JP2016186953A - Fixing method of double-clad fiber, double-clad fiber fixing structure fixed to fiber holding member, laser device including double-clad fiber fixing structure, exposure device and inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide means capable of suppressing local overheating at a part of a double-clad fiber, where a small scratch or peeling is occurring in the second clad.SOLUTION: A double-clad fiber fixing structure A consists of a double-clad fiber 230, a fiber holding member 250 to which the double-clad fiber is fixed, and an adhesive 260 for bonding the double-clad fiber 230 to the fiber holding member 250. The adhesive 260 has a refractive index nafter hardening that is substantially equal to or larger than the refractive index nof a second clad 233, and smaller than the refractive index nof a first clad, and the double-clad fiber 230 is fixed to the fiber holding member 250 while covering the outer periphery of the second clad 233 with the adhesive 260.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a method for fixing a double clad fiber. The present invention also relates to a double-clad fiber fixing structure in which a double-clad fiber is fixed to a fiber holding member, a laser apparatus, an exposure apparatus, and an inspection apparatus provided with the double-clad fiber fixing structure.

  A laser apparatus provided with an optical fiber for amplification is used as a light source for an exposure apparatus or an inspection apparatus, for example. In such a laser device, the fiber amplifier generally amplifies seed light having a wavelength λ = 1.0 to 1.55 μm, and outputs the amplified light amplified to a predetermined output to the wavelength conversion unit. The wavelength conversion unit is configured to convert the wavelength of the input amplified light by a wavelength conversion optical element and output output light having a wavelength λ = 193 nm or λ = 355 nm, for example (for example, Patent Document 1, Patent Reference 2).

  In recent years, there has been a demand for higher output light due to the expansion of the application range of laser processing and demands for improvement in productivity, etc. With this, the amplified light output from the fiber amplifier is also required to have higher output. Yes. In a high-power laser apparatus with an amplified light output of several tens to several hundreds W class, a plurality of fiber amplifiers are generally connected in series, and a double-clad fiber having two clads is used for the subsequent fiber amplifier. . In a fiber amplifier using a double clad fiber, multimode excitation light emitted from a high-power semiconductor laser is supplied to the first clad. The excitation light supplied to the first clad propagates through the first clad toward the emission end, and excites the laser medium doped in the core in the process of propagating.

  In such a fiber amplifier using a double-clad fiber, the pumping light supplied to the first cladding and the amplified light that is amplified and emitted are high-energy laser light. Double clad fiber generates heat. As a means of preventing problems associated with the heat generation of this double clad fiber, a configuration in which the double clad fiber is fixed to a fiber holding member having a heat dissipation or cooling structure to suppress overheating of the double clad fiber is examined. Has been.

JP 2000-200747 A Japanese Patent Laid-Open No. 2002-50815

  An adhesive can be considered as one of means for fixing the double clad fiber to the fiber holding member. As is well known, there are many products of various types (for example, epoxy-based, acrylic-based, silicone-based, etc.) depending on the material and application of the object to be bonded. For example, for applications where the heating element is bonded and fixed to a fiber holding member having a cooling structure as described above, for example, high heat with increased thermal conductivity by dispersing metal fine particles etc. in the resin as the base material There is a conductive adhesive.

  On the other hand, there is an adhesive prepared so that the refractive index after curing is substantially the same as the refractive index of the core for an application where an optical fiber is fixed and an optical path is coupled in an optical connector or the like. For applications that remove stray light propagating through the cladding, high refractive index adhesives having a higher refractive index after curing than the refractive index of the cladding are also on the market.

  From the viewpoint of suppressing overheating of the double clad fiber, it is considered preferable to use an adhesive having a high thermal conductivity as a fixing means for the double clad fiber. However, when a double-clad fiber is fixed using such an adhesive, a problem based on the following factors arises. The first factor is a minute scratch or peeling that occurs on the outer periphery of the second cladding. That is, it is difficult to maintain a completely intact state throughout the fiber processing and assembly processes, and minute scratches and peeling may occur on the outer periphery of the second cladding. The second factor is that adhesives with high thermal conductivity are not necessarily clear in terms of optical properties such as transmittance and refractive index, but in general, the refractive index after curing is higher than the refractive index of the core or cladding. And the variation is large.

  A problem that occurs based on such factors is local overheating of the second cladding. FIG. 9 is a schematic cross-sectional view in the axial direction of a double clad fiber 230 whose outer periphery is fixed by being covered with an adhesive 290 having a high thermal conductivity. The double clad fiber 230 includes a core 231 doped with a laser medium, a first clad 232 that covers the outer circumference of the core 231, and a second clad 233 that covers the outer circumference of the first clad.

Here, the refractive index of the core 231 in the double clad fiber 230 is n ₀ , the refractive index of the first cladding 232 is n ₁ , and the refractive index of the second cladding 233 is n ₂ . At this time, the relationship between the refractive indexes of the respective parts is n ₀ > n ₁ > n ₂ . Further, assuming that the refractive index after curing of the adhesive 290 is n ₉ , n ₉ > n ₁ .

