JPH02123302A - Beam shape correcting prism - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a beam shape correction prism for an optical head used in an optical disk device or the like.

[Prior Art] Laser light emitted from a semiconductor laser has a large divergence angle, and is a beam with different divergence angles in a direction perpendicular to and parallel to the p-n junction surface of the semiconductor laser, Generally, the divergence angle is large in the direction perpendicular to the bonding surface and small in the parallel direction, so the optical axis cross section has an elliptical distribution.

Therefore, various beam shaping prisms for semiconductor lasers have been proposed for condensing the laser light of the semiconductor laser having an elliptical distribution into a circular spot and converting it into a parallel beam having a circular or quasi-circular distribution. The applicant of this application has disclosed the r-semiconductor laser beam-shaping prism 1 of JP-A-63-163322, the "beam-shaping prism" of JP-A-63-197901, and the r-beam shaping prism of JP-A-63-197902. In particular, it prevents fluctuations in the beam exit angle due to changes in wavelength caused by temperature changes and changes in the refractive index of prisms, resulting in relative misalignment between the write and read beams and erase beams in optical disk devices. We are proposing a beam shaping prism that has no

Furthermore, a high-performance semiconductor laser pen that reduces the angular change of the emitted laser output light due to temperature changes and does not produce astigmatism has been proposed in JP-A No. 60-205420 entitled ``Semiconductor Laser Pen''.

These conventional optical heads for optical disk devices all require a beam shaping prism, a polarizing beam splitter (PBS) composed of two prisms, or a phaseless beam splitter.

Furthermore, in the above-mentioned R-beam shaping prism 1 of JP-A No. 63-197901, it is proposed to combine a beam shaping prism with a deflection beam splitter or a phaseless beam splitter. too,
Three types of prisms, each with a different refractive index, were required.

FIG. 3 is a principle diagram of a conventional beam shape correction prism, and as shown, it is formed by combining one prism with a refractive index nl and two prisms with a refractive index n2.

[Problem to be Solved by the Invention] However, since the conventional beam shape correction prism is formed as described above, at least three constituent elements, that is, prisms are required, resulting in the problem that it is not possible to reduce the cost. It had a point.

Therefore, the beam shape correcting prism of the present invention was created in view of this problem, and it is an object of the present invention to provide a beam shape correcting prism that can be configured with even two constituent elements, that is, two prisms, and which can reduce costs. That purpose.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the beam shape correction prism of the present invention has the following configuration. 1st of rate nl
The refractive index when the beam is incident on a medium at an incident angle θ and refracted at a refraction angle φ is further incident on a second medium with a refractive index n2 at an incident angle α and refracted at a refraction angle β. The wavelength dependence is d n n 1
n 2□, and n+'= n
z = dλ no s expressed as □
n.

The following relationship is substantially satisfied, and a deflection beam splitter or a phaseless beam splitter is formed between the first medium and the second medium.

Preferably, the refraction angle from the first medium to the second medium is 45°.

[Operation] The beam enters the first medium of refractive index n+ from the medium of refractive index n0 at an incident angle θ, is refracted at a refraction angle φ, and then enters the second medium of refractive index n2 at an incident angle α. When configured to be refracted at a refraction angle β, the beam passes through a polarizing beam splitter or a phaseless beam splitter formed between the first medium and the second medium.

Preferably, the refraction angle from the first medium to the second medium is 45 degrees so that the laser beam passes through.

[Examples] Preferred embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a principle diagram of a beam shape correction prism.

In FIG. 1, a semiconductor laser 5 and a collimating lens 7 are shown.
A first prism 1 having reflective surfaces IA and IB having a refractive index n1 and a second prism 2 having a refractive index n2 are held in a positional relationship as shown in the figure by holding means (not shown), respectively. has been done.

Further, at the boundary surface 3 between the first prism 1 and the second prism 2, a multilayer film is formed by vapor deposition or the like on the reflective surface of either the first prism l or the second prism 2, and a deflection beam splitter, Alternatively, a phaseless beam splitter is formed.

