JP6108398B2 - Light modulation system control method, light modulation system, and optical body used therefor - Google Patents

Description

  The present invention relates to a method for controlling a light modulation system, a light modulation system, and an optical body used therefor.

With the increase in the density of information recording media, it is required to increase the writing speed of the recording media. Recently, a magneto-optical writing method that can dramatically increase the information writing speed in a magnetic recording medium has been proposed and demonstrated. This is a method to perform bit writing by reversing the magnetization in the recording medium with pulsed light in the order of femtoseconds to picoseconds, but the magnetization direction of the recording medium can be controlled by the polarization state of the light used at the time of writing. Become. That is, the reversal of magnetization can be controlled depending on whether it is right circularly polarized light or left circularly polarized light (that is, depending on the sign of the rotation ellipticity). Furthermore, it is also possible to write the light and shade according to the rotation direction ratio on the recording medium. In order to realize such a magneto-optical writing method capable of increasing the speed, an optical modulation system that quickly controls the polarization state of light is indispensable.
See Patent Documents 1 to 4 as documents disclosing techniques related to the present invention.

WO2011 / 043309 JP 2010-145913 A JP 2006-201472 A JP 07-333579 A

  However, at present, there is no known device capable of switching between right circularly polarized light and left circularly polarized light at high speed, which is suitable for writing to the recording medium and is driven with a small size and low power.

The inventors of the present invention have made extensive studies in order to solve such problems, and have focused on the device (optical body) disclosed in Patent Document 1.
This optical body can arbitrarily adjust the polarization angle of linearly polarized light, and is configured as follows.
As shown in FIG. 1, the optical body includes a first reflective layer 2 in which nine layers of tantalum oxide 2a and silicon oxide 2b are alternately laminated on SGGG (gallium / gadolinium / garnet substrate) 1. It is formed as a mirror. A magneto-optical material layer 3 made of bismuth, yttrium, and garnet is formed on the first reflective layer 2. Further, a refractive index variable layer 5 made of PLZT sandwiched between transparent electrodes (ITO) 4 a and 4 b from both sides is laminated on the magneto-optical material layer 3. Further, on the outer side, a second reflective layer 6 in which 18 layers of tantalum oxide 6a and silicon oxide 6b are alternately laminated is formed as a Bragg mirror.

  In the optical body configured as described above, when laser light, which is linearly polarized light, is incident as incident light from the first layer 1 side, it passes through the magneto-optical material layer 3 made of bismuth, yttrium, and garnet, and rotates clockwise. It is converted into polarized light and counterclockwise circularly polarized light. Here, there is a phase difference between right circularly polarized light and left circularly polarized light. This phase difference can be changed by controlling the electric field applied to the refractive index variable layer 5. Furthermore, since the incident light is subjected to multiple reflection between the first layer 1 and the second layer 6, the phase difference is amplified.

  Therefore, even when the phase difference between the right circularly polarized light and the left circularly polarized light generated by the magneto-optical effect of the magneto-optical material layer 3 is slight, when the light is emitted from the first layer 1, the phase difference Is a significant size. The phase difference between the right circularly polarized light and the left circularly polarized light thus amplified returns to linearly polarized light when passing through the magneto-optical material layer 3, and the angle of the plane of polarization rotates according to the phase difference. . Therefore, the rotation angle of the polarization plane of the outgoing light is modulated with respect to the incoming light.

Here, if the refractive index of the refractive index variable layer 5 is controlled, the rotation angle modulation of the polarization plane of the outgoing light with respect to the incident light can be arbitrarily controlled within a large range. When a light modulation system is constructed using this optical body, the polarization state of light can be controlled very quickly. For this reason, it can be an optical modulation system suitable for a writing method that requires extremely fast modulation of the polarization state of light, such as the magneto-optical writing method described above.
The characteristics (voltage-rotation angle characteristics) of this optical body are shown in FIGS. 2 and 3 (FIGS. 11 and 9 of Patent Document 1).

