JP4557022B2 - Laminated phase difference plate, projection type image device - Google Patents

Description

  The present invention relates to a laminated phase difference plate formed by laminating a plurality of crystal plates and a projection type video apparatus using the laminated phase plate.

Conventionally, a laminated retardation plate as disclosed in Patent Document 1 is known as an optical element that is used in a liquid crystal projector or the like and aligns the polarization of incident light from a light source.
This laminated phase difference plate is composed of two phase difference plates made of a quartz substrate. The phase difference plate is bonded so that crystal optical axes (hereinafter referred to as optical axes) intersect.
This laminated retardation plate functions as a half-wave retardation plate and converts the polarization plane of incident light into a polarization plane rotated by 90 °. Depending on the light source, this incident light can be selected from any of the three-color wavelength band (approximately 400 nm to 700 nm), the blue wavelength band (approximately 400 nm to 500 nm), the green wavelength band (approximately 500 nm to 600 nm), and the red wavelength band (approximately 600 nm to 700 nm). It belongs to the wavelength band.
As disclosed in Patent Document 2, a liquid crystal projector or the like uses various optical elements to take out light in the above-mentioned plurality of wavelength bands from a light source, and gradation these light with a liquid crystal shutter, and then again these To project video information. A large number of retardation plates are used in the optical path constituted by these optical elements. The light incident on these retardation plates belongs to any one of the above-described wavelength bands. The above-mentioned wavelength band range is an example, and other ranges are set based on the design of the liquid crystal projector.

JP 2004-170853 A JP 2006-330282 A

  In the laminated phase difference plate disclosed in Patent Document 1, the thickness of the two phase difference plates is set to 100 μm as an optimum condition in the embodiment. Further, the cutting directions of the two retardation plates from the quartz crystal are both Z-cut, and the optical axis azimuth angles are set to 19 ° and 64 °, respectively. This design improves the polarization conversion efficiency in the wavelength range of 400 nm to 700 nm.

However, the above-described conventional laminated phase difference plate is insufficient for further demand for improvement in polarization conversion efficiency in the wavelength band of incident light. This polarization conversion efficiency indicates, for example, the rate of conversion in the case of polarization from P wave to S wave. If all P waves are polarized and converted to S wave, it is indicated as an ideal value of 1.00. The closer the polarization conversion efficiency is to the ideal value of 1.00, the smaller the amount of light that has passed through the laminated retardation plate, and the more suitable it is for producing a liquid crystal projector having a bright image.
In addition, laminated phase difference plates for incident light in various wavelength bands are used in liquid crystal projectors, and means that can improve the polarization conversion efficiency optimum for each wavelength band have been proposed in the past. Was not.

  The present invention pays attention to the above-mentioned problems, and provides a laminated retardation plate suitable for the wavelength band of light and a projection type image device using the laminated retardation plate, which has improved polarization conversion efficiency compared to the prior art. With the goal.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.
Application Example 1 A laminated retardation plate according to Application Example 1 includes a first retardation plate having a phase difference Γ′a and a second retardation plate having a phase difference Γ′b with respect to light having a wavelength λ. Each optical axis is stacked so as to intersect, and is converted into linearly polarized light obtained by rotating the polarization plane of linearly polarized light that is incident in the wavelength range of λ1 to λ2 (where λ1 <λ <λ2) by 90 degrees, and then emitted. It is a laminated phase difference plate, wherein the first phase difference plate and the second phase difference plate are formed from a Y-cut quartz substrate, and the polarization plane of the incident linearly polarized light and the optical of the first phase difference plate The optical axis azimuth θa is the angle formed with the axis, and the optical axis azimuth θb is the angle formed between the polarization plane of the incident linearly polarized light and the optical axis of the second retardation plate. The relationship between the angle θa and the optical axis azimuth angle θb satisfies θb = θa + α, 0 ° <θa <45 °, and 40 ° <α <50 °. When the refractive index of ordinary light of the first retardation plate is Noa, the refractive index of extraordinary light is Nea, and the thickness is da, the phase difference Γ′a of the first retardation plate and polarization conversion Efficiency Ta is
Γ′a = 2 × π × da × (Nea-Noa) / λ,
Ta = 4 × (sin ² θa) × (cos (2θa)) × (sin ² (Γ′a / 2))
When the refractive index of ordinary light of the second retardation plate is Nob, the refractive index of extraordinary light is Neb, and the thickness is db, the phase difference Γ′b of the second retardation plate is The polarization conversion efficiency Tb is
Γ′b = 2 × π × db × (Neb−Nob) / λ,
Tb = 4 × (sin ² θb) × (cos (2θb)) × (sin ² (Γ′b / 2))
And the phase difference Γ′a and the phase difference Γ′b are
Γ′a = Γa + ΔΓa,
Γ′b = Γb + ΔΓb,
Γa = 180 °,
Γb = 180 °
And the relationship between ΔΓa and ΔΓb satisfies the following expression (1) .

The first retardation plate and the second retardation plate polish the quartz base material cut from the quartz raw stone, and the thickness of the substrate before bonding is processed to the target value of the designed thickness. The amount of deviation between the processed thickness value and the designed thickness target value affects the amount of deviation between the first retardation plate and the target value of the phase difference of the light transmitted through the second retardation plate. . If the phase difference of the second phase difference plate is controlled with respect to the amount of deviation from the target value of the phase difference of the first phase difference plate, the phase difference of the light beam transmitted through the upper air laminated phase difference plate after bonding The amount of deviation from the target value can be reduced, and the polarization conversion efficiency can be improved.
Therefore, the amount of deviation ΔΓb from the design target value of the phase difference Γb of the second phase difference plate is changed from the amount of deviation ΔΓa of the phase difference Γa of the first phase difference plate from the design target value to the value of the second phase difference plate. A means for obtaining from the optical axis azimuth angle θb was found. By this means, when the retardation plates are bonded, the first retardation plate having a deviation amount ΔΓa from the design target value of the phase difference Γa and the deviation of the optimum phase difference Γb from the design target value. A second retardation plate having an amount ΔΓb can be laminated together. The laminated retardation plate obtained by this means cancels out the amount of deviation ΔΓa from the design target value of the phase difference Γa with the amount of deviation ΔΓb from the design target value of the phase difference Γb, and therefore has high polarization conversion efficiency. it can.

