CN2531411Y - Optical modulator - Google Patents

Abstract

The utility model relates to a light modulator, comprising a waveguide divided into two branches (11, 12), ground electrodes (13, 14) disposed on the two sides of the waveguide branches, and a working electrode (15) disposed between the two waveguide branches. The working electrode includes two parts of a RF electrode (151) and a DC offset electrode (152), the ground electrodes comprise two parts of RF ground electrodes (131, 141) and DC offset ground electrodes (132, 142). Unlike the prior art, the RF ground electrodes (131, 141) are different in length. The length proportion is determined by chirp coefficient, which meets the relational expression k = (a+1) / (1-a), wherein, k is the length proportion of the two electrodes, a is the chirp coefficient, which is determined according to the actual needs. The utility model improves the MZ modulator which is used to modulate intensity originally, the two symmetric RF ground electrodes are changed into asymmetric, resulting in that the phases Psi a and Psi b generated by the two branches are different, so the (Psi a + Psi b) / 2 is not equal to zero, so the chirp modulation is realized during the intensity modulation, thus solving the problems that in the prior art the chirp and the intensity modulations are not synchronous.

Description

A kind of photomodulator

Technical field

The utility model belongs to optical communication technique, is specifically related to the phase place and the intensity modulated technology of light.

Background technology

The modulator of realizing the conversion of high-speed data electric light is the Primary Component of fibre-optic transmission system (FOTS) at present, at present with Mach-Zehnder (MZ, Mach-Zehnder) interfere for the intensity modulator of principle be the most frequently used a kind of.Commercial MZ modulator adopts the cascode symmetrical structure of electrode frequently, and promptly the structure of the structure of optical waveguide and electrode all is to adopt symmetrical structure.Fig. 1 is the vertical view of MZ modulator, and the black thick line among the figure is represented waveguide exactly, and waveguide arm 11,12 is two arms of modulator again, is to adopt symmetrical structure.The square frame of waveguide both sides is represented electrode 13,14,15, also is to adopt symmetrical structure, and wherein the electrode 15 in the middle of the waveguide arm 11,12 is a working electrode, and the electrode 13,14 of branch road both sides is a ground electrode.As shown in the figure, light is injected after the MZ modulator, is divided into two bundles and transmits in the waveguide arm 11 and 12 of two symmetries, carries out intensity modulated simultaneously under the modulation voltage that electrode 13,14,15 provides.The electrode 13,14,15 of MZ modulator is divided into two parts usually again: radio frequency (RF) electrode 131,141,151 and direct current biasing (DC Bias) electrode 132,142,152.Radio-frequency electrode is near the input end of modulator, and the direct current biasing electrode is near the output terminal of modulator.

For the MZ modulator, the phase shift that its modulator electrode causes is directly proportional with voltage.Respectively with two arms 11,12 about a and the b representative, dc offset voltage is elected V as below _πInput light superposes after through two arms, and the output after the stack can be expressed as: $E={\mathrm{\ψ}}_0\exp [-j(w_{0}t+\frac{{\mathrm{\ψ}}_a+{\mathrm{\ψ}}_b}{2})]\cos \frac{{\mathrm{\ψ}}_a-{\mathrm{\ψ}}_b}{2},$

Wherein ψ a and ψ b are respectively the phase shift that the radio-frequency electrode in the underarm causes.In the MZ modulator of symmetrical structure, ψ _a=-ψ _b, at this moment flashlight can be reduced to:

E＝ψ ₀ exp[-j(w ₀t)]cosψ _a

The physical meaning of warbling is time dependent phase place.Depend on owing to warble

The MZ modulator of symmetrical structure can be realized zero intensity modulated of warbling as can be seen from this expression formula.

Long Distance Transmission studies show that to have the modulation signal of necessarily warbling and can help the system transmissions optimization in Properties.When carrying out intensity modulated, take suitable phase modulation (PM) can improve transmission performance in other words.Adopting phase-modulator independently is a kind of method of warbling of realizing.The benefit of this method is to regulate warbling, but adopting the potential problems of phase-modulator is the synchronous existing problems of high speed signal, the drive signal synchronism stability that is intensity modulator and phase-modulator has difficulties, and this just causes difficulty for the commercialization of phase-modulator.

Summary of the invention

The purpose of this utility model just is existing photomodulator is improved, and makes the MZ modulator that can only be used for intensity modulated at present simultaneously can carry out phase modulation (PM), can effectively solve stationary problem of the prior art.

