CN112505976B - Optical signal amplification method - Google Patents

Abstract

The present invention provides an optical signal amplifying method, comprising: receiving a first optical signal to be amplified, generating a second optical signal through the first optical signal and a pumping optical device; passing the second optical signal through a Raman fiber amplifier Amplify to obtain a third optical signal; the third optical signal passes through the first second-order optical nonlinear Bragg reflection waveguide to generate a fourth optical signal, and the fourth optical signal also includes an invalid signal; the fourth optical signal passes through the second optical signal. Phase-sensitive amplification of the second-order optical nonlinear Bragg-reflecting waveguide to generate a fifth optical signal. Through the method of the present invention, on the one hand, the noise index of the optical fiber amplifier can be effectively reduced, and the optical signal-to-noise ratio of the system can be improved; process noise, effectively improving the optical signal-to-noise ratio.

Description

A kind of optical signal amplification method

technical field

The present invention relates to an optical communication system, in particular to an optical signal amplification method.

Background technique

In an optical communication network, information is transmitted in the form of optical signals through optical fibers, and optical fibers are thin glass filaments that can transmit signals over long distances. Optical communication equipment mainly includes optical communication equipment, optical access equipment, and optical transmission equipment. In an optical fiber network, the original information needs to be modulated to be transmitted, and common modulation methods include phase shift keying (PSK), frequency shift keying (FSK), amplitude shift keying (ASK) and quadrature amplitude modulation ( QAM).

Phase Shift Keying (PSK): A modulation technique in which the phase of the carrier is used to represent the information of the input signal. There are two types of phase shift keying: absolute phase shift and relative phase shift. Phase modulation based on the phase of the unmodulated carrier is called absolute phase shifting. Taking binary phase modulation as an example, when the symbol is "1", the modulated carrier is in phase with the unmodulated carrier; when the symbol is "0", the modulated carrier and the unmodulated carrier are in reverse phase; "1" and "0" ”, the carrier phase difference after modulation is 180°.

The modulation method in which the change of the carrier frequency is controlled by a digital signal is called frequency shift keying. The amplitude keying is implemented by ASK, which modulates the amplitude of the sine wave according to the difference of the signal. Amplitude keying can be achieved with multipliers and switching circuits. The carrier is turned on or off under the control of the digital signal 1 or 0. When the signal is 1, the carrier is turned on, and a carrier appears on the transmission channel; when the signal is 0, the carrier is turned off, and the transmission channel No carrier transmission on it. Then at the receiving end, we can restore the 1 and 0 of the digital signal according to the presence or absence of the carrier. The frequency bandwidth for binary amplitude keyed signals is twice the width of the binary baseband signal.

Quadrature Amplitude Modulation (QAM, Quadrature Amplitude Modulation) is a modulation method that performs amplitude modulation on two quadrature carriers. These two carriers are usually sine waves with a phase difference of 90 degrees (π/2) and are therefore called quadrature carriers.

With the continuous improvement of the data transmission rate of the optical network, it has reached the T/s level at present, and the requirements for the optical signal-to-noise ratio (OSNR) are getting higher and higher. In the high-speed optical network, the noise accumulated by the cascade of optical amplifiers has a great impact on the optical signal-to-noise ratio, which indirectly increases the number of optical-electrical-optical conversions and increases the cost of signal transmission. .

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the above problem, and to provide a method for amplifying an optical signal, so as to solve the problem that the OSNR of the optical signal is required to be as high as possible in the process of high-speed optical network transmission.

