Superconducting electro-optic modulator

Abstract

This invention relates to a superconducting optical modulator, comprising: a Mach-Zehnder interference structure, wherein the modulation arm waveguide of the Mach-Zehnder interference structure includes a first modulation arm waveguide and a second modulation arm waveguide; and a superconducting modulation electrode, wherein the traveling-wave electrode of the superconducting modulation electrode is an asymmetric coplanar waveguide electrode structure with unequal gap widths on both sides, the traveling-wave electrode including a first traveling-wave electrode and a second traveling-wave electrode connected in parallel, the first traveling-wave electrode and the second traveling-wave electrode respectively acting on the first modulation arm waveguide and the second modulation arm waveguide to achieve modulation of the phase of the optical signal in the Mach-Zehnder interference structure. This invention enables long-distance effective modulation on a small-size chip, thereby significantly reducing the half-wave voltage required by the modulator and meeting the low half-wave voltage and high bandwidth requirements of superconducting optical interconnect applications.

Description

Technical Field

[0001] This invention relates to the field of cross-temperature zone interconnection technology, and in particular to a superconducting optical modulator. Background Technology

[0002] Among existing cross-temperature zone data transmission schemes, optical fiber links have inherent advantages over coaxial cable schemes in terms of physical principles: optical transmission relies on photons rather than charge carriers, has no conductor ohmic heat loss, and has a lower heat load; the bandwidth of optical carriers is much larger than that of electrical signals, enabling higher capacity data transmission; optical signals and electromagnetic signals are not coupled, and are naturally unaffected by electromagnetic crosstalk and interference. Therefore, in cross-temperature zone interconnection of low-temperature superconducting systems, optoelectronic links are a better choice, and low-temperature electro-optic modulators are the core devices for realizing electro-optic signal conversion.

[0003] However, the application of existing electro-optic modulators at low temperatures is limited. For example, silicon-based electro-optic modulators suffer from significant reductions in modulation efficiency and tuning capability at low temperatures due to carrier freeze-drying and thermo-optical failure. Micro-ring resonant electro-optic modulators based on group III / V materials have an inherent trade-off between low power consumption and high-speed modulation because both the driving voltage and modulation bandwidth are limited by the full width at half maximum (FWHM) spectrum characteristics of the resonant cavity. Mach-Zehnder electro-optic modulators based on lithium niobate substrates have driving voltage and modulation bandwidth that depend on the effective modulation length, making it impossible to achieve both high-speed data transmission and low driving voltage simultaneously. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a superconducting optical modulator that can simultaneously achieve low driving voltage and high bandwidth.

[0005] The technical solution adopted by this invention to solve its technical problem is: to provide a superconducting optical modulator, comprising: The Mach-Zehnder interferometer structure includes a first modulation arm waveguide and a second modulation arm waveguide. A superconducting modulation electrode, wherein the traveling wave electrode of the superconducting modulation electrode is an asymmetric coplanar waveguide electrode structure with unequal gap widths between the electrodes on both sides, the traveling wave electrode includes a first traveling wave electrode and a second traveling wave electrode connected in parallel, the first traveling wave electrode and the second traveling wave electrode acting on the first modulation arm waveguide and the second modulation arm waveguide respectively, so as to achieve modulation of the phase of the optical signal in the Mach-Zehnder interference structure.

[0006] Furthermore, the modulation arm waveguide is always located on the narrow gap side of the asymmetric coplanar waveguide electrode structure.

[0007] Furthermore, both the first traveling wave electrode and the second traveling wave electrode include a multi-segment straight electrode structure, which is connected by a curved electrode structure to form a reciprocating serpentine structure.

[0008] Furthermore, the signal electrode of the curved electrode structure spans the corresponding modulation arm waveguide, so that the electrode gap width on both sides of the asymmetric coplanar waveguide electrode structure is exchanged before and after the span.

[0009] Furthermore, the first traveling wave electrode and the second traveling wave electrode are mirror-symmetrically distributed about the common central axis between them, and in the straight electrode structure of the first traveling wave electrode and the second traveling wave electrode, the narrow gap side is located either close to the common central axis or away from the common central axis.

[0010] Furthermore, the straight electrode structures of the same traveling wave electrode are arranged in parallel.

[0011] Furthermore, in the straight electrode structure of the same traveling wave electrode, the modulation electric field formed on the narrow gap side has the same direction.

