10 Gbit symmetric PONs. Our device operates as a wavelength multiplexer/demultiplexer, simultaneously coupling and combining/splitting two optical signals at the wavelengths of λ_1=1270 nm and λ_2=1577 nm. The coupler is based on engineering a surface grating coupler to obtain opposite radiation angles for the two respective wavelengths. To achieve a higher coupling efficiency, the material platform thicknesses were optimized as a tradeoff between the waveguide propagation loss and the substrate reflectivity. By judiciously choosing the period (Λ=500 nm) and the duty cycle (DC=55%) of the grating section, an efficient dual-band grating coupler is designed with a minimum feature size of 225 nm. The coupler was fabricated in ST Crolles using their 300 mm SOI platform and 193-nm deep-ultraviolet lithography, demonstrating that large-scale fabrication is feasible. Measured fiber-chip coupling efficiencies were -4.9 dB and -5.2 dB with a 3-dB bandwidth of >27 nm and 56 nm at λ_1=1270 nm and λ_2=1577 nm, respectively.

Efficient power splitting is a fundamental function in silicon photonics integrated circuits and, consequently, compact power splitters with low losses over a broad bandwidth are sought after. Symmetric Y-junctions, consisting of a stem waveguide branching into two diverging arms, are typically used. However, the finite resolution of current photonic fabrication technologies results in a limited minimum feature size (MFS) of the tip between the splitter arms, penalizing fundamental transverse electric mode (TE0) since its intensity maximum coincides with the central region of the splitter. In this work, we propose a novel high-performance power splitter based on a symmetric Y-junction incorporating subwavelength metamaterials. Our device performance was simulated using 3D finite-difference time-domain method, considering two different fabrication resolution limits. In the worst-case resolution scenario (i.e., MFS of 100 nm), the device shows excess loss (EL) as low as 0.5 dB for both the TE0 mode and the first-order transverse electric mode (TE1) in a 300 nm bandwidth (1300 nm - 1600 nm). For the high-resolution fabrication process (i.e., MFS of 50 nm), total EL is further reduced under 0.3 dB over a bandwidth of 250 nm (1350 nm - 1600 nm). A proof-of-concept device was fabricated with electron beam lithography using SOI wafers with a 220-nm-thick Si layer and a SiO2 upper cladding. Preliminary experimental results show negligible losses for the TE0 mode over a broad bandwidth of 180 nm (i.e., 1500 nm - 1680 nm), for both fabrication scenarios (100 nm and 50 nm MFS).

We propose a novel three-dimensional (3-D) continuously tunable delay line based on high performance 3-D tunable directional couplers (DCs) driven by graphene heaters. The device includes a continuously tunable delay line section and 2 bit discretely tunable delay line section, the former can be considered as 1 bit discretely tunable delay line structure, the latter includes two delay units and three switch units. We set the maximum delay tuning range of the continuously tunable delay line section equal to incremental delay step ∆t of discretely tunable delay line section, so that the tuning is continuous over the entire delay range. The use of the graphene electrode by placing in direct contact with the upper waveguide core combined with the air slots formed on both sides of the graphene electrode can improve the heating efficiency. The proposed delay line has an optimal dimension of 25 mm × 6.8 mm (length × width). The simulation results show crosstalks are less than -21.6 dB over the whole C-band and less than ~-45.2 dB (OFF state) at 1550 nm. The delay line is capable of operation for continuously tuning and the delay time is linearly dependent on K. And the continuously tuning delay range is from 0 to 200 ps over minimum 3 dB bandwidth of <10 GHz. The minimum 3 dB bandwidth of our proposed device is four times larger than that of a continuously tunable delay line constructed with a typical 2×2 asymmetric MZI.

In this work, we analyze a horizontal slot waveguide configuration, which evaluates the potential for an integration of barium titanate (BTO) based modulators into a photonic integrated circuit (PIC) technology based on siliconon- insulator (SOI) wafer. The waveguide configuration consists of a doped crystal silicon layer, a Ba_0:7Sr_0:3TiO₃ (BST) template layer, a barium titanate (BTO) layer and a doped poly-silicon layer on top. In contrast to current approaches, we analyze the performance of this waveguide-structure by using a vertical electrode configuration that is formed by the doped silicon layer. In this way, the electric field strength is dramatically increased compared to current horizontal electrode configuration.

