Mode division multiplexing all-optical regenerative device

Abstract

The application discloses a mode division multiplexing all-optical regenerative device, which comprises a polarization controller, a few-mode amplifier, an optical coupler, a few-mode nonlinear optical fiber, an optical carrier extractor and an optical phase shifter. Mode division multiplexing signals of multi-level pulse amplitude modulation from different users can be simultaneously regenerated by the mode division multiplexing all-optical regenerative device, the regenerated mode division multiplexing signals are amplified and shaped, and the power transfer curve of each mode channel is not affected by the change of other mode levels.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical communication, and more particularly relates to a mode division multiplexing all-optical regenerator. BACKGROUND

[0002] With the explosive growth of network traffic, the capacity of optical networks will soon be exhausted, and the transmission capacity of single-mode fiber communication systems is gradually approaching the nonlinear Shannon limit. In order to meet the increasing capacity demand of optical networks, the space division multiplexing technology is used to overcome the Shannon limit and improve the data capacity of optical fibers. The mode division multiplexing technology is also increasingly valued, and each mode is regarded as an independent data channel. Like single-mode fiber communication systems, in order to increase the transmission distance of mode division multiplexing signals, an erbium-doped fiber amplifier is indispensable, but it will also introduce spontaneous emission noise. In the mode division multiplexing system, mode crosstalk is inevitable in the transmission fiber and will be aggravated with the increase of signal transmission distance. At the same time, mode crosstalk will be introduced in the mode division multiplexing switching node and optical switching chip and other devices. The degradation of spontaneous emission noise and mode crosstalk to the signal is intolerable for long-distance transmission systems, which limits the signal transmission capacity and transmission distance of space division multiplexing. In order to reduce or suppress the influence of the above degradation factors, the mode division multiplexing system also needs corresponding all-optical regenerative technology.

[0003] In single-mode fiber communication systems, all-optical regenerative technology has been deeply studied. Using self-phase modulation, cross-phase modulation, four-wave mixing and other nonlinear effects, many regenerators with MZI (Mach-Zehnder interferometer) or NOLM (nonlinear optical loop mirror) structure have been proposed. And with the wide application of PAM (pulse amplitude modulation) signals, simultaneous regeneration of multiple amplitudes has become a research focus. Parameter optimization and device cascading of MZI and NOLM structures can achieve multi-level amplitude shaping regeneration. For the regeneration of mode division multiplexing systems, mode division multiplexing signals can be demultiplexed to single-mode for all-optical regeneration, but this is very costly. At present, due to the interference of nonlinear effects between modes, there is no mode division multiplexing all-optical regenerative device that can simultaneously realize multi-level amplitude regeneration of multiple signal modes. Therefore, a mode division multiplexing all-optical regenerative device capable of simultaneously regenerating each channel of the mode division multiplexing signal is indispensable. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a mode division multiplexing all-optical regenerative device which can regenerate the degraded mode division multiplexing signal, and the power transfer curve of each mode channel after regeneration will not be affected by the change of other mode levels.

[0005] To achieve the above-mentioned purposes, the application discloses a mode division multiplexing all-optical regenerative device, which is characterized by comprising a polarization controller, a few-mode amplifier, an optical coupler, a few-mode nonlinear fiber, an optical carrier extractor and an optical phase shifter.

[0006] The multi-level pulse amplitude modulation signals from different users carried by different fiber modes form a deteriorated mode division multiplexing signal in the fiber.

[0007] The deteriorated mode division multiplexing signal is input into the first few-mode amplifier after being adjusted by the first polarization controller for amplification, and then the amplified mode division multiplexing signal is divided into two paths by the first optical coupler.

[0008] Among them, one path of the mode division multiplexing signal is input into the optical carrier extractor to obtain a mode carrier, the mode carrier is amplified by the second few-mode amplifier, and two mode carriers are obtained by the second optical coupler; the other path of the mode division multiplexing signal is input into the third optical coupler together with one mode carrier output by the second optical coupler after the second polarization controller.

[0009] The other mode carrier output by the second optical coupler is input into one input port of the fourth optical coupler after being phase-shifted by the optical phase shifter; the third optical coupler inputs the mode division multiplexing signal and the other mode carrier output by the second optical coupler into the few-mode nonlinear fiber, the signals of each mode and the mode carrier generate mode self-phase modulation and intermodal cross-phase modulation in the few-mode nonlinear fiber, and then are input into the other input port of the fourth optical coupler, and finally the regenerated mode division multiplexing signal is output through the fourth optical coupler.

