InP-Based Monolithically Integrated Photonic Devices for Digital Coherent Transmission

We comprehensively review InP-based monolithically integrated photonic devices for digital coherent transmission. A single-stripe tunable laser consisting of the tunable distributed amplification-chirped sampled grating-distributed reflector structure has yielded the high fiber output power of more than +17 dBm and the narrow spectral linewidth of less than 200 kHz, which achieved sufficient properties for 16-ary quadrature amplitude modulation (16QAM). A dual-polarization in-phase and quadrature modulator module with the Mach-Zehnder modulator array accomplished 16QAM modulation for 224 Gb/s at a low differential driving voltage of 2.5 V
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. A photodetector monolithically integrated with a 90° hybrid presented a high responsivity (> 0.130 A/W over C-band) and the stable operation with low dark current over 5000 h in the accelerated aging test (test condition: -7.5 V at 175 °C). Demodulation of 224 Gb/s DP-16QAM modulated signals was demonstrated as the compact coherent receiver using this photodetector. A wide 3-dB bandwidth of more than 40 GHz for 400 Gb/s DP-16QAM by 64 GBaud operation was also realized as the receiver thanks to p-i-n-photodiodes with a high-speed response.