Electric control 3D optical waveguide switch using phase change material

Abstract

A vertical directional coupler or switch includes a lower waveguide and an upper waveguide integrated with an optical phase change material disposed between the lower waveguide and the upper waveguide to control the direction of optical coupling between the lower waveguide and the upper waveguide.

Description

[0001] This application is a divisional application of a patent application with application number 2020800768679, application date November 18, 2020, and invention name “Electrically controlled 3D optical waveguide switch using phase change materials”.

[0002] Cross-references to related patents and applications

[0003] This application claims the patent application filed on November 19, 2019, entitled

[0004] The invention claims the benefit of U.S. Provisional Patent Application No. 62 / 937,470 for “Electrically-controllable 3D optical wave guide switch modeling with phase change materials,” the disclosure of which is hereby incorporated herein by reference.

[0005] The technology disclosed in this article is related to the technology disclosed in U.S. Patent No. 9,368,720, entitled “Method to make Phase-Change Material RF Switches with Thermal Dielectrics”, issued on June 14, 2016, the disclosure of which is hereby incorporated by reference herein.

[0006] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0007] none Technical Field

[0008] The disclosed technology relates to optical switches. Background Art

[0009] Modern microelectronics applications in defense and commercial sectors are expanding toward cognitive RF and image processing, autonomy, machine learning, and artificial intelligence. These applications require processing of big data and face performance challenges associated with: 1) memory bottlenecks, or 2) latency and significant power consumption associated with data transfer between computing chips. To overcome data latency and power consumption issues, innovative approaches to high-aggregate bandwidth data paths between computing chips are needed that consume less energy than traditional electrical interfaces.

[0010] Given that conventional CMOS scaling no longer meets computing performance requirements, the International Technology Roadmap for Semiconductors (ITRS) emphasizes the importance of interconnect innovation and 3D integration.

[0011] Furthermore, the reconfigurability of the interconnect fabric, combined with reconfigurable memory, should enhance the computational performance of Networks-on-Chip (NoCs). Given the slowdown of Moore’s Law, current state-of-the-art (SOA) microprocessor chips rely on parallelism to improve computational performance. For example, Intel’s 1.28Tflop NoC consists of 80 CPU blocks and consumes about 90 watts. The inter-chip network operates at 4GHz, a 10x8 2D mesh. A major issue is that as the technology scales, the charging and discharging of the interconnect wires results in increased latency. Low-loss photonic switching fabrics can potentially enable significantly lower power efficiency in optical interconnect links to reach aggressive targets below 1pJ / bit, which would enable parallelism in scaling multi-core NoCs for high-performance computing.

[0012] In the article entitled "CMOS-Compatible Scalable Photonic Switch Architecture Using 3D-Integrated Deposited Silicon Materials for High-Performance Data Center Networks", Proceedings 2011 Conference on Lasers and Electro-Optics paper OMM2 by Biberman et al., the disclosure of which is hereby incorporated by reference herein, an existing switch having dielectric silicon nitride input waveguides and output waveguides located in different planes is described, which uses polysilicon electro-optical materials to control the optical coupling between these input waveguides and output waveguides. See Figure 1 of that article. Since the refractive index change produced by the electro-optics of the silicon material is very small, the silicon is formed into a ring resonator to enhance the effect of the refractive index change. Therefore, the spectral width of the switch operation is quite small.

[0013] A prior art switch that uses phase changes in PCM to control the switch is described in an article by Zhang et al. (Optics Letters, v.43, n.1, Jan. 2018, pp.94-97), the disclosure of which is hereby incorporated by reference herein. See Figure 2. However, its input waveguide and output waveguide are located in the same plane instead of two different planes. In addition, R. Soref et al. published the concept of electro-optical switching at 1550nm using a two-state GeSe phase change layer (see Opt. Express, vol. 23, p. 1536-1546, 2015), the disclosure of which is hereby incorporated by reference herein. However, the device is an optical switch with a single Si waveguide embedded in a GeSe PCM layer, and is not a directional coupler.

[0014] PCM materials have also been proposed for use in memory devices. See Wong et al., "Phase Change Memory", Proceeding of the IEEE, Vol. 98, No. 12, Dec 2010 pp 2201-2227, the disclosure of which is hereby incorporated by reference herein.

[0015] The technology disclosed herein is related to and improves upon the technology disclosed in U.S. Patent No. 9,368,720 issued on June 14, 2016, in that, for example, a better layout is provided when the disclosed switch is used in a crossbar switch design. The disclosure of U.S. Patent No. 9,368,720 is hereby incorporated herein by reference.

