Waveguide optical amplifier and optical amplification system

Abstract

A waveguide optical amplifier and an optical amplification system. The waveguide optical amplifier comprises a substrate, an outer cladding layer, an inner cladding layer, and a core layer, wherein the outer cladding layer, the inner cladding layer and the core layer are all located on one side of the substrate; the core layer comprises N waveguides arranged in parallel, and each of the N waveguides is used for transmitting signal light; the inner cladding layer covers the N waveguides, and the inner cladding layer is used for transmitting multi-mode pump light; the outer cladding layer covers the inner cladding layer; and the refractive indexes of the core layer, the inner cladding layer and the outer cladding layer sequentially decrease. The waveguide optical amplifier can use a multi-mode pump as a pump source, so that the cost is low.

Description

Waveguide optical amplifiers and optical amplification systems

[0001] This application claims priority to Chinese Patent Application No. 202510396888.3, ​​filed on March 28, 2025, entitled "Waveguide Optical Amplifier and Optical Amplification System", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of optical communication technology, and in particular to a waveguide optical amplifier and an optical amplification system. Background Technology

[0003] A waveguide optical amplifier is an optical amplifier that uses a waveguide structure to limit the propagation path of light and introduces a gain medium within the waveguide to amplify the power of the light.

[0004] In related technologies, waveguide optical amplifiers include a substrate and a core layer and a cladding layer located on one side of the substrate. The core layer includes at least one waveguide, and the cladding layer covers each waveguide. Signal light and single-mode pump light are simultaneously transmitted in the waveguides, thereby amplifying the signal light.

[0005] In this type of waveguide optical amplifier, each waveguide requires a single-mode pump to provide single-mode pump light. However, the high cost of single-mode pumps limits the application of this type of waveguide optical amplifier. Summary of the Invention

[0006] This application provides a waveguide optical amplifier and an optical amplification system. The waveguide optical amplifier can amplify signal light in multiple waveguides using multimode pump light, which helps to reduce costs.

[0007] In a first aspect, this application provides a waveguide optical amplifier. The waveguide optical amplifier includes a substrate, an outer cladding layer, an inner cladding layer, and a core layer, wherein the outer cladding layer, the inner cladding layer, and the core layer are all located on one side of the substrate. The core layer includes N waveguides arranged in parallel, each of the N waveguides being used to transmit signal light, where N is a positive integer. The inner cladding layer covers the N waveguides and is used to transmit multimode pump light. The outer cladding layer covers the inner cladding layer. The refractive indices of the core layer, the inner cladding layer, and the outer cladding layer decrease sequentially.

[0008] In this application, an inner cladding layer is incorporated to allow multimode pump light to propagate within the inner cladding, thereby amplifying the signal light propagating in the waveguide. Since multimode pump light can be used to amplify the signal light, a multimode pump can be used as the pump source instead of a single-mode pump. Given that the cost per watt of a single-mode pump is significantly higher than that of a multimode pump, using a multimode pump as the pump source can significantly reduce costs. Furthermore, multimode pumps do not require a thermoelectric cooler (TEC), and using a multimode pump as the pump source helps reduce the overall power consumption of the optical amplification system, further reducing costs.

[0009] In some examples, the inner cladding is a single, integral structure that encloses the N waveguides. That is, the N waveguides share a single inner cladding, and the multimode pump light within this cladding can simultaneously amplify the signal light in multiple waveguides. When a multimode pump is used as the pump source, the power of the provided multimode pump light is typically high, while the pump power required by the signal light in a single waveguide is usually low. Therefore, by sharing the multimode pump light among the signal light in multiple waveguides, the power requirements of the pump light for the signal light in each waveguide can be met.

[0010] In other examples, the inner cladding comprises N sub-claddings, each of which clads one of the N waveguides. Thus, each waveguide is amplified by the multimode pump light from its corresponding sub-cladding, allowing for individual adjustment of the power of the multimode pump light used in each waveguide to meet the different gain requirements of the signal light in each waveguide.

[0011] In a first possible implementation, the inner cladding covers the outer peripheral wall of each waveguide. The refractive index difference between the inner cladding and the waveguide confines the signal light within the waveguide for transmission.

[0012] In a second possible implementation, the inner cladding covers all surfaces of the outer peripheral wall of each waveguide except for the top surface of the waveguide, which is the surface of the waveguide furthest from the substrate. The refractive difference between the waveguide and air, and the refractive index difference between the waveguide and the inner cladding, confine the signal light within the waveguide for transmission.

[0013] In this second possible implementation, the outer cladding layer can cover the surfaces of the inner cladding layer except for its top and end faces. The top surface of the inner cladding layer is the surface furthest from the substrate, and the end faces are the sides where the waveguide's end faces are located. In this case, the top surface of the inner cladding layer is also clad with air. The refractive index difference between the inner cladding layer and air, and the refractive index difference between the inner and outer cladding layers, can confine the multimode pump light within the inner cladding layer for transmission. When the waveguide and inner cladding layer share air as the cladding layer, it simplifies the fabrication process of the waveguide optical amplifier.

[0014] Optionally, the element doped in any of the N waveguides is selected from the following elements: erbium (Er), ytterbium (Yb), neodymium (Nd), and thulium (Tm). In practical applications, appropriate elements can be selected for doping based on the wavelength of the signal light to be amplified.

[0015] Optionally, N is greater than 1. When N is greater than 1, the integration density of the waveguide optical amplifier can be increased.

[0016] In some examples, at least two of the N waveguides are doped with different elements. This allows for the transmission of signal light at different wavelengths in waveguides doped with different elements, thus amplifying the signal light at different wavelengths. For example, one waveguide is doped with Er, another with Yb, and yet another with Tm.

