Patent Application
20160337727
The present invention relates to a system and method for photonics, and, in particular, to a system and method for a photonic structure.
Data centers route massive quantities of data. Currently, data centers may have a throughput of 5-10 terabytes per second, which is expected to drastically increase in the future. Data centers contain huge numbers of racks of servers, racks of storage devices, and other racks often with top-of-rack (TOR) switches, all of which are interconnected via massive centralized packet switching resources. In data centers, electrical packet switches are used to route all data packets, irrespective of packet properties, in these data centers.
Photonic packet switching may be useful in data centers due to the fast speed of photonic switching. However, photonic buffers are problematic to create. Photonic switching architectures may reduce or eliminate the use of photonic buffers. To address the lack of photonic storage and buffering, photonic switches may utilize accurate timing, with the input photonic signals being accurately aligned in time at the inputs of the photonic switch by generating these signals via electronic means in switch peripherals, such as the TOR. For switched entities (e.g. packets) from different inputs to avoid collision at the output of a central switch, the differences in timing at the input (input skew) plus the set up time for a photonic switch may be shorter than the gap time between photonic packets or containers. A source of delay and skew is the optical path length light travels along the optical switch. The optical paths have a non-zero average length, which introduces an average delay, and a non-zero variation in optical path length, introducing skew. A large skew may reduce or eliminate the inter-packet or inter-container gap, leading to errors. Even if the inputs are aligned in time to remove this input skew, when the different paths through the central switch have different physical lengths, skew is reintroduced, resulting in a degradation of the inter-packet gap, leading to difficulties in discriminating packet boundaries in the destination peripheral or, for large skew, causing overlapping or clipping of switched entities corrupting the data flow. Hence delay and skew through a photonic switch are problematic.
An embodiment photonic structure includes a plurality of input stage cards including a first input stage card and a second input stage card, where the first input stage card is parallel to the second input stage card, where a first plane is at an edge of the plurality of input stage cards, and where the first plane is orthogonal to the plurality of input stage cards. The photonic structure also includes a plurality of center stage cards optically coupled to the plurality of input stage cards, where the plurality of center stage cards includes a first center stage card and a second center stage card, where the first center stage card is orthogonal to the first input stage card and the second input stage card, where the second center stage card is orthogonal to the first input stage card and the second input stage card, where the first plane is at a first edge of the plurality of center stage cards and orthogonal to the plurality of center stage cards, where a second plane is at a second edge of the plurality of center stage cards, where the second plane is parallel to the first plane, where the first center stage card is directly optically coupled to the first input stage card and the second input stage card, and where the second center stage card is directly optically coupled to the first input stage card and the second input stage card. Additionally, the photonic structure includes a plurality of output stage cards optically coupled to the plurality of center stage cards, where the plurality of output stage cards includes a first output stage card and a second output stage card, where the first output stage card is orthogonal to the first center stage card and the second center stage card, where the second output stage card is orthogonal to the first center stage card and the second center stage card, where the second plane is at an edge of the plurality of output stage cards, where the second plane is orthogonal to the plurality of output cards, where the first output stage card is directly optically coupled to the first center stage card and the second center stage card, and where the second output stage card is directly optically coupled to the first center stage card and the second center stage card. An embodiment optical connection includes a first array of holes on a first side of a registration plate and an array of grooves having a plurality of end stops on a second side of the registration plate. The optical connection also includes a first plurality of graded refractive index (GRIN) lenses inserted into the first array of holes, where the first plurality of GRIN lenses includes a first GRIN lens in a first hole of the first array of holes and a second plurality of GRIN lenses inserted in grooves of the array of grooves, where the first side of the registration plate is opposite the second side of the registration plate, where the second plurality of GRIN lenses includes a second GRIN lens in a first groove of the array of grooves opposite the first GRIN lens, and where the first GRIN lens is optically coupled to the second GRIN lens by an air gap in the first hole.
In one example, the first GRIN lens has a first diameter, where the second GRIN lens has a second diameter, and where the first diameter is smaller than the second diameter, and where the first lens is configured to propagate light to the second lens. In another example, the second plurality of GRIN lenses is configured to slide in along the array of grooves.
An embodiment registration plate includes a row of holes and a groove configured to receive a card along the row of holes, where the card includes a row of non-contact optical connectors, and where the groove is configured to align the row of non-contact optical connectors with the row of holes. The registration plate also includes an end stop at an end of the groove, where the end stop is configured to align the row of non-contact optical connectors with the row of holes.
