JPH0798881A - Optical pickup device - Google Patents

Abstract

PURPOSE:To surely set the prescribed temperature even under the high environmental temperature with a compact and simple structure by arranging 1st and 2nd Peltier elements in superposition. CONSTITUTION:A Peltier element 21 is arranged so that one pole thereof is brought into thermal contact with the substrate in a light source part 1, and a Peltier element 21 is arranged so taht a low-temp. side pole thereof is brought into close contact with the other pole of the Peltier element 21 in superposition. A heat sink 3 formed with many heat radiating fins at the high-temp. side pole of the Peltier element 22 is thermally coupled and densely arranged. As for the short-wavelength laser light which is converted and emitted from the nonlinear optical element is bent, for example, the light pass thereof is bent by the mirror, and the laser light is introduced to the outside of a package 105 through the window of the package 105, passed through the objective lens of the objective lens driving device, and then focused on the optical disk.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides an optical pickup device, in particular, a pumping semiconductor laser, a light source section having a laser medium pumped by laser light from the semiconductor laser, that is, a solid-state laser, and a nonlinear optical element. The present invention relates to an optical pickup device.

[0002]

2. Description of the Related Art Compact discs, laser discs,
Light used for recording and reproducing on an optical disk such as a magneto-optical disk is desired to have a shorter wavelength in order to improve recording density and reproduction resolution.

As such a light source, a structure is provided in which a light source section having a pumping semiconductor laser, a laser medium, and a nonlinear optical element is provided, and the laser medium of the semiconductor laser 1 is pumped to extract the laser medium. Proposal of a laser light generator capable of obtaining low power consumption and high power density by introducing light as a fundamental wave into a non-linear optical element and obtaining laser light of a short wavelength due to, for example, a second harmonic from the non-linear optical element It is out of order (for example, Japanese Patent Laid-Open No. 1-1433)
77).

By the way, in such a laser light generator, the pumping semiconductor laser is always kept at a predetermined temperature so as to be kept in a state of oscillating light of a predetermined wavelength that efficiently pumps the laser medium. Need to be controlled.

On the other hand, the laser medium also needs to be kept at a predetermined temperature. For this laser medium, for example, it is cut in a wedge shape, and the laser medium is moved and adjusted with respect to the optical path. By selecting the optical path length depending on which position of the wedge-shaped laser medium the optical path passes through, the temperature to be held exactly matches the set temperature in the pumping semiconductor laser, It is possible to set both temperatures with the temperature controller.

As shown in the sectional view of the schematic structure of FIG. 7, the temperature control device includes a heat source unit 1 having a pumping semiconductor laser, a laser medium, and a nonlinear optical element, as described above. Peltier element 2 of single stage
Are placed. In this Peltier element 2, for example, a large number of pellets having a Peltier effect are arranged between substrates 4 facing each other, one substrate side is commonly used as a low temperature side, that is, a cooling side pole, and the other side is commonly used as a high temperature side, that is, It is configured as a pole on the heat generation side.

Then, the temperature of the exciting semiconductor laser of the light source section 1 is detected by a temperature detecting element such as a thermistor,
As a result, the power P supplied to the Peltier device 2 (= current I ·
The voltage V) is controlled to cool the light source unit 1, and the light source unit 1 is maintained at a predetermined temperature.

In this case, a so-called heat sink 3 having a heat dissipation fin having a high heat conductivity and a large surface area is formed as a light source portion 1 of the Peltier element 2 for reliable temperature control, that is, sufficient heat dissipation. A configuration is employed in which the electrode is thermally coupled to the pole on the side opposite to the coupling portion.

Therefore, the above-mentioned short-wavelength laser light generator is used for recording or reproducing on various optical disks,
Alternatively, when used as a light source of an optical pickup that performs both of them, the temperature control device, a heat sink, and the like are mounted on the optical pickup together with the light source unit 1 including the excitation semiconductor laser, the laser medium, and the nonlinear optical element described above. .

