JP4783749B2 - Beam splitting element - Google Patents

Description

  The present invention relates to a polarization hologram element having a function of transmitting or diffracting an element by a polarization component of an incident light beam, and more particularly to a light beam splitting element that divides an incident light beam from one light source into two or more light beams.

  The following have been proposed as conventional techniques related to the polarization hologram element.

  Patent Document 1 discloses an optical anisotropic diffraction element in which a diffraction grating shape is formed on an isotropic substrate, and a groove having the diffraction grating shape is filled with an optical anisotropic material.

  In Patent Document 2, a photopolymerizable liquid crystal is used, exposure is performed by a method such as interference exposure in a horizontally aligned state, and an external field is applied to an unexposed portion after the liquid crystal in the exposed portion is periodically polymerized and solidified. A hologram element that reacts and solidifies in a vertically aligned state is disclosed.

  In Patent Document 3, two-beam interference exposure is performed by controlling an optical medium including a liquid crystal and a polymer within a specific temperature range corresponding to the N-I point of the liquid crystal. A hologram element having a structure oriented in various directions is disclosed.

  Moreover, what is shown to the following patent document 4 is known as a prior art regarding light beam splitting.

  Japanese Patent Application Laid-Open No. H10-260260 divides a beam from a common light source in an optical scanning device and an image forming apparatus, causes the beams to enter different reflecting mirrors, and scans different surfaces to be scanned. The light division here is realized by a method such as a half mirror prism or a combination of a half mirror and a mirror.

  By the way, in recent years, a technique for converting a semiconductor laser into a multi-beam has progressed and is being applied to, for example, an electrophotographic image forming apparatus used in a laser printer, a digital copying machine, a plain paper fax machine, and the like. With regard to this electrophotographic image forming apparatus, colorization and speeding-up have progressed, and tandem-compatible image forming apparatuses having a plurality of (usually four) photoconductors have become widespread. However, in the case of such a tandem method, with an increase in the number of light sources, an increase in the number of parts, a color shift due to a wavelength difference between a plurality of light sources, and a cost increase occur. In addition, the deterioration of the semiconductor laser is cited as a cause of the failure of the writing unit. When the number of light sources increases, the probability of failure increases and the recyclability deteriorates.

Therefore, in order to reduce the number of light sources and the number of parts and reduce the cost, a method of dividing the beam from the common light source has been proposed. In the above-mentioned Patent Document 4, the light beam is divided by the following means. .
(1) Method using a half mirror prism (2) Method combining a half mirror and a mirror (3) Method of spatially dividing an emitted beam by providing a plurality of openings

  Here, since the mirrors are used as the separating means in both the methods (1) and (2), the beam spot diameter is likely to be deteriorated due to the influence of the variation in the surface accuracy of the mirror and the influence of the arrangement error. Further, the half mirror prism used in 1) is very expensive, resulting in an increase in cost. The method of combining the half mirror and the mirror shown in 2) is difficult to arrange the layout, and has an opening angle in the deflection rotation plane, so that the optical characteristics such as the beam spot diameter deteriorate. Further, the method of dividing a light beam by a plurality of openings has problems such as insufficient light quantity and increased beam spot diameter because the peripheral part of the beam from the light source is used.

  Therefore, as a light beam separation element, there is an element in which hologram elements are arranged in multiple stages, light is divided by transmission and diffraction of the preceding hologram element, and an optical axis of the divided light is adjusted by transmission and diffraction of the latter hologram element. .

  However, in the case of the optical separation element using the above-described hologram element, since the hologram element has temperature dependence, there is a problem in that the power of the light beam fluctuates due to temperature change.

Further, in Patent Document 5, the element temperature at which the diffraction efficiency takes a minimum value is in the range of 25 ° C. to 70 ° C., and the element has alternating regions where the refractive index anisotropy and the temperature dependence of the refractive index are different. A hologram element having an arrayed structure is disclosed.
Japanese Patent Laid-Open No. 10-92004 Japanese Patent Laid-Open No. 11-271536 JP 2000-212465 A JP 2005-92129 A JP 2003-270419 A

  A configuration in which hologram elements (including diffraction gratings) are stacked as a beam splitting element can be realized in a small size and at a relatively low cost. However, the optical characteristic (diffraction efficiency) of the hologram element is easily affected by temperature, and there is a problem that the light beam splitting efficiency changes depending on the temperature environment. The cause of the change in the optical characteristics may be an influence of a change in the refractive index of the hologram material, a change in the hologram structure due to expansion or contraction, and the like.

  Patent Document 5 discloses a material that reduces the temperature dependency of the hologram element by adjusting the material. However, the adjustment by the material limits the selection material as the hologram material, and it is difficult to realize highly efficient characteristics. Become.

  In general, it is important for the characteristics of the optical element to stably maintain high efficiency even when the temperature in the apparatus used or the ambient environment changes. It is important that the characteristics of the optical system used in the above-described electrophotographic image forming apparatus and the like maintain stable and high efficiency even with changes in temperature in the apparatus and changes in the surrounding environment.

  An object of the present invention is to provide a low-cost beam splitting element having high temperature efficiency and good temperature characteristics, which solves the above-mentioned problems, in a beam splitting system that splits a beam from a common light source using a hologram element. is there.

  The light beam splitting element of the present invention has a periodic structure composed of a region exhibiting optical anisotropy and a region exhibiting optical isotropy, and two or more hologram elements having different temperature characteristics of transmitted light or diffracted light. A light beam splitting element that is combined with the first hologram element, the second hologram element, and the third hologram element on the light incident side, and splits the light by transmission and diffraction of the first hologram element. The transmitted light of the first hologram element is applied to the third hologram element, the diffracted light of the first hologram element is applied to the second hologram element, and the divided light is transmitted and diffracted by the second hologram element. And the light intensity of the divided transmitted light from the first hologram element is adjusted by the transmission of the third hologram element, so that the incident light flux is reduced to two or more light fluxes. Divided and characterized in that it emitted.

  Further, the temperature characteristic of the transmitted light or diffracted light of the hologram element in the present invention is set by the film thickness of the periodic structure of the hologram.

  In the invention, the temperature characteristic of the transmitted light or diffracted light of the hologram element is set by the refractive index modulation amount amplitude generated by the periodic structure of the hologram.

Further, in the present invention, the film thicknesses of the first hologram element, the second hologram element, and the third hologram element are T ₁ , T ₂ , and T ₃ , respectively, and the + 1st order light or the −1st order light has the maximum diffraction efficiency. If the thickness of the hologram element and Tmax, _{T 1} is less than _{T 2, T 3} is good greater than _{T 2,} and Tmax is set between _{T 1} and _{T 2.}

The film thickness T ₃ of the third hologram element may be approximately twice the film thickness Tmax of the hologram element.

In the present invention, the film thicknesses T1 and T2 of the periodic structure of the first hologram element and the second hologram element described above are preferably in a relationship of | Tmax−T1 |> | Tmax−T2 | .

Further, the present invention, the thickness T ₁ of the periodic structure of the first hologram element described above is better to approximately half of the thickness T ₂ of the periodic structure of the second hologram element.

  Further, the present invention provides a periodic structure of the hologram element in which a composition comprising a non-polymerizable liquid crystal, a polymerizable monomer or prepolymer, and a photopolymerization initiator is held between a pair of transparent substrates, Using a polymer-dispersed liquid crystal hologram element in which a periodic phase separation structure consisting of a polymer layer and a non-polymerizable liquid crystal layer is formed by subjecting an object to multi-beam interference exposure of two or more beams. Good.

  The present invention has a periodic structure composed of a region exhibiting optical anisotropy and a region exhibiting optical isotropy, and is a light beam formed by combining two or more hologram elements having different temperature characteristics of transmitted light or diffracted light. The splitting element is arranged with the first hologram element, the second hologram element, and the third hologram element on the light incident side, thereby reducing the diffraction efficiency of the first hologram due to temperature rise and the second hologram. The increase in diffraction efficiency can be canceled, and the fluctuation due to the temperature of the second diffracted deflected light in the divided light beam is suppressed, so that the temperature characteristics of the light beam dividing element are improved. Further, by arranging the third hologram 3, even if the transmittance of the first transmitted straight light from the first hologram increases due to the temperature rise, it is canceled by the transmitted light efficiency characteristic of the third hologram, and the temperature is increased. Regardless of this, a constant transmittance can be obtained.

  In addition, by setting the film thickness of the first hologram element to be small, the allowable range of the incident angle dependency is wide.

  In addition, a liquid crystal hologram produced by interference exposure can be duplicated, so that the cost can be reduced. By arranging the liquid crystal hologram elements in multiple stages, a low-cost beam splitting element can be provided.

  Embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated in order to avoid duplication of description.

