JP2014178642A - Optical device and writing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel optical device and writing method.SOLUTION: The optical device of the present invention comprises: a photorefractive cell 100 including electrodes 21, 21 which sandwich a photorefractive layer 24; an interference light irradiating light source 31 which irradiates the photorefractive layer 24 with interference light; an electric field application device 32 which applies electric field to the photorefractive layer 24; and a control section 35. When writing of information to the photorefractive layer 24 is performed, the control section 35 controls an action of the electric field application device 32 so as to apply electric field having inverted polarities between a writing preparation period and a writing period subsequent to the preparation period to the photorefractive layer 24, and controls an action of the interference light irradiating light source 31 so as to irradiate interference light in the writing period.

Description

  The present invention relates to an optical device using a photorefractive material and a method for writing information into a photorefractive layer.

  In a photorefractive material, when light having a light-dark intensity distribution is irradiated, a refractive index change corresponding to the intensity distribution occurs. On the other hand, when the light having a uniform intensity without distribution is irradiated, the changed refractive index is restored. Due to this property, photorefractive materials have been studied for application to hologram reproduction, image calculation filters, and the like. Further, among photorefractive materials, an orientation enhancement type (orientation enhancement type) photorefractive material has attracted attention because of its excellent performance and the ability to produce a large-area device.

  However, an optical device using a photorefractive material generally has an insufficient response speed. If the response speed of the optical device can be improved, application to various fields that require a high-speed response such as image processing, dynamic holography, interference measurement, and optical recording is expected.

  The response speed of the orientation-enhancing photorefractive material depends on the external electric field (driving electric field) intensity and the writing light intensity. Therefore, the response speed of the optical device increases as the external electric field is higher or the write light intensity is higher.

  Non-Patent Document 1 reports that the response speed is increased by setting the external electric field applied to the photorefractive material to a steady electric field having a high electric field (for example, an electric field strength exceeding 100 V / μm).

  Further, in Non-Patent Document 2, by using an instantaneous electric field (pulse electric field) instead of a steady electric field, the response speed is increased by applying a high electric field exceeding 100 V / μm instantaneously only at the time of writing. It has been reported.

Furthermore, Non-Patent Document 3 reports that a response speed of 0.3 ms was achieved using an optical pulse with high light intensity (4 mJ / cm ² ) (E = 90 V / μm).

D. Wright, et. Al., Appl. Phys. Lett. 73, (1998) 1490. Sava Tay, et.al., Nature 451, (2008) 694. M. Eralp, et.al., Appl. Phys. Lett. 89, (2006) 114105.

  However, when a high electric field is applied to the photorefractive material as described in Non-Patent Document 1, dielectric breakdown and destabilization of the material occur.

  On the other hand, as described in Non-Patent Document 2, when an instantaneous electric field is used, application of a high electric field can be limited only to writing, but the response speed can be made faster than several milliseconds. Have difficulty.

  Further, since Non-Patent Document 3 uses a large-sized laser device, there is a problem that it is not suitable as a general-purpose device.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an optical device using an alignment-enhanced photorefractive material capable of realizing a relatively fast and stable response with a relatively simple configuration. And providing a method of writing information to the photorefractive layer.

  In order to solve the above-described problems, the present invention provides a photorefractive cell including a photorefractive layer including an orientation-enhancing organic photorefractive material and a pair of electrodes sandwiching the photorefractive layer, and interference light in the photorefractive layer. An interference light irradiation device that irradiates the photorefractive layer via the pair of electrodes, and a control unit that controls operations of the interference light irradiation device and the electric field application device. And when writing information to the photorefractive layer, the control unit applies an electric field whose polarity is inverted between a write preparation period and a write period subsequent to the preparation period to the photorefractive layer. Control the operation of the application device, and the interference during the writing period It controls the operation of the interference light irradiation apparatus to irradiate, to provide an optical device.

  According to the above optical device, a coercive electric field is generated in the photorefractive layer due to the accumulated electric charge generated from the impurities contained in the material due to the application of the electric field in the writing preparation period. In the subsequent writing period, the coercive electric field is not reversed simultaneously with the external electric field and is maintained for a certain period. Therefore, the coercive electric field generated in the photorefractive layer is superimposed on the external electric field after the polarity inversion, and the effective electric field is enhanced. In the control unit, control is performed so that writing by interference light is performed while the effective electric field is enhanced, so that the response speed can be increased while suppressing the influence on the photorefractive layer and the like.

