JPH02213823A - Light wavelength converting device - Google Patents

Abstract

PURPOSE:To facilitate optical adjusting operation and to obtain a high-level wavelength-converted wave by enabling a convergence optical system to adjust independently the positions of a 1st lens which is relatively small in the absolute value of the focal length and a 2nd lens which is relatively large and arranged on a laser light source side. CONSTITUTION:The convergence optical system 20 which converges a basic wave into a small beam spot and irradiates the waveguide part end surface of a light wavelength converting element 10 with the beam spot is equipped with the 1st lens 21 which is relatively small in the absolute value of the focal length and the 2nd lens 22 which is relatively large in the absolute value of the focal length and arranged on the light source side as compared with the 1st lens 21, and the position of the 2nd lens 22 is adjustable independently of the 1st lens 21. Namely, when the focal length absolute values of the 1st and 2nd lenses 21 and 22 are denoted as f1 and f2, the ratio f1/f2 of the absolute values of both the focal lengths is set small and then the beam spot position is adjusted finely by moving the 2nd lens 22 greatly by the quantity required to move the beam spot position by a certain quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical wavelength conversion device that converts a fundamental wave into a second harmonic of half the wavelength of the fundamental wave. The present invention relates to an optical wavelength conversion device with an improved optical system for inputting to a wavelength conversion element.

(Prior Art) Various attempts have been made to convert the wavelength of laser light (shorten the wavelength) by utilizing second harmonic generation using nonlinear optical materials. Specifically, an optical wavelength conversion element that performs wavelength conversion in this manner is, for example, as shown in [Fundamentals of Optoelectronics JA, YARIV, translated by Kunio Tada and Takeshi Kamiya (Maruzen Co., Ltd.), p.200-204. The bulk crystal type is well known. However, since this optical wavelength conversion element uses the birefringence of the crystal to satisfy the phase matching condition, there is a problem in that even if the nonlinearity is large, a material with no or small birefringence cannot be used.

As an optical wavelength conversion element that can solve the above problems,
A so-called fiber type has been proposed. This optical wavelength conversion element is an optical fiber whose cladding is filled with a core made of a nonlinear optical material, and is published in Journal of the Micro-Optics Research Group of the Japan Society of Applied Physics Vol. 3.
No, 2. An example is shown on pages 28-32. Since this fiber-type optical wavelength conversion element can easily achieve phase matching between the fundamental wave and the second harmonic, research on this fiber-type optical wavelength conversion element has been actively conducted recently. .

Also, for example, JP-A-63-15233, JP-A-63-15
As shown in Japanese Patent No. 234, a two-dimensional optical waveguide type optical wavelength conversion element in which a two-dimensional optical waveguide made of a nonlinear optical material is formed between two substrates serving as a cladding portion is also known. Furthermore, a three-dimensional optical waveguide-type optical wavelength conversion element is also known in which a three-dimensional optical waveguide made of a nonlinear optical material is embedded in a glass substrate and emits a second harmonic wave into the glass substrate. These two-dimensional or three-dimensional optical waveguide type optical wavelength conversion elements also have the above-mentioned features.

Further, in the specification of Japanese Patent Application No. 63-72752, it is described in detail that the sum frequency and the difference frequency are similarly generated by the fiber type wavelength conversion element. Regarding generation of sum-difference frequency in a waveguide type optical wavelength conversion element, a patent application filed in 1986
It is described in detail in the specification of No. 3-72753.

Furthermore, third harmonic generation using third-order nonlinearity is also fully possible.

In the optical waveguide type (including fiber type) optical wavelength conversion elements listed above, the waveguide section is mainly formed from a nonlinear optical material, but the cladding section only or the waveguide section Both the cladding portion and the cladding portion may be formed from a nonlinear optical material. That is, a part of the guided light traveling through the waveguide seeps into the cladding part as an evanescent wave, so if the cladding part is made of a nonlinear optical material, this evanescent wave can be wavelength converted.

