Optical signal amplification method and device for optical fiber radio frequency transmission

Abstract

The invention discloses an optical signal amplification method and device for optical fiber radio frequency transmission, and the method comprises the steps: carrying out the power division of a received optical signal at two ends of a bidirectional optical fiber radio frequency transmission system, and enabling one path to be used for recovering a radio frequency signal; and the other path is used for generating a pumping signal after being amplified, the pumping signal is reversely injected into the original optical fiber link through the bidirectional optical device, and the received optical signal is amplified by utilizing stimulated Brillouin scattering (SBS). Benefited from the narrow-band gain spectrum (-30MHz) of the SBS, compared with an optical fiber radio frequency transmission amplification mode based on a bidirectional erbium-doped optical fiber amplifier, the optical signal amplification method can effectively reduce amplified spontaneous emission (ASE) noise and improve the signal-to-noise ratio of a recovered radio frequency signal, thereby improving the stability of frequency transmission. Meanwhile, due to the high gain characteristic of SBS, the optical signal amplification method can support amplification of weak optical signals, and the radio frequency transmission distance of the single-hop optical fiber is expected to be remarkably expanded.

Description

Technical Field

[0001] The present invention relates to the field of optical communication and optical transmission, and in particular to a method and device for amplifying optical signals transmitted by optical fiber radio frequency frequency based on stimulated Brillouin scattering. Background Art

[0002] High-precision time and frequency transmission technology has broad application prospects in scientific research, major infrastructure construction, national defense industry, etc. With the in-depth study of the noise generation mechanism of the transmission system and the factors restricting the accuracy improvement, optical fiber RF frequency transmission technology has made significant progress and developed three major technical trends: long-distance transmission, high-precision maintenance and distributed applications.

[0003] In the fiber RF frequency transmission system, erbium-doped fiber amplifiers (EDFA) are widely used to amplify C-band optical signals because the radiation transition spectrum of erbium ions covers the entire C-band. Most of the fiber RF frequency transmission systems reported so far use bidirectional erbium-doped fiber amplifiers (bi-EDFA) for optical signal amplification.

[0004] However, this solution faces two major challenges in practical application:

[0005] (1) Using bi-EDFA to amplify optical signals can easily cause self-oscillation and introduce a large amount of ASE noise, reducing the signal-to-noise ratio.

[0006] (2) For long-span applications, it is not convenient to place bi-EDFA in the middle. If EDFA is used for amplification at the end point, the input signal may be lower than the threshold and the gain may be insufficient, while using multi-stage amplification will introduce too much ASE noise.

[0007] Therefore, the study of low-noise and high-gain optical amplification technology is of great significance to fiber frequency transmission. On the one hand, it can reduce noise, improve signal-to-noise ratio, and reduce the background noise of the frequency transmission system. On the other hand, it can provide a possible solution for practical single-hop long-span applications. Summary of the invention

[0008] The present invention aims to solve the above technical problems and proposes an optical signal amplification device and method for optical fiber RF frequency transmission. By using this method to amplify optical signals, single-hop long-span optical fiber RF frequency transmission can be achieved while obtaining high signal-to-noise ratio and high gain.

[0009] On the one hand, the present invention provides a method for amplifying optical signals for optical fiber radio frequency transmission, which is characterized in that it includes:

[0010] The received optical signal is split into two parts, one for recovering the RF signal and the other for generating the pump signal.

[0011] amplifying, modulating and filtering the optical signal used to generate the pump signal to generate the pump signal;

[0012] The amplified pump signal is injected back into the original optical fiber link through a bidirectional optical device;

[0013] The received optical signal is amplified using stimulated Brillouin scattering (SBS).

[0014] The optical signal used to generate the pump signal is subjected to carrier suppressed double sideband modulation or carrier suppressed upper sideband modulation through an electro-optic modulator, and then a first-order upper sideband signal is filtered out through a bandpass filter as a pump signal, and the frequency of the modulated signal loaded on the electro-optic modulator is equal to the Brillouin frequency shift corresponding to the first-order upper sideband signal.

[0015] After the pump signal is released, the power reaches or exceeds the SBS threshold power.

