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.
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Chirped-grating spectrometer-on-a-chip
We demonstrate an on-chip spectrometer readily integrable with CMOS electronics. The structure is comprised of a SiO2/Si3N4/SiO2waveguide atop a silicon substrate. A transversely chirped grating is fabricated, in a single-step optical lithography process, on a portion of the waveguide to provide angle and wavelength dependent coupling to the guided mode. The spectral and angular information is encoded in the spatial dependence of the grating period. A uniform pitch grating area, separated from the collection area by an unpatterned propagation region, provides the out-coupling to a CMOS detector array. A resolution of 0.3 nm at 633 nm with a spectral coverage tunable across the visible and NIR (to ∼ 1 µm limited by the Si photodetector) by changing the angle of incidence, is demonstrated without the need for any signal processing deconvolution. This on-chip spectrometer concept will cost effectively enable a broad range of applications that are beyond the reach of current integrated spectroscopic technologies.
more » « less- NSF-PAR ID:
- 10181025
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optics Express
- Volume:
- 28
- Issue:
- 17
- ISSN:
- 1094-4087; OPEXFF
- Page Range / eLocation ID:
- Article No. 24501
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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