JPH103047A - Light source device for two beam scanning - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light source device for two beam scanning easy to adjust and change the pitch of a scanning line and capable of effectively making the bent and the deviation of pitch of a scanning line smaller without making the light source side of an optical scanning system larger. SOLUTION: By adjusting the tilt angle Σ of the arranging direction 1-1 of two collimator lenses 2a, 2b to the arranging direction 5-1 of a reflection surface 51 and a beam splitting surface 52 in a composite prism member 5, a distance (d) between optical axes of two collimators in the optical path after the beam splitting surface 52 is made adjustable. By shifting at least one of two light emitting sources 1a, 1b from the optical axis of the corresponding collimator lens, by the shifting direction and shifted amount, the degree of approach in the main scanning corresponding direction and the degree of separation in the sub-scanning corresponding direction of the respective beams in the optical path after the beam splitting surface 52 are made to be adjustable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a two-beam scanning light source device.

[0002]

2. Description of the Related Art In order to speed up image recording by optical scanning, a multi-beam scanning system for scanning a plurality of scanning lines at once is intended. As one form of the multi-beam scanning method, there is a “two-beam scanning method” using beams from two light emitting sources.

The problem with the multi-beam scanning method is that
The “scanning line”, which is the trajectory of light scanning by a beam, is remarkably easy to bend as compared with the ordinary single beam scanning method, and the “pitch deviation” of the scanning line (the difference between the maximum value and the minimum value (The ratio to the designed scanning line interval) is likely to be large.

[0004] As a method for effectively reducing the bending and the pitch deviation of the scanning line, those described in JP-A-7-209596 and JP-A-6-18802 are known.
However, the former requires a special optical arrangement called "telecentric", and in order to realize this, a cylinder lens between the light source device and the optical deflector, and an aperture between this cylinder lens and the light source device are required. It is necessary to increase the interval between the light sources, which causes an increase in the size of the light source side of the optical scanning device.

In the latter, the position of the imaging optical system provided between the optical deflector and the surface to be scanned and the aperture is conjugated by a cylinder lens provided between the aperture and the optical deflector. Therefore, applicable optical systems are limited.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the present invention makes it easy to adjust or change the scanning line pitch, without bending the scanning line or increasing the scanning line without increasing the size of the light source side of the optical scanning optical system. It is an object of the present invention to realize a novel two-beam scanning light source device capable of effectively reducing the pitch deviation of the light source.

[0007]

According to the light source device for two-beam scanning of the present invention, "after independently collimating beams from two independent light-emitting sources, they approach each other in the main scanning direction and move in the sub-scanning direction. Is a light source device that combines and emits as two beams moving away from each other.

[0008] An optical scanning device using the light source device is as follows.
As a general optical scanning device, a parallel beam from a light source device is scanned in a sub-scanning direction by a cylinder lens (sub-scanning is performed on a virtual optical path in which the optical path from the light source to the surface to be scanned is linearly developed along the optical axis. (In a direction corresponding to the direction parallel to the main scanning direction) to form a long line image in the main scanning corresponding direction (a direction corresponding to the main scanning direction on the virtual optical path in parallel). Deflected by a polygon mirror having a deflecting / reflecting surface in the vicinity of the image forming position, and the deflecting beam is condensed as a light spot on the surface to be scanned by an anamorphic image forming optical system having a surface tilt correction function, and optical scanning is performed. belongs to.

An anamorphic imaging optical system usually has a long toroidal lens, a long cylinder lens, and the like as "optical elements for correcting surface tilt". In the imaging optical system, generally, the starting point of the deflection by the deflection anti-slope surface and the position of the surface to be scanned have a conjugate relationship with respect to the sub-scanning corresponding direction.

[0010] The two-beam scanning light source device according to the first aspect of the present invention is characterized in that "the degree of approach of the two beams in the main scanning direction and the degree of the distance in the sub-scanning direction, and two collimating lenses for collimating the two beams. , The optical axis interval in the sub-scanning corresponding direction after the synthesis is adjustable ".

Here, with reference to FIG. 3, the above “degree of approach” and “degree of distance” will be described. FIG. 3A is an explanatory diagram showing the state of the two beams L ₁ and L ₂ synthesized and emitted from the two-beam scanning light source device 100 as viewed in the sub-scanning corresponding direction. The vertical direction in FIG. 3A is the “main scanning corresponding direction”. As shown in FIG.
The two beams L ₁ and L _{2 that} are combined and emitted gradually approach each other in the main scanning corresponding direction after the emission, and the position in the figure: P
At the intersection. The intersection angle α between the beams L ₁ and L _{2 at} the intersection position P is referred to as “approach degree”.

