We present the design of a compact channel drop filter based on 2D photonic crystals on silicon-on-insulator platform. The proposed device consists of three channel sections with line defect waveguides as the bus and drop waveguides and L3 cavity as the resonator. The input and output ends of the bus waveguide are connected to silicon strip waveguides through tapered waveguide regions for efficient mode transmission. Each L3 cavity filters one resonant wavelength, which will be coupled to the drop waveguide. The effect of the size and position of the structural parameters on the proper selection of resonant wavelengths and drop efficiencies is studied. The device performance has been numerically analyzed, and thermal stability is studied using the 3D finite-difference time-domain method. The proposed device can filter three wavelengths in the C-band with minimum channel spacing of 3.03 nm. With the tapered-coupled bus waveguide, drop efficiency has been improved from 77% to 91%, and the quality factor and linewidth are found as 5042 and 0.31 nm, respectively. The footprint of the filter is 116 μm2 per channel section. The proposed device is suitable for practical wavelength division multiplexing applications in optical communication systems.
A compact microring resonator (MRR) and its implementation for polarization rotation-based all-optical switching are proposed. The polarization rotation has been achieved by enhancing geometry-induced birefringence of the device and with the insertion of polarization rotator in the race-track-shaped MRR. The proposed device has been modeled using Jones matrix and the finite-difference time-domain simulation method. The insertion loss and the extinction ratio have been found to be −0.13 and 19.39 dB, respectively.
The performance of a bidirectional silicon mode-division (de)multiplexer has been analyzed in the radio over fiber passive optical network system. The device uses two grating-assisted contra-directional coupler sections to demultiplex the transmitted fundamental, first-order, and second-order quasi-transverse electric (TE) modes. A bandwidth of 791 GHz and acceptable crosstalks of −25.73 dB (TE0m), −10.30 dB (TE1m), and −11.84 dB (TE2m) have been achieved from the 2.5D finite-difference time-domain method at a wavelength of 1550 nm. The system uses parabolic index multimode fiber (MMF) and free-space optics channels alternatively. A 120-Gbps data rate has been obtained using differential quadrature phase-shift keying scheme and hybrid mode-division multiplexing techniques. The system maintains an acceptable bit error rate (≤10 − 12) over transmission distances of ≤5.3 km MMF and ≤1.9 km for free-space optics link with receiver sensitivities of ≥ − 26.2 and ≥ − 24.8 dBm, respectively.
A silicon Mach–Zehnder modulator (MZM) with quasi-TM mode propagation is investigated for non-return-to-zero on–off keying modulation. The quasi-TM PN phase shifter phase-loss characteristics have been determined and shown to exhibit better performance compared to quasi-TE phase shifter with the same waveguide cross-sectional area and device parameters. The phase shifter modulation efficiency is 1.02 V.cm. The MZM transfer characteristics are determined for the dual-arm push–pull driving scheme, and a traveling-wave electrode structure is employed to enhance the device bandwidth. A 3-dB bandwidth of 74 GHz is obtained at 2.5-V reverse bias. The modulator high-speed characteristics are studied for different data rates over single-mode fiber transmission. A 30-km fiber transmission with an open eye at 160 Gbps with 2-V peak-to-peak drive is obtained with an extinction ratio of 2.3 dB and bit-error-rate (BER) of ∼2.77 × 10 − 06. The effect of fiber dispersion on the BER shows dispersion tolerance from 0 to −1.73 ps . nm − 1 . km − 1 for 30-km fiber transmission below the hard-decision forward error correction threshold at 100-Gbps operation.
We present the effect of losses and nonlinearity on the behavior of modulation instability (MI) in thulium-doped fiber amplifier (TDFA) operational in S and near-C bands. Based on a derived analytical model, the relative change in maximum integrated gain at the respective perturbation frequency was observed and compared with lossless TDFAs. At an estimated small-signal attenuation of 0.36 (corresponding to small-signal attenuation coefficient α = 0.01 / m), a frequency shift of 1.44 THz with a reduction in integrated gain of 45 dB was obtained for an input signal power of 250 mW. For the same set of parameters, the effect of nonlinear and loss factor was calculated and compared with present day state-of-the-art erbium-doped fiber amplifiers. The analysis helped in the selection of optimum values for small-signal gain coefficient (g0 = 0.21 / m) and TDFA length (L = 100 m) to maximize the integrated gain of the perturbations for different input signal powers. The special case pertaining to nonideal conditions with respect to the large amplitude of input perturbations was solved numerically. Dipole relaxation time was estimated (450 fs) from the results and compared with the theoretically calculated value (318 fs) for TDFAs. The results obtained can be used constructively in the selection of optimum parameters and perturbation frequency value for the design of TDFA lasers in which MI acts as an active saturable absorber.
The mode, loss, and dispersion characteristics of a buried strip waveguide have been calculated for coarse wavelength division multiplexing wavelengths. Process simulation has been used to form the graded-index core by germanium implantation in silicon. Quasivectorial finite-difference method has been used to calculate the number of propagating modes, effective indices, material absorption, mode confinement, and the dispersion parameters. The scattering loss has been determined from the Payne–Lacey model. The zero dispersion for higher-order modes occurs in the O-band, which is suitable for short-reach multimodal applications. The usable waveguide length and number of modes have been characterized and are limited by the mode with highest propagation loss/dispersion and lowest mode confinement, respectively.
