Canon LV Series パンフレット

4-1

The laser light emitted by a semiconductor laser is positioned
so that it is a linearly polarized beam with respect to the z-
axis. Then, a collimator lens makes it into a parallel light
beam. The grating array direction of this parallel light beam is
the direction of the y-axis, and the diffraction grating with a
grating pitch d divides the beam into two light beams by a
diffraction angle of q. Here, the equation d sin 

θ = λ holds.

These two light beams pass through a first lens and are then
irradiated into an E/O frequency shifter consisting of electro-
optical crystals. After that, they are diffracted by a second lens
before irradiated to the object moving at a velocity of V,
which is being measured. The incidence angle of the two 
irradiated light beams is 

θ'.

The first and second lenses form an afocal optical system with
a magnification of m, and the aberration is corrected so that
sin 

θ / sin θ' = m.

The two light beams that are now modified to have a
frequency difference fR by the E/O frequency shifter are then
irradiated to the object to be measured, and the diffused
beams coming back from the object proceed through the
second lens and a condensing lens, eventually reaching the
photo diode. The beat signal (i.e., the Doppler frequency) of
these light beams containing the speed information obtained

Y

X

Z

Photo Diode

S-100Z Optical Structure

Object to be measured

E/O Frequency Shifter

Collimator 
Lens

Condensing Lens

Semiconductor Laser

Diffraction Grating

Afocal Optical System

here is F=2V/md+fR, independent of the laser frequency; in
addition, it is possible to measure the velocity from an object
that is originally in a still state.
By signal-processing this Doppler frequency, the unit displays
the velocity and sends the F/V output and pulse output.