JP2012173361A - Optical attenuator and optical attenuator module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical attenuator having high durability and stable transmittance characteristics.SOLUTION: At least one of both sides of a transparent glass substrate in an incident light wavelength range includes a plurality of light transmission areas with different light transmittances. The light transmission area comprises a part that is formed with a microstructure formed by repetition of a rugged pattern having such a dimension as causing incident light to diffract and openings having such a dimension as not causing the incident light to diffract. The light transmittance of the light transmission area comprising the microstructure and the openings is set by a 0-order light transmittance of the microstructure and an opening ratio of the opening.

Description

  The present invention is a light including an optical attenuator that is an element for reducing the amount of light to a desired level in an apparatus that uses light, such as a laser processing apparatus, and an operation unit that adjusts the amount of light to a desired level using the optical attenuator. The present invention relates to an attenuator module.

  As the optical attenuator, there is a variable optical attenuator that can attenuate the amount of light to a plurality of levels. The variable optical attenuators are roughly classified into three types: (1) butterfly method, (2) polarization method, and (3) film distribution method.

  The butterfly method utilizes the incident angle dependency of the transmittance of the dielectric multilayer film, and the transmittance is changed by tilting the element. This method is widely adopted because it does not cause a difference in transmittance within the beam diameter and can be downsized including the operation unit.

  The polarization method is a method in which a polarizing plate and a (λ / 2) wave plate are arranged on the optical path of laser light, and the transmittance is changed by relatively rotating the polarizing plate or the (λ / 2) wave plate. . Some use a polarizing beam splitter (PBS) instead of a polarizing plate. Although the polarization method is easy to realize, it does not function unless the light beam to be attenuated is linearly polarized light or a light beam close thereto, and does not function with circularly polarized light or random polarized light.

  The film distribution method is an element in which the transmittance is changed for each place by changing the film thickness for each place when forming a dielectric multilayer film or a metal thin film. However, the transmittance characteristics of the thin film change depending on the operating temperature, and the amount of incident light that is not transmitted is absorbed by the element, so that the temperature of the element itself rises, and the physical film thickness of the thin film increases accordingly. The transmittance changes. In high performance thin films having a large absorption coefficient, the temperature rise is more prominent. Therefore, in order to enable actual use, there is a problem in that it is necessary to continue irradiation with laser and wait until the element temperature becomes constant and the transmittance is stabilized. In addition, the use of a high-power laser may damage the thin film and make it unusable.

  Therefore, at present, the butterfly method, which has no transmittance distribution within the beam diameter, can cope with random polarization, and can cope with the downsizing of the entire apparatus, is mainly used.

  Both methods use thin films. Thin films are expensive due to their poor yield. In particular, a high-performance thin film has a higher yield because the film thickness must be strictly controlled, and the price is further increased due to the fact that the thin film material is expensive.

  In both the butterfly method and the film distribution method, those using a dielectric multilayer film, when the optical attenuator is used in a high output optical system such as a YAG laser processing apparatus, the thin film absorbs the laser beam and the thin film material is sublimated. For example, durability is an issue.

  In either method, the light beam is transmitted through the thin film. The transmittance characteristic of the thin film varies depending on the operating temperature. Further, in any case, the amount of incident light that is not transmitted is absorbed by the element, so that the physical thickness of the thin film changes and the transmittance changes as the temperature of the element itself increases. In high performance thin films having a large absorption coefficient, the temperature rise is more prominent. Therefore, in order to enable actual use, it has been necessary to continue irradiation with the laser and wait until the element temperature becomes constant and the transmittance is stabilized.

  Since the conventional method uses a thin film and has a large wavelength dependency and a narrow wavelength range, a dedicated optical element is required for each laser wavelength to be used.

  In the butterfly method, the incident angle is changed in order to change the transmittance. However, the thin film has a large dependency on the incident angle with respect to the optical characteristic, and the characteristic changes greatly with a slight difference in the incident angle. .

  An object of the present invention is to provide an optical attenuator having high durability and stable transmittance characteristics, and an optical attenuator module using the optical attenuator.

  The optical attenuator of the present invention is provided with a plurality of light transmission regions having different light transmittances on at least one of the front and back surfaces of a glass substrate that is transparent in the wavelength range of incident light. Includes a portion in which a fine structure formed by repetition of a concavo-convex pattern having a size causing diffraction is formed and an opening having a size in which incident light does not cause diffraction. The size of the opening is smaller than the beam diameter of the incident light.