(Problem to be Solved by the Invention) However, in the optical waveguide type (including fiber type) optical wavelength conversion element as described above, in order to increase the optical density and increase the wavelength conversion efficiency, it is necessary to The cross-sectional dimension of the wave portion (for example, the core diameter for a fiber type device, the waveguide thickness for a two-dimensional optical waveguide type device) is 1 to 2 μm.
It is often made extremely small. Conventionally, a widely used method for inputting a fundamental wave into such a waveguide is to focus the fundamental wave into a small spot using a focusing optical system and irradiate it onto the end face of the waveguide. When the cross-sectional dimension of the optical element is small as described above, it is necessary to perform optical adjustment with an accuracy of about ±0.1 μm. This will be explained in detail below using an example.

For example, as shown in FIG. 4, a laser beam 15 emitted from a semiconductor laser 16, which is a fundamental wave light source, is passed through a collimator lens 17 to become parallel light, and then passed through an anamorphic prism pair 18 to form a beam cross-sectional shape. Let us consider the case where the beam is made into a perfect circle, focused into a small spot by the focusing lens 50, and irradiated onto the end face of the core 52 of the fiber type optical wavelength conversion element 51. Here, it is assumed that the focal lengths of the collimator lens 17 and the focusing lens 50 are 8 mm and 4 mm, respectively, the diameter of the core 52 is 1.2 μm1, and the spot diameter of the laser beam 15 is the same <1.2 μm. Further, the positional tolerance (in the xSy direction perpendicular to the optical axis) of the narrowed spot with respect to the core end face is approximately ±0.1 μm. The optical adjustments for irradiating the spot of the laser beam 15 concentrically and with the same diameter on the end surface of the core 52 are: ■ Position adjustment of the optical wavelength conversion element 51 ■ Position adjustment of the converging lens 50 ■ Position of the collimator lens 17 Adjustment ■ Considering that it is performed by adjusting the position of the semiconductor laser 16, the tolerance for position adjustment for ■ and ■ is ±0.1 μm, and the tolerance for ■ and ■ is ±0.2 μm. Adjusting the system is extremely difficult.

On the other hand, in order to facilitate the optical adjustment described above, a virtual fiber has been proposed in which a gradient index rod lens is attached to the input end of the optical fiber. Although such a rod lens can be employed, even if it does so, the above-mentioned tolerance will only be about twice as large, and it will not be a significant improvement.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an optical wavelength conversion device that can easily perform optical adjustment for efficiently injecting a fundamental wave from the end face of a waveguide. That is.

(Means for Solving the Problems) The optical wavelength conversion device according to the present invention includes the above-mentioned optical waveguide type optical wavelength conversion element, that is, a cladding portion and a cladding portion with a higher refractive index than the cladding portion. an optical wavelength conversion element having a waveguide section arranged in the waveguide section, at least one of the cladding section and the waveguide section being formed of a nonlinear optical material, and converting the wavelength of a fundamental wave guided through the waveguide section; , an optical wavelength conversion device comprising a laser light source that emits laser light as a fundamental wave, and a focusing optical system that focuses the laser light into a small spot and irradiates the end face of the waveguide, wherein the focusing optical system has a focal point. A first lens with a relatively small absolute value of distance, and a first lens with a relatively large absolute value of focal length.
and a second lens arranged closer to the laser light source than the lens, and the second lens is characterized in that its position can be adjusted independently of the first lens. .

(Function) In the above configuration, when the absolute value of the focal length of the first and second lenses is respectively flsfZ, the amount of movement ΔX of the second lens in the direction perpendicular to the optical axis, and the amount of movement due to this movement. The amount of movement ΔX of the beam spot in the same direction has the following relationship.

ΔX” (ft/fz) ΔX −・−−−−
(1) On the other hand, the amount of movement Δ2 of the second lens in the optical axis direction,
The amount of movement of the beam spot in the same direction due to this movement ΔZ
has the following relationship.