[0016] The disclosed switch is intended to use an optical phase change material (abbreviated as "O-PCM" or simply "PCM" in this document and the accompanying drawings) to switch light of 1550nm wavelength commonly used in optical communication systems to achieve switching. Other materials besides the materials disclosed herein can also be used with switches intended to switch light of other wavelengths. Summary of the invention

[0017] In one aspect, the technology of the present disclosure provides an optical coupler (or switch) structure in which a vertical coupler has both lower and upper SiN waveguides with very low loss (preferably 0.1 dB / cm) and a very thin O-PCM material is disposed therebetween to control the coupler switch. The O-PCM is preferably a GeSe alloy with an optical bandgap greater than 1 eV. The two control electrodes are connected by a thermal shunt to provide effective transient heating without interfering with the optical field. The switch can be manufactured using a monolithic process without the need for conventional wafer bonding techniques. By vertically separating the two silicon nitride waveguides, optical losses are significantly reduced compared to a planar geometry where the two silicon nitride waveguides must intersect. Compared to a directional coupler array based on a planar O-PCM switch, the O-PCM switch of the present disclosure with a multi-stage, low-loss SiN waveguide achieves a highly flexible crossing structure with a reduced number of waveguide crossings.

[0018] In another aspect, the disclosed technology provides a vertical coupler switch including lower and upper SiN waveguides, and the lower and upper SiN waveguides integrate an O-PCM material disposed between the lower and upper waveguides for controlling optical coupling between the lower and upper waveguides.

[0019] In another aspect, the disclosed technology provides a vertical directional coupler or switch, which includes lower and upper waveguides, and the lower and upper waveguides are integrated with an optical phase change material disposed between the lower and upper waveguides for controlling the optical coupling between the lower and upper waveguides. The lower and upper waveguides are preferably formed of SiN, and the optical phase change material is preferably formed of GeSe or a GeSe alloy.

[0020] In yet another aspect, the disclosed technology provides a crossbar switch comprising a plurality of vertical couplers or switches, the crossbar switch further comprising a plurality of input and output waveguides, the plurality of input and output waveguides being arranged in a grid-like pattern that crosses one another in different layers of the crossbar switch, the plurality of vertical couplers or switches being disposed at intersections of the plurality of input and output waveguides, wherein (i) upper waveguides of a subset of vertical directional couplers or switches are coupled in series with one another and with a selected one of the input or output waveguides of the crossbar switch, (ii) lower waveguides of different subsets of vertical directional couplers or switches are coupled in series with one another and with a selected different one of the input or output waveguides of the crossbar switch, and (iii) an optical phase change material is disposed between the lower and upper waveguides to control optical coupling between the lower and upper waveguides in each of the plurality of vertical couplers or switches. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 depicts a prior art switch having dielectric silicon nitride input and output waveguides located in different planes and using polysilicon electro-optical material to control the optical coupling between those input and output waveguides.

[0022] FIG. 2 depicts a prior art switch that uses phase changes in a PCM to control switching.

[0023] FIG3( a ) provides a perspective view of an individual 3D O-PCM switch device (preferably used for sixteen positions in the four-by-four crossbar of FIG3( c )). The individual 3D O-PCM switch device has low-loss SiN input and output waveguides located on different layers of the 3D structure, and an O-PCM switch structure located between the two SiN waveguides.

[0024] FIG3( b ) is an exploded view of the SiN input waveguide and output waveguide and the O-PCM switch structure, wherein the SiN input waveguide and output waveguide are located at different layers of the structure, and the O-PCM switch structure is located between the two SiN input and output waveguides. For clarity of representation, the SiN material embedded in the PCM material (in the preferred embodiment) is omitted.

[0025] FIG. 3( c ) is a perspective schematic diagram of an optical phase change material (O-PCM or PCM only) crossbar switch having four input waveguides and four output waveguides in this embodiment.

[0026] FIG3( d ) depicts a cross-sectional view of the O-PCM switch of FIG3( c ), showing the relative positions of the SiN waveguide embedded in SiO 2 , the PCM switch, the heater, and the heat shunt.

[0027] Figure 3(e) depicts a graph similar to Figure 3(c) and 3(d) 4 is a cross-sectional view of another embodiment of an O-PCM switch showing the relative positions of the SiN waveguide, PCM switch, heater and heat shunt, but in this embodiment the heat shunt surrounds the PCM within the PCM switch.

[0028] FIG4( a) shows an HFSS simulation of an O-PCM-based 3D bidirectional coupler switch of the present disclosure, wherein the O-PCM material is preferably integrated in a middle waveguide or a short waveguide disposed between the upper and lower waveguides. The table in the figure lists the simulated light intensity in the waveguide in the region adjacent to the middle waveguide or the short waveguide, expressed in arbitrary power units per unit area.

[0029] Figure 4(b) to Figure 4(c) It is depicted that light will either couple out of the bottom waveguide and into the upper waveguide (a "crossover" configuration or state), or remain in the bottom waveguide (a "through" configuration or state), depending on the phase of the O-PCM material.

