[Paper Review] Ultra-wideband Waveguide-coupled Photodiodes Heterogeneously Integrated on a Thin-film Lithium Niobate Platform

Chao Wei, Youren Yu+8 more|arXiv (Cornell University)|May 13, 2023

Photonic and Optical Devices26 references5 citations

TL;DR

This paper presents the first heterogeneously integrated, waveguide-coupled InP/InGaAs modified uni-traveling carrier (MUTC) photodiodes on a thin-film lithium niobate (TFLN) platform, achieving a record 3-dB bandwidth of 110 GHz and 0.4 A/W responsivity at 1550 nm. The integration leverages wafer-level heterogeneous bonding to enable high-speed, compact, and scalable photonic integrated circuits with enhanced optical confinement and electro-optic performance.

ABSTRACT

With the advantages of large electro-optical coefficient, wide transparency window, and strong optical confinement, thin-film lithium niobate (TFLN) technique has enabled the development of various high-performance optoelectronics devices, ranging from the ultra-wideband electro-optic modulators to the high-efficient quantum sources. However, the TFLN platform does not natively promise lasers and photodiodes. This study presents an InP/InGaAs modified uni-traveling carrier (MUTC) photodiodes heterogeneously integrated on the TFLN platform with a record-high 3-dB bandwidth of 110 GHz and a responsivity of 0.4 A/W at a 1550-nm wavelength. It is implemented on a wafer-level TFLN-InP heterogeneous integration platform and is suitable for the large-scale, multi-function, and high-performance TFLN photonic integrated circuits.

Motivation & Objective

• To overcome the lack of native photodetectors on thin-film lithium niobate (TFLN) platforms for high-speed photonic integration.
• To enable wafer-scale, heterogeneous integration of high-performance photodiodes with TFLN waveguides for scalable photonic circuits.
• To achieve ultra-wideband operation (≥100 GHz) with high responsivity at 1550 nm for applications in optical communications and sensing.
• To demonstrate compatibility with existing TFLN-based devices such as modulators and quantum sources in a multi-functional platform.

Proposed method

• Heterogeneous integration of InP/InGaAs MUTC photodiodes onto a thin-film lithium niobate (TFLN) platform using wafer-level bonding techniques.
• Design of waveguide-coupled photodiodes to efficiently couple light from TFLN waveguides into the InP-based absorber region.
• Use of a modified uni-traveling carrier (MUTC) structure to reduce transit time and increase bandwidth.
• Optimization of the photodiode’s Schottky contact and intrinsic layer thickness to balance bandwidth and responsivity.
• Employment of a transfer-printing process for precise alignment and high-yield integration of III-V materials on TFLN substrates.
• Characterization of RF and optical performance using S-parameter measurements and responsivity testing at 1550 nm.

Experimental results

Research questions

• RQ1 Can high-bandwidth photodiodes be effectively integrated on a TFLN platform that lacks native photodetectors?
• RQ2 What is the maximum achievable bandwidth of a waveguide-coupled photodiode when heterogeneously integrated on TFLN?
• RQ3 How does the responsivity of the integrated photodiode compare to state-of-the-art devices at 1550 nm?
• RQ4 Can wafer-level heterogeneous integration enable scalable, multi-functional photonic integrated circuits on TFLN?
• RQ5 What are the key design and process parameters that determine the bandwidth and responsivity of such integrated photodiodes?

Key findings

• The integrated photodiode achieves a record 3-dB electrical bandwidth of 110 GHz, demonstrating ultra-wideband operation.
• The device exhibits a responsivity of 0.4 A/W at 1550 nm, indicating high quantum efficiency and effective light coupling.
• The waveguide-coupled design enables efficient optical power transfer from TFLN waveguides to the III-V absorber layer.
• The wafer-level heterogeneous integration process ensures high yield and compatibility with large-scale photonic integrated circuits.
• The TFLN platform supports both high-speed photodetection and existing functionalities like electro-optic modulation, enabling full photonic integration.
• The results validate the feasibility of building high-performance, multi-functional photonic integrated circuits on a single TFLN substrate.