ΔZ= (ft/fz) 2 Δz・・・・・・
(2) In this way, in the device of the present invention, the amount of movement of the second lens required to move the beam spot position by a certain predetermined amount is determined by the ratio of the absolute values of both focal lengths (fl/fz).
It can be made large enough by setting small.

In other words, in this device, the beam spot position can be finely adjusted by moving the second lens significantly.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows an optical wavelength conversion device according to an embodiment of the present invention. This optical wavelength conversion device includes, for example, a fiber-type optical wavelength conversion element 1o, a semiconductor laser 16 that emits a laser beam 15 as a fundamental wave to be wavelength converted, and inputs this laser beam 15 into an optical wavelength conversion element 10. It has a focusing optical system 2o for focusing.

As shown in detail in FIG. 2, the above-mentioned optical wavelength conversion element 10 is as follows.
This is an optical fiber in which a core 11 made of a nonlinear optical material is filled in a hollow portion at the center of a cladding 12. As the nonlinear optical material, it is preferable to use an organic nonlinear optical material with high wavelength conversion efficiency. In this example, 3,5-dimethyl-1-(4nitrophenyl)pyrazole (hereinafter referred to as PR
A) forms the core 11. In addition,
A method for producing a fiber-type optical wavelength conversion element using such an organic nonlinear optical material as a core is described in detail in, for example, Japanese Patent Laid-Open No. 62-231945.

Semiconductor laser (wavelength: 870
The laser beam (fundamental wave) 15, which is a diverging beam emitted from the laser beam (nm) 1
The cross-sectional shape of the beam is shaped into a perfect circle, and the beam is further focused by the focusing optical system 20, and the beam is focused on the end face 11a of the core 11.
The light is focused on a small spot P with the same diameter (1.2 μm in this example) at the top. Thereby, the laser beam 15 enters into the optical wavelength conversion element lo. This fundamental wave 15 has a wavelength of 1/2 (-4
35 nm) into the second harmonic 15'. This second harmonic wave 15' is radiated into the cladding 12, undergoes repeated total reflection between the interface between the outer surface of the cladding 12 and the surrounding medium (usually air), and travels inside the element 10 toward the end face side. Phase matching is
The waveguide mode in the core part of the fundamental wave 15 and the second harmonic 15
′ (in the case of so-called Cerenkov radiation).

From the output end face fob of the optical wavelength conversion element 10, the second
A beam 15'' containing harmonics 15' is emitted. This emitted beam 15'' is passed through a filter (not shown), and a second
Only the harmonic 15' is extracted and used.

Here, in order to increase the input coupling efficiency to the optical wavelength conversion element IO, the laser beam 15 focused on the small beam spot P as described above is applied to the core end surface 11a with an accuracy of, for example, ±0.1 μm. It is necessary to irradiate accurately concentrically and with the same diameter. Therefore, in this device, the focusing optical system 20 includes a first lens (convex lens) 21 with a focal length fl-4 mm and a focal length fz = 2 which is sufficiently longer than that.
00 mm, and a second lens (convex lens) 22 arranged closer to the semiconductor laser 16 than the first lens 21. The second lens 22 is held in a holding frame 24 that is separate from the holding frame 23 of the first lens 21, and independently of the first lens 21 in the optical axis direction 2.
It is possible to move in the XS''/direction that is perpendicular to the optical axis direction and perpendicular to each other.

In the above equation (1), if ΔX-0.1 μm,
In this case f 1/ f z -4/200 = 0.02
Therefore, Δx-5 μm. In other words,
If the position of the second lens 22 in the x and y directions can be adjusted with an error of ±5 μm (this is fully possible), the position of the beam spot P in the X% and Y directions can be adjusted with an error of ±0.1 μm.
It can be done with high precision using m.

Similarly, regarding the two-direction position adjustment of the beam spot P, from the equation (2) above, ΔZ = (4/200) 2Δ2, so the allowable error of the beam spot position can be calculated as ΔZ-±
If it is 1 μm, it will be Δ2−±2.5 mm.