An embodiment device includes an optical macromodule and a plurality of flexible waveguide extensions having a surface. The device also includes a plurality of graded refractive index (GRIN) lenses, where the plurality of flexible waveguide extensions are optically coupled between the optical macromodule and the plurality of GRIN lenses.
The foregoing has outlined rather broadly the features of an embodiment of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of embodiments of the invention will be described hereinafter, which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.
It should be understood at the outset that although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.
In photonic switching, skew occurs from the difference in propagation time of light through different optical paths. For example, it is desirable for the skew to be much smaller than the inter-packet gap (IPG) between photonic packets, so the majority of the IPG may be used for photonic switch setup. Table 1 below illustrates various approaches for 100 Gb/s data streams and packet flows.
A CLOS switch configuration may be used in a photonic switching fabric.
For example, photonic CLOS switch 300 has a physical crosspoint set up time from about 1 ns to about 5 ns although the connection maps for the switch may be completed over a much longer period by a parallel/serial pipelined processing process. Additional details on pipelined processing are further discussed in U.S. patent application Ser. No. 14/455,034 filed on Aug. 8, 2014, and entitled “System and Method for Photonic Networks,” which this application incorporates hereby by reference.
CLOS switch 300 contains input signals 302 which are fed to first stage fabrics 304, which are X by Y switches. Junctoring pattern of connections 306 connects first stage fabrics 304 and second stage fabrics 308, which are Z by Z switches. X, Y, and Z are positive integers. Also, junctoring pattern of non-contact optical connectors 290 connect second stage fabrics 308 and third stage fabrics 292, which are Y by X switches, to connect every fabric in each stage equally to every fabric in the next stage of the switch. Making the switch dilating improves its blocking characteristics. Third stage fabrics 292 produce outputs 294 from input signals 302 which have traversed the three stages. Four first stage fabrics 304, second stage fabrics 308, and third stage fabrics 292 are pictured, but more stages (e.g. 5-stage CLOS) or fabrics per stage may be used. In an example of a 3 stage CLOS, there are the same number (Z) of first stage fabrics 304 and third stage fabrics 292, with a different number (Y) of second stage fabrics 308, where Y is equal to Z times the number of first stage outputs per stage module divided by the number of second stage inputs per stage module. As an example, a switch of 1024 input ports, built from 32×64 input stages, 32×32 center stages and 64×32 output stages has 32 input stage modules, 64 center stage modules, and 32 output stage modules. The effective input and output port count of CLOS switch 300 is equal to the number of first stage fabrics (Z) multiplied by X, for the input port count, by the number of third stage fabrics (Z) multiplied by X for the output port count. In an example, Y is equal to 2X−1, and CLOS switch 300 is at the non-blocking threshold. In another example, X is equal to Y, and CLOS switch 300 is conditionally non-blocking. In this example, existing circuits may be rearranged to clear some new paths. A non-blocking switch is a switch that connects N inputs to N outputs in any combination, irrespective of the traffic configuration on other inputs or outputs. A similar structure can be created with five stages for larger fabrics, with two first stages in series and two third stages in series.
An input stage, center stage, or output stage card may contain a pair of crosspoint switches or a single crosspoint switch. Alternatively, the cards are more complex. In some technologies, such as electro-optic Silicon crosspoint switches, the switching performance is highly polarization dependent. The input optical signal may be split into two polarizations, one matching the crosspoint switch's best polarization plane and one orthogonal to it, which is then rotated ninety degrees before being fed into a second crosspoint switch. After switching, one of the signals is rotated ninety degrees, and the two signals are combined to create the original signal. This may be achieved in a PIC or a combination of PICs on a macromodule, which provides high throughput and may incorporate amplification to reduce stage losses, and polarization diversity for polarization-agnostic operation.
A photonic switch with four shelves, each of around 250 mm in height, may fit a one meter rack height. When switch commutation is used, two photonic switches fit in a single rack with commutator elements in a small volume in an adjacent rack. However, inter-rack cabling via an over the top overhead structure significantly adds to the delay. Commutators may be placed into a central location between the switches, adding 250 to 500 mm to the rack height, leading to a rack height of about 2.25 to about 2.5 meters. Alternatively, the commutators are distributed into the input and output stage shelves, leading to a wider shelf. Additional details on commutator based photonic switches and packaging are further discussed in U.S. patent application Ser. No. 14/508,676 filed on Oct. 7, 2014, and entitled “System and Method for Commutation in Photonic Switching,” which this application incorporates hereby by reference. When commutation is not used, a single switch occupies about 1 meter of rack height.
