Magnetically activated photonic switches and switch fabrics employing the same

Various embodiments of the present invention are directed to photonic switches and switch fabrics employing the photonic switches. In one embodiment of the present invention, a photonic switch comprises a first waveguide disposed on a surface of a substrate in proximity to an opening in the substrate, and a second waveguide crossing the first waveguide and positioned in proximity to the opening in the substrate. The photonic switch includes a tunable microring resonator disposed on the surface of the substrate adjacent to the first waveguide and the second waveguide and configured with an opening aligned with the opening in the substrate. The photonic switch also includes a wire having a first end and a second end and configured to pass through the opening in the microring and the opening in the substrate.

TECHNICAL FIELD

Embodiments of the present invention are directed to photonic switches and photonic-switch-based switch fabrics.

BACKGROUND

Switch fabrics are typically employed for “raw” data switching from input ports to output ports of various kinds of devices, including processors, memory, circuit boards, servers, storage servers, external network connections or any other data processing, storing, or transmitting device. However, switch fabrics can often be a data processing bottleneck for many different kinds of computing environments. A typical switch fabric, for example, can limit the scope of a computing environment's ability to handle the ever increasing data processing and transmission needs of many applications, because many switch fabrics are fabricated to accommodate only the “port-rate of the day” and the “port-count of the day” and are not fabricated to accommodate larger bandwidths that may be needed to effectively accommodate future applications. In particular, the amount and frequency with which data is exchanged between certain devices can be larger for some devices than for others, and the use of low-latency, metal-signal lines employed by most switch fabrics also have limited bandwidths. As a result, the amount of data that can be transmitted between devices may not be well matched to the data transfer needs of the devices employed by an application at each point in time, which often results in data processing delays. In addition, the use of signal lines necessitates considerable power consumption in order to transmit electrical signals between devices.

A number of the issues associated with electrical signals transmitted via signal lines can be significantly reduced by encoding the same information in electromagnetic, radiation (“EMR”) that is transmitted via waveguides. First, the data transmission rate can be increased significantly due to the much larger bandwidth provided by waveguides. Second, power consumption per transmitted bit is lower for EMR transmitted via waveguides than for transmitting the same data in electrical signals via signal lines. Third, degradation or loss per unit length is much less for EMR transmitted via waveguides than for electrical signals transmitted via signal lines. Physicists and engineers have recognized a need for fast switching devices that can accommodate data encoded EMR as a medium for transmitting massive amounts of data between various kinds of data processing, storing, or transmitting devices.

SUMMARY

Various embodiments of the present invention are directed to photonic switches and switch fabrics employing the photonic switches. In one embodiment of the present invention, a photonic switch comprises a first waveguide disposed on a surface of a substrate in proximity to an opening in the substrate, and a second waveguide crossing the first waveguide and positioned in proximity to the opening in the substrate. The photonic switch includes a tunable microring resonator disposed on the surface of the substrate adjacent to the first waveguide and the second waveguide and configured with an opening aligned with the opening in the substrate. The photonic switch also includes a wire having a first end and a second end and configured to pass through the opening in the microring and the opening in the substrate.

DETAILED DESCRIPTION

Embodiments of the present invention are directed to photonic switches and to switch fabrics employing the same photonic switches. These embodiments employ at least one microring resonator having resonance frequencies that are tunable by inducing a local, solenoidal magnetic field within the microrings. The magnetic field can be induced by passing a current through a wire running through the microring opening. A magneto-optical effect causes circular birefringence within the microrings. In other words, a different phase velocity exists for EMR waves with opposite circular polarizations circulating within the microrings. The circulating EMR ways can be considered to recombine upon emergence from the magnetized microring but with a net phase offset, resulting in a rotation of the angle of linear polarization. Unlike conventional electronic switches and switch fabrics, photonic switches and switch fabrics of the present invention consume less power, provide a higher bandwidth, and do not suffer from substantial loss over longer distances.

In the following description, the terms “photonic” and “photonically” refer to devices that operate with classical and/or quantized EMR having wavelengths that are not limited to just the visible portion of the electromagnetic spectrum. In the various photonic switch and switch fabric embodiments described below, a number of structurally similar components comprising the same materials have been provided with the same reference numerals and, in the interest of brevity, an explanation of their structure and function is not repeated.

