JP2011054273A - Polarization diffraction element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical head device capable of performing a stable signal detection when recording and reproducing information of an optical disk. <P>SOLUTION: A polarization diffraction element 1 does not act as a diffraction grating to incident light of a first linearly polarized light beam to be emitted light from a semiconductor laser 5 to transmit the incident light, but acts as a diffraction grating to incident light of a second linearly polarized light beam, to be a reflected returned light from the optical disk 7, in a polarization direction orthogonal to the first linearly polarized light beam to diffract incident light, and is made of a birefringent material. The polarization diffraction element 1 is prepared and disposed in an optical path between the light source 5 and a beam splitter 4 of the optical head device. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical head device used for recording and reproducing information on an optical recording medium such as an optical disk.

  For example, information is written on an information recording surface of an optical recording medium such as an optical disc such as a CD or a DVD or a magneto-optical disc (hereinafter collectively referred to as “optical disc”) (hereinafter referred to as “recording”), or Various optical head devices that read (hereinafter referred to as “reproduction”) information on an information recording surface are used.

  FIG. 6 is a side view schematically showing an example of a conventional optical head device. The emitted light from the semiconductor laser 5 is reflected by a reflection film (not shown) formed on the surface of the beam splitter 4 on the semiconductor laser 5 side, and is focused on the information recording surface of the optical disc 7 by the objective lens 3. Here, the reflection film is a partial reflection film that transmits a part of incident light and reflects the remaining light. The reflected light from the optical disk 7 is transmitted again through the objective lens 3, and part of the light is transmitted through the beam splitter 4, then condensed on the light receiving surface of the photodetector 6, and the remaining light is reflected on the reflecting film of the beam splitter 4. The light is reflected by the laser beam and returned to the light emitting point of the semiconductor laser 5. In the photodetector 6, the received light is converted into an electrical signal, the electrical signal corresponding to the received light amount is amplified by an amplifier, and the gain is appropriately corrected by an automatic gain correction circuit to adjust the signal level within a certain range. Is output.

  As a configuration of the optical head device, a collimator lens may be disposed between the beam splitter 4 and the objective lens 3, or a cylindrical lens or a concave lens may be disposed between the beam splitter 4 and the photodetector 6. . In addition, there is an optical head device configured using two semiconductor lasers for a wavelength of 790 nm for CD and two semiconductor lasers for a wavelength of 650 nm for DVD.

  In such an optical head device, when the reflected return light from the information recording surface of the optical disk is incident on the light emitting point of the semiconductor laser used as the light source, the intensity of the emitted light from the semiconductor laser becomes unstable, resulting in accurate information recording. Further, there arises a problem that reproduction cannot be performed. In order to solve this problem, a circuit that superimposes a high frequency current of several hundred MHz on the drive current of the power supply for the semiconductor laser is provided, and the return light and the oscillation light are changed by changing the oscillation mode of the semiconductor laser from the single mode to the multimode. And the output light intensity is stabilized.

  In addition, a quarter-wave plate 2 having a phase difference of π / 2 with respect to the oscillation wavelength of the semiconductor laser is disposed in the optical path between the semiconductor laser and the objective lens, and the return light travels back and forth through the quarter-wave plate. The output light intensity is stabilized by reducing the interference between the return light and the oscillation light by changing the polarization state of the oscillation light from the polarization state of the oscillation light. However, when the output power of the semiconductor laser is increased in order to record information on the information recording surface of an optical disc such as a CD-R or CD-RW at high speed, the intensity of the return light to the light emitting point of the semiconductor laser also increases. There is a problem that the intensity of the emitted light of the semiconductor laser becomes unstable and stable recording and reproduction cannot be performed.

  An object of the present invention is to provide an optical head device capable of stable signal detection at the time of recording and reproducing information on an optical disk in an optical head device using a relatively high-power semiconductor laser as a light source in view of the above circumstances. To do.

