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We developed an inter-chip optical link using direct optical wire (DOW) bonding by open-to-air polymerization. An arch-shaped wire was drawn from a tip in a similar way to a metal wire, but the wire was formed from a polymer solution that solidified in the air during wiring. The DOW bonding was examined for silicon photonic chips where grating couplers are integrated for input/output coupling. Cone-shaped studs were formed at the ends of the wire, and their geometry was optimized using finite-difference time-domain simulation to give a mode conversion function. Although the polymer wire had a multimode scale of 7 µm, the wire bonding between the grating couplers showed a relatively low insertion loss of 5.8 dB at a wavelength of 1590 nm compared to a conventional connection using single-mode fiber blocks. It also showed a larger wavelength tolerance within the range of ∼1520–1590 nm. DOW bonding between a grating coupler and a single-mode fiber were also examined to verify the feasibility of out-of-plane connection with edge-coupling devices. The grating-to-fiber wire link also exhibited a large wavelength tolerance.

We demonstrated the low-loss channel and slot waveguides using Germanium-on-insulator for the mid-infrared range. In N2 purge state for measuring propagation loss, 1.40 and 1.98 dB/cm of the channel and slot waveguide, respectively, were obtained.

Conventional photon detectors necessarily face critical challenges regarding strong wavelength-selective response and narrow spectral bandwidth, which are undesirable for spectroscopic applications requiring a wide spectral range. With this perspective, herein, we overcome these challenges through a free-carrier absorption-based waveguide-integrated bolometer for infrared spectroscopic sensors on a silicon-on-insulator (SOI) platform featuring a spectrally flat response at near-infrared (NIR) range (1520-1620 nm). An in-depth thermal analysis was conducted with a systematic investigation of geometry dependence on the detectors. We achieved great performances: temperature coefficient of resistance (TCR) of -3.786%/K and sensitivity of -26.75%/mW with a low wavelength dependency, which are record-high values among reported waveguide bolometers so far, to our knowledge. In addition, a clear on-off response with the rise/fall time of 24.2/29.2 µs and a 3-dB roll-off frequency of ∼22 kHz were obtained, sufficient for a wide range of sensing applications. Together with the possibility of expanding an operation range to the mid-infrared (MIR) band, as well as simplicity in the detector architecture, our work here presents a novel strategy for integrated photodetectors covering NIR to MIR at room temperature for the development of the future silicon photonic sensors with ultrawide spectral bandwidth.

In this paper, we systematically investigated tailoring bolometric properties of a proposed heat-sensitive TiO

The authors demonstrate integrated 1D optical phased arrays (OPAs) for wide-angle 2D beam-steering. The 2D OPA consists of 16 1D transversal steering OPAs whose radiators have different grating periods, to assign different longitudinal angles. The transversal steering of each OPA is performed by the phase control of the p-i-n electro-optic phase shifter array. The 1D transversal steering OPAs operate serially, changing the longitudinal radiation angle. The grating radiators were designed with an array pitch of 2 μm, and a varying period in the range of 610-710 nm. The entire 16 × (1 × 16) OPAs were integrated into a small area of 26.5 mm 2 . The obtained transversal/longitudinal beam-steering range was 46°/44°, respectively, with a wavelength of 1560 nm, which enables wide 2D beam-steering.

The authors demonstrate the collimation of a vertically diverged beam emitted from a silicon-based end-fire optical phased array (OPA) using an aspheric cylindrical lens. A micro-cylindrical lens with a numerical aperture of 0.8 was placed near the focal length in front of an 1 × 16 end-fire OPA with a half-wavelength (775 nm) radiator array pitch for a 1550 nm wavelength. The lens provided a great collimation effect, reducing the vertical divergence angle from 95.6° to 6.7° during horizontal beam steering over ±30°. The horizontal divergence angle showed some expansion, from 7.6° to 10°, due to the angle-dependant curvature of the lens and the distance to the lens surface.

We systematically investigated the electrical characteristics of TiOx/Ti/TiOx tri-layer film for optical gas sensors on Ge-on-insulator platform. It was found that noise-equivalent- temperature-difference, which is strongly associated with limit-of-detection of gas sensors, could reach 14.56 mK.

Supplemental Document for the Manuscript

Optical slot waveguide was demonstrated in the mid-infrared at 4.2 μm for gas sensing application on Germanium-on-silicon platform. 0.47 ppm of limit-of-detection for carbon dioxide can be achieved with enhanced confinement factor and propagation loss.

We demonstrate the on-chip monitoring of far-field patterns in a silicon-based optical phased array (OPA) using a planar diffractor and traveling-wave photodetectors (PDs) integrated at the end of the radiator array. To reproduce the diffraction patterns within a silicon slab, the planar diffractor is designed with a diffraction region surrounded by an absorptive boundary and seven discrete outlet waveguides. Each outlet waveguide is linked to the photon-assisted tunneling PD which has a silicon p - n junction and is operated under a reverse bias to detect a sub-bandgap wavelength, 1.3 µm. With the 1 × 16 OPA and seven detectors, the positions of the main beams aligned to specific directions in the free space were clearly monitored.