CN215986791U

CN215986791U - High-speed modulator

Info

Publication number: CN215986791U
Application number: CN202120710515.6U
Authority: CN
Inventors: 陆明之
Original assignee: Ningbo Yuanxin Optoelectronic Technology Co ltd
Current assignee: Ningbo Yuanxin Optoelectronic Technology Co ltd
Priority date: 2021-04-07
Filing date: 2021-04-07
Publication date: 2022-03-08
Anticipated expiration: 2031-04-07

Abstract

The utility model discloses a high-speed modulator, which comprises an optical waveguide structure and a traveling wave electrode structure, wherein the optical waveguide structure comprises a first optical waveguide arm and a second optical waveguide arm, the traveling wave electrode comprises a grounding electrode and a signal wire, the signal wire applies electric fields or voltages in opposite directions to the first optical waveguide arm and the second optical waveguide arm, the first optical waveguide arm and the second optical waveguide arm are both of a folding structure, and the signal wire is folded along with the first optical waveguide arm and the second optical waveguide arm, so that the electric fields or voltages applied to the first optical waveguide arm and the second optical waveguide arm are kept unchanged, or the electric fields or voltages applied to the first optical waveguide arm and the second optical waveguide arm are synchronously changed. Compared with the prior art, the utility model has the advantages that: the folding structure of the optical waveguide is matched with a ground-signal-ground coplanar waveguide traveling wave electrode structure to realize the modulation addition of light at different sections of the waveguide, so that the optical waveguide has longer phase shift waveguide length within the limited device length, and simultaneously, the bandwidth can be ensured to meet the application requirement.

Description

High-speed modulator

Technical Field

The utility model relates to an optical component, in particular to a high-speed modulator.

Background

With the continuous development of optical communication systems, the requirements for the transmission rate of optical communication are continuously increased, and the requirements for the performance of the modulator are also higher and higher. The performance of the traditional direct modulation laser or the electroabsorption modulation laser can meet the requirement of data transmission at medium and short distances, but breakthrough progress is difficult to be made on signal transmission at ultra-long distances and ultra-high transmission rates, so that a Mach-Zehnder (MZ) modulator based on phase modulation becomes a non-choice of the ultra-high performance modulator of this generation and even the next generation. High-speed MZ modulators that are commercially available today include conventional bulk-material lithium niobate modulators, silicon optical modulators, and indium phosphide-based modulators, while thin-film lithium niobate modulators are also favored by the industry because of their excellent electro-optic performance and low material cost, and are well-established as the solution to be used in next-generation high-speed modulators. During the operation of these modulators, due to the high operating voltage, high bandwidth drivers capable of outputting high voltage are required, and these drivers are usually very expensive, which is one of the important reasons for the high cost of the application of these modulators.

The typical MZ modulator is based on the principle that a beam splitter is used to split an optical signal into two beams, an electric field is applied to a material, the electro-optic effect of the material is utilized to change the refractive index of the material, so that the phases of the optical signals of the two arms are changed, and finally the optical signals with the phase difference between the two arms are combined by a beam combiner and the phase difference is converted into an intensity signal. For example, a coplanar waveguide line electrode structure and a modulator disclosed in chinese patent application No. 202010409764.1, or a silicon-based lithium niobate high-speed optical modulator and a method for manufacturing the same disclosed in chinese patent application No. 201710255559.2.

A very important criterion of the modulator is, among others, the voltage required to cause the pi phase shift, i.e. the half-wave voltage. The size of the half-wave voltage determines the working voltage of the modulator, if the half-wave voltage of the modulator is reduced to be below 1.5V, the driving power supply of the modulator can be provided by a CMOS circuit, and the application cost of the modulator is greatly reduced; due to the characteristics of phase modulation, the phase modulation arm length of the modulator can only be increased with the aim of reducing the half-wave voltage of the device under the same waveguide structure and traveling wave electrode structure (c.wang, m.zhang, x.chen, m.bertrand, a.shams-Ansari, s.chandrasekhar, p.winzer, and m.local, "Integrated lithium anode electro-optical modulation CMOS operating at-compatible" Nature 562, 101-one 104 (2018)).

In fact, increasing the modulation arm length of the modulator will reduce the modulation bandwidth of the device to some extent and effectively reduce the half-wave voltage to below 1.5V, but the result of this is that the length of the device is above 2cm unless the half-wave voltage-length product (V) is reached in the future_πL) is reduced, otherwise a large reduction in the length of the device is difficult. The excessive device length makes the device encounter no less difficulty in commercialization, and the size of the device becomes a difficult problem to be solved in the packaging process.

In summary, it is difficult to maintain a small device size in the case of implementing a low half-wave voltage in the MZ modulator of today, and it is urgently needed to implement a high-speed modulator with a low half-wave voltage and a small size on a chip.

