CN1756986A - Optical attenuator and optical head device - Google Patents

Abstract

The present invention provides an optical attenuator reducing variations in optical attenuation amount in response to temperature change, and an optical head device having properties excellent in recording and reproducing an information. An optical attenuator comprising a liquid crystal element having spirally arranged molecules in which a liquid crystal layer 107 is sandwiched between transparent electrodes 103 and 104, and a polarizing beam splitter 110 whose transmittance is changed depending on a polarization state, wherein the ordinary refractive index (no) and the extraordinary refractive index (ne) of liquid crystal, the angle ([theta]pt) of liquid crystal molecules against the transparent substrate surfaces, the thickness (d) of the liquid crystal layer 107 and the wavelength ( lambda ) of incident light, constituent elements are configured so that the value A satisfies the range of from 0.5 to 1.5 in the conditional formula defined by the formula (1): <DF NUM=''(1)''>A = DELTA n . d DIVIDED lambda </DF> wherein <DF> DELTA n = no . ne/ <SQRT>n<2>o . cos<2>([theta]pt) + n<2>e . sin<2>([theta]pt)</SQRT> - no </DF>.

Description

Optical attenuator and optic probe device

Technical field

The present invention relates to optical attenuator and optic probe device, relate in particular to the optic probe device using for optical recording media is carried out to record and regenerating information and be arranged on the optical attenuator on optic probe device.

Background technology

In recent years, extensively utilization can by irradiating, light records and/or the optical recording media of regenerating information.As such optical recording media, known have such as form the read-only class CD-ROM etc. of fine convex-concave pattern on substrate according to the information of record.

In addition, as this optical recording media, known have such as magneto-optic disk such utilize kerr effect carry out regenerating information photomagneto disk, have to utilize the phase change disc of the signal recording layer that phase-change material forms and on the signal recording layer being formed by organic dyestuff, forms as CD-R and record the CD-R etc. that difference that mark detection record the reflectivity of mark at this is carried out regenerating information.

On the other hand, for the various video disc recordings to above-mentioned and/or the various information of regenerating, also developing the various record regenerators with optic probe device.The optical recording medias such as CD-R are recorded and/or the optic probe device of regenerating information in, when recorded information, the light quantity focusing on optical recording media need to be increased, but when regenerating information, this light quantity need to be reduced by object lens etc.

In order to meet this needs, be the outgoing light quantity that the electric current that is input to the semiconductor laser of emergent light by change changes semiconductor laser till now.Yet the semiconductor laser of some use, when input current being diminished in order to reduce outgoing light quantity, exists noise to increase or the unsettled problem of outgoing light quantity.

A kind of structure for this reason proposing is, by use optical attenuator on this optic probe device simultaneously, make to CD, to irradiate the little high-quality laser of noise with miniwatt, for example, to having suppressed as far as possible that the high-quality information of noise records and/or regenerate (, JP 2002-260269 communique).

In addition, as the optical attenuator using on such optic probe device, known have a structure that has combined polarising beam splitter (PBS) and liquid crystal cell, this liquid crystal cell is to form like this, by adding that the voltage of regulation changes the sharp polarized state of light of incident, and pass through polarising beam splitter with this polarization state, control like this optical transmission ratio that incides optical recording media.

Summary of the invention

The problem existing when environment temperature changes is, due to the ordinary refraction index of liquid crystal and very optical index change, so utilize the damping capacity of the optical attenuator generation of liquid crystal cell to change.

In addition, in the optic probe device of optical attenuator has been installed, when inciding the polarization state of the polarisation of light direction etc. of liquid crystal cell and change, owing to arriving the transmission light quantity of optical recording media, change a lot, so need to accurately control the polarization direction of the incident light of directive liquid crystal cell, thus because polarization direction adjustment causes cost to rise and yield rate reduces.