[0010] The application achieves the above-mentioned purposes in the following way:

[0011] The application discloses a mode division multiplexing all-optical regenerative device, which is characterized by comprising a polarization controller, a few-mode amplifier, an optical coupler, a few-mode nonlinear fiber, an optical carrier extractor and an optical phase shifter; the multi-level pulse amplitude modulation mode division multiplexing signals from different users can be simultaneously regenerated by the mode division multiplexing all-optical regenerative device, the regenerated mode division multiplexing signals are amplified and shaped, and the power transfer curves of each mode channel are not affected by the changes of other mode levels.

[0012] Meanwhile, the application also has the following beneficial effects:

[0013] (1) In the few-mode nonlinear fiber, the coefficient of intermodal cross-phase modulation is an integer multiple of the coefficient of mode self-phase modulation, so that the level change of each signal mode will generate cross-phase modulation with a positive integer multiple period on other signal modes, the power transfer function of each signal mode will not be affected by the level change of other signal modes and remains unchanged, and the regenerative device can simultaneously regenerate each mode in the mode division multiplexing signal.

[0014] (2), the light phase shifter adjusts the phase of the mode carrier, aligns the working point position of the power transfer curve of each mode channel at the output end with the level of the multi-level pulse amplitude modulation signal PAM signal, and realizes optimal regeneration. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a specific embodiment architecture diagram of a mode division multiplexing all-optical regeneration device of the present application.

[0016] Figure 2 is the refractive index distribution diagram of the optimized design of the few-mode nonlinear optical fiber.

[0017] Figure 3 is the power transfer curve diagram of the LP01 and LP11e mode channels.

[0018] Figure 4 is the waveform diagram of the degraded and regenerated PAM4 signals of the LP01 mode channel.

[0019] Figure 5 is the waveform diagram of the degraded and regenerated PAM4 signals of the LP11e mode channel. DETAILED DESCRIPTION

[0020] The specific embodiments of the present application will be described below in conjunction with the accompanying drawings, so that those skilled in the art can better understand the present application. It should be particularly noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present application, these descriptions will be omitted here.

[0021] EMBODIMENT

[0022] Figure 1 is a specific embodiment architecture diagram of a mode division multiplexing all-optical regeneration device of the present application.

[0023] In this embodiment, as shown in Figure 1 , a mode division multiplexing all-optical regeneration device of the present application comprises a polarization controller, a few-mode amplifier, an optical coupler, a few-mode nonlinear optical fiber, an optical carrier extractor, and a light phase shifter.

[0024] As shown in Figure 1 , the multi-level pulse amplitude modulation signals carried by different optical fiber modes from different users form a degraded mode division multiplexing signal in the optical fiber.

[0025] The degraded mode division multiplexing signal is input to the few-mode amplifier 1 after being adjusted by the polarization controller 1, and then the amplified mode division multiplexing signal is divided into two paths by the optical coupler 1.

[0026] In the embodiment, the mode gain of the few-mode amplifier 1 can be adjusted according to the minimum level interval of each mode input, and after adjustment, the minimum level interval of each mode in the mode division multiplexing signal entering the few-mode nonlinear optical fiber is ensured to remain unchanged. For example, when the minimum level interval of the LP01 mode and the LP11e mode input is 10 mW, the mode gain of the two modes is 17.401 dB and 17.397 dB respectively.

[0027] Among them, one mode division multiplexing signal is input into the optical carrier extractor to obtain a mode carrier, and the mode carrier is amplified by the few-mode amplifier 2 and then split by the optical coupler 2 to obtain two mode carriers; the other mode division multiplexing signal is input into the optical coupler 3 together with one mode carrier output by the optical coupler 2 after passing through the polarization controller 2;

[0028] The other mode carrier output by the optical coupler 2 is input into one input port of the optical coupler 4 after phase shifting by the optical phase shifter; the mode division multiplexing signal and the other mode carrier output by the optical coupler 2 are input into the few-mode nonlinear optical fiber by the optical coupler 3, and the signal of each mode and the mode carrier generate mode self-phase modulation and intermodal cross-phase modulation in the few-mode nonlinear optical fiber, and then input into the other input port of the optical coupler 4, and finally output the regenerated mode division multiplexing signal through the optical coupler 4.