[0016] On the other hand, the present invention also provides an optical signal amplifying device for optical fiber radio frequency transmission, characterized in that it comprises:

[0017] An optical coupler, whose input end is connected to an external input optical signal, is used to divide the received optical signal into two paths, one for recovering the radio frequency signal and the other for generating a pump signal;

[0018] a pump signal generating unit, whose input end is connected to the output end of the optical coupler, comprising a first optical amplifier, an electro-optic modulator, a second optical bandpass filter, a second optical amplifier, a polarization controller and a radio frequency signal source, wherein the input end of the electro-optic modulator is connected to the output end of the first optical amplifier, the radio frequency end is connected to the radio frequency signal source, and the output end is connected to the input end of the second optical bandpass filter; the electro-optic modulator is used to perform carrier suppressed double sideband modulation or carrier suppressed upper sideband modulation on the amplified optical signal; the radio frequency signal source is used to provide a modulation signal for the electro-optic modulator, the frequency of the modulation signal loaded on the electro-optic modulator is equal to the Brillouin frequency shift corresponding to the first-order upper sideband signal; the second optical bandpass filter is used to filter out the first-order upper sideband signal of the modulated optical signal, that is, the pump signal; the second optical amplifier amplifies the filtered pump signal to above the SBS threshold power; the polarization controller is used to modulate the polarization state of the pump signal to maximize the Brillouin gain, and utilizes the stimulated Brillouin scattering effect to amplify the received optical signal transmitted in the optical fiber link through the injected pump signal;

[0019] An optical circulator has three ports and is used for circulating transmission of optical signals.

[0020] Electro-optic modulator, with a modulation bandwidth greater than the Brillouin frequency shift (~11 GHz) of a 1550 nm laser in a single-mode fiber, can achieve carrier suppressed double sideband modulation or carrier suppressed upper sideband modulation.

[0021] Compared with the prior art, the beneficial effects of the present invention are: by utilizing the narrowband and high gain characteristics of SBS, this optical signal amplification method can effectively reduce ASE noise, improve the signal-to-noise ratio of the input transceiver signal, and thus improve the stability of frequency transmission. This optical signal amplification method supports the amplification of weak optical signals and is expected to significantly increase the single-hop optical fiber RF frequency transmission distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the optical path of an optical signal amplifying device for optical fiber radio frequency transmission according to Embodiment 1 of the present invention;

[0023] Figure 2 This is a schematic diagram of the optical path of an optical signal amplifying device for optical fiber radio frequency transmission according to Embodiment 2 of the present invention;

[0024] Figure 3 It is a schematic diagram of the principle of achieving SBS optical signal amplification by generating a pump signal through carrier suppressed double sideband modulation;

[0025] Figure 4 It is a schematic diagram of the principle of achieving SBS optical signal amplification by generating a pump signal through carrier suppression upper sideband modulation. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with examples and drawings. This example is implemented based on the technical solution of the present invention, and provides a detailed implementation method and a specific workflow, but the protection scope of the present invention is not limited to the following examples.

[0027] Figure 1 The optical path diagram of the optical signal amplifying device for optical fiber radio frequency transmission in embodiment 1 of the present invention includes an optical coupler 1-1, an optical circulator 1-2, a first optical bandpass filter 1-3, a first optical amplifier 1-4, an electro-optical modulator (EOM) 1-5, an RF signal source 1-6, a second optical bandpass filter 1-7, a second optical amplifier 1-8 and a polarization controller 1-9. The input end of the optical coupler 1-1 is connected to an external input optical signal (carrier frequency is f c), and the output ends are respectively connected to port 2 of the optical circulator 1-2 and the input end of the first optical amplifier 1-4. The output end of the first optical amplifier 1-4 is connected to the input end of the electro-optical modulator 1-5, the RF signal source 1-6 is connected to the RF port of the electro-optical modulator, and the output end of the electro-optical modulator is connected to the input end of the second optical bandpass filter 1-7. The output end of the second optical bandpass filter is connected to the input end of the second optical amplifier 1-8. The output end of the second optical amplifier is connected to the port of the optical circulator 1 through the polarization controller 1-9. The port 3 of the optical circulator is connected to the input port of the first optical bandpass filter 1-3, and the latter's output port outputs the amplified optical signal (carrier frequency is f c ).