[0017] In other examples, the N waveguides are doped with the same element. This allows signal light of the same wavelength to be transmitted through the N waveguides, thus amplifying the signal light of the same wavelength. For example, all N waveguides are doped with Er.

[0018] Optionally, the waveguide optical amplifier further includes an end-face coupling structure or a top-face coupling structure located in the inner cladding. The end-face coupling structure is used to inject the multimode pump light into the inner cladding from its end face, and the top-face coupling structure is used to inject the multimode pump light into the inner cladding from its top face. Multimode pump light can be injected into the inner cladding through coupling structures built into it.

[0019] For example, the end-face coupling structure can be a strip-shaped coupled waveguide; the top-face coupling structure can be a reflective structure or a vertically coupled grating, etc.

[0020] Optionally, the waveguide optical amplifier further includes an end-face coupler or a top-face coupler. The end-face coupler contacts the end face of the inner cladding and is used to inject the multimode pump light from the end face of the inner cladding into the inner cladding. The top-face coupler contacts the top face of the inner cladding and is used to inject the multimode pump light from the top face of the inner cladding into the inner cladding. Multimode pump light can also be injected into the inner cladding via a coupler disposed outside the inner cladding.

[0021] For example, the end-face coupler is formed by N signal fibers and multiple pump fibers fused together and tapered; the N signal fibers correspond one-to-one with the N waveguides, each of the N signal fibers is used to output signal light to the corresponding waveguide, and the multiple pump fibers are located around the N signal fibers, at least a portion of which is used to output the multimode pump light to the inner cladding. This end-face coupler enables the injection of multimode pump light into the inner cladding while simultaneously injecting signal light into the corresponding waveguide.

[0022] For example, the top surface coupler includes a microprism, etc.

[0023] Optionally, the waveguide optical amplifier further includes a pump light fading structure located on the surface of the inner cladding away from the substrate and at a position away from where the multimode pump light is injected into the inner cladding. By setting the pump light fading structure at a position away from where the multimode pump light is injected into the inner cladding, the thermal effect generated by unabsorbed multimode pump light can be suppressed, which is beneficial to improving the stability of the waveguide optical amplifier's performance and avoiding material damage to the waveguide optical amplifier caused by thermal effects.

[0024] Alternatively, the pump light extraction structure can adopt any of the following three structures:

[0025] The first type is a light-absorbing material located on the surface of the inner cladding away from the substrate.

[0026] The second type is a light-transmitting material located on the surface of the inner cladding away from the substrate, wherein the refractive index of the light-transmitting material is greater than that of the inner cladding.

[0027] The third type is a roughened structure located on the surface of the inner cladding that is far from the substrate.

[0028] All three structures can extract unabsorbed multimode pump light from the inner cladding.

[0029] Secondly, an optical amplification system is provided, including a pump source and the waveguide optical amplifier provided in the first aspect. The pump source is used to provide pump light to the waveguide optical amplifier.

[0030] Optionally, the pump source includes at least one of a multimode pump and a single-mode pump. The multimode pump is used to provide the aforementioned multimode pump light, and the single-mode pump is used to provide single-mode pump light. When the pump source includes single-mode pump light, the single-mode pump light needs to be transmitted in the waveguide simultaneously with the signal light to amplify the signal light. Attached Figure Description

[0031] Figure 1 is a three-dimensional structural schematic diagram of a waveguide optical amplifier provided in an embodiment of this application;

[0032] Figure 2 is a schematic diagram of the end face structure of the waveguide optical amplifier in Figure 1;

[0033] Figure 3 is a schematic diagram of the side structure of the waveguide optical amplifier in Figure 1;

[0034] Figure 4 is a schematic diagram of the end face structure of another waveguide optical amplifier provided in an embodiment of this application;

[0035] Figure 5 is a schematic diagram of the end face structure of another waveguide optical amplifier provided in an embodiment of this application;

[0036] Figure 6 is a schematic diagram of the end face structure of another waveguide optical amplifier provided in an embodiment of this application;

[0037] Figure 7 is a schematic diagram of the end face structure of another waveguide optical amplifier provided in an embodiment of this application;

[0038] Figure 8 is a schematic diagram of the arrangement of pump optical fiber and signal optical fiber provided in an embodiment of this application;

[0039] Figure 9 is a schematic diagram of another arrangement of pump fiber and signal fiber provided in an embodiment of this application;

[0040] Figure 10 is a schematic diagram of an end-face coupler provided in an embodiment of this application;

[0041] Figure 11 is a schematic diagram of another waveguide optical amplifier provided in an embodiment of this application;

[0042] Figure 12 is a schematic diagram of another waveguide optical amplifier provided in an embodiment of this application;

[0043] Figure 13 is a schematic diagram of another waveguide optical amplifier provided in an embodiment of this application;

[0044] Figure 14 is a schematic diagram of a vertically coupled grating provided in an embodiment of this application;

[0045] Figure 15 is a schematic diagram of another waveguide optical amplifier provided in an embodiment of this application;

[0046] Figure 16 is a schematic cross-sectional view of another waveguide optical amplifier provided in an embodiment of this application;

[0047] Figure 17 is a schematic diagram of a cross-sectional structure of the waveguide optical amplifier shown in Figure 16 from another direction;

[0048] Figure 18 is a schematic diagram of another cross-sectional structure of the waveguide optical amplifier shown in Figure 16 from another direction. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0050] Figure 1 is a schematic diagram of a waveguide optical amplifier provided in an embodiment of this application. Figure 2 is a schematic diagram of the end face structure of the waveguide optical amplifier in Figure 1. Figure 3 is a schematic diagram of the side structure of the waveguide optical amplifier in Figure 1. As shown in Figures 1-3, the waveguide optical amplifier includes: a substrate 1, an outer cladding layer 4, an inner cladding layer 3, and a core layer 2, all located on one side of the substrate 1. The core layer 2 includes N waveguides 21 arranged in parallel, each waveguide 21 used to transmit signal light, where N is a positive integer. The inner cladding layer 3 covers the N waveguides 21 and is used to transmit multimode pump light. The outer cladding layer 4 covers the inner cladding layer 3. The refractive indices of the core layer 2, inner cladding layer 3, and outer cladding layer 4 decrease sequentially.

