JPH0814663B2 - Collimating lens for semiconductor laser - Google Patents

Description

TECHNICAL FIELD The present invention relates to a collimating lens for a semiconductor laser.

(Prior Art) A semiconductor laser has been generally used as a light source for an optical pickup of an optical disc system, a laser printer, and the like.

As is well known, the laser light emitted from a semiconductor laser is a divergent light beam, and a collimator lens is used to couple this divergent light beam.

The collimator lens and the semiconductor laser have a positional relationship such that the light emitting point of the semiconductor laser occupies the focal position of the collimator lens, and are integrated with each other by a holder.

By the way, a light source device in which a semiconductor laser and a collimator lens are integrated by a holder is designed and manufactured in accordance with a predetermined reference temperature, for example, 20 ° C. The ambient temperature to the device is quite large depending on the time and place,
It is not uncommon to fluctuate, for example, fluctuate in the temperature range of 0 to 60 ° C.

As described above, when the environmental temperature of the light source device deviates from the reference temperature, the light flux emitted from the collimator lens is not a parallel light flux, which hinders focusing of the optical pickup and writing in the optical printer. There are two causes for this.

The first reason is that the holder that integrally holds the semiconductor laser and the collimator lens undergoes thermal deformation according to the temperature change, and the position of the semiconductor laser deviates from the focus of the collimator lens.

The second cause is a change in the oscillation wavelength of the semiconductor laser due to a change in temperature. That is, the wavelength of the laser light emitted from the semiconductor laser changes with temperature, and when the light wavelength changes like this, the refractive index of the collimator lens changes due to the dispersibility of the collimator lens, which is apparently collimated. It appears as a change in the focal length of the lens.

Conventionally, as a method for solving such a problem, on the one hand, the semiconductor laser is temperature-controlled to stabilize the laser wavelength, and on the other hand, the holder is made of two or more materials having different linear expansion coefficients. However, there is known a method in which the positional relationship between the collimator lens and the semiconductor laser is made substantially constant regardless of the temperature change (Japanese Patent Laid-Open No. Sho 61-187).
59-15206).

However, in this conventional method, the cost of the holder is high, and the temperature control of the semiconductor laser causes a high cost.

(Object) The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a semiconductor laser for a semiconductor laser that does not require temperature control of the semiconductor laser and can also manufacture a holder at low cost. To provide a new collimator lens.

(Configuration) Hereinafter, the present invention will be described.

The collimator lens of the present invention is for coupling a divergent light beam from a semiconductor laser. Therefore, the collimator lens is integrated with the semiconductor laser by the holder while maintaining a predetermined positional relationship with the semiconductor laser.

Now, the collimating lens of the present invention is shown in FIG.
As shown in FIG. 1, the convex lens 12 is composed of two lenses in one group.
And the concave lens 14 and these lenses 12, 14
Are joined together.

The left side of FIG. 1 is the image side, that is, the side from which light is emitted, and the convex lens 12 is arranged on this side. The right side of FIG. 1 is the light source side, that is, the semiconductor laser side, and the concave lens 14 is arranged on this side. The emission point of the semiconductor laser is placed at point p on the optical axis AX. Reference numeral 16 represents a cover glass of the semiconductor laser.

For the convex lens 12, the refractive index is n ₁ , the Abbe number is υ ₁ , the focal length is f ₁ , and for the concave lens 14, the refractive index is n ₂ , the Abbe number is υ
₂ and the focal length is f ₂ . However, the Abbe number υ ₁ , υ ₂ is d
For lines.

The focal length of the entire system is f. Further, as shown in FIG. 1, the radius of curvature of the i-th lens surface is r _i (i = 1 to 3) and the distance between the lens surfaces is d _i (i =
1-2).

Then, the _{n 1, n 2, υ 1} , υ 2, f 1, f 2, f, and r ₂ satisfy the following conditions.

(I) n ₁ <n ₂ (ii) r ₂ <0 The principle of the present invention is as follows.

FIG. 2 shows a light source device using the collimator lens 10 of the present invention.

