JP2002090543A - Polarizing function element, optical isolator element, optical isolator and laser diode module - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a high-precision polarizing function element that is easy to handle such as cutting and washing, and that is inexpensive and small, and that has better performance. SOLUTION: A plurality of parallel metal gratings 2a,.
a '... are filled with dielectrics 2b, 2b' ... or the dielectric gratings 2b, 2b 'are filled with metals 2a, 2a'.
The entire laminated film of the flat polarizing films 2, 2 'filled with ... and the dielectric films 3, 3' formed on the polarizing film is provided on the surface of the substrate 1 as a polarizing film and an anti-reflection film. .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization function element constituting a polarization filter, an optical isolator element constituting an optical isolator, an optical isolator comprising an optical isolator element, and a laser diode module having an optical isolator. It is about improvement.

[0002]

2. Description of the Related Art Generally, when an optical isolator is exemplified,
The optical isolator includes at least a Faraday rotator, a polarizer on the light incident side and the light emitting side, and a magnet for providing a magnetic field parallel to the optical axis direction.

In the structure, a polarizing prism or a polarizing glass is used as a polarizer. Since it is necessary to precisely determine the mutual angle of the polarizer between the incident side and the output side via a Faraday rotator, it takes time and effort to assemble, and the product price becomes high as an optical isolator. In addition, since two polarizers are separately provided on the incident side and the output side via the Faraday rotator, there is a limit in downsizing.

In order to make the optical isolator inexpensive and compact, it has been proposed to provide a conductive metal grating on both sides of a Faraday rotator as a polarizing film whose optical axes are inclined at 45 degrees to each other (particularly). Kaihei 7-49468
issue).

[0005] The isolator element is obtained by mass-producing a metal grid by forming a metal grid on a Faraday rotator of about several cm ² by vacuum evaporation or the like, and then cutting it into a size of about 1 mm to 3 mm square.

[0006] When the isolator element is cut, the polarizing film has irregularities due to the spacing between the metal gratings and the metal grating. Therefore, such a polarizing film is liable to be damaged or contaminated. You need to pay attention to it. In addition, since the polarization surface has irregularities, it is difficult to form a non-reflection film by further laminating another optical film on the polarization surface due to the gaps between the metal gratings.

On the other hand, a magneto-optical crystal having a Faraday effect is provided, a number of parallel grooves having a predetermined width and depth are provided on the surface of the magneto-optical crystal, and a metal layer is filled in the grooves as a metal lattice. Has proposed a flat polarizer-integrated Faraday rotator (Japanese Patent No. 3067026).

According to the Faraday rotator integrated with the polarizer, there is no problem such as breakage or contamination of the polarizing film, but the parallel width of the mirror is maintained at a predetermined width and the dimension depth is larger than the width. Since a large number of grooves are provided on the surface of a hard magneto-optical crystal such as garnet, this processing is extremely difficult in practice. It is also difficult to precisely control the processing of digging a minute groove exactly to a predetermined depth and filling the groove with a metal layer.

[0009]

SUMMARY OF THE INVENTION According to the present invention, even if a plurality of parallel metal grids are provided on the surface of the substrate, the cutting,
It is an object of the present invention to provide a polarizing function element which can be easily handled such as washing, has high accuracy, is excellent in light transmittance and polarization performance, and can be configured inexpensively and compactly, and an optical isolator element.

It is another object of the present invention to provide an optical isolator which is highly accurate, has excellent characteristics, is inexpensive, and can be made compact.

A further object of the present invention is to provide a laser diode module having a large oscillation output and a stable output for the same electric input.

[0012]

According to a first aspect of the present invention, there is provided a polarizing function element, wherein a plurality of parallel metal gratings are provided on a surface of a substrate, and the gaps between the metal gratings are filled with a dielectric material. It is configured by providing a flat polarizing film in which a dielectric grating is filled with metal as a polarizing film and an anti-reflection film on the surface of a substrate.

According to a second aspect of the present invention, there is provided a polarizing function element, wherein a gap between a plurality of parallel metal gratings is filled with a dielectric or a dielectric grating is filled with a metal; The entire laminated film with a dielectric film formed thereon is provided as a polarizing film and an anti-reflection film on the surface of the substrate.

The polarizing function element according to the third aspect of the present invention is configured such that the metal grating of the polarizing film is positioned in parallel with each other, and the polarizing film and the antireflection film are provided on both sides of the substrate.

