CN111913309A - Lithium niobate electro-optical switch with ultra-large bandwidth - Google Patents

Lithium niobate electro-optical switch with ultra-large bandwidth Download PDF

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CN111913309A
CN111913309A CN202010741293.4A CN202010741293A CN111913309A CN 111913309 A CN111913309 A CN 111913309A CN 202010741293 A CN202010741293 A CN 202010741293A CN 111913309 A CN111913309 A CN 111913309A
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waveguide
lithium niobate
ultra
phase shifter
gradual change
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何赛灵
黄强盛
林宗兴
陈楷旋
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Zhejiang University ZJU
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Zhejiang University ZJU
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
    • G02F1/0305—Constructional arrangements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/125—Bends, branchings or intersections
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
    • G02F1/0305—Constructional arrangements
    • G02F1/0316—Electrodes
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12035—Materials
    • G02B2006/1204—Lithium niobate (LiNbO3)
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12083—Constructional arrangements
    • G02B2006/12085—Integrated
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12133—Functions
    • G02B2006/12159—Interferometer

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  • Nonlinear Science (AREA)
  • Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
  • Optical Integrated Circuits (AREA)

Abstract

The invention discloses a lithium niobate electro-optical switch with ultra-large bandwidth. The lithium niobate electro-optical switch with the ultra-large bandwidth comprises a plurality of cascaded equal-arm Mach-Zehnder interferometers. The equal-arm Mach-Zehnder interferometer sequentially comprises a gradual change input waveguide, a 3dB beam splitter, a split curved waveguide, a phase shifter, a close curved waveguide, a 3dB beam combiner and a gradual change output waveguide from input to output. The invention can realize the optical switch with ultra-high extinction ratio in the ultra-wide bandwidth range controlled by single voltage by setting the lengths of the phase shifters of a plurality of equal-arm Mach-Zehnder interferometers in the cascade structure, and can also be used as a compact integrated light chopper or an ultra-wide bandwidth modulator.

Description

Lithium niobate electro-optical switch with ultra-large bandwidth
Technical Field
The invention relates to the field of integrated optoelectronic devices, in particular to a lithium niobate electro-optical switch with ultra-large bandwidth.
Background
Integrated photonics is a powerful platform. Compared with a free space optical system, the optical system can improve the performance and stability of the optical system and simultaneously realize the advantages of low cost, small size, replacement and the like. Over the past decade, significant efforts have been made to develop integrated photonic platforms with low loss in the communications band, most typically silicon-based photonics.
Integrated photonic devices in the visible band have received less attention. The visible light band is involved in many fields of application, including optical imaging, biosensing, biomedicine, optogenetics, and the like. For example, alkali and alkaline earth metals, such as cesium, calcium and sodium, are key elements in modern precision optical frequency metrology, magnetic measurements and quantum computing, with atomic transition lines in the visible and near-visible spectral ranges.
Driven by these applications, many materials have been investigated for use in visible light photonic platforms, including silicon dioxide, silicon nitride, aluminum nitride, lithium niobate, and the like. The lithium niobate is a negative uniaxial crystal, has a very large transparent window covering a 400-5000 nm waveband, has a very large electro-optic coefficient and strong optical nonlinearity, and is very suitable for manufacturing modulators and switches and generating nonlinear processes such as wavelength conversion. Optical waveguides in earlier lithium niobate optical devices were formed based on titanium diffusion or annealed proton exchange, and the refractive index difference was very small, so the size of the overall device was usually very large, which is not conducive to the need for large-scale dense integration. In recent years, however, lithium niobate thin films have rapidly developed. The waveguide structure based on the lithium niobate thin film has the advantages of large refractive index difference, small waveguide size, compatibility with CMOS and the like, thereby receiving wide attention. Because the transparent window of the lithium niobate covers the whole visible light wave band, the lithium niobate thin film is a very good choice for the visible light wave band integrated photon platform.
