JP2005077659A - Optical element and optical pickup device using the element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element, in which requests to reduce the size and the cost are met and optical performance is improved, and to provide an optical pickup device which uses the element. <P>SOLUTION: An optically transmissive substrate 16 is provided with at least a surface 18, which has micronized periodic structures 17 and has a function equivalent to a 1/4 wave plate and a surface 21 which has micronized periodic structures 20 and has functions equivalent to those of a polarized beam splitter. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical element and an optical pickup device using the optical element, and more particularly to an optical element having a function as a polarization separating element and a function as a quarter wavelength plate, and an optical pickup apparatus including the optical element. .

  Conventionally, as an optical element for an optical pickup used in an optical pickup apparatus, there are an objective lens, a collimator lens, a cylindrical lens, a quarter wavelength plate (QWP), a polarization beam splitter (PBS) as a polarization separation element, and the like. .

  FIG. 6 shows an example of a conventional optical pickup device constituted by such an optical element.

  The optical pickup device 1 includes a diffraction grating 3, a polarization beam splitter 4, a quarter wavelength plate 5, a collimator lens 6, and an objective lens 7, which are arranged separately from light emitted from a light source 2 such as a laser diode. Are sequentially transmitted to irradiate the optical recording medium 9, and the reflected light is transmitted through the objective lens 7 and the quarter-wave plate 5, and then in the direction orthogonal to the transmission direction in the polarization beam splitter 4. It is designed to reflect.

  The reason why the light is reflected by the polarization beam splitter 4 is that the polarization of the light changes when it passes through the quarter-wave plate 5 twice. For example, if the light from the light source 2 is s-polarized light, the light transmitted through the quarter-wave plate 5 twice is p-polarized light.

  The light reflected by the polarization beam splitter 4 is collected by the cylindrical lens 10 and then received by the photodetector 11 to be used as read data or the like.

JP 2000-182266 A

  By the way, in recent years, demands for downsizing and cost reduction of such optical elements and optical pickup devices using the optical elements are increasing. In order to satisfy such demands, the number of parts is reduced and assembly is performed. It is effective to simplify the process.

  However, the quarter-wave plate 5 used as a glass optical element has a structure in which a liquid crystal sheet called a phase film is sandwiched between two glass substrates, so the number of parts increases. In addition, the optical performance has a drawback that transmitted wavefront aberrations are likely to occur.

  Furthermore, since the polarizing beam splitter 4 as another glass optical element has a structure in which block-shaped glass is bonded, high-precision bonding is required at the time of bonding, resulting in a complicated assembly process. As a result, the cost increased.

  Therefore, as a result of diligent research, the present inventor has achieved a reduction in the number of parts by realizing an optical element in which a quarter-wave plate and a polarization separation element are integrated using a recent micro-processing technique such as a nano-processing technique. In addition, the present invention has been made to realize the simplification of the assembly process and the improvement of the optical performance.

  The present invention has been made in view of the above points, and can satisfy the demands for miniaturization and cost reduction, and at the same time, an optical element capable of improving optical performance, and an optical pickup using the same. The object is to provide an apparatus.

  In order to achieve the above-described object, the optical element according to claim 1 of the present invention is characterized in that a light-transmitting substrate has at least a surface having a function equivalent to a quarter-wave plate made of a fine periodic structure, and a fine periodicity. And a surface having a function equivalent to a polarization separation element having a structure.

  According to such a configuration, an optical element in which the quarter-wave plate and the polarization separation element are integrated can be realized. As a result, the number of parts is reduced, the assembly process is simplified, The transmitted wavefront aberration can be reduced by reducing the number of light transmission interfaces that contribute to the light transmission of the optical element.

  The optical element according to claim 2 is characterized in that, in claim 1, a surface having a function corresponding to the ¼ wavelength plate and a surface having a function corresponding to the polarization separating element are mutually connected to each other on the light transmitting substrate. It exists in the point arrange | positioned on a different surface.

  And according to such a structure, the manufacturing process was further simplified by forming the surface which has a function equivalent to a quarter wavelength plate, and the surface which has a function equivalent to a polarization separation element more simply. An optical element can be realized.

  The optical pickup device according to claim 3 has at least a surface having a function equivalent to a quarter-wave plate made of a fine periodic structure and a function equivalent to a polarization separation element made of a fine periodic structure on a light-transmitting substrate. And an optical element provided with a surface having the same.

