JPH11160639A - Beam combining optical element and optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a new beam combining optical element for beams emitted from plural light sources. SOLUTION: This beam combining optical element 16 is constituted so that the independent beams emitted from the plural light sources are combining as the beams mutually forming a very small angle. Then, the element 16 is formed of a transparent material and provided with a first surface 16A for refracting the beam emitted from one light source 10 and making it incident, a second surface 16B for refracting the beam emitted from the different light source 11 and making it incident and an emitting surface 16C for emitting the beam made incident from the first surface 16A and the different beam made incident from the second surface 16B. The beam made incident from the first surface 16A is emitted from the emitting surface 16c as it is and the beam made incident from the second surface 16B is emitted from the emitting surface 16C after it is totally reflected on the first surface 16A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a beam combining optical element and an optical scanning device.

[0002]

2. Description of the Related Art Independent beams from a plurality of light sources are condensed on the same surface to be scanned as a plurality of light spots separated in the sub-scanning direction, and a plurality of lines on the surface to be scanned are simultaneously scanned by light. Multi-beam optical scanning device,
It is intended to realize an optical scanning device in which the independent beams are condensed as light spots on separate scanning surfaces to perform optical scanning and simultaneously write a plurality of electrostatic latent images.

In such an optical scanning device, beams emitted from a plurality of light sources are combined as beams that form a small angle with each other. As such beam combining, there is a method utilizing the polarization state of a beam. That is, a semiconductor laser that emits a beam in a linearly polarized state is used as a light source, and each beam from the two semiconductor lasers is applied to an optical element having a polarization separation film by P and S with respect to the polarization separation film.
The beam is incident as polarized light, and the beam is synthesized using reflection and transmission by the polarization separation film. In this case, a half-wave plate is generally used for one beam in order to make the polarization planes of the beams orthogonal to each other.

Although such beam combining is effective,
Since an optical element having a polarization separation film and a half-wave plate are expensive, the cost of the optical scanning device is increased.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel and inexpensive beam combining optical element for combining beams from a plurality of light sources and a novel optical scanning device using the beam combining optical element. And

[0006]

The beam synthesizing optical element of the present invention is a "beam synthesizing optical element for synthesizing independent beams from a plurality of light sources as beams at a small angle to each other". Features (Claim 1). That is, the beam combining optical element is formed of a transparent material and has a first surface on which a beam from one light source is refracted and incident, and a second surface on which a beam from another light source is refracted and incident. , An exit surface for emitting a beam incident from the first surface and another beam incident from the second surface. Then, the beam made incident from the first surface is emitted from the emission surface as it is, and the beam made incident from the second surface is emitted from the emission surface after being totally reflected by the first surface.

[0007] As described above, the beam combining optical element of the present invention performs beam combining using only the refraction and reflection of a beam. Therefore, the beam combining optical element is compared with a conventional one using a polarization separation film or a half-wave plate. It can be realized at low cost.

According to a second aspect of the present invention, there is provided an optical scanning device, comprising: combining a plurality of independent beams from a plurality of light sources as beams forming a small angle with each other; and combining the combined plurality of beams with a common optical deflector. An optical scanning device that deflects and converges each deflected beam on a surface to be scanned by a common scanning and imaging optical system as a plurality of light spots separated in the sub-scanning direction, and optically scans a plurality of lines simultaneously on the surface to be scanned. " Wherein the beam combining optical element according to claim 1 is used as a beam combining optical element for combining a plurality of independent beams from a plurality of light sources into beams forming a small angle with each other.

[0009] In the optical scanning apparatus according to the second aspect, at least two of the plurality of beam-combined beams are:
It is possible to have an angle in the main scanning corresponding direction (claim 3). With this configuration, of the light spots that simultaneously scan the same surface to be scanned simultaneously, the light spots of at least two beams are individually detected on the light scanning start side, and the start of scanning of each line is individually determined. It becomes possible to control.
In the optical scanning device according to the second aspect, at least two of the plurality of beam-combined beams can have an angle in the sub-scanning corresponding direction (claim 4). In this way, the scanning imaging optical system provides the “at least the same region in the main scanning corresponding direction (the direction corresponding to the main scanning direction on the optical path from the light source to the surface to be scanned)” to the at least two beams.
Can be used for light spot imaging, so that the imaging characteristics of these beams in the main scanning direction can be similar to each other.

