JP2002267969A - Optical element using multibeam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element which uses the multibeams emitted from an optical waveguide element and is small in size and is stable by arraying a plurality of waveguides constituted as the optical waveguide element at a high density. SOLUTION: Semiconductor lasers 10 are arrayed at the exit end face of a semiconductor laser array 20 so as to form laser beams having a size X in the respective arraying directions of the semiconductor lasers narrower than the size Y in the direction perpendicular thereto, thereby, the size over the entire part of the optical system is made smaller.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording apparatus such as a laser printer which scans and prints a large number of laser beams emitted from a plurality of semiconductor lasers, that is, multiple beams.

[0002]

2. Description of the Related Art In a laser printer using a multi-beam, the rotation speed of a rotary polygon mirror and the light modulation speed can be reduced by the number of multi-beams.

FIG. 3 is a schematic diagram of a laser printer using a semiconductor laser array 20 in which a plurality of laser elements are formed in parallel by being integrated on a semiconductor substrate. In the figure, each of the multi-beams emitted from the semiconductor laser array 20 is collimated by a collimator lens 1, the beam width is expanded by lenses 2 and 3 as beam expanders, and the photosensitive drum 7 is scanned by a rotary polygon mirror 5. are doing. Cylindrical lens 4
Is for correcting a scanning line pitch error on the photosensitive drum due to the inclination of the reflection surface of the rotary polygon mirror 5.

The scanning lens 6 narrows the beam scanned by the rotary polygon mirror 5 onto the photosensitive drum 7. Since the beam interval of the multi-beams narrowed down on the photosensitive drum is larger than the spot diameter 8 as shown in FIG. 3, the multi-beams are scanned obliquely with respect to the scanning direction, and the intervals between the scanning lines are adjusted appropriately. I have to. Note that a virtual plane including a beam scanned by the rotating polygon mirror is called a scanning plane, a direction parallel to the scanning plane and perpendicular to the optical axis is defined as an x direction, and a direction perpendicular to the scanning plane is defined as a y direction.

FIG. 4 shows a state of beam emission from an end face 22 of a conventional semiconductor laser array 20. The optical waveguide 23 from which the beam is emitted is thinner in the layer direction, that is, the y direction, and longer in the array arrangement direction X. The thinning in the layer direction is because forming a defect-free, high-quality layer is a difficult process and requires a lot of time to deposit the layer.

On the other hand, in the horizontal direction, that is, in the x direction, the layer thickness is made thinner and conversely longer, and the volume of laser light guided is increased, thereby increasing the laser light amplification factor.
In addition, if the length is long in the x direction, fine processing becomes easy. However, with such a conventional waveguide end face, an optical system used in an optical recording apparatus becomes extremely large, the entire apparatus becomes large, and the stability due to cost and environmental temperature is not good.

Hereinafter, the cause of the increase in the size of the optical system will be described.

FIG. 5 shows a state in which the beam from the semiconductor laser array 20 is emitted from the end face 22 and then expanded by diffraction at a location called a far field, which is farther from the emission end. Due to diffraction, a narrow beam width widens at the exit end, and a wide beam narrows at the exit end.
In the vicinity of the collimator lens 1, an elliptical shape 25 as shown
Beam cross-sectional shape.

FIGS. 6 and 7 show emission from a semiconductor laser array.
Of the optical system until the focused beam forms an image on the photosensitive drum.
It shows the status of the game propagation. Figure 6 is parallel to the scanning plane
FIG. 7 shows the direction from the direction perpendicular to the scanning plane.
This is defined as the y direction in the optical system viewed. In the figure,
F, f,_1,f_2,f_3,f
₆And the focal length of the cylindrical lens 4 is f_cAnd

In FIG. 6, a beam emitted from the optical waveguide is emitted from the collimator lens 1, becomes parallel light, and enters the beam expanders 2 and 3. The beam emitted from the beam expander 3 becomes parallel light, is scanned by the rotating polygon mirror 5, and is narrowed down on the photosensitive drum 7 by the scanning lens 6.

