CN104836625A - Dual-parallel Mach-Zehnder modulator (DPMZM) high-linearity microwave photonic link implementation system - Google Patents

Abstract

The invention relates to a dual-parallel Mach-Zehnder modulator (DPMZM) high-linearity microwave photonic link implementation system. The dual-parallel Mach-Zehnder modulator (DPMZM) high-linearity microwave photonic link implementation system includes a laser, a signal source, a DPMZM, an electric splitter, an electric attenuator, a direct current power source and a photoelectric detector; radio frequency signals generated by the signal source are divided into two paths through the electric power splitter, wherein one path is connected with an uplink sub modulator, and the other path is connected with a downlink sub modulator through the electric attenuator; the laser is connected with an optical input port of the DPMZM; the direct current power source controls the phase states of the bias points of the DPMZM and the optical signals of the DPMZM; and the optical signals outputted by the DPMZM are connected with the photoelectric detector through optical fiber transmission, so that direct detection can be performed, and frequency beating can be completed in the photoelectric detector, and therefore, third-order intermodulation interference can be inhibited. According to the dual-parallel Mach-Zehnder modulator (DPMZM) high-linearity microwave photonic link implementation system of the invention, asymmetric power distribution is performed on radio frequency signals in the two optical wave interference paths of the DPMZM, so that the modulation depth of the two sub modulators of the DPMZM can be changed and precisely controlled; the optimal bias points of the sub modulators are set; and therefore, third-order intermodulation interference can be inhibited to the largest extent, and the linearity of a microwave photonic link can be improved.

Description

A kind of high linearity microwave photon link based on DPMZM realizes system

Technical field

The present invention relates to a kind of high linearity microwave photon link and realize system, particularly relate to a kind of based on two parallel MZ Mach-Zehnder (the Dual-Parallel Mach-ZehnderModulator of asymmetric power division, DPMZM) high linearity microwave photon link realizes system, belongs to microwave photon Signal transmissions and processing technology field.

Background technology

Microwave photonics is the new branch of science that microwave is combined with photon technology, and wherein the Microwave photonics technology branch such as Optical Generation of Millimeter Wave Signals, optical fiber radio (ROF) technology, Optically controlled microwave technology becomes the focus of recent domestic research.Microwave photon link, as the optimized integration of these technology, has the features such as large, the non-linear rejection ability of transmission capacity is strong, electromagnetism interference.The broadband rf signal received can be modulated to area of light and carry out long range propagation, multichannel distribution and process, can also effectively reduce its volume, weight and power consumption by the system integration.Therefore military and civilian field is widely applied to, as fields such as electronic warfare, radar, remote sensing, radio communication, cable TVs (CATV).

The linearity is one of important indicator characterizing microwave photon link performance, and the size of Spurious Free Dynamic Range (Spurious-Free Dynamic Range, SFDR) represents the quality of the linearity.Nonlinear response by waveguide affects, and radiofrequency signal electrooptic modulation process can bring certain nonlinear distortion to microwave photon link, affects the linearity of microwave photon link.Wherein third order intermodulation interference (Third-OrderIntermodulation, IMD3) is the most important nonlinear terms of the influential system linearity, and it drops in radiofrequency signal frequency band, is difficult to be eliminated by filter.The appearance of third order intermodulation interference can have a strong impact on the receptivity of microwave photon link to broadband rf signal.The microwave photon link that therefore will realize high linearity just means will do better suppression to third order intermodulation interference.

In microwave photon link, the electro-optic external modulation module bearing electro-optic conversion is the critical component affecting linearity performance.In multiple electro-optic external modulation module, the electrooptic modulation module being core with MZ Mach-Zehnder (MZM), due to the advantage of its high speed, High Extinction Ratio, filter with low insertion loss, is most widely used.Owing to only there is an optical interference path in single MZM, third order intermodulation interference components and fundametal compoment have identical variation tendency with modulation depth, and do not have the bias point of utilizable effective suppression third order intermodulation interference.Therefore the electro-optic external modulation module design that third order intermodulation can be suppressed to disturb will be found, need the mode adopting two or more MZM cascade or parallel connection, increase optical interference path, control the information such as phase delay between the light intensity in different path, modulation depth, bias point and path, the third order intermodulation interference mismatch that different electrooptic modulation process is produced, cancels out each other.In the design of two MZM parallel connections, along with the appearance of the integrated electro-optic modulator DPMZM of commercialization, the high linearity microwave photon link studied based on DPMZM becomes study hotspot in recent years.