  And according to such a structure, the optical pick-up apparatus using the optical element with which the quarter wavelength plate and the polarization separation element were integrated can be implement | achieved, As a result, a number of parts can be reduced and it can assemble It is possible to reduce the transmitted wavefront aberration by simplifying the process and further reducing the number of light transmission interfaces of the optical element.

  According to a fourth aspect of the present invention, there is provided the optical pickup device according to the third aspect, wherein the surface of the optical element having a function corresponding to the quarter-wave plate and the surface having a function corresponding to the polarization separation element are the light. It exists in the point arrange | positioned on the mutually different surface of a transparent substrate.

  And according to such a structure, the manufacturing process was further simplified by forming the surface which has a function equivalent to a quarter wavelength plate, and the surface which has a function equivalent to a polarization separation element more simply. An optical pickup device using an optical element can be realized.

  According to the optical element of the first aspect, it is possible to satisfy the demands for miniaturization and cost reduction, and to realize an optical element capable of improving the optical performance by reducing the transmitted wavefront aberration. it can.

  According to the optical element according to the second aspect, in addition to the effect of the optical element according to the first aspect, a further inexpensive optical element can be realized.

  According to the optical device of the third aspect of the present invention, it is possible to realize an optical pickup device that can satisfy the demands for miniaturization and cost reduction, and can reduce the transmitted wavefront aberration and improve the optical performance. Can do.

  According to the optical device of the fourth aspect, in addition to the effect of the optical pickup device according to the third aspect, a further inexpensive optical pickup device can be realized.

  Hereinafter, an optical element according to an embodiment of the present invention and an optical pickup apparatus including the optical element will be described with reference to FIG.

  Note that the same reference numerals are used for the same or similar parts in the basic configuration as in the prior art.

  As shown in FIG. 1, the optical element 15 in this embodiment includes a subwavelength structure 17 as a fine periodic structure on one surface (a lower surface in FIG. 1) of a light-transmitting substrate 16 made of glass or the like. A surface 18 having a function equivalent to a / 4 wavelength plate is provided.

  The sub-wavelength structure 17 constituting the surface 18 is a structure formed using a fine processing technique such as a nano processing technique so that the formation pitch (uneven pitch) is smaller than the wavelength of light used. The structure shown in FIG. 1 is formed in a lattice shape having a rectangular cross section, but other cross sectional shapes can also be selected.

Moreover, as a material constituting the sub-wavelength structure 17, a material such as SiN _X or Si (preferably having a refractive index of 2.0 or more) can be appropriately selected.

  Furthermore, the optical element 15 in the present embodiment corresponds to a polarization separation element (polarization beam splitter) composed of a sub-wavelength structure 20 as a fine periodic structure on the other surface (upper surface in FIG. 1) of the light transmissive substrate 16. A surface 21 having a function is provided.

  This sub-wavelength structure 20 is also a structure formed in a size smaller than the wavelength of light used for forming pitch by using a fine processing technique such as a nano-processing technique like the sub-wavelength structure 17 described above. .

  In FIG. 1, a sub-wavelength structure 20 constituting the surface 21 is a so-called wire grid type sub-wavelength structure in which metals such as Au are arranged in a lattice pattern.

  As a constituent material of the sub-wavelength structure 20, a material such as Ag, Cu, or Al can be selected in addition to Au.

For example, a multilayer structure made of Si or SiO ₂ may be disposed on the surface of the light transmissive substrate 16 without being limited to the wire grid.

  Thus, in the present embodiment, the surface 18 having a function equivalent to a quarter-wave plate made of the sub-wavelength structure 17 and the surface 21 having a function equivalent to a polarization separation element made of the sub-wavelength structure 20 are provided. By providing the same light-transmitting substrate 16, it is possible to realize the optical element 15 in which the quarter-wave plate and the polarization separation element are integrated.

  As a result, the number of parts of the optical element 15 can be reduced, the assembly process can be simplified, and the number of light transmission interfaces of the optical element 15 can be reduced to reduce transmitted wavefront aberration (see FIG. 2). ).

  Further, if the transmitted wavefront aberration of the same level as that of the present situation is allowed, the tolerance of the transmitted wavefront accuracy can be relaxed, and further cost reduction can be realized by improving the yield.

