CN102761374B - Radio frequency photon link system - Google Patents

Abstract

The invention relates to the field of a radio frequency photo-electronic technology and discloses a radio frequency photon link system. The radio frequency photon link system comprises a pre-microwave circuit and a radio frequency photon link, wherein the radio frequency photon link comprises a laser device, a polarization controller, a photo-electronic modulator and a detector. The pre-microwave circuit designed on the basis of a JFET (Junction Field-Effect Transistor) integrates a pre-distortion function and a pre-discharge function, so that the gain of the radio frequency photon link can be greatly improved, and the noise coefficient is reduced; and the three-step non-linear distortion component of the whole radio frequency photon link system can be restrained by introducing pre-distortion.

Description

Radio frequency photon chain-circuit system

Technical field

The present invention relates to radio frequency photoelectron technology field, particularly a kind of radio frequency photon chain-circuit system.

Background technology

Radio frequency optoelectronics is the emerging cross discipline that microwave and photon technology combine, and has large bandwidth, a many advantages such as volume is little, lightweight, loss is little, anti-electromagnetic interference, low dispersion, is paid close attention to widely and studies; Radio frequency photon link is as the core of this technology, can receive microwave signal and microwave signal output is provided, in light territory, radiofrequency signal is directly transmitted to control and process, be widely applied to the fields such as electronic warfare, radar, remote sensing, sensing network, radio communication, cable TV.

The performance parameter of radio frequency photon link mainly comprises gain, noise factor and dynamic range.Traditional radio frequency photon link utilization pre-low-noise amplifier, the gain that can effectively improve chain-circuit system, improves the output signal-to-noise ratio of signal, but also will worsen the dynamic range of system simultaneously; And adopt traditional predistortion circuit, although can effectively suppress the third-order non-linear crosstalk of system, the insertion loss of circuit also will cause the gain of whole system to reduce simultaneously, worsens the noise factor of system.So it is most important how to improve the research of property indices of chain-circuit system simultaneously, this is the prerequisite that can radio frequency photon link large-scale application.

Therefore, be necessary to design a kind of Simple And Practical, have the preposition microwave circuit of putting in advance with predistortion function concurrently, can improve gain, noise factor and the dynamic range of chain-circuit system simultaneously.

Summary of the invention

(1) technical problem that will solve

The technical problem to be solved in the present invention is: how to design a kind of preposition microwave circuit, the gain of conventional radio frequency photon chain-circuit system is improved, noise factor reduces, and third-order non-linear crosstalk is inhibited.

(2) technical scheme

In order to solve the problems of the technologies described above, the invention provides a kind of radio frequency photon chain-circuit system, comprise preposition microwave circuit and radio frequency photon link, described radio frequency photon link comprises laser, Polarization Controller, electrooptic modulator and detector;

Described laser is for generation of light carrier;

Described Polarization Controller, is connected between described laser and electrooptic modulator, for the polarization state of the light carrier of laser output is adjusted into consistent with the main shaft of electrooptic modulator;

Described preposition microwave circuit, is connected with described electrooptic modulator, for the input radio frequency signal receiving is amplified, increases the modulation depth of described electrooptic modulator, and suppresses the third-order non-linear crosstalk of described radio frequency photon chain-circuit system;

Described electrooptic modulator, for being modulated to described light carrier by described input radio frequency signal;

Described detector, is connected with described electrooptic modulator, for converting the light signal obtaining after described electrooptic modulator modulation to the signal of telecommunication, to recover described input radio frequency signal.

Preferably, described preposition microwave circuit comprises JFET field effect transistor, and the transfer characteristic curve of described JFET field effect transistor meets square law relationship.

Preferably, described preposition microwave circuit comprises: JFET field effect transistor, two inductance L 1, L2, two capacitor C 1, C2, two resistance R _s, R _l, wherein, the grid of described JFET field effect transistor connects one end of capacitor C 1 and one end of inductance L 1, and drain electrode connects one end of capacitor C 2 and one end of inductance L 2, source ground; The other end of described capacitor C 1 connects source resistance R _sone end, resistance R _sother end connecting signal source V _inone end, described signal source V _inother end ground connection; The other end of capacitor C 2 connects load resistance R _lone end, load resistance R _lother end ground connection.

Preferably, the other end of described inductance L 1 connects gate bias voltage, and the other end of described inductance L 2 connects drain electrode direct voltage.

(3) beneficial effect

Technique scheme tool has the following advantages: the preposition microwave circuit that the present invention is based on the design of JFET field effect transistor integrates predistortion and pre-playing function, can improve greatly the gain of chain-circuit system, noise-reduction coefficient, and by introducing predistortion, can suppress the third-order non-linear distortion component of whole system.

