Patent Description:
As an example of fiber structure-related techniques of the related art, Patent Literature <NUM> describes an optical element in which graphene is attached to a fiber end surface as a saturable absorber for a fiber laser. <page <NUM> a>.

In the related art, the adhesiveness between the saturable absorber and the optical fiber may not be sufficient and there is room for improvement in terms of the adhesiveness between the saturable absorber and the optical fiber.

In this regard, an object of one aspect of the present invention is <CIT> a saturable absorber containing carbon nanowalls, wherein the carbon nanowall is doped with a substance having a number of valence electrons different from that of carbon. The carbon nanowall comprises a plurality of graphite pieces or graphene arranged in parallel in the same direction. <CIT> also relates to a light source for outputting excitation light, an oscillator having an optical gain medium and a saturable absorption element, and emitting laser light using the light output from the excitation light, wherein the saturable absorption element is made of carbon A laser device comprising nanowalls. <CIT> relates to an optical connection structure characterized by a solid viscous connection member having refractive-index matching property being adheringly disposed in a single layer state between the end faces of mutually opposing optical transmission media or between the end face of an optical transmission medium and an optical component that are mutually opposing. <CIT> relates to a Fabry-Perot resonator having a high gain optical fiber and a saturable absorber between two mirrors, a laser diode for supplying pumping light power to the resonator, a laser diode current supply circuit, and a laser diode output power A passive mode-locked optical fiber laser composed of a coupler for supplying to a resonator, an isolator for laser output, and an optical fiber for coupling them. A V Tausenev et al is about "<NPL>. to provide a fiber structure, a pulse laser device, a supercontinuum light source, and a production method for a fiber structure enabling adhesiveness enhancement between a saturable absorber and an optical fiber.

A fiber structure according to one aspect of the present invention includes first and second optical fibers disposed such that tip portions thereof butt and a sheet-shaped saturable absorber sandwiched between the tip portion of the first optical fiber and the tip portion of the second optical fiber. Each of the tip portions of the first optical fiber and the second optical fiber has a core, a cladding provided around the core, and a ferrule provided around the cladding. The tip portion of the first optical fiber has a protruding shape protruding to a tip side. The saturable absorber has an adhering part at least adhering to the core of the first optical fiber and a non-adhering part present around the adhering part and not adhering to the tip portion of the first optical fiber.

In the fiber structure, the saturable absorber sandwiched between the tip portion of the first optical fiber and the tip portion of the second optical fiber has the adhering part at least adhering to the core of the first optical fiber and the non-adhering part present around the adhering part and not adhering to the tip portion of the first optical fiber when viewed in the thickness direction of the saturable absorber. In other words, between the saturable absorber and the tip portion of the first optical fiber, a play part where these do not adhere is present. Accordingly, even if air bubbles are generated between the saturable absorber and the tip portion when, for example, the saturable absorber is placed in the tip portion of the first optical fiber, the air bubbles are capable of easily escaping to the surrounding space by means of the play part and it is possible to suppress the air bubbles having an effect to cause a decline in the adhesiveness between the saturable absorber and the first optical fiber. In other words, the adhesiveness between the saturable absorber and the first optical fiber can be enhanced.

In the fiber structure according to one aspect of the present invention, the adhering part may adhere to the core and the cladding of the first optical fiber. The tip portion of the first optical fiber and the tip portion of the second optical fiber may butt such that a dent corresponding to a shape of the cladding of the first optical fiber adhering at the adhering part is formed in the saturable absorber. In this case, the first optical fiber and the second optical fiber are capable of sandwiching the saturable absorber with sufficient force, the heat conduction of the saturable absorber, eventually thermal diffusion, is improved, the life of the saturable absorber can be extended, and durability enhancement can be achieved.

In the fiber structure according to one aspect of the present invention, the tip portion of the second optical fiber may have a protruding shape protruding to a tip side. The adhering part may at least adhere to the core of the second optical fiber. The non-adhering part may not adhere to the tip portion of the second optical fiber. In this case, between the saturable absorber and the tip portion of the second optical fiber, a play part where these do not adhere is present. Accordingly, even if air bubbles are generated between, for example, the saturable absorber and the second optical fiber, the air bubbles are capable of easily escaping to the surrounding space by means of the play part and it is possible to suppress the air bubbles having an effect to cause a decline in the adhesiveness between the saturable absorber and the second optical fiber. In other words, the adhesiveness between the saturable absorber and the second optical fiber can be enhanced.

In the fiber structure according to one aspect of the present invention, the adhering part may adhere to the core and the cladding of the second optical fiber. The tip portion of the first optical fiber and the tip portion of the second optical fiber may butt such that a dent corresponding to a shape of the cladding of the second optical fiber adhering at the adhering part is formed in the saturable absorber. In this case, the first optical fiber and the second optical fiber are capable of sandwiching the saturable absorber with sufficient force, the heat conduction of the saturable absorber, eventually thermal diffusion, is improved, the life of the saturable absorber can be extended, and durability enhancement can be achieved.

In the fiber structure according to one aspect of the present invention, an outer edge of the saturable absorber may be positioned inside an outer edge of at least one of the first optical fiber and the second optical fiber when viewed in a thickness direction of the saturable absorber. In this case, the saturable absorber is less likely to peel off than in a case where, for example, the outer edge of the saturable absorber is positioned outside the outer edges of the first optical fiber and the second optical fiber when viewed in the thickness direction. As a result, the adhesiveness between the saturable absorber and at least one of the first and second optical fibers can be further enhanced.

A fiber structure according to one aspect of the present invention includes first and second optical fibers disposed such that tip portions thereof butt and a sheet-shaped saturable absorber sandwiched between the tip portion of the first optical fiber and the tip portion of the second optical fiber. An outer edge of the saturable absorber is positioned inside an outer edge of at least one of the first optical fiber and the second optical fiber when viewed in a thickness direction of the saturable absorber.

In the fiber structure, the outer edge of the saturable absorber is positioned inside the outer edge of at least one of the first optical fiber and the second optical fiber when viewed in the thickness direction of the saturable absorber. Accordingly, the saturable absorber is less likely to peel off than in a case where, for example, the outer edge of the saturable absorber is positioned outside the outer edges of the first optical fiber and the second optical fiber when viewed in the thickness direction. As a result, the adhesiveness between the saturable absorber and at least one of the first and second optical fibers can be enhanced.

In the fiber structure according to one aspect of the present invention, the saturable absorber may have a polygonal shape in which a corner portion is square-chamfered or round-chamfered when viewed in the thickness direction of the saturable absorber. In this case, the saturable absorber is less likely to peel off than in a case where the saturable absorber is not chamfered. As a result, the adhesiveness between the saturable absorber and the first optical fiber can be further enhanced.

In the fiber structure according to one aspect of the present invention, the saturable absorber may have a circular shape, an elliptical shape, or an oval shape when viewed in the thickness direction of the saturable absorber. In this case, the saturable absorber is less likely to peel off than in a case where the saturable absorber has, for example, a polygonal shape. As a result, the adhesiveness between the saturable absorber and the first optical fiber can be further enhanced.

In the fiber structure according to one aspect of the present invention, the saturable absorber may contain a sheet-shaped resin and a plurality of carbon nanotubes dispersed in the resin. In this case, the saturable absorber can be formed from the resin and the carbon nanotubes.

A pulse laser device according to one aspect of the present invention includes the fiber structure. In the pulse laser device as well as the fiber structure, the adhesiveness between the saturable absorber and the first optical fiber can be enhanced.

A supercontinuum light source according to one aspect of the present invention includes the pulse laser device. In the supercontinuum light source as well as the fiber structure, the adhesiveness between the saturable absorber and the first optical fiber can be enhanced.

A production method for a fiber structure according to one aspect of the present invention includes a first step of preparing a sheet-shaped saturable absorption material and first and second optical fibers, a second step of forming a sheet-shaped saturable absorber by punching the saturable absorption material, a third step of adsorbing the saturable absorber with an adsorption instrument, a fourth step of placing the saturable absorber adsorbed by the adsorption instrument in a tip portion of the first optical fiber, and a fifth step of causing the tip portion of the first optical fiber and a tip portion of the second optical fiber to butt such that the saturable absorber is sandwiched between the tip portion of the first optical fiber and the tip portion of the second optical fiber. Each of the tip portions of the first optical fiber and the second optical fiber has a core, a cladding provided around the core, and a ferrule provided around the cladding. The tip portion of the first optical fiber has a protruding shape protruding to a tip side. In the fourth step, the saturable absorber is placed in the tip portion of the first optical fiber such that an adhering part at least adhering to the core of the first optical fiber and a non-adhering part present around the adhering part and not adhering to the tip portion of the first optical fiber are formed in the saturable absorber.

