CN100401110C - Optical element group for optical read-write head and its manufacturing method - Google Patents

Abstract

The invention provides an optical element group for optical read-write head, which does not contain a Quarter Wave Plate (QWP), and the optical element group comprises a plurality of optical elements, wherein at least two optical elements are respectively provided with an optical coating film generating phase difference to change the polarization state of light beams so as to lead emergent light to become circularly polarized light, and the circularly polarized light is incident on an optical storage medium and finally becomes a signal light beam received by an optical detector.

Description

Optical element group for optical read/write head and manufacturing method thereof

technical field

The invention relates to an optical read-write device, and in particular to an optical read-write head.

Background technique

The technology of storing data on CDs and DVDs and accessing the data stored on them through optical read-write devices is well known. Usually, the reading and writing of data is carried out by the action of optical read-write heads; The principle of taking out the disc is to focus the laser beam on the data storage surface of the disc first, and then pass the signal beam reflected by the disc surface through a photodetector to convert it into an electronic signal; the experimental results have confirmed that if When the laser beam incident on the optical disc is a circularly polarized light, the resulting signal beam is better. Therefore, making the incident beam on the optical disc into a circularly polarized light becomes one of the optical design conditions of the optical pick-up head.

Fig. 1A has shown a traditional optical read-write head, and this optical read-write head comprises a laser diode 101 for DVD reading and writing, a laser diode 103 for CD reading and writing, a polarized beam splitter (polarized beamsplitter) 105, a Polarization beam splitter 107, a mirror (folding mirror) 109, a quarter wave plate (quarter wavelengh plate; QWP) 111 and a light detector 113; Laser diodes 101 and 103 are used to generate laser beams, laser The light beam is in a linearly polarized state after being emitted from the laser diode, that is, there is no phase difference between its two vertical components (referred to as S-wave and P-wave respectively); polarization beam splitters 105 and 107 are used to separate the different components of the light beam. The polarization components (S-wave and P-wave) are reflected or transmitted; the mirror 109 is used to reflect the beam to change the direction of the beam; and the quarter-wave plate 111 is used to adjust the polarization of the beam state, so that there is a phase difference between the S-wave and P-wave of the beam. When the phase difference between the S-wave and the P-wave reaches +90 degrees or +270 degrees (that is, -90 degrees), the incident A 90-degree phase difference is generated on the beam of the disc, and then the beam is converted into circularly polarized light to generate a better signal beam; the photodetector 113 is used to receive the signal beam reflected from the disc surface.

In addition, after the CD laser diode 103 emits light, there are S-wave components and P-wave components perpendicular to each other, and their initial intensities are represented by I _S1 and I _P1 respectively, assuming the initial phase difference δ _SP =0°, as shown in Figure 1B As shown, when it is incident on the polarizing beam splitter 107, the penetration efficiencies of the S-wave and the P-wave are respectively 90% and 0%, as shown by the solid line in FIG. The penetration efficiencies of -wave and P-wave are 70% and 20% respectively, as shown in the solid line of Figure 1D, the characteristics of polarized beam splitter 107 and reflector 109 are shown in Table 1;

Penetration rate Polarizing Beamsplitter Reflector S-wave 90% 70% P-wave 0% 20%

Table 1

Therefore, the intensity I _S of the S-wave after being reflected by the polarizing beam splitter 107 becomes 0, and the intensity I P of the P-wave after being reflected by the polarizing beam splitter 107 = I _P1 × 90% = 0.9I _P1 ; then _the S-wave is again Intensity I _S =0×70%=0 after reflection by reflector 109, and P-wave intensity I _P =0.9I _P1 ×20%=0.18I _P1 after reflection by reflector 109, then pass through polarized beam splitter 107 and After the reflector 109, the P-wave energy I _P of the light beam = 0.18I _P1 , while the S-wave energy I _S disappears completely, and before the light beam enters the optical disc, it will pass through the quarter-wave plate 111 again, making it a The circular polarization state, as shown in Figure 1E. It can be seen from the foregoing that although the light beam can be finally made into a circularly polarized state, the S-wave energy is completely lost and not utilized.

Contents of the invention

The present invention provides an optical element group for an optical read-write head, the optical element group does not contain a quarter wave plate (quarter wavelength plate; QWP), and the optical element group includes data located on an optical path An optical element, wherein at least two optical elements each have an optical coating that changes the polarization state of the light beam, so that an outgoing light traveling along the optical path becomes a circularly polarized light, and the circularly polarized light is incident on an optical storage medium, and Finally, it becomes a signal light beam received by a light detector. The invention also provides a manufacturing method of the aforementioned optical element group.

Since the optical element group provided by the present invention does not contain a quarter-wave plate, the cost of the quarter-wave plate can be saved, and problems caused by poor quality and poor assembly of the quarter-wave plate can also be avoided. Problem; In addition, the phase difference of the present invention is produced by the combination of different optical elements, therefore, the polarization state of the light beam can be adjusted to the polarization state with higher transmission or reflection efficiency of each optical element by using the coating on each optical element , so that better signal strength can be obtained.

