JP4800254B2 - Wavelength selective diffraction element, optical pickup, optical information processing apparatus, and optical information processing method - Google Patents

Description

  The present invention relates to a light-selective diffractive element having different diffraction characteristics depending on the wavelength of light, an optical pickup that includes the same and performs recording / reproduction of an optical recording medium, an optical information processing apparatus and an optical information processing method using the same .

  Conventionally, an optical information processing apparatus for processing information on an optical recording medium such as an optical disc such as a DVD or CD, and an optical pickup for recording / reproducing the optical recording medium provided in the optical information processing apparatus have been known. For example, as disclosed in, for example, [Patent Document 1] and [Patent Document 2], an optical pickup and an optical information processing apparatus corresponding to a plurality of types of optical recording media have been proposed.

The optical pickup described in [Patent Document 1] includes light-selective diffractive elements having different diffractive characteristics according to the wavelength of light so as to correspond to a plurality of types of optical recording media.
This light selective diffractive element aims to solve the following problems.
When a conventional diffraction element such as a three-beam generating diffraction element or a hologram diffraction element is used in combination with a two-wavelength semiconductor laser, diffracted light is generated for any incident light of two wavelengths, which is not desired. Unnecessary diffracted light becomes stray light and enters the photodetector, and information cannot be recorded or reproduced.
・ Since unnecessary diffracted light is generated, the amount of light is lost and the signal light is reduced.

  Therefore, the light-selective diffraction element described in [Patent Document 1] includes a periodic concavo-convex portion formed on a transparent substrate and a filling portion that fills the periodic concavo-convex portion with respect to light of two different wavelengths. In the diffractive element used, any one of the concavo-convex member constituting the periodic concavo-convex part and the filling member constituting the filling part is made of a material containing a red organic pigment, and the other is made of a material containing a transparent inorganic substance. The refractive index of the member and the refractive index of the filling member are substantially the same for the light of one wavelength and are different for the light of the other wavelength.

JP 2002-350625 A JP 2004-145915 A

However, such a wavelength selective diffraction element has the following problems.
One of the two types of materials used is an organic material, but the organic material has lower heat resistance than an inorganic material such as glass, and is therefore unsuitable for optical instruments used at high temperatures.
Organic materials are weak in light resistance as compared with inorganic materials, and are not suitable for optical devices that receive high-power light or short-wavelength light.
-Requires a glass substrate to hold both sides of the diffractive structure.

  The present invention includes a wavelength-selective diffractive element and a wavelength-selective diffractive element that can prevent or suppress the generation of unnecessary diffracted light while solving such a problem while ensuring appropriate diffraction efficiency for a plurality of different wavelengths. An object of the present invention is to provide an optical pickup, an optical information processing apparatus using the same, and an optical information processing method.

  In order to achieve the above object, the invention described in claim 1 is characterized in that the first substrate that transmits at least the first wavelength light and the second wavelength light that are different from each other, and the first substrate alternately. A first portion formed by a first material and a second portion formed by a second material, the refractive index of the first material and the refractive index of the second material, And the first portion comprises a first subwavelength structure having a pitch smaller than the first wavelength and the second wavelength, and the effective refractive index of the first subwavelength structure and the second The refractive indices of the materials are in wavelength selective diffractive elements that are substantially equal to each other for light of the first wavelength and substantially different from each other for light of the second wavelength.

  According to a second aspect of the present invention, in the wavelength selective diffraction element according to the first aspect, the second substrate that transmits the light transmitted through the first substrate and the second substrate are alternately disposed along the second substrate. The third portion formed of the third material and the fourth portion formed of the fourth material, and the refractive index of the third material and the refractive index of the fourth material are different from each other. The third portion includes a second sub-wavelength structure having a pitch smaller than the first wavelength and the second wavelength, and the effective refractive index of the second sub-wavelength structure and the refractive index of the fourth material. Are substantially equal to each other with respect to the light having the second wavelength and substantially different from each other with respect to the light having the first wavelength.

  According to a third aspect of the present invention, in the wavelength selective diffraction element according to the second aspect, the first substrate and the second substrate are integrated.

  According to a fourth aspect of the present invention, there is provided a first emission unit that emits light having a first wavelength, a second emission unit that emits light having a second wavelength, and light emitted from the first emission unit. And an optical system for condensing the light emitted from the second emitting means on the optical recording medium, a light receiving means for receiving the reflected light from the optical recording medium, the first emitting means and the second 4. An optical pickup having a wavelength selective diffraction element according to claim 1, which is disposed between an emitting means and the optical system.

  According to a fifth aspect of the present invention, there is provided an optical information processing apparatus comprising the optical pickup according to the fourth aspect, wherein the optical pickup processes information on an optical recording medium.

  According to a sixth aspect of the present invention, there is provided an optical information processing method for processing information on an optical recording medium using the optical pickup according to the fourth aspect.

  The present invention is formed by a first substrate that transmits at least light having a first wavelength and light having a second wavelength that are different from each other, and a first material that is alternately disposed along the first substrate. A first portion formed by the second material and a second portion formed by the second material, wherein the refractive index of the first material and the refractive index of the second material are different from each other. A first subwavelength structure having a pitch smaller than the first wavelength and the second wavelength, wherein the effective refractive index of the first subwavelength structure and the refractive index of the second material are the first wavelength. Are substantially equal to each other, and are substantially different from each other with respect to the second wavelength light, so that the first wavelength light is transmitted and the second By adjusting the effective refractive index of the first subwavelength structure to diffract light of wavelength, at least By realizing a large change in the refractive index between two wavelengths in the sub-wavelength structure, the sub-wavelength structure adjusts the chromatic dispersion characteristics of the refractive index, so there are low material constraints, and high temperature, high power and short wavelength light In this case, it is only necessary to use an inorganic material, and even in this case, the range of materials that can be selected is wide, and since it can be easily created simultaneously by photolithography and nanoimprint techniques, it is an oxide that is more resistant to heat than organic materials. Inorganic materials such as thin films can be selected and can be applied to optical equipment used at high temperatures, and inorganic materials such as oxide thin films that are more resistant to light than organic materials can be selected. An optical machine that uses a beam, for example, a device equipped with a blue semiconductor laser, or a high-power laser beam, for example, a high-power laser used for an optical pickup for high-speed recording In addition, it can be easily manufactured at the same time by a photolithographic technique, and does not require a bonding process of a glass substrate holding a diffraction grating. As long as the substrate thickness is sufficient, the thickness can be reduced to, for example, about 100 μm, and the weight can be reduced. While achieving these, it is not necessary to ensure appropriate diffraction efficiency for different wavelengths. It is possible to provide a wavelength-selective diffraction element that can prevent or suppress generation of diffracted light.

  Formed by a second substrate that transmits light transmitted through the first substrate, a third portion formed by the third material, and a fourth material that are alternately disposed along the second substrate. The refractive index of the third material and the refractive index of the fourth material are different from each other, and the third portion has a pitch smaller than the first wavelength and the second wavelength. A second sub-wavelength structure having an effective refractive index of the second sub-wavelength structure and a refractive index of the fourth material substantially equal to each other for light of the second wavelength, If the light of the first wavelength is substantially different from each other, the first sub-wavelength structure is effective so that the light of the first wavelength is transmitted and the light of the second wavelength is diffracted. In addition to adjusting the refractive index, light of the second wavelength is transmitted and light of the first wavelength is diffracted In this way, by adjusting the effective refractive index of the second sub-wavelength structure, a large change in the refractive index between at least two wavelengths is realized in the sub-wavelength structure. In order to make adjustments, the material restrictions are low, and when using high-temperature, high-power or short-wavelength light, it is sufficient to use inorganic materials. Even in this case, the range of materials that can be selected is wide, and photolithography techniques and nanoimprint techniques Since a large number can be easily created at the same time, it is possible to select inorganic materials such as oxide thin films that are more resistant to heat than organic materials, and it can also be applied to optical equipment used at high temperatures. It is possible to select an inorganic material such as a strong oxide thin film, a short wavelength light beam such as a device equipped with a blue semiconductor laser, or a high power light beam such as a high-speed recording device. It can also be applied to optical equipment using high-power lasers used in optical pickups, etc., and can easily be manufactured simultaneously by photolithography, and requires a glass substrate bonding process that holds the diffraction grating. However, it is only necessary to have a substrate thickness that is essentially a thin-film element and gives the element strength, so that it can be thinned and reduced to about 100 μm, for example. It is possible to provide a wavelength selective diffractive element capable of ensuring an appropriate diffraction efficiency with respect to the wavelength and preventing or suppressing generation of unnecessary diffracted light.

