## 1 Introduction  
Optical instruments based on off-axis interferometry can find many applications in metrology and industrial applications for measuring different parameters in optics metrology, such as refractive index, lens parameters, etc., as reported [1; 2; 3]. However, it is a difficult and time-consuming work [4] to align optical elements of interferometers, especially in off-axis measurement optical systems [5; 6; 7; 8].  
Sometimes, the optical alignment needs expensive additional assistance of wavefront sensor, laser tracker or photoelectric auto-collimator to achieve high alignment accuracy. An array of speckles or diffraction light spots can also be used for aided optical system adjustment. Generally, such controllable focus optical function requires that the optical systems be implied by moving optical components mechanically, and some by the internal liquid [9] or outer driven force to generate the surface deformation of the zoom components. However, those mechanical systems responses slow, and it is not easy to realize miniaturization design. [PERSON] [10] from Arizona optical center used the computer-generated hologram (CGH) to project optical array marks in the measurement of the astronomical telescope primary mirror. The CGH could produce focus spots and crossing speckles with designed focal length and space coordinates so the astronomical telescope primary mirror could be positioned precisely after adjustment.  
To find a new cost-effective approach to overcome the difficulty in off-axis optical alignment and measurement, we conduct a study on using a programmable optical system to generate a space position controllable focus light spots array to aid the alignment process. The idea is to use the liquid crystal on silicon spatial light modulator (LCoS-SLM) to generate an off-axis light spots array.  
Compared with the deformable micro-mirror [11], the LCoS-SLM could be digitally controlled at the pixel level to realize more flexible functions such as the generation of optical arrays. For example,Huang et al. [12] studied the method to produce high-quality optical vortex arrays. [PERSON] et al. [13] worked on the generation of diffraction light spots array for optical scanning and tracking with the SLM. The LCoS-SLM could be calibrated [14] and compensated for making its phase response character better in optical applications [15], and the nonlinearity phase response has been researched as well [16; 17; 18; 19] to find methods to achieve correct phase modulation performance in its applications. The compensation phase modulation calculation is also a key technique [19]. Based on these studies, the LCoS-SLM could be employed to generate light spot arrays to help the optical alignment.  
In principle, an optical alignment procedure could be done in optical surface measurement in an off-axis optical measurement system using the LCoS-SLM as an optical compensator between the incident light and outgoing light. With the proposed optical setup, the off-axis system could generate a focus spots array, which could be employed to adjust the alignment according to some predesigned physical marks (Figure 1a) near the tested optical surface first, shown as Figure 1b. After rotation and translation adjustment, the sample surface could be aligned and positioned precisely. Moreover, then the LCoS-SLM could be used to generate the measurement wavefront and project it to the sample surface to get surface data.