JPH0243503A - Composite optical element - Google Patents

Abstract

PURPOSE:To obtain a high NA (the stop-down angle of a lens) and to make it possible to integrate the title composite optical element with other optical elements by laminating one or more grating elements to a grating element obtained by forming a protection layer on the upper surface of a grating layer. CONSTITUTION:A composite Fresnel lens 1 is constituted by forming a Fresnel lens layer 12 on the upper surface of a glass (transparent) base 11, forming a protection layer 13 on the upper surface of the lens layer 12 to constitute an optical element body 1a and forming a Fresnel lens layer 14 on the protection layer 13 of the optical element body 1a. A two layer type high NA Fresnel lens 1 is arranged oppositely to an LD chip 3 and a beam forming grating 2 is stuck to the base side (plan face) of the Fresnel lens. Beams radiated from the LD chip 3 are collimated by the lens 1 and circular beams are formed by the grating 2 and projected. Consequently, a high NA lens with high efficiency and a small axial aberration can be obtained and the degree of integration can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a composite optical element in which grating elements are laminated.

(B) Conventional technology Conventional composite optical elements, such as composite grating elements, have a structure in which a grating layer is formed on each of the front and back surfaces of a glass substrate, or a structure in which the back surfaces of two glass substrates each having a grating layer on the front surface are bonded together. are known.

(C) Problems to be Solved by the Invention In the above-mentioned conventional composite grating element, the number of gratings that can be composited is limited to two layers.

Therefore, there is a disadvantage that the field of application is limited.

Furthermore, since this composite grating element does not have a flat surface portion, it has the disadvantage that it cannot be integrated with other optical elements.

By the way, in recent years, optical pickup objective lenses and LD
A high NA Fresnel lens is required as a collimating lens. However, with Fresnel lenses,
The higher the NA (lens aperture angle), the smaller the grating minimum period. The relationship between NA and the minimum period is expressed by the following equation.

λ Δ= NA Here, Δ is the minimum period and λ is the wavelength.

For the objective lens of the pickup, N of 0.45 or more is recommended.
A is determined, and therefore the minimum period is about 1.7 μm. Therefore, manufacturing accuracy is very difficult, and there are problems such as a decrease in efficiency due to manufacturing errors and the occurrence of axial aberrations. Furthermore, as the period becomes smaller, the deviation from the phase shift function (theoretical error) becomes larger, leading to a decrease in efficiency. In this way, Fresnel lenses have high N, with high efficiency and low aberration.
It was very difficult to obtain an A lens. In addition, since Fresnel lenses have large off-axis aberrations, it is very difficult to align the optical axis, and a lens with an NAo of 45 can reduce off-axis aberrations to 0.01.
In order to make the angle deviation less than 0.016 (deg
) (see Figure 3).

For this reason, conventionally, for example, an LD collimator with a beam shaping function used mainly as a light source for writeable optical discs is constructed by combining a high NA collimator lens 41 and a beam shaping prism 42, as shown in FIG. was.

The light from the semiconductor laser light source 43 located near the focal point is
A collimator lens 41 converts the parallel light into parallel light, and a beam shaping prism 42 shapes the parallel light into a circular beam for emission. However, this combination structure has disadvantages such as the high NA collimator lens and beam shaping prism being expensive and the collimator itself becoming large.

This invention solves the above-mentioned problems and achieves high NA,
Moreover, it is an object of the present invention to provide a composite optical element that can be integrated with other optical elements.

(d) Means and operation for solving the problem In order to achieve this object, the composite optical element of the present invention has the following configuration.

A composite optical element is constructed by laminating one or more grating elements on a grating element which has a grating layer on the upper surface of a transparent substrate and a protective layer on the upper surface of the grating layer.

In a composite optical element having such a configuration, the base grating element is constructed by forming a grating layer on the upper surface of a transparent substrate, and forming a protective layer (for example, UV curable resin) on the upper surface of this grating layer. There is. By laminating a grating element on the upper surface of this protective layer, a composite optical element in which at least one surface is a flat surface for integration (for integration with other optical elements) and two layers of grating elements is obtained. It will be done. Further, when a protective layer with a flat top surface is formed on the grating element located above these two layers, a third layer of the grating element can be further laminated on this protective layer. In other words, it is possible to obtain a composite optical element in which three or more layers of grating elements are laminated. Therefore, various kinds of optical element bodies (for example, a composite Fresnel lens) can be combined without any limit to the number, and the field of application of the 711Z can be dramatically expanded. Furthermore, since this composite optical element has a flat surface (flat tt3 surface on the substrate side), the degree of integration with other optical elements can be improved.

Such compound optical elements (e.g. compound Fresnel lens)
In order to obtain a lens with NAo of 45,
For example, in a two-layer type (a laminate with two lens layers), NAo
, 24, and in the three-layer type (a laminate with three lens layers), N
Ao, 16 is a good thing. Therefore, such a Fresnel lens has a large minimum period and a small deviation from the phase shift function, so it is highly efficient and has a high NA with small axial aberration.
It becomes a lens.

Furthermore, since off-axis aberrations are also reduced, the tolerance for angular misalignment is increased and alignment of the optical axes is facilitated.

(E) Embodiment FIGS. 1(A) and 1(B) are explanatory diagrams showing a specific embodiment of the composite optical element according to the present invention. In the example, a high NA composite Fresnel lens is illustrated.