FIG. 7 shows the propagation state of the light beam (principal light beam) at the center of the two beams emitted from the two optical waveguides. The light beams emitted from the beam expanders 2 and 3 intersect almost at the position of the rotary polygon mirror 5, so that the size of the rotary polygon mirror 5 does not increase even if multiple beams are used. Therefore, the rotary polygon mirror 5 is arranged almost at the focal position of the lens 3.

If the diameter of the beam emitted from the optical waveguide in the x direction (scanning direction) is dx, the beam diameter d _7x narrowed down on the photosensitive drum is given by the following equation.

D _7x = d _x f ₂ f ₆ / f ₁ f ₃ (1) Next, consider FIG. After the beam in the y direction perpendicular to the scanning direction exits the lens 3, it is narrowed by the cylindrical lens 4 to the position of the rotary polygon mirror 5 with a beam diameter d _5y . The focused beam is again focused on the photosensitive drum by the scanning lens 6 at _d7y . The magnification m is given by m = _d7y / _d5y . When the rotary polygon mirror 5 rotates, the reflection surface of the rotary polygon mirror moves before and after the optical axis. The beam diameter d _5y to be narrowed down to the rotary polygon mirror 5 so that the moving range falls within the focus depth of the narrowed beam.
Needs to be set large to some extent. That is, the magnification m is not too large.

A beam emitted from an optical waveguide of a semiconductor laser
The diameter in the y direction (scanning direction) of the _yThen
Beam diameter d narrowed down on the ram_7yIs given by
You.

[0015] _{d 7y = d y mf 2 f} c / f 1 f 3 ...... (2) usually, because it is d _7x = d _7y, equation (1), related from the equation (2) of the following equation.

F _c = d _x f ₆ / d _y m (3) As in the conventional case, the beam emitted from the optical waveguide is long in the array direction as shown in FIG. 4, that is, d _x / d If d _y is large, the focal length f _c of the cylindrical lens 4 from the equation (3) is increased. For the focal length f ₆ of the scanning lens 6 is to ensure a large scanning width, the focal length is long.

On the other hand, there is a problem in setting the magnification m to a large value as described above.
_Has a large focal length fc. The focal length f ₃ of the lens 3 constituting the beam expander is 6, as is apparent from FIG. 7, which should be greater than the focal length f _c of the cylindrical lens 4.

As described above, since the beam 25 emitted from the semiconductor laser array 20 in FIG. 8 is narrow in the array arrangement direction, it is necessary to greatly expand the beam.
The focal lengths of the lens 3 and the cylindrical lens 4 become longer. In the multi-beam scanning, the multi-beams are configured to intersect at the position of the rotary polygon mirror 5 so that the size of the rotary polygon mirror 5 is substantially the same as that of a single beam.

Therefore, the distance between the lens 3 and the rotary polygon mirror 5 must be set to the focal length of the lens 3, and the distance between the lenses 2 and 3 constituting the beam expander is the distance between the lenses 2 and 3. Since the focal length is set to the sum of the focal lengths, as a result, the distance of the optical system from the semiconductor laser array 20 to the rotary polygon mirror 5 becomes longer, and the entire optical system becomes larger. As the size of the optical system increases, the cost increases, and the rigidity of the optical bench holding the optical system becomes insufficient. Therefore, there is a problem that the optical system becomes unstable even when the environmental temperature changes. Incidentally, JP-A-9-159960 can be cited as this kind of technique.

[0020]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to reduce the size of an optical system, such as a semiconductor laser array, which uses multiple beams from an optical waveguide, and to maintain the optical system even when the ambient temperature changes. Reduce the deviation of the entire system,
Be stable.

[0021]

In order to solve the above-mentioned problems, a laser beam having a width smaller than a dimension in a direction perpendicular to the dimension in the arrangement direction of each semiconductor laser is provided on an emitting end face of the semiconductor laser array. In an optical element using a multi-beam.

[0022]

DETAILED DESCRIPTION OF THE INVENTION Namely, in order to solve the problems described above, in the analysis described above, i.e., in formula _{(3) f c = d x} f 6 / d y m ...... (3), d x By reducing the value of / d _y , the cylindrical lens 4
The focal length f _c is reduced, the focal length of the lens 3 constituting the beam expander is reduced, thereby reducing the size of the optical system even in a multi-beam optical system.