Description of drawings

1A-1E are diagrams showing the composition of optical components and the characteristics of each optical component of a conventional optical read-write head.

2A-2E are diagrams showing the composition of the optical elements and the characteristics of each optical element of the optical read-write head according to the present invention.

3A-3D are graphs showing the relationship between the phase difference generated by the optical element group and the wavelength of the light beam according to the present invention.

Fig. 4 is an illustration of an optical design according to the present invention.

Detailed ways

2A is a schematic diagram of an optical element group used for an optical read-write head in a preferred embodiment of the present invention. The optical element group includes a laser diode 201 for DVD reading and writing, a laser diode 203 for CD reading and writing, and a laser diode 203 for CD reading and writing. A polarized beam splitter 205 with an optical coating 204, a polarized beam splitter 207 with an optical coating 206, a mirror 209 with an optical coating 208, and a photodetector 211; laser diodes 201 and 203 are used to generate The laser beams for reading and writing DVDs and CDs, polarized beam splitters 205 and 207 are used to reflect or transmit different polarization components in the beams, and the mirror 209 is used to reflect the beams to change the direction of the beams. The optical coatings 204, 206 and 208 on the beam splitters 205, 207 and the reflector 209 can cause a phase difference between the two vertical components of the light beam (referred to as S-wave and P-wave respectively) to adjust the polarization of the light beam state, when the phase difference between the S-wave and the P-wave reaches +90 degrees or +270 degrees (that is, -90 degrees), the light beam incident on the optical disc can be made into circularly polarized light; the photodetector 211 is used for Receive the signal light beam reflected from the disc surface and convert it into an electronic signal.

Generally speaking, the laser diode 201 used for DVD reading and writing has a wavelength of 660 nanometers, and then the polarization beam splitters 205, 207 and the reflector 209 with optical coatings 204, 206 and 208 that generate phase differences can be designed respectively. , so that the relationship between the generated phase difference and the wavelength of the beam is shown in Figures 3A, 3B and 3C, respectively. In this way, when the laser beam passes through the polarization beam splitters 205, 207 and When reflecting mirror 209, its phase difference total will be as shown in Figure 3D, when the wavelength of laser beam is 660 nanometers, because optical coating 204,206 and 208 can make S-wave and P-wave of laser beam generate respectively The phase difference of θ ₁ , θ ₂ and θ ₃ , and make θ ₁ , θ ₂ and θ ₃ satisfy the following conditions:

θ ₁ +θ ₂ +θ ₃ = 90° or 270°(1)

Therefore, according to the optical element group of the present invention, the light beam incident on the optical disk can be made into circularly polarized light, which is the same as the effect produced by the quarter-wave plate, so the quarter-wave plate can be omitted; The number and types of optical components can be increased or decreased by the personnel according to their needs. Usually, the optical components used in optical read-write heads include laser diodes, polarized beam splitters, gratings, and folding mirrors. ), a polarizer, and a collimator to generate phase differences such as θ ₁ , θ ₂ , etc. of the light beams respectively, and make the total of them +/-90 degrees, so as to achieve the purpose of generating circularly polarized light.

In addition, the present invention can also use the principle of phase difference to convert the polarization state of the light beam to a state with higher transmission or reflection efficiency, that is, the principle of phase difference can be used to coat the optical element according to the required The achieved phase difference and reflectance/transmittance take into account the selection of material type, number of layers and thickness. When designing optical components, as shown in Figure 4, the following formulas can be used:

Tan2α＝[2 I _S0 I _P0 Cos(s, p phase shift)]/I _S0 ² -I _P0 ² (2)

I _S0 and I _P0 respectively represent the reflection/transmission intensity of the optical element with a coating that produces a phase difference for the beam, and (s, p phase shift) represent the S-wave and P-wave of the optical element with a coating that produces a phase difference for the beam. The phase difference generated between the waves, the angle α represents the angle between the long axis of the elliptically polarized light and the S-wave coordinate axis.

Taking Fig. 2A as an example, after the CD laser diode 203 emits light, there are S-wave components and P-wave components perpendicular to each other, and their initial intensities are represented by I _S1 and I _P1 respectively, assuming the initial phase difference δ _SP =0° , as shown in Figure 2B, when it is incident on the polarization beam splitter 207 with a coating that produces a phase difference, the penetration efficiencies of the S-wave and the P-wave are 90% and 0%, respectively, as shown by the solid line in Figure 2C As shown, if it is incident on the reflector 209 with a coating that produces a phase difference, the penetration efficiencies of the S-wave and the P-wave are 70% and 20%, respectively, as shown by the solid line in Figure 2D. However, according to the present invention In the embodiment, the polarization beam splitter 207 and the reflector 209 have optical coatings 206 and 208 that can generate a phase difference respectively, and the optical coatings 206 and 208 can respectively generate 70° and 200° between the S-wave and the P-wave The phase difference is shown in the dotted ellipses in Figure 2C and 2D, respectively, and the characteristics of the polarized beam splitter and the reflector are shown in Table 2;

