JP4742630B2 - Reflective optical element and optical pickup device - Google Patents

Description

  The present invention relates to a phase difference adjusting film capable of controlling the polarization state of reflected light, in particular, a phase difference adjusting film that reflects light so as not to cause a phase change of polarized light, and light of a plurality of wavelengths in different polarization states. The present invention relates to a reflective optical element having a phase difference adjusting film that reflects the light so that the polarization state matches. The present invention also relates to an optical pickup device having such a reflective optical element.

  Conventionally, as a reflective optical element, a metal reflection mirror in which a metal film (for example, aluminum or silver) is vapor-deposited on a glass material, or a dielectric reflection mirror in which dielectric films are vapor-deposited in multiple layers is known. A mirror described in Non-Patent Document 1 is disclosed as an example of a dielectric reflecting mirror. This mirror is a high reflectivity mirror for laser.

Supervision of Shigetaro Ogura “Design, Fabrication and Evaluation Technology of Optical Thin Films at Production Sites” Technical Information Association p.240

  When a polarized light beam is incident on such a metal reflection mirror or dielectric reflection mirror, a phase difference is generated between P-polarized light and S-polarized light, and the polarization state is changed. For example, even if linearly polarized light enters the mirror, it changes to elliptically polarized light after reflection. Therefore, when such a reflection mirror is used in an optical device using polarized light, desired characteristics cannot be obtained due to a change in polarization state.

  In the case of a dielectric reflecting mirror, for a specific wavelength, it is possible to suppress the phase difference by devising the film thickness and the film material, but a very large number of layers are required. In addition, it is very difficult to prevent phase differences with respect to a plurality of wavelengths.

  Regarding the reflectivity, the metal reflection mirror has little change in reflectivity depending on the wavelength, but cannot obtain a high reflectivity. In the case of a dielectric reflecting mirror, a very large number of layers is required to obtain a high reflectance for a plurality of wavelengths. Also, it is very difficult to achieve both high reflectivity and phase compensation.

  The present invention has been made in view of the above points, and an object of the present invention is to easily provide a reflective optical element having a reflective film that has a high reflectance and does not generate a phase difference. Another object of the present invention is to easily provide a reflective optical element having a reflective film having a high reflectance and capable of controlling a phase difference with respect to a wavelength.

In order to achieve the above object, an optical pickup device according to a first aspect of the present invention includes a first light source that emits light of a first wavelength, a second light source that emits light of a second wavelength, A reflective optical element that bends the optical path of light from the light source, the reflective optical element having a prism and a phase difference adjusting film formed on the reflecting surface of the prism, and the phase difference adjusting film is incident on the prism The light of the first wavelength is reflected so that the polarization state thereof does not substantially change, and the light of the second wavelength incident on the prism is substantially the same as the polarization state of the light of the first wavelength. It is reflected so that it becomes.

An optical pickup device according to a second aspect of the invention is the optical pickup device according to the first aspect , further comprising a quarter-wave plate between the first and second light sources that emit linearly polarized light and the reflective optical element. The quarter-wave plate converts linearly polarized light from the first light source into circularly polarized light, and the reflective optical element reflects and emits light of the first and second wavelengths as circularly polarized light. To do.

An optical pickup device according to a third aspect of the invention emits light having a first wavelength λ1 (395 nm <λ1 <425 nm) and light having a second wavelength λ2 (630 nm <λ2 <690 nm). A second light source, a third light source that emits light of a third wavelength λ3 (740 nm <λ3 <870 nm), and a reflective optical element that bends the optical path of light from the first, second, and third light sources. The reflective optical element includes a prism and a phase difference adjusting film formed on the reflecting surface of the prism, and the phase difference adjusting film is one of the first, second, and third light incident on the prism. Reflect the polarization state of the light of the wavelength so that it does not substantially change, and make the polarization state of the light of the remaining two wavelengths substantially the same as the polarization state of the reflected light so that the polarization state does not change It is characterized by being reflected on.

An optical pickup device according to a fourth aspect of the present invention is the optical pickup device according to the third aspect , wherein a quarter-wave plate is disposed between the first, second and third light sources that emit linearly polarized light and the reflective optical element. The quarter-wave plate converts linearly polarized light from any one light source into circularly polarized light, and the reflective optical element reflects the light of the first, second, and third wavelengths as circularly polarized light. It is characterized by injecting.

A reflective optical element according to a fifth aspect is the reflective optical element according to any one of the first to fourth aspects, wherein the retardation adjustment film is formed on a total reflection surface of the prism.

  A phase difference adjusting film is formed at the interface between the optically transparent medium and air, and the light is reflected in the medium, so that the polarization component of light having a predetermined wavelength incident at a predetermined incident angle is obtained. It is possible to prevent a phase difference from occurring. Further, even if there are wavelength fluctuations and incident angle fluctuations for light of a plurality of wavelengths, the reflectance can be maintained almost 100%. Furthermore, it is possible to prevent a phase difference from occurring even if there are wavelength fluctuations and incident angle fluctuations for light of a plurality of wavelengths.

