KR100681903B1 - Optical information reconstructing apparatus, optical information recoding/reconstructing apparatus, method of measuring diffraction efficiency for optical information processing apparatus - Google Patents

Abstract

An optical information reproducer, an optical information recording/reproducing device, and a diffraction efficiency measurement method of an optical information processing device are provided to measure diffraction efficiency by detecting/comparing lightness of a reference beam before the reference beam is incident on an optical information storage medium and/with lightness of a beam which passes through the medium, thus faster and exacter diffraction efficiency is measured. A reproducing optical system(101) guides a beam scanned from a beam source(100) to an optical information storage medium(140). The first lightness detector(130) detects lightness of the beam by being positioned on the optical system(101). The second lightness detector(150) detects lightness of a beam which passes through the medium(140). An operator(170) compares the lightness of the detected beams to operate diffraction efficiency of the beams. An optical information detector(160) detects optical information reproduced by the beam which passes through the medium(140).

Description

Optical information reconstructing apparatus, optical information recoding / reconstructing apparatus, method of measuring diffraction efficiency for optical information processing apparatus}

1 is a block diagram showing an optical information reproducing apparatus according to an embodiment of the present invention.

2 is a block diagram showing an optical information recording and reproducing apparatus according to an embodiment of the present invention. 3 is a flowchart illustrating a diffraction efficiency measuring method using Equation 1 in the optical information processing apparatus according to the embodiment of the present invention.

4 is a flowchart illustrating a diffraction efficiency measuring method using Equation 2 in the optical information processing apparatus according to another embodiment of the present invention.

** Description of the symbols for the main parts of the drawings **

100 ... light source

110 ... angle adjustable mirror

120 ... actuator

130 first light intensity detector

150 ... 2nd Light Detector

The present invention relates to a method for measuring diffraction effects of an optical information reproducing apparatus, an optical information recording and reproducing apparatus, and an optical information processing apparatus, and more particularly, diffraction for measuring diffraction efficiency of reference light for processing holographic optical information. A method of measuring diffraction efficiency of an optical information reproducing apparatus, an optical information recording and reproducing apparatus, and an optical information processing apparatus capable of measuring efficiency.

The holographic optical information processing device stores data by irradiating a storage medium with an optical modulated signal beam and a reference beam that intersects the signal light to form an interference pattern on the storage medium. . In the reproduction of optical information, only the reference light is incident on the interference fringe of the storage medium, and at this time, the optical information input to the storage medium is reproduced by diffraction of light generated in the interference fringe.

In addition, the holographic light processing apparatus may store the data in multiple ways by irradiating the reference light with one beam spot at different angles. In addition, the multi-input data can be reproduced by irradiating only the reference light at different angles during reproduction. At this time, the better the diffraction efficiency of the output signal light, the better the reproduction efficiency of the optical information. Therefore, it is desirable to be able to exhibit the optimum diffraction efficiency when angular multiplexing the light.

The prior art of the holographic light processing apparatus is Korean Patent Publication No. 2000-20835. In the conventional techniques known with the patent, in order to measure the diffraction efficiency of light, a signal light reproduced during reproduction of optical information is detected by an optical detector such as a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS), and The amount of light detected in all the pixels of the information detector is summed and then the diffraction efficiency is measured through a complex computational process.

The conventional method of measuring diffraction efficiency has a problem in that the DSP (Digital Signal Processor), which needs to perform signal processing in parallel due to the sum of the light amounts of all the pixels of the optical information detector and also undergoes a complicated calculation process, has a problem. In addition, since the conventional method does not process the diffraction efficiency of the light in real time, the reproduction efficiency of the optical information is deteriorated because the optical information cannot be detected and reproduced in the optimal diffraction state.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to diffract light by detecting and comparing the amount of light passing through the optical information storage medium with the amount of light before the reference light incident on the optical information storage medium. It is an object of the present invention to provide an optical information reproducing apparatus capable of measuring the efficiency.

Another object of the present invention is to record the optical information to measure the diffraction efficiency by detecting and comparing the amount of light before entering the reference light incident on the optical information storage medium and the amount of light passing through the optical information storage medium to reproduce the optical information It is to provide a playback device.