In the optical scanning device according to the second, third or fourth aspect of the present invention, it is possible to make "a plurality of beams combined cross each other in the vicinity of a deflecting reflection surface in an optical deflector". . In this way, the area of the deflecting and reflecting surface can be effectively reduced, and the optical deflector can be made compact. In the optical scanning device according to the second, third, fourth, or fifth aspect, "a beam incident on the first surface from outside may be P-polarized with respect to the first surface" (claim 6). The beam incident on the first surface is refracted from the first surface and enters the beam combining optical element. When the incident beam is P-polarized light, the incident angle is set to an angle close to the Brewster angle. Light loss due to reflection on the surface 1 can be effectively reduced. Further, in the optical scanning device according to any one of claims 2 to 6, "the light emission amount of each light source is adjusted such that the light intensities of the plurality of beams combined by the beam combining optical element are substantially equal. (Claim 7). In this manner, a plurality of lines on the surface to be scanned can be simultaneously scanned with light spots having the same light intensity.

[0011] In the optical scanning device according to any one of claims 2 to 7, "each of the plurality of beam-combined beams is elongated between the beam combining optical element and the optical deflector in the main scanning corresponding direction. It has a line image forming optical system for forming a line image near the deflecting and reflecting surface of the optical deflector, and the common scanning and image forming optical system moves the vicinity of the deflecting and reflecting surface and the position of the surface to be scanned in the sub-scanning corresponding direction. (In the direction corresponding to the sub-scanning direction on the optical path from the light source to the surface to be scanned), the relationship is substantially conjugated. " By doing so, when a rotating two-sided mirror or a rotating polygonal mirror is used as the optical deflector, the influence of surface tilt can be eliminated. In the case of the optical scanning device according to the eighth aspect, as in the fourth aspect of the present invention, "a plurality of beams combined are
In the case of "crossing in the vicinity of the deflecting reflection surface of the optical deflector", the scanning imaging optical system causes each beam to be a predetermined part in the It is natural that they are separated by intervals.

[0012] In the optical scanning device according to any one of claims 2 to 8, the "interval in the sub-scanning direction" of the plurality of light spots for simultaneously scanning the surface to be scanned is an integral multiple of the pitch of the scanning line. In particular, adjacent lines can be simultaneously scanned as the "interval corresponding to the pixel density" (claim 9). In such an optical scanning method for simultaneously scanning adjacent lines, modulation of a light spot is easy.

The beam combining optical element according to the present invention can combine three or more beams, but can easily combine two beams from two light sources. Therefore, in the optical scanning device according to any one of claims 2 to 9,
It goes without saying that the number of independent light sources can be two (claim 10). In this case, the angle of incidence of the beam incident on the first surface of the beam combining optical element from the first light source and the angle of incidence of the beam incident on the second surface of the beam combining optical element from the second light source (Embodiment 11), the beam width of each light beam emitted from the beam combining optical element can be made substantially equal to each other even if the coupling and beam shaping of the beam from each light source are performed in exactly the same manner. The spot diameter of the light spot formed on the scanning surface can be made substantially the same.

