Differential erbium-doped optical fiber amplifier structure based on polarization multiplexing

Abstract

The invention belongs to the field of erbium-doped optical fiber amplifiers, and provides a differential erbium-doped optical fiber amplifier structure based on polarization multiplexing. According to the structure, two paths of optical signals are adjusted to be in an orthogonal polarization state, are combined through the polarization beam combiner and then are sent into the single-path erbium-doped optical fiber to be uniformly amplified, so that the consistency of a signal path and a noise source is kept in the amplification process. And the amplified optical signals are demultiplexed by the polarization beam splitter and then are respectively output, so that efficient optical signal amplification and common-mode noise suppression are realized. According to the scheme, the problem of differential offset failure caused by noise non-common mode in a traditional double-amplifier structure is solved, and the signal-to-noise ratio and the system stability of differential detection are improved.

Description

Technical Field

[0001] The present invention belongs to the field of erbium-doped fiber amplifiers, and in particular relates to a differential erbium-doped fiber amplifier structure based on polarization multiplexing. Background Art

[0002] With the growing demand for electromagnetic environment measurements in space, traditional antenna and receiver-based measurement methods, due to their large size, susceptibility to interference, and limited bandwidth, are no longer able to meet the requirements for high-sensitivity, wide-bandwidth, and low-disturbance measurement of electromagnetic signals in complex space environments. In recent years, electromagnetic wave measurement systems based on photoelectric detection have gradually become a research hotspot due to their advantages such as small size, wide bandwidth, and strong anti-interference capabilities.

[0003] To further eliminate environmental interference and system noise floor, a differential detection architecture is often employed. This architecture uses a differential electric field sensor and a differential photodetector to receive and process signals. This theoretically effectively suppresses common-mode noise and significantly improves the system's signal-to-noise ratio (SNR). In practical systems, the optical signal emitted by a light source must sequentially pass through multiple optical devices, such as optical fibers, modulators, and waveguides. Each stage of the device introduces insertion loss, causing the optical power to continuously decrease during transmission. The optical signal ultimately reaching the photodetector is relatively low in power, impacting the SNR and sensitivity of the entire system.

[0004] To compensate for the decreased sensitivity caused by optical power attenuation, an optical amplifier is typically introduced before the photodetector to amplify the optical signal. However, if two independent optical amplifiers are used in a differential detection structure, the amplified noise introduced by each amplifier, due to its independent spontaneous emission, thermal noise, and gain fluctuation, often lacks common-mode characteristics. This inconsistency can lead to an increase in residual noise after differential processing, thereby weakening the noise suppression advantage of the differential structure and even introducing new interference terms. Summary of the Invention

[0005] To address the shortcomings of the existing technology, the present invention proposes a differential optical signal amplification structure based on polarization multiplexing. This structure adjusts the two differential optical signals to orthogonal polarization states and performs polarization multiplexing before amplification, allowing them to share the same optical amplification path. This ensures gain consistency and common noise sources for the two signals during the amplification process. After amplification, polarization demultiplexing is then used to restore the two signals and connect them to differential photodetectors. By reducing the introduction of non-common-mode noise, the noise cancellation efficiency in differential detection is significantly improved.

[0006] The technical solutions of the present invention are as follows:

[0007] A differential erbium-doped fiber amplifier structure based on polarization multiplexing includes an optical isolator, a polarization controller, a polarization combiner, a pump light source, a wavelength division multiplexer, an erbium-doped fiber and a polarization beam splitter;

[0008] The optical isolator includes a first, a second and a third, a fourth optical isolator, wherein the first and second optical isolators are connected after the two input ports, and the third and fourth optical isolators are connected before the two output ports, and are used to prevent interference from reflected light.

[0009] Preferably, the operating wavelength of the optical isolator is 1550 nm, and the insertion loss is less than 0.5 dB.

[0010] The polarization controller is located after the second optical isolator and is used to adjust the polarization direction of the input signal of the channel so that it forms an orthogonal polarization state with the optical signal of another channel.

[0011] Preferably, the polarization controller can realize the control of polarization of light in any direction in the 1550nm band, and the insertion loss is less than 0.5dB.

[0012] The polarization beam combiner is used to combine two optical signals in orthogonal polarization states into one polarization composite optical signal.

[0013] Preferably, the central operating wavelength of the polarization beam combiner is 1550 nm, the insertion loss is less than 0.5 dB, and the polarization extinction ratio is not less than 20 dB.

[0014] The wavelength division multiplexer is arranged between the polarization combiner, the pump light source and the erbium-doped optical fiber, and is used to combine the 980nm pump light and the 1550nm signal light and input them into the erbium-doped optical fiber.

[0015] Preferably, the wavelength division multiplexer is a 980 / 1550nm dual-channel WDM beam combining device with an isolation of not less than 30dB and a low insertion loss of less than 0.8dB.

[0016] The erbium-doped optical fiber is used to uniformly amplify the composite input orthogonal polarization light signals.

[0017] Preferably, the erbium-doped fiber is 5 to 6 meters long and has a gain bandwidth covering 1525 nm to 1565 nm.

[0018] The polarization beam splitter is arranged after the erbium-doped optical fiber and is used to separate the amplified polarization composite optical signal into two output signals according to its polarization direction.

