Miniature Two-Photon Microscopic Imaging Using Dielectric Metalens.

Miniature two-photon microscopy has emerged as a powerful technique for investigating brain activity in freely moving animals. Ongoing research objectives include reducing probe weight and minimizing animal behavior constraints caused by probe attachment. Employing dielectric metalenses, which enable the use of sizable optical components in flat device structures while maintaining imaging resolution, is a promising solution for addressing these challenges.

Linewidth-related residual intensity modulation in lithium niobate phase modulators.

We present a modified model for residual intensity modulation (RIM) observed in lithium niobate phase modulators, which is suitable for both narrow linewidth and wide linewidth lasers. This model is based on two key points leading to RIM: one is the optical propagation loss, which is proportional to the applied voltage, and the other is the interference between an injected wave and its reflection from the lithium niobate substrate. In order to verify the model, the RIM is measured accurately with different linewidths of input lasers respectively.

Realization of Hollow-Core Photonic-Crystal Fiber Optic Gyro Based on Low-Noise Multi-Frequency Lasers with Intermediate-Frequency Difference.

Mainly focusing on the demand for a novel resonator optic gyro based on a hollow-core photonic-crystal fiber (HC-RFOG), we achieve a multi-frequency lasers generation with low relative phase noise via an acousto-optic modulation of light from a single laser diode. We design a homologous heterodyne digital optical phase-locked loop (HHD-OPLL), based on which we realize the low-noise multi-frequency lasers (LNMFLs) with an intermediate frequency difference. The noise between the lasers with a 20 MHz difference is 0.

Resonant fiber optic gyroscope with three-frequency differential detection by sideband locking.

A new scheme of three-frequency differential detection with a sideband locking technique is firstly proposed to suppress backscattering noise for improving the accuracy of resonator fiber optic gyroscope (RFOG). In the system we proposed, one light path is divided into three paths and sinusoidal wave modulations of different frequencies are respectively applied to generate the sideband. The first-order sidebands of the three channels of light in the cavity are locked to the adjacent three resonance peaks by sideband locking technique.

Free spectral range measurement using homologous heterodyne optical phase-locked loop based on acousto-optic modulation.

We demonstrate a homologous heterodyne optical phase-locked loop for free spectral range measurement of a fiber ring resonator. In this loop, the frequency noise within the 10 Hz bandwidth is reduced by more than 40 dB from 147.350 to 0.

Design of low-crosstalk polarizing resonator and homologous multi-frequency differential detection for hollow-core photonic-crystal fiber optic gyro.

In order to suppress the undesired polarization in the hollow-core photonic-crystal fiber (HCPCF) resonator and reduce the loss of the resonator, we realize a low-crosstalk polarizing resonator with the polarization-correlated phase modulation technique (PCPM). In addition, we put forward a homologous multi-frequency differential detection scheme, with which the backscattering noise and the backreflection noise of the gyro can be well suppressed. Finally, we realize a hollow-core photonic-crystal fiber optic gyro based on the low-crosstalk polarizing resonator and the homologous multi-frequency differential detection.

Passive compensation of intensity and polarization-induced noise by a quadrature demodulation technique in a resonator optic gyroscope.

Polarization-induced noise is a dominant noise that seriously hinders the progress of resonator optic gyroscopes. Many countermeasures have been developed but showed insufficient performance. In this paper, we propose a quadrature demodulation technique (QDT) that adopts references of both sine and cosine to demodulate the signal.

Suppression of backscattering-induced noise by sideband locking based on high and low modulation frequencies in ROG.

Backscattering-induced noise is a dominant noise in a resonant optic gyroscope (ROG). This paper proposes a method to suppress the carrier and backscattering-induced noise with a sideband locking technique. The resonant cavity can be taken as a band-pass filter, and the carrier frequency component can be located at the stop-band while one sideband is locked to the cavity resonance.

Improvement of long-term stability of hollow-core photonic-crystal fiber optic gyro based on single-polarization resonator.

To improve long-term stability, we present a single-polarization resonator optic gyro based on a hollow-core photonic-crystal fiber (HCPCF), utilizing a micro-optical polarizing coupler formed by pairs of collimators and a series of polarization-dependent devices. We build the mathematical model of the polarization noise of the proposed gyro and experimentally validate the elimination of the undesired polarization eigenstate, which is the basis of the system's improved long-term stability. We use multi-modulation to suppress the backscattering noise and the closed-loop detection method to eliminate the effect of fluctuating output power on the gyro bias.

Real-time free spectral range measurement based on optical single-sideband technique.

We demonstrate a real-time scheme for measuring the free spectral range (FSR) of a high-aspect-ratio SiN waveguide ring resonator with a fiber-based hybrid unbalanced Mach-Zehnder modulator (MZM) using an optical single-sideband technique. Resonance-tracking loops were established with the Pound-Drever-Hall technique for locking resonance modes. A relative precision of 3.

Analysis of polarization noise in transmissive single-beam-splitter resonator optic gyro based on hollow-core photonic-crystal fiber.

We realize a transmissive single-beam-splitter resonator optic gyro based on a hollow-core photonic-crystal fiber (HCPCF), utilizing a micro-optical coupler formed by pairs of lenses and one filter, which is a new type of resonator fiber optic gyro based on the HCPCF (HC-RFOG). We build a mathematical model of the polarization noise based on the transfer function of this novel transmissive single-beam-splitter resonator. We construct a HC-RFOG and simulate and validate the effects of polarization noise on the gyro system.

Transmissive single-beam-splitter resonator optic gyro based on a hollow-core photonic-crystal fiber.

We propose a transmissive single-beam-splitter resonator optic gyro based on a hollow-core photonic-crystal fiber (HCPCF), which is a new regime of resonator fiber optical gyro based on an HCPCF, a hollow-core resonator fiber optical gyro (HC-RFOG), for the first time, to the best of our knowledge. We evaluate the transfer function of this novel transmissive single-beam-splitter resonator, and the resonance characteristics are simulated to optimize the element parameters. We utilize a micro-optical coupler formed by pairs of lenses and one filter to realize this novel resonator.

Suppression of backreflection error in resonator integrated optic gyro by the phase difference traversal method.

The phase difference traversal (PDT) method is proposed to suppress the backreflection-induced error in resonator integrated optic gyro (RIOG). Theoretical analysis shows that the backreflection-induced zero-bias fluctuation is periodical and sine/cosine-like. By forcing the phase difference between the CW and CCW incident light to traverse the interval [0, 2π] repeatedly and rapidly enough, the fluctuation can be low-pass filtered and, hence, the backreflection-induced error can be effectively suppressed.

Reduction of angle random walk by in-phase triangular phase modulation technique for resonator integrated optic gyro.

In a resonator integrated optic gyro (RIOG) employing a planar optical waveguide ring, the interference between backreflected light and signal light will not only cause nonreciprocal drift of cw and ccw resonance frequencies, but also deteriorate the original signal waveform of the resonator output. If contra-phase triangular phase modulation (CPM) were applied, a cosine-like ripple, whose initial phase varies randomly, would superpose upon the quasi-square waveform of the resonator output, resulting in increment of noise and the gyro's angle random walk (ARW). Therefore, in-phase triangular phase modulation (IPM) technique is proposed and used to eliminate the ripple and improve the waveform quality of the resonator output, and the gyro's ARW is obviously reduced from 3 to 0.