  Moreover, it is preferable that the said control part controls operation | movement of the said electric field application apparatus and interference light irradiation apparatus so that irradiation of the said interference light may be started within 1 second from the start of the said writing period.

  According to the above method, since the writing is performed when the effective electric field is most enhanced, the response speed can be further increased.

  The writing preparation period and the writing period are preferably continuous.

  According to the above method, since the writing is performed when the effective electric field is most enhanced, the response speed can be further increased.

  It is preferable to use a pulse electric field having a pulse width of 1 millisecond or more and 1 second or less as an electric field applied to the photorefractive layer in the writing preparation period and the writing period.

  According to the above configuration, since the application time of the electric field is short, high-speed writing can be realized while suppressing the influence on the photorefractive layer and the like.

  The irradiation time of the interference light in the writing period is preferably in the range of 0.1 milliseconds to 1 second.

  According to the above configuration, it is possible to obtain a sufficient response speed while suppressing the influence on the photorefractive layer and the like.

  The photorefractive cell preferably includes a functional layer for maintaining or enhancing an effective electric field acting on the photorefractive layer. Note that the functional layer is provided, for example, between the photorefractive layer and at least one of the pair of electrodes.

  According to the above configuration, since the effective electric field applied to the photorefractive layer can be increased or maintained for a predetermined period, it is possible to further speed up the response and maintain information recording (memory property).

  The functional layer is preferably selected from any one of a ferroelectric layer, a coercive electric field forming layer, and a block layer that suppresses charge transfer between the electrode and the photorefractive layer.

  Further, as a specific aspect of the optical device according to the present invention, the orientation-enhancing organic photorefractive material is at least selected from the group consisting of a carbazole derivative polymer, a phenylene vinylene derivative polymer, and a tetraphenyldiaminobiphenyl derivative polymer. One type of compound is included as a photoconductive molecule, and at least one type of dye selected from the group consisting of azo dyes, dicyanostyrene derivatives, dicyanomethylene dihydrofuran derivatives, and polyene derivatives is included as a birefringent optical dye.

  The present invention also relates to a method for writing information to a photorefractive layer including an orientation-enhancing organic photorefractive material, wherein an electric field whose polarity is inverted between a write preparation period and a write period subsequent to the preparation period is described above. There is provided a writing method including applying to a photorefractive layer and irradiating the photorefractive layer with interference light in the writing period.

  In addition, as an example of the writing method, a photorefractive layer including a photorefractive layer including an orientation-enhancing organic photorefractive material and a pair of electrodes sandwiching the photorefractive layer, and interference that irradiates the photorefractive layer with interference light. A method of driving an optical device comprising a light irradiation device and an electric field application device that applies an electric field to the photorefractive layer via the pair of electrodes, when writing information to the photorefractive layer, There is a driving method in which an electric field whose polarity is reversed in a writing preparation period and a writing period subsequent to the preparation period is applied to the photorefractive layer, and the interference light is irradiated in the writing period.

  According to the above driving method, the response speed can be increased while suppressing the influence on the photorefractive layer and the like.

  According to the present invention, there is provided an optical device using an orientation-enhancing photorefractive material and a method for writing information to a photorefractive layer, which can realize a relatively fast and stable response with a relatively simple configuration. Can do.

It is a figure which shows schematic structure of the optical device which concerns on one Embodiment of this invention. It is a wave form diagram of the electric field (upper side) applied to the optical device which concerns on one Embodiment of this invention, and the writing light (lower side) irradiated. It is a figure explaining the drive principle of the optical device which concerns on one Embodiment of this invention. It is a figure which shows the modification of the drive method of the optical device which concerns on one Embodiment of this invention. It is a figure which shows the outline of the arrangement | positioning relationship between the sandwich cell and various optical systems of the non-degenerate four-wave mixing evaluation apparatus which concerns on one Example of this invention. It is a wave form diagram which shows the timing of the pulse electric field applied to the sandwich cell which concerns on one Example of this invention, the change of a reference beam, object light, and optical writing. It is a figure which shows the measurement result of the diffracted light intensity which concerns on one Example of this invention.

<1. Optical device>
Hereinafter, the optical device according to the present embodiment will be described in detail with reference to FIGS. 1 and 2.

