Because of the high index contrast, current silicon photonics based optical phased arrays cannot achieve small beam divergence and large field-of-view simultaneously without increasing fabrication complexity. To resolve the dilemma, we propose an ultra-long waveguide grating antenna formed by placing subwavelength segments within the evanescent field of a conventional strip waveguide. Bound state in the continuum effect is leveraged to suppress the sidewall emission. As a proof of concept, we theoretically demonstrated a millimeter-long through-etched waveguide grating antenna with a divergence angle of 0.081° and a feature size compatible with current silicon photonics foundries.

Current gradient-index (GRIN) lens based proximal-driven intracoronary optical coherence tomography (ICOCT) probes consist of a spacer and a GRIN lens with large gradient constant. This design provides great flexibility to control beam profiles, but the spacer length should be well controlled to obtain desired beam profiles and thus it sets an obstacle in mass catheter fabrication. Besides, although GRIN lens with large gradient constant can provide tight focus spot, it has short depth of focus and fast-expanded beam which leads to poor lateral resolution for deep tissue. In this paper, a type of spacer-removed probe is demonstrated with a small gradient constant GRIN lens. This design simplifies the fabrication process and is suitable for mass production. The output beam of the catheter is a narrow nearly collimated light beam, referred to as pencil beam here. The full width at half maximum beam size varies from 35.1 µm to 75.3 µm in air over 3-mm range. Probe design principles are elaborated with probe/catheter fabrication and performance test. The in vivo imaging of the catheter was verified by a clinical ICOCT system. Those results prove that this novel pencil-beam scanning catheter is potentially a good choice for ICOCT systems.

We propose and demonstrate a multi-point, self-adaptive fiber ultrasonic sensor based on fiber Bragg gratings (FBGs). The sensor is constructed from matched FBG pairs (FBGPs) and a tunable optical filter in a fiber ring laser. FBGPs with different Bragg wavelengths are used as both the comb filter to produce potential lasing lines and the ultrasonic sensing elements. The ultrasonic signal is directly detected by monitoring the intensity response at each laser channel to the cold-cavity loss modulation from the spectral shift of matched FBGPs. The laser channel between the FBGPs is actively switched using the tunable optical filter, thereby achieving multi-point and switchable detection yet avoiding mode competition in the lasers. Meanwhile, to achieve self-adaptability, the two FBGs of the FBGP are fixed side by side at the same location of the structure such that both FBGs respond similarly to static strain and temperature variation. The multi-point system is highly promising for the robustness in the practical applications because it is insensitive to static strain ranging over 1400° and temperature variation from 20 °C to 50 °C, respectively.

This work theoretically investigates the relative intensity noise (RIN) and spectral linewidth characteristics of epitaxial quantum dot (QD) lasers on silicon subject to optical injection. The results show that the RIN of QD lasers can be reduced by optical injection, hence a reduction of 10 dB is achieved which leads to a RIN as low as −167.5 dB/Hz in the stable injection-locked area. Furthermore, the spectral linewidth of the QD laser can be greatly improved through the optical injection locked scheme. It is reduced from 556.5 kHz to 9 kHz with injection ratio of −60 dB and can be further reduced down to 1.5 Hz with injection ratio of 0 dB. This work provides an effective method for designing low intensity noise and ultra-narrow linewidth QD laser sources for photonics integrated circuits on silicon.

Subwavelength grating metamaterial (SGM) waveguide is typically treated as a homogeneous medium without considering intra-waveguide reflection. However, this approximation is not always valid, especially in resonators. In this paper, we show that the reflection-induced mutual coupling between the clock-wise and counter-clock-wise resonant modes in a subwavelength grating metamaterial waveguide ring resonator (SGMRR) breaks the degeneracy of the two modes, leading to the formation of Autler–Townes splitting. This phenomenon could be leveraged to improve the detection limit of SGMRR-based sensors.