JP3511776B2 - Optical deflection element, method of manufacturing optical deflection element, and image forming apparatus - 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 deflecting element, a method of manufacturing the optical deflecting element, and an image forming apparatus, and more particularly to deflecting a light beam incident on an optical waveguide formed of a thin film within the optical waveguide. The present invention relates to an optical deflector, a method for manufacturing the optical deflector, and an image forming apparatus using the optical deflector such as a laser printer, a digital copying machine, and a facsimile.

[0002]

2. Description of the Related Art An optical scanning device using a light beam used in a laser beam printer, a digital copying machine, a facsimile, etc., is a rotary polygonal mirror (polygon mirror) for deflecting a light beam from a gas laser or a semiconductor laser.
And an f.theta. Lens that focuses the light beam reflected by the rotating polygon mirror in a state of constant velocity linear motion on the image forming surface of the photoconductor or the like. An optical scanning device using such a polygon mirror is
Since the motor rotates the polygon mirror at high speed, there is a problem in durability and noise is generated during high speed rotation. Further, considering these durability and noise, there is a problem that the optical scanning speed is limited by the number of rotations of the motor.

Therefore, an optical waveguide type optical deflector utilizing the acousto-optic effect is expected (CSTsai, IEEE Tr.
ans.Circuits and Syst.vol.CAS-26 (1979) 1072., JP-A-52-68307, JP-B-63-64765, etc.). This optical waveguide type optical deflector is made of LiN
An optical waveguide made of bO ₃ or ZnO, an incident means for coupling the light beam into the optical waveguide, and a surface acoustic wave for deflecting the light beam in the optical waveguide by the acousto-optic effect are provided. It is provided with a comb-shaped electrode (transducer) to be excited and an emitting means for emitting the deflected light beam from the optical waveguide. Further, in order to efficiently emit the light beam, a thin film lens or the like can be added to the light deflection element as necessary. These optical waveguide type optical deflection elements have no mechanical moving parts like polygon mirrors, and thus have the advantages of being noiseless, highly reliable, and compact. There is.

As another optical deflecting element having no mechanically movable part, a prism type optical deflecting element using a material having an electro-optical effect having a higher modulation speed than an acousto-optical effect is known ( A.Yariv, Optical Electronics, 4th e
d. (New York, Rinehart and Winston, 1991) pp.336-339
, Q.Chen, et al., J. LightwaveTech.vol.12 (1994) 1401
, JP-A-62-47627, etc.). In contrast to the acousto-optic effect-based optical deflection element that deflects the light beam with the excited surface acoustic waves, the electro-optic effect-based optical deflection element allows the optical waveguide to be periodically input to the optical waveguide by inputting a signal to the electrode. A large change in the refractive index is given, and the light beam is deflected by the change in the refractive index.

When an image forming apparatus is constructed using the above-mentioned light deflection element, the deflection of the light beam of the light deflection element is used as the main scanning, and the main scanning direction of the projection surface of the photoconductor or the like irradiated with the light beam is used. When the main scanning and the sub scanning are performed with the movement in the intersecting direction as the sub scanning, the image plane in which the scanning lines formed by the main scanning are continuous in the sub scanning direction can be formed on the projection surface. An image can be formed by synchronizing the scanning (main scanning and sub-scanning) and changing the intensity of the light beam according to the image data corresponding to the density of the image. recently,
It is required to form an output such as a high-quality print in a short time, that is, to increase the scanning speed.

[0006]

However, in the conventional optical scanning device, when high-speed scanning is performed by one light beam deflected by the optical deflecting element by the acousto-optic effect, it is deflected by the excited surface acoustic wave. There is a problem that the deflection speed is limited and the scanning speed has an upper limit value.

On the other hand, the light deflection element based on the electro-optic effect is
Since the electro-optical switching speed is high, the problem that the scanning speed has the upper limit value does not occur, but there is a limit to the modulation speed of the driver for modulating the intensity of the light beam incident on the optical waveguide according to the image data. However, there is a problem that the scanning speed is limited by this modulation speed.

In order to solve this problem, the apparent modulation speed can be increased by scanning a plurality of light beams substantially at the same time.

However, in order to simultaneously scan a plurality of light beams, the respective deflections corresponding to the plurality of light beams are maintained so that the intervals of the scanning lines of several tens of microns are maintained on the image plane so that unevenness does not occur. It is necessary to adjust the optical axis for positioning the element with high accuracy. Optical axis adjustment to achieve such position accuracy is possible experimentally,
This is not practical because the structure becomes complicated and a delicate and long adjustment time is required.

In view of the above facts, the present invention provides a light deflection element having a simple structure and capable of deflecting a plurality of scanning lines formed by a plurality of light beams substantially simultaneously while maintaining a predetermined interval. Is the purpose.

In addition to the above objects, it is another object of the present invention to obtain a method of manufacturing a light deflecting element that can easily manufacture the light deflecting element, and an image forming apparatus using the light deflecting element.

[0012]

In order to achieve the above object, an optical deflecting element of the present invention comprises an optical waveguide which is formed of a thin film and which emits an incident light beam from an end, and an optical waveguide which is incident on the optical waveguide. A plurality of waveguides each provided with a deflection means for deflecting the light beam, and the deflection directions of the light beams deflected by the respective deflection means of the plurality of waveguides substantially coincide with each other, and A single substrate provided with each of the plurality of waveguides so that the light beams are emitted from different positions in the intersecting direction.

In this optical deflecting element, a plurality of waveguides including an optical waveguide and a deflecting means are provided on a single substrate. Each of the plurality of waveguides is composed of an optical waveguide and a deflecting means. The optical waveguide is formed of a thin film and emits the incident light beam from the end portion, and the deflecting means deflects the light beam incident on the optical waveguide. The plurality of waveguides are provided on the substrate such that the deflection directions of the light beams deflected by the respective deflection means are substantially the same. Therefore, the light beam emitted from the end of the optical waveguide is deflected in substantially the same direction. Along with this, the plurality of waveguides are respectively provided on the substrate so that the light beams are emitted from different positions in the direction intersecting the deflection direction. Therefore,
The emitted light beam is emitted with a step at different positions at the end of the optical waveguide. As a result, the light beams are deflected from the end of the optical waveguide in substantially the same direction and emitted from different positions. Therefore, without adjusting the optical axis for positioning the light deflection element with high accuracy, the plurality of light beams are simultaneously scanned or the plurality of light beams are selected while maintaining the distance between the adjacent light beams at a predetermined distance. Can be scanned.

According to a second aspect of the present invention, the deflecting means includes a transducer that excites a surface acoustic wave according to an input signal, and the light beam incident by the acousto-optic effect that causes diffraction by the surface acoustic wave. Can be deflected. Further, as described in claim 3, the deflecting means includes an electrode for changing the refractive index with respect to the optical waveguide in response to an input signal, and is incident by an electro-optical effect that causes diffraction by the change in the refractive index. The deflected light beam can be deflected.

Next, the manufacturing method of the optical deflecting element of the present invention is as follows.
Formed by forming one flat substrate with a predetermined thickness and vertical and horizontal lengths in a predetermined length in a stepwise manner so that the surface portion of a predetermined width in either one of the vertical and horizontal directions forms a predetermined step in the thickness direction. On each surface of the stepped substrate, a thin film optical waveguide for emitting the incident light beam from the end is formed. Since the substrate is thus formed in a stepped shape, there is a step between the surface portions of the formed stepped substrate. Therefore, if the thin film optical waveguide is formed in the same manner for each surface portion, without adjusting the optical axis for positioning the optical deflecting element with high accuracy, while maintaining the interval between adjacent light beams at a predetermined interval, It is possible to obtain an optical deflection element capable of simultaneously scanning a plurality of light beams or selectively scanning a plurality of light beams.

As another method of manufacturing the light deflecting element, a plane portion having a predetermined width in one of the vertical and horizontal directions is thick on one flat substrate having a predetermined thickness and a predetermined horizontal and vertical length. The underlying clad layer or the same material layer as the substrate is formed stepwise so as to form a predetermined step in the vertical direction, and the incident light beam is emitted from the end to each of the formed surface portions. In this way, since the step-like base is formed on the substrate by forming the step-like film on the flat substrate, if the optical waveguide of the thin film is formed in the same manner for each surface portion, the optical deflection element can be formed. Without adjusting the optical axis for high-precision positioning,
While maintaining the interval between adjacent light beams at a predetermined interval,
It is possible to obtain an optical deflection element capable of simultaneously scanning a plurality of light beams or selectively scanning a plurality of light beams.

