KR100477680B1 - Optical pickup - Google Patents

Abstract

Disclosed is an optical pickup apparatus capable of eliminating birefringence due to nonuniformity of an optical recording medium using a polarizing beam splitter.

The disclosed optical pickup apparatus includes a light source; A beam splitter for converting a traveling path of the incident light; An objective lens for focusing the light incident through the beam splitter to form a light spot on the optical recording medium; A polarization beam splitter disposed on an optical path between the beam splitter and the objective lens to transmit incident light of one polarization and reflect light of another polarization; A first photodetector for receiving light of one polarization transmitted through the polarization beam splitter among the light reflected from the optical recording medium; And a second photodetector for receiving light of another polarization reflected by the polarization beam splitter among the light reflected by the optical recording medium.

In addition, the disclosed optical pickup device comprises a light source; A beam splitter for converting a traveling path of the incident light; An objective lens for focusing the light incident through the beam splitter to form a light spot on the optical recording medium; A polarization beam splitter provided on a traveling path of light incident through the beam splitter, for transmitting light of one polarized light and reflecting light of another polarization; A first photodetector for transmitting light of one polarization incident through the polarization beam splitter; And a second photodetector for receiving light of another polarization reflected by the polarization beam splitter.

Description

Optical pickup device

The present invention relates to an optical pickup apparatus capable of removing birefringence due to non-uniformity of an optical recording medium. Specifically, a birefringence due to non-uniformity of an optical recording medium can be removed using a polarizing beam splitter. An optical pickup apparatus.

In general, an optical pickup apparatus records information on an optical recording medium or reproduces the recorded information by using light irradiated from a light source.

1 is a schematic view showing an optical arrangement of an optical pickup apparatus employing a conventional beam splitter.

As shown in the drawing, the optical pickup apparatus includes a light source 1 for irradiating light, a beam splitter 5 for changing a traveling direction of incident light, and an optical path between the beam splitter 5 and the optical recording medium 13. An objective lens 11 arranged to focus the incident light on the optical recording medium 13 and parallel to the diverging light incident on the optical path between the beam splitter 5 and the objective lens 11 A collimating lens 7 for light, and a photodetector 17 for reflecting light from the optical recording medium 13 and receiving light through the beam splitter 5 to detect an information signal and an error signal. do.

The beam splitter 5 is a polarizing beam splitter that reflects light of one polarization and transmits light of another polarization among incident light. That is, in the optical arrangement shown in FIG. 1, the light incident from the light source 1 is reflected to the optical recording medium 13, and the light reflected from the optical recording medium 13 is transmitted to the optical recording medium 13. Face toward the photodetector 17.

Meanwhile, a quarter wave plate 9 is further provided on the optical path between the beam splitter 5 and the objective lens 11 so that circularly polarized light is incident on the optical recording medium 13. This quarter wave plate 9 converts the incident linearly polarized light into circularly polarized light and the circularly polarized light into linearly polarized light.

Each of the photodetectors 17 includes a plurality of dividers each independently receiving and photoelectrically converting light, and by selectively differentially amplifying and summing signals from each of the dividers to the optical recording medium 13. The recorded information signal, track error signal, and focus error signal are detected.

The 3-beam method is widely used as a method of detecting the track error signal. To this end, a grating 3 is further provided on the optical path between the light source 1 and the beam splitter 5 to diffract and transmit incident light to 0th order light, ± 1st order light, ± 2nd order light, ...

In addition, the astigmatism method is widely used as a method for detecting a focus error signal. To this end, an astigmatism lens 15 is disposed between the beam splitter 5 and the photodetector 17 to be inclined in a direction opposite to the inclined direction of the beam splitter 6 to correct the coma aberration. It is further provided.

On the other hand, the optical recording medium 13 is a disc type optical recording medium such as a compact disc (CD) and a digital multifunction disc (DVD). The optical recording medium 13 is manufactured by inserting a resin into the mold and imprinting the resin, so that the resin may be unevenly formed in the space within the mold. The density of the optical recording medium changes according to this degree of nonuniformity. Therefore, when recording / reproducing information on portions having different densities of the optical recording medium, the refractive angles of the incident light are changed as they pass through the media having different refractive indices. Therefore, the nonuniformity of the medium acts as a birefringence phenomenon.

