JP2605933B2 - Beam shaping lens and short wavelength laser light source - Google Patents

Description

The present invention relates to a light beam shaping lens for a light wavelength conversion element and a light beam shaping lens used in the field of optical information processing using coherent light or in the field of optical measurement and control. It relates to the short-wavelength laser light source used.

2. Description of the Related Art FIG. 9 shows a configuration diagram of a conventional short wavelength laser light source. In FIG. 9, 21 is a semiconductor laser, 24 is a collimator lens, 25 is a focus lens, and 27 is a light wavelength conversion element. The semiconductor laser 21 mounted on the mount 20 emits the fundamental wave P1. The generated fundamental wave P1 is collimated by the collimator lens 24, and after the polarization direction is rotated by 90 degrees by the half-wave plate 26, the condensed light is condensed by the focus lens 25 and is reflected by the optical waveguide 2 formed on the light wavelength conversion element 27. It enters the optical waveguide 2 from the end. The light is converted into a harmonic P2 in the optical waveguide 2 and emitted to the outside. The harmonic P2 emitted to the outside is converted into parallel light by the light beam shaping lens 30. The shaping of a harmonic (wavelength: 0.42 μm) of a fundamental wave having a wavelength of 0.84 μm by a conventional light beam shaping lens will be described in detail with reference to FIG. FIG. 10 is a sectional view of the light wavelength conversion element 21 and the conventional light beam shaping lens 30. (See Ito et al., JP-A-1-280720) The light beam shaping lens 30 has a conical shape that is symmetrical about the a-axis, and the apex 31 of the cone is the peak of the Cherenkov light, which is a harmonic of the light wavelength conversion element 21. It is on the side opposite to the emission surface 3. When light of the fundamental wave P1 from the semiconductor laser is incident on the incident surface 5 of the buried optical waveguide 2 formed on the LiNbO ₃ substrate 1, the effective refractive index of the guided mode of the fundamental wave and the effective refractive index of the higher harmonic wave are increased. When the condition for equality is satisfied, the LiNbO ₃ substrate 1
The light of the harmonic P2, which is the Cherenkov light, is efficiently radiated therein and operates as an optical wavelength conversion element. When radiated out of the substrate, the harmonic P2 is refracted by Snell's law and radiated at a larger angle with respect to the a-axis. This Cherenkov light is made parallel by the light beam shaping lens 30. The light beam shaping lens 30 functions like a prism in one section. For this reason, the Cherenkov light is parallel to all of the figures shown in FIG. 10 when the figure is rotated around the rotationally symmetric axis a. Explaining concretely using numerical values, when laser light having a wavelength of 840 nm is incident on the light wavelength conversion element, the emission angle φ from LiNbO ₃ becomes 52 degrees, and the glass material LaK14 (refractive index 1.716, wavelength 420 n
33 m is obtained as the apex angle α using m). When the light beam shaping lens 30 manufactured under these conditions is arranged in front of the light wavelength conversion element 21 and the vertex 31 of the light beam shaping lens 30 is placed on an extension of the optical waveguide 2, the harmonic P2 becomes parallel to the a-axis and a The Cerenkov light, which is a harmonic wave around the axis, has a parallel height.

PROBLEM TO BE SOLVED BY THE INVENTION As described above, in the conventional light beam shaping lens, it is actually difficult to convert the light into perfect parallel light, and it has been difficult to collect harmonics to the diffraction limit. That is, the apex angle α of the light beam shaping lens is uniquely determined by the emission angle φ of the harmonic, and conversely, when the oscillation wavelength of the semiconductor laser is shifted or when the spectrum of the oscillation wavelength is wide, after passing through the light beam shaping lens. The light deviates from the parallel light, or becomes light in which the harmonics have a spread. This will be described in detail with reference to the drawings. FIG. 11 shows a cross section of a conventional light beam shaping lens. The harmonics P2 emitted from the optical wavelength conversion element 21 have different wavelengths, so that the emission angle from the optical wavelength conversion element differs. For example, in the light beam shaping lens 30 designed to be parallel to the wavelength λ1, an angle shift from the a-axis occurs for a harmonic of the wavelength λ2.
For this reason, there is a problem that if light deviated from such parallel light is condensed, it becomes difficult to collect light due to aberration.