As a result of detailed examination of such an optical body, the following characteristics were noticed.
When the voltage applied to the refractive index variable layer was changed, the rotation ellipticity (rotation direction was one direction) also changed with the rotation angle, and there was a maximum point (peak: maximum absolute value) in the change. Since the rotation angle corresponding to the voltage causing the peak is small, the voltage causing the peak and the range of the voltages before and after the peak are generally not used when controlling the rotation angle of the polarization plane of the linearly polarized light. As a result of examining the range of such voltages in detail, the present inventors have found that there is a peak in the above-described rotational ellipticity, and the voltage applied to the refractive index variable layer from zero voltage to the voltage corresponding to the peak. I noticed that when I swept, the rotation ellipticity changed linearly. At zero voltage, the ellipticity of rotation was zero.
In such spheroid characteristics (voltage-rotational ellipticity), the absolute value of the rotational ellipticity decreases from the peak to the rotational ellipticity (= 0) corresponding to zero voltage, and this decreasing tendency can be further promoted. I thought that the sign of the rotation ellipticity might be reversed.
Therefore, the layer structure of the optical body described in Patent Document 1, particularly the peak wavelength of the rotation angle was changed. Specifically, the peak wavelength λ2 (resonance wavelength in the optical body) of the rotation angle is slightly increased with respect to the wavelength λ1 of the incident light. Incidentally, in the optical body described in Patent Document 1, the wavelength λ1 of the incident light is matched with the peak wavelength λ2 of the rotation angle. This is because the rotation angle changes greatly before and after the peak wavelength λ2.
FIG. 5 shows the characteristics when the wavelength λ1 of the incident light is smaller than the peak wavelength λ2 of the rotation angle.
This characteristic was obtained by simulation based on the matrix approach. See M. Inoue, T. Fujii, “A theoretical analysis of magneto-optical Faraday effect of YIG films with random multilayer structure”, Appl. Phys. 81, 317 (1997). This document is then incorporated as part of this specification.
A specific layer structure of the optical body will be described later.

From the results of FIG. 5, it can be seen that when the voltage is changed, the sign of the rotation ellipticity is reversed at the peak of the rotation angle. That is, the direction of rotation is reversed.
Furthermore, there is a peak in each code (that is, in each rotation direction). When this peak is used, the effect of each rotation direction can be efficiently reflected on the recording medium, and since the transmittance also shows the maximum value at each peak, a high output can be secured.

The present invention has been made based on the above findings found by the present inventors, and the first aspect thereof is defined as follows.
A light source that emits first light of a first wavelength λ1,
An optical body that uses the first light as incident light, has a peak of the rotation angle of the polarization plane at the second wavelength λ2, and outputs the second light as output light. An optical body having a variable refractive index layer and a magneto-optical material layer present between the reflective layers of
A method of controlling a light modulation system comprising: a refractive index control unit capable of controlling a refractive index of the refractive index variable layer to a first refractive index and a second refractive index;
While making the second wavelength λ2 corresponding to the peak of the rotation angle of the optical body larger than the wavelength λ1 of the incident light,
In the first refractive index, the second light is elliptically polarized light in a first direction, and in the second refractive index, the second light is elliptically polarized light in a second direction. A method for controlling an optical modulation system for controlling a refractive index of a variable-index layer.

According to the optical modulation system of the first aspect defined as described above, as is clear from the new characteristic found by the present inventors (see FIG. 5), the voltage is adjusted to adjust the refractive index variable layer. When the refractive index is the first refractive index, the output light (second light) is elliptically polarized light in the first direction, and the refractive index of the refractive index variable layer is changed to the second refractive index by changing the voltage. Sometimes, the output light (second light) may have a different sign from the first direction, that is, a rotation direction (second rotation direction) different from the first direction.
Since the refractive index of the refractive index variable layer can be changed by voltage switching, the rotation direction of the output light can be switched at high speed.

Here, as is apparent from FIG. 5, since there are peaks (maximum points) in the first direction and the second direction, the rotation angle of the optical body can be used so that the rotation ellipticity of both peaks can be used. It is preferable to define the wavelength λ2 corresponding to the peak.
Of course, the difference can be written on the recording medium by using regions where different rotation directions can be obtained (different signs of the rotation ellipticity) other than the peak value of the rotation ellipticity. Furthermore, since the rotation ellipticity changes linearly, by selecting the voltage (that is, the refractive index) as appropriate, in addition to the rotation in two directions, the intermediate value (light / dark) is written to the storage medium. You can also.