  Further, as shown in FIG. 1, a surface 18 having a function equivalent to a ¼ wavelength plate (hereinafter referred to as “¼ wavelength plate-side functional surface 18”) and a surface 21 having a function corresponding to a polarization separation element ( (Hereinafter referred to as “polarized light separating element-side functional surface 21”) can be formed on the different surfaces of the light-transmitting substrate 16 to form the functional surfaces 18 and 21 more simply. The optical element 15 with a simplified manufacturing process can be realized.

  The quarter-wave plate side functional surface 18 and the polarization separation element side functional surface 21 may be laminated on one surface side of the light transmissive substrate 16. Even in this case, both the functional surfaces 18 and 21 can ensure a function corresponding to a quarter wavelength plate and a function equivalent to a polarization separation element, respectively. Reduction, simplification of the assembly process, and reduction of transmitted wavefront aberration can be achieved.

  Further, in addition to the above configuration, an AR film as an antireflection film is disposed between the outer surface of the polarization separation element side functional surface 21 or between the light transmitting substrate 16 and the polarization separation element side functional surface 21. It may be. Thereby, an optical element with further improved optical performance can be realized.

  As shown in FIG. 2, the optical element having the above configuration can constitute an optical pickup device 23 together with other optical elements.

  The optical pickup device 23 has a diffraction grating 3 that is arranged orthogonal to the optical axis of the light source light in the traveling direction of the light source light emitted from the light source 2 such as a laser diode. In the light transmission direction of the diffraction grating 3, the optical element 15 of the present invention has a predetermined inclination angle (for example, with respect to the optical axis of the light source light so that the polarization separation element side functional surface 18 faces the diffraction grating 3 side. 45 °).

  Further, in the light transmission direction of the optical element 15, the collimator lens 6, the objective lens 7, and the optical recording medium 9 are sequentially disposed so as to be orthogonal to the optical axis of the light source light. , 7 and 9 are faced with the quarter-wave plate-side functional surface 18 having a predetermined inclination angle (for example, 45 °).

  Furthermore, in the reflection direction of the light reflected from the optical recording medium 9 in the optical element 15, the cylindrical lens 10 and the photodetector 11 as the light receiving element are sequentially arranged so as to be orthogonal to the optical axis of the reflected light from the optical element 15. Has been.

  Unlike the conventional optical pickup device 23 in which the quarter-wave plate and the polarizing beam splitter are separately provided, the function of the quarter-wave plate and the polarizing beam splitter is one optical element. 15 is integrated. As a result, the number of parts (the number of optical elements) of the optical pickup device 23 is reduced, and accordingly, downsizing and cost reduction of the optical pickup device 23 are realized. Further, the number of surfaces of the light transmission interface of the optical element is reduced and the transmitted wavefront aberration is reduced, so that the error rate is reduced and the performance of the optical pickup device 23 itself is improved. With such an optical pickup device 23, good performance is expected even when using light with a shorter wavelength, such as a DVD or a blue laser.

  And in order to read the data of the optical recording medium 9 by such an optical pick-up apparatus 23, first, the light source light radiate | emitted from the light source 2 permeate | transmits an optical element through a diffraction grating. At this time, the transmission interface of the light source light is an interface with the air of the polarization separation element side functional surface 21, an interface with the air of the light transmissive substrate 16 (two surfaces), and the air of the quarter wavelength plate side functional surface 18. There are a total of four interfaces, and the number of light transmission interfaces is reduced as compared with the conventional configuration. In the conventional configuration, only the transmission interface of the quarter wavelength plate 5 requires four surfaces, and if the transmission interface of the polarizing beam splitter 4 is added to this, more transmission interfaces are required than those of the present invention. Was.

  The transmitted light that has passed through the optical element 15 passes through the collimator lens 6 and is then focused and irradiated on the recording surface of the optical recording medium 9 by the objective lens 7.

  The irradiation light applied to the optical recording medium 9 is reflected by the recording surface, and the reflected light travels in the direction opposite to the traveling direction of the irradiation light and passes through the objective lens 7 and the collimator lens 6. The light enters the quarter-wave plate-side functional surface 18 of the optical element 15 and is reflected by the quarter-wave plate-side functional surface 18.

  Next, the reflected light reflected by the quarter-wave plate-side functional surface 18 is received by the photodetector after passing through the cylindrical lens. Thereby, the recording data of the optical recording medium contained in the reflected light is read out.

