Tandem Configuration of Microrings and Arrayed Waveguide Gratings for a High-Resolution and Broadband Stationary Optical Spectrometer at 860 nm

Abstract

Stationary optical spectrometers with both high spectral resolution and broad bandwidth at 800 nm −900 nm are needed in the high speed biosensing and bioimaging systems. Here we present an integrated spectrometer which uses a pair of fixed wavelength microring resonators (MRR) integrated in tandem with a pair of identical arrayed waveguide gratings (AWG). The use of narrow-line-width MRRs in the primary stage offers highspectral resolution with an ultracompact footprint. The broadband AWG in the secondary stage provides a wide free spectral range (FSR). The AWG is designed to have channel spacing equal to the FSR of the MRR, so that the cyclically dropped wavelengths that cannot be distinguished by the MRR can be well separated by the secondary-stage AWG. By interleaving the resonances of the MRRs, high spectral resolution and wide optical bandwidth are attained. The proof-of-concept demonstration was implemented on a silicon nitride platform for 860 nm center wavelength. We interleaved two MRRs and integrated them with two 35-channel AWGs. The spectrometer has 70 wavelength channels within an overall size of 1.15 mm × 1.25 mm. The channel spacing is 0.75 nm, and the optical bandwidth is 57.5 nm.

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.…”

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

“…Integrated spectrometers based on various designs and working principles have been demonstrated since the early 1990s. Conventional integrated spectrometers utilize dispersive optics or narrowband filters to separate the spectral content of the incident signal into an array of photodetectors. − The spectral resolution of dispersive optic-based spectrometers is limited by the length of the optical path because it is inversely proportional to the optical path. Narrowband filters selecting a specific wavelength of light allow spectrometers to be more compact.…”

“…The high spectral resolution is possibly achieved by introducing multiple filters with narrow channel spacing. However, the spectral bandwidth is fundamentally limited by the free spectral range (FSR). ,, For the silicon ring resonator with acceptable bend loss, the bend radius should be larger than 5 μm, indicating an FSR no larger than 19 nm around 1550 nm. Another challenge lies in inevitable fabrication imperfections for the large-scale filter array, which is crucial for small channel spacing.…”

Dual-Polarization Bandwidth-Bridged Bandpass Sampling Fourier Transform Spectrometer from Visible to Near-Infrared on a Silicon Nitride Platform

“…However, the development of on-chip spectrometers based on photonic integrated circuits (PICs) has shown great promise in the sense that they can offer low-cost, portable, and robust spectroscopy, along with low power consumption and high reliability . In recent decades, a myriad of on-chip spectrometer devices have been demonstrated based on different operating schemes, such as dispersive optics using arrayed waveguide gratings (AWGs), − echelle grating, metasurface elements, arrayed narrow-band filters, computational spectral reconstruction-based systems, and Fourier transform spectroscopy (FTS). Dispersive spectrometers, often called grating spectrometers or scanning spectroscopy, splits the wavelengths of input light into separate spectral ranges and collects each wavelength individually.…”

“…Dispersive spectrometers, often called grating spectrometers or scanning spectroscopy, splits the wavelengths of input light into separate spectral ranges and collects each wavelength individually. A lot of grating-based devices have been studied and reported with sub-nanometer resolution in the visible (VIS) to near-infrared (NIR) range, − ,, but the gratings or slits on a dispersive device limit the amount of energy reaching the detector and the scan speed of spectroscopy because the individual wavelengths across the bandwidth have to be measured separately. Meanwhile, FTS is a technique that measures the spectrum with the interference of light instead of dispersion, so it does not separate energy into individual wavelengths for measuring the spectrum, offering advantages including high optical throughput and a multiplexing advantage, and, in turn, a larger signal-to-noise ratio (SNR) and faster data collection speed compared to the grating-based dispersive counterparts.…”