JP3060327B2 - Plastic lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a plastic lens .
The present invention relates to an optical system including a plastic lens which can have any astigmatism as required.

[0002]

2. Description of the Related Art In recent years, plastic lenses have been used for various purposes. However, plastic lenses generally have internal strain due to a polymer material and have optically birefringence. The birefringence distribution often has a pattern that causes astigmatism in a linearly polarized light field, particularly in the case of a biconvex lens. In addition, plastic lenses often generate astigmatism, especially in molded products, because asymmetry occurs in the lens surface shape.

For example, plastic aspherical lenses are often used for laser optical system lenses such as optical disk lenses and laser beam printer lenses. This plastic lens mainly uses an acrylic copolymer resin having PMMA or MMA as a base material. These acrylic resins have a negative sign of birefringence, and the absolute value of the magnitude of birefringence is about one digit smaller than that of other resins such as polycarbonate and polystyrene. Generally, a plastic aspherical lens for an optical disk using an acrylic resin has a maximum value δmax of an absolute value of a phase difference δ due to birefringence within the effective diameter of the lens.
0 °>δmax> −40 °, and the astigmatism due to birefringence was within an allowable value for an optical disc lens. However, acrylic resins have low birefringence and are suitable for optical disc lenses, but have high water absorption and are liable to change in performance due to humidity. Also, heat resistance is not so high. On the other hand, there is polycarbonate as a resin other than acrylic resin, which is generally suitable for lens use. This resin is superior to acrylic resin in both moisture absorption resistance and heat resistance, but has too large a birefringence and is not suitable for an objective lens for an optical disk. In other words, if a plastic lens material that has excellent heat resistance and moisture absorption resistance, but has a large birefringence and is manufactured by a normal mold processing and molding method so that the lens surface shape does not have asymmetry, the optical disk In the case of a lens for use, as shown in FIG. 1, astigmatism caused by birefringence exceeds the standard of lens performance.

[0004] The above two causes of astigmatism occur in FIG.
~ As shown in Fig. 3, there is a dependency on the direction of linear polarization and the direction of the gate (entrance of material at the time of molding) of the lens.
Conventionally, no lens has been set in consideration of these relationships.

[0005]

In the prior art, a technique for providing arbitrary astigmatism in the same lens system has not been established. To generate the necessary astigmatism, the lens must be replaced or replaced. I had to change the design. The present invention is an optical system that includes a plastic lens having astigmatism caused by birefringence, and an astigmatism caused by asymmetry of the lens surface shape, plug with respect to the polarization direction of the incident
By rotating the stick lens, the same lens system can have any astigmatism.

[0006]

[Means for Solving the Problems] In order to solve the above problem,
In the optical system of the present invention, astigmatism caused by birefringence
The difference and the astigmatism caused by the asymmetry of the lens surface shape.
Gate direction when molding plastic lenses
The plastic so that the polarization direction of the emitted light substantially matches
It is characterized by the arrangement of cleanse.

In addition, astigmatism caused by birefringence and
With astigmatism caused by the asymmetry of the lens surface shape
Plastic lens, birefringence within effective lens diameter
A plastic lens having a maximum phase difference δmax of + 50 ° <δmax <+ 120 ° due to folding is arranged such that astigmatism caused by the birefringence is compensated by astigmatism caused by the lens surface shape. It is characterized by.

In addition, astigmatism caused by birefringence and Len
With astigmatism caused by the asymmetry of the
The gate direction during molding of the plastic lens is
So that it becomes a direction rotated by about 90 ° with respect to the light direction,
Disposing the plastic lens with respect to the polarization direction
It is characterized by having.

Also, astigmatism caused by birefringence and
With astigmatism caused by the asymmetry of the lens surface shape
Rotate plastic lens with respect to polarization direction of incident light
By doing so, it is noted that arbitrary astigmatism was given.
Sign. Also, astigmatism caused by birefringence and the lens
With astigmatism caused by surface asymmetry
The gate direction during molding of the stick lens is
So that it is a direction rotated by a predetermined angle with respect to the direction,
Disposing the plastic lens with respect to the polarization direction
It is characterized by having.

[0010]

FIG. 1 shows the state of astigmatism of a plastic lens .
The symbols are schematically represented, and the number of symbols indicates the magnitude of astigmatism. Injection-molded plastic lenses generally produce birefringence symmetrical with respect to the gate direction. Astigmatism due to this birefringence is caused by rotating the gate direction with respect to the polarization direction of the incident light, as shown in FIG. The characteristic is that the sign of astigmatism changes when viewed from the direction. On the other hand, astigmatism caused by asymmetry of the lens surface shape is such that when the gate direction is rotated with respect to the polarization direction of the incident light, the sign of the astigmatism does not change when viewed from the gate direction as shown in FIG. There is a feature.

