JPH07234317A - Polarizing optical element and polarizing optical device - Google Patents

Abstract

PURPOSE:To reduce the cost of the polarizing optical element and increase the selectivity of a plane of polarization, to facilitate the assembly of an applied equipment, and to widen the application range. CONSTITUTION:A birefringent material film 34 is provided on a blaze diffraction grating 33 formed on a glass substrate 32. Consequently, this element is lower in cost than structure which is formed entirely of a birefringent material, and the selectivity of a plane of polarization is made higher than that when only the blaze diffraction grating 33 is used through the synergism of the blaze diffraction grating 33 and birefringent material film 34. Further, restrictions on the angle of incidence of even the light in a short-wavelength range are realized because of the presence of the birefringent material film 34, so the assembly of the applied equipment is easy and the application range is wide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing optical element for selecting a plane of polarization and a polarizing optical device using the polarizing optical element.

[0002]

2. Description of the Related Art FIG. 5 shows a magneto-optical disk head using a first conventional example of the present invention. The magneto-optical disk head 11 includes a polarization beam splitter 12, a Wollaston prism 13, a lens 14, and a photodetector 15.
And a laser diode 16 and an objective lens 17.

In the magneto-optical disk head 11, a large proportion of the light 21 emitted from the laser diode 16 and incident on the polarization beam splitter 12 is reflected by the polarization beam splitter 12 and transmitted through the objective lens 17. And enters the magneto-optical disk 22. The light 21 that has entered the magneto-optical disk 22 has its polarization plane rotated according to the recording signal, is reflected, passes through the objective lens 17, and then enters the polarization beam splitter 12 again.

Of the light 21 reflected by the magneto-optical disk 22 and incident on the polarization beam splitter 12, a large proportion of the light 21 having a polarization plane orthogonal to the polarization plane of the light 21 incident on the magneto-optical disk 22. And the magneto-optical disk 22
A predetermined proportion of the light 21 having the same polarization plane as that of the light 21 incident on the polarization beam splitter 12 is transmitted.

Therefore, compared with the light 21 reflected by the magneto-optical disk 22 and incident on the polarization beam splitter 12,
In the light 21 transmitted through this polarization beam splitter 12,
The proportion of the light 21 having a polarization plane orthogonal to the polarization plane of the light 21 incident on the magneto-optical disk 22 is increased.

The light 21 that has passed through the polarization beam splitter 12 and has entered the Wollaston prism 13 is split into two lights 21 having mutually orthogonal polarization planes, and the lens 1
After passing through 4, the light enters the photodetector 15. Then, the recording signal of the magneto-optical disk 22 is obtained by detecting the rotation of the polarization plane from the light 21 incident on the photodetector 15.

FIG. 6 shows a magneto-optical disk head using the second conventional example of the present invention. The magneto-optical disk head 23 includes a Wollaston prism 13 and a lens 14 in the magneto-optical disk head 11 shown in FIG.
And the polarization beam splitter 2 instead of the photodetector 15.
4 and photodiodes 25a and 25b.

The polarization beam splitter 24 includes a polarization film 24a similar to the polarization film 12a of the polarization beam splitter 12.
Besides, a total reflection film 24b is also provided. Then, the polarization beam splitters 12 and 24 and the photodiode 25
The laser couplers 26 a and 25 b are integrated.

The magneto-optical disk head 23 shown in FIG.
The light 21 reflected by the magneto-optical disk 22 and transmitted through the polarization beam splitter 12 as in the case of the magneto-optical disk head 11 shown in FIG. It is split into two lights 21. The light 21 transmitted through the polarizing film 24a enters the photodiode 25a, and
The light 21 reflected by a is incident on the photodiode 25b after being reflected by the total reflection film 24b.

In a magneto-optical disk head, in general, the proportion of the light 21 reflected by the magneto-optical disk 22 that has a polarization plane orthogonal to the polarization plane of the light 21 incident on the magneto-optical disk 22. Of the first polarizing optical element for increasing the light intensity and two lights 21 having polarization planes orthogonal to each other with respect to the light 21 transmitted through the first polarizing optical element.
A second polarizing optical element for splitting is required.

