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Inverse-designed photonic circuits for fully passive, bias-free Kerr-based nonreciprocal transmission and routing
Ki Youl Yang, Jinhie Skarda, Michele Cotrufo, Avik Dutt, Geun Ho Ahn, Dries Vercruysse, Shanhui Fan, Andrea Alù, Jelena Vučković
TL;DR
Integrated optical isolation remains challenging because of high insertion loss and other integration barriers. This work uses inverse-designed Kerr resonators for passive, bias-free nonreciprocal transmission and routing, including a cascaded device and an on-chip ranging demonstration. The cascade achieves near-unity transmission across a broad nonreciprocal intensity range, and the device supports distance measurement up to 60 m.
Problem
Integrated optical isolation in large-scale photonics remains elusive, with high insertion loss, weak magneto-optical effects, and material incompatibility among the stated challenges.
Source: p. 1Method
The authors use inverse-designed Kerr Fano resonators for passive, bias-free transmission and routing, then cascade Fano and Lorentzian resonators to increase the nonreciprocal intensity range while preserving high transmission.
Source: pp. 1–2Results
Near-unity transmission (T > 99%) was obtained over a NRIR > 6 dB, and the device demonstrated distance measurements up to 60 m.
Source: p. 2Takeaways & Limitations
The demonstrated nonreciprocal circuit is practically relevant to chip-scale LIDAR distance measurement using a fully passive, bias-free device.
Source: p. 2These nonlinearity-based devices are mainly useful for pulsed or periodic sources because of dynamic reciprocity constraints.
Source: p. 6
Abstract
from arXiv · showhide
Nonreciprocal devices such as isolators and circulators are key enabling technologies for communication systems, both at microwave and optical frequencies. While nonreciprocal devices based on magnetic effects are available for free-space and fibre-optic communication systems, their on-chip integration has been challenging, primarily due to the concomitant high insertion loss, weak magneto-optical effects, and material incompatibility. We show that Kerr nonlinear resonators can be used to achieve all-passive, low-loss, bias-free, broadband nonreciprocal transmission and routing for applications in photonic systems such as chip-scale LIDAR. A multi-port nonlinear Fano resonator is used as an on-chip, all-optical router for frequency comb based distance measurement. Since time-reversal symmetry imposes stringent limitations on the operating power range and transmission of a single nonlinear resonator, we implement a cascaded Fano-Lorentzian resonator system that overcomes these limitations and significantly improves the insertion loss, bandwidth and non-reciprocal power range of current state-of-the-art devices. This work provides a platform-independent design for nonreciprocal transmission and routing that are ideally suited for photonic integration.
Appendix I: Characterization of inverse-design-reflectors
The appendix characterizes inverse-designed reflectors by comparing measured reflectance with simulation and checking measured reflectance against design targets.
Appendix I: Characterization of inverse-design-reflectors
- The measured reflectance spectrum agrees with the numerical simulation of the fabricated inverse-designed structure.The spectrum compares measured blue dots with the simulated red curve.Source: Figure S1 · p. 9
- At 1550 nm, measured reflectances are shown against 60%, 80%, 95%, and 99% design targets; the main-text Fano resonators use the 60% and 80% designs.Source: Figure S1 · p. 9
- Reflectance was characterized using Fabry–Perot resonators with identical reflectors at both ends and measured finesse.The measured spectrum showed fair agreement with finite-difference time-domain simulation.Source: Appendix I · p. 9
Appendix II: Operation of a Fano device – spectral bandwidth, operation power
The appendix measures forward and backward transmission of a single Fano resonator across laser wavelengths at fixed input power.
Appendix II: Operation of a Fano device – spectral bandwidth, operation power
- The spectral measurement uses a single Fano resonator with 80% reflectance and a 2.28 µm offset from the resonator midplane.Source: Appendix II: Operation of a Fano… · p. 9
- Transmission in both propagation directions is measured as laser detuning from the Fano resonance changes.Source: Appendix II: Operation of a Fano… · p. 9
- The wavelength sweep holds CW input power constant at 14 dBm loaded in the silicon waveguide, with no counter-propagating waves.Source: Appendix II: Operation of a Fano… · p. 9
Appendix III: Nonreciprocal transmission of pulsed signal in an asymmetric Fano resonator
The pulsed-signal isolation experiment compares forward and backward transmission while varying backward input intensity, using delayed pulse trains to avoid pulse overlap.
Appendix III: Nonreciprocal transmission of pulsed signal in an asymmetric Fano resonator
- The 10 MHz pulse trains propagate in both directions with a slight time delay to avoid overlap, and their transmissions are recorded in real time.Source: Appendix III: Nonreciprocal… · p. 9
- Forward pulse trains are launched at intensities that make the device highly transmissive, while backward-pulse transmission is read at varying backward input intensities.Source: Appendix III: Nonreciprocal… · p. 10
- The setup routes transmitted signals from the input and output ports to a fast photodetector through optical circulators.Source: Figure S3 · p. 10