Review

Miniaturization of optical spectrometers

See allHide authors and affiliations

Science  29 Jan 2021:
Vol. 371, Issue 6528, eabe0722
DOI: 10.1126/science.abe0722

You are currently viewing the abstract.

View Full Text

Log in to view the full text

Log in through your institution

Log in through your institution

Miniaturizing spectrometers

Optical spectroscopy is a widely used characterization tool in industrial and research laboratory settings for chemical fingerprinting and analysis. High-end spectrometers are typically benchtop based with bulky optical components, moving parts, and long path lengths, and they can deliver a wealth of information with ultrahigh precision and bandwidth. There is, however, a drive toward miniaturization of spectrometers, in which concepts in nanophotonics are used to control light on much smaller scales. Yang et al. reviewed recent developments in spectrometry systems, including various fabrication approaches of nanophotonics systems and the software that computationally determines the spectra, that strive to shrink their footprint and open up applications in portable spectroscopy.

Science, this issue p. eabe0722

Structured Abstract

BACKGROUND

Optical spectrometry is one of the most powerful and widely used characterization tools in scientific and industrial research. Benchtop laboratory spectrometer systems—characterized by bulky optical components, moving parts, and long path lengths—can deliver unparalleled, ultrafine resolution and wide spectral ranges. However, a rapidly growing application space exists for spectral analysis where the need for reduced physical dimensions, cost, or power consumption takes precedence over the need for high performance. The demand for portable or handheld spectral analysis devices requires shrinking of these systems down to centimeter-scale footprints. More extreme miniaturization to submillimeter length scales would open a range of opportunities for in situ analysis, with potential for integration into lab-on-a-chip systems, smartphones, or even spectrometer-per-pixel snapshot hyperspectral imaging devices. Toward this aim, an approach that involves simply scaling down benchtop systems (with miniaturized gratings and reflective optics) becomes constrained as a result of the complex fabrication involved and the inherent proportionality of resolution to path length in dispersion-based systems.

ADVANCES

A wide variety of miniaturized spectrometer systems have emerged since the early 1990s. These can be grouped into four broad categories according to the underlying strategies they use for spectral characterization: (i) those that have tried to push the boundaries of miniaturization using a conventional benchtop strategy, where light interacts with miniaturized dispersive optics such that different spectral components are spatially separated when arriving at a detector array; (ii) narrowband filters, which can be used to selectively transmit light with specific wavelengths, such that analysis of complete spectra can be achieved either with a single filter (the transmissive properties of which can be varied over time) or by passing light through an array of multiple unique narrowband filters, each mounted onto its own detector; (iii) Fourier transform systems, where integrated interferometers [such as those based on microelectromechanical systems (MEMS) components] can be used to produce temporal or spatial interferograms, which are then computationally converted to a readable spectrum; and (iv) a newly emerging paradigm of microspectrometers, in which computational techniques are used to approximate or reconstruct an incident light spectrum from precalibrated spectral response information encoded within a set of broadband detectors or filters.

OUTLOOK

We now stand at a watershed where this field is yielding ultracompact microspectrometer systems with performance and footprint near those viable for integrated applications such as lab-on-a-chip systems, smartphones, and spectral imagers. Until recently, advancement has been inspired by and has benefited from wider technological trends in the production of hardware. For instance, earlier dispersion-based strategies have been improved through optimization of high-precision microfabrication, lithographic, and etching techniques to produce ever more scaled-down gratings and optics. In parallel, the development of MEMS components has enabled ultracompact, electronically driven moving parts for miniaturized Fourier transform interferometer–based devices. However, as the physical size and cost of processing power have fallen sharply over the past 15 years, the emergence of reconstructive microspectrometers has heralded a fundamental shift in the field, where developments in the software will shoulder much of the burden for enhancing device performance while footprints continue to shrink. Maturation of the algorithmic strategies behind these devices will likely see the incorporation of machine learning–based techniques, which increasingly will be able to compensate for the compromises in detector performance necessitated by further miniaturization. This represents a promising route toward ultracompact high-performance systems and the emergence of spectral analysis in a host of previously inaccessible platforms in scientific research, industry, and consumer electronics.

Strategies toward ultracompact microspectrometers.

Schemes for miniaturized spectral sensing systems based on dispersive optics, narrowband filters, Fourier transform interferometers, and computational spectral reconstruction schemes have all emerged over the past three decades.

Abstract

Spectroscopic analysis is one of the most widely used analytical tools in scientific research and industry. Although laboratory benchtop spectrometer systems offer superlative resolution and spectral range, their miniaturization is crucial for applications where portability is paramount or where in situ measurements must be made. Advancement in this field over the past three decades is now yielding microspectrometers with performance and footprint near those viable for lab-on-a-chip systems, smartphones, and other consumer technologies. We summarize the technologies that have emerged toward achieving these aims—including miniaturized dispersive optics, narrowband filter systems, Fourier transform interferometers, and reconstructive microspectrometers—and discuss the challenges associated with improving spectral resolution while device dimensions shrink ever further.

View Full Text

Stay Connected to Science