C + L + U hybrid doped fiber and amplifier

Abstract

The invention discloses a C + L + U hybrid doped optical fiber and an amplifier. An optical fiber core comprises a first doping system, an isolation system and a second doping system in sequence from inside to outside; the first doping system and the second doping system are respectively one of a bismuth doping system and an erbium doping system, and are physically separated through an isolation system; the amplifier relates to one unit or two units, and when one unit is used, the mixed doped optical fiber is matched with a C + L + U broadband light source to realize full-band amplification; for the two units, the erbium-doped optical fiber and the bismuth-doped optical fiber are used for series connection, combination and amplification respectively, the erbium-doped optical fiber amplifies C + L wave band signal light, and the bismuth-doped optical fiber amplifies L + U wave band signal light. The structure is simple, the erbium-bismuth co-doping problem is solved through the layered doping design, and the advantages of being low in cost, compact in structure and wide in gain bandwidth are achieved.

Description

Technical Field

[0001] This invention belongs to the field of optical communication technology, specifically relating to a C+L+U hybrid doped optical fiber and an amplifier. Background Technology

[0002] To cope with the ever-increasing traffic demands of the 5G era, network operators need to maximize network capacity in a cost-effective manner. Utilizing bands other than the C-band as a means to increase transmission capacity is receiving increasing attention. Currently, there are solutions to extend the C-band to the adjacent L-band. For example, patent CN116960714A proposes a discrete erbium-doped amplifier that can amplify C+L band signals. However, this requires separating the C+L band into two independent C-band and L-band signals, amplifying them separately, and then combining them using wavelength division multiplexing (WDM). This results in the loss of several wavelengths (3-5nm bandwidth) in the middle of the frequency band due to WDM, leading to high coupling loss and poor stability. Patent CN111698033A utilizes a hybrid fiber amplifier with two modules: an erbium-doped fiber amplifier and an integrated Raman amplifier. However, the gain control of this hybrid fiber amplifier is extremely complex and difficult to implement. Currently, there is no commercially available technology that can simultaneously amplify C+L+U bands while controlling their gain.

[0003] In the prior art, patent CN116679373A discloses an active silica fiber in the L+ and L+U bands doped with two or more ions selected from bismuth, germanium, erbium, ytterbium, lanthanum, and thulium; patent CN202010073619.0 discloses a Bi / Er / La / Al co-doped L-band or C+L-band silica fiber; patent CN117849937A discloses an S+C+L-band ultra-wideband gain fiber with a dual-core structure having Tm-doped inner core and Er-doped outer core; patent CN118666490A incorporates bismuth, phosphorus, and... The invention discloses an O- and E-band extended active optical fiber and its preparation method by incorporating control elements into the fiber core; CN118409387A discloses a U-band active optical fiber with a core layer co-doped with germanium, bismuth and lanthanide ions. However, the above-mentioned existing technologies have defects such as incomplete band coverage (only some bands, no full band connection), complex gain control (discrete modules or hybrid structures lead to high loss and poor coordination), material process bottlenecks (bismuth doping has high loss, multi-layer structure is difficult to mass produce) and low system integration (requires additional devices leading to high cost), which cannot meet the 5G ultra-wideband optical amplification requirements.

[0004] Regarding the gain fiber for ultrawideband amplification of C+L+U, SV Firstov proposed to achieve simultaneous amplification of the C+L+U bands through erbium-bismuth mixed doping. However, this method also has the following problems: the mixed doping of erbium (Er) and bismuth (Bi) causes the upconversion luminescence and excited-state absorption of the two ions to affect each other. Moreover, the two ions have similar radii, and in the twisted germanium silicate glass, there is mutual competition and suppression in the vacancies entering the glass.

[0005] Therefore, those skilled in the art are dedicated to developing a C+L+U hybrid doped optical fiber and amplifier. Summary of the Invention

[0006] Therefore, in view of the above-mentioned defects of the prior art, the present invention solves at least the following technical problems: solving the problem of narrow gain spectral width in existing optical fiber signal amplification, and solving the energy and structural competition that exists when erbium (Er) and bismuth (Bi) are co-doped in optical fibers.