Research both domestic and external proposes multiple design for the high linearity microwave photon link based on DPMZM.Comprising y-branch waveguide beam intensity ratio and radio-frequency power ratio in change DPMZM, dual-polarization is utilized to suppress IMD3 in conjunction with DPMZM, Digital Signal Processing is utilized to suppress IMD3 after photodetection, and research Dual Drive DPMZM tetra-motor phases relations, change bias point and suppress IMD3 etc.But in above scheme, IMD3 suppresses insufficient, fails to realize the microwave photon link of high linearity.

Existing DPMZM microwave photon link exemplary implementations:

(1)Guanghao Zhu,“A Broadband Linearized Coherent AnalogFiber-Optic Link Employing Dual Parallel Mach–Zehnder Modulators，”Photonics Technology Letters，vol.21,no.21，2009.

This article utilizes DPMZM to achieve the microwave photon link of linearizing Double Sideband Suppressed Carrier modulation.By strict control inputs with export y-branch waveguide light intensity, utilize interfere the principle that disappears mutually make upper and lower two along separate routes in the third order intermodulation interference that produces cancel out each other, reach and suppress third order intermodulation interference, improve the object of the microwave photon link linearity.

This system can effectively improve the microwave photon link linearity, but needs the light intensity of the two y-branch waveguides to DPMZM strictly to control, and this is be difficult to realize in area of light, and does not have ripe goods shelf products to use at present, implements difficulty larger.

(2) analogy pine, a kind of " method realizing high linearity microwave photon link based on Dual Drive DPMZM.CN201210499691.5”。

The patent proposes a kind of high linearity system of the DPMZM microwave photon link based on radiofrequency signal phase control, the method is by the bias point of microwave signal phase relation between four electrodes controlling up-downgoing sub-modulator and the sub-modulator of up-downgoing, after link receiving terminal is with photodiode direct-detection, achieve the suppression to third order intermodulation, effectively improve the microwave photon link linearity.

This patent, by changing signal phase relation between Different electrodes, realizes third order intermodulation AF panel.This kind of method requires accurately to control respectively the phase place of four tunnel radiofrequency signals, and during practical operation, system is comparatively complicated, propose rigors, and the stability of a system caused by electric phase shifter is poor to the technological level of optics.

Summary of the invention

Technical problem to be solved by this invention is: complicated for project organization in prior art, and IMD3 suppresses insufficient, fail the deficiency of the microwave photon link realizing high linearity, provide a kind of high linearity microwave photon link based on DPMZM and realize system.By carrying out asymmetric power division to the radiofrequency signal in DPMZM two-way optical interference path, change and the accurate sub-modulators modulate degree of depth of control DPMZM two, corresponding two sub-modulator just bias points are set, inhibit third order intermodulation to disturb to the full extent, improve the microwave photon link linearity.The method realizes simple, utilizes existing commercial devices to complete.

The technical solution adopted in the present invention is: a kind of high linearity microwave photon link based on DPMZM realizes system, comprising: laser, signal source, DPMZM, electric shunt, electrical attenuator, DC power supply and photodetector;

Described DPMZM comprises up sub-modulator, descending sub-modulator and phase-modulator;

The radiofrequency signal that described signal source produces is divided into two-way through electric power splitter, and wherein a road is directly connected with the rf inputs mouth of up sub-modulator, and another road carries out being connected with the rf inputs mouth of descending sub-modulator after power attenuation through electrical attenuator;

Described laser is connected with the light input end mouth of DPMZM, for DPMZM exports a road light carrier, and the bias point of described DC power control DPMZM and the phase state of DPMZM light signal;

The light signal that described DPMZM exports is connected to photodetector through Optical Fiber Transmission and carries out direct detection, and completes beat frequency in photodetector, thus realizes the suppression to third order intermodulation interference.

The bias point of described DC power control DPMZM and the phase state of DPMZM light signal; Be specially:

Described DC power supply provides three road DC bias signal for DPMZM, wherein two-way DC bias signal controls the bias point of up sub-modulator and descending sub-modulator respectively, 3rd road DC bias signal drives the phase-modulator in DPMZM, the phase state of control DPMZM uplink optical signal and downlink optical signal.

The little 20dB of power of the up sub-modulator radiofrequency signal of power ratio input of the descending sub-modulator radiofrequency signal of described input.

