KR100926935B1 - Optical pickup system and optical output calibration method - Google Patents

Abstract

An optical pickup system and an optical output correction method are disclosed. The disclosed optical pickup system includes: an optical pickup that irradiates light onto an optical recording medium and detects reflected light, the optical pickup actively correcting aberrations; And an optical output control unit configured to correct the amount of light generated by actively correcting the aberration to control the amount of light irradiated to the optical recording medium. In addition, the method for correcting the light output is applied to the step of detecting a portion of the light emitted from the light source; Correcting the sensitivity of the monitoring photodetector by reflecting the change in the light output of the remaining light output from the objective lens generated by actively correcting the aberration generated in the process of irradiating the remaining light of the light emitted from the light source to the optical recording medium It characterized in that it comprises a.

Description

Optical pick up system and method for compensating optical output

The present invention relates to an optical pickup system and an optical output correction method applied thereto, and more particularly, to an optical pickup system reflecting a change in the amount of light generated by driving an aberration correction optical system for aberration correction and an optical output correction applied thereto. It is about a method.

Optical pickup includes a light source for generating light having a specific wavelength, an objective lens that focuses light on an optical recording medium, and a photodetector for detecting a signal by receiving reflected light reflected from the optical recording medium and converting the signal into an electrical signal. And an optical system for guiding the light generated from the light source toward the optical recording medium and guiding the light beam of the reflected light toward the photodetector. The output power of the light source must be maintained at a constant level set at the time of recording or reproduction for normal recording / reproduction. To this end, the optical pickup is provided with a monitoring photodetector for controlling the output of the laser diode (LD) to be kept constant. The monitoring photodetector is installed inside the light source or outside the light source to convert the intensity of light output from the light source into a current signal to detect the output power of the light source.

On the other hand, an aberration correction optical system for correcting aberration generated in the optical system of the information recording / reproducing apparatus is provided in the optical pickup. By the way, even if the same amount of light is emitted from the light source, the amount of light finally output from the objective lens may be changed by this aberration correction optical system. In particular, when a beam splitter for splitting light into the monitoring photodetector is disposed between the light source and the aberration correction optical system, there is a problem in that the amount of light varied by the aberration correction optical system is not properly monitored.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical pickup system and an optical output correction method capable of correctly detecting the amount of light varied by the aberration correction optical system.

The optical pickup system according to the present invention,

An optical pickup that irradiates light onto the optical recording medium and detects reflected light, the optical pickup actively correcting aberrations; And

And an optical output control unit for correcting the amount of light generated by actively correcting the aberration to control the amount of light irradiated to the optical recording medium.

In addition, the light output correction method according to the present invention,

In the optical pickup system for driving the aberration correction optical system to correct the aberration,

Detecting some of the light emitted from the light source; And

Correcting the sensitivity of the monitoring photodetector by reflecting the change in the amount of light of the remaining light output from the objective lens generated by actively correcting the aberration generated in the process of irradiating the remaining light of the light emitted from the light source to the optical recording medium It characterized in that it comprises a step.

The optical pickup system and the optical output correction method according to the present invention by reflecting the problem solving means as described above by reflecting the change in the amount of light according to the aberration correction, by compensating the thrust sensitivity of the monitoring photodetector, through the objective lens to the optical recording medium The amount of light outputted can be kept constant at all times.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the examples exemplified below are not intended to limit the scope of the present invention, but are provided to fully explain the present invention to those skilled in the art. In the drawings, like reference numerals refer to like elements, and the size of each element in the drawings may be exaggerated for clarity and convenience of description.

1 is a view schematically showing an optical pickup system according to a first embodiment of the present invention.

Referring to FIG. 1, an optical pickup system according to an exemplary embodiment includes an optical pickup 100 that irradiates light onto an optical recording medium D and detects reflected light, and a circuit unit that controls the optical pickup 100. 200).

