CN203069927U - Electro-optical waveguide used for superspeed electro-optic sampling - Google Patents

Abstract

The utility model is applicable to the field of optic devices and provides an electro-optical waveguide used for superspeed electro-optical sampling. The electro-optical waveguide comprises an AlGaAs sandwich layer and AlGaAs claddings positioned on the two sides of the AlGaAs sandwich layer, and electrodes are respectively arranged on the outer sides of the AlGaAs claddings on the two sides; the AlGaAs claddings on the two sides have the same refracting index to input femto-second laser and the refracting index of the AlGaAs claddings to the input femto-second laser is lower than that of the AlGaAs sandwich layer to input femto-second laser. According to the utility model, AlGaAs optical waveguide is taken as an electro-optical crystal for transmitting femto-second laser. Therefore, the half-wave voltage is reduced greatly, and the sensitivity in detection is enhanced.

Description

The electro-optical transducer that can be used for the hypervelocity electro optic sampling

Technical field

The utility model belongs to the optical device field, relates in particular to a kind of electro-optical transducer that can be used for the hypervelocity electro optic sampling.

Background technology

The electro optic sampling technology has very important meaning in the ultrafast opto-electronics field, this technology proposes in nineteen eighty-two in the people such as Valdmanis by U.S. Rochester university.The electro optic sampling system is " sampling gate " with ultrashort light pulse, changes by the light intensity of measuring electric signal modulation to be measured, realizes the test to hypervelocity electron device or circuit.This technology has the bandwidth less than the temporal resolution below the 1ps level and THz level, owing to need not to extract electric charge from measured device or circuit, therefore system under test (SUT) is not almost had electromagnetic interference (EMI) simultaneously.These advantages make it be subjected to the scientific research personnel and more and more pay attention to.

In the electro optic sampling technology, one of its Primary Component is electro-optic crystal.Usually adopting the thickness of electro-optic crystal is the hundreds of micron, because the electrooptical coefficient of electro-optic crystal is smaller at present, thereby will have enough voltage could make that the light of different directions polarization has enough phase differential in the output face.Usually half-wave voltage is wanted several kilovolts, and the electric signal that we need survey often has only several volts, even littler, and this has just limited the sensitivity of detectable signal greatly.Reduce the thickness of electro-optic crystal significantly, can reduce half-wave voltage, make the detection difficulty of electric signal reduce greatly, improve the signal to noise ratio (S/N ratio) of surveying.But reduce the thickness of electro-optic crystal significantly, also can bring certain problem.When electro-optic crystal thickness is very little, waveguiding effect can be very obvious when light transmitted in this crystal, at this moment needs to consider waveguiding effect to the influence of detectable signal, so just can make detection more accurate.

The utility model content

Technical problem to be solved in the utility model is to provide a kind of electro-optical transducer for the hypervelocity electro optic sampling, is intended to improve the sensitivity of detection.

The utility model is achieved in that a kind of electro-optical transducer for the hypervelocity electro optic sampling, and described electro-optical transducer comprises the AlGaAs sandwich layer and be positioned at the AlGaAs covering of described AlGaAs sandwich layer both sides that the outside of the AlGaAs covering of described both sides is respectively equipped with electrode; The AlGaAs covering of described both sides is identical to the refractive index of the femtosecond laser of input, and is lower than described AlGaAs sandwich layer to the refractive index of the femtosecond laser of input.

Further, the AlGaAs covering of described both sides satisfies following relation to refractive index and the described AlGaAs sandwich layer of the femtosecond laser of input to the refractive index of the femtosecond laser imported:

$\sqrt{n_1^2-{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_2^2}\frac{\mathrm{\&pi;}}{\mathrm{\&lambda;}}\mathrm{aR}<\frac{\mathrm{\&pi;}}{2},$ Wherein, n ₁, n ₂Be respectively the refractive index of waveguide core layer and covering, a is the thickness of waveguide core layer, and λ is the wavelength of the femtosecond laser of incident.