[0007] This invention discloses a C+L+U hybrid doped optical fiber and an amplifier. The fiber core consists of a first doping system, an isolation system, and a second doping system from the inside out. The first doping system and the second doping system are respectively a bismuth doping system and an erbium doping system, and are physically separated by the isolation system. Furthermore, the first doping system is a bismuth-doped germanium silicate system, and the second doping system is an erbium-doped silicate system; or the first doping system is an erbium-doped silicate system, and the second doping system is a bismuth-doped germanium silicate system; the isolation system is composed of Ge, F, and Si elements; Furthermore, the bismuth-doped germanium silicate system is composed of silicon tetrahedra and germanium tetrahedra, and its porosity is lower than that of the erbium-doped silicate system; the erbium-doped silicate system is composed of silicon tetrahedra, and its porosity is higher than that of the bismuth-doped germanium silicate system. Furthermore, the isolation system is used to block the energy transfer paths of erbium ions and bismuth ions, avoiding energy competition when the two are mixed and doped. Further, in the first doping system, the doping content of bismuth is 0.001–0.5 wt%, and the doping content of germanium is 10–50 wt%; in the second doping system, the doping content of erbium is 0.01–1 wt%; or in the first doping system, the doping content of erbium is 0.01–1 wt%, and in the second doping system, the doping content of bismuth is 0.001–0.5 wt%, and the doping content of germanium is 10–50 wt%. Furthermore, the first and second doped systems are also doped with at least one of Al, La, Ce, Yb, Zr, and Nd, with a doping content of 0.001–0.5 wt%. Furthermore, the bismuth-doped germanium silicate system is used to amplify L+U band signal light, and the erbium-doped silicate system is used to amplify C+L band signal light; This invention also discloses a C+L+U hybrid doped fiber amplifier, comprising one or two amplification units: when there is one amplification unit, it includes the aforementioned hybrid doped fiber, pump laser, signal optical path, wavelength division multiplexer, and optical isolator; when there are two amplification units, the first unit includes bismuth-doped germanium silicate fiber, pump laser, signal optical path, wavelength division multiplexer, and optical isolator, and the second unit includes erbium-doped silicate fiber, pump laser, signal optical path, wavelength division multiplexer, and optical isolator; Furthermore, the pump laser is connected to the wavelength division multiplexer: when the amplifier is a single amplification unit structure, it provides pump energy to the hybrid doped fiber; when the amplifier is a two amplification unit structure, it provides pump energy to the bismuth-germanium silicate fiber of the first unit and the erbium-doped silicate fiber of the second unit, respectively. Furthermore, the amplifier has a gain bandwidth covering 1527–1700 nm, a bandwidth of 173 nm, and a fluorescence emission intensity of -32.7 dBm at 1650 nm.

[0008] In summary, compared with the prior art, the above-described technical solutions conceived in this invention have at least the following beneficial effects: 1. This invention can achieve ultra-wideband gain amplification, especially in the band range adjacent to the C-band. The C-band is already commercially available, and the L-band is under development. It can not only be combined with the L-band to expand the bandwidth of optical fiber communication, but also with the U-band to expand the bandwidth of optical fiber communication. It can meet the current bandwidth growth requirements in the field of optical communication. It has the advantages of compact structure, easy implementation, wide amplification spectrum, and ability to achieve broadband high gain. It can be applied to communication band expansion, mid-infrared laser light sources and other related fields. 2. This invention addresses the challenges of energy and structural competition in erbium-bismuth co-doping by disclosing a layered doping system and an isolation layer doping system. The two-layer doping ensures the stability of the two-layer glass structure and also prevents the two ions from interfering with each other in terms of energy level transition radiation wavelength and bandwidth. Attached Figure Description

[0009] Figure 1 This is a cross-sectional view of the optical fiber doped layer of the present invention; Figure 2 This is a diagram of the microscopic coordination environment structure of the erbium-doped optical fiber of the present invention; Figure 3 This is a diagram of the micro-coordination environment structure of the bismuth-doped optical fiber of the present invention; Figure 4 This is a structural diagram of the fiber optic amplifier containing two amplification units according to the present invention; Figure 5 This is a structural diagram of the fiber optic amplifier containing one amplification unit according to the present invention; Figure 6 This is an amplified spontaneous emission spectrum of Embodiment 5 of the present invention.