According to a fourth aspect of the present invention, in the optical isolator element, a plurality of parallel metal gratings are provided on the surface of the substrate. Is filled with a dielectric or a dielectric grating is filled with a metal, and a laminated film of a dielectric film formed on the polarizing film as a polarizing film and an anti-reflection film. It is configured such that the metal grid is provided on both sides of the substrate at an angle corresponding to the Faraday rotation angle.

According to a fifth aspect of the present invention, in the optical isolator element, the substrate is provided with a Faraday rotating crystal that is magnetically saturated without an external magnetic field.

An optical isolator according to a sixth aspect of the present invention is constructed by assembling the optical isolator element according to the fourth or fifth aspect.

A laser diode module according to a seventh aspect of the present invention is configured by mounting the optical isolator according to the sixth aspect.

[0019]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an optical isolator shown in FIG. 1; FIG. An element and an optical isolator shown in FIG. 5 and an optical isolator element shown in FIG. 6 are mounted to constitute a laser diode module. In FIGS. 1 to 4, the thickness of the substrate is omitted in the middle as shown by a dashed line. In addition, components common to the embodiments are denoted by the same reference numerals.

The polarization functional element shown in FIG. 1 includes an element substrate 1 and a plurality of parallel metal gratings 2a.
a flat polarizing film 2 made of a dielectric 2b filling the interval of a ...
Is provided on the surface of the substrate 1 as a polarizing film and an anti-reflection film.

As a specific example of the polarization function element, silicon (Si) is used as the element substrate 1, and a metal lattice 2a of tantalum (Ta) and a dielectric material of silicon dioxide (SiO ₂ ) which fills an interval between the metal lattices 2a. Polarizing film 2 flat from body 2b
Formed as a polarizing film and an anti-reflection film.

In this case, the width of the metal grids 2a is 45.
nm, the width of the dielectric 2b of silicon dioxide: 55 nm, the refractive index can be formed to be 1.87 with respect to light having a wavelength of 1.55 μm. When the thickness of the flat polarizing film 2 is formed to be 390 nm, an effective polarizing film and anti-reflection function is exhibited.

In the polarizing function element having such a configuration, the flat polarizing film 2 in which the intervals between the plurality of parallel metal gratings 2a are filled with the dielectrics 2b is used as the polarizing film and the anti-reflection film. In addition to being easy to handle such as washing, it can be formed with high precision, and a flat polarizing film 2 functioning as a polarizing film and an anti-reflection film is formed integrally with the element substrate 1 so as to be inexpensive and compact. it can.

The polarization functional element shown in FIG. 2 includes an element substrate 1 and a plurality of parallel metal gratings 2a.
The entire laminated film of a flat polarizing film 2 composed of a dielectric 2b that fills the space of a ... and a dielectric film 3 formed on the polarizing film 2 is formed as a polarizing film and an anti-reflection film. It is constituted by providing on the surface of.

As a specific example of the polarizing function element, a transparent glass (material: BK-7 glass) is used as an element substrate 1, a metal grid 2a of aluminum (Al), and a metal grid 2a.
... dielectrics 2b of silicon dioxide (SiO ₂ ) to fill the intervals
The flat polarizing film 2 is formed from the above, and a dielectric film 3 of silicon dioxide (SiO ₂ ) is formed on the polarizing film 2 so as to form the entire laminated film as an anti-reflection film. Can be

In this case, assuming that the corresponding wavelength is 1.55 μm, the width of the aluminum metal grids 2a is 50n.
m, the width of the dielectric 2b of silicon dioxide: 50 nm, the thickness of the polarizing film 2: 388 nm, and the thickness of the dielectric film 3 of silicon dioxide: 388 nm. The refractive index of the glass substrate 1 is 1.51, and the refractive index of the polarizing film 2 is 1.8.
2. The silicon dioxide dielectric film 3 can be formed with a refractive index of 1.46 and a polarization extinction ratio of 30 dB.

In the polarizing function element thus constructed, a flat polarizing film 2 in which a plurality of parallel metal gratings 2a are filled with dielectrics 2b, and a dielectric film 3 provided on the flat polarizing film 2 are provided. Since the entire laminated film is used as a polarizing film and a non-reflective film, it is easy to handle such as cutting and washing, and can be formed to be a high-precision one. Since the entire laminated film in which the film 3 is superimposed on the polarizing film 2 is formed as a non-reflective film, it can be configured to have more excellent light transmittance and polarization performance.

