JP2013190589A - Polarizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer which is capable of reducing an influence of nonlinear optical effects of a dielectric.SOLUTION: A polarizer 1 has a fiber coupler structure having a coupling part 3 where two hollow core optical fibers 2 are coupled in a lengthwise direction. The portions transmitting light are hollow core parts of the hollow core optical fibers.

Description

  The present invention relates to a polarizer. More specifically, the present invention relates to a polarizer that extracts linearly polarized light in a specific direction from natural light or linearly polarized light in a certain direction.

  In recent years, optical communication technology that enables high-speed data communication has been widely adopted in the information communication field. Further, a polarizer is known as one of optical components used in an optical communication system. Such a polarizer is an element that extracts linearly polarized light in a specific direction from natural light oscillating in all directions or linearly polarized light oscillating in a certain direction. That is, the polarizer has a function of selectively transmitting a polarization component in a specific direction in incident light and blocking a polarization component in a direction orthogonal to the polarization component.

  Further, the polarizer is an indispensable optical component for eliminating the instability of the optical circuit due to the fluctuation of the polarization. As polarizers used for optical communication, optical measurement, and the like, waveguide-type polarizers, bulk-type polarizers, and intermediate polarizers between waveguide-type and bulk-type have been proposed (for example, patents). (See Literature 1 or Patent Literature 2).

Japanese Patent Laid-Open No. 5-93683 JP 7-27935 A

  By the way, in recent years, the influence of the nonlinear optical effect of the dielectric in the optical component has become a problem, and in order not to be affected by this, it is desirable that the light transmitting portion is hollow. On the other hand, photonic band gap fibers, Bragg fibers, and the like have been developed as hollow optical transmission media. However, optical components such as polarizers do not have a hollow structure, and only have a structure that passes through a finite-length dielectric regardless of whether they are a bulk type or a waveguide type. A polarizer having a structure that passes through a dielectric cannot avoid the influence of various nonlinear optical effects.

  The present invention has been made in view of the above-described problems, and provides a polarizer capable of reducing the influence of a nonlinear optical effect of a dielectric.

  In order to achieve the above object, in the polarizer of the present invention, the light transmitting portion of the coupling portion is a hollow core portion.

  Specifically, the polarizer of the present invention has a fiber coupler structure having a coupling portion in which two hollow core optical fibers are coupled in the longitudinal direction, and the light transmitting portion is the hollow core of the hollow core optical fiber. It is a part.

  The polarizer of the present invention is characterized in that, in the above-described present invention, the two hollow core optical fibers are two photonic band gap fibers.

  In the polarizer of the present invention, in the above-described present invention, the lattice spacing of the hollow core portion in the two photonic band gap fibers is D, and a pair of adjacent lattices in the grating formed in the photonic band gap fiber. Is a lattice spacing of Λ, and the normalized lattice spacing D / Λ of the hollow core portion in the two photonic bandgap fibers per lattice spacing Λ is 3 or more and 4 or less.

  In the polarizer of the present invention, in the above-described present invention, the lattice spacing of the hollow core portion in the two photonic band gap fibers is D, and a pair of adjacent lattices in the grating formed in the photonic band gap fiber. Is a lattice spacing of Λ, and the normalized lattice spacing D / Λ of the hollow core portion in the two photonic band gap fibers per lattice spacing Λ is 6 or more and less than 8.

In the polarizer of the present invention, in the above-described present invention, when the length of the coupling portion is x-polarized light and y-polarized light are respectively Lx and Ly, and m and n are arbitrary integers of 0 or more. ,
Lx × 2 × m = Ly × (2 × n + 1) (1)
Or
Lx × (2 × m + 1) = Ly × 2 × n (2)
It is characterized by being. However, neither Lx nor Ly is 0.

  In the polarizer of the present invention, in the above-described present invention, the lattice spacing of the hollow core portion in the two photonic band gap fibers is D, and a pair of adjacent lattices in the grating formed in the photonic band gap fiber. Is a lattice spacing of Λ, and the normalized lattice spacing D / Λ of the hollow core portion in the two photonic band gap fibers per lattice spacing Λ is approximately 5.

  The polarizer of the present invention is characterized in that, in the above invention, the length of the coupling portion is Lx × m where the coupling length of x-polarized light is Lx. However, m = 1, 2, or 3.