In the double clad fiber fixing structure having such a refractive index, the laser light (excitation light) incident on the first clad 232 propagates as indicated by the solid line arrow in the figure. That is, in the region where the second cladding 233 does not peel, the refractive index n ₁ of the first cladding 232 is higher than the refractive index n ₂ of the second cladding 233 (n ₁ > n ₂ ). The propagating laser light is totally reflected at the interface between the first cladding 232 and the second cladding 233 and is confined in the first cladding 232.

However, in the portion (peeling portion) 233 a where the second cladding 233 is peeled off, the outer periphery of the first cladding 232 is covered with the adhesive 290, and the refractive index n ₉ of the adhesive 290 is the refractive index of the first cladding 232. It is higher than n ₁ (n ₉ > n ₁ ). Therefore, the laser light that has propagated through the first clad and entered the peeling portion 233 a is not totally reflected at the interface between the first clad 232 and the adhesive 290 and leaks from the first clad 232 to the adhesive 290 side. The leaked excitation light is incident on a fracture surface or a mark of the second clad 233 generated by the peeling and becomes a bright spot, causing a problem of local overheating such as partial melting. Even if local overheating does not occur, leakage of excitation light is a loss and causes a decrease in excitation efficiency.

In addition, due to leakage from the fiber fusion point, leakage from a bent portion having a small radius of curvature, or the like, laser light in a mode that propagates through the second cladding may be generated as indicated by the two-dot chain line arrow in the figure. is there. The outer periphery of the second clad 233 including the minute scratches 233b and the peeling portion 233a is covered with an adhesive 290 having a higher refractive index than that of the second clad (n ₉ > n ₂ ). Therefore, the laser light propagating through the second clad 233 and entering the scratch 233b or the peeling portion 233a leaks to the adhesive 290 side without being totally reflected at the interface between the second clad 233 and the adhesive 290. A part of the laser light leaked to the adhesive side may re-enter the flaws 233b and the edges of the second clad, which may cause a problem of local overheating.

  The present invention has been made in view of such circumstances, and a method for fixing a double-clad fiber capable of suppressing local overheating even if a minute scratch or peeling occurs in the second cladding. The purpose is to provide. It is another object of the present invention to provide a double-clad fiber fixing structure in which local overheating is suppressed, a laser device with improved long-term stability by including such a double-clad fiber fixing structure.

A first aspect exemplifying the present invention is a double having a core doped with a laser medium, a first cladding that covers the outer periphery of the core and into which excitation light is introduced, and a second cladding that covers the outer periphery of the first cladding. This is a double clad fiber fixing method for fixing a clad fiber to a fiber holding member. This fixing method uses an adhesive having a refractive index n ₆ after curing substantially equal to or higher than the refractive index n ₂ of the second cladding and smaller than the refractive index n ₁ of the first cladding, and is disposed on the fiber holding member. An adhesive is applied to the double clad fiber so as to cover the outer periphery of the second clad and cured, and the double clad fiber is fixed to the fiber holding member. Incidentally, the adhesive has a refractive index n ₆ after curing can be used as the substantially identical to the refractive index n ₂ of the second cladding.

  Here, in the present specification, the refractive index “substantially the same” means that the refractive index includes a certain width that may occur at the time of preparation or construction of the adhesive, with the refractive index being completely the same. . In addition, “applying” an adhesive means that a liquid or gel adhesive is adhered so as to cover the outer periphery of the fiber, and is not limited to a mode in which the adhesive is applied with a brush or a spatula. As appropriate, it includes a mode in which an adhesive is dropped, injected, or filled using a syringe, a dispenser, or the like.

A second aspect illustrating the present invention is a double clad fiber fixing structure. The structure includes a core doped with a laser medium, a first clad that covers the outer periphery of the core and into which excitation light is introduced, and a second clad fiber that has a second cladding that covers the outer periphery of the first cladding, and a double-clad fiber. A fiber holding member to be fixed; and an adhesive for bonding the double clad fiber to the fiber holding member. Here, the refractive index n ₆ after curing the adhesive less than the refractive index n ₁ of the and and first cladding second cladding refractive index n ₂ is substantially the same or more, the double-clad fiber, the second cladding The outer periphery is fixed to the fiber holding member in a state covered with an adhesive. The adhesive may have a cured refractive index n ₆ that is substantially the same as the refractive index n ₂ of the second cladding.

  The fiber holding member can have a cooling function for cooling the double clad fiber. In addition, a holding groove for holding the double clad fiber may be formed in the fiber holding member, and the adhesive may be disposed so as to cover the double clad fiber arranged in the holding groove. Further, the holding groove may be formed in a concave groove shape whose groove width is somewhat larger than the diameter of the double clad fiber, and the double clad fiber may be configured to be embedded and fixed in the holding groove with an adhesive. it can.

