Multichannel frequency-selective switch employing anarrayed-waveguide grating multiplexer with fold-back optical paths

The optimized configuration of an N-channel frequency-selective 2×2 switch based on an arrayed-waveguide grating (AWG) (2N+1)×(2N+1) multiplexer is proposed that offers significant crosstalk reduction and loss-imbalance equalization. The optimization is achieved by employing fold-back optical paths instead of loop-back paths. A switch constructed with a silica-based AWG 16×16 multiplexer demonstrates coherent crosstalk of less than -30 dB in the transmitting frequency-division-multiplexed (FDM) channels; the gain in optimization is more than 15 dB. The largest loss-difference among the seven FDM channels is simultaneously reduced from 4.5 dB to 1.6 dB. These improvements will extend the cascadable number of nodes in all-optical FDM networks     

Loss-imbalance equalization in arrayed waveguide-grating (AWG)multiplexer cascades

How to connect arrayed-waveguide-grating (AWG) multiplexers in cascade is discussed with the goal of equalizing the loss imbalance among frequency-division-multiplexed (FDM) channels. This paper proposes to average the FDM-channel loss over the cascaded multiplexers by shifting port connections between each adjacent multiplexer. A simulation predicts that, in a cascade of M periodic N×N multiplexers, shifting the connections by N/M reduces the loss imbalance from MΔα to Δα/M where Δα [dB] denotes the loss imbalance per multiplexer. This improvement will extend the cascadable node number in all-optical FDM networks. The prediction is confirmed experimentally in an optical add-drop filter (M=2) constructed with a silica-based AWG 16×16 multiplexer; the largest loss difference among 15 FDM channels is reduced from 5.0 dB to 1.5 dB. This paper also reports that imperfect multiplexer periodicity due to waveguide dispersion restricts the equalizable frequency bandwidth to less than several free spectral ranges (FSR's)     

FDM-channel selection filter using arrayed-waveguide gratingmultiplexer with input and output switches

A novel configuration is reported for a tunable channel-selection filter that employs an arrayed-waveguide grating (AWG) multiplexer and optical switches. The filter requires only 2(√N-1) 1×2 switch elements to select one of N frequency-division-multiplexed (FDM) channels. A filter for 100 GHz-spaced 16 FDM channels is demonstrated with an AWG 16×16 multiplexer and six 1×2 switches     

Factors affecting the design of optical FDM informationdistribution systems

Major factors affecting optical frequency division multiplexing (FDM) distribution system design are described. In particular, multiplexing/distribution configuration and channel-selection methods are compared from the viewpoint of the number of channels, the number of subscribers, and the transmission distance. The applicability of optical fiber amplifiers to the optical FDM information-distribution network is also discussed. The experimental results of a 5 GHz spaced 16-channel FDM distribution/transmission at 622 Mb/s, using a waveguide frequency-selection switch (tunable filter) and a multicarrier frequency-stabilization technique, are also discussed     

Architectures and performance of AWG-based optical switching nodes for IP networks

In order to support the continuous growth of transmission capacity demand, optical packet switching technology is emerging as a strong candidate, promising to allow fast dynamic allocation of wavelength-division multiplexing (channels, combined with a high degree of statistical resource sharing). This work addresses the design of optical switch architectures, based on previous proposals available in the technical literature that use an arrayed waveguide grating (AWG) device to route packets. Since the port number of currently available AWGs is a limiting factor, we propose two new modified structures which better exploit the switching capability of this component in the wavelength domain. Since a limited hardware complexity is a key requirement for all-optical switches, due to the high cost of optical components, these different node configurations are compared in terms of complexity. Traffic performance of these new structures in a full optical packet switching scenario is also examined.     

Packet loss and delay performance of feedback and feed-forwardarrayed-waveguide gratings-based optical packet switches with WDMinputs-outputs

This paper analyzes the packet loss and delay performance of an arrayed-waveguide-grating-based (AWG) optical packet switch developed within the EPSRC-funded project WASPNET (wavelength switched packet network). Two node designs are proposed based on feedback and feed-forward strategies, using sharing among multiple wavelengths to assist in contention resolution. The feedback configuration allows packet priority routing at the expense of using a larger AWG. An analytical framework has been established to compute the packet loss probability and delay under Bernoulli traffic, justified by simulation. A packet loss probability of less than 10^-9 was obtained with a buffer depth per wavelength of 10 for a switch size of 16 inputs-outputs, four wavelengths per input at a uniform Bernoulli traffic load of 0.8 per wavelength. The mean delay is less than 0.5 timeslots at the same buffer depth per wavelength     

