JP2008261903A - Dispersion control fiber with void, optical transmission system and optical delay circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dispersion control fiber with void whose controllability of dispersion is improved by a simple structure. <P>SOLUTION: The dispersion control fiber with void includes: a core having a radius a<SB>1</SB>; a ring core which is formed concentrically with the core, has an inner diameter a<SB>2</SB>larger than a<SB>1</SB>and has an outer diameter a<SB>3</SB>larger than a<SB>2</SB>; a plurality of voids formed between the core and the ring core; and a clad with which the outside of the ring core is covered, wherein the coupling wavelength λ<SB>p</SB>at which propagation constants of waveguide mode on the core and the ring core become equal is set to exist in the vicinity of the usage wavelength band. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a dispersion control fiber with holes, an optical transmission system, and an optical delay circuit.

  In a high-speed optical transmission system, waveform distortion due to accumulated chromatic dispersion causes a signal error and degrades transmission characteristics. In recent years, wavelength division multiplexing (WDM) transmission has been widely used, and the wavelength band used is not a single wavelength but a wide wavelength. Therefore, in a high-speed WDM transmission system, it is necessary to compensate the accumulated dispersion over a wide wavelength band.

  Dispersion compensation techniques for compensating cumulative dispersion in a WDM transmission system have been studied based on various techniques such as dispersion compensation fiber (DCF), fiber Bragg grating, and signal regeneration in an electrical stage. In particular, DCF is widely used because it has good connectivity with optical fiber transmission lines and has wide bandwidth. In the DCF, since the loss increases in proportion to the fiber length, it is desirable that the compensation amount per unit length is large. Further, in order to compensate for a plurality of wavelength channels in the used wavelength band at once, it is desirable to compensate for the dispersion slope at the same time. Up to now, DCFs having various structures that have a large compensation amount and can perform slope compensation have been reported.

  In order to reduce the influence of dispersion in a long distance transmission line such as a core network, a dispersion shifted fiber (DSF) having a zero dispersion wavelength in the 1550 nm band is widely used. Since the DSF has a dispersion of about −20 ps / nm · km in the wavelength 1310 nm band, the transmission characteristics in the wavelength band deteriorate. Therefore, for the DSF, it is necessary to perform dispersion compensation with a DCF having positive dispersion in the wavelength 1310 nm band. However, with conventional DCF, material dispersion is dominant at 1310 nm, and it is difficult to achieve positive dispersion. In recent years, an optical fiber called a photonic crystal fiber (PCF) having holes in the fiber has attracted attention. Since the PCF can shift the zero dispersion wavelength to the short wavelength side, positive dispersion can be obtained in the 1310 nm band. In Non-Patent Document 1, dispersion compensation in the 1310 nm band of DSF is realized using PCF.

  Furthermore, in order to realize an advanced optical transmission system, a demand for an optical signal buffer is increasing. Therefore, in recent years, an optical delay circuit using a nonlinear effect in an optical fiber or an optical device has been widely studied, and recently, a delay of 800 ps has been realized.

  In Non-Patent Document 2, in the hole assist fiber, the distance c between the fiber core and the holes provided around the fiber core is an important parameter in bending and connection loss characteristics. A hole-assist fiber design technique is described in which, by setting the number of holes to 2 or more at the position of the hole distance c with respect to the radius a, the region in which the holes are provided can be effectively regarded as the same refractive index. ing.

K. Nakajima et al., "Dispersion Compesation of Dispersion-Shifted Fiber at 1310 nm using Photonic Crystal Fiber", ECOC2006 Proceeding, Tu.3.3.5, September 2006 K. Nakajima et al., "Hole-Assisted Fiber Design for Small Bending and Splice Losses", IEEE Photonics Technology Letters, vol.15, no.12, December 2003, p.1737-1739

  However, in a general DCF, the compensation amount is about −100 ps / nm · km to −200 ps / nm · km, and the structure becomes complicated in order to obtain a larger compensation amount. Further, the dispersion in the 1310 nm band in the PCF of Non-Patent Document 1 is about several tens of ps / nm · km, and it is difficult to simultaneously control the dispersion slope. In the conventional delay circuit using the non-linear effect, the delay time is about 0.01 ns to 1 ns, and the circuit configuration is complicated.

  Accordingly, the present invention has been proposed in view of the above-described problems, and provides a dispersion control fiber with holes, an optical transmission system, and an optical delay circuit with improved controllability of dispersion with a simple structure. Objective.

The dispersion control fiber with holes according to the first invention for solving the above-described problem is formed of a circular core region having a radius a ₁ and a concentric shape with the circular core region, and the inner diameter is larger than the a _{1. 2,} a ring-shaped core region having an outer diameter of larger a ₃ than the a _2, a plurality of pores formed between the circular core region and the ring-shaped core region, the ring-shaped core A dispersion control fiber with holes having a cladding region covering the outside of the region, wherein a coupling wavelength λ _{P in} which the propagation constants of the waveguide modes in the circular core region and the ring-shaped core region are equal is It has in the vicinity.

The dispersion control fiber with holes according to the second invention for solving the above-described problem is a dispersion control fiber with holes according to the first invention, wherein the number of the holes is 3 or more, and the diameter of the holes is , D is the distance from the axial center to the hole c / 2, and the circular core region and the ring-shaped core region have relative refractive indexes of Δ ₁ and Δ ₂ with respect to the refractive index of the cladding region, respectively. When there is a difference, the coupling wavelength λ _P satisfies the following expression.

The dispersion control fiber with holes according to the third invention for solving the above-described problem is the dispersion control fiber with holes according to the first or second invention, wherein the coupling wavelength λ _P has a wavelength of 1260 nm to 1625 nm. It is a range.

The dispersion control fiber with holes according to the fourth invention for solving the above-described problem is a dispersion control fiber with holes according to the third invention, wherein the normalized hole position c / 2a ₁ is 1.08 to 1.58, the relative refractive index difference Δ ₁ is 1.0 to 1.6%, the relative refractive index difference Δ ₂ is 0.0 to 0.78%, and a normalized ring core The inner diameter a ₂ / a ₁ is 5 or less, and the normalized ring core outer diameter a ₃ / a ₁ is 7 or less.

Pores with distributed control fiber according to a fifth invention for solving the above problems, a pore with distributed control fiber according to any one of the first to fourth invention, in the coupling wavelength lambda _P The wavelength dispersion is −200 ps / nm · km or less.