In the embodiments shown in FIGS. 1 and 2, a case where one or more flat polarizing films or the entire laminated film is provided on one surface of the element substrate 1 as a polarizing film and an anti-reflection film has been described, as shown in FIG. Are filled with dielectrics 2b... 2b ′.
By forming the 2 ′ metal gratings 2a... 2a ′... In parallel with each other, they can be provided on both sides of the element substrate 1 as a polarizing film and an anti-reflection film.

As a specific example, silicon (Si) is used as the element substrate 1 and tantalum (Ta) metal lattices 2a.
2a ', and dielectrics 2b, 2b' of silicon dioxide (SiO ₂ ) filling the spaces between the metal gratings 2a, 2a ', and the like, form flat polarizing films 2, 2'. , 2 '
The dielectric films 3 and 3 ′ of magnesium fluoride (MgF ₂ ) are formed on top of this to form the entire laminated film as an anti-reflection film.

In this case, assuming that the corresponding wavelength is 1.55 μm, the width of the tantalum metal lattices 2a.
120 nm, width of silicon dioxide dielectrics 2b ..., 2b '...: 100 nm, thickness of polarizing films 2, 2': 180 nm,
Thickness of dielectric films 3, 3 'of magnesium fluoride: 290
It may be set to about nm. The refractive index of the silicon substrate 1 is 3.5, the refractive index of the polarizing films 2, 2 'is 2.2, the refractive index of the magnesium fluoride dielectric films 3, 3' is 1.38.
Thus, a polarizing extinction ratio of 48 dB can be formed.

In the polarizing function element thus configured, by providing the polarizing film and the anti-reflection film on both sides of the substrate 1, the performance as the polarizing function element can be improved, and the polarization extinction ratio can be increased.

The optical isolator element shown in FIG. 4 has a flat Faraday rotating crystal as a substrate 1 and a plurality of parallel metal gratings 2a, 2a '... Filled with dielectrics 2b, 2b'. The entire laminated film of the polarizing films 2 and 2 ′ and the dielectric films 3 and 3 ′ formed on the polarizing films 2 and 2 ′ is a polarizing film and a non-reflection film. Metal grid 2
a, 2a 'are inclined at an angle of about 45 degrees corresponding to the Faraday rotation angle (the inclination direction is indicated by a dotted line in the drawing), and a polarizing film and an anti-reflection film are provided on both surfaces of the substrate 1. Have been.

As a specific example, a substrate 1 is made of TbBiFe garnet, which is a Faraday rotating crystal, and silver (A)
g) of the metal grids 2a, 2a ',.
..., 2a 'dielectric 2b of ... silicon dioxide to fill the gap of the (SiO ₂₎ ..., 2b' ... 'is formed and the polarizing film 2, 2' flat polarizing 2,2 from and superimposed on the film To form dielectric films 3 and 3 ′ of magnesium fluoride (MgF ₂ ), and to form the entire laminated film as an anti-reflection film.

In this case, when the corresponding wavelength is 1.55 μm, the thickness of the Faraday rotating crystal substrate 1 (rotational thickness at 45 degrees): 470 μm, the silver metal lattices 2a.
Width: 50 nm, silicon dioxide dielectrics 2b ..., 2b '...
Width: 50 nm, thickness of the polarizing films 2 and 2 ′: 200 nm,
Thickness of dielectric films 3, 3 'of magnesium fluoride: 350
It may be set to about nm. The refractive index of the Faraday rotating crystal substrate 1 is 2.35, and the refractive indices of the polarizing films 2 and 2 ′ are:
2.02, the refractive index of the magnesium fluoride dielectric films 3 and 3 'is 1.38, and the isolator characteristics can be 42 dB.

In addition, when the corresponding wavelength is 1.31 μm, the thickness of the Faraday rotating crystal substrate 1 (rotational thickness at 45 °): 400 μm, the width of the silver metal lattices 2a. Of the dielectrics 2b ..., 2b '...: 50 nm, the thickness of the polarizing films 2, 2': 190 nm, and the thickness of the magnesium fluoride dielectric films 3, 3 ': 330 n
m may be set. The refractive index of the Faraday rotating crystal substrate 1 is 2.35, and the refractive indices of the polarizing films 2 and 2 ′ are:
2.05, the refractive index of the magnesium fluoride dielectric films 3 and 3 ′ is 1.38, and the isolator characteristics are 41 dB.

