KR0175536B1 - Multichannel Optical Frequency Alignment Method and Multichannel Optical Frequency Alignment Method Using Optical Fiber Michelson Interferometric Optical Filter in Multichannel Optical Transmission System - Google Patents

Abstract

In a multi-channel optical transmission system using an optical frequency (or wavelength) division multiplexing technique, an optical filter composed of an optical fiber Michelson interferometer is used to set the multi-channel optical frequencies at a pseudo-interval (or a sequential boiling interval) (Or sequential boiling interval) of the multi-channel optical frequencies, the crosstalk caused by the four-wave mixing of the optical fibers can be efficiently suppressed, and a compatible system can be realized by efficiently aligning the multi-channel frequencies Channel optical frequency-aligning method and a multi-channel optical frequency aligning apparatus using an optical fiber Michelson interferometer type optical filter in a multi-channel optical transmission system.

Description

Multichannel Optical Frequency Alignment Method and Multichannel Optical Frequency Alignment Method Using Optical Fiber Michelson Interferometric Optical Filter in Multichannel Optical Transmission System

FIG. 1 is a block diagram of a Michelson interferometer type optical filter composed of optical fibers having different chromatic dispersion according to the present invention. FIG.

FIG. 2 is a characteristic diagram showing the calculation of the optical frequency (or wavelength) transmission characteristics of FIG.

FIG. 3 is a block diagram of a multi-channel optical transmission system using a Michelson interferometer type optical filter according to the present invention;

DESCRIPTION OF THE REFERENCE NUMERALS

1: input of interferometer 2: optical isolator

3: optical fiber coupler 4, 5: optical fiber

6, 7: Faraday rotating mirror (FRM)

8: Optical fiber output stage 11: Multichannel light source (LD)

12: first optical fiber coupler (or optical fiber splitter) (FC)

13, 17: second and third optical fiber couplers (FC)

14: Michelson interferometer type optical filter (FMIF) using optical fibers with different chromatic dispersion

15: Optical frequency stabilization circuit (FSC) 16: External modulator (EM)

The present invention relates to a multichannel optical frequency alignment method and a multichannel optical frequency alignment apparatus using an optical fiber Michelson interferometer type optical filter in a multichannel optical transmission system and, more particularly, to a multichannel optical frequency alignment method and a multichannel optical frequency alignment apparatus using an optical frequency (or wavelength) The optical fiber Michelson interferometer type optical filter is constructed so that the transmitted or reflected optical frequencies have pseudo-interval (or sequential boiling interval) characteristics by using optical fibers having different chromatic dispersion in the transmission system, Or a sequential boiling interval) of the multi-channel optical frequency.

In general, a multichannel optical transmission system using optical frequency (or wavelength) division multiplexing technology has a 1550 nm wavelength region of an Erbium Doped Fiber Amplifier (EDFA) having a bandwidth of about 4 THz (about 30 nm) (TDM: Time Division Multiplexed) signals on each channel and transmitting them on multiple channels, thereby realizing a transmission system of several hundred Gb / s to several Tb / s. The color injection of the optical fiber is a major factor limiting the performance of a high-speed long-distance optical transmission system, and can be effectively controlled by using a dispersion-shifted fiber (DSF) having zero dispersion in the wavelength region of 1550 nm. However, the use of a dispersion-shifted optical fiber (DSF) having a small chromatic dispersion value reduces the phase difference between transmission channel frequencies in a multi-channel optical frequency division multiplexing transmission system, so that the four wave mixing of the optical fibers generates new frequency components, Thereby causing crosstalk, which is a major factor in deteriorating system performance.

In order to suppress the four-wave mixing of the optical fiber, a method of increasing the frequency interval of the transmission channel or adjusting the chromatic dispersion value of the optical fiber to increase the phase difference between the channel frequencies to lower the efficiency of lowering the four- Are arranged at non-uniform intervals so that the frequency components generated by the four-wave mixing of the optical fibers are located outside the filter region of the transmission channel or the receiving end. In this case, a method of aligning the multichannel frequencies is to arrange and control the multichannel frequencies at equal intervals using the equal-interval optical frequency transmission characteristic of a reference resonator such as a fiber Fabry-Perot (FFP) resonator, And the multi-channel frequency is aligned and controlled at a boiling interval. In particular, in the N-channel system, the frequency difference between any two channels {n _ij = n _i -n _j (i, j = 1, 2, ..., N, i ≠ j) It is possible to prevent the frequency components generated by the four-wave mixing of the optical fibers from overlapping the transmission channel by setting the channels to have different values. However, since the transmission bandwidth is significantly increased compared to the case of the equal interval and the frequency intervals between adjacent channels of the transmission channel do not have a constant functional relation, the optical frequency transmission characteristic of the reference resonator should be selectively used Therefore, it is difficult to align and control the multi-channel optical frequency.

Accordingly, the present invention provides a multi-channel optical transmission system using an optical frequency (or wavelength) division multiplexing technique, in which multichannel optical frequencies are set at a pseudo-interval (or a sequential boiling interval) by using an optical filter composed of an optical fiber Michelson interferometer, By efficiently aligning multichannel optical frequencies set at a pseudo-uniform interval (or a sequential boiling interval), the crosstalk caused by the four-wave mixing of the optical fibers can be efficiently suppressed, and a compatible system And the like.

According to an aspect of the present invention, there is provided a multi-channel frequency aligning method for a multi-channel optical transmission system, including: setting a multi-channel frequency in pseudo-interval or sequential boiling intervals in which frequency intervals of a transmission channel are sequentially increased or decreased; The optical fiber coupler includes a first optical fiber coupler for separating the optical outputs of the respective light sources, a second optical fiber coupler for separating optical outputs of the first optical fiber couplers and the second optical fiber couplers, A Michelson interferometer type optical filter including an optical fiber having different chromatic dispersion and having an optical output coupled through the second optical fiber coupler as an input; The optical output of the optical fiber Michelson interferometer type optical filter composed of different optical fibers is detected An optical frequency stabilizing circuit having a function of regulating the temperature and injection current of the channel light sources, a respective external modulator inputting some other optical outputs coming through the first optical fiber coupler, And a third fiber coupler having optical outputs as inputs.

According to the present invention, in a multi-channel optical transmission system using an optical frequency (or wavelength) division multiplexing technique, multi-channel optical frequencies are set to pseudo-interval (or sequential boiling interval) And a multi-channel optical frequency is set to a pseudo-interval (or a sequential boiling interval) by using the optical filter, and the set multi-channel optical frequencies are stably aligned. Therefore, by setting all the frequency intervals between adjacent channels differently while maintaining the total transmission bandwidth constant, it is possible to efficiently utilize the region transmission band of the zero dispersion wavelength of the optical fiber in the multi-channel optical transmission system, Can be efficiently suppressed.

In addition, by ensuring a constant defined functional relationship defined by the characteristics of a fiber-optic Michelson interferometric optical filter between frequency intervals, a compatible system capable of easily aligning multi-channel frequencies between different systems Can be configured.

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

FIG. 1 is a configuration diagram of a Michelson interferometer type optical filter composed of optical fibers having different chromatic dispersion according to the present invention. In FIG. 1, reference numeral 1 denotes an input end of an interferometer, 2 denotes an output signal of an interferometer Is an optical isolator used as a means for blocking components. (3) is an optical fiber coupler that divides the optical signal by 50 to 50, (4) and (5) are optical fibers having different chromatic dispersion that constitute the two paths of the interferometer, and the optical fibers have different lengths. (6) and (7) are Faraday rotating mirrors, which are used as a means to prevent the interference characteristics of the interferometer from changing due to the polarization changes that the optical signal travels through the two optical fibers (4) and (5) , And (8) are optical fiber output stages.

The optical signals input to the interferometer are divided into 50 to 50 by the optical fiber coupler 3 and then proceed to the optical fibers 4 and 5 respectively and are reflected by the paradiometer mirrors 6 and 7, Are combined by the optical fiber coupler 3 again via paths 4 and 5, respectively. At this time, the two optical signals traveling through the optical fibers 4 and 5 travel in different optical paths (the product of the refractive index and the length of the optical fiber), and the interference signal due to the path difference is output to the output terminal 8 . The intensity of the output signal of the Michelson interferometer is as follows.

Here, lambda and lambda ₀ are the frequency (or wavelength) of the optical signal and the reference optical frequency (or wavelength)

n ₁ (?), n ₂ (?): Refractive index of optical fibers (4) and (5)

l ₁ , l ₂ : the length of the optical fibers (4) and (5)

k: visibility of the interference fringe

[Delta] [phi] ([lambda]) is the phase difference according to the optical path difference between the two optical fibers.

That is, the phase difference Δφ (λ), which affects the output characteristics of the interferometer, is determined by the difference between the optical paths of the two optical fibers 4 and 5, and the optical path is defined as the product of the refractive index and length of the optical fiber , The chromatic dispersion and the length of the two optical fibers 4 and 5 are changed, so that the transmitted optical frequency and frequency interval can be adjusted.

The refractive index of the optical fiber has a chromatic dispersion characteristic that varies depending on the optical frequency (or wavelength). If the two optical fibers 4 and 5 have the same chromatic dispersion characteristics, the intensity of the output signal of the interferometer shows a periodic variation with respect to the optical frequency (or wavelength). However, if the difference in chromatic dispersion between the two optical fibers 4 and 5 is large, the chromatic dispersion of the optical fiber monotonically increases or decreases according to the optical frequency (or wavelength), and thus the Michelson interferometer Type optical filter exhibits pseudo-uniform (or sequential boiling interval) optical frequency (or wavelength) transmission characteristics.

FIG. 2 is a characteristic diagram showing the calculation of the optical frequency (or wavelength) transmission characteristic of FIG. 1. The chromatic dispersion of the two optical fibers 4 and 5 is 17 ps / nm, km, -80 ps / The lengths were assumed to be 10 cm and 5 cm, respectively. When the group delay of the two optical fibers 4 and 5 is assumed to be the same at a wavelength of 1530 nm, there are 13 transmission peaks between the wavelengths of 1544 nm and 1566 nm, (1.34 nm, 1.24 nm, 1.15 nm, 1.08 nm, 1.03 nm, 0.97 nm, 0.93 nm, 0.90 nm, 0.86 nm, 0.83 nm, 0.81 nm and 0.78 nm in the wavelength region) can do.

FIG. 3 is a block diagram of a multi-channel optical transmission system using a Michelson interferometer type optical filter according to the present invention.

This is an example of a system configuration for efficiently aligning and easily controlling multi-channel frequencies set at a pseudo-uniform interval (or a sequential boiling interval) using a Michelson interferometer type optical filter composed of optical fibers having different chromatic dispersion. Reference numeral 11 denotes a multichannel light source in which optical frequencies are arranged at predetermined intervals (or consecutively spaced intervals), and reference numeral 12 denotes a first optical fiber coupler (1 × 2 optical fiber coupler or optical fiber splitter) , And separates the light output of each light source. A part of the optical output separated through each first optical fiber coupler is combined through the second optical fiber coupler (Nx1 optical fiber coupler) of (13) and input to the optical fiber Michelson interferometer type optical filter 14. (14) is a Michelson interferometer type optical filter composed of optical fibers having different chromatic dispersion, and has a pseudo-uniform (or sequential boiling interval) optical frequency (or wavelength) transmission characteristic. When the optical frequency of the multi-channel light sources 11 inputted to the optical fiber Michelson interferometer type optical filter 14 is fluctuated, the optical output is changed. The optical frequency stabilizing circuit 15 is a circuit for adjusting the temperature and injection current of the multichannel light sources 11 by detecting a change in optical output of the optical fiber Michelson interferometer type optical filter 14 according to a change in optical frequency . That is, each of the multi-channel light sources 11 stably arranges pseudo-interval (or sequentially consecutively spaced) multi-channel optical frequencies through an optical fiber Michelson interferometer type optical filter 14 and an optical frequency stabilization circuit 15 . On the other hand, some of the other optical outputs coming through the first optical fiber coupler 12 have stable frequency characteristics and are modulated through the external modulator 16 while maintaining a predetermined pseudo constant interval (or sequential boiling interval) (N × 1 optical fiber coupler) 17 and transmitted.

According to the present invention, since the multi-channel frequency alignment method using a pseudo-interval (or sequential boiling interval) optical filter composed of an optical fiber Michelson interferometer has a constant functional relationship between adjacent channels, It is possible to easily realize alignment and control of multi-channel optical frequencies set at equal intervals (or sequential boiling intervals), thereby effectively suppressing crosstalk caused by four-wave mixing of optical fibers, Band can be fully utilized, and a multi-channel optical transmission system compatible with each other can be realized.

Claims (7)

A first optical fiber coupler for separating the light outputs of the respective light sources, a second optical fiber coupler for separating the light outputs of the light sources separated through the first optical fiber coupler, A Michelson interferometer type optical filter composed of an optical fiber having different chromatic dispersion with an optical output integrated through the second optical fiber coupler as an input and an optical fiber composed of optical fibers having different chromatic dispersion An optical frequency stabilization circuit having a function of adjusting a temperature and an injection current of the multi-channel light sources by sensing a change in light output of the Michelson interferometer type optical filter; A third optical fiber coupler for inputting optical outputs modulated through the respective external modulators, The multi-channel optical frequency alignment apparatus using the Michelson optical fiber interferometer type optical filter in a channel Mai optical transmission system, characterized in that consisting of. 2. The optical fiber michelson interferometer type optical filter according to claim 1, wherein the optical fiber Michelson interferometer type optical filter composed of optical fibers having different chromatic aberration comprises an input end of an interferometer that receives an optical signal as input and an output terminal of an interferometer , Optical fiber couplers that divide the optical signal into two equally spaced optical fibers, optical fibers with different chromatic dispersion that constitute the two paths of the interference crosstalk, and polarization changes experienced when the optical signal travels through the respective optical fibers And a plurality of parallel mirrors for preventing an interference characteristic of the interferometer from changing, and an optical fiber output terminal for outputting an optical signal. In the multi-channel optical transmission system, a multichannel optical fiber using an optical fiber Michelson interferometer type optical filter Frequency alignment device. In a multi-channel transmission system using an optical frequency division multiplexing technique, the multi-channel optical transmission system is characterized in that the frequency intervals of the transmission channels are arranged to increase or decrease sequentially, but multi-channel frequencies are set at pseudo- Multichannel Optical Frequency Alignment Method Using Optical Fiber Michelson Interferometric Optical Filter. 4. The multi-channel optical transmission system according to claim 3, wherein the frequencies are set so that the frequency intervals between adjacent channels of the multi-channel frequencies arranged to increase or decrease sequentially have a certain functional relationship. Multichannel optical frequency alignment method using optical filter. The multi-channel optical transmission system according to claim 3 or 4, wherein an optical filter composed of an optical fiber Michelson interferometer is used to align the multi-channel optical frequencies set at the pseudo-interval or the sequential boiling interval, A multi - channel optical frequency alignment method using an interferometer type optical filter. 4. The multi-channel optical transmission system according to claim 3, wherein the optical fiber Michelson interferometer type optical filter uses optical fibers having different chromatic dispersion so as to have pseudo-uniform or sequential unequal spacing optical frequency transmission characteristics. Multichannel Optical Frequency Alignment Method Using Michelson Interferometric Optical Filter. And a paradigm mirror is used to suppress a change in the polarization characteristics of the optical signal due to the optical fiber constituting the two paths of the optical fiber Michelson interferometer. In the multi-channel optical transmission system, Optical frequency alignment method.