  A hole dispersion control fiber according to a sixth aspect of the present invention that solves the above-described problem is a hole dispersion control fiber according to any one of the first to fifth aspects, wherein the dispersion control fiber has a wavelength dispersion of 1550 nm. The ratio to the dispersion slope is in the range of 230 nm to 530 nm.

  A dispersion control fiber with holes according to a seventh invention that solves the above-described problem is a dispersion control fiber with holes according to any one of the first to fourth inventions, wherein the zero dispersion wavelength is from 1300 nm to It is characterized by being in the range of 1324 nm.

Pores with distributed control fiber according to the eighth invention for solving the above problems, a pore with distributed control fiber according to any one of the first to fourth invention, in the coupling wavelength lambda _P The dispersion value of chromatic dispersion in the LP02 mode is positive.

  The dispersion control fiber with holes according to the ninth invention for solving the above-mentioned problem is a dispersion control fiber with holes according to the eighth invention, wherein the ratio of the chromatic dispersion of the LP02 mode at the wavelength of 1310 nm to the dispersion slope is It is in the range of −150 nm to −280 nm.

10 holes with distributed control fiber according to the invention for solving the above problems, a pore with distributed control fiber according to any one of the first to fourth invention, in the coupling wavelength lambda _P The group velocity is 0.2043 × 10 ⁶ km / s or less.

  An optical transmission system according to an eleventh aspect of the present invention for solving the above-described problems includes an optical fiber having positive dispersion in a used wavelength band and a dispersion control fiber with holes according to any one of the first to seventh aspects. It is characterized by including.

  An optical transmission system according to a twelfth invention for solving the above-described problem is the optical transmission system according to the eleventh invention, wherein an optical fiber having positive dispersion in the used wavelength band is zero at a wavelength of 1300 nm to 1324 nm. It has a dispersion wavelength.

  An optical transmission system according to a thirteenth invention for solving the above-described problem includes an optical fiber having a zero dispersion wavelength at a wavelength of 1300 nm to 1324 nm, and a dispersion control fiber with holes according to the seventh invention. To do.

  An optical transmission system according to a fourteenth invention for solving the above-described problem includes an optical fiber having negative dispersion in a wavelength 1310 nm band, and a dispersion control fiber with holes according to the seventh or eighth invention. Features.

  An optical transmission system according to a fifteenth invention for solving the above-described problem is the optical transmission system according to the fourteenth invention, wherein an optical fiber having negative dispersion in the wavelength 1310 nm band is zero at wavelengths 1525 nm to 1575 nm. It has a dispersion wavelength.

  An optical transmission system according to a sixteenth invention for solving the above-described problem is the optical transmission system according to the fourteenth or fifteenth invention, wherein the mode converter performs mode conversion between the LP01 mode and the LP02 mode. It is characterized by having.

  An optical delay circuit according to a seventeenth aspect of the present invention for solving the above-described problems is composed of the dispersion control fiber with holes according to the tenth aspect of the present invention and a wavelength conversion element that performs wavelength conversion between the wavelengths. And

  According to the present invention, there is an effect that the controllability of dispersion is high and the design is easy, and the manufacturability is good due to the simple structure.

  Furthermore, a large negative or positive dispersion can be realized as compared with the conventional DCF, and the effect of high dispersion compensation efficiency is achieved.

  Furthermore, there is an effect that the used wavelength band can be designed flexibly and easily.

  Furthermore, there is an effect that a delay of a large optical signal can be obtained with a simple circuit configuration as compared with the prior art.

  Hereinafter, the best mode for carrying out the present invention will be described in detail based on examples.

Hereinafter, the dispersion control fiber with holes according to the first embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic cross-sectional view of a dispersion control fiber with holes according to a first embodiment of the present invention.

As shown in FIG. 1, the dispersion control fiber with holes according to the present embodiment has a core (circular core region) 1 having a radius a ₁ located in the center in a cross section perpendicular to the longitudinal direction, A ring core (ring-shaped core region) 2 having an inner diameter a ₂ larger than a ₁ and an outer diameter a ₃ larger than a ₂ is formed concentrically with the core 1, and an outer side of the ring core 2. It has a clad (cladding region) 3 to be covered, and a hole 4 formed at a distance of c / 2 from the axis and having a diameter d. The refractive indexes of the core 1, the ring core 2 and the clad 3 are n ₁ , n ₂ and n ₃ , respectively. The relative refractive index differences Δ ₁ and Δ ₂ of the core 1 and the ring core 2 with respect to the cladding 3 are defined by the following equation (2).

Here, if the holes 4 are arranged across two or more regions having different refractive indexes, it becomes very difficult to manufacture. Therefore, the holes 4 are located between the core 1 and the ring core 2 a _{1 to} a. A range of ₂ is preferable.

FIG. 2 shows an effective refractive index distribution in the radial direction of the dispersion control fiber with holes according to the first embodiment of the present invention. As described in Non-Patent Document 2 described above, the hole layer 41 that is a portion of a _{1 to} a ₂ can be effectively regarded as a layer having the same refractive index. Therefore, although the number of holes is six here, the same effect can be obtained even with a structure having fewer or more holes. However, since the problem of birefringence occurs when the number of holes is 2, the number of holes is preferably 3 or more.

Here, FIG. 3 shows an outline for explaining the operation principle of the dispersion control fiber with holes according to the first embodiment of the present invention. FIG. 3A is a distribution diagram of the refractive index of the dispersion control fiber with holes according to the first embodiment of the present invention, and FIG. 3B is a waveguide including only the core region. FIG. 3C is a distribution diagram of the waveguide mode in the case where it is a waveguide composed of a hole layer and a ring-shaped core region, and FIG. Is a distribution diagram of the waveguide mode when the wavelength λ is smaller than the coupling wavelength λ _P , and FIG. 3E is a distribution diagram of the waveguide mode when the wavelength λ is the same as the coupling wavelength λ _P. FIG. 3F is a distribution diagram of the waveguide mode when the wavelength λ is larger than the coupling wavelength λ _P. A dotted line in FIG. 3 represents a waveguide mode distribution in each waveguide. The coupling wavelength λ _P is a wavelength at which the propagation constant of the waveguide mode of the waveguide shown in FIG. 3B is equal to the propagation constant of the waveguide mode of the waveguide shown in FIG.