In the fourth step of the production method for a fiber structure, the saturable absorber is placed in the tip portion of the first optical fiber such that the adhering part at least adhering to the core of the first optical fiber and the non-adhering part present around the adhering part and not adhering to the tip portion of the first optical fiber are formed in the saturable absorber. In other words, between the saturable absorber and the tip portion of the first optical fiber, a play part where these do not adhere is present. Accordingly, even if air bubbles are generated between the saturable absorber and the tip portion when, for example, the saturable absorber is placed in the tip portion of the first optical fiber, the air bubbles are capable of easily escaping to the surrounding space by means of the play part and it is possible to suppress the air bubbles having an effect to cause a decline in the adhesiveness between the saturable absorber and the first optical fiber. In other words, the adhesiveness between the saturable absorber and the first optical fiber can be enhanced. As a result, after the fourth step, falling of the saturable absorber from the tip portion of the first optical fiber is suppressed.

In the production method for a fiber structure according to one aspect of the present invention, in the fourth step, the saturable absorber may be placed in the tip portion of the first optical fiber such that the adhering part adheres to the core and the cladding of the first optical fiber. In the fifth step, the tip portion of the first optical fiber and the tip portion of the second optical fiber may be caused to butt such that a dent corresponding to a shape of the cladding of the first optical fiber adhering at the adhering part is formed in the saturable absorber. In this case, the first optical fiber and the second optical fiber are capable of sandwiching the saturable absorber with sufficient force, the heat conduction of the saturable absorber, eventually thermal diffusion, is improved, the life of the saturable absorber can be extended, and durability enhancement can be achieved.

In the production method for a fiber structure according to one aspect of the present invention, the tip portion of the second optical fiber may have a protruding shape protruding to a tip side. In the fifth step, the tip portion of the first optical fiber and the tip portion of the second optical fiber may be caused to butt such that the adhering part at least adheres to the core of the second optical fiber and the non-adhering part does not adhere to the tip portion of the second optical fiber. In this case, between the saturable absorber and the tip portion of the second optical fiber, a play part where these do not adhere is present. Accordingly, even if air bubbles are generated between, for example, the saturable absorber and the second optical fiber with the tip portion of the first optical fiber and the tip portion of the second optical fiber butting, the air bubbles are capable of easily escaping to the surrounding space by means of the play part and it is possible to suppress the air bubbles having an effect to cause a decline in the adhesiveness between the saturable absorber and the second optical fiber. In other words, the adhesiveness between the saturable absorber and the second optical fiber can be enhanced.

In the production method for a fiber structure according to one aspect of the present invention, in the fifth step, the tip portion of the first optical fiber and the tip portion of the second optical fiber may be caused to butt such that a dent corresponding to a shape of the cladding of the second optical fiber adhering at the adhering part is formed in the saturable absorber. In this case, the first optical fiber and the second optical fiber are capable of sandwiching the saturable absorber with sufficient force, the heat conduction of the saturable absorber, eventually thermal diffusion, is improved, the life of the saturable absorber can be extended, and durability enhancement can be achieved.

In the production method for a fiber structure according to one aspect of the present invention, in the fourth step, the saturable absorber may be placed in the tip portion of the first optical fiber such that an outer edge of the saturable absorber is positioned inside an outer edge of the first optical fiber when viewed in a thickness direction of the saturable absorber. In this case, the saturable absorber is less likely to peel off than in a case where, for example, the saturable absorber is placed in the tip portion of the first optical fiber such that the outer edge of the saturable absorber is positioned outside the outer edge of the first optical fiber when viewed in the thickness direction. As a result, the adhesiveness between the saturable absorber and the first optical fiber can be further enhanced.

In the production method for a fiber structure according to one aspect of the present invention, in the fifth step, the tip portion of the first optical fiber and the tip portion of the second optical fiber may be caused to butt such that the outer edge of the saturable absorber is positioned inside an outer edge of the second optical fiber when viewed in the thickness direction of the saturable absorber. In this case, the saturable absorber is less likely to peel off than in a case where, for example, the tip portion of the first optical fiber and the tip portion of the second optical fiber butt such that the outer edge of the saturable absorber is positioned outside the outer edge of the second optical fiber when viewed in the thickness direction of the saturable absorber. As a result, the adhesiveness between the saturable absorber and the second optical fiber can be further enhanced.

In the production method for a fiber structure according to one aspect of the present invention, in the fourth step, a Newton ring containing interference fringes generated at the non-adhering part of the saturable absorber may be formed in the saturable absorber. In this case, by observing the Newton ring, it is possible to easily grasp the state where the adhering part of the saturable absorber at least adheres to the core and the non-adhering part of the saturable absorber does not adhere to the tip portion of the first optical fiber.

A production method for a fiber structure according to one aspect of the present invention includes a first step of preparing a sheet-shaped saturable absorption material and first and second optical fibers, a second step of forming a sheet-shaped saturable absorber by punching the saturable absorption material, a third step of adsorbing the saturable absorber with an adsorption instrument, a fourth step of placing the saturable absorber adsorbed by the adsorption instrument in a tip portion of the first optical fiber, and a fifth step of causing the tip portion of the first optical fiber and a tip portion of the second optical fiber to butt such that the saturable absorber is sandwiched between the tip portion of the first optical fiber and the tip portion of the second optical fiber. In the fourth step, the saturable absorber is placed in the tip portion of the first optical fiber such that an outer edge of the saturable absorber is positioned inside an outer edge of the first optical fiber when viewed in a thickness direction of the saturable absorber.

In the fourth step of the production method for a fiber structure, the saturable absorber is placed in the tip portion of the first optical fiber such that the outer edge of the saturable absorber is positioned inside the outer edge of the first optical fiber when viewed in the thickness direction. Accordingly, the saturable absorber is less likely to peel off than in a case where, for example, the saturable absorber is placed in the tip portion of the first optical fiber such that the outer edge of the saturable absorber is positioned outside the outer edge of the first optical fiber when viewed in the thickness direction. As a result, the adhesiveness between the saturable absorber and the first optical fiber can be enhanced.

In the production method for a fiber structure according to one aspect of the present invention, in the fifth step, the tip portion of the first optical fiber and the tip portion of the second optical fiber may be caused to butt such that the outer edge of the saturable absorber is positioned inside an outer edge of the second optical fiber when viewed in the thickness direction of the saturable absorber. In this case, the saturable absorber is less likely to peel off than in a case where, for example, the tip portion of the first optical fiber and the tip portion of the second optical fiber butt such that the outer edge of the saturable absorber is positioned outside the outer edge of the second optical fiber when viewed in the thickness direction of the saturable absorber. As a result, the adhesiveness between the saturable absorber and the second optical fiber can be enhanced.

The production method for a fiber structure according to one aspect of the present invention may further include a sixth step of accommodating the tip portion of the first optical fiber and the tip portion of the second optical fiber in a housing. In this case, the saturable absorber is accommodated in the housing together with the tip portion of the first optical fiber and the tip portion of the second optical fiber. As a result, deterioration of the saturable absorber attributable to oxidation can be suppressed. As a result, the life of the saturable absorber can be sufficient and durability enhancement can be achieved.

In the production method for a fiber structure according to one aspect of the present invention, the saturable absorber may have a polygonal shape in which a corner portion is square-chamfered or round-chamfered when viewed in the thickness direction of the saturable absorber. In this case, the saturable absorber is less likely to peel off than in a case where the saturable absorber is not chamfered. As a result, the adhesiveness between the saturable absorber and the first optical fiber can be further enhanced.

In the production method for a fiber structure according to one aspect of the present invention, the saturable absorber may have a circular shape, an elliptical shape, or an oval shape when viewed in the thickness direction of the saturable absorber. In this case, the saturable absorber is less likely to peel off than in a case where the saturable absorber has, for example, a polygonal shape. As a result, the adhesiveness between the saturable absorber and the first optical fiber can be further enhanced.

According to one aspect of the present invention, it is possible to provide a fiber structure, a pulse laser device, a supercontinuum light source, and a production method for a fiber structure enabling adhesiveness enhancement between a saturable absorber and an optical fiber.

Hereinafter, an embodiment will be described in detail with reference to the drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals with redundant description omitted.

As illustrated in <FIG>, a supercontinuum light source <NUM> is a light source generating supercontinuum light. The supercontinuum light source <NUM> includes a pulse laser device <NUM>, a fiber amplifier <NUM>, a pulse compression fiber <NUM>, and a highly non-linear optical fiber <NUM>.

The pulse laser device <NUM> is a ring-type laser oscillator. Details of the pulse laser device <NUM> will be described later. The output end of the pulse laser device <NUM> is connected to the fiber amplifier <NUM>. The output end of the fiber amplifier <NUM> is connected to the pulse compression fiber <NUM>. The output end of the pulse compression fiber <NUM> is connected to the highly non-linear optical fiber <NUM>. The highly non-linear optical fiber <NUM> is a highly non-linear fiber generating supercontinuum light. The highly non-linear optical fiber <NUM> expands the spectral width of input pulsed light by the non-linear optical effect and converts it into supercontinuum light. The supercontinuum light is output from the output end of the highly non-linear optical fiber <NUM>.