  If the first substrate and the second substrate are integrated, the first sub-wavelength structure is configured to transmit the first wavelength light and diffract the second wavelength light. By adjusting the effective refractive index of the second sub-wavelength structure so that the second wavelength light is transmitted and the first wavelength light is diffracted in addition to adjusting the effective refractive index of By realizing a large change in the refractive index between at least two wavelengths in the sub-wavelength structure, the sub-wavelength structure adjusts the chromatic dispersion characteristics of the refractive index, so there are low material constraints, high temperature, high power and short wavelength In the case of using light, an inorganic material may be used. Even in this case, the range of materials that can be selected is wide, and a large number of materials can be easily attached to the first substrate and the second substrate simultaneously by a photolithography method or a nanoimprint method. Do the matching This makes it possible to select inorganic materials such as oxide thin films that are more heat resistant than organic materials, and can be applied to optical equipment used at high temperatures, as well as oxidation that is more resistant to light than organic materials. It is possible to select an inorganic material such as a thin film, and to an optical device using a short-wavelength light beam, for example, a device equipped with a blue semiconductor laser, or a high-power laser beam, for example, a high-power laser used for an optical pickup for high-speed recording. It is also applicable, and can be easily manufactured at the same time by a photolithographic technique, and does not require a bonding process of a glass substrate holding a diffraction grating, and is essentially a thin film element having element strength. As long as the substrate thickness is sufficient, the thickness can be reduced to, for example, about 100 μm, and the weight can be reduced. Provided is a wavelength-selective diffractive element that can be easily manufactured and that can secure appropriate diffraction efficiency for a plurality of different wavelengths and prevent or suppress generation of unnecessary diffracted light. be able to.

  The present invention includes a first emitting unit that emits light having a first wavelength, a second emitting unit that emits light having a second wavelength, the light emitted from the first emitting unit, and the second An optical system for condensing the light emitted from the emitting means on the optical recording medium; a light receiving means for receiving the reflected light from the optical recording medium; the first emitting means and the second emitting means; Since the optical pickup has the wavelength selective diffraction element according to any one of claims 1 to 3 disposed between the optical system and the optical system, the wavelength selective diffraction element having the above-described effect is provided. In addition, the optical pickup can be applied to an optical device used at a high temperature, and an optical pickup for high-speed recording using a short-wavelength light beam, for example, a device equipped with a blue semiconductor laser, or a strong light beam, for example, a high-power laser. A small, high performance optical pin It is possible to provide a backup.

  Since the present invention is an optical information processing apparatus having the optical pickup according to claim 4 and processing information on an optical recording medium by this optical pickup, the optical pick-up having the above-described effect is provided, and at a high temperature. Compact and high-performance optical information that can be used and can be used with short-wavelength light beams, such as equipment with a blue semiconductor laser, and high-power lasers, such as high-power light beams, such as high-speed recording optical pickups A processing device can be provided.

  Since the present invention is an optical information processing method for processing information on an optical recording medium using the optical pickup according to claim 4, it can be used at a high temperature using an optical pick having the above-described effects, To provide a small and high-performance optical information processing method capable of using a high-power laser in a short-wavelength light beam, for example, a device equipped with a blue semiconductor laser, or a high-power light beam, for example, an optical pickup for high-speed recording Can do.

  FIG. 1 shows an outline of an optical information processing apparatus to which the present invention is applied. The optical information processing apparatus processes information of an optical recording medium called a plurality of types of optical recording media, that is, optical disks. Examples of the optical recording medium include CDs, CD-Rs, DVDs, and the like having a plurality of types with different substrate thicknesses and recording densities.

  Processing of information on the optical recording medium includes reproduction of information recorded on the optical recording medium, recording of information on the optical recording medium, and the like. In the optical information processing apparatus 100 of this embodiment, such reproduction and recording are performed. It is possible to do both.

  The optical information processing apparatus 100 includes a spindle motor 11 that rotates the optical recording medium 10, an optical pickup 20 that is used for recording and reproducing information signals in processing information on the optical recording medium 10, and an optical pickup 20. A feed motor 12 for moving to the inner and outer periphery of the optical recording medium 10, a modulation / demodulation circuit 13 for performing predetermined modulation and demodulation processing, a servo control circuit 14 for performing servo control of the optical pickup 20, and the like, and an optical information processing apparatus And a system controller 15 that controls the entire system 100.

  The spindle motor 11 is driven and controlled by a servo control circuit 14 and is driven to rotate at a predetermined rotational speed. The optical recording medium 10 to be recorded and reproduced is chucked on the drive shaft 11a of the spindle motor 11 and rotated at a predetermined rotational speed by the spindle motor 11 driven and controlled by the servo control circuit 14.

  The modem circuit 13 is connected to the system controller 15 and the external circuit 16. When recording an information signal on the optical recording medium 10, the modulation / demodulation circuit 13 receives a signal to be recorded on the optical recording medium 10 from the external circuit 16 under the control of the system controller 15, and performs predetermined modulation on the signal. Apply processing. The signal modulated by the modem circuit 13 is supplied to the optical pickup 20.

  When reproducing the information signal from the optical recording medium 10, the modulation / demodulation circuit 13 receives the reproduction signal reproduced from the optical recording medium 10 from the optical pickup 20 under the control of the system controller 15, and outputs the reproduced signal to the reproduction signal. A predetermined demodulation process is performed. The signal demodulated by the modem circuit 13 is output from the modem circuit 13 to the external circuit 16.

  The feed motor 12 is for moving the optical pickup 20 to a predetermined position in the radial direction of the optical recording medium 10 when recording and reproducing the information signal, and based on a control signal from the servo control circuit 14. Driven. That is, the feed motor 12 is connected to the servo control circuit 14 and is controlled by the servo control circuit 14.

  The servo control circuit 14 controls the feed motor 12 so that the optical pickup 20 is moved to a predetermined position facing the optical recording medium 10 under the control of the system controller 15. The servo control circuit 14 is also connected to the spindle motor 11, and controls the operation of the spindle motor 11 under the control of the system controller 15. As described above, the servo control circuit 14 controls the spindle motor 11 so that the optical recording medium 10 is rotationally driven at a predetermined rotational speed when information signals are recorded and reproduced on the optical recording medium 10.

  When recording and reproducing information signals to and from the optical recording medium 10, the optical pickup 20 irradiates the optical recording medium 10 that is rotationally driven with laser light and detects the return light. The optical pickup 20 is connected to the modulation / demodulation circuit 13. When recording an information signal, a signal input from the external circuit 16 and subjected to a predetermined modulation process by the modulation / demodulation circuit 13 is supplied to the optical pickup 20.

  Based on the signal supplied from the modem circuit 13, the optical pickup 20 irradiates the optical recording medium 10 with laser light that has been subjected to light intensity modulation. Further, when reproducing the information signal, the optical pickup 20 irradiates the rotationally driven optical recording medium 10 with a constant output laser beam, and a reproduction signal is generated from the return light. The reproduction signal is supplied to the modem circuit 13.

  The optical pickup 20 is also connected to the servo control circuit 14. At the time of recording / reproducing the information signal, a focus servo signal and a tracking servo signal are generated from the return light reflected and returned by the optical recording medium 10 that is driven to rotate, and these servo signals are supplied to the servo control circuit 14. The

FIG. 2 is a schematic configuration diagram of an optical pickup to which the present invention is applied.
The optical pickup 20 of this embodiment performs reproduction and recording of a plurality of types of optical recording media 10 having different substrate thicknesses and recording densities, such as CDs, CD-Rs, and DVDs.

  The optical pickup 20 includes a first laser diode 21 serving as a first emitting unit that emits a first laser beam L1 having a wavelength of 780 nm as light having a first wavelength, and light having a second wavelength. The second laser diode 22 as the second emitting means for emitting the second laser light L2 having a wavelength of 660 nm band has a two-wavelength light source 23 housed in a common package.

  The optical pickup 20 also includes a diffraction element 30 as a wavelength selective diffraction element that diffracts the first laser light L1 and the second laser light L2 emitted from the two-wavelength light source 23 to generate three beams, and a diffraction element. An optical system Lo common to the laser beams L1 and L2 for condensing the first laser beam L1 and the second laser beam L2 that have passed 30 onto the recording surface 10a of the optical recording medium 10 is provided. .

  The optical pickup 20 is also reflected light reflected by the recording surface 10a of the optical recording medium 10 and has returned through the common optical system Lo and returned light Lr1, Lr2 of the first laser light L1 and the second laser light L2. Are provided with an optical axis adjusting element 27 that corrects the optical axis deviation and a common light receiving element 28 as a light receiving means for receiving the return lights Lr1 and Lr2.

  As the two-wavelength light source 23, either a monolithic type in which a two-wavelength light source is formed on the same semiconductor substrate or a hybrid type in which individual chips are incorporated can be adopted.

  The common optical system Lo converts the emitted laser beams L1 and L2 and the return beams Lr1 and Lr2 into a plate-like beam splitter 24 and collimates the emitted laser beams L1 and L2 guided by the beam splitter 24. A collimating lens 25 and an objective lens 26 for converging outgoing laser beams L1 and L2 transmitted through the collimating lens 25 onto the recording surface 10a of the optical recording medium 10 are provided.

