CN1170932A - Optical pickup - Google Patents

Abstract

An optical head, compatible with discs of different formats, comprising: - a first light source emitting light of a certain wavelength; - a second light source emitting light with a wavelength different from that emitted by the first light source; The light emitted by the first and second light sources is focused on the recording medium; the optical path conversion device is arranged on the optical path between the first and the second light source to change the propagation path of the incident light; a first light detector is used for receiving Light emitted from the first light source and incident through the recording medium and the optical path conversion device; a second photodetector for receiving light emitted from the second light source and incident through the recording medium and the optical path conversion device.

Description

optical head

The invention relates to an optical head, in particular to an optical head capable of being compatible with disc recording media of different formats.

An optical head suitable for a digital video disc player (DVDP) that can record and reproduce information at a high density should be able to record and reproduce not only on a digital video disc (DVD), but also on a CD-like recording medium, such as a compact disc (CD), CD-R (re-recordable), CD-I, CD-G, etc. record and reproduce for compatibility.

However, the standard thickness of existing CD-type discs is 1.2 mm, and the standard thickness of DVDs is 0.6 mm due to allowable disc tilt errors, numerical apertures of objective lenses, and the like. Therefore, when the information recorded on the CD is recorded and reproduced by the optical head of the DVD, spherical aberration occurs due to the difference in its thickness. Due to this spherical aberration, it is impossible to obtain a sufficient light intensity for recording an information signal, or signal deterioration occurs at the time of reproduction.

Likewise, light sources for reproducing DVDs and CDs have different wavelengths, wherein the existing light sources for reproducing CDs have a wavelength of approximately 780 nm, while those for reproducing DVDs have a wavelength of approximately 650 nm.

A conventional compatible optical head capable of recording and reproducing information on discs having different formats as described above, comprising a light source emitting at a wavelength of approximately 650 nm, suitable for DVD format, but having an improved structure, which This structure can compensate for the difference in thickness of the discs used, so that discs of different formats can be interchangeably used in a device having such a compatible optical head. In this case, the light intensity drops by about 5% compared to an optical head using a light source emitting light of a wavelength of 780nm, but since it is within the allowable range of reproduction, such a problem is not serious.

However, when a CD-R, which is one of CDs, is used, a difference in sensitivity occurs when using a light source emitting light of a wavelength of 650 nm compared to using a light source emitting light of a wavelength of 780 nm. That is, since the CD-R has an organic dye film recording layer, the difference in reflectance depending on the wavelength is remarkable, as shown in FIG. 1 . Then, when light having a wavelength of about 650 nm is used, the reflectance falls within 10%, which makes it impossible to reproduce the signal.

In order to overcome the above problems, as shown in FIG. 9, a conventional compatible optical head is designed, which includes a first light source 21 emitting light with a wavelength of 650nm and a second light source 31 emitting light with a wavelength of 780nm. The first light source 21 is suitable for a relatively thin disc 10a, such as a DVD disc, and the second light source 31 is suitable for a relatively thick disc 10b, such as a CD disc.

The light emitted by the first light source 21 is reflected by the polarizing beam splitter 23 , passes through the interference filter 33 , the λ/4 optical path difference plate 11 and the holographic element 13 , and is focused onto the optical disc 10 by the objective lens 15 . The interference filter 33 reflects the light emitted by the second light source 31 to the optical disc 10 and then passes the light reflected by the optical disc 10 .

Since the diameter of the light emitted by the first light source 21 is larger than that of the diffraction pattern formed on the center of the hologram element 13, the light is not diffracted, even after the light passes through the hologram element 13, that is, it is zero-order diffracted light. , which is focused on the relatively thin optical disc 10a. In addition, the light emitted from the second light source 31 is diffracted by the diffraction pattern when passing through the hologram element 13, becomes +1st order light, and is focused on the relatively thick optical disc 10b.

Compatible optical head can use CD-R as recording medium when using two light sources. However, the use of a holographic element on which a diffractive pattern is formed would make assembly and optical placement difficult. Furthermore, due to the use of optical detectors, precise adjustment of the optical axes of the light from the two light sources is required.

The object of the present invention is to provide a compatible optical head which is compatible with different formats of optical discs and has a simple structure, so as to overcome the above-mentioned problems.

In order to achieve the above object, the provided compatible optical head includes: a first light source that emits light of a certain wavelength; a second light source whose wavelength of light is different from that of the light emitted by the first light source; and the light emitted by the second light source are respectively focused on the objective lens on the recording medium; an optical path conversion device arranged between the first and second light sources and the objective lens is used to change the propagation path of the incident light; a first photodetector, It is used to receive the light emitted from the first light source and incident through the recording medium and the optical path conversion device; a second photodetector is used to receive the light emitted from the second light source and incident through the recording medium and the optical path conversion device .

