KR100199773B1 - Collecting optical system for laser diode using spherical lenses - Google Patents

Abstract

According to the present invention, when the ratio of the length of the horizontal axis (X) and the vertical axis (Y) of the beam diverging region of the laser diode (Laser-Diode) is different, five spherical lenses are used to make the circular shape requiring the focused beam shape. The present invention relates to a laser optical focusing optical system used, wherein the first and second lenses 10 and 20 and the planar convex third legs 30 each having a predetermined curvature are disposed on a straight line at a predetermined interval to form a third lens ( The first lens group 100 is configured so that the direction of the beam through the 30 is parallel, and the fourth and fifth lenses 40 and 50 having both sides of the predetermined curvature are arranged at a predetermined interval on a straight line. And a second lens group 200 to focus the beam through the fifth lens 50, and the first lens group 100 and the second lens group 200 are aligned in a straight line at a predetermined interval. Because it is arranged to be arranged, it is cheaper than the lens for focusing optical system using expensive cylinder lens or 6 spherical lens It can be processed in a cost and saving processing in accordance with the reduction in the number of lenses and airborne, the characterized in that the arrangement of the lens easier.

Description

Focusing Optics for Laser Diodes Using Five Spherical Lenses

1 is a schematic diagram showing the distribution of an emitting area and an emitting beam of a general laser diode.

FIG. 2 is a front view and cross-sectional view of the emitting beam of the laser diode of FIG.

3 (a), (b), and (c) show traces of vertical focusing, traces of horizontal focusing, and six spherical lenses of a conventional laser diode focusing optical system, respectively. Trace chart of focused optical system for laser diode.

4 (a) and 4 (b) are traces of vertical focusing and traces of horizontal focusing of the laser optical focusing optical system according to the present invention, respectively.

5 (a) and 5 (b) show aberration diagrams of FIGS. 4 (a) and 4 (b), respectively.

6 is an exemplary view through a linewidth selection apparatus in the focusing optical system of the present invention.

* Explanation of symbols for main parts of the drawings

100: first lens group 200: second lens group

300: line width selector 10 50: Lens

LD: laser diode EA: divergence area

LS: Light Spot

The present invention relates to an optical system for focusing a laser beam (Beam) through a laser diode (Laser-Diode), and more particularly, the ratio of the length of the horizontal axis (X) and the vertical axis (Y) of the beam diverging region of the laser diode In this case, it relates to a focusing optical system for laser diodes using five spherical lenses to make a circular shape requiring the shape of the focused beam to be elliptical.

FIG. 1 is a schematic diagram showing distributions of an emitting area and an emitting beam of a general laser diode, and the horizontal axis X of the emitting area EA that emits a beam from a laser diode LD currently used. ) And the length of the longitudinal axis (Y) has a remarkable difference.

Therefore, the diverging beam emitted by the horizontal axis X, which is the long axis of the diverging area EA, has a vertical divergence angle ( ), The diverging beam emitted by the longitudinal axis Y of the diverging area EA has a horizontal divergence angle ( ).

As can be seen in FIG. 1, when the length of the horizontal axis X of the diverging region EA is greater than the length of the vertical axis Y, the vertical divergence angle ( ) Is the horizontal divergence angle ( It has a characteristic larger than).

The reason for this is a phenomenon related to the diffraction theory of the beam, which indicates the general property of the divergent beam of the laser diode.

FIG. 2 is a front view of the laser diode of FIG. 1 and a cross-sectional view of an emitting beam, which shows the shape of a beam which is emitted by the laser beam in the diverging area EA of the laser diode LD.

Here, the part of the area A is mainly the distribution of the horizontal component of the laser beam emitted in the diverging area EA, and the part of the area B is mainly the vertical component of the laser beam emitted in the diverging area EA. Distribution.