Means for Solving the Problems The present invention enables perfect parallel emission of a harmonic pattern after passing through a light beam shaping lens by adding a new device to the shaping lens of Cerenkov light in order to solve the above problems. Things.

For this purpose, the light beam shaping lens of the present invention is made of a material that is transparent to Cerenkov light radiated from the light wavelength conversion element formed of the substrate on which the optical waveguide is formed and has a large wavelength dispersion, and has a first conical portion. And a means having a portion having the shape of the second cone and the center axis of the first cone coincides with the center axis of the second cone.

Further, the short wavelength laser light source of the present invention is a light wavelength conversion element comprising a substrate on which an optical waveguide is formed, and a light beam shaping made of a material which is transparent to Cerenkov light emitted from the light wavelength conversion element and has a large wavelength dispersion. A lens and a semiconductor laser, wherein the light beam shaping lens is positioned in an extended line of the Cerenkov light emitted from the optical wavelength conversion element, and the vertex of the cone is arranged on the extension of the optical waveguide, and the Cerenkov of the optical wavelength conversion element is disposed. Means is used in which the light emitting surface side and the apex of the cone are arranged to face each other.

Function By the above means, it is possible to convert the Cherenkov light, which is a higher harmonic wave emitted in different directions for different wavelengths emitted from the optical wavelength conversion element, into a complete parallel light, and to condense it to the diffraction limit. Becomes

Embodiment An embodiment of the short wavelength laser light source of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of a blue laser light source, which is a kind of short wavelength laser light source constituted by using the light beam shaping lens of the present invention. This blue laser light source is composed of a light wavelength conversion element 27 composed of a LiNbO ₃ substrate on which an optical waveguide 2 manufactured by a proton exchange method is formed, a light beam shaping lens 30, a semiconductor laser 21, and a high frequency power supply which is a power supply for driving the semiconductor laser 21. Basically configured. Optical waveguide (proton exchange optical waveguide) fabricated on LiNbO ₃ substrate 1 by proton exchange method
Has good uniformity of generated harmonics. The operation of the blue laser light source will be briefly described. The fundamental wave P1 emitted from the high-frequency driven semiconductor laser 21 is a collimator lens
After being converted into parallel light by 24, the light enters the optical waveguide 2 formed in the light wavelength conversion element 27 by the focus lens 25. Here, the semiconductor plate 26 is for adjusting the polarization directions of the semiconductor laser 21 and the optical waveguide 2. The incident fundamental wave P2 is converted into a high frequency P2 by the optical waveguide 2, radiated into the LiNbO ₃ substrate 1, and emitted from the end face to the outside of the optical wavelength conversion element 27. Since this high frequency P2 becomes Cerenkov ring-shaped divergent light (Cherenkov light), it is collimated by the light beam shaping length 30 and emitted to the front of the blue laser light source.

Next, the operation of the light beam shaping lens of the present invention will be described in detail with reference to the drawings. FIG. 2 is a sectional view of the light wavelength conversion element 27 and the light beam lens 30. The beam shaping lens 30 is a
A portion 30 that is rotationally symmetric about the axis and has a first conical shape
a and a second conical portion 30b.
The central axis of the first conical shape and the central axis of the second conical shape are both the a-axis and coincide with each other. The difference from the conventional light beam shaping lens is that the apex 31 is opposed to the emission surface 3 side of the harmonic of the light wavelength conversion element 27 and that a material having a large wavelength dispersion is used. In addition, unlike the past, 2
With two conical parts. In FIG. 2, the emission angle θ of the high frequency P2 generated from the fundamental wave P1 into the substrate is represented by the following equation.

cos θ = N / n where n is a high-frequency refractive index, and N is an effective refractive index of a fundamental wave to be guided, and draws a substantially symmetrical Cherenkov ring about an a-axis which is an extension of the optical waveguide. This is generally called Cerenkov light. Further, the refractive index of the substrate is wavelength-dependent, so that the emission angle θ depends on the wavelength of the fundamental wave.