Further, a photoreceptor for forming an image, a charging means for uniformly charging the photoreceptor, an exposing means for irradiating the photoreceptor with light to form a latent image, and the latent image In an image forming apparatus provided with a developing means for visualizing, as the exposing means, an optical waveguide formed from a thin film and emitting an incident light beam from an end portion, and a light beam incident on the optical waveguide are deflected. A plurality of waveguides each provided with a deflection means, and each of the deflection directions of the light beam deflected by each deflection means of the plurality of waveguides substantially match,
A single substrate provided with each of the plurality of waveguides so that the light beams are emitted from different positions in a direction intersecting with the deflection direction, and a light source for making the light beams incident on each of the optical waveguides. By using the optical deflecting element configured as described above, there is no need to adjust the optical axis for positioning the optical deflecting element with high accuracy, and to prevent unevenness while maintaining the scanning lines at a predetermined interval on the image surface. It is possible to simultaneously scan a plurality of light beams or selectively scan a plurality of light beams.

The deflection of the light beam in the solid state element is known to be electro-optical deflection, acousto-optical deflection, magneto-optical deflection, etc., but in the present invention, it is easy to control. It is preferable to use the deflecting means for deflecting the light beam by the acousto-optically effective deflection or the electro-optically effective deflection because it is easy to manufacture.

The acousto-optic effective deflecting means excites a surface acoustic wave (hereinafter referred to as SAW) in an optical waveguide of a piezoelectric thin film, and deflects an incident light beam by black diffraction by the SAW. A transducer such as a comb electrode that excites the SAW is a parallel comb electrode, a chirp electrode in which the pitch between the electrode fingers is changed in the SAW propagation direction,
An electrode in which a plurality of these electrodes are arranged at different angles, a chirp electrode in which the angle between the electrode fingers is inclined, a curved interdigital electrode, a curved electrode in which the distance between the electrode fingers changes in the electrode length direction, and a pitch between the electrode fingers It is possible to use an electrode or the like in which a plurality of different electrodes are arranged at different angles, and it is also possible to multiple-diffract the light beam in the optical waveguide using any one of the above electrodes. The SAW modulation can use digital modulation or analog modulation.

On the other hand, in the electro-optically effective deflecting means, electrodes such as comb-shaped electrodes are arranged on the surface of the thin film optical waveguide, and a voltage is applied between the comb-shaped electrodes so that the refractive index of the thin film optical waveguide is increased. The incident light beam is black-diffracted and deflected by the diffraction grating due to the change, or is deflected by the prism type deflection element utilizing the change in the refractive index of the prism shape having two sides which are not parallel to each other. It is preferable to use a prism-type deflecting element because it is difficult to obtain a practically sufficient resolution in the deflecting means that deflects by applying a voltage to the comb-shaped electrode. The prism type deflection element has a prism-shaped polarization domain inversion portion having two sides that are not parallel to each other, and is different between the prism-shaped polarization domain inversion portion and other portions by applying a voltage between the upper and lower electrodes. Generates a refractive index. In this case, the upper electrode may have a prism-shaped pattern having two sides that are not parallel to each other, and a portion having different refractive indexes corresponding to the electrode pattern may be generated by applying a voltage between the electrodes. .

As an optical waveguide material applicable for forming the optical waveguide of the present invention, LiNbO ₃ , LiTaO ₃ , Zn is used when an acousto-optical deflecting means is used.
O, Pb (Zr, Ti) O ₃ (PZT), (Pb, L
a) (Zr, Ti) O ₃ (PLZT) is typically used. This optical waveguide material is, for example, L
In the case of iNbO ₃ , a LiNbO ₃ single crystal wafer is coated with Ti.
After vapor deposition of Ti, LiNbO _{3 was} added at about 1000 ° C.
Optical waveguide manufactured by diffusing into
Optical waveguide prepared by proton exchange of iNbO ₃ single crystal wafer, LiNbO ₃ on LiTaO ₃ single crystal substrate
An optical waveguide in which a thin film is vapor-phase epitaxially grown by Rf-magnetron sputtering, an optical waveguide in which a LiNbO ₃ thin film is solid-phase epitaxially grown on an α-Al ₂ O ₃ single crystal substrate by a sol-gel method, and the like can be used. In the case of ZnO, a c-axis oriented ZnO thin film prepared by electron beam evaporation or Rf-magnetron sputtering on a glass substrate as an optical waveguide can be used. Further, in the case of PLZT, an optical waveguide in which a PLZT thin film is vapor-phase epitaxially grown on a MgO substrate by ion beam sputtering, and an optical waveguide in which a PLZT thin film is vapor-phase epitaxially grown on an epitaxial MgO buffer layer on a GaAs substrate by Rf magnetron sputtering, SrTi
An optical waveguide or the like in which a PLZT thin film is solid-phase epitaxially grown on an O ₃ substrate by a sol-gel method can be used.

On the other hand, when an electro-optical deflecting means is used
Is a ferroelectric thin film.
As ABO₃In positive-type perovskite-type oxides, positive
As a tetragonal, orthorhombic or pseudo-cubic system, for example BaTi
O₃, PbTiO₃, Pb_{1- x}La_x(Zr_yT
i_1-y)_{1-x / 4}O₃(Depending on the values of x and y, PZT, P
LT, PLZT), Pb (Mg_1/3Nb_2/3) O₃, K
NbO₃As a hexagonal system, for example, LiNbO
₃, LiTaO₃There are ferroelectrics typified by
Sung in the bronze type oxide_xBa_1-xNb₂
O₆, Pb_xBa_1-xNb₂O₆Etc. Also, above
In addition to materials, Bi_FourTi₃O₁₂, Pb₂KNb _FiveO₁₅,
K₃Li₂Nb_FiveO₁₅, Further substituted derivatives of the above materials, etc.
There is.

As the electrode, a metal electrode such as Pt or Al or a transparent oxide electrode such as ITO having a refractive index smaller than that of the optical waveguide can be used.

A clad layer having a smaller refractive index than the optical waveguide can be provided between the optical waveguide and the electrode (upper electrode or lower electrode). For example, when a clad layer is provided between the optical waveguide and the upper electrode, any material may be used for the upper electrode, but it is desirable to use a transparent oxide electrode such as ITO because it causes an increase in driving voltage. . As the lower electrode, a conductive or semiconductive single crystal substrate or a conductive or semiconductive epitaxial or oriented thin film provided between the substrate and the optical waveguide can be used. When such a lower electrode is used, Nb-doped SrTiO ₃ , Al-doped ZnO, In ₂ O ₃ , R having a smaller refractive index than the optical waveguide.
uO ₂ , BaPbO ₃ , SrRuO ₃ , YBa ₂ Cu ₃
O _7-x , SrVO ₃ , LaNiO ₃ , La _0.5 Sr _0.5
An oxide such as CoO ₃ is preferable, but Pd, Pt, Al,
It is also effective to use a metal such as Au or Ag. The conductive or semiconductive single crystal substrate or the conductive or semiconductive epitaxial or oriented thin film is preferably selected according to the crystal structure of the ferroelectric thin film. The conductive or semi-conductive thin film or the single crystal substrate used as the upper electrode or the lower electrode has a resistivity in the range of about 10 ⁻⁶ Ω · cm to 10 ³ Ω · cm. If the resistivity is negligible, it can be used as the upper electrode or the lower electrode. Further, an upper electrode material or a lower electrode material having an appropriate carrier mobility can be selected depending on the deflection speed or the modulation speed.

The laser used as the light source is, for example, a gas laser such as He-Ne or AlGaAs.
Compound semiconductor lasers such as or these lasers
An array or the like can be used. Laser light generated by laser oscillation is prism coupling, butt coupling (or end coupling), grating coupling, evanescent field
It is introduced into the optical waveguide by a method selected from coupling and the like.

Suitable thin film lenses are mode index lenses, Reneburg lenses, geodesic lenses, Fresnel lenses, grating lenses and the like.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

First, the deflection with an acousto-optical effect in the optical waveguide to which the present invention is applicable will be described.

For example, by using the piezoelectric effect of the LiNbO ₃ thin film, surface acoustic waves (SAW) can be excited via a transducer. Since the SAW periodically changes the refractive index of the thin film, the laser light coupled into the ferroelectric thin film that intersects with the SAW is incident on the acousto-optic effect under the Bragg condition of the following equation (1). Causes Bragg reflection.

Mλ = 2Λsin θ _B (1) where m: order of diffracted laser λ: wavelength of laser Λ: wavelength of SAW θ _B : Bragg angle (deflection angle × 1/2)

At this time, the input frequency to the transducer
That the wavelength Λ of the SAW changes by modulating the
Due to Bragg angle θ_BChange to take advantage of
The light can be scanned. This frequency sweep
Generally, digital modulation is used to
The SAW frequency that intersects the beam width is changed in appropriate steps.
And the SAW frequency over the beam width of the laser light is
It is constant. Acousto-optic for digital modulation during effective deflection
Laser light spot diameter, number of spots, spots
The travel time is determined as follows. Laser light in optical waveguide
Beam width of D _l, The focal length of the imaging lens is F_lTosure
For example, the diffraction limit spot diameter 2ω (1 / e²Diameter) is the following
It can be expressed by equation (2). At this time, the resolution laser scan
Number of pots N _dCan be expressed by the following equation (3).