For achieving the above object, a kind of photomodulator that the utility model proposes comprises the waveguide that is divided into two branch roads, two ground electrodes and the working electrode between two waveguide arms in the waveguide arm both sides, described working electrode comprises radio-frequency electrode and direct current biasing electrode two parts again, described two ground electrodes comprise radio frequency ground electrode and direct current biasing ground electrode two parts again, radio-frequency electrode and radio frequency ground electrode are near light input end, direct current biasing electrode and direct current biasing ground electrode are near light output end, and it is characterized in that: the length of the radio frequency ground electrode in described two ground electrodes is inequality.

In the above-mentioned photomodulator, described radio-frequency electrode and the wherein long isometric and aligned in position of radio frequency ground electrode, described direct current biasing electrode and two isometric and aligned in position of direct current biasing ground electrode, short radio frequency ground electrode is with the radio frequency ground electrode of length and an end of radio-frequency electrode align.

In the above-mentioned photomodulator, the length ratio of described two radio frequency ground electrodes is definite according to chirp coefficient, satisfies to concern k=(a+1)/(1-a), and wherein k is the length ratio of two electrodes, and a is a chirp coefficient, determines according to actual needs.

Improve because the utility model is the MZ modulator that will originally be used for intensity modulated, the radio frequency ground electrode of two symmetries is made into asymmetric, the phase place ψ a and the ψ b size that cause radio-frequency electrode to produce are unequal, so Non-vanishing, thus in intensity modulated, realize warbling modulation, so just can solve asynchronous problem of warbling with intensity modulated of the prior art.And the size of the modulation of warbling can also realize by the length ratio of regulating two ground electrodes.

Below in conjunction with the drawings and specific embodiments the utility model is elaborated.

Description of drawings

The MZ modulator structure figure that Fig. 1 is traditional;

The MZ modulator structure synoptic diagram that Fig. 2 the utility model provides.

Embodiment

Utilize the prior art part that the definition of ψ a and ψ b etc. is described specific implementation of the present utility model.

From expression formula $E={\mathrm{\ψ}}_0\exp [-j(w_{0}t+\frac{{\mathrm{\ψ}}_a+{\mathrm{\ψ}}_b}{2})]\cos \frac{{\mathrm{\ψ}}_a-{\mathrm{\ψ}}_b}{2},$ As can be seen: the photomodulator existence is warbled if desired, just must allow The Xiang Buwei constant.Because the direct current biasing electrode adopts symmetrical structure, Item depends on the phase place that is produced by radio-frequency electrode _RFWith _RF

Chirp coefficient size α can use the absolute value representation of expression. $\mathrm{\α}=\frac{{\mathrm{\ψ}}_a^{\mathrm{RF}}+{\mathrm{\ψ}}_b^{\mathrm{RF}}}{{\mathrm{\ψ}}_a^{\mathrm{RF}}-{\mathrm{\ψ}}_b^{\mathrm{RF}}}$

If ${\mathrm{\ψ}}_a^{\mathrm{RF}}=-{\mathrm{\ψ}}_b^{\mathrm{RF}},$ Warble is zero.

Therefore, in order to realize the modulation of warbling, the utility model adopts the modulator of structure shown in Figure 2, the same with prior art shown in Figure 1, this cascode electrode MZ modulator frequently comprises the waveguide of representing with black thick line, and waveguide is divided into two branch roads 21,22 again, is to adopt symmetrical structure.The square frame of waveguide both sides is represented electrode 23,24,25, and wherein the electrode 25 in the middle of the waveguide arm 21,22 is a working electrode, and the electrode 23,24 of branch road both sides is a ground electrode.Light is injected after the MZ modulator, is divided into two bundles and transmits in the waveguide arm 21 and 22 of two symmetries, carries out intensity modulated simultaneously under the modulation voltage that electrode 23,24,25 provides.The ground electrode 23,24 of MZ modulator is divided into two parts usually again: radio frequency (RF) ground electrode 231,241 and direct current biasing (DC Bias) ground electrode 232,242.Working electrode is separated into two parts also: radio-frequency electrode 251 and direct current biasing electrode 252, radio-frequency electrode and radio frequency ground electrode are near the input end of modulator, and direct current biasing electrode and direct current biasing ground electrode are near the output terminal of modulator.Direct current biasing ground electrode 232,242 and direct current biasing electrode 252 are isometric, and align on the position.Unlike the prior art be radio frequency ground electrode the 231, the 241st wherein, asymmetric, as shown in Figure 2, wherein the length of radio frequency ground electrode 231,241 is different, but one of the length in the length of radio-frequency electrode 251 and the ground electrode 241,251 is isometric, and alignment, above length is short down among the figure is example, so radio-frequency electrode 251 is just isometric with long radio frequency ground electrode 231, and alignment.It is long down to go up weak point, and at this moment, radio-frequency electrode 251 is just the same long with radio frequency ground electrode 241.It can also be seen that in Fig. 2 wherein short radio frequency ground electrode 241 aligns with long radio frequency ground electrode 231, radio-frequency electrode 251 1 ends (right side).With with represent the up and down length of two radio frequency ground electrodes 231,241 respectively, at this moment chirp coefficient size α just can be expressed as: $\mathrm{\α}=\frac{L_a-L_b}{L_a+L_b}$

