WO2022134109A1

WO2022134109A1 - Fiber amplifier, wavelength division multiplexing system, and optical communication device

Info

Publication number: WO2022134109A1
Application number: PCT/CN2020/139709
Authority: WO
Inventors: 张鹏; 肖孟本; 董红超
Original assignee: 华为技术有限公司
Priority date: 2020-12-25
Filing date: 2020-12-25
Publication date: 2022-06-30
Also published as: CN115552812A

Abstract

The embodiments of the present application relate to the technical field of optical communication, and provide a fiber amplifier, a wavelength division multiplexing system, and an optical communication device. The fiber amplifier comprises: a first pump light source and a first gain fiber, the first pump light source being used for coupling pump light to the first gain fiber, and the first gain fiber comprising a first fiber core and first cladding that wraps the outer part of the first fiber core. The first fiber core has a gain medium, and the first fiber core is formed with a plurality of first gratings arranged along the length direction of the first gain fiber. The first gratings can couple a base mode of the first fiber core to a high-order mold of the first cladding transmitted in the same direction as the base mode.

Description

Optical fiber amplifier, wavelength division multiplexing system and optical communication equipment

technical field

The present application relates to the technical field of optical communication, and in particular, to an optical fiber amplifier, a wavelength division multiplexing system, and an optical communication device.

Background technique

In the field of optical communication, rare earth fiber amplifiers are widely used, especially Erbium Doped Fiber Amplifier (EDFA). The room mainly includes pump light source 01 and Erbium Doped Fiber (Erbium Doped Fiber, EDF) 02 and so on. Among them, EDF02 is the core structure of EDFA, and the gain spectral characteristics of EDF02 determine the bandwidth of EDFA. As shown in Figure 2, the gain spectrum of EDF02 is mainly concentrated in the C-band, so that the EDFA is mainly concentrated in the C-band, with a bandwidth of more than 30 nanometers, which in turn supports the expansion of communication capacity in recent decades.

With the explosive growth of communication capacity, the bandwidth needs to be widened, and the existing EDF concentrated in the C band can no longer meet the demand. In this case, the gain spectrum of the EDF needs to be expanded. For example, as shown in Figure 2, the gain profile of the EDF needs to be extended to the S-band (S band) and to the L-band (L band). As can be seen from Figure 2, whether it is extended to the S band or to the L band, the gain of the EDF will drop sharply, and the amplification performance of the EDFA will drop sharply. In addition, widening the bandwidth will also lead to gain. The flatness becomes worse (for example, if the bandwidth is doubled, the gain flatness is degraded by about ten dB).

Fig. 3 is another existing EDFA structure diagram, including a first EDF 021 and a second EDF 022, the first pump light source 011 is used to provide pump light to the first EDF 021, and the second pump light source 012 is used for The second EDF 022 is supplied with pump light, and a gain flattening filter (Gain Flattening Filter, GFF) 03 is provided between the first EDF 021 and the second EDF 022.

In the EDFA shown in Figure 3, a two-stage optical amplifier (that is, with a first EDF 021 and a second EDF 022) and GFF03 are used to remove the gain peak to expand the bandwidth. As shown in Figure 4, a better gain can be obtained. flatness.

However, as shown in FIG. 4 , the gain improvement of the EDFA is still limited, so the amplification performance of the EDFA is limited, and it still cannot meet the demand for the explosive growth of communication capacity. Besides, as shown in Figure 4, the depth of GFF03 is too large, which deteriorates the noise performance of the EDFA, and even makes the EDFA unusable.

SUMMARY OF THE INVENTION

Embodiments of the present application provide an optical fiber amplifier, a wavelength division multiplexing system, and an optical communication device. The main purpose is to provide an optical fiber amplifier that can increase the gain and reduce the noise figure on the premise of realizing a wide frequency band and a flat gain.

