Broadband and High-Resolution Integrated Spectrometer Based on a Tunable FSR-Free Optical Filter Array

Abstract

Integrated spectrometers provide the possibility of compact, low-cost portable spectroscopy sensing, which is the critical component of the lab-on-a-chip system. However, using existing on-chip designs is challenging to realize a high-resolution miniature spectrometer over a broad wavelength range. Here, we demonstrate an on-chip time-sampling narrowband filter array spectrometer that enables simultaneous acquisition of high-resolution spectra via optical Fabry−Peŕot cavities and a large spectral range with tunable free spectral range free filters. Two spectrometers consisting of five and seven filter cells with a compact footprint are fabricated and experimentally characterized, demonstrating a resolution of <0.43 and <0.51 nm and a spectral range of 73.2 and 102.7 nm, respectively. Unknown broad bandwidth input signal spectra can be successfully retrieved. Integrating more filter cells with thermal isolation trenches can dramatically boost the operational spectral range. Such spectrometers may open up new pathways toward spectral analytical applications.

Integrated Single-Resonator Spectrometer beyond the Free-Spectral-Range Limit

“…Due to the inherent trade-off between linewidths and free spectral ranges (FSRs), however, it is challenging to simultaneously attain high resolutions and broad bandwidths in filter-based spectrometers. This issue can be resolved to a limited extent by sorting FSRs with extra demultiplexers − or paralleling multiple FSR-free photonic-crystal (PhC) nanobeam cavities. − Nevertheless, these approaches will eventually raise the device footprint and layout complexity. Also, the FSR broadening of nanobeam cavities is typically accompanied by the tightly confined mode volume, resulting in a narrow tuning range and an increase in aggregate power consumption. , For FTSs, the unknown spectrum is retrieved in the Fourier domain from a modulated interferogram.…”

“…For instance, frequency-domain optical coherence tomography (OCT) requires a <85 pm spectral resolution and a >75 nm bandwidth (around the 1300 nm wavelength) to accomplish a <10 μm depth resolution and a >5 mm imaging depth . It is feasible to circumvent the FSR limit by exploiting tandem filters or parallel nanocavities, − in which temporal and spatial decorrelations are combined. In spite of this, the scalability of these schemes is basically compromised by larger footprints and higher power arising from a greater number of cascaded resonators.…”

“…Also, the FSR broadening of nanobeam cavities is typically accompanied by the tightly confined mode volume, resulting in a narrow tuning range and an increase in aggregate power consumption. 19,20 For FTSs, the unknown spectrum is retrieved in the Fourier domain from a modulated interferogram. Various schemes, e.g., spatial heterodyne Mach−Zehnder interferometers (MZIs), 22−26 tunable/switchable MZIs, 27−30 and stationary-wave interferometers, 31−33 have been reported to implement the chip-scale Fourier spectrometry.…”

“…This issue can be resolved to a limited extent by sorting FSRs with extra demultiplexers − or paralleling multiple FSR-free photonic-crystal (PhC) nanobeam cavities. − Nevertheless, these approaches will eventually raise the device footprint and layout complexity. Also, the FSR broadening of nanobeam cavities is typically accompanied by the tightly confined mode volume, resulting in a narrow tuning range and an increase in aggregate power consumption. , For FTSs, the unknown spectrum is retrieved in the Fourier domain from a modulated interferogram. Various schemes, e.g., spatial heterodyne Mach–Zehnder interferometers (MZIs), − tunable/switchable MZIs, − and stationary-wave interferometers, − have been reported to implement the chip-scale Fourier spectrometry.…”

Planar photonic chips with tailored dispersion relations for high-efficient spectrographic devices

“…Thus, much attention is focused on improving the signal-to-noise ratio, while the spectral resolution is always been ignored 31,35,36 . To improve the spectral resolution, many state-of-the-art techniques have employed tunable narrowband filters 37,38,39,40 . However, the challenge lies in inevitable fabrication imperfections for the large-scale complex devices.…”