KR20010060737A - Optical fiber compensator for the simultaneous compensation of polarization mode dispersion and chromatic dispersion - Google Patents

Abstract

PURPOSE: An optical fiber compensator for compensating polarization mode dispersion and chromatic dispersion is provided to make the communication service of high quality possible with the low cost by compensating dispersion of the polarizing mode and color necessary in the communication of high speed and high quality at the same time. CONSTITUTION: The optical fiber compensator for compensating polarization mode dispersion and chromatic dispersion includes nodes(10,20), the sending side single mode fiber(110), the polarizing light maintaining fiber(120), a polarizing light controller(130), the single mode optical fiber(140) and an optical connector(150). The polarizing light maintaining fiber(120) is extended from the sending side single mode fiber(110) and has a bragg grating(125) for compensating dispersion of color with controlling the reflex delay time of each wavelength of the optical signal. The polarizing light controller(130) arranges the low speed axis of the sending side single mode fiber(110) and the high speed axis of the polarizing light maintaining fiber(120). The single mode optical fiber(140) is connected to the receiving side node(20). The optical connector(150) detects the optical signal of the wavelength needed from the optical signal reflected from the polarizing light maintaining fiber(120).

Description

Optical fiber compensator for compensating polarization mode dispersion and color dispersion {OPTICAL FIBER COMPENSATOR FOR THE SIMULTANEOUS COMPENSATION OF POLARIZATION MODE DISPERSION AND CHROMATIC DISPERSION}

The present invention relates to an optical fiber compensator for compensating polarization mode dispersion and chromatic dispersion of an optical signal transmitted through an optical fiber in an optical communication network, and more particularly, in a single channel transmission of an optical communication network. The present invention also relates to an optical fiber compensator capable of simultaneously compensating polarization mode dispersion and color dispersion, which are optical transmission distortions of an optical signal transmitted along an optical fiber during wavelength division multiplexing transmission, which is a multi-channel transmission method.

In general, when an optical signal is transmitted through an optical fiber in an optical communication network, as the optical wave progresses, material dispersion according to the wavelength and waveguide dispersion due to the difference in dielectric constant between the waveguides according to the characteristics of the material constituting the fiber. Affected by color dispersion. In particular, a single-mode optical fiber has two polarization states perpendicular to the direction of propagation of the light waves. Ideally, these polarization states should be identical to each other, but in reality the propagation speeds on the axes differ due to the dielectric constant in those directions. Differential group delay is caused, resulting in polarization mode dispersion. For example, using a single-mode optical fiber with a chromatic dispersion coefficient of about 17 ps / nm / km, when transmitting an optical signal of 10 Gbps speed in the wavelength range of 1550 nm, the maximum transmission power can be transmitted while maintaining a power penalty of 1 dB or less. The distance is about 60 km. In addition, as the transmission speed increases, the transmittable distance decreases because the spread of the optical signal increases. For this reason, bit error rate and power penalty increase when transmitting an optical signal at high speed.

Various schemes for compensating the aforementioned color dispersion and polarization mode dispersion have been proposed. FIGS. 1A and 1B illustrate a configuration of an optical fiber that compensates color dispersion, and FIG. 2 illustrates a configuration of an optical fiber that compensates polarization mode dispersion. Illustrated.

First, FIG. 1A uses distributed compensation fiber 14 in the middle of a single mode fiber 12 connected between nodes 10 and 20. The wavelength division multiplexed optical signals λ ₁ , λ ₂ , λ ₃ ,..., Λ _n provided from the transmission node 10 are subjected to chromatic dispersion and polarization mode dispersion as they are guided through the single mode fiber 12. do. In this case, the distributed compensation fiber 14 disposed between the single mode fibers 12 compensates the color dispersion of the optical signal and provides the color dispersion compensated optical signal to the single mode fiber 12 connected to the receiving node 20 side. do.

FIG. 1B illustrates an optical circulator 24 arranged in the middle of the single mode fiber 22 connected between the nodes 10 and 20 as a compensation scheme different from that of FIG. 1A, and extending from the optical circulator 24. 26 shows a chromatic dispersion compensation scheme in which a grating 28 is formed. The wavelength division multiplexed optical signals λ ₁ , λ ₂ , λ ₃ ,..., Λ _n provided from the transmission node 10 are subjected to chromatic dispersion and polarization mode dispersion as they are guided in the single mode fiber 22. . At this time, the single mode fiber 26 compensates the color dispersion by adjusting the reflection delay time of the optical signal by wavelength by its fiber grating 28, and the compensated optical signal is received by the receiving node 20 through the optical circulator 24. Can be delivered and extracted.

However, the scheme shown in Figs. 1A and 1B is fundamentally limited in compensating only color dispersion. In addition, the dispersion compensation fiber and the optical circulator used in these methods are expensive, there is a problem that takes up a lot of installation area.

Referring to FIG. 2, there is shown a configuration of an optical fiber network using polarization maintaining fibers to compensate polarization mode dispersion. As shown, the fiber connected between the nodes 10, 20 is comprised of a single mode fiber 32 and a polarization maintaining fiber 36, and a polarization controller between these fibers 32, 36. 34 is disposed.

The polarization controller 34 functions to align the polarization axes of the single mode fiber 32 and the polarization maintaining fiber 36, and the polarization maintenance fiber 36 compensates for the polarization axis speed difference. Accordingly, the wavelength division multiplexed optical signals λ ₁ , λ ₂ , λ ₃ ,..., Λ _n provided from the transmission node 10 are guided by the single mode fiber 32 to reduce color dispersion and polarization mode dispersion. As is the case, polarization mode dispersion is compensated through the polarization maintaining fiber 36 and then transferred to the receiving node 20. However, the scheme shown in FIG. 2 also fundamentally only compensates for the polarization mode dispersion but does not compensate for color dispersion.

Therefore, the conventional distributed compensation fiber networks shown in Figs. 1 and 2 described above should be used separately from each other, which is a major factor in the increase of the cost of the entire network. There is a problem of being lowered.

Therefore, an object of the present invention is to provide an optical fiber compensator capable of simultaneously compensating for color dispersion and polarization mode dispersion of an optical signal.

According to an aspect of the present invention, an optical fiber compensator for compensating color dispersion and polarization mode dispersion of an optical signal includes: a transmission-side single mode fiber coupled to a transmission-side node for guiding a wavelength division multiplexing optical signal; To compensate for color dispersion of the optical signal provided from the transmission single mode fiber, the receiving side has Bragg gratings formed at different grating intervals for each wavelength of the optical signal, and a polarization mode due to the differential group speed delay of the optical signal. A polarization maintaining fiber having a variable length proportional to the differential group speed delay to compensate dispersion; A polarization controller disposed between the single mode fiber and the polarization maintaining fiber to adjust polarization axis alignment; A single mode fiber connected to a receiving node to receive an optical signal reflected from the bragg grating of the polarization maintaining fiber; And an optical coupler for extracting an optical signal having a wavelength required for the receiving node from the optical signal reflected from the polarization mode fiber and received at the receiving single mode fiber.

1A and 1B are diagrams showing the configuration of a fiber for color dispersion compensation in the prior art;

2 is a diagram showing a fiber configuration for compensating polarization mode dispersion in the prior art;

3 is a diagram showing a fiber configuration for simultaneously compensating for color dispersion and polarization mode dispersion in accordance with the present invention.

<Description of the symbols for the main parts of the drawings>

10, 20: nodes 22, 32, 110, 140: single-mode fiber

24: optical circulator 34, 130: polarization regulator

36, 120: polarization maintaining fiber 125: Bragg grating

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

3 shows a configuration of an optical fiber compensator capable of simultaneously compensating for color dispersion and polarization mode dispersion according to the present invention. As shown, the dispersion compensation optical fiber compensator of the present invention comprises a polarization maintaining fiber 120 extending from the transmitting side single mode fiber 110, a single mode optical fiber 140 connected to the receiving node 20 and a polarization maintaining fiber. And a 2 * 2 optical coupler 150 for extracting the optical signal of the required wavelength from the optical signal reflected from the 120.

Polarization maintaining fiber 120 has a Bragg grating 125 formed in accordance with the present invention. The Bragg grating 125 is formed at different grating periods or intervals for each wavelength of the optical signal to compensate for color dispersion by adjusting the reflection delay time for each wavelength of the optical signal. More specifically, the Bragg grating 125 is formed at intervals that gradually become shorter in the low frequency side direction of the optical signal and at intervals that gradually widen in the high frequency side direction of the optical signal. Therefore, the reflection delay time of the optical signal on the low frequency side is shortened and the reflection delay time of the optical signal on the high frequency side is shortened according to the interval of Bragg grating 125 so that the optical signal of all wavelengths reflected by the Bragg grating 125 is reflected. The reflection delay time will be the same, which in turn can compensate for color dispersion.

The method of forming the grating interval can be implemented as in Equation 1 described below.

In Equation 1, Is the propagation constant of the optical signal, Denotes the grating period. In this case, when the wavelength traveling in the same direction is reflected it can be represented by the following equation (2).

In Equation 2, Is the effective refractive index, Represents the wavelength. Thus, grating Equation 2 Expanded with respect to, the following equation (3).

Therefore, by forming intervals of different gratings in a manner corresponding to the wavelength of the input optical signal, different reflection delay times for each wavelength can be adjusted to compensate for color dispersion.

In addition, the polarization maintaining fiber 120 compensates for the polarization mode dispersion due to the differential group velocity delay of the transmitted optical signal by adjusting its overall physical length l as described in Equation 4 below.

In Equation 4, T _DGD represents the measured differential group speed delay, L _B is the bit length of the polarization maintaining fiber 120, τ _g represents the delay time of the polarization maintaining fiber 120, L represents the reciprocating length of the polarization maintaining fiber 120, that is, 2 * l. These bit lengths L _B and the delay time τ _g may be expressed as Equations 5 and 6, respectively.

In Equations 5 and 6, | n _x -n _y | represents a difference in refractive index between the x and y axes of the polarization maintaining fiber 120. The delay speed τ _g of the polarization maintaining fiber 120 can be calculated from Equations 5 and 6, and the reciprocating length of the polarization maintaining fiber 120 is proportional to the differential group speed delay T _DGD measured using the delay speed τ _g . By adjusting (L), the polarization mode dispersion of the optical signal can be compensated.

Meanwhile, the polarization controller 130 performs a polarization axis alignment function of aligning a low speed axis of the single mode fiber 110 and a high speed axis of the polarization maintaining fiber 120.

The optical coupler 150 is input through the single mode fiber 110 according to the alignment of the polarization axis of the single mode fiber 110 and the polarization maintaining fiber 120 by the polarization controller 130 and the grating of the polarization maintaining fiber 120 ( An optical signal having a wavelength required by the receiving node 20 is extracted from the optical signal reflected at 125 and reflected back to the single mode fiber 140 of the receiving node 20.

In addition, the single-mode fiber 140 on the receiving side has a fiber 145 extending through the optical coupler 150, the end of the fiber 145, the optical signal reflected from the polarization maintaining fiber 120 is the receiving side It is roughly processed so as not to be reflected toward the single mode fiber 140.

The optical fiber structure for dispersion compensation of the present invention having the above-described configuration will be briefly described as follows.

The wavelength division multiplexed optical signals (λ ₁ , λ ₂ , λ ₃ ,..., Λ _n ) at the transmitting node 10 are transmitted through the single mode fiber 110 to receive color dispersion and polarization mode dispersion. . At this time, the optical signal is aligned once the polarization axis by the polarization controller 130, it is provided to the polarization maintaining fiber 120 through the optical coupler (150). In the polarization maintaining fiber 120, the optical signal is adjusted to the reflection delay time for each wavelength according to the adjusted length l of the polarization maintaining fiber 120 and the brag grating 125 to the optical coupler 150. After being reflected, only the optical signal having the required wavelength is reflected to the single mode fiber 140 of the receiving node 20 and extracted and input to the node 20. Accordingly, the optical signal guided through the single mode fiber 110 is provided to the receiving node as an optical signal in which both color dispersion and polarization mode dispersion are compensated through the above-described path.

Therefore, according to the present invention, polarization mode dispersion and chromatic dispersion compensation, which are essential for high speed and high quality communication in short channel and multi channel optical communication, can be simultaneously compensated by a single polarization maintaining fiber. As a result, signal transparency, low cost, and improved installation operability will enable high-quality communications services in high-speed, high-capacity backbone networks and high-speed metro-WDM.

Claims (4)

In the optical fiber compensator for compensating the color dispersion and polarization mode dispersion of the optical signal, It has Bragg gratings formed at different grating intervals for each wavelength of the optical signal to compensate for color dispersion of the optical signal provided from a transmission-side single mode fiber connected to a transmission-side node that guides the wavelength division multiplexing optical signal. A polarization maintaining fiber having a variable length proportional to the differential group speed delay to compensate polarization mode dispersion due to the differential group speed delay of the signal; A single mode fiber connected to a receiving node to receive an optical signal reflected from the bragg grating of the polarization maintaining fiber; And an optical coupler configured to extract an optical signal having a wavelength required for the receiving node from the optical signal reflected from the polarization maintaining fiber and received at the receiving single mode fiber. The Bragg grating formed in the polarization maintaining fiber is formed at intervals that gradually become shorter in the low frequency side direction of the optical signal, and is formed at intervals that gradually widen in the high frequency side direction of the optical signal. An optical fiber compensator for dispersion compensation. The method of claim 1, wherein the length of the polarization maintaining fiber is Where T _DGD represents the differential group speed delay, L _B is the bit length of the polarization maintaining fiber, τ _g represents the delay time of the polarization maintaining fiber, and L is the polarization An optical fiber compensator for dispersion compensation, characterized in that it represents a reciprocating length of a holding fiber. The dispersion compensation element of claim 1, wherein the receiving side single mode fiber has an end extending through the optical coupler, and the end is roughly processed so that an optical signal reflected from the polarization maintaining fiber is not reflected. Fiber optic compensator.