  FIG. 1 is a diagram showing a schematic configuration of an optical device according to an embodiment of the present invention. FIG. 2 is a waveform diagram of the electric field applied to the optical device and the irradiated write light according to an embodiment of the present invention.

  As shown in FIG. 1, the optical device 200 according to the present embodiment includes a photorefractive cell 100, an interference light irradiation light source (interference light irradiation device) 31, an electric field application device 32, an electric field application device 32, and interference light irradiation. At least a control unit 35 for controlling the operation of the light source 31 is provided.

(Photorefractive cell 100)
The photorefractive cell 100 is disposed between a photorefractive layer 24 containing an orientation-enhancing organic photoactive material, a pair of electrodes 21 and 21 sandwiching the photorefractive layer 24, and between the photorefractive layer 24 and the pair of electrodes 21. The functional layer 25 is provided. The electrode 21 is composed of a transparent electrode such as an indium tin oxide (ITO) electrode. The functional layer 25 is, for example, a transparent insulating layer (an example of a block layer). In this case, the functional layer 25 is applied to suppress charge injection from the electrode 21 and to effectively act on an external electric field described later. Moreover, the electrode 21 is formed on the surface of the translucent board | substrate 22, such as a glass substrate or a plastic substrate, and becomes the structure of the transparent electrode substrates 23 * 23.

  The interference light irradiation light source 31 is configured to include a plurality of laser light sources, for example, and irradiates an arbitrary position on the photorefractive layer 24 with interference light interfered with the laser light.

(Orientation-enhancing organic photorefractive material)
An orientation-enhancing organic photorefractive material is an organic photorefractive material containing at least a photoconductive molecule and a birefringent optical dye (birefringent optical chromophore), and the orientation state of the birefringent optical dye is an internal electric field ( Widely refers to materials that change due to the generation of a spatial electric field. The generation of an internal electric field refers to an electric field generated in the material when the alignment-enhanced photorefractive material is irradiated with interference light, that is, an electric field that generates a photorefractive effect.

  A birefringent optical dye is an organic dye that produces birefringence when oriented. The type of the birefringent optical dye is not particularly limited, but it is desirable that the birefringent optical dye has a structure exhibiting large birefringence as a single molecule. Specific examples include azo dyes, dicyanostyrene derivatives, dicyanomethylene dihydrofuran derivatives and polyene derivatives. Examples of the azo dye include 2,5-dimethyl-4- (paraphenylazo) anisole (DMNPAA) and 1- (2′-ethylhexyloxy) -2,5-dimethyl-4- (4 ″ -nitrophenylazo). Benzene (EHDNPB) is mentioned. Examples of the dicyanostyrene derivatives include 2- [4-bis (2-methoxyethyl) amino] benzylidene] malononitrile (AODST) and 4-homopiperidinobenzylidene-malonitrile (7-DCST). Examples of the dicyanomethylene dihydrofuran derivative include 2-dicyanomethylene-3-cyano-5,5-dimethyl-4- (4′-dihexylaminophenyl) -2,5-dihydrofuran (DCDHF-6). It is done. Furthermore, examples of the polyene derivative include 2-N, N-dihexyluamino-7-dicyanomethylidenyl-3,4,5,6,10-pentahydronaphthalene (DHADC-MPN). Moreover, a birefringent optical dye may be used individually by 1 type, and may be used in combination of 2 or more types. The blending amount of the birefringent optical dye is not particularly limited as long as it is appropriately determined according to the combination with other constituent materials, and the like. For example, the orientation-enhancing organic photorefractive material (total is 100% by weight; It is 20 to 50% by weight.

  A photoconductive molecule is an organic compound that absorbs interference light generated by a light source for writing a signal to generate positive and negative charges (photocarriers) and transports the photocarrier. The type of the photoconductive molecule is not particularly limited, and specific examples include a carbazole derivative polymer, a phenylene vinylene derivative polymer, and a tetraphenyldiaminobiphenyl derivative polymer. Examples of the carbazole derivative polymer include polyvinyl carbazole (PVK) and poly [methyl-3- (9-carbazolyl) -propylsiloxane] (PSX). Examples of the phenylene vinylene derivative polymer include poly (arylene vinylene) copolymer triphenylamine dimer polyphenylene vinylene (TPD-PPV) and poly [1,4-phenylene-1,2-di (4-benzyloxyphenyl) vinylene. ] (DBOP-PPV). Furthermore, examples of the tetraphenyldiaminobiphenyl derivative polymer include poly (acrylic tetraphenyldiaminobiphenol) (PATPD). Moreover, a photoconductive molecule may be used individually by 1 type, and may be used in combination of 2 or more types. When a dicyanostyrene derivative is used as the birefringent optical dye, it is preferable to use a carbazole derivative polymer or a tetraphenyldiaminobiphenyl derivative polymer as the photoconductive molecule. The blending amount of the photoconductive molecule is not particularly limited as long as it is appropriately determined depending on the combination with other constituent materials, and is, for example, 35 to 60% by weight in the orientation-enhancing organic photorefractive material.