[0028] The method of amplifying the input optical signal by the device is as follows:

[0029] Input optical signal (carrier frequency is f c ) is divided into two paths by the optical coupler 1-1. One path is first amplified by the first optical amplifier 1-4, and then input to the electro-optical modulator 1-5 for carrier suppressed double sideband modulation or carrier suppressed upper sideband modulation, and then the first-order upper sideband signal (frequency f) is filtered out by the second optical bandpass filter 1-7. c +f b ). The modulation signal is provided by the RF signal source 1-6, and the modulation frequency is equal to the Brillouin frequency shift f corresponding to the upper sideband signal b . After the upper sideband signal is amplified by the second optical amplifier 1-8 to above the SBS threshold power, it is injected into the optical fiber link from port 1 of the optical circulator 1-2 and the optical coupler after passing through the polarization controller 1-9. The polarization controller is used to modulate the polarization state of the pump light to maximize the Brillouin gain. The other output of the optical coupler passes through port 2 of the optical circulator and is output from port 3, and then input into the first optical bandpass filter 1-3 to filter out the backscattered pump signal. When the SBS that occurs is strong, the power of the optical signal output by the first optical bandpass filter will increase significantly.

[0030] Figure 2 This is a schematic diagram of the optical path of an optical signal amplifying device for optical fiber radio frequency transmission in Example 2 of the present invention, including an optical circulator 2-1, an optical coupler 2-2, a first optical bandpass filter 2-3, a first optical amplifier 2-4, an electro-optical modulator (EOM) 2-5, an RF signal source 2-6, a second optical bandpass filter 2-7, a second optical amplifier 2-8, and a polarization controller 2-9. The 2 ports of the optical circulator 2-1 are connected to the external input optical signal (carrier frequency is f c), port 3 is connected to the input end of optical coupler 2-2, and one output port of the optical coupler is connected to the input port of the first optical amplifier 2-4. The output end of the first optical amplifier is connected to the input end of the electro-optical modulator 2-5, the RF signal source 2-6 is connected to the RF port of the electro-optical modulator, and the output end of the electro-optical modulator is connected to the input end of the second optical bandpass filter 2-7. The output end of the second optical bandpass filter is connected to the input end of the second optical amplifier 2-8. The output end of the second optical amplifier is connected to the port of optical circulator 1 through the polarization controller 2-9. Another output port of the optical coupler is connected to the input port of the first optical bandpass filter 2-3, and the latter's output port outputs the amplified optical signal (carrier frequency is f c ).

[0031] The method of amplifying the input optical signal may also be as follows:

[0032] Input optical signal (carrier frequency is f c ) is input through the 2-port of the optical circulator 2-1 and output from the 3-port, and then input to the optical coupler 2-2, and then the optical signal is equally divided into two paths by the second optical coupler. One of the paths is amplified by the first optical amplifier 2-4, and then input to the electro-optical modulator 2-5 for carrier suppressed double sideband modulation or carrier suppressed upper sideband modulation, and then the first-order upper sideband signal (frequency f) is filtered out by the second optical bandpass filter 2-7. c +f b ). The modulation signal is provided by the RF signal source 2-6, and the modulation frequency is equal to the Brillouin frequency shift f corresponding to the upper sideband signal. b . After the upper sideband signal is amplified by the second optical amplifier 2-8 to above the SBS threshold power, it is injected into the optical fiber link from port 1 of the optical circulator after passing through the polarization controller 2-9. The polarization controller is used to modulate the polarization state of the pump light to maximize the Brillouin gain. Since the pump signal does not pass through the optical coupler, a 3dB insertion loss is avoided. The other output of the optical coupler is input to the first optical bandpass filter 2-3 to filter out the backscattered pump signal. When a strong SBS occurs in the optical fiber link, the power of the optical signal output by the first optical bandpass filter will increase significantly.

[0033] Figure 3 It is a schematic diagram of the principle of achieving SBS optical signal amplification by generating a pump signal through carrier suppressed double sideband modulation; Figure 4 This is a schematic diagram of the principle of SBS optical signal amplification by generating a pump signal through carrier suppression upper sideband modulation. Stimulated Brillouin scattering is a nonlinear optical phenomenon that occurs in media such as optical fibers. When high-intensity light waves interact with acoustic waves in the medium, part of the energy of the light waves is transferred to the acoustic waves, and scattered light is generated. This process can be used to amplify optical signals.