According to a twelfth aspect of the present invention, there is provided an optical scanning apparatus comprising: "combining a plurality of independent beams from a plurality of light sources as beams forming a small angle with each other; and combining the combined beams by a common optical deflector. Deflected, separates each deflected beam from each other, condenses each separated deflected beam as a light spot on a separate scanned part by a corresponding scanning imaging optical system, and separates each scanned part separately. Optical scanning device for optical scanning "
Wherein a plurality of independent beams from a plurality of light sources are
A beam combining optical element according to claim 1 is used as a beam combining optical element for combining beams forming a small angle with each other.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, numerals 10 and 11 are semiconductor lasers as "light sources", numerals 12 and 13 are coupling lenses, numerals 14 and 15 are apertures, numeral 16 is a beam combining optical element, numeral 17 Is a cylindrical lens as a “line image forming optical system”, reference numeral 18 is a rotating polygon mirror as an “optical deflector”, reference numeral 19 is an fθ lens as a “scanning optical system”, and reference numeral 20 is a “scanning surface”. Reference numeral 21 denotes a beam detecting element formed by a photo sensor. Semiconductor laser 1
The beams radiated from 0 and 11 are coupled to subsequent optical systems by coupling lenses 12 and 13, respectively. The coupling action of the coupling lenses 12 and 13 is a “collimating action”, and the coupled light fluxes become “parallel light fluxes”. Each of the coupled beams is blocked by the apertures 14 and 15 at the periphery of the light beam, and is "beam-shaped" into a predetermined light beam cross-sectional shape. The beam-shaped beams are combined by the beam combining optical element 16 as “beams that make a small angle to each other”, are focused by the cylindrical lens 17 in the sub-scanning corresponding direction (the direction perpendicular to the drawing), and are An image is formed in the vicinity of the deflecting reflection surface as a long line image in the main scanning corresponding direction. Note that a “concave cylindrical mirror” can be used instead of the cylindrical lens 17.

Each beam reflected by the deflecting / reflecting surface of the rotary polygon mirror 18 is incident on the fθ lens 19 while being deflected at a constant angular velocity with the rotation of the rotary polygon mirror 18 at a constant speed. The light is condensed on the top as “two light spots separated in the sub-scanning direction”, and the scanning line L
Optical scanning is performed simultaneously on two lines of 1 and L2. fθ lens 19
Prior to the start of optical scanning, each beam transmitted through is sequentially detected by the beam detecting element 21, and a synchronization signal for starting optical scanning by each beam is issued based on a detection signal for each beam. The interval (pitch) between the scanning lines L1 and L2 that are simultaneously scanned by each beam is set to “an interval corresponding to the pixel density (for example, 42.3 μm if the pixel density is 600 dpi)”.

The beam combining optical element 16 is a "transparent material"
And has a first surface 16A, a second surface 16B, and an emission surface 16C. The beam having passed through the aperture 14 enters the first surface 16A, is refracted, enters the beam combining optical element 16, and exits from the exit surface 16C.
The beam passing through the aperture 15 is converted to a second surface 16B.
Is incident on the beam combining optical element 16 and
After being totally reflected by the surface 16A, the light exits from the exit surface 16C. The two beams emitted from the emission surface 16C form a “small angle” with each other, and intersect at the position of the deflecting reflection surface of the rotary polygon mirror 18 in FIG.

That is, the beam synthesizing optical element 16 is a beam synthesizing optical element for synthesizing independent beams from the plurality of light sources 10 and 11 as beams forming a small angle with each other, and is formed of a transparent material. A first surface 16A for refracting a beam from one light source 10 and entering the same, a second surface 16B for refracting and entering a beam from another light source 11, a beam incident from the first surface, And an emission surface for emitting another beam incident from the second surface,
The beam incident from the first surface 16A is emitted directly from the emission surface 16C, and the beam incident from the second surface 16B is totally reflected by the first surface 16A and then emitted from the emission surface 16C. (Claim 1).

The optical scanning device shown in FIG. 1 combines a plurality of independent beams from a plurality of light sources 10 and 11 as beams forming a small angle with each other, and combines the combined beams with a common light deflection. The beam is deflected by a beam splitter 18, and each deflected beam is condensed as a plurality of light spots separated in the sub-scanning direction on a surface 20 to be scanned by a common scanning / imaging optical system 19 to simultaneously scan a plurality of lines on the surface to be scanned. 2. A beam combining optical element according to claim 1, wherein the beam combining optical element combines a plurality of independent beams from the plurality of light sources and 11 into beams forming a small angle with each other.
No. 6 is used (claim 2). Then, at least two of the plurality of beams obtained by the beam combining have an angle in the main scanning corresponding direction (claim 3). in this way,
Since the two beams combined are separated from each other in the direction corresponding to the main scanning, each light beam deflected by the rotary polygon mirror 18 can be individually detected by the beam detecting element 21 to start writing of each of the scanning lines L1 and L2. Timing can be set, and good two-beam scanning can be performed. In the embodiment shown in FIG. 1, the directions of the beams emitted from the semiconductor lasers 10 and 11 are adjusted so that the two light spots condensed on the surface to be scanned are separated from each other in the sub-scanning direction. In the direction orthogonal to the drawing of FIG.

