Embodiment
Below, the optical information reproduction method that describes optical information reproducing apparatus, optical information recorder/transcriber with reference to the accompanying drawings in detail and utilize described device.
In the following description, the function of consideration element defines its title.Thereby, the title of element should be interpreted as qualification technology member, also can be called other titles in the art.
The example of optical information reproducing apparatus at first, is described with reference to Fig. 1.As shown in the figure, optical information reproducing apparatus 100 comprises light source 110, polarized light beam splitter 120, interim beam splitter 130, overlapping optical system 140, Focused Optical system 160 and sensing element 170.
Light source 110 emissions have light beams of predetermined wavelengths L.Be preferably from light source 110 emitted light beams L and be formed parallel beam and for having excellent coherence's the laser beam of plane wave type.For example, light beam L preferably has the wavelength that is suitable for storing holographic data.
The interim light beam A that polarized light beam splitter 120 will be divided into the reference beam R that is used for reproduction optical information and be used to generate the first auxiliary beam A1 and the second auxiliary beam A2 from light source 110 emitted light beams.Polarized light beam splitter 120 has the polarization beam splitting face 120a that has been used for partially and light beam L has been carried out beam splitting.Polarized light beam splitter 120a is used for the interim light beam of transmission (P light beam) A and reflected reference beam (S light beam) S.
Special light source regulating element 124 can be set, and this light source regulating element 124 is used to regulate the reference beam R and the first auxiliary beam A1 and the second auxiliary beam A2 that are gone out by polarized light beam splitter 120 beam splitting.Light source regulating element 124 can be provided as polaroid, sensitization wave filter or the like.Light source regulating element 124 is set to accurately regulate light intensity and the uniformity coefficient of reference beam R and the first auxiliary beam A1 and the second auxiliary beam A2, and this light source regulating element 124 is not set can be guaranteed in the characteristic of reference beam R and interim light beam A the time.
Can use non-polarized light beam beam splitter (not shown) to replace polarized light beam splitter 120.In this case, can use S polaroid and P polaroid to replace light source regulating element 124, S polaroid and P polaroid are respectively applied for reference beam R and the interim light beam A that will be gone out by the beam splitting of non-polarized light beam beam splitter institute and play inclined to one side be S light beam and P light beam.
The interim light beam A that interim beam splitter 130 is used for being gone out by polarized light beam splitter 120 beam splitting is divided into the first auxiliary beam A1 and the second auxiliary beam A2.Interim beam splitter 130 is arranged on the path that interim light beam A passes through.Interim beam splitter 130 can be provided as prism spectroscope, holographic spectroscope or the like.
On the light path of the reference beam R that is separated by polarized light beam splitter 120, also be provided with a plurality of catoptrons 126 that are used for reference beam R guiding overlapping optical system 140.Catoptron 126 is preferably the Galvano mirror of the light path that is used to regulate reference beam R.
Overlapping optical system 140 is used to be parallel to the optical axis ground overlapping first auxiliary beam A1 and the second auxiliary beam A2 and reference beam R.Overlapping optical system 140 comprises light beam overlapping device 142, refracting telescope 150 and condenser lens 146.
Light beam overlapping device 142 has the overlapping face 142a that is used for the transmission first auxiliary beam A1 and the second auxiliary beam A2 and reflected reference beam R.By the overlapping face 142a transmission first auxiliary beam A1 and the second auxiliary beam A2 and reflected reference beam R, thereby make light beam overlap.
The reference beam R that overlaps by light beam overlapping device 142 and the first auxiliary beam A1 and the second auxiliary beam A2 incide Focused Optical system 160 by refracting telescope 150.Refracting telescope 150 is preferably formed by the Galvano mirror.
Focused Optical system 160 is used for the reference beam R that will overlap and the first auxiliary beam A1 and the second auxiliary beam A2 and is input to recording medium D.Focused Optical system 160 comprises a plurality of condenser lenses 162.The light path of passing through Focused Optical system 160 of the first auxiliary beam A1 and the second auxiliary beam A2 preferably has equal length.Inciding the first auxiliary beam A1 on the recording medium D and the light intensity of the second auxiliary beam A2 should be equal to each other or be equal to each other in error range as much as possible.
Sensing element 170 is used to read reference beam R and the first auxiliary beam A1 and the second auxiliary beam A2 that incides on the recording medium D.Sensing element 170 comprises reading optical beam beam splitter 172, reconstruction beam detecting device 174 and auxiliary beam detecting device 176.