As illustrated in <FIG>, the pulse laser device <NUM> constitutes an ultra-short pulse (femtosecond) laser device. The pulse laser device <NUM> includes an excitation light source <NUM>, an amplification optical fiber <NUM>, and a fiber structure <NUM>. The excitation light source <NUM> where the fiber structure <NUM> is disposed on the optical path of an optical fiber <NUM> configured in a loop shape is, for example, a laser diode. Continuous light from the excitation light source <NUM> is input to the amplification optical fiber <NUM> and circulates in only one direction. The fiber structure <NUM> is a structure including a saturable absorber <NUM>. Details of the fiber structure <NUM> will be described later.

The saturable absorber <NUM> is a material, and the light transparency of the material changes depending on the intensity of incident light. The saturable absorber <NUM> absorbs the incident light in a linear region where the incident light intensity is weak. When the incident light intensity reaches a high level, the absorption of the saturable absorber <NUM> decreases and the incident light is transmitted through the saturable absorber <NUM>. In the pulse laser device <NUM>, the amplitude of oscillating laser light fluctuates at a high frequency with time due to a noise component, and thus light with a high level of incident light intensity is transmitted without being absorbed by the saturable absorber <NUM> and becomes pulsed light. The pulsed light is superposed on continuous light circulating in a ring-type resonator, the intensity is increased by stimulated emission being promoted, and the transmission of the pulsed light through the saturable absorber <NUM> becomes more likely. While the pulsed light circulates in the ring-type resonator while growing in this manner, the saturable absorption characteristics of the saturable absorber <NUM>, the fiber non-linear effect, and the wavelength dispersion effect result in pulsed light generation. The generated optical pulse is separated and output.

Next, the fiber structure <NUM> will be specifically described.

As illustrated in <FIG> and <FIG>, the fiber structure <NUM> includes a first optical fiber <NUM>, a second optical fiber <NUM>, the saturable absorber <NUM>, and a housing <NUM>. The first optical fiber <NUM> and the second optical fiber <NUM> are single-mode fibers. The first optical fiber <NUM> and the second optical fiber <NUM> are disposed such that a tip portion 110a of the first optical fiber <NUM> and a tip portion 120a of the second optical fiber <NUM> butt. The first optical fiber <NUM> and the second optical fiber <NUM> are disposed such that a first axis X1 of the first optical fiber <NUM> and a second axis X2 of the second optical fiber <NUM> coincide. A first end surface 110b of the first optical fiber <NUM> and a second end surface 120b of the second optical fiber <NUM> face each other.

The first optical fiber <NUM> has a first core <NUM>, a first cladding <NUM>, a first ferrule <NUM>, and a first ferrule holding portion <NUM>. The first core <NUM> extends along the first axis X1 of the first optical fiber <NUM>. The first cladding <NUM> is provided around the first core <NUM>. The first cladding <NUM> covers the periphery of the first core <NUM>. The first cladding <NUM> extends along the first axis X1. The first ferrule <NUM> is a cylindrical body formed of ceramics. The tip sides of the first core <NUM> and the first cladding <NUM> are inserted in the first ferrule <NUM>. The first ferrule <NUM> is provided around the first cladding <NUM> on the tip side of the first cladding <NUM>. The first ferrule <NUM> covers the periphery of the tip side of the first cladding <NUM>. The first ferrule <NUM> extends along the first axis X1. In this manner, the tip portion 110a of the first optical fiber <NUM> has the first core <NUM>, the first cladding <NUM>, and the first ferrule <NUM>.

The tip portion 110a of the first optical fiber <NUM> has a protruding shape protruding to the tip side and has a function of preventing return light by being polished diagonally. The tip portion 110a having the protruding shape is formed so as to taper toward the tip side from the base end side of the first optical fiber <NUM>. The outer diameter of the tip portion 110a having the protruding shape gradually decreases toward the tip side from the base end side of the first optical fiber <NUM>. The tip surface of the first core <NUM>, the tip surface of the first cladding <NUM>, and the tip surface of the first ferrule <NUM> constitute the same first end surface 110b. The first end surface 110b is a bowl-shaped (spherical) curved surface. The first end surface 110b has a circular shape when viewed in the direction along the first axis X1 of the first optical fiber <NUM>. The first ferrule <NUM> includes a first inclined surface 110c inclined in a direction away from the first axis X1 from the first end surface 110b toward the base end side of the first optical fiber <NUM>. The first inclined surface 110c has, for example, the shape of a side surface of a truncated cone. In this manner, the surface of the tip portion 110a having the protruding shape includes the first end surface 110b and the first inclined surface 110c.

Likewise, the second optical fiber <NUM> has a second core <NUM>, a second cladding <NUM>, a second ferrule <NUM>, and a second ferrule holding portion <NUM>. The second core <NUM> extends along the second axis X2 of the second optical fiber <NUM>. The second cladding <NUM> is provided around the second core <NUM>. The second cladding <NUM> covers the periphery of the second core <NUM>. The second cladding <NUM> extends along the second axis X2. The second ferrule <NUM> is a cylindrical body formed of ceramics. The tip sides of the second core <NUM> and the second cladding <NUM> are inserted in the second ferrule <NUM>. The second ferrule <NUM> is provided around the second cladding <NUM> on the tip side of the second cladding <NUM>. The second ferrule <NUM> covers the periphery of the tip side of the second cladding <NUM>. The second ferrule <NUM> extends along the second axis X2. In this manner, the tip portion 120a of the second optical fiber <NUM> has the second core <NUM>, the second cladding <NUM>, and the second ferrule <NUM>.

The tip portion 120a of the second optical fiber <NUM> has a protruding shape protruding to the tip side and has a function of preventing return light by being polished diagonally. The tip portion 120a having the protruding shape is formed so as to taper toward the tip side from the base end side of the second optical fiber <NUM>. The outer diameter of the tip portion 120a having the protruding shape gradually decreases toward the tip side from the base end side of the second optical fiber <NUM>. The tip surface of the second core <NUM>, the tip surface of the second cladding <NUM>, and the tip surface of the second ferrule <NUM> constitute the same second end surface 120b. The second end surface 120b is a bowl-shaped (spherical) curved surface. The second end surface 120b has a circular shape when viewed in the direction along the second axis X2 of the second optical fiber <NUM>. The second ferrule <NUM> includes a second inclined surface 120c inclined in a direction away from the second axis X2 from the second end surface 120b toward the base end side of the second optical fiber <NUM>. The second inclined surface 120c has, for example, the shape of a side surface of a truncated cone. In this manner, the surface of the tip portion 120a having the protruding shape includes the second end surface 120b and the second inclined surface 120c.

The saturable absorber <NUM> is a material for ultra-short pulse laser device mode lock. As illustrated in <FIG>, the saturable absorber <NUM> is a sheet-shaped sheet body containing carbon nanotubes. The saturable absorber <NUM> has, for example, a circular shape when viewed in the thickness direction of the saturable absorber <NUM> (hereinafter, also simply referred to as "thickness direction"). The diameter of the saturable absorber <NUM> is smaller than the diameters of the first ferrule <NUM> and the second ferrule <NUM>. The diameter of the saturable absorber <NUM> is larger than the outer diameters of the first cladding <NUM> and the second cladding <NUM>. The saturable absorber <NUM> is disposed between the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM>.

The saturable absorber <NUM> is provided so as to overlap the first core <NUM>, the first cladding <NUM>, and the first ferrule <NUM> when viewed in the thickness direction. The saturable absorber <NUM> is provided so as to include the first core <NUM>, the first cladding <NUM>, and the inner edge portion (tip surfaces) of the first ferrule <NUM> when viewed in the thickness direction. The outer edge of the saturable absorber <NUM> is positioned inside the outer edge of the first optical fiber <NUM> when viewed in the thickness direction. The outer edge of the saturable absorber <NUM> is positioned inside the outer edge of the first ferrule <NUM> when viewed in the thickness direction. The outer edge of the saturable absorber <NUM> is positioned inside the outer edge of the first end surface 110b and outside the outer edge of the first cladding <NUM> when viewed in the thickness direction.

Likewise, the saturable absorber <NUM> is provided so as to overlap the second core <NUM>, the second cladding <NUM>, and the second ferrule <NUM> when viewed in the thickness direction. The saturable absorber <NUM> is provided so as to include the second core <NUM>, the second cladding <NUM>, and the inner edge portion (tip surfaces) of the second ferrule <NUM> when viewed in the thickness direction. The outer edge of the saturable absorber <NUM> is positioned inside the outer edge of the second optical fiber <NUM> when viewed in the thickness direction. The outer edge of the saturable absorber <NUM> is positioned inside the outer edge of the second ferrule <NUM> when viewed in the thickness direction. The outer edge of the saturable absorber <NUM> is positioned inside the outer edge of the second end surface 120b and outside the outer edge of the second cladding <NUM> when viewed in the thickness direction.

