JPH01206682A - Semiconductor laser beam source - Google Patents

Abstract

PURPOSE:To make the fluctuation of projecting laser rays in a projecting angle due to a temperature change as small as possible by a method wherein an unequally spaced diffraction grating is composed of a material which has such a thermal expansion coefficient that the fluctuation of a projecting angle can be almost compensated for with the change of the unequally spaced diffraction grating in a focal length due to a temperature change. CONSTITUTION:A semiconductor laser diode chip (LD chip) 1 is fixed to a heat sink 3, and a transparent substrate provided with a Fresnel lens 2 is disposed in front of the LD chip 1. A material forming the Fresnel lens 2 expands or contracts with the change of temperature T. When the lens material expands thermally due to the rise of a temperature T, the period of a lens pattern increases, and consequently the focal length of the Fresnel lens 2 grows larger. Therefore, the fluctuations of the focal length of the Fresnel lens 2 due to the change of an oscillating wavelength of the LD chip 1 caused by a temperature change and due to the thermal expansion and contraction of the lens material are made to act cancelling each other. By these processes, a projecting laser beam can be prevented from fluctuating in a projecting angle.

Description

Detailed Description of the Invention Summary of the Invention In a light source that includes a semiconductor laser and a Fresnel lens that shapes its emitted light, a change in the focal length of the Fresnel lens due to a change in the oscillation wavelength of the semiconductor laser due to a temperature change. The Fresnel lens was constructed from a material with a coefficient of thermal expansion that was almost canceled out by changes in the focal length of the Fresnel lens caused by thermal expansion.

BACKGROUND OF THE INVENTION The present invention relates to a semiconductor laser light source, and more particularly, to a semiconductor laser light source that converts diffused (divergent) emitted light from a semiconductor laser into parallel light using an unequally spaced diffraction grating (for example, a Fresnel lens) and emits it into space. .

The oscillation wavelength of a semiconductor laser fluctuates due to temperature changes.

When the wavelength of the incident light changes, the focal length of the Fresnel lens changes. Furthermore, the focal length of the Fresnel lens changes as it expands and contracts due to temperature changes. Changes in the focal length of the Fresnel lens due to fluctuations in the oscillation wavelength of the semiconductor laser and changes in the focal length due to thermal expansion and contraction of the Fresnel lens itself generally work in a direction that cancels each other out, but (1) Usually they do not cancel each other out completely. Can not. Therefore, the shape of the laser beam shaped by the Fresnel lens changes as the temperature changes. In other words, what should be parallel light becomes divergent light or convergent light. In addition, in the case of divergent light or convergent light, the divergence angle or convergence angle changes.

Summary of the Invention The present invention aims to minimize variations in the output angle of the emitted light due to temperature changes in a semiconductor laser light source in which the laser light output from the semiconductor laser is shaped and emitted using an unevenly spaced diffraction grating. do.

The semiconductor laser light source according to the present invention suppresses the change in the focal length of the non-uniformly spaced diffraction grating caused by the change in the oscillation wavelength of the semiconductor laser due to temperature change to the change in the focal length of the non-uniformly spaced diffraction grating caused by thermal expansion. It is characterized in that the unevenly spaced diffraction grating is constructed of a material having a coefficient of thermal expansion that is almost compensated for by changes.

According to this invention, the change in the focal length of the non-uniformly spaced diffraction grating due to the change in the wavelength of the laser beam is almost canceled out by the change in the focal length due to the thermal expansion of the non-uniformly spaced diffraction grating.
Fluctuations in the output angle of the output laser beam due to temperature changes become smaller. Therefore, even if there is a temperature change, the collimated light will remain parallel, and the divergent light will have a divergent angle.

The convergence angle hardly changes.

DESCRIPTION OF EMBODIMENTS FIG. 1 is a partially cutaway perspective view showing an embodiment of a semiconductor laser light source according to the present invention. FIG. 2 is a partially cutaway front view of the semiconductor laser light source shown in FIG. 1 with the cap removed.

Referring to these figures, the heat sink 3 is fixed to the substantially central position of the stem 6. This heat sink 3 may be formed integrally with the stem 6. A semiconductor laser diode chip (LD chip) 1 is fixed on the heat sink 3. This LD chip 1 is stem 6
(This is the optical axis of the emitted light).