FIG. 1Ashows an isometric view of a first photonic switch100in accordance with embodiments of the present invention. The photonic switch100includes a first ridge waveguide102, a second ridge waveguide104intersecting the first waveguide102, and a tunable microring resonator (“microring”)106, all of which are disposed on a surface of a substrate108. The photonic switch100also includes a wire110passing through an opening112in the microring106and an opening (not shown) in the substrate108.FIG. 1Bshows an exploded isometric view of the photonic switch100with the first and second waveguides102and104and the microring106lifted above the substrate108in accordance with embodiments of the present invention.FIG. 1Breveals an opening114through the substrate108in approximate alignment with the opening112in the microring106. The openings112and114allow the wire110to pass through the substrate108and the microring106. The wire110extends approximately perpendicular to the substrate108.

The waveguides102and104can be comprised of a column IV semiconductor, such as Si and Ge, or a compound III-V semiconductor, where Roman numerals III and V refer to elements in the third and fifth columns of the Periodic Table of the Elements. Examples of suitable compound III-V semiconductors are InP, InAs, GaP, GaN, GaAs, and InxGa1-xAsyP1-y, where the parameters x and y can range between 0 and 1. The choice of composition x and y are well-known in the art. The waveguides can be comprised of other suitable material having a refractive index that is greater than the substrate108. The substrate108can be comprised of a material having a lower refractive index than the waveguides102and104. For example, the substrate108can be comprised of SiO2, Si3N4, Al2O3, or another suitable dielectric insulating material. The combination of materials selected for the substrate108and the waveguides102and104may depend on matching the lattice constant of the materials selected for the waveguides102and104with the lattice constant of the materials selected for the substrate108. The wire110can be comprised of silver, gold, copper, nickel, chromium, platinum, aluminum, an alloy thereof, or any other suitable conductor.

Although the wire110shown inFIG. 1has a circular cross-section, embodiments of the present invention are not so limited. The wire110can also have square, rectangular, elliptical, or more complex cross sections. The wire110may also have many different widths or diameters and aspect ratios or eccentricities, and the wire110may have nanoscale to microscale cross-sectional dimensions. For example, the diameter of the wire110may range from about 1-2 microns. The waveguides102and104can be single-mode waveguides with cross-sectional dimensions ranging from about 400-600 nm in width by about 150-450 nm in height. Preferably, these cross-sectional dimensions can be about 500 nm in width by about 250 nm in height, but these dimensions can vary depending on the implementation. Although the intersecting waveguides102and104appear inFIG. 1to intersect at about 90°, in other embodiments, the waveguides102and104can intersect at angles other than 90°, such as angles ranging from about 45° to about 90°. The microring may have an outer diameter of about 7-15 microns and an inner diameter as large as about 10 microns.

The microring106shown inFIG. 1represents many different kinds of suitable microrings that can be used in the photonic switch100. In other words, the microring106can actually be comprised of a number of different materials and components, two of which are described below with reference toFIGS. 2 and 3.

FIG. 2Ashows an isometric view of a first tunable microring resonator200disposed on a portion of the substrate108in accordance with embodiments of the present invention. As shown inFIG. 2A, a portion of the wire110passes through the opening112.FIG. 2Bshows a cross-sectional view of the microring200along a line2B-2B, shown inFIG. 2A, in accordance with embodiments of the present invention. The wire110passes through the opening112in the microring200and the opening114in the substrate108.FIG. 2Balso reveals that the microring200includes an inner microring202disposed on a surface of the substrate108. At least a portion of the outer surface of the inner microring202is covered with a magnetic material204. The inner microring202can be comprised of a column IV semiconductor or a compound III-V semiconductor, such as InP, InAs, GaP, GaN, GaAs, or InxGa1-xAsyP1-y, as described above with reference to the waveguides102and104. The inner microring202can be doped with suitable paramagnetic impurities, such as Mn, Or, Ni, Fe, Co, alloys thereof, rare earth ions, like terbium. The inner microring202can also be comprised of commonly used materials for the 700-1100 nm wavelength range, such as terbium doped borosilicate glass and terbium gallium garnet crystal (Tb3Ga5O12) that have the largest Faraday rotation angles. The magnetic material204coats at least a portion of the outer surface of the inner microring202and can be comprised of a “soft” ferromagnetic material, such as Ni, Fe, permalloy, which contains about 20% Fe and about 80% Ni and has a very small coercive field, or another suitable ferromagnetic material.