FIG. 3B shows a light source device 1 for two-beam scanning.
The state of the two beams L ₁ and L ₂ synthesized and emitted from 00 when viewed from the main scanning corresponding direction is illustrated in an explanatory diagram.
The vertical direction in FIG. 3B is the sub-scanning corresponding direction.
In FIG. 3B, reference numerals AX ₁ and AX ₂ denote the optical axes of the two collimating lenses in the two-beam scanning light source device after the beam combination, and correspond to the sub-scanning directions of the optical axes AX ₁ and AX _2. Can be adjusted as described above.

As shown in FIG. 3B, the two beams L ₁ and L ₂ emitted from the two-beam scanning light source device 100 gradually move away from each other in the sub-scanning corresponding direction after the emission. In other words, the beams L ₁ and L ₂ advance so as to travel in different directions from the intersection position: q, with the position: q in FIG. 3B as the intersection position. The virtual intersection angle β of the beams L ₁ and L _{2 at} the intersection position: q is referred to as “degree of distance”. If the optical system extending from the two-beam scanning light source device to the surface to be scanned is determined, the crossing angle β determines the interval between the light spots on the surface to be scanned in the sub-scanning direction, that is, the pitch of the scanning lines.

If the distance between the optical axes AX ₁ and AX ₂ is adjusted while keeping the distance, that is, the intersection angle β, constant, it is easy to displace the intersection position q in the left-right direction in FIG. 3B. Will be appreciated.

In the two-beam scanning system, when the position of the "two line images" in which the two beams emitted from the two-beam scanning light source device are formed by the cylinder lens is shifted in the main scanning corresponding direction, the two deflected beams are formed. On the other hand, the “surface tilt correction function” operates differently, and a large bending is likely to occur in the scanning line.

As in the two-beam scanning light source device of the present invention, when the two beams emitted from the light source device are brought closer to each other in the main scanning direction, the two beams can intersect in the main scanning direction. , Intersection position (Fig. 3
By setting the position (a): P) near the starting point of the deflection by the deflecting reflection surface, the surface tilt correction effect can be applied to each beam in the main scanning direction in the same manner, and the scanning line can be greatly bent. Can be effectively reduced.

In the above-described optical scanning device, the two deflection beams generally cross each other between the surface to be scanned and the starting point of the deflection in the sub-scanning corresponding direction. In such an optical scanning device, the “pitch deviation” of a scanning line in two-beam scanning is used.
Is strongly affected by the surface tilt correction optical element used in the imaging optical system.

In order to avoid this, the intersection of the two deflected beams in the direction corresponding to the sub-scanning direction should be set near the above-mentioned surface tilt correction optical element (ie, on the scanning surface than the object-side focal position of the surface tilt correction optical element). Side). This is because the operation of the optical element for correcting surface tilt becomes substantially the same for each of the two beams.

The “intersecting position of the deflected two beams in the sub-scanning corresponding direction” is the intersecting position q in FIG. 3B by an optical element between the two-beam scanning light source device and the intersecting position. Are conjugate positions. Therefore, by adjusting the distance between the optical axes AX ₁ and AX ₂ in FIG. 3B to adjust the position of the intersection position: q, the two beams L ₁ and L ₂ deflected in the sub-scanning direction are adjusted. The intersection position can be easily located near the optical element for correcting surface tilt, and thus the pitch deviation can be effectively reduced.

According to a second aspect of the present invention, a two-beam scanning light source device includes two collimating lenses, two light emitting sources, and a combining prism member. "Two collimating lenses"
Are arranged at a predetermined distance from each other and with their optical axes parallel. “Two light sources” are provided corresponding to each of these collimating lenses. As a light emitting source, an LD (semiconductor laser) element or an LED (light emitting diode) element can be used. Two light sources are independent
For example, in the case where the LD element is used as a light emitting source, it means that the light emitting sources are “separate from each other as LD elements”.

