JP2002006211A - Temperature compensation lens and optical device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a temperature compensation lens (collimator lens) capable of more easily performing a focusing correction in accordance with a temperature fluctuation, and to obtain an optical device using temperature compensation lens. SOLUTION: The temperature compensation lens is provided with at least one positive lens and at least one negative lens, and two or more lenses are formed of different lens materials, and provided that the refractive index of material for an i-th lens in order form the exit side of a luminous flux is expressed by (ni), the rate-ofchange of the refractive index (ni) with reference to the temperature rise (dt) is expressed by dni/dt (1/ deg.C), and the power of the i-th lens is expressed by ϕi (1/mm), a conditional expression (1) should be satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature compensating lens and an optical apparatus using the same, and more particularly, to appropriately compose a temperature compensating lens to easily correct a focus due to a temperature fluctuation. The present invention relates to a collimator lens used in a scanning optical device, or a condensing lens (imaging lens) used in a digital image reading device or the like.

[0002]

2. Description of the Related Art Conventionally, in a scanning optical device used in an image forming apparatus such as a laser beam printer or a digital copying machine, a light beam emitted from a light source means after being modulated in accordance with an image signal is output to, for example, a rotating polygon mirror (polygon mirror). )
The light is periodically deflected by an optical deflector, and is focused on a photosensitive recording medium (photosensitive drum) surface in the form of a spot by an imaging optical system having fθ characteristics, and the surface is optically scanned to record an image. Is going.

FIG. 11 is a schematic view of a main part of a conventional optical scanning device.

In FIG. 1, a substantially parallel light beam emitted from a laser unit 111 enters a cylindrical lens 112 having a predetermined refractive power only in the sub-scanning direction. Of the substantially parallel light beams that have entered the cylindrical lens 112, they are emitted as they are as substantially parallel light beams in the main scanning section. In the sub-scan section, the light is converged and formed as a substantially linear image on the deflecting surface 113a of the optical deflector 113 composed of a rotating polygon mirror. Then, the deflection surface 113 of the optical deflector 113
The light beam deflected and reflected at a is imaged on a photosensitive drum surface 116 as a surface to be scanned by an imaging optical system (fθ lens system) 117 including a spherical lens 114 and a toric lens 115 having fθ characteristics, and Arrow A deflector 113
The photosensitive drum surface 116.
Image information is recorded by optically scanning the upper part in the direction of arrow B (main scanning direction).

FIG. 12 shows the laser unit 1 shown in FIG.
FIG. 11 is an enlarged explanatory view of FIG. In the figure, 121 is a semiconductor laser as a light source, 122 is a base, 123 is a lens barrel holder, 124 is a lens barrel, 125 is a convex lens (collimator lens), and 126 is a diaphragm. In the figure, the light beam emitted from the semiconductor laser 121 is converted into a substantially parallel light beam by a convex lens 125, and is emitted after being restricted by a stop 126.

In recent years, as the performance of a scanning optical device has become higher with a higher performance of a printer or the like, drawing with a smaller spot diameter has been required, and a bright optical system with a small Fno has been required. The adoption of a bright optical system with a small Fno reduces the depth of focus, so that it is necessary to take a countermeasure against a change in focus due to an environmental change (particularly, a temperature change).

[0007] For example, as a countermeasure, there is a method in which the lens barrel shape of the collimator lens shown in FIG. There is a method of correcting focus fluctuation by combining with wavelength fluctuation of a laser light source.

[0008]

However, the above-described correction method has limitations due to mechanical restrictions on the lens barrel shape,
There are various problems such as an increase in cost caused by newly introducing a diffractive optical element. Various proposals have conventionally been made to balance the mechanical deformation of the collimator lens, the change in the refractive index, the change in the shape, and the movement of the focus due to the mode hop of the laser light source, but no specific method is disclosed. Did not.

It is an object of the present invention to provide a temperature compensating lens which makes it easier to correct the focus due to temperature fluctuation by appropriately setting each lens constituting the temperature compensating lens, and an optical device using the same.

