JP3474904B2 - Light head - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for recording, reproducing, and erasing information using reflected light from an optical information recording medium. 2. Description of the Related Art The structure of a conventional optical head will be described with reference to FIG. The light emitted from the laser light source 1 is incident on the grating diffraction surface 3 of the holographic grating 2 to be separated into a 0th-order light 4a and ± 1st-order lights 4b and 4c, and an objective lens (not shown). ) To form a light spot on the surface of an optical disk (not shown) as an optical information recording medium. On the disk surface, information is read using the zero-order light 4a, the ± first-order lights 4b and 4c detect the track state, become reflected light, and enter the holographic grating 2 again, so that the laser light source The light is separated into transmitted light traveling toward 1 and diffracted light traveling toward the light receiving element 7. In this case, the diffracted light is the first-order diffracted light 5a, 5a.
b, 5c and first-order diffracted lights 6a, 6b, 6c are split into two sets of light and guided to six light receiving surfaces a to f on the light receiving element 7. FIGS. 15A to 15C show light spot shapes on the surface of the light receiving element 7, wherein FIGS. 15B and 15C show when the disk surface is in focus, and FIGS. This shows the situation when the surface is near or far from the time of focusing. Here, the focus error signal Fe is detected by using the wedge prism method, and the track error signal Te and the reproduction signal Rf are detected by using the three-beam method. The calculation formula is as follows: Fe = (a + d)-(b + c) Te = ef Rf = a + b + c + d As described above, by arranging the laser light source 1 and the light receiving element 7 on the same plane and using the holographic grating 2, stable signal detection can be performed at a small size and at low cost. [0003] In the prior art shown in FIG.
Since the holographic grating 2 has only a function of simply splitting light, diffracted light that is emitted from the laser light source 1 and incident on the holographic grating 2 and is not irradiated to the optical disk is generated, or the holographic grating is reflected from the disk surface and holographically reflected. Of the light that has reentered the graphic grating 2, transmitted light that is not guided to the light receiving element 7 is generated, so that the light use efficiency is poor. Such a phenomenon of a decrease in light use efficiency does not cause much problem in a read-only optical head (CD, LD, etc.). Sufficient light power cannot be obtained at the time of recording, or an expensive and high-output laser light source must be used to obtain such sufficient light power, which is contrary to miniaturization and cost reduction. Results. According to the present invention, recording and erasing of information are performed by condensing light emitted from a laser light source by an objective lens and irradiating an optical information recording medium with a light spot. In addition, in an optical head for reproducing information or the like by guiding reflected light from the optical information recording medium to a light receiving element, a polarizing film is formed on one surface on an optical path between the laser light source and the objective lens. And a prism having a reflective film formed on a surface facing the surface of the polarizing film with a certain plate thickness, is disposed on an optical path through which light emitted from the laser light source does not pass, and the optical information recording by the reflective film is performed. A transmissive diffraction element having a diffraction grating that guides only the reflected light to the light receiving element on the optical path through which the reflected light from the medium is disposed between the prism and the laser light source , The light emitted from the laser light source is transmitted through the transmission type diffraction element.
, The laser light source and the light receiving element were arranged close to each other and housed in the same package. According to the present invention, the light emitted from the laser light source passes through the diffraction grating of the transmission type diffraction element. Since only the reflected light from the optical information recording medium passes through and all the diffracted light that has passed through is guided to the light receiving element, the amount of light applied to the optical information recording medium is reduced or the surface of the medium is reduced. It is possible to eliminate the problem that a part of the reflected light amount from the light is not guided to the light receiving element, to increase the light use efficiency, and to use a low-power laser light source. An embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 shows the entire configuration of an optical head, and the light a emitted from a semiconductor laser 8 as a laser light source is shown in FIG.
Is collimated by a collimating lens 9, condensed by an objective lens 11 via a quarter-wave plate 10, and irradiated on a surface of an optical disc 12 as an optical information recording medium, thereby recording, reproducing, and reproducing information. Erasing or the like is performed. In the present embodiment, in such an optical head, the polarizing film 1 is entirely formed on the optical path between the semiconductor laser 8 and the objective lens 11.
