JP2003057418A - Prism, optical device and optical disk drive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a prism configured to emit two light beams having a different wavelength by making bevels before and after incidence on the prism perpendicular while reducing the emission angle deviation of the two light beams. SOLUTION: A first light beam with a wavelength λ1 and a second light beam with a wavelength λ2 (λ1<λ2) are made incident on the prism at different incidence angles of θ1in and θ1in+Δθ (Δθ<0) from a first plane, respectively, the first and second light beams are reflected on a second plane (internal reflection), and the first and second light beams are again emitted from the first plane. The prism consists of a transparent material having a refractive index n1 (wavelength λ1). An optical constant is set so that the beam intensity distribution of the first and second light beams is shaped from an ellipse (before incidence) into an near circle (after emission), an exit angle deviation from the prism of the first and second light beams is reduced, and the emission light bevels of the first and second light beams are perpendicular to incident light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prism through which two light rays pass, an optical device such as an optical pickup equipped with the prism, and an optical disk drive device equipped with the optical device.

[0002]

2. Description of the Related Art FIG. 5 shows a schematic configuration of an optical device (optical pickup) using a conventional two-wavelength light source. In FIG. 5, the divergent light emitted from the semiconductor laser 11, which is each light source, becomes a parallel light beam by the collimator lens 12, and the angle is almost perpendicular to the information recording medium 16 by the beam shaping prism 13 and the reflection mirror 14. It is changed and focused on the information recording surface of the information recording medium 16 by the objective lens 15. The reflected light from the information recording medium 16 passes through the same optical path, is reflected by the beam splitter 17, the optical path is bent 90 °, and is condensed on the light receiving element 19 by the detection lens 18.

By the way, in the optical device having the configuration shown in FIG. 5, one light source is arranged on the optical axis of the collimator lens 12, but the other light source is arranged at a position off the optical axis of the collimator lens 12. Therefore, the collimator lens 12
The emitted light is obliquely incident on the objective lens 15, and aberration is generated in the light condensed on the information recording surface of the information recording medium 16. Therefore, in order to solve such a problem, in the optical pickup disclosed in Japanese Patent Laid-Open No. 11-296893, as shown in FIG. 6, one of a first light source of wavelength λ1 and a second light source of wavelength λ2 ( λ1 <λ2), the incident angle of the beam having a large wavelength of the light source to the beam shaping prism 13 is
By making the incident angle of the beam having a small wavelength smaller than that of the beam, the beam-shaping prism exit angles of the respective beams are matched to make the beam entering the objective lens vertical.

[0004]

However, as shown in FIG.
In the shape and arrangement of the beam shaping prism 13 as shown in FIG. 6, the inclination angle ρ becomes large before and after the incidence of light rays, and it is necessary to lengthen the layout of the optical components in the beam traveling direction.
That is, there is a problem that the size of the optical device becomes large.

The present invention has been made in view of the above circumstances, and provides a prism having a configuration in which two light beams having different wavelengths are emitted with the inclination angle before and after the incidence on the prism being made right while reducing the emission angle deviation. Further, an optical device having a configuration in which beam shaping is performed by using the prism, the tilt angle before and after the incidence of the prism is made to be a right angle while the deviation of the two beam emission angles is made small, and the optical arrangement can be made compact. It is an object of the present invention to provide a compact optical disk drive device equipped with the optical device.

[0006]

In order to achieve the above object, the invention according to claim 1 provides a first light beam having a wavelength λ1 and a second light beam having a wavelength λ2 (λ1 <λ2) from the first surface. Incidents are made at different incident angles θ1in and θ1in + Δθ (Δθ <0), the first ray and the second ray are reflected (internal reflection) on the second surface, and the first ray and the second ray are again reflected from the first surface. In a prism that emits light rays and is made of a transparent material with a refractive index n1 (wavelength λ1), the beam intensity distribution of the first light ray and the second light ray is shaped from an ellipse (before incidence) to a substantially circle (after emission). ,
The optical constants are set so that the prism exit angle deviation between the first light ray and the second light ray is reduced and the inclination angle of the emitted light with respect to the incident light of the first light ray and the second light ray becomes a right angle. Characterize.