For switching stages which are orthogonally connected, and circuit packs which are not physically orthogonal, but are organized in an orderly row of vertical units, the orthogonal connections may be achieved through a fiber shuffle.
In one example, optical path lengths in circuit packs and shelves are long (several meters) and the optical path lengths in the optical shuffle are very long. It is desirable for the optical path lengths to be matched to provide lower differential lengths than the limits given in Table 1, for example, within about 0.2% to about 4% of their overall length.
Table 2 illustrates a variety of sources of delay for the physical design illustrated in
Only 525 ps of the uncompensated skew is from photonic functionality, with the remainder from the packaging and inter-stage interconnections. It is desirable to reduce the uncompensated skew from the packaging and inter-stage interconnections. Designing the optical path lengths of each component to be the same optical path length, and hence have the same propagation delay, reduces the skew. However, this increases the overall delay, for example by about half of the value of the removed skew.
The macromodules 831, 817, and 833 contain the active photonic functionality which may contain hybridized Si-PIC or InGaAsP/InP switch cell arrays or crosspoint switches, optical amplifiers such as semiconductor optical amplifiers (SOAs), and electronic control chips, as well as monolithically integrated dense arrays of optical interconnect, including low loss optical crossings, optical power splitters and combiners and/or polarization splitters, combiners and rotators. Instead of SOAs, when the waveguides are SiO2, 980 nm optically pumped erbium doped waveguide amplifiers (EDWA) may be used.
Macromodule 831 is fed from the external optical inputs via a lithographically defined waveguide array 824, which may be a polymer on polymer waveguide array, from input ribbon fiber cable connector 822. The processed/switched outputs of macromodule 831 are fed via waveguide array 826 with a known geometry to a series of expanded beam non-contact connectors, such as graded index lens (GRIN) connectors 828. The exiting facet of the GRIN lens (as well as the entry facet of its mating lens) may be anti-reflection coated to avoid the air gap between the two components acting as an optically resonant cavity.
The center stage also contains a macromodule 817, which contains similar functions to those of 813 but is dimensionally and functionally customized to the role of a center stage switching stage. Macromodule 817 receives its inputs via the receive side of the GRIN connectors 828, via controlled length optical paths. After its switching/processing the macromodule outputs are coupled to the center stage output connectors, connector 835 where they are coupled into the output stage card via its input connector, connector 835, and passed through controlled length optical connection path 827 into the macromodule 833. The switched/processed output from this macromodule exits the switch via controlled length optical links 825 and output connector 823.
The non-contact connectors may be mounted using precision etched V-groove technology directly on the macromodule substrate. When V-grooves are directly etched on the macromodule substrate, the width of the macromodule is extended to match the apertures in the mid-planes, increasing the size of the macromodule.
In another example, the optical expanded beam connectors are mounted off the macromodule using polymer waveguide based mechanically compliant extensions, such as mechanically compliant extension with integrated waveguides 880 in
In Si PIC photonic switching matrices, each cell is controlled, both for switching state (connections on or off) and optimization (optimum on-off contrast). Control may be achieved by mounting a control application specific integrated circuit (ASIC) above the optically active layer of the Si PIC and using direct chip-to-chip connections across the interface to densely couple the two chips. The Si-PIC is mounted with its optically active surface down, so it can couple to the macromodule substrate, and the control chip is mounted to the Si PIC chip for electrical connections via the Si PIC chip. The pair is mounted over a hole in the macromodule, with the Si PIC chip optically active surface down, so the edge areas of the Si PIC chip couple optically to the macromodule and the Si PIC chip picks up electrical connections from the macromodule both for its own use and for propagation to the control chip. Besides the control ASICs on the Si PIC chips, SOAs and optionally SOA controllers have electrical connections and metallic traces. Integrated circuit (IC) tracing metal may be used for connectivity.