A PBS prism (polarizing beam splitter) 13 as a prism having a reflective film 13b formed on a surface opposite to the surface of the polarizing film 13a with a certain thickness.
Was arranged. Further, a transmission type diffraction grating 14 having a diffraction grating 15 is disposed between the PBS prism 13 and the semiconductor laser 8. The diffraction grating 15 is
a formed on a portion of the laser beam a
Is reflected on the optical path through which the light does not pass and the reflected light b from the optical disc 12 is reflected on the optical path through the PBS prism 13.
It is arranged so that only the light is guided to the light receiving element 16. FIG. 2A shows a grating shape of the diffraction grating 15, which is divided into regions (here, regions 15a to 15c) in order to detect a focus error signal Fe and a track error signal Te. Accordingly, the light receiving element 16 is also divided into multiple regions (four regions here) according to the number of divisions of the diffraction grating 15. As described above, various division methods of the diffraction grating 15 and the light receiving element 16 can be considered depending on the signal detection method. The semiconductor laser 8 and the light receiving element 16 are in the same package 17.
(TO-5, etc.). In such a configuration, the semiconductor laser 8
Is reflected by the polarizing film 13a of the PBS prism 13, is converted into parallel light by the collimating lens 9, becomes circularly polarized by the quarter wavelength plate 10, and becomes the objective lens 11. And irradiates the light onto the surface of the optical disk 12, thereby recording and erasing information. Further, the reflected light b from the optical disk 12 follows an optical path opposite to the incident optical path, becomes linearly polarized light whose direction is changed by 90 ° from the outgoing light a by the 波長 wavelength plate 10, and the polarized light of the PBS prism 13. After being transmitted through the film 13a and reflected by the reflection film 13b, the light is guided to the diffraction grating 15 of the transmission type diffraction element 14. This diffraction grating 15 has a plurality of regions 15a to 15c.
Therefore, the reflected light b is split by this and detected by the light receiving element 16. Thus, the information reproduction signal Rf, the focus error signal Fe, and the track error signal Tr can be detected. As described above, on the optical path through which the light a emitted from the semiconductor laser 8 does not pass through the diffraction grating 15 of the transmission type diffraction element 14, and the reflected light b
The reflected light b placed on the optical path through the S prism 13
By adopting an optical isolator configuration in which only the light is guided to the light receiving element 16, the amount of outgoing light “a” applied to the optical disk 12 is reduced or a part of the amount of reflected light “b” from the disk surface is reduced. It is possible to eliminate the phenomenon of light loss that the light is not guided to the light receiving element 16, and it is possible to increase the light use efficiency as compared with the related art. In this way, light loss is small and light use efficiency can be increased,
A low-power laser light source can be used, thereby realizing a low-cost optical head. Here, since the semiconductor laser 8 and the light receiving element 16 are integrated in the package 17, the size can be reduced and the operation can be performed stably with time. Next, a first modification of the present invention will be described with reference to FIGS. The description of the same parts as those of the embodiment of the present invention is omitted, and the same parts are denoted by the same reference numerals. In the above-described embodiment of the present invention, the transmission type diffraction element 14 is used, but in this modification , a reflection type diffraction element 19 is used instead. That is, as shown in FIG. 3, a PBS prism 13 having a polarizing film 13a formed on one surface is disposed on an optical path between the semiconductor laser 8 and the objective lens 11, and the polarizing film 13a of the PBS prism 13 is formed. -Type diffraction element 19 having a diffraction grating 18 on a surface opposite to the set surface with a certain thickness (plate thickness) t