[0010]

The temperature compensation lens according to the first aspect of the present invention has at least one positive lens and at least one negative lens, of which two or more lenses are mutually made of materials. Differently, the refractive index of the material of the i-th lens is ni, the rate of change of the refractive index ni with respect to the temperature rise dt is dni / dt (1 / ° C.), and the power of the i-th lens is φi from the emission side of the light beam. (1 / mm)

[0011]

(Equation 2)

M: the total number of lenses.

According to a second aspect of the present invention, in the first aspect, the at least one negative lens is made of a material having a positive refractive index change.

According to a third aspect of the present invention, in the second aspect, the at least one positive lens is made of a material having a negative refractive index change.

According to a fourth aspect of the present invention, in the third aspect of the invention, at least one of the positive lenses has a refractive index change rate with respect to temperature made of a material having the positive refractive index change. It is characterized by being smaller than the rate of change.

According to a fifth aspect of the present invention, in the third or fourth aspect of the present invention, a positive lens made of a material having a negative refractive index change is located on the most exit side of the light beam.

According to a sixth aspect of the present invention, in the first aspect of the present invention, the temperature compensating lens comprises four or less lenses.

An optical device according to a seventh aspect of the present invention is characterized in that a light beam emitted from a light source is converted into a substantially parallel light beam by using the temperature compensation lens according to any one of the first to sixth embodiments. .

According to an eighth aspect of the present invention, in the seventh aspect of the present invention, an amount of change of the output wavefront of the temperature compensation lens due to a temperature change is a change amount of a wavelength of a light beam emitted from the light source of 5 nm.
Is 0.5 wavelength or less, and changes in a direction in which the focal length increases with a positive wavelength change.

According to a ninth aspect of the present invention, there is provided an optical device using the temperature compensation lens according to any one of the first to sixth aspects.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Numerical Example 1 FIG. 1 is a sectional view of a main part of a first embodiment when a temperature compensation lens according to the present invention is used in, for example, a laser unit of a scanning optical device as an optical device (to be described later). FIG. 7 is a lens cross-sectional view of Numerical Example 1.

In FIG. 1, reference numeral 1 denotes light source means (laser light source).
, For example, a semiconductor laser. Reference numeral 2 denotes a temperature compensating lens which functions as a collimator lens for converting a light beam emitted from the light source means 1 into a substantially parallel light beam. Hereinafter, for the sake of convenience, the temperature compensating lens 2 is treated as the i-th lens from the light-emitting side of the light beam. The collimator lens 2 serving as a temperature compensating lens in the present embodiment is a first lens G having a negative (negative refractive power) in order from a light beam output side (a stop 3 side).
1. The lens comprises four lenses: a positive (positive refractive power) second lens G2, a negative third lens G3, and a positive fourth lens G4. First, second, third and fourth four lenses G
1, G2, G3, and G4 are placed in a lens barrel 17 made of metal or resin, the position of which is determined using a spacer or a barrel shape, and fixed with a retaining ring or the like.
Reference numeral 3 denotes an aperture, which restricts a light beam passing through the collimator lens 2. 17 is a lens barrel, 18 is a barrel holder, and 19 is a base.

In FIG. 1, a divergent light beam emitted from a semiconductor laser 1 becomes a substantially parallel light beam after refraction through a collimator lens 2, passes through a stop 3, and enters a cylindrical lens (not shown) of a scanning optical device described later.

In the present embodiment, as shown in Numerical Example 1 described later, a glass material (trade name: S-bs17, OHARA CORPORATION) in which the negative first lens G1 has a positive refractive index change.
The second positive lens G2 is made of a glass material having a negative refractive index change (trade name: S-bal3, OHARA Co., Ltd.), and the third negative lens G3 is made of a positive refractive index change. The fourth positive lens G4 is made of a glass material (trade name S-bs17, OHARA CORPORATION) having a positive refractive index change.
The refractive index change rate (dn / dt) of the positive second lens G2 with respect to the temperature is set to be smaller than the refractive index change rate (dn / dt) of the negative first and third lenses G1 and G3 with respect to the temperature. are doing.

