CGH encoding with variable step size search

In the field of aspheric testing, Computer-Generated Hologram (CGH) technology has been widely used. For CGH encoding, when applying the conventional encoding method to achieve highly accurate coding, it will use an amount of data that is often up to tens or even hundreds of GB. Therefore, in order to achieve high encoding accuracy with a small amount of encoded data, we propose a variable step size CGH encoding method. This method first obtains CGH fringe distribution through finding isophase surface, then selects different sampling steps by calculating the phase distribution gradient so that the CGH achieves high precision coding using as few points as possible. Finally, the method was used to CGH encode, then the resulting CGH was manufactured to test an aspheric surface. The test result is 3.142 nm (RMS). In order to verify the credibility of the test results, we design and make a compensator to test the same aspheric surface. The test result is 3.645 nm (RMS). The difference between the two results is 1.291 nm (RMS), and shows that the encoding method can meet the requirements of high-precision testing of aspheric surfaces.