Fabrication-tolerant Fourier transform spectrometer on silicon with broad bandwidth and high resolution

Abstract

We report an advanced Fourier transform spectrometer (FTS) on silicon with significant improvement compared with our previous demonstration in [Nat. Commun. 9, 665 (2018)2041-1723]. We retrieve a broadband spectrum (7 THz around 193 THz) with 0.11 THz or sub nm resolution, more than 3 times higher than previously demonstrated [Nat. Commun. 9, 665 (2018)2041-1723]. Moreover, it effectively solves the issue of fabrication variation in waveguide width, which is a common issue in silicon photonics. The structure is a balanced Mach–Zehnder interferometer with 10 cm long serpentine waveguides. Quasi-continuous optical path difference between the two arms is induced by changing the effective index of one arm using an integrated heater. The serpentine arms utilize wide multi-mode waveguides at the straight sections to reduce propagation loss and narrow single-mode waveguides at the bending sections to keep the footprint compact and avoid modal crosstalk. The reduction of propagation loss leads to higher spectral efficiency, larger dynamic range, and better signal-to-noise ratio. Also, for the first time to our knowledge, we perform a thorough systematic analysis on how the fabrication variation on the waveguide widths can affect its performance. Additionally, we demonstrate that using wide waveguides efficiently leads to a fabrication-tolerant device. This work could further pave the way towards a mature silicon-based FTS operating with both broad bandwidth (over 60 nm) and high resolution suitable for integration with various mobile platforms.

Advances in cost-effective integrated spectrometers

“…Recently, two different mechanisms of achieving temporal modulation of the OPD are demonstrated. First one is similar with SH-FTS in the sense that the OPDs are also in the form of varying physical length difference, but optical switches are employed to dynamically change the physical pathway and realize the temporal modulation of OPD 86 , as shown in Fig. 10d .…”

Scalable On‐Chip Microdisk Resonator Spectrometer

“…[1] The micro-spectrometers sharing the same ideas with the benchtop counterparts, such as dispersive optics and Fourier transforms interferometers, have degraded resolving power since the spectral resolution scales inversely with its footprint. [2][3][4][5][6][7][8][9][10][11][12] In recent years, reconstructive micro-spectrometers based on computational algorithms exploring spectral-to-spatial mapping have been extensively investigated due to superior performances of the spectral resolution and operation bandwidth. [13][14][15][16][17][18][19][20][21] Diverse integrated photonic structures, such as random scattering media, [16][17][18][19] evanescently coupled multimode spiral waveguide, [20] and linear coherent integrated networks [21] are utilized to design a reconstructive micro-spectrometer.…”

Design of broadband spectrum sampling filter for on-chip computational spectrometers

“…Researchers have employed this type of spectrometer to retrieve a broadband spectrum (7 THz to 193 THz) with sub nm resolution. [8] However, the measurement time of the FTS is too long due to the slow thermo-optical effect.…”