  Further, even when light of a plurality of wavelengths having different polarization states is incident, the light can be reflected with substantially the same polarization state with a reflectance of almost 100%. In particular, when the interface is a total reflection surface, the high reflectance and the phase difference can be easily adjusted with a small number of layers.

  Further, by using such a reflective optical element having a phase difference adjusting film in an optical pickup device, it is possible to prevent a decrease in signal intensity and return light to the laser, thereby improving signal detection accuracy. In addition, the optical pickup device can be thinned.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an optical pickup device 1 according to the first embodiment. FIG. 1A is a top view of the optical pickup device 1, and FIG. 1B is a side view of the optical pickup device 1. The optical pickup device 1 is a device that records information on an optical disc that is an optical information recording medium and / or reproduces information from the optical disc. The optical disk 20 includes a first optical disk (for example, a next-generation high-density optical disk using a blue laser) and a second optical disk (for example, a DVD) having a transparent substrate thickness t1, and a transparent substrate thickness t2 different from t1. There are three types of three optical discs (for example, CD). Here, the thickness t1 = 0.6 mm and t2 = 1.2 mm of the transparent substrate. The first optical disk using blue light may be a disk having a thickness t3 (for example, t3 = 0.1 mm) different from the thickness t1 of the transparent substrate.

  The optical pickup device 1 includes a first semiconductor laser 11 that is a first light source, a second semiconductor laser 12 that is a second light source, and a third semiconductor laser 13 that is a third light source as light sources. The first semiconductor laser 11 emits linearly polarized light having a first wavelength λ1 (395 nm ≦ λ1 ≦ 425 nm), the second semiconductor laser 12 emits linearly polarized light having a second wavelength λ2 (630 nm ≦ λ2 ≦ 690 nm), The third semiconductor laser 13 emits linearly polarized light having a third wavelength λ3 (third wavelength λ3: 740 nm ≦ λ3 ≦ 870 nm). The first light source, the second light source, and the third light source are selected according to the type of the optical disk on which information is recorded and / or reproduced.

  The light sources 11, 12 and 13, the combiners 31 and 32, the polarization beam splitter 80, the collimator lens 40, the ¼ wavelength plate 50, the photodetector 14, the toric lens 90 and the reflective optical element 60 of the optical pickup device 1 The optical pickup device 1 is thinned by being arranged on a plane parallel to the information recording surface.

  Hereinafter, the operation for reproducing information in the order of the optical path will be briefly described. The linearly polarized divergent light beam emitted from the first semiconductor laser 11, the second semiconductor laser 12, or the third semiconductor laser 13 is incident on the collimator lens 40 via the beam combiners 31 and 32 and the polarization beam splitter 80, and is parallel light. Is converted to The beam combiners 31 and 32 superimpose the optical paths from the light sources 11, 12 and 13 on the same optical path. Parallel light that is linearly polarized light is converted into circularly polarized light by the quarter-wave plate 50. The quarter-wave plate 50 functions as a quarter-wave plate for the three wavelengths λ1, λ2, and λ3. For example, the quarter-wave plate 50 is formed by laminating a plurality of phase plates so that their optical axes are inclined with respect to each other so as to form a predetermined angle. The parallel light transmitted through the quarter-wave plate 50 is incident on the objective lens 70 after the optical path is bent by 90 ° by the reflective optical element 60. The light incident on the objective lens 70 is condensed on the information recording surface of the optical disc 20 to form a spot. A diffractive optical element is provided on the lens surface of the objective lens 70, and the optical power of the objective lens 70 varies depending on the wavelength. As a result, a spot position (in the optical axis direction) corresponding to the thickness of the transparent substrate of the optical disc 20 is obtained.

  The reflective optical element 60 is used to reduce the thickness of the optical pickup device 1 in the objective lens optical axis direction. That is, the light path is bent at a right angle by the reflective optical element 60, whereby the light sources 11, 12, 13, combiners 31, 32, polarizing beam splitter 80, collimator lens 40, 1/4 wavelength plate 50, photodetector 14 and reflection optics. The element 60 and the like can be arranged on a plane perpendicular to the optical axis of the objective lens 70 (a plane parallel to the recording surface of the optical disc 20), and the thickness can be reduced.

  Incident light from the light source to the optical disc 20 becomes reflected light modulated by information pits on the information recording surface, and follows an optical path opposite to the incident light. The reflected light is converted from circularly polarized light to linearly polarized light orthogonal to the laser radiation light by the quarter-wave plate 50. The reflected light is reflected by the polarization beam splitter 80, enters the common photodetector 14 via the toric lens 90, and is detected as a signal.