Further, described lambda1-wavelength is 1.064 μ m, and the refractive index of the AlGaAs covering of described both sides is 3.52, and thickness is 8 μ m; The refractive index of described AlGaAs sandwich layer is 3.53, and thickness is 2 μ m.

Further, the field distribution of the light that conducts in the described electro-optical transducer is the linear combination of two orthogonal mode fields, and the phase differential of two orthogonal modes in described electro-optical transducer output cross section is linear change with impressed voltage.

The utility model utilizes the AlGaAs optical waveguide to transmit femtosecond laser as electro-optic crystal, thereby can reduce half-wave voltage greatly, improves the sensitivity of surveying.

Description of drawings

Fig. 1 is the variation synoptic diagram of AlGaAs crystal index ellipsoid main shaft when extra electric field of providing of the utility model;

Fig. 2 is the planar waveguide structural representation that the utility model provides;

Fig. 3 is the TE that the utility model provides ₀Mould and TM ₀Mould is exported the phase differential in cross section with the synoptic diagram that concerns of on-load voltage variation in waveguide.

Embodiment

In order to make the purpose of this utility model, technical scheme and advantage clearer, below in conjunction with drawings and Examples, the utility model is further elaborated.Should be appreciated that specific embodiment described herein only in order to explaining the utility model, and be not used in restriction the utility model.

The propagation law of light in crystal deferred to electromagnetic theory of light, and the method for geometry of utilizing index ellipsoid can be complete and express the refractive index that characterizes the crystal optics characteristic easily and distribute in the value of space all directions.Extra electric field is to the influence of crystal optics characteristic, and the variation of size, shape and orientation that can be by index ellipsoid is described.

The AlGaAs crystal belongs to

Crystal class, its three four-fold axis of symmetry are its crystalline axis direction, and three axles (x, y z) can exchange.

Point group is isotropic crystal, its refractive index n ₀The ellipsoid equation be:

$x^2+{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HDA00002851043300013.png"\; state="\{\{state\}\}">y</figure-callout>}}^2+z^2={\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HDA00002851043300011.png,HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_0^2---\left(1\right)$

In the formula (1), x, y, three coordinates of z are got crystalline axis direction, as shown in Figure 1.At extra electric field E (E _x, E _y, E _z) act on down, induction index ellipsoid equation is:

$\frac{x^2+{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HDA00002851043300013.png"\; state="\{\{state\}\}">y</figure-callout>}}^2+z^2}{{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HDA00002851043300011.png,HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_0^2}+2{\mathrm{\&gamma;}}_{41}(E_x\mathrm{yz}+E_y\mathrm{zx}+E_z\mathrm{xy})=1---\left(2\right)$

Wherein, γ ₄₁Be electrooptical coefficient.The direction of extra electric field has three kinds of possible situations in the practical application: electric field is perpendicular to (001) face, perpendicular to (110) face or perpendicular to (111) face.Electric field is discussed perpendicular to the situation of (001) face (namely along the z direction of principal axis) in the utility model.This moment E _x=E _y=0, E _z=| E|, so induction index ellipsoid equation is:

$\frac{x^2+{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HDA00002851043300013.png"\; state="\{\{state\}\}">y</figure-callout>}}^2+z^2}{{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HDA00002851043300011.png,HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_0^2}+2{\mathrm{\&gamma;}}_{41}{E}_z\mathrm{xy}=1---\left(3\right)$

The appearance of cross term xy means that the main shaft of index ellipsoid around the z axle rotation has taken place, and is the convenience of computing, can be with its main shaftization.If new main shaft has rotated the α angle around the z axle, then new (xyz) old (x ' y ' z') pass between the coordinate is:

x=x′cosα-y′sinα

y=x′sinα+y′cosα

z=z′ (4)

With (4) substitution (3) Shi Kede:

$(\frac{1}{{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HDA00002851043300011.png,HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_0^2}+2{\mathrm{\&gamma;}}_{41}{E}_z\sin \mathrm{\&alpha;}\cos \mathrm{\&alpha;})x^{\&prime;2}$

