JP2003177295A - Lens system and optical head device equipped with temperature compensating function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent performance degradation by canceling the change of the focal distance of a lens system due to temperature change and the change of the linear expansion of a supporting member for a lens system due to the temperature change. <P>SOLUTION: This lens system 1 is provided with collimating lenses 2 and 3 and a light source or a photodetector 5 and has constitution where they are attached to the same supporting member 4. When a distance between the lens group and the light source or the photodetector 5 is changed because of the change of the linear expansion in the optical axis direction of the member 4 due to the temperature change, the change amount of the focal distance of the lens group caused by the change of the refractive index and the change of the linear expansion of the respective lenses due to the temperature change is regulated to be equal to the change amount of the distance. Thus, collimating accuracy is improved. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for preventing performance deterioration due to temperature change in a lens system including a collimating lens group and a light source or a light receiving section.

[0002]

2. Description of the Related Art As an apparatus having a lens system and a light source or a light receiving portion mounted on the same supporting member, for example, an optical head device (or optical pickup) used for signal reading or signal recording of an optical disc is used. Can be mentioned.

FIG. 6 schematically shows a main part of such a configuration example.

A lens a (shown as a single lens in the figure) and a light source (semiconductor laser) b are mounted on a mount portion c, and the lens a is a collimating lens, and the light emitted from the light source b is collimated. It has the role of making light.

By the way, in such a lens system, a change in the ambient environment, for example, a temperature change is a problem, and a change in the distance between the lens a and the light source b, a change in the wavelength of the light source itself, or a change in the power of the lens itself. The focal length shifts due to the change.

That is, as shown in FIG. 6A, the lens a on the mount portion c is in the state before the temperature change.
While the distance between the light source and the light source b was "X0",
In the state after the temperature change, due to the linear expansion of the mount part c,
As exaggeratedly shown in the figure (B), it becomes "X1" and extends in the optical axis direction. As a result, in the figure (A), as shown by the light rays d, d, the light transmitted through the lens a was emitted as parallel light, but in the state after the temperature change shown in the figure (B), As shown by the light rays e, e, the transmitted light of the lens a deviates from the state of parallel light.

[0007]

As described above, due to the influence of the temperature change, it becomes impossible for the light emitting system to accurately keep the light emitted from the lens as parallel light, and in the light receiving system, the incident light that has passed through the lens. Out of focus, etc.,
In an optical head device or the like using such a lens system, there is a problem that characteristics may deteriorate when the temperature changes.

Particularly, in the case of a lens system such as an optical disc having a high NA (numerical aperture), which requires a strict requirement for collimation accuracy, a change in linear expansion of the mount portion and a change in focal length of the lens system occur. The difference causes performance deterioration.

Therefore, it is difficult to be affected by temperature changes due to design changes such as attachment and support structure of lenses and light sources, and glass materials and arrangement in the lens system, or adjustment or correction means for temperature compensation is taken. Although a method is conceivable, there remain inconveniences such as a complicated structure and a hindrance to downsizing and cost reduction.

An object of the present invention is to prevent performance deterioration by canceling out the change in focal length of the lens system due to temperature change and the change in linear expansion of the supporting member of the lens system due to temperature change.

[0011]

In order to solve the above-mentioned problems, the present invention is directed to a linear expansion change amount in the optical axis direction of a supporting member for supporting a collimating lens group and a light source or a light receiving portion. In addition, the material and power arrangement of each lens are specified so that the change in the combined focal length of the lens group due to the change in the refractive index of each lens due to the temperature change and the change in the linear expansion of the lens in the optical axis direction becomes equal. Is.

Therefore, according to the present invention, the temperature variation can be compensated by offsetting the variation in the distance between the lens group and the light source or the light receiving section by the variation in the combined focal length of the lens group. it can.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to temperature compensation in a lens system having a structure in which a collimating lens group and a light source or a light receiving section are attached to the same supporting member. Suitable for application.

When the focal length (synthetic focal length) of the synthetic lens system relating to the collimating lens group is "F" and the variation due to the temperature change is "ΔF", ΔF can be calculated from the following formula. .