[0034] The optical signal to be amplified consists of a carrier wave (frequency fc ) and two first-order sidebands (frequency f c ±f rf , f rf The optical signal to be amplified is modulated by an electro-optic modulator, and the frequency of the modulated signal is the Brillouin frequency shift f corresponding to the pump optical signal. b , the calculation formula is

[0035]

[0036] Where c is the speed of light, n is the refractive index of the optical fiber, v a is the speed of sound in the optical fiber. Usually, the pump light signal needs to be amplified to more than twice the SBS threshold power and injected into the optical fiber where the input signal is located, and then the SBS phenomenon will be observed. By properly adjusting the polarization state of the pump signal, it can be observed that the initial signal has obtained a significant gain. The highest gain can be obtained by adjusting the polarization state of the pump signal. The gain spectrum can be calculated by formula (2)

[0037]

[0038] where g b is the Brillouin coefficient of single-mode fiber, A eff is the effective mode field area of ​​the optical fiber, A p is the pump laser amplitude, Δf is the pump-signal frequency deviation, 2π / Γ b is the gain spectrum width B b Therefore, the optical signal-to-noise ratio improvement can be calculated by formula (3):

[0039] ΔOSNR≈B s / [B b +(B s -B b ) / G b ],#(3)#

[0040] Among them B s is the ASE noise bandwidth, which is numerically equal to the bandwidth of the optical filter at the output side of the pump generation module, G b The Brillouin gain is the effective amplification of the optical signal and the improvement of OSNR by precisely controlling the power, frequency and polarization state of the pump signal.

Claims

1. A method for amplifying optical signals for optical fiber radio frequency transmission, characterized in that: include: The received optical signal is split into two parts, one for recovering the RF signal and the other for generating the pump signal. amplifying, modulating and filtering the optical signal used to generate the pump signal to generate the pump signal; The amplified pump signal is injected back into the original optical fiber link through a bidirectional optical device; The received optical signal is amplified using stimulated Brillouin scattering (SBS).

2. The optical signal amplification method for optical fiber radio frequency transmission according to claim 1, characterized in that: The optical signal used to generate the pump signal is subjected to carrier suppressed double sideband modulation or carrier suppressed upper sideband modulation through an electro-optic modulator, and then a first-order upper sideband signal is filtered out through a bandpass filter as a pump signal, and the frequency of the modulated signal loaded on the electro-optic modulator is equal to the Brillouin frequency shift corresponding to the first-order upper sideband signal.

3. The optical signal amplification method for optical fiber radio frequency transmission according to claim 2, characterized in that: After the pump signal is amplified, the power reaches or exceeds the SBS threshold power.

4. An optical signal amplifying device for optical fiber radio frequency transmission, characterized in that: include: An optical coupler, whose input end is connected to an external input optical signal, is used to divide the received optical signal into two paths, one for recovering the radio frequency signal and the other for generating a pump signal; a pump signal generating unit, whose input end is connected to an output end of the optical coupler, comprising a first optical amplifier, an electro-optic modulator, a second optical bandpass filter, a second optical amplifier, a polarization controller and a radio frequency signal source, wherein the input end of the electro-optic modulator is connected to the output end of the first optical amplifier, the radio frequency end is connected to the radio frequency signal source, and the output end is connected to the input end of the second optical bandpass filter; the electro-optic modulator is used to perform carrier suppressed double sideband modulation or carrier suppressed upper sideband modulation on the amplified optical signal; the radio frequency signal source is used to provide a modulation signal for the electro-optic modulator, and the modulation frequency is equal to the Brillouin frequency shift corresponding to the first-order upper sideband signal; the second optical bandpass filter is used to filter out the first-order upper sideband signal of the modulated optical signal, that is, the pump signal; the second optical amplifier amplifies the filtered pump signal to above the SBS threshold power; the polarization controller is used to modulate the polarization state of the pump signal to maximize the Brillouin gain, and utilizes the stimulated Brillouin scattering effect to amplify the received optical signal transmitted in the optical fiber link through the injected pump signal; The optical circulator has three ports for injecting a pump optical signal into an original optical fiber link and outputting an optical signal received from the optical fiber link.

5. An optical signal amplification device for optical fiber radio frequency transmission, characterized in that: The electro-optical modulator is a modulator capable of realizing carrier suppressed double sideband modulation or carrier suppressed upper sideband modulation, and includes an intensity modulator and an IQ modulator.

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