Therefore, in the magneto-optical disk heads 11 and 23 shown in FIGS. 5 and 6, the polarization beam splitter 12 is used as the first polarizing optical element, and the wall light is used as the second polarizing optical element. The Ton prism 13 or the polarization beam splitter 24 is used. Further, as these polarizing optical elements, in addition, an echelette-type blazed diffraction grating and an optical element in which a grating made by a proton exchange method is formed on a substrate made of LiNbO ₃ which is a birefringent material are considered.

[0012]

However, in the polarization beam splitters 12 and 24 having the polarization films 12a and 24a, which are dielectric multilayer films, the light beam 21 for obtaining desired performance is obtained.
The angle of incidence is severely limited, and it is not easy to assemble the magneto-optical disk heads 11 and 23. Also, since the Wollaston prism 13 has no choice but to be a transmission type,
Since the degree of freedom in designing the magneto-optical disk heads 11 and 23 is low and the lens 14 and the photodetector 15 need to be separated from the Wollaston prism 13, it is difficult to miniaturize the magneto-optical disk heads 11 and 23. .

In the echelette-type blazed diffraction grating, if the light 21 having a wavelength of about 780 nm which is generally used in the magneto-optical disk heads 11 and 23 is used, the incident angle of the light 21 must be strictly limited. ,
It is possible to obtain a selection ratio lower than the selection ratio of the polarization plane of about 1: 100 required for the magneto-optical disk heads 11 and 23. Therefore, it is difficult to use this blaze diffraction grating alone for the magneto-optical disk heads 11 and 23.

On the other hand, in the optical element in which the lattice is formed on the substrate made of LiNbO ₃ by the proton exchange method, a high selection ratio of the polarization plane can be obtained, but the cost of LiNbO ₃ itself is high and the proton exchange method is stable. Since it is difficult to carry out the operation, the overall cost is high.

[0015]

A polarizing optical element 31, 36, 44, 45, 54, 55 according to claim 1 comprises a diffraction grating 3
It is characterized in that a birefringent material film 34 is provided on the surface 3.

The polarizing optical elements 31, 36, 4 according to claim 2
4, 45, 54 and 55 are characterized in that, in the polarizing optical element according to claim 1, the diffraction grating 33 is a blazed diffraction grating.

The polarizing optical elements 31, 36 and 4 of claim 3
4, 45, 54 and 55 are characterized in that, in the polarizing optical element according to claim 1 or 2, the birefringent material film 34 is an inorganic ferroelectric film.

The polarizing optical elements 31, 36, 4 according to claim 4
Nos. 4, 45, 54 and 55 are characterized in that, in the polarizing optical element according to claim 1 or 2, the birefringent material film 34 is an organic ferroelectric film.

The polarizing optical elements 31, 36 and 4 of claim 5
4, 45, 54 and 55 are the dielectric multilayer films 35 on the surfaces facing the diffraction grating 33 in the polarizing optical elements 31, 36, 44, 45, 54 and 55 according to any one of claims 1 to 4.
Corresponding to the optical constants of the substrate 32 on which the diffraction grating 33 is formed and the dielectric multilayer film 35, one of the two lights 21 having polarization planes orthogonal to each other is mainly It is characterized in that the light is transmitted through and the other is mainly reflected, both are transmitted, or both are reflected.

According to a sixth aspect of the present invention, there is provided the polarizing optical device 42 according to the second aspect.
The first polarizing optical element 44 according to claim 5, wherein one of the two lights 21 is mainly transmitted and the other is mainly reflected, and the first polarizing optical element 44 is fixed to the first portion of the prism 43. These two lights 21 are incident on the second portion of the prism 43 on which the two lights 21 transmitted through the polarizing optical element 44 are incident.
The second polarizing optical element 45 according to claim 5, wherein one of the two is mainly transmitted and the other is mainly reflected,
A first photo-detecting element 48a is fixed to the side of the second polarizing optical element 45 opposite to the second portion, and the two light reflected by the second polarizing optical element 45 are provided. The second photodetector element 48b is fixed to the third portion of the prism 43 on which the light 21 is incident.