[0015]

[Equation 1]

In the above equation, "fi" indicates the focal length of each lens, "dαi" indicates the coefficient of linear expansion (rate of change) of the ith lens due to temperature change, and "dni" indicates the first. The refractive index change coefficient by the temperature change about the i-th lens is shown. Further, “Σ” means the sum of the natural number variable “i” for the first to Nth lenses (“N” indicates the number of lenses).

Then, "dni" and "dαi" are defined by the following equations (the subscript "i" representing the lens number is omitted).

[0018]

[Equation 2]

Here, “Δn” represents a finite change in the refractive index with temperature, and “Δα” represents a finite change in the linear expansion coefficient with temperature.

Therefore, the value of "dni" for each lens is determined by the change in the refractive index of the lens material with temperature, and the value of "dαi" for each lens is determined by the change in the linear expansion of the lens material with temperature. 1] As shown in the equation,
For the value obtained by subtracting the reciprocal of “dni” from “dαi” divided by “fi”, the total sum for the variable i is calculated and the value of F is 2
By multiplying by the power, the temperature change amount “ΔF” can be obtained for the combined focal length “F” of the lens group.

Then, the support member for supporting the lens group, the light source or the light receiving portion linearly expands (or contracts) due to a temperature change.
When the change in the distance between the lens group and the light source or the light receiving unit is described as “ΔX”, the above ΔF
Have the same sign and the same size (ΔX−ΔF = 0),
The change due to temperature can be offset. That is, with respect to the linear expansion change ΔX of the support member in the optical axis direction caused by the temperature change, the refractive index change “Δn” of each lens due to the temperature change and the linear expansion change “Δ of the lens in the optical axis direction.
If it is specified that the condition that the variation “ΔF” in the combined focal length due to α is equal, ideal temperature compensation can be realized.

However, in reality, it is difficult to strictly satisfy the condition of "ΔX = ΔF" over the desired temperature range. Therefore, a certain allowable range "ε" is set and "| ΔX-Δ" is set.
The lens system may be designed under the condition of F | <ε (for example, about 20 μm is set as a practical ε value).

In the above formula [1], "1 / d
“Ni” is given a negative sign, and taking into account that it is proportional to the reciprocal of Δn, a lens or lens group having a positive lens power formed of a material whose refractive index change due to temperature change is small, and a temperature An example is a combination of a lens or a lens group having a negative lens power, which is made of a material having a large change in refractive index due to a change.

Then, in the above equation [1], "dα
a lens or a lens group having a positive lens power formed of a material having a large linear expansion change due to temperature change, considering that the sign of “i” is positive and this is proportional to “1-Δα”; An example is a combination of a lens or a lens group having a negative lens power, which is made of a material whose linear expansion change due to temperature change is small.

Generally, plastic is mentioned as a material having a large change in refractive index due to temperature change (showing a negative value as a change rate), and glass is mentioned as a material having a small change in refractive index due to temperature change. In the latter case, among optical glasses, there are PBH4, PBH3, etc. (made by OHARA) as a material having a relatively large refractive index change, and S-FSL as a material having a relatively small refractive index change.
5, S-FTL10 etc. (made by OHARA).

Further, as a material having a large linear expansion change due to a temperature change, there may be mentioned plastic, and as a material having a small linear expansion change due to a temperature change, there may be mentioned a glass. As relatively large materials, there are S-FSL5, S-FPL51 and the like (manufactured by OHARA), and as materials having a relatively small change in linear expansion, there are S-LAH60, S-YGH51 and the like (manufactured by OHARA).

FIG. 1 schematically shows an example of the configuration of a lens system according to the present invention. FIG. 1A shows a state before temperature change, and FIG. 1B shows a state after temperature change. Shows.

In the lens system 1 shown in this example, the lens group consisting of the convex lens 2 and the concave lens 3 is a supporting member (mounting portion).
The light source or the light receiving unit 5 is attached to the support member 4 while being attached to the support member 4.