This optical pickup is required to be movable in the direction along its radial direction with respect to a rotating optical disc, and it is desired that the optical pickup be downsized as a whole and its access be made. Since it is necessary to shorten the time as much as possible, the overall weight of this optical pickup is required to be constructed as light as possible.

On the other hand, in the above-mentioned laser light generator as a light source, it is desired to have a structure capable of performing stable cooling by performing sufficient cooling even under a high ambient temperature and always maintaining a predetermined temperature. .

However, in the temperature control device having the above-mentioned structure, the temperature control, especially the cooling, is not always sufficiently performed, and a problem occurs in long-term continuous use.

Now, consider the conventional structure shown in FIG. 7, that is, a model in which a single-stage Peltier device 2 is provided.

In this case, for simplification, the thermal contact resistance of the thermal coupling portion of each part, the thermal resistance of the Peltier element 2 to the substrate 4 in the Peltier element 2 and the like are ignored.

Generally, the efficiency η of a Peltier device is given by
Given in.

[0016]

## EQU1 ## η = {αTcI− (1/2) rI ² −k · Δ
T} / (αΔTI + krI ² )

Here, αI> 0 and k> 0.

Α is the Seebeck coefficient of the Peltier device. T
_H is the high temperature side (heat generation side) of the Peltier element. Tc
Is the temperature on the low temperature side (cooling side) of the Peltier element, that is, the control target temperature. I is the current supplied to the Peltier device. r is
Electric resistance of Peltier element. k is the thermal conductance of the Peltier element. ΔT = T _H -Tc

Here, the electric resistance r and the thermal conductance K of the Peltier device can be expressed by r = ρL / A k = λA / L, where A and L are the cross-sectional area and height per one stage of the Peltier device. Here, ρ is the resistivity of the Peltier element, and λ is the thermal conductivity.

Here, assuming that A / L is the shape variable x, the electric resistance r and the thermal conductance k are functions of x.

According to Equation 1, the smaller ΔT, the better the efficiency η.

In the optical pickup, since the temperature of the light source section 1, that is, the semiconductor laser and the laser medium is kept constant, Tc = constant.
Lowering T _H can reduce ΔT and improve efficiency η.

Therefore, the heat sink 3 is provided to transfer heat to the outside air to reduce T _H. In this case, the exhaust heat amount Q _out of the Peltier element can be expressed by the following equation 2.

[0024]

[Number 2] _{Q out = hS out (T H} -T air)

Here, h is the heat transfer coefficient from the heat sink to the outside air, S _out is the heat sink area, and T _air is the outside air temperature.

Now, assuming that Q _out is constant, T _H
The following two methods are conceivable as methods for lowering the value.

(I) Increase the heat transfer coefficient h. (Ii) Increase the heat sink area S _out .

In order to increase the heat transfer coefficient h, it can be considered to provide a cooling fan for forced cooling. However, in this way, a cooling fan is provided for (i),
Increasing the heat sink area in the above (ii) is not preferable because it increases the weight and size of the optical pickup.

[0029]

SUMMARY OF THE INVENTION The present invention relates to a solid-state laser configuration having the above-described pumping semiconductor laser and an optical pickup using a laser light generator having a nonlinear optical element as a wavelength conversion element as a light source,
A lightweight structure is adopted so that a predetermined temperature can be reliably set even under a high environmental temperature.

[0030]

The present invention is shown in FIGS. 1 and 2, as shown in FIG. 1 and FIG. 2, respectively, which are schematic sectional views of respective examples of the light source structure of the optical pickup according to the present invention. Although not shown, an optical pickup device including a pumping semiconductor laser, a laser medium pumped by laser light from the semiconductor laser, and a light source unit 1 having a non-linear optical element is at least the first
The Peltier device 21 and the second Peltier device 22 are arranged so as to overlap each other. That is, at least two or more Peltier elements are arranged.

Then, one pole of the first Peltier element 21 is thermally coupled to the light source unit 1, and the second Peltier element 22 is connected.
Of the first Peltier element 21 is thermally coupled to the other pole of the first Peltier element 21.

