JPS61193106A - Functional optical element - Google Patents

Abstract

PURPOSE:To obtain a functional optical element having no dependency on the polarization characteristic of used light by forming a phase diffraction grating arranging two substances having optical axes different to each other alternately. CONSTITUTION:A functional optical element is formed of triangular wave grating using a substance 1 and 2. The optical axis of the substance 1 is arranged in the direction of grooves of the grating and the optical axis of the substance 2 is arranged in the direction of the row of the grating. A rectangular grating is formed in the element using the substances 1 and 2. Further, the optical axis of the substance 1 is arranged in the direction of the grooves of the grating and the optical axis of the substance 2 is arranged in the perpendicular direction to the arranged surface of the grating. Such substances having the specified optical axes are those represented by so-called optically anisotropic substances such as LiNbO3, LiTaO3, PLZT, liquid crystal, SiO2, CdS, CaCO3, ZrO2, Al2O3, MgF2, etc. The two substances for forming a phase diffraction grating may be different to each other or same.

Description

[Detailed description of the invention] (1) Technical field The present invention is for optical recording, optical coupling, and optical communication.

The present invention relates to a functional optical element suitable as a device for various devices such as those for optical calculation.

(2) Prior Art Conventionally, various diffraction gratings have been applied as single-function optical elements, and are used, for example, as a 1-spectrometer, a 9-branch multiplexer, or a reflector. Recently, with the addition of applications in semiconductor lasers and optical integrated circuits, it has become an even more important optical element.

Among the various types of diffraction gratings mentioned above, one of the phase type diffraction gratings generally uses methods such as forming irregularities on the surface or changing the refractive index inside the medium as a means for imparting a phase change. The medium used in such a diffraction grating is usually composed of an optically isotropic material and exhibits its original function regardless of the polarization characteristics of the light used. However, in recent years, there have been increasing opportunities for diffraction gratings to be constructed of optically anisotropic materials such as crystals having a predetermined optical axis. in this case,
The characteristics of the diffraction grating change depending on the polarization direction of the light used.

Therefore, unless a laser or the like is used as a light source and linearly polarized light is used, it is necessary to linearly polarize the light in a predetermined direction via a polarizing plate, and at this stage the light utilization efficiency is greatly reduced. .

(3) Summary of the Invention An object of the present invention is to eliminate the conventional drawbacks and provide a novel functional optical element that does not depend on the polarization characteristics of the light used.

In order to achieve the above object, the functional optical element according to the present invention is characterized in that a phase type diffraction grating is formed by alternately arranging two materials having different directions of optical axes. A substance having an axis is a substance represented by a so-called optically anisotropic substance, for example, LiNbO3, Li
TaO3, PLZT.

Gd2 (MoOa)3, B14Tt30t2゜Bi
t2SiO12, GaAs, Si, ZnTe.

As2Se3, Se, AsGe5eS, BaTi
O3, TiO2, KDP, DKDP, ADP.

ZnO, MnB1, Ba2NaNb5015. liquid crystal,
5i02. CdS, CaCO3, ZrO2゜Al2O3
, MgF2, etc. In addition, the two materials forming the above-mentioned phase-type diffraction grating in the present invention may be different materials or the same material.In short, when creating the functional optical element, the direction of the optical axis is determined. can be set arbitrarily, and the decision whether to use different materials or the same material is determined by the function provided to the single-function optical element, ease of manufacture, etc.

Furthermore, although the optical axes of the two alternately arranged materials are normally used in the same manner, there are also restrictions on the materials that can be used with different optical axes, constraints on the production of the device, and the present device. Various forms are conceivable depending on the conditions regarding the specifications, etc.

By using this functional optical element, you can, for example, not only split and polarize light, but also extract a predetermined linearly polarized light from light with arbitrary polarization characteristics, or combine two linearly polarized lights with different polarization directions. It can perform various functions such as dividing. Furthermore, it is also possible to provide an imaging function by changing the shape of the diffraction grating. The reason why this device has such multiple functions is that the diffraction grating is formed from two materials with different optical axes, and the two materials have different refractive indexes depending on the polarization component of the light used. This is because it was actively applied to diffraction gratings.

This element can also be made into a transmissive type and a reflective type.In the case of a transmissive type, the constituent members must have transparency to the light used, and in the case of a reflective type, the substrate or It is necessary to use a reflective material or provide a reflective film for the predetermined member.