From the characteristics shown in FIG. 5, it was newly found that both the rotation angle and the rotation ellipticity change with the change of voltage. More specifically, both the rotation ellipticity and the rotation angle change linearly in the voltage range from zero to its peak.
The existence of such characteristics can be known only after the voltage is swept beyond the general use range (up to a rotation angle close to zero) in the optical body described in Patent Document 1. This characteristic can also be obtained when the wavelength λ2 corresponding to the peak of the rotation angle of the optical body is equal to the wavelength λ1 of the input light.
Based on the above knowledge, another second aspect of the present invention is defined as follows.
A light modulator comprising an optical body having a pair of reflective layers, a refractive index variable layer and a magneto-optical material layer existing between the pair of reflective layers;
A method of controlling an optical modulation system comprising: a refractive index control unit capable of controlling a refractive index of the refractive index variable layer to a first refractive index and a second refractive index;
A control method of a light modulation system for controlling a refractive index of a refractive index variable layer so as to change both a rotation angle and an ellipticity of a polarization plane of the second light.
In this light modulation system control method, both the rotation angle and ellipticity of the polarization plane of the second light can be changed by changing the refractive index of the refractive index variable layer.

  In the optical body described in Patent Document 1, the rotation angle of the polarization plane is controlled by using the output light as the linearly polarized light with respect to the incident light that is the linearly polarized light. The basic structure of the optical body of the present invention is the same as that of the optical body described in Patent Document 1, but by adjusting the reflectance of the pair of reflective layers, the surface opposite to the incident surface of the incident light More circularly polarized output light can be extracted.

It is a schematic cross section of the optical body described as an Example in Patent Document 1. FIG. 11 is a graph showing voltage-rotation angle and voltage-phase for an optical modulation system described in Patent Document 1 (FIG. 11 of Patent Document 1). It is a graph which shows the wavelength-rotation angle about the light modulation system described in patent document 1 (FIG. 9 of patent document 1). 1 is a schematic diagram of a light modulation system according to an embodiment of the present invention. It is a graph which shows the relationship between the applied voltage in transmitted light, a Faraday rotation angle, a Faraday rotation ellipticity, and the transmittance | permeability. It is a graph which shows the relationship between the change of the refractive index in transmitted light, Faraday rotation angle, Faraday rotation ellipticity, and transmittance. It is a graph which shows the relationship between the applied voltage in reflected light, a Kerr rotation angle, a Kerr rotation ellipticity, and a reflectance. It is a graph which shows the relationship between the change of the refractive index in reflected light, a Kerr rotation angle, a Kerr rotation ellipticity, and a reflectance.

Hereinafter, the light modulation system of the present invention will be described in detail.
As shown in FIG. 4, the light modulation system includes an optical body 10, a light source 20, and a refractive index control unit 30.
The optical body 10 has a structure in which a first reflective layer 12, a magneto-optical material layer 13, a refractive index variable layer 14 sandwiched between translucent electrodes 14a and 14b, and a second reflective layer 15 are sequentially laminated on a substrate 11. It is.
Although the material of the board | substrate 11 can be selected arbitrarily, SGGG is employable similarly to a prior art example (refer FIG. 1).
Both the first reflective layer 12 and the second reflective layer 15 can employ a Bragg mirror layer or a metal film made of a dielectric multilayer film.
When a black mirror layer is employed as the reflection layer, the material and film thickness of the dielectric layer pair constituting the repeating unit of the dielectric multilayer film are Bragg reflection conditions (d = λ / 4: where λ is the value of each layer The optical wavelength, d can be arbitrarily selected according to the wavelength of the incident light and the application, provided that the film thickness satisfies the condition (d is the film thickness of each layer). Specifically, a combination of silicon oxide (SiO ₂ ) and tantalum oxide (Ta ₂ O ₅ ) as a pair of dielectric layers, silicon oxide (SiO ₂ ) and silicon (Si), silicon oxide (SiO ₂ ) and oxide aluminum (Al ₂ O _3), and the like.

