JP3526154B2 - Optical scanning recording device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning recording apparatus for recording a continuous tone image on a recording material by scanning recording light whose intensity is modulated based on an image signal on the recording material. is there.

[0002]

2. Description of the Related Art Conventionally, a light for recording a continuous tone image on a recording material by modulating the intensity of the recording light on the basis of an image signal indicating the continuous tone image and scanning the recording light on the recording material. Various scanning recording devices are provided.

[0003]

In the optical scanning recording apparatus of this type, in order to record an image with a higher gradation, it is necessary to make the dynamic range of the recording light large. Therefore, it is conceivable to apply an optical modulator having a large extinction ratio, but of course, this extinction ratio also has an upper limit, which naturally limits the dynamic range of the recording light.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an optical scanning recording apparatus capable of recording a dynamic image of recording light with an extremely wide range and recording an image with high gradation. is there.

[0005]

The optical scanning recording apparatus according to the present invention, as described above, records the modulated recording light with the optical modulating means for intensity-modulating the recording light based on the image signal indicating the continuous tone image. In an optical scanning recording apparatus having a scanning means for scanning on a material, an optical wavelength conversion means for wavelength-converting the intensity-modulated recording light by a non-linear optical effect is provided, and the recording light after the wavelength conversion is used as a recording material. The above is designed to be scanned.

[0006] Note that the above light modulating means and the light wavelength converting unit, which are integrally formed with each other by using the same substrate Ru is used.

More specifically, more specifically,
The electro-optical effect and the nonlinear optical effect.
The angle θ between the surface of the electric crystal and the Z axis of the crystal is 0.
Ferroelectric bond cut so that ° <θ <90 °
Crystal substrate, a plurality of optical waveguides formed on this substrate, and
Electrodes for applying a voltage to at least one of these optical waveguides
And a plurality of light guides according to the applied state of the voltage.
Light is controlled by controlling the transfer of guided light between waveguides.
Is used as the optical wavelength conversion means.
The optical waveguide on the downstream side of the electrode in the waveguide direction.
The one composed of the wavelength conversion part formed in the
Be done.

[0008] Then the wavelength converter, the ferroelectric crystal spontaneous polarization direction of the substrate is 180 ° reversal of the free-onset polarization direction parallel to the extending building domain reversals periodically arranged periodic domain comprising It is composed of an inverted structure.

When the optical waveguide is formed by proton exchange and annealing and the wavelength conversion portion is formed by the periodic domain inversion structure formed in the optical waveguide, the angle θ is θ ≦ 20 °. It is desirable to be in the range.

When the optical waveguide is formed by proton exchange and annealing as described above, and the wavelength conversion portion is formed by the periodic domain inversion structure formed in the optical waveguide, the angle θ is 0.2. It may be in the range of ° ≦ θ, more preferably in the range of 0.5 ° ≦ θ.

More specifically, the ferroelectric crystal substrate is more specifically cut by a plane perpendicular to the axis obtained by rotating the Y axis of the crystal by 3 ° in the YZ plane toward the Z axis. , Z
It is preferable to use one that is cut by a plane perpendicular to the axis rotated by 87 ° on the X axis side in the ZX plane.

More specifically, as the ferroelectric substance forming the substrate, more specifically, LiNb _x Ta _1-x O ₃ (0 ≦ x ≦ 1),
Alternatively, those doped with MgO or ZnO are preferably used.

Further, when the substrate formed by cutting the ferroelectric crystal as described above is used, more preferably, the optical waveguide is formed so as to extend in the X-axis or Y-axis direction of the substrate in the wavelength conversion section. The wavelength converter is composed of the periodic domain inversion structure formed in the optical waveguide.

Further preferably, as the above-mentioned optical waveguide,
A plurality of optical waveguides forming a directional optical coupler are provided, and the electrodes are arranged so that optical coupling between these optical waveguides can be controlled by applying a voltage. Further books
In the optical scanning recording apparatus of the invention, the extinction ratio of the optical modulator is 10 dB.
It is desirable to be configured as described above.

