KR20000023409A - Optical amplifying unit and optical transmission system - Google Patents

Abstract

PURPOSE: An optical amplifier and an optical transmission system are provided to amplify an optimum optical signal by utilizing an amplified fiber, a pump source, and a coupler. CONSTITUTION: An optical transmission system comprises an optical transmission device(10),an optical reception device(20), an optical fiber link, and an optical amplification device(100,100'). The optical transmission device transmits an optical signal within the transmission wave band more than 1570nm. The optical reception device receives the transmitted optical signal. The optical fiber link combines the transmission device to the optical reception device. The optical amplification device is combined by the optical fiber link. The optical amplification device comprises an input(101), an output(102), and optical amplifiers(104,104'). The optical amplifiers comprise amplified fibers(108,113,114), pump sources(109,110,115,116), and optical couplers(111,112,117,118).

Description

Optical amplification device and optical transmission system {OPTICAL AMPLIFYING UNIT AND OPTICAL TRANSMISSION SYSTEM}

The present invention relates to an optical amplification apparatus, an optical transmission system for use for optical communication, in particular a wavelength division multiplexing (WDM) optical transmission system using the optical amplification apparatus.

In a WDM optical transmission system, transmission signals including various optical channels are sent on the same line (including at least an optical amplifier) by a wavelength division multiplexing method. The transmitted channels can be digital or analog and can be distinguished because each of them is associated with a particular wavelength.

Currently, long distance high capacity optical transmission systems use optical fiber amplifiers that do not require OE / EO conversion unlike previously used electronic regenerators. Optical fiber amplifiers are preset with a core doped with one or more rare earths to amplify optical signals due to stimulated radiation when excited by pump radiation. It includes a fiber optic of a long length. Optical fibers doped with erbium (Er) have been developed for use with both optical amplifiers and lasers. These devices are of great importance because their operating wavelengths coincide with a third window for the optical fiber around 1550 nm. European (EP) Patent Application No. 98110594.3 under Applicant's name proposes a 32 channel WDM optical transmission system using erbium doped optical amplifiers (EDFAs) in the wavelength bands of 1529-1535 nm and 1541-1561 nm.

For example, several methods have been proposed to improve system performance in terms of amplification gain and amplification band.

One technique for improving the system performance consists of doping together erbium-doped amplified fibers with ytterbium (Yb). Doping active fibers together with erbium and ytterbium provides much greater flexibility in the choice of pump wavelengths, as well as broadening the pump absorption band from 800 nm to 1100 nm, as well as higher absorption cross sections and ytterbium dopants ( dopant) greatly increases the absorption of the ground state because of solubility. The ytterbium ions absorb many pump lights and subsequent mutual relaxation between the ytterbium and the adjacent ions of erbium allows the absorbed energy to be transferred to the erbium system. Grobb et al. ("Optical Amplifiers Doped Together with Er / Yb of + 24.6dBm Output Power Pumped by Diode-pumped Nd: YLF Lasers", Electronics Letters, 1992, 28, (13) pp 1275-1276) and the paper by Maker and Ferguson ("1.56 micrometer Yb-sensitized Er fiber lasers pumped by diode-pumped Nd: YAG and Nd: YLF lasers", Electronics Letters As described by 1988, 24, (18), pp. 1160-1161, the accompanying co-doping technique uses fiber amplifiers and lasers through direct pumping at the long wavelength tail of the ytterbium absorption spectrum. Can be applied to effectively excite them. This pumping is suitably performed by means of diode-pumped solid state lasers, for example 1047 nm Nd: YLF lasers or Nd: YAG lasers.

Co-doped amplified fibers with erbium and ytterbium for amplifying communication signals are further described in European patent application EP0803944A2 and US Pat. No. 5,225,925. The European patent application 0803944A2 has a multistage Er-dough which operates within a wavelength band of 1544-1562 nm and has a first stage comprising Er and Al and a second stage comprising Er and additional rare earth elements, eg Yb. It refers to a doped fiber amplifier (EDFA). Such multi-stage EDFAs can have advantageous properties within the above-mentioned wavelength bands over all erbium amplification systems, such as a relatively wide uniform gain region, and a relatively high output power, without significant degradation of the noise form. Applicants, however, have no advantage in terms of the amplification proposed in EP0803944A2, which is limited to the number of channels transmitted, still in the relatively narrow (large developed) 1544-1562 nm band. Moreover, the second step of Er / Yb is pumped by means of a diode-pumped Nd-doped fiber laser emitting 1064 nm. The pump source used mainly for the excitation of mono-modal amplified fibers is relatively expensive and impaired.

U. S. Patent 5,225, 925 relates to an optical fiber for sourcing or amplifying light signals in a single transverse mode. The fiber includes main glass doped with erbium (Er) and a photosensitizer such as ytterbium (Yb) or iron (Fe). Preferably the main glass is doped silica glass (eg doped phosphate or borate). Applicant noted that the U. S. Patent 5,225, 925, because of the shape of its gain curve, was not particularly suitable for WDM transmission and was adapted for transmission of a single channel of 1535 nm. Moreover, such amplified fibers are adapted to be pumped by means of diode-pumped Nd-doped fiber lasers having the disadvantages mentioned above.

None of EP0803944A2 and US Pat. No. 5,225,925 mention amplification by Er / Yb-doped optical amplifiers of signals in wavelength bands other than the transmission band around 1550 nm.

Improvements in Er / Yb amplified fibers have been achieved by cladding pumping techniques that include pumping active fibers in the inner cladding region surrounding the core instead of directly in the core. Cladding pumping is a technique that allows high power, wide stripe diodes to be employed as an efficient, low cost, small dimension pump for double-clad rare earth doped single mode fibers. Output powers from hundreds of milliwatts to tens of watts can be obtained by this technique. As an example, Er / Yb fibers pumped by a diode array at 980 nm are described in Minelly et al. ("Diode Array of Fiber Lasers and Amplifiers Doped with Er3 / Yb3, IEEE Photonics Technology Letters, 1993," 5, (3), pp. 301-303. The erbium- ytterbium co-doped design provides much higher ground for erbium in the band of about 980 nm than single doped erbium fibers. This results in a much shorter optimum length The technique of inserting the pump radiation out of the core into part of the fiber (same as the outer core or as the inner cladding) Perceptible), for example, described in International Patent Application (PCT) No. 95/10868 and US Pat. No. 5696782.

Several methods have been proposed to increase the number of channels to be transmitted. One way to increase the number of channels is to narrow the channel spacing. However, narrowing the channel spacing exacerbates nonlinear effects such as cross-phase modulation or mixing of four waves, and requires precise wavelength control of the optical transmitters. Applicants have witnessed that channel spacing lower than 50 GHz is difficult to achieve substantially for the above reasons.

Another way to increase the number of channels is to widen the available wavelength band within the low loss region of the fiber. One key technique is optical amplification within this wavelength band over a conventional 1550 nm transmission band. In particular, the high wavelength band around 1590 nm and more precisely the high wavelength band between 1565 nm and 1620 nm are very promising for long distance light transmission in that very high numbers of channels can be allocated within that band. If the 1565-1620nm band optical amplifier must handle a high number of channels, the spectral gain characteristics of such amplifiers are fundamental to optimize the performance and cost of the system. The use of a 1590 nm transmission wavelength region of erbium doped fiber amplifiers parallel to the 1530-1550 wavelength regions is attractive and has been considered recently. As an additional advantage, employing the 1590 nm wavelength range makes it possible to use distributed shifted fibers for WDM transmission without any degradation caused by the mixing of the four waves. Many of the details in the patent and non-patent literature describe amplification in the high wavelength transmission band (from 1565 nm to 1620 nm). All these documents only consider erbium-doped fiber amplifiers.

The following documents suggest several methods for extending the available bands for high-wavelength transmission bands.

U.S. Patent 5,500,764 discloses erbium doped SiO ₂ -Al ₂ O ₃ -GeO ₂ pumped by 1.55 micrometers and 1.47 micrometer light sources and adapted to amplify optical signals between 1.57 micrometers and 1.61 micrometers. It relates to a single mode optical fiber (distance between 150 m and 200 m).

Ono et al. (“Er3 + -doped fiber amplifiers with uniform gain for WDM signals in the 1.57 to 1.60 micrometer wavelength range”, IEEE PHOTONICS TECHNOLOGY LETTERS, Vol. 9, No. 5, May 1997 , pp. 596-599, disclose a fiber amplifier based on Er + 3-doped silica with uniform gain for 1.58 micrometer band WDM signals. In this paper, different fiber lengths were tested and the authors found that 200 meters was the optimal length of erbium-doped fibers (EDF) for making EDFAs with high gain and low noise.

Masuda et al. ("Broadband, Uniform Gain, Erbium Doped Fiber Amplifiers with 3DB Bandwidths Less Than 50nm", ELECTRONICS LETTERS, 5th June 1997, Vol. 33, No. 12, pp. 1070-1072 is a two-stage erbium-doped 52 nm band (1556-1608 nm) for silicate erbium-doped fiber amplifiers and a 50 nm band (1554-1604 nm) for fluoride erbium-doped fiber amplifiers We propose a scheme with fibers and an intermediate equalizer. In the case of silicate erbium doped fiber amplifiers, the two stages include 50m EDF and 26m EDF, respectively.

Joley et al. ("Proof of Negligible Multipath Interference and Low PMD in Ultra Homogeneous Wideband EDFAs Using Highly Doped Erbium Fibers", "Optical Amplifiers and Their Applications" Conference, Vail, Colorado, July 27-29 1998, TuD2-1 / 124-127), a wide band that reaches maximum external power greater than +18.3 dBm at 1570 and amplifies signals in the 1585 nm band using 45 m erbium fiber Suggest EDFA.

It is an object of the present invention to provide an optical amplification apparatus for use in optical communications.