A transparent substrate 4 provided with a Fresnel lens 2 is arranged in front of the LD chip 1. Fresnel lens 2 is located at the center of substrate 4. A Fresnel lens has a concentric pattern of protrusions and recesses, and uses Fresnel diffraction of light due to the pattern of protrusions and recesses to perform a lens action (condensing light, collimating, etc.). There are two types of concavo-convex patterns of Fresnel lenses, such as a step-like pattern and a blazed pattern. As a means for shaping the laser light beam, it is possible to use other forms of non-uniformly spaced diffraction gratings, such as diffraction gratings formed on both sides in directions perpendicular to each other, and the pitch of these diffraction gratings being wider in the center and narrowing towards the sides. It is also possible to use a nonuniformly spaced diffraction grating that acts as a lens. Such an unevenly spaced diffraction grating including the Fresnel lens 2 may be formed integrally with the transparent substrate 4, or may be made separately and attached to the substrate 4.

The substrate 4 is fixed at both ends to two support blocks 5, which are fixed to a stem 6 on both sides of the heat sink 3. Considering the X and Y axes in two directions perpendicular to the Z axis, the width of the support block 5 is long in the Y direction, and the center of this width is on the X axis. Further, the two support blocks 5 are located at equal distances from the Z-axis center in the X-axis direction. The substrate 4 is then fixed to the block 5 at a position where the Z axis passes through the center of the Fresnel lens 2.

Further, a Fresnel lens 2 is provided at a position to collimate the diffused laser light emitted from the LD chip 1.

A heat sink 3 to which an LD chip 1 is fixed; a substrate 4 provided with a Fresnel lens 2; In this case, a cap 7 is provided to cover the entire block 5 to which the plate 4 is fixed, and is fixed to the stem 6 by CanSeal, adhesive, or other method.

A hole is made at the top of the cap 7, and a transparent plate (
(plastic, glass, etc.) 8 are provided to constitute the window. The laser beam collimated by the Fresnel lens 2 is emitted to the outside through the transparent plate 8.

Needless to say, the LD chip 1 is connected to a terminal 9 provided insulated on the stem 6 by wire bonding or the like.

Since the optical system including the LD chip 1 and the Fresnel lens 2 is housed within the cap 7, the influence of the external environment is extremely reduced. It is especially protected from dust adhesion.

Further, the LD chip 1 and the Fresnel lens 2 are located on the central axis Z of the stem 6, and the Fresnel lens 2 is located on the substrate 4.
Further, the substrate 4 and the support block 5 have a symmetrical shape with respect to the X-axis and the Y-axis and are arranged in such a manner. Therefore, due to temperature changes, the substrate 4. Even if the support block 5 (although the thermal expansion of the support block is extremely small in this embodiment) expands or contracts, they thermally expand or contract in the same direction in a plane perpendicular to the Z axis (XY plane). Therefore, the LD chip 1 and Fresnel lens 2 are always on the Z-axis, and the optical axis is never deflected from the Z-axis. Since the substrate 4 on which the Fresnel lens 2 is provided is firmly fixed by the two support blocks 5, it is resistant to vibrations and shocks.

Generally, when the temperature T of the LD chip 1 increases, the oscillation wavelength λ tends to become longer.

On the other hand, the period Δ of the concavo-convex pattern of the Fresnel lens is a function of the wavelength λ of the light used (incident light) and the focal length f of the lens. When we consider this cycle to be constant,
As the wavelength λ of light increases, the focal length #Lf decreases.

Fresnel lens 2. The feed that forms this also expands and contracts as the temperature T changes. Thermal expansion of the lens feed due to an increase in temperature T increases the period of the lens pattern, thereby increasing the focal length f of the Fresnel lens 2.

Therefore, the focal length fluctuation of the Fresnel lens 2 due to the change in the oscillation wavelength of the LD chip 1 due to temperature change,
The focal length fluctuations caused by thermal expansion and contraction of the material of the Fresnel lens 2 act in a direction that cancels each other out.

Generally, the change in focal length due to a change in the oscillation wavelength of the LD chip 1 is larger than the change in focal length due to the material of the lens 2.

Therefore, in the present invention, the Fresnel lens 2 is constructed using a material with an extremely large coefficient of thermal expansion, and the change in focal length caused by the thermal expansion of the lens feed is widened, and the change in focal length caused by the variation in the emission wavelength of the LD chip 1 is reduced. The lens is designed to almost cancel out any changes in focal length.

In this embodiment, the heat sink 3 and the support block 5 are made of feed having such a small coefficient of thermal expansion that its thermal expansion and contraction due to temperature changes can be ignored. As a result, the distance between the LD chip 1 and the Fresnel lens 2 can be considered to be approximately constant regardless of temperature changes. An example of a material having a coefficient of thermal expansion so small that thermal expansion and contraction can be ignored is Kovar (coefficient of thermal expansion: 4.8 x 10-6/''C).

