Yishen Qiu

Polarization-independent drop filters based on photonic crystal self-collimation ring resonators.

We report here a polarization-independent drop filter (PIDF) based on a photonic crystal self-collimation ring resonator (SCRR). Despite of the large birefringence associated with the polarization-dependent dispersion properties, we demonstrate a PIDF based on multiple-beam interference theory and polarization peak matching (PPM) technique. The PIDF performance was also investigated based on finite-difference time-domain (FDTD) technique, with excellent agreement between the theory and the simulation. For the designed drop wavelength of 1550 nm, the polarization-independent free spectral range is about 36.1 nm, which covers the whole optical communication C-band window. The proposed PIDFs are highly desirable for applications in photonic integrated circuits (PICs).

Photonic NOT and NOR gates based on a single compact photonic crystal ring resonator

New all-optical NOT and NOR logic gates based on a single ultracompact photonic crystal ring resonator (PCRR) have been proposed. The PCRR was formed by removing the line defect along the GammaM direction instead of the conventional GammaX direction in a square-pattern cylindrical silicon-rod photonic crystal structure. The behavior of the proposed logic gates is qualitatively analyzed with the theory of beam interference and then numerically investigated by use of the two-dimensional finite-difference time-domain method. No nonlinear material is required with less than a 2.2 microm effective ring radius. The wavelengths of the input signal and the probe signal are the same. This new device can potentially be used in on-chip photonic logic-integrated circuits.

High-current-sensitivity all-fiber current sensor based on fiber loop architecture

In this paper, we demonstrate a novel all-fiber current sensor using ordinary silica fiber. The sensor employs a fiber solenoid as a current sensor head, which improves the current sensitivity by allowing optical signals to traverse the sensor head repeatedly. Theory and experiment prove that the improvement in sensitivity increases periodically with the number of repetitions of optical signals circulating round the loop.

Temperature and Vibration Robustness of Reflecting All-Fiber Current Sensor Using Common Single-Mode Fiber

Temperature and vibration robustness of a reflecting all-fiber current sensor (AFCS) using a common single-mode fiber (SMF) are analyzed theoretically and experimentally. The effect of the birefringence condition of the sensing fiber on the temperature and vibration sensitivity of the AFCS is shown via theoretical models. The temperature and vibration sensitivity of the AFCS using an orthoconjugate retroreflector are almost entirely independent of the birefringence condition of the fiber. Thus, this configuration is preferable for a reflecting AFCS using an SMF. The experimentally observed temperature and vibration sensitivity of AFCSs using different fibers and configurations support this conclusion.

Polarization-independent Fabry–Perot interferometer in a hole-type silicon photonic crystal

We propose and numerically demonstrate a polarization-independent Fabry-Perot interferometer (PI-FPI) based on the self-collimation effect in a hole-type silicon photonic crystal (PhC). By use of the polarization peak matching method, a resonance frequency of the transverse-electric modes can equal that of the transverse-magnetic modes in the PI-FPI, although the transmission spectra are quite polarization dependent due to birefringence of the PhC. For the operating wavelength of 1550 nm, the PI free spectral range of the PI-FPI is up to 32.3 nm, which nearly covers the whole optical communication C-band window. With its small dimensions, simple structure, and silicon-based material, this PI-FPI may play an important role in photonic integrated circuits.

Coherence theory of a laser beam passing through a moving diffuser

We present the general coherence theory for laser beams passing through a moving diffuser. The temporal coherence of laser beams passing through a moving diffuser depends on two characteristic temporal scales: the laser coherence time and the mean time it takes the diffuser to move past a phase correlation area. In most applications, the former is much shorter than the latter. Our theoretical analysis shows the spatial coherence area of light scattered from a moving diffuser decreases while the coherence time remains unchanged. The conclusion has been confirmed by experiments using a Michelson interferometer and it is not in accordance with the original coherence theory in which both the temporal and spatial coherence of light scattered by a moving diffuser decrease. We also developed a method based on the theory of eigenvalues to calculate the speckle contrast on a screen illuminated by light transmitted through a moving diffuser.

Optical logic operations with self-pumped phase-conjugation output in photorefractive materials

Abstract By using the induced and erasable self-pumped phase-conjugation in photorefractive materials, OR, NOR and NOT logic functions can be performed. The signal-to-noise (logic 1/0) ratio at the output is extremely large. Such logic operations can be combined to implement more complex functions or any logic system.

Speckle contrast in near field scattering limited by time coherence

The relationship between the speckle contrast of scattered light in near field and longitudinal distance that is perpendicular to scattering surface is investigated. The experiment indicates that when using the laser illumination source with proper time coherence length, the curve of speckle contrast vs. longitudinal distance appears minimum turning point. The position and value of minimum point are decided by the coherence of light and scattering matter. It is easy to obtain the correlation area of scattered light by measuring the minimum point position and the illuminated area. Comparing to traditional scattering technique, this method can simultaneously measure the roughness parameters of surface height variance and surface height correlation area.

Power calculation of wavelength tunable Yb3+:LSO laser

A theoretical model is presented describing continuous-wave operation about wavelength tunable Yb(3+):LSO (Yb(3+):Lu(2)SiO(5)) laser. In LSO host, Yb(3+) ion occupies two different Lu(3+) sites and the spectrum exhibits the inhomogeneously broadened property. Working as a computable model, it takes into account the pump absorption saturation, the re-absorption of laser, and the full spectral information of the laser transition. The calculated results are compared with the experimental results, and it verifies the validity of the model. Then the laser performances for different Yb(3+) concentration, crystal length, and the transmission of the output mirror are predicted.

Modal analysis of ultra-compact channel filters based on race-track photonic crystal ring resonators

A new channel drop filter (CDF) is proposed based on a race-track photonic crystal ring resonator composed of square-lattice cylindrical silicon rods in air. By using a two-dimensional finite-difference, time-domain numerical technique, the modal behavior of two representative CDFs, parallel and perpendicular, has been analyzed. The analyses include the impact of additional scatterer size, scatterer amount and their position on the performance of proposed CDFs, such as drop efficiency and quality factor (Q). For the parallel CDF, about 130 spectral Q and 99% drop efficiency can be optimally achieved at 1363 nm channel with 0.145 periodicity scatterer size, whereas for the perpendicular one, about 180 spectral Q and 99% drop efficiency can be optimally obtained at 1366 nm channel with 0.165 periodicity scatterer size. By increasing the number of scatterers, the efficiency of both configurations can be enhanced. No obvious variation is obtained by changing the scatterer position.