  In the optical pickup 20 having such a configuration, when information is reproduced from a CD-R serving as the optical recording medium 10, the first laser light L1 having a wavelength of 780 nm is emitted from the first laser light source 21.

  The first laser beam L1 enters the diffractive element 30 to enter the common optical system Lo, passes through the beam splitter 24 and the collimator lens 25, and then is incident on the recording surface 10a of the CD-R by the objective lens 26. Converge as.

  The return light Lr1 of the first laser light L1 reflected by the recording surface 10a is condensed on the common light receiving element 28 via the objective lens 26, the collimating lens 25, the beam splitter 24, and the optical axis adjusting element 27, and the common light receiving element. The CD-R information is reproduced by the signal detected at 28.

  When reproducing information on a DVD as the optical recording medium 10, the second laser light source 22 emits a second laser beam L2 having a wavelength of 660 nm. Similarly to the first laser light L2, the second laser light L2 enters the common optical system Lo by entering the diffraction element 30, and is converged as a light spot on the recording surface 10a of the DVD by the objective lens 26. The return light Lr2 of the second laser light L2 reflected by the recording surface 10a is condensed on the common light receiving element 28 via the beam splitter 24. Information reproduction of a DVD is performed by a signal detected by the common light receiving element 28.

  The diffraction element 30 has a first diffraction grating surface 31 disposed on the two-wavelength light source 23 side, and a second diffraction grating surface 32 disposed on the beam splitter 24 side, on both surfaces thereof. A diffraction grating surface is formed.

  The diffractive element 30 performs the tracking error detection by the three-beam method, that is, the three-spot method, so that the first laser beam L1 having a long wavelength of 780 nm and the second laser beam having a short wavelength of 660 nm emitted from the two-wavelength light source 23 are used. This is for diffracting both L2 and generating three beams.

  As shown in FIG. 3, the first diffraction grating surface 31 diffracts the 780 nm laser beam L1 on the long wavelength side at an angle α and transmits the 660 nm laser beam L2 on the short wavelength side as it is without being diffracted. Conversely, the second diffraction grating surface 32 transmits the 780 nm laser beam L1 on the long wavelength side as it is without being diffracted, and diffracts the 660 nm laser beam L2 on the short wavelength side at an angle β.

  As shown in the figure, the grating pitch P1 of the periodic grating 31a formed on the first diffraction grating surface 31 and the grating pitch P2 of the periodic grating 32a formed on the second diffraction grating surface 32 are shown. And the grating pitch P2 is larger than the grating pitch P1.

These diffraction angles α and β are obtained as values satisfying the following expression using the grating pitch P1 and the grating pitch P2, where Λ1 is the wavelength of the laser beam L1 and Λ2 is the wavelength of the laser beam L2.
sin (α) = Λ1 / P1
sin (β) = Λ2 / P2

  FIG. 4 shows the relationship between the direction of the periodic grating 31 a formed on the first diffraction grating surface 31 and the direction of the periodic grating 32 a formed on the second diffraction grating surface 32. FIG. 4A shows the arrangement positions of the first diffraction grating surface 31 and the second diffraction grating surface 32 in the diffraction element 30, and FIGS. Corresponding to the illustrated positions of the first diffraction grating surface 31 and the second diffraction grating surface 32 in FIG. 5, the formation modes of the periodic gratings 31 a and 32 a of the first diffraction grating surface 31 and the second diffraction grating surface 32, respectively. Show. In FIG. 4A, symbols d1 and d2 indicate the groove depths of the periodic gratings 31a and 32a, respectively.

  As can be seen from the comparison of FIGS. 5B and 5C, the direction of the periodic grating 31a and the direction of the periodic grating 32a form a predetermined angle θ. In other words, the direction of the periodic grating 32a with respect to the direction of the periodic grating 31a is inclined by an angle θ around the optical axis.

  As a result, the diffraction direction of the short-wavelength laser light L2 by the second diffraction grating surface 32 is an angle around the optical axis with respect to the diffraction direction of the long-wavelength laser light L1 by the first diffraction grating surface 31. The direction is inclined by θ.

This angle θ is set in accordance with the spot position of the beam in different types of optical recording media.
FIG. 5 is an explanatory diagram showing spot positions of the laser beams L1 and L2 for reproducing different types of optical recording media 10, and a method for setting the angle θ will be described with reference to this drawing.

  The spot positions of the three beams of the long-wavelength laser light L1 on the recording surface 10a of the optical recording medium 10 are shifted from the main spot L1M in the vertical direction and the horizontal direction from the main spot L1M, and the main spot L1M in both directions. The first sub-spot L1A and the second sub-spot L1B are located symmetrically with respect to the center.

  At this time, the spot position of the three beams of the laser light L2 on the short wavelength side is a main spot L2M that overlaps with the main spot L1M, is shifted from the main spot L2M in the vertical direction and the horizontal direction, and is main in both directions. A first sub-spot L2A and a second sub-spot L2B are located symmetrically around the spot L2M.

  Then, due to the difference in track pitch, the sub-spots L1A and L1B of the first laser beam L1 and the sub-spots L2A and L2B of the second laser beam L2 need to be positioned at an angle θ around the optical axis. is there.

  Since the angle θ coincides with the angle formed by the direction of the periodic grating 31a and the direction of the periodic grating 32a around the optical axis, the first diffraction grating surface 31 and the second diffraction grating surface 31 A diffraction grating surface 32 is formed on the diffraction element 30. For this purpose, it is sufficient to adjust the rotation of the first diffraction grating surface 31 or the second diffraction grating surface 32 of the diffraction element 30 around the optical axis.

  By adjusting the angle formed by the direction of the periodic grating 31a and the direction of the periodic grating 32a around the optical axis to θ, each of the laser beams L1 and L2 transmitted through the diffractive element 30 can be transmitted from the optical recording medium 10 respectively. A light spot is formed at an appropriate position.

Similarly, the spot forming position of the three beams formed on the light receiving surface of the common light receiving element 28 can be adjusted.
FIG. 6 shows the light receiving surface of the common light receiving element 28 that receives return light from different types of optical recording media 10. As shown in the figure, the common light receiving element 28 includes, on the light receiving surface 28a, a four-divided main light receiving portion 33 that receives the first and second return lights Lr1 and Lr2 shown in FIG. This is a differential push-pull type having a split-type light-receiving surface and having two split-type sub-light-receiving portions 34 and 35 arranged symmetrically around the light-receiving portion 33.

  As shown in the figure, the first return light Lr1 is condensed as a main beam receiving part 33 as a main return spot R1M as three beams, and the first and second sub light receiving parts 34 and 35 are first and second sub-lights. Condensed as return spots R1A and R1B. As shown in the figure, the second return light Lr2 is condensed as a main beam receiving portion 33 as a main return spot R2M as three beams, and the first and second sub-light receiving portions 34 and 35 are first and second sub-lights. Condensed as return spots R2A and R2B.

  When the centers of the main return spots R1M and R2M are aligned, the first and second return lights Lr1 and Lr2 are changed to the sub return spots R1A and R1B of the first laser beam Lr1 due to the difference in the track pitch of the optical recording medium 10. The straight line connecting the sub return spots R2A and R2B of the second laser light with respect to the connecting straight line is condensed on the light receiving surface 28a with an angle θ around the optical axis. This angle θ coincides with the angle formed between the direction of the periodic grating 31a and the direction of the periodic grating 32a around the optical axis. Therefore, in the diffraction element 30, by setting the angle to θ, the return lights Lr1 and Lr2 are condensed on the light receiving surface 28a in such a manner.

The grating pitches P1 and P2 shown in FIG. 3 influence the diffraction angles α and β. These diffraction angles α and β influence the distance between the main spots L1M and L2M and the first sub-spots L1A and L2A and the second sub-spots L1B and L2B. The diffraction angles α and β influence the distance between the main return spots R1M and R2M and the first sub return spots R1A and R2A and the second sub spots R1B and R2B.
Accordingly, the grating pitches P1 and P2 are selected so that the sub-beams are arranged at predetermined positions of the optical recording medium 10 and the common light receiving element 28.

  In the diffractive element 30 used in the optical pickup 20, the ratio of the 0th order transmission efficiency to the 1st order diffraction efficiency (± 1st order diffracted light efficiency / 0th order light transmittance) takes a value in the range of about 0.05 to 0.30. It is like that.

  Here, if the diffraction efficiencies of the diffraction elements 30 used for the CD and the DVD are greatly different for each wavelength of light, it is difficult to adjust the gain of the common light receiving element 28, and the amount of sub-beams is too small, resulting in increased noise and recording / reproduction characteristics. Deterioration occurs. On the other hand, if the sub-beam intensity is too high, the main beam intensity is reduced and the recording power is reduced. Therefore, a higher-power semiconductor laser is required. In addition, recording on the disk with sub-beams may occur, and the recording characteristics may deteriorate.

