All-optical flip-flop based on vertical cavity semiconductor optical amplifiers.

We report the operation of an all-optical set-reset (SR) flip-flop based on vertical cavity semiconductor optical amplifiers (VCSOAs). This flip-flop is cascadable, has low optical switching power (~10 microW), and has the potential to be integrated on a small footprint (~100 microm(2)). The flip-flop is composed of two cross-coupled electrically pumped VCSOA inverters and uses the principles of cross-gain modulation, polarization gain anisotropy, and highly nonlinear gain characteristics to achieve flip-flop functionality. We believe that, when integrated on chip, this type of all-optical flip-flop opens new prospects for implementing all-optical fast memories and timing regeneration circuits.

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.

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.

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.

Observation of wavelength and multiple bistabilities in 850nm Vertical-Cavity Semiconductor Optical Amplifiers (VCSOAs).

Both wavelength bistability (WB) and multiple bistability (MB) were predicted theoretically by Adams' model in resonant optical amplifiers. We report here, for the first time to our knowledge, their experimental observation in 850nm Vertical-Cavity Semiconductor Optical Amplifiers (VCSOA). Clockwise hysteresis of WB is observed at constant input power while the input wavelength is swept across the gain window. MB is observed at a fixed operation wavelength biased on the long-wavelength side of the two separated Polarization-Dependent Gain (PDG) windows of the VCSOA by sweeping the optical input. The polarization of the input is set to a fixed angle with respect to the two intrinsic principal axes of the VCSOA. Two MB levels were experimentally observed at 160muW and 320muW, respectively. These observations are in good agreement with theoretical prediction by Adams' model and may lead to multi-valued optical information manipulation.

Optical bistability in vertical-cavity semiconductor optical amplifiers.

We present an overview of the properties and applications of optical bistability in vertical-cavity semiconductor optical amplifiers (VCSOAs). The basic physics and analytical models of this optical nonlinearity are discussed. Experimental results obtained from a VCSOA operated in the 850 nm wavelength region are presented. 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 muW when the device is biased at 98% of its lasing threshold. Numerical simulations based on the Fabry-Perot resonator model and rate equations we developed show good agreement with our experimental observations. In addition, a low input intensity high contrast (10:1) optical and gate and 2R regeneration are demonstrated. We believe that bistable VCSOAs can significantly advance the prospect of a dense two-dimensional array of low-switching-intensity all-optical logic and memory elements.

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.

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.

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.