FIG. 3 shows another embodiment as an explanatory diagram of only a characteristic portion. FIG. 3 shows the beam combining optical element 1.
6 is an explanatory view in which the optical path after 6 is linearly developed up to the surface to be scanned 20, and the vertical direction in the figure is the sub-scanning corresponding direction. The “light source side portion” from the semiconductor lasers 10 and 11 as light sources to the beam combining optical element 16 is rotated 90 degrees around the “optical axis of the cylindrical lens 17” from the state of FIG. The two beams combined by the combining optical element 16 "have an angle in the direction corresponding to the sub-scanning" (claim 4). These two beams "intersect near the deflecting reflection surface of the optical deflector (rotating polygon mirror 18)" (claim 5). In this case, as described above, the image forming position of the “long line image in the main scanning corresponding direction” formed by each beam so that the light spot of each beam is separated on the surface to be scanned 20 in the sub-scanning direction. (Which is in a conjugate relationship with the scanned surface 20 by the fθ lens 19) is displaced from the beam crossing position.

In the embodiment shown in FIG. 3, the semiconductor lasers 10, 11 and the coupling lenses 12, 13,
The apertures 14 and 15 are in the same plane shown in the drawing, and therefore, the two beams combined are not separated in the main scanning corresponding direction (the direction perpendicular to the drawing). For this reason, the imaging action of the fθ lens 19 with respect to the two beams that scan the surface to be scanned 20 is substantially the same in the main scanning corresponding direction. Image characteristics are equal to each other, and good multi-beam optical scanning can be realized. Also,
Scan lines L1 and L2 scanned simultaneously by each beam
Are set to intervals corresponding to the pixel density.

In each of the embodiments shown in FIGS. 1 and 3, the number of independent light sources is two (claim 10).
The interval in the sub-scanning direction of a plurality of light spots that simultaneously scan 0 is an interval corresponding to the pixel density (claim 9), and the beam is synthesized between the beam combining optical element 16 and the optical deflector 18. A line image forming optical system 17 for forming each of the plurality of beams as a long line image in the main scanning direction in the vicinity of the deflecting and reflecting surface of the optical deflector 18 has a common scanning image forming optical system 19. The vicinity of the deflecting reflection surface and the position of the surface to be scanned are substantially conjugated in the direction corresponding to the sub-scanning.

FIG. 4 shows an optical scanning device according to an embodiment of the present invention. In order to avoid complication, the same reference numerals as those in FIG. The optical scanning device according to the embodiment shown in FIG. 4 combines a plurality of independent beams from a plurality of light sources 10 and 11 as beams forming a small angle with each other, and combines the combined beams into a common optical deflector. (Rotating polygon mirror 18), separates the respective deflected beams from each other, and separates the deflected beams on separate scanned portions (the peripheral surfaces of photoconductors 20A and 20B) by the corresponding scanning and imaging optical system. An optical scanning device that condenses light beams as light spots and individually optically scans each scanned portion, and combines a plurality of independent beams from a plurality of light sources 10 and 11 as beams forming a small angle with each other. The beam combining optical element according to claim 1 is used as the beam combining optical element 16 to perform.