  First, a schematic configuration of a light beam splitting element which is a premise of the present invention will be described with reference to FIGS. 1 and 2 are schematic views showing a schematic configuration of a light beam splitting element that is a premise of the present invention. Although the first transmitted straight light from the first hologram element does not pass through the second hologram element, FIG. As shown in FIG. 2, the second hologram element is arranged to transmit.

  A light beam splitting element 100 shown in FIG. 1 is configured by arranging a first hologram element 1 and a second hologram element 2 in multiple stages. The first hologram element 1 is provided with a hologram layer 13 between the translucent substrates 11 and 12, and the second hologram element 2 is provided with a hologram layer 23 between the translucent substrates 21 and 22.

  The principle of operation of the light beam splitting element 100 in which the first hologram element 1 and the second hologram element 2 are arranged in multiple stages is that the incident light beam 10 is diffracted by the first hologram element 1 by the diffracted deflected light 10b and the transmitted straight light 10a. Divided into two light beams, the deflected light 10b by diffraction becomes deflected light 20b deflected again by the diffraction by the second hologram element 2, and the optical axis (traveling direction) and light intensity of the divided two light beams can be set.

   Here, the deflected light diffracted by the first hologram element 1 is the first diffracted deflected light 10 b, and the deflected light diffracted again by the second hologram element 2 is “2 diffracted deflected light 20 b, the straight light transmitted by the first hologram element 1. Is defined as first transmitted straight light 10a, and straight light transmitted again by the second hologram element 2 is defined as second transmitted straight light 20a.

  In FIG. 1, the first transmitted straight light 10 a from the first hologram element 1 does not pass through the second hologram element 2. On the other hand, the configuration shown in FIG. 2 is arranged such that the first transmitted straight light 10 a from the first hologram element 1 is transmitted through the second hologram element 2.

  As shown in FIG. 2, when the first transmitted straight light 10 a passes through the second hologram element 2, the transmittance is increased by a phase difference plate (not shown) before entering the second hologram element 2. It is desirable to set the polarization direction.

  As shown in FIG. 3, the light beam splitting element 100 may be configured. In the configuration shown in FIG. 3, a substrate 15 is used which serves as both a substrate used on the light emitting side of the first hologram element 1 and a substrate used on the light incident side of the second hologram element 2. In this case, the thickness of the substrate 15 is appropriately set according to the light receiving positions (interval distance of the divided light beams) of the second transmitted straight light 20a and the second diffracted deflected light 20b.

  As described above, as shown in FIGS. 1 to 3, by arranging the first hologram element 1 and the second hologram element 2 in multiple stages, the optical axis (traveling direction) and light of two light beams divided from one light beam are obtained. The strength can be set.

  Here, a volume hologram element model will be described with reference to FIG. FIG. 4 is a schematic diagram showing a model of a cross-sectional structure of the volume hologram element.

This hologram element has a periodic structure of an optically anisotropic region and an optically isotropic region. The refractive index modulation amount of the periodic structure is Δn _H , the thickness of the periodic structure is T, the grating pitch of the periodic structure is p, the period The lattice inclination of the structure is defined as φ.

In general, the diffraction angle θ of the hologram can be expressed by θ = sin ⁻¹ (λ / p), and is determined by the wavelength λ of the incident light beam and the grating pitch p of the hologram. That is, the diffraction angle θ can be set by the hologram grating pitch p.

The diffraction efficiency depends on the refractive index modulation amount (or refractive index difference) Δn _H generated from the grating periodic structure and the thickness T of the periodic structure. By optimizing these parameters, the ideal diffraction efficiency is obtained. Is obtained. The maximum diffraction efficiency that can be theoretically obtained varies depending on the type of hologram, but volume holograms (refractive index modulation holograms) can obtain very high diffraction efficiency (theoretical value: 100%), and are incident angles that satisfy the Bragg diffraction condition. By setting θ _in and the grating inclination φ, the efficiency of the diffracted light of a specific order (particularly, + 1st order or −1st order) can be set.

  That is, in the light beam splitting element 100 shown in FIGS. 1, 2, and 3, the incident light beam is set by setting the grating inclination φ of the first hologram 1 and the second hologram 2 to be the same (satisfying the Bragg diffraction condition). The first diffracted deflected light 10b diffracted from 10 can be re-diffracted with high efficiency into the second diffracted deflected light 20b parallel to the incident optical axis 10 (first transmitted straight traveling light 10a).

  Next, the operation principle of the optical function of the hologram element that can be used for the above light beam splitting element will be described.

  FIG. 5 shows a schematic configuration of a deflecting hologram element using a holographic polymer dispersed liquid crystal (HPDLC: Holographic Polymer Dispersed Liquid Crystal).

  In the polarization hologram element 1 (2), a region 1a showing optical anisotropy (birefringence) and a region 1b showing optical isotropy are periodically formed between a pair of substrates 11, 12 (21, 22). ing. As the functional operation, for example, as shown in FIG. 6 (a), the polarization direction incident on the element is s-polarized light (here, perpendicular to the periodic array direction which is the direction perpendicular to the paper surface), and the isotropic region 1b When the refractive index n and one refractive index no of the birefringent region 1a are n = no, light is transmitted as it is. Further, as shown in FIG. 6B, the incident polarization direction is p-polarized light (here, parallel to the periodic arrangement direction which is the horizontal direction on the paper surface), and the refractive index n and birefringence of the isotropic region 1b. When the other refractive index ne of the region 1a is n ≠ ne, the light is diffracted. In this manner, transmission and diffraction are selected depending on the polarization direction of incident light. In the example shown in FIG. 6, p-polarized light is diffracted and s-polarized light is transmitted. However, depending on the refractive index of the periodic structure, p-polarized light may be transmitted and s-polarized light may be diffracted.

  Further, in FIG. 5, the periodic structure of the optically anisotropic region 1a and the optically isotropic region 1b is shown as being sandwiched between the substrates 11, 12 (21, 22), but is not limited thereto. The film may be formed on a single substrate or not on the substrate.

Here, the polarization hologram element shown in FIGS. 5 and 6 is a volume type refractive index modulation hologram. As described above, the diffraction efficiency is the product Δn _H · T of the hologram refractive index modulation amount Δn _H and the thickness T. Depending on the refractive index modulation amount Δn _{H of the} region exhibiting optical anisotropy in the specific polarization direction and the region exhibiting optical isotropy, the thickness T (film thickness or cell gap) of the periodic structure of the hologram element The diffraction efficiency can be set as appropriate. The grating inclination φ shown in FIG. 5 is a vector perpendicular to the periodic structure, and the relationship is 45 ° <φ <135 ° with the periodic structure arrangement plane as a reference (0 °).

  Regarding the temperature dependency of the hologram element, the refractive index of a substance existing in the hologram periodic structure (two regions having different refractive indexes, for example, a birefringent region and an isotropic region) is generally temperature dependent. When the environmental temperature changes, it is difficult to always maintain a constant refractive index. This change in refractive index due to temperature leads to fluctuations in diffraction efficiency and a decrease in polarization selectivity, which is a serious problem in practical use in the configuration of the light beam splitting element of the present invention. Here, the polarization selectivity is defined as the ratio between the diffraction efficiency of s-polarized light and the diffraction efficiency of p-polarized light. For example, when the light beam splitting element as in the present invention is applied to a projection image device such as a projector, the change in the splitting efficiency from the light beam splitting element is reflected as unevenness in intensity in the projected image, which may lead to a decrease in contrast. Further, when applied to an electrophotographic image forming apparatus such as a laser printer, the change in the division efficiency affects each dot of the printed image, which may lead to problems such as fine line collapse and color unevenness.

Next, the temperature dependence of the hologram element will be described. FIG. 7 shows the relationship between the refractive index modulation amount Δn _H of the volume type refractive index modulation hologram and the diffraction efficiency. The refractive index modulation amount Δn _H shown here is a difference in height of the refractive index distribution inside the hologram element shown in FIGS. 4 and 5, but Δn _H is | no−n | for simplicity of explanation. Or | ne−n |. The diffraction efficiency as [Delta] n _H increases rises, [Delta] n _H _max when [Delta] n _H is maximum, becomes theoretically diffraction efficiency of 100%, the diffraction efficiency [Delta] n _H exceeds the maximum slide into reduced.

  FIG. 8 is a characteristic diagram showing the general temperature dependence of the refractive index n of the isotropic region 1b and the refractive indexes no and ne of the birefringent region 1a. As shown in FIG. 8, as the temperature rises, the absolute values of the refractive indexes n, no, and ne change, and | no-n | and | ne-n | change relatively.

As described above, along with the change in the refractive index due to the temperature rise, the diffraction efficiency of the hologram element greatly varies depending on the temperature. That is, when the maximum diffraction efficiency is set, Δn _H decreases with increasing temperature, and the diffraction efficiency tends to decrease (arrow in FIG. 7). Here, in order to generally obtain high diffraction efficiency, Δn _H must be large to some extent. Therefore, in order to obtain high diffraction efficiency, it is preferable to set | ne−n | as Δn _H.