The direct current biasing point of described up sub-modulator is set to 148 °, and the direct current biasing point of descending sub-modulator is set to 30 °, and the direct current biasing point of phase-modulator is arranged on minimum transfer point.

The present invention's advantage is compared with prior art:

(1) in DPMZM microwave photon link, the present invention gives up RF signal power in existing method and is averagely allocated to the method for two sub-modulators, adopt asymmetric power division in conjunction with the method for corresponding modulator Bias point control, maximum suppression IMD3 component, compared with traditional microwave photon link, the present invention can effectively improve the microwave photon link linearity;

(2) compared with existing microwave photon link linearity optimization method, the present invention is by controlling RF signal power distribution ratio and the realization of two-way direct current biasing point, only have three variable elements, do not need strictly to control DPMZM inside light intensity and signal phase, stability is higher;

(3) the present invention completes and suppresses IMD3 before photodetection, can realize multichannel wavelength-division/time division multiplexing, in multidiameter delay structure, be easy to integrated approach, decrease system unit quantity, improve the reusability of system in Optical Fiber Transmission;

(4) technological level of the present invention to opto-electronic device does not have rigors, and rely on ripe goods shelf products to realize, implementation complexity is lower, has versatility and replicability.

Accompanying drawing explanation

Fig. 1 is the present invention's asymmetric power division DPMZM microwave photon link schematic diagram;

Fig. 2 is DPMZM cut-away view of the present invention;

Fig. 3 is spectrogram before and after DPMZM microwave photon link IMD3 suppresses, wherein, a () distributes spectrogram before and after DPMZM microwave photon link IMD3 suppression for adopting symmetric power, (b) suppresses front and back spectrogram for adopting asymmetric power division DPMZM microwave photon link IMD3 in the present invention;

Fig. 4 is that verification system of the present invention obtains SFDR performance curve.

Embodiment

In FIG, a kind of high linearity microwave photon link based on DPMZM provided by the invention realizes system, comprising: laser, signal source, DPMZM, electric shunt, electrical attenuator, DC power supply and photodetector;

Described DPMZM comprises up sub-modulator, descending sub-modulator and phase-modulator;

The radiofrequency signal that described signal source produces is divided into two-way through electric power splitter, and wherein a road is directly connected with the rf inputs mouth of up sub-modulator, and another road carries out being connected with the rf inputs mouth of descending sub-modulator after power attenuation through electrical attenuator;

Described laser is connected with the light input end mouth of DPMZM, for DPMZM exports a road light carrier, and the bias point of described DC power control DPMZM and the phase state of DPMZM light signal; Described DC power supply provides three road DC bias signal for DPMZM, wherein two-way DC bias signal controls the bias point of up sub-modulator and descending sub-modulator respectively, 3rd road DC bias signal drives the phase-modulator in DPMZM, the phase state of control DPMZM uplink optical signal and downlink optical signal;

The light signal that described DPMZM exports is connected to photodetector through Optical Fiber Transmission and carries out direct detection, and completes beat frequency in photodetector, thus realizes the suppression to third order intermodulation interference.

In fig. 2, DPMZM inside is made up of up sub-modulator MZM1, a descending sub-modulator MZM2 and phase-modulator PM.There are an optical signal input mouth and a light signal output end mouth; Two radio-frequency (RF) signal input end mouth (a), (b), be connected to the drive electrode of up sub-modulator and descending sub-modulator respectively, complete electrooptic modulation; Three direct current (DC) biases input port (c), (d), (e), port (c), (d) are connected to up sub-modulator and descending sub-modulator respectively, control sub-modulator bias point, port (e) is connected to PM, controls light signal phase place.

Signal source 2 output frequency is ω _rFradiofrequency signal, the two-way being divided into power not after electric power splitter 3 and electrical attenuator 4 adjust waiting, is connected to DPMZM radio-frequency (RF) signal input end mouth (a) and (b) respectively.Inputting up sub-modulator signal amplitude is V _rF, inputting descending sub-modulator signal amplitude is r*V _rF.It is 2 θ that DC power supply 6 is supplied to up sub-modulator bias voltage angle value ₁, connectivity port (c), being supplied to descending sub-modulator bias voltage angle value is 2 θ ₂, connectivity port (d).DC power supply 6 provides bias voltage to drive PM, and connectivity port (e), is arranged on minimum transfer point (180 °).

