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 optical transport network,100Gb/s DP-QPSK (Dual polarization quadrature phase-shift keying) receiver based on polarization multiplexing and multi-phase modulation format has being paid important attention. Compared with the direct detection, coherent detection technology of the100Gb/s DP-QPSK receiver can achieve high-performance signal demodulation and can greatly improve the optical signal noise ratio. So, the research of100Gb/s DP-QPSK receiver has significant economic value and wide range of practical prospects. This thesis spreads out discussions around the theory analysis, design optimization, and test results of the PLC (planar lightwave circuits) based100Gb/s DP-QPSK receiver as follows:(1) A new SWT (segmented waveguide taper) mode adapter for a polarization mode converter is proposed and demonstrated, and this polarization mode converter can be used in the front end of the100Gb/s DP-QPSK receiver for the polarization conversion. It is proved that this SWT mode adapter requires no vertical tapering process but can enlarge the mode size both in vertical and horizontal direction. The segmented waveguide of the SWT mode adapter is capable of changing the effective refractive index of the waveguide both in the vertical and horizontal direction, so it can both change the mode size of the vertical and horizontal direction. This feature avoids the problem of the mode size in the vertical direction can not be changed in traditional mode converter. Our newly designed polarization mode converter based on the0.75%-Δ silica waveguide is able to reduce the excess loss induced by quartz half waveplate significantly from5dB to less than1.5dB, and the polarization conversion efficiency of this polarization mode converter is very high which can meet the requirements of100Gb/s DP-QPSK receiver.(2) A traditional90°hybrid and a PBS (polarization beam splitter) integrated90°hybrid are systematically researched, including the theoretical design, fabrication and test. First, I (inphase) branch and Q (quadrature) branch phase difference, insertion loss and insertion loss consistency of traditional90°hybrid is tested. The test results indicate that the I 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, insertion loss, insertion loss consistency and PER (polarization extinction ratio) of PBS integrated90°hybrid is tested. The test results indicate that the I branch and Q branch phase difference is within±4°, insertion loss is of less than11.5dB and12dB when the input is signal 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 of90°hybrid and a high-speed PD (photodiodes) array is proposed. The output waveguide of90°hybrid is polished into a45°angle in this hybrid integrated program. The four output spots of90°hybrid and four active areas of1×4PD array can be seen clearly only use infrared light and infrared CCD (charge-coupled device). This scheme avoids the low accuracy of traditional mechanical mark, affect the high frequency characteristics of the1×4PD array when bonding gold wire on the PD pad to monitor the current of the PD, significantly complicate the device assembly and increase cost when using microlens. The coupling efficiency of the output waveguide of90°hybrid and1×4PD array is very high in this hybrid integrated program. Based on this proposed coupling scheme, the responsivity variation for the100Gb/s DP-QPSK receiver is less than±0.18dB for all PD channels in an environment temperature range of-5℃to80℃.(4) A high speed transmission board and a high speed package transmission board is designed and tested. First, the model of high speed transmission line is designed by HFSS design software. Secondly, a high frequency test platform is conducted to test the high frequency performance of the high speed transmission board and a high speed package transmission board. The test platform contains a lightwave component analyzer, a probe station, and two differential coplanar waveguide probes. The test results show that the high speed transmission board meets the requirements of100Gb/s DP-QPSK receiver, while high speed package transmission board doesn’t meet the requirements of100Gb/s DP-QPSK receiver, which needs for further improvements.