Looking at the case where the density of the optical recording medium 13 satisfies the desired standard and the incident light is irradiated to each of the unsatisfactory parts, the optical recording medium 13 has different refractive phenomena as described above. Therefore, the angle of refraction becomes different so that the light is divided into light of a desired polarization and light of a different polarization. The magnitude of this polarization depends on the degree of birefringence.

The beam splitter 5 is adapted to reflect and transmit characteristics in accordance with the polarization characteristics of the laser beam irradiated from the light source 1, and transmits only normal polarized light to the photodetector 17. That is, light of abnormally polarized light does not form in the photodetector 17. Therefore, a problem arises in that the amount of light received is small for the portion where the density of the optical recording medium 13 is changed.

In addition, since the optical recording medium 13 is mounted on a spindle motor (not shown) and rotates, information is periodically performed on a portion whose density is changed. . Such periodicity also causes errors in signal reproduction and signal change, thereby degrading reproduction ability.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide an optical pickup apparatus capable of removing birefringence due to nonuniformity of an optical recording medium using a polarizing beam splitter.

An optical pickup apparatus according to the present invention for achieving the above object comprises a light source for irradiating laser light; A beam splitter for reflecting a part of the incident light and transmitting a remainder straight to convert the traveling path of the incident light; An objective lens for focusing light incident through the beam splitter to form an optical spot on an optical recording medium; A polarization beam splitter disposed on an optical path between the beam splitter and the objective lens to transmit incident light of one polarization and reflect light of another polarization; A first photodetector for transmitting the polarization beam splitter among the light reflected by the optical recording medium and receiving light of one polarization incident through the beam splitter; And a second photodetector for receiving light of another polarization reflected by the polarization beam splitter among the light reflected from the optical recording medium, wherein the information signal and the error from the signals detected by the first and second photodetectors are included. It is characterized in that the signal can be detected.

In addition, the optical pickup device according to the present invention comprises a light source for irradiating laser light; A beam splitter for reflecting a part of the incident light and transmitting a remainder straight to convert the traveling path of the incident light; An objective lens for focusing light incident through the beam splitter to form an optical spot on an optical recording medium; A polarization beam splitter which is reflected on the optical recording medium and provided on a traveling path of light incident through the beam splitter, and transmits light of one polarization incident and reflects light of another polarization; A first photodetector configured to receive light of one polarization incident through the polarization beam splitter; And a second photodetector configured to receive light of another polarization reflected by the polarization beam splitter, wherein the second photodetector is configured to detect an information signal and an error signal from signals detected through the first and second photodetectors. It is done.

Hereinafter, an optical pickup apparatus according to exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2, an optical pickup apparatus according to an exemplary embodiment of the present invention focuses a light source 21 for irradiating laser light L, a beam splitter 25 for converting a traveling path of incident light, and incident light. An objective lens 29 for forming a light spot on the optical recording medium 31 and an optical path between the beam splitter 25 and the objective lens 29 so that light of one polarization is transmitted straight through and another polarization is transmitted. Polarization beam splitter (41) for reflecting light and first and second photodetectors (35) (45) for receiving information reflected from the optical recording medium (31) to detect information signals and error signals. do.

The beam splitter 25 divides the incident light by a predetermined light quantity ratio, for example, a ratio of 50:50, partially reflects the light, and transmits the remaining light to change the path of the incident light. Therefore, when the light source 21 is disposed as shown in FIG. 2, the laser light L irradiated from the light source 21 is incident on the beam splitter 25, a part of which is reflected and the other is transmitted. do. At this time, the reflected light is used as the effective light. On the other hand, in the light reflected from the optical recording medium 31, the light transmitted by the beam screener 25 is used as the effective light.

Here, the light source 21 is composed of a semiconductor laser diode to irradiate light of a specific polarization. Therefore, the light irradiated from the light source 21 and reflected by the beam splitter 25 becomes light having a specific polarization direction.

On the other hand, in the optical arrangement of the light source 21 and the beam splitter 25, it may be arranged so that the light transmitted through the beam splitter 25 can be used as the effective light.

Light incident from the light source 21 and reflected by the beam splitter 25 is focused by the objective lens 29 to form a light spot on the optical recording medium 31. As such, the light directed to the optical recording medium 31 has a specific polarization direction according to the polarization characteristic of the light source 21.