An example of compensation for the focal length variation described above will be described in detail below.

The focal length variation coefficient of the material of the Fresnel lens 2 is given by the following equation.

(1/f)(a f/aT)-2a-r (1) Here, α is the coefficient of linear expansion of the material of the Fresnel lens 2, and is given by the following equation.

a= (1/R) (aR/JT) (2) m
m Rm is the radius of each zone of the Fresnel lens.

= 8 = Furthermore, γ is the wavelength change coefficient of the LD chip 1 and is given by the following equation.

γ=(1/λ)(aλ/9T') (3
) When formula (1) is transformed, it becomes the following formula.

(,llf/δT) = f (2a-7) (
4) llf/aT of the second equation (4) for a given γ
It is sufficient to select a material for the Fresnel lens 2 having α such that the value of ) is zero or close to zero.

For example, allyl diglycol carbonate (CR-39) is used as a material for the Fresnel lens 2. The coefficient of thermal expansion α of this material is extremely large α-1,2XLO”
-4/'C. Also, GaAj2As is used for LD chip 1.
When using a system semiconductor laser, the wavelength change coefficient γ of a certain type of LD chip is γ = 2.923XIO'/'C(λ
=0.78μm, aλ/aT=0.228nm
/'C). Further, the focal length f of the Fresnel lens 2 is set to f = 1 [mm]. Substitute these values into equation (4). (J f/, 13 T) = I
Xl0-3X (2Xl, 2 XIO-2,923X
l0-4) --5,23X10-8 [m/'C] =
-0,0528[μm/'C The temperature dependence of the focal length f can be suppressed to an extremely small value in this way, and the emitted light can be kept parallel regardless of temperature changes.

FIG. 3 shows the directivity angle temperature dependence (20° C. standard) of various Fresnel lens materials and plastic lenses. When acrylic resin (PMMA) is used as the Fresnel lens material.

Compared to the case where a plastic lens (convex lens) is used as the lens, when the above-mentioned allyl diglycol carbonate is used as the Fresnel φ lens material, the exit angle of the emitted light can be kept almost constant regardless of temperature changes. I understand.

In the above example, it is assumed that the thermal expansion and contraction of the heat sink 3 and the support block 5 can be ignored, but the present invention is applicable even when these thermal expansion and contraction cannot be ignored. next.

A case will be described in which thermal expansion and contraction of the heat sink 3 and the support block 5 are taken into account.

In FIG. 1, the length of the heat sink 3 in the Z-axis direction is a, the length of the support block 5 in the Z-axis direction is b, and the linear expansion coefficient of the heat sink 3 is a t .

Let the linear expansion coefficient of the support block 5 be bl.

The distance from the exit surface of the LD chip 1 to the Fresnel lens 2 is equal to the set focal length f, and f=ba.

The focal length variation evaluation function F is given by the following equation.

F = (setting focal length) +ΔTi [variation attributable to thermal expansion of heat sink and support block co-(variation attributable to thermal expansion of Fresnel lens) + (
Variation due to oscillation wavelength)) = f + ΔTf[-b(a-b)-a f]-2
fα +fγ (5) In order to set F=f (=constant) regardless of temperature changes, the following equation should hold true.

t [b (a b ) a t f ]
2 f α+fγl−0 (6) The materials (a + bt ) + of the heat sink 3 and the support block 5 and their lengths a and b may be set so that equation (6) holds true. α.

γ and f are the same as those in the above embodiment.

For example, heat sink 3 is made of Kovar' copper (
b = 1.65xLO-5/'C) and their lengths are a = 21.3mm, b = 22.3m
If m, then equation (6) holds true, and F=f.

As a result, the output angle of the two output light beams does not change depending on the temperature.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway perspective view showing an embodiment of a semiconductor laser light source according to the present invention, Fig. 2 is a partially cutaway front view with the cap shown in Fig. 1 removed, and Fig. 3 shows various materials. 2 is a graph showing the temperature dependence of the orientation angle of a Fresnel lens and a plastic lens. 1...LD chip, 2...Fresnel lens. that's all

Claims (1)

[Claims] Thermal expansion such that the change in the focal length of the non-uniformly spaced diffraction grating due to the change in the oscillation wavelength of the semiconductor laser due to temperature change is almost compensated for by the change in the focal length of the non-uniformly spaced diffraction grating due to thermal expansion. A semiconductor laser light source that consists of an unevenly spaced diffraction grating made of materials with coefficients.