KR20110096914A - Multi optical pick up - Google Patents

Abstract

The multi-optic pick-up according to the invention is, for example, a half-grating of simple structure divided into a first grating region for separating a laser beam of a first wavelength and a second grating region for separating a laser beam of a second wavelength. (Half Grating) is installed in a specific position in the optical path before the laser beam of the first wavelength and the laser beam of the second wavelength is superimposed, thereby specially used for phase shift grating, wavelength selective grating, double-sided grating, etc. Since it is not necessary to use a manufactured high-cost optical device, it is possible to reduce the manufacturing cost of the optical pickup, and to improve the productivity and performance of the optical pickup.

Description

Multi Optical Pick Up

The present invention relates to multi-optical pickup for recording or reading data on various types of optical discs such as CDs, DVDs, BDs and the like, for example.

1 shows a configuration of an embodiment of a general optical pickup. For example, the optical pickup includes an objective lens 11, a collimator lens 12, a beam splitter 13, and a grating ( 14), laser diode 15, photo detector 16, actuator 17, and the like.

The optical pickup may record or read data by firing a laser beam on various types of optical discs 10 such as CDs, DVDs, BDs, and the like. .

On the other hand, the laser diode (LD) 15 is a light emitting device, for example, in the case of a CD-LD (CD-LD), emits a red laser beam of 785nm wavelength, DVD In the case of the laser diode (DVD-LD), a red laser beam having a wavelength of 660 nm is emitted, and in the case of a BD-LD, the blue laser beam having a wavelength of 405 nm is emitted.

And. The grating (GT) 14 is a grating element. The grating 14 includes a main beam, a first sub beam 1, and a second laser beam emitted from the laser diode 15. The beam splitter (BS) 13 reflects the separated main beam and the sub beams by diffraction into sub beams 2 and splits the beams.

In addition, the collimator lens (CL) 12 converts the reflected main beam and the sub-beams from diffused light to horizontal light, and the object lens 11 (OL) For example, as shown in FIG. 1, the main beam and the sub-beams converted into the horizontal light are focused on a track formed on the optical disc 10.

After the light is collected on the track of the optical disk, the reflected main and sub beams pass through the objective lens 11, the collimator lens 12, and the beam splitter 13, and the photo detector PD. Detector 16 is received.

For example, as shown in FIG. 2, the photo detector 16 may be a light receiving element, and a 12 split photo detector may be used. The main beam may include A, which is formed at the center of the photo detector. Received in the B, C, D region, the first sub-beam (Sub Beam 1) of the sub-beams, is received in the E, F, G, H region formed on the left side of the photo detector, the second sub-beam 2) is received in the I, J, K, L areas formed on the right side of the photo detector.

The A, B, C, and D signals photoelectrically converted by the A, B, C, and D regions are output as a main push pull (MPP) signal by a subtractor (unsigned), and the main The push-pull signal has a value of MPP = (A + D)-(B + C).

Also, the E, F, G, and H signals photoelectrically converted by the E, F, G, and H regions are output as a first sub push pull (SPP1) signal by a subtractor (unsigned). The first sub-push pull signal has a value of SPP1 = (E + H)-(F + G), and the I, J, K, L signal photoelectrically converted by the I, J, K, L region. Is output as a second sub push pull (SPP2) signal by a subtractor (unsigned), and the second sub push pull signal is represented by SPP2 = (I + L)-(J + K). Value.

Meanwhile, the first sub push pull signal SPP1 and the second sub push pull signal SPP2 are summed and amplified by an adder (unsigned) and a predetermined gain (Gain = k) (k (SPP1 +). SPP2) and a subtractor (unsigned), which are subtracted from the main push pull signal MPP and output as a differential push pull signal (DPP), wherein the differential push pull signal (DPP) is DPP = MPP-k (SPP1 + SPP2).

The differential push-pull (DPP) signal, as is widely known, controls a driving voltage applied to the actuator 17 to move the objective lens 11 in a left-right direction. Tracking) is used in the servo control operation, for example, as shown in Figure 3, the main push pull (MPP) signal, and the first push pull (SPP1) signal and the second push pull (SPP2) signal It has a 180 degree retardation value.

