[Paper Review] A versatile, inexpensive integrated photonics platform

Jeffrey M. Shainline, Sonia Buckley+7 more|arXiv (Cornell University)|Nov 7, 2016

Photonic and Optical Devices72 references17 citations

TL;DR

This paper presents a low-cost, versatile integrated photonics platform using near-ambient temperature deposition of SiN waveguides and superconducting nanowire single-photon detectors (SNSPDs) with i-line lithography. The process enables high-accuracy, scalable fabrication of passive devices like Mach-Zehnder interferometers and ring resonators, and achieves robust, process-agnostic fiber packaging compatible with operation from 1 K to 160 °C, enabling applications in quantum photonics and nonlinear optics with high detection efficiency and low loss.

ABSTRACT

We present an approach to fabrication and packaging of integrated photonic devices that utilizes waveguide and detector layers deposited at near-ambient temperature. All lithography is performed with a 365 nm i-line stepper, facilitating low cost and high scalability. We have shown low-loss SiN waveguides, high-$Q$ ring resonators, critically coupled ring resonators, 50/50 beam splitters, Mach-Zehnder interferometers (MZIs) and a process-agnostic fiber packaging scheme. We have further explored the utility of this process for applications in nonlinear optics and quantum photonics. We demonstrate spectral tailoring and octave-spanning supercontinuum generation as well as the integration of superconducting nanowire single photon detectors with MZIs and channel-dropping filters. The packaging approach is suitable for operation up to 160 \degree C as well as below 1 K. The process is well suited for augmentation of existing foundry capabilities or as a stand-alone process.

Motivation & Objective

• To develop a low-cost, scalable integrated photonics fabrication process compatible with diverse substrates and foundry workflows.
• To enable high-accuracy, low-loss passive photonic devices using i-line stepper lithography and near-ambient temperature deposition.
• To integrate superconducting nanowire single-photon detectors (SNSPDs) with on-chip photonic circuits for quantum optical applications.
• To create a process-agnostic fiber packaging scheme functional from 1 K to 160 °C for broad application compatibility.
• To demonstrate the platform’s utility in nonlinear optics and quantum photonics through supercontinuum generation and on-chip detector integration.

Proposed method

• Deposits SiN waveguiding layers via plasma-enhanced chemical vapor deposition (PECVD) at <65 °C using N₂ and SiH₄ precursors.
• Uses i-line stepper (365 nm) for all lithography steps, enabling low-cost, high-scalability fabrication.
• Deposits WSi-based SNSPDs via sputtering at near-ambient temperatures for compatibility with backend-of-line (BEOL) integration.
• Employs a process-agnostic fiber packaging method using alignment markers and epoxy bonding, functional from 1 K to 160 °C.
• Integrates SNSPDs with Mach-Zehnder interferometers and channel-dropping filters via direct waveguide coupling.
• Utilizes dispersion-engineered waveguides and ring resonators to achieve high Q-factors (>10⁶) and critical coupling.

Experimental results

Research questions

• RQ1 Can a low-cost, scalable photonic platform be developed using standard i-line lithography and near-ambient temperature deposition?
• RQ2 Can high-accuracy, low-loss SiN waveguides and high-Q resonators be fabricated with this approach?
• RQ3 Can superconducting nanowire single-photon detectors be effectively integrated with on-chip photonic circuits using this process?
• RQ4 Can the fiber packaging scheme achieve reliable, high-throughput coupling across extreme temperatures (1 K to 160 °C)?
• RQ5 Can this platform support advanced applications such as octave-spanning supercontinuum generation and quantum photonic circuits?

Key findings

• Low-loss SiN waveguides with propagation loss of ~0.2 dB/cm were achieved using PECVD deposition at <65 °C.
• High-Q ring resonators with Q-factors exceeding 10⁶ were demonstrated, enabling critical coupling and high extinction ratios.
• A 50/50 Mach-Zehnder interferometer (MZI) exhibited nearly 30 dB extinction depth in spectral response, indicating high visibility and low crosstalk.
• Waveguide-integrated SNSPDs achieved near-identical performance across multiple devices, with extinction >20 dB observed in four-channel dropping filters.
• The fiber packaging scheme enabled stable coupling over a wide temperature range, from 1 K to 160 °C, with no degradation in performance.
• Octave-spanning supercontinuum generation was demonstrated using spectral tailoring and a frequency comb, confirming nonlinear optical utility.