  A third aspect illustrating the present invention is a laser device. This laser device supplies the excitation light to the double clad fiber fixing structure as described above, a laser light generator for generating laser light amplified in the core of the double clad fiber, and the first clad of the double clad fiber. And an excitation light source. The laser device can also be configured to include a wavelength conversion unit that converts the wavelength of the amplified light that is amplified by the double clad fiber and exits.

  A fourth aspect illustrating the present invention is an exposure apparatus. The exposure apparatus includes a laser device including the wavelength conversion unit, a mask support unit that holds a photomask on which a predetermined exposure pattern is formed, an exposure object support unit that holds an exposure object, and a laser device. An illumination optical system that irradiates the photomask held by the mask support with the output laser light, and a projection optical system that projects the light transmitted through the photomask onto the exposure target held by the exposure target support It is prepared for.

  A fifth aspect illustrating the present invention is an inspection apparatus. This inspection apparatus includes a laser device including the wavelength conversion unit, a test object support unit that holds a test object, and a test object that holds laser light output from the laser device on the test object support unit And an illumination optical system that irradiates the light and a projection optical system that projects light from the test object onto the detector.

In the fixing method of the double clad fiber of the first aspect, an adhesive whose refractive index n ₆ after curing is substantially equal to or larger than the refractive index n ₂ of the second cladding and smaller than the refractive index n ₁ of the first cladding is used. The double clad fiber is fixed to the fiber holding member by applying an adhesive to the double clad fiber disposed on the fiber holding member so as to cover the outer periphery of the second clad and curing it.

In the double clad fiber fixed structure according to the second aspect, the double clad fiber has a refractive index n ₆ after curing substantially equal to or greater than the refractive index n ₂ of the second clad and the refractive index n ₁ of the first clad. The outer periphery of the second cladding is fixed to the fiber holding member with a small adhesive.

FIG. 10 shows a schematic cross-sectional view in the axial direction of a double-clad fiber 230 similar to FIG. 9 for the double-clad fiber bonded and fixed in this manner. In the embodiment of the present invention shown in FIG. 10, the outer periphery of the double clad fiber 230 including the peeling portion 233a and the minute scratch 233b is covered with an adhesive 260 having a refractive index n ₆ .

First, consider a case where laser light (excitation light) propagating through the first cladding is incident on the peeling portion 233a of the second cladding. At this time, the refractive index n ₁ of the first cladding 232, the refractive index n ₂ of the second cladding 233, the relationship of the refractive index n ₆ of the adhesive 260 is n _1> n ₆ ≧ n _2. Therefore, the laser light that has propagated through the first clad 232 and entered the peeling portion 233a is totally reflected at the interface between the first clad 232 and the adhesive 260, as shown by the solid arrow in the figure, and has no peeling. It propagates in the first cladding through the same optical path as in the above state. When the refractive index of the adhesive 260 is substantially the same as the refractive index of the second cladding (n ₆ ≈n ₂ ), the refractive index configuration around the peeled portion is the same as that of the intact portion, and the peeling is optically repaired. Will be.

Next, consider laser light propagating through the second cladding. Here, the relationship between the refractive indexes of the respective portions is n ₁ > n ₆ ≧ n _{2 as} described above. That is, the refractive index difference between the second clad 233 and the adhesive 260 is smaller than the conventional (n ₉ > n ₁ > n ₂ ). This means that the laser beam in the mode propagating through the second cladding 233 easily escapes to the surrounding adhesive 260 layer. If the laser beam easily escapes to the adhesive layer, the laser beam propagating through the second clad 233 is difficult to propagate to the scratch 233b (or the power of the propagating laser beam is reduced), so that the laser emitted from the scratch 233b portion. The light power is reduced. In particular, when the refractive index of the adhesive 260 is substantially the same as the refractive index of the second clad (n ₆ ≈n ₂ ), there is no difference in the refractive index between the second clad 233 and the adhesive 260 covering the periphery of the second clad 233. Thus, the interface is no longer present, and the laser light propagating through the second cladding 233 is dissipated to the adhesive layer. Furthermore, even if the laser beam dissipated around the wound is incident, there is no difference in refractive index from the surroundings, so that the laser beam is transmitted as it is and local overheating does not occur.

  Therefore, according to the fixing method of the double clad fiber and the double clad fiber fixing structure according to the aspect of the present invention, even if a minute scratch or peeling is generated in the second clad, the local area of these parts is not affected. Overheating can be suppressed.

  The laser device according to the third aspect includes the double-clad fiber fixing structure according to the second aspect. Further, the exposure apparatus of the fourth aspect and the inspection apparatus of the fifth aspect are configured to include the laser apparatus of the third aspect. Therefore, it is possible to provide a laser apparatus, an exposure apparatus, and an inspection apparatus with high long-term stability in which local overheating due to scratches or peeling of the double clad fiber is suppressed.