2ω = (4 / π) · (λ · F _l / D _l ) ... (2) N _d = 2Δθ _B · F / 2ω = (π / 4) · τ · Δf _d ... ( 3)

Here, τ is the transit time of the SAW with respect to the beam width of the laser light, and when the SAW is digital modulation, it is the spot moving time t _d shown in the following equation (4). In this case, the SAW passage time (spot movement time) can be shortened by reducing the beam width of the laser beam and / or selecting an optical waveguide material having a high SAW speed.

T _d = τ = (D _l / v) (4) The number N _d of resolution laser spots is Δf _{d in the} SAW frequency band and δf _d (= the frequency change required for diffraction). 1
/ Τ), it can be expressed as shown in the following equation (5).

N _d ≈Δf _d / δf _d = τ · Δf _d = D _l / v · Δf _d ··· (5) As described above, when the spot moving time is shortened, the number of spots is reduced and when the number of spots is increased. The spot movement time is long. Therefore, in order to increase the number of spots without changing the spot moving time, it is effective to widen the band of the transducer.

Further, depending on the SAW transit time τ and the number of resolution laser spots N _d , the scanning speed (spot moving time) t _d can be transformed using the above equation (5) to obtain the following (6).
It can be expressed by a formula.

T _d ≈τ × N _d ≈τ × τ · Δf _d = τ ² · Δf _d (6) As will be described later, in the present embodiment, a plurality of laser beams are deflected simultaneously. Since the photoconductor can be exposed (by scanning), the apparent scanning speed can be improved by 1 / m when the number of beams is m, as shown in the following expression (7).

T _m = td / m ≈ (τ × N _d ) / m = (τ × τ · Δf _d ) / m = (τ ² · Δf _d ) / m (7)

In the case of analog modulation, since the SAW frequency continuously changes over the beam width of the laser light, the portion of the optical waveguide through which the SAW propagates also functions as a Fresnel zone lens and is diffracted. The laser light is deflected and condensed at the same time. In this case, if the frequency band of SAW by analog modulation within the beam width of the laser light is δf _a , the focal length F can be expressed by the following equation (8), and the spot diameter d at the focal position can be expressed by the following (9). Can be expressed as

F = Dv / (λδf _a ) = (v ² / λ) · (τ / δf _a ) (8) d = v / δf _a (9) Further, the modulation sweep time (analog modulation time width) ) and T _a, the SAW of the frequency band by analog modulation Delta] f _a
When the scanning speed t _a is expressed by the following equation (10), the resolution laser spot number N _a expressed by the following equation (11).

T _a = T _a −τ (10) N _a = (T _a −τ) / T _a · (τ · Δf _a ) (11) Also, in this case, the same will be described later. As described above, since a plurality of laser beams can be simultaneously deflected (scanned) to expose the photoconductor, as shown in the following formula (12), when the number of beams is m, the apparent scanning speed is 1 / m. Can be improved.

T _m = t _a / m≈ (T _a −τ) / m (12)

Next, the electro-optically effective deflection will be described. In the electro-optic effect, the relationship between the refractive index n and the electric field E can be expressed by the following equation (13).

N = n ⁰ + aE + bE ² + cE ³ + ... (13) This equation (13) is applied to a material having a crystal structure with a symmetry center.
As for the change in refractive index due to the electric field, the odd-order terms disappear and the next (1
It can be expressed by equation 4).

Δn = n ⁰ −n = −bE ² −... (14) The quadratic term of the equation (14) is called the Kerr effect, and is generally expressed by the following equation (15). It is represented by.

Δn = −½Rn ³ E ² (15) On the other hand, in the material having a crystal structure without a symmetry center, the change in the refractive index due to the electric field leaves odd-order terms, and the following equation (16) Can be expressed as

Δn = n ⁰ −n = −aE−bE ² −... (16) The first-order term of the equation (16) is Pockels.
s) Effect, which is generally expressed by the following equation (17).

Δn = −½rn ³ E (17) These effects can be seen only in a substance having a crystal structure with no center of symmetry, that is, a piezoelectric substance or a ferroelectric substance. In reality, as the electric field is increased, the refractive index changes in such a manner that the Kerr effect is gradually superimposed on the Pockels effect.

When using such an electro-optical effect, a ferroelectric substance having a crystal structure with no symmetry center and a high coefficient is used, and LiNbO ₃ and PLZT are typical. When a local electric field is applied to a ferroelectric such as a PLZT thin film, the refractive index at that portion is lowered as described above, and the direction of laser light can be switched (switched) by Bragg reflection or total reflection. In the case of this EO (electro-optic effect) modulation, the spot movement time (switching time) is on the order of picoseconds because it is not limited by the movement time of the phonon such as an optical deflection element utilizing the acousto-optic effect and is due to polarization. Extremely fast.

When a predetermined electric field is applied to the comb electrodes,
As shown in FIG. 1, the refractive index n when no electric field is applied
_The refractive index of the thin film (optical waveguide) changes so that the portions 12 having a refractive index n ₂ different from ₁ are periodically (periodically indicated by the interval A in FIG. 1). When the refractive index changes periodically in this way, the incident laser light 10 is Bragg-reflected at the portion 12 under the Bragg condition shown by the above equation (1). As a result, the incident laser light 10
Becomes the Bragg reflection, that is, the deflected laser light 14.

Since the Bragg angle is a minute angle, in order to deflect (scan) the laser light in a range, many electrodes are arranged and the addressing is performed so that the changing cycle of the refractive index is changed according to the deflection angle. Is preferably performed.

On the other hand, as shown in FIG. 2, media having different refractive indices (mediums shown by refractive index n ₁ and refractive index n ₂ in FIG. 2)
In order for light to be totally reflected at the boundary of, the total reflection condition of the following equation must be satisfied.

Θ ≧ θ _T = sin ⁻¹ (n ₂ / n ₁ ), where θ _T : incident angle (critical angle) n ₁ : refractive index of the material of the optical waveguide n ₂ : refractive index of the lower refractive index portion n ₂ <n ₁ Here, when the decrease in the refractive index is due to the Kerr effect, Δn = ½Rn ³ E ² as described above, so the incident angle θ _T can be expressed by the following equation.

Θ _T = sin ⁻¹ (n ₂ / n ₁ ) = sin ⁻¹ {(n ₁ −Δn) / n ₁ } = sin ⁻¹ (1-1 / 2Rn ² E)

The Pockels coefficient of LiNbO ₃ having a refractive index n ₀ = 2.286 (633 nm) is r ₃₃ = 30.8.
× 10 ^-12 m / V, so 100 kV / cm
When applied, the refractive index changes by 2 × 10 ⁻³ , and the maximum change θmax in the traveling direction of the laser light is obtained at the critical angle θ _T as follows.

Θmax = (90−θ _T ) × 2 = {90−sin ⁻¹ (n ₂ / n ₁ )} × 2 = (90 ° −87.60 °) × 2 = 2.40 ° × 2 = 4.80 °

In addition to the above, a prism type light deflection element is known as an element having an electro-optical effect. Figure 3
The description will be made using the medium 20 in which the hypotenuse portions of the two prisms 22 and 24 having the same shape having a length of 1 and a height of D and having different refractive indices are joined as shown in FIG. Light L incident on this medium 20
When _A is passed through a prism 22 having a refractive index n _a, its transit time tau _a for the speed of light in the prism 22 and c _a, the following (1
It can be expressed by the equation (8), and when c is the speed of light in a vacuum, the following (1
It can be expressed by equation (9). Similarly, the transit time τ _b of the light L _B passing through the prism 24 having the refractive index n _b can be expressed by the following equation (20).

Τ _a = l / c _a (18) τ _a = l / c _a = l / c · n _a (19) τ _b = l / c _b = l / c · n _b ... (20)

Therefore, the difference Δτ between the transit times of the lights L _A and L _B is given by the following (2), where n _a = n + Δn> n _b = n.
It can be expressed by the formula 1).

Δτ = 1 / c (n _a −n _b ) = 1 / cΔn (21) Due to the difference Δτ in transit time, the difference Δy in the position of the wavefront before exiting the prism is It can be expressed by equation (22).

Δy = c _b · Δτ = c / n _b · l / c · Δn = l Δn / n (22) This is equivalent to refraction of the beam axis in the prism, and its angle is expressed by the following equation (23). Can be expressed as

Θ _D ≈tan (θ _D ) = − Δy / D = −lΔn / Dn (23) Further, the angle when the light is emitted from the prism according to Snell's law can be expressed by the following equation (24), and n _air · sin θ _O = sin θ _O = n · sin θ _D ··· (24) The angle θ _O can be expressed by the following equation.

