U.S. patent number 3,759,603 [Application Number 05/201,652] was granted by the patent office on 1973-09-18 for acousto-optical light deflector having increased band width and short access time.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Hans Eschler.
United States Patent |
3,759,603 |
Eschler |
September 18, 1973 |
ACOUSTO-OPTICAL LIGHT DEFLECTOR HAVING INCREASED BAND WIDTH AND
SHORT ACCESS TIME
Abstract
An acousto-optical light deflector employs a crystal as a sound
medium which is energized by way of a piezo-electric trandsducer
with ultrasonic waves to deflect a light beam incident
approximately parallel with the sound wave fronts as a function of
the ultrasonic frequency. The deflector also comprises a control
apparatus for supplying the piezo-electric transducer with a
controllable variable frequency and is charactrized by the
provision of several piezo-electric transducers which are designed
for consecutive frequency ranges and which are juxtaposed on the
sound medium.
Inventors: |
Eschler; Hans (Muenchen,
DT) |
Assignee: |
Siemens Aktiengesellschaft
(N/A)
|
Family
ID: |
5791040 |
Appl.
No.: |
05/201,652 |
Filed: |
November 24, 1971 |
Foreign Application Priority Data
|
|
|
|
|
Dec 15, 1970 [DT] |
|
|
P 20 61 694.8 |
|
Current U.S.
Class: |
359/311;
359/313 |
Current CPC
Class: |
G02F
1/332 (20130101) |
Current International
Class: |
G02F
1/33 (20060101); G02F 1/29 (20060101); G02f
001/32 () |
Field of
Search: |
;350/161 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wibert; Ronald L.
Assistant Examiner: McGraw; V. P.
Claims
I claim:
1. An acousto-optical light deflector comprising a crystal employed
as a sonic medium, a plurality of piezo-electric transducers
carried on said crystal, said piezo-electric transducers comprising
crystal plates carried on said crystal sound medium and angularly
disposed with respect to one another, each of said transducers
having an individual frequency range adjacent to the frequency
ranges of the other said transducers and energizable with
ultrasonic energy to produce sonic wave fronts in said crystal as a
function of the energizing frequency for deflecting a light beam
incident approximately parallel with said sonic wave fronts, and
control apparatus for supplying said piezo-electric transducers
with a controllable variable frequency.
2. An acousto-optical light deflector according to claim 1, wherein
said piezo-electric transducers are carried by said crystal
juxtaposed and parallel and are electrically connected to each
other and to said control apparatus.
3. An acousto-optical light deflector according to claim 1, wherein
said piezo-electric transducers are constructed from different
crystal materials so that the sonic amplitudes radiated by the
transducers are aligned with each other.
4. An acousto-optical light deflector according to claim 1, wherein
said transducers are constructed such that the frequencies of
adjacent transducers coincide in partial frequency ranges below
their half power points.
5. An acousto-optical light deflector according to claim 1, wherein
said control apparatus includes a fixed frequency oscillator, a
variable frequency oscillator and a mixer connected between said
oscillators and said transducers for superposing said fixed and
variable frequencies to provide a control frequency.
6. An acousto-optical light deflector according to claim 1, wherein
said control apparatus includes a plurality of fixed frequency
oscillators each having a different frequency, a bus bar connected
to said transducers, and a plurality of electronic switches
connected between said oscillators and said bus bar for selectively
connecting said oscillators to said transducers.
7. An acousto-optical light deflector according to claim 6, wherein
the total frequency range is divided into octaves and said bus bar
is provided as a plurality of buses each associated with a separate
octave, and a plurality of low pass filters each interposed between
a separate bus and said transducers.
8. An acousto-optical light deflector according to claim 1, wherein
said transducers are connected with said crystal by cold pressing
in a vacuum and comprising a low melting point compound interposed
between said transducers and said crystal.
9. An acousto-optical light deflector according to claim 8, wherein
said low melting compound comprises indium.
10. An acousto-optical light deflector according to claim 8,
wherein said low melting compound comprises thalium.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a light deflector having several
transducers for consecutive frequency ranges arranged in
juxtaposition, and further relates to an acousto-optical light
deflector comprising a crystal which is utilized as a sound medium
and which is energized by way of a piezo-electric converter with
ultrasonic waves to deflect a light ray incident approximately
parallel with the wave fronts as a function of the ultrasonic
frequency, and also to control apparatus for supplying the
piezo-electric transducer with a controllable variable
frequency.
2. Description of the Prior Art
The principle of acousto-optical light deflection has been known
for a long period of time. It is based on the light diffraction by
ultrasonic waves. When an ultrasonic wave is transmitted through a
medium, for example, a crystal, whereby pressure fluctuations are
produced in the crystal, a light ray incident in the direction of
the wave front is diffracted in a manner similar to that
accomplished by a diffraction grating.
