Dynamic Free-Spectral-Range Measurement for Fiber Resonator Based on Digital-Heterodyne Optical Phase-Locked Loop

We propose a novel scheme, based on digital-heterodyne optical phase-locked loop with whole-fiber circuit, to dynamically measure the free-spectral-range of a fiber resonator. The optical phase-locked loop is established with a differential frequency-modulation module consists of a pair of acousto-optic modulators. The resonance-tracking loop is derived with the Pound-Drever-Hall technique for locking the heterodyne frequency of the OPLL on the frequency difference between adjacent resonance modes. A stable locking accuracy of about 7 × 10?9 and a dynamic locking accuracy of about 5 × 10?8 are achieved with the FSR of 8.155 MHz, indicating a bias stability of the resonator fiber optic gyro of about 0.1?/h with 10 Hz bandwidth. In addition, the thermal drift coefficient of the FSR is measured as 0.1 Hz/?C. This shows remarkable potential for realizing advanced optical measurement systems, such as the resonant fiber optic gyro, and so on.

Three-Dimensional Planar Metallic Lenses Based on Concentric Rings with Modulated Subwavelength Width

A kind of Subwavelength Planar Metallic Lenses (SPMLs) is proposed to realize far-field optical focusing in the visible range based on concentric rings with modulated width in a silver film. The width of each metallic ring is mutative so that the radiation fields of surface plasmon polaritons can be controlled and the relevant phase retardations can be modulated to make a beam focus at the desired position. For comparison, the Subwavelength Planar Dielectric Lenses (SPDLs) structured on silica glass with the same concentric ring shapes as SPMLs are analyzed, although without opaque metal coating on SPDLs, the computational results show that SPMLs can support higher intensity focal spot, narrower full-width half-maximum beam width, and longer depth of focus at the focal region under certain lens thickness due to the coupling of surface plasomon polaritons, diffracted evanescent waves and propagated electromagnetic waves.

Femtosecond fiber laser at 780 nm for two-photon autofluorescence imaging

We present an Er-doped fiber(Er:fiber)-based femtosecond laser at 780 nm with 256 MHz repetition rate, 191 fs pulse duration, and over 1 W average power.Apart from the careful third-order dispersion management, we introduce moderate self-phase modulation to broaden the output spectrum of the Er:fiber amplifier and achieve 193 fs pulse duration and 2.43W average power.Over 40% frequency doubling efficiency is obtained by a periodically poled lithium niobate crystal.Delivering through a hollow-core photonic bandgap fiber, this robust laser becomes an ideal and convenient light source for two-photon autofluorescence imaging.

Improving long-term temperature bias stability of an integrated optical gyroscope employing a Si_(3)N_(4)resonator

The presence of polarization noise generated by the waveguide resonator limits the performance of a resonant integrated optical gyroscope(RIOG).Using silicon nitride(Si_(3)N_(4))to fabricate a waveguide with an ultralowaspect-ratio can result in a resonator that only supports light transmission in a single-polarization state,suppressing polarization noise.We successfully fabricated a Si_(3)N_(4)resonator with a bending radius of 17.5 mm,a finesse(F)of 150,a quality factor(Q)of 1.54×10^(7),and a propagation loss of 1.2 d B/m.The Si_(3)N_(4)resonator was used to construct a double closed-loop RIOG that showed long-term bias stability(3600 s)of 13.2°/h at room temperature,14.8°/h at 40℃,21.2°/h at 50℃,and 23.6°/h at 60℃.We believe this to be the best performance reported to date for a Si_(3)N_(4)resonator-based RIOG.This advancement paves the way for the wider application of RIOGs.