  The glass transition temperature (Tg) of the orientation-enhancing organic photorefractive material is not particularly limited as long as the glass transition temperature (Tg) is appropriately set according to the operating temperature. However, when assuming a material that operates near room temperature, an example of the glass transition temperature is − It is in the range of 40 ° C. or higher and 30 ° C. or lower. For example, when a material for fixing an optical signal such as an image is assumed, it is preferable to set the glass transition temperature sufficiently higher than room temperature. In that case, an example of the glass transition temperature is in the range of 100 ° C. to 250 ° C.

  The orientation enhancing organic photorefractive material may further contain other components. Specific examples of the other components include a plasticizer and a sensitizing dye.

  One of the roles of the plasticizer is to adjust the glass transition temperature of the orientation-enhancing organic photorefractive material to a desired value. The type of plasticizer is not particularly limited, and electrically stable nonpolar molecules and charge transporting molecules are used. Specific examples include ethyl carbazole (ECz), ethyl hexyl carbazole (EHCz), and benzyl butyl phthalate (BBP). Moreover, a plasticizer may be used individually by 1 type and may be used in combination of 2 or more types. The blending amount of the plasticizer may be appropriately determined according to the combination with other constituent materials and the like, and is not particularly limited. For example, it is 0 to 30% by weight in the orientation-enhancing organic photorefractive material.

The role of the sensitizing dye is to increase charge generation at the wavelength of the light source used. The type of the sensitizing dye is not particularly limited. Specifically, for example, buckminsterfullerene (C ₆₀ ), phenyl C61 butyric acid methyl ester (PCBM) and 2,4,7-trinitro-9-fluorenone (TNF), 9 -(Dicyanomethylene) -2,4,7-trinitrofluorene (TNFM). Moreover, a sensitizing dye may be used individually by 1 type, and may be used in combination of 2 or more types. The blending amount of the sensitizing dye is not particularly limited as long as it is appropriately determined depending on the combination with other constituent materials, and is, for example, 0 to 5% by weight in the orientation-enhancing organic photorefractive material.
(Functional layer 25)
The optical device 200 preferably includes one or more functional layers 25 between the photorefractive layer 24 and at least one of the pair of electrodes 21 and 21. The functional layer 25 is preferably provided between the photorefractive layer 24 and each of the pair of electrodes 21 and 21. The functional layer 25 is a translucent layer.

  The functional layer 25 refers to a layer having a function of maintaining or enhancing the effective electric field applied to the photorefractive layer 24. Examples of the functional layer 25 include a block layer, a ferroelectric layer, and a coercive electric field forming layer. If the functional layer 25 is provided, the effective electric field applied to the photorefractive layer 24 can be increased or maintained for a predetermined period of time, so that it is possible to further increase the response speed and maintain information recording (memory property). It becomes.

The block layer refers to a layer having a function of shielding charge transfer at the electrode interface. Specific examples of the block layer include a SiO ₂ layer as a transparent insulating layer, an insulating polymer layer, and an insulating organic thin film layer. According to such a block layer, the cancellation of the internal charge due to the charge injection into the photorefractive layer 24 is suppressed, or the outflow of the internal charge to the electrode 21 is suppressed.

  A ferroelectric layer refers to a layer that has the function of maintaining internal charge distribution and enhancing internal charge using spontaneous polarization. Specific examples of the ferroelectric layer include a ferroelectric polymer such as PVDF, an ionic liquid, and a ferroelectric liquid crystal.

  The coercive electric field forming layer refers to a layer having a function of attaching the coercive electric field forming layer outside the photorefractive layer. Specific examples of the coercive electric field forming layer include ionic liquid and ferroelectric liquid crystal. In addition, what is necessary is just to seal in a layer so that it may not leak when using an ionic liquid.

