A broadband silicon photonic-integrated-circuit based RF spectrum analyzer with 10 MHz spectral resolution

TL;DR

This paper presents a silicon photonic integrated circuit RF spectrum analyzer achieving 10 MHz spectral resolution over 10 GHz bandwidth, combining high resolution, broad bandwidth, and fast update rate in a compact device.

Contribution

It introduces a novel PIC-based RF spectrum analyzer with record-high resolution and a new encoding scheme for fast, wideband RF spectrum analysis.

Findings

Achieved 100 MHz resolution at 1550 nm wavelength.

Resolved RF tones separated by 10 MHz over 10 GHz bandwidth.

Operates as a single-shot spectrometer supporting fast updates.

Abstract

Designing miniaturized optical spectrometers is an increasingly active area of research as spectrometers are crucial components for a wide range of applications including chemical and material analysis, medical diagnostics, classical and quantum sensing, characterization of light sources, and radio frequency (RF) spectrum analysis. Among these applications, designing on-chip spectrometers for RF spectrum analysis is particularly challenging since it requires combining high resolution and large bandwidth with a fast update rate. Existing chip-scale spectrometers cannot achieve the resolution required for RF analysis, setting aside challenges in maintaining a fast update rate and broad bandwidth. In this work, we address these challenges by introducing a silicon photonic integrated circuit (PIC)-based RF spectrum analyzer that combines an ultra-high-resolution speckle spectrometer with an interferometric RF-to-optical encoding scheme. The PIC-based speckle spectrometer uses a path-mismatched multimode interferometer with inverse designed splitters to compensate for waveguide loss, enabling a record-high resolution of 100 MHz (0.8 pm at a wavelength of 1550 nm). To further improve the resolution of the overall RF spectrum analyzer, we modify the RF-to-optical encoding scheme by directing the RF signal through a path mismatched interferometer and encoding the outputs of the RF interferometer on separate optical carriers. This further reduces the RF spectral correlation width of the combined system, enabling the RF spectrum analyzer to resolve RF tones separated by 10 MHz across a bandwidth of 10 GHz. Since this approach operates as a single-shot spectrometer, it can support fast update rates, providing a path to compact, persistent wideband RF spectrum analysis.