CN104065414A - Dynamic range expanding method based on modulator offset point information acquisition - Google Patents

Abstract

The invention relates to a dynamic range expanding method based on modulator offset point information acquisition. The method is characterized by comprising the following steps: firstly, establishing a numerical model, and providing a digital compensation algorithm; secondly, revealing the relation between a compensation coefficient and a modulator offset point; secondly, detecting the modulator output power to obtain the specific angle of the offset point; lastly, counteracting a distortion compensation coefficient with non-linear distortion of a modulator to obtain linear output. By adopting the method, nonlinear distortion of the modulator can be counteracted without accurately acquiring the specific propagation model of a system or accurately estimating system characteristic parameters. The difficulty in accurate parameter estimation in a digital domain in the prior art is avoided. The method can be widely applied to various optical links.

Description

A kind of dynamic range method for improving based on modulator bias point acquisition of information

Technical field

The present invention relates to a kind of dynamic range method for improving based on modulator bias point acquisition of information, relate in particular to a kind of method that Digital Signal Processing (DSP) linearization technique based on working point acquisition of information promotes dynamic range.

Background technology

Spurious Free Dynamic Range (SFDR) is one of most important performance index of analog optical link, has comprehensively embodied a system and has overcome noise effect, processes the ability of small-signal and overcome the ability that nonlinear distortion affects, processes and receive strong signal.Externally, under the effect of intensity modulator unintentional nonlinearity characteristic, in output signal, there is distortion and disturb, comprise harmonic distortion and crosstalk etc., cause the Spurious Free Dynamic Range of analog optical link limited.

In prior art, a kind of crosstalk based on backward Digital Signal Processing suppresses technology, as shown in Figure 1, the rear distortion compensation technology of DSP is after accurately knowing the Mathematical Modeling of ssystem transfer function, by the corresponding inverse function of DSP technical construction, thereby the crosstalk component amplitude that the crosstalk component that assurance is produced by modulator inherent nonlinearity generates with digital signal processor equates and single spin-echo, thereby the two is cancelled out each other, reach the object that nonlinear distortion suppresses.

But this scheme need to accurately be known the object that TRANSFER MODEL that system is concrete is estimated to reach distortion compensation coefficient; Need in addition accurately to estimate as detection of optical power, responsiveness etc. system features parameter, otherwise can cause the malfunctioning of distortion compensation.

In sum, the problem that the technology of existing dynamic range method for improving exists is TRANSFER MODEL and the accurate estimating system characteristic parameter that need to accurately know that system is concrete, has brought the difficulty of carrying out accurate parameter Estimation at numeric field.

Summary of the invention

(1) technical problem that will solve

The technical problem to be solved in the present invention is just to provide a kind of dynamic range method for improving, do not need accurately to know TRANSFER MODEL that system is concrete and accurately estimating system characteristic parameter just can offset the nonlinear distortion of modulator-demodulator.

(2) technical scheme

In order to solve the problems of the technologies described above, the invention provides a kind of dynamic range method for improving based on modulator bias point acquisition of information, it is characterized in that, comprise the following steps:

Step 1: set up Mathematical Modeling, propose digital compensation algorithm;

Step 2: disclose the relation between penalty coefficient and modulator bias point;

Step 3: detect by modulator Output optical power, know the concrete angle of bias point;

Step 4: the nonlinear distortion of distortion compensation function and modulator offsets, obtains linearisation output.

Preferably, described modulator is arranged on quadrature bias point bias point in addition.

Preferably, described method realizes equivalent frequency spectrum shift by light territory, and high-frequency signal is transformed in intermediate-freuqncy signal or baseband signal.