In the present invention, the first Peltier element 21 serves as the temperature control means of the light source unit 1 and the second Peltier element 22 serves as the main heat radiation means in the above-mentioned structure.

[0033]

According to the structure of the present invention, at least the first Peltier element 21 thermally coupled to the light source section 1 and the second Peltier element 22 thermally coupled to the first Peltier element 21. Since the two-stage Peltier element is provided, efficient cooling can be performed.

That is, the equation 3 holds for the energy balance of the Peltier element, and the equation 4 holds for the heat absorption amount Q _ab of the Peltier element.

[0035]

[Number 3] _{Q out = Q ab + P =} Q ab + α (T H -Tc) I + rI 2

[0036]

[Number 4] _{Q ab = αTcI- (1 / 2rI} 2) -k (T H -Tc)

Now, regarding the single-stage Peltier element, when the characteristics, dimensions, temperature conditions, etc. are as follows, the heat absorption amount Q _ab = 1.2 [W], Seebeck coefficient α = 205 × 10 ⁻⁶ [V / K], resistivity ρ = 1.22 × 10 ⁻⁵ [Ωm], thermal conductivity λ = 1.53 [W / m · K], low temperature side temperature Tc = 25 [° C.], height L = 1 .43 [mm], cross-sectional area A = 0.5 [mm ² ], heat sink area = 0.03 [m ² ] High temperature under heat transfer coefficient = 8 [W / m ² K] between heat sink and outside air The relationship between the side temperature T _H , the efficiency η, and the supplied power P is as shown in FIG. In FIG. 3, the curve 31 shows the efficiency η (Q _ab / P), and the curve 32 shows the supply power P [W]. According to this, when the efficiency η temperature T _H rises, and when T _H = 80 ° C., η falls to 0.3 or less, and the Peltier exhaust heat amount of the equation 3 and the heat sink discharge of the equation 2 are released. When the heat quantity becomes unbalanced and the temperature rises beyond this, control becomes impossible.

However, even if T _H is 80 ° C. or higher, for example 90 ° C., the Peltier devices 21 and 22 in two stages or more share the control, so that each Peltier device is controlled at a low temperature, for example. Since the operation is performed in the high efficiency η range near 40 ° C., it is possible to effectively perform cooling, that is, temperature control even at a high temperature of 80 ° C. or higher.

As described above, in the present invention, a plurality of stages of Peltier elements are provided. However, since this Peltier element is extremely lightweight and small in size as compared with a heat sink and a cooling fan, this Peltier element is used. The burden on the optical pickup due to the provision of a plurality of stages does not pose a problem.

Further, in the present invention, the temperature control of the light source unit 1 which requires high accuracy as described above and the cooling for surely performing this control are realized by adopting the Peltier element structure of at least two stages. Since the Peltier element 2 of the first stage can effectively dissipate and cool the temperature rise even when the laser beam is continuously oscillated for a long period of time, the second Peltier element 6 can subtly share the laser beam. That is, highly accurate temperature control can be performed.

[0041]

Embodiments of the optical pickup according to the present invention will be described. The pickup according to the invention, as usual,
For example, as shown in the perspective view of the outline of the optical pickup 101 in FIG. 4, the optical pickup 103 according to the present invention is movably arranged along the radial direction of the rotating optical disc 101 as shown by an arrow 102.

The optical pickup 103 has a light source section structure 105 having a light source section 1, as shown in FIG.
And the laser light extracted from the optical disk 101.
It has an objective lens driving device 105 having an objective lens for condensing the light into an image.

The light source unit structure 105 has a package 105 in which the light source unit 1 is housed. The light source unit 1 includes an excitation semiconductor laser 106, a laser medium 107 excited by laser light from the semiconductor laser 106, and a nonlinear optical element 108.

The semiconductor laser 106 is mounted on the mounting table 109 having good thermal conductivity while being thermally closely coupled thereto. A condenser lens 110 and a lens fixing block 111 having good thermal conductivity are fixed to the condenser 106 and arranged in the optical rear stage of the laser 106.