Due to the physically orthogonal structure between the input stages and the center stages, and between the center stages and the third stages, the optical connections are direct. The connections are made with expanded beam non-contact optical connectors which propagate a beam from one connector half to the other. The facing facets of the two connector halves are efficiently anti-reflective coated to avoid forming a small resonant cavity between the two halves. The connectors are non-contacting with an air gap, facilitating the insertion and removal of individual center stage modules. The active photonics of the switching cards is carried on optical substrates or macromodules backed with a strength member, for example nickel plated steel or duralumin, which may also carry a control electronics printed circuit board on one side.
The electronic boards may be mounted above or below the optical process area of the card. Alternately, the electronics boards are all above or all below the optical processing area. The latter approach simplifies the packaging and facilitates the electronics plugging into a conventional backplane. However, former approach using two card configurations alternately doubles the spacing between the electronics boards relative to the photonic boards, facilitating more headroom for bulky electrical components with good cooling airflow while keeping the photonic spacing minimized to accommodate smaller photonic modules and optical connector pitch. In one example, the photonic macromodule carrier area is of the order for about 28 to about 96 square inches, most of which is tracking to the connector field. The use of SOA or other optical amplifiers such as EDWA compensates for losses through the crosspoint PICs hybridized on the macromodules, as well as compensating for the losses of SiO2 or Si waveguide structures.
In one example, optical modules have a pitch of about 3-6 mm and electronic modules have a spacing of twice the photonic spacing at about 6-12 mm. This results in the optical connectors having a pitch of 3-6 mm which leads to the following connector array sizes for the connectors between the input stage and the center stage, as shown in Table 3. For small switches, the resultant length of the connector array facilitates the integration of the connector array, the tracking to it, and the macromodule active photonic component on one substrate, as is shown in
Table 4 below illustrates the propagation delay and skew for photonic structure 810. The fiber shuffle delay is eliminated, and the fiber shuffle is replaced by direct orthogonal connections between macromodules using a two part GRIN lens expanded beam free space connector. The delay between devices is from optical traces from mounted GRIN lenses for expanded beam free space connections. Of the switch cards, 4 cm of each is on a PIC with the balance on the macromodule. The macromodule may be larger to provide traces to connectors. The overall delay for the structure illustrated in
The modules have a variety of elements. A module may contain a heat spreader, which may be a precision metal or thermally conductive ceramic strength plate. A large area hybridized macromodule has a substrate which supports a dense array of lithographically defined low loss optical connections, including optical crossovers and/or multiple layers of optical interconnectivity to provide the connectivity between the various hybridized photonic components and PICs as well as monolithic integrated waveguide components, such as optical power splitters and combiners, polarization splitters, rotators and combiners, and optical couplers in and out of the hybridized photonic components, such as the PICs and SOAs, as wells into couplings into waveguide extensions to optical connectors and metalized electrical connections. Thus, the substrate also supports hybridized and monolithic photonic and hybridized electronic functions and building blocks. Also, a macromodule either directly contains or connects to extensions to precision mounted expanded beam non-contact optical connectors spaced precisely along one or two opposing sides of the macromodule and coupled directly or via extensions to macromodule waveguides of other modules. The macromodule also contains a hybridized SOA and its electronic control functions or monolithic EDWA amplification capacity. EDWAs may use an on-board or may use an external high optical power pump laser at 980 nm. Additionally, the module structure plate that is carrying the photonic macromodule also carries a PCB or other form of dense electrical module for the electronic control, such as the SMC or GFC functions, or other electrical functions.
The photonic functionality is contained in macromodule 168, which contains the functionality shown in
Control circuit board 164 performs electronics functions, such as SMC functions, associated with the input stage switch. Control circuit board 164 contains a card, PCB, or module which provides electronics control to the switch and communicates with the per-Si PIC overlay electronic chips, which provide per-switch cell control and optimization. The controller circuit board also implements the SMC function for the input ports connected to its associated input stage switch card. Electronic connectors 166 couple control circuit board 164 to other cards.
The photonic functionality is contained in macromodule 238, which contains the functionality of
Control circuit board 224 performs electronics functions, such as GFC functions, associated with the output stage switch. Control circuit board 224 contains a card, PCB, or module which provides electronics control to the switch and communicates with the per-Si-PIC overlay electronic chips, which provide per-switch cell control and optimization. The controller card also implements the GFC function for the input ports connected to its associated input stage switch card.