Application Example 2 In the laminated phase difference plate according to Application Example 1, when λ1 = 400 nm and λ2 = 700 nm, the thickness da of the first retardation plate is in the range of 24 μm to 31 μm , and The thickness db of the second retardation plate is in the range of 24 μm to 31 μm .

  The laminated phase difference plate in which the first retardation plate having the thickness in the range and the second retardation plate having the thickness in the range are bonded together by the method according to the application example has a wavelength of 400 nm to 700 nm. In the incident light in the region, it is possible to obtain a high polarization conversion efficiency as compared with the conventional laminated phase difference plate.

Application Example 3 In the laminated phase difference plate according to Application Example 1, when λ1 = 400 nm and λ2 = 500 nm, the thickness da of the first retardation plate is in the range of 21 μm to 26 μm , and The thickness db of the second retardation plate is in the range of 21 μm to 26 μm .

  The laminated retardation plate obtained by bonding the first retardation plate having the thickness in the range and the second retardation plate having the thickness in the range by the method according to the application example has a wavelength of 400 nm to 500 nm. In the incident light in the region, it is possible to obtain a high polarization conversion efficiency as compared with the conventional laminated phase difference plate.

Application Example 4 In the laminated phase difference plate according to Application Example 1, when λ1 = 500 nm and λ2 = 600 nm, the laminated phase difference plate according to the application example described above, The thickness da is in the range of 25 μm to 35 μm , and the thickness db of the second retardation plate is in the range of 25 μm to 35 μm .

  The laminated phase difference plate in which the first retardation plate having the thickness in the range and the second retardation plate having the thickness in the range are bonded together by the method according to the application example has a wavelength of 500 nm to 600 nm. In the incident light in the region, it is possible to obtain a high polarization conversion efficiency as compared with the conventional laminated phase difference plate.

Application Example 5 In the laminated phase difference plate according to Application Example 1, when λ1 = 600 nm and λ2 = 700 nm, the laminated phase difference plate according to the application example described above, The thickness da is in the range of 24 μm to 47 μm , and the thickness db of the second retardation plate is in the range of 24 μm to 47 μm .

  A laminated retardation plate obtained by bonding a first retardation plate having a thickness in the above range and a second retardation plate having a thickness in the above range by the method according to the application example has a wavelength of 600 nm to 700 nm. In the incident light in the region, it is possible to obtain a high polarization conversion efficiency as compared with the conventional laminated phase difference plate.

Application Example 6 A projection type video apparatus according to Application Example 6 is characterized in that at least one of the laminated retardation plates according to Application Examples 1 to 5 is used.

  In the projection type video apparatus using the laminated phase difference plate whose polarization conversion efficiency is improved as compared with the prior art, the light utilization efficiency is improved, and a brighter image can be displayed even if a light source having the same luminance is adopted. In particular, in a projection-type video apparatus that uses a combination of light sources in a plurality of different wavelength ranges, a phase difference plate having the highest polarization conversion efficiency can be used for each wavelength range of the light sources, so that the light utilization efficiency can be improved. .

  Hereinafter, embodiments of a laminated retardation plate according to the present invention will be described with reference to the drawings. In addition, the plate | board thickness of the laminated phase difference plate in each following embodiment, an optical axis azimuth, polarization conversion efficiency, etc. were obtained based on the following formula | equation (2), Formula (3), Mueller determinant, etc.

ここで、Γ：位相差、ｄ：板厚、Ｎｅ：異常光線屈折率、Ｎｏ：常光線屈折率、λ：波長、Ｔ：偏光変換効率、θ：光学軸方位角を表す。
上記の式により、５ｎｍ間隔の波長ごとに偏光変換効率を得て、偏光変換効率の理想値１．００との差を乖離値とした。目的とする波長領域において、それぞれの乖離値を累積して累積乖離値を得た。

Here, Γ: retardation, d: plate thickness, Ne: extraordinary ray refractive index, No: ordinary ray refractive index, λ: wavelength, T: polarization conversion efficiency, θ: optical axis azimuth.
From the above formula, polarization conversion efficiency was obtained for each wavelength of 5 nm intervals, and the difference from the ideal value 1.00 of the polarization conversion efficiency was defined as the deviation value. In the target wavelength region, the accumulated divergence values were obtained by accumulating the respective divergence values.

(First embodiment)
FIG. 1 is an explanatory diagram for explaining the laminated retardation plate of the first embodiment. FIG. 1 is a diagram illustrating polarization conversion of incident light, and FIG. 2 is a diagram illustrating an optical axis azimuth angle.
As shown in FIG. 1, the laminated phase difference plate 1 includes a first phase difference plate 10 and a second phase difference plate 20.
As shown in FIG. 2, the first retardation plate 10 and the second retardation plate 20 are bonded together so that the optical axes 11 and 21 intersect each other.

FIG. 3 shows a Poincare sphere of a half-wave retardation plate according to the present invention. Therefore, a method for minimizing the phase difference deviation of the half-wave retardation plate using the Poincare sphere will be described. First, the setting condition is the incident polarization plane: the horizontal direction in FIG.
First retardation plate: retardation Γa = 180 °
Optical axis azimuth; θa
Second retardation plate: retardation Γb = 180 °
Optical axis azimuth; θb
Then, the polarization state of the light transmitted through the first retardation plate and the second retardation plate can be considered as follows.

  The function of the half-wave retardation plate is to rotate the plane of polarization approximately 90 °, and this is represented by the Poincare sphere at coordinates P0 (S1, S2, S3) = (1, 0, 0). To the coordinate P2 (-1, 0, 0). Therefore, the start point is set as a coordinate P0 as an intersection of the S1 axis and the spherical surface. Next, the rotation axis R1 is set at a position where the S1 axis is rotated counterclockwise by 2θa. P0 is rotated clockwise by phase difference 180 ° with the R1 axis as the rotation axis, and the point reached is defined as P1. Next, the rotation axis R2 is set at a position obtained by rotating the S1 axis counterclockwise by 2θb. P1 is rotated in the clockwise direction by 180 degrees around the R2 axis as a rotation axis, and the point reached is defined as P2.