[0030] Figure 5 An O-PCM switch is shown with a heat shunt that effectively transfers the required heat to the O-PCM layer. Thermal model of transient heating of the PCM at 5 nJ / μm 2 For clarity of presentation, the SiN material of the short waveguide used with the PCM is omitted. DETAILED DESCRIPTION

[0031] The following description is presented to enable one of ordinary skill in the art to make and use the invention and to incorporate it into the context of a particular application. Various modifications and uses in different applications will be apparent to those skilled in the art, and the general principles defined herein can be applied to a wide range of embodiments. Therefore, the present invention is not intended to be limited to the embodiments presented, but rather to be given the widest scope consistent with the principles and novel features disclosed herein.

[0032] In the following specific embodiments, many specific details are set forth to provide a more thorough understanding of the present invention. However, it is apparent to those skilled in the art that the present invention may be practiced without being limited to these specific details. In other cases, to avoid obscuring the present invention, well-known structures and devices are shown in block diagram form rather than in detail.

[0033] The reader's attention is directed to (i) all papers and documents filed concurrently with this specification and disclosed to the public for inspection with this specification (the contents of all such papers and documents are incorporated herein by reference), and (ii) all other papers and documents incorporated herein by reference (but not actually filed with this specification).

[0034] Unless expressly stated otherwise, all features disclosed in this specification (including any accompanying claims, abstracts and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose. Therefore, unless expressly stated otherwise, each feature disclosed is only an example of a general series of equivalent or similar features.

[0035] In addition, any element in the claims that does not explicitly state a "means" for performing a specific function, or a "step" for performing a specific function, should not be interpreted as a "means" or "step" clause as provided in 35 USC Section 112, Paragraph 6. In particular, the "step of" or "act of" used in the claims herein is not intended to invoke the provisions of 35 USC 112, Paragraph 6.

[0036] like Figure 3(a) to Figure 3(d) As shown, the technology disclosed herein provides a coupler switch structure using an optical phase change material (O-PCM), wherein the vertical directional coupler switch design includes a lower waveguide (WG) 10 and an upper waveguide (WG) 12 formed of a very low loss material such as SiN, and an O-PCM material 14 located therebetween to control the optical coupler switch structure 8. The state of the O-PCM material 14 is changed by a heater 29. In FIG. 3( a), the heater 29 is depicted as being in close proximity to the O-PCM material 14, but in certain embodiments, it may be more convenient to position the heater 29 away from the O-PCM material 14 whose state is controlled by the heater 29, as will be seen, for example, with reference to FIG. 3( d). For reasons discussed below, the O-PCM material 14 is preferably formed of GeSe or a GeSe alloy.

[0037] FIG3( a) depicts a single optocoupler switch structure 8, while FIG3( c) shows a perspective schematic diagram of an optical phase change material (O-PCM) crossbar switch having four input (or in this embodiment, thru) waveguides (In1 to In4) 10 and four output (or in this embodiment, cross) waveguides (Out1 to Out4) 12 connected by sixteen optocoupler switch structures 8, each of which is depicted in more detail in FIG3( a). Of course, since typically a crossbar switch will have more than four inputs and more than four outputs, the number of optocoupler switch structures 8 used in a crossbar arrangement can be much greater than the sixteen depicted in FIG3( c).

[0038] Control of the various heaters 29 (heating or not) is accomplished by circuitry in, for example, an application specific integrated circuit (ASIC) 28, and the array of optocoupler switch structures 8 forming the crossbar switch of FIG3(c) may be provided on the ASIC 28. The ASIC 28 may conveniently be formed from CMOS devices, although other or additional semiconductor technologies may be used instead of (or in addition to) CMOS if desired.

[0039] In the crossbar switch of FIG3(c), if desired, the input (or through) waveguides 10 and the output (or crossover) waveguides 12 can be interchanged, so that its input waveguides (In1 to In4) become outputs and its output waveguides (Out1 to Out4) become inputs. If desired, the upper and lower waveguides can also be interchanged.

[0040] FIG3( d ) is a schematic cross-sectional view of a single optical coupling switch structure 8 depicted in FIG3( a ).

[0041] The gap size between waveguides is preferably finely controlled by a nanoscale material deposition process, which greatly reduces process variability in switch manufacturing compared to 2D lateral switch designs where the gap is defined by photolithography and etching processes.

[0042] By vertically separating the upper waveguide 12 (the straight waveguide in the embodiment of FIG. 3( c)) and the lower waveguide 10 (the crossed waveguide in the embodiment of FIG. 3( c)), the through state loss is significantly reduced compared to the planar geometry where the crossed waveguide and the straight waveguide intersect. The 3D O-PCM switch structure 8 and the multi-stage low-loss waveguides 10, 12 are preferably both formed of SiN, achieving a highly flexible crossbar switch architecture (e.g., as shown in FIG. 3( c)), reducing the number of waveguide crossings, and thereby greatly reducing optical losses in the crossbar switch matrix. The waveguide crossing occurs in a region 15 where the upper waveguide 12 is first bent to extend parallel to the lower waveguide 10 over a short straight segment or portion 12S of each upper waveguide 12 where it is set parallel to the underlying lower waveguide 10 for a distance corresponding to the length segment 12S and then bent again (see non-straight portion 12NL) to be set again in a direction more or less orthogonal to the direction of the straight-through waveguide 10. The input waveguide and the output waveguide have a limited optical coupling length or region 15 (e.g., a length of 20 μm to 30 μm) to couple light through the O-PCM switch structure disposed therebetween. The coupling length is ideally set by efficient optical coupling with minimal optical losses in the O-PCM switch structure.