The saturable absorber <NUM> is sandwiched between the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM>. Specifically, the saturable absorber <NUM> is sandwiched between the first end surface 110b and the second end surface 120b. The saturable absorber <NUM> includes an adhering part <NUM> adhering to the first end surface 110b and the second end surface 120b and a non-adhering part <NUM> not adhering to the first end surface 110b and the second end surface 120b. "Not adhering" includes being away (separated). "Not adhering" includes a gap (space) being present inbetween. The same applies to the following "not adhering". The adhering part <NUM> has a circular shape when viewed in the thickness direction. The non-adhering part <NUM> has a circular ring shape and is present around the adhering part <NUM> when viewed in the thickness direction.

The adhering part <NUM> adheres to a first region 110b1 of the first end surface 110b. The non-adhering part <NUM> does not adhere to a second region 110b2 of the first end surface 110b. The first region 110b1 has a circular shape when viewed in the direction along the first axis X1. The second region 110b2 has a circular ring shape and is present around the first region 110b1 when viewed in the direction along the first axis X1. The first region 110b1 includes the tip surface of the first core <NUM>, the tip surface of the first cladding <NUM>, and the inner edge portion of the tip surface of the first ferrule <NUM>. The second region 110b2 includes the outer edge portion of the tip surface of the first ferrule <NUM>. In other words, the adhering part <NUM> of the saturable absorber <NUM> adheres to the first core <NUM>, the first cladding <NUM>, and the inner edge portion of the first ferrule <NUM>. The non-adhering part <NUM> of the saturable absorber <NUM> does not adhere to the outer edge portion of the first ferrule <NUM>.

Likewise, the adhering part <NUM> adheres to a third region 120b1 of the second end surface 120b. The non-adhering part <NUM> does not adhere to a fourth region 120b2 of the second end surface 120b. The non-adhering part <NUM> is separated from the fourth region 120b2 of the second end surface 120b. The non-adhering part <NUM> is away from the fourth region 120b2 of the second end surface 120b. The third region 120b1 has a circular shape when viewed in the direction along the second axis X2. The fourth region 120b2 has a circular ring shape and is present around the third region 120b1 when viewed in the direction along the second axis X2. The third region 120b1 includes the tip surface of the second core <NUM>, the tip surface of the second cladding <NUM>, and the inner edge portion of the tip surface of the second ferrule <NUM>. The fourth region 120b2 includes the outer edge portion of the tip surface of the second ferrule <NUM>. In other words, the adhering part <NUM> of the saturable absorber <NUM> adheres to the second core <NUM>, the second cladding <NUM>, and the inner edge portion of the second ferrule <NUM>. The non-adhering part <NUM> of the saturable absorber <NUM> does not adhere to the outer edge portion of the second ferrule <NUM>.

It should be noted that the shapes of the adhering part <NUM>, the non-adhering part <NUM>, the first region 110b1, the second region 110b2, the third region 120b1, and the fourth region 120b2 are not particularly limited and shapes other than the shapes described above may be used depending on, for example, the mode of contact between the saturable absorber <NUM> and the first and second end surfaces 110b and 120b.

A dent (see <FIG> and <FIG>) corresponding to the shape of the first cladding <NUM> of the first optical fiber <NUM> adhering at the adhering part <NUM> is formed in the saturable absorber <NUM>. The dent has a shape along the outer edge of the first cladding <NUM>. Likewise, a dent corresponding to the shape of the second cladding <NUM> of the second optical fiber <NUM> adhering at the adhering part <NUM> is formed in the saturable absorber <NUM>. The dent has a shape along the outer edge of the second cladding <NUM>.

The saturable absorber <NUM> contains a sheet-shaped resin and the plurality of carbon nanotubes dispersed in the resin. A material having excellent heat resistance is used as the resin. The carbon nanotubes have the saturable absorption characteristics of absorbing light in the <NUM>,<NUM> band and the absorption decreasing when the incident light intensity reaches a high level.

The first optical fiber <NUM> and the second optical fiber <NUM> are fixed to the housing <NUM> in a state of being pressed in the direction of mutual approach. As a result, the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM> are pressed in the direction of mutual approach. The saturable absorber <NUM> is sandwiched by and between the first end surface 110b and the second end surface 120b.

The first ferrule holding portion <NUM> and the second ferrule holding portion <NUM> have a circular tube shape. The first ferrule holding portion <NUM> holds the first ferrule <NUM>. The first ferrule holding portion <NUM> is coaxially attached to the base end side of the first ferrule <NUM>. The inner portion of the first ferrule holding portion <NUM> communicates with the inner portion of the first ferrule <NUM>. The second ferrule holding portion <NUM> holds the second ferrule <NUM>. The second ferrule holding portion <NUM> is coaxially attached to the base end side of the second ferrule <NUM>. The inner portion of the second ferrule holding portion <NUM> communicates with the inner portion of the second ferrule <NUM>.

The housing <NUM> has a sleeve <NUM> and a package <NUM>. The sleeve <NUM> is a split sleeve having a C-shaped cross section. An axially extending slit is formed in the sleeve <NUM>. The sleeve <NUM> has an elastic force tightening the end portions of the first optical fiber <NUM> and the second optical fiber <NUM> inserted therein. A space K in the sleeve <NUM> communicates with the outside of the sleeve <NUM> via the slit.

The package <NUM> has an elongated shape. The package <NUM> has a divided structure in which a plurality of members are fitted together. The fitting part is bonded with a sealing material such as an epoxy adhesive for vacuum airtightness. The package <NUM> is formed of stainless steel, aluminum, brass, or the like. A space K1 is formed in the package <NUM>. The space K1 of the package <NUM> is in an airtight state. The space K1 is defined by the inner surface of the package <NUM> and the outer surface of the sleeve <NUM>. The space K1 includes the space K in the sleeve <NUM>. The space K1 communicates with the space K via the above-described slit of the sleeve <NUM>. The space K1 contains the saturable absorber <NUM> in the package <NUM>. The space K1 constitutes the surrounding space of the saturable absorber <NUM>.

Through holes <NUM> and <NUM> communicating with the space K1 are formed along the longitudinal direction in the package <NUM>. With the middle portion of the sleeve <NUM> positioned in the space K1, one end portion and the other end portion of the sleeve <NUM> are fitted in the through holes <NUM> and <NUM>, respectively. The first ferrule <NUM> is inserted in the through hole <NUM>. The second ferrule <NUM> is inserted in the through hole <NUM>.

The through hole <NUM> has an end portion that includes an opening <NUM> increased in diameter via a step. The first ferrule holding portion <NUM> is inserted in the opening <NUM>. With the first ferrule holding portion <NUM> inserted, a bottom surface 145a of the opening <NUM> is separated from the end surface of the first ferrule holding portion <NUM> (has a gap with respect to the end surface). The through hole <NUM> has an end portion that includes an opening <NUM> increased in diameter via a step. The second ferrule holding portion <NUM> is inserted in the opening <NUM>. With the second ferrule holding portion <NUM> inserted, a bottom surface 146a of the opening <NUM> is separated from the end surface of the second ferrule holding portion <NUM> (has a gap with respect to the end surface).

A first tip tube <NUM> extending along a direction intersecting with the longitudinal direction is joined to the package <NUM>. The first tip tube <NUM> communicates with the space K1. The first tip tube <NUM> is a glass or metal tube used when gas is discharged from the space K1 (the space K1 is vacuumized) and when the space K1 is filled with an inert gas or liquid. The first tip tube <NUM> is blocked such that the space K1 is in an airtight state.

The space between the package <NUM> and the first ferrule holding portion <NUM> (that is, between the package <NUM> and the first ferrule <NUM>) is bonded and sealed by a sealing material S. The space between the package <NUM> and the second ferrule holding portion <NUM> (that is, between the package <NUM> and the second ferrule <NUM>) is bonded and sealed by the sealing material S. The space between the package <NUM> and the first tip tube <NUM> is bonded and sealed by the sealing material S. The sealing material S is, for example, solder, a brazing material, or an epoxy adhesive for vacuum airtightness having a function as an adhesive. The space between the package <NUM> and the first ferrule holding portion <NUM>, the space between the package <NUM> and the second ferrule holding portion <NUM>, and the space between the package <NUM> and the first tip tube <NUM> may be bonded and sealed, for example, by welding.

Next, a method for producing the fiber structure <NUM> will be described.

First, a sheet-shaped sheet member (saturable absorption material) 130N (see <FIG>), the first optical fiber <NUM>, and the second optical fiber <NUM> are prepared (first step). The sheet member 130N is formed by dispersing a plurality of carbon nanotubes in a sheet-shaped resin. The sheet member 130N is prepared by a general known method. The sheet-shaped saturable absorber <NUM> is formed by punching the sheet member 130N (second step). Specifically, as illustrated in (a) of <FIG>, the sheet member 130N is installed between, for example, a punch 130d of a hand punch 130c and a die 130e. As illustrated in (b) of <FIG>, the sheet member 130N is cut and the saturable absorber <NUM> is formed by pressing the punch 130d toward the die 130e.

