The way to ensure control of the optical signal/noise ratio in the receiver, a method of optical telecommunications (options), telecommunications, optical amplifier and an active fiber

 

(57) Abstract:

The invention relates to a telecommunications system that includes optical amplifiers included cascade, and intended mainly for multiplex transmission with separation of wavelengths, and the combination of dopants in an optical fiber allows to achieve a high signal-to-noise for all channels in the specified wavelength range even when there are multiple signals simultaneously introduced into the fiber, which is achievable technical result. 6 c. and 39 C.p. f-crystals, 16 ill., table 1.

The present invention relates to communication systems with optical amplifiers and can operate in transmission mode with frequency division and multiplexing of channels (multiplexing) (hereinafter referred to as the M-transfer).

For WDM transmission needed more channels or transmitted signals, independent from each other and sent over the same fiber optic line by sealing channels (multiplexing) in the optical frequency range; transmitting channels, which can be both digital and analog, are separated from each other, because each of them works on its particular frequency.

When using amplifiers, in particular, an optical amplifier, it is required that the identity of the frequency characteristics of all transmission channels; in addition, to ensure transmission to a large number of channels frequency band in which the amplifier must be sufficiently wide.

The optical amplifier is based on the property fluorescense of dopant (dopant), in particular erbium entered into the body of fiber-optic light guide. The erbium excited by paging the light energy becomes high level of emission in the wavelength range corresponding to the minimum light attenuation in optical fibers based on silicon.

When through the optical fiber with the introduction of a erbium, which is supported in the excited state, passes the light signal having a wavelength corresponding to such a high level of emissions, it causes a transition of the atoms of the excited erbium lower energy level, light and stimulated emission at the wavelength of this signal, which creates the effect of amplification of the signal.

At levels below the excited state is also a place of spontaneous decay energy ATO the range forced the issue, corresponding to the amplification of a signal.

Light emission generated by the pumping light energy in the activated doping an impurity of the optical fiber, can occur at a number of wavelengths characteristic of such doped substances, resulting in the source of the fluorescence spectrum in the fiber.

In order to achieve the best possible signal in the fiber of the type in question along with providing a high signal-to-noise ratio acceptable for reliable reception of the signal in the optical communication distance is also used signal generated by the laser source with a wavelength corresponding to the maximum (expected frequency) curve of the fluorescence spectrum in the fiber containing alloying impurity, or the peak of the emission.

On the other hand, fiber doped with erbium, are characterized by an emission spectrum with a peak width limited whose parameters vary depending on the properties of glassy systems, in which erbium is introduced as a dopant, and the spectrum of such a high intensity of interest in the wavelength range close to the mentioned peak, which gives grounds to consider the possibility of what I fibers, doped with erbium, the characteristic irregularity of the spectrum of the emission, which identifies opportunities to achieve a uniform gain across the entire desired frequency band.

To ensure substantially flat characteristics of gain, i.e., more constant gain at different wavelengths by eliminating sources of noise due to spontaneous emission, can be used in filter elements, such as those described, for example, in patents EP 426222, EP 441211 and EP 417441, authored by the present Applicant.

In these patents, however, does not describe the operation of the amplifiers in the mode frequency separation and compaction (multiplexing) channels, and is not the work of several amplifiers included cascade relative to each other.

The spectral shape of the emission radiation to a large extent depends on dopant (dopant) present in the core of the optical fiber to increase the refractive index, for example, that shown in U.S. patent 5282079, where it is established that fluorescence spectrum of an optical fiber doped with aluminum/erbium has a less pronounced peak than the spectrum of the optical fiber doped with germanium-but has a numerical aperture (CHA), 0.15.

Materials ECOC'93. ThC12.1, pages 1-4, addressed the fiber for an optical amplifier doped Al and La, and has a very low sensitivity to hydrogen; described fiber with additives Al had a numerical aperture of 0.16, and the fiber with the addition of Al and La - 0,30.

Materials ECOC'93, Th4, pages 181-184, was considered optical amplifiers with fiber, alloyed erbium; also described the experiments conducted with the fibers, the core of which was doped with aluminum, aluminum-germanium and lanthanum/aluminum. The best results, apparently, was achieved with fibers, doped Al/La.

In the journal Electronics Letters, 6 june 1991, vol. 27, N 12, pp. 1065 - 1067 noted that in the optical fiber amplifiers doped with erbium, the introduction of additives corundum allows to obtain the characteristic gain more flat shape and of greater magnitude; in article compared the fiber amplifiers doped with aluminium, germanium and erbium amplifiers in the fiber with the addition of lanthanum, germanium and erbium and it was argued that in the latter case produces the largest alignment of gain characteristics.

Materials ECOC'91, TuPSl-3, pages 285-288 described the use of fiber type Al22O3- SiO2with the addition of erbium; was obtained numerical aperture (CHA) 0,31 and concentration of erbium 231018cm-3.

Materials ECOC'89, received in the last turn, PDA 8, pp. 33-36, September 10 to 14, 1989, describes an experiment with twelve optical amplifiers erbium-doped fiber connected in a cascade configuration; used single-ended signal with a wavelength of 1,536 μm. It was noted that for the stable operation requires the ability to control the wavelength of the signal in the range of 0.01 nm taking into account the fact that the value of the binary error rate (CSD) quickly fall from her change.

In U.S. patent 5117303 described optical transmission consisting of a synchronized optical amplifiers, which, as follows from the above calculations, when operating in the saturation mode provide high signal-to-noise ratio.

Described amplifiers included erbium doped fiber with a core of Al2O3- SiO2; this involved the use of filters. Settlement is Yu get these same characteristics were not conducted.

According to the present invention it was found that when a specific combination of additives introduced into the body of the active optical fiber, it becomes possible to obtain fiber, providing a high numeric aperture and such radiation spectrum, which makes possible the creation of such optical amplifiers (in particular, in systems with frequency multiplexing), which have homogeneous characteristics for a stand-alone amplifier, and for a group of amplifiers connected in a cascade configuration.