The photonic functionality is contained in macromodule 272, which contains two single polarization crosspoint switches, for example two 32×32 Si-PICs, or an AWG-R, such as a 32×32 AWG-R, or an 80×80 AWG-R, up to 64 SOAs with 32×32 Si-PICs or up to 160 SOAs in multi-SOA arrays with an AWG-R of 80×80 ports, plus polarization splitters, rotators, and combiners. Although the AWG-R is polarization-agnostic, the SOAs exhibit polarization-dependent properties, and may be used as pairs between polarization splitters, rotators and combiners. Macromodule 272 is coupled via optical flexible precision length extensions, which may be used to equalize path lengths. Optical connectors 268 and 271 are optical non-contact expanded beam connectors used to directly optically couple the center stage card to each input stage card and each output stage card.
Control circuit board 264 performs electronics functions, such as fabric control functions, for the center stage switch, and may implement the center stage controller (CSC) function, which collects connection data from the SMC and GFC once they have finished their negotiations, to build a center stage connection map if an AWG-R is not used. Control circuit board 264 contains a card, PCB, or module which provides electronics control to the switch and communicates with the per-Si PIC overlay electronic chips, which provide per-switch cell control and optimization. The controller card is coupled to retracting electrical connector 266, a two part connector (the other part being on the mating mid-plane) which facilitates slide-in insertion of the circuit module across the face of the connector.
Macromodule 272 may contain crosspoint switches, like the macromodule shown in
Substrate 338 carries electro-optic transmitter array 350, which is configured to convert electrical signals received via high speed bus 354 from orthogonal mapper board 334. Also, opto-electric receiver array 348 is configured to convert optical signals to electrical signals and transmit them along high speed bus 352 to orthogonal mapper board 334. Electro-optic transmitter array 350 is coupled to area 344 for silica optical interconnect on silica or silicon. Alternatively, the non-contact optical connectors 340 and 347 may be coupled to the opto-electric receiver array 348 and electro-optic transmitter array 350 via flexible optical connection arrays as per the photonic switching cards. Area 344 is coupled to non-contact optical connectors 347, optical non-contact expanded beam connectors. Additionally, opto-electric receiver array 348 is coupled to area 342 with optical interconnect, which is coupled to non-contact optical connectors 340, optical non-contact expanded beam connectors. The optical interconnect areas equalize the path lengths. The optical non-contact connectors directly couple the orthogonal mapper card to each input stage card and each output stage card. Orthogonal mapper cards 330 and 360 communicate with the SMCs of the input stage switching cards and the GFCs of the output stage switching cards. System timing reference 339 generates system clock timing for the overall switch and the dependent TOR-located functions, such as packet splitters and combiners.
Orthogonal mapper board 334 performs orthogonal mapper routing functions. Orthogonal mapper board 334 may contain a processor and/or application specific integrated circuit (ASIC). The orthogonal mapper board is coupled to refracting electrical connector 336, a slide-in connector. The operation of the orthogonal mapper is described in U.S. patent application Ser. No. 14/455,034.
Mid-plane 372 has aperture 376, and mid-plane 394 has aperture 388, which are in the center of the mid-planes. Aperture 376 is for non-contact expanded beam optical connectors for communications between the input stage switch cards and the center stage switching cards and orthogonal mapper cards. Similarly, aperture 388 is for non-contact expanded beam optical connectors to communicate from center stage switching cards and orthogonal mapper cards to output stage switching cards. Both mid-plane apertures contain a registration plate not shown in
Electrical connectors 378 and 374 are on mid-plane 372, while electrical connectors 392 and 386 are on mid-plane 394. Electrical connectors 378, 374, 392, and 386 are vertically mounted multi-pin electrical connectors. Non-contact optical connectors 184 of the input stage cards may protrude through aperture 376, and non-contact optical connectors 230 of the output stage cards may protrude through aperture 388 to within a fraction of a millimeter or a millimeter or two of the slid in non-contact optical connectors 340 and 347 of the center stage cards.
Electrical connectors 396 and 390 on mid-plane 394 are horizontally mounted connectors on the inner surface of mid-plane 394. Electrical connectors 396 and 390 are for slide-in insertion connections, so the center stage insert-able module is slid in to the slot horizontally across the face of the two vertical mid-planes. The connector contacts on the plug-in module may be retractable to facilitate this slide-action insertion, for example with a cam action activated by rotating a connector release lever.