  Therefore, the groove depths d1 and d2 of the periodic gratings 31a and 32a shown in FIG. 4A are adjusted. The relationship between the groove depths d1 and d2 and the diffraction efficiency of the diffractive element 30 will be described later. By selecting the groove depths d1 and d2, the ratio between the 0th-order transmission efficiency and the first-order diffraction efficiency is within the above range. Can be stored.

  Note that the diffraction element 30 has a configuration in which the first diffraction grating surface 31 and the second diffraction grating surface 32 are integrally formed, but the first diffraction element having only the first diffraction grating surface 31 is provided. And a second diffraction element having only the second diffraction grating surface 32 may be used. In this configuration, the angle θ described above can be adjusted after each diffraction grating is manufactured by the rotation of the first diffraction element and the second diffraction element around the optical axis.

  Further, in the configuration in which the first diffractive element and the second diffractive element are separated, in order to facilitate adjustment such as position adjustment when incorporating them into the optical pickup 20, both diffractive elements are connected by a common holder or the like. It can be configured so that it can be supported and rotated integrally around the optical axis. Further, in such a separated configuration, the diffraction grating surfaces may be arranged to face each other.

The diffractive element 30, the first diffractive element, and the second diffractive element are all light-selective diffractive elements having different diffraction characteristics according to the wavelength of light.
Hereinafter, a light selective diffraction element to which the present invention is applied will be described.

  As shown in FIG. 7, the light-selective diffractive element 40 extends in the horizontal direction and vertical direction of FIG. 7 with a size of about several mm square, and has a light L2 having a first wavelength λ1 and a second wavelength λ2. By the first material alternately disposed on the substrate 43 along the left-right direction in FIG. 7 in the extending direction of the substrate 43. It has a sub-wavelength structure 41 as a first sub-wavelength structure, which is a first portion formed, and a projecting portion 42, which is a second portion formed of a second material.

  The lights L1 and L2 correspond to the first and second laser beams emitted from the first and second laser diodes 21 and 22, respectively, and the wavelengths λ1 and λ2 are the wavelengths Λ2 (= 660 nm) and Λ1 ( = 780 nm), and the sub-wavelength structure 41 and the protrusions 42 correspond to the first diffraction grating surface 31.

  The sub-wavelength structures 41 and the protrusions 42 are alternately arranged in a line shape in the direction perpendicular to the paper surface of FIG. 7, and form a periodic structure that is larger than the wavelengths λ1 and λ2. This period, that is, each grating period of the diffraction grating is sufficiently longer than the wavelengths λ1 and λ2, for example, 20 to 100 μm.

  The first material is quartz, and the second material is Ta205, which is a high dielectric material, which are different from each other and have different refractive indexes. For example, the refractive indexes of quartz and Ta205 are 1.456 and 2.309, respectively, for the wavelength λ1, and the refractive indexes of quartz and Ta205 are 1.454 and 2.261, respectively, for the wavelength λ2.

  The material of the substrate 43 is also quartz, which is a transparent substrate. As the material of the substrate 43 and the projecting portion 42, a material having a refractive index difference between the wavelength λ1 and the wavelength λ2 of 0.005 or less, such as quartz, is preferable, and the refractive index used for optical equipment is 1.6 or less. General glass materials (such as BK7) and resin materials can be used.

  The sub-wavelength structure 41 has a periodic structure having a fine structure with a pitch of 400 nm or less, which is smaller than the wavelengths λ1 and λ2, and exhibits structural birefringence. Structural birefringence is a TE wave that is a polarization component parallel to the stripe and a polarization component that is perpendicular to the stripe when two types of media having different refractive indexes are arranged in a stripe shape with a period shorter than the wavelength of light. It means that the refractive index is different from that of a certain TE wave and a birefringence action occurs.

  Here, for the following explanation, the terminology of a fine concavo-convex structure having a rectangular cross section like the sub-wavelength structure 41 will be described with reference to FIG. The unevenness of the fine uneven structure has a rectangular wave shape in cross section, and the rectangular wave unevenness is formed in a uniform cross section in a direction perpendicular to the paper surface of FIG. Therefore, the convex part in the fine concavo-convex structure forms a long ridge in a direction perpendicular to the drawing, and the concave part forms a long ridge in a direction perpendicular to the drawing. The convex portion forming the ridge is called a land, and the concave portion forming the ridge is called a space.

The pitch P of the fine concavo-convex structure having a rectangular wave cross section is the sum of a pair of land, space land width a, and space width b. The height of the land with respect to the bottom of the space is defined as the groove depth d. The groove depth d corresponds to the groove depths d1 and d2.
At this time, the filling factor f is represented by a / P. A large filling factor f indicates that the land width a occupying the pitch P is large.

  When the fine concavo-convex structure is a sub-wavelength structure as in this embodiment, the incident light incident on the fine concavo-convex structure from the air region is a polarization component that vibrates parallel to the land longitudinal direction, that is, the direction perpendicular to the paper surface in FIG. For a certain TE component and a TM component that is a polarization component that vibrates parallel to the periodic direction of the fine concavo-convex structure, that is, the left-right direction in FIG. 8, the fine concavo-convex structure acts like a medium having a different refractive index. Is expressed.

  When the effective refractive index in the sub-wavelength structure 41 is n // for the TE component and n⊥ for the TM component, these effective refractive indexes, that is, light in an arbitrary polarization direction pass through the fine uneven structure such as the sub-wavelength structure 41. The refractive index felt when the subwavelength structure 41 is formed is expressed as follows using the refractive index n of the material on which the sub-wavelength structure 41 is formed and the filling factor f of the fine concavo-convex structure.

That is, assuming that laser beams L2 and L1 having wavelengths λ1 and λ2 larger than the period of the sub-wavelength structure 41 are perpendicularly incident, the polarization directions of the laser beams L2 and L1 that are the incident light are Depending on whether the TE direction is parallel to the space extending direction or the TM direction is perpendicular, the effective refractive index of the sub-wavelength structure 41 is given by the above formulas 1 and 2, respectively.
Further, the phase difference ψ is expressed by the following Expression 3.

  Therefore, it can be seen that the phase difference ψ can be arbitrarily adjusted by appropriately selecting the filling factor f and the groove depth d.

FIG. 9 shows the relationship between the filling factor when the light L2 having the wavelength λ1 is incident on the sub-wavelength structure 41 formed of Ta205, and the effective refractive indexes in the TE direction and the TM direction. This relationship is obtained by the above formulas 1 and 2. As already described, the refractive index of Ta205 itself is 2.309 for wavelength λ1, which corresponds to the case where the filling factor f is 1, that is, the case where no space is formed.
As shown in FIG. 9, by changing the polarization direction of the incident light between the TE direction and the TM direction of the sub-wavelength structure 41, the effective refractive index is between the above formula 1 and the above formula 2. Change.

  In FIG. 10, the relationship between the wavelength of incident light and the refractive index is compared between the effective refractive index in the TE direction and the refractive index of quartz when the filling factor f of the sub-wavelength structure 41 formed of Ta205 is 0.26. A correlation diagram is shown.

  Under this condition, the effective refractive index in the TE direction of the sub-wavelength structure 41 is 1.456 at the wavelength λ1 and 1.436 at the wavelength λ2, and the difference between them is 0.024. Compared to the difference in refractive index between wavelengths λ1 and λ2 in a general glass material (BK7, etc.) having a refractive index of 1.6 or less, which is used in optical equipment, as described above, is 0.005 or less. It can be seen that a large difference in refractive index occurs.

  On the other hand, the effective refractive index in the TE direction of the sub-wavelength structure 41 at the wavelength λ1 is 1.456, which is substantially equal to the refractive index of quartz. Note that, substantially, here, it is determined based on whether or not there is no optical influence when used in the optical pickup 20 and the optical information processing apparatus 100 (the same applies to the entire application). .

  Thus, the effective refractive index of the sub-wavelength structure 41 can be changed by the refractive index of the material used and the filling factor f. Further, as apparent from the above equation 1, when the sub-wavelength structure 41 is formed, the effective refractive index is smaller than the refractive index of the material. Therefore, in order to obtain an effective refractive index equivalent to the refractive index of the protruding portion 42 in the sub-wavelength structure 41, the refractive index of the material forming the sub-wavelength structure 41 is set to be higher than the refractive index of the material forming the protruding portion 42. It needs to be bigger.

  In consideration of the above, the light-selective diffraction element 40 includes a sub-wavelength structure 41 formed of the Ta 205, a protrusion 42 formed of quartz, and a substrate 43. The direction of the diffraction grating determined by the period of the sub-wavelength structure 41 and the protrusion 42 and the direction of the sub-wavelength grating of the sub-wavelength structure 41 are parallel, and the polarization directions of the incident lights L1 and L2 are the diffraction grating and the sub-wavelength. TE direction parallel to the grating.

  The sub-wavelength structure 41 has a filling factor f of 0.26, and an effective refractive index of 1.456 for the wavelength λ1 and 1.436 for the wavelength λ2. The refractive index of the protrusion 42 is 1.456 for the wavelength λ1 and 1.436 for the wavelength λ2. Under these conditions, the effective refractive index of the sub-wavelength structure 41 and the refractive index of the protrusion 42 are substantially equal to each other for the wavelength λ1. The groove depth is d1 as shown in FIG. 7, which corresponds to d1 described above.