SUMMERY OF THE UTILITY MODEL

The technical problem to be solved by the present invention is to provide a high-speed modulator, which can reduce the half-wave voltage of the device without increasing the length of the device, and can ensure that the bandwidth of the device meets the application requirements.

The technical scheme adopted by the utility model for solving the technical problems is as follows: a high-speed modulator comprising an optical waveguide structure and a traveling wave electrode structure, said optical waveguide structure comprising a first optical waveguide arm and a second optical waveguide arm, said traveling wave electrode comprising a ground electrode and a signal line, said signal line applying electric fields or voltages of opposite directions to the first optical waveguide arm and the second optical waveguide arm, characterized in that: the first optical waveguide arm and the second optical waveguide arm are both of a folded structure, and the signal line is folded along with the first optical waveguide arm and the second optical waveguide arm, so that electric fields or voltages applied to the first optical waveguide arm and the second optical waveguide arm are kept unchanged, or the electric fields or voltages applied to the first optical waveguide arm and the second optical waveguide arm are synchronously changed.

According to an aspect of the present invention, the electric field or voltage on the two optical waveguide arms remains constant, the first and second optical waveguide arms each include a straight arm and a curved arm connected between two adjacent straight arms, the straight arm of each first optical waveguide arm has the straight arm of the corresponding second optical waveguide arm, and the curved arm of each first optical waveguide arm has the curved arm of the corresponding second optical waveguide arm; the straight arm of the first optical waveguide arm and the straight arm corresponding to the second optical waveguide arm are arranged in parallel at intervals, and the bent arm of the first optical waveguide arm and the bent arm of the second optical waveguide arm are crossed with each other; the traveling wave electrode is of a single driving structure, the signal line comprises an input electrode, a middle electrode and an output electrode, the middle electrode comprises a straight electrode and a bent electrode, the straight electrode corresponds to the straight arm of the first optical waveguide arm or the second optical waveguide arm, and the straight electrode is located between the straight arms corresponding to the first optical waveguide arm and the second optical waveguide arm.

According to an aspect of the present invention, the electric fields or voltages on the two optical waveguide arms are changed synchronously, the first optical waveguide arm and the second optical waveguide arm each include a straight arm and a curved arm connected between adjacent two straight arms, the straight arm of each first optical waveguide arm has the straight arm of the corresponding second optical waveguide arm, and the curved arm of each first optical waveguide arm has the curved arm of the corresponding second optical waveguide arm; the straight arm of the first optical waveguide arm and the straight arm corresponding to the second optical waveguide arm are arranged in parallel at intervals, and the bent arm of the first optical waveguide arm and the bent arm corresponding to the second optical waveguide arm are arranged in parallel at intervals and do not intersect with each other; the traveling wave electrode is of a dual-drive structure with two signal lines, wherein one signal line comprises a first input electrode, a first middle electrode and a first output electrode, and the other signal line comprises a second input electrode, a second middle electrode and a second output electrode; each intermediate electrode comprises a straight electrode and a bent electrode, the straight electrode of the first intermediate electrode is arranged in parallel with the straight arm corresponding to the first optical waveguide arm, the bent electrode of the first intermediate electrode is intersected with the bent arm corresponding to the first optical waveguide arm, the straight electrode of the second intermediate electrode is arranged in parallel with the straight arm corresponding to the second optical waveguide arm, and the bent electrode of the second intermediate electrode is intersected with the bent arm corresponding to the second optical waveguide arm.

In order to realize the input, modulation and output of light, the optical waveguide structure comprises a first beam splitter and a second beam splitter, an input optical waveguide as an input end of the waveguide structure, an output optical waveguide as an output end of the waveguide structure, and one end of each of the first optical waveguide arm and the second optical waveguide arm is connected to the output end of the first beam splitter, the other end of each of the first optical waveguide arm and the second optical waveguide arm is connected to the input end of the second beam splitter, and the output optical waveguide is connected to the output end of the second beam splitter.

In order to reduce the coupling loss of the device, the optical waveguide structure further comprises an input optical waveguide serving as an input end of the waveguide structure and an output optical waveguide serving as an output end of the waveguide structure, and the input optical waveguide and the output optical waveguide both adopt a mode spot converter structure.

Compared with the prior art, the utility model has the advantages that: the optical waveguide structure is set to be a folding structure, and the modulation addition of light in different sections of the waveguide is realized by matching with a ground-signal-ground coplanar waveguide traveling wave electrode structure, so that the optical waveguide structure can have longer phase-shift waveguide length, namely longer optical length and phase-shift length, in the limited device length, and meanwhile, the bandwidth can be ensured to meet the application requirement; the electro-optical effects of the two arms are opposite in direction, the phase change caused by modulation is opposite, a natural push-pull effect is formed, half-wave voltage of the modulator is reduced, and the voltage required by pi phase shift is caused; the microwave phase velocity of the traveling wave electrode is designed to be matched with the group velocity of light so as to obtain higher modulation bandwidth; the length of the traveling wave electrode is the same as that of the optical waveguide in the modulation process, matching of the optical signal and the electric signal is kept, and bandwidth attenuation caused by mismatching of signal propagation length is reduced.