As described above, the diffraction efficiency of the hologram element depends on the product Δn _H · T of the refractive index modulation amount Δn _H and the thickness (hologram layer) T. Since the film thickness T is held by a spacer or a curable material, the change due to temperature rise is small. That is, it is considered that the fluctuation of the diffraction efficiency due to the temperature rise is greatly influenced by the temperature change of the refractive index modulation amount Δn _H. The magnitude of the refractive index modulation amount depends on the hologram material to be used and the manufacturing method, but generally it is about 0.04 for a hologram using a photopolymer, and a liquid crystal material exhibiting high birefringence is used. In a conventional liquid crystal hologram, it is about 0.15. The refractive index modulation amount can be selected to some extent depending on the material, and a larger refractive index modulation amount is advantageous for obtaining high efficiency.

The temperature characteristics of the light beam splitting element will be described. When the refractive index modulation amount is constant in a constant temperature environment (for example, room temperature), the relationship between the diffraction efficiency and the transmittance of the volume type refractive index modulation hologram element and the film thickness is as shown in FIG. As described above, the volume type refractive index modulation hologram element theoretically has a maximum diffraction efficiency of 100%, and the relationship between the diffraction efficiency and the transmittance is 100% as a whole. The film thickness (cell gap) of the hologram layer at which a maximum diffraction efficiency of 100% is obtained is T ₂ , the diffraction efficiency is 50% (transmittance is 50%), and the film thickness (cell gap) of the hologram layer is T ₁ . The _{T 1} = T 2/2. As shown in FIG. 10, the diffraction efficiency and the transmittance change corresponding to the film thickness like a sine curve and a cosine curve.

  Here, when polarization hologram elements having the same hologram layer thickness (cell gap) are arranged in multiple stages as the first hologram 1 and the second hologram 2, and the incident polarization direction is parallel to the arrangement direction of the hologram periodic structure The light beam splitting element will be described with reference to FIGS.

As shown in FIG. 10, in T ₂ where the film thickness (cell gap) of the hologram layers 13 and 23 of the element obtains the maximum diffraction efficiency, all light is diffracted by the first hologram element 1 and the second hologram Re-diffracted by element 2. That is, the first transmitted straight light is not generated, only the optical axis is shifted, and the light beam is not divided.

Further, as shown in FIG. 11, in T ₁ where the film thickness (cell gap) of the hologram layers 13 and 23 of the element obtains half of the maximum diffraction efficiency, the first hologram element 1 Although the light beam is equally divided into the first diffracted light beam 10b, the second diffracted light beam is also divided evenly in the second hologram element 2, so that the light emitted from the elements 1 and 2 arranged in multiple stages is three. It becomes a luminous flux and the intensity varies.

  A configuration in which holograms having different hologram layer thicknesses (cell gaps) are arranged in multiple stages as the first hologram 1 and the second hologram 2 will be described with reference to FIG.

In this configuration, the incident polarization direction is parallel to the arrangement direction of the hologram periodic structure, and the film thickness of the hologram layer 13 is set to T ₁ (T ₂ / T) as shown in FIG. 12 for the first hologram element 1 and the second hologram element 2. 2), when the thickness of the hologram layer 23 and _{T 2,} the first diffraction efficiency of the hologram element 1 is 50%, the transmittance becomes 50%, the diffraction efficiency of the second hologram element 2 is 100%, transmittance 0%. That is, as shown in FIG. 13, the first transmissive straight light 10a and the first diffracted deflected light 10b are output from the first hologram element 1, the first diffracted deflected light 10b is diffracted by the second hologram element 2, and the second Output as diffracted deflection light 20b. In the light beam splitting element 100 having this configuration, the two light beams can be split evenly at a rate of 50% for the second diffracted deflection light 20b and 50% for the efficiency of the first transmitted straight light 10a.

Here, in order to explain the reduction in variation of the splitting efficiency due to temperature in the configuration of the light beam splitting element as described above, the relationship between Δn _H · T and the diffraction efficiency is further shown in FIGS. 13 and 14 regarding the temperature characteristics of the hologram element. First hologram 1 of the thickness of the hologram layer 13 is T _1, the change in the diffraction efficiency thickness of the hologram layer 23 by the second temperature increase of the hologram 2 of T ₂ indicated by the arrow. It is assumed that the refractive index modulation amount Δn _H is constant regardless of the film thickness T. Those shown in FIG. 13, the first diffraction efficiency of the hologram 1 has set the thickness T ₁ of the hologram layer 13 to be 50%, the film of the hologram layer 23 in which the second hologram 2 is the diffraction efficiency is 100% than the thickness Tmax, it is set to a thickness T ₂ which is reduced a little thickness. Further, in the example shown in FIG. 14, the film thickness T ₁ of the hologram layer 13 is set so that the diffraction efficiency of the first hologram 1 is 50%, and the hologram layer 23 in which the diffraction efficiency of the second hologram 2 is 100%. than the film thickness Tmax, is set to the film thickness T ₂ with an increased a little thickness.

  In the case shown in FIG. 13, the diffraction efficiency of both the first hologram 1 and the second hologram 2 is lowered due to the temperature rise. On the other hand, in FIG. 14, the diffraction efficiency of the first hologram 1 is reduced due to the temperature rise, but the diffraction efficiency of the second hologram 2 is once increased and then decreased.

  From FIG. 13 and FIG. 14, the film thickness T of the hologram is set to be smaller than the film thickness Tmax for obtaining the maximum diffraction efficiency. Thus, it can be seen that the diffraction efficiency once increases and decreases as the temperature rises.

Therefore, in the configuration in which the first hologram 1 and the second hologram 2 having hologram layers having different film thicknesses (cell gaps) are arranged in multiple stages, the film thickness T ₁ of the first hologram 1 is a film thickness that obtains the maximum diffraction efficiency. less than T _max, the thickness _{T 2} of the second hologram 2 is set larger than the thickness _{T max} to obtain maximum diffraction efficiency. With this configuration, it is possible to cancel the decrease in the diffraction efficiency of the first hologram 1 and the increase in the diffraction efficiency of the second hologram 2 due to a temperature increase. Therefore, fluctuations due to the temperature of the second diffracted deflected light 20b in the divided light beam are suppressed, and the temperature characteristics of the light beam dividing element are improved.

In addition, in the configuration shown in FIGS. 1, 2, and 12, in order to increase the efficiency of the divided light beam, first, the diffraction efficiency for dividing the light beam substantially equally by the first hologram 1 is obtained. This can be realized by configuring the hologram layers of the first hologram 1 and the second hologram 2 so as to obtain a high diffraction efficiency. That is, it means that the diffraction efficiency of the second hologram 2 should be higher than the diffraction efficiency of the first hologram 1, and the higher the diffraction efficiency is, the closer to _{Tmax at} which the maximum diffraction efficiency can be obtained. Therefore, the difference | T _max −T ₂ | between the film thickness of the hologram layer 23 of the second hologram 2 and T _max for obtaining the maximum diffraction efficiency is the film thickness T ₁ of the hologram layer 13 of the first hologram 1. difference in _{T max} of the maximum diffraction efficiency is obtained _{| T} max -T ₁ | can be set high efficiency of split light beams with a smaller than.

Furthermore, from the relationship between the diffraction efficiency and the film thickness in FIG. 9, the film thickness T ₁ of the hologram layer 12 of the first hologram element 1 is set to approximately half the film thickness T ₂ of the hologram layer 23 of the second hologram element 2. Thus, the intensities of the divided light beams can be set to be approximately equal.

Here, in the above description in which the temperature characteristic of the diffraction efficiency is set by the film thickness T (element cell gap) of the hologram, it is assumed that the refractive index modulation amount Δn _H of the hologram is constant. Actually, a substantially constant refractive index modulation amount Δn _H can be obtained by fixing the material used for the hologram and the manufacturing conditions.

Further, as shown in FIGS. 13 and 14, the diffraction efficiency of the hologram is related to Δn _H · T. Therefore, in the above description, the film thickness T is constant, and the diffraction efficiency of the hologram is controlled by the refractive index modulation amount Δn _H. Temperature characteristics can also be set. The refractive index modulation amount Δn _H of the hologram can be adjusted to some extent depending on the material and production conditions.

Even if the first hologram element and the second hologram element having different film thickness T and refractive index modulation amount Δn _H are used, there is no problem as long as the temperature characteristics can be improved as a light beam splitting element.

  Next, the schematic configuration of the light beam splitting element according to the embodiment of the present invention is shown in FIGS. In the configuration of this embodiment, the first holographic element 1, the second holographic element 2, and the holographic element 3 are arranged, and the first transmissive straight light 10 a obtained by dividing the third holographic element 3 by the first hologram 1. Is adjusted (temperature characteristic compensation). The first transmitted straight light 10a passes through the third hologram element 3 and is output as the third transmitted straight light 30a.