Apertures 380 and 382 on mid-plane 372 facilitate input stage air plenum airflow in the center area and to cool the center stage cards.
Mid-plane interconnect 384 and 398 is a mid-plane interconnect PCB or flexi-circuit between mid-plane 372 and mid-plane 394.
In
In
In
In
The input stage modules 446 are fully populated with 32 units in
There may be cover plate(s) over the open vertical faces of the horizontally inserted center stage cards. These may be partitioned into strip plates or platelets to reduce air loss while changing cards.
Next, in step 984, the optical signals are switched by the input stage optical cards, for example by optical crosspoint switches. The delays in the optical switching paths through the input stage optical cards low and have a low skew.
Then, in step 986, the switched optical signals from step 984 are coupled to the center stage cards. An array of non-contact optical connectors is used to couple each input stage card to each center stage card. The non-contact optical connectors may include two aligned GRIN lenses with an air gap between the GRIN lenses. The input stage optical cards are orthogonal to the center stage optical cards, facilitating a low delay and skew in the connection.
Next, in step 988, the optical signals are switched by the center stage optical cards. The optical signals may be switched using crosspoint optical switches or AWG-Rs. The optical paths through the center stage cards are short and have a low skew.
In step 990, the switched optical signals from step 988 are coupled to the output stage cards, which are orthogonal to the center stage cards. An array of non-contact optical connectors is used to directly couple each center stage card to each output stage card. The non-contact optical connectors may include two aligned GRIN lenses with an air gap between the GRIN lenses.
Then, in step 992, the optical signals are switched by the output stage cards, for example by optical crosspoint switches. The delays in the optical switching paths through the output stage optical cards are low and have a low skew.
Finally, in step 994, the switched optical signals from step 992 are transmitted, for example using optical fibers. The optical path lengths through the photonic structure a low delay and a low skew.
The waveguide in the macromodule substrate may have a very small cross-section, depending on the waveguide design and choice of waveguide material. An example silica waveguide has a width of from about 3 μm to about 8 μm. Some silicon waveguides may have sub-micron dimensions. These waveguides may be brought out to the substrate edge of the macromodules and directly coupled to the next stage modules. However, the small mode field diameter needs extreme precision in the alignment of the waveguides in the two substrates. Also, the macromodule edges would be in intimate contact with no air gap and may have significant losses.
In an embodiment, the mode-field is expanded in a mode field expander. The mode field expander is a tapered expanding cross sectional waveguide. The expanded beam is aligned to an edge fiber attach mechanism or a GRIN lens to create an expanded beam connector. The lens projects a nominally parallel sided beam which may be propagated in air.
The beam propagates about one to two millimeters across an air gap, when it impinges on another GRIN lens, which focuses the parallel beam to reconstruct the mode field spot. When the two GRIN lenses are identical, the reconstructed mode field spot is the same size as the source mode field spot. On the other hand, when the second GRIN lens is longer and has a larger diameter and increased focal length, the mode field spot on the received side is larger.
On the other hand,
An embodiment uses a projection from a smaller lens to a larger lens.
When lenses are laterally offset, using a receiving lens which is larger than the projecting lens may have better performance.
The use of dissimilar lens areas introduces an overall mismatch or loss in the connector, even when aligned.
The two parts of the expanded beam non-contact connectors are aligned accurately to remain within these tolerances. The connector halves are carried on separate plug-in modules, one inserting conventionally and one slid into place across the face of mid-planes. In one example, to align the connectors of the vertically oriented input stage or output stage modules with the connectors of the horizontally inserted center stage modules, both halves of every connector associated with the first stage/center stage and second stage/output stage interfaces are aligned to a common registration detail or point on the mid-planes where these connectors meet.
The registration plate is made from a highly stable material with approximately the same coefficient of expansion as the substrate controlling the GRIN lens pitch. Registration plate 680 has a precision two dimensional array of tapered holes 686, which are slightly larger than the non-contact optical connectors. The GRIN lenses may be in protective sleeves. One plate is fixed to each of the mid-planes, providing a reference guide into which the pluggable module (i.e. input and output stage modules) expanded beam optical connectors meet during the last part of the travel of the module down the plug-in card guides. Registration details 682, for example a metal spike, may be attached to either end of the macromodule row of expanded beam connector lenses. The registration detail enters the precision plate just before the expanding beam connectors, and tends to center the expanded beam connectors. Also, the lens array substrate may be resiliently mounted on the carrier to provide a small degree of compliance, so the overall pluggable input stage or output stage module position registration does not compete with the macromodule optical alignment to the aperture registration plate.