[0015]

When the fundamental wave is wavelength-converted by the nonlinear optical effect, the intensity of the wavelength-converted wave is known to be proportional to the square of the fundamental wave intensity. Therefore, in the optical scanning recording apparatus of the present invention in which the recording light after the intensity modulation is wavelength-converted, the dynamic range of the modulated recording light (fundamental wave) input to the optical wavelength conversion means is, for example, 1.
When it is a digit, the dynamic range of the recording light after wavelength conversion is expanded to two digits. If the dynamic range of the recording light is expanded in this way, it is possible to record an image with extremely high gradation.

Further, especially when the light modulating means and the light wavelength converting means are formed on a common substrate, the device can be made compact, and further, the optical position adjustment of these both means is unnecessary. it can.

Further, in forming the light modulating means and the light wavelength converting means on a common substrate, the angle θ formed between the surface of the substrate and the Z axis of the ferroelectric crystal is 0 ° <as the substrate.
If you use the one that is cut so that θ <90 °,
Both a high extinction ratio and a high wavelength conversion efficiency can be obtained. Hereinafter, that point will be described in detail.

When an X-cut or Y-cut ferroelectric crystal substrate is used, the wavelength conversion efficiency of the wavelength converter is significantly lower than when a Z-cut substrate is used. When using a substrate that is cut so that the angle θ between the surface of the substrate and the Z axis of the ferroelectric crystal is 0 ° <θ <90 °, the wavelength conversion efficiency is about the same as when using a Z-cut substrate. Is obtained.

Further, when a substrate cut so that the angle θ formed by the surface of the substrate and the Z axis of the ferroelectric crystal is 0 ° <θ <90 °, the extinction ratio in electro-optical light modulation is used. Of 15 dB or more can be secured as in the case of using an X-cut or Y-cut substrate.

On the other hand, since the intensity of the wavelength converted wave is proportional to the square of the fundamental wave intensity as described above, when the extinction ratio in electro-optical light modulation is 10 dB, the extinction ratio of the wavelength converted wave is 20 dB. Therefore, if the extinction ratio in electro-optical light modulation is 15 dB or more as described above, the converted wavelength is 20 dB which is generally required for high gradation image recording.
The above extinction ratio is secured.

Therefore, in the present invention, if a substrate cut so that the angle θ formed by the substrate surface and the Z axis of the ferroelectric crystal is 0 ° <θ <90 °, a high extinction ratio and a high wavelength conversion are obtained. The efficiency can be obtained together.

Further, in the present invention, since the recording light for scanning the recording material has a short wavelength by wavelength conversion, for example, blue modulated light is obtained and used for color image recording, or the recording density is increased. The effect of being able to do so is also obtained.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a perspective shape of an optical scanning recording apparatus according to the first embodiment of the present invention. As shown in the figure, this optical scanning recording apparatus has an optical waveguide element 1 that performs optical modulation and optical wavelength conversion, and an optical scanning unit 2 that scans recording light on a recording material. Figure 2
Indicates the planar shape of the optical waveguide device 1. In FIG. 1, the size ratio between the optical waveguide device 1 and the optical scanning unit 2 is different from the actual size, and the former is enlarged for easy understanding.

First, the optical waveguide device 1 will be described.
This optical waveguide device 1 includes two channel optical waveguides 11 and 12 formed by, for example, proton exchange on a crystal substrate 10 of LiNbO ₃ (hereinafter, referred to as MgO-LN) doped with 5 mol% of MgO, and these. It has flat plate-shaped electrodes 13, 14A and 14B formed on the sides of the optical waveguides 11 and 12, respectively, and a wavelength conversion section 15 formed on one optical waveguide 12.

A laser beam 21 having a wavelength of 950 nm emitted from a semiconductor laser 20 is input to one channel optical waveguide 11. In this example, this semiconductor laser 20
Are directly coupled to the substrate 10 at the end face portion of the optical waveguide 11. However, the present invention is not limited to this, and the semiconductor laser 20 may be disposed apart from the substrate 10 and the laser beam 21 converged by the optical system may be applied to the end face portion of the optical waveguide 11 and input to the optical waveguide 11. Good. The longitudinal mode of the semiconductor laser 20 is locked by a known method.

