CN103095379A - Method for realizing high linearity microwave photon link based on dual drive dual-parallel mach-zehnder modulator (DPMZM) - Google Patents

Abstract

The invention provides a method for realizing a high linearity microwave photon link based on a dual drive dual-parallel mach-zehnder modulator (DPMZM). According to the method, by controlling phase relations of microwave signals among four electrodes of two sub-mach-zehnder modulators (MZM) of the dual drive DPMZM and offset points of the two MZMs of the dual drive DPMZM, after directly detecting an receiving end of the link by a photodiode (PD), complete restraint of third-order interception is achieved, and thus the high linearity microwave photon link is realized.

Description

A kind of method that realizes high linearity microwave photon link based on two driving DPMZM

Technical field

The present invention relates to realize in a kind of microwave photon link the method for high linearity, more particularly, a kind of high linearity method that relates to microwave photon link based on the two parallel MZ Mach-Zehnders (Dual-Parallel Mach-Zehnder Modulator, DPMZM) of two drivings.

Background technology

In recent years, Microwave photonics is development ambit rapidly, and it is large that the microwave photon link has transmission capacity, and anti-electromagnetic interference does not have traditional advantages such as electricity bottleneck.Microwave photonics is being communicated by letter, sensing, and there is very important application in the fields such as national defence.Wherein, the microwave photon link of great dynamic range is the research direction that in this field, remarks are paid close attention to.

The dynamic range of microwave photon link refers to minimum signal that link can transmit and the power bracket between peak signal.It is subject to the restriction of two key factors: the one, and the noise of system, the 2nd, system non-linear.For the microwave photon link of realizing great dynamic range just needs lower link noise and the system linear degree of Geng Gao.

Because the external modulation link is compared the internal modulation link and do not warbled, the direct-detection mode is compared more simple economy of relevant detection mode, therefore, and the main external modulation direct-detection link that adopts in present microwave photon link.In external modulation direct-detection link, the photoelectric external modulator of bearing the electric light conversion is the Primary Component of system link, and link transmission function and link-quality are played crucial influence.In multiple electrooptic modulator, MZ Mach-Zehnder (MZM) is due to its high speed, High Extinction Ratio, low insertion loss and to make the advantage such as simple be to use maximum electrooptic modulators in microwave current photon link.

The non-linear meeting of the transfer function of electrooptic modulator brings distortion to link, affects the system linear degree.Wherein third order intermodulation (Third-Order Intermodulation, IMD3) is to affect the most important nonlinear terms of system linear degree.Therefore, the high linearity that realize link just means and will do better inhibition to IMD3.

Research since the nineties in last century is found, single MZM has the available bias point that suppresses the second harmonic, but therefore the bias point that there is no utilizable inhibition third order intermodulation will find the modulation scheme that suppresses third order intermodulation, needs to adopt cascade or MZ modulator in parallel.In scheme in parallel, along with the integrated two parallel MZ Mach-Zehnder (DPMZM) that commercialization occurred, research becomes in recent years study hotspot based on the linearisation of the microwave photon link of DPMZM.

Research both domestic and external has proposed the linearized solution of multiple inhibition IMD3 for the high linear microwave photon link based on DPMZM.Comprising DPMZM is adopted different power-division ratios, utilize dual-polarization in conjunction with the DPMZM IMD3 that disinthibites, and the single different bias point combinations that drive DPMZM of research, by to its upper arm MZM modulated microwave signal, underarm MZM only transmits carrier wave, then regulates the phase difference of the sub-MZM of the first two to reach the inhibition to IMD3 by the 3rd MZM.But above these schemes all could not realize the inhibition fully to IMD3 in theory.

Summary of the invention

Present in the research of high linear microwave photon link in order to overcome, also there is no can suppress fully theoretically the linearized solution of IMD3.The present invention proposes a kind ofly in the microwave photon link, suppress based on two driving DPMZM the method that IMD3 realizes high linearity fully.

The technical solution adopted in the present invention is, at transmitting terminal, the rf signal of different frequency carried out being loaded into four electrodes of the two DPMZM of driving of electrooptic modulator after phase control, then two sub-MZM up and down of DPMZM are carried out identical quadrature biasing.DPMZM is output as and has loaded the light signal after the rf signal, at receiving terminal, carries out direct-detection with photodiode (Photodiode, PD), the signal of telecommunication that after the electric light conversion, reduction loads before obtaining.

The invention has the beneficial effects as follows, in the microwave photon link, realized the inhibition fully to third order intermodulation.And what adopt is the integrated two DPMZM of driving modulators of commercialization, and direct-detection mode simple in structure.

Description of drawings

The present invention is further described below in conjunction with drawings and Examples.

Fig. 1 illustrates entire block diagram of the present invention.

Fig. 2 is shown specifically electrical signal phase control section of the present invention and the two DPMZM of driving biasing control section.

Fig. 3 illustrates the two DPMZM of driving modulator input and output spectrogram of the present invention.