For this reason, when the gate direction is arranged so as to coincide with the polarization direction as shown in FIGS. 2 and 3A, the astigmatism due to birefringence and the astigmatism due to the surface shape are enhanced.
Large astigmatism is generated as shown in FIG. 4A. Conversely, when the arrangement is as shown by B in FIGS. 2 and 3, astigmatism due to birefringence and astigmatism due to the surface shape cancel each other, and astigmatism can be reduced as shown in FIG. 4B. Of course, if the astigmatism due to the birefringence and the astigmatism due to the surface shape have the same magnitude, the astigmatism can be completely corrected. In addition, by rotating to an intermediate position as shown in FIG. 5, any astigmatism can be obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A plastic resin used in the optical system of the present invention.
The following is a specific example of a lens . Examples of materials for plastic lenses include a resin obtained by copolymerizing polycarbonate with positive sign birefringence and styrene with negative sign birefringence, or a polyolefin copolymer resin with a positive sign or a polyolefin non-copolymer resin. There are resins and the like.

Example 1 As a material, a resin sample obtained by copolymerizing styrene with polycarbonate was used. As for the birefringence within the effective diameter of the lens, the maximum value of the phase difference δ was δmax = + 80 °. When there is no asymmetry in the lens surface shape, the astigmatism is reduced to Zernik.
When represented by the aberration coefficient of e, 0.04 in the arrangement of FIG. 4A.
λrms, and 0.04λrms in the arrangement of FIG. 4B. On the other hand, by giving asymmetry to the lens surface shape, 0.07λrms in FIG. 4A and 0.01λrms in FIG.
4B, a lens with small astigmatism suitable as an objective lens for an optical disk could be obtained in the arrangement of FIG. 4B.

The asymmetry of the lens surface shape naturally occurs at the time of molding the lens. As a specific means for positively assimilating the lens shape, there is a method of forming the lens during molding.
There are a method of giving asymmetry and a method of giving asymmetry according to molding conditions at the time of molding.

Example 2 Using the plastic lens of Example 1 and the arrangement of FIG. 4A, a lens system in which the astigmatism of the plastic lens was enhanced was obtained.

Example 3 In a single lens using a polyolefin-based resin, astigmatism due to birefringence was 0.04λrms when represented by a Zernike aberration coefficient. The astigmatism due to the asymmetry of the lens surface shape was 0.03λrms. When this lens is rotated by 30 ° with respect to the polarization direction as shown in FIG. 5A, the astigmatism is 0.06λrms.
As shown in FIG. 5B, when the gate direction was rotated by 60 ° with respect to the polarization direction, the astigmatism was 0.03λrms.

[0017]

The optical system of the present invention according to the present invention, as described above, the optical
By simply changing the orientation of the plastic lens in the system, the amount of astigmatism can be changed as desired, not only to offset the astigmatism generated in other places, but also to positively astigmatize it. Even when using aberrations, the amount of generation can be freely adjusted, which is extremely convenient.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing astigmatism generally possessed by a plastic lens.

FIG. 2 is an explanatory diagram of astigmatism caused by birefringence of a plastic lens.

FIG. 3 is an explanatory diagram of astigmatism caused by asymmetry of the surface shape of a plastic lens.

FIG. 4 is a conceptual diagram showing a change in astigmatism due to the arrangement of a plastic lens.

FIG. 5 is a conceptual diagram showing a change in astigmatism due to another arrangement of a plastic lens.

────────────────────────────────────────────────── ─── Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 3/02-3/08 G02B 9/00-17/08 G02B 21/02-21/04 G02B 25 / 00-25/04 G02B 27/28 JICST file (JOIS) Birefringence * Astigmatism WPI (DIALOG) [birefringen? + Double * reflect? ] * Lens * [asymmetric? + Dissy mmet? ] * PY = 1990: 1991

Claims (5)

(57) [Claims] 1. Astigmatism caused by birefringence and lens surface
Plus with astigmatism caused by shape asymmetry
Gate direction during tic lens molding and polarization of incident light
The plastic lens is arranged so that the
Optics including a plastic lens characterized by being placed
system. 2. Astigmatism caused by birefringence and lens
With astigmatism caused by surface asymmetry
Stick lens with birefringence within the effective lens diameter
The maximum value δmax of the resulting phase difference δ is + 50 ° <δmax <+ 120 ° so that the astigmatism caused by the birefringence is compensated by the astigmatism caused by the lens surface shape. An optical system that includes a plastic lens as a feature. 3. Astigmatism caused by birefringence and lens surface
Plus with astigmatism caused by shape asymmetry
The gate direction during molding of the tic lens is
Direction so as to be rotated by approximately 90 ° with respect to the
Make sure that the plastic lens is
And an optical system including a plastic lens. 4. Astigmatism caused by birefringence and lens
With astigmatism caused by surface asymmetry
Rotate the stick lens with respect to the polarization direction of the incident light.
The feature is that it has arbitrary astigmatism
An optical system that includes a plastic lens. 5. Astigmatism caused by birefringence and lens surface
Plus with astigmatism caused by shape asymmetry
The gate direction during molding of the tic lens is
To the direction rotated by a predetermined angle with respect to the
The plastic lens was arranged with respect to the polarization direction.
An optical system including a plastic lens.