A quarter wavelength plate 112, for example, is arranged on the incident side of the pumping laser light of the laser medium 107.
The resonator 200 is constituted by the wave plate 112, the laser medium 107, and the nonlinear optical element 108.

The laser medium 107 is, for example, Nd: YAG.
The laser light from the semiconductor laser light for excitation is condensed by the lens 110 and introduced into the laser medium 107 via the quarter-wave plate 112.

The incident surface of the quarter-wave plate 112 for the excitation laser light transmits the excitation laser light (for example, a wavelength of 810 nm) and has a wavelength-selective reflection surface 113 for reflecting the laser light generated by the laser medium 107. And The end face of the nonlinear optical element 108 for deriving the wavelength-converted light is a reflecting surface 114 that reflects the fundamental wave, that is, the light of the wavelength generated from the laser medium 107, and transmits the wavelength-converted light, for example, the second harmonic. .

The nonlinear optical element 108 is, for example, KTP.
(KTiOPO ₄ ), for example, the above-mentioned N
The fundamental wave light by the laser light from the laser medium 107 made of d: YAG, for example, the second harmonic (532) of 1064 nm
(nm) is transmitted through the reflecting surface 114 and output.

In this configuration, the quarter-wave plate 112
Is a birefringent element used in the laser light source disclosed in Japanese Patent Application Laid-Open No. 1-220870, which stably and efficiently outputs laser light of the second harmonic emitted as output laser light. .

The above-mentioned resonator 200, that is, the laser medium 107 and the like is installed on the good heat conductive fixed block 117.

The mounting table 109 of the semiconductor laser 106, the lens 110, and the fixed blocks 111 and 117 of the resonator 200 are, for example, thermally and tightly coupled on a common substrate 118 having good thermal conductivity, and are mutually predetermined. The light source unit 1 is configured by arranging them while maintaining the positional relationship.

Then, the first Peltier element 21 is arranged in the light source unit 1 so that the pole on one side thereof is brought into thermal contact with the light source unit 1, in the illustrated example, the substrate 118. Further, the second Peltier element 22 is placed on the other side pole of the first Peltier element 21 so as to be in close contact with the low temperature side pole of the second Peltier element 22. A heat sink 3 having a large number of heat radiation fins 119 is thermally and tightly coupled to the high temperature side pole of the second Peltier element 22.

In the first and second Peltier elements 21 and 22, semiconductor pellets having a Peltier effect between the substrates 4 made of, for example, Al ₂ O ₃ and having metal deposited on both ends are arranged. A normal configuration can be adopted.

In the example of FIGS. 1 and 5, when the second Peltier element 22 is arranged outside the package 105,
In the above example, both Peltier elements 21 and 22 are both arranged in the package 105.

Then, the short-wavelength laser light, which has been wavelength-converted and emitted from the nonlinear optical element 108, has its optical path bent by, for example, a mirror 115, and the package 10
5 out of the package 105 through the window 116,
This is made to pass through the objective lens of the objective lens driving device 5 and is focused on the optical disc 101, as shown by the broken line in FIG.

In the above-mentioned light source assembly, if the temperature on the low temperature side, that is, the control target temperature Tc, the heat absorption amount Q _ab , and the use environment temperature are restricted, the optimum shape variable x that minimizes the power consumption is determined. Now, in the case of controlling the first Peltier device 21 so that ΔT = 20 ° C.,
A curve 61 in FIG. 6 is obtained when the power consumption is optimized with respect to the outside air temperature, although the power consumption is optimized to be the minimum.
The boundary condition in this case is the heat transfer coefficient h = 8 [W / m ² K] of the heat sink 3, and the heat absorption amount Q _ab = 1.2 [W] and the Seebeck coefficient α = 205 × 10 ⁻ for the Peltier element. ⁶ [V / K], resistivity ρ = 1.22 × 10 ⁻⁵ [Ωm], thermal conductivity λ = 1.53 [W / mK], low temperature side temperature Tc = 25 [° C], height L = 1.43 [mm], cross-sectional area A = 0.5 [mm ² ].