  According to the above, in order for P2 to reach (-1, 0, 0), the optical axis azimuth angle θa and the optical axis azimuth angle θb need only satisfy the following conditions. The phase difference α is set to ± 5 ° of the set value in consideration of the bonding accuracy.

FIG. 4 shows a view of the Poincare sphere of FIG. 3 as viewed from the S3 axis. The rotation axis R1 when moving from the coordinate P0 to the coordinate P1 is at a position rotated by 2θa from the S1 axis. The rotation axis R2 when moving from the coordinate P1 to the coordinate P2 is at a position rotated by 2θb from the S1 axis.
Therefore, the center of the Poincare sphere is O, the angle formed by the coordinates P0, P1, and the center O is ∠P0-O-P1, and the angle formed by the coordinates P1, the coordinates P2, and the center O is ∠P1-O-P2. Then,

  FIG. 5 is a diagram linearly representing the phase difference when the polarized light moves from the coordinate P0 to the coordinate P2 on the equator plane of the Poincare sphere in FIG. The equator plane from the coordinate P0 through the coordinate P1 to P2 should be represented by a curve, but is represented by a straight line for easy understanding. rx is a rotation radius when moving from the coordinate P0 to the coordinate P1 using the R1 axis as a rotation axis. Further, rz is a rotation radius when moving from the coordinate P1 to the coordinate P2 using the R2 axis as a rotation axis. In the first retardation plate processed so as to move from P0 to P1 with the radius of rotation r1 at the Poincare sphere, if the processing accuracy of the thickness of the retardation plate deviates from the design value, it cannot move to P1 but becomes P1x. . In the second retardation plate that is processed so as to move from P1 to P2 with the rotation radius rz, if P1 is processed so as to be P1z, P1−P1x = P1−P1z, and the position can be accurately moved to P2. A laminated retardation plate having a function of a half-wave retardation plate can be provided.

  If L = P1-P1x = P1-P1z,

式（８）及び式（９）より

From formula (8) and formula (9)

ポアンカレ球の半径をｋとすると

If the radius of the Poincare sphere is k

式（１０）、式（１１）、および式（１２）より

From Formula (10), Formula (11), and Formula (12)

上記より、ずれ量ΔΓｂは以下の式に導かれる。

From the above, the deviation amount ΔΓb is derived from the following equation.

  In the laminated phase plate in which a plurality of phase difference plates are combined and bonded, using Equation (1), phase difference plates having optimum phase differences ΔΓ can be combined. By selecting this formula (1), the phase difference as the laminated phase difference plate becomes the target value as described in the Poincare sphere, and the polarization conversion efficiency becomes the best.

FIG. 6 shows the thicknesses of the first retardation plate and the second retardation plate of the laminated retardation plate having the optimum phase difference obtained from the equation (1) in accordance with the equation (2) and the equation (3). As shown.
There are various such suitable combinations depending on the optical axis azimuth. Only when the optical axis azimuth angle θa is 22.5 °, the thickness of the two sheets does not depend on the optical axis azimuth angle θa, and the same thickness is always the optimum value.

  Table 1 shows the polarization conversion efficiency of a laminated phase plate in which a first retardation plate having a thickness T1 and a second retardation plate having a thickness T2 are bonded together. These are results obtained by combining the plate thicknesses under the conditions shown in FIG. F, G, and H are combined on a line indicating an optimum condition, and J and K are laminated phase plates that deviate from the line, that is, a combination that is not optimal. The polarization conversion efficiency loss indicates a ratio of a portion that does not reach the polarization conversion efficiency 1.00 shown by the gray area divergence range 56 in FIG. The larger this ratio, the lower the retardation of the laminated phase difference plate. Accordingly, the smaller the polarization conversion efficiency loss, the better. F, G, and H have higher polarization conversion efficiency because the polarization conversion efficiency loss is smaller than that of J and K. That is, the laminated phase difference plate combined using the condition along the solid line portion shown in FIG. 7, that is, the expression (1), can obtain high polarization conversion efficiency.

Next, an embodiment relating to a range of plate thicknesses suitable for wavelength dependency of the laminated phase plates optimally combined using Expression (1) will be described.
The laminated phase difference plate 1 shown in FIG. 1 is formed so that the thicknesses of the first phase difference plate 10 and the second phase difference plate 20 are in the range of 23.80 μm to 31.39 μm. The first retardation plate 10 and the second retardation plate 20 are formed with substantially the same thickness.
The first retardation plate 10 and the second retardation plate 20 are formed from a Y-cut quartz substrate in which the optical axes 11 and 12 exist along the plate surface.

In the laminated phase difference plate 1, the optical axis azimuth angle θa of the first phase difference plate 10 and the optical axis azimuth angle θb of the second phase difference plate 20 are expressed by Equations (2), (3), Mueller determinants, and the like. Is set.
The optical axis azimuth angle θa and the optical axis azimuth angle θb represent the angles formed by the optical axes 11 and 12 with respect to the horizontal vibration surfaces 13 and 14 of the incident light counterclockwise from the vibration surfaces 13 and 14.
Here, the settable range of the optical axis azimuth θa and the optical axis azimuth θb in the thickness range of the first retardation plate 10 and the second retardation plate 20 is exemplified.

