JPH1073761A - Beam shaping optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to suppress the change in angular magnification to a smaller level even if the incident angle of luminous fluxes changes by setting the incident angles of the reference rays to the respective luminous flux transmission faces of prisms of a beam shaping optical system at specific angles. SOLUTION: The incident angles of the reference rays to the respective luminous flux transmission surfaces of the first and second prisms of the beam shaping optical system having the two wedge-shaped prisms having the main sections parallel with each other are so set as to satisfy the conditions expressed by the equation. As a result, the primary component (secondary component of the exit angle) of the change in the angular magnification by a difference in the incident angles may be suppressed and the error in the image formation position may be made smaller in the case the images of the luminous fluxes emitted from the first and second prisms are formed on an objective surface. The difference in the exit angle by the change in the incident angle may be suppressed in the quantity of the occurrence of itself. A distortion aberration is imparted to a rotationally symmetrical collimating lens, by which the distortion aberration occurring in the error of the exit angle of the beam shaping optical system is nearly offset.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam shaping optical system for shaping a sectional shape of a light beam, a light source device using the beam shaping optical system, and an imaging optical system.

[0002]

2. Description of the Related Art This type of beam shaping optical system is, for example,
This is disclosed in JP-A-60-175018. As shown in FIG. 7, the beam shaping optical system disclosed in the first embodiment of the publication includes first and second wedge-shaped prisms 1 and 2 arranged in order from the incident side on the left side in the figure. It has the effect of shaping the cross section of a laser beam emitted from a semiconductor laser having an elliptical far-field pattern into a circular shape. The main sections of the prisms 1 and 2 are parallel to each other. Note that the main section of the wedge-shaped prism refers to a plane perpendicular to a ridge line which is an intersection line of two refraction surfaces through which a light beam passes (or an intersection line of an extension surface thereof when the refraction surfaces do not intersect).

In optical devices such as an optical disk device, a magneto-optical disk device, and a laser printer using a semiconductor laser as a light source, the above-described optical devices are generally used in order to effectively use the amount of light and maintain symmetry of a spot formed on a target surface. A simple beam shaping optical system is used. In the above-described optical apparatus, a method of performing processing in parallel with a plurality of light beams has been developed in order to improve the input / output speed of information. As a light source of an apparatus using a plurality of light beams, a multipoint light emitting semiconductor laser having three or more light emitting points in one element tends to be used in order to make the apparatus compact. The principal rays of the light beam emitted from each light emitting point of the multi-point light emitting semiconductor laser emit at different angles from each other at a predetermined angle.

[0004]

However, the conventional beam shaping optical system described in the above publication is designed to correct the cross-sectional shape of a single light beam incident at a predetermined reference angle. When a plurality of light beams having different emission angles, such as light beams emitted from a point-emitting semiconductor laser, are incident, there is a problem that an angular magnification for a light beam incident at an angle other than the reference angle is significantly different from an angular magnification for a light beam incident at a reference angle. is there. Table 1 below shows the incident angle φ (deg.) To the first prism 1 and the exit angle ω (de) from the second prism 2 calculated based on the data of the conventional example described in the above publication.
g.), and the ideal exit angle ψ (deg.) expressed as the product of the paraxial magnification γ ₀ (0.669041 in this example) and the incident angle φ when the magnification is constant. Angle magnification γ at incident angle, change rate γ ′ based on paraxial magnification (= (γ ₀ −γ) /
γ ₀ ) and the exit angle error δ (deg.)
The relationship is shown below.

[0005]

[Table 1] Incident angle φ Exit angle ω Ideal exit angle ψ Angle magnification γ Change rate γ 'Exit angle error δ -2.0 -1.33272 -1.33808 0.66636 0.40% 0.00536 -1.6 -1.06710 -1.07047 0.66694 0.31% 0.00337 -1.2 -0.80098- 0.80285 0.66748 0.23% 0.00187 -0.8 -0.53440 -0.53523 0.66800 0.16% 0.00083 -0.4 -0.26739 -0.26762 0.66848 0.08% 0.00023 0.0 0.00000 0.00000--0.00000 0.4 0.26774 0.26762 0.66935 -0.05% 0.00012 0.8 0.53584 0.53523 0.66980 -0.11% 0.00061 1.2 0.80422 0.80285 0.67018 -0.17% 0.00137 1.6 1.07286 1.07047 0.67054 -0.22% 0.00239 2.0 1.34173 1.33808 0.67087 -0.27% 0.00365

As described above, in the conventional beam shaping optical system, since the change in the angular magnification due to the difference in the incident angle is relatively large, when applied to the optical system of the apparatus using the above-described multi-point light emitting semiconductor laser, Even when the light emitting points on the laser are formed at equal intervals, the distance between the spots formed on the medium due to the difference in the angle of incidence of the luminous flux from each light emitting point of the semiconductor laser to the beam shaping optical system Becomes uneven. Further, the conventional beam shaping optical system has a component in which the exit angle error with respect to the change of the incident angle is represented by a second-order or higher order even function of the incident angle as shown by a broken line in FIG. On the other hand, the distortion aberration of a rotationally symmetric optical system such as a collimator lens or an objective lens is a function of an odd number of the third or higher order of the incident angle. Even if the objective lens or the like has distortion, the distortion due to the beam shaping optical system cannot be corrected.

The present invention has been made in view of the above-mentioned problems of the prior art, and provides a beam shaping optical system capable of suppressing a change in angular magnification to be small even when an incident angle of a light beam changes. A light source device that emits a plurality of light beams using the beam shaping optical system, and
It is an object of the present invention to provide an imaging optical system that can form a plurality of light beams emitted from light emitting points at regular intervals on a target surface at regular intervals.

[0008]

In order to achieve the above object, a beam shaping optical system according to the present invention is a beam shaping optical system having two wedge-shaped prisms whose main cross sections are parallel to each other. The incident angle of the reference light beam with respect to each light flux transmitting surface is set so as to satisfy the following condition (1). The “reference light beam” is defined as a light beam that enters at an angle at which a specified angular magnification is obtained.

[0009]

(Equation 2)

By satisfying the above condition (1), the primary component (secondary component of the exit angle) of the change in the angular magnification due to the difference in the incident angle can be suppressed, and the luminous flux exiting the prism can be reflected on the target surface. In the case where the image is formed, the error of the image forming position can be reduced. For example, when the incident light makes 1 deg. (0.017453 rad.) With respect to the reference light, Σα _j = 0.
If 02, the difference in injection angle is 0.017453 rad. × 0.02
= 0.00035 rad. The error of the image position on the image plane is represented by an integral value of the angular magnification, and a factor of 1/2 is applied. For example, the image point of the reference ray at the incident angle of 0 deg.
If two image points of the deg. ray are arranged at an interval of 1 mm, from 0.00035 / 2 × 1 mm = 0.001774 mm, one image point is 1 + 0.000174 mm from the center image point and the other image point is The point is formed at a position of -1 + 0.000174 mm from the central imaging point.

Next, the process of deriving the above conditional expression will be described below. Note that the symbol “Π” in the equation is an operation symbol indicating the product of all elements. Beam entire system shaping optical system comprising a plurality of prisms are assumed to consist of the L plane from the first surface, when incident on the first surface, the inclination with respect to the reference ray is the ray P is delta ₁ Consider the working angular magnification.

The ratio of the rate of change of the angular magnification per unit change in the incident angle on the j-th surface counted from the incident side to the angular magnification of this surface is ε _j , and the ratio of the reference light beam to the j-th surface is The difference between the incident angle and the incident angle of the ray P is Δ _j , the angular magnification of the j-th surface with respect to the reference ray is γ _j , and the angular magnification of the entire system with respect to the ray P is Γ (Δ ₁ ). The angular magnification of the entire system with respect to the reference ray is Γ (0). Since the angle difference of the light beam P with respect to the reference light beam is converted by the angular magnification of each light beam transmitting surface, the difference between the incident angle of the reference light beam and the light beam P with respect to each light beam transmitting surface is represented by the following equation (2). , (Δ ₁ ) of the entire system with respect to the light ray P is as shown in the following equation (3).