The optical path conversion device includes: a first beam splitter located on the optical path between the first light source and the objective lens, used to reflect the light emitted by the first light source to the recording medium, and then pass the light reflected by the recording medium to the first light detector A device; a second beam splitter located on the optical path between the first beam splitter and the objective lens, used to reflect the light emitted by the second light source to the recording medium, and pass the light reflected by the recording medium; a second beam splitter located at the first The third beam splitter on the optical path between the first beam splitter and the second beam splitter is used to reflect the light emitted by the second light source, reflected by the recording medium and passed through the second beam splitter to the second light detector.

According to another aspect of the present invention, the optical path conversion device includes: a first beam splitter located on the optical path between the first light source and the objective lens, used to reflect the light emitted by the first light source to the recording medium, and reflect the light emitted by the recording medium The light leads to the first photodetector; a second beam splitter located on the optical path between the first beam splitter and the objective lens is used to reflect the light emitted by the second light source to the recording medium, and through the reflection by the recording medium A third beam splitter on the optical path between the objective lens and the second beam splitter, used to transmit the light emitted by the first and second light sources to the recording medium, and transmit the light emitted from the first light source, and then the light reflected by the recording medium, and reflect the light emitted by the light source and reflected by the recording medium to the second photodetector.

According to still another aspect of the present invention, the optical path conversion device includes: a first beam splitter located on the optical path between the first light source and the objective lens, used to transmit the light emitted by the first light source to the recording medium, and reflect the light from the recording medium The light is reflected to the first photodetector; a second beam splitter located on the optical path between the second light source and the objective lens is used to reflect the light emitted by the second light source and send the light reflected by the recording medium to the second photodetector A third beam splitter positioned on the optical path between the first beam splitter and the objective lens is used to reflect the light emitted from the second light source and reflected by the second beam splitter to the recording medium, and reflect the light reflected by the recording medium The light is reflected to the second beam splitter.

According to yet another aspect of the present invention, the first light source and the first photodetector are arranged adjacent to each other to form a first assembly.

Above-mentioned purpose and advantage of the present invention will be clearer by referring to the preferred embodiment of the present invention in detail with reference to accompanying drawing, wherein:

Fig. 1 is the graph of light source wavelength and reflectivity when adopting CD-R as recording medium;

Fig. 2 is a schematic diagram of the optical layout of a conventional compatible optical head;

3 is a schematic diagram of an optical arrangement of a compatible optical head according to a first embodiment of the present invention;

4 is a schematic diagram of an optical arrangement of a compatible optical head according to a second embodiment of the present invention;

5 is a schematic diagram of an optical arrangement of a compatible optical head according to a third embodiment of the present invention;

6 is a schematic diagram of an optical arrangement of a compatible optical head according to a fourth embodiment of the present invention;

FIG. 7 is a schematic cross-sectional view of an embodiment of the first assembly employed in FIG. 6 .

As shown in Figure 3, the compatible optical head of the first embodiment of the present invention includes: the first and the second light source 51 and 61 that generate and emit laser light; the first, the second and the third beam splitter 53, 63 and 65 , they are arranged on the optical path as an optical path conversion device to change the propagation path of the incident light; an objective lens 41 is used to focus the light emitted by the light sources 51 and 61 onto the recording medium 10; and the first and second photodetectors 57 and 69 for receiving light reflected by the recording medium 10, and detecting information signals and error signals.

The first light source 51 generates and emits light having a wavelength of about 650 nm, which can record and reproduce information on a relatively thin optical disc 10a such as a DVD, DVD-ROM disc. The second light source 61 generates and emits light with a wavelength of about 780nm, which can record and reproduce information on a relatively thick optical disc 10b, such as a CD type, especially a CD-R disc.

The first and second light sources 51 and 61 are arranged on different optical paths, and one of them is selectively driven according to the type of recording medium. Here, the driving mechanism of the first and second light sources 51 and 61 adopts a manual operation method, that is, the user selects a light source suitable for a certain recording medium 10, or an automatic operation method, that is, the operator can A separate detector (not shown) for detecting the type of recording medium 10 loaded in the player selects the light source. Since the aforementioned driving mechanisms are well known, their detailed descriptions are omitted.

The objective lens 41 focuses the light emitted from the first and second light sources 51 and 61 to form a light spot on the recording medium 10 . The objective lens 41 is driven by an actuator (not shown) that is driven based on a focus error signal and a tracking error signal.

