Optical amplifier and optical circuit

Abstract

Provided is an optical amplifier having a high degree of integration and a small number of components that is suited for a wide wavelength band.　An optical amplifier (200) according to the present disclosure is characterized by comprising: a first optical circuit (201) that includes a band demultiplexing unit (203n) that demultiplexes input signal light for each of a plurality of wavelengths, and a first combiner array (205n) that is an array of first combiners (205) that merge and output signal light for each demultiplexed wavelength with pump light; a second optical circuit (202) that includes a band multiplexing unit (207n) that multiplexes the signal light; a fiber array (206n) that is connected between the first optical circuit (201) and the second optical circuit (202) and amplifies signal light outputted from each of the first combiners of the first optical circuit and is an array of fiber amplifiers (206); and a substrate in which the first optical circuit (201), the second optical circuit (202), and the fiber array (206n) are formed as waveguide structures for each wavelength.

Description

Optical amplifier and optical circuit

[0001] The present disclosure relates to an optical amplifier, and more particularly to an optical amplifier that amplifies signal light using a fiber amplifier.

[0002] As the capacity of optical communication networks continues to increase, multi-band transmission that utilizes wide bandwidths of light has attracted attention, and research and development is progressing (Non-Patent Document 1). Multi-band transmission utilizes wide bandwidths such as L-band and S-band in addition to the C-band that is generally used for long-distance transmission.

[0003] Optical amplifiers used in such long-distance optical transmission include optical fiber amplifiers such as lumped Raman amplifiers and rare-earth doped fiber amplifiers. In transmission using multiple bands, such as multi-band transmission, multiple types of optical fiber amplifiers are prepared, one for each band. For example, rare-earth doped fiber amplifiers can accommodate different wavelengths by changing the type of doped atom or the length of the fiber. Furthermore, lumped Raman amplifiers can accommodate different wavelengths by changing the wavelength of the pump light.

[0004] 1(a) and 1(b) are diagrams showing optical amplifiers compatible with a single wavelength. 1(a) shows a configuration in which pump light is input in the same direction as the signal light, and 1(b) shows a configuration in which pump light is input in the opposite direction to the signal light. In these configurations, input signal light 103 is combined (FIG. 1(a)) or removed (FIG. 1(a)) with pump light 104 having a wavelength corresponding to the input signal light by a combiner 105. The signal light is then input to a fiber amplifier 106 for amplification, and input to a combiner 107, where pump light 108 is removed (FIG. 1(a)) or combined (FIG. 1(b)). In these configurations, the fiber amplifier 106 can be formed by a lumped Raman amplifier or a rare-earth doped fiber amplifier.

[0005] Benjamin J. Puttnam, Ruben S. Luis, Georg Rademacher, Lidia Galdino, Domanic Lavery, Tobias A. Eriksson, Yoshinari Awaji, Hideaki Furukawa, Polina Bayvel, and Naoya Wada, "0.61 Pb / s S, C, and L-Band Transmission in a 125μm Diameter 4-Core Fiber Using a Single Wideband Comb Source," J. Lightwave Technol., 2021, 39, 1027-1032K. Suzuki et al., "A Transponder Aggregator With Efficient Use of Filtering Function for Transponder Noise Suppression," in Journal of Lightwave Technology, May15, 2023, vol. 41, no. 10, pp. 3074-3083

[0006] However, when an optical amplifier compatible with a single wavelength as shown in Fig. 1 is directly applied to multiband transmission using multiple bands, the optical amplifier structure becomes complex and the number of components becomes large. That is, when multiple wavelengths are used, it is necessary to separate signal light 103 input from optical fiber 102 into wavelengths, combine / remove pump light 104 from these separated signal lights using combiner 105, amplify each signal light using fiber amplifier 206, and further combine / remove pump light 108 from each signal light using combiner 107, and combine the signal lights of all wavelengths and couple them to optical fiber 110. For this reason, it is necessary to prepare a combiner and fiber amplifier for each wavelength, which increases the number of components and complicates the structure.

