JP3037962B2 - Optical scanning device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical scanning device.

2. Description of the Related Art An optical scanning device that optically scans a surface to be scanned by deflecting a light beam by an optical deflecting device is well known in relation to a laser printer, a digital copying machine, a laser facsimile, and the like.

The optical scanning lens is used in such an optical scanning device.
A lens for forming an image on a surface to be scanned with a light beam deflected by a light deflector as a light spot, and various fθ lenses have been conventionally proposed.

The applicant has previously proposed a single lens having an approximate fθ function (Japanese Patent Application No. 62-304737).

[Problems to be Solved by the Invention] Although the single lens having the approximate fθ function enables wide-area optical scanning, the uniformity of the optical scanning by the light spot and the correction of the field curvature are realized by the single lens. Therefore, if the uniformity, that is, the linearity of the optical scanning is increased, the field curvature cannot be sufficiently corrected, and it is difficult to increase the density of the optical scanning.

The present invention has been made in view of the above-mentioned circumstances, and a purpose thereof is to further improve the single lens having the approximate fθ function described above, thereby achieving excellent linearity and excellent correction of field curvature. It is an object of the present invention to provide an optical scanning device using a novel optical scanning lens.

[Means for Solving the Problems] Hereinafter, the present invention will be described.

An optical scanning device according to the present invention includes a light source device that emits a light beam,
A focusing optical system for converting the light beam from the light source device into a focused light beam, a deflecting device for deflecting the focused light beam by the focusing optical system at a constant angular velocity, and further focusing the focused light beam deflected by the deflecting device. A light scanning lens for forming an image on the surface to be scanned in the form of a light spot and scanning at substantially constant speed.

The optical scanning lens is "a lens for further converging a converged light beam deflected at a constant angular velocity to form an image as a light spot on the surface to be scanned, and for optically scanning the surface to be scanned substantially uniformly". , "A single lens having a focal length f of a material having a refractive index n".

The optical scanning lens in the optical scanning device according to claim 1, wherein the optical scanning lens is a spherical lens, and has a curvature of a first surface (a surface on which a focused light beam is incident: the same applies hereinafter) as indicated by reference numeral 5A in FIG. Assuming that the radius is R ₁ and the radius of curvature of the second surface (the surface on the side where the imaging light flux exits: the same applies hereinafter) is R ₂ , R ₁ > 0 and | R ₁ | <
| R ₂ |, where t is the entrance pupil distance measured from the front principal point, and s is the distance from the front principal point to the natural focal point of the incident focused light: (1-I) −8.0 <(nf / t) + (f / s) <− 3.5 (1-II) −0.4 <(t / f) <− 0.15

The optical scanning lens in the optical scanning device according to claim 2 is a first lens.
As shown by reference numeral 5B in FIG. (II), the radius of curvature of the first surface is
R ₁ , when the radius of curvature of the second surface on the optical axis is R ₂ , R ₂ > 0 and | R ₁ |> | R ₂ , the entrance pupil distance measured from the front principal point is t, and the front principal point Where s is the distance from to the natural focal point of the incident focused light: (2-I) -7 <(nf / t) + (f / s) <-0.6 (2-II) -0.41 <(t / f) Satisfies the condition of <−0.13.

The second surface are aspherical and the conical constant K and the fourth-order aspherical coefficients A ₄ in this aspherical surface, (2-III) 0.8 × 10 -8 <(A 4 /K)<3.0×10 - ⁸ conditions are satisfied.

The optical scanning lens in the optical scanning device according to claim 3 is a first lens.
As shown by reference numeral 5C in FIG. (III), the radius of curvature of the first surface is R
_1, the radius of curvature the optical axis of the second face and in R _1> 0 when the _{R 2 | R 1 | <|} R 2 | a is the entrance pupil distance measured from the front principal point t, front principal point Where s is the distance from to the natural focal point of the incident focused light: (3-I) -8 <(nf / t) + (f / s) <-3.5 (3-II) -0.4 <(t / f) Satisfies the condition of <−0.15.

The first surface is aspherical and the conical constant K and the fourth-order aspherical coefficients A _4, in this non-spherical (3-III) -0.6 × 10 -8 <(A 4 /K)<-0.3×10 ^-8 is satisfied.

