CN1213339C - Method and device for realizing dynamic tunable chatter by using mach-zehnder modulator - Google Patents

Abstract

The present invention provides a chirping dynamic state adjusting method which utilizes an MZ modulator. The MZ modulator is a common ground electrode structure. The present invention is characterized in that the magnitude of chirping can be adjusted by changing the radio frequency voltage of a radio frequency electrode of the MZ modulator; the chirping factor a is equal to the ratio of the phase shift sum (psi-[a]+[RF]+psi-[b]+[RF]) to the phase shift difference (psi-[a]+[RF]-psi-[b]+[RF]), and the phase shift sum and the phase shift difference are caused by the radio frequency voltage of an upper branch circuit and a lower branch circuit. The present invention realizes the chirping dynamic state adjusting method and a device thereof by utilizing the MZ modulator, the magnitude of the generated chirping can be simply and exactly controlled by adjusting the driving voltage, and simultaneously, the present invention realizes the intensity modulation and phase modulation, and improves the transmission performance of an optical fiber transmission system.

Description

A kind of Mach-Zehnder modulator realize the warbling method and device thereof of dynamic adjustable of utilizing

Technical field

The present invention relates to fiber optic communication field, especially relate to the method and the device thereof that in fibre-optic transmission system (FOTS), carry out intensity modulated and phase modulation (PM).

Background technology

Mach-Zehnder (Mach-Zehnder) modulator is called the MZ modulator again, is the Primary Component of changing in order to the electric light of realizing high-speed data in the fibre-optic transmission system (FOTS).From electrode position, the MZ modulator has two kinds of structures usually: cascode is electrode structure and common ground electrode structure frequently.Cascode frequently electrode structure is meant and adopts two ground electrodes and a radio-frequency electrode, promptly radio-frequency electrode in the middle of two waveguides and two ground electrodes respectively in the both sides of waveguide.Altogether the structure of ground electrode is then opposite: adopts two radio-frequency electrodes and a ground electrode, promptly ground electrode in two waveguides centres and two radio-frequency electrodes respectively in the both sides of waveguide.Usually the MZ modulator adopts symmetrical structure, that is, the structure of waveguide and the structure of electrode all are symmetrical.Be the vertical view of bilateral driving (symmetry is the ground electrode structure altogether) MZ modulator as shown in Figure 1.Black thick line among the figure is represented waveguide exactly, and the square frame of waveguide both sides is represented electrode.Two arms are in two waveguides again, hereinafter referred to as branch road up and down, add that at branch road up and down driving voltage realizes modulation respectively.The electrode of modulator is divided into two parts: radio frequency (RF) electrode and direct current biasing (DC Bias) electrode, radio-frequency electrode is near the input end of modulator, formed with the traveling wave electrode that lays respectively at the waveguide both sides by being positioned at the middle ground electrode of two waveguides, the direct current biasing electrode is formed with the ground electrode that lays respectively at the waveguide both sides by being positioned at the middle direct current biasing electrode of two waveguides near the output terminal of modulator.

What is called is warbled and is meant time dependent phase place.The MZ modulator is based on such principle: the phase shift that modulator electrode causes is directly proportional with voltage.Respectively with branch road about a and the b representative, can be expressed as below through the output after the optical superposition of two branch roads:

$E={\mathrm{\ψ}}_0\exp [-j(w_{0}t+\frac{{\mathrm{\ψ}}_a+{\mathrm{\ψ}}_b}{2})]\cos \frac{{\mathrm{\ψ}}_a-{\mathrm{\ψ}}_b}{2},$ ψ _aAnd ψ _bThe phase shift that branch road causes about being respectively.

From the expression formula of front as can be seen: because the size not influence of dc offset voltage to warbling only needs to consider that radio-frequency electrode cause additive phase ψ _a ^RFAnd ψ _b ^RFWhat produced warbles.If ${\mathrm{\ψ}}_a^{\mathrm{RF}}=-{\mathrm{\ψ}}_b^{\mathrm{RF}},$ Then warble is zero.

Studies show that the modulation of warbling additional suitable on the basis of intensity modulated (or claiming phase modulation (PM)) helps the system transmissions optimization in Properties, suitable in other words phase modulation (PM) bond strength modulation can improve transmission performance.But existing MZ modulator is a symmetrical structure, and the radio-frequency voltage on the branch road equates about being added in, and therefore, existing MZ modulator can only be realized zero intensity modulated of warbling.

Summary of the invention

The objective of the invention is to solve in the present fibre-optic transmission system (FOTS), when using the MZ modulator to carry out intensity modulated, can not carry out the problem of phase modulation (PM), and a kind of MZ of utilization modulator realize the warbling method of dynamic adjustable proposed, promptly, additional suitable phase modulation (PM) on the basis of intensity modulated is to improve the system transmissions performance of fibre-optic transmission system (FOTS).

