Electrostatic comb driven integrated waveguide MEMS optical switch based on adiabatic coupler

Abstract

The application discloses an electrostatic comb driven integrated waveguide MEMS optical switch based on an adiabatic coupler. The switch unit comprises a substrate, a mechanical driving structure and an adiabatic coupler, the adiabatic coupler comprises a fixed conical waveguide and a movable conical waveguide arranged in parallel, the movable conical waveguide is connected with the mechanical driving structure, the two waveguide structures are the same, the length is the same but the width gradient direction is opposite, and the two waveguides are arranged in central symmetry. The application realizes the effect of optical path switching by driving the separated adiabatic coupler through the electrostatic comb, and has the advantages of a large bandwidth range, low insertion loss, low crosstalk, high extinction ratio, simple manufacturing process, low processing cost, low power consumption, strong scalability and the like.

Description

Technical Field

[0001] This invention relates to an optical switch in the field of integrated optoelectronic devices, specifically to an integrated waveguide MEMS optical switch and its array that achieves optical path adjustment by adjusting the spacing between two tapered waveguides in an adiabatic coupler through an electrostatic comb drive. Background Technology

[0002] In recent years, the scale of data center networks has expanded rapidly. With the mature application of new technologies such as 5G, IoT, cloud computing, and artificial intelligence, network data traffic has increased dramatically. This has placed new demands on data center networks, urgently requiring higher-performance data centers to support the rapid development of the digital economy, which is based on these technologies. Against this backdrop, optical interconnect technology has rapidly emerged due to its advantages over traditional electrical interconnect, such as high bandwidth and low power consumption, providing a solution for improving data center performance. Optical interconnect has now become a key technology for large-scale data centers.

[0003] With the development of optical interconnects, their scale and complexity are constantly expanding, making flexible reconfiguration a new challenge. Large-scale N×N optical switch arrays are key devices for achieving flexible reconfiguration of optical interconnects and have become a research focus. Various optical switch structures based on different platforms have been proposed, such as optical switches based on micromechanical systems (MEMS) and integrated waveguide optical switches based on Mach-Zehnder interferometers (MZI).

[0004] Among numerous optical switch structures, MEMS-based optical switches have attracted significant attention due to their low loss, high speed, high reliability, and strong scalability. Large-scale MEMS-based optical switch arrays have been applied in data center networks. MEMS-based optical switches are further divided into free-space switches and integrated waveguide optical switches. For free-space optical switches, the optical signal propagates and switches in free space after entering the switch from the optical fiber, and is then received by the output optical fiber. Currently, most optical switches in data center networks are free-space optical switches. MEMS-based free-space switches offer good scalability, and can currently achieve hundreds of ports while maintaining low insertion loss and low crosstalk. However, the switching time of such switches is relatively long, typically in the range of milliseconds to tens of milliseconds, limiting the reconfiguration speed of large-scale data centers. In integrated waveguide optical switches, the optical signal is confined within the integrated waveguide after entering the chip from the input optical fiber, and the optical path switching is achieved through the integrated waveguide structure and mechanical structure. In recent years, MEMS-based integrated waveguide optical switches have made significant progress, achieving sub-microsecond fast switching times, low insertion loss, low crosstalk, and a large number of ports. MEMS-based integrated waveguide optical switches are expected to overcome the current limitations of optical switch arrays and be applied to large-scale optical interconnect networks. Summary of the Invention

[0005] In view of the above background technology, the purpose of this invention is to provide an integrated waveguide MEMS optical switch and N×N array based on an adiabatic coupler driven by an electrostatic comb. This switch applies a driving voltage to a fixed electrostatic comb, causing it to attract an attraction between itself and a grounded movable electrostatic comb, thereby driving the movable electrostatic comb to move. Furthermore, the movable tapered waveguide in the adiabatic coupler is driven by a transmission rod to change the distance between it and the fixed tapered waveguide, thus achieving the effect of optical path switching.

[0006] The technical solution adopted in this invention is:

[0007] The present invention includes at least one switching unit. Each switching unit includes a substrate and a mechanical drive structure and an adiabatic coupler placed on the substrate. The adiabatic coupler mainly includes a fixed tapered waveguide and a movable tapered waveguide. The fixed tapered waveguide is kept fixed. Both the fixed tapered waveguide and the movable tapered waveguide are arranged parallel to each other along the moving direction perpendicular to the mechanical drive structure. Both ends of the fixed tapered waveguide are connected to curved waveguides. Both ends of the movable tapered waveguide are connected to the mechanical drive structure through a pair of multimode interference cross waveguide structures. The mechanical drive structure drives the movable tapered waveguide to move closer to or away from the fixed tapered waveguide.

[0008] Each end of the movable conical waveguide is sequentially connected to a first curved waveguide in a loop shape, a cross-shaped multimode interference cross waveguide, and a second curved waveguide in a loop shape. The cross-shaped multimode interference cross waveguide consists of a longer one and a shorter one. The longer one consists of a pair of symmetrical mode evolution conical waveguides and a long multimode wide waveguide. The wide ends of the pair of mode evolution conical waveguides are connected to both ends of the long multimode wide waveguide, and the narrow ends are connected to the two curved waveguides in a loop shape. The shorter one is a short multimode wide waveguide. One end of the short multimode wide waveguide is connected to the mechanical drive structure, and the other end is not connected. The longer one of the cross-shaped multimode interference cross waveguides is used for optical signal transmission, and the shorter one is used for mechanical fixation.