[0013]

(Equation 3)

Here, in the range where the equation (4) is satisfied, the above equation (3) is expressed as the equation (5). Defining the rate of change of the angular magnification for each surface as α _j as in the following equation (6),
(5) is expressed as in equation (7). From equation (7), in order to reduce the change in angular magnification of the entire system due to the change of the incident angle (change in the delta ₁₎ gamma (delta ₁₎ It can be seen that the Shigumaarufa _j may be brought closer to zero.

[0015]

(Equation 4)

Next, the above-mentioned change in the angular magnification will be described using the refractive index of the medium. Assuming that the j-th surface of the beam shaping optical system is a boundary surface, the refractive index of the medium on the entrance side and the exit side is;
The relationship between the incident angle and the refraction angle is defined by Snell's law represented by the following equation (8). When the angular magnification γ _j of this boundary surface is calculated based on Snell's law, it is as shown in the following equation (9).

[0017]

(Equation 5)

Equation (9) is differentiated to obtain a change rate γ _j ′ of the angular magnification γ _j.
Is obtained as shown in Expression (10). Further, the ratio ε _j of the rate of change of the angular magnification per unit change amount of the incident angle with respect to the angular magnification of this surface is a change in which the angular magnification γ _j represented by the above equation (10) is a denominator and a differential value. Using the rate γ _j ′ as a numerator, the following equation (11) is used.

[0019]

(Equation 6)

The beam shaping optical system of the present invention uses the γ _j and ε _j obtained as described above so that Σα _j defined by the above equation (6) approaches 0, specifically, The angle of incidence on each light transmitting surface is determined so that the absolute value of Σα _j is smaller than 0.020. Further, in the beam shaping optical system of the present invention, the principal ray of the light beam emitted from a single light emitting point and refracted by each light beam transmitting surface of the prism is:
It is characterized in that it is set to be included in a single main section.

By arranging the beam shaping optical system according to the present invention at a position where a plurality of light beams emitted from a light source having a plurality of light emitting points and converted into parallel light beams by a collimating lens are made incident, a plurality of shaped parallel light beams are obtained. Can be configured. According to the configuration of the present invention, the generation amount itself of the exit angle error due to the change in the incident angle of the beam shaping optical system can be suppressed to be small. In the configuration of the invention,
Expressing the exit angle error as a polynomial with the incident angle as a variable,
The third order term is the main component that determines the value of the polynomial. Therefore, by giving a distortion (proportional to the cube of the incident angle) to the rotationally symmetric collimating lens, the distortion caused by the exit angle error of the beam shaping optical system can be almost canceled. The distortion given to the collimator lens is a distortion in the negative direction when a parallel light beam is incident from the beam shaping optical system side and the imaging performance is evaluated on the imaging surface on the light source side.

Further, when the beam shaping optical system according to the present invention is used in a light beam imaging optical system, the light beam from the light source device having the above-described configuration is formed into an image on an object surface by an objective lens. . Further, similarly to the case of the above-described collimating lens, the objective lens can be provided with a distortion that cancels the distortion caused by the beam shaping optical system. The distortion given to the objective lens is a distortion in a positive direction when a parallel light beam is incident from the beam shaping optical system side and the imaging performance is evaluated on the target surface. When the beam shaping optical system is used as a light source device as described above or as an imaging optical system, a plurality of light emitting points are arranged so as to be arranged in a line in a direction parallel to the main cross section, or a plurality of light emitting points are mainly used. They are arranged so as to be two-dimensionally arranged in a direction parallel to and perpendicular to the cross section.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a beam shaping optical system according to the present invention will be described below. FIG. 1 shows an optical system of a magneto-optical disk device as a light beam imaging optical system using a beam shaping optical system according to the present invention.