The first aspect of the present invention relates to methods enable control signal-to-noise ratio of the optical signal reception in a predetermined wavelength range for optical telecommunication systems, containing

optical transmitter

- optical receiver,

- fiber-optic line that connects the above-mentioned transmitter and receiver, and

at least one optical amplifier in an active optical fiber located along the above lines, where the above-mentioned active fiber has a line of radiation, characterized by a zone of high radiation of some wavelengths, which includes viewpodcast reduced emissions.

The present invention allows to improve the characteristic of the radiation due to the choice or dosage of dopants in the active fiber.

In particular, the above predefined wavelength range is between 1530 and 1560 nm; more preferred is a range between 1525 and 1560 nm.

In a preferred execution of the signal-to-noise ratio for the optical signal measured at a width of 0.5 nm filter, exceeded 15 dB.

In a preferred execution of the invention the above system contains at least two optical amplifier in an active optical fiber arranged in series along the above-mentioned fiber-optic lines.

In a preferred version of the invention a method of selecting dopant for fiber includes a base fluorescent dopant and at least one additional dopant interacting with the above main dopants in the glass lattice of the active optical fiber, with the objective of reducing the level above plot reduced emissions to values less than 1 dB with respect to the magnitude of the radiation in at least one of the adjacent zones in the above range. As the main dopant naibin and lanthanum (in the form of the respective oxides).

The second aspect of the present invention relates to a method of optical communication comprising the steps:

- generate at least one optical signal with a predetermined wavelength from the corresponding range of wavelengths;

- make the above signal over fiber optic telecommunication lines,

- at least one-time gain above the optical signal at least one optical amplifier in an active fiber and

- reception of the above signal through a receiver, characterized in that the active optical fiber in at least one of the amplifiers has a main fluorescent dopant and at least one additional dopant interacting with the above main dopants in the glass lattice of the active fiber, which leads to the amplification of a for the above-mentioned optical signal above a predetermined wavelength in the above-mentioned optical amplifier in an active optical fiber. In the absence of a means for filtering the gain, as measured at an input power of -20 dBm, differs less than 1.6 dB from the corresponding amplification of the signal at a different wavelength hetenyi, characterized by the fact that the signal-to-noise ratio for the optical signal in the receiver, measured at a width of 0.5 nm filter is not less than 15 dB for a single signal from the above-mentioned range, and in the presence of two or more signals having different wavelengths included in the specified range that are simultaneously fed to the input of the above amplifier, and this is done for each of these optical signals.

In particular, this method includes a procedure of at least two-stage amplification of the above-mentioned optical signal using respective optical amplifiers in an active fiber along the above-mentioned fiber optic communication lines.

Used in this method, the above-mentioned optical amplifier includes an active optical fiber, the core of which is doped with erbium, fulfilling the role of primary fluorescent dopant. In addition, the core is doped with at least two additional gopastami, which interact with the above main dopants. In a preferred execution of them are aluminum, germanium and lanthanum (in the form of the respective oxides).

A fourth aspect of the present Opticheskie signals in a predetermined wavelength range,

- receiving station,

- fiber-optic line that connects the above-mentioned transmitting and receiving stations, and

at least two of the optical amplifier in an active fiber connected in series along the above lines, which are connected to each other to ensure the passage of the above-mentioned optical signals from the above transmitting station to the above receiving station and are characterized by the fact that at least one of them contains the active optical fiber based on silica with a core alloy of at least one additional dopants. These amplifiers are connected to each other in such a manner as to provide at the receiving station the signal-to-noise ratio measured at the width of the filter of 0.5 mm, at least 15 dB for signals with wavelengths in the specified range; and as for a single signal from this range and in the presence of two or more signals having different wavelengths included in the specified range that are simultaneously fed to the input of the above amplifier, and this is done for each of these optical signals.

As the main dopant most preferred assetstudio oxides).

Most preferred is the situation where the bandwidth is in the range from 1530 to 1560 nm.

In a preferred execution of the fiber described in the present invention comprises at least three series-connected optical amplifier; at least one of them contains the active optical fiber, the core of which is doped with aluminum, germanium, lanthanum and erbium (in the form of the respective oxides).

The fifth aspect of the present invention relates to an optical amplifier in an active fiber containing

- at least one period of active fibers based on silicon

- pumping means for said active fiber, providing optical energy pumping at the wavelength of pumping,

- a means of interfacing between the specified active fiber with optical pumping and one or more transmitted signals with wavelengths within a predefined range of the transmission, characterized in that the said active optical fiber has alloy core with at least one main fluorescent dopants and at least one additional dopants, nahodyashayasa active fiber, the maximum change in gain for the two signals in the transmission at various wavelengths in the specified range, measured at an input power of -20 dBm, less than 2.5 dB.

In the preferred implementation of the main amplifier fluorescent dopants is erbium oxide, and more dopanti - aluminum, germanium and lanthanum (in the form of the respective oxides).

In particular, the above optical amplifier in an active fiber has the above-mentioned predetermined wavelength range (which was provided with the correction gain reduction) characteristic emission level which is higher than 1 dB relative to the level of emission in at least one of the related fields in the specified range, which in the preferred implementation does not exceed 0.5 dB.

The above predefined wavelength range is between 1530 and 1560 nm; more preferred is a range between 1525 and 1560 nm.

In a preferred execution of the specified active fiber has a numerical aperture of more than 0.15.

Another aspect of the present invention relates to an active optical fiber, in particular, to optical amplifiers teleko is Gavino with at least one main fluorescent dopants and at least one additional dopants, being in functional communication, through which the emission characteristic of the specified fiber in the specified range of wavelengths for pumping the fiber light energy delivered from the site with lower values (more than 1 dB compared to the emission levels of at least one of the adjacent zones in the specified range) and in the preferred implementation does not exceed 0.5 dB.

For the above-mentioned active fiber as the main fluorescent dopant most preferred is the choice of erbium (as oxide), and as an additional dopants - germanium, aluminum, and lanthanum (in the form of the respective oxides).