Are bonded and fixed and provided integrally. In such a configuration, the optical disk 12
Reflected light b from the polarizing film 13 in the PBS prism 13
reflective diffractive element 1 that is transmitted through a and disposed on the opposite surface
The light is diffracted by the nine diffraction gratings 18, and all the diffracted light is guided to the light receiving element 16. This reflection type diffraction element 1
Also in the case of No. 9, various signals can be easily detected by dividing the area similarly to the transmission type diffraction element 14. Accordingly, since the reflection type diffraction element 19 is used as the reflection type, the diffraction grating 18 is arranged on the surface on the other side of the polarizing film 13a when viewed from the emission light side. Outgoing light a does not pass through the diffraction grating 18 toward the optical disk 12,
Since the plate thickness t between the surface of the polarizing film 13a and the surface on the side of the diffraction grating 18 can be reduced and the plate thickness t can have a certain range of change, the light receiving element as shown in FIG. The position P of the focal point on the 16 surfaces can be set relatively arbitrarily according to the thickness D of the light receiving substrate. In addition, since the outgoing light a from the semiconductor laser 8 toward the optical disk 12 does not transmit as in the case of the substrate 14a of the transmission type diffraction element 14 described above, compared with the transmission type, it is necessary to adjust the assembly of the diffraction grating 18. The emitted light a does not fluctuate and stable assembly adjustment can be performed. In addition, also in the case of the present embodiment, it is possible to increase the light use efficiency and realize a low-cost optical head. Next, a second variant of the present invention FIGS. 5-6
It will be described based on. In addition, the embodiment of the present invention described above and
The description of the same parts as those of the first modified example is omitted, and the same reference numerals are used for the same parts. In the above-described embodiment of the present invention, the PBS prism 13 is used, but in this modification , a polarization splitting element is used instead. That is, as shown in FIG. 5, a polarization splitting function (P) having different emission angles depending on the polarization direction on the optical path between the semiconductor laser 8 and the objective lens 11.
A function is to dispose a Wollaston prism 20 as a polarization splitting element having a function of angularly separating polarized light and S-polarized light. Accordingly, the reflected light b from the optical disc 12 is guided to the light receiving element 16 on the optical path through which the light a emitted from the semiconductor laser 8 does not pass and the reflected light b from the optical disk 12 passes through the Wollaston prism 20. The transmission type diffraction element 14 having the diffraction grating 15 was provided. The Wollaston prism 20 generally has a higher extinction ratio and a higher separation angle accuracy than other prisms. Therefore, the reason why the separation angle accuracy is increased will be described with respect to an example in which the separation angle accuracy is compared with that of the PBS prism 13 as shown in FIGS. First,
In the PBS prism 13 of (b), the outgoing light a and the reflected light b
Is performed by adjusting the plate thickness t.
However, if the plate thickness t becomes t + to due to an error, the position of the condensing point shifts from point P to point Q. In general, since the accuracy of the plate thickness t is about ± 0.1 mm, it can be expected that the positional deviation amount Δ of the light-converging point is also about Δ = ± 0.1 mm. On the other hand, in the Wollaston prism 20 of (a), the separation between the output light a and the reflected light b is performed by the separation angle θ.
It is done by adjusting. In this case, the separation angle θ
Is about ± 0.03 °, and assuming that the distance between the Wollaston prism 20 and the light receiving element 16 is 5 mm, the positional deviation amount Δ of the focal point P is Δ = 5 tan 0.03 ° = 0.0026 mm. This Δ value is found to be about 1/50 smaller than the Δ value of the PBS prism 13. For this reason, the Wollaston prism 2 is smaller than the PBS prism 13.
