The resonant layer effect (RLE) is investigated for a multilayer structure with iron nanoinclusions. The RLE tuning and strength are analyzed as a function of nanoinclusion filling factor and resonant, cladding and guiding layers thicknesses. Crossing, splitting, and quasidegeneration of modes in the structure dispersion diagram are discussed, along with its relation to the RL effect detuning and structure-coupling regime. For the range of parameters considered, multiple resonances are tunable in the multilayer structure. Optimized RLE TE and TM polarizers are proposed for operation at 1550 nm based on modal loss and field confinement calculations. For the TE-pass polarizer, a 201.1-dB rejection ratio and 3.85-dB/cm insertion loss are obtained, while for the TM-pass polarizer, a 95.6-dB rejection ratio and 4.41-dB/cm insertion loss are achieved.
This work describes an in-fiber Michelson interferometer inclinometer which is sensitive to curvature applied in the tapered region. The performance of this inclinometer is evaluated by calculating the variation of the fringe visibility near the 1550 nm spectral range as a function of the tilt angle. It is presented the results of four experimental measurements and calculated the average and standard deviation of those measurements. The results indicate a good response of the sensor within the angular range between 3° and 6°. The average of those four measurements is around -0.15/° and the greatest standard deviation is about 5.5%.
In this work, a remote curvature sensor using a standard OTDR as the interrogation system is presented. This approach uses a core diameter mismatch sensor which is formed by a short section of a multimode fiber, with a length of 3 mm, sandwiched between two singlemode fibers. In this case, the attenuation of the optical signal will vary as the fiber is bent allowing interrogating the sensor with OTDR technology. Preliminary results indicate a resolution range of ~0.0003 cm- 1, sensitivity in the range of ~-208.46 dB/cm-1 and a variation of 2.67 dB in the OTDR trace within the bend radius range.
In this paper it is proposed an interrogation system based on OTDR for fiber loop mirror intensity sensors. The system has been characterized in order to obtain its maximum dynamic range. The technique demonstrated good linearity with a – 13.3 dB/mm slope. A 0.027 mm resolution was achieved. The proposed interrogation system permits multiplexing of around 10 sensors and showed to be an alternative technique for multiplexing and remote sensing.
This work presents numerical results related to an in-line Mach-Zehnder interferometer used as a refractive index sensor. The in-line Mach-Zehnder is based on abrupt tapers in standard single mode optical fiber. Numerical simulations were carried out using commercial software based on Beam Propagation Method in order to analyze the sensitivity response in terms of wavelength shift when this sensor is bent at certain radii of curvature. We realized that application of bending in the In-line Mach-Zehnder interferometer enhanced considerably the sensitivity of this sensor to the external refractive index. The best result was achieved for a radius of curvature of 10 mm (~500 nm/RIU for the refractive index range of 1.33 to 1.41) improving the sensitivity about eight times in comparison with the case with no bent.
One of the major issues in the modeling of subwavelength optical materials resides in how to compute the effective properties of such media. An efficient technique must be able to describe appropriately the electromagnetic response of the overall structure. Within this context, this work is focused on the calculation of effective parameters of metallic silver nanowires embedded in alumina background. An algorithm based on modal propagation is considered in order to estimate the refractive index at the visible spectrum. The resonances obtained in the computing model are compared to the predictions of analytical Bruggeman and Maxell-Garnett theories and analyzed by regarding excitation of surface modes at the metal-dielectric interface.
In this work, we address a study of the spectral reflectance of silver nanowire metamaterials in the visible and near-infrared regions. To this end, several samples were fabricated with different fill-ratios and lattice constants, and their respective optical responses characterized in terms of these parameters. We perform a direct comparison between the collected experimental data with the values predicted by different analytical homogenization models to provide a better understanding of the effective optical behavior of this kind of metamaterials.