The present invention realizes through the following scheme:

An optical signal amplifying method, comprising: receiving a first optical signal to be amplified, and generating a second optical signal by using the first optical signal and a pump optical device;

Amplifying the second optical signal through a Raman fiber amplifier to obtain a third optical signal;

The third optical signal generates a fourth optical signal through the first second-order optical nonlinear Bragg reflection waveguide, and the fourth optical signal further includes a null signal;

Phase-sensitive amplification of the fourth optical signal through the second second-order optical nonlinear Bragg reflection waveguide to generate a fifth optical signal;

The pump light device includes at least one pump light source, a wave combiner, and a control module;

The control module is used to detect and control the working state of the pump light source;

The second-order optical nonlinear Bragg reflection waveguide is composed of a central cavity and two p-type Bragg mirrors, the central defect layer is made of AlGaAs material with a thickness of 1 μm, the upper and lower Bragg mirrors are selected from AlGaAs/GaAs material with a thickness of 120 nm/700 nm, and The central cavity has the same high index of refraction as the Bragg mirror.

Preferably, in the optical signal amplification method, the first optical signal includes at least one wavelength channel for wavelength division multiplexing.

Preferably, in the optical signal amplifying method, the wavelength channel is modulated by orthogonal dual polarization, including parts of the X pole and the Y pole.

Preferably, in the optical signal amplification method, the wavelength channel is mainly modulated by PSK, FSK, ASK, and QAM.

Preferably, in the optical signal amplification method, the pump light and the invalid signal are removed by wavelength selection for the fifth optical signal.

Preferably, in the optical signal amplification method, the pump light is linearly polarized light or circularly polarized light.

Preferably, in the optical signal amplification method, the pump light source is a pump laser with a wavelength range of 1455-1510 nm.

Preferably, in the optical signal amplification method, the invalid signal is a conjugate signal of the first optical signal.

Preferably, in the optical signal amplification method, the wavelengths of the invalid signal and the first optical signal are equidistant from the wavelength of the pump light.

Preferably, in the optical signal amplification method, the Raman fiber amplifier includes: a wave combiner, a second pump light, a first isolator, a second isolator and a gain flattening filter; wherein,

The common end of the multiplexer is connected to the output end of the first isolator, the reflection end of the multiplexer is connected to the second pump light, and the transmission end of the multiplexer is isolated from the second The output end of the second isolator is connected to the input end of the gain flattening filter, and the output end of the gain flattening filter is used as the output end of the Raman fiber amplifier.

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

In the invention, the original optical signal is firstly pumped by pumping light, then a Raman fiber amplifier is used to amplify the optical signal, and the final amplified signal is obtained by processing the optical signal twice through the second-order optical nonlinear Bragg reflection waveguide. Through the above method, on the one hand, the noise index of the fiber amplifier can be effectively reduced, and the optical signal-to-noise ratio of the system can be improved; At the same time, it has better carrier confinement, improves the thermal stability of the reflected waveguide, obtains a larger current characteristic temperature, and can also suppress the refractive index guide, ensuring that Reflective waveguide for efficient light field suppression.

Description of drawings

FIG. 1 is a flow chart of the method of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. The indicated orientation or positional relationship is based on the orientation or positional relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the indicated device or element must have a specific orientation or a specific orientation. construction and operation, and therefore should not be construed as limiting the invention. Furthermore, the terms "first", "second", and "third" are used for descriptive purposes only and should not be construed to indicate or imply relative importance. In the description of the present invention, it should be noted that the terms "installed", "connected", "connected" and "arranged" should be understood in a broad sense, unless otherwise expressly specified and limited, for example, it may be a fixed connection, or It can be a detachable connection or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal communication between the two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in specific situations. The embodiments of the present invention will be described below based on the overall structure of the present invention.

1 shows a flowchart of an optical signal amplifying method according to the present invention, the method includes: receiving a first optical signal to be amplified, and generating a second optical signal by using the first optical signal and a pumping optical device;

Amplifying the second optical signal through a Raman fiber amplifier to obtain a third optical signal;

The third optical signal generates a fourth optical signal through the first second-order optical nonlinear Bragg reflection waveguide, and the fourth optical signal further includes a null signal;

Phase-sensitive amplification of the fourth optical signal through the second second-order optical nonlinear Bragg reflection waveguide to generate a fifth optical signal;

The pump light device includes at least one pump light source, a wave combiner, and a control module;

The control module is used to detect and control the working state of the pump light source;