It is another object of the present invention to provide a method for measuring diffraction efficiency of an optical information processing apparatus which detects and compares an amount of light before incident on an optical information storage medium and an amount of light passing through the optical information storage medium to process the optical information. It is for.

An optical information reproducing apparatus according to the present invention for achieving the above object is a light source, a first light amount sensor for detecting the amount of light is located on the optical system for guiding the light scanned from the light source to the optical information storage medium, A second light quantity detector for detecting the light quantity of the light passing through the optical information storage medium, a calculation unit comparing the light quantity of the light detected by the first light quantity detector and the second light quantity detector, and calculating a diffraction efficiency of the light; And an optical information detector for detecting optical information reproduced by the light passing through the information storage medium.

The first light amount detector may include a transmissive plate through which the light is transmitted and a portion of the light is reflected, and a photodiode for sensing the light reflected from the transmissive plate.

The second light amount detector may include a photodiode for detecting the light passing through the optical information storage medium.

The light detected by the second light amount detector may be a zero order beam of light incident on the optical information storage medium.

The optical system may include an angle adjusting mirror that adjusts an angle of incidence of the light according to a result calculated by the calculating unit.

In accordance with an aspect of the present invention, an optical information recording and reproducing apparatus includes: a light source, a beam splitter for dividing light provided from the light source, and loading data into one light separated from the beam splitter to enter an optical information storage medium. A signal light optical system, a reference light optical system for guiding another light separated from the polarization beam splitter, to the optical information storage medium, and a first light amount detector positioned on the reference light optical system to sense the amount of light. A second light quantity sensor for detecting a light quantity of the light passing through the light, a calculation unit comparing the light quantity of the light detected by the first light quantity detector and the second light quantity detector to calculate a diffraction efficiency of the light, and passing through the optical information storage medium And an optical information detector for detecting optical information reproduced by one light.

A third light quantity detector is positioned between the light source and the beam splitter, and the calculating unit reflects the transmissivity of the beam splitter to the light quantity detected by the second light quantity detector and is detected by the third light quantity detector. The amount of light can be compared and calculated.

The transmittance of the beam splitter may be obtained by comparing light amounts of light detected by the first light amount detector and the third light amount detector.

The first light amount detector and the third light amount detector may each include a transmissive plate through which the light is transmitted and a portion of the light is reflected, and a photodiode sensing the light reflected from the transmissive plate.

The second light amount detector may be a photodiode, and the second light amount detector may detect a zero order beam of the light passing through the optical information storage medium.

The reference light optical system may be provided with an angle adjusting mirror for adjusting the incident angle of the light according to the diffraction efficiency calculated by the calculating unit .

Diffraction efficiency measuring method of the optical information processing apparatus according to the present invention for achieving the above object is incident light to the optical information storage medium storing the optical information, detecting the amount of light before entering the optical information storage medium Detecting the amount of light diffracted to a position different from the diffraction position of the regenerated light passing through the optical information storage medium to the optical information detector, the amount of light detected before being incident on the optical information storage medium, and And comparing the amount of light diffracted to the different position passing through the optical information storage medium to measure the diffraction efficiency of the light in the optical information storage medium.

The light diffracted to the other position may be zero order light of light incident on the optical information storage medium. When the diffraction efficiency is lower than the set diffraction efficiency, the angle at which the light is incident on the optical information storage medium may be changed. The set diffraction efficiency may be a diffraction efficiency of another reproducing light previously measured.

Hereinafter, a method of measuring diffraction efficiency of the optical information reproducing apparatus, the optical information recording and reproducing apparatus, and the optical information processing apparatus according to the embodiment of the present invention configured as described above will be described. In the description of the following embodiments, the names of each component may be referred to by other names in the art. However, if the functional similarity and identity thereof, even if the modified embodiment can be adopted may be equivalent configuration. In addition, the symbols added to each component is described for convenience of description. However, the contents shown in the drawings in which these symbols are described do not limit each component to the ranges in the drawings. Similarly, even if an embodiment in which the configuration on the drawings is partially modified is employed, it can be regarded as an equivalent configuration if there is functional similarity and identity.

1 shows an optical information reproducing apparatus according to an embodiment of the present invention. As shown in FIG. 1, the optical information reproducing apparatus is for reproducing recorded optical information, and the recorded optical information may be a holographic interference fringe.