[0007] In addition, the realization of higher capacity transmission by utilizing spatial multiplexing transmission technologies such as multi-core fiber (MCF) and multi-fiber in combination with multi-band is also being considered. For example, when using uncoupled MCF or multi-fiber, the above-mentioned fiber amplifiers are required several times the number of spatial channels, making the above-mentioned problem more pronounced.

[0008] The present disclosure has been made in consideration of the above-mentioned problems, and its purpose is to provide an optical amplifier that is compatible with a wide wavelength band, has a high degree of integration, and has a small number of parts.

[0009] An optical amplifier according to one aspect of an embodiment of the present invention is characterized by comprising: a first optical circuit including a band demultiplexing unit that demultiplexes input signal light into a plurality of wavelengths and a first combiner array that is an arrangement of first combiners that combine the signal light for each demultiplexed wavelength with pump light and output the combined signal light; a second optical circuit including a band demultiplexing unit that combines the signal light; a fiber array that is an arrangement of fiber amplifiers connected between the first optical circuit and the second optical circuit and that amplifies and outputs the signal light output from each first combiner of the first optical circuit; and a substrate on which the first optical circuit, the second optical circuit, and the fiber array are formed as waveguide structures for each of the wavelengths.

[0010] According to the present disclosure, an optical amplifier that is compatible with a wide wavelength band, has a high degree of integration, and has a small number of parts is provided.

[0011] 3(a) and (b) are diagrams showing an optical amplifier compatible with a single wavelength; FIG. 3(a) and (b) are diagrams illustrating a waveguide structure compatible with a multicore fiber; FIG. 3(b) is a diagram illustrating a connection configuration between the multilayer waveguide shown in FIG. 3(b) and an amplifier fiber array; FIG. 3(a) and (b) are diagrams illustrating an optical amplifier compatible with an embodiment of the present invention; FIG. 3(b) is a diagram ...

[0012] Various embodiments of the present disclosure will be described in detail below with reference to the drawings. The same or similar reference numerals indicate the same or similar elements, and redundant description may be omitted. Materials and numerical values ​​are for illustrative purposes only and are not intended to limit the technical scope of the present disclosure. The following description is an example, and some configurations may be omitted or modified, or additional configurations may be added, as long as they do not deviate from the gist of one embodiment of the present disclosure.

[0013] 2 is a diagram schematically illustrating an optical amplifier according to one embodiment of the present invention. The optical amplifier 200 according to this embodiment is configured to include optical circuits 201 and 202, each equipped with a combiner and the like, and a fiber array 206n made up of a plurality of fiber amplifiers 206 provided between the optical circuits 201 and 202. The first optical circuit 201 is connected to an optical fiber 102 for inputting a plurality of signal lights having different wavelengths.

[0014] The first optical circuit 201 includes a band demultiplexing unit 203n that demultiplexes input signal light into multiple wavelength bands, and a combiner array 205n that is an arrangement of combiners 205 that combines the demultiplexed signal light for each wavelength with pump light 104. Furthermore, the pump light 104 corresponding to that wavelength is input to each combiner 205. With this configuration, each combiner 205 combines the input pump light with the signal light and outputs the combined signal to the fiber amplifier 206. Meanwhile, the second optical circuit 202 includes a combiner array 207n that is an arrangement of combiners 207 that removes pump light 108 from the amplified signal light input from the fiber amplifier 206, and a band combining unit 209n that combines the signal light from each combiner 207. Furthermore, the removed pump light 108 is output from each combiner 207. With this configuration, each combiner 207 outputs a signal light that has been amplified and from which the pump light has been removed, and these signal lights for each wavelength are multiplexed in the band multiplexing section 209 n and output to the optical fiber 110 .

[0015] In this embodiment, the band demultiplexing unit 203n and combiner array 205n and fiber array 206n that constitute the optical circuit 201, and the combiner array 205n and band multiplexing unit 209n that constitute the optical circuit 202 are formed on a single substrate as waveguide devices for each wavelength, thereby making it possible to obtain an optical amplifier with a high degree of integration and a small number of parts.