Drawings

Fig. 1 is a schematic diagram of an optical waveguide structure of a high-speed modulator according to a first embodiment of the present invention.

Fig. 2 is a schematic structural diagram of a traveling-wave electrode of a high-speed modulator according to a first embodiment of the present invention.

Fig. 3 is a schematic cross-sectional structure diagram of an optical waveguide according to a first embodiment of the present invention.

Fig. 4 is a schematic diagram of an optical waveguide structure of a high-speed modulator according to a second embodiment of the utility model.

Fig. 5 is a schematic diagram of a traveling-wave electrode structure of a high-speed modulator according to a second embodiment of the present invention.

Fig. 6 is a diagram showing simulation results of the depth of the optical waveguide, the electrode spacing, the half-wave voltage, and the loss of the optical waveguide mode in the first and second embodiments of the present invention.

Fig. 7 is a simulation diagram of characteristic impedance of an optical waveguide structure and a simulation result diagram of microwave phase refractive index according to the first and second embodiments of the present invention.

Fig. 8 is a diagram of bandwidth simulation and calculation results according to the first and second embodiments of the present invention.

Detailed Description

The utility model is described in further detail below with reference to the accompanying examples.

Example one

Referring to fig. 1-3, a high speed modulator includes an optical waveguide structure and a traveling wave electrode structure, the optical waveguide structure being shown in dashed lines in fig. 2.

The optical waveguide structure includes a first input optical waveguide 11, a second input optical waveguide 12, a first splitter 13, a first optical waveguide arm 14, a second optical waveguide arm 15, a second splitter 16, a first output optical waveguide 17, and a second output optical waveguide 18. The first input optical waveguide 11 and the second input optical waveguide 12 serve as input ends of the optical waveguide structure, and the first output optical waveguide 17 and the second output optical waveguide 18 serve as output ends of the optical waveguide structure. The beam splitter may be a multimode interference coupler.

The first beam splitter 13 and the second beam splitter 16 are both 2 × 2 multimode interference couplers. The first input optical waveguide 11 and the second input optical waveguide 12 are connected to two input ends of a first splitter 13, respectively, and the first optical waveguide arm 14 and the second optical waveguide arm 15 are connected to two output ends of the first splitter 13, respectively.

The first optical waveguide arm 14 is an integral structure and includes a first straight arm 141, a first curved arm 142, a second straight arm 143, a second curved arm 144, and a third straight arm 145, which are connected in sequence. The second optical waveguide arm 15 is an integral structure, and includes a fourth straight arm 151, a third curved arm 152, a fifth straight arm 153, a fourth curved arm 154, and a sixth straight arm 155, which are connected in this order. Each straight arm of the first optical waveguide arm 14 corresponds to one straight arm of the second optical waveguide arm 15, and each curved arm of the first optical waveguide arm 14 corresponds to one curved arm of the second optical waveguide arm 15.

One end of the first straight arm 141 is connected to one output end of the first beam splitter 13, the other end of the first straight arm is connected to one end of the first bending arm 142, the other end of the first bending arm 142 is connected to one end of the second straight arm 143, the other end of the second straight arm 143 is connected to one end of the second bending arm 144, the other end of the second bending arm 144 is connected to one end of the third straight arm 145, and the other end of the third straight arm 145 is connected to one input end of the second beam splitter 16. One end of the fourth straight arm 151 is connected to the other output end of the first beam splitter 13, the other end of the fourth straight arm 151 is connected to one end of the third curved arm 152, the other end of the third curved arm 152 is connected to one end of the fifth straight arm 153, the other end of the fifth straight arm 153 is connected to one end of the fourth curved arm 154, the other end of the fourth curved arm 154 is connected to one end of the sixth straight arm 155, and the other end of the sixth straight arm 155 is connected to the other input end of the second beam splitter 16. The first output optical waveguide 17 and the second output optical waveguide 18 are connected to two output terminals of the second splitter 16, respectively.

The first rectilinear arm 141, the second rectilinear arm 143, the third rectilinear arm 145, the fourth rectilinear arm 151, the fifth rectilinear arm 153, and the sixth rectilinear arm 155 are arranged in parallel, and each extends in the left-right direction as viewed in fig. 1 and 2. The straight arms of the first optical waveguide arm 14 and the straight arms of the second optical waveguide arm 15 are arranged alternately, that is, the fourth straight arm 151, the first straight arm 141, the fifth straight arm 153, the second straight arm 143, the sixth straight arm 155, and the third straight arm 145. Thus, the first curved arm 142 and the third curved arm 152 have a first intersection 191 and the second curved arm 144 and the fourth curved arm 154 have a second intersection 192.

