We present a fiber-optic extrinsic Fabry-Perot interferometer pressure sensor based on a nanothick silver diaphragm. The sensing diaphragm, with a thickness measured in a few hundreds of nanometers, is fabricated by the electroless plating method, which provides a simple fabrication process involving a high-quality diaphragm at a low cost. The sensor exhibits a relatively linear response within the pressure variation range of 0-50 kPa, with a high pressure sensitivity of 70.5 nm/kPa. This sensor is expected to have potential applications in the field of highly sensitive pressure sensors.

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This study proposes a high-precision compensation system using an on-machine noncontact measuring system to improve the manufacturing accuracy and efficiency of largediameter aspheric mirrors by reducing profile errors arising from tool setting errors and machine positioning errors. By measuring a standard hemisphere, the assembly tilt angle of the measurement sensor can be calibrated. The grinding wheel setting offset can be calculated by comparing the measured profile and the ideal profile, and the profile error caused by wheel offset can be reduced by adjusting the grinding origin coordinate. According to the normal unit vector and residual error in the Z direction of the measuring points, the normal residual errors corresponding to the grinding points could be generated as well as the compensation grinding numerical control (NC) program. An 800-mm-diameter K9 mirror was ground to verify the proposed compensation grinding method. The profile error was reduced from 65 to 35 μm during the semi-finish grinding stage. By using the compensation grinding path, the profile accuracy was improved from 35 to 8 μm in the fine grinding stage. The proposed compensation method effectively improves the profile accuracy and manufacturing efficiency for grinding large-diameter aspheric mirrors.

A novel temperature-insensitive strain sensor, based on an in-line Mach-Zehnder interferometer, is fabricated by concatenating two waist-enlarged fiber tapers separated by a short piece of photonic crystal fiber. The interference spectrum of the proposed sensor is analyzed in detail. Experimental results demonstrate that this sensor has a strain sensitivity of 3.02 pm/µε and maintains the temperature insensitivity feature. The proposed sensor has great potential in diverse sensing applications due to its advantages, such as its compact size, low cost, and simple fabrication process.OCIS In-line fiber-optic Mach-Zehnder (MZ) interferometric sensors have attracted great interest due to their unique advantages, including their compact size, low cost, high sensitivity, immunity to electromagnetic interference, and ruggedness even in corrosive and other harsh environments [1−4] . The operating principle of the MZ sensors is based on inter-modal interference, which arises from the phase difference between the involved interfering modes, primarily including the core mode and cladding modes excited in the sensing fiber. Thus far, a number of in-line fiber-optic MZ interferometric sensors based on various configurations have been reported in the literature. To excite cladding modes or couple the core mode to cladding modes, many different methods are employed to construct such sensors, including long period gratings (LPGs) [5−7] and mismatched or misaligned core diameter and fiber tapers [8−14] . Based on the abovementioned methods, these sensors show good performance in the applications of sensing temperature, strain, bending, and refractive index. However, one constant drawback of these sensors is the cross-interference between different measurands, such as a strain sensor with an undesirable thermal sensitivity. To address this issue one has to design sensing heads with athermal packages or simultaneously and independently measure strain and temperature; however, this always increases the complexity of the sensor and seriously limits the practical application of the fiber sensor.In this letter, we propose and experimentally demonstrate a novel in-line MZ interferometric sensor, which is formed by splicing a piece of photonic crystal fiber (PCF) between two pieces of a conventional single-mode fiber (SMF). A waist-enlarged fiber taper, which possesses much better physical strength than the waist-reduced taper, is introduced into our proposed structure (Fig. 1). At the first splicing point, the core mode of the lead-in SMF excites the cladding modes, in which a taper region formed by air holes collapse in PCF, and then couple back into the lead-out SMF after the second splicing point. Consequently, the light from the lead-out SMF shows an interference pattern with a fringe contrast of more than 15 dB. The experimental result demonstrates that the proposed sensor has a strain sensitivity of 3.02 pm/µε to the axial strain. It also maintains the temperatureinsensitive feature. Furthermore, this type of sensor has a much...

This paper presents a method to improve the alignment accuracy of mask in linear scale projection lithography, in which the adjacent pixel gray square variance method of CCD image is used to find the best position of the focal length of the motherboard and then realize the alignment of the focal plane. Two image positions in the focal plane from the CCD are compared the traits overlap through the image splicing principle, and to establish the correction of four typical errors on the basis of the whole grating errors. At the same time, using the rotation error of the mask to summarize Grayscale Variation Function of CCD Image, and threshold functions are used to express the factors including wave crests of the amplitude, period error and phase error, which govern the rotation accuracy and weight alignment accuracy expression of the four error factors is established. In the experiment, it is finally corrected the slope of the mask and be adjusted the same direction of the slide plate with the help of dual-frequency laser interferometer, the influence of alignment error on lithography accuracy was discussed and verified in the static case and the CCD maximum resolution pixel corresponds to 0.1 μm, the accuracy of scale is 0.79 μm in only 200 mm measurement range.