The first and second photodetectors 57 and 69 respectively receive the light emitted by the first light source 51 and the second light source 61 and incident through the recording medium 10 and the first, second and third beam splitters 53, 63 and 65. . The first and second photodetectors 57 and 69 include at least two light receiving plates (not shown) for receiving incident light and generating electrical signals corresponding to the amount of light. The electrical signals output from the first and second photodetectors 57 and 69 are differentiated and/or summed and amplified for detecting information signals, tracking error signals and focus error signals.

The first beam splitter 53 is located on the optical path between the first light source 51 and the objective lens 41, and reflects the light emitted by the first light source 51 to the recording medium 10, and then passes the light reflected by the recording medium 10 to the first photodetector 57 . The first beam splitter 53 passes a part of the incident light at a certain ratio and reflects the rest of the light. Preferably, the first beam splitter 53 is planar as shown, but it may also be a cube formed by combining two triangles. Here, the arrangement of the first light source and the first photodetector can be considered in accordance with a cube-type structure.

The second beam splitter 63 is located on the optical path between the first beam splitter 53 and the objective lens 41 , reflects the light emitted by the second light source 61 onto the recording medium 10 , and passes the light reflected by the recording medium 10 through the beam splitter.

In addition, the third beam splitter 65 is located on the optical path between the first and second beam splitters 53 and 63, and changes the propagation optical path so that the light emitted by the first light source 61 passes through the second beam splitter 63 and is recorded by the The light reflected by the medium 10 is directed to the second photodetector 69 . Each of the first, second and third beam splitters 53, 63 and 65 may be coated to selectively pass or reflect light in a certain wavelength region.

The second and third beam splitters 63 and 65 may be planar or cubic. In the case that the second and third beam splitters 63 and 65 are planar, the astigmatism caused by the inclination of the two beam splitters 63 and 65 should not occur when the light emitted by the first light source 51 passes through, so , as shown, the second and third beam splitters 63 and 65 are inclined in opposite directions to cancel mutual astigmatism. Preferably, the inclination angle between the second and third beam splitters 63 and 65 is 90°.

A collimator lens 45 is also arranged on the optical path between the objective lens 41 and the second beam splitter 63 . Since the first light source 51 is located at the focal point of the collimator lens 45, the light emitted from the first light source and passed through the collimator lens 45 becomes parallel light. In addition, since the second light source is located away from the focus position of the collimator lens 45, that is, at a position shorter than the focal length, the light A emitted from the second light source 61 and passed through the collimator lens 45 diverges to become almost parallel light. of light. As described above, the divergence of the light emitted by the second light source 61 through the collimator lens 45 can prevent the occurrence of spherical aberration due to the wavelength of the light source and the recording medium 10 when manufacturing the objective lens 41 for a relatively thin optical disc 10a. Caused by a thickness difference between.

Light emitted from the first light source 51 and passed through the collimator lens 45 and the objective lens 41 is focused on the relatively thin recording medium 10a. Light emitted from the second light source 61 and passed through the collimator lens 45 and the objective lens 41 is focused on the relatively thick recording medium 10b.

In addition, a first sensor lens 55 is provided on the optical path between the first beam splitter 53 and the first photodetector 57 to control the focusing of the light incident on the first photodetector 57 . The first sensor transmission 55 facilitates the optical arrangement of the first light detector 57 . In addition, the curvature of the first sensor lens 55 can be controlled so that the horizontal focus position of light passing through the first sensor lens 55 is different from its vertical focus position, which causes astigmatism. Thus, the first photodetector 57 can detect the focus error signal according to the astigmatism method.

A second sensor lens 67 is also provided on the optical path between the third beam splitter 65 and the second photodetector 69 . The structure and function of the second sensor lens 67 are basically the same as those of the first sensor lens 55 .

A compatible optical head according to the second embodiment of the present invention is shown in FIG. 4 . In the drawings, the same reference numerals as in Fig. 3 denote the same elements. Referring to Fig. 4, a second beam splitter 163 is arranged on the optical path between the first beam splitter 53 and the objective lens 41, and reflects the light emitted from the second light source 61 to the recording medium 10, and then reflects from the recording medium of incident light.

A third beam splitter 165 is located on the optical path between the objective lens 41 and the second beam splitter 163, and through the incident light from the first and second light sources 51 and 61, the light emitted by the second light source 61 from the recording medium The light reflected by 10 is directed to the second photodetector 69.

Here, it is preferable that the second and third beam splitters 163 and 165 are in the shape of a cube as shown in FIG. 4 so that the shape of the light emitted from the second light source 61 will not be deformed due to astigmatism.