On the other hand, the main push-pull (MPP) signal and the differential push-pull (DPP) signal have the same phase value to each other, for example, in the main push-pull (MPP) signal and the sub-push-pull (SPP) signal, Even if abnormal offset values exist, the differential push-pull (DPP) signal is calculated by the value of DPP = MPP-k (SPP1 + SPP2), and thus exists in the main push-pull signal and the sub push-pull signal. The offset values cancel each other so that a stable differential push-pull signal is always output.

Accordingly, the tracking servo control operation is performed by using a differential push-pull (DPP) signal that is not affected by the abnormal offset value as described above. Recently, CD, DVD, or DVD is performed. Multi-Pick Ups for recording or reading data on different types of optical discs such as (DVD) and BD (BD) have been developed and released and commercialized.

4 illustrates an embodiment of a general multi-optic pickup. For example, the multi-pickup includes an objective lens 21, a collimator lens 22, a beam splitter 23, The multi-grating 24, the multi-laser diode 25, the multi-photo detector 26, the actuator 27, and the like are included.

Meanwhile, the multi-laser diode 25 selectively emits a unique laser beam corresponding to the type of the optical disc. For example, the multi-laser diode 25 may include a CD and a DVD laser diode (CD). / DVD-LD), it emits a red laser beam of 785nm wavelength for CD, or emits a red laser beam of 660nm wavelength for DVD.

When the multi-photo detector 26 is, for example, a CD and DVD photo detector (CD / DVD-PD), as shown in FIG. 4, a CD photo detector (for example, PD1 = CD-). PD) and DVD photodetector (eg PD2 = DVD-PD) are integrally formed.

In addition, when the multi-grating 24 is, for example, CD and DVD combined grating (CD / DVD-GT), as shown in FIG. 4, a phase shift grating manufactured in a special shape is shown. This can be used.

However, the phase shift grating is, as is well known, a high-cost optical element specially manufactured in the shape of a grating so that the phase difference between the main beam and the sub beams is 180 degrees, so that the manufacturing cost of the multi-optic pickup is increased. There is a problem.

In addition, since the phase shift grating has a poor radial shift characteristic, as is widely known, the light efficiency is extremely lowered unless it is precisely placed in the center of the laser beam, thereby improving productivity and performance of the optical pickup. There is a problem that is reduced.

On the other hand, the multi-grating 24, in addition to the phase shift grating specially manufactured as described above, may be used, as is well known, wavelength selective grating, or double-sided grating, in the case of the wavelength selective grating or double-sided grating Similarly, since it is a specially manufactured high-priced optical element, the manufacturing cost of the multi-optical pickup is increased, and precise design and control are required, which leads to a problem that the productivity and performance of the optical pickup are deteriorated.

For example, the present invention provides a simple structure of half grating divided into a first grating region for separating a laser beam of a first wavelength and a second grating region for separating a laser beam of a second wavelength. The present invention is to provide a multi-optic pickup for improving the manufacturing cost and productivity of the multi-optic pickup by using it for a multi-optic pickup such as a combined CD, DVD and optical pickup.

The multi-optical pickup according to the present invention includes a light emitting device for emitting one of a laser beam of a first wavelength and a laser beam of a second wavelength, and the emitted laser beam as a main beam and first and second sub beams. In a multi-optical pickup comprising a grating element for separating, the grating element includes a first grating region for separating the laser beam of the first wavelength and a first grating region for separating the laser beam of the second wavelength. It is divided into two grating regions, and installed in front of the light emitting device, characterized in that installed in a specific position of the optical path before the laser beam of the first wavelength and the laser beam of the second wavelength overlap,

In addition, the spacing and inclination of the gratings formed in the first grating region is different from the spacing and inclination of the gratings formed in the second grating region,

In addition, the specific position of the optical path in which the grating element is provided, characterized in that the laser beam of the first wavelength and the laser beam of the second wavelength is provided at the position just before the overlap,

The first grating region may separate the laser beam for the DVD, and the second grating region may separate the laser beam for the CD.