The invention provides a kind of optical attenuator, described optical attenuator comprises: liquid crystal cell, wherein on two opposed surfaces separately of transparency carrier, form transparency electrode, between described transparency electrode, clip liquid crystal layer, the direction of the liquid crystal molecule in described liquid crystal layer is twisted into spiral fashion around the axle of the thickness direction of described liquid crystal layer simultaneously; Different with the polarized state of light of incident with transmissivity, at least one polarization transmission element, in the described optical attenuator forming like this, make to form the ordinary refraction index (n of the liquid crystal of described liquid crystal cell _o) and unusual optical index (n _e), with the liquid crystal molecule of the described transparency carrier adjacency angle (θ with respect to the surperficial formation of transparency carrier _pt), in the 1st conditional expression with the definition of (1) formula, meet A value between the thickness (d) of liquid crystal layer and incident light wavelength (λ) in from 0.5 to 1.5 scope.

$A=\frac{\mathrm{\&Delta;n}\&CenterDot;d}{\mathrm{\&lambda;}}\&CenterDot;\&CenterDot;\&CenterDot;\left(1\right)$

In formula,

$\mathrm{\&Delta;n}=n_o\&CenterDot;n_e/\sqrt{n_o^2\&CenterDot;{\cos }^2\left({\mathrm{\&theta;}}_{\mathrm{pt}}\right)+{\mathrm{<figure-callout\; id="2"\; label="n\; e"\; filenames="A20048000605900172.png,A20048000605900181.png"\; state="\{\{state\}\}">n</figure-callout>}}_e^{}\&CenterDot;{\sin }^2\left({\mathrm{\&theta;}}_{\mathrm{pt}}\right)}-n_o$

In addition, provide a kind of above-mentioned optical attenuator of such formation, the angle (θ that two directions of orientation separately of the liquid crystal molecule adjacent with two described transparency carriers are formed _t), incide the light quantity (P of described optical attenuator _in) and the light quantity (P of described optical attenuator outgoing _out) between meet the 2nd conditional expression with the definition of (2) formula (wherein, dim light constant B is-60, and angle variables C value is in from 60 to 90 scope).

${\mathrm{\&theta;}}_t=\frac{P_{\mathrm{out}}\&CenterDot;C}{P_{\mathrm{in}}}+C\&CenterDot;\&CenterDot;\&CenterDot;\left(2\right)$

In addition, provide a kind of above-mentioned optical attenuator, described optical attenuator has two described polarization transmission elements, and configures respectively a described polarization transmission element in incident one side of light and outgoing one side of light of described liquid crystal.

In addition, provide that a kind of at least one is the above-mentioned optical attenuator of diffraction efficiency with the different polarized light diffraction element in the polarization direction of incident light in two described polarization transmission elements.

In addition, provide at least one and the integrated above-mentioned optical attenuator of described liquid crystal cell in a kind of two described polarization transmission elements.

In addition, provide a kind of described liquid crystal cell to there is the above-mentioned optical attenuator of nematic crystal.

In addition, the above-mentioned optical attenuator that provides a kind of described transparency carrier to be formed by glass.

In addition, provide a kind of optic probe device, described optical head comprises: light source; Emergent light from this light source is focused on to the focalizer of using on optical recording media; The catoptrical photodetector that the emergent light that detection focuses on is reflected by optical recording media; In light path in light path between light source and optical recording media or between optical recording media and photodetector, utilize impressed voltage to change the optical attenuator of the light quantity of transmitted light; And the voltage-operated device that adds voltage to this optical attenuator, feature is that described optical attenuator is above-mentioned optical attenuator.

In addition, provide a kind of above-mentioned optic probe device, described optic probe device is that optical recording media is regenerated and the optic probe device of recorded information, and on optical recording media, carries out the light quantity P of the focusing that regenerating information uses ₁with the light quantity P that carries out the focusing that recorded information uses ₂the P of ratio ₁/ P ₂value in 0.2～0.8 scope.