The optical system shown in FIG. 1 uses, as a light source, a multi-point light emitting semiconductor laser 10 having three light emitting points on the same substrate, and uses a collimator lens 20 to collimate three divergent lights emitted from the semiconductor laser 10. And a beam shaping optical system 3 composed of two wedge-shaped prisms 31 and 32
0 is used to correct each cross-sectional shape.

The light beam emitted from the semiconductor laser 10 is divergent light having a different divergence angle in directions orthogonal to each other when viewed from the direction facing the light beam. The divergence angle is small in a direction parallel to the bonding surface of the pn junction and large in a direction perpendicular to the bonding surface. Therefore, the collimator lens 20
Has a cross-sectional shape of an ellipse in which the radius in the direction parallel to the junction surface of the pn junction is smaller than the radius in the direction perpendicular thereto. On the other hand, the emission point of the multi-point emission semiconductor laser is pn
The collimator lens 2 is arranged along a direction parallel to the joint surface of the junction, and the principal rays of each light beam have an angle difference from each other in a plane parallel to the joint surface of the pn junction.
At the point when 0 is emitted, three elliptical light beams whose major and minor axis directions match each other are in a state of juxtaposition along the minor axis direction. The junction surface of the pn junction of the semiconductor laser 10 is shown in FIG.
In the X direction within the plane of the drawing. The beam shaping optical system 30 has a light flux transmission surface perpendicular to the main cross section parallel to the X direction, and by expanding the diameter of each light flux in the X direction, the cross sectional shape of the light flux is made circular. It has a function to get closer.

The light beam emitted from the beam shaping optical system 30 and transmitted through the half mirror prism 41 is divided into two lenses 42
a and 42b, the light enters the objective lens 43 via a relay lens system 42, and is converged by the objective lens and becomes independent on the recording surface of the optical disk 44 as the target surface.
To form two beam spots. The beam spots are formed at equal intervals along the X direction in the figure.

The reflected light from the magneto-optical disk 44 enters the half mirror prism 41 via the objective lens 43 and the relay lens system 42. The light beam reflected by the half mirror surface is rotated by 45 ° in the polarization direction by the half-wave plate 51, and separated into two linearly polarized light components in which the vibration directions of the electric field vectors are orthogonal to each other by the polarized light beam splitter 52. The light enters the light receiving elements 54a and 54b via the optical lenses 53a and 53b. Light receiving elements 54a, 54b
Is a known multi-segment sensor, and outputs a tracking error signal and a focusing error signal. By taking the difference between the outputs of the two light receiving elements 54a and 54b, the magnetic signal recorded on the magneto-optical disk 44 can be read.

The specific configuration of the beam shaping optical system 30 is as follows.
As shown in FIG. An axis parallel to the optical axis of the collimator lens 20 is defined as a reference axis Fx, and the angle of the reference axis with respect to the normal of the j-th surface counted from the incident side on the left side in the drawing (from the normal to the reference axis). An acute angle and a positive sign in the clockwise direction in the figure) is β _j , and an incident angle of the reference ray incident along the reference axis with respect to the j-th surface is θ _j . Assuming that the refractive index of the medium on the incident side from the j-th surface is n _0j and the refractive index of the medium on the exit side is n _1j , the configuration of the beam shaping optical system 30 is as shown in Table 2.

[0029]

TABLE 2 Surface number _{β n 0 n 1 θ γ ε} α 1 52.389 1.00000 1.63552 52.3890 0.4265 -1.0619 -1.0619 2 15.725 1.63552 1.00000 7.6938 1.6611 -0.2377 -0.1014 3 -33.556 1.00000 1.59631 61.9291 0.3537 1.6405 1.1623 4 0.000 1.59631 1.00000 0.0000 1.5963 0.0000 0.0000

The angular magnification γ _j of each light transmitting surface and the rate of change of the angular magnification per unit change of the incident angle on the j-th surface counted from the incident side of the change in the angular magnification with respect to the angular magnification of this surface The ratio ε _j and the rate of change α _j of the angular magnification for each surface are as shown in Table 2. In this configuration, the product of γj Πγ _j = 0.
4000, the sum of α _j Σα _j = −0.0010, and the above condition
(1) is satisfied.