Next, temperature compensation according to the present invention will be described.

Normally, in the use state of the apparatus, the following changes occur in the apparatus shown in FIG. 1 as the environmental temperature changes.

(1) The wavelength of the laser light source 1 changes. The amount of change depends on the type of the laser light source, but is, for example, 0.2 m in a normal 5 mw to 30 mw semiconductor laser.
It changes by about nm / ° C.

(2) As a change in the mechanical shape, the lens barrel 17 and the barrel holder 18 expand due to a rise in temperature. As a method of correcting the elongation of the lens barrel 17 and the barrel holder 18, a method of performing reverse correction using thermal deformation using two or more types of materials (bimetal)
Is well known. However, it is difficult to make a large correction with the configuration of the lens barrel 17 and the barrel holder 18 shown in FIG. That is, this method has a limitation due to mechanical restrictions.

(3) The shape of the lens itself changes. When the lens shape changes due to the temperature rise, the power of the lens decreases.

In this embodiment, the refractive index of the lens material changes as follows due to an increase in the environmental temperature. In the following description, the description will be made in the form of a change in the focus position when a light beam enters from the stop side (so-called reverse tracing).

That is, the power of the negative first lens G1 is originally low, but changes in the direction of reducing the focus due to a positive refractive index change. Since the positive second lens G2 has a negative refractive index change, it changes in the direction in which the focus is extended. The negative third lens G3 changes in the direction in which the focus is extended by increasing the negative power due to the positive refractive index change. Positive fourth lens G
Reference numeral 4 has a positive refractive index change and changes in a direction to reduce the focus due to a temperature rise.

The sum of these changes is the focus change caused by the temperature rise. In most cases, deformation of the lens barrel 17 and the barrel holder 18 due to thermal expansion is large, and a change in the direction to correct this is required.

That is, in the present embodiment, the refractive index of the material of the i-th lens is ni and the rate of change of the refractive index ni with respect to the temperature rise dt is dni / dt.
(1 / ° C.), and the power (refractive power) of the i-th lens is φ
When i (1 / mm),

[0034]

(Equation 3)

M: total number of lenses By setting each lens so as to satisfy the following condition, the focal length of the lens is changed so as to increase as the temperature rises. As a result, a temperature compensating lens that can easily correct the focus due to the temperature fluctuation is obtained.

Conditional expression (1) defines the total amount of focus variation of each lens caused by a temperature change. If the upper limit of conditional expression (1) is exceeded, focus correction becomes difficult, which is not good. .

In this embodiment, a material having a negative refractive index change is particularly used for the positive second lens G2, so that the lens back (back focus) is effectively improved in the extending direction. If the lens is configured to extend in the direction in which the focal length of the lens is extended, it can be said that the thermal expansion of the lens barrel offsets the distance of the laser chip from moving away, and is advantageous in terms of temperature compensation. The temperature compensation can be more easily performed by compensating the bimetal structure of the lens barrel to add the surplus amount due to the offset and the amount generated by other factors.

As described above, in the present embodiment, by setting each lens so as to satisfy the conditional expression (1) as described above, a change in focus with respect to the temperature of the lens itself is reduced, or a direction in which the lens back extends due to a rise in temperature. That is, it is possible to approach the direction in which the deformation of the lens barrel is corrected. Specifically, by using a glass material having a small change in the refractive index with respect to the temperature rise for the positive lens and using a glass material having a large change in the refractive index with respect to the temperature rise for the negative lens, the focus due to temperature fluctuation can be reduced. It is possible to obtain a temperature compensating lens that can be easily corrected.

It is ^preferable to set the lower limit of conditional expression (1) to -10 ^-6 . If the lower limit value of the conditional expression (1) is exceeded, the focus changes in the direction in which the focus extends beyond the extension of the lens barrel, and it becomes difficult to correct the focus due to temperature fluctuation, which is not good.

