Junzhen Jiang

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.

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.

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.

Optical channel drop filters based on 45° photonic crystal ring resonators

A new optical channel drop filter was proposed based on two-dimensional (2D) 45° photonic crystal ring resonators. Its spectral information including intensity, dropped efficiency and quality factor affected by different physical parameters were numerically analyzed with 2D finite-difference time-domain technique. Near 100% dropped efficiency can be achieved at 1550-nm channel.

Multichannel high-current-sensitivity all-fiber current sensor

In this paper, we demonstrate a novel all-fiber current sensor using ordinary silica fiber and the fiber loop architecture that can be used to improve current sensitivity. In order to improve the efficiency of the sensor and reduce cost, we present a multichannel all-fiber current sensor based on the principle of time-division multiplexing. To illustrate the principle, we show the typical dual-channel all-fiber current sensor in our experiment. It shows that the currents at two different points can be measured simultaneously. In addition, we find by measurement that the dual-channel fiber current sensor has good linear responses dependence of the variation of the degree of polarization ∆P on the current intensity I for two channels respectively. Every channel is affected by the current alone, requires a separate calibration.

Hybrid Structure Multichannel All-Fiber Current Sensor

We have experimentally developed a hybrid-structure multi-channel all-fiber current sensor with ordinary silica fiber using fiber loop architecture. According to the rationale of time division multiplexing, the sensor combines parallel and serial structures. The purpose of the hybrid-structure multi-channel all-fiber current sensor is to get more information from the different measured points simultaneously. In addition, the hybrid-structure fiber current sensor exhibited a good linear response for each channel. A three-channel experiment was performed in the study and showed that the system could detect different current positions. Each channel could individually detect the current and needed a separate calibration system. Furthermore, the three channels will not affect each other.

Tunable drop filters based on photonic crystal self-collimation ring resonators

A tunable drop filter (TDF) based on two-dimensional photonic crystal (PC) self-collimation ring resonator (SCRR) is proposed. The PC consisting of square-lattice air cylinders in silicon has square-shaped equal frequency contours (EFCs) in the wavevector space at the frequencies between 0.172-0.188c/a for TE modes. The SCRR includes two mirrors and two splitters. The air holes inside the SCRR are infiltrated with a kind of liquid crystal whose ordinary and extraordinary refractive indices are 1.522 and 1.706, respectively. The effective refractive index neff of liquid crystal depends on the applied electric field. Simulated with the FDTD method, the transmission spectra at the drop port of SCRR are in the shape of sinusoidal curves with uniform peak spacing between 0.172-0.188c/a. Transmission peaks will shift to the lower frequencies when neff is increased. When neff changes from 1.522 to 1.706, the peaks will experience red-shift over 0.003c/a. So this SCRR can work as a tunable drop filter. For the operating wavelength around 1550nm, its dimensions are only tens of microns.

Overlap Spectrum Fiber Bragg Grating Sensor Based on Light Power Demodulation

Demodulation is a bottleneck for applications involving fiber Bragg gratings (FBGs). An overlap spectrum FBG sensor based on a light power demodulation method is presented in this paper. The demodulation method uses two chirp FBGs (cFBGs) of which the reflection spectra partially overlap each other. The light power variation of the overlap spectrum can be linked to changes in the measurand, and the sensor function can be realized via this relationship. A temperature experiment showed that the relationship between the overlap power spectrum of the FBG sensor and temperature had good linearity and agreed with the theoretical analysis.

Multichannel all fiber current sensor based on the single polarimetric detection and loop scheme

A multichannel all fiber current sensor that can be used to measure currents at different positions simultaneously is presented in the paper. Each sensor head uses single-polarization single-mode devices and loop scheme to realize current measurement. All the sensor heads are connected via a series structure and the measured results are received by only one photo-detector based on the principle of time-division multiplexing. Theory and experiment prove that the sensor is feasible.

A Loop All-Fiber Current Sensor Based on Single-Polarization Single-Mode Couplers

Low current sensitivity and insufficient system stability are two key problems in all-fiber current sensor (AFCS) studies. In order to solve the two problems, a novel AFCS combining single-polarization single-mode (SPSM) couplers and a loop structure is presented in this paper with a design that incorporates the advantages of both SPSM couplers and a loop structure. SPSM couplers are shown to simplify the AFCS system and reduce the risk of interference, and the loop structure can enhance the current sensitivity. Both theory and experiment prove that the new AFCS can simultaneously overcome two prevalent obstacles of low current sensitivity and low stability.