Penetration rate Polarizing Beamsplitter Reflector S-wave 90% 70% P-wave 0% 20% Phase difference δ_S-P 70° 200°

Table 2

Therefore, when the laser beam is incident on the polarization beam splitter 207, the optical coating 206 will redistribute the energy of the beam, and cause a phase difference of 70° between the S-wave and the P-wave, so that the laser beam becomes elliptically polarized, And adjust the long axis of the ellipse to the direction close to the P-wave (because the P-wave reflection efficiency is higher), so that when passing through the polarization beam splitter 207 with a coating that produces a phase difference, when δ _SP =70° , Is=0.15I _S1 , Ip=0.95I _P1 .

Next, when passing through the reflector 209 with a coating that produces a phase difference, the same principle is used to concentrate most of the energy of the phase design in the direction of the _P -wave. The reflection mirror 209 has no energy to pass through, even if the penetration efficiency of the reflection mirror 209 with a coating that produces a phase difference is very large, it cannot be utilized. The difference is δ _SP =70°, Is=0.15I _S1 , Ip=0.95I _P1 when the polarized beam splitter 207 with the coating that produces phase difference emits light, if the reflector 209 with the coating that produces phase difference is designed, it will The generated phase difference δ _SP =200° concentrates the energy transfer to the P-wave direction. In this way, the overall energy after passing through the reflective mirrors 207 and 209 with the coating that generates the phase difference will become Is=0.13I _S1 , Ip=0.13I _P1 , generally speaking, I _S1 will be equal to I _P1 , so not only the overall energy of the beam will be stronger than that of the existing technology, but also the total phase difference can be δ _SP =70+200=270° or -90°, as shown in Figure 2E, achieves the effect of circular polarization while increasing efficiency and causing the desired polarization phenomenon.

Since the optical element group provided by the present invention uses an optical coating that produces a phase difference on the optical element to achieve the purpose of producing a phase difference, it does not contain a quarter-wave plate, so a quarter-wave can be omitted The cost of the plate can also avoid the problems caused by the poor quality of the quarter-wave plate and the poor assembly; in addition, the phase difference of the present invention is produced by the combination of different optical elements, so the coating on each optical element can be used The polarization state of the light beam is adjusted to the polarization state with higher transmission or reflection efficiency of each optical element, so that better signal strength can be obtained.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person familiar with the art may make various equivalent changes or replacements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be defined by the appended claims of the application.

Claims (12)

1. optical elements sets that is used for optical read/write head, this optical elements sets comprises several optical elements, wherein respectively have an optical coating that produces phase differential at least two these optical elements,, make an emergent light become a circularly polarized light to change the polarized state of light beam; And in this optical elements sets, do not contain a quarter-wave plate.

2. the optical elements sets that is used for optical read/write head as claimed in claim 1 is characterized in that, this optically coated this optical element of at least one tool is a laser beam generator.

3. the optical elements sets that is used for optical read/write head as claimed in claim 1 is characterized in that, this optically coated this optical element of at least one tool is a polar biased spectroscope.

4. the optical elements sets that is used for optical read/write head as claimed in claim 1 is characterized in that, this optically coated this optical element of at least one tool is a catoptron.

5. the optical elements sets that is used for optical read/write head as claimed in claim 1 is characterized in that, this optically coated this optical element of at least one tool is a collimating apparatus.

6. the optical elements sets that is used for optical read/write head as claimed in claim 1 is characterized in that, the polarization state of the also adjustable lay the grain bundle of this optical coating, and this signal beams that this photo-detector is received has the highest signal intensity.

7. manufacture method that is used for the optical elements sets of optical read/write head, this optical elements sets comprises several optical elements, to produce a circularly polarized light; And in this optical elements sets, do not contain a quarter-wave plate; This method is included on two these optical elements at least respectively adheres to an optical coating, and this optical coating can produce phase differential, to change the polarized state of light beam, makes an emergent light become this circularly polarized light.

8. the manufacture method that is used for the optical elements sets of optical read/write head as claimed in claim 7 is characterized in that, this optically coated this optical element of at least one tool is a laser beam generator.

9. the manufacture method that is used for the optical elements sets of optical read/write head as claimed in claim 7 is characterized in that, this optically coated this optical element of at least one tool is a spectroscope.

10. the manufacture method that is used for the optical elements sets of optical read/write head as claimed in claim 7 is characterized in that, this optically coated this optical element of at least one tool is a catoptron.

11. the manufacture method that is used for the optical elements sets of optical read/write head as claimed in claim 7 is characterized in that, this optically coated this optical element of at least one tool is a collimating apparatus.

12. the manufacture method that is used for the optical elements sets of optical read/write head as claimed in claim 7 is characterized in that, the polarization state of the also adjustable lay the grain bundle of this optical coating, and this signal beams that this photo-detector is received has the highest signal intensity.

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