The registration plate is attached to the mid-plane so the non-contact optical connectors enter a series of tapering holes which, along with the registration detail, guide them to a known fixed position in the two axes of the plane of the mid-plane, with a tolerance relative to the registration plate, equivalent to the tapered hole positional tolerance plus spacing between the minimum hole diameter at the small end of the taper and the diameter of the expanded beam lens. To facilitate accurate spacing of the lenses, the lenses are mounted to the macromodule while held in a positional jig, relying on accurate inter-lens spacing, accurate lithography on the macromodule substrate, and the use of waveguide mode expanders to produce the required positional accuracy. The jig has a sufficiently tight tolerance for the row of lenses to be aligned to the substrate by aligning the lenses at each end. When this is achieved, the jig may have a higher tolerance than the margins in the registration plate-to-lens diameter tolerances, thereby avoiding binding the holes from the lens offset.
The center stage card is slide-inserted and aligned. The center stage non-contact optical connectors clear the mid-plane component of the electrical slid-in connector. This may be achieved by placing the optical connectors higher or lower than the electrical connectors, so they pass above or below the electrical connector as they slide in place. The optical connector may pass through the electrical component when the diameter is smaller than the opened connector slow width for a clamshell type connector which closes after module insertion. The clamshell action is either on the pluggable module or the backplane. In another example, the input stage and output stage expanded beam connectors protrude further through the registration plate, which may be mounted further into the center stage cavity than the mid-plane.
The slide-in non-contact optical connectors are aligned to the registration plate in two axes, the axis along which the plug-in module slides, and the axis orthogonal to this, up and down the mid-plane. The third axis, the distance between the two ends of the mating pair of the optical connector (the air gap) is handled by the tolerance of the two non-contact optical connectors for the size of the air gap. The air gap has a range which is more than the range of actual gaps. A parallel sided optical beam from a GRIN lens may be sent many tens of centimeters in air, for example in a three dimensional (3)D micro-electro-mechanical system (MEMS) switch, so an air gap of about 0.5 mm to about 2 mm is not problematic when there is no optical resonance in the air gap. Therefore the lens surfaces are anti-reflection coated to avoid resonances in the air gap.
The vertical alignment may be addressed by using lenses and/or registration details, such as a metal spike, which slide into a precision groove on the center stage module side of the registration plate. For example, groove 692 may be used. The groove is accurately positioned relative to the tapered holes, and is wider than the width of the expanded beam optical connector lenses or the registration detail, so it constrains them in a vertical direction to a tolerance based on the positional tolerances of the groove on the registration plate plus the slack or gap between the groove width and the lens diameter or registration detail diameter. The lenses are in a straight line without bow in the macromodule. Silica on silicon may be prone to bowing, because the two materials expand at a different rate. This may be reduced by growing a silica layer on the back of the silicon substrate of the macromodule.
The horizontal alignment along the slide-in path may be achieved using a precision end to the slide-in groove in the registration plate, for example end stop 684, so the face of the registration detail is stopped at the correct distance down the groove. A precision end stop for a single connector block per circuit pack side constrains the center stage connectors horizontally. For multiple connector blocks, a graduated or stepped groove width with precision taper end stops may be used. There is a tolerance between the groove end on the input stage slide and the groove on the output stage side. When the macromodule is mounted slightly resiliently, and is pressured into the direction of the insertion, when it reaches the end stops of the grooves, it rotates a small fraction of a degree to simultaneously pick up on both end-stops. This causes the center stage macromodule to be slightly twisted, but does not have a significant impact on the alignment of the expanded beam connector components.
Along the groove, components include a input stage or output stage lens, with a registration plate hole tolerance and slack of Lh, while the registration plate manufacturing tolerance in the horizontal direction, from the groove end reference to the center of the registration plate along the groove is Rh. Also, in the horizontal direction, the center stage lens position-registration detail position tolerance is Ch. The vertical direction across the groove, the tolerances include the input stage or output stage lens-registration plate hole tolerances and slack of Lv, the registration plate manufacturing tolerances in the vertical direction, in the groove vertical tolerances and slack and the centering of the groove on the registration plate holes is Rv, and the center stage lens position-registration detail position tolerance is C. The overall horizontal tolerance is given by:
T
h
=L
b
+R
h
+C
h,
and the overall vertical tolerance is given by:
T
v
=L
v
+R
v
+C
v.