  In the polarizer according to the present invention, in the above-described present invention, the fiber coupler structure is formed by polishing the side surfaces of the two hollow core optical fibers into a flat shape, and the hollow core portions of the two hollow core optical fibers are formed with each other. It is characterized in that it includes a coupling portion in which the two hollow core optical fibers are coupled in close proximity to each other, or a coupling portion in which the two hollow core optical fibers are stretched and coupled in the longitudinal direction of the hollow core optical fiber.

  In the polarizer of the present invention, a hollow core optical fiber is used as a hollow optical transmission medium, and a light transmitting portion is a hollow core portion of the hollow core optical fiber, so that light normally passes through a dielectric. Compared with a polarizer, the optical component is less affected by the nonlinear optical effect.

It is the schematic which showed the one aspect | mode of the polarizer which concerns on this invention. It is the elements on larger scale around the coupling | bond part of a polarizer. It is AA sectional drawing of FIG. It is the figure which showed the relationship between the bond length of x polarized light and y polarized light with respect to D / Λ. It is the schematic diagram which calculated and showed the branching characteristic of each polarized light when changing the length of a coupling part. It is the schematic diagram which calculated and showed the branching characteristic of each polarized light when changing the length of a coupling part. It is the schematic diagram which calculated and showed the branching characteristic of each polarized light when changing the length of a coupling part.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

  FIG. 1 is a schematic view showing an aspect of a polarizer 1 according to the present invention, FIG. 2 is a partially enlarged view of the periphery of a coupling portion 3 of the polarizer 1, and FIG. 3 is a cross-sectional view taken along line AA in FIG. Respectively.

  As shown in FIG. 1, a polarizer 1 according to the present invention includes photonic bandgap fibers (PBF) 21 and 22, which are two hollow core optical fibers 2, in the longitudinal direction (the arrow direction in FIG. 1). The so-called fiber coupler structure having the coupling portion 3 coupled to () is configured.

  As described above, in the polarizer 1, the two hollow core optical fibers 2 are composed of the two photonic band gap fibers (the first photonic band gap fiber 21 and the second photonic band gap fiber 22). Such an embodiment is shown. Further, as shown in FIG. 2, the polarizer 1 has light transmitting portions as the hollow core portions 51 and 52 of the photonic band gap fibers 21 and 22 that are the hollow core optical fibers 2, and the light transmitting portions. There is no dielectric.

  The fiber coupler structure that constitutes the polarizer 1 of the present invention is, for example, Canadian Instrumentation & Research, Polarization-Maintaining Coupler: http: // www. cirl. com / 954 p. As disclosed in php and the like, the hollow core portions 51 and 52 of the photonic band gap fibers 21 and 22 are brought close to each other after the side surfaces of the two photonic band gap fibers 21 and 22 are polished into a flat shape. Thus, it is possible to employ a polishing type fiber coupler structure that is coupled by evanescent coupling or the like. In addition, two photonic bandgap fibers 21 and 22 are heated and melted and bonded by evanescent bonding or the like, and if necessary, the bonded portion 3 is stretched and thinned to bring the hollow core portions 51 and 52 closer to each other. A coupler structure or the like may be employed.

  A cross-sectional structure of the coupling portion 3 is shown in FIG. Two photonic gap fibers (first photonic band gap fiber 21 and second photonic band gap fiber 22) are equal in diameter and have a lattice 41 that is a plurality of holes arranged at equal intervals. In addition, a clad made of glass such as quartz glass including 42 and hollow core portions 51 and 52 made of a hollow region where such glass does not exist are formed. Alternatively, it may be a multi-core fiber.

  Here, in the cross-sectional structure shown in FIG. 3, the direction along the axis connecting the centers of the two hollow core parts 51 and 52 is the x direction, and the direction orthogonal to the x direction in the cross-sectional view is the y direction. Moreover, the lattice spacing of the hollow core portions 51 and 52 in the two photonic band gap fibers 21 and 22 is D, and the lattices of a pair of adjacent lattices in the lattices 41 and 42 constituting the photonic band gap fibers 21 and 22 When the interval is Λ, the lattice interval D / Λ (normalized lattice interval) of the hollow core portions 51 and 52 per lattice interval Λ of the gratings 41 and 42, the polarization in the x direction (x polarization), and the polarization in the y direction ( FIG. 4 shows the relationship between the coupling length L / Λ (normalized coupling length) per lattice spacing Λ of the gratings 41 and 42 when the coupling length of y-polarized light is L (Lx, Ly).

