Avago’s 850nm oxide VCSEL for applications requiring modulation at 25-28G has been designed for -3dB bandwidths in excess of 18GHz over an extended temperature range of 0-85C. The VCSEL has been optimized to minimize DBR mirror thermal resistivity, electrical resistance and optical losses from free carrier absorption. The active region is designed for superior differential gain to enable high optical bandwidths. The small-signal modulation response has been characterized and the large-signal eye diagrams show excellent high-speed performance. Characterization data on other link parameters such as relative intensity noise and spectral width will also be presented.
In this paper, the noise properties of vertical cavity semiconductor optical amplifiers (VCSOAs) operated in reflection mode are studied. Expressions for noise sources contributing to the total noise detected at amplifier output are derived, based on the photon statistics master equations. The noise figure, defined as the degradation of signal-to-noise ratio (SNR), is analyzed using the assumption that spontaneous emission-signal beat noise dominates. The analysis shows that the noise figure of reflection mode VCSOAs has the same values as that in transmission mode as long as amplifier gain is high (G>>1). Furthermore, simulations depict the dependence of noise figure on device parameters and bias conditions, as well as reveal the importance of the low reflectivity front mirror and the high reflectivity rear mirror for low noise operation. In addition, the noise figure analysis results are compared with experimental measurements, in which amplified spontaneous emission (ASE) power is measured by an optical spectrum analyzer and the noise figure is obtained from the ASE power and the amplifier gain. The measured data are in good agreement with the theoretical predictions.
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.
Vertical cavity semiconductor optical amplifiers (VCSOAs) are attractive devices for use in coherent optical amplification, especially where 2-D amplifier arrays are required. However, the coherence preservation quality of a VCSOA depends strongly on the bias condition, resonant wavelength mismatch, and the optical input power level. We characterize the coherence degree of a VCSOA as a function of these parameters by measuring interference fringe visibility with an interferometer. The dominant factors influencing the contrast of the fringes are the ratio of coherent, stimulated emission photons to amplified spontaneous emission (ASE) photons, and the spectral distortion of the amplified signal. Mostly, the overall gain and the saturation characteristic of the amplifier determine the ratio of stimulated emission to ASE. The spectral distortion of the signal is due to the narrow gain window of the VCSOA, but the effect significantly degrades the visibility only for relatively large wavelength mismatch from the gain peak. Analytic expressions may be used to identify the optimal bias current and optical input power to maximize the amplifier gain and visibility of the interference.
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.