  The light transmittance of the light transmission region constituted by the fine structure and the opening is set by the zero-order light transmittance of the fine structure and the opening ratio of the opening. The aperture ratio is the ratio of the apertures per unit area, and is specifically set by the size of the apertures and the intervals at which the apertures are arranged. Light incident on the fine structure is not absorbed by the optical attenuator element, but is emitted from the optical attenuator element as first-order diffracted light or second-order diffracted light in addition to zero-order diffracted light. In the opening, the light incident on the opening of the incident light is transmitted without being diffracted. The light transmittance of the light transmission region is defined as the ratio of the amount of outgoing light to the amount of incident light. In this case, the emitted light is the sum of the amount of 0th-order light transmitted through the fine structure and the emitted light transmitted through the opening. The fine structure can have various 0th-order light transmittances, and some of them have zero-order light transmittance.

  The pitch of the fine structure composed of the concavo-convex pattern is equal to or greater than the magnitude at which incident light diffracts. Specifically, the pitch of the fine structure is preferably in the range of 2 to 600 times the incident light wavelength. This range is determined as follows. The condition under which diffraction occurs is “pitch> incident light wavelength”. However, in a region where the pitch is equal to the incident light wavelength, the transmittance does not become zero even if the depth of the fine pattern of the fine structure is changed. FIG. 3 shows the relationship between the depth of the concavo-convex pattern having a fine structure and the transmittance of zero-order diffracted light. The incident light wavelength of the data in FIG. 3 is 1064 nm, and the filling factor (FF) is 0.5. A filling factor shows the ratio of the convex part with respect to a pitch in an uneven | corrugated pattern. For example, when the pitch is 2 μm, the transmittance of the 0th-order diffracted light is about 7% when the depth of the uneven pattern with a fine structure is 1.4 μm. In order to make the transmittance of the 0th-order diffracted light closer to 0%, the lower limit of the pitch of the fine structure needs to be at least twice the wavelength used. The upper limit of the pitch of the fine structure is not limited from the condition that diffraction occurs. However, since the diffraction angle decreases as the pitch of the fine structure increases, it becomes difficult to separate the 0th-order diffracted light (diffraction angle is 0 °) from the 1st-order diffracted light. For example, if the pitch is 100 times the incident light wavelength, the diffraction angle of the first order diffracted light is 0.57 °, if it is 500 times, it is 0.12 ° if it is 575 times, if it is 0.75, if it is 0.10 ° and 1000 times. 0.06 °. From the viewpoint of separating the 0th-order diffracted light and the 1st-order diffracted light, the upper limit of the pitch is about 600 times the incident light wavelength.

  Further, the depth of the concave portion of the fine structure is suitably 0.1% to 80% of the pitch. This range is determined as follows. According to the result of FIG. 3, for example, if the pitch is a fine structure of 2 μm, the depth of the concave portion of the fine structure is about 0 to 1.4 μm in order to change the transmittance of the 0th order diffracted light from the maximum value to the minimum value. It is necessary to change within the range. The depth of the concave portion of the fine structure at this time corresponds to 0% to 70% of the pitch. Similarly, Table 1 summarizes the relationship up to a pitch of 20 μm.

  As shown in FIG. 2, the transmittance of the 0th-order diffracted light takes a minimum value when the filling factor is 0.5. Therefore, from the results of Table 1, when the pitch is 1.5 μm, the depth of the concave portion of the microstructure is Must be 80% of the pitch. If the pitch is 20 μm, the depth of the concave portion of the fine structure is good at 6% of the pitch. If the pitch is further increased, the depth of the concave portion of the fine structure can be reduced. Since the pitch has an upper limit from a practical viewpoint, the depth of the concave portion of the fine structure cannot be reduced as much as possible, and the limit is about 0.1%.

  Since the fine structure is formed by dry etching, in the embodiment in which the fine structure having a different filling factor is formed on one glass substrate, the depth of the concave portion is shallow in a region having a large filling factor and deep in a region having a small filling factor. .

  The light transmission region includes those having only an opening without having a fine structure. In this case, the light transmittance of the light transmission region is 100%.

  Furthermore, the light transmission region includes a region having only a fine structure without an opening. In this case, the light transmittance of the 0th-order diffracted light in the light transmission region is set to a predetermined value depending on the pitch of the fine structure and the filling factor, and the light transmittance of the 0th-order diffracted light is zero.