  FIG. 4 is a result of numerical analysis of a change in operating characteristics when the core interval of the fiber coupler structure in the polarizer 1 (the lattice interval of the hollow core portions 51 and 52 and the lattice interval of the lattices 41 and 42) is changed. Specifically, the range of D / Λ from 3 to 7 is graphed while the lattice spacing Λ is 2.5 μm and D / Λ is changed in the range of 3 to 8.

  Such D / Λ is preferably about 3 or more and less than 8. When D / Λ is less than 3, the glass portion serving as the partition between the two cores disappears, so that the coupler structure is not obtained. When D / Λ is large, there is a margin in the manufacturing deviation of the polarizer, but when D / Λ is 8 or more, the normalized coupling length reaches 400,000. If the normalized coupling length is 400000, it means that the coupling length reaches 1 m when Λ is 2.5 μm. If the coupling length is 1 m or longer, the length of the coupling portion 3 is too long, and it may be difficult to manufacture the polarizer 1.

  Moreover, it is preferable that the length L of the coupling portion 3 of the polarizer 1 is approximately several mm to 1 m in view of the manufacturing method and stability.

  Hereinafter, an appropriate design of the polarizer 1 in a predetermined D / Λ within the above-described range of D / Λ will be described.

(1) D / Λ = 3 or more and 4 or less FIG. 5 shows the length of the coupling unit 3 on the assumption that the ratio of the coupling length of y-polarized light to the coupling length of x-polarized light is y: x = 10: 9. It is the schematic diagram which computed and showed the branching characteristic (branch characteristic of light intensity) of each polarization | polarized-light when changing the length. The horizontal axis represents the length of the coupling portion 3, and the vertical axis represents the light intensity of the photonic bandgap fiber (for example, the first photonic bandgap fiber 21). Note that the exact calculation for each polarizer 1 is performed using the coupling length as a parameter.

  When D / Λ is 3 or more and 4 or less and the polarizer 1 is used as a fiber coupler, for example, the length of the coupling portion 3 of the polarizer 1 is set to an operating point such as point A in FIG. To produce a fiber coupler so that there is no difference in the branching characteristics due to polarized light. Point A is a point where all the light of the optical fiber 1 is transferred to the optical fiber 2 in both the x polarization and the y polarization, that is, the intensity of the optical fiber 1 becomes zero. What is necessary is just to produce the polarizer 1 of the length which becomes an operating point of A point. This length can be obtained as the actual length by multiplying the normalized coupling length of FIG. 4 by the lattice spacing Λ.

  Further, as shown in FIG. 5 described above, in the polarizer having the configuration shown in FIGS. 1 to 3, the coupling length slightly differs depending on the polarization direction of light when D / Λ is in the range of 3 to 4. (The bond length of y-polarized light is longer than the bond length of x-polarized light). For this reason, when the length of the coupling portion 3 is increased, the difference in the coupling length is accumulated, and at the point B in FIG. 5, the polarization power of the first photonic band gap fiber 21 is the second photonic band gap. The light intensity of the polarization of the second photonic bandgap fiber 22 can remain in the first photonic bandgap fiber 21 with 100% transition to the fiber 22.

  In this case, in the present invention, the operation as the polarizer 1 is realized by designing the length of the coupling portion 3 of the polarizer 1 to a length that becomes an operating point such as point B in FIG. As shown in FIG. 5, the light intensity in the photonic bandgap fiber 21 at point B is approximately 100% for y-polarized light and approximately 0% for x-polarized light. Since only the y-polarized light exists in the photonic band gap fiber 21, the polarizer 1 operates as a polarizer. Alternatively, a point where y-polarized light is approximately 0% and x-polarized light is approximately 100% may be selected.

In order to obtain a point where y-polarized light is approximately 100% and x-polarized light is approximately 0%, or y-polarized light is approximately 0% and x-polarized light is approximately 100%, FIG. X-polarized light and y-polarized light coupling lengths, respectively, Lx and Ly, and m and n are arbitrary integers of 0 or more.
Lx × (2 × m + 1) = Ly × 2 × n (3)
Or Lx × 2 × m = Ly × (2 × n + 1) (4)
M and n may be selected so that However, neither Lx nor Ly is 0.

