Pi-Gang Luan

Photonic-crystal beam splitters

This work studies two-dimensional photonic crystal beam splitters with two input ports and two output ports. The beam splitter structure consists of two orthogonally crossed line defects and one point defect in square-lattice photonic crystals. The point defect is positioned at the intersection of the line defects to divide the input power into output ports. If the position and the size of the point defect are varied, the power of two output ports can be identical. The beam splitters can be used in photonic crystal Mach-Zehnder interferometers or switches. The simulation results show that a large bandwidth of the extinction ratio larger than 20 dB can be obtained while two beams are interfered in the beam splitters. This enables photonic crystal beam splitters to be used in fiber optic communication systems.

Enhanced light emission from InAs quantum dots in single-defect photonic crystal microcavities at room temperature

The optical properties of InAs quantum dots with photonic crystal microcavity emitting near 1.3μm were investigated at room temperature. The photoluminescence (PL) intensity for quantum dots in cavity was enhanced by two orders of magnitude. The large PL enhancement was attributed to the effects combining the improved extraction efficiency and the enhanced spontaneous emission rate due to the Purcell effect. A threefold Purcell enhancement is observed at room temperature, which is predominantly achieved by the very small mode volume of the photonic crystal microcavity.

Novel design of organic one-dimensional photonic crystal filter

We present a new structure of one-dimensional photonic crystal filter which is more efficiently than traditional designs. To combine periodic and gradually-increasing-thickness structures of one-dimensional photonic crystals can enlarge the photonic band gap.

Visible frequency of achromatic quadrants wave plates using the artificial birefringence

We have demonstrated the zero dispersion quarter wave plates in visible frequency range. The quarter wave plates were produced by using the subwavelength-period gratings to form the birefringence film. Taking this feature, we can design quarter wave plates for use in wide frequency range by the effective medium theory (EMT).

Two-dimensional photonic crystal beamsplitters

We demonstrate a beamsplitter in 2-dimensional square-lattice photonic crystals with two orthogonal line defects, and a point defect placed in the intersection of the two line defects. This structure divides the input power into each output ports. The size and position of the point defect has been varied to observe the related output power. The 2/spl times/2 beamsplitter can divide input power into each output port identically. This beamsplitter may be used in photonic crystal Mach-Zehnder interferometers or switches.

Design of omnidirectional reflector air-waveguide

In this paper, we study the structure of air-waveguide surrounded by omnidirectional reflectors for both vertical and horizontal confinements. The structure is designed for the fabrication processes using GaAs-based materials and their oxides with which the omnidirectional reflectors have been demonstrated elsewhere. The vertical and horizontal confinements are achieved by the omnidirectional reflectors consisting of AlGaAs/AlGaAs -oxide multilayers and AlGaAs/air multilayers, respectively. Due to large index difference between GaAs (n=3.53) and AlAs-oxide (n=1.56), large photonic band gap can be obtained. In our design, AlGaAs (n=3.2) and AlGaAs-oxide (n=2.2) are used as the materials for growth of multilayers. The band structure of the omnidirectional reflector is calculated by transfer matrix method. For the AlGaAs/air multilayers, with the thickness ratio of the AlGaAs/air multilayers to be 40%/60%, the normalized band gap that is in the range between 0.18 to 0.34 and 0.45 to 0.62 exists only for the TE mode. With a pulsed input light of the wavelength at 1.55 /spl mu/m launched at the position of z=0, the entrance of the air-waveguide, the propagation loss is calculated. The minimum propagation loss is 0.23 dB//spl mu/m for the wavelength at 1.596 /spl mu/m. By tuning the structure of the omnidirectional reflector and the air-waveguide, for example by increasing the period of the multilayers, the propagation loss can still be decreased.