Table 3 below shows the incident angle φ (deg.) To the first prism 31 and the second prism 3 according to the configuration of the above embodiment.
2 and the paraxial magnification γ0 assuming that the magnification is constant (0.40006 in this example).
6) and the incident angle φ, the ideal exit angle ψ (deg.), The angular magnification γ at each incident angle, and the change rate γ ′ based on the paraxial magnification (= (γ ₀ −γ) / γ ₀ ) and the exit angle error δ (deg.) represented by ω−ψ.

[0032]

[Table 3] Incident angle φ Exit angle ω Ideal exit angle ψ Angle magnification γ Change rate γ 'Exit angle error δ -2.0 -0.79919 -0.80013 0.39960 0.12% 0.00094 -1.6 -0.63962 -0.64011 0.39976 0.08% 0.00049 -1.2 -0.47988- 0.48008 0.39990 0.04% 0.00020 -0.8 -0.31999 -0.32005 0.39999 0.02% 0.00006 -0.4 -0.16002 -0.16003 0.40005 0.00% 0.00001 0.0 0.00000 0.00000--0.00000 0.4 0.16002 0.16003 0.40005 0.00% -0.00001 0.8 0.31999 0.32005 0.39999 0.02% -0.00006 1.2 0.47987 0.48008 0.39989 0.04% -0.00021 1.6 0.63961 0.64011 0.39976 0.08% -0.00050 2.0 0.79918 0.80013 0.39959 0.12% -0.00095

The relationship between the incident angle and the exit angle error in this configuration is shown by the solid line in the graph of FIG. The broken line in the figure shows the emission angle error δ of the beam shaping optical system described in the gazette described in the related art section for comparison. By comparing Table 1 and Table 3, it can be understood that the beam shaping optical system according to the embodiment has a smaller rate of change in angular magnification due to a difference in incident angle than the conventional example. Further, as shown in the graph of FIG. 3, the emission angle error δ between the ideal emission angle and the actual emission angle when there is no change in the angular magnification is within the range of the incident angle ± 2 deg. / 4 ~
It can be reduced to about 1/5. Further, in the conventional example, the exit angle error δ appears as a function of the second order or more and even order of the incident angle, but in the example of the embodiment, it is expressed as a function of the third order or more of the odd order.

Incidentally, as in the above embodiment, the magneto-optical disk is used.
When used as a beam shaping optical system for
A 1.6 μm track-width magneto-optical device commonly used today
Image position due to the difference in angular magnification when applied to optical discs
Level at which misalignment is detected as a tracking error
If we try to keep it below, the sum of the rate of change of angular magnification Σα _j
Condition that the absolute value of is less than 0.003
(1) Stricter conditions are required to be satisfied. Implementation form
Beam shaping optics can meet these more demanding requirements
Suitable for application to the optical system of magneto-optical disks
ing.

Next, a description will be given of the distortion caused by the beam shaping optical system constituted by combining the above-described prisms, and means for correcting the distortion. The distortion generated by the beam shaping optical system includes
First, the aberration based on the exit angle error due to the change in the angular magnification due to the difference in the incident angle, and second, the lateral magnification of the imaging system is the tangent ratio (tanφ / tanω) between the incident angle φ and the exit angle ω. Whereas, the angular magnification of the beam shaping optics is
There is an aberration based on the mismatch defined by (φ / ω).

The distortion caused by the first cause can be reduced by minimizing the change in the angular magnification with respect to the change in the incident angle as in the embodiment, but the beam shaping optics is realized by combining two wedge prisms. In the case of constructing a system, since the angular magnification cannot be made completely constant, it always occurs although it is smaller than the conventional example.
In the beam shaping optical system of the embodiment, the distortion due to the change in the angular magnification is 0.030 × φ with respect to the incident angle φ (deg.).
Occurs at a rate of ² %.

On the other hand, distortion due to the second cause occurs even when the angular magnification is constant with respect to the change in the incident angle. Generally, in imaging via an optical system, the height (image height) of an image point corresponding to one object point from the optical axis is determined by the tangent of the incident angle of the principal ray to the lens and the focal length of the lens. Is determined by On the other hand, since the angular magnification γ of the beam shaping optical system defines that the relationship between the incident angle φ and the exit angle ω is γ · φ = ω, distortion occurs in an image when the angular magnification γ is applied. . In order to prevent distortion, it is necessary to set the relationship between the incident angle φ and the exit angle ω so that γ · tan φ = tan ω. Is difficult to have.

Since the following Table 4 shows only the distortion caused by the second cause, the case where the beam diameter is enlarged in one direction by an ideal beam shaping optical system in which the angular magnification does not change due to the difference in the incident angle is shown. And the amount of distortion generated in the beam shaping optical system by the second cause is shown. ω ₀ (deg.) is equal to γ
・ Ideal injection angle when tanφ = tanω ₀ is satisfied, ω
(deg.) is a calculated exit angle when the beam shaping optical system satisfies γ · φ = ω, and it is assumed that the angular magnification γ is constant at 0.400 in each case. D is the distortion represented as the ratio of the difference between the calculated exit angle ω and the ideal exit angle ω ₀ (ω ₀ −ω) / ω. In this case, the incident angle φ (deg.) Is 0.00
Distortion occurs at a rate of 86 × φ ² %.

[0039]

[Table 4] Incident angle φ Ideal exit angle ω ₀ Calculated exit angle ω Distortion D 0.0 0.0000 0.000 0.000% 1.0 0.4000 0.400 0.009% 2.0 0.8003 0.800 0.034% 3.0 1.2009 1.200 0.077% 4.0 1.6022 1.600 0.140% 5.0 2.0043 2.000 0.220% 6.0 2.4074 2.400 0.310% 7.0 2.8118 2.800 0.420% 8.0 3.2176 3.200 0.550% 9.0 3.6251 3.600 0.700% 10.0 4.0344 4.000 0.860%

The distortion generated by the beam shaping optical system 30 according to the embodiment has an aberration of 0.1 due to the first and second causes.
030 × φ ² % and 0.0086 × φ ² %, and 0.039 × φ ² %. Therefore, if the incident angle is 2 deg., A distortion of 0.16% occurs. The distortion generated by the beam shaping optical system 30 is:
Correction can be made by offsetting with another lens system. In the optical system of the magneto-optical disk device, the collimator lens 2
By intentionally giving the objective lens 43 a distortion aberration that cancels out the distortion caused by the beam shaping optical system 30, the occurrence of distortion as the whole system can be suppressed.

When the collimating lens 20 is given a distortion, when a parallel light beam is incident from the beam shaping optical system 30 side and the imaging performance is evaluated on the imaging surface on the light source side, the negative direction Distortion. On the other hand, in the case where the objective lens 43 has distortion, a parallel light beam is made incident from the beam shaping optical system 30 side and the magneto-optical disk 44 is provided.
When the imaging performance is evaluated on the target surface where is located, the distortion becomes a positive direction.

In order to cancel the distortion caused by the exit angle error of the beam shaping optical system 30 of the embodiment, the collimating lens 20 needs to have an incident angle φ _c (deg.) With respect to the collimating lens 20. A negative distortion of 0.039 × φ _c ² % is provided. FIG. 4 is a lens diagram showing a specific configuration example of the collimator lens 20 having such a distortion. The collimating lens 20 is a semiconductor laser 1
0 in order from the cover glass 12 side, the first lens 21 which is a meniscus positive lens, and the negative second lens 21 bonded to each other.
Lens 22, positive third lens 23, positive fourth lens 2
4, the biconcave negative fifth lens 25, and the biconvex positive sixth lens
It is composed of a lens 26.