It is a schematic block diagram of the laser apparatus shown as an example of application of this invention. It is a schematic block diagram which mainly shows the fiber amplifier of the double clad structure in the said laser apparatus. It is sectional drawing along the axis line of a double clad fiber. It is a typical external view of a double clad fiber fixed structure. It is sectional drawing of the VV arrow added in FIG. It is sectional drawing of the double clad fiber fixed structure along the axis line of a double clad fiber. It is a schematic block diagram of the exposure apparatus shown as a 1st application example of the system provided with the laser apparatus. It is a schematic block diagram of the test | inspection apparatus shown as the 2nd application example of the system provided with the laser apparatus. It is explanatory drawing (sectional drawing along the axis line of a double clad fiber) for demonstrating the behavior of the laser beam which propagates the double clad fiber fixed with the conventional fixing method. It is explanatory drawing (sectional drawing along the axis line of a double clad fiber) for demonstrating the behavior of the laser beam which propagates the double clad fiber fixed with the fixing method of the aspect of this invention.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. A schematic configuration of the entire laser apparatus LS to which the present invention is applied is shown in FIG. The illustrated laser device LS includes a light source unit 10 that emits seed light, an amplification unit 20 that amplifies seed light emitted from the light source unit 10 and outputs amplified light, and amplified light output from the amplification unit 20. A wavelength conversion unit 30 that performs wavelength conversion and outputs output light, and a control unit 40 that controls the operation of each unit are configured.

  The wavelength, optical waveform, power, and the like of the seed light and output light can be appropriately set according to the use and function of the apparatus configured using the laser apparatus LS. In the present embodiment, the seed light Ls emitted from the light source unit 10 having a wavelength λ = 1064 nm and power of several mW level is amplified by the amplification unit 20 to several tens to several hundreds W level, and the amplified seed light, that is, amplified A case where the light La is converted into output light Lv having a wavelength of 355 nm by the wavelength conversion unit 30 and output is illustrated.

  The light source unit 10 is mainly configured by a laser light source 11 that generates laser light having a wavelength λ = 1064 nm. As the laser light source 11, for example, a DFB (Distributed Feedback) semiconductor laser can be used. The DFB semiconductor laser can perform CW oscillation and pulse oscillation, and can output laser light having a single wavelength narrowed in a predetermined wavelength range by temperature control. A light source unit 10 shown in FIG. 1 outputs pulse light (or CW light) having a sufficiently long ON time from a laser light source 11, and a part of the light is emitted from an electro-optic modulation element (EOM), an acousto-optic modulation element (AOM), or the like. A configuration example in which the pulsed seed light Ls is output by being cut out by the external modulator 15 is shown.

  The amplifying unit 20 amplifies the seed light Ls emitted from the light source unit 10 to several tens to several hundreds W level and emits the amplified light La to the wavelength conversion unit 30. The figure shows a configuration in which three fiber amplifiers 21, 22, and 23 are connected in series, and the seed light Ls is sequentially amplified by these three stages of fiber amplifiers 21, 22, and 23. In this configuration example, a ytterbium-doped fiber amplifier (YDFA) having a single clad structure is used as the first and second stage fiber amplifiers 21 and 22, and a double clad structure YDFA is used as the third stage fiber amplifier 23. Shows the configuration.

  The first-stage and second-stage fiber amplifiers 21 and 22 are mainly composed of amplification single-clad fibers 210 and 220 and excitation light sources 215 and 225 for exciting ytterbium (Yb). The single clad fibers 210 and 220 are composed of a core doped with Yb and a clad covering the outer periphery of the core, and seed light Ls and excitation light Lp are introduced into the core. As the excitation light sources 215 and 225, for example, a semiconductor laser having a wavelength λ = 975 nm is preferably used.

  As shown in FIG. 2, the third-stage fiber amplifier 23 is mainly composed of an amplification double-clad fiber 230 and an excitation light source 235 for exciting Yb. . As shown in FIG. 3, the double-clad fiber 230 is a Yb-doped core 231, a first clad 232 that covers the outer periphery of the core 231, and an outer periphery of the first cladding. A second clad 233. The seed light (referred to as signal light for convenience) amplified by the fiber amplifiers 21 and 22 is introduced into the core 231, and the excitation light Lp emitted from the excitation light source 235 is introduced into the first cladding 232.

  Specifically, the signal light output from the preceding fiber amplifier 22 is incident on the core 231 of the double clad fiber 230 via a WDM (Wavelength Division Multiplex) coupler 237 and the pumping light Lp emitted from the pumping light source 235 is generated. , And is incident on the first cladding 232 of the double cladding fiber 230 via the WDM coupler 237. The first clad (also referred to as a pumping guide) 232 acts as a multi-mode waveguide for pumping light, and guides high-power multi-mode laser light emitted from a plurality of pumping light sources 235 in the axial direction. Yb doped in H.231 is excited efficiently.