表２は、第１の位相差板１０及び第２の位相差板２０の上記３種類の板厚における光学軸方位角θａ及び光学軸方位角θｂの設定可能範囲を示したものである。
表２に示すように、板厚が下限値の２３．８０μｍの場合には、光学軸方位角θａは、２１．７°〜２３．３°の範囲、光学軸方位角θｂは、６６．７°〜６８．３°の範囲である。
板厚が略中心値の２７．７３μｍの場合には、光学軸方位角θａは、１２．０°〜３３．０°の範囲、光学軸方位角θｂは、５７．０°〜７８．０°の範囲である。
板厚が上限値の３１．３９μｍの場合には、光学軸方位角θａは、２１．４°〜２３．６°の範囲、光学軸方位角θｂは、６６．４°〜６８．６°の範囲である。

Table 2 shows the settable ranges of the optical axis azimuth angle θa and the optical axis azimuth angle θb in the three types of thicknesses of the first phase difference plate 10 and the second phase difference plate 20.
As shown in Table 2, when the plate thickness is the lower limit of 23.80 μm, the optical axis azimuth θa is in the range of 21.7 ° to 23.3 °, and the optical axis azimuth θb is 66.7. It is in the range of ° to 68.3 °.
When the plate thickness is approximately 27.73 μm, the optical axis azimuth θa is in the range of 12.0 ° to 33.0 °, and the optical axis azimuth θb is 57.0 ° to 78.0 °. Range.
When the plate thickness is 31.39 μm, which is the upper limit, the optical axis azimuth θa is in the range of 21.4 ° to 23.6 °, and the optical axis azimuth θb is in the range of 66.4 ° to 68.6 °. It is a range.

The optical axis azimuth angle θb is a value obtained by adding α to the set value of the optical axis azimuth angle θa. The value of the optical axis azimuth angle θb is calculated by setting the angle α formed by the optical axis azimuth angle θa and the optical axis azimuth angle θb to 45 °.
The angle α formed by the optical axis azimuth angle θa and the optical axis azimuth angle θb is not limited to 45 °, and an angle different from 45 ° can be set by a combination of the plate thickness and the optical axis azimuth angle θa. is there.

  In the above configuration, the laminated phase difference plate 1 shown in FIG. 1 functions as a ½ wavelength phase difference plate. In this laminated phase difference plate 1, when the linearly polarized light 30 that is the P-polarized component of the incident light is incident, the phase of the linearly polarized light 30 is shifted by 180 °, so that the plane of polarization is rotated by 90 °, and the linearly polarized light that is the S-polarized component. Polarized light is converted into polarized light 40 and emitted.

  Here, the polarization conversion efficiency from the P-polarized component to the S-polarized component by the multilayered retardation plate 1 of the first embodiment will be described with respect to the result of comparison with the conventional multilayered retardation plate using the cumulative divergence value. To do.

FIG. 8 is a graph for explaining the accumulated divergence value. As shown in FIG. 8, the cumulative divergence value is obtained by obtaining the polarization conversion efficiency for each wavelength of the incident light at intervals of 5 nm and using the difference from the ideal value 1.00 of the polarization conversion efficiency as the divergence value. It is a value accumulated over the entire corresponding wavelength region.
For example, in FIG. 8, when the wavelength is 650 nm, the polarization conversion efficiency is 0.97, and the deviation value 55 is 1.00−0.97 = 0.03. The cumulative divergence value is obtained over the entire corresponding wavelength region as described above, and the result is accumulated.
The cumulative divergence value represents the approximate area of the divergence range 56 in the graph of FIG. 8, and the smaller the value, the higher the polarization conversion efficiency.

FIG. 9 shows the cumulative polarization conversion efficiency of the multilayer retardation plate of the first embodiment and the polarization conversion efficiency of the multilayer retardation plate of the prior art in the thickness of the retardation plate in the wavelength region of 400 nm to 700 nm. It is the graph compared using the deviation value. The calculation is performed assuming that the first retardation plate and the second retardation plate are substantially equal.
Here, the horizontal axis of FIG. 9 represents the plate thickness of the phase difference plate, and the vertical axis of FIG. 9 represents the cumulative deviation value. The same applies to FIGS. 12, 13, and 14 below.

In FIG. 9, a curve 60 is a line connecting cumulative divergence values at each plate thickness.
A straight line 70 is a line obtained by drawing the cumulative divergence value of the conventional phase difference plate in parallel with the horizontal axis. If it is below the straight line 70, it means that the accumulated divergence value is smaller than that of the prior art laminated phase difference plate. In addition, the said polarization conversion efficiency of the prior art was computed from patent document 1. FIG.

  As shown in FIG. 9, the laminated phase difference plate 1 has a thickness of 24 μm to 31 μm in the thickness of each of the first phase difference plate 10 and the second phase difference plate 20, and the accumulated divergence value is the conventional level. It is below the phase difference plate, and it can be seen that the polarization conversion efficiency is improved as compared with the conventional laminated phase difference plate. In this thickness range, the polarization conversion efficiency can be further improved by combining the first retardation plate and the second retardation plate using the formula (1).

  The laminated phase difference plate 1 having the above plate thickness can obtain higher polarization conversion efficiency than the conventional laminated phase difference plate in a wavelength region of 400 nm to 700 nm. In the optimization of the plate thickness range described above, the two phase plates are substantially equal, but by combining the optimization of the two plate thicknesses according to the formula (1) with the setting of the plate thickness range, a further 400 nm to High polarization conversion efficiency can be obtained in a wavelength region of 700 nm.

Here, an example of an optical element for polarization conversion using the laminated retardation plate 1 of the first embodiment will be described.
FIG. 10 is a main part configuration diagram of a polarization beam splitter (hereinafter referred to as PBS (Polarization Beam Splitter)) 2 as an optical element for polarization conversion provided with the laminated retardation plate of the first embodiment.
As shown in FIG. 10, the PBS 2 has a plurality of laminated phase difference plates 1 at predetermined positions on the light emission side in a prism array 50 in which a polarization separation film 52 is formed on the slope of a prism 51 made of glass or the like. It is prepared for.
The PBS 2 has a polarization conversion function in which when randomly polarized light is incident as incident light from the left side of FIG. 10, the polarization components are aligned in the PBS 2 and emitted to the right side of FIG.

Here, the polarization conversion function of the PBS 2 will be described. When randomly polarized incident light is incident on the PBS 2, in the first path 53, the P-polarized component of the incident light is transmitted through the polarization separation film 52 due to its optical characteristics and enters the laminated phase difference plate 1. 1 is subjected to polarization conversion, and the plane of polarization is rotated by 90 ° and emitted as an S-polarized component.
In the second path 54, the S-polarized component of the incident light is reflected by the polarization separation film 52 to the lower side in FIG. 10 due to its optical characteristics, and further reflected to the right by the lower polarization separation film 52. , S-polarized light components are emitted.
As a result, the PBS 2 emits most of the randomly polarized incident light after being converted into the S-polarized component.