The present invention will be described in detail below using examples.

(4) Example Figures 1 (A) to (C) show examples of the basic configuration of this functional optical element, and 1 and 2 are materials whose optical axes have different directions, respectively.
Reference numeral 3 indicates the incident light, and 4 and 4' indicate mutually orthogonal polarization components of the incident light 3, respectively. The configuration examples shown in FIG. 1 are all transmission type elements, and the optical axis and the direction of the polarized light component of the incident light 3 are indicated by → marks and Φ marks, respectively, to facilitate understanding of FIG. 1.

The element shown in FIG. 1(A) has substances 1 and 2 forming a triangular wave-like lattice, and the optical axis of each substance 1 is in the groove direction of the lattice (perpendicular to the paper), and substance 2 is in the lattice arrangement direction. (towards the left and right of the page). In the element shown in FIG. 1(B), substances 1 and 2 form a rectangular grating, and each optical axis is perpendicular to the groove direction of the grating for substance 1 and to the array plane of the diffraction grating for substance 2. facing the direction.

In the element shown in FIG. 1(C), the optical axis directions of the substances 1 and 2 are the same as in FIG. 1(B), and the diffraction grating formed by the two substances 1 and 2 has a sine wave shape.

In the functional optical element of this embodiment, the optical axis directions of the two substances 1 and 2 constituting the element are orthogonal in space, but do not necessarily need to be orthogonal; It is sufficient that the optical axis directions of the two substances 1 and 2 intersect, and the arrangement is determined based on various constraints as described above. However, in general, this functional optical element functions better when the relative angular difference θ (as seen from the incident light) between the two optical axis directions satisfies θ≧30'. Hereinafter, an example of the function of the present functional optical element will be explained using the drawings.

Figures 2 (A) and (B) are functional explanatory diagrams of this functional optical element, in which the same members and symbols as in Figure 1 are given the same numbers, 5 and 5' are higher-order diffracted lights, and 6 is a zero. The following shows the transmitted light.

In the element shown in FIG. 1(A), substances 1 and 2 form a rectangular diffraction grating, and the optical axis of substance 1 is in the groove direction of the diffraction grating, and the optical axis of substance 2 is in the direction in which the diffraction gratings are arranged. are orthogonal to each other.

In general, light having a random polarization direction, in other words, light having arbitrary polarization characteristics, can be divided into two orthogonal components 4.4' as shown in FIG. In the element shown in FIG. 2(A), the polarized light component 4 of the incident light 3 is parallel to the optical axis of the substance 1, and the extraordinary refractive index ne of the substance 1 is sensed. Furthermore, the ordinary refractive index n'o of the substance 2 is felt perpendicularly to the optical axis direction of the substance 2. Further, the polarized light component 4' of the incident light 3 senses the ordinary refractive index no of the substance 1 and the extraordinary refractive index αe of the substance 2. Therefore, mutually orthogonal polarization components 4 of the incident light 3,
4' can be considered to pass independently through diffraction gratings made of materials with refractive indices ne and rI'o, and no and n'e, respectively. Here, the refractive index difference Δn of the grating for one polarization component is
For polarization component 4, Δ1=lne-n'ol.

For the polarization component 4', when expressed as Δα = lno-ffel, by setting Δn = Δn', the diffraction grating of the single-function optical element can be expressed as if it were made of an isotropic material. It exerts the same diffraction effect on polarized light components, and therefore can function effectively for light having arbitrary polarization characteristics.

Hereinafter, an example of fabrication of the device according to FIG. 2(A) and results of performance evaluation will be described. After slicing the TiO2 crystal along the crystal axis and forming it into a plate shape of 50 x 50 x 1 mm, both sides were polished.
Two cleaned transparent substrates are prepared. Apply RD-200ON (a negative resist manufactured by Hitachi, Ltd.) on the surfaces of these two substrates using a spinner, and perform a prescribed pre-bake.
Thereafter, a grating made of resist with a pitch of 1.61 Lm and a thickness of 4000 people was formed by mask exposure and development. However, the direction in which the diffraction gratings are arranged on both substrates is such that one is in the direction of the crystal axis and the other is in the direction perpendicular to the crystal axis. Subsequently, the four substrate surfaces were etched to a depth of 1.54 lumens by an etching method using a CF4-O2 mixed gas, and then the resist was removed using a resist remover.