[0043] A relatively short waveguide 19, preferably mainly formed of SiN, is preferably disposed between upper and lower waveguides disposed in parallel to each other, so that the length of the short waveguide 19 is preferably approximately equal to the length of the straight section 12S of the waveguide 12. The short waveguide 19 has an O-PCM material 14 sandwiched between upper and lower portions 18 (preferably formed of SiN) of the short waveguide or PCM waveguide 19, and preferably in the middle between the upper and lower surfaces of the short waveguide or PCM waveguide 19. Each waveguide 19 is disposed parallel to the waveguide 10, and is also disposed parallel to the short section 12S of the waveguide 12 at each 3D O-PCM switch structure 8. The length of the section 12S is preferably shorter than the spacing between adjacent waveguides 10 (the spacing is preferably about 50 μm, as shown in FIG. 3( c)). The short section waveguide 19 is a switchable waveguide that couples adjacent input waveguides 10 and output waveguides 12S. Depending on the phase of PCM chosen (amorphous or crystalline), the optical properties of the short waveguide 19 of, for example, SiN / PCM / SiN will change, making the coupling normally open for amorphous PCM switching or normally closed for crystalline PCM switching.

[0044] The heater 29 may be positioned proximate to the O-PCM material 14 as shown in the embodiments of Figures 3(a) and 3(c), or may be positioned further away as shown in the embodiments of Figures 3(d) and 3(e), where the heater 29 is spaced a distance d from the PCM and heat is transferred to (or from) an area proximate to the O-PCM 14 via the heat shunt channel 16. The heat shunt channel 16 is preferably a material that is an efficient conductor of thermal energy, such as AlN, SiC, or diamond, that is transparent at the frequency of light in the waveguides 10 and 12 (preferably transparent at a wavelength of 1550 nm for these communication system embodiments). The heater 29 is preferably spaced at least a distance d from the O-PCM 14 to help minimize interference with the optical field in the waveguide 19. Figure 5 A metal heating element 29e is depicted within the heater 29 in FIG.

[0045] The lower waveguide 10 may be embedded in a SiO2 cladding material 20 having a total thickness of, for example, about 1 μm. The cladding material 20 may be disposed directly on the ASIC 28, and the thickness of the lower waveguide 10 may be about a quarter wavelength or thicker. Between the lower surface of the short waveguide 19 and the upper surface of the lower waveguide 10 is a SiO2 cladding material 22 having a thickness of, for example, about 0.3 μm, thereby separating the lower surface of the short waveguide 19 and the upper surface of the lower waveguide 10 by the thickness of the SiO2 cladding material 22. The short waveguide 19 (composed of the upper and lower waveguide portions 18 and the O-PCM material 14 sandwiched therebetween) has a total thickness of, for example, about 1100 nm, as described below.

[0046] SiO cladding material 24 is formed above the short waveguide 19 and covers the top surface of the short waveguide 19 with a thickness of about 0.3 μm, thereby separating the upper surface of the short waveguide 19 from the lower surface of the upper waveguide 12 by the thickness (0.3 μm) of the SiO cladding material 24 covering the upper surface of the short waveguide 19. The thickness of the cladding materials 20 and 22 present between the waveguides 10, 12 and the short waveguide 19 in these areas is preferably about 0.3 μm, respectively. The thickness of the upper waveguide 10 may be about a quarter wavelength or thicker.

[0047] The length of the short waveguide 19 is selected to provide sufficient optical coupling between the segments of the upper waveguide 12 and the lower waveguide 10 for switching light between their crossed state and their straight-through state when the two are parallel to each other (as described below). If the short waveguide 19 is long enough, the SiN portion 18 of the waveguide 19 can be omitted or reduced, and the waveguide 19 can then only include or mainly include the O-PCM material 14. Preferably, the thickness of the O-PCM material 14 is about 100nm, while the thickness of the SiN portions 18 of the waveguide 19 is preferably about 500nm. The O-PCM material 14 is preferably about 500nm wide, while the SiN layer 18 can be slightly wider than the O-PCM material 18, which is preferably about 700nm wide. Alternatively, the O-PCM material 14 and the SiN layer 18 can be the same width. The above dimensions are used for one embodiment of the disclosed switch, which is intended to switch light of 1550nm wavelength commonly used in optical communication systems.

[0048] The upper waveguide 12 (including its segment 12S) is then covered by a top cladding layer of SiO2 which may be about 10 μm thick. The widths of the lower waveguide, the short waveguide and the upper waveguide are preferably the same or about 700 nm.