[0016] In the above configuration, the optical fiber 102 for inputting the signal light or the optical fiber 110 for outputting the signal light may be one or more. Furthermore, the integration of the optical waveguide device may be such that all elements are integrated on one chip or are divided into multiple chips.

[0017] In the above configuration, the band demultiplexing unit 203n and the band combining unit 209n can be configured with wavelength division multiplexing (WDM) couplers 203 and 209. In the combiner array 205n, methods for combining the pump light 104 with the signal light (not shown) include combining using a conventional coupler and combining using a WDM coupler 209 utilizing the difference in wavelength between the pump light 104 and the signal light. While conventional couplers inherently result in power loss during combining, the use of a WDM coupler 209 enables combining without loss in principle. Furthermore, the combiner 207, which removes the pump light 108 from the signal light, must be separated by wavelength using the WDM coupler 209. If the pump light is sufficiently attenuated in the amplifier fiber array 206n or other regions, a combiner for removing the pump light from the signal light is not necessary. Ordinary couplers include directional couplers, MZIs, Y-branching, and multimode interference. WDM couplers can also include directional couplers, MZIs, etc. It is obvious that the effects of the present invention can be achieved even when other waveguide-type WDM couplers are used.

[0018] In this embodiment, the WDM coupler and combiner are integrated, allowing the pump light source to be shared, and the number of different amplifiers for each band can be reduced.

[0019] Therefore, according to the present disclosure, it is possible to provide an optical amplifier that is compatible with a wide wavelength band, has a high degree of integration, and has a small number of parts.

[0020] In this embodiment, as described above, the fiber array 206n in which the fiber amplifiers 206 are arranged is in the form of a multi-core fiber (MCF) as a waveguide device.

[0021] In the case of a single-core fiber configuration, the coupling between the fiber and the waveguide can be arranged one-dimensionally, and the cores of the waveguide device can be arranged in a single row. This is the structure of a typical planar lightwave circuit and is the simplest configuration.

[0022] 3(a) and (b) are diagrams illustrating a waveguide structure compatible with a multicore fiber. When an MCF has two cores, adjusting the angle of the MCF so that all the cores of the MCF are aligned in a row allows the cores of the waveguide device to be aligned in a row. A similar method can also be used when the waveguide has three or more cores, as long as the cores are aligned in a row. As shown in FIG. 3(a), the optical waveguide in this case is composed of an underclad 302, a core 303, and an overclad 304, and the core 303 is aligned horizontally relative to the wafer (substrate) 301. The cross section of the fiber amplifier 206 corresponds to the core 303.

[0023] On the other hand, when an MCF has three or more cores, the optical waveguide cores can be multi-layered to enable connection between the MCF and the waveguide. As shown in FIG. 3(b), for example, a two-layer waveguide is composed of an underclad 302, a first core 303a, a first overclad 304a, a second core 303b on the first overclad 304a, and a second overclad 304b. The cross section of the fiber amplifier 206 in FIG. 2 corresponds to the cores 303a and 303b. Three or more layers can be constructed by forming additional cores and overclads on the overclad. For example, when a four-core MCF is used, in which four cores are arranged at the vertices of a parallelogram, rectangle, or square, two parallel cores can be connected to a waveguide in the same layer to enable connection to a two-layer waveguide. This configuration allows the optical signals of each spatial channel of the MCF to be treated individually and connected to a combiner array 205n via a band demultiplexer 203n. In this case, other waveguides, such as the combiner array 205n, can remain multilayer waveguides, or can be prepared separately as single-layer waveguide devices and connected. The fiber amplifier 206 can be an MCF, but the above configuration allows for the use of a single-core one. When using optical fiber for a single-core amplifier, if the waveguide connected to the amplifier fiber array 206n is multilayered, the height of the fiber array must also be adjusted. In this case, fibers can be connected to each layer of the waveguide in separate locations, or the fiber amplifiers 206 can be arranged in steps to form blocks. For example, by placing the fiber amplifiers 206 in V-shaped grooves 401 of different heights (groove depths), blocks of fiber arrays 206n can be created with fiber amplifiers 206 arranged at different heights (Figure 4).