Polymeric optical waveguide circuits formed using silicone resin

Polymeric optical waveguides fabricated using a newly developed silicone resin have a low birefringence as well as low propagation loss and good environmental stability. Optical waveguide circuits including a directional coupler, an arrayed waveguide grating (AWG) multi/demultiplexer, and a digital thermooptic (TO) switch are successfully realized using the silicone resin     

A 16-channel frequency selection switch for optical FDMdistribution systems

The performance of a 5-GHz-spaced, 16-channel frequency selection switch (FS-SW) for optical frequency division multiplexing (FDM) distribution systems is described. The silica waveguide-type FS-SW is constructed with four serially connected periodic filters integrated on a silicon chip. The required crosstalk level for each periodic filter of the FS-SW was estimated to be -21.0 dB for a 16-channel FS-SW and 23.6 dB for a 128-channel FS-SW. Crosstalk can be independent of the power coupling ratio of the 3-dB-coupler regions by choosing suitable connecting configurations for the periodic filters. A controller for the switch is also described and the desired channel can be selected successfully from among 16 optical carriers under an average crosstalk level of less than -20 dB     

WDM-PON中基于AWG的新型OVPN研究

在波分复用无源光网络(WDM-PON)中,提出了一种基于阵列波导光栅(AWG)的新型光虚拟专用网(OVPN)。OVPN采用环形结构,在不同光网络单元(ONU)之间使用波长通道直接通信,不仅保证了ONU之间通信的安全性,而且提高了网络生存性。分别从光功率损耗和系统误码率(BER)进行了数值分析,结果表明,本文结构不仅增加了通信的安全性,而且仅使用4个波长就能实现16个ONU的相互联接,从而节省了波长资源,且具有很强的抗串扰能力。     

Bidirectional optical cross connects for multiwavelength ringnetworks using single arrayed waveguide grating router

Bidirectional optical cross connects (BOXCs) using a single arrayed waveguide grating router and tunable fiber Bragg gratings (FBGs) have been proposed for multiwavelength bidirectional WDM ring networks. Two types of structures in fold-back and loop-back configurations have been considered and their feasibility has been demonstrated experimentally. The performances of two proposed structures have been investigated and compared in terms of crosstalk characteristics and backscattering suppression capability. The performance of the fold-back configuration is less vulnerable to the crosstalk of the arrayed waveguide grating (AWG) router. On the contrary, the BOXCs in loop-back configuration suppress backscattered signals effectively without using optical bandpass filters and, thus, have good scalability and are more cost effective. Therefore, the choice between two structures will depend on the crosstalk requirement in the BOXCs and the characteristics of the AWG router. In transmission of 2.5-Gb/s signals, the power penalty of 0.5 dB has been observed at BER of 10^-9 in both structures. Expansion of the proposed 2×2 structure to N × N adopting multistage structure has been discussed. The limitation on the maximum scale due to spectral bandwidth narrowing has been considered     

Impact of crosstalk in an arrayed-waveguide router on an opticaladd-drop multiplexer

The impact of crosstalk in an arrayed-waveguide (AWG) router on the performance of an N-channel optical add-drop multiplexer (OADM), with m add/drop channels and n-pass channels is theoretically investigated. A single arrayed-waveguide router is simultaneously used for multiplexing and demultiplexing. This results in crosstalk not only from the incoming channels, but from the outgoing channels as well. We show that the performance of the OADM degrades as either N or m are increased, suggesting that the number of channels in a network based on OADM's is limited by crosstalk in the AWG router. When an optical filter is added at the output of the OADM the digital signal-to-noise ratio Q is independent of N and m, and within a few tenths of a decibel of the perfect filtering case     

AWG作光路分插复用器串扰对信道数的影响

研究了阵列波导路由器作光路分插复用器（OADM）串扰的影响,其路由器含有m个上路/下路信道和n个传输信道。理论分析表明:随着上路/下路信道m和传输信道n的增加,串扰使OADM的信噪比QCT,成非线性下降、由于在阵列波导路由器中存在串扰,限制了基于 OADM的网络复用信道数。     

Spectral efficiency of optical FDM systems impaired by phase noise

The required frequency spacings between channels in an optical frequency division multiplexing (FDM) network are considered. The minimum permissible spacings consistent with meeting bit error rate (BER) objectives are derived. The assumed transmission uses on-off keying (OOK), at a data rate 1/T (in bits per second), via external modulation of a laser source having linewidth β (in hertz). The assumed receiver consists of an optical channel selection filter followed by a p-i-n photodiode and a postdetection integrate-and-dump circuit. The analysis estimates the adjacent channel interference (ACI)-induced floor on BER for the middle of three FDM channels, as a function of frequency spacing and linewidth-to-bit rate ratio (βT). For BER=10^-9 and βT ranging from 0.32 to 5.12, the required channel spacing ranges from 5.2 to 27.5 bit rates. The multiplying factors associated with using (wide-deviation) frequency shift keying (FSK), coherent (heterodyne) detection, and infinitely many FDM channels, respectively, are estimated to be 2.0, at most 3.0, and at most 1.37     

