Experiment on Channel-switching Add/Drop Multiplexer in a Multi-channel WDM System

A channel-switching optical add/drop multiplexer with tunable fiber Bragg grating tuned by equivalent-intensity cantilever beam is proposed and experimentally demonstrated. The no-chirped linearly tuning range is about 6.1 nm, which enables it to add or drop 8 channels with channel spacing 100 GHz. It is used in a 4-channel WDM system to test its capability. The adjacent channel isolation is not less than 24 dB. 4-channel lasers modulated by 1.2 Gb/s Non-Return-to-Zero format (NRZ), \{Return-to-Zero\} format (RZ) and 2.5 GHz analogue signals are dropped by the device after transmission over 100 km and the results are given.     

Design and analysis of two-dimensional photonic crystals channel filter

A novel three-port channel add/drop filter consisting of two waveguides and two cavities is proposed. One is used for a resonant tunneling-based channel add/drop operation from the bus waveguide to the add/drop waveguide, while the other is used to realize the wavelength-selective reflection feedback in the bus waveguide. By means of coupled mode theory in time, the conditions to achieve 100% add efficiency are derived thoroughly. Based on these theoretical analysis, the channel add filter and some other multi-channel filters are designed in two-dimensional photonic crystals (2D PCs) with square lattice of dielectric rods in air. The numerical results by using the finite-difference time-domain (FDTD) method demonstrate almost complete channel add/drop tunneling at resonance via the three-port systems.     

A 32-channel 100 GHz wavelength division multiplexer by interleaving two silicon arrayed waveguide gratings

A 32-channel wavelength division multiplexer with 100 GHz spacing is designed and fabricated by interleaving two silicon arrayed waveguide gratings (AWGs). It has a parallel structure consisting of two silicon 16-channel AWGs with 200 GHz spacing and a Mach-Zehnder interferometer (MZI) with 200 GHz free spectral range. The 16 channels of one silicon AWG are interleaved with those of the other AWG in spectrum, but with an identical spacing of 200 GHz. For the composed wavelength division multiplexer, the experiment results reveal 32 wavelength channels in C-band, a wavelength spacing of 100 GHz, and a channel crosstalk lower than -15 dB.     

4 × 25 GHz uni-traveling carrier photodiode arrays monolithic with In P-based AWG demultiplexers using the selective area growth technique

We use the selective area growth(SAG) technique to monolithically integrate In P-based 4-channel arrayed waveguide gratings(AWGs) with uni-traveling carrier photodiode arrays at the O-band. Two kinds of channel spacing demultiplexers of 20 nm and 800 GHz are adopted for potential 100 Gbps coarse wavelength division multiplexing and local area network wavelength division multiplexing systems, with an evanescent coupling plan to facilitate the SAG technique into device fabrication. The monolithic chips in both channel spacings exhibit uniform bandwidths over 25 GHz and a photodiode responsivity of 0.81 A/W for each channel, in agreement with the simulated quantum efficiency of 80%. Cross talk levels are below-20 d B for both channel spacing chips.     

Polarization Insensitive Ion-Exchanged Arrayed-Waveguide Grating Multiplexers in Glass

Wavelength multiplexers based on the arrayed-waveguide grating (AWG) principle are fabricated with ion-exchanged waveguides in glass for 1550 nm. The insertion loss is 6 and 4 dB with a cross talk of 15 and 20 dB for 8-channel 50 GHz and 4-channel 100 GHz devices, respectively. The AWGs are almost polarization insensitive because the refractive index profile of the waveguides is nearly concentric and the waveguides are diffused into stress-free glass substrates. The transverse electric transverse magnetic (TETM) shift of the wavelength response is only 0.02 nm (2.5GHz) for an 8-channel 50 GHz AWG. The temperature sensitivity is 1.4 GHz C.     

Investigation of wavelength division multiplexing ring network topology to enhance the system capacity

In this paper, we have investigated the wavelength division multiplexed (WDM) system using ring network topology. This network is used to increase the capacity with eight optical add/drop multiplexers (OADMs) by using dispersion compensating fiber and semiconductor optical amplifier (SOA) to achieve a distance up to 1600 km. It is observed that network shows the acceptable results at 15 Gbps data rate with 100 GHz channel spacing. The OADM nodes are also varied to investigate the network performance in the term of BER and Q-factor.     

基于光子晶体的三端口分插复用器

提出了一种新的基于对称全反射壁的光子晶体分插复用器,与其他类型的光子晶体复用器相比,无需对介质柱进行复杂的调节即可实现100%上/下载,方便实际制造.提出的理论模型与基于二维时域有限差分(FDTD)法的数值实验相当吻合,显示出这种器件具有优良的上/下载性能.     

基于多模干涉耦合器的阵列波导光栅设计研究

研究了基于多模干涉(MMI)耦合器的阵列波导光栅(AWG).通过模式传输分析方法,分析了多模干涉耦合器及阵列波导;并给出在硅基底上的二氧化硅波导上四通道100 GHz-AWG普通结构和紧凑结构的设计结果.     

Dynamic-channel-equalizer using in-line channel power monitor and electronic variable optical attenuator

We propose and demonstrate a polarization-insensitive dynamic-channel-equalizer (DCE) for compensating erbium-doped-fiber-amplifier (EDFA) amplified signals after dynamic optical add/drop. The DCE can be monolithically integrated on silicon-on-insulator (SOI) platform and is potentially low cost and compact. The DCE can compensate complicated gain slope shape, which may be generated in cascaded EDFAs or deliberate channel add/drop, based on individual channel equalization. Fifteen-decibel receiver sensitivity improvement at 10 Gb/s bit-error-rate (BER) measurement of 10⁻⁹ was achieved in the compensated channel by removing cross-gain-modulation generated by neighboring channel add/drop.     

Analysis and Compensation of Polarization Mode Dispersion in Single Channel,WDM and 32-channel DWDM Fiber Optic System

One of the most serious impairments which limit the data rate in long distance and high speed transmission systems is Polarization Mode Dispersion (PMD). PMD is negligible when data rate is low (i.e. in Mb/s or few Gb/s) but it will affect the high data rate transmission systems (10^s of Gb/s, Tb/s etc.), as the pulse broadening severely distorts the signal during transmission. Thus it is necessary to compensate the PMD in both single and multichannel fiber optic transmission system due to increase in the traffic demand. This paper deals with a Deterministic Differential Group Delay (DDGD) method to compensate the PMD in single channel, by delaying the fast polarization component and wavelength independent Polarization Maintaining Fiber (PMF) method for multichannel PMD compensation. The DDGD method efficiently compensates the PMD upto 45 ps in single channel 40 Gb/s transmission systems. The State of Polarization (SOP) before and after the PMD and after compensation is analyzed by means of Poincare Sphere. By using PM Fiber method, simultaneous and effective compensation of PMD in multichannel system is achieved. Here, the simulation has been carried out for 4-channel (40 Gb/s), 8-channel (80 Gb/s), 16-channel (160 Gb/s) WDM systems and 32-channel (320 Gb/s) DWDM fiber optic system with each channel having the data rate of 10 Gb/s and the results of PMD compensation for all the channels are analyzed. It is seen that the PMD compensation is achieved upto 90 ps 87 ps, 84 ps and 80 ps in 4-channel, 8-channel, 16-channel WDM systems and 32-channel DWDM systems respectively. As very high data rate of 100 Gb/s and above are in practice now-a-days, compensation of PMD is enhanced to 1.6 Tb/s (16 × 100 Gb/s) data rate for 16-channel by PMF method and 74 ps of broadening is compensated effectively.     

Impact of the all-optical gain-clamping technique on the transience characteristics of cascaded discrete fiber Raman amplifiers

We theoretically analyse the dynamic response of amplifier cascades involving combinations of unclamped and gain-clamped discrete fiber Raman amplifiers (DFRAs) in the worst possible case of power transients. We consider a 64-channel system in which all of the channels except one (i.e. the surviving channel) are modulated to simulate channel add/drop. We vary the number and the position of the gain-clamped DFRAs in the cascade to determine whether a cascade in which only a few amplifiers are gain-clamped (referred to as a mixed cascade) can be as effective as a cascade comprising all gain-clamped amplifiers for controlling the power transients within tolerable limits (for example, 1 dB). We take into account the location of the surviving channel and the operational regime of the amplifiers. Our results show that the location of the gain-clamped DFRAs in a mixed cascade affects the transient characteristics and that it is possible to control the transients within tolerable limits.     

Tunable add/drop channel coupler based on an acousto-optic tunable filter and a tapered fiber

We report a tunable add/drop channel coupler based on an acousto-optic tunable filter and a tapered fiber. The coupling efficiency and central wavelength of the add/drop channel coupler are tunable by simply tuning the power and frequency of the driving radio frequency signal. Further possible improvements on the configuration are also discussed.     

Tunable Optical Add/Drop Multiplexers Using Cascaded Mach Zehnder Coupler

A tunable add/drop filter based on Cascaded Mach Zehnder (CMZ) coupler using SiO₂/silicon oxinitride (SiON) is presented with its mathematical model. The increase of filtered width (i.e., free spectral response) and lowering of crosstalk for this filter are optimized using its mathematical model with truncated binomial coupler distribution. The number of wavelength channels with 100 GHz (0.8 nm) channel spacing for 5-stage (M = 9, r = 2) truncated binomial CMZ filter with index contrast ∼5% at -20 dB crosstalk and the bending loss of 0.1 dB per MZ section are obtained as ∼37 (free spectral range of 31 nm). It is seen that if during the fabrication process, waveguide core width w is increased or decreased by 0.1 μm (in percentage terms ∼±6.6%), the crosstalk is slightly increased by ∼7%. Thermal tuning for wavelength channels is achieved by thin film heater with low power thermooptic delay line structure which reduces the heating power by ∼1.58 times in comparison to the conventional structure.     

An all-fiber optical temporal differentiator for wavelength-division-multiplexed system based on twin-core fiber

A multichannel optical temporal differentiator implemented based on twin-core fiber for wavelength-division-multiplexed (WDM) system is proposed. The key feature of the proposed temporal differentiator is that WDM signals at nominal central frequencies can be simultaneously processed. As an example, a 16-channel WDM first-order optical temporal differentiator is designed and numerically proved, the central frequencies are located at the nominal central frequencies which are suggested in IUT-T G.692 recommendation. The designed device is practically feasible and offer the operation bandwidth of 33.5 GHz and the channel spacing of 100 GHz. Furthermore, the channel numbers can be easily expand to 32, 64, even 128. Performance analysis results show a good accuracy calculating the first-order time differentiation of the standard WDM signals centered at the nominal central frequencies with high energetic efficiency.     

Tunable Optical Add/Drop Multiplexers Using Cascaded Mach Zehnder Coupler

Abstract

A tunable add/drop filter based on Cascaded Mach Zehnder (CMZ) coupler using SiO₂/silicon oxinitride (SiON) is presented with its mathematical model. The increase of filtered width (i.e., free spectral response) and lowering of crosstalk for this filter are optimized using its mathematical model with truncated binomial coupler distribution. The number of wavelength channels with 100 GHz (0.8 nm) channel spacing for 5-stage (M = 9, r = 2) truncated binomial CMZ filter with index contrast ～5% at ?20 dB crosstalk and the bending loss of 0.1 dB per MZ section are obtained as ～37 (free spectral range of 31 nm). It is seen that if during the fabrication process, waveguide core width w is increased or decreased by 0.1 μm (in percentage terms ～±6.6%), the crosstalk is slightly increased by ～7%. Thermal tuning for wavelength channels is achieved by thin film heater with low power thermooptic delay line structure which reduces the heating power by ～1.58 times in comparison to the conventional structure.     

利用光纤光栅对实现双波长增益控制掺铒光纤放大器特性的实验研究

控制激光的弛豫振荡和空间烧孔现象的存在 ,对全光增益控制掺铒光纤放大器 (EDFA)的性能产生劣化影响。采用一种新颖简单的利用两对光纤光栅对形成谐振腔结构 ,实现双波长增益控制掺铒光纤放大器。由两个不同波长的激光共同承担增益控制的任务 ,降低了控制激光引起的空间烧孔现象和瞬态输出变化。在动态工作条件下 ,双波长激光增益控制掺铒光纤放大器显示出优越的特性 ,适用范围扩展为普通单波长增益控制掺铒光纤放大器的两倍 ,能够适应 0～ 43kHz的上下载频率。     

Optimization of a 2D photonic crystal add/drop multiplexer based on contra-directional coupling

We present a highly integrated add/drop multiplexer, where the contra-directional coupling is realized by phase matching two photonic crystal waveguides. The device band structure, the corresponding transmission and drop spectra, and the coupling length are carefully analysed. Different device configurations are discussed and by tailoring the coupling factor, we optimize the frequency response of the filter, obtaining a -sized channel selector, characterized by a very high drop efficiency.     

Soliton pulses generation and filtering using micro-ring resonators for DWDM-based soliton communication

We propose a new optical system that can be used to form the multi-soliton pulses within the micro-ring resonators. The system consists of two micro-ring resonators and an add/drop multiplexer that can be integrated into a single system. The large bandwidth signal is generated by using a soliton pulse propagating in a Kerr-type nonlinear medium. The tuned soliton pulses in either spatial or temporal modes are obtained by using the add/drop multiplexer. Results obtained have shown that the multi-soliton pulses can be localized coherently within the micro-ring waveguide. This is shown that the generation of the multi-soliton pulses within the micro-ring resonator is achieved, which is available for long-distance communication with dense wavelength division multiplexing (DWDM). The significant increase in channel number and spacing are obtained, whereas the large free spectrum range (FSR) of 600 pm is achieved.     

Hybrid Integration of 1 × 12 Metal-Semiconductor-Metal Photodetector and Polyimide Waveguide Array

We report here a demonstration of hybrid integration of a 1 × 12 metal-semiconductor-metal (MSM) photodetector array and polyimide channel waveguides via 45° total-internal-reflection (TIR) micro-couplers. The two-layer polyimide waveguide array was constructed using Ultradel 9120D for the core and Ultradel 9020 for the lower cladding layer. The coupling loss and propagation loss of the waveguide are 0.2dB and 0.21 dB/cm, respectively. The cross talk of the adjacent channels is -32 dB. The MSM photodetector array was fabricated on a semi-insulated GaAs wafer. The photodetectors are integrated to operate in the conventional vertical illumination mode. We measured the external quantum-efficiency and 3 dB bandwidth of the integrated MSM photodetectors at 0.4 A/W and 2.648 GHz, respectively. The aggregate 3 dB bandwidth of the 12-channel integrated system is 32 GHz.     

Quantum key distribution using the localized soliton pulses via a wavelength router in the optical network

We propose a new system of a continuous variable quantum key distribution via a wavelength router in the optical networks. A large bandwidth signal is generated by a soliton pulse propagating within the micro ring resonator, which is allowed to form the continuous wavelength with large tunable channel capacity. There are two forms of localized soliton pulses proposed. Firstly, the required information is transmitted via the localized temporal soliton pulse. Secondly, the continuous variable quantum key distribution is formed by using the localized spatial soliton pulse via a quantum router and networks, which is formed by using and optical add/drop multiplexer incorporating in the network. The localized soliton pulses are available for add/drop signals to/from the optical network, where the high security and capacity information can be performed.