[0019] Preferably, the operating center wavelength of the polarization beam splitter is 1550 nm, the insertion loss is less than 0.5 dB, and the polarization extinction ratio is not less than 20 dB.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This paper proposes a dual-channel common optical amplification method based on polarization multiplexing. By modulating two differential signals into orthogonal polarization states and combining them for amplification, this method ensures that the two signals have the same noise background during the amplification process, significantly improving the ability to suppress common-mode noise in differential detection. This method is compact and suitable for integration, effectively solving the cancellation failure problem caused by different noise sources in traditional differential structures, and provides a stable and feasible solution for high-fidelity extraction of weak signals in applications such as electromagnetic field optical measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. By referring to the drawings, the features and advantages of the present invention can be more clearly understood. The drawings are schematic and should not be understood as limiting the present invention in any way. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0023] Figure 1 It is a schematic diagram of the system structure of the differential erbium-doped fiber amplifier of the present invention.

[0024] Figure 2 It is a schematic diagram of the polarization multiplexing principle of the present invention.

[0025] Figure 3 It is a schematic diagram of the polarization demultiplexing principle of the present invention.

[0026] Figure 4 It is a schematic diagram of the present invention for eliminating common-mode noise after signal amplification. DETAILED DESCRIPTION

[0027] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present invention and the features therein can be combined with each other without conflict.

[0028] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0029] The working principle of the differential erbium-doped fiber amplifier structure based on polarization multiplexing of the present invention is as follows:

[0030] If two optical signals have perpendicular polarization states, they can propagate independently along the fast and slow axes of an optical fiber without interfering with each other. That is, if one optical signal is horizontally polarized and the other vertically polarized, they can be coupled into different principal axes of a polarization-maintaining fiber for transmission.

[0031] Based on this principle, two optical signals that originally needed to be amplified separately are adjusted to mutually orthogonal polarization states. Then, a polarization combiner is used to combine them into a single signal and feed it into the same erbium-doped fiber amplifier. Because the two polarization states correspond to different propagation directions, they do not interfere with each other in the fiber, allowing both signals to be amplified simultaneously without introducing additional differential noise.

[0032] Furthermore, by introducing a polarization beam splitter after amplification, the two beams can be separated again and directed to the two channels of a balanced photodetector. This allows differential optical amplification to be performed by a single amplifier, improving system consistency and suppressing the introduction of asymmetric noise.

[0033] The above principle is verified through a specific example below.

[0034] Example 1

[0035] The present invention provides a differential erbium-doped fiber amplifier structure based on polarization multiplexing, such as Figure 1 shown.

[0036] Figure 4 The present invention demonstrates the effect of suppressing common mode noise when the pulse light passing through the differential electric field sensor is amplified and the signal is received by the differential photodetector. Figure 4 (a) and Figure 4 (b) The detection results when the two optical signals are connected to the photodetector and the spectrum analyzer separately. Figure 4 (c) shows the detection effect when two optical signals are simultaneously connected to a differential photodetector and a spectrum analyzer. The results show that while effectively amplifying the optical signal, the system suppresses common-mode noise by over 10 dB. This demonstrates that the differential photodetector structure of the present invention not only achieves signal amplification without introducing additional noise, but also exhibits excellent noise suppression and system stability.

[0037] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A differential erbium-doped fiber amplifier structure based on polarization multiplexing, characterized in that: The optical fiber includes a first input end, a second input end, a first output end, a second output end, an optical isolator, a polarization controller, a polarization combiner, a pump light source, a wavelength division multiplexer, an erbium-doped optical fiber and a polarization beam splitter.

2. The differential erbium-doped fiber amplifier structure according to claim 1, characterized in that: The first input end is connected to a first optical isolator.

3. The differential erbium-doped fiber amplifier structure according to claim 1, characterized in that: The second input end is connected to the second optical isolator.

4. The differential erbium-doped fiber amplifier structure according to claim 1, characterized in that: The first optical isolator is connected to the polarization controller.

5. The differential erbium-doped fiber amplifier structure according to claim 1, characterized in that: The second optical isolator is connected to the polarization beam combiner.

6. The differential erbium-doped fiber amplifier structure according to claim 1, characterized in that: The polarization controller is connected to the polarization beam combiner.

7. The differential erbium-doped fiber amplifier structure according to claim 1, characterized in that: The polarization beam combiner is connected to the wavelength division multiplexer.

8. The differential erbium-doped fiber amplifier structure according to claim 1, characterized in that: The pump light source is a 980nm pump light source.

9. The differential erbium-doped fiber amplifier structure according to claim 1, characterized in that: The pump light source is connected to a wavelength division multiplexer.

10. The differential erbium-doped fiber amplifier structure according to claim 1, characterized in that: The wavelength division multiplexer is connected to the erbium-doped optical fiber.

11. The differential erbium-doped fiber amplifier structure according to claim 1, characterized in that: The erbium-doped optical fiber is connected to a polarization beam splitter.

12. The differential erbium-doped fiber amplifier structure according to claim 1, characterized in that: The polarization beam splitter is connected to the third optical isolator.

13. The differential erbium-doped fiber amplifier structure according to claim 1, characterized in that: The polarization beam splitter is connected to the fourth optical isolator.

14. The differential erbium-doped fiber amplifier structure according to claim 1, characterized in that: The third optical isolator is connected to the first output end.

15. The differential erbium-doped fiber amplifier structure according to claim 1, characterized in that: The fourth optical isolator is connected to the second output end.

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