[0029] In the embodiment, the structure of the few-mode nonlinear optical fiber is specially designed, and after the design is completed, the refractive index distribution of the few-mode nonlinear optical fiber satisfies that the coefficient of intermodal cross-phase modulation is an integer multiple of the coefficient of mode self-phase modulation. For example, the cross-phase modulation coefficient between the LP01 mode and the LP11e mode is m times of the self-phase modulation coefficient of the LP01 mode, and the cross-phase modulation coefficient between the LP11e mode and the LP01 mode is m times of the self-phase modulation coefficient of the LP11e mode, and m and m are positive integers. The minimum level change of the LP01 mode will produce a cross-phase modulation phase shift of m times of the period to the LP11e mode signal, and the minimum level change of the LP11e mode will produce a cross-phase modulation phase shift of m times of the period to the LP01 mode signal. The power transfer function of the LP01 mode and the LP11e mode signal will not be affected by the change of the signal level of each other and will remain unchanged. 01 The m 01 times of the self-phase modulation coefficient of the LP01 mode 11e The m 01 times of the self-phase modulation coefficient of the LP11e mode 11e are positive integers. The minimum level change of the LP01 mode will produce a cross-phase modulation phase shift of m 01 times of the period to the LP11e mode signal, and the minimum level change of the LP11e mode will produce a cross-phase modulation phase shift of m 11e times of the period to the LP01 mode signal. The power transfer function of the LP01 mode and the LP11e mode signal will not be affected by the change of the signal level of each other and will remain unchanged. In the embodiment, the refractive index distribution of the few-mode nonlinear optical fiber optimized by design is shown in Figure 2 , at this time m 01 and m 11e are both 1.

[0030] In the embodiment, the optical phase shifters are used to adjust the phases of the mode carriers, and after phase shifting, the working point positions of the power transfer curves of the mode division multiplexed signals of each mode at the output end are aligned with the levels of the multi-level pulse amplitude modulation (PAM) signals. In the process of adjusting the phases of the mode carriers, when the phases of the mode carriers are increased or decreased, the step-shaped power transfer function curve can be moved to the left or right. For example, the four levels of the LP01 mode and the LP11e mode PAM4 signals are 10 mW, 20 mW, 30 mW and 40 mW respectively, when the phase shifts of the two optical phase shifters are both 142.19°, the working points are aligned with the levels of the deteriorated signals, and the regenerative device can achieve the best regeneration effect, and the power transfer curve is as shown in Figure 3 .

[0031] In the embodiment, the mode division multiplexed all-optical regenerative device simultaneously regenerates the deteriorated LP01 mode and LP11e mode PAM4 signals, and the power waveforms of the deteriorated and regenerated PAM4 signals of the LP01 mode and the LP11e mode are as shown in Figure 4 and Figure 5 It can be seen that the noises of the two signal modes are well suppressed, and the signal powers are both amplified.

[0032] Although the above describes the specific embodiments of the present application in order to facilitate the understanding of the present application by those skilled in the art, it should be clear that the present application is not limited to the scope of the specific embodiments, and for those skilled in the art, it is obvious that various changes are within the spirit and scope of the present application defined and determined by the appended claims, and all the inventions utilizing the concept of the present application are within the scope of protection.

Claims

1. A mode-multiplexing all-optical regeneration device, characterized in that, include: Polarization controller, few-mode amplifier, optical coupler, few-mode nonlinear fiber, optical carrier extractor, optical phase shifter; Multilevel pulse amplitude modulation signals from different users, carried by different fiber modes, form degraded mode-division multiplexed signals in the optical fiber; The degraded mode-division multiplexed signal is adjusted by the first polarization controller and then input to the first few-mode amplifier for amplification. The amplified mode-division multiplexed signal is then split into two paths through the first optical coupler. One of the mode-division multiplexed signals is sent to the optical carrier extractor to obtain the mode carrier. After the mode carrier is amplified by the second few-mode amplifier, it is split by the second optical coupler to obtain two mode carriers. The other mode-division multiplexed signal is sent to the third optical coupler together with the mode carrier output by the second optical coupler after passing through the second polarization controller. The other mode carrier output from the second optical coupler is phase-shifted by an optical phase shifter and then sent to one input port of the fourth optical coupler. The third optical coupler inputs the mode-division multiplexed signal and the mode carrier output from the second optical coupler together into the few-mode nonlinear fiber. In the few-mode nonlinear fiber, each mode signal and the mode carrier generate mode self-phase modulation and inter-mode cross-phase modulation, and then sends them to another input port of the fourth optical coupler. Finally, the regenerated mode-division multiplexed signal is output through the fourth optical coupler. The refractive index distribution of the few-mode nonlinear fiber satisfies the following condition: the coefficient of intermode cross-phase modulation is an integer multiple of the coefficient of mode self-phase modulation. The optical phase shifter adjusts the phase of the mode carrier, and after phase shifting, it satisfies the following: the operating point position of the power transfer curve of each mode channel at the output end is aligned with the level of the multi-level pulse amplitude modulation signal.

2. The mode-division multiplexing all-optical regeneration device according to claim 1, characterized in that, The first few-mode amplifier adjusts the gain of each mode according to the minimum level interval of each mode input, and after adjustment, ensures that the minimum level interval of each mode entering the few-mode nonlinear fiber in the mode-division multiplexed signal remains unchanged.

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