As illustrated in (c) of <FIG>, the saturable absorber <NUM> is adsorbed by an adsorption instrument 130f (third step). Specifically, the adsorption instrument 130f adsorbs the surface of the saturable absorber <NUM> that is on the side opposite to the back surface pressed by the punch 130d.

As illustrated in (a) of <FIG>, the saturable absorber <NUM> adsorbed by the adsorption instrument 130f is placed in the tip portion 110a of the first optical fiber <NUM> (fourth step). Specifically, the saturable absorber <NUM> is placed in the tip portion 110a of the first optical fiber <NUM> such that the back surface of the saturable absorber <NUM> abuts against the first end surface 110b of the first optical fiber <NUM>. The saturable absorber <NUM> is placed so as to overlap the first core <NUM>, the first cladding <NUM>, and the first ferrule <NUM> when viewed in the thickness direction. The saturable absorber <NUM> is placed such that the outer edge is positioned inside the outer edge of the first optical fiber <NUM> when viewed in the thickness direction.

The saturable absorber <NUM> is placed such that the adhering part <NUM> adhering to the first core <NUM>, the first cladding <NUM>, and the inner edge portion of the first ferrule <NUM> and the non-adhering part <NUM> present around the adhering part <NUM> and not adhering to the outer edge portion of the first ferrule <NUM> are formed in the saturable absorber <NUM>.

When the saturable absorber <NUM> is placed in the tip portion 110a of the first optical fiber <NUM>, the saturable absorber <NUM> and the first end surface 110b adhere to each other as a result of the interaction between the interfaces caused by static electricity, intermolecular force, or the like. The adhesion force between the saturable absorber <NUM> and the first end surface 110b (that is, the degree of the interaction between the interfaces caused by the static electricity, intermolecular force, or the like) is larger than the weight of the saturable absorber <NUM> itself. Accordingly, when the saturable absorber <NUM> is placed on the first end surface 110b, the adhesion force makes it difficult for the saturable absorber <NUM> to fall from the first end surface 110b. As illustrated in (b) of <FIG>, the first optical fiber <NUM> is inserted into the through hole <NUM> of the package <NUM> and the second optical fiber <NUM> is inserted into the through hole <NUM> of the package <NUM> in this state. At this time, the saturable absorber <NUM> is held on the first end surface 110b by the adhesion force, and thus the first optical fiber <NUM> can be inserted without the saturable absorber <NUM> falling from the first end surface 110b. Workability is improved as a result.

In the fourth step, a Newton ring containing interference fringes generated at the non-adhering part <NUM> of the saturable absorber <NUM> is formed in the saturable absorber <NUM>. As illustrated in (a) of <FIG>, after the saturable absorber <NUM> is placed (mounted) in the tip portion 110a of the first optical fiber <NUM>, the Newton ring can be observed via the saturable absorber <NUM> in the direction along the first axis X1 by means of, for example, a microscope. As illustrated in (b) of <FIG>, a Newton ring <NUM> is formed at the non-adhering part <NUM> of the saturable absorber <NUM>, which is present around the adhering part <NUM> adhering to the first optical fiber <NUM>. It should be noted that the illustration of the first optical fiber <NUM> is simplified in <FIG>. <FIG> is a photographic view illustrating the Newton ring <NUM> observed in the saturable absorber <NUM>. In <FIG>, the middle black circular region is the adhering part <NUM> and the black annular ring outside the adhering part <NUM> is the Newton ring <NUM>.

As illustrated in <FIG>, the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM> are caused to butt such that the saturable absorber <NUM> is sandwiched between the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM> (fifth step).

In the fifth step, the saturable absorber <NUM> overlaps the second core <NUM>, the second cladding <NUM>, and the second ferrule <NUM> when viewed in the thickness direction. In the fifth step, the outer edge of the saturable absorber <NUM> is positioned inside the outer edge of the second optical fiber <NUM> when viewed in the thickness direction. In the fifth step, the adhering part <NUM> of the saturable absorber <NUM> adheres to the second core <NUM>, the second cladding <NUM>, and the inner edge portion of the second ferrule <NUM>. In the fifth step, the non-adhering part <NUM> of the saturable absorber <NUM> does not adhere to the outer edge portion of the second ferrule <NUM>.

In the fifth step, the dent (see <FIG> and <FIG>) corresponding to the shape of the first cladding <NUM> of the first optical fiber <NUM> adhering at the adhering part <NUM> is formed in the saturable absorber <NUM>. Likewise, the dent corresponding to the shape of the second cladding <NUM> of the second optical fiber <NUM> adhering at the adhering part <NUM> is formed in the saturable absorber <NUM>.

In the fifth step, the first optical fiber <NUM> and the second optical fiber <NUM> are pressed so as to approach each other. In this pressed state, the space between the package <NUM> and the first ferrule holding portion <NUM> is bonded and sealed by the sealing material S and the space between the package <NUM> and the second ferrule holding portion <NUM> is bonded and sealed by the sealing material S. As a result, the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM> are accommodated in the housing <NUM> (sixth step). The first tip tube <NUM> is attached to an exhaust stand, and the space K1 is vacuumized via the first tip tube <NUM>. Then, a part of the first tip tube <NUM> is removed and blocked.

As described above, in the fiber structure <NUM>, the saturable absorber <NUM> sandwiched between the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM> has the adhering part <NUM> adhering to the first core <NUM>, the first cladding <NUM>, and the inner edge portion of the first ferrule <NUM> of the first optical fiber <NUM> and the non-adhering part <NUM> present around the adhering part <NUM> and not adhering to the outer edge portion of the first ferrule <NUM> when viewed in the thickness direction. In other words, between the saturable absorber <NUM> (non-adhering part <NUM>) and the tip portion 110a (second region 110b2) of the first optical fiber <NUM>, a play part where these do not adhere is present. Accordingly, even if air bubbles are generated between the saturable absorber <NUM> and the tip portion 110a when, for example, the saturable absorber <NUM> is placed in the tip portion 110a of the first optical fiber <NUM>, the air bubbles are capable of easily escaping to the surrounding space by means of the play part and it is possible to suppress the air bubbles having an effect to cause a decline in the adhesiveness between the saturable absorber <NUM> and the first optical fiber <NUM>. In other words, the adhesiveness between the saturable absorber <NUM> and the first optical fiber <NUM> can be enhanced. When the adhesiveness between the saturable absorber <NUM> and the first optical fiber <NUM> is high, the heat conduction of the saturable absorber <NUM>, eventually thermal diffusion, is improved, the life of the saturable absorber <NUM> can be extended, and durability enhancement can be achieved. When the adhesiveness between the saturable absorber <NUM> and the first optical fiber <NUM> is high, the saturable absorber <NUM> is unlikely to fall from the first optical fiber <NUM> when, for example, the abutment of the first optical fiber <NUM> and the second optical fiber <NUM> is released.

In the fiber structure <NUM>, the adhering part <NUM> adheres to the first core <NUM> and the first cladding <NUM> of the first optical fiber <NUM>. The tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM> butt such that the dent corresponding to the shape of the first cladding <NUM> of the first optical fiber <NUM> adhering at the adhering part <NUM> is formed in the saturable absorber <NUM>. As a result, the saturable absorber <NUM> is sandwiched between the first optical fiber <NUM> and the second optical fiber <NUM> such that the dent is formed. In this case, the first optical fiber <NUM> and the second optical fiber <NUM> are capable of sandwiching the saturable absorber <NUM> with sufficient and appropriate force, the heat conduction of the saturable absorber <NUM>, eventually thermal diffusion, is improved, the life of the saturable absorber <NUM> can be extended, and durability enhancement can be achieved.

In the fiber structure <NUM>, the tip portion 120a of the second optical fiber <NUM> has a protruding shape protruding to the tip side. The adhering part <NUM> of the saturable absorber <NUM> adheres to the second core <NUM>, the second cladding, and the inner edge portion of the second ferrule <NUM> of the second optical fiber <NUM>. The non-adhering part <NUM> of the saturable absorber <NUM> does not adhere to the outer edge portion of the second ferrule <NUM>. In other words, between the saturable absorber <NUM> (non-adhering part <NUM>) and the outer edge portion (fourth region 120b2) of the second ferrule <NUM>, a play part where these do not adhere is present. Accordingly, even if air bubbles are generated between, for example, the saturable absorber <NUM> and the second optical fiber <NUM>, the air bubbles are capable of easily escaping to the surrounding space by means of the play part and it is possible to suppress the air bubbles having an effect to cause a decline in the adhesiveness between the saturable absorber <NUM> and the second optical fiber <NUM>. In other words, the adhesiveness between the saturable absorber <NUM> and the second optical fiber <NUM> can be enhanced.

