Vertical-cavity Semiconductor Optical Amplifiers Research Articles

Bistabilities of Birefringent Vertical-Cavity Semiconductor Optical Amplifiers With Antiresonant Reflecting Optical Waveguide

Bistable characteristics of birefringent antiresonant reflecting-optical-waveguide (ARROW) vertical-cavity semiconductor optical amplifiers (VCSOA) under external optical injection with multi-mode profile and arbitrary polarization orientation are investigated theoretically. It is found that the presence of ARROW can realize stable single-mode bistable switching in VCSOAs. Furthermore, with suitable design of the bias current profile, it can be shown that ARROW VCSOAs with a large core diameter (i.e., ges 50 mum) can sustain stable single-mode bistable switching.

Optical Flip-Flop Using Bistable Vertical-Cavity Semiconductor Optical Amplifiers With Anti-Resonant Reflecting Optical Waveguide

Flip-flop operations of anti-resonant reflecting-optical-waveguide (ARROW) vertical-cavity semiconductor optical amplifiers (VCSOAs) under the influence of undesired high-order injection modes are investigated theoretically. Three types of flip-flop operations, namely: (1) flip-flop triggered by optical injection, (2) inverse flip-flop triggered by optical injection, and (3) flip-flop triggered by injection current, are to be considered in the studies. It is found that with the presence of ARROW, all three types of optical flip-flop are insensitive to high-order injection modes, and stable single-mode flip-flop can be maintained in the operation.

All-optical flip-flop operation of VCSOA

An all-optical flip-flop, the memory of which is based on dispersive bistability in a single vertical cavity semiconductor optical amplifier, is demonstrated experimentally. Flip-flop control is achieved using two mechanisms: cross-phase modulation to set the flip-flop and cross-gain modulation of the holding beam within a remote SOA to reset it. Optical control signals are sub-milliwatt in power and derived from a single 5 ns, 1539 nm initial pulse. Flip-flop operation at 1542 nm is polarisation insensitive to control signals and achieved with an on-off contrast greater than 3 dB.

Homoclinic Snaking in a Semiconductor-Based Optical System

We report on experimental observations of homoclinic snaking in a vertical-cavity semiconductor optical amplifier. Our observations in a quasi-one-dimensional and two-dimensional configurations agree qualitatively well with what is expected from recent theoretical and numerical studies. In particular, we show the bifurcation sequence leading to a snaking bifurcation diagram linking single localized states to "localized patterns" or clusters of localized states and demonstrate a parameter region where cluster states are inhibited.

Potential of InGaAs/GaAs Quantum Dots for Applications in Vertical Cavity Semiconductor Optical Amplifiers

The use of InGaAs/GaAs quantum dots (QDs) in vertical cavity semiconductor optical amplifiers (VCSOAs) is proposed and analyzed. The results underline the distinctive differences between practical designs for QD vertical cavity semiconductor lasers and QD-VCSOAs. By means of a QD rate-equation scheme that accounts for both homogeneous and inhomogeneous broadening and the VCSOA cavity characteristics, the effects of material properties are identified. The design routes outlined here ensure the suitability of QD-VCSOAs for high-speed applications (>100 Gb/s) that rely on the fast carrier dynamics.

Polarisation effects on the nonlinear optical characteristics of a 1.55 µm vertical-cavity semiconductor optical amplifier

The effect of polarisation on the nonlinear optical properties of a 1550 nm vertical-cavity semiconductor optical amplifier (VCSOA) subjected to external optical injection into the two orthogonal polarisations of the fundamental mode has been studied experimentally. Clockwise nonlinear switching with very high on–off contrast ratio between the output states, exceeding 50:1, is reported. It is also shown that the use of polarised light gives a reduction to only some tens of microwatts of the input power requirements needed for clockwise nonlinear switching with high on–off contrast ratio. This represents at least one order of magnitude decrease in comparison with previously reported results either in VCSOAs or in edge-emitting devices. These results offer promise for the potential use of VCSOAs for all-optical signal processing as well as for optical interconnects and all-optical switching/routing applications.

Bistability and nonlinear gain in 1.55μm vertical cavity semiconductor optical amplifiers: Theory and experiments

We report experimental measurements of power and wavelength optical bistability and nonlinear gain in two 1.55μm vertical-cavity semiconductor optical amplifiers operated in reflection. Anticlockwise and clockwise nonlinear switching and bistability, both with high on-off contrast ratio up to 3.5:1, have been observed in the optical power and wavelength domains. Theoretical modeling gives excellent agreement with the experimental measurements.