Next, the emission angle φ from the LiNbO ₃ substrate 1 can be expressed by the following equation to satisfy Snell's law.

φ = sin ⁻¹ [nsin θ] As described above, the emission angle φ also changes due to a change in wavelength. That is, φ also changes due to the change in the emission angle θ and the refractive index n due to the wavelength change. FIG. 3 shows the change of the emission angle with respect to the wavelength of the fundamental wave. As the wavelength becomes shorter, the emission angle φ becomes larger. The beam shaping lens 30 is made of a material having a large wavelength dispersion.
Inside, the light having the wavelength λ ₁ , which is a shorter wavelength, has a larger refractive index than the light having the longer wavelength λ ₂ , and the light having the wavelength λ ₁ bends more. Therefore, if the apex angles α1 and α2 of the light beam shaping lens 30 are selected using a material having a large wavelength dispersion, the light beams having different emission angles can be made parallel. Here, the apex angle is an angle from the a-axis which is the central axis.

Description will be made below using specific numerical values. In this embodiment, LiNbO ₃ having a large dispersion is used as a material of the light beam shaping lens. Abbe's number is 18. The Abbe number ν is smaller for a material having a larger dispersion and is defined by the following equation.

ν = (n _d −1) / (n _f −n _c ) where n _d , n _f , and n _c are wavelengths of 587 nm, 486 nm, and 656 n, respectively.
The refractive index at m. The apex angle was calculated so that the harmonics became parallel to the a-axis, and the apex angle α1 was 72 degrees and α2 was 81.5 degrees.
Although the semiconductor laser wavelength generated a mode hop of ± 0.2 nm from 415.0 nm, the higher harmonic emitted from the light beam shaping lens was completely parallel light around the a-axis.

Next, a method for manufacturing a blue laser light source, which is a kind of short wavelength laser light source, will be described. As a method of manufacturing a short wavelength laser light source, first, an optical wavelength conversion element is mounted on a mount 20 in FIG.
The surface on which 27 optical waveguides 2 were formed was bonded. next
A focus lens 25 and a semiconductor plate 26 having an NA of 0.6 were inserted into the mount 20 and fixed. Next, after inserting the collimator lens 24 and the semiconductor laser 21 having an NA of 0.3, the semiconductor laser
Then, the collimator lens 24 and the semiconductor laser 21 are moved so that the fundamental wave P1 is focused on the incident portion of the optical waveguide 2 of the optical wavelength conversion element 27 so that the output harmonic wave P2 is maximized and fixed. Was done. After that, the beam shaping lens 30
Was mounted on the mount 20. The light beam shaping lens 30 was cut in half to be fixed to the mount 20. Optical wavelength conversion element 27
The vertex 31 of the light beam shaping lens 30 is arranged on an extension of the optical waveguide 2 formed in the above, so that the harmonic P2 is emitted in parallel. In FIG. 1, the semiconductor laser 21 has an oscillation wavelength of 830 nm, a constant current is applied from a CW power supply, and a sine-shaped high frequency (1 GHz) is applied from a high-frequency power supply, and a fundamental wave P1 having an average power of 40 mW is emitted. This fundamental wave P1 is the lens 24,2
Using 5 and the half-wave plate 26, the light was incident on the optical wavelength conversion element 27, and a harmonic P2 was generated. In this optical wavelength conversion element 27, a fundamental wave P1 of 25 mW was incident inside the optical waveguide 2, a harmonic of 1.2 mW was obtained, and the total conversion efficiency was 3%. The emitted high frequency P2 was collimated by the light beam shaping lens 30 and had a divergence angle of 1 mmrad or less. The one using the conventional light beam shaping lens was 10 mmrad. By using the light beam shaping lens of the present invention as in this embodiment, the parallelism can be greatly improved.

In addition, it was confirmed that a light shaping lens was effective for generating harmonics by using an optical wavelength conversion element using a fundamental wave with a wavelength of 0.65 to 1.6 μm, and that the emitted light from a short-wavelength laser light source was collimated. did.