Accompanying drawing explanation

Fig. 1 is the high-performance radio-frequency photon chain-circuit system frame diagram based on preposition microwave circuit that the present invention adopts;

Fig. 2 a is the structure chart of the preposition microwave circuit that adopts of the present invention, the I-V working curve that Fig. 2 b is JFET and transfer characteristic curve figure;

Fig. 3 is system configuration schematic diagram of the present invention.

Wherein, 101: radio frequency photon chain-circuit system; 102: preposition microwave circuit; 103: radio frequency photon link; 1: laser; 2: Mach-Zehnder intensity modulator; 3: Polarization Controller; 4: detector.

Embodiment

Below in conjunction with drawings and Examples, the specific embodiment of the present invention is described in further detail.Following examples are used for illustrating the present invention, but are not used for limiting the scope of the invention.

The embodiment of the present invention adopts the simulated photons link based on Mach-Zehnder intensity modulator to describe as example, but do not limit the scope of the invention, no matter lithium niobate modulator or electroabsorption modulator, no matter be directly in harmonious proportion and transfer to other localities, as long as exist the modulated process of third-order non-linear distortion all can contain.

System 101 structures of the embodiment of the present invention as shown in Figure 1, comprise preposition microwave circuit 102 and 103 two modules of radio frequency photon link, and wherein the output signal of preposition microwave circuit is using the input signal as photon link.Described radio frequency photon link 103 comprises laser 1, Polarization Controller 3, Mach-Zehnder intensity modulator 2 and detector 4; Described laser 1 is for generation of light carrier; Described Polarization Controller 3, is connected between described laser 1 and Mach-Zehnder intensity modulator 2, for the polarization state of the light carrier of laser 1 output is adjusted into consistent with the main shaft of Mach-Zehnder intensity modulator 2; Described preposition microwave circuit 102, be connected with described Mach-Zehnder intensity modulator 2, for the input radio frequency signal receiving is amplified, increase the modulation depth of described Mach-Zehnder intensity modulator 2, and suppress the third-order non-linear crosstalk of photon chain-circuit system; Described Mach-Zehnder intensity modulator 2, for being modulated to described light carrier by described input radio frequency signal; Described detector 4, is connected with described Mach-Zehnder intensity modulator 2, for converting the light signal obtaining after described Mach-Zehnder intensity modulator 2 modulation to the signal of telecommunication, to recover described input radio frequency signal.

The structure chart of preposition microwave circuit as shown in Figure 2 a, comprising: JFET field effect transistor, two inductance L 1, L2, two capacitor C 1, C2, two resistance R _s, R _l, wherein, the grid G of described JFET field effect transistor connects one end of capacitor C 1 and one end of inductance L 1, and drain D connects one end of capacitor C 2 and one end of inductance L 2, source S ground connection; The other end of described capacitor C 1 connects source resistance R _sone end, source resistance R _sother end connecting signal source V _inone end, the other end ground connection of described signal source; The other end of capacitor C 2 connects load resistance R _lone end, load resistance R _lother end ground connection.The other end of described inductance L 1 connects gate bias voltage V _bias, the other end of described inductance L 2 connects drain electrode direct voltage V _dc.The nucleus module of this preposition microwave circuit is JFET field effect transistor, comprises grid, drain electrode and source electrode, and as shown in Figure 2 b, this curve will be done detailed explanation in the back for the I-V working curve of JFET field effect transistor and transmission characteristic curve.By control grid bias voltage V _biasand input signal source V _insize, can be so that JFET field effect transistor works in Class A mode of operation (Class A), load resistance R _lsize according to the drain electrode direct voltage V of JFET field effect transistor characteristic and drain electrode _dcdetermine.In addition, in preposition microwave circuit, two capacitor C 1, C2 are for isolated DC signal, and two inductance L 1, L2 are used for isolating AC signal.

The similar microwave amplifier of groundwork principle of this preposition microwave circuit has utilized the non-linear transfer characteristic of JFET field effect transistor simultaneously, makes this preposition microwave amplifiercation circuit have predistortion function.

Preposition microwave circuit can improve gain, noise factor and the third-order non-linear distortion performance of conventional radio frequency photon chain-circuit system simultaneously, will launch respectively explanation from this three aspects: below.

One, gain

As shown in Figure 1, the gain that the preposition microwave circuit of the first order provides is G ₁, the gain of the radio frequency photon link of the second level is G ₂, the gain G of the radio frequency photon chain-circuit system of the two composition meets and is related to G=G ₁g ₂, because the gain of JFET field effect transistor is higher, so this preposition microwave circuit can greatly improve the gain index of whole radio frequency photon chain-circuit system.