Regarding the light source or the light receiving section 5, for example, when applied to an optical head device, a semiconductor laser is used in the light emitting system, and a light receiving element such as a photodiode is used in the light receiving system. That is, in the light emitting system, the light emitted from the semiconductor laser is emitted through the convex lens 2 after passing through the concave lens 3, and in the light receiving system, the light incident on the convex lens 2 reaches the light receiving element through the concave lens 3.

For the convex lens 2, a material exhibiting a low refractive index change and a high linear expansion change with respect to temperature change is used, and the concave lens 3 shows a high refractive index change with respect to temperature change, and A material exhibiting a low linear expansion change is used. That is, the respective tendencies of the refractive index change and the linear expansion change are defined to be opposite to each other according to the difference in the sign of the lens power (see the above [Formula 1] and [Formula 2].

The support member 4 is made by, for example, magnesium die casting or the like.

In the state before the temperature change shown in FIG.
The distance between the lens group on the support member 4 and the light source or the light receiving unit 5 is “X0”, and for example, in the case of a light emitting system,
The light emitted from the light source passes through each lens and becomes parallel light.

Assuming that the temperature of the lens system is changed, for example, the temperature is changed to a high temperature side (temperature rise), FIG.
As shown in an exaggerated manner, due to the linear expansion of the support member 4, the distance between the lens group and the light source or the light receiving unit 5 becomes “X1”, and extends in the optical axis direction.

As a result, the focal length of the convex lens 2 is shortened by the change of the refractive index due to the temperature change and the change of the curvature by the linear expansion, and the concave lens 3 is changed by the temperature change and the refractive index. The change in the curvature due to the linear expansion extends the focal length.

However, as described above, the convex lens 2
Is made of a material that has a small change in refractive index and a large change in linear expansion with respect to temperature changes, and therefore the amount of change in focal length is small. Further, since the concave lens 3 is made of a material having a large change in refractive index and a small change in linear expansion with respect to temperature change, the amount of change in focal length is large.

Therefore, the focal length of the entire lens system becomes longer as the temperature changes to the higher temperature side. If the change in the focal length is made equal to the change “ΔX = X1−X0” due to the linear expansion of the support member 4, the influence due to the temperature change can be eliminated. That is, by appropriately designing the refractive index change coefficient and the linear expansion coefficient with temperature for each lens, the change in the focal length of the lens system due to the temperature change and the extension amount due to the linear expansion of the support member 4 are regulated to the same degree. It is possible to reduce the influence of the shift of the focal length.

As a result, in the case of a light emitting system, FIG.
Even if the distance between the lens group and the light source extends in the optical axis direction as shown by the solid line in (B), the light transmitted through each lens is emitted as parallel light. It should be noted that the light rays shown by the broken lines in the figure are comparatively showing the light rays before the temperature change.

In the above description, the case where the temperature rises is described. However, it is needless to say that the temperature compensation is performed even when the temperature drops and the influence of the shift of the focal length is reduced. Further, in the above example, the lens configuration in which one convex lens and one concave lens are combined has been described, but the present invention is not limited to this, and for example, a lens group having a positive lens power composed of a plurality of lenses or a plurality of lenses. A configuration using a lens group with negative lens power consisting of
Various embodiments are possible.

FIG. 2 is a schematic view showing only the main part of the configuration for application to the optical head device 6.

The recording medium 7 is constructed so as to be able to read or record optical signals, and light is irradiated through the objective lens 8 provided in the optical head device 6. still,
Although illustration is omitted, driving control in the focus direction and the tracking direction is performed by a driving device (biaxial actuator) that supports the objective lens 8.

The optical head device 6 includes a light source, a light receiving section, and a lens system. That is, the light emitted from the semiconductor laser 9 becomes parallel light by the collimating lens 10 (shown as a single lens in the drawing), and the beam splitter 11 is used.
The objective lens 8 is irradiated with the light through a λ / 4 wavelength plate or the like. Further, the return light from the recording medium 7 goes through the objective lens 8 and follows the reverse of the forward path, and is transmitted from the beam splitter 11 through the lens 12 (shown as a single lens in the figure) to the light receiving element 1.
Reach 3.