Reading optical beam beam splitter 172 is used for the reconstruction beam that reproduces during by recording medium D at the first auxiliary beam A1 and the second auxiliary beam A2 and reference beam R is carried out beam splitting.Reading optical beam beam splitter 172 is transmitted to auxiliary beam detecting device 176 with the first auxiliary beam A1 and the second auxiliary beam A2, and reference beam R is reflexed to reconstruction beam detecting device 174.
Reconstruction beam detecting device 174 is used to detect the reconstruction beam that reproduces from recording medium D in response to reference beam R.Reconstruction beam detecting device 174 can adopt the image sensing device that has such as the pel array of CCD (charge-coupled image sensor) and CMOS (complementary metal oxide semiconductor (CMOS)) device.
Auxiliary beam detecting device 176 detects when utilizing reference beam reproduction optical information the together first auxiliary beam A1 of diffraction and intensity and the position of the second auxiliary beam A2 with reference beam R.Auxiliary beam detecting device 176 is determined the droop error of reference beam R and recording medium D based on testing result.Auxiliary beam detecting device 176 adopt be arranged as with the corresponding a plurality of photodiode P1 of moving area of the first auxiliary beam A1 by recording medium D and the second auxiliary beam A2 ... and Pn (referring to Fig. 9 and Figure 10).
Photodiode P1 ... and the arrangement of Pn should be longer than the total length apart from d and the first auxiliary beam A1 and the displacement of the second auxiliary beam A2 when tilting between the incidence point of the first auxiliary beam A1 and the second auxiliary beam A2.Capable of being combined and arrange at least several to dozens of photodiodes P1 ... and Pn.Can adopt CCD or cmos device as auxiliary beam detecting device 176.Can be suitable for embodiment ground and revise and adopt any part.
The inclination angle of the recording medium D that is used for determining that the first auxiliary beam A1 and the second auxiliary beam A2 pass through by the intensity of the auxiliary beam detecting device 176 detected first auxiliary beam A1 and the second auxiliary beam A2 and position.
When the first auxiliary beam A1 and the second auxiliary beam A2 together are refracted with reference beam R, can measure the light intensity of the first auxiliary beam A1 and the second auxiliary beam A2 and the inclination angle that recording medium D is determined in the position by recording medium D the time.
Below, with the reproduction that is described in briefly in the optical information reproducing apparatus optical information.
110 emission light beam L come reproduction optical information from light source.Is reference beam R and interim light beam A by polarized light beam splitter 120 with institute's emitted light beams L beam splitting.Regulate the reference beam R of institute's beam splitting and the characteristic (for example, intensity, uniformity coefficient and polarizability) of interim light beam A by light source regulating element 124.Is the first auxiliary beam A1 and the second auxiliary beam A2 by interim beam splitter 130 with the interim light beam A beam splitting through regulating.
The first auxiliary beam A1 and the second auxiliary beam A2 of institute's beam splitting incide on the overlapping optical system 140, to overlap with reference beam R.Inciding the first auxiliary beam A1 on the overlapping optical system 140 and the second auxiliary beam A2 and reference beam R overlaps to be parallel to optical axis and to propagate into refracting telescope 150.Incide on the recording medium D with reference beam R and with the first auxiliary beam A1 and the second auxiliary beam A2 that reference beam overlaps mutually by refracting telescope 150.
Incide reference beam R on the recording medium D and be formed on interference figure refraction on the recording medium D, thereby generate reconstruction beam.Read reconstruction beam by reconstruction beam detecting device 174.
The first auxiliary beam A1 and the second auxiliary beam A2 incide the same position place on the recording medium D of reference beam R incident.At this moment, reference beam R can be with the first auxiliary beam A1 and the second together incident of auxiliary beam A2, perhaps only the incident first auxiliary beam A1 and the second auxiliary beam A2.First auxiliary beam A1 of incident and the intensity of the second auxiliary beam A2 should be equal to each other or be equal to each other in error range as much as possible.
The first auxiliary beam A1 and the second auxiliary beam A2 that incide on the recording medium D detect by recording medium D and by auxiliary beam detecting device 176.Auxiliary beam detecting device 176 detects intensity and the position of the detected first auxiliary beam A1 and the second auxiliary beam A2.