Two, noise factor

Because the noise factor of the preposition microwave circuit of the first order is NF ₁, the noise factor of the radio frequency photon link of the second level is NF ₂so the noise factor NF of whole radio frequency photon chain-circuit system meets:

$\mathrm{NF}={\mathrm{NF}}_1+\frac{{\mathrm{NF}}_2}{G_1}---\left(1\right)$

Because the noise factor of JFET field effect transistor is very low, and gain is higher, so the noise factor of whole radio frequency photon chain-circuit system is by the preposition microwave circuit a little more than the first order, and be far smaller than the radio frequency photon link of the second level, so this preposition microwave circuit can greatly improve the noise factor of traditional analog photon link.

Three, third-order non-linear crosstalk

This preposition microwave circuit, except pre-playing function, has also utilized the non-linear transmission characteristic of JFET field effect transistor, has predistortion function.

The predistortion function of this preposition microwave circuit is mainly realized by the non-linear transmission characteristic of JFET field effect transistor, can offset non-linear in electrooptic modulation process, thereby reaches the effect that suppresses third-order non-linear intermodulation.

The transfer curve relation of JFET field effect transistor as shown in Figure 2 b, can be expressed as:

$\begin{array}{cc}{i}_D=I_{\mathrm{DSS}}{(1-\frac{v_{\mathrm{GS}}}{V_P})}^2& (V_P\≤v_{\mathrm{GS}}\≤0)\end{array}---\left(2\right)$

I wherein _dcurrent drain current for JFET field effect transistor; I _dSSfor saturated drain current; v _gSfor gate source voltage, it is also the applied signal voltage of whole system; V _pfor grid source pinch-off voltage.

If JFET field effect transistor works in Class A mode of operation (Class A) pattern, have the transfer function of preposition microwave circuit to meet:

$v_o=[I_{\mathrm{DC}}-I_{\mathrm{DSS}}{(1-\frac{v_{\mathrm{GS}}}{V_P})}^2]R_L$

$=I_{\mathrm{DC}}{R}_L-I_{\mathrm{DSS}}{R}_L+\frac{2I_{\mathrm{DSS}}{R}_L{v}_{\mathrm{GS}}}{V_P}-\frac{I_{\mathrm{DSS}}{R}_L{v}_{\mathrm{GS}}^2}{V_P}---\left(3\right)$

V wherein _ofor the output voltage of preposition microwave circuit, I _dCfor the drain electrode direct voltage of JFET field effect transistor, R _lfor load resistance.By output voltage v _oafter straight, obtain v _m, and:

$v_m=\frac{2I_{\mathrm{DSS}}{R}_L{v}_{\mathrm{GS}}}{V_P}-\frac{I_{\mathrm{DSS}}{R}_L{v}_{\mathrm{GS}}^2}{V_P}=b_1{v}_{\mathrm{GS}}+b_2{v}_{\mathrm{GS}}^2---\left(4\right)$

Wherein $b_1=\frac{2I_{\mathrm{DSS}}{R}_L}{V_P},$ $b_2=\frac{I_{\mathrm{DSS}}{R}_L}{V_P}.$

Radio frequency photon chain-circuit system of the present invention comprises laser, electrooptic modulator and detector, suppose that the electrooptic modulator that the present invention adopts is Mach-Zehnder intensity modulator, detector is direct detection, chain-circuit system structure as shown in Figure 3, electrooptic modulator in Fig. 3 has rf input port and direct current biasing end, radio frequency input is signal input port, and direct current biasing is used for loading direct voltage.The transfer function of radio frequency photon link can be expressed as:

$I_{\mathrm{out}}=\mathrm{\γ}{P}_{\mathrm{in}}[1+\cos \left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}(V_M+v_m)\right)]$

$=\mathrm{\γ}{P}_{\mathrm{in}}[1-\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\sin \left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}{V}_M\right)v_m-\frac{{\mathrm{\π}}^2}{2V_{\mathrm{\π}}^2}\cos \left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}{V}_M\right)v_m^2+\frac{{\mathrm{\π}}^3}{6V_{\mathrm{\π}}^3}\sin \left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}{V}_M\right)v_m^3]---\left(5\right)$

