In this paper, ultrahigh-Q factor racetrack microring resonators (MRRs) are demonstrated based on silica planar lightwave circuits (PLCs) platform. A loaded ultrahigh-Q factor Q_load of 1.83 × 10⁶ is obtained. The MRRs are packaged with fiber-to-fiber loss of ~5 dB. A notch depth of 3 dB and ~137 pm FSR are observed. These MRRs show great potential in optical communications as filters. Moreover, the devices are suitable used in monolithic integration and hybrid integration with other devices, especially in external cavity lasers (ECLs) to realize ultranarrow linewidths.

In this paper, electro-absorption variable optical attenuators (VOAs) have been designed and fabricated on silicon-on-insulator material with a 3 μm thick top silicon layer. We have simulated the impact of doping distance, doping width, doping depth, doping concentration, and doping length on VOA’s power consumption at 20 dB attenuation. We have found that the power consumption of VOA at 20 dB attenuation will decrease as the doping distance and doping width get smaller, while the doping depth and doping concentration get larger. We have further demonstrated that the power consumption can also be reduced by increasing the doping length and by taking a series structure theoretically. In this paper, VOAs with different doping structures, doping distances, doping widths, and doping lengths have been fabricated, and the tested results have verified our theoretical analysis. With doping distance of 8 μm, doping width of 15 μm, doping length of 1 cm, doping concentration of $1\times {10}^{19}{\mathrm{cm}}^{-3}$, and doping depth of 0.9 μm, the power consumption of the series VOA at 20 dB attenuation is 470 mW, and the rising/falling time is 54 ns/49.5 ns.

We experimentally demonstrate efficient light emission enhancement from Si with Er/O co-implanting coupled to 2-D hexagonal photonic crystal (PC) double-heterostructure microcavity fabricated on silicon-on-insulator. A single sharp resonant peak with 1552.2 nm communication wavelength dominates the photoluminescence (PL) spectrum and 35-fold PL intensity enhancement is obtained compared to the case of identically implanted silicon-on-insulator wafer at room temperature. The obvious red-shift and degraded Q-factor of resonant peak are present with the excitation power increasing, and the maximum measured Q-factor of 3829 is found at 1.5 mW power. The resonant peak is observed to shift depending on the structural parameters of PC.

A miniature Fourier transform spectrometer is proposed using a thin-film lithium niobate electro-optical modulator instead of the conventional modulator made by titanium diffusion in lithium niobate. The modulator was fabricated by a contact lithography process, and its voltage-length and optical waveguide loss were 2.26 V·cm and 1.01 dB/cm, respectively. Based on the wavelength dispersion of the half-wave voltage of the fabricated modulator, the emission spectrum of the input signal was retrieved by Fourier transform processing of the interferogram, and the analysis of the experimental data of monochromatic light shows that the proposed miniaturized FTS can effectively identify the input signal wavelength.

Quantum Key Distribution (QKD) is gaining significant interest due to its theoretical guarantee of unconditional security. Integrated optics offers distinct advantages compared to bulk optics, including high stability, flexibility, controllability, and robustness. We develop a planar lightwave circuit (PLC) silica asymmetric Mach-Zehnder interferometer (AMZI) module with temperature system at an accuracy of 0.1 ℃ including an AMZI chip with a 400ps delay and a single-chip microcomputer. The silica AMZI module is used to encode at Alice, and the same low loss AMZI module is used to decode at Bob at a clock repetition rate of 156 MHz. Two intensity states Z -basis (|0ñ, |1ñ) and two phase states X-basis (|+ñ, |-ñ) are prepared at Alice and detected at Bob successfully. The extinction ratio of |0ñ and |1ñ between first-slot and third-slot are about 17 dB. And the interference visibility of |+ñ, |-ñ between interference max and min of second-slot are about 88%. The estimated secret key rate and the quantum bit error rate (QBER) using a simulation model for a transmission distance of 20 km is 16.3 kbps and 0.0384, respectively.