$+(\frac{1}{{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HDA00002851043300011.png,HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_0^2}-2{\mathrm{\&gamma;}}_{41}{E}_z\sin \mathrm{\&beta;}\cos \mathrm{\&alpha;})y^{\&prime;2}$

$+\frac{1}{{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HDA00002851043300011.png,HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_0^2}{z}^{\&prime;2}+2{\mathrm{\&gamma;}}_{41}{x}^{\&prime;}{y}^{\&prime;}({\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA00002851043300013.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&alpha;}-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="HDA00002851043300013.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&alpha;})=1---\left(5\right)$

Since x ', y ', z' is three major axes orientations of induction index ellipsoid, then the following formula cross term should be zero, so:

α=±45° (6)

When face applied, induction index ellipsoid main shaft will be around z axle rotation 45 degree along (001) for this explanation extra electric field, and as shown in Figure 1, this corner and electric field level are irrelevant, but rotation direction is relevant with direction of an electric field.° then respond to the index ellipsoid main shaftization if get α=45, its equation is:

$(\frac{1}{{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HDA00002851043300011.png,HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_0^2}+{\mathrm{\&gamma;}}_{41}{E}_z)x^{\&prime;2}+(\frac{1}{{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HDA00002851043300011.png,HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_0^2}-{\mathrm{\&gamma;}}_{41}{E}_z)y^{\&prime;2}+\frac{1}{{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HDA00002851043300011.png,HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_0^2}{z}^{\&prime;2}=1---\left(7\right)$

γ ₄₁The order of magnitude be 10 ^-12M/V, γ usually ₄₁E＜＜1 utilizes binomial theorem, can derive three main shaft induction refractive indexes and be respectively:

$n_x^{\&prime;}={\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HDA00002851043300011.png,HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_0+\frac{1}{2}{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HDA00002851043300011.png,HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_0^3{\mathrm{\&gamma;}}_{41}{E}_z$

$n_y^{\&prime;}=n_0-\frac{1}{2}{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HDA00002851043300011.png,HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_0^3{\mathrm{\&gamma;}}_{41}{E}_z$

$n_z^{\&prime;}=n_0---\left(8\right)$

This moment, crystal became biaxial crystal by isotropy.

Above-described is the electrooptical effect of AlGaAs crystal, further describes the transport property of AlGaAs optical waveguide below.The designed AlGaAs optical waveguide of the utility model is symmetrical planar waveguide, and as shown in Figure 2, its sandwich layer and both sides covering all are Al _xGa _1-xThe As material.The ratio difference of Al, the refractive index of crystal is just different, ratio by control Al can make the refractive index of both sides covering identical, the refractive index of refractive index ratio covering that simultaneously can sandwich layer is slightly high, for example can be by extra doped with Al in waveguide, and make the doping of Al in the covering be higher than the doping of Al in the sandwich layer.Skin at the both sides covering all plates electrode then, just can be to AlGaAs crystal on-load voltage.

The transport property of AlGaAs optical waveguide when not powering up

When not powering up, the AlGaAs crystal is isotropic body.Utilizing electromagnetic theory to derive can get, and when light transmits along the y' direction in this waveguide, can be decomposed into two quasi-modes, i.e. TE mould (transverse electric mode) and TM mould (transverse magnetic wave).The TE mould includes only three field component E _x', H _y', H _z', the TM mould also includes only three field component H _x', E _y', E _z', TE mould and TM mould are mutually orthogonal.The field distribution of conducting in this waveguide can be regarded the linear combination of these two kinds of patterns as.The secular equation of TE mould and TM mould is respectively:

$\tan \left(\mathrm{ha}\right)=\frac{2\mathrm{hq}}{h^2-q^2}---\left(9\right)$

$\tan \left(\mathrm{ha}\right)=\frac{2\frac{n_1^2}{{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_2^2}\mathrm{hq}}{h^2-\frac{n_1^4}{{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_2^4}{q}^2}---\left(10\right)$