Next, a description will be given of a second embodiment in which the light beam shaping lens of the present invention is made of LiNbO ₃ as in the first embodiment. In FIG. 4, reference numeral 30 denotes a light beam shaping lens, which is a vertex 31 of a convex first conical portion and a second shaved portion.
Has a vertex 32 of a conical portion. The vertical angle α1 is 60
Degrees, α2 is 99.9 degrees. In this embodiment, the fundamental wave output by driving the 830 nm semiconductor laser at high frequency is coupled to the optical wavelength conversion element, and the generated harmonic P2 has a spectrum spread from wavelengths λ1 to λ2. FIG. 5 shows the spread angle from the a-axis with respect to the wavelength of the harmonic after passing through the light beam shaping lens. Actually, harmonics are ± 1 around 415nm
It has a spectral spread of nm. Therefore, the conventional light beam shaping lens had a divergence angle of ± 0.1 degrees, but the light beam shaping lens of the present invention no longer spreads. As shown in this example, the spread could be completely suppressed by using the light beam shaping lens of the present invention.

Next, a description will be given of a _third embodiment in which the light beam shaping lens of the present invention is made of LiNbO ₃ as in the first embodiment. In FIG. 6, reference numeral 27 denotes an optical wavelength conversion element in which the optical waveguide 2 is formed, and reference numeral 30 denotes a light beam shaping lens. The apex 31 of the cone opposes the emission surface 3 of the harmonic of the optical wavelength conversion element 27.
In the light beam shaping lens 30 of this embodiment, there is only one vertex 31 of the cone, and lens processing is simple. The apex angle α1 was 66.2 degrees. Thereby, a parallel light of 2 mmrad or less was obtained. If the apex angle of the cone is less than 60 degrees, the light beam shaping lens becomes too large, so that it is not practical.

Next, a description will be given of a fourth embodiment in which the light beam shaping lens of the present invention is made of a glass material SFS9 as a material. SFS9 is a SF-based glass material that is transparent to harmonics having a wavelength of 415 nm, and has a small Abbe number of 24. In FIG.
Reference numeral 30 denotes a light beam shaping lens having vertices 31 and 32 of a cone. The light beam shaping lens of this embodiment is characterized in that since the material is a glass material, the lens processing is simple and the material is inexpensive. The vertex angle α1 was 68 degrees and α2 was 73 degrees. This gives 2m
Parallel light of mrad or less was obtained.

In this example, SFS9 was used as a material.
Highly dispersed glass materials having an Abbe number of 30 or less, such as 0, are also inexpensive and effective.

Next, as a fifth embodiment, an example in which the light beam shaping lens of the present invention is applied to an organic nonlinear material will be described. FIG. 8 shows the configuration of this embodiment. Reference numeral 27 denotes an optical wavelength conversion element in which MNA, which is an organic nonlinear material, is formed as an optical waveguide 2 in a glass fiber 1a, and reference numeral 30 denotes a light beam shaping lens using ZnS as a material. ZnS has a short absorption edge of 360 nm and a very large dispersion. The fundamental wave P1 emitted from the semiconductor laser propagates in the optical waveguide 2 made of MNA, is converted into a higher harmonic wave P2, propagates through the cladding made of glass, and is emitted to the outside. this
The light with a wide emission angle due to the spectrum spread was completely collimated and emitted by the light beam shaping lens 30 made of ZnS.

Next, an optical information processing apparatus in which the short wavelength laser light source of the present invention is applied to reading of an optical disk will be described as a sixth embodiment. As described in the second embodiment, the harmonic wave is made completely parallel by the light beam shaping lens without spreading. After passing through the polarizing beam splitter, these harmonics are condensed by a focusing lens and form a 0.6 μm spot on the optical disk. The reflected signal again passes through the polarization beam splitter and then enters the light receiver. 2m by high frequency driving at 960MHz using semiconductor laser with wavelength 0.84μm and output 40mW
W harmonics were emitted.

As described above, by using the light beam shaping lens of the present invention as a short-wavelength laser light source in which a semiconductor laser is driven at a high frequency, it is possible to collect light to the diffraction limit and to extract a high-power harmonic. For this reason, it is possible to narrow the spot to half of the reading system of an optical disk using a 0.8 μm band semiconductor laser which has been conventionally used, and to improve the recording density of the optical disk four times.

