Optical switch controllable by vertically moving MEMS structure

Abstract

MEMS-actuated optical switches can be implemented on photonic chips. These switches are small, generally planar, simple to implement, and contain only one moving MEMS component per switch. The switches exhibit low optical loss, require low power to operate, are simple to control, and are easy to integrate with other optical devices. Each switch has two optical waveguides that are optically coupled in the on switch state and uncoupled in the off switch state. An end section or a middle section of one of the two waveguides can translate between the on and off states to affect the coupling. Alternatively, a coupling frustration can translate between the on and off states to affect the coupling.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application is related to U.S. patent application Ser. No. 16 / 586,249, filed Sep. 27, 2019, and entitled "Optical Switch Controllable by Vertical Motion MEMS Structure," the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to optical switches, and more particularly to MEMS actuated optical switches that may be implemented on a photonic chip. [Background technology]

[0003] In many integrated photonic applications, a binary optical switch is needed to direct light from an input waveguide to one of two output waveguides. In some applications, several binary optical switches are interconnected to form a 1×N type, N×M type, or other type of optical switch network. Ideally, a binary optical switch should have low optical loss, require low power to operate, be small, simple to control, and easy to integrate with other optical devices, regardless of the output to which the light is coupled.

[0004] Examples of systems that may include optical switches include Light Detection and Ranging (sometimes referred to as Laser Imaging, Detection, and Ranging) (LiDAR) and image projectors. Such systems emit or receive collimated optical beams (visible or invisible from a human perspective) in directions that can be controlled with high precision, and these beams often need to be steered or swept to locate or track targets. Similarly, laser communication systems sometimes need to steer optical beams, such as to initially establish a line-of-sight communication channel between two terminals, or later to track whether one or both of the terminals move. Modern optical systems often require small, nearly planar optical switch networks implemented on photonic chips, such as for driving arrays of emitters for LiDAR and image projectors. See, for example, U.S. Patent Publication No. 2018 / 0175961, entitled “Integrated MEMS Switches for Selectively Coupling Light In and Out of a Waveguide,” the entire contents of which are incorporated by reference into this specification for all purposes.

[0005] A common method for implementing optical switches in integrated photonic circuits involves the use of a Mach-Zehnder interferometer and a phase shifter. In such circuits, the relative phase of two arms directs light to a selected output. The phase shift can be implemented and controlled in several known ways, such as thermal tuning. Phase-shifter-based Mach-Zehnder switches are analog devices that can switch any amount of power between two outputs. For many applications, this is advantageous, but for applications where binary switching is desired, very precise control of the phase between the two arms is necessary to obtain low losses and good attenuation. Such precise phase control demands complex control systems, especially when environmental factors such as temperature can affect the phase of the light propagation.

[0006] Tae Joon Seok, et al., "Large-scale broadband digital silicon photonic switches with vertical adiabatic couplers," Optica, Vol. 3, No. 1, pp. 64-70, January 2016 ("Seok") and Tae Joon Seok, et al., "Large-scale broadband digital silicon photonic switches with vertical adiabatic couplers: supplemental material" ("Seok Supplement"), describe a MEMS-actuated optical switching matrix composed of multiple orthogonally intersecting, typically uncoupled waveguides. Sangyoon Han, et al., "Large-scale silicon photonic switches with movable directional couplers," Optica, Vol. 2, No. 4, pp. 370-375, April 2015 ("Han") discloses another MEMS-actuated optical switching matrix composed of multiple vertically intersecting, typically uncoupled waveguides. In Seok and Han, a separate switch cell is placed at each waveguide intersection. When a switch cell is activated, it bidirectionally couples the two intersecting waveguides. Thus, the switching matrix can act as a crossbar switch, where each row of the switching matrix can be coupled to a desired column of the switching matrix.

[0007] However, each Seok switch cell requires a pair of back-to-back adiabatic couplers on separate MEMS actuators, and each Han switch cell requires a pair of back-to-back resonant couplers on a MEMS actuator. In each case, the two couplers are distinct from the intersecting waveguides, and in Seok, the two couplers can be actuated independently. To turn on the switch cell, both couplers must be moved so that each of the two couplers is in close proximity to a respective one of the two intersecting waveguides. In the on state, light from one of the two intersecting waveguides couples into one of the couplers. The light then propagates to the other coupler, and then light couples from the other coupler into the other of the two intersecting waveguides. Thus, the two couplers are in close proximity to each other of the two intersecting waveguides. Evanescent coupling is required in the on switch cell, which introduces losses. The two orthogonal waveguides are stationary. Only the coupler moves. The coupler is not physically part of any of the waveguides. The coupler does not extend beyond the switch cell. In contrast, each waveguide extends beyond the switch cell in both directions. Each switch cell is bidirectional, i.e., light can propagate through the on switch cell between two intersecting waveguides in either direction or both directions simultaneously. However, simpler optical switches with lower losses and that can be implemented on a photonic chip would be preferable. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] US Patent Publication No. 2018 / 0175961 Summary of the Invention [Means for solving the problem]

[0009] An embodiment of the present invention provides an optical switch. The optical switch has a design wavelength. The optical switch includes a photonic chip. The first input / output port includes a first optical waveguide disposed on the photonic chip. The second input / output port includes a second optical waveguide distinct from the first optical waveguide and disposed on the photonic chip. A first end portion of the second optical waveguide is disposed proximate to an intermediate portion of the first optical waveguide.

[0010] A MEMS structure is disposed on the photonic chip, the MEMS structure having a translatable portion configured to translate in response to a control signal.

[0011] The translatable optical component includes one of (a) an intermediate portion of the first optical waveguide and (b) a first end portion of the second optical waveguide, i.e., the translatable optical component, in any given embodiment, includes either (a) an intermediate portion of the first optical waveguide or (b) a first end portion of the second optical waveguide, but not both (a) and (b).

[0012] The translatable portion of the MEMS structure is configured to mechanically couple to the translatable optical component to thereby translate it between at least a first (on) position and a second (off) position, where in the first (on) position, the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide are coupled to each other with a coupling efficiency of at least about 85% at the design wavelength. Evanescent coupling In the second (off) position, the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide are coupled to each other with a coupling efficiency of up to about 10% at the design wavelength. Evanescent coupling The electrodes are spaced far enough apart so that the electrodes are spaced far enough apart ... so that the electrodes

[0013] In any embodiment, when the translatable optical component is in the first position, the first input / output port is a single Evanescent coupling The single input / output port may be optically coupled to the second input / output port via a single Evanescent couplingmay be between the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide. Specifically, one of (a) the intermediate portion of the first optical waveguide and (b) the first end portion of the second optical waveguide is configured to translate. That is, in any given embodiment, either (a) the intermediate portion of the first optical waveguide is configured to translate or (b) the first end portion of the second optical waveguide is configured to translate, but not both (a) and (b).

[0014] In any embodiment, the optical switch may have an outer boundary that defines a minimally sized rectangular area that includes the translatable optical components and the MEMS structure. The first and second input / output ports may be arranged outside the outer boundary. Each end of the first optical waveguide may be arranged outside the outer boundary. An intermediate portion of the first optical waveguide may be disposed within the outer boundary. A first end portion of the second optical waveguide may be disposed within the outer boundary. A second end of the second optical waveguide, opposite the first end portion, may be disposed outside the outer boundary. The MEMS structure may be disposed within the outer boundary.

[0015] In any embodiment, the translatable optical component may include an intermediate portion of the first optical waveguide.

[0016] In some embodiments, in both the first position and the second position, the intermediate portion of the first optical waveguide is aligned above the first end portion of the second optical waveguide when viewed normal to the photonic chip. The intermediate portion of the first optical waveguide may be configured to translate relative to the photonic chip in a plane that intersects the first end portion of the second optical waveguide.