The invention according to claim 2 is characterized in that, in the prism according to claim 1, the optical constants are set so that the beam intensity distribution of the first light ray becomes a circle. Further, the invention according to claim 3 is characterized in that, in the prism according to claim 1, the optical constant is set so that the beam intensity distribution of the second light ray becomes a circle. The invention according to claim 4 provides the prism according to claim 1,
It is characterized in that the optical constants are set so that the prism output angle deviation between the first light ray and the second light ray becomes 0 °. Further, in the invention according to claim 5, in the prism according to claim 4, the optical constant is set so that the beam intensity distribution of at least one of the first light ray and the second light ray becomes a circle. Characterize. Furthermore, claim 6
The invention according to claim 1 is characterized in that in the prism according to any one of claims 1 to 5, a transparent material having a refractive index n ≧ 1.7 is used.

The invention according to claim 7 is an optical device, comprising: a first light source for emitting a first light beam having a wavelength λ1; and a second light source for emitting a second light beam having a wavelength λ2. Item 1
It is characterized in that the prism according to any one of to 6 is provided. The invention according to claim 8 is that, in the optical device according to claim 7, the position of the prism is adjusted in the incident ray direction so that the prism exit positions of the first ray and the second ray coincide with each other. Characterize.

According to a ninth aspect of the present invention, in the optical disc drive device for irradiating the information recording medium with a light beam to record, reproduce or erase information, the optical device is the optical device according to the seventh or eighth aspect. An optical device is used.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the configuration, operation and action of the present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 is a sectional view of a prism showing an embodiment of the present invention. Figure 1
In, the first light ray of wavelength λ1 and the second light ray of wavelength λ2 (λ1 <λ2) are incident from the first surface of the prism 3 at different incident angles θ1in and θ1in + Δθ (Δθ <0). At this time, the two light rays travel toward the second surface at refraction angles θ1out and θ2out. Then, the two light rays are incident on the second surface at incident angles φ1in and φ2in, are reflected (internally reflected) at reflection angles φ1out and φ2out, and head toward the first surface again. Then, it is incident on the first surface at incident angles ψ1in and ψ2in, and the refraction angle ψ1ou
Emit at t, ψ2out. Here, assuming that the space other than the prism is filled with air (refractive index: n = 1), the apex angle of the prism is α, the refractive index of the wavelength λ1 is n1, and the refractive index of the wavelength λ2 is n2. The angle in the plane can be expressed as follows.

[0011]   θ1out = arcsin {(1 / n1) sinθ1in} (1)   θ2out = arcsin {(1 / n2) sin (θ1in + Δθ)} (2)   φ1out = φ1in = θ1out-α (3)   φ2out = φ2in = θ2out−α (4)   ψ1in = φ1out-α (5)   ψ2in = φ2out-α (6)   ψ1out = arcsin {(1 / n1) sin ψ1in} (7)   ψ2out = arcsin {(1 / n2) sin ψ2in} (8)

The beam shaping magnification M1 of the first light beam
Then, the beam shaping magnification M2 of the second light ray can be represented by the product of the shaping magnifications at the refraction portions of the equations (1) and (2) and the refraction portions of the equations (7) and (8). M1 = (cosθ1out / cosθ1in) × (cosψ1out / cosψ1in) (9) M2 = (cosθ2out / cos (θ1in + Δθ)) × (cosψ2out / cosψ2in) (10)

Since the exit angles of the first light ray and the second light ray from the prism 3 can be expressed by the equations (7) and (8), the exit angle deviation Δψ12out of the first light ray and the second light ray is The formula below
It becomes (11). Δψ12out = | ψ1out−ψ2out | (11) Further, the tilt angle ρ of the prism output light with respect to the prism input light
1 and ρ2 are given by the following equations (12) and (13). ρ1 = | θ1in−ψ1out | ... (12) ρ2 = | θ2in−ψ2out | ... (13)

Here, the following value determined by the initial setting of the prism is called an optical constant of the prism. Incident angle of first light ray: θ1in Vertical angle of prism: α Refractive index for first light ray (wavelength λ1): n1 Refractive index for second light ray (wavelength λ2): n2

Next, the structure of claim 1 will be described. Since the conventional transmission type beam shaping prism as shown in FIG. 6 does not have a means for turning the traveling direction of the light beam, the light source is arranged at a position bent at a refraction angle set by the beam shaping magnification, or another surface is used. Since it is reflected by, the optical device becomes large. On the other hand, in the prism 3 having the structure of claim 1 shown in FIG. 1, the two light rays can be freely changed in the traveling direction by being reflected (internal reflection) by the second surface of the prism. However, at the same time, the beam shaping must be performed on the first surface, and the emission direction of the light rays must be set finely. Therefore, instead of simply reflecting the light with a 45 ° mirror, the conditional expression (12), Set the optimum optical constant in (13).