To achieve the above object, the embodiments of the present application adopt the following technical solutions:

In a first aspect, the present application provides a fiber amplifier, the fiber amplifier includes: a first pump light source and a first gain fiber, the first pump light source is used to couple the pump light to the first gain fiber, and the first gain fiber The optical fiber includes a first core and a first cladding clad outside the first core, the first core has a gain medium, and the first core is formed with a plurality of first gain fibers arranged along the length direction of the first gain fiber. A grating; wherein the first grating is capable of coupling the fundamental mode of the first fiber core to the higher-order mode of the first cladding layer propagating in the same direction as the fundamental mode.

In the fiber amplifier provided in the embodiment of the present application, the first pump light source provides the pump light to the first gain fiber, so that the gain medium in the first core of the first gain fiber is converted from low energy by the pump light under the action of the pump light. level transition to a high energy level to realize the amplification of the optical signal. Also, since the first grating is formed on the first core, and the first grating can couple the fundamental mode of the first core to the high-order mode propagating in the same direction as the fundamental mode of the first cladding, in this case, through the The first grating can remove the gain peak and realize the filtering effect. In particular, in the fiber amplifier of the present application, the first gain fiber is also performing filtering while amplifying the optical signal, suppressing the gain competition and making the emission cross section smaller. The signals in the signal bands of 100% (for example, S-band and L-band) can be sufficiently amplified to increase the gain over the entire bandwidth, and at the same time, the gain-flattening filter depth will be reduced and the noise performance will be greatly improved.

In a possible implementation manner of the first aspect, the period Λ1 of the first grating satisfies:

Wherein, λ1 _res is the center wavelength of the gain spectrum of the first gain fiber;

is the effective refractive index of the fundamental mode of the first core;

is the effective refractive index of the m-th mode of the first cladding layer, m is a positive integer greater than 1; the period Λ1 of the first grating is the spacing between every two adjacent first gratings.

In a possible implementation manner of the first aspect, the fiber amplifier further includes: a second pump light source and a second gain fiber, the second pump light source is used to couple the pump light to the second gain fiber, and the first gain fiber The light output end is connected with the light input end of the second gain fiber, the second gain fiber includes a second core and a second cladding clad outside the second core, and the second core has a gain medium. In this case, the first pump light source and the first gain fiber form a first-stage amplifying structure, and the second pump light source and the second gain fiber form a second-stage amplifying structure. Through two-stage amplification, the high gain requirement of the fiber amplifier can be met. .

In a possible implementation manner of the first aspect, the fiber amplifier includes three or more pump light sources and gain fibers.

In a possible implementation manner of the first aspect, the second fiber core is formed with a plurality of second gratings arranged along the length direction of the second gain fiber; the second gratings can couple the fundamental mode of the second fiber core to the second cladding The higher-order mode of the second fiber core is transmitted in the same direction as the fundamental mode of the second fiber core; the period Λ2 of the second grating satisfies:

Wherein, λ2 _res is the center wavelength of the target filter gain spectrum of the second gain fiber;

is the effective refractive index of the fundamental mode of the second core;

is the effective refractive index of the m-th mode of the second cladding layer, m is a positive integer greater than 1; the period Λ2 of the second grating is the spacing between every two adjacent second gratings.

By arranging gratings in both the first gain fiber of the first-stage amplification and the second gain fiber of the second-stage amplification, the distributed gain flatness is realized, the gain competition in the large emission cross-section band is suppressed, and the gain is fully amplified. As a result, the gain over the entire bandwidth can be increased, and the gain-flattening filter depth can be reduced, greatly improving the noise performance.

In a possible implementation manner of the first aspect, the period Λ1 of the first grating is equal to the period Λ2 of the second grating.

In a possible implementation manner of the first aspect, the period Λ1 of the first grating is greater than or smaller than the period Λ2 of the second grating.

In a possible implementation manner of the first aspect, the gain medium is rare earth ions. so that the gain fiber forms a rare earth doped fiber.

In a possible implementation manner of the first aspect, the rare earth ions are selected from at least one of Er ³⁺ , Tm ³⁺ , Ho ³⁺ or Yb ³⁺ .