[0012] Furthermore, the portion of the curved electrode structure near the straight electrode structure integrates a dielectric bridge structure, which spans the asymmetric coplanar waveguide electrode structure and connects the ground lines on both sides.

[0013] Furthermore, the first modulation arm waveguide and the second modulation arm waveguide have the same length, and the first traveling wave electrode and the second traveling wave electrode have the same length.

[0014] Furthermore, both the input beam splitter and the output beam combiner of the Mach-Zehnder interference structure are 50:50 beam splitting ratio structures.

[0015] Furthermore, the superconducting modulation electrode also includes a power splitter and a power combiner. The power splitter is a power-equal output structure used to connect the input terminals of the first traveling wave electrode and the second traveling wave electrode. The power combiner is an equal-power combining structure used to connect the output terminals of the first traveling wave electrode and the second traveling wave electrode.

[0016] Beneficial effects By adopting the above-mentioned technical solution, the present invention has the following advantages and positive effects compared with the prior art: This invention employs an asymmetric CPW structure with unequal gaps on both sides and places the modulation arm waveguide on the narrow gap side of the CPW structure. This ensures that the optical waveguide is always located on the narrow gap side with high electric field intensity during transmission, thereby maximizing the electro-optic interaction efficiency, improving modulation efficiency in principle, and reducing half-wave voltage. Furthermore, by combining a waveguide cross-line structure with curved electrodes, the direction of the electric field acting on the single-sided modulation arm remains consistent, achieving effective superposition of the modulation signals. This invention constructs a push-pull structure by placing the two optical waveguides in different side gaps of the coplanar waveguide (CPW) electrodes, thereby modulating the two modulation arms in opposite phases. This invention maintains impedance continuity in the curved region and suppresses resonance caused by the curved structure by placing grounded dielectric bridges at positions close to the straight electrode structure in the curved electrode structure, thus ensuring good transmission characteristics of the electrode in a wide frequency band. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the low-temperature electro-optic modulator structure according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the asymmetric CPW structure and optical waveguide according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the dielectric bridge structure according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the bending structure according to an embodiment of the present invention; Figure 5 This is a comparison diagram of the electric field intensity of symmetrical and asymmetrical CPW structures in the embodiments of the present invention; Figure 6 This is a schematic diagram of the bent traveling wave electrode structure according to an embodiment of the present invention; Figure 7 This is a comparison diagram of the S-parameters of transmission lines with and without a dielectric bridge structure according to embodiments of the present invention; Detailed Implementation

[0018] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0019] Embodiments of the present invention relate to a cryogenic electro-optic modulator based on a Mach-Zehnder interferometer structure, such as... Figure 1 As shown, it mainly consists of two parts: a Mach-Zehnder interference structure and a superconducting modulation electrode.

[0020] The Mach-Zehnder interferometer structure comprises an input beam splitter waveguide, a first modulation arm waveguide, a second modulation arm waveguide, and an output beam combiner waveguide connected in sequence. Both the first and second modulation arms include straight and curved waveguide sections, arranged side-by-side between the input beam splitter waveguide and the output beam combiner waveguide. The waveguide structure is responsible for optical signal transmission. The optical signal enters the MMI beam splitter structure through the optical input port on the left. The split optical signal is output with equal amplitude and in phase. The input beam splitter waveguide and the output beam combiner waveguide can employ a 50:50 beam splitting ratio.

[0021] The superconducting modulation electrode receives the modulation electrical signal and modulates the phase of the optical signal in the Mach-Zehnder interference structure. It includes a split T-junction power divider, a combiner T-junction power divider, and a first and second bent traveling wave electrode with an integrated dielectric bridge structure. The materials of the split T-junction power divider, the combiner T-junction power divider, the first bent traveling wave electrode, and the second bent traveling wave electrode can be superconducting niobium. The split T-junction power divider can adopt an equal amplitude and in-phase output structure, and the combiner T-junction power divider can adopt an equal power combiner structure.

[0022] Two traveling-wave electrodes are connected in parallel and act on the first and second modulation arm waveguides of the Mach-Zehnder interference structure, respectively. Both the first and second curved traveling-wave electrodes are asymmetric coplanar waveguide (CPW) electrode structures with unequal gaps on both sides, resulting in unequal electric field strengths within the gaps. The first and second modulation arm waveguides are located on the narrow gap sides of the first and second traveling-wave electrodes, respectively.