Θ _O = sin ⁻¹ (n · sin θ _D ) = n · θ _D = −n · lΔn / Dn = −lΔn / D

Here, assuming that the two prisms have polarization axes in opposite directions and an electric field is applied in a direction parallel to the z-axis, from the above equation (17), the refractive indices n _a and n _b are (25) and (26), and the difference Δn between these refractive indices
(= N _a −n _b ) can be expressed by the following equation (27).

N _a = n ₀ −1/2 rn ₀ ³ E ・ ・ ・ (25) n _b = n ₀ +1/2 rn ₀ ³ E ・ ・ ・ (26) Δn = −rn ₀ ³ E ・ ・ ・ (27) )

Therefore, assuming that the applied voltage is V and the thickness of the prism is d, the angle θ ₀ can be expressed by the following equation (28).
The laser light can be deflected in proportion to the electric field or voltage.

Θ ₀ = −lΔn / D = 1 / D · rn ₀ ³ E = l / D · rn ₀ ³ (V / d) (28)

If instead of two prisms a triangular electrode is placed at the position of prism 22 in FIG. 3 and an electric field is applied parallel to the z-axis, the indices of refraction n _a , n _b are
It can be expressed by the following equations (29) and (30), and the difference Δn (= n _a −n _b ) between these refractive indices can be expressed by the following equation (31).

N _a = n ₀ −1/2 rn ₀ ³ E ・ ・ ・ (29) n _b = n ₀・ ・ ・ (30) Δn = −1 / 2 rn ₀ ³ E ・ ・ ・ (31)

Therefore, assuming that the applied voltage is V and the thickness of the medium is d, the angle θ ₀ can be expressed by the following equation (32), and the laser beam can be deflected in proportion to the electric field or the voltage.

Θ ₀ = −lΔn / D = 1 / D · ½rn ₀ ³ E = l / 2D · rn ₀ ³ (V / d) (32)

As such an element, an optical scanning element 42 using a Ti diffusion type single crystal LiNbO ₃ optical waveguide or a proton exchange type single crystal LiNbO ₃ optical waveguide as shown in FIGS. 4 and 5 has been studied. . This optical scanning element 42
The optical waveguide 36 having the polarization domain inversion portion (prism portion) 30 is provided on the insulating substrate 38, and the lower electrode 40 is provided below the insulating substrate 38. A glad layer 34 and an upper electrode 32 are sequentially provided on the optical waveguide 36.

When such electro-optical deflection is used, since the electro-optical switching speed is very high, there is no problem of the upper limit of the laser scanning speed.
There is a problem that the modulation speed of the driver has an upper limit and the laser recording speed cannot be increased. However, as will be described later, since it becomes possible to simultaneously scan a plurality of laser beams to expose the photoconductor, the apparent scanning speed is improved to 1 / m as described above when the number of beams is m. It is possible to

In consideration of the above principle, the optical deflecting element of the embodiment to which the present invention is applicable is provided with a plurality of optical waveguides which are provided on a single substrate and arranged in steps and formed of a thin film. And a light source including a plurality of lasers for injecting a plurality of light beams into the optical waveguide or a laser array for oscillating a plurality of laser beams, and an incident means thereof.
In the optical waveguide, a thin film lens that shapes the light beam as needed, and means for deflecting the light beam are provided.
As a means for emitting each deflected light beam to the outside of the optical waveguide, it is composed of optically polished end faces corresponding to each light beam, which are installed at different positions in a stepwise direction in the film thickness direction. .

As the emitting means for emitting the deflected light beam to the outside of the optical waveguide, it is possible to practically use a grating or a prism in addition to the end face of the optical deflecting element. The present inventors have proposed a deflecting element for a plurality of beams using a grating or a prism as the emitting means (see Japanese Patent Application No. 7-152743).

By the way, since the acousto-optical or electro-optical deflection element has a relatively small deflection angle, various measures have been taken to widen the deflection angle. In order to expand the deflection angle, expansion of the band in the deflecting section and multiple diffraction have been studied, but this has been accompanied by complication and size increase of the element.

However, by using the end face of the light deflecting element as the emitting means, the refraction at the end face according to Snell's law when light propagates from a medium having a high refractive index to a medium having a low refractive index can be utilized, which is about 1.5 times. Therefore, the deflection angle can be increased by about 3 times. Further, the processing of the light deflecting element for forming the end face of the light deflecting element as the emitting means is relatively simple, and is particularly excellent in that it does not cause the element to become large or complicated.

The above light deflection element can be manufactured as follows. First, steps are formed on the light deflection element by physically or chemically polishing one flat substrate, or by using the same material as the substrate or a different material on the one flat substrate. A thin film is deposited in steps. The step interval is determined in combination with the optical system, and is determined in consideration of the image spot diameter, the scanning line density, the magnification of the condensing optical system for obtaining the image spot, and the like. However, it is preferable to form the light-deflecting element in the range of 0.1 μm to 200 μm for manufacturing reasons. If the step interval is too small, it is difficult to secure the processing accuracy during polishing or the film thickness accuracy when depositing a thin film.If the step interval is too large, it will take a long time for processing or deposition. It takes time, the throughput is deteriorated, and the cost of the light deflection element is increased. As a method of polishing the substrate, a general polishing method such as submerged polishing using an abrasive and a polisher, mechanical polishing such as mechanochemical polishing, ion milling, dry or wet etching, or a combination of these methods is used. be able to. Also, when depositing a thin film to form steps, it is desirable to homoepitaxially grow the same material as the substrate, heteroepitaxially grow a different material, or grow an oriented thin film. This means that when a thin film for optical waveguide is formed on this substrate, if there is an amorphous layer or a polycrystalline layer on the substrate surface,
This is because the quality of the optical waveguide deteriorates, the loss in the optical waveguide increases, and it becomes unsuitable for practical use.

An optical deflector is manufactured by forming the above-mentioned thin film optical waveguide on the substrate manufactured as described above. If the waveguide of the thin film using a LiNbO ₃ single crystal wafer, LiNbO ₃ was deposited on Ti the single crystal wafer by diffusing into LiNbO ₃ and Ti at about 1000 ° C, or LiNbO ₃ single crystal When an epitaxial thin film is prepared by exchanging protons on a wafer, electron beam evaporation, flash evaporation,
Ion plating, Rf-magnetron sputtering, ion beam sputtering, laser ablation, MBE, CVD, plasma CVD,
It is prepared by a vapor phase growth method selected from MOCVD and the like, and a solid phase growth method of a thin film prepared by a wet process such as a sol-gel method and a MOD method.

The laser beam emitted from the optical waveguide exposes the photoconductor through a focusing optical system such as a collimator lens, an aperture, and an F.theta. Lens, and the laser beam is scanned by the main scanning by deflection and the photoconductor. By sub-scanning (rotating) the drum or belt, a plurality of lines (scanning lines) can be simultaneously scanned or interlaced scanned.

The step intervals of the plurality of optical waveguides are predetermined depending on the combination of the condensing optical system and the light deflection element, but the light source emits three or more laser beams,
When deflecting three or more laser beams, it is preferable to arrange the steps at equal intervals.

Further, the laser light emitted from the end face of the light deflection element has a divergence angle in the film thickness direction. The laser beam having this divergence angle is collimated by the collimator lens and then passed through the aperture, whereby the beam shape can be shaped and the beam position can be adjusted.
In this case, by arbitrarily selecting the shape and insertion position of the aperture, it is possible to form an image at a predetermined position even if the exit position on the end face is arbitrarily arranged. That is, the image forming positions of the respective beams in the sub-scanning direction are such that the apertures corresponding to the respective beams are shifted at equal intervals, and the image plane at the aperture positions can be imaged on the drum surface at a predetermined magnification. By selecting the system, it becomes possible to maintain the scanning line interval. On the other hand, when the emission end faces are not arranged at equal intervals, there are problems such as a reduction in transmission efficiency at the aperture and non-uniformity of the beam shape, resulting in an increase in variations in beam quality among the beams. . Further, when the light deflection element is used in the image forming apparatus, the image quality is deteriorated. On the other hand, when steps are arranged at equal intervals, the emission position, aperture position, and image formation position are arranged on a straight line, which suppresses variations in beam quality between beams and achieves high image quality. It becomes possible to do.

Next, the first embodiment will be described in detail.
The first embodiment is an application of an optical deflecting element for performing acousto-optical deflection to the present invention.