In addition to the optical disk, the present invention can be used for an optical information processing apparatus such as a laser printer and a plate making machine, which requires light collection.

In the embodiment, the substrate has a large nonlinear optical constant.
Although LiNbO ₃ was used, it is also recommended to use a ferroelectric substance such as LiNbO ₃ or KNbO ₃ , an organic substance, or a substrate with a large nonlinear optical constant such as a compound semiconductor such as ZnS if it can generate high frequency by Cherenkov radiation. it can.

Effect of the Invention As described above, according to the light beam shaping lens of the present invention, by giving a large wavelength dispersion to the material, the semiconductor laser is driven at a high frequency, and the spectrum of the harmonic emitted from the light wavelength conversion element is broadened. Even in the case where the wavelength of the semiconductor laser hops, the harmonics can be made parallel, and the light can be focused to the diffraction limit.

A short-wavelength laser light source incorporating the light beam shaping lens can emit a parallel laser light having a very small spread of 1 mmrad or less, and its practical value is extremely large.

As an optical information processing apparatus incorporating the above short wavelength laser light source, high output and stable short wavelength light can be used, and the recording density and sensitivity are greatly improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a short-wavelength laser light source according to the first embodiment of the present invention, FIG. 2 is a sectional view of a light beam shaping lens according to the first embodiment of the present invention, and FIG. FIG. 4 is a graph showing the dependence of a harmonic emission angle on wavelength, FIG. 4 is a sectional view of a light beam shaping lens according to a second embodiment of the present invention, FIG. FIG. 7 is a sectional view of a light beam shaping lens according to a third embodiment of the present invention, FIG. 7 is a sectional view of a light beam shaping lens according to a fourth embodiment of the present invention, and FIG. FIG. 9 is a sectional view of a conventional short-wavelength laser light source, FIG. 10 is a sectional view of a conventional light-beam shaping lens, and FIG. 11 is a sectional view of a conventional light-beam shaping lens. FIG. It is. 1 ...... LiNbO ₃ substrate, 2 ...... waveguide, 21 ...... semiconductor laser, 27 ...... light wavelength conversion device, 30 ...... beam shaping lens, P2
……harmonic.

Claims (10)

(57) [Claims] A first conical portion made of a material which is transparent to Cerenkov light radiated from an optical wavelength conversion element comprising a substrate on which an optical waveguide is formed and has a large wavelength dispersion, and a second conical portion; A light beam shaping lens having a portion having a conical shape, wherein a central axis of the first cone coincides with a central axis of the second cone. 2. An optical wavelength conversion device comprising a substrate on which an optical waveguide is formed, a light beam shaping lens comprising a material transparent to Cerenkov light radiated from the optical wavelength conversion device and having a large wavelength dispersion, and a semiconductor laser. Wherein the light beam shaping lens is located on an extension of the Cerenkov light emitted from the light wavelength conversion element, and a vertex of a cone is arranged on the extension of the optical waveguide, and the Cerenkov light emission surface side of the front light wavelength conversion element is provided. And a vertex of the cone is arranged to oppose each other. 3. The method according to claim 1, wherein the substrate on which the optical waveguide is formed is LiNb _X Ta.
_{1-X O 3 (0 ≦} X ≦ 1) beam shaping lens according to claim (1), wherein the using the substrate. 4. The method according to claim 1, wherein the substrate on which the optical waveguide is formed is LiNb _X Ta.
_3. The short-wavelength laser light source according to claim 2, wherein a _1- XO.sub.3 (0.ltoreq.X.ltoreq.1) substrate is used. 5. The light beam shaping lens according to claim 1, wherein a SF-based glass material is used as a material. 6. The short-wavelength laser light source according to claim 2, wherein a SF-based glass material is used. 7. The light beam shaping lens according to claim 1, wherein LiNbO ₃ is used as a material. 8. The short-wavelength laser light source according to claim 2, wherein LiNbO ₃ is used as a material. 9. The light beam shaping lens according to claim 1, wherein a material having an Abbe number of 30 or less is used. 10. The short-wavelength laser light source according to claim 2, wherein a material having an Abbe number of 30 or less is used.