In a possible implementation manner of the first aspect, the fiber amplifier further includes a wavelength coupling device, and the wavelength coupling device is used for coupling the pump light and the signal light. By setting the wavelength coupling device, the coupling amount of the pump light signal light can be improved.

In a possible implementation manner of the first aspect, the optical fiber amplifier further includes an isolator.

In a second aspect, the present application provides a wavelength division multiplexing system, the wavelength division multiplexing system includes: a wavelength division multiplexer, a transmission optical fiber, a demultiplexer, and any implementation manner of the first aspect above. The light input end of the fiber amplifier is connected with the wavelength division multiplexer through the transmission fiber; the light output end of the fiber amplifier is connected with the wavelength division multiplexer through the transmission fiber.

In the wavelength division multiplexing system provided by the embodiments of the present application, the optical fiber amplifier in any of the implementation manners of the above-mentioned first aspect is included. While amplifying the optical signal, the first gain fiber of the fiber amplifier is also filtering, which suppresses the gain competition, so that the signal in the signal band (for example, the S-band and the L-band) with small emission cross-section can be fully amplified, so that the Increasing the gain across the entire bandwidth also reduces the gain-flattening filter depth, greatly improving noise performance. In order to increase the bandwidth and gain of the wavelength division multiplexing system, the gain is flattened, and the noise figure is also smaller.

In a third aspect, the present application further provides an optical communication device, including the optical fiber amplifier of any implementation manner of the foregoing first aspect or the wavelength division multiplexing system of the foregoing second aspect.

The optical communication device provided by the embodiment of the present application includes the optical fiber amplifier of the above-mentioned embodiment. Therefore, the optical communication device provided by the embodiment of the present application and the optical fiber amplifier of the above-mentioned technical solution can solve the same technical problem and achieve the same expected effect.

Description of drawings

Fig. 1 is the structural representation of a kind of erbium-doped fiber amplifier in the prior art;

Fig. 2 is the gain spectrum diagram of erbium-doped fiber;

3 is a schematic structural diagram of another erbium-doped fiber amplifier in the prior art;

Fig. 4 is the gain spectrum diagram and the noise figure spectrum diagram of the structure shown in Fig. 3;

FIG. 5 is a schematic structural diagram of a wavelength division multiplexing system according to an embodiment of the application;

6 is a schematic structural diagram of an optical fiber amplifier according to an embodiment of the application;

7 is a schematic structural diagram of an optical fiber amplifier according to an embodiment of the application;

FIG. 8 is a schematic structural diagram of an optical fiber amplifier according to an embodiment of the application;

9 is a schematic structural diagram of an erbium-doped fiber in a fiber amplifier according to an embodiment of the application;

Fig. 10 is the insertion loss spectrum diagram of the existing filter;

11 is an insertion loss spectrum diagram of a grating according to an embodiment of the application;

12 is a gain spectrum diagram of a gain fiber according to an embodiment of the application;

13 is a schematic structural diagram of another optical fiber amplifier according to an embodiment of the application;

14 is a schematic structural diagram of another optical fiber amplifier according to an embodiment of the application;

15 is a schematic structural diagram of an erbium-doped fiber in a fiber amplifier according to an embodiment of the application;

16 is a gain spectrum diagram and a noise figure spectrum diagram of the fiber amplifier according to the embodiment of the application;

17 is a schematic structural diagram of another fiber amplifier according to an embodiment of the application;

18 is a schematic structural diagram of another optical fiber amplifier according to an embodiment of the application;

19 is a schematic structural diagram of another fiber amplifier according to an embodiment of the application;

FIG. 20 is a partial structural schematic diagram of a chip integrated with a silicon waveguide according to an embodiment of the present application.