A value of 0 makes it possible to reduce the degree of variation of the positional deviation amount Δ based on the accuracy of each component, thereby reducing the ratio of the detected signal offset. Therefore, by using the Wollaston prism 20 having the polarization splitting function, the extinction ratio and the accuracy of the polarization splitting angle can be further improved, and the variation of the assembly error can be reduced. The yield can be improved and a low-cost optical head can be obtained. The polarization separation element is not limited to the Wollaston prism 20, but may be a lotion prism, a Senarmont prism, or any other element having a polarization separation function in which the light emission angle varies depending on the polarization direction. FIG. 7 shows a third modification of the present invention . Although the Wollaston prism 20 is disposed between the semiconductor laser 8 and the collimating lens 9 in the configuration of FIG. 5 described above, here, the Wollaston prism 20 is disposed between the collimating lens 9 and the 波長 wavelength plate 10. It is arranged. By arranging the Wollaston prism 20 in the parallel optical path in this way, it is possible to provide a margin for the arrangement space as compared with the case where the Wollaston prism 20 is arranged in the convergent optical path as in the modification of FIG. Accuracy is eased, and assembly adjustment is facilitated. By using the collimating lens 9 having a large NA to enhance the light use efficiency, the working distance (the distance between the semiconductor laser 8 and the collimating lens 9) may be reduced, and the Wollaston prism 20 may not be arranged. However, there is no problem if the arrangement is as in the present modification . Next, a fourth modification of the present invention will be described with reference to FIG. Note that the above-described embodiment of the present invention and the first,
The description of the same parts as in the second modification is omitted, and the same parts are denoted by the same reference numerals. In this modification, the embodiment of the present invention or the second embodiment
In the optical head of the modified example, a transmission type diffraction element 14 having a diffraction grating 15 is provided on a window cap 17a of a package 17 in which a semiconductor laser 8 and a light receiving element 16 are sealed.
Are integrally attached. The semiconductor laser 8 and the light receiving element 16 are mounted on the side and top of the stem 17b, respectively. The diffraction grating 1 is located above the light receiving element 16.
5 is arranged facing the inside of the cap, and the substrate 1
Both ends of 4a are fixed to the upper inner wall of the window cap 17a. Thereby, in the package 17,
Since the semiconductor laser 8, the light receiving element 16, and the diffraction grating 15 are integrated, the size can be further reduced. In addition, it is possible to stabilize the assembly by such an integrated structure, and by arranging the lattice surface toward the inside of the cap, it is strong against dust and scratches, and further stabilization can be achieved. . Furthermore, if a method (knife edge method) in which the diffraction grating 15 is not adjusted in the optical axis direction is adopted, the window cap 17a
Can be finely adjusted and fixed at the time of sealing, and assembly can be performed easily. Next, a fifth modification will be described with reference to FIGS. Note that the above-described embodiment of the present invention and the first,
The description of the same parts as in the second modification is omitted, and the same parts are denoted by the same reference numerals. In each of the embodiments and the modified examples described above, the function of splitting the light constituting the optical isolator (diffraction gratings 15 and 18) and the function of separating the polarization (PBS prism 1)
3, although Wollaston prism 20) and has been described for the case that has been each separately present, in this modification, these two
One function is realized by one element. That is, as shown in FIG. 9, on the optical path between the semiconductor laser 8 and the objective lens 11, a diffraction grating 2 having a light splitting function and a polarization splitting function whose diffraction efficiency changes according to the polarization direction.
1a and 21b are arranged close to each other so as to face each other. These diffraction gratings 21a and 21b are
2a and 22b are formed on one surface, respectively. In this case, the reason why the grating is arranged obliquely with respect to the optical axis is to make a black angle with respect to the light, and the separation angle is reduced by using two gratings.
Diffraction angle fluctuation due to wavelength fluctuation can be canceled. FIGS. 10A and 10B show diffraction gratings 21a and 2a.
1B shows the lattice shape of FIG. Diffraction grating 21a,
21b (diffraction grating 2
1a) is formed such that the grating pitch or the grating vector direction is different. Hereinafter, a case where the diffraction efficiency has a small pitch (1 μm or less), a deep groove (an aspect ratio of 1.5 or more), and a high-density deep groove lattice shape will be described. In such a configuration, the semiconductor laser 8
The light a emitted from the optical disk 12 has a polarization direction perpendicular to the grating, so that about 90 to 100% of the light is transmitted as it is without being diffracted, is irradiated on the surface of the optical disk 12, and is reflected from the optical disk 12. The light b is rotated in the polarization direction by 90 ° by the quarter-wave plate 10 and travels in a polarization state parallel to the grating, and is diffracted by the two diffraction gratings 21a and 21b with an efficiency of about 90 to 100%, respectively. Light receiving element 16
Head to. Since the diffraction grating 21a is divided into a plurality of regions, it can correspond to various signal detection methods. Therefore, by using two diffraction gratings 21a and 21b whose diffraction efficiency changes depending on the polarization direction, the number of components can be reduced, and the diffraction angle fluctuation due to wavelength fluctuation, which is a drawback of the diffraction grating itself, is also reduced. Can be canceled. Also, the two diffraction gratings 21a, 21
b are arranged close to each other to minimize the occurrence of astigmatism. Further, if the two prisms 22a and 22b are integrated, a cube having no grating surface on the light incident side surface can be obtained. Since it becomes a prism, handling becomes easy. FIG. 11 shows a sixth modification. The diffraction gratings 21a and 21b are formed on both sides of a thin substrate 24, and the substrate 24 is mounted above the window cap 17a constituting the package 17 in a state inclined with respect to the optical axis. In this way, by integrating the two diffraction gratings 21a and 21b together with the semiconductor laser 8 and the light receiving element 16, a more compact configuration can be achieved. FIG. 12 shows a seventh modification. 9 and 11 described above, two diffraction gratings 2 are used.
