JP2005242250A - Method and apparatus for manufacturing grating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and apparatus for manufacturing a grating that reduce the effect by reflection and have superior mass productivity in the method of manufacturing the grating by a phase masking method. <P>SOLUTION: In the method of manufacturing the grating by the phase masking method, the angle that is made by the incidence direction of the interference light, which is projected into a plane whose normal is a grating vector of the grating preformed in a phase mask, with the normal to the phase mask side is made larger than 0 degree and smaller than 60 degrees, so that the reflection light generated at the backside and surface of the phase mask can be separated from main light. Consequently, the grating is formed in a core by using the interference light consisting of only the main light, thereby reducing the effect of the reflection light and manufacturing the grating with high quality. Also, an anti-reflection film becomes unnecessary so that the apparatus for manufacturing the grating is provided which is superior in the mass productivity. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a grating manufacturing method and apparatus for forming a grating in an optical component by exposure using a phase mask, and in particular, the relationship between the incident angle of light incident on a phase mask and the width of light used for exposure. It is related with the manufacturing method of the grating which can improve the characteristic of a grating, and can form the characteristic stably, and its manufacturing apparatus.

  For example, a phase mask method is widely known as an example of manufacturing a grating as a periodic modulation structure in an optical component. The phase mask method will be briefly described with reference to FIG.

  FIG. 10A is a diagram showing an arrangement configuration of various parts for carrying out the phase mask method, and FIG. 10B is a diagram when the configuration of FIG. 10A is viewed from the A direction. is there. As shown in the figure, this configuration is a quartz-type material 101 to which a substance having photosensitivity is added in advance, and a substrate-type mask arranged in parallel with the longitudinal direction of the quartz-type material 101. The phase mask 102 has concave grooves formed on the surface at predetermined intervals, and a light source (not shown) that irradiates the quartz material 101 with the exposure beam light 103 through the phase mask 102. At this time, the concave groove surface (that is, the lattice surface 102a) of the phase mask 102 is disposed on the quartz-based material 101 side.

  In such a configuration, when the exposure beam light 103 emitted from the light source is irradiated onto the phase mask 102, the exposure beam light 103 is diffracted to a specific angle by the change of the optical phase on the grating surface 102a. A periodic intensity distribution (hereinafter referred to as an interference region 104) is generated in the vicinity of the phase mask 102 due to the interference of the ± first-order diffracted light 105 of the diffracted light. If a quartz-based material is placed in the interference region 104, a grating is written inside.

  At the time of formation, by appropriately designing the shape of the grating, it is possible to suppress the diffraction to the 0th order light and increase the intensity of the diffracted light to the ± 1st order light. Specifically, the diffraction to the 0th order light can be 1 to 3% or less, and the diffraction to the ± 1st order light can be about 35% each.

  As a typical part using this phase mask method, there is an optical part in which a periodic perturbation of refractive index change is created in the quartz-based material 101 having the above-described characteristics. The quartz material 101 can be used as an optical filter that reflects or emits a specific wavelength when a periodic perturbation is applied. In particular, when an optical fiber is used as the silica-based material 101, the silica-based material 101 is called an optical fiber grating and is widely used in the fields of optical communication and sensors.

In order to change the refractive index of the quartz-based material 101 using the phase mask method, it is necessary to change the refractive index according to the intensity of the exposure beam light 103. The property of changing the refractive index by light irradiation is called photosensitivity, and this photosensitivity varies depending on the wavelength of light to be irradiated and the substance, and usually an ultraviolet laser having a wavelength of about 250 nm is used as irradiation light. Patent Documents 1 to 8 describe a method for manufacturing a grating using the above-described manufacturing method.
JP 2000-89045 A JP-T-2001-502443 Japanese Patent Laid-Open No. 7-140311 Japanese Patent Laid-Open No. 9-265017 JP-A-10-48450 Japanese Patent Laid-Open No. 11-6923 Japanese Patent Laid-Open No. 11-6924 JP-A-11-344621

  By the way, when light is incident on the phase mask 102, light is reflected on the surface of the phase mask 102 due to a difference in refractive index. This is because reflection corresponding to the difference in refractive index, that is, Fresnel reflection, occurs due to the difference in refractive index between synthetic quartz, which is the material of the phase mask 102, and the surrounding air.