In the fiber structure <NUM>, the adhering part <NUM> adheres to the second core <NUM> and the second cladding <NUM> of the second optical fiber <NUM>. The tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM> butt such that the dent corresponding to the shape of the second cladding <NUM> of the second optical fiber <NUM> adhering at the adhering part <NUM> is formed in the saturable absorber <NUM>. As a result, the saturable absorber <NUM> is sandwiched between the first optical fiber <NUM> and the second optical fiber <NUM> such that the dent is formed. In this case, the first optical fiber <NUM> and the second optical fiber <NUM> are capable of sandwiching the saturable absorber <NUM> with sufficient force, the heat conduction of the saturable absorber <NUM>, eventually thermal diffusion, is improved, the life of the saturable absorber <NUM> can be extended, and durability enhancement can be achieved.

(a) of <FIG> is a photographic view illustrating a dent <NUM> formed in the saturable absorber <NUM>. (b) of <FIG> is an enlarged view of the B portion of (a) of <FIG>. As illustrated in (a) and (b) of <FIG>, the dent <NUM> is formed in the saturable absorber <NUM> when the saturable absorber <NUM> is sandwiched between the first optical fiber <NUM> and the second optical fiber <NUM>. The dent <NUM> is formed by leaving the shape of the outer edge of the first cladding <NUM> or the outer edge of the second cladding <NUM>. By means of the dent <NUM> formed in the saturable absorber <NUM>, it can be confirmed that the saturable absorber <NUM> appropriately overlapped the first core <NUM> and the first cladding <NUM> or the second core <NUM> and the second cladding <NUM>. In addition, by means of the dent <NUM> formed in the saturable absorber <NUM>, it can be confirmed that the first optical fiber <NUM> and the second optical fiber <NUM> sandwiched the saturable absorber <NUM> with appropriate force.

(a) of <FIG> is a photographic view illustrating the dent <NUM> formed in the saturable absorber <NUM>. (b) of <FIG> is a photographic view illustrating the result of observing the dent <NUM> with a polarizing microscope. When the saturable absorber <NUM> is pressurized and stress is generated about the pressurized part in the saturable absorber <NUM>, birefringence occurs at the pressurized part where the stress is generated when the saturable absorber <NUM> is irradiated with randomly polarized light. Accordingly, the pressurized part appears to shine when, for example, cross Nicol observation is performed by means of a polarizing microscope. Accordingly, the dent <NUM>, which is a circular stress or cladding mark caused by sandwiching the saturable absorber <NUM> between the first optical fiber <NUM> and the second optical fiber <NUM>, is brighter than, for example, parts other than the dent <NUM> as illustrated in (a) and (b) of <FIG> in, for example, cross Nicol observation by means of a polarizing microscope. In other words, it can be seen that the dent <NUM> in the saturable absorber <NUM> can be visualized by observing the saturable absorber <NUM> with a polarizing microscope.

In a punching-based saturable absorber formation process, a burr may be formed in the edge portion of the saturable absorber. As illustrated in <FIG>, when a saturable absorber 130A formed by general punching is placed on a glass plate <NUM> and observed in the thickness direction of the saturable absorber 130A by means of, for example, a microscope, it can be seen that interference fringes <NUM> are formed at a part of the edge portion of the saturable absorber 130A as illustrated in <FIG>. It is conceivable that this is because the saturable absorber 130A is lifted by a burr <NUM> formed in the edge portion of the saturable absorber 130A as illustrated in <FIG> and the lifting results in gap formation between the saturable absorber 130A and the glass plate <NUM>. It should be noted that the interference fringes are about a contact part <NUM> between the saturable absorber 130A and the glass plate <NUM> (see <FIG>). When the burr <NUM> is formed in the edge portion of the saturable absorber 130A as described above, the gap formation between the saturable absorber 130A and the glass plate <NUM> may result in a decline in the adhesiveness between the saturable absorber 130A and the glass plate <NUM>.

In this regard, in the fiber structure <NUM>, the play parts where these do not adhere are present between the saturable absorber <NUM> (non-adhering part <NUM>) and the outer edge portion (second region 110b2) of the first ferrule <NUM> and between the saturable absorber <NUM> (non-adhering part <NUM>) and the outer edge portion (fourth region 120b2) of the second ferrule <NUM> as described above. Accordingly, even if a burr is formed in, for example, the edge portion of the saturable absorber <NUM>, it is possible to suppress a decline in the adhesiveness between the saturable absorber <NUM> and the first and second optical fibers <NUM> and <NUM> attributable to the burr. In other words, it is possible to enhance the adhesiveness between the saturable absorber <NUM> and the first and second optical fibers <NUM> and <NUM> by sufficiently using the interaction between the interfaces caused by, for example, static electricity, intermolecular force, or the like. In addition, the adhesiveness between the saturable absorber <NUM> and the first optical fiber <NUM> is enhanced even when the saturable absorber <NUM> is placed in the tip portion 110a of the first optical fiber <NUM>, and thus falling of the saturable absorber <NUM> from the first optical fiber <NUM> is suppressed.

In the fiber structure <NUM>, the outer edge of the saturable absorber <NUM> is positioned inside the outer edges of the first optical fiber <NUM> and the second optical fiber <NUM> when viewed in the thickness direction. The diameter of the saturable absorber <NUM> is smaller than the diameters of the first optical fiber <NUM> and the second optical fiber <NUM> as compared with a case where, for example, the outer edge of the saturable absorber is positioned outside the outer edges of the first optical fiber <NUM> and the second optical fiber <NUM> when viewed in the thickness direction, and thus no impact is likely to be applied from the sheet end portion of the saturable absorber <NUM>. Accordingly, the adhesion force of the saturable absorber <NUM> with respect to the first optical fiber <NUM> and the second optical fiber <NUM> is improved and the saturable absorber <NUM> is unlikely to peel off. As a result, the adhesiveness between the saturable absorber <NUM> and the first and second optical fibers <NUM> and <NUM> can be further enhanced.

In the fiber structure <NUM>, the saturable absorber <NUM> has a circular shape when viewed in the thickness direction. When the saturable absorber has, for example, a polygonal shape when viewed in the thickness direction, the saturable absorber is likely to peel off from its corner portion. On the other hand, the saturable absorber <NUM> has a circular shape when viewed in the thickness direction, and thus the saturable absorber <NUM> is unlikely to peel off from the first optical fiber <NUM> and the second optical fiber <NUM>. As a result, the adhesiveness between the saturable absorber <NUM> and the first and second optical fibers <NUM> and <NUM> can be further enhanced.

In the fiber structure <NUM>, the saturable absorber <NUM> contains the sheet-shaped resin and the plurality of carbon nanotubes dispersed in the resin. As a result, the saturable absorber <NUM> can be formed from the resin and the carbon nanotubes.

The pulse laser device <NUM> includes the fiber structure <NUM>. The pulse laser device <NUM> as well as the fiber structure <NUM> has actions and effects such as being capable of enhancing the adhesiveness between the saturable absorber <NUM> and the first optical fiber <NUM>.

The supercontinuum light source <NUM> includes the pulse laser device <NUM>. The supercontinuum light source <NUM> as well as the fiber structure <NUM> has actions and effects such as being capable of enhancing the adhesiveness between the saturable absorber <NUM> and the first optical fiber <NUM>.

When the first optical fiber <NUM> is pressed to the second optical fiber <NUM> side, it is difficult to further press the first optical fiber <NUM> if the first optical fiber <NUM> and the package <NUM> are already in contact (mechanical interference). In other words, a gap between the package <NUM> and the first optical fiber <NUM> (or the first ferrule holding portion <NUM>) is necessary in order to realize the pressing. The same applies to the second optical fiber <NUM>.

In this regard, in the fiber structure <NUM>, a gap is formed between the package <NUM> (bottom surface 145a of the opening <NUM>) and the end surface of the first ferrule holding portion <NUM>. A gap is formed between the package <NUM> (bottom surface 146a of the opening <NUM>) and the end surface of the second ferrule holding portion <NUM>. As a result, the first optical fiber <NUM> and the second optical fiber <NUM> can be pressed against each other.

In the fourth step of the method for producing the fiber structure <NUM>, the saturable absorber <NUM> is placed in the tip portion 110a of the first optical fiber <NUM> such that the adhering part <NUM> adhering to the first core <NUM>, the first cladding <NUM>, and the inner edge portion of the first ferrule <NUM> of the first optical fiber <NUM> and the non-adhering part <NUM> present around the adhering part <NUM> and not adhering to the outer edge portion of the first ferrule <NUM> are formed in the saturable absorber <NUM>. In other words, between the saturable absorber <NUM> (non-adhering part <NUM>) and the outer edge portion (second region 110b2) of the first ferrule <NUM>, the play part where these do not adhere is present. Accordingly, even if air bubbles are generated between the saturable absorber <NUM> and the tip portion 110a when, for example, the saturable absorber <NUM> is placed in the tip portion 110a of the first optical fiber <NUM>, the air bubbles are capable of easily escaping to the surrounding space by means of the play part and it is possible to suppress the air bubbles having an effect to cause a decline in the adhesiveness between the saturable absorber <NUM> and the first optical fiber <NUM>. In other words, the adhesiveness between the saturable absorber <NUM> and the first optical fiber <NUM> can be enhanced. When the adhesiveness between the saturable absorber <NUM> and the first optical fiber <NUM> is high, the heat conduction of the saturable absorber <NUM>, eventually thermal diffusion, is improved, the life of the saturable absorber <NUM> can be extended, and durability enhancement can be achieved. When the adhesiveness between the saturable absorber <NUM> and the first optical fiber <NUM> is high, the saturable absorber <NUM> is unlikely to fall from the first optical fiber <NUM>.