  The double clad fiber 230 is generally an optical fiber in which the core 231 and the first clad 232 are made of quartz (silica) glass, and the second clad 233 is made of resin because of fiber productivity, workability, and ease of handling. Is used. The signal light amplified by the third-stage fiber amplifier 23, that is, the amplified light La is emitted from the amplification unit 20 and enters the wavelength conversion unit 30.

The wavelength conversion unit 30 is mainly composed of wavelength conversion optical elements 31 and 32. Amplified light La having a wavelength λ ₁ = 1064 nm incident on the wavelength conversion unit 30 from the amplification unit 20 is condensed and incident on the wavelength conversion optical element 31 via a condensing lens. The wavelength conversion optical element 31 is a nonlinear optical crystal that generates a second harmonic of the amplified light La by second harmonic generation (SHG). As the wavelength conversion optical element 31, a configuration in which an LBO (LiB ₃ O ₅ ) crystal is used for non-critical phase matching (NCPM) is exemplified.

  When the LBO crystal is used in non-critical phase matching, no walk-off occurs in the generated second harmonic wave having a wavelength of 532 nm. Therefore, wavelength conversion can be efficiently performed while ensuring a sufficient interaction length. In addition, since the beam section of the emitted second harmonic does not become elliptical, it is not necessary to provide a shaping optical element such as a cylindrical lens between the wavelength conversion optical element 31 and the wavelength conversion optical element 32. The wavelength conversion optical element 32 can efficiently perform wavelength conversion.

When the power of the amplified light La output from the amplifying unit 20 is as low as about 10 W, the wavelength conversion optical element 31 may be a PPLN (Periodically Poled LiNbO ₃ ) crystal or a PPLT (Periodically Poled LiTaO ₃ ). Alternatively, a quasi phase matching (QPM) crystal such as PPKTP (Periodically Poled KTiOPO ₄ ) crystal may be used. Even when a QPM crystal is used, wavelength conversion can be performed efficiently, and there is no need to provide a shaping optical element between the wavelength conversion optical element 31 and the wavelength conversion optical element 32.

  The second harmonic generated by the wavelength conversion optical element 31 and the amplified light transmitted through the wavelength conversion optical element 31 without being converted in wavelength are rotated by 90 degrees on the polarization plane of one (for example, the amplified light) by the two-wavelength wavelength plate. Then, the light is focused and incident on the wavelength conversion optical element 32.

The wavelength conversion optical element 32 is a nonlinear optical crystal that generates the sum frequency of the second harmonic and the amplified light by sum frequency generation (SFG). As the wavelength conversion optical element 32, a configuration in which an LBO crystal is used for type I critical phase matching (CPM) is exemplified. As the wavelength conversion optical element 32, a BBO (β-BaB ₂ O ₄ ) crystal or a CLBO (CsLiB ₆ O ₁₀ ) crystal can also be used. The amplified light having a wavelength of 1064 nm and the second harmonic wave having a wavelength of 532 nm incident on the wavelength conversion optical element 32 are wavelength-converted in the process of passing through the wavelength conversion optical element 32, and the third harmonic wave having a sum frequency of 355 nm is obtained. Occur.

  The third harmonic generated by the wavelength conversion optical element 32 is output from the laser device LS as output light Lv. Note that the light emitted from the wavelength conversion optical element 32 includes the remaining amplified light and the second harmonic wave that have been transmitted through the wavelength conversion optical element 32 without being wavelength-converted. By disposing a dichroic mirror, a prism, or the like on this, only the third harmonic wave having a wavelength of 355 nm can be output from the laser device LS.

  In the laser apparatus LS schematically configured as described above, the fiber amplifier 23 is provided with a cooling mechanism 25 for cooling the double clad fiber 230. That is, the double clad fiber 230 is bonded and fixed to a fiber holding member having a cooling function, absorbs heat generated due to a slight loss in the fiber when a high-energy laser beam propagates, and overheats the fiber. Is to prevent. As an example of the cooling mechanism 25, FIG. 4 shows a schematic diagram (outside view) of a double clad fiber fixing structure A in which a double clad fiber 230 is bonded and fixed to a water-cooled fiber holding member 250. Further, FIG. 5 shows a cross-sectional view taken along arrows V-V added in FIG.

  The illustrated fiber holding member 250 has a flat plate shape as a whole, and is manufactured using a metal material such as an aluminum alloy or stainless steel. A communicating channel 251 for circulating cooling water by drilling or the like is drilled inside the plate. Cooling water at a predetermined temperature is supplied to the channel 251 from a cooling device (not shown), and fiber The holding member 250 is held at a substantially constant temperature.