This connection is such that the straight arms of the first optical waveguide arm 14 and the second optical waveguide arm 15 are always kept in a relatively fixed positional relationship, that is, the straight arm of the first optical waveguide arm 14 is located above (above in plan view) the straight arm of the second optical waveguide arm 15 at a corresponding position as viewed in fig. 1 and 2. The intersection of the two optical waveguide arms can be adjusted in distance so that the intersection is 90 degrees perpendicular to reduce loss and crosstalk caused by the crossing of the optical waveguides.

Preferably, the input optical waveguide and the output optical waveguide may adopt a gradually widening structure or a mode spot converter structure to reduce the coupling loss of the device. The input/output optical waveguide and the two optical waveguide arms are single mode waveguides, and the connection part of the single mode waveguide and the multimode waveguide region of the multimode interference coupler can adopt tapered graded waveguides, so that the connection loss is reduced. The appropriate waveguide etch depth and waveguide width can be selected to adjust the mode size in the optical waveguide so that the modulation electric field can better act on the core layer of the optical waveguide without causing large additional waveguide loss.

The microwave phase velocity of the traveling wave electrode is designed to match the group velocity of the light to obtain a higher modulation bandwidth. The traveling wave electrode structure is a single driving structure and comprises a grounding electrode 21, an input electrode 22, an intermediate electrode 23 and an output electrode 24, wherein the grounding electrode 21 covers the optical waveguide structure, and the input electrode 22, the intermediate electrode 23 and the output electrode 24 form a signal line. The input electrode 22 serves as an input terminal of a signal line, and the output electrode 24 serves as an output terminal of the signal line. The optical waveguide structure may be located outside the ground electrode 21 area only at the input and output sections, using a single input traveling wave electrode structure in conjunction with a crossed optical waveguide structure to achieve superposition of the modulation on each segment of the optical waveguide modulation on the phase modulation arm. The size design and the optical waveguide structure design of each part are all enabled to enable the characteristic impedance to be close to 50 ohms so as to reduce the reflection of radio-frequency signals during inputting, outputting and transmitting on the electrodes, and therefore the modulation bandwidth is increased. The size design of the modulating portion of the traveling wave electrode (intermediate electrode 23) and the design of the optical waveguide structure can be changed so that the magnitude of the microwave phase velocity is as close as possible to the group velocity of light to reduce the bandwidth attenuation caused by the mismatch of the microwave phase velocity and the group velocity of light.

The input electrode 22 is connected to the fourth rectilinear arm 151 on the side away from the first rectilinear arm 141, and is connected to the third rectilinear arm 145 on the side away from the sixth rectilinear arm 155. The intermediate electrode 23 is connected between the input electrode 22 and the output electrode 24, and is an integral structure including a first straight electrode 231, a first bent electrode 232, a second straight electrode 233, a second bent electrode 234 and a third straight electrode 235, which are connected in sequence, wherein one end of the first straight electrode 231 is connected with the input electrode 22, the connection position may be a bent shape, the other end of the first straight electrode 231 is connected with one end of the first bent electrode 232, the other end of the first bent electrode 232 is connected with one end of the second straight electrode 233, the other end of the second straight electrode 233 is connected with one end of the second bent electrode 234, the other end of the second bent electrode 234 is connected with one end of the third straight electrode 235, the other end of the third straight electrode 235 is connected with the output electrode 24, and the connection position may be a bent shape. Each straight arm of the first optical waveguide arm 14 corresponds to one straight electrode of the intermediate electrode 23, and each bent arm of the first optical waveguide arm 14 corresponds to one bent electrode of the intermediate electrode 23.

The first rectilinear electrode 231 is located between the fourth rectilinear arm 151 and the first rectilinear arm 141, the second rectilinear electrode 233 is located between the fifth rectilinear arm 153 and the second rectilinear arm 143, and the third rectilinear electrode 235 is located between the sixth rectilinear arm 155 and the third rectilinear arm 145. Preferably, the straight arms are parallel to each other, i.e. a 180 ° turn is made at each curved arm. That is, when the positions of the first optical waveguide arm 14 and the second optical waveguide arm 15 are interchanged, the direction of the electric field of the intermediate electrode 23 is also changed. Thus, the electric field or voltage applied to each of the first optical waveguide arm 14 and the second optical waveguide arm 15 is kept constant, and the opposite electric field or voltage is applied to both optical waveguide arms at all times.