[0017] In some embodiments, the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide are configured such that when the intermediate portion of the first optical waveguide is in the first position, the intermediate portion of the first optical waveguide resonantly optically couples with the first end portion of the second optical waveguide with a coupling efficiency of at least about 85% at the design wavelength.

[0018] In some embodiments, the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide are configured such that when the intermediate portion of the first optical waveguide is in the first position, the intermediate portion of the first optical waveguide adiabatically and optically couples with the first end portion of the second optical waveguide with a coupling efficiency of at least about 85% at the design wavelength.

[0019] In some embodiments, in both the first position and the second position, the intermediate portion of the first optical waveguide is laterally displaced from the first end portion of the second optical waveguide when viewed normal to the photonic chip. The intermediate portion of the first optical waveguide may be configured to translate in a plane that does not intersect the first end portion of the second optical waveguide.

[0020] In some embodiments, the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide are configured such that when the intermediate portion of the first optical waveguide is in the first position, the intermediate portion of the first optical waveguide resonantly optically couples with the first end portion of the second optical waveguide with a coupling efficiency of at least about 85% at the design wavelength.

[0021] In some embodiments, the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide are configured such that when the intermediate portion of the first optical waveguide is in the first position, the intermediate portion of the first optical waveguide adiabatically and optically couples with the first end portion of the second optical waveguide with a coupling efficiency of at least about 85% at the design wavelength.

[0022] In some embodiments, the translatable optical component includes a first end portion of the second optical waveguide.

[0023] In some embodiments, in both the first position and the second position, the first end portion of the second optical waveguide is aligned above the intermediate portion of the first optical waveguide. The first end portion of the second optical waveguide may be configured to translate relative to the photonic chip in a plane that intersects the intermediate portion of the first optical waveguide.

[0024] In some embodiments, the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide are configured such that when the intermediate portion of the first optical waveguide is in the first position, the intermediate portion of the first optical waveguide resonantly optically couples with the first end portion of the second optical waveguide with a coupling efficiency of at least about 85% at the design wavelength.

[0025] In some embodiments, the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide are configured such that when the intermediate portion of the first optical waveguide is in the first position, the intermediate portion of the first optical waveguide adiabatically and optically couples with the first end portion of the second optical waveguide with a coupling efficiency of at least about 85% at the design wavelength.

[0026] In some embodiments, in both the first position and the second position, the first end portion of the second optical waveguide is laterally displaced from the intermediate portion of the first optical waveguide when viewed normal to the photonic chip. The first end portion of the second optical waveguide may be configured to translate in a plane that does not intersect the intermediate portion of the first optical waveguide.

[0027] In some embodiments, the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide are configured such that when the intermediate portion of the first optical waveguide is in the first position, the intermediate portion of the first optical waveguide resonantly optically couples with the first end portion of the second optical waveguide with a coupling efficiency of at least about 85% at the design wavelength.

[0028] In some embodiments, the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide are configured such that when the intermediate portion of the first optical waveguide is in the first position, the intermediate portion of the first optical waveguide adiabatically and optically couples with the first end portion of the second optical waveguide with a coupling efficiency of at least about 85% at the design wavelength.

[0029] Another embodiment of the present invention provides an optical switch having a design wavelength, the optical switch including a photonic chip and a translatable optical coupling frustration.

[0030] A first optical waveguide is disposed on the photonic chip, the first optical waveguide having an intermediate portion.

[0031] A second optical waveguide, distinct from the first optical waveguide, is disposed on the photonic chip. The second optical waveguide has a first end portion. The first end portion is stationary relative to an intermediate portion of the first optical waveguide. The first end portion is coupled to the intermediate portion of the first optical waveguide with a coupling efficiency of at least about 85% at a design wavelength in the absence of optical coupling frustrations. Evanescent coupling The first optical waveguide is located sufficiently close to the intermediate portion thereof so as to

[0032] A MEMS structure is disposed on the photonic chip. The MEMS structure has a translatable portion mechanically coupled to the optical coupling frustrator. The MEMS structure is configured to translate the optical coupling frustrator between at least a first position and a second position in response to a control signal. The first position is proximate to at least one of an intermediate portion of the first optical waveguide and a first end portion of the second optical waveguide. That is, in the first position, the optical coupling frustrator is proximate to the intermediate portion of the first optical waveguide and / or the first end portion of the second optical waveguide. The second position is spaced apart from at least one of the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide.

[0033] In the first position, the optical coupling frustration provides a coupling efficiency of greater than about 10% at the design wavelength between the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide. Evanescent coupling In the second position, the optical coupling frustration is sufficiently close to the intermediate portion of the first optical waveguide and / or the first end portion of the second optical waveguide to prevent a coupling efficiency of at least about 85% at the design wavelength between the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide. Evanescent coupling the first end portion of the second optical waveguide so as to allow

[0034] In some embodiments, in both the first position and the second position, the optical coupling frustration is aligned above at least a portion of at least one of the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide when viewed normal to the photonic chip.

[0035] In some embodiments, in both the first position and the second position, the optical coupling frustration is laterally displaced from an intermediate portion of the first optical waveguide and a first end portion of the second optical waveguide when viewed normal to the photonic chip.

[0036] In some embodiments, in the first position, the light coupling frustrated is proximate to a middle portion of the first light guide, and in the second position, the light coupling frustrated is spaced apart from the middle portion of the first light guide.

[0037] In some embodiments, in the first position, the optical coupling frustration is proximate to the first end portion of the second optical waveguide, and in the second position, the optical coupling frustration is spaced from the first end portion of the second optical waveguide. The present invention provides, for example, the following items. (Item 1) 1. An optical switch having a design wavelength, the optical switch comprising: A photonic chip, a translatable optical coupling frustrated element; a first optical waveguide disposed on the photonic chip, the first optical waveguide having an intermediate portion; a second optical waveguide, the second optical waveguide being distinct from the first optical waveguide, the second optical waveguide being disposed on the photonic chip, the second optical waveguide having a first end portion, the first end portion being stationary with respect to an intermediate portion of the first optical waveguide and being sufficiently proximate to an intermediate portion of the first optical waveguide such that, in the absence of the optical coupling frustration, the second optical waveguide evanescently couples with the intermediate portion of the first optical waveguide with a coupling efficiency of at least about 85% at the design wavelength; a MEMS structure disposed on the photonic chip, the MEMS structure having a translatable portion mechanically coupled to the optical coupling frustrator and configured to translate the optical coupling frustrator in response to a control signal between at least (a) a first position proximate to at least one of an intermediate portion of the first optical waveguide and a first end portion of the second optical waveguide, and (b) a second position spaced apart from at least one of an intermediate portion of the first optical waveguide and a first end portion of the second optical waveguide; Equipped with in the first position, the optical coupling frustration is sufficiently close to at least one of an intermediate portion of the first optical waveguide and a first end portion of the second optical waveguide to prevent evanescent coupling between the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide with a coupling efficiency of greater than about 10% at the design wavelength; an optical switch, wherein in the second position, the optical coupling frustration is sufficiently spaced from at least one of an intermediate portion of the first optical waveguide and a first end portion of the second optical waveguide to enable evanescent coupling between the intermediate portion of the first optical waveguide and a first end portion of the second optical waveguide with a coupling efficiency of at least about 85% at the design wavelength. (Item 2) 2. The optical switch of claim 1, wherein in both the first and second positions, the optical coupling frustration is aligned above at least a portion of at least one of an intermediate portion of the first optical waveguide and a first end portion of the second optical waveguide when viewed in a direction normal to the photonic chip. (Item 3) 2. The optical switch of claim 1, wherein in both the first and second positions, the optical coupling frustration is laterally displaced from an intermediate portion of the first optical waveguide and a first end portion of the second optical waveguide when viewed normal to the photonic chip. (Item 4) 2. The optical switch of claim 1, wherein in the first position, the optical coupling frustration is proximate to an intermediate portion of the first optical waveguide, and in the second position, the optical coupling frustration is spaced from the intermediate portion of the first optical waveguide. (Item 5) 2. The optical switch of claim 1, wherein in the first position, the optical coupling frustration is proximate to a first end portion of the second optical waveguide, and in the second position, the optical coupling frustration is spaced apart from the first end portion of the second optical waveguide. [Brief description of the drawings]

[0038] The present invention will be more fully understood from the following detailed description of specific embodiments taken in conjunction with the drawings, in which:

[0039] [Figure 1] Figure 1 is a perspective view illustrating the general principles of an optical switch according to some embodiments of the invention. Subsequent figures illustrate various aspects of individual embodiments of the switch of Figure 1.