That is, according to the present invention, in an optical recording apparatus that emits multi-beams arranged in a row from a multi-beam generating section and scans the optical recording material collectively, the multi-beam generating section includes a single substrate. A semiconductor laser array having a plurality of semiconductor lasers formed thereon, and a single-mode laser beam emitted from the semiconductor laser array has a dimension in the direction of arrangement of the semiconductor laser array at the emission laser end face larger than the dimension in the perpendicular direction. The beam has a narrow width.

Alternatively, besides the semiconductor laser array, an optical waveguide element provided with a plurality of optical waveguides for transmitting light from a plurality of semiconductor lasers to a single substrate on a single substrate is used. Each of the multi-beams emitted from the optical waveguide may be configured such that the dimension in the array arrangement direction is a beam having a width narrower than the dimension in the orthogonal direction at the optical waveguide emission end.

Hereinafter, specific embodiments of the present invention will be described. Semiconductor laser array 2 as an optical element used in the present invention
FIG. 2 shows a beam exit end face of the optical waveguide element 9 or 0. The waveguide end is narrow in a direction parallel to the waveguide arrangement direction. For this reason, the beam 16 emitted from the optical waveguide has an elliptical shape having a narrow width in the direction parallel to the arrangement direction.

That is, the beam 16 is formed such that the dimension in the arrangement direction of the semiconductor lasers 10 is narrower than the dimension in the perpendicular direction. Since the output beam is narrowed in the arrangement direction, the coupling between the laser beam and the adjacent optical waveguide can be kept small even if the interval between the optical waveguides is narrowed, and the optical waveguide array can be arranged with high density. 9D is an end face of the optical waveguide element 9, and 15 is a cross-sectional shape of the optical waveguides 9A and 9B.

FIG. 1 shows the shape of a beam propagating through the optical waveguide element 9 of the present invention. The light from the plurality of semiconductor lasers 10 passes through the corresponding single mode light through the optical fiber 11, and the plurality of optical waveguides 9A, 9A,
9B. Since the light emitted from the optical fiber 11 has a light intensity distribution having a circular cross section, the optical waveguide 9
In order to efficiently guide light to A and 9B, the light incident side 9C has a circular cross-sectional shape as shown by A in the beam. Here, 9D is the end face of the optical waveguide element 9, 15 is the cross-sectional shape of the optical waveguides 9A and 9B, and 16 is the cross-sectional shape of the beam.

At the emission ends 9D of the optical waveguides 9A and 9B, the beam is formed to have an elliptical shape as indicated by B as described above. That is, at the emission end 9D, the dimension X in the arrangement direction of the semiconductor lasers 10 is arranged so as to form a laser beam having a width smaller than the dimension Y in the perpendicular direction. The light emitted from the optical waveguides 9A and 9B is diffracted.
As shown in the figure, the laser beam has a cross-sectional shape having a long width in the arrangement direction of the optical waveguides 9A and 9B.

In the optical system analysis using FIGS. 6 and 7, the derived equation (3) is as follows.

F _c = d _x f ₆ / d _y m (3) In the optical waveguide device 9 of the present invention shown in FIG.
Since the ratio d _x / d _y of the cross-sectional shape of the beam emitted from the end 9B can be set to a small value, the cylindrical lens 4
Can be the focal length f _c of the small, FIG. 6,
The lens 3 constituting the beam expander as described in FIG.
Is also reduced, and the entire optical system can be reduced.

That is, if the beam emitting end face of the semiconductor laser array 20 or the optical waveguide element 9 is narrow in the arrangement direction, the emitted beam radiates at a large divergence angle by diffraction, so that the beam emitted from the lens 3 is emitted. Has a large beam width even if the beam expansion rates of the lenses 2 and 3 are small, and can be narrowed down to a minute light spot by the lens 6. Since the ratio of expanding the beams of the lenses 2 and 3 is given by the ratio of the focal lengths of the lenses 2 and 3, the focal length of the lens 3 can be reduced and the optical system can be made compact.