On the other hand, as described above, the optical recording medium 31 causes birefringence due to the nonuniformity of the medium caused during the manufacturing process. Therefore, the light reflected from the optical recording medium 31 is divided into light having polarization characteristics such as incident light and light having different polarization characteristics.

The polarization beam splitter 41 transmits light of one polarization incident from the light source 21 toward the objective lens 29. Further, among the light incident on the optical recording medium 31, light of the same polarization as the light incident on the light source 21 is transmitted, and another polarization caused by the nonuniformity of the medium constituting the optical recording medium 31. Light reflects. That is, the light reflected from the optical recording medium 31 and re-incident to the polarization beam splitter 41 is divided into a first path La and a second path Lb.

When looking at the structure of the polarizing beam splitter 41, it may have a cubic structure or a plate-like structure as shown.

The collimating lens 27 may further include a collimating lens 27 configured to focus incident light on the optical path between the beam splitter 25 and the objective lens 29 so that the light directed toward the objective lens 29 becomes parallel light. Do.

The first photodetector 35 receives light incident upon branching from the polarization beam splitter 41 to the first path La, and the second photodetector 45 at the polarization beam splitter 41. The light incident on the second path Lb is received. In this way, the information signal and the error signal can be detected by summing and / or differentialting the electrical signals received through the first and second photodetectors 35 and 41 and photoelectrically converted.

Through the first and second photodetectors 35 and 45, the three-beam method is widely used as a method of detecting the track error signal. To this end, a grating 23 is further provided on the optical path between the light source 21 and the beam splitter 25 to diffract and transmit incident light to 0th order light, ± 1st order light,.

In addition, the astigmatism method is widely used as a method for detecting a focus error signal. To this end, an astigmatism lens 33 is further provided between the beam splitter 25 and the first photodetector 35. The astigmatism lens 35 is also arranged in a direction opposite to the inclination direction of the beam splitter 25 so as to correct coma aberration. The astigmatism lens 33 is formed of a concave-shaped yaw lens, which transmits incident light straight in a direction in which the cross-sectional shape is rectangular, and at least one surface is concave as shown in the cross-sectional shape. Is divergently transmitted to allow astigmatism light to enter the first photodetector 35.

Referring to FIG. 3, the first photodetector 35 includes first to fourth split plates A ₁ , B ₁ , C ₁ , and D ₁ arranged in a zi-shaped shape, and the first to fourth split plates ( And fifth and sixth partition plates E ₁ and F ₁ arranged on both sides of A ₁ , B ₁ , C ₁ , and D ₁ , respectively, to detect track error signals.

Referring to FIG. 4, the second photodetector 45 according to the first embodiment of the present invention includes the seventh to tenth partition plates A ₂ , B ₂ , C ₂ , and D ₂ arranged in the shape of 田. do.

Therefore, the signals detected in each of the first to fourth split plates A ₁ , B ₁ , C ₁ , and D ₁ , and the seventh to tenth split plates A ₂ , B ₂ , C ₂ , and D _2. Each of the detected signals is added, and each of the summed signals is differentially and / or added to detect a focus error signal and an information signal.

That is, a focus error signal (FES) is obtained as a sum signal of focus error signals detected by each of the first and second photodetectors 35 and 45. This is expressed as equation (1).

An information signal RFS includes the first to fourth split plates A ₁ , B ₁ , C ₁ , and D ₁ , and the seventh to tenth split plates A ₂ , B ₂ , and C _2. , D ₂ ) summing the received and photoconverted signals in each. This is expressed as equation (2).

On the other hand, the track error signal (TES) is from the first order diffraction light received by the fifth split plate E ₁ and the sixth split plate F ₁ of the light divided by the grating 23, respectively. Is detected. That is, the track error signal is detected by differentially amplifying a signal received and photoelectrically converted into each of the fifth and sixth partition plates E ₁ and F ₁ . If this is expressed as equation (3).

As described above, the polarization beam splitter 41 is employed to guide the light of the other polarization caused by the nonuniformity of the optical recording medium 31 to the second path Lb, and the second photodetector 45 is Further, by receiving the light, the periodicity of the detection signal caused by the birefringence can be eliminated, and the amount of detection of the information signal and the focus error signal can be increased, thereby improving the signal reproduction capability.

FIG. 5 illustrates a structure according to another embodiment of the second photodetector 45 of FIG. 2. The second photodetector 45 includes seventh to tenth split plates A ₂ , B ₂ , C ₂ and D ₂ , and the seventh to tenth split plates A ₂ , B ₂ , C ₂ and D _2. And eleventh and twelfth partition plates E ₂ and F ₂ disposed on both sides thereof.