FIGS. 2C-2Dshow how magnetic moments of the materials comprising the microring200are changed when a current is applied to the wire110in accordance with embodiments of the present invention. The magnetic moments are represented by directional arrows, such as directional arrow206. InFIG. 2C, when no current is applied to the wire110, the magnetic moments are randomly oriented. However, when a current208is applied to the wire110, as shown inFIG. 2D, the magnetic moments are aligned with the direction of the solenoidal magnetic field210induced by the current in the wire110.

FIG. 3Ashows an isometric view of a second tunable microring resonator300disposed on a portion of the substrate108in accordance with embodiments of the present invention. The wire110passes through the opening112.FIG. 3Aalso shows that the microring300is comprised of an inner microring302, an outer microring304, and a segment306.FIG. 3Bshows a cross-sectional view of the microring300along a line3B-3B, shown inFIG. 3A, in accordance with embodiments of the present invention. The wire110passes through the opening112in the microring300and the opening114in the substrate108.FIGS. 3A-3Balso reveal a segment306covering a portion of the outer surface of the outer microring304and a pinning stub308attached to at least a portion of the outer surface of the segment306. The inner microring302can be comprised of an intrinsic column IV semiconductor, such as Si or Ge, or an intrinsic compound III-V semiconductor, such as GaN or InxGa1-xAsyP1-y, as described above. The outer microring304can be comprised of SiO2, Al2O3, Si3N4, or another suitable dielectric material. The segment306covering a portion of the outer microring304can be comprised of a ferromagnetic material, such as Ni, Fe, permalloy, or another suitable ferromagnetic materials. The pinning stub308can be comprised of an antiferromagnetic material, such as FeMn, NiO, Cr2O3, or another suitable antiferromagnetic material.

FIGS. 3C-3Dshow how magnetic moments of the segment306are changed when a current is applied to the wire110in accordance with embodiments of the present invention. The pinning stub308can be deposited and positioned on the segment306in order to align the magnetic moments of the segment306into a particular direction. For example, as shown inFIG. 3C, when no current is applied to the wire110, the magnetic moments of the segment306can be oriented in the direction represented by the directional arrows, such as directional arrow310. However, when a current312is applied to the wire110, as shown inFIG. 3D, the magnetic moments of the segment306are aligned with the direction of the solenoidal magnetic field circulating in the direction314is created.

The microrings200and300have resonance frequencies that can be tuned by interaction of the corresponding circular-microring modes with the local magnetization induced or changed by the solenoid magnetic field created by the current flowing through the wire110. The microrings200and300use a magneto-optical effect to evanescently couple EMR to and from the waveguides102and104. The resonance frequencies of the microrings200and300cause EMR waves to be decomposed into two circularly polarized waves which propagate at different speeds. For example, EMR waves that are circulating within the microrings200and300with opposite circular polarizations have different phase velocities when the solenoidal magnetic field is created. These waves recombine upon emergence from the microrings200and300. However, because of the difference in propagation speed they emerge with a net phase difference, resulting in a rotation of the angle of linear polarization. The resonance frequency or wavelength supported by the microrings200and300shifts. Thus, the current applied to the wire110can be used to actively control evanescent coupling of EMR between the waveguides102and104and the microrings200and300.

The photonic switch100is operated by applying an appropriate current or voltage to the wire110. This can be accomplished by attaching a wire to each end of the wire110as described below with reference toFIGS. 4 and 5.

FIG. 4shows an isometric view of the photonic switch100and wires402and404attached to the ends of the wire110in accordance with embodiments of the present invention. Although the wires402and404appear to be perpendicular to one another and horizontal to the plane of the substrate108, the wires402and404can be arranged in any suitable configuration for supplying current or voltage to the wire110. As shown inFIG. 4, the flow of current through the wires404,110, and402is represented by directional arrows406,408, and410. The current flows from the wire404into the wire110and out along the wire402. In other embodiments, the current can of course be reversed.