Accompanying drawing explanation

Fig. 1 means the side view of an example of optical attenuator of the present invention.

Fig. 2 means the figure of the direction of orientation of lcd segment and the axis of homology of polarization transmission element.

Fig. 3 means at twist angle (θ _t) be 60 Simulation results figure while spending.

Fig. 4 means at twist angle (θ _t) be 42 Simulation results figure while spending.

Fig. 5 means at twist angle (θ _t) be 10 Simulation results figure while spending.

Fig. 6 means the Simulation results figure when making dim light amount be 20 ± 3%.

Fig. 7 means the Simulation results figure when making dim light amount be 80 ± 3%.

Fig. 8 means that the double refraction amount (Δ n) at liquid crystal is the Simulation results figure of 0.108 o'clock.

Fig. 9 means that the double refraction amount (Δ n) at liquid crystal is the Simulation results figure of 0.136 o'clock.

Figure 10 means the summary construction diagram of an example of optic probe device of the present invention.

Figure 11 be to the angular deflection amount of the incident polarization direction of lcd segment as parameter, represent transmission optics attenuator light intensity to being added in the figure of relation of the voltage of liquid crystal layer.

Figure 12 means the side view of other examples of optical attenuator of the present invention.

Figure 13 means when light incident side configuration polarization transmission element, measure the figure of the incident polarization light direction skew of this optical attenuator and an example of the relation between beam intensity ratio.

Embodiment

Fig. 1 represents an example of optical attenuator of the present invention.It arranges the transparency electrodes such as ITO 103 and 104 on the transparency carriers such as glass, plastics 101 and 102.Form again the alignment films such as polyimide 105 and 106, implementing to configure two transparency carriers after the orientation process such as friction, make to separate the gap at uniform interval and mutually opposed, and by the peripheries that bond such as bonding agent (not shown), forming unit structure.In unit, the inner liquid crystal of enclosing, forms liquid crystal layer 107.As liquid crystal, can use for example nematic crystal, also can add chiral material.

Transparency electrode 103 with 104 with can add that from outside the Control of Voltage part 109 of voltage is connected, form lcd segment 130.Can to liquid crystal molecule 108, carry out orientation process like this, make it in the boundary surface of polyimide and liquid crystal layer with respect to polyimide face angulation, and this angle is made as to pretwist angle (θ _pt).The direction of liquid crystal molecule is twisted into spiral fashion around the axle of the thickness direction of liquid crystal layer.Polarization transmission element 110 be transmissivity with incident polarized state of light different elements.In Fig. 1, the light being attenuated incides lcd segment 130 from transparency carrier 101 sides, from transparency carrier 102 outgoing, incides polarization transmission element 110.Polarization transmission element 110 is preferably at least configured in the rear one-level with respect to the lcd segment 130 of the working direction of light.

Fig. 2 be illustrated in the alignment films on liquid crystal layer and each transparency carrier each boundary surface liquid crystal molecule each direction of orientation 202 and 203 and the axis of homology 201 of polarization transmission element between relation.The only linearly polarized light that incides this optical attenuator, polarization direction is along X-axis.Direction of orientation 202 at the liquid crystal molecule of the boundary surface of the alignment films of the transparent substrate side of the light incident side of lcd segment 130 (in Fig. 1 105) and liquid crystal layer is made as pretwist angle (θ in Fig. 2 with the angle that X-axis forms _p), each direction of orientation 202 and 203 angles that form are made as twist angle (θ in Fig. 2 _t).Although pretwist angle and twist angle be restriction not, from the simplicity of making, to consider, twist angle is preferably 5～90 degree.In addition, the ordinary refraction index of liquid crystal is made as to n _o, very optical index is made as n _o, the thickness of liquid crystal layer is made as d _oand the optical wavelength of dim light is made as to λ.