The present invention includes a light source, an objective lens that condenses light emitted from the light source onto an optical recording medium, a photodetector that detects reflected light from the optical recording medium, and light emitted from the light source as the objective. A beam splitter that reflects to the lens side and transmits part of the reflected light from the optical recording medium to the photodetector side and reflects the remaining part of the reflected light to the light source side, and the optical recording medium An optical head device for recording and reproducing information, wherein the following polarizing diffraction element made of a birefringent material is installed in an optical path between the light source and the beam splitter. An optical head device is provided.
Polarization diffraction element:
When the first linearly polarized light that is emitted from the light source is incident on the polarizing diffraction element, it acts as a diffraction grating for generating three beams for incident light detection on the optical recording medium, 50% or more of the first linearly polarized light is transmitted in a straight line as zero-order diffracted light, and the second linearly polarized light having a polarization direction orthogonal to the first linearly polarized light is reflected light from the optical recording medium. When entering the polarizing diffraction element, it acts as a diffraction grating that keeps the second linearly polarized light away from the light source, and diffracts 90% or more of the second linearly polarized light.

Further, the polarizing diffraction element is processed to be a ordinary refractive index n _o and extraordinary refractive index _{n e (n o ≠ n e} ) cross-sectional shape birefringent material having a stepped d periodic bumpy isotropic refractive index transparent material having a refractive index n _s is filled in the concave _{portion, | n e -n s | ×} d is a factor (m + 1/2) of the wavelength λ of the incident light (m comprises 0 | N _o −n _s | × d is in the range from (k + 1/4) to (k + 1/12) times the wavelength λ of the incident light (k is a positive integer including 0). An optical head device is provided. Furthermore, the phase difference of the transmitted light with respect to the incident light of the first linearly polarized light is an odd multiple of π / 2 in the polarizing diffraction element or in the optical path between the polarizing diffraction element and the objective lens. There is provided the above optical head device in which a phase plate is provided, and the incident light of the first linearly polarized light is converted into the second linearly polarized light by reciprocating through the phase plate.

  In the optical head device using the polarizing diffraction element according to the present invention, the return light to the light emitting point of the semiconductor laser is eliminated, so that the oscillation light intensity of the semiconductor laser is stable and stable signal detection during recording and reproduction of information on the optical disk. Can do. Polarization diffraction that has both a diffraction grating function for generating three beams for signal detection including information on the optical disk and a function for blocking the return light to the light emitting point of the semiconductor laser without increasing the number of parts. An optical head device composed of elements is realized.

1 is a side view showing an example of the configuration of an optical head device according to the present invention. It is a figure which shows an example of the polarization | polarized-light diffraction element in this invention, (a) The side view which shows a mode that the 1st linearly polarized light was incident as an outward path, (b) The side surface which shows a mode that the 2nd linearly polarized light was incident as a return path Figure. It is a figure which shows the other example of the polarizing diffraction element in this invention, (a) The side view which shows a mode that the 1st linearly polarized light was incident as an outward path, (b) The mode that the 2nd linearly polarized light was incident as a return path FIG. It is a figure which shows another example of the polarizing diffraction element in this invention, (a) A side view which shows a mode that the 1st linearly polarized light was incident as an outward path, (b) A state where the 2nd linearly polarized light was incident as a return path FIG. It is a figure which shows another example of the polarizing diffraction element in this invention, (a) A side view which shows a mode that the 1st linearly polarized light was incident as an outward path, (b) A state where the 2nd linearly polarized light was incident as a return path FIG. The side view which shows the outline of a structure of the conventional optical head apparatus.

  FIG. 1 is a side view schematically showing an example of the optical head device of the present invention. The configuration of the conventional optical head device shown in FIG. 6 is the same as that of the conventional optical head device shown in FIG. 6 except that the polarizing diffractive element 1 is installed in the optical path between the semiconductor laser 5 which is a light source emitting the first linearly polarized light and the beam splitter 4. is there. Therefore, the same reference numerals as those in FIG. 6 denote the same elements. The polarizing diffractive element 1 does not act as a diffraction grating for incident light of the first linearly polarized light emitted from a light source (semiconductor laser), transmits incident light, and is reflected light from an optical recording medium. The incident light of the second linearly polarized light having the polarization direction orthogonal to the first linearly polarized light acts as a diffraction grating and diffracts the incident light away from the light source.