[0024] 5 is a diagram showing a schematic diagram of an optical amplifier according to one embodiment of the present invention. The optical amplifier 500 according to this embodiment is configured to include optical circuits 501 and 502, each equipped with a combiner and the like, and a fiber array 206n made up of a plurality of fiber amplifiers 206 provided between the optical circuits 501 and 502.

[0025] In cases where multiple signals of the same band are input from multiple fiber amplifiers 206, or where pump light 104 of a common wavelength in a nearby wavelength band can be used, the pump light source 104n can also be shared. The pump light 104 is input to the splitter 505 of the optical amplifier 500 shown in FIG. 5. A laser diode (LD) or the like is used as the pump light source 104n. A high-power pump light source can be branched and multiplexed into signal light of multiple spatial channels via multiple combiners 207 of the combiner array 207n. This branching is possible using a waveguide coupler. In this embodiment, the splitter 505 is included in the optical circuit 501. By integrating the combiner array 205n and the splitter 505 on the same chip, it is possible to reduce the number of light sources and the number of components (FIG. 5).

[0026] It is desirable that pump light branched from the same LD share the same wavelength band or adjacent wavelength bands.

[0027] [Embodiment 3] In the configurations up to embodiment 3, the pump light 104 is input from the same direction as the signal light, but the optical fiber pump will also work if it is input from the opposite direction. In this case, the pump light source 104n is connected to the combiner array 207n on the output side of the amplifier fiber array 206n. Furthermore, the combiner array 205n on the input side to the amplifier fiber array 206n may be an isolator that transmits light in only one direction, and does not need to be on the same chip. In this case, a fiber-type isolator or the like can be used.

[0028] [Embodiment 4] The sizes of the propagation modes propagating through the aforementioned single-core fiber, MCF, fiber amplifier 206, and waveguide often differ, so connecting them as is can result in loss due to mode mismatch.

[0029] This problem can be solved by adding a spot size converter (SSC) to the waveguide, which converts the size of the propagation mode.Spot size converters (SSCs) include those that form segments in the waveguide and those that gradually change the thickness of the waveguide.

[0030] 6A is a schematic diagram showing an optical amplifier according to one embodiment of the present invention. The optical amplifier 600 according to this embodiment includes optical circuits 601a and 602a, each equipped with a combiner and the like, and a fiber array 206n made up of a plurality of fiber amplifiers 206 provided between the optical circuits 601a and 602a. A gain flattening filter (GFF) 601 is provided between the fiber amplifier 206 and the combiner 207. Hereinafter, the gain flattening filter will be referred to as GFF.

[0031] 6, by incorporating a GFF 601 between the amplifier fiber array 206n and the combiner array 207n, it is possible to flatten the gain spectrum in the fiber amplifier 206. GFFs made of dielectric multilayer films or waveguide elements have been reported, and these can also be applied to the GFF 601.

[0032] For example, in the case of an optical amplifier 600a having a fiber attached, the dielectric multilayer GFF 601 can be connected to an optical fiber for the amplifier, and the other fiber of the GFF 601 can be connected to a waveguide (FIG. 6(a)).

[0033] 6(b) is a schematic diagram showing an optical amplifier according to one embodiment of the present invention. The optical amplifier 600b according to this embodiment is configured to include optical circuits 601b and 602b, each equipped with a combiner and the like, and a fiber array 206n made up of a plurality of fiber amplifiers 206 provided between the optical circuits 601b and 602b. A GFF 601 is provided in the optical circuit 601b between the fiber amplifier 206 and the combiner 207.