As shown in FIG. 8A, the image forming apparatus 48 of the present embodiment includes a semiconductor laser 52 and a substrate 54.
And an optical deflection element 50 having an optical waveguide 56 as a main element. Three laser beams deflected at a predetermined angle are emitted from the light deflection element 50 (details will be described later). A condensing optical system 66 including an fθ lens and a photoconductor 64 are sequentially provided on the laser beam emission side of the light deflection element 50. Further, the image forming apparatus 48 includes the deflection control circuit 68A,
The controller 68 includes a laser drive circuit 68B and a rotation control circuit 68C.

This condensing optical system 66 is composed of a collimator lens 66A, a slit-shaped aperture 66B corresponding to each laser beam and provided at intervals of about 20 μm, a first lens 66C and a second lens 66D. It is composed of a θ lens. In this condensing optical system 66, each of the laser beams that are acousto-optically deflected and emitted from the emission end face to the outside of the optical waveguide is approximately doubled so that the beam interval of the laser beams on the photoconductor 64 is 42 μm. To magnify and image.

In the present embodiment, the deflection control circuit 68A of the control device 68 changes the laser beam to SA by the acousto-optic effect.
It is a circuit for exciting W. This deflection control circuit 6
By applying a voltage from 8A, the laser light is scanned on the photoconductor 64 in a predetermined direction (the arrow X direction in FIG. 8B, the main scanning direction). Further, the laser drive circuit 68B is
It is a circuit for controlling the intensity of laser light emitted from the semiconductor laser 52 and the emission time (exposure time).
The rotation control circuit 68C is a circuit for rotating or stepping the photoconductor 64 at a constant speed in a predetermined direction (arrow Y direction in FIG. 8A, sub-scanning direction).

The laser drive circuit 68B described above is
The semiconductor laser 52 is subjected to pulse width modulation or amplitude modulation based on image data supplied from a host computer (not shown) or the like. This image data is data corresponding to the image formed on the photoconductor 64. In this case, the laser light emitted by the drive by the laser drive circuit 68B is synchronized with the deflection control circuit 68A and the rotation control circuit 68C, and the deflection angle of the light beam deflected by the deflection control circuit 68A is the main angle during image formation. The position of the photoconductor 64 that corresponds to the position in the scanning direction and that is rotated by the rotation control circuit 68C corresponds to the position in the sub-scanning direction during image formation. A two-dimensional image can be formed on the photoconductor 64 by the main scanning and the sub scanning.

The image forming apparatus 48 also includes a charging device 90 for uniformly charging the photoconductor 64 and a developing device 92 for visualizing the image formed as a latent image on the photoconductor 64. An image is visualized by the charging device 90 and the developing device 92. That is, the photoconductor 64 is uniformly charged in advance by the charging device 90, and a latent image is formed on the photoconductor 64 by exposing the photoconductor 64 to the exposed portion. The latent image thus formed on the photoconductor 64 is visualized on a copying material such as paper or film by the developing device 92.

As shown in FIG. 6, the optical deflection of this embodiment is
The element 50 has three laser beams 52 ₁, 52₂, 52₃
Equipped with a three-spot type semiconductor laser 52 that emits
There is. This semiconductor laser 52 is
Laser light output of about 20mW, total 60mW
Using a 3-spot laser diode array
It The emission side of this semiconductor laser 52 will be described later.
Optical waveguide 56 having a predetermined step in a stepped manner₁5,
6₂, 56₃A single crystal conductive substrate 54 on which the
It has been burned.

Optical waveguide 56₁Laser light 52₁Incidence of
On the side, the incident laser light 52 ₁(Width D = 8 mm
Mode index lens for collimating
58 ₁Is provided. In addition, the optical waveguide 56₁Has
SAW61₁Electrode 60 for exciting₁Is provided.
Optical waveguide 56₁The end face of the laser light in the traveling direction will be described later.
Laser light 52 that is polished to₁The optical waveguide 56
₁It has the function of ejecting to the outside. The optical waveguide 56
₂, 56₃Since they have the same configuration, description thereof will be omitted.

The light deflection element 50 is manufactured as follows.
Made. First, α-Al₂O₃Single crystal material (rectangle
Form) and prepare this α-Al₂O ₃Full surface of single crystal material
Is SiO₂Polishing with abrasive grains (mechanochemical polishing
Sing). After that, do not shift this material a specified length.
By partially mechanochemical polishing
Therefore, the step height is 20 μm and three steps are used.
The substrate 54 having is formed (see FIG. 7). This board 54
With a detergent and solvent, and then
After performing the etching process, the step portion on the substrate 54
Solid phase epitaxial growth by sol-gel method
By doing LiNbO₃Thin film optical waveguide 56₁5,
6₂, 56₃To form. Next, the optical waveguide 56₁, 56
₂, 56₃One of the end faces is polished to form the incident end face 62A.
And polishing the other end face to form the injection end face 62B.
To do.

Further, the optical waveguide 56₁On the mode in
Dex lens 58₁And the pitch between electrode fingers is changed
Set chirp electrode 60₁To provide. Similarly, the optical waveguide 5
6₂On top is the mode index lens 58₂And J
Charp electrode 60₂The optical waveguide 56₃On top
Index lens 58₃And chirp electrode 60 ₃
To provide. Further, it is emitted from the semiconductor laser 52.
Laser light 52₁~ 52₃Each of the optical waveguides 56₁~ 5
6₃Butt coupling to be incident on
Therefore, the semiconductor laser 52 is fixed directly on the incident end face 62A.
Is determined. In this way, the acousto-optical light deflection element 5
Create 0.

Next, the operation of the image forming apparatus of this embodiment will be described. First, the optical deflection element 50, is emitted three laser light in the semiconductor laser 52 is incident on each of the thin film optical waveguide 56 _{1-56 3.} Optical waveguide 56 ₁
The laser light 52 ₁ incident on the
After being collimated by the lens 58 ₁ to have a beam width D = 8 mm, it is digitally modulated and deflected by the chirp electrode 60 _{1 in} the SAW propagation direction (the arrow direction of SAW 61 ₁ shown in FIG. 6). Deflected laser beam is emitted from the optical waveguide 56 ₁ of the exit end face 62B to the optical waveguide 56 ₁ outside, a collimator lens 66A, an aperture 66B corresponding to the laser light 52 _1, and the light collecting optical system according to F · theta lens 66 And the beam spacing on the photoconductor 64 is 42 μm.
Is imaged so that Further, the laser beam 52 ₂ incident on the waveguide 56 ₂ provided at a predetermined step is collimated by the mode index lens 58 ₂ and the chirp electrode 60 _{2 is} directed in the SAW propagation direction (arrow direction of SAW 61 ₂ shown in FIG. 6). Is digitally modulated and deflected by.
Laser light 52 ₂ after deflection emitted from the exit end face 62B of the optical waveguide 56 ₂ to the optical waveguide 56 ₂ outside condensing optical system 6
After 6, the image is formed on the photoconductor 64 so that the beam interval is 42 μm. Similarly, the laser light 52 ₃ incident on the waveguide 56 ₃ provided with a predetermined step is collimated by the mode index lens 58 ₃ and the chirp electrode 60 is formed in the SAW propagation direction (the arrow direction of SAW 61 ₃ shown in FIG. 6). Digitally modulated and deflected by ₃ . The deflected laser light 52 ₃ is emitted from the exit end face 62 of the optical waveguide 56 _3.
Emitted from B to the optical waveguide 56 ₃ outside, through the focusing optical system 66, the beam interval is imaged so as to 42μm on the photosensitive member 64.

Each laser beam deflected as described above and emitted from the optical waveguide is collected by the condensing optical system 6 such as an fθ lens.
The photosensitive member 64 is exposed through 6 to the photosensitive member 64. The deflection in the optical deflector 50 is performed by main scanning (arrow X in FIG. 8).
(Scanning in the direction), the same deflection is simultaneously performed for each laser beam, and sub-scanning (scanning in the direction of arrow Y in FIG. 8) due to movement of the laser beam during rotation of the photosensitive member 64 is performed. Simultaneous scanning every 3 lines is performed,
Interlaced scanning is performed every three lines in the sub-scanning direction (rotational direction of the photosensitive drum).

The photosensitive member 64 is uniformly charged in advance by the charging device 90, and a latent image is formed on the photosensitive member 64 by simultaneous scanning. The latent image formed on the photoconductor 64 after the simultaneous scanning is performed by the developing device 92.
It is visualized as a copy material such as paper or film.

The respective laser beams deflected and emitted from the optical waveguide are emitted with a step in substantially the same direction. That is, the deflection direction (main scanning direction and sub-scanning direction) corresponding to the step of the optical waveguide formed in a step shape
Are fired from different positions. Therefore, the plurality of laser beams emitted from the light deflection element 50 are three substantially parallel laser beams directed in the same direction. Since these laser lights can be deflected (main scanning) at the same time,
Three laser beams, which are maintained in a substantially parallel state in the same direction, are emitted from the light deflection element 50. Therefore,
Simultaneous scanning (deflection) of a plurality of laser beams,
It is not necessary to provide a complicated adjusting device or finely adjust the optical axis in order to maintain the spacing of the scanning lines of several tens of microns on the image surface of No. 4 and prevent unevenness. Only by condensing the light onto the photoconductor 64 via 66, it is possible to perform scanning while maintaining a constant scanning line interval.