  In addition, the functional layer 25 may have a configuration in which the layers having the different functions described above are overlapped. Further, when one or more functional layers 25 are provided between the photorefractive layer 24 and each of the pair of electrodes 21 and 21, the pair of functional layers 25 and 25 are symmetrical with the photorefractive layer 24 interposed therebetween. It may be configured to have the same type of layer at various positions, or may be configured to be an asymmetric layer with the photorefractive layer 24 interposed therebetween.

  The functional layer 25 is formed by, for example, further forming a film on the surface of the transparent electrode substrate 23 on which the electrode 21 is formed.

  In the case where a plurality of photorefractive layers are provided, the functional layer can be provided as an intermediate layer between photorefractive layers, for example.

(Control unit 35)
The control unit 35 controls the operation of the electric field application device 32 and the interference light irradiation light source 31, and is configured by a computer, for example. When writing information to the photorefractive layer 24, as shown in FIG. 2, the controller 35 includes a series of periods including a first period (write preparation period) and a second period (write period) subsequent to the first period. In the sequence, the operation of the electric field applying device 32 is controlled so that an electric field whose polarity is inverted between the first period and the second period is applied to the photorefractive layer 24 through the pair of electrodes 21 and 21 (FIG. 2). Upper waveform). Further, the operation of the interference light irradiation light source 31 is controlled so that the interference light (writing light) irradiated by the interference light irradiation light source 31 is irradiated to the photorefractive layer 24 in the second period. As described above, the timing of applying the electric field of the electric field applying device 32, the application time of the electric field, the control of the polarity inversion of the electric field, and the operation control of the interference light irradiation light source 31 are performed in association with each other in the control unit 35. . The control operation by the control unit 35 is described in <2. This will be described in detail in the section “Driving method of optical device>”.

  When the optical device 200 reads information recorded on the photorefractive layer 24 by irradiation of interference light as a signal, the optical device 200 may further include a read light irradiation device 33 and a photodetector 34 as recording / reproducing means. The reading light irradiation device 33 irradiates the photorefractive layer 24 with reading light having a wavelength corresponding to the recorded information, and the diffracted light (signal) generated as a result of the irradiation is detected by the photodetector 34.

  The type of the optical device 200 is not particularly limited as long as it uses a photorefractive effect, but is preferably a device that requires a high-speed response in units of milliseconds or less or sub-milliseconds. Examples of the optical device 200 include an image display device such as a hologram device, an optical arithmetic device, a photorefractive phase conjugate mirror, an optical recording device, and an image adjustment filter. The optical device 200 can be used, for example, in the technical fields of real-time stereoscopic hologram display, moving object detection, moving object velocity analysis, and three-dimensional real-time imaging such as pathological tissue.

<2. Driving method of optical device>
Hereinafter, the driving method of the optical device 200 shown in FIG. 1 will be described in more detail with reference to FIGS. As shown in the upper side of FIG. 2, the voltage is maintained at the sustain voltage (0 V in FIG. 2) before writing. When writing is performed, first, the photorefractive layer 24 is used as the first period (writing preparation period). A reference electric field (writing preparation electric field) is applied. For example, in FIG. 2, the reference electric field is shown as a positive external electric field. By applying the reference electric field, a coercive electric field is generated in the photorefractive layer 24 due to accumulated charges generated from impurities contained in the material.

  Subsequent to the first period, in the second period (writing period), the polarity of the external electric field applied to the photorefractive layer 24 is instantaneously reversed. In FIG. 2, a negative external electric field (writing electric field) is applied to the photorefractive layer 24 in the second period with respect to the positive reference electric field in the first period. When the polarity of the external electric field applied to the photorefractive layer 24 is instantaneously reversed in this way, the coercive electric field inside the photorefractive layer 24 is not reversed at the same time as the external electric field and is maintained for a certain period. Therefore, in the second period, an effective electric field in which the coercive electric field is superimposed on the external electric field is applied to the photorefractive layer 24. As a result, in the second period, the effective electric field applied to the photorefractive layer 24 is reinforced (enhanced) by the coercive electric field. If writing by interference light is performed while the effective electric field is enhanced (see the lower side of FIG. 2), high-speed writing can be realized while suppressing deterioration of the photorefractive layer 24. FIG. 3 is a graph showing the relationship between the external electric field applied to the photorefractive layer 24, the coercive electric field formed, and the effective electric field in the first period and the second period.

