Raman optical fiber amplifier and optical amplification assembly

Abstract

The invention provides a Raman optical fiber amplifier and an optical amplification assembly, and belongs to the technical field of optical communication. In the Raman optical fiber amplifier provided by the invention, two output ends of an optical path switching unit are correspondingly connected with two input ends of a polarization beam combiner. The light path switching unit can alternately transmit two paths of pump light with different wavelengths to two output ends of the light path switching unit according to a target frequency, so that the two paths of pump light can alternately enter different input ends of the polarization beam combiner. Therefore, the polarization beam combiner can output a polarization pulse sequence after carrying out cross-polarization beam combination on the received two paths of pump light, and in the polarization pulse sequence, two polarization pulses with different wavelengths and the same polarization direction are staggered in time, so that SRS transfer between the pump light with different wavelengths can be effectively reduced, the NF of a short-wave signal is reduced, and the transmission efficiency of the short-wave signal is improved. And the performance of the optical communication system is improved.

Description

Technical Field

[0001] This application relates to the field of optical communication technologies, and particularly to a Raman fiber amplifier and an optical amplification component. Background Art

[0002] In order to double the capacity of an optical communication system without changing the transmission distance, systematic improvements need to be made in aspects such as optical fibers, optical fiber amplifiers (referred to as optical amplifiers for short), wavelength selective switches, system compensation, debugging, and design.

[0003] Commonly used optical fiber amplifiers in optical communication systems include erbium-doped fiber amplifiers (EDFAs) and Raman fiber amplifiers (RFAs), etc. Among them, EDFAs are limited by the 3-decibel (dB) quantum noise limit. For RFAs, such as distributed RFAs (DRAs), their equivalent noise figure (NF) can be less than 3 dB.

[0004] However, for the C+L band, RFAs have a short-wave performance bottleneck. Because compared with the C band, the wavelength range of the first-order pump light in the C+L band is large, and the transfer of stimulated Raman scattering (SRS) between pumps will affect the NF of short-wave signals, severely limiting the system performance. Among them, the C band refers to the conventional band, and the L band refers to the long band. Summary of the Invention

[0005] This application provides a Raman fiber amplifier and an optical amplification component, which can solve the technical problem of the short-wave performance bottleneck existing in RFAs in related technologies.

[0006] In a first aspect, an RFA is provided, which includes: a first pump source, a second pump source, an optical path switching unit, a first polarization beam combiner, and a first coupler. The first pump source is configured to output a first pump light with a first wavelength; the second pump source is configured to output a second pump light with a second wavelength, the second wavelength is different from the first wavelength, and both are within a first wavelength range. The input ends of the optical path switching unit are respectively connected to the first pump source and the second pump source, the first output end of the optical path switching unit is connected to the first input end of the first polarization beam combiner, the second output end of the optical path switching unit is connected to the second input end of the first polarization beam combiner, and the optical path switching unit is configured to alternately transmit the first pump light and the second pump light to the first output end and the second output end according to a target frequency. The first polarization beam combiner is configured to orthogonally polarize and combine the first pump light and the second pump light transmitted by the optical path switching unit, and then transmit the combined light to the first coupler. The first coupler is configured to couple the received pump light to an optical fiber.

[0007] In the RFA provided by this application, the optical path switching unit can alternately incident two pump lights with different wavelengths to different input ends of the polarization beam combiner according to a target frequency. Thus, after the polarization beam combiner orthogonally polarizes and combines the two received pump lights, a polarization pulse sequence can be output. In this polarization pulse sequence, two polarization pulses with different wavelengths but the same polarization direction are staggered in time. Therefore, the SRS transfer between pump lights with different wavelengths can be effectively reduced, the NF of the short-wave signal can be reduced, and the performance of the optical communication system can be improved.

[0008] Optionally, the optical path switching unit can be an optical switch or a wavelength selective switch. Among them, the optical switch can be a mechanical optical switch or a non-mechanical optical switch. The mechanical optical switch can change the optical path of the pump light by moving an optical fiber or an optical element. The non-mechanical optical switch can rely on the electro-optic effect, magneto-optic effect, acousto-optic effect, or thermo-optic effect to change the waveguide refractive index so as to change the optical path of the pump light.

[0009] Optionally, the RFA can further include: a third pump source, a fourth pump source, a first polarization beam combining depolarizer, and a second coupler. The third pump source is configured to output a third pump light with a third wavelength; the fourth pump source is configured to output a fourth pump light with a fourth wavelength, the third wavelength and the fourth wavelength are both within the first wavelength range, and the first wavelength, the second wavelength, the third wavelength, and the fourth wavelength are different from each other. The first polarization beam combining depolarizer is configured to polarize and combine and then depolarize the third pump light and the fourth pump light, and then transmit the combined light to the second coupler; the first polarization beam combiner is configured to transmit the orthogonally polarized and combined pump light to the second coupler. The second coupler is configured to couple the received pump light to the first coupler.

[0010] The RFA provided by this application can effectively improve the Raman gain of the RFA and provide a flat Raman gain spectrum by using multiple pump sources. Moreover, by using a first polarization beam combining depolarizer to combine two input linearly polarized pump lights and then depolarize the combined linearly polarized light, the polarization dependent gain (PDG) of the RFA can be effectively reduced.

[0011] Optionally, the RFA may further include: a fifth pump source, a sixth pump source, and a second polarization beam combiner. The fifth pump source is used to output a fifth pump light with a fifth wavelength; the sixth pump source is used to output a sixth pump light with a sixth wavelength. Both the fifth wavelength and the sixth wavelength are within a first wavelength range, and the first wavelength, the second wavelength, the fifth wavelength, and the sixth wavelength are different from each other. The input end of the optical path switching unit is also respectively connected to the fifth pump source and the sixth pump source. The third output end of the optical path switching unit is connected to the first input end of the second polarization beam combiner, and the fourth output end of the optical path switching unit is connected to the second input end of the second polarization beam combiner. The optical path switching unit is further configured to alternately transmit the fifth pump light and the sixth pump light to the third output end and the fourth output end according to the target frequency. The second polarization beam combiner is configured to orthogonally polarize and combine the received fifth pump light and sixth pump light and then transmit them to the first coupler.