Needless to say, "radius of curvature on the optical axis" means "radius of a tangent sphere contacting the lens surface at the intersection of the optical axis and the lens surface." The unit of the numerical value in the conditions (2-III) and (3-III) is mm- ³ .

The light scanning device according to any one of claims 1 to 3 emits a light beam as schematically shown in FIG.
A focusing optical system 2 for converting a light beam from the light source device into a focused light beam, and a deflecting device (denoted by 3 to indicate a deflecting / reflecting surface thereof) for deflecting the focused light beam by the focusing optical system 2 at a constant angular velocity. An optical scanning lens 5 for further converging the converged light beam deflected by the deflector to form an image on the surface 6 to be scanned in the form of a light spot so as to scan at substantially constant speed. The optical scanning lens 5 is one of the optical scanning lenses 5A, 5B, and 5C described with reference to FIG.

The light scanning device according to claim 4, as schematically shown as a specific example in FIG. 3, a light source device Q for emitting a light beam, and a focusing optical system for converting the light beam from the light source device Q into a focused light beam. 2, a deflecting device (denoted by 3 for a deflecting and reflecting surface) for deflecting the converged light beam by the converging optical system 2 at a constant angular velocity, and further converges the converged light beam deflected by the deflector to scan the surface to be scanned. And an optical scanning lens 5 for forming an image in the form of a light spot and scanning at substantially constant speed. The optical scanning lens 5 is one of the optical scanning lenses 5A, 5B, and 5C shown in FIG. 1, and a field curvature in the sub scanning direction is provided between the optical scanning lens 5 and the surface 6 to be scanned. Has a long cylindrical lens 8 as a correction optical system for correcting.

[Operation] FIG. 2 is a drawing in which the optical scanning device of claims 1 to 3 is developed along the optical path of the principal ray from the light source to the surface to be scanned, and the main scanning direction is the vertical direction. Therefore, in this drawing, the direction orthogonal to the drawing corresponds to the sub-scanning direction.

In the figure, reference symbol Q indicates a light source device. As the light source device Q, an LD or an LED is used. Here, an LD is assumed.
Reference numeral 1 denotes a surface passing through the light emitting portion of the light source device Q and orthogonal to the optical axis;
That is, it indicates the object plane.

The divergent light emitted from the light source device Q is converted into a convergent light beam by a converging lens 2 as a converging optical system, deflected by a deflecting / reflecting surface 3 of a deflecting device, and incident on an optical scanning lens 5. A rotating polygon mirror, a pyramidal mirror, or the like is used as the deflecting device.

If there is no light scanning lens 5, the light beam converged by the condenser lens 2 is focused at the position of the “natural focal point” Q ′ on the image plane 7 of the condenser lens 2. When the condensed light beam is deflected by the operation of the deflecting device, the focal point moves on the arc 4. . When the deflecting device is a rotary polygon mirror, the deflecting light beam has a deflecting origin slightly fluctuating on the optical axis, so that the trajectory of the convergence point does not become a complete arc but has a shape close to the arc 4.

The optical scanning lens 5 is provided between the deflecting / reflecting surface 3 and the scanned surface 6. The optical scanning lens 5 has a positive refractive power, further focuses the incident convergent light beam, and forms an image substantially as a light spot on the surface 6 to be scanned. In other words, the optical scanning lens 5 ideally sets the “movement trajectory by deflection” of the natural focal point by the condenser lens 2 as an imaginary light source object position, and conjugates the imaginary light source object position with the surface 6 to be scanned. It has the function of linking.

Accordingly, as shown in FIG. 2, the front principal point H of the optical scanning lens 5 is formed.
S 'by measuring the distance from the rear principal point H' to the surface 6 to be scanned in the direction of the arrow.
Then, assuming that the focal length of the optical scanning lens 5 is f, a relationship of (1 / s) − (1 / s ′) = − 1 / f is established.

The distance from the front principal point H to the position of the entrance pupil (the starting point of deflection by the deflecting and reflecting surface 3) is measured in the direction of the arrow, and is represented by t. Further, the refractive index of the material of the optical scanning lens 5 is represented by n. The signs of the distances s, s', and t follow the rules of geometric optics.