In order to achieve ultrahigh data capacity and to overcome the wireless spectrum crunch, 5G is going to adopt millimeter-wave (mmW) frequencies (30 GHz – 300 GHz). To generate high-quality mmW signals by lasers, it requires optical sources with ultra-narrow optical linewidth and low relative intensity noise (RIN). In recent years, we have developed InAs/InP quantum dot (QD) multi-wavelength lasers (MWLs) around 1550 nm with the frequency spacing from 10 GHz to 1000 GHz. Those QD MWLs have very low RIN, ultra-narrow optical linewidth, small timing jitters, compact size, low power consumption and the ability for hybrid integration with silicon substrates. In this paper we present a buried heterostructure (BH) C-band InAs/InP 25-GHz QD MWL with phase noise and RIN of less than 500 kHz and -130 dB/Hz for its individual channel, respectively. By using this QD MWL a photonic aided radio-over-fiber (RoF) quadrature amplitude modulated (QAM) signal wireless delivery at 25 GHz is successfully demonstrated through 25.22 km standard single-mode fiber (SSMF) with a data capacity of 16 Gbit/s (16QAM x 4GBaud). We have also presented a monolithic BH QD dual-wavelength (DW) DFB laser as an optical beat source for mmW signal generation. The BH QD DW-DFB laser with the optical linewidth of 16 KHz and the RIN of -158 dB/Hz is capable of generating spectrally pure mmW signals between 46 GHz and 48 GHz. By using it, we have demonstrated a real time 24-Gbit/s (64QAM x 4GBaud) data bandwidth wireless communication system operating at 47.2-GHz carrier over 25-km SSMF.

Free-space coupled membrane photonic devices are highly desirable for 3D optical interconnects, free space communications, imaging, sensing, and ranging applications. Based on transfer printing processes, heterogeneously integrated active photonic crystal devices can be built on the common silicon platform. In this talk, I will report recent progresses related to hybrid integrated photonic crystal surface-emitting membrane lasers on silicon substrate, based on QW gain material and transition metal dichalcogenide monolayers. Issues to be discussed related to thermal performance, charge injection, and scaling towards energy efficient optical interconnects.

Sources that can produce single photons in the telecom band, capable of traveling long distances over optical fibers, are of great interest for long-haul quantum communications. In recent years, there has been a major drive to demonstrate single-photon sources (SPSs) for quantum key distribution to provide secure communications over long distances. Nanowires containing a single quantum dot emitting around 1μm have been proven to be viable source to emit a very pure photon with multiphoton probability below 1% [1]. Extending the emission wavelength to the telecom window seemed inevitable to fully exploit the available architecture of long-haul fiber-based quantum optical networks. In this invited talk, we will report on our recent results on the fabrication of InAsP single quantum dot embedded within an InP photonic waveguide nanowire for single photon emission at telecom band. In particular, we outline the importance of the photonic waveguide design for optimum photons generation and coupling to the external optics. Manipulating the dot growth conditions as well as engineering the band structure around the dot (dot-in-a-rod configuration) are some of the approaches [2, 3] that have been applied to achieve emission at 1310nm and will be presented. SPS operating at 1310nm with multiple photon probability below 2% is achieved 4K. [1] D. Dalacu, K. Mnaymneh, J. Lapointe, X. Wu, P. J. Poole, G. Bulgarini, V. Zwiller and M. Reimer, Nano Letters 12, 5919 (2012). [2] S. Haffouz, K. D. Zeuner, D. Dalacu, P. J. Poole, J. Lapointe, D. Poitras, K. Mnaymneh, X. Wu, M. Couillard, M. Korkusinski, E. Schöll, K. D. Jöns, V. Zwiller, and R. L. Williams. Nano Letters 18, 3047 (2018). [3] S. Haffouz, P. J. Poole, J. Jin, X. Wu, K. Mnaymneh, D. Dalacu, and R. L. Williams., Appl. Phys. Lett. 117, 113102 (2020).