The search for new doping material in S and near-C band communication window could prove as a boon for data traffic to which Thulium fits the slot optimally. The paper presents the performance estimation of Thulium doped fiber amplifiers (TDFAs) through ion-ion interaction mechanism (IM) effects consisting of homogeneous up-conversion (HUC) and pair induced quenching (PIQ) processes, also called clustering effect. Typically, the IM effects were studied as detrimental effect on signal gain, but in this work it was shown that they can also act as aiding mechanisms for early population inversion and lasing conditions at relatively lower pump power. Design parameters of TDFA were studied by carrying out the computational simulations on MatLab and OptiSystem 16 based on the mathematical model. The obtained results infers about the constructive nature of the IM effects. The optimum performance estimation parameters TDFA length was determined as 100 m with dopant area of 1μm. Due to the interplay of IM effect the optimum pump power was determined as 450 mW and signal gain of 20.32 dB instead of 650 mW when no IM effect was considered. The signal wavelength for minimum noise figure was calculated as 1460 nm. The work presented may be considered as a step closer to S and near-C band fiber optic communication systems.
In this paper, mathematical model and simulations displaying the phenomenon of modal instability (MI) in 1050 nm pumped heavily doped Thulium (Tm3+) fiber amplifier is presented. Pulse splitting effect through MI with variation in chirp parameter and non-linear fiber length was modeled and simulated. The pulses considered were sech, Gaussian, and super-Gaussian type. Model was computationally solved on MatLab and the results were verified by incorporating similar conditions and parameters on OptiSystem 16 simulation platform. Results concludes the optimum non linear length (LNL) and the chirp parameter (C = 12) which has to be taken so as to obtain continues time domain pulse train as well as linearly spaced frequency combs. The repetition rate of 500 MHz for 4 ps pulse at 1460 nm with peak sub-pulse energy of 8 nJ was obtained and has been reported to the first time (under MI mechanism) to the authors' knowledge. Optimum TDFA length was concluded as 375 m at which MI phenomenon was triggered.
This paper analyzes a germanium-doped silicon traveling wave Mach-Zehnder modulator (TWMZM) for high speed operation at 1550 nm wavelength. Single arm drive modulator performance using non-return-to-zero on-off keying (NRZ-OOK) driving scheme has been investigated. The phase-loss characteristics of the graded-index silicon-germanium PN phase shifter have been determined numerically. The traveling wave electrode has been designed for 1.5 mm long phase shifter. The 3 dB modulation bandwidth of the designed TWMZM is calculated to be 31 GHz at -2 V and an error-free operation of 59 Gbps has been obtained for 2 V peak-to-peak drive voltage with an extinction of ~6 dB.
In this paper, a grating assisted MDM-PDM hybrid (de)multiplexer based on the silicon-on-insulator (SOI) platform has been proposed and analyzed using coupled mode theory with effective index method (EIM). The proposed device consists of a multimode wide waveguide and five single mode narrow waveguides. The quasi- TE/TM modes of the wide waveguide are phase matched with the respective contra-propagating fundamental quasi-TE/TM modes of the single mode narrow waveguides. The phase matching conditions are satisfied by using different period gratings, which are surface corrugated on the wide waveguide. The proposed device structure exhibits good crosstalk, insertion loss, and return loss values.
Multiple transition levels covering S and near-C bands (1460 to 1565 nm) of thulium-doped fiber amplifiers (TDFAs) allows them as potential alternative to erbium-doped fiber amplifiers (EDFAs) hence getting employed in dense wavelength division multiplexing (DWDM) in optical fiber communication. We present overmodulation gain dynamics (OGD) on TDFAs using the EDFA’s Bononi and Rusch (1998) model. The paper portrays overmodulation of digital optical communication signal, of which amplitude was modulated by low-frequency (∼100 kHz), for line-surveillance and management control of optical information in DWDM TDFA systems. Signal-to-signal and signal-to-amplified spontaneous emission (ASE) transfer functions were derived to predict the system’s performance under high input signal power conditions and its variation on input modulation indices. Difference of −10.3 dB (0.093 W) in output signal gain was observed at 1490 nm signal wavelength with ASE. Output modulation index of 15% having high pass signal characteristics as of a lead compensator was observed with the applied signal frequency sweep. Overmodulation sensitivity for various levels of input signal power demonstrates undesirable 30% increment in the output modulation index at 8 dBm and 1490 nm signal wavelength, respectively, at corner frequency.
Paper presents Opto-Mechanical intrusion sensor fence with FBGs attached to mechanical accelerometers and strain
sensors, optimized on SolidWorks 2013 for desired frequency to 35 Hz, picking up accelerations/ strains and its
deployment for perimeter security. The accelerometer structure consists of inertial mass supported by an L-shaped
modified cantilever beam having non-uniform cross section area connected to base by a thin neck element which acts as
strain concentrated centre hence an optimum zone for FBG sensors placement. Bragg wavelength shifts were obtained
on Optigrating software for the obtained strain values on mechanical assembly of fence. CFD wind analysis is performed
on the assembly to obtain the spot for accelerometer’s placement to avoid false alarms up to wind velocities of 20 m/s.
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