Bragg reflection waveguide is a one-dimensional photonic crystal material with line defects, which consists of upper and lower Bragg reflectors (DBR) and a central cavity, and the central cavity forms a line defect optically, and the light transmission direction is perpendicular to the refraction of the DBR rate modulation direction. The DBR is composed of alternating high and low refractive index materials with refractive indices n1 and n2, respectively, and the thicknesses of the high and low refractive index layers are d1 and d2, respectively. The refractive index and thickness of the central defect layer are m and n, respectively. Bragg scattering occurs when light propagates in this periodic dielectric material, creating a photonic band gap, and when the optical transmission constant lies within the photonic band gap, light cannot travel in this particular direction.

AlGaAs material has been used in the semiconductor industry for many years, and compared with the equivalent GaAs PIN structure, it can effectively improve the return loss, insertion loss and P-1db index. In order to improve the conductive properties, the second-order optical nonlinear Bragg reflection waveguide is composed of an N-type central cavity and two p-type Bragg mirrors. The central defect layer is made of AlGaAs material with a thickness of 1 μm, and the upper and lower Bragg mirrors are selected with a thickness of 120nm/700nm. AlGaAs/GaAs material, and the central cavity has the same high refractive index as the Bragg mirror. The thickness of 1 μm can take into account both the electrical and optical properties of the Bragg-reflecting waveguide.

Optical pumping is a process that uses light to raise electrons from a lower energy level in an atom or molecule to a higher energy level. By being used in lasing structures, the lasing medium is pumped to achieve population inversion. In practical applications, the pumping of light is often incoherent due to the transitional spectral linewidth and undesirable effects such as hyperfine structure trapping and radiative trapping.

The control module further includes a microprocessor, a pumping light source driving unit, a light source working performance collecting unit and a temperature control unit; the circuits are connected by a data line and a control line. When the output power of the pump laser light source needs to be controlled, the microprocessor outputs the data to the pump light source driving unit through the control signal line CS; at the same time, the microprocessor outputs data to the pump light source driving unit through the second control signal data line, and then passes through the second control signal data line. After amplification, it is sent to the bias current input terminal of the pump light source. Optical pumping can effectively realize the energy level transition of the original signal light, but the signal light of different wavelengths has different energy level difference, which requires the pump light to meet the transition requirements of the signal light of different wavelengths. Through the pump light driving unit, the output power of the pump light can be effectively adjusted, which greatly improves the flexibility and applicability of the method.

When the tube core temperature of the pump light source needs to be controlled, the microprocessor outputs the control information to the temperature control unit; when the pump light source is controlled, the corresponding performance needs to be detected for more accurate feedback adjustment. During the pumping process, the pump light will burst out a great amount of energy in a short period of time, causing the temperature of the entire pump light source to rise rapidly. Constant temperature control will greatly affect the life and stability of the pump light element. The temperature of the pump light source is monitored by the temperature control unit, which can ensure the stable and reliable operation of the pump light source.

Aluminum Gallium Arsenide is a new type of semiconductor material. The ALGAAS-based material with a thickness of 1 μm is arranged in the central layer, and its refractive index is the same as that of the high refractive index layer of the Bragg reflector, which can suppress the refractive index guide and ensure that the Bragg reflection waveguide can Effective light field confinement.