(2) D / Λ = 6 or more and less than 8 Next, when D / Λ is 6 or more in FIG. 4, the coupling length of x-polarized light and y-polarized light is different from 1.5 times to 2.5 times. State (a state in which the coupling length of y-polarized light is 1.5 to 2.5 times longer than the coupling length of x-polarized light).

  FIG. 6 is a schematic diagram of calculation of the branching characteristics of each polarization when the length of the coupling portion 3 is changed when D / Λ is 6 or more. In FIG. 6, it is assumed that the ratio of the bond length of x-polarized light and the bond length of y-polarized light is 1: 2.

  If the fiber coupler having the branching characteristics shown in FIG. 6 is designed to the length of the point C shown in FIG. 6, the operation as the polarizer 1 can be realized. That is, the point C corresponds to the coupling length of y-polarized light, and the light intensity in the photonic band gap fiber 21 is approximately 0% for y-polarized light and approximately 100% for x-polarized light. Since there is only x-polarized light in the photonic band gap fiber 21, the polarizer 1 operates as a polarizer. Alternatively, a point where y-polarized light is approximately 100% and x-polarized light is approximately 0% may be selected.

In order to obtain a point where y-polarized light is approximately 0% and x-polarized light is approximately 100%, or a point where y-polarized light is approximately 100% and x-polarized light is approximately 0%, FIG. X-polarized light and y-polarized light coupling lengths, respectively, Lx and Ly, and m and n are arbitrary integers of 0 or more.
Lx × 2 × m = Ly × (2 × n + 1) (5)
Or Lx × (2 × m + 1) = Ly × 2 × n (6)
M and n may be selected so that However, neither Lx nor Ly is 0.

  In this structure, light incident on one of the two photonic bandgap fibers 21 and 22 (for example, the first photonic bandgap fiber 21) is incident on the other photonic bandgap fiber. Since only one reciprocation is made to the band gap fiber (for example, the second photonic band gap fiber 22), the polarizer 1 with further reduced non-linearity than the design shown in FIG. 4 can be realized.

  On the other hand, when D / Λ is 8 or more, the normalized coupling length reaches 400000 as described above. That the bond length reaches 400,000 means that the bond length reaches 1 m when Λ is 2.5 μm. When the coupling length is 1 m, the length of the coupling portion 3 is too long, and it may be difficult to manufacture the polarizer 1. Therefore, D / Λ is preferably less than 8.

(3) When D / Λ = approximately 5 When D / Λ is approximately 5 in FIG. 4, the two central core portions 51 and 52 of the photonic bandgap fibers 22 and 22 constituting the polarizer 1. Only the polarization in the polarization direction perpendicular to the axis connecting the centers of the two is in a state in which the coupling length is resonantly increased.

  FIG. 7 is a schematic diagram of the branching characteristics of each polarized light in this region. In FIG. 7, it is assumed that the ratio of the bond length of y-polarized light to the bond length of x-polarized light is 10: 1. In the fiber coupler having the branching characteristics shown in FIG. 7, the operation as the polarizer 1 can be realized by designing the length of the coupling portion to the length of the point D. The point D corresponds to the coupling length of x-polarized light, and the x-polarized light intensity in the photonic band gap fiber 21 is zero. That is, since there is only y-polarized light in the photonic bandgap fiber 21, the polarizer 1 operates as a polarizer that transmits only y-polarized light.

  In order to obtain a point at which the y-polarized light is approximately 100% and the x-polarized light is approximately 0%, the coupling length of the x-polarized light is obtained and, when Lx is obtained, the length of the coupling portion is Lx × m may be used. m = 1, 2, or 3; If m = 3 or less, a function as a polarizer can be expected. However, since the ratio of y-polarized light is the largest because m = 1, it is desirable to set the length of the coupling portion to Lx.

  In this structure, light incident on one of the two photonic bandgap fibers 21 and 22 (for example, the first photonic bandgap fiber 21) is incident on the other photonic bandgap fiber. Since, for example, the second photonic bandgap fiber 22 has not been transferred, nonlinearity can be reduced most.