The data that are used as the inclination angle of the incident angle of reading reference beam R and recording medium D by the intensity of the auxiliary beam detecting device 176 detected first auxiliary beam A1 and the second auxiliary beam A2 and position.
The example of optical information recorder/transcriber is described with reference to Fig. 2 and Fig. 3 below.Optical information recorder/transcriber 200 has the structure of adding the optical system that is used for generating the signal beams S of recording optical information to above-mentioned optical information reproducing apparatus 100.The structure identical with optical information reproducing apparatus 100 will be not described in detail.
As shown in Figures 2 and 3, optical information recorder/transcriber 200 comprises light source 210, non-polarized light beam beam splitter 220a, polarized light beam splitter 220b, interim beam splitter 230a, overlapping optical system 240, refracting telescope 250, Focused Optical system 260 and sensing element 270.
Light source 210, polarized light beam splitter 220b, interim beam splitter 230, overlapping optical system 240, refracting telescope 250, Focused Optical system 260 and sensing element 270 are similar to those elements in the above-mentioned optical information reproducing apparatus, thereby omit the detailed description to them.
Non-polarized light beam beam splitter 220a is used for carrying out beam splitting from light source 210 emitted light beams L to form signal beams S and reference beam R.Light beams was risen partially to form signal beams S by light source regulating element 222a in a branch of minute.Another light beam of institute's beam splitting incides that polarized light beam splitter 220b goes up and is reference beam R and interim light beam A by beam splitting.
To be risen by the light beams that the beam splitting of non-polarized light beam beam splitter 220a institute goes out by light source regulating element 222a is that the P light beam is to form signal beams S partially.The light path of signal beams S is provided with optical gate (shutter) 224a, spatial light modulator 228 and fourier transform lens 229.
The light path of optical gate 224a shutoff signal light beam S the time from recording medium D reproduction optical information.Spatial light modulator 228 with data load to signal beams S.Fourier transform lens 229 comes figure signal light beam S by Fourier transform, and will be input to recording medium D through the signal beams S of conversion.
Spatial light modulator 228 can adopt TFT LC (film transistor type liquid crystal) device of representing active-matrix device, STN LC (super-twist nematic liquid crystal) device, Ferro LC device, PDLC (Polymer Dispersed Liquid Crystal) device or the plasma addressed LC device of representing passive matrix device.
To describe the record of optical information recorder/transcriber below and reproduce operation.
The operation of recording optical information is at first described.From light source 210 emission light beam L.Is a pair of light beam that is used to generate signal beams S and reference beam R by non-polarized light beam beam splitter 220a with institute's emitted light beams L beam splitting.By light source regulating element 222a one light beams of institute's beam splitting is risen and to be the P light beam partially, and be converted into signal beams S.
At signal beams S by in the spatial light modulator 228, utilize spatial light modulator 228 with data load to signal beams S.The signal beams S that is loaded with data on it incides on the recording medium by fourier transform lens 229.
Another light beam by non-polarized light beam beam splitter 220a beam splitting incides on the polarized light beam splitter 220b, and is reference beam R and interim light beam A by beam splitting.Interim light beam A need not to be used for recording optical information, thus by optical gate 224b cross-section (intersected).
The reference beam R that is gone out by polarized light beam splitter 220b beam splitting incides on the overlapping optical system 240 by a plurality of catoptrons 226.The reference beam R that incides on the overlapping optical system 240 incides on the recording medium D by refracting telescope 250 and Focused Optical system 260.
On recording medium D, form the holographic interference pattern by signal beams S and the reference beam R that incides on the recording medium D.This holographic interference pattern is the data that are used to reproduce recording medium D.
The operation of reproduction optical information will be described below.From light source 210 emission light beam L.Is a pair of light beam that is used to generate signal beams S and reference beam R by non-polarized light beam beam splitter 220a with institute's emitted light beams L beam splitting.Come the cross-section light beam that is used to generate signal beams S by optical gate 224a.
Another light beam that is gone out by non-polarized light beam beam splitter 220a beam splitting incides on the polarized light beam splitter 220b, and is reference beam R and interim light beam A by beam splitting.Reference beam R incides on the overlapping optical system 240 by a plurality of catoptrons 226.