Preferably, said method comprising the steps of:

Step 1: set up Mathematical Modeling, y=a ₀+ a ₁x+a ₂x ²+ a ₃x ³;

Ignore above higher harmonic components three times, by x (t)=ρ (t) cos (ω _mt), described in substitution in Mathematical Modeling, obtain base band

Fundamental frequency $y_1\left(t\right)=[a_1+\frac{{3a}_3}{4}A{\left(t\right)}^2]\·A\left(t\right)\cos \left({\mathrm{\ω}}_{m}t\right)$

Digital compensation algorithm is proposed:

$\begin{array}{c}{y}_1^{\′}=y_0^{\mathrm{\γ}}{y}_1\≈a_0^{\mathrm{\γ}}{a}_1(1+\frac{{\mathrm{\γ}}_{a2}}{{2a}_0}{A}^2+\frac{{3a}_3}{{4a}_1}{A}^2)\·A\cos {\mathrm{\ω}}_{m}t\\ =a_0^{\mathrm{\γ}}{a}_{1}A\cos {\mathrm{\ω}}_{m}t\end{array}$

Step 2: disclose the relation between penalty coefficient and modulator bias point:

When penalty coefficient γ meets time, distortion is inhibited;

Intensity modulated link transfer function is:

Calculating the now relation table between penalty coefficient and modulator bias point is shown:

$\mathrm{\γ}=\frac{1+\sin \mathrm{\φ}}{2\sin \mathrm{\φ}};$

Step 3: detect by modulator Output optical power, know the concrete angle φ of bias point;

Step 4: according to the concrete angle φ of the bias point obtaining in step 3, calculate distortion compensation coefficient gamma by step 2, and bring γ into distortion compensation algorithm in step 1.

(3) beneficial effect

Dynamic range method for improving based on modulator bias point acquisition of information of the present invention, model Mathematical Modeling, proposes digital compensation algorithm; Then disclose the relation between penalty coefficient and modulator bias point; , by modulator output power detect, know the concrete angle of bias point thereafter; The nonlinear distortion of last distortion compensation function and modulator offsets, and obtains linearisation output.Method provided by the invention, do not need accurately to know TRANSFER MODEL that system is concrete and accurately estimating system characteristic parameter just can offset the nonlinear distortion of modulator-demodulator.Avoided prior art at numeric field, to carry out the difficulty of accurate parameter Estimation.

Accompanying drawing explanation

In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, to the accompanying drawing of required use in embodiment or description of the Prior Art be briefly described below, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skills, do not paying under the prerequisite of creative work, can also obtain according to these accompanying drawings other accompanying drawing.

Fig. 1: the crosstalk based on Digital Signal Processing backward suppresses the electrical block diagram of technology;

Fig. 2: the structural principle schematic diagram of a kind of dynamic range method for improving based on modulator bias point acquisition of information provided by the invention;

Fig. 3: DSP processing logic algorithm flow schematic diagram of the present invention;

Fig. 4: the electrical block diagram of a kind of dynamic range method for improving based on modulator bias point acquisition of information provided by the invention;

Embodiment

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

A kind of dynamic range method for improving based on modulator bias point acquisition of information that this enforcement provides as shown in Figure 2, first by the clear and definite Modulation and Nonlinear intrinsic numeric of modeling analysis model, utilize base band and working point information extraction structure penalty function, complete the counteracting of distortion.Concrete implementation procedure is as follows.

When first Mach of input increases Dare modulator (MZM1) electrode centers frequency, be ω m two-tone signal:

x(t)＝ρ(t)cos(ω _mt) (1)

ρ (t)=2A wherein _mcos (Δ t) is the equivalent envelope of input two-tone signal, the actual margin that Am is two-tone signal, the angular frequency difference that 2 Δs are two-tone signal.Because MZM1 adopts the working point of low biasing, finally survey the harmonic components that output signal comprises all levels time, can represent nonlinear transfer function by general Taylor series expansion model:

y＝a ₀+a ₁x+a ₂x ²+a ₃x ³(2)

Because the amplitude of high-order harmonic wave has the characteristic die-offing, the impact on system under small-signal model is fainter, therefore in above-mentioned expression formula, has ignored three times above higher harmonic components.(1) is brought in (2), and by digital filtering, the expression formula that can obtain respectively base band and fundamental component is:

$y_0\left(t\right)=a_0+\frac{a_2}{2}A{\left(t\right)}^2---\left(3\right)$

$y_1\left(t\right)=[a_1+\frac{{3a}_3}{4}A{\left(t\right)}^2]\·A\left(t\right)\cos \left({\mathrm{\ω}}_{m}t\right)---\left(4\right);$