In the optical isolator element configured as described above, the polarizing film and the anti-reflection film on both surfaces exhibit a polarizing function and also function to increase the light transmittance. An isolator can be configured.

Depending on the optical isolator element, FIG.
As shown in the figure, a magnet 4 having a cylindrical shape or the like and a holder 5 made of stainless steel are provided. In addition, by assembling the whole including the magnet 4 inside the holder 5, it is possible to configure an inexpensive and compact optical isolator with high performance, excellent characteristics, and low cost.

Instead of the optical isolator element according to the embodiment shown in FIG. 5, an optical isolator can be constituted by providing, as the element substrate 1, a Faraday rotating crystal that is magnetically saturated without an external magnetic field. As the Faraday rotating crystal, for example, a hard magnetic garnet which is magnetically saturated without an external magnetic field in garnet (Japanese Patent Laid-Open No. 9-328)
398) Tb-Bi-Fe-Ga-Al-O based substrate.

According to the isolator element having the Faraday rotation crystal which is magnetically saturated without the external magnetic field as the element substrate 1, there is no need to mount a magnet, so that a cheaper and smaller optical isolator can be constructed.

A laser diode module can be configured as shown in FIG. 6 using any of the optical isolators of the above-described embodiments. This laser diode module
In addition to the optical isolator 10, a semiconductor laser chip 11 used as a light source, a heat sink 12 for the semiconductor laser chip 11, a cylindrical lens 13 for condensing laser light oscillated from the semiconductor laser chip 11, and an optical fiber 1
4, a zirconia ferrule 15 for fixing the optical fiber 14 and a module case 16 are provided.

In the laser diode module configured as described above, the oscillation output can be increased with respect to the same electrical input and the output can be stabilized as compared with the configuration including the optical isolator using the conventional polarizing film. .

In order to inspect the characteristics, the corresponding wavelength according to the present invention: 1.55 μm (first), the corresponding wavelength: 1.31
A 10 μm (second) optical isolator element is provided, each having 10 μm (second) optical isolator elements.
No. 468), 10 optical isolators each having a corresponding wavelength of 1.55 μm (third) and a corresponding wavelength of 1.31 μm (fourth), and the isolation and transmission loss characteristics for each light were compared and examined. . The result is shown in Table 1 below.
And it was confirmed that the product of the present invention was superior to the conventional product.

[0043]

[Table 1]

In the above-described embodiment, the garnet of BK-7 glass, silicon crystal, Faraday rotating crystal or hard magnetic garnet which is magnetically saturated without an external magnetic field is exemplified as the element substrate. Substrates can also be used. For example, lead glass, germanium crystal,
Cadmium, manganese, mercury, tellurium, and the like can be cited as Faraday rotators other than niobate lithium crystals and garnets.

In the above-described embodiment, the dielectric film 3
Although the description has been given based on the case where 3 ′ is formed as a single layer film, it may be formed as a multilayer film by combining dielectric materials having different refractive indexes.

The above-described embodiments are merely examples, and do not limit the present invention in any way. Therefore, there is no intention to exclude what is equivalent to each embodiment of the present invention or a part thereof, and various modifications can be made within the scope of the present invention as claimed. For example, although the above-described embodiment has been described in terms of filling the space between the metal grids with a dielectric, this must be interpreted as being substantially equivalent to the expression of filling the space between the dielectric grids with a metal. No.

[0047]

As described above, according to the polarization functional element according to the first aspect of the present invention, the interval between the plurality of parallel metal gratings is filled with the dielectric or the interval between the dielectric gratings is filled with the metal. By providing a flat polarizing film as a polarizing film and a non-reflective film on the surface of the substrate, handling such as cutting and washing can be easily performed and a highly accurate film can be formed. Since they are integrally formed, they can be configured to be inexpensive and small.

According to the polarizing function element of the second aspect of the present invention, a flat polarizing film in which a gap between a plurality of parallel metal grids is filled with a dielectric or a gap between the dielectric grids is filled with a metal,
By providing the entire laminated film with the dielectric film formed on the flat polarizing film as a polarizing film and an anti-reflection film on the surface of the substrate, it is easy to handle such as cutting and washing, and it is highly accurate. In addition to being inexpensive and compact, it is possible to form a dielectric film on a polarizing film, so that it has better performance than an anti-reflection film that can be formed on various substrates. Can be configured.