The length of the signal line of the traveling wave electrode structure is equal to the length of the optical waveguide structure. The bent part of the traveling wave electrode structure is designed, and the equivalent length of the bent part is equal to the length of the corresponding optical waveguide so as to reduce the mismatch of signals. The input and output ends of the electrode and the input and output ends of the optical waveguide are in the mutually vertical direction by utilizing the bending structure of the electrode, so that the test or the packaging of the device is convenient. I.e. with reference to fig. 2, the direction of the first input optical waveguide 11 and the second input optical waveguide 12 is preferably perpendicular to the direction of the input electrode 22. The appropriate electrode-to-waveguide spacing can be selected to allow the modulating electric field to act better on the core of the optical waveguide without causing large additional waveguide losses.

The first optical waveguide arm 14, the second optical waveguide arm 15, and the intermediate electrode 23 may be bent more times, as long as the relative positions are maintained. The term "integral structure" as used herein refers to an integral extension, and "connected" is used to describe the positional relationship between two adjacent segments, and does not mean that an external mechanism is required to facilitate the connection.

The traveling wave electrode structure shown in this embodiment is a variation of a typical coplanar microstrip structure, and is composed of a signal line and two coplanar large-area grounds, so as to conduct a high-frequency signal to pass through the device for final output.

In this embodiment, the optical waveguide structure is an x-cut lithium niobate thin film wafer on silicon, and as shown in fig. 3, the optical waveguide cross-sectional structure of the first embodiment of the present invention is a schematic view of an optical waveguide cross-section structure, which sequentially includes, from bottom to top, a substrate 101, a buried layer 102, a thin film 103, a gold electrode 104, and a cap layer 105, where the substrate 101 is a silicon substrate, the buried layer 102 is a silicon oxide layer, the thin film 103 is an x-cut lithium niobate thin film, and the cap layer 105 is silicon oxide. Preferably, the buried layer 102 has a thickness of 2 μm, the membrane 103 has a thickness of 0.6 μm, the optical waveguide is a shallow etched waveguide, the ridge height is selected to be 0.3 μm, the gold electrode 104 has a thickness of 0.9 μm, and the cap layer 105 has a thickness of 0.8 μm.

The electro-optic effect of the material is related to the direction of the electric field, and the signal on one electrode is V_RFThe refractive indexes of the two arms can be changed towards different directions simultaneously, for example, when the electric field directions in the x-cut thin-film lithium niobate material are respectively towards the + y direction and the-y direction, the modulation phase difference of the two arms is twice that of the single arm, so that the half-wave voltage is one half of that of the single arm.

The first optical waveguide arm 14 and the second optical waveguide arm 15 can utilize heightThe phase of the optical waveguide is modulated to the working point by a fast biaser or by an independent bias electrode by using a thermo-optic effect, an electro-optic effect or other modes, and then a high-speed modulation electric signal V is added to the electrode corresponding to the first optical waveguide arm 14_RF1The electric field applied to the first optical waveguide arm 14 can change the refractive index of the material by the electro-optic effect to change the mode effective refractive index Δ n in the optical waveguide_eff1Second optical waveguide arm 15 is applied with high-speed modulation signal V_RF2The mode effective refractive index on the optical waveguide is changed to Δ n_eff2The change in phase on the two waveguide arms can then be expressed as:

in the above formula, λ is the wavelength of the incident light of the high-speed modulator, and L is the length of the phase shift region of the optical waveguide arm.

Referring to fig. 2, the working principle of the present embodiment is as follows:

incident light generated by laser output by an external laser in an end-face coupling or vertical coupling mode enters a first input optical waveguide 11 or a second input optical waveguide 12, and is divided into two beams by a first beam splitter 13, and the two beams enter a first optical waveguide arm 14 and a second optical waveguide arm 15 respectively; meanwhile, a high-speed RF signal is input from the input electrode 22 into the phase modulation arm (middle electrode 23) region of the modulator, modulated in the phase modulation arm region, light and the modulation signal propagate forward at the same speed on the modulation arm, the modulation signal modulates the phases of the upper and lower optical waveguide arms to be opposite in the process of propagating to the right (l.arizmedia, "Photonic applications of lithium nitride crystals," physical states solidi (a)201,253 minus 283 (2004)), and the effective refractive indexes of the two optical waveguide arms are respectively changed, so that the phases of the optical signals of the two optical waveguide arms are respectively changed, and high-speed modulation of low voltage is realized. After passing through the first intersection 191 of the optical waveguide structure, the optical signals of the two optical waveguide arms propagate to the left, the first optical waveguide arm 14 is still above the second optical waveguide arm 15, the traveling wave electrode also propagates to the left through the first bending electrode 232, and the modulation signal is mutually accumulated in the leftward modulation process and the first rightward modulation process according to the property of the lithium niobate material; after the direction is turned for many times, the two beams of light convert the phase difference signal of the two arms into an intensity signal of the light in the second beam splitter 16, and the modulation of the light is completed. Namely, the two optical waveguide arms are applied with opposite phase shift electric fields or voltages to cause opposite phase changes, finally, the phase difference of the two arms is the sum of the phase modulations of the two arms, and the phase difference is converted into intensity information after passing through the multimode interference coupler, so that the phase modulation function is realized.