The "combining prism member" combines two beams emitted from two light sources and collimated by the corresponding collimating lenses. That is, the synthetic prism member is
The reflecting surface and the beam splitting surface are parallel to each other and separated by a predetermined distance. The reflecting surface reflects the beam collimated by one collimating lens toward the beam splitting surface. The beam split surface reflects the beam reflected by the reflecting surface,
The beam collimated by the other collimating lens is transmitted. In this way, a beam reflected by the beam splitting surface and a beam transmitted through the beam splitting surface are radiated as two combined beams.

The inclination angle of the "arrangement direction of the two collimating lenses" with respect to the "arrangement direction of the reflection surface and the beam split surface" in the combining prism member is adjustable. By adjusting the inclination angle, the inclination angle after the beam split surface can be adjusted. The distance between the optical axes of the two collimating lenses in the sub-scanning direction in the optical path can be adjusted.

At least one of the two light sources is
It can be deployed offset from the optical axis of the corresponding collimating lens, and the degree of approach of each beam on the optical path after the beam split plane in the main scanning corresponding direction and the sub-scanning corresponding direction depend on the shifting direction and the shifting amount of the shifted light source. Is adjustable.

The “beam splitting surface” in the above-mentioned composite prism member may be, for example, a “semi-transmissive mirror surface”, but the semi-transmissive mirror surface has low light use efficiency. Therefore, if the “two light sources” are “independent LD elements”, the emitted beam is substantially in a linearly polarized state, so that a half-wave plate is provided between one light source and the combining prism member. By setting the beam splitting surface of the combining prism as a “polarizing beam splitting surface” (claim 3), the utilization factor of light can be increased. In this case, each independent LD
The element may be adjustable in rotation about the chief ray of the radiation beam (claim 4).

According to a fifth aspect of the present invention, in the two-beam scanning light source device according to the second, third or fourth aspect, after adjusting each adjustable portion,
This is a two-beam scanning light source device that is integrally fixed as a whole.

[0026]

FIG. 1 shows an embodiment of the present invention.
In (a), the vertical direction is the sub-scanning corresponding direction, the direction orthogonal to the drawing is the main scanning corresponding direction, and in (b), the horizontal direction is the main scanning corresponding direction, and the vertical direction is the sub-scanning corresponding direction.

In FIG. 1A, two independent light emitting sources 1a and 1b are "LD elements", and have two collimating lenses 2a and 2b and aperture plates 3a and 3 having openings.
b is held by the holder 10 together with the light emitting sources 1a and 1b.

The two collimating lenses 2a and 2b are "separated by a predetermined distance from each other and have their optical axes parallel".
Is fixedly held. Aperture plates 3a, 3b are provided in holes formed along the optical axis of the collimators 2a, 2b.

The light emitting sources 1a and 1b are provided in holding holes provided on the incident side of the collimating lenses 2a and 2b, respectively. The holding hole is larger than the engaging portion of the light emitting source held by the holding hole, and the light emitting sources 1a and 1b adjust the position of the light emitting portion in the direction orthogonal to the optical axis of the corresponding collimating lens 2a or 2b. In this manner, the holder 10 can be fixed to the holder 10 in such an adjusted state.

The combining prism member 5 is a transparent optical element and has a reflecting surface 51 and a deflecting beam splitting surface 52 which are parallel to each other and separated by a predetermined distance. The half-wave plate 4 is fixedly provided (claim 3).

As shown in FIG. 1A, when viewed in the sub-scanning corresponding direction (vertical direction in the figure), the light emitting portion of the light emitting source 1a is "in the same plane as the optical axis of the collimating lens 2a". , the beam L ₁ is transmitted through the polarization beam splitting surface 52 as shown.

The beam emitted from the light emitting source 1b is collimated by a collimating lens 2b,
Is turned by 90 degrees, and is sequentially reflected by the reflecting surface 51 and the polarizing beam splitting surface 52 to form the beam L _2.
Inject as

When the optical axis AX ₂ of the collimating lens 2b is extended toward the combining prism member 5 and reflected by the reflecting surface 51 and the deflecting beam splitting surface 52 in the same manner as a light beam, as shown in FIG. (in FIG. 1 (a), the beam L is ₁ and overlaps) the optical axis optical axis AX ₁ of the collimator lens 2a and spacing in the sub-scanning direction: forming a d.