  In FIG. 15, the arrangement order is the first hologram 1, the second hologram 2, and the third hologram 3 from the incident light side. However, if the light intensity of the divided first transmitted straight light 10 a can be adjusted, the second hologram 2. And the third hologram 3 may be arranged on the incident side, and the arrangement order thereof may be either. Further, as long as the functions of the second hologram 2 and the third hologram 3 are the same, they may be in the same position.

  Here, in the light beam splitting element having the configuration in which the first hologram 1 and the second hologram 2 are arranged, the first diffracted deflected light among the first diffracted deflected light 10b and the first transmitted straight traveling light 10a split from the first hologram 1 is used. As described above, the temperature characteristic of the diffraction efficiency is canceled by setting the film thickness of the hologram elements 2 to be arranged 10b, and the temperature characteristic of the second diffracted deflected light 20b emitted from the second hologram 2 is improved. However, the temperature characteristics of the first transmitted straight light 10a are not improved. Therefore, by further arranging the third hologram element 3 on the optical axis of the first transmitted straight light 10a, the change in efficiency due to temperature can be improved even for the first transmitted straight light 10a.

As shown in FIG. 9, the film thickness T ₃ of the third holograms to be arranged is initially set so that the transmittance is approximately 100% or the diffraction efficiency is approximately 0%, and the transmittance decreases as the temperature rises. It is preferable to exhibit characteristics that increase efficiency. By additionally arranging the third hologram 3 having such characteristics, the transmitted light efficiency of the third hologram 3 is increased even if the transmittance of the first transmitted straight light 10a from the first hologram 1 increases due to the temperature rise. Canceled by the characteristics, a constant transmittance can be obtained regardless of the temperature.

Next, as temperature characteristics of the divided light flux of the hologram element in this embodiment, FIG. 17 and FIG. 18 show the relationship between Δn _H · T, transmittance, and diffraction efficiency. First hologram 1 having a thickness T _1, a second hologram having a thickness T _2, the transmittance and the change of the diffraction efficiency due to temperature rise of the third hologram of thickness T ₃ are indicated by arrows. Here, it is assumed that the refractive index modulation amount Δn _H is constant regardless of the film thickness T.

  In FIG. 17, the transmittance of the first hologram 1 increases and the transmittance of the second hologram 2 and the third hologram 3 decreases due to the temperature rise. In FIG. 18, the diffraction efficiency of the first hologram 1 decreases and the diffraction efficiency of the second hologram 2 and the third hologram 3 increases due to the temperature rise.

  As described above, from FIG. 17 and FIG. 18, the hologram film thickness T is set smaller than the film thickness Tmax for obtaining the maximum diffraction efficiency, so that the diffraction efficiency decreases due to the temperature rise, and the film thickness Tmax for obtaining the maximum diffraction efficiency. It can be seen that the diffraction efficiency increases as the temperature rises by setting a larger value. Further, in the vicinity of the film thickness of 2 Tmax, the diffraction efficiency is approximately 0% and the transmittance is approximately 100%, and it can be seen that the diffraction efficiency increases and the transmittance decreases with increasing temperature.

Therefore, the first hologram 1, the second hologram 2, the third hologram 3, and the hologram elements are arranged in multiple stages, and the film thicknesses of the holograms are set so that the temperature characteristics of the holograms are different. Thickness T ₁ of the first hologram 1 is smaller than the thickness T _max to obtain maximum diffraction efficiency, the thickness T ₂ of the second hologram 2 is set larger than the thickness T _max to obtain maximum diffraction efficiency, and a third hologram The film thickness T ₃ of ₃ is set larger than the film thickness T ₂ of the second hologram 2. With this configuration, the decrease in the diffraction efficiency of the first hologram 1 and the increase in the diffraction efficiency of the second hologram 2 due to the temperature increase are canceled, and further, the increase in the transmittance of the first hologram 1 and the third hologram due to the temperature increase. 3 is reduced. Therefore, fluctuations due to the temperature of the two split light beams are suppressed, and the temperature characteristics of the light beam splitting element are improved.

Here, since it is generally preferable for the optical element to have high light utilization efficiency, it is preferable that the light beam splitting element also has high splitting efficiency. Therefore, as shown in FIGS. 17 and 18, by setting the film thickness T ₃ of the third hologram to approximately twice the film thickness Tmax for obtaining the maximum diffraction efficiency, the transmittance of the third hologram 3 is initially approximately 100%. A very high efficiency is exhibited and a high light utilization efficiency can be obtained as a light beam splitting element. Next, a reference example of the present invention will be described with reference to FIG. FIG. 19 is a schematic diagram showing a schematic configuration of a light beam splitter in a reference example of the present invention. In the second embodiment, the first hologram element 1 and the second hologram elements 213 and 23 have the same film thickness (cell gap) T. The incident polarization direction is set so that the ratio of the intensity of the p-polarized component and the s-polarized component of the incident light is substantially equal. In such a configuration, it is necessary to adjust the setting of the incident polarization direction, etc., but since they have the same film thickness, they can be realized by an element by a production process under a certain condition, so that productivity can be improved.

As described above, in a configuration in which hologram elements having the same film thickness (cell gap) of the hologram layer are arranged in multiple stages, a hologram element having a film thickness (cell gap) T _max that maximizes diffraction efficiency is used. When the incident polarization direction is substantially parallel (p polarization) and perpendicular (s polarization) to the periodic structure of the hologram element, the light beam is not split.

  This depends on the light intensity of the incident polarization component (p-polarized light and s-polarized light) to the hologram element. When the polarization direction parallel to the arrangement direction of the periodic structure is incident as shown in FIG. Since there is almost no s-polarized component and almost a p-polarized component, the incident light hardly generates transmitted light related to the s-polarized component, and only diffracted light related to the p-polarized component is generated.

  Here, as shown in FIG. 21, when the polarization direction is slightly inclined from the direction parallel to the arrangement direction of the periodic structure, the intensity of the incident light is divided into an s-polarized component and a p-polarized component. As a proportion, the p-polarized component is larger than the s-polarized component, so that diffracted light related to the p-polarized component is generated more and transmitted light related to the s-polarized component is generated a little. Further, as shown in FIG. 22, when the polarization direction is inclined by 45 ° (135 °) from the direction parallel to the arrangement direction of the periodic structure, the intensity of the incident light is equal to the s-polarization component and the p-polarization component. Therefore, the diffracted light related to the p-polarized component and the transmitted light related to the s-polarized component are equalized. Thus, the ratio of the first diffracted polarized light and the first transmitted straight light of the first hologram element 1 depends on the ratio of the light intensity of the s-polarized component and the p-polarized component of the incident light. In addition, the average refractive index of the periodic structure also changes depending on the incident polarization direction, and is slightly caused by the ratio of the first diffracted deflected light and the first transmitted straight light.

  As shown in FIGS. 21 and 22, linearly polarized light having a polarization direction different from the arrangement direction of the periodic structure is incident, and the intensities of the p-polarized component and the s-polarized component are appropriately adjusted. Thus, the p-polarized component becomes the first diffracted polarized light 10b, and the s-polarized component becomes the first transmitted straight light 10a. Next, in the second hologram element 2, the p-polarization component becomes the second diffracted deflection light 20b, the s-deflection component becomes the second transmitted straight light 20a, and the light beam is split.

  Here, the incident polarization direction can be set by a general retardation plate, and a polarizing plate, a Glan-Thompson prism, a half-wave plate, or the like can be used. In addition, when polarized light such as LD is used as the light source, it can be set by rotating the light source.

As described above, the hologram element has temperature dependency. Therefore, the relationship between Δn _H · T and diffraction efficiency of the hologram element was examined by varying the film thickness of the hologram layer of the hologram element. 23, 24, and 25 show the relationship between Δn _H · T and the diffraction efficiency of the hologram element. A change in diffraction efficiency due to a temperature rise of each hologram element is indicated by an arrow. However, it is assumed that the refractive index modulation amount Δn _H is constant regardless of the film thickness T.

FIG. 22 shows a case where the film thicknesses (cell gaps) T ₁ and T ₂ of the hologram layers 13 and 23 of the first hologram element 1 and the second hologram element ₂ are the same as the film thickness T _max for obtaining the maximum diffraction efficiency. Show. In this case, the diffraction efficiency of all of the first hologram 1, the second hologram 2, and the third hologram 3 is reduced due to the temperature rise.

