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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 MZIsmore »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.« less

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.

We designed and demonstrated an on-chip Fourier transform spectrometer on Si3N4-on-SiO2 using an array of Mach-Zehnder interferometers (MZIs) for 𝜆 = 600~1000 nm. The retrieval of an input spectrum is demonstrated by the interconnect simulation.

Abstract With success of silicon photonics having mature to foundry-readiness, the intrinsic limitations of the weak electro-optic effects in Silicon limit further device development. To overcome this, heterogeneous integration of emerging electrooptic materials into Si or SiN platforms are a promising path to deliver <1fJ/bit device-level efficiency, 50+Ghz fast switching, and <10's um^2 compact footprints. Graphene's Pauli blocking enables intriguing opportunities for device performance to include broadband absorption, unity-strong index modulation, low contact resistance. Similarly, ITO has shown ENZ behavior, and tunability for EOMs or EAMs. Here we review recent modulator advances all heterogeneously integrated on Si or SiN such as a) a DBR-enabled photonic 60 GHz graphene EAM, b) a hybrid plasmon graphene EAM of 100aJ/bit efficiency, d) the first ITO- based MZI showing a VpL = 0.52 V-mm, and e) a plasmonic ITO MZI with a record low VpL = 11 V- um. We conclude by discussing modulator scaling laws for a roadmap to achieve 10's aJ/bit devices.

Mid-infrared trace gas sensing is a rapidly developing field with wide range of applications. Although CRDS, TDLAS, FTIR and others, can provide parts per billion and in some cases, parts per trillion sensitivities, these systems require bulky and expensive optical elements and, furthermore, are very sensitive to beam alignment and have significant size and weight that place constrains on their applications in the field, particularly for airborne or handheld platforms. Monolithic integration of light sources and detectors with an optically transparent passive photonics platform is required to enable a compact trace gas sensing system that is robust to vibrations and physical stress. Since the most efficient quantum cascade lasers (QCLs) demonstrated are in the InP platform, the choice of InGaAs-InP for passive photonics eliminates the need for costly wafer bonding versus silicon, germanium of GaAs, that would require optically absorbing bonding interfaces. The InGaAs-InP material platform can potentially cover the entire λ=3-15μm molecular fingerprint region. In this paper, we experimentally demonstrate monolithic integration of QCL, quantum cascade detector (QCD) and suspended membrane sub-wavelength waveguides in a fully monolithic InGaAs/InP material system. The transverse magnetic polarized QCL emission is efficiently coupled into an underlying InGaAs suspended membrane subwavelength waveguide. In additionmore »to low-loss compact waveguide bends, the suspended membrane architecture offers a high analyte overlap integral with the analyte. The propagating light is absorbed at the peak absorbance wavelength of the selected analyte gas and the transduced signal is detected by the integrated QCD. Gas sensing will be demonstrated« less

Chemicals are best recognized by their unique wavelength specific optical absorption signatures in the molecular fingerprint region from λ=3-15μm. In recent years, photonic devices on chips are increasingly being used for chemical and biological sensing. Silicon has been the material of choice of the photonics industry over the last decade due to its easy integration with silicon electronics as well as its optical transparency in the near-infrared telecom wavelengths. Silicon is optically transparent from 1.1 μm to 8 μm with research from several groups in the mid-IR. However, intrinsic material losses in silicon exceed 2dB/cm after λ~7μm (~0.25dB/cm at λ=6μm). In addition to the waveguiding core, an appropriate transparent cladding is also required. Available core-cladding choices such as Ge-GaAs, GaAs-AlGaAs, InGaAs-InP would need suspended membrane photonic crystal waveguide geometries. However, since the most efficient QCLs demonstrated are in the InP platform, the choice of InGaAs-InP eliminates need for wafer bonding versus other choices. The InGaAs-InP material platform can also potentially cover the entire molecular fingerprint region from λ=3-15μm. At long wavelengths, in monolithic architectures integrating lasers, detectors and passive sensor photonic components without wafer bonding, compact passive photonic integrated circuit (PIC) components are desirable to reduce expensive epi material lossmore »in passive PIC etched areas. In this paper, we consider miniaturization of waveguide bends and polarization rotators. We experimentally demonstrate suspended membrane subwavelength waveguide bends with compact sub-50μm bend radius and compact sub-300μm long polarization rotators in the InGaAs/InP material system. Measurements are centered at λ=6.15μm for sensing ammonia« less