  The light transmittance of the 0th-order diffracted light with a fine structure is set by the pitch and the filling factor. However, as will be described later, the filling factor approaches 0 or 1 when attempting to increase the transmittance. This means that the width of the convex part or concave part of the fine-concave uneven pattern becomes narrow. If the pattern width is 1 μm or less, it cannot be resolved by a conventional reduction optical exposure machine (stepper) for semiconductors in a photolithography process. Therefore, it becomes difficult to secure the light amount in the high transmittance region. Specifically, it becomes difficult to ensure a transmittance of 90% or higher for 0th-order diffracted light. As a method for solving this problem, there is an electron beam drawing (EB drawing) method, but there is a disadvantage that the drawing time becomes long and the cost becomes high.

  Therefore, in the present invention, the light transmittance is adjusted by the combination of the fine structure and the opening.

  The microstructure can be set to have a predetermined 0th-order diffracted light transmittance, but can also be set so that the 0th-order diffracted light transmittance is zero.

  The aperture ratio can be adjusted so that the opening has a predetermined light transmittance, which is particularly effective for setting the light transmittance correctly in a high transmittance region. In the present invention, some light transmission regions are constituted by a portion where a fine structure is formed and an opening having an area smaller than the beam diameter of incident light and having no pattern.

  In one embodiment of the present invention, the fine structure has a constant pitch, and the fine structures of all the light transmission regions can have the same fine structure composed of concave and convex patterns having the same pitch and filling factor. In that case, the fine structure of the light transmission region is set such that the pitch, the filling factor, and the depth of the concavo-convex pattern are set so that the light transmittance of the 0th-order diffracted light becomes substantially 0 with respect to the wavelength of the incident light. Can be.

  In this embodiment, by controlling the size and layout of the opening, diffraction is not generated in the opening. Therefore, when a synthetic quartz glass substrate having a refractive index of 1.0 is used, the light transmittance is set to 0 to 92. % Can be adjusted.

  Further, in this embodiment, the ratio of the fine structure line to the space (1: 1 when the filling factor is 0.5) remains constant, and the space width needs to be narrowed over the entire light transmission region. Therefore, the space width can be set up to the resolution limit of the stepper. That is, since the pitch can be reduced, the degree of freedom in designing the diffraction angle is increased, and it is possible to cope with a short wavelength. As a result, as an advantage at the time of manufacture, it can be manufactured using a conventional exposure apparatus, and when the 0th-order diffracted light transmittance of the fine structure is set to 0, in order to control the 0th-order light transmittance, a pattern-free portion ( It is only necessary to adjust the layout and dimensions of the openings, and this design is easy.

  In another embodiment, the fine structure has a constant pitch, the pitch of the fine structure of all the light transmission regions is equal, and the filling factor indicating the ratio of the convex portion to the pitch is different between the different light transmission regions. It can also be done. In this embodiment, the light transmittance of the light transmission region can be set by adjusting the filling factor of the fine structure, the size and layout of the opening. Also in this case, since diffraction is not generated at the opening, when a synthetic quartz glass substrate having a refractive index of 1.0 is used, the light transmittance can be adjusted in the range of 0 to 92%.

  A plurality of light transmission regions are arranged along a straight line on the surface of the glass substrate, and the aperture ratio of the opening can be set to be different for each light transmission region.

  Further, a plurality of light transmission regions are arranged along the circumferential direction on the surface of the glass substrate, and the aperture ratio of the opening can be set to be different for each light transmission region. .

  An antireflection structure having a concavo-convex structure having a pitch equal to or less than half the wavelength of incident light may be formed on the surface of the concavo-convex pattern having a fine structure and the surface of the opening.

  The optical attenuator module of the present invention includes the optical attenuator of the present invention and a moving mechanism for displacing the glass substrate so that the incident position of incident light with respect to the light transmission region moves between the light transmission regions.

  Further, by combining two or more attenuators, it is possible to obtain a light attenuation rate larger than that of one attenuator.

  When the incident light is linearly polarized light, it is preferable that a (λ / 4) wavelength plate is disposed on the light incident side of the optical attenuator module.

  In one embodiment of the optical attenuator module, a first optical branching means for branching out and extracting a part of incident light from the optical attenuator module, and a second optical element for branching out and extracting a part of outgoing light from the optical attenuator module. Capturing the detection signals of the first and second light receiving elements and the first and second light receiving elements, respectively, which receive and detect the light extracted by the light branching means, the first and second light branching means, And a moving mechanism control device for controlling a moving mechanism for displacing the glass substrate of the optical attenuator so that the level ratio of the detection signal corresponds to the set attenuation rate.