[0010] 101 - First doping system, 102 - Isolation system, 103 - Second doping system, 201 - First amplification unit, 301 - Second amplification unit, 211 / 212 / 311 / 312 - Optical isolator, 213 / 214 / 313 / 314 - Wavelength division multiplexer, 216 / 217 / 316 / 317 Pump laser, 215 - Bismuth-doped fiber, 315 - Erbium-doped fiber, 201' - Amplification unit, 215' - Erbium-bismuth fiber. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0012] To facilitate understanding, before introducing the embodiments of this application, the terms or concepts that may be involved in the embodiments of this application will be introduced first. It should be understood that the basic concepts introduced below are simply explained using examples described in the current related art, and the specific names are not limited in this application.

[0013] Regarding network formations, optical fiber is essentially a type of glass. Glass is a rigid structure, and a rigid structure is a three-dimensional network-like irregular framework. This three-dimensional network-like framework structure is the network formation in glass. The network formation determines the basic structure and many important properties of glass. For example, silica glass is composed of a three-dimensional random framework of silicon-oxygen tetrahedra. The network structure is complete and robust, giving fused silica glass very high melting and softening temperatures, strong mechanical strength, and a low coefficient of thermal expansion. Taking common silica optical fiber as an example, the random network model considers that the most basic unit composing this type of glass is a silicon-oxygen tetrahedron (SiO4) formed by a silicon atom and four surrounding oxygen atoms. The silicon atom is located at the center of the tetrahedron, and the four oxygen atoms are located at the vertices of the tetrahedron. The silicon and oxygen atoms are bonded together by covalent bonds. Each silicon-oxygen tetrahedron is connected to other silicon-oxygen tetrahedra through the oxygen atoms at the vertices, forming a three-dimensional spatial network. The network connection method of the network formation is that the silicon-oxygen tetrahedra are interconnected through shared oxygen atoms (bridging oxygen). These connections are irregular, resulting in a lack of long-range order in the three-dimensional network structure of the glass, but a certain degree of short-range order exists in local regions. For example, in quartz glass, silicon-oxygen tetrahedra are connected at various angles, forming a highly cross-linked three-dimensional network without obvious periodic repeating units. Overall, silicon-oxygen tetrahedra are randomly distributed in three-dimensional space, forming a continuous, gapless network structure. However, due to the irregularity of the silicon-oxygen tetrahedra connections, there are voids or channels of varying sizes in the network. The size and shape of these voids are also irregular. In active optical fibers, rare earth ions, such as erbium and bismuth ions, enter through the void lattice formed in the network forging body. As described above, the silicate system mentioned in this invention uses silicon-oxygen tetrahedra to form the glass network framework. In the germanium silicate system mentioned in this invention, there is also a germanium tetrahedron, GeO4, as another network forging body. Therefore, the germanium silicate system has two tetrahedral structures that share oxygen atoms on the germanium-oxygen bonds, forming a three-dimensional irregular network structure of alternating GeO4 and SiO4. Compared to silicate systems, germanium silicate systems have a more twisted and crowded network structure with fewer voids, thus reducing the likelihood of rare-earth ions entering the network. Erbium ions, with their larger radius than bismuth ions, are more likely to enter the voids within the germanium silicate network, potentially preventing erbium from entering. Therefore, designing two separate, non-interfering doped layers can overcome the difficulty of rare-earth ion doping into the microstructure. Furthermore, germanium silicate glass structures have lower porosity, making them more suitable for bismuth ions, while silicate glass structures have higher porosity, making them more suitable for erbium ions.

