相位误差对阵列波导光栅传输特性的影响

研究了阵列波导光栅 (AWG)制作过程中产生的误差所引起的相位误差对AWG传输特性的影响。非随机误差引起的相位误差使信道的中心波长产生漂移 ,研究表明波导宽度 0 0 2 μm的变化将引起中心波长漂移 0 1nm。随机误差所产生的随机相位误差将恶化AWG的串扰特性 ,计算表明 ,最大随机误差为 0 0 0 0 0 4rad μm时 ,串扰将增加 4 2dB。     

相位误差对AWG波分复用器非相邻通道串扰影响的分析

分析了工艺制作过程中引入的阵列波导相位误差以及由其所引起的非相邻通道间串扰性能的劣化,给出了相应的分析公式.利用该公式,可以简捷地分析所设计的AWG型器件的非相邻通道串扰水平,为优化AWG型器件的设计提供依据.     

Crosstalk reduction in N×N WDM multi/demultiplexers bycascading small arrayed waveguide gratings (AWG's)

This paper shows a new scheme which improves the crosstalk performance of large optical multi/demultiplexers, a key component in wavelength division multiplexing (WDM) systems. This scheme uses arrayed waveguide gratings (AWG's) of various sizes and requires no additional equipment. It is well known that a large multi/demultiplexer can be constructed by cascading small multi/demultiplexers. We have studied the impact of the number and size of AWG stages on crosstalk performance. This paper proves that to obtain a multistage multi/demultiplexer with minimum crosstalk, the total channel number of each AWG stage must be minimized. For example, cascading 10-channel AWG's and 11-channel AWG's improves the crosstalk performance of a 110-channel multi/demultiplexer by about 7.5 dB. Furthermore, the crosstalk performance degradation due to fabrication error is theoretically investigated taking channel bandwidth into account. Optimum design parameters of multistage AWG's are introduced: When the AWG suppression ratio is 30 dB and the ratio of channel bandwidth to channel spacing is about 0.24, the degradation in crosstalk performance due to fabrication error is minimized. The tradeoff between the crosstalk performance and the efficiency in terms of hardware and wavelength are also discussed. It is discovered that this simple scheme can yield a crosstalk-free WDM router. Crosstalk reduction obtained by this scheme allows the realization of flexible multiwavelength networks based on wavelength routing     

氟化聚合物光谱响应平坦化阵列波导光栅的优化设计和制备

本文基于阵列波导光栅(AWG)的传输理论,利用含氟聚合物(PFS-co-GMA)共聚物材料,对17×17信道光谱响应平坦化AWG波分复用器进行了参数优化.由于在聚合物阵列波导光栅器件的制备过程中,选用了反应离子刻蚀(RIE)工艺和蒸汽回溶技术,形成的梯形截面波导芯,使AWG传输的光产生相位移,导致传输光谱移动,引起串扰...     

工艺误差对AWG串扰特性的影响

分析了阵列波导光栅器件的制作过程中引入的各种工艺误差。对波导尺寸误差、折射率误差以及长度误差进行了等效,并计算了位相误差和振幅误差的方差。最后分析了位相误差和振幅误差对阵列波导光栅的频谱特性尤其是相邻通道间的串扰特性的影响。     

The role of photomask resolution on the performance ofarrayed-waveguide grating devices

The crosstalk performance of an arrayed-waveguide grating (AWG) multiplexer or demultiplexer is primarily caused by random optical phase errors introduced in the arrayed waveguides. Because the layout of waveguides on a wafer is patterned via photomask through the photolithography process, the resolution of a photomask has a direct influence on the phase errors of an AWG. The paper presents a theoretical analysis on the phase error caused by photomask resolution and other basic design parameters. Both calculation and measurement results show that a high-resolution photomask (better than 25 nm) is a critical requirement to produce low-crosstalk (less than -30 dB) AWG demultiplexers. We also investigate the effect of nonideal power distribution in the arrayed waveguides because it contributes considerable phase errors when material impurity is not well controlled during wafer fabrication. Basic criteria of power profile truncation, number of grating waveguides, and material index variation are also summarized     

Measurement of slowly varying component in phase error distribution of a large-channel-spacing arrayed-waveguide grating

It has been difficult to measure the phase error distribution of a large-channel-spacing arrayed-waveguide grating (AWG) with optical low coherence interferometry (OLCI). In this reported work OLCI was successfully used to measure the slowly varying component in the distribution of a 1 THz-spaced AWG that was the primary filter in an ultra-high-density multi/demultiplexer. The spectral sidelobe of the AWG can be reduced by using the component to achieve the lowest possible accumulated crosstalk in the multi/demultiplexer.     