FIG. 5shows a second isometric view of the photonic switch100and wires502and504attached to the ends of the wire110in accordance with embodiments of the present invention. As shown inFIG. 5, the wire502is also attached to a third wire506which, in turn, is attached to a fourth wire508that passes under the wire504. The current flows from the wire504into the wire110and from the wire110to the wire502as indicated by directional arrows510-512. The current then flows from the wire506and out through the wire508as indicated by directional arrow513.

An appropriate current applied to the wire110, as shown inFIGS. 4 and 5, generates a magnetic field of magnitude M in the adjacent microring106. This magnetic field shifts the resonance of the microring106such that a substantially portion of the EMR transmitted in one of the intersecting waveguides can be coupled into the other. In other words, depending on how the microring106is configured, the magnetic field can be used to determine whether or not the microring106is able to support EMR of a particular frequency, ω. The microring106can be operated in the photonic switch100in two ways. A first way is described below with reference toFIG. 6, and a second way is described below with reference toFIG. 7.

FIGS. 6A-6Bshow top views of the photonic switch100operated in a first way in accordance with embodiments of the present invention. In certain embodiments, the materials and dimensions of the microring300can be selected such that the microring300does not have resonance with, or cannot support, a channel λ with the frequency ω transmitted along the waveguide104. As a result, after inputting the channel λ into the waveguide104, as shown inFIG. 6A, the channel λ passes the microring300unaffected, passes through the intersection602and out along the remainder of the waveguide104, as shown inFIG. 6A. Note that some loss of the channel λ intensity may occur at the intersection602. This loss may occur as a result of a portion of the channel λ spilling over into the intersecting waveguide102due to diffraction at the corners of the intersection602. This spillover occurs in both directions of the waveguide102, but the intensity of the EMR entering the intersecting waveguide102is insignificant when compared to the intensity of the channel λ that continues to propagate along the waveguide104.

Next, as shown inFIG. 6B, applying an appropriate current to the wire110, as described above with reference toFIGS. 4 and 5, generates a magnetic field around the microring300. This magnetic field shifts the resonance of the microring300into resonance with the frequency ω of the channel λ transmitted along the waveguide104. As a result, a substantial portion of the channel λ propagating along the waveguide104can be evanescently couple into the microring300, circulate within the microring300, and evanescently couple from the microring300into the intersecting waveguide102. The channel λ then propagates along the waveguide102. Here, loss of the channel λ intensity may occur as a result of a portion of the channel λ not evanescently coupling into the microring300and continuing to propagate along the waveguide104, and loss may occur again at the intersection602.

FIGS. 7A-7Bshow top views of the photonic switch100operated in a second way in accordance with embodiments of the present invention. In other embodiments, the materials and dimensions of the microring300can be selected so that the microring300has resonance with the frequency ω of the channel λ without generating the magnetic field as described above. As shown inFIG. 7A, because the microring300can support the channel λ, a substantial portion of the channel λ can evanescently couple into the microring300, circulate within the microring300, and evanescently couple from the microring300into the intersecting waveguide1.02. The channel λ then propagates along the waveguide102. Loss of the channel λ intensity may occur at the intersection602, and a portion of the channel λ may not evanescently couple into the microring300leaving a portion to propagate along the waveguide104.

Next, as shown inFIG. 7B, applying an appropriate current to the wire110, as described above with reference toFIGS. 4 and 5, generates a magnetic, field around the microring300. This magnetic field shifts the resonance of the microring300the frequency ω of the channel λ. As a result, the channel λ passes the microring300unaffected, passes through the intersection602and out along the remainder of the waveguide104. As described above, loss of the channel λ intensity may occur at the intersection602, but the intensity of the EMR entering the intersecting waveguide102is not significant when compared to the intensity of the channel λ that continues to propagate along the waveguide104.