  Here, when the signal light is reflected by the polarization beam splitter 80, if the polarization state is disturbed from the linearly polarized light, the intensity of the signal light to the photodetector 14 becomes weak and the detection accuracy decreases. Further, return light to the laser is generated, which makes the oscillation of the laser unstable. In order to reduce the influence of the polarization disturbance caused by the optical disk 20, a circularly polarized spot is formed on the optical disk 20. Further, in order to bend the optical path, a reflection optical element 60 is used instead of a general reflection mirror. FIG. 2 shows the reflective optical element 60.

  In the reflective optical element 60 that bends the optical path, a phase difference adjusting reflective film 62 is formed on the reflective surface 61 a of the prism 61. In general, when light is incident on an interface having different refractive indexes, the reflectivity and phase difference change with respect to the P-polarized light and S-polarized light with respect to the incident surface, and as a result, the polarization state changes. In particular, when the incident angle is as large as 45 ° as in the present embodiment, the influence is great. In the present embodiment, the phase difference adjusting reflection film 62 is formed on the reflection surface 61a, and a phase difference is generated between polarized light components orthogonal to each other with respect to light of the first, second, and third wavelengths. Is configured to not. Since the polarization state does not change due to reflection, circularly polarized light is incident on the optical disc 20, and the signal light (return path) transmitted through the quarter-wave plate 50 is converted into linearly polarized light. As a result, signal light hardly leaks to the light source side.

  With conventional dielectric reflecting mirrors, it is possible to increase the reflectivity for light of three wavelengths, but it is very difficult to produce a phase difference at the same time, even for two different wavelengths. It is difficult to. Also, increasing the number of layers does not prevent the generation of a phase difference. The phase difference adjusting reflective film 62 of the present embodiment is provided at the interface between an optically dense medium (prism medium, eg, glass) and an optically sparse medium (air), and light is reflected in the prism medium. Is done. As a result, it is possible to prevent a phase difference from occurring for light having a plurality of wavelengths.

  Antireflection films corresponding to the three wavelengths λ1, λ2, and λ3 are formed on the incident surface 61b and the exit surface 61c of the prism 61 to prevent loss of light amount and noise due to reflected light. Further, the entrance surface 61b and the exit surface 61c are surfaces perpendicular to the optical axis, thereby preventing the generation of astigmatism. Since light enters the antireflection film perpendicularly, no phase difference is generated by the antireflection film.

  FIG. 3 is a diagram showing a schematic configuration of an optical pickup apparatus 100 according to the second embodiment of the present invention. FIG. 3A is a top view of the optical pickup device 100, and FIG. 3B is a side view of the optical pickup device 100.

  The optical pickup device 100 includes a first semiconductor laser 111 as a first light source, a second semiconductor laser 112 as a second light source, and a third semiconductor laser 113 as a third light source as light sources. The first semiconductor laser 111 emits light having a first wavelength λ1 = 405 nm, the second semiconductor laser 112 emits light having a second wavelength λ2 = 660 nm, and the third semiconductor laser 113 emits light having a third wavelength λ3 = It emits light at 780 nm. The first light source, the second light source, and the third light source are integrated as a single light source unit 110, and the light emission point of the second light source and the light emission point of the third light source are substantially the same. . The light emission point of the first light source is slightly different in position from the light emission points of the second and third light sources (for example, 0.5 mm). The first light source, the second light source, and the third light source are selected according to the type of the optical disk on which information is recorded and / or reproduced. In FIG. 3, the optical path of the light flux emitted from the first light source is shown, and the light flux from the second and third light sources is omitted in order to avoid complication of the drawing.

  The light source unit 110, the polarizing beam splitter 180, the quarter-wave plate 150, the photodetector 114, the toric lens 190, and the reflective optical element 160 are arranged on a plane parallel to the information recording surface of the optical disc 20. The height of the pickup device 100 is reduced.

  Hereinafter, the operation for reproducing information in the order of the optical path will be described. The linearly polarized divergent light beam emitted from the first semiconductor laser 111, the second semiconductor laser 112, or the third semiconductor laser 113 is incident on the collimator lens 140 via the polarization beam splitter 180 and converted into parallel light. The polarization state of the parallel light that is linearly polarized light is converted by the quarter-wave plate 150. The quarter-wave plate 150 gives a 90 ° phase difference to polarization components orthogonal to each other with respect to the first wavelength light, and converts the first wavelength light from linearly polarized light into circularly polarized light. The parallel light transmitted through the quarter-wave plate 150 is incident on the objective lens 170 after the optical path is bent by 90 ° by the reflective optical element 160, and is condensed on the information recording surface of the optical disc 20, thereby forming a spot. A diffractive optical element is provided on the lens surface of the objective lens 170, the optical power varies depending on the wavelength, and a spot position (optical axis direction) corresponding to the thickness of the transparent substrate of the optical disc 20 is obtained.

  Incident light on the optical disc 20 becomes reflected light modulated by information pits on the information recording surface, and follows an optical path opposite to the incident light. The reflected light is converted into linearly polarized light (a polarization direction orthogonal to the laser radiation light) by the ¼ wavelength plate 150 and reflected by the polarizing beam splitter 180. The polarizing beam splitter 180 has a first reflecting surface 181 and a second reflecting surface 182. The first reflecting surface 181 and the second reflecting surface 182 will be described later. The light having the first wavelength λ 1 is reflected by the first reflecting surface 181. Light having the second and third wavelengths λ <b> 2 and λ <b> 3 passes through the first reflecting surface 181 and is then reflected by the second reflecting surface 182. The light reflected by the polarization beam splitter 180 enters the photodetector 114 common to the three wavelengths of light via the toric lens 190 and is detected as a signal.

  Here, the quarter-wave plate 150 gives a 90 ° phase difference to the polarization components orthogonal to each other with respect to the light of the first wavelength, but 55.2 ° with respect to the light of the second wavelength. Therefore, a phase difference of 46.7 ° is given to the light of the third wavelength. A general quarter-wave plate (for example, using birefringence) acts as a quarter-wave plate only for a specific wavelength. Therefore, even if the reflective optical element that bends the optical path by 90 ° does not give a phase change to the polarized light, the light of the second and third wavelengths cannot be converted from linearly polarized light to circularly polarized light. On the other hand, with respect to the signal light (return path), the quarter-wave plate 150 does not function as a quarter-wave plate with respect to the light of the second and third wavelengths. It does not become linearly polarized light. As a result, the amount of light detected by the photodetector 114 is lost. Unnecessary return light is incident on the second or third semiconductor laser, which makes the operation of the laser unstable.

  The reflective optical element 160 of the present embodiment adjusts the relationship between the wavelength and the phase difference at a predetermined incident angle, that is, a phase difference adjustment that generates a desired phase difference in the polarization component of the light having the predetermined wavelength. A reflective film 162 is formed. Specifically, the phase difference adjusting reflective film 162 does not generate a phase difference with respect to the polarized light having the first wavelength, and 34.8 ° with respect to the polarized light having the second wavelength. A phase difference of 43.3 ° is generated for the polarized light. Therefore, the light reflected by the reflective optical element 160 is converted into circularly polarized light at any wavelength.

  On the other hand, the signal light reflected by the optical disc 20 is reflected by the reflective optical element 160, and the above-described phase difference is generated with respect to the light of the second and third wavelengths. In other words, with respect to the return path, the reflective optical element 160 is different from the light of the different wavelengths (the light of the first, second, and third wavelengths) incident in the same polarization state (circularly polarized light). It can also be said that the phase difference of the polarization is not changed for the light of the first wavelength, and a predetermined phase difference is generated for the light of the second and third wavelengths. As a result, the light transmitted through the quarter-wave plate 150 in a reciprocating manner is converted into linearly polarized light that is orthogonal to the linearly polarized light in the forward path at any wavelength.

  The first reflecting surface 181 transmits the P-polarized light having the first wavelength λ1, the light having the second wavelength λ2 and the third wavelength λ3, and reflects the S-polarized light having the first wavelength λ1 ( Long-wavelength transmission type) polarization separation characteristics. Further, the second reflecting surface 182 transmits the light having the first wavelength λ1 and the P-polarized light having the second wavelength λ2 and the third wavelength λ3, and S having the second wavelength λ2 and the third wavelength λ3. It has a dichroic (short wavelength transmission type) polarization separation characteristic that reflects polarized light. The second reflection surface 182 reflects the light of the second and third wavelengths λ2 and λ3 at a position different from the light of the first wavelength λ1. The interval between the first reflecting surface and the second reflecting surface is set to 1 / √2 times the interval between the light emitting position of the first light source and the light emitting positions of the second and third light sources. As a result, the light emission positions of the second and third light sources are different from the light emission position of the first light source, but the light is condensed at the same position on the photodetector 114 via the toric lens 190. The first reflecting surface 181 is formed on the inclined surface of the right-angle prism on the optical disc 20 side among the right-angle prisms constituting the polarization beam splitter 180. This is because the light of the first wavelength (blue light) has a smaller amount of light emission than the other two colors of light and is largely absorbed by the adhesive, so that it does not pass through the adhesive layer.

  It is preferable that the phase difference adjusting reflection films 62 and 162 are composed of 5 layers or more and 80 layers or less by combining media selected from at least two groups among three groups of media having the following refractive index ranges. .

1.30 <n1 <1.50
1.55 <n2 <1.85
1.90 <n3 <2.60
However,
n1 is the refractive index of the first group of media,
n2 is the refractive index of the second group of media,
n3 is the refractive index of the third group of media,
It is.