[0012] In the solution provided by this application, the optical path switching unit can be connected to multiple groups of pump sources, where each group of pump sources includes two pump sources with different wavelengths. Moreover, for the two pump sources in each group of pump sources, the optical path switching unit can alternately incident the pump lights output by the two pump sources to different input ends of the polarization beam combiner according to the target frequency. Thereby, the SRS transfer between the pump lights with different wavelengths in the RFA can be further reduced, and then the NF of the short-wave signal can be reduced, improving the performance of the optical communication system.

[0013] Optionally, the first wavelength range may be from 1400 nanometers to 1520 nanometers. The pump light within the first wavelength range can also be referred to as the first-order pump light, and the pump source that outputs the first-order pump light can also be referred to as the first-order pump source.

[0014] Optionally, the RFA may further include: a seventh pump source, an eighth pump source, a second polarization beam combining depolarizer, and a third coupler. The seventh pump source is configured to output a seventh pump light with a seventh wavelength; the eighth pump source is configured to output an eighth pump light with an eighth wavelength, the eighth wavelength is different from the seventh wavelength, and both are within a second wavelength range, and the upper limit of the second wavelength range is less than the lower limit of the first wavelength range. The second polarization beam combining depolarizer is configured to perform polarization beam combining and depolarization on the seventh pump light and the eighth pump light, and then transmit them to the third coupler; the third coupler is configured to couple the received pump light to the optical fiber.

[0015] The pump light within the second wavelength range may also be referred to as second-order pump light or higher-order pump light, and the pump source that outputs the second-order or higher-order pump light may also be referred to as a second-order pump source or a higher-order pump source. Among them, the second-order pump light can extend the transmission distance of the first-order pump light in the optical fiber, thereby effectively reducing the NF of the RFA.

[0016] Optionally, the second wavelength range is from 1200 nanometers to 1399 nanometers.

[0017] Optionally, the Raman fiber amplifier further includes: a drive circuit, which can be used to control the optical path switching unit to switch the transmission path of the pump light according to the target frequency. Among them, the drive circuit may include a pulse generator, and the pulse generator can output a square wave signal with adjustable frequency, duty cycle, and modulation depth.

[0018] Optionally, the range of the target frequency may be from 10 kilohertz (kHz) to 1 megahertz (MHz).

[0019] Optionally, the transmission direction of the pump light coupled by the RFA into the optical fiber is opposite to the transmission direction of the signal light in the optical fiber. That is to say, the RFA may be a backward optical amplifier. The wavelength range of the signal light transmitted in the optical fiber may be from 1520 nanometers to 1630 nanometers.

[0020] In a second aspect, another Raman fiber amplifier (RFA) is provided, which includes: a first pump source, a second pump source, an optical path switching unit, a first polarization beam combiner, a depolarizer, a fourth coupler, and a first coupler. The first pump source is configured to output a first pump light with a first wavelength; the second pump source is configured to output a second pump light with a second wavelength, where the second wavelength is different from the first wavelength and both are within a first wavelength range. The input end of the optical path switching unit is connected to the first pump source, the first output end of the optical path switching unit is connected to the first input end of the first polarization beam combiner, the second output end of the optical path switching unit is connected to the second input end of the first polarization beam combiner, and the optical path switching unit is configured to alternately transmit the first pump light to the first output end and the second output end according to a target frequency. The first polarization beam combiner is configured to orthogonally combine the received pump lights and then transmit them to the fourth coupler; the depolarizer is configured to depolarize the second pump light and then transmit it to the fourth coupler. The fourth coupler is configured to couple the received pump lights to the first coupler; the first coupler is configured to couple the received pump lights to an optical fiber.

[0021] The optical path switching unit can alternately incident the first pump light to different input ends of the polarization beam combiner according to a target frequency. Thus, after the polarization beam combiner orthogonally combines the received first pump light, a polarization pulse sequence can be output. In this polarization pulse sequence, the polarization pulses in different polarization directions of the first pump light are staggered in time. Therefore, the stimulated Raman scattering (SRS) transfer between the first pump light and the depolarized second pump light can be effectively reduced, the noise figure (NF) of the short-wave signal can be reduced, and the performance of the optical communication system can be improved.

[0022] In a third aspect, an optical amplification component is provided, which includes: a cascaded RFA and erbium-doped fiber amplifier (EDFA); where the RFA is the RFA provided in the first aspect or the second aspect above.

[0023] In summary, the present application provides a Raman fiber amplifier and an optical amplification component. In the solution provided by the present application, the two output ends of the optical path switching unit are correspondingly connected to the two input ends of the polarization beam combiner. The optical path switching unit can alternately transmit two pump lights with different wavelengths to its two output ends according to a target frequency, so that the two pump lights can alternately enter different input ends of the polarization beam combiner. Thus, after the polarization beam combiner orthogonally combines the two received pump lights, a polarization pulse sequence can be output. In this polarization pulse sequence, two polarization pulses with different wavelengths but the same polarization direction are staggered in time. Therefore, the SRS transfer between pump lights with different wavelengths can be effectively reduced, the NF of the short-wave signal can be reduced, and the performance of the optical communication system can be improved. Description of the Drawings

[0024] Figure 1It is a schematic structural diagram of an optical communication system provided by an embodiment of the present application;

[0025] Figure 2 It is a schematic structural diagram of an RFA provided by an embodiment of the present application;

[0026] Figure 3 It is a schematic diagram of an optical path switching unit switching the optical path of pump light provided by an embodiment of the present application;

[0027] Figure 4 It is a schematic diagram of a polarization pulse sequence output by a polarization beam combiner provided by an embodiment of the present application;

[0028] Figure 5 It is another schematic structural diagram of an RFA provided by an embodiment of the present application;

[0029] Figure 6 It is still another schematic structural diagram of an RFA provided by an embodiment of the present application;

