Quantum key distribution can realize unconditional security of communication. Here, a quantum decoding chip based on silica-on-silicon planar lightwave circuit (PLC) platform, which is compatible for multiprotocol has been demonstrated. PLC technology provides stability, high integration, and practicality for the chip, whereas silica-on-silicon material makes it low loss and low cost. The chip is integrated with three variable optical splitters, two asymmetric Mach–Zehnder interferometers, and four variable directional couplers. The interference visibility is investigated by self-interfering method, and the results showed it is high to 98.2% under temperature control. The extinction ratio for the phase states is kept between 23 and 25 dB for 6 h without active phase correction.
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/𝑠. 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 2μm 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).
This paper reports a planar structure InGaAs/InP avalanche photodetector focal plane arrays. Their material structure use separate absorption, grading, charge and multiplication layer. The pixel pitch of 8×8 format detectors is 250 μm. The breakdown voltage (VBD) is typically in the range of 65 to 70 V for most of the devices on the same wafer. The typical dark current at 90% of VBD is 3 nA, dark currents as low as 0.5 nA at 90% of VBD have also been observed for some diodes, corresponding to a dark current density of 1 × 10-5 A/cm2. The photocurrent starts to increase at the "punch-through" voltage Vp of 43 V. The responsivity at 1.55 μm is 0.91 A/W at unity gain and the multiplication layer is estimated to be 1.2 μm. Each device on the same wafer has excellent characteristics and high uniformity through measurement, laying a solid foundation for 3D imaging laser radar systems.
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