In this embodiment, the second photodetector 45 is distinguished in terms of the eleventh and twelfth partition plates E ₂ and F ₂ , and each of the partition plates forming the first photodetector 35, The optical arrangement of the seventh to tenth split plates A ₂ , B ₂ , C ₂ , and D ₂ is substantially the same as the structure according to the embodiment of FIG. 4, through which the focus error signal and the information signal are divided. Since the manner of detecting is also substantially the same, a detailed description thereof will be omitted.

According to this embodiment, the track error signal (TES: Track Error Signal) is respectively received by the photo-fifth partition plate (E ₁₎ and a sixth partition plate (F ₁₎ divided by the grating (23) ± 1 It is detected from the next diffraction light and the ± first order diffraction light received on the eleventh split plate E ₂ and the twelfth split plate F ₂ , respectively.

In this way, the second photodetector 45 further includes the eleventh and twelfth partition plates E ₂ (F ₂ ), so that the fifth and sixth split plates E _{1 of} the first photodetector 35 are provided. The track error signal sensitivity can be increased by detecting the track error signal using the signal detected at (F ₁ ).

Referring to FIG. 6, an optical pickup apparatus according to another exemplary embodiment of the present invention focuses a light source 21 for irradiating laser light L, a beam splitter 25 for converting a traveling path of incident light, and incident light. An objective lens 29 for forming a light spot on the optical recording medium 31, a polarizing beam splitter 61 provided on a traveling path of light reflected from the optical recording medium and incident through the beam splitter; A first photodetector 35 for receiving light of one polarization incident through the polarization beam splitter 61 and a second photodetector for receiving light of another polarization reflected by the polarization beam splitter 61 ( 65).

Here, it is preferable to further include a collimating lens 27 for focusing the incident light on the optical path between the beam splitter 25 and the objective lens 29 so that the light directed to the objective lens 29 becomes parallel light. Do.

Incident light is incident on the optical path between the light source 21 and the beam splitter 25 so that the track error signal can be detected by the 3-beam method through the first and second photodetectors 35 and 65. It is preferable to further include a grating 23 for diffraction and transmission with 0th order light, ± 1st order light, ..., and the like.

As described above, in the optical pickup apparatus according to the present embodiment having an optical configuration and arrangement, a polarizing beam splitter 61 is disposed between the beam splitter 25 and the first and second photodetectors 35 and 65. In the points arranged in, there are differences, but other parts are substantially the same, so a detailed description thereof will be omitted.

The polarizing beam splitter 61 transmits light of one polarization among the light incident through the beam splitter 25 to be directed to the first photodetector 35, and forms a medium for forming the optical recording medium 31. Light of other polarizations caused by the nonuniformity of is reflected and directed to the second photodetector 45.

Each of the beam splitter 25 and the polarizing beam splitter 61 has a flat plate-like structure in which reflective surfaces 25a and 61a reflecting a part of incident light are inclined on the optical path. Thus, by employing the flat plate structure, the cost can be reduced and the size and weight can be reduced as compared with the case where the cubic structure is used.

In addition, it is preferable that the inclination direction of the beam splitter 25 and the inclination direction of the polarization beam splitter 61 are opposite to each other, as shown in FIG. 6. In this way, by arranging the beam splitter 25 and the polarizing beam splitter 61, it is possible to correct the coma aberration caused by adopting a flat plate type structure and tilting it.

The partition structures of each of the first and second photodetectors 35 and 65 are as shown in FIGS. 3 to 5, and the signals received by the first and second photodetectors 35 and 65. The information signal and the error signal can be detected by summing and / or differentially as shown in Equation 1 to Equation 4 above.

As described above, the optical pickup apparatus according to the embodiment of the present invention configured uses the polarization beam splitter to induce light caused by the nonuniformity of the optical recording medium to another path, and to receive the light induced in the other path. And a second photodetector to detect the information signal and the error signal using both the light received by the first and the second photodetector, thereby eliminating the periodicity of the detection signal caused by the nonuniformity of the optical recording medium. Can be. In addition, the amount of information signal and error signal detection can be increased, thereby improving signal reproduction capability.

1 is a schematic view showing an optical arrangement of a conventional optical pickup device.