In addition, the first grating region is characterized in that a plurality of gratings are formed at a tighter spacing and a greater angle of inclination than the second grating region,

In addition, the specific position where the grating element is installed, is calculated by the following formula,

,

,

Where f _{CL _ DVD} is the focal length from the DVD light emitting element to the collimator lens, NA _{OL_DVD} is the numerical aperture of the DVD objective lens, f _{OL _ DVD} is the focal length from the DVD objective lens to the DVD recording layer, and f _{CL _ CD} is the focal length from the CD emitting element to the collimator lens, NA _{OL _ CD} is the numerical aperture of the CD objective lens, f _{OL _ CD} is the focal length from the CD objective lens to the CD recording layer, and x _DVD Is the radius of the first grating area through which the laser beam for the DVD is transmitted, x _CD is the radius of the second grating area through which the CD laser beam is transmitted, and x _DVD + x _CD is the physical separation between the DVD light emitting device and the CD light emitting device. The distance, and y _DVD and y _CD are the same value, it is characterized in that the specific position where the grid element is installed.

The multi-optic pick-up according to the invention is, for example, a half-grating of simple structure divided into a first grating region for separating a laser beam of a first wavelength and a second grating region for separating a laser beam of a second wavelength. (Half Grating) is installed in a specific position in the optical path before the laser beam of the first wavelength and the laser beam of the second wavelength is superimposed, thereby specially used for phase shift grating, wavelength selective grating, double-sided grating, etc. Since it is not necessary to use a manufactured high-cost optical device, it is possible to reduce the manufacturing cost of the optical pickup, and to improve the productivity and performance of the optical pickup.

1 illustrates an embodiment of a general optical pickup,
2 illustrates an embodiment of an output process of a general differential push-pull (DPP) signal.
3 shows a graph of an embodiment for general push-pull signals,
4 illustrates an embodiment of a general multi-optical pickup,
5 illustrates an embodiment of a multi-optical pickup according to the present invention;
6 illustrates an embodiment in which half grating according to the present invention is installed at a specific position,
FIG. 7 illustrates an embodiment in which a laser beam is separated by a first grating region and a second grating region of a half grating according to the present invention.
8 and 9 show an embodiment for determining the optimal installation position of the half grating according to the present invention,
10 illustrates an embodiment in which half grating according to the present invention is installed in close proximity to a laser diode.

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

The present invention can be applied to a multi-optic pickup for selectively firing any one of laser beams of different wavelengths. For example, a CD and DVD combined optical pickup, or a DVD and BD It can be applied to various types of multi optical pickups such as a combined optical pickup.

Meanwhile, the multi-optic pickup according to the present invention includes, for example, a first grating region for separating a laser beam of a first wavelength into a main beam and sub beams, and a laser beam of a second wavelength into a main beam and sub beams. A simple grating is used, in which the second grating region for separation is divided with respect to the center, and in the present invention, this is called half grating.

As a multi-optical pickup using the half grating, for example, a CD and DVD (CD / DVD) combined optical pickup will be described in detail.

5 shows an embodiment of the multi-optical pickup according to the present invention. The multi-optic pickup includes, for example, an objective lens 21, a collimator lens 22, a beam splitter 23, and a half grating. 34, the multi-laser diode 25, the multi-photo detector 26, the actuator 27, etc. are comprised.

In addition, the multi-laser diode 25 is a light emitting device, and selectively emits a unique laser beam corresponding to the type of the optical disc. For example, the multi-laser diode 25 is a combination of CD and DVD. In the case of a laser diode (CD / DVD-LD), either a red laser beam of 785 nm wavelength for CD or a red laser beam of 660 nm wavelength for DVD is selectively fired.

In addition, the multi-photo detector 26 includes a plurality of photo detectors corresponding to the types of laser beams emitted by the multi-laser diode 25, for example, the multi-laser diode 25 ) Is a CD and DVD combined photo detector (CD / DVD-PD), as shown in FIG. 5, a CD photo detector (eg PD1 = CD-PD) and a DVD photo detector (eg PD2 = DVD-PD) is integrally formed.