Optical switches are a key device in the field of integrated photonics, and are used to control the presence or absence of optical signals to achieve specific goals. The principle of realizing the optical switch mainly comprises a thermo-optic effect, an electro-optic effect, an acousto-optic effect and the like. Over the past decade, researchers have focused on optical switches placed primarily in the communications band, and have proposed various configurations. Then, in the visible band, the operation of the optical switch may be much less and less. The main reasons of the method can be two, namely, the method is suitable for visible light wave bands and is not provided with a plurality of integrated photon platforms capable of manufacturing high-performance optical switches; secondly, the wavelength of the visible light wave band is too small, the dispersion is too large, and compared with the communication wave band, it is more difficult to realize the optical switch with ultra-large bandwidth and ultra-high extinction ratio in the visible light wave band.
In gas detection, a chopper can be used for modulating light emitted by a light source into light with a certain frequency, and the light is matched with a lock-in amplifier for use, so that the influence of noise with other frequencies on a system can be reduced, and the signal-to-noise ratio of a detection result is improved. The chopper used therein is usually a mechanical device, generally composed of a rotating chopper and a control device thereof, which periodically interrupts light by the continuous rotation of the chopper, thereby modulating continuous light into light having a certain frequency.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a lithium niobate electro-optical switch with an ultra-large bandwidth, which can realize that the extinction ratio is less than-20 dB in the whole 400-900 nm wave band.
A lithium niobate electro-optical switch with ultra-large bandwidth comprises a plurality of equal-arm Mach-Zehnder interferometers which are sequentially connected end to form cascade connection, wherein waveguide structures in the equal-arm Mach-Zehnder interferometers are based on a lithium niobate thin film platform; the equal-arm Mach-Zehnder interferometer sequentially comprises a gradual change input waveguide, a 3dB beam splitter, a split curved waveguide, a phase shifter, a close curved waveguide, a 3dB beam combiner and a gradual change output waveguide from input to output; the 3dB beam splitter comprises a beam splitting middle waveguide, a beam splitting upper waveguide and a beam splitting lower waveguide; wherein, the gradual change input waveguide is connected with the beam splitting intermediate waveguide; the split curved waveguide comprises an upper split curved waveguide and a lower split curved waveguide; one end of the upper split curved waveguide is connected with the beam splitting upper waveguide, and one end of the lower split curved waveguide is connected with the beam splitting lower waveguide; the phase shifter comprises an upper phase shifter and a lower phase shifter, wherein the upper phase shifter comprises an upper straight waveguide, a signal electrode and an upper grounding electrode, and the lower phase shifter comprises a lower straight waveguide, a signal electrode and a lower grounding electrode; the close-to-bend waveguide comprises an upper close-to-bend waveguide and a lower close-to-bend waveguide; the 3dB beam combiner comprises a beam combining middle waveguide, a beam combining upper waveguide and a beam combining lower waveguide; one end of an upper straight waveguide of the upper phase shifter is connected with an upper near curved waveguide, and one end of a lower straight waveguide is connected with a lower near curved waveguide; one end close to the bent waveguide at the upper part is connected with the beam combining upper waveguide of the 3dB beam combiner, and one end close to the bent waveguide at the lower part is connected with the beam combining lower waveguide of the 3dB beam combiner; the combined beam intermediate waveguide is connected with the gradual change output waveguide.
The optical switch is provided with a plurality of cascaded equal-arm Mach-Zehnder interferometers, and the number of the cascaded Mach-Zehnder interferometers and the length of the corresponding phase shifter are selected to realize the ultrahigh extinction ratio in the required ultrahigh bandwidth range.
The substrate of the lithium niobate thin film platform is lithium niobate, the buried oxide layer is silicon dioxide, the covering layer is silicon dioxide, and the waveguide structure layer is x-cut thin film lithium niobate; the side wall of the waveguide has an inclined angle theta; the operating mode used in the waveguide is the TE fundamental mode.