[0034] This is also possible with optical amplifier 600b, which is configured such that after the optical fiber for the amplifier is connected to the waveguide, a groove is formed so as to straddle the waveguide and GFF 601 is inserted into the groove. In the case of optical amplifier 600b, the degree of integration can be improved by integrating GFF 601 and combiner array 207n, etc., on the same chip. Also, in Figure 6(b), a GFF is disposed individually for each waveguide, but one GFF may be disposed so as to straddle multiple waveguides.

[0035] The GFF 601 using a waveguide element can be realized, for example, by a configuration in which Mach-Zehnder interferometer (MZI) circuits are connected in multiple stages, or by a configuration using other interferometers such as a ring resonator, and can be applied to the optical amplifiers 601a and 601b of this embodiment. Furthermore, in addition to an MZI circuit, it can also be realized by using other interferometers such as a ring resonator, and in the case of a waveguide element, the degree of integration can be improved by integrating the GFF 601 and the combiner array 207n, etc., on the same chip.

[0036] 7a is a diagram showing a schematic diagram of an optical amplifier according to one embodiment of the present invention. The optical amplifier 700a according to this embodiment is configured to include optical circuits 701a and 702a, each equipped with a combiner and the like, and a fiber array 206n consisting of a plurality of fiber amplifiers 206 provided between the optical circuits 701a and 702a. The optical circuit 701a includes a VOA 704 and a splitter 705.

[0037] Because the intensity of signal light varies between optical fibers and bands, it is desirable to be able to adjust the amount of amplification. This problem can be solved by using an optical amplifier 700a configured by adding a variable optical attenuator (VOA) 704 to a splitter 705 that splits the pump light 104 (FIG. 7a). To integrate the splitter 705 on the same chip, it is desirable to form the VOA and the splitter 705 using an optical waveguide. Hereinafter, the variable optical attenuator will be referred to as a VOA. In this embodiment, the VOA 704 and splitter 705 are included in the optical circuit 701a. As an optical waveguide VOA 704, one using an MZI has been reported (Non-Patent Document 10), and an MZI can also be applied to the VOA 704. Integrating the combiner array 205n, VOA 704, and splitter 705 on the same chip reduces the number of light sources and the number of components.

[0038] 7b is a diagram showing a schematic diagram of an optical amplifier according to one embodiment of the present invention. The optical amplifier 700b according to this embodiment is configured to include optical circuits 701b and 702b, each equipped with a combiner and the like, and a fiber array 206n consisting of a plurality of fiber amplifiers 206 provided between the optical circuits 701b and 702b. The optical circuit 701a includes a combiner 205n, a VOA 704, and a splitter 505.

[0039] Furthermore, by employing a waveguide-type splitter 705b with an adjustable splitting ratio in the optical amplifier 700b, it is possible to adjust the gain of the amplifier while making more effective use of the light from the pump light source than by employing a VOA 704 (FIG. 7b). A configuration using an MZI can also be employed for this adjustable waveguide-type splitter 705 (Non-Patent Document 2). By integrating the combiner array 205n and the splitter 705b on the same chip, it is possible to reduce the number of light sources and the number of components.

[0040] [Embodiment 7] For the optical circuits and optical amplifiers described in Embodiments 1 to 6, the integration density on a single chip can be improved by fabricating the waveguides connecting to the input and output sides of the amplifier optical amplifier 800 on the same chip 803 (Figure 8). This not only improves integration density, but also has the advantage of integrating the input and output fibers of optical signals into a single fiber block 804 consisting of multiple fibers, allowing simultaneous connection to the waveguide device chip. Another advantage is that the input and output ends of the amplifier optical fiber array 806n are also integrated into the same block, allowing simultaneous connection to the waveguide device chip. Furthermore, while Figure 8 shows the amplifier optical fiber array 806n and the optical fibers 102 and 110 for inputting and outputting optical signals located on both sides of the chip 803, they can also be arranged in the same direction using bent waveguides. In this case, both the fibers for inputting and outputting optical signals and the amplifier optical fibers are integrated into a single fiber block 804, allowing simultaneous connection to the waveguide device chip.