In view of the above-described characteristics, an optical system arranged in a lens group is used to focus the divergent laser beam to a desired size. The divergence area EA of a laser diode LD that is commonly used is 50 The horizontal axis (X) and 1.0 A light spot (LS) having a minimum intensity distribution (i.e., a desired laser beam size) of a desired incident beam has a diameter of long and short axes of 206, respectively. , 204 It must be.

The reason for setting the size of the laser beam is to generate a desired TEMOO mode when inducing the size of the beam generated from the laser diode LD to a crystal (not shown) which is a pumping medium. This is because the intensity distribution of the minimum incident beam.

Laser diodes (LD), which are generally used to satisfy the above conditions, have different lengths of vertical and horizontal diverging regions (EA), so that the focusing optical system is composed of a combination of cylindrical, cylindrical or toroidal lenses. The diameter of the major and minor axis of the desired light spot LS is 206, respectively. , 204 Although it is designed to be, but the disadvantage that the distance of each lens disposed is not only long, there is a problem that the number of lenses required and the need to use an expensive lens is inherent.

In order to solve this problem, as shown in FIG. The horizontal axis (X) and 1.0 Using the laser diode LD having the diverging region EA of the longitudinal axis Y of the beam, the minimum intensity distribution of the desired incident beam, that is, the diameters of the long and short axes of the laser beam , 204 In order to obtain a light spot LS having an in size, each lens 1 is used by using a spherical lens 1 and each cylindrical lens 2,3. 3) was made to have a predetermined curvature (Power) and placed at a predetermined interval to obtain the desired diameter of the incident beam.

However, the cylinder lens used here is very expensive (about 10 times more) than the general lens, and it is very difficult to design and process the curvature of the cylinder lens, as well as increase the processing time and achieve the desired light spot. The arrangement is not easy and there is a problem that the space occupied by the lens is enlarged due to the size of the cylinder lens.

In addition, a focusing optical system using six spherical lenses as shown in FIG. 3 (c) has been proposed to solve this problem.

However, the problem of alignment remains because the distance between the lenses is short, the processing tolerance is tight and the distance between the upper surfaces (the center distance from 62 to LS) is short.

The present invention has been made to solve the above problems, and it is easy to design and process the curvature of the lens by using a low-cost general lens rather than an expensive cylinder lens, it is possible to save the processing time of the lens and the lens It is an object of the present invention to provide a focusing optical system for a laser diode, which facilitates the arrangement of the.

As a means for achieving the above object, the first and second lenses having a predetermined curvature on both sides and the planar third lens are arranged at a predetermined interval on a straight line so that the direction of the beam through the third lens proceeds in parallel. A first lens group; A second lens group having fourth and fifth lenses having predetermined curvatures on both sides at predetermined intervals on a straight line to focus the direction of the beam through the fifth lens, wherein the first lens group and the second lens group are provided; This is achieved by allowing the lens group to be disposed at a predetermined interval on a straight line.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

4 (a) and 4 (b) show traces of vertical focusing and horizontal focusing of a laser diode focusing optical system according to the present invention. And a first lens group in which the second lenses 10 and 20 and the flat convex third lens 30 are arranged at a predetermined interval on a straight line so that the direction of the beam through the third lens 30 proceeds in parallel. 100 and second and second lenses having a predetermined curvature on both sides thereof are arranged at a predetermined interval on a straight line so that the direction of the beam through the fifth lens 50 is focused. The lens group 200 is provided, and the first lens group 100 and the second lens group 200 are arranged in a straight line at predetermined intervals.

The converging optical system of the present invention configured as described above has almost zero aberration with respect to the portion of the region A, which is the distribution of the horizontal component of the laser beam emitted from the diverging region EA, as shown in FIG. 0), and a portion of the region B, which is a distribution of the vertical component of the laser beam emitted from the diverging region EA, has a predetermined distribution aberration so that the desired cross section of the light spot LS can be It can be shaped.

That is, the horizontal divergence angle ( The numerical aperture (NA: Numeral Aperture) of the focusing optical system composed of the lens group corresponding to the divergence width And the vertical divergence angle ( The numerical aperture of the focusing optical system composed of lens groups corresponding to the divergence width In the case of designing the focusing optical system of the present invention, the NA in the diverging region EA of the laser diode LD is Until the aberration is completely removed, the NA aberration is distributed as needed in the diverging region EA of the laser diode LD to make a light spot LS of a desired focused beam.

For example, the characteristics of the SDL-2352-P1, which is a model of the laser diode LD used in the present invention, will be described. The horizontal axis (X) and 1.0 It consists of a configuration having a vertical axis (Y) of, and the vertical divergence angle ( This 32 , Horizontal divergence angle ( ) 12 to be.

When focusing the laser beam of this characteristic to guide the size of the beam generated from the laser diode (LD) to the crystal pumping medium, the intensity distribution of the minimum incident beam to generate the desired TEMOO mode The diameter of the long axis and short axis of the light spot LS is each 206 , 204 In order to ensure that the total magnification of the focusing optical system of the present invention to 4 times, the horizontal divergence angle ( 12 Numerical aperture by (NA ) Indicates residual aberration 3 Degree, and the vertical divergence angle ( ) 32 Numerical aperture by (NA ) Indicates residual aberration 100 When the degree is generated, it is possible to create a cross-sectional size of the desired light spot LS.

The residual aberrations considered here are COMA and spherical aberrations, which are 50 lengths in the horizontal axis (X), the long axis of the diverging region (EA) of the laser diode (LD) compared to the size of the required system. Is less than the desired length of the light spot LS, the amount of generation of aberration is weak and excluded from the present invention, and spherical aberration is mainly considered among the residual aberrations.

The design data of the converging optical system for making the desired cross-sectional size of the light spot LS is as follows.

wavelength( ) 810 Each lens 10 having a refractive index n of 1.71068 50, the curvature of the first surface 11 of the first lens 10, unit 1 / ) Is -0.0183646, the curvature of the second surface 12 is -0.02, the curvature of the first surface 21 of the second lens 20 is -0.055759, the curvature of the second surface 22 is -0.0097948 The curvature of the first surface 31 of the third lens 30 is 0.000000, the curvature of the second surface 32 is -0.045241, and the curvature of the first surface 41 of the fourth lens 40 is 0.136612, the curvature of the second surface 42 is 0.153846, the curvature of the first surface 51 of the fifth lens 50 is 0.004, the curvature of the second surface 52 is 0.019802, and each lens 10 50, the center distance (Distance) of the first surface and the second surface is 2.0 The center distance from the diverging region EA of the laser diode LD to the first surface 11 of the first lens 10 is 6.312. The center distance from the second surface 12 of the first lens 10 to the first surface 21 of the second lens 20 is 0.5. The center distance from the second surface 22 of the second lens 20 to the first surface 31 of the third lens 30 is 0.5. The center distance from the second surface 32 of the third lens 30 to the first surface 41 of the fourth lens 40 is 15.0. The center distance from the second surface 42 of the fourth lens 40 to the first surface 51 of the fifth lens 50 is 1.5. The center distance from the second surface 52 of the fifth lens 50 to the light spot LS is 43.391. to be.

Here, the center distance from the diverging region EA of the laser diode LD to the first surface 11 of the first lens 10 is 6. The reason for this is that the output beam of the laser diode (LD) is high power, so 0.1w / unit per unit area is minimized in order to minimize the damage of the COATING surface which may be caused by using the laser beam. This is because a distance capable of maintaining the following incident intensity is required.

FIG. 5 (a) is a transverse aberration of FIG. 4 (a), and the horizontal divergence angle ( ) 12 If the residual aberration 3 5 (b) is the aberration diagram of FIG. 4 (b), and the vertical divergence angle ( This 32 If the residual aberration 100 It is about to occur.

FIG. 6 is an exemplary diagram in which a linewidth selecting device 300 is included in the focusing optical system of the present invention, and in the embodiment of the present invention, three lenses 10 are illustrated. The beam path was kept parallel between the first lens group 100 composed of 30 and the second lens group 200 composed of two lenses 40 and 50, which is necessary, that is, pumping. In order to increase the efficiency, the linewidth selector 300 (eg, Etalon, etc.) may be used to select the line width of the laser beam.

As described above, the present invention can configure the optical system that can use the etaron to increase the pumping efficiency by selecting the line width of the laser beam, to secure the working distance by increasing the center distance to the light spot The center distance from the diverging region EA of the laser diode LD to the first surface 11 of the first lens 10 may be increased to reduce the possibility of damage to the lens coating surface. In addition to increasing tolerances in design, it is possible not only to improve the stability of machining, but also to process at a lower cost than the lenses for focusing optical systems using expensive cylinder lenses or six spherical lenses. According to the present invention, it is possible to save processing time and facilitate the disposition of the lens.

Claims (14)

A laser diode (LD) for emitting a laser beam; The ratio of the length of the horizontal axis (X) to the vertical axis (Y) is set differently so that the vertical divergence angle ( ) Is the horizontal divergence angle ( A diverging region EA formed to be larger than); The first and second lenses 10 and 20 and the flat convex third lens 30 having both surfaces having predetermined curvatures are disposed at a predetermined interval on a straight line so that the beams through the third lens 30 are parallel to each other. A first lens group 100 for proceeding; The second lens group 200 having the second and fourth lenses 40 and 50 having predetermined curvatures on both sides at a predetermined interval on a straight line to focus the direction of the beam through the fifth lens 50. And the first lens group and the second lens group are arranged to be arranged at a predetermined interval in a straight line. 5. The laser diode of claim 1, wherein the first lens 10 has a curvature of −0.0183646 and a second curvature of −0.02 of the second surface 12. Focusing optical system. The laser diode of claim 1, wherein the curvature of the first surface 21 is -0.055759 and the curvature of the second surface 22 is -0.0097948. Focusing optical system. The focusing optical system of claim 1, wherein the third lens has a curvature of 0.000000 and a second curvature of −0.045241. The focusing optical system of claim 1, wherein the curvature of the first lens is 0.136612 and the curvature of the second surface is 0.153846. The focusing method of claim 1, wherein the fifth lens 50 has a curvature of 0.004 and a curvature of a second surface 52 of 0.019802. Optical system. The lens of claim 1, wherein each of the lenses (10) 60, the center distance (Distance) of the first surface and the second surface is 2.0 Focusing optical system for a laser diode using five spherical lenses characterized in that. The center distance from the diverging region EA of the laser diode LD to the first surface 11 of the first lens 10 is 6.312. Focusing optical system for a laser diode using five spherical lenses characterized in that. The center distance from the second surface 12 of the first lens 10 to the first surface 21 of the second lens 20 is 0.5. Focusing optical system for a laser diode using five spherical lenses characterized in that. The center distance from the second surface 22 of the second lens 20 to the first surface 31 of the third lens 30 is 0.5. Focusing optical system for a laser diode using five spherical lenses characterized in that. The center distance from the second surface 32 of the third lens 30 to the first surface 41 of the fourth lens 40 is 15.0. Focusing optical system for a laser diode using five spherical lenses characterized in that. The center distance from the second surface 42 of the fourth lens 40 to the first surface 51 of the fifth lens 50 is 1.5. Focusing total light for laser diodes using five spherical lenses characterized in that. The center distance from the second surface 52 of the fifth lens 50 to the light spot LS is 43.391. Focusing optical system for a laser diode, characterized in that. 12. The line width selection device 300 is interposed between the second surface 32 of the third lens 30 and the first surface 41 of the fourth lens 40. Focusing optical system for laser diodes using five spherical lenses.