An all-optical switch of Mach－Zehnder interferometer type using an active fibre ring resonator

We propose an all-optical switch of the Mach－Zehnder interferometer type using an active nonlinear ring resonator and analyse the significance of the parameter A, a product of gain and total loss, for performing an ideal 1 by 2 switch. We found that in the range of 1-κ≤A≤\sqrt{1-κ}, the increment of A can compensate the losses inside the ring, therefore increase the finesse of the ring and enhance the nonlinearity contribution to reduce the switching power threshold effectively. We also emphasize the importance of the initial switching point and discuss the feasibility of utilizing a high-nonlinear fibre in the ring.     

SiO2 Waveguide Resonator Used in an Integrated Optical Gyroscope

An integrated optical waveguide resonator based on a SiO2 waveguide is proposed, fabricated and tested. The method of designing the resonator is also presented. The optimal splitting ratio of the coupler is gained by simulating the relationship between the splitting ratio of the key coupler in the resonator and the resonator＇s finesse with resonance depth. The calculated fundamental detection limit of this integrated optical vcaveguide resonator is 1.6°/h. Finally, a micro-optical gyroscope system based on the integrated waveguide resonator is built, and the measured resonator＇s finesse F is close to 70 under fluctuating temperature. To the best of our knowledge, the present F is the best result to date. For the coupler splitting rate the experimental results have fixed errors with the simulation results caused by fabrication processes which can be easily eliminated, implying that the method of design is effective and applicable.     

基于开环振荡器阵列磁振荡效应的全光开关

We demonstrate an all-optical switching of the magnetic resonance properties associated with a metallic Split Ring Resonator（SRR） array. The periodically spaced elements are fabricated on a high-resistivity silicon wafer and probed by using conventional Terahertz （THz） time-domain spectroscopy. We use a continuous-wave laser diode to generate carriers in the gaps of the SRR elements. Using a sufficient power, this opti- cal excitation can create an effective short gap, which would switch the resonant properties of the metamaterial from that of an SRR array to that of a closed ring resonator array and leads to dramatic changes in the THz transmission. In the present experiment, the optically induced switching is associated with the magnetic reso- nance. However, with appropriate changes in the device structure, this approach can be extended to switch a medium with a negative real index of refraction to a medium with a positive real index of refraction. This opens the way to creat a broad new range of active devices.     

Coupled resonator-induced transparency on a three-ring resonator

The coupled resonator-induced transparency(CRIT) phenomenon, which is analogous to electromagnetically induced transparency in atomic systems, can occur in an original integrated optical resonator system due to the coherent interference of the coupled optical resonators. The system was composed of three ring resonators on silicon, each with the same cavity size, and the optical coupling to the input and output ports was achieved using grating with a power coupling efficiency of 36%. A CRIT resonance whose spectrum shows a narrow transparency peak with a low group velocity was demonstrated.The quality factor of the ring resonator can attain a value up to 6×10~4, and the harmonic wavelength can be controlled by adjusting the temperature. The through and drop transmission spectra of the resonator are reconciled well with each other and also consistent well with the theoretical analysis.     

Experimental study of nonlinear switching characteristics of conventional 2×2 fused tapered couplers

The nonlinear switching characteristics of fused fiber directional couplers were studied experimentally. By using femtosecond laser pulses with pulse width of 100 fs and wavelength of about 1550 nm from a system of Ti:sapphire laser and optical parametric amplifier (OPA), the nonlinear switching properties of a null coupler and a 100% coupler were measured. The experimental results were coincident with the simulations based on nonlinear propagation equations in fiber by using super-mode theory. Nonlinear loss in fiber was also measured to get the injected power at the coupler. After deducting the nonlinear loss and input efficiency, the nonlinear switching critical peak powers for a 100% and a null fused couplers were calculated to be 9410 and 9440 W, respectively. The nonlinear loss parameter PN in an expression of αNL=αP/PN was obtained to be PN = 0.23 W.     

Controllable time delay using slow/fast light in active fiber ring resonators with gain manipulation

We propose to generate controllable time delay using slow/fast light in fiber ring resonators with gain manipulation.The dispersion and group delay of active fiber ring resonator can be controlled by manipulating its gain level below the lasing threshold.Controllability of the negative group delay in the undercoupled regime and the positive group delay in the overcoupled regime is theoretically demonstrated.Besides,large group delay can be obtained accompanied by signal gain in active ring resonators.In addition,we describe wide bandwidth and large group delay in 4-stage cascaded ring resonators.     

All-fibre micro-ring resonator based on tapered microfibre

In this paper, bendloss characteristics of an optical fibre are investigated in detail, and the results show that the resonator with a smaller ring radius, wider free spectrum range （FSR）, higher fineness （f） and quality-factor （Q） can be achieved by using microfibres. Based on the improved fused taper technique, a high-quality microfibre with 5 ttm radius has been fabricated, and an all-fibre micro-ring resonator with a radius of only 500μm is realized using self-coiling coupling method. The good-resonant characteristic makes the all-fibre device be expected to avoid bendloss and connection loss associated with planar waveguide integration.     

A controllable coupling structure for silicon microring resonators based on adiabatic elimination

Optical microring resonators are extensively employed in a wide range of physical studies and applications due to the resonance enhancement property.Incorporating coupling control of a microring resonator is necessary in many scenarios,but modifications are essentially added to the resonator and impair the capability of optical enhancement.Here,we propose a flexible coupling structure based on adiabatic elimination that allows low-loss active coupling control without any modifications to the resonators.The self-coupling coefficient can be monotonically or non-monotonically controllable by the proposed coupler,potentially at a high speed.The characteristic of the coupler when implemented in silicon microring resonators is investigated in detail using substantiated analytical theory and experiments.This work provides a general method in coupling control while ensuring the resonance enhancement property,making active coupling control in a resonator-waveguide system feasible.     

Influence of group—velocity mismatch on soliton switching in a nonlinear fibre coupler

In this work, the influence of group-velocity mismatch on soliton self-routing pulse switching in a nonlinear fibre coupler is discussed in detail by the use of both variational approach and numerical simulation. The results obtained show that the group-velocity mismatch leads to the relative displacement between the two orthogonal polarization modes, increase of the critical power, and reduction of the elimination-light ratio. For sub-ps pulse, the influence cannot be neglected.     

Fabrication of the high power input coupler for BEPCⅡ superconducting cavities

The BEPCII storage ring adopts two 500 MHz superconducting cavities (SCC). Each one is equipped with a 500 MHz input power coupler. The coupler is to feed 150 kW power in continuous wave (CW) mode with both standing and traveling wave modes. Due to high power feeding and high frequency of the coupler, its fabrication is a big challenge. The fabrication started with two key components,the window and the antenna. Up to now, two sets including windows and antennas have been made by IHEP. And a 270 kW RF power in CW has passed through the coupler during the high power test. The fabrication details are presented in this paper.