[0041] 9 is a diagram showing yet another configuration of a fiber amplifier including the optical circuit of Embodiment 7. The fiber amplifier 900 of FIG. 9 is configured such that the optical fibers 102 and 110 for signal light and the amplification fiber 806 in the optical circuit of FIG. 8 are all connected at a single end face of the chip 301. If the fiber 111 from the pump light source 104 is also connected at the end face of the same optical circuit 901 using a splitter (a waveguide-type variable optical branch with an adjustable branching ratio) 905, it becomes possible to connect all of the fibers 906n required for the fiber amplifier 900 together in a single fiber block 804. The optical circuit 901 and all of the fibers can be aligned and connected in a single process.

[0042] The order of connecting the fibers is not limited to the configuration in Fig. 9. Also, the combiner 207n that removes the pump light from the signal light may be omitted.

[0043] [Embodiment 8] Depending on the wavelength, not only the wavelength of the pump light but also the type and length of the amplifier fiber can be changed. For example, in the case of an optical amplifier using a rare-earth doped fiber, if the wavelength length changes, the doping atom and length must be adjusted. Therefore, the type and length of the optical fiber for the amplifier are selected for each band according to the wavelength.

[0044] The present disclosure is applicable to the technical fields of optical amplifiers and optical circuits.

Claims

1. An optical amplifier comprising: a first optical circuit including: a band demultiplexing section that demultiplexes input signal light into a plurality of wavelengths; and a first combiner array that is an arrangement of first combiners that combine the demultiplexed signal light for each wavelength with pump light and output the combined signal light; a second optical circuit including: a band multiplexing section that combines signal light; a fiber array that is an arrangement of fiber amplifiers that is connected between the first optical circuit and the second optical circuit and that amplifies and outputs the signal light output from each first combiner of the first optical circuit; and a substrate on which the first optical circuit, the second optical circuit, and the fiber array are formed as a waveguide structure for each wavelength.

2. The optical amplifier according to claim 1, wherein the plurality of fiber amplifiers are different in length or type.

3. The optical amplifier according to claim 1, wherein the fiber amplifier is characterized in that a two-core multicore fiber (MCF) inputs and outputs the signal light at the first combiner, the two-core multicore fiber (MCF) is connected to a waveguide device, and two cores of the two-core multicore fiber (MCF) are arranged parallel to a plane in which the waveguide exists.

4. The optical amplifier according to claim 1, wherein the fiber amplifier is a multicore fiber (MCF) having three or more cores that inputs and outputs the signal light at the first combiner, the multicore fiber (MCF) having three or more cores is connected to a waveguide device, and the waveguide device has multiple layers of cores.

5. The optical amplifier according to claim 1, wherein a pump light source is connected to said first combiner array separately from said signal light.

6. The optical amplifier according to claim 1, wherein the first combiner and an optical splitter are optically connected, and pump light is input via the optical splitter.

7. The optical amplifier according to claim 1, wherein the first combiner and the optical splitter are integrated on the same chip.

8. An optical amplifier according to claim 1, wherein the fiber amplifier and a gain flattening filter (GFF) are optically connected, and the waveguide to which the fiber amplifier is connected has the function of the GFF.

9. An optical amplifier according to claim 1, characterized in that the first combiner array and an optical splitter are optically connected, the branching ratio of the optical splitter is variable or the optical splitter is optically connected to an element having a VOA function, and the optical splitter and VOA are configured with optical waveguides.

10. An optical amplifier according to claim 1, wherein said fiber amplifier and the fiber through which said signal light is input and output are arranged so as to be in contact with the same optical waveguide device chip.

11. An optical circuit including a band demultiplexing section that demultiplexes input signal light into multiple wavelengths, and a combiner array that is an arrangement of combiners that combines the signal light for each demultiplexed wavelength with pump light and outputs the combined signal light.

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