Although the reference numerals 1a and 21b are arranged on a converging optical path between the semiconductor laser 8 and the collimating lens 9, here, the diffraction gratings 21a and 21b are connected to the collimating lens 9 and the 1/4 wavelength plate 1 respectively.
It is arranged on a parallel optical path between 0. Since the diffraction gratings 21a and 21b are formed on the two prisms 22a and 22b and the substrate that is a parallel flat plate, astigmatism is likely to occur when divergent light is incident. Occurrence of astigmatism becomes extremely small, whereby the collimator lens 9 having a large NA can be used similarly to the third modification of FIG. 7 described above, and the light use efficiency can be improved. In addition, since the angles of the light incident on the diffraction gratings 21a and 21b are all black angles, the extinction ratio is improved and the noise due to the return light of the emitted light a can be reduced. Next, an eighth modification will be described with reference to FIG. The above-described embodiments of the present invention, the first to fifth embodiments
The description of the same parts as those of the modification is omitted, and the same reference numerals are used for the same parts. This modification is a modification of the above-described embodiment and each modification.
This is an example in which the element having the light separation function described in the example , the diffraction grating, and the laser light source are integrated. FIG. 13A shows a PBS prism 13 having a polarizing film 13a and a diffraction grating 1 according to an embodiment of the present invention (see FIG. 1).
5, a transmission type diffraction element 14 having a semiconductor laser 8,
The light receiving element 16 is integrally formed. FIG.
(B) shows the polarizing film 1 in the first modification (see FIG. 3).
A PBS prism 13 having 3a, a reflection type diffraction element 19 having a diffraction grating 18, a semiconductor laser 8, and a light receiving element 16 are integrally formed. FIG. 13 (c)
In the second modification , a Wollaston prism 20 having a polarization splitting function, a transmission type diffraction element 14 having a diffraction grating 15, a semiconductor laser 8, and a light receiving element 16 in the second modification (see FIG. 5) are integrally formed. Things. FIG. 13 (d)
In the fifth modification , the diffraction gratings 21a and 21b having the light separation function and the polarization separation function in the fifth modified example (see FIG. 9), the semiconductor laser 8, and the light receiving element 16 are integrally formed. This makes it possible to achieve further downsizing with stability over time. Further, by making the housing plastic, weight reduction can be achieved, and high-speed access can be realized. Further, by sealing the semiconductor laser 8 directly using an element having a polarization splitting function or a diffraction grating, the window cap 17a becomes unnecessary, and the manufacturing process can be simplified. In addition, TO
It is also conceivable to attach it to a stem other than the existing package 17, such as -5. Even in such a case, the manufacturing process can be simplified and reliability can be ensured. According to the present invention, recording and erasing of information are performed by condensing the light emitted from a laser light source by an objective lens and irradiating the optical information recording medium with a light spot.
In an optical head that reproduces information by guiding the reflected light from the optical information recording medium to a light receiving element, a polarizing film is formed on the entire surface of the optical path between the laser light source and the objective lens, and A prism on which a reflection film is formed on a surface facing the surface of the polarizing film with a certain plate thickness is disposed, and on the optical path through which light emitted from the laser light source does not pass and from the optical information recording medium by the reflection film. a transmission type diffraction element is reflecting light having a diffraction grating that guides only the reflected light on the optical path through the prism to the light receiving element, before
Disposed between serial prism and said laser light source, the laser
Light emitted from a light source passes through the transmission diffraction element.