[0030] Figure 7 It is another schematic diagram of an optical path switching unit switching the optical path of pump light provided by an embodiment of the present application;

[0031] Figure 8 It is another schematic diagram of a polarization pulse sequence output by a polarization beam combiner provided by an embodiment of the present application;

[0032] Figure 9 It is yet another schematic structural diagram of an RFA provided by an embodiment of the present application;

[0033] Figure 10 It is still another schematic diagram of an optical path switching unit switching the optical path of pump light provided by an embodiment of the present application;

[0034] Figure 11 It is still another schematic diagram of a polarization pulse sequence output by a polarization beam combiner provided by an embodiment of the present application;

[0035] Figure 12 It is yet another schematic structural diagram of an RFA provided by an embodiment of the present application;

[0036] Figure 13 It is a schematic structural diagram of an optical amplification component provided by an embodiment of the present application. Detailed implementation manners

[0037] The following describes in detail the Raman fiber amplifier and the optical amplification component provided by the embodiments of the present application with reference to the accompanying drawings.

[0038] The next-generation optical communication system will evolve from 400G*80 wavelength to 800G*80 wavelength, and the transmission performance challenges of the 800G*80 wavelength system are huge. Among them, 800G refers to a data transmission rate of 800 gigabits per second (Gbps), and 80 wavelength refers to the number of channels of the wavelength division multiplexing system being 80. For the C+L band, since the wavelength of its short-wave signal is around 1527 nm, and the upper limit of the wavelength range of the first-order pump light is 1520 nm, the upper limit of the wavelength of this first-order pump light is relatively close to the wavelength of the short-wave signal. Therefore, it will affect the amplifier spontaneous emission (ASE) noise of the short-wave signal. Moreover, since the long-wave pump light in the first-order pump light can be used to provide gain for the long-wave signal, and the short-wave pump light is used to provide gain for the short-wave signal, the SRS transfer between the pumps will affect the transmission distance of the short-wave pump light, and thus affect the NF of the short-wave signal.

[0039] In order to reduce the SRS transfer between the pumps, in some embodiments, a pump time domain modulation (TDM) scheme can be adopted. In this pump TDM scheme, the drive circuit can modulate the continuous light emitted by the laser into pulsed light (i.e., pump light pulses). However, modulating the continuous light into pulsed light in this scheme will result in pump power loss.

[0040] In some other embodiments, the laser still operates at continuous power, that is, the laser still outputs continuous Raman pump light, and the Raman pump light provided by the longest-wave pump and the shortest-wave pump lasers is adjusted by optical elements. Among them, the optical elements include a polarization controller or a phase controller, etc. By modulating the optical elements at a given period, and using devices such as a coupler, an optical fiber delay line, and a polarization beam combiner, a series of pump light pulses are provided at the output of the polarization beam combiner at the modulation frequency. However, what is output in this embodiment is still a series of pump light pulses. Moreover, to achieve the same gain, the peak power of the pump light pulses needs to be doubled, and thus the average power of the pump light pulses is the same as the power of the continuous light. However, too high a peak power of the pump light pulses will result in too large double Rayleigh scattering (DRS), and ultimately the achieved NF gain is reduced. In addition, this embodiment requires the use of an optical fiber delay line to achieve a half-cycle delay for both wavelengths, but the wavelengths are different and their delays are inconsistent. Therefore, the engineering implementation difficulty of this embodiment is relatively high.

[0041] An embodiment of the present application provides an RFA, which can keep the pump source (i.e., the laser) operating at a continuous power to avoid power loss caused by TDM. Moreover, the RFA can keep the average power and peak power of the RFA output unchanged with a relatively low engineering implementation difficulty, so as to reduce DRS in the optical fiber, thereby effectively improving the pumping performance and obtaining the NF gain of the short-wave signal.

[0042] Figure 1 is a schematic structural diagram of an optical communication system provided by an embodiment of the present application. As Figure 1 shown, the system may include: a plurality of optical transponder units (OTUs) deployed at the sending end, a multiplexer (MUX), an optical amplification unit (OAU), an optical fiber, a demultiplexer (DEMUX), and a plurality of OTUs deployed at the receiving end. Among them, the plurality of OTUs at the sending end can convert the service signals to be transmitted into optical signals of corresponding wavelengths. The multiplexer (which can also be called a combiner) can combine a plurality of optical signals of different wavelengths onto one optical fiber and transmit them in the optical fiber. Referring to Figure 1 it can be seen that after the optical signal is transmitted for a certain distance, it needs to be optically amplified by the OAU. The OAU can usually be an EDFA. However, for a link with limited performance or an ultra-long haul link, the OAU may include the RFA provided by an embodiment of the present application. For example, the OAU may include a cascaded RFA and an EDFA.

[0043] Figure 2 is a schematic structural diagram of an RFA provided by an embodiment of the present application. As Figure 2 shown, the RFA includes: a first pump source 01, a second pump source 02, an optical path switching unit 03, a first polarization beam combiner 04, and a first coupler 05.

[0044] Among them, the first pump source 01 is used to output a first pump light of a first wavelength λ1. The second pump source 02 is used to output a second pump light of a second wavelength λ2. The second wavelength λ2 is different from the first wavelength λ1, and both are within the first wavelength range. Optionally, the first wavelength range can be from 1400 nanometers (nm) to 1520 nm. The pump light in this first wavelength range can also be called first-order pump light. Correspondingly, the pump sources (such as the first pump source 01 and the second pump source 02) used to output this first-order pump light can also be called first-order pump sources.

[0045] The two input ends of the optical path switching unit 03 are respectively connected to the first pump source 01 and the second pump source 02. For example, referring to Figure 2, the first input end I1 of the optical path switching unit 03 is connected to the first pump source 01, and the second input end I2 of the optical path switching unit 03 is connected to the second pump source 02. The first output end O1 of the optical path switching unit 03 is connected to the first input end of the first polarization beam combiner 04, and the second output end O2 of the optical path switching unit 03 is connected to the second input end of the first polarization beam combiner 04. The optical path switching unit 03 is used to alternately transmit the first pump light and the second pump light to the first output end O1 and the second output end O2 according to the target frequency.

