The process of Zernike mode detection with a Shack-Hartmann wavefront sensor is computationally extensive. A holographic modal wavefront sensor has therefore evolved to process the data optically by use of the concept of equal and opposite phase bias. Recently, a multiplexed computer-generated hologram (CGH) technique was developed in which the output is in the form of bright dots that specify the presence and strength of a specific Zernike mode. We propose a wavefront sensor using the concept of phase biasing in the latter technique such that the output is a pair of bright dots for each mode to be sensed. A normalized difference signal between the intensities of the two dots is proportional to the amplitude of the sensed Zernike mode. In our method the number of holograms to be multiplexed is decreased, thereby reducing the modal cross talk significantly. We validated the proposed method through simulation studies for several cases. The simulation results demonstrate simultaneous wavefront detection of lower-order Zernike modes with a resolution better than λ/50 for the wide measurement range of ±3.5λ with much reduced cross talk at high speed.

Differential modal Zernike wavefront sensor employing a computer-generated hologram: a proposal

A Fresnel-like structure is required for various kinds of applications, such as contact lenses in the biomedical field, solar concentrators in the energy industry, wave-front correctors for display technology, and beam shaping for illumination systems. In this report, the author provides a simple iterative algorithm that can generate prism structures on arbitrary curved surfaces in an analytical form. Using this algorithm, a spreadsheet program can easily generate the profile of prism structures for optical software simulation. Moreover, a noniterative formulation is derived in order to reduce the design procedures. Comparisons between iterative and noniterative formulations prove the feasibility and robustness of the present approach.

Fresnel-like prism structure generating algorithm on a curved surface with iterative and noniterative forms.

High sampling frequency Shack-Hartmann wave front sensor is used to measure the dynamic wavefront error in adaptive optics system. Its output signal must be processed by wave front processor.In this paper, the method of real time processing for high sampling frequency Shack-Hartmann wave frontsensor was discussed. As an example, the results for 2900 Hi Shack-Hartmann wave front sensor was given.

Research of the real time processing technology for high sampling frequency shack-hartmann wavefront sensor

Fresnel-like prism arrays are designed using geometric ray optics and fabricated on a curved surface according to specific focal length requirements. In this study, the tolerance of Fresnel-like prism structures on arbitrary surfaces was investigated. Compact equations (iterative and non-iterative) based on analytical formulation can be helpful in exploring the sensitivity associated with the fabrication of Fresnel-like structures. The curved surface in this study revealed a linear relationship between maximum angular tolerance and the angle of incident rays. An understanding of such linearity is a key issue in the fabrication of lenses as well as in the sensitivity formulae used for optical structures in the development of next-generation optics.

Angular tolerance and sensitivity for designing Fresnel-like prism structures with arbitrary surface profiles

High positional resolution position sensitive detector (PSD) is strongly desired in high-precision position and angle measurement systems. However, a method that can enhance the positional resolution of most types of PSDs is promising but not reported. In this work, the barrel distortion is introduced deliberately in a two dimensional (2-D) pin-cushion PSD to enhance its positional resolution, through changing the sheet resistance ratio of photosensitive area and border resistor. This method has the effect of improving the positional resolution of PSD in the entire photosensitive area. PSDs with free of distortion and barrel distortion are fabricated and tested to verify that the resolution of PSD with barrel distortion is higher than PSD with free of distortion. Multi-layer feed-forward (MLF) neural network is used to correct position errors and improve the linearity of PSD with barrel distortion to about 0.02% of nonlinearity. Consequently, a high resolution and high linearity PSD is proposed and demonstrated using the method of barrel distortion, and corrected by MLF neural work. It's worth noting that this method can be used to improve the positional resolution of most types of PSDs, without increasing the structure complexity, manufacturing cost and pressure on the back-end signal processing circuit.

High Positional Resolution Pin-Cushion Position Sensitive Detector by Deliberately Introducing Barrel Distortion

A novel PSD-based Hartmann-Shack wavefront sensor(HSWFS) prototype has been developed. Compared with the conventional CCD-based HSWFS, it can operate at very high sampling rate, and it only has very short readout delaytime. In this paper, the PSD-based HSWFS is described in details, and the performances of the PSD-based HSWFS and the CCD-based HSWFS are compared.

PSD-based Shack-Hartmann wavefront sensor

A novel PSD-based Hartmann-Shack wavefront sensor (HSWFS) prototype has been developed, which employs a 4X4 PSD array as the detector to measure the displacements of the sub-aperture spots. Compared with the conventional CCD-based HSWFS, it can operate at very high sampling rate, and it only has very short readout delay time. Our system can measure wavefront at frame rate up to 5KHz, and the detected wavefront error is less than A / 50 (λ = 632.8wn). In this paper the experimental results are given. The measurement error of the PSD-based HSWFS for a given aberrated plate is compared with the measure result of the Zygo interferometer.

Performance of the PSD-based hartmann-shack wavefront sensor

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PSD-based Shack-Hartmann wavefront sensor

Performance of the PSD-based hartmann-shack wavefront sensor