[0051] In this embodiment, A covering B means that A is attached to at least a portion of the sidewall of B. In Figure 1, the inner cladding 3 is a monolithic structure that covers N waveguides 21. That is, the N waveguides 21 share a single inner cladding 3.

[0052] Waveguide 21 includes two end faces 21a and an outer peripheral wall connected between the two end faces 21a and surrounding the two end faces 21a.

[0053] The inner cladding layer 3 covers the outer peripheral wall of each waveguide 21. The outer cladding layer 4 covers the outer peripheral wall of the inner cladding layer 3. In this way, when signal light is injected into the waveguide 21, the inner cladding layer 3 can confine the signal light to propagate within the waveguide 21; and when multimode pump light is injected into the inner cladding layer 3, the outer cladding layer 4 can confine the multimode pump light to propagate within the inner cladding layer 3.

[0054] Optionally, the signal light transmitted in waveguide 21 can be single-mode light.

[0055] In this embodiment, the type of element doped in waveguide 21 is not limited; for example, it can be Er, Yb, Nd, and Tm. In practical applications, appropriate elements can be selected for doping based on the wavelength of the signal light to be amplified.

[0056] In one possible implementation, the N waveguides 21 are doped with the same element. For example, each waveguide 21 is doped with Er. In this way, signal light of the same band can be transmitted in the N waveguides 21 to amplify the signal light of the same band.

[0057] In another possible approach, at least two of the N waveguides 21 are doped with different elements. This allows for the transmission of signal light of different wavelengths in waveguides 21 doped with different elements, thereby amplifying the signal light of different wavelengths.

[0058] For example, N equals 3, and the three waveguides 21 are doped with different elements. For instance, one waveguide 21 is doped with Er or Yb, one waveguide 21 is doped with Nd, and another waveguide 21 is doped with Tm. The Er- or Yb-doped waveguide 21 can be used to amplify signal light in the conventional (C) band and / or long wavelength (L) band, the Nd-doped waveguide 21 can be used to amplify signal light in the original (O) band, and the Tm-doped waveguide 21 can be used to amplify signal light in one or more bands of the extended (E) band, short wavelength (S) band, and ultra-long wavelength (U) band.

[0059] In this embodiment, the refractive indices of the core layer 2, inner cladding layer 3, and outer cladding layer 4 are not limited. As long as the difference between the refractive index of the core layer 2 and the refractive index of the inner cladding layer 3 is sufficient to cause total internal reflection of the signal light on the inner wall of the waveguide 21, and the difference between the refractive index of the inner cladding layer 3 and the refractive index of the outer cladding layer 4 is sufficient to cause total internal reflection of the multimode pump light on the inner wall of the inner cladding layer 3, it is acceptable.

[0060] Optionally, the substrate 1 can be a silicon (Si) substrate, a silicon carbide (SiC) substrate, or a quartz substrate, etc.; the outer cladding layer 4 is formed of silicon dioxide (SiO2); the inner cladding layer 3 is formed of germanium (Ge) doped SiO2 or silicon oxynitride (SiON); and the core layer 2 is formed of silicon nitride (SiN).

[0061] In Figures 1-3, waveguide 21 is a straight line. However, the shape of waveguide 21 is not limited in the embodiments of this application. It can also be wavy, zigzag or spiral, as long as multiple waveguides 21 are arranged side by side.

[0062] Figure 1-3 illustrates an example where N equals 3. In other embodiments, N can be equal to 1 or any other value greater than 1. For example, the value of N ranges from 2 to 64. For instance, N equals 4, 8, 16, or 32. When N is greater than 1, the waveguide optical amplifier has a higher integration density; therefore, the following illustrations will focus on the case where N is greater than 1.

[0063] In operation, signal light is injected into the waveguide for propagation within it, while multimode pump light is injected into the inner cladding for propagation within that cladding. Since the inner cladding covers the waveguide, the energy of the multimode pump light within it can be transferred to the signal light in the waveguide, amplifying it. Because multimode pump light can be used to amplify the signal light, it can be used as the pump source instead of a single-mode pump. Given that the cost per watt of a single-mode pump is significantly higher than that of a multimode pump, using a multimode pump as the pump source can significantly reduce costs. Furthermore, multimode pumps do not require a TEC (Transmission Controlled Energy), which helps reduce the overall power consumption of the optical amplification system.

[0064] Furthermore, when a multimode pump is used as the pump source, the power of the multimode pump light it provides is usually relatively high, while the pump power required for the signal light in a single waveguide is usually relatively low. In the embodiments of this application, multiple waveguides share a single cladding layer, and the multimode pump light simultaneously amplifies the signal light in multiple waveguides, thus fully utilizing the energy of the multimode pump light provided by the multimode pump.