$=a_0+a_1{v}_m+a_2{v}_m^2+a_3{v}_m^3$

Wherein, I _outfor link output current, the conversion efficiency that γ is detector, P _infor laser output power, V _πfor the half-wave voltage of electrooptic modulator, V _mfor the DC offset voltage of electrooptic modulator, v _mrF signal voltage for input.In addition, a ₀=γ P _in, $a_1=\frac{\mathrm{\π\γ}{P}_{\mathrm{in}}}{V_{\mathrm{\π}}}\sin \left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}{V}_M\right),$ $a_2=-\frac{{\mathrm{\π}}^2\mathrm{\γ}{P}_{\mathrm{in}}}{2V_{\mathrm{\π}}^2}\cos \left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}{V}_M\right),$ $a_3=-\frac{{\mathrm{\π}}^3\mathrm{\γ}{P}_{\mathrm{in}}}{6V_{\mathrm{\π}}^3}\cos \left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}{V}_M\right).$ So total link transmission function meets:

$I_{\mathrm{out}}=a_0+a_1{v}_m+a_2{v}_m^2+a_3{v}_m^3$

$=a_0+a_1(b_1{v}_{\mathrm{GS}}+b_2{v}_{\mathrm{GS}}^2)+a_2{(b_1{v}_{\mathrm{GS}}+b_2{v}_{\mathrm{GS}}^2)}^2+a_3{(b_1{v}_{\mathrm{GS}}+b_2{v}_{\mathrm{GS}}^2)}^3$ （6）

$=a_0+a_1{b}_1{v}_{\mathrm{GS}}+(a_1{b}_2+a_2{b}_1^2)v_{\mathrm{GS}}^2+({2a}_2{b}_1{b}_2+a_3{b}_1)v_{\mathrm{GS}}^3$

$+(a_2{b}_2^2+3a_1{b}_1^2{b}_2)v_{\mathrm{GS}}^4+3a_3{b}_2^2{b}_1{v}_{\mathrm{GS}}^5+a_3{b}_2^3{v}_{\mathrm{GS}}^6$

From formula (6), can find out, as long as meet relational expression can eliminate third order distortion item,

$\tan \left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}{V}_M\right)=-\frac{3V_{\mathrm{\π}}{I}_{\mathrm{DSS}}{R}_L}{\mathrm{\π}{V}_P}$

By above-mentioned analysis, can reach a conclusion, preposition microwave circuit proposed by the invention can improve gain, noise factor and the third-order non-linear crosstalk of radio frequency photon chain-circuit system effectively simultaneously.

As can be seen from the above embodiments, the preposition microwave circuit that the present invention is based on the design of JFET field effect transistor integrates predistortion and pre-playing function, can improve greatly the gain of chain-circuit system, noise-reduction coefficient, and by introducing predistortion, can suppress the third-order non-linear distortion component of whole system.

The above is only the preferred embodiment of the present invention; it should be pointed out that for those skilled in the art, do not departing under the prerequisite of the technology of the present invention principle; can also make some improvement and replacement, these improvement and replacement also should be considered as protection scope of the present invention.

Claims (1)

1. a radio frequency photon chain-circuit system, is characterized in that, comprises preposition microwave circuit and radio frequency photon link, and described radio frequency photon link comprises laser, Polarization Controller, electrooptic modulator and detector;

Described laser is for generation of light carrier;

Described Polarization Controller, is connected between described laser and electrooptic modulator, for the polarization state of the light carrier of laser output is adjusted into consistent with the main shaft of electrooptic modulator;

Described preposition microwave circuit, is connected with described electrooptic modulator, for the input radio frequency signal receiving is amplified, increases the modulation depth of described electrooptic modulator, and suppresses the third-order non-linear crosstalk of described radio frequency photon chain-circuit system;

Described electrooptic modulator, for being modulated to described light carrier by described input radio frequency signal;

Described detector, is connected with described electrooptic modulator, for converting the light signal obtaining after described electrooptic modulator modulation to the signal of telecommunication, to recover described input radio frequency signal;

Described preposition microwave circuit comprises JFET field effect transistor, and the transfer characteristic curve of described JFET field effect transistor meets square law relationship;

Described preposition microwave circuit also comprises: two inductance L 1, L2, two capacitor C 1, C2, two resistance R _s, R _l, wherein, the grid of described JFET field effect transistor connects one end of capacitor C 1 and one end of inductance L 1, and drain electrode connects one end of capacitor C 2 and one end of inductance L 2, source ground; The other end of described capacitor C 1 connects source resistance R _sone end, source resistance R _sother end connecting signal source V _inone end, the other end ground connection of described signal source; The other end of capacitor C 2 connects load resistance R _lone end, load resistance R _lother end ground connection;

The other end of described inductance L 1 connects gate bias voltage V _bias, the other end of described inductance L 2 connects drain electrode direct voltage V _dc.