Jibo Bai

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.

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.

Fabry-perot interferometer in a rod-type photonic crystal based on self-collimation

Low-loss Fabry-Perot interferometer consisting of two reflectors in a rod-type photonic crystal based-on the self-collimation effect is proposed and investigated. Free spectral range and peaks frequencies of its transmission decrease when the resonant cavity length increases. By raising the reflector reflectivity, the quality factor of peaks can be easily improved.

Folded Mach-Zehnder interferometer based on photonic crystal self-collimation effect

A Folded Mach-Zehnder interferometer (FMZI) in a two-dimensional photonic crystal is proposed. The FMZI consists of one splitter and several mirrors. Light propagates between them employing self-collimation effect. Its two interfering branches have different path lengths. The two complementary transmission spectra at two FMZI output ports are both in the shape of sinusoidal curves and have a uniform peak spacing in the frequency range from 0.255c/a to 0.270c/a. The peak spacing becomes smaller when the length difference between the two branches is increased. As self-collimation light beams can cross each other without coupling, this FMZI is much smaller than non-folded interference-type filters in photonic crystals. This FMZI may work as a wavelength division demultiplexer in high-density photonic integrated circuits.

Wavelength interleaver in a two-dimensional rod-type photonic crystal

A theoretical model of wavelength interleaver, which is based on an asymmetric Mach-Zehnder interferometer (AMZI) constructed in a two-dimensional photonic crystal (2D PhC), is proposed and numerically demonstrated. The 2D PhC consists of a square lattice of dielectric cylindrical rods in air. The AMZI includes two mirrors and two splitters. Light propagates between them employing self-collimation effect. The two interferometer branches have different path lengths. By using the finite-difference time-domain method, the calculation results show that the transmission spectra at two AMZI output ports are in the shape of sinusoidal curves and have a uniform peak spacing in the frequency range from 0.191c/a to 0.200c/a. When the path length of the longer branch is increased and the shorter one is fixed, the peaks shift to the lower frequencies and the peak spacing decreases nonlinearly. Consequently, the transmission can be designed to meet various application demands by changing the length difference between the two branches. For the dimensions of the wavelength interleaver are about tens of central wavelengths, it may be applied in future photonic integrated circuits.

Fabry-Perot Etalon in Hole-type Photonic Crystal as an Optical Sensor

A Fabry-Perot (FP) etalon constructed in a two-dimensional photonic crystal (2D PhC) utilizing self-collimation effect is proposed and investigated. The 2D PhC consists of a square lattice of air holes in silicon. It has square-shaped equal frequency contours (EFCs) in the frequency range of 0.275-0.295c/a for TE modes. The FP proposed consists of two PhC reflectors and one cavity between them. Light propagates in the photonic crystal employing self-collimation effect. The two reflectors have reflectivities of around 97.5% in the frequency range 0.275-0.295c/a. The FDTD calculation results show that the transmission spectrum of the FP etalon has a uniform peak spacing between 0.275c/a and 0.295c/a. The transmission spectrum shifts to the lower frequency as the refractive index of a fluid filling in the air holes in the FP cavity is increased. Therefore this etalon can work as an optical sensor for a gas and a liquid. The fluids whose refractive index vary within 1.0-1.5 can be sensed and detected. Its dimensions are only about tens of microns when the central operating wavelength is equal to 1550nm. So it can be applied as a micro-scale sensor.