Due to A (t) in (3) second ²existence, in the signal demodulating, except there is fundamental frequency signal component, also exist significant third order intermodulation distortion component.But can notice extra modulation product A (t) ²be present in baseband signal equally.Utilize small-signal approximate, and suppose following distortion compensation logical algorithm establishment:

$\begin{array}{c}{y}_1^{\′}=y_0^{\mathrm{\γ}}{y}_1\≈a_0^{\mathrm{\γ}}{a}_1(1+\frac{{\mathrm{\γ}}_{a2}}{{2a}_0}{A}^2+\frac{{3a}_3}{{4a}_1}{A}^2)\·A\cos {\mathrm{\ω}}_{m}t\\ =a_0^{\mathrm{\γ}}{a}_{1}A\cos {\mathrm{\ω}}_{m}t\end{array}---\left(5\right)$

From above formula, can by the optimization of parameter, complete the inhibition of nonlinear distortion, when γ meets following formula, third order intermodulation distortion in theory (IMD3) is eliminated completely:

$\mathrm{\γ}=-\frac{3}{2}\frac{a_0}{a_2}\frac{a_3}{a_1}---\left(6\right)$

Above-mentioned logical algorithm is general Mathematical Modeling, applicable to the distortion compensation of any type non linear system, is certainly also applicable to intensity modulated-direct-detection (IM-DD) analog optical link system based on MZM.But it should be noted that and should build corresponding non-linear transfer curve Mathematical Modeling for concrete system performance, determine a ₀～a ₃deng each characteristic coefficient.By effective Mathematical Models, know each characteristic parameter, be the key that guarantees that follow-up distortion compensation correctly completes.The IM-DD simulated photons system that is set to low bias state for working point, transfer function can be expressed as:

Wherein V π is the half-wave voltage at input electrical signal frequency place, for the angular deviation value of relative quadrature bias point is put in modulator real work, for the responsiveness of detector (PD), I _pDfor surveying photoelectric current, Z _pDequivalent matched impedance for PD.Expansion by (7) can be known a ₀～a ₃characteristic parameter, bring in (6) and can obtain:

$\mathrm{\γ}=\frac{1+\sin \mathrm{\φ}}{2\sin \mathrm{\φ}}---\left(8\right)$

Coefficient gamma is only information-related with modulator bias point, and not affected by other factors, therefore can be obtained and be determined unique compensating factor γ by the concrete state in working point.Without accurately knowing the concrete parameters of link, avoided carrying out at numeric field the difficulty of accurate parameter Estimation, only need the Obtaining Accurate of working point can complete the digital post-compensation of nonlinear distortion, greatly reduce the complexity of logical algorithm.The method is applicable to have the system of light territory frequency down-conversion function, has just had extra insertion loss, but can, in conjunction with the advantage of the low biasing technique of modulator, provide extra gain advantage.

The electrical block diagram of a kind of dynamic range method for improving based on modulator bias point acquisition of information that as shown in Figure 4, the present embodiment provides; In Fig. 4, the output CW wavelength of laser is that 1550nm, light source output power are the continuous light wave of 16dBm, and MZM1 is biased in φ=-43o, and second Mach increases Dare modulator (MZM2) and be operated in quadrature bias point.The two-tone signal injecting lays respectively at 3.040 and 3.040GHz, and local oscillator (LO) signal frequency is 3GHz, has finally produced the intermediate-freuqncy signal (IF) that is positioned at 40MHz and 41MHz.The detection simulation signal of telecommunication is converted to digital signal through 14,200MS/s analog to digital converter (ADC, ADlink), through follow-up digital processing.Utilize the working point of the control modulator that bias control circuit that business can be used can be stable.

When the two-tone signal power injecting is that 2dBm, LO signal power are 16dBm and when the luminous power of injection PD is 3dBm, the frequency spectrum of the intermediate-freuqncy signal that experimental study demodulates and respective quadrature tonal signal thereof.For without linearizing system, carrier wave-crosstalk is than being 36.1dB, and distortion effect is comparatively serious, the digital linearization technology that adopts the present embodiment to propose, and carrier wave-crosstalk ratio is greater than 58dB, and distortion component is significantly suppressed.When power remains 3dBm before PD, compare with the system of quadrature bias state, adopt the method to there is the gain advantage of extra 7.2dB.