"Numerical Example 2" FIG. 2 is a lens sectional view of Numerical Example 2 of the present invention to be described later.

In Numerical Embodiment 2 shown in FIG. 2, a collimator lens 12 as a temperature compensating lens is composed of a positive first lens G1 and a negative second lens G2 in order from the light exit side (aperture side). Make up. The first positive lens G1 is made of a glass material having a negative refractive index change (trade name S-
bal3, OHARA CORPORATION) and a negative second lens G
2 is a glass material having a positive refractive index change (trade name: S-ti
h11, Ohara Corporation).

In the numerical example 2, the positive first lens G1
Has a negative refractive index change, so that it changes in the direction to extend the focus. The negative second lens G2 changes in the direction in which the focus is extended by increasing the negative power due to the positive refractive index change.

The total of these changes is the focus change caused by the temperature rise.
Also, as shown in Table 1 below, each lens is set so as to satisfy the conditional expression (1). This makes it possible to reduce the change in focus with respect to the temperature of the lens itself, or to approach the direction in which the lens back extends due to the temperature rise, that is, the direction in which the deformation of the lens barrel is corrected. Specifically, by using a glass material having a small change in refractive index with respect to temperature rise for the positive lens as described above, and using a glass material having a large change in refractive index with respect to temperature rise for the negative lens, temperature fluctuation Temperature compensation lens in which focus correction can be made easier.

"Numerical Embodiment 3" FIG. 3 is a lens sectional view of Numerical Embodiment 3 of the present invention, which will be described later.

In Numerical Example 3 shown in FIG. 3, the collimator lens 22 as a temperature compensating lens includes a first positive lens G1, a second negative lens G2, and a positive first lens G in order from the light beam exit side (aperture side). It is composed of three lenses G3. The first positive lens G1 is a glass material having a negative refractive index change (trade name: S-lam3, OHARA CORPORATION)
The negative second lens G2 is made of a glass material having a positive refractive index change (trade name: S-tih10, Ohara Co., Ltd.), and the positive third lens G3 is made of a glass material having a positive refractive index change. (Trade name: S-lah64, OHARA CORPORATION).

In the third embodiment, the positive first lens G1
Has a negative refractive index change, so that it changes in the direction to extend the focus. The negative second lens G2 changes in the direction in which the focus is extended by increasing the negative power due to the positive refractive index change. Since the positive third lens G3 has a positive refractive index change, the third lens G3 changes in a direction to reduce the focus due to a temperature rise.

The total of these changes is the focus change caused by the temperature rise.
Also, as shown in Table 1 below, each lens is set so as to satisfy the conditional expression (1). This makes it possible to reduce the change in focus with respect to the temperature of the lens itself, or to approach the direction in which the lens back extends due to the temperature rise, that is, the direction in which the deformation of the lens barrel is corrected. Specifically, by using a glass material having a small change in refractive index with respect to temperature rise for the positive lens as described above, and using a glass material having a large change in refractive index with respect to temperature rise for the negative lens, temperature fluctuation Temperature compensation lens in which focus correction can be made easier.

In Numerical Embodiments 2 and 3, the positive first lens G1 made of a material having a negative refractive index change is disposed on the most outgoing side of the light beam.

FIG. 4, FIG. 5, and FIG. 6 are wave front aberration diagrams of Numerical Examples 1, 2, and 3 of the present invention, respectively. As shown in each wavefront aberration diagram, it can be seen that good optical performance is obtained by favorably correcting aberrations.

"Numerical Examples" Next, numerical data of the temperature compensation lens (collimator lens) of the present invention, glass materials of each lens, and numerical examples 1, 2, 3 of the refractive index change rate of the glass material with respect to the temperature. Is shown.

Each of Numerical Examples 1, 2, and 3 is described from the light beam exit side (stop side). In a numerical example, r0
Is the aperture, ri is the radius of curvature of the i-th lens surface in order from the light-emitting side, di is the i-th lens thickness and air spacing in order from the light-emitting side, and ni and νi are each the light-emitting side from the light emitting side. Refractive index and Abbe number of the material of the i-th lens, dn
i / dt is the rate of change of the refractive index of the i-th lens from the light beam output side.