[0046] The first polarization beam combiner 04 is used to orthogonally combine the first pump light and the second pump light transmitted by the optical path switching unit 03 and then transmit them to the first coupler 05. The first coupler 05 is used to couple the received pump light into the optical fiber. Among them, the first coupler 05 can be a wavelength division multiplexer (WDM), which can couple lights of different wavelengths into one optical fiber. The input pigtail of the first polarization beam combiner 04 can be polarization-maintaining optical fiber, and the output pigtail can be single-mode optical fiber.

[0047] It can be understood that after receiving two paths of pump light through two input ends, the optical path switching unit 03 can output the two paths of pump light through its two output ends, where each output end is used to output one path of pump light, and the pump lights output by the two output ends are different. In the embodiment of the present application, as Figure 3 shown, the optical path switching unit 03 alternately transmitting the first pump light and the second pump light to the first output end O1 and the second output end O2 according to the target frequency may mean that: in the first time period t1, the first pump light received by the first input end I1 is transmitted to the first output end O1, and the second pump light received by the second input end I2 is transmitted to the second output end O2. In the second time period t2, the optical path is switched, the first pump light received by the first input end I1 is transmitted to the second output end O2, and the second pump light received by the second input end I2 is transmitted to the first output end O1.

[0048] Among them, the duration of the first time period t1 and the duration of the second time period t2 may be equal. The target frequency f may satisfy: f = 1 / (t1 + t2), and the target frequency f may be from 10 kHz to 1 MHz. The optical path switching unit 03 can alternately repeat the states of the first time period t1 and the second time period t2 to realize modulating the transmission paths of the first pump light and the second pump light according to the target frequency.

[0049] It can also be understood that the first pump light output by the first pump source 01 and the second pump light output by the second pump source 02 are both linearly polarized lights, and the polarization directions of the linearly polarized lights are indefinite. After the first polarization beam combiner 04 receives the first pump light and the second pump light transmitted by the optical path switching unit 03, the two pump lights can be combined into one beam. Moreover, the crystal optical axes aligned with the two input ends of the first polarization beam combiner 04 are different. The first polarization beam combiner 04 can modulate the pump light received by its first input end into pump light with a first polarization direction X (i.e., X-polarized light), and can modulate the pump light received by its second input end into pump light with a second polarization direction Y (i.e., Y-polarized light). Among them, the first polarization direction X is orthogonal to the second polarization direction Y.

[0050] Combined with the working principle of the optical path switching unit 03 described above, referring to Figure 4 , in the first time period t1, the pump light output by the first polarization beam combiner 04 may include pump light with a first wavelength λ1 in the first polarization direction X and pump light with a second wavelength λ2 in the second polarization direction Y. In the second time period t2, the pump light output by the first polarization beam combiner 04 may include pump light with a second wavelength λ2 in the first polarization direction X and pump light with a first wavelength λ1 in the second polarization direction Y.

[0051] From Figure 4 it can be seen that within each time period, the polarization directions of the pump light with the first wavelength λ1 and the pump light with the second wavelength λ2 are orthogonal, that is, the polarization pulses of the pump lights with two different wavelengths in the same polarization direction do not overlap, or it can be understood that the pump lights with two wavelengths in the same polarization direction are completely staggered in time. Thus, it can be ensured that there is no power transfer (i.e., SRS transfer) between the pump light with the first wavelength λ1 and the pump light with the second wavelength λ2, and the NF performance benefit of the short-wave signal is achieved.

[0052] Assuming that the adjacent first time period t1 and the second time period t2 are a time unit, then as Figure 4 shown, within each time unit, the pump light with the first wavelength λ1 and the pump light with the second wavelength λ2 both include polarization pulses in the first polarization direction X and polarization pulses in the second polarization direction Y, and the two polarization pulses are orthogonal. It can be understood that for the signal, when the time unit is small enough, the signal cannot distinguish, that is, no polarization-related gain will be generated. And the Raman gain is determined by the average power of the pump light. In the embodiment of the present application, since the pump light output by the first polarization beam combiner 04 can be equivalent to a continuous wave, its average power remains unchanged and the peak power remains unchanged. Thus, the power loss caused by time modulation can be effectively avoided, and the bidirectional Rayleigh scattering in the optical fiber can be effectively reduced, thereby improving the pump performance and obtaining the NF benefit.

[0053] Optionally, in the embodiments of the present application, the optical path switching unit 03 may be an optical device capable of adjusting the transmission path of the pump light according to the target frequency, and both its input pigtail and output pigtail may be polarization-maintaining fibers. For example, the optical path switching unit 03 may be an optical switch or a wavelength selection switch (WSS). Among them, the optical switch may be a mechanical optical switch or a non-mechanical optical switch. The mechanical optical switch can change the optical path of the pump light by moving optical fibers or optical elements. Exemplarily, the mechanical optical switch may include a moving optical fiber, a moving sleeve, a moving collimator, a moving mirror, a moving prism, and a moving coupler, etc. The non-mechanical optical switch may be an optical switch that relies on the electro-optic effect, magneto-optic effect, acousto-optic effect, or thermo-optic effect to change the waveguide refractive index, thereby changing the optical path of the pump light.

[0054] Figure 5 It is a schematic structural diagram of another RFA provided by the embodiments of the present application. Optionally, as Figure 5 shown, the RFA may further include: a third pump source 06, a fourth pump source 07, a first polarization beam combining and depolarizing device 08, and a second coupler 09.

[0055] Among them, the third pump source 06 is used to output the third pump light with the third wavelength λ3, and the fourth pump source 07 is used to output the fourth pump light with the fourth wavelength λ4. The third wavelength λ3 and the fourth wavelength λ4 are both within the first wavelength range, and the first wavelength λ1, the second wavelength λ2, the third wavelength λ3, and the fourth wavelength λ4 are different from each other. For example, the first wavelength λ1 to the fourth wavelength λ4 may satisfy: λ2 < λ3 < λ4 < λ1. That is to say, the first pump light with the first wavelength λ1 may be the longest wavelength pump among the four pump lights, and the second pump light with the second wavelength λ2 may be the shortest wavelength pump among the four pump lights.