A method of hybrid integration of quantum dot microdisk lasers with silicon wafer is proposed and realized. In addition to the possibility of combining microlasers with various silicon-based electronic and photonic devices, this makes it possible to significantly improve heat removal from the active region of the microlaser. The thermal resistance normalized to the mesa area reaches the level of about 0.002 (K/W)*cm², which is significantly lower than the corresponding values of QD microlasers on GaAs substrate and monolithically grown on Si. As a result, the threshold current as well as current-induced shift of emission wavelength are reduced in continuous-wave regime.

Lasing properties of the two-dimensional (2D) distributed feedback (DFB) lasers can be engineered by replacing either the gain medium or periodic structures necessary for the feedback mechanism. Quasicrystals are the intermediate class between the periodic and random structures. They have high rotational symmetry and more favorable for the generation of photonic bandgap as compared to periodic structures. In our experiment, we designed a pentagonal prism for the holographic lithography to construct a long-range 10-fold rotational symmetry, which exhibits 2D quasiperiodic structures. A solution-processable colloidal quantum dots (CQDs) was spin-coated on the resultant 2D quasicrystals. An analytical model based on the cavity mode coupling effect was developed to predict the output performance of the 2D DFB CQDs photonic quasicrystals laser. The respective optically pumped 2D photonic quasicrystal samples exhibit multi-wavelength lasing emission in different directions due to long-range rotational symmetry. The five DFB lasing spots are symmetrically distributed in the 2D space, the center of the lasing spots is similar to a star shape. The derived analytical model predictions are in line with the experimental results.

Features of the all-fiber heavily erbium-doped laser operation in passive Q-switched regime with a repetition rate of pulses up to 700 kHz and pulse duration 70 ns without the use of an additional nonlinear optical elements have been investigated. The generation dynamics of the heavily erbium-doped fiber laser assembled according to the classical Fabry-Perot scheme with two mirrors under continuous direct core pumping at the 976 nm and 1490 nm wavelength was studied. Passive Qswitching in heavily erbium-doped lasers is realized due to effect, which is opposite to the saturable absorption. The absorption grows with the field intensity instead of being saturated. The reason for the appearance of pulses is the existence of ion pairs at high erbium concentrations. This creates an effective absorption dependent on levels’ populations of ion pairs.

Linearly polarized quantum sources with high purity and well-defined polarization angles are the fundamental blocks in the photonic quantum technological evolution. However, due to the orientation of the dipole moment with the quantum emitters, the polarization state of the emitted photons is intrinsically limited. Therefore, it is impossible to generate arbitrary linear polarization states simultaneously. Here, we propose a new concept of versatilely generating linearly polarized emission based on a quantum metasurface platform that combines nano-diamonds containing color centers with metasurface-decorated waveguides. By tailoring the size and orientation of the slit meta-atom on the waveguide, linearly polarized emission with arbitrary polarization angles can be achieved with the degree of linear polarization larger than 0.999.

An acousto-optic tunable filter (AOTF) based on a paratellurite crystal for tuning the radiation wavelength of a copper vapor laser has been calculated and manufactured. The geometry of acousto-optic interaction in AOTF for performing wide-angle spectral-selective diffraction is based on the parallelism of the incident and diffracted light tangents to the wave surfaces. The system of equations for the above conditions is solved and the maximum numerical aperture of the filter in the scattering plane is determined. It has been found that the required angle of deviation of the acoustic wave vector from the [110] direction leads, due to the large elastic anisotropy of paratellurite, to a significant deviation of the group velocity vector, or energy flux. This angle between the vectors of the phase and group velocities can be tens of degrees, which makes it necessary to manufacture an acousto-optic cell of a special shape. In addition, when deviating from the [110] direction, this also leads to a change in the velocity of elastic waves, in this case to its increase and, as a result, to a decrease in the efficiency of acousto-optic interaction. It is calculated that the maximum numerical aperture in the diffraction plane is obtained at an angle of deviation of the elastic wave vector from the [110] direction by approximately 18 degrees. In this case, the numerical aperture in the diffraction plane is almost twice the numerical aperture in the orthogonal plane. Therefore, for the case of the same numerical aperture, it is sufficient to choose an angle of about 10 degrees. The paper presents a mathematical description and calculation results for the main characteristics of an acousto-optic tunable filter. Based on the performed studies, an acousto-optic tunable filter for controlling the parameters of a copper vapor laser at two radiation wavelengths λ₁ = 510.6 nm and λ₂ = 578.2 nm was fabricated and experimentally investigated.