[0009] The fixed and movable tapered waveguides have the same structure, both being a tapered waveguide with a gradually changing width. The fixed and movable tapered waveguides have the same length but their widths change in opposite directions. The input width of the fixed tapered waveguide is the same as the output width of the movable tapered waveguide, and the output width of the fixed tapered waveguide is the same as the input width of the movable tapered waveguide. The gap between the fixed and movable tapered waveguides remains constant.

[0010] The mechanical drive structure includes an electrostatic comb driver consisting of a fixed electrostatic comb and a movable electrostatic comb, a T-shaped transmission structure, and three sets of fixed islands and spring structures;

[0011] The T-shaped transmission structure is suspended above the base. The top rod of the T-shaped transmission structure is parallel to the movable conical waveguide, and the bottom rod is perpendicular to the movable conical waveguide. Starting from the end closest to the movable conical waveguide, the bottom rod of the T-shaped transmission structure is arranged sequentially along the length direction with the first set of fixed islands and spring structures, the second set of fixed islands and spring structures, and the third set of fixed islands and spring structures. All three sets of fixed islands and spring structures are connected to the T-shaped transmission structure.

[0012] Electrostatic comb drivers are arranged on both sides of the T-shaped transmission structure between the second set of fixed islands and spring structures and the third set of fixed islands and spring structures. Each electrostatic comb driver includes a pair of fixed electrostatic combs and a pair of movable electrostatic combs. The fixed electrostatic combs are fixed to the base. The pair of fixed electrostatic combs are symmetrically distributed on both sides of the length of the bottom rod of the T-shaped transmission structure and are not connected to the bottom rod of the T-shaped transmission structure. The movable electrostatic combs are suspended above the base. The pair of movable electrostatic combs are symmetrically distributed on both sides of the length of the bottom rod of the T-shaped transmission structure. One end of the pair of movable electrostatic combs near the bottom rod of the T-shaped transmission structure is fixedly connected to the side of the bottom rod. The comb teeth of the fixed electrostatic combs and the movable electrostatic combs are arranged in opposite directions and interlaced.

[0013] The first set of fixed islands and spring structures mainly consists of a fixed island and a pair of semi-folded springs. The fixed island is fixed to the base. Both ends of the fixed island are connected to the bottom of the T-shaped transmission structure near the movable tapered waveguide via the semi-folded springs and the bottom of the T-shaped transmission structure. The semi-folded springs are suspended above the base.

[0014] The semi-folding spring is a suspended structure, consisting of a spring handle and two beams connected to both ends of the spring handle and perpendicular to the length direction of the spring handle. Both beams extend toward the same side away from the spring handle and are respectively connected to a fixed island and a T-shaped transmission structure.

[0015] The second set of fixed islands and spring structures are the same as the third set of fixed islands and spring structures, each consisting of four fixed islands and a pair of folding springs. The fixed islands are fixed to the base. Two fixed islands are grouped together among the four fixed islands. One group of fixed islands is arranged on the same side of the bottom rod of the T-shaped transmission structure, and the two groups of fixed islands are arranged on both sides of the bottom rod of the T-shaped transmission structure. The two fixed islands on the same side are connected to the side of the bottom rod of the T-shaped transmission structure by a folding spring, which is suspended above the base.

[0016] The folding spring is a suspended structure, comprising a spring handle, two short beams connected to both ends of the spring handle and perpendicular to the length direction of the spring handle, and two long beams connected to the middle of the spring handle and perpendicular to the length direction of the spring handle. One end of each of the two short beams is connected to both ends of the spring handle, and the other end of each of the two short beams away from the spring handle is connected to two fixed islands on the same side of the bottom rod of the T-shaped transmission structure. One end of each of the two long beams is connected to two points in the middle of the spring handle, and the other end of each of the two long beams away from the spring handle is connected to two points on the same side of the bottom rod of the T-shaped transmission structure.

[0017] The pair of fixed electrostatic combs are connected to an external circuit, and the light switch is controlled by applying or removing voltage to the pair of fixed electrostatic combs.

[0018] The fixed electrostatic comb is connected to an external circuit. A potential difference is generated between the applied voltage and the moving electrostatic comb, creating an attractive force between them. The moving electrostatic comb moves closer to the fixed comb. The connection between the moving electrostatic comb and the base of the T-shaped transmission structure causes the entire T-shaped transmission structure to displace perpendicular to the length of the fixed tapered waveguide. The connection between the top edge of the T-shaped transmission structure and the multimode interference cross waveguide further causes the movable tapered waveguide to displace perpendicular to the length of the fixed tapered waveguide. Simultaneously, the three sets of springs connected to the T-shaped transmission structure undergo elastic deformation. Adjusting the voltage applied by the external circuit controls the displacement of the movable tapered waveguide, thus regulating the distance between the fixed and movable tapered waveguides, thereby enabling the integrated waveguide MEMS optical switch to switch the optical propagation path.

