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.
As a powerful and noninvasive tool, laser trapping has been widely applied for the confinement and physiological study of biological cells and organelles. Researchers have used the single spot laser trap to hold individual sperm and quantitatively evaluated the motile force generated by a sperm. Early studies revealed the relationship between sperm motility and swimming behavior and helped the investigations in medical aspects of sperm activity. As sperm chemotaxis draws more and more interest in fertilization research, the studies on sperm-egg communication may help to explain male or female infertility and provide exciting new approaches to contraception. However, single spot laser trapping can only be used to investigate an individual target, which has limits in efficiency and throughput. To study the chemotactic response of sperm to eggs and to characterize sperm motility, an annular laser trap with a diameter of several hundred microns is designed, simulated with ray tracing tool, and implemented. An axicon transforms the wavefront such that the laser beam is incident on the microscope objective from all directions while filling the back aperture completely for high efficiency trapping. A trapping experiment with microspheres is carried out to evaluate the system performance. The power requirement for annular sperm trapping is determined experimentally and compared with theoretical calculations. With a chemo-attractant located in the center and sperm approaching from all directions, the annular laser trapping could serve as a speed bump for sperm so that motility characterization and fertility sorting can be performed efficiently.
The compactness of VCSELs (Vertical Cavity Surface Emitting Lasers) provides them the ability to meet the demands of current biochip technologies. In earlier research, optical trapping of live biological cells and microspheres based on VCSEL array has been realized in the form of parallel static traps on a translation stage. In microfluidic systems (lab-on-a-chip devices), the background flow introduces complexity and uncertainty in velocity and force analysis on target microparticles, making the capability of transporting biological objects without moving sample highly desirable. Moreover independently controllable traps offer more flexibility in microparticle manipulation. In this paper, a microscope-integrated VCSEL trapping system capable of independent control and batch processing of microparticles is devised and demonstrated. Optical design considerations for keeping stable trapping performance while multiplexing are addressed. Both a single optical trap and a trap array can be controlled independently by tilting mirror while their relative depth can be adjusted without power loses in optical system. In the micromanipulator, a single VCSEL trap serves as a collector and distributor, while a VCSEL array provides the carrier for synchronous processing and small range shift. Potential improvement based on two independently controlled VCSEL arrays is discussed and related applications are investigated.