WO2018174179A1 - Modulateur optique - Google Patents

Modulateur optique Download PDF

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Publication number
WO2018174179A1
WO2018174179A1 PCT/JP2018/011467 JP2018011467W WO2018174179A1 WO 2018174179 A1 WO2018174179 A1 WO 2018174179A1 JP 2018011467 W JP2018011467 W JP 2018011467W WO 2018174179 A1 WO2018174179 A1 WO 2018174179A1
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optical
line
optical modulator
modulation
waveguide
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PCT/JP2018/011467
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English (en)
Japanese (ja)
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榎原　晃
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公立大学法人兵庫県立大学
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Priority to JP2019506980A priority Critical patent/JP7037199B2/ja
Publication of WO2018174179A1 publication Critical patent/WO2018174179A1/fr

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  • the present invention relates to an optical modulator that is used to modulate light with an electrical signal when transmitting large-capacity information through an optical fiber or transmitting an optical fiber of a radio signal.
  • the optical modulator is a key device in such a system.
  • optical modulators are required to operate at high frequencies such as the millimeter wave band.
  • modulation efficiency increases due to increased loss and structural problems. descend. Therefore, a high-efficiency optical modulator is expected even in a high frequency band such as a millimeter wave band.
  • an optical modulator using an electro-optic effect has been used.
  • FIG. 8A is a plan view showing a configuration of a general optical modulator according to Conventional Example 1.
  • FIG. 8B is a longitudinal sectional view taken along line E-E 'of the optical modulator of FIG. 8A.
  • the optical modulator according to Conventional Example 1 includes a substrate 51, an optical waveguide 52, a buffer layer 53, a modulation electrode 54, and ground electrodes (ground electrodes) 55 and 56.
  • the substrate 51 is a z-cut substrate of lithium niobate having an electro-optic effect.
  • the optical waveguide 52 is formed on the surface of the substrate 51 by thermal diffusion of metal titanium, and the input optical waveguide 52a, a pair of phase modulation waveguides 52b and 52c branched from the input optical waveguide 52a, and an output optical waveguide in which they are joined 52d and constitutes a Mach-Zehnder interferometer.
  • the modulation electrode 54 is disposed immediately above one of the phase modulation waveguides (here, the phase modulation waveguide 52b).
  • the buffer layer 53 is a thin film for preventing a part of light propagating through the optical waveguide 52 from being absorbed by the modulation electrode 54 and the ground electrodes 55 and 56.
  • the phase modulation waveguides 52b and 52c are perpendicular to the phase modulation waveguides 52b and 52c as indicated by the electric force lines 151 and 152, respectively. Since electric fields having directions opposite to each other are applied to the directions, the directions of refractive index change due to the electro-optic effect in the phase modulation waveguides 52b and 52c are opposite to each other. For this reason, the input light 57 to the input optical waveguide 52a is bisected and undergoes phase modulation in opposite directions when propagating through the phase modulation waveguides 52b and 52c, and this propagation light is transmitted to the output optical waveguide 52d. The light intensity is modulated by interference at the time of merging, and becomes output light 58.
  • FIG. 9 is a plan view showing a configuration of an optical modulator according to Conventional Example 2 disclosed in Patent Document 1.
  • FIG. 9 is a plan view showing a configuration of an optical modulator according to Conventional Example 2 disclosed in Patent Document 1.
  • the optical modulator according to Conventional Example 2 includes an optical path (optical waveguide) 68 having electro-optic effect characteristics, a modulation electrode 61 formed along the optical path 68 for applying an electric field to the optical path, Common electrodes (grounding electrodes) 66 and 67 formed to face the modulation electrode 61 and stubs 64 and 65 obliquely connected to substantially the center of the modulation electrode 61, and a wiring 62 and a tapered shape at the connection portion.
  • a power supply line including the transformer 63 is connected. Then, by opening the end of the modulation electrode 61, the resonance operation is performed, and the modulation efficiency is increased.
  • the stubs 64 and 65 have a function for impedance matching so that the modulated wave is efficiently input to the modulation electrode 61 without being reflected.
  • FIG. 10 is a longitudinal sectional view showing a configuration of an optical modulator according to Conventional Example 3 disclosed in Patent Document 2.
  • an optical waveguide 72 having an electro-optic effect is formed on a thin plate 71 having a thickness of about 10 ⁇ m, and a modulation electrode is arranged so as to sandwich the thin plate 71.
  • the modulation electrode includes a first electrode on the upper surface of the thin plate 71 and a second electrode on the lower surface of the thin plate, the first electrode includes a signal electrode 74 and a ground electrode 75a, and the second electrode serves as a ground electrode 75b.