The number of repetitions of the dielectric layer pair can be arbitrarily selected. However, when the same dielectric pair is adopted for the first reflection layer and the second reflection layer, the second number of repetitions is determined by the number of repetitions of the first reflection layer. It is assumed that the number of repetitions of the reflective layer is large. When a combination of silicon oxide (SiO ₂ ) and tantalum oxide (Ta ₂ O ₅ ) is adopted as a pair of dielectric layers, the first reflective layer is 3 pairs or more, and the second reflective layer is 5 pairs or more. It is preferable to do. More preferably, the first reflective layer is 5 pairs or more, and the second reflective layer is 7 pairs or more.
Examples of the metal layer include a single layer film or a multilayer film of aluminum, platinum, gold, silver, and alloys thereof.

  In this optical body, incident light is incident on the first reflective layer 12, and light transmitted from the second reflective layer 15 side is used as output light. This output light becomes elliptically polarized light.

The distance between the first layer and the second layer is m × λ / 2 (where m is a natural number and λ is an optical wavelength between the first layer and the second layer). Thereby, the space | interval of a 1st layer and a 2nd layer corresponds with the width | variety of the node of an optical wavelength.
Here, the optical wavelength is defined by λ ₀ / n. λ ₀ is the wavelength of incident light in vacuum, and n is the effective refractive index. When only one kind of material layer is interposed between the first layer and the second layer, the effective refractive index n is equal to the refractive index of the material. When a plurality of material layers are interposed between the first layer and the second layer, the refractive index is obtained when a layer in which a plurality of different materials are continuous is regarded as one layer of one material. For example, when the refractive index and film thickness of one of two consecutive layers are n ₁ and d ₁ and the other is n ₂ and d ₂ , (n ₁ × d ₁ + n ₂ × d ₂ ) / (d ₁ + N ₂ ) is an effective refractive index of two consecutive layers.

From the viewpoint of ease of design, when a plurality of layers are interposed between the first layer and the second layer, the thickness of each layer should be a natural number times (optical wavelength / 2 of each layer). Is preferred. For example, when the layer A and the layer B are interposed between the first layer and the second layer, the thicknesses of the layer A and the layer B are (m ₁ × λ _A ) / 2, (m ₂ × λ _B ) / 2. Here, λ _A is the optical wavelength of layer A, and λ _B is the optical wavelength of layer B. With this design, even when a plurality of layers are interposed between the first layer and the second layer, the distance between the first layer and the second layer is m × λ / 2 ( Here, m is a natural number, and λ is an optical wavelength between the first layer and the second layer). When a translucent electrode layer is interposed between the first layer and the second layer, it is preferable that the translucent electrode layer also maintains the above relationship.

In the above, when defining the distance between the first layer and the second layer, and when defining the thickness of each layer in the plurality of layers interposed between the first layer and the second layer An optical wavelength λ is used. This optical wavelength λ can have some margin. This is because it is extremely difficult to accurately control the thickness of each layer on the order of nm. Further, even if there is a slight margin (preferably within ± 10%, more preferably within ± 5%), modulation suitable for the purpose can be performed.
As described above, the first layer and the second layer are preferably reflective layers, but when at least one of the first layer and the second layer is a dielectric multilayer (Bragg mirror layer), When some or all of the dielectric layers constituting the multilayer are formed of a refractive index variable layer such as a magneto-optic material or an electro-optic material, these layers may also contribute to the light modulation function.

  The magneto-optic material constituting the magneto-optic material layer 13 has a magneto-optic effect (Faraday effect, Kerr effect), and when linearly polarized light passes through the magneto-optic material, it passes through the elliptically polarized light (right circle) (Polarized light) and counterclockwise elliptically polarized light (left circularly polarized light). At this time, there is a phase difference between the right circularly polarized light and the left circularly polarized light. Since this magneto-optical material has nonreciprocity, the phase difference is maintained when the right circularly polarized light and the left circularly polarized light with phase difference are again passed through the magneto-optical material and converted back to linearly polarized light. It appears as rotation (change in angle) of the polarization plane of linearly polarized light.