On the other hand, the half grating 34, for example, as shown in Figure 5, the first grating area (Area1) and the second wavelength for separating the laser beam of the first wavelength into the main beam and the sub-beams, The second grating area (Area2) for separating the laser beam into the main beam and the sub beams is manufactured in a simple structure divided into two centers.

In addition, the gratings formed in the first grating region and the gratings formed in the second region have different intervals and inclinations. For example, the first grating region Area1 has a red color of 660 nm wavelength for DVD. When the laser beam is separated into the main beam and the sub beams, and the second grating area Area2 separates the red laser beam of the 785 nm wavelength for the CD into the main beam and the sub beams, as shown in FIG. 5. The lattice formed in the first lattice area Area1 is formed more densely than the lattice formed in the second lattice area Area2.

In addition, the gratings formed in the first grating area Area1 have a larger angle of inclination than those of the gratings formed in the second grating area Area2, as shown in FIG. 6. This is because the track pitch of the DVD (eg DVD_Track Pitch = 0.74um) is narrower than the track pitch of the CD (eg CD_Track Pitch 1.64um).

Meanwhile, the half grating 34 manufactured as described above is installed in front of the multi-laser diode 25. For example, as shown in FIG. 7, the laser beam for CD and the laser beam for CD overlap each other. It is installed at a specific position on the optical path that is not.

The specific position is a multi-laser in which the DVD laser beam is incident only in the first grating region Area1 of the half grating, and the CD laser beam is incident only in the second grating region Area2 of the half grating. The distance d with the diode 25 should be determined.

For example, as shown in FIG. 8, when the laser beam for DVD is fired, the separation distance between the first grating region Area1 of the half grating 34 and the laser diode for DVD_LD is y _DVD . If the effective radius of the first grating region through which the DVD laser beam is transmitted is x _DVD , the following Equation (1) can be derived.

.. 수식(1)

.. Formula (1)

Here, f _{CL _ DVD} is a focal length from the laser diode for DVD (DVD_LD) to the collimator lens CL (for example, f _{CL _ DVD} = 16 mm), and NA _{OL _ DVD} is the numerical aperture of the DVD objective lens ( Example: NA _{OL_DVD} = 0.65), and f _{OL _ DVD} is the focal length (e.g., 3.22 mm) from the DVD objective to the DVD recording layer.

On the other hand, as is widely known, since the numerical aperture of the objective lens is NA = nSinθ, for example, in the case of FIG. 8, NA _{OL_DVD} = nSinb = n (a / f _{OL_DVD} ), where n is the _{regulation ratio of} air. Assuming 1, eventually a = f _{OL _ DVD} X NA _{OL _ DVD} , which is the focal length f _{OL _ DVD} from the center of the DVD objective to the DVD recording layer and the focal length c from the right side of the DVD objective to the DVD recording layer. Because it is the same.

Thus, y _DVD : x _DVD = f _{CL _ DVD} : a = f _{CL _ DVD} : (f _{OL _ DVD} Since xNA _{OL _ DVD} ), the above formula (1) can be derived.

As shown in FIG. 9, when the CD laser beam is emitted, the separation distance between the second grating area Area2 of the half grating 34 and the CD laser diode CD_LD is y _CD . If the effective radius of the second grating region through which the laser beam for CD is transmitted is x _CD , the following equation (2) can be derived.

.. 수식(2)

.. Formula (2)

Here, f _{CL _ CD,} the focal length of the CD laser diode (CD_LD) for up to a collimator lens (CL) (for example: f _{CL_CD} = 16.1mm) and, NA _{OL _ CD} has a numerical aperture of the CD objective lens (for example, : NA _{OL_CD} = 0.53), and f _{OL _ CD} is the focal length (eg, 3.24 mm) from the CD objective to the CD recording layer.

On the other hand, as described above, since the numerical aperture of the objective lens is NA = nSinθ, for example, in the case of FIG. 9, NA _{OL_CD} = nSinf = n (e / f _{OL_CD} ), where n is the _{regulation ratio of} air. Assuming 1, eventually e = f _{OL _ CD} X NA _{OL _ CD} , which is essentially the focal length (f _{OL _ CD} ) from the center of the CD objective to the CD recording layer and the focal length (g) from the left side of the CD objective to the CD recording layer. Because it is the same.

Thus, y _CD : x _CD = f _{CL _ CVD} : e = f _{CL _ CD} : (f _{OL _ CD} X NA _{OL _ CD} ), so that the above formula (2) can be derived.

On the other hand, the sum of the x _DVD and x _CD is the physical separation distance between the DVD laser diode (DVD_LD) and the CD laser diode (CD_LD), for example, as shown in Fig. 8 or 9, x _DVD + x _CD = 0.11 mm, and y _DVD and y _CD are equal to each other as the distance d between the half grating 34 and the multi-laser diode 25.

Accordingly, y _DVD satisfying the above formulas (1) and equation (2), and a _DVD + x _CD x = 0.11mm and, y = y _DVD condition of d = _CD Alternatively, when y _CD is calculated, the value of the specific position d on the optical path in which the DVD laser beam and the CD laser beam do not overlap with each other is calculated as d = 463 um.

Meanwhile, the half grating 34 may be installed closer to the multi laser diode 25 than the specific position d, for example, as shown in FIG. 10.

Or more, preferred embodiments of the present invention described above, for the purpose of illustration, those skilled in the art, within the technical spirit and the technical scope of the present invention disclosed in the appended claims below, to further improve various other embodiments Changes, substitutions or additions will be possible.

10 optical disc 11 objective lens
12 collimator lens 13 beam splitter
14 grating 15 laser diode
16: Photo detector 17: Actuator
21: objective lens 22: collimator lens
23 beam splitter 24 multi-grating
25: multi-laser diode 26: multi-photo detector
27: Actuator 34: Half Grating

Claims (6)

A light emitting device for emitting one of the laser beam of the first wavelength and the laser beam of the second wavelength;
In the multi-optical pickup comprising a grating element for separating the emitted laser beam into the main beam and the first and second sub-beams,
The grating element is divided into a first grating region for separating the laser beam of the first wavelength and a second grating region for separating the laser beam of the second wavelength,
It is provided in front of the light emitting element, the multi-optical pickup, characterized in that installed in a specific position of the optical path before the laser beam of the first wavelength and the laser beam of the second wavelength overlap. The method of claim 1,
The spacing and the slope of the gratings formed in the first grating region are different from the spacing and the slope of the gratings formed in the second grating region. The method of claim 1,
The specific position of the optical path in which the grating element is provided is provided at a position just before the laser beam of the first wavelength and the laser beam of the second wavelength are overlapped. The method of claim 1,
The first grating region separates the laser beam for the DVD, and the second grating region separates the laser beam for the CD. The method of claim 4, wherein
And a plurality of gratings are formed in the first grating area at a denser interval and a larger angle of inclination than the second grating area. The method of claim 4, wherein
The specific position where the grating element is installed is calculated by the following equation,

,

Where f _{CL _ DVD} is the focal length from the DVD light emitting element to the collimator lens, NA _{OL _ DVD} is the numerical aperture of the DVD objective lens, and f _{OL _ DVD} is the focal length from the DVD objective lens to the DVD recording layer. ,
f _{CL _ CD} is the focal length from the CD emitting element to the collimator lens, NA _{OL _ CD} is the numerical aperture of the CD objective lens, f _{OL_CD} is the focal length from the CD objective lens to the CD recording layer,
x _DVD is the radius of the first lattice region through which the laser beam for _DVD is transmitted, x _CD is the radius of the second lattice region through which the CD laser beam is transmitted, and x _DVD + x _CD is the distance between the DVD light emitting element and the CD light emitting element. The physical separation distance, and y _DVD and y _CD are the same value, characterized in that the particular location where the grating element is installed.

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