The dispersion control fiber with holes according to the first embodiment of the present invention is composed of a waveguide composed of only the core 1 (see the solid line shown in FIG. 3B), the hole layer 41 and the ring core 2. It can be considered that this is a coupled system of waveguides (see the solid line shown in FIG. 3C). In the coupling system of two waveguides as described above, as shown in FIGS. 3 (d), 3 (e), and 3 (f), a rapid change in the propagation constant occurs at the coupling wavelength λ _P. As a result, a large dispersion value can be obtained. In order to form a waveguide in the waveguide shown in FIG. 3B and the waveguide shown in FIG. 3C, the refractive index of the core 1 and the refractive index of the ring core 2 are larger than the refractive index of the cladding 3. There is a need. Further, the absolute value of dispersion at λ _P can be increased by increasing the distance between the core 1 and the ring core 2 or decreasing the refractive index of the layer (hole layer 41) between the core 1 and the ring core 2. it can. In the conventional reduction of the refractive index by addition of fluorine, there is a limit to the amount of addition of the refractive index because of the limit in production, but in this embodiment, the refraction of the hole layer 41 is easily made depending on the size of the hole 4. It is possible to reduce the rate.

FIG. 4 shows the relationship between the hole position and chromatic dispersion in the dispersion control fiber with holes according to the first embodiment of the present invention. Here, the radius a ₁ of the core 1 is 1.5 μm, the standardized ring core inner diameter a ₂ / a ₁ is 3.0, the standardized ring core outer diameter a ₃ / a ₁ is 5.0, and the standardized holes The diameter d / 2a ₁ was 0.4, the relative refractive index difference Δ ₁ of the core ₁ was 1.5%, and the relative refractive index difference Δ ₂ of the ring core ₂ was 0.3%. In FIG. 4, the solid line, the broken line, the dotted line, and the alternate long and short dash line represent cases where the normalized hole position c / 2a ₁ is 1.2, 1.4, 1.5, and 1.6, respectively. As shown in FIG. 4, it can be seen that a very large negative dispersion value of −1000 ps / nm · km to −3000 ps / nm · km can be obtained in the dispersion control fiber with holes. The wavelength at which the absolute value of dispersion is the largest corresponds to the coupling wavelength λ _P. Here, the relationship between the coupling wavelength λ _P and the normalized hole position c / 2a ₁ is shown in FIG. As shown in FIG. 5, the coupling wavelength λ _P can be designed in an arbitrary wavelength band such as a wavelength 1310 nm band or a 1550 nm band by moving the position of the hole 4 close to the core 1 and changing the hole position. Therefore, according to the dispersion control fiber with holes according to the present embodiment, it is possible to obtain negative dispersion having a large absolute value in an arbitrary wavelength band. The coupling wavelength λ _P can be approximated by the following equation (3) from FIGS. 4 and 5.

For example, in FIGS. 4 and 5, k ₀₁ = 477.8 and k ₁ = 725.4 are obtained.

FIG. 6 shows the relationship between the hole diameter and the chromatic dispersion in the dispersion control fiber with holes according to the first embodiment of the present invention. Here, the radius a ₁ of the core ₁ , the normalized ring core inner diameter a ₂ / a ₁ , the normalized ring core outer diameter a ₃ / a ₁ , the relative refractive index difference Δ _{1 of} the core ₁ , and the relative refractive index difference Δ _{2 of the} ring core _2. Is the same as FIG. 4, and the normalized hole position c / 2a ₁ is 1.5. The solid line, broken line, dotted line, alternate long and short dash line in the figure represents the case where the normalized hole diameter d / 2a ₁ is 0.2, 0.3, 0.4, 0.5, and 0.6, respectively. To express.

As shown in this figure, as the holes 4 are made smaller, negative dispersion and negative dispersion slope can be realized in a wider band, and as the holes 4 are made larger, the absolute value of dispersion at an arbitrary wavelength can be made larger. In FIG. 6, similarly to FIG. 4, the wavelength at which the absolute value of dispersion is the largest corresponds to the coupling wavelength λ _P. Here, the relationship between the coupling wavelength λ _P and the normalized hole diameter d / 2a ₁ is shown in FIG. The coupling wavelength λ _P can be approximated by the following equation (4) from FIGS. 6 and 7.

For example, in FIGS. 6 and 7, k ₀₂ = 1556.3, k ₂₁ = 849.6, and k ₂₂ = 11.14.

Here, FIG. 8 shows the relationship between the relative refractive index difference Δ ₁ of the core ₁ and the wavelength dispersion in the dispersion control fiber with holes according to the first embodiment of the present invention. Here, the normalized hole diameter d / 2a ₁ , the radius a ₁ of the core ₁ , the normalized ring core inner diameter a ₂ / a ₁ , the normalized ring core outer diameter a ₃ / a ₁ , and the relative refractive index difference Δ _{2 of the} ring core ₂ Is the same as FIG. 4, and the normalized hole position c / 2a ₁ is 1.5. The solid line, broken line, and dotted line in the figure represent cases where the relative refractive index difference Δ ₁ of the core ₁ is 1.4%, 1.5%, and 1.6%, respectively.

As shown in this figure, it is understood that the coupling wavelength λ _P is on the long wavelength side by increasing the relative refractive index difference Δ ₁ of the core 1. In FIG. 8, similarly to FIG. 4, the wavelength at which the absolute value of dispersion is the largest corresponds to the coupling wavelength λ _P. Here, the relationship between the coupling wavelength λ _P and the relative refractive index difference Δ ₁ of the core 1 is shown in FIG. The coupling wavelength λ _P can be approximated by the following equation (5) from FIGS. 8 and 9.

For example, in FIGS. 8 and 9, k ₀₃ = 619.9 and k ₃ = 63182 are obtained.

FIG. 10 shows the relationship between the relative refractive index difference Δ ₂ of the ring core ₂ and the chromatic dispersion in the dispersion control fiber with holes according to the first embodiment of the present invention. Here, the normalized hole position c / 2a ₁ , the normalized hole diameter d / 2a ₁ , the radius a ₁ of the core ₁ , the normalized ring core inner diameter a ₂ / a ₁ , the normalized ring core outer diameter a ₃ / a ₁ Is the same as in FIG. 8, and the relative refractive index difference Δ ₁ of the core ₁ is 1.5%. The solid line, broken line, dotted line, alternate long and short dash line in the figure indicate that the relative refractive index difference Δ ₂ of the ring core ₂ is 0.6%, 0.4%, 0.3%, 0.2%,. This represents the case of 0%.