Further, in the conventional optical device using the beam shaping prism, the two light beams emitted from another light source have different angles in the traveling direction as shown in FIG. On the other hand, in the prism having the structure of claim 1 shown in FIG. 1, the deviation is corrected by utilizing the difference in the refractive index depending on the wavelengths of the two light rays. In general, when the transparent material forming the prism is a glass material, the shorter wavelength has a higher refractive index. Therefore,
By making the prism incident angle of the short-wavelength light more obtuse than the long-wavelength light, the refraction angle inside the prism is increased, and the prism exit angle is matched between the short-wavelength light and the long-wavelength light.
At this time, an optical constant is set so that the above-mentioned conditional expression (11) approaches 0.

Generally, the emitted light of a semiconductor laser is
Since the divergence angle of the divergent light differs between the axis parallel to the active layer and the axis perpendicular to the active layer, the intensity distribution of the rays collimated by the collimator lens has an elliptical shape. Therefore, by setting the beam shaping direction of the prism in the minor axis direction of the ellipse, the beam shape of the emitted light approaches a circle (conditional expressions (9) and (10)).

Next, the structure of claim 2 is characterized in that, in the prism of the structure of claim 1, the optical constant is set so that the beam intensity distribution of the first light ray becomes a circle. In particular, the beam shaping magnification is set for a light beam having a short wavelength. For example, the wavelength of the first ray is λ1 = 6
It is assumed that the wavelength of the second light ray is 60 nm, the wavelength of the second light ray is λ2 = 780 nm, and the angle deviation of the incident light is Δθ = 0.6 °. Further, the ratio of the major axis to the minor axis of the ellipse of the incident light intensity distribution shape of the short wavelength light is 2.
If it is 5: 1, M1 may be set to 2.5. Further, the emission angle deviation Δψ12out is ˜0 °, and the inclination angle of the emitted light with respect to the incident light of the first and second rays is ρ1≈ρ2≈90 °.
If desired, the prisms are designed as shown in Tables 1 and 2 below from the above equations (9) to (13). At this time, a glass material EFD4 was used as the transparent material forming the prism.

[0019]

[Table 1]

[0020]

[Table 2]

Next, in the structure of claim 3, in the prism of the structure of claim 1, the optical constant is set so that the beam intensity distribution of the second light ray becomes a circle. In particular, the beam shaping magnification is set for a light beam having a short wavelength. For example, the wavelength of the first ray is λ1 = 6
It is assumed that the wavelength of the second light ray is 60 nm, the wavelength of the second light ray is λ2 = 780 nm, and the angle deviation of the incident light is Δθ = 0.6 °. In addition, the ratio of the major axis to the minor axis of the ellipse of the incident light intensity distribution shape of the long wavelength light is 2.
If it is 5: 1, M1 may be set to 2.5. When it is desired to set the emission angle deviation Δψ12out to be 0 ° and the inclination angle of the emitted light with respect to the incident light of the first and second rays to be ρ1≈ρ2≈90 °, the prisms can be defined by the following formulas (9) to (13). It is designed as shown in Tables 3 and 4. At this time, a glass material EFD4 was used as the transparent material forming the prism.

[0022]

[Table 3]

[0023]

[Table 4]

Next, in the structure of claim 4, in the prism of the structure of claim 1, the prism exit angle deviation Δψ12out of the first light beam of wavelength λ1 and the second light beam of wavelength λ2 is 0 °. , Set the optical constants. For example, the wavelength of the first light ray is λ1 = 660 nm, the wavelength of the second light ray is λ2 = 780 nm, and the angle deviation of the incident light is Δθ = 0.6 °.
Suppose Further, it is assumed that the ratio of the major axis to the minor axis of the ellipse of the incident light intensity distribution shape of the first and second rays is approximately 2.7: 1.
Further, the emission angle deviation Δψ12out = 0 °, the inclination angle of the emitted light with respect to the incident light of the first and second rays is ρ1≈ρ2≈90 °.
Such a prism is designed as shown in Tables 5 and 6 below from the above equations (9) to (13). At this time, a glass material EFD8 was used as the transparent material forming the prism.