[0056] The first polarization beam combining and depolarizing device 08 is used to perform polarization beam combining and depolarization on the third pump light and the fourth pump light (i.e., the unmodulated pump light), and then transmit it to the second coupler 09. That is to say, the first polarization beam combining and depolarizing device 08 can combine two input linearly polarized lights, then depolarize the combined linearly polarized light, and finally output unpolarized light to the second coupler 09.

[0057] The first polarization beam combiner 04 can be used to transmit the orthogonally polarized combined pump light to the second coupler 09. The second coupler 09 is used to couple the received pump light (i.e., the depolarized pump light transmitted by the first polarization beam combining depolarizer 08 and the orthogonally polarized combined pump light transmitted by the first polarization beam combiner 04) to the first coupler 05. It can be seen from this that the orthogonally polarized combined pump light output by the first polarization beam combiner 04 can be transmitted to the first coupler 05 through the second coupler 09. Among them, the second coupler 09 can also be a wavelength division multiplexer.

[0058] In the embodiment of the present application, by using multiple first-order pump sources, the Raman gain of the RFA can be effectively improved, and a flat Raman gain spectrum can be provided. It can be understood that the gain of the RFA is related to the polarization state of light. When the polarization direction of the pump light is orthogonal to the polarization direction of the signal light, the gain is small, and when the polarization direction of the pump light is the same as the polarization direction of the signal light, the gain is large. In the embodiment of the present application, by using a polarization beam combining depolarizer to combine two input linearly polarized lights and then depolarize the combined linearly polarized light, the PDG of the RFA can be effectively reduced.

[0059] In a possible example, the first polarization beam combining depolarizer 08 can also have an isolation function, that is, the first polarization beam combining depolarizer 08 can be an isolator polarization beamcombiner with depolarizer (IPBCD). Among them, the isolator in the IPBCD can isolate the reflected light to avoid damaging the pump source.

[0060] Figure 6 It is a schematic structural diagram of another RFA provided by the embodiment of the present application. Optionally, as Figure 6 shown, the RFA may further include: a fifth pump source 10, a sixth pump source 11, and a second polarization beam combiner 12.

[0061] The fifth pump source 10 is used to output the fifth pump light with a fifth wavelength λ5. The sixth pump source 11 is used to output the sixth pump light with a sixth wavelength λ6. The fifth wavelength λ5 and the sixth wavelength λ6 are both within the first wavelength range, and the first wavelength λ1, the second wavelength λ2, the fifth wavelength λ5, and the sixth wavelength λ6 are all different from each other.

[0062] The input end of the optical path switching unit 03 is also respectively connected to the fifth pump source 10 and the sixth pump source 11. For example, referring to Figure 6 and Figure 7, the third input end I3 of the optical path switching unit 03 is connected to the fifth pump source 10, and the fourth input end I4 is connected to the sixth pump source 11. The third output end O3 of the optical path switching unit 03 is connected to the first input end of the second polarization beam combiner 12, and the fourth output end O4 of the optical path switching unit 03 is connected to the second input end of the second polarization beam combiner 12. The optical path switching unit 03 is further configured to alternately transmit the fifth pump light and the sixth pump light to the third output end O3 and the fourth output end O4 according to the target frequency.

[0063] The second polarization beam combiner 12 is configured to perform orthogonal polarization beam combination on the received fifth pump light and sixth pump light, and then transmit them to the first coupler 05.

[0064] It can be understood that, as Figure 7 shown, the optical path switching unit 03 alternately transmitting the fifth pump light and the sixth pump light to the third output end O3 and the fourth output end O4 according to the target frequency may mean that: in the first time period t1, the fifth pump light received by the third input end I3 is transmitted to the third output end O3, and the sixth pump light received by the fourth input end I4 is transmitted to the fourth output end O4. In the second time period t2, the optical path is switched, the fifth pump light received by the third input end I3 is transmitted to the fourth output end O4, and the sixth pump light received by the fourth input end I4 is transmitted to the third output end O3.

[0065] It can also be understood that both the fifth pump light output by the fifth pump source 10 and the sixth pump light output by the sixth pump source 11 are linearly polarized lights, and the polarization directions of the linearly polarized lights are uncertain. After the second polarization beam combiner 12 receives the fifth pump light and the sixth pump light transmitted by the optical path switching unit 03, the two pump lights can be combined into one beam. Moreover, the second polarization beam combiner 12 can modulate the pump light received by its first input end into pump light with the first polarization direction X, and can modulate the pump light received by its second input end into pump light with the second polarization direction Y.

[0066] Based on the above analysis, it can be known that referring to Figure 8 , in the first time period t1, the pump light output by the second polarization beam combiner 12 may include pump light with the fifth wavelength λ5 in the first polarization direction X and pump light with the sixth wavelength λ6 in the second polarization direction Y. In the second time period t2, the pump light output by the second polarization beam combiner 12 may include pump light with the sixth wavelength λ6 in the first polarization direction X and pump light with the fifth wavelength λ5 in the second polarization direction Y.

[0067] Since the polarization directions of the pump light with the fifth wavelength λ5 and the pump light with the sixth wavelength λ6 are orthogonal in each time period, that is, the pump lights with two wavelengths in the same polarization direction are completely staggered in time. Thus, it can be ensured that there is no power transfer between the pump light with the fifth wavelength λ5 and the pump light with the sixth wavelength λ6, and the NF performance gain of the short-wave signal is achieved. Moreover, in each time unit, the pump light with the fifth wavelength λ5 and the pump light with the sixth wavelength λ6 both include polarization pulses with the first polarization direction X and polarization pulses with the second polarization direction Y, and these two types of polarization pulses are orthogonal. It can be understood that for the signal, when the time unit is small enough, the signal cannot distinguish, that is, the polarization-dependent gain will not be generated. And the Raman gain is determined by the average power of the pump light. In the embodiment of the present application, since the pump light output by the second polarization beam combiner 12 is equivalent to a continuous wave, its average power remains unchanged and the peak power remains unchanged. Thus, the power loss caused by time modulation can be effectively avoided, and the bidirectional Rayleigh scattering in the optical fiber can be effectively reduced, thereby improving the pump performance and obtaining the NF gain.