As can be seen, the size of chirp coefficient depends on the ratio of radio-frequency electrode brachium $k=\frac{L_a}{L_b},$ The chirp coefficient that this structure obtains can not surpass 1.Following formula can be rewritten as: $k=\frac{a+1}{1-a}$

Therefore, in concrete the application, can chirp coefficient size according to actual needs determine the length ratio of radio-frequency electrode in the modulator.Table 1 is the relations of two radio-frequency electrode length than k and chirp coefficient α.

Table 1

Two radio-frequency electrode length compare k	Chirp coefficient α
		1	0
2	0.33
		3	0.5
4	0.6
		5	0.67
6	0.7
		7	0.75

In actual applications, chirp coefficient α has positive and negative.In the utility model patent, the positive and negative of chirp coefficient α can be by regulating bias current _DCRealize.

When:

(1) $c\·V^{\mathrm{DC}}\·L^{\mathrm{DC}}=\frac{\mathrm{\π}}{2},$ At this moment warble to just chirp coefficient $\mathrm{\α}=\frac{L_a-L_b}{L_a+L_b}.$

(2) $c\·V^{\mathrm{DC}}\·L^{\mathrm{DC}}=-\frac{\mathrm{\π}}{2}$ Or $c\·V^{\mathrm{DC}}\·L^{\mathrm{DC}}=\frac{3}{2}\mathrm{\π},$ At this moment warble to negative chirp coefficient $\mathrm{\α}=\frac{L_a-L_b}{L_a+L_b}.$

Wherein be coupling constant, it is relevant with the refractive index of waveguiding structure and material. _RFBe the crest voltage of radio-frequency electrode, its value is relevant with the length of coupling constant and radio-frequency electrode.L ^DCBe the length of direct current biasing electrode.

L wherein _bRelation below the still length of the shorter radio-frequency electrode of expression, so value satisfies:

0≤L _b≤L _a。

In conjunction with above embodiment, the asymmetric radio-frequency electrode structure of the utility model employing can be carried out the phase modulation (PM) or the modulation of warbling when realizing intensity modulated as can be seen.Because phase modulation (PM) and intensity modulated are carried out simultaneously, so can solve the stationary problem of two kinds of modulation.

Claims (3)

1, a kind of photomodulator comprises and is divided into two branch roads (21,22) waveguide, be positioned at waveguide arm (21,22) two of both sides ground electrodes (23) and be positioned at two waveguide arms (21,22) working electrode between (25), described working electrode (25) comprises radio-frequency electrode (251) and direct current biasing electrode (252) two parts again, described two ground electrodes (23,24) comprise radio frequency ground electrode (231 again, 241) and direct current biasing ground electrode (232,242) two parts, radio-frequency electrode (251) and radio frequency ground electrode (231,241) near light input end, direct current biasing electrode (252) and direct current biasing ground electrode (232,242) near light output end, it is characterized in that: described two ground electrodes (23,24) the radio frequency ground electrode (231 in, 241) length is inequality.

2, photomodulator as claimed in claim 1, it is characterized in that: described radio-frequency electrode (251) and the wherein long isometric and aligned in position of radio frequency ground electrode (231), described direct current biasing electrode (252) and the isometric and aligned in position of two direct current biasing ground electrodes (232,242), short radio frequency ground electrode (241) is with the radio frequency ground electrode (231) of length and an end of radio-frequency electrode (251) align.

3, photomodulator as claimed in claim 1, it is characterized in that: the length ratio of radio frequency ground electrode (231,241) is determined according to chirp coefficient in described two ground electrodes (23,24), satisfy and concern k=(a+1)/(1-a), wherein k is the length ratio of two radio frequency ground electrodes, a is a chirp coefficient, determines according to actual needs.

Images