[0014] Regarding energy conversion, the gain amplification principle of an amplifier involves the pump source providing energy to amplify the signal light, causing rare-earth ions to transition from the ground state to an excited state, thus achieving particle inversion. The 4f electron shell of rare-earth ions possesses metastable energy levels, such as Er... 3+ The ground state is 4 I 15 / 2 The excited state is 4 I 13 / 2 (Corresponding to a wavelength of 1550 nm). When irradiated by pump light (such as a 980 nm or 1480 nm laser), ions absorb energy and transition to a higher energy level. Under sufficiently strong pump light, the number of ions in the higher energy level (metastable state) exceeds that in the ground state, resulting in population inversion. This is a necessary condition for optical amplification. For Er ions, the pump light (e.g., 980 nm or 1480 nm) will... 3+ From the ground state 4 I 15 / 2 Stimulate 4 I 11 / 2 or 4 I 13 / 2 The energy level is reduced to a metastable state through nonradiative relaxation. 4 I 13 / 2 Then, it radiatively transitions back to the ground state. 4 I 15 / 2 It emits photons at ~1550 nm (C-band). When an L-band signal light is input, due to the energy and energy level of the longer wavelength band of the L-band... 4 I 13 / 2 With energy level 4 I 9 / 2 Since the energy difference is relatively close, the erbium ion in the metastable upper energy level can easily absorb long-wavelength signal photons and then transition to the next energy level. 4 I 9 / 2 This leads to attenuation of long-wavelength signals in the L-band. 3+Without any excitation, ions are in their ground state. When the pump light intensity is moderate, the ions absorb the energy of the pump light and transition to higher energy levels. Different wavelengths of the pump light result in different higher energy levels to which the ions transition. In the metastable state, the particles have a longer lifetime, and particles excited by the pump light continuously converge towards this energy level through non-radiative transitions, achieving population inversion. Similarly, for bismuth ions, under pump light excitation, bismuth ions also undergo energy level transitions, amplifying the signal. Bismuth ions are highly sensitive to their surrounding environment; the absorption peak shifts with changes in the fiber doping composition and matrix, corresponding to Bi ions transitioning to different energy levels and undergoing population inversion at different wavelengths. For example, in a germanium silicate matrix, bismuth forms two active centers, BAC-Si and BAC-Ge, which correspond to upconversion luminescence near 1430 nm and 1600 nm, respectively. This invention designs an isolation system to prevent the two gain media, erbium and bismuth, from entering each other's doping system during layered doping, which would cause the emission and absorption peaks of the two rare earth ions to overlap. During this stimulated emission and upconversion luminescence process, bismuth ions and erbium ions may compete for energy transfer and energy conversion.

[0015] like Figure 1 As shown in the figure, this invention discloses a C+L+U hybrid doped optical fiber, the core of which, from the inside out, consists of a first doping system, an isolation system, and a second doping system. The first and second doping systems are respectively a bismuth doping system and an erbium doping system, and are physically separated by the isolation system. The isolation system is used to block the energy transfer path between erbium ions and bismuth ions, avoiding both competition in energy conversion and structural competition.

[0016] The first doping system is a bismuth-doped germanium silicate system, and the second doping system is an erbium-doped silicate system; or the first doping system is an erbium-doped silicate system, and the second doping system is a bismuth-doped germanium silicate system; the isolation system consists of Ge, F, and Si elements. The bismuth-doped germanium silicate system is used to amplify L+U band signal light, and the erbium-doped silicate system is used to amplify C+L band signal light.

[0017] like Figure 2-3 As shown, the first doping system is a bismuth-doped germanium silicate system composed of silicon tetrahedra and germanium tetrahedra with low porosity, and the second doping system is an erbium-doped silicate system composed of silicon tetrahedra with high porosity; or the first doping system is an erbium-doped silicate system composed of silicon tetrahedra with high porosity, and the second doping system is a bismuth-doped germanium silicate system composed of silicon tetrahedra and germanium tetrahedra with low porosity.

[0018] In the first doping system, the doping content of bismuth is 0.001–0.5 wt%, and the doping content of germanium is 10–50 wt%; in the second doping system, the doping content of erbium is 0.01–1 wt%; or in the first doping system, the doping content of erbium is 0.01–1 wt%, and in the second doping system, the doping content of bismuth is 0.001–0.5 wt%, and the doping content of germanium is 10–50 wt%. Both the first and second doping systems are further doped with at least one of Al, La, Ce, Yb, Zr, and Nd, with a doping content of 0.001–0.5 wt%.