According to a seventh aspect of the present invention, there is provided the polarizing optical device 52 according to the second aspect.
The first polarizing optical element 54 according to claim 5, wherein one of the two lights 21 is mainly transmitted and the other is mainly reflected, and the first polarizing optical element 54 is fixed to the first portion of the prism 53. The second polarizing optical element 5 according to claim 5, wherein both of the two lights 21 are reflected by a second portion of the prism 43 on which the two lights 21 transmitted through the polarizing optical element 54 are incident.
5 is fixed, and the second polarizing optical element 55 is fixed.
At the third and fourth portions of the prism 53 on which the one and the other lights 21 reflected by the incident light respectively enter.
The light detecting elements 58a and 58b are fixed.

[0022]

The polarizing optical elements 31, 36 and 4 according to claims 1 to 4.
In Nos. 4, 45, 54, and 55, since the birefringent material film 34 is provided on the diffraction grating 33, the diffraction grating 33 can be formed of a material different from the birefringent material. On the other hand, due to the synergistic action of the diffraction grating 33 and the birefringent material film 34,
The selectivity of the plane of polarization is enhanced as compared with the case where only the diffraction grating 33 is used. Moreover, due to the presence of the birefringent material film 34, the restriction on the incident angle is relaxed even for the light 21 in the short wavelength region.

The polarizing optical elements 31, 36 and 4 of claim 5
In Nos. 4, 45, 54 and 55, the transmission type, the reflection type or the transmission reflection type is selected by selecting the optical constants of the substrate 32 on which the diffraction grating 33 is formed and the dielectric multilayer film 35. be able to.

Polarizing optical devices 42 and 52 according to claims 6 and 7.
Then, the first and second polarizing optical elements 44, 45, 5
4, 55 and the first and second photodetector elements 48a, 48
All of b, 58a, and 58b are fixed to the prisms 43 and 53.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First to fourth embodiments of the present invention will be described below with reference to FIGS. The components corresponding to those of the first and second conventional examples shown in FIGS. 5 and 6 are designated by the same reference numerals.

FIG. 1 shows a method of manufacturing the polarizing optical element of the first embodiment. In order to manufacture the polarizing optical element 31 of the first embodiment, as shown in FIG.
The blaze diffraction grating 33 is formed on the surface of the glass substrate 32 by cutting with a scoring machine. Then, Figure 1
As shown in (b), a birefringent material film 34, which is an inorganic ferroelectric film such as a LiNbO ₃ film or an organic polymer ferroelectric film such as a liquid crystal film, is formed on the blazed diffraction grating 33.

When the inorganic ferroelectric film is formed as the birefringent material film 34, in order to maintain the anisotropy of the inorganic ferroelectric film, for example, when the inorganic ferroelectric film is formed by the CVD method, the temperature and the atmosphere are changed. When the gas or the like is controlled and the vapor deposition method is used, the vapor deposition angle or the like is controlled. In addition, the birefringent material film 34
When forming a liquid crystal film or the like, the surface of the glass substrate 32 having the blazed diffraction grating 33 formed thereon is subjected to a surface treatment in order to maintain the orientation of the liquid crystal film or the like.

Next, as shown in FIG. 1C, a dielectric multilayer film 35 is formed on the back surface of the glass substrate 32 to complete the polarizing optical element 31. At this time, by selecting a combination of optical constants of the glass substrate 32 and the dielectric multilayer film 35, when two lights having polarization planes orthogonal to each other enter the polarizing optical element 31, the two lights Select either a transmissive type that both transmit at different angles, a reflective type that both reflect at different angles, or a transflective type that one of the two lights mainly transmits and the other mainly reflects To do.

In the first embodiment described above, the blaze diffraction grating 33 is formed on the glass substrate 32, and the glass substrate 32 is low in cost, but a substrate other than the glass substrate 32 can be used. The pitch and shape of the blazed diffraction grating 33, the birefringent material film 34, and the dielectric multilayer film 3 are also included.
The film thickness and the like of No. 5 can be appropriately selected according to the type of light source used, applied equipment, and the like.