In a preferred execution, the content of lanthanum in the core of the optical fiber (in the form of oxide) exceeds 0.1% by mol, more preferably the content is not less than 0.2% by mole.

In a preferred implementation of the germanium concentration in the core optovoloknu (oxide) exceeds 5% and the molar ratio between the content of germanium and lanthanum (as oxides) in the core of the optical fiber is in the range from 10 to 100, more preferably the ratio is 50.

In a preferred execution, the content of aluminum in the core of the optical fiber (in the form of oxide) Anenii content of erbium in the core of the optical fiber (in the form of oxide) is between 20 and 5000 ppm to 1 mol, more preferably the content from 100 to 1000 ppm 1 mol.

In a preferred execution of the numerical aperture of the fiber exceeds 0,18.

In Fig. 1 shows a diagram of the amplifier.

In Fig. 2 shows an amplifier circuit with a notch filter.

In Fig. 3 shows a diagram of the experimental setup to determine the spectral emission curves for different types of fiber.

In Fig. 4 shows the spectral emission curves for different types of fiber obtained using the experimental setup depicted in Fig. 3.

In Fig. 5 shows the characteristics of the gain of the amplifier shown in Fig. 1, signals having different wavelengths and two different level of the source power, and fiber described in the present invention.

In Fig. 6 shows the characteristics of the gain of the amplifier shown in Fig. 2, signals having different wavelengths and three different levels of input power, and fiber described in the present invention.

In Fig. 7 shows the characteristics of the gain of the amplifier shown in Fig. 2, signals having different wavelengths and three different levels of input installation contains multiple cascades of amplifiers, which provides multiplexing of two signals with different wavelengths in one line.

In Fig. 9 shows curves characterizing the value of the binary error rate (CSD), measured using the experimental setup shown in Fig. 8. Used a variety of amplifiers.

In Fig. 10 shows the experimental scheme of the transmitting installation, containing several cascades of amplifiers, which provides multiplexing of four signals with different wavelengths in one line.

In Fig. 11 shows the power levels of the output signal of the first amplification stage in the experimental setup, shown in Fig. 10. Used amplifiers described in this invention.

In Fig. 12 shows the power levels of the signal at the output of the second amplification stage in the experimental setup, shown in Fig. 10.

In Fig. 13 shows the power levels of the signal at the output of the third amplification stage in the experimental setup, shown in Fig. 10.

In Fig. 14 shows the power levels of the signal at the output of the fourth amplifier in the pilot's actions in the pilot plant it is shown in Fig. 10.

In Fig. 16 shows the power levels of the signal at the output of the preamplifier in the experimental setup, shown in Fig. 10.

Used amplifiers known type.

As shown in Fig. 1, the amplifier is used as the amplifier optical fiber, contains one fiber optic light guide 1, doped with erbium, with a corresponding pump laser 2 associated, moreover, with dichroic connector 3; one optical gate 4 is located to the optical fiber 1 (amplified signal), whereas the second optical valve 5 is located after the active fiber of the fiber.

Usually (but not necessarily) dichroic connector 3 is located after the active fiber (as shown in the figure), providing the pump energy in a counter signal.

The amplifier also includes a second erbium doped optical fiber, the optical fiber 6, which is connected with the corresponding pump laser 7 through dichroic connector 8, which in the given example is also connected to a source of pumping in vstrechnoy direction, thus, the optical valve 9 is located after the fiber optic light guide 6.

Lasers of this type are produced, for example, a company LASERTRON INC., 37, North Avenue, Burlington., MA (US).

Dichroic connectors 3, 8 are made by melting the optical fiber of single mode fiber with a wavelength of 980 nm and a bandwidth of 1530-1560 nm. Fluctuations of the output power < 0.2 dB depending on polarization.

Dichroic connectors of the aforementioned type are well known and common in the market. For example, they are issued by companies GOULD Inc., Fibre Optic Division, Baymeadow Drive, Gelm Burnie, MD (US) and SIFAM Ltd., Fibre Optic Division, Woodland Road, Torguay, Devon (GB).

The optical valves 4, 5, 9 control of polarization does not depend on the polarization of the transmitted signal. They are characterized by the parameter isolation greater than 35 dB, and a reflectivity less than 50 dB.

Used valves models MDL 1-15 PIPT-A SIN 1016 company ISOWAVE, 64 Hording Avenue, Dover, New Jersey, US.

In Fig. 2 is a diagram of an alternative implementation of the amplifier, in which corresponding elements have the same numbers as in Fig. 1.

In this amplifier, the elements which perform the same functions as in the amplifier, opiasaniye optical path of the core of two types. One of them is coaxial relative to the connected to the filter fiber optic cable and the other is shifted relative to the center and cut edges. The detailed description is given in the patents EP 441211 and EP 417441 used in this work as reference material.

This filter shall be of such dimensions to provide communication with an offset relative to the center core for wavelengths corresponding to the part of the emission spectrum of the amplifier; boundary cutoff offset from the center core provides the scattering of trapped radiation in the shell fibers, interrupting communications with the main core.

In the above example dvuhseriynyy filter 10 has the following characteristics: wavelength range for which you provided the link in the second core BW (-3 dB) - 8-10 nm; filter length - 35 mm

The filter size is selected in such a way that provides maximum attenuation of the peak emission of the active fiber.

Alternatively, in the conducted experiments we used filters with the following characteristics: attenuations1530 nm to 5 dB or weakening ins1532 nm - 11 dB.

This filter is designed to henia fiber, with the aim of obtaining the maximum possible constant (or "flat") characteristics of the amplifier gain for different values of the wavelength.

This requirement is especially important for tasks OM - transfer where you need the most uniform gain for each channel.

In the above amplifiers have been used various types of active fiber doped with erbium. Their composition and optical characteristics shown in the table.

The composition analysis was carried out at the preliminary stage (before pulling the fiber) using the electron microprobe in combination with scanning electron microscope (SEM Hitachi).

The analysis was conducted at 1300 increases at discrete points along the diameter and separated from each other by 200 ám.

Mentioned fibers were made by the method of vacuum metallization in the tube made of quartz glass.

In the above-mentioned fibers introduction Germany as dopant in the matrix SiO2in the fiber core was produced in the synthesis phase.

Introduction erbium, aluminium oxide and lanthanum into the fibers produced by the method of "doping solution," in which an aqueous solution of chloride dopant contact is.

In more detail, the method of doping the solution described, for example, in U.S. patent 5282079, which is used in this work as reference material.

The greater the value of the numerical aperture (CHA) in A fiber compared with other fibers was caused by the fact that in the manufacture of fiber core was not made modification of the liquid reagent used in the manufacture of fiber C (Al/Ge/Er), in particular, was not made to seal the source of Germany.

Thus, the consistent introduction of lanthanum and aluminum by the method of doping the solution leads to a higher value of refractive index than expected. In addition, there are other unexpected improvements in amplification and transmission, which will be described later.

In Fig. 3 shows a diagram of the experimental setup to determine the spectral emission curves for different types of fiber: spectral emission curves measured for active fibers A, B, C, D, shown in Fig. 4.

The laser diode pump 11, operating at a wavelength of 980 nm, was connected through a dichroic connector 12 (wavelength 980 nm, band width 1550 nm) to the active Testov">

The laser diode 11 had a capacity of about 60 mW (optical fiber 13). The active fiber 13 had a length corresponding to the effective gain for the selected power pump; for the studied fibers, each of which had the same content of erbium, this length corresponded to 11 PM

For fibers with different content of erbium appropriate length may be determined based on known criteria.

Optical spectrum analyzer was a model TQ8345 company ADVANTEST CORPORATION, Shinjuku - NS Bldg. 2 - 4-1 Nishi Shinjuku, Shinjuku - ku Tokyo (JP).

The measurements were carried out by pumping the fiber radiation with a wavelength of 980 nm; recorded spectrum of the spontaneous emission fiber.

The results obtained are shown in Fig. 4, where curve 15 corresponds to the fiber A, the curve 16 - fiber B, the curve 17 - fiber C and the curve 18 - fiber D.

As follows from these graphs, the spectrum emission for fibers B, C, and D has a main peak intensity at a wavelength of 1532,5 nm and the subsequent zone of high emission in the region of large wavelengths up to about 1560-1565 nm, which includes the second strongly broadened peak.

A comparative analysis of the curves 16 and 17 (fiber B and C, respectively) shows that more slotno D, curve 18) leads to higher levels of radiation in the range 1535-1560.

On the other hand, for all fibers B, C, and D reducing emissions was observed in the spectrum d (located approximately between 1535 and 1540 nm) between the primary and the second emission peak; in this area the level of emissions below the maximum level in adjacent areas (including primary and second peaks) at least 2 dB. It is marked on the figure by a link h to the curve 16 and well seen for the curves 17 and 18.

On the contrary, from the curve 15 it follows that in these experimental conditions for fibers in A zone d does not have a significant decrease in the level of radiation (or where it is still visible, it is in all cases below 0.5 dB).

In addition, the curve 15 shows that the maximum emission for A fiber occurs at lower wavelengths than for fibers B, C, and D. This maximum is approximately 1530 nm; fiber has a high level of emissions, up to 1520 nm.

Amplifiers, the circuit of which is shown in Fig. 1 and 2, were produced on the fiber A.

The first active fiber fiber 1 was about 8 m in length, while the second active fiber 6 had a length of about 15 and 13 m, respectively, for usilitel two different power levels of the input signal to the amplifier, it is shown in Fig. 1. In Fig. 6 shows the characteristics of gain at different wavelengths for three different power levels of the input signal for the amplifier shown in Fig. 2.

In particular, the curve 19 in Fig. 5 corresponds to the input of the power amplifier shown in Fig. 1, equal to -20 dBm, while the curve 20 corresponds to the input power of -25 dBm.

In turn, the curve 21 in Fig. 6 corresponds to the input of the power amplifier shown in Fig. 2, is equal to - 20 dBm, while curve 22 corresponds to the input power of 25 dBm, and curve 23 - 30 dBm.

As follows from these figures, in particular from a comparison of the curves 19 and 21, corresponding to the power level of 20 dBm, which is especially interesting for your communications needs, both in the absence and in the presence of a filter using a fiber with a core alloy (in addition to erbium) oxide, germanium and lanthanum, leads to substantial alignment of gain characteristics, especially in the area between 1536 and 1540 nm. This result is achieved in the absence of the filter.

In particular, in the absence of a filter at -20 dBm, the difference in gain between signals with different wavelengths was less than 1.6 dB, and the gain of the amplifier, it is shown in Fig. 2 and made of fiber C (Al/Ge/Er), for signals having different wavelengths and three different levels of input power.

In particular, the curve 24 in Fig. 6 corresponds to the input signal power equal to - 20 dBm, curve 25 corresponds to a power of 25 dBm, and curve 26 - 30 dBm.

At -20 dBm, the difference in amplification for signals with different wavelengths was about 2.1 dB.

The comparison of the obtained results allows us to conclude that the use of fiber A (Al/Ge/La/Er) in the amplifier without filter results in a much more uniform gain characteristic than using fiber C (Al/Ge/Er) in the amplifier with a filter.

Have performed experiments on the transmission of signals over long distances. Use the amplifiers shown in Fig. 1 and 2, made of either fiber A (Al/Ge/La/Er), or from fiber C (Al/Ge/Er) connected in a cascade configuration, i.e. sequentially. One of the used experimental setups shown in Fig. 8.

The first and second signals 27, 28 with wavelengths1= 1536 nm and2= 1556 nm was applied through the multiplexer 30 to the fiber optic light guide 29.

The first attenuator 31 is placed after the amplifier 32a; celebrites 32, 32', 32", 32"'.

The receiver 33 is placed after the optical demultiplexer 34 containing an interference filter with a bandwidth of 1 nm at 3 dB, which was carried out breeding recorded signal.

Signals 27, 28, generated by the respective laser had a power of 0 dBm each; total power, switched the light guide 29, was 0 dBm (taking into account losses in the connecting links is 3 dB).

The multiplexer 30, which was the "switch 1x2", was manufactured by E-TEK DYNAMICS INC., 1885 Lundy Aven., San Jose, GA (US).

The amplifier 32a was a fiber amplifier, which is a commercial product and has the following characteristics: input power of -5 to +2 dBm; output power -13 dBm; working wavelength 1530-1560 nm.

This amplifier had no notch filter.

Model was used for TPA/E-12, available from the applicant. The amplifier contains the active fiber type C, doped with erbium (Al/Ge/Er).

It was assumed that the power amplifier operates in saturation mode, in which output power is directly dependent on the pump power, which is described in detail in the patent EP 439867, the underside of the amplifier 32 total optical power of approximately - 18 dBm.

Quality attenuators 31 was used devices company JDS FITEL INC., 570 Heston Drive, Nepean (Ottawa), Ontario (CA) model Va5. Each attenuator is provided attenuation corresponding to approximately 100 km of fiber.

Amplifiers 32, 32', 32", 32"' were identical and each of them provided a gain of about 30 dB at both wavelengths2,3when the total output power of +12 dBm.

The signal 27 with wavelength = 1536 nm was directly modelirovaniya at 2.5 Gbit/s, were generated HGV laser forming part of SDH terminal model SIX-1/16, manufactured by Philips of the Netherlands BV, 2500B, Gravenhage 6 (NID), with receiver 33.

The signal 28 with a wavelength of = 1556 nm there is a continuous signal (SHF) and were generated in the system by laser model MG094813 at a power level of 0 dBm, manufactured by the Banks of Corporatian, Minato-ku 5-10-27, Tokyo, Japan. Used interference filter 34 model TB4500 produced by the aforementioned firm JDS of Fitel, Inc.

Experiment 1.

In the first experiment were used amplifiers for fiber A (Al/Ge/La/Er), the scheme of which is shown in Fig. 1 and in which there is no notch filter 10.

Experiment 2.

In this experiment we used the amplifiers n the UNT (frequency) error bit in the amplifier 33 was measured by the change in the average received signal power with wavelength 1(1536 nm).

The experimental results shown in the graph of Fig. 9, where the curve 35 refers to the experiment 1, and curve 36 to experiment 2.

As shown in the graph of Fig. 9, the gain of a single amplifier fiber A (Al/Ge/La/Er), equipped with a notch filter, is precisely the same and even more uniform, as the amplifier fiber without A notch filter 10 and with cascading enabled, the signal with a wavelength of 1536 nm has a significantly higher error rate in bits with equal received power.

Experiment 3.

The second experimental scheme is shown in Fig. 10. There are four test signal 37, 38, 39, 40 wavelengths = 1536 nm, = 1556 nm, = 1550 nm and = 1544 nm served on the fiber 41 through the wave multiplexer 42.

The level of the input signal is regulated by predevaluation (corrector) 43. With the power amplifier 44, the signals are fed into the tract containing four linear amplifier 45, 45', 45", 45"', between which enabled attenuators 46 to simulate a length of optical fiber.

The receiving device includes a preamplifier 47, the optical demultiplexer 48 and the receiver 49.

Signals are generated respectively PGV laser (with u is to them in the terminal, representing the receiver 49; DFB laser with a wavelength of 1556 nm with a continuous emissions produced by the BANKS; the DFB laser with a wavelength of 1550 nm and a continuous emission, also manufactured by the BANKS; ECL laser (with emitter connections) with variable wavelength, pre-installed on a wave of 1544 nm, with a continuous emissions model HP81678A manufactured by Hewlett Packard, Raquel (USA).

Prerequisites 43 consists of four attenuators manufactured by JDS, in which the attenuation is determined depending on the optical power of the respective channel.

The multiplexer 42 is made on the splitter 1x4 manufactured by the above company E-TECH DYNAMICS.

The amplifier is a model TPA/E-13, commercially available and supplied the above mentioned suppliers.

Amplifiers 45, 45', 45", 45"' identical to each other and each has a gain of about 30 dB when the total output power of +12 dBm.

Diagram of the amplifier shown in Fig. 1; they are built on the fiber A (Al/Ge/La/Er).

Each of the attenuators 46 provides attenuation of 30 dB, which corresponds to a fiber length of 100 km

It uses optical attenuators model VA5, is adage preamp, has the following characteristics: gain is 22 dB; noise factor of 4.5 dB; output power from -26 to -11 dB; operating wavelength - 1530-1560 nm.

Here we have used the model RPA/E-F, freely sold by the Supplier and is built on the active fiber C (Al/Ge/Er).

The preamplifier is intended for the reception of signals with a very low level (for example, -50 dB) and the gain to the level of power (up to feed on the receiving device), providing the necessary amplitude-frequency characteristic.

The optical demultiplexer 48 is a tunable filter, Fabry-Perot, with a bandwidth of 0.8 nm -3 dB, included in the preamplifier 47.

During the experiment the filter Fabry-Perot was configured at wavelength = 1536 nm (called the critical wavelength) pilot-tone signal, which is generated by the transmitter 37.

The receiver 49 is a SDH terminal device model SIX-1/16 sold by Philips of the Netherlands BV, 2500B, Gravenhage (NID.).

In Fig. 11 to 15 illustrate the behavior of signals in successive stages, in particular at the inputs of the amplifiers 45, 45', 45" and 45"', respectively, and also at the input of the preamplifier 47.

This correction was carried out in such a way that it is ensured alignment optical signal-to-noise ratio at the output of the preamplifier 47.

In successive amplification stages can be observed that the lower level of the gain curve in the range of small wavelengths due to the above-mentioned effect of saturation, whereas the optical signal-to-noise ratio in each channel remains high (With/S dB at = 0.5 nm) to the output of the preamplifier 47.

When the experiment was conducted with the use of amplifiers in the circuit of Fig. 2, having an active fiber type C and the notch filter, it was found a significant decrease of the signal power on the waves 1536 and 1544 nm and a strong detuning of the optical signal to noise between different channels, as can be seen from the graph of Fig. 16, which shows the power of signals in different channels at the input of the preamplifier; even more significant deterioration detected in the channel with wavelength = 1540 nm.

In this case, the pre-correction would reduce the imbalance between the channels is abotut on the waves 1535 and 1540 nm); however, when such correction is not in all cases possible to achieve acceptable signal-to-noise ratio for all signals within the operating range of wavelengths. So, to enable this correction channels would have to be set very high initial weakening of the most important channels (C = 1550 and 1556 nm), which would have led to very low values of the ratio signal/noise (of the order of 8-10 dB) that will make it impossible for high-quality reception of signals.

Better results are achieved when using amplifiers with notch filter and an optical fiber of the Al/Ge/Er, the reason why consider the fact that the fiber has A curve issue, practically free from decay or local minima of considerable size, and in particular from a minimum in the wavelength range close to the peak emission wave 1535-1540 nm.

In fact, it is believed that when multiple signals with different wavelengths at the same time served in the fiber, the presence of decay or local minimum in the curve of the emission is clearly present in the spectrum in contrast to other fibers with which comparison is made) causes low gain signals corresponding to such downturns, compared with signals which drove at wavelengths adjacent ranges recovers the energy of the pump to the signal, which is saturated at low output value (i.e., this level after amplification no longer depends on its input values, and only depends on the pump power, is present in the fiber, which leads to increments of the difference between the levels of different signals).

In the case of cascaded amplifiers and broadband transmission mode such effect increment takes place in each stage and believe that is the reason appears to irregularities in the frequency response, which can not be compensated by pre-correction or other methods mentioned above.

It was noted that the above-mentioned effect takes place for signals on the decay curve of the emission due to competition amplification of the signals at wavelengths adjacent to the waves on the decline, while he (the effect) is not in respect of signals with wavelengths that lie on the boundaries of the useful range (at least to a certain extent), although at such wavelengths the amount of emission can be completely the same or lower than the amount mentioned downturn.

In accordance with the present invention the introduction of Al/Ge/Er fiber resulted in an unexpected decrease of such a local minimum emissions, although this Al/La/Er, and Al/Ge/Er fiber have a significant drop in emissions in waves 1535-1540 nm, and therefore on the basis of information about the parameters of such well-known fibers would have to be excluded the conclusion that the useful aspects of the behavior of fiber Al/Ge/La/Er, but at the same time, such a fiber would be able to provide a multiplex transmission with signal amplification at a certain wavelength.

However, unexpectedly, in accordance with another and even more important aspect was revealed that the presence of a peak inside area with high emission of the existence of the mentioned decline near this peak, or in any case when the functional relation (negative) with adjacent areas has been the cause of not enough high values of signal-to-noise ratio for signals related to this recession, and that the active fiber finds its inherent ability to eliminate or reduce this decline, it helps to solve the problem of providing broadband in the presence of one or more amplifiers.

Therefore, in accordance with the present invention it was found that the active fiber, dopanti which provide emission curve with a relatively high level in the frequency band, mainly loose the Oh band (that would be the cause of the significant difference of the communication signals at different wavelengths within the said band of wavelengths, multiplexing in the fiber), allows the formation of amplifiers, especially suitable for use in a line containing at least two series-connected optical amplifier with frequency division multiplexing signals, which ensures high performance.

In accordance with another aspect of the present invention it was found that the control signal-to-noise considered here the transmission systems can be carried out not only by the use of filters or assumptions narrowed frequency band of transmission signals (which allows you to avoid including unwanted areas of wavelengths), but also by selecting dopant and its dosage in the body of the active fiber amplifier, allowing the curve of emission can be concentrated in a fairly wide band (i.e., expanded to 1526-1560 nm, or at least until the 1530-1560 nm), without lifting amplify the signal to an undesirable level in one or more specific areas of the curve issue, although it has a peak emission in the band.

In functional terms it is considered that, as already explained above, the presence of high-emission areas adjacent to the tion of the signal amplification at wavelengths, corresponding to such a decline.

In relation to the emission (or spectral) curve, with relatively high values, believe that in this band the fiber has an issue, the value of which exceeds the emission outside this band, providing increased signal in said band; in the form of indicator such zone is defined as the area enclosed between two boundary values at which the emission of 3 dB lower than at the wavelength enclosed in this interval or band (preferably in almost constant zone interval). In fact, this band corresponds to the area in which may be received useful gain.

In the peak emission believe its amount of emission in the wavelength range, which is much higher than in areas of the spectrum outside this range, the result is a different nature of the signals supplied to the optical fiber at wavelengths both inside and outside this range.

As for the differences in acceleration, it is considered that matters of differences of more than 2 dB between the signals on the most important and less important wavelengths in a specified band (when input power is equal to or less than - 20dBm).

Otnositel, in which there is a secondary minimum of emission, the value of which is less than the value of emission on any of the boundaries of the above-mentioned range, and a value less than the given value, the maximum values of the emission in a continuous wavelength ranges (in particular, as the main peak of the erbium emission at wavelengths below downturn, and a secondary peak at higher wavelengths), according to the present invention it is also believed that given the magnitude of the decline, which is more than 0.5 dB, in particular greater than 1 dB, leads to noticeable effects.

It was also found that in the linear amplifier used in the system, has a number of cascaded amplifiers, the use of a notch filter, which can reduce the intensity of the main peak of emission by education largely flat gain curve of the individual amplifiers is not possible to avoid the above described effect.

In fact, the notch filter in the circuit, which includes several cascaded amplifiers is attenuating element working in the area of the working strip, lying below the center, and the effect produced by them, inevitably expands towards the zone of emission decay curve; this effect oslableniyu in the zone of recession or local minimum.

The use equivalent to the filter means to weaken or otherwise to limit the emission main peak, such as described in patent EP 426222, does not lead to significant differences in performance.

Finally, in accordance with the present invention should the content of lanthanum in the body of the fiber in the preferred amount of more than 0.1% by mol and the content of germanium in the amount of more than 5% by mole, and the ratio Ge/La is preferably maintained at a level of 50 (but in any event within 10 to 2100).

The presence of lanthanum in the fiber allows to increase the content of germanium and aluminum, which results in a large numerical aperture (>0.18 and preferably not less than 0.2), which leads to an important advantage from the point of view of efficiency gain and a more uniform amplitude-frequency characteristics in the working band.

In addition, the presence of lanthanum allows to increase the content in the fiber erbium without increasing effect of inclusions, the content of erbium can reach from 20 to 5000 ppm, and even more, but preferably from 100 to 1000 ppm.

When detailed consideration in respect of the use of linear amplifiers of the amplifier, designed for a signal of very low intensity (for example, -50 dBm) and gain it before feeding it to the receiving device.

In addition, it should be noted that although there has been described a two-stage amplifiers using two serial and separately pumped pieces of active fiber, in accordance with the present invention it can also work and single-stage amplifiers, for example, corresponding to the diagrams mentioned in the patents EP 426222 and EP 439867, amplifiers, differing from each other in type, such as single-stage and two-stage amplifiers can be used together in the same scheme. In addition, when there are special requirements in dual-stage amplifiers one of them can be performed on the optical fiber according to the present invention.

On the other hand, a specialist in the art, taking into account the above considerations, will be able to determine the specific operating conditions and the specific content of dopant, appropriate to the intended application to achieve the required characteristics.

When using the present invention by a specialist working with fibers provided is in the desired wavelength range, will be able in combination with a secondary gopastami, interacting with each other, to define a specific dopant and their dosages to obtain the desired shape of the curve of the emission fiber and the corresponding performance of amplifiers and amplifier systems (lasers, optical horoscopes and so on), as well as obtain the necessary signal-to-noise ratio in the operating frequency band.

For a particular area of technology that is of interest to the Applicant, he was limited to case studies of the use of erbium as the main dopant and germanium, aluminum and lanthanum, are introduced into the fiber in the form of their oxides, as secondary dopants, because the results of these studies were sufficient to solve technical problems.

The information contained in the present description of the invention, can be used by persons of average skill to solve interesting problems, which may be similar to or different from those described above, provided that they have the same technical basis, by the investigations of various dopants or their specific dosages, using the results of experiments described here, as well as functional relationships between reconcile to abandon individual dopants or combinations of them, if, when examined separately, they give unsatisfactory results in systems that contain them, from the point of view of the signal-to-noise ratio, because some combinations can result in higher performance, which can be seen on the example of the present invention.

1. The way to ensure control of the optical signal/noise ratio at the reception in a predetermined wavelength range in the optical telecommunication system containing an optical transmitter for transmitting at least two signals of different wavelengths, prisoners in the specified wavelength range, optical receiver, fiber optic line connecting the specified transmitter and receiver to send these at least two signals, and at least one optical amplifier in an active optical fiber located along a specified line, and the specified active fiber has a curve emission area with high emission in the wavelength range, includes the specified predefined wavelength range, within which there is a decline in emissions compared with adjacent areas, characterized in that eliminate or reduce the specified emission decay curve by selecting and dispensing alloying Parmesan choose between 1530 and 1560 nm.

3. The method according to p. 2, wherein the pre-defined area wavelengths choose between 1525 and 1560 nm.

4. The method according to p. 1, characterized in that the ratio of the optical signal/noise ratio of more than 15 dB, measured with a filter with a bandwidth of 0.5 nm.

5. The method according to p. 1, wherein the telecommunications system includes at least two optical amplifier in an active optical fiber arranged in series along the specified fiber-optic lines.

6. The method according to p. 1, characterized in that the fiber is chosen basic fluorescent doping impurity and at least one additional alloying impurity interacting with the main alloying an impurity in the glass lattice of the active fiber to reduce the decline in emissions to values less than 1 dB with respect to the value of emission in at least one of the adjacent zones in the above-mentioned range.

7. The method according to p. 6, characterized in that as the main dopant choose erbium in the form of its oxide and at least two additional dopant, interacting with the main alloying impurity in the body of the active fiber.

8. The method according to p. 7, characterized in that as the - Armani, aluminum, and lanthanum in the form of their oxides, interacting with the main alloying impurity in the body of the active fiber.

9. Method of optical telecommunications, which generate at least one optical signal with a predetermined wavelength in a wavelength range serves this signal in optical fiber optic telecommunications, amplify the optical signal at least once at least one optical amplifier in an active fiber and accept the said signal receiver, wherein the active optical fiber at least one of the optical amplifiers contains basic fluorescent doping impurity and at least one additional alloying impurity, which interacts with the main alloying an impurity in the glass lattice of the active optical fiber, thus amplify the optical signal at a given wavelength optical amplifier in an active optical fiber, measure the input power, which is -20 dBm, the gain differs less than 1.6 dB from the corresponding amplification of the signal at a different wavelength in the above range in the absence of filtration media.

10. The method of optical Telecom band, served this signal in fiber optic telecommunications, amplify the optical signal at least once at least one optical amplifier in an active optical fiber, signal receiver, wherein the at least one optical amplifier in an active fiber contains the active fiber silicon-based body, which enter at least one main fluorescent doping impurity and at least one additional alloying impurity, which is chosen and dosed so that the ratio of the optical signal/noise ratio in the receiver, the measured filter with a bandwidth of 0.5 nm, has a value of at least 15 dB for signals with a wavelength included in the range.

11. The method according to p. 10, characterized in that the ratio of the optical signal/noise ratio in the receiver, the measured filter with a bandwidth of 0.5 nm, has a value not less than 15 dB in the presence of at least two signals with different wavelengths, which simultaneously serves on the amplifier that applies to each of the optical signals.

12. The method according to p. 9 or 10, characterized in that it includes the steps of amplifying an optical signal at least twice the corresponding optical>13. The method according to PP.9 and 10, characterized in that the operating range of wavelengths choose between 1530 and 1560 nm.

14. The method according to p. 13, characterized in that the operating range of wavelengths choose between 1525 and 1560 nm.

15. The method according to p. 9 or 10, characterized in that the optical amplifier in an active fiber contains erbium as the primary dopant and at least two additional dopant, which interact with the main alloying impurity.

16. The method according to p. 15, characterized in that as an additional dopants, which interact with the main alloying impurity, choose aluminum, germanium and lanthanum in the form of their oxides.

17. The telecommunications system containing a transmitting station, generating optical signals in a predetermined wavelength range, a receiving station, fiber optic connection line between the transmitting and receiving stations, at least two of the optical amplifier in an active optical fibers, connected in series to a communication line and connected to each other for transmission of optical signals from the transmitting station to the receiving station, wherein at least one of the optical amplifiers crescenta alloying impurity and at least one additional alloying impurity, moreover, the amplifiers are connected to each other and configured to provide at the receiving station the optical signal-to-noise ratio, as measured by the filter with a bandwidth of 0.5 nm and having a value not less than 15 dB for signals with wavelength, a member of the working range.

18. The system under item 17, characterized in that the ratio of the optical signal/noise ratio at the receiving station, the measured filter with a bandwidth of 0.5 nm, has a value not less than 15 dB in the presence of at least two signals with different wavelengths within the operating range simultaneously supplied to the amplifier for each signal.

19. The system under item 17, characterized in that the main alloying impurity is erbium in the form of its oxide.

20. The system under item 17, wherein the additional alloying impurities are aluminum, germanium and lanthanum in the form of their oxides.

21. The system under item 17, characterized in that the specified transmission range selected between 1530 and 1560 nm.

22. The system under item 17, characterized in that the at least three optical amplifier connected in series in the connection line.

23. The system according to p. 22, characterized in that at least one of the cascaded lanthanum and erbium in the form of their oxides.

24. Optical amplifier in an active optical fiber containing at least one active segment fibers based on silicon, a means of pumping the active fiber made with the possibility of input optical power and the pump wavelength of the pump, the connecting means for the optical power of the pump in the active optical fiber and one or more transmission signals with the wavelengths of the transmission within the transmission range, wherein the active fiber contains at least one main fluorescent alloying additive and at least one additional alloying additive associated functional relationship with each other to such an extent, the difference in gain between the two signals having different wavelengths transfer within the above range, measured at an input power of -20 dBm, is less than 2.5 dB in the absence of filtration media related to the active fiber.

25. The optical amplifier according to p. 24, characterized in that as the main fluorescent dopant selected erbium in the form of its oxide.

26. The optical amplifier according to p. 25, characterized in that as an additional dopants wybranie has a curve issue without falling in a given range of wavelengths, which would exceed the 1 dB relative value of emission in at least one of the adjacent zones in this range.

28. The optical amplifier according to p. 27, characterized in that the curve of the issue is busts size is not more than 0.5 dB with respect to the value of emission in at least one of the adjacent zones of the given range.

29. The optical amplifier under item 24, wherein the specified wavelength range of the transmission is selected between 1530 and 1560 nm, preferably between 1525 and 1560 nm.

30. The optical amplifier according to p. 24, characterized in that the active fiber has a numerical aperture of more than 0.15.

31. The optical amplifier according to p. 24, characterized in that it contains two active optics based on silicon, with corresponding pumping means, at least one of which contains at least one main fluorescent dopants and at least one of the additional dopants that are functionally associated with each other to such an extent that differences in maximum gain between two signals with different wavelengths of transmission, measured at an input power of -20 dBm, does not exceed 2.5 dB in the absence of filtering that is associated with Pro-active, characterized in that it has a numerical aperture of more than 0.15, and contains at least one main fluorescent doping impurity and at least one additional alloying materials, functionally related to each other, in this case the curve of the emission fiber in a predetermined wavelength range in the presence of pump light energy supplied to the fiber, has no drops bigger than 1 dB relative value of emission in at least one of the neighboring zones of the given range.

33. Active fiber under item 32, characterized in that the curve of the issue is busts size is not more than 0.5 dB with respect to the value of emission in at least one of the adjacent zones of the given range.

34. Active fiber under item 32, characterized in that as the main fluorescent dopant selected erbium in the form of its oxide.

35. Active fiber by p. 34, characterized in that as an additional dopants selected aluminum, germanium and lanthanum in the form of their oxides.

36. Active fiber by p. 34, characterized in that the content of lanthanum in the body of the fiber in the form of its oxide is more than 0.1% to 1 mol.

37. Active fiber by p. 35, ex is 38. Active fiber by p. 34, wherein the content of germanium in the body of the fiber in the form of its oxide is 5% to 1 mol.

39. Active fiber on p. 38, characterized in that the molar ratio of the content of lanthanum to the content of germanium in the form of their oxides in the body of the fiber is 10 to 100.

40. Active fiber on p. 38, characterized in that the molar ratio of the content of lanthanum to the content of germanium in the form of their oxides in the body of the fiber is about 50.

41. Active fiber by p. 34, characterized in that the aluminium content in the form of its oxide in the body of the fiber is more than 1% per 1 mol.

42. Active fiber by p. 41, characterized in that the aluminium content in the form of its oxide in the body of the fiber is more than 2% on 1 mol.

43. Active fiber by p. 34, characterized in that the content of erbium in the form of its oxide in the body of the fiber is 20 to 5000 ppm 1 mol.

44. Active fiber on p. 43, characterized in that the content of erbium in the form of its oxide in the body of the fiber is 100 - 1000 ppm 1 mol.

45. Active fiber by p. 34, characterized in that the fiber has a numerical aperture of more than 0.18.

 

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