The width of the beam splitting middle waveguide is gradually changed from wide to narrow, the widths of the beam splitting upper waveguide and the beam splitting lower waveguide are gradually changed from narrow to wide, and gaps between the beam splitting middle waveguide and the beam splitting upper waveguide and between the beam splitting lower waveguide in the whole gradual change process are kept unchanged.
The upper straight waveguide and the lower straight waveguide are used for connecting the input and the output of the optical field; the signal electrode and the upper grounding electrode are arranged on the left side and the right side of the upper straight waveguide and are used for being connected with a signal source; the signal electrode and the lower grounding electrode are arranged on the left side and the right side of the lower straight waveguide and are used for being connected with a signal source; under a push-pull structure (GSG), a signal electrode is connected to the positive end of a signal source, and an upper grounding electrode and a lower grounding electrode are connected to the negative end of the signal source together; when the signal source voltage is zero, in the upper phase shifter and the lower phase shifter, the effective refractive indexes of TE fundamental modes in the upper straight waveguide and the lower straight waveguide are not changed, and the phase difference of the light fields output by the upper straight waveguide and the lower straight waveguide is 0; when the signal source voltage is not zero, a phase difference exists between the light fields finally output by the upper straight waveguide and the lower straight waveguide.
When the signal source voltage is half-wave voltage, the phase difference of the light fields finally output by the upper straight waveguide and the lower straight waveguide is pi, the effective refractive index variation of the TE fundamental mode is equal to a large inverse sign, and the half-wave voltage is reduced by half.
The width of the beam combination middle waveguide is gradually changed from narrow to wide, the widths of the beam combination upper waveguide and the beam combination lower waveguide are gradually changed from wide to narrow, and gaps among the beam combination middle waveguide, the beam combination upper waveguide and the beam combination lower waveguide are kept unchanged in the whole gradual change process; when the phase difference of the optical fields input into the beam combination upper waveguide and the beam combination lower waveguide is 0, the optical field combination beam enters a TE fundamental mode of the beam combination middle waveguide after gradual change; when the phase difference of the optical fields input into the upper beam combination waveguide and the lower beam combination waveguide is pi, the optical field combination beam enters a TE high-order mode of the middle beam combination waveguide after gradual change, and if the width of the output waveguide is controlled to gradually change to a single-mode width, the TE high-order mode is changed into a radiation mode and is lost.
The invention has the beneficial effects that:
(1) the invention adopts a thin film lithium niobate platform, the minimum part size is 100nm, the prior art can process, and the manufacture is relatively simple;
(2) the 3dB beam splitter and the 3dB beam combiner are formed by utilizing three gradient waveguides in the equal-arm Mach-Zehnder interferometer, and the 3dB beam splitter and the 3dB beam combiner can realize ultra-low loss beam splitting and beam combining in an ultra-large bandwidth;
(3) the waveguide oxide buried layer and the covering layer are thicker, the distance between the electrode and the waveguide is longer, the curvature radius of the bent waveguide is larger, and the loss caused by the electrode and the waveguide is negligible theoretically;
(4) the invention utilizes a plurality of cascaded equal-arm Mach-Zehnder interferometers, and the grounding electrodes of the phase shifter parts of the equal-arm Mach-Zehnder interferometers are connected with the negative end of a control signal together, and the signal electrodes are connected with the positive end of the control signal together, so that the whole structure can be controlled by a single voltage.
(5) The invention utilizes a plurality of cascaded equal-arm Mach-Zehnder interferometers, and the spectral transmittance of the whole structure is the product of the spectral transmittances of the corresponding equal-arm Mach-Zehnder interferometers, so that the ultra-high extinction in an ultra-large bandwidth range can be realized.
Drawings
FIG. 1 is a top view of the structure of an equal arm Mach-Zehnder interferometer.
FIG. 2 is a cross-sectional view of a waveguide in an equal arm Mach-Zehnder interferometer.
FIG. 3 is a cross-sectional view of an upper phase shifter in an equal arm Mach-Zehnder interferometer.
Fig. 4 is a single-ended output diagram of a 3dB splitter in an equal-arm mach-zehnder interferometer.