Reference number:

01-pump light source; 02-EDF; 021-first EDF; 022-second EDF; 03-GFF;

101-first pump light source; 102-second pump light source; 103-third pump light source; 201-first gain fiber; 202-second gain fiber; 203-third gain fiber; 211-first fiber core; 212-second core; 221-first cladding; 222-second cladding; 23-first grating; 24-second grating; 3-isolator; 4-wavelength coupling device; 5-silicon waveguide ; 6-chip.

Detailed ways

The technical terms involved in this application are explained below.

Gain (Gain), which represents the power amplification factor of the amplifier, expressed by the common logarithm of the ratio of output power to input power, and the unit is decibel (dB). The higher the gain, the better the performance of this amplifier.

Insertion Loss (IL), which represents the ratio of the outgoing light intensity to the incident light intensity after a light energy is transmitted through the insertion device. The lower the insertion loss, the smaller the loss or attenuation of the optical signal.

Noise Figure (NF), which represents the ratio of the signal-to-noise ratio at the input end of the amplifier to the signal-to-noise ratio at the output end. The smaller the noise figure, the better the noise performance of the amplifier.

The technical solutions involved in the present application are introduced below.

In the optical communication line in the optical communication equipment, the optical signal will be lost with the long-distance transmission of the signal. Therefore, generally in the optical communication equipment, a fiber amplifier needs to be installed to amplify the attenuated optical signal.

Figure 5 shows a structural diagram of a wavelength division multiplex (WDM) system applied in an optical communication setting. The WDM includes multiple light sources, wavelength division multiplexers, transmission fibers, fiber amplifiers, A wavelength division multiplexer and multiple detectors, wherein, at the transmitting end of the WDM system, a wavelength division multiplexer is used to combine the optical signals of different wavelengths emitted by multiple light sources, and the combined optical signals are transmitted through the transmission fiber. To the fiber amplifier, the fiber amplifier amplifies the attenuated optical signal, and the amplified optical signal is sent to the transmission fiber for transmission. The signals are sent to different detectors.

The optical fiber amplifier in the above-mentioned optical communication equipment usually adopts the rare earth optical fiber amplifier, because the rare earth optical fiber amplifier can directly amplify the optical signal, and can make the optical-electrical-optical relay into an all-optical relay.

In addition, in the optical communication equipment other than the above-mentioned WDM, fiber amplifiers may also be set in other optical communication equipment, such as the ytterbium-doped fiber amplifier in the high-power fiber laser, the power of the master oscillator in the lidar Amplifier (Master Oscillator Power-Amplifier, MOPA) and so on.

With the explosive growth of communication capacity, a C band with wavelengths of 1520nm-1560nm, S-band with wavelengths of 1480nm-1520nm and L-band with wavelengths of 1560nm-1620nm are needed to increase the bandwidth. However, in order to achieve high bandwidth, gain and noise figure need to be sacrificed.

The embodiments of the present application provide an optical fiber amplifier, which can improve the gain, reduce the noise factor, and make the gain flat on the premise of realizing high bandwidth, so as to meet the requirements of communication use.

A fiber amplifier is given below, and the specific structure is shown in the following description.

As shown in FIG. 6 is a structural diagram of a fiber amplifier. Between the input end (input) and the output end (output) of the fiber amplifier, it includes: a first pump light source 101 and a first gain fiber 201, a first The pump light source 101 is used to couple the pump light to the first gain fiber 201 . In this way, the pump light provided by the first pump light source 101 excites the medium (eg, rare earth ions) used for gain in the first gain fiber 201 to transition from a low energy level to a high energy level, so as to amplify the optical signal.

Here, the pumping light of the first pumping light source 101 may be as shown in FIG. 6 , the transmission direction of the pumping light in the first gain fiber 201 (as shown by the dashed line with an arrow in the figure) and the gain fiber 201 The transmission directions of the signal light (shown by the solid lines with arrows in the figure) are the same. Such a first pump light source 101 may be referred to as a forward pump light source.

The pumping light of the first pumping light source 101 may be as shown in FIG. The transmission direction of the signal light (shown by the solid line with arrows in the figure) is opposite. Such a first pump light source 101 may be referred to as a back pump light source.

