JP3368986B2 - Optical scanning recording device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning recording apparatus,
More specifically, an electrode is formed close to an optical waveguide having an electro-optic effect, and the recording light is modulated by a waveguide-type electro-optic element that modulates the guided light according to the voltage applied to the electrode. The present invention relates to an optical scanning recording apparatus described above. 2. Description of the Related Art Conventionally, a light beam is modulated based on a given recording signal, and the modulated light beam is scanned on a photosensitive recording material, for example.
2. Description of the Related Art An optical scanning recording apparatus for recording, on a recording material, an image, a sound, and the like carried by the signal is known. [0003] In this type of optical scanning recording apparatus,
It has also been proposed to use a waveguide-type electro-optical element disclosed in, for example, JP-A-2-931 for modulating a light beam. This waveguide-type electro-optical element includes an optical waveguide having an electro-optical effect, and a grid electrode (hereinafter referred to as an EOG electrode) formed thereon to form an electro-optic grating on the optical waveguide. ) And a drive circuit for applying a voltage to the EOG electrode, wherein the guided light guided through the optical waveguide is selectively diffracted in accordance with the voltage application state to the EOG electrode. . When such a waveguide type electro-optical element is used, when one of the diffracted light and the undiffracted light (zero-order light) is used as the recording light, the recording light is used in accordance with the presence or absence or degree of diffraction. Can be modulated. Further, for example, JAPANESE JOURNAL OF APPL
IED PHYSICS (Japanese Journal of Applied Physics) Vol.20, No.4, April, 1981 p
As shown on pages 733 to 737, two channel optical waveguides forming a directional coupler are formed on a substrate having an electro-optical effect, and a plate-like electrode is arranged on each channel optical waveguide. There is also known a waveguide type electro-optical element in which guided light guided through a channel optical waveguide is selectively transferred to the other channel optical waveguide in accordance with a voltage application state to the electrode. With such a waveguide-type electro-optical element, light emitted from the other channel optical waveguide can be used as recording light, and the recording light can be modulated based on the voltage applied to the electrodes. On the other hand, as a recording light source, a semiconductor laser has been conventionally used in many cases. If this small and light semiconductor laser is used in combination with the above-mentioned waveguide type electro-optical element, it is extremely advantageous in reducing the size and weight of the optical scanning recording apparatus. By the way, in the above-mentioned waveguide type electro-optical element, in order to avoid light scattering and light absorption by the electrode, SiO ₂ is provided between the electrode and the optical waveguide.
, Al ₂ O _3, or the it is necessary to form a buffer layer made of, in the waveguide type electro-optical device having a buffer layer, a phenomenon that DC drift has been observed to be susceptible to occur. Although the characteristic of the applied voltage V versus the diffraction efficiency η is originally as shown in FIG. 7A, the DC drift changes as shown in FIG. 7B as the voltage is continuously applied to the electrodes. It is a phenomenon that does. For example, when such a DC drift occurs in a waveguide type electro-optical element applied to an image recording apparatus, it becomes difficult to control a recording light amount level and a sufficient extinction ratio cannot be secured. It becomes impossible to record images. As a method of suppressing the DC drift, for example, “Experimental 4 × 4 Optical Switchimg Network”
As shown in "Electronics Letters Vol. 12, No. 22 1976, a method of superimposing a high-frequency voltage on a voltage applied to an electrode is known. On the other hand, a semiconductor laser used as a recording light source is known. There is a problem of so-called mode hopping in which the amount of light and the oscillation wavelength fluctuate due to a change in ambient temperature, etc. As a countermeasure against this mode hopping, for example, Japanese Patent Laid-Open No. 59-9 / 1984
As disclosed in Japanese Patent No. 086, it has been considered that a semiconductor laser is driven by a high-frequency current to oscillate in multiple longitudinal modes. However, in an optical scanning recording apparatus using the above-mentioned waveguide type electro-optical element for modulating a light beam and using a semiconductor laser as a recording light source, a high frequency voltage is applied to an electrode applied voltage as a measure against DC drift. Superimposed,
When the semiconductor laser is driven by a high-frequency current as a mode hopping countermeasure, problems such as deterioration of the image quality of a recorded image and sound quality of a recorded sound may occur. An object of the present invention is to provide an optical scanning recording apparatus capable of preventing such a problem. An optical scanning recording apparatus according to the present invention comprises: an optical waveguide having an electro-optic effect; a semiconductor laser for causing a light beam to enter the optical waveguide; and a frequency f _{l applied to the} semiconductor laser. A semiconductor laser driving circuit for supplying a high-frequency current, at least one pair of electrodes formed close to the optical waveguide, and applying a voltage, which is amplitude-modulated based on a given recording signal, between these electrodes. A modulating circuit for modulating a light beam propagating through the optical waveguide, a scanning unit for scanning the light beam emitted from the optical waveguide on a recording material, and a voltage applied to the electrode, f _d <|
f _l -2f _e | the relationship (where f _d is the bandwidth of the recording signal) is characterized in that and means for superimposing a high frequency voltage of frequency f _e satisfying. According to the study of the present inventors,
As described above, while the semiconductor laser is driven by the high-frequency current, the problem that occurs when the waveguide-type electro-optical element is driven by the high-frequency superimposed voltage has been found to be caused by two high-frequency beats. . Hereinafter, this beat will be described in detail with reference to FIG. The drive current I of the semiconductor laser is a high-frequency current as shown in FIG. (1), if the frequency is assumed to be f _l, the light intensity P _l as is shown in FIG. (2) in the same waveform as the drive current I, that is periodically changed at a frequency f _l. On the other hand, in the above-described waveguide type electro-optical element having the EOG electrode, the voltage V applied to the electrode is as shown in FIG.
As shown in FIG. 7, it is assumed that the amplitude is modulated based on the image signal D in FIG. 7 (7), and a high-frequency voltage having a frequency f _e is superimposed thereon. In that case, if the intensity of the guided light incident on the EOG electrode portion is constant, the light intensity P _e of the guided light after passing through the electrode portion, as shown in FIG. 4, the frequency 2f _e Changes periodically. That is, if there is no DC drift, the relationship between the applied voltage V and the diffraction efficiency η is η = sin ² AV (A: constant) as shown in FIG. even when even a negative time, the same diffraction efficiency η equal absolute value of the voltage obtained, the frequency of the light intensity P _e is twice the 2f _e voltage frequency. [0018] Therefore, if the actual intensity of the guided light incident on the EOG electrode portion is periodically changed at a frequency f _l, as described above, the guided light after passing through the electrode portion,
F _l -2f _e | | difference between the two frequencies of the beat component frequency occurs. If this beat frequency is the band f of the recording signal
_{If d} is included, the light intensity P of the recording light fluctuates due to the influence of the beat component as shown in FIG. However, in the present invention, the beat frequency |
f _l -2f _e | is recorded so is higher than the bandwidth f _d signal D, as a beat component shown in FIG. (5) are incorporated into the intensity of the recording light changes due to the recording signal D, beat components Prevents the recording light intensity P from being in correspondence with the recording signal D due to the influence of. [0020] The above _{f d <| f l -2f e} | a becomes satisfying magnitude relation of the frequencies, f _l> the case of 2f _e to (1) in FIG. 4, the f _l <2f _e The case is shown in FIG. As described above, according to the present invention, as a countermeasure against DC drift, a high frequency voltage is superimposed on an electrode applied voltage,
Further, even if the semiconductor laser is driven by a high-frequency current as a mode hopping countermeasure, it is possible to prevent problems such as deterioration of the image quality of a recorded image and sound quality of a recorded sound. Embodiments of the present invention will be described below in detail with reference to the embodiments shown in the drawings. FIG. 1 shows an optical scanning recording apparatus according to an embodiment of the present invention. FIGS. 2 and 3 show a waveguide type electro-optical element 1 used in the optical scanning recording apparatus. As shown in FIG. 1, a semiconductor laser 19 emits a light beam 20 serving as recording light. The semiconductor laser 19 is driven by the high-frequency current I emitted from the oscillator 18 and oscillates in multiple longitudinal modes in order to prevent the occurrence of the mode hopping described above. The light beam 20 in the divergent light state is converted into parallel light by the collimator lens 21 and then modulated based on the image signal D in the waveguide-type electro-optical element 1 as described later. The high-frequency current I for driving the semiconductor laser 19 has a waveform shown in FIG. 6A, and the light intensity P _l of the light beam 20 before entering the waveguide type electro-optical element 1.
Changes periodically with the same waveform as the drive current I as shown in FIG. The modulated light beam 20A is incident on a polygon mirror (rotating polygon mirror) 22 serving as a main scanning means, is reflected and deflected, passes through a scanning lens 23 composed of, for example, an fθ lens, and then, reaches a cylindrical platen 24. While converging on the held photosensitive material 25, it is main-scanned in the direction of arrow X. The cylindrical platen 24 is rotated in the direction of the arrow Y by the motor 26 constituting the sub-scanning means together therewith. By the above, photosensitive material
25 is scanned two-dimensionally by the modulated light beam 20A, where a continuous tone image carried by the image signal D is recorded. Next, the modulation of the light beam 20A by the waveguide-type electro-optical element 1 will be described in detail with reference to FIGS. This waveguide-type electro-optical element includes a thin-film optical waveguide 11 formed on a LiNbO ₃ substrate 10 doped with MgO, a buffer layer 12 made of an SiO ₂ film formed thereon, EO formed on
A G electrode 13, a linear grating for light input (Linear Grating Coupler: hereinafter referred to as LGC) 14 and an LGC 15 for light output formed on the surface of the optical waveguide 11 with the EOG electrode 13 being separated from each other; And a drive circuit 16 for applying a voltage to the EOG electrode 13. The semiconductor laser 19 has a light beam 20
The optical waveguide 11 passes through the obliquely cut end face 10 a of the optical waveguide 11.
Is transmitted so as to be incident on the LGC14 portion. Accordingly, the light beam 20 is diffracted by the LGC 14 and enters the optical waveguide 11, and travels in the optical waveguide 11 in the direction of arrow A in the waveguide mode. This light beam (guided light) 20 is applied to an EOG electrode
Although guided through the portion corresponding to 13, the guided light 20 travels straight when no voltage is applied to the EOG electrode 13. On the other hand, when a voltage is applied to the EOG electrode 13 from the drive circuit 16, the refractive index of the optical waveguide 11 having an electro-optic effect changes, and a diffraction grating is formed in the optical waveguide 11, and the guided light 20 is converted by the diffraction grating. Diffracts. The light beam 20A diffracted as described above and the non-diffracted light beam (zero-order light) 20
B is diffracted toward the substrate 10 in the LGC 15 and this substrate 10
Out of the element from the obliquely cut end face 10b. Since the diffraction efficiency η changes according to the value of the voltage V applied to the EOG electrode 13 as shown in FIG. 7, the light beam 20A emitted out of the device is It can be modulated according to the value. The control of the applied voltage V based on the image signal D
It is as follows. The image signal D composed of a voltage signal takes a value for each pixel, for example, as shown in (7) of FIG. 6, and the image signal D is input to the mixing amplifier 17 of FIG. The high-frequency voltage V _RF frequency f _e output from the oscillator 16 is input to the mixing amplifier 17, the voltage V which the high-frequency voltage V _RF is superimposed on the image signal D
(The waveform is (3) in FIG. 6) is applied to the EOG electrode 13. [0031] In this case, if it is if the intensity of the light beam (guided light) 20 which enters the portion facing the EOG electrode 13 is constant, the light intensity P _e of the light beam 20A after passing through this portion FIG as shown in 6 (4), periodically changes at a frequency 2f _e. Therefore, the light beam 20 incident on the portion that actually faces the EOG electrode 13 intensity P _l is 6 (2)
The frequency f _l equal to the frequency of the high-frequency current I as shown in FIG.
, The light beam 20A after passing through the electrode facing portion has a difference | f between these two frequencies.
_l -2f _e | of the beat component of the frequency occurs. In the present embodiment, the band f _d of a frequency f _l is 500 MHz, also the image signal D of the high frequency current I 50
MHz, for which the frequency f of the high-frequency voltage V _RF
e is assumed to be 200 MHz. At this time, the beat frequency f
_l -2f _e = a 100 MHz, the bandwidth f _d of the image signal D
Therefore, it is possible to prevent the light intensity P of the light beam 20A, which is the recording light, from fluctuating due to the influence of the beat and fail to correspond to the recording signal D. The reason is as described in detail above. When the above-mentioned beat occurs, the light beam 20A, which is the recording light, should be irradiated to one pixel as shown in FIG. 5 (1). However, if the frequencies _fl and _fe are set so that the beat frequency becomes relatively high, the light beam 20A is irradiated as shown in FIG. 3 (3), and the integration effect on the recording material is reduced. Working, the recorded image has almost no beat effect. Although the embodiment applied to the flying spot type image recording apparatus has been described above, the present invention is applicable not only to an image recording apparatus but also to an apparatus for recording audio signals and various data on a magneto-optical disk or the like. However, the present invention can be similarly applied.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic perspective view of an optical scanning recording apparatus according to an embodiment of the present invention. FIG. 2 is a plan view of a waveguide type electro-optical element used in the optical scanning recording apparatus. 3 is a side view of the waveguide type electro-optical element. FIG. 4 is a semiconductor laser driving current frequency _fl , a driving voltage frequency _fe of the waveguide type electro-optical element, and an image signal band f _{d in the} optical scanning recording apparatus. FIG. 5 is a schematic diagram illustrating the effect of a beat component on a recorded image. FIG. 6 is a graph illustrating waveforms of signals in the optical scanning recording apparatus. FIG. 7 is a schematic diagram illustrating a DC drift. Figure [description of symbols] 1 waveguide type electro-optical element 10 MgO-doped LiNbO ₃ substrate 11 thin-film optical waveguide 12 buffer layer 13 EOG electrodes 16 oscillator 17 mixing amplifier 18 the oscillator 19 semiconductor laser 20 light beam 20A diffracted light beam 21 Li Meter lens 22 a polygon mirror 24 cylindrical platen 25 photosensitive material

Claims (1)

(57) an optical waveguide having a [Claims 1 electro-optical effect, a semiconductor laser light is incident beam into the optical waveguide, the semiconductor supplying a high frequency current having a frequency f _l to this laser diode A laser driving circuit; at least one pair of electrodes formed close to the optical waveguide; and applying an amplitude-modulated voltage between these electrodes based on a given recording signal to propagate the optical waveguide. a modulation circuit for modulating the light beam, scanning means for scanning the light beam emitted from the optical waveguide on the recording material, the voltage applied to the _{electrode, f d <| f l -2f} e |
Means for superimposing a high-frequency voltage having a frequency f _e that satisfies the following relationship (where f _d is the band of the recording signal).