Next, the beam width in a direction perpendicular to the arrangement direction of the semiconductor laser array 20 or the optical waveguide elements 9 will be described. If the beam width in the direction perpendicular to the arrangement direction of the optical waveguide elements 9 is wide, the outgoing beam emits at a small divergence angle by diffraction. For this reason, the beam width in the direction in which the lenses 2 and 3 as beam expanders are emitted becomes narrow, and the focal length of the cylindrical lens 4 becomes small in order to narrow the position of the rotary polygon mirror 5 with a desired beam width. ,
Even if the focal length of the lens 3 is small, the cylindrical lens 4 can be accommodated between the lens 3 and the position of the rotary polygon mirror 5.

[0033]

As described above, the optical waveguide device for generating a multi-beam according to the present invention can form an array of optical waveguides at high density and can reduce the size of the entire optical system.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a beam propagating through an optical waveguide device shown as an embodiment of the present invention.

FIG. 2 is a diagram showing a beam emitting end face in the optical waveguide device of FIG. 1;

FIG. 3 is a diagram showing a conventional laser printer optical system using a semiconductor laser array.

FIG. 4 is a view showing an output beam at a light output end of the semiconductor laser array of FIG. 3;

FIG. 5 is an explanatory view showing a beam emitted from the semiconductor laser array of FIG. 3;

FIG. 6 is a diagram showing a beam emitted from a conventional semiconductor laser array or optical waveguide element viewed from a direction parallel to a scanning surface.

FIG. 7 is a diagram of a beam emitted from a conventional optical waveguide element viewed from a direction perpendicular to a scanning surface.

FIG. 8 is a diagram showing principal rays of two beams emitted from a conventional optical waveguide element viewed from a direction parallel to a scanning surface.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Collimator lens, 2,3 ... lens, 4 ... Cylindrical lens, 5 ... Rotating polygon mirror, 6 ... Scanning lens, 7 ... Photosensitive drum, 8 ... Light spot array, 9 ... Optical waveguide element, 9A, 9B
... Optical waveguide, 9C ... Incoming side, 9D ... Outgoing side, 10 ... Semiconductor laser, 11 ... Optical fiber, 20 ... Semiconductor laser array, 17 ... End face of optical waveguide element, 15 ... Cross-sectional shape of optical waveguide, 16 ... Cross-sectional shape.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C362 AA14 AA15 AA36 AA43 BA60 BA67 DA08 2H045 BA22 BA33 5C051 AA02 CA07 DA02 DB02 DB22 DB24 DB25 DB30 DC02 DC04 DC07 5C072 AA03 BA13 BA17 DA02 DA04 DA07 DA21 HA02 HA06 HA13 XA

Claims (4)

[Claims] 1. An optical recording apparatus for scanning a laser beam from a semiconductor laser array having a plurality of semiconductor lasers arranged in parallel on an optical recording material through a lens system. An optical element using a multi-beam, wherein the semiconductor lasers are arranged so as to form a laser beam having a width narrower than the dimension in the direction perpendicular to the dimension in the arrangement direction of each of the semiconductor lasers. 2. An optical recording apparatus in which a laser beam from a semiconductor laser array in which a plurality of semiconductor lasers are arranged in parallel passes through a lens system and is collectively scanned on an optical recording material. Connecting an optical waveguide to each of the lasers, and arranging on the emission end face of the optical waveguide a laser beam having a width smaller than a dimension in a direction perpendicular to a dimension in an arrangement direction of each of the semiconductor lasers; An optical element using a multi-beam, characterized by the following. 3. The semiconductor laser array according to claim 1, wherein the semiconductor laser array is arranged on the emission end face such that a dimension in an arrangement direction of each of the semiconductor lasers is smaller than a dimension in a perpendicular direction. Optical element using multiple beams. 4. The optical recording apparatus according to claim 1, wherein a plurality of laser beams output from the emission end of said semiconductor laser array or said optical waveguide are collectively scanned on a photosensitive material by a rotary polygon mirror. An optical element using the multi-beam described in 1 or 2.