The collimator lens 10 is fitted in the cell 22 and screwed to the hollow cylindrical holder 20.

On the other hand, the semiconductor laser 30 is screwed to the holder 21, and the holder 21 is screwed to the holder 20 to be integrated with the holder 20.

Now, let ΔT be the deviation of the environmental temperature from the reference temperature,
The linear expansion coefficient of the holder 20 is α.

Since the optical distance between the principal point on the light source side of the collimator lens 10 and the light emitting point of the semiconductor laser is f at the reference temperature, the distance between the principal point on the light source side and the light emitting point is the temperature change Δ. With respect to T, due to thermal deformation of the holder 20, it changes by Δl = f · α · ΔT (1). If standardized as f = 1, Δl = α · ΔT (2).

On the other hand, as is well known, the change δλ in the emission wavelength of the semiconductor laser is proportional to ΔT. That is, δλ = β · ΔT (3) Therefore, Is obtained. If you put this in equation (2), Is obtained.

Therefore, if the focal length of the collimator lens changes by Δl ′ when f = 1 when the wavelength λ shifts by δλ, the temperature change ΔT can be obtained by setting Δl′l ′. Since the positional deviation between the collimator lens and the semiconductor laser due to the above is canceled by the change in the focal length due to the change in wavelength, the parallel light flux is always emitted from the light source device regardless of the change in the environmental temperature.

Now, generally, in a semiconductor laser, temperature change Δ
Wavelength change ratio β giving wavelength change δλ for T
Is 0.2 to 0.3 nm / deg. Further, aluminum or aluminum die cast is generally used as a material for the holding body 20, and the linear expansion coefficient α of these materials is
For aluminum, α = 23 × 10 ^-6 ₁ / deg, and for aluminum die casting, α = 20 × 10 ^-6 ₁ / deg.

Using equation (4) above, α = 20 × 10 ⁻⁶ to 23 × 10 ⁻⁶ , β
= 0.2 to 0.3, the variation region of Δl is the wavelength change δ
For λ, 67 × 10 ^-6 δλ Δl 115 × 10 ^-6 δλ (5) Therefore, the axial chromatic aberration ΔC is δλ = 10 nm
Is 0.67 × 10 ^-3 ΔC1.15 × 10 ^-3 (6).

Therefore, the axial chromatic aberration of the collimator lens may be increased so as to satisfy the expression (6).

Here, the above conditional expressions (i), (ii), and (iii) will be described. Condition (i) n ₁ <n ₂ is a condition for reducing the residual spherical aberration. This condition also allows the absolute value of r ₂ to be large, so that condition (i) is advantageous in lens processing.

Condition (ii) r ₂ <0, the first face is a condition for correcting under negative spherical aberration terms generated by the third surface (i), negative spherical aberration when the r ₂ 0 It becomes impossible to correct due to the occurrence of.

Condition (iii) Is a condition for increasing the axial chromatic aberration. Above the lower limit, the axial chromatic aberration becomes small, and the thermal deformation of the holder cannot be canceled out. Standard temperature of 20 by satisfying the above conditions
In the case of 0 ° C., it is possible to obtain a parallel light flux substantially constantly at an environmental temperature of 0 ° to 60 ° C.

 Hereinafter, four specific examples will be shown.

(Example 1) f = 1.0 NA = 0.14 r 1 = 0.6795 d 1 = 0.2375, n 1 = 1.63553 υ 1 = 33.84 r 2 = -0.4913 d 2 = 0.1159, n 2 = 1.81961 υ 2 = 37.54 r 3 = - 1.7410 I = 0.030, ΔC = 0.68 × 10 ^-3 The aberration diagram of this example is shown in FIG.

In addition, also in this embodiment and the following embodiments, Where n ₁ and n ₂ are values for a wavelength of 780 nm, and ΔC is a wavelength of 79
The difference between the focal lengths of 0 nm and 780 nm is shown.

(Example 2) f = 1.0, NA = 0.17 r 1 = 0.662 d 1 = 0.2847 n 1 = 1.60909 υ 1 = 36.3 r 2 = -0.396 d 2 = 0.1368 n 2 = 1.70399 υ 2 = 64.2 r 3 = -1.956 I = 0.040, ΔC = 0.77 × 10 ⁻³ (Example 3) f = 1.0, NA = 0.17 r ₁ = 0.7159 d ₁ = 0.133 n ₁ = 1.71221 υ ₁ = 28.31 r ₂ = −0.5161 d ₂ = 0.1467 n ₂ = 1.81961 υ ₂ = 37.3 r ₃ = -3.575 I = 0.044 △ C = 0.92 × 10 ^-3 (Example 4) f = 1.0, NA = 0.17 r ₁ = 0.7849 d ₁ = 0.1069 n ₁ = 1.76605 υ ₁ = ₁ 25.7 r ₂ = -0.4402 d ₂ = 0.2722 n ₂ = 1.81961 υ ₂ = 37.3 r ₃ = -4.805 I = 0.058 ΔC = 1.07 × 10 ^-3 Aberration diagrams for Examples 2, 3 and 4 are shown as 5, shown in FIG. As is clear from these aberration diagrams, the aberrations are satisfactorily corrected in each of the examples.

For comparison, an example of what is conventionally known as a collimating lens for semiconductor lasers will be given.

(Comparative example) r ₁ = 0.6377 d ₁ = 0.1333 n ₁ = 1.51118 υ ₁ = 64.2 r ₂ = -0.4604 d ₂ = 0.1333 n ₂ = 1.76605 υ ₂ = 25.7 r ₃ = -0.9753 With this collimating lens, the wavelength is 780 nm. Focal length f ₇₈₀ = 0.99997, focal length f _{790 at} wavelength 790 nm
= 1.00007 and ΔC = f ₇₉₀ −f ₇₈₀ = 0.1 × 10 ⁻³ , the axial chromatic aberration is small and the positional deviation due to thermal deformation of the holder cannot be corrected. Also The value of is -0.0002. The value of I is so small because ν ₁ > ν ₂ , n ₁ <n ₂ .

In the present invention, by combining glass materials such that υ ₁ <υ ₂ , I
The size of is enlarged.

(Effect) As described above, according to the present invention, a novel collimating lens for a semiconductor laser can be provided. Since this collimator lens is configured as described above, it becomes possible to manufacture the holder for holding it with a single material at low cost. Further, it is not necessary to control the temperature of the semiconductor laser. Therefore, a light source device with a simple structure and low cost can be realized.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the configuration of the collimator lens according to the present invention, FIG. 2 is a diagram for explaining the use state of the collimator lens of the present invention, and FIGS. 3 to 6 are aberration diagrams. is there. 10 ... Collimating lens, 12 ... Convex lens, 14 ... Concave lens, 30 ... Semiconductor laser

Claims (1)

[Claims] 1. A collimating lens for coupling a divergent light beam from a semiconductor laser, which is integrated with the semiconductor laser by a holder and maintains a predetermined positional relationship with the semiconductor laser, and a side from which the light beam is emitted. From the semiconductor laser side to the semiconductor laser side, in which a convex lens and a concave lens are arranged in this order, a two-group construction is used. The refractive index of the convex lens is n ₁ , the refractive index of the concave lens is n ₂ , and the Abbe line for the d-line of the convex lens ₁ the number [nu, ₂ the Abbe number [nu respect to the d-line of the concave _lens, the focal length of the convex lens f _1, a focal length of the concave lens f _2, a focal length of the entire system f, and the radius of curvature of the second face and r ₂ Then, these are (I) n ₁ <n ₂ (II) r ₂ <0 (III) f [{1 / (f ₁ ν ₁ )} + {1 / (f ₂ ν ₂ )}] ≧ 0.03 When the holding body is deformed due to temperature change, Change in the distance between the Torenzu, characterized by being configured so as to be offset by the axial chromatic aberration of the collimator lens by the oscillation wavelength change of the semiconductor laser due to the temperature change, the semiconductor laser collimating lens.