Matthias Gross

Parallel transport of biological cells using individually addressable VCSEL arrays as optical tweezers

We have demonstrated the use of vertical cavity surface emitting lasers (VCSELs) for optical trapping and active manipulation of live biological cells and microspheres. We have experimentally verified that the Laguerre‐Gaussian laser mode output from the VCSEL functions just as well as the traditional Gaussian fundamental laser mode for optically trapping biological cells and may be preferable since the highest intensity of the Laguerre‐Gaussian mode is located at the outer ring of the optical aperture, which allows for stronger optical confinement to be obtained for a lower total power. Another advantage that VCSELs have over conventional gas and diode lasers is their ability to be manufactured in an array form. Using a 2 � 2 array of VCSELs, the simultaneous and independent transport of four human red blood cells is demonstrated indicating that much larger two-dimensional VCSEL arrays can be used as individually addressable optical tweezers in biological chips and systems. This parallel transport capability will have a significant impact in currently developing biochip array and assay technologies through the facilitation of the selection, relocation, and precision placement of cells. # 2002 Elsevier Science B.V. All rights reserved.

VCSEL Arrays as Micromanipulators in Chip-Based Biosystems

The potential use of vertical cavity surface emitting laser (VCSEL) arrays for applications in cell analysis and tissue engineering is investigated by means of parallel optical trapping and active manipulation of biological cells on microfluidic chips. The simultaneous and independent transport of nine cells using a 3×3 array of VCSELs has been demonstrated experimentally; indicating that larger 2-dimensional array transport using individually addressable tweezers is achievable with VCSEL array devices. The transport properties of VCSEL tweezers have been investigated for various types of cells including 3T3 Murine fibroblasts, yeast, rat primary hepatocytes and human red blood cells. Due to the low relative index of refraction between the biological cell and surrounding medium and the relatively low optical power available with present VCSELs, the Laguerre-Gaussian laser mode output of the VCSEL is more favorable to use in an optical tweezer since the highest intensity is located at the outer ring of the optical aperture, producing stronger optical confinement at lower power levels. For larger biological cells or cells with a lower relative index of refraction, the power limitations of a single VCSEL were overcome through the binning of several VCSELs together by combining the outputs of a sub-array of VCSELs into a collective optical tweezer. A comprehensive analysis and simulation of how the VCSELs’ pitch and output beam divergence influence the operation of the resultant optical tweezer array is presented along with our experimental data. Employing the methods of parallel array transport and the binning of multiple VCSEL outputs, allows for the manipulation and spatial arrangement of different types of cells in a co-culture so as to facilitate the formation of engineered tissues.

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.

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.

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.

All-optical oscillator based on a single bistable Vertical-Cavity Semiconductor Optical Amplifier (VCSOA)

A novel all-optical oscillator is demonstrated for the first time by employing a cascadable VCSOA inverter in a closed optical loop, which generates a self-sustained square-like waveform with ~80 ps switching time and 5:1 extinction ratio.

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.