An optical information reproducing apparatus according to a preferred embodiment of the present invention includes a light source 100. The light source 100 generates laser light having a predetermined wavelength (hereinafter referred to as a reference beam) for reproducing optical information.

The reference light b1 oscillated by the light source 100 passes through a reproducing optical system 101. The optical system 101 includes an angle adjusting mirror 110 and a lens (unsigned). An actuator 120 for operating the angle adjustment mirror 110 is coupled to the angle adjustment mirror 110. The angle adjustment mirror 110 may be adopted a galvano mirror (Galvano mirror). In this case, the actuator 120 may be a piezo device.

The reference light b1 passing through the optical system 101 is incident on a transparent optical data storage medium 140 in which optical information is stored. The optical information storage medium 140 is made of a material whose optical characteristics such as refractive index, dielectric constant, and reflectance change according to the intensity of the reference light b1 when the reference light b1 is incident.

The optical information storage medium 140 is made of a transparent material through which light passes. Next to the optical information storage medium 140 is an optical information detector 160 for detecting the optical information reproduced by the reference light (b1) passing through the optical information storage medium 140. The optical information detector 160 may be a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS).

On the other hand, between the optical information storage medium 140 and the angle adjustment mirror 110 to detect the beam intensity of the reference light (b1) reflected from the angle adjustment mirror 110 to the optical information storage medium 140 (b1) The first light amount detector 130 is installed. The first light amount detector 130 includes a transmission plate 131 through which most of the reference light b1 passing through the optical system is transmitted, and some of the light is reflected.

The transmission plate 131 transmits approximately 99% of the reference light b1 and reflects about 1%. The first light amount detector 130 includes a photodiode 132 that detects 1% of light reflected from the transmission plate 131 together with the transmission plate 131. On the other hand, it is not necessary to detect the total amount of light for the amount of light. Since the change in the amount of light is detected as a comparison value with the second light amount detector 150 to be described later, the amount of light detected is sufficient to generate a detection signal.

 In addition, a second light amount detector 150 for detecting a light amount of the light b2 passing through the optical information storage medium 140 is provided. The second light amount detector 150 may be provided as a photodiode 150. The second light amount detector 150 detects a zero order beam b2 of the light b2 that has passed through the optical information storage medium 140. Therefore, the light transmittance in the optical information storage medium 140 due to the change in the amount of light can be obtained. This light transmittance becomes the diffraction efficiency of the optical information storage medium 140. That is, the diffraction efficiency may be indirectly measured by detecting the zero-order light b2 even if the optical information storage medium 140 does not measure the diffracted reproduction light.

Therefore, the optical information reproducing apparatus includes a calculation unit 170 for calculating the diffraction efficiency of the light by comparing the light amounts of the light detected by the first light amount detector 130 and the second light amount sensor 150. The controller 180 adjusts the reflection angle of the angle adjustment mirror 110 according to the measurement result of the calculation unit 170. The calculation unit 170 calculates the diffraction efficiency of the light by the calculation as shown in Equation 1 below.

η represents the diffraction efficiency. In addition, Id represents a light quantity value detected by the second light quantity detector 150, and I0 represents a light quantity value detected by the first light quantity detector 130. Therefore, the diffraction efficiency is measured as a percentage as a comparison value between the detected value detected by the first light amount detector 130 and the detected value detected by the second light amount detector 150.

Next, an embodiment of an optical information recording and reproducing apparatus according to an embodiment of the present invention will be described. 2 is a block diagram showing an optical information recording and reproducing apparatus according to an embodiment of the present invention.

As shown in FIG. 2, the optical information recording and reproducing apparatus according to the embodiment of the present invention includes a light source 200. The light source 200 oscillates the light b3 having a predetermined wavelength. A beam splitter 210 for dividing the light b3 oscillated from the light source 200 is positioned on the path of the light oscillated from the light source 200. The beam splitter 210 may be a polarization beam splitter that polarizes light b3.

And a signal light optical system (unsigned) which loads data into one light separated from the beam splitter 210 (hereinafter referred to as "signal light") and enters the optical information storage medium 250. The signal light optical system loads predetermined optical information into a spatial light modulator (SLM) 270 in the signal light split from the beam splitter 210. A lens system (unsigned), such as a Fourier transform lens, is provided between the spatial light modulator 270 and the optical information storage medium 250. The optical information recorded on the optical information storage medium 250 may be a holographic interference fringe. The optical information storage medium 250 is made of a transparent material as already mentioned. For a detailed description thereof, please refer to the above-described case of the optical information reproducing apparatus.