[0019] The fixed tapered waveguide, movable tapered waveguide, T-shaped transmission structure, three sets of fixed islands and spring structure and electrostatic comb driver are made of the same material and have the same thickness. The entire switching unit structure or N×N array can be fabricated using monolithic integrated processing.

[0020] The fixed conical waveguide, movable conical waveguide, T-shaped transmission structure, semi-folded spring, folded spring and movable electrostatic comb are all suspended structures that are released through corrosion of the buried layer.

[0021] In this invention, the fixing island and the fixing member are both connected to the base through the buried layer, and the rest are suspended.

[0022] The N×N optical switch array should include at least four of the above-mentioned integrated waveguide MEMS optical switch units. Adjacent switch units are connected by single-mode waveguides and waveguide cross-connections. The connection method between switch units can adopt, but is not limited to, Benes, Cross-Bar and other topologies.

[0023] The innovation of this invention lies mainly in the innovative use of an adiabatic coupler composed of a movable tapered waveguide 3 and a fixed tapered waveguide 2 in an optical switch. The principle is the adiabatic evolution of the mode. Compared with coupling structures based on interference principles such as directional couplers and micro-bend directional couplers, it has the fundamental advantages of large process tolerance, ultra-large bandwidth, and ultra-low loss. By setting the above-mentioned adiabatic coupler in the above-mentioned optical switch, it can bring about the advantages of larger process tolerance, larger bandwidth, and lower loss.

[0024] The beneficial effects of this invention are:

[0025] (1) The present invention uses only one type of material, has a simple structure, and has low manufacturing cost;

[0026] (2) The switching unit has low insertion loss, low crosstalk and high extinction ratio in a wide wavelength range and a wide processing tolerance range;

[0027] (3) The switching unit adopts a capacitor-type driving method, and the energy consumption of the switching unit is extremely low;

[0028] (4) The switching unit has two input ports and two output ports. This 2×2 switching unit can be cascaded into a large-scale optical switch array using various topologies, and has strong scalability.

[0029] In summary, this invention achieves optical path switching by driving separate thermally adiabatic couplers with an electrostatic comb, and has significant advantages such as a large bandwidth range, low insertion loss, low crosstalk, high extinction ratio, simple manufacturing process, low processing cost, low power consumption, and strong scalability. Attached Figure Description

[0030] Figure 1 This is a top view of the structure of the present invention in its initial state (OFF);

[0031] Figure 2 yes Figure 1 Cross-sectional view of line A-A';

[0032] Figure 3 yes Figure 1 Cross-sectional view of B-B';

[0033] Figure 4 This is a top view of the structure of the present invention after voltage is applied (ON);

[0034] Figure 5 These are schematic diagrams of a fixed tapered waveguide and a movable tapered waveguide;

[0035] Figure 6 This is a schematic diagram of an N×N integrated waveguide MEMS optical switch structure based on the Benes topology.

[0036] Figure 7 shows the optical field transmission diagrams of the thermal coupler portion of the present invention in OFF and ON states. Figure 7(a) shows the optical field transmission diagram of the thermal coupler in OFF state, and Figure 7(b) shows the optical field transmission diagram of the thermal coupler in ON state.

[0037] In the figure: 1. First group of fixed island and spring structure, 2. Fixed tapered waveguide, 3. Moving tapered waveguide, 4. T-shaped transmission structure, 5. Second group of fixed island and spring structure, 6. Fixed electrostatic comb, 7. Moving electrostatic comb, 8. Third group of fixed island and spring structure, 9. Buried layer, 10. Substrate. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the scope of protection of the present invention.

[0039] like Figure 1 and Figure 4 As shown, the present invention mainly includes at least one switching unit. Each switching unit includes a substrate 10 and a mechanical drive structure and an adiabatic coupler placed on the substrate. The adiabatic coupler mainly includes a fixed tapered waveguide 2 and a movable tapered waveguide 3. The fixed tapered waveguide 2 is kept fixed. Both the fixed tapered waveguide 2 and the movable tapered waveguide 3 are arranged parallel to each other along the direction of movement perpendicular to the mechanical drive structure. Both ends of the fixed tapered waveguide 2 are connected to S-shaped curved waveguides, which serve as the input / output terminals of the switching unit. The fixed tapered waveguide 2 is fixed by connecting to external components through the curved waveguides at both ends and by supporting the fixed tapered waveguide 2. The two ends of the movable tapered waveguide 3 are connected to the T-shaped transmission structure 4 of the mechanical drive structure through a pair of multimode interference cross waveguide structures. The mechanical drive structure drives the movable tapered waveguide 3 to move closer to or away from the fixed tapered waveguide 2.

[0040] Both the fixed tapered waveguide and the movable tapered waveguide include a set of curved waveguides at both ends, and a portion of the curved waveguides is a width-gradient waveguide, whose width gradually changes from the width at the end of the tapered waveguide to the width of a single-mode waveguide. Both the fixed tapered waveguide 2 and the movable tapered waveguide 3 increase structural flexibility by incorporating curved waveguides.

