|Posted date||Nov 2, 2018|
|International application number||2018JP011467|
|International publication number||WO 2018174179|
|Date of international filing||Mar 22, 2018|
|Date of international publication||Sep 27, 2018|
|Abstract||The optical modulator pertaining to the present invention is provided with: an optical waveguide having two branching optical waveguides, the optical waveguide being formed on a waveguide substrate in which at least a portion thereof has an electro-optical effect; and a modulating electrode provided with first lines disposed facing each other so as to sandwich the two branching optical waveguides, and second and third lines, the first through third line conductors being electromagnetically coupled with each other and having line lengths so as to essentially resonate with an inputted high-frequency signal for optical modulation. In the optical modulator, the modulating electrode is disposed so that voltages having mutually different signs are induced in the second line and the third line, respectively, and the modulating electrode is excited on the basis of the high-frequency signal for optical modulation.|
|Outline of related art and contending technology||
Elimination of the dead zones of the radio wave, an apartment or office for the purpose of distributing signals to a wireless, radio over fiber system and referred to as a radio signal and the direct modulation, an optical fiber radio signal transmission and is returned to a distant radiating system has been attracting attention.
The optical modulator, in such a system is a key device.In recent years, with the high frequency radio signal, the optical modulator is at a high frequency millimeter wave band or the like are required to operate, in general the higher the frequency and the loss of the structure of the problem of an increase in the modulation efficiency is decreased.Therefore, the millimeter wave band with high efficiency even at a high frequency band such as an optical modulator is expected.Conventional, for example a high frequency millimeter wave band high-quality signal light modulation, using an electro-optical effect optical modulator has been used.
Fig. 8A is an example of a conventional optical modulator 1 according to the general plan view showing the configuration of the present invention.In addition, the light modulator 8A Fig. 8B is an E-E ' is a vertical cross-sectional view taken along the line.
Fig. 8A and in Fig. 8B, the optical modulator according to the conventional example 1, substrate 51, the optical waveguide 52, the buffer layer 53, the modulation electrode 54, the ground electrode 55, 56 are provided.Here, the substrate 51, the electro-optical effect from the z-cut substrate of lithium niobate. 52 Is an optical waveguide, the surface of the substrate 51 formed by thermal diffusion of titanium metal, and the input optical waveguide 52a, a pair of bifurcated from the phase modulation waveguide 52b, and 52c, they are merged with the optical waveguide 52d and the output, constitute a Mach-Zehnder interferometer.Z direction for the change in the refractive index by the electric field, the phase modulation waveguide 54 is one of the modulation electrodes (here the phase modulation waveguide 52b) are positioned directly above.The buffer layer 53, the optical waveguide 52 a portion of the light propagated through the modulation electrode 54 and the ground electrode 55, 56 in order to prevent absorbed by a thin film.
Configured as described above and in the optical modulator according to the conventional example 1, the modulation electrode 59 is applied to the modulated wave 54, as shown in the electric line 151,152, and the phase modulation waveguide 52b is 52c, the vertical directions opposite to each other since the electric field is applied, the phase modulation waveguide 52b, 52c in the direction of the refractive index change caused by the electro-optical effect and in the opposite direction.Therefore, the input optical waveguide 52a to 57 is input, the phase modulation waveguide halves 52b, 52c propagate in opposite directions when the light undergoes phase modulation, the propagation light is output to the optical waveguide 52d when the merging of the interference light intensity is modulated, and output light 58.
Fig. 9 is, in the conventional example disclosed in Patent Document 1 2 is a plan view showing the configuration of the optical modulator according to the present invention.
9 In FIG., 2 is the optical modulator according to the conventional example, the electro-optical effect characteristics and the optical path (optical waveguide) 68, 68 formed along the optical path, for applying an electric field in the optical path 61 and the modulation electrode, modulating electrode 61 is formed so as to face the common electrode (ground electrode) 66, 67 and, a modulator electrode 61 substantially in the center of the stub connected at 64, and 65, the connection wiring pattern 62 and the tapered transformer to the feed lines 63 are connected to each other.Then, the modulation electrode 61 to the open end of the resonance operation is performed, the modulation efficiency is enhanced.Stub 64, 65 is, not reflected in the modulated wave input to the modulation electrode 61 efficiently as, a function for achieving impedance matching.
Fig. 10 is, in the conventional example disclosed in Patent Document 2 3 showing a configuration of the optical modulator according to a longitudinal sectional view.
10 In FIG., 3 is the optical modulator according to the conventional example, about 10μm of the thickness of the electro-optical effect to the thin plate 71 is formed in the optical waveguide 72, the modulation electrodes so as to sandwich the thin plate 71 is disposed.As a modulation electrode, the first electrode 1 and the upper surface of the thin plate 71, the first electrode 2 and the lower surface of the thin plate, the first signal electrode is 1 75a and 74 and the ground electrode, the first electrode 2 and the ground electrode 75b.The buffer layer 73a, light 73b propagating through the waveguide 72 a portion of the light absorbed by the modulating electrode in order to prevent a thin film. 71 Is a thin plate 77 the support substrate via the adhesive layer 76 is adhered to.Of the optical modulator of the present configuration is characterized in that, as shown in Fig. 8A as compared with a general optical modulator, the signal electrode 74 and the thin plate 71 formed on the back surface of the ground electrode 73b and the electric field generated by the voltage between the light modulation to be employed.Thus, the modulation efficiency is improved.