As in the embodiments of FIGS. 1 and 3 described above, the beams from the semiconductor lasers 10 and 11 are converted into parallel light beams by the coupling lenses 12 and 13, and are shaped by the apertures 14 and 15. The two beams combined by the beam combining optical element 16 form a small angle with each other, and are rotated by a rotary polygon mirror 18 by a cylindrical lens 17.
In the vicinity of the deflecting / reflecting surface as a long line image in the main scanning corresponding direction, and cross each other. After passing through the scanning imaging lens 191, the deflected light beams are separated from each other. That is, the beam from the semiconductor laser 10 is reflected by the mirrors 203 and 2.
At 04, the optical path is bent, transmitted through the lens 201, reflected by the mirror 205, condensed as a light spot on the photoconductor 20A, and optically scans the photoconductor 20A. When the beam from the semiconductor laser 11 passes through the scanning imaging lens 191, it passes through the lens 202, is reflected by the mirror 206, is condensed as a light spot on the photoconductor 20 B, and optically scans the photoconductor 20 B. . The scanning imaging lens 191 and the lens 201 form a “scanning optical system” corresponding to the beam from the semiconductor laser 10, and the scanning imaging lens 191 and the lens 202 correspond to the “beam from the semiconductor laser 11” A scanning imaging optical system "is constituted. These scanning image forming optical systems have optical performances equivalent to each other, and have a function (fθ characteristic) of equalizing the speed of light scanning by each light spot.

The configuration as shown in FIG. 4 can form a two-color image by making the color of the toner for developing the electrostatic latent image formed by each beam different. Is performed twice with different toner colors, so that it can be used for color image formation.
"Perform the two-color process twice with different toner colors"
In FIG. 4, two sets of components as shown in FIG. 4 may be directly arranged in the conveying direction of the image carrying sheet. In the configuration shown in FIG. 4, the transfer of the toner image from each photoconductor is performed twice. You may return it.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific embodiment of the beam combining optical element 16 will be described with reference to FIG. As shown in FIG. 2, the beam combining optical element 16 has a quadrilateral “plan view shape”, and as shown in the figure, four corners: θ ₁ , θ ₂ , θ ₃ , θ ₄ , the first theta ₁₁ and the refraction angle: angle of incidence of the plane 16A:
θ ₁₂ , the incident angle on the second surface 16B: θ ₂₁ and the refraction angle: θ ₂₂ , the incident / reflective angle of total reflection on the first surface 16A: θ ₂₃ , and the incident angle of each beam on the exit surface: 16C:
θ ₁₃ and θ ₂₄ and emission angles θ ₁₄ and θ ₂₅ are determined, and the refractive index of the transparent material of the beam combining optical element 16 is set to N.

By the transparent material of N = 1.5118, θ
₁ = 40.85 degrees, θ ₂ = 136.85 degrees, θ ₃ = 47.
3 degrees, θ ₄ = 135 degrees, and the incident angle: θ ₁₁ = 75
Degrees, θ ₂₁ = 75 degrees, other angles (unit: degrees)
Is determined as follows. θ ₁₂ = 39.7, θ ₁₃ = 1.15, θ ₁₄ = 1.74, θ
₂₂ = 39.7, θ ₂₃ = 42, θ ₂₄ = 1.15, θ ₂₅ =
1.74 The angle formed by the two combined beams: θ = 3.48 degrees, which is a “small angle”. The condition that the beam incident from the second surface 16B is totally reflected by the first surface 16A is as follows:
θ ₂₃ is larger than 41.4 degrees, and in this embodiment, θ ₂₃ = 42 degrees satisfies this condition. The small angle formed by the two combined beams: θ = 3.48 degrees
In the embodiment as shown in FIG. 1, when the deflected light beam has an angle of 3.48 degrees in the main scanning corresponding direction, the angle is sufficient for each beam detection element 21 to detect each beam separately.

Here, the invention according to claim 6 will be described.
FIG. 5 shows the relationship between the reflectance and the incident angle (horizontal axis) when a beam is incident on a transparent body having a refractive index of 1.5. The tendency shown in FIG. 5 is general. Even when the refractive index is 1.51118 described in the embodiment, the relationship between the incident angle and the reflectance is substantially the same as that in FIG. It is desirable that the angle of incidence of the beam incident from the outside on the first surface 16A of the beam combining optical element be "60 degrees or more". At this time, considering the light use efficiency, it is preferable that the beam incident from the outside on the first surface 16A be taken into the beam combining optical element as much as possible by refraction. The smaller the reflectivity, the better. For such a reason, it is better to set "a beam incident from the outside on the first surface as" P-polarized light having a lower reflectance "with respect to the first surface (claim 6)".

