JPH1195027A - Polarizing element of multilayer structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optionally design the center wavelength and the wavelength range from a vertical wave to oblique wave by stacking a grating layers with grating pitch smaller than the wavelength of applied light, through void layers or dielectric layers, and specifying the thickness of each layer. SOLUTION: Grating layers with a grating pitch smaller than the wavelength of the light are stacked through void layers or dielectric layers, and the thickness of each layer is to be about a quarter of either wavelength of two orthogonal polarized components of the light in each layer. That is, when grating structure is formed of isotropic material, and the grating pitch is made smaller than the wavelength, an effective refractive index in the direction of an arrow mark L (perpendicular to a grating face) differs between polarized light in a TE direction of the electric field and polarized light in a TM direction out of light entering this grating, and the refractive index of polarized light in the TM direction is larger. Such a grating is horizontally sliced and stacked with thin layers of isotropic material (or different material) placed in between, and its stack pitch P is to satisfy the effective refractive index of TE or TM polarized light × P=1/4 wavelength + 1/4 wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing element having a multilayer structure and a polarizing beam splitter.

[0002]

2. Description of the Related Art In general, a polarizing element using a birefringent crystal is used. In addition, a multilayer film of an isotropic substance using Brewster reflection is used as a polarizing beam splitter. The one using a crystal is expensive, the size of the optical device in the optical axis direction is large, the size of the optical device is large, and when it is used as a beam splitter, there is a drawback that the take-out angle of orthogonal bi-polarized light is narrow. Since the multilayer polarizing beam splitter also uses Brewster reflection, the directional relationship among incident light, reflected light, and transmitted light is determined by the Brewster angle, and in the configuration of an optical device, the arrangement of various optical elements is greatly restricted. .

[0003]

SUMMARY OF THE INVENTION The present invention relates to the relationship between the input and output angles and the polarization characteristics (eg, usable wavelength range, reflectance,
It is an object of the present invention to provide a polarizing element whose transmittance can be designed as required.

[0004]

SUMMARY OF THE INVENTION Gratings with a grating spacing smaller than the wavelength are spaced apart, or an isotropic layer is interposed in the spacing, and the thickness of the grating and each of the spacings is used in each layer. A laminated structure or a birefringent material film and an isotropic material film, each having a thickness of about 光 of the wavelength of light, are laminated.
Provided is a multilayer film in which one or two layers of the birefringent substance and the isotropic substance are further provided with a thickness of about 1/4 of the wavelength of light in the layer, and a thickness of 1/8 wavelength before and after the laminate.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Assuming that a grating structure as shown in FIG. 1B is made of an isotropic material and the grating pitch is smaller than the wavelength, the light incident on the grating causes the electric field to be polarized in the TE direction and in the TM direction. The effective refractive index in the direction of arrow L (perpendicular to the lattice plane) is different from that of polarized light, and the refractive index of the polarized light in the TM direction is larger. For example, in the case of GaAs, the grating pitch D = 0.31 μm, d / D for light having a wavelength of 1.55 μm (in air).
= 0.4, the ratio between the refractive indices of both the TM and TE polarized lights is 2.
443 / 1.304 = 1.873, which is larger than the ratio of calcite at a wavelength of 1.55 μm of 1.106.
Now, such a grid is horizontally sliced, with a thin layer of the same isotropic substance (may be different) interposed therebetween as shown in FIG. 1A, and the stacking pitch P is set to TE or TM.
The effective refractive index of any polarized light × P = approximately 波長 wavelength + ／ wavelength (e.g., 250 nm for 1.55 μm). With respect to the polarized light, the vertical reflection with respect to the normal incidence is strengthened by the interference of multiple reflections, and a large reflectance is obtained. Since such a relationship does not hold for polarized light orthogonal to the polarized light, there is no reflected light and the transmittance increases.
Thus, it is possible to separate two orthogonal components of polarized light with respect to vertical incident reflection. Of course, it is also possible to separate the orthogonally polarized light with respect to oblique incidence by setting the stacking pitch appropriately.

FIG. 2 shows a multilayer film in which an anisotropic substance A and an isotropic substance I are alternately laminated.
In particular, a ８ wavelength layer of an anisotropic substance is provided at the light incident end, and an 異 方 性 wavelength thick anisotropic substance layer is provided at the light exit end face. It has been found that by bringing the anisotropic substance substrate IB into contact, the polarization characteristics are further improved as compared with the case of merely having a quarter-wave thickness alternately laminated film.

The structure shown in FIG. 1 is manufactured, for example, as follows. As shown in FIG. 3, several atomic layers of an AlAs layer 2 are formed on a GaAs substrate 1 (a), a GaAs layer 3 is formed thereon (b), a photoresist is coated, and a lattice pattern is printed by a holographic exposure wave. By developing, a mask 4 having a lattice pattern is formed (c), and this is vertically etched by ion beam etching to form a GaAs lattice (d). At this time, since the etching rate of the AlAs layer is extremely lower than that of GaAs, the AlAs layer is hardly etched.
A GaAs-only lattice is obtained. Here, the thickness of the GaAs layer 3 is formed to be 実 効 wavelength as the effective wavelength in the GaAs lattice of the used wavelength. Next, the GaAs substrate 1 is etched so that the thickness of the combined layer of the GaAs substrate 1 and the AlAs layer becomes ４ of the effective wavelength of the used light in the layer. By stacking, (e) the structure of FIG. 1 is obtained.