  In the optical attenuator of the present invention, the light transmittance is adjusted by the fine structure of the concavo-convex pattern formed on the surface of the glass substrate and the opening without the concavo-convex pattern. Is stable, excellent in durability, and can be manufactured at low cost because it does not use a thin film process. Furthermore, since the glass material has less wavelength dependency, it can exhibit excellent effects such as obtaining broadband characteristics with respect to the light rays used.

(A) is a schematic sectional drawing which shows the uneven | corrugated pattern of a fine structure, (B) is a schematic plan view. It is a graph which shows the relationship between the filling factor (FF) in a fine structure, and the transmittance | permeability of 0th-order diffracted light. It is a graph which shows the relationship between the depth of the uneven | corrugated pattern of a fine structure, and the transmittance | permeability of 0th-order diffracted light. It is an enlarged plan view which shows a part of one light transmissive area | region in one Example. It is a flowchart which shows the size of the opening part in one Example, and the design method of a layout. It is a graph which shows the light transmittance with respect to the size / pitch of the opening part in one Example. It is a graph which shows the relationship between the position (beam incident position) on the straight line of the Example in which a light transmittance changes along a straight line, and the light transmittance of 0th-order light. (A) is a schematic plan view of an embodiment in which the light transmittance changes along the circumferential direction, and (B) is a partially enlarged plan view thereof. It is a graph which shows the light transmittance change in one Example and a comparative example. It is a partial top view which shows the fine structure of a comparative example. It is a flowchart of the process of manufacturing one Example. It is a schematic sectional drawing of one Example. It is a block diagram which shows one Example of an optical attenuator module.

  1A and 1B schematically show a microstructure formed in the light transmission region of the optical attenuator of one embodiment. The fine structure used in the present invention has a constant pitch, but the uneven filling factor may be constant even if the light transmission region is different, and may be different if the light transmission region is different. FIG. 1 does not show a light transmission region, but shows only a fine structure and explains its function. (A) is sectional drawing along the direction where the filling factor of the uneven | corrugated shape of a fine structure is changing, (B) is a top view of the both ends.

  The glass substrate 2 is a transparent material at least in the wavelength range of incident light, and is not particularly limited. For example, quartz glass or borosilicate glass can be used. Pyrex (registered trademark) and Tempax (registered trademark) can be used as the borosilicate glass. A fine structure 4 is formed on one surface of the glass substrate 2. The fine structure 4 is composed of a repeating uneven pattern. The concavo-convex pattern is a line-and-space pattern composed of convex portions (lines) 6 and grooves (spaces) 8 extending in the direction perpendicular to the paper surface. The pitch P composed of a set of irregularities in the irregular pattern is constant. The line width of the convex portion 6 is L, and the width of the groove 8 is S. P = L + S, and L / P is a filling factor (FF). D is the depth of the groove 8.

  The uneven pattern of fine structure has a constant pitch P with respect to the horizontal direction (straight line direction) shown in the figure, and the filling factor is 0.5 at the left end and almost 1.0 at the right end. From the left to the right in the figure, the filling factor continuously changes in the range from 0.5 to almost 1.

  Incident light enters from one surface of the optical attenuator, passes through the other surface, and becomes outgoing light. The pitch P of the concavo-convex pattern is set in the range of 2 to 600 times the wavelength of the incident light. Now, for example, laser light having a wavelength of 1064 nm is used as incident light, and the pitch P is set to 20 μm. However, the pitch P is an example, and can be set as appropriate as long as the incident light is in a range where diffraction occurs. Here, an example is shown in which laser light having a wavelength of 1064 nm is used as incident light, but the same applies to incident light having other wavelengths. For example, when laser light having a wavelength of 266 nm is used as incident light, it is appropriate to set the pitch P to 5 μm.

  When incident light enters the fine structure 4, diffraction occurs, and first-order diffracted light and second-order diffracted light are generated in addition to zero-order diffracted light transmitted in the same direction as the incident light. Since each diffracted light has a different emission direction, by guiding only the 0th-order diffracted light to be incident on the object, the transmittance of the emitted light with respect to the incident light is reduced by the generation of diffracted light other than the 0th-order diffracted light. To do.