FIG. 2 shows a polarizing optical element which is the second embodiment. The polarizing optical element 36 of the second embodiment.
Has substantially the same structure as that of the first embodiment shown in FIG. 1 except that the dielectric multilayer film 35 is formed on the birefringent material film 34, not on the back surface of the glass substrate 32. In addition, the same operational effects as those of the first embodiment can be obtained.

FIG. 3 shows a laser coupler which is a polarizing optical device as a third embodiment and a magneto-optical disk head which uses this laser coupler. This magneto-optical disk head 41 has substantially the same configuration as the magneto-optical disk head 23 shown in FIG. 6 except that a laser coupler 42 is used instead of the laser coupler 26.

The laser coupler 42 has a prism 43 having a trapezoidal cross section, and the transmissive / reflective polarizing optical element 44 as in the first or second embodiment shown in FIGS. It is fixed on the slope facing the laser diode 16. A transmissive / reflective polarizing optical element 45 is also fixed to the portion of the bottom surface of the prism 43 on the polarizing optical element 44 side.

On the other hand, a total reflection film 46 is fixed on the top surface of the prism 43, and on the bottom surface of the prism 43, a polarizing optical element 45 and an adhesive layer 47 in a portion other than the polarizing optical element 45 are provided. Two photodiodes 48a and 48b are fixed via the.

In the magneto-optical disk head 41, a large proportion of the light 21 emitted from the laser diode 16 and incident on the polarizing optical element 44 is reflected by the polarizing optical element 44, and the objective lens 17 passes through. The light passes through and enters the magneto-optical disk 22. The light 21 reflected by the magneto-optical disk 22 and transmitted through the objective lens 17 enters the polarizing optical element 44, and is the same as the magneto-optical disk heads 11 and 23 shown in FIGS. In the state where the ratio of the light 21 having a polarization plane orthogonal to the polarization plane of the light 21 incident on the beam 22 is increased, the polarizing optical element 4
Through 4.

The prism 4 is transmitted through the polarizing optical element 44.
The light 21 that has entered the light source 3 is separated by the polarizing optical element 45 into two lights 21 having polarization planes orthogonal to each other. The light 21 transmitted through the polarizing optical element 45 enters the photodiode 48a, and the light 21 reflected by the polarizing optical element 45 is reflected by the total reflection film 46 and then enters the photodiode 48b.

FIG. 4 shows a laser coupler as a polarizing optical device and a magneto-optical disk head using this laser coupler as a fourth embodiment. The magneto-optical disk head 51 has substantially the same configuration as the magneto-optical disk head 41 shown in FIG. 3 except that a laser coupler 52 is used instead of the laser coupler 42.

Like the laser coupler 42, the laser coupler 52 also has a prism 53 having a trapezoidal cross section. The prism 53 has an inclined surface facing the laser diode 16 and is similar to the polarizing optical element 44. A transflective polarizing optical element 54 is fixed. But the prism 5
In the part of the bottom surface of 3 on the polarizing optical element 54 side,
The reflective polarizing optical element 55 is fixed.

On the other hand, a total reflection film 56 is fixed to the top surface of the prism 53, and of the bottom surface of the prism 53,
In the portion where the light 21 reflected by the total reflection film 56 is incident,
Two photodiodes 58a and 58b are fixed.

Even with this magneto-optical disk head 51, as shown in FIG.
Similarly to the case of the magneto-optical disk head 41 shown in FIG.
A large proportion of the light 21 incident on is reflected by the polarizing optical element 54, passes through the objective lens 17, and enters the magneto-optical disk 22. The light 21 reflected by the magneto-optical disk 22 and transmitted through the objective lens 17 is incident on the polarizing optical element 54 and has a polarization plane orthogonal to the polarization plane of the light 21 incident on the magneto-optical disk 22. The light is transmitted through the polarizing optical element 54 in a state where the ratio is increased.

The prism 5 is transmitted through the polarizing optical element 54.
The light 21 that has entered the light source 3 is separated by the polarizing optical element 55 into two lights 21 having mutually orthogonal polarization planes. The two separated lights 21 are both reflected by the polarizing optical element 55, but their reflection angles are different from each other, and after being reflected by the total reflection film 46, they are respectively separated by the photodiodes 58a and 58b. Incident on.