The pump light of the first pump light source 101 can be as shown in FIG. 8 , the first pump light source 101 has two, one of which is the transmission direction of the pump light of the first pump light source in the first gain fiber 201 It is opposite to the transmission direction of the signal light in the gain fiber 201 , and the transmission direction of the other first pump light source in the first gain fiber 201 is consistent with the transmission direction of the signal light in the gain fiber 201 . Such a first pump light source 101 may be referred to as a bidirectional pump light source.

FIG. 9 shows a structural diagram of the first gain fiber 201 in FIG. 6 . The first gain fiber 201 includes a first core 211 and a first cladding 221 clad outside the first core 211. The first fiber The core 211 has a gain medium therein. In addition, a plurality of first gratings 23 are also included. The plurality of first gratings 23 are formed on the first fiber core 211 and arranged along the length direction of the first gain fiber.

The above-mentioned first grating 23 is a long period grating, that is to say, with reference to FIG. 9 , along the transmission direction P of the first gain fiber, the first grating 23 can couple the fundamental mode LP01 in the first fiber core 211 to the first gain fiber. The higher-order mode LP0m in a cladding layer 221 in the same direction as the fundamental mode LP01, m is a positive integer greater than 1.

In this way, after the fundamental mode signal of the first fiber core 211 is coupled to the high-order mode in the first cladding layer 221, it will be lost during the continuous transmission in the P direction in the first cladding layer, so that the first cladding layer will be lost. The gain fiber 201 implements filtering to attenuate the gain competition effect of high gain wavelengths.

Since the first gain fiber 201 suppresses the gain competition of the large emission cross-section band while achieving amplification, the signal bands with smaller emission cross-section (for example, the S band and the L band) can also occupy sufficient pump light or reverse The number of transferred particles was fully amplified. As a result, the gain over the entire bandwidth can be increased, and the gain-flattening filter depth can be reduced, greatly improving the noise performance.

When a gain flattening filter (Gain Flattening Filter, GFF) is used in the fiber amplifier, FIG. 10 shows the insertion loss spectrum of the filter customized based on the gain spectrum of the first gain fiber. When the gain fiber described in FIG. 7 is used, FIG. 11 shows the insertion loss spectrum of each first grating customized based on the gain spectrum of the first gain fiber.

It can be seen from Figure 10 that the insertion loss depth of this filter is relatively large, reaching close to 40dB. This filter can be called a discrete gain flattening filter. However, it can be seen from Fig. 11 that the insertion loss depth of each first grating is only less than 0.8dB. Through the arrangement of these multiple first gratings less than 0.8dB along the transmission direction, the gain fiber can achieve The gain is flat, so a gain fiber with a plurality of first gratings can be called a distributed gain flattening filter.

When the fiber amplifier only includes the first pump light source 101 and the first gain fiber 201 shown in FIG. 6 , the formed fiber amplifier can be called a first-stage amplifier. During specific implementation, the gain spectrum of the first grating can be customized according to the gain spectrum of the first gain fiber 201 and the quantity of the first grating, so that the first gain spectrum capable of realizing the customized gain spectrum can be written on the first gain fiber 201 . A grating, and the period Λ1 of the first grating 23 satisfies:

Wherein, λ1 _res is the center wavelength of the gain spectrum of the first gain fiber 201;

is the effective refractive index of the fundamental mode of the first core 211;

is the effective refractive index of the m-th mode of the first cladding layer 221 , and m is a positive integer greater than 1.

It should be noted that the period Λ1 of the first grating is the length from one refractive index change point to an adjacent refractive index change point. That is, as shown in FIG. 9 , the period Λ1 of the first grating is the distance D between every two adjacent first gratings 23 .

It should be noted that: the center wavelength of the gain spectrum of the first gain fiber 201 refers to: as shown in FIG. 12 , the light energy of λ _res is the largest at the wavelength between 1520 nm and 1540 nm, then λ _res is the center wavelength.