As described above, the light-emitting portion of the light-emitting source 1b is shifted from the optical axis of the collimator lens 2b in the direction corresponding to the sub-scan, so that the beam L ₂ reflected by the reflecting surface 51 and the deflecting beam split surface 52 is , degree away in the sub-scanning direction: beta only, inclined relative to the beam L _1.
The degree of separation: β is determined so that light spots are condensed at a desired pitch on the surface to be scanned.

FIG. 1B shows the state of FIG.
(A) is an explanatory diagram illustrating a state viewed from the emission side of the combined beam.

Explaining each symbol in the figure, the distance: Δ
P is the distance between the central part of the reflecting surface 51 and the deflected beam splitting surface 52 in the synthetic prism member 5, and this distance: Δ
P is the “distance between the reflecting surface and the deflecting beam splitting surface” and is the “predetermined distance”. Distance: ΔC is the distance between the optical axes of the two collimating lenses 2a and 2b, and is a “predetermined distance”. In the embodiment being described, the distance: ΔP
And ΔC are set equal. Angle: σ is the direction of arrangement of the reflecting surface 51 and the deflecting beam splitting surface 52 in the synthetic prism member 5 (chain line 5-1 in FIG. 1B).
Is the inclination angle in the arrangement direction of the two collimating lenses 2a and 2b (the chain line 1-1 in FIG. 1B).
Since the inclination angle is σ, the arrangement interval of the collimating lenses 2a and 2b is “ΔC · cosσ” in the sub-scanning corresponding direction and “ΔC · sin σ” in the main scanning corresponding direction.

The interval: δ ₁ is the “shift amount” between the optical axis of the collimating lens 2 a and the light emitting portion 1 a 1 of the light emitting source 1 a in the main scanning corresponding direction. In this embodiment, the light emitting portion 1 a 1 is in the main scanning corresponding direction. Only collimating lens 2a
Is off the optical axis. In contrast, the light emitting portion 1b1 of the light emitting source 1b is from the optical axis of the collimator lens 2b, the amount of shift in the main scanning corresponding direction: [delta] ₂ shifted, the sub-scanning direction to the shift amount at the same time: and [delta] ₃ shifted. Therefore, the “shift direction” of the light emitting unit 1b1 is determined by these shift amounts: δ ₂ and δ ₃ .

The shift amount emitting portion 1a1 from the optical axis of the collimator lens 1a: By offset by [delta] _1, the beam L ₁ emitted from the synthesizing prism member 5, but inclined with respect to the optical axis AX _1, the inclination exclusively Since this occurs only in the main scanning corresponding direction, the optical axis AX ₁ in FIG.
It is drawn on top of each other and the beams L ₁ and.

On the other hand, the light emitting portion 1b1 is a collimating lens 2
The beam L ₂ emitted from the combining prism member 5 is shifted from the optical axis b in the main / sub-scanning corresponding directions.
Is both main and sub-scanning corresponding direction inclined with respect to the optical axis AX _2.
"Slope of beam L ₂ with respect to the optical axis AX ₂ in the sub-scanning corresponding direction" in this case is the aforementioned away index: is beta.

As shown in FIG. 1B, the light emitting units 1a1,
1b1 indicates that the directions of deviation from the optical axis of the corresponding collimating lens are opposite to each other in the main scanning corresponding direction, that is,
Since the light-emitting portions 1a1 and 1b1 are shifted away from each other in the main scanning direction (shift amounts: δ ₁ and δ ₂ ), the beams L ₁ and L ₂ emitted from the combining prism 5 are mutually shifted in the main scanning direction. To get closer to each other. Therefore, by adjusting the shift amounts: δ ₁ and δ ₂ , the “approach degree” can be adjusted.

Based on the same considerations, the distance: β can be adjusted by adjusting the shift amount: δ ₃ , and the deflection beam split surface 5 can be adjusted by adjusting the angle: σ.
It will be easily understood that the optical axis interval d in the sub-scanning corresponding direction of the optical axes AX ₁ and AX ₂ in the second and subsequent directions can be adjusted.

As described above, the inclination angle: σ and the shift amount:
After adjusting δ ₁ , δ ₂ , and δ ₃ , the holder 10, the light emitting sources 1 a, 1 b, and the composite prism member 5 can be integrated by appropriate unillustrated integrating means (adhesion, screwing means, housing, etc.). The light source device for two-beam scanning according to claim 5 can be realized.