A number of the photonic switches100can be assembled to form a switch fabric that can be used to transmit channels between various kinds of data processing, storing, or transmitting devices.FIG. 8shows an exploded isometric view of a first switch fabric800in accordance with embodiments of the present invention. The switch fabric800includes a first set of three approximately parallel801-803waveguides intersecting a second set of three approximately parallel waveguides805-807all of which are disposed on a surface of a substrate808. The switch fabric800includes nine photonic switches811-819disposed on the surface of the substrate808. Each photonic switch is positioned in proximity to the intersection of two intersecting ridge waveguides, as described above with reference toFIG. 1. As shown inFIG. 8, the switch fabric800also includes a first set of three wires821-823and a second set of three wires825-827located at approximately right angles to the first set of wire821-823. For simplicity of illustration, the wires821-823and the wires825-827are shown detached from the wires of the photonic switches811-819. During operation of the switch fabric800, the wires in the first set of wires821-823are electronically coupled to the wires in the columns of photonic switches, and the wires in the second set of wires825-827can be photonically coupled to the wires in the rows of photonic switches. For example, the wire821can be electronically coupled to the wires of the photonic switches811,814, and817, and the wire825can be electronically coupled to the wires of the photonic switches811,812, and813. Note that the switch fabric800can be scaled down or up to accommodate any number of intersecting waveguides and photonic switches.

The photonic switches811-819can be configured and operated in accordance with the two different operational embodiments described above with reference toFIGS. 6 and 7. For the sake of brevity, the following is a description of the operation of the switch fabric800in accordance with the operational embodiment described above with reference toFIG. 6. In other words, it is assumed that the photonic switches811-819are configured to operate in accordance with the embodiment described above with reference toFIG. 6. The switch fabric800receives three different channels λ1, λ2, and λ3on the three waveguides801-803, respectively. The photonic switches811-819can be configured so that the associated microrings are not resonant with the channels λ1, λ2, and λ3propagating along the waveguides801-803, respectively. For example, the photonic switches811-813may have associated microrings that are configured to not be in resonance with the channel λ1, and, therefore, the channel λ1is not evanescently coupled via the associated microrings into the intersecting waveguides805-807. The photonic switches811-819can also be configured so that when an appropriate current is applied to the associated wires, the microrings are resonant with the channels λ1, λ2, and λ3propagating along the waveguides801-803. For example, when an appropriate current is applied to the wire of the photonic switch811via the wires821and825, the associated microring is resonant with the channel λ1such that the channel λ1evanescently couples into the waveguide805. When an appropriate current is applied to the wire of the photonic switch816via the wires823and826, the associated microring is resonant with the channel λ2such that the channel λ2evanescently couples into the waveguide807.

In other embodiments, rather than placing the waveguide layer and substrate808between the first set of wires821-823and the second set of wires825-827, the wires running through the photonic switches811-819can each be connected to wires as described above with reference toFIG. 5. In other words, each of the wires running through a microring of the photonic switches811-819can be connected to two wires, such as wires504and502, and wires, such as wire506, can pass through openings in the substrate808to connect with wires, such as wire508.

In order to reduce loss of a channel due to diffraction at a waveguide intersection, such as intersection602, in other embodiments, the intersecting waveguides, such as waveguides102and104, can be replaced by a first waveguide that is overlain by a second waveguide.FIG. 9shows an isometric view of a second photonic switch900in accordance with embodiments of the present invention. The photonic switch900includes a first ridge waveguide902, a second ridge waveguide904overlaying the first waveguide902, and a microring906. The first waveguide902and the microring906are disposed on a substrate908, and the second waveguide904can be in contact with the first waveguide902or suspended above the first waveguide902by a support (not shown). Although the microring906can be configured as described above with reference toFIGS. 2 and 3, the height of the microring906is greater than the height of the microring106in order to evanescently couple a channel resonating in the microring906into the waveguide904. The photonic switch900also includes a portion of a wire910passing through an opening912in the microring906and an opening (not shown) in the substrate908. The photonic switch can be comprised of the same materials as the first photonic switch100and operated in the same manner as described above with reference toFIGS. 6 and 7. In addition, configuring the photonic switch900with separate first and second waveguides902and904may reduce the amount of loss due to diffraction, as described above with reference toFIGS. 6 and 7.

In other embodiments, the first waveguide902can be fabricated on a surface of the a substrate, as shown inFIG. 9, and the second waveguide904can also be fabricated on the same substrate but with the waveguide904arching over the first waveguide902where the two waveguides cross. This configuration employs the shorter microring106and the same coupling as the photonic switch900but without the diffraction associated with the waveguides of the photonic switch100.

In other embodiments, the photonic switch900can also be employed as photonic switches in switch fabrics.FIG. 10shows an exploded isometric view of a second switch fabric1000in accordance with embodiments of the present invention. The switch fabric1000includes a first set of three approximately parallel waveguides1001-1003and a second set of three approximately parallel waveguides1005-1007that overlay the first set of waveguides1001-1003. The waveguides1001-1003are disposed on the surface of a substrate1008. The switch fabric1000also includes nine photonic switches1011-1019disposed on the surface of the substrate1008. The photonic switches1011-1019are positioned in proximity to two overlaying ridge waveguides, as described above with reference toFIG. 9. As shown inFIG. 10, the switch fabric1000also includes a first set of three wires1021-1023and a second set of three wires1025-1027located at approximately right angles to the first set of wire1021-1023. For simplicity of illustration, the wires1021-1023and the wires1025-1027are shown detached from the wires of the photonic switches1011-1019. The wires in the first set of wires1021-1023are electronically coupled to the wires in the columns of photonic switches, and the wires in the second set of wires1025-1027can be photonically coupled to the wires in the rows of photonic switches. For example, the wire1021can be electronically coupled to the wires of the photonic switches1011,1014, and1017, and the wire1025can be electronically coupled to the wires of the photonic switches1011,1012, and1013. The photonic switches1011-1019can operated in the same manner as the photonic switches of the switch800described above with reference toFIG. 8. Note that the switch fabric1000can be scaled down or up to accommodate any number of overlapping waveguides and photonic switches.

In order to reduce the loss associated with not fully evanescently coupling a channel into a first microring, as described above with reference toFIGS. 6 and 7, a second microring can be employed.FIG. 11shows an isometric view of a third photonic switch1100in accordance with embodiments of the present invention. The photonic switch1100is identical to the photonic switch100except the photonic switch1100includes an additional tunable microring resonator1202disposed on the surface of a substrate1104opposite the microring906. The photonic switch1100also includes a second wire1106passing through an opening1108in the microring1102and an opening (not shown) in the substrate1104. The elements of the photonic switch1100can be comprised of the same materials as the first photonic switch100, and the microring1102can have the same configuration and be comprised of the same materials as the microrings200and300described above with reference toFIGS. 2 and 3.

The microrings106and1102are operated by applying appropriate currents to the wires110and1106, as described above with reference toFIGS. 6 and 7. For example, the microrings106and1102can be configured in the same manner as the microrings described above with reference toFIG. 6. Applying an appropriate current to the wire110causes the resonance of the microring106to shift into resonance with a channel propagating along the waveguide104. Although, a substantial portion of this channel evanescently couples from the waveguide104into the waveguide102via the microring106, a portion of the channel may continue to propagate beyond the intersection602. Applying an appropriate second current to the wire1106causes the resonance of the microring1102to shift into resonance with the channel, evanescently coupling more of the channel into the waveguide102. As a result, loss resulting from a portion of the channel passing the microring106without being coupled into the microring106may be reduced by including the microring1102.

In other embodiments, the channel loss prevention measures of the photonic switches900and1100can be combined to form a fourth photonic switch.FIG. 12shows an isometric view of a fourth photonic switch1200in accordance with embodiments of the present invention. The photonic switch1200is identical to the photonic switch900except the photonic switch1200includes an additional tunable microring resonator1202disposed on the surface of a substrate1204and a wire1206passing through a hole1208in the microring1202and a hole (not shown) in the substrate1204. The elements of the photonic switch1200can be comprised of the same materials as the first photonic switch100, and the microring1202can have the same configuration and be comprised of the same materials as the microrings200and300described above with reference toFIGS. 2 and 3.

Although the present invention has been described in terms of particular embodiments, it is not intended that the invention be limited to these embodiments. Modifications within the spirit of the invention will be apparent to those skilled in the art. For example, in other embodiments of the present invention, those skilled in the art will immediately recognize that the switch fabric800can be modified to include the photonic switches1100at intersecting waveguides, and that the switch fabric1000can be modified to include the photonic switches1200at the overlaying waveguides.