The curvature radii R ₁ and R ₂ of each surface of the optical scanning lens of claim 1 are
R ₁ > 0 and | R ₁ | <| R ₂ |, and the distances t and s satisfy the above-mentioned conditions (1-I) and (1-II).

Since R ₁ > 0 and | R ₁₁ | <| R ₂ |, the first surface has a convex shape, and the second surface can be any of a flat surface, a convex surface, and a concave surface. Therefore, as the lens form of the optical scanning lens of the first aspect, a convex flat / biconvex / convex meniscus form is possible.

The condition (1-I) is a condition for making the diameter of the light spot for optically scanning the surface to be scanned uniform in the main scanning direction. If the lower limit is exceeded, the curvature of field in the main scanning direction greatly expands toward the underside at the intermediate image height, and the light spot diameter in the main scanning direction cannot be kept uniform. If the upper limit is exceeded, the curvature of field in the main scanning direction falls to the underside at the entire image height, and the light spot diameter in the main scanning direction cannot be kept uniform.

When the value goes below the lower limit of the condition (1-II), the optical scanning lens becomes too large and practicality is lost. If the upper limit is exceeded, the linearity deteriorates, and it becomes impossible to correct the deviation from the constant velocity by electrical signal processing during optical scanning. The range in which the deviation from the uniform velocity during the optical scanning can be corrected by electrical signal processing means “substantially constant velocity” in the present invention.

The curvature radii R ₁ and R ₂ of each surface of the optical scanning lens according to claim ₂ are:
R ₂ <0 and | R ₁ |> | R ₂ |, and the distances t and s satisfy the above-mentioned conditions (1-I) and (1-II).

Since R ₂ <0 and | R ₁ |> | R ₂ |, the second surface has a convex shape, and the first surface can be any of a flat surface, a convex surface, and a concave surface. Therefore, as the lens form of the optical scanning lens of the second aspect, a plano-convex, bi-convex, convex meniscus form is possible.

In the optical scanning lens as claimed in claim 2 is the conic constant K and the fourth-order aspherical coefficients A ₄ second surface is a non-spherical surface satisfies the above conditions (2-III).

As is well known, when y is the distance from the optical axis and x is the amount of aspheric surface, the radius of curvature on the optical axis is R. Is a curved surface obtained by rotating the curve around the optical axis, the conic constant is K in the above equation, and A ₄ is a coefficient of y ⁴ .

Each of the conditions (2-I) and (2-III) is a condition for reducing the fluctuation of the diameter of the light spot in the main scanning direction and making the diameter in the same direction uniform.

When the lower limit of the condition (2-I) is exceeded, the field curvature in the main scanning direction becomes a shape which is greatly expanded to an underside at an intermediate image height, and
If the upper limit is exceeded, the curvature of field in the main scanning direction falls to the under side at the entire image height.

If the lower limit of the condition (2-III) is exceeded, the field curvature in the main scanning direction falls to the over side at the entire image height, and if the upper limit is exceeded, the field curvature in the scanning direction falls to the under side at the full image height.

Therefore, if the values are out of the range of the conditions (2-I) and (2-III), the diameter of the light spot in the main scanning direction cannot be kept uniform because of the curvature of field in the main scanning direction.

If the lower limit of the above condition (2-II) is exceeded, the optical scanning lens becomes too large and loses practicality. Condition (2-
If the upper limit of II) is exceeded, the linearity of optical scanning deteriorates, and the deviation from the uniform velocity cannot be corrected by electrical signal processing.

The rate radii R ₁ and R ₂ of the optical scanning lens according to claim 3 are R ₁ > 0,
And | R ₁ | <| R ₂ |, and the distances t and s satisfy the above-mentioned conditions (3-I) and (3-II).

Since R ₁ > 0 and | R ₁ | <| R ₂ |, the first surface has a convex shape, and the second surface can be any of a flat surface, a convex surface, and a concave surface. Therefore, the lens form of the optical scanning lens according to the third aspect can be a convex flat / biconvex / convex meniscus form.