On the other hand, the electrode 13 is connected to a modulation drive circuit 25 which receives an image signal S carrying blue information of a color continuous tone image, and the electrodes 14A and 14B are grounded. Also the wavelength converter
Reference numeral 15 has a periodic domain inversion structure in which the domain inversion portion 16 in which the spontaneous polarization (domain) of the MgO-LN substrate 10 is inverted is repeated at a predetermined period.

A method of making the optical waveguide device 1 having the above structure will be described below. As shown in FIG. 3, the substrate 10 is a ferroelectric substance MgO having an electro-optical effect and a non-linear optical effect.
-A product obtained by cutting and polishing an LN ingot 10 'in a plane perpendicular to the Y'axis obtained by rotating the Y axis in the YZ plane by θ = 3 ° on the Z axis side (3 ° Y cut It is a substrate) and is monopolarized to have a thickness of 0.3 mm, for example. Note that the angle θ is exaggerated in FIG.

On the surfaces 10a and 10b of the MgO-LN substrate 10 thus formed, as shown in FIG. 4, comb electrodes are formed, respectively.
30, comb-shaped electrode on the + Z side with the plate electrode 31 attached
When a pulse voltage is applied between both electrodes 30 and 31 such that 30 is a positive potential and the plate electrode 31 located on the −Z side is a negative potential, as shown in FIG. The direction of the spontaneous polarization of the substrate 10 which was oriented in the opposite direction is inverted in the voltage application portion, and the domain inversion portion 16 is formed. The direction of the spontaneous polarization is inclined by θ = 3 ° with respect to the substrate surface 10a, so that the polarization direction of the domain inversion portion 16 is also inclined with respect to the substrate surface 10a.

The surfaces 10a, 10 of the MgO-LN substrate 10 are
a direction parallel to b and orthogonal to the X axis, and the substrate surface 10a,
The directions perpendicular to 10b are the Z-axis direction and the Y-axis direction, respectively.
Since the angle θ is 3 ° with respect to the axial direction, these directions are referred to as the Z ′ direction and the Y ′ direction for convenience.

Next, on the MgO-LN substrate 10, the channel optical waveguides 11 and 12 are formed by well-known photolithography.
A mask of metal (Ta in this example) having an opening corresponding to the shape is formed. After that, the MgO-LN substrate 10 is
After dipping in pyrophosphoric acid heated to 160 ° C. for 64 minutes for proton exchange to remove the Ta mask with an etching solution, it is annealed in air at 350 ° C. for 1 hour.

By the above processing, the channel optical waveguides 11 and 12 as shown in FIGS. 1 and 2 are formed. At this time, the channel optical waveguide 12 is formed such that the portion where the domain inversion portions 16 are formed extends along the direction in which the domain inversion portions 16 are arranged.

Next, the -X plane and the + X plane including the end faces of the channel optical waveguides 11 and 12 of the MgO-LN substrate 10 are optically polished to complete the optical waveguide device 1.

As shown in FIGS. 1 and 2, in the optical waveguide device 1 having the above-described structure, the laser beam 21 is input to one of the channel optical waveguides 12 and guided therethrough, and the two optical beams are guided in accordance with a potential difference V described later. The other channel optical waveguide 11 is transferred at a portion (coupling portion) where the waveguides 11 and 12 are close to each other.

The laser beam 21 guided through the channel optical waveguide 12 has a wavelength of ½ in the wavelength conversion section 15, that is,
Converted to the blue second harmonic wave 22 of 475 nm. That is, in the wavelength conversion unit 15, the laser beam 21 as the fundamental wave and the second harmonic 22 thereof are formed by the periodic domain inversion structure in which the domain inversion unit 16 is periodically repeated in the waveguide direction of the laser beam 21. Phase matching (so-called pseudo phase matching) is performed. In this example, the length of the optical waveguide 12 in the portion where the periodic domain inversion structure is formed, that is, the interaction length L for wavelength conversion is 10 mm.

Here, the electrodes 14A and 14B are held at the ground potential in the coupling portion of the two channel optical waveguides 11 and 12. On the other hand, a variable voltage is applied to the electrode 13 from the modulation drive circuit 25, and the transfer of the laser beam 21 is controlled according to the potential difference V between the electrode 13 and the electrodes 14A and 14B.