  Since such a polarizing diffraction element 1 is installed, the second linearly polarized light reflected by the optical disk and further reflected by the beam splitter 4 is diffracted and does not reach the semiconductor laser. The intensity becomes stable, and as a result, accurate information recording and reproduction of the optical head device can be performed. Here, when the incident light is diffracted away from the semiconductor laser, it may be avoided not to reach the semiconductor laser at all, but the light emitting point of the semiconductor laser may be avoided. Here, this case is also included. The polarizing diffraction element 1 is made of a birefringent material, and examples of the birefringent material include an optical crystal and a polymer liquid crystal. From the viewpoint of ease of productivity and the like, it is preferable to use a polymer liquid crystal.

FIG. 2 is a side view showing one example of the configuration of the polarizing diffraction element in the present invention. A diffractive element 10 which is a polarizing diffractive element has a cross section of a birefringent material 13 having an ordinary light refractive index n _o and an extraordinary light refractive index n _e (n _o ≠ n _e ) on one surface of a translucent flat substrate 11. shape is machined so as to be periodically uneven shaped step d, to fill the isotropic refractive index transparent material 14 having a refractive index n _s in the recess. In addition, the isotropic refractive index transparent material 14 is sandwiched between the translucent flat substrate 11 and the translucent flat substrate 12. An antireflection film may be formed at the interface between the light-transmitting flat substrate 11 and the light-transmitting flat substrate 12 with air.

Here, substantially with equal isotropic refractive index transparent material 14 for example the refractive index _{n s} is the ordinary refractive index _{n o, | n e -n s} | × d is the oscillation wavelength λ of the semiconductor laser 5 (m + 1/2 ) Is a step d which is a multiple (m is a positive integer including 0). Here, m is preferably 0, 1 or 2. If it is 3 or more, the level difference d becomes large, which is not preferable in terms of production efficiency. When m is 0, the production efficiency is highest and particularly preferable.

The diffractive element 10 having such a structure is mounted on the optical head device as the polarizing diffractive element 1 in FIG. 1, and the first linearly polarized light of the emitted light from the semiconductor laser 5 is applied to the diffractive element 10 by ordinary light polarization (FIG. ) Is placed so as to be incident as ◎). At this time, the concave-convex periodic structure of the birefringent material 13 functions as an isotropic refractive index layer because the ordinary light refractive index n _o and the refractive index n _s are substantially equal, and the incident light of the first linearly polarized light Transmits straight without being diffracted.

The linearly polarized light that has passed through the polarizing diffraction element 1 (diffraction element 10) is reflected by the optical disc 7, so that it travels back and forth through the quarter-wave plate 2, and part of the second linearly polarized light is the beam splitter 4. And is incident on the light detector 6 as signal light, and the rest is reflected by a reflective film (not shown) of the beam splitter 4 and returns to the polarizing diffractive element 1 (diffractive element 10) as incident light. . At this time, the polarization direction of the return (return) light becomes the extraordinary light linear polarization (← → in FIG. 2B) which is the second linear polarization, which is orthogonal to the polarization direction of the forward linear polarization toward the optical disk. Therefore, the concavo-convex periodic structure of the birefringent material 13 has a phase difference of 2π × (n _e −n _s ) × d / λ, that is, 2π × λ × (m + 1/2) / λ, and a phase difference of π (m = 0). It may act as a phase diffraction grating. Since most of the return light is diffracted as higher-order light of ± 1st order or higher, there is little return light that is transmitted straight through and collected at the light emitting point of the semiconductor laser 5.

  Further, the diffraction angle θ of the Q-order diffracted light generated according to the grating pitch P of the concavo-convex periodic structure of the birefringent material 13 has a relationship of sin θ = Qλ / P with respect to the wavelength λ of the incident light. Here, Q takes values of ± 1, ± 2,. Since the diffracted light closest to the light emitting point of the semiconductor laser 5 is ± first order diffracted light, the grating pitch is such that the ± first order diffracted light is diffracted into a region that does not affect the oscillation of the semiconductor laser 5, that is, a region that does not overlap the light emitting point. Set P. Specifically, the lattice pitch P is preferably 50 μm or less.