The working principle of RFA is based on the stimulated Raman scattering (SRS) effect in the fiber, which can be explained from the viewpoint of quantum mechanics as: a pump photon is incident on the fiber, the electrons in the fiber are excited and transition from the ground state to the virtual energy level, Then the electrons in the virtual energy level return to the high energy level of the vibrational state under the induction of the signal light, and at the same time emit a low-frequency Stokes. In the fiber, the vibrational energy level above the ground state has a large range, so the Raman gain has a wide spectrum (3dB bandwidth is about 6-7THz), and there is a main peak near the frequency shift of 13.2THz. If the weak signal light and the strong pump light are transmitted in the fiber at the same time, and the wavelength of the signal light is within the Raman gain spectrum of the pump light, then a part of the energy is transferred from the pump light to the signal light to realize the amplification of the signal light. This principle of amplifier is called RFA. Its characteristics are: (1) It can achieve full-band amplification, and the Raman scattering gain wavelength is mainly determined by the pump wavelength, so selecting the appropriate wavelength pump can theoretically achieve any wavelength amplification; (2) The gain medium is a transmission fiber. By itself, it can amplify the optical signal online to realize long-distance relayless transmission and long-distance pumping, especially suitable for occasions where it is inconvenient to set up repeaters such as submarine optical cable communication, and because the amplification is distributed along the optical fiber rather than concentrated, the optical fiber The signal power everywhere in the RFA is small, which can reduce the interference of nonlinear effects, especially the four-wave mixing (FWM) effect; (3) The noise figure (NF) of RFA is lower than that of EDFA. (4) The gain spectrum is wide, and a wide and flat gain spectrum can be achieved by pumping with multiple wavelengths. In the embodiment of the present invention, the Raman fiber amplifier is used in the front stage, which can effectively take into account various wavelength signals and improve the amplification distance. When the second-order Bragg reflection grating is subsequently connected, the connection distance and pump can be set more flexibly. pump wavelength and pump power.

RFA can be divided into two types: discrete and distributed. Among them, the gain fiber used in discrete RFA is relatively short, generally several kilometers; the pump light and the signal light transmitted in the same direction are called forward pump, and vice versa It is called backward pumping, and pumping in two directions at the same time is called bidirectional pumping. Compared with the forward pump, the use of the backward pump can avoid the crosstalk of the pump noise into the signal, so that the noise of the amplifier is lower, and the polarization dependence of the backward pump is also smaller. Therefore, in the present invention, a bidirectional pumping driving method is preferably adopted.

Since the Bragg reflection waveguide with second-order optical nonlinearity used is a solid-state semiconductor element, many elements of the optical amplifier are integrated on a semiconductor platform, which can effectively lower noise and reduce costs.

Preferably, in the optical signal amplification method, the first optical signal includes at least one wavelength channel for wavelength division multiplexing.

Preferably, in the optical signal amplifying method, the wavelength channel is modulated by orthogonal dual polarization, including parts of the X pole and the Y pole.

Preferably, in the optical signal amplification method, the wavelength channel is mainly modulated by PSK, FSK, ASK, and QAM.

Phase Shift Keying (PSK): A modulation technique in which the phase of the carrier is used to represent the information of the input signal. There are two types of phase shift keying: absolute phase shift and relative phase shift. The modulation method in which the change of the carrier frequency is controlled by a digital signal is called frequency shift keying. The amplitude keying is implemented by ASK, which modulates the amplitude of the sine wave according to the difference of the signal. Quadrature Amplitude Modulation (QAM, Quadrature Amplitude Modulation) is a modulation method that performs amplitude modulation on two quadrature carriers.

Preferably, in the optical signal amplification method, the pump light and the invalid signal are removed by wavelength selection for the fifth optical signal.

The fifth optical signal already contains the original pump light and invalid light. For the valid signal, the above-mentioned pump light and invalid light are noise, so they need to be eliminated, and wavelength selection is a very effective one. filter method.

Preferably, in the optical signal amplification method, the pump light is linearly polarized light or circularly polarized light.

In order to avoid adverse effects such as transitional spectral line width and hyperfine structure trapping and radiation trapping, the pumping of light is often incoherent, so the pumping light can be set to polarized light in different directions, linearly polarized light and circularly polarized light Each light has different characteristics and advantages, and those skilled in the art can choose according to needs.

Preferably, in the optical signal amplification method, the pump light source is a pump laser with a wavelength range of 1455-1510 nm.

The pump laser group includes at least two different pump wavelengths, so that the deficiency of the signal light gain of different wavelength bands can be compensated.

Preferably, in the optical signal amplification method, the invalid signal is a conjugate signal of the first optical signal.

Preferably, in the optical signal amplification method, the wavelengths of the invalid signal and the first optical signal are equidistant from the wavelength of the pump light.