According to the polarizing function element of the present invention, the metal of the polarizing film formed by filling the space between the plurality of parallel metal gratings with a dielectric or filling the space between the dielectric gratings with a metal. By providing the polarizing film and the anti-reflection film on both sides of the substrate with the gratings positioned in parallel with each other, the performance as a polarization functional element can be improved, and the polarization extinction ratio can be increased.

According to the optical isolator element of the fourth aspect of the present invention, the Faraday rotation crystal is used as a substrate, and the interval between a plurality of parallel metal lattices is filled with a dielectric, or the interval between the dielectric lattices is filled with a metal. The entire laminated film of the buried flat polarizing film and the dielectric film formed on the polarizing film is a polarizing film and an anti-reflection film, and the metal grating of each polarizing film is set at an angle corresponding to the Faraday rotation angle. Since the polarizing film and the anti-reflection film on both surfaces function to increase the light transmittance and suppress the reflectivity by being inclined and provided on both surfaces of the substrate, it can be configured to have low light loss and excellent characteristics.

According to the optical isolator element of the fifth aspect of the present invention, since the Faraday rotating crystal that is magnetically saturated without an external magnetic field is provided as the element substrate, it is not necessary to mount a magnet, so An inexpensive and compact optical isolator can be configured.

According to the optical isolator according to the sixth aspect of the present invention, by assembling the optical isolator element according to the fourth or fifth aspect, the optical isolator can be configured to have high performance, excellent characteristics, low cost and small size.

According to the laser diode module according to the seventh aspect of the present invention, by mounting the optical isolator according to the sixth aspect, the oscillation output is large and the output is stable for the same electric input. Can be configured.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a polarization functional element according to one embodiment of the present invention.

FIG. 2 is an explanatory view showing a polarization functional element according to another embodiment of the present invention.

FIG. 3 is an explanatory view showing a polarization functional element according to still another embodiment of the present invention.

FIG. 4 is an explanatory view showing an optical isolator element according to the present invention.

FIG. 5 is an explanatory diagram showing an optical isolator according to the present invention.

FIG. 6 is an explanatory view showing a laser diode module according to the present invention.

[Description of Signs] 1 Substrate 2a ..., 2a '... Metal lattice 2b ..., 2b' ... Dielectric 2, 2 'Polarizing film 3, 3' Dielectric film 10 Optical isolator

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Nobuo Imaizumi 3-8-22 Nitta, Adachi-ku, Tokyo Namiki Seiki Co., Ltd. F term (reference) 2H037 AA01 BA03 CA10 DA01 DA03 DA04 DA05 DA06 2H049 BA05 BA08 BA45 BB03 BB42 BC25 2H079 AA03 BA02 CA06 DA12 2H099 AA01 BA02 CA02 DA05 5F073 AB27 AB28 AB30 FA06

Claims (7)

[Claims] 1. A polarizing function element in which a plurality of parallel metal gratings are provided on the surface of a substrate. A polarizing function element provided on a surface of a substrate as a reflection film. 2. The method according to claim 1, wherein an entire laminated film of the flat polarizing film and a dielectric film formed on the polarizing film is provided on the surface of the substrate as a polarizing film and an anti-reflection film. Item 2. The polarization functional element according to Item 1. 3. The polarizing function element according to claim 1, wherein the polarizing film and the anti-reflection film are provided on both sides of the substrate with the metal grating of the polarizing film positioned in parallel with each other. 4. A polarizing function element in which a plurality of parallel metal gratings are provided on a surface of a substrate, wherein a Faraday rotation crystal is used as a substrate, and a gap between the plurality of parallel metal gratings is filled with a dielectric or a dielectric grating is provided. The entire laminated film consisting of a flat polarizing film filled with metal and a dielectric film formed on top of the polarizing film was used as a polarizing film and an anti-reflection film, and the metal grating of each polarizing film corresponded to the Faraday rotation angle. An optical isolator element provided on both sides of a substrate at an angle. 5. The optical isolator element according to claim 4, wherein the substrate comprises a Faraday rotating crystal that is magnetically saturated without an external magnetic field. 6. An optical isolator comprising the optical isolator element according to claim 4 or 5. 7. A laser diode module comprising the optical isolator according to claim 6.