[Paper Review] Active-cavity photonic molecule optical data wavelength converter for silicon photonics platforms

Hayk Gevorgyan, Anatol Khilo+1 more|arXiv (Cornell University)|May 11, 2020

Photonic and Optical Devices4 citations

TL;DR

This paper demonstrates a CMOS-compatible, electrically driven active-cavity photonic molecule wavelength converter in silicon photonics that enables efficient, on-chip optical data wavelength conversion using low-voltage RF drive signals. It achieves up to -13 dB conversion efficiency with 6 GHz bandwidth for 24 GHz wavelength shifts and -18 dB efficiency with 4.8 GHz bandwidth for 56 GHz shifts, successfully converting 4 Gbps NRZ optical data without external optical or high-power RF pumps.

ABSTRACT

We demonstrate an optical data wavelength converter based on an electrically driven photonic molecule structure comprising two coupled active silicon microring resonators. The converter, supplied by a continuous-wave (CW) microwave drive signal equal in frequency to the desired wavelength shift, replicates an input optical signal at a new wavelength. The optical coupled-cavity system matches supermode resonances to the input and wavelength-converted optical waves maximizing the conversion efficiency. Two device designs that perform wavelength up- and down-conversion by 0.19 nm (24 GHz) with -13 dB conversion efficiency and 6 GHz bandwidth; and by 0.45 nm (56 GHz) with -18 dB efficiency and 5 GHz bandwidth are demonstrated. A 4 Gbps non-return-to-zero (NRZ) optical data stream is shifted in wavelength and successfully recovered. This architecture accepts CMOS-level RF drive voltages and can be integrated in monolithic CMOS electronic-photonic platforms with a simple signal source circuit as part of a self-contained subsystem on chip that generates and carries out the wavelength conversion, requiring no high-frequency (optical or electrical) and high-power external pump input to the chip. This type of device may become a new standard element in the component libraries of silicon and CMOS photonics processes.

Motivation & Objective

• To develop a low-power, on-chip optical wavelength converter for silicon photonics that avoids reliance on high-power optical pumps.
• To overcome the efficiency roll-off limitations of single-cavity modulators by using coupled active microring resonators.
• To enable bidirectional wavelength conversion (up- and down-conversion) with high efficiency using only CMOS-level RF drive voltages.
• To integrate the wavelength conversion function monolithically with electronic circuits on a single chip, eliminating external high-frequency or high-power inputs.
• To establish a new component for silicon and CMOS photonic process design kits (PDKs) enabling wavelength-division multiplexing-based signal processing.

Proposed method

• The device uses two electrically driven, coupled active silicon microring resonators forming a photonic molecule with symmetric and antisymmetric supermodes.
• Electrical modulation via RF signals at 24 GHz or 56 GHz induces frequency translation between the supermodes, shifting the input signal to a new wavelength.
• The system is designed so that the input signal excites one supermode, and the RF drive couples energy to the other, enabling efficient wavelength conversion.
• Theoretical modeling uses a coupled-mode theory framework to predict conversion efficiency, with the response analogous to a second-order frequency-translating filter.
• The converter is biased at -1.5 V DC and driven with 4 V peak-to-peak RF signals at the target frequency to achieve phase modulation and resonance tuning.
• On-chip integration with CMOS electronics allows self-contained operation using only DC power and on-chip RF signal generation.

Experimental results

Research questions

• RQ1 Can a dual-active-cavity photonic molecule structure in silicon photonics achieve efficient, low-power optical wavelength conversion without requiring external optical pumps?
• RQ2 How does the coupling between two active microring resonators enable bidirectional wavelength conversion with high efficiency and wide bandwidth?
• RQ3 To what extent can conversion efficiency and bandwidth be improved using CMOS-compatible RF drive signals and on-chip signal generation?
• RQ4 Can such a device be monolithically integrated with electronic circuits to form a self-contained, pump-free subsystem on a single chip?
• RQ5 What is the maximum data rate achievable with this architecture, and how is it limited by external filtering and device bandwidth?

Key findings

• The device demonstrated wavelength conversion with -13 dB efficiency and 6 GHz bandwidth for a 24 GHz shift (±0.19 nm), and -18 dB efficiency with 4.8 GHz bandwidth for a 56 GHz shift (±0.45 nm).
• A 4 Gbps non-return-to-zero (NRZ) optical data stream was successfully shifted in wavelength and recovered, with eye diagrams confirming signal integrity.
• The system supports bidirectional operation: up-conversion in one direction and down-conversion in the opposite, with equal efficiency.
• The conversion efficiency is 15–50 dB higher than that of single-cavity modulators, overcoming the photon lifetime-limited efficiency roll-off.
• The device operates using only CMOS-level RF drive voltages and DC power, with no need for external high-frequency or high-power optical inputs.
• The theoretical model based on coupled-mode theory accurately predicts the measured conversion efficiency and response shape, validating the design approach.