As shown in this figure, it is understood that the coupling wavelength λ _P is on the short wavelength side by increasing the relative refractive index difference Δ ₂ of the ring core 2. In FIG. 10, as in FIG. 4, the wavelength at which the absolute value of dispersion is the largest corresponds to the coupling wavelength λ _P. It can be seen that when the relative refractive index difference Δ _{2 of the} ring core 2 is 0.2% or less, the coupling wavelength λ _P is substantially constant, and the absolute value of dispersion increases. Here, the relationship between the coupling wavelength λ _P and the relative refractive index difference Δ ₂ of the ring core 2 is shown in FIG. Coupling wavelength lambda _P, from FIGS. 10 and 11, lambda _P can be approximated by the following equation (6).

For example, in FIG. 10 and FIG. 11, k ₀₄ = 1618.8, k ₄₁ = 938.6, and k ₄₂ = −6.04 × 10 ⁶ .

FIG. 12 shows the relationship between the normalized ring core inner diameter a ₂ / a ₁ and chromatic dispersion in the dispersion control fiber with holes according to the first embodiment of the present invention. Here, the normalized hole position c / 2a ₁ , the normalized hole diameter d / 2a ₁ , the radius a ₁ of the core ₁ , the normalized ring core outer diameter a ₃ / a ₁ , and the relative refractive index difference Δ _{1 of the} core ₁ Is the same as FIG. 10, and the relative refractive index difference Δ ₂ of the ring core ₂ is 0.3%. The solid line, broken line, dotted line, and alternate long and short dash line in the figure represent cases where the normalized ring core inner diameter a ₂ / a ₁ is 2.5, 3.0, 3.5, and 4.0, respectively.

As shown in this figure, it can be seen that the coupling wavelength λ _P becomes the longer wavelength side by increasing the normalized ring core inner diameter a ₂ / a ₁ . Here, the relationship between the coupling wavelength λ _P and the normalized ring core inner diameter a ₂ / a ₁ is shown in FIG. The coupling wavelength λ _P can be approximated by the following equation (7) from FIG. 12 and FIG.

For example, in FIGS. 12 and 13, k ₀₅ = 1560.9, k ₅₁ = −13.64, and k ₅₂ = 5.455 are obtained.

FIG. 14 shows the relationship between the normalized ring core outer diameter a ₃ / a ₁ and the chromatic dispersion in the dispersion control fiber with holes according to the first embodiment of the present invention. Here, the normalized hole position c / 2a ₁ , the normalized hole diameter d / 2a ₁ , the radius a _{1 of} the core 1, the relative refractive index difference Δ _{1 of} the core ₁ , and the relative refractive index difference Δ ₂ of the ring core ₂ are: 12, the normalized ring core inner diameter a ₂ / a ₁ was set to 3. A solid line, a broken line, and a dotted line in the figure represent cases where the normalized ring core outer diameter a ₃ / a ₁ is 4.0, 5.0, and 6.0, respectively.

As shown in this figure, it can be seen that the coupling wavelength λ _P becomes the shorter wavelength side by increasing the normalized ring core outer diameter a ₃ / a ₁ . In FIG. 14, as in FIG. 4, the wavelength at which the absolute value of dispersion is the largest corresponds to the coupling wavelength λ _P. Here, the relationship between the coupling wavelength λ _P and the normalized ring core outer diameter a ₃ / a ₁ is shown in FIG. The coupling wavelength λ _P can be approximated by the following equation (8) from FIG. 14 and FIG.

For example, in FIGS. 14 and 15, k ₀₆ = 1010.5, k ₆₁ = 178.8, and k ₆₂ = −13.41 are obtained.

Here, assuming that the coupling wavelength λ _P is expressed by a linear combination of dependencies corresponding to the individual parameters of λ _P shown in equations (3) to (8), the following equation (9) Can be represented.

Here, as an example, when the coefficient k _ij (i = 1, 2,..., J = 1, 2) is obtained from FIGS. Further, k ₀ is determined to be −993.5. In this way, by obtaining the coefficient k representing the structure dependence of the coupling wavelength λ _P and using Equation (9), λ _P can be designed to an arbitrary wavelength, and as a result, a negative value having a large absolute value in an arbitrary wavelength band can be obtained. Is obtained.

When the used wavelength band is a communication wavelength band generally used in optical communication (O to L band: 1260 nm to 1625 nm), in order to set λ _P within the range of 1260 nm to 1625 nm, the equations (3) to (8) Using the formula, the design range of the structural parameter is as follows.

  Further, from the structural characteristics shown in FIGS. 1 and 2, the following equation (11) is obtained.

From the equations (10) and (11), the normalized hole diameter d / 2a ₁ needs to be designed as the following equation (12).

Therefore, the coupling wavelength λ _P can be designed to be 1260 nm to 1625 nm by satisfying the expressions (10) to (12). Here, from the viewpoint of manufacturing, the radius a _{1 of the} core 1 is preferably 0.5 μm or more. Further, since the waveguide mode of the core becomes dominant when the core 1 becomes larger and the controllability of the coupling wavelength λ _P is lowered, a ₁ is preferably 2.0 μm or less.

Hereinafter, an optical transmission system using a dispersion control fiber with holes according to a second embodiment of the present invention will be described with reference to the drawings. In this system, the control fiber with holes according to the first embodiment of the present invention described above is used. The present embodiment is an optical transmission system of one method for performing dispersion compensation of a normal single mode fiber (SMF) and a dispersion shifted fiber (DSF).
FIG. 16 is a configuration diagram of an optical transmission system using a dispersion control fiber with holes according to a second embodiment of the present invention.

  In general, the chromatic dispersion of SMF becomes zero at wavelengths of 1300 nm to 1324 nm, increases monotonously with respect to the wavelength, and takes a positive value of about 17 ps / nm · km in the wavelength 1550 nm band. Therefore, SMF dispersion at 1550 nm can be compensated by connecting an optical fiber having negative dispersion in the wavelength band. Furthermore, in order to compensate over a wide band centering on the wavelength, it is necessary to compensate for the dispersion slope of the SMF at the same time. As a parameter indicating the compensation performance of dispersion and dispersion slope, a dispersion compensation rate η represented by the following equation (13) is known.

Where λ is a wavelength, D _T and S _T represent the dispersion value and dispersion slope of the compensated fiber (eg, SMF), and Dc and Sc are compensation fibers (eg, according to the first embodiment of the present invention). The dispersion value and dispersion slope of the dispersion control fiber with holes). When η is 1, the compensation performance is the best. Here, the value of the dispersion vs. dispersion slope ratio D _T / S _T in SMF wavelength 1550nm is generally about 330 nm.

