Coupled Waveguide Photodiodes Research Articles

High responsivity evanescently coupled waveguide photodiode using spot-size converter and distributed Bragg reflector at 1.55 μm wavelength

InGaAs/InP waveguide photodiode, one of the most crucial devices in optical modules, has proven to be beneficial for exponential data communication. However, improving responsivity with a high 3 dB bandwidth remains a challenge for various photodetector designs. In this letter, a multi-layers SiO2/SiNx distributed Bragg reflector and a spot-size converter are both employed and improve responsivity by 61%. An optimized optical matching layer and a spot-size converter combined with the reflector lead to a 0.66 A/W responsivity at 1550 nm wavelength. 3 dB bandwidth of the device can achieve 85 GHz with a 3μm × 10 μm active area. The responsivity improvement indicates a higher quantum efficiency and signal-to-noise ratio. It could be beneficial for high speed optical communication and other applications.

InP-Based Butt-Joint Coupled Waveguide Photodiodes Integrated With Various Functions for 100 GBaud Coherent Detection

This paper reports on the performance of an InP-based butt-joint (BJ) coupled waveguide photodiode (PD) for 100 GBaud coherent detection. We adopt a dual-layer absorber comprised of p- and i-type GaInAs absorption layers to enhance the advantage of BJ coupled waveguide PDs which overcome the tradeoff between high responsivity and wide bandwidth. As a result, a responsivity as high as 0.90 A/W over the C-band and a wide 3 dB bandwidth of 71 GHz have been successfully obtained at a reverse bias voltage of 2.5 V. Towards the realization of compact coherent modules without complicated assembly processes, we have also fabricated a compact photonic integrated circuit (PIC) chip (Chip size: 2.6 × 4.1 mm) configured by 12 BJ coupled waveguide PDs and various optical functions, such as 90° hybrids and variable optical attenuators (VOAs) through the InP-based monolithic integration technology. An integrated coherent transmitter-receiver optical sub-assembly (IC-TROSA) employing the PIC has exhibited receiver performance sufficient for 100 GBaud coherent detection.

Design and fabrication of multi-channel photodetector array monolithic with arrayed waveguide grating**Project supported by the National High Technology Research and Development Program of China (Grant Nos. 2013AA031401, 2015AA016902, and 2015AA016904), the National Natural Science Foundation of China (Grant Nos. 61176053, 61274069, and 61435002), and the National Basic Research Program of China (Grant Nos. 2012CB933503 and 2013CB932904).

We have provided optical simulations of the evanescently coupled waveguide photodiodes integrated with a 13-channels AWGs. The photodiode could exhibit high internal efficiency by appropriate choice of layers geometry and refractive index. Aseamless joint structure has been designed and fabricated for integrating the output waveguides of AWGs with the evanescently coupled waveguide photodiode array. The highest simulation quantum efficiency could achieve 92% when the matching layer thickness of the PD is 120 nm and the insertion length is 2 μm. The fabricated PD with 320-nm-thick matching layer and 2-μm-length insertion matching layer present a responsivity of 0.87 A/W.

Design and optimization of evanescently coupled waveguide photodiodes

We present the design and optimization of evanescently coupled waveguide photodiodes (EC-WPDs) based on the coupling modes theory and the beam propagation method. Efficient focalization of the optical power in the absorber is achieved by an appropriate choice of index matching layers of EC-WPDs. Numerical simulation shows that high-speed (40 GHz), high quantum efficiency (81%) and high linearity photodiodes can be achieved, and EC-WPDs are promising devices for future optical communication systems.

Novel directional coupled waveguide photodiode–concept and preliminary results

A novel photodiode is presented using a directional coupler incorporated with a UTC style photodiode with 0.88 A/W responsivity and 35 dBm OIP3 at 25 mA. The device responsivity is characterized at various photocurrents up to 10 mA and the OIP3 is measured up to 25 mA and 10 GHz. Additionally, the device capacitance is measured and used to model the capacitance limited OIP3 of the device. The failure of the device was compared to a traditional waveguide photodiode showing burnout no longer occurs at the front of the device and demonstrated the potential of the new design to control the photocurrent density profile for a waveguide style photodiode.

Dual Evanescently Coupled Waveguide Photodiodes with High Reliability for over 40-Gbps Optical Communication Systems

For over 40-Gbps optical communication systems, phase coded modulation formats, like differential phase shift keying (DPSK) and quadrature phase shift keying (QPSK), are very important for signal frequency efficiency and long-reach transmission. In such systems, differential receivers which regenerate phase signals are key components. Dual Photo Diodes (dual PDs) are key semiconductor devices which determine the receiver performance. Each PD of the dual PDs should realize high speed performance, high responsibility and high input power operation capability. Highly symmetrical characteristics between the two PDs should be also realized, thus the dual PDs are desired to be monolithically integrated to one chip. In this paper, we describe the design, fabrication, characteristics and reliability of monolithically integrated dual evanescently coupled waveguide photodiodes (EC-WG-PDs) for the purpose described above. The structure of the EC-WG-PDs offers the attractive advantages of high speed performance, high responsivity and high input power operation. Furthermore, their fabrication process is suitable for the integration of two PDs on one ship. First, the optimization was done for high products of 3-dB bandwidth and responsivity for 43-Gbps DPSK receivers. Excellent characteristics (50GHz bandwidth with a responsivity of 0.95A/W), and high reliability were demonstrated. The other type of optimization was done for ultra high speed operation up to 100-Gbps. The fabricated PDs exhibited the 3dB-bandwidth of 80GHz with a responsivity of 0.25A/W. Furthermore, 43-Gbps RZ-DPSK receivers including the dual EC-WG-PDs based on the former optimization and differential transimpedance amplifiers (TIAs) newly developed for the purpose were also presented. Clear and symmetrical eye openings were observed for both ports. The OSNR characteristics exhibited 14.3dB at a bit error rate of 10-3 that is able to be recovery with FEC. These performances are enough for practical use in 43-Gbps RZ-DPSK systems.

InP-Based High-Speed Photodetectors

This paper provides an overview on recent advances of InP-based photodetectors for high-speed fiber-optic applications, with emphasis on evanescently coupled waveguide photodiodes, balanced receivers, and distributed traveling wave photodetectors.

Recent Advances in Ultra-High-Speed Waveguide Photodiodes for Optical Communication Systems

This paper describes the recent advances in semiconductor photodiodes for use in ultra-high-speed optical systems. We developed two types of waveguide photodiodes (WG-PD) — an evanescently coupled waveguide photodiode (EC-WG-PD) and a separated-absorption-and-multiplication waveguide avalanche photodiode (WG-APD). The EC-WG-PD is very robust under high optical input operation because of its distribution of photo current density along the light propagation. The EC-WG-PD simultaneously exhibited a high external quantum efficiency of 70% for both 1310 and 1550nm, and a wide bandwidth of more than 40GHz. The WG-APD, on the other hand, has a wide bandwidth of 36.5GHz and a gain-bandwidth product of 170GHz as a result of its small waveguide mesa structure and a thin multiplication layer. Record high receiver sensitivity of -19.6dBm at 40Gbps was achieved. Additionally, a monolithically integrated dual EC-WG-PD for differential phase shift-keying (DPSK) systems was developed. Each PD has equivalent characteristics with 3-dB-down bandwidth of more than 40GHz and external quantum efficiency of 70% at 1550nm.