The optical pickup 100 includes a light source 110, a beam split 120 that splits a part of the light emitted from the light source 110, a monitoring photodetector 130 that detects a part of the split light, A collimating lens 140 for shaping the remaining light of the light emitted from the light source 110 into parallel light, an objective lens 160 for irradiating the light recorded with the parallel light onto the optical recording medium D; It may include a main photodetector 180 for detecting the light reflected from the optical recording medium (D). The light source 110 may be a semiconductor laser diode emitting a laser beam of a predetermined wavelength. In the present embodiment, an optical configuration in which one light source 110 is employed is described as an example. However, the present invention includes a plurality of light sources 110 to substantially support an optical pickup system that is compatible with various types of optical recording media. The same may apply. The mirror 150 serves to fold the optical path so that light can be irradiated perpendicular to the recording medium D. Furthermore, the optical pickup may further include a mirror 150 that folds the optical path for proper placement of the optical elements, and may further include a detection lens 170 disposed in front of the main photodetector 180. Although the plate type mirror 150 is illustrated in the drawing, the present invention is not limited thereto. For example, a beam splitter such as a wedge type may be employed. The detection lens 170 allows the light spot to be properly formed on the main photodetector 180. For example, an astigmatism lens may be employed to detect the focus error signal by the astigmatism method.

The beam splitter 120 is an example of an optical splitter that splits some light to monitor light output. As the beam splitter 120, for example, a polarizing beam splitter may be used. For example, when the light source 110 employs a semiconductor laser diode that mainly emits light of the P-polarized component and partially emits light of the S-polarized component, a part of the S-polarized component is monitored by using a polarizing beam splitter. It can be used for the recording, and the main light of the P polarization component can be used for recording / reproducing. The beam splitter 120 also separates the light incident on the optical recording medium D and the light reflected from the optical recording medium D. In order to effectively separate the incident light and the reflected light, the polarization direction of the light incident on the optical recording medium D is further interposed between the beam splitter 120 and the objective lens 160 through a quarter wave plate (not shown). And the polarization direction of the light reflected from the optical recording medium D can be perpendicular.

The monitoring photodetector 130 is a front monitoring type for detecting a part of the light emitted from the light source 110, and particularly collimating used as an aberration correction optical system for correcting aberration as described later. Light that does not pass through the lens 140 is detected. The light output signal detected by the monitoring photodetector 130 is fed back to the light source 110 through the light output controller 250 as described below. The monitoring photodetector 130 detects that the output power increases or decreases due to a temperature characteristic of a light source such as a semiconductor laser diode, thereby keeping the output of the light source 110 constant. In particular, the present embodiment, by appropriately compensating the sensitivity of the monitoring photodetector 130, by suppressing the change in the amount of light caused by the movement of the collimating lens 140, which will be described later to provide a constant amount of light on the optical recording medium (D) Allow light to be irradiated.

The collimating lens 140 is a lens for shaping incident light into parallel light. The collimating lens 140 and the collimating lens driving unit 145 for driving the collimating lens 140 in the optical axis direction are examples of an aberration correcting optical system that actively corrects aberration. The optical pickup optical system requires a device for correcting coma aberration caused by the tilt of the optical recording medium, coma aberration caused by the tilt of the optical recording medium when the objective lens shifts. Furthermore, in the case of a compatible optical pickup optical system, it is necessary to correct spherical aberration generated in the wavelength of the light source or the thickness difference of the optical recording medium corresponding to various formats such as CD, DVD, BD or HD-DVD. This embodiment corrects this aberration by moving the collimating lens 140 in parallel in the optical axis direction.

The circuit unit 200 may include a signal processor 210, a controller 220, an aberration correcting optical system driver 230, a light source driver 240, and an optical output controller 250.

The signal processor 210 reads information from the reflected light detected by the main photodetector 180, extracts a servo error signal, and sends the signal to the controller. The controller 220 controls the light source 110 through the light source driver 240 and the light output controller 250, and controls the collimating lens 140 through the aberration correcting optical system driver 230.

The control unit 220 sends an aberration correction signal to the aberration correction optical system driver 230 to correct the aberration of the optical pickup optical system, and transmits an aberration correction signal to the optical output control unit to correct the sensitivity of the monitoring photodetector 130. Also send 250).