Here, an example of the projection type video apparatus using the above PBS will be described. FIG. 11 is a main part configuration diagram of an example of a projection type video apparatus having a plurality of light sources.
As shown in FIG. 11, the PBS is used as a polarization conversion element 540 or a polarization conversion element 541.
This projection type video apparatus has a lamp 501 and a reflector 511 as a white light source. The light guided from this light source is dispersed or condensed by the multi-lens 531, multi-lens 532, etc., and is incident on the polarization conversion element 540 using the PBS. The white light source described above is natural light having a wavelength band of approximately 400 nm to 700 nm. Since the PBS using the multilayered phase difference plate 1 according to the first embodiment has high polarization conversion efficiency, the light from the light source is used. It can be used effectively. Therefore, it is possible to provide a projection type video apparatus with excellent brightness.

A light source 502 shown in FIG. 11 is a monochromatic light source made of a light emitting diode. The light guided from this light source is dispersed or condensed by the multi-lens 533, the multi-lens 534, etc., and enters the polarization conversion element 541 using the PBS. For example, the monochromatic light source can provide light belonging to any one of a blue wavelength band (approximately 400 nm to 500 nm), a green wavelength band (approximately 500 nm to 600 nm), and a red wavelength band (approximately 600 nm to 700 nm). A PBS suitable for such a polarization conversion element will be described in the following embodiment.
Note that FIG. 11 is shown as an example, and the present invention may be suitably used for a projection type video apparatus with only a white light source using a lamp or a projection type video apparatus with only a plurality of monochromatic light sources.

(Second Embodiment)
The laminated phase difference plate in each of the following embodiments including the laminated phase difference plate of the second embodiment is different from the laminated phase difference plate of the first embodiment in that the first phase difference plate and the second phase difference plate. The thickness range of the retardation plate and the range of the optical axis azimuth are different.
In the following description of each embodiment, FIGS. 1 and 2 will be shared, and the difference from the laminated retardation plate of the first embodiment will be mainly described by partially replacing the reference numerals in FIGS. 1 and 2. In addition, the code | symbol before replacement is shown first with a parenthesis.

As shown in FIGS. 1 and 2, the laminated retardation film 101 (1) of the second embodiment includes a first retardation film 110 (10) and a second retardation film 120 (20). It consists of
The laminated phase difference plate 101 is formed so that the thickness of each of the first phase difference plate 110 and the second phase difference plate 120 is in the range of 20.73 μm to 26.34 μm. The first retardation plate 110 and the second retardation plate 120 are formed with substantially the same thickness.
In the laminated phase difference plate 101, the first phase difference plate 110 and the second phase difference plate 120 are formed from a Y-cut quartz crystal substrate.

In the laminated phase difference plate 101, the optical axis azimuth angle θa of the first phase difference plate 110 and the optical axis azimuth angle θb of the second phase difference plate 120 are expressed by Equation (2), Equation (3), Mueller determinant, and the like. Is set.
Here, a settable range of the optical axis azimuth θa and the optical axis azimuth θb in the thickness range of the first retardation plate 110 and the second retardation plate 120 is illustrated.

表３は、第１の位相差板１１０及び第２の位相差板１２０の上記３種類の板厚における光学軸方位角θａ及び光学軸方位角θｂの設定可能範囲を示したものである。
表３に示すように、板厚が下限値の２０．７３μｍの場合には、光学軸方位角θａは、２１．４°〜２３．６°の範囲、光学軸方位角θｂは、６６．４°〜６８．６°の範囲である。
板厚が略中心値の２３．６１μｍの場合には、光学軸方位角θａは、１１．５°〜３３．５°の範囲、光学軸方位角θｂは、５６．５°〜７８．５°の範囲である。
板厚が上限値の２６．３４μｍの場合には、光学軸方位角θａは、２１．３°〜２３．７°の範囲、光学軸方位角θｂは、６６．３°〜６８．７°の範囲である。

Table 3 shows a settable range of the optical axis azimuth angle θa and the optical axis azimuth angle θb in the three types of plate thicknesses of the first phase difference plate 110 and the second phase difference plate 120.
As shown in Table 3, when the plate thickness is the lower limit of 20.73 μm, the optical axis azimuth θa is in the range of 21.4 ° to 23.6 °, and the optical axis azimuth θb is 66.4. It is in the range of ° to 68.6 °.
When the plate thickness is approximately the center value of 23.61 μm, the optical axis azimuth θa is in the range of 11.5 ° to 33.5 °, and the optical axis azimuth θb is 56.5 ° to 78.5 °. Range.
When the plate thickness is 26.34 μm, which is the upper limit value, the optical axis azimuth θa is in the range of 21.3 ° to 23.7 °, and the optical axis azimuth θb is in the range of 66.3 ° to 68.7 °. It is a range.

The value of the optical axis azimuth angle θb is calculated by setting the angle α formed by the optical axis azimuth angle θa and the optical axis azimuth angle θb to 45 °. Therefore, the optical axis azimuth angle θb is a value obtained by adding 45 ° to the set value of the optical axis azimuth angle θa.
The angle α formed by the optical axis azimuth angle θa and the optical axis azimuth angle θb is not limited to 45 °, and an angle different from 45 ° can be set by a combination of the plate thickness and the optical axis azimuth angle θa. is there.

  With the above configuration, the laminated retardation plate 101 functions as a half-wave retardation plate. As a result, when the linearly polarized light 30 that is the P-polarized component of the incident light is incident on the laminated phase difference plate 101, the plane of polarization of the linearly polarized light 30 is shifted by 180 °, and the polarization plane is rotated by 90 °. The light is converted into linearly polarized light 40, which is a component, and emitted.