In such a configuration, the beam B emitted from the semiconductor laser 5 passes through an air layer with a refractive index of no, enters the first prism 1 at an angle θ, is refracted at an angle φ, and passes through the first prism 1 at an angle θ. 1, the light enters the second prism 2 at an incident angle α and is then refracted at an angle β.

Here, the beam shaping correction factor m is cosφ cosβ m wealth COSθ COSα It will be expressed as

Therefore, the color ratio of the beam spread of a general semiconductor laser 5, that is, the color ratio of angles perpendicular to and parallel to the optical axis direction is 2.
4, β=45°, and furthermore, the first prism 1
When the material of the prism 2 is βSc7 manufactured by Hoya Corporation or β7 manufactured by Ohara Corporation, and the material of the second prism 2 is LaFL6, at the laser wavelength λ=830 nm, dn.

-1,844X 10-' nm-'d λ n2 -, -3.296 x 10-' nm-'d λ As a result, θ=67,462°.

FIG. 2 is a diagram illustrating the principle of a beam shape correction prism showing a specific example of an incident angle of θ: 67,462°. In Figure 2, the apex angle is 90.76 as shown.
When the angle is 7°, the beam shaping correction factor m = 2.43
becomes.

Here, when calculating the change in angle β when a ±10 nm variation occurs with respect to the fundamental wavelength of the laser, λ = 830 nm, we get: 128200 m...β = 45°000012 '''λ
== 830nm...β= 45.000051°λ=1340nm ---β= 45.000012°, Δβ±,. 7. is Δβ±tonm44 × 1
It is calculated as 0-'deg.

By the way, in βSC7 which is a single glass, m=
When 2.43 and θ=71.3', Δφ±1or
tm="li:5.6 x 10-'d"eg.

In addition, when ejecting from a medium, the light is further multiplied by n2, so it becomes 6.6X10''''deg, which is about 1/100 of that of a single medium.

When used as a polarizing beam splitter or a phaseless beam splitter, the beam passes from the first prism 1 to the second prism 2, and the reflected light from the disk is used to be reflected on the polarizing beam splitter or beam splitter surface, so β =45° should be guaranteed.

FIG. 4 is a characteristic diagram showing the deflection beam splitter characteristics calculated based on the above conditions, with wavelength plotted on the horizontal axis.
It also shows the transmittance on the vertical axis.

[Effects of the Invention] As described above, the present invention can provide a beam shape correction prism that can be configured with even two constituent elements, that is, two prisms, and can reduce costs.

[Brief explanation of drawings]

Fig. 1 is a diagram of the principle of the beam shape correction prism, Fig. 2 is a diagram of the principle of the beam shape correction prism showing a specific example of the incident angle of θ = 67, 462°, and Fig. 3 is the principle diagram of the beam shape correction prism. FIG. 4 is a diagram showing the principle of a conventional beam shape correction prism. FIG. 4 is a characteristic diagram showing the deflection beam splitter characteristics calculated based on the above conditions. In the figure, 1...first prism, 2...second prism,
3...Multilayer film, n7...Refractive index.

Claims (2)

[Claims] (1) A beam enters a first medium with a refractive index n_1 at an incident angle θ from a medium with a refractive index n_0, is refracted at a refraction angle φ, and then enters a second medium with a refractive index n_2 at an incident angle α. When configured to refract at a refraction angle β, the wavelength dependence of the refractive index is dn/dλ, and n_1'=n_1/n_0, n_2
' = n_2/n_0, the relationship ▲There are mathematical formulas, chemical formulas, tables, etc.▼ is approximately satisfied, and a deflection beam splitter or a phaseless beam splitter is installed at the boundary between the first medium and the second medium. A beam shape correction prism that forms a beam shape. (2) The refraction angle from the first medium to the second medium is 45
2. The beam shape correction prism according to claim 1, wherein the beam shape correction prism has an angle of .degree.