Detector-Only Spectrometer Based on Structurally Colored Silicon Nanowires and a Reconstruction Algorithm

Abstract

Spectroscopy is a cornerstone in the field of optics. Conventional spectrometers generally require two elements. The first provides wavelength selectivity, for example, diffraction grating or Michelson interferometer. The second is a detector (or detector array). Many applications would benefit from very small and lightweight spectrometers. This motivates us to investigate what may be regarded as an ultimate level of miniaturization for a spectrometer, in which it consists solely of a detector array. We demonstrate a chip containing 24 pixels, each comprising a silicon nanowire (Si NW) array photodetector formed above a planar photodetector. The NWs are structurally colored, enabling us to engineer the responsivity spectra of all photodetectors in the chip. Each pixel thus combines wavelength selectivity and photodetection functions. We demonstrate the use of our chip to reconstruct the spectrum of an unknown light source impinging upon it. This is achieved by an algorithm that takes as its inputs the measured photocurrents from the pixels and a library of their responsivity spectra.

On‐Chip Measurement of Photoluminescence with High Sensitivity Monolithic Spectrometer

“…On‐chip spectroscopy is of great interest due to its prevalence in both scientific research and technology applications. [ 1–4 ] Currently, rapid development of footprint shrinking is available for microspectrometer chips through the instrumentality of sophisticated light splitting techniques [ 5–9 ] such as quantum dot filters [ 10 ] or photonic structures. [ 11–14 ] In such devices, the primary shortcoming lies in key sensor performance metrics, including sensitivity and resolution, scale inversely with the effective optical path length, and light–matter interaction volume.…”

Recent Advances in Vertically Aligned Nanowires for Photonics Applications

“…In recent years, nanowires originated from a wide variety of materials have arisen as a centerpiece for optoelectronic applications such as sensors, solar cells, optical filters, displays, light-emitting diodes and photodetectors [1][2][3][4][5][6][7][8][9][10][11][12]. Tractable but outstanding, optical features of nanowire arrays achieved by modulating its physical properties (e.g., diameter, height and pitch) allow to confine and absorb the incident light considerably, albeit its compact configuration.…”

Visible to long-wave infrared chip-scale spectrometers based on photodetectors with tailored responsivities and multispectral filters

“…Fishnet microspectrometer measured (red) and reference (blue) broad-and narrow-band sample spectra (g) and (h). Reprint permission obtained from [47,48].…”

“…Microspectrometer chips have been formed from a single compositionally-engineered semiconductor nanowire where the elemental composition and thus band gap energy and optical absorption spectrum vary with position along the nanowire [46]. Other examples consist of sets of structurally colored silicon PIN photodiodes comprised of either arrayed vertical nanowires [47] or high contrast gratings (HCGs) [48], where each pixel in the spectrometer has a unique responsivity, tailored through control of the geometry. These three filter-free designs represent in some sense the ultimate miniaturization of spectrometers, as they consist of only one component.…”

“…To estimate the incident spectrum, S(λ) using equation (1) and real experimental data there exist several linear regression methods. Researchers have used techniques such simulated annealing [44,48,49], recursive least squares [38,40,47], Tikhonov (L 2 ) regularization [39,45,48,50], Lasso (L 1 ) regularization [51], as well as non-negative least squares [47,52], since S(λ) is always non-negative. These methods are used in place of direct matrix inversion [49] or computing the Moore-Penrose inverse or using singular-value decomposition method as the regularization parameter introduced helps reduce the impact of random noise and measurement errors in either of the measured photoresponses or the responsivities [49].…”