  In particular, as shown in FIG. 11, the reflection of light on the grating surface 102a is diffracted in the same manner as the transmitted light, and the diffraction efficiency of the reflected light is maximized for ± 1st order diffracted light. The ± 1st order diffracted light reflected by the grating surface 102a is reflected again by the back surface (surface on which no grating is formed) of the phase mask 102 and interferes with the ± 1st order diffracted light. That is, in the figure, ± first-order diffracted light α and reflected light β are overlapped to generate an interference region. For this reason, there is a problem that the interference pattern formed by the diffraction of ± first-order light is disturbed.

  Furthermore, if the thickness of the phase mask 102 varies for each manufacturing rod in such a state, the phase of the diffracted light due to reflection changes, so that the interference condition changes and the diffracted light intensity also varies. The fluctuation of the thickness of the phase mask usually leads to a problem that uniform interference fringes cannot be obtained from light having wavelengths of 248 nm and 244 nm used as exposure beam light.

  In order to solve such a problem, a method of providing an antireflection film 111 on the back surface of the phase mask 102 as shown in FIG. 12 has been proposed. The antireflection film 111 is formed by a method of forming a dielectric film on a substrate and has a characteristic of suppressing reflection at a specific wavelength. Usually, dielectrics having different refractive indexes are formed in multiple layers. Due to the presence of the antireflection film 111, it is possible to reduce the reflection on the back surface of the substrate, which is usually about 4%, to 0.5% or less, and ± 1st order light reflected on the phase mask diffraction surface is reflected on the back surface of the mask Without passing through. For this reason, interference with reflected light as seen in FIG. 11 can be suppressed.

  However, this antireflection film 111 has the following problems. In order to fabricate the grating, the light incident on the phase mask 102 normally uses ultraviolet light around 240 nm, but when this ultraviolet light is incident on the antireflection film 111 for a long time or with high intensity, the characteristics of the antireflection film 111 change. As a result, the reflection suppressing function is lowered. For this reason, when the grating is mass-produced using the same phase mask, there is a problem that the grating characteristic is deteriorated due to the deterioration of the antireflection film 111, and as a result, a low-quality optical component may be produced. Further, when the antireflection film 111 is deteriorated, there is a problem that the reflected light cannot be sufficiently removed and interference fringes with high definition cannot be obtained.

  In order to prevent this, it is necessary to remove the existing antireflection film 111 and attach a new antireflection film before the antireflection film 111 deteriorates, but this hinders mass production.

  Furthermore, since the phase mask 102 is gradually contaminated by use in the manufacturing process, it needs to be cleaned periodically. Usually, chemical cleaning is performed using a solution of acid or alkali. However, since the antireflection film 111 deteriorates even in this chemical cleaning, it is necessary to reattach the antireflection film 111 every time cleaning is performed.

  The present invention has been made in view of the above problems, and its purpose is to reduce the influence of reflection by a method that does not use an antireflection film in a grating manufacturing method using a phase mask method, and to provide an excellent mass productivity. It is in providing a manufacturing method and its manufacturing apparatus.

  According to the first aspect of the present invention, a quartz material including at least a core to which an additive having photosensitivity to ultraviolet light is added and a clad covering the core is disposed, and is parallel to the arrangement direction of the quartz material. A plate-like phase mask is arranged so that the interference light that emits monochromatic light in the ultraviolet region is irradiated through the phase mask, and a grating that periodically changes the refractive index is produced in the core. The angle between the incident direction of the interference light projected in the plane having the grating vector of the grating formed in advance on the phase mask as a normal and the normal to the phase mask surface is 0 degree. The gist is that it is larger than 60 degrees.

According to a second aspect of the present invention, in the method for manufacturing a grating according to the first aspect, the thickness t of the phase mask and a half of the phase light perpendicular to the phase mask grating vector of the interference light incident on the phase mask. The relationship between the value width w and the angle θ formed between the incident direction of the interference light projected in the plane having the normal to the grating vector of the phase mask and the normal to the phase mask surface satisfies the following equation:

And the gist is that it is smaller than 60 degrees.