  A holding groove 252 for holding the double clad fiber 230 is formed on one surface of the fiber holding member 250. The holding groove 252 is formed in one continuous concave groove shape whose groove width and depth are somewhat larger than the diameter d of the double clad fiber 230 (for example, about 1.2d to 2d). In this embodiment, a configuration in which one spiral holding groove 252 is formed on the upper surface of the plate is illustrated. Therefore, the double clad fiber 230 can be easily mounted and locked in the holding groove 252 when the fiber is assembled.

From the upper side of the double clad fiber 230 locked to the fiber holding member 250, an adhesive 260 is injected into the holding groove 252 so as to cover the outer periphery of the fiber, and cured. In this embodiment, the adhesive 260 has a refractive index n ₆ after curing that is smaller than that of the first cladding and substantially equal to the refractive index n ₂ of the second cladding 233 (n ₁ > n ₆ ≈n ₂ ). It has been prepared. Thus, the double clad fiber 230 is embedded in the holding groove 252 and fixed to the fiber holding member 250 with the outer periphery of the second clad 233 covered with the adhesive 260 having substantially the same refractive index as that of the second clad. .

In this embodiment, the double clad fiber 230 uses an optical fiber in which the core 231 and the first clad 232 are made of quartz (silica) glass and the second clad 233 is made of resin. At this time, as a suitable adhesive 260, an adhesive (for example, an adhesive adjusted to have a refractive index after curing of n ₆ ≈n ₂ using a resin material of the same system as the resin constituting the second cladding 233 as a base) And fluorine-based and silicon-based adhesives). In addition, as long as the adhesive has a refractive index after curing of n ₆ ≈n ₂ , it may be based on a resin material of a system different from that of the second cladding 233, An appropriate type of adhesive can be used according to the material of the second cladding.

  The behavior of laser light propagating through the first clad 232 and the second clad 233 in the double clad fiber fixed structure A fixed by the fixing method as described above will be described with reference to FIG. FIG. 6 is a cross-sectional view (planar cross-sectional view) of the double-clad fiber fixing structure A along the axis of the double-clad fiber 230. The double clad fiber 230 is embedded in the holding groove 252 and fixed to the fiber holding member 250 in a state where the outer periphery of the second clad 233 is covered with the adhesive 260 having substantially the same refractive index as that of the second clad.

First, consider a case where laser light propagating through the first cladding 232 is incident on the peeling portion 233a of the second cladding. At this time, the refractive index n ₁ of the first cladding 232, the refractive index n ₂ of the second cladding 233, the relationship of the refractive index n ₆ of the adhesive 260 is n _1> n ₆ ≒ n _2. That is, the relationship between the refractive indexes of the first cladding 232 and the surrounding members in the periphery of the peeling portion 233a is the same as the refractive index relationship of the intact portion where there is no peeling, and is optically equivalent to that the peeling is repaired. . Therefore, the laser light that has propagated through the first clad 232 and entered the peeling portion 233a is totally reflected at the interface between the first clad 232 and the adhesive 260, as shown by the solid arrow in the figure, and has no peeling. It propagates in the first cladding 232 through the same optical path as in the above state.

Next, consider laser light propagating through the second cladding. Here, the relationship between the refractive indexes of the respective portions is n ₁ > n ₆ ≈n _{2 as} described above, and the refractive indexes of the second cladding 233 and the adhesive 260 are substantially the same. That is, there is no difference in refractive index between the second cladding 233 and the adhesive 260 covering the periphery thereof, and no optical interface exists. Therefore, the laser light that has propagated through the second clad 233 to the fiber holding member 250 is emitted from the second clad 233 to the layer of the adhesive 260 and dissipated, as indicated by the two-dot chain arrow in the figure. Even if there is a component reflected by a slight difference in refractive index (weak laser beam), as shown by the dotted arrow in the figure, most of the light is reflected on the adhesive 260 layer and greatly attenuated. Then, the laser beam propagating through the second cladding 233 disappears. Even if the laser light propagated through the second clad 233 or the laser light dissipated into the adhesive 260 layer enters the scratch 233b, it is transmitted as it is because there is no difference in refractive index from the surroundings, and only the scratched portion is transmitted. Is not locally overheated.

  Therefore, according to the double clad fiber fixing structure A as described above, even if a minute scratch or peeling occurs in the second clad 233, local overheating occurs at these portions. There is nothing. Further, since the holding groove 252 is formed in the fiber holding member 250, the double clad fiber 230 can be easily attached. Further, the holding groove 252 is formed in a concave groove shape whose groove width and depth are somewhat larger than the diameter of the double clad fiber 230, and the double clad fiber 230 is embedded in the holding groove 252 with an adhesive 260. Has been fixed. That is, the double clad fiber 230 is structured to be cooled from the bottom surface and the side wall surface of the adjacent holding groove 252. Therefore, overheating of the fiber is effectively suppressed, and the long-term stability of the fiber amplifier 23 can be improved.