  Therefore, the effective refractive index of the sub-wavelength structure 41 and the refractive index of the protrusion 42 are substantially equal to the light L2 having the wavelength λ1, and therefore, as shown in FIG. The light L2 is not diffracted and only the 0th order light is generated.

  Further, since the effective refractive index of the sub-wavelength structure 41 and the refractive index of the protruding portion 42 are substantially different from each other with respect to the light L1 having the wavelength λ2, the wavelength as shown in FIG. The light L1 having the wavelength of λ2 is diffracted, and 0th-order light and ± 1st-order light are generated. The ± first-order light is collected by the first sub spot L1A and the second sub spot L1B shown in FIG. 5 and the first sub return spot R1A and the second sub spot R1B shown in FIG. Corresponds to light.

  FIG. 11 shows the groove depth dependence of the zero-order transmittance and the first-order diffraction efficiency of the light-selective diffraction element 40 having the sub-wavelength structure 41 having a pitch P of 0.3 μm and a filling factor f of 0.26. Are shown in comparison with wavelengths λ1 and λ2. The pitch P corresponds to the pitch P1 shown in FIG.

  As is apparent from FIG. 11A, at the wavelength λ1, as described above, the effective refractive index of the sub-wavelength structure 41 and the refractive index of the protruding portion 42 are not substantially different, so that diffracted light is not generated. The first-order diffraction efficiency is zero.

  On the other hand, at the wavelength λ2, as is apparent from FIG. 11B, the zero-order transmission depends on the difference between the effective refractive index of the sub-wavelength structure 41 and the refractive index of the protrusion 42 and the groove depth d1. The rate and first-order diffraction efficiency vary.

  From these facts, in applications such as optical equipment using the optical selective diffraction element 40, for example, the usage conditions of the optical pickup 20 and the optical information processing apparatus 100, that is, the diffraction element 30 used in the optical pickup 20 as described above, 0 Since the diffraction ratio between the second-order transmission efficiency and the first-order diffraction efficiency is in the range of about 0.05 to 0.30, the groove depth d1 is adjusted to take a value that the diffraction ratio takes. ing.

  For example, as can be seen from FIG. 11B, when the groove depth d1 is 5.5 μm, the 0th-order transmittance is 0.86 and the first-order diffraction efficiency is 0.06 at the wavelength λ2. .07. At the wavelength λ1, the 0th-order transmittance is approximately 1, and the diffraction efficiencies of ± 1st order diffracted light and higher order diffracted light are both 0.5% or less. Therefore, in the light selective diffraction element 40, if the groove depth d1 is 5.5 μm, a diffraction function having wavelength selectivity at two wavelengths λ1 and λ2 is substantially secured.

  FIG. 12 shows a light selective diffraction element 50 to which the present invention is applied. The light-selective diffraction element 50 will be described mainly with respect to the differences from the light-selective diffraction element 40.

  The light selective diffractive element 40 transmits the light L2 having the wavelength λ1, and diffracts the light L1 having the wavelength λ2. The light selective diffractive element 50 diffracts the light L2 having the wavelength λ1, The light L1 having the wavelength λ2 is transmitted.

  The light selective diffractive element 50 corresponds to the sub-wavelength structure 41 corresponding to the sub-wavelength structure 41 and the sub-wavelength structure 51 as the second sub-wavelength structure, which is the third portion formed of the third material. And a protrusion 52 that is a fourth portion formed of the fourth material, and a substrate 53 that is a second substrate corresponding to the substrate 43.

  By appropriately selecting the effective refractive index of the sub-wavelength structure 51 and the refractive index of the protrusion 52 by selecting the third and fourth materials and the filling factor f of the sub-wavelength structure 51, the wavelength λ1 The light L2 is diffracted and the light L1 having the wavelength λ2 is transmitted.

  Such a characteristic is obtained by the light selective diffraction grating 50 functioning as a diffraction grating for the light L2 having the wavelength λ1 and transmitting straight through the light L1 having the wavelength λ2 without performing diffraction. The diffraction efficiency is adjusted by changing the grating shape such as the groove depth d2 and the filling factor f of the sub-wavelength structure 51, and the angle of the diffracted light is adjusted by the size of the grating pitch P of the sub-wavelength structure 51. The groove depth d2 corresponds to d2 shown in FIG. 3 and the like, and the grating pitch P corresponds to the pitch P2 shown in FIG. The sub-wavelength structure 51 and the protruding portion 52 correspond to the second diffraction grating surface 32.

  In FIG. 13, the relationship between the wavelength of incident light and the refractive index is compared between the effective refractive index in the TE direction and the refractive index of quartz when the filling factor f of the sub-wavelength structure 51 formed of Ta205 is 0.27. A correlation diagram is shown.

  Under this condition, the effective refractive index in the TE direction of the sub-wavelength structure 51 is 1.474 at the wavelength λ1 and 1.454 at the wavelength λ2, and the difference between these is 0.020. Compared to the difference in refractive index between wavelengths λ1 and λ2 in a general glass material (BK7, etc.) having a refractive index of 1.6 or less, which is used in optical equipment, as described above, is 0.005 or less. It can be seen that a large difference in refractive index occurs.

  On the other hand, the effective refractive index in the TE direction of the sub-wavelength structure 51 at the wavelength λ2 is 1.456, which is substantially equal to the refractive index of quartz. Thus, the effective refractive index of the sub-wavelength structure 41 can be changed by the refractive index of the material used and the filling factor f.

  Considering the above, the light selective diffraction element 50 includes a sub-wavelength structure 51 formed of the Ta 205, a protruding portion 52 formed of quartz, and a substrate 53. The direction of the diffraction grating determined by the period of the sub-wavelength structure 51 and the protrusion 52 and the direction of the sub-wavelength grating of the sub-wavelength structure 51 are parallel, and the polarization directions of the incident lights L1 and L2 are the diffraction grating and the sub-wavelength. TE direction parallel to the grating.

  The filling factor f of the sub-wavelength structure 51 is 0.27, and the effective refractive index is 1.474 for the wavelength λ1 and 1.454 for the wavelength λ2. The refractive index of the protrusion 52 is 1.456 for the wavelength λ1 and 1.454 for the wavelength λ2. Under these conditions, the effective refractive index of the sub-wavelength structure 41 and the refractive index of the protrusion 42 are substantially equal to each other for the wavelength λ2. The groove depth is d2 as shown in FIG. 12, which corresponds to d2 described above.

  Therefore, the effective refractive index of the sub-wavelength structure 51 and the refractive index of the protrusion 52 are substantially different from each other with respect to the light L1 having the wavelength λ1, so that the wavelength as shown in FIG. The light L2 having a wavelength of λ1 is diffracted to generate zero-order light and ± first-order light. The ± first-order light is collected by the first sub-spot L2A and the second sub-spot L2B shown in FIG. 5 and the first sub-return spot R2A and the second sub-spot R2B shown in FIG. Corresponds to light.

  Further, since the effective refractive index of the sub-wavelength structure 51 and the refractive index of the projecting portion 52 are substantially equal to the light L2 having the wavelength λ2, as shown in FIG. The light L1 is not diffracted and only the 0th order light is generated.

  FIG. 14 shows the groove depth dependence of the zero-order transmittance and the first-order diffraction efficiency of the light-selective diffraction element 50 having the sub-wavelength structure 51 having a pitch P of 0.3 μm and a filling factor f of 0.27. Are shown in comparison with wavelengths λ1 and λ2. The pitch P corresponds to the pitch P2 shown in FIG.

  As apparent from FIG. 14A, at the wavelength λ1, the zero-order transmittance and 1 are dependent on the difference between the effective refractive index of the sub-wavelength structure 51 and the refractive index of the protrusion 52 and the groove depth d2. The next diffraction efficiency changes.

  On the other hand, at the wavelength λ2, the effective refractive index of the sub-wavelength structure 51 and the refractive index of the protruding portion 52 are not substantially different as described above, and as is apparent from FIG. Does not occur, and the first-order diffraction efficiency is zero.

  From these facts, in applications such as optical equipment using the optically selective diffraction element 50, for example, the usage conditions of the optical pickup 20 and the optical information processing apparatus 100, that is, the diffraction element 30 used in the optical pickup 20 as described above, 0 Since the diffraction ratio between the second-order transmission efficiency and the first-order diffraction efficiency is in the range of about 0.05 to 0.30, the groove depth d2 is adjusted to take the value that the diffraction ratio takes. ing.