  • the buffer layers 73a and 73b are thin films for preventing a part of light propagating through the optical waveguide 72 from being absorbed by the modulation electrode.
  • the thin plate 71 is bonded to the support substrate 77 through the adhesive layer 76.
  • the characteristic of the optical modulator of this configuration is that the electric field generated by the voltage between the signal electrode 74 and the ground electrode 73b formed on the back surface of the thin plate 71 is also light as compared with the general optical modulator shown in FIG. 8A. It can be used for modulation. Thereby, the modulation efficiency is improved.
  • FIG. 11A is a plan view showing a configuration of an optical modulator according to Conventional Example 4 disclosed in Patent Document 3.
  • FIG. 11B is a longitudinal sectional view taken along line FF ′ when the propagation mode M11 is excited by the parallel coupling line 33 of FIG. 11A
  • FIG. 11C is a propagation mode M12 of the parallel coupling line 33 of FIG. 11A.
  • FIG. 6 is a longitudinal sectional view taken along line FF ′ when is excited.
  • a surface portion of a substrate 31 having an electrooptic effect such as a lithium tantalate (LiTaO 3 ) single crystal or a lithium niobate (LiNbO 3 ) single crystal, is formed using a proton exchange method using benzoic acid or the like.
  • An optical waveguide 32 is provided.
  • the optical waveguide 32 is branched into two branch optical waveguides 32a and 32b at two branch points 38a and 38b, and the input light input from the entrance-side optical waveguide 32x is branched at one branch point 38a. After passing through the two branch optical waveguides 32a and 32b, the other branch point 38b is configured to travel through the common exit-side optical waveguide 32y.
  • a parallel coupling line 33 including three lines 33a, 33b, and 33c extending along the branched optical waveguides 32a and 32b of the optical waveguide 32 is provided.
  • the inner ends of the lines 33a and 33b are formed so as to be positioned immediately above the center of the branch optical waveguides 32a and 32b.
  • the line 33c is located between the two lines 33a and 33b. Both ends of each line 33a, 33b, 33c are connected to each other via connection lines 36a, 36b.
  • an input line 35 for applying an input signal that is connected to one line 33 b of the parallel coupling line 33 and causes the parallel coupling line 33 to resonate is provided.
  • the lines 33a to 33c, the connection lines 36a and 36b, and the input line 35 of the parallel coupling line 33 are respectively configured by a metal film such as aluminum or gold formed by using a process such as vacuum deposition, photolithography, and etching. ing.
  • a ground plane 34 formed using a metal film deposition method or the like is provided on the back surface of the substrate 31.
  • the input light is introduced from the entrance-side optical waveguide 32x and undergoes a light modulation action when passing through the branched optical waveguides 32a and 32b as follows.
  • a high frequency signal is input from the input line 35 and resonance occurs in the lines 33a, 33b, and 33c of the parallel coupling line 33
  • the gaps 37a and 37b are represented by electric lines of force as indicated by dotted lines in FIG. 11B.
  • An electric field is generated.
  • the refractive index of the material constituting the branched optical waveguides 32a and 32b changes according to the electric field strength. Accordingly, in the exit side optical waveguide 32y, interference between the two light beams that have passed through the branched optical waveguides 32a and 32b occurs, and the intensity of the output light changes due to this interference, thereby operating as a light intensity modulator.
  • the propagation mode M11 of FIG. 11B since the electric fields 131 and 132 in the upside down direction are applied to the two branch optical waveguides 32a and 32b, a phase difference occurs in the light wave, and interference occurs in the exit side optical waveguide 32y.
  • the light modulation element of this embodiment functions as a light intensity modulator.
  • the position of the branch optical waveguide 32b is shifted so that the directions of the electric fields 131 and 133 formed in the branch optical waveguides 32b and 32b are opposite to each other.
  • the coupling line formed by the three lines 33a, 33b, and 33c is used as the modulation electrode, so that the center of the coupled line formed by the three lines 33a, 33b, and 33c is obtained.
  • High-efficiency optical modulation is performed using a propagation mode in which the line 33c is 0 and the voltages on both lines have opposite signs.
  • the coupling line formed by the three lines 33a, 33b, and 33c is used as the modulation electrode, so that the center of the coupled line formed by the three lines 33a, 33b, and 33c is obtained.
  • High-efficiency optical modulation is performed using a propagation mode in which voltages between the line 33c and the lines 33a and 33b on both sides have opposite signs.