The light output controller 250 compensates the sensitivity of the monitoring photodetector 130 by reflecting the change in the amount of light generated by the aberration correction of the collimating lens of the light output from the objective lens 160, and referring to FIG. 2. , A comparator 260, a gain selector 270, and an output unit 280.

The comparator 260 gives an appropriate gain to the light output signal detected by the monitoring photodetector 130 and transmits the light output signal to the light source driver 240 through the output unit 280. At this time, the gain selector 270 is configured to obtain an appropriate light output compensation gain from the aberration correction signal input from the controller 220 so that the gain gain reflects the light output compensation gain reflecting the light amount change generated by the aberration correction optical system. Is selected and input to the comparator 260. This optical output compensation gain will be described later. The comparator 260 reflects the light output compensation gain selected by the gain selector 270, thereby transmitting the corrected light output signal to the light source driver 240 through the output unit 280.

Next, referring to FIGS. 3A to 3C and 4, the optical output of the light output through the objective lens is changed as the collimating lens moves in the optical axis direction for aberration correction.

3A shows that the collimating lens 140 is in position. Based on this, in FIG. 3B, the collimating lens 140 is moved toward the light source 110, and in FIG. 3C, the collimating lens 140 is moved toward the objective lens 160. At this time, reference numeral A denoted by a dotted line indicates the correct position shown in FIG. 3A.

Referring to FIGS. 3A to 3C, when the collimating lens 140 moves from the correct position A toward the light source 110, the degree of shaping the emitted light into parallel light is changed, so that the objective lens 160 From the standpoint of view, the amount of light incident and output is different. However, from the standpoint of the monitoring photodetector 130 which detects the light split from the beam splitter 120 between the light source 110 and the collimating lens 140, the movement of the collimating lens 140 is not reflected. The light output will be detected.

An example of the change in the light output of the objective lens according to the movement of the collimating lens is well illustrated in FIG. 4. In FIG. 4, the light output efficiency of the objective lens refers to a ratio of the light output from the objective lens to the light output from the light source. The absolute value and the slope of the graph shown in FIG. 4 may vary according to design variables such as magnification and transmittance of the optical system, and also depending on the maximum amount of movement of the collimating lens.

Referring to FIG. 4, when the amount of movement of the collimating lens is moved toward the light source 110 as shown in FIG. 3B, that is, when the amount of movement in the graph is negative, the optical output efficiency of the objective lens is reduced compared to the normal position. . On the other hand, when the amount of movement of the collimating lens is moved toward the objective lens 160 as shown in FIG. 3C, that is, when the amount of movement in the graph is positive, the light output efficiency of the objective lens is increased compared to the exact position. have. As such, even if the light output from the light source is constant, the light output from the objective lens may vary according to the movement of the collimating lens. In general, the sensitivity of the photodetector monitoring photodetector is controlled within ± 5% or ± 10% of the standard value when the light output and temperature change.The optical output variation in the objective lens driven by the collimating lens is controlled by the type of optical system. Although it varies depending on the structure, the amount of movement of the collimating lens, and the like, the change is over 7% or more, so that it is difficult to adjust the stable light output only by the conventional method.

Accordingly, the present embodiment reflects the amount of variation in the light output according to the amount of movement of the collimating lens, thereby correcting the sensitivity of the monitoring photodetector. 5 is a graph illustrating an optical output correction gain according to the movement of the collimating lens.

The light output correction gain of the monitoring photodetector represents the variation in the light output in the objective lens when the collimating lens position is shifted based on the light output value in the objective lens when the specific collimating lens position is referenced. This light output correction gain can be obtained by directly measuring the objective lens output level according to the collimating lens position variation when the output of the light source is constant, or obtained through simulation calculation. This light output correction gain can be calculated by, for example, Equation 1 below.

y = -0.0063x ² + 0.0659x + 0.09997

In this case, x is the amount of movement of the collimating lens, y means the light output correction gain, the crystal coefficient R ² is given by 1. This optical output correction gain is approximately proportional to the square of the collimating lens position shift amount, and is indicated by a solid line in FIG. As indicated by the dotted line in FIG. 5, the equation given by Equation 1 may be approximated by Equation 2 below, which is linearly proportional to the amount of movement of the collimating lens, and the crystal coefficient R ² is given as 0.9971.

y = 0.0659x + 0.9972

Even if the optical output correction gain is determined as shown in Equation 2, the deviation is not large. Therefore, when the optical output control unit 250 of FIG. 1 reflects the optical output correction gain, the circuit configuration can be made simpler. Equations 1 and 2 are exemplary and may vary depending on the type and structure of the optical system and the amount of movement of the collimating lens.