Examples of the magneto-optical material exhibiting such a magneto-optical effect include a ferromagnetic material, an antiferromagnetic material, a ferrimagnetic material, and a paramagnetic material. As a translucent ferromagnetic material exhibiting a Faraday effect, materials for magnetic storage media such as CdCo, spinel ferrite such as CoFe ₂ O ₄ , hexagonal ferrite such as PbFe ₁₂ O ₁₉ , and CdCr ₂ S ₄ Chalcogenides, ferrites, chromated trihalides such as CrCl ₃ , garnets such as Y ₃ Fe ₅ O ₁₂ (BiY) ₃ Fe ₅ O ₁₂ , manganic acid compounds such as (LaSr) MoO ₃ , europium compounds such as EuO And a metal thin film made of Fe and its alloy, a thin film made of Co and its alloy, a thin film made of Mn and its alloy, and other organic materials such as Fe ₂ O ₄ and polyethylene.

  Examples of the light-transmitting antiferromagnetic material that exhibits the Faraday effect include manganese oxide.

Paramagnetic materials exhibit a magneto-optical effect by applying a magnetic field from the outside.
As a translucent paramagnetic material exhibiting a Faraday effect, rare earth Al-substituted garnet such as Tb ₃ AlO ₁₂ , GGG (Gd ₃ Ga ₅ O ₁₂ ), gas such as oxygen, liquid such as water, solid such as potassium chloride , GGG (Gd ₃ Ga ₅ O ₁₂ ), GGS and other glasses.
When a short wavelength such as blue light is to be modulated, it is preferable to employ TAG and TGG. This is because the short wavelength is hardly absorbed.
The magnetic material layer can be a single layer or a plurality of layers. In the case of a plurality of layers, the layers constituting the plurality of layers may be the same material or different materials.

The refractive index variable layer 14 changes the refractive index in the light passing direction with respect to the light passing therethrough.
Examples of a material for forming the refractive index variable layer 14 include an electro-optic material, an acousto-optic material, and a mature optical material. Electro-optic materials are materials whose refractive index changes when an electric field is applied. Examples include PZT (PbZr _0.25 Ti _0.48 O ₃ ), PLZT, PLHT, SBN, LT, LN, KDP, DKDP, BNN, KTN, and BTO. be able to.
When the refractive index variable layer 14 is formed of an electro-optic material, the refractive index can be changed and controlled by controlling the electric field applied to the variable refractive index layer. In order to apply an electric field to the refractive index variable layer, a configuration in which the refractive index variable layer is sandwiched between the translucent electrodes 14a and 14b can be adopted as described in Patent Document 1. Of course, an electric field may be applied from the outside of the optical body. In this case, the direction of application of the electric field is not limited to being perpendicular to the in-plane direction of the refractive index variable layer, but may be inclined.

The acousto-optic material is a material in which the refractive index changes due to the application of stress and strain. PZT (PbZr _0.25 Ti _0.48 O ₃ ), LT, LN, Al ₂ O ₃ , Y ₃ Al ₅ O ₁₂ , Si, SiO ₂ Etc.
When the refractive index variable layer 14 is formed of an acousto-optic material, it can be controlled by changing the refractive index by controlling the stress applied to the refractive index variable layer 14. In order to apply stress to the refractive index variable layer 14, it is conceivable that the refractive index variable layer is sandwiched between light-transmitting piezoelectric elements.

  A thermo-optic material is a material whose refractive index changes with temperature. When a refractive index variable layer corresponding to liquid crystal is formed of a thermo-optic material, the refractive index is controlled by controlling the heat applied to the variable refractive index layer. It can be controlled by changing the rate. In order to control the temperature of the refractive index variable layer, for example, a heater may be provided.

  The refractive index variable layer 14 may be a single layer or a plurality of layers. In the case of a plurality of layers, the layers constituting the plurality of layers may be the same material or different materials.