Fig. 5 is a graph of spectral transmittance for an equal-arm mach-zehnder interferometer MZI1 phase shifter section length of L1=3 mm.
Fig. 6 is a graph of spectral transmittance for an equal-arm mach-zehnder interferometer MZI2 phase shifter section length of L2=5 mm.
Fig. 7 is a graph of spectral transmittance for an equal-arm mach-zehnder interferometer MZI3 phase shifter section length of L3=8 mm.
Fig. 8 is a graph of spectral transmittance for an equal-arm mach-zehnder interferometer MZI4 phase shifter section length of L4=12 mm.
Fig. 9 is a structural plan view of the ultra-large bandwidth lithium niobate electro-optical switch composed of a plurality of cascaded equiarm mach-zehnder interferometers (in the figure, the number of the equiarm mach-zehnder interferometers is four).
FIG. 10 is a loss plot for a very large bandwidth lithium niobate electro-optical switch comprised of four cascaded equal arm Mach-Zehnder interferometers.
FIG. 11 is a graph of the extinction ratio of a very large bandwidth lithium niobate electro-optical switch comprised of four cascaded, equal arm Mach-Zehnder interferometers.
Detailed Description
The invention is further illustrated with reference to the following figures and examples.
FIG. 1 is a top view of the structure of an equal arm Mach-Zehnder interferometer. The equal-arm Mach-Zehnder interferometer sequentially comprises a gradual change input waveguide 1, a 3dB beam splitter, a split curved waveguide, a phase shifter, a near curved waveguide, a 3dB beam combiner and a gradual change output waveguide 17 from input to output; the 3dB beam splitter comprises a beam splitting middle waveguide 2, a beam splitting upper waveguide 4 and a beam splitting lower waveguide 3; wherein, the gradual change input waveguide 1 is connected with the beam splitting intermediate waveguide 2; the split curved waveguide comprises an upper split curved waveguide 6 and a lower split curved waveguide 5; wherein, one end of the upper divided curved waveguide 6 is connected with the beam splitting upper waveguide 4, and one end of the lower divided curved waveguide 5 is connected with the beam splitting lower waveguide 3; the phase shifter comprises an upper phase shifter and a lower phase shifter, wherein the upper phase shifter comprises an upper straight waveguide 8, a signal electrode 10 and an upper grounding electrode 11, and the lower phase shifter comprises a lower straight waveguide 7, a signal electrode 10 and a lower grounding electrode 9; the approach bending waveguide comprises an upper approach bending waveguide 13 and a lower approach bending waveguide 12; the 3dB beam combiner comprises a beam combining middle waveguide 16, a beam combining upper waveguide 15 and a beam combining lower waveguide 14; wherein, one end of the upper straight waveguide 8 of the upper phase shifter is connected with the upper near curved waveguide 13, and one end of the lower straight waveguide 7 is connected with the lower near curved waveguide 12; one end of the upper bent waveguide 13 close to the upper beam combining waveguide 15 of the 3dB beam combiner is connected, and one end of the lower bent waveguide 12 close to the lower beam combining waveguide 14 of the 3dB beam combiner is connected; the beam combining intermediate waveguide 16 is connected to a tapered output waveguide 17.