When liquid crystal layer is added to the voltage below upper threshold voltage, the light by lcd segment generally becomes elliptically polarized light from linearly polarized light.Then, suppose by adding that voltage drives liquid crystal molecule, for example, to make liquid crystal molecule direction unanimously towards direction of an electric field.At this moment, the linearly polarized light of incident lcd segment does not change polarization state and directly passes through same as before lcd segment.Can control the voltage that is added in lcd segment and change the polarized state of light by lcd segment, then control by the light quantity of the light of polarization transmission element.

Here, liquid crystal layer is divided into N decile along thickness d direction, can thinks a little the set of N sheet uniaxiality birefringent plate of each optic axis distortion.At the thickness direction of liquid crystal layer, when surrounding's liquid crystal molecule of the imaginary axis of thickness direction does not have distortion, with following formula, represent phasic difference Γ at this moment.

$\mathrm{\&Gamma;}=\frac{2\mathrm{\&pi;}\&CenterDot;\mathrm{\&Delta;n}\&CenterDot;d}{\mathrm{\&lambda;}}$

In formula, $\mathrm{\&Delta;n}=n_o\&CenterDot;n_e/\sqrt{n_o^2\&CenterDot;{\cos }^2\left({\mathrm{\&theta;}}_{\mathrm{pt}}\right)+{\mathrm{<figure-callout\; id="2"\; label="n\; e"\; filenames="A20048000605900172.png,A20048000605900181.png"\; state="\{\{state\}\}">n</figure-callout>}}_e^{}\&CenterDot;{\sin }^2\left({\mathrm{\&theta;}}_{\mathrm{pt}}\right)}-n_o$

If suppose that in thickness direction distortion be uniformly, by the phasic difference separately of the birefringent plate of N decile, be Γ/N.If represent to incide the polarized state of light of lcd segment and by the polarized state of light of lcd segment with Stokes' parameter, and be made as respectively S _inand S _out, can be expressed as

$S_{\mathrm{in}}=\left(\begin{array}{c}1\\ 1\\ 0\\ 0\end{array}\right)$

$S_{\mathrm{out}}=\left(\begin{array}{c}1\\ S_1\\ S_2\\ {\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="A20048000605900172.png,A20048000605900181.png"\; state="\{\{state\}\}">S</figure-callout>}}_3\end{array}\right)$

Utilize mueller matrices, they are expressed as

S _out＝R(θ _p)·R(θ _t/N) ^(N-1)·[W(Γ/N)·R(-θ _p/N)] ^(N-1)·W(Γ/N)·R(-θ _p)·S _in

In formula

$W\left(x\right)=\left[\begin{array}{cccc}1& 0& 0& 0\\ 0& 1& 0& 0\\ 0& 0& \cos \left(x\right)& -\sin \left(x\right)\\ 0& 0& \sin \left(x\right)& \cos \left(x\right)\end{array}\right]$

Suppose that polarization transmission element is that transmissivity is 100% in X-direction, the desirable polariscope of the uniaxiality that is 0% in Y direction, the transmissivity P of this optical attenuator _outfor

$P_{\mathrm{out}}=\frac{{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="A20048000605900181.png"\; state="\{\{state\}\}">S</figure-callout>}}_1+1}{2}$

, become n _o, n _e, d, θ _t, θ _p, θ _ptfunction with λ.By calculating P _out, can access the desirable attenuation rate of this attenuator.

Fig. 3, Fig. 4 and Fig. 5 represent simulation result.In each result, establish the double refraction amount (Δ n)=0.1005 of liquid crystal, wavelength (λ)=405nm.Wherein with Δ n definition double refraction amount.In Fig. 3,4 and 5 result, twist angle (θ _t) be respectively 60 degree, 42 degree and 10 degree.The transverse axis of each figure is that the thickness (d) of liquid crystal layer is cell gap, and the longitudinal axis is pretwist angle (θ _p), with curve, represented the thickness of the liquid crystal layer that dim light amount is 50 ± 3% and the relation between pretwist angle.Can know, that dim light amount is 50 ± 3%, pretwist angle with respect to the distribution (angle distribution) of the thickness of liquid crystal layer with twist angle (θ _t) size and change, especially at twist angle (θ _twhen)=42 are spent (situation of Fig. 4), the distribution of solution is very wide.

