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Magnetorheological finishing (MRF) is usually used to remove subsurface defects (SSD) of workpieces to improve the laser-induced damage threshold due to its low stress. Although MRF has been widely used to remove surface defects and SSD, the evolution and removal mechanism of surface scratches under MRF have not been fully elucidated. A systematic study is conducted on the scratch removal process and removal ability of MRF. First, an experimental study on the removal of scratches with different depths is carried out, and the effect of the scratch depth on the removal efficiency is analyzed. Second, when the scratches are removed, the processing is performed in two directions: parallel and perpendicular to the scratch. Thereby, the relationship between the scratch removal efficiency (SRE) and the processing direction is analyzed. Finally, based on the scratch removal process and mechanism, an innovative method for efficient scratch removal using a sacrificial layer is proposed. The effectiveness of this method is verified by experiments. This method can significantly improve the SRE of MRF. [ABSTRACT FROM AUTHOR]

The physical mechanism in efficiency droop of GaN-based light-emitting diodes (LEDs) was investigated using a modified rate equation model considering inhomogeneous carrier distribution and was compared with the measured result. On this basis, the efficiency droop effect on the performance of a code division multiple access (CDMA) visible-light communication (VLC) system using GaN-based LEDs was also analyzed. The results reveal that the obvious transmitted signal error under the effect of LED efficiency droop leads to performance deterioration of multiuser CDMA VLC systems. Also, the performance of CDMA VLC systems is reduced with the user number increase due to LED efficiency droop. The bit error rate of a CDMA VLC system was further calculated for different branch signal levels and bias currents. It is demonstrated that the efficiency droop effect on the performance of CDMA VLC systems can be alleviated by adjusting the branch signal level and the bias current. [ABSTRACT FROM AUTHOR]

For a high precision interferometric fiber optic gyroscope (IFOG) under temperature control, a short start-up time and small temperature drift are important for its applications. The start-up time and the temperature drift of IFOG with the same fiber length but with a different fiber coil layer number are investigated and compared. Simulation by finite difference time domain method is done to illustrate the existence of optimal layer number for the fiber coil wound by the quadrupolar method. Theoretical analysis is then provided and a closed-form formulation is given to calculate the optimal layer number of the fiber coil, which can effectively reduce both the start-up time and temperature drift of IFOG. Our study is meaningful in improving the thermal performance of the fiber coil. [ABSTRACT FROM AUTHOR]

An optical setup for the nonorthogonal two-axis Lloyd’s mirror interferometer, which is composed of a nonorthogonal type of mirror-substrate assembly and a newly designed beam expansion assembly, is proposed to fabricate highly precise two-dimensional (2-D) diffraction scale gratings having uniform pattern structures over a wide area. The beam expansion assembly is designed in such a way that a thin collimated laser beam is at first generated by a small collimating lens to carry out a precise polarization modulation control of subdivided wavefronts in the beam, followed by the generation of a collimated laser beam with the expansion of the thin collimated laser beam by using a beam expander. Since a pair of high-precision half-wavelength plates made of crystalline quartz can be employed in the newly designed optical setup, a much better polarization modulation control can be expected, compared to the conventional optical setup in which low-precision large-size half-wavelength plates made of polycarbonate should have been employed. To verify the effectiveness of the proposed optical setup, theoretical calculations and some basic experiments are carried out by using a prototype optical setup to demonstrate the feasibility of the proposed optical setup for fabrication of highly precise 2-D scale gratings. [ABSTRACT FROM AUTHOR]

A high pumping-power fiber combiner for backward pumping configurations is fabricated and demonstrated by manufacturing process refinement. The pump power handling capability of every pump fiber can extend to 600 W, corresponding to the average pump coupling efficiency of 94.83%. Totally, 2.67-kW output power with the beam quality factor M² of 1.41 was obtained, using this combiner in the fiber amplifier experimental setup. In addition, the temperature of the splicing region was less than 50.0°C in the designed combiner under the action of circulating cooling water. The experimental results prove that the designed combiner is a promising integrated all-fiber device for multikilowatt continuous-wave fiber laser with excellent beam quality. [ABSTRACT FROM AUTHOR]

Amultiprobe surface encoder for opticalmetrology of six-degree-of-freedom(six-DOF) planar motions is presented. The surface encoder is composed of an planar scale grating with identical microstructures in - and -axes and an optical sensor head. In the optical sensor head, three paralleled laser beams were used as laser probes. After being divided by a beam splitter, the three laser probes were projected onto the scale grating and a reference grating with identical microstructures, respectively. For each probe, the first-order positive and negative diffraction beams along the - and -directions from the scale grating and from the reference grating superimposed with each other and four pieces of interference signals were generated. Three-DOF translational motions of the scale grating Δx, Δy, and Δz can be obtained simultaneously from the interference signals of each probe. Three-DOF angular error motions θx, θy, and θz can also be calculated simultaneously from differences of displacement output variations and the geometric relationship among the three probes. A prototype optical sensor head was designed, constructed, and evaluated. Experimental results verified that this surface encoder could provide measurement resolutions of subnanometer and better than 0.1 arc sec for three-DOF translational motions and three-DOF angular error motions, respectively. [ABSTRACT FROM AUTHOR]