A compatible optical head according to the third embodiment of the present invention is shown in FIG. 5 . In the drawings, the same reference numerals denote the same elements. According to the characteristics of this embodiment, the third beam splitter 65 is located on the optical path between the first beam splitter 53 and the objective lens 41, and reflects the light emitted by the second light source 61 to the recording medium 10, and reflects light from the recording medium 10 reflected incident light.

The second beam splitter 63 is located on the optical path between the second light source 61 and the third beam splitter 65 , and directs the incident light from the third beam splitter to the second light detector 69 .

Preferably, the first, second and third beam splitters 53, 63 and 65 are flat as shown in FIG. In the figure, the first beam splitter 53 and the third beam splitter 65 are relatively inclined. Also, the first light source 51 is on a straight line with the first beam splitter 53 , the third beam splitter 65 , the objective lens 41 and the recording medium 10 .

The first, second and third beam splitters 53, 63 and 65 may be cuboidal or flat as described above.

See Fig. 6, a kind of compatible optical head of the fourth embodiment of the present invention, it comprises first and second optical assembly 70 and 80, is used for emitting the light of different wavelength, and receives the light reflected by recording medium 10 simultaneously Light; Objective lens 41, the light that first and second optical assembly 70 and 80 sends is focused on the recording surface of recording medium 10; An optical path conversion device, such as a beam splitter 47, is arranged on the optical path, to change incident light transmission path. The same reference numerals as in previous figures denote the same elements.

According to a feature of this embodiment, the light source and photodetector are combined into an optical assembly. In this case, there is no need to insert the first beam splitter 53 (see FIG. 3 ) and the third beam splitter 65 in the optical path. Therefore, since there is only one beam splitter 47 as the optical path conversion device, the structure of the optical system can be simplified and the utilization rate of light can be improved.

One of the first and second optical assemblies 70 and 80 may consist of a light source and a light detector as shown in FIGS. 3 to 5 .

The first optical component 70 can be used when the beam splitter 47 has a cube-shaped structure, and its composition is shown in FIG. 7 . In Fig. 7, the first optical assembly 70 includes, a substrate 71, on which the first light source 151 and the first photodetector 157 are arranged, and the housing 72 covers the first light source 151 and the first photodetector 157, on the housing There is also an emission window 73 in which a holographic element 74 is arranged.

When the first light source 151 is an edge emitting laser, the first light source 151 is connected to the substrate 71 through the mount 75 . In addition, the first optical assembly 70 includes a plurality of lead wires 76 penetrating through and fixed on the substrate 71 for driving the first light source 151 and the first light detector 157 .

The hologram element 74 directs the light emitted from the first light source 151 to the recording medium shown in FIG. 6 , and diffracts the light reflected by the recording medium 10 toward the first photodetector 157 .

The structure of the second optical assembly 80 of Fig. 6 is similar to the structure of the first optical assembly 70, the difference is that the wavelengths of the light emitted by the second light source (not shown) and the light detected by the second photodetector are different The wavelength of the light from the first light source 151 and the first photodetector.

When the beam splitter 47 is shaped as an inclined plate, the hologram elements 74 of the first and second optical assemblies 70 and 80 are disposed on the optical path at an oblique angle opposite to that of the beam splitter 47 . Thus, distortion of light incident on the recording medium 10 from the first light source 51 can be prevented.

A compatible optical head according to the present invention includes first and second light sources emitting light of different wavelengths, and compatibly uses optical discs of different thicknesses by selectively driving one light source according to the type of recording medium used, and can To prevent data destruction during reproduction of information recorded on a CD-like disc, especially a CD-R disc having an organic dye film recording layer on the disc. In addition, the selective use of two light sources can increase the service life of the optical head, and the use of two light detectors also facilitates the arrangement of the optical path of each component.

Claims (17)

1. compatible optical head, it comprises:

One emission has first light source of predetermined wavelength;

One emission wavelength is different from the secondary light source that described first light source sends optical wavelength;

One object lens, the light that is used for respectively described first and second light sources being sent focuses on recording medium;

One optical path switching device, on the light path between described first and second light sources, described object lens are used to change the travel path of incident light;

One first photo-detector, be used to receive send by described first light source and via the light of described recording medium and described optical path switching device incident;

One second photo-detector, be used to receive send by described secondary light source and via the light of described recording medium and described optical path switching device incident.

2. compatible optical head as claimed in claim 1, wherein, described optical path switching device comprises:

One first beam splitter on light path between described first light source and the described object lens, the light that is used for being sent by described first light source reflexes to described recording medium, and will be by described first photo-detector of the light directive of described recording medium reflection;

One second beam splitter on light path between described first beam splitter and the described object lens, the light that is used for being sent by described secondary light source reflexes to described recording medium, and transmits the light by described recording medium reflection;

One the 3rd beam splitter on light path between described first and second beam splitters, be used for send from described secondary light source, by recording medium reflection and the light reflection by described second beam splitter to described second photo-detector.

3. compatible optical head as claimed in claim 2 also comprises, collimation lens, be used for be incident between described first and second light sources and described object lens on diverging light become directional light or approximately parallel light.

4. compatible optical head as claimed in claim 3, wherein, described secondary light source is positioned at the focal length of described collimation lens, make by described secondary light source send and light by described collimation lens with certain angular dispersed.

5. compatible optical head as claimed in claim 2 also comprises, first sensor lens are used to regulate the focusing of the incident light on the light path that incides at least one described first and second photo-detector.

6. compatible optical head as claimed in claim 1, wherein, described optical path switching device comprises:

One first beam splitter on light path between described first light source and the described object lens, the light that is used for being sent by described first light source reflexes to described recording medium, and will be by described first photo-detector of the light directive of described recording medium reflection;

One second beam splitter on light path between described first beam splitter and the described object lens, the light that is used for being sent by described secondary light source reflexes to described recording medium, and will be by the light by described recording medium reflection;

One second beam splitter on light path between described object lens and described second beam splitter, be used for and be mapped to described recording medium by the light that described first and second light sources send, and by send by described first light source and by the light of described recording medium reflection, and will send by described light source and reflex to described second photo-detector by the light of described recording medium reflection.

7. compatible optical head as claimed in claim 6 also comprises: collimation lens are used for and will are incident between described first and second light sources on the light path and the diverging light on the object lens becomes to directional light or is similar to parallel light.

8. compatible optical head as claimed in claim 7, wherein, described secondary light source is positioned at the focal length of described collimation lens, makes by described secondary light source to send, also pass through the light of collimation lens with certain angular dispersed.

9. compatible optical head as claimed in claim 6 also comprises, first sensor lens are used for regulating the focusing of the light on one that incides described at least first and second photo-detectors.

10. compatible optical head as claimed in claim 1, wherein, described optical path switching device comprises:

One first beam splitter on light path between described first light source and the described object lens is used for the described recording medium of light directive that will be sent by described first light source, and will be reflexed to described first photo-detector by the light of described recording medium reflection;

One is positioned at second beam splitter on the light path between described secondary light source and described object lens, is used to reflect the light that sends from described secondary light source, and will be by described second photo-detector of the light directive of described recording medium reflection; With

One the 3rd beam splitter on light path between described first beam splitter and the described object lens, be used for sending by described secondary light source, reflex to described recording medium by the light of described second beam splitter reflection, and the light of described recording medium reflection is reflexed to described second beam splitter.

11. the compatible optical head as claim 10 also comprises, collimation lens are used for the light path and the diverging light on the described object lens that incide between described first and second light sources are changed into directional light or approximately parallel light.

12. as the compatible optical head of claim 11, wherein, described secondary light source is positioned at the focal length of described collimation lens, makes light that send from secondary light source, by described collimation lens with certain angular dispersed.

13. the compatible optical head as claim 10 also comprises, first sensor lens are used for regulating the focusing of the light on one the light path that is incident on described at least first and second photo-detectors.

14. compatible optical head as claimed in claim 1, wherein, described first light source and described first photo-detector are installed toward each other, constitute one first assembly.

15. as the compatible optical head of claim 14, wherein, described first assembly comprises:

One substrate, described first light source and described first photo-detector are installed on the described substrate;

One shell has the emitter window by the light that sends from described first light source, and first light source and described first photo-detector are stated in described casing cover residence;

One holographic element is placed in the described emitter window, is used for light that send from described first light source and described object lens of process and the reception of described recording medium is directed to described first photo-detector.

16. compatible optical head as claimed in claim 1, wherein, described secondary light source and the arrangement adjacent to each other of second photo-detector constitute one second assembly.

17. as the compatible optical head of claim 16, wherein, described second assembly comprises:

One substrate is installed described secondary light source and described second detector on this substrate;

One shell has the emitter window by the light that sends from described secondary light source, and secondary light source and described second photo-detector are stated in this casing cover residence;

One holographic element is placed in the described emitter window, and the light that will be sent by described secondary light source and receive via described object lens and recording medium is directed to described secondary light source.

Images