[0049] These dimensions and materials set forth in the preceding paragraphs may be varied if deemed useful by one skilled in the art, particularly for embodiments of the disclosed switches that switch other wavelengths of light.

[0050] The embodiment of Figure 3(e) is similar to the embodiment of Figure 3(d), but in this embodiment the heat shunt 16 surrounds the PCM 14 within the short PCM waveguide 19, and thus the SiN portion 18 of the short or PCM waveguide abuts the heat shunt 16 surrounding the PCM 14. The thermal characteristics of this embodiment may be better than the embodiment of Figure 3(d), but the optical characteristics may be worse due to the presence of some heat shunt material 16 between the PCM 14 and the SiN portion 18 of the short or PCM waveguide 19.

[0051] The O-PCM material 14 changes state when heated by one or more electrically controlled heaters 29, which may be thermally coupled to the O-PCM material 14 by one or more thermal shunts 16, preferably formed of AlN, unless the electrically controlled heaters 29 are disposed sufficiently close to the O-PCM material 14 that the thermal shunts may be omitted. However, if the electrically controlled heaters 29 are disposed closer than Figure 3(d) and 3(e) If the depicted distance d (half wavelength at 1550 nm) is closer, the heater 29 should be designed to prevent it from being disturbed by the light field in the short waveguide 19.

[0052] Now refer to Figure 4(a) to Figure 4(c)The operation of the switch 8 is explained. When the O-PCM material 14 is crystalline (see FIG. 4( b)), the input light remains in the lower (through state) SiN waveguide 10. When the O-PCM material 14 is heated to become amorphous (see FIG. 4( c)), the input light is coupled from the lower waveguide 10 to the upper waveguide 12 (cross state). The O-PCM material 14 is preferably disposed in a short waveguide 18, and is preferably 0.5 μm wide, 0.1 μm high and 30 μm long, and is separated from the SiN waveguides 10, 12 by a distance of about 0.5 μm, which may be noted to be preferably less than the half-wavelength distance d.

[0053] By applying appropriate electrical pulses (set and reset) from IC 28 to heater 29 via electrical connection 31, PCM material 14 can be instantaneously changed between its crystalline (see FIG. 4(b)) and amorphous (see FIG. 4(c)) states. When heater 29 receives a relatively large amount of peak energy in a relatively short period of time, heater 29 resets PCM material 14 to its amorphous (see FIG. 4(c)) state. Conversely, when heater 29 receives a relatively small amount of peak energy in a relatively long period of time, heater 29 sets PCM material 14 to its crystalline (see FIG. 4(b)) state. See Wong et al., “Phase Change Memory”, Proceeding of the IEEE, Vol. 98, No. 12, Dec 2010 pp 2201-2227, the disclosure of which is hereby incorporated by reference herein, for a more detailed discussion of this phenomenon.

[0054] from Figure 4(a) to Figure 4(c) It can be seen that the coupling between the waveguides is very efficient... When the structure 8 is in its crossed state, substantially all of the light in the lower waveguide 12 is coupled into the upper waveguide 10 (see 4(c)) because the O-PCMWG material 14 is in its amorphous (heated) state. This is because the 3D vertical directional coupler 8 includes vertically aligned waveguides 10, 12 and 19 that are close to each other and arranged parallel to each other over the length of the short waveguide 19, thus providing efficient coupling compared to conventional lateral directional couplers.

[0055] Furthermore, it should now be clear that light can enter from either end of the disclosed coupler and thus exit from the other end. The disclosed coupler can operate bi-directionally. Furthermore, it should be further clear that light can enter one of the waveguides 10 or 12 and exit the other of the waveguides 10 and 12 when the O-PCM material 14 is in its amorphous state (and thus the disclosed coupler is then in its crossover state), or light can remain in the waveguide when the O-PCM material 14 is in its crystalline state (and thus the disclosed coupler is then in its straight-through state).

[0056] Waveguides 10 and 12 and portion 18 of waveguide 19 are preferably formed of SiN because SiN waveguides are known to have low optical losses at a wavelength of 1550 nm commonly used in optical communication systems. Other waveguide materials may be used but may have greater optical losses. GeSe is preferably selected for O-PCM material 14 because GeSe has a sufficient optical bandgap (1 eV to 2 eV) to minimize optical losses at the above 1550 nm wavelength compared to other -PCM materials such as GeTe.