[0040] [Diagram 2] FIG. 2 is a perspective view of an embodiment of the optical switch of FIG. 1 in which an end of one waveguide is positioned directly above a middle portion of another waveguide in accordance with an embodiment of the present invention.

[0041] [Diagram 3] FIG. 3 is a side view of the optical switch of FIG. 2 according to one embodiment of the present invention.

[0042] [Figure 4]FIG. 4 is a perspective view of another embodiment of the optical switch of FIG. 1 in which an end of one waveguide is positioned directly beneath a middle portion of the other waveguide in accordance with an embodiment of the present invention.

[0043] [Diagram 5] FIG. 5 is a side view of the optical switch of FIG. 4 according to one embodiment of the present invention.

[0044] [Figure 6] Figure 6 is a perspective view of yet another embodiment of the optical switch of Figure 1 in which an end of one waveguide is aligned over a middle portion of another waveguide in accordance with an embodiment of the present invention. Figure 6 shows the optical switch in an off state.

[0045] [Figure 7] FIG. 7 is a side view of the optical switch of FIG. 6 in an off state according to one embodiment of the present invention.

[0046] [Figure 8] FIG. 8 is a perspective view of the optical switch of FIGS. 6 and 7, showing the optical switch in an on state according to one embodiment of the present invention.

[0047] [Figure 9] FIG. 9 is a side view of the optical switch of FIGS. 6-8 in an on state according to one embodiment of the present invention.

[0048] [Figure 10] Figures 10 and 11 are respective cross-sectional views of the optical switch of Figures 6-9 according to one embodiment of the present invention, Figure 10 shows the optical switch in an OFF state and Figure 11 shows the optical switch in an ON state. [Figure 11] Figures 10 and 11 are respective cross-sectional views of the optical switch of Figures 6-9 according to one embodiment of the present invention, Figure 10 shows the optical switch in an OFF state and Figure 11 shows the optical switch in an ON state.

[0049] [Figure 12]Figures 12 and 13 are separate perspective views of the optical switch of Figures 6-11 with the translatable portion of the MEMS structure shown in wireframe, according to one embodiment of the present invention. Figure 12 shows the optical switch in an off state, and Figure 13 shows the optical switch in an on state. [Figure 13] Figures 12 and 13 are separate perspective views of the optical switch of Figures 6-11 with the translatable portion of the MEMS structure shown in wireframe, according to one embodiment of the present invention. Figure 12 shows the optical switch in an off state, and Figure 13 shows the optical switch in an on state.

[0050] [Figure 14] Figures 14 and 15 are separate perspective views of another embodiment of the optical switch of Figure 1 in which an end of one waveguide is positioned laterally displaced from a middle portion of the other waveguide, in accordance with an embodiment of the present invention, Figure 14 shows the optical switch in an off state and Figure 15 shows the optical switch in an on state. [Figure 15] Figures 14 and 15 are separate perspective views of another embodiment of the optical switch of Figure 1 in which an end of one waveguide is positioned laterally displaced from a middle portion of the other waveguide, in accordance with an embodiment of the present invention, Figure 14 shows the optical switch in an off state and Figure 15 shows the optical switch in an on state.

[0051] [Figure 16] FIG. 16 is a perspective view of an optical switch according to an optional embodiment of the invention in which a translatable optical component translates in a plane across another waveguide.

[0052] [Figure 17] FIG. 17 is a perspective view of an optical switch including a resonant coupler according to some embodiments of the present invention.

[0053] [Figure 18] FIG. 18 is a perspective view of an optical switch including an adiabatic coupler according to some embodiments of the present invention.

[0054] [Figure 19] FIG. 19 is a perspective view of yet another embodiment of the optical switch of FIG. 1 in which a vertically translatable coupling frustration is used to control whether two optical waveguides couple, in accordance with an embodiment of the present invention.

[0055] [Figure 20] 20, 21, and 22 are perspective views of alternative embodiments of the optical switch of FIG. 19, according to separate embodiments of the present invention. [Figure 21] 20, 21, and 22 are perspective views of alternative embodiments of the optical switch of FIG. 19, according to separate embodiments of the present invention. [Figure 22] 20, 21, and 22 are perspective views of alternative embodiments of the optical switch of FIG. 19, according to separate embodiments of the present invention.

[0056] [Diagram 23] 23 and 24 show the results of a computer simulation of the optical switch of FIG. 19 in the on and off states, respectively. [Figure 24] 23 and 24 show the results of a computer simulation of the optical switch of FIG. 19 in the on and off states, respectively.

[0057] [Diagram 25] Figures 25 and 26 are perspective views of yet another embodiment of the optical switch of Figure 1, in which an adiabatic coupler is disposed below a middle portion of the other waveguide, according to an embodiment of the present invention. In Figures 25 and 26, the translatable portion of the MEMS structure is shown in wire frame. Figure 25 shows the optical switch in an OFF state, and Figure 26 shows the optical switch in an ON state. [Figure 26]Figures 25 and 26 are perspective views of yet another embodiment of the optical switch of Figure 1, in which an adiabatic coupler is disposed below a middle portion of the other waveguide, according to an embodiment of the present invention. In Figures 25 and 26, the translatable portion of the MEMS structure is shown in wire frame. Figure 25 shows the optical switch in an OFF state, and Figure 26 shows the optical switch in an ON state.

[0058] [Figure 27] 27, 28, 29, and 30 show the results of computer simulations of the optical switches of FIGS. [Figure 28] 27, 28, 29, and 30 show the results of computer simulations of the optical switches of FIGS. [Figure 29] 27, 28, 29, and 30 show the results of computer simulations of the optical switches of FIGS. [Diagram 30] 27, 28, 29, and 30 show the results of computer simulations of the optical switches of FIGS.

[0059] [Diagram 31] Figure 31 is a top view, Figure 32 is a side view (optical switch in off state), Figure 33 is a side view (optical switch in on state), and Figure 34 is a cross-sectional view of a portion of a MEMS structure for translating a waveguide or coupling frustration according to an embodiment of the invention. The MEMS structure may be used in any of the optical switches described herein. [Diagram 32] Figure 31 is a top view, Figure 32 is a side view (optical switch in off state), Figure 33 is a side view (optical switch in on state), and Figure 34 is a cross-sectional view of a portion of a MEMS structure for translating a waveguide or coupling frustration according to an embodiment of the invention. The MEMS structure may be used in any of the optical switches described herein. [Diagram 33]Figure 31 is a top view, Figure 32 is a side view (optical switch in off state), Figure 33 is a side view (optical switch in on state), and Figure 34 is a cross-sectional view of a portion of a MEMS structure for translating a waveguide or coupling frustration according to an embodiment of the invention. The MEMS structure may be used in any of the optical switches described herein. [Diagram 34] Figure 31 is a top view, Figure 32 is a side view (optical switch in off state), Figure 33 is a side view (optical switch in on state), and Figure 34 is a cross-sectional view of a portion of a MEMS structure for translating a waveguide or coupling frustration according to an embodiment of the invention. The MEMS structure may be used in any of the optical switches described herein.

