Masaru Takechi

InP-Based p-i-n-Photodiode Array Integrated With 90

This paper reports on the performance of an InP-based p-i-n-photodiode array monolithically integrated with a 90° hybrid consisting of multimode interference structures using the butt-joint regrowth and its application to compact 100 Gb/s coherent receivers. A responsivity including total loss of 8.2 dB in the waveguide was as high as 0.14 A/W, and responsivity imbalance of all channels was less than ±0.5 dB. The wide 3-dB bandwidth of 26 GHz at a low reverse bias voltage of 1.6 V was obtained under high optical input power conditions (photocurrent = 2.5 mA). The stable dark current was achieved in the accelerated aging test (test condition: -5 V at 175 °C) over 2000 h. Finally, the excellent common mode rejection ratio with low loss imbalance of 90° hybrids (less than -20 dB up to 25 GHz) and demodulation of 128 Gb/s dual polarization quadrature phase-shift keying modulated signals were demonstrated for the compact coherent receiver (package body size: 15 mm × 26 mm × 5.5 mm).

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For coherent detection using multi-level modulation formats, we demonstrated small responsivity imbalance of the InP-based p-i-n photodiode array monolithically integrated with the 90° hybrid consisting of 2 × 4 and 2 × 2 multimode interference structures and a 45° phase shifter. Responsivity imbalance of the In-phase and Quadrature channels was less than ±0.2 dB over the C-band by the adoption of the asymmetric waveguide phase shifter which functions as the 45° phase shifter, and its good reproducibility was indicated from the standard deviation for each wafer. Furthermore, excellent common mode rejection ratio below -25 dB was also confirmed from the coherent receiver with this integrated device. These results prove that this structure is very useful for stable manufacturability of the 90° hybrid.

Hybrid Using Butt-Joint Regrowth for Compact 100 Gb/s Coherent Receiver

The InP-based pin-photodiode array monolithically integrated with a 90° hybrid and spot-size converters was realized using selective embedding regrowth for compact 100Gb/s coherent receivers. The low dark current of less than 500 pA up to 85 °C was attained by InP passivation effect in four-channel pin-photodiodes. As a receiver using these photodiode arrays, a receiver responsivity including total loss of 6.7 dB in the 90° hybrid and intrinsic loss of 3 dB in the polarization beam splitter was higher than 0.060A/W between −5 °C and 85 °C through the integration of the spot-size converter. Responsivity imbalance of the In-phase and Quadrature channels was also less than 0.5 dB over the C-band.

Small responsivity imbalance of InP-based p-i-n photodiode array monolithically integrated with 90° hybrid using asymmetric waveguide phase shifter for coherent detection

We demonstrate a high responsivity of 64 GBaud micro intradyne coherent receivers (Micro-ICR) operating at the wavelength range from 1565 nm to 1612 nm (L-band). The package body size is 12.0 mm × 22.7 mm × 4.5 mm, which is fully compliant with OIF implementation agreement. A newly developed InP-based photonic integrated circuit (InPPIC) for the L-band High-Bandwidth Micro-ICR is composed of the high-speed p-i-n-photodiode array (f3dB > 40GHz) and a 90° hybrid waveguide consisting of MMIs which is designed to obtain high transmittance over the L-band. They are monolithically integrated through butt-joint regrowth in which a GaInAs absorption layer of the photodiode is directly connected with a GaInAsP core layer of the 90° hybrid in order to achieve the high responsivity with high optical coupling efficiency. Furthermore, the optical couplings between optical fibers and InP-PICs are realized by low optical loss micro optics. Receiver responsivities of more than 65 mA/W for signal input and local input are achieved within the L-band at 25°C. The wide 3-dB bandwidth of 40 GHz is also confirmed using high-bandwidth TIA. These values are comparable to the coherent receiver for 64 GBaud C-band applications. This receiver module is very promising for the increase of transmission capacity through expansion of operation wavelength (C-band and L-band).