That is, when the potential difference V is 0 (zero), the laser beam 21 guided through the channel optical waveguide 12
Are basically transferred to the optical waveguide 11, and as the potential difference V increases, the transfer amount decreases, and conversely, the amount of light guided through the optical waveguide 12 increases. When V is a predetermined value Vπ, there is no transition and the laser beam 21 basically guides all through the optical waveguide 12. Therefore, by controlling the voltage applied to the electrode 13 based on the image signal S, the intensity of the laser beam 21 guided through the channel optical waveguide 12 can be modulated, and thus the blue second harmonic wave 22 is converted into the image signal. The intensity can be modulated based on S.

Next, the optical scanning section 2 will be described. This optical scanning unit 2 is provided with the blue second harmonic wave 22 and the green recording light.
23, and a rotary polygon mirror (polygon mirror) 41 as a main scanning unit arranged so that the red recording light 24 is incident thereon,
The light 22, 23 reflected and deflected by this rotating polygon mirror 41 and
The fθ lens 42 for converging the 24 on the predetermined scanning plane regardless of the deflection angle and the color photosensitive recording material 40 are indicated by the arrow y.
And a sub-scanning unit 43 that conveys the image at a constant speed.

The above-mentioned 3 which is reflected and deflected by the rotary polygon mirror 41.
The colored lights 22, 23, and 24 perform main scanning on the recording material 40 in the arrow x direction substantially orthogonal to the arrow y direction. At the same time, the recording material 40 is conveyed by the sub-scanning means 43 as described above, and the sub-scanning is performed.

The green recording light 23 and the red recording light 24 are
Intensity modulation is performed on the basis of an image signal carrying green information and an image signal carrying red information of a color continuous tone image. These lights 23 and 24, and the blue second harmonic
The two-dimensional scanning of 22 on the recording material 40 as described above records a continuous color image on the recording material 40.

Next, the results of examining the wavelength conversion efficiency and extinction ratio of the optical waveguide device 1 and the offset voltage Vo will be described. The offset voltage Vo is, as shown in FIG. 7, how much the voltage V _{1 at} which the minimum optical output is obtained is offset from the voltage 0 in the relationship between the voltage applied to the electrode 13 and the optical output to the channel optical waveguide 12 side. In this example, the voltage V ₁ and the voltage V at which the maximum light output is obtained are shown.
The difference from ₂ is expressed as a ratio (%) to Vπ. The extinction ratio is a value before wavelength conversion.

For comparison, instead of the above-mentioned substrate 10, as shown in FIG. 6, an MgO-LN ingot 10 "is replaced with an axis Z" whose Z axis is rotated 87 ° toward the X axis in the ZX plane. Substrate obtained by cutting and polishing on a vertical surface (87 ° Z-cut substrate)
(A second embodiment of the present invention), and a conventionally known Z-cut substrate, X-cut substrate, and Y
The wavelength conversion efficiency, the extinction ratio, and the offset voltage Vo were similarly examined for the one using the cut substrate. In addition, those optical waveguide elements, except for the cut orientation of the substrate,
Basically, all of them have the same structure as the optical waveguide device 1. However, when the 87 ° Z-cut substrate is used, the optical waveguide is formed so as to extend in the Y-axis direction. The results are shown below (Table 1).

[0042]

[Table 1]

In this (Table 1), the wavelength conversion efficiency is indicated by the conversion efficiency η. The conversion efficiency η is the power of the fundamental laser beam 21 PFM (mW), the second harmonic 22
When the power of P _SHG (mW) and the interaction length are L (mm), η (% / Wcm ² ) = P _FM / P _SHG × 1000 × (10 / L)
It is given by ² .

As shown here, in the optical scanning recording apparatus according to the first and second embodiments of the present invention, while the wavelength conversion efficiency as high as that when using the Z-cut substrate is obtained, Extinction ratio is X-cut substrate or Y
It is 15 dB or more as in the case of using a cut substrate.

As described above, the intensity of the second harmonic wave 22 is proportional to the square of the intensity of the laser beam 21, which is the fundamental wave. Therefore, the extinction ratio of electro-optical light modulation by applying a voltage to the electrode 13 is 10 dB. Then the extinction ratio of the second harmonic 22 is 20 dB
Becomes Therefore, when the extinction ratio in electro-optical light modulation is 15 dB or more as described above, the second harmonic 22 is generally required for high gradation image recording.
An extinction ratio of dB or more is secured. Thereby, the recording material
By making the dynamic range of the second harmonic wave 22 scanning over 40 large, it is possible to record an extremely high gradation continuous tone image.