[0065] In the embodiments shown in Figures 1-3, the inner cladding layer 3 of the integrated structure is integrally formed. The outer cladding layer 4 and the core layer 2 can be formed on the substrate 1 first, and then the target region of the outer cladding layer 4 can be doped using a doping process, or the target region of the outer cladding layer 4 can be laser-modified to change the refractive index of the target region, thereby obtaining the inner cladding layer 3. Here, the target region is the area in the outer cladding layer 4 located around the waveguide 21 where the refractive index needs to be increased.

[0066] In other embodiments, the outer cladding layer and the inner cladding layer can be fabricated in layers. For example, the outer cladding layer 4 includes a lower outer cladding layer and an upper outer cladding layer, and the inner cladding layer 3 includes a lower inner cladding layer and an upper inner cladding layer. The lower outer cladding layer, the lower inner cladding layer, the core layer, the upper inner cladding layer, and the upper outer cladding layer are sequentially stacked on the substrate 1 in a direction away from the substrate 1. The waveguide optical amplifier with this structure can be formed using photolithography (or overlay process). In this case, the integral inner cladding layer 3 is formed by connecting the lower inner cladding layer and the upper inner cladding layer.

[0067] Figure 4 is a schematic diagram of the end face structure of another waveguide optical amplifier provided in an embodiment of this application. The difference between the waveguide optical amplifier shown in Figure 1 and the one shown in Figure 4 is that the structure of the inner cladding is different.

[0068] As shown in Figure 4, the inner cladding 3 includes N sub-claddings 31 arranged at intervals, each sub-cladding 31 covering a waveguide 21, and the waveguides 21 covered by different sub-claddings 31 are different. The outer cladding 4 covers the outer perimeter of all sub-claddings 31.

[0069] In this embodiment, each waveguide is amplified by multimode pump light from a corresponding sub-cladding. The power of the multimode pump light used in each waveguide can be adjusted individually to meet the different gain requirements of the signal light in each waveguide.

[0070] In practice, the multimode pump light in these multiple sub-cladding layers can be provided by one or more multimode pumps. When the multimode pump light in the multiple sub-cladding layers is provided by multiple multimode pumps, each multimode pump can provide multimode pump light for one or more sub-cladding layers.

[0071] Since multimode pumps can provide high power multimode pump light, when a multimode pump provides multimode pump light for multiple subcladding layers, the output of the multimode pump can be connected to multiple pump fibers through a beam splitter, with each pump fiber used to provide multimode pump light for one subcladding layer.

[0072] Figure 5 is a schematic diagram of another waveguide optical amplifier provided in an embodiment of this application. The difference between this waveguide optical amplifier and the one shown in Figure 1 is that the positions of the inner cladding layer and the core layer are different.

[0073] As shown in Figure 5, the inner cladding 3 covers all surfaces of the outer peripheral wall of each waveguide 21 except for the top surface of the waveguide 21. The top surface of the waveguide 21 is the surface of the waveguide 21 that is away from the substrate 1. That is, the top surface of the waveguide 21 is exposed.

[0074] In this embodiment, the top surface of the inner cladding layer 3 is also exposed, meaning that the top surface of the inner cladding layer 3 is not covered by the outer cladding layer 4. Thus, the top surfaces of the core layer 2 and the inner cladding layer 3 share an air cladding. Since the refractive index of air is lower than that of the core layer 2 and the inner cladding layer 3, the signal light can still be confined within the waveguide 21 for transmission, while the multimode pump light can be confined within the inner cladding layer 3 for transmission.

[0075] Compared to the waveguide amplifier shown in Figure 1, the fabrication process is simpler. Furthermore, using air as the cladding provides stronger light confinement. Additionally, in this structure, multimode pump light can be directly injected into the inner cladding from the top surface of the inner cladding 3, simplifying implementation.

[0076] Figure 6 is a schematic diagram of another waveguide optical amplifier provided in an embodiment of this application. The difference between this waveguide optical amplifier and the one shown in Figure 5 lies in the positions of the inner cladding layer and the core layer. In the embodiment shown in Figure 5, both the top surface of the inner cladding layer 3 and the top surface of the waveguide 21 are exposed. In other embodiments, only the top surface of the inner cladding layer 3 may be exposed, while the top surface of the waveguide 21 may be covered by the inner cladding layer 3.

[0077] Figure 7 is a schematic diagram of another waveguide optical amplifier provided in an embodiment of this application. The difference between this waveguide optical amplifier and the one shown in Figure 2 is that the positions of the inner cladding layer and the core layer are different.

[0078] As shown in Figure 7, each sub-cladding 31 of the inner cladding 3 covers the outer peripheral wall of the corresponding waveguide 21 except for the top surface of the waveguide 21.

[0079] In Figure 7, the top surface of waveguide 21 and the top surface of inner cladding 3 share an air cladding. Since the refractive index of air is less than that of core layer 2 and inner cladding 3, the signal light can still be confined to waveguide 21 for transmission, while the multimode pump light is confined to inner cladding 3 for transmission.

[0080] It should be noted that in the embodiment shown in Figure 7, both the top surface of the inner cladding layer 3 and the top surface of the waveguide 21 are exposed. In other embodiments, only the top surface of the inner cladding layer 3 may be exposed while the top surface of the waveguide 21 is covered by the inner cladding layer 3.

[0081] The following explains the method of injecting multimode pump light into the inner cladding.

[0082] In a first possible implementation, multimode pump light is injected into the inner cladding from its end face. The end face of the inner cladding is connected to its top surface, and the end face of the inner cladding is the surface on which the end face of the waveguide is located.

[0083] In this case, the injection methods of multimode pump light include, but are not limited to, the following three.

[0084] Method 1: Align the output end face of the pump fiber with the end face of the inner cladding to directly inject the multimode pump light output from the pump fiber into the inner cladding.