[0041] Each end of the movable tapered waveguide 3 is sequentially connected to a first loop-shaped bent waveguide, a cross-shaped multimode interference cross waveguide, and a second loop-shaped bent waveguide. The cross-shaped multimode interference cross waveguide consists of a longer and a shorter one. The longer one comprises a pair of symmetrical mode evolution tapered waveguides and a long multimode wide waveguide. The wide ends of the pair of mode evolution tapered waveguides are connected to both ends of the long multimode wide waveguide, and the narrow ends are connected to the two loop-shaped bent waveguides. The shorter one is a short multimode wide waveguide, with one end connected to the T-shaped transmission structure 4 of the mechanical drive structure, and the other end unconnected. The longer of the cross-shaped multimode interference cross waveguides is used for optical signal transmission, and the shorter one is used for mechanical fixation. The other end of the second bent waveguide, which is not connected to the multimode interference cross waveguide, serves as the input / output terminal of the switching unit.

[0042] Each multimode interference cross waveguide contains a pair of adiabatic tapered waveguides and a pair of orthogonal multimode wide waveguides. The two ends of the multimode wide waveguide perpendicular to the length direction of the fixed tapered waveguide are connected to an adiabatic tapered waveguide, realizing the mutual adiabatic evolution between the modes in the multimode waveguide and the modes in the single-mode waveguide. The multimode wide waveguide parallel to the length direction of the fixed tapered waveguide is not used to propagate signals. One end is connected to the T-shaped transmission structure, and the other end is unconnected.

[0043] When the movable tapered waveguide and its two connected loops approach the fixed tapered waveguide under the drive of the MEMS drive device, the two form an adiabatic coupler. The outer ends of both the fixed tapered waveguide and the movable tapered waveguide are connected to single-mode waveguides. Optical signals are input and output through single-mode waveguides, and adjacent switching units in the N×N array are also connected to each other through single-mode waveguides.

[0044] Adjacent switching units are interconnected through the curved waveguides of the switching units, which serve as the input and output waveguides of the switching units.

[0045] like Figure 5 As shown, the fixed tapered waveguide 2 and the movable tapered waveguide 3 have the same structure, both being tapered waveguides with a gradually changing width. The fixed tapered waveguide 2 and the movable tapered waveguide 3 have the same length, but the direction of the width change is opposite along the waveguide direction. The width of the input end of the fixed tapered waveguide 2 is the same as the width of the output end of the movable tapered waveguide 3, and the width of the output end of the fixed tapered waveguide 2 is the same as the width of the input end of the movable tapered waveguide 3. The gap between the fixed tapered waveguide 2 and the movable tapered waveguide 3 remains constant, so that the fixed tapered waveguide 2 and the movable tapered waveguide 3 are ultimately arranged in a centrally symmetrical manner.

[0046] The mechanical drive structure includes an electrostatic comb driver consisting of a fixed electrostatic comb 6 and a movable electrostatic comb 7, a T-shaped transmission structure 4, and three sets of fixed islands and spring structures 1, 5, and 8. The set of fixed islands and spring structures closest to the movable tapered waveguide is the first set, and the two sets of fixed islands and spring structures furthest from the movable tapered waveguide are the second and third sets, respectively. Openings are evenly distributed on the T-shaped transmission structure to allow the entry of chemical reagents that corrode the buried layer. The three sets of fixed islands and springs are distributed along the length of the base of the T-shaped transmission structure.

[0047] The T-shaped transmission structure 4 is suspended above the base 10. The top rod of the T-shaped transmission structure 4 is parallel to the movable conical waveguide 3, and the bottom rod is perpendicular to the movable conical waveguide 3. Starting from the end closest to the movable conical waveguide 3, the bottom rod of the T-shaped transmission structure 4 is arranged sequentially along its length with the first set of fixed islands and spring structures 1, the second set of fixed islands and spring structures 5, and the third set of fixed islands and spring structures 8. The first set of fixed islands and spring structures 1, the second set of fixed islands and spring structures 5, and the third set of fixed islands and spring structures 8 are all connected to the T-shaped transmission structure 4. The T-shaped transmission structure 4 is connected to the movable electrostatic comb 7.

[0048] Electrostatic comb drivers are arranged on both sides of the T-shaped transmission structure 4 between the second set of fixed islands and spring structures 5 and the third set of fixed islands and spring structures 8. The electrostatic comb drivers include a pair of fixed electrostatic combs 6 and a pair of movable electrostatic combs 7. The fixed electrostatic combs 6 are fixed to the base 10. The pair of fixed electrostatic combs 6 are symmetrically distributed on both sides of the bottom rod of the T-shaped transmission structure 4 along its length and are not connected to the bottom rod of the T-shaped transmission structure 4. They are fixed to the base 10 near the second set of fixed islands and spring structures 5 and are supported by the buried layer 9 below. The movable electrostatic combs 7 are suspended above the base 10 and are suspended structures. The pair of movable electrostatic combs 7 are symmetrically distributed on both sides of the bottom rod of the T-shaped transmission structure 4 along its length and are located near the third set of fixed islands and spring structures 8. The end of the pair of movable electrostatic combs 7 near the bottom rod of the T-shaped transmission structure 4 is fixedly connected to the side of the bottom rod, and the end away from the bottom rod of the T-shaped transmission structure 4 is not connected. The comb teeth of the fixed electrostatic combs 6 and movable electrostatic combs 7 on both sides of the bottom rod of the T-shaped transmission structure 4 are opposite and interlaced.