The performance of the light deflection element 50 of this embodiment is as follows.
If the bandwidth of the transducer is Δf = 800 MHz and the wavelength of the laser is λ0 = 780 nm, the scanning time t _d is 11.3 ms / line for each laser beam, but 3
Since the lines are simultaneously scanned, the apparent scanning time tm is 2.8 ms / line. The present inventor conducted an experiment of exposing the photoconductor under these conditions, and found that it was 600 dot / inc.
The result is that h can be printed on A4 size paper at about 3 sheets per minute, and a practical printing speed is realized.

Here, the conventional optical waveguide type optical deflector is caused by a loss (incident loss) in which the intensity of the laser light is reduced when the laser light is incident on the optical waveguide, a scattering of the laser light in the optical waveguide, and the like. There are a loss of light intensity (scattering loss), a loss of light intensity when deflecting laser light (deflection loss), and a loss of light intensity when emitting laser light from an optical waveguide (emission loss). Due to these losses, the intensity of the laser light reaching the photoconductor changes, and the energy density on the photoconductor when exposed to the laser light changes. For this reason, in an image forming apparatus such as a facsimile, there is a problem that uneven printing occurs.

On the other hand, in this embodiment, since the semiconductor laser capable of emitting three laser beams is used, even if there is a loss of the laser beam, the exposure energy density three times that of the single beam laser can be obtained. Thus, the exposure energy density on the photoconductor required for exposing the photoconductor can be sufficiently obtained.

Further, in this embodiment, since each deflected laser beam is emitted to the outside of the optical waveguide, the emission position is shifted at a constant interval in the film thickness direction of the optical waveguide, that is, in the sub-scanning direction of the scanning line. By arranging an aperture on the optical axis of each laser beam and taking a configuration in which the focusing optical system 66 magnifies the image approximately twice, the positional accuracy between the emitted beams is determined by the optical deflection element. And about twice the mechanical accuracy of these optical systems. Therefore, if the processing accuracy of the mechanical polishing is about ± 0.5 μm, the positional accuracy between the emitted laser beams is about ± 1 μm, and the positional accuracy can be greatly improved.

Next, a second embodiment will be described. In addition,
Since this embodiment has a configuration similar to that of the above-described embodiment, the same portions are denoted by the same reference numerals and detailed description thereof will be omitted. Further, in the present embodiment, as shown in FIG. 9, a plurality of (two in the present embodiment) chirp electrodes are arranged for one laser beam to increase the deflection angle.

The optical deflection element 50A of this embodiment is manufactured as follows. In the first embodiment, the substrate 54 has three
Although the steps are formed, in the present embodiment, the substrate 54 having the two steps is formed, and the optical waveguide of the ZnO thin film is formed on the α-Al ₂ O ₃ single crystal substrate in the same manner as the above embodiment. Are produced (FIG. 9). On the optical waveguide 56 ₁ ,
A mode index lens 58 ₁ , a first chirp electrode 60 ₁₁ and a second chirp electrode 60 _{12 in} which the pitch between the electrode fingers is changed are sequentially provided. Similarly, a thin film optical waveguide 56 ₂
A mode index lens 58 ₂ , a first chirp electrode 60 ₂₁ and a second chirp electrode 60 ₂₂ are provided on the top.
Further, the semiconductor laser 52A of the present embodiment uses a dual beam laser diode array,
The ZnO thin film is directly fixed and coupled to the end face of the optical waveguide. In this way, the acousto-optical light deflection element 50A
To make.

In the image forming apparatus of this embodiment, as shown in FIG. 10, the optical deflection element 50 of FIG.
6 _1, 56 ₂ in place of the two-stage light deflector 50A having an image forming apparatus and substantially the same structure as in FIG.

Next, the operation of the image forming apparatus of this embodiment will be described. First, in the light deflection element 50A, two laser beams are emitted from the semiconductor laser 52A and are incident on the optical waveguides 56 ₁ and 56 ₂ , respectively. Each laser beam incident on the optical waveguide is a mode index lens 58.
After being collimated by the first chirp electrode 6
It is diffracted and deflected twice by being digitally modulated by 0 ₁₁ and 60 ₂₁ and further digitally modulated by the second chirp electrodes 60 ₁₂ and 60 ₂₂ . This doubles the deflection angle. The deflected laser light is emitted by an end face that is emitted at the position of the emission end face at an interval of 20 μm in the film thickness direction of the optical waveguide and is emitted to the outside of the optical waveguide. The photoconductor is exposed at 600 dots / inch through the condensing optical system 66. The scanning of the laser beam onto the photosensitive member is interlaced by every two lines by main scanning by deflection and sub-scanning by rotation of the photosensitive drum. Also in this case, approximately 2
Since the image is magnified twice, the positional accuracy between the emitted beams is about twice as high as the mechanical accuracy of the light deflection element 50A and these optical systems. That is, if the processing accuracy of the mechanical polishing is set to approximately ± 0.5 μm, the positional accuracy between the injection beams becomes approximately ± 1 μm, and the positional accuracy can be greatly improved.

Next, a third embodiment will be described. Since this embodiment has a configuration similar to that of the above-described embodiment, the same portions are denoted by the same reference numerals and detailed description thereof is omitted. Further, in the present embodiment, as shown in FIG. 11, the laser light is introduced into the optical waveguide by prism coupling.

The light deflection element 50B of this embodiment is manufactured as follows. After using the α-Al ₂ O ₃ single crystal material and performing the same polishing (mechanochemical polishing) and etching treatment in a hydrochloric acid aqueous solution (chemical etching) as in the above-described embodiment to provide three steps of about 40 μm, , Thin film optical waveguides 56 ₁ , 56 ₂ , 56 by diffusing Ti into each of the stepped portions on the substrate 54.
Forming ₃ Next, the optical waveguides 56 ₁ , 56 ₂ , and 56 ₃
One of the end faces is polished to form an injection end face 62B.

As shown in FIG. 11, this optical waveguide 5
6 _1, 56 _2, 56 ₃ of the other end face side optical waveguide 5
6 _1, 56 _2, 56 ₃ of the each prism coupling 59 _1, 59 _2, 59 ₃ are provided. Laser light is introduced into the optical waveguide by each of these prism couplings 59 ₁ , 59 ₂ , 59 ₃ .

The semiconductor laser 52B of this embodiment is
Constructed separately from the substrate and optical waveguide, it contains a 3-spot laser diode array and a collimating lens. The semiconductor laser 52B emits three collimated laser beams 52 ₁ , 52 ₂ , and 52 ₃ .

The image forming apparatus according to the present embodiment has the same structure as that shown in FIG. 8, and therefore the optical deflecting element 50 shown in FIG. 8 will be described in place of the optical deflecting element 50B. In addition, in the present embodiment, the optical magnification of the condensing optical system 66 is set to the same magnification, and each of the slit-shaped apertures 64B is provided with a shift of about 40 μm corresponding to the laser light. There is.

Next, the operation of the image forming apparatus of this embodiment
Will be explained. First, in the light deflection element 50B, the semiconductor laser
Laser beams collimated at the laser 52B
Is ejected and the prism coupling 59₁, 59₂,
59 ₃By optical waveguide 56₁, 56₂, 56₃Enter
Is shot. Each laser light incident on the optical waveguide is char
Diffraction by being digitally modulated by the electrode 60
Be deflected. The deflected laser light is emitted from the exit end face.
With a space of 40 μm in the film thickness direction of the optical waveguide.
It is emitted by the end face that emits outside the arranged optical waveguide,
Photoconductor via a condensing optical system 66 such as an aperture and a lens
To expose. The scanning of the laser light onto the photoconductor is by deflection.
Main scan and sub-scan by rotation of the photosensitive drum
Scanning is performed simultaneously for each scan. In this case, enlarge the image to approximately 1x
The position accuracy between each output beam is
Equal to the mechanical precision of the child 50B and these optical systems.
It That is, the processing accuracy of mechanical polishing is approximately ±
If it is 0.5 μm, the positional accuracy between each emitted beam is approximately ±
0.5 μm, which can greatly improve the position accuracy.
it can.

Next, a fourth embodiment will be described. In addition,
Since this embodiment has a configuration similar to that of the above-described embodiment, the same portions are denoted by the same reference numerals and detailed description thereof will be omitted.

