Title: On-Chip Digital Fourier-Transform Spectrometer Using a Thermo-Optical Michelson Grating Interferometer
This theoretical modeling and simulation paper
presents designs and projected performance of an on-chip digital
Fourier transform spectrometer using a thermo-optical (TO)
Michelson grating interferometer operating at∼1550 and 2000 nm
for silicon-on-insulator and for germanium-on-silicon technological
platforms, respectively. The Michelson interferometer arms
consist of two unbalanced tunable optical delay lines operating in
the reflection mode. They are comprised of a cascade connection
of waveguide Bragg grating resonators (WBGRs) separated by a
piece of straight waveguide with lengths designed according to the
spectrometer resolution requirements. The length of eachWBGRis
chosen according to the Butterworth filter technique to provide one
resonant spectral profile with a bandwidth twice that of the spectrometer
bandwidth. A selectable optical path difference (OPD)
between the arms is obtained by shifting the notch in the reflectivity
spectrum along the wavelength axis by means of a low-power TO
heater stripe atop the WBGR, inducing an OPD that depends on
the line position of the WBGR affected by TO switching.We examined
the device performances in terms of signal recostruction in the
radio-frequency (RF) spectrum analysis application at 1 GHz and
at 1.5 GHz of spectrometer resolution. The investigation demonstrated
that high-quality spectrum reconstruction is obtained for
both Lorentzian and arbitrary input signals with a bandwidth
up to 40 GHz. We also show that spectrum reconstruction of
100–200 GHz RF band input signals is feasible in the Ge-on-Si
chips. more »« less
An ultra‐high resolution Fourier transform spectrometer (FTS) realized in silicon photonic platform that can operate with broad band, narrow band as well as a combination of broad band and narrow band signals is reported. The ultra‐high resolution of the spectrometer is achieved by exploiting multiple techniques: a Michelson interferometer (MI) structure to increase the optical path delay (OPD), a hybrid waveguide design to reduce insertion loss, an optimized heater and air trenches to achieve higher thermal efficiency. Moreover, to further increase the OPD of the spectrometer to increase its resolution, a novel multiple interferometers approach is employed which combines balanced MI withNstatically imbalanced MIs, thereby increasing the OPD of a single MI by factor ofN+ 1. An FTS spectrometer consisting ofN= 2 such MIs is fabricated and experimentally characterized using unknown broad bandwidth input signal spectra of about 180 nm centered around 1550 nm, a narrow line laser input signal, and a combination of broad and narrow band signals demonstrating spectral resolution of about 0.16 nm.
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.
We present an ultra-compact single-shot spectrometer on silicon platform for sparse spectrum reconstruction. It consists of 32 stratified waveguide filters (SWFs) with diverse transmission spectra for sampling the unknown spectrum of the input signal and a specially designed ultra-compact structure for splitting the incident signal into those 32 filters with low power imbalance. Each SWF has a footprint less than 1 µm × 30 µm, while the 1 × 32 splitter and 32 filters in total occupy an area of about 35 µm × 260 µm, which to the best of our knowledge, is the smallest footprint spectrometer realized on silicon photonic platform. Experimental characteristics of the fabricated spectrometer demonstrate a broad operating bandwidth of 180 nm centered at 1550 nm and narrowband peaks with 0.45 nm Full-Width-Half-Maximum (FWHM) can be clearly resolved. This concept can also be implemented using other material platforms for operation in optical spectral bands of interest for various applications.