On the other hand, in FIG. 23, the film thicknesses T ₁ and T ₂ of the hologram layers 13 and 23 of the first hologram element 1 and the second hologram element ₂ are the same, and the film thickness T _max for obtaining the maximum diffraction efficiency. It shows a case where the relationship is larger than that. In this case, the diffraction efficiency of both the first hologram 1 and the second hologram 2 once increases due to the temperature rise and then decreases. From this, when the film thicknesses (cell gaps) T ₁ and T ₂ of the hologram layers of the first hologram element 1 and the second hologram element ₂ are substantially the same, the film thickness is equal to or less than the film thickness T _max for obtaining the maximum diffraction efficiency. In both the first hologram 1 and the second hologram 2, the diffraction efficiency is lowered due to the temperature rise, and the temperature characteristics of the light beam splitting element 100 are significantly deteriorated.

However, even when the film thicknesses T ₁ and T ₂ of the hologram layers of the first and second hologram elements 1 and ₂ are substantially the same, the film thicknesses T ₁ and T ₂ have the maximum diffraction efficiency as shown in FIG. Since the diffraction efficiency of both the first hologram 1 and the second hologram 2 increases once due to temperature rise and then decreases due to being larger than the film thickness T _max to be obtained, there is a slight fluctuation, but high diffraction efficiency over a wide temperature range. And the temperature characteristics of the light beam splitting element 100 are improved.

FIG. 24 shows a case where the film thicknesses (cell gaps) T ₁ and T ₂ of the hologram layers 13 and 23 of the first hologram element 1 and the second hologram element 2 have a magnitude relationship with respect to T _max. Show. In this case, the diffraction efficiency of the first hologram 1 decreases and the diffraction efficiency of the second hologram 2 increases due to the temperature rise. That is, the film thickness (cell gap) of the hologram layer is set so that the diffraction efficiencies are substantially the same, and the polarization direction of incident polarized light is set so that the intensity ratio of the p-polarized component and the s-polarized component is substantially equal. In the light beam splitting element having the configuration in which the first hologram 1 and the second hologram 2 are arranged in multiple stages, it is preferable to set the film thickness as follows. Thickness _{T 1} of the first hologram 1 of the hologram layer 13 is smaller than the thickness _{T max} to obtain maximum diffraction efficiency, the thickness _{T 2} of the second hologram 2 of the hologram layer 23 than the thickness _{T max} to obtain maximum diffraction efficiency By setting a large value, a decrease in the diffraction efficiency of the first hologram 1 and an increase in the diffraction efficiency of the second hologram 2 due to a temperature increase are canceled, and the temperature characteristics of the divided light beam (second diffraction deflection light) are improved.

  FIG. 25 shows an ideal relationship between the diffraction efficiency of the light beam splitting element 100 and the incident polarization direction in the configuration as shown in FIG. From FIG. 25, when the incident polarization direction is approximately 45 ° or approximately 135 ° (45 ° + 90 °) with respect to the arrangement direction of the periodic structure, the splitting balance of the light beam is approximately 50%, which depends on the application. However, it is possible to obtain characteristics that do not cause a problem as a general optical element. Specifically, from FIG. 25, the light flux balance is in the range of 40% to 60% in the range of 43 ° ± 3 ° with respect to the arrangement direction of the periodic structure of the incident polarization direction. There are no problems.

  In addition, when a quarter wave plate is used as a phase difference plate for setting the incident polarization direction, and circularly polarized light or elliptically polarized light is used, in the circularly polarized light, as shown in FIG. The intensity | strength of a polarization component is set equally and incident light can be divided | segmented equally. Even in elliptically polarized light, the ratio of the intensity of the p-polarized component and the s-polarized component can be set by appropriately setting the azimuth angle. In FIG. 27, the circularly polarized light is rotated counterclockwise, but the rotation direction may be either left or right. When circularly polarized light is incident in this way, the axis only needs to be set with respect to the polarization direction on the light source side, and setting of the polarization direction to the polarization hologram element becomes unnecessary.

  A schematic configuration of the light beam splitting element according to the second embodiment of the present invention is shown in FIGS. In this embodiment, the light amount adjusting means 4 is provided in the subsequent stage of the first hologram 2 and the third hologram 3. 28 and 29 are schematically illustrated separately from the hologram element, but may be integrated with the hologram element as long as a desired light beam can be adjusted and does not affect other light beams. Here, as the light amount adjusting means 4, a general ND filter, a phase difference plate, or the like can be used. Thus, when the light quantity adjustment means 4 is provided, the intensity | strength of the divided | segmented light beam can be set, respectively. That is, when the intensity of one light beam divided due to the temperature rise decreases, the intensity of the other light beam can be adjusted by the light amount adjusting means 4 so that the intensity of the divided light beam can be kept substantially the same, and the temperature characteristics are good. A beam splitting device can be realized.

  Here, as the hologram element used for the light beam splitting element 100 in the configuration of the present invention, as shown in FIG. 30A and FIG. 30B as long as it shows temperature dependence and the grating pitch and grating inclination can be set. As described above, those having a periodic structure composed of a region exhibiting optical anisotropy and a region exhibiting optical isotropy can be used. For example, the periodic structure can be combined with each other by forming a grating groove in an isotropic medium or birefringent medium and filling the isotropic medium or birefringent medium.

  The grating grooves having a periodic structure can be formed by photolithography and etching, cutting, forming technique, or the like. As the isotropic medium, a transparent resin such as a photopolymer, or an optical glass material such as quartz or BK7 can be used. However, it is not limited to this as long as it does not have birefringence. As the birefringent medium, a polymer birefringent film (polymer film), liquid crystal, or the like can be used.

  Examples of the method for forming the periodic structure include a general mask exposure method using a stepper on a hologram recording material, a direct drawing method using an electron beam, a direct drawing method using a laser beam, and a two-beam interference exposure method.

As the recording material, the following general photosensitive materials can be used. For example, dichromated gelatin, photoclock material, photothermoplastic, electro-optic crystal (eg, ferroelectric oxide: LiNbO ₃ , BaTiO ₃ crystal, etc.), photoresist, photopolymer, polymer liquid crystal and polymer dispersed liquid crystal and so on.

  In particular, a photopolymer having high versatility can record a refractive index modulation type hologram, so that high diffraction efficiency can be obtained, and since there is almost no graininess, a hologram with high resolution and low noise can be obtained. Photopolymers are composed of a wide variety of materials and can be broadly classified into photocrosslinking types and photopolymerization types. Some photopolymerization types require development and others do not. Materials that do not require a development step can be classified into (a) a polymer, a monomer, (b) a monomer, a monomer, (c) an inactive component (low molecule), and a monomer in terms of composition. Components (a) and (c) are selected so that a large refractive index difference is generated between the monomer polymerization material and the polymer or low molecular weight compound. (B) is composed of two types of monomers having different refractive indexes. (1) Monomer having different photopolymerizability, (2) Photopolymerizable and thermally polymerizable monomer, (3) Photoradical polymerizable and light. There are combinations of cationically polymerizable monomers.

  Among the materials described above, photopolymerizable photopolymers such as photopolymers and photoresists can be selected from a wide range of resolution, exposure sensitivity, and photosensitive wavelength band, have excellent environmental resistance, and have flexibility in film thickness and size. is there. Moreover, since the granularity is low, high diffraction efficiency and high transparency can be obtained as the characteristics of the hologram.

  In the case of a refractive index modulation type hologram having a high diffraction efficiency, the larger the difference in refractive index modulation of the periodic structure in the recorded hologram region, the smaller the optimum film thickness for obtaining high efficiency. Changes in diffraction efficiency depending on fluctuations and incident angles can be reduced. That is, it is possible to realize a hologram having a wide tolerance range with respect to wavelength variation and incident angle of the obtained high diffraction efficiency characteristics. Photosensitive materials that can increase the difference in refractive index modulation of the periodic structure include polymer birefringent films exhibiting birefringence, polymer liquid crystals, and polymer dispersed liquid crystals.

  A polymer birefringent film is a polymer film that has birefringence by stretching a polymer film and orienting polymer chains, and can be easily mass-produced with a stamper, etc. There is an advantage that an element can be manufactured. Examples of the polymer material for the stretched polymer film include, but are not limited to, polyolefins, polyacrylates, polycarbonate (PC), polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA), polystyrene, and the like. It is not a thing.

  The polymer liquid crystal and the polymer dispersed liquid crystal are compositions composed of any one or a mixture of a polymerizable liquid crystal, a non-polymerizable liquid crystal, a polymerizable monomer or a prepolymer, and a photopolymerization initiator. As the polymerizable liquid crystal monomer, a liquid crystal acrylate monomer or the like can be used, and as the non-polymerizable liquid crystal, a general liquid crystal having refractive index anisotropy can be used. The phase structure may be any of nematic, cholesteric, and smectic types.

  As the polymerizable monomer or prepolymer thereof, photopolymerization, photocrosslinkable monomers, oligomers, prepolymers and mixtures thereof can be used. In addition to the above, a thermal polymerization inhibitor, a plasticizer, and the like may be added.

