CN106772789A - A low nonlinear coefficient few-mode fiber - Google Patents

Abstract

The invention provides a low nonlinear coefficient few-mode optical fiber; the refractive index of the fiber core is distributed in a graded manner, so that three-mode few-mode operation of optical fiber communication C-band low nonlinear coefficient and low differential mode group delay is realized, and the nonlinear coefficient and the differential mode group delay are distributed flatly in the C-band range; the optical fiber has the characteristics that the optical fiber has wide application prospect in the fields of optical fiber communication few-mode transmission, mobile communication Front-haul few-mode transmission and the like.

Description

A low nonlinear coefficient few-mode fiber

technical field

The invention relates to an optical fiber waveguide structure, in particular to a low nonlinear coefficient few-mode optical fiber, which can be applied in the fields of optical fiber communication, optical information processing and the like.

Background technique

Optical fiber is an important transmission medium for optical fiber communication systems; with the further development of optical fiber manufacturing technology, people realized a low-loss optical fiber with a loss of about 0.2dB/km in the 1550nm band in 1979; low-loss optical fiber started a revolution in the field of optical fiber communication In 1995, the commercialization of erbium-doped fiber amplifiers working in the 1550nm band led to the great development of optical fiber communication and nonlinear fiber optics; various types of optical fibers and optical fiber communication systems were widely used [1 G. P. Agrawal, Nonlinear Fiber Optics, 5e, Elsevier Inc. Elsevier (Singapore) Pte Ltd. 2012, 1-648].

In order to solve the transmission quality problems caused by fiber nonlinearity in single-mode fiber optic communication systems, the industry has adopted a solution to reduce fiber nonlinearity by using large effective area fibers. In recent years, the few-mode fiber used in the field of space-division multiplexing optical fiber communication is one of the frontier research hotspots of fiber optics; in order to reduce the nonlinear effect of fiber, the literature [2 He Wen, HongjunZheng, Benyuan Zhu and Guifang Li, Experimental Demonstration of Long-Distance Analog Transmission over Few-Mode Fibers. OFC2015, M3E.2, 2015, 1-3] Using Few-Mode Fiber with 130µm ² -mode field area in the 1550 nm band reduces the third-order intermodulation distortion of the analog transmission signal by 3 dB , improving the signal spurious-free dynamic range by 1.5 dB; literature [3 Mukasa K, Imamura K, Sugizaki R. Multi-core Few-mode optical fibers with large Aeff. European Conference and Exhibition on Optical Communications. 2012: 1-3] proposed 170µm ² (LP ₀₁ ) and 250µm ² (LP ₁₁ ) large effective area few-mode fibers; literature [4 Kasahara M, Saitoh K, Sakamoto T, et al.Design of Three-Spatial-Mode Ring-Core Fiber. Journal of LightwaveTechnology, 2014, 32(7): 1337-1343.] proposed a large effective area annular core few-mode fiber with adjustable mode field area from 80 to ^360µm2 ; literature [5 Mingjun Li, et al. Low delay and large effective areafew-mode fibers for mode-division multiplexing. IEEE Opto-Electronics and Communications Conference, 2012:495-496.] proposed large effective area and low differential modes with mode field areas of 186µm ² (LP ₀₁ ) and 242µm ² (LP ₁₁ ) Few-mode fiber with group delay, and demonstrated 100 km few-mode transmission experiment. It can be seen that in order to reduce the nonlinear coefficient of the fiber, increasing the effective mode field area of the fiber is also an effective solution for the space division multiplexed few-mode fiber; mode group delay; and the refractive index gradient distribution can effectively reduce the differential mode group delay[6 Sillard P, Bigot-Astruc M, Molin D. Few-ModeFibers for Mode-Division-Multiplexed Systems [J]. Journal of LightwaveTechnology 2014 , 32(16):2824-2829]; the research on few-mode fibers with large effective mode field area, low nonlinear coefficient, and graded distribution of refractive index is very important; the research challenge of few-mode fibers is to achieve low nonlinearity with wide bandwidth coefficient, low differential mode group delay for few-mode operation.

Contents of the invention

With the support of the National Natural Science Foundation of China (No. 61671227 and 61431009), the Natural Science Foundation of Shandong Province (ZR2011FM015), and the special funds of the "Taishan Scholars" construction project, the present invention proposes a low nonlinear coefficient few-mode optical fiber. The refractive index of the optical fiber is The gradient distribution realizes the three-mode few-mode operation with low nonlinear coefficient and low differential mode group delay in the C-band of optical fiber communication, and gives the variation law of various characteristics of the proposed few-mode fiber with the incident wavelength; for mobile communication The practical application of Front-haul few-mode transmission provides support.

The technical solution adopted by the present invention to solve its technical problems is:

The cross-section of the low nonlinear coefficient few-mode optical fiber proposed by the present invention is generally composed of a pure silica matrix cladding and a doped silica core; the outer diameter of the core of the optical fiber, the outer diameter of the cladding and the perfect match The outer diameter of the layer corresponds to 26µm, 100µm and 150µm in turn; the core radius and refractive index distribution are designed to be balanced; the refractive index of the fiber cladding, core center and perfect matching layer are 1.4440, 1.4449 and 1.4440 respectively; the refraction from the core center to the cladding The rate is a gradual distribution; the refractive index follows the equation

(1)

Set, where n ₁ represents the center refractive index of the fiber core, n ₂ represents the cladding refractive index, r represents the distance from any point in the fiber to the axis, is the outer diameter of the fiber core; the characteristics of the few-mode fiber are studied by the full vector finite element method.

The beneficial effects of the present invention are as follows:

1. A low nonlinear coefficient few-mode optical fiber is proposed; its refractive index has a gradual distribution, which realizes the three-mode few-mode operation with low nonlinear coefficient and low differential mode group delay in the C-band of optical fiber communication, and the nonlinear coefficient and differential mode group delays have a flat distribution in the C-band range;

2. The characteristics of this optical fiber make it have broad application prospects in the fields of optical fiber communication few-mode transmission and Front-haul few-mode transmission.

Description of drawings

Fig. 1 is the cross-sectional schematic diagram and the refractive index profile diagram of the low nonlinear coefficient few-mode optical fiber of the present invention; Wherein Fig. 1 (a) is the optical fiber cross-sectional schematic diagram, R1 is the core outer diameter, R2 is the cladding outer diameter, R3 is The outer diameter of the perfect matching layer; Figure 1(b) is a distribution diagram of the optical fiber refractive index;

Figure 2 is the electric field distribution diagram of the linear polarization modes LP01, LP11a and LP11b when the incident light wavelength is 1.550 µm;

Figure 3 shows the variation of the effective mode field area and nonlinear coefficient of the few-mode fiber with the wavelength of the incident light; the solid lines with stars and small circles in Figure 3(a) represent the effective mode field area of LP01 and LP11 with the wavelength of the incident light, respectively. ; the solid lines with stars and small circles in Fig. 3(b) represent the nonlinear coefficients of LP01 and LP11 as a function of the wavelength of incident light, respectively;

Figure 4 shows the variation of the dispersion of few-mode fiber with the wavelength of the incident light. The dotted line, dotted line and solid line in Figure 4(a) represent the material dispersion, waveguide dispersion and total dispersion of the mode LP01 respectively; Figure 4(b) points Lines, dotted lines and solid lines represent the material dispersion, waveguide dispersion and total dispersion of mode LP11, respectively;

Figure 5 shows the variation of the differential mode group delay DMGD of LP11 and LP01 with the wavelength of the incident light.

detailed description

The technical solution of the present invention will be described in detail below in conjunction with the embodiments and drawings, but the scope of protection is not limited thereto.

Embodiment 1 See Figure 1, which is a cross-sectional schematic diagram (a) and a refractive index distribution diagram (b) of a low nonlinear coefficient few-mode fiber of the present invention. The cross-section of the low nonlinear coefficient few-mode fiber is made of pure Silicon matrix cladding and doped silica core; the radii of the circles in the figure are denoted as R1, R2 and R3 respectively, corresponding to the outer diameter of the core, the outer diameter of the cladding and the outer diameter of the perfect matching layer in turn, where R1= 26 µm, R2=100 µm, R3=150 µm. Balanced design of core radius and refractive index distribution; the refractive index of the fiber cladding, core center and perfect matching layer are 1.4440, 1.4449 and 1.4440 respectively; the refractive index from the core center to the cladding is set according to equation (1), showing a gradual change distribution; the characteristics of the few-mode fiber were studied by using the full vector finite element method.

Fig. 2 shows the electric field distribution of the linear polarization modes LP01, LP11a and LP11b when the incident light wavelength is 1.550 µm. LP11a and LP11b are degenerate modes; their effective mode field area and parameters such as nonlinear coefficients are the same, and they will be represented by LP11 in the following discussion.

Figure 3 shows the variation of the effective mode field area and nonlinear coefficient of the few-mode fiber with the wavelength of the incident light, and the solid lines with stars and small circles in Figure 3(a) indicate that the effective mode field area of LP01 and LP11 varies with the wavelength of the incident light ; the solid lines with stars and small circles in Figure 3(b) represent the nonlinear coefficients of LP01 and LP11 as a function of the wavelength of the incident light, respectively. It can be seen from Figure 3 that the effective mode area of the LP01 and LP11 modes of the few-mode fiber is very large, much larger than the effective mode area of the standard single-mode fiber, and increases with the increase of the incident light wavelength; the effective mode area of the LP11 mode increases more quick. The nonlinear coefficients of LP01 and LP11 modes of few-mode fibers are very small, much smaller than those of standard single-mode fibers, and decrease with the increase of the incident light wavelength, and both have a flat distribution in the C-band of optical fiber communication; LP01 and LP11 modes are non-linear. The linear coefficients differ very little.

Figure 4 shows the variation of the dispersion of few-mode fiber with the wavelength of the incident light. The dotted line, dotted line and solid line in Figure 4(a) represent the material dispersion, waveguide dispersion and total dispersion of the mode LP01 respectively; Figure 4(b) points Lines, dotted lines, and solid lines represent the material dispersion, waveguide dispersion, and total dispersion of mode LP11, respectively. It can be seen from Fig. 4 that the waveguide dispersions of modes LP01 and LP11 are both small, resulting in their total dispersion being approximately equal to the material dispersion. The total dispersion of modes LP01 and LP11 becomes larger with the increase of incident light wavelength. In the 1550 nm band, the total dispersion of modes LP01 and LP11 is consistent with that of literature [5].

Figure 5 shows the variation of the differential mode group delay DMGD of LP11 and LP01 with the wavelength of the incident light. It can be obtained from Figure 5 that the differential mode group delay DMGD of LP11 and LP01 is very small and gradually decreases with the increase of the incident light wavelength; Communication C-band is flat distribution. The differential mode group delay is on the same order of magnitude as the DMGD in [5].

In short, the few-mode optical fiber proposed by the present invention realizes the few-mode operation with low nonlinear coefficient and low differential mode group delay in the C-band of optical fiber communication, and the nonlinear coefficient and differential mode group delay are flatly distributed in the C-band range; The characteristics of the optical fiber make it have broad application prospects in the fields of optical fiber communication few-mode transmission, Front-haul few-mode transmission and other fields.

It should be noted that the specific implementation is only a representative example of the present invention, and obviously the technical solution of the present invention is not limited to the above-mentioned embodiments, and many variations are possible. Those of ordinary skill in the art, based on the disclosure of the present invention or obtained without objection from the written description of the document, should be considered as the protection scope of this patent.

Claims (2)

1. A low nonlinear coefficient few-mode optical fiber is characterized in that: the cross section is composed of a doped silica fiber core and a pure silica matrix cladding on the whole; the core outer diameter, cladding of the optical fiber The outer diameter and the outer diameter of the perfect matching layer correspond to 26 µm, 100 µm and 150 µm in turn; the refractive index of the fiber cladding, core center and perfect matching layer are 1.4440, 1.4449 and 1.4440 respectively; the refractive index from the center of the core to the cladding is gradually changing type distribution; the refractive index follows the equation (1) setting, where n ₁ represents the center refractive index of the fiber core, n ₂ represents the cladding refractive index, r represents the distance from any point in the fiber to the axis, a = 26 µm is the outer diameter of the fiber core, . 2. according to the described optical fiber of claim 1, it is characterized in that, realized the three-mode few-mode operation of optical fiber communication C band low nonlinear coefficient, low differential mode group time delay, and nonlinear coefficient and differential mode group time delay are in C The distribution is flat in the band range.