2 is a schematic view showing an optical arrangement of the optical pickup device according to an embodiment of the present invention.

3 is a view showing the first photodetector of FIG.

4 illustrates an embodiment of the second photodetector of FIG. 2.

FIG. 5 shows another embodiment of the second photodetector of FIG. 2. FIG.

6 is a schematic diagram showing an optical arrangement of an optical pickup apparatus according to another embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

21 ... light source 23 ... grading

25 ... beam splitter 27 ... collimating lens

29.Objective lens 31.Optical recording medium

33 ... astigmatism lens 35 ... first photodetector

41,61 ... polarized beam splitter 45,65 ... second photodetector

Claims (8)

A light source for irradiating laser light; A beam splitter for reflecting a part of the incident light and transmitting a remainder straight to convert the traveling path of the incident light; An objective lens for focusing light incident through the beam splitter to form an optical spot on an optical recording medium; A polarization beam splitter disposed on an optical path between the beam splitter and the objective lens to transmit incident light of one polarization and reflect light of another polarization; A first photodetector for transmitting the polarization beam splitter among the light reflected by the optical recording medium and receiving light of one polarization incident through the beam splitter; A second photodetector for receiving light of another polarization reflected by the polarization beam splitter among the light reflected by the optical recording medium; An astigmatism lens disposed on an optical path on the beam splitter and the first photodetector to generate astigmatism; and including information signals and error signals from signals detected through the first and second photodetectors. An optical pickup apparatus, characterized by being able to detect. delete A light source for irradiating laser light; A beam splitter having a flattened structure in which a part of the incident light is reflected and the remaining part is transmitted in a straight line, thereby converting a traveling path of the incident light, the reflecting surface reflecting a part of the incident light inclined on the optical path; An objective lens for focusing light incident through the beam splitter to form an optical spot on an optical recording medium; Reflecting surface which is reflected on the optical recording medium and provided on the traveling path of the incident light through the beam splitter, transmits light of one polarized light and reflects light of another polarized light, reflecting part of the incident light A polarizing beam splitter having a flattened structure disposed on the optical path inclined in a direction opposite to the ordinary direction of the beam splitter; A first photodetector configured to receive light of one polarization incident through the polarization beam splitter; And a second photodetector configured to receive light of another polarization reflected by the polarization beam splitter, wherein the information signal and the error signal can be detected from the signals detected through the first and second photodetectors. Optical pickup device. delete The method according to claim 1 or 3, The first photodetector, The first to fourth split plates A ₁ , B ₁ , C ₁ , D ₁ , and the first to fourth split plates A ₁ , B ₁ , C ₁ , D ₁ , respectively; And fifth and sixth partition plates E ₁ and F ₁ capable of detecting an error signal, The second photodetector, Seventh to tenth partition plates (A ₂ , B ₂ , C ₂ , D ₂ ) are provided, A signal detected in each of the first to fourth split plates and a signal detected in each of the seventh to tenth split plates are summed, and the summed signals are differentially and / or summed to add a focus error signal and an information signal. Optical pickup device, characterized in that to be able to detect. The method according to claim 1 or 3, The first photodetector, First to fourth split plates A ₁ , B ₁ , C ₁ , D ₁ , and first to fourth split plates A ₁ , B ₁ , C ₁ , D ₁ , respectively; 5 and a sixth partition plate E ₁ , F ₁ , The second photodetector, 7th to 10th split plates A ₂ , B ₂ , C ₂ and D ₂ , and the 7th to 10th split plates A ₂ , B ₂ , C ₂ and D ₂ , which are respectively disposed on both sides Eleven and twelfth partition plates (E ₂ , F ₂ ), A signal detected in each of the first to fourth split plates and a signal detected in each of the seventh to tenth split plates are summed, and the summed signals are differentially and / or summed to add a focus error signal and an information signal. Detect The signal detected in each of the fifth and sixth partition plates and the signals detected in each of the eleventh and twelfth partition plates are summed, and the sum of the summed signals can be differentially detected to detect the track error signal. Optical pickup device characterized in that. The method according to claim 1 or 3, And a grating disposed on an optical path between the light source and the beam splitter to diffract and transmit incident light into at least three lights. The method according to claim 1 or 3, And a collimating lens disposed on an optical path between the beam splitter and the objective lens to focus incident divergent light to become parallel light.