  As the photopolymerization initiator, a known material can be used, and the addition amount varies depending on the absorbance of each material with respect to the wavelength of light to be irradiated, and is appropriately adjusted depending on the exposure conditions during replication.

  The composition comprising the above-described photosensitive material can form a periodic structure having a refractive index distribution that differs depending on the polarization direction by appropriately setting the exposure conditions (the amount of refractive index modulation in the periodic structure depends on the polarization direction). Different).

  Examples of the composition include a holographic polymer dispersed liquid crystal (HPDLC) in which a non-polymerizable liquid crystal and a photopolymerization initiator are dispersed in a polymer monomer, or a mixture of a polymerizable liquid crystal and a photopolymerization initiator. And photo-cured liquid crystal (PPLC: Photo-Polymerized Liquid Crystal).

  Next, a hologram element using HPDLC will be described as a hologram element that can be used in the light beam splitting element of the present invention. The case where an interference fringe is exposed to the above composition will be described. FIG. 33 shows a cross-sectional configuration of HPDLC before interference exposure. In this configuration, a composition 50 in which a non-polymerizable liquid crystal molecule, a polymerizable monomer or prepolymer, and a photopolymerization initiator (not shown) are uniformly mixed is sandwiched between two transparent substrates 51 and 52. FIG. 34 schematically shows a hologram formation process by phase separation, where FIG. 34A is a cross-sectional view showing an exposure state, FIG. 34B is a cross-sectional view when phase separation is performed after exposure, c) is a top view in the case of phase separation. As shown in FIG. 34 (a), the intensity distribution of the interference fringes is shown for the composition 30 in which the non-polymerizable liquid crystal molecules, the polymerizable monomer or prepolymer, and the photopolymerization initiator (not shown) are uniformly mixed. Interference exposure is performed in such a state. By this exposure, as shown in FIGS. 34 (b) and 34 (c), the monomer moves in the bright part of the interference fringe (phase separation between the polymer and the liquid crystal) and cures, and the liquid crystal remains in the dark part of the interference fringe, The liquid crystal is oriented in a specific direction by being pulled by the polymer cured in the bright part. Because of this orientation, one of the incident polarized light beams orthogonal to each other transmits almost no refractive index change. The polarization direction perpendicular to this is aligned with the direction in which the liquid crystal is aligned and the refractive index is large, so that the incident light is diffracted with a periodic refractive index change. Thus, HPDLC functions as a polarizing diffraction grating.

  In PPLC, a liquid crystal having a photopolymerizable sensitive group is sealed between a transparent electrode (ITO) and a substrate having an alignment layer for aligning liquid crystal to horizontally align the liquid crystal. When the interference fringes are exposed to this, liquid crystal molecules are polymerized and cured in the bright portions of the fringes. On the other hand, the liquid crystal molecules in the dark part of the stripe remain without being cured. Next, light is irradiated while applying a voltage between the transparent electrodes sandwiching the liquid crystal layer. At this time, the liquid crystal in the dark portion is oriented in the direction perpendicular to the substrate by applying a voltage and cured by light. As described above, the alignment of the liquid crystal has a horizontal / vertical periodic structure corresponding to the bright and dark interference fringes. When polarized light perpendicular to the diffraction grating recorded in this way is incident, even if there is horizontal / vertical orientation in one polarization direction (coincident with the minor axis direction of the horizontally aligned liquid crystal molecules), no change in refractive index is felt. Most of the incident light is transmitted, and in the direction perpendicular to this, the incident light almost diffracts with a change in the refractive index due to the horizontal / vertical alignment in line with the long axis direction of the horizontally aligned liquid crystal molecules.

  As described above, a polarization hologram having polarization selectivity can be produced by phase separation accompanying the polymerization reaction of the composition material, or a change in orientation due to the polymerization reaction and the external field.

  As a method for forming a hologram recording photosensitive material, a general solvent film forming method can be applied, and spin coating or dipping on a single substrate, capillary action or injection by vacuum into a cell composed of a counter substrate. There are methods.

  Hereinafter, the present invention will be described in more detail with reference to specific examples, reference examples, and comparative examples, but the present invention is not limited to the following examples.

Example 1
An antireflection film for blue light and red light is formed on one side of a 0.7 mm thick glass substrate, and a bead spacer having a diameter of about 4 μm to 12 μm is prepared, and each bead spacer corresponding to the hologram layer to be formed is mixed. Two glass substrates were bonded together with the agent. The adhesive was applied to two locations on the edge of the substrate on the surface opposite to the antireflection film forming surface.

  Next, a composition composed of a mixture of the following materials (1) to (5) is injected into the cell by a capillary method while being heated on a hot plate, and a composition layer that becomes a hologram layer having a thickness of about 5 μm to 20 μm is formed. Formed. In addition, since this composition was reactive to light having a shorter wavelength than green, it was handled in a dark room using red light.

(1) Nematic liquid crystal (Merck Δε> 0) 25 parts by weight (2) Urethane prepolymer (manufactured by Kyoeisha Chemical) 75 parts by weight (3) Diacrylate (manufactured by Kyoeisha Chemical) 10 parts by weight (4) Methacrylate (manufactured by Kyoeisha Chemical) 5 parts by weight (5) Bisacylphosphine oxide photopolymerization initiator (Ciba Geigy) 1 part by weight

When the above composition was injected into the cell and the properties thereof were examined, this composition was isotropic at room temperature.

  Next, a two-beam interference exposure system using a He—Cd laser having a wavelength of 442 nm was prepared. The laser light is divided and expanded to be parallel light, and interference fringes having a period of about 1 μm are generated corresponding to the interference fringes of two-beam interference. With the cell substrate heated, two-beam interference exposure was performed for about 1 minute to produce a liquid crystal hologram element. At this time, it was set so that the two light beams were incident after tilting about 7 degrees with respect to one incident optical axis.

  For evaluating the characteristics of the liquid crystal hologram element, the prepared element was irradiated with linearly polarized laser light having a wavelength of 655 nm, and the 0th-order light and the + 1st-order diffracted light intensity with respect to the incident light intensity were measured. The device is adjusted by using an ND filter so that the incident light intensity is about 5 mW, a linearly polarizing plate and a half-wave plate are arranged in the incident optical path, and the optical axis of the half-wave plate is rotated by 45 degrees, thereby providing an element. The incident polarization direction (p-polarized light, s-polarized light) can be switched. At this time, the p-polarized light was in a direction orthogonal to the interference fringes at the time of interference exposure, and the s-polarized light was in the direction of the interference fringes.

  For evaluating the characteristics of the liquid crystal hologram element, the produced element was irradiated with linearly polarized laser light having a wavelength of 655 nm, and the 0th-order light and the + 1st-order diffracted light intensity with respect to the incident light intensity were measured. The incident light intensity is adjusted using an ND filter so that the incident light intensity is about 5 mW, a linearly polarizing plate and a half-wave plate are arranged in the incident light path, and the optical axis of the half-wave plate is rotated 45 degrees to enter the element. The polarization direction (p-polarized light, s-polarized light) can be switched. At this time, the p-polarized light was in a direction orthogonal to the interference fringes at the time of interference exposure, and the s-polarized light was in the direction of the interference fringes.

  FIG. 33 shows the characteristics of diffraction efficiency in p-polarization of a liquid crystal hologram element having a film thickness of 5 μm to 20 μm. FIG. 33 also shows the theoretical value of the lattice structure designed by the above-described interference exposure system (Kogelnik's coupled wave theory). From the comparison of the theoretical value and the actual measurement value, it can be seen that the designed hologram structure is made. The maximum diffraction efficiency is obtained when the film thickness is 9 μm. When the film thickness is 9 μm or less, which obtains the maximum efficiency from the temperature characteristics of the diffraction efficiency of the hologram element shown in FIG. 34, the diffraction efficiency decreases as the temperature rises. It can be seen that the diffraction efficiency increases as the temperature rises when the film thickness is 9 μm or more. Thus, it can be seen that the temperature characteristic of the diffraction efficiency can be set by setting the film thickness.

(Reference Example 1)
A reference example of the light beam splitting element which is a premise of the present invention will be described.

  Using the two elements of the liquid crystal hologram thus produced, a beam splitting element was produced by arranging in multiple stages as shown in FIG. The incident polarization direction to the element was p-polarized light, and the distance between array elements was about 10 mm. The film thicknesses of the first hologram element and the second hologram element are set as appropriate, and the incident light of the first transmitted straight light (first light beam) and the second diffracted deflected light (second light beam) of the light beam splitting element with the film thickness set is set. The temperature characteristics of light utilization efficiency were evaluated.