[0060] [Diagram 35] Figure 35 is a top view and Figure 36 is a cross-sectional view of a portion of a MEMS structure for translating a waveguide or coupling frustration according to another embodiment of the invention. The MEMS structure may be used in any of the optical switches described herein. [Diagram 36] Figure 35 is a top view and Figure 36 is a cross-sectional view of a portion of a MEMS structure for translating a waveguide or coupling frustration according to another embodiment of the invention. The MEMS structure may be used in any of the optical switches described herein.

[0061] [Figure 37] 37 and 38 are side views of a MEMS structure in respective off and on positions according to another embodiment of the present invention. The MEMS structure may be used in any of the optical switches described herein. [Figure 38] 37 and 38 are side views of a MEMS structure in respective off and on positions according to another embodiment of the present invention. The MEMS structure may be used in any of the optical switches described herein.

[0062] [Figure 39] 39 is a top view of a MEMS structure in an on position according to another embodiment of the present invention.The MEMS structure may be used in any of the optical switches described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0063] Detailed Description of Specific Embodiments Embodiments of the present invention provide MEMS-actuated optical switches that can be implemented on a photonic chip. These optical switches are small, generally planar, simple to implement, and, unlike Seok, contain only one moving MEMS component per optical switch, and unlike Seok or Han, contain only one moving MEMS component per optical switch. Evanescent coupling The switch exhibits low optical losses, requires low power to operate, is small, simple to control, and easy to integrate with other optical devices. Optical Switches - Overview

[0064] FIG. 1 is a perspective view of an optical switch 100 fabricated on a photonic chip 102 according to some embodiments of the present invention. The general principles of the optical switch 100 are described with reference to FIG. 1, and various aspects of the optical switch 100 are described below with reference to other figures. These aspects include (a) whether an end portion of one waveguide is adjacent to or above a middle portion of another waveguide, (b) whether the end portion is above or below the middle portion, (c) whether the two waveguides are resonantly or adiabatically coupled in the on state, (d) the number of possible switch states (e.g., a binary on / off optical switch has two states), (e) the optical component that translates to change the switch state, and (f) the nature of the translatable optical component (e.g., whether it is an optical coupler or a coupling frustration). These aspects can be combined in various ways, some of which are described herein. These aspects and combinations of aspects can vary between embodiments.

[0065] Optical switch 100 includes two optical waveguides 104 and 106 and has a design wavelength that may encompass a range of wavelengths. Waveguides 104 and 106 are attached to photonic chip 102 and positioned on, above, or below surface 108 of photonic chip 102. Waveguides 104 and 106 are made of suitable materials and are sized and engineered to support the propagation of optical signals within the design wavelength with low loss, as is well known in the art. A translatable optical component on the side of another waveguide

[0066] The relative placement of the end portion 110 of the waveguide 106 and the intermediate portion 112 of the other waveguide 104 represents one aspect of the optical switch 100 that may vary among various embodiments. In the embodiment shown in FIG. 1, the end portion 110 of the waveguide 106 and the intermediate portion 112 of the other waveguide 104 are laterally disposed adjacent to one another when viewed from above (normal to the surface 108) of the photonic chip 102. That is, the end portion 110 of the waveguide 106 is spaced the same distance from the surface 108 of the photonic chip 102 as the intermediate portion 112 of the other waveguide 104 is spaced from the surface 108, at least in the on-state, and the end portion 110 of the waveguide 106 is displaced a lateral distance 114 from the other waveguide 104 when viewed from above (normal to the surface 108). Thus, an end portion 110 of one waveguide 106 and an intermediate portion 112 of the other waveguide 104 lie side-by-side on the surface 108 of the photonic chip 102 when viewed from above, normal to the surface 108 . A translatable optical component aligned above another waveguide

[0067] However, in some other embodiments, exemplified by the optical switch 200 shown in FIGS. 2 and 3, the end portion 110 may be positioned and aligned above the intermediate portion 112 of the other waveguide 104 when viewed from above, normal to the surface 108. A support structure 202 elevates and supports the waveguide 106 above the other waveguide 104. Optionally, the waveguide 106 can return to the surface 108 beyond the optical switch 200. It should be appreciated that in some applications, the two waveguides 104 and 106 do not need to be positioned on the same or similar layer, as in Seok and Han. It should also be appreciated that not having the two waveguides 104 and 106 on the same or similar layer allows for the implementation of an optical switch with only a single coupler per switch cell, rather than two couplers, as in Seok and Han.

[0068] In some other embodiments, exemplified by the optical switch 400 shown in Figures 4 and 5, the end portion 110 of the optical waveguide 106 may be positioned and aligned below the intermediate portion 112 of the other waveguide 104 when viewed from above, normal to the surface 108, as discussed in more detail herein.

[0069] Returning to FIG. 1, most optical switches 100 are binary in that they have exactly two states, typically "on" and "off," and switch light from an input path 116 (one of the two optical waveguides 104 or 106) to exactly one of two output paths 118 or 120. One output path 118 may be a continuation of the input path 116 of the optical waveguide 104, while the other output path 120 typically follows the other optical waveguide 106. Both the input path 118 and the output path 120 extend beyond the optical switch 100. However, one of the two optical paths 118 or 120 terminates within the optical switch 100. That is, only one end of the two optical paths 118 or 120 is located within the optical switch 100. In contrast, the back-to-back couplers in the Seok or Han switch cells do not extend beyond the switch cell. That is, each end of each back-to-back combiner in Seok and Han is populated with its respective switch cell.

[0070] The optical switch 100 includes at least first and second input / output ports 130 and 132, optionally a third input / output port 134, and optionally a fourth input / output port (not shown). Regardless of the number of input / output ports on a given optical switch 100, the input / output ports 130-134 are representative. The input / output ports 130-134 may be defined by cross sections of their respective optical waveguides 104 and 106, as indicated by the dashed lines. The input / output ports 130-134 serve as individual interfaces between the optical switch 100 and other optical components, such as light sources, photodetectors, or other optical switches distinct from the optical switch 100 (not shown). Each input / output port 130-134 provides a means for obtaining optical signals into or out of the optical switch 100 from or to another optical component, i.e., other than the optical switch 100. Input / output ports 130 - 134 are used to inject light into and receive light from optical switch 100 .

[0071] The optical switch 100 controls how light received through one of the input / output ports 130-134 is directed to the other of the input / output ports 130-134. As described, the input / output ports 130-134 serve as individual interfaces to the optical switch 100. Thus, the input / output ports 130-134 are not components through which light propagates within the optical switch 100. Under the present definition of an input / output port, the translatable optical couplers in Seok or Han are not input / output ports because each Seok or Han translatable optical coupler is entirely internal to a given optical switch cell and each Seok or Han translatable optical coupler only transmits light within the optical switch cell, not between the optical switch cell and another optical component. The Seok and Han translatable optical couplers are not interfaces between the optical switch cell and other optical components. The on / off nature of the optical switch 100 may be considered to describe whether light from the input path 116 is switched or not switched to the output path 120 .

[0072] In the on-state, the two optical waveguides 104 and 106 mutually interact with each other with an efficiency of at least about 85% at the design wavelength. Evanescently coupled , so that depending on which waveguide 104 and / or 106 acts as the input waveguide, light propagating along the input waveguide 104 couples to the other waveguide 106, or vice versa, or coupling in both directions occurs. The coupling occurs within region 122. The coupling can be resonant and / or adiabatic.

[0073] In the off state, the two waveguides are Evanescently coupled No or two waveguides have an efficiency of less than about 10%. Evanescently coupled , so that light propagating along one of the two waveguides 104 or 106 does not substantially couple into the other waveguide, but instead continues to propagate along the input waveguide. As used herein, a coupling efficiency of less than about 10% is considered to be uncoupled. When the optical switch 100 is in the off state, light from the input path 116 propagates along the waveguide 104 to the output path 118. The output path 118 may continue to another optical switch (not shown) or another optical element (not shown), or the output path 118 may terminate beyond the optical switch 100.