  It shows that the transmittance of the 0th-order diffracted light changes depending on the filling factor. In the example of FIG. 1, a Tempax (registered trademark) glass substrate having a thickness of 1.0 mm is used as the glass substrate 2, the pitch P of the fine structure 4 is 20 μm, and the depth d of the groove 8 is 1.2 μm. FIG. 2 shows the measurement results of the filling factor and the transmittance of the 0th-order diffracted light when circularly polarized monochromatic light having a wavelength of 1064 nm is incident as incident light in a direction perpendicular to the surface of the substrate 2. When the filling factor is 0.5, the line width L and the groove width S are equal as shown in the left end of FIG. According to this result, when the filling factor is 0.5, the diffracted light becomes first-order or higher-order diffracted light, and the transmittance of light emitted in the same direction as the incident light as zero-order diffracted light is zero. When the filling factor is smaller or larger than 0.5, the transmittance increases, and as the filling factor approaches 0 and 1, almost only the 0th-order diffracted light is present. In the example of FIG. 1, the filling factor is formed so as to change within a range from 0.5 to approximately 1. Therefore, if the incident position of the incident light is displaced from the left to the right in FIG. The transmittance can be varied in the range from 0 to nearly 100%.

  Since the groove width S decreases as the filling factor approaches 1, the method of forming the glass substrate by dry etching cannot be continuously manufactured to 0. When simultaneously forming patterns having different filling factors, the depth d of the groove varies depending on the size of the filling factor. The smaller the filling factor, the wider the groove, so that deeper grooves are formed. The larger the filling factor, the shallower the groove.

  FIG. 4 is an enlarged plan view showing a part of one light transmission region in the optical attenuator of one embodiment.

  A quartz glass substrate is used as a glass substrate which is a transparent material at least in the wavelength range of incident light, and a plurality of light transmission regions are formed on one surface thereof. FIG. 4 shows a part of one light transmission region 11. This light transmission region 11 is composed of a portion where a fine structure 12 is formed that is formed by repeating a concave and convex pattern large enough to cause the incident light to diffract, and an opening 14 large enough to prevent the incident light from diffracting. . The light transmissive region 11 includes only the fine structure 12 and only the opening portion. Here, the light transmissive region including both the fine structure 12 and the opening portion 14 will be described.

  The incident light to the optical attenuator is not particularly limited. However, an incident light with a wavelength of 1064 nm and a beam diameter of 4 mm has an incident angle with respect to the optical attenuator of 0 degree, that is, a direction perpendicular to the surface of the optical attenuator. It is assumed to be incident on

  The fine structure 4 is set so that the amount of transmitted zero-order diffracted light is not zero. Specifically, the pitch P of the concavo-convex pattern of the fine structure 4 is 20 μm, the line width of the concavo-convex pattern is 18.5 μm (filling factor is 0.925), and the height of the convex portion of the concave and convex pattern (the same as the depth of the concave portion) ) Is set to 1.2 μm. This fine structure 4 has a transmittance of 73% for zero-order diffracted light with respect to incident light having a wavelength of 1064 nm. Therefore, in this embodiment, the light transmittance of the 0th order light in the light transmitting region is determined by the 0th order diffracted light transmittance of the fine structure 4 and the aperture ratio of the opening 14.

  The size of the opening 14 is not diffracted at the wavelength of the incident light and is small with respect to the beam diameter of the incident light. As shown in FIG. 5, the size and arrangement of the openings 14 are determined so that no diffracted light is generated and the light transmittance is a desired value.

  Specifically, the following four light transmission regions were created. The size of the light transmission region is a square with a side of 6 mm.

(1) The openings 14 have a diameter of 0.4 mm and are arranged at intervals of 2 mm (P0). In this case, the 0th-order light transmittance was 81.7%.

(2) The openings 14 have a diameter of 0.4 mm and are arranged at intervals of 1.5 mm (P0). In this case, the 0th-order light transmittance was 88.5%.

(3) The openings 14 have a diameter of 0.4 mm and are arranged at 1 mm intervals (P0). In this case, the 0th-order light transmittance was 90.1%.

(4) The openings 14 have a diameter of 0.4 mm and are arranged at intervals of 0.5 mm (P0). In this case, the 0th-order light transmittance was 94%.

  In order to show that a wider light transmittance range can be set in the opening, the light transmittance is measured when the diameter (size) of the opening 14 is 0.4 mm and the arrangement interval (pitch P0) is variously changed. The results are shown in FIG. In FIG. 6, the horizontal axis represents the ratio between the interval (pitch P <b> 0) at which the openings 14 are arranged and the diameter (size).