  The enhancement time and enhancement strength (see FIG. 3) of the effective electric field applied to the photorefractive layer 24 in the second period are controlled by adjusting the electric field amplitude and electric field pulse width of the reference electric field applied in the first period. Can do. In order to increase the effective electric field enhancement time and enhancement strength, it is better that the electric field amplitude (absolute value) and electric field pulse width of the reference electric field are larger. However, from the viewpoint of obtaining a sufficient response speed while suppressing the load on the photorefractive layer 24, the electric field amplitude (absolute value) of the reference electric field is preferably in the range of 10 V / μm to 300 V / μm, More preferably, it is in the range of 50 V / μm to 300 V / μm, and more preferably in the range of 100 V / μm to 300 V / μm. The electric field pulse width of the reference electric field (corresponding to the electric field application time) is preferably in the range of 0.1 milliseconds to 1 second, and preferably in the range of 1 millisecond to 0.5 seconds. More preferably.

  Further, from the viewpoint of obtaining a sufficient response speed while suppressing the load on the photorefractive layer 24, the electric field amplitude (absolute value) of the external electric field (writing electric field) applied to the photorefractive layer in the second period is 10 V / μm. Above, it is preferably in the range of 300 V / μm or less, more preferably in the range of 50 V / μm or more and 300 V / μm or less, and in the range of 100 V / μm or more and 300 V / μm or less. Further preferred. Further, the electric field pulse width (corresponding to the electric field application time) of the writing electric field is preferably within a range of 0.1 milliseconds to 1 second, and preferably within a range of 1 millisecond to 0.5 seconds. More preferably, it is more preferably in the range of 1 millisecond or more and 0.1 second or less.

  After the second period, the voltage is returned to the sustain voltage again. As described above, a series of sequences from the sustain voltage to the sustain voltage through the first period and the second period may be repeatedly performed.

  2 and 3 show examples in which a pulse electric field having the same electric field amplitude (absolute value) and the same electric field pulse width is applied in the first period and the second period except that the polarity is reversed. You may apply the pulse electric field from which an electric field amplitude and an electric field pulse width differ in a 1st period and a 2nd period. Alternatively, a negative electric field may be applied in the first period, and a positive electric field may be applied in the second period. Furthermore, as long as the effect of enhancing the effective electric field applied to the photorefractive layer 24 in the second period is maintained, a short transition period (for example, between the first period and the second period, for example) A period when the voltage is 0 or the like may be provided. However, it is preferable that the first period and the second period are continuous without providing a transition period or the like. Further, in the case where the first period and the second period are repeated as two cycles or more continuously, the electric field of the second period applied for writing information is applied to the next consecutive writing preparation period (first period). It may also be used as an electric field.

  Optical writing is performed in the second period in which the external electric field applied to the photorefractive layer 24 is inverted, as shown on the lower side of FIG. The optical writing may be performed simultaneously with the reversal of the external electric field (start of the second period) or may be performed at any timing in the second period, but immediately after the reversal of the external electric field. Since the coercive electric field superimposed on the external electric field is the largest, it is preferable to perform optical writing within 1 second at the same time as the reversal of the external electric field. More preferably, it is more preferable to perform optical writing simultaneously with reversal of the external electric field. The optical writing timing and the optical pulse width can be controlled by controlling the emission of the interference light with a liquid crystal shutter (DisplayTech, LV2500-AC, etc.) provided in the interference light irradiation light source 31, for example.

Also, optical writing intensity to photorefractive layer 24 is 10mW ^/ cm ² ~1000mW ^/ cm 2 is preferred, for example, 100 mW / cm ^2. Further, the light pulse width in the interference light irradiation is preferably 1 femtosecond to 1 second, for example, 1 millisecond to 15 milliseconds. Moreover, the irradiation time of the interference light in one writing is not particularly limited, but is, for example, 1 femtosecond to 1 second or less, and 0.1 millisecond or more and 1 second or less.

<3. Modified Example of Driving Method of Optical Device>
2 and 3, a pulse electric field having the same electric field amplitude (absolute value) and the same electric field pulse width is applied in the first period (writing preparation period) and the second period (preparation period) except that the polarity is reversed. Thus, the driving method in which optical writing is performed only once in the second period has been described. However, for example, a driving method as shown in FIG. 4 may be adopted.