[0074] Although discussed in the context of a binary optical switch, the principles disclosed herein may be used mutatis mutandis to construct optical switches with more than two states and / or more than two optical paths and / or optical switches that split input light among output paths according to a control signal, such that each output path of the multiple output paths simultaneously receives a non-zero portion, e.g., more than 10%, of the input light. Several such non-binary optical switches are described herein. The number of states of the optical switch is one aspect of the optical switch 100. Whether the input light is switched to substantially only one output path, or alternatively, the input light is split among multiple output paths, is another aspect of the optical switch 100.

[0075] Returning again to Figure 1, a MEMS structure 124 is disposed on or within the photonic chip 102. At least a portion (not shown) of the MEMS structure 124 is configured to translate, as indicated by double arrow 126, in response to a control signal 128, such as along an axis perpendicular to the surface 108 of the photonic chip 102. The MEMS structure 124 may include a flexure and a spaced apart electrode (not shown) that are electrostatically attracted to each other in response to a control voltage (derived from the control signal 128) applied to the electrodes or electromagnetic structures to translate the translatable portion of the MEMS structure 124.

[0076] The translatable portion of MEMS structure 124 is mechanically coupled to a translatable optical component (not shown in FIG. 1 but described in detail herein) and configured to translate the translatable optical component along axis 126. Translation of the translatable optical component from a first position to a second position changes optical switch 100 from one state to another, e.g., from an off state to an on state. In FIG. 1 , MEMS structure 124 is shown to the right of both waveguides 104 and 106, although in some embodiments (described with respect to other figures), MEMS structure 124 is disposed to the left of one or both of waveguides 104 and 106 and / or above or below one or both of waveguides 104 and 106.

[0077] As described, one side of the optical switch 100 involves the relative placement of the end portion 110 of one waveguide 106 and the middle portion 112 of the other waveguide 104. Figure 6 illustrates an optical switch 600 in which the end portion 110 of one waveguide 106 is aligned above the middle portion 112 of the other waveguide 104. Thus, in this embodiment, the placement side of the end portion 110 and middle portion 112 may be described as aligned above.

[0078] In this embodiment, the end portion 110 is mechanically coupled to the MEMS structure 124 (omitted from FIG. 6 for clarity) and translates in response to translation of a translatable portion of the MEMS structure 124, as indicated by double arrow 602. Thus, in this embodiment, the end portion 110 is the translatable optical component described above. The end portion 110 translates between (a) an OFF position distal to the intermediate portion 112 (as illustrated in FIGS. 6 and 7) and (b) an ON position proximate to the intermediate portion 112 (as illustrated in FIGS. 8 and 9). A flexible portion 604 facilitates the translation of the end portion 110, while the remainder of the waveguide 106 remains stationary relative to the photonic chip 102.

[0079] In the off position (FIGS. 6 and 7), the end portion 110 is far enough away from the intermediate portion 112 to prevent coupling between the end portion 110 and the intermediate portion 112. However, in the on position (FIGS. 8 and 9), the end portion 110 is close enough to, but not necessarily in intimate contact with, the intermediate portion 112 to provide coupling between the end portion 110 and the intermediate portion 112 with a coupling efficiency of at least about 85% at the design wavelength.

[0080] In this embodiment, the end portion 110 of the waveguide 106 remains vertically aligned above the intermediate portion 112 of the other waveguide 104 as it translates, regardless of whether the end portion 110 is in the off position or the on position. Thus, the end portion 110 can be described as translating vertically directly above the intermediate portion 112 of the other waveguide 104.

[0081] The MEMS structure 124 may define a volume enclosing the end portion 110 of the waveguide 106 and the middle portion 112 of the other waveguide 104, as shown in FIG. 6 by the dashed rectangular prism 606. FIGS. 10 and 11 are cross-sectional views of the MEMS structure 124 as viewed from a cross-sectional plane 608 (FIG. 6). FIGS. 12 and 13 are simplified perspective views of the optical switch 600 with the translatable portion of the MEMS structure 124 shown as a wire frame. FIGS. 10 and 12 illustrate the MEMS structure 124 when the end portion 110 is in the off position, i.e., the optical switch 600 is in the off state, and FIGS. 11 and 13 illustrate the MEMS structure 124 when the end portion 110 is in the on position, i.e., the optical switch 600 is in the on state.

[0082] As shown in Figures 10 and 11, the MEMS structure 124 may include a counter electrode 1000 that can be charged to an appropriate voltage and attracted to encourage translation of the end portion 110 between the OFF and ON positions. The MEMS structure 124 should include mechanical stops 1002 to limit the travel of the end portion 110, i.e., to ensure a small gap between the end portion 110 and the middle portion 112 in the ON position. The stops should also be designed to have a minimum contact area with the moving MEMS element to prevent "stiction" (van der Waals or mirror charge-based adhesion). The electrodes 1000, stops 1002, and other details have been omitted from the wireframe diagrams (Figures 12 and 13) for simplicity. Translation of the middle part of the waveguide

[0083] As discussed with respect to Figures 4 and 5, in the optical switch 400, the end portion 110 of the waveguide 106 is positioned below and aligned with the middle portion 112 of the other waveguide 104. The support structure 202 elevates and supports the waveguide 104 above the waveguide 106. In this embodiment, the middle portion 112 translates between an OFF position (shown in solid lines) and an ON position (shown in dashed lines in Figure 5), as indicated by a double arrow 402. In such an embodiment, a translatable portion of the MEMS structure 124 (not shown in Figures 4 and 5 for clarity) is mechanically coupled to the middle portion 112 and translates the middle portion 112 between the OFF position and the ON position. In such an embodiment, the middle portion 112 of the waveguide 104 is supported and translated by the translatable portion of the MEMS structure 124. 12 and 13 may be modified to place the middle portion 112 above the wireframe and the end portion 110 of the waveguide 106 below the wireframe. In other respects, optical switch 400 is similar to optical switch 600 described herein. A translatable optical component on the side of another waveguide

[0084] Figures 14 and 15 illustrate an optical switch 1400, which is similar to the optical switch 600 shown in Figures 6-13, except that the end portion 110 of the waveguide 106 is not aligned above the intermediate portion 112 of the other waveguide 104. Instead, according to this embodiment, in both the on and off positions, the end portion 110 is displaced laterally a distance 114 from the other waveguide 104 when viewed from above (normal to the surface 108).

[0085] FIG. 14 illustrates the optical switch 1400 in an off state, and FIG. 15 illustrates the optical switch 1400 in an on state. As in the optical switch 600 described with respect to FIGS. 6-13, in the optical switch 1400, the end portion 110 translates vertically, as indicated by the double arrow 1402. However, the end portion 110 of the waveguide 106 remains vertically misaligned with the middle portion 112 of the other waveguide 104, regardless of whether the end portion 110 is in the off or on position. In this embodiment, in the on state, the end portion 110 of the waveguide 106 and the middle portion 112 of the other waveguide 104 laterally couple, as indicated by the coupling region 122 in FIG. 15. Thus, in this embodiment, the end portion 110 is the translatable optical component described above.

[0086] A MEMS structure similar to the MEMS structure 124 shown in Figures 10-13 (not shown in Figures 14 and 15 for clarity) may be used to translate the end portion 110, although the end portion 110 and the intermediate portion 112 are laterally displaced from each other. The MEMS structure 124 described with respect to Figures 10-13 has flexures on both sides of the translatable optical component (the coupler), but if the translatable optical component translates in a plane that does not intersect another waveguide (as in Figures 14 and 15), the MEMS structure 124 may have a flexure on only one side, and the MEMS structure 124 may be anchored on only one side, as described below with respect to Figures 35 and 36. The end portion 110 may be described as translating vertically adjacent to the intermediate portion 112 of the other waveguide 104. Thus, in this embodiment, the dispositional sides of end portion 110 and intermediate portion 112 may be described as adjacent, side-by-side, or misaligned.