In this specification, “translucency” refers to a characteristic of transmitting incident light (modulation target light) and is not limited to so-called transparency (translucency for visible light). In addition, the refractive index variable layer necessarily has translucency.
Materials having a Kerr effect include R ₃ Fe ₅ O ₁₂ (R-rare earth elements such as Bi, Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), MFe Spinel ferrite such as ₂ O ₄ (M = Mn, Fe, Co, Ni, Cu, Mg, Li _0.5 Fe _0.5 ), MFe ₂ O ₄ (M = Ba, Pb, Sr, Ca, Ni _0.5 Fe _0.5 , Ag Hexagonal ferrite such as _0.5 La _0.5 ), polycrystalline film composed of MnBi, PtCo, EuO, PtMnSb, Gd-Co, Gd-Fe, Dy-Fe, Tb-Fe, Gd-Tb-Fe, Gd-Dy- Rare earth single transition metal thin films such as Fe, Tb-Fe-Co, Gd-Tb-Fe-Co, (Gd-Fe) -Bi, (Gd-Fe) -Sn, Nd-Dy-Fe-Co, and A composite film made of a thin film made of a material can be mentioned.

  When the magneto-optical material layer is made light transmissive, a multilayer structure in which a laminate of the magneto-optical material layer and the refractive index variable layer is repeated can also be adopted. When this multilayer structure is adopted, each magneto-optic material layer is preferably formed of the same material, but it is not excluded to form it with different materials. Similarly, each refractive index variable layer is preferably formed of the same material, but may be formed of different materials.

The light source 20 can output linearly polarized light, and for example, a semiconductor laser device can be used. Let λ1 be the wavelength of incident light output from the light source.
Here, when the peak wavelength of the rotation angle of the optical body 10 is λ2, λ1 <λ2. Thereby, when the refractive index of the refractive index variable layer 14 is changed, the sign of the rotational ellipticity of the output elliptically polarized light can be reversed, and a peak value can be obtained in each rotational direction.
The peak wavelength of the rotation angle refers to a wavelength at which the input light can be angularly polarized most efficiently in the optical body.
In the optical body, the peak wavelength can be controlled by controlling the material and / or thickness of the magneto-optical material layer.
In the examples described below, the wavelength λ1 of incident light is 800.0 nm, and the peak wavelength λ2 of the rotation angle in the optical body is 800.5 nm.

The refractive index control unit 30 changes the refractive index of the refractive index variable layer 14 and applies desired energy to the refractive index variable layer 14 according to the characteristics of the refractive index variable layer 14.
A method in which the refractive index variable layer 14 is formed of an electro-optic material and the refractive index is controlled by applying an electric field thereto is preferable because the refractive index can be switched at high speed with a simple configuration. More specifically, a refractive index variable layer made of an electro-optic material is sandwiched between a pair of translucent electrodes, and the voltage applied to the pair of translucent electrodes is switched, thereby allowing the refractive index variable layer to be refracted easily and at high speed. The rate can be controlled arbitrarily.

  An optical modulation system according to an embodiment of the present invention will be described below with reference to FIG.

<Semiconductor laser device>
The semiconductor laser device 20 can emit a laser beam of 800 nm.

<Optical body>
The optical body 10 has nine layers of tantalum oxide 12a and silicon oxide 12b alternately stacked on SGGG (gallium, gadolinium, garnet substrate: Gd _2.68 Ca _0.32 Ga _4.04 Mg _0.32 Zr _0.64 O ₁₂ ) 11. The first reflective layer 12 is formed as a Bragg mirror. A magneto-optical material layer 13 made of bismuth, yttrium, and garnet is formed on the first reflective layer 12. Further, on the magneto-optical material layer 13, a refractive index variable layer 14 made of PLZT sandwiched between transparent electrodes (ITO) 14a and 14b from both sides is laminated. Further, a second reflective layer 15 in which nine layers of tantalum oxide 15a and silicon oxide 15b are alternately stacked is formed as a Bragg mirror on the outer side.