  FIG. 4A shows information written by performing multiple times of optical writing on the same region in the second period (writing period) after the external electric field applied to the photorefractive layer 24 is reversed. This is an example in which the integrated value of is used as a signal. The second period can be, for example, several milliseconds or less.

  (B) in FIG. 4 shows that the electric field amplitude (absolute value) of the pulse electric field applied in the second period is larger than that in the first period, and the electric field pulse width is smaller than that in the first period. This is an example of a driving method in which optical writing is repeated by repeating a period multiple times. A high-speed response is realized by shortening the second period (writing period).

  (C) in FIG. 4 shows that repeated optical writing is performed at a high speed by applying a pulse electric field having a high electric field amplitude instantaneously in the first period and setting the second period to the minimum period necessary for optical writing. It is an example of the drive method to perform.

  Note that both the driving methods shown in FIGS. 2 and 4 use the application of a pulsed electric field, so that the electric field application time can be shortened compared to the case where a steady electric field is applied. Therefore, damage and deterioration of the material caused by application of an electric field can be reduced.

  Hereinafter, the present invention will be described in further detail with reference to examples.

[Preparation of sandwich cell as a characterization sample]
(Orientation-enhancing organic photorefractive material)
The alignment-enhancing organic photorefractive material (hereinafter referred to as organic PR material) used in the examples is 59.4% by weight of polyvinyl carbazole as a photoconductive molecule, 10% by weight of EHCz as a plasticizer, and as a sensitizing dye. It contains 0.6% by weight of fullerene and 30% by weight of AODCST as a birefringent optical dye as a constituent component.

(Production of ITO glass substrate with functional layer)
Two ITO glass substrates with functional layers were produced by forming an insulating polymer material (fluorine polymer resin) as a functional layer on the surface of the ITO glass substrate on which the electrodes were patterned on the side having the electrodes.

(Preparation of characteristic evaluation sample)
A sandwich cell (corresponding to the photorefractive cell 100 shown in FIG. 1) in which an organic PR material is sandwiched between two ITO glass substrates with a functional layer using a polyimide film as a spacer is produced, and characteristics evaluation in each example shown below Used as a sample.

[Example 1: Influence on light-induced refractive index change by driving using inversion pulse electric field]
In this embodiment, when the pulse electric field is applied to the sandwich cell simultaneously with optical writing (normal driving), after applying the pulse electric field (writing preparation period), the pulse electric field is applied with the polarity reversed (writing period). ) In the case where optical writing was performed simultaneously with polarity reversal (reversal drive), the rising speed of the photoinduced refractive index change was examined.

  If the magnitude of the light-induced refractive index change occurring in the organic PR material is Δn, and the diffracted light intensity obtained by irradiating the organic PR material with the readout light is I, the magnitude of the light-induced refractive index change Δn and the diffracted light intensity The relationship of I can be expressed by the following formula.

Therefore, the magnitude Δn of the light-induced refractive index change was evaluated by the diffracted light intensity I.

(Electric field application conditions)
An ITO glass substrate constituting the sandwich cell was connected to a terminal of a high voltage amplifier device (Matsusada Precision, HCOR-10) via a lead wire. Then, a pulse electric field having an electric field amplitude of 60 V / μm was applied for a pulse width of 0.5 seconds (normal pulse electric field application), then inverted to −60 V / μm, and a pulse width of 0.5 seconds was applied (inverted pulse electric field application). .

(Non-degenerate four-wave mixing measurement device)
For the evaluation of the diffracted light intensity, the non-degenerate four-wave mixing measurement system shown in FIG. 5 was used. FIG. 5 schematically shows the positional relationship between the sandwich cell and various optical systems. In the figure, 7 is a sandwich cell, 3 is readout light, 4 is diffracted light, 1 is reference light (writing light (interference light)), 2 is object light (writing light (interference light)), and 6 is a tilt angle ( (60 °), 5 means a crossing angle (writing angle) (10 °). A He—Ne laser (CVI Melles Griot, 05LHP151) was used as the interference light irradiation light source. After being separated into two by a prism beam splitter, the interference light irradiation device was formed by causing interference on a sandwich cell (organic PR material). As the readout light 3, a 808 nm semiconductor laser (Solab, CPS 808) is used, and the diffracted light 4 generated from the sandwich cell (organic PR material) is detected by a photodiode (Solab, PDA 100A), and a storage oscilloscope (Lecroy, WaveRunner). 64Xi-A).