  For example, as can be seen from FIG. 14A, when the groove depth d2 is 4.5 μm, the 0th-order transmittance is 0.86 and the first-order diffraction efficiency is 0.06 at the wavelength λ1, so the diffraction ratio is 0. .07. At the wavelength λ2, the 0th-order transmittance is approximately 1, and the diffraction efficiencies of ± 1st-order diffracted light and higher-order diffracted light are both 0.5% or less. Therefore, in the light selective diffraction element 50, when the groove depth d2 is 4.5 μm, a diffraction function having wavelength selectivity at two wavelengths λ1 and λ2 is substantially secured.

  FIG. 15 shows a light selective diffraction element 60 to which the present invention is applied. The light selective diffractive element 60 is a combination of the light selective diffractive element 40 and the light selective diffractive element 50, and the substrate 43 and the substrate 53 are shared to form a substrate 63. This corresponds to the diffraction element 30. The light selective diffractive element 40 and the light selective diffractive element 50 correspond to the above-described first diffractive element and second diffractive element, respectively, from which the diffractive element 30 is separated.

  Since the substrate 43 and the substrate 53 are made common, the substrate 63 has the same configuration as that of the light transmitted through the substrate 43 by the substrate 53. In addition, about the structure with which the light selective diffraction element 40 and the light selective diffraction element 50 were equipped, the polarization direction of light L1, L2, etc., the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As shown in FIG. 5A, the light selective diffraction element 60 diffracts the light L2 having the wavelength λ1 at the sub-wavelength structure 41 and the projecting portion 42, and the sub-wavelength structure 51 and the projecting portion. The part 52 is transparent. That is, only the portion of the sub-wavelength structure 41 and the protruding portion 42 functions as a diffraction grating.

  On the other hand, as shown in FIG. 5B, the light selective diffraction element 60 transmits the light L1 having the wavelength λ2 through the sub-wavelength structure 41 and the projecting portion 42, and the sub-wavelength structure 51. Diffraction occurs at the portion with the protrusion 52. That is, only the portion of the sub-wavelength structure 51 and the protruding portion 52 functions as a diffraction grating.

  As described above, in the light selective diffraction element 60, one compounded element functions as a diffraction element independently for each of the two wavelengths λ1 and λ2. Therefore, it can be used as the diffraction element 30.

  Although the diffraction element 30, the first and second diffraction elements, and the light selective diffraction elements 40, 50, and 60 have been described above, various modifications can be made thereto.

  That is, the wavelength λ1 is set to 660 nm, the wavelength λ2 is set to 780 nm, and the description has been given focusing on the two wavelengths. However, other wavelengths may be used. The wavelength of the incident light is in the visible light region to the infrared light region, that is, in the range of 300 to 1600 nm. As is clear from FIGS. 10 and 16, the difference in refractive index between the two wavelengths increases as the difference between the two wavelengths increases.

  The wavelength to be used is not limited to two wavelengths, and can also be applied to an optical apparatus using three or more wavelengths equipped with three or more laser beams.

  The incident light to the diffraction grating has been described as being perpendicularly incident on the diffraction grating, but is not limited to normal incidence, and may be configured to be incident obliquely.

  The polarization direction of the incident light to the diffraction element does not need to be the TE direction, and may be the TM direction. In this case, as is clear from FIG. 9, the effective refractive index is different. The polarization direction may be between the TE direction and the TM direction. In this case, the refractive index is intermediate between the effective refractive index in the TE direction and the effective refractive index in the TM direction.

  In the above example, the grating direction of the diffraction grating and the grating direction of the sub-wavelength structure are parallel as shown in FIG. 16 (a), but are parallel as shown in FIGS. 16 (b) and 16 (c). It does not have to be. FIG. 4C shows the case where the diffraction grating direction and the grating direction of the sub-wavelength structure are perpendicular, and FIG. 5B shows the case where the angle is an intermediate angle between FIG. ing. Since the effective refractive index changes according to the grating direction of the sub-wavelength structure, it is possible to select the grating direction of the sub-wavelength structure so that a desired effective refractive index is obtained.

  The cross-sectional shape of the sub-wavelength structure grating is not limited to a rectangular shape, and may be a trapezoidal shape, a triangular shape, a partial circular shape, or a partial elliptical shape. What is necessary is just to adjust a filling factor according to this shape so that it may meet the desired effective refractive index.

  Similarly, the cross-sectional shape of the portion where the sub-wavelength structure is not formed is not limited to a rectangular shape, but is a trapezoidal shape, a triangular shape, a partial circular shape, or a partial elliptical shape. There may be. The groove depth may be adjusted according to the shape so as to meet the desired diffraction efficiency.

  You may form with the material from which the member of the part made into the protrusion part in the above-mentioned example and the part demonstrated as a board | substrate differ.

  As shown in FIG. 17, the sub-wavelength structure may be formed also in the portion described as the protruding portion in the above example.

  As shown in FIG. 18, the height of the land of the subwavelength structure, in other words, the depth of the space or the groove depth d3 is shallower than the height h of the projecting portion in the above example, and the subwavelength structure is It may be formed only at the upper end in the portion between the projecting portions.

  A method for manufacturing the above-described photoselective diffraction element will be described. In this manufacturing method, the sub-wavelength structure is first formed on the substrate, and then the protrusion is formed. In order to form the sub-wavelength structure, a mold having a shape obtained by inverting the sub-wavelength structure is required according to the shape of the sub-wavelength structure. Therefore, a method for manufacturing the mold will be described.

  First, with reference to FIG. 19 thru | or FIG. 21, the manufacturing method of the light selective diffraction element except the light selective diffraction element shown in FIG. 18 is demonstrated. FIG. 19 shows a method for manufacturing a mold as a nanoimprint substrate, FIG. 20 shows a method for manufacturing a subwavelength structure, and FIG. 21 shows a method for manufacturing a protruding portion. The mold manufacturing method is the same as the method for manufacturing the photoselective diffraction element shown in FIG.

  In forming the mold, a flat silicon substrate 71 as shown in FIG. 19A is prepared. This silicon substrate 71 is for forming an electron beam drawing resist layer 72 on its surface, and this surface is a crystal plane (110). X-ray diffraction analysis is performed on the silicon substrate 71 in advance to measure the deviation between the surface / polished surface and the crystal axis and the deviation between the substrate orientation flat direction and the crystal axis. From this measurement result, the end surface 71a after wet etching, which will be described later with reference to FIG. 8C, is made to appear as a wall of a surface {111} having a shape maintaining the resist pattern pitch and line width. The line direction and orientation flat direction are aligned with a dedicated jig.

  Then, an electron beam drawing resist layer 72 is formed on the silicon substrate 71. The electron beam drawing resist layer 72 is formed by applying and prebaking an electron beam drawing resist on the silicon substrate 71. Thereby, electron beam drawing substrate preparation is performed, and then drawing with an electron beam is performed. Drawing with an electron beam is performed by a program determined and designed in advance according to drawing conditions that vary depending on the pitch and line width of the target product.

  After the drawing, as shown in FIG. 5B, development and rinsing are performed to leave the electron beam drawing resist layer 72 in a predetermined shape, thereby forming a resist pattern. The shape of the resist portion corresponds to the shape of the land portion in the subwavelength structure to be formed.

  As shown in FIG. 3C, the silicon substrate 71 is subjected to alkaline wet etching with KOH using the resist pattern as a mask. The silicon substrate 71 is etched in the depth direction in the same shape as the resist pattern. At this time, the silicon substrate 71 is etched in the depth direction with the same bit and the same line width as the resist pattern, and the wall formed thereby appears as the end surface 71a of the surface {111} which is the wet etching end surface.

  As shown in FIG. 4D, the electron beam drawing resist layer 72 is peeled off to form a silicon mold, that is, a mold 73. The reference numerals in FIG. 4D indicate that the portions have substantially the same size as the corresponding reference portions shown in FIG.

  FIG. 19 (e) is an overhead view of the mold 73, and the part shown in FIG. 19 (d) is provided as a part thereof. (A)-(d) of the figure shows the state expanded compared with the figure (e). The mold 73 may be formed of a light transmissive material.

  In forming the sub-wavelength structure using the mold 73, as shown in FIG. 20A, a UV curable resin 75, which is a transfer resin, is applied to a glass substrate 74 as a product substrate corresponding to the above-described substrate. To do.

  As shown in FIG. 5B, the mold 73 is pressed from above to perform nanoimprint transfer. Since the UV curable resin 75 which is a transfer material has a sufficiently low viscosity, the shape transfer is performed by entering the unevenness of the mold 73.

  As shown in FIG. 2C, UV irradiation is performed from the glass substrate 74 side, which is a light transmitting material, and the UV curable resin 75 is cured. In addition, although the mold 73 manufactured by the manufacturing method shown in FIG. 19 is used, when a photocurable resin is used as the nanoimprint material, it is preferable to use a light transmitting mold such as a quartz substrate. desirable. The quartz substrate mold can be manufactured using the nanoimprint technique shown here as it is. In this case, the difference is that the unevenness is reversed. A thermosetting resin can also be used as the nanoimprint material instead of the UV curable resin 75. In this case, the curing is performed by heating.

