DE19945143A1 - Optical transmission system - Google Patents

Abstract

The invention relates to an optical transmission system (OTS), consisting of a plurality of optical fiber link sections (FDS), each with an optical fiber (SSMF) and a dispersion compensation unit (DCF), in which dispersion compensation units (DCF) are provided, which the fiber dispersion (d) of several Compensate fiber section sections (FDS¶1¶ to FDS¶4¶) in such a way that the remaining dispersion (D¶rest¶) per compensated fiber section section (FDS¶1¶ to FDS¶4¶) is at least almost equally by the same amount of dispersion (DELTAD ) increases.

Description

The invention relates to an optical transmission system standing with several optical fiber sections an optical fiber and a dispersion compensation unit.

For all optical transmission systems with high data throughput rates, also with the WDM principle (Wavelength Division multiplexing) working transmission systems, who through the in the transmission of optical signals over optical fibers occurring chromatic dispersion and Self-phase modulation (SPM) distortion in the transmitted appropriate optical data signal - see here Gray and joy: "Optical communication technology - an introduction tion ", Springer-Verlag, 3rd edition, 1991, pp. 120-126.

Such distortions of the optical data to be transmitted signals depend among other things on the input power of the optical data signal. Furthermore, such Distortions the regeneration-free transmission range an optical transmission system, d. H. the opti cal transmission path over which an optical data signal can be transmitted without regeneration or "3R- Regeneration "(electronic data regeneration with regard to the amplitude, edge and the clock of an optically transmitted telten, digital data signal or data stream) must be led.

To avoid such distortions of the optical data signal to compensate for the transmission of optical signals suitable dispersions via standard optical monomode fibers compensation units provided or one to the optical Transmission route adapted dispersion management turned on puts. Such optical transmission systems are used for this purpose  predominantly un in several optical fiber sections subdivided, in which the respectively in the considered optical Fiber stretch section caused fiber dispersion with Complete or with the help of a dispersion compensation unit is partially compensated.

Such dispersion compensation units are an example wise designed as special optical fibers in which through a special choice of the refractive index profile in the fiber core and the surrounding cladding layers of the optical fiber the dispersion or fiber dispersion, in particular in the 1550 nm Window takes very high negative values. With the help of the dispersion-compensating fiber, high negative dispersion values can be determined by the optical Transmission fibers effectively created dispersion contributions be compensated. In addition, the maximum number of optical fiber sections or the regenerations free range of the optical transmission system through the Eye diagram ("eye-opening") of the output of the respective optical fiber section section adjacent optical Da tensignals determined. This results in a maximum Range for a regeneration-free transmission of an op table data signal, which is additionally by the optical Si gnal-noise ratio of the transmission medium determined is.

In optical transmission systems implemented so far different dispersion management concepts follows, with the optimal dispersion compensation of an opti transmission path by using pre and / or post-compensated or differently over- or under-comm performed optical fiber sections becomes. Depending on the fiber dispersion, a be certain distance can be transmitted without regeneration.

For this purpose from DER FERMELDE-ENGINEER:
"Wavelength division multiplexing technology in future photonic networks", A. Ehrhardt et. al., 53rd volume, issues 5 and 6, May / June 1999, pp. 18-24 known that the system optimum for dispersion compensation of an optical transmission system can be achieved with a dispersion compensation of less than 100%. Furthermore, it is apparent from the above-mentioned publication that the chromatic fiber dispersion can be compensated for by a certain part by fiber non-linearities.

The object of the present invention is therefore an optical transmission system of the type mentioned to design such that the dispersion compensation ver is improved and / or reduced by the signal distortions graceful, regeneration-free bridgeable transmission range te is increased. The task is based on that in the Oberbe grabbed by the features specified by claim 1 characteristic features solved.

According to the invention, the object is achieved by an optical transmission Solution solved in the dispersion compensation units are provided, the fiber dispersion of several fibers Compensate sections of the track so that the remaining Residual dispersion per compensated fiber section at least almost evenly around the same dispersion amount increases. The advantage of the invention almost evenly distributed undercompensation over the one individual optical fiber sections compared to systems with full compensation almost doubled the transmission range that can be bridged without regeneration enables d. H. in the respective fiber section is undercompensated until the remaining Dispersion a multiple of the Disper according to the invention amount corresponds, with the remaining dispersion along the optical transmission path per fiber section increases by the amount of dispersion.  

According to a further embodiment of the invention, the op table transmission system through fiber nonlinearities and the fiber dispersion caused, accumulated residual Dispersion that is almost linear with increasing data rate decreases - claim 2. The non-linear effect self-phase mo dulation and the Group Velocity Dispersion (GVD) are the original thing for the accumulated residual dispersion at the end of the last th fiber section of the optical transmission link ke. They are with fully compensated fiber sections almost independent of the input power of the optical Da tens signals and influence each other, d. H. the Self-phase modulation can be dispersion-compensating Have effect. Furthermore, with increasing data the group velocity dispersion in the optical fibers while the self-phase modulation remains almost unchanged. Thus, the self-phase modulation (SPM) carries in the optical Transmission system for dispersion compensation, the dispersion-compensating effect of self-phase modulation (SPM) with increasing data rate regarding the Group Velo city dispersion becomes lower, d. H. the accumulated residual Dispersion decreases with increasing data rate.

According to a further embodiment of the invention Dispersion compensation units to compensate for the fiber dispersion of all optical fiber sections seen - claim 3. Takes advantage in all Fiber link sections of the optical transmission system the residual dispersion at least almost uniformly the same dispersion contribution, so the maximum regene ration-free bridgeable transmission range realized become.

All optical fiber sections of the optical transmission system almost the same length on - on saying 4, in addition to the optical fibers of the fiber sections a minimum length of 20 kilometers exhibit - claim 6. With a minimum length of about 20 kilos  have the meter due to the fiber dispersion and the fiber signal distortions caused by nonlinearities almost the maximum value. By dividing the optical transmission system in almost the same length of optical fiber sections cuts, the number of which is due to the regeneration-free bridging optical transmission path and the accumulated Residual disperison can be determined by a simple modu lare construction with regard to dispersion compensation and the transmission range that can be bridged without regeneration optimized optical transmission system can be realized. In particular, due to the resulting symmetrical Structure of the optical transmission system is particularly advantageous operate in a bidirectional operating mode - On saying 7.

Advantageous further developments and training of the Invention according optical transmission system are in the further Claims described.

The invention is intended to be based on a basic circuit picture and two diagrams are explained in more detail.

Fig. 1 shows the basic structure of an optical transmission system,

Fig. 2 shows a diagram of the dispersion management scheme according to the invention and

Fig. 3 shows in a further diagram the regeneration freely bridgeable number of compensated fiber sections depending on the distributed under- or over-compensation.

In Fig. 1, an optical transmission system OTS is shown schematically, which has an optical transmitter TU and an optical receiver RU. The optical transmission device TU is connected via N optical, each with an input I and an output E fiber link sections FDS ₁ to FDS _N to the optical receiving device RU, each having an optical amplifier EDFA, an optical fiber SSMF and an optical dispersion compensation unit DCU exhibit.

A first and Nth optical fiber section FDS ₁ , FDS _N are shown by way of example in FIG. 1, a second to N - 1st fiber section FDS ₂ to FDS _{N-1 being} indicated by a dotted line. Furthermore, the first optical fiber section FDS ₁ consists of a first optical amplifier EDFA ₁ , a first optical fiber SSMF ₁ , for example an optical standard single-mode fiber, and a first optical dispersion compensation unit DCU ₁ , being between the first optical Fiber SSMF ₁ and the first optical dispersion compensation unit DCU ₁ still an optical preamplifier - not shown in Fig. 1 - can be provided. Analogously, the Nth optical fiber link section FDS _{N has} an Nth optical amplifier EFDA _N , an Nth optical fiber SSMF _N and an Nth optical dispersion compensation unit DCU _N. Analogously, a further optical preamplifier - not shown in FIG. 1 - can also be provided here between the Nth optical fiber SSMF _N and the Nth optical dispersion compensation unit DCU _N.

The optical data signal or the optical data stream OS is transmitted by the optical transmitter TU to the input I of the first optical fiber section FDS ₁ . Within the first optical fiber section FDS ₁ , the optical data signal OS is amplified with the aid of the first optical amplifier EDFA ₁ and transmitted via the first optical fiber SSMF ₁ to the first dispersion compensation unit DCU ₁ . In the first dispersion compensation unit DCU ₁ , the signal _{distortions of} the optical data signal OS caused by the optical transmission via the first optical fiber SSMF ₁ except for a first residual dispersion D _rest1 , which in the case of the first dispersion compensation unit DCU ₁ corresponds to the inventive dispersion amount ΔD , compensated. The specified residual dispersion D _rest is a fraction of the accumulated residual dispersion D _akk which is determined by the number N of the optical fiber link sections FDS and which increases almost uniformly with each compensated fiber link section FDS by almost the same dispersion amount ΔD.

The accumulated residual dispersion D _akk is caused by the fiber nonlinearities and the fiber dispersion and is present at the end of the Nth fiber segment section FDS _N. For putting in accumulated residual dispersion D is _AKK at the end of the N-th fiber link section FDS _N not Siert compen due to the required for recovering the data from the optical data signal OS parameters for the eye diagram "eye-opening". Thus, the optical data signal OS present at the output E of the first optical fiber section FDS _{1 is} not completely dispersion-compensated, but is compensated for.

Analogously, the optical data signal OS is transmitted via the further optical fiber link sections FDS to the input I of the Nth optical fiber link section FDS _N. The optical data signal OS present at the input I of the Nth optical fiber link section FDS _N is amplified with the aid of the Nth optical amplifier EDFA _N and transmitted via the Nth optical fiber SSMF _N to the Nth dispersion compensation unit DCU _N. In the Nth dispersion compensation unit DCU _N , the fiber dispersion of the optical data signal OS caused by the Nth optical fiber SSMF _{N is} partially compensated, from which it can be seen that the residual dispersion D _{rest of} the optical data signal OS is almost uniformly around the predetermined one dispersion amount .DELTA.D rises and after the N-th dispersion compensation of the accumulated residual dispersion D corresponds _AKK. The optical data signal OS present at the output E of the Nth optical fiber link section FDS _N is transmitted to the optical receiving device RU and, if necessary, is subjected to a 3R regeneration before further processing - not shown in FIG. 1.

In Fig. 2 by way of example an inventive dispersion management scheme DCS reference to a diagram schematically made. It is clear from this that the optical transmission system OTS according to the invention is composed of several optical fiber sections FDS, each of which has an optical fiber SSMF and a dispersion compensation unit DCF, for example a dispersion-compensating fiber. To explain the dispersion management scheme DCS according to the invention, the number of optical fiber sections is limited to four (N = 4), so that in Fig. 2 are a first, second, third and fourth optical fiber section FDS ₁ , FDS ₂ , FDS ₃ , FDS ₄ are shown, where in the first optical fiber section FDS ₁ a first optical fiber SSMF ₁ and a first optical dispersion compensation unit DCF ₁ , the second optical fiber section FDS _{2 section} a second optical fiber SSMF ₂ and a second optical dispersion compensation unit DCF ₂ , the third optical fiber section FDS _{3 has} a third optical fiber SSMF ₃ and a third optical dispersion compensation unit DCF ₃ and the fourth optical fiber section FDS _{4 has} a fourth optical fiber SSMF ₄ and a fourth optical dispersion compensation unit DCF ₄ . Here, for the dispersion management scheme DCS of the exemplary embodiment, for example, almost the same length is selected for the first to fourth optical fibers SSMF ₁ to SSMF ₄ and for the first to fourth dispersion-compensating fibers DCF ₁ to DCF ₄ .

The diagram has a horizontal (abscissa) and a ver tical axis (ordinate) x, d on, whereby by the horizontal Axis the distance x from the optical transmitter TU or the range of optical data transmission and through the vertical axis d the fiber dispersion d in the respective  optical fiber SSMF or in the dispersion-compensating Fiber DCF is shown.

It is clear from FIG. 2 that the fiber dispersion of an optical data signal OS present at the input I of the first optical fiber link section FDS ₁ from the optical transmitter TU (x = 0) increases linearly along the first optical fiber SSMF ₁ and at the end of the first optical fiber x ₁ assumes a first maximum dispersion _amount D _max1 . The first maximum dispersion _amount D _max1 is partially compensated for with the aid of the first dispersion compensation unit DCF ₁ or the first dispersion-compensating fiber, ie at the end of the first dispersion-compensating fiber x _{2 there} is a first residual dispersion D _rest1 , which is at the output E of the first dispersion compensation unit DCF ₁ corresponds to the dispersion amount ΔD.

The subsequent second optical fiber SSMF ₂ increases the fiber dispersion d from the first residual dispersion D _rest1 to a second maximum dispersion _amount D _max2 , which is present at the end of the second dispersion-compensating fiber x ₃ . The second maximum dispersion _amount D _max2 is _compensated with the aid of the second dispersion compensation unit DCF ₂ or the second dispersion-compensating fiber until the second residual dispersion D _{rest2 corresponds} to twice the dispersion amount ΔD, ie the remaining residual dispersion D _rest increases evenly per optical fiber section section FDS by the amount of dispersion ΔD. Thus, at the end of the second dispersion-compensating fiber x _{4, there is} a second residual dispersion D _rest2 , which at the output E of the second dispersion compensation unit or the second dispersion-compensating fiber DCF ₂ corresponds to twice the dispersion amount ΔD.

The optical data signal OS transmitted from the second dispersion-compensating fiber DCF ₂ to the third optical fiber SSMF ₃ experiences in the third optical fiber SSMF ₃ as in turn signal distortions caused by the fiber dispersion d, which at the end of the third optical fiber x _{5 has} a third maximum _{Accept the amount of} dispersion D _max3 . The third dispersion _amount D _max3 is _{undercompensated} by the third optical dispersion compensation unit DCF _{3 in} such a way that the remaining third residual dispersion D _{rest3 corresponds} to three times the dispersion amount ΔD according to the invention, ie the residual dispersion D _rest takes x at the end of the third dispersion-compensating fiber _{6 shows} a third residual dispersion D _rest3 , which has increased again by the dispersion amount ΔD in comparison to the second residual dispersion D _rest2 .

Furthermore, the optical data signal OS present at the output E of the third dispersion-compensating fiber DCF _{3 is} transmitted to the fourth and last optical fiber SSMF _{4 of} the optical transmission system OTS. It is clear from FIG. 2 that the fiber dispersion d continues to increase and at the end of the fourth optical fiber x _{7 has} a fourth maximum dispersion _amount D _max4 . By means of the fourth Dis persionskompensationseinheit DCF ₄ of the fourth maximum dispersion amount D is _{max4 AKK} reduced to the amount of the accumulated residual dispersion D, which corresponds to four times the amount of dispersion to the invention OF INVENTION .DELTA.D. Thus, at the end of the optical transmission link or at the end of the fourth fiber link section x _8, the remaining residual dispersion D _{rest of} the optical transmission system OTS has the amount of the accumulated residual dispersion D _akk .

The inventive “division” of the accumulated residual dispersion D _akk calculated or estimated for the respective optical transmission system OTS into a fixed number of fiber link sections FDS almost doubles the transmission range x ₈ that can be bridged without regeneration. In this case, the fiber link sections FDS of the optical transmission system, regardless of the length of the respective optical fiber SSMF, are each undercompensated except for a residual dispersion D _rest determined by the accumulated residual dispersion D _akk , the residual dispersion D of fiber link section FDS ₁ Faserstrec kenabschnitt FDS ₂ increases by the same amount of dispersion.

In comparison to the respective fiber section FDS of an optical transmission system OTS completely com Penetrating dispersion management scheme DCS can be achieved through the dispersion management scheme DCS according to the invention th under-compensation that can be bridged without regeneration Range can be increased significantly, which leads to a savings cost-intensive electrical 3R Regeneration facilities leads.

Furthermore, due to the symmetrical structure of the optical transmission system OTS shown in FIG. 2, bidirectional data transmission over the considered fiber link sections FDS can be realized in a simple manner.

In addition, an optical fiber SSMF and a Disper sions compensation unit DCF fiber sections cut FDS designed as an optical transmission module M. his. Thus the OTS optical transmission system can a series connection of such optical transmission modules M are formed. Such a modular design facilitate tert the realization of an optical transmission link or expansion of an existing optical transmission stretch considerably in practice.

Furthermore, the use of the distributed under-compensation according to the invention is particularly advantageous in optical transmission systems which, because of the data transmission using a plurality of transmission channels, have a strong cross-phase modulation (XPM) as an effect which limits the transmission ranges which can be bridged freely and regeneratively. This strong cross-phase modulation (XPM) can be suppressed by the provision according to the invention of a small, local residual dispersion D _rest at the end of a fiber section FDS. Thus, not only the self-phase modulation (SPM) is suppressed by the distributed under-compensation according to the invention, but the influence of the cross-phase modulation (XPM) is substantially reduced almost simultaneously.

In Fig. 3, the regeneration freely bridgeable number of the compensated fiber stretch sections nfs is shown in a further diagram as a function of the distributed undercompensation or overcompensation uoc for different input powers P4dBm, P6dBm, P9dBm, P12dBm, P15dBm of the optical data signal OS.

The further diagram has a horizontal (abscissa) and a vertical axis (ordinate) uoc, nfs, whereby by the horizontal axis that intended for dispersion compensation Scheme "under- or overcompensation" of the optical transmission system OTS and through the vertical axis nfs the number of the compensated fiber sections FDS of the optical Transmission system OTS is shown. He lets himself out of that know that by the even accommodation according to the invention pensation of several fiber link sections FDS an increase the transmission range that can be bridged without regeneration can be achieved. The regeneration-free bridgeable transfer range is shown in the further diagram by the number of the compensated fiber sections FDS of the optical Transmission system OTS clarified.

For this purpose, a first to fifth optical data signal OS1 to OS5 an optical test transmission system OTS leads, each a different input power P exhibit. The first optical data signal OS1 has egg ne input power of 4 dBm, the second optical data signal OS2 an input power of 6 dBm, the third optical Da tensignal OS3 an input power of 9 dBm, the fourth op  table data signal OS4 an input power of 12 dBm as well the fifth optical data signal OS5 has an input power of 15 dBm.

The increase in the transmission range that can be bridged without regeneration is particularly evident in the curve profile for the first optical data signal OS1, since the first optical data signal OS1 with undercompensation of approximately 0.5 km of a standard single-mode fiber (SSMF) over almost 120 fiber sections FDS can be transmitted without regeneration. Here, the respective fiber section section FDS is compensated by the dispersion-compensating fiber DCF to the extent that a residual dispersion D _rest is present, which corresponds to an uncompensated optical fiber piece of the length of half a kilometer (0.5 km).

Claims (8)

1. Optical transmission system (OTS) consisting of several optical fiber link sections (FDS), each with an optical fiber (SSMF) and a dispersion compensation unit (DCF), characterized in that dispersion compensation units (DCF ₁ to DCF _Q ) are provided which provide the fiber dispersion (d) Compensate for several fiber sections (FDS ₁ to FDS _q ) in such a way that the remaining dispersion (D _rest ) per compensated fiber section (FDS ₁ to FDS ₄ ) increases at least almost equally by the same amount of dispersion (ΔD) . 2. Optical transmission system according to claim 1, characterized in that the optical transmission system (OTS) has a non-linearities caused by fiber and the fiber dispersion (d), accumulated residual dispersion (D _akk ), which decreases almost linearly with increasing data rate. 3. Optical transmission system according to one of claims 1 or 2, characterized in that the dispersion compensation units (DCF ₁ to DCF ₄ ) for compensating the fiber dispersion (d) of all optical fiber sections (FDS ₁ to FDS ₄ ) are provided. 4. Optical transmission system according to one of claims 1 to 3, characterized in that all optical fiber sections (FDS ₁ to FDS ₄ ) of the optical transmission system (OTS) have almost the same length. 5. Optical transmission system according to one of claims 1 to 4, characterized in that an optical fiber (SSMF ₁ ) and a Dispersionskom compensation unit (DCF ₁ ) having fiber link section (FDS ₁ ) realizes an optical transmission module (M). 5. Optical transmission system according to claim 4, characterized, that the optical transmission system (OTS) consists of several in Se rie arranged optical transmission modules (M) formed can be. 6. Optical transmission system according to one of claims 1 until 5, characterized, that the optical fibers (SSMF) of the fiber link sections (FDS) have a minimum length of 20 kilometers. 7. Optical transmission system according to one of claims 1 or 6, characterized, that the optical transmission system (OTS) is bidirectional len operating mode.