Under the same conditions, the case where the Peltier device shown in FIG. 7 has a single stage is shown by the curve 62 in FIG. With this conventional configuration, there is no solution under the above conditions when the outside air temperature exceeds 60.5 ° C. That is, temperature control is impossible even if the shape of the Peltier element is optimized.

On the other hand, according to the configuration of the present invention, it is possible to operate at a higher temperature than the conventional configuration.

In the example described above, the second Peltier element 22
However, as shown in FIG. 2, the second Peltier device 22 is arranged outside the package, or the package itself is used as a heat sink. Various modifications and changes can be made.

In the illustrated example, the Peltier device is the substrate 4
This is a case where the structure is thermally coupled to the package or the heat sink 3 via, but it is desirable to exclude each substrate of each Peltier element 21 and 22 including this substrate 4. Explaining with this, in the place where the aforementioned, for simplicity of explanation, the temperature of the temperature T _H and the heat sink 3 of the hot side of the Peltier element is a case of the identical, in practice between them There is a temperature difference.

[0061] Now, the temperature of the heat sink 3 and T _HS,
Considering the one-dimensional model for simplicity, the following formula 3 is obtained.

[0062]

[Equation 5] _{Q out = (T H -T HS} ) · λ p S p / L p

Λ _p , S _p and L _p are the thermal conductivity, area and thickness of the substrate, respectively.

When this is transformed, the equation 4 is obtained.

[0065]

[Equation 6] T _H = (Q _out · L _p / λ _p · S _p ) + T _HS

Therefore, in order to lower T _H , it is conceivable to reduce L _p or increase λ _p and S _p , but it is effective to eliminate the substrate of the Peltier element. .

[0067]

According to the configuration of the present invention, the first Peltier element 21 thermally coupled to the light source section 1 and the second Peltier element 22 thermally coupled to the first Peltier element 21.
By providing at least two stages of Peltier elements, it is apparently efficient from the above, and reliable and stable temperature control can be performed even under a high outside air temperature.

Therefore, according to the present invention, it is possible to reduce the size of the heat sink, and in some cases to omit the heat sink, and also to reduce the size of the heat sink when a fan for forced cooling is provided depending on the surrounding conditions of use. be able to.

Further, according to the present invention, since the Peltier device has at least two stages, the temperature control of the light source section 1 which requires high accuracy as described above and the cooling for surely performing this control are performed. Since the Peltier element 2 of the first stage can effectively dissipate and cool the temperature rise even when the laser beam is continuously oscillated for a long period of time, the second Peltier element 6 can subtly share the laser beam. That is, the benefit is large in practical use, such as highly accurate temperature control.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a main part of an example of an optical pickup according to the present invention.

FIG. 2 is a schematic cross-sectional view of a main part of another example of the optical pickup according to the present invention.

FIG. 3 is a diagram showing the relationship between the efficiency of a Peltier element and the temperature of supplied power.

FIG. 4 is a perspective view of an example of the present invention.

FIG. 5 is a schematic cross-sectional view of a main part of an example of an optical pickup according to the present invention.

FIG. 6 is a diagram showing the outside air temperature dependence of the power consumption of the conventional pickup and the present invention.

FIG. 7 is a schematic cross-sectional view of a main part of a conventional optical pickup.

[Explanation of symbols]

 1 Light Source Section 21 First Peltier Element 22 Second Peltier Element 3 Heat Sink

Claims (2)

[Claims] 1. An optical pickup device comprising a pumping semiconductor laser, a laser medium pumped by laser light from the semiconductor laser, and a light source section having a non-linear optical element, wherein at least a first Peltier element is provided. And a second Peltier element are overlapped with each other, and one pole of the first Peltier element is thermally coupled to the light source unit, and the low-temperature side pole of the second Peltier element is the first Peltier element. An optical pickup device characterized by being thermally coupled to the other pole of the. 2. The optical pickup device according to claim 1, wherein the first Peltier element serves as temperature control means for the light source section, and the second Peltier element serves as main heat radiation means.