Table 1 also shows the calculation results of the conditional expression (1). In Table 1, the description is given from the light-emitting side, and the cover glass without power is excluded.

As shown in Table 1, in any of the numerical examples, by using a material having a negative refractive index change for at least one positive lens, the direction in which the focus is elongated with respect to the temperature rise, or almost It is configured to change to zero.

[Numerical Example 1] f = 33.01806 glass material 10 ⁻⁶ / ° C. r0 = aperture d0 = 1.00 r1 = -101.800 d1 = 2.50 n1 = 1.51329 ν1 = 64.1 s-bsl dn1 / dt = 2.6 r2 = ∞ d2 = 12.0 r3 = 32.173 d3 = 3.85 n2 = 1.56738 ν2 = 53.0 s-bal3 dn2 / dt = -0.7 r4 = -21.206 d4 = 3.99 r5 = -13.043 d5 = 1.35 n3 = 1.71925 ν3 = 28.5 s-tih10 dn3 / dt = 2.4 r6 = 207.994 d6 = 0.87 r7 = 21.041 d7 = 3.46 n4 = 1.51329 ν4 = 64.1 s-bsl7 dn4 / dt = 2.6 r8 = -24.087 d8 = 15.0 r9 = ∞ d9 = 0.30 n5 = 1.51329 ν5 = 64.1 s-bsl7 dn5 /dt=2.6 r 10 = ∞ [Numerical Example 2] f = 28.29966 Glass material 10 ^-6 / ° C r1 = 18.024 d1 = 3.50 n1 = 1.56738 ν1 = 53.0 s-bal3 dn1 / dt = -0.7 r2 = -11.791 d2 = 0.00 r3 = -12.052 d3 = 2.00 n2 = 1.77406 ν2 = 25.7 s-tih11 dn2 / dt = 1.0 r4 = -37.449 d4 = 6.30 r5 = ∞ d5 = 0.30 n3 = 1.51329 ν3 = 64.1 s-bsl7 dn3 / dt = 2.6 r6 = ∞ [Numerical example 3] f = 23.97112 Glass material 10 ^-6 / ° C r1 = 49.968 d1 = 2.04 n1 = 1.71153 ν1 = 47.9 s-lam3 dn1 / dt = -0.4 r2 = -14.474 d2 = 0.00 r3 =- 14.563 d3 = 1.58 n2 = 1.77406 ν2 = 25.7 s-tih10 dn2 / dt = 2.4 r4 = -250.149 d4 = 10.97 r5 = 15.256 d5 = 1.46 n3 = 1.78188 ν3 = 47.4 s-lah64 dn3 / dt = 4.2 r6 = 43.646 d6 = 5.00 r7 = ∞ d7 = 0.30 n4 = 1.51329 ν4 = 64.1 s-bsl7 dn4 / dt = 2.6 r8 = -∞

[0055]

[Table 1]

The units of dn / dt in the above table are 10 ⁻⁶ / ° C., φ /
The value of (n-1) × dn / dt is × 10 ⁻⁶ .

[Scanning Optical Apparatus] FIG. 7 is a top view of the essential parts when the temperature compensating lens (collimator lens) of any one of the numerical embodiments 1, 2 and 3 is used in a scanning optical apparatus as an optical apparatus. Shows a state in which each element is projected in the main scanning section. FIG. 8 is a side view of a main part of FIG. 7, showing a state where each element is projected in the sub-scanning cross section. FIG.
FIG. 10 is a developed view when developed in the main scanning direction along the light beam, and FIG. 10 is a developed view when developed in the sub-scanning direction in FIG.

In the figure, reference numeral 1 denotes a light source means, which is composed of, for example, a semiconductor laser. 2 is Numerical Examples 1, 2 and 2,
3, which converts a divergent light beam emitted from the semiconductor laser 1 into a substantially parallel light beam. Reference numeral 3 denotes a stop (slit member), which restricts a passing light beam (light amount).