Suppress for realizing maximized IMD3, control electrical attenuator attenuation, make the radiofrequency signal of input port (b) and the RF signal power of input port (a) than being 20dB, the best direct current biasing point of the sub-modulator of up-downgoing is respectively 148 ° and 30 °.Corresponding r=0.1,2 θ ₁=148 °, 2 θ ₂=30 °.Up-downgoing sub-modulator output optical signal analytical expression can be expressed as:

$\left\{\begin{array}{c}{E}_{\mathrm{MZM}1}\left(t\right)=\frac{1}{\sqrt{2}}{E}_{\mathrm{in}}\left(t\right)[\exp ({\mathrm{\θ}}_1+m\cos \left(\mathrm{\ωt}\right))+\exp (-{\mathrm{\θ}}_1-m\cos \left(\mathrm{\ωt}\right))]\\ =\sqrt{2}{E}_{\mathrm{in}}\left(t\right)\cos ({\mathrm{\θ}}_1+m\cos \left(\mathrm{\ωt}\right))\\ E_{\mathrm{MZM}2}\left(t\right)=\frac{1}{\sqrt{2}}{E}_{\mathrm{in}}\left(t\right)[\exp ({\mathrm{\θ}}_2+r*m\cos \left(\mathrm{\ωt}\right))+\exp (-{\mathrm{\θ}}_2-r*m\cos \left(\mathrm{\ωt}\right))]\\ =\sqrt{2}{E}_{\mathrm{in}}\left(t\right)\cos ({\mathrm{\θ}}_2+r*m\cos \left(\mathrm{\ωt}\right))\end{array}\right.---\left(1\right)$

DPMZM output optical signal expression formula is the difference of two formulas above:

$\begin{array}{c}{E}_{\mathrm{OUT}}\left(t\right)=E_{\mathrm{MZM}1}\left(t\right)-E_{\mathrm{MZM}2}\left(t\right)\\ =\sqrt{2}{E}_{\mathrm{in}}\left(t\right)[\cos ({\mathrm{\θ}}_1+m\cos \left(\mathrm{\ωt}\right))-\cos ({\mathrm{\θ}}_2+r*m\cos \left(\mathrm{\ωt}\right))]\end{array}---\left(2\right)$

Carry out direct-detection through photodetector 7, if conversion efficiency is R, output photoelectric stream I (t) is:

$\begin{array}{c}I\left(t\right)={\mathrm{RE}}_{\mathrm{OUT}}\left(t\right)*\stackrel{\‾}{E_{\mathrm{OUT}}\left(t\right)}\\ ={\mathrm{RP}}_{\mathrm{in}}\left(t\right)[2+\cos (2{\mathrm{\θ}}_1+2m\cos \left(\mathrm{\ωt}\right))+\cos (2{\mathrm{\θ}}_2+2r*m\cos \left(\mathrm{\ωt}\right))\\ -4\cos ({\mathrm{\θ}}_1+m\cos \left(\mathrm{\ωt}\right))\cos ({\mathrm{\θ}}_2+r*m\cos \left(\mathrm{\ωt}\right))\end{array}---\left(3\right)$

I ₀(t)=RP _int () is the probe current of modulator when being operated in maximum transmitted point.If m (v)=mcos ω t, m (v) be dimensionless, linear function about input voltage v.For small-signal input, DPMZM microwave photon link transfer function can be expressed as:

$\begin{array}{c}f\left(m\left(v\right)\right)=\frac{I\left(t\right)}{I_0\left(t\right)}\\ =\left(\begin{array}{c}\frac{1}{4}(1+\cos {\mathrm{\θ}}_1+\cos {\mathrm{\θ}}_2-\cos {\mathrm{\θ}}_1\cos {\mathrm{\θ}}_2)+\frac{1}{2}m\left(v\right)*(\sin 2{\mathrm{\θ}}_1+r\sin 2{\mathrm{\θ}}_2-2\sin {\mathrm{\θ}}_1\cos {\mathrm{\θ}}_2-2r\cos {\mathrm{\θ}}_1\sin {\mathrm{\θ}}_2)+...\\ +\frac{1}{12}m{\left(v\right)}^3*(2\sin 2{\mathrm{\θ}}_1+2r^3\sin 2{\mathrm{\θ}}_2-(1+3r^2)\sin {\mathrm{\θ}}_1\cos {\mathrm{\θ}}_2-r(3+r^2)\cos {\mathrm{\θ}}_1\sin {\mathrm{\θ}}_2)+......\end{array}\right)\end{array}---\left(4\right)$

Wherein, m (v) item component and m (v) ³item component characterizes the IMD3 item that first-harmonic item and nonlinear effect in microwave photon link cause respectively.Make m (v) ³item component coefficient equals zero, and can third order intermodulation be suppressed completely to disturb.