[0019] This invention also discloses a C+L+U hybrid-doped fiber amplifier, which comprises one or two amplification units. When it is a single amplification unit, it includes the aforementioned hybrid-doped fiber, pump laser, signal optical path, wavelength division multiplexer, and optical isolator. When it is a double amplification unit, the first unit includes a bismuth-doped germanium silicate fiber, pump laser, signal optical path, wavelength division multiplexer, and optical isolator; the second unit includes an erbium-doped silicate fiber, pump laser, signal optical path, wavelength division multiplexer, and optical isolator. The pump laser is connected to the wavelength division multiplexer: when the amplifier is a single amplification unit structure, it provides pump energy to the aforementioned hybrid-doped fiber; when the amplifier is a double amplification unit structure, it provides pump energy to the bismuth-doped germanium silicate fiber of the first unit and the erbium-doped silicate fiber of the second unit, respectively. The C+L+U band amplifier with one or two units designed in this invention has good commercial prospects and provides a solution for multi-band WDM systems in industry and academia.

[0020] Example 1 A C+L+U band fiber amplifier, such as Figure 4 As shown, it includes two amplification units. The first amplification unit 201 includes optical isolators 211 and 212, wavelength division multiplexers 213 and 214, bismuth-doped fiber 215, and pump lasers 216 and 217. The second amplification unit 301 includes optical isolators 311 and 312, wavelength division multiplexers 313 and 314, erbium-doped fiber 315, and pump lasers 316 and 317. The composition of the erbium-doped fiber is: 0.05 wt% erbium doping and 0.005 wt% aluminum doping. The composition of the bismuth-doped fiber is: 0.002 wt% bismuth doping, 40 wt% germanium doping, and 0.02 wt% lanthanum doping.

[0021] Example 2 A C+L+U band fiber amplifier, such as Figure 4As shown, it includes two amplification units. The first amplification unit 201 includes optical isolators 211 and 212, wavelength division multiplexers 213 and 214, bismuth-doped fiber 215, and pump lasers 216 and 217. The second amplification unit 301 includes optical isolators 311 and 312, wavelength division multiplexers 313 and 314, erbium-doped fiber 315, and pump lasers 316 and 317. The composition of the erbium-doped fiber is: 0.02 wt% erbium and 0.025 wt% aluminum. The composition of the bismuth-doped fiber is: 0.005 wt% bismuth, 40 wt% germanium, and 0.02 wt% lanthanum.

[0022] Example 3 A C+L+U band fiber amplifier, such as Figure 5 As shown, the device includes an amplification unit 201', which comprises optical isolators 211 and 212, wavelength division multiplexers 213 and 214, erbium-bismuth fiber 215', and pump lasers 216 and 217. The layered doping structure of the erbium-bismuth fiber, from the inside out, consists of a first doping system, a Ge / F / Si doping system, and an erbium silicate system. The first doping system comprises 0.05 wt% erbium and 0.005 wt% aluminum; the Ge / F / Si doping system comprises 5 wt% germanium and 0.8 wt% fluorine; and the second doping system comprises 0.005 wt% bismuth, 0.003 wt% lanthanum, and 40 wt% germanium.

[0023] Example 4 A C+L+U band fiber amplifier includes an amplification unit 201', which comprises optical isolators 211 and 212, wavelength division multiplexers 213 and 214, erbium-bismuth fiber 215', and pump lasers 216 and 217. The erbium-bismuth fiber has a layered doping structure from the inside out consisting of a first doping system, a Ge / F / Si doping system, and an erbium silicate system. The first doping system comprises 0.005 wt% bismuth, 0.003 wt% lanthanum, and 40 wt% germanium. The Ge / F / Si doping system comprises 5 wt% germanium and 0.8 wt% fluorine. The second doping system comprises 0.05 wt% erbium and 0.005 wt% aluminum.

[0024] Example 5 A C+L+U band fiber amplifier includes an amplification unit 201', which comprises optical isolators 211 and 212, wavelength division multiplexers 213 and 214, erbium-bismuth fiber 215', and pump lasers 216 and 217. The erbium-bismuth fiber has a layered doping structure consisting of a first doping system, a Ge / F / Si doping system, and an erbium silicate system from the inside out. The first doping system comprises 0.005 wt% bismuth, 0.003 wt% lanthanum, and 40 wt% germanium. The Ge / F / Si doping system comprises 5 wt% germanium and 0.8 wt% fluorine. The second doping system comprises 0.03 wt% erbium and 0.007 wt% aluminum.