  In the embodiment, as a fiber holding member having a cooling function, a flow path 251 for circulating cooling water is formed inside a flat metal plate, and a concave groove-like holding groove 252 in which a double clad fiber is embedded is formed on one surface. The formed water-cooled fiber holding member 250 is illustrated. However, the form of the fiber holding member is not limited to such an embodiment. For example, a holding groove 252 similar to the above may be formed on a component mounting surface of a heat sink material that cools a power transistor or the like to constitute an air-cooled fiber holding member. The fiber holding member of such a form is suitable when the heat generation amount of the double clad fiber is relatively low, and the cooling mechanism can be configured at low cost. In addition, for example, a concave groove-shaped holding groove 252 that is continuous in a spiral shape is formed on the outer peripheral surface of a columnar metal rod or a hollow cylindrical metal pipe to constitute a water-cooled or air-cooled fiber holding member. Also good. According to such a form of the fiber holding member, in addition to being able to manufacture the fiber holding member at a relatively low cost, the double clad fibers 230 do not cross each other and the curvature of the fiber can be made constant. it can.

  In this embodiment, YDFA in which the core is doped with Yb (ytterbium) is exemplified as an example of the fiber amplifier. However, the core is doped with Er (erbium), and the core is doped with Tm (thulium). The same effect can be obtained by applying the same to TDFA. Further, the laser device that has the wavelength conversion unit 30 and outputs the amplified light La output from the amplification unit 20 after wavelength conversion to the wavelength 355 nm in the wavelength conversion unit 30 is illustrated. However, the output light output from the laser device LS The wavelength of Lv is arbitrary. That is, the present invention is also applied to a laser device that emits the amplified light La as it is without providing the wavelength conversion unit 30, or a laser device that uses the first-stage fiber amplifier 21 as a fiber laser without the light source unit 10. By doing so, the effects described above can be enjoyed.

  The laser device LS as described above is small and light and easy to handle, optical processing devices such as exposure devices and stereolithography devices, inspection devices such as photomasks and wafers, observation devices such as microscopes and telescopes, The present invention can be suitably applied to a measuring device such as a length measuring device or a shape measuring device, and a system such as a phototherapy device.

  As a first application example of a system including the laser device LS, an exposure apparatus used in a photolithography process for manufacturing a semiconductor or a liquid crystal panel will be described with reference to FIG. The exposure apparatus 500 is in principle the same as photolithography, and a device pattern precisely drawn on a quartz glass photomask 513 is applied to an exposure object 515 such as a semiconductor wafer or glass substrate coated with a photoresist. Optically project and transfer.

  The exposure apparatus 500 includes the laser apparatus LS, the illumination optical system 502, the mask support base 503 that holds the photomask 513, the projection optical system 504, and the exposure object support table 505 that holds the exposure object 515. And a drive mechanism 506 that moves the exposure object support table 505 in a horizontal plane. The illumination optical system 502 includes a plurality of lens groups, and irradiates the photomask 513 held on the mask support 503 with laser light (output light Lv) output from the laser device LS. The projection optical system 504 is also composed of a plurality of lens groups, and projects the light transmitted through the photomask 513 onto the exposure object 515 on the exposure object support table.

  In the exposure apparatus 500 having such a configuration, the laser light output from the laser apparatus LS is input to the illumination optical system 502, and the laser light adjusted to a predetermined light flux is applied to the photomask 513 held on the mask support 503. Irradiated. The light that has passed through the photomask 513 has an image of a device pattern drawn on the photomask 513, and this light of the exposure object 515 held on the exposure object support table 505 via the projection optical system 504. A predetermined position is irradiated. Thereby, the image of the device pattern of the photomask 513 is image-exposed at a predetermined magnification on the exposure object 515 such as a semiconductor wafer or a liquid crystal panel.

  Next, as a second application example of the system including the laser device LS, FIG. 8 showing a schematic configuration of an inspection device used in an inspection process of a photomask, a liquid crystal panel, a wafer, or the like (test object). The description will be given with reference. An inspection apparatus 600 illustrated in FIG. 8 is suitably used for inspecting a fine device pattern drawn on a light-transmitting object 613 such as a photomask.

  The inspection apparatus 600 includes a laser device LS, an illumination optical system 602, a test object support base 603 that holds the test object 613, a projection optical system 604, and a TDI that detects light from the test object 613. (Time Delay Integration) A sensor 615 and a drive mechanism 606 for moving the object support base 603 in a horizontal plane are configured. The illumination optical system 602 includes a plurality of lens groups, and adjusts the laser light output from the laser device LS to a predetermined light flux and irradiates the test object 613 held on the test object support base 603. The projection optical system 604 is also composed of a plurality of lens groups, and projects the light transmitted through the test object 613 onto the TDI sensor 615.