  As shown in FIG. 20D, a mold release process for removing the mold 73 is performed. On the glass substrate 74, an imprint resin layer 76 formed of a layer of UV curable resin 75 is formed. The imprint resin layer 76 covers the entire surface of the glass substrate 74. That is, a thin layer is also formed as a layer in a portion corresponding to the convex portion of the mold 73.

  As shown in FIG. 5E, the layer is removed by O 2 dry etching, the thin layer corresponding to the convex portion of the mold 73 is removed, and the glass substrate 74 is exposed at this portion. As the dry etching apparatus, a high-density plasma etching apparatus such as a TCP apparatus or an NLD apparatus is used.

The etching conditions are as follows.
・ Gas type: Oxygen gas (O2)
・ Gas introduction amount: 20sccm
・ Pressure: 0.4Pa
・ Resin etching rate: 30 nm / second ・ Upper bias power: 1 kW
・ Lower bias power: 60W

  Subsequently, a coating film forming process shown in FIG. In this process, the substrate subjected to the layer removal process is taken out, and a sol-gel material 77, which is a high refractive material, is removed by a spinner. It is applied to the part where the land is formed and prebaked. Such application and pre-baking are repeated according to the required height. Finally, post-baking is performed, and the sol-gel material 77 is completely cured to obtain the state shown in FIG. At this time, the material shrinks slightly.

The conditions for the coating film forming process are as follows.
-JSR nanocomposite material use, photosensitive sol-gel material containing inorganic ultrafine particles, refractive index 1.90
・ Model number: Z-7503 is mixed with high refractive index ultrafine particles to increase the refractive index of the base material. ・ Material of high refractive index ultrafine particles: Ta205 material ・ Particle size of high refractive index ultrafine particles: 10 nm or less ・ Viscosity: 10 mPa s
・ Curing: Light irradiation energy amount 400mj / cm2 * 120 seconds

  As shown in FIG. 5G, the imprint resin layer 76 is removed and an imprint film removal process is performed. The removal process is performed by, for example, a method of removing an organic resin material by performing CAROS cleaning, that is, cleaning with a mixed solution of sulfuric acid and hydrogen peroxide. Thereby, the sub-wavelength structure 78 is formed on the glass substrate 74.

  In forming the protrusions between the sub-wavelength structures 78, as shown in FIG. 21A, the mask resist layer is formed so as to fill the space portion of the sub-wavelength structures 78 over the entire surface of the glass substrate 74. 79 is formed. The mask / resist layer 79 becomes a resist.

  As shown in FIG. 6B, an exposure mask pattern 80 is formed on the mask / resist layer 79 in a portion corresponding to the sub-wavelength structure 78, and as shown in FIG. Exposure is performed from the pattern 80 side, and development and rinsing are performed to remove the exposure mask pattern 80, and the mask / resist layer 79 remains in the space portion of the sub-wavelength structure 78, as shown in FIG. And Thereby, the patterning in which the glass substrate 74 is exposed in the portion corresponding to the protruding portion is performed.

  As shown in FIG. 4E, a sol-gel material 81, which is a low refractive index material, is applied to the gap portion of the mask resist layer 79 where the glass substrate 74 is exposed, and is cured by baking. At this time, the sol-gel material 81 is applied, and the baking process by pre-baking and post-baking is performed in the same manner as the coating film forming process shown in FIG.

Conditions for such low refractive index material application and baking are as follows.
・ Uses JSR nanocomposite material ・ Model number: Z-7503
Material: photosensitive sol-gel material containing inorganic ultrafine particles, refractive index 1.45
・ Ultrafine particle size: 10 nm or less ・ Viscosity: 1 mPa · s
・ Curing: Light irradiation energy amount 400mj / cm2 * 120 seconds

  As shown in FIG. 21 (f), the mask / resist layer 79 is removed, and a diffraction grating including a sub-wavelength structure 78 having a high refractive index structure and a projecting portion 82 having a low refractive index structure. A light selective diffraction element 84 having the structure 83 is obtained. This diffraction grating structure 83 corresponds to the first diffraction grating surface 31 shown in FIG.

  If necessary, the surface of the glass substrate 74 on which the diffraction grating structure 83 is not formed is subjected to the processing shown in FIGS. 20 and 21A to 21F, and the diffraction grating structure 83 is also formed on the surface. Then, as shown in FIG. 5G, the light selective diffraction element 84 having the diffraction grating structure 83 on both surfaces of the glass substrate 74 can be formed. The light selective diffraction element 84 corresponds to the above-described diffraction element 30 and light selective diffraction element 60.

  In this case, when forming the diffraction grating structure 83 for the second time, if necessary, a mold having a shape different from the mold 73 used for forming the diffraction grating structure 83 for the first time is shown in FIG. Manufacture and use the indicated process. This is because the diffraction grating structure 83 formed at the second time is different in optical characteristics from the diffraction grating structure 83 formed at the first time, and therefore the shape such as the space width may be different from the diffraction grating structure 83 formed at the first time. is there. The diffraction grating structure 83 formed for the second time corresponds to the second diffraction grating surface 32 shown in FIG.

  By varying the pitch, groove depth, refractive index, and the like of the sub-wavelength structure 78 formed on each surface of the glass substrate 74, the light-selective diffraction element 84 corresponding to the diffraction element 30 and the light-selective diffraction element 60 described above. Can be manufactured.

  As a method for forming the diffraction grating structure 83 on both sides, in addition to the method for performing the above-described treatment on both sides of one glass substrate 74 as described above, different diffraction grating structures on one side of each of the two glass substrates 74. 83, and the glass substrate 74 is joined and integrated.

  With reference to FIGS. 22 and 23, a method of manufacturing the photoselective diffraction element shown in FIG. 18 will be described. FIG. 22 shows a manufacturing method of the sub-wavelength structure, and FIG. 23 shows a manufacturing method of the protruding portion. Since FIG. 22 corresponds to FIG. 19 and FIG. 23 corresponds to FIG. 20, the same parts as those shown in FIG. 19 and FIG.

  The mold 73 to be used can be manufactured in the same manner as the manufacturing method shown in FIG. However, the height of the convex portion corresponding to the sub-wavelength structure provided in the mold 73 is formed corresponding to the groove depth d3 shown in FIG. 18 which is the groove depth of the sub-wavelength structure to be formed. .

  In forming the sub-wavelength structure using the mold 73, as shown in FIG. 22A, a high refractive index layer 90 is made of a high refractive index material on a glass substrate 74 as a product substrate corresponding to the above-described substrate. Then, a UV curable resin 75 that is a transfer resin is applied on the high refractive index layer 90.

  The high refractive index layer 90 is mainly different from the manufacturing method described above. Since the high refractive index layer 90 is a portion that forms a thickness corresponding to the difference between the groove depth d3 and the height h of the protrusion shown in FIG. 18, the height is adjusted to the same height as the thickness. The

The conditions for the coating film forming process are as follows.
-JSR nanocomposite material use, photosensitive sol-gel material containing inorganic ultrafine particles, refractive index 1.90
・ Model number: Z-7503 is mixed with high refractive index ultrafine particles to increase the refractive index of the base material. ・ Material of high refractive index ultrafine particles: Ta205 material ・ Particle size of high refractive index ultrafine particles: 10 nm or less ・ Viscosity: 10 mPa s
・ Curing: Light irradiation energy amount 400mj / cm2 * 120 seconds

From FIG. 22B to FIG. 22D, the transfer process, the curing process, and the mold release process are performed as in FIG. 20B to FIG. 20D.
When the layer removal process is performed in FIG. 22E, a part of the high refractive index layer 90 where a land having a sub-wavelength structure is to be formed is exposed by removing the layer.

  Subsequently, a coating film forming process shown in FIG. In this process, a sol-gel material 77, which is a high refractive material, is applied to a portion where a land having a sub-wavelength structure, where the high refractive index layer 90 is exposed, and the sol-gel material 77 is completely cured. Thus, the state shown in FIG.

  As shown in FIG. 6G, the imprint resin layer 76 is removed to remove the imprint film, and the sub-wavelength formed by the high refractive index layer 90 and the sol-gel material 77 on the glass substrate 74 is processed. Structure 91 is formed. However, in this state, the high refractive index layer 90 also extends to the portion where the protruding portion is to be formed. This portion of the high refractive index layer 90 is removed in the process of forming the protrusions shown in FIG.

  In forming the protrusions, a mask / resist layer 79 should be formed as shown in FIG. 23 (a), and then a subwavelength structure should be finally formed as shown in FIG. 23 (b). An exposure mask pattern 80 is formed in a portion corresponding to the portion, and exposure is performed from the exposure mask pattern 80 side as shown in FIG.

  As shown in FIG. 4D, development and rinsing are performed to remove the exposure mask pattern 80 and a portion where the projecting portion of the high refractive index layer 90 is to be formed. The mask / resist layer 79 remains in the space portion.

  As shown in FIG. 4E, a sol-gel material 81, which is a low refractive index material, is applied to the gap portion of the mask resist layer 79 where the glass substrate 74 is exposed, and is cured by baking.