When especially the thickness of liquid crystal layer is near 3.5 μ m, the distribution of solution is very wide.The distribution of separating is extensively extraordinary, because can increase the tolerance to the foozle of parameter, especially in the refractive index of liquid crystal, can suppress the variation of dim light amount during with variation of ambient temperature.

Equally, to dim light amount, be 20 ± 3% and 80 ± 3% results of calculating, also exist and make the wide twist angle (θ of angle distribution _t), each dim light amount is respectively to 60 degree and 24 degree.In Fig. 6 and Fig. 7, represent simulation result respectively.While being 50 ± 3% with dim light amount, (situation of Fig. 4) is the same, especially near the thickness of liquid crystal layer is 3.5 μ m, has the wide region of angle distribution.

At the double refraction amount (Δ n) of liquid crystal, be then 0.108 and 0.136 o'clock, the wide twist angle (θ of angle distribution when dim light amount is 50 ± 3% _t) calculate result the same twist angle (θ during with Δ n=0.1005 _t) be 42 degree.In Fig. 8 and Fig. 9, represent result.Can know, especially the wide liquid crystal layer of angle distribution has the tendency that its thickness reduces with Δ n increase, and the result that repeats emulation is known, and the pass between Δ n, d and λ is

$A=\frac{\mathrm{\&Delta;n}\&CenterDot;d}{\mathrm{\&lambda;}}$

(A is the scope from 0.5 to 1.5, is preferably 0.75～0.95.), in addition, twist angle (θ in this case _t) and transmissivity (P _out) between pass be

${\mathrm{\&theta;}}_t=\frac{P_{\mathrm{out}}\&CenterDot;B}{P_{\mathrm{in}}}+C$

(B is that-60, C is from 60 to 90 value, is preferably from 65 to 75 value).

If selection meets the parameter (n of the lcd segment of these conditions _o, n _e, d, θ _t, θ _p, θ _pt) make lcd segment, can increase the tolerance to the foozle of parameter, especially in the refractive index of liquid crystal, can suppress the variation of dim light amount during with variation of ambient temperature.

Then the situation that, the polarization direction of the incident light of the optical attenuator of consideration Fig. 1 changes.For example, incident light is linearly polarized light, and during along the X-direction polarization of Fig. 2, and the in the situation that of rotation centered by Z axis in polarization direction, the example that the light intensity of transmission optics attenuator adds voltage with respect to liquid crystal layer as shown in figure 11.Polarization direction and X-direction relativity shift that three curve tables in Figure 11 are shown into the linearly polarized light of penetrating are respectively three kinds of situations of 3 degree, 0 degree and-3 degree.Due to the relativity shift of such polarization direction, near light intensity voltage 0V changes.

; when using this optical attenuator; for example, by liquid crystal layer being added respectively to the voltage of 5V and 0V strengthens (5V) or weakens in the situation of light intensity of (0V) transmission; due to the polarization direction of linearly polarized light and the relativity shift of X-direction of incident, so the beam intensity ratio under voltage separately changes.On the contrary, in order not make light intensity change, just need to accurately control the polarization direction of the linearly polarized light of incident.

Figure 12 represents other examples of optical attenuator of the present invention.In addition, the label identical with the label using in Fig. 1 represents identical element.Light incident side (transparency carrier 101 sides) by the light at lcd segment configures the 2nd polarization transmission element 120, when inciding the polarisation of light direction of this optical attenuator and change, owing to there being the 2nd polarization transmission element 120, so the polarisation of light to lcd segment incident is stable, described beam intensity ratio does not change, therefore fine.Polarization direction skew when Figure 13 is illustrated in light incident side configuration polarization transmission element, that detect this optical attenuator of incident and an example of beam intensity ratio, the result while simultaneously representing not configure polarization transmission element.

