Optical encoder based on a nondiffractive beam III

Abstract

In two preceding works (Appl. Opt.47, 2201-2206, 2008; Appl. Opt.48, 414-424, 2009) we introduced the design of an optical encoder based on a nondiffractive beam and studied the dependence of its performance on its parameters (e.g., grating pitch, photodetector size). In those works we proposed different optimization criteria and concluded that the proposed design provides an output sinusoidal signal with high contrast and very low harmonic distortion, while having remarkable tolerance to variations in its parameters and to mechanical perturbations. In this work we (1) study how to improve the system performance by means of selecting appropriate photodetector geometry, (2) study the system performance for different nondiffractive beam geometries, and (3) quantify the output signal tolerance to vertical and lateral misalignment between the centers of the nondiffractive beam and the photodetector. As a consequence, we obtain new sets of optimal parameters that significantly improve the system performance and enhance its tolerance to mechanical perturbations and fabrication errors.

Performance of an optical encoder based on a nondiffractive beam implemented with a specific photodetection integrated circuit and a diffractive optical element

“…Vertical misalignments between the NDB and the photodetector of the same magnitude than lateral misalignments of Figs. 11 and 12 cause much lower changes in the photocurrents, a result previously stated in one of our previous works [19].…”

“…There are several types of NDB [24], but, in a previous work [19], we showed that the best performance of the encoder is achieved with a zero-order Bessel beam. This NDB can be produced with an axicon and a slit-lens system, for example [25][26][27].…”

“…In 2008, we proposed an optical encoder based on a nondiffractive beam (NDB) [13] and presented some experimental results and a theoretical model to understand, analyze, and optimize its performance [18,19]. The main characteristic of this design is its excellent stability, which is due to the propagation invariance of the NDBs, thus allowing higher tolerances under variations in the distance between the scale and the moving head.…”

Self‐configuration system and frequency characterization of a programmable photodetector ASIC

“…In previous works, 1–3 our group stated the advantages of using optical encoders based on non‐diffracting beams (NDB), mainly related to the stability and mechanical tolerances. In those articles, it was also proven that the functionality of the NDB encoder is optimized if the detector has a particular detectivity pattern, namely, the function.…”