[0049] Fixed islands are all rectangular in structure, such as Figure 2 and Figure 3 As shown, both the fixed island and the fixed electrostatic comb 6 are connected to the substrate 10 through the buried layer 9, while the rest are not connected to the substrate 10.

[0050] The first set of fixed island and spring structure 1 mainly consists of a fixed island and a pair of semi-folded springs. The fixed island is connected and fixed to the base 10 through the buried layer 9. The fixed island is fixed to the base 10. Both ends of the fixed island are connected to the bottom rod of the T-shaped transmission structure 4 near the movable tapered waveguide 3 through the semi-folded springs and the bottom rod of the T-shaped transmission structure 4. The semi-folded springs are suspended in the base 10.

[0051] The semi-folding spring in the first fixed island spring structure 1 is a suspended structure, consisting of a spring handle and two beams connected to both ends of the spring handle and perpendicular to the length direction of the spring handle. Both beams extend toward the same side away from the spring handle and are respectively connected to the fixed island and the T-shaped transmission structure 4.

[0052] The second set of fixed islands and spring structure 5 has the same structure as the third set of fixed islands and spring structure 8, both consisting of four fixed islands and a pair of folding springs. The fixed islands are connected and fixed to the base 10 through the buried layer 9. The fixed islands are fixed to the base 10. Among the four fixed islands, two fixed islands form a group. One group of fixed islands is arranged on the same side of the bottom rod of the T-shaped transmission structure 4. The two groups of fixed islands are arranged on both sides of the bottom rod of the T-shaped transmission structure 4. The two fixed islands on the same side under one group of fixed islands are connected to the side of the bottom rod of the T-shaped transmission structure 4 through a folding spring. The folding spring is suspended in the base 10.

[0053] The folding springs in the second group of fixed islands and spring structures 5 and the third group of fixed islands and spring structures 8 are suspended structures, consisting of a spring handle, two short beams connected to both ends of the spring handle and perpendicular to the length direction of the spring handle, and two long beams connected to the middle of the spring handle and perpendicular to the length direction of the spring handle. One end of each of the two short beams is connected to both ends of the spring handle, and the other end of each of the two short beams away from the spring handle is connected to two fixed islands located on the same side of the length direction of the bottom rod of the T-shaped transmission structure 4. One end of each of the two long beams is connected to two points in the middle of the spring handle, and the other end of each of the two long beams away from the spring handle is connected to two points located on the same side of the length direction of the bottom rod of the T-shaped transmission structure 4.

[0054] A pair of fixed electrostatic combs 6 are connected to an external circuit. The optical switch is controlled by applying or removing voltage to the pair of fixed electrostatic combs 6. The top layer structure and silicon substrate 10, except for the fixed electrostatic combs 6, are all grounded.

[0055] A voltage is applied to a pair of fixed electrostatic combs 6, generating an attractive or repulsive force that drives the movable electrostatic comb 7 to move closer to or away from the fixed electrostatic combs 6. This, in turn, drives the T-shaped transmission structure 4 to move the movable tapered waveguide 3 closer to or away from the fixed tapered waveguide 2 under the elastic control of three sets of fixed islands and spring structures 1, 5, and 8. This controls the coupling / contact connection between the movable tapered waveguide 3 and the fixed tapered waveguide 2, thereby achieving the control of the optical switch.

[0056] The implementation process of this invention is as follows:

[0057] When an external circuit applies voltage to a pair of fixed electrostatic combs 6, the fixed electrostatic combs 6 generate an attractive force on the movable electrostatic combs 7, causing the movable electrostatic combs 7 to move toward the fixed electrostatic combs 6. The part of the movable electrostatic combs 7 connected to the bottom rod of the T-shaped transmission structure 4 causes the entire T-shaped transmission structure 4 to move perpendicular to the length direction of the movable tapered waveguide 3. Then, the part of the movable tapered waveguide 3 connected to the top edge of the T-shaped transmission structure 4 causes the movable tapered waveguide 3 to move closer to the fixed tapered waveguide 2. The movement of the T-shaped transmission structure 4 causes the semi-folded spring in the first set of fixed islands and spring structures 1 and the folded springs in the second and third sets of fixed islands and spring structures 5 and 8 to undergo elastic deformation.

[0058] The distance between the movable tapered waveguide 3 and the fixed tapered waveguide 2 can be controlled by adjusting the voltage applied to a pair of fixed electrostatic combs 6. When the two are close enough, the optical propagation path can be controlled.

[0059] In the embodiment, the electrostatic comb drivers 6 and 7 are placed between the second set of fixed islands and spring structures 5 and the third set of fixed islands and spring structures 8. The two sets of fixed islands and spring structures 5 and 8 help to increase the stability of the electrostatic comb drivers 6 and 7 during operation.