Preferably, the Raman fiber amplifier includes: a wave combiner, a second pump light, a first isolator, a second isolator and a gain flattening filter; wherein,

The common end of the multiplexer is connected to the output end of the first isolator, the reflection end of the multiplexer is connected to the second pump light, and the transmission end of the multiplexer is isolated from the second The output end of the second isolator is connected to the input end of the gain flattening filter, and the output end of the gain flattening filter is used as the output end of the Raman fiber amplifier.

Preferably, in the optical signal amplification method, the Raman fiber amplifier further comprises a nonlinear optical fiber, and the nonlinear optical fiber is arranged at the transmission end of the wave combiner and the input end of the second isolator between.

In the several embodiments provided in this application, it should be understood that the disclosed apparatus and method may be implemented in other manners. The device embodiments described above are only illustrative. For example, the division of the units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components may be combined, or Can be integrated into another system, or some features can be ignored, or not implemented. In addition, the coupling, or direct coupling, or communication connection between the components shown or discussed may be through some interfaces, and the indirect coupling or communication connection of devices or units may be electrical, mechanical or other forms. of.

The embodiments of the present invention have been described above, but those skilled in the art should understand that these are only examples, and those skilled in the art can make various changes to the embodiments without departing from the principles and essence of the present invention. or modification, but these changes and modifications all fall into the protection scope of the present invention.

Claims (7)

1. An optical signal amplification method, comprising: receiving a first optical signal to be amplified, and generating a second optical signal through the first optical signal and a pump optical device;

amplifying the second optical signal through a Raman fiber amplifier to obtain a third optical signal;

the third optical signal is passed through a first second order optical nonlinear bragg reflection waveguide to generate a fourth optical signal, the fourth optical signal further comprising an invalid signal;

performing phase-sensitive amplification on the fourth optical signal through a second-order optical nonlinear Bragg reflection waveguide to generate a fifth optical signal;

removing the pumping light and the invalid signal by selecting the wavelength of the fifth optical signal;

the pumping light device comprises at least one pumping light source, a wave combiner and a control module;

the control module is used for realizing the detection and control of the working state of the pump light source;

the second-order optical nonlinear Bragg reflection waveguide consists of a central cavity and two p-type Bragg reflectors, wherein the central defect layer is made of AlGaAs material with the thickness of 1 mu m, the upper Bragg reflector and the lower Bragg reflector are made of AlGaAs/GaAs material with the thickness of 120nm/700nm and are alternately made of AlGaAs material and GaAs material, and the high refractive indexes of the central cavity and the Bragg reflectors are the same;

the nulling signal is a conjugate signal of the first optical signal, and the wavelengths of the nulling signal and the first optical signal are equidistant from the wavelength of the pump light.

2. The optical signal amplification method of claim 1, wherein the first optical signal comprises at least one wavelength channel for wavelength division multiplexing.

3. Optical signal amplification method according to claim 2, characterized in that the wavelength channels are modulated by orthogonal dual polarization, comprising portions of X-and Y-poles.

4. The optical signal amplification method of claim 2 wherein the wavelength channel is modulated by PSK, FSK, ASK or QAM.

5. The optical signal amplification method of claim 1, wherein the pump light is linearly polarized light or circularly polarized light.

6. The optical signal amplification method of claim 5, wherein the pump light source is a pump laser having a wavelength ranging from 1455 nm to 1510 nm.

7. The optical signal amplification method according to claim 1, wherein the raman fiber amplifier comprises: the optical fiber amplifier comprises a wave combiner, second pump light, a first isolator, a second isolator and a gain flattening filter; wherein,

the common end of the wave combiner is connected with the output end of the first isolator, the reflection end of the wave combiner is connected with the second pump light, the transmission end of the wave combiner is connected with the input end of the second isolator, the output end of the second isolator is connected with the input end of the gain flattening filter, and the output end of the gain flattening filter is used as the output end of the Raman fiber amplifier.

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