  If the number is below the lower limit of the number of layers, there is no tolerance for wavelength fluctuations and incident angle fluctuations, and it is impossible to cope with wavelength fluctuations and incident angle fluctuations in use. If the upper limit is exceeded, productivity is inferior, and performance deterioration due to film thickness variation or the like tends to occur.

  The incident angle θ to the phase difference adjusting reflective film 62 is preferably 30 ° or more and 80 ° or less. If this condition is not satisfied, it is difficult to correct the phase difference. Especially for a plurality of wavelengths, it is very difficult to correct the phase difference.

  Further, it is preferable that the reflection surface 61a of the prism satisfies the total reflection condition when the phase difference adjusting reflection films 62 and 162 are not provided. When the phase difference adjusting reflection films 62 and 162 are formed on the interface satisfying the total reflection condition to form a reflection surface, a high reflectance of almost 100% can be easily obtained. Since the reflectance can be ensured by total reflection, the phase difference adjusting reflection film only has to play a role of adjusting the phase difference of polarized light. Therefore, the number of layers of the retardation adjusting reflective film can be reduced (for example, 20 layers or less). A specific configuration will be described later.

  The phase difference adjusting reflective film does not need to have a characteristic that does not completely change the polarization state of incident light or a characteristic that completely matches the polarization state of certain light with the polarization state of other light. It is sufficient that desired characteristics can be obtained for the entire optical system. In the case of the optical pickup device, it is sufficient that the detection signals of the photodetectors 14 and 114 are not weakened or the return light to the laser does not have an adverse effect. Specifically, it is preferable that the phase difference adjusting reflective film has the same phase difference within ± 10 °, more preferably within ± 5 °. More specifically, in the case of the first embodiment, it is preferable to suppress the occurrence of a phase difference due to reflection within ± 10 °, more preferably within ± 5 °. In the case of the second embodiment, it is preferable to align the phase differences of light of each wavelength after reflection within ± 10 °, more preferably within ± 5 °.

  When a phase difference of ± 10 ° or more occurs, the signal light component returns to the light path on the light source side, and the S / N ratio decreases due to the decrease in the intensity of the signal light, and the oscillation of the light source (laser diode) becomes unstable. A problem occurs. The above problem can be solved by suppressing the reflection phase difference generated by the phase difference adjusting reflective film to within ± 10 °. The effect is further increased by making the generation of the reflection phase difference within ± 5 °.

  As described above, the phase difference adjusting reflection film is formed at the interface between the optically transparent medium and air, and the phase difference adjusting reflection film reflects the light in the medium so that a predetermined incident angle is obtained. It is possible to prevent a phase difference from occurring in the polarization component of incident light having a predetermined wavelength. Further, even for light of a plurality of wavelengths, the reflectivity can be maintained nearly 100% regardless of wavelength variation and incident angle variation. Furthermore, it is possible to prevent a phase difference from occurring regardless of wavelength variation or incident angle variation in light having a plurality of wavelengths.

  Moreover, even if the polarization states of the light of a plurality of wavelengths are different, it can be reflected with substantially the same polarization state with a reflectance of almost 100%.

  In particular, when the interface is a total reflection surface, it is possible to easily achieve high reflectivity and adjust the phase difference with a small number of layers.

  Further, by using such a reflective optical element having a phase difference adjusting reflective film in an optical pickup device, it is possible to prevent a reduction in signal intensity and return light to the laser, thereby improving the signal detection accuracy and the optical pickup device. Can be made thinner.

  Hereinafter, the configuration of the reflective optical element used in the optical pickup device embodying the present invention will be described more specifically with reference to film configuration data and the like. In any of the embodiments, as shown in FIG. 2, a phase difference adjusting reflection film is formed on the inclined surface 61a of the right-angle prism 61 having a right-angled isosceles triangle shape. Incident light enters the prism perpendicularly, is totally reflected by the inclined surface 61a (incident angle 45 °), and the 90 ° optical path is bent and emitted perpendicularly to the prism exit surface.

Example 1
The phase difference adjusting reflective film of the first embodiment is a multilayer film that does not change the phase difference of incident polarized light having a predetermined wavelength at a predetermined incident angle. 17 layers comprising a TiO ₂ compound (nd = 2.05), SiO ₂ (nd = 1.46), and Al ₂ O ₃ (nd = 1.62) on the slope of a prism having a refractive index of nd = 1.62. The multilayer film is formed. The refractive index nd is a refractive index with respect to d-line (587.6 nm).

  4, 5 and 6 show the reflection characteristics of the retardation adjusting reflective film when the incident angles are 43 °, 45 ° and 47 °, respectively. The horizontal axis represents wavelength (unit: nm), and the vertical axis represents reflectivity (unit:%). The solid line indicates the reflectance of S-polarized light, and the broken line indicates the reflectance of P-polarized light. The reflectivity is almost 100% at any angle. For convenience of drawing, only the range of 400 nm to 900 nm is described, but even at 395 nm, the reflectance is 95.5% or more.