Subsequently, the optical information recording and reproducing apparatus includes a reference light optical system (unsigned) for guiding light separated from the beam splitter 210 (hereinafter referred to as "reference beam") to the optical information storage medium 250. The reference light optical system includes an angle adjusting mirror 220 for guiding the reference light b2 to the optical information storage medium 250. In addition, the optical information storage medium 250 is provided with an optical information detector 280 that detects reproduced light diffracted and reproduced from the optical information storage medium 250.

Meanwhile, a first light amount detector 240 is installed between the angle adjusting mirror 220 and the optical information storage medium 250 in the optical path of the reference optical system. In addition, a second light amount detector 260 for detecting zero order light b2 of the reference light transmitted through the optical information storage medium 250 is installed, and a third light quantity detector 260 is disposed on the optical path between the light source 200 and the beam splitter 210. The light quantity detector 290 is installed.

The first light amount detector 240 is a transmissive plate 241 through which the majority of the reference light b2 is transmitted so as to sense the amount of light reflected by the angle adjustment mirror 220 and proceeds to the optical information storage medium 250. And a photodiode 242 that senses some reflected light at 241.

The second light amount detector 260 may be a photodiode for detecting the reference light b2 passing through the optical information storage medium 250. Subsequently, the third light amount detector 290 transmits and reflects a part of the light b3 emitted from the light source 200 and reflects a part of the third light detector 290. Photodiode 292 is included.

In addition, the optical information recording and reproducing apparatus includes an operation unit 300 for calculating the diffraction efficiency of the light by comparing the light amount of the light detected by the first light amount detector 240, the second light amount detector 260, and the third light amount detector 290. The controller 310 may adjust the reflection angle of the angle adjustment mirror 220 positioned before the second light amount detector 260 according to the measurement result of the calculation unit 300. Here, the calculation unit 300 measures the diffraction efficiency of light by the calculation as shown in Equation 2 below.

η Represents the diffraction efficiency. In addition, Id represents a light quantity value detected by the second light intensity detector 260, and I0 represents a light quantity value detected by the third light quantity detector 290. And a denotes the transmittance of the reference light split from the beam splitter 210, i.e., a denotes the intensity "I1" of the light detected by the first light intensity detector 240 and the intensity "I0 of the light detected by the third light intensity detector 290. Is the comparison value.

Therefore, the diffraction efficiency reflects the transmissivity of the beam splitter 210 to the amount of light detected by the first light amount detector 240, thereby comparing the amount of light detected by the third light amount detector 290. Can be obtained.

On the other hand, the optical information recording and reproducing apparatus according to the embodiment of the present invention may measure the diffraction efficiency using Equation 1 applied to the optical information reproducing apparatus, which is another embodiment. In this case, the first light intensity detector 240 and the second light intensity detector 260 may be utilized.

Hereinafter, an embodiment of a diffraction efficiency measuring method of an optical information processing apparatus according to an embodiment of the present invention will be described with reference to the drawings. The optical information processing apparatus in this embodiment may be either the above-described optical information reproducing apparatus or the optical information recording and reproducing apparatus. Therefore, in the following diffraction efficiency measurement method, although an embodiment is described by dividing into Equation 1 and Equation 2, the description of the embodiment is intended to help understand the technical idea of the present invention and to limit the technical idea of the present invention. It should be noted that not.

3 is a flowchart illustrating a diffraction efficiency measuring method using Equation 1 in the optical information processing apparatus according to the embodiment of the present invention.

As shown in FIG. 1 and FIG. 3, the diffraction efficiency measuring method according to Equation 1 is incident on the optical information storage medium 140 in which optical information is stored. Optical information is recorded in the optical information storage medium 140 in the form of a diffraction grating. The first light amount detector 130 detects the amount of light before being incident on the optical information storage medium 140. Next, the amount of light diffracted to a position different from the diffraction position of the regenerated light passing through the optical information storage medium 140 to the optical information detector 160 is detected by the second light amount detector 150 (S100). In this case, the other position may be the zero-order light b2 of the reference light incident on the optical information storage medium 140.