  In this embodiment, the fine structure 4 is set so that the transmitted light amount of the zero-order diffracted light becomes zero. Specifically, the pitch P of the concavo-convex pattern of the fine structure 4 is 20 μm, the line width of the concavo-convex pattern is 10 μm (filling factor is 0.5), and the height of the convex portion of the concave / convex pattern is the same as the depth of the concave portion. It is set to be 1.2 μm. As shown in FIG. 2, the fine structure 4 has zero transmission light of zero-order diffracted light with respect to incident light having a wavelength of 1064 nm. Therefore, in this embodiment, the light transmittance of the 0th-order light in the light transmission region is determined only by the aperture ratio of the opening 14.

  The incident light of the measurement which obtained the measurement result of FIG. 6 was measured by three types with a wavelength of 1064 nm and beam diameters of 2 mm, 4 mm and 8 mm. The incident angle with respect to the optical attenuator is 0 degree. According to this result, even if the light transmittance of the 0th-order diffracted light from the fine structure portion is 0, a wide range of light transmittance from 0 to 90% can be realized by arranging the opening 14. I understand.

  Thus, the light transmission regions set so as to have different light transmittances depending on the fine structure and the opening may be arranged along a straight line on the glass substrate or may be arranged on the circumference. .

  The pitch P of the concavo-convex pattern of the fine structure 4 is 20 μm, the line width of the concavo-convex pattern is 10 μm (filling factor is 0.5), and the convex part of the concavo-convex pattern so that the transmitted light amount of the zero-order diffracted light of the fine structure 4 becomes zero In the element set so that the height (the same as the depth of the recess) is 1.2 μm, the diameter (size) of the opening 14 is set to 0.4 mm in the same manner as the measurement data of FIG. The following examples were obtained by arranging regions with different intervals (pitch P0) arranged along a straight line of the glass substrate. That is, in FIG. 6, the horizontal axis represents the ratio between the interval at which the openings 14 are arranged and the diameter, but in this embodiment, the openings 14 are arranged so that the position on the straight line of the glass substrate and the light transmittance are linear. The area | region where the ratio of the space | interval which arrange | positions and a diameter differs is arrange | positioned along the straight line of a glass substrate. In this example, the relationship between the position on the straight line of the glass substrate (beam incident position) and the light transmittance when the light transmittance of the zero-order light is measured with incident light having a wavelength of 1064 nm and a beam diameter of 4 mm is shown. 7 shows. The data in FIG. 7 corresponds to the beam diameter of 4 mm in the data in FIG. Here, the horizontal axis of FIG. 7 represents the dimension of the optical attenuator in which 11 regions having different ratios of the interval between the openings 14 and the diameter are disposed (the dimension in the straight line direction in which 11 regions are disposed). However, this dimension is arbitrary and may be longer or shorter.

  By arranging regions having different light transmittances of the 0th order light in a straight line as in this embodiment, the light attenuator is moved along the straight line with respect to the incident light, whereby the light transmittance of the 0th order light is moved. Can be changed.

  FIG. 8 shows an embodiment in which light transmission regions having different light transmittances are arranged on the circumference. A light transmission region is arranged along the circumference on one surface of the disk-shaped glass substrate 16. Reference numeral 18 schematically shows a light transmission region. The light transmission region 18 is the same as the structure shown in FIG. 4, and the portion where the fine structure 12 composed of a repetitive concavo-convex pattern in which incident light diffracts is formed, and the incident light does not diffract. The opening 14 is formed. In this embodiment, the fine structure 12 is formed so that the light transmittance of the 0th-order diffracted light becomes 0 with respect to the wavelength of incident light to be used. Such a light transmission region 18 is arranged along the circumference of the substrate 16. The 0th-order light transmittance of the light transmission region 18 is set to increase in a range of 4 to 94% with respect to 0 to 360 ° of the rotation angle of the substrate 16 depending on the size of the opening 14 and the arrangement interval. Has been.

  The relationship between the light transmittance and the rotation angle is shown as data “with opening” in FIG. 9. The beam incident position on the horizontal axis is the rotation angle of the substrate 16.

  FIG. 10 shows a comparative example in which the light transmittance of the 0th-order diffracted light is changed only by a fine structure without providing an opening. In this comparative example, the filling factor is formed to change along the circumferential direction. The fine-concave pattern is formed as a repeated pattern of protrusions 9 and grooves 10 extending in the radial direction from the center of the circle. Also in the comparative example, the pitch P of the uneven pattern with a fine structure is set uniformly along the circumferential direction, and the filling factor is formed so as to continuously change along the circumferential direction.