The specific numerical configuration of the collimating lens 20 is shown in Table 5 below. The surface numbers in the table are given from the sixth lens 26 side along the light incident direction when the performance is evaluated, and the first and second surfaces are the sixth lens 26, and the third and fourth surfaces are the same. Fifth lens 25, hereinafter the fifth surface to the first
One surface is a fourth, third, second, and first lens 24, 23, 2
Nos. 2 and 21 and the twelfth and thirteenth surfaces are the cover glass 12
Is shown. The symbol FNo. In the table is the F number, f is the focal length, φ _cmax is the maximum incident angle from the cover glass 12 side, r
Is the radius of curvature, d is the distance between the surfaces, n780 is the refractive index of the medium at a wavelength of 780 nm, and vd is its Abbe number.

[0044]

[Table 5]

FIG. 5 shows that the collimating lens 20 having the above-described configuration is provided from the beam shaping optical system 30 side, that is, the sixth lens.
It is a graph which shows the performance at the time of making a parallel light flux enter from the lens 26 side, (A) is spherical aberration SA and sine condition SC,
(B) shows distortion. FIG. 6 is a ray diagram when the collimating lens and the beam shaping optical system 30 are combined. 3 of the light emitting surface 10a of the semiconductor laser 10
The divergent light beams emitted from the two light emitting points are
0, the beam is converted into a parallel beam, and the beam shaping optical system 3
0 at different incident angles. The beam shaping optical system enlarges the beam diameter in the X direction, which is the arrangement direction of the light emitting points, and emits three parallel beams at different angles.

Table 6 shows the performance when the collimating lens 20 and the beam shaping optical system 30 are combined, and there is no distortion due to the above-mentioned first and second causes with respect to the incident angle φ. Ideal image height hi, actual image height h
r, the value of distortion D obtained by (hr-hi) / hi.

[0047]

[Table 6] Incident angle φ (deg.) Ideal image height hi Real image height hr Distortion D -2.0 0.485266 0.485200 -0.01% -1.6 0.388156 0.388114 -0.01% -1.2 0.291084 0.291062 -0.01% -0.8 0.194040 0.194032 0.00% -0.4 0.097015 0.097014 0.00% 0.0 0.000000 0.000000 0.00% 0.4 -0.097015 -0.097016 0.00% 0.8 -0.194040 -0.194037 0.00% 1.2 -0.291084 -0.391063 -0.01% 1.6 -0.388156 -0.388092 -0.02% 2.0 -0.485266 -0.485121 -0.03%

As shown in Table 6 above, by canceling out the distortion caused by the collimating lens 20 and the distortion caused by the beam shaping optical system 30, for example, when the incident angle is 2 deg. .12% of the distortion of the beam shaping optical system 30 as a whole -0.1.
03%, which is about 1/4.

In the above embodiment, a light source whose light emitting points are arranged in a straight line is used.
Light sources arranged in a dimension can also be used. in this case,
The emission angle error based on the shift of the light emitting point in the direction parallel to the main section can be reduced by using a configuration equivalent to the embodiment. On the other hand, in the direction perpendicular to the main section, the prism has no angular magnification, so that the exit angle error based on the deviation of the light emitting point in this direction can be suppressed to a relatively small value.

[0050]

As described above, according to the present invention, the change in the angular magnification due to the difference in the incident angle of the beam shaping optical system can be reduced. Therefore, even if the incident angle of the light beam changes, the magnification of the beam shaping does not change.For example, when adjusting the emission direction of the light beam, only the incident angle of the parallel light beam incident on the beam shaping optical system is changed. The beam shaping optical system itself need not be adjusted. Also, when shaping a plurality of light beams having different incident angles,
Since each magnification acting on each light beam can be made constant, when multiple light beams emitted from the beam shaping optical system are imaged on the target surface, the image forming points of the light beams incident at a certain angle difference are fixed. It can be formed at intervals.