  The polarizer 1 of the present invention described above uses the hollow core optical fiber 2 such as the photonic bandgap fibers 21 and 22 as the hollow optical transmission medium, and the hollow portions of the fibers 21 and 22 where the light transmission portion is applied. Since the core portions 51 and 52 are used, the structure does not allow light to pass through the dielectric, and the optical component is less affected by the nonlinear optical effect than the conventional polarizer 1.

  The embodiment described above is an example of the implementation of the present invention, and the present invention is not limited to such an embodiment.

  For example, in the above-described embodiment, the branching characteristics of FIGS. 5 to 7 are assumed on the assumption that the relationship between the coupling length of y-polarized light and the coupling length of x-polarized light is a predetermined ratio. The relationship between the coupling lengths is not limited to the above-described ratio, and each of the cases where the length of the coupling unit 3 is changed assuming that the relationship between the coupling length of y-polarized light and the coupling length of x-polarized light is an arbitrary ratio. The polarizer 1 may be designed from a predetermined operating point after calculating the polarization branching characteristics and creating diagrams corresponding to FIGS. 5 to 7.

  Further, in the above-described embodiment, the photonic band gap fibers 21 and 22 are described as examples of the hollow core optical fiber 2, but the hollow core optical fiber 2 has a concentric refractive index distribution in addition to this. A Bragg fiber or the like may also be used.

  The present invention is a polarizer using a hollow core optical fiber such as a photonic bandgap fiber and having the hollow core portion of such a fiber as a light transmitting portion, and can be expected to reduce the influence of the nonlinear optical effect. The availability is high.

DESCRIPTION OF SYMBOLS 1 Polarizer 2 Photonic band gap fiber (hollow core optical fiber)
21 1st photonic band gap fiber 22 2nd photonic band gap fiber 3 coupling | bond part 41 grating | lattice (1st photonic band gap fiber)
42 grating (second photonic bandgap fiber)
51 Hollow core (first photonic bandgap fiber)
52 Hollow core (second photonic bandgap fiber)
D Lattice spacing of hollow core Λ Lattice spacing of lattice

Claims (8)

  A polarizer having a fiber coupler structure having a coupling portion in which two hollow core optical fibers are coupled in the longitudinal direction, and a light transmitting portion is a hollow core portion of the hollow core optical fiber.   The polarizer according to claim 1, wherein the two hollow core optical fibers are two photonic band gap fibers.   The lattice spacing of the hollow core portion in the two photonic band gap fibers is D, and the lattice spacing of a pair of adjacent lattices in the lattice formed in the photonic band gap fiber is Λ. 3. The polarizer according to claim 2, wherein the normalized lattice spacing D / Λ of the hollow core portion in the two photonic band gap fibers is 3 or more and 4 or less.   The lattice spacing of the hollow core portion in the two photonic band gap fibers is D, and the lattice spacing of a pair of adjacent lattices in the lattice formed in the photonic band gap fiber is Λ. 3. The polarizer according to claim 2, wherein a normalized lattice interval D / Λ of a hollow core portion in the two photonic band gap fibers is 6 or more and less than 8. 4. When the length of the coupling portion is x-polarized light and y-polarized light are respectively Lx and Ly, and m and n are arbitrary integers of 0 or more,
Lx × 2 × m = Ly × (2 × n + 1) (1)
Or
Lx × (2 × m + 1) = Ly × 2 × n (2)
The polarizer according to claim 3 or 4, wherein the polarizer is. However, neither Lx nor Ly is 0.   The lattice spacing of the hollow core portion in the two photonic band gap fibers is D, and the lattice spacing of a pair of adjacent lattices in the lattice formed in the photonic band gap fiber is Λ. 5. The polarizer according to claim 4, wherein the standardized lattice spacing D / Λ of the hollow core portion in the two photonic band gap fibers is approximately 5. 5.   The polarizer according to claim 6, wherein the length of the coupling portion is Lx × m where the coupling length of x-polarized light is Lx. However, m = 1, 2, or 3.   The fiber coupler structure is formed by polishing the side surfaces of the two hollow core optical fibers into a flat shape, and connecting the hollow core portions of the two hollow core optical fibers close to each other, or the two The polarizer according to any one of claims 1 to 7, further comprising: a coupling portion obtained by stretching and joining the hollow core optical fibers in the longitudinal direction of the hollow core optical fibers.

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