  The grating pattern of the concavo-convex periodic structure is usually linear when the grating is viewed from above, but it can also be divided into areas with different grating directions of the linear grating, or a hologram pattern with a curved grating instead of a linear grating. Good. As a result, in an optical head device using a high-power semiconductor laser as a light source, almost no return light is collected at the light emitting point of the semiconductor laser, and the oscillation light intensity of the semiconductor laser is stabilized as described above. Stable signal detection can be performed during recording and reproduction.

  FIG. 3 is a side view showing another example of the configuration of the polarizing diffraction element according to the present invention ((a) shows a state where the first polarized light is incident as an outward path, and (b) shows a second polarized light as a return path. Shows the incident state.) As a signal detection method for reproducing information on an optical disc, a three-beam method using three beams, which is generally used, is applied to one surface of the translucent flat substrate 12 in the diffraction element 20. A diffraction grating 15 for generating a sub beam to be used for tracking of the optical disk is formed. The diffraction efficiency of the diffraction grating 15 does not depend on the polarization direction. The other configuration is the same as the configuration of the diffraction element 10 in FIG. 2, and the same reference numerals as those in FIG. 2 denote the same elements as those in FIG.

  By using the diffraction element 20 having such a structure in the optical head device as the polarizing diffraction element 1 of FIG. 1, a stable signal at the time of recording and reproducing information on the optical disk without increasing the number of parts and the weight of the optical head device. This is preferable because it can be detected. That is, it is preferable that a diffraction grating whose diffraction efficiency does not depend on the polarization direction, which is used as a three-beam generating element for detecting a signal of reflected light, is further formed on the polarizing diffraction element.

  FIG. 4 is a side view showing another example of the configuration of the polarizing diffraction element according to the present invention ((a) shows a state where the first polarized light is incident as the forward path, and (b) the second polarized light is incident as the backward path. Shows how it was done.) 1 is disposed instead of the quarter-wave plate 2 disposed in the optical path between the beam splitter 4 and the objective lens 3 of the optical head device of FIG. The diffractive element 30 which is a polarizing diffractive element has a phase difference of π between the translucent flat substrate 11 and the translucent flat substrate 12 using the isotropic refractive index transparent material 14 and the translucent adhesive 17. The phase plate 16 that is an odd multiple of / 2 is sandwiched. The other configuration is the same as the configuration of the diffraction element 20 in FIG. 3, and the same reference numerals as those in FIG. 3 denote the same elements as those in FIG. As the phase plate 16, an organic thin film phase plate or a crystal phase plate having a phase difference generating function such as a polycarbonate birefringent film or a polymer liquid crystal is used.

  By disposing the diffraction element 30 having such a structure as the polarizing diffraction element 1 of FIG. 1 so that the birefringent material 13 is on the semiconductor laser 5 side, the number of parts and the weight of the optical head device are reduced. It is preferable because stable signal detection can be performed at the time of recording / reproducing the signal of the optical disk. In addition, a phase plate may be installed in the optical path between the polarizing diffraction element and the objective lens.

  FIG. 5 is a side view showing still another example of the configuration of the polarizing diffraction element in the present invention ((a) shows a state in which the first polarized light is incident as the forward path, and (b) the second polarized light is in the return path. Shows the incident state.) In the polarizing diffraction element 30 shown in FIG. 4, the polarizing diffraction grating having the birefringent material 13 as a constituent element and the diffraction grating 15 formed on one surface of the translucent flat substrate 12 are separately formed. Has been.

  However, the diffraction element 40 shown in FIG. 5 has only a polarizing diffraction grating having the birefringent material 13 as a constituent element, and this diffraction grating 40 also functions as the diffraction grating 15 of FIG. Yes. That is, as shown in FIG. 5A, in the first linearly polarized light, ± first-order diffracted light is generated together with zero-order diffracted light, resulting in a total of three beams. As shown in FIG. 5B, ± first-order diffracted light is generated from the first linearly polarized light, and this diffracted light is deflected so as to avoid the light source (that is, away from the light source). 5 that are the same as those in FIG. 4 represent the same elements as those in FIG.