The light source device thus obtained has two independent light sources.
After the beams from the two light emitting sources 1a and 1b are separately collimated, they are combined and emitted as two beams that approach each other in the main scanning direction and move away from each other in the sub-scanning direction.

In the embodiment of FIG. 1, the light emitting sources 1a,
Since 1b is an LD element, the emitted beam is substantially linearly polarized by a laser beam, and the plane of polarization is in the direction of arrangement of the optical axes of the collimating lenses 2a and 2b (FIG. 1).
(B) in the direction indicated by the chain line 1-1). On the other hand, when the polarization plane of the beam is parallel to the chain line 5-1 in FIG. 1B, the polarization beam split plane 52 completely reflects the beam and sets the polarization plane orthogonal to the chain line 5-1. It has the property of completely transmitting the beam it has.

Therefore, in the embodiment of FIG.
If the angle in FIG. 1B: σ is not 0, the light emitting sources 1a,
1b is part of the polarization beam splitting surface 52
Therefore, the light is reflected and transmitted, respectively, and the light use efficiency is poor.

Therefore, according to the third aspect of the present invention, as shown in FIG. 2, each of the LDs which are two independent light emitting sources 1a and 1b.
Let the element be "rotatably adjustable about the chief ray of the radiation beam (parallel to the optical axis of the corresponding collimating lens)." By adjusting the rotation of each LD element, the directions 1a10 and 1b10 of the polarization plane of the radiation beam are adjusted, and the polarization reflection surface of the combining prism member 5 transmits all of the incident light beams from the light emission source 1a to emit light. Source 1
By reflecting all the beams from b,
Two-beam scanning with good light use efficiency becomes possible.

FIG. 4 is an explanatory diagram showing an optical scanning device using the two-beam scanning light source device 41 of the present invention. 2
The beam scanning light source device 41 has a configuration as described above,
The direction of the polarization plane of the beam from each LD element is adjusted so that the light use efficiency is maximized (claim 3).

In FIG. 4, the light source device 4 for two-beam scanning
The two beams emitted from 1 are both collimated by two collimating lenses, and enter the cylinder lens 43. The cylinder lens 43 has a positive power only in the sub-scanning corresponding direction, focuses the two beams only in the sub-scanning corresponding direction, and forms two linear images long in the main scanning corresponding direction.

The polygon mirror, which is an optical deflector, has a deflecting / reflecting surface 44 near an image forming position of the two line images and deflects two beams. The deflected two beams are input to the fθ lens 4
5 and a long lens (optical element for correcting surface tilt) 46 form an image on the surface to be scanned (the peripheral surface of the drum-shaped photoconductive photoreceptor 48) in the sub-scanning direction. Accordingly, the light is converged as two light spots that scan the surface to be scanned simultaneously. The long lens 46 is a "long toroidal lens"
It is.

In FIG. 4, the beam transmitted through the long lens 46 has its optical path bent by an optical path bending mirror 47, and is condensed on a photoconductive photosensitive member 48 whose peripheral surface matches the surface to be scanned. Optical scanning of the body surface. Thus, the surface to be scanned is optically scanned on two scanning lines simultaneously.

FIG. 5 shows the optical arrangement in the “virtual optical path” described above, in which the area from the two-beam scanning light source device 41 to the surface to be scanned 48 is linearly developed along the optical axis.
In FIG. 3, the vertical direction is the main scanning corresponding direction, and in FIG. 3B, the vertical direction is the sub scanning corresponding direction.

As shown in FIG. 5A, the beams L ₁ and L ₂ from the two-beam scanning light source device 41 are radiated so as to approach each other with an approaching degree α in the main scanning corresponding direction. Intersecting position: P is set at the position of the deflecting reflection surface 44.

As a result, the “surface tilt correction effect” by the fθ lens 45 and the long lens 46 acts on the beams L ₁ and L ₂ in the main scanning direction in the same manner, and it is effective to generate a large bend in the scanning line. Can be reduced.

As shown in FIG. 5B, two beams L
_1, L ₂ moves away index: with β away from each other, the position between the starting point of deflection and the scanned surface 48 in the sub-scanning corresponding direction: cross each other at Q. The position in the sub-scanning corresponding direction: Q is a conjugate point with respect to the position: q (branch position of the beams L ₁ and L ₂ in the sub-scanning corresponding direction) by the cylinder lens 43, the fθ lens 45, and the long lens 46. Therefore, the position q is adjusted by adjusting the inclination angle: σ, and the position, which is the conjugate point, is changed to the vicinity of the long lens 46 which is the optical element for correcting surface tilt (the long lens 46 and the surface to be scanned). 48), the effects on the beams L ₁ and L ₂ of the long lens 46 can be made substantially similar to each other, and the pitch deviation can be effectively reduced.