[0060] like Figure 1 As shown, when the integrated waveguide MEMS optical switch in the embodiment is in its natural state (OFF state without voltage), the distance between the movable tapered waveguide 3 and the fixed tapered waveguide 2 is relatively large, and there is no optical signal coupling between the tapered waveguides 2 and 3. In this state, there is a large distance between the comb teeth of the fixed electrostatic comb 6 and the movable electrostatic comb 7 along the length of the bottom rod of the T-shaped transmission structure. This distance is greater than the distance between the movable tapered waveguide 3 and the fixed tapered waveguide 2 in the natural state, to prevent the two tapered waveguides from getting close together, i.e., in a state of... Figure 4 When the ON state is shown, the teeth of the electrostatic comb 6 and 7 collide.

[0061] like Figure 4 As shown, when the integrated waveguide MEMS optical switch in the embodiment is in the ON state with a certain bias applied, the movable tapered waveguide 3 approaches the fixed tapered waveguide 2, and a small gap is maintained between the two tapered waveguides. At this time, the two tapered waveguides form a directional thermally adiabatic coupler, and the optical signal can undergo thermal evolution to realize the path switching of the optical signal.

[0062] During the transition of the integrated waveguide MEMS optical switch in this embodiment from a natural OFF state to an ON state, the fixed electrostatic comb 6 is kept under voltage. The voltage is adjusted to stabilize the movable tapered waveguide 3 at a certain distance from the fixed tapered waveguide 2. When the integrated waveguide MEMS optical switch in this embodiment needs to switch from an ON state to an OFF state, the bias voltage applied to the fixed electrostatic comb 6 can be removed.

[0063] In this embodiment, the fixed tapered waveguide 2 and the movable tapered waveguide 3 are used for optical transmission. The fixed tapered waveguide 2 has single-mode bent waveguides connected at both ends, and the movable tapered waveguide 3 has single-mode bent waveguides and multimode interference cross waveguides connected at both ends. The buried layers beneath both the fixed tapered waveguide 2 and the movable tapered waveguide 3 are hollowed out, making both suspended waveguide structures. The fixed tapered waveguide 2 remains stationary, while the movable tapered waveguide 3 can be brought close to the fixed tapered waveguide 2 to form an adiabatic directional coupler. The lengths of the fixed tapered waveguide 2 and the movable tapered waveguide 3, as well as the gap between them, should support the adiabatic evolution of the optical signal within them.

[0064] In practice, the top layer structures of the thermal coupler and the electrostatic comb driver are made of the same material, and they are on the same plane regardless of whether the buried layer is hollowed out. For the entire switching structure, except for the fixed island and the fixed electrostatic comb 6 which are supported by the buried layer, the other structures are all suspended structures, and all of the suspended structures except for the fixed tapered waveguide 2 can be moved.

[0065] In practice, the top-layer structures of the thermal coupler and the electrostatic comb driver are made of the same material, enabling monolithic integrated fabrication. The integrated waveguide MEMS optical switch in this embodiment has a 2×2 port structure, which can be connected into an N×N switch array according to different topologies. Furthermore, the size of the N×N array can be increased by adding more switch units.

[0066] Figure 6 This diagram illustrates a 4×4 switch array cascaded using a Benes topology. The 4×4 array comprises six switch units: switch units 1 and 2 form the first stage, switch units 3 and 4 form the second stage, and switch units 5 and 6 form the third stage. Switch units in different stages are interconnected via straight waveguides or cross waveguides. The two output ports of switch unit 1 in the first stage are connected to one of the input ports of switch units 3 and 4 in the second stage, respectively. Similarly, the two output ports of switch unit 2 in the first stage are connected to the remaining input ports of switch units 3 and 4 in the second stage. The connections between the second-stage and third-stage switch units are similar.

[0067] The following describes the working process of the integrated waveguide MEMS optical switch in this invention:

[0068] Figure 1 When the switch is in the OFF state, no bias voltage is applied to the fixed electrostatic comb 6, and a large gap is maintained between the fixed electrostatic comb 6 and the movable electrostatic comb 7, as well as between the fixed tapered waveguide 2 and the movable tapered waveguide 3. At this time, for signals input from below the fixed tapered waveguide 2, due to the greater distance of the movable tapered waveguide 3, the signal will be output from above the fixed tapered waveguide 2 unaffected. Similarly, optical signals input from below the movable tapered waveguide 3 will also be output from above the movable tapered waveguide 3 unaffected.

[0069] When a certain voltage is applied to the fixed electrostatic comb 6, an induced charge is generated on the movable electrostatic comb 7, creating an electrostatic attraction between them. Under the action of this electrostatic attraction, the movable electrostatic comb 7 moves closer to the fixed electrostatic comb 6. The T-shaped transmission structure 4 moves along a direction perpendicular to the length of the movable tapered waveguide 3, pulling one end of the spring in the three sets of fixed islands and spring structures, causing it to deform. When the elastic force generated by the deformation balances the electrostatic force between the electrostatic comb teeth, the entire mechanical structure reaches a state of equilibrium.

[0070] As the applied voltage increases, the electrostatic force generated between the fixed electrostatic comb 6 and the movable electrostatic comb 7 becomes greater, the displacement generated when the mechanical structure reaches equilibrium becomes greater, and the moving distance of the movable tapered waveguide 3 becomes greater, bringing it closer to the movable tapered waveguide 2.

