Pengyue Wen

Observation of bistability in a Vertical-Cavity Semiconductor Optical Amplifier (VCSOA)

We report, the first time to our knowledge, an observation of optical bistability in a Vertical-Cavity Semiconductor Optical Amplifier (VCSOA) operated in reflection mode. Counterclockwise hysteresis loops are obtained over a range of initial phase detuning and bias currents. One hysteresis loop is observed experimentally with an input power as low as 2 ìW when the device is biased at 98% of its lasing threshold. We also numerically simulate the optical bistability and obtain good agreement with our experimental observations. Bistable VCSOAs significantly advances the prospect of dense 2-D array of low switching-intensity all-optical logic and memory elements.

Vertical-cavity optical AND gate

Abstract We have demonstrated, the first time to our knowledge, a low-input intensity high-contrast (10:1) optical AND gate based on the differential gain (optical bistability) observed in an 850 nm GaAs vertical-cavity semiconductor optical amplifier (VCSOA). The input switching power is about 6 μW, which equals to the intensity of 16 nW / μm 2 . It is about 2 orders of magnitude lower than in in-plane semiconductor optical amplifiers. In the experiment the device also shows an optical gain of 10 dB.

Observation of counterclockwise, clockwise and butterfly bistabilty in 1550 nm VCSOAs.

In this paper, we report counter-clockwise, clockwise, and, for the first time to our knowledge, butterfly bistability in 1550 nm Vertical Cavity Semiconductor Optical Amplifiers (VCSOA). Bistable operation is experimentally observed for bias currents ranging from 66-122% of threshold with switching powers as low as 2 microW. These switching powers are two orders of magnitude lower than any previous results in 1550 nm VCSOAs. These switching powers are consistent with previous reports on optical bistability in 850 nm VCSOAs and provide an important step towards the realization of small footprint, low power optical logic/switching elements in the 1550 nm wavelength band.

Nonlinear gain in vertical-cavity semiconductor optical amplifiers

We report on the wavelength-dependent nonlinear-gain properties of a vertical-cavity semiconductor optical amplifier. A step-like output versus input transfer curve and bistability are found on the long wavelength side of the resonant peak. The characteristics are caused by a dispersive nonlinearity arising from gain saturation in the device. The nonlinear transfer of the amplifier could be used for logic regeneration and all-optical logic operations, while the optical injection power required to switch the device is an order of magnitude lower than previously reported with edge-emitting devices.

Integration of optoelectronic array devices for cell transport and sorting

Current biochip technologies typically rely on electrostatic or mechanical forces for the transport and sorting of biological samples such as single cells. In this paper we have investigated how optical pressure forces can be effectively used for the manipulation of cells and switching in a microfluidic system. By projecting the optical beams externally non-contact between the control devices and the sample chip is possible thus allowing the sample chips to be disposable which reduces the chance of cross-contamination. In one implementation we have shown that vertical cavity surface emitting laser (VCSEL) array devices used as parallel optical tweezer arrays can increase the parallelism of sample manipulation on a chip. We have demonstrated the use of a high-order Laguerre-Gaussian mode VCSEL for optical tweezing of polystyrene microspheres and live cells. We have also shown that optical pressure forces from higher- power sources can be used for the switching of particles within microfluidic channels. Both the attractive gradient force and the scattering force of a focused optical beam have been used to direct small particles flowing through junctions molded in PDMS. We believe that by integrating optical array devices for simultaneous detection and manipulation, highly parallel and low-cost analysis and sorting devices may be achieved.

Cascadable all-optical inverter based on a nonlinear vertical-cavity semiconductor optical amplifier

We report, for the first time to our knowledge, the operation of a cascadable, low-optical-switching-power(~10 microW) small-area (~100 microm(2)) high-speed (80 ps fall time) all-optical inverter. This inverter employs cross-gain modulation, polarization gain anisotropy, and highly nonlinear gain characteristics of an electrically pumped vertical-cavity semiconductor optical amplifier (VCSOA). The measured transfer characteristics of such an optical inverter resemble those of standard electronic metal-oxide semiconductor field-effect transistor-based inverters exhibiting high noise margin and high extinction ratio (~9.3 dB), making VCSOAs an ideal building block for all-optical logic and memory.

Rate Equations for modeling dispersive nonlinearity in Fabry-Perot semiconductor optical amplifiers

We model the non-linear gain characteristics of a Fabry-Perot semiconductor optical amplifier using a modified photon density rate equation. Good agreement is found with experimental results, with the simulation accurately reproducing all the major characteristics of the amplifier. To our knowledge, this is the first calculation using only the rate equations that accurately predicts the gain and nonlinear behavior of FPSOAs.

Polarization anisotropy in vertical-cavity semiconductor optical amplifiers

The polarization-dependent gain (PDG) characteristics of a vertical-cavity semiconductor optical amplifier (VCSOA) are measured, and the case of the PDG is determined. It is often assumed that the polarization states of a VCSOA are degenerate because of the circular geometry of the device. This assumption is not true in practice, and it is found that VCSOAs possess a dominant linear polarization state and a small difference in frequency between polarization states. The difference in resonant frequencies causes the PDG of the VCSOA. Measurements of the polarization state show that the cause of the splitting is electro-optic birefringence.

New photon density rate equation for Fabry-Perot semiconductor optical amplifiers (FP SOAs)

Two different approaches are commonly used for Fabry-Perot Semiconductor Optical Amplifiers (FP SOAs) performance analysis: the Fabry-Perot resonator approach and rate equation approach. Compared with the Fabry-Perot resonator approach, the rate equation approach is more powerful because noise and mode-related performance analysis can be included. However, it has been shown that the results based on Fabry-perot approach contains multiplicative factor which arise from an explicit consideration of the resonator and those factors are missing in the rate equation approach. As a result, the existing rate equations provide a poor description of FP SOAs. Our analysis shows that this is due to the fact that the interference between the injected optical field and the intracavity optical field has not been taken into account properly. In this paper, a new photon density rate equation for Fabry-Perot semiconductor optical amplifiers is derived based on the electric field rate equation. By taking this interference into account, our derivation shows that the input coupling term in the photon density rate equation is a function of the top and bottom mirror reflectivity, as well as the bias condition. Optical gain predictions from this new photon density rate equation match well with experimental measurements.

Misalignment correction for optical interconnects using vertical cavity semiconductor optical amplifiers

In board-to-board optical interconnects, the misalignment between the board and the backplane connections can cause both optical loss and interchannel cross talk. A vertical cavity semiconductor optical amplifier (VCSOA) is proposed to correct optical misalignment in an optical connector between the board and the backplane. Angular or lateral misalignment can be corrected with the designed module. The correction ability is determined by the acceptance angle of the VCSOA, which was characterized to be 9.4 degrees full angle at a 3 dB gain drop for a 30 microW optical signal at 1 GHz. The lateral misalignment correction ability is 0.16f, where f is the focal length of the mini lens to converge the input light onto the VCSOA.