Activity

Due to the limited processing accuracy of the platform and unevenness of the glass substrate itself, a holographic lithography system is prone to out-of-focus imaging problems; therefore, the real-time focusing components are critical for holographic lithography systems. In this paper, a real-time focus monitoring and adjusting system using an electrically tunable lens (ETL) for large-area lithography is introduced. Combined with the ETL, the limited depth of field of the microscopic objective has been effectively expanded, and the automatic focusing evaluation and adjustment are achieved. The development, including simulation using Zemax, optics system design and implementation, experiments, and evaluation are demonstrated in this paper. The results show that the out-of-focus problem in our large-area holographic lithography system has been significantly alleviated.With the development of high-power lasers for aerospace, electronics, etc., the demand for large-aperture planar optical elements has become more urgent, along with the demand for measurement methods. read more In this paper, the design of a 300 mm aperture vertical Fizeau spatial-temporal phase-shifting interferometer is discussed. Based on position difference between laser sources, the spatial phase-shifting technique is achieved by generating a laser source array on the focal plane of the collimation lens, and four pairs of coherent beams with different phase shifts are integrated in a vertical Fizeau interference system. Combined with a tunable laser diode, a temporal phase-shifting technique can be realized in any pair of coherent beams through wavelength tuning. The key techniques, which include laser duplication to introduce different phase shifts, conjugate imaging, and separation for interferograms, and assembly for a transmission flat, are demonstrated. The systematic error and position mismatch error of interferograms are eliminated. Comparison experiments are conducted between spatial and temporal phase-shifting techniques. A dynamic water surface is also measured to verify its capacity for detecting dynamic objects.This paper reports beam wave intensity fluctuations in uplink (ground-to-satellite) laser beam transmission caused by atmospheric turbulence. Intensity fluctuation in the strong region was apparently induced by uplink measurement in previous experiments. Statistical values of the uplink fluctuation were estimated by numerical calculation using moment equation analysis with thin phase screen approximation. The beam profile of the uplink, the scintillation index, and the covariance of the uplink intensity fluctuation were calculated using models of the refractive index structure constant. The generation of strong intensity variation was explained as the result of a speckle pattern on the receiving plane at the satellite produced by atmospheric turbulence when scanned along with trajectory of the satellite.We designed and simulated a diode laser with output power of more than 10 kW and a line shape beam spot of approximately $14 – 58\;\rm mm \times 1.6\;\rm mm$14-58mm×1.6mm ($\rm 1/e^2$1/e2 width). The diode laser was assembled with high fill factor diode laser bars that can be cooled with filtered tap water. The diode laser bar was beam shaped with a tilted cylindrical lens array to twist the slow axis of individual emitters by 90 deg, and then the slow axis was collimated with a single cylindrical lens. From the simulation, 20 laser diode bars with the same wavelength formed a diode laser optical stack with an output power of more than 3.5 kW, a beam spot of $31\;\rm mm \times 12\;\rm mm$31mm×12mm size, and full divergence angles of around 6 mrad in both the horizontal and vertical directions. Then, three laser diode optical stacks with different wavelengths were wavelength-multiplexed to obtain an output power of more than 10 kW. Finally, the diode laser optical stack was transformed by simple cylindrical lenses to form a line shape spot with a working distance longer than 250 mm. Our diode laser design is much simpler than previous devices with similar output power and can find various applications such as high-speed laser cladding.We present a graphene-based optical leaky wave antenna (OLWA) with diamond-shaped perturbations. The leaky wave antenna is created by applying diamond-shaped graphene perturbations to a Si3N4 waveguide. The leaky wave behavior is observed by changing the graphene chemical potential. Results in the form of leakage power, normalized directivity, and reflectance, transmittance, leakage power, normalized directivity, and normalized E-field are presented. The half power beamwidth (HPBW) of 1.2° is achieved by this antenna. The reflectance and transmittance are in a very low wavelength range between 1.4 and 1.6 µm throughout. The leakage of power is more for the lower graphene chemical potential. The graphene-based design is also compared to a gold-based design and silicon-based design to show the leakage comparison. The designed graphene-based OLWA can be used in medical sensing devices.Thermal-induced errors have a significant impact on the environmental adaptability of a fiber optic gyroscope (FOG). Reasonable winding methods can reduce and offset the thermal-induced errors. However, complex methods put higher requirements on winding accuracy. By adding additional winding layers on the outer surface of the fiber coil, an improved winding method to reduce the temperature error of FOG is proposed in this paper. Simulations in temperature-control conditions and time-varying temperature conditions are performed. Simulation and experimental results show that additional winding layers lead to a satisfactory reduction of thermal-induced rate errors. With parameter estimation and error compensation, thermal-induced errors can be further reduced.In this paper, we introduce a cryogen-adaptive sensor based on a micro-electromechanical system (MEMS) for level measurement of cryogenic fluids. The sensor is fabricated by an optical fiber inserted in a glass ferrule and an integrated Fabry-Perot (FP) chip using the MEMS technique. We carried a liquid nitrogen level measurement experiment to verify the performance of the sensor and a low coherent interference system is used to transform the liquid level to absolute phase. The measuring range is 24 cm and can be expanded more widely. The experimental results show that the sensor has a good monotonic linear response (coefficient determination $\rm R^2 \gt 0.998$R2>0.998), and the measurement error is less than $ \pm 5\;\rm mm$±5mm in liquid nitrogen. The excellent cryogenic temperature performance from $ – 260^\circ \rm C$-260∘C to $ – 100^\circ \rm C$-100∘C also is demonstrated, which shows the potential application in level measurement of various cryogenic liquids.