A fully integrated efficient surface plasmon coupler composed of a non-tapered waveguide is designed for the infrared through rigorous numerical and theoretical studies. To study such structures, a general methodology to study rigorously discontinuities in open waveguides is used. It relies on a full vector description given by Maxwell’s equations in the framework of the finite element method. In our case, the discontinuities are provided by the graphene patches that are modelled as 2D conductivity pieces. The leaky modes of the invariant structure are first computed and then injected as incident fields in the full structure with the graphene patches and sheet using a scattered field approach. This method we recently published allows to compute all the field and energy quantities needed to characterize the investigated couplers. These couplers are designed to work on the far infrared regime. TAS, a special chalcogenide glass is considered for the guiding layer. The studied waveguide is a rib waveguide. The input part of the studied device is the bare rib waveguide. Following the propagation axis, the device is composed of the coupler region, made of a finite number of graphene patches located just above the core guiding layer. The role of this coupler is to generate electromagnetic fields in the next continuous graphene sheet (also located on the top of the core layer) where the surface plasmon polariton part of the field is propagating. The graphene properties are the ones provided by the Kubo formula. The studied device is fully integrated and no out of plane waves have to be considered, only electromagnetic fields propagating inside the structures are considered. Parametric numerical studies as a function of the waveguide thickness and of the duty cycle parameter describing the coupling patches have been conducted in order to maximize the plasmonic part of the generated field near the graphene layer. Several waveguide and coupler configurations with realistic parameter have been obtained proving a highly efficient and fully integrated coupler. Among these configurations, one where the mode coupling between the main mode and higher orders modes is minimized is of particular interest for practical applications.

In this paper, we discuss the principle of coupling an optical signal to an optical resonator. We give the broad outlines of the principle and the experimental parameters then we look at how to optimize this coupling using finite element simulations.

We consider a setup designed to study infrared radiation reflected from liquid and solid substances located on various substrates in this work. We describe the optical and principal scheme for the experimental setup. We use a laser setup that contains one Alpes Lasers quantum-cascade laser chip with a tuning range 1000 - 1300 1/cm with peak power up to 480 mW and 1 MHz repetition rate. Setup includes two HgCdTe thermoelectrically cooled sensors as reference and signal detector. Each sensor is equipped TEC controller, and the amplifier is mounted. The signal is digitized using a 24-bit ADC with a frequency of 1.5 MHz. Measurement time is about 1 sec. Recently experimentally reached sensitivity is less than one microgram per square cm on various substrates. We estimate the device's possible weight to about 5 kg and the sensitivity of about microgram per square cm. This work presents the results of processing the diffuse reflectance spectra. The diffuse reflectance spectra have low selectivity. So, we use calculational algorithms based on Kramers-Kronig transformations with extrapolation of spectra and phase correction. For substance identification using diffuse reflectance spectra, we use database consists of about 20 substances.

We report on a new method for fabrication of saturable absorbers for operation in ring fiber lasers as a mode-locking element taking advantages of the manufacturing technologies of fiber couplers and microfiber tapers coated with carbon nanotubes. It is demonstrated in the experiment that the transmittance of the fabricated saturable absorber increases with an increase of the input radiation power. Also, we have shown that the fabricated saturable absorber enables generation of picosecond soliton pulses in ring fiber laser configuration.