[0068] Figure 6 The illustrated embodiment is described by taking the optical path switching unit 03 connected to two groups of pump sources as an example. Among them, each group of pump sources includes two pump sources with different wavelengths. For example, the first pump source 01 and the second pump source 02 are a group of pump sources, and the fifth pump source 10 and the sixth pump source 11 are a group of pump sources. It can also be understood that the RFA may further include more groups of pump sources connected to the optical path switching unit 03, and a polarization beam combiner corresponding to each group of pump sources. For example, referring to Figure 7 , the RFA may include n + 1 pump sources, and the n + 1 pump sources can output pump lights with n + 1 different wavelengths. Correspondingly, the optical path switching unit 03 has n + 1 input ends and n + 1 output ends. Each adjacent two output ends are connected to a polarization beam combiner and correspond to a group of pump sources.

[0069] Among them, for the two pump sources with different wavelengths included in each group of pump sources, the optical path switching unit 03 can alternately transmit the two pump lights output by the two pump sources to the two output ends according to the target frequency, and transmit them to a corresponding polarization beam combiner through the two output ends. Each polarization beam combiner can output a polarization pulse sequence, and in this polarization pulse sequence, the polarization pulses of the two pump lights with different wavelengths in the same polarization direction do not overlap, that is, the polarization pulses of the two different wavelengths in the same polarization direction are completely staggered in time.

[0070] In the embodiments of the present application, the wavelengths of the pump light output by the two pump sources included in each group of pump sources may satisfy that the wavelength of the longer-wavelength pump light is the wavelength closest to the peak wavelength of the Raman gain spectrum of the shorter-wavelength pump light among the wavelengths of all the pump sources included in the RFA. That is to say, the two pump sources in each group of pump sources may be the two pump sources with relatively serious SRS transfer. Thus, it can be ensured that the optical path switching unit 03 and a corresponding polarization beam combiner can effectively reduce the SRS transfer between the two pump sources to achieve a greater NF gain.

[0071] For example, referring to Figure 7 , assuming that the RFA includes n + 1 first-order pump sources, and the wavelengths of the first-order pump light output by the n + 1 first-order pump sources are λ1 to λn+1 in sequence. If the wavelength of the pump light output by a certain first-order pump source is the target wavelength, then the other first-order pump source in the group with this first-order pump source may be the first-order pump source among the n + 1 first-order pump sources whose output pump light wavelength is closest to the peak wavelength of the Raman gain spectrum of the pump light with the target wavelength. That is to say, the wavelength of the first-order pump light output by the other first-order pump source may be the wavelength among λ1 to λn+1 that is closest to the peak wavelength of the Raman gain spectrum of the target wavelength.

[0072] Optionally, as Figure 5 and Figure 6 shown, the RFA provided by the embodiments of the present application may further include: a seventh pump source 13, an eighth pump source 14, a second polarization beam combining depolarizer 15, and a third coupler 16.

[0073] The seventh pump source 13 is used to output the seventh pump light with a seventh wavelength λ7, and the eighth pump source 14 is used to output the eighth pump light with an eighth wavelength λ8. The eighth wavelength λ8 is different from the seventh wavelength λ7 and both are within the second wavelength range.

[0074] The second polarization beam combining depolarizer 15 is used to perform polarization beam combining and depolarization on the seventh pump light and the eighth pump light (i.e., the unmodulated pump light) and then transmit it to the third coupler 16. The third coupler 16 is used to couple the received pump light into the optical fiber. The third coupler 16 may also be a wavelength division multiplexer.

[0075] In the embodiments of the present application, the upper limit of the second wavelength range may be less than the lower limit of the first wavelength range. For example, the second wavelength range may be from 1200 nm to 1399 nm. The pump light in the second wavelength range may be referred to as second-order pump light or higher-order pump light, and the pump source for outputting the second-order or higher-order pump light may also be referred to as a second-order pump source or a higher-order pump source. It can be understood that the pump light in the second wavelength range can extend the transmission distance of the first-order pump light in the optical fiber, thereby effectively reducing the NF of the RFA.

[0076] Optionally, as Figure 5 shown, the RFA may further include: a drive circuit 17, which can be used to control the optical path switching unit 03 to switch the transmission path of the pump light according to the target frequency. By way of example, the drive circuit 17 may include a pulse generator that is capable of outputting a square wave signal with adjustable frequency, duty cycle, and modulation depth.

[0077] Optionally, in the embodiments of the present application, the transmission direction of the pump light coupled by the RFA to the optical fiber is opposite to the transmission direction of the signal light in the optical fiber. That is to say, the RFA may be a backward optical amplifier.

[0078] Among them, the pump light coupled by the RFA to the optical fiber may at least include the pump light coupled by the first coupler 05. Alternatively, in addition to the pump light coupled by the first coupler 05, it may further include the pump light coupled by the third coupler 16. The signal light transmitted in the optical fiber may be a wavelength division multiplexing signal, and its wavelength range may be from 1520 nm to 1630 nm.

[0079] Optionally, the pump sources (such as a first-order pump source and a second-order pump source) in the embodiments of the present application may include semiconductor lasers, fiber lasers, and / or solid-state lasers. The polarization beam combining depolarizers (such as the first polarization beam combining depolarizer 08 and the second polarization beam combining depolarizer 15) in the embodiments of the present application may be composed of different quartz crystals, birefringent crystals, and / or optical rotation plates. Moreover, its input pigtail fiber may be a polarization-maintaining fiber, and the output pigtail fiber may be a single-mode fiber. The input pigtail fiber of the polarization beam combiner in the embodiments of the present application may be a polarization-maintaining fiber, which can combine two linearly polarized lights, and the output pigtail fiber may be a single-mode fiber.