By r=0.1,2 θ ₁=148 °, 2 θ ₂bring formula (4) into for=30 °, the DPMZM microwave photon link transfer function obtained can be expressed as:

In formula (5), IMD3 item m (v) ³coefficient be 0, and the coefficient of first-harmonic item m (v) is not 0, therefore present invention achieves and suppresses the maximization of IMD3.In Fig. 3, (a) distributes for adopting symmetric power, and three direct current (DC) biases are all operated in the DPMZM microwave photon link output signal spectrum figure of orthogonal points.B () is for adopting the high linearity microwave photon link output signal spectrum figure of asymmetric power division DPMZM in the present invention.After can finding out linearization process, IMD3 rejection ratio reaches more than 62dB, than improving about 40dB before linearisation.

In Fig. 4, dotted line and be respectively the SFDR curve of DPMZM microwave photon link before and after linearisation that experimental verification obtains shown in realizing.The high linearity microwave photon link of the asymmetric power division DPMZM of the present invention can be found out by microwave photon link SFDR by 105.5dBHz ^2/3be increased to 128dBHz ^4/5above.

Existing DPMZM microwave photon link system configuration adopts symmetric power to distribute, and realizes linearization process by changing the mode such as radiofrequency signal phase difference and light carrier delay between the sub-modulator of up-downgoing.Electricity phase shifter and light delay facility environment less stable, be difficult to maintain Best Point.

The present invention and existing DPMZM microwave photon link are distinguished and are in overall construction design: the present invention adopts an electric power splitter and electrical attenuator to replace multiple electric phase shifter in existing scheme and light delay equipment.Do not need through repeatedly phase shift process, effective suppression of third order intermodulation interference can be realized.

The present invention and existing DPMZM microwave photon link are distinguished and are on technology realizes: the present invention for cutting point, adopts the mode of asymmetric power division to change the modulation depth of the sub-modulator of up-downgoing with RF signal power difference.Control modulator just bias point simultaneously.Keep fundametal compoment constant, complete the suppression to third order intermodulation interference.Without the need to repeatedly changing radiofrequency signal phase place, optimum state can be maintained for a long time, effectively improving the DPMZM microwave photon link linearity.

The content that the present invention is not described in detail belongs to general knowledge as well known to those skilled in the art.

Claims (4)

1. the high linearity microwave photon link based on DPMZM realizes a system, it is characterized in that comprising: laser, signal source, DPMZM, electric shunt, electrical attenuator, DC power supply and photodetector;

Described DPMZM comprises up sub-modulator, descending sub-modulator and phase-modulator;

The radiofrequency signal that described signal source produces is divided into two-way through electric power splitter, and wherein a road is directly connected with the rf inputs mouth of up sub-modulator, and another road carries out being connected with the rf inputs mouth of descending sub-modulator after power attenuation through electrical attenuator;

Described laser is connected with the light input end mouth of DPMZM, for DPMZM exports a road light carrier, and the bias point of described DC power control DPMZM and the phase state of DPMZM light signal;

The light signal that described DPMZM exports is connected to photodetector through Optical Fiber Transmission and carries out direct detection, and completes beat frequency in photodetector, thus realizes the suppression to third order intermodulation interference.

2. a kind of high linearity microwave photon link based on DPMZM realizes system according to claim 1, it is characterized in that: the bias point of described DC power control DPMZM and the phase state of DPMZM light signal; Be specially:

Described DC power supply provides three road DC bias signal for DPMZM, wherein two-way DC bias signal controls the bias point of up sub-modulator and descending sub-modulator respectively, 3rd road DC bias signal drives the phase-modulator in DPMZM, the phase state of control DPMZM uplink optical signal and downlink optical signal.

3. a kind of high linearity microwave photon link based on DPMZM realizes system according to claim 1, it is characterized in that: the little 20dB of power of the up sub-modulator radiofrequency signal of power ratio input of the descending sub-modulator radiofrequency signal of described input.

4. a kind of high linearity microwave photon link based on asymmetric power division DPMZM realizes system according to claim 2, it is characterized in that: the direct current biasing point of described up sub-modulator is set to 148 °, the direct current biasing point of descending sub-modulator is set to 30 °, and the direct current biasing point of phase-modulator is arranged on minimum transfer point.