Is the first auxiliary beam A1 and the second auxiliary beam A2 by auxiliary beam light splitting optical system 230 with interim light beam A beam splitting.The first auxiliary beam A1 and the second auxiliary beam A2 incide on the overlapping optical system 240 and with reference beam R and overlap mutually.The first auxiliary beam A1 that will overlap by refracting telescope 250 and the second auxiliary beam A2 and reference beam R guiding Focused Optical system 260.
The reference beam R and the first auxiliary beam A1 and the second auxiliary beam A2 incide on the recording medium D by Focused Optical system 260.Utilization is formed on the reference beam R that the interference figure on the recording medium D will incide on the recording medium D and is converted to reconstruction beam.The reconstruction beam by recording medium D and the first auxiliary beam A1 and the second auxiliary beam A2 incide and read on the optical system 270.
It is separated from each other to incide the reconstruction beam read on the optical system 270 and the first auxiliary beam A1 and the second auxiliary beam A2 by reading optical beam beam splitter 272.Read reconstruction beam by reconstruction beam detecting device 274, read the first auxiliary beam A1 and the second auxiliary beam A2 by auxiliary beam detecting device 276.
Employing is by the intensity of the auxiliary beam detecting device 276 detected first auxiliary beam A1 and the second auxiliary beam A2 and the position data as the inclination angle of incident angle of reading reference beam R and recording medium D.
Use description in above-mentioned optical information reproducing apparatus and optical information recorder/transcriber, proofread and correct the method for the droop error of recording medium below.Come indicating member with the Reference numeral in the optical information reproducing apparatus.These members also can be indicated by the Reference numeral in optical information recorder/transcriber.Alternatively, they can be included in the modified example of the present invention.
With reference to Fig. 4 optical information reproduction method according to exemplary embodiment is described.
As shown in Figure 4, in optical information reproduction method, reference beam R incides on the recording medium D.The first auxiliary beam A1 and the second auxiliary beam A2 can be with the reference beam R incidents of inciding on the recording medium D (light beam input step (S110)).
On recording medium D, form the holographic interference pattern to produce the diffraction of light beam according to angular multiplexed method.The first auxiliary beam A1 and the second auxiliary beam A2 incide the same position place on the recording medium D.First auxiliary beam A1 of incident and the intensity of the second auxiliary beam A2 should be equal to each other or be equal to each other in error range as much as possible.
Incide the first auxiliary beam A1 on the recording medium D and the second auxiliary beam A2 in by recording medium D by the interference figure diffraction that is formed on the recording medium D.Detect first diffracted auxiliary beam A1 and the second auxiliary beam A2 (detecting step (S120)) by auxiliary beam detecting device 176.When detecting the first auxiliary beam A1 and the second auxiliary beam A2, measure light intensity and the position of the first auxiliary beam A1 and the second auxiliary beam A2.Utilization be arranged on a plurality of photodiode P1 on the auxiliary beam detecting device 176 ... and Pn comes sensing first auxiliary beam A1 and the second auxiliary beam A2 (referring to Fig. 9 and Figure 10).
When reading the first auxiliary beam A1 and the second auxiliary beam A2 fully, the sense information of the first auxiliary beam A1 and the second auxiliary beam A2 and the previous set information of the first auxiliary beam A1 and the second auxiliary beam A2 are compared, to determine that whether therebetween difference is less than specification error value (comparison step (S130)).The specification error value is to satisfy the value of optimum Working, and can be in advance the duty that is associated with difference except that the specification error value be stored in the look-up table.
When difference during, carry out by reference beam R is input to recording medium 110 and the reproduction optical information processing less than the specification error value.When difference during, judge that the incident angle of the reference beam R that is determined by the inclination angle of recording medium D is not " Bragg angle ", the inclination angle of recording medium D incorrect (determining step (S140)) thus greater than the specification error value.
By repeatedly the first auxiliary beam A1 and the second auxiliary beam A2 being input to same position and repeatedly detected value and specification error value being compared, can determine the inclination angle of storage medium D more accurately.
Compare by detected value and setting value, be provided with the incident angle (incident angle is provided with step (S150)) of reference beam R the first auxiliary beam A1 and the second auxiliary beam A2.By will with reference beam R together the first auxiliary beam A1 of incident and the light intensity of the second auxiliary beam A2 compare, can calculate the incident angle of reference beam R.By the comparison of the first auxiliary beam A1 and the second auxiliary beam A2, can determine the incident angle of reference beam R based on the position that occurs little difference or minimal difference between the first auxiliary beam A1 and the second auxiliary beam A2.
