Xi Fengjie

Performance analysis of multiplexed phase computer-generated hologram for modal wavefront sensing

We investigate the performance and capability of a holographic modal wavefront sensor (HMWS) that is based on a multiplexed phase computer-generated hologram (MPCGH). The theoretical treatments of the HMWS are presented with scalar diffraction approximations and Fourier analysis. Several MPCGHs have been designed with different linear carrier frequencies, by using of the multiplexed coding scheme we have proposed, and by coding some common Zernike modes. The numerical simulation is carried out to investigate the performance of the HMWS to detect particular aberration mode(s), by considering the effect of different carrier frequency selections and the capability of coding a large number of modes. The results exhibit the expected characteristics of a corresponding symmetric spot pair, and indicate that the wavefront distorted by a particular Zernike mode(s) can be retrieved immediately through solving the amplitude of each mode coded in MPCGHs through the response curves of the HMWS.

Modal wavefront sensor based on binary phase-only multiplexed computer-generated hologram

We propose an approach for implementing a modal wavefront sensor using a binary phase-only multiplexed computer-generated hologram (BPMCGH). To simplify the coding and fabricating processes, a model based on tilt plane reference waves and an effective coding scheme for BPMCGH have been developed. The necessary number of subholograms to be recorded or coded is significantly reduced, from two or even more to just one per aberration mode, accordingly. The numerical and experimental demonstration results are presented and discussed and show that this approach is convenient for producing a BPMCGH and efficient for sensing the aberration modes.

High-diffractive-efficiency defocus grating for wavefront curvature sensing

The optimum phase defocus grating for wavefront curvature sensing is proposed. It features an equidistantly quantized, binary-phase-step defocus grating with a phase-step height of pi. The diffractive efficiency of the phase defocus grating is theoretically computed. The optical transfer function is obtained. The optimum phase defocus grating is fabricated. The high diffractive efficiencies of the +/-1 diffraction orders are verified experimentally, the average values of which are 38.08% and 40.36%, respectively.

Frequency analysis of wavefront curvature sensing: optimum propagation distance and multi-z wavefront curvature sensing

In this paper we determine the optimum propagation distance between measurement planes and the plane of the lens in a wavefront curvature sensor with the diffraction optics approach. From the diffraction viewpoint, the measured wavefront aberration can be decomposed into Fourier harmonics at various frequencies. The curvature signal produced by a single harmonic is analyzed with the wave propagation transfer function approach, which is the frequency analysis of wavefront curvature sensing. The intensity of the curvature signal is a sine function of the product of the propagation distance and the squared frequency. To maximize the curvature signal, the optimum propagation distance is proposed as one quarter of the Talbot length at the critical frequency (average power point at which the power spectrum density is the average power spectrum density). Following the determination of the propagation distance, the intensity of the curvature signal varies sinusoidally with the squared frequencies, vanishing at some higher frequency bands just like a comb filter. To cover these insensitive bands, wavefront curvature sensing with dual propagation distances or with multi-propagation distances is proposed.

Application of optical system simulation software Seelight in adaptive optics

The optical system simulation software Seelight is a system simulation software with independent intellectual property rights which can simulate beam generation, atmospheric transmission and adaptive beam control. The software provides an effective simulation tool for the application fields of optical system. In this article, we introduce the basic structure of Seelight software, the running interface, and the main modules of model libraries. Using the basic models of adaptive optics to build adaptive optics simulation systems, including the PZT deformable mirror module and the Hartmann wavefront sensor module, which improves the beam quality of the far field by correcting the wavefront aberration due to beam propagation through atmosphere. The correction effect of adaptive optics simulation system is verified under the different turbulence intensity, it is clear that correction residual greatly increased with the increasing of turbulence intensity. The Seelight software can be used to simulate various optical systems including adaptive optics system, and the system can be validated and optimized.

Low order aberrations compensation by direct adjustment of the reflective beam shaper in slab laser

A direct method for compensation of low order aberrations with large PV value was presented in this paper. In which, the relationship between the optical layout parameters and the output aberration coefficients were derived by ray matrix method. Then, the adjustment parameters calculated by the equations were used to change the optical layout parameters to compensate the low order aberrations with defocus and astigmatism. The effectiveness of this method was verified by simulations based on the optical models built in a optical design software. It shows that the low order aberrations can be accurately compensated to a level below 0.5λ by the direct method.