[0023] The first and second modulation arm waveguides can be configured to have equal lengths, as can the first and second curved traveling wave electrodes. Both the first and second curved traveling wave electrodes include a ring electrode structure and a straight electrode structure. Adjacent straight electrode structures are connected by the ring electrode structure to form a reciprocating serpentine structure. The ring electrode structure can be a semi-circular ring structure, with the signal line of the CPW electrode crossing either the first or second modulation arm waveguide at the center of the semi-circular ring, allowing the gap dimensions on both sides of the asymmetric coplanar waveguide to change before and after the crossing. In both the first and second curved traveling wave electrodes, the straight electrodes are arranged in parallel, and the direction of the modulation electric field generated by the electrical signal on the narrow gap side remains consistent within the same modulation arm.

[0024] An electrical signal is input through the CPW electrode, output in phase and equal amplitude to two asymmetric CPW electrodes via a T-type power divider, and the split electrical signal modulates one of the split optical signals. In some preferred embodiments, a dielectric bridge structure can be integrated on the traveling wave electrode to achieve long-distance modulation within a limited area through the curved structure. Dielectric bridges are placed before and after the curved structure to optimize impedance continuity and suppress resonance caused by the curved structure. Placing the optical waveguide on one side of the narrow gap of the asymmetric CPW electrode improves modulation efficiency, and the modulation electric field directions in the two modulation arms are reversed by adjusting the relative positions of the optical waveguide and the electrode.

[0025] Specifically, the first and second traveling-wave electrodes can be arranged in a mirror-symmetrical configuration about their common central axis. Furthermore, in the straight electrode structures of both electrodes, the narrow gap sides are either located close to or far from the common central axis. In this way, after the optical signal undergoes phase modulation in opposite directions, interference occurs in the right-side MMI beam-combining region, and the final modulated optical signal is output from the right-side optical output port.

[0026] Due to the introduction of the curved structure, it is impossible to place waveguides on both sides of the CPW gap for effective modulation. Therefore, an asymmetric CPW structure is used to enhance the electric field within one side of the gap to improve modulation efficiency. The relative positions of the asymmetric CPW electrode structure and the optical waveguide are as follows: Figure 2 As shown, by adjusting the sizes of gap1 and gap2 on both sides of the CPW to be inconsistent, a higher electric field is generated on the narrow gap side. Placing the optical waveguide on the narrow gap side can achieve higher modulation efficiency, thereby reducing the voltage required for modulation.

[0027] The schematic diagram of the dielectric bridge structure is as follows: Figure 3 As shown, by using a titanium thin film cross-line structure to connect the ground lines on both sides of the asymmetric CPW, the impedance continuity of the bent structure is optimized, the resonance caused by the bent structure is effectively suppressed, and a high-bandwidth traveling wave electrode is realized.

[0028] The schematic diagram of the bending structure is as follows: Figure 4 As shown, by using a signal line across the optical waveguide in a curved structure, the electric field direction remains constant in the modulation arm on one side. Combined with the low ohmic loss of the superconducting metal, a consistent signal amplitude is maintained over long distances, achieving effective modulation over long distances. This significantly reduces the half-wave voltage without affecting the bandwidth.

[0029] The following is a specific application example of a long-distance superconducting transmission line according to the embodiments, and the scheme is as follows: The example compares the electric field intensity in the gaps between the two sides of a symmetrical CPW structure and an asymmetrical CPW structure under the same impedance. The results are as follows. Figure 5 As shown, where Figure 5 (a) shows the electric field distribution of the asymmetric CPW. Figure 5 (b) shows the electric field distribution diagram of the CPW. Calculate the average electric field intensity in the central region of the two structures, respectively. and That is, the electric field strength on the narrow gap side of the asymmetric CPW structure increases by about 90%, so the half-wave voltage required for the same modulation length is smaller.

[0030] The aforementioned bent superconducting traveling wave electrode structure was fabricated, and its schematic diagram is shown below. Figure 6As shown, the transmission bandwidth of bent superconducting electrodes with and without dielectric bridge structures was compared, and the results are as follows. Figure 7 As shown, the integrated dielectric bridge significantly improves the resonant point caused by the curved structure, achieving high electrical bandwidth, indicating that the curved electrode structure of the integrated dielectric bridge is suitable for the electrode application requirements of cryogenic electro-optic modulators.

