JPH0248886B2 - KORIMEETAARENZUKEI - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a collimator lens system for obtaining parallel light flux from a monochromatic light source. Since a monochromatic light source such as a semiconductor laser is used as a light source, the collimator lens system does not require correction of chromatic aberration. However, in order to increase the utilization efficiency of the diverging light beam from the light source, it is necessary to reduce the F value of the collimator lens system. Furthermore, in order to reduce the size, weight, and cost of the lens system, it is required to reduce the number of lenses in the lens system. This is desirable from the standpoint of increasing light transmittance and reducing the adverse effects of light reflected by the lens surface. Furthermore, the collimator lens system is required to have performance close to that of an ideal lens, and is also required to have good performance against off-axis light caused by installation errors and the like. That is, it is necessary to satisfactorily correct spherical aberration, coma aberration, and astigmatism. An object of the present invention is to provide a collimator lens system for semiconductor lasers that satisfies the above requirements. The details of the collimator lens system of the present invention will be explained below. As is clear from FIG. 1, the collimator lens system of the present invention has a first lens having a positive refractive power and having a convex surface on the light exit side in order from the light exit side.
It is composed of two lenses, a lens _L1 and a second lens _L2 having a concave surface on the light beam exit side, and satisfies the following conditions. (1) 0.6<r ₁ /f<2.1 (2) |r ₂ |/f>1.5 (3) −0.25>r ₃ /f>−2.1 (4) r ₄ /f<−0.3 By the way, f is the total The focal length of the system, r ₁ is the radius of curvature of the surface of the first lens L ₁ on the light flux exit side, r ₂ is the radius of curvature of the surface of the first lens L ₁ on the light flux input side, and r ₃ is the radius of curvature of the surface of the first lens L ₁ on the light flux input side. The radius of curvature of the surface on the light beam exit side, r ₄ is the radius of curvature of the surface of the second lens L ₂ on the light beam incident side. First, the shape of the lens will be described. Considering spherical aberration, a concave surface is generally required to correct the spherical aberration caused by a positive lens.
In addition, when considering good correction of comatic aberration, it is better to suppress the comatic aberration generated by each lens, and it is better to make the light flux exit side of the first lens _L1 and the light flux input side of the second lens _L2 a strongly concave surface. is not desirable. Therefore, the light flux exit side of the second lens _L2 is made concave.
Since the diverging light flux enters the second lens, the fourth lens
The luminous flux width at r ₄ is relatively narrow, and the luminous flux width at the third surface r ₃ is relatively wide, but the wider the luminous flux width, the _greater the spherical aberration that occurs on that surface. Although the occurrence of aberration is small, the occurrence of spherical aberration due to the concave surface of the third surface _r3 becomes large, which is useful for correcting the spherical aberration. That is, the first lens L ₁
By using a positive lens and making the second lens _L2 into the shape described above, spherical aberration and comatic aberration can be well corrected, the F number is small, and it is possible to design a two-element collimator lens system. Become. Next, conditions for configuring the collimator lens system of the present invention will be explained. As described above, in the present invention, by making the surface of the first lens L ₁ on the light beam exit side (from which a parallel light beam is emitted) a convex surface, the spherical aberration, coma aberration, and coma aberration occurring in the first lens L ₁ can be reduced. is kept relatively small,
In addition to enabling good correction of various aberrations, the second
By making the surface of the light beam exit side of the lens L ₂ a concave surface, the spherical aberration occurring in the first lens can be well corrected, and furthermore, due to the relationship between the concave surface and the surface of the second lens L ₂ on the light beam entrance side. This makes it possible to effectively correct coma aberration. Condition (1) is a condition for properly correcting spherical aberration and coma aberration in the above. If the lower limit of this condition is exceeded, spherical aberration will be insufficiently corrected. If the upper limit of this condition is exceeded, spherical aberration will be overcorrected and extroverted coma will occur. Condition (2) is a condition for satisfactorily correcting spherical aberration and coma aberration. If this condition is not met, spherical aberration will be overcorrected and extroverted comatic aberration will occur. Condition (3) relates to good correction of spherical aberration. If the upper limit of this condition is exceeded, spherical aberration will be overcorrected, and coma aberration will not be able to be corrected well. Furthermore, if the lower limit of this condition is exceeded, inward comatic aberration will occur. Condition (4) relates to good correction of coma aberration. If this condition is not met, spherical aberration will be over-corrected, and comatic aberration will not be properly corrected. Examples according to the present invention are shown below. Example 1

【table】 Example 2

【table】 Example 3

【table】 Example 4

【table】 Example 5

【table】 Example 6

【table】 Example 7

【table】 Example 8

[Table] However, r ₁ , r ₂ , r ₃ , r ₄ are the radius of curvature of each surface viewed from the light beam exit side, and d ₁ , d ₂ , d ₃ are the thickness and thickness of each lens viewed from the light beam exit side in order. Air spacing, n ₁ , n ₂
are the refractive indexes of each lens at a wavelength of 780 nm, ν ₁ , ν ₂
is the Abbe number of each lens for the d-line. As is clear from the above, according to the present invention, it is possible to provide a collimator lens system having a two-lens configuration, which is small and lightweight, and has a bright F value of 3.5 or less.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of the lens system according to the present invention, Figure 2
9 to 9 are aberration diagrams of Examples 1 to 8, respectively. _L1 ...first lens, _L2 ...second lens, G...cover glass.

Claims (1)

[Scope of Claims] 1. In a collimator lens system for a semiconductor laser for obtaining parallel light flux from a monochromatic light source, in order from the light flux exit side, a first lens with a positive refractive power having a convex surface on the light flux exit side and a first lens on the light flux exit side the second having a concave surface;
A collimator lens system consisting of two lenses and satisfying the following conditions: 0.6<r ₁ /f<2.1 | r ₂ |/f>1.5 −0.25>r ₃ /f> -2.1 r ₄ /f<-0.3, where f is the focal length of the entire system, r ₁ is the radius of curvature of the surface of the first lens on the light exit side, and r ₂ is the radius of curvature of the surface of the first lens on the light incidence side , r ₃ is the radius of curvature of the surface of the second lens on the light flux exit side, and r ₄ is the radius of curvature of the surface of the second lens on the light flux incident side.