阵列波导光栅插入损耗的降低

阵列波导光栅（AWG Arrayed Waveguide Grating）是实现多通道密集波分复用（DWDM Dense Wavelength Division Multiplexing)光网络的理想器件,插入损耗是它的一个重要性能指标。本文介绍了多种减小AWG插入损耗的方法,并在此基础上,分析了如何使用楔形波导结构来降低模式失配所导致的耦合损耗。这种方法可以在不增加器件制作难度的同时大大降低AWG的插入损耗,并且适用于各种材料和结构的AWG器件设计。     

A simple expression for optical FDM network scale considering fiberfour-wave mixing and optical amplifier noise

Possible transmission distance and number of channels are studied in optical FDM (frequency division multiplexed) systems. Optical amplifier noise and fiber four-wave mixing, which respectively restrict input power to a repeater and input power to a fiber, are taken into account. A simple analytical expression is derived for evaluating FDM network scale by using a Gaussian noise approximation. Calculation examples are also presented     

Photonic FDM multichannel selector using coherent opticaltransversal filter

This paper describes a photonic frequency-division-multiplexing (FDM) multichannel selector using a coherent optical transversal filter and discusses its application to a photonic FDM highway switch. The selector can select several arbitrary channels out of several multiplexed frequency channels. The selector function takes advantage of the fact that the filter can express arbitrary frequency characteristics. An experimental 16-tap filter is fabricated according to silica-based-waveguide technology, which can monolithically integrate a variety of optical components. Arbitrary channel selection and signal transmission characteristics are confirmed by measuring the frequency characteristics of the selector and the bit-error-rate performance     

Characterization of 1/spl times/N broadcast and 2/spl times/N multicast packet switching using active-vertical-coupler-based optical crosspoint switch

This paper reports the expansion of a novel optical multicast scheme to 1-to-4 and 2-to-4 configurations using an active-vertical-coupler (AVC)-based optical crosspoint switch (OXS) matrix. A 1-to-4 broadcast experiment has been carried out first, with only 0.5 dB excess loss per signal split. Input signals with two wavelengths are then fed into one row of OXS to investigate the effect of wavelength-division multiplexing on the 1-to-4 multicast switching. Finally, combining both, the expanded 2-to-N multicast is also achieved with an N value up to 4. The switching characteristics, switched signal quality, and optical signal-to-noise ratio (OSNR) have been investigated in different configurations. Power penalties of less than 4.5 dB are found in worst case switched signals in the 2-to-4 configuration. Slow OSNR degradation in line with previous prediction is also observed. The measured results confirm the excellent multicast switching characteristics nearly free from power splitting loss in this device.     

Client-configurable eight-channel optical add/drop multiplexerusing micromachining technology

A client-configurable optical add/drop multiplexer (OADM) is demonstrated using a micromachined 8×6 matrix switch. The matrix switch can be configured to add/drop any of the eight input channels from/to any of the six add/drop ports. For the switching fabric, the insertion loss is 2~3 dB for the dropped channels and 8~9 dB for the added channels by using the backsides of the micromirror switches. The switching extinction ratio is over 40 dB, the crosstalk between channels is less than -40 dB, and they are equipment-limited in this experiment     

TWC and AWG based optical switching structure for OVPN in WDM-PON

Considering the influence of more random atmospheric turbulence,worse pointing errors and highly dynamic link on the transmission performance of mobile multiple-input multiple-output(MIMO)free space optics(FSO)communication systems,this paper establishes a channel model for the mobile platform.Based on the combination of Alamouti space-time code and time hopping ultra-wide band(TH-UWB)communications,a novel repetition space-time coding(RSTC)method for mobile 2×2 free-space optical communications with pulse position modulation(PPM)is developed.In particular,two decoding methods of equal gain combining(EGC)maximum likelihood detection(MLD)and correlation matrix detection(CMD)are derived.When a quasi-static fading and weak turbulence channel model are considered,simulation results show that whether the channel state information(CSI)is known or not,the coding system demonstrates more significant performance of the symbol error rate(SER)than the uncoding.In other words,transmitting diversity can be achieved while conveying the information only through the time delays of the modulated signals transmitted from different antennas.CMD has almost the same effect of signal combining with maximal ratio combining(MRC).However,when the channel correlation increases,SER performance of the coding 2×2 system degrades significantly.