Here, in the dispersion control fiber with holes according to the present embodiment, a large negative dispersion can be obtained at the wavelength by designing the coupling wavelength λ _P to a desired wavelength as shown in the first embodiment. Therefore, by setting the coupling wavelength λ _P in the 1550 nm band, it is possible to compensate for positive dispersion in the wavelength band. Furthermore, it is more preferable to design the dispersion at the coupling wavelength λ _{P to} be −200 ps / nm · km or less because the dispersion can be compensated more efficiently than the conventional dispersion compensating fiber (DCF). Further, by setting the dispersion-to-dispersion slope ratio D / S at a wavelength of 1550 nm to 230 nm to 530 nm, the dispersion compensation rate with respect to the SMF is within 1 ± 0.3, and it is more preferable because wideband dispersion compensation can be performed.

Further, the dispersion compensation fiber with holes according to the present embodiment has a negative dispersion at the zero dispersion wavelength by setting the coupling wavelength λ _P longer than the zero dispersion wavelength as shown in the first embodiment. A slope is obtained. Since the SMF has a monotonically increasing dispersion with respect to the wavelength as described above, the dispersion slope at the zero dispersion wavelength is positive. Therefore, dispersion compensation in the vicinity of the zero dispersion wavelength of the SMF can be realized by designing the zero dispersion wavelength of the dispersion control fiber with holes according to the present embodiment to a wavelength equivalent to that of the SMF and connecting it to the SMF. Here, since the zero dispersion wavelength of the SMF is 1300 nm to 1324 nm, when performing dispersion compensation near the zero dispersion wavelength of the SMF, the zero dispersion wavelength of the dispersion control fiber with holes according to the present embodiment is set to 1300 nm to 1324 nm. It is necessary to be in the range.

On the other hand, in the DSF, the zero dispersion wavelength is in the 1550 nm band, and is positive dispersion on the longer wavelength side than the zero dispersion wavelength. Positive dispersion on the longer wavelength side than the zero dispersion wavelength of the DSF can be compensated for by an optical fiber having negative dispersion in the wavelength band as in the case of the SMF. By designing the coupling wavelength λ _P on the longer wavelength side than the zero dispersion wavelength using the dispersion control fiber with holes according to the present embodiment, a large negative dispersion can be obtained in the wavelength band, and the above-mentioned SMF As in the case, efficient dispersion compensation can be performed.

  As shown in FIG. 16, the optical transmission system includes a transmitter 51 that emits an optical signal, a single mode fiber 52 having one end connected to the transmitter 51, and the other end side of the single mode optical fiber 52. And a dispersion control fiber 53 with holes connected thereto. To the other end of the dispersion control fiber 53 with holes, a light receiver 54 that receives an optical signal transmitted through the fibers is connected. The single mode fiber 52 represents, for example, SMF or DSF. The optical signal is incident on the single mode fiber 52 from the transmitter 51, and the optical signal transmitted through the single mode fiber 52 is compensated for dispersion in the dispersion control fiber 53 with holes and received by the receiver 54. Here, the description has been given using the optical transmission system in which the dispersion control fiber 53 with holes is arranged at the rear stage of the single mode fiber 52. However, the dispersion control fiber with holes is arranged at the front stage of the single mode fiber, or the front stage and the rear stage. The optical transmission system may be arranged in both. The transmitter 51 and the receiver 54 are an example of a part that introduces an optical signal into the single mode fiber 52 and a part that receives an optical signal that has passed through the single mode fiber 52. Alternatively, an optical transmission system may be used as a connection with other optical network.

FIG. 17 shows chromatic dispersion characteristics in the optical transmission system according to the present embodiment. FIG. 17A shows a dispersion control fiber with holes, in which the radius a ₁ of the core 1 is 1.5 μm, the normalized ring core inner diameter a ₂ / a ₁ is 3.0, and the normalized ring core inner diameter a ₂ / a. ₁ is 5.0, the normalized hole position c / 2a ₁ is 1.5, the normalized hole diameter d / 2a ₁ is 0.4, and the relative refractive index difference Δ ₁ of the core ₁ is 1.5. FIG. 17B shows the chromatic dispersion characteristics when the relative refractive index difference Δ ₂ of the ring core 2 is 0.345%, and FIG. 17B shows the chromatic dispersion characteristics of the SMF before the dispersion compensation and the compensation It is a figure showing the wavelength dispersion characteristic after performing (SMF + dispersion control fiber with a hole). As shown in FIG. 17A, the coupling wavelength λ _P was 1551 nm. The dispersion control fiber with holes according to the present embodiment realizes a dispersion value of about −1500 ps / nm · km, and performs SMF compensation at a distance of about 1/100 of the SMF distance. Can do. Further, as shown in FIG. 17B, it can be seen that the absolute value of chromatic dispersion is reduced to 1 ps / nm · km or less in the wavelength range of 1550 nm ± 6 nm.

FIG. 18 shows chromatic dispersion characteristics when dispersion compensation is performed in the vicinity of the zero dispersion wavelength of the SMF in the optical transmission system according to the present embodiment. Here, in the dispersion control fiber with holes, the radius a ₁ of the core 1 is 1.5 μm, the normalized ring core inner diameter a ₂ / a ₁ is 3.0, and the normalized ring core outer diameter a ₃ / a ₁ is 5 0.0, the normalized hole position c / 2a ₁ is 1.5, the normalized hole diameter d / 2a ₁ is 0.4, the relative refractive index difference Δ ₁ of the core ₁ is 1.5%, and the ring core 2 relative refractive index difference Δ ₂ = 0.6%. At this time, the coupling wavelength λ _P was 1407 nm. A solid line, a broken line, and a dotted line represent chromatic dispersion before dispersion compensation of SMF, chromatic dispersion of dispersion control fiber with holes, and chromatic dispersion after compensation (SMF + dispersion control fiber with holes), respectively. From this figure, it is possible to compensate for the absolute value of the dispersion slope to 0.04 ps / nm ² / km or less, which is half or less of SMF, at the zero dispersion wavelength ± 10 nm of SMF by using a dispersion control fiber with holes. . Therefore, according to the dispersion control fiber with holes according to the present embodiment, the zero dispersion wavelength can be designed in the 1310 nm band, and a negative dispersion slope can be realized in the 1310 nm band. Therefore, dispersion compensation in the vicinity of the zero dispersion wavelength of the SMF can be achieved. realizable.