(Comparative example of Reference Example 1)
As a hologram configuration in which the diffraction efficiency decreases as the temperature rises, a beam splitting element is formed by combining two holograms in which the film thickness of the first hologram 1 is 4.5 μm and the film thickness of the second hologram 2 is 9 μm. did. FIG. 35 shows the temperature characteristics of the light utilization efficiency of this light beam splitting element. As shown in FIG. 35, the efficiency of the first light beam and the second light beam is equally divided by about 50% near room temperature. However, as the temperature rises, the splitting efficiency changes. At around 50 ° C., the first light flux is about 60% and the second light flux is about 40%. As the temperature changes, the efficiency of both the first light flux and the second light flux changes, and the intensity difference between the light fluxes is as large as about 20%. In the case of such characteristics, it is necessary to correct the temperature characteristics of the first light beam and the second light beam, respectively.

(Reference Example 1-1)
Element for reducing the influence of light quantity fluctuation due to temperature As a hologram configuration in which the diffraction efficiency decreases and increases as the temperature rises, the first hologram 1 has a film thickness of 4.5 μm and the second hologram 2 has a film thickness. A beam splitting element in which two holograms having a size of 11.5 μm were combined was prepared. FIG. 36 shows the temperature characteristics of the light utilization efficiency of this light beam splitting element. In the vicinity of room temperature, the first light beam is divided by about 50% and the second light beam is divided by about 40%. In the splitting efficiency accompanying the temperature rise, the first light flux is about 60% around 50 ° C., but the second light flux hardly changes and remains about 40%. As described above, the variation of the second light flux due to the temperature is reduced. Compared with Comparative Example 1, the intensity difference of each light beam is the same, but only the temperature characteristic of the first light beam needs to be corrected, and correction is easy.

(Reference Example 1-2)
Element for reducing the influence of light quantity variation due to temperature and the difference in intensity of each light beam As a hologram configuration in which the diffraction efficiency decreases and increases with increasing temperature, the film thickness of the first hologram 1 is 4.9 μm, the second A light beam splitting element in which two holograms having a hologram film thickness of 11 μm were combined was prepared. FIG. 37 shows the temperature characteristics of the light utilization efficiency of this light beam splitting element. In the vicinity of room temperature, the first light beam is approximately 45% and the second light beam is approximately 48% and is divided approximately evenly. Here, the splitting efficiency changes as the temperature rises, but in the vicinity of 50 ° C., the first light flux is about 53% and the second light flux is about 45%, and the influence of the light amount fluctuation due to temperature is reduced. Further, in the temperature range of room temperature to 50 ° C., the efficiency change of the first light beam and the second light beam is about ± 5%, and the intensity difference of each light beam is about 10%. The difference in intensity is also small.

(Example)
Example for reducing the influence of light quantity variation due to temperature and the difference in intensity of each light beam Further, using the three elements of the hologram produced as described above, a light beam splitting element was produced in a multi-stage arrangement as shown in FIG. Similarly, the temperature characteristics of the light utilization efficiency with respect to the incident light of the third transmitted straight light (first light beam) and the second diffracted deflected light (second light beam) of the light beam splitting element were evaluated.

  As a hologram configuration in which the diffraction efficiency decreases and increases with increasing temperature, the film thickness of the first hologram 1 is 5 μm, the film thickness of the second hologram 2 is 12 μm, and the film thickness of the third hologram 3 is 18 μm. A light beam splitting element combining three holograms was prepared. The temperature characteristics of the light utilization efficiency are shown in FIG. In addition, a light beam splitting element formed by two hologram elements having a film thickness of the first hologram 1 of 5 μm and a film thickness of the second hologram 2 of 12 μm is prepared, temperature characteristics of light utilization efficiency are evaluated, and the results are shown. It is shown in 2.

  38 and Table 1, in the embodiment of the present invention, in the vicinity of the room temperature, the first light flux is approximately 43% and the second light flux is approximately 43% and is approximately equally divided. Here, the splitting efficiency hardly changes as the temperature rises, the first light flux is about 44% and the second light flux is about 44% near 50 ° C. Therefore, in the temperature range of room temperature to 50 ° C., the efficiency change of the first light beam and the second light beam is within about ± 1%, and it is not necessary to correct the temperature characteristics.

  Further, comparing the characteristics of Table 1 and Table 2, it can be seen that the temperature characteristics are further improved by providing the third hologram element.

(Reference Example 2)
Here, using the two elements of the hologram produced as described above, a beam splitting element was produced by arranging in multiple stages as shown in FIG. The incident polarization direction to the element was a polarization direction rotated by 45 ° from the p-polarized light, and the distance between the array elements was about 10 mm. The film thicknesses of the first hologram element 1 and the second hologram element 2 are set as appropriate, and the first transmitted straight light (first light beam) and the second diffracted deflected light (second light beam) are incident on the light beam splitting element having the film thickness set. The temperature characteristics of light utilization efficiency with respect to light were evaluated.

(Reference Example 2-Comparative Example 1)
As a hologram configuration in which the diffraction efficiency decreases as the temperature rises, a light beam splitting element was prepared by combining two holograms in which the film thickness of the first hologram 1 was 9 μm and the film thickness of the second hologram 2 was 9 μm. FIG. 39 shows the temperature characteristics of the light utilization efficiency of this light beam splitting element. Near the room temperature, the efficiency of the first light beam and the second light beam is equally divided by about 50%. However, as the temperature rises, the splitting efficiency changes, and in the vicinity of 50 ° C., the first light flux is about 52% and the second light flux is about 45%, and the intensity difference between each light flux is as large as 7%. The effect of characteristic fluctuation due to temperature is large.

(Reference Example 2-1)
Element for reducing the influence of light quantity variation due to temperature and the difference in intensity of each light beam As a hologram configuration in which the diffraction efficiency decreases and increases with increasing temperature, the film thickness of the first hologram 1 is 9 μm, A light beam splitting element in which two holograms having a film thickness of 10 μm were combined was prepared. FIG. 40 shows the temperature characteristics of the light utilization efficiency of this light beam splitting element. Near the room temperature, the efficiency of the first light beam and the second light beam is equally divided by about 50%. However, as the temperature rises, the splitting efficiency changes slightly. At around 50 ° C., the first luminous flux is about 52% and the second luminous flux is about 47%. The intensity difference between the luminous fluxes is 5%. Compared to the above Reference Example 2-Comparative Example 1, the influence of the characteristic variation due to temperature was reduced.

(Reference Example 3)
Here, using the two elements of the hologram produced as described above, a beam splitting element was produced by arranging in multiple stages as shown in FIG. The incident polarization direction to the element was a polarization direction rotated by 45 ° from the p-polarized light, and the distance between the array elements was about 10 mm. The film thicknesses of the first hologram element 1 and the second hologram element 2 are set as appropriate, and the first transmitted straight light (first light beam) and the second diffracted deflected light (second light beam) are incident on the light beam splitting element having the film thickness set. The temperature characteristics of light utilization efficiency with respect to light were evaluated. The light amount adjusting means 4 was installed only after the first hologram element.

(Reference Example 3-Comparative Example 1)
As a hologram configuration in which the diffraction efficiency decreases and increases as the temperature rises, a beam splitting element that combines two holograms with the first hologram 1 having a film thickness of 8 μm and the second hologram 2 having a film thickness of 10 μm is prepared. did. FIG. 41 shows the temperature characteristics of the light utilization efficiency of this light beam splitting element. Near the room temperature, the efficiency of the first light beam and the second light beam is divided by 52% and 46%, respectively. As the temperature rises, the splitting efficiency hardly changes. In the vicinity of 50 ° C., the first light flux is about 56% and the second light flux is about 43%. However, the difference in intensity of each light beam is as large as 6 to 13% in the vicinity of room temperature to 50 ° C.

(Reference Example 3)
Element for reducing the influence of light quantity variation due to temperature and intensity difference of each light beam As a hologram configuration in which the diffraction efficiency decreases and increases as the temperature rises, the first hologram has a film thickness of 8 μm and the second hologram 2 Two holograms having a film thickness of 10 μm were combined, and a light beam splitting element in which an ND filter having a transmittance of 85% was installed as the light quantity adjusting means 4 after the first hologram element 1 was prepared. FIG. 42 shows the temperature characteristics of the light utilization efficiency of this light beam splitting element. Near the room temperature, the efficiency of the first light beam and the second light beam is equally divided by about 45%. As the temperature rises, the splitting efficiency hardly changes. In the vicinity of 50 ° C., the first luminous flux is about 47% and the second luminous flux is about 43%. In the vicinity of room temperature to 50 ° C., the intensity difference of each light beam is as small as ± 2%. Reference Example 3 Compared with Comparative Example 1, the intensity difference between the light beams was small.

  As described above, in the configuration of the light beam splitting element that combines the holograms having different temperature characteristics, the light beam splitting element in which the variation in the splitting efficiency characteristic due to the temperature change is suppressed by setting the temperature characteristic of the hologram by the film thickness. It was confirmed that it was realized.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims for patent.