The angle of diffraction therefore depends on the distance of the
pressure maxima, that is, however, on the wave length and/or the
frequency of the ultrasonic wave. If the direction of incidence of
the light ray against the wave front is inclined by a small angle,
a Bragg reflection of the light ray can be observed at the wave
fronts. In order for a Bragg reflection to occur, however, the
angle of incidence must suffice for the Bragg condition. This
principle and its advantages, as well as various applications were
described in 1966 by E. I. Gordon in the article "A Review of
Acousto-Optical Deflection and Modulation Devices" in the
publication Applied Optics, Vol. 5, No. 10, page 1629 et seq.,
October 1966.
In the article "Television Display Using Acoustic Deflection and
Modulation of Coherent Light" by A. Korpel, R. Adler, P. Desmares
and W. Watson and published in Applied Optics, Vol. 5, No. 10, page
1667 et seq., October 1966, the authors describe how a larger
number of deflection directions can be obtained. As it is known,
the Bragg reflection requires the acoustical wave fronts to be
symmetrical with respect to the incident and diffracted light ray.
If the Bragg angle is to be modified, the acoustic wave front must
change its direction. This is accomplished by a special arrangement
and electronic circuitry of the phased array, whose combined wave
fronts change their direction when the frequency is modified. In
that way, a change of the ultrasonic frequency from 19 to 35 MHz
and a light ray deflection changing in proportion thereto is
attainable.
In the periodical "Japan J. Apl. Phys. 8," page 811, 1969, N.
Uchida and H. Ivaski report on an additional structure regarding a
two-dimensional acousto-optical light deflector wherein a sound
frequency modification was achieved between 48 and 63 MHz through
the utilization of a special design.
The frequency bandwidth and the so-called capacity speed product
(CSP) connected therewith of acousto-optical light deflectors (the
number of resolvable spots per switching time) are limited by the
varying sonic radiation output of the piezo-electric transducers at
different frequencies and the solid direction of incidence (Bragg
condition). Therefore, the bandwidth of the known acousto-optical
light deflectors has been limited to a maximum of about one
octave.
Acousto-optical light deflectors are utilized where a rapid light
deflection is important. In order to scan a major surface with a
light ray, perhaps for profile measurement, the deflectability of
the light ray should be provided up to large angles of deflection,
which corresponds to an effective approachability of the deflection
crystal having a large bandwidth.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide an
increase in the number of deflection angles and to increase for
that purpose the bandwidth of an acousto-optical deflector to a
range encompassing more than one octave.
According to the invention, the foregoing objective is achieved
through the provision of several piezo-electric transducers which
are designed for consecutive frequency ranges and juxtaposed on a
sound medium, the transducers increasing the sound frequency
bandwidth to values up to 300 MHz and maintaining the deflection
efficiency effectively constant over a larger range than heretofore
known.
The crystal plates used as piezo-electric transducers are
preferably arranged at an angle on the sound medium so that the
deflection of the incident light ray can remain stable.
The piezo-electric transducers may also be advantageously arranged
in a partial area of a phased array, that is, instead of being
tilted with respect to each other, they may be arranged juxtaposed
and parallel and electrically series connected to a variable
oscillator.
It is advantageous to construct the transducers from such different
crystal materials so that the amplitudes radiated by the
transducers are aligned with each other.
Moreover, the transducers are preferably dimensioned in such a
manner that the frequencies coincide, for which in case of two
adjacent frequencies, the deflection efficiency drops to half the
maximum value. The degree of deflection effect is then actually
constant over a major frequency range.
A control apparatus may advantageously be provided with an
oscillator of a fixed frequency and with an oscillator of variable
frequency, as well as with a mixing device in which the fixed and
the variable frequencies are superposed in order to obtain the
control frequencies. Another possibility resides in the control
apparatus being provided with a number of oscillators whose
frequencies are invariable and connected by way of electronic
switches and a bus bar arrangement with one or several transducers.
In order to avoid interfering higher waves, the entire frequency
range is advantageously divided into octaves by supplying the
frequencies of different octaves to separate bus bars which are
provided with low pass filters.
The transducers should be connected with the crystal utilized as a
sonic medium, preferably by cold pressing, in vacuum, under the
interposition of compounds having a low melting point, such as
indium, thalium, etc.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of the invention, its
organization, construction and operation will best be understood
from the following detailed description taken in conjunction with
the accompanying drawings, in which:
FIG. 1 is a pictorial and schematic representation of an
acousto-optical light deflector having increased bandwidth;
FIG. 2 is a graphical illustration of the total deflection
efficiency effect of the multiple transducer deflector;
FIG. 3 illustrates a phased array design of an acousto-optical
deflector;
FIG. 4 is a block diagram illustration of an oscillator which is
synchronizable throughout the entire frequency range; and
FIG. 5 is a block diagram representation for a digitalized control
of the transducers.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1, a deflector crystal 1 is illustrated as a sound medium.
The deflector crystal 1 carries three acoustic transducers 2, 3 and
4 with different frequency ranges of the sound radiation, namely,
f1 to f2, f2 to f3, and f3 to f4. The three transducers 2, 3 and 4
may be connected in parallel and connected to a high frequency
oscillator 5. Each transducer actually represents a band-pass
filter and accommodates an electrical output only in its
corresponding frequency band. The transducers deliver the absorbed
energy to the deflection crystal in the form of ultrasonic waves,
whereby compressions 6 are produced in the deflection crystal. The
distance of the illustrated compression lines corresponds to the
wave lengths of the ultrasonic waves. If a laser beam enters the
deflection crystal 1 from a fixed predetermined direction, it is
deflected at the wave fronts 6 according to the Bragg condition.
The incident laser beam 7 is deflected, depending on the ultrasonic
frequency present, into the direction 8, 9 or 10. The number of
possible directions of deflection of the laser beam is a function
of the number of acousto-optical transducers and their usable
frequency bandwidths.
It may also be advantageous to traverse the light beam as rapidly
as possible over different directions of deflection. The scale for
the efficiency of the light deflector is the so-called capacity
speed product CSP. It is only a function of the bandwidth of the
deflector and the expression .DELTA.f/2 applied. With the structure
described, bandwidths between 100 and 300 MHz and capacity speed
products of about 2 .times. 10.sup.8 seconds .sup.-.sup.1 are
possible.
FIG. 2 is a graphical illustration of the degree of deflection
effect .eta. with respect to the frequency f. The degree of effect
is understood to mean the relation of deflected to incidence
luminous intensity. FIG. 2 illustrates that each of the three
transducers 2, 3 and 4 has a respective degree of effect of .eta.
1, .eta. 2 and/or .eta. 3, which has a maximum value at the
corresponding central frequencies f1, f2 and f3. The degrees of
effect drop off on both sides of these central frequencies. The
central frequencies f1, f2 and f3 are spaced such that the degrees
of effect bisect where they have dropped by three decibels. From
these three curves, a total degree of effect of .eta. .sub.ges =
.eta. 1 + .eta. 2 + .eta. 3, as represented in the drawing. The
degree of effect of a transducer is a function of the data of the
sound medium, the light wavelength of the incident beam, the
dimensions of the transducer and the sound or sonic performance. At
sufficiently high sonic performance, 100 percent of the radiated
light can be deflected, because no performance is lost under the
alternating effect of the light waves with the sonic field.
The manner of operation of a phased array design is illustrated in
FIG. 3. Here again, the crystal 1 is employed as a sonic medium and
carries three transducers 2, 3 and 4 which are juxtaposed parallel
with each other. The transducers are electrically series-connected
with a variable oscillator 5, so that at a time when the transducer
3 causes at a certain distance a compression 36 in the crystal,
compressions 37 and 38 shifted by .lambda. /2 are generated by the
transducers 2 and 4. The compressions 36, 37 and 38 can be
consolidated into a single compression line 39 extending obliquely
in the crystal. In this way compressions extending obliquely and
shifted by .lambda. are produced in the crystal, whose oblique
position depends on the oscillator frequency.
FIG. 4 illustrates how a variable control of the transducers is
made possible with a fixed and a variable oscillator. In FIG. 4, an
oscillator 10 has a fixed frequency fa and a variable oscillator 11
provides frequencies of fb and fc, whereby the frequency fb is
greater than the frequency fa. Both frequencies are superposed in a
mixer 12 and supplied to the transducers by way of a low pass
filter 13 for frequencies which are less than fc-fa and by way of a
broad band amplifier 14. The low pass filter 13 is utilized to
eliminate the upper frequency waves from influencing the deflection
of the luminous beam.
FIG. 5 illustrates a block circuit diagram for a digitalized
approach for energizing the transducers. Here, the oscillators 15,
16 and 17 have separate fixed frequencies f15, f16 and f17,
respectively, and are consolidated by way of a bus bar 22 as a
first group of oscillators, and the oscillators 18, 19, 20 and 21
have fixed frequencies f18, f19, f20 and f21, respectively, which
are consolidated by means of a bus bar 23 as a second group of
oscillators. One frequency octave is contained in each group. A
desired frequency can be switched to a bus bar from one of the
switching inputs 24 or 25 by way of an appropriate switch gate 26.
Therefore, higher waves are created which are prevented from
traversing the low pass filters 27 and 28. The selected frequency
f15, f16 . . . or f21 passes to the transducers by way of a wide
band amplifier 29.
The foregoing has described acousto-optical light deflectors and
means for operating such deflectors with increased bandwidth.
Although the foregoing description has been made by reference to
certain illustrative embodiments, many changes and modifications
thereof may become apparent to those skilled in the art without
departing from the spirit and scope of my invention. Therefore, it
will be appreciated that I intend to include within the patent
warranted hereon all such changes and modifications as may
reasonably and properly be included within the scope of my
contribution to the art.
* * * * *