5, unlike the ordinary refractive index _{n o} and extraordinary refractive index _{n e (n o ≠ n e} ) the refractive index _{n s} of the isotropic refractive index transparent material 14 of the birefringent material 13, | _{n e} - n _s | × d is a step d that is (m + 1/2) times the oscillation wavelength λ of the semiconductor laser (m is a positive integer including 0), and | n _o −n _s | × d is the oscillation wavelength λ It is preferable that the range is (k + 1/4) times (k + 1/12) times (k is an integer including 0). Here, m and k are preferably 0, 1 or 2. If it is 3 or more, the level difference d becomes large, which is not preferable in terms of production efficiency. When m and k are 0, the production efficiency is highest and particularly preferable.

  The diffractive element 40 having such a structure is used as the polarizing diffractive element 1 in FIG. 1, and the birefringent material 13 is on the semiconductor laser 5 side. In the optical head device, the first linearly polarized light emitted from the semiconductor laser 5 is The birefringent material 13 is preferably disposed so as to be incident as ordinary light polarized light. With this arrangement, the number of parts and the weight of the optical head device are reduced, and stable signal detection can be performed during recording and reproduction of information on the optical disk.

At this time, uneven periodic structure of birefringent material 13 on the forward pass is the phase difference is _{2π × (n o -n s)} × d / λ, i.e. 2π × λ × (k + 1 /4) / λ from 2 [pi × lambda Since it is up to x (k + 1/12) / λ, it acts as a phase diffraction grating with a phase difference of π / 2 to π / 6 (it may be k = 0). About 0% 0th order diffracted light and 20% to about 3% ± 1st order diffracted light are calculated, and by appropriately setting the grating pitch of the concavo-convex periodic structure, a 3-beam generating element for signal detection including information on the optical disk is obtained. Can do.

The linearly polarized light of the 0th order diffracted light and the ± 1st order diffracted light transmitted through the birefringent material 13 passes through the phase plate 16 and then becomes circularly polarized light, which is emitted from the diffraction element 40, reflected by the optical disk, and returned as light again. The light enters the diffraction element 40. After passing through the phase plate 16, the light enters the birefringent material 13 as an extraordinary light polarized light having a polarization direction orthogonal to the outgoing ordinary light polarized light. At this time, the concavo-convex periodic structure of the birefringent material 13 has a phase difference of 2π × (n _e −n _s ) × d / λ (that is, 2π × λ × (m + 1/2) / λ) and a phase difference of π Most of the return light is high-order diffracted light of ± 1st order or higher, so that the amount of return light that is transmitted straight and collected at the light emitting point of the semiconductor laser is small. Here, m = 0 may be set.

  By using the diffraction element 40 having such a structure, only one polarizing diffraction grating can function as a three-beam generating element for signal detection including information on the optical disk and return light to the light emitting point of the semiconductor laser. The deflecting function can be realized at the same time. As a result, the number of parts and the weight of the optical head device are reduced as described above, and stable signal detection can be performed during recording and reproduction of information on the optical disk.

"Example 1"
First, the diffraction element used in the optical head device of this example will be described with reference to FIG. On the other surface of the glass substrate is a light-transmissive flat substrate 11 on which the antireflection film is formed on one surface, the ordinary refractive index n _o as a birefringent material 13 is 1.55 and the extraordinary refractive index n _e Was formed, and a concavo-convex periodic structure having a linear lattice pitch of 5 μm and a recess depth of 2.6 μm was produced by photolithography and etching techniques. In addition, after a SiO ₂ film having a thickness of 0.24 μm is formed on the outer surface of the translucent flat substrate 12, a diffraction grating having a grating pitch of 25 μm and an uneven step of 0.24 μm by photolithography and etching techniques. 15 was prepared, and an antireflection film was formed on the surface.