[0080] Optionally, as Figure 5 and Figure 6 shown, the RFA provided in the embodiments of the present application may further have a first end P1 and a second end P2. Among them, the first end P1 may also be referred to as the inlet end, which can be used to connect the link optical fiber. The second end P2 may also be referred to as the outlet end, which can be used to connect the link optical fiber or a subsequent optical amplifier (such as an EDFA).

[0081] In summary, the present application provides an RFA. In the RFA provided by the present application, two output ends of the optical path switching unit are correspondingly connected to two input ends of the polarization beam combiner. The optical path switching unit can alternately transmit two pump beams with different wavelengths to its two output ends according to the target frequency, so that the two pump beams can alternately enter different input ends of the polarization beam combiner. Thus, after orthogonally polarization combining the two pump beams received by the polarization beam combiner, a polarization pulse sequence can be output. In the polarization pulse sequence, two polarization pulses with different wavelengths but the same polarization direction are staggered in time. Therefore, the SRS transfer between pump beams with different wavelengths can be effectively reduced, the NF of the short-wave signal can be reduced, and the performance of the optical communication system can be improved.

[0082] Another embodiment of the present application provides an RFA. As Figure 9 shown, the RFA includes: a first pump source 01, a second pump source 02, an optical path switching unit 03, a first polarization beam combiner 04, a depolarizer 17, a fourth coupler 18, and a first coupler 05.

[0083] Among them, the first pump source 01 is used to output a first pump beam with a first wavelength λ1. The second pump source 02 is used to output a second pump beam with a second wavelength λ2. The second wavelength λ2 is different from the first wavelength λ1, and both are within the first wavelength range. The first wavelength range can be 1400 nm to 1520 nm.

[0084] The input end of the optical path switching unit 03 is connected to the first pump source 01. The first output end O1 of the optical path switching unit 03 is connected to the first input end of the first polarization beam combiner 04. The second output end O2 of the optical path switching unit 03 is connected to the second input end of the first polarization beam combiner 04. The optical path switching unit 03 is used to alternately transmit the first pump beam to the first output end O1 and the second output end O2 according to the target frequency.

[0085] The first polarization beam combiner 04 is used to orthogonally polarization combine the received pump beams and then transmit them to the fourth coupler 18.

[0086] The depolarizer 17 is used to depolarize the second pump beam and then transmit it to the fourth coupler 18. As Figure 9 described, the depolarizer 17 can be an IPBCD.

[0087] The fourth coupler 18 is used to couple the received pump beams to the first coupler 05. The first coupler 05 is used to couple the received pump beams to the optical fiber.

[0088] In the embodiment of the present application, as Figure 10As shown, the optical path switching unit 03 alternately transmits the first pump light to the first output end O1 and the second output end O2 according to the target frequency, which may mean that: in the first time period t1, the first pump light received by the input end I1 is transmitted to the first output end O1. In the second time period t2, the optical path is switched, and the first pump light received by the input end I1 is transmitted to the second output end O2.

[0089] Wherein, the duration of the first time period t1 may be equal to the duration of the second time period t2. The target frequency may be from 10 kHz to 1 MHz. The optical path switching unit 03 may alternately repeat the states of the first time period t1 and the second time period t2 to modulate the transmission path of the first pump light according to the target frequency.

[0090] It can also be understood that the first pump light output by the first pump source 01 is linearly polarized light, and the polarization direction of the linearly polarized light is indefinite. After receiving the first pump light transmitted by the optical path switching unit 03, the first polarization beam combiner 04 can combine the first pump light. Moreover, the first polarization beam combiner 04 can modulate the pump light received by its first input end into pump light with the first polarization direction X, and can modulate the pump light received by its second input end into pump light with the second polarization direction Y. Wherein, the first polarization direction X is orthogonal to the second polarization direction Y.

[0091] Combined with the working principle of the optical path switching unit 03 described above, refer to Figure 11 , in the first time period t1, the pump light output by the first polarization beam combiner 04 may include pump light with the first wavelength λ1 in the first polarization direction X. In the second time period t2, the pump light output by the first polarization beam combiner 04 may include pump light with the first wavelength λ1 in the second polarization direction Y.

[0092] From Figure 11 it can be seen that within each time period, the X-polarization pulse and the Y-polarization pulse of the pump light with the first wavelength λ1 are completely staggered in time. After the second pump light with the second wavelength λ2 is depolarized and combined with the polarization pulse sequence output by the first polarization beam combiner 04, there is less power transfer with the pump light with the first wavelength λ1, thereby avoiding affecting the NF of the short-wave signal.

[0093] Optionally, as Figure 12 shown, the RFA may further include a third pump source 06, a fourth pump source 07, a first polarization beam combining depolarizer 08, and a second coupler 09. The functions of the third pump source 06, the fourth pump source 07, the first polarization beam combining depolarizer 08, and the second coupler 09 may refer to the description of the foregoing embodiments and will not be elaborated here.

[0094] Optionally, continue to refer to Figure 12, the RFA may further include a seventh pump source 13, an eighth pump source 14, a second polarization beam combining depolarizer 15, and a third coupler 16. The functions of the seventh pump source 13, the eighth pump source 14, the second polarization beam combining depolarizer 15, and the third coupler 16 may refer to the descriptions of the foregoing embodiments, and will not be elaborated herein.

[0095] An embodiment of the present application also provides an optical amplification component, such as Figure 13 shown, the optical amplification component includes: a cascaded RFA and EDFA; wherein, the RFA may be the RFA provided in the foregoing embodiment.

[0096] The optical amplification component may also be referred to as a hybrid optical amplification unit, and the RFA and EDFA in the hybrid optical amplification unit may be integrated on a single board. Optionally, the EDFA may be a pluggable amplifier.

[0097] Optionally, the optical amplification component provided by the embodiment of the present application may be used for backward amplification of the signal light in the C+L band of an optical communication system.

[0098] In the embodiments of the present application, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance. The term "at least one" means one or more, and "a plurality" means two or more.