In the embodiment of FIG. 1, ΔP = ΔC =
12 mm, tilt angle: σ = 9.5 degrees, shift amount: δ ₁ = δ ₂
= 0.046 mm, δ ₃ = 0.006 mm, and good two-beam scanning with little bending of the scanning line and small pitch deviation was realized.

[0056]

As described above, according to the present invention, a novel light source device for two-beam scanning can be realized. In the light source device for two-beam scanning according to the present invention, the two beams to be radiated move away from each other in the direction corresponding to the sub-scanning, approach each other in the direction corresponding to the main scanning, the degree of separation in the direction corresponding to the sub-scanning, and the radiation of the two collimating lenses. Since the distance between the optical axes of the beams and the degree of approach in the main scanning direction can be adjusted, it is easy to adjust and change the scanning line pitch, and it is possible to effectively reduce the bending of the scanning line and the pitch deviation of the scanning line to obtain a good light. Scanning becomes possible, and the light source side of the optical scanning optical system does not increase in size. The invention according to claim 3 is:
Light use efficiency is good.

[Brief description of the drawings]

FIG. 1 is a diagram for describing one embodiment of the present invention.

FIG. 2 is a diagram for explaining a characteristic portion of the embodiment of the invention described in claim 3;

FIG. 3 is a diagram for explaining the distance between two beams emitted from the two-beam scanning light source device of the present invention;

FIG. 4 is a diagram showing an example of an embodiment of an optical scanning device using a two-beam scanning essential element source device according to the present invention.

FIG. 5 is a diagram for explaining a state of two beams emitted from a two-beam scanning light source device in the optical scanning device of FIG. 4;

[Explanation of symbols]

 1a, 1b LD element as a light emitting source 2a, 2b Collimating lens 4 1/2 wavelength plate 5 Synthetic prism member

Claims (5)

[Claims] 1. A light source device for separately collimating beams from two independent light-emitting sources and then combining and radiating them as two beams approaching each other in a main scanning direction and moving away from each other in a sub-scanning direction. The proximity of the two beams in the main scanning corresponding direction;
A light source device for two-beam scanning, wherein a distance in a sub-scanning corresponding direction and an optical axis interval of two collimating lenses for collimating the two beams in a sub-scanning corresponding direction after beam combining are adjustable. 2. The light source device for two-beam scanning according to claim 1, wherein two collimating lenses are provided at a predetermined distance from each other and arranged in parallel with the optical axis, and each of the collimating lenses corresponds to the collimating lens. Provided 2
One light source, a reflecting surface and a beam splitting surface are parallel to each other and are separated by a predetermined distance. A beam collimated by one collimating lens is transmitted through the beam splitting surface, and the other collimating A combining prism member for combining the two beams by sequentially reflecting the beam collimated by the lens on the reflecting surface and the beam splitting surface, and the arrangement direction of the reflecting surface and the beam splitting surface in the combining prism member In contrast, by adjusting the inclination angle of the two collimating lenses in the arrangement direction, the distance between the optical axes of the two collimating lenses in the sub-scanning direction in the optical path after the beam splitting plane is adjustable. And at least one of the two light sources is displaced from the optical axis of the corresponding collimating lens. In this manner, the degree of approach of each beam in the optical path after the beam splitting plane in the main scanning corresponding direction and the degree of separation in the sub-scanning corresponding direction can be adjusted by the shifting direction and the shifting amount of the light emitting source to be shifted. A light source device for two-beam scanning characterized by the above-mentioned. 3. The two-beam scanning optical system according to claim 2, wherein the two light sources are independent LD elements, and a half-wave plate is provided between one of the light sources and the combining prism member. A light source device for two-beam scanning, wherein the beam splitting surface of the combining prism is a polarizing beam splitting surface. 4. The two-beam scanning light source device according to claim 3, wherein each LD element is rotatable around a principal ray of the radiation beam. 5. The light source device for two-beam scanning according to claim 2, wherein the adjustable portions are adjusted and then fixed as a whole.