FIG. 1(A) shows a composite Fresnel lens in which two lens layers are laminated.

This composite Fresnel lens l has a glass (transparent) substrate 11
A Fresnel lens layer 12 is formed on the upper surface, a protective layer 13 is formed on the upper surface of this lens layer 12 to constitute an optical element body 1a, and a Fresnel lens layer 14 is formed on the protective layer 13 of this optical element body 1a. It is configured as follows. For example, the optical element A1! A lens layer 12 is formed by depositing ZnS, which is an inorganic material, on (Sukumba) by a vacuum thin film forming method (for example, vacuum evaporation technology), and a UV curing resin is applied to this lens layer 12 to integrate the glass substrate 11. By adhering and curing the UV curing resin by irradiating ultraviolet rays, a lens layer 1''2 is obtained which is peeled off from the stamper and adhered to the substrate 11.A UV curing resin is applied to a certain thickness on this lens layer 12,
The protective film 13 is formed by setting the resin film as a flat surface and irradiating it with ultraviolet rays to harden the resin. Then, the lens layer 12 obtained in the same manner as described above is adhered onto this protective film 13.

FIG. 1(B) shows a Fresnel lens in which three lens layers are laminated.

This Fresnel lens is the second layer of the two-layer Fresnel lens obtained in FIG.
5 is provided, and a lens layer 16 is formed on this protective layer 15.

Two-layer Fresnel lens in Figure 1 (A) and Figure 1 (B)
In any of the three-layer Fresnel lenses, the back surface of the Os plate 11 on the glass substrate 11 side) is a flat surface,
It is set to allow integration with other optical elements.

When such a composite Fresnel lens is used, the NA0.
In order to obtain a lens with a diameter of 45, NA0.24 is used for a two-layer Fresnel lens [FIG. 1(A)], and NAO016 is used for a three-layer Fresnel lens (FIG. 1(B)). Therefore, the minimum period is large and the deviation from the phase shift function is small, resulting in a high NA lens with high efficiency and small axial aberration. In addition, off-axis aberrations are also reduced, and the tolerance for angular misalignment is increased, making it easier to align the optical axes.

Further, since the lens has a curvature, the NA of a normal aspherical lens is controlled to be within about 0.5 to 0.6.

However, since the Fresnel lens is a flat plate, the NA is not limited and can be increased without limit by adding multiple layers.

For example, by laminating four layers of Fresnel lenses with NA of 0.24, a lens with NA of about 0.7 can be obtained, and when used as a pink-up objective lens, the spot diameter is 1/2 that of the conventional (NAo, 45). This increases the recording density of optical discs by four times.

FIG. 2 is an explanatory diagram showing an LD collimator with a beam shaping function using an example composite Fresnel lens.

In this application example, a two-layer high-NA Fresnel lens shown in Fig. 1 (Δ) is placed facing the LD chip 3, and a grating 2 for beam molding is bonded to the substrate side (flat surface) of the Fresnel lens. This shows an example of the accumulation. The diverging light from the LD chip 3 is shaped into a circular beam by the high NA Fresnel lens shaping grating 2 of the embodiment and is emitted. This integrated example of the LD collimator with a beam shaping function can achieve smaller size, lighter weight, stability, and lower resolution than the conventional example (FIG. 4). In particular, reduction in access time, which is the biggest problem with optical discs, can be achieved by reducing the weight.

(f) Effects of the Invention In the present invention, as described above, the grating element is provided with a grating layer on the upper surface of the transparent substrate, and a protective layer is provided on the upper surface of this grating layer. On the layer, 1
Since it was decided to laminate a plurality of lens layers, at least one surface has a flat surface for integration with other optical elements,
Moreover, a high NA optical element including multiple lens layers can be provided.

In the composite optical element of this invention, various types of optical elements (
Since the number of grating elements (grating elements) can be stacked without any limit, the field of application will expand dramatically.

Furthermore, in the case of a composite Fresnel lens, a high NA lens with high efficiency and small axial aberration can be obtained. In addition, off-axis aberrations are also reduced, and the tolerance for angular misalignment is increased, making it easier to align the optical axes. Furthermore, since it is a compound lens with multiple lens layers and has the ability to be integrated with the moon and other optical elements, the degree of integration is reduced and the lens can be made smaller and lighter in applications.
It has an excellent effect of achieving the purpose of the invention.

[Brief explanation of the drawing]

FIG. 1(A) is an explanatory diagram showing a two-layer Fresnel lens according to the embodiment, FIG. 1(B) is an explanatory diagram showing a three-layer Fresnel lens according to the embodiment, and FIG. 2 is an explanatory diagram showing the Fresnel lens according to the embodiment. An explanatory diagram showing the used LD collimator with beam shaping function, Figure 3 is an explanatory diagram showing the relationship between Fresnel lens NA, angular deviation, and wavelength, and Figure 4 shows the conventional L D collimator with beam shaping function. It is an explanatory view showing a D collimator. 1: Composite Fresnel lens, 11 glass substrate, 12.1
4/16: Fresnel lens layer, 13/15: Ho:! ! layer.

Claims (1)

[Claims] (1) A composite optical element characterized in that one or more grating elements are laminated on a grating element comprising a grating layer on the upper surface of a transparent substrate and a protective layer on the upper surface of the grating layer.