  In addition to the optical pickup apparatus shown in FIG. 2, for example, an optical pickup apparatus having an arrangement configuration of optical elements as shown in FIG. 3 may be adopted.

  The optical pickup device 24 shown in FIG. 3 is different from that shown in FIG. 2 in that the optical element 15 is arranged with the quarter-wave plate-side functional surface 18 facing the light source 2 side. The light source light reflected by the / 4 wavelength plate-side functional surface 18 is reflected to the optical recording medium 9 side via the reflection mirror 25 so that the light source light is incident on the recording surface of the optical recording medium 9.

  Then, the reflected light incident on and reflected by the optical recording medium 9 is reflected to the optical element 15 side through the reflecting mirror 25 and then transmitted through the optical element 15 to be received by the photodetector 11. ing. In FIG. 3, the quarter-wave plate-side functional surface 18 of the optical element 15 functions so that the reflected light from the reflection mirror 25 is not reflected to the light source 2 side.

  In such an optical pickup device 24 as well, as in the case shown in FIG. 2, the optical pickup device 24 can be reduced in size, cost, and optical performance.

  In the present embodiment, a sample having a polarization separating element side functional surface 21 specifically configured to have a size as shown in FIG. 4 and a quarter wavelength plate side having a size as shown in FIG. The optical characteristics of the sample provided with the functional surface 18 were tested using the RCWA method.

The results are shown in Table 1 and Table 2 below.

  Table 1 shows the light quantity ratio (extinction ratio, reflection ratio) set on the glass substrate (BK7). This Table 1 shows the polarization separation element (polarization light) of the polarization separation element side functional surface shown in FIG. It becomes an index indicating the performance as a beam splitter.

As shown in Table 1, the reflection ratio at 785 nm, which is the use wavelength of CD, was -20 dB, which was a sufficiently usable value.

  Table 2 shows retardation (phase delay amount δφ) data indicating the characteristics of the quarter-wave plate-side functional surface.

  As shown in Table 2, the retardation value was δφ = 87.6 ° at the operating wavelength of 785 nm with respect to 90 ° required for the quarter-wave plate.

  This value is a sufficiently usable value in view of the fact that the tolerance of the current quarter wavelength plate is about 90 ± 4 °.

  Thus, it can be seen that the optical element in the present invention can exhibit optical performance that can sufficiently replace the quarter-wave plate and the polarization separation element, which have been conventionally separated.

  In addition, this invention is not limited to embodiment mentioned above, A various change is possible as needed.

Sectional drawing which shows typically embodiment of the optical element which concerns on this invention The block diagram which shows embodiment of the optical pick-up apparatus which concerns on this invention FIG. 2 is a configuration diagram showing another embodiment different from FIG. 2 in the embodiment of the optical pickup device according to the present invention. Explanatory drawing which showed the specific dimension of the polarization separation element side functional surface used for a characteristic test in embodiment of the optical element which concerns on this invention Explanatory drawing which showed the specific dimension of the 1/4 wavelength plate side functional surface used for a characteristic test in embodiment of the optical element which concerns on this invention. Configuration diagram showing an optical element conventionally employed and an optical pickup device using the same

Explanation of symbols

DESCRIPTION OF SYMBOLS 15 Optical element 16 Light transmissive board | substrate 17 Subwavelength structure 18 1/4 wavelength plate side functional surface 20 Subwavelength structure 21 Polarization separation element side functional surface 23,24 Optical pick-up apparatus

Claims (4)

An optical device comprising a light-transmitting substrate having at least a surface having a function equivalent to a quarter-wave plate having a fine periodic structure and a surface having a function corresponding to a polarization separation element having a fine periodic structure. element. 2. The surface having a function corresponding to the ¼ wavelength plate and the surface having a function corresponding to the polarization separation element are disposed on different surfaces of the light transmitting substrate. An optical element according to 1. An optical element having at least a surface having a function equivalent to a quarter-wave plate made of a fine periodic structure and a surface having a function equivalent to a polarization separation element made of a fine periodic structure was used on the light transmissive substrate. An optical pickup device characterized by the above. The surface of the optical element having a function equivalent to the ¼ wavelength plate and the surface having a function corresponding to the polarization separation element are disposed on different surfaces of the light-transmitting substrate. The optical pickup device according to claim 3.