[0025] The amplified spontaneous emission spectrum of Example 5 is as follows: Figure 6 In Example 5, the amplified spontaneous emission spectrum of the optical fiber covers the 1527–1700 nm band (with a bandwidth of 173 nm), indicating that it can effectively amplify signals in the C+L+U band. The optical fiber provided by this invention achieves a fluorescence emission intensity of -32.7 dBm at 1650 nm. This performance not only verifies the broadband amplification capability but also meets the application requirements of high-efficiency optical amplifiers and lasers outside the current C-band.

[0026] The description in this specification is merely illustrative of the invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the content of this specification or exceed the scope defined in the claims, they should all fall within the protection scope of this invention.

Claims

1. A C+L+U hybrid doped optical fiber, characterized in that, The fiber core consists of a first doping system, an isolation system, and a second doping system from the inside out; the first doping system and the second doping system are respectively a bismuth doping system and an erbium doping system, and are physically separated by the isolation system.

2. The C+L+U hybrid doped optical fiber according to claim 1, characterized in that, The first doping system is a bismuth-doped germanium silicate system, and the second doping system is an erbium-doped silicate system; or the first doping system is an erbium-doped silicate system, and the second doping system is a bismuth-doped germanium silicate system; the isolation system is composed of Ge, F, and Si elements.

3. The C+L+U hybrid doped optical fiber according to claim 2, characterized in that, The bismuth-doped germanium silicate system is composed of silicon tetrahedra and germanium tetrahedra, and has a lower porosity than the erbium-doped silicate system; the erbium-doped silicate system is composed of silicon tetrahedra, and has a higher porosity than the bismuth-doped germanium silicate system.

4. The C+L+U hybrid doped optical fiber according to claim 3, characterized in that, The isolation system is used to block the energy transfer path between erbium ions and bismuth ions, thus avoiding energy competition when the two are mixed and doped.

5. The C+L+U hybrid doped optical fiber according to claim 4, characterized in that, The first doping system contains 0.001–0.5 wt% bismuth and 10–50 wt% germanium; the second doping system contains 0.01–1 wt% erbium; or the first doping system contains 0.01–1 wt% erbium, the second doping system contains 0.001–0.5 wt% bismuth and 10–50 wt% germanium.

6. The C+L+U hybrid doped optical fiber according to claim 5, characterized in that, The first and second doping systems are further doped with at least one of Al, La, Ce, Yb, Zr and Nd, with a doping content of 0.001 to 0.5 wt%.

7. The C+L+U hybrid doped optical fiber according to claim 2, characterized in that, The bismuth-doped germanium silicate system is used to amplify L+U band signal light, and the erbium-doped silicate system is used to amplify C+L band signal light.

8. A C+L+U hybrid doped fiber amplifier, characterized in that, It includes one or two amplification units: when it is one amplification unit, it includes the hybrid doped fiber, pump laser, signal optical path, wavelength division multiplexer and optical isolator as described in any one of claims 1-7; when it is two amplification units, the first unit includes bismuth-doped germanium silicate fiber, pump laser, signal optical path, wavelength division multiplexer and optical isolator, and the second unit includes erbium-doped silicate fiber, pump laser, signal optical path, wavelength division multiplexer and optical isolator.

9. The C+L+U hybrid doped fiber amplifier according to claim 8, characterized in that, The pump laser is connected to the wavelength division multiplexer: when the amplifier is a single amplification unit structure, it provides pump energy to the hybrid doped fiber according to any one of claims 1-7; when the amplifier is a two amplification unit structure, it provides pump energy to the bismuth-germanium silicate fiber of the first unit and the erbium-doped silicate fiber of the second unit, respectively.

10. The C+L+U hybrid doped fiber amplifier according to claim 8, characterized in that, The amplifier has a gain bandwidth covering 1527–1700 nm, a bandwidth of 173 nm, and a fluorescence emission intensity of -32.7 dBm at 1650 nm.

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