When the intensity of the light is detected by the first light amount detector 130 and the second light amount detector 150, the calculation unit 170 calculates the diffraction efficiency according to Equation 1 (S110). And the value for the diffraction efficiency obtained at this time is transmitted to the controller 180.

The controller 180 compares the detected diffraction efficiency with the diffraction efficiency previously calculated and input (S120). The previously calculated diffraction efficiency may be one preset in an optimal state, or may be a superior diffraction efficiency among the previously calculated diffraction efficiency.

Subsequently, the controller 180 determines whether the calculated diffraction efficiency result is less than the previously calculated and input diffraction efficiency (S130). At this time, if the diffraction efficiency is reduced, the controller 180 transmits a control signal to the actuator 120 to adjust the reflection angle of the angle control mirror 110 (S140). The angle control signal may be an operation signal for various angles preset and input to the controller 180.

When the angle is adjusted, the first light amount detector 130 and the second light amount detector 150 detect the diffraction efficiency of the light, and then repeat the above-described process to find the angle generating the optimal diffraction efficiency. On the other hand, when the angle at which the diffraction efficiency is optimal is found, that is, the position where the diffraction efficiency does not decrease from the previously calculated and input diffraction efficiency is found, the measurement of the diffraction efficiency is stopped, and the optical information is detected by the optical information detector 160. That is, when it is determined that the rotational efficiency is optimal, the optical information detector 160 operates to detect the reproduction light with respect to the diffraction efficiency in the optimal state (S150).

4 is a flowchart illustrating a diffraction efficiency measuring method using Equation 2 in the optical information processing apparatus according to another embodiment of the present invention. In the case of the embodiment of Figure 4 is to measure the diffraction efficiency in consideration of this when the intensity of the light emitted from the laser as a light source changes over time.

As shown in FIG. 2 and FIG. 4, the diffraction efficiency measuring method according to Equation 2 is incident on the beam splitter 210. The light then splits and propagates in the beam splitter 210. In this case, before the light is incident on the beam splitter 210, the light intensity is detected by using the third light amount detector 290.

Of the light split by the beam splitter 210, the light traveling to the angle adjusting mirror 220 (hereinafter referred to as “reference light b1”) is reflected by the angle adjusting mirror 220 to store the optical information storing the optical information ( Proceed to 250).

Then, the light amount of the reference light b1 is detected by the first light amount detector 240 before being incident on the optical information storage medium 250 (S200). Next, the second light amount detector 260 detects the light amount of the light b2 diffracted to a position different from the diffraction position of the regenerated light passing through the optical information storage medium 250 to the optical information detector 280. The other position may be zero order light of reference light incident on the optical information storage medium 250 (S210).

When the intensity of light is detected by the first light amount detector 240, the second light amount detector 260, and the third light amount detector 290, the calculation unit 300 calculates the diffraction efficiency according to Equation 2 (B220). And the value for the diffraction efficiency obtained at this time is transmitted to the controller 310. The controller 310 compares the detected diffraction efficiency with the diffraction efficiency previously calculated and input (S230).

The controller 310 determines whether the calculated diffraction efficiency result is less than the previously calculated and input diffraction efficiency value (S250). If the diffraction efficiency is decreased, the controller 310 controls the reflection angle of the angle control mirror 220. The adjustment signal is transmitted to the angle adjustment mirror 220 to adjust the degree. The angle control signal may be an operation signal for various angles which are preset and input to the controller 310 (S240).

When the angle is adjusted, the first light amount detector 240, the second light amount detector 260, and the third light amount detector 290 detect the diffraction efficiency of the light, and then repeat the above process to obtain the optimum diffraction efficiency. Find the angle you are generating. When the angle at which the diffraction efficiency is optimal is found, the optical information detection proceeds to the optical information detector 280 (S260).

In the optical information reproducing apparatus, the optical information recording and reproducing apparatus, and the diffraction efficiency measuring method of the optical information processing apparatus according to the embodiment of the present invention as described above, a component having other additional functions is added. Or it may be replaced by another component. However, if the modified other embodiment includes the essential components of the present invention, and to sense the intensity of light before passing through the optical information storage medium and the optical information storage medium to measure the diffraction efficiency of the present invention It should be considered to be included in the category.

