We demonstrate a low current and high bandwidth waveguide photodetector by selective area growth technique. The waveguide photodiode has been fully fabricated by a photonic integration process. The photodiode epitaxial structure is selectively regrown on wafer with SiO2-masked SOA mesas. Before SAG of photodetector layers, SOA mesas are etched into non-reentrant configuration. The SAG process is carried out in low-pressure MOCVD reactor at a high growth temperature of 680 °≅ and growth rate of 5Å/đť‘ . Combination of low-speed Ar/Cl2/CH4 dry etching and wet etching is used to define PD mesas. PD mesas are arranged <300μm away from SOA mesa to minimize the growth rate enhancement of SAG. The photodetector is evanescently coupled with a 2ÎĽm wide rib waveguide defined by ICP etching. The PD is passivated with 600nm SiO2 by PECVD. The fabricated waveguide photodiode exhibits a dark current of 242pA at -3V, fiber-to-chip responsivity up to 0.18A/W and 3dB electrical bandwidth of 20GHz. The performance shows hardly no compromise when comparing to that of normal discrete devices. Those results lay good foundations for high-function photonic integration circuits in near future.
A parallel array with 8 high speed surface-illuminated pin photodetectors (PDs) is designed and fabricated. The effect of absorption layer thickness on PD responsivity and bandwidth is analyzed, and the material structure is optimized accordingly. The photodetector array, which is based on the Indium Phosphorus (InP) Platform, is manufactured by Metalorganic Chemical Vapor Deposition (MOCVD) and contact photolithography. Each detector has a photosensitive surface diameter of 20μm and a depletion layer thickness of 1.0μm. All 8 pin-PDs exhibit a uniform responsivity over 0.7A/W at 1310nm and a low dark current of below 4nA at 1V reverse bias. In addition, the 8 pin-PDs exhibit a uniform -3dB bandwidth of 20GHz. The experimental results agree well with the theoretical values. The photodetector array, which has a cost-effective and simple manufacturing process, could potentially operate at a total transmission rate beyond 200Gbps for fiber optic communication applications and can be integrated with other optoelectronic devices.
We propose a polarization insensitive multimode interference coupler (MMI) design for optical 90° hybrid. The 90° hybrid used in coherent receiver application is based on the Indium Phosphorus (InP) platform, which can realize monolithic integration with detectors. By using the three dimension beam propagation method, a 90° hybrid based on a polarization insensitive MMI has been designed and optimized. We find that there is an ideal interference length for both transverse electric (TE) mode and transverse magnetic (TM) mode in this structure. Using the designed 90° hybrid, we demonstrate the common mode rejection ratios for in-phase channels and quadrature channels better than -20 dB and the phase errors better than ±3° in an ideal interference length range. The phase errors of the I-channel and Q-channel less than ±4° when the interference length is 480μm across the C band (1535-1560 nm).
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