A dual-pass fiber amplifier with wideband gain flatness realized by a coupler and a grating

Abstract

The present application provides a kind of double-pass fiber amplifier with wideband gain flatness realized by coupler and grating.The coupler, polarization controller and adjustable attenuator constitute a fiber loop mirror.The fiber loop mirror, gain fiber and fiber grating constitute a resonant cavity to generate new pump laser, and realize double-pumping together with pump.The first amplified signal is reflected back to the gain fiber for secondary amplification by the fiber loop mirror, and finally output by the three-port circulator to realize signal double-pass.The polarization controller and adjustable attenuator are used to control the power of new pump and gain flatness.The present application uses existing technology and product conditions to design the structure of fiber amplifier, retains the advantages of fiber amplifier, and realizes wideband signal double-pass amplification with high gain while maintaining gain flatness.

Description

Technical Field

[0001] This invention relates to a two-pass fiber amplifier that achieves broadband gain flatness using a coupler and a grating. It relates to the field of fiber amplifiers. Background Technology

[0002] Fiber optic amplifiers represent a fundamental revolution in fiber optic communication and are a key technology for realizing high-speed, high-capacity fiber optic communication systems. Wavelength division multiplexing (WDM), especially dense WDM, has significantly increased communication bandwidth, becoming a hot topic in current development and application. Its development has also placed higher demands on fiber optic amplifiers. Operating bandwidth, gain flatness, and gain value, as important indicators for evaluating optical amplifier performance, have received widespread attention in the design and application of fiber optic amplifiers.

[0003] Current fiber optic communication primarily operates in the C-band, with only a small portion of the low-loss communication window being utilized. This is mainly limited by the operating bandwidth of fiber optic amplifiers. Dual-wavelength pumping can effectively extend the operating bandwidth of fiber optic amplifiers, but traditional dual-wavelength pumped optical amplifiers require at least two pumps, resulting in higher costs. Furthermore, the amplification of broadband optical signals necessitates addressing the issue of pump-signal beamforming, and dual-wavelength pumping configurations impose even more stringent requirements on beamforming. Gain flatness is also crucial for broadband amplifier applications; only optical amplifiers with flat gain can be successfully used in practical communications. Achieving broadband gain flatness is currently a hot research topic. Additionally, gain flattening typically involves stripping away the high-gain portion to achieve flatness, which reduces the gain value of the optical amplifier.

[0004] This patent describes a dual-pass fiber amplifier that achieves broadband gain flatness using couplers and gratings. Its all-fiber structure, when applied to optical communication systems, eliminates the need for photoelectric conversion and facilitates easy connection to fiber optic systems. This amplifier utilizes existing components in its design. By forming a resonant cavity within the amplifier and employing a single pump to achieve dual-wavelength pumping, costs are effectively saved and the gain bandwidth is extended. Furthermore, only single-wavelength signal combining needs to be considered. A ring mirror, constructed using a coupler and polarization controller, controls broadband gain flatness. The dual-pass structure enables double signal amplification, further enhancing the amplifier's gain. Summary of the Invention

[0005] To address the shortcomings of the existing technology, this invention provides a dual-pass fiber amplifier that achieves broadband gain flatness using a coupler and a grating.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A dual-pass fiber amplifier that achieves broadband gain flatness using a coupler and a grating is composed of a pump (1), an isolator (2), a three-port circulator (3), a wavelength division multiplexer (4), a fiber grating (5), a gain fiber (6), a coupler (7), a polarization controller (8), and an adjustable attenuator (9).

[0007] The pump (1) passes through an isolator (2), a wavelength division multiplexer (4), and a fiber grating (5) before being input into the gain fiber (6). A coupler (7), a polarization controller (8), and an adjustable attenuator (9) together form a fiber optic ring mirror. The polarization controller (8) and the adjustable attenuator (9) are used to control the reflection of the fiber optic ring mirror. The fiber optic ring mirror and the fiber grating (5) form a linear resonant cavity, which, together with the gain fiber (6) and the pump (1), generates a laser with a wavelength different from that of the pump (1). The newly generated pump laser, along with the pump (1), acts on the amplifier; dual pumping helps to broaden the amplifier's gain bandwidth.

[0008] The signal is input from port a and output from port b of the three-port circulator (3), and is first amplified by passing through the wavelength division multiplexer (4) and fiber optic grating (5) into the gain fiber (6). The first amplified signal is reflected back to the gain fiber (6) by a fiber optic ring mirror composed of coupler (7), polarization controller (8), and adjustable attenuator (9) for secondary amplification. The second amplified signal passes through the fiber optic grating (5) and wavelength division multiplexer (4), and is input from port b and output from port c of the three-port fiber optic circulator (3). This achieves dual-pass signal transmission for the fiber optic amplifier, which can improve the amplifier's gain. Simultaneously, adjusting the polarization controller (8) can flatten the amplifier's gain.