The thickness of each layer is as follows.
First reflective layer 12: optical length λ = 800.5 nm
(Total thickness of tantalum oxide 12a and silicon oxide 12b)
Second reflective layer 15: optical length λ = 800.5 nm
(Total thickness of tantalum oxide 15a and silicon oxide 15b)
Magneto-optic material layer 13 (bismuth / yttrium / garnet): m = 4
Here, m is a natural number (1, 2, 3,...).
Refractive index variable layer 15 (PLZT): m = 1
Here, m is a natural number (1, 2, 3,...).
Transparent electrodes (ITO) 14a, 14b:
In the simulation described later, it is assumed that the translucent electrode does not have a thickness, and the material is completely translucent and does not have an electrical resistance.

  Each of these layers can be formed by sputtering. However, the method is not limited to the sputtering method, and general-purpose thin film manufacturing techniques such as a PVD method such as an evaporation method, an ion plating method, a spray method, and an ion beam irradiation method, and a CVD method can be applied.

<Refractive index control unit>
The refractive index control unit 30 includes a power source capable of applying a predetermined potential between the transparent electrodes (ITO) 14a and 4b, and is connected to the transparent electrodes (ITO) 14a and 14b. The details of the application control by the refractive index control unit 30 will be described in the section of simulation calculation described later.

  With respect to the light modulation system configured as described above, a simulation calculation is performed by the matrix approach method when the laser beam, which is linearly polarized light, is incident as incident light from the first layer 11 side using the semiconductor laser device 20. It was. Simulated calculations were performed for both transmitted and reflected light.

<For transmitted light>
The result of the simulation calculation in the case of transmitted light is shown in FIGS.
FIG. 5 is a graph showing the relationship between the voltage applied to the refractive index variable layer 14 made of PLZT, the Faraday rotation angle, the Faraday rotation ellipticity, and the transmittance. From this graph, it can be seen that there is a peak of Faraday rotation angle when the applied voltage is around 0.26V, and there is a peak of Faraday rotation ellipticity with positive and negative on both sides slightly shifted from the peak. I understood. It was also found that the Faraday rotation ellipticity peak coincides with the position of the maximum transmittance peak.

  On the other hand, FIG. 6 is a graph showing the relationship between the refractive index change Δn of the refractive index variable layer 15 in transmitted light, the Faraday rotation angle, the Faraday rotation ellipticity, and the transmittance. From this graph, there is a peak of Faraday rotation angle when the refractive index change Δn is around 0.0075, and there is a peak of Faraday rotation ellipticity with positive and negative on both sides slightly shifted from the peak. I found out that It was also found that the Faraday rotation ellipticity peak coincides with the position of the maximum transmittance peak.

<In the case of reflected light>
The result of the simulation calculation in the case of reflected light is shown in FIGS.
FIG. 7 is a graph showing the relationship between the change in refractive index of transmitted light and the Kerr rotation angle, Kerr rotation ellipticity, and transmittance.
It is a graph which shows the relationship between the change of the refractive index of the refractive index variable layer 15 in transmitted light, Kerr rotation angle, Kerr rotation ellipticity, and transmittance. From this graph, a peak of the Kerr rotation angle exists when the applied voltage is around 0.26 V, and a peak of the Kerr rotation ellipticity that reverses positive and negative exists on both sides slightly shifted from the peak. I understood that. It was also found that the Kerr rotation ellipticity peak coincides with the position of the maximum transmittance peak.
On the other hand, FIG. 8 is a graph showing the relationship between the refractive index change (Δn) and the Kerr rotation angle, Kerr rotation ellipticity, and transmittance. From this graph, there is a Kerr rotation angle peak near a refractive index change Δn of around 0.0075, and there are Kerr rotation ellipticity peaks that are opposite to each other on both sides slightly shifted from the peak. I found out that It was also found that the Kerr rotation ellipticity peak coincides with the position of the maximum transmittance peak.

  In this example, laser light having a wavelength λ1 = 800.0 nm is used as incident light, and the peak wavelength in the optical body is set to λ2 = 800.5 nm.