[0025]

[Table 5]

[0026]

[Table 6]

Next, in the structure of claim 5, in the prism of the structure of claim 4, the optical constant is set so that the beam intensity distribution of at least one of the first light ray and the second light ray becomes a circle. However, here, in particular, the emission angle deviation Δψ12out of the rays of two wavelengths is 0.
In addition to setting the angle to 0, the beam shaping magnification is set for one of the two wavelengths.
For example, the wavelength of the first light ray is λ1 = 660 nm, the wavelength of the second light ray is λ2 = 780 nm, and the angular deviation of the incident light is Δ.
It is assumed that θ = 0.6 °. Also, assuming that the ratio of the major axis to the minor axis of the ellipse of the incident light intensity distribution shape of the short wavelength light is 2.5: 1,
It is assumed that the beam shaping magnification is set for this ray. Emission angle deviation Δφ12 out = 0 °, M1 = 2.5, inclination angle of emission light with respect to incident light of first and second rays is ρ1≈ρ2≈
The prism having a 90 ° angle is designed as shown in the following Tables 7 and 8 from the above-mentioned equations (9) to (13). At this time, a glass material EFD4 was used as the transparent material forming the prism.

[0028]

[Table 7]

[0029]

[Table 8]

Next, in the structure of claim 6, in the prism of any one of claims 1 to 5, the refractive index n ≧ 1.
The transparent material of No. 7 is used. here,
Assuming that the wavelength of the first light ray is λ1 = 660 nm and the wavelength of the second light ray is λ2 = 780 nm, the angle deviation of the incident light with respect to these two light rays is Δθ ≦ 1 °, and the shaping magnification of the first light ray is Of M1 to 2.5 and an emission angle deviation of Δψ12 out = 0, the inclination angle ρ of the emitted light with respect to the incident light and the refractive index n1 of the transparent material (for example, glass material) forming the prism are The relationship is shown in FIG. Therefore, by using a transparent material (eg, glass material) having a refractive index of n ≧ 1.7, the tilt angle ρ can be made to be a right angle.

Next, the optical device according to claim 7 has a wavelength λ1.
A first light source that emits a first light beam, a second light source that emits a second light beam having a wavelength λ2, and the prism according to any one of claims 1 to 6. And Figure 3
FIG. 1 is a schematic configuration diagram of an optical device showing an embodiment of the present invention, which shows a configuration example of an optical device used as an optical pickup of an optical disc drive device. In FIG. 3, a first light source 1-1 that emits a first light beam having a wavelength λ1 and a second light source 1-2 that emits a second light beam having a wavelength λ2 are provided in the light source unit 1. And a semiconductor laser (L
The divergent light emitted from either one of D) becomes a parallel light beam by the collimator lens 2, is shaped into a beam by the prism 3, and is deflected in a substantially orthogonal direction along the optical path, passes through the beam splitter 7, and is a rising mirror. 4 information recording medium (compact disc (CD) type optical disc, or digital versatile disc (DVD))
(The optical disk of the system, etc.) 6, the angle is changed in a direction substantially perpendicular to the optical recording medium, and the light is focused on the information recording surface of the information recording medium 6 by the objective lens 5. The reflected light from the information recording medium 6 passes through the same optical path and is reflected by the beam splitter 7 to travel the optical path 90.
The light is bent and is focused on the light receiving element 9 by the detection lens 8.

According to the optical device having the structure shown in FIG.
The prism 3 having the configuration described in any one of 1 to 6 is mounted, and the prism 3 has at least a beam intensity distribution of the first light ray and the second light ray from an ellipse (before incidence) to a substantially circular shape (emission). The optical constants are adjusted so that the prism output angle deviation between the first and second rays is reduced and the inclination angle of the emitted light with respect to the incident light of the first and second rays becomes a right angle. Is set. Therefore, since the inclination angle of the emitted light with respect to the incident light becomes a right angle, the layout of the light sources 1-1 and 1-2 and other components becomes easy, and the light sources 1-1 and 1-2 become easy.
Since the prism can be arranged at right angles to the traveling direction of the prism output light, the optical device can be downsized.