Further, the lens system used in combination with the beam shaping optical system is intentionally provided with a distortion which cancels the distortion caused by the exit angle error of the beam shaping optical system, so that the entire system can be improved. The amount of generation of distortion can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an optical system of a magneto-optical disk device to which a beam shaping optical system according to an embodiment is applied.

FIG. 2 is an enlarged explanatory diagram of a beam shaping optical system according to the embodiment.

FIG. 3 is a graph showing a comparison of an error of an emission angle between the beam shaping optical system shown in FIG. 2 and a beam shaping optical system of a conventional example.

FIG. 4 is a lens diagram of a collimating lens according to the embodiment.

FIG. 5 is an aberration diagram of the collimator lens of FIG. 4 alone;

FIG. 6 is an explanatory diagram showing an optical path when the beam shaping optical system of FIG. 2 and the collimator lens of FIG. 4 are combined.

FIG. 7 is an explanatory diagram of a prism showing a conventional beam shaping optical system.

[Explanation of symbols]

 Reference Signs List 10 semiconductor laser 20 collimating lens 30 beam shaping optical system 31 first prism 32 second prism 43 objective lens

Claims (13)

[Claims] 1. A beam shaping optical system having two wedge-shaped prisms whose main cross sections are parallel to each other, wherein an incident angle of a reference light beam with respect to each light flux transmitting surface of the prism is defined by the following condition (1).
A beam shaping optical system characterized by being set so as to satisfy the following. (Equation 1) 2. The beam shaping according to claim 1, wherein a principal ray of a light beam emitted from a single light emitting point and refracted by each light beam transmitting surface of the prism is included in the main cross section. prism. 3. A light source device using the beam shaping optical system according to claim 1, comprising: a light source having a plurality of light emitting points; and a collimating lens for converting a light beam emitted from the light source into a parallel light beam. A light source device, wherein the beam shaping optical system is disposed at a position where a plurality of light beams emitted from the collimator lens are incident. 4. A light emitting device according to claim 3, wherein said plurality of light emitting points are arranged in a line in a direction parallel to said main cross section.
The light source device according to item 1. 5. The light source device according to claim 3, wherein the collimating lens has a distortion that cancels a distortion caused by the beam shaping optical system. 6. The collimating lens has a negative distortion when a parallel light beam is incident from the beam shaping optical system side and the imaging performance is evaluated on an imaging surface on the light source side. The light source device according to claim 5, wherein 7. The light source device according to claim 3, wherein the light source is a multipoint light emitting semiconductor laser. 8. A light source having a plurality of light-emitting points, a collimating lens for converting a light beam emitted from the light source into a parallel light beam, and two light-emitting points disposed at positions where a plurality of light beams emitted from the collimating lens are incident. A light source device comprising: a beam shaping optical system having the above prism; wherein the collimating lens has a distortion that cancels a distortion caused by the beam shaping optical system. 9. The collimating lens has a negative distortion when a parallel light beam is incident from the beam shaping optical system side and the imaging performance is evaluated on an imaging surface on the light source side. The light source device according to claim 8, wherein 10. The light source device according to claim 9, wherein the plurality of light emitting points are arranged in a line in a direction parallel to the main cross section. 11. A light source having a plurality of light-emitting points, a collimator lens for converting a light beam emitted from the light source into a parallel light beam, and two or more light-emitting devices for shaping a cross-sectional shape of the plurality of light beams emitted from the collimator lens. A beam shaping optical system having a prism, and an objective lens for imaging a plurality of light beams shaped by the beam shaping optical system on a target surface, wherein the objective lens is provided on the target surface caused by the beam shaping optical system. An imaging optical system having a distortion that cancels the distortion described above. 12. The objective lens according to claim 1, wherein the objective lens has a positive distortion when a parallel light beam is incident from the beam shaping optical system side and the imaging performance is evaluated on the target surface. 12. The imaging optical system according to item 11. 13. The imaging optical system according to claim 12, wherein the plurality of light emitting points are arranged in a line in a direction parallel to the main cross section.