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1. Monolithic Integration of Si3N4 Ring Resonator and On-Chip Fourier Transform Spectrometer for The Lab-On-A-Chip Biosensor

   Yoo, Kyoungmin ; Chen, Ray T. ( May 2022 , Cleo)

   Jiang, Wei ; Alan Wang (Ed.)

   We demonstrated the monolithically integrated biosensor with micro-ring-resonator (MRR) and spatial-heterodyne Fourier-transform-spectrometer (SH-FTS) on Si3N4-on-SiO2, substituting the external optical spectrum analyzer. The spectrum is retrieved from SH-FTS with the bulk sensitivity of 42.9 nm/RIU. 

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2. Near-Infrared Lab-on-a-Chip Optical Biosensor with Micro Ring Resonator and Fourier Transform Spectrometer on SOI platform

   https://doi.org/10.1364/CLEO_SI.2023.SF2E.1  

   Yoo, Kyoung Min ; Fan, Kang-Chieh ; An, Yue ; Hlaing, May ; Jain, Sourabh ; Chen, Ray T. ( January 2023 , CLEO 2023)

   We demonstrated the design and experimental results of the near-infrared lab-on-a-chip optical biosensor platform that monolithically integrates the micro-ring-resonator and the on-chip spectrometer on the SOI wafer with the limit of detection of 0.042 RIU.

    

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3. Dual-Polarization Bandwidth-Bridged On-Chip Bandpass Sampling Fourier Transform Spectrometer from Visible to Near-Infrared on a Silicon Nitride Platform

   https://doi.org/0000-0002-9181-4266  

   Yoo, Kyoung Min ; Chen, Ray T. ( July 2022 , ACS photonics)

   Jelena Vuckovic (Ed.)

   On-chip broadband optical spectrometers that cover the entire tissue transparency window (λ = 650–1050 nm) with high resolution are highly demanded for miniaturized biosensing and bioimaging applications. The standard spatial heterodyne Fourier transform spectrometer (SHFTS) requires a large number of Mach–Zehnder interferometer (MZI) arrays to obtain a broad spectral bandwidth while maintaining high resolution. Here, we propose a novel type of SHFTS integrated with a subwavelength grating coupler (SWGC) for the dual-polarization bandpass sampling on the Si3N4 platform to solve the intrinsic trade-off limitation between the bandwidth and resolution of the SHFTS without having an outrageous number of MZI arrays or adding additional active photonic components. By applying the bandpass sampling theorem, the continuous broadband input spectrum is divided into multiple narrow-band channels through tuning the phase-matching condition of the SWGC with different polarization and coupling angles. Thereby, it is able to reconstruct each band separately far beyond the Nyquist criterion without aliasing error or degrading the resolution. We experimentally demonstrated the broadband spectrum retrieval results with the overall bandwidth coverage of 400 nm, bridging the wavelengths from 650 to 1050 nm, with a resolution of 2–5 nm. The bandpass sampling SHFTS is designed to have 32 linearly unbalanced MZIs with the maximum optical path length difference of 93 μm within an overall footprint size of 4.7 mm × 0.65 mm, and the coupling angles of SWGC are varied from 0° to 32° to cover the entire tissue transparency window. 

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4. On-Chip Digital Fourier-Transform Spectrometer Using a Thermo-Optical Michelson Grating Interferometer

   Richard A. Soref, Francesco De ( November 2018 , Journal of lightwave technology)

   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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5. Miniaturized integrated spectrometer using a silicon ring-grating design

   https://doi.org/10.1364/OE.424443  

   Alshamrani, Naif ; Grieco, Andrew ; Hong, Brandon ; Fainman, Yeshaiahu ( May 2021 , Optics Express)

   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.

    

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