JPS6149650B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-frequency driven acousto-optic element used in laser recording devices and the like.

Conventionally, a multifrequency acousto-optic device has been used as an optical modulator in a laser recording device, and is constructed by attaching one transducer 1 to an acoustic medium 2, as shown in FIG. Then, a plurality of carrier waves of different frequencies ₁ , ₂ , _. and primary light ₁₁ ,
₁₂ ,... are emitted. This primary light ₁₁ ,
₁₂ , . . . are divided into a plurality of parts corresponding to the driving frequencies ₁ , ₂ , . . . and become modulated light according to the image signal. In this case, the acousto-optic element has a frequency characteristic as shown in FIG. 2, and a broadband one is used and driven at multiple frequencies around the center frequency. However, the driving frequencies ₁ , ₂ , . . . fall within one band as shown in FIG. 2, and the modulation efficiency of each frequency varies depending on the state of other frequencies, resulting in cross-modulation.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a multi-frequency driven acousto-optic element that does not cause cross modulation.

Embodiments of the present invention will be described below with reference to the drawings.

In this embodiment, a transducer 1 is used as shown in FIG.
is multiple 1 corresponding to driving frequencies ₁ , ₂ , and _3.
1 , 1 ₂ , and 1 ₃ and attached to the acoustic medium 2 . This transducer 1 ₁ , 1 ₂ , 1
₃ are driven by the outputs of drive systems 3 to 5, respectively, that is, the frequencies ₁ , ₂ , ₃ ( ₁ < ₂ <
₃ ) The carrier wave amplitude-modulated with the image signal is applied, and the light beams 6 to 8 from the laser are each Bragg-diffracted by the acoustic medium 2, thereby performing optical modulation corresponding to the image signal and producing modulated light. 9 to 11 are obtained. In this case, light beams 6 to 8 have driving frequencies
The light beams are made incident on the acoustic medium 2 in accordance with bragg angles θ ₁ to θ ₃ determined by ₁ to ₃ , and are optically modulated by the outputs of the drive systems 3 to 5, respectively. Now, the driving frequency is i, the black angle is θi, the wavelength of the incident light beam is λ,
If the speed of sound is ν, then θi=λi/ν (1). Further, the coils 12-14 are connected in parallel (or in series) with the transducers _{11-13 ,} respectively, and the acoustic medium 2 is grounded. Since the transducers 1 ₁ to 1 ₃ serve as capacitive loads, the coil 12
〜14 to form a resonant circuit and each drive frequency _1〜
It resonates at ₃ . Therefore, transducer 1 ₁ ~
₁₃ , if the coils 12 to 14 were not present, the frequency characteristics would be as shown by the broken line in Figure 4, but with the provision of the coils 12 to 14, the Q becomes higher and the frequency characteristics become steeper, as shown by the solid line in Figure 4. Become. Then, the center frequencies (resonant frequencies) of the frequency characteristics are appropriately selected for each of the resonant circuits of the transducers ₁₁ to ₁₃ and the coils 12 to 14, and the driving frequencies ₁ to 14 are set to these.
When laser beams 6 to 8 are made incident on the acoustic medium 2 at black angles θ _{1 to θ 3} corresponding to their center frequencies, frequency characteristics as shown in FIG. 5 are obtained, and each Drive frequencies ₁ to ₃ are in separate bands, and cross-modulation is completely eliminated.

The light beams 6 to 8 may be obtained by separate lasers 15 to 17 as shown in FIG. 6, but they may also be obtained by one laser 18, half mirrors 19, 20, and mirror 21 as shown in FIG. can. Furthermore, in a laser recording device, a method has been proposed in which a plurality of modulated lights are scanned on a photoreceptor drum by an optical scanner, and scanning is divided into multiple parts in the main scanning direction and each modulated light is used. When the multi-frequency drive acousto-optic element is used as an optical modulator in the system, the lenses 22 to 24 on the incident side of the acousto-optic element as shown in FIG.
The focusing surface P may be placed behind the acousto-optic element. Further, as shown in FIG. 9, the focusing surfaces P of the lenses 22 to 24 are placed in front of the acousto-optic element, and the focusing surfaces P and the surface of the photoreceptor drum are conjugated.
The upper beam pitch may be set to a desired beam pitch on the photoreceptor drum surface by the magnification of the conjugate optical system.

As described above, in the multi-frequency driven acousto-optic element according to the present invention, the transducer is divided into a plurality of parts corresponding to the driving frequency, and a plurality of inductance elements that resonate with each of these transducers at each driving frequency are provided. Since a plurality of light beams are made incident in accordance with the black angle corresponding to each driving frequency, each driving frequency falls into a separate band and cross-modulation does not occur.

[Brief explanation of the drawing]

FIG. 1 is a front view showing a conventional multi-frequency drive acousto-optic element, FIG. 2 is a characteristic curve diagram showing the frequency characteristics of the same acousto-optic element, and FIG. 3 is a schematic front view showing an embodiment of the present invention. , FIGS. 4 and 5 are characteristic curve diagrams for explaining the same embodiment, and FIGS. ₆ to ₉ are schematic front views showing usage examples of the present invention. Jusa, 2... Acoustic medium, 6-8... Incident light, 9-11... Modulated light,
12-14...Coil.

Claims (1)

[Claims] 1 Equipped with a plurality of transducers corresponding to a plurality of drive frequencies, and a plurality of inductance elements each resonating with the plurality of transducers at a plurality of drive frequencies, so that a plurality of light beams can be transmitted at a plurality of drive frequencies. A multi-frequency driven acousto-optic element characterized in that the incident light is adjusted to a corresponding black angle.