  According to a third aspect of the present invention, in the method for manufacturing a grating according to the first or second aspect, the interference light is moved along the core region of the quartz-based material while maintaining the incident angle of the interference light. This is the gist.

  The gist of the present invention described in claim 4 is the method for producing a grating according to any one of claims 1 to 3, wherein the quartz material is an optical fiber.

  According to a fifth aspect of the present invention, there is provided a quartz-based material including at least a core to which an additive having photosensitivity to ultraviolet light is added and a clad covering the core, and is disposed in parallel with an arrangement direction of the quartz-based material. A grating manufacturing apparatus comprising at least a plate-shaped phase mask and a light source for irradiating the quartz-based material with interference light through the phase mask, wherein the grating is formed in advance on the phase mask The light source is arranged so that an angle formed between an incident direction of interference light projected in a plane having a vector as a normal line and a normal line to the phase mask surface is larger than 0 degree and smaller than 60 degrees. Is the gist.

According to a sixth aspect of the present invention, in the grating manufacturing apparatus according to the fifth aspect, the thickness t of the phase mask and a half of the phase light perpendicular to the phase vector of the interference mask incident on the phase mask. The relationship between the value width w and the angle θ formed between the incident direction of the interference light projected in the plane having the normal to the grating vector of the phase mask and the normal to the phase mask surface satisfies the following equation:

And the gist is that it is smaller than 60 degrees.

  According to a seventh aspect of the present invention, in the grating manufacturing apparatus according to the fifth or sixth aspect, the interference light is moved along the core region of the quartz-based material while maintaining the incident angle of the interference light. The gist is to have moving means.

  The gist of the present invention according to claim 8 is the grating manufacturing apparatus according to claims 5 to 7, wherein the quartz-based material is an optical fiber.

  According to the present invention, in the grating manufacturing method by the phase mask method, the incident direction of the interference light projected in the plane having the grating vector of the grating formed in advance on the phase mask as the normal line, and the method for the phase mask surface By making the angle formed with the line larger than 0 degrees and smaller than 60 degrees, the reflected light generated on the back and front surfaces of the phase mask can be separated from the main light. Thereby, since the grating can be formed in the core using the interference light consisting only of the main light, the influence of the reflected light can be reduced and a high quality grating can be manufactured. Moreover, since an antireflection film is not required, a grating manufacturing apparatus excellent in mass productivity can be provided. Also, a grating longer than the width of the interference light can be produced by relatively moving the interference light and the phase mask while maintaining the incident angle of the interference light.

  The present invention provides a grating manufacturing method that solves instability during grating fabrication due to reflection on the back surface of the phase mask by appropriately setting the thickness of the phase mask, the beam width of incident light, and the incident angle of interference light, and It is the manufacturing apparatus.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  First, the basic configuration for fabricating a grating is almost as shown in FIG. A side view when the exposure beam light 103 is incident on the phase mask 102 is as shown in FIG. That is, since the exposure beam 103 is normally incident on the surface of the phase mask 102, as shown in FIG. 10B, the quartz material 101, the phase mask 102, and the exposure beam 103 used for exposure are used. Is the arrangement relationship shown in FIG.

  In such an arrangement, the intensity change is caused by multiple reflection occurring on both surfaces of the phase mask 102 as described above.

  Here, the present inventor has found that the influence on the exposure due to multiple reflection can be reduced by causing the exposure beam light 103 to enter the phase mask 102 obliquely. This is shown in the oblique incidence in FIG. FIG. 13 is an optical path diagram when the exposure beam 103 is incident obliquely. As shown in the figure, the light β reflected by the front and back surfaces of the phase mask 102 is shifted from the optical path of so-called non-reflected light (main light α) used mainly at the time of exposure.

  Therefore, the intensity modulation of the light due to the interference between the light β reflected from the back surface and the front surface of the phase mask 102 and the main light α is also reduced. As a result, the reflected light β is excluded from the exposure beam light 103 and only the main light α is obtained. Can do.

