High-speed integrated photodetectors for 40-Gbit/s applications

Abstract

Photonic integrated photodetectors are built by combining guided-wave, optoelectronic and microwave devices. They offer high conversion efficiency, extremely high speed operation and high power linearity up to 20 mW of optical power. A careful design of the applied spot size converter allows an optimized fiber-chip coupling and polarization insensitive performance of the photodiodes. Recent results of electro-optic sampling measurements reveal 3 dB-and 6 dB-bandwidth of 64 GHz and 100 GHz, respectively, as well as an excellent phase linearity up to 160 GHz. Further integration of two photodiodes leads to e.g. 40 GHz balanced detectors enabling DPSK transmission for longhaul systems. Using optical pre-amplification an excellent sensitivity of -32 dBm was achieved at 40 Gbit/s.

High-speed, waveguide photodiodes

“…In addition several structural enhancements and modifications have been incorporated onto the chip; these include: (1) integration of the bias tee on chip, (2) integration of a 50-Ω termination resistor, (3) fabrication of the complete waveguide stack from semi-insulating materials, (4) achieving efficient coupling to short, low-capacitance photodiodes, (5) utilization of thin depleted absorbing layers to minimize the carrier transit component of the bandwidth, and (6) air bridge connections to coplanar contact pads. Photodiodes of this type have achieved 100-GHz bandwidth, 53-GHz bandwidth-efficiency product, polarization dependent loss of 0.9 dB, and ± 2 μm vertical and horizontal alignment tolerances [10]. The 1-dB saturation point of the RF output power has reached -8 dBm at 100 GHz.…”

“…In one approach, the transition region consists of laterally [5][6][7] or vertically [8,9] tapered layers that adiabatically transfer the light from an underlying dilute waveguide to a photodiode on top of the transition region. In recent years, this structure has been refined and optimized to achieve high coupling efficiency between an optical fiber input and the photodiode and to extend bandwidths to 100 GHz and beyond [10][11][12]. In addition several structural enhancements and modifications have been incorporated onto the chip; these include: (1) integration of the bias tee on chip, (2) integration of a 50-Ω termination resistor, (3) fabrication of the complete waveguide stack from semi-insulating materials, (4) achieving efficient coupling to short, low-capacitance photodiodes, (5) utilization of thin depleted absorbing layers to minimize the carrier transit component of the bandwidth, and (6) air bridge connections to coplanar contact pads.…”