As described above, in the light modulation system according to the first embodiment, by controlling the voltage applied to the refractive index variable layer 14, the transmitted elliptical or reflected light of the laser light has a rotation ellipticity peak that is opposite in polarity. A unique effect of being present can be achieved.
For this reason, it can be used as a light source for writing in a recording medium that controls the reversal of magnetization depending on whether the light used for writing is right circularly polarized light or left circularly polarized light. In addition, the change in the applied voltage appears as a change in the electric field applied to the refractive index variable layer, and the refractive index can be controlled at high speed, so that high-speed writing is possible.

12, 15 ... reflective layer (12 ... first reflective layer, 15 ... second reflective layer)
10, 20... Light modulator (10... Optical body, 20... Semiconductor laser device (light source))
DESCRIPTION OF SYMBOLS 14 ... Refractive index variable layer 13 ... Magneto-optical material layer 14a, 14b, 30 ... Refractive index control part (14a, 14b ... Transparent electrode, 30 ... Potential generator)

Claims (9)

A light source that emits first light of a first wavelength λ1,
An optical body that uses the first light as incident light, has a rotation angle peak at the second wavelength λ2, and outputs the second light as output light, comprising a pair of reflective layers and the pair of reflective layers An optical body having a refractive index variable layer and a magneto-optical material layer existing between
A method of controlling a light modulation system comprising: a refractive index control unit capable of controlling a refractive index of the refractive index variable layer to a first refractive index and a second refractive index;
While making the second wavelength λ2 corresponding to the peak of the rotation angle of the optical body larger than the wavelength λ1 of the incident light,
In the first refractive index, the second light is elliptically polarized light in a first direction, and in the second refractive index, the second light is elliptically polarized light in a second direction. A method for controlling an optical modulation system for controlling a refractive index of a variable-index layer.   The absolute value of the rotational ellipticity of the elliptically polarized light in the first direction becomes the maximum at the first refractive index, and the absolute value of the rotational ellipticity of the elliptically polarized light in the second direction at the first refractive index. The control method according to claim 1, wherein control is performed so as to maximize the value.   The control method according to claim 2, wherein the refractive index variable layer is made of an electro-optic material whose refractive index is changed by an electric field, and the refractive index control unit controls an electric field applied to the refractive index variable layer. An optical body having a pair of reflective layers, a refractive index variable layer and a magneto-optical material layer present between the pair of reflective layers;
A refractive index control unit capable of controlling a refractive index of the refractive index variable layer to a first refractive index and a second refractive index, wherein linearly polarized light is input and elliptically polarized light is output. A control method,
A method for controlling a light modulation system, wherein the refractive index of the refractive index variable layer is controlled so as to change both the rotation angle and the rotation ellipticity of the elliptically polarized light.   The control method according to claim 4, wherein the refractive index variable layer is made of an electro-optic material whose refractive index is changed by an electric field, and the refractive index control unit controls an electric field applied to the refractive index variable layer. A light source that emits first light of a first wavelength λ1,
An optical body that uses the first light as incident light, has a rotation angle peak at the second wavelength λ2, and outputs the second light as output light, comprising a pair of reflective layers and the pair of reflective layers An optical body having a refractive index variable layer and a magneto-optical material layer existing between
A refractive index control unit capable of controlling a refractive index of the refractive index variable layer to a first refractive index and a second refractive index;
In the first refractive index, the second light is elliptically polarized light in a first direction, and in the second refractive index, the second light is elliptically polarized light in a second direction. A control unit for controlling the refractive index of the variable rate layer,
The light modulation system, wherein the second wavelength λ2 corresponding to the rotation angle peak of the optical body is larger than the wavelength λ1 of the incident light.   The absolute value of the ellipticity of the elliptically polarized light in the first direction is the maximum at the first refractive index, and the absolute value of the ellipticity of the elliptically polarized light in the second direction is the maximum at the second refractive index. The system of claim 6.   The system according to claim 7, wherein the refractive index variable layer is made of an electro-optic material whose refractive index is changed by an electric field, and the refractive index control unit controls an electric field applied to the refractive index variable layer. The system according to claim 8, wherein the refractive index control unit includes a pair of transparent electrodes sandwiching the refractive index variable layer.

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