Fig. 11A is, in the conventional example disclosed in Patent Document 3 4 is a plan view showing the configuration of the optical modulator according to the present invention.In addition, Fig. 11B is a parallel coupling line 11A of the M11 propagation mode is excited in the 33 when the F-F of the 'vertical cross-sectional view taken along the line, parallel coupling line 11A of Fig. 11C is a propagation mode in the 33 M12 when the excitation of F-F' is a vertical cross-sectional view taken along the line.
Fig. 11A in, (LiTaO 3) single crystal of lithium tantalate, lithium niobate (LiNbO 3) single crystal substrate having an electrooptic effect such as surface portion 31, such as a proton exchange method using a benzoic acid is used to form the optical waveguide 32 is provided.The optical waveguide 32, 38a one branching point of the 2, 38b 2 optical waveguide 32a in two branches, and branches to step 32b, the optical waveguide 32x on the inlet side of the input light is input from one of the branch point 2 branches to branch 38a of the optical waveguide 32a, after passing through the 32b, the outlet side of the common branch point 38b of the other optical waveguide 32y is configured such as the one shown.
Further, on the substrate 31, each branch of the optical waveguide 32 the optical waveguide 32a, 32b extend along one line 3 33a, 33b, 33c from the parallel coupling line 33 is provided.Each of the line 33a, each of the inner end 33b, each branch optical waveguide 32a, 32b so as to be positioned directly above a nearly central portion of the formed.In addition, line 33c is, one line 2 33a, 33b are positioned in the middle.Each of the line 33a, 33b, both end portions of the 33c, the connecting lines 36a, 36b are connected to one another via.Further, on the substrate 31, 1 of the parallel coupling line 33 one line 33b connected to the coupling line 33 to cause the parallel resonance of the input signal is applied to the input line 35 is provided.Each line of the parallel coupling line 33 33a-33c, the connecting lines 36a, 36b and 35 is the input line, a vacuum deposition method, a photolithography and etching processes such as aluminum or gold and the like formed using a metal film are respectively constituted.In addition, the back surface of the substrate 31, a metal film formed using the evaporation method or the like provided on the ground plane 34.
The input light, introduced from the inlet side optical waveguide 32x, each branch optical waveguide 32a, passes through 32b, as described below, is exposed to the light modulator.From the input line 35 and the high frequency signal is input, each line of the parallel coupling line 33 33a, 33b, 33c resonance occurs, each gap section 37a, 37b as shown by a dotted line in Fig. 11B electric lines of force represented by the electric field is generated.Then, by electro-optical effect, the optical waveguide branches 32a, 32b having a refractive index of the material constituting the change according to electric field intensity.Therefore, in the outlet side optical waveguide 32y, the optical waveguide branches 32a, 32b and 2 passes through one of the light interference occurs, this interference causes the intensity of output light changes, the optical intensity modulator operates.
Here, the coupling line 3 of line 33a-33c in parallel to the first electrode 33, usually, there is the propagation mode of the type 3, in one mode of propagation 2 of the M11, 11B and M12 will be described below with reference to Fig. 11C.
Fig. 11B mode of propagation in M11, 2 of the optical waveguide branches 32a, 32b in the reverse direction in the vertical electric field applied to the word line 131,132, a phase difference to the light exit side in the optical waveguide 32y since the interference occurs, the light modulation element of the present embodiment, functions as an optical intensity modulator.On the other hand, in the Fig. 11C mode of propagation M12, the optical waveguide branches 32b, 32b to 131,133 of the electric field formed so as to opposite to the direction, the position of the branch optical waveguide 32b is shifted.
Fig. 11B is composed of the propagation mode of the optical modulator is M11, 3 of line 33a, 33b, 33c coupling line can be used in the modulation electrode, 33a of the line 3, 33b, the center of the coupling line 33c by line 0 on both sides of the line 33c is the voltage of the opposite sign to each other in a propagation mode of the light modulation is performed using a high efficiency.Fig. 11C is composed of the propagation mode of the optical modulator is M12, 3 of line 33a, 33b, 33c coupling line can be used in the modulation electrode, 33a of the line 3, 33b, 33c and 33c at the center of the coupling line by line, 33a on both sides of the line, the voltage of the opposite sign to each other between the 33b propagation mode and a high efficiency by using light modulation is performed.In this case, the optical waveguide 32a, and 32b, 33a of the line 3, 33b, 33c and the arrangement relationship is, in Fig. 11a, is slightly different from the Fig. 11b.More specifically, four-branch optical waveguide 32b the lower side of the position of the line 33c has moved so as to spans and are disposed.
|Scope of claims||
|IPC(International Patent Classification)||
National States: AE AG AL AM AO AT AU AZ BA BB BG BH BN BR BW BY BZ CA CH CL CN CO CR CU CZ DE DJ DK DM DO DZ EC EE EG ES FI GB GD GE GH GM GT HN HR HU ID IL IN IR IS JO JP KE KG KH KN KP KR KW KZ LA LC LK LR LS LU LY MA MD ME MG MK MN MW MX MY MZ NA NG NI NO NZ OM PA PE PG PH PL PT QA RO RS RU RW SA SC SD SE SG SK SL SM ST SV SY TH TJ TM TN TR TT TZ UA UG US UZ VC VN ZA ZM ZW
ARIPO: BW GH GM KE LR LS MW MZ NA RW SD SL SZ TZ UG ZM ZW
EAPO: AM AZ BY KG KZ RU TJ TM
EPO: AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR
OAPI: BF BJ CF CG CI CM GA GN GQ GW KM ML MR NE SN ST TD TG
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