  The present invention can be used for an optical scanning device, an image forming apparatus, a projection image forming apparatus, and the like used for a laser printer, a digital copying machine, a plain paper fax machine, and the like.

It is a schematic diagram which shows schematic structure of the light beam splitting element used as the premise of this invention. It is a schematic diagram which shows schematic structure of the light beam splitting element used as the premise of this invention. It is a schematic diagram which shows schematic structure of the light beam splitting element used as the premise of this invention. It is a schematic diagram which shows the model of the cross-section of a volume hologram element. It is a schematic diagram which shows the model of the cross-section of a hologram element. It is a typical sectional view showing the composition of a hologram element. It is a schematic diagram which shows the functional operation | movement of a hologram element. Is a graph showing the relationship of the refractive index modulation [Delta] n _H and the diffraction efficiency of the volume type refractive index modulation hologram. FIG. 6 is a characteristic diagram showing general temperature dependence of the refractive index n of an isotropic region and the refractive indexes no and ne of a birefringent region. It is a figure which shows the relationship between the diffraction efficiency of a volume type refractive index modulation hologram element, the transmittance | permeability, and a film thickness. It is a schematic diagram showing a light beam splitting element in which polarization hologram elements having the same hologram layer thickness are arranged in multiple stages as a first hologram and a second hologram. It is a schematic diagram showing a light beam splitting element in which polarization hologram elements having the same hologram layer thickness are arranged in multiple stages as a first hologram and a second hologram. It is a schematic diagram which shows schematic structure of the light beam splitting element in embodiment of this invention. FIG. 6 is a characteristic diagram showing a relationship between Δn _H · T and diffraction efficiency. It is a characteristic diagram showing the relationship between the diffraction efficiency [Delta] n H _· T. It is a schematic diagram which shows schematic structure of the light beam splitting element in embodiment of this invention. It is a schematic diagram which shows schematic structure of the light beam splitting element in embodiment of this invention. It is a characteristic diagram showing the relationship between the diffraction efficiency [Delta] n H _· T in the embodiment of the present invention. It is a characteristic diagram showing the relationship between the diffraction efficiency [Delta] n H _· T in the embodiment of the present invention. It is a schematic diagram which shows schematic structure of the light beam splitting element used as the premise of this invention. It is a schematic diagram which shows a mode that the light of the polarization direction parallel to the arrangement direction of a periodic structure injects into the hologram element of the light beam splitting element concerning embodiment of this invention. It is a schematic diagram which shows a mode that a polarization direction inclines a little from the direction parallel to the arrangement direction of a periodic structure in the hologram element of the light beam splitting element concerning embodiment of this invention. It is a schematic diagram which shows a mode that the polarization direction inclines 45 degrees from the direction parallel to the arrangement direction of a periodic structure in the hologram element of the light beam splitting element concerning embodiment of this invention. FIG. 6 is a characteristic diagram showing a relationship between Δn _H · T of a hologram element and diffraction efficiency. FIG. 6 is a characteristic diagram showing a relationship between Δn _H · T of a hologram element and diffraction efficiency. FIG. 6 is a characteristic diagram showing a relationship between Δn _H · T of a hologram element and diffraction efficiency. It is a figure which shows the ideal relationship between the light utilization efficiency of a light beam splitting element, and an incident deflection direction. It is a figure which shows a mode that the light beam deflected by the circular deflection | deviation or the elliptical deflection using the quarter wavelength plate as a phase board was entered into the light beam splitting device concerning embodiment of this invention. It is a schematic diagram which shows schematic structure of the light beam splitting element in 2nd Embodiment of this invention. It is a schematic diagram which shows schematic structure of the light beam splitting element in 2nd Embodiment of this invention. It is a schematic diagram which shows an example of the hologram element used for this invention. It is a schematic diagram which shows the cross-sectional structure before the interference exposure of the liquid crystal hologram element used for this invention. The hologram formation process by phase separation is shown, (a) is a schematic sectional view during exposure, (b) is a schematic sectional view in a phase-separated state, and (c) is a schematic top view in a phase-separated state. is there. It is a characteristic view which shows the characteristic of the diffraction efficiency in p deflection | deviation of the liquid crystal hologram element with a film thickness of 5 micrometers-20 micrometers. It is a characteristic view which shows the temperature characteristic of the diffraction efficiency of a liquid crystal hologram element with a film thickness of 5 micrometers-18 micrometers. It is a figure which shows the temperature characteristic of the light utilization efficiency of the light beam splitting element which combined the two holograms with which the film thickness of the 1st hologram was 4.5 micrometers and the film thickness of the 2nd hologram was 9 micrometers. It is a figure which shows the temperature characteristic of the light utilization efficiency of the light beam splitting element which combined the two holograms whose film thickness of the 1st hologram was 4.5 micrometers, and whose film thickness of the 2nd hologram was 11.5 micrometers. It is a figure which shows the temperature characteristic of the light utilization efficiency of the light beam splitting element which combined the two holograms with which the film thickness of the 1st hologram was 4.9 micrometers and the film thickness of the 2nd hologram was 11 micrometers. It is a figure which shows the temperature characteristic of the light utilization efficiency which concerns on the Example of this invention, The film thickness of the 1st hologram was 5 micrometers, the film thickness of the 2nd hologram was 12 micrometers, and the film thickness of the 3rd hologram was 18 micrometers. . It is a figure which shows the temperature characteristic of the light utilization efficiency of the light beam splitting element which combined the two holograms with which the film thickness of the 1st hologram was 9 micrometers and the film thickness of the 2nd hologram was 9 micrometers. It is a figure which shows the temperature characteristic of the light utilization efficiency of the light beam splitting element which combined the two holograms with which the film thickness of the 1st hologram was 9 micrometers and the film thickness of the 2nd hologram was 10 micrometers. It is a figure which shows the temperature characteristic of the light utilization efficiency of the light beam splitting element which combined the two holograms whose film thickness of the 1st hologram was 8 micrometers, and whose film thickness of the 2nd hologram was 10 micrometers. Temperature characteristics of light use efficiency of a beam splitting element in which two holograms having a film thickness of the first hologram of 8 μm and a film thickness of the second hologram 2 of 10 μm are combined and a light amount adjusting means is provided after the first hologram element 1 FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 1st hologram element, 2nd hologram element, 3rd hologram element, 4, Light quantity adjustment means, 11, 12, 21, 22, 31, 32 Substrate, 13, 23, 33 Hologram layer, 100 Light beam splitting element

Claims (8)

  It is a light beam splitting element comprising a combination of two or more hologram elements having a periodic structure composed of a region exhibiting optical anisotropy and a region exhibiting optical isotropy, and having different temperature characteristics of transmitted light or diffracted light. The first hologram element, the second hologram element, and the third hologram element are arranged with respect to the light incident side, and light is divided by transmission and diffraction of the first hologram element. Transmitted light is applied to the third hologram element, diffracted light of the first hologram element is applied to the second hologram element, and the optical axis of the divided light is adjusted by transmission and diffraction of the second hologram element. The light intensity of the split transmitted light from the first hologram element is adjusted by the transmission of the third hologram element, and the incident light beam is divided into two or more light beams and emitted. Light beam splitting element according to symptoms.   The light beam splitting element according to claim 1, wherein the temperature characteristic of the transmitted light or diffracted light of the hologram element is set by the film thickness of the periodic structure of the hologram.   The light beam splitting element according to claim 1, wherein the temperature characteristic of the transmitted light or diffracted light of the hologram element is set by a refractive index modulation amount amplitude generated by a periodic structure of the hologram. The film thicknesses of the first hologram element, the second hologram element, and the third hologram element are T ₁ , T ₂ , and T ₃ , respectively. 4, wherein T ₁ is smaller than T ₂ , T ₃ is larger than T ₂ , and Tmax is between T ₁ and T _2. The light beam splitting element described. 5. The light beam splitting element according to claim 4, wherein the film thickness T3 of the _third hologram element is approximately twice the film thickness Tmax of the hologram element. 5. The light beam splitting element according to claim 4, wherein the film thicknesses T < b > 1 and T < b > 2 of the periodic structure of the first hologram element and the second hologram element have a relationship of | Tmax−T1 |> | Tmax−T2 | . The thickness T ₁ of the periodic structure of the first hologram element, beam splitting element according to claim 4 or 6, characterized in that a substantially half thickness T ₂ of the periodic structure of the second hologram element.   The hologram element has a periodic structure in which a composition comprising a non-polymerizable liquid crystal, a polymerizable monomer or prepolymer, and a photopolymerization initiator is held between a pair of transparent substrates, and the composition is more than two luminous fluxes. 2. A polymer-dispersed liquid crystal hologram element in which a periodic phase separation structure of a layer mainly composed of a polymer and a layer mainly composed of a non-polymerizable liquid crystal is formed by multibeam interference exposure. The light beam splitting element according to any one of 1 to 7.

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