Next, in the present embodiment, a method of correcting light output will be described.

Referring back to FIG. 1, the light output system 100 detects some of the light emitted from the light source 110. For this purpose, the beam splitter 120 branches some of the emitted light toward the monitoring photodetector 130. In addition, the remaining light from the light source 110 is irradiated to the optical recording medium (D), and the collimating lens 140 is actively corrected by driving the collimating lens 140 in response to the aberration generated in this process. In this case, the optical output correction gain according to the amount of movement of the collimating lens 140 is recorded in a predetermined memory of the circuit unit 200, so that the optical output controller 250 refers to this or is previously input to the optical output controller 250. The sensitivity of the monitoring photodetector 130 is corrected by reflecting the optical output correction gain. That is, the light output correction gain according to the amount of movement of the collimating lens 140 is reflected in the gain applied to the light output signal detected by the monitoring photodetector 130. By controlling the light output of the light source 110 on the basis of the product of the light output signal detected by the monitoring photodetector 130 multiplied by the light output correction gain according to the amount of movement of the collimating lens 140, the objective lens 160 The amount of light outputted can be kept constant.

6 is a diagram schematically illustrating an optical pickup system according to a second embodiment of the present invention.

Referring to FIG. 6, the optical pickup system according to the present exemplary embodiment includes an optical pickup 300 for irradiating light onto the optical recording medium D and detecting reflected light, and a circuit unit for controlling the optical pickup 300. 400).

The optical pickup 300 includes a light source 110, a beam split 120, a monitoring photodetector 130, a collimating lens 140 ′, a mirror 150, a liquid crystal lens 340, The objective lens 160, the detection lens 170, and the main photodetector 180 may be included. The circuit unit 400 may include a signal processor 210, a controller 220, an aberration correction optical system driver 430, a light source driver 240, and an optical output controller 250.

This embodiment is substantially the same as the above embodiment except that the liquid crystal lens 340 is employed as the aberration correction optical system for actively correcting the aberration. Therefore, the same reference numerals are attached to members substantially the same as the above-described embodiment, and detailed description thereof will be omitted.

The collimating lens 140 'of the present embodiment is a lens for shaping incident light into parallel light and is not driven dynamically unlike the above-described embodiment.

On the other hand, the present embodiment is provided with a liquid crystal lens 340, to actively correct the generated aberration. 6 illustrates a case in which the liquid crystal lens 340 is disposed adjacent to the objective lens 160, but is not limited thereto. For example, the liquid crystal lens 340 may be disposed adjacent to the collimating lens 140 ′.

The liquid crystal lens 340 is an element in which liquid crystals are arranged in a predetermined direction as a voltage is applied, an example of which is illustrated in FIG. 7. Referring to FIG. 7, the liquid crystal lens 340 has a liquid crystal layer 345 interposed between two transparent substrates 341 and 348, and a liquid crystal layer 345 so that a voltage can be applied to the liquid crystal layer 345. Transparent electrode layers 342 and 347 are provided between the transparent substrates 341 and 348. Furthermore, in order to improve the alignment of the liquid crystal layer 345, alignment layers 343 and 346 may be further interposed. When a voltage is applied to the liquid crystal element 340 by the aberration correction optical system driver 430, the arrangement of the liquid crystal molecules changes, thereby obtaining a phase difference distribution corresponding to the inverse of the aberration to be corrected. By such a configuration, the liquid crystal lens 340 can actively correct the aberration, while a change in the amount of light occurs in accordance with the driving of the liquid crystal lens 340 as in the light amount change caused by the dynamic driving of the collimating lens described above. Can be.