In some embodiments, if the first stage of amplification can meet the gain requirement, the structure shown in FIG. 6 can be adopted. In other embodiments, when the gain achieved by the first-stage amplification cannot meet the requirements, a second-stage amplification, or a third-stage amplification, or more stages of amplification may be used.

Figure 13 shows a two-stage amplifying fiber amplifier, which includes a first pump light source 101 and a first gain fiber 201 between an input end and an output end of the fiber amplifier: a second The pump light source 102 and the second gain fiber 202 are coupled and connected with the light input end of the second gain fiber 202 and the light output end of the first gain fiber 201 .

The first pump light source 101 is used to couple the pump light to the first gain fiber 201 to excite the gain medium in the first gain fiber 201 to transition from a low energy level to a high energy level to achieve first-level amplification of the optical signal.

The second pump light source 102 is used to couple the pump light to the second gain fiber 202 to excite the gain medium in the second gain fiber 202 to transition from a low energy level to a high energy level, thereby realizing the second-level amplification of the optical signal. The desired gain requirement is then achieved through bipolar amplification.

Also, referring to FIG. 15 , the second gain fiber 202 also includes a second core 212 and a second cladding 222 clad outside the second core 212 .

In specific implementation, the core material and cladding material of the first gain fiber 201 and the second gain fiber 202 may be the same, but during the specific wiring, one end of the first gain fiber 201 is connected to the second gain fiber 202 One end is welded so that the two are coupled.

When designing the grating, there are three implementations, the first is to set the grating only on the first gain fiber, and not to set the grating on the second gain fiber; the second is to set the grating only on the second gain fiber, not on the second gain fiber A grating is set on a gain fiber; the third is to set a grating on the first gain fiber, and a grating is also set on the second gain fiber. Whether to write gratings on both gain fibers depends on the gain spectrum and noise figure spectrum of the final fiber amplifier. The noise figure achieved by the first embodiment is smaller than the noise figure achieved by the third embodiment, then the grating is only written on the first gain fiber or the second gain fiber. If the first and second embodiments achieve If the noise figure is higher than that achieved by the third embodiment, gratings are written on both the first gain fiber and the second gain fiber.

As shown in FIG. 14, when gratings are written on both the first gain fiber 201 and the second gain fiber 202, in order to describe the characteristics of the gratings on the two gain fibers clearly, the grating on the second gain fiber 201 can be called the first gain fiber. Two gratings 24 .

In the first gain fiber 201, a plurality of first gratings 23 are arranged along the transmission direction of the first gain fiber 201 to couple the fundamental mode in the first core to the fundamental mode of the first cladding and the first core High-order modes in the same direction to achieve first-order filtering.

In the second gain fiber 201, a plurality of second gratings 24 are arranged along the transmission direction of the second gain fiber 202 to couple the fundamental mode in the second core to the fundamental mode of the second cladding and the second core The high-order mode in the same direction is used to realize the second-stage filtering effect. Through the two-stage filtering, the gain competition of the large emission cross-section band is suppressed, so that the signal bands with small emission cross-section (for example, the S band and the L band) are fully amplified. As a result, the gain over the entire bandwidth can be increased, and the gain-flattening filter depth can be reduced, greatly improving the noise performance.

When gratings are written on both the first gain fiber 201 and the second gain fiber 202, and the gain spectrum of the first gain fiber 201 and the gain spectrum of the second gain fiber 202 are consistent, the first gain fiber 201 and The second gain fiber 202 is regarded as a total fiber, in this case, each grating gain spectrum can be customized according to the gain spectrum of the total fiber, and the first grating 23 written on the first gain fiber 201 and the first grating written on the first The periods of the second gratings 24 on the two gain fibers 202 are equal. After applying the first gain fiber with the first grating written on it and the second gain fiber written with the second grating on the fiber amplifier, if the final gain spectrum has a large fluctuation, the first grating and the second grating can be adjusted. cycle.