  In the present embodiment, a method for compensating for dispersion in the 1310 nm band or 1550 nm band in the SMF or DSF with zero dispersion wavelength has been described. However, the single mode fiber of the optical transmission system according to the present embodiment is not limited to the SMF and DSF. However, by appropriately designing the dispersion control fiber with holes, it is effective in compensating for the dispersion slope near the positive dispersion or zero dispersion wavelength of any optical fiber in any wavelength band.

  An optical transmission system according to the third embodiment of the present invention will be described below with reference to the drawings. The present embodiment is an optical transmission system of one method that performs dispersion compensation in a 1310 nm band of a general DSF using LP02 mode chromatic dispersion of a dispersion control fiber with holes.

  The dispersion of the DSF increases monotonously with wavelength, and generally becomes a zero dispersion wavelength in the 1550 nm band. Therefore, it has a negative dispersion of about −20 ps / nm · km in the 1310 nm band. Therefore, in order to compensate the dispersion of the DSF in the 1310 nm band, an optical fiber having positive dispersion in the wavelength band is required. Furthermore, in order to perform dispersion compensation over a wide band in the 1310 nm band of DSF, it is necessary to compensate for dispersion and dispersion slope simultaneously. As shown in the above equation (13), dispersion and dispersion slope compensation are realized by matching the dispersion-to-dispersion slope ratio in the wavelength band between the compensating fiber and the compensated fiber. Here, the dispersion characteristics of the DSF at 1310 nm are a negative dispersion and a positive dispersion slope, and the dispersion-to-dispersion slope ratio is about −220 ps / nm · km.

FIG. 19 shows chromatic dispersion characteristics of the LP01 mode and the LP02 mode in the dispersion control fiber with holes according to the third embodiment of the present invention. Here, in the dispersion control fiber with holes according to the present embodiment, the radius a ₁ of the core ₁ is 1.5 μm, the normalized ring core inner diameter a ₂ / a ₁ is 3.0, and the normalized ring core outer diameter a _3. / A ₁ is 5.0, the normalized hole position c / 2a ₁ is 1.5, the normalized hole diameter d / 2a ₁ is 0.4, and the relative refractive index difference Δ ₁ of the core ₁ is 1. The relative refractive index difference Δ ₂ of the ring core ₂ was 0.7%. As shown in this figure, it can be seen that a large dispersion exceeding several hundred ps / nm · km is obtained in the wavelength 1310 nm band for the LP02 mode. The dispersion characteristics of the LP02 mode are symmetric with those of the LP01 mode. In the dispersion control fiber with holes according to the present embodiment, since the coupling wavelength λ _P can be designed in the wavelength 1310 nm band, large positive dispersion can be realized in the wavelength band by using the LP02 mode.

Further, the dispersion of the LP02 mode monotonously decreases with respect to the wavelength on the longer wavelength side than the coupling wavelength λ _P. Therefore, by designing the coupling wavelength λ _P to be shorter than the used wavelength band (for example, 1310 nm), positive dispersion and negative dispersion slope are obtained in the used wavelength band, and DSF dispersion or dispersion slope compensation is obtained. Is possible. More preferably, by setting the dispersion-to-dispersion slope ratio of the dispersion control fiber with holes in the range of −150 nm to −280 nm, the dispersion compensation ratio η at 1310 nm with respect to the DSF can be 1 ± 0.3.

  FIG. 20 shows the configuration of an optical transmission system when dispersion compensation is performed for an optical fiber having negative dispersion in the wavelength 1310 nm band by using the dispersion control fiber with holes according to the third embodiment of the present invention. As shown in this figure, the optical transmission system includes a transmitter 61 that emits an optical signal, a negative dispersion fiber 62 having one end connected to the transmitter 61 and having negative dispersion in the 1310 nm band, and the negative dispersion fiber. And a mode converter 63 that is connected to the other end of 62 and converts the optical signal transmitted through the negative dispersion fiber 62 into the LP02 mode. One end of a dispersion control fiber 64 with holes is connected to the mode converter 63. The other end of the dispersion control fiber 64 is connected to a light receiver 65 that receives an optical signal transmitted through the fiber. The optical signal is incident on the negative dispersion fiber 62 from the transmitter 61, the dispersion is compensated in the dispersion control fiber 64 with holes, and is received by the light receiver 65. More preferably, the optical signal transmitted through the negative dispersion fiber 62 is converted into the LP02 mode by the mode converter 63, so that the connection characteristic with the dispersion control fiber 64 with a hole in the subsequent stage is improved. Here, the mode converter 63 and the dispersion control fiber 64 with holes are described using an optical transmission system arranged at the subsequent stage of the negative dispersion fiber 62. However, the mode converter and the dispersion control fiber with holes are made of a negative dispersion fiber. The optical transmission system may be arranged in the front stage or both the front stage and the rear stage. The transmitter 61 and the receiver 65 are an example of a part that introduces an optical signal into the negative dispersion fiber 62 and a part that receives an optical signal that has passed through the dispersion control fiber with holes. An optical transmission system may be used as a connection with a fiber or another optical network.

FIG. 21 shows chromatic dispersion characteristics when chromatic dispersion in the wavelength 1310 nm band of the DSF is compensated for using the dispersion control fiber with holes according to the third embodiment of the present invention. FIG. 21 (a) shows a normalized ring core in the dispersion control fiber with holes according to this embodiment, in which the radius a ₁ of the core ₁ is 1.5 μm, the normalized ring core inner diameter a ₂ / a ₁ is 3.0. The outer diameter a ₃ / a ₁ is 5.0, the normalized hole position c / 2a ₁ is 1.5, the normalized hole diameter d / 2a ₁ is 0.4, and the relative refractive index difference of the core 1 FIG. 21B is a diagram showing wavelength dispersion characteristics of the LP02 mode when Δ ₁ is 1.5% and the relative refractive index difference Δ ₂ of the ring core 2 is 0.725%, and FIG. 21B performs dispersion compensation. It is a figure showing the wavelength dispersion characteristic of the wavelength dispersion characteristic of front DSF, and after performing compensation (DSF + dispersion control fiber with a hole). As shown in FIG. 21A, the coupling wavelength λ _P was 1309 nm. The dispersion control fiber with holes according to this embodiment realizes a dispersion value of about 1400 ps / nm · km, and performs DSF dispersion compensation with a length of about 1/70 of the fiber length of the DSF. Can do. Further, as shown in FIG. 21B, the absolute value of dispersion is compensated to 1 ps / nm · km or less at a wavelength of 1310 nm ± 4 nm.