[0087] 1, if the waveguide 104 continues to another optical switch (not shown) or another optical component (not shown), the waveguide 104 may be referred to as a "bus" waveguide and the other waveguide 106 may be referred to as a "pick-off" waveguide because the other waveguide 106 "pick-offs" light from the bus waveguide when the optical switch 100 is in the on state. As explained above, one aspect of the optical switch 100 is the relative vertical position of the middle portion 112 of the bus waveguide and the end portion 110 of the pick-off waveguide. FIGS. 2, 3, and 6-14 show optical switches 200, 600, and 1400 in which the end portion 110 of the pick-off waveguide 106 is positioned higher than the middle portion 112 of the bus waveguide 104 relative to the photonic chip 102, at least in the off state. 4 and 5, on the other hand, show an optical switch 400 in which the end portion 110 of the intake waveguide 106 is positioned lower than the intermediate portion 112 of the bus waveguide 104. In the embodiment shown in FIG.

[0088] Another aspect of the optical switch 100 is the relative horizontal position of the intermediate portion 112 of the bus waveguide and the end portion 110 of the intake waveguide. FIGS. 2-13 show optical switches 200, 400, and 600 in which the end portion 110 of the intake waveguide is vertically aligned with the intermediate portion 112 of the bus waveguide. In these embodiments, the translatable optical component, whether the end portion 110 or the intermediate portion 112, translates in a plane 1600 that crosses the other waveguide, as shown in FIG. 16. The translatable optical component translates along an axis, as indicated by the double arrow 1602. On the other hand, FIGS. 14 and 15 show an optical switch 1400 in which the end portion 110 of the intake waveguide is displaced laterally and is therefore not vertically aligned with the intermediate portion 112 of the bus waveguide. In this embodiment, the translatable optical component translates in a plane that does not intersect the other waveguide. Translatable Optical Components

[0089] Another aspect of the optical switch 100 involves the nature of the translatable optical components, which can affect the type of coupling (adiabatic or resonant) that occurs when the optical switch is in the on state. Figure 17 is a perspective view of an optical switch in which the end portion 110 of one waveguide 106 and the middle portion 112 of the other waveguide 104 have approximately equal effective refractive indices at the design wavelength. In this case, when the end portion 110 and the middle portion 112 are in the on position, the coupling between the end portion 110 and the middle portion 112 is resonant.

[0090] Several factors affect the refractive index, including material and dimensions. Thus, one way to make the effective refractive index approximately equal is to make the end portions 110 and the intermediate portions 112 of the same material and have their respective dimensions approximately equal. However, if the end portions 110 and the intermediate portions 112 are made of different materials, their respective effective refractive indexes can be made approximately equal by adjusting their respective dimensions, as is well known to those skilled in the art. Similarly, if the respective dimensions of the end portions 110 and the intermediate portions 112 are different, they can be made to have approximately equal effective refractive indexes by careful selection of their respective materials.

[0091] In the resonant coupler, optical power is transferred between the two waveguides 104 and 106 due to the symmetric and asymmetric modes having different propagation velocities. If the length of the resonant coupler is appropriately selected, the input power can be arbitrarily divided between the output waveguides, as known to those skilled in the art. Unless otherwise indicated, in the embodiments described herein, the resonant coupler is designed to transfer as much power as is practical, and thus the optical switch can be considered to be an on / off switch. However, in other embodiments, the length of the resonant coupler is selected such that when the optical switch is in the on state, less than as much power as is practical is transferred, and the remainder of the power continues through the other waveguide.

[0092] Thus, for a resonant coupler, it is important to precisely control the relative position of the coupled portions of waveguides 104 and 106 when the optical switch is in the on state, because the resonant coupling is highly dependent on the spacing between waveguides 104 and 106. This can be accomplished by constraining the motion of the MEMS structure to approximately vertical motion only, and by including a physical stop, such as stop 1002 (FIG. 10), for the MEMS structure to rest on when in the on position.

[0093] Matching the effective refractive index of the end portion 110 and the intermediate portion 112 and constraining the motion of the MEMS structure is difficult to achieve. To avoid this difficulty, in some embodiments, as shown in FIG. 18, when the two waveguides 104 and 106 have different refractive indices, at least one of the end portion 110 or the intermediate portion 112 is tapered to promote adiabatic coupling between the end portion 110 and the intermediate portion 112 when the optical switch is in the on state. In the embodiment shown in FIG. 18, the end portion 110 of the waveguide 106 is tapered to form an adiabatic coupler 1800. The materials and dimensions of the end portion 110 and the intermediate portion 112 should be selected such that the effective refractive index of the guided mode in the adiabatic coupler 1800 is initially less than the effective mode refractive index of the other waveguide 104, and the effective mode refractive index gradually increases to a value above the effective mode refractive index of the other waveguide 104 in the direction in which the input light propagates. Power is transferred between the two waveguides 104 and 106 as their respective effective refractive indices intersect.

[0094] Such a tapered coupler 1800 is relatively tolerant to slight misalignments or slight displacements of one or both of the waveguides 104 and 106, manufacturing non-idealities, material variations between optical switches, etc. On the other hand, processing tolerances must be held tight for resonant couplers.

[0095] Any of the optical switches described herein may employ adiabatic or resonant couplers, as discussed with respect to Figures 17-18. Additionally, resonant coupling may provide wavelength selectivity, which may have the potential benefit of background noise reduction or wavelength multiplexing / demultiplexing through a series of optical switches. Optical coupling "frustrator"

[0096] FIG. 19 is a perspective view of an optical switch 1900 according to another embodiment of the present invention. Similar to the optical switch 1400 shown in FIGS. 14 and 15, the two waveguides 104 and 106 are laterally displaced a distance 114 from each other. However, unlike the optical switch 1400, neither the waveguides 104 or 106 (neither the end portion 110 of one waveguide 106 nor the middle portion 112 of the other waveguide) are translated. Instead, the end portion 110 of the waveguide 106 and the middle portion 112 of the other waveguide 104 are fixed in position relative to the photonic chip 102 such that the middle portion 112 is coupled to the end portion 110 with a coupling efficiency of at least 85% at the design wavelength. By keeping both waveguides fixed in position, tighter tolerances on the waveguide spacing can be ensured. As described, precise control of the relative positions of the coupled portions of waveguides 104 and 106 when the optical switch is in the on state is important for efficient resonant coupling. In contrast, the prior art optical switch by Seok and Han translates the two couplers, which can create alignment and spacing problems.

[0097] In optical switch 1900, the translatable optical component is a membrane 1902 ("optically coupled frustration") disposed above end portion 110 of waveguide 106. Membrane 1902 is mechanically coupled to a translatable portion of MEMS structure 124 (not shown for clarity). Thus, the translatable portion of MEMS structure 124 translates membrane 1902 vertically, as indicated by double arrow 1904, in a manner similar to the way that the translatable portion of MEMS structure 124 translates end portion 110 of waveguide 106 in optical switch 1400. MEMS structure 124 is similar to MEMS structure 124 described with respect to optical switch 1400 shown in FIGS. 14 and 15.

[0098] The material and dimensions of the membrane 1902 and the distance 1904 over which it translates are selected such that when the membrane 1902 is in a first position (the "on" position) distal to the end portion 110, there is minimal or negligible interaction between the membrane 1902 and the end portion 110 of the waveguide 106, and light couples from the first waveguide 104 into the second waveguide 106 with at least about 85% efficiency, however, when the membrane 1902 is in a second position (the "off" position) proximate the end portion 110, the membrane 1902 strongly interacts with the end portion 110. This interaction prevents coupling between the two waveguides 104 and 106 by breaking the symmetry between the two waveguides 104 and 106. The symmetry breaking prevents the existence of the symmetric and asymmetric modes described above, so that no coupling occurs between the two waveguides 104 and 106. When the coupling frustration 1902 is in the off position, the two waveguides 104 and 106 are no longer in phase, so power cannot be coupled between the waveguides 104 and 106.

