Patent Application
20080205212
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2007-050311, filed Feb. 28, 2007, the entire contents of which are incorporated herein by reference.
1. Field
One embodiment of the present invention relates to an information recording/reproducing apparatus and an information recording/reproducing method, which can record information on an information recording medium capable of recording information by using light with two wavelengths.
2. Description of the Related Art
In optical discs such as a DVD-R disc and a DVD-RW available on the market, address information is previously recorded in a land pre-pit, and a record mark is formed on a wobbled pre-groove.
A reproducing signal from a land pre-pit or a pre-groove is used for reproducing address information or as a tracking servo signal. For stable tracking and correct reproduction of address information, the shape of a land pre-pit or a pre-groove is optimized such that a reproducing signal becomes larger.
A current optical disc drive also adopts a method of optimizing recording conditions, such as a recording power and a recording pulse width, in order to realize more stable information recording.
For example, Japanese Patent Application Publication (KOKAI) No. 2001-266362 discloses
a) a large detection signal is obtained from a land pre-pit to ensure the reliability of reproduction from address information recorded in a land pre-pit, and
b) a large track displacement detection signal is obtained from a pre-groove to ensure high tracking stability at the time of forming a record mark, when a record mark is newly recorded on an information recording medium having a pre-groove and a land pre-pit.
In the Japanese Patent Application Publication (KOKAI) No. 2004-192679 explains an example of calculating optimum recording power, or optimizing recording conditions when recording information, based on a detected value of an optical phase difference among optical discs.
In the Japanese Patent Application Publication (KOKAI) No. 6-131688 discloses an example using a reproducing light sources and a recording light source, which are different in the wavelength of output laser beams.
However, in a read-only DVD-ROM disc, address information and tracks are formed by a record mark formed in an emboss pit, and a land pre-pit and a pre-groove are not formed. Therefore, a read-only optical disc drive is optimized for reproducing information of a record mark, and if a reproducing signal of a land pre-pit or pre-groove specific to a recording optical disc is mixed there, it becomes a noise component. In this case, even if a recording condition is an optimized recording mark, a reproducing characteristic is degraded.
In the example shown in the Publication No. 2001-266362, as the wavelength of a laser beam for tracking when recording a record mark is the same as the wavelength of a laser beam for reproducing information from a record mark, the following problems occur.
1. A crosstalk signal from a land pre-pit is mixed into a reproducing signal from a record mark, and the characteristic of a reproducing signal from a record mark is degraded, and the reliability of reproduction from a record mark is largely lowered.
2. By the influence of a diffracted light from a pre-groove, the characteristic of track displacement detection by a differential phase detect (DPD) method is degraded, and the stability of detection of a track displacement from a record mark is lowered.
3. As a DC level from a pre-groove is decreased upon reproduction, the amplitude of a reproducing signal from a record mark is lowered, and the reliability of reproduction from a record mark is largely lowered.
Even by changing the wavelengths of laser beams for recording and reproducing as shown in the Publication No. 2004-192679 or 6-131688, it is difficult to increase the amplitude of a signal upon reproduction as indicated in the Publication No. 2001-266362.
As described above, there is a problem that the record mark reading characteristic is different between a current DVD-R/DVD-RW disc and a read-only DVD-ROM.
A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention.
Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment of the invention, an optical head device for recording information on a recording medium which reflects light from a first light source to output light with a first wavelength by a predetermined light power, and diffracts a little light from a second light source to output a light with a second wavelength longer than the light with a first wavelength from the first light source in a non-recording state, comprising: an objective lens which condenses the light from the first and second light sources on a recording layer of a recording medium; an actuator which movably holds the objective lens to permit focusing to match a focal position of the objective lens with a recording layer of a recording medium, and to permit tracking to match the light condensed by the objective lens with a predetermined position in the radial direction of a recording medium; and a photodetector which outputs a signal corresponding to the light power mount of a reflected light from a recording layer of a recording medium captured by the objective lens, wherein recording information on a recording layer of a recording medium by the light emitted from the second light source, simultaneously outputting light from the first and second light sources, controlling a position of the objective lens in the direction of an optical axis by the light emitted from the first or second light source and reflected from recording layer of a recording medium, and controlling a position of the object lens in the radial direction of a recording medium by the output of the photo-detector which detects a component of the light emitted from the first light source and reflected from a recording layer of a recording medium, and wherein reproducing information recorded on a recording medium is only by the light emitted from the second light source, and controlling a position of the objective lens in the direction of an optical axis and in the radial direction of a recording medium by the output of the photo-detector which detects a component of the light emitted from the second light source and reflected from a recording layer of a recording medium.
Embodiments of this invention will be described in detail with reference to the drawings.
An optical disc drive (disc drive) 1 shown in
The PUH 101 includes a first semiconductor laser element (LD 1) 113 capable of outputting a laser beam with a first wavelength, a second semiconductor laser element (LD 2) 115 capable of outputting a laser beam with a second wavelength longer than the first wavelength, an objective lens 151 which guides laser beams from the first and second laser elements to a recording surface of an optical disc D, and captures a reflected laser beam reflected from the recording surface of the optical disc D, and an actuator (ACT) 111 holding the objective lens 151, as explained later.
The PUH 101 has a monitoring photodetector (APC-PD, in
The optical disc drive 1 has a CPU 21, a RAM 23, a ROM 25 and an interface 27, which are connected to a bus 11. The bus 11 is connected to a signal processing circuit 61 to give a predetermined characteristic to the output from the D-PD 105 of the PUH 101, a servo circuit 63 to control a position of an ACT 111 by using the output from the signal processing circuit 61, and a data reproducing circuit 65 to reproduce data (information) recorded in the optical disc D from the output of the signal processing circuit. The bus 11 is also connected to a PLL circuit 67, a laser drive circuit (laser diode driver, LDD) 51, and a disc motor control circuit 41. The LDD 51 includes a laser control circuit 53 and a modulation circuit 55, controls the strengths and waveforms of laser beams output from the first and second laser elements mounted in the PUH 101, and controls the output and stop of a laser beam. The LDD 51 can drive the first and second semiconductor laser elements at the same time.
In the optical disc drive 1 shown in
The modulation circuit 55 modulates recording data supplied from a host set (an external apparatus) connected through the interface 27, at the time of recording information, and supplies the modulated data to the laser control circuit 53.
The laser control circuit 53 supplies a writing signal to at least one of the first and second laser elements in the PUH 101, at the time of recording information (at the time of forming a mark), based on the modulated data supplied from the modulation circuit 55. At the time of reproducing information, a laser beam fixed to a reproducing power is supplied to at least one of the first and second laser elements of the PUH 101.
The laser beam according to a signal supplied from the laser control circuit 53 output from the PUH 101 is focused on the optical disc D. A monitoring signal corresponding to the intensity of a laser beam is generated by a monitoring PD 103 of the PUH 101, and output to the laser control circuit 55. Then, a writing signal is adjusted.
An output signal based on a reflected light from the optical disc D is generated by the data PD 105 of the PUH 101, and supplied to the servo circuit 63 and data reproducing circuit 65 through the signal processing circuit 61. The signal processing circuit 61 generates a focus error signal and a tracking signal, and outputs them to the servo circuit 63.
The servo circuit 63 generates a focusing control signal and a tracking signal for controlling the position of the ACT 111, and outputs them to not-shown focus coil and tracking coil of the ACT 111. As a result, a laser beam condensed on the recording surface of the optical disc D by an objective lens of the ACT 111 is controlled to be just-focused on the recording layer of the recording surface of the optical disc D, and then controlled to follow a track.
The output from the signal processing circuit 61 supplied from the data reproducing circuit 65 is reproduced as recorded data (on the optical disk D), based on a reproducing clock signal from the phase-locked loop (PLL) circuit 67.