Furthermore, using the homogeneous refractive index transparent resin, which is an isotropic refractive index transparent material 14 having a refractive index n _s = 1.55, the concave portions processed into the concavo-convex shape of the polymer liquid crystal layer were filled. Further, a quarter-wave plate 16 made of a polycarbonate birefringent film is sandwiched between two glass substrates which are translucent flat substrates 11 and 12, and a translucent adhesive having the same refractive index as that of a homogeneous refractive transparent resin. The diffraction element 30 was produced by bonding with the material 17. Here, the quarter-wave plate 16 made of a polycarbonate birefringent film has a phase difference of transmitted light of π / with respect to the incident linearly polarized light of the semiconductor laser 5 having an oscillation wavelength λ of 790 nm used in the optical head device. 2 was used.

  The diffractive element 30 having such a structure is mounted on the optical head device as the polarizing diffractive element 1 of FIG. 1, and the linearly polarized light emitted from the semiconductor laser 5 is converted into ordinary light polarized light (first linearly polarized light) in the polymer liquid crystal layer. It arrange | positioned so that it might inject. At this time, the light transmitted through the diffractive element 30 is not diffracted by the rugged periodic structure of the polymer liquid crystal layer, but the diffraction grating 15 generates 0th-order diffracted light and ± 1st-order diffracted light. Used as 3 beams for signal detection. The generated diffracted light was about 83% 0th order diffracted light and about 7% ± 1st order diffracted light with respect to the incident light, and the emitted light was circularly polarized light.

  Further, 85% of the incident light is reflected by a reflection film (not shown) formed on the surface of the beam splitter 4, and is condensed on the information recording surface of the optical disk by the objective lens 3, and reflected light from the information recording surface. And diverged. Of this diverged reflected light, 15% of the light is again transmitted through the beam splitter 4 by the objective lens 3 and condensed on the light receiving surface of the photodetector 6, and the remaining 85% is reflected by the beam splitter 4 and returned. The light was incident on the polarizing diffraction element 1 (diffraction element 30).

  The light incident on the polarizing diffraction element 1 (diffraction element 30) passes through the quarter-wave plate 16 and becomes an extraordinary light polarized light (second linearly polarized light) and enters a diffraction grating made of a polymer liquid crystal. More than 95% of the light is diffused as high-order diffracted light of ± 1st order or higher, and the light collected at the light emitting point of the semiconductor laser 5 becomes almost zero. As a result, in an optical head device using a high-power semiconductor laser as a light source, the oscillation light intensity of the semiconductor laser was stabilized, and stable signal detection was possible during recording and reproduction of information on the optical disk.

"Example 2"
First, the diffraction element used in the optical head device of this example will be described with reference to FIG. On the other surface of the glass substrate is a light-transmissive flat substrate 11 on which the antireflection film is formed on one surface, the ordinary refractive index n _o as a birefringent material 13 is 1.55 and the extraordinary refractive index n _e A polymer liquid crystal layer of 1.70 was formed, and a concavo-convex periodic structure with a linear lattice pitch of 25 μm and a recess depth of 1.9 μm was produced by photolithography and etching techniques. An antireflection film was formed on one side of the translucent flat substrate 12.

Furthermore, using the homogeneous refractive index transparent resin, which is an isotropic refractive index transparent material 14 having a refractive index n _s = 1.49, the concave portions processed into the concavo-convex shape of the polymer liquid crystal layer were filled. Further, a quarter-wave plate 16 made of a polycarbonate birefringent film is sandwiched between two glass substrates which are translucent flat substrates 11 and 12, and a translucent adhesive having the same refractive index as that of a homogeneous refractive transparent resin. The diffraction element 40 was produced by bonding with the material 17. Here, the quarter-wave plate 16 made of a polycarbonate birefringent film has a phase difference of transmitted light of π / with respect to the incident linearly polarized light of the semiconductor laser 5 having an oscillation wavelength λ of 790 nm used in the optical head device. 2 was used.

The diffractive element 40 having such a structure is mounted on the optical head device as the polarizing diffractive element 1 of FIG. 1, and the linearly polarized light of the emitted light from the semiconductor laser 5 is polarized on the polarizing diffraction grating made of a polymer liquid crystal layer. It arrange | positioned so that it may inject as (1st linearly polarized light). At this time, the concave-convex periodic structure of the polymer liquid crystal layer acts as a phase diffraction grating having a phase difference of 2π × (n _o −n _s ) × d / λ, that is, a phase difference of 0.29π, and is approximately 81 with respect to incident light. % 0th order diffracted light and about 8% ± 1st order diffracted light were generated. The outgoing light was circularly polarized. The 0th-order diffracted light and ± 1st-order diffracted light were used as three beams for signal detection including information on the optical disk.