  FIG. 7 shows the phase difference characteristics of the phase difference adjusting reflective film when the incident angles are 43 °, 45 °, and 47 °. The horizontal axis represents wavelength (unit: nm), and the vertical axis represents phase difference (unit: °). At any angle, the phase difference is substantially zero with respect to the first wavelength λ1, the second wavelength λ2, and the third wavelength λ3. For convenience of drawing, only the range of 400 nm to 900 nm is shown, but even at 390 nm, the phase difference is suppressed to 2 ° or less.

The film configuration of the phase difference adjusting reflective film is shown below. This film configuration is designed using commercially available thin film design software with a target of 100% reflectivity and zero phase difference between P-polarized light and S-polarized light when reflected near 405 nm, 630 nm, and 780 nm. It has been done. The layer numbers are listed in order from the prism side.
[Layer number] [Material] [Physical film thickness (nm)]
1 SiO ₂ 30.88
2 Al ₂ O ₃ 47.77
3 SiO ₂ 86.31
4 Al ₂ O ₃ 9.11.
5 SiO ₂ 414.72
6 Al ₂ O ₃ 28.79
7 SiO ₂ 151.63
8 Al ₂ O ₃ 169.36
9 SiO ₂ 85.01
10 Al ₂ O ₃ 110.51
11 SiO ₂ 124.0
12 Al ₂ O ₃ 20.15
13 A compound of TiO ₂ 87.27
14 Al ₂ O ₃ 25.55
15 A compound of TiO ₂ 12.32.
16 Al ₂ O ₃ 57.96
17 SiO ₂ 109.9
《Comparative example》
The comparative example is a surface reflecting mirror having the shape shown in FIG. A 57-layer reflective film 262 made of TiO ₂ (nd = 2.30) and SiO ₂ (nd = 1.46) is formed on a glass plane having a refractive index nd = 1.52. The refractive index nd is a refractive index with respect to d-line (587.6 nm).

  FIG. 15 shows the reflection characteristics of the reflective film at an incident angle of 45 °. The horizontal axis represents wavelength (unit: nm), and the vertical axis represents reflectivity (unit:%). The solid line indicates the reflectance of S-polarized light, and the broken line indicates the reflectance of P-polarized light. The reflectivity is almost 100% for the light having the wavelength λ1, the wavelength of the second light source, and the wavelength λ3 of the third light source. For convenience of drawing, only the range from 400 nm to 900 nm is shown, but even at 395 nm, the reflectance is 96% or more.

  FIG. 16 shows the retardation characteristics of the reflective film at an incident angle of 45 °. The horizontal axis represents wavelength (unit: nm), and the vertical axis represents phase difference (unit: °). As shown in FIG. 16, in the plane reflection mirror, even if 57 multilayer films are stacked, the wavelength λ1, the wavelength λ2 of the second light source, and the wavelength λ3 of the third light source, The phase difference cannot be made zero. At the same time as high reflectivity, the phase difference of one wavelength can be made zero at most.

The film configuration of the comparative example is shown below. This film configuration is designed using a commercially available thin film design software with a target of 100% reflectivity and zero phase difference between P-polarized light and S-polarized light when reflected near 405 nm, 660 nm, and 780 nm. It has been done. The layer numbers are listed in order from the prism side.
[Layer number] [Material] [Physical film thickness (nm)]
1 TiO ₂ 53.14
2 SiO ₂ 94.22
3 TiO ₂ 54.66
4 SiO ₂ 100.39
5 TiO ₂ 53.73
6 SiO ₂ 67.36
7 TiO ₂ 50.08
8 SiO ₂ 97.79
9 TiO ₂ 54.13
10 SiO ₂ 87.24
11 TiO ₂ 45.98
12 SiO ₂ 94.79
13 TiO ₂ 59.41
14 SiO ₂ 108.41
15 TiO ₂ 61.43
16 SiO ₂ 146.31
17 TiO ₂ 62.99
18 SiO ₂ 102.13
19 TiO ₂ 59.65
20 SiO ₂ 122.32
21 TiO ₂ 72.19
22 SiO ₂ 124.14
23 TiO ₂ 70.22
24 SiO ₂ 120.11
25 TiO ₂ 88.9
26 SiO ₂ 122.56
27 TiO ₂ 103.01
28 SiO ₂ 124.22
29 TiO ₂ 72.48
30 SiO ₂ 144.67
31 TiO ₂ 78.68
32 SiO ₂ 125.95
33 TiO ₂ 101.44
34 SiO ₂ 129.54
35 TiO ₂ 104.25
36 SiO ₂ 119.95
37 TiO ₂ 101.56
38 SiO ₂ 167.94
39 TiO ₂ 106.1
40 SiO ₂ 113.72
41 TiO ₂ 117.51
42 SiO ₂ 90.07
43 TiO ₂ 39.07
44 SiO ₂ 240.38
45 TiO ₂ 123.57
46 SiO ₂ 235.95
47 TiO ₂ 41.87
48 SiO ₂ 234.3
49 TiO ₂ 42.55
50 SiO ₂ 232.73
51 TiO ₂ 119.28
52 SiO ₂ 82.55
53 TiO ₂ 117.28
54 SiO ₂ 243.22
55 TiO ₂ 53.88
56 SiO ₂ 249.52
57 TiO ₂ 80.55
Example 2
The phase difference adjusting reflective film of the first embodiment is a multilayer film that does not change the phase difference of incident polarized light having a predetermined wavelength at a predetermined incident angle. A multilayer film of 14 layers made of Ta ₂ O ₅ , SiO _2, and Al ₂ O ₃ is formed on the slope of the prism having a refractive index nd = 1.77.