  • the positional relationship between the optical waveguides 32a and 32b and the three lines 33a, 33b, and 33c is slightly different from those in FIGS. 11a and 11b. More specifically, the arrangement is such that the position of the branch optical waveguide 32b is moved so as to be placed under the line 33c.
  • the optical modulator according to Conventional Example 3 has been proposed with the object of improving this point.
  • the electric field induced between the signal electrode 74 and the ground electrode 75a is directed in the lateral direction, and the electric field is distributed outside the optical waveguide 72, and is not related to light modulation. . Therefore, in Conventional Example 3, only a part of the electric field induced by the modulation signal contributes to the light modulation. If the electric field distribution spreading outside the optical waveguide can be reduced, it is considered that the modulation efficiency can be further improved.
  • the modulation efficiency is improved by using the resonator type modulation electrode.
  • a part of the modulation signal propagating through the modulation electrode is radiated into the substrate as a surface wave.
  • This phenomenon is due to the fact that the substrate operates as a dielectric waveguide, and the modulation signal propagating in the modulation electrode is combined with the propagation wave in the substrate.
  • the modulation signal is resonated to accumulate energy in the modulation electrode to achieve high modulation efficiency.
  • the modulation efficiency is remarkably lowered.
  • An object of the present invention is to solve the above-described problems and to provide an optical modulator capable of performing optical modulation with higher efficiency than ultra-high frequency signals such as millimeter wave bands as compared with the prior art. .
  • An optical modulator includes: An optical waveguide having at least a portion formed on a waveguide substrate having an electro-optic effect and having two branched optical waveguides; The first and second and third lines arranged opposite to each other so as to sandwich the two branch optical waveguides, and are electromagnetically coupled to each other and inputted as an optical modulation high-frequency signal And a modulation electrode comprising first to third line conductors having a line length that substantially resonates with respect to the optical modulator, The modulation electrode is arranged such that voltages of different signs are induced between the second line and the third line based on the high-frequency signal for light modulation, and the modulation electrode is excited. It is characterized by that.
  • the optical modulator according to the present invention it is possible to realize an optical modulator having higher efficiency than a conventional technique even for a high-frequency signal such as a millimeter wave band.
  • FIG. 1B is a longitudinal sectional view taken along line A-A ′ of the optical modulator of FIG. 1A.
  • FIG. 1A and 1B are longitudinal sectional views showing the polarities of voltages generated in line conductors 14, 15a and 15b and the electric field distribution in a waveguide substrate 11 when the optical modulator of FIG. 1A and FIG. 1B is in a propagation mode M1.
  • 1A and 1B are longitudinal sectional views showing the polarities of voltages generated in line conductors 14, 15a and 15b and the electric field distribution in a waveguide substrate 11 in the propagation mode M2 of the optical modulator of FIGS. 1A and 1B.
  • FIGS. 1A and 1B are longitudinal sectional views showing the polarities of voltages generated in line conductors 14, 15a, and 15b and the electric field distribution in a waveguide substrate 11 in the propagation mode M3 of the optical modulator of FIGS. 1A and 1B. It is a top view which shows the structural example of the optical modulator which concerns on Embodiment 2 of this invention.
  • FIG. 3B is a longitudinal sectional view taken along line B-B ′ of the optical modulator of FIG. 3A. It is a top view which shows the structural example of the optical modulator which concerns on the modification of Embodiment 2 of this invention. It is a top view which shows the structural example of the optical modulator which concerns on Embodiment 3 of this invention.
  • FIG. 5B is a longitudinal sectional view taken along line C-C ′ of the optical modulator of FIG. 5A. It is a top view which shows the structural example of the optical modulator which concerns on Embodiment 4 of this invention.
  • FIG. 6B is a longitudinal sectional view taken along line D-D ′ of the optical modulator in FIG. 6A. It is an electromagnetic field analysis simulation result with respect to the optical modulator of FIG. 1A and FIG. 1B, and is a graph showing frequency characteristics of reflection loss.
  • 10 is a plan view showing a configuration of an optical modulator according to Conventional Example 1.
  • FIG. FIG. 8B is a longitudinal sectional view taken along line E-E ′ of the optical modulator in FIG. 8A.
  • FIG. 10 is a plan view showing a configuration of an optical modulator according to Conventional Example 2.
  • FIG. It is a longitudinal cross-sectional view which shows the structure of the optical modulator which concerns on the prior art example 3.
  • 10 is a plan view showing a configuration of an optical modulator according to Conventional Example 4.
  • FIG. 11B is a longitudinal sectional view taken along line F-F ′ in the propagation mode M11 of the optical modulator in FIG. 11A.