[0099] 19, the coupling frustration 1902 is disposed only over the end portion 110 of the waveguide 106, while in another embodiment, shown in Figure 20, in an optical switch 2000, the coupling frustration 1902 is disposed across the middle portion 112 of the other waveguide 104. In yet another embodiment, shown in Figure 21, in an optical switch 2100, the coupling frustration 1902 is disposed, to some extent, across both the end portion 110 of one waveguide 106 and the middle portion 112 of the other waveguide 104.

[0100] Placing the coupling frustrator 1902 above only the end portion 110 of the waveguide 106, as in optical switch 1900 (FIG. 19), has advantages. For example, light does not couple as strongly into the coupling frustrator 1902, and the coupling frustrator 1902 may be made from an optically lossy material. If the coupling frustrator 1902 is placed above the waveguide 104, it should be made thin enough that it does not have guided modes of its own, and the coupling frustrator 1902 should have low optical loss.

[0101] In another embodiment shown in FIG. 22, in an optical switch 2200, an end portion 110 of one waveguide 106 is aligned above a middle portion 112 of the other waveguide 104. As in optical switches 1900, 2000, and 2100, the end portion 110 and middle portion 112 are positioned close enough together to couple in the absence of a coupling frustrated 2202. However, unlike optical switches 1900-2100, in optical switch 2200, optical frustrated 2202 translates vertically (2204) along a side of the two waveguides 104 and 106. That is, optical frustrated 2202 is displaced laterally a distance 114 away from the two waveguides 104 and 106, and optical frustrated 2202 translates in a plane (not shown) that does not intersect the two waveguides 104 and 106.

[0102] In the optical switch embodiments 1900-2200 that translate the optical frustrator 1902 or 2202, the light does not necessarily have to pass through the volume defined by the MEMS structure 124. Thus, the light may possibly Evanescent interactions 23 and 24, no light is incident on the material of the MEMS structure 124 except for 1900 nm. Thus, materials that exhibit some optical loss can be used for the MEMS structure 124, which is important in that wavelengths around 900 nm are of particular interest in some applications. These wavelengths are absorbed by silicon with an absorption length similar to that modeled in FIGS. 23 and 24 (discussed below). Other MEMS devices may be unable to tolerate these optical losses in their individual waveguides. However, as shown in FIGS. 23 and 24, these optical losses can be tolerated in the MEMS optical frustrator 1902 or 2202, allowing silicon to be used as the material for the MEMS structure 124. This is important because silicon is a preferred material for MEMS devices due to its physical and electrical properties and its ease of processing.

[0103] In yet other embodiments of the optical switch (not shown), in which the two waveguides 104 and 106 are either arranged one on top of the other as in FIG. 22 or side-by-side as in FIG. 19, the coupling frustration may translate laterally rather than vertically, so long as, in the off state, the coupling frustration is sufficiently close to one of the waveguides so as to shift the effective refractive index of the propagating mode of that waveguide relative to the other waveguide. Combined side of optical switch

[0104] As described, the optical switches described herein involve various aspects including (a) whether an end portion of one waveguide is adjacent to or on top of an intermediate portion of another waveguide, (b) whether the end portion is above or below the intermediate portion, (c) whether the two waveguides are resonantly or adiabatically coupled in the on state, (d) the number of possible switch states, (e) the optical components that translate to change the switch state, and (f) the nature of the translatable optical components. These aspects may be combined in various ways. For example, the optical switch 200 described with reference to FIGS. 2-4 may include a resonant coupler or an adiabatic coupler. Similarly, the optical switch 400 described with reference to FIGS. 4-5 may also include a resonant coupler or an adiabatic coupler. Outer boundary of the optical switch

[0105] The optical switch 100 has an outer boundary 136 ( FIG. 1 ) that defines a minimum sized rectangular area that includes the translatable optical components and the MEMS structure 124. The outer boundary 136 is the minimum rectangular area on the photonic chip 102 that includes the MEMS structure 124 and the translatable optical components, which may be the intermediate portion 112 of the first optical waveguide 104 or the end portion 110 of the second optical waveguide 106. As can be seen in FIG. 1 , the input / output ports 130-134 are all located outside the outer boundary 136. Each end (not shown) of the first optical waveguide 104 is located outside the outer boundary 136. The intermediate portion 112 of the first optical waveguide 104 is located within the outer boundary 136. The first end portion 110 of the second optical waveguide 106 is located within the outer boundary 136. A second end (not shown) of the second optical waveguide 106, opposite the first end portion 110, is disposed outside of the outer boundary 136. The MEMS structure 124 is disposed within the outer boundary 136. Computer Simulation

[0106] 23 and 24 show the results of a computer simulation of the optical switch 1900 (FIG. 19) performed using the Bidirectional Eigenmode extension and varFDTD engine of Mode Solutions software from Lumerical, Inc. The simulation includes an extra bend in the waveguide beyond that shown in FIG. 19 to separate the input and output waveguides. Table 1 lists example device parameters used in the simulation. FIG. 23 shows the results of a simulation of the optical switch 1900 in the on state, i.e., the coupling frustrated 1902 is distal from the end portion 110 of the waveguide. FIG. 24 shows the results of a simulation of the optical switch 1900 in the off state, i.e., the coupling frustrated 1902 is proximal to the end portion 110. The film material simulated was chosen to have significant optical loss (absorption length of about 100 microns) and yet the performance of the optical switch 1900 was still excellent. As can be seen from Figures 23 and 24, the optical switch 1900 exhibits low optical loss and excellent attenuation in both states. [Table 1]

[0107] 25 and 26 are perspective views of an optical switch 2500 including an adiabatic coupler 2502 disposed below the intermediate portion 112 of the other waveguide 104. The adiabatic coupler was described with respect to FIG. 18. Other aspects of the optical switch 2500 are similar to other embodiments described herein such as with respect to FIGS. 4, 5, 10, 11, and 18. FIGS. 25 and 26 illustrate the translatable portion of the MEMS structure 124 as a wireframe. FIG. 25 illustrates the MEMS structure 124 when the optical switch 2500 is in an off state, i.e., the intermediate portion 112 is distal from the adiabatic coupler 2502, and FIG. 26 illustrates the MEMS structure 124 when the optical switch 2500 is in an on state, i.e., the intermediate portion 112 is proximate to the adiabatic coupler 2502. Arrows 2504 indicate the path of light propagation through optical switch 2500 from waveguide 104 to waveguide 106 .

[0108] 27, 28, 29, and 30 show computer simulation results for optical switch 2500. Table 2 lists example device parameters used in the simulations. [Table 2]

[0109] Figures 27 and 29 depict graphs of optical power (mode profile) at various xy coordinates in a cross-section of optical switch 2500, i.e., at the beginning (in the direction of light propagation) of adiabatic coupler 2502, as viewed from cross-sectional plane 2506, when optical switch 2500 is in its off and on states, respectively. Figures 28 and 30 depict graphs of optical power (mode profile) at various xy coordinates in a cross-section of optical switch 2500, i.e., at the end (in the direction of light propagation) of adiabatic coupler 2502, as viewed from cross-sectional plane 2508, when optical switch 2500 is in its off and on states, respectively.

[0110] In Figures 27-30, position 2700 represents the bus waveguide 104 and position 2702 represents the other waveguide 106. When the optical switch 2500 is in the off state, the propagating mode remains confined to the upper bus waveguide 104 (position 2700), as can be seen in Figures 27 and 28, i.e., no light is coupled into the adiabatic coupler 2502. However, when the optical switch 2500 is in the on state, the propagating mode can be seen in the bus waveguide 104 at an x-position corresponding to the beginning of the adiabatic coupler 2502 (Figure 29), but with an x-position corresponding to the end of the adiabatic coupler 2502, the propagating mode is coupled from the bus waveguide 104 to the bottom waveguide 106, with most of the power being confined within the bottom waveguide 106 (Figure 30).