[0085] Among them, the pump fiber is used to transmit multimode pump light, and the signal fiber is used to transmit signal light.

[0086] In practice, when signal light is injected into the waveguide from its end face, the output end face of the pump fiber can be aligned with the end face of the inner cladding, and the output end face of the signal fiber can be aligned with the end face of the waveguide, thereby simultaneously injecting the signal light and multimode pump light into the waveguide amplifier.

[0087] Figure 8 is a schematic diagram of the arrangement of signal fibers and pump fibers provided in an embodiment of this application. As shown in Figure 8, multiple pump fibers 51 are located around N signal fibers 52. The N signal fibers 52 correspond one-to-one with the N waveguides 21, and each signal fiber 52 is used to output signal light to the corresponding waveguide 21. At least a portion of the multiple pump fibers 51 are used to output multimode pump light. In this case, the signal light output by the signal fiber 52 directly enters the corresponding waveguide 21, and the multimode pump light output by the pump fiber 51 directly enters the inner cladding 3.

[0088] The arrangement shown in Figure 8 is suitable for the case where N waveguides 21 share a single inner cladding 3 as shown in Figures 1 and 3. For the case where each waveguide 21 has its own sub-cladding 31 as shown in Figures 2 and 4, the arrangement shown in Figure 9 can be used.

[0089] For example, in Figure 9, a pump fiber 51 is disposed next to (e.g., below) each signal fiber 52. In other embodiments, two pump fibers 51 may be disposed next to each signal fiber 52, for example, one pump fiber 51 is disposed above and one below each signal fiber 52. Here, "above" refers to the side away from the substrate 1, and "below" refers to the side closer to the substrate 1.

[0090] In the examples shown in Figures 8 and 9, the pump fiber 51 is a multimode fiber, and the signal fiber 52 is a single-mode fiber or a multimode fiber.

[0091] Optionally, a mode converter or lens or similar structure can be provided between the output end face of the pump fiber 51 and the end face of the inner cladding 3 to better couple the multimode pump light output from the pump fiber 51 to the inner cladding; and / or, a mode converter or lens or similar structure can be provided between the output end face of the signal fiber 52 and the end face of the waveguide 21 to better couple the signal light output from the signal fiber 52 to the corresponding waveguide 21.

[0092] In other embodiments, pump fiber 51 and signal fiber 52 are the same fiber, in which case pump fiber 51 and signal fiber 52 can be double-clad fibers. The core of the double-clad fiber is used to transmit signal light, and the inner cladding of the double-clad fiber is used to transmit multimode pump light. Using double-clad fibers to transmit both signal light and multimode pump light simultaneously is advantageous for end-to-end mating with the inner cladding while maintaining a relatively small inner cladding size, thereby achieving a larger core-to-cladding ratio.

[0093] Optionally, the double-clad fiber can be a multi-core fiber, which has multiple cores. In implementation, the arrangement of the cores can be the same as the arrangement of the N waveguides, so that each core can be aligned with one waveguide.

[0094] Method 2: Inject multimode pump light into the inner cladding through an end-face coupler located on one side of the end face of the inner cladding.

[0095] When the pump fiber 51 is a multimode fiber, since the diameter of the multimode fiber is relatively large, if the output end face of the multimode fiber is directly aligned with the inner cladding, there may be a problem of mode field diameter mismatch. Therefore, after arranging N signal fibers and multiple pump fibers, fused tapering can be performed to obtain an end face coupler with one end larger than the other. The end face coupler can simultaneously inject the signal light into the corresponding waveguide and inject the multimode pump light into the inner cladding.

[0096] Figure 10 is a schematic diagram of an end-face coupler provided in an embodiment of this application. As shown in Figure 10, the end-face coupler is formed by N signal optical fibers 52 and multiple pump optical fibers 51 arranged in the manner shown in Figure 7, which are fused tapered.

[0097] By aligning the small end of the end-face coupler with the end faces of the inner cladding and waveguide, the multimode pump light and signal light received from the large end of the end-face coupler can be injected into the inner cladding and waveguide from the small end of the end-face coupler.

[0098] In the case of N waveguides sharing an inner cladding as shown in Figures 1, 3, and 5, when the end-face coupler includes multiple pump fibers, the pump fibers can be divided into two groups. One group of pump fibers is connected to a multimode pump, and the other group of pump fibers is connected to another multimode pump, thus playing a role of mutual backup and improving the reliability of the optical amplification system.

[0099] In the case of each waveguide having a separate sub-cladding as shown in Figures 2 and 4, each waveguide corresponds to an end-face coupler. When the end-face coupler includes multiple pump fibers, the pump fibers can be divided into two groups. One group of pump fibers is connected to a multimode pump, and the other group of pump fibers is connected to another multimode pump, thereby playing a role of mutual backup and improving the reliability of the optical amplification system.

[0100] Method 3: Multimode pump light is injected into the inner cladding through an end-face coupling structure set in the inner cladding.

[0101] For example, the end-face coupling structure is a strip-shaped coupled waveguide, with one end face located in the end face of the inner cladding and the other end located in the inner cladding. The end face of each strip-shaped coupled waveguide is aligned with the output end face of a pump fiber, allowing multimode pump light output from the pump fiber to be input into the strip-shaped coupled waveguide. After propagating along the strip-shaped coupled waveguide, the multimode pump light is injected into the inner cladding from the other end of the strip-shaped coupled waveguide.

[0102] In practice, the cross-sectional area of ​​the strip-coupled waveguide is larger than the cross-sectional area of ​​the waveguide used to transmit signal light. Here, the cross-section is a section perpendicular to the extension direction (or length direction) of the waveguide.