[0057] Figure 5 The control electrode of the disclosed invention is shown coupled to the 3D optical switch design disclosed herein. In order to construct an electrically programmable 3D O-PCM switch 8 with low optical losses based on a metal heater 29, we want to position the heater 29 at a distance d of at least half a wavelength (preferably 0.7 μm (half wavelength of 1550 nm)). In addition, to achieve improved thermal coupling between the heater grid and the O-PCM waveguide, we utilized our existing AlN thermal shunt technology disclosed in U.S. Patent No. 9,368,720, the disclosure of which is hereby incorporated herein by reference. The high (1.5 W / (cm*K)) thermal conductivity AlN layer is a dielectric thermal shunt with an optical refractive index of 2.02+j0.00002, close to that of a SiN waveguide. AlN provides an ideal optical index close to that of SiN and has an ideal thermal conductivity, enabling it to act as a thermal shunt 16. Simulations of the optical modes in the 3D thermal splitter O-PCM switch show that the optical modes are well confined, as shown in Figure 4(a). Figure 5 shows the applied 0.5μsec8mW / μm 2 Transient thermal modeling of the electrical pulses was performed and it was verified that the heat was well confined within the O-PCM material 14 and the switching energy was sufficient to produce an electrothermal cycle shorter than a few μsec including heating and cooling steps.

[0058] The switch disclosed herein takes advantage of the optical coupler structure, wherein the vertical directional coupler switch design has very low loss (preferably 0.1 dB / cm) lower and upper SiN waveguides 12, 10, and a very thin O-PCM material 14 disposed therebetween for controlling the directional coupler switch 8. Preferably, the O-PCM material 14 is GeSe or a GeSe alloy with an optical bandgap preferably greater than 1 eV. The control electrode 31 can provide a channel from the CMOS IC 28 to provide power to the heater 29 and conduct heat back to the CMOS IC 28 when the heater is not powered, and by separating the electrode 29 even further than the heater 29, the electrode 29 provides efficient transient heating (by providing electrical pulses to the heater 29) and efficient transient cooling (by making the O-PCM material 14 an efficient thermal and electrical conductor, such as Cu) of the O-PCM material 14 without interfering with the optical field in the waveguides 10, 12.

[0059] By vertically separating the two SiN waveguides 10, 12, optical losses are significantly reduced compared to a planar geometry where two silicon nitride waveguides must intersect. Since the O-PCM waveguide 19 is disposed between the top 10 and bottom 12 waveguides, and when the O-PCM material 14 in the waveguide 19 changes to its crystalline state, its refractive index is completely different from that of the waveguides 10, 12, isolation occurs between the waveguides 10, 12. Conversely, when the O-PCM material 14 in the waveguide 19 changes to its amorphous state, its refractive index approximates that of the waveguides 10, 12, and thus isolation no longer occurs between the waveguides 10, 12 and light moves from one waveguide to the other. The disclosed 3D O-PCM switch with multi-stage, low-loss SiN waveguides enables a highly flexible crossbar architecture with a reduced number of waveguide crossings.

[0060] When the PCM is amorphous, the PCM acts as a low-loss dielectric material, not much different from the lower and upper SiN waveguides 18. Incident light in the waveguide 10 can be coupled to the upper waveguide 12. Conversely, when the PCM is crystalline, the PCM becomes metallic and optically lossy. Light cannot be coupled to the output waveguide.

[0061] The vertical separation of the SiN waveguides 10, 12 is referenced relative to the figure (particularly Figure 3(d) and 3(e)), and it will be apparent to one skilled in the art that the disclosed embodiments may be used or operated in any desired orientation. Therefore, the term "vertical" or reference thereto herein (and in the appended claims) is not intended to limit how the disclosed embodiments may be utilized or operated. Furthermore, if desired, the positions of the upper and lower waveguides 12, 10 may be reversed, so that the upper waveguide 12 thereafter takes the position of the lower waveguide and the lower waveguide 10 thereafter takes the position of the upper waveguide.

[0062] The drawings of this application are presented in black and white, but Figure 3(a) , 3(b) , 3(d), 4(a) to Figure 4(c) and 5 Color versions of the drawings can be found in Appendix A of the U.S. patent application to which priority is claimed. The color versions of these drawings present certain information slightly more clearly than the black and white versions, so persons interested in this technology may wish to request a color copy of Appendix A from the U.S. Patent and Trademark Office.

[0063] Having now described the invention in accordance with the requirements of the patent law, those skilled in the art will understand how to change and modify the invention to meet their specific requirements or conditions. Such changes and modifications can be made without departing from the scope and spirit of the invention disclosed herein.

[0064] According to the requirements of the patent law, for the purpose of illustration and disclosure, the foregoing specific implementation of the exemplary embodiment is presented. It is not intended to be exhaustive or to limit the invention to the precise form described, but only to enable other technical personnel in the field to understand how the invention is applicable to a specific purpose or implementation. For those skilled in the art, the possibility of modification and change will now be obvious. The description of the exemplary embodiments is not intended to be limiting, and these exemplary embodiments may include tolerances, feature sizes, specific operating conditions, engineering specifications, etc., and may vary with the implementation or due to changes in the prior art, so no limitation should be implied. The applicant has reached this disclosure with respect to the prior art, but improvements are also considered, and future modifications may be made in view of these improvements, that is, according to the prior art at the time. The scope of the present invention is intended to be defined by the written claims and applicable equivalents. Unless expressly stated, the reference to the claim element in the singular form is not intended to mean "one and only one". In addition, any element, component or method or process step in the present disclosure is not intended to be dedicated to the public, regardless of whether the element, component or step is clearly stated in the claim. No claim element herein shall be construed under the provisions of 35 U.S.C. Sec. 112, sixth paragraph, unless the element is expressly referenced by the phrase “means for…,” and no method or process step herein shall be construed under those provisions unless one or more steps are expressly recited by the phrase “comprising the steps of….”