Although not shown, regarding the lens 10 and the semiconductor laser 9, and the lens 12 and the light receiving element 13,
Each is attached to the same support member.

In the present invention, the lens 10 and the lens 12 are formed as a lens group, and the combination of the lens groups caused by the change in the refractive index of each lens due to the temperature change and the change in the linear expansion of the lens in the optical axis direction. The difference between the variation of the focal length and the variation of the linear expansion of the support member in the optical axis direction is set to zero or a value near it (a permissible value including zero).

That is, the focal length change due to the temperature change in the composite lens system including the lens (or lens group) having a positive lens power and the lens (or lens group) having a negative lens power, and the corresponding lens The lens system is designed so that the linear expansion change due to the temperature change of the support member of the system cancels each other out.

As the lens material, a plastic material can be used, but when a glass material having a small change in refractive index and a small change in linear expansion due to temperature change is used, temperature compensation can be effectively realized by the present invention. You can Further, in the application to an optical disc device, it is useful for temperature compensation in the case of a high NA, that is, a lens system to which high collimation accuracy is imposed.

[0046]

EXAMPLE FIG. 3 shows a configuration according to Example 1, which is a first glass lens L1 having a positive lens power.
And a second glass lens L2 having a negative lens power are bonded together.

Then, the lens L2 and the semiconductor laser LS
A lens L3 having no power is arranged at an intermediate position between and, which is a cover glass.

Each lens and the semiconductor laser LS are mounted on a supporting member (mounting part) 4_1.

When the focal length of the lens system at the light source wavelength of 405 nm (nanometer) is "f" and the linear expansion coefficient of the supporting member is "αm", in this example, f = 25.0 (m)
m) and αm = 1.01010.

The structure and arrangement of the lens system are shown in table form as follows.

[0051]

[Table 1]

The meaning of each symbol in the above table is as follows.

“No”: Surface number attached to lens surface “r”: Curvature radius of lens surface (unit: mm) “d”: Surface spacing (unit: mm) “n”: d line (light source wavelength 587. Refractive index “ν” at 56 nm) ... Abbe number at d-line (light source wavelength 587.56 nm).

Regarding the surface number, the left side surface of the lens L1 is defined as "1", and the surface number is defined to increase toward the right side. Regarding the surface spacing, the i-th and (i + 1) -th spacings are described in the i-th row in the table (this also applies to Tables 2 and 3 described later). ).

In this embodiment, the lens L1 is refracted.
The temperature coefficient of the rate is −5.65 × 10 ^-6/ ° C, linear expansion section
The number is 90 × 10^-7/ ° C, and the lens L2
And the temperature coefficient of the refractive index is 8.08 × 10^-6/ ° C,
Linear expansion coefficient is 67 × 10^-7/ ° C.

FIG. 4 shows the configuration according to the second embodiment, which is a lens group in which a first glass lens L1 having a positive lens power and a second glass lens L2 having a negative lens power are bonded together. And the third glass lens L3 having a positive lens power has a configuration of three elements in two groups.

Then, the lens L3 and the semiconductor laser LS
A cover glass L4 having no power is arranged between and.

The lenses L1 to L3 and the semiconductor laser LS are mounted on a supporting member (mounting part) 4_2.

In this example, f = 11.0 (mm), αm =
It is 1.00055.

The structure and arrangement of the lens system are shown in a table format as follows.

[0061]

[Table 2]

The meaning of each symbol in the above table is as described above.

In this embodiment, the lens L1 has a temperature coefficient of refractive index of 0.19 × 10 ⁻⁶ / ° C and the linear expansion coefficient of 88 × 10 ⁻⁷ / ° C. The temperature coefficient of the coefficient is 12.54 × 10 ⁻⁶ / ° C and the linear expansion coefficient is 82 × 10 ⁻⁷ / ° C. The temperature coefficient of the refractive index of the lens L3 is 0.19 × 1.
The coefficient of expansion is 0 ^-6 / ° C and the coefficient of linear expansion is 88 × 10 ^-7 / ° C.