Here, the results of comparing the polarization conversion efficiency of the P-polarized component to the S-polarized component by the laminated retardation plate 101 with those of the conventional laminated retardation plate are shown in FIG.
FIG. 12 is a graph comparing the polarization conversion efficiency of the laminated phase difference plate 101 and the polarization conversion efficiency of the conventional laminated phase difference plate using the accumulated divergence values at each thickness in the wavelength region of 400 nm to 500 nm. is there.

In FIG. 12, a curve 160 is a line connecting the accumulated divergence values at each plate thickness of the laminated phase difference plate 101.
A straight line 170 is a line obtained by drawing the cumulative divergence value of the conventional phase difference plate in parallel with the horizontal axis.

  As shown in FIG. 12, the laminated phase difference plate 101 has a thickness of 21 μm to 26 μm in the thickness of each of the first phase difference plate 110 and the second phase difference plate 120, and the accumulated divergence value is the conventional level. It is lower than the phase difference plate, and it can be seen that the polarization conversion efficiency is higher than that of the conventional laminated phase difference plate.

The laminated retardation plate 101 can obtain higher polarization conversion efficiency than the conventional laminated retardation plate in the wavelength region of 400 nm to 500 nm. In the optimization of the plate thickness range described above, the two phase plates are substantially equal, but by combining the optimization of the two plate thicknesses according to the formula (1) with the setting of the plate thickness range, a further 400 nm to High polarization conversion efficiency can be obtained in a wavelength region of 500 nm.
The laminated phase difference plate 101 of the second embodiment is used for an optical element such as PBS like the laminated phase difference plate 1 of the first embodiment, and the incident light has a blue wavelength band (approximately 400 nm to 500 nm). Is preferable because of high polarization conversion efficiency.

(Third embodiment)
As shown in FIG. 2, the laminated phase difference plate 201 (1) of the third embodiment is configured to include a first phase difference plate 210 (10) and a second phase difference plate 220 (20). ing.
The laminated phase difference plate 201 is formed so that the thickness of each of the first phase difference plate 210 and the second phase difference plate 220 is in the range of 24.04 μm to 35.28 μm. The first retardation plate 210 and the second retardation plate 220 are formed with substantially the same thickness.
In the laminated phase difference plate 201, a first phase difference plate 210 and a second phase difference plate 220 are formed from a Y-cut quartz crystal substrate.

In the laminated phase difference plate 201, the optical axis azimuth angle θa of the first phase difference plate 210 and the optical axis azimuth angle θb of the second phase difference plate 220 are expressed by Equation (1), Equation (2), Mueller determinant, and the like. Is set.
Here, a settable range of the optical axis azimuth angle θa and the optical axis azimuth angle θb in the thickness range of the first retardation plate 210 and the second retardation plate 220 is illustrated.

表４は、第１の位相差板２１０及び第２の位相差板２２０の上記３種類の板厚における光学軸方位角θａ及び光学軸方位角θｂの設定可能範囲を示したものである。
表４に示すように、板厚が下限値の２４．０４μｍの場合には、光学軸方位角θａは、２１．２°〜２３．８°の範囲、光学軸方位角θｂは、６６．２°〜６８．８°の範囲である。
板厚が略中心値の２９．７７μｍの場合には、光学軸方位角θａは、−４．２°〜４９．２°の範囲、光学軸方位角θｂは、４０．８°〜９４．２°の範囲である。
板厚が上限値の３５．２８μｍの場合には、光学軸方位角θａは、２２．２°〜２２．８°の範囲、光学軸方位角θｂは、６７．２°〜６７．８°の範囲である。

Table 4 shows the settable ranges of the optical axis azimuth angle θa and the optical axis azimuth angle θb in the three types of thicknesses of the first phase difference plate 210 and the second phase difference plate 220.
As shown in Table 4, when the plate thickness is the lower limit of 24.04 μm, the optical axis azimuth θa is in the range of 21.2 ° to 23.8 °, and the optical axis azimuth θb is 66.2. It is in the range of ° to 68.8 °.
When the plate thickness is approximately 29.77 μm, the optical axis azimuth θa is in the range of −4.2 ° to 49.2 °, and the optical axis azimuth θb is 40.8 ° to 94.2. It is in the range of °.
When the plate thickness is 35.28 μm, the upper limit, the optical axis azimuth θa is in the range of 22.2 ° to 22.8 °, and the optical axis azimuth θb is in the range of 67.2 ° to 67.8 °. It is a range.

The value of the optical axis azimuth angle θb is calculated by setting the angle α formed by the optical axis azimuth angle θa and the optical axis azimuth angle θb to 45 °. Therefore, the optical axis azimuth angle θb is a value obtained by adding 45 ° to the set value of the optical axis azimuth angle θa.
The angle α formed by the optical axis azimuth angle θa and the optical axis azimuth angle θb is not limited to 45 °, and an angle different from 45 ° can be set by a combination of the plate thickness and the optical axis azimuth angle θa. is there.

  With the above configuration, the laminated retardation plate 201 functions as a half-wave retardation plate. As a result, when the linearly polarized light 30 that is the P-polarized component of the incident light is incident on the laminated retardation plate 201, the plane of polarization of the linearly polarized light 30 is shifted by 180 °, and the polarization plane is rotated by 90 °. The light is converted into linearly polarized light 40, which is a component, and emitted.

Here, the result of comparing the polarization conversion efficiency of the P-polarized component to the S-polarized component by the laminated retardation plate 201 with that of the conventional laminated retardation plate is shown in FIG.
FIG. 13 compares the polarization conversion efficiency of the laminated phase difference plate 201 with the polarization conversion efficiency of the prior art laminated quartz phase difference plate using the accumulated divergence values at each thickness in the wavelength region of 500 nm to 600 nm. It is a graph.

In FIG. 13, a curve 260 is a line connecting the accumulated divergence values at the respective plate thicknesses of the laminated phase difference plate 201.
A straight line 270 is a line obtained by drawing the cumulative divergence value of the conventional phase difference plate in parallel with the horizontal axis.

