Reconstructive spectrometer using a photonic crystal cavity

Abstract

Optical spectrometers have propelled scientific and technological advancements in a wide range of fields. While sophisticated systems with excellent performance metrics are serving well in controlled laboratory environments, many applications require systems that are portable, economical, and robust to optical misalignment. Here, we propose and demonstrate a spectrometer that uses a planar one-dimensional photonic crystal cavity as a dispersive element and a reconstructive computational algorithm to extract spectral information from spatial patterns. The simple fabrication and planar architecture of the photonic crystal cavity render our spectrometry platform economical and robust to optical misalignment. The reconstructive algorithm allows miniaturization and portability. The intensity transmitted by the photonic crystal cavity has a wavelength-dependent spatial profile. We generate the spatial transmittance function of the system using finite-difference time-domain method and also estimate the dispersion relation. The transmittance function serves as a transfer function in our reconstructive algorithm. We show accurate estimation of various kinds of input spectra. We also show that the spectral resolution of the system depends on the cavity linewidth that can be improved by increasing the number of periodic layers in distributed Bragg mirrors. Finally, we experimentally estimate the center wavelength and linewidth of the spectrum of an unknown light emitting diode. The estimated values are in good agreement with the values measured using a commercial spectrometer.

Sparsity for Ultrafast Material Identification

“…[ 22 ] By taking advantage of the sparsity of the problem, we could substantially reduce the number of measurements and thus make material identification fast, inexpensive, and portable. [ 23–45 ]…”

Determining the transfer function of a reconstructive spectrometer using measurements at two wavelengths

“…© 2023 Optica Publishing Group https://doi.org/10.1364/OL.494412 Introduction. Reconstructive spectrometers recover an input frequency spectrum by solving an inverse problem using different computational algorithms [1][2][3][4][5][6][7][8][9]. These compact spectrometers offer high resolution and break the inevitable size-resolution trade-off of conventional spectrometers.…”

“…Their operating principle relies on mapping the spatial information to the spectral information using the transfer function of the system, which is the pre-calibrated system response. Different platforms such as patterned photonic crystals [10][11][12], disordered photonic structures [2], photonic crystal cavities [1,13,14], miniaturized microdonut resonators [15], integrated micro-ring resonator with diffraction gratings [16], arrayed waveguide gratings [17], variable material absorption [18], spectral filters [19,20], surface plasmon polaritons [21], and dielectric metasurfaces [22], have been used to demonstrate reconstructive spectrometers. Prior to our recent work [1], most of these demonstrations relied on complex and expensive fabrication techniques and were sensitive to optical misalignment.…”

“…Different platforms such as patterned photonic crystals [10][11][12], disordered photonic structures [2], photonic crystal cavities [1,13,14], miniaturized microdonut resonators [15], integrated micro-ring resonator with diffraction gratings [16], arrayed waveguide gratings [17], variable material absorption [18], spectral filters [19,20], surface plasmon polaritons [21], and dielectric metasurfaces [22], have been used to demonstrate reconstructive spectrometers. Prior to our recent work [1], most of these demonstrations relied on complex and expensive fabrication techniques and were sensitive to optical misalignment. Our demonstration utilized a scalable fabrication technique, a low-cost web camera, and a computational reconstruction technique to reliably reconstruct the input spectrum in the presence of noise and optical misalignment.…”

“…A critical issue that remains unaddressed by the state-ofthe-art reconstructive spectrometers, including our recent work [1], is the requirement of a tunable and narrowband source to generate the transfer function of the system for use in the reconstruction algorithm. This requirement increases the cost of development of the spectrometer and hinders wide deployment in the field.…”