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.

Two-wavelength switching with 1.55 µm VCSOA

Two-wavelength switching of a signal beam by a control signal at a different wavelength is demonstrated for the first time in a 1550 nm vertical cavity semiconductor optical amplifier (VCSOA). This result offers promise for the use of VCSOAs in all-optical switching/routing applications.

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.

Two-wavelength switching with 1550 nm semiconductor laser amplifiers

Feature Issue on Photonics in SwitchingTwo-wavelength switching operation between two signals at different wavelengths is reported using the optical bistability occurring in two different semiconductor laser amplifiers. With this technique an optical signal can be set in either of the optical input wavelengths by appropriate choice of the powers of the input signals. Switching of a signal beam by another control beam at different wavelength is reported experimentally with a 1550 nm distributed feedback semiconductor optical amplifier. Also, a theoretical model has been generated to analyze the wavelength switching operation with a novel amplifier type--the 1550 nm vertical cavity semiconductor optical amplifier (VCSOA). Using a 1550 nm VCSOA, wavelength switching operation is reported with a calculated input power below 1 μW. This low input power requirement for switching added to the high-frequency response of the VCSOA, and the ease of fabricating 2D arrays of these devices due to the vertical structure, makes the VCSOA a very interesting device for use in optical switching applications in the optical telecommunication networks.

Effects of parallel and orthogonal polarization on nonlinear optical characteristics of a 1550 nm VCSOA

Experimental observation of Optical Bistability (OB) and nonlinear gain is reported in a 1550-nm Vertical Cavity Semiconductor Optical Amplifier (VCSOA) under parallel and orthogonal polarized optical injection into the two orthogonal polarizations of the fundamental mode. Different nonlinear switching mechanisms, including anticlockwise and clockwise nonlinear gain and bistability, have been found when the polarization of the externally injected signal matches that of the injected mode, whilst a linear response is measured when the polarization is orthogonal to that of the mode under injection. This diversity of behavior with input polarization offers promise for the potential use of VCSOAs for all-optical signal processing and all-optical switching/routing applications.

Influence of Thermal Effects on Cross-Gain Modulation Characteristics in VCSOA

We study theoretically and numerically the influence of thermal effects on the cross-gain modulation (XGM) characteristics of vertical-cavity semiconductor-optical amplifiers. We show that heating of the device may lead to noticeable modifications of the XGM efficiency spectrum, leading even to negative XGM efficiency, in good agreement with recent experimental results

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.

Optical bistability and nonlinear gain in 1.55 µm VCSOA

An experimental observation of power and wavelength optical bistability and nonlinear gain in a 1550 nm vertical-cavity semiconductor optical amplifier (VCSOA) operated in reflection and biased above and below threshold is reported. Two distinct types of optical bistability, clockwise and anticlockwise, are observed.

Design and analysis of large-area vertical-cavity semiconductor optical amplifiers with anti-resonant reflecting optical waveguide

The optical characteristics of antiresonant reflecting optical waveguide (ARROW) vertical-cavity semiconductor optical amplifiers (VCSOAs) are investigated theoretically. Influence of spatial hole burning (SHB) and thermal lensing on the stability of the amplified output signal is taken into consideration in the studies. A design rule, which can be used to deduce the optimized dimensions of ARROW, is developed to achieve spatially stable single-spot amplified output-signal in large-area VCSOAs. It can be shown that a high saturation power yet stable output signal can be achieved in large-area ARROW VCSOAs simultaneously.

Slow-light in a vertical-cavity semiconductor optical amplifier

This paper discusses the effect of slow-light in Vertical-Cavity Semiconductor Optical Amplifiers. A Fabry-Perot model is used to predict the group delay (GD) and GD-bandwidth performance of a VCSOA operated in reflection in the linear regime. It is shown that the GD depends on all cavity parameters while the GDxGD-bandwidth product only depends on the gain. Experimental demonstration with a 1300nm GaInNAs VCSOA is used to validate the model and demonstrate tunable GDs between 25 and 100 ps by varying the VCSOA gain. Experimental distortion of the signals induced by nonlinear effects is also presented.