Laser-operated apparatus for data and signal recording

A laser-operated apparatus for data and signaling recording makes use of a laser-beam source whose laser beam is directed at the Bragg angle into a tellurium dioxide monocrystal provided with an array of ultrasonic transducers, each of which is energized independently by at least one amplitude modulated very high frequency carrier. The individual transducer segments generate respective beams within the body of the crystal which, upon emerging, represent individual information channels which are separately controllable to provide the data and information recordal.

FIELD OF THE INVENTION 
The invention relates to a laser operated apparatus for data and signal 
recording comprising a laser light source, a multi-channel acousto-optical 
intensity modulator (preferably also serving as an active beam 
distributing means); a beam deflecting system synchronized with said 
modulator, light-sensitive information recording means, passive optical 
elements for directing the laser beams, and control means for coordinating 
the operation of the apparatus. 
BACKGROUND OF THE INVENTION 
As it is known, the more economical operation of recently available 
fast-working computers necessitates rapid recordal of the computer output 
data. Such output data are recorded mainly by line printers, but the 
significance of microfilm operated output systems is always increasing. 
The most widely used fast line printers are either of the mechanical or of 
the electrostatic types. The maximum speed of the faster electrostatic 
line printers is about 6000 lines/min. These line printers are very 
expensive and their manufacture is complicated. In microfilm systems the 
characters are displayed on the screen of a cathode ray tube and from here 
the characters are imaged by an optical system with a large aperture to 
the recording microfilm. The speed of such systems can be as high as 
30,000 lines/min. 
Because of their different operational principles the character generators 
of the two above mentioned systems cannot be interchanged. Laser operated 
character generators, besides their high speeds (about 50,000 to 150,000 
lines/min), have the great advantage that they can be used both for line 
printers and for microfilm outputs; this changeover requires only the 
simple replacement of their output optics. 
There is an apparatus known (for instance produced by Siemens (AG), in 
which the multi-directional deflection of a laser beam is carried out by a 
rotating polygon-shaped mirror, while the intensity modulation and the 
generation of the vertical column of a character point matrix are 
performed by a multi-channel acousto-optical modulator. 
The operation of the multi-channel modulator is based on the selectivity of 
the acousto-optical Bragg diffraction. More particularly when several 
oscillator output signals with different frequencies are coupled to a 
single ultrasound transducer of an acousto-optical cell simultaneously, 
there will be as many deflected outgoing laser beams as there are 
oscillators. These deflected beams can be spatially separated from each 
other and their intensity can easily be modulated almost independently by 
changing the output powers of the oscillators. The multi-channel modulator 
requires the use of an amplitude adder which is a complicated device and a 
high power linear amplifier. The controlling electronic circuitry become 
particularly complicated and expensive when the number of the channels, 
for improving the character quality, exceeds about 10 or 20. 
In laser-operated line printer produced by IBM the intensity modulation is 
effected magneto-optically the line-directional deflection is carried out 
by a rotating polygonal mirror, and the generation of the characters 
occurs within the point matrix by lines i.e. on a miniraster. This makes 
the synchronization complicated and expensive, while due to the sequential 
mode of operation the bandwidth of the modulator should be high. 
In a line printer produced by the RCA corporation the generation of the 
characters occurs in minirasters (altogether 19 pieces). This has the same 
drawbacks as mentioned in connection with the IBM system. 
There are also known systems designed for producing microfilms such as the 
laser-operated character generators of Datalight Inc., of Stromberg 
Datagraphix Inc., and of the 3M Co., the operation of these systems is 
similar to that of the Siemens system with the exception that the 
line-directional deflection is carried out by a swinging mirror. The 
characters are composed on a 7.times.5 or 9.times.7 point matrix. 
Due to the use of an adder-type multi-channel modulator, the number of 
raster points in the column direction (7 and 9) within the point matrix 
cannot be noticably increased further economically. The further 
improvement of the quality of the characters can be reached only by 
generating miniraster based characters which is both complicated and 
expensive. 