Wherein, n ₁, n ₂Be respectively the refractive index of waveguide core layer and covering, a is the thickness of waveguide core layer,

$h=\sqrt{n_1^2{\mathrm{<figure-callout\; id="0"\; label="k"\; filenames="HDA00002851043300011.png,HDA00002851043300013.png"\; state="\{\{state\}\}">k</figure-callout>}}_0^2-{\mathrm{\&beta;}}^2},$ $q=\sqrt{{\mathrm{\&beta;}}^2-{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_2^2{\mathrm{<figure-callout\; id="0"\; label="k"\; filenames="HDA00002851043300011.png,HDA00002851043300013.png"\; state="\{\{state\}\}">k</figure-callout>}}_0^2},$ ${\mathrm{<figure-callout\; id="0"\; label="k"\; filenames="HDA00002851043300011.png,HDA00002851043300013.png"\; state="\{\{state\}\}">k</figure-callout>}}_0=\frac{2\mathrm{\&pi;}}{\mathrm{\&lambda;}},$ λ is the wavelength of the femtosecond laser of incident, and β is propagation constant.By finding the solution above-mentioned two equations, can obtain the propagation constant β of TE mould and TM mould respectively, and then can find the solution phase place variation, the mould field distribution isotype characteristic of light in waveguide.Phase differential at any m of waveguide output terminal rank TE mould and n rank TM mould is:

Wherein, L is waveguide length.

The TE mould that can exist in the waveguide and the number of TM mould equate that they all are to be determined by following parameters:

$V=\sqrt{n_1^2-{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_2^2}\frac{\mathrm{\&pi;}}{\mathrm{\&lambda;}}a---\left(12\right)$

When The time, only may there be a TE mould and TM mould, i.e. a TE in the waveguide ₀Mould and TM ₀Mould.And TE in the waveguide ₀Mould and TM ₀The intensity size of mould is determined by field distribution and the polarization direction of incident light.

The transport property of AlGaAs optical waveguide when powering up

When at the AlGaAs optical waveguide outside on-load voltage, according to the electrooptical effect of introducing previously as can be known, the AlGaAs crystal has become biaxial crystal.Wherein, z' direction crystal refractive index n ₀Constant, and x', y' direction crystal refractive index become respectively

With

Because the change of refractive index is very little with respect to original crystal refractive index, thereby the still approximate establishment of scalar Helmholtz equation, the pattern in the waveguide still can be decomposed into TE mould and TM mould.Wherein the electric field component of TM mould mainly is along the z' direction, and z' direction crystal refractive index n ₀Constant, thereby mode propagation constant β is constant.The electric field component of TE mould is along the x' direction, and change has taken place the refractive index of x' direction, thereby mode propagation constant β also changes.The phase differential of any m of waveguide output terminal rank TE mould and n rank TM mould is become by (11):

The change amount of the propagation constant β of TE mould can be obtained by (9).

In hypervelocity electro optic sampling technology, we can design structure and the index distribution of waveguide, make only to have TE in the waveguide ₀Mould and TM ₀Mould.If load a voltage in the waveguide covering outside, can make TE ₀The propagation constant of mould changes, and TM ₀The propagation constant of mould is constant, thereby can change the phase differential of the pattern of two electric field mutually perpendicular direction vibrations of output terminal, and then changes the polarization state of outgoing beam, and we just can utilize this waveguide to survey ultrafast electric signal like this.

The last relation that pattern phase differential and impressed voltage are discussed again.When lambda1-wavelength adopts 1.064 μ m, by control Al _xGa _1-xThe ratio of As crystal Al can be so that waveguide core layer and cladding index be respectively 3.53 and 3.52.Under the situation that satisfies single mode condition (12), we arrange core layer thickness a is 2 μ m, only has TE like this in waveguide ₀Mould and TM ₀Mould.Waveguide both sides cladding thickness all is 8 μ m, and waveguide length is 1mm.Can obtain TE according to (9), (10) ₀Mould and TM ₀The propagation constant of mould, and then can get according to formula (11), do not powering up under the situation, at output cross section TE ₀Mould and TM ₀The phase differential of mould is 0.068.Powering up under the situation, because waveguide core layer and clad crystal change of refractive are respectively on the x' direction that causes of linear electro-optic effect:

$\mathrm{\&Delta;}{n_{1x}}^{\&prime;}=\frac{1}{2}{n}_1^3{\mathrm{\&gamma;}}_{41}{E}_z---\left(14\right)$

$\mathrm{\&Delta;}{n_{2x}}^{\&prime;}=\frac{1}{2}{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA00002851043300013.png"\; state="\{\{state\}\}">n</figure-callout>}}_2^3{\mathrm{\&gamma;}}_{41}{E}_z---\left(15\right)$

According to (9), (10), (13), (14) and (15), we can obtain TE by numerical evaluation ₀Mould and TM ₀Mould is in the phase differential in waveguide output cross section and the relation of on-load voltage, as shown in Figure 3.As shown in Figure 3, on-load voltage and TE ₀Mould and TM ₀Mould is linear at the phase differential in waveguide output cross section.What particularly point out is, making phase differential change the required impressed voltage of π is 335V, and namely half-wave voltage is 335V, and the half-wave voltage in this voltage ratio tradition hypervelocity electro optic sampling technology reduces about 1 order of magnitude.Like this, by adopting AlGaAs optical waveguide transmission laser, can reduce half-wave voltage greatly, this also means presses the ability of acquisition of signal to strengthen greatly to light current, under the constant situation of other condition, can make detectivity improve about order of magnitude.

The utility model proposes and utilize the AlGaAs optical waveguide to transmit femtosecond laser as electro-optic crystal, thereby can reduce half-wave voltage greatly, improve the sensitivity of surveying.At first studied in the literary composition and powering up and do not power up the transport property of laser in the AlGaAs optical waveguide under the situation, and then with concrete model TE mould, the phase differential of TM mould and the relation between the impressed voltage have been discussed, the result shows, on-load voltage and TE ₀Mould and TM ₀Mould is linear at the phase differential in waveguide output cross section.Especially adopt the AlGaAs electro-optical transducer to transmit femtosecond laser, can make half-wave voltage reduce an order of magnitude than classic method, thereby can improve the detectivity to weak signal greatly.

The above only is preferred embodiment of the present utility model; not in order to limit the utility model; all any modifications of within spirit of the present utility model and principle, doing, be equal to and replace and improvement etc., all should be included within the protection domain of the present utility model.

Claims (4)

1. an electro-optical transducer that can be used for the hypervelocity electro optic sampling is characterized in that, described electro-optical transducer comprises the AlGaAs sandwich layer and be positioned at the AlGaAs covering of described AlGaAs sandwich layer both sides that the outside of the AlGaAs covering of described both sides is respectively equipped with electrode; The AlGaAs covering of described both sides is identical to the refractive index of the femtosecond laser of input, and is lower than described AlGaAs sandwich layer to the refractive index of the femtosecond laser of input.

2. electro-optical transducer as claimed in claim 1 is characterized in that, the AlGaAs covering of described both sides satisfies following relation to refractive index and the described AlGaAs sandwich layer of the femtosecond laser of input to the refractive index of the femtosecond laser imported:

Wherein, n ₁, n ₂Be respectively the refractive index of waveguide core layer and covering, a is the thickness of waveguide core layer, and λ is the wavelength of the femtosecond laser of incident.

3. electro-optical transducer as claimed in claim 2 is characterized in that, described lambda1-wavelength is 1.064 μ m, and the refractive index of the AlGaAs covering of described both sides is 3.52, and thickness is 8 μ m; The refractive index of described AlGaAs sandwich layer is 3.53, and thickness is 2 μ m.

4. electro-optical transducer as claimed in claim 3, it is characterized in that, the field distribution of the light that conducts in the described electro-optical transducer is the linear combination of two orthogonal mode fields, and the phase differential of two orthogonal modes in described electro-optical transducer output cross section is linear change with impressed voltage.

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