  As shown in FIG. 6F, a diffraction grating having a sub-wavelength structure 91 having a high refractive index structure and a projecting portion 82 having a low refractive index structure by removing the mask / resist layer 79. A light selective diffraction element 93 having the structure 92 is obtained. The diffraction grating structure 92 corresponds to the first diffraction grating surface 31 shown in FIG.

  Also in this case, if necessary, a diffraction grating structure 92 is also formed on the surface of the glass substrate 74 on which the diffraction grating structure 83 is not formed, and as shown in FIG. A light selective diffraction element 93 having a diffraction grating structure 92 can be formed. The light selective diffraction element 93 corresponds to the diffraction element 30 and the light selective diffraction element 60 described above. The diffraction grating structure 92 formed for the second time corresponds to the second diffraction grating surface 32 shown in FIG.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.

  For example, in the above-described embodiment, the first wavelength is λ1, the second wavelength is λ2, and the effective refractive index of the first sub-wavelength structure and the refractive index of the second material are relative to the light of wavelength λ1. Are substantially equal and substantially different for light of wavelength λ2, but the effective refractive index of the first subwavelength structure and the refractive index of the second material are A substantially different structure may be used for light of substantially the same wavelength λ1.

  In the above-described embodiment, the optical pickup 20 and the optical information processing apparatus 100 corresponding to two wavelengths with the optical recording medium as DVD and CD have been described. However, the optical pickup 20 and the optical information processing apparatus 100 are blue-violet laser light having a wavelength of 405 nm band. It may be compatible with Blu-rBy using HD, or two wavelengths of HD DVD and DVD.

  In the above-described embodiment, two laser light sources are provided as light sources. However, the present invention can also be applied to a multi-light source type optical pickup and an optical information processing apparatus provided with three or more laser light sources.

  The above-described embodiment is an example in which a dedicated diffraction grating is provided for each of CD and DVD. For example, in the case of using a 1-beam system instead of a 3-beam system for CD, it is suitable for DVD. Only the second diffraction grating such as the light-selective diffraction element 50 having diffraction efficiency may be provided.

  The transmittance may be adjusted by changing the duty of the diffraction grating, that is, the ratio of the convex portion occupying one period of the grating, in other words, the region where the sub-wavelength structure is formed.

  Furthermore, as shown in FIG. 24, the light-selective diffractive element includes, for example, a grating groove of a diffraction grating forming the light-selective diffractive element itself or a sub-wavelength structure as disclosed in [Patent Document 2]. A structure may be adopted in which the diffraction grating is divided into regions shifted for each of the regions X1, X2, and X3 to improve the quality of the signal to be detected.

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

It is a functional block diagram of the optical information processing apparatus to which the present invention is applied. It is a schematic block diagram of the optical pick-up with which this invention was equipped with the optical information processing apparatus shown in FIG. FIG. 3 is a schematic front view of a wavelength selective diffraction element to which the present invention is applied, which is provided in the optical pickup shown in FIG. 2. FIG. 4 is a trihedral view of the wavelength selective circuit element shown in FIG. 3. FIG. 4 is a schematic front view of an optical recording medium showing an aspect of an optical spot formed on the optical recording medium by the wavelength selective circuit element shown in FIG. 3. FIG. 4 is a schematic front view of the light receiving means showing an aspect of a light spot formed on the light receiving means by the wavelength selective circuit element shown in FIG. 3. It is a typical front view of another wavelength selective diffraction element to which the present invention is applied. It is a schematic diagram for demonstrating the term of each part which comprises a subwavelength structure. FIG. 8 is a correlation diagram illustrating a relationship between a filling factor and an effective refractive index for each polarization direction of the wavelength selective diffraction element illustrated in FIG. 7. FIG. 8 is a correlation diagram comparing the relationship between the wavelength of incident light and the refractive index of the wavelength-selective diffraction element shown in FIG. 7 between the effective refractive index in the TE direction and the refractive index of quartz at a predetermined filling factor. FIG. 8 is a correlation diagram showing the groove depth dependence of the 0th order transmittance and the 1st order diffraction efficiency of the wavelength selective diffraction element shown in FIG. 7 in comparison with wavelengths λ1 and λ2. It is a typical front view of another wavelength selective diffraction element to which the present invention is applied. FIG. 13 is a correlation diagram comparing the relationship between the wavelength of incident light and the refractive index of the wavelength selective diffraction element shown in FIG. 12 between the effective refractive index in the TE direction and the refractive index of quartz at a predetermined filling factor. FIG. 13 is a correlation diagram showing the groove depth dependence of the zero-order transmittance and the first-order diffraction efficiency of the wavelength-selective diffraction element shown in FIG. 12 by comparing the wavelengths λ1 and λ2. It is a typical front view of another wavelength selective diffraction element to which the present invention is applied. It is a perspective view of the example of composition of a wavelength selective diffraction element when the field relation between the grating direction of a diffraction grating of a wavelength selective diffraction element, and the grating direction of a subwavelength structure is varied. It is a schematic perspective view of the wavelength selective element which formed the subwavelength structure in the 2nd part. FIG. 6 is a schematic front view of a wavelength selective element to which the present invention is applied, having a sub-wavelength structure of another configuration. It is a flowchart of the manufacturing method of the type | mold for manufacturing the wavelength selective diffraction element to which this invention is applied. It is a flowchart of the manufacturing method which manufactures the sub wavelength structure of the wavelength selective diffraction element to which this invention was applied using the type | mold manufactured with the manufacturing method shown in FIG. It is a flowchart of the manufacturing method which manufactures the wavelength selective diffraction element to which this invention is applied by manufacturing a 2nd part following the manufacturing method shown in FIG. FIG. 20 is a flowchart of a manufacturing method for manufacturing the sub-wavelength structure of the wavelength selective diffraction element shown in FIG. 18 using a mold manufactured by the manufacturing method shown in FIG. 19. It is a flowchart of the manufacturing method which manufactures the wavelength-selective diffraction element shown in FIG. 18 by manufacturing the 2nd part following the manufacturing method shown in FIG. It is a perspective view of a wavelength selective diffraction element to which the present invention is applied, formed by shifting the grating grooves of the diffraction grating.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical recording medium 20 Optical pick-up 21 1st emitting means 22 2nd emitting means 28 Light receiving means 30 Wavelength selective diffraction element 40 Wavelength selective diffraction element 41 1st part, 1st subwavelength structure 42 2nd Portion 43 First substrate 50 Wavelength-selective diffraction element 51 Third portion, second sub-wavelength structure 52 Fourth portion 53 Second substrate 60 Wavelength-selective diffraction element 74 First and second substrate 78 First DESCRIPTION OF SYMBOLS 1, 3rd part, 1st, 2nd subwavelength structure 82 2nd, 4th part 84 Wavelength selective diffraction element 91 1st, 3rd part, 1st, 2nd subwavelength structure 93 Wavelength Selective diffraction element 100 Optical information processing device L ₀ Optical system L1 Light of second wavelength L2 Light of first wavelength n //, n 屈折 Effective refractive index P Pitch λ1 First wavelength λ2 Second wavelength

Claims (6)

A first substrate that transmits at least a first wavelength light and a second wavelength light different from each other;
A first portion formed by a first material and a second portion formed by a second material, alternately disposed along the first substrate;
The refractive index of the first material and the refractive index of the second material are different from each other,
The first portion comprises a first subwavelength structure having a pitch smaller than the first wavelength and the second wavelength;
The effective refractive index of the first subwavelength structure and the refractive index of the second material are substantially equal to each other for light of the first wavelength, and substantially for light of the second wavelength. Different wavelength-selective diffraction elements. In the wavelength selective diffraction element according to claim 1,
A second substrate that transmits light transmitted through the first substrate;
A third portion formed by a third material and a fourth portion formed by a fourth material, alternately disposed along the second substrate;
The refractive index of the third material and the refractive index of the fourth material are different from each other.
The third portion comprises a second subwavelength structure having a pitch smaller than the first wavelength and the second wavelength;
The effective refractive index of the second subwavelength structure and the refractive index of the fourth material are substantially equal to each other for the second wavelength light and substantially equal to the first wavelength light. A wavelength-selective diffraction element characterized by being different from each other.   3. The wavelength selective diffraction element according to claim 2, wherein the first substrate and the second substrate are integrated. First emission means for emitting light of a first wavelength;
Second emission means for emitting light of a second wavelength;
An optical system for condensing the light emitted from the first emitting means and the light emitted from the second emitting means on the optical recording medium;
A light receiving means for receiving reflected light from the optical recording medium;
An optical pickup comprising the wavelength selective diffraction element according to any one of claims 1 to 3, which is disposed between the first emission means and the second emission means and the optical system.   An optical information processing apparatus comprising the optical pickup according to claim 4 and processing information on an optical recording medium by the optical pickup.   An optical information processing method for processing information on an optical recording medium using the optical pickup according to claim 4.

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