In the fourth step of the method for producing the fiber structure <NUM>, the saturable absorber <NUM> is placed in the tip portion of the first optical fiber <NUM> such that the adhering part <NUM> adheres to the first core <NUM> and the first cladding <NUM> of the first optical fiber <NUM>. In the fifth step, the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM> butt such that the dent corresponding to the shape of the first cladding <NUM> of the first optical fiber <NUM> adhering at the adhering part <NUM> is formed in the saturable absorber <NUM>. As a result, the saturable absorber <NUM> is sandwiched between the first optical fiber <NUM> and the second optical fiber <NUM> such that the dent is formed. In this case, the first optical fiber <NUM> and the second optical fiber <NUM> are capable of sandwiching the saturable absorber <NUM> with sufficient force, the heat conduction of the saturable absorber <NUM>, eventually thermal diffusion, is improved, the life of the saturable absorber <NUM> can be extended, and durability enhancement can be achieved.

In the method for producing the fiber structure <NUM>, the tip portion 120a of the second optical fiber <NUM> has a protruding shape protruding to the tip side. In the fifth step, the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM> butt such that the adhering part <NUM> adheres to the second core <NUM>, the second cladding <NUM>, and the inner edge portion of the second ferrule <NUM> of the second optical fiber <NUM> and the non-adhering part <NUM> does not adhere to the outer edge portion of the second ferrule <NUM>. In other words, between the saturable absorber <NUM> (non-adhering part <NUM>) and the outer edge portion (fourth region 120b2) of the second ferrule <NUM>, the play part where these do not adhere is present. Accordingly, even if air bubbles are generated between, for example, the saturable absorber <NUM> and the second optical fiber <NUM> with the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM> butting, the air bubbles are capable of easily escaping to the surrounding space by means of the play part and it is possible to suppress the air bubbles having an effect to cause a decline in the adhesiveness between the saturable absorber <NUM> and the second optical fiber <NUM>. In other words, the adhesiveness between the saturable absorber <NUM> and the second optical fiber <NUM> can be enhanced.

In the fifth step of the method for producing the fiber structure <NUM>, the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM> butt such that the dent corresponding to the shape of the second cladding <NUM> of the second optical fiber <NUM> adhering at the adhering part <NUM> is formed in the saturable absorber <NUM>. As a result, the saturable absorber <NUM> is sandwiched between the first optical fiber <NUM> and the second optical fiber <NUM> such that the dent is formed. In this case, the first optical fiber <NUM> and the second optical fiber <NUM> are capable of sandwiching the saturable absorber <NUM> with sufficient force, the heat conduction of the saturable absorber <NUM>, eventually thermal diffusion, is improved, the life of the saturable absorber <NUM> can be extended, and durability enhancement can be achieved.

In the fourth step of the method for producing the fiber structure <NUM>, the saturable absorber <NUM> is placed in the tip portion 110a of the first optical fiber <NUM> such that the outer edge is positioned inside the outer edge of the first optical fiber <NUM> when viewed in the thickness direction. As compared with, for example, a case where the saturable absorber is placed in the tip portion 110a of the first optical fiber <NUM> such that the outer edge is positioned outside the outer edge of the first optical fiber <NUM> when viewed in the thickness direction, the diameter of the saturable absorber <NUM> is smaller than the diameter of the first optical fiber <NUM>, and thus no impact is likely to be applied from the sheet end portion of the saturable absorber <NUM>. Accordingly, the adhesion force of the saturable absorber <NUM> with respect to the first optical fiber <NUM> is improved and the saturable absorber <NUM> is unlikely to peel off. As a result, the adhesiveness between the saturable absorber <NUM> and the first optical fiber <NUM> can be further enhanced.

In the fifth step of the method for producing the fiber structure <NUM>, the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM> butt such that the outer edge of the saturable absorber <NUM> is positioned inside the outer edge of the second optical fiber <NUM> when viewed in the thickness direction. As compared with, for example, a case where the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM> butt such that the outer edge of the saturable absorber is positioned outside the outer edge of the second optical fiber <NUM> when viewed in the thickness direction, the diameter of the saturable absorber <NUM> is smaller than the diameter of the second optical fiber <NUM>, and thus no impact is likely to be applied from the sheet end portion of the saturable absorber <NUM>. Accordingly, the adhesion force of the saturable absorber <NUM> with respect to the second optical fiber <NUM> is improved and the saturable absorber <NUM> is unlikely to peel off. As a result, the adhesiveness between the saturable absorber <NUM> and the second optical fiber <NUM> can be further enhanced.

In the fourth step of the method for producing the fiber structure <NUM>, the Newton ring <NUM> containing the interference fringes generated at the non-adhering part <NUM> of the saturable absorber <NUM> is formed in the saturable absorber <NUM>. Accordingly, by observing the Newton ring <NUM>, it is possible to easily grasp the state where the adhering part <NUM> of the saturable absorber <NUM> adheres to the first core <NUM>, the first cladding <NUM>, and the inner edge portion of the first ferrule <NUM> and the non-adhering part <NUM> of the saturable absorber <NUM> does not adhere to the outer edge portion of the first ferrule <NUM>.

The method for producing the fiber structure <NUM> includes the sixth step of accommodating the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM> in the housing <NUM>. Accordingly, the saturable absorber <NUM> can be accommodated in the housing <NUM> together with the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM>. As a result, deterioration of the saturable absorber <NUM> attributable to oxidation can be suppressed. Accordingly, the life of the saturable absorber <NUM> can be extended and durability enhancement can be achieved.

In the method for producing the fiber structure <NUM>, the saturable absorber <NUM> is circular when viewed in the thickness direction. As a result, the adhesiveness between the saturable absorber <NUM> and the first and second optical fibers <NUM> and <NUM> can be further enhanced as described above.

It should be noted that the above effect in the case of burr formation in the edge portion of the saturable absorber <NUM> is similarly exhibited in the method for producing the fiber structure <NUM>.

As illustrated in (a) and (b) of <FIG>, in the saturable absorber <NUM>, the distance from the center to the edge portion is more uniform than in a polygonal saturable absorber 130B. As a result, the center of the saturable absorber <NUM> can be more easily aligned with the center of the tip portion 110a of the first optical fiber <NUM> (here, the center of the first cladding <NUM>). In other words, the saturable absorber <NUM> can be easily placed in the tip portion 110a of the first optical fiber <NUM>. As a result, in the fiber structure <NUM>, the saturable absorber <NUM> and the first optical fiber <NUM> can be accurately positioned relative to each other.

In the circular saturable absorber <NUM> as compared with the polygonal saturable absorber 130B, the size (area) of the saturable absorber <NUM> can be reduced with the area of the adhering part <NUM> with respect to the first optical fiber <NUM> constant. As a result, the center of the saturable absorber <NUM> can be more easily aligned with the center of the tip portion 110a of the first optical fiber <NUM>. In other words, the saturable absorber <NUM> can be more easily placed in the tip portion 110a of the first optical fiber <NUM>. As a result, in the fiber structure <NUM>, the saturable absorber <NUM> and the first optical fiber <NUM> can be more accurately positioned relative to each other. In addition, when the saturable absorber <NUM> is placed in the tip portion 110a of the first optical fiber <NUM>, there is no need to pay attention to the corner portion protruding from the first ferrule <NUM>, and thus workability is improved.

(a) to (f) of <FIG> are photographic views illustrating the Newton ring. As illustrated in (a) to (f) of <FIG>, the size of the adhering part <NUM> with respect to the first optical fiber <NUM> in each of the saturable absorbers <NUM> and 130B can be observed by observing the Newton ring <NUM>. When the saturable absorber <NUM> is used, the diameter of the adhering part <NUM> is approximately <NUM> to <NUM>. The diameter of the adhering part <NUM> is approximately <NUM> when the saturable absorber 130B is used. As described above, the size of the adhering part <NUM> does not tend to change depending on the shape of the saturable absorber. The adhesion ratio between the saturable absorber <NUM> and the first optical fiber <NUM> (area of the adhering part <NUM>/area of the saturable absorber <NUM>) is approximately <NUM>% to <NUM>%.