OBJECT OF THE INVENTION 
The object of the invention is to provide a laser operated character 
generator by which the quality of the characters can be further increased 
without a miniraster mode, which comprises comparatively a few optical 
elements of commercial quality, has a simple mechanical construction and 
can be manufactured economically. 
SUMMARY OF THE INVENTION 
The basic principle of the invention lies in the fact that a 
multi-segmented ultrasound transducer is provided in the multi-channel 
intensity modulator, and to the respective ultrasound transducing segments 
a control unit is coupled which excites the associated segment by a 
compound very high frequency signal having discrete component frequencies 
and this unit adjusts the amplitudes of the component frequencies by 
gating according to predetermined conditions.

SPECIFIC DESCRIPTION 
Referring now to FIG. 1 a laser 101 is shown producing an output beam 102 
which after passing through a polarization forming plate 103 passes 
through confocal telephoto optics consisting of a collecting lens 104 and 
a dispersing lens 105. 
The beam diameter decreases by the ratio of the focal distances of the 
collecting lens 104 and the dispersing lens 105 whereupon the beam passes 
through a multi-channel intensity modulator 106, at the same time the neck 
of the beam, which has a Gaussian intensity distribution, gets longer, 
whereby the beam diameter will be nearly constant below each of the 1, 2, 
. . . N ultrasound transducer segments 107 of the intensity modulator 106. 
The undeflected and deflected beams 108 and 109 leaving the multi-channel 
intensity modulator 106 pass through beam-expanding optics consisting of 
diverting and collecting lenses 110 and 111 and are reflected by a 
swinging mirror 112. After being reflected from the mirror the beams fall 
on a so-called copying cylinder 113 of an electrostatic copying device 
which rotates with a constant angular speed and is coated with a 
photoconductive layer. The size of each of the raster points thus formed 
depends on the diameter of the beams leaving the lens 111, on the optical 
path-length measured between the lens 111 and the cylinder 113 and on the 
wavelength of the laser. The lenses 104, 105 and 110 can be of average 
commercial quality, while the lens 111 should be a normal camera objective 
with a focal length to diameter ratio of at least 2.8. By moving the 
camera optics along the beam path the vertical size of the characters can 
be changed. As this optics is arranged ahead of the swinging mirror 112, 
the line length will be unchanged during such movements. The undeflected 
laser beam with the exception of an angular extremity is fully covered by 
a knife-edge bar 114 during its full scanning range, whereby it cannot 
reach the cylinder. The swinging mirror 112 swings around an axis 115 with 
an angular amplitude of 10.degree. to 30.degree.. Due to this swinging 
movement the deflected beams move along the generatrix of the cylinder 113 
in the direction of the arrow 116. By modulating the intensity of the 
respective deflected beams in a properly synchronized way with the 
movement of the swinging mirror 112, a series sequence of characters can 
be produced along the generatrix of the cylinder; the characters also can 
be imaged on a screen, or can be used for producing an alphanumerical 
display. The time-dependence of the angular displacement of the swinging 
mirror 112 can be either saw-tooth shaped and sinusoidal. In case of 
sinusoidal movements the quasi-linear section of the sine curve around the 
zero-crossing can be used for generating characters. A small apertured 
photo detector 117 arranged beside the vertical end face of the knife-edge 
bar 114 detects the undeflected but by the swinging mirror 112 
periodically diverted laser beam 108 and provides respective pulses at the 
instances when the swinging mirror 112 is in the corresponding angular 
extreme position. These pulses are used for the synchronization of the 
multi-channel intensity modulator 106. 
It should be noted that instead of the swinging mirror 112 a polygon-shaped 
mirror or an acousto-optical light deflecting means can also be used. In 
this latter case both in front and behind the deflecting means respective 
additional supplementary beam-forming optical elements should be provided. 
In the place of the copying cylinder any other light-sensitive material 
(e.g. microfilm) can be used. 
The operation of the multi-channel intensity modulator 106, by which 
excellent character quality can be attained, will be described in 
connection with FIG. 2. 
The laser beam 102 is directed into a tellurium dioxide monocrystal 118 in 
a direction corresponding to the crystalline indices of (001). The crystal 
plate normal to the direction defined by the crystalline indices of (110) 
a shear oscillating ultrasound transducer 107 is provided comprising N 
separate segment pieces. A compound high-frequency signal is coupled to 
each of these segments generated by the proper superposition of the output 
signals of n separate VHF oscillators 119 (very high frequency 
oscillators). The output signals of these oscillators 119 are transferred 
after passing through respective gates 120 and dynamic level equalizers 
121 to inputs of adders 122 and from the outputs of the adders 122 through 
power amplifiers 123 to the ultrasound transducing segments. The 
frequencies of the oscillators 119 are substantially evenly distributed 
within their operational frequency range (e.g. in connection with a 
wave-length of 6328 A of a He-Ne laser this range can be between 20 and 60 
Mc/s). 
In the tellurium dioxide crystal above the respective segments n separate 
phase-lattices will be formed being superimposed onto each other. 
The incoming laser beam incident upon the crystal in the so called Bragg 
angle will be deflected with angles corresponding to the respective 
frequencies coupled to the individual segments, whereby separate outgoing 
beams 109 are generated. The intensity of any one of these outgoing beams 
can be modulated or controlled, independently of the intensity of the 
other beams, by a control signal coupled to control inputs 124 of the gate 
120 and the dynamic lever equalizer 121 associated with that particular 
beam. On the basis of practically realizable crystal sizes and of 
acousto-optical calculations N can be even as high as 120. The maximum 
value of n is limited by economic considerations. Supposing the still 
economical values for n to be about 3 to 5, the maximum number of channels 
can reach even N.times.n=60 to 100. When using 20 to 30 channels the 
quality of the characters is almost as good as it is in normal printing. 
The control of the character generator shown in FIG. 3 occurs by means of a 
gated VHF unit 125 with adjustable gain and this unit 125 comprises the 
gates 120, the dynamic level equalizers 121, the adders 122 and the power 
amplifiers 123 shown in FIG. 2. 
The control inputs 124 are driven by a digital character generating unit 
128 wih gating pulses 124 shown in FIG. 4, and in response to such control 
signals the units 125 controls the multi-channel intensity modulator 106 
to produce the deflected beams 109 defining the columns of the 
point-matrix. The syncronization between the swinging mirror and the 
multi-channel modulation can be of either of two alternatives. In the 
first version a synchronizing signal delivered by the photo detector 117 
(FIG. 1) triggers the reading of the character content from the digital 
character generating unit 128. According to the second version it is the 
digital character generating unit 128 that produces a starting signal for 
an electronic driving unit 127 adapted to drive the swinging mirror 112 by 
energizing a deflecting coil 126 for the swinging mirror, so that the 
deflection of the swinging mirror starts simultaneously with the reading 
of the characters. 
The starting signal 130 of the electronic driving unit 127 and a time 
diagram 131 corresponding to the momentary angular position of the 
swinging mirror 112 are also illustrated in FIG. 4. The signals 124' shown 
in FIG. 4 correspond to an example for n=1 and N=7 as defined in 
connection with FIG. 2. 
The circuit arrangement shown in FIG. 3 has a data transfer channel input 
132 which, when the apparatus is used as line printer or as a computer 
output to microfilm or as a plotter, provides through an interface an 
operational connection with the computer. 
It should also be noted that the arrangement shown in FIG. 1 is somewhat 
modified in a computer output to microfilm mode because an additional lens 
system is arranged directly behind the swinging mirror 112 which, 
depending on the actual width of the microfilm, scales down the line-width 
(and proportionally therewith also the size of the raster points) to be 
between about 0.5 to 5 centimeters. 
The focal surface of this additional lens system is preferably a planar 
surface but depending on the manner in which the microfilm is guided it 
can be a spherical surface too. 
In plotter mode only one of the channels of the multi-channel modulator 106 
is used, and the recording of the picture information to be displayed is 
carried out in separate raster lines. The control can be received from a 
computer, from a television camera, or from any other suitable data or 
signal generating device.