The Research On100Gb/s DP-QPSK Receiver Based On Planar Lightwave Circuit

Recently, in order to meet the continuous growth in demand for capacity of the opticaltransport network,100Gb/s DP-QPSK (Dual polarization quadrature phase-shift keying)receiver based on polarization multiplexing and multi-phase modulation format has beingpaid important attention. Compared with the direct detection, coherent detection technologyof the100Gb/s DP-QPSK receiver can achieve high-performance signal demodulation andcan greatly improve the optical signal noise ratio. So, the research of100Gb/s DP-QPSKreceiver has significant economic value and wide range of practical prospects. This thesisspreads out discussions around the theory analysis, design optimization, and test results ofthe PLC (planar lightwave circuits) based100Gb/s DP-QPSK receiver as follows:(1) A new SWT (segmented waveguide taper) mode adapter for a polarization modeconverter is proposed and demonstrated, and this polarization mode converter can be usedin the front end of the100Gb/s DP-QPSK receiver for the polarization conversion. It isproved that this SWT mode adapter requires no vertical tapering process but can enlarge themode size both in vertical and horizontal direction. The segmented waveguide of the SWTmode adapter is capable of changing the effective refractive index of the waveguide both inthe vertical and horizontal direction, so it can both change the mode size of the vertical andhorizontal direction. This feature avoids the problem of the mode size in the verticaldirection can not be changed in traditional mode converter. Our newly designedpolarization mode converter based on the0.75%-Δ silica waveguide is able to reduce theexcess loss induced by quartz half waveplate significantly from5dB to less than1.5dB,and the polarization conversion efficiency of this polarization mode converter is very highwhich can meet the requirements of100Gb/s DP-QPSK receiver.(2) A traditional90hybrid and a PBS (polarization beam splitter) integrated90hybrid are systematically researched, including the theoretical design, fabrication and test.First, I (inphase) branch and Q (quadrature) branch phase difference, insertion loss andinsertion loss consistency of traditional90hybrid is tested. The test results indicate that theI branch and Q branch phase difference is within±5°, insertion loss is between7.05dB and8.05dB, and insertion loss consistency is within1dB, which can meet the requirements of 100Gb/s DP-QPSK receiver. Secondly, I branch and Q branch phase difference, insertionloss, insertion loss consistency and PER (polarization extinction ratio) of PBS integrated90hybrid is tested. The test results indicate that the I branch and Q branch phasedifference is within±4°, insertion loss is of less than11.5dB and12dB when the input issignal light and local oscillator light respectively, insertion loss consistency is within1dB,the PER of signal light and local oscillator light PBS is less than-18dB and less than-22dB respectively. Therefore, further improvement of the PER of signal light PBS is required.(3) A new hybrid integrated program of the output waveguide of90ohybrid and ahigh-speed PD (photodiodes) array is proposed. The output waveguide of90ohybrid ispolished into a45°angle in this hybrid integrated program. The four output spots of90ohybrid and four active areas of1×4PD array can be seen clearly only use infrared lightand infrared CCD (charge-coupled device). This scheme avoids the low accuracy oftraditional mechanical mark, affect the high frequency characteristics of the1×4PD arraywhen bonding gold wire on the PD pad to monitor the current of the PD, significantlycomplicate the device assembly and increase cost when using microlens. The couplingefficiency of the output waveguide of90ohybrid and1×4PD array is very high in thishybrid integrated program. Based on this proposed coupling scheme, the responsivityvariation for the100Gb/s DP-QPSK receiver is less than±0.18dB for all PD channels inan environment temperature range of-5℃to80℃.(4) A high speed transmission board and a high speed package transmission board isdesigned and tested. First, the model of high speed transmission line is designed by HFSSdesign software. Secondly, a high frequency test platform is conducted to test the highfrequency performance of the high speed transmission board and a high speed packagetransmission board. The test platform contains a lightwave component analyzer, a probestation, and two differential coplanar waveguide probes. The test results show that the highspeed transmission board meets the requirements of100Gb/s DP-QPSK receiver, whilehigh speed package transmission board doesn’t meet the requirements of100Gb/sDP-QPSK receiver, which needs for further improvements.