The light deflection element of this embodiment is manufactured as follows. In the second embodiment, two steps of steps are formed on the substrate 54 made of the α-Al ₂ O ₃ single crystal material. However, in the present embodiment, the LiTaO ₃ single crystal material is used and the single LiTaO ₃ is used. LiTaO ₃ is homoepitaxially grown by Rf-magnetron sputtering to 1.0 μm on the ₃ single crystal substrate with half of the substrate being masked to form two steps. Next, an optical waveguide is produced by growing an optical waveguide of an epitaxial LiNbO ₃ thin film by 1.0 μm on the formed two-step substrate by the Rf sputtering method. It should be noted that one chirp electrode is formed on the optical waveguide corresponding to the laser beam, and on the optical waveguide 56 ₁ , a mode index lens 58 ₁ and a chirp electrode 60 ₁₁ with a pitch between the electrode fingers changed are sequentially arranged. A mode index lens 5 is provided on the optical waveguide 56 _2.
8 ₂ and a chirp electrode 60 ₂₁ are provided (FIG. 9). In this way, an acousto-optical light deflection element is manufactured.

The image forming apparatus according to the present embodiment has substantially the same structure as that shown in FIG. In this embodiment, the condensing optical system 66 sets the optical magnification to about 20 times without using the slit-shaped aperture. In addition, S is generated by each of the chirp electrodes 60 ₁₁ and 60 _21.
The control for exciting the AW adopts analog modulation.

Next, the operation of the image forming apparatus of this embodiment will be described. First, in the light deflection element, the semiconductor laser 5
In 2A, two laser beams are emitted and made incident on the optical waveguides 56 ₁ and 56 ₂ , respectively. Each laser beam incident on the optical waveguide is collimated by the mode index lens 58 and then diffracted and deflected by being analog-modulated by the chirp electrode. The laser beam deflected and emitted from the end face passes through a condensing optical system 66 that does not use an aperture, is magnified about 20 times, and is imaged on the surface of the photoconductor. The scanning of the laser beam onto the photosensitive member is performed simultaneously every two lines by main scanning by deflection and sub-scanning by rotation of the photosensitive drum.

In this embodiment, since the analog modulation is used, the scanning speed is 85 μs / line which is two orders of magnitude faster than the scanning speed by digital modulation.
Printing of 00 dpi / inch is possible on 60 sheets or more per minute on A4 size paper. But such high density,
At a high scanning speed, the scanning exposure speed is limited by the speed of the video rate for modulating the laser light rather than the scanning speed of the laser light, and the video rate requires about 800 Mbps. It is difficult to realize such a high video rate for one semiconductor laser, and
bps is the upper limit. In this embodiment, since two laser beams can be simultaneously scanned and exposed, the video rate for one laser beam is the same at 400 Mbps, but the apparent video rate is 8 times the number of laser beams.
Since it becomes 00 Mbps, it is possible to realize high-speed scanning exposure that is twice as fast as the case of using a semiconductor laser that emits one laser beam. Further, since the beam positional accuracy can be 0.1 μm or less in terms of film thickness accuracy, the positional accuracy between the emitted beams is 2 μm or less, and the positional accuracy can be significantly improved.

Next, a fifth embodiment will be described. In addition,
Since this embodiment has a configuration similar to that of the above-described embodiment, the same portions are denoted by the same reference numerals and detailed description thereof will be omitted. In the second embodiment, laser light is incident from the end face of the optical waveguide, but in the present embodiment, a grating is formed on the optical waveguide and the laser light is introduced into the optical waveguide by this grating.

The light deflection element 50C of this embodiment is manufactured as follows. Using a material of MgO single crystal, a PLT thin film having a smaller refractive index than the PZT thin film as a cladding layer is formed on this single MgO single crystal substrate by masking half of the substrate by Rf-magnetron sputtering. , 0.9 μm epitaxial growth to form two steps. Next, an optical waveguide is produced by growing an optical waveguide of an epitaxial PZT thin film on the formed two-step stepped substrate by Rf sputtering to a thickness of 0.9 μm.

As shown in FIG. 12, on the optical waveguide 56 ₁ , the grating 57 ₁ , the first chirp electrode 60 ₁₁ and the second chirp electrode 60 _{12 with the} pitch between the electrode fingers changed.
Are provided in order. Similarly, a grating 57 ₂ , a first chirp electrode 60 ₂₁ and a second chirp electrode 60 ₂₂ are provided on the optical waveguide 56 ₂ . Further, the semiconductor laser 52C of the present embodiment includes a dual beam laser diode array and a collimator lens. The semiconductor laser 52C emits _two collimated laser beams 52 ₁ and 52 ₂ . In this way, the acousto-optical light deflection element 50A is manufactured.

Since the structure of the image forming apparatus of this embodiment is substantially the same as that of the image forming apparatus shown in FIG. 10, detailed description thereof will be omitted. In the present embodiment,
The condensing optical system 66 has an optical magnification set to about 23 times without using a slit-shaped aperture.

Next, the operation of the image forming apparatus of this embodiment
Will be explained. First, collimation from the semiconductor laser 50C
Laser light 52 emitted₁The grating
57₁By optical waveguide 56₁Will be introduced to. Incident
Laser light 52₁Is the first chirp electrode 60₁₁By
Digitally modulated, and further the second chirp electrode 60₁₂To
Therefore, by being digitally modulated, it is diffracted twice and deflected.
To be done. This doubles the deflection angle. Biased
Laser light 52₁From the end face 62B to the optical waveguide 56₁Outside
Is ejected. Similarly, laser light 52₂Is a great
57₂By optical waveguide 56₂Introduced in
Charp electrode 60 _{twenty one}And the second chirp electrode 60_{twenty two}By
It is diffracted and deflected twice by being digitally modulated
It Polarized laser light 52₂Is light from the end face 62B
Waveguide 56₂It is ejected to the outside.

In this embodiment, the laser light is magnified about 23 times by the condensing optical system 66 and focused on the surface of the photoconductor, so that the positional accuracy between the emitted laser lights is about 2 μm. , The position accuracy can be greatly improved.

Next, a sixth embodiment will be described. The sixth embodiment is an application of the present invention to an optical deflecting element that performs electro-optical deflection. Since the present embodiment has a configuration substantially similar to that of the above-described embodiments, the same parts are designated by the same reference numerals and detailed description thereof will be omitted.

As shown in FIG. 13, the resistivity is about 5 mΩ ·
cm-500 mΩ · cm Nb-doped SrTiO ₃ (1
00) Using a single crystal material, a conductive substrate 74 having a step height of 20 μm and three steps is formed by mechanochemical polishing and chemical etching as in the first embodiment. Epitaxial PLZT (12/40/60) is formed on each of the steps of the substrate 74.
Optical waveguide 76 ₁ of the thin film, 76 _2, 76 ₃ is growth.
These optical waveguides 76 _1, 76 _2, 76 _3, thickness dw
= 600 nm, εw = 1300, r = 120 × 10 ⁻¹²
It is a PLZT layer of m / V, and is manufactured as follows by solid phase epitaxial growth using the sol-gel method.

First, anhydrous lead acetate Pb (CH ₃ CO
O) ₂ , lanthanum isopropoxide La (O-iso-C
₃ H ₇ ) ₃ , zirconium isopropoxide Zr (O
-iso- C ₃ H _{7) 4,} and titanium isopropoxide T
i a _{(O-iso- C 3 H 7} ) 4 as a starting material, was dissolved in 2-methoxyethanol, then distillation was carried out for 6 hours 1
The mixture was refluxed for 8 hours, and finally the Pb concentration was 0.6M P
A precursor solution for LZT (12/40/60) is obtained. Further, this precursor solution is spin-coated on the substrate. All the above operations are performed in an N ₂ atmosphere. next,
350 ° C by raising the temperature at 10 ° C / sec in a humidified O ₂ atmosphere
After holding at C, the temperature is kept at 650 ° C. Finally, the electric furnace is turned off and cooled. As a result, the first PZT thin film having a film thickness of about 100 nm is solid-phase epitaxially grown.
By repeating this a predetermined number of times (five times in the present embodiment), an epitaxial PLZ with a total film thickness of 600 nm is obtained.
A T thin film is obtained. The crystallographic relationship is PLZT (100)
// Nb-SrTiO ₃ (100), in-plane orientation PLZT
A structure of [001] // Nb-SrTiO ₃ [001] is obtained.

Optical waveguide 76 ₁ of each of these PLZT thin films
To 76 ₃ on the resistivity of about 1 M.OMEGA · cm, thickness to form an electrode array 80 _1, 80 _2, 80 ₃ of the prism type of ITO transparent conductive oxide thin film of about 100 nm. Further, both end faces of the substrate 74 and the optical waveguide 76 _{1-76 3,} the above-described embodiment and likewise polished to the incident end surface 62A
And the emission end face 62B. On the incident end face 62A,
The semiconductor laser 52 is directly fixed and butt coupled.

