Zhongchang Zhuo

Electromagnetically induced photonic bandgap in hot Cs atoms

Three-level Λ-type thermal Cs atoms are used to demonstrate the phenomenon of a photonic bandgap induced by quantum coherence with a standing wave (SW). We observed the transmitted signals of probe field driven by several kinds of SW, which are formed by a strong forward-traveling field and a backward-traveling field when a mirror reflects the forward-traveling beam. Considering Doppler inhomogeneous broadenings with a SW drive, we employ Fourier transformation to solve density-matrix equations for simulation results. The simulation results are found to be consistent with the experimental results.

Fabrication of a tilted fiber Bragg grating with a designed reflection spectrum profile

A method of fabricating a tilted fiber Bragg grating (TFBG) with a designed reflection spectrum profile is proposed and demonstrated experimentally. In a reflective TFBG the central wavelength and the reflectivity are dependent on the tilt angles. Controlling the rate at which the tilt angle is continuously varied and the exposure dose in the UV-light writing process permits accurate control of the bandwidth and reflectivity of the grating. The experimental result agrees well with TFBG theory and calculation.

Group velocity control of a light pulse using giant nonlinearities

In this paper, we propose and demonstrate a scheme to enhance nonlinearities of a probe pulse at both cross-phase modulation (XPM) and self-phase modulation (SPM) in a four-level system. Based on standing wave grating generated by counter-propagating resonant signal fields and an additional off-resonant coupling field, a giant nonlinear refractive index of the resonant probe field is obtained with absorption suppressed. Group velocity of the probe pulse can be controlled by both XPM and SPM nonlinearities.

A bistable system with an electromagnetically induced grating

We propose a scheme of a bistable system with an electromagnetically induced grating and analyse the optical bistabilities in the system. The stationary equations describing the system have been derived. This bistable system shows typical hysteresis behaviour.

Fabrication of planar optical waveguide material on silicon by flame hydrolysis deposition

SiO2 thick films were deposited on silicon wafer (2 inches in diameter) as buffer layer for fabricating planar optical wave-guide by flame hydrolysis deposition (FHD) method. The deposition speed is as high as 8μ+m per minute. Then the deposited films were consolidated in electric furnaces in vacuum or air ambience at the temperature of 1380°C. As a result, transparent vitreous silica (or called silica glass) and semi-transparent cristobalite films were obtained. The thickness of the vitreous silica films is up to 40μm, and this kind of films is suitable for buffer layer of planar wave-guide. SiO2 thick films doped with GeO2 were obtained by the same process to fabricate the core layer. Finally, several factors affecting the consolidated silica films were discussed in detail.

Observation of electromagnetically induced photonic band gaps in hot two-level atoms

In this paper, two-level thermal Cs atoms are used to observe electromagnetically induced photonic band gaps with a strong symmetric and two types of asymmetric standing-wave (SW) driving fields. One main band and two sidebands are measured for the transmitted and reflected spectra. We carry out physical interpretation about the observations in SW-dressed atom picture and employ method of Fourier transformation to solve density-matrix equations for hot two-level system to simulate the experimental results. The numerical analyses are consistent with the experimental observations for properties of electromagnetically induced photonic band gaps.

Enhanced group velocity dispersion and nonlinearity for a weak field using quantum coherence

We propose a scheme in a four level atomic system to enhance group velocity dispersion and nonlinearity for a weak field using photonic bandgap created by quantum coherence with standing fields, where weak probe pulse propagates fast or slowly controlled by interaction between atoms and coherent fields.

Photon switch by Fano interference in a double quantum well structure

In this paper, we demonstrate a weak photon switch by Fano interference in a double quantum well structure. GaAs/AlGaAs and InGaAs/AlAs heterostructures are taken as switch media to show that the weak switch can work at different wavelength by choosing materials and structures. We also estimate the order of the switch power and show that this photon switch by Fano interference in coupled double quantum well structures is a weak optical switch that can be used to realize one optical beam control another beam.