The reproduced data reproduced by the data reproducing circuit 65 is output to a host set (an external apparatus) or a storage device (an HDD or a work memory) through the interface circuit 27.
It is needless to say that the disc motor control circuit 41, modulation circuit 55 (LDD 51), laser control circuit 53 (LDD 51), servo circuit 63, data reproducing circuit 65, and PLL circuit 67 are controlled by the central processing unit (CPU) 21. The CPU 21 controls all operations of the optical disc drive 1, according to operation commands supplied from the host set through the interface circuit 27. The CPU 21 uses the random access memory (RAM) 23 as a work area, and is operated according to a program stored in the read-only memory (ROM) 25. This is not substantially different from a known disc drive apparatus, and explanation will be omitted.
Next, an explanation will be given on a photodetector incorporated in an optical head (PUH) of the optical disc drive shown in
The data PDIC 105 has a main photodetecting area at a position in the optical head (PUH 101,
Each photodetecting area receives light with a wavelength 1 (400 to 410 nm), outputs a push-pull (PP) signal usable for a focus error signal and a tracking error signal, and outputs a data reproducing signal, or radio frequency (RF) signal from an area to receive light with a wavelength 2 (650 to 680 nm).
For example, the data PDIC 105 shown in
It is possible to obtain a focus error signal by using the outputs of four channels (CH) of the central (main) photodetecting area. Further, it is also possible to obtain a differential phase detection (DPD) signal by using the outputs of four channels of the central area. Therefore, it is possible to perform tracking even for an optical disc having a record mark (a string of pits) by DPD by using a laser beam with the wavelength 2.
The monitoring PDIC 103 is provided at a predetermined position in the optical head (PUH) 101, and has a photodetecting area 103-1 to receive light with the wavelength 1 (400 to 410 nm), and a photodetecting area 103-2 to receive light with the wavelength 2 (650 to 680 nm), as shown in
A filter or a polarizer 123 may be provided between the PDIC 103 and a beam splitter (a dichroic prism described later with reference to
In current DVD-R and DVD-RW discs, 650±5 nm is assumed to be a wavelength of light for reproducing. Therefore, a laser beam with a wavelength of 650 nm can be obtained by using the PUH 101 of the optical disc drive shown in
Actually, an optical disc having a wide usable wavelength range is advantageous in cost performance, and reproducible by a 650±5 nm laser beam. Therefore, one of wavelengths of a laser beam to be output from a laser element mounted in the PUH 101 is decided to 650±5 nm.
A wavelength λw used for a laser beam used for tracking may be any value shorter than 650 nm. In contrast, as a laser beam (a semiconductor laser source) with a wavelength of 405 nm has been used in the HD DVD and Blu-ray disc (BD) standards, one of wavelengths of a laser beam to be output from a laser element mounted in the PUH 101 is desirably 405±5 nm.
As recording is performed by using light with a wavelength of 650 nm, the characteristic (absorbance) of the recording layer of the optical disc shown in
Namely, the characteristic of the recording layer of the optical disc shown in
Therefore, by using a recording layer having the absorbance (reflectivity) shown in
The depth of land/groove specific to an optical disc can be obtained from the result of simulation showing the relationship between the groove depth and push-pull signal amplitude when a laser beam with a wavelength of 405 nm is condensed by an objective lens with a numerical aperture (NA) of 0.65, as shown in
Namely, the push-pull signal amplitude is very large in
For example, when the depth of a groove of a recording layer of an optical disc D is 20 nm, the width of a push-pull signal is large for a laser beam with the wavelength 1 (405 nm), but small for a laser beam with the wavelength 2 (650 nm). By giving such a groove to the recording layer of the optical disc D, a push-pull signal is substantially not output when reproducing the optical disc D with a laser beam with the wavelength 2, after recording a signal on an optical disc by tracking by a laser beam with the wavelength 1. As a result, the influence of a track cross (crosstalk) in a focus signal is reduced, and stable focusing is possible. Even when reproducing a recorded optical disc by a second laser beam by using optional optical head and optical disc drive specific to a current DVD standard optical disc, as a record mark (a string of pits) is recorded, tracking in the DPD method is possible, and no problem arises from the fact that a push-pull signal is not output.
An optical head (PUH) 101 shown in
The wavelength of a laser beam output from the first laser element (LD 1) 113 is 405±5 nm (400 to 410 nm), and blue, as already explained.
The wavelength of a laser beam output from the second laser element (LD 2) 115 is 650 to 680 nm (or 650±15 nm), and red, as already explained.
The dichroic prism 121 transmits most (over 90%) of a laser beam with a first wavelength, and reflects most (over 90%) of a laser beam with a second wavelength.
The polarization beam splitter 131 transmits a p-polarized light beam, and reflects an s-polarized light beam.
The APC PDIC 103 consists of two or more photodetecting areas (usually, one main area and two sub-areas on both sides) partitioned by division lines intersecting at right angles, as shown in
As shown in
The data PDIC 105 consists of two or more photodetecting areas (usually, one main area and two sub-areas on both sides) partitioned by division lines intersection at right angles, as shown in
In the optical head (PUH) 101 shown in
The light with the first wavelength (indicated by a solid line) passes through the dichroic prism 121, and the light with the second wavelength (indicated by a broken line) reflects on the dichroic prism 121. The first laser element (LD 1) 113 and second laser element (LD2) 115 are arranged, so that the output lights with the first and second wavelengths are positioned on the same axial line.
The light with the first wavelength passing through the dichroic prism 121 and the light with the second wavelength reflected from the dichroic prism 121 are transmitted through the polarization beam splitter 131, converted to parallel light by the collimator lens (CL) 141, transmitted through a not-shown λ4 plate, given a predetermined convergence by the objective lens (OL) 151, and condensed on the recording layer of the recording surface of the optical disc D.
The reflected laser beams (the laser beams with the first and second wavelengths overlapped) reflected from the recording surface of the optical disc D are captured by the objective lens 151, converted to parallel light, transmitted through a not-shown λ/4 plate and turned 90 degree compared with the laser beam having the polarizing direction toward the optical disc D, and changed from a p-polarized beam to a s-polarized beam.
The reflected laser beam transmitted through the %/4 plate is given convergence by the collimator lens 141, and applied to the polarization beam splitter 131. At this time, as the polarizing direction is changed to a s-polarization, then the reflected laser beam is reflected toward the data PDIC 105.
Thereafter, the reflected laser beam is photoelectrically converted by the PDIC 105, and supplied to the signal processing circuit 61 (refer to
A laser beam with the first wavelength reflected from the dichroic prism 121 by a predetermined ratio and a laser beam with the second wavelength passing through the dichroic prism 121 by a predetermined ratio are guided to the APC PDIC 103, photoelectrically converted by the PDIC 103, and supplied to the laser control circuit 53 (refer to
An optical head (PUH) 201 shown in
The data PDIC 105 obtains a focus error signal and an RF signal from a laser beam with the second wavelength output from the main photodetecting area diagrammatically shown in
Namely, as a laser beam with the wavelength 2 is used for focusing, a spot of a laser beam with the wavelength 2 emitted from the objective lens (OL) 151 can be condensed without defocusing. By obtaining a tracking error signal from a laser beam with the wavelength 1, even if a recording layer of an optical disc is displaced from a focal position of the objective lens 151, a tracking error signal can be obtained without being so influenced in contradistinction to an RF signal.
The output of the APC PDIC 103 is used for setting the intensity of a laser beam output from each laser element, as in the example of
In an optical head (PUH) 301 shown in
By using the PUH 301 shown in
In an optical head (PUH) 401 shown in
By using the PUH 401 shown in
In an optical head (PUH) 501 shown in
By using the optical head (PUH) shown in
A PUH 601 shown in
Namely, a focus of a laser beam with the wavelength 2 is corrected by adjusting the position of the movable (relay) lens 681 to obtain a best RF signal with the wavelength 2, thereby realizing stable focus control compared with a system (
As in a PUH 701 shown in
In the system shown in
For example, by simultaneously lighting the laser element (LD 1) 113 for the wavelength 1 and the laser element (LD 2) 115 for the second wavelength, and by obtaining focus error signals of both laser elements at the same time, it is possible to detect a focus displacement of a laser beam with each wavelength (a displacement from a focus position of an objective lens), to perform focusing and tracking by using a laser beam with the wavelength 1, and to perform recording by using a laser beam with the wavelength 2.
For example, when recording, a predetermined offset may be added to a focus error signal, so that a size of the beam spot becomes minimum with respect to light with the wavelength 2. And for example, In this case, by adjusting an optical path length of a laser beam with at least one of the wavelengths by a corresponding movable (relay) lens, as in the system shown in
As explained above, it is possible to record information at a highly increased speed (several or several ten times higher) on a write-once optical disc (a recording medium), which outputs a push-pull signal when receiving a laser beam with the wavelength 1 (400 to 410 nm) of the present invention and outputs almost no push-pull signal when receiving a laser beam with the wavelength 2 (650 to 680 nm), by using a laser beam with the second wavelength 2 for recording.
Namely, according to the invention, when recording data on a write-once optical disc medium, which outputs a push-pull signal when receiving a laser beam with the wavelength 1 (400 to 410 nm) of the present invention and outputs almost no push-pull signal when receiving a laser beam with the wavelength 2 (650 to 680 nm), as it is impossible to follow (track) a face wobble before recording with the wavelength 2, a record mark to permit reading a signal by light with the wavelength 2 is formed on the medium by tracking with the wavelength 1, or by recording by light with the wavelength 1 or 2. As tracking by light with the wavelength 2 is possible by using the DPD method after recording, reproduction is possible only by light with the wavelength 2.
Further, according to the invention, as a maximum output of semiconductor laser having the wavelength 2 is larger than the output of a semiconductor laser having the wavelength 1, recording at a highly increased speed is possible by using a semiconductor laser having the wavelength 2. Further, as the wavelength 2 is longer than the wavelength 1, it is necessary to increase NA in order to realize the same spot size. But, when a spreading angle and optical magnification of a laser beam from LD are equal in the wavelengths 1 and 2, a beam using efficiency is increased when the NA is high. Therefore, from this point of view, recording by using the wavelength 2 is advantageous in the power.
Further, when the working distances of the wavelengths 1 and 2 are different when recording, there arise a problem that when focusing by using the wavelength 1, and the light with the wavelength 2 is defocused and a spot of the wavelength 2 cannot be condensed. According to the invention, in the example shown in
Namely, by using the invention, it is possible to record data on a write-once optical disc medium, which outputs a push-pull signal when receiving a laser beam with the wavelength 1 (400 to 410 nm) of the present invention and outputs almost no push-pull signal when receiving a laser beam with the wavelength 2 (650 to 680 nm), by the same wavelength as a reproducing wavelength, by tracking by using a laser beam with the wavelength 1, and by recording by using a laser beam with the wavelength 2. Namely, when recording on a medium, it is easily possible to optimize recording conditions to obtain the best quality of a reproducing signal. In addition, when reproducing data, it is possible to obtain a reproducing signal with good quality with less influences of land pre-pit and pre-groove.
Further, in a semiconductor laser used for an optical disc drive, a laser beam with the wavelength 2 is lower in cost and larger in output. Therefore, it is possible to manufacture at low cost an optical disc drive capable of recording on a write-once optical disc which outputs a push-pull signal when receiving a laser beam with the wavelength 1 (400 to 410 nm) of the present invention and outputs almost no push-pull signal when receiving a laser beam with the wavelength 2 (650 to 680 nm), at a highly increased speed.
While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. What is claimed is:
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-050311 | Feb 2007 | JP | national |
