We measure linear optical dispersion, nonlinear refraction and two-photon absorption in a silicon waveguide at 1.54 μm wavelength. The total dispersion in the silicon waveguide was found to be $\text{−9.1\hspace{0.17em}}\mathrm{fs/(nm cm)}.$ At 1.54 μm wavelength, the two-photon absorption coefficient was found to be 0.45 cm/GW and a π phase shift from self-phase modulation was observed in optical pulses of 60 W peak-coupled power, generated from an amplified gain-switched laser diode.

Pulse transit time (PTT) has attracted much interest for cuffless blood pressure (BP) measurement. However, its limited accuracy is one of the main problems preventing its widespread acceptance. Arterial BP oscillates mainly at high frequency (HF) because of respiratory activity, and at low frequency (LF) because of vasomotor tone. Prior studies suggested that PTT can track BP variation in HF range, but was inadequate to follow the LF variation, which is probably the main reason for its unsatisfactory accuracy. This paper presents a new indicator, the photoplethysmogram intensity ratio (PIR), which can be affected by changes in the arterial diameter, and, thus, trace the LF variation of BP. Spectral analysis of BP, PTT, PIR, and respiratory signal confirmed that PTT was related to BP in HF at the respiratory frequency, while PIR was associated with BP in LF range. We, therefore, develop a novel BP estimation algorithm by using both PTT and PIR. The proposed algorithm was validated on 27 healthy subjects with continuous Finapres BP as reference. The results showed that the mean ± standard deviation (SD) for the estimated systolic, diastolic, and mean BP with the proposed method against reference were -0.37 ± 5.21, -0.08 ± 4.06, -0.18 ± 4.13 mmHg, and mean absolute difference (MAD) were 4.09, 3.18, 3.18 mmHg, respectively. Furthermore, the proposed method outperformed the two most cited PTT algorithms for about 2 mmHg in SD and MAD. These results demonstrated that the proposed BP model using PIR and PTT can estimate continuous BP with improved accuracy.

Waves that are perfectly confined in the continuous spectrum of radiating waves without interaction with them are known as bound states in the continuum (BICs). Despite recent discoveries of BICs in nanophotonics, full routing and control of BICs have not yet been explored. Here, we experimentally demonstrate BICs in a fundamentally new photonic architecture by patterning a low-refractive-index material on a high-refractive-index substrate, where dissipation to the substrate continuum is eliminated by engineering the geometric parameters. Pivotal BIC-based photonic components are demonstrated, including waveguides, microcavities, directional couplers, and modulators. Therefore, this work presents the critical step of photonic integrated circuits with BICs, and enables the exploration of new single-crystal materials on an integrated photonic platform without the fabrication challenges of patterning the single-crystal materials. The demonstrated lithium niobate platform will facilitate development of functional photonic integrated circuits for optical communications, nonlinear optics at the single photon level, as well as scalable photonic quantum information processors.

We describe a shallow-etched diffractive waveguide grating coupler which achieves efficient coupling between single-mode fiber and a silicon-on-insulator optical waveguide. By the appropriate choice of waveguide/grating thicknesses and varying the coupling strength of the grating coupler via tailoring its fill factor to optimize the mode matching, a coupling loss of only 1.2 dB was obtained for each fiber/silicon waveguide interface. The coupling strength and effective refractive index of grating with different fill factors were also characterized to confirm the design simulations. The back reflection was suppressed by varying the coupling strength, leading to further enhancement of the coupling efficiency.