Due to assembly processes in microelectronics packaging, semiconductor materials are under undesired stresses, which become more important at extreme thermo-mechanical operating conditions. Investigations of the performances of the semiconductors is very challenging, because each assembly is a complex structure with many materials with very different physical-chemical properties. Remarkable is the determination of local stresses trough optical techniques, like Raman spectroscopy. Focus of this study is the monitoring of stress induced on silicon chips after bonding. Three bonding processes are investigated: soldering using a eutectic AuSn preform, sintering using a commercial Ag sintering paste, sintering using an in-house developed sintering paste made by surface enhanced etched brass particles dispersed in polyethylene glycol 600. In all cases, the Si-chip is bonded to a Cu substrate. The stress distribution after AuSn-soldering presents a homogeneous pattern, while after Ag- and Cu-sintering an axial distribution along the diagonal is observed. The samples are investigated at three temperatures: -50, 20, and 180 °C. The stress phenomena are higher for the assemblies made via AuSn-soldering, with stress value above 600 MPa. The results are discussed in term of compressive and tensile strain and thermal expansion coefficients.

Nanophotonic devices are the very fundamental functions in a photonic integrated circuit, which have led to a revolutionary development in many fascinating applications. Toward this end, researches have demonstrated different kinds of nanostructures that are made from plasmonic and dielectric materials, including optical waveguides, ring resonators, photonic crystal resonators, nanoapertures, and nanoantennas. Plasmonics is considered to be the most promising candidate for the next generation of integrated chip-scale technology. In particular, using plasmonic nanoantennas, optical field enhancement and confinement can be achieved with deeply subwavelength range, leading to strong light–matter coupling and with enhanced optical forces. Another reason for the use of plasmonics is its ease of integration with other photonic waveguides for optical information processing at nanoscales. As predicted by Maxwell’s equations, light fields have linear momentum and thus can generate optical forces on tiny objects via momentum transfer. Nanoantennas utilize optical forces to trap and manipulate small particles at relatively low incident intensities. For the field of nanoscience, the on-chip ability to handle single nanoparticles at the integrated devices is quite advantageous. Various nanoparticles have been trapped, including polystyrene and gold nanoparticles. Traditionally, gold has been used as the material of choice in plasmonics because of their relatively good optical properties and chemical stability. Advances in plasmonic materials research have ushered in alternative materials. Among them, copper particularly has attracted significant attention because of its good plasmonic properties and abundant quantity. Copper is comparably cheap, which is compatible with industry-standard fabrication processes, such as the complementary metal-oxide-semiconductor (CMOS) technology, and has been widely used in microelectronics. In this work, we demonstrate a coupled T-shaped Cu plasmonic nanoantenna for the optical trapping of single dielectric nanoparticles and investigate its plasmonic and optical properties interacting with an infrared trapping laser. The electric field enhancement (and thus optical force), temperature rise, and induced fluid velocity it provides are quite similar in comparison to those provided by the Au nanoantenna design. Cu is cheap and compatible with standard microelectronic fabrication technologies. Large local field enhancements mean that low incident power can be utilized. In addition, we show that the oxidization effects on the Cu surface have a weak influence on trapping characteristics compared to pure Cu nanoantenna, and the Si heat sink substrate can reduce the temperature rise in water. Our results verify that T-shaped Cu nanoantennas are robust as nanophotonic devices for optical information manipulation at nanoscales. They could also be used to manipulate and investigate single quantum emitters and small molecules. Beyond this, we anticipate a multitude of topics of Cu nanostructures could be performed for future optical computer investigation and lab-on-a-chip application.