Here, in order to perform optical writing at an arbitrary timing and an arbitrary optical pulse width, a liquid crystal shutter is disposed on the optical path of the writing light 2 (object light), and the timing is controlled by a function generator (Tektronix, AFG3021B). It was. The writing light intensity of writing light 1 and 2 to the sandwich cell (organic PR material) was 65 mW / cm ² , respectively. The total light intensity at the time of writing is 130 mW / cm ² . The light pulse width of the writing light 2 (object light) was 10 milliseconds, and writing for one pulse was performed (that is, the irradiation time of the interference light was 10 milliseconds).

  FIG. 6 is a waveform diagram showing the pulse electric field applied to the sandwich cell, reference light and object light changes, and optical writing timing in this embodiment. Interference light is generated only under conditions in which the reference light (corresponding to the writing light 1) and the object light (corresponding to the writing light 2) are irradiated simultaneously, and writing to the organic PR material is performed. As shown in FIG. 6, in the normal drive, a pulse electric field was applied, and in the inversion pulse electric field drive (inversion drive), the pulse electric field was inverted and optical writing was performed at the same time.

(Results of comparison of inversion drive and normal drive diffracted light intensity)
The measurement results are shown in FIG. The horizontal axis represents time (seconds). The vertical axis represents the diffracted light intensity I. As shown in FIG. 7, by driving the inversion pulse electric field, a higher diffracted light intensity was obtained at a higher speed than the conventional pulse electric field drive which is a conventional method. Therefore, it was found that the response speed of the organic PR material can be increased by reversing the electric field and simultaneously performing optical writing.

  The present invention can be used for an optical device using a photorefractive material.

21 Electrode 24 Photorefractive layer 25 Functional layer 31 Interference light irradiation light source (interference light irradiation device)
32 Electric field application device 35 Control unit 100 Photorefractive cell 200 Optical device

Claims (9)

A photorefractive cell comprising a photorefractive layer containing an orientation-enhancing organic photorefractive material and a pair of electrodes sandwiching the photorefractive layer;
An interference light irradiation device for irradiating the photorefractive layer with interference light;
An electric field applying device for applying an electric field to the photorefractive layer via the pair of electrodes;
A controller that controls the operation of the interference light irradiation device and the electric field application device,
When writing information to the photorefractive layer, the control unit applies an electric field applying device that applies an electric field whose polarity is reversed between a write preparation period and a write period subsequent to the preparation period to the photorefractive layer. An optical device that controls the operation of the interference light irradiation apparatus so as to irradiate the interference light during the writing period.   The optical device according to claim 1, wherein the control unit controls operations of the electric field application device and the interference light irradiation device so as to start irradiation of the interference light within one second from the start of the writing period.   The optical device according to claim 1, wherein the writing preparation period and the writing period are continuous.   The light according to any one of claims 1 to 3, wherein a pulse electric field having a pulse width of 1 millisecond or more and 1 second or less is used as an electric field applied to the photorefractive layer in the writing preparation period and the writing period. device.   The optical device according to any one of claims 1 to 4, wherein an irradiation time of the interference light in the writing period is in a range of 0.1 milliseconds to 1 second.   The optical device according to any one of claims 1 to 5, wherein the photorefractive cell includes a functional layer for maintaining or enhancing an effective electric field acting on the photorefractive layer.   The optical device according to claim 6, wherein the functional layer is selected from any one of a ferroelectric layer, a coercive electric field forming layer, and a block layer that suppresses charge transfer between the electrode and the photorefractive layer. The orientation-enhancing organic photorefractive material is
Containing at least one compound selected from the group consisting of a carbazole derivative polymer, a phenylene vinylene derivative polymer, and a tetraphenyldiaminobiphenyl derivative polymer as a photoconductive molecule, and
The at least one pigment | dye selected from the group which consists of an azo pigment | dye, a dicyano styrene derivative, a dicyano methylene dihydrofuran derivative, and a polyene derivative is included as a birefringent optical pigment | dye in any one of Claims 1-7. Optical device. A method of writing information to a photorefractive layer containing an alignment-enhanced organic photorefractive material,
A writing method, comprising: applying an electric field whose polarity is reversed between a writing preparation period and a writing period subsequent to the preparation period to the photorefractive layer, and irradiating the photorefractive layer with interference light in the writing period.

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