The multilayer film shown in FIG. 2 is manufactured as follows.
As shown in FIG. 4, a single-crystal substrate 11 is prepared, and a single-crystal layer 12 of a birefringent substance is grown thereon by an epitaxial growth method so as to have a thickness of 1/4 of the wavelength used (a). An isotropic material layer 13 is formed thereon to a quarter wavelength thickness by a vapor deposition method or the like (b). Another isotropic material layer 14 is formed thereon to a thickness that can provide mechanical strength (c), and the substrate 11 is dissolved and removed (d). The laminates obtained in the steps (a) and (b) are bonded to each other facing each other (e). This adhesion is absorbed only by contact if the mutual surfaces are flat at the atomic layer level. Otherwise, it is adsorbed by alcohol.
Hereinafter, after (e), the portion of the substrate 11 is dissolved away, and (a) to
The substrate 11 of (e) in units of the laminate made in (b)
Is dissolved (adhesion) (adsorption), and the step of (f) is repeated a predetermined number of times.

FIG. 5 shows a characteristic example of the structure shown in FIG.
This example uses GaAs, and the laminated structure is expressed by the following equation. GaAs / [(1/4) (FB) / (1/4) (GaAs)] × 6 (1/4) (FB) / GaAs where FB is the lattice structure portion of FIG. Means (1 /
4) is a 1/4 wavelength layer, and x6 is 1 / F of FB and GaAs.
This means that four sets of four wavelength layers are stacked and six sets (12 layers as the number of layers) are stacked, and the quarter wavelength layer stacking part is a lattice layer on both end faces, and a GaAs layer is appropriately formed thereon. Thickness is provided to maintain mechanical strength. As can be seen from FIG. 5, the TE light reflectance is approximately 100% and the TM light reflectance is approximately 0% in a wavelength range of 1.3 to 1.7 μm centering on the wavelength 1.50 μm.
It has become. A reflectance of 0% means that the transmittance is about 10%.
0%.

FIG. 6 shows the characteristics of an alternately laminated film having a quarter-wavelength layer of an anisotropic and isotropic material. The anisotropic material is calcite, the isotropic material is titanium oxide, and the composition formula of the film is as follows. As below. Air / (1/8) (CaCO ₃ ) / [(1/4) (Ti
O ₂ ) / (１ ／) (CaCO ₃ )] × 20 / (1 /
4) (TiO ₂ ) / (1/8) (CaCO ₃ ) / TiO
₂ This laminated film is air on one side and titanium oxide on the other side, which also serves as a support substrate. Both the incident end faces of the film are calcite, and the other medium can be seen as air on one side and TiO _{2 on} the other. The center wavelength of the TM polarized light is 1.55 μm, and the center is 1.32 to 1.4 μm.
The reflectance of light is approximately 100%, the reflectance of TM light is 20 to 60%, and the transmittance is 80 to 40%.

FIG. 7 shows a structure in which a structural polarization element is applied to a semiconductor laser, wherein B is a GaAs substrate, S is a laser part, and a part P on which projections on both sides are arranged is a polarization element part. This element has an alternating arrangement of a lattice layer and an air layer, and corresponds to a dielectric layer in the example of FIG. 1 in which an air layer is used. Since the resonance is established with respect to the polarized light in this vibration direction, the emitted light is a laser beam whose electric field is only polarized in this direction.

[0012]

According to the present invention, the separation of orthogonally polarized light from the normal incidence reflection, which was impossible with the conventional polarizing element, is possible. The grating pitch, the stacking interval, and the thickness of the dielectric layer are also possible. There are many degrees of freedom in design, such as
From vertical incidence to oblique incidence, it is possible to selectively design the center wavelength used, usable wavelength range, etc., and it can respond to various requirements quite freely. It is a big contributor to

[Brief description of the drawings]

FIG. 1 illustrates an embodiment of the present invention.

FIG. 2 is a diagram showing another embodiment of the present invention.

FIG. 3 is a view showing a manufacturing method of the embodiment shown in FIG. 1;

FIG. 4 is a view showing a manufacturing method of the embodiment of FIG. 2;

FIG. 5 is a diagram showing characteristics of the embodiment of FIG. 1;

FIG. 6 is a diagram showing characteristics of the embodiment of FIG. 2;

FIG. 7 is a perspective view showing still another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 GaAs substrate 2 AlAs layer 3 GaAs layer 4 Mask of lattice pattern 11 Single crystal substrate 12 Birefringent material layer 13 Isotropic material layer

Claims (2)

[Claims] 1. A grating layer having a grating pitch smaller than a wavelength of light to be used is stacked via a gap layer or a conductive layer, and the thickness of each layer is determined by any one of two orthogonal polarization components of the light to be used in each layer. A multilayer structure polarizing element characterized in that the wavelength is about 程度 of the wavelength. 2. The laminate according to claim 1, wherein the anisotropic conductive layer and the isotropic conductive layer each have a thickness of about ４ of the wavelength of each of the two orthogonally polarized light components used in each layer. 1 /
A multilayer polarizing element comprising an anisotropic conductive layer having a thickness of eight wavelengths.