Since the beam from the semiconductor laser 10 and the beam from the semiconductor laser 11 generally have different angles of incidence on the entrance surface and the exit surface, the semiconductor laser 1
If the light emission intensities of 0 and 11 are the same, the intensities of the two beams emitted from the beam combining optical element may be different from each other due to the difference in the reflectance on each surface. Therefore, in such a case, it is preferable to adjust the light emission amounts of the respective light sources so that the light intensities of the plurality of beams combined by the beam combining optical element become substantially equal.

Incidentally, the semiconductor laser 1 shown in FIG.
The in-plane luminous flux diameters of the beams (parallel luminous flux) from 0 and 11 to the beam combining optical element 16 are E ₁ and E ₂ , respectively, and the luminous flux diameters of these beams emitted from the beam combining optical element 16 are shown in FIG. Let E ₁ ′ and E ₂ ′ be E ₁ ′ = E ₁ · cos θ ₁₂ · cos θ ₁₄ / cos θ ₁₁ · c
os θ ₁₃ E ₂ '= E ₂ · cos θ ₂₂ · cos θ ₂₄ / cos θ ₂₁ · c
the osθ _23. Here, the angles: θ ₁₃ , θ ₁₄ , θ ₂₃ , and θ ₂₄ are all small angles of about several degrees, so that “cos θ ₁₃ {cos θ ₁₄ }
cos θ ₂₃ ≒ cos θ ₂₄ ≒ 1 ”and the refraction angle:
θ ₁₂ and θ ₂₂ depend on the incident angles θ ₁₁ and θ ₂₁ , respectively.
Therefore, to make E ₁ ′ / E ₁ ≒ E ₂ ′ / E ₂ , cos θ
₁₂ / cos θ ₁₁ ≒ cos θ ₂₂ / cos θ ₂₁ , and the refraction angles θ ₁₂ and θ ₂₂ are the refraction angles for the same material, so that if the incident angles θ ₁₁ and θ ₂₁ are equal, the refraction angles are also equal to each other. Therefore, if the incident angles θ ₁₁ and θ ₂₁ to the beam combining optical element 16 are made substantially equal, that is, the first light source 1
0 from the beam incident angle of incident on the first surface 16A of the beam combining optical element 16: a theta _11, the incident angle of the beam entering from the second light source 11 on the second surface 16B of the beam combining optical element 16: If θ ₂₁ is substantially equal (claim 11), E ₁ ′
/ E ₁ ≒ E ₂ ′ / E ₂ holds, and the beam combining optical element 1
By making the luminous flux widths of the two beams incident on the beam 6 the same, the luminous flux widths of the two beams emitted from the beam combining optical element 16 can be made equal, and the two beams having substantially the same diameter on the surface to be scanned by these emitted two beams. You can get a spot. That is, according to the eleventh aspect, the semiconductor laser 1
Coupling lenses 12 and 13 for coupling beams from 0 and 11 and aperture 1 for beam shaping
The same light source can be used for each of the light sources 4 and 15, and the beams from each light source can be similarly coupled and shaped similarly. The optical characteristics of the coupling lens and the shape of the aperture need to be different for each light source. There is no. In the above example, in the above-described embodiment and example, the incident angle is set equal to θ ₁₁ = θ ₂₁ = 75 degrees, and the two incident angles are set equal. In the above embodiments and examples,
The case where two beams are combined by the beam combining optical element 16 has been described, but two or more beams can be made incident on the first surface 16A and / or the second surface 16B to combine three or more beams. Needless to say.

[0031]

As described above, according to the present invention, a novel beam combining optical element and optical scanning device can be realized. The beam combining optical element of the present invention can perform beam combining irrespective of the polarization state of the beam, and can be realized at low cost because an expensive half-wave plate and a polarization separation film are not used. Also,
The optical scanning device of the present invention can be realized at low cost by using the beam combining optical element.

[Brief description of the drawings]

FIG. 1 is an optical scanning device according to the present invention,
FIG. 3 is a diagram for describing one embodiment.