The functional optical element shown in FIG. 2(A) was produced by closely attaching these two substrates with their respective gratings interlocked. In addition, the ordinary refractive index no of TiO2 for light with a wavelength of 8300 is 2
．． 51 ordinary refractive index ne is 2.78. Therefore, Δn=
It becomes 0.27.

Now, in a phase type diffraction grating forming a single functional optical element, the order in which transmitted diffracted light exists is given by the following equation.

Here, 0 is the wavelength of the incident light, Δ is the pitch of the diffraction grating,
m represents the order of transmitted diffracted light. The light used to evaluate the performance of this functional optical element was light with a random polarization direction (input Q
= 8300 people), and by substituting each condition into the above equation, the orders m of the diffracted light that may exist are -1, 0, and 1. Furthermore, the diffraction efficiency η0 of the zero-order transmitted diffracted light in a rectangular diffraction grating like the present element can be expressed by the following equation (1).

-rto=-Ar-(1+cos (2w"")
) --- (1) λ0 In equation (1), Δn-T=(+10m) in o (m=o, 1.2, 3.
-----)---When (2) is satisfied, η0=Q and zero-order transmitted diffracted light does not exist, and each condition of this example is (
As shown in the figure, the diffracted light that satisfies the equation 2) is only the ±1st-order diffracted light 5.5'. Furthermore, since the lattice shape is symmetrical, the energy distribution between the +1st-order diffracted light 5 and the 11st-order diffracted light 5' is equal, resulting in an overall light utilization efficiency of over 80% and an S/N ratio of over 100:1. became.

The element according to FIG. 2(B) is a polarizing plate or a polarizing plate.

It is a functional optical element having a function similar to a polarizing beam splitter, and 6 indicates zero-order transmitted light.

Here, the optical axis direction of the substance 1 is the groove direction of the diffraction grating, and the optical axis direction of the substance 2 is a direction perpendicular to the diffraction grating surface, so that they are orthogonal to each other. Further, in this element, substance 1 and substance 2 form a triangular wave-like lattice. In this device, substances 1 and 2 are the same substance. (no=n'o
, ne=n'e) When incident light 3 having arbitrary polarization characteristics is incident on a non-element, the polarization component 4 of the incident light 3 is a substance l
The extraordinary refractive index ne of substance 2 and the ordinary refractive index n'o of substance 2 are felt.

Moreover, the polarization component 4' is the ordinary refractive index no of the substance 1 and the substance IR2
The ordinary refractive index n'0 is felt. Therefore, for the polarization component 4 of the incident light 3, the refractive index ne and rl'Q.

For polarization component 4', there are diffraction gratings with refractive indices no and n'O. However, as mentioned above, no=n'
Since o, ne=n'e, the polarized light component 4' has no substantial diffraction grating, and passes through this element without any problem, becoming zero-order transmitted light 6. Also, polarization component 4 is Δn:1ne-no
It is diffracted by a diffraction grating of l.

In equation (3) for the diffraction efficiency of the zero-order transmitted diffracted light in the triangular wave diffraction grating shown below, if conditions are set so that ηO-0, the polarized light component 4 becomes the higher-order diffracted light 5. .5' and is emitted. In this way, it is possible to extract a predetermined linearly polarized light from light having a random polarization direction.

η0 = sinc (π””) −m−(3
) Input 0 When linearly polarized light is extracted from a normal polarizing plate, the light loss is as much as 70%, but with this element, the light loss is about 50%.

The functions of this functional optical element using Fig. 2 are only one example of the functions of this element, and various functions can be achieved by changing the lattice shape formed by substances 1 and 2, the optical axis direction of both substances, etc. It is possible to have Also, Fresnel lens is used as an application.

Needless to say, it can be used for curved gratings, grating couplers, 6FB lasers, etc.

(5) As described in detail of the invention, although the functional optical element according to the present invention is made of an optically anisotropic material, it functions effectively for light having arbitrary polarization characteristics. , and is an optical element having multiple functions.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the configuration of a functional optical element according to the present invention. FIG. 2 is a functional explanatory diagram of the functional optical element according to the present invention. 1.2--A substance with a predetermined optical axis 3---=-Incoming light 4, 4'----Polarized light components orthogonal to each other 5, 5'
---First higher-order diffracted light 6-----First transmitted light

Claims (1)

[Claims] (1) A functional optical element characterized in that two materials having optical axes in different directions are arranged alternately and a phase type diffraction grating is formed by the two materials.