[0103] Optionally, the end-face coupling structure may further include a mode converter connected to one end of the strip-coupled waveguide, which may be a tapered waveguide. The large end of the tapered waveguide is the input end, coupled to the output end face of the pump fiber, and the small end of the tapered waveguide is the output end, connected to one end of the strip-coupled waveguide.

[0104] Alternatively, when the end-face coupling structure only includes a strip coupling waveguide, a mode converter or lens or other structure can be set between the output end face of the pump fiber 51 and the end face of the inner cladding 3 to better couple the multimode pump light output from the pump fiber 51 to the strip coupling waveguide.

[0105] In the case of N waveguides sharing a single cladding as shown in Figures 1, 3, and 5, the cladding contains one or more end-face coupling structures. When the cladding contains multiple end-face coupling structures, these structures can be divided into two groups. One group's pump fiber is connected to a multimode pump, while the other group's pump fiber is connected to another multimode pump. This provides mutual backup and improves the reliability of the optical amplification system.

[0106] In Figures 2 and 4 above, each waveguide has a separate sub-cladding, and each sub-cladding contains one or more end-face coupling structures. When a sub-cladding contains multiple end-face coupling structures, these structures can be divided into two groups. One group of end-face coupling structures connects the pump fiber to a multimode pump, while the other group connects the pump fiber to another multimode pump. This provides mutual backup and improves the reliability of the optical amplification system.

[0107] In a second possible implementation, multimode pump light is injected into the inner cladding from its top surface. In this case, the injection methods of the multimode pump light include, but are not limited to, the following.

[0108] Method 1: Align the output end face of the pump fiber with the top face of the inner cladding to directly inject the multimode pump light output from the pump fiber into the inner cladding.

[0109] Figure 11 is a schematic diagram of another waveguide optical amplifier provided in an embodiment of this application. As shown in Figure 11, a notch 41 is provided in the outer cladding 4 near the input end of the waveguide 21, exposing part of the top surface of the inner cladding 3. The output end face of the pump fiber 51 is attached to the top surface of the inner cladding 3 in the notch 41.

[0110] The output end face of the pump fiber 51 is an inclined plane at an acute angle to the centerline of the pump fiber. This facilitates the transmission of the multimode pump light output from the pump fiber within the inner cladding.

[0111] It should be noted that when the outer cladding 4 does not cover the top surface of the inner cladding 3, the output end face of the pump fiber 41 can be directly attached to the top surface of the inner cladding 3.

[0112] In this case, signal light can be injected into the waveguide from the end face of waveguide 21.

[0113] Method 2: Inject multimode pump light into the inner cladding through a top surface coupler located on the top surface of the inner cladding.

[0114] For example, the top surface coupler can be a microprism.

[0115] Figure 12 is a schematic diagram of another waveguide optical amplifier provided in an embodiment of this application. As shown in Figure 12, the waveguide optical amplifier further includes a microprism 6. The bottom surface of the microprism 6 is attached to the top surface of the inner cladding 3. The arrows in Figure 12 indicate the propagation path of the multimode pump light, which enters from the side of the microprism 6, passes through the bottom surface of the microprism 6, and then enters the inner cladding 3.

[0116] In this case, signal light can be injected into the waveguide from the end face of waveguide 21.

[0117] Method 3: Inject multimode pump light into the inner cladding by using a top-coupling structure located in the inner cladding.

[0118] In some examples, the top-coupling structure can be a vertically coupled grating. This vertically coupled grating can transform multimode pump light propagating perpendicular to the top surface of the inner cladding into multimode pump light propagating parallel to the top surface of the inner cladding, thereby enabling the multimode pump light output from the pump fiber to propagate within the inner cladding.

[0119] In one possible implementation, the multimode pump light is injected into the cladding through a vertically coupled grating, and the signal light is injected into the waveguide from its end face. In another possible implementation, both the multimode pump light and the signal light are injected through vertically coupled gratings. In this other possible implementation, a vertically coupled grating is provided at the input end of each waveguide. The centerline of the signal fiber is perpendicular to or at a small angle to the top surface of the cladding. The vertically coupled grating corresponding to each waveguide can convert signal light propagating perpendicular to the top surface of the cladding into signal light propagating parallel to the top surface of the cladding, thereby enabling the signal light to propagate in the corresponding waveguide.

[0120] Figure 13 is a cross-sectional schematic diagram of another waveguide optical amplifier provided in an embodiment of this application. As shown in Figure 13, the structure of this waveguide optical amplifier is basically the same as that of the waveguide optical amplifier in Figure 6. The difference is that the waveguide optical amplifier in Figure 13 also includes a vertical coupling grating 7, which is embedded in the inner cladding 3 and is used to inject multimode pump light into the inner cladding. In implementation, the top surface of the vertical coupling grating 7 can be flush with the top surface of the inner cladding 3 or the top surface of the vertical coupling grating 7 can be covered by the inner cladding 3.

[0121] Figure 14 is a schematic diagram of a vertically coupled grating provided in an embodiment of this application. As shown in Figure 14, the vertically coupled grating 7 includes a grating array 71 and a tapered waveguide 72. The large end of the tapered waveguide 72 is arranged close to the grating array 71, and the small end of the tapered waveguide 72 is the output end. When multimode pump light is incident along a direction perpendicular to the top surface of the vertically coupled grating 7, due to the diffraction effect, it will become light along a direction parallel to the top surface of the inner cladding 3, and propagate along the tapered waveguide 72 until it is injected into the inner cladding 3.

[0122] The grating array 71 includes a plurality of parallel strip structures 71a and a filling structure 71b filling the spaces between the strip structures 71a. The refractive index of the filling structure 71b is different from that of the strip structures 71a.