Fig. 4 illustrates the input and output electricity spectrogram of the whole link of the present invention.

Embodiment

In Fig. 1, microwave photon chain route transmitting terminal A and receiving terminal B form.Transmitting terminal A part, be loaded on four drive electrodes of electro-optical modulation device DPMZM (3) after the rf signal that microwave source (1) sends different frequency is sent into the phase control module (2) that is comprised of electric phase shifter, DPMZM (3) is comprised of its up sub-MZM (4) and descending sub-MZM (5).Receiving terminal B part is carried out direct-detection with photodiode PD (6).

In Fig. 2, microwave source (1) sends two frequencies and is respectively w ₁And w ₂Rf signal

With

Be loaded into four drive electrode a of two sub-MZM (4) (5) of DPMZM (3) after process phase control (2), b, c is on d.For up sub-MZM (4), radiofrequency signal With

First pass through electric phase shifter PS before being loaded into electrode a ₂Carry out the phase shift of 90 degree, be loaded into electrode b and do not carry out phase shift.For descending sub-MZM (5), radiofrequency signal

With the electric phase shifter PS of process ₁The 180 dephased radiofrequency signals of degree have been carried out

First pass through electric phase shifter PS before being loaded into electrode c ₃Carry out the phase shift of-90 degree, be loaded into electrode d and do not carry out phase shift.

Through after top phase control (2), be loaded into four electrode a of DPMZM (3), b, c, the driving voltage on d can be expressed as respectively:

$V_{11}\left(t\right)=V_m[\cos (w_{1}t+\frac{\mathrm{\π}}{2})+\cos (w_{2}t+\frac{\mathrm{\π}}{2})]---\left(1\right)$

V ₁₂(t)＝V _m[cos(w ₁t)+cos(w ₂t)] (2)

$V_{21}\left(t\right)=V_m[\cos (w_{1}t-\frac{\mathrm{\π}}{2})+\cos (w_{2}t+\frac{\mathrm{\π}}{2})]---\left(3\right)$

V ₂₂(t)＝V _m[cos(w ₁t)+cos(w ₂t+π)] (4)

Two the sub-MZM (4) (5) that suppose DPMZM (3) have identical half-wave voltage V _π, with two sub-MZM (4) (5) DC driven e, f all is biased in V _π/ 2 quadrature bias points carry out single-side band modulation.

The light signal of up sub-MZM (4) output of DPMZM (3) can be expressed as:

$E_{\mathrm{out}1}\left(t\right)=E_{\mathrm{in}}\left(t\right)\underset{k=-\∞}{\overset{\∞}{\mathrm{\Σ}}}\underset{l=-\∞}{\overset{\∞}{\mathrm{\Σ}}}{J}_k\left(m\right)J_l\left(m\right)e^{i(k{w}_{1}t+l{w}_{2}t)}[{(-1)}^{k+l}{e}^{j\frac{\mathrm{\π}}{4}}+{\left(i\right)}^{k+l}{e}^{-j\frac{\mathrm{\π}}{4}}]---\left(5\right)$

In formula (5), m=π V _m/ V _π, E _in(t) be to send by laser (0) light field of sending into DPMZM (3).The light signal of descending sub-MZM (5) output of DPMZM (3) can be expressed as:

$E_{\mathrm{out}2}\left(t\right)=E_{\mathrm{in}}\left(t\right)\underset{k=-\∞}{\overset{\∞}{\mathrm{\Σ}}}\underset{l=-8}{\overset{\∞}{\mathrm{\Σ}}}{(-1)}^l{J}_k\left(m\right)J_l\left(m\right)e^{l(k{w}_{1}t+{\mathrm{lw}}_{2}t)}[e^{j\frac{\mathrm{\π}}{4}}+{\left(i\right)}^{k+l}{e}^{-j\frac{\mathrm{\π}}{4}}]---\left(6\right)$

The output optical signal of DPMZM (3) is the output sum of two sub-MZM (4) (5).

In Fig. 3, be (h) w for laser (0) output center frequency _cThe spectrum schematic diagram, (i) be the spectrum schematic diagram of up sub-MZM (4) output optical signal of DPMZM (3), two frequencies that loaded through output after phase control (2) are w ₁And w ₂Radiofrequency signal, be the upper sideband modulation.(j) be the spectrum schematic diagram of descending sub-MZM (5) output optical signal of DPMZM (3), two frequencies that loaded through output after phase control (2) are w ₁And w ₂Radiofrequency signal, be the lower sideband modulation.(k) be the spectrum schematic diagram of DPMZM (3) output optical signal, be the output spectrum sum of sub-MZM (4) and sub-MZM (5).