[0071] When the gap between the movable tapered waveguide 3 and the fixed tapered waveguide 2 is reduced to a certain extent, the movable tapered waveguide 3 and the fixed tapered waveguide 2 form an adiabatic directional coupler, which is the ON state of the switch.

[0072] Figure 4 Describing the ON state of the switch, in this state, the fixed tapered waveguide 2 and the movable tapered waveguide 3 form an adiabatic directional coupler. At this time, for an optical signal input from below the fixed tapered waveguide 2, due to the close proximity to the movable tapered waveguide 3, the optical signal in the fixed tapered waveguide 2 will adiabatically evolve into the movable tapered waveguide 3 and be output from above the movable tapered waveguide 3. To return the switch to the OFF state, simply remove the voltage applied to the fixed electrostatic comb 6. After the electrostatic force is removed, the mechanical structure is no longer in equilibrium and will return to the initial OFF state under the elastic force generated by the spring deformation. This completes the switch state switching and achieves the adjustment of the light propagation path.

[0073] The integrated waveguide MEMS optical switch described in this embodiment has two input ports and two output ports, making it a 2×2 optical switch. This offers greater scalability compared to a 1×2 optical switch with one input port and two output ports. A 1×2 optical switch typically employs a cross-bar topology, requiring up to N optical switch units to form an N×N array. 2 The 2×2 silicon-based MEMS optical switch can also adopt the Benes topology, as shown in Figure 7. Only N (log₂N-0.5) optical switch units are needed to form an N×N switch array. Besides the Benes topology, other topologies can also be used for the switch array of the switch units in this invention.

[0074] The following describes specific implementations of the present invention:

[0075] Silicon-on-insulator (SOI) was chosen as the implementation platform, with a 220nm thick silicon top layer, a 2µm thick silicon dioxide buried layer, and a silicon substrate. The considered wavelength range is 1500nm to 1600nm, using TE-polarized optical signals. The fixed tapered waveguide has widths of 400nm and 300nm at its two ends, while the movable tapered waveguide has widths of 300nm and 400nm at its two ends. Both have the same length of 120µm. The distance between the fixed and movable tapered waveguides is 1µm in the OFF state and 100nm in the ON state.

[0076] The optical performance of the device was simulated and verified using the three-dimensional finite-difference time-domain (3D-FDTD) method. In the OFF state, the incident light field propagates almost entirely along the fixed tapered waveguide, as shown in Figure 7(a). Low loss and high extinction ratio are achieved in the 1500nm to 1600nm wavelength range, with a loss of less than 0.04dB and crosstalk below -30dB. When a voltage is applied to the fixed electrostatic comb, the moving electrostatic comb pushes the movable tapered waveguide to the fixed tapered waveguide through a T-shaped transmission structure. When the gap between the two is 100nm, the switch enters the ON state. At this time, the incident light field evolves almost adiabatically into the movable tapered waveguide, as shown in Figure 7(b). When the switch is in the OFF state, low loss and high extinction ratio are achieved in the 1500nm to 1600nm wavelength range, with a loss of less than 0.03dB and crosstalk below -25dB. Therefore, the integrated waveguide MEMS optical switch proposed in this invention can achieve ultra-large bandwidth, ultra-low loss, high extinction ratio and ultra-low energy consumption.

[0077] The above embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. An electrostatic comb driven adiabatic coupler based integrated waveguide MEMS optical switch, characterized in that: it comprises at least one switching unit, each switching unit comprising a substrate (10) and a mechanical driving structure and an adiabatic coupler disposed on the substrate, the adiabatic coupler comprising a fixed tapered waveguide (2) and a movable tapered waveguide (3), the fixed tapered waveguide (2) being fixed, the fixed tapered waveguide (2) and the movable tapered waveguide (3) being arranged in parallel along a direction perpendicular to the movement direction of the mechanical driving structure, both ends of the fixed tapered waveguide (2) being connected with a bent waveguide, both ends of the movable tapered waveguide (3) being connected with the mechanical driving structure through a pair of multimode interference cross waveguide structures, the movable tapered waveguide (3) being driven by the mechanical driving structure to move close to or away from the fixed tapered waveguide (2); the mechanical driving structure comprising an electrostatic comb driver composed of a fixed electrostatic comb (6) and a movable electrostatic comb (7), a T-shaped transmission structure (4), and three groups of fixed island and spring structures (1, 5, 8); the T-shaped transmission structure (4) is suspended on the substrate (10), the top rod part of the T-shaped transmission structure (4) is parallel to the movable tapered waveguide (3), and the bottom rod part is perpendicular to the movable tapered waveguide (3), the bottom rod part of the T-shaped transmission structure (4) is sequentially arranged with the first group of fixed island and spring structure (1), the second group of fixed island and spring structure (5), and the third group of fixed island and spring structure (8) from one end close to the movable tapered waveguide (3) along the length direction, and the first group of fixed island and spring structure (1), the second group of fixed island and spring structure (5), and the third group of fixed island and spring structure (8) are all connected with the T-shaped transmission structure (4); the electrostatic comb driver is arranged on both sides of the T-shaped transmission structure (4) between the second group of fixed island and spring structure (5) and the third group of fixed island and spring structure (8), the electrostatic comb driver comprising a pair of fixed electrostatic combs (6) and a pair of movable electrostatic combs (7), the fixed electrostatic combs (6) being fixed to the substrate (10), the pair of fixed electrostatic combs (6) being symmetrically distributed on both sides of the length direction of the bottom rod part of the T-shaped transmission structure (4) and having no connection between the bottom rod part of the T-shaped transmission structure (4); the movable electrostatic combs (7) are suspended on the substrate (10), the pair of movable electrostatic combs (7) being symmetrically distributed on both sides of the length direction of the bottom rod part of the T-shaped transmission structure (4), and one end of the pair of movable electrostatic combs (7) close to the bottom rod part of the T-shaped transmission structure (4) being fixedly connected with the side edge of the bottom rod part; the comb teeth of the fixed electrostatic combs (6) and the movable electrostatic combs (7) are oppositely and staggeringly distributed.