When a color image is recorded as in this example, it is necessary that the green recording light 23 and the red recording light 24 have basically the same dynamic range as the second harmonic 22. There is. In order to do so, for example, the green recording light 23 and the red recording light 24 are also the second harmonics obtained by wavelength-converting each fundamental wave of a predetermined wavelength, and the fundamental waves are converted before the wavelength conversion. May be configured to be modulated. Further, as the light source for the recording light 24 of red color in particular, the semiconductor laser may be used as it is without being combined with the light wavelength conversion means.

The optical scanning recording apparatus of the present invention can be configured to record not only color images but also monochrome images. Even in that case, the same effect can be obtained that a high dynamic range of recording light can be secured and a continuous tone image of high gradation can be recorded.

[0048]

[0049]

[0050]

[0051]

Further, in the present invention, the above-mentioned JP-A-7-2 is used.
As shown in Japanese Patent No. 94860, by superposing a high frequency on the voltage applied to the electrode 13, the above-mentioned problem of DC drift can be solved and an extinction ratio of 20 dB or more can be obtained.

Further, the embodiment using the 3 ° Y-cut substrate and the 87 ° Z-cut substrate, that is, the substrate in which the angle θ between the substrate surface and the Z axis is 3 ° has been described above.
The present invention is not limited to the substrate in which θ is 3 °, but 0 ° <θ
Basically, the same effect as described above can be obtained by using all the substrates in the range of <90 °. However, in the case where the optical waveguide is formed by proton exchange and annealing and the wavelength conversion part is configured by the periodic domain inversion structure, in order to obtain wavelength conversion efficiency almost equal to that when using the Z-cut substrate, 0.2 ° ≦ It is desirable to use a substrate in the range of θ ≦ 20 °, more preferably in the range of 0.5 ° ≦ θ ≦ 20 °.

That is, when the optical waveguide is formed by proton exchange and annealing, the range of θ at which the waveguide mode is not cut off is 20 ° or less. In this case, the field distribution of the guided mode is 1.2 μ at the shallowest.
It will be about m. Correspondingly, in order to make the depth of the domain inversion portion 1.2 μm or more, θ should be 0.2 ° or more. On the other hand, in order to facilitate the light input to the optical waveguide, it is desirable that the field distribution of the guided mode be 1.4 μm or more, and correspondingly, the domain inversion depth should be 1.4 μm.
In order to make m or more, θ may be 0.5 ° or more.

Further, the optical scanning recording apparatus of the present invention is not limited to the above-mentioned proton exchange optical waveguide, but may be constructed by providing other Ti diffusion optical waveguide or the like.

The substrate forming the optical waveguide is also the above-mentioned M
Not only the LiNbO ₃ substrate doped with gO, but also other LiNbO ₃ substrates and LiNbO doped with ZnO
₃ substrate, may be LiTaO ₃ substrate, the MgO and ZnO utilizing doped LiTaO ₃ substrate.

[Brief description of drawings]

FIG. 1 is a perspective view of an optical scanning recording apparatus according to a first embodiment of the present invention.

FIG. 2 is a plan view of an optical waveguide device used in the optical scanning recording device.

FIG. 3 is a schematic diagram illustrating a cut state of a substrate used for the optical waveguide device.

FIG. 4 is a schematic perspective view showing how the optical waveguide device is produced.

FIG. 5 is a schematic perspective view showing a domain inversion portion formed in the optical waveguide device.

FIG. 6 is a schematic diagram illustrating a cut state of the optical waveguide device substrate used in the second embodiment of the present invention.

FIG. 7 is a graph showing a schematic relationship between an applied voltage and an optical output of the electro-optical modulator.

FIG. 8 is a graph illustrating a bias voltage in an electro-optical light modulator.