In addition, polarization transmission element can be used to polymkeric substance and add the such absorption-type polariscope of pigment after stretching, or as line grating, polarising beam splitter, by polarization direction, changes the element of light path and then change actual transmission.Especially, the diffraction efficiency polarization diffraction device different with the polarization direction of incident light can slimming, in addition because being also easy to realize miniaturization with lcd segment is integrated.As polarization diffraction device, can utilize liquid crystal, high molecule liquid crystal or lithium niobate (LiNbO ₃) etc. birefringent medium make.

In addition, lcd segment with polarization transmission element is integrated can realize miniaturization and and reduce component number, so very good.

In addition, Figure 10 represents the optical attenuator of making to be like this contained in an example on optic probe device.Optical attenuator of the present invention consists of liquid crystal cell 3, polarization transmission element 4 and 12, and is arranged between collimation lens 2 and quarter wave plate 8.From the light of semiconductor laser 1 outgoing, by collimation lens 2, become directional light, after transmission-polarizing transmissive element 12, transflective liquid crystal element 3.Utilize voltage-operated device 11 to add from outside voltage to liquid crystal cell 3.The light transmission-polarizing transmissive element 4 of transflective liquid crystal element 3.Polarization transmission element 4 is the elements when the light outgoing to this element incident, according to the change of polarized direction of incident light to the light quantity of optical recording media outgoing, can use polarization beam apparatus, prism or the diffraction grating that contains line grating, deflection diffraction element etc.In the example of Figure 10, polarization beam apparatus, as polarization transmission element 4, is used as to polarization transmission element 12 by polarization diffraction device.In addition, can polarization transmission element 4 and 12 and liquid crystal cell 3 paste, form integrated.The light of transmission-polarizing transmissive element 4, after transmission quarter wave plate 8, focuses on optical recording media 7 by the condenser lens 5 being contained on driver 6.

The light being reflected by optical recording media 7 advances along the opposite direction of above-mentioned light path.In the example of Figure 10, owing to having used polarization beam apparatus as polarization transmission element 4, so be polarized after transmissive element 4 reflections along the progressive light of negative side of light path, by condenser lens 9, focus on and arrive photodetector 10.At this moment, by to liquid crystal cell 3 (in fact, the transparency electrode forming to the surface that forms the transparency carrier of liquid crystal cell) add multiple different voltage, change the polarisation of light direction of transflective liquid crystal element 3, thereby focus on the light quantity on optical recording media after can changing transmission-polarizing transmissive element 4.

Reasonable situation is, carry out optical recording media information regeneration use focus on the light quantity P on optical recording media ₁the light quantity P of the focusing of using with the information recording that carries out optical recording media ₂ratio P ₁/ P ₂the value in 0.2～0.8 scope, but preferably in the value of 0.3～0.6 scope.If this light amount ratio, when to optical recording media recorded information, can be 100% light quantity setting, carry out fully recording of information, on the other hand, when regeneration, if be the value of 20～80% (0.2～0.8) scope of the light quantity while recording light quantity setting, and then be set as the value of 30～50% (0.3～0.6) scope, owing to can carry out the regeneration of information in the situation that S/N is large, and can be to optical recording media writing information, so relatively good.

Below, represent embodiment.