[0111] Dimensions for one implementation of optical switch 2500 using silicon nitride for waveguides 104 and 106 are provided in Table 2. The overall length and waveguide dimensions of optical switch 2500 can be adjusted depending on the desired total size and required performance of optical switch 2500. Other materials, such as silicon, sapphire, titanium dioxide, diamond, silicon carbide, and chalcogenide glasses, can also be used for the waveguides depending on the desired wavelengths of operation and optical power to be addressed by optical switch 2500. Additional / alternative structures and / or materials

[0112] FIG. 31 is a top view, FIG. 32 is a side view (optical switch in off state), FIG. 33 is a side view (optical switch in on state), and FIG. 34 is a cross-sectional view of a portion of a MEMS structure 124 for translating a waveguide or coupling frustration according to an embodiment of the present invention. The thickness dimensions of FIG. 34 (about 100 nm and about 300 nm, respectively) are example dimensions that work well for an embodiment that includes silicon-rich silicon nitride material and operates at a wavelength of about 1,550 nm. However, in other embodiments, the thickness, waveguide material, and wavelength may vary depending on design choices. The distance 3300 (FIG. 33) is about 100 μm or longer in some embodiments to accommodate tension in the actuation region. The present MEMS structure 124 is mainly applicable to optical switches in which two waveguides 104 and 106 are arranged one above the other. Ideally, a waveguide material, which is likely to be an electrical insulator, is deposited on top of the MEMS structural material and on top of the electrodes. Alternatively, the MEMS structural material may be deposited on top of the waveguide material. However, this results in an electrical insulator between the top and bottom electrodes.

[0113] FIG. 35 is a top view and FIG. 36 is a cross-sectional view of a portion of a MEMS structure 124 for translating a waveguide or coupling frustration according to another embodiment of the present invention. The thin slab between the waveguide and the pad for actuation shown in FIG. 35 is optional. Although FIG. 36 shows the upper waveguide directly above the lower waveguide, the lower waveguide does not have to be directly below the upper waveguide. The thickness dimensions of FIG. 34 (about 100 nm and about 300 nm, respectively) are example dimensions that work well for an embodiment that includes a silicon-rich silicon nitride material and operates at a wavelength of about 1,550 nm. However, in other embodiments, the thickness, waveguide material, and wavelength can vary depending on design choices. Side views of the switch off and on states are similar to FIGS. 32 and 33. The present MEMS structure 124 is primarily applicable to optical switches where the translating upper layer may be anchored to only one side, such as in embodiments shown in Figures 14, 15, and 22, in which a portion of a waveguide or coupling frustration translates vertically along the side of one or more other waveguides.

[0114] In situations where actuation occurs on only one side, as in Figures 35-36, a stop may be used to prevent contact between the upper and lower waveguides. A single electrode pair would otherwise likely result in a tilted upper waveguide, at least when the MEMS structure is actuated, as opposed to one electrode pair on each side of the waveguide. The stop flattens the actuated portion of the MEMS structure.

[0115] 37 and 38 are side views of a MEMS structure 124 in respective off and on states according to another embodiment of the invention. In this embodiment, rather than a pair of electrodes that electrostatically attract or repel each other, a piezoelectric material is used for actuation. The piezoelectric material expands or contracts in response to an actuation voltage applied to the top conductor. This expansion or contraction results in bending of the MEMS structure as shown in FIG. 38. A lower stop limits the translation of the MEMS structure, thus flattening it to the right.

[0116] 39 is a top view of a MEMS structure 124 in an on state according to another embodiment of the present invention. This MEMS structure 124 may be used, for example, to translate a coupling frustration. The top 3900 of the MEMS structure 124 is shown diagrammatically only to expose the components below the top, including the end portion 110 of the waveguide 106. Arrows 3902 indicate the path taken by light as it is coupled from the waveguide 104 to the waveguide 106. The top 3900 may be perforated to allow air to flow through the perforations as the top translates, reducing friction with the air.

[0117] The waveguides and / or MEMS structures described herein may alternatively be made from aluminum nitride, depending on the design wavelength of the optical switch. The MEMS structures described herein may alternatively be made from scandium aluminum nitride or various metals.

[0118] The present invention is described through the exemplary embodiments described above, but modifications and variations to the illustrated embodiments may be made without departing from the inventive concept disclosed herein. For example, specific parameter values ​​such as dimensions and materials may be recited in relation to the disclosed embodiments within the scope of the present invention, but the values ​​of all parameters may vary over a wide range to suit different applications. Unless otherwise indicated in the context or understood by a person skilled in the art, terms such as "about" mean within ±20%.

[0119] As used herein, including the claims, the term "and / or" when used in connection with a list of items means one or more of the items in the list, i.e., at least one of the items in the list, but not necessarily all of the items in the list. As used herein, including the claims, the term "or" when used in connection with a list of items means one or more of the items in the list, i.e., at least one of the items in the list, but not necessarily all of the items in the list. "Or" does not mean "exclusive or" unless otherwise indicated.

[0120] The disclosed aspects or portions thereof may be combined in ways not recited above and / or not expressly claimed. In addition, the embodiments disclosed herein may suitably be practiced in the absence of any element not specifically disclosed herein. Thus, the present invention should not be considered as limited to the disclosed embodiments.

Claims

1. 1. An optical switch having a design wavelength, the optical switch comprising: A photonic chip, a translatable optical coupling frustrated element; a first optical waveguide disposed on the photonic chip, the first optical waveguide having an intermediate portion; a second optical waveguide distinct from the first optical waveguide, the second optical waveguide disposed on the photonic chip and having a first end portion, the first end portion being stationary with respect to an intermediate portion of the first optical waveguide, the first end portion being sufficiently close to an intermediate portion of the first optical waveguide such that the first end portion evanescently couples with the intermediate portion of the first optical waveguide in the absence of the optical coupling frustration, and a coupling efficiency between the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide is at least about 85% at the design wavelength; a MEMS structure disposed on the photonic chip, the MEMS structure having a translatable portion mechanically coupled to the optical coupling frustrator, the translatable portion configured to translate the optical coupling frustrator in response to a control signal between at least (a) a first position proximate to at least one of the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide, and (b) a second position spaced apart from the at least one of the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide; Equipped with in the first position, the optical coupling frustrator is sufficiently proximate to at least one of the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide to prevent evanescent coupling between the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide, and a coupling efficiency between the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide is less than about 10% at the design wavelength; an optical switch, wherein in the second position, the optical coupling frustration is sufficiently spaced from at least one of the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide to enable evanescent coupling between the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide, and a coupling efficiency between the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide is at least about 85% at the design wavelength.

2. 2. The optical switch of claim 1, wherein in both the first and second positions, the optical coupling frustration is aligned above at least a portion of at least one of the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide when viewed normal to the photonic chip.

3. 2. The optical switch of claim 1, wherein in both the first and second positions, the optical coupling frustration is laterally displaced from the intermediate portion of the first optical waveguide and the first end portion of the second optical waveguide when viewed normal to the photonic chip.

4. 2. The optical switch of claim 1, wherein in the first position, the optical coupling frustration is proximate to the intermediate portion of the first optical waveguide, and in the second position, the optical coupling frustration is spaced from the intermediate portion of the first optical waveguide.

5. 2. The optical switch of claim 1, wherein in the first position, the optical coupling frustration is proximate to the first end portion of the second optical waveguide, and in the second position, the optical coupling frustration is spaced from the first end portion of the second optical waveguide.

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