Patent ID: 7064898

Claim:
An optoelectronic device comprising: a light emitter for emitting a light beam on a reflection medium, a light-beam-dividing element having a first diffraction grating region and a second diffraction grating region located in the vicinity of the first diffraction grating region, being located between the light emitter and the reflection medium, and a photodetector for receiving light diffracted at the diffraction grating region of the light-beam-dividing element, among returning light beams reflected by the reflection medium, wherein an entire light beam emitted from the light emitter enters the first diffraction grating region and is reflected by the reflection medium, whereby the photodetector receives only a portion of the returning light that passes through the first diffraction grating region, the second diffraction grating region prevents the portion of the returning light beams which enters the second diffraction grating region from entering the photodetector, where the returning light beams are ±first order diffracted light generated when a light beam emitted from the light emitter enters the first diffraction grating region and is reflected by the reflection medium, and the second diffraction grating region prevents the light beam emitted from the light emitter from reaching the reflection medium.