As described above, the method for measuring diffraction efficiency of the optical information reproducing apparatus, the optical information recording and reproducing apparatus, and the optical information processing apparatus stores the amount of light before the incident light of the reference light incident on the optical information storage medium and reproduces the optical information. By detecting and comparing the amount of light that has passed through the medium to measure the diffraction efficiency of the light, it is possible to measure the diffraction efficiency more quickly and accurately, and also to reflect the measured diffraction efficiency as quickly as possible when reproducing the optical information. There is an effect to improve more.

Claims (16)

Light source; An optical system for guiding the light scanned from the light source to an optical information storage medium; A first light amount detector positioned on the optical system to sense a light amount of the light; A second light amount detector for detecting a light amount of the light passing through the optical information storage medium; A calculator configured to calculate a diffraction efficiency of the light by comparing the light amount of the light detected by the first light amount detector and the second light amount detector; And an optical information detector for detecting optical information reproduced by the light passing through the optical information storage medium. The light detector according to claim 1, wherein the first light amount detector includes a transmission plate through which the light is transmitted and a part of the light is reflected, and a photodiode for sensing the light reflected from the transmission plate. Information player. The optical information reproducing apparatus according to claim 1, wherein the second light quantity detector includes a photodiode for detecting the light passing through the optical information storage medium. The optical information reproducing apparatus according to claim 1, wherein the light detected by the second light quantity detector is a zero order beam of light incident on the optical information storage medium. The optical information reproducing apparatus according to claim 1, wherein the optical system includes an angle adjusting mirror which adjusts an angle of incidence of the light according to a result calculated by the calculating unit. Light source; A beam splitter dividing light provided from the light source; A signal light optical system which loads data into one light separated from the beam splitter and enters an optical information storage medium; A reference light optical system for guiding another light separated from the polarizing beam splitter to the optical information storage medium; A first light amount detector positioned on the reference light optical system to sense a light amount of the light; A second light amount detector for detecting a light amount of the light passing through the optical information storage medium; A calculating unit for comparing the light quantity of the light detected by the first light quantity detector and the second light quantity detector to calculate a diffraction efficiency of the light; And an optical information detector for detecting optical information reproduced by the light passing through the optical information storage medium. The method of claim 6, wherein a third light amount detector is positioned between the light source and the beam splitter, and the calculating unit reflects a transmissivity of the beam splitter to the amount of light detected by the second light amount detector. Optical information recording and reproducing apparatus, characterized in that for calculating by comparing the amount of light detected by the three-light detector. 8. The optical information recording and reproducing apparatus according to claim 7, wherein the transmittance of the beam splitter is obtained by comparing the light quantity of the light detected by the first light quantity detector and the third light quantity detector. The photodiode of claim 8, wherein each of the first light amount detector and the third light amount detector includes a transmission plate through which the light is transmitted and a portion of the light is reflected, and a photodiode sensing the light reflected from the transmission plate. Optical information recording and reproducing apparatus comprising a. 7. The optical information recording and reproducing apparatus according to claim 6, wherein the second light intensity sensor is a photodiode. The optical information recording and reproducing apparatus according to claim 6, wherein the second light quantity detector detects a zero order beam of the light passing through the optical information storage medium. 7. The optical information recording and reproducing apparatus according to claim 6, wherein the reference light optical system is provided with an angle adjusting mirror for adjusting the incident angle of the light according to the diffraction efficiency calculated by the calculating unit. Entering light into an optical information storage medium storing optical information; Detecting an amount of light of the light before being incident on the optical information storage medium; Detecting an amount of light diffracted to a position different from a diffraction position of the regenerated light passing through the optical information storage medium to the optical information detector; Measuring the diffraction efficiency of the light in the optical information storage medium by comparing the amount of light detected before entering the optical information storage medium with the amount of light diffracted to the other position passing through the optical information storage medium. Method for measuring diffraction efficiency of an optical information processing device, characterized in that. The method of claim 13, wherein the light diffracted to the other position is zero-order light of light incident on the optical information storage medium. 15. The method of claim 13, wherein the angle at which the light is incident on the optical information storage medium is changed when the diffraction efficiency is lower than the set diffraction efficiency. 16. The method of claim 15, wherein the set diffraction efficiency is a diffraction efficiency of another reproduced light measured previously.

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