[0065] The concepts of the present invention include the following:

[0066] Concept 1: An optical coupler or switch structure comprising two waveguides disposed in different layers of the optical coupler or switch structure and comprising an optical phase change material disposed between the two waveguides for controlling optical coupling between the two waveguides.

[0067] Concept 2: The optical coupler or switch structure of Concept 1 wherein said two waveguides are formed of SiN or SiN alloys and said optical phase change material is GeSe or GeSe alloy having an optical bandgap greater than 1 eV.

[0068] Concept 3: The optical coupler or switch structure of Concept 1 or 2 wherein an electrically controlled heater is thermally coupled to said optical phase change material via a thermal shunt to provide transient heating of said optical phase change material in response to an electrical signal applied to said heater.

[0069] Concept 4: An optical coupler or switch structure according to any of Concepts 1 to 3, wherein one of the two waveguides has a straight portion, wherein the straight portion is arranged parallel to the other of the two waveguides, and the one of the two waveguides has an additional non-straight portion in optical communication with the straight portion, and the non-straight portion allows the one of the two waveguides to cross over the other of the two waveguides.

[0070] Concept 5: A vertical directional coupler or switch comprising a lower waveguide and an upper waveguide, the lower waveguide and the upper waveguide integrating an optical phase change material disposed between the lower waveguide and the upper waveguide for controlling optical coupling between the lower waveguide and the upper waveguide.

[0071] Concept 6: The vertical directional coupler or switch of Concept 5 wherein said lower waveguide and said upper waveguide are formed of SiN or a SiN alloy.

[0072] Concept 7: The vertical directional coupler or switch of Concept 5 or 6 wherein said optical phase change material is a material having an optical bandgap greater than 1 eV.

[0073] Concept 8: The vertical directional coupler or switch of any of Concepts 5 to 7 wherein said optical phase change material is GeSe or a GeSe alloy.

[0074] Concept 9: A vertical directional coupler or switch according to any of Concepts 5 to 8, further comprising an electrically operated heater connected to the thermal shunt, wherein the electrically operated heater is used to provide transient heating of the optical phase change material through the thermal shunt without interrupting the optical field in either the lower waveguide or the upper waveguide.

[0075] Concept 10: The vertical directional coupler or switch of Concept 9 wherein four sides of said optical phase change material are surrounded by a portion of said thermal shunt.

[0076] Concept 11. The vertical directional coupler or switch of Concept 9 wherein said optical phase change material abuts said thermal shunt on opposing side surfaces of said optical phase change material.

[0077] Concept 12: The vertical directional coupler or switch of any of Concepts 5 to 11 wherein said optical phase change material is disposed in another waveguide consisting essentially of SiN or a SiN alloy.

[0078] Concept 13: The vertical directional coupler or switch of any of Concepts 5 to 12 wherein said optical phase change material is disposed in another waveguide disposed between a predetermined portion of said upper waveguide and a predetermined portion of said lower waveguide.

[0079] Concept 14: The vertical directional coupler or switch of Concept 12 or 13 wherein said another waveguide, said predetermined portion of said upper waveguide and said predetermined portion of said lower waveguide are all arranged parallel to each other.

[0080] Concept 15: The vertical directional coupler or switch of any of Concepts 5 to 14 wherein said optical phase change material is disposed within another waveguide disposed parallel to a predetermined portion of said upper waveguide and a predetermined portion of said lower waveguide.

[0081] Concept 16: The vertical directional coupler or switch of Concept 15 wherein said another waveguide has a length substantially shorter than either of said upper waveguide and said lower waveguide.

[0082] Concept 17: A vertical directional coupler or switch according to any of Concepts 5 to 16, wherein one of the two waveguides has a straight portion arranged parallel to the other of the two waveguides, and the one of the two waveguides has an additional non-straight portion in optical communication with the straight portion, and the non-straight portion allows the one of the two waveguides to cross over the other of the two waveguides.

[0083] Concept 18: A cross switch comprising a plurality of vertical directional couplers or switches according to claim 5, the cross switch further comprising a plurality of input waveguides and a plurality of output waveguides, the plurality of input waveguides and the plurality of output waveguides being arranged in different layers of the cross switch in a grid-like pattern that crosses each other, the plurality of vertical directional couplers or the switches being arranged so that the plurality of input waveguides and the plurality of output waveguides cross each other, wherein upper waveguides of a subset of the plurality of vertical directional couplers or the switches are coupled in series with each other and with a selected one of the plurality of input waveguides or the plurality of output waveguides of the cross switch, and wherein lower waveguides of different subsets of the plurality of vertical directional couplers or the switches are coupled in series with each other and with a different selected one of the plurality of input waveguides or the plurality of output waveguides of the cross switch.