We experimentally demonstrate a compact Fourier Transform on-chip spectrometer based on spatially heterodyned array of Michelson interferometers (MIs) in a silicon-on-insulator (SOI) platform. We demonstrate that with the same progressive geometric path length difference between the spatially heterodyned arrayed interferometer arms, MIs double the optical phase delays and thus double the wavelength resolution (δλ=0.8nm) compared to Mach-Zehnder interferometers (MZIs) (δλ=1.6nm). Our proof-of-concept device demonstrates one method to address the bandwidth-resolution tradeoff inherent in on-chip FTIRs, which gains in significance for optical sensing applications requiring single digit picometers resolution in compact on-chip form factors
We introduce and experimentally demonstrate a miniaturized integrated spectrometer operating over a broad bandwidth in the short-wavelength infrared (SWIR) spectrum that combines an add-drop ring resonator narrow band filter with a distributed Bragg reflector (DBR) based broadband filter realized in a silicon photonic platform. The contra-directional coupling DBR filter in this design consists of a pair of waveguide sidewall gratings that act as a broadband filter (i.e., 3.9 nm). The re-directed beam is then fed into the ring resonator which functions as a narrowband filter (i.e., 0.121 nm). In this scheme the free spectral range (FSR) limitation of the ring resonator is overcome by using the DBR as a filter to isolate a single ring resonance line. The overall design of the spectrometer is further simplified by simultaneously tuning both components through the thermo-optic effect. Moreover, several ring-grating spectrometer cells with different central wavelengths can be stacked in cascade in order to cover a broader spectrum bandwidth. This can be done by centering each unit cell on a different center wavelength such that the maximum range of one-unit cell corresponds to the minimum range of the next unit cell. This configuration enables high spectral resolution over a large spectral bandwidth and high extinction ratio (ER), making it suitable for a wide variety of applications.
Richard A. Soref, Francesco De. On-Chip Digital Fourier-Transform Spectrometer Using a Thermo-Optical Michelson Grating Interferometer. Retrieved from https://par.nsf.gov/biblio/10093696. Journal of lightwave technology 36.22
Richard A. Soref, Francesco De. On-Chip Digital Fourier-Transform Spectrometer Using a Thermo-Optical Michelson Grating Interferometer. Journal of lightwave technology, 36 (22). Retrieved from https://par.nsf.gov/biblio/10093696.
Richard A. Soref, Francesco De.
"On-Chip Digital Fourier-Transform Spectrometer Using a Thermo-Optical Michelson Grating Interferometer". Journal of lightwave technology 36 (22). Country unknown/Code not available. https://par.nsf.gov/biblio/10093696.
@article{osti_10093696,
place = {Country unknown/Code not available},
title = {On-Chip Digital Fourier-Transform Spectrometer Using a Thermo-Optical Michelson Grating Interferometer},
url = {https://par.nsf.gov/biblio/10093696},
abstractNote = {This theoretical modeling and simulation paper presents designs and projected performance of an on-chip digital Fourier transform spectrometer using a thermo-optical (TO) Michelson grating interferometer operating at∼1550 and 2000 nm for silicon-on-insulator and for germanium-on-silicon technological platforms, respectively. The Michelson interferometer arms consist of two unbalanced tunable optical delay lines operating in the reflection mode. They are comprised of a cascade connection of waveguide Bragg grating resonators (WBGRs) separated by a piece of straight waveguide with lengths designed according to the spectrometer resolution requirements. The length of eachWBGRis chosen according to the Butterworth filter technique to provide one resonant spectral profile with a bandwidth twice that of the spectrometer bandwidth. A selectable optical path difference (OPD) between the arms is obtained by shifting the notch in the reflectivity spectrum along the wavelength axis by means of a low-power TO heater stripe atop the WBGR, inducing an OPD that depends on the line position of the WBGR affected by TO switching.We examined the device performances in terms of signal recostruction in the radio-frequency (RF) spectrum analysis application at 1 GHz and at 1.5 GHz of spectrometer resolution. The investigation demonstrated that high-quality spectrum reconstruction is obtained for both Lorentzian and arbitrary input signals with a bandwidth up to 40 GHz. We also show that spectrum reconstruction of 100–200 GHz RF band input signals is feasible in the Ge-on-Si chips.},
journal = {Journal of lightwave technology},
volume = {36},
number = {22},
author = {Richard A. Soref, Francesco De},
}
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