The droop error of recording medium D is proofreaied and correct to form the default incident angle (aligning step (S160)) of reference beam R.Can be by the inclination angle of recording medium D being proofreaied and correct or the incident angle of reference beam R is proofreaied and correct the correction of carrying out the droop error of recording medium D.
Describe the light beam input step (S110) of optical information reproduction method in detail with reference to Fig. 5.
In light beam input step (S110), scan the optical information (scanning step (S112)) that is stored in the position of reference beam R incident according to angular multiplexed method to the reference beam R (the perhaps first auxiliary beam A1 and the second auxiliary beam A2) on the recording medium D by oblique incidence.
The reference beam R and the first auxiliary beam A1 that suppose to incide on the recording medium D have identical light intensity with the second auxiliary beam A2." θ " the expression first auxiliary beam A1 and the second auxiliary beam A2 incide the angle on the recording medium D.
Light intensity-angle Selection the curve of the optical information that scans has been shown among Fig. 6 and Fig. 7.
The synoptic diagram of light intensity-angle Selection curve that Fig. 6 is an illustration when not having the multiplexing optical information that is stored in the recording medium.As shown in the figure, when the light intensity with the first auxiliary beam A1 of equal angular incident and the second auxiliary beam A2 is positioned at same position place on two slopes of peak curve, the inclination angle of recording medium D is formed the feasible diffraction efficiency maximum that incides the reference beam R on the recording medium D, this means that the incident angle of the reference beam R that is determined by the inclination angle of recording medium D is positioned at " Bragg angle ".
The synoptic diagram of light intensity-angle Selection curve that Fig. 7 is an illustration when the multiplexing optical information that is stored in the recording medium.As shown in the figure, when locating with predetermined difference value t with the light intensity of the first auxiliary beam A1 of equal angular incident and the second auxiliary beam A2, the incident angle of the reference beam R that is determined by the inclination angle of recording medium D is not positioned at " Bragg angle " to be located, and this means that the diffraction efficiency of reference beam R reduces.
Be described below with reference to Fig. 7.Be stored in optical information (scanning step (S112)) among the recording medium D by utilizing angular multiplexed method to scan with angular multiplexed method.The position that has the optical information of largest light intensity in the optical information that scans is set to reference position Rmax (reference position is provided with step (S114)).
Adopt reference position Rmax that the optical information that is used as benchmark in the optical information that scans is set.Reference position Rmax is as the benchmark that reproduces other optical information in angular multiplexed information.
After the reference position Rmax of optical information is set, the signal area 1 (signal area is provided with step (S116)) of reconstruction beam is set based on reference position Rmax.Signal area 1 is used for easily moving between many angular multiplexed optical information by getting rid of at the noise that generates between many angular multiplexed optical information according to reference position Rmax.
Signal area 1 can be determined by the steady state value k that before is provided with at reference position Rmax.Steady state value k is the value between 0 and 1, and the position of the reconstruction beam in the signal area 1 is lower than reference position Rmax all the time.Steady state value k can change according to device state being set, and can be set to according to the average intensity of the optical information that scans variable.
When reference position Rmax is set as mentioned above, can come to determine inversely reference position Rmax by largest light intensity A1max and the A2max that utilizes the first auxiliary beam A1 and the second auxiliary beam A2 corresponding to reference position Rmax.
Owing to have constant clearance between the reference position A2max of the reference position A1max of first auxiliary beam and second auxiliary beam, so the reference position A1max that can be by reading first auxiliary beam and the reference position A2max of second auxiliary beam calculate reference position Rmax inversely.
When the reference position A1max that utilizes first auxiliary beam and second auxiliary beam and A2max determine reference position Rmax, satisfy R<k*Rmax and A1<k*A1max and A2<k*A2max simultaneously and satisfy Rmax>A1max and the position of Rmax>A2max and A1max=A2max is set to reference position Rmax.
Reference position Rmax reverse determined to can be used to when the reproduction optical information to find out the optical information of reproduction when reference beam R departs from particular optical information owing to various errors or external action.
In this manner, finished the light beam input step (S110) that reference beam R is input to signal area 1.
Describe the detection step (S120) of optical information reproduction method below in detail with reference to Fig. 8 and Fig. 9.