When gratings are written on both the first gain fiber 201 and the second gain fiber 202, and the gain spectrum of the first gain fiber 201 and the gain spectrum of the second gain fiber 202 are inconsistent, according to the gain of the first gain fiber 201 The spectral type of the first grating 23 is customized, and the second grating 24 is customized according to the gain spectral type of the second gain fiber 202, and the period Λ1 of the first grating 23 and the period Λ2 of the second grating 24 respectively satisfy:

is the effective refractive index of the fundamental mode of the first core;

is the effective refractive index of the mth order mode of the first cladding, m is a positive integer greater than 1; λ2 _res is the center wavelength of the target filter gain spectrum of the second gain fiber;

is the effective refractive index of the fundamental mode of the second core;

is the effective refractive index of the m-th mode of the second cladding, and m is a positive integer greater than 1.

In this case, the period Λ1 of the first grating 23 may be larger than the period Λ2 of the second grating 24 , or the period Λ1 of the first grating 23 may be smaller than the period Λ2 of the second grating 24 .

It should be noted that the definition of the period of the second grating is the same as the definition of the period of the first grating.

FIG. 16 shows the gain spectrum and noise figure spectrum of the C-band and L-band when gratings are written on both the first gain fiber and the second gain fiber of the fiber amplifier structure shown in FIG. 14 . The C-band and L-band gain profiles and noise figure profiles of the two-stage fiber amplifier using GFF are compared, and the results are as follows:

When the pump light conditions applied by the first pump light source and the second pump light source are the same, in FIG. 4, the existing fiber amplifier can only achieve a gain of less than 12dB, but, as shown in FIG. 16, the embodiment of the present application Fiber amplifiers can achieve gains close to 12dB. Therefore, the fiber amplifier of the present application can significantly increase the gain.

When the pump light conditions applied by the first pump light source and the second pump light source are the same, in Figure 4, the noise figure of the existing fiber amplifier is degraded to close to 12dB, which is quite different from the actual demand. However, as shown in Figure 4 16. The noise figure of the optical fiber amplifier of the embodiment of the present application is less than 5 dB. Therefore, the optical fiber amplifier of the present application can significantly improve the noise performance.

Figure 17 shows a three-stage amplifying fiber amplifier, which includes: a first pump light source 101 and a first gain fiber 201 between the input end (input) and the output end (output) of the fiber amplifier, and the second pump The pump light source 102 and the second gain fiber 202, the third pump light source 103 and the third gain fiber 203, the light input end of the second gain fiber 202 is coupled to the light output end of the first gain fiber 201, and the second gain fiber 202 The light output end is coupled and connected to the light input end of the third gain fiber 203 .

In addition, gratings are written on the first gain fiber 201 , the second gain fiber 202 and the third gain fiber 203 .

Fig. 18 shows another three-stage amplification fiber amplifier. The difference from Fig. 17 is that gratings are written on the first gain fiber 201 and the third gain fiber 203, but the second gain fiber 202 is not written with gratings.

Like the above-mentioned two-stage fiber amplifier, whether gratings are to be written on the first gain fiber 201, the second gain fiber 202 and the third gain fiber 203, it is necessary to follow: when the gain of the final fiber amplifier meets the requirements, Which structure has a smaller noise figure, choose which method.

The gain fiber described above may be a rare earth fiber. Wherein, the rare earth ions doped in the core can be at least one of Er ³⁺ , Tm ³⁺ , Ho ³⁺ or Yb ³⁺ , that is to say, it can be doped with a rare earth ion, or it can be At least two rare earth ions are incorporated.

In some embodiments, in conjunction with FIG. 19 , the fiber amplifier further includes an isolator 3, and the isolator 3 is arranged at the light input end and the light output end of the gain fiber (201, 202), so as to filter out the spontaneously amplified reverse amplification in the fiber Radiation (Amplified Spontaneous Emission, ASE), avoid ASE to interfere with the optical signal, reduce the amplification performance of the fiber amplifier.