[0123] Figure 14 illustrates the grating array 71 including a strip structure 71a as an example. In other embodiments, the strip structure 71a can be replaced with a fan structure.

[0124] In other embodiments, the vertically coupled grating 7 may include only the grating array 71, without the tapered waveguide 72.

[0125] When the signal light is injected into the waveguide using a vertically coupled grating, the structure shown in Figure 14 can be used.

[0126] In other examples, the top-coupling structure can be a reflective structure disposed within the inner cladding. In a first possible implementation, the reflective structure is used to inject multimode pump light, with the signal light injected from the end face of the waveguide. In this first possible implementation, the reflective structure passes through the inner cladding but not through the waveguide. In a second possible implementation, both the multimode pump light and the signal light are injected through the reflective structure. In this second possible implementation, the reflective structure passes through the inner cladding and all the waveguides.

[0127] Figure 15 is a schematic cross-sectional view of another waveguide optical amplifier provided in an embodiment of this application. As shown in Figure 15, a groove 3a is formed in the inner cladding 3 by etching or other methods. Part of the sidewall of the groove 3a is a slope 3b. The slope 3b can reflect the multimode pump light whose propagation direction is perpendicular to the top surface of the inner cladding 3, transforming it into multimode pump light whose propagation direction is parallel to the top surface of the inner cladding 3. This slope is the aforementioned reflection structure.

[0128] In practice, the depth of the groove 3a is determined by the mode size of the multimode pump light, with the aim of reflecting all the multimode pump light incident on the waveguide amplifier, in order to avoid energy waste.

[0129] Optionally, the waveguide optical amplifier further includes a pump light fading structure located on the top surface of the inner cladding and away from the multimode pump light injection point into the inner cladding. For example, it could be located on the top surface of the inner cladding and near the output end of the waveguide.

[0130] When multimode pump light propagates within the inner cladding, it may not be completely absorbed by the gain medium in the waveguide. This unabsorbed multimode pump light can be converted into heat, causing localized temperature rises, affecting the performance of the waveguide amplifier, and even damaging the waveguide amplifier material. By placing a pump light extraction structure at a location far from the multimode pump light injection inner cladding, the thermal effects generated by the unabsorbed multimode pump light can be suppressed.

[0131] For example, the pump light extraction structure can adopt any of the following three structures.

[0132] The first type is a light-absorbing material located on the top surface of the inner cladding, which is the pump light-exiting structure.

[0133] Light-absorbing materials include, but are not limited to, resins or metals.

[0134] Figure 16 is a schematic cross-sectional view of another waveguide optical amplifier provided in an embodiment of this application. As shown in Figure 16, the outer cladding 4 has a window 42 that exposes the top surface of the inner cladding 3, and the light-absorbing material 8 is located in the window 42. The window 42 is located away from the multimode pump light injection into the inner cladding. For example, in Figure 16, it is located away from the groove 3a.

[0135] It should be noted that, for ease of depiction, the distance between the groove 3a and the window 42 in Figure 16 is relatively close, and is only used to indicate the relative position between the two, and does not represent the actual size ratio of each structure of the waveguide optical amplifier.

[0136] Figure 17 is a schematic cross-sectional view of the waveguide optical amplifier in Figure 16 from another direction. The cross-section in Figure 17 is perpendicular to the cross-section in Figure 16. As shown in Figure 17, when the top surface of waveguide 21 is covered by the inner cladding 3, the orthographic projection of the light-absorbing material 8 on the surface of the substrate 1 can overlap with the orthographic projection of waveguide 21 on the surface of the substrate 1. That is, the light-absorbing material 8 can pass over the waveguide 21 without affecting the transmission of signal light.

[0137] Figure 18 is a schematic diagram of another cross-sectional structure of the waveguide optical amplifier in Figure 16 from another direction. The cross-section in Figure 18 is perpendicular to the cross-section in Figure 16. As shown in Figure 18, when the top surface of waveguide 21 is not covered by the inner cladding layer 3, the orthographic projection of the light-absorbing material 8 on the surface of the substrate 1 does not overlap with the orthographic projection of waveguide 21 on the surface of the substrate 1. That is, the light-absorbing material 8 does not pass over the waveguide 21 to avoid affecting the transmission of signal light.

[0138] The second type is a light-transmitting structure for pump light output, which is a light-transmitting material located on the top surface of the inner cladding. The refractive index of the light-transmitting material is greater than that of the inner cladding.

[0139] When the refractive index of the light-transmitting material is greater than that of the inner cladding, the total internal reflection condition of the multimode pump light in the inner cladding can be disrupted, allowing the multimode pump light to exit from the inner cladding. Similar to the structure shown in Figure 16, the light-transmitting material can be placed in the window of the outer cladding 4.

[0140] The third type is a coarsened structure formed on the top surface of the inner cladding, where the pump light is directed out.

[0141] The roughened structure can disrupt the total internal reflection condition of the multimode pump light in the inner cladding, allowing the multimode pump light to exit from the inner cladding. This roughened structure can be formed by etching or other methods. Similar to the structure shown in Figure 16, the roughened structure can be placed in a window of the outer cladding 4.

[0142] In implementation, the pump light extraction structure can also adopt any other structure that can destroy the total internal reflection of the multimode pump light, and the embodiments of this application do not limit this.

[0143] It should be noted that Figure 16 illustrates an example of multimode pump light being injected into the inner cladding through a reflective structure disposed in the inner cladding. The pump light extraction structure can be combined with an optical waveguide amplifier employing any of the aforementioned multimode pump light injection methods.