Measurement of phase and amplitude error distributions in InP-basedarrayed-waveguide grating multi/demultiplexers

The authors have measured the phase and amplitude error distributions in an InP-based arrayed-waveguide grating (AWG) multi/demultiplexer using Fourier transform spectroscopy and signal data processing. The signal data processing technique was based on wavenumber scale transformation and was applied to reduce the effect of second-order dispersion in a measured interferogram. The results reveal that the main origins of the crosstalk and dispersion in an InP-based AWG are random and slowly-varying phase errors, respectively     

Estimation of waveguide phase error in silica-based waveguides

A new estimation method is proposed in order to clarify waveguide phase error factors. Using the proposed method, it is possible to analyze such factors as core size error and refractive index error, which cause optical phase error in waveguides. This method is applied to silica-based waveguides to estimate the waveguide phase error. This revealed an average core size error of 2.1×10^-3 μm and an average refractive index error of 1.9×10^-6. Finally, based on the measured phase error values, the optimum arrayed-waveguide grating (AWG) configuration is considered with a view to achieving low crosstalk     

New concept in long-reach PON Planning: BER-aware wavelength allocation

With the use of arrayed-waveguide grating (AWG) and erbium-doped-fiber amplifier (EDFA), the long-reach passive optical network (LR-PON) can provide enormous bandwidth over large distances. However, these new technologies can also deteriorate the receivers' bit-error rate (BER) performance. By bringing the concept of BER-awareness into network planning, we can alleviate the performance deterioration, which could in turn lead to simpler design of receiver and thus lower the total cost of LR-PON.The effects of AWG and EDFA on BER are studied in this paper. An analytical model of BER performance is developed as a function of the output port location in the AWG and the distance of the receiver from the AWG. Not only does the proposed model capture the power loss caused by AWG, but it also accounts for several transmission impairments, including the beat noise due to inter-channel crosstalk in the AWG, the amplified spontaneous emission (ASE) noise related to EDFA, and the thermal noise related to the receiver. Based on this model, we propose both short-term and long-term distance-aware wavelength allocation schemes, which balance the BER among the optical network units (ONUs) at different distance. Simulation results show that average BER improves and the relative standard deviation decreases.     

Crosstalk Loss Requirements for PCM Transmission

We present in this paper a unified approach to the crosstalk interference problem arising in PCM transmission on paired cables. For bipolar signaling, and three types of commonly used channel shaping, viz., cosine, raised cosine, and Gaussian, we present the minimum average near-end crosstalk (NEXT) and far-end crosstalk (FEXT) loss requirements at any transmission rate as a function of repeater spacing and number of interfering pairs so as to meet a desired error rate objective. This will aid in indicating if new cables need to be developed for a proposed rate of transmission or, for a given cable, the error margin available for degradations other than crosstalk can be readily determined. Extension to other coding schemes is indicated, and crosstalk compatibility is examined for mixedTsystems, such asT1,T1C, andT2. Graphical results are presented to readily aid in system design of anyTcarrier with repeater spacings up to 70 dB.     

An optimal signal design for band-limited asynchronous DS-CDMAcommunications

An optimal signal design for band-limited, asynchronous, direct-sequence code-division multiple-access (DS-CDMA) communications with aperiodic random spreading sequences and a conventional matched filter receiver is considered in an additive white Gaussian noise (AWGN) channel. With bandwidth defined in the strict sense, two optimization problems are solved under finite bandwidth and zero interchip interference constraints. First, a chip waveform optimization is performed given the system bandwidth, the data symbol transmission rate, and the processing gain. A technique to characterize a band-limited chip waveform with a finite number of parameters is developed, and it is used to derive optimum chip waveforms which minimize the effect of multiple-access interference (MAI) for any energy and delay profile of users. Next, a joint optimization of the processing gain and the chip waveform is performed, given the system bandwidth and the data symbol transmission rate. A sufficient condition for a system to have lower average probability of bit error for any energy profile is found, and it is used to derive some design strategies. It is shown that the flat spectrum pulse with the processing gain leading to zero excess bandwidth results in the minimum average probability of bit error. Design examples and numerical results are also provided     

一种降低列阵波导光栅相邻信道串扰的方法

阵列波导光栅 (AWG)作为波长滤波器在光通信领域具有很大的应用前景。串扰是影响阵列波导光栅应用的重要因素之一。为了降低阵列波导光栅相邻信道的串扰 ,本文提出并研究了一种降低阵列波导光栅的新方法。该方法利用阵列波导光栅的衍射特点性 ,通过调节阵列波导光栅的自由光谱范围 (FSR)、罗兰圆焦距和阵列波导数目 ,使得各信道信号的输出极小值处于其它信道输出波导中心 ,无次极大处于其它波导中 ,从而降低了阵列波导光栅的串扰 ,特别是相邻信道之间的串扰。通过光束传播方法 (BPM)的模拟了具有不同FSR的 1× 16阵列波导光栅 ,结果显示 ,该方法能将相邻信道之间的串扰降低约 5 .7dB。     

Wideband microwave filter constructed by asymmetrical compact microstrip resonator and floating plate coupling structure

The realisation of a microwave filter is presented by using the asymmetrical compact microstrip resonator and floating plate coupling structures. The filter demonstrates the properties of low insertion loss, wide pass bandwidth and two controllable transmission zeros, which results in fast roll-off responses near to the corner frequencies of the passband. It also has the advantages of compact size, ease of fabrication and absence of via holes. An X-band prototype with 34% fractional bandwidth was designed and fabricated to verify the proposed design concept. Good agreement between simulation and measurement was obtained.     

硅基二氧化硅阵列波导光栅相位误差数值分析

采用传输函数法对硅基二氧化硅阵列波导光栅(AWG)的相位系统误差和随机误差进行了详细的分析. 系统误差的模拟结果表明阵列波导的有效折射率和相邻阵列波导长度差ΔL的偏移将会对使中心波长λ0偏离设计值，平板波导有效折射率、阵列波导的间距、罗兰圆聚焦长度R的偏移会使通道间隔偏离设计值. 随机误差的模拟结果表明相邻阵列波导长度差、阵列波导中芯区折射率、芯区宽度、芯区厚度的随机波动对AWG的串扰影响较大，而波导上、下包层折射率的波动对AWG串扰影响较小.     

Sharp-Rejection Wideband Bandstop Filters

In this letter, a novel transmission line configuration has been proposed to design a sharp-rejection, bandstop filter (BSF) with wide rejection bandwidth. The rejection bandwidth and the level of rejection are controlled by the characteristic impedances of the transmission lines. Design equations are obtained by using a lossless transmission line model. The proposed design has been verified in microstrip line by fabricating a prototype BSF of -20 dB fractional bandwidth of 100% at a stopband center frequency f₀ = 1.5 GHz. The filter structure is simple and easy to fabricate.     

Fabrication of 17×17 polymer/Si arrayed waveguide grating with flat spectral response using steam-redissolution technique

Arrayed waveguide grating(AWG) is a key device in the wavelength-division multiplexing(WDM) system, and the flat spectral response of the AWG device is required.In this paper,the RIE process has been improved.By using the steam-redissolution technique,the insertion loss and the crosstalk have been reduced.Experimental results show that the central wavelength is 1550.86 nm,the channel spectral response flatness is about 1.5 dB,3-dB bandwidth is about 0.478 nm,insertion loss is 10.5 dB,and crosstalk is abo...     

用于FBG解调的AWG芯片的设计、仿真与制备

设计、仿真并制备了一种用于光纤布拉格光栅(FBG)解调的阵列波导光栅(AWG)芯片。该芯片基于SOI衬底进行制备,并在AWG的输入/输出波导、阵列波导与平板波导之间采用双刻蚀结构进行优化。经仿真,该AWG的插入损耗为1.5dB,串扰小于 -20dB,3dB带宽为1.5nm。优化后的AWG芯片采用深紫外光刻技术、电感耦合等离子体等技术制备。经测试,该AWG的插入损耗为3dB,串扰小于 -20dB,3dB带宽为2.3nm。搭建了基于该AWG的解调系统,解调实验结果表明,该系统在0.8nm范围内的解调精度可达11.26pm,波长分辨率为6pm。     

Optimum Pulse Shapes for Pulse-Amplitude Modulation Data Transmission Using Vestigial Sideband Modulation

When designing pulse-amplitude modulation (PAM) systems for use over bandpass channels having restricted bandwidth, one may be led to use single-sideband (SSB) or vestigial sideband (VSB) transmission in order to maximize transmission rate. Carefully shaped pulses must be used to minimize degradation due to intersymbol interference (isi). In this paper VSB pulses are derived that have no inherent isi, and in addition have maximum immunity in a mean-squared-error (MSE) sense to timing and carrier phase errors. The results here generalize on those of Franks who treated the SSB case. The optimum VSB pulses are shown to be identical to those of Franks at the band edges, and to have vestigial roll-off characteristics of a similar discontinuous nature. It is also shown that one may allocate available bandwidth to the vestigial roll-off band band and Nyquist roll-off band in any way desired. The final performance for the optimum pulse depends only on the total bandwidth used. These results are shown to apply as well to a system employing a matched filter. The case of random timing and phase errors is also considered, and optimum pulses are again found. Several mathematical properties of the optimal pulses are given physical justification and geometric insight through error ellipses, and optimal signal shapes are plotted for various cases of special interest.     

17×17 硅基聚合物信道箱形光谱阵列波导光栅的制备

Arrayed waveguide grating (AWG) is a key device in wavelength-division multiplexing (WDM) system, and the flat spectral response of the AWG device is required. In this paper, the RIE process has been improved. By using the steam- redissolution technique, the insertion loss and the crosstalk have been reduced. Experimental results show that the central wavelength is 1550.86nm, and 3-dB bandwidth is about 0.478 nm, insertion loss is 10.5 dB, crosstalk is about –22 dB. The insertion loss of an AWG device is reduced by about 3 dB for the central channel and 4.5 dB for the edge channels, and the crosstalk is reduced by 2.5 dB after the steam- redissolution.