[0031] This embodiment of the cryogenic electro-optic modulator combines a thin-film lithium niobate platform and superconducting metal electrodes, utilizing the low ohmic loss of the superconducting metal and the linear electro-optic coefficient of lithium niobate to achieve effective modulation over long distances. The modulator uses a multimode interference coupler (MMI) and a T-type power divider to split and combine the optical and electrical signals, respectively. The two split electrical signals act on their corresponding optical waveguides. By placing the two optical waveguides in the gaps on different sides of the coplanar waveguide (CPW) electrodes, the two modulation arms are modulated in opposite phases, thus forming a push-pull structure. Furthermore, to enhance modulation efficiency, an asymmetric CPW structure with unequal gaps on both sides is employed, combined with a bent electrode and waveguide crossover structure. This ensures that the optical waveguide remains on the narrow gap side with high electric field strength throughout transmission, and the electric field direction on each modulation arm remains consistent, achieving effective superposition of the modulated signals. Additionally, grounded dielectric bridges are placed before and after the bent electrode structure to maintain impedance continuity in the bent region, suppress resonance caused by the bent structure, and ensure good transmission characteristics of the electrodes over a wide bandwidth. This structural design enables long-distance effective modulation on a small-sized chip, thereby significantly reducing the half-wave voltage required by the modulator. At the same time, the application of a dielectric bridge structure optimizes the transmission characteristics of the electrodes, realizing a low-half-wave voltage and high-bandwidth cryogenic electro-optic modulator that meets the requirements of superconducting optical interconnect applications.

Claims

1. A superconducting optical modulator, characterized in that, include: The Mach-Zehnder interferometer structure includes a first modulation arm waveguide and a second modulation arm waveguide. A superconducting modulation electrode, wherein the traveling wave electrode of the superconducting modulation electrode is an asymmetric coplanar waveguide electrode structure with unequal gap widths between the electrodes on both sides, the traveling wave electrode includes a first traveling wave electrode and a second traveling wave electrode connected in parallel, the first traveling wave electrode and the second traveling wave electrode acting on the first modulation arm waveguide and the second modulation arm waveguide respectively, so as to achieve modulation of the phase of the optical signal in the Mach-Zehnder interference structure.

2. The superconducting optical modulator according to claim 1, characterized in that, The modulation arm waveguide is always located on the narrow gap side of the asymmetric coplanar waveguide electrode structure.

3. The superconducting optical modulator according to claim 2, characterized in that, Both the first traveling wave electrode and the second traveling wave electrode include a multi-segment straight electrode structure, which is connected by a curved electrode structure to form a reciprocating serpentine structure.

4. The superconducting optical modulator according to claim 3, characterized in that, The signal electrode of the curved electrode structure crosses the corresponding modulation arm waveguide, so that the electrode gap width on both sides of the asymmetric coplanar waveguide electrode structure is exchanged before and after crossing.

5. The superconducting optical modulator according to claim 4, characterized in that, The first traveling wave electrode and the second traveling wave electrode are mirror-symmetrically distributed about the common central axis between them, and in the straight electrode structure of the first traveling wave electrode and the second traveling wave electrode, the narrow gap side is located either close to the common central axis or away from the common central axis.

6. The superconducting optical modulator according to claim 3, characterized in that, The straight electrode structures of the same traveling wave electrode are arranged in parallel.

7. The superconducting optical modulator according to claim 3, characterized in that, In the straight electrode structure of the same traveling wave electrode, the modulation electric field formed on the narrow gap side acts in the same phase modulation direction as the corresponding modulation arm waveguide.

8. The superconducting optical modulator according to claim 3, characterized in that, The portion of the curved electrode structure near the straight electrode structure integrates a dielectric bridge structure, which spans the asymmetric coplanar waveguide electrode structure and connects to the ground lines on both sides.

9. The superconducting optical modulator according to claim 1, characterized in that, The first modulation arm waveguide and the second modulation arm waveguide have the same length, and the first traveling wave electrode and the second traveling wave electrode have the same length.

10. The superconducting optical modulator according to claim 1, characterized in that, The superconducting modulation electrode further includes a shunt power divider and a combiner power divider. The shunt power divider is an equal-amplitude, in-phase output structure used to connect the input terminals of the first traveling wave electrode and the second traveling wave electrode. The combiner power divider is an equal-power combiner structure used to connect the output terminals of the first traveling wave electrode and the second traveling wave electrode.

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