By the structure, the higher effective modulation length is realized in the limited device length, and the half-wave voltage value of the unit device length is obviously reduced; in addition, because the beam splitter and the beam combiner of the modulator both adopt 2 multiplied by 2 multimode interference couplers, higher extinction ratio can be realized under specific input and output ports.

Example two

Referring to fig. 4 and 5, the difference from the first embodiment is that the positions of the first optical waveguide arm 14 and the second optical waveguide arm 15 are interchanged during the extension process, that is, the first bending arm 142 and the third bending arm 152 are arranged side by side, the second bending arm 144 and the fourth bending arm 154 are arranged side by side, the bending arc length (including the radius) of the first bending arm 142 is smaller than that of the third bending arm 152, and the bending arc length (including the radius) of the second bending arm 144 is larger than that of the fourth bending arm 154. Thus, the first optical waveguide arm 14 and the second optical waveguide arm 15 extend so as to be always parallel to each other without any intersection therebetween, and each straight arm includes, from bottom to top in fig. 4, a fourth straight arm 151, a first straight arm 141, a second straight arm 143, a fifth straight arm 153, a sixth straight arm 155, and a third straight arm 145.

The traveling wave electrodes are of a dual-drive structure, and the two input electrodes are respectively the first input electrode 221 and the second input electrode 222, the same two intermediate electrodes are respectively the first intermediate electrode 231 and the second intermediate electrode 232, and the same two output electrodes 24 are respectively the first output electrode 241 and the second output electrode 242. The traveling wave electrode structure realizes the superposition of the modulation of each section of optical waveguide on the phase modulation arm by matching a dual-drive traveling wave electrode structure with a simple bent folded optical waveguide. The input and output portions may use a bent structure such that the lengths of the input and output portions of the two signal lines are the same to reduce the mismatch of signals.

The first middle electrode 231 is an integrated structure and includes a first straight electrode 2311, a first bent electrode 2312, a second straight electrode 2313, a second bent electrode 2314 and a third straight electrode 2315 which are connected in sequence; the second intermediate electrode 232 is an integral structure and includes a fourth straight-line electrode 2321, a second curved electrode 2322, a fifth straight-line electrode 2323, a fourth curved electrode 2324 and a sixth straight-line electrode 2325 which are connected in sequence. The first bent electrode 2312 of the first intermediate electrode 231 and the third bent electrode 2322 of the second intermediate electrode 232 are arranged in parallel, and the second bent electrode 2314 of the first intermediate electrode 231 and the fourth bent electrode 2324 of the second intermediate electrode 232 are arranged in parallel in the same manner as the bent arms of the first optical waveguide arm 14 and the second optical waveguide arm 15 are arranged in parallel.

The first rectilinear electrode 2311 of the first intermediate electrode 231 is located on the side of the first rectilinear arm 141 of the first optical waveguide arm 14 away from the fourth rectilinear arm 151 of the second optical waveguide arm 15, the second rectilinear electrode 2313 is located on the side of the second rectilinear arm 143 facing the fifth rectilinear arm 153, and the third rectilinear electrode 2315 is located on the side of the third rectilinear arm 145 away from the sixth rectilinear arm 155. The fourth rectilinear electrode 2321 of the second intermediate electrode 232 is located on the side of the fourth rectilinear arm 151 of the second optical waveguide arm 15 facing the first rectilinear arm 141 of the first optical waveguide arm 14, the fifth rectilinear electrode 2323 is located on the side of the fifth rectilinear arm 153 away from the second rectilinear arm 143, and the sixth rectilinear electrode 2325 is located on the side of the sixth rectilinear arm 155 facing the third rectilinear arm 145.

That is, the first intermediate electrode 231 extends along the first optical waveguide arm 14 and intersects the first optical waveguide arm 14 at each bending, and the second intermediate electrode 232 extends along the second optical waveguide arm 15 and intersects the second optical waveguide arm 15 at each bending.

V exists when the modulation signals applied to the two optical waveguide arms_RF1＝-V_RF2When the two-arm modulation signal is a differential signal, the voltageChange to 2V_RF1Thus the half wave voltage is one half of the single arm modulation.

Referring to fig. 4, the working principle of the present embodiment is as follows:

incident light generated by laser output by an external laser in an end-face coupling or vertical coupling mode enters a first input optical waveguide 11 or a second input optical waveguide 12, and is divided into two beams by a first beam splitter 13, and the two beams enter a first optical waveguide arm 14 and a second optical waveguide arm 15 respectively; simultaneously, high speed differential RF signal (V)_RFand-V_RF) Entering the phase modulation arm (first intermediate electrode 231 and second intermediate electrode 232) area of the modulator by the first input electrode 221 and the second input electrode 222 respectively, where the modulated light and the modulation signal propagate forward on the modulation arm at the same speed, and the modulation electrode is always above the modulated optical waveguide during the forward propagation, so that the modulation on each segment of the modulated optical waveguide is cumulative; after the direction is turned for many times, the two beams of light convert the phase difference signal of the two arms into an intensity signal of the light in the second beam splitter 16, and the modulation of the light is completed.

First, in the dc case of a high-speed modulator, the change Δ n of the refractive index of the lithium niobate material in the electrostatic field can be expressed as the following formula:

in the above formula, n_eIs the extraordinary refractive index of lithium niobate, E_z(x, z) is the electric field along the z direction. Thus the change in effective refractive index Δ n_effCan be expressed as the following equation:

in the above formula e_z(x, z) is the optical field intensity of the TE mode in the optical waveguide structure, and gamma represents the optical field limiting factor of the mode in the lithium niobate waveguide. Therefore, when light travels a certain distance L in the waveguide, the phase change of the light can be representedThe following formula:

when the phase change is pi, the voltage applied to the electrode is the half-wave voltage V of the device_πThe voltage-length constant V can be calculated_πL can be expressed as the following equation:

the limiting factor gamma can be calculated through simulation of an electrostatic field, so that V is obtained_πAnd L. FIG. 6 is a graph showing simulation results of different optical waveguide etching depths and electrode distances under the conditions that the length L is equal to 0.5cm and the optical waveguide width is 1.5 μm, wherein the etching depth of 0.3 μm and the electrode distance of 5 μm are selected from the graph as the optical waveguide structures of the first embodiment and the second embodiment, and the simulation results of the optical waveguide loss are 0.1dB/cm and V is equal to V_πThe simulation result of L was 1.75V · cm. On the basis of the simulation result, the length of each of the three modulation arms in the first and second embodiments is 0.4cm, so that the effective modulation arm length is 1.2cm, corresponding to the simulated half-wave voltage V_πIs 1.46V.

Next, the characteristic impedance and the microwave refractive index of the optical waveguide structure are simulated and calculated by using a finite element calculation method, and a simulated value and a characteristic impedance value of the microwave refractive index are about 50 ohms when the width of the metal electrode is 12.5 μm and the thickness of the silicon oxide cap layer is 0.8 μm, as shown in fig. 7, the radio frequency simulation result of the optical waveguide structure of the first embodiment and the second embodiment is obtained.

The theoretical electro-optic response curve can be obtained through the radio frequency simulation result, and can be represented by the following formula:

in the above formula, alpha is the attenuation constant of the electrode, and L is the length of the electrodeDegree, b is given by the equation

Definition of wherein n_μIs the refractive index of microwave, n_oThe parameter b represents the mismatch between the refractive index of the microwave and the refractive index of the group of light.

FIG. 8 shows the electro-optic response curve calculated by the above formula, and it can be seen from the curve in the figure that the theoretical 3-dB bandwidth value of the first and second embodiments can reach 40 GHz.

In the two embodiments, the optical waveguides are both single-mode waveguides, the interference region of the multimode interference coupler is actually multimode waveguides, and the two are connected by adopting the tapered graded waveguides, so that the loss during connection can be greatly reduced.

As can be seen from the above description, the high-speed modulators provided in the first and second embodiments of the present invention effectively realize the folding of the long-arm long MZ modulator using the bent and/or crossed folded waveguide structure (the "folding" in the present invention refers to the folding on a plane, such as the paper surface shown in fig. 1 or fig. 4, rather than the folding in the direction of the through electrode) and the traveling-wave electrode structure of the coplanar waveguide. The utility model has the characteristics of small half-wave voltage, large manufacturing tolerance and high extinction ratio, and can realize a high-performance high-speed modulator with small length.

In addition, the selection of the chip material of the device can be changed into other phase modulation materials, the optical waveguide structure of the device can be correspondingly changed along with the change of the material, and the length of the device can be reduced through the idea of the utility model. The etching depth and width of the optical waveguide can be adjusted to obtain different modulation effects, which can affect the half-wave voltage and waveguide loss of theoretical modulation. The spacing of the metal can be adjusted to achieve different modulation effects, which can affect the half-wave voltage and waveguide loss of the theoretical modulation. The radio frequency parameters of the device can be adjusted by adjusting the thickness or the material of the upper cover layer silicon oxide and the lower cover layer silicon oxide. The radio frequency parameters of the device can be adjusted by adjusting the width of the metal electrode, the metal thickness and the metal spacing width. More or less folds can be realized by adjusting the bending times of the waveguide and the electrode and the direction of the output waveguide, so as to obtain different required half-wave voltages and 3-dB electro-optic response bandwidths. The termination of the modulation signal can be realized by externally connecting a 50 ohm terminal resistor with the high-frequency probe or connecting the 50 ohm terminal resistor with a gold wire or manufacturing the 50 ohm terminal resistor on a chip.

Claims

1. A high-speed modulator comprising an optical waveguide structure comprising a first optical waveguide arm (14) and a second optical waveguide arm (15), and a traveling-wave electrode structure comprising a ground electrode (21) and a signal line applying electric fields or voltages of opposite directions to the first optical waveguide arm (14) and the second optical waveguide arm (15), characterized in that: the first optical waveguide arm (14) and the second optical waveguide arm (15) are both of a folded structure, and the signal line is folded along with the first optical waveguide arm (14) and the second optical waveguide arm (15), so that the electric field or voltage applied to the first optical waveguide arm (14) and the second optical waveguide arm (15) is kept constant, or the electric field or voltage applied to the first optical waveguide arm (14) and the second optical waveguide arm (15) is synchronously changed; the waveguide structure further comprises an input optical waveguide serving as an input end of the waveguide structure and an output optical waveguide serving as an output end of the waveguide structure, and the input optical waveguide and the output optical waveguide both adopt a spot size converter structure.

2. The high speed modulator of claim 1, wherein: the first optical waveguide arm (14) and the second optical waveguide arm (15) each comprise a straight arm and a curved arm connected between two adjacent straight arms, the straight arm of each first optical waveguide arm (14) has a corresponding straight arm of the second optical waveguide arm (15), and the curved arm of each first optical waveguide arm (14) has a corresponding curved arm of the second optical waveguide arm (15); the straight arm of the first optical waveguide arm (14) and the corresponding straight arm of the second optical waveguide arm (15) are arranged at intervals in parallel, and the bent arm of the first optical waveguide arm (14) and the bent arm of the second optical waveguide arm (15) are crossed with each other; the traveling wave electrode is of a single driving structure, the signal line comprises an input electrode (22), an intermediate electrode (23) and an output electrode (24), the intermediate electrode (23) comprises a straight electrode and a bent electrode, the straight electrode corresponds to a straight arm of the first optical waveguide arm (14) or the second optical waveguide arm (15), and the straight electrode is located between the straight arms corresponding to the first optical waveguide arm (14) and the second optical waveguide arm (15).

3. The high speed modulator of claim 1, wherein: the first optical waveguide arm (14) and the second optical waveguide arm (15) each comprise a straight arm and a curved arm connected between two adjacent straight arms, the straight arm of each first optical waveguide arm (14) has a corresponding straight arm of the second optical waveguide arm (15), and the curved arm of each first optical waveguide arm (14) has a corresponding curved arm of the second optical waveguide arm (15); the straight arms of the first optical waveguide arm (14) and the corresponding straight arms of the second optical waveguide arm (15) are arranged at intervals in parallel, and the bent arms of the first optical waveguide arm (14) and the corresponding bent arms of the second optical waveguide arm (15) are arranged at intervals in parallel and do not intersect with each other; the traveling wave electrode is in a dual-drive structure with two signal lines, wherein one signal line comprises a first input electrode (221), a first intermediate electrode (231) and a first output electrode (241), and the other signal line comprises a second input electrode (222), a second intermediate electrode (232) and a second output electrode (242); each intermediate electrode comprises a straight electrode and a bent electrode, the straight electrode of the first intermediate electrode (231) is arranged in parallel with the straight arm corresponding to the first optical waveguide arm (14), the bent electrode of the first intermediate electrode (231) is intersected with the bent arm corresponding to the first optical waveguide arm (14), the straight electrode of the second intermediate electrode (232) is arranged in parallel with the straight arm corresponding to the second optical waveguide arm (15), and the bent electrode of the second intermediate electrode (232) is intersected with the bent arm corresponding to the second optical waveguide arm (15).

4. The high speed modulator of claim 1, wherein: the optical waveguide structure comprises an input optical waveguide as an input end of the waveguide structure, an output optical waveguide as an output end of the waveguide structure, a first beam splitter (13) and a second beam splitter (16), the input optical waveguide is connected to the input end of the first beam splitter (13), one end of each of a first optical waveguide arm (14) and a second optical waveguide arm (15) is connected to the output end of the first beam splitter (13), the other end of each of the first optical waveguide arm (14) and the second optical waveguide arm (15) is connected to the input end of the second beam splitter (16), and the output optical waveguide is connected to the output end of the second beam splitter (16).