Referring back to FIG. 6, the specific value of the light output correction gain for compensating for the change in the amount of light according to the driving of the liquid crystal lens 340 may be directly measured or obtained through simulation calculation, and the light output controller 250 may be obtained. ) May correct the sensitivity of the monitoring photodetector 130 by reflecting the optical output correction gain.

Such an optical pickup system and an optical output correction method of the present invention have been described with reference to the embodiments shown in the drawings for clarity, but these are merely exemplary, and various modifications and equivalents may be made by those skilled in the art. It will be appreciated that other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the appended claims.

1 is a view schematically showing an optical pickup system according to a first embodiment of the present invention.

FIG. 2 is a block diagram schematically illustrating an optical output controller applied to the optical pickup system illustrated in FIG. 1.

3A to 3C are diagrams illustrating that the light output of light output through the objective lens changes as the collimating lens moves in the optical axis direction for aberration correction.

4 is a graph showing the light output efficiency of the objective lens according to the movement of the collimating lens.

5 is a graph illustrating an optical output correction gain according to the movement of the collimating lens.

6 is a diagram schematically illustrating an optical pickup system according to a second embodiment of the present invention.

FIG. 7 is a cross-sectional view schematically illustrating an example of a liquid crystal lens applied to the optical pickup system shown in FIG. 6.

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

100,300 ... optical pickup 110 ... light source

120 ... beam splitter 130 ... monitoring photodetector

140,140 '... collimating lens 145 ... collimating lens drive unit

150 ... mirror 160 ... objective lens

170 .. Detecting lens 180 ... main photodetector

200, 400 circuit circuit 210 signal processing unit

220 Control unit 230,430 Aberration correction optical system driver

240 ... light source driver 250 ... light output controller

260 ... Comparators 270 ... Gain Selection

280 ... output 340 ... liquid crystal lens

D ... optical recording media

Claims (8)

An optical pickup that irradiates light onto the optical recording medium and detects reflected light, the optical pickup actively correcting aberrations; And And an optical output control unit configured to correct the amount of light generated by actively correcting the aberration to control the amount of light irradiated to the optical recording medium. The optical pickup, A light source unit having at least one light source; An optical branch part which splits the light emitted from the light source part into first light and second light; A monitoring photodetector for detecting the branched first light; An aberration correction optical system for actively correcting aberration generated when irradiating the branched second light onto an optical recording medium; And And an objective lens for irradiating the optical recording medium with the second light via the aberration correction optical system. The light output control unit, The optical pickup system of claim 2, wherein the sensitivity of the monitoring photodetector is compensated by reflecting a change in the amount of light generated by the aberration correction of the aberration correction optical system of the second light output from the objective lens. delete The method of claim 1, The aberration correction optical system includes at least one collimating lens moving in the optical axis direction or at least one liquid crystal lens driven in response to a voltage. The method according to claim 1 or 3, The aberration correction optical system, Correcting at least one of spherical aberration caused by the thickness difference of the optical recording medium, coma aberration caused by the tilt of the optical recording medium, and coma aberration caused by the tilt of the optical recording medium when the objective lens shifts. Optical pickup system characterized in that. delete In the optical pickup system for driving the aberration correction optical system to correct the aberration, Detecting some of the light emitted from the light source; And Correcting the sensitivity of the monitoring photodetector by reflecting the change in the amount of light of the remaining light output from the objective lens generated by actively correcting the aberration generated in the process of irradiating the remaining light of the light emitted from the light source to the optical recording medium It includes; Correction of the sensitivity of the monitoring photodetector is characterized by reflecting the light output correction gain generated in accordance with the aberration correction of the aberration correction optical system to a gain applied to the optical output signal detected by the monitoring photodetector. Optical output calibration method of optical pickup system. delete The method of claim 6, By controlling the light output of the light source unit on the basis of the product of the light output signal detected by the monitoring photodetector multiplied by the light output correction gain generated in accordance with the aberration correction of the aberration correction optical system, the light output of the second light output from the objective lens The optical output correction method of the optical pickup system, characterized in that the amount of light is kept constant.

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