Next, the operation of the image forming apparatus of this embodiment will be described. First, the light deflector 70, each of the laser beams 52 ₁ to 52 ₃ emitted from the semiconductor laser 52 is introduced into the corresponding optical waveguide 76 _{1-76 3.} P
Each optical waveguide 76 _1-76 of LZT thin film _3, the upper provided with ITO transparent conductive oxide thin film (electrode array 80 ₁ -
80 ₃₎ and Nb-doped SrTiO ₃ (100) because of the high refractive index than the single crystal substrate 74, the laser light 52 ₁
To 52 ₃ is confined in the optical waveguide. Each laser beam 52 which is incident _{1-52 3} electrode array 80 _{1-80 3}
By applying a voltage between the substrate 74 and the substrate 74, a change in the refractive index occurs and the light is deflected. Each deflected laser light 52 ₁ ~
52 ₃ is emitted from the exit end face 62B with a spacing step in the thickness direction (about 20 [mu] m), a collimator lens 66A, a slit-shaped aperture 66B arranged staggered at 20 [mu] m intervals corresponding to each laser beam, and F・
The photoconductor 64 is exposed through the condensing optical system 66 by the θ lens.

Further, the laser on the photosensitive member may be lost due to a loss at the time of coupling the laser light to the optical waveguide, a loss due to scattering of the laser light in the optical waveguide, a loss at the time of emitting the laser light from the optical waveguide, and the like. Although the exposure energy density of light decreases, a semiconductor laser that can emit three laser beams can be used in this embodiment; therefore, a semiconductor that emits one laser beam even if there is a loss of laser light. It is possible to obtain an exposure energy density that is about three times that of a laser, and it is possible to obtain a sufficient exposure energy density of laser light on the photoconductor required for exposing the photoconductor. Moreover, since the magnification of the condensing optical system is about 2 times,
The positional accuracy between the emitted laser beams is twice as high as the mechanical accuracy of the light deflection element and these optical systems. That is,
If the processing accuracy of the mechanical polishing is about ± 0.5 μm, the positional accuracy between the emitted beams becomes approximately ± 1.0 μm, and the positional accuracy between the emitted beams can be improved.

As described above, the light deflection elements of the above-described embodiments can simultaneously scan or interlace with a plurality of light beams, so that the scanning speed (deflection speed) of laser light and the recording speed can be improved. You can Therefore, the range of use can be expanded to image forming apparatuses such as laser printers, digital copying machines, and facsimiles.

Further, each deflected laser light is emitted from the end face to the outside of the optical waveguide, and the position of the emission end face is shifted at a constant interval in the film thickness direction of the waveguide, that is, in the sub-scanning direction of the scanning line. Since the configuration is arranged, it is possible to improve the positional accuracy between the emitted beams, and it is possible to substantially enlarge the deflection angle according to Snell's law when the laser beam is emitted from the end face and use it. Become.

Further, the image forming apparatus of each of the above-mentioned embodiments can form an image at a high scanning speed by using the light deflection element for exposing the photosensitive member.

The light deflection element of the above embodiment has been described as an example used for the exposure of the image forming apparatus. Specifically, a laser for drawing a plurality of scanning lines with a light beam to form an image. Suitable for use in printers, digital copiers, facsimiles, etc., and use optical deflection elements for optical elements used in general optoelectronics including optical disk pickups, optical switches for optical communication and optical computers, etc. be able to.

[0132]

As described above, according to the optical deflecting element of the present invention, the optical deflecting element is formed by forming a plurality of waveguides including the optical waveguide and the deflecting means on a single substrate with steps. , The light beams emitted from the respective ends of the plurality of optical waveguides are deflected in substantially the same direction, and are emitted from different positions in the direction intersecting the deflection direction, so that the optical deflection element is positioned with high accuracy. The effect that the plurality of light beams can be simultaneously scanned or the plurality of light beams can be selectively scanned while maintaining the distance between the adjacent light beams at a predetermined distance without adjusting the optical axis for There is.

Further, according to the method of manufacturing an optical deflecting element of the present invention, the light beam is formed by forming one flat substrate in a stepwise manner so that the surface portion having a predetermined width has a predetermined step in the thickness direction. Since a plurality of thin-film optical waveguides that emit light from the end can be formed, it is possible to easily obtain an optical deflection element that does not require optical axis adjustment for positioning the optical deflection element with high accuracy. Also, by forming a step clad layer of the underlying clad layer or the same material as the substrate on a single flat substrate, it is possible to form a plurality of thin film optical waveguides that emit a light beam from the end, and It is possible to obtain an optical deflecting element that does not require optical axis adjustment for positioning the element with high accuracy.

Further, according to the image forming apparatus of the present invention,
Since the optical beam can be irradiated onto the photoconductor by the light deflecting element which does not require the optical axis adjustment for positioning the light deflecting element with high accuracy to form a latent image, the light deflecting element can be positioned with high accuracy. There is an effect that an image can be formed at a high scanning speed without causing unevenness while maintaining a predetermined interval between scanning lines on the image surface without adjusting the optical axis.

[Brief description of drawings]

FIG. 1 is an explanatory diagram for explaining Bragg diffraction.

FIG. 2 is an explanatory diagram for explaining total reflection.

FIG. 3 is a conceptual configuration diagram of a prism type deflection element.

FIG. 4 is a top view showing an optical waveguide type prism deflecting element.

FIG. 5 is a cross-sectional view showing an optical waveguide type prism deflecting element.

FIG. 6 is a schematic diagram showing an optical deflection element according to the first embodiment.

FIG. 7 is a partial cross-sectional view of FIG.

FIG. 8 is a schematic configuration diagram showing an image forming apparatus using an optical deflecting element according to the first embodiment.

FIG. 9 is a schematic view showing an optical deflection element according to a second embodiment.

FIG. 10 is a schematic configuration diagram showing an image forming apparatus using an optical deflecting element according to a second embodiment.

FIG. 11 is a schematic view showing an optical deflecting element according to a third embodiment.

FIG. 12 is a schematic configuration diagram showing an optical deflecting element according to a fifth embodiment.

FIG. 13 is a schematic configuration diagram showing an optical deflecting element according to a sixth embodiment.

[Explanation of symbols]

50 Optical deflection element 52 Semiconductor laser 54 substrate 56 Optical Waveguide 58 mode index lens 60 electrodes

Claims (6)

(57) [Claims] 1. A plurality of waveguides each comprising an optical waveguide formed of a thin film and emitting an incident light beam from an end portion, and a deflection means for deflecting the incident light beam into the optical waveguide. The deflection directions of the light beams deflected by the deflection means of the plurality of waveguides are substantially the same, and the plurality of light guides are emitted so that the light beams are emitted from different positions in a direction intersecting the deflection direction. An optical deflection element comprising: a single substrate provided with each of the waveguides; 2. The deflecting means includes a transducer for exciting a surface acoustic wave according to an input signal, and deflects an incident light beam by an acousto-optic effect that causes diffraction by the surface acoustic wave. Claim 1
The light deflection element according to. 3. The deflecting means includes an electrode that changes the refractive index of the optical waveguide according to an input signal, and deflects the incident light beam by an electro-optical effect that causes diffraction due to the change of the refractive index. The optical deflection element according to claim 1, wherein 4. A flat substrate having a predetermined thickness and vertical and horizontal lengths each having a predetermined length is stepped so that a surface portion having a predetermined width in one of the vertical and horizontal directions forms a predetermined step in the thickness direction. A method of manufacturing an optical deflecting element, comprising forming a thin film optical waveguide for emitting an incident light beam from an end portion on each surface portion of a formed stepped substrate. 5. A substrate having a predetermined thickness and a predetermined length and width on a single flat substrate such that a surface portion having a predetermined width in one of the length and width forms a predetermined step in the thickness direction. A method of manufacturing an optical deflecting element, which comprises forming a clad layer or a layer of the same material as a substrate in a stepwise manner, and forming a thin film optical waveguide for emitting an incident light beam from an end on each formed surface. 6. A photosensitive member for forming an image, a charging unit for uniformly charging the photosensitive member, an exposing unit for irradiating the photosensitive member with light to form a latent image, and the latent image In an image forming apparatus including a developing unit for visualizing, the exposing unit deflects the light beam incident on the optical waveguide, the optical waveguide being formed of a thin film and emitting the incident light beam from an end thereof. A plurality of waveguides each including a deflecting unit and a deflection direction of a light beam deflected by each deflecting unit of the plurality of waveguides substantially coincide with each other, and different positions in a direction intersecting the deflection direction. And a light source for injecting a light beam into each of the optical waveguides, and a single substrate provided with each of the plurality of waveguides so that the light beam is emitted from the optical deflector. Image formation characterized by Location.