In Fig. 4, the signal of telecommunication that the light signal of DPMZM (3) output obtains after detecting through PD (6) can be expressed as under small-signal model:

$i\left(t\right)=R*{\left|E_{\mathrm{in}}\left(t\right)\right|}^2\left(\begin{array}{c}8+8m(\cos \left(w_{1}t\right)+\sin \left(w_{2}t\right))+{2m}^2(-2+\cos \left({2w}_{1}t\right)-\cos \left({2w}_{2}t\right))\\ -\frac{2}{3}{m}^3(9\cos \left(w_{1}t\right)-\cos \left({3w}_{1}t\right)+9\cos \left({2w}_{2}t\right)+\sin \left(3w_{2}t\right))\end{array}\right)+O{\left(m\right)}^4---\left(7\right)$

In formula (7), R is the responsiveness of PD (6).The formula medium frequency is w ₁And w ₂The radiofrequency signal item exported for link of item, and frequency is 2w ₁-w ₂And 2w ₂-w ₁The third order intermodulation item be zero, therefore realized the inhibition fully to third order intermodulation.In Fig. 4, (p) being the electricity spectrum schematic diagram of microwave source (1) output, is (q) the electricity spectrum schematic diagram after PD (6) detects, and (q) medium frequency is 2w ₁-w ₂And 2w ₂-w ₁The third order intermodulation item do not exist.

Claims (5)

1. high linearity method based on the microwave photon link of the two parallel MZ Mach-Zehnders (Dual-Parallel Mach-Zehnder Modulator, DPMZM) of two drivings, the method comprises following 3 points:

(1) at transmitting terminal, signal of telecommunication part, the electrical signal phase relation between four electrodes of two sub-MZM of the two driving of control inputs DPMZM;

(2) at transmitting terminal, photoelectricity modulating part, the bias point of two sub-MZM of control DPMZM;

(3) at receiving terminal, adopt direct-detection, after photodiode (Photodiode, PD) opto-electronic conversion, realize the inhibition fully to third order intermodulation;

Realize high linearizing microwave photon link according to above 3.

2. the method for claim 1, wherein first signal of telecommunication part at the link transmitting terminal, frequency is w ₁And w ₂Radiofrequency signal

With

Be specially through the phase difference relation that is loaded into after phase control on pair four electrodes of two sub-MZM that drive DPMZM:

(1) for up sub-MZM, radiofrequency signal

With

Carry out 90 phase shifts of spending before being loaded into the upper arm electrode, be loaded into the underarm electrode and do not carry out phase shift;

(2) for descending sub-MZM, radiofrequency signal

With passed through 180 degree phase shifts

Carry out-90 phase shifts of spending before being loaded into the upper arm electrode, be loaded into the underarm electrode and do not carry out phase shift.

3. the method for claim 1, wherein second point is in the photoelectricity modulating part of link transmitting terminal, and the bias point of two sub-MZM of DPMZM all carries out single-side band modulation at identical quadrature bias point, and result is respectively upper sideband modulation and lower sideband modulation.

4. method as claimed in claim 3, the analytical expression of DPMZM upper arm MZM output optical signal can be expressed as:

$E_{\mathrm{out}1}\left(t\right)=E_{\mathrm{in}}\left(t\right)\underset{k=-\∞}{\overset{\∞}{\mathrm{\Σ}}}\underset{l=-\∞}{\overset{\∞}{\mathrm{\Σ}}}{J}_k\left(m\right)J_l\left(m\right)e^{i(k{w}_{1}t+l{w}_{2}t)}[{(-1)}^{k+l}{e}^{j\frac{\mathrm{\π}}{4}}+{\left(i\right)}^{k+l}{e}^{-j\frac{\mathrm{\π}}{4}}]---\left(\text{1}\right)$

The analytical expression of underarm MZM output optical signal can be expressed as:

$E_{\mathrm{out}2}\left(t\right)=E_{\mathrm{in}}\left(t\right)\underset{k=-\∞}{\overset{\∞}{\mathrm{\Σ}}}\underset{l=-8}{\overset{\∞}{\mathrm{\Σ}}}{(-1)}^l{J}_k\left(m\right)J_l\left(m\right)e^{l(k{w}_{1}t+{\mathrm{lw}}_{2}t)}[e^{j\frac{\mathrm{\π}}{4}}+{\left(i\right)}^{k+l}{e}^{-j\frac{\mathrm{\π}}{4}}]---\left(2\right)$

The light signal analytical expression of DPMZM output is top two formula sums.

5. the method for claim 1, thirdly at receiving terminal, after adopting the PD direct-detection, the signal of telecommunication expression formula that obtains can be expressed as:

$i\left(t\right)=R*{\left|E_{\mathrm{in}}\left(t\right)\right|}^2\left(\begin{array}{c}8+8m(\cos \left(w_{1}t\right)+\sin \left(w_{2}t\right))+{2m}^2(-2+\cos \left({2w}_{1}t\right)-\cos \left({2w}_{2}t\right))\\ -\frac{2}{3}{m}^3(9\cos \left(w_{1}t\right)-\cos \left({3w}_{1}t\right)+9\cos \left({2w}_{2}t\right)+\sin \left(3w_{2}t\right))\end{array}\right)+O{\left(m\right)}^4---\left(3\right)$

Wherein, the third order intermodulation item is suppressed fully.

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