The object of the present invention is achieved like this, a kind of MZ of utilization modulator realize the warbling method of dynamic adjustable, described MZ modulator is for being total to the ground electrode structure, it is characterized in that, regulate the size of warbling by the radio-frequency voltage on the radio-frequency electrode that changes common ground electrode structure MZ modulator, described chirp coefficient size a equals the caused phase shift of radio-frequency voltage and the (ψ of branch road up and down _a ^RF+ ψ _b ^RF) with the caused phase shift difference (ψ of radio-frequency voltage of branch road up and down _a ^Rf-ψ _b ^RF) ratio.

This method further comprises, adjusts the symbol that the dc offset voltage scalable is warbled.

When described MZ modulator was symmetrical structure, described chirp coefficient size (α) equaled the radio-frequency voltage sum (V of branch road up and down _a ^RF+ V _b ^RF) with the poor (V of the radio-frequency voltage of branch road up and down _a ^RF-V _b ^RF) ratio.

Method of the present invention can adopt the MZ modulator of existing symmetrical structure to realize, can also adopt the MZ modulator of dissymmetrical structure provided by the present invention to realize.MZ modulator of the present invention is to adopt ground electrode structure altogether, it is characterized in that the length of two radio-frequency electrodes of described MZ modulator can be unequal, also can equate.

Implement the MZ of utilization modulator of the present invention realize the warbling method and the device thereof of dynamic adjustable, can simply and accurately control the size of warbling that produces by regulating driving voltage, realize intensity modulated and phase modulation (PM) simultaneously, thereby improved the system transmissions performance of fibre-optic transmission system (FOTS).

Description of drawings

Fig. 1 is the existing symmetry vertical view of the MZ modulator of ground electrode structure altogether;

Fig. 2 is the asymmetric vertical view of the MZ modulator of ground electrode structure altogether of the present invention.

Embodiment

According to the modulation principle of foregoing MZ modulator, exist if desired and warble, just must allow

Item is non-vanishing, and is not constant.Because the size not influence of dc offset voltage to warbling only needs to consider that radio-frequency electrode causes additive phase ψ _a ^RFAnd ψ _b ^RFWhat produced warbles.Chirp coefficient size a can use the absolute value of following expression, and its symbol need be considered the position of direct current biasing point.

$a=\frac{{\mathrm{\ψ}}_a^{\mathrm{RF}}+{\mathrm{\ψ}}_b^{\mathrm{RF}}}{{\mathrm{\ψ}}_a^{\mathrm{RF}}-{\mathrm{\ψ}}_b^{\mathrm{Rf}}}$

If ${\mathrm{\ψ}}_a^{\mathrm{RF}}=-{\mathrm{\ψ}}_b^{\mathrm{RF}},$ Warbling is zero, if ψ _a ^RFAnd ψ _b ^RFDifference will produce and warble,

The present invention realizes the dynamic modulation of warbling of bilateral driving MZ modulator by adjusting radio-frequency voltage mode.MZ is depended in the generation of warbling, and up and down the additive phase that produces of branch road is asymmetric.Asymmetricly mainly contain two sources: one, adopt asymmetric waveguiding structure or radio-frequency electrode structure; Two, the driving voltage difference that loads in two waveguides.Driving voltage generally comprises the voltage that loads on the voltage that loads on the radio-frequency electrode and the direct current biasing electrode, but in the present invention, because the size not influence of dc offset voltage to warbling only needs to consider that the voltage that loads on the radio-frequency electrode is radio-frequency voltage.

The length of supposing the radio-frequency electrode of branch road a is L _a ^RF, the length of the radio-frequency electrode of branch road b is L _b ^RF, the radio-frequency voltage of two branch roads is respectively V _a ^RFAnd V _b ^RFIf adopt dissymmetrical structure or V _a ^RFAnd V _b ^RFVary in size, then the phase place that produces of both sides is asymmetric, at this moment will produce and warble, chirp coefficient can be expressed as:

$a=\left|\frac{V_a^{\mathrm{Rf}}{L}_a^{\mathrm{RF}}+V_b^{\mathrm{RF}}{L}_b^{\mathrm{RF}}}{V_a^{\mathrm{RF}}{L}_a^{\mathrm{RF}}-V_b^{\mathrm{RF}}{L}_b^{\mathrm{RF}}}\right|$

In one embodiment of the invention, the inventive method is to adopt the MZ modulator of existing symmetrical structure to realize.Because the length of waveguide and electrode is fixed, the key of the dynamic modulation that realizes warbling is choosing of driving voltage.

Suppose $k_1=L_a^{\mathrm{RF}}/L_b^{\mathrm{RF}},k_2=|V_a^{\mathrm{RF}}/V_b^{\mathrm{RF}}|$

At this moment electrode structure for symmetry has $L_a^{\mathrm{RF}}=L_b^{\mathrm{RF}},$ k ₁=1, chirp coefficient can be expressed as:

$a=\frac{V_a^{\mathrm{RF}}-V_b^{\mathrm{RF}}}{V_a^{\mathrm{RF}}+V_b^{\mathrm{RF}}}$

The adjusting of chirp coefficient can be by changing V as can be seen _a ^RFAnd V _b ^RFRealize.Expression formula above the degree rewriting of design, like this:

$V_a^{\mathrm{RF}}=k_2{V}_b^{\mathrm{RF}}=\frac{1+a}{k_1(1-a)}{V}_b^{\mathrm{RF}}$

Can pass through fixedly V during practical operation _b ^RFSize, by changing V _a ^RFSize adjustment warble.Can certainly change two radio-frequency voltages simultaneously.