Since the laser light source and the light receiving element are arranged close to each other and housed in the same package, the amount of light applied to the optical information recording medium is reduced or a part of the amount of light reflected from the medium surface is reduced to the light receiving element as in the related art. It is possible to eliminate the problem of being no longer guided, improve the light use efficiency, and realize a low-cost optical head using a low-output laser light source. ## EQU00001 ##

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an optical path diagram showing an overall configuration of an optical head according to an embodiment of the present invention. FIG. 2A is a front view showing a region-divided diffraction grating, and FIG. 2B is a front view showing a multi-divided light receiving element. FIG. 3 is an optical path diagram showing a partial configuration of an optical head according to a first modification . FIG. 4 is an optical path diagram showing a positional relationship of light reflected by a polarizing film surface and a grating surface. FIG. 5 is an optical path diagram showing an overall configuration of an optical head according to a second modification . 6A is an optical path diagram showing an optical path separation state by a Wollaston prism, and FIG. 6B is an optical path diagram showing an optical path separation state by a PBS prism. FIG. 7 is an optical path diagram showing a configuration of an optical head when a polarization splitting element is arranged in a parallel optical path. FIG. 8 is a vertical sectional side view showing a configuration inside a package of an optical head according to a fourth modified example. FIG. 9 is an optical path diagram showing a partial configuration of an optical head according to a fifth modification . FIGS. 10A and 10B show a fifth modification , in which FIG. 10A is a front view showing a diffraction grating divided into regions, and FIG. 10B is a front view showing a diffraction grating not divided into regions. FIG. 11 is a longitudinal sectional side view showing a configuration inside a package of an optical head according to a sixth modified example . FIG. 12 is an optical path diagram showing a configuration of an optical head when a prism having a diffraction grating according to a seventh modified example is arranged in a parallel optical path. FIG. 13 is a side view showing a configuration of a package section of various optical heads according to an eighth modification . FIG. 14 is a perspective view showing an optical path separation state when a conventional diffraction element is used. FIG. 15 is a front view showing various light spot states on the light receiving surface of the light receiving element. Explanation of code 8 laser light source 11 objective lens 12 optical information recording medium 13 prism 13a polarizing film 14 transmission type diffraction element 15 diffraction grating 16 light receiving element 17a cap 18 diffraction grating 19 reflection type diffraction element 20 polarization separation element 21a, 21b diffraction Lattice 24 substrate

   ────────────────────────────────────────────────── ─── Continuation of front page       (56) References JP-A-4-67452 (JP, A)                 JP-A-2-29943 (JP, A)                 JP-A-3-125340 (JP, A)                 JP-A-3-192305 (JP, A)                 JP-A-62-8347 (JP, A)                 JP-A-3-250437 (JP, A)                 JP-A-4-276319 (JP, A)                 JP-A-1-313988 (JP, A)                 JP-A-3-254448 (JP, A)                 JP-A-62-141652 (JP, A)

Claims (1)

(57) [Claims 1] The recording and erasing of information is performed by condensing the light emitted from a laser light source with an objective lens and irradiating the optical information recording medium with a light spot. In an optical head that reproduces information by guiding the reflected light from the optical information recording medium to a light receiving element, a polarizing film is formed on the entire surface of the optical path between the laser light source and the objective lens, and A prism on which a reflection film is formed on a surface facing the surface of the polarizing film with a certain plate thickness is disposed, and on the optical path through which light emitted from the laser light source does not pass and from the optical information recording medium by the reflection film. A transmission type diffraction element having a diffraction grating that guides only the reflected light to the light receiving element on an optical path through the prism,
The laser light source is disposed between the laser light sources.
An optical head , wherein the laser light source and the light receiving element are arranged close to each other and housed in the same package by the emitted light passing through the transmission type diffraction element .