  Further, 85% of the incident light is reflected by a reflection film (not shown) formed on the surface of the beam splitter 4, and is condensed on the information recording surface of the optical disk by the objective lens 3, and reflected light from the information recording surface. And diverged. Of this diverged reflected light, 15% of the light is again transmitted through the beam splitter 4 by the objective lens 3 and condensed on the light receiving surface of the photodetector 6, and the remaining 85% is reflected by the beam splitter 4 and returned. The light was incident on the polarizing diffraction element 1 (diffraction element 40).

  The light incident on the polarizing diffractive element 1 (diffractive element 40) is transmitted through the quarter-wave plate 16 to become extraordinary light polarized light (second linearly polarized light) and incident on a diffraction grating made of a polymer liquid crystal. More than 95% of the light is diffused as high-order diffracted light of ± 1st order or higher, and the light collected at the light emitting point of the semiconductor laser 5 becomes almost zero. As a result, in an optical head device using a high-power semiconductor laser as a light source, the oscillation light intensity of the semiconductor laser was stabilized, and stable signal detection was possible during recording and reproduction of information on the optical disk.

  In this example, only one polarizing diffraction element is used to generate three signal detection beams including information on the optical disk in the forward path, and diffract the return light to the light emitting point of the semiconductor laser in the backward path. The same effect was obtained with a simple configuration.

1: Polarization diffraction elements 10, 20, 30, 40: Diffraction element 2, 16: 1/4 wavelength plate (phase plate)
3: Objective lens 4: Beam splitter 5: Semiconductor laser 6: Photo detector 7: Optical disc (optical recording medium)
11, 12: Translucent flat substrate 13: Birefringent material 14, 17: Isotropic refractive index transparent material (translucent adhesive)
15: Diffraction grating

Claims (3)

A light source;
An objective lens for condensing the light emitted from the light source onto an optical recording medium;
A photodetector for detecting reflected light from the optical recording medium;
A beam that reflects light emitted from the light source toward the objective lens and transmits part of the light reflected from the optical recording medium toward the photodetector and reflects the remaining portion of the reflected light toward the light source. An optical head device that includes a splitter and records and reproduces information on the optical recording medium, and includes the following polarizing diffraction element made of a birefringent material in an optical path between the light source and the beam splitter An optical head device comprising:
Polarization diffraction element:
When the first linearly polarized light that is emitted from the light source is incident on the polarizing diffraction element, it acts as a diffraction grating for generating three beams for incident light detection on the optical recording medium, 50% or more of the first linearly polarized light is transmitted straight as 0th order diffracted light,
When the second linearly polarized light that is reflected from the optical recording medium and has a polarization direction orthogonal to the first linearly polarized light is incident on the polarizing diffraction element, the second linearly polarized light is emitted from the light source. It acts as a diffraction grating that keeps away, and diffracts 90% or more of the second linearly polarized light. The polarizing diffraction element is processed to be a ordinary refractive index n _o and extraordinary refractive index _{n e (n o ≠ n e} ) cross-sectional shape birefringent material having a stepped d periodical uneven, the The concave portion is filled with an isotropic refractive index transparent material having a refractive index n _s , and | n _e −n _s | × d is (m + 1/2) times the wavelength λ of incident light (m is a positive value including 0 The number | n _o −n _s | × d ranges from (k + 1/4) to (k + 1/12) times the wavelength λ of the incident light (k is a positive integer including 0). 2. An optical head device according to 1.   The phase difference of the transmitted light with respect to the incident light of the first linearly polarized light is an odd multiple of π / 2 in the polarizing diffractive element or in the optical path between the polarizing diffractive element and the objective lens. 3. The optical head according to claim 1, further comprising a phase plate, wherein the incident light of the first linearly polarized light is converted into the second linearly polarized light by reciprocating through the phase plate. 4. apparatus.

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