In the optical scanning lens as claimed in claim 3 is the conic constant K and the fourth-order aspherical coefficients A ₄ first surface a non-spherical surface satisfies the above conditions (3-III).

Each of the conditions (3-I) and (3-III) is a condition for reducing the fluctuation of the diameter of the light spot in the main scanning direction and making the diameter in the same direction uniform.

When the lower limit of the condition (3-I) is exceeded, the field curvature in the main scanning direction becomes large at the intermediate image height and expands to the under side, and when the upper limit is exceeded, the field curvature in the main scanning direction becomes the full image height. It falls to the under side.

If the lower limit of the condition (3-III) is exceeded, the field curvature in the main scanning direction falls to the under side at the entire image height, and if the upper limit is exceeded, the field curvature in the main scanning direction falls to the over side at the full image height.

Therefore, if the values deviate from the ranges of the conditions (3-I) and (3-III), the diameter of the light spot in the main scanning direction cannot be kept uniform because of the curvature of field in the main scanning direction.

If the lower limit of the above condition (3-II) is exceeded, the optical scanning lens becomes too large and loses practicality. Condition (3-
If the upper limit of II) is exceeded, the linearity of optical scanning deteriorates, and the deviation from the uniform velocity cannot be corrected by electrical signal processing.

[Examples] Specific examples will be described below.

In each embodiment, as shown in FIG. ₁ , the radius of curvature of the first surface of the optical scanning lens is R ₁ , the radius of curvature of the second surface is R ₂ , and the distance between these lens surfaces is d ₁ . The refractive index of the material of the optical scanning lens is n. Further, the distance between the deflecting reflecting surface 3 of the deflecting device and the first surface is d ₀ , and the distance between the second surface and the scanned surface 6 is D. When the lens surface is an aspherical surface, the above-mentioned radius of curvature means, of course, the radius of curvature on the optical axis.

Also, X represents the parameter in the conditions (1-I), (2-I), and (3-I): (nf / t) + (f / s), and Y represents the condition (1-II), (2-I). II), (3-II) parameters: t
Represents / f. In addition, Z is the condition (2-III), (3-III)
Represents A ₄ / K. F, s, t are the distances described with reference to FIG. The light source device Q and the condenser lens 2 can be set arbitrarily within a range that satisfies the numerical values of each embodiment.

First, three specific examples of the optical scanning lens used in the optical scanning device shown in FIG. 2 will be described. The optical scanning lens is a convex flat lens in the first embodiment, a convex meniscus lens in the second embodiment, and a biconvex lens in the third embodiment.

Example 1 f = 326.349, S = 160, t = −70, X = −6.19, Y = −0.214 R ₁ R ₂ d ₀ d ₁ D n 250 ∞ 70 20 93.538 1.766 Maximum total deflection angle: 80 degrees, light Scanning width: 217.1 Linearity: 7.7% or less FIG. 4 shows field curvature in the main scanning direction of the first embodiment.

Example 2 f = 430.157, s = 103.732, t = −66.268, X = −7.32, Y = −0.154 R ₁ R ₂ d ₀ d ₁ D n 250 1000 70 20 66.65 1.766 Maximum total deflection angle: 85 °, light Scanning width: 217.1 Linearity: 18.2% or less FIG. 5 shows field curvature in the main scanning direction of the second embodiment.

Example 3 f = 221.408, S = 214.238, t = −75.762, X = −4.13, Y = −0.342 R ₁ R ₂ d ₀ d ₁ D n 250 −500 70 30 97.357 1.766 Maximum total deflection angle: 90 degrees, Optical scanning: 217.1 Linearity: 32.2% or less FIG. 6 shows the field curvature in the main scanning direction of the third embodiment.

In the first to third embodiments, the field curvature in the main scanning direction is satisfactorily corrected, but the field curvature in the sub-scanning direction (not shown) is slightly too large. However, such field curvature in the sub-scanning direction can be satisfactorily corrected by using a long cylindrical lens as a correction optical system as in the optical scanning device of the fourth aspect. Hereinafter, an embodiment of the optical scanning device according to claim 4 will be described. As described above, the optical scanning device according to the fourth aspect is roughly as shown in FIG.

The surface distance between the exit side lens surface of the optical scanning lens 5 and the entrance side lens surface of the long cylindrical lens 8 is d ₂ , the thickness of the long cylindrical lens 8 is d ₃ , and the exit side lens of the long cylindrical lens 8. the distance between the surface and the scan surface and d _4.

The radius of curvature of the entrance / exit side lens surface of the long cylindrical lens 8 is R _3X , R _{4X in} the main scanning direction, R _3Y , R _{4Y in the} sub scanning direction, and the focal length is f _X , Let f _{Y be} the refractive index of the lens material n ′.

 Embodiment 4 is an embodiment of the optical scanning device according to claim 4.

Example 4 f = 326.349, s = 160, t = −70, X = −6.19, Y = −0.214 R ₁ R ₂ d ₀ d ₁ n 250 ∞ 70 20 1.766 R _3X R _3Y R _4X R _4Y n ′ d ₂ d ₃ d ₄ ∞ 12.0 ∞ 485 1.485 67.0 3.0 24.518 f _X = ∞, f _Y = 24.742 Maximum total deflection angle: 80 degrees, optical scanning width: 217.1 Linearity: 7.6% or less Main and sub scanning directions according to the fourth embodiment FIG. 7 shows the curvature of field. The solid line indicates the field curvature in the sub-scanning direction. Similarly to the main scanning direction, the curvature of field in the sub-scanning direction is well corrected.

 Next, three embodiments of the optical scanning device according to claim 2 will be described.

The aspheric coefficients other than A ₄ In aspherical second surface all zero.

Example 5 f = 200, s = 300, t = −66.111, X = −4.78, Y = −0.33056, Z = 2.33 × 10 ⁻⁸ R ₁ R ₂ d ₀ d ₁ D n ∞−160.0 55 20 120 1.8 Aspherical surface K = −3.43, A ₄ = −8.0 × 10 ⁻⁸ Maximum deflection angle: 108 degrees, effective main scanning width: 286.0, linearity: 8% or less FIG. 8 shows the field curvature in the main scanning direction of this embodiment. Is shown.
Although the linearity is slightly low, the deviation from the constant speed of the optical scanning can be sufficiently corrected electrically at this level. With this degree of linearity, the field curvature in the main scanning direction is the eighth
It is corrected very well as shown in the figure.

Example 6 f = 200, s = 301.811, t = −70.489, X = −4.44, Y = −0.35245, Z = 1.15 × 10 ⁻⁸ R ₁ R ₂ d ₀ d ₁ Dn 800 −197.778 61.5 20 118.067 1.8 Aspheric surface K = 4.0, A ₄ = −4.6 × 10 ⁻⁸ Maximum deflection angle: 85.6 degrees, effective main scanning width: 222.8, linearity: −1.4 to 2.5% FIG. 9 shows an image of this embodiment in the main scanning direction. Shows surface curvature.

Example 7 f = 200, s = 301.811, t = −70.489, X = −4.44, Y = −0.35245, Z = 1.0 × 10 ⁻⁸ R ₁ R ₂ d ₀ d ₁ Dn 800 −197.778 61.5 20 118.067 1.8 Aspherical surface K = −1.0, A ₄ = −1 × 10 ⁻⁸ Maximum deflection angle: 85.6 degrees, effective main scanning width: 222.0, linearity: −1.0 to 1.8% FIG. 10 shows the main scanning direction of this embodiment. Fig. 4 shows field curvature.

In all of Examples 5 to 7, the curvature of field in the main scanning direction is well corrected, and the diameter of the light spot in the main scanning direction can be effectively made uniform.

For comparison, FIG. 11 shows an example of the curvature of field in the main scanning direction when the first and second surfaces are spherical surfaces and the linearity is -1.0 to 0.6%. When the first and second surfaces are spherical, if the linearity is set to the above level, the curvature of field in the main scanning direction will generally be almost the same as that shown in FIG. The linearity of this comparative example is almost the same as that of the seventh embodiment, but in the seventh embodiment, the curvature of field in the main scanning direction is corrected more favorably by using an aspheric surface.

In each of the fifth to seventh embodiments, the field curvature in the sub-scanning direction is slightly increased due to the favorable correction of the field curvature in the main scanning direction. There is no practical problem because the correction can be made by various methods, for example, by using a long cylindrical lens or a long toroidal lens for correction without affecting the good field curvature.

Hereinafter, three examples of the optical scanning device according to claim 3 will be described.

Aspherical coefficients other than A ₄ In aspherical first surface are both zero.

Example 8 f = 326.349, s = 160, t = −70 X = −6.19, Y = −0.214, Z = −0.33 × 10 ⁻⁸ R ₁ R ₂ d ₀ d ₁ Dn 250 ∞ 70 20 93.538 1.766 Non spherical _{K = -14.0, a 4 = 4.65} × 10 -8 maximum deflection angle: 80 degrees, the effective main scanning width: 223.6, linearity: 7.5% or less Fig. 12, the main scanning direction of the field curvature of this embodiment Show. With this degree of linearity, the curvature of field in the main scanning direction is corrected very well as shown in FIG.

Example 9 f = 326.349, s = 160, t = −70 X = −6.19, Y = −0.214, Z = −0.4 × 10 ⁻⁸ R ₁ R ₂ d ₀ d ₁ Dn 250 ∞ 70 20 93.538 1.766 Non Spherical surface K = −10, A ₄ = 4.0 × 10 ⁻⁸ Maximum deflection angle: 80 degrees, effective main scanning width: 221.4, linearity: −0.9 to 5.5% FIG. 13 shows the image plane in the main scanning direction of this embodiment. Indicates curvature.

Example 10 f = 221.408, s = 214.238, t = −75.762 X = −4.13, Y = −0.342, Z = −0.5 × 10 ⁻⁸ R ₁ R ₂ d ₀ d ₁ Dn 250 −500 70 30 97.357 1.766 aspheric _{K = -7.0, a 4 = 3.5} × 10 -8 maximum deflection angle: 88 degrees, the effective main scanning width: 216.4, Riniaritei: 27.4% or less Figure 14, the image plane in the main scanning direction of this embodiment curvature Is shown. Although the linearity is slightly low, the deviation from the constant speed of the optical scanning can be sufficiently corrected electrically at this level.

In each embodiment, the curvature of field in the light scanning direction is well corrected, and the diameter of the light spot in the main scanning direction can be effectively made uniform.

For comparison, FIG. 15 shows an example of the curvature of field in the main scanning direction when the first and second surfaces use spherical surfaces and the linearity is -1.1 to 0.6%. When the first and second surfaces are spherical, if the linearity is set to the above level, the curvature of field in the main scanning direction will generally be almost the same as that shown in FIG.

The linearity of this comparative example is almost the same as that of the ninth embodiment, but in the second embodiment, the curvature of field in the main scanning direction is more favorably corrected by using an aspheric surface.

In each of the eighth to tenth embodiments, the field curvature in the sub-scanning direction is slightly increased due to the favorable correction of the field curvature in the main scanning direction. There is no practical problem because the correction can be made by various methods without affecting the goodness of the present invention, for example, by using a long cylindrical lens or a long toroidal lens for correction.

[Effects of the Invention] As described above, according to the present invention, a novel optical scanning device can be provided.

In the optical scanning device of the present invention, since the optical scanning lens is configured as described above, the field curvature in the main scanning direction can be satisfactorily corrected. Therefore, by configuring an optical scanning device using this optical scanning lens, the diameter of the light spot in the main scanning direction can be made uniform, and high-density optical scanning can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an optical scanning lens used in the optical scanning device of the present invention. FIGS. 2 and 3 are diagrams for explaining the optical scanning device of the present invention. 6 to 6 are diagrams showing the field curvature in the main scanning direction for each of the first to third embodiments, FIG. 7 is a diagram showing the field curvature in the main and sub-scanning directions for the fourth embodiment, and FIGS. FIG. 10 shows Example 5
7 is a diagram showing field curvature in the main scanning direction for each of No. 7;
FIG. 11 is a diagram showing image surface curvature in the main scanning direction according to a comparative example of the optical scanning lens according to claim 2, and FIGS. 12 to 14 are image surfaces in the main scanning direction according to Examples 8 to 10, respectively. FIG. 15 is a view showing curvature, and FIG. 15 is a view showing curvature of field in the main scanning direction according to a comparative example of the optical scanning lens of claim 3. Q: light source device, 2: condensing lens, 3: deflecting / reflecting surface, 5A, 5B, 5C: optical scanning lens, 6: scanned surface, Q '
…… Natural focusing point

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-54-98627 (JP, A) JP-A-61-147211 (JP, A) JP-A-1-99013 (JP, A) JP-A-58-1983 93021 (JP, A) JP-A-61-172109 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (4)

(57) [Claims] 1. A light source device for emitting a light beam, a focusing optical system for converting a light beam from the light source device into a focused light beam, a deflecting device for deflecting the focused light beam by the focusing optical system at an equal angular velocity, and An optical scanning lens for further converging the converged light beam deflected by the deflecting device, forming an image on the surface to be scanned in a light spot shape, and scanning at a substantially constant speed, and wherein the optical scanning lens has A single lens having a focal length f is formed of a material having a refractive index n. The radius of curvature of the first surface is R ₁ , and the radius of curvature of the second surface is R _2.
Where R ₁ > 0 and | R ₁ | <| R ₂ |, and the entrance pupil distance measured from the front principal point of the optical scanning lens is t, and the natural value of the incident focused light from the front principal point is t. Assuming that the distance to the focal point is s, the following expression holds: (1-I) -8.0 <(nf / t) + (f / s) <-3.5 (1-II) -0.4 <(t / f) <-0.15 An optical scanning device, which satisfies a condition. 2. A light source device for emitting a light beam, a focusing optical system for converting a light beam from the light source device into a focused light beam, a deflecting device for deflecting the focused light beam by the focusing optical system at an equal angular velocity, and An optical scanning lens for further converging the converged light beam deflected by the deflecting device, forming an image on the surface to be scanned in a light spot shape, and scanning at a substantially constant speed, and wherein the optical scanning lens has A single lens having a focal length f is formed of a material having a refractive index n, the second surface is aspheric, and the radius of curvature of the first surface is
R ₁ , when the radius of curvature of the second surface on the optical axis is R ₂ , R ₂ <
0, and | R ₁ |> | R ₂ |, and the conic constant K and the fourth-order aspheric coefficient A _{4 of the} aspheric surface of the second surface are: (2-III) 0.8 × 10 ⁻⁸ (mm ^-3 ) <(A ₄ /K)<3.0×10 ^-8 (mm
^-3 ) When the following condition is satisfied, the entrance pupil distance measured from the front principal point of the optical scanning lens is t, and the distance from the front principal point to the natural focal point of the incident focused light is s. -I) An optical scanning device characterized by satisfying a condition of -7 <(nf / t) + (f / s) <-0.6 (2-II) -0.41 <(t / f) <-0.13. 3. A light source device for emitting a light beam, a focusing optical system for converting the light beam from the light source device into a focused light beam, a deflecting device for deflecting the focused light beam by the focusing optical system at an equal angular velocity, and An optical scanning lens for further converging the converged light beam deflected by the deflecting device, forming an image on the surface to be scanned in a light spot shape, and scanning at a substantially constant speed, and wherein the optical scanning lens has The first surface is aspherical, the radius of curvature of the first surface on the optical axis is R ₁ , the radius of curvature of the second surface is R _2, and the first surface is aspherical. When R ₁ >
0, and | R ₁ | <| R ₂ |, and the conic constant K and the fourth-order aspheric coefficient A _{4 in the} aspheric surface of the first surface are: (3-III) −0.6 × 10 ⁻⁸ ( mm ^-3 ) <(A ₄ /K)<−0.3×10
^-8 (mm ^-3 ) is satisfied, and the entrance pupil distance measured from the front principal point of the optical scanning lens is t, and the distance from the front principal point to the natural focal point of the incident focused light is s. Wherein (3-I) -8 <(nf / t) + (f / s) <-3.5 (3-II) -0.4 <(t / f) <-0.15 Optical scanning device. 4. The optical scanning device according to claim 1, wherein a correction optical system for correcting curvature of field in the sub-scanning direction is provided between the optical scanning lens and the surface to be scanned. An optical scanning device comprising a length cylindrical lens.