The development of an interferometric optical fiber inclinometer is described in this paper. A weak tapered region is
induced in a standard single mode fiber in the vicinity of the cleaved fiber tip, using a standard fusion splicer. In this
situation an in-fiber Michelson interferometer is constructed that is sensitive to curvature applied in the tapered region. It
is shown that depending on the angular range, fringe visibility and/or peak position depend strongly on the applied
curvature enabling low cost dielectric inclinometer to be setup that is suitable for high voltage applications. It is
presented an analysis of the sensor response by means of experimental measurements and manipulation of these
experimental data through computational simulations. The results coming from the numerical simulations indicate a
good performance of the sensor within range of angular variation between 3 and 6 degrees and 10 and 14 degrees. A low
cost strategy to interrogate the response of sensor using electrically modulated fiber Bragg gratings, a photodetector and
frequency analysis is described. The results presented by this electric interrogation technique show a good sensitivity in
the range 3.5 to 5.5 degrees.
It is reported a LPG dynamic interrogation technique based on the modulation of fibre Bragg gratings located in the
readout unit that permits to attenuate the effect of the 1/f noise of the electronics in the resolution of the LPG-based
sensing head. The concept is tested to detect variations of the external refractive index and a resolution of 2.0×10-4 NIR
was achieved without system optimization. Additionally, the effect in the sensor resolution when introducing Erbium and
Raman optical amplification is experimentally investigated.
KEYWORDS: Raman spectroscopy, Amplifiers, Optical amplifiers, Wave propagation, L band, Fiber amplifiers, Signal attenuation, Single mode fibers, Nonlinear optics, High power fiber amplifiers
A quantitative study on the impact of pump-pump interaction in wide band Raman amplifiers in the S, C and L bands is reported here.
For this purpose, the nonlinear coupled Raman equations are written in a novel format separating the different mechanisms which
contribute to gain profile, among them, pump-pump interaction. The study is applied to a modern low loss fiber under three pump
excitation. The minimum total pump power required to pump-pump interaction mechanisms is investigated for the co and couter
propagating amplifier configuration. These threshold power level is significantly different for both configurations. In the co
propagating configuration it is independent on the amplifier length while for the counter propagating configuration it is dependent on
the amplifier length. to affect gain profile is dependent on fiber length for the counter propagation amplifier configuration while it is independent on fiber length for the co-propagating configuration. Further, a sensitivity analysis of gain flatness as a function of the
central pump wavelength power is conduction for both amplifier configurations. The counter propagation configuration is less
sensitive to center wavelength power level variation when compared to the co propagating configuration.
The analysis of a subcarrier multiplexing free space optical transmission system with ASK electrical
modulation is presented in this paper. The designed system based on SCM-ASK-FSO allows the optimized
exploration of the available spectral frequency bandwidth. The performance for the SCM - FSO subsystem
obtained using ASK electrical modulation was evaluated in terms of eye diagram and bit error rate.
It was verified that the FSO channel does not generate intermodulation between the subcarriers, allowing a
uniform interchannel spacing. The necessity of the channel insertion was evaluated as a function of the
reduction in the distance between the system transceivers. SCM techniques integrated to a FSO system
operating at 1550 nm were simulated with the commercial software Optisystems from Optiwave, Inc.
Studies considering different modulation techniques used in the integration of subcarrier multiplexing
(SCM) optical transmission systems are presented in this paper. The analysis of SCM systems operating in
the 1550 nm signal wavelength range involves ASK, QPSK, 16QAM and 64QAM electrical modulations.
From experimental results and by numerical simulation, the frequency response of the fibre for the ODSB and
OSSB systems is obtained. The simulated results suggest that using dispersion compensating fibre (DCF) it is
possible to compensate the dispersive effect in optical fibre for ODSB signals, allowing the system to get
OSSB similar frequency response. SCM systems simulations were performed using the commercial software
Optisystems from Optiwave, Inc. The system bandwidth increase was analysed in terms of fibre length and
dispersion considering different links, subcarrier spacing and number of subcarriers. From experimental
results, the intermodulation effect, generated by the optical fibre, is verified and indicated the necessity of
using unequal spacing between the subcarriers, which is a factor that limits the SCM systems' performance.
The performance of a Subcarrier Multiplexing (SCM) optical fibre system using QPSK modulation is analysed in this paper. Our results will show that it is possible to increase the system bandwidth by controlling the input optical power. Various fibre dispersion values and subcarrier channel spacing are used in order to check the bandwidth increase proportional to the optical power. The transmission bandwidth was studied in terms of fibre dispersion and input optical power. The frequency response was measured and computed. Limitations imposed by nonlinear distortions mainly due to interplay between dispersion and self-phase modulation are verified as well. The analysis to the SCM_QPSK transmission system such as the subcarrier channel spacing, signal input power, available frequency bandwidth under the fibre specifications and system conditions operation will be explored in a specific application. It means applying this technique after setting the requirements necessary to the operation of an optical ground-wire (OPGW) already installed system. The results showed an increase of the transmission bandwidth as the optical power increases. For QPSK modulation, power penalties smaller than 1 dB were obtained only for channel spacing higher than 1.2 multiplied by the symbol rate. Experimental measurements obtained in the literature were used to validate our results. Eye opening and received eye diagrams will be evaluated in order to have a simpler receiver layout and make the entire system more reliable, since it will become more robust to error disturbance, maintenance is easier and system upgrades will be facilitated.
In this paper we analyze by simulation a measured amplified single channel 40 Gb/s communication system composed by standard fiber. Two different commercial simulation tools are used to perform the calculations. Experimental results were reproduced in such distinct simulation environments that allowed calibrating and predicting the system performance when new parameter settings are taken into evaluation. The simulation results indicate that at least 10 dB less power is required to achieve the same BER simply using an optimized receiver. That result enabled to have the same BER and also allowed removing the EDFA. Since one device such as an EDFA could be eliminated of the layout, with less optical power being required in the receiver, fiber spans as short as lengths that eliminate the dispersion compensation have been considered.
All-optical wavelength conversion using cross-gain modulation in a semiconductor optical amplifier is one of the simplest and most common techniques to perform such operation. However, the finite gain recovery time of the amplifier causes severe distortion and pattern dependence at high bit-rates. The present work shows that it is possible to reduce the pattern dependence of the output converted signal using a fiber Bragg grating operating on its transmission edge. A wavelength converter using the non-linear effect of cross-gain modulation in a semiconductor optical amplifier can be assembled in the co-propagating and counter-propagating modes. The advantage of the counter-propagating mode is the possibility of an assembly without an optical filter in the output of the converter to filter the input signal, however this scheme introduces crosstalk in WDM systems, due to the residual facets reflectivity of the semiconductor optical amplifier. In this paper we analyze by simulation using commercial software, the improvement in the frequency response of a wavelength converter based on cross gain modulation in semiconductor optical amplifier in the counter-propagating mode using a fiber Bragg grating. The simulation results show that, with the fiber Bragg grating in the output of the converter, the pattern dependence of the converted signal is reduced. This paper also shows the advantages and disadvantages of the counter-propagating mode.
We evaluate the performance of a wavelength conversion technique
based on the modulation of the amplified spontaneous emission of
semiconductor optical amplifiers through simulation software. Unlike conventional conversion technique the ASE-XGM does not require a CW probe signal. The converted wavelength is determined by an optical filter, which slices the modulated ASE spectrum. We focus on bit error rate (BER)conversion performance of a 2.5 Gbit/s non-return to zero, pseudo-random sequence of order 11. BER values better than 10-9 are achieved for signal input power ranging from -6 dBm to 0 dBm, and for a slicing filter centered around 0.4 nm red shifted from signal wavelength.
This work presents the results of the study on the longitudinal modes behavior in an erbium doped fiber ring laser that uses two optical fibers--one mechanic and another electric. The operation of both filters is combined to cover the whole spectral range corresponding to the erbium fluorescence. The influence of the cavity length, host matrix and combination of two optical filters on the mode suppression and performance of the laser is discussed. We obtained the match conditions for operation of the optical filters which better improve the laser performance. An estimate of the relative intensity noise due to the introduction of the laser in a communication system is also presented.
The optimized power performance and the spectral tunability modeling of Erbium-doped fiber ring lasers are presented together with the measurement of the relative intensity noise. A Figure of Merit and an optimization procedure are defined in order to obtain maximum output power for a given pump power aiming the project design. Two tunable Erbium-doped fiber ring lasers were assembled. Their tunabilities are modeled and compared to the experimental results. Good agreement was obtained. We achieved a 32 nm tuning range, limited by the tuning range of the filter used. A relative intensity noise < - 120 dB/Hz, which enables to externally modulate such lasers up to 2.5 Gb/s, was also obtained.
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