In some embodiments, in conjunction with FIG. 19 , the fiber amplifier further includes a wavelength coupling device 4 for coupling the pump light and the slave signal light. The wavelength coupling device 4 has three ports, the first port is connected with the optical fiber for transmitting signal light, the second port is connected with the pump light source, and the third port is connected with the gain fiber.

In addition, the long-period grating mentioned above can also be applied to silicon waveguides. For example, referring to FIG. 20 , an electro-optical modulator (not shown in the figure) is generally integrated on the chip 6 . The silicon waveguide 5 connected to the electro-optic modulator, in the silicon waveguide 5, includes a core and a cladding clad outside the core, and the above-mentioned long period grating can be written on the core to improve gain and reduce noise coefficient.

The appearance of the silicon waveguide 5 may be a rectangular waveguide as shown in FIG. 20 or a ridge waveguide.

In the description of this specification, the particular features, structures, materials or characteristics may be combined in any suitable manner in any one or more embodiments or examples.

The above are only specific embodiments of the present application, but the protection scope of the present application is not limited to this. should be covered within the scope of protection of this application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

An optical fiber amplifier, characterized in that it includes:

the first pump light source;

a first gain fiber, the first pump light source is used for coupling pump light to the first gain fiber, the first gain fiber includes a first core and a cladding outside the first core a first cladding layer, wherein the first fiber core has a gain medium, and the first fiber core is formed with a plurality of first gratings arranged along the length direction of the first gain fiber;

Wherein, the first grating can couple the fundamental mode of the first fiber core to a higher-order mode of the first cladding that propagates in the same direction as the fundamental mode.
The fiber amplifier according to claim 1, wherein the period Λ1 of the first grating satisfies:

Wherein, λ1 res is the center wavelength of the gain spectrum of the first gain fiber;

is the effective refractive index of the fundamental mode of the first fiber core;

is the effective refractive index of the m-th order mode of the first cladding, and m is a positive integer greater than 1;

The period Λ1 of the first grating is the interval between every two adjacent first gratings.
The optical fiber amplifier according to claim 1 or 2, wherein the optical fiber amplifier further comprises:

the second pump light source;

a second gain fiber, the second pump light source is used for coupling pump light to the second gain fiber, and the light output end of the first gain fiber is connected to the light input end of the second gain fiber, The second gain fiber includes a second core and a second cladding outside the second core, the second core having a gain medium therein.
The fiber amplifier according to claim 3, wherein the second fiber core is formed with a plurality of second gratings arranged along the length direction of the second gain fiber; The fundamental mode of the second core is coupled to a higher-order mode of the second cladding that propagates in the same direction as the fundamental mode of the second core;

The period Λ2 of the second grating satisfies:

Wherein, λ2 res is the center wavelength of the target filter gain spectrum of the second gain fiber;

is the effective refractive index of the fundamental mode of the second core;

is the effective refractive index of the m-th order mode of the second cladding, and m is a positive integer greater than 1;

The period Λ2 of the second grating is the interval between every two adjacent second gratings.
The fiber amplifier according to claim 4, wherein the period Λ1 of the first grating is equal to the period Λ2 of the second grating.
The fiber amplifier according to claim 4, wherein the period Λ1 of the first grating is greater than or smaller than the period Λ2 of the second grating.
The fiber amplifier according to any one of claims 1-6, wherein the gain medium is rare earth ions, so that the gain fiber forms a rare earth doped fiber.
A wavelength division multiplexing system, comprising:

wavelength division multiplexer;

transmission fiber;

The optical fiber amplifier according to any one of claims 1 to 7, wherein the light input end of the optical fiber amplifier is connected to the wavelength division multiplexer through the transmission fiber;

A demultiplexer, wherein the light output end of the optical fiber amplifier is connected to the demultiplexer through the transmission fiber.
An optical communication device, comprising:

The optical fiber amplifier according to any one of claims 1 to 7, or the wavelength division multiplexing system according to claim 8.