Detect the first auxiliary beam A1 and the second auxiliary beam A2 by auxiliary beam detecting device 176 by recording medium D.Auxiliary beam detecting device 176 comprise a plurality of photodiode P1 ... and Pn, and by with these photodiodes P1 ... and Pn be divided into a plurality of detecting units (U1 ... and Un) detect the first auxiliary beam A1 and the second auxiliary beam A2 (detecting unit partiting step (S122); Referring to Fig. 9 and Figure 10).
Detecting unit U1 ... and Un detects the first auxiliary beam A1 and the second auxiliary beam A2 by recording medium D, thus from detecting unit U1 ... and find out detecting unit among the Un and have time peaked detecting unit U2 with maximum detected value.After finding out detecting unit and having time peaked detecting unit U2, the detected value of detecting unit U1 and U2 is compared (detected value comparison step (S124)) mutually with maximum detected value.
Incide situation on two photodiode Pn and the Pn+1 owing to exist among the first auxiliary beam A1 and the second auxiliary beam A2 each all to incide situation and auxiliary beam A1 or an A2 on the photodiode Pn exactly in the mode that overlaps, so need be provided with to detecting unit Un.
May occur as shown in Figure 9 detecting each situation among the first auxiliary beam A1 and the second auxiliary beam A2, and detect one or more situation among auxiliary beam A1 and the A2 according to the mode that overlaps by a plurality of photodiode Pn and Pn+1 by a photodiode Pn.
When detecting one of the first auxiliary beam A1 and second auxiliary beam A2 by a photodiode, the photodiode P1 from be arranged in auxiliary beam detecting device 176 ... and select to have the photodiode (hereinafter being called " P2 ") of maximum detected value among the Pn.Photodiode P2 and two photodiodes that are positioned at the both sides of photodiode P2 are set to the first detecting unit U1, and photodiode is divided into detecting unit U2 by 3 adjacent photodiode are combined ... and Un.
Calculate the light intensity of detecting unit U1 and U2, find out detecting unit U1 with largest light intensity and detecting unit U2 then with inferior largest light intensity.Then, the light intensity of the first detecting unit U1 is compared with the light intensity of the second detecting unit U2.
As shown in figure 10, when auxiliary beam A1 and A2 with the mode that overlaps focus on one or more photodiode P1 ... and Pn is when going up, by according to auxiliary beam A1 and A2 are focused on mode identical on the photodiode with photodiode P1 ... and Pn be divided into detecting unit U2 ... and Un, can measure the light intensity of the first auxiliary beam A1 and the second auxiliary beam A2.
Measurement by between the auxiliary beam detecting device 176 detected first auxiliary beam A1 and the second auxiliary beam A2 apart from d.Detect the photodiode of largest light intensity and detect distance between the photodiode of time largest light intensity by calculating, can obtain the distance between the first auxiliary beam A1 and the second auxiliary beam A2.Can be than the detection distance between the definite more accurately first auxiliary beam A1 of the predeterminable range between the first auxiliary beam A1 and the second auxiliary beam A2 and the second auxiliary beam A2.
When the inclination angle of recording medium D is too big, because one of the first auxiliary beam A1 and second auxiliary beam A2 may depart from the zone of auxiliary beam detecting device 176, so will measure the distance between the first auxiliary beam A1 and the second auxiliary beam A2.In this case, auxiliary beam detecting device 176 can detect an auxiliary beam and by auxiliary beam detecting device 176 detected another light beams (for example, the noise light beam that generates when the diffraction) as auxiliary beam.
In this manner, by utilizing light beam, can calculate the incident angle of the reference beam R that incides on the recording medium D or the inclination angle of the recording medium D that reference beam R is incided in response to reference beam R and the first auxiliary beam A1 and second auxiliary beam A2 reproduction.
The incident angle of reference beam R or the inclination angle of recording medium D are controlled in the inclination angle that calculates of the recording medium D that can be incided based on the incident angle that calculates that incides the reference beam R on the recording medium D or reference beam R.
As previously mentioned, in optical information reproducing apparatus, optical information recorder/transcriber and optical information reproduction method according to an exemplary embodiment of the present invention, by make reference beam and a pair of auxiliary beam by recording medium, detect reference beam by recording medium and auxiliary beam with the inclination angle of determining recording medium and determine whether to occur droop error, can come correct for tilt errors.