Chirp coefficient is that 1 situation reflects in above-mentioned formula of reduction, at this moment corresponding to V _b ^RFSize be zero.

If a, the voltage of b two arms is in-phase voltage, and at this moment chirp coefficient is less than 1, if a, the voltage of b two arms is reverse voltage, and at this moment chirp coefficient is greater than 1.

What table 1 provided is the ratio of the driving voltage of branch road up and down and the corresponding relation of corresponding chirp coefficient.

The ratio of the driving voltage of branch road and the relation of corresponding chirp coefficient about table 1. symmetrical structure

At this moment the size of chirp coefficient depends on that directly radio-frequency voltage is poor as can be seen: pressure reduction is big more, and it is big more to warble.

Positive and negative can the putting by direct current biasing of warbling adjusted.For just warbling, bias point is selected in The place is not biased voltage, warbles for negative.

In another embodiment of the present invention, can also adopt the MZ modulator of dissymmetrical structure to realize method of the present invention.

As shown in Figure 2, dissymmetrical structure shows that the length of two traveling wave electrodes of radio frequency (RF) electrode is unequal.The length of two traveling wave electrodes is respectively L _a ^RFAnd L _b ^RFIf, $V_a^{\mathrm{RF}}>V_b^{\mathrm{RF}},$ At this moment can adopt $L_a^{\mathrm{RF}}>L_b^{\mathrm{RF}}$ Structure.L _bValue satisfy below relation: $0\≤L_b^{\mathrm{RF}}\≤L_a^{\mathrm{RF}}.$

Suppose $k_1=L_a^{\mathrm{RF}}/L_b^{\mathrm{RF}},k_2=V_a^{\mathrm{RF}}/V_b^{\mathrm{RF}},$ Its voltage ratio is as shown in table 2:

The ratio of the driving voltage of branch road and the relation following (dissymmetrical structure) of corresponding chirp coefficient about the table 2.

Method of the present invention and device thereof can be used for the NRZ sign indicating number of 2.5Gbit/s, 10Gbit/s and 40Gbit/s and higher or lower speed and realize the light emission module of various RZ sign indicating number transmission systems.

Claims (8)

1, a kind of Mach-Zehnder MZ modulator realize warbling method of dynamic adjustable of utilizing, described MZ modulator is for being total to the ground electrode structure, it is characterized in that, regulate the size of warbling by the radio-frequency voltage on the radio-frequency electrode that changes the MZ modulator, described chirp coefficient size a equals the caused phase shift of radio-frequency voltage and the (ψ of branch road up and down _a ^RF+ ψ _b ^RF) with the caused phase shift difference (ψ of radio-frequency voltage of branch road up and down _a ^RF-ψ _b ^RF) ratio.

2, Mach-Zehnder MZ modulator realize the warbling method of dynamic adjustable of utilizing according to claim 1 is characterized in that, adjusts the symbol that the dc offset voltage scalable is warbled.

3, Mach-Zehnder MZ modulator realize the warbling method of dynamic adjustable of utilizing according to claim 1 and 2 is characterized in that described MZ modulator is a symmetrical structure, and described chirp coefficient size a equals the radio-frequency voltage sum (V of branch road up and down _a ^RF+ V _b ^RF) with the poor (V of the radio-frequency voltage of branch road up and down _a ^RF-V _b ^RF) ratio.

4, Mach-Zehnder MZ modulator realize the warbling method of dynamic adjustable of utilizing according to claim 1 is characterized in that, fixes the size of a radio-frequency voltage, realizes the dynamic adjustable of warbling by regulating another radio-frequency voltage.

5, Mach-Zehnder MZ modulator realize the warbling method of dynamic adjustable of utilizing according to claim 1 is characterized in that, realizes that by the homophase radio-frequency voltage on the radio-frequency electrode that changes the MZ modulator chirp coefficient is less than 1 adjusting.

6, Mach-Zehnder MZ modulator realize the warbling method of dynamic adjustable of utilizing according to claim 1 is characterized in that, realizes that by the anti-phase radio-frequency voltage on the radio-frequency electrode that changes the MZ modulator chirp coefficient is greater than 1 adjusting.

7, a kind of MZ modulator of realizing the described method of claim 1 is characterized in that, the equal in length of two radio-frequency electrodes of described MZ modulator.

8, a kind of MZ modulator of realizing the described method of claim 1 is characterized in that, the length of two radio-frequency electrodes of described MZ modulator is unequal.

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