With the success of the Webb telescope, dispersed fringe sensing (DFS), with the significant merit of a large capture range, is proving to be a promising cophasing approach for a large-aperture segmented telescope. In this Letter, a novel, to the best of our knowledge, piston error extraction method based on principal component analysis (PCA) technology is proposed. In this method, all the one-dimension intensity distributions along the dispersion axis for different interference positions are regarded as a set of random phase-shifted interference signals. PCA technology is utilized to obtain its corresponding continuous principal phase and the piston error could be directly estimated proportionally from the slope of the phase–wavenumber line. This method avoids nonlinear operations, similar to Shi’s traditional framework; no active move is needed for fine cophasing, and the method is also free of characteristic constant calibration in sidelobe peak displacement- and slope-based methods. Preliminary simulations of the method’s coarse-then-fine cophasing ability with high accuracy are presented here to show its potential.

A dispersed fringe sensor (DFS) is a promising approach for sensing the large-scale piston error for segmented mirror systems. In this Letter, a novel method, to the best of our knowledge, for piston sensing based on a digital dispersed fringe (DDF), which is generated by wavelength tuning, is introduced. By continuously changing the wavelength of light passing through the sensor, a collection of far-field spot arrays can be acquired, which are used to construct the DDF with steps of accumulation and stacking in sequence for each inter-segment region. A correlation-based method is applied to extract the encoded piston information from the DDF. The method greatly eases the demanding hardware requirement in traditional DFS and shows high efficiency for the reason that it could simultaneously measure all of the relative piston settings; in addition, it exhibits strong robustness to noise.

The coefficient of thermal expansion (CTE) is an important property of ultra-low expansion (ULE) glass, and the ultrasonic velocity method has shown excellent performance for the nondestructive measurement of CTE in large ULE glass. In this method, the accurate acquisition of the ultrasonic velocity in ULE glass is necessary. Herein, we present a correlation method to determine the ultrasonic TOF in ULE glass and to further obtain the ultrasonic longitudinal wave velocity ($c_{\mathrm{L}}$) indirectly. The performance of this method was verified by simulations. Considering the dependence of $c_{\mathrm{L}}$ on temperature (T), we carried out the derivation of the analytical model between $c_{\mathrm{L}}$ and T. Based on reasonable constant assumptions in the physical sense, a $c_{\mathrm{L}}$–T exponential model was produced, and some experimental results support this model. Additional experiments were carried out to validate the accuracy of the $c_{\mathrm{L}}$–T exponential model. The studies we conducted indicate that the $c_{\mathrm{L}}$–T exponential model can reliably predict the ultrasonic velocity in ULE glass at different temperatures, providing a means for the nondestructive CTE measurement of large ULE glass at a specified temperature.

The CLP Publishing collects CLP journals and partnered optics and photonics journals, and provides readers an optical publishing platform with global influence. SPIE, OSA, CUP. Chinese Laser Press (CLP), established by Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences (CAS) and Chinese Optical Society (COS) in 2009, nowadays publishes eight journals and manages three online platforms.

The fiber bundle (FB) optical system is widely used in many fields, such as medical imaging and military reconnaissance, owing to its advantages of high design freedom, small volume, and light weight. The traditional theory for the optical transfer function is not suitable for such a discrete sampling optical system. Researchers have developed numerical calculation methods to analyze the imaging quality of the discrete sampling optical system, in which the geometric model needs to be established and the coupling region needs to be determined. We have developed a simple and computationally efficient imaging theory that is suitable for various combinations of FB and CCD detectors. The coupling modulation transfer function (coupling-MTF) of discrete sampling optical systems of square-arrangement fiber bundles (SFBs) and hexagonal-arrangement fiber bundles (HFBs) are analyzed. Simulation results demonstrate that although SFB has a higher coupling-MTF than HFB, the latter is more convenient in coupling alignment operation. Our results have proven the effectiveness and universality of the proposed theory, and it can be used to guide the system design.