Fabrication, polarisation and wavelength insensitive optical switch/attenuator based on adiabatic mode multiplexer

Experimental results of an adiabatic mode multiplexer (AMM) based novel 2/spl times/2 optical switch/variable optical attenuator that consists of a symmetric Y-branch interferometer (mode converter) and adiabatic mode multiplexer/demultiplexer pair are presented. It is shown that both normally cross and bar designs have identical optical performance. Extinction ratio without thermal activation is wavelength independent. Over C-band the attenuation at -20 dB varies by less than 0.3 dB and polarisation dependent loss is less than 1 dB. It is proved that the mode converter plays a dominant role in polarisation state sensitivity at high attenuation values and can be optimised by varying interferometer arm length. Since an AMM-based switch does not require process optimisation steps it can be fabricated within a process optimised for other optical devices.     

Uni- and bidirectional 4λ×560 Mb/s transmissionsystems using WDM devices based on wavelength-selective fusedsingle-mode fiber couplers

Four-wavelength-channel wavelength-division multiplexing (WDM) lab transmission system experiments with buried heterostructure (BH) lasers at 1200-, 1240-, 1280-, and 1320-nm wavelengths, all-fiber WDM devices, and 20-km single-mode link fiber at a 560-Mb/s bit rate demonstrated that unidirectional and bidirectional WDM transmission systems could be operated successfully by using all-fiber 4λ multiplexing, 4λ demultiplexing, or 4λ multiplexing/demultiplexing devices with a low insertion loss per wavelength channel (2.1-4.7 dB), enough optical far-end crosstalk attenuation (18-37 dB), and high optical near-end crosstalk attenuation (43-49 dB). It is concluded that the four-wavelength-channel WDM lab transmission system at 560 Mb/s mainly used as a test bed is not representative of future unidirectional trunk WDM systems. Such systems favor distributed feedback (DFB) lasers in the 1500-1560-nm wavelength range where fiber attenuation is lower than in the 1200-1320 nm wavelength range and where 1500-nm DFB lasers with a smaller linewidth do not limit the repeater distance as much because of mode partition noise     

Variable optical attenuator based on a cutoff modulator withtapered waveguides in polymers

A variable optical attenuator was demonstrated by using a thermooptic cutoff modulator in polymers. It combined horizontally and vertically tapered waveguide structures to improve both the attenuation efficiency and the fiber coupling. The rib height of the waveguides in the input and output region was chosen to achieve minimum fiber coupling loss. For the waveguide in the active region with the electrodes, the rib height was reduced and the width was tapered in order to enhance the attenuation performance by weakening the mode confinement. The two waveguides with different rib heights were connected smoothly by employing a vertical taper, which was realized by utilizing two steps of reactive ion etching with a shadow mask. Then a fiber coupler built in a silicon block was attached directly to the output end of the device. A fraction of the main attenuator output was tapped and fed back to the electrical driver to achieve constant output regardless of variations in input light power and polarization. The measured insertion loss of the attenuator was 2.5 dB at 1550 nm. The dynamic range was more than 20 dB with an electrical power consumption of 160 mW. And the optical response time was faster than 1.5 ms. The effect of polarization on the attenuation was reduced to 0.1 dB by employing a continuous electronic feedback control. The wavelength uniformity was as small as 0.3 dB over the range from 1530 to 1560 nm. Finally, the attenuator was successfully used to regulate channel powers within 0.4 dB in a wavelength division multiplexed transmission system     

基于SOI的16通道VMUX器件单片集成

本文制作了基于绝缘体上硅(SOI)材料的16通道的光功率可调波分复用器(VMUX),并且采用了脊形波导结构。该器件是由信道间隔100GHz的阵列波导光栅(AWG)及电光型可调光衰减器(VOA)组成,该VOA采用了侧向p-i-n二极管结构。该VMUX器件的插入损耗为9.1dB,串扰为10dB。VOA在衰减量为20dB时的注入电流为60.74mA。器件的整体尺寸为2.9×1mm2。该VMUX器件具备优异的16通道波分复用及光功率均衡的性能。     

Polarization-Dependent Gain in SOA-Based Optical Multistage Interconnection Networks

The small polarization dependence (< 1 dB) of optical components becomes significant in optical multistage interconnection networks. The cumulative effect can ultimately limit physical layer scalability by changing the maximum number of internal nodes that optical packets can traverse error free. It is shown that for nodes based on commercial semiconductor optical amplifier (SOA) switches with polarization-dependent gains of less than 0.35 dB, the maximum number of cascaded nodes changes by as much as 20 nodes, depending on both the packet wavelength and its state of polarization. This deviation in the number of nodes could correspond to a 100-fold decrease in the number of interconnected ports of an optical interconnection network such as the data vortex. This dramatic effect is explained in terms of optical signal-to-noise ratio degradation due to accumulated amplified spontaneous emission noise originating from the SOA device in the node     

A computer controlled narrow bandpass optical tunable filter usinga Fourier diffraction grating in the range of 1.3-1.55 μm

A novel tunable filter using a Fourier grating is studied and discussed. It consists of a Fourier grating, a collimator lens, single-mode fibers, and a computer controlled rotary actuator. It has very low polarization dependence of less than 0.3 dB, an insertion loss of less than 3 dB, and a narrow bandwidth of 1.5 nm. Wavelength selection was realized by rotating the grating, which was controlled by a computer. The device is able to select the light at the desired wavelength from more than 100 WDM optical data streams with 2 nm spacing in the range of 1.3-1.55 μm     

Wavelength add-drop switching using tilting micromirrors

This paper describes a single-mode optical fiber switch which routes individual signals into and out of a wavelength multiplexed data stream without interrupting the remaining channels. The switch uses free-space optical wavelength multiplexing and a column of micromechanical tilt-mirrors to switch 16 channels at 200 GHz spacing from 1531 to 1556 nm. The electrostatically actuated tilt mirrors use an 80 V peak-to-peak 300 KHz sinusoidal drive signal to switch between ±10° with a 20 μs response. The total fiber-to-fiber insertion loss for the packaged switch is 5 dB for the passed signals and 8 dB for added and dropped signals, with 0.2 dB polarization dependence. Switching contrast was 30 dB or more for all 16 channels and all input and output states. We demonstrate operation by switching 622 Mb/s data on eight wavelength channels between the two input and output ports with negligible eye closure     

Polarization independent, integrated optical, acoustically tunablewavelength filters/switches with tapered acoustical directional coupler

Enhanced sidelobe suppression of the filter characteristics of tunable acousto-optical mode converters in LiNbO₃ has been achieved using for the first time tapered acoustical directional couplers. A sidelobe suppression of more than 15.5 dB could be demonstrated in a single stage device. By combining the mode converter with two integrated optical polarization splitters a polarization independent filter/wavelength selective switch has been fabricated with less than 3 dB intrinsic insertion loss, a polarization dependence of less than 1 dB, and a sidelobe suppression exceeding 14 dB     

Noise figure of saturated 1310-nm polarization insensitive multiple-quantum-well optical amplifiers

The noise figure degradation due to saturation by amplified spontaneous emission of high-gain 1310-nm polarization insensitive multiple-quantum-well optical amplifiers has been investigated systematically by studying amplifiers of different lengths. It is found that the intrinsic noise figure of 4 dB of a device with 20-dB single-pass gain is degraded to about 5 dB for a device having 36-dB single-pass gain. This degradation in noise figure is very modest, compared to results reported earlier for semiconductor optical amplifiers with bulk-gain media, illustrating the benefits of using a quantum-well gain medium in semiconductor optical amplifiers.     

Polarization selection and sensitivity of external cavityvertical-cavity surface-emitting laser diodes

A theoretical analysis has been undertaken of the polarization properties of birefringent vertical-cavity surface-emitting lasers (VCSELs) subject to weak optical feedback in an external cavity configuration. Attention is focussed on the competition between two orthogonal polarizations of the fundamental (LP₀₁) transverse mode of the device. It is shown that control of the emission polarization can be exercised even for very small external reflectivities (10^-4%) by appropriate choice of optical feedback delays. The polarization selectivity is shown to be dependent upon the strength of optical feedback. Polarization is also shown to be highly sensitive to small changes in optical feedback delay. Thermally induced wavelength shift is shown to affect polarization behaviour     

Bit error rate performance for wavelength conversion at 20 Gbit/s

Wavelength conversion at 20 Gbit/s, to longer and shorter wavelength, is achieved using cross gain-compression in a semiconductor optical amplifier. Quantitative performance is assessed from the bit error rate data at 20 Gbit/s, for the first time for any wavelength conversion scheme. For conversion of 10 nm to a shorter wavelength, the penalty is 2.6 dB     

5-Gb/s XOR optical gate based on cross-polarization modulation insemiconductor optical amplifiers

We demonstrate a new design for a XOR optical gate operating in the GHz regime using the cross-polarization modulation effect in a semiconductor optical amplifier. Dynamic and optically controlled polarization rotation in the devices is used to control the output power of the device. Static extinction ratio of the order of 20 dB can be obtained. Bit rate doubling at rate of 1.2 and 2.5 Gb/s have been demonstrated     

Widely tunable polarization-independent all-optical wavelengthconverter using a semiconductor optical amplifier

We report a polarization-independent widely tunable four-wave mixing wavelength converter using polarization diversity and broad-band orthogonal pumps in a single semiconductor optical amplifier. The conversion efficiency is nearly constant (less than 3-dB variation) over a 36-nm range with less than 0.34 dB polarization sensitivity. The power penalty at 10^-9 bit error rate for a 10-Gb/s signal is less than 0.9 dB     

光正交频分复用信号垂直泵浦全光波长变换研究

理论分析了一种基于垂直泵浦结构光半导体放大器(SOA)的偏振无关光正交频分复用(OOFDM)信号波长变换模型,实验证明了基于SOA-四波混频(FWM)的OOFDM信号波长变换的可行性,观测到OOFDM在SOA引入噪声而带来的信号劣化。实验成功实现了2.5Gbit/s光OFDM信号的波长变换,其误码率为1×10-3的接收机功率代价可以忽略,其极化敏感度小于3dB。     

High-Speed Mode-Locked Quantum-Dot Lasers and Optical Amplifiers

Recent results on GaAs-based high-speed mode-locked quantum-dot (QD) lasers and optical amplifiers with an operation wavelength centered at 1290 nm are reviewed and their complex dependence on device and operating parameters is discussed on the basis of experimental data obtained with integrated fiber-based QD device modules. Hybrid and passive mode locking of QD lasers with repetition frequencies between 5 and 80 GHz, sub-ps pulse widths, ultralow timing jitter down to 190 fs, high output peak power beyond 1 W, and suppression of Q-switching are reported, showing the large potential of this class of devices for O-band optical fiber applications. Results on cw and dynamical characterization of QD semiconductor optical amplifiers (SOAs) are presented. QD amplifiers exhibit a close-to-ideal noise figure of 4 dB and demonstrate multiwavelength amplification of three coarse wavelength division multiplexing (CWDM) wavelengths simultaneously. Modelling of QD polarization dependence shows that it should be possible to achieve polarization insensitive SOAs using vertically coupled QD stacks. Amplification of ultrafast 80 GHz optical combs and bit-error-free data signal amplification at 40 Gb/s with QD SOAs show the potential for their application in future 100 Gb Ethernet networks.     

2$,times,$ 2 InP Optical Switching Matrix Based on Carrier-Induced Effects for 1.55-$mu$m Applications

This letter demonstrates a 2times2 low optical crosstalk and low power consumption switching matrix device based on carrier-induced effects on an InP substrate. The matrix device comprises two digital optical switches (DOSs) with a wide multimode Y-junction associated with a sinusoidal passive integrated optical circuit with an optimized X-crossing. The passive structure was designed using a two-dimensional beam propagation method (BPM) and the entire InP-InGaAsP-InP DOS was designed using a semivectorial three-dimensional BPM. The fabricated 2times2 InP switching matrix heterostructure with lambdag=1.3 mum exhibits optical crosstalk as low as -30.5 dB for drive current of 52 mA at 1.55-mum wavelength. Maximum crosstalk change of 4 dB is measured under optical polarization variation.     

Four-channel tunable optical notch filter using InGaAsP/InPreflection gratings

A new tunable optical notch filter for use in wavelength division multiplexing (WDM) transmission system has been fabricated in the InGaAsP/InP material system for use at 1.55 μm. The device uses tunable reflection gratings in a waveguide to control the channels (4 in this case). Crosstalk levels between 9 dB and 20 dB have been measured, depending on the channel. System experiments at 150 Mb/s show less than 1 dB crosstalk penalty at 10^-9 bit-error rate     

A 1×8 InP/InGaAsP optical matrix switch with low insertionloss and high crosstalk suppression

We present a current controlled passive 1×8 InP/InGaAsP optical matrix switch for routing applications at wavelength 1.55 μm. It is realized in a tree architecture and has integrated tapers for efficient fiber butt coupling. An AR coated device has average fiber-chip-fiber insertion losses of 6.8 and 6.3 dB for TE and TM polarizations, respectively. The homogeneity of the eight outputs is better than 0.3 dB in each polarization state. The crosstalk suppression is better than 19 dB. The performance of the device indicates that large InP-based switching matrices can be realized     

MOEMS variable optical attenuator with improved dynamic characteristics based on robust design

The design and preliminary data of a novel microoptoelectromechanical systems variable optical attenuator (VOA) driven by a pair of V-beam electrothermal actuators is described. This VOA deploys a face-to-face arranged pair of 45/spl deg/ tilted mirrors in front of two coaxially aligned lensed fibers to form retro-reflection planar light path for attenuation. The initial insertion loss is 0.7 dB at 1550 nm and the maximum dynamic range of attenuation is 50 dB, respectively. The polarization-dependent loss is measured as 0.15 dB at 20-dB attenuation. The dynamic attenuation deviation is less than /spl plusmn/0.36 dB at 20-dB attenuation with respect to 20-G shock of periodical mechanical vibration at 1 K Hz, in which it complies with requirements of the Telcordia GR1221 regulations.     

Superimposed phase gratings in planar optical waveguides forwavelength demultiplexing applications

A theoretical analysis of superimposed phase gratings in planar optical waveguides for wavelength demultiplexing applications is developed. Using coupled-mode theory, it is shown that the coupling between the gratings affects diffraction characteristics for output beams of close angular or wavelength separation. Nevertheless, taking into account the coupling effects and adjusting critical parameters, high-performance devices are found to be achievable in carefully designed structures. The authors predict that wavelength demultiplexers having efficiencies larger than 95%, angular and wavelength separation smaller than 0.2° and 20 Å, respectively, and crosstalk attenuation lower than -40 dB are possible