The manufacturing method is the same for both the example and the comparative example, and a resist pattern was formed by a photolithography process using a semiconductor reduction optical exposure machine, and the pattern was transferred to a glass substrate by dry etching.
Also in the comparative example, the filling factor is designed so that the relationship between the light transmittance and the rotation angle is the same as that in the embodiment of FIG. However, in the high transmittance region, the width of the groove of the concavo-convex pattern with a fine structure becomes narrow, and it becomes impossible to process as designed. The relationship between the light transmittance and the rotation angle of the comparative example is also shown as “no opening” in FIG. It can be seen that the high transmittance region is not processed as designed.

  As can be seen from the result of FIG. 9, a predetermined light transmittance can be realized even by a fine structure except for the high transmission region. Therefore, as another embodiment, as in the comparative example, a fine structure and an opening that can adjust the light transmittance of the 0th-order diffracted light are combined. The opening is arranged particularly in the light transmission region for the high transmission region.

  FIG. 11 schematically shows one method for producing the optical attenuator of the present invention. The microstructure and the opening are formed simultaneously. For example, a synthetic glass substrate is used as the substrate, and a photoresist layer is applied to the substrate surface. The photoresist may be either a negative type or a positive type. Here, a positive type is used as an example. The photoresist is exposed using a reduction optical exposure machine, and development and rinsing are performed to form a resist pattern. When the substrate is anisotropically dry-etched using the resist pattern as a mask, a pattern including the fine structure 12 and the opening 14 as shown in FIG. 12 is formed on the substrate.

  The optical attenuator of the present invention can also be manufactured by a nanoimprint method in which a pattern is transferred to a resin layer using a mold, and the transferred pattern is transferred again to a substrate by etching.

  The optical attenuator is preferably formed with an antireflection structure (ARS structure) on the surface of the concave-convex pattern having a fine structure and the surface of the opening. The antireflection structure is a concavo-convex structure that is finer than the concavo-convex pattern of the fine structure, and is a concavo-convex structure having a pitch of half or less of the wavelength of incident light. An example of the antireflection structure is an uneven structure having a pitch of 200 nm and a depth of 130 nm. By forming the concavo-convex structure uniformly on the surface of the convex and concave surfaces of the fine concavo-convex pattern and the surface of the opening, the light transmittance near 1064 nm can be maintained at 99%. Become.

  Such an antireflection structure is formed on the surface of the glass substrate before forming the concave / convex pattern of fine structure and the opening by a photoengraving and etching method or a nanoimprint method. After that, an uneven pattern and an opening having a fine structure are formed. However, the formation of an antireflection structure in advance does not hinder the formation of an uneven pattern and an opening having a fine structure.

  FIG. 13 schematically shows an embodiment of the optical attenuator module. In one embodiment, the optical attenuator 60 is provided with a moving mechanism 61. According to the configuration of the optical attenuator 60, the moving mechanism 61 changes the light transmittance by changing the incident position of the incident light to the optical attenuator 60 by linearly moving the optical attenuator 60, or the optical attenuator. The light transmittance is changed by changing the incident position of the incident light with respect to the optical attenuator 60 by rotating 60 around the rotation center.

  An optical splitter 66 is disposed on the optical path of the laser incident light 64 as a first optical branching means for branching out a part 68 of the laser incident light 64 incident on the optical attenuator 60 from the laser light source 62. The optical splitter 66 is provided, for example, such that a glass substrate transparent to the laser light 64 is inclined so as to reflect and extract a part of the incident light 64. In the laser light source 60, since the oscillated laser light is linearly polarized light, a (λ / 4) wavelength plate is provided to change the laser light to circularly polarized light, and the laser light 64 emitted from the laser light source 60 has circularly polarized light. .

  An optical splitter 72 is disposed on the optical path of the laser output light 70 as second optical branching means for branching and extracting a part 74 of the output light 70 that has passed through the optical attenuator 60. The optical splitter 72 is also provided, for example, such that a glass substrate transparent to the laser light 64 is inclined so as to reflect and take out a part of the outgoing light 70.

  For example, a photodiode 76 is arranged as a first light receiving element to receive and detect the light 68 extracted as part of the incident light by the optical splitter 66, and the light extracted as part of the outgoing light by the optical splitter 72. For example, a photodiode 78 is disposed as a second light receiving element to receive and detect 74.