[0009] In the above scheme, the reflection wavelength of the fiber grating (5) is within the gain wavelength of the gain fiber (6), and the reflection wavelength and reflectivity can be adjusted as needed.

[0010] In the above scheme, the gain fiber (6) is an active fiber doped with rare earth ions or a bismuth-doped fiber.

[0011] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and will become apparent from the description or may be learned by practice of the invention. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a schematic diagram of a dual-pass fiber amplifier structure that uses a coupler and a grating to achieve broadband gain flatness, as provided in Embodiment 1 of the present invention. Detailed Implementation

[0014] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0015] Example 1 This invention provides a dual-pass fiber amplifier structure that uses a coupler and a grating to achieve broadband gain flatness, as shown in the embodiment of the invention. Figure 1 As shown. The amplifier consists of a pump (1), an isolator (2), a three-port circulator (3), a wavelength division multiplexer (4), a fiber grating (5), a gain fiber (6), a coupler (7), a polarization controller (8), and an adjustable attenuator (9). The pump (1) passes through the isolator (2) to the wavelength division multiplexer (4), and then through the fiber grating (5) into the gain fiber (6). The coupler (7), polarization controller (8), and adjustable attenuator (9) form a fiber optic ring mirror that can reflect broadband light. The fiber grating (5), coupler (7), polarization controller (8), and adjustable attenuator (9) together form a linear resonant cavity. Adding the pump (1) and the gain fiber (6) can generate a new laser with a wavelength different from the pump wavelength. The polarization controller (8) and the adjustable attenuator (9) work together to adjust the power of the new laser. The new laser and the pump (1) together act as the pump for the amplifier, achieving dual pumping, which can extend the gain bandwidth of the amplifier. The signal is input from port a and output from port b of the three-port circulator (3), passes through the wavelength division multiplexer (4) and fiber optic grating (5) and enters the gain fiber (6) for initial amplification. Then, it is reflected back to the gain fiber (6) by a fiber optic ring mirror composed of coupler (7), polarization controller (8), and adjustable attenuator (9) for secondary amplification. The amplified signal then passes through the fiber optic grating (5) and wavelength division multiplexer (4) and is input from port b and output from port c of the three-port circulator (3). The polarization controller (8) in the amplifier is used to achieve gain flattening of the amplifier.

[0016] A preferred example of this embodiment is: the pump (1) wavelength is 1240nm, the gain fiber (6) is bismuth-doped fiber, the fiber grating (5) is a 1310nm Bragg grating with a reflectivity of 99%, and the splitting ratio of the coupler (7) is 50:50.

Claims

1. A dual-pass fiber amplifier that achieves broadband gain flatness using a coupler and a grating, the amplifier is composed of a pump (1), an isolator (2), a three-port circulator (3), a wavelength division multiplexer (4), a fiber grating (5), a gain fiber (6), a coupler (7), a polarization controller (8), and an adjustable attenuator (9). The pump (1) passes through the isolator (2), the wavelength division multiplexer (4), and the fiber grating (5) before entering the gain fiber (6). The coupler (7), the polarization controller (8), and the adjustable attenuator (9) together form a fiber ring mirror. The polarization controller (8) and the adjustable attenuator (9) are used to control the reflection of the fiber ring mirror. The fiber ring mirror and the fiber grating (5) form a linear resonant cavity, which works together with the gain fiber (6) and the pump (1) to produce a different... The newly generated pump laser, along with the pump (1) wavelength, acts on the amplifier. Dual pumping helps to broaden the gain bandwidth of the amplifier. The signal is input from port a and output from port b of the three-port circulator (3). After passing through the wavelength division multiplexer (4) and fiber optic grating (5), it is input into the gain fiber (6) and amplified for the first time. The amplified signal is reflected back to the gain fiber (6) by the fiber optic ring mirror composed of coupler (7), polarization controller (8) and adjustable attenuator (9) and amplified a second time. The amplified signal passes through fiber optic grating (5) and wavelength division multiplexer (4) and is input from port b and output from port c of the three-port fiber optic circulator (3). This achieves dual signal transmission of the fiber optic amplifier, which can improve the gain of the amplifier. At the same time, adjusting the polarization controller (8) can flatten the gain of the amplifier.

2. A dual-pass fiber amplifier using a coupler and grating to achieve broadband gain flatness according to claim 1, characterized in that, The reflection wavelength of the fiber grating (5) is within the gain wavelength of the gain fiber (6), and the reflection wavelength and reflectivity can be adjusted as needed.

3. A dual-pass fiber amplifier using a coupler and grating to achieve broadband gain flatness according to claim 1, characterized in that, The gain fiber (6) is an active fiber doped with rare earth ions or a bismuth-doped fiber.

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