The optical attenuator that to have made the light extinction rate that uses under wavelength 405nm be 36.5%.The details of manufacture is described with Fig. 1 and Fig. 2 below.First in lcd segment, on the glass transparent substrate 101 and 102 that is 1.0mm at the thickness of Fig. 1, utilize sputtering method to generate the nesa coating being formed by ITO that thickness is 30nm, then utilize photoetching process and wet etching to form figure, form like this transparency electrode 103 and 104.Utilize the alignment films 105 and 106 of aniline printing method polyimide of the about 50nm of coating thickness in the transparency electrode 103 and 104 of transparency carrier 101 and 102, then sintering.Utilizing cloth to implement friction orientation to the alignment films 105 of polyimide film and 106 processes.At this moment, liquid crystal molecule 108 is around the axle distortion of the thickness direction of liquid crystal layer 107.Utilize silk screen print method on transparency carrier 101, to print the encapsulant (not shown) of epoxy series.In the encapsulant of epoxy series (not shown), having mixed respectively diameter that the thickness of maintenance medium crystal layer uses and be the fiber spacing body 3% (mass ratio converts, below identical) of 3.6 μ m and having obtained the tectal diameter of electric conductivity of having implemented on surface that the electric conductivity between transparency carrier 101 and 102 uses is the baton round 2% of 4 μ m.Overlapping transparency carrier 101 and 102 makes after position alignment, at the temperature of 170 degree, 6 * 10 ⁴n/m ²pressure under crimping forming unit.Utilize vacuum impregnation in the unit of making, to inject nematic crystal and form liquid crystal layer 107, and with UV bonding agent (not shown) sealing-in inlet, formation profile is the liquid crystal cell of 8mm * 10mm rectangle.This liquid crystal cell can add voltage from outside to liquid crystal layer by transparency electrode 103 and 104.The parameter of liquid crystal cell (lcd segment of optical attenuator) is set as, θ _p=-10 degree, θ _t=50 degree, Δ n=0.1005, d=3.6.

The liquid crystal cell of making is represented to be combined in optic probe device as Figure 10.The polarization transmission element 4 configuring in optic probe device is that polarization beam apparatus and polarization transmission element 12 are that liquid crystal cell 3 is set between polarization diffraction device, utilizes and controls this liquid crystal cell from the output voltage of voltage-operated device 11.Emergent light from semiconductor laser 1 is the order transmission of polarization beam apparatus, quarter wave plate 8 according to collimation lens 2, polarization transmission element 12, liquid crystal cell 3, polarization transmission element 4, when transmission remains on after the condenser lens 5 on driver 6, focus on optical recording media 7.The light focusing on is reflected by optical recording media 7, according to the order transmission of condenser lens 5 and quarter wave plate, and after polarization direction generation 90 degree variations, is polarized beam splitter reflection, is then directed to photodetector 10.

At this moment, liquid crystal cell 3 is added to voltage, and configure photodetector on the position of optical recording media 7, detect the light quantity of the light being focused, the voltage that result adds liquid crystal cell is 0.4V _rmswhen (1kHz rectangle exchange), be 37% (to establish and add that voltage is 10V _rmslight quantity when (rectangle of 1kHz exchanges) is 100%), can be by liquid crystal being added to voltage changes the light quantity that focuses on the light on optical recording media 7.While utilizing this optic probe device to optical recording media recorded information, liquid crystal cell 3 is added to voltage 10V _rms(rectangle of 1kHz exchanges), increase focuses on the light quantity of the light of optical recording media 7, when from optical recording media regenerating information, does not change the output power of semiconductor laser 1, and the voltage that liquid crystal cell 3 is applied is made as to 0.4V _rms(rectangle of 1kHz exchanges), makes the light quantity that focuses on optical recording media reduce to 37%.Like this, under low noise, carry out the regeneration of information.In addition, environment temperature is changed from 10 ℃ to 60 ℃, but in the change of having confirmed dim light amount is suppressed among a small circle.

