Advances in cost-effective integrated spectrometers

Abstract

The proliferation of Internet-of-Things has promoted a wide variety of emerging applications that require compact, lightweight, and low-cost optical spectrometers. While substantial progresses have been made in the miniaturization of spectrometers, most of them are with a major focus on the technical side but tend to feature a lower technology readiness level for manufacturability. More importantly, in spite of the advancement in miniaturized spectrometers, their performance and the metrics of real-life applications have seldomly been connected but are highly important. This review paper shows the market trend for chip-scale spectrometers and analyzes the key metrics that are required to adopt miniaturized spectrometers in real-life applications. Recent progress addressing the challenges of miniaturization of spectrometers is summarized, paying a special attention to the CMOS-compatible fabrication platform that shows a clear pathway to massive production. Insights for ways forward are also presented.

Fig. 1. Market penetration rates for compact spectrometers; yellow and red bars represent the rates in 2019 and 2024, respectively.

Reprinted from ref. with permission from Tematys

Fig. 2. Forecasts for spectrometer modules of various sizes.

Reprinted from ref. with permission from Tematys

Fig. 3. Approximate positions of the vibrational mode assignments of exemplary functional groups in the NIR band.

Reprinted from ref. with permission from Metrohm

Fig. 4. Summary of the spectrometer specifications for the detections of various biomarkers based on published demonstrations.

Solid and dashed lines correspond to in-vivo and in-vitro testing, respectively

Fig. 5. Summary of the spectrometer specifications for industrial applications based on published demonstrations.

Solid and dash line represent NIR and Raman spectroscopy, respectively

Fig. 6. Working principles of on-chip spectrometers.

Schematic illustration of the underlying principles for different on-chip integrated spectrometers, including WdM spectrometers based on (a) dispersive structure, (b) arrayed or tunable narrowband filters, and WM spectrometers based on (c) Fourier-transform spectrometers formed by tunable Mach–Zehnder interferometers, and (d) broadband filter or detector arrays with distinctive spectral responses for computational spectrum reconstruction, respectively

Fig. 7. PCG based spectrometers on silicon photonics platform.

a Schematic illustration of a PCG spectrometer. b SEM image of a silicon PCG spectrometer. c–e PCG spectrometers with Bragg reflectors, photonics crystal reflector, and coating grating with silver films, respectively. b Reprinted from ref. with permissions from IEEE Publishing. c Reprinted with permission from ref. . Copyright 2014 American Chemical Society. d Reprinted from ref. with permission from IOP Publishing. e Reprinted from ref. with permission from IEEE Publishing

Fig. 8. AWG based spectrometers on silicon photonics platform.

a AWG with MMIs for compact footprint. b AWG with reflectors to reduce half of the size. c, d AWGs with advanced star couplers and wide waveguides to reduce channel cross-talk^,. a Adapted from ref. with permission from IEEE Publishing. b Reprinted from ref. with permission from IEEE Publishing. c Reprinted from ref. with permission from IEEE Publishing. d Reprinted from ref. with permission from IEEE Publishing

Fig. 9. Narrowband-filters based spectrometers on silicon photonics platform.

a Schematic of a cascaded MZI filters based spectrometer. b Spectrum tailoring of cascaded MZI filters based spectrometers by optimizing the couplers at each MZI. c Schematic of a ring resonators array based spectrometer. d Cascaded Bragg gratings based spectrometer. e Spectrometer composed of both AWG and ring resonators. a Reprinted from ref. with permission from IEEE Publishing. b Reprinted from ref. with permission from IEEE Publishing. c Reprinted from ref. with permission from Optica Publishing Group. d Reprinted from ref. with permission from Optica Publishing Group. e Reprinted from ref. with permission from IEEE Publishing

Fig. 10. Fourier transform spectrometers on silicon photonics platform.

a General framework of a FTS. b, c FTS on silicon photonics with OPDs introduced by an array of imbalanced MZIs^,. d, e FTS on silicon photonics with OPDs tunable in time domain^,. f The state-of-the-art work on silicon TH-FTS with 180 nm bandwidth and 0.16 nm resolution. a Reprinted from ref. with permission from John Wiley and Sons. b Reprinted with permission from ref. . © Optica Publishing Group. c Reprinted with permission from ref. . © Optica Publishing Group. d Reprinted by permission from Springer Nature: Nature Communications ref. , 2018. e Reprinted by permission from Springer Nature: Nature Communications ref. , 2018. f Reprinted from ref. with permission from John Wiley and Sons

Fig. 11. Computational spectrometers on silicon photonics platform.

a General schematic for computational spectrometers. b The first demonstration of computational spectrometers. c–e The recently demonstrated computational spectrometers on silicon photonics using disordered medium, ultra-long multimode waveguide and stratified waveguide filters, respectively. b Reprinted with permission from ref. . © Optica Publishing Group. c Reprinted by permission from Springer Nature: Nature Photonics ref. , 2013. d Reprinted with permission from ref. . © Optica Publishing Group. e Reprinted by permission from Springer Nature: Nature Communications ref. , 2021

Fig. 12. Conceptual illustrations of some promising technological paths toward the next-generation integrated spectrometers.

a Computational spectrometers based on active path reconfiguration rather than passive power splitting. b Programmable spectrometers based on reconfigurable PICs. c Parallelism in the design of spectrometer systems