  As shown in FIG. 13, the laminated phase difference plate 201 has a thickness of 25 μm to 35 μm in the thickness of each of the first phase difference plate 210 and the second phase difference plate 220, and the accumulated divergence value is the conventional level. It can be seen that the polarization conversion efficiency is higher than that of the prior art laminated phase difference plate.

The laminated retardation plate 201 can obtain higher polarization conversion efficiency than the conventional laminated retardation plate in a wavelength region of 500 nm to 600 nm. In the optimization of the plate thickness range, the two phase plates are substantially equal, but by combining the optimization of the two plate thicknesses according to the equation (1) with the setting of the plate thickness range, the thickness of 500 nm to High polarization conversion efficiency can be obtained in a wavelength region of 600 nm.
The laminated phase difference plate 201 of the third embodiment is used for an optical element such as PBS like the laminated phase difference plate 1 of the first embodiment, and the incident light has a green wavelength band (approximately 500 nm to 600 nm). Is preferable because of high polarization conversion efficiency.

(Fourth embodiment)
As shown in FIG. 2, the laminated retardation film 301 (1) of the fourth embodiment includes a first retardation film 310 (10) and a second retardation film 320 (20). ing.
The laminated phase difference plate 301 is formed such that the thickness of each of the first phase difference plate 310 and the second phase difference plate 320 is in the range of 23.98 μm to 47.41 μm. The first retardation plate 310 and the second retardation plate 320 are formed with substantially the same thickness.
In the laminated phase difference plate 301, the first phase difference plate 310 and the second phase difference plate 320 are formed from a Y-cut quartz crystal substrate.

In the laminated phase difference plate 301, the optical axis azimuth angle θa of the first phase difference plate 310 and the optical axis azimuth angle θb of the second phase difference plate 320 are expressed by equations (1), (2), Mueller determinant, and the like. Is set.
Here, a settable range of the optical axis azimuth angle θa and the optical axis azimuth angle θb in the thickness range of the first phase difference plate 310 and the second phase difference plate 320 is illustrated.

表５は、第１の位相差板３１０及び第２の位相差板３２０の上記３種類の板厚における光学軸方位角θａ及び光学軸方位角θｂの設定可能範囲を示したものである。
表５に示すように、板厚が下限値の２３．９８μｍの場合には、光学軸方位角θａは、２１．１°〜２３．９°の範囲、光学軸方位角θｂは、６６．１°〜６８．９°の範囲である。
板厚が略中心値の３５．７６μｍの場合には、光学軸方位角θａは、０．０°〜１８０．０°の範囲、光学軸方位角θｂは、４５．０°〜２２５．０°の範囲である。
板厚が上限値の４７．４１μｍの場合には、光学軸方位角θａは、２１．１°〜２３．９°の範囲、光学軸方位角θｂは、６６．１°〜６８．９°の範囲である。

Table 5 shows a settable range of the optical axis azimuth angle θa and the optical axis azimuth angle θb in the three types of thicknesses of the first phase difference plate 310 and the second phase difference plate 320.
As shown in Table 5, when the plate thickness is the lower limit of 23.98 μm, the optical axis azimuth θa is in the range of 21.1 ° to 23.9 °, and the optical axis azimuth θb is 66.1. It is the range of ° to 68.9 °.
When the plate thickness is 35.76 μm, which is a substantially central value, the optical axis azimuth θa is in the range of 0.0 ° to 180.0 °, and the optical axis azimuth θb is 45.0 ° to 225.0 °. Range.
When the plate thickness is 47.41 μm, which is the upper limit, the optical axis azimuth θa is in the range of 21.1 ° to 23.9 °, and the optical axis azimuth θb is in the range of 66.1 ° to 68.9 °. It is a range.

The value of the optical axis azimuth angle θb is calculated by setting the angle α formed by the optical axis azimuth angle θa and the optical axis azimuth angle θb to 45 °. Therefore, the optical axis azimuth angle θb is a value obtained by adding 45 ° to the set value of the optical axis azimuth angle θa.
The angle α formed by the optical axis azimuth angle θa and the optical axis azimuth angle θb is not limited to 45 °, and an angle different from 45 ° can be set by a combination of the plate thickness and the optical axis azimuth angle θa. is there.

  With the above configuration, the laminated retardation plate 301 functions as a half-wave retardation plate. As a result, when the linearly polarized light 30 that is the P-polarized component of the incident light is incident on the laminated retardation plate 301, the plane of polarization of the linearly polarized light 30 is shifted by 180 °, and the polarization plane is rotated by 90 °. The light is converted into linearly polarized light 40, which is a component, and emitted.

Here, FIG. 7 shows a result of comparing the polarization conversion efficiency of the P-polarized component into the S-polarized component by the laminated retardation plate 301 with that of the conventional laminated retardation plate.
FIG. 14 is a graph comparing the polarization conversion efficiency of the multilayer retardation plate 301 and the polarization conversion efficiency of the multilayer retardation plate of the prior art using the accumulated divergence values at each plate thickness in the wavelength region of 600 nm to 700 nm. It is.

  In FIG. 14, a curve 360 is a line connecting the accumulated divergence values at the respective plate thicknesses of the laminated phase difference plate 301. A straight line 370 is a line obtained by drawing the cumulative divergence value of the conventional phase difference plate in parallel with the horizontal axis.

  As shown in FIG. 14, the laminated phase difference plate 301 has a thickness of 24 μm to 47 μm in the thickness of each of the first phase difference plate 310 and the second phase difference plate 320, and the accumulated divergence value is the conventional level. It can be seen that the polarization conversion efficiency is higher than that of the prior art laminated phase difference plate.

The laminated retardation plate 301 can obtain higher polarization conversion efficiency than the conventional laminated retardation plate in the wavelength region of 600 nm to 700 nm. In the optimization of the plate thickness range, the two phase plates are substantially equal, but by combining the optimization of the two plate thicknesses according to the formula (1) with the setting of the plate thickness range, the thickness of the plate is further increased from 600 nm. High polarization conversion efficiency can be obtained in a wavelength region of 700 nm.
Note that the laminated retardation film 301 of the fourth embodiment is used for an optical element such as PBS similarly to the laminated retardation film 1 of the first embodiment, and the incident light has a red wavelength band (approximately 600 nm to 700 nm). Is preferable because of high polarization conversion efficiency.