工业上的实用性

在本发明中，提供一种随环境温度变化而衰减量的变化小的光衰减器、 另外随入射光的偏振方向等偏振状态的变化而衰减量的变化小的光衰减器、 进行信息的记录和再生特性好的装有所述光衰减器的光头装置。

另外，该光衰减器在波为1550nm频带等近红外波区域也能利用， 例如可用作为光通信系统的可变光衰减器等。

Claims (9)

1. an optical attenuator, described optical attenuator comprises: liquid crystal cell, wherein on the opposed surface separately of two transparency carriers, form transparency electrode, between described transparency electrode, clip liquid crystal layer, the direction of the liquid crystal molecule in described liquid crystal layer is twisted into spiral fashion around the axle of the thickness direction of described liquid crystal layer simultaneously; Different with the polarized state of light of incident with transmissivity, at least one polarization transmission element,

It is characterized in that, in the described optical attenuator forming like this, make to form the ordinary refraction index (n of the liquid crystal of described liquid crystal cell _o) and unusual optical index (n _e), with the liquid crystal molecule of the described transparency carrier adjacency angle (θ with respect to the surperficial formation of transparency carrier _pt), in the 1st conditional expression with the definition of (1) formula, meet A value between the thickness (d) of liquid crystal layer and incident light wavelength (λ) in from 0.5 to 1.5 scope.

$A=\frac{\mathrm{\&Delta;n}\&CenterDot;d}{\mathrm{\&lambda;}}$ $\left(1\right)$

In formula,

$\mathrm{\&Delta;n}=n_o\&CenterDot;n_e/\sqrt{n_o^2\&CenterDot;{\cos }^2\left({\mathrm{\&theta;}}_{\mathrm{pt}}\right)+n_e^2\&CenterDot;{\sin }^2\left({\mathrm{\&theta;}}_{\mathrm{pt}}\right)}-n_o$

2. optical attenuator as claimed in claim 1, is characterized in that, forms so described optical attenuator, the angle (θ that two directions of orientation separately of the liquid crystal molecule adjacent with two described transparency carriers are formed _t), incide the light quantity (P of described optical attenuator _in) and from the light quantity (P of described optical attenuator outgoing _out) between meet the 2nd conditional expression with the definition of (2) formula (wherein, dim light constant B is-60, and angle variables C value is in from 60 to 90 scope).

${\mathrm{\&theta;}}_t=\frac{P_{\mathrm{out}}\&CenterDot;B}{P_{\mathrm{in}}}+C...\left(2\right)$

3. optical attenuator as claimed in claim 1 or 2, is characterized in that, has two described polarization transmission elements, and configures respectively a described polarization transmission element in incident one side of light and outgoing one side of light of described liquid crystal.

4. optical attenuator as claimed in claim 3, is characterized in that, in two described polarization transmission elements, at least one is for diffraction efficiency is with the different polarized light diffraction element in the polarization direction of incident light.

5. the optical attenuator as described in claim 3 or 4, is characterized in that, in two described polarization transmission elements, at least one and described liquid crystal cell are integrated.

6. if claim 1 is to the optical attenuator as described in any one of claim 5, it is characterized in that, described liquid crystal cell has nematic crystal.

7. if claim 1 is to the optical attenuator as described in any one of claim 6, it is characterized in that, described transparency carrier consists of glass.

8. an optic probe device, described optic probe device comprises: light source; Emergent light from this light source is focused on to the focalizer of using on optical recording media; The catoptrical photodetector that the emergent light that detection focuses on is reflected by optical recording media; In light path in light path between light source and optical recording media or between optical recording media and photodetector, utilize additional on voltage change the optical attenuator of the light quantity of transmitted light; And the voltage-operated device that adds voltage to this optical attenuator, it is characterized in that,

Described optical attenuator is that claim 1 is to the optical attenuator described in any one of claim 7.

9. optic probe device as claimed in claim 8, is characterized in that, described optic probe device is that optical recording media is regenerated and the optic probe device of recorded information, and on optical recording media, carries out the light quantity P of the focusing that regenerating information uses ₁with the light quantity P that carries out the focusing that recorded information uses ₂the P of ratio ₁/ P ₂value in 0.2～0.8 scope.

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