  In the present embodiment, a technique for performing dispersion compensation at a DSF of 1310 nm has been described. However, the technique and the optical transmission system according to the present embodiment are not limited to the above-described ranges. By appropriately designing the dispersion control fiber with holes, it becomes possible to compensate for the negative dispersion of any optical fiber at any wavelength.

  An optical delay circuit according to the fourth embodiment of the present invention will be described below with reference to the drawings. This circuit is a technique for realizing a group delay of 1 nm / km or more in an arbitrary wavelength band.

In the dispersion control fiber with holes according to the present embodiment, since the chromatic dispersion changes abruptly in the vicinity of the coupling wavelength λP, the group velocity of the light wave also changes. FIG. 22 shows the wavelength characteristics of the group velocity in the dispersion control fiber with holes according to the fourth embodiment of the present invention. Here, in the dispersion control fiber with holes according to the present embodiment, the radius a ₁ of the core ₁ is 1.5 μm, the normalized ring core inner diameter a ₂ / a ₁ is 3.0, and the normalized ring core outer diameter a _3. / A ₁ is 5.0, the normalized hole position c / 2a ₁ is 1.5, the normalized hole diameter d / 2a ₁ is 0.6, and the relative refractive index difference Δ ₁ of the core ₁ is 1. The relative refractive index difference Δ ₂ of the ring core ₂ was 0.3%. At this time, the coupling wavelength λ _P is 1555 nm. In FIG. 22, a solid line and a broken line represent the dispersion control fiber with holes and the SMF, respectively. As shown in FIG. 22, it can be seen that the group velocity of the dispersion control fiber with holes is slower than the group velocity of SMF at a wavelength of 1560 nm or less. Therefore, by using the dispersion control fiber with holes according to the present embodiment, it is possible to efficiently delay the light as compared with the conventional optical fiber delay device. In order to obtain a group delay of 1 ns / km or more from SMF at a wavelength of 1550 nm, the group velocity at the coupling wavelength λ _P of the dispersion control fiber with holes according to the present embodiment is 0.2043 × 10 ⁶ km / s or less. Preferably there is.

FIG. 23 shows a configuration of an optical delay circuit using the dispersion control fiber with holes according to the present embodiment. As shown in this figure, the optical delay circuit includes a wavelength conversion element 72 to which an optical signal 71 is input, a dispersion control fiber 73 with holes connected to one end of the wavelength conversion element 72, and the dispersion control with holes. The other end side of the fiber is connected and has a wavelength conversion element 74 that outputs an optical signal. In this optical delay circuit, a controller 76 for controlling ON / OFF of operation of wavelength conversion elements (hereinafter referred to as elements) 72 and 74 is provided. When the wavelength of the input optical signal 71 and the output optical signal 74 is λ ₁ and the elements 72 and 75 are in the ON state by the controller 76, the wavelength λ ₁ is converted into the wavelength λ ₂ in the element 72. It is assumed that wavelength λ ₂ is converted to wavelength λ ₁ . That is, when the elements 72 and 75 are in the ON state, the optical signal of λ ₂ propagates through the holey dispersion control fiber 73, and when the elements 72 and 75 are in the OFF state, the optical signal of λ ₁ propagates. Here, assuming that the fiber length in the dispersion control fiber 73 with holes is L and the group velocity is v _g (λ), the arrival time τ from the input end to the output end is expressed by the following equation (14). .

  Here, the time for passing through the elements 72 and 75 is sufficiently shorter than the time for propagating through the fiber 73 and can be ignored. From the above equation (14), the following equation (15) can be obtained. By turning on the elements 72 and 75, light delay can be caused.

Here, the dispersion control fiber 73 with a hole is preferable because it has a rapid change in group velocity near the coupling wavelength λ _P , and can generate a larger optical delay than the above equation (15).

Here, the case where the dispersion control fiber with holes shown in FIG. 22 is used as an example is shown below. If the fiber length L is 1 km, the wavelength λ ₁ is 1570 nm, and the wavelength λ ₂ is 1540 nm, an optical delay of about 100 ns can be generated from FIG. In addition, the delay amount can be arbitrarily designed by changing the wavelength λ ₂ after wavelength conversion by a signal from the controller 76.

  The present invention can be used as a dispersion compensating fiber that cancels out positive dispersion at a wavelength of 1310 nm and negative dispersion at a wavelength of 1550 nm. It can also be used as an optical delay device.

It is a schematic sectional drawing of the dispersion control fiber with a hole concerning the 1st example of the present invention. It is a distribution map of the effective refractive index in the radial direction of the dispersion control fiber with holes according to the first embodiment of the present invention. It is the schematic for demonstrating the operating principle of the dispersion control fiber with a hole which concerns on 1st Example of this invention. It is a figure which shows the relationship between a hole position and wavelength dispersion in the dispersion control fiber with a hole which concerns on 1st Example of this invention. It is a figure which shows the relationship between coupling wavelength (lambda) _P and the normalized hole position c / 2a1 in the dispersion control fiber with a hole which concerns on _1st Example of this invention. It is a figure which shows the relationship between a hole diameter and wavelength dispersion in the dispersion control fiber with a hole which concerns on 1st Example of this invention. It is a figure which shows the relationship between coupling wavelength (lambda) _P and the normalized hole diameter d / 2a1 in the dispersion control fiber with a hole which concerns on _1st Example of this invention. It is a figure which shows the relationship between the relative refractive index difference (DELTA) ₁ of a core, and wavelength dispersion in the dispersion control fiber with a hole which concerns on _1st Example of this invention. It is a figure which shows the relationship between the coupling wavelength (lambda) _P and the relative refractive index difference (DELTA) ₁ of a core in the dispersion control fiber with a hole concerning the 1st Example of this invention. It is a figure which shows the relationship between the relative refractive index difference (DELTA) ₂ of a ring core, and wavelength dispersion in the dispersion control fiber with a hole which concerns on 1st Example of this invention. It is a figure which shows the relationship between coupling wavelength (lambda) _P and the relative refractive index difference (DELTA) ₂ of a ring core in the dispersion control fiber with a hole which concerns on 1st Example of this invention. In pores with distributed control fiber according to a first embodiment of the present invention showing the relationship between the normalized ring core inner diameter a ₂ / a ₁ and the wavelength dispersion. In pores with distributed control fiber according to a first embodiment of the present invention, showing a relationship between the coupling wavelength lambda _P and the normalized ring core inner diameter a ₂ / a _1. In pores with distributed control fiber according to a first embodiment of the present invention, it is a graph showing the relationship between the normalized ring core outer diameter a ₃ / a ₁ and the wavelength dispersion. In pores with distributed control fiber according to a first embodiment of the present invention, showing a relationship between the coupling wavelength lambda _P and the normalized ring core outer diameter a ₃ / a _1. It is a block diagram of the optical transmission system using the dispersion control fiber with a hole concerning the 2nd example of the present invention. It is a figure which shows the chromatic dispersion characteristic in the optical transmission system which concerns on the 2nd Example of this invention. It is a figure which shows the wavelength dispersion characteristic when dispersion compensation is carried out near the zero dispersion wavelength of the single mode fiber in the optical transmission system according to the second embodiment of the present invention. It is a figure which shows the wavelength dispersion characteristic of LP01 mode and LP02 mode in the dispersion control fiber with a hole concerning the 3rd Example of this invention. It is a figure which shows the structure of the optical transmission system when performing dispersion compensation of the optical fiber which has negative dispersion | distribution in wavelength 1310nm band using the dispersion control fiber with a hole which concerns on 3rd Example of this invention. It is a figure which shows the chromatic dispersion characteristic when compensating the chromatic dispersion in the wavelength 1310nm band of DSF using the dispersion | distribution control fiber with a hole which concerns on the 3rd Example of this invention. It is a figure which shows the wavelength characteristic of group velocity in the dispersion control fiber with a hole which concerns on the 4th Example of this invention. It is a figure which shows the structure of the optical delay circuit using the dispersion control fiber with a hole concerning the 4th Example of this invention.

Explanation of symbols

1 Core 2 Ring core 3 Clad 4 Hole 41 Hole layer 51, 61 Transmitter 52 Single mode fiber 53, 64, 73 Dispersion control fiber 54, 65 with hole Receiver 62 1310nm negative dispersion fiber 63 Mode converter 71 Input Optical signal 72, 75 Wavelength conversion element 74 Output optical signal 76 Controller a ₁ Core radius a ₂ Ring core inner diameter a ₃ Ring core outer diameter c Hole position d Hole diameter n ₁ Core refractive index n ₂ Ring core Refractive index n ₃ Cladding refractive index

Claims (17)

A circular core region having a radius a _1, a ring shape formed concentrically with the circular core region, an inner diameter a ₂ larger than the a ₁ , and an outer diameter a ₃ larger than the a ₂ A dispersion control fiber with a hole having a core region, a plurality of holes formed between the circular core region and the ring-shaped core region, and a cladding region covering the outside of the ring-shaped core region, ,
A dispersion control fiber with holes, wherein a coupling wavelength λ _{P at} which propagation constants of waveguide modes in the circular core region and the ring-shaped core region are equal is provided in the vicinity of a used wavelength band. The dispersion control fiber with holes according to claim 1,
The number of the holes is three or more,
The diameter of the hole is d, the distance from the axial center to the hole is c / 2, and the circular core region and the ring-shaped core region are Δ ₁ and Δ with respect to the refractive index of the cladding region, respectively. _When the relative refractive index difference is _2, the coupling wavelength λ _P satisfies the following formula:

The dispersion control fiber with holes according to claim 1 or 2,
The dispersion control fiber with holes, wherein the coupling wavelength λ _P is in the range of 1260 nm to 1625 nm. The dispersion control fiber with holes according to claim 3,
The normalized hole position c / 2a ₁ is 1.08 to 1.58, the relative refractive index difference Δ ₁ is 1.0 to 1.6%, and the relative refractive index difference Δ ₂ is 0. .0 to 0.78%, normalized ring core inner diameter a ₂ / a ₁ is 5 or less, and normalized ring core outer diameter a ₃ / a ₁ is 7 or less Distributed control fiber. It is a dispersion control fiber with a hole according to any one of claims 1 to 4,
A dispersion control fiber with holes, wherein chromatic dispersion at the coupling wavelength λ _P is −200 ps / nm · km or less. The dispersion control fiber with holes according to any one of claims 1 to 5,
A dispersion control fiber with holes, wherein a ratio of chromatic dispersion to a dispersion slope at a wavelength of 1550 nm is in a range of 230 nm to 530 nm. It is a dispersion control fiber with a hole according to any one of claims 1 to 4,
A dispersion control fiber with holes, wherein a zero dispersion wavelength is in a range of 1300 nm to 1324 nm. It is a dispersion control fiber with a hole according to any one of claims 1 to 4,
A dispersion control fiber with holes, wherein a dispersion value of chromatic dispersion of the LP02 mode at the coupling wavelength λ _P is positive. The dispersion control fiber with holes according to claim 8,
A dispersion control fiber with holes, wherein a ratio of chromatic dispersion of LP02 mode at a wavelength of 1310 nm to a dispersion slope is in a range of −150 nm to −280 nm. The dispersion control fiber with holes according to any one of claims 1 to 4,
A dispersion control fiber with holes, wherein a group velocity at the coupling wavelength λ _P is 0.2043 × 10 ⁶ km / s or less. An optical transmission system comprising: an optical fiber having positive dispersion in a used wavelength band; and the dispersion control fiber with holes according to any one of claims 1 to 7. The optical transmission system according to claim 11, comprising:
An optical transmission system, wherein the optical fiber having positive dispersion in the used wavelength band has a zero dispersion wavelength at a wavelength of 1300 nm to 1324 nm. An optical transmission system comprising: an optical fiber having a zero dispersion wavelength at a wavelength of 1300 nm to 1324 nm; and a dispersion control fiber with holes according to claim 7. An optical transmission system comprising: an optical fiber having negative dispersion in a wavelength 1310 nm band; and the dispersion control fiber with holes according to claim 7 or 8. The optical transmission system according to claim 14,
The optical transmission system, wherein the optical fiber having negative dispersion in the wavelength 1310 nm band has a zero dispersion wavelength in the wavelength range of 1525 nm to 1575 nm. The optical transmission system according to claim 14 or 15,
An optical transmission system comprising a mode converter that performs mode conversion between an LP01 mode and an LP02 mode. An optical delay circuit comprising: the dispersion control fiber with holes according to claim 10; and a wavelength conversion element that performs wavelength conversion between the wavelengths.

Images