The output background noise density recording is-162dBm/Hz, for shot noise limited.By IM-DD analog optical link system after test frequency down conversion, export IF signal power (dBm) with input rf signal power (dBm) variation relation, along with injecting the lifting of RF two-tone signal power, survey intermediate-freuqncy signal (40MHz & 41MHz) power and be the lifting of phase uniform velocity thereupon, slope is 1.System without distortion compensation, record crosstalk component (39MHz & 42MHz) power and be the speed increment of 3 times with injecting RF two-tone signal power, illustrate that this system is third order intermodulation distortion limited, dynamic range is 103.2dB@1Hz; Through DSP linearisation, record crosstalk component (39MHz & 42MHz) power and be the speed increment of 5 times with injecting RF two-tone signal power, the main crosstalk constrained type that five rank crosstalks are system, third order intermodulation distortion is inhibited completely, dynamic range reaches 123.3dB@1Hz, has effectively improved the dynamic range characteristics of analog optical link.

Above execution mode is only for the present invention is described, but not limitation of the present invention.Although the present invention is had been described in detail with reference to embodiment, those of ordinary skill in the art is to be understood that, technical scheme of the present invention is carried out to various combinations, revises or is equal to replacement, do not depart from the spirit and scope of technical solution of the present invention, all should be encompassed in the middle of claim scope of the present invention.

Claims (4)

1. the dynamic range method for improving based on modulator bias point acquisition of information, is characterized in that, comprises the following steps:

Step 1: set up Mathematical Modeling, propose digital compensation algorithm;

Step 2: disclose the relation between penalty coefficient and modulator bias point;

Step 3: detect by modulator Output optical power, know the concrete angle of bias point;

Step 4: the nonlinear distortion of distortion compensation function and modulator offsets, obtains linearisation output.

2. method according to claim 1, is characterized in that, described modulator is arranged on the bias point beyond quadrature bias point.

3. method according to claim 1, is characterized in that, described method realizes equivalent frequency spectrum shift by light territory, and high-frequency signal is transformed in intermediate-freuqncy signal or baseband signal.

4. method according to claim 2, is characterized in that, comprises the following steps:

Step 1: set up Mathematical Modeling, y=a ₀+ a ₁x+a ₂x ²+ a ₃x ³;

Ignore above higher harmonic components three times, by x (t)=ρ (t) cos (ω _mt), described in substitution in Mathematical Modeling, obtain base band

Fundamental frequency $y_1\left(t\right)=[a_1+\frac{{3a}_3}{4}A{\left(t\right)}^2]\·A\left(t\right)\cos \left({\mathrm{\ω}}_{m}t\right)---\left(4\right);$

Digital compensation algorithm is proposed:

$\begin{array}{c}{y}_1^{\′}=y_0^{\mathrm{\γ}}{y}_1\≈a_0^{\mathrm{\γ}}{a}_1(1+\frac{{\mathrm{\γ}}_{a2}}{{2a}_0}{A}^2+\frac{{3a}_3}{{4a}_1}{A}^2)\·A\cos {\mathrm{\ω}}_{m}t\\ =a_0^{\mathrm{\γ}}{a}_{1}A\cos {\mathrm{\ω}}_{m}t\end{array}$

Step 2: disclose the relation between penalty coefficient and modulator bias point:

When penalty coefficient γ meets time, distortion is inhibited;

Intensity modulated link transfer function is:

Calculating the now relation table between penalty coefficient and modulator bias point is shown:

$\mathrm{\γ}=\frac{1+\sin \mathrm{\φ}}{2\sin \mathrm{\φ}};$

Step 3: detect by modulator Output optical power, know the concrete angle φ of bias point;

Step 4: according to the concrete angle φ of the bias point obtaining in step 3, calculate distortion compensation coefficient gamma by step 2, and bring γ into distortion compensation algorithm in step 1.