Next, the optical device according to claim 8 is the optical device according to claim 7.
In addition to the above configuration, the position of the prism 3 is adjusted in the incident light ray direction so that the prism exit positions of the first light ray and the second light ray coincide with each other. FIG. 4 is a schematic configuration diagram of an optical device showing another embodiment of the present invention, which shows a configuration example of an optical device used as an optical pickup of an optical disc drive device. In FIG.
Those denoted by the same reference numerals as those in FIG. 3 are similar components and operate in the same manner. Here, in the structure of claim 8, as shown in FIG. 4, the prism 3 for the first light ray and the second light ray is used.
Of the prism 3 so that the emission positions on the first surface of the
Is arranged by adjusting the position in the direction of the arrow in the figure, and by making the prism exit positions of the first light ray and the second light ray coincide in this way, It is possible to reduce the optical axis shift of the second light beam.

Next, the invention according to claim 9 is an optical disk drive device for irradiating a light beam onto an information recording medium by an optical device to record or reproduce or erase information, and the optical device according to claim 7 or 8 It is characterized in that an optical device having the configuration is used. More specifically, in the optical pickup section of the optical disc drive device, as shown in FIG.
Alternatively, the optical device having the configuration shown in FIG. 4 is mounted, and the optical device having the configuration shown in FIG. 3 or FIG. Has the effect of

Although illustration of the entire optical disk drive device is omitted, the optical disk drive device includes a disk drive unit that holds a CD or DVD optical disk, which is the information recording medium 6, and is rotationally driven by a motor, as shown in FIG. Figure 4
An optical pickup (optical device) having a configuration as shown in
Signal detection for detecting a focus error signal, a tracking error signal, and an information signal by detecting an output signal of a support / moving mechanism portion that supports the optical pickup and moves along the recording surface of the optical disc 6 and a light receiving element 9 of the optical pickup. The circuit, the actuator of the disk drive unit and the optical pickup (the actuator that moves the objective lens in the focus direction and the tracking direction) and the light based on the focus error signal and the tracking error signal from the signal detection circuit or the input information from the operation unit. It is composed of a control circuit for controlling the support / movement mechanism part of the pickup device, an input / output circuit used for connection with an external device, and an operation part for making various settings.

[0036]

As described above, according to the first aspect of the invention, the first light ray having the wavelength λ1 and the second light ray having the wavelength λ2 (λ1 <λ2) have different incident angles θ from the first surface.
1 in, θ1 in + Δθ (Δθ <0) is incident, the first ray and the second ray are reflected (internal reflection) on the second surface, and the first ray and the second ray are emitted again from the first surface. , Refractive index n1
In a prism made of a transparent material of (wavelength λ1), the beam intensity distribution of the first light ray and the second light ray is shaped from an ellipse (before incidence) to a substantially circle (after emission), and By setting the optical constants so that the deviation of the prism exit angle of the ray of light is small and the inclination angle of the emitted light with respect to the incident light of the first ray and the second ray becomes a right angle, Since the inclination angle is right, the layout of the light source and other parts is easy. Moreover, since the deviation of the emission angles of the light rays of the two wavelengths is small, it is possible to reduce the occurrence of aberration when the light rays of the two wavelengths pass through the lens. Further, since the intensity distribution of the light rays becomes substantially circular, it is possible to form spots that are narrowed in both directions in the condensing optical system.

In the invention according to claim 2, in the prism according to claim 1, the optical constant is set so that the beam intensity distribution of the first light ray becomes a circle.
In addition to the above effect, the beam intensity distribution has a circular shape, especially for a light beam having a short wavelength, so that a smaller spot can be formed. Further, in the invention according to claim 3, in the prism according to claim 1, the optical constant is set so that the beam intensity distribution of the second light ray becomes circular,
In addition to the effect of the first aspect, especially for a light beam having a long wavelength, the beam intensity distribution has a circular shape, so that a smaller spot can be formed. Further, in the invention according to claim 4, in the prism according to claim 1, the optical constant is set so that the deviation of the prism exit angles of the first light ray and the second light ray is 0 °. In addition to the effect of 1, the emission angle deviation of the rays of two wavelengths becomes 0,
Since the condenser lens can be arranged perpendicularly to the light rays of the two wavelengths, it is possible to further reduce the occurrence of aberration when passing through the lens. In the invention according to claim 5, claim 4
In the prism described above, by setting the optical constants so that the beam intensity distribution of at least one of the first light ray and the second light ray is circular, in addition to the effect of claim 4, With respect to the light beam having the wavelength of, since the intensity distribution has a circular shape, it is possible to form a smaller spot. Furthermore, the invention according to claim 6 is characterized in that, in the prism according to any one of claims 1 to 5, a transparent material having a refractive index n ≧ 1.7 is used. In the case where is 660 nm and 780 nm, the effect according to any one of claims 1 to 5 can be obtained.