The width of the gradual change input waveguide 1 is gradually changed from 200nm to 800nm, the gradual change length is 100 mu m, and the gradual change input waveguide is used for inputting an equal arm Mach-Zehnder interferometer optical field and controlling the single-mode operation of the waveguide; the waveguide width of the beam splitting middle waveguide 2 is gradually changed from 800nm to 100nm, the waveguide widths of the beam splitting upper waveguide 4 and the beam splitting lower waveguide 3 are gradually changed from 100nm to 800nm, the gradual change length is 300 mu m, and in the gradual change process, gaps Gap =110nm between the beam splitting middle waveguide 2 and the beam splitting upper waveguide 4 and the beam splitting lower waveguide 3 are kept unchanged; the upper and lower divided curved waveguides 6 and 5 have a waveguide width of 800nm and a longitudinal span Lx=160 μm and transverse span Ly=10 μm; the widths of the upper straight waveguide 8 and the lower straight waveguide 7 are 800 nm; the electrode structure adopts a push-pull structure, namely GSG, wherein G represents a grounding electrode, S represents a signal electrode, and the length of the phase shifter part is L; the waveguide width of the upper near curved waveguide 13 and the lower near curved waveguide 12 is 800nm, and the longitudinal span is Lx=160 μm and transverse span Ly=10 μm; the waveguide width of the combined beam middle waveguide 16 is gradually changed from 100nm to 800nm, the waveguide widths of the combined beam upper waveguide 15 and the combined beam lower waveguide 14 are gradually changed from 800nm to 100nm, the gradual change length is 300 mu m, and in the gradual change process, gaps Gap =110nm between the combined beam middle waveguide 16 and the combined beam upper waveguide 15 and the combined beam lower waveguide 14 are kept unchanged; gradually-increasing type electric applianceThe width of the variable output waveguide 17 is graded from 800nm to 200nm, and the grading length is 100 μm, which is used for the loss and filtering of the TE high-order mode.
FIG. 2 is a cross-sectional view of a waveguide in the equal-arm Mach-Zehnder interferometer, the waveguide is based on a lithium niobate thin film platform, and the waveguide structure is a ridge waveguide. Wherein the substrate 18 is lithium niobate with the thickness of 400 μm; buried oxide layer 19 is silicon dioxide and is 2 μm thick; the waveguide structure layer 20 is an x-cut lithium niobate thin film, the total thickness of which is H =130nm, and the unetched thickness is Hslab=90 nm; the side walls of the waveguide present an angle of inclination θ, typically around 60 °, the waveguide width being W; the capping layer 21 is silicon dioxide and has a thickness of 2 μm. Fig. 3 is a cross-sectional view of an upper phase shifter in an equiarm mach-zehnder interferometer, the added parts being a signal electrode 11, an upper ground electrode 10, and gold as an electrode material, the thickness and width of the electrode being 600nm and 10.16 μm, respectively, and the distance between the electrode and the waveguide being G =7 μm, compared to fig. 2. The cross-sectional view of the lower phase shifter is similar.
FIG. 4 is a single-ended output diagram of a 3dB beam splitter in an equal-arm Mach-Zehnder interferometer, where the single-ended output is very close to 50% within the entire 400-900 nm band. Therefore, the 3dB beam splitter can realize 50:50 light splitting with ultralow loss in an overlarge bandwidth.
FIGS. 5, 6, 7 and 8 are graphs of spectral transmittance corresponding to the case where the equal-arm Mach-Zehnder interferometer in FIG. 1 is applied with a static voltage of 3.3V and the case where the phase shifter has a length of 3mm, 5mm, 8mm and 12mm, respectively. As can be seen from fig. 5, 6, 7, and 8, when the voltage applied to the electrodes of the equal-arm mach-zehnder interferometer is not changed and the length L of the phase shifter portion is changed, the corresponding output spectrum changes with the change of the length L of the phase shifter portion, and only a very small band can satisfy the requirement of high extinction ratio, and cannot satisfy the requirement of ultrahigh extinction ratio within the ultra-large bandwidth. Therefore, the optical switch based on the single equal-arm Mach-Zehnder interferometer cannot meet the requirement of ultrahigh extinction ratio in an ultra-large bandwidth in a visible light wave band. And a plurality of cascade equal-arm Mach-Zehnder interferometers are adopted, and the spectral transmittance of the whole structure is the product of the spectral transmittance of each equal-arm Mach-Zehnder interferometer. By reasonably selecting the number of cascaded Mach-Zehnder interferometers and the length of the corresponding phase shifter, the ultrahigh extinction ratio can be realized within the required ultrahigh bandwidth range.
Fig. 9 is a structural plan view of a super-large bandwidth lithium niobate electro-optical switch composed of a plurality of cascaded equal-arm mach-zehnder interferometers, where the number of the equal-arm mach-zehnder interferometers in this embodiment is four. The four equal-arm mach-zehnder interferometers MZI1, MZI2, MZI3, MZI4 have exactly the same parameters as the equal-arm mach-zehnder interferometer described in fig. 1, except for the phase shifter section length. The lengths of the phase shifters of the four equal-arm Mach-Zehnder interferometers are L1=3mm，L2=5mm，L3=8mm，L4=12 mm. The grounding electrodes of the phase shifter parts of the four equal-arm Mach-Zehnder interferometers are connected to the negative end of a control signal, and the signal electrodes of the phase shifter parts are connected to the positive end of the control signal, so that the whole structure can be controlled by a single voltage.
Since buried oxide layer 18 and capping layer 21 are thicker, the bend radius separating the bend waveguide, near the bend waveguide, is larger, the electrode is farther from the waveguide, the transmission loss, the bend loss, and the loss due to the electrode of the waveguide are negligible, and only the losses of the 3dB beam splitter and the 3dB beam combiner are considered. FIG. 10 is a loss plot for a very large bandwidth lithium niobate electro-optical switch comprised of four cascaded equal arm Mach-Zehnder interferometers. As can be seen from FIG. 10, the loss is theoretically less than 0.25dB over the entire 400-900 nm wide band range, which is attributed to the ultra-large bandwidth and ultra-low loss of the operation of the 3dB beam splitter and 3dB beam combiner.
FIG. 11 is a graph of the extinction ratio of a very large bandwidth lithium niobate electro-optical switch comprised of four cascaded, equal arm Mach-Zehnder interferometers. As can be seen from FIG. 11, the extinction ratio is less than-20 dB in the whole ultra-large bandwidth range of 400-900 nm. The ultra-large bandwidth covers the whole visible light wave band and part of the near infrared wave band. Near 900nm, the extinction ratio is less than-25 dB, so the bandwidth still has the potential to continue to expand.
The above-described embodiments are intended to illustrate rather than to limit the invention, and any modifications and variations of the present invention are within the spirit of the invention and the scope of the appended claims.

Claims (7)

1. A lithium niobate electro-optical switch with ultra-large bandwidth is characterized in that: the optical switch comprises a plurality of equal-arm Mach-Zehnder interferometers which are sequentially connected end to form cascade connection, and a waveguide structure in the equal-arm Mach-Zehnder interferometers is based on a lithium niobate thin film platform; the equal-arm Mach-Zehnder interferometer sequentially comprises a gradual change input waveguide, a 3dB beam splitter, a split curved waveguide, a phase shifter, a close curved waveguide, a 3dB beam combiner and a gradual change output waveguide from input to output; the 3dB beam splitter comprises a beam splitting middle waveguide, a beam splitting upper waveguide and a beam splitting lower waveguide; wherein, the gradual change input waveguide is connected with the beam splitting intermediate waveguide; the split curved waveguide comprises an upper split curved waveguide and a lower split curved waveguide; one end of the upper split curved waveguide is connected with the beam splitting upper waveguide, and one end of the lower split curved waveguide is connected with the beam splitting lower waveguide; the phase shifter comprises an upper phase shifter and a lower phase shifter, wherein the upper phase shifter comprises an upper straight waveguide, a signal electrode and an upper grounding electrode, and the lower phase shifter comprises a lower straight waveguide, a signal electrode and a lower grounding electrode; the close-to-bend waveguide comprises an upper close-to-bend waveguide and a lower close-to-bend waveguide; the 3dB beam combiner comprises a beam combining middle waveguide, a beam combining upper waveguide and a beam combining lower waveguide; one end of an upper straight waveguide of the upper phase shifter is connected with an upper near curved waveguide, and one end of a lower straight waveguide is connected with a lower near curved waveguide; one end close to the bent waveguide at the upper part is connected with the beam combining upper waveguide of the 3dB beam combiner, and one end close to the bent waveguide at the lower part is connected with the beam combining lower waveguide of the 3dB beam combiner; the combined beam intermediate waveguide is connected with the gradual change output waveguide.
2. The ultra-large bandwidth lithium niobate electro-optic switch of claim 1, wherein: the optical switch is provided with a plurality of cascaded equal-arm Mach-Zehnder interferometers, and the number of the cascaded Mach-Zehnder interferometers and the length of the corresponding phase shifter are selected to realize the ultrahigh extinction ratio in the required ultrahigh bandwidth range.
3. The ultra-large bandwidth lithium niobate electro-optic switch of claim 1, wherein: the substrate of the lithium niobate thin film platform is lithium niobate, the buried oxide layer is silicon dioxide, the covering layer is silicon dioxide, and the waveguide structure layer is x-cut thin film lithium niobate; the side wall of the waveguide has an inclined angle theta; the operating mode used in the waveguide is the TE fundamental mode.
4. The ultra-large bandwidth lithium niobate electro-optic switch of claim 1, wherein: the width of the beam splitting middle waveguide is gradually changed from wide to narrow, the widths of the beam splitting upper waveguide and the beam splitting lower waveguide are gradually changed from narrow to wide, and gaps between the beam splitting middle waveguide and the beam splitting upper waveguide and between the beam splitting lower waveguide in the whole gradual change process are kept unchanged.
5. The ultra-large bandwidth lithium niobate electro-optic switch of claim 1, wherein: the upper straight waveguide and the lower straight waveguide are used for connecting the input and the output of the optical field; the signal electrode and the upper grounding electrode are arranged on the left side and the right side of the upper straight waveguide and are used for being connected with a signal source; the signal electrode and the lower grounding electrode are arranged on the left side and the right side of the lower straight waveguide and are used for being connected with a signal source; under the push-pull structure, a signal electrode is connected to the positive end of a signal source, and an upper grounding electrode and a lower grounding electrode are connected to the negative end of the signal source together; when the signal source voltage is zero, in the upper phase shifter and the lower phase shifter, the effective refractive indexes of TE fundamental modes in the upper straight waveguide and the lower straight waveguide are not changed, and the phase difference of the light fields output by the upper straight waveguide and the lower straight waveguide is 0; when the signal source voltage is not zero, a phase difference exists between the light fields finally output by the upper straight waveguide and the lower straight waveguide.
6. The ultra-large bandwidth lithium niobate electro-optic switch of claim 5, wherein: when the signal source voltage is half-wave voltage, the phase difference of the light fields finally output by the upper straight waveguide and the lower straight waveguide is pi, the effective refractive index variation of the TE fundamental mode is equal to a large inverse sign, and the half-wave voltage is reduced by half.
7. The ultra-large bandwidth lithium niobate electro-optic switch of claim 1, wherein: the width of the beam combination middle waveguide is gradually changed from narrow to wide, the widths of the beam combination upper waveguide and the beam combination lower waveguide are gradually changed from wide to narrow, and gaps among the beam combination middle waveguide, the beam combination upper waveguide and the beam combination lower waveguide are kept unchanged in the whole gradual change process; when the phase difference of the optical fields input into the beam combination upper waveguide and the beam combination lower waveguide is 0, the optical field combination beam enters a TE fundamental mode of the beam combination middle waveguide after gradual change; when the phase difference of the optical fields input into the upper beam combination waveguide and the lower beam combination waveguide is pi, the optical field combination beam enters a TE high-order mode of the middle beam combination waveguide after gradual change, and if the width of the output waveguide is controlled to gradually change to a single-mode width, the TE high-order mode is changed into a radiation mode and is lost.
CN202010741293.4A 2020-07-29 2020-07-29 Lithium niobate electro-optical switch with ultra-large bandwidth Pending CN111913309A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113534564A (en) * 2021-07-14 2021-10-22 华中科技大学 Method and device for improving scanning angle of optical phased array

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113534564A (en) * 2021-07-14 2021-10-22 华中科技大学 Method and device for improving scanning angle of optical phased array

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