By the way, when the saturable absorber <NUM> is placed in the tip portion 110a of the first optical fiber <NUM>, the size of the adhering part <NUM> between the saturable absorber <NUM> and the tip portion 110a depends only on the radius of curvature of the first end surface 110b without depending on the parameters of the saturable absorber <NUM> (when the saturable absorber <NUM> maintains a flat sheet shape). This is because the adhering part <NUM> is a point-of-contact component between the first end surface 110b of the first optical fiber <NUM> and the saturable absorber <NUM>.

<FIG> is a photographic view illustrating the Newton ring observed in the saturable absorber <NUM>. After the saturable absorber <NUM> is placed in the tip portion 110a of the first optical fiber <NUM>, the adhering part <NUM> may move before and after the saturable absorber <NUM> is sandwiched between the first optical fiber <NUM> and the second optical fiber <NUM>. After the placement of the saturable absorber <NUM> in the tip portion 110a of the first optical fiber <NUM>, the Newton ring <NUM> was observed before the sandwiching of the saturable absorber <NUM> between the first optical fiber <NUM> and the second optical fiber <NUM>. Then, the saturable absorber <NUM> was sandwiched between the first optical fiber <NUM> and the second optical fiber <NUM>, the first optical fiber <NUM> and the saturable absorber <NUM> were removed from the second optical fiber 120after, for example, <NUM> hours, and the Newton ring <NUM> was observed again.

As illustrated in (a) of <FIG>, the Newton ring <NUM> is formed at a position away from the first cladding <NUM> after the saturable absorber <NUM> is placed in the tip portion 110a of the first optical fiber <NUM> and before the saturable absorber <NUM> is sandwiched between the first optical fiber <NUM> and the second optical fiber <NUM>. On the other hand, as illustrated in (b) of <FIG>, the Newton ring <NUM> moves in the direction of the first cladding <NUM> after the saturable absorber <NUM> is sandwiched between the first optical fiber <NUM> and the second optical fiber <NUM> and then the first optical fiber <NUM> and the saturable absorber <NUM> are removed from the second optical fiber <NUM>.

As described above, one aspect of the present invention is not limited to the above-described embodiment and may be modified or applied to those that differ without changing the scope described in each claim.

Although an example in which the first inclined surface 110c of the first optical fiber <NUM> is a side surface of a truncated cone is illustrated in the above embodiment, the first inclined surface 110c may be a curved surface continuously connected to the first end surface 110b. In other words, the tip-side end surface of the first optical fiber <NUM> may be a bowl-shaped (spherical) curved surface protruding to the tip side. In the above embodiment, the tip-side end surface of the first optical fiber <NUM> may be configured by a flat surface and a curved surface.

Although an example in which the second inclined surface 120c of the second optical fiber <NUM> is a side surface of a truncated cone is illustrated in the above embodiment, the second inclined surface 120c may be a curved surface continuously connected to the second end surface 120b. In other words, the tip-side end surface of the second optical fiber <NUM> may be a bowl-shaped (spherical) curved surface protruding to the tip side. In the above embodiment, the tip-side end surface of the second optical fiber <NUM> may be configured by a flat surface and a curved surface.

Although an example in which both the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM> have a protruding shape protruding to the tip side is illustrated in the above embodiment, the tip portion 120a of the second optical fiber <NUM> may not have a protruding shape. For example, the tip portion 120a of the second optical fiber <NUM> may have a columnar shape and the outer diameter of the tip portion 120a of the second optical fiber <NUM> may match the outer diameter of the base end side of the second optical fiber <NUM>.

Although an example in which the adhering part <NUM> of the saturable absorber <NUM> adheres to the first core <NUM>, the first cladding <NUM>, and the inner edge portion of the first ferrule <NUM> of the first optical fiber <NUM> is illustrated in the above embodiment, the adhering part <NUM> may not adhere to the first cladding <NUM> and the inner edge portion of the first ferrule <NUM>. The adhering part <NUM> may at least adhere to the first core <NUM>.

Although an example in which the adhering part <NUM> of the saturable absorber <NUM> adheres to the second core <NUM>, the second cladding <NUM>, and the inner edge portion of the second ferrule <NUM> of the second optical fiber <NUM> is illustrated in the above embodiment, the adhering part <NUM> may not adhere to the second cladding <NUM> and the inner edge portion of the second ferrule <NUM>. The adhering part <NUM> may at least adhere to the second core <NUM>.

Although an example in which the outer edge of the saturable absorber <NUM> is positioned inside the outer edges of both the first optical fiber <NUM> and the second optical fiber <NUM> when viewed in the thickness direction is illustrated in the above embodiment, the outer edge of the saturable absorber <NUM> may not be positioned inside the outer edge of the second optical fiber <NUM> insofar as the outer edge of the saturable absorber <NUM> is positioned inside the outer edge of the first optical fiber <NUM> when viewed in the thickness direction. For example, when viewed in the thickness direction, the outer edge of the saturable absorber <NUM> may coincide with the outer edge of the second optical fiber <NUM> or may be positioned outside the outer edge of the second optical fiber <NUM>. The outer edge of the saturable absorber <NUM> may not be positioned inside the outer edge of the first optical fiber <NUM> insofar as the outer edge of the saturable absorber <NUM> is positioned inside the outer edge of the second optical fiber <NUM> when viewed in the thickness direction. For example, when viewed in the thickness direction, the outer edge of the saturable absorber <NUM> may coincide with the outer edge of the first optical fiber <NUM> or may be positioned outside the outer edge of the first optical fiber <NUM>. The outer edge of the saturable absorber <NUM> may be positioned inside the outer edge of at least one of the first optical fiber <NUM> and the second optical fiber <NUM> when viewed in the thickness direction.

Although an example in which the tip portion 110a of the first optical fiber <NUM> and the tip portion 120a of the second optical fiber <NUM> have a protruding shape and the saturable absorber <NUM> is provided with a configuration having the adhering part <NUM> and the non-adhering part <NUM> is described in the above embodiment, the present invention is not limited thereto. The configuration may not be provided when the outer edge of the saturable absorber <NUM> is positioned inside the outer edge of at least one of the first optical fiber <NUM> and the second optical fiber <NUM> when viewed in the thickness direction.

Although an example in which the saturable absorber <NUM> is circular when viewed in the thickness direction is illustrated in the above embodiment, the saturable absorber <NUM> may have an elliptical shape or an oval shape (that is, a rounded rectangular shape or a track shape) when viewed in the thickness direction. In this case, the saturable absorber <NUM> is unlikely to peel off from the first optical fiber <NUM> and the second optical fiber <NUM> as in a case where the saturable absorber <NUM> is circular when viewed in the thickness direction. As a result, the adhesiveness between the saturable absorber <NUM> and the first and second optical fibers <NUM> and <NUM> can be further enhanced.

Although an example in which the saturable absorber <NUM> is circular when viewed in the thickness direction is illustrated in the above embodiment, the saturable absorber <NUM>, when viewed in the thickness direction, may be polygonal with its corner portion square-chamfered or round-chamfered. The square chamfering is so-called C chamfering. The round chamfering is so-called R chamfering. In this case, the saturable absorber <NUM> is less likely to peel off, as in a case where the saturable absorber <NUM> is circular when viewed in the thickness direction, than in a case where the saturable absorber <NUM> has a corner portion. As a result, the adhesiveness between the saturable absorber <NUM> and the first and second optical fibers <NUM> and <NUM> can be further enhanced.

Although an example in which the saturable absorber <NUM> is a sheet-shaped sheet body containing carbon nanotubes is illustrated in the above embodiment, the saturable absorber <NUM> may be a semiconductor substrate. Examples of the semiconductor substrate include a semiconductor substrate manufactured by BATOP GmbH, having a size of <NUM> by <NUM> (five square millimeters), and having a thickness of hundreds of micrometers.

Claim 1:
A fiber structure comprising:
first and second optical fibers (<NUM>, <NUM>) disposed such that tip portions (110a, 120a) thereof butt; and
a sheet-shaped saturable absorber (<NUM>) sandwiched between the tip portion (110a) of the first optical fiber (<NUM>) and the tip portion (120a) of the second optical fiber (<NUM>), wherein
each of the tip portions (110a, 120a) of the first optical fiber (<NUM>) and the second optical fiber (<NUM>) has a core (<NUM>, <NUM>), a cladding (<NUM>, <NUM>) provided around the core (<NUM>, <NUM>), and a ferrule (<NUM>, <NUM>) provided around the cladding (<NUM>, <NUM>),
the tip portion (110a) of the first optical fiber (<NUM>) has a protruding shape protruding to a tip side,
characterised in that
the saturable absorber (<NUM>) has an adhering part (<NUM>) at least adhering to the core (<NUM>) of the first optical fiber (<NUM>) and a non-adhering part (<NUM>) present around the adhering part (<NUM>) and not adhering to the tip portion (110a) of the first optical fiber (<NUM>).