[0099] The term "and / or" in the present application is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0100] As described above, the above are only optional embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present application can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A Raman fiber amplifier, characterized in that, The Raman fiber amplifier includes: a first pump source, a second pump source, an optical path switching unit, a first polarization beam combiner, and a first coupler; The first pump source is configured to output a first pump light with a first wavelength; The second pump source is configured to output a second pump light with a second wavelength, the second wavelength is different from the first wavelength, and both are within a first wavelength range; The input ends of the optical path switching unit are respectively connected to the first pump source and the second pump source. The first output end of the optical path switching unit is connected to the first input end of the first polarization beam combiner, and the second output end of the optical path switching unit is connected to the second input end of the first polarization beam combiner. The optical path switching unit is configured to alternately transmit the first pump light and the second pump light to the first output end and the second output end according to a target frequency; The first polarization beam combiner is configured to orthogonally polarize and combine the first pump light and the second pump light transmitted by the optical path switching unit, and then transmit the combined light to the first coupler; The first coupler is configured to couple the received pump light into an optical fiber.

2. The Raman fiber amplifier according to claim 1, wherein The optical path switching unit is an optical switch or a wavelength selective switch.

3. The Raman fiber amplifier according to claim 1 or 2, characterized in that, The Raman fiber amplifier further includes: a third pump source, a fourth pump source, a first polarization beam combining depolarizer, and a second coupler; The third pump source is configured to output a third pump light with a third wavelength; The fourth pump source is configured to output a fourth pump light with a fourth wavelength. The third wavelength and the fourth wavelength are both within the first wavelength range, and the first wavelength, the second wavelength, the third wavelength, and the fourth wavelength are different from each other; The first polarization beam combining depolarizer is configured to polarize and combine and depolarize the third pump light and the fourth pump light, and then transmit the combined light to the second coupler; The first polarization beam combiner is configured to transmit the orthogonally polarized and combined pump light to the second coupler; The second coupler is configured to couple the received pump light into the first coupler.

4. The Raman fiber amplifier according to any one of claims 1 to 3, characterized in that, The Raman fiber amplifier further includes: a fifth pump source, a sixth pump source, and a second polarization beam combiner; The fifth pump source is configured to output a fifth pump light with a fifth wavelength; The sixth pump source is configured to output a sixth pump light with a sixth wavelength. The fifth wavelength and the sixth wavelength are both within the first wavelength range, and the first wavelength, the second wavelength, the fifth wavelength, and the sixth wavelength are different from each other; The input ends of the optical path switching unit are further respectively connected to the fifth pump source and the sixth pump source. The third output end of the optical path switching unit is connected to the first input end of the second polarization beam combiner, and the fourth output end of the optical path switching unit is connected to the second input end of the second polarization beam combiner. The optical path switching unit is further configured to alternately transmit the fifth pump light and the sixth pump light to the third output end and the fourth output end according to the target frequency; The second polarization beam combiner is configured to orthogonally polarize and combine the received fifth pump light and sixth pump light, and then transmit the combined light to the first coupler.

5. The Raman fiber amplifier according to any one of claims 1 to 4, characterized in that, The first wavelength range is from 1400 nanometers to 1520 nanometers.

6. The Raman fiber amplifier according to any one of claims 1 to 5, characterized in that The Raman fiber amplifier further includes: a seventh pump source, an eighth pump source, a second polarization beam combining depolarizer, and a third coupler; The seventh pump source is configured to output a seventh pump light with a seventh wavelength; The eighth pump source is configured to output an eighth pump light with an eighth wavelength, the eighth wavelength is different from the seventh wavelength, and both are within a second wavelength range, and the upper limit of the second wavelength range is less than the lower limit of the first wavelength range; The second polarization beam combining depolarizer is configured to perform polarization beam combining and depolarization on the seventh pump light and the eighth pump light, and then transmit them to the third coupler; The third coupler is configured to couple the received pump light to the optical fiber.

7. The Raman fiber amplifier according to claim 6, characterized in that, The second wavelength range is from 1200 nanometers to 1399 nanometers.

8. The Raman fiber amplifier according to any one of claims 1 to 7, characterized in that, The Raman fiber amplifier further includes: a drive circuit, and the drive circuit is configured to control the optical path switching unit to switch the transmission path of the pump light according to the target frequency.

9. The Raman fiber amplifier according to any one of claims 1 to 8, characterized in that, The range of the target frequency is from 10 kilohertz to 1 megahertz.

10. The Raman fiber amplifier according to any one of claims 1 to 9, characterized in that, The transmission direction of the pump light coupled by the Raman fiber amplifier to the optical fiber is opposite to the transmission direction of the signal light in the optical fiber.

11. A Raman fiber amplifier, characterized in that, The Raman fiber amplifier includes: a first pump source, a second pump source, an optical path switching unit, a first polarization beam combiner, a depolarizer, a fourth coupler, and a first coupler; The first pump source is configured to output a first pump light with a first wavelength; The second pump source is configured to output a second pump light with a second wavelength, the second wavelength is different from the first wavelength, and both are within the first wavelength range; The input end of the optical path switching unit is connected to the first pump source, the first output end of the optical path switching unit is connected to the first input end of the first polarization beam combiner, the second output end of the optical path switching unit is connected to the second input end of the first polarization beam combiner, and the optical path switching unit is configured to alternately transmit the first pump light to the first output end and the second output end according to the target frequency; The first polarization beam combiner is configured to perform orthogonal polarization beam combining on the received pump light and then transmit it to the fourth coupler; The depolarizer is configured to perform depolarization on the second pump light and then transmit it to the fourth coupler; The fourth coupler is configured to couple the received pump light to the first coupler; The first coupler is configured to couple the received pump light to the optical fiber.

12. An optical amplification component, characterized in that, The optical amplification component includes: a cascaded Raman fiber amplifier and an erbium-doped fiber amplifier; wherein, the Raman fiber amplifier is the Raman fiber amplifier according to any one of claims 1 to 11.

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