Reference numeral 4 denotes a cylindrical lens (cylinder lens) having a predetermined refracting power only in the sub-scanning direction, and a deflecting surface of an optical deflector 6 to be described later in the main scanning section in a main scanning section. (Reflection surface) 6a is formed as a substantially linear image.

Reference numeral 9 denotes a folding mirror which reflects the light beam transmitted through the cylindrical lens 4 toward the optical deflector 6. Each element such as the collimator lens 2, the diaphragm 3, the cylindrical lens 4, and the return mirror 9 constitutes one element of the incident optical system 11, respectively.

Reference numeral 6 denotes an optical deflector, which comprises, for example, a rotating polygon mirror (polygon mirror) and is rotated at a constant speed in a direction indicated by an arrow A in the figure by driving means (not shown) such as a motor.

Reference numeral 12 denotes an image forming optical system having a light condensing function and fθ characteristics, and includes a single fθ lens (fθ lens system) 5;
A cylindrical mirror 7 having a predetermined refractive power only in the sub-scanning direction, and forms a deflected light beam from the optical deflector 6 on the surface 8 to be scanned; The tilt of the deflecting surface 6a is corrected by making the deflecting surface 6a and the scanned surface 8 have a substantially conjugate relationship. lens 5 also constitutes one element of the incident optical system 11. The fθ lens system may be composed of a plurality of lenses.

Reference numeral 8 denotes a photosensitive drum surface as a surface to be scanned.

In this embodiment, in the main scanning section shown in FIG. 7, a divergent light beam emitted from the semiconductor laser 1 is converted into a substantially parallel light beam by the collimator lens 2, and the light beam (light amount) is restricted by the stop 3. Incident on the cylindrical lens 4. The substantially parallel light beam incident on the cylindrical lens 4 exits as it is, passes through the fθ lens 5 via the folding mirror 9, and enters the deflection surface 6a from substantially the center of the deflection angle of the optical deflector 6 (front incidence). ). At this time, the light beam incident on the light deflector 6 is incident on the deflecting surface 6a of the light deflector 6 in a state wider than the width of the deflecting surface 6a in the main scanning direction (overfield optical system). The light beam deflected and reflected by the deflecting surface 6a of the optical deflector 6 is converged by passing through the fθ lens 5 again, and is guided onto the photosensitive drum surface 8 via the cylindrical mirror 7.

On the other hand, in the sub-scanning section shown in FIG. 8, the divergent light beam emitted from the semiconductor laser 1 is converted into a substantially parallel light beam by the collimator lens 2, and the light beam (light amount) is restricted by the stop 3 to form a cylindrical lens. 4 is incident. The substantially parallel light beam that has entered the cylindrical lens 4 converges, passes through the fθ lens 5 via the return mirror 9, and enters the deflection surface 6a of the optical deflector 6 at a predetermined angle (ε / 2). An image is formed on the deflection surface 6a as a substantially linear image (a linear image elongated in the main scanning direction) (oblique incidence optical system). The light beam deflected and reflected by the deflecting surface 6a of the optical deflector 6 passes through the fθ lens 5 again, is converged by the cylindrical mirror 7, and is guided onto the photosensitive drum surface 8.
By rotating the light deflector 6 in the direction of arrow R, the surface of the photosensitive drum 8 is moved in the direction of arrow S (main scanning direction).
Optical scanning. Thus, an image is recorded on the photosensitive drum surface 8 as a recording medium.

In the above-described scanning optical device, when the wavefront emitted from the collimator lens 2 changes due to a temperature change, the spot diameter on the photosensitive drum surface 8 changes. Normally, this change amount is a problem for a scanning optical apparatus in which the change amount of the wavelength (light source wavelength) of the light beam emitted from the light source exceeds 0.5 nm with respect to the change amount of 5 nm. Therefore, in this embodiment, by using any one of the collimator lenses shown in Numerical Examples 1, 2, and 3, the change due to the temperature change of the output wavefront of the collimator lens is changed by 5 nm in the light source wavelength. Is set to 0.5 wavelength or less, thereby changing the focal length in the direction in which the focal length increases with respect to a positive wavelength change, thereby solving the above problem.