In the invention according to claim 7, as an optical device, a first light source for emitting a first light beam of wavelength λ1 and a second light source for emitting a second light beam of wavelength λ2 are provided.
Since the light source can be arranged at right angles to the traveling direction of the prism-emitted light by providing the prism described in any one of 1 to 6, the optical device can be downsized. Also,
According to an eighth aspect of the invention, in the optical device according to the seventh aspect, the position of the prism is adjusted in the incident light ray direction so that the prism emission positions of the first light ray and the second light ray coincide with each other. Therefore, in addition to the effect of the seventh aspect, in the optical device in which the prism is adjusted in the light beam incident direction, there is no optical axis shift between the two light beams, so that the signal characteristic of the optical device is improved.

According to a ninth aspect of the present invention, in the optical disc drive device for irradiating the information recording medium with a light beam to record or reproduce or erase information, the optical device is the optical device according to the seventh aspect. By using the optical device, the optical device according to the seventh or eighth aspect has a compact shape, and therefore, there is an effect that it does not take up space in the drive and the drive design is facilitated.

[Brief description of drawings]

FIG. 1 is a sectional view of a prism showing an embodiment of the present invention.

FIG. 2 is a tilt angle ρ of emitted light with respect to incident light of a prism according to the present invention, and a refractive index n1 of a transparent material forming the prism.
It is a figure which shows the relationship of.

FIG. 3 is a schematic configuration diagram of an optical device (optical pickup) showing an embodiment of the present invention.

FIG. 4 is a schematic configuration diagram of an optical device (optical pickup) showing another embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of an optical device (optical pickup) using a conventional two-wavelength light source.

FIG. 6 is an explanatory diagram of a relationship between incident light and emitted light when two light rays having different wavelengths are incident on a conventional beam shaping prism.

[Explanation of symbols]

1: Light source unit 1-1: First light source 1-2: Second light source 2: Collimator lens 3: Prism 4: Standing mirror 5: Objective lens 6: Information recording medium 7: Beam splitter 8: Detection lens 9: Light receiving element

Claims (9)

[Claims] 1. A first light ray having a wavelength λ1 and a second light ray having a wavelength λ2 (λ1 <λ2) are incident from the first surface at different incident angles θ1in and θ1in + Δθ (Δθ <0), respectively. In a prism made of a transparent material having a refractive index n1 (wavelength λ1), which reflects (internally reflects) the first light ray and the second light ray and again emits the first light ray and the second light ray from the first surface. , The beam intensity distribution of the first ray and the second ray is shaped from an ellipse (before incidence) to a substantially circle (after emission) to reduce the deviation of the prism exit angle between the first and second rays. The prism is characterized in that the optical constants are set so that the inclination angle of the emitted light with respect to the incident light of the first light ray and the second light ray becomes a right angle. 2. The prism according to claim 1, wherein the optical constant is set so that the beam intensity distribution of the first light ray becomes a circle. 3. The prism according to claim 1, wherein an optical constant is set so that the beam intensity distribution of the second light ray becomes a circle. 4. The prism according to claim 1, wherein an optical constant is set such that the deviation of the prism exit angle between the first light ray and the second light ray is 0 °. 5. The prism according to claim 4, wherein the optical constant is set so that the beam intensity distribution of at least one of the first light ray and the second light ray becomes a circle. 6. A prism according to claim 1, wherein a transparent material having a refractive index n ≧ 1.7 is used. 7. A first light source that emits a first light beam of wavelength λ1 and a second light source that emits a second light beam of wavelength λ2.
An optical device comprising the prism according to claim 1. 8. The optical device according to claim 7, wherein the position of the prism is adjusted in the direction of the incident light beam so that the exit positions of the prism of the first light beam and the second light beam coincide with each other. . 9. An optical disk drive device for irradiating an information recording medium with a light beam to record, reproduce, or erase information by an optical device, wherein the optical device according to claim 7 is used as the optical device. An optical disk drive device characterized by: