CN110289539A - A Broadband Multidimensional Optical Fiber Amplifier - Google Patents

Abstract

The invention discloses a kind of broadband multidimensional fiber amplifiers, are mainly used in space division multiplexing communication system.It includes signal input port, pump ports, WDM, fan-in bundling device, the clad doped rare earth doped fiber of multidimensional mono-/bis-is fanned out to bundling device, and long-period fiber grating is formed by combining.Present invention mainly solves the signals of multi-core optical fiber transmission line to relay scale-up problem.Multi-core optical fiber can be again introduced into using the amplified signal of technical solution of the present invention to be transmitted, until signal is downloaded or reaches receiving end.There is good compatibility using the Transmission system of this amplifier construction, it is at low cost, the characteristics of dilatation good reliability.

Description

A Broadband Multidimensional Optical Fiber Amplifier

(1) Technical field

The invention relates to an optical fiber amplifier in the field of space division multiplexing in optical fiber communication.

(2) Background technology

The research on space division multiplexing technology started from Japan. Space division multiplexing technology has rapidly increased the capacity of optical fiber communication from Tb/s to Pb/s, laying a technical foundation for future optical fiber communication. According to literature reports, in 2015, B.J.Puttnam et al. reported that a 2.15Pb/s signal was transmitted in a 22-core optical fiber, and the transmission distance was 31km, breaking the world record for the transmission capacity of a single optical fiber. But no one has reported a 22-core erbium-doped fiber amplifier. The current research mainly focuses on the 7-core erbium-doped fiber amplifier. The pumping and signal fan-in/fan-out are performed by the tapered fiber coupler. Since the tapered fiber coupler matches the mode field, the insertion loss of the fiber fusion is reduced, and the The practicability of the multi-core fiber amplifier is improved. Erbium has a main emission peak at 1530nm, and its amplification in the C band is a very mature technology. However, L-band signals are also used in existing transmission systems. At the same time, due to the development of optical fiber manufacturing technology, the current optical fiber has completely eliminated the loss of the water peak near 1385nm, so that the communication window can be further extended to the S-band. It is still difficult to realize the optical fiber amplifier across three communication bands in space division multiplexing technology. The current amplifier has the problem of uneven gain of multi-channel signals, and the bandwidth of the amplifier is not large enough, which limits the number of wavelength division multiplexing channels.

Patent CN104051937A discloses a high-power multi-core fiber laser, which is composed of fiber coupler, doped fiber, fiber grating and so on. The function it realizes is to obtain high-power optical fiber laser, which does not involve broadband spectral output, and the multi-core optical fiber of this patent is not doped with various rare earth materials.

Patent CN101719621A discloses a high-power multi-band multi-core fiber laser, which is characterized in that a fiber reflection grating is loaded at both ends of a multi-core multi-doped fiber or a high-reflectivity film is coated on the end face of the fiber to form a A fiber resonator to increase the pumping efficiency of the pump light. This patent does not adjust the flatness of the output spectrum, and its reflective grating is mainly used for frequency selection.

Patent CN101771233A discloses a high-power multi-band multi-layer rare earth ion doped ring core laser, which is characterized in that the optical fiber is composed of multiple layers of different doped materials, and different rare earth ions are excited in different layers. In addition, a fiber grating or a fiber end reflective film for pump light is loaded at both ends of the fiber to achieve the function of improving the pumping efficiency, but it does not adjust the flatness of the output spectrum.

Patent CN104035166A discloses a high-power laser beam combiner based on multi-core optical fiber. This patent realizes the beam combining function of multiple laser signals. Compared with this patent, there is no doping of various materials. The realized function is to combine multiple beams in the multi-core fiber to obtain a high-power output beam. , there is no corresponding adjustment and processing for the output spectrum.

Patent CN205122987U discloses a multi-core fiber laser, which consists of an NX1 fiber pump coupler, a multi-core active fiber, and a multi-core fiber grating. From the perspective of mechanism, the multi-core active optical fiber of this device does not involve a variety of rare earth ion doping, and does not mention broadband amplification and gain flatness.

Patent CN103682961A discloses an ultra-broadband fiber optic light source system and a method for realizing a fiber optic light source. The patent combines erbium-doped and bismuth-doped active optical fibers to obtain a broadband ultra-fluorescent light source. This patent uses two sets of active optical fiber pumping structures, and its device integration is insufficient, and it does not design for spectral flatness, nor does it reveal the theoretical problem of crosstalk using multi-core optical fibers.

Patent CN200320112294.4 discloses an ultra-broadband optical fiber light source, which includes an optical fiber, a semiconductor laser, an optical isolator, an erbium-doped optical fiber, a reflector, and a wavelength division multiplexing coupler. Structurally, the patent uses forward pumping and backward pumping and mirrors to increase pumping efficiency. The flat range of the output spectrum is 65nm. The patent innovates on the structure of the amplifier, but does not involve innovations in doping and multi-core amplification.

Patent CN201310560042.6 discloses an ultra-broadband light source based on co-doped erbium, thulium and neodymium. The optical fiber in this patent is prepared by co-doping three rare earth elements of erbium, thulium and neodymium. Through the excitation of pump light, an ultra-broadband light source based on spontaneous emission is generated. The broadband output light wave has a wavelength range of 1280nm-1625nm, which has no corresponding design for spectral flatness, and only has a single fiber core in structure. This patent does not disclose the crosstalk problem of using multi-core optical fiber, and does not consider the problem of high gain.

Patent CN201380044137.0 discloses a multi-core optical fiber amplifier. It describes the function of a multi-core doped optical fiber that can achieve amplification under the action of pump light. It can realize multi-core amplification and multi-mode multi-mode amplification. However, this patent does not reveal the problem of multi-core optical fiber crosstalk, does not disclose the mechanism of doping rare earth elements to obtain a broadband amplification effect, and does not use gain flattening technology.

To sum up, in order to solve the relay amplification problem of the transmission system combining space division multiplexing and broadband wavelength division multiplexing, it is necessary to overcome the problem of crosstalk, broadband amplification and gain flatness, etc., and there is no existing solution in the current technology , therefore, how to realize broadband multi-dimensional fiber amplification is an urgent problem to be solved.

(3) Contents of the invention

The purpose of the present invention is to manufacture a broadband multi-dimensional optical fiber amplifier, which is mainly used in space division multiplexing communication systems. It adopts a multi-core design, and each core is co-doped with one or more oxides in ZrO ₂ /SbO ₂ /Yb ₂ O ₃ /Al ₂ O ₃ /La ₂ O ₃ /Er ₂ O ₃ , the doping concentrations of different cores are strictly the same. This design is to hope that the signal gain generated under the same length is basically the same after passing through the long-period fiber grating. The signal enters from the input port and is input to the multi-core rare earth-doped fiber through the fan-in beam combiner. At the same time, the pump light is also coupled to the multi-core rare-earth-doped fiber through the fan-in beam combiner. The multi-core rare earth-doped fiber is connected to the fan-out beam combiner. It is followed by a long-period fiber grating and other combinations. There are two schemes for the whole system: scheme one is a multi-core double-clad rare-earth-doped fiber, which has N-1 cores and no core in the center, which is only used as the pump energy receiving end. N-1 signal lights are connected to the multi-core double-clad rare earth-doped optical fiber through a fan-in beam combiner with N-1 cores (the center core is pure silica). Multiple multi-mode laser pumping sources are input to the multi-core double-clad rare earth-doped fiber through a double-clad fan-in beam combiner. The multi-core double-clad rare-earth-doped optical fiber is connected to the fan-out beam combiner, and the long-period fiber grating is connected behind it. The second option is that N signals pass through N single-mode fibers, and N single-mode pumps are input to N fiber-core fan-in beam combiners through N WDMs. The fan-in beam combiner and multi-core single-clad rare earth doped The optical fiber is connected, and then connected to the fan-out beam combiner, and then connected to the long-period fiber grating. The fan-out beam combiner is also N single-mode optical fibers, and each single-mode optical fiber is aligned with each core of the multi-core single-clad rare earth-doped optical fiber. Here we are talking about N fiber cores, where N is any integer between 7 and 37.

The fluorescence emission width of erbium ion is closely related to the structure of its surrounding ligands. When Er ₂ O ₃ is co-doped with other oxides, a new small energy level structure is generated due to the splitting of the erbium energy level induced by the crystal field around the erbium ion. The first is the splitting of the upper energy level, resulting in a small energy level structure. The second is the splitting of the ground state energy level, resulting in a small energy level structure. Since the electronic transition occurs from the upper energy level to the ground state energy level, the more small energy levels are split into each energy level, the more electronic transitions are in multiple states, which is the mechanism of emission spectrum broadening. Compared with common erbium-doped fiber amplifiers, the spectrum width of the invention reaches 75nm, ranging from 1525nm to 1600nm.

We choose Er ₂ O ₃ co-doped ZrO ₂ /SbO ₂ /Yb ₂ O ₃ /Al ₂ O ₃ /La ₂ O ₃ oxides, the first is to change the crystal field around the erbium ions. Secondly, the absorption cross section of the pump light can be increased, and the increase of the absorption cross section can shorten the length of the optical fiber and reduce the loss.

For space division multiplexing technology, 7-core is the most mature research at present, but as the need for capacity expansion continues to increase, the multi-core amplifying fiber we designed can have a structure of up to 37 cores, which can support a maximum communication capacity of 37 times . Broadband multi-dimensional fiber amplifiers can use single-mode pumping, and the number of them is not less than the number of fiber cores. If multi-mode high-power pumping is used, the number of pump lasers can be greatly reduced. But this amplifier amplifies N-way (single-clad) and N-1-way (double-clad) signals at the same time, and can prevent crosstalk between signals.

In communication systems, crosstalk always leads to an increase in the bit error rate and is therefore a phenomenon that must be suppressed. However, for space division multiplexing, it is impossible to completely eliminate crosstalk. We can obtain optimized design parameters through simulation so that the crosstalk coefficient between fiber cores is less than -45dB/100m.

In the space division multiplexing communication system, the amplified signal needs to be flat, and the gains of multiple fiber cores must be the same. Here, we connect a customized long-period fiber grating to the amplified signal of each fiber core to achieve signal flattening. To ensure that the gain of multiple cores is the same, firstly, the doping concentration of each core needs to be the same, and secondly, the absorption of each core needs to reach saturated absorption. The multi-core doped rare earth fiber has an optimized length, so that the broadband The gain and flatness of each fiber core of the multidimensional fiber amplifier are close to the same.

Using a single-stage amplifier design, the width of the ASE spectrum can reach 90nm under optimized pumping parameters. When the small signal power is -30dBm, the average output signal gain is 20.7dB, and the average noise is 5.6dB. The amplification bandwidth reaches 75nm (from 1525nm to 1600nm).

Broadband multi-dimensional optical fiber amplifier is an indispensable and important link in the space division multiplexing communication system, and it mainly undertakes the signal relay amplification function in the multi-core optical fiber transmission line. The amplified signal enters the multi-core optical fiber again for transmission until the signal is downloaded or reaches the receiving end. In this transmission system, dense wavelength division multiplexing, amplitude-phase orthogonal multiplexing, polarization multiplexing, time division multiplexing and space division multiplexing can be supported, and the maximum system transmission capacity exceeding Pb/s can be supported (1Pb/s =1000Tb/s=1000000Gb/s). The transmission system constructed by using this amplification system has the characteristics of good compatibility, low cost, and good expansion reliability.

(4) Description of drawings

Figure 1 is a cross-sectional view of a 7-core rare-earth-doped optical fiber, where 1 represents the core. 2 indicates the cladding of the core. 3 represents the concave cladding of the core. 4 denotes a silica cladding. 4 The outer layer is coated with conventional paint (not shown in the figure) is a multi-core single-clad rare earth-doped optical fiber. 4 The outer layer is coated with low refractive index paint (not shown in the figure) is the multi-core double-clad rare earth-doped optical fiber.

Fig. 2 is a cross-sectional view of a 19-core rare-earth-doped optical fiber, where 5 denotes a core. 6 represents the cladding of the core. 7 represents the concave cladding of the core. 8 denotes a silica cladding. 8 The outer layer is coated with conventional paint (not shown in the figure) is a multi-core single-clad rare earth-doped optical fiber. 8 The outer layer is coated with low refractive index paint (not shown in the figure) is the multi-core double-clad rare earth-doped optical fiber.

Fig. 3 Ultra-wideband high-gain amplification scheme of multi-dimensional parallel amplification. 9 of them are multimode pump ports. 10 is a single-mode signal port, and there are N-1 ports in total. 11 is a double-clad fan-in beam combiner. 12 is a multi-core double-clad rare-earth-doped optical fiber, which has no core at the center and has N-1 cores in total. 13 is a fan-out beam combiner. 14 is a long-period fiber grating, and there are N-1 pieces in total. Wherein N is any integer between 7 and 37. A-A is a cross-sectional side view. It can be seen that there is no core in the center of the multi-core double-clad rare earth-doped fiber, and there are only N-1 cores.

Figure 4 is a multi-core single cladding rare earth doped fiber amplifier scheme. Among them, there are 15 single-mode pump ports, N in total. 16 is a single-mode signal port, a total of N. 17 is WDM for signal and pumping, N in total. 18 is a fan-in beam combiner. 19 is a multi-core single-clad rare-earth-doped optical fiber, which has N cores. 20 is a fan-out beam combiner. 21 is a long-period fiber grating, and there are N pieces in total. N is any integer between 7-37.

Fig. 5 is the gain spectrum and noise spectrum of the broadband multidimensional fiber amplifier, and its amplification bandwidth reaches above 75nm (from 1525nm to 1600nm).

(5) Specific implementation methods

Examples are described in further detail below.

A 7-core single-clad fiber broadband amplifier: 7 common single-mode fibers are used as signal ports, connected to 7 980/1550nm WDMs, and 7 single-mode pumps are connected to the WDM pump ports. The core spacing of the 7-core single-clad rare-earth doped fiber is 41 μm, and the crosstalk of 100 test is -52.5dB. The rare earth doped in each core is ZrO ₂ /Yb ₂ O ₃ /Al ₂ O ₃ /Er ₂ O ₃ , and the uniformly doped rare earth preform obtained was stretched and cut to obtain 7 small preforms, 7 A small preform rod is then stacked to form a 7-core single cladding doped rare earth optical fiber. This ensures the consistency of the doping concentration of each fiber core. The crosstalk value of the 7-fiber fan-in combiner is -50.5dB, and the maximum insertion loss is 1.1dB. The crosstalk value of the 7-fiber fan-out combiner is -51.2dB, and the maximum insertion loss is 1.2dB. Seven custom-made long-period fiber gratings flatten and filter the output spectrum, and the full-spectrum gain difference is ±1.3dB.

A 19-core double-clad fiber broadband amplifier: 18 ordinary single-mode fibers are used as signal ports, and 3 multimode pumps are connected from three multimode pump ports. The core spacing of the 18-core single-clad rare-earth doped fiber is 30 μm, and the crosstalk of 100 test is -48.6dB. The rare earth doped in each fiber core is ZrO ₂ /Yb ₂ O ₃ /Al ₂ O ₃ /Er ₂ O ₃ , and the uniformly doped rare earth preform obtained was stretched and cut to obtain 18 small preforms, 18 A small preform rod plus a non-doped core rod is stacked to form a 19-core preform rod, which is drawn into a double-clad doped rare-earth optical fiber and coated with a low-refractive index coating. This ensures the consistency of the doping concentration of each fiber core. The crosstalk value of the 18-fiber fan-in combiner is -47.5dB, and the maximum insertion loss is 1.5dB. The crosstalk value of the 18-fiber fan-out combiner is -48.2dB, and the maximum insertion loss is 1.6dB. 18 custom-made long-period fiber gratings flatten and filter the output spectrum, and the gain difference of the full spectrum is ±1.3dB.

A 37-core single-clad fiber broadband amplifier: 37 common single-mode fibers are used as signal ports, connected to 37 980/1550nm WDMs, and 37 single-mode pumps are connected to the WDM pump ports. The core spacing of the 37-core single-clad rare-earth doped fiber is 30 μm, and the crosstalk of the 100-core test is -47.5dB. The rare earth doped in each fiber core is ZrO ₂ /Yb ₂ O ₃ /Al ₂ O ₃ /Er ₂ O ₃ , and the obtained uniformly doped rare earth preform was stretched and cut to obtain 37 small preforms, 37 A small prefabricated rod is then stacked to form 37 core single-clad doped rare earth optical fibers. This ensures the consistency of the doping concentration of each fiber core. The crosstalk value of the 37-core fan-in combiner is -47.6dB, and the maximum insertion loss is 2.1dB. The crosstalk value of the 37-core fan-out combiner is -47.2dB, and the maximum insertion loss is 1.9dB. 37 custom-made long-period fiber gratings flatten and filter the output spectrum, and the full-spectrum gain difference is ±1.5dB.

Although the design parameters in the above embodiments are preferred, and the above embodiments have also described the present invention in detail, those skilled in the art can understand that various modifications can be made to these embodiments without departing from the raw materials and purpose of the present invention. Changes, modifications, substitutions and variations, the scope of the present invention is defined by the claims and their equivalents.

Claims (7)

1. A broadband multidimensional optical fiber amplifier, which includes signal input, WDM, fan-in beam combiner, multiple pump laser sources, multi-core single/double-clad rare earth-doped optical fiber, fan-out beam combiner, long-period fiber grating, etc. . 2. multi-core single/double-clad rare earth-doped optical fiber as claimed in claim 1, it has N (N is any integer between 7～37) fiber cores, co-doped in each fiber core The mixed oxide is one or more of ZrO ₂ /SbO ₂ /Yb ₂ O ₃ /Al ₂ O ₃ /La ₂ O ₃ /Er ₂ O ₃ , and the doping concentrations of different cores are strictly the same. 3. The optical fiber according to claim 1, characterized in that: scheme one is a double-clad rare-earth-doped optical fiber, the quartz cladding is the first cladding, and the low-refractive index coating is the second cladding, without WDM coupling pumping, The multimode pump is directly coupled from the central core of the fan-in combiner/fan-out combiner, and the output is composed of a fan-out combiner fused with a long-period fiber grating; the second scheme is that the signal of each fiber core and the single-mode pump are composed of WDM coupling, then from a fan-in combiner to a single-clad rare-earth-doped fiber, which contains silica cladding and a common coating, and the output consists of a fan-out combiner fused to a long-period fiber grating. 4. The optical fiber according to claim 1, characterized in that the number of cores of the multi-core rare earth-doped optical fiber is 7-37, and the crosstalk coefficient between the cores is less than -45dB/100m. 5. The optical fiber according to claim 1, wherein both the fan-in beam combiner and the fan-out beam combiner are from N single-mode fibers to N cores of multi-core rare earth-doped fibers. 6. The optical fiber according to claim 1, wherein the N single-mode optical fibers of the fan-out combiner are spliced with N customized long-period fiber gratings to flatten the gain spectrum of the N optical fibers. 7. by the described optical fiber amplifier of claim 1, it is characterized in that: can support to amplify N road (single clad layer) and N-1 road (double clad layer) signal simultaneously on transmission link, and can prevent generation between signal crosstalk.