  A moving mechanism control device 80 is provided for taking in the detection signals of the photodiodes 76 and 78 and controlling the moving mechanism 61 so that the level ratio of the detection signals corresponds to the set attenuation rate. The moving mechanism control device 80 is a computer system including a computer and an interface.

  When this optical attenuator module is applied to a laser processing apparatus, the laser beam that has passed through the optical attenuator 60 is applied to an object 82 that is a workpiece.

  Since the ratio of the light extracted by the optical splitters 66 and 72 is known in advance, the attenuation rate of the laser light by the optical splitters 66 and 72 is also known in advance. Since the attenuation rate by the optical attenuator 60 can be obtained from the level ratio of the detection signals of the photodiodes 76 and 78, the intensity of the laser light applied to the object 82 can also be obtained.

2 Glass substrate 4,12 Fine structure 6 Convex part (line)
8 groove
DESCRIPTION OF SYMBOLS 9 Protrusion part 10 Groove | channel 11 Light transmissive area | region 14 Aperture part 60 Optical attenuator 16 Laser oscillator 18 Light receiver 61 Moving mechanism 62 Laser light source 64 Laser incident light 66 Optical splitter 68 as 1st optical branching means 68 Part of laser incident light 70 Outgoing light consisting of 0th-order diffracted light 72 Optical splitter as second light branching means 74 Part of outgoing light 76 Photodiode as first light receiving element 78 Photodiode as second light receiving element 80 Moving mechanism control device

Claims (12)

An optical attenuator that attenuates incident light,
A plurality of light transmission regions having different light transmittances are provided on at least one of the front and back surfaces of a glass substrate that is transparent in the wavelength range of incident light,
The light transmissive region includes a portion formed with a fine structure formed by repetition of a concavo-convex pattern of a size that causes incident light to diffract and an opening having a size that does not cause diffraction of the incident light,
The light transmittance of the light transmission region composed of the fine structure and the opening is set by the zero-order light transmittance of the fine structure and the opening ratio of the opening. Attenuator.   2. The light according to claim 1, wherein the fine structure has a constant pitch, and the fine structures of all the light transmission regions are the same fine structure composed of a concavo-convex pattern having the same pitch and a filling factor indicating a ratio of a convex portion to the pitch. Attenuator.   The pitch, filling factor, and depth of the concavo-convex pattern are set so that the fine structure of the light transmission region has a zero-order light transmittance of substantially zero with respect to the wavelength of incident light. Light attenuator.   The pitch of the fine structure is constant, the pitches of the fine structures of all the light transmission regions are equal, and the filling factor indicating the ratio of the convex portion to the pitch is different between the different light transmission regions. The optical attenuator described.   A plurality of the light transmission regions are arranged along a straight line on the surface of the glass substrate, and the aperture ratio of the opening is set to be different for each light transmission region. The optical attenuator as described in any one of Claims.   A plurality of the light transmission regions are arranged along a circumferential direction on the surface of the glass substrate, and the aperture ratio of the opening is set to be different for each light transmission region. 5. The optical attenuator according to any one of 4 above.   The light according to any one of claims 1 to 6, wherein a concavo-convex antireflection structure having a pitch equal to or less than half the wavelength of incident light is formed on a surface of the concavo-convex pattern of the fine structure and a surface of the opening. Attenuator. An optical attenuator according to any one of claims 1 to 7,
A moving mechanism for displacing the glass substrate so that an incident position of incident light with respect to the light transmitting region moves between the light transmitting regions;
Optical attenuator module with   The optical attenuator module according to claim 8, further comprising a condenser lens for reducing a beam diameter of incident light with respect to the optical attenuator and a condenser lens for receiving 0th-order diffracted light transmitted through the optical attenuator.   The optical attenuator module according to claim 8 or 9, wherein two or more attenuators are combined to obtain an optical attenuation factor larger than that of one attenuator.   The optical attenuator module according to any one of claims 8 to 10, wherein the incident light is linearly polarized light, and a (λ / 4) wave plate is disposed on the light incident side of the optical attenuator module. First optical branching means for branching out and extracting a part of incident light of the optical attenuator module;
Second light branching means for branching and extracting a part of the emitted light of the optical attenuator module;
First and second light receiving elements that respectively receive and detect light extracted by the first and second light branching units;
A moving mechanism control device that takes in detection signals of the first and second light receiving elements and controls the moving mechanism so that a level ratio of the detection signals corresponds to a set attenuation rate;
The optical attenuator module according to any one of claims 8 to 11, further comprising: