A Dual Four-Quadrant Photodetector Based on Near-Infrared Enhanced Nanometer Black Silicon

In this paper, a new preparation process of nanometer black silicon is proposed, by which high trapping optical Se-doped black silicon material is prepared by nanosecond pulsed laser ablation of high-resistance silicon coated with Se film in HF gas atmosphere. The results indicate that the average absorptivity of 400–2200 nm band before annealing is 96.81%, and the absorptivity maintains at 81.28% after annealing at 600 degrees. Meanwhile, black silicon prepared under the new technology is used in double four-quadrant photodetector, the results show that, at a reversed bias of 50 V, the average unit responsiveness is 0.528 A/W at 1060 nm and 0.102 A/W at 1180 nm, and the average dark current is 2 nA at inner quadrants and 8 nA at outer quadrants. The dual four-quadrant photodetector based on near-infrared enhanced black silicon has the advantages of high responsiveness, low dark current, fast response and low crosstalk, hence it is appropriate for a series of direction of applications, such as night vision detection and medical field.

Spot-Centroid Determination Algorithms in Semiactive Laser Photodiodes for Artillery Applications

Precision of guided projectiles depends equally on the accuracy in determining the coordinates of the objective and on the exactness of the measurement devices utilized for position and attitude calculation of the projectile. Development of algorithms for low-cost high-precision terminal guidance systems is a cornerstone in research in this field. Semiactive laser (SAL) kits, and particularly quadrant detector devices, have been developed to improve precision in guided weapons. Photodetection system can be functionally divided into two main parts: sensing and processing. The sensed signal is processed to estimate the spot coordinates, i.e., the laser footprint, which provides some information regarding projectile-target relative position, to obtain the needed information for the navigation and guidance algorithms. The electrical intensities that a real sensor provides under laboratory conditions are compared to a mathematical model based on area intersection calculations to simulate the intensities on real flights. Then, four different processing algorithms, two of them rational, and the other two logarithmic, are tested for different spot sizes, which are nonlinear. Proposing an interpolation algorithm based on the four electrical intensities obtained in a semiactive laser quadrant photodetector, laser footprint center estimation is improved for artillery applications. Finally, an example illustrating a projectile flight is employed to compare real and calculated laser footprints in order to select the best algorithm for artillery applications.

Axial Calibration of QPD Signal based on Stuck Bead Method for Optical Trapping Applications

Calibration of axial quadrant photodetector (QPD) signal to the trapped bead position in an optical tweezer is important to measure the quantitative mechanical parameter in axial (laser propagation) direction. An alternative calibration based on the Stuck Bead Method (SBM) was proposed in this study. 3 µm polystyrene beads were stuck at the surface of glass coverslip and moved axially around the laser focus. QPD was used to obtain the position dependent intensity profile at three different laser powers (19.8 mW, 34.1 mW, 48.5 mW). The QPD signal-to-distance calibration value was consistent at 26 mV/µm for the used bead at the three laser powers. It was found that the calibration values are independent of laser powers and limited by the resolution of distance adjustment.