Although the temperature compensation lens is used as a collimator lens in this embodiment, it may be used as an imaging lens. Further, although the temperature compensation lens is used in the scanning optical device, the invention is not limited to this, and it may be used in other optical devices, for example, other devices such as an interference device and a digital image reading device.

[0068]

According to the present invention, by appropriately setting each lens constituting the temperature compensating lens as described above, it is possible to more easily correct the focus due to temperature fluctuation, and an optical apparatus using the same. Can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a first embodiment when a temperature compensation lens of the present invention is used in a laser unit of a scanning optical device.

FIG. 2 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 3 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 4 is a diagram illustrating various aberrations of Numerical Example 1 of the present invention.

FIG. 5 is a diagram illustrating various aberrations of Numerical Example 2 of the present invention.

FIG. 6 is a diagram showing various aberrations of Numerical Example 3 of the present invention.

FIG. 7 is a top view of a main part of the optical device of the present invention.

FIG. 8 is a side view of a main part of the optical device of the present invention.

FIG. 9 is a developed view when developed in the main scanning direction along the light beam.

FIG. 10 is a developed view when developed in the sub-scanning direction along the light beam.

FIG. 11 is a schematic view of a main part of a conventional scanning optical device.

FIG. 12 is an explanatory view of the laser unit of FIG. 11;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Light source means 2, 12, 22 Temperature compensation lens (collimator lens) 3 Aperture 4 Cylindrical lens 5 fθ lens 6 Optical deflector 7 Cylindrical mirror 8 Scanning surface 11 Incident optical system 12 Imaging optical system 16 Aperture 17 Lens barrel 18 lens barrel holder 19 base G1 first lens G2 second lens G3 third lens G4 fourth lens

Continued on the front page F term (reference) 2C362 AA46 BA84 2H045 CB15 CB22 2H087 KA19 NA08 PA02 PA03 PA05 PA18 PB03 PB04 PB05 QA02 QA03 QA14 QA18 QA21 QA22 QA25 QA26 QA41 QA46 5C072 AA12 BA01 XA03 DA04

Claims (9)

[Claims] At least one positive lens and at least one negative lens, wherein two or more lenses have different materials from each other, and a material of an i-th lens in order from a light emitting side. Is the refractive index of ni, and the rate of change of the refractive index ni to the temperature rise dt is d.
ni / dt (1 / ° C.), and the power of the i-th lens is φ
When i (1 / mm), m: Total number of lenses A temperature-compensating lens specially satisfying the following condition. 2. The temperature compensating lens according to claim 1, wherein said at least one negative lens is made of a material having a positive refractive index change. 3. The temperature compensation lens according to claim 2, wherein said at least one positive lens is made of a material having a negative refractive index change. 4. The method according to claim 1, wherein at least one of the positive lenses has a refractive index change rate with respect to temperature smaller than that of the negative lens made of a material having the positive refractive index change. The temperature compensation lens according to claim 3, wherein 5. The temperature compensating lens according to claim 3, wherein a positive lens made of a material having a negative refractive index change is located at the most exit side of the light beam. 6. The temperature compensating lens according to claim 1, wherein the temperature compensating lens comprises four or less lenses. 7. An optical device using the temperature compensation lens according to claim 1 to convert a light beam emitted from a light source into a substantially parallel light beam. 8. A change in temperature of an output wavefront of the temperature compensating lens due to a temperature change is 0.5 wavelength or less for a change in wavelength of a light beam emitted from the light source of 5 nm, and a focus for a positive wavelength change. The optical device according to claim 7, wherein the distance changes in a direction in which the distance increases. 9. An optical device using the temperature compensation lens according to claim 1. Description: