A micro-displacement encoder using a thin-film resonant photodetector with directional sensitivity

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5 Citations (Scopus)


A micro-displacement encoder based on compact Moiré configuration is developed using a resonant photodetector with directional sensitivity for oblique incidence. The photodetector consists of a thin-film silicon photodiode and a resonant grating (index grating). The fabricated photodetector is directly located in a Fresnel image zone of a scale grating. Therefore, the optical arrangement of the proposed encoder is simple. Using a guided-mode resonance, the photodetector detects selectively the interference of the 1st-order beams diffracted from the scale grating, while suppressing the sensitivity for the 0th-order beam. The 0th-order beam causes undesired signal modulation for the air gap fluctuation of the encoder. In the experiment, sub-micron resolution and robustness to the air gap variation have been confirmed. The directional sensitivity and the encoder performances have also been analyzed theoretically.

Original languageEnglish
Pages (from-to)1087-1094
Number of pages8
JournalJournal of Optics A: Pure and Applied Optics
Issue number11
Publication statusPublished - 2007 Nov 1


  • Directional sensitivity
  • Micro-displacement encoder
  • Resonant grating
  • Thin-film resonant photodetector

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics


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