  Therefore, if the incident beam angle is equal to or larger than the angle at which the exposure light beam 103 that is not reflected and the reflected light that is reflected once on the front and back surfaces of the phase mask 102 do not overlap, the influence of interference by the reflected light is reduced. Can be eliminated.

  Here, it demonstrates more concretely with reference to Fig.1 (a). As shown in the figure, the grating device has a quartz material 101 including at least a core to which an additive having photosensitivity to ultraviolet light is added in advance, and a clad covering the core, and a quartz material 101. A plate-like phase mask 102 arranged in parallel with the arrangement direction of the light source and a light source that emits interference light that changes the refractive index of the core, and is arranged so as to enter the quartz-based material 101 via the phase mask 102. And at least a light source (not shown).

  Here, one of the features of the present invention is that the incident direction of the interference light in which the exposure light beam 103 emitted from the light source is projected in a plane normal to the grating vector of the grating surface 102a formed in advance on the phase mask 102. And an angle formed by the normal to the phase mask surface is set to be within a range larger than 0 degree and smaller than 60 degrees.

  Here, the “phase mask grating vector” indicates a direction in which a plurality of concave grooves carved on the surface of the phase mask 102 changes. Therefore, “in the plane with the normal of the lattice vector of the phase mask” means a two-dimensional plane perpendicular to the direction of the lattice vector. Further, the “incident direction of the exposure beam light projected in the plane with the normal of the grating vector of the phase mask” is the incident direction of the exposure beam light 103 incident obliquely with respect to the phase mask 102, Specifically, it indicates the direction projected on the two-dimensional plane.

  In other words, referring to FIG. 1 (a), it indicates an angle in a two-dimensional plane represented by the X axis and the Y axis, where the X axis is 0 degrees and the Y axis is 90 degrees. The incident angle θ is assumed to be within the range of 0 to 60 degrees.

In such a configuration, the light incident on the phase mask 102 having the thickness t and the refractive index n at the incident angle θ changes from the traveling direction due to refraction and is emitted from a point separated from the incident position by the distance d. Here, as described above, the incident angle θ is defined as an angle formed between the incident direction of the exposure beam light projected on the plane having the grating mask vector of the phase mask as a normal and the normal to the phase mask surface. Further, at this time, the interval between the reflection positions when incident light (also referred to as exposure beam light) is reflected by the surface of the phase mask 102, that is, the distance d can be expressed by Expression (1).

If the exposure beam light width viewed from the side surface of the phase mask 102 is equal to or smaller than the value of Expression (1), the reflected light can be exposed without overlapping the main light as shown in FIG. It becomes.

  That is, when Expression (2) is satisfied, the exposure light beams do not overlap each other, and stable exposure characteristics can be realized.

  However, when the incident angle to the phase mask is 60 degrees or more, reflection on the back surface of the phase mask increases rapidly, and therefore an incident angle of 60 degrees or more is not desirable. This is shown in FIG.

  FIG. 2 shows the measured laser power that is transmitted when the second harmonic (ArSHG laser) of an argon ion laser is incident on a synthetic quartz substrate and the incident angle is changed by rotating the quartz substrate.

  The polarization direction of the laser is a direction perpendicular to the rotation axis of the quartz substrate, and the data is normalized by the power at an incident angle of 60 degrees. According to this result, it was confirmed that when the incident angle exceeds 60 degrees, the transmittance rapidly deteriorates (that is, the reflection on the quartz substrate increases rapidly).

  Therefore, if the incident angle is set to 60 degrees or more, the laser power passing through the phase mask is reduced. Therefore, the incident angle θ is preferably set to 60 degrees or less.

  Further, as a method of making the exposure beam light incident at a predetermined angle on the phase mask 102, there are methods shown in FIGS. Here, considering the adjustment of the optical system and the design of the exposure apparatus, it is desirable that either the phase mask or the exposure beam light is parallel or perpendicular to a reference surface such as a surface plate.

  By doing so, the positional relationship with other jigs can be accurately determined. Considering these, one of the methods of exposing the phase mask 102 at an angle is to maintain the exposure beam 103 parallel or perpendicular to the reference surface such as the surface plate 113 as shown in FIGS. In this state, the angle of the phase mask 102 is changed.

  In the case of this method, there is an advantage that various angles can be accommodated by attaching a goniometer stage or a rotary stage to a jig for fixing the phase mask 102. At that time, it is desirable that a scale indicating the angle is attached to the gonio stage or the rotary stage because it can be easily adjusted to a desired angle.

  On the other hand, as shown in FIG. 4 or FIG. 6, there is a method in which the exposure beam light 103 is incident obliquely while maintaining the phase mask 102 perpendicular or parallel to a reference surface such as a surface plate 113.

  This method has the advantage that it is not necessary to move the phase mask 102. In other words, since the method of fixing the phase mask 102 is very important in grating fabrication, a structure that can fix the phase mask by the same method as the conventional exposure method is advantageous.

  Next, Embodiment 1 according to the present invention will be described with reference to FIGS.

  First, an experiment was conducted to confirm how the intensity of light diffracted by the phase mask 102 changes when the incident angle of the exposure beam light is changed.

  A second harmonic (ArSHG: wavelength 244 nm) of an argon ion laser is incident on a phase mask 102 made of synthetic quartz having a thickness of 2.3 mm, and the exposure beam 103 is moved in the direction of the lattice vector of the phase mask 102. The intensity of ± first-order diffracted light 105 was measured. The center period of the phase mask 102 is 1070 nm. The beam diameter when the exposure beam light is incident on the phase mask is 2.3 mm in the grating vector direction and 0.25 mm in the direction perpendicular to the grating vector.

  However, the beam diameter here refers to the full width at half maximum of each axis of the exposure beam light intensity. When the incident angle to the phase mask 102 is changed from 0 degree to 6.5 degrees, the intensity of the first-order diffracted light 105 at each angle is measured as a result of measuring the position of the phase mask 102 in the grating vector direction. Is shown in FIG.

  When the incident angle is 0 degree, it can be confirmed that a periodic intensity change occurs in the longitudinal direction of the phase mask due to interference by reflected light on the front and back surfaces of the phase mask. It was also confirmed that the amplitude of the intensity modulation became smaller as the incident angle was increased.

  This is shown in FIG. FIG. 8 is a plot in which the horizontal axis represents the incident angle and the vertical axis represents the intensity modulation component of the first-order diffracted light illustrated in FIG. However, the magnitude of the amplitude is normalized by the value when the incident angle is 0 degree. In addition, the straight line in FIG. 8 is obtained by calculating the degree of overlap between incident light that is reflected once on the front and back surfaces of the phase mask and incident light that is not reflected when the incident angle is changed. It is. It was confirmed that an intensity change due to multiple reflections on the front and back surfaces of the phase mask can be suppressed by appropriately setting the incident angle of light incident on the phase mask.

  Next, Embodiment 2 according to the present invention will be described with reference to FIGS.

  The result of actually producing a fiber grating based on the result of Example 1 is shown. FIGS. 9A to 9C show the results of measuring the transmission characteristics of fiber gratings manufactured by changing the incident angle to 0 degrees, 3.9 degrees, and 6.5 degrees, respectively.

  The conditions other than the incident angle are all the same as in Example 1, and the single mode fiber that was left in a high-pressure hydrogen atmosphere at 55 degrees and 10 [MPa] for 5 days to increase the photosensitivity was used in Example 1. This is a result of producing a 50 mm grating using the same phase mask (substrate thickness 2.3 mm, center period 1070 nm, chirp rate 0.14 nm / cm).

  When the incident angle is 0 degree, it can be confirmed that the periodic fluctuation of the diffraction intensity observed in Example 1 also affects the transmission spectrum. In addition, it was confirmed that when the incident angle was set to 6.5 degrees, no periodic fluctuation was observed in the transmission spectrum, and the manufactured grating characteristics could be improved by appropriately adjusting the incident angle of the exposure beam light. .

It is the schematic which shows the structure of the grating manufacturing apparatus which concerns on embodiment of this invention. It is a graph which shows the experimental result which measured the transmittance | permeability with respect to an incident angle. It is the schematic which shows one structural example of the grating manufacturing apparatus which concerns on embodiment of this invention. It is the schematic which shows the other structural example of the grating manufacturing apparatus which concerns on embodiment of this invention. It is the schematic which shows the further another structural example of the grating manufacturing apparatus which concerns on embodiment of this invention. It is the schematic which shows the other structural example of the grating manufacturing apparatus which concerns on embodiment of this invention. It is a graph which shows the result of having measured the change by the position to the grating vector direction of the phase mask 102 about the intensity | strength of the 1st-order diffracted light 105 with respect to an incident angle. It is the graph which showed the intensity | strength modulation component of the 1st-order diffracted light with respect to an incident angle. It is a graph which shows the result of having measured the transmission characteristic of the fiber grating at the time of changing an incident angle. It is the schematic which shows the structure of the manufacturing apparatus of the conventional grating. It is the figure which modeled the optical path when multiple reflection arises with the phase mask in the manufacturing apparatus of the conventional grating. It is the figure which modeled the optical path of the reflected light at the time of providing the antireflection film in one surface of the phase mask in the manufacturing apparatus of the conventional grating. It is the figure which modeled the optical path of the interference light at the time of making incident beam light incline with respect to a phase mask surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Optical component 102 ... Phase mask 102a ... Concave groove surface 103 ... Light (exposure beam light)
104 ... Interference region 105 ... ± 1st order diffracted light 111 ... Antireflection film 113 ... Surface plate

Claims (8)

Placing a quartz-based material including at least a core to which an additive having photosensitivity to ultraviolet light and a clad covering the core are arranged, and a plate-like phase mask so as to be parallel to the arrangement direction of the quartz-based material , And irradiating interference light that emits monochromatic light in the ultraviolet region through the phase mask, and forming a refractive index that periodically varies in the core,
The angle formed by the incident direction of the interference light projected in the plane having the grating vector of the grating formed in advance on the phase mask as a normal and the normal to the phase mask surface is larger than 0 degree and 60 degrees. A method for producing a grating, characterized in that it is smaller. The phase mask thickness t, the half-value width w perpendicular to the phase mask grating vector of the interference light incident on the phase mask, and a plane normal to the phase mask grating vector are projected. The relationship between the incident direction of the interference light and the angle θ formed by the normal to the phase mask surface satisfies the following equation:

The method for manufacturing a grating according to claim 1, wherein the angle is smaller than 60 degrees.   3. The method of manufacturing a grating according to claim 1, wherein the interference light is moved along the core region of the quartz-based material while maintaining the incident angle of the interference light.   4. The method of manufacturing a grating according to claim 1, wherein the quartz material is an optical fiber. A quartz-based material including at least a core to which an additive having photosensitivity to ultraviolet light is added and a clad covering the core, and a plate-like phase mask disposed in parallel with the direction in which the quartz-based material is disposed; A grating manufacturing apparatus comprising at least a light source that irradiates the quartz-based material with interference light through the phase mask,
The angle formed by the incident direction of the interference light projected in the plane having the grating vector of the grating formed in advance on the phase mask as a normal and the normal to the phase mask surface is larger than 0 degree and 60 degrees. An apparatus for manufacturing a grating, wherein the light source is arranged so as to be smaller. The phase mask thickness t, the half-value width w perpendicular to the phase mask grating vector of the interference light incident on the phase mask, and a plane normal to the phase mask grating vector are projected. The relationship between the incident direction of the interference light and the angle θ formed by the normal to the phase mask surface satisfies the following equation:

6. The grating manufacturing apparatus according to claim 5, wherein the angle is less than 60 degrees.   The grating manufacturing apparatus according to claim 5, further comprising a moving unit that moves the interference light along a core region of the quartz-based material while maintaining an incident angle of the interference light. The grating manufacturing apparatus according to claim 5, wherein the quartz material is an optical fiber.

Images