2. The electrostatic comb driven adiabatic coupler based integrated waveguide MEMS optical switch according to claim 1, characterized in that: ​ The movable tapered waveguide (3) is connected with a first curved waveguide, a cross-shaped multimode interference cross waveguide and a second curved waveguide in sequence at each end, the cross-shaped multimode interference cross waveguide is composed of a longer one and a shorter one, the longer one is composed of a pair of symmetrical mode evolution tapered waveguides and a long multimode wide waveguide, the wide ends of the pair of mode evolution tapered waveguides are connected with the two ends of the long multimode wide waveguide respectively, the narrow ends are connected with the two curved waveguides respectively, the shorter one is a short multimode wide waveguide, one end of the short multimode wide waveguide is connected with the mechanical driving structure.

3. The electrostatic comb-driven adiabatic coupler-based integrated waveguide MEMS optical switch of claim 1, wherein: The fixed tapered waveguide (2) and the movable tapered waveguide (3) have the same structure, and are both tapered waveguides with gradually changing width, the fixed tapered waveguide (2) and the movable tapered waveguide (3) have the same length but opposite directions of width change, the input end width of the fixed tapered waveguide (2) is the same as the output end width of the movable tapered waveguide (3), the output end width of the fixed tapered waveguide (2) is the same as the input end width of the movable tapered waveguide (3), and the gap between the fixed tapered waveguide (2) and the movable tapered waveguide (3) is always kept unchanged.

4. The electrostatic comb-driven adiabatic coupler-based integrated waveguide MEMS optical switch of claim 1, wherein: The first fixed island and spring structure (1) is composed of a fixed island and a pair of half-folded springs, the fixed island is fixed on the substrate (10), the two ends of the fixed island are connected to one end of the movable tapered waveguide (3) through a half-folded spring and a bottom rod of the T-shaped transmission structure (4), and the half-folded spring is suspended on the substrate (10).

5. The electrostatic comb-driven adiabatic coupler-based integrated waveguide MEMS optical switch of claim 4, wherein: The half-folded spring is a suspended structure, which comprises a spring handle and two beams connected to the two ends of the spring handle and perpendicular to the length direction of the spring handle, and the two beams extend towards the same side away from the spring handle and are connected to the fixed island and the T-shaped transmission structure (4) respectively.

6. The electrostatic comb-driven adiabatic coupler-based integrated waveguide MEMS optical switch of claim 1, wherein: The second fixed island and spring structure (5) and the third fixed island and spring structure (8) have the same structure, and are both composed of four fixed islands and a pair of folded springs; the fixed islands are fixed on the substrate (10), two fixed islands in the four fixed islands form a group, the fixed islands in the same group are arranged on the same side of the bottom rod of the T-shaped transmission structure (4), the two groups of fixed islands are arranged on the two sides of the bottom rod of the T-shaped transmission structure (4) respectively, the two fixed islands on the same side are connected through a folded spring and a side of the bottom rod of the T-shaped transmission structure (4), and the folded spring is suspended on the substrate (10).

7. The electrostatic comb-driven adiabatic coupler-based integrated waveguide MEMS optical switch of claim 6, wherein: The folding spring is a suspended structure, comprising a spring handle, two short beams connected to both ends of the spring handle and perpendicular to the length direction of the spring handle, and two long beams connected to the middle part of the spring handle and perpendicular to the length direction of the spring handle, one end of the two short beams is connected to both ends of the spring handle respectively, the other end of the two short beams away from the spring handle is connected to two fixed islands on the same side of the bottom rod part of the T-shaped transmission structure (4) respectively, one end of the two long beams is connected to the middle part of the spring handle respectively, the other end of the two long beams away from the spring handle is connected to two places on the same side of the bottom rod part of the T-shaped transmission structure (4) respectively.

8. The electrostatic comb-driven adiabatic coupler-based integrated waveguide MEMS optical switch of claim 1, wherein: The pair of fixed electrostatic combs (6) are connected with external circuits, and the control of the optical switch is realized by applying or removing voltage to the pair of fixed electrostatic combs (6).

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