[Explanation of symbols]

1 Optical Waveguide Element 2 Optical Scanning Section 10 MgO Doped LiNbO ₃ Substrate 11, 12, 50, 51 Channel Optical Waveguide 13, 14A, 14B Electrode 15 Wavelength Converter 16 Domain Inverter 20 Semiconductor Laser 21 Laser Beam (Fundamental Wave) 22 2 harmonics 25 modulation drive circuit 30 comb-shaped electrode 31 flat plate electrode 40 recording material 41 rotating polygon mirror 43 sub-scanning means 60, 61 3 dB coupler section

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-2-13929 (JP, A) JP-A-6-273817 (JP, A) JP-A-4-333835 (JP, A) 1983 ULTRASONICS SY MPOSIUM, 1983, 527-530 (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 1/37

Claims (11)

(57) [Claims] 1. A light modulator for intensity-modulating recording light based on an image signal representing a continuous tone image, a light wavelength converter for wavelength-converting the intensity-modulated recording light by a non-linear optical effect, and a wavelength converter. Scanning means for scanning the recorded recording light on the recording material, wherein the light modulating means forms a ferroelectric crystal having an electro-optical effect and a non-linear optical effect, the surface of the ferroelectric crystal forming the Z axis of the crystal. A ferroelectric crystal substrate cut so that the angle θ is 0 ° <θ <90 °, a plurality of optical waveguides formed on this substrate, and a voltage is applied to at least one of these optical waveguides. An electrode, and is configured to modulate light by controlling transfer of guided light between the plurality of optical waveguides in accordance with the applied state of the voltage, wherein the optical wavelength conversion means is configured to Also in the waveguide direction Is composed from the wavelength conversion portion formed on the optical waveguide at the side, the wavelength conversion unit, the ferroelectric parallel to extend the spontaneous polarization of the faces by 180 ° reversal of the free-onset polarization orientation of the crystal substrate
Optical scanning recording apparatus characterized by building domain reversals is composed of periodic domain inversion structure formed by periodically arranged. 2. The optical waveguide is formed by proton exchange and annealing, the wavelength conversion portion is formed of a periodic domain inversion structure formed in the optical waveguide, and the angle θ is θ ≦ 20 °. The optical scanning recording apparatus according to claim 1 , wherein the optical scanning recording apparatus is in the following range. 3. The optical waveguide is formed by proton exchange and annealing, the wavelength conversion portion is formed by a periodic domain inversion structure formed in the optical waveguide, and the angle θ is 0.2 ° ≦ θ 3. The optical scanning recording apparatus according to claim 1 , wherein the optical scanning recording apparatus is in the following range. 4. The optical scanning recording apparatus according to claim 3, wherein the angle θ is in a range of 0.5 ° ≦ θ. 5. The ferroelectric crystal substrate is cut in a plane perpendicular to an axis obtained by rotating the Y axis of the crystal in the YZ plane by 3 ° to the Z axis side. Claim 1
4. The optical scanning recording device according to any one of 1 to 4 . 6. The ferroelectric crystal substrate is cut on a plane perpendicular to an axis obtained by rotating the Z axis of the crystal in the ZX plane by 87 ° to the X axis side. Claim 1
4. The optical scanning recording device according to any one of 1 to 4 . 7. The ferroelectric material is LiNb _x Ta.
_{1-x O 3 (0 ≦} x ≦ 1) or optical scanning recording apparatus according to claim 1 to 6 any one of claims, characterized in that the MgO or ZnO, it is one that is doped. 8. The optical waveguide is formed so as to extend in the X-axis direction of a substrate in the wavelength conversion section, and the wavelength conversion section is constituted by a periodic domain inversion structure formed in the optical waveguide. Claims 1 to 7 characterized
The optical scanning recording apparatus according to any one of claims 1. 9. The optical waveguide is formed in the wavelength conversion section so as to extend in the Y-axis direction of the substrate, and the wavelength conversion section is constituted by a periodic domain inversion structure formed in the optical waveguide. Claims 1 to 7 characterized
The optical scanning recording apparatus according to any one of claims 1. 10. A plurality of optical waveguides forming a directional optical coupler are provided as the optical waveguides, and the electrodes are
The optical coupling between these optical waveguides is arranged so as to be controllable by applying a voltage.
9. The optical scanning recording device according to any one of 9 above. 11. The extinction ratio of the optical modulator is 10 dB or more.
Is characterized by 11. Any one of claims 1 to 10
The optical scanning recording device described.