In other words, the position adjustment of the second lens 22 in two directions is ±2'.
, if it is possible to adjust the position of the beam spot P in two directions with an error of ±1 μm (this is also possible).
It can be done with high precision.

Note that even if the second lens 22 with a long focal length is used as described above, the laser beam 15 that is focused on the core end face 11a is ultimately focused on the first lens with a short focal length of f1-4 mm.
Since the light is emitted from the lens 21, the device does not become unnecessarily long.

Next, a second embodiment of the present invention will be described with reference to FIG. In this FIG. 3, elements equivalent to those in FIG. 2 are given the same numbers, and explanations thereof will be omitted unless particularly necessary. In this device, the focusing optical system 20 includes a third lens 33 in addition to the first lens 21 and second lens 22 described above. In this example, the focal length f3 of this third lens 33 is
=2000mm. This third lens 33 is also held in a holding frame 34 different from the holding frames 23.24 described above, and its position can be adjusted independently of the first and second lenses 21.22.

In this case, ΔX=(fx/f3)ΔX, so ΔX=(4/2000)ΔX. Therefore, by moving this third lens 33 and adjusting the position of the beam sub-P in the x and y directions, the first
Compared to the embodiment, optical adjustment can be performed with an order of magnitude higher precision.

In this configuration, it is convenient to use the second lens 22 for comparatively rough fine adjustments and to use the third lens 33 for extremely precise fine adjustments.

In the embodiments described above, a convex lens is used as the second lens 22, but in the present invention, a concave lens may be used as the second lens. Furthermore, the first, second, and third lenses are not limited to single lenses, and combination lenses may be used.

Furthermore, the present invention is similarly applicable to cases where the above-mentioned two-dimensional or three-dimensional optical waveguide type optical wavelength conversion element is used other than the fiber type optical wavelength conversion element. The present invention is applicable not only to the case of converting to a wave, but also to the case of converting to the above-mentioned third harmonic.

(Effects of the Invention) As explained in detail above, in the optical wavelength conversion device of the present invention, a focusing optical system that focuses the fundamental wave into a small beam spot and irradiates it onto the end face of the waveguide of the optical wavelength conversion element, or A first lens having a relatively small absolute value, and a second lens having a relatively large absolute value of focal length and disposed closer to the light source than the first lens. Since the position of the second lens can be adjusted independently of the second lens, even if the position of the second lens is adjusted with relatively rough accuracy, the position of the beam spot can be adjusted with extremely high accuracy. Therefore, according to this device, optical adjustment is facilitated, the fundamental wave input efficiency to the optical wavelength conversion element is increased, and
It becomes possible to obtain high-intensity wavelength-converted waves.

[Brief explanation of the drawing]

Figure 1 is a schematic side view showing an eleventh embodiment of the present invention, Figure 2 is a perspective view showing details of the optical wavelength conversion element of the device of the first embodiment, and Figure 3 is a second embodiment of the present invention. Schematic side view showing an example. FIG. 4 is a schematic side view showing an example of a conventional optical wavelength conversion device. 10... Optical wavelength conversion element 11... Core 12...
・Clad 15...Laser light (fundamental wave)]
6... Semiconductor laser 17... Collimator lens 20... Focusing optical system 21... First lens 22... Second lens 23.24.34.
...Holding frame 33...Third lens

Claims (1)

[Scope of Claims] It has a cladding part and a waveguide part having a higher refractive index and disposed within the cladding part, and at least one of the cladding part and the waveguide part is made of a nonlinear optical material. Become,
an optical wavelength conversion element that converts the wavelength of the fundamental wave guided through the waveguide; a laser light source that emits laser light as the fundamental wave; and a laser light source that focuses the laser light into a small spot and irradiates it onto the end face of the waveguide. In an optical wavelength conversion device comprising a focusing optical system, the focusing optical system includes a first lens having a relatively small absolute value of the focal length, and a first lens having a relatively large absolute value of the focal length.
and a second lens disposed closer to the laser light source than the lens, the second lens being able to adjust its position independently of the first lens. Device.