Claims

1. An optical coupler or switch structure, comprising two waveguides arranged in different layers of the optical coupler or the switch structure, and comprising an optical phase change material arranged between the two waveguides for controlling optical coupling between the two waveguides, wherein the optical phase change material is arranged in a third waveguide located between the first two waveguides, wherein the first two waveguides and the third waveguide are formed of SiN or a SiN alloy, and the optical phase change material is GeSe or a GeSe alloy having an optical band gap greater than 1eV.

2. An optical coupler or switch structure according to claim 1, wherein an electrically controlled heater is thermally coupled to the optical phase change material in the third waveguide through a thermal shunt to provide transient heating of the optical phase change material in response to an electrical signal applied to the heater.

3. The optical coupler or switch structure of claim 1 , wherein one of the two waveguides has a straight portion, wherein the straight portion is arranged in parallel to the other of the two waveguides and the third waveguide, and the one of the two waveguides has an additional non-straight portion in optical communication with the straight portion, wherein the non-straight portion allows the one of the two waveguides to cross over the other of the two waveguides.

4. A vertical directional coupler or switch, comprising a lower waveguide and an upper waveguide, wherein the lower waveguide and the upper waveguide are integrated with an optical phase change material arranged in another waveguide, wherein the optical phase change material mainly comprises SiN or SiN alloy, and the other waveguide is arranged between the lower waveguide and the upper waveguide for controlling the optical coupling between the lower waveguide and the upper waveguide.

5. The vertical directional coupler or switch of claim 4, wherein the lower waveguide and the upper waveguide are formed of SiN or a SiN alloy.

6. The vertical directional coupler or switch of claim 4, wherein the optical phase change material is a material having an optical band gap greater than 1 eV.

7. The vertical directional coupler or switch according to claim 4, wherein the optical phase change material is GeSe or a GeSe alloy.

8. The vertical directional coupler or switch of claim 4, further comprising an electrically operated heater connected to the thermal shunt, the electrically operated heater being used to provide transient heating of the optical phase change material through the thermal shunt without interrupting the optical field in either the lower waveguide or the upper waveguide.

9. The vertical directional coupler or switch of claim 8, wherein four sides of the optical phase change material are surrounded by a portion of the thermal shunt.

10. The vertical directional coupler or switch of claim 8, wherein the optical phase change material abuts the thermal shunt on two opposing side surfaces of the optical phase change material.

11. The vertical directional coupler or switch according to claim 4, wherein the optical phase change material is disposed in the other waveguide, and the other waveguide is disposed between a predetermined portion of the upper waveguide and a predetermined portion of the lower waveguide.

12. The vertical directional coupler or switch according to claim 11, wherein the another waveguide, the predetermined portion of the upper waveguide, and the predetermined portion of the lower waveguide are all arranged parallel to each other.

13. The vertical directional coupler or switch of claim 4, wherein the optical phase change material is disposed within the other waveguide, and the other waveguide is disposed parallel to a predetermined portion of the upper waveguide and a predetermined portion of the lower waveguide.

14. The vertical directional coupler or switch of claim 4, wherein the length of the further waveguide is substantially shorter than that of either of the upper waveguide and the lower waveguide.

15. A vertical directional coupler or switch according to claim 4, wherein one of the two waveguides has a straight portion arranged parallel to the other of the two waveguides, and the one of the two waveguides has an additional non-straight portion in optical communication with the straight portion, and the non-straight portion allows the one of the two waveguides to cross over the other of the two waveguides.

16. A crossbar switch comprising a plurality of vertical directional couplers or switches according to claim 4, the crossbar switch further comprising a plurality of input waveguides and a plurality of output waveguides, the plurality of input waveguides and the plurality of output waveguides being arranged in different layers of the crossbar switch in a grid-like pattern that crosses each other, the plurality of vertical directional couplers or the switches according to claim 4 being arranged so that the plurality of input waveguides and the plurality of output waveguides cross each other, wherein upper waveguides of a subset of the plurality of vertical directional couplers or the switches are coupled in series with each other and with a selected one of the plurality of input waveguides or the plurality of output waveguides of the crossbar switch, and wherein lower waveguides of different subsets of the plurality of vertical directional couplers or the switches are coupled in series with each other and with a selected different one of the plurality of input waveguides or the plurality of output waveguides of the crossbar switch.

17. The optical coupler or switch structure of claim 1, wherein the third waveguide is separated from the two waveguides by a layer of SiO2 material.

18. The vertical directional coupler or switch of claim 4, wherein the further waveguide is spaced apart from the lower waveguide and the upper waveguide by a layer of SiO2 material.

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