  8, 9, and 10 show the reflection characteristics of the phase difference adjusting reflective film when the incident angles are 43 °, 45 °, and 47 °, respectively. The horizontal axis represents wavelength (unit: nm), and the vertical axis represents reflectivity (unit:%). The solid line indicates the reflectance of S-polarized light, and the broken line indicates the reflectance of P-polarized light. The reflectivity is almost 100% at any angle. For convenience of drawing, only the range of 400 nm to 900 nm is described, but even at 395 nm, the reflectance is 95.5% or more.

  FIG. 11 shows the phase difference characteristics of the phase difference adjusting reflective film when the incident angles are 43 °, 45 °, and 47 °. The horizontal axis represents wavelength (unit: nm), and the vertical axis represents phase difference (unit: °). At any angle, the phase difference is substantially zero with respect to the first wavelength λ1, the second wavelength λ2, and the third wavelength λ3. For convenience of drawing, only the range of 400 nm to 900 nm is shown, but even at 390 nm, the phase difference is suppressed to 2 ° or less.

The film configuration of the phase difference adjusting reflective film is shown below. This film configuration is designed using a commercially available thin film design software with a target of 100% reflectivity and zero phase difference between P-polarized light and S-polarized light when reflected near 405 nm, 660 nm, and 780 nm. It has been done. The layer numbers are listed in order from the prism side.
[Layer number] [Material] [Physical film thickness (nm)]
1 Al ₂ O ₃ 66.68
2 Ta ₂ O ₅ 13.57
3 Al ₂ O ₃ 165.56
4 SiO ₂ 119.52
5 Al ₂ O ₃ 31.72
6 SiO ₂ 245.29
7 Al ₂ O ₃ 205.35
8 SiO ₂ 75.06
9 Al ₂ O ₃ 73.44
10 SiO ₂ 189.56
11 Al ₂ O ₃ 48.92
12 Ta ₂ O ₅ 147.73
13 Al ₂ O ₃ 56.11
14 SiO ₂ 92.73
Example 3
The phase difference adjusting reflective film of the second embodiment is a film for setting the phase difference of incident polarized light having a predetermined wavelength at a predetermined incident angle to a desired value. A 12-layer multilayer film made of SiO ₂ and Al ₂ O ₃ is formed on the slope of a prism having a refractive index nd = 1.77.
FIG. 12 shows the reflection characteristics of the phase difference adjusting reflective film when the incident angle is 45 °. The horizontal axis represents wavelength (unit: nm), and the vertical axis represents reflectivity (unit:%). The solid line indicates the reflectance of S-polarized light, and the broken line indicates the reflectance of P-polarized light. The reflectivity is almost 100%.

  FIG. 13 shows the phase difference characteristics of the phase difference adjusting reflective film when the incident angle is 45 °. The horizontal axis represents wavelength (unit: nm), and the vertical axis represents phase difference (unit: °). The phase difference with respect to the first wavelength λ1 is 0.17 °, the phase difference with respect to the second wavelength λ2 is 34.38 °, and the phase difference with respect to the third wavelength λ3 is 43.31 °. The phase difference adjusting reflection film compensates for the shortage of the phase difference generated by the quarter wavelength plate 150 described above. For convenience of drawing, only the range of 400 nm to 900 nm is shown, but even at 390 nm, the phase difference is suppressed to 1 ° or less.