FIG. 5 shows the configuration according to the third embodiment, which is a lens group in which a first glass lens L1 having a positive lens power and a second glass lens L2 having a negative lens power are bonded together. And the third glass lens L3 having a positive lens power has a configuration of three elements in two groups.

The lens L3 and the semiconductor laser LS
A cover glass L4 having no power is arranged between and.

The lenses L1 to L3 and the semiconductor laser LS are mounted on a supporting member (mounting part) 4_3.

In this example, f = 10.2 (mm) and αm =
It is 1.00055.

The structure and arrangement of the lens system are shown in a tabular form as follows.

[0069]

[Table 3]

The meaning of each symbol in the above table is as described above.

The values of the temperature coefficient of linear refractive index and the coefficient of linear expansion of the lenses L1 to L3 are the same as those of the lenses L1 to L3 of the second embodiment.

According to each of the embodiments described above, even if the distance between the light source or the light receiving portion and the lens group changes due to the linear expansion (or contraction) of the support member due to the temperature change,
Since the change in the focal length of the lens system occurs to the same degree and the temperature compensation is performed, the following advantages can be obtained.

Even if the temperature changes in the light emitting system, the light emitted from the lens system can be accurately kept parallel.

Even if the temperature changes in the light receiving system, it is possible to accurately maintain the position of the focal point where the parallel light is focused.

By making the system itself including the lens group supported by the same member and the light source or the light receiving portion have a temperature compensating function, it is possible to suppress the influence of temperature change on the characteristics as much as possible when applied to the optical head device. .

[0076]

As is apparent from the above description, according to the inventions according to claims 1 and 6, the lens changes with respect to the distance change ΔX between the lens group and the light source or the light receiving section. By compensating with the change ΔF in the combined focal length of the system, temperature compensation can be performed, and therefore the configuration is not complicated and the cost is not significantly increased. In addition, when applied to the optical head device, it is difficult to receive a change in ambient temperature, so that performance and reliability can be improved.

According to the inventions of claims 2 and 7,
By designing the temperature change amount ΔF of the focal length in consideration of the refractive index change coefficient and the linear expansion coefficient of each lens due to the temperature change, ΔF can be regulated to a value substantially equal to the distance change amount ΔX. .

Claim 3, Claim 4, Claim 8, and Claim 9
According to the invention of claim 1, by selecting the materials having different tendencies of the change of the refractive index and the change of the linear expansion due to the temperature change according to the sign (positive or negative) of the lens power, the design of the lens system can be facilitated. Can be prevented from becoming complicated.

According to the fifth and tenth aspects of the present invention, precise temperature compensation can be performed when a glass lens having a small change in refractive index and a small change in linear expansion is used.
Higher performance is possible.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a configuration of a lens system according to the present invention, in which FIG. 1A shows a state before a temperature change,
The figure (B) shows the state after the temperature change.

FIG. 2 is a diagram illustrating a main part of a configuration of an optical head device.

FIG. 3 is a view showing an embodiment of the present invention together with FIGS. 4 and 5, and this drawing is an explanatory view of the first embodiment.

FIG. 4 is an explanatory diagram of a second embodiment.

FIG. 5 is an explanatory diagram of a third embodiment.

FIG. 6 is a diagram showing a conventional configuration example, in which (A) shows a state before temperature change, and (B) shows a state after temperature change.

[Explanation of symbols]

1 ... Lens system, 2, 3 ... Lens, 4, 4_1, 4_2,
4_3 ... Support member, 5 ... Light source or light receiving section, 6 ... Optical head device, 7 ... Recording medium, L1 to L3 ... Lens

Continued front page    F-term (reference) 2H044 AH01 AH05 AH14                 2H087 KA13 LA25 NA08 PA01 PA02                       PA18 PB02 PB03 QA02 QA05                       QA07 QA14 QA22 QA25 QA33                       QA37 QA41 QA42 QA45 RA42                       UA01                 5D119 AA01 AA03 AA11 AA22 AA50                       BA01 BB01 BB02 BB03 DA01                       DA05 FA05 JA02 JB01 JB03                       JB04 JB06                 5D789 AA01 AA03 AA11 AA22 AA50                       BA01 BB01 BB02 BB03 DA01                       DA05 FA05 JA02 JB01 JB03                       JB04 JB06