For the lens axes to be aligned within a distance Da:
D
a
2
=T
h
2
+T
v
2.
When Th=Tv=T:
D
a
=T√{square root over (2)}.
The individual tolerances and the target value for Da may be set by the design of the lens system. In one example, a 1.8 mm GRIN lens has an about 6 mm connection pitch, with a registration plate hole array area of about (6)*32=192 mm, or about 6.6 inches on a side, while the electronics cards may have a pitch of about 12 mm. This leads to a photonics card pitch of about 6 mm, for a registration plate of about 192 mm square. The overall packaging density is may be limited by the electronics pitch.
The center stage module slides through the mid-plane electrical connector and makes contact through mating connections with the electrical connector. This may be achieved by retracting the electrical connections on one part of the two mating parts of each of the mating connectors, and advancing the connections again once the module is inserted. Such connectors have been known since the early 1980s when they were explored as a solution to connector insertion forces before low insertion force connectors were developed.
The macromodule substrate may be silicon or silica on silicon. For small switching modules with limited port counts, the macromodule may act as a carrier and interconnect for the photonic functionality, as well as providing the optical tracking to the inter-module connectors. For high port count switches, the length of the inter-module connector array becomes large, and the macromodule is sized to provide only the interconnect, monolithic components and integrated components hybridization of the switch stage photonic functionality, with the interconnect to the inter-stage connectors such as the GRIN lens connectors being provided by precision extensions as detailed in
There both optical and electrical coupling to and from the macromodule from the hybridized components. In one example, illustrated by
Polarization splitting, combining, and rotation functions are performed, for example directly on the macromodule substrate. One example silicon nitrate on silicon-on-insulator (SOI) polarization splitter based on TM0-TE1 mode conversion, such as waveguide 860 illustrated in
Amplification may be achieved by hybridizing semiconductor optical amplifier arrays and their controllers on the substrate. Alternatively EDWAs are built into the substrate. An EDWA array uses a high power 980 nm optical pump source rather than an electrical power source for SOAs.
Next, in step 624, the center stage cards are inserted between the two mid-planes. The center stage cards are slid between the two mid-planes. Retractable electrical connectors are retracted during insertion. Optical non-contact connectors are aligned with the optical non-contact optical connectors in the input stage cards, so each center stage card is directly optically connected to each input stage card. The optical connectors are aligned using the registration plate in the aperture of the mid-plane. Alternate center stage cards are inserted with the electrical connectors above and below the optical connectors. The center stage cards have two sets of optical non-contact connectors on opposite sides of the card to directly couple to the input stage cards and the output stage cards. Both are aligned using registration cards in an aperture in the corresponding mid-plane.
Then, in step 626, orthogonal mapper cards are inserted. In one example, two orthogonal mappers are inserted. In one example, one orthogonal mapper card is inserted above the center stage cards, and the other orthogonal mapper card is inserted below the center stage cards. In another example, the orthogonal mapper cards are all at the top, all at the bottom, or interspersed with the center stage cards. The orthogonal mapper cards have a retractable electrical connector which is retracted while the orthogonal mapper cards are slid between the two mid-planes. The orthogonal mapper cards also have optical non-contact connectors on opposite sides, which are aligned using registration plates in apertures in the mid-planes. The orthogonal mapper cards all have a direct optical connection to each input stage card and each output stage card.
Finally, in step 628, the output stage cards are plugged in to the second mid-plane. The output stage cards have an electrical connector, which is plugged in to the mid-plane, and an optical non-contact connector, which is inserted in to the registration plate in the aperture of the mid-plane. Each output stage card is directly optically connected to each center stage card and each orthogonal mapper card. The electrical connectors are alternately above and below the non-contact optical connectors.
Sub-equipped lower capacity switches may omit the insertion of a portion of each set of cards in each stage. When X % of input and output cards are provisioned and ≧X % of center stage cards are provisioned to maintain dilation levels, the resultant switch capacity is X % of the maximum. Hence, when 26 of 32 input and output cards are provisioned the switch capacