JPS63188109A - Distributed refractive index optical system - Google Patents

Abstract

PURPOSE:To sufficiently correct aberrations by providing the first area which has a convex and consists of a uniform medium, the second area which is brought into contact with the first area on the side opposite to the convex and has a refractive index distribution in the direction approximately vertical to the optical axis, and the third area which is brought into contact with the second area on the opposite side of the first area and consists of a uniform medium. CONSTITUTION:Plano-convex lenses 1 and 2 consisting of a uniform medium and an optical member 3 which has a refractive index distribution in the direction approximately vertical to an optical axis AX and has planes in both ends (luminous flux incidence and exit faces) constitute a spherical lens. The plane-convex lens 1 is closely brought into contact with the plane on the opposite side of a light emitting element 4 of the optical member 3, and the face on the side opposite to te light emitting element 4 of the plano-convex lens 2 is closely brought into contact with the plane on the side of the light emitting element 4 of the optical member. Consequently, the light emitting element 4 is closely brought into contact with the convex of the plano- convex lens 2 and a light emission point 4a of the light emitting element 4 is placed near the apex of the convex of the plano-convex lens 2. Thus, the spherical aberration and the coma are corrected.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to a refractive index distribution type optical system having a region with a refractive index distribution within a light passage region of the optical system, and in particular, converts divergent light emitted from a light source into parallel light. The present invention relates to a refractive index distribution type optical system suitable for converting parallel light into a converging target.

[Prior art]

Conventionally, this type of refractive index gradient optical system is generally used with a component of the optical system, such as a lens, separated from a light source or a light receiving element by a predetermined distance.

JP-A-58-205122 discloses the above-mentioned refractive index distribution type optical system. This optical system is composed of a plano-convex lens made of a homogeneous medium and a gradient index lens with flat surfaces at both ends.

However, in the conventional optical system as shown in Japanese Patent Application Laid-open No. 58-205132, in addition to alignment between each element,
For example, it is necessary to adjust the distance between the light source, the light receiving element, and the optical system, and a lot of time is spent on assembly and adjustment work.

On the other hand, as one means of solving the above-mentioned problems, it is possible to use a light source or a light receiving element in close contact with an element of an optical system.

As an example of this form, there is a method in which a light source such as a light emitting element is brought into close contact with a ball lens, as shown in, for example, Japanese Patent Laid-Open Nos. 58-68990 and 60-9181. According to this method, by using a medium with a refractive index of around 2.0 as the medium of the ball lens, it is possible to convert the divergent light from the light emitting element into a substantially parallel beam of light.

However, in this type of optical system, when trying to obtain a practically necessary numerical aperture NA, residual aberration becomes large, making it impossible to use it for precise purposes.

Another possibility is to make the end face of the spherical lens aspherical in order to correct the residual aberrations mentioned above, but in order to properly correct spherical aberration and coma aberration, it is necessary to provide an aperture inside the lens, which is difficult to manufacture. At the same time, the correction of aberrations themselves cannot be said to be sufficient.

[Summary of the invention]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, an object of the present invention is to provide a gradient index optical system that is easy to assemble and adjust and has high performance.

In order to achieve the above object, a gradient index optical system according to the present invention includes a first region having a convex surface and made of a homogeneous medium, and a first region that is in contact with the first region on the opposite side of the convex surface and that is aligned with the optical axis. It is characterized by having a second region having a refractive index distribution in a substantially vertical direction, and a third region that is in contact with the second region on the opposite side from the first region and is made of a homogeneous medium.

According to the present invention, it is possible to provide an optical system that has a practically sufficient numerical aperture NA and can sufficiently correct aberrations.

In particular, since the light-emitting element and the light-receiving element can be used in close contact with the end face of the optical system element, assembly and adjustment are facilitated. Further, since the refractive index gradient optical system of the present invention has a substantially single structure, the optical system itself can be easily assembled and adjusted, and is highly suitable for mass production.

Furthermore, the above-mentioned No. 1. Second. It is also possible to construct the third regions from different members and bond them together to form an optical system with a single structure. In this case, it is preferable to select the shape of each member so that each bonding surface has a flat shape.

Further features of the invention are described in the Examples below.

(Example) FIG. 1 is a sectional view showing an example of a gradient index optical system according to the present invention.

In the figure, 1 and 2 are plano-convex lenses made of a homogeneous medium, 3 is an optical member having a refractive index distribution in a direction substantially perpendicular to the optical axis AX, and having flat surfaces at both ends (light exit surface). The optical member 3 constitutes a spherical lens. 4 is a light emitting element, 4a is a light emitting point of the light emitting element 4, and A is a parallel light beam.

Note that d+, di, and s are symbols indicating parameters of this optical system, and represent the axial distance between each surface.

The plano-convex lens 1 is a lens whose surface on the light emitting element 4 side is flat and the other surface is a convex surface with a radius of curvature rl, and is in close contact with the plane of the optical member 3 on the side opposite to the light emitting element 4.

On the other hand, the surface of the plano-convex lens 2 on the light emitting element 4 side has a radius of curvature r,
This lens has a convex surface and a flat surface, and the other surface, that is, the surface opposite to the light emitting element 4, and the flat surface of the optical member 3 on the light emitting element 4 side are in close contact with each other.

Therefore, the optical system of this embodiment has a single structure in which the plano-convex lens 1.2 and the optical member 3 are bonded together by a predetermined method.

Further, the light emitting element 4 is in close contact with the convex surface of the plano-convex lens 2,
The light emitting point 4a of the light emitting element 4 is located near the apex of the convex surface of the plano-convex lens 2.

The refractive index distribution formed in the optical member 3 is N(ρ)!, where the refractive index on the axis is NO%, the distance from the optical axis is ρ, and the refractive index at the distance ρ is N(ρ)! NO+N1p”+
It is expressed as N2 p' +-. Furthermore, Nl, N2. ...
indicates the refractive index distribution coefficient.

Further, in this embodiment, the refractive index of the homogeneous medium constituting the plano-convex lens 1.2 is set to "I r 13."

In FIG. 1, the light beam emitted from the light emitting point 4a of the light emitting element 4 is transmitted through the plano-convex lens 2. The optical member 3 degrees passes through the plano-convex lens 1 one after another, and is emitted from the plano-convex lens 1 as a parallel light beam λ.

Here, the light flux emitted from the light emitting point 4a is affected by the red surface of the plano-convex lens 2 and the optical member 3, the refractive index distribution of the optical member 3, the interface between the optical member 3 and the plano-convex lens 1, and the interface between the plano-convex lens 1 and air. undergoes refraction.

According to the optical system of this embodiment, although the configuration is simple, the divergent light beam emitted from the light emitting point 4a can be converted into a parallel light beam with aberrations well corrected. This is mainly due to the formation of the refractive index distribution region within the optical system and the setting of the region at an appropriate position within the optical system. Spherical aberration and coma aberration can be favorably corrected by appropriately determining this refractive index distribution region and the refractive conditions for each refractive surface.

It is generally known that various aberrations can be corrected by forming a refractive index distribution in an optical element such as a lens. However, if the refractive index distribution region is simply formed near a refractive surface such as a convex surface, spherical aberration can be corrected, but coma aberration remains.

Therefore, in the optical system of this embodiment, the refractive index distribution region, that is, the optical member 3, is placed at a predetermined distance from the convex surface of the plano-convex lens 1, and both spherical aberration and comatic aberration are corrected for high NA. are doing.

Incidentally, the optical member 3 is located near the center of curvature of the convex surface of the plano-convex lens 1.

Further, the refractive index distribution formed in the optical member 3 has a distribution in which the refractive index gradually increases as it moves away from the optical axis, and has a function equivalent to a lens having substantially negative power or zero power. is fulfilled.

Therefore, among the light rays incident on the optical member 3, the rays that pass through a position farther from the optical axis are subjected to a stronger diverging effect, which has a function that opposes the converging effect on the convex surface of the plano-convex lens 1. The convex surface of the plano-convex lens 1 excessively refracts light rays that pass off-axis, particularly at positions far away from the optical axis, so this excessive refraction is canceled out by the divergence effect produced by the refractive index distribution.
It performs good aberration correction.

Specific examples of the present invention will be shown below.

Table 1 below shows numerical examples 1 to 4 of the present gradient index optical system, and the outline of the optical system represented by these numerical examples 1 to 4 is shown in the lens cross-sectional view shown in FIG. 1 above. Match.

In the table, r++rz is the radius of curvature of the convex surface of the plano-convex lens 1.2 in FIG. 1, n l * n 2 is the refractive index of the plano-convex lens 1.2, and No is the optical member 3 in FIG. On-axis refractive index, Nl, N2°Ns, Na is the refractive index distribution coefficient,
Similarly, Δn is the maximum refractive index difference within the effective diameter of the optical member 3,
f indicates the focal length of the entire system, and NA indicates the numerical aperture.

In addition, in all of Examples 1 to 4, the shape-related parameter r
l * r2 * dl * dl * am are common values. Note that dl + dl r dl are plano-convex lenses 1. Optical member 3. The design shows the axial thickness of the plano-convex lens 2, and was designed for light with a wavelength λ=780 nm.

Table 1 Example 1゜N A -0,35, f -5,34 r1 Tomi aO1r, 5=-5,0, dl=4.5, a,=t, 01ds=4.5, n,=l
O1n,=Z.

No "1.5, Nl = 1.32307X10-2N
2 = 3.92461X10-' Ns = -2,22646xlO-'N4"-5,4781X10-' Δn=0.0197 Example 2° NA 0.35, f-thickness 5.30 r, w5.o, r2=-5,0 d,=4.5, d2=1.0, d3=4.5nt=1.
94410, n=-1, 9441ONo-1,5, N,
=O Nt =4.17051X10-" Ns "-1,84454X10-' N4 Snow-5.478txlO-' Δ n=o, o053 Example 3°NA=0.35, f=5.31 r1=5. 0, r, =-5, O d, = 4.5, d2 = 1.0, d, = 4.5n+ = l
O, n= =2.0 No=1.54, N1 work 1.18425X10-”
N2 =3.91288x 10-' N3 =-1,16390X10-' N4 =-7,79214x 10-'Δ n-0,0
178 Example 4゜N A = 0.35, f snow 5.25 r, = 5.0, r2 = -5,0 d, = 4.5, d2 = 1.0, d, = 4.5nl = 2
．． ．． 0%n2 = 2hO N0 = t, 61, N, = 9.62360X10-'N2
=3.88232xlO-' N3 =-1,56168X10-' N4 =-1,41240xlO-' Δn=o, o149 Figures 2 (A) to (C) are shown in Example 3 of the numerical examples above. An aberration diagram of the optical system is shown, and wavefront aberration is described here.

In FIG. 2, (A) shows that the light emitting point 4a shown in FIG. 1 is 0.1 mm1 off-axis from the optical axis! ff position, (
B) shows the wavefront aberration when the light emitting point 4a is located off-axis by 0.05 mm1i from the optical axis, and (C) shows the wavefront aberration when the light emitting point 4a is on the optical axis. ' Note that M indicates the meridional direction and S indicates the sagittal direction.

As can be seen from the aberration diagrams in FIGS. 2(A) to 2(C), the present refractive index distribution type optical system can satisfactorily correct aberrations. Further, although the aberration diagram is shown here only for Example 3 in Table 1 as an example, similar performance was obtained for other Examples as well.

Although one embodiment of the present invention has been specifically described above, the form of the gradient index optical system of the present invention is not limited to the above embodiment.

In the above embodiment, the present gradient index optical system is used to convert diverging light into parallel light, but it can also be used, for example, as a condenser lens to converge a light beam. This can be easily understood by considering the parallel light beam as incident light in FIG.

Further, the light emitting element 4 in FIG. 1 includes a semiconductor laser, an LED, a light source with a pinhole surface, an output end of an optical fiber, and the like. Furthermore, when this optical system is used as the above-mentioned condensing lens, the light-receiving elements used in close contact with the optical system include optical sensors such as phototransistors and CCDs, the input end of optical fibers, and reflective films such as aluminum films. .

In the numerical example shown in Table 1, d, -d3, nl = n2
For the case of 42.0, dl /d3,
The value of nl/n2 may be any value.

Further, according to the optical system shown in the same numerical example, the wall thickness of the optical member 3 is about 1/10 of the wall thickness of the entire optical system, but this wall thickness ratio also depends on the specifications and manufacturing. It can be set arbitrarily to suit the problem.

In addition, in the same numerical example, the thickness of the entire optical system is standardized as 10, but the size of the optical system of the present invention should be arbitrary in accordance with the application and specifications.

FIG. 3 is a sectional view showing a modification of the gradient index optical system shown in FIG. 1. In the figure, numeral 21 indicates a parallel plate, and the same members as those shown in FIG.

In the optical system shown in FIG.
is in close contact with the convex surface of the plano-convex lens 2. However, the refractive surface on the light emitting point 4a side of the member in contact with the light emitting element 4 does not affect aberrations by giving it a radius of curvature greater than a certain degree.

Therefore, in the optical system of this embodiment, a parallel plate 21 is arranged in place of the plano-convex lens 2, and the plano-convex lens 1, the optical member 3, and the parallel plate 21 are bonded together to form the system. Note that the parallel plate 21 is made of a homogeneous medium.

According to the configuration of this embodiment, since the parallel flat plate 21 having a simple shape is used instead of the plano-convex lens 2, manufacturing becomes easy. Moreover, since the end faces of the light receiving element and the light emitting element that are brought into close contact with the end faces of the optical system elements are usually flat, the parallel plate 2
The use of No. 1 is also effective in terms of ease of adhesion.

Further, even the structure shown in the cross-sectional view of FIG. 3 is no different from the structure shown in the cross-sectional view of FIG. 1 in terms of optical performance.

That is, even in the optical system shown in FIG. 3, aberrations can be corrected well. The wavefront aberration at this time is equivalent to that shown in FIG.

Incidentally, a numerical example of the optical system shown in FIG. 3 is intentionally not shown. This is because in the embodiment shown in Table 1, r2
This is because simply setting =■ is sufficient to serve as a numerical example of this embodiment.

Furthermore, it goes without saying that each element constituting the present optical system does not necessarily have a portion through which the light rays do not pass. Examples of this are shown in FIGS. 4(A) to 4(D).

Figures (A) and (B) show the shape of the optical member 3 having a refractive index distribution when a portion of the optical member 3 through which the light rays do not pass is cut. Optical members of the type that have a refractive index gradient in the direction perpendicular to the optical axis (gradient index lenses) used in the optical system of the present invention have large diameters due to restrictions on the refractive index distribution forming method. Difficult to make. Therefore, such a shape with a small diameter is advantageous in terms of fabrication.

Also, if a diameter is small, the refractive index difference Δn
can be held small, which is also advantageous in manufacturing.

Further, the refractive index difference Δn in the numerical examples shown in Table 1 is also based on consideration of only the portion through which the light ray passes.

Incidentally, the value of Δn in each example in Table 1 is within 0.02, and it can be easily produced by a normal ion exchange method.

Figure 4 (C), CD) shows plano-convex lens 1 and plano-convex lens 2.
Alternatively, the shape of the parallel plate 21 is obtained by cutting the portion through which the light rays do not pass.

Note that here, the optical member 3 and the plano-convex lens 2 or the parallel plate 21
Although the diameters of the light emitting elements 4 and 4 are drawn to be the same, they do not have to be the same.

Next, in the optical system of the present invention, a diaphragm for shielding light may be provided at an appropriate location.

Figures 4 (E) and (F) are the same figure (A), respectively.

A diaphragm S is provided around the optical member 3 of the optical system shown in (B). Further, (G) and (H) in the same figure are those in which an aperture S is provided near the convex surface of the plano-convex lens 1 of the optical system shown in (C) and (D) in the same figure, respectively. The position of this diaphragm S is not limited to the illustrated location, but may be placed at any position deemed appropriate depending on the application. Further, the diaphragm S may be formed not only from a specific light-shielding member, but also by applying a light-shielding material to some of the constituent elements of the present optical system.

Next, an application example of the optical system of the present invention will be described.

FIG. 5(A) shows a device in which a semiconductor laser 41 as a light emitting element is bonded to the optical system of the present invention.

41a and 41b in the figure are light emitting points of the semiconductor laser 41. Here, these light emitting points 41a.

It is assumed that 41b can be turned ON10FF independently.

The device shown in FIG. 2A forms a collimated laser beam emitting light source device 5 as a whole. Figure 5 (B) is
) shows a laser beam printer constructed using the light source device 5 of FIG. In the figure, 5 is a light source device for emitting a parallel laser beam, 6 is a polygon mirror, and 7 is an f-
θ lens, 8 is a photosensitive drum. On the photosensitive surface of the photosensitive drum 8, the light source device 5 is arranged so that the scanning direction of the laser beam and the arrangement direction of the two spots are perpendicular to each other. This printer uses two laser beams to write information at the same time, which has a significant effect on improving printing speed. In this example, the number of laser emission points is set to 2.
However, the present invention is not limited to this, and three or more may be used, or one may be used as in the conventional case.

Next, other application examples of the optical system of the present invention will be described.

FIG. 6(A) shows an embodiment of an optical fiber human output device. This embodiment is an example in which an optical fiber 9 is used as a light emitting element or a light receiving element in the present refractive index gradient optical system.

According to this device, it is possible to efficiently input parallel light into the fiber 9 while suppressing the occurrence of aberrations, and vice versa.
It is possible to convert the emitted light from a parallel light into parallel light with a certain width and output it.

FIG. 6(B) shows an optical fiber coupling device 10 in which two of the present gradient index optical systems are disposed facing each other.

According to this device, the light emitted from the fiber 9' can be efficiently input into the fiber 9.

The optical system of the application example shown in Figs. 5 and 6 is
Although it has the form shown in Figure (F), it goes without saying that it is not limited to this.

The present refractive index gradient optical system shown in each of the embodiments and application examples described above is an optical system having a single structure by bonding three members together.

However, according to the present invention, a region having a refractive index distribution in which the refractive index changes in a direction perpendicular to the optical axis is formed in a specific region of a single member, and a curved surface is formed on the end face of the member. An optical system equivalent to the optical system of the example can be obtained.

It goes without saying that the use of a single member in this manner makes manufacturing easier. Also in this case, it is preferable that the curved surface and the refractive index distribution region be spaced apart by a specific distance.

Therefore, to restate the main features of the present invention, it has at least three regions adjacent to each other, the middle part of the regions is a refractive index distribution region, the region adjacent to the region is formed of a homogeneous medium, and the entire system is At least one of the light flux incident surfaces is a curved surface.

〔Effect of the invention〕

As described above, the refractive index gradient optical system according to the present invention is an excellent optical system that can satisfactorily correct various aberrations even though it has a simple configuration consisting of a single structure.

In particular, it is effective to place a light-emitting element or a light-receiving element in close contact with the end face of an optical system component and use it as a light-emitting (or light source) device or a light-receiving device. It is possible to satisfactorily correct both.

By having such an effect, there is no need to adjust the distance between the light emitting element or light receiving element and the optical system, and there is no need to align the components of the optical system. It is easier to assemble and adjust the equipment that uses it. Therefore, it can significantly contribute to cost reduction and simplification.

Furthermore, each element constituting the optical system is easily available and has a simple configuration, so it does not require much effort to create.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one embodiment of a gradient index optical system according to the present invention. FIG. 2 is a wavefront aberration diagram of a specific example of the optical system shown in FIG. 1. FIG. 3 is a sectional view showing a modification of the embodiment shown in FIG. 1. FIGS. 4A to 4H are cross-sectional views showing other embodiments of the gradient index optical system according to the present invention. FIGS. 5(A) and 5(B) are diagrams showing an application example of the present refractive index distribution type optical system. FIGS. 6(A) and 6(B) are diagrams showing other application examples of the present refractive index distribution type optical system. 1, 2-----One plano-convex lens 3-----Optical member 4 having one refractive index distribution---One--Light emitting element 4 a---------- One light emitting point B11 ----------- Parallel light beam A X ----------- One optical axis

Claims (2)

[Claims] (1) a first region having a convex surface and made of a homogeneous medium; a second region that is in contact with the first region on the opposite side of the convex surface and has a refractive index distribution in a direction substantially perpendicular to the optical axis; A gradient index optical system comprising: a third region that is in contact with the second region on a side opposite to the first region and is made of a homogeneous medium. (2) The gradient index optical system according to claim (1), wherein the first, second, and third regions are each made of different members and are bonded together. .