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. Then, the carrier will be suppressed by the cavity itself, which will reduce the interference with carrier backscattering. For the adoption of different modulation frequencies in clockwise (CW) and counter-clockwise (CCW) directions, the first-order sidebands of CW and CCW have a frequency offset to each other. Therefore, the first-order sideband backscattering can be eliminated when the sideband is locked to the cavity resonance. Also, both high and low modulation frequencies are applied to the phase modulator, which will further suppress the carrier, and the demodulation of low frequency will reduce the sensitivity to phase fluctuation noise in the system. The method has low requirements for parameter accuracy or device performance.

Imaging of guided waves using an all-fiber reflection-based NSOM with self-compensation of a phase drift.

A phase-resolved reflection-based near-field scanning optical microscopy (NSOM) technique with an original all-fiber configuration is presented. Our system consists of an intrinsically phase-stable common-path interferometer. The reflection from the waveguide input facet or from an integrated fiber Bragg grating is used as the reference beam. This arrangement effectively suppresses the phase drift caused by environmental fluctuations. By raster scanning a silicon atomic force microscope probe, we measure the complex near fields of the propagating and stationary waves in silicon nanowaveguides. Our robust, align-free, cost-effective, and shot-noise-limited near-field imaging technique paves the way for versatile optical characterizations of nanophotonic structures on a chip.

Full control of far-field radiation via photonic integrated circuits decorated with plasmonic nanoantennas.

We theoretically develop a hybrid architecture consisting of photonic integrated circuit and plasmonic nanoantennas to fully control optical far-field radiation with unprecedented flexibility. By exploiting asymmetric and lateral excitation from silicon waveguides, single gold nanorod and cascaded nanorod pair can function as component radiation pixels, featured by full 2π phase coverage and nanoscale footprint. These radiation pixels allow us to design scalable on-chip devices in a wavefront engineering fashion. We numerically demonstrate beam collimation with 30° out of the incident plane and nearly diffraction limited divergence angle. We also present high-numerical-aperture (NA) beam focusing with NA ≈0.65 and vector beam generation (the radially-polarized mode) with the mode similarity greater than 44%. This concept and approach constitutes a designable optical platform, which might be a future bridge between integrated photonics and metasurface functionalities.

Analysis of low F-number dual micro-axilens array with binary structures by rigorous electromagnetic theory.

We investigate a two-dimensional low F-number dual micro-axilens array with binary structures based on a rigorous electromagnetic theory. The focal characteristics of a binary dual micro-axilens array (BDMA), including axial performances (focal depth and focal shift) and transverse performances (focal spot size and diffraction efficiency), have been analyzed in detail for different F-numbers, different incident polarization (TE and TM) waves, and different distances between micro-axilens. Numerical results reveal that the interference effect of a BDMA is not very evident, which is useful for building a BDMA with a high fill factor, and the focal characteristics of a BDMA are sensitive to the polarization of an incident wave. The comparative results have also shown that the diffraction efficiency of a BDMA will increase and the focal spot size of a BDMS will decrease when the F-number increases, for both TE polarization and TM polarization, respectively. It is expected that this investigation will provide useful insight into the design of micro-optical elements with high integration.

Binary sub-wavelength diffractive lenses with long focal depth and high transverse resolution.

This study explores two-dimensional binary sub-wavelength diffractive lenses (BSDLs) for implementing long focal depth and high transverse resolution based on the rigorous electromagnetic theory and the finite-difference time-domain method. Focusing performances, such as the actual focal depth, the ratio between the focal depth of the designed BSDL and the focal depth of the conventional sub-wavelength lens and the spot size of the central lobe at the actual focal plane, for different f-numbers, have been studied in the case of TE incidence polarization wave. The rigorous numerical results indicate that the designed BSDLs indeed have long focal depth and high transverse resolution by modulating the binary sub-wavelength characteristic sizes. Because BSDLs have the ability for monolithic integration and can require only single step fabrication, the investigations may provide useful information for BSDLs' application in micro-optical systems.

[Influence of polarization maintaining fibers and polarizer on the lightwave spectrum].

The parameters of polarization maintaining fibers and polarizer, and the splicing angles between them have important influence on the spectral characteristics of lightwave propagating in them. The transmission model of lightwave was established using Jones matrix. For the first time, the effect of degree of polarization, fiber lengths, splicing angles between fibers and between fiber and component on the output spectrum was discussed. It was indicated that the shape of output spectrum of the unpolarized lightwave will not change when the splicing angles between fibers and between fiber and component were not zero, while there were periodical functions added to the output spectrum of polarized of partially polarized lightwave. The result that when the angles were constants, the longer the fibers were, the smaller the periods of periodical functions, and that when the fiber lengths were constants, in a certain range the bigger the angles, the larger the amplitudes of periodical functions, was achieved. The conclusions were verified by experiments and they could supply theoretical guidance for the systems using polarization maintaining fibers and polarizer.