  In the description of the first to fourth embodiments, the PBS is exemplified as the use of the laminated phase difference plates 1, 101, 201, 301. However, the present invention is not limited to this. For example, the cross prism 590 shown in FIG. You may use for the phase plate 572 or the phase plate 573 installed nearby.

Explanatory drawing of the polarization | polarized-light of a laminated phase difference plate. Explanatory drawing of the optical axis direction of a laminated phase difference plate. The figure which shows a Poincare sphere. The figure which showed the Poincare sphere from S3 axial direction. The figure which showed on the straight line the polarization | polarized-light of the equatorial plane of a Poincare sphere. The graph which shows the combination of the board thickness of the suitable two phase plate of this invention. The graph which shows a comparative example with the combination of the plate | board thickness of the suitable two phase plate of this invention. The graph explaining the accumulation deviation value in the embodiment of the present invention. The graph which compared the accumulated divergence value of the lamination | stacking phase difference plate in 1st Embodiment, and the lamination | stacking phase difference plate of a prior art. The principal part block diagram of PBS provided with the laminated phase difference plate. The principal part block diagram of the projection type imaging device provided with the laminated phase difference plate. The graph which compared the cumulative deviation value of the lamination | stacking phase difference plate in 2nd Embodiment, and the lamination | stacking phase difference plate of a prior art. The graph which compared the accumulated deviation value of the lamination | stacking phase difference plate in 3rd Embodiment, and the lamination | stacking phase difference plate of a prior art. The graph which compared the accumulated divergence value of the lamination | stacking phase difference plate in 4th Embodiment, and the lamination | stacking phase difference plate of a prior art.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,101,201,301 ... Laminated phase difference plate, 2 ... PBS, 10,110,210,310 ... 1st phase difference plate, 11, 12, 21 ... Optical axis, 13, 14 ... Vibrating surface, 20, 120, 220, 320 ... second retardation plate, 30, 40 ... linearly polarized light, 50 ... prism array, 51 ... prism, 52 ... polarization separation film, 53 ... first path, 54 ... second path, 55 ... Deviation value, 56 ... Deviation range, 60, 160, 260, 360 ... Curve, 70, 170, 270, 370 ... Straight line, 501 ... Lamp, 502 ... Light source, 511 ... Reflector, 531, 532, 533, 534 ... Multi Lens, 540, 541... Polarization conversion element, 572, 573... Phase plate, 590... Cross prism, O .. Center, R1, R2... Rotating axis, T1, T2. , ΔΓb ... Deviation amount, θa: optical axis azimuth angle of first retardation plate, θb: optical axis azimuth angle of second retardation plate.

Claims (6)

A first retardation plate having a phase difference Γ′a and a second retardation plate having a phase difference Γ′b with respect to light having a wavelength λ are laminated so that the optical axes intersect with each other;
A laminated phase difference plate that converts linearly polarized light that is incident in a range of wavelengths λ1 to λ2 (where λ1 <λ <λ2) into a linearly polarized light that is rotated by 90 degrees, and emits the linearly polarized light;
The first retardation plate and the second retardation plate are formed from a Y-cut quartz substrate,
An angle formed between the polarization plane of the incident linearly polarized light and the optical axis of the first retardation plate is defined as an optical axis azimuth angle θa,
When the angle formed between the polarization plane of the incident linearly polarized light and the optical axis of the second retardation plate is defined as an optical axis azimuth angle θb, the relationship between the optical axis azimuth angle θa and the optical axis azimuth angle θb is as follows. ,
θb = θa + α,
0 ° <θa <45 °,
40 ° <α <50 °
Satisfied,
When the refractive index of ordinary light of the first retardation plate is Noa, the refractive index of extraordinary light is Nea, and the thickness is da, the phase difference Γ′a of the first retardation plate and the polarization conversion efficiency Ta Is
Γ′a = 2 × π × da × (Nea-Noa) / λ,
Ta = 4 × (sin ² θa) × (cos (2θa)) × (sin ² (Γ′a / 2))
Satisfied,
When the refractive index of the ordinary ray of the second retardation plate is Nob, the refractive index of the extraordinary ray is Neb, and the thickness is db, the phase difference Γ′b of the second retardation plate and the polarization conversion efficiency Tb Is
Γ′b = 2 × π × db × (Neb−Nob) / λ,
Tb = 4 × (sin ² θb) × (cos (2θb)) × (sin ² (Γ′b / 2))
Satisfied,
The phase difference Γ′a and the phase difference Γ′b are:
Γ′a = Γa + ΔΓa,
Γ′b = Γb + ΔΓb,
Γa = 180 °,
Γb = 180 °
Satisfied,
A laminated phase difference plate, wherein the relationship between ΔΓa and ΔΓb satisfies the following expression (1).

In claim 1,
When λ1 = 400 nm and λ2 = 700 nm,
A laminated phase difference plate, wherein a thickness da of the first phase difference plate is in a range of 24 μm to 31 μm, and a thickness db of the second phase difference plate is in a range of 24 μm to 31 μm. In claim 1,
When λ1 = 400 nm and λ2 = 500 nm,
2. The laminate according to claim 1, wherein a thickness da of the first retardation plate is in a range of 21 μm to 26 μm, and a thickness db of the second retardation plate is in a range of 21 μm to 26 μm. Phase difference plate. In claim 1,
When λ1 = 500 nm and λ2 = 600 nm,
2. The laminate according to claim 1, wherein a thickness da of the first retardation plate is in a range of 25 μm to 35 μm, and a thickness db of the second retardation plate is in a range of 25 μm to 35 μm. Phase difference plate. In claim 1,
When λ1 = 600 nm and λ2 = 700 nm,
2. The laminate according to claim 1, wherein a thickness da of the first retardation plate is in a range of 24 μm to 47 μm, and a thickness db of the second retardation plate is in a range of 24 μm to 47 μm. Phase difference plate. A projection-type image device,
A projection type video apparatus using the laminated phase difference plate according to any one of claims 1 to 5.

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