FIG. 2 is a diagram for explaining one embodiment of a beam combining optical element.

FIG. 3 shows the optical scanning device according to the second, fourth, and fifth aspects of the present invention;
It is a figure for explaining another embodiment.

FIG. 4 is a diagram for explaining an optical scanning device according to a twelfth embodiment of the present invention;

FIG. 5 is a diagram for explaining the invention described in claim 6;

[Explanation of symbols]

 10, 11 Semiconductor laser 12, 13 Coupling lens 14, 15 Aperture 16 Beam combining optical element 17 Cylindrical lens 18 Rotating polygon mirror 19 fθ lens 20 Photoconductor

Claims (12)

[Claims] 1. A beam combining optical element for combining independent beams from a plurality of light sources as beams forming a small angle with respect to each other. The beam combining optical element is formed of a transparent material, and refracts a beam from one light source to be incident. A first surface to be refracted, a second surface for refracting a beam from another light source to enter, a beam incident from the first surface, and another beam incident from the second surface. Having a light exit surface, the beam incident from the first surface is directly emitted from the light exit surface, and the beam incident from the second surface is totally reflected by the first surface. A beam combining optical element for emitting light from the emission surface. 2. A method according to claim 1, wherein a plurality of independent beams from a plurality of light sources are combined as beams at a small angle to each other, and the combined plurality of beams are deflected by a common optical deflector. In an optical scanning device that converges on the surface to be scanned by the imaging optical system as a plurality of light spots separated in the sub-scanning direction and optically scans the surface to be scanned simultaneously by a plurality of lines, a plurality of light sources independent from a plurality of light sources are provided. 2. An optical scanning device using the beam combining optical element according to claim 1 as a beam combining optical element for combining the beams as beams forming a small angle with each other. 3. The optical scanning device according to claim 2, wherein at least two of the plurality of beam-combined beams have an angle in the main scanning corresponding direction. 4. The optical scanning device according to claim 2, wherein at least two of the plurality of beam-combined beams have an angle in the sub-scanning corresponding direction. 5. The optical scanning device according to claim 2, wherein a plurality of beams combined cross each other near a deflecting reflection surface of the optical deflector. 6. The optical scanning device according to claim 2, wherein a beam incident on the first surface from the outside is P-polarized light with respect to the first surface. apparatus. 7. The optical scanning device according to claim 2, wherein the light emission amounts of the respective light sources are adjusted such that the light intensities of the plurality of beams combined by the beam combining optical element become substantially equal. An optical scanning device characterized by adjusting. 8. An optical scanning device according to claim 2, wherein each of the plurality of beam-combined beams is arranged between the beam combining optical element and the optical deflector in the main scanning corresponding direction. It has a line image forming optical system for forming a long line image near the deflection reflecting surface of the optical deflector, and the common scanning image forming optical system has a sub-scanning position near the deflection reflecting surface and the position of the surface to be scanned. An optical scanning device having a substantially conjugate relationship in a scanning corresponding direction. 9. The optical scanning device according to claim 2, wherein a distance in a sub-scanning direction between a plurality of light spots for simultaneously scanning a surface to be scanned is a distance corresponding to a pixel density. An optical scanning device characterized by the above-mentioned. 10. The optical scanning device according to claim 2, wherein the number of independent light sources is two. 11. An optical scanning device according to claim 10, wherein an incident angle of a beam incident on a first surface of the beam combining optical element from a first light source, and an incident angle of the beam combining optical element from a second light source. An optical scanning device, wherein incident angles of beams incident on the second surface are substantially equal. 12. A plurality of independent beams from a plurality of light sources are combined as beams at a small angle to each other, the combined beams are deflected by a common optical deflector, and the respective deflected beams are separated from each other. In the optical scanning device, each of the separated polarized beams is condensed as a light spot on a separate scanned portion by a corresponding scanning and imaging optical system, and each scanned portion is individually optically scanned. 2. An optical scanning device, comprising: the beam combining optical element according to claim 1 as a beam combining optical element that combines a plurality of independent beams from a light source into beams that form a small angle with each other.