Compressive single pixel imaging (C-SPI) is a novel imaging technique able to reconstruct images using only a single pixel detector and a partial measurement of the scene. This technique uses different structured illumination, generated by a spatial modulator, to illuminate the scene and measures the reflected or transmitted light intensities. This compressive stage allows for a sub-Nyquist set of measurements, which significantly increases the technique efficiency, while maintaining a good reconstruction image quality. An experimental setup was developed to study the ability of C-SPI to determine the lifetime and mean intensity of an oxygen sensitive biomarker (Pt(II) ring-fused chlorins). This biomarker phosphorescence is quenched in the presence of oxygen resulting in smaller intensity and lifetime. A structured illumination system was used to stimulate the sample with Hadamard patterns, in the range between 428 nm and 620 nm, while a photodiode collected the emitted light peaking at 756nm. The imaged scene was composed of two toluene solutions with the same biomarker concentration (1 μM), one in the presence of oxygen and the other in its absence. The images were reconstructed using total variation minimization by augmented lagrangian and alternating direction algorithms (TVAL3) with compressive ratios of 25%, 10% and 5%. The proposed method was able to spatially locate the sample contained in a deoxygenated environment in two distinct spatial locations. The deoxygenated sample lifetime and mean intensity of the reconstructed images were, respectively, approximate 20 μs and 2.1×10^-3 AU, for the first location, and 20 μs and 4.0×10^-3 AU for the second location. Regarding the oxygenated sample, the results were scattered in a long range for lifetime but achieved a mean intensity of approximately 4.8×10^-5 AU. Consistent results were obtained for the three compression ratios without major loss in image quality. The proposed method showed that SPI has the ability to perform simultaneous phosphorescence lifetime and intensity imaging. The introduction of compressive sensing makes this technology more attractive to practical applications because it lowers the amount of time necessary to image the sample. The C-SPI is a simple and less expensive technique because it dismisses the use of a fast two dimensional detector (CCD) and the associated electronics, as well as mechanical scanning procedures. Also, multiple single pixel detectors, sensitive to different wavelengths, can make these instruments versatile and allow for simultaneous phosphorescence biomarkers analysis. The next steps in the research will be to study changes in the sample concentration and different percentages of dissolved oxygen.

In this paper, we consider an integrated optical system designed to analyze the composition of ambient air. The optical system consists of a dynamic Michelson interferometer and a multi-pass White gas cell. We use steady state IR radiation source, that is integrated in the system. IR Radiation is modulated by passing through the interferometer, and then enters a multi-pass gas cell. We use two MCT TE cooled photodetector as reference and signal detectors. To digitize registered signal, we use a 24-bit ADC. For the described system, the sensitivity limit is about ppb levels, that allows detecting volatile substances at the maximum permissible concentrations. Described FTIR spectroscopy systems can be used for ambient air analysis and for breathomics applications.

In integrated photonics, the calculation of the solutions regarding the propagation equations modes may be summed up as a problem with eigenvalues and eigenvectors to be solved. Based on such global principle, we have investigated the ability to monitor the impact of a lack of material (or void) on the evolution of eigenvalues of waveguides. To this end, specific families of resonators have been designed with several slits nano-inscribed upon them. The signal resonant light is then characterized while considering the whole geometry taking account of the void: thus, it contains the information regarding the pre-defined recessed volume. The UV 210 polymer is processed (deep UV 248 nm) so as to shape specific slots within a set of waveguides. Then, such waveguides have been re-looped as micro-resonators circuits with a view to measuring experimentally relevant variations of the eigenvalue considering the Free Spectral Range (FSR) associated with resonances. Experiments allowed us to highlight such changes in effective indices clearly correlated to the amount of void. As the lack of material reaches 10% (imprinted within space), a noticeable variation can be observed. It made possible to measure the impact of a given lack of material (defined grooved volume) within the cyclic resonators, on the measured and normalized FSR optical quantity showing then a dynamic evolution close to 1.5%. Moreover, simulations have been carried out so as to confirm the experimental measurements: accordingly, the relevant results allow us to validate a quantified description regarding the hollowed out volume (or mass recessed). Then, by way of the COMSOL software, apt simulations allowed us to confirm the measured evolution in agreement with experiments. This study provides a way to evaluate the global dynamic ranging effect due to a given mass hollowed out from such looped structures as regards the entailed spectral signature linked to the eigenvalues.

In this study, we are interested in giant tapers operating in a totally Multi-Mode Interference (MMI) regime capable of producing still an adequate single-mode field at the output. The idea is therefore to provide an answer on a possible giant acceptable limit of such MMI tapers still causing a single-mode output and then determining which opto-geometric parameters on this simple mathematical object and geometry act on the behavior. To this end, we have defined energy criteria per volume at the output. We consider families of tapers with a constant height corresponding to the output rib waveguide and a triangle shape. Each taper is defined by its input size, its length and its output size. The objective is to determine the minimum length of the taper to get enough energy or the desired guided mode(s) in the output waveguide. Two various approaches have been investigated and compared: numerical simulations by a finite element method (COMSOL) and a pure mathematical and geometrical study in conditions of total reflection on the walls of the taper plus a specific plane transformation. When the length of the taper increases, the energy increases in the core up to a limit value and decreases in the cladding. The size of the output guide is fixed to w_s = 2 microns and the input size of the taper varies from typically 6 microns to `giant' 400 microns. Four kinds of behavior were identified. For small lengths all the energy is reflected by the walls of the taper. For first intermediate lengths a part of the light is difused in the cladding and the other part is guided to the output guide. For following intermediate lengths the major part of the light is guided to the output guide with multi-modes propagation. Lastly for greater lengths only the fundamental guided mode appears in the output guide.

Visible light communication (VLC) allows the dual use of lighting and wireless communication systems by modulation of illumination devices. However, to increase the performance, typically, beam-forming measures are taken creating pencil beams, thus contradicting the illumination purpose. In order to optimize the performance trade off between efficient illumination and communication, the switching capabilities of illumination LEDs are examined. Illumination LEDs with standard drivers and without beam-forming show limited applicability for communication purposes as they are not optimized for the necessary switching capability (f ≈11 MHz) and coherence. Methods to enhance the electrical current by pre-equalisation, biasing, carrier sweeping and current shaping are examined in respect to the illumination LED's communication performance. A novel driver scheme is derived which achieves considerably higher switching frequencies (f ≥100 MHz) without employing beamforming at the illumination LED. This driver is able to obtain a data rate of up to 200 Mbit/s at a distance of 3.2 m, using on-off keying (OOK) modulation technique. Therefore, it is feasible to apply the LED driver by implementing standardised illumination devices in VLC systems.

The optoelectronic proliferation of liquid crystals based passive microwave and millimetre-wave reconfigurable technology relies not only upon low-cost micro-fabrication techniques, but also on high-fidelity yet efficient device design and simulation methodologies based on an in-depth understanding of the complex coupling between waveguiding geometries and multi-material systems through multi-physics models. While closed-form analytical solutions are not possible for multi-volume complex geometries, numerically attempting the problem is of research and development interest, in particular for gaining fundamental insights on the coupling between liquid crystals optoelectronic response and millimetre-wave interactions, hence producing guidelines for in-house code development of specific optoelectronic device prototypes without resorting to commercial off the shelf software. To this end and by way of illustration, this work proposes a novel mixed-signal dielectric-partitioning model for local polarisation and tunability analysis into a liquid crystals based shielded coplanar waveguide tunable delay line targeting applications in the 57-66 GHz band. Due to the transverse electromagnetic nature of the fully enclosed coplanar waveguide structure, the traditional two-step approach (liquid crystals’ quasi-electrostatic simulation in microscopic scale progressing to millimetre-wave simulation in macroscopic scale) could be rearranged into one single stage in terms of the molecular directors with respect to the identical electric vector field distributions. The proposed standalone and quasi-analytical model is verified by experimental measurements implemented on a 0–π tunable true-time-delay phase shifter, with a 7.94% improvement in the predicting accuracy of the effective line length required, and a huge reduction in computational costs as compared with the traditional two-step method. The proposed efficient model is envisioned to inform the development of highly efficient in silico tools with high fidelity for liquid crystals based reconfigurable applications beyond displays.

By simulating tight focusing of vector beams with azimuthal polarization of fractional order, the effect of the deviation of the beam order from m = 2 (i.e., the case when the backflow is observed at the center of the focal spot) was investigated. It was shown that the reverse flow is retained in the center of the spot even with a significant deviation of the beam order from m = 2 - it is retained up to m = 1.55.