Another object of the present invention is to provide an optical transmission system using the optical amplifying apparatus, in particular a wavelength division multiplexing optical transmission system.

It is yet another object of the present invention to provide an optical amplification device adapted for use in analog CATV systems.

Applicants note that the line EDFA adapted to amplify optical signals within the high wavelength band can amplify an optical signal with an input power with a maximum power value of nearly -10 dBm to less than 19 dBm, ie a maximum gain of nearly 29 dB. I witnessed it. An input power of nearly -10 dBm is typical for optical amplifiers in long distance transmission systems as an appropriate reference value. Although lower input power has higher gains for lower power input signals than for EDFAs, in this case ASE (amplified spontaneous emission) is a value that causes the signal-to-noise ratio to be low. To increase. Conversely, signal input powers of -10 dBm or more, which can be obtained as an example of damage to the transmission fiber length, saturate its gain, leading to waste of unwanted energy. An optical transmission system that transmits 64 channels between 1575 nm and 1602 nm and uses EDFAs will provide maximum power per channel at the output of the line EDFAs of about 0.2 dBm and will limit the maximum span length to substantially less than 100 km in length. will be.

Applicants further observed that the curve of gain versus erbium concentration in erbium-doped activated fibers of predetermined length has an increase and decrease to a maximum corresponding to the optimal value of erbium concentration. Higher gains can only be obtained by increasing the length of the active region doped with erbium, ie by increasing the length of the active fiber. Conventional long-haul WDM optical transmission systems using erbium doped activated fibers require fiber lengths of several hundred meters to reach relatively high gains. Indeed, special erbium-doped activated fibers with a larger core diameter are used, which allows for a relatively high gain with a fiber length down to 30-40 m.

Applicants have found that transmission systems including erbium- ytterbium co-doped amplifiers in the 1565-1620 nm band provide very high performance, especially for erbium doped optical amplifiers. In particular, Applicants note that an optical amplification device comprising an erbium and ytterbium-doped fiber amplifier optimized in terms of length and doping has a very uniform amplification band (± 0.5 dB in the wavelength region where it is located above 1565 nm and has a width of at least 27 nm. ) And very high gains. In more detail, Applicants note that an optical amplification device comprising an optimized erbium- ytterbium-doped fiber amplifier provides an output signal power of up to 23 dBm in response to an input of nearly -10 dBm power in the wavelength region of 1575-1602 nm. I found it possible. Applicants have furthermore found that such high power can be reached by including an erbium doped preamplifier into the optical amplification device, preferably including a preamplifier.

In addition, the Applicant has observed that for erbium-ytterbium-doped fibers, the increasing region in the droid-erbium concentration curve extends far more than erbium-doped fibers and relatively short active fibers within the 1565-1620nm band. It has been found that it can be used. Applicants have found that the optimum fiber length of the active fiber can be chosen to minimize the gain slope of the considered wavelength band depending on the erbium concentration in the active fiber of the amplifier and the system parameters such as single power at the input of the amplifier. It was.

Moreover, Applicants have found that high pump performances in the high wavelength bands considered can be obtained using erbium- ytterbium double-clad fibers taking the advantage of multimode pumping machinery.

Furthermore, the Applicant has found that the amplification apparatus described above can be advantageously used in long distance WDM transmission systems to obtain high transmission efficiency in the wavelength range up to 1620 nm. In particular, Applicant notes that a wideband long-haul WDM transmission system divides its wavelength transmission band into three sub-bands corresponding to 1529-1535 nm, 1541-1561 nm and 1575-1602 nm, and It has been found that at least Er / Yb can be realized by means of amplifying the subbands of 1575-1602 nm by means of an optical amplification device coupled with an accompanying doped amplifier, preferably an Er doped preamplifier. By way of example, such a wide band allows for efficient transmission of 64 channels with a spacing of 50 GHz.

Furthermore, Applicants note that the high gain that the Er / Yb in the high wavelength band can be achieved by means of a co-doped amplifier means that a WDM transmission system in the 1575-1602 nm band is equal to 130 Km between subsequent amplification steps, or It has been found that it can include fiber spacing with larger lengths.

According to a first aspect, the present invention provides an optical transmission device adapted to transmit an optical signal in a transmission wavelength band above 1570 nm, an optical reception device for receiving the optical signal, and optical coupling of the transmission device to the reception device. And an optical fiber link, an optical amplification device coupled along the link. The optical amplifying apparatus has an amplifying wavelength band including the transmission wavelength band, and an input for input of the optical signal from the link and an output for outputting the optical signal from the link and amplifying the optical signal. An optical amplifier positioned between the input and output, the optical amplifier including an amplifying fiber, a pump source for generating pump radiation, and an optical coupler for optically coupling the pump source to the amplifying fiber. . The amplified fiber comprises an optical fiber doped with erbium and ytterbium.

In particular, the optical amplifying device has a power gain much greater than 29 dB when the optical signal has an input power of at least -10.5 dBm and a wavelength within the amplifying wavelength band. Advantageously, said optical amplifying apparatus has a power gain of at least 31 dB when said optical signal has an input power of at least -10.5 dBm and a wavelength within said amplification band. More preferably the optical amplifying device has a power gain of at least 33 dB when the optical signal has an input power of at least -10.5 dBm and a wavelength within the amplifying wavelength band.

Preferably, the width of the amplification wavelength band is at least 15 nm more preferably at least 27 nm.

Preferably, the lower wavelength limit of the amplification wavelength is equal to or greater than 1575 nm.

Preferably, the optical amplifying apparatus has a gain variation lower than 1 dB within the amplifying wavelength band.

Advantageously, said optical transmission system further comprises an optical preamplifier positioned for preamplifying said optical signal between an input of said optical amplifying device and said optical amplifier.

Preferably, the amplifying fiber has a core having an erbium concentration between approximately 600 ppm and 1000 ppm.

Preferably, the amplifying fiber has a core having a ratio between an ybium concentration and an ytterbium concentration between about 5: 1 and 30: 1.

Preferably, the amplifying fiber has a length of less than 30m and more preferably less than 13m.

Preferably, the amplifying fiber is a double-clad fiber having a core, an inner cladding surrounding the core and an outer cladding surrounding the inner cladding.

Advantageously, said optical link comprises optical fiber spacings having a length of at least 130Km.

In a second aspect, the invention provides an optical signal having a wavelength within one wavelength band, said wavelength band having a lower limit of much greater than 1570 nm;

Supplying the signal to an optical link;

Amplifying the signal along the optical link; And

And receiving said optical signal from said optical link, said amplifying step feeding said signal into an active fiber doped with erbium and ytterbium.

Preferably, the supplying step includes a step of supplying the signal to one end of the active fiber, the active fiber having a ytterbium concentration and an erbium concentration such that the power gain of the optical signal at its other end is at least 25 dB. And length.

More preferably, the supplying step has a step of supplying the signal to one end, wherein the active fiber has a length, erbium concentration and ytterbium such that the power gain of the optical signal is at least 31 dB at the other end of the active fiber. Has a concentration.

Preferably, the wavelength band has a width of at least 27 nm.

In another aspect, the present invention relates to an optical amplifying apparatus for amplifying optical signals in an optical transmission system. The optical amplifying device has an amplifying wavelength band having a width of at least 15 nm and a lower limit wavelength limit much greater than 1570 nm. The optical amplification apparatus includes an amplifying fiber, a pump source for generating pump radiation and an optical coupler for optically coupling the pump source to the amplifying fiber, the optical fiber comprising optical fibers doped with erbium and ytterbium. Characterized in that. The foregoing general description and the following detailed description are by way of example only and do not limit the claims of the invention. The practice and the following description of the invention suggest further advantages and objects of the invention.

1 is a block diagram of an optical transmission system consistent with the present invention.

FIG. 2 is a qualitative graph of the spectral gain characteristics of the optical transmission system of FIG. 1 with signal transmission bands BB, RB1 and RB2 designation.

3 is a detailed diagram of the multiplexing portion of the optical transmission system in FIG.

4 is a detailed diagram of the transmitter power amplifier portion of the optical transmission system in FIG.

5 is a filter performance shape graph of the non-emphasis filter for a transmitter power amplifier of the present invention.

6 is a detailed diagram of the intermediate station of the optical transmission system in FIG.

7 is a detailed diagram of a receiver preamplifier of the optical transmission system in FIG.

FIG. 8 is a detailed diagram of the demultiplexing portion of the light transmission system in FIG. 1.

9 is a schematic representation of a first embodiment of an optical amplifying apparatus according to the present invention.

10A and 10B are equation simulation results obtained with the optical amplifier of FIG. 9 in the case of two-channel transmission.

11A, 11B and 11C show the results of additional equation simulations obtained with the optical amplifier of FIG. 9 in the case of two channel transmission.

12A and 12B are schematic representations of the experimental arrangement used to test the optical amplification device of FIG. 9.

13A and 13B show experimental results obtained with the experimental arrangement of FIGS. 12A and 12B in the case of two channel transmission.

14A and 14B show experimental results obtained with the experimental arrangement of FIGS. 12A and 12B in the case of transmission of 64 channels.

15 is a schematic representation of a second embodiment of an optical amplifying apparatus according to the present invention.

16 is a schematic representation of a third embodiment of an optical amplifying apparatus according to the present invention.

17A and 17B are schematic representations of multi-mode pumping of double cladding fibers and of double cladding fibers used in an optical amplification apparatus.

Referring to FIG. 1, the optical transmission system 1 includes a first fiber terminal 30, a second terminal location 20, an optical fiber line 30 connecting the two terminal locations 10, 20, and At least one line position 40 located between the terminal positions 10 and 20 along the optical fiber line 30.

For simplicity, the light transmission system 1 described below is unidirectional. That is, the signals travel from one terminal location to another (in the present case, from the first terminal location to the second terminal location). However, any consideration that follows is intended to be reasonably considered for a bidirectional system in which signals travel in both directions. Moreover, although the optical transmission system 1 has been adapted to transmit up to 128 channels, the number of channels from the following description is not a limiting feature for the scope and principle of the present invention and more than 128 channels are required for a specific optical transmission system. It will be apparent that it can be used in dependence upon. The first terminal position 10 preferably comprises a multiplexing portion (MUX) 11, a transmitter power amplifier portion (TPA) 12 and a plurality of input channels 16. The second terminal position 20 preferably comprises a receiver preamplifier (RPA) portion 14, a demultiplexing portion (DMUX) 15 and a plurality of output channels 17.

Each input channel 16 is received by the multiplexing portion 11. Although the multiplexing portion 11, which will be described below with reference to FIG. 3, may alternatively group the input channels 16 to a number less than 3 or greater than 3, the input channels 16 are preferably selected. The three sub-bands referred to as the blue band RB1, the first red band RB2, and the second red band RB3 are multiplexed or grouped.

The three subbands BB, RB1, RB2 are then subbands or combined contiguously separated by a TPA portion 12, at least one line position 40 and a second terminal position 20. Received by light bands. Portions of the optical fiber lines 30 adjoin at least one line position 40 together with the TPA portion 12, the RPA portion 14 and possibly other line positions 40 (not shown). The TPA portion 12, which will be described later with reference to FIG. 4, receives, amplifies, and optimizes the subbands BB, RB1, RB2 separated from the multiplexing portion 11. Then combine them into a single wideband (SWB) for transmission on the first portion of the optical fiber line 30. The line position 40, which will be described later with reference to FIG. 6, receives its single wideband (SWB) and subdivids the single wideband (SWB) into the three subbands (BB, RB1, RB2), ultimately. Add and drop signals in each subband BB, RB1, RB2, and amplify and optimize those three subbands BB, RB1, RB2. Then recombine them into a single wide band (SWB). Line position 40 may be provided with known add / drop multiplexers (OADM) of known shape for the adding and dropping operations.

The second portion of the optical fiber line 30 couples the output of the line position 40 to another position 40 (not shown) or to the RPA portion 14 of the second terminal position 20. . The RPA portion 14, which will be described later with reference to FIG. 7, also amplifies and optimizes the single wideband SWB. The single wide band SWB can then be divided into three subbands BB, RB1 and RB2 before outputting them.

The non-multiplexing portion 15 to be described later with reference to FIG. 8 receives three subbands BB, RB1 and RB2 from the RPA portion 14 and the three subbands BB, RB1 and RB2. ) Is divided by the individual wavelengths of the output channels 17. The number of input channels 16 and output channels 17 may not be equivalent due to the fact that some channels may be added or dropped within line position 40 (or line positions).

According to the above, the optical link for each subband BB, RB1, RB2 is defined between the corresponding input of the TPA part 12 and the corresponding output of the RPA part 14.

FIG. 2 is a qualitative graph of the spectral radiated regions of amplifiers used in an optical transmission system corresponding to different gains for signals traveling through fiber link and other allocations of the three subbands BB, RB1, RB2. . In particular, the first subband BB preferably covers an area between 1529 nm and 1535 nm corresponding to the first amplified wavelength region of the erbium-doped fiber amplifiers and allocates up to 16 channels; The second subband RB1 falls between 1541 nm and 1561 nm, corresponding to the second amplified wavelength region of the erbium-doped fiber amplifiers, and allocates up to 48 channels; The third subband RB2 covers an area between 1575 nm and 1602 nm corresponding to the amplified wavelength region of the erbium / ytterbium doped fiber amplifiers according to the present invention and allocates up to 64 channels. Although the gain spectral graph of erbium / ytterbium doped fiber amplifiers provides the best performance in terms of 1575 nm-1602 nm area amplification, channels can be advantageously allocated down to 1565 nm and up to 1620 nm. More specifically, Applicants note that the lower limit of 1570 nm is preferred for channel assignment in the RB2 band because of the shape of the power spectrum of the fiber doped with ER / Yb in this wavelength range.

In the proposed 128 channel system, adjacent channels have a predetermined interval of 50 GHz. Alternatively, the frequency spacing may not be equivalent to mitigate the mixing of the four known waves.

In the erbium amplification band, the BB band includes a substantial hump in the gain response while the RB1 and RB2 bands have very uniform gain characteristics. As described below, in order to use an erbium-doped fiber spectral emission region in the BB band, the optical transmission system 1 uses equalization means for equalizing gain characteristics in that region. As a result, by dividing the erbium-doped 1529-1602 nm fiber spectral emission region into three subregions, each comprising a BB band, an RB1 band, and an RB2 band, the optical transmission system 1 is efficient for dense WDM. Erbium-doped fiber spectral radiant regions can be used and provided.

The following provides a more detailed description of the various modules of the invention depicted in FIG.

3 shows a more detailed portion of the multiplexing portion 11 of the first terminal position 10. The first terminal position 10 is in addition to the multiplexing portion 11 and the TPA portion 12 (not shown in FIG. 3), such as an optical line terminal portion (OLTE) 41 and a wavelength converter portion (WCS) ( 42).

OLTE 41, which can communicate with standard line terminating equipment for use in SONET, ATM, IP, or SDH systems, transmits / receives (TX) within the same amount of channels in the WDM system 10. / RX) device (not shown). In a suitable embodiment, the OLTE 41 has 128 TX / RX devices. In the multiplexing portion 11, the OLTE 41 transmits a plurality of signals at a normal wavelength. As shown in FIG. 3, in a suitable embodiment, the OLTE 41 may store 16 (16) channels of the first group, 48 (48) channels of the second group and 64 (64) channels of the third group. Output. However, as indicated above, the number of channels may vary depending on the needs and needs of a particular optical transmission system.

As will be readily appreciated by one of ordinary skill in the art, OLTE 41 may have a smaller set of OLTEs, such as three, that will supply information frequencies to WCS 42. Thus, the WCS 42 includes 128 wavelength converter modules WCM1-WCM128.

Devices WCM1-WCM16 each receive one of the first group of signals emitted from OLTE 41, and devices WCM17-WCM64 each of the second group emitted from the OLTE 41. Receive any one of the signals, and devices WCM65-WCM128 each receive one of the third group of signals from the OLTE 41. Each device is capable of converting a signal from a normal wavelength to a selected wavelength and retransmitting the signal. The devices can receive and retransmit signals in standard form such as OC-48 or STM-16, but the preferred operation of the WCM1-128 is clear for the particular data type adopted.

Each WCM1-128 preferably has a photodiode (not shown) for receiving an optical signal from the OLTE 41 and converting it into an electrical signal, a laser or a light source (not shown) for generating a fixed carrier wavelength. And an electron light modulator, such as a Mark-Zehnder modulator (not shown) that externally modulates the fixed carrier wavelength with the electrical signal. Alternatively each WCM1-128 has a photodiode (not shown) with a laser diode directly modulated with an electrical signal to convert the received wavelength into a carrier wavelength of the laser diode. As an additional alternative, each WCM1-128 receives an optical signal (eg according to SDH or SONET) from the end of the trunk fiber line, for example via a wavelength demultiplexer and converts it into an electrical signal. A module having a high sensitivity receiver and a direct modulation or an external modulation laser source. This latter alternative allows for the reproduction of signals from the output of transmission and trunk fiber lines in the inventive optical communication system, which allows to extend the length of the entire link.

Although FIG. 3 shows that the signals are provided and generated by the combination of OLTE 41 and the devices WCM1-WCM128, the signals may be generated or provided directly by a source without limitation to their roots. Can be.

The multiplexing portion 11 comprises three wavelength multiplexers (WMs) 43, 44 and 45. For the appropriate 128-128 channel system, each selected wavelength signal output from devices WCM1-WCM16 is received by WM 43 and each selected wavelength signal output from devices WCM 17-WCM64. Is received by the WM 44 and each selected wavelength signal output from the devices WCM65-WCM128 is received by the WM 45. WMs 43, 44 and 45 combine the received signals of the three bands BB, RB1 and RB2 into three respective wavelength division multiplexed signals. As shown in FIG. 3, the WM 43 is a 16 channel wavelength multiplexer, such as a conventional 1x16 planar light splitter. WM 44 is a 48 channel wavelength multiplexer, such as a conventional 1x64 planar optical splitter with 16 unused ports. WM 45 is a 64 channel wavelength multiplexer, such as a conventional 1x64 planar optical splitter. Each multiplexer may include a second port (eg, 2X16 and 2X64 splitters) for providing an optical transmission system 1 having an optical supervisory channel (not shown). In addition, the WMs 43, 44, 45 may have more inputs than used by the system to provide space for system growth. As an example, a wavelength multiplexer using inert Silica on Silicon (SiO ₂ -Si) or Silica on Silica (SiO ₂ -SiO ₂ ) technology can be used by those of ordinary skill in the art to determine insertion losses. Can be used for the WMs to reduce. Examples are an arrayed waveguide grating (AWG), fiber grating, and interference filter.

Referring to FIG. 4, the bands BB, RB1 and RB2 output from the multiplexing portion 11 are received by the TPA portion 12. The signals in the bands BB, RB1, RB2 are from the OLTE 41, the WCS 42, and from a source different from the shape of the WMs 43, 44, 45 depicted in FIG. It may be provided as. By way of example, the signals in the bands BB, RB1, RB2 may be generated by the user and supplied directly to the TPA portion 12 without departing from the intention of the invention described in more detail below. have.

The TPA portion 12 comprises three amplifier portions 51, 52, 53, a coupling filter 54, and an equalization filter 61 for each band BB, RB1, and RB2. The amplifier portions 51, 52 are preferably erbium-doped two-stage fiber amplifiers (although other rare earth-doped fiber amplifiers may be used), while in accordance with the present invention the amplifier portion 53 is shown in FIGS. And erbium- ytterbium doped (Er / Yb) fiber amplifiers, which will be described in detail with reference to FIG.

The outputs of the amplifiers 51, 52, 53 are received by a filter 54 which combines the bands BB, RB1 and RB2 into a single wide band SWB.

Each of the amplifiers 51 and 52 is pumped by one or two laser diodes to provide a gain for the signals it amplifies. The characteristics of each amplifier, including its length and pump wavelength, are chosen to optimize the performance of the amplifier for the particular subband it amplifies. By way of example, the first stage of the amplifier portions 51 and 52 may be pumped with a laser diode (not shown) operating at 980 nm to amplify the band BB and RB1, respectively, in a linear or saturation region. have. Suitable laser diodes are available from the applicant. The laser diodes are commonly available on the market as 980/1550 WDM couplers, e.g., E-Tek Dynamics Inc. (1885 Lundy Ave. San Jose, CA USA), San Jose-C. Can be combined into the optical path of the preamplifiers using the model name SWDM0915SPR from TEK DYNAMICS, INC. The 980 nm laser diode provides a low noise form for amplifiers compared to other possible pump wavelengths.

The second stage of each amplifier portion 51-53 preferably operates in saturation. The second stage of the amplifier portion 51 is preferably another 980 nm pump (not shown) which is doped with erbium and combined with the optical path of the band BB using the WDM coupler (not shown) described above. To amplify the band (BB). The 980 nm pump provides a better shape and noise shape for signals in signals in the low band region covering 1529-35 nm. The second stage of the amplifier portion 52 preferably amplifies the band RB1 with a laser diode pump source erbium-doped and operating at 1480 nm. Such laser diodes have the same model name (FOL1402PAX-1) supplied by JDS Fitel, Inc., located at 570 Heston Drive, Nepean, Ontario Canada. Available in the market. The 1480 nm pump provides a better form of saturated conversion efficiency required in the band RB1 for a much larger number of channels in the region covering 1542-61 nm. Alternatively higher power 980 nm pump lasers or multiplexed 980 nm pump sources may be used. Portion 53 will be described in detail with reference to FIGS. 9, 15, and 16.

A filter 61 is located in the RB1 band amplifier for assistance in equalizing SNR and signal levels at the system output across the band RB1. In particular, the filter 61 is provided with a non-emphasis filter for attenuating the region of high amplification wavelengths in the band RB1. If used, the non-emphasis filter may use a long period Bragg Grating Technology, a split-beam fourier filter, or the like. For example, the non-emphasis filter may have an operating wavelength range of 1541-1561 nm. And have peak transmission wavelengths at 1541-1542 nm and 1559-1560 nm and a relatively lower constant transmission for wavelengths between these peak values. 5 illustrates the relative reduction performance or filter shape of the preferred non-highlight filter 61. The graph of FIG. 5 shows that the non-highlight filter 61 has a region of peak transmission around 1542 nm and 1560 nm, and a region of relatively constant or uniform decrease between about 1546 nm and 1556 nm. The non-highlight filter 61 for erbium-doped fiber amplifiers needs to add only a 3-4 dB reduction in wavelengths between the peaks to help uniformize the gain response across the high band. The non-highlight filter 61 may have a reduction characteristic different from that shown in FIG. 5 depending on the gain-uniformity requirements of the actual system employed, such as the wavelength of the dopant used in the fiber amplifiers or the pump source for those amplifiers. have.

Alternatively, the non-highlighting filter 61 can be omitted and the non-highlighting operation at the multiplex portion 11 of the first terminal position 10 by means of calibrated reduction. Can be obtained.

The amplified bands BB, RB1, RB2 output from the amplifiers 51, 52, 53, respectively, after passing through the TPA 12 are received by the filter 54. Filter 54 is a band combination filter and is, for example, two cascaded interference filters with three ports (not shown), a first coupling combining the band BB and band RB1, the And a second coupling between the bands BB / RB1 and the band RB2 provided by the first filter with a band RB2.

Inserts for optical monitors (not shown) and service lines can be added at the common port via WDM 1480/1550 interference filters (not shown) at wavelengths different from communication channels, for example at 1480 nm. The optical monitor detects optical signals to ensure that there is no breakdown in the optical transmission system 1. The service line insertion is used to manage telemetry, surveillance, performance and data monitoring, control and housekeeping, and voice frequency order wire through alarm supervision channels. Provide access for line service modules. The single light band output from the filter 54 of the TPA portion 12 is the length of the transmission fiber (not shown) of the optical fiber line 30, such as 100 Km, which attenuates the signals within the single light band (SWB). Pass through. As a result, line position 40 receives and amplifies the signals within the single wide band (SWB). As shown in FIG. 6, line position 40 includes several amplifiers (AMP) 64-69, three filters 70-72, equalization filter (EQ) 74, and three OADM stages. (75-77).

The filter 70 receives the single wide band SWB and separates the band RB2 from the bands BB, RB1. The amplifier 64 receives and amplifies the band BB and the band RB1. So filter 71 receives the output from amplifier 64 and separates the bands BB, RB1. The band BB is received by the first OADM step 75 which is equalized by the equalization filter 74 and the predetermined signals are dropped and / or added and further further amplified by the amplifier. The band RB1 already passed through the non-highlight filter 61 in the TPA 12 is first amplified by the amplifier 66 and then the predetermined signals are dropped and / or added and further added to the amplifier 67. Is received by the second OADM step 76 which is amplified by. The band RB2 is first received by a third OADM stage 77 which is amplified by the amplifiers 68 and then the predetermined signals are dropped and / or added and further amplified by the amplifier 69. . The amplified bands BB, RB1, RB2 are then recombined by the filter 72 into the single wide band SWB.

The amplifier 64 receiving the single wideband (SWB) preferably has a single optical fiber amplifier operated in a linear region. That is, amplifier 64 is operated with its output power dependent on its input power. Depending on the actual tooling, the amplifier 64 may alternatively be a single stage or multistage amplifier. By operating it in a linear condition, the amplifier 64 helps to ensure independence of relative power between the bands BB, RB1. In other words, with an amplifier operating under linear conditions, the output power (and signal-to-noise ratio) of the individual channels in either of the two bands BB, RB1 is added or removed from the other subbands BB, RB1. If it doesn't, it doesn't change seriously. In order to obtain robustness for the presence of all or some of the channels in a density WDM system, the first stage amplifiers (amplifiers 64 and 68) are placed in an unsaturated region and line before extracting portions of the channels for separation equalization and amplification. It must be operated in position 40. In a suitable embodiment, the amplifiers 64, 68 are erbium pumped in the accompanying-propagation direction with a laser diode (not shown) pumped at 980 nm to obtain a noise figure that is preferably less than 5.5 dB for each band. Doped fiber amplifiers.

Filter 71 is for example a three port device, preferably a drop port for feeding the band BB into an equalization filter 74 and a reflection port for feeding the band RB1 into the amplifier 66. an interference filter having a port).

Amplifier 66 is preferably a single erbium doped fiber amplifier that operates in saturation such that its output power is substantially independent of its input power. In this method, the amplifier 66 performs an operation of adding a power boost to the channels in the band RB1 compared to the channels in the band BB. Because of the much larger number of channels in the band RB1 compared to the band BB in the appropriate embodiment, i.e. at 48 channels opposite 16, the channels in the band RB1 typically turn off the amplifier 64. When passing through, they will all have low gains. As a result, the amplifier 66 helps to balance the power for the channels in the band RB1 compared to the band BB. Of course, an amplifier 66 may not be required for other arrangements of channels between the bands BB, RB1 or alternatively may be required on the band BB side of the line position 40. .

For the channels of the band RB1, the amplifiers 64, 66 can be seen together as two stage amplifiers having a first stage operated in shaping mode and a second stage operating in saturation. To help stabilize the output power between the channels in the band RB1, the amplifiers 64, 66 are preferably pumped as the same laser diode pump source. In this way, as described in EP695049, the extra pump power from the amplifier 64 is provided to the amplifier 66. In detail, line position 40 includes a WDM coupler positioned between amplifier 71 and filter 71 which extracts 980 nm of pump light remaining at the output of amplifier 64. This WDM coupler can be, for example, a model name (SWDMCPR3PS110) supplied by E-Tek Dynamics Inc., located at Rundy Avenue 1885, San Jose, California. The output from this WDM coupler is fed to a second WDM coupler of the same type (not shown) located in the optical path after amplifier 66. These two couplers are coupled by an optical fiber 78 which transmits the redundant 980 nm pump signals with a relatively low loss. The second WDM coupler passes the excess 980 nm pump power into the amplifier 66 in the counter-propagation direction.

From the amplifier 66, the signals in the band RB1 are transferred to an OADM stage 76, an example of known type of OADM. From the OADM stage 76 the signals of band RB1 are fed to amplifier 67. For the appropriate erbium-doped fiber amplifier, amplifier 67 is for example from a laser diode source (not shown) with pump power exceeding the laser (not shown) driving amplifiers 64, 66. Has a pump wavelength of 1480 nm. The 1480 nm wavelength provides good conversion efficiency for high output power output compared to other pump wavelengths for erbium doped fibers. Alternatively, a group of multiplexed pump sources such as a high power 980 nm pump source or two pump sources at 980 nm or one at 975 nm and the other at 986 nm can be used to drive the amplifier 67. . Amplifier 67 preferably operates in saturation to provide the power boost with signals in band RB1. And if desired, it can be equipped with a multi-stage amplifier.

After passing through the amplifier 64 and the filter 71, the band BB enters the equalization filter 74. As mentioned above, the gain characteristic for the erbium doped spectral radiant region has a peak or hump in the band BB region but remains very uniform in the region of the band RB1. As a result, when the band BB or the single wide band SWB (including the BB band) is amplified with an erbium-doped fiber amplifier, the channels in the region of the band BB are amplified unevenly. Also, as mentioned above, when equalization means are applied to overcome the problem of inequality, the equalization means are applied over the entire spectrum of the channel, resulting in continuous gain disparities. However, by dividing the channels of the spectrum into bands BB and RB1, reduced in-band equalization of the band BB will provide adequate uniformity of gain characteristics for the channels of the band BB. Can be.

In a suitable embodiment, the equalization filter 74 has two ports of devices based on a long term chirped bragg grating technique that gives selected attenuation at different wavelengths. For example, the equalization filter 74 for the band BB may have an operating wavelength range from 1529 nm to 1536 nm with a wavelength at the valley bottom between 1530.3 nm and 1530.7 nm. Equalization filter 74 may be combined in a dependent form with other filters (not shown) and need to be used alone to provide an optimum filter shape and thus to provide gain equalization for the particular amplifiers used in the WDM system 1. There is no. Equalization filter 74 may be manufactured by one of ordinary skill in the art or may be obtained from many suppliers in the art. It should be understood that the particular structure used for the equalization filter 74 is within the scope of skilled artisans and may include, for example, specialized Bragg grating, interference filters, or mark-gendered optical filters such as long term gratings. do.

The signals of the band BB from the equalization filter 74 are transferred to the OADM stage 75 which is the same type of the OADM stage 76 and then to the amplifier 65. With an appropriate erbium doped fiber amplifier, amplifier 65 is provided by a laser diode source (not shown) and via a WDM coupler (not shown) in the optical path for pumping the amplifier 65 in the opposite propagation direction. Combined pump wavelength of 980 nm. Since the channels in the band BB pass through both amplifiers 64 and 65, equalization filter 74 can compensate for the gain imbalance caused by the two amplifiers. Thus, the drop in decibels for the equalization filter should be determined according to the line power requirement for the band BB and the overall amplification. The amplifier 65 preferably operates in saturation to provide a power boost to the signals in the band BB, and can be configured as a multistage amplifier if desired.

The band RB2 is received from the fiber amplifier 68, which is an erbium-doped fiber amplifier, preferably pumped with 980 nm or 1480 nm pump light, depending on the requirements of the system. From amplifier 68, the channels of band RB2 are transferred to OADM 77, which is the same type of OADM steps 75 and 76, for example, and then to amplifier 69. According to the present invention, the amplifier 69 will be described in detail with reference to FIGS. 9, 15 and 16 as an erbium / ytterbium co-doped amplifier adapted to amplify the band RB2.

After passing through the amplifiers 65, 67, 69, respectively, the amplified BB, RB1, RB2 bands are then recombined by the filter 72 into the single optical band (SWB). Like filter 54 of FIG. 4, filter 72 may include, for example, two cascaded three-port filters (not shown). The first couples the RB1 band and the BB band, and the second couples the RB2 band and the BB and RB1 bands provided by the first filter.

Like the TPA portion 12, the line position 40 may also include service line insertion and extraction through an optical monitor and, for example, a WDM 1480/1550 interference filter (not shown). One or more of these elements may be included at any of the interconnection points of the line location 40.

In addition to amplifiers 64-69, filters 70-72 and 74, and OADM steps 75-77, line position 40 may occur during transmission of signals along a long distance communication link. A dispersion compensation module (DCM) (not shown) for compensation for chromatic dispersion may be included. The DCM (not shown) preferably consists of sub-devices combined with one or more of the upper ones of the amplifiers 65, 67 and 69 to compensate for the dispersion of the channels in the BB, RB1 and RB2 bands. Can be taken. For example, the DCM (not shown) may have an optical circulator having a first port connected to receive channels in one or more of the three bands BB, RB1, RB2. A chirped bragg grating may be attached to the second port of the circulator. The channels will exit the second port and will be reflected in the information transmitted Bragg grating to compensate for color dispersion. The dispersion compensated signals will then exit the next port of a continuous transmission circulator within the WDM system. Devices other than chirped bragg grating, such as the length of the dispersion compensation fiber, may be used for color dispersion compensation. The design and use of the DCM portion does not limit the present invention and the DCM portion may be employed or omitted within the WDM system 1 depending on the overall need for system tooling. After the line position 40, the combined single wide band (SWB) signal passes through the length of the long distance light transmission fiber of the optical fiber line 30. If the distance between the first and second terminal positions 10 and 20 is long enough to cause attenuation of the optical signals, for example as long as 100 km, one or more additional line positions 40 providing amplification may be used. Can be. In a practical arrangement, five spans of long distance transmission fibers are used (each span having a length to provide 0,22 dB / Km power loss and nearly 25 dB total span loss). Separated by four amplification line positions 40.

Following the last span of the transmission fiber, the RPA portion 14 receives the single wide band (SWB) from the last line position 40 and at the end of the communication link the single wide band (SWB) for reception and detection. Prepare the signals of). As shown in FIG. 7, RPA portion 14 includes amplifiers (AMP) 81-85, filters 86 and 87, equalization filter 88, and, if necessary, three router modules ( 91-93). Filter 86 receives a single wide band (SWB) and separates the band RB2 from the BB and RB1 bands. Amplifier 81 is preferably doped with erbium and amplifies the BB and RB1 bands to help improve the signal-to-noise ratio for the channels in the BB and RB1 bands. As an example, amplifier 81 may be pumped with a pump at any other wavelength or with a 980 nm pump to provide a low noise shape for the amplifier. The BB and RB1 bands are in turn separated by a filter 87. With TPA portion 12 and line position 40, amplifiers 82 and 83 amplify the BB band and RB1 band with 980 nm pumping, respectively. In order to stabilize the output power between the channels in the RB1 band, the amplifiers 81 and 83 preferably have the same by using a coupling optical fiber 89 which transmits an extra 980 nm pump signal with a relatively low loss. It is pumped with a 980nm laser diode pump. In particular, amplifier 81 is associated with a WDM coupler located between amplifier 81 and filter 87 and extracting the 980 nm pump light that remains at the output of amplifier 81. This WDM coupler may be, for example, a model number (SWDMCPR3PS110) supplied by E-Tek Dynamics, Inc., located at Rundy Avenue 1885, San Jose, CA. The output from the WDM coupler is fed to a second WDM coupler of the same type located in the optical path after amplifier 83. The two couplers are coupled by an optical fiber 89 which transmits a residual 980 nm pump signal with a relatively low loss. The second WDM coupler passes its remaining 980 nm pump power into the amplifier 83 in the opposite propagation direction. Thus, the amplifiers 81-83, the filter 87, and the equalization filter 88 are identical to the amplifiers 64, 65, 67, the filter 71 and the equalization filter 74 at the line position 40. Each function can be performed and configured into identical or equivalent parts depending on the overall system requirements.

Amplifier 84 combines with filter 86 to receive and amplify the RB2 band. By way of example, amplifier 84 is the same erbium doped amplifier as amplifier 86 of FIG. The RB2 band channels are then received by amplification 85 which is an erbium doped amplifier of a known type as an example.

The RPA portion 14 further has a routing step that allows adapting the channel spacing in the BB, RB1, RB2 bands with the channel separation capacity of the demultiplexing portion 15. In particular, if the channel separation capacity of the demultiplexing portion 15 is for a relatively wide channel spacing (eg 100 GHz grid) while the channels in the WDM system 1 are at a dense interval (50 GHz) then RPA Portion 14 may include the routing step 90 shown in FIG. 7. Other structures may be added to the RPA portion 14 depending on the channel separation capacity of the demultiplexing portion 15.

The routing step 90 has three router modules 91-93. Each router module 91-93 divides each band into two subbands, each subband containing half of the channels of its corresponding band. For example, if the BB band has 16 channels λ ₁ -λ ₁₆ and each is separated by 50 GHz, then the router module 91 divides the BB band by channels λ ₁ , λ separated by 100 GHz. Channels λ ₁ , λ ₂ , λ separated by a first subband BB ′ having ₂ , λ ₃ ,..., Λ ₁₅ and 100 GHz and interleaved with the channels in the subband. ₃ ,..., Λ ₁₆ ). In a similar manner, the router module 92, 93 may divide the band RB1 and the band RB2 into first subbands RB1 'and RB2' and second subbands RB1 " and RB2 ", respectively. Divide by)

Each router module 91-93 includes, for example, a coupler (not shown) having a first series of bragg gratings attached to the first port and a second series of gratings attached to the second port. The bragg grating attached to the first port has reflection wavelengths corresponding to all other channels (eg even channels), while the bragg grating attached to the second port is applied to its remaining channels (eg odd channels). Will have corresponding reflection wavelengths. This grating arrangement also serves to divide the single input path into two output paths with twice the channel-to-channel spacing.

After passing through the RPA portion 14, the bands BB, RB1, RB2 or their respective subbands are received by the demultiplexing portion 15. As shown in FIG. 8, the demultiplexing portion 15 receives its respective subbands BB ′, BB ″, RB1 ′, RB1 ″, RB2 ′, RB2 ″ and its output channels 17. Six wavelength demultiplexers (WDs) 95 ', 95' ', 96', 96 '', 97 ', 97' '. The demultiplexing portion 15 further comprises receiving devices RX1-RX128 for receiving its output channels 17. The wavelength demultiplexers preferably have arranged waveguide grating devices but alternative structures are contemplated to achieve the same or similar wavelength separation. As an example, demultiplex the channels in interference filters, Fabry Perot filters or subbands BB ', BB' ', RB1', RB1 '', RB2 ', RB2' '. In-fiber bragg grating can be used as a conventional method.

In a suitable embodiment, the demultiplexer portion 15 combines the interference filter and the AWG filter technique. Alternatively, Fabry-Perot filters or in-fiber bragg grating can be used. WDs 95 'and 95'', preferably eight channel demultiplexers with interference filters, receive and demultiplex the first subband BB' and the second subband BB '', respectively. In particular, WD 95 'demultiplexes channels λ ₁ , λ ₃ ,..., Λ ₁₅ and WD 95''has channels λ ₂ , λ ₄ , ..., λ ₁₅ ) demultiplex. However, both WD 95 'and 95''may be 1 × 8 type AWG 100 GHz demultiplexers. Similarly, WDs 96 ', 96''receive and demultiplex the first subband RB1' and the second subband RB1 '', respectively, to make channels λ ₁₇ -λ ₆₄ . do. WDs 97 ′, 97 ″ receive and multiplex first subband RB2 ′ and second subband RB2 ″, respectively, to create channels λ ₆₅ -λ ₁₂₈ . Both WD (96 ', 96'') can be 1X32 type AWG 100 GHz demultiplexers installed below to use only 24 of the available demultiplexers ports, and both WD (97', 97 '') It can be a 1x32 type AWG 100 GHz demultiplexers using all available demultiplexer ports. The output channels 17 consist of individual channels demultiplexed by WDs 95 ', 95'',96', 96 '', 97 ', 97'', each of the output channels 17 Is received by any one of the receiving devices RX1-RX128.

9 illustrates an erbium / ytterbium fiber amplification apparatus 100 adapted for use in the optical transmission system to amplify the band RB2 in accordance with the present invention. In particular, the amplifying apparatus 100 is suitable embodiments of the amplifier portions 53 of FIG. 4 and the amplifier portions 69 of FIG. 6.

The amplification apparatus 100 includes an input 101, an output 102, an erbium fiber preamplifier 103, and an erbium / ytterbium fiber amplifier 104. The preamplifier 103 and the amplifier 104 are arranged in series and the preamplifier 103 is between the input 101 and the amplifier 104 to provide a first amplification to the RB2 channels received at the input 101. Is located in.

The amplification device 100 also preferably has first and second isolators 105, 106. The first isolator 105 is positioned between the preamplifier 103 and the amplifier 104 and is adapted to block light directed from the amplifier 104 toward the preamplifier 103. The second isolator 106 is positioned between the amplifier 104 and the output 102 and is adapted to block the light directed from the output 102 towards the optical amplifier 104.

The preamplifier 103 may be, for example, a known type of single stage erbium doped fiber amplifier pumped at 980 nm and / or 1480 nm depending on system requirements. The total length of the erbium doped active fibers in the preamplifier is preferably between 80 nm and 150 nm. Preamplifier 103 receives band RB2 from input 101 and amplifies its RB2 channels at a first power level up to 15-17 dBm, for example. The first amplification performed by preamplifier 103 allows to reach a high power level at the output of amplifier 104 as will be seen later. Preamplifier 103 also allows to improve the noise figure (NF) of amplifying device 100 and equalize the RB2 band channels.

The amplifier 104 is a single stage fiber amplifier with bidirectional pumping that includes an amplified optical fiber 108 having a preset length.

Applicants have determined that the optimum overall length of the active fiber can be found dependent on system parameters such as single input power and erbium concentration in the active fiber in order to minimize its gain slope within the considered wavelength band.

Applicants can accept the total length of the active fiber between 10 nm and 20 nm with about 15-17 dBm at the input of the amplifier 104 and with an erbium concentration in the active fiber of the amplifier 104 in the region indicated below. You get a reasonably low gain slope, and the minimum gain slope is obtained for a total fiber length of nearly 12m.

Amplifier 104 further includes first and second pump lasers 109 and 110 for providing pump radiation to the amplified optical fiber 108, and the first and second pump lasers 109 and 110. First and second WDM optical couplers 111 and 112 that couple light from the amplified optical fibers 108.

The optical fiber 108 is preferably a double-clad fiber of the type described below with reference to FIG. 17A, which is preferably the not-in-scale portion of the optical fiber 108. The fiber 108 is a core 140 having a first refractive index or refractive index n1, surrounding the core 140 and coaxial with the core 140 and having a second refractive index n2 ( an inner cladding 141 with n2 <n1, and an outer cladding surrounding the inner cladding 141 and coaxial with respect to the inner cladding 141 and having a third refractive index n3 (n3 <n2) An outer cladding 142. As shown in FIG. 17B, under normal operating conditions of the amplifying device 100, the transmitted signal is confined into the core 140, while the pump radiation is supplied into the inner cladding 141 and the active medium. Are sequentially absorbed by the core 140 to excite them. The fiber 108 preferably has an outer diameter of the outer cladding 142 of 90 micrometers, an outer diameter of the inner cladding 141 of 65 micrometers and an outer diameter of the core 140 of about 5 micrometers. Core 140 is preferably made of SiO ₂ / P ₂ O ₅ / Al ₂ O ₃ co-doped with Er / Yb. In more detail, core 140 preferably has a weight percent of P ₂ O 5 greater than 10 percent (preferably 20 percent), a weight percent of Al ₂ O ₃ lower than ₂ percent, an erbium concentration between 600 ppm and 1000 ppm and 1000 ppm and It has a ytterbium concentration between 20000 ppm. The ratio between ytterbium and erbium concentrations is preferably between 10: 1 and 30: 1, more preferably about 20: 1. The difference in refractive index between the core 140 and the inner cladding 141 is preferably Δn = n ₁ -n ₂ = 0.013 +/− 0.002, and the difference in refractive index between the inner cladding 141 and the outer cladding 142 is preferably Δn '= n ₂ -n ₃ = 0.017 +/- 0.003 (mainly due to fluorine (F) doping of the outer cladding 142). The core 140 and inner cladding 141 define a single mode waveguide for guiding the transmission signals having a first numerical aperture NA1 = 0.19 +/- 0.02, while the inner cladding 141 and the outer cladding 142 defines a guiding multi-mode waveguide of the pump radii with the second numerical aperture NA2 = 0.22 +/- 0.01.

To make the fiber 108, two different preforms (not shown) are used. A first preform was used to obtain the core 140 and the inner cladding 141 and SiO ₂ and P ₂ O by means of MCVD method (chemical vapor deposition method: another method known as CVD method) into pure silica preform. ₅ is deposited and then introduced by introducing aluminum and rare earth erbium and ytterbium by known solution doping methods. The first preform is operated to obtain a preset geometric ratio between the core 140 and the inner cladding 141.

A commercial second preform is used to obtain the outer cladding 142. The second preform has a central region of pure SiO ₂ and a peripheral region of SiO ₂ doped with fluorine. The central region of the second preform is removed to obtain a central longitudinal hole into which the first preform is introduced. The three layers of preforms thus obtained are flowed out in the usual way to obtain the optical fiber 108.

With reference to FIG. 9, the pump lasers 109, 110 are multi-mode wide-range lasers with an emission wavelength included in the wavelength region 920-980 nm, for example at 920 nm, each pumping nearly 400 mW into the optical fiber 108. Is adapted to provide power. As an example the pump lasers 109, 110 may be a model number (MECP7PR6) supplied by E-Tek Dynamics Inc., located at Rundy Avenue 1885, San Jose, CA.

The first and second couplers 111 and 112 are micro optical (mirror or mirror type) WDM couplers located at both ends of the optical fiber 108. Couplers 111, 112 include first, second, and third access fibers, respectively, as indicated in two cases having 111a, 111b, 111c and 112a, 112b, 112c. Each of the couplers 111, 112 is furthermore not in shape but a converging lens system which directs the beam of light between its access fibers, for example an inclined segment indicated with 111d and 112d respectively. It includes a selective reflective surface, such as a dichroic mirror, which is represented graphically. The actual tilt of the dichroic or heterogeneous mirror inside the coupler depends on the direction of the incoming light beams carrying the signal and pump radiation. The selective reflective surface in couplers 111 and 112 is transparent to the wavelengths of the RB2 band channels and reflects to the wavelengths of the pumping radiation. In this way, the RB2 band channels pass through the reflective surface substantially without loss, while the pump radiation is reflected by the reflective surface into the cladding of the amplifying fiber 108. Alternatively, each coupler 111, 112 has a selective reflecting surface that reflects on the wavelengths of the RB2 band channels and transmits to the wavelength of the pumping radiation.

Coupler 111 has its first access fiber 111a optically coupled with the output of preamplifier 103 (via isolator 105) to receive the preamplified RB2 band channels, and pump radiation. Second access fibers 111b optically coupled with the pump laser 109 to receive the amplified fiber for feeding both the RB2 band channels and pump radiation to the fiber 108 in the same propagation direction. It has a third access fiber 111c optically coupled to the input of 108.

Coupler 112 receives the pump radiation and the first access fiber 112a optically coupled with output 102 (via isolator 105) to transmit the amplified RB2 band channels to output 102. To receive the amplified RB2 band channels from the second access fiber 112b and the amplified fiber 108 optically coupled to the pump laser 110 and to pump pump laser in the opposite propagation direction with respect to the transmitted signals. It has a third access fiber 112c optically coupled with the output of the amplifying fiber 108 to feed its pump radiation generated by 110 to the fiber 108.

The first access fibers 111a and 112a are single mode fibers having a wavelength cutoff of 1300 nm ± 30 nm, a cladding diameter of 125 μm and a numerical aperture NA = 0.2. The second access fibers 111b and 112b have a core diameter of 65 micrometers, a cladding diameter of 90 micrometers and a numerical aperture NA = 0.22. The third access fibers 111c and 112c have the same chemical and geometrical characteristics of the amplifying fiber 108 but have no active doping.

Couplers 111, 112 have an insertion loss of approximately 1,02 dB measured at 1550 nm for optical signals passing from first access fiber 111a / 112a to third access fiber 111c, 112c or vice versa, It has an insertion loss of approximately 0.22 dB measured at 980 nm for the optical signals passing from the second access fibers 111b and 112b to the third access fibers 111c and 112c or vice versa. Moreover, the couplers 111 and 112 are much larger than the 30 dB optical isolation and the second and third access fibers measured at 980 nm between the first access fibers 111a / 112a and the third access fibers 111c / 112c. Has an optical isolation much greater than 20 dB measured at 1550 nm in between.

10A and 10B show numerical simulations of two channel transmissions through the amplification apparatus 100. Both channels had an input power of -13.5 dBm (at input 101) and were selected at 1575 nm and 1602 nm as examples at the extremes of the RB2 band. In particular, FIGS. 10A and 10B show estimated spectra and estimated power of the two channels, each represented in a shape by means of two different cross marks at the output of preamplifier 103 and at the output of amplifier 104, respectively. Show the levels.

11A, 11B and 11C show additional numerical results related to transmission through the optical amplifier 104 of the above two channels at 1575 nm and 1602 nm. In particular, this calculation simulates the transmission of those two channels through the line amplification portion including the Er / Yb amplifier 104 which is not preceded by the preamplifier 103. 11A, 11B and 11C show the ASE (amplification) on the length of the active Er / Yb fiber z for different input signal powers of -12 dBm per channel, +5 dBm per channel and +10 dBm per channel, respectively. Stimulus radiation) and signal power dependence. The results show that in the absence of preamplification 103, limitations are imposed on the input signal power region by using only Er / Yb accompanied doped amplification fibers to amplify the RB2 band channels, for example. Signals with power per channel have a relatively low gain. This is considered to be due to the high fluorescence peak at 1536 nm of Er / Yb accompanied doped fibers. In fact, if the low signal powers in the bandwidth (1575nm-1602nm) are fed directly to the amplifier 104, its signal gain is saturated by the accumulation of amplified spontaneous emission (ASE) and a low output power is obtained. The result is that the use of a preamplifier, such as the use of an erbium doped preamplifier, is advantageous to ensure high saturation output power within its limited configuration. Because the use of only Er / Yb-doped amplified fibers to impose high amplification efficiency and saturation output power imposes a lower limit on the input signal (almost 0 dBm). On the other hand, its limited combined shape (Er doped preamplifier and Er / Yb accompanied doped power amplifier) allows for high efficiency and high saturation output power for input powers down to -20 dBm. This strong saturation avoids over-amplified spontaneous accumulation outside of the signal bandwidth. However, an alternative amplification step that is less appropriate than the previously described amplification scheme may include cascaded connections of Er / Yb-doped doped amplification fibers with the addition of filters to suppress the amplified spontaneous emission. . This arrangement can be advantageously used as a power amplifier stage with relatively high input power signals, but according to the above it can suffer substantial waste of energy, especially amplified spontaneous emission after receiving very low power level input signals. Such energy waste may be experienced in the first stage, which tends to produce high values of.

12A and 12B show experimental devices used to test the amplification device 100. The experimental apparatus of FIG. 12A includes a preamplifier 103, a light generator 150 for exporting optical signals into the input of the preamplifier 103, and an optical spectrum analyzer 152 for detecting the spectrum at the output of the preamplifier 103. ). In particular, generator 150 is preferably a laser array 64 each of which generates each wavelength in the RB2 band. In the experimental setup of FIG. 12B, the amplifier 104 can be added in series to the preamplifier 103 and the optical spectrum analyzer 152 detects the spectrum at the output of the amplifier 104. Attenuation filters 151 and 151 ′ may be included in the experimental apparatus of FIGS. 12A and 12B for the safety of the light spectrum analyzer 152. Furthermore, a power meter (not shown) may be added to the experimental devices of FIGS. 12A and 12B to monitor optical power at the output of preamplifier 103 and at the output of amplifier 104, respectively.

13A and 13B show an optical spectrum analyzer 152 in response to an input signal comprising two channels at 1575 nm and 1602 nm having a total power of approximately -10.5 dBm (equivalent to approximately -13.5 dBm of power per channel). By means of means, the detected spectra are shown at the output of the preamplifier 103 and at the output of the amplifier 104 respectively. No attenuation filter was included in this case. Because optical power at the output of preamplifier 103 and amplifier 104 respectively is not dangerous for the spectrum analyzer 152. In the spectra of FIGS. 13A and 13B, the power peaks of the two detected channels overlap with the power radiation of the preamplifier 103 and the combined power emissions of the preamplifier 103 and the amplifier 104, respectively. do. These experimental results confirm the numerical results of FIGS. 10A and 10B. In particular, the experimental results in FIG. 13B show that for all RB2 bands, the amplifier 100 amplifies a -10.5 dBm input power signal (such as two -13.5 dBm channels) to reach a full saturation output of nearly 23 dBm. Show that you can. In other words, a power gain much greater than 33 dB was obtained for input signals in the RB2 band and input optical power of nearly -10 dBm. The gain spectral curve of the cascade preamplifier 103 and amplifier 104 arrangement is nearly uniform and has a variation of 0.55 dB at 1575 nm and 1602 nm, ie between both ends of its RB2 band.

14A and 14B show experimental power spectra detected with an overall input signal power of approximately -9.5 dBm and with the arrangement of FIGS. 12A and 12B for a 64 channel case. In this case, attenuation filters 151 (20 dB attenuation) and 151 '(25 dB attenuation) were added for the safety of the optical spectrum analyzer 152. Saturated output power of nearly 22 dBm was detected at the output of amplifier 104 by a power meter having the arrangement of FIG. 12B. This power is slightly lower than that detected in the case of two channel transmissions. The power difference seen in these two experiments is probably not due to the difference in the number of channels combining the signals, but due to the difference in the other characteristics of the optical connectors and preamplifiers used in the two experiments. This leaves room for further optimization by, for example, increasing the pump power or improving the amplifier design to reach higher saturation output power. In particular, Applicants have determined that output powers up to 26 dBm can be reached with an input power of nearly -10 dBm by steaming the pump above 400 mW and by optimizing its optical connection.

13 and 14 show that the optical amplification device of the present invention has a power gain much greater than 25 dB when its optical signals have an input power of about -10.5 dBm or -9.5 dBm and have wavelengths between 1575 nm and 1602 nm. Allow. In particular, with the inventive optical amplification device operating within the stated conditions (eg at least -10.5 dBm input power), a power gain of much greater than 31 dB and especially a power gain of much greater than 33 dB has been demonstrated. . These values are much higher than the 29 dB seen with erbium doped amplifiers under the same conditions.

In Fig. 15, a second embodiment of an amplifying apparatus for use in the optical transmission system 1 for amplifying the RB2 band is illustrated. The amplifier 100 'of FIG. 15 differs from the amplifier 100 of FIG. 9 only in the structure of the erbium / ytterbium amplifier as indicated here by 104'. The other optical elements of the amplifying apparatus 101 'are indicated with the same reference numerals as the corresponding elements in FIG.

The amplifier 104 ′ is a double stage amplifier with accompanying propagation pumping, with first and second amplified fibers 113 and 114, first and second amplified optical fibers 113 and 114 doped with erbium and ytterbium. The first and second pump lasers 115 and 116 and the first and second pump lasers 115 and 116, respectively, to provide pump radiation, respectively, and the first and second amplified optical fibers 113 and 114, respectively. First and second micro-optical (mirror) WDM optical couplers 117 and 118 for optical coupling to the two, and preferably both to suppress the portion of the amplified spontaneous emission of the amplifying fibers 113 and 114. Noise cancellation filter 119 located between the amplification stages.

The first and second amplified fibers 113, 114 include two stretches of the same erbium / ytterbium fiber as an example, and preferably include two stretches of the same type of fiber 108 of FIG. 9. Fiber lengths can be selected depending on the system requirements.

The pump lasers 115, 116 are, for example, multiple shaped lasers of the same type of pump lasers 109, 110 with pumping power of nearly 400 mW and provide pumping radii between 920 nm and 980 nm.

Couplers 117 and 118 are micro optical couplers of the same type couplers 111 and 112 of FIG. In particular, each of the micro-optical couplers 117, 118 includes a focusing lens system and, for example, a selective reflective surface that is transparent to the wavelengths of the RB2 band channels and reflects to the wavelength of the pumping radiation. In this way, the RB2 band channels pass through the reflective surface substantially without loss, while the pump radii respectively pass into the cladding of the amplifying fibers 113 and 114 in the same direction with respect to the transmitted signals. Reflected by the reflective surface.

The noise canceling filter 119 is positioned between the amplifying fiber 113 and the coupler 118, and amplifying fibers 113 and 114 to improve the performance of the amplifying device 100 'in terms of channel equalization and output power. Its amplified spontaneous emission is applied to filter. Another elimination filter (not shown) may be located in addition to or alternatively to filter 119 between isolator 106 and output 102. The amplification portion 100 'can provide nearly 22 dBm of saturated output power with nearly 10 dBm of input signal power.

16 is a third embodiment of an amplification apparatus adapted to be used in the system 1 to amplify the RB2 band. The amplifying device 100 ″ of FIG. 15 differs from the amplifying device 100 of FIG. 9 and the amplifying device 100 ′ of FIG. 15 only in the erbium / ytterbium amplifier structure, as indicated herein by 104 ″.

The amplifier 104 '' is a double stage amplifier with bidirectional pumping, the first and second amplifying fibers 120 and 121 co-doped with erbium and ytterbium, and pump radiating the first and second active fibers 120 First and second pump lasers 122 and 123 for providing to the first and second pump lasers, respectively, and first and second WDM optical couplers 124 for bidirectionally coupling the first pump laser to the first fiber 120. 125, amplification of third and fourth WDM optocouplers 126 and 127, and fibers 120 and 121 for bidirectionally coupling the second pump laser 123 to the second fiber 121 And a noise canceling filter 128 for suppressing the spontaneous radiated part.

The first and second active fibers 120, 121 are preferably the same double-clad fibers as the fiber 108 in Fig. 9 having respective lengths that can be selected depending on the system requirements. The pump lasers 122, 123 are, for example, multiple shaped lasers of the same type of pump lasers 109, 110 that provide pumping radii between 920 nm and 980 nm with a pumping power of 400 mW.

Couplers 124-127 are adapted to supply pump radiation into the inner cladding of the active fibers 120, 121. Couplers 124 and 126 are preferably dissolved fiber WDM couplers of the 960/1550 nm or 920/1550 nm type. By way of example, couplers 124 and 126 are models MW9850-P05 made by the applicant. More specifically, coupler 124 is sandwiched between pump laser 122 and fiber 120, and coupler 126 is sandwiched between pump laser 123 and fiber 121. Each of the couplers 124, 126 has a first access fiber receiving the RB2 band channels, a second access fiber receiving a pump radiation, and approximately 50 percent of the RB2 band channels and pump radiation power (typically About 48 percent) to the corresponding amplifying fibers 120 and 121, and a fourth access fiber to which the remaining pump radii- tion (nearly 50 percent of the pump radiant power) is conveyed. Preferably, the first and third access fibers are opposite ends of the same double-clad fiber, while the second and fourth access fibers are opposite ends of the same multi-shaped fiber.

The couplers 125, 127 are preferably micro-optical (mirror type) WDM couplers of the same type couplers 111, 112 of FIG. 9. Each of these is located on the opposite side of its corresponding fiber amplifier 120, 121 relative to its corresponding dissolved fiber coupler 124, 126. Each micro optocoupler 125, 127 receives a first access fiber optically coupled to an active fiber 120, 121, the redundant pump radii and has a loss not greater than 0.3 dB, more precisely about 0.22 dB By means of each optical fiber 130, 131 to transfer into the fourth access fiber of its corresponding dissolved fiber coupler 124, 126 in order to pass into each active fiber 120, 121 in the opposite propagation direction with a loss of A second access fiber coupled, and a third access fiber carrying the amplified transmission signals. Each micro optocoupler 125,127 has a signal pass band that includes the RB2 band such that the RB2 band channels are transmitted with very low loss. The particular coupling arrangement described previously is adapted to supply about 85 percent of the pump power generated by each pump laser 122, 123 to each fiber amplifier 120, 121. Therefore, very high efficiency pumping is provided.

Like the amplifying portion 100 'of FIG. 15, the amplifying portion 100' is adapted to provide a saturated output power of up to 22 dBm with an input power of approximately -10 dBm.

Detailed and various changes, materials, steps, and arrangements of the parts exemplified and described above to explain the nature of the present invention are to be understood as those of ordinary skill in the art and scope of the present invention as expressed in the appended claims. Can be made by them.

By way of example, a transmission system may be made with a transmission wavelength band including all bands and only the RB2 band, or a portion of the RB2 band or a band comprising the RB2 band. A transmission system adapted to transmit only in the RB2 band is, for example, a transmission device generating 64 channels with a spacing of 50 GHz at 2,5 Gbit / s, an optical link coupled to one end of the transmission device, And a receiving device coupled to the other end.

The optical link can have a fiber span (or span) even longer than 130Km between subsequent steps, each fiber span introducing about 28dB of loss (using fibers with a loss of about 0.22 dB / Km). .

Claims (33)

An optical transmission device 10 adapted to transmit an optical signal within a transmission wavelength band of 1570 nm or more; An optical receiver 20 for receiving the optical signal; An optical fiber link optically coupling the transmitting device to the receiving device; And And optical amplification apparatuses 100 and 100 'coupled along the link. The optical amplifying apparatus has an amplifying wavelength band including the transmission wavelength band, an input for input 101 of the optical signal from the link, an output 102 for outputting the optical signal into the link, and Consisting of optical amplifiers 104, 104 'positioned between the input 101 and the output 102 to amplify an optical signal, The optical amplifiers 104, 104 'are amplified fibers 108; 113, 114, pump sources 109, 110; 115, 116 for generating pump radiation, and the pump sources 109, 110; 115, 116 and optical couplers 111, 112; 117, 118 for optically coupling the amplification fibers 108; 113, 114, and The amplifying fiber (108; 113, 114) comprises an optical fiber doped with erbium and ytterbium. 2. The optical amplification apparatus (100; 100 ') has a power gain of greater than 29 dB when the optical signal has an input power of at least -10.5 dBm and a wavelength within the amplification wavelength band. Optical transmission system. 3. The optical amplifying apparatus (100) according to any one of claims 1 and 2, wherein the optical amplifying apparatus (100; 100 ') has a power of at least 31 dB when the optical signal has an input power of at least -10.5 dBm and a wavelength within the amplifying wavelength band. Optical transmission system characterized in that it has a gain. 3. The optical amplifying apparatus (100) of claim 1, wherein the optical amplifying apparatus (100; 100 ') has a power of at least 33 dB when the optical signal has an input power of at least -10.5 dB and a wavelength within the amplification wavelength. Optical transmission system characterized in that it has a gain. The optical transmission system according to claim 1, wherein the width of the amplified wavelength band is at least 15 nm. The optical transmission system according to any one of claims 1 to 2, wherein the width of the amplified wavelength band is at least 27 nm. The optical transmission system according to claim 1, wherein the lower wavelength limit of the amplified wavelength band is much greater than or equal to 1575 nm. 3. Optical transmission system according to any one of the preceding claims, characterized in that the optical amplification device (100; 100 ') has a gain variation lower than 1 dB within the amplification wavelength band. 3. An optical device as claimed in any preceding claim, located between the input (101) of the optical amplification device (100; 100 ') and the optical amplifiers (104; 104') for preamplifying the optical signal. And a further optical preamplifier. The optical transmission system according to any one of claims 1 to 2, wherein the amplifying fiber comprises SiO ₂ , P ₂ O ₅ , Al ₂ O ₃ and is doped together with Er / Yb. The optical transmission system according to any one of claims 1 to 2, wherein the amplifying fiber has a core (140) having an erbium concentration of approximately 600 ppm to 1000 ppm. The optical transmission system according to any one of claims 1 to 2, wherein the amplifying fiber has a core (140) having a ytterbium concentration of approximately 1000 ppm to 20000 ppm. The optical transmission system according to any one of claims 1 to 2, wherein the amplifying fiber has a core having a concentration ratio of erbium and ytterbium between about 5: 1 and 30: 1. The amplifying fiber of claim 1, wherein the amplifying fiber has a core having a weight percent of P ₂ O ₅ , which is much larger than 10 percent, and a weight percent of Al ₂ O _{3, which} is lower than 2 percent. An optical transmission system characterized by the above. The optical transmission system according to any one of claims 1 to 2, wherein the amplifying fiber has a length lower than 30 m. The optical transmission system according to any one of claims 1 to 2, wherein the amplifying fiber has a length lower than 13m. The amplification fiber according to any one of the preceding claims, wherein the amplifying fiber has a double- having a core (140), an inner cladding (141) surrounding the core, and an outer cladding (142) surrounding the inner cladding. Optical transmission system, characterized in that the clad fiber. 3. Light transmission system according to any one of the preceding claims, wherein the pump source (109, 110; 115, 116) has an emission wavelength between 920 nm and 982 nm. 3. Light transmission system according to any one of the preceding claims, wherein the pump source (109, 110; 115, 116) is a multimode wide area laser. The optical amplifier (104; 104 ') is a single-stage fiber amplifier (104) having bidirectional pumping, wherein the amplifying fiber (108), two pump sources (109). 110, and two optical couplers 111, coupled at opposite ends of the amplifying fiber 108, each of which couples each one of the two pump sources 109, 110 to the amplifying fiber 108. 112). 21. The optical transmission system according to claim 20, wherein the two optical couplers (109, 110) are micro optical WDM couplers. 3. The optical amplifier (104) (104 ') according to any one of claims 1 to 2, wherein the optical amplifiers (104; 104') are double stage amplifiers with accompanying propagation pumping, wherein each stage of the double stage amplifiers is amplified fibers (113, 114), And a pump source (115, 116) and an optical coupler (117, 118). 23. The optical transmission system of claim 22 wherein the coupler (117, 118) in each stage of the double stage amplifier (104 ') is a micro optical WDM coupler. The optical transmission system according to any one of claims 1 to 2, characterized in that it comprises a plurality of optical transmission devices at different wavelengths. The optical transmission system according to any one of claims 1 to 2, wherein the optical link has intervals of optical fibers having a length of at least 130 km. The optical transmission system according to claim 1, wherein the optical transmission system has a wavelength transmission band having a width of at least 53 nm. Generating an optical signal having a wavelength within the wavelength band, the wavelength band having a lower limit much greater than 1570 nm; Supplying the signal to an optical link; Amplifying the signal along the optical link; And Receiving the optical signal from the optical link; And And said amplifying step comprises feeding said signal into an active fiber doped with erbium and ytterbium. 28. The optical power supply of claim 27, wherein the supplying step feeds the signal to one end of the active fiber with an input power of at least -10.5 dBm, wherein the active fiber is the optical power of the optical signal at the opposite end of the active fiber. And a length, erbium concentration and ytterbium concentration such that is at least 29 dB. 28. The method of claim 27, wherein the supplying step comprises supplying the signal to one end of the active fiber with an input power of at least -10.5 dBm, the active fiber being the optical at the other end of the active fiber. And a length, erbium concentration, and ytterbium concentration such that the optical power of the signal is at least 31 dB. 30. The method of any of claims 27-29, wherein the wavelength band has a width of at least 27 nm. 30. The method of any one of claims 27 to 29, further comprising preamplifying the optical signal before feeding the optical signal to the active fiber. 30. The method of any of claims 27 to 29, further comprising the step of pumping the active fiber with a multi-mode pump radiation having a wavelength between 920 nm and 980 nm. Way. Has an amplification wavelength with a lower wavelength limit much greater than 1570 nm and a width of at least 15 nm, Amplifying fibers 108; 113, 114, pump sources generating pump radii 109, 110; 115, 116 and pump sources 109, 110; 115, 116 to the amplifying fibers 108; 113, 114 Optical couplers (111, 112; 117, 118) for optical coupling with And wherein said amplifying fiber (108; 113, 114) comprises an optical fiber doped with erbium and ytterbium.