  • FIG. 11B is a longitudinal sectional view taken along line F-F ′ in the propagation mode M12 of the optical modulator of FIG. 11A.
  • FIG. FIG. 1A is a plan view showing a configuration example of an optical modulator according to Embodiment 1 of the present invention.
  • FIG. 1B is a longitudinal sectional view taken along the line AA ′ of the optical modulator of FIG. 1A.
  • an optical modulator includes a waveguide substrate 11, an optical waveguide 12 provided on the waveguide substrate 11, and a buffer layer 13 provided on the upper surface of the waveguide substrate 11.
  • a line conductor 19 c provided on the upper surface, a support substrate 20 that is a dielectric substrate supporting the waveguide substrate 11, and a ground conductor 21 disposed on the back surface of the support substrate 20 are configured.
  • each of the line conductors 14, 15a, 15b is a microstrip line having a common ground conductor 21 made of a metal thin film, and the three line conductors 14, 15a, 15b are close to each other so as to be electromagnetically coupled to each other. Therefore, three coupled lines that are electromagnetically coupled to each other are formed, and simultaneously operate as modulation electrodes.
  • the line conductor 19c also constitutes the feed line 19 which is a microstrip line having the ground conductor 21 in common.
  • the line conductor 19c disposed close to the line conductor 15b via the gap 18 is capacitively coupled to the line conductor 15b.
  • the optical waveguide 12 is disposed at two opposing portions 17 sandwiched between both sides of the line conductor 14 of the waveguide substrate 11 and one side of the line conductor 15, and the two line conductors 15a and 15b have both ends thereof. They are short-circuited by the short-circuit portion 22.
  • the waveguide substrate 11 is made of a z-cut substrate of lithium niobate (LiNbO 3 ) having an electro-optic effect (the z axis in crystal engineering faces a direction perpendicular to the waveguide substrate 11).
  • the optical waveguide 12 is formed on the surface of the waveguide substrate 11 by thermal diffusion of titanium metal.
  • the input light 25 is introduced into the optical waveguide 12, branched into two at the branching portion 23, and after passing through the facing portion 17, the light is combined at the multiplexing portion 24, and a Mach-Zehnder interferometer that becomes the output light 26 is obtained. It is composed.
  • a buffer layer 13 made of silicon oxide or the like is formed on the upper surface of the waveguide substrate 11 in order to suppress attenuation of light waves in the optical waveguide 12, and a metal thin film or the like is formed on the buffer layer 13.
  • One line conductor 14 is formed. Further, on the lower surface of the waveguide substrate 11, two line conductors 15 a and 15 b made of a metal thin film or the like are arranged in parallel with the line conductor 14 with a gap 16 therebetween, and both sides of the line conductor 14 are connected. The portions on the inner side (gap portion 16 side) of the line conductors 15a and 15b face each other with the waveguide substrate 11 in between.
  • the waveguide substrate 11 is fixed on a support substrate 20 made of sapphire (single crystal alumina) or the like.
  • FIG. 2A is a longitudinal sectional view showing the polarity of the voltage generated in the line conductors 14, 15a and 15b and the electric field distribution in the waveguide substrate 11 when the optical modulator of FIG. 1A and FIG. 1B is in the propagation mode M1.
  • FIG. 2B is a longitudinal sectional view showing the polarity of the voltage generated in the line conductors 14, 15 a and 15 b and the electric field distribution in the waveguide substrate 11 when the optical modulator of FIG. 1A and FIG. 1B is in the propagation mode M 2.
  • FIG. 2A is a longitudinal sectional view showing the polarity of the voltage generated in the line conductors 14, 15 a and 15 b and the electric field distribution in the waveguide substrate 11 when the optical modulator of FIG. 1A and FIG. 1B is in the propagation mode M 2.
  • 2C is a longitudinal sectional view showing the polarity of the voltage generated in the line conductors 14, 15 a and 15 b and the electric field distribution in the waveguide substrate 11 in the propagation mode M3 of the optical modulator of FIGS. 1A and 1B. 2A to 2C, the line conductor 19c is not shown.
  • the electric field distribution generates strong electric fields 101 and 102 concentrated on the opposing portion 17, and the two opposing portions 17 are in opposite directions. Since the electric fields 101 and 102 are applied to the optical waveguide 12 having the electro-optic effect, the refractive indexes of the two optical waveguides 12 passing through the facing portion 17 change in directions opposite to each other.
  • the input light 25 to the optical waveguide 12 is divided into two and propagates through the respective optical waveguides 12, where they undergo phase modulation in opposite directions, interfere with each other at the multiplexing unit 24, and the light intensity is modulated.
  • the modulation signal input to the feed line 19 excites the propagation mode M2, and the propagation mode M2 repeats reflection at both ends of the modulation electrode, thereby causing resonance at a frequency determined by the length of the line conductor.
  • the energy of the modulation signal is accumulated in the modulation electrode due to resonance, the voltage amplitude of the propagation mode M2 is increased, and a large voltage is induced. Thereby, highly efficient light modulation is realized.
  • the electric field generated by the propagation mode M2 is generated only in a limited region of the facing portion 17, as shown in FIG. 2B. Therefore, since the energy of the input modulation signal is efficiently used for inducing the electric field, an improvement in modulation efficiency can be expected as compared with the conventional example 1 in FIG. 8B. Moreover, since the space
  • the thin plate-like waveguide substrate 11 and the support substrate 20 made of sapphire having a relatively low dielectric constant the equivalent dielectric constant of the substrate viewed from the propagation wave in the modulation electrode can be greatly reduced. Therefore, it is possible to effectively suppress the modulation signal from leaking to the surface wave. This is particularly effective when the modulation electrode is used as a resonator as in this embodiment.
  • the equivalent dielectric constant of the substrate viewed from the propagation wave in the modulation electrode can be greatly reduced, so that the velocity between the propagation wave and the light wave can be reduced. The difference can be reduced, and the modulation efficiency can be improved accordingly.
  • the power supply of the modulation signal will be described.
  • the degree of coupling between the high-frequency signal input to the feed line 19 of the line conductor 19c and the resonance mode that resonates with the modulation electrode can be adjusted.
  • the positional relationship corresponding to the optimum degree of coupling all the energy of the high-frequency signal input to the feed line 19 is converted into the resonance mode, and the efficiency is further improved.
  • the resonance frequencies are also different. Therefore, the resonance mode of the propagation mode M2 can be selectively excited by adjusting the length of the line conductor so that the propagation mode M2 resonates at a desired frequency.
  • the positional relationship and the degree of coupling between the feed line 19 and the modulation electrode will be described below.
  • the line conductors 14, 15a, 15b, the line conductor 19c are substantially orthogonal.
  • the tip of the line conductor 19c is extended, and the gap 18 is formed in the line conductor 15b on the line conductor 19c side.
  • the degree of coupling can be increased by disposing the cover so as to be deeply covered.
  • the line conductor 19c is not necessarily arranged at the center of the line conductor 15b as shown in FIG. 1A.
  • the degree of coupling is the largest, and the degree of coupling can be reduced by shifting to the end.
  • FIG. 7 is a graph showing the electromagnetic loss analysis simulation results for the optical modulators of FIGS. 1A and 1B and showing the frequency characteristics of reflection loss (S 11 ).
  • the horizontal axis represents the frequency (GHz) of the input high-frequency signal
  • the vertical axis represents the reflection loss (dB).
  • the reflection is greatly reduced at the assumed resonance frequency (around 10 GHz), and it can be seen that almost all of the input signal power is coupled to the modulation electrode. Since the resonance frequency can be adjusted by the lengths of the line conductors 15a and 15b, it is possible to resonate at a desired frequency.
  • a resonator structure in which both ends of the line conductors 15a and 15b are short-circuited by the short-circuit portion 22 is used as the modulation electrode, but the ends of the line conductors 15a and 15b are opened without being short-circuited, or
  • the resonator structure can also be configured by short-circuiting one and opening the other, which is also effective.
  • a traveling wave structure that propagates the propagation mode M2 excited by a high frequency signal without resonating in the same direction as the light wave in the optical waveguide 12 is also effective.
  • the two optical waveguides 12 change in refractive index in the same direction, and cannot be modulated.
  • FIG. FIG. 3A is a plan view showing a configuration example of an optical modulator according to Embodiment 2 of the present invention.
  • 3B is a longitudinal sectional view taken along line BB ′ of the optical modulator of FIG. 3A.
  • the same reference numerals as those in FIGS. 1A and 1B are assigned to the same or corresponding components as those in FIGS. 1A and 1B (Embodiment 1). Description of these components is omitted unless necessary.
  • the optical modulator according to the second embodiment is different in the following points from the optical modulator according to the first embodiment in FIGS. 1A and 1B.
  • the line conductors 15 a and 15 b are provided on the upper surface of the waveguide substrate 11, and the line conductor 14 is provided on the lower surface of the waveguide substrate 11.
  • the tip of the line conductor 19c is disposed close to the side of the line conductor 15b via the gap 18, and the line conductor 19c is capacitively coupled to the line conductor 15b. The resonance mode is excited.
  • Other configurations are the same as those of the optical modulator according to the first embodiment.
  • a mode corresponding to the propagation mode M2 in FIG. 2B is excited in which the voltage of the line conductor 14 is 0 and the voltages of the line conductors 15a and 15b on both sides are opposite signs.
  • an electric field in which electric lines of force are represented by 101 and 102 is generated.
  • strong electric fields 101 and 102 in opposite directions are generated in the two opposing portions 17, and efficient light modulation can be performed on the same principle as in the first embodiment.
  • FIG. 4 is a plan view showing a configuration example of an optical modulator according to a modification of the second embodiment of the present invention.
  • the modified example of the second embodiment is inductive coupling by eliminating the gap 18 and directly connecting the line conductor 19c and the line conductor 15b as compared with the second embodiment of FIG. 3A. The method is used.
  • the degree of coupling is determined by the position in the longitudinal direction on the line conductor 15b to which the line conductor 19c is connected.
  • a larger degree of coupling than the capacitive coupling by the gap 18 can be easily obtained.
  • FIG. FIG. 5A is a plan view showing a configuration example of an optical modulator according to Embodiment 3 of the present invention.
  • FIG. 5B is a longitudinal sectional view taken along the line CC ′ of the optical modulator of FIG. 5A.
  • the same reference numerals as those in FIG. 1A and FIG. Description of these components is omitted unless necessary.
  • Embodiment 3 provided the cavity part 27 in the part in which the line conductors 15a and 15b were installed in the upper surface of the support substrate 20.
  • FIG. It is characterized by that. The rest is the same as in the first embodiment. Hereinafter, the difference will be described in detail.
  • the equivalent dielectric constant of the substrate viewed from the propagation wave in the modulation electrode can be greatly reduced.
  • this effect can be further enhanced in the optical modulator according to the third embodiment. That is, since the line conductors 15a and 15b are in contact with the air at the cavity portion 27, the equivalent dielectric constant of the substrate as seen from the propagation wave in the modulation electrode is further reduced, thereby further increasing the surface of the modulation signal. Suppression of leakage to the wave and speed matching between the propagation wave and the light wave in the modulation electrode are realized, and the modulation efficiency is further improved. Even if the depth of the hollow portion 27 is small, it is effective. However, if the depth is larger than the width of the gap portion 16, a great effect is exhibited.
  • FIG. 6A is a plan view showing a configuration example of an optical modulator according to Embodiment 4 of the present invention.
  • FIG. 6B is a longitudinal sectional view taken along line DD ′ of the optical modulator of FIG. 6A. 6A and 6B, the same reference numerals as those in FIGS. 5A and 5B are assigned to the same or corresponding components as those in the third embodiment in FIGS. 5A and 5B. Description of these components is omitted unless necessary.
  • the fourth embodiment is characterized in that a conductor film 28 is formed on the bottom surface of the cavity portion 27 of the third embodiment, as compared with the third embodiment of FIGS. 5A and 5B.
  • the rest is the same as in the third embodiment.
  • the difference will be described in detail.
  • the optical modulator When the conductor film 28 is formed on the bottom surface of the cavity portion 27, when the optical modulator operates in the propagation mode M2, the voltage difference between the line conductors 15a and 15b and the conductor film 28 is also generated in the cavity portion 27. An electric field is induced. For this reason, the dielectric constant felt by the propagating wave is strongly influenced by the dielectric constant of the air in the hollow portion 27 and decreases. Therefore, in the fourth embodiment, compared with the third embodiment, the propagation speed of the propagation wave in the modulation electrode is further increased, and the speed with the light wave in the optical waveguide 12 is further matched, so that the complete speed is achieved. Matching is also possible.
  • the electric field generated in the cavity portion 27 does not contribute to the light modulation, but the dielectric constant of air in the cavity portion 27 is much smaller than that of a general waveguide substrate such as lithium niobate.
  • the energy of the electric field generated in 27 is much smaller than the electric field energy generated in the waveguide substrate 11. Therefore, the decrease in modulation efficiency due to the electric field generated in the cavity portion 27 is negligible, and the influence of the improvement in modulation efficiency due to the speed matching effect is greater.
  • the interval between the optical waveguides 12 constituting the Mach-Zehnder interferometer is 50 ⁇ m
  • the thickness of the support substrate 20 made of sapphire single crystal is 0.5 mm
  • the thickness of the waveguide substrate 11 made of z-cut lithium niobate is 10 ⁇ m
  • the width of the line conductor 14 is 55 ⁇ m
  • the width of the line conductors 15 a and 15 b is 225 ⁇ m
  • the width of the gap 16 is 45 ⁇ m
  • the length of the line conductors 15 a and 15 b is 6.9 mm
  • the overlapping length of the gap 18 10 GHz when the length of the line conductor 15b and the tip of the line conductor 19c in the plan view is 20 ⁇ m
  • the depth of the cavity 27 is 30 ⁇ m
  • the line width of the line conductor 19c is 0.1 mm.
  • the desirable dimensions of each part will be described.
  • a thinner one is advantageous for improving modulation efficiency.
  • the mechanical strength in the fourth embodiment and the mechanical strength in the fourth embodiment is increased.
  • a range of 5 ⁇ m to 100 ⁇ m is highly effective, and a thickness of about 10 ⁇ m is most desirable.
  • the interval between the optical waveguides 12 constituting the Mach-Zehnder interferometer is usually about 20 to 500 ⁇ m.
  • the width of the facing portion 17 is desirably about 5 times or less the thickness of the waveguide substrate 11. From these dimensions, the width of the gap 16 is inevitably determined.
  • the line widths of the line conductors 15a and 15b are narrowed, the characteristic impedance of the propagation wave becomes higher and a higher electric field can be created, but conversely, there is an effect that propagation loss increases. For this reason, depending on the thickness and material of the line conductors 15a and 15b, there is no general optimum value.
  • the waveguide substrate 11 and the support substrate 20 are generally half or more of the width of the line conductor 14. If the thickness is set in a range smaller than the combined length, the effect of the present invention is exhibited.
  • the height (depth) of the hollow portion 27 is effective if the depth is small, but a great effect is exhibited particularly if it is about the width of the gap portion 16 or more.
  • the dielectric constant and refractive index of the waveguide substrate 11, the dielectric constant of the support substrate 20, the line conductors 14, 15a is influenced by many factors such as the size of 15b and the frequency of the modulation signal, it is effective if it is 1/10 or more of the width of the gap 16.
  • the buffer layer 13 is formed in order to suppress attenuation of the light wave in the optical waveguide 12, and a material having a refractive index lower than that of the waveguide substrate 11 is desirable, and a material other than silicon oxide may be used. Further, the thickness of the buffer layer 13 is preferably about 1/50 to 1/10 of the wavelength of the light wave to be used, but it is not always necessary for the light modulation operation, and may not be formed.
  • the material of the waveguide substrate 11 is preferably an electro-optic crystal, lithium niobate or lithium tantalate, which has mechanical strength, but is not necessarily limited to these materials. Further, since only the portion of the optical waveguide 12 needs to have the electro-optic effect, a thin plate is made of another material having mechanical strength, and the optical waveguide having the electro-optic effect is partially built therein. But you can. In such a method, an organic material or a ceramic material having an electro-optic effect can be used.
  • the support substrate 20 may be any material that can support the waveguide substrate 11, and may not necessarily be sapphire. However, as described above, a material having a low dielectric constant is desirable, and a material having a smaller dielectric loss with respect to the modulation signal is desirable.
  • the support substrate 20 it is more preferable to use a material having a lower dielectric constant than the waveguide substrate 11 for the support substrate 20. Further, depending on the situation, it is necessary to sandwich an adhesive for bonding the support substrate 20 and the waveguide substrate 11 between them.
  • the operating frequency (corresponding to the resonant frequency of the resonant electrode) is 10 GHz
  • the electrode spacing for applying an electric field to the optical waveguide is unified to 10 ⁇ m
  • the maximum electric field strength between the electrodes and the electrode length when signals of the same input power are input is shown below.
  • the comparison of the modulation efficiency when operated between the two optical modulators was performed using commercially available electromagnetic field analysis software HFSS (manufactured by Ansys Japan).
  • the analysis conditions were that the operating frequency (corresponding to the resonance frequency) was 10 GHz, each conductor was a gold thick film with a film thickness of 10 ⁇ m, and the distance between the line electrodes at the position where the waveguide was present was 10 ⁇ m.
  • the shape is as described above in the optical modulator according to the fourth embodiment.
  • the substrate 31 is a z-cut lithium niobate crystal having a thickness of 0.5 mm, and the line widths of the lines 33a, 33b, and 33c are 50 ⁇ m, 50 ⁇ m, and 30 ⁇ m, respectively. .
  • the gaps 37a and 37b are both 10 ⁇ m in order to match the conditions with the optical modulator according to the fourth embodiment.
  • the input line 35 of the conventional example 4 is connected to a position (0.8 mm from the center of the resonator electrode) that can be matched with the second resonance mode at a frequency of 10 GHz.
  • Table 1 summarizes the maximum electric field strength between the electrodes where the optical waveguide is located and the resonator length when the signal of the resonance frequency is input.
  • Table 2 summarizes the operation speed, modulation voltage, size, and advantages of the optical modulators according to the comparative example and the embodiment.
  • the line conductor 14 and the line conductors 15a and 15b are formed close to each other with the buffer layer 13, the optical waveguides 12 and 12 and the waveguide substrate 11 interposed therebetween and electromagnetically coupled to each other.
  • a modulation electrode for modulating an optical signal propagating through the optical waveguides 12 and 12 according to a high-frequency signal input via 19 is configured.
  • the line conductors 15a and 15b are formed to face the optical waveguides 12 and 12 branched into two.
  • the line conductors 14, 15a, 15b have a line length that substantially resonates with respect to the input high-frequency signal.
  • the waveguide substrate 11 has an upper surface and a lower surface that are substantially parallel to each other.
  • the line conductor 14 is formed on the upper surface of the waveguide substrate 11 having the two branched optical waveguides 12 and 12 through the buffer layer 13, while the line conductors 15 a and 15 b are conductive. It is formed on the lower surface of the waveguide substrate 11.
  • the line conductors 15a and 15b are formed on the upper surface of the waveguide substrate 11 having the two branched optical waveguides 12 and 12 via the buffer layer 13, while the line conductor 14 is the waveguide substrate. 11 is formed on the lower surface.
  • the line conductor 19c may be formed so as to be electromagnetically, capacitively, or directly coupled to any of the line conductors 14, 15a, 15b.
  • the conductor film 28 may be formed so as to face the line conductors 15a and 15b in at least a part of the hollow portion 27.
  • an electro-optic optical modulator having higher efficiency than a conventional technique can be realized even for a high-frequency signal such as a millimeter wave band.

Landscapes

  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

Selon la présente invention, le modulateur optique comprend : un guide d'onde optique ayant deux guides d'onde optiques de ramification, le guide d'onde optique étant formé sur un substrat de guide d'onde dans lequel au moins une partie associée a un effet électro-optique ; et une électrode de modulation pourvue de premières lignes disposées en regard l'une de l'autre de façon à prendre en sandwich les deux guides d'onde optiques de ramification, et des deuxième et troisième lignes, les premier à troisième conducteurs de ligne étant couplés électromagnétiquement l'un à l'autre et ayant des longueurs de ligne de façon à résonner essentiellement avec un signal haute fréquence entré destiné à une modulation optique. Dans le modulateur optique, l'électrode de modulation est disposée de telle sorte que des tensions ayant des signes mutuellement différents sont induites dans la deuxième ligne et la troisième ligne, respectivement, et l'électrode de modulation est excitée sur la base du signal haute fréquence destiné à une modulation optique.
PCT/JP2018/011467 2017-03-23 2018-03-22 Modulateur optique WO2018174179A1 (fr)

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KR20230048067A (ko) 2020-08-04 2023-04-10 산텐 세이야꾸 가부시키가이샤 근시 치료, 근시 예방 및/또는 근시 진행 억제를 위한 의약

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US8409114B2 (en) 2007-08-02 2013-04-02 Boston Scientific Scimed, Inc. Composite elongate medical device including distal tubular member
US9072874B2 (en) 2011-05-13 2015-07-07 Boston Scientific Scimed, Inc. Medical devices with a heat transfer region and a heat sink region and methods for manufacturing medical devices

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WO2005019913A1 (fr) * 2003-08-21 2005-03-03 Ngk Insulators, Ltd. Dispositif de guide d'ondes optique et modulateur optique de type a onde itinerante
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JP2003156723A (ja) * 2001-09-05 2003-05-30 Ngk Insulators Ltd 光導波路デバイス、光変調器、光変調器の実装構造および光導波路基板の支持部材
JP2004062158A (ja) * 2002-06-03 2004-02-26 Matsushita Electric Ind Co Ltd 光変調素子及び通信システム
WO2005019913A1 (fr) * 2003-08-21 2005-03-03 Ngk Insulators, Ltd. Dispositif de guide d'ondes optique et modulateur optique de type a onde itinerante
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2020166050A (ja) * 2019-03-28 2020-10-08 住友大阪セメント株式会社 光制御素子
JP7218652B2 (ja) 2019-03-28 2023-02-07 住友大阪セメント株式会社 光制御素子
KR20230048067A (ko) 2020-08-04 2023-04-10 산텐 세이야꾸 가부시키가이샤 근시 치료, 근시 예방 및/또는 근시 진행 억제를 위한 의약

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