[0144] This application also provides an optical amplification system. The optical amplification system includes a pump source and any of the aforementioned waveguide optical amplifiers. The pump source is used to provide pump light to the waveguide optical amplifier.

[0145] Optionally, the pump light source includes at least one of a multimode pump and a single-mode pump.

[0146] In some examples, the pump source includes a multimode pump but not a single-mode pump, with the multimode pump providing the multimode pump light propagating in the inner cladding to amplify the signal light in all waveguides.

[0147] In other examples, the pump source includes a single-mode pump but not a multi-mode pump, wherein the single-mode pump light provided by the single-mode pump is transmitted in the waveguide simultaneously with the signal light to amplify the signal light.

[0148] In other examples, the pump source includes single-mode pumps and multi-mode pumps. In at least a portion of the waveguide, the single-mode pump light provided by the single-mode pump is transmitted simultaneously with the signal light, while the multi-mode pump light provided by the multi-mode pump is transmitted within the inner cladding. In waveguides that simultaneously transmit single-mode pump light and signal light, the signal light is amplified by both the single-mode and multi-mode pump lights. This configuration satisfies the gain requirements of the signal light in each waveguide.

[0149] For example, the signal light in one waveguide and the signal light in another waveguide may have different gains under the action of multimode pump light in the inner cladding. In order to balance the gain of the signal light in the two waveguides, a single-mode pump light can be input into the waveguide where the signal light with the lower gain is located, so that the gain of the signal light increases.

[0150] When the pump source includes a single-mode pump and the signal light is injected into the waveguide from the end face, the single-mode pump light and the signal light can be combined into one path using a multiplexing device, and then injected into the corresponding waveguide from the end face. When the pump source includes a single-mode pump and the signal light is injected into the waveguide from the top surface of the inner cladding, for example, the single-mode pump light can be injected into the corresponding waveguide from the end face, or the single-mode pump light and the signal light can be combined into one path using a multiplexing device, and then injected into the corresponding waveguide from the top surface of the waveguide through a top surface coupling structure (such as the aforementioned reflection structure).

[0151] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this application pertains. The terms “first,” “second,” “third,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms “an” or “a” and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms “comprising” or “including” and similar terms mean that the elements or objects preceding “comprising” or “including” encompass the elements or objects listed following “comprising” or “including” and their equivalents, and do not exclude other elements or objects. The “multiple” mentioned in the embodiments of this application refers to two or more. A and / or B indicate three possibilities: A; B; and A and B.

[0152] The above is merely one embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

A waveguide optical amplifier, characterized in that, include: The system comprises a substrate, an outer cladding layer, an inner cladding layer, and a core layer, wherein the outer cladding layer, the inner cladding layer, and the core layer are all located on one side of the substrate. The core layer includes N waveguides arranged in parallel, each of which is used to transmit signal light, where N is a positive integer; The inner cladding layer covers the N waveguides and is used to transmit multimode pump light. The outer cladding layer covers the inner cladding layer; The refractive indices of the core layer, the inner cladding layer, and the outer cladding layer decrease sequentially. The waveguide optical amplifier according to claim 1 is characterized in that, The inner cladding is a single, integral structure that covers the N waveguides; or... The inner cladding includes N sub-claddings, each of which covers one of the N waveguides. The waveguide optical amplifier according to claim 1 or 2 is characterized in that, The inner cladding covers the outer peripheral wall of each waveguide; or... The inner cladding covers all surfaces of the outer peripheral wall of each waveguide except for the top surface of the waveguide, which is the surface of the waveguide furthest from the substrate. The waveguide optical amplifier according to any one of claims 1 to 3 is characterized in that, N is greater than 1, at least two of the N waveguides are doped with different elements; or, the N waveguides are doped with the same element. The waveguide optical amplifier according to any one of claims 1 to 4 is characterized in that, The element doped in any of the N waveguides is selected from the following elements: Erbium (Er), Ytterbium (Yb), Neodymium (Nd), and Thulium (Tm). The waveguide optical amplifier according to any one of claims 1 to 5 is characterized in that, The waveguide optical amplifier further includes an end-face coupling structure or a top-face coupling structure located in the inner cladding. The end-face coupling structure is used to inject the multimode pump light from the end face of the inner cladding into the inner cladding, and the top-face coupling structure is used to inject the multimode pump light from the top face of the inner cladding into the inner cladding; or... The waveguide optical amplifier further includes an end-face coupler or a top-face coupler. The end-face coupler contacts the end face of the inner cladding and is used to inject the multimode pump light from the end face of the inner cladding into the inner cladding. The top-face coupler contacts the top face of the inner cladding and is used to inject the multimode pump light from the top face of the inner cladding into the inner cladding. The waveguide optical amplifier according to any one of claims 1 to 6 is characterized in that, The waveguide optical amplifier also includes an end-face coupler, which is formed by N signal fibers and multiple pump fibers fused tapered. The N signal optical fibers correspond one-to-one with the N waveguides. Each of the N signal optical fibers is used to output signal light to the corresponding waveguide. The multiple pump optical fibers are located around the N signal optical fibers. At least a portion of the multiple pump optical fibers is used to output the multimode pump light to the inner cladding. The waveguide optical amplifier according to any one of claims 1 to 7 is characterized in that, The waveguide optical amplifier further includes a pump light fading structure located on the surface of the inner cladding away from the substrate and at a position away from where the multimode pump light is injected into the inner cladding. An optical amplification system, characterized in that, include: The pump source and the waveguide optical amplifier as described in any one of claims 1 to 8, wherein the pump source is used to provide pump light for the waveguide optical amplifier. The optical amplification system according to claim 9 is characterized in that, The pump light source includes at least one of a multimode pump and a single-mode pump.

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