The film configuration of the phase difference adjusting reflective film is shown below. This film configuration uses commercially available thin-film design software, with respect to the reflectance, 100% for light near 405 nm, 660 nm, and 780 nm, and for the phase difference, zero for light near 405 nm, near 660 nm. The target is designed to be 34.8 ° with respect to light and 43.3 ° with respect to light in the vicinity of 780 nm. The layer numbers are listed in order from the prism side.
[Layer number] [Material] [Physical film thickness (nm)]
1 SiO ₂ 165.97
2 Al ₂ O ₃ 238.15
3 SiO ₂ 164.27
4 Al ₂ O ₃ 77.36
5 SiO ₂ 176.52
6 Al ₂ O ₃ 179.27
7 SiO ₂ 98.26
8 Al ₂ O ₃ 71.92
9 SiO ₂ 253.77
10 Al ₂ O ₃ 40.86
11 SiO ₂ 28.47
12 Al ₂ O ₃ 164.15
The reflective optical element described in the above embodiment is a single element with a bending angle of 90 °, but the bending angle is not limited to 90 °. Further, a plurality of optical elements (for example, prisms) and the reflective optical element may be joined. Furthermore, the reflective optical element may be used not only in an optical pickup device but also in an optical system or an optical device that uses polarized light as an element that bends an optical path.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows schematic structure of the optical pick-up apparatus which is the 1st Embodiment of this invention, (a) Top view and (b) Side view. It is a figure which shows the reflective optical element which is one Embodiment of this invention. It is a figure which shows schematic structure of the optical pick-up apparatus which is the 2nd Embodiment of this invention, (a) Top view and (b) Side view. 6 is a graph showing reflection characteristics (incident angle: 43 °) of the phase difference adjusting film of Example 1. 6 is a graph showing reflection characteristics (incident angle: 45 °) of the phase difference adjusting film of Example 1. 6 is a graph showing reflection characteristics (incident angle: 47 °) of the phase difference adjusting film of Example 1. 3 is a graph showing the phase difference characteristics of the phase difference adjusting film of Example 1. 6 is a graph showing the reflection characteristics (incident angle of 43 °) of the phase difference adjusting film of Example 2. 6 is a graph showing reflection characteristics (incident angle: 45 °) of the phase difference adjusting film of Example 2. 6 is a graph showing the reflection characteristics (incident angle: 47 °) of the phase difference adjusting film of Example 2. 6 is a graph showing the phase difference characteristics of the phase difference adjusting film of Example 2. 10 is a graph showing the reflection characteristics (incident angle: 45 °) of the phase difference adjusting film of Example 3. 10 is a graph showing the phase difference characteristics (incident angle 45 °) of the phase difference adjusting film of Example 3. It is a figure which shows the reflective optical element of a comparative example. It is a graph which shows the reflective characteristic (incident angle of 45 degrees) of the reflective film of a comparative example. It is a graph which shows the phase difference characteristic (incident angle 45 degrees) of the reflecting film of a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,100 Optical pick-up apparatus 11,111 1st semiconductor laser 12,112 2nd semiconductor laser 13,113 3rd semiconductor laser 14,114 Photodetector 60,160 Reflective optical element 61 Prism 62a Reflecting surface (slope)
61b Entrance surface 62c Exit surface 62, 162 Phase difference adjusting film 70, 170 Objective lens 50, 150 1/4 wavelength plate

Claims (5)

A first light source that emits light of a first wavelength;
A second light source that emits light of a second wavelength;
A reflective optical element that bends the optical path of light from the light source;
The reflective optical element has a prism and a phase difference adjusting film formed on the reflecting surface of the prism,
The phase difference adjusting film reflects the light having the first wavelength incident on the prism so that the polarization state does not substantially change, and reflects the light having the second wavelength incident on the prism having the first wavelength in the polarization state. An optical pickup device that reflects light so as to be substantially the same as the polarization state of the light. A quarter-wave plate between the first and second light sources that emit linearly polarized light and the reflective optical element;
The quarter-wave plate converts linearly polarized light from the first light source into circularly polarized light, and the reflective optical element reflects and emits light of the first and second wavelengths as circularly polarized light. The optical pickup device according to claim 2 . A first light source that emits light of a first wavelength λ1 (395 nm <λ1 <425 nm);
A second light source that emits light of a second wavelength λ2 (630 nm <λ2 <690 nm);
A third light source that emits light of a third wavelength λ3 (740 nm <λ3 <870 nm);
A reflective optical element that bends the optical path of light from the first, second, and third light sources;
The reflective optical element has a prism and a phase difference adjusting film formed on the reflecting surface of the prism,
The phase difference adjusting film reflects the polarization state of the light of any one of the first, second, and third wavelengths incident on the prism so as not to substantially change, and changes the polarization state of the remaining two wavelengths of light. An optical pickup device that reflects light so as to be substantially the same as the polarization state of the reflected light so that the polarization state does not change. A quarter-wave plate between the first, second and third light sources that emit linearly polarized light and the reflective optical element;
The quarter-wave plate converts linearly polarized light from any one light source into circularly polarized light, and the reflective optical element reflects and emits light of the first, second, and third wavelengths as circularly polarized light. The optical pickup device according to claim 3 . The phase difference adjusting film, an optical pickup device according to any one of claims 1 to 4, characterized in that it is formed on the total reflection surface of the prism.

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