Claims (10)

[Claims] 1. A lens system having a temperature compensating function, comprising a collimating lens group and a light source or a light-receiving unit mounted on the same supporting member, wherein the optical axis direction of the supporting member is caused by a temperature change. Is specified so that the change in the refractive index of each lens due to the temperature change and the change in the combined focal length of the lens group due to the change in the linear expansion of the lens in the optical axis direction are equal to the change in the linear expansion. A lens system with a temperature compensation function that is characterized by 2. A lens system having a temperature compensation function according to claim 1, wherein the refractive index change coefficient of each lens due to temperature change is “dn
i ”, the linear expansion coefficient of each lens due to temperature change is“ dαi ”,
When the focal length of each lens is “fi”, the combined focal length of the lens group is “F”, and the temperature change of the combined focal length is “ΔF”, “ΔF = F ² · {Σ (1 / fi) ・ (dαi-1 / dn
i)} ”(where“ Σ ”means the sum of the natural number variable“ i ”for the first to Nth lenses.
“N” indicates the number of lenses. ) Is obtained by
A lens system having a temperature compensating function, characterized in that the distance change ΔX between a lens group and a light source or a light-receiving unit that occurs when the temperature changes are made to have substantially the same size with the same sign. 3. A lens system having a temperature compensation function according to claim 1, wherein a lens or lens group having a positive lens power and made of a material whose refractive index change due to temperature change is small, and refraction due to temperature change. A lens system having a temperature compensating function, comprising a lens or a lens group having a negative lens power formed of a material having a large rate change. 4. A lens system having a temperature compensation function according to claim 1, wherein a lens or lens group having a positive lens power and made of a material having a large linear expansion change due to temperature change, and a line due to temperature change. A lens system having a temperature compensating function, comprising a lens or a lens group having a negative lens power formed of a material having a small expansion change. 5. The lens system having a temperature compensating function according to claim 1, wherein the lens or the lens group is made of a glass material. 6. A structure in which a light source and a light receiving unit and a lens group for collimation are provided to read or record a signal from a recording medium, and the lens group and the light source or the light receiving unit are attached to the same supporting member. In the optical head device having the above, due to the change in the linear expansion in the optical axis direction of the supporting member caused by the temperature change, the change in the refractive index of each lens and the linear expansion change in the optical axis direction of the lens due to the temperature change An optical head device, characterized in that it is defined so that the variation of the combined focal length of the lens groups becomes equal. 7. The optical head device according to claim 6, wherein the refractive index change coefficient of each lens due to temperature change is “dn
i ”, the linear expansion coefficient of each lens due to temperature change is“ dαi ”,
When the focal length of each lens is “fi”, the combined focal length of the lens group is “F”, and the temperature change of the combined focal length is “ΔF”, “ΔF = F ² · {Σ (1 / fi) ・ (dαi-1 / dn
i)} ”(where“ Σ ”means the sum of the natural number variable“ i ”for the first to Nth lenses.
“N” indicates the number of lenses. ) Is obtained by
An optical head device characterized in that the distance change ΔX between a lens group and a light source or a light-receiving unit that occurs when the temperature changes is made to have substantially the same size with the same reference sign. 8. The optical head device according to claim 6, wherein the lens or lens group having a positive lens power and made of a material having a small change in refractive index due to temperature change, and the material having a large change in refractive index due to temperature change And a lens or lens group having a negative lens power formed in 1. 9. The optical head device according to claim 6, wherein the lens or lens group having a positive lens power and made of a material having a large linear expansion change due to temperature change, and the material having a small linear expansion change due to temperature change. And a lens or lens group having a negative lens power formed in 1. 10. The optical head device according to claim 6, wherein the lens or the lens group is made of a glass material.