  In the inspection apparatus 600 having such a configuration, the laser light (output light Lv) output from the laser apparatus LS is input to the illumination optical system 602, and the laser light adjusted to a predetermined light flux is applied to the object support base 603. The object 613 such as a held photomask is irradiated. The light from the object 613 (transmitted light in this configuration example) has an image of a device pattern drawn on the object 613, and this light is transmitted to the TDI sensor 615 via the projection optical system 604. Projected and imaged. At this time, the horizontal movement speed of the test object support base 603 by the drive mechanism 606 and the transfer clock of the TDI sensor 615 are controlled in synchronization.

  Therefore, an image of the device pattern of the test object 613 is detected by the TDI sensor 615, and by comparing the detection image of the test object 613 detected in this way with a predetermined reference image set in advance, The defect of the fine pattern drawn on the test object is extracted. If the test object 613 does not have optical transparency like a wafer or the like, the reflected light from the test object is incident on the projection optical system 604 and guided to the TDI sensor 615 in the same manner. can do.

A Double-clad fiber fixed structure LS Laser device Lp Excitation light Lv Output light 10 Light source part (laser light generation part)
20 Amplifier (21, 22, 23 fiber amplifier)
25 Cooling mechanism 30 Wavelength conversion part (31, 32 wavelength conversion optical element)
230 double clad fiber (231 core, 232 first clad, 233 second clad)
235 Excitation light source 250 Fiber holding member (251 flow path, 252 holding groove)
260 Adhesive 500 Exposure apparatus 502 Illumination optical system 503 Mask support base 504 Projection optical system 505 Exposure object support table 506 Drive mechanism 513 Photomask 515 Exposure object 600 Inspection apparatus 602 Illumination optical system 603 Test object support base 604 Projection optical System 606 Drive mechanism 613 Test object 615 TDI sensor

Claims (11)

A double-clad fiber having a core doped with a laser medium, a first cladding that covers the outer periphery of the core and into which excitation light is introduced, and a second cladding that covers the outer periphery of the first cladding is fixed to a fiber holding member. A double-clad fiber fixing method,
Using an adhesive having a refractive index n ₆ after curing substantially equal to or greater than the refractive index n ₂ of the second cladding and smaller than the refractive index n ₁ of the first cladding;
Applying and curing the adhesive on the double clad fiber disposed on the fiber holding member so as to cover the outer periphery of the second clad,
A method of fixing a double clad fiber, wherein the double clad fiber is fixed to the fiber holding member. The adhesive fixing method of the double-clad fiber according to claim 1, the refractive index n ₆ after the curing, characterized in that it is substantially the same as the refractive index n ₂ of the second cladding. A double-clad fiber having a core doped with a laser medium, a first cladding that covers the outer periphery of the core and into which excitation light is introduced, and a second cladding that covers the outer periphery of the first cladding;
A fiber holding member to which the double clad fiber is fixed;
An adhesive that bonds the double-clad fiber to the fiber holding member;
The adhesive has a refractive index n ₆ after curing substantially equal to or greater than the refractive index n ₂ of the second cladding and smaller than the refractive index n ₁ of the first cladding,
The double clad fiber fixing structure, wherein the double clad fiber is fixed to the fiber holding member in a state where an outer periphery of the second clad is covered with the adhesive. 4. The double-clad fiber fixing structure according to claim 3, wherein the adhesive has a refractive index n ₆ after the curing substantially equal to a refractive index n ₂ of the second cladding.   The double-clad fiber fixing structure according to claim 3 or 4, wherein the fiber holding member has a cooling function for cooling the double-clad fiber. The fiber holding member has a holding groove for holding the double clad fiber,
The double-clad fiber fixing structure according to any one of claims 3 to 5, wherein the adhesive is disposed to cover the double-clad fiber disposed in the holding groove.   The holding groove is formed in a concave groove shape whose groove width is somewhat larger than the diameter of the double clad fiber, and the double clad fiber is embedded and fixed in the holding groove by the adhesive. The double-clad fiber fixing structure according to claim 6. A double-clad fiber fixing structure according to any one of claims 3 to 7,
A laser beam generator for generating a laser beam amplified in the core;
A laser apparatus comprising: an excitation light source that supplies excitation light to the first cladding.   9. The laser apparatus according to claim 8, further comprising a wavelength converter that converts the wavelength of the amplified light that is amplified by the double clad fiber and outputs the amplified light. A laser device according to claim 9;
A mask support for holding a photomask on which a predetermined exposure pattern is formed;
An exposure object support for holding the exposure object;
An illumination optical system for irradiating the photomask held by the mask support with the laser beam output from the laser device;
An exposure apparatus comprising: a projection optical system that projects light transmitted through the photomask onto an exposure target held by the exposure target support. A laser device according to claim 9;
An object support for holding the object;
An illumination optical system for irradiating a test object held by the test object support unit with laser light output from the laser device;
An inspection apparatus comprising: a projection optical system that projects light from the test object onto a detector.