In the third and fourth embodiments described above, the polarizing optical element according to the invention of the present application is applied to a laser coupler for a magneto-optical disk head, but it separates return light in optical fiber communication or the like. The polarizing optical element according to the present invention can be applied to an optical isolator and the like.

[0042]

Since the diffraction grating can be made of a material different from the birefringent material, the entire polarization optical element is made of the birefringent material. The cost can be reduced as compared with the structure.
On the other hand, since the selectivity of the polarization plane is enhanced as compared with the case where each of the diffraction grating and the birefringent material film is independent, the selectivity of the polarization plane is high. Moreover, since the restriction on the incident angle is loose even for light in the short wavelength region, it is easy to assemble applicable equipment,
Wide application range.

The polarizing optical element according to claim 5 is a transmission type,
Since either the reflective type or the transmissive reflective type can be selected, the degree of freedom in designing the applied device is high, and the transmissive reflective type or the reflective type can be selected to downsize the applied device.

In the polarizing optical device according to claims 6 and 7, both of the first and second polarizing optical elements and the first and second photodetecting elements which are low in cost and have high selectivity of the polarization plane are provided. Since it is fixed to the prism, not only the cost of the applied device can be reduced and the selectivity of the polarization plane can be enhanced, but also the applied device can be easily assembled and the applied device can be downsized.

[Brief description of drawings]

FIG. 1 is a side view showing a manufacturing method according to a first embodiment of the present invention in the order of steps.

FIG. 2 is a side view of a second embodiment of the present invention.

FIG. 3 is a side view of a third embodiment of the invention of the present application.

FIG. 4 is a side view of a fourth embodiment of the present invention.

FIG. 5 is a side view of a first conventional example of the invention of the present application.

FIG. 6 is a side view of a second conventional example of the invention of the present application.

[Explanation of symbols]

 21 Light 31 Polarizing Optical Element 32 Glass Substrate 33 Blazed Diffraction Grating 34 Birefringent Material Film 35 Dielectric Multilayer Film 36 Polarizing Optical Element 42 Laser Coupler 43 Prism 44 Polarizing Optical Element 45 Polarizing Optical Element 48a Photodiode 48b Photodiode 52 Laser Coupler 53 Prism 54 Polarizing Optical Element 55 Polarizing Optical Element 58a Photodiode 58b Photodiode

Claims (7)

[Claims] 1. A polarizing optical element comprising a birefringent material film provided on a diffraction grating. 2. The polarizing optical element according to claim 1, wherein the diffraction grating is a blazed diffraction grating. 3. The polarizing optical element according to claim 1, wherein the birefringent material film is an inorganic ferroelectric film. 4. The polarizing optical element according to claim 1, wherein the birefringent material film is an organic ferroelectric film. 5. A dielectric multilayer film is provided on a surface facing the diffraction grating, and the dielectric multilayer film and the dielectric multilayer film are orthogonal to each other corresponding to optical constants of the substrate and the dielectric multilayer film. One of the two lights having a polarization plane is mainly transmitted and the other is mainly reflected, both are transmitted, or both are reflected. A polarizing optical element according to item. 6. The first polarizing optical element according to claim 5, wherein one of the two lights is mainly transmitted and the other is mainly reflected, wherein the first polarizing optical element is fixed to the first portion of the prism, 6. One of these two lights is mainly transmitted and the other is mainly reflected by the second portion of the prism on which the two lights transmitted through the first polarizing optical element are incident.
The second polarizing optical element described in the above is fixed, and the first photo-detecting element is fixed to the side opposite to the second portion of the second polarizing optical element, The second optical detecting element is fixed to the third portion of the prism on which the two lights reflected by the second polarizing optical element are incident. 7. The first polarizing optical element according to claim 5, wherein one of the two lights is mainly transmitted and the other is mainly reflected, and the first polarizing optical element is fixed to the first portion of the prism, The second polarizing optical element according to claim 5, wherein both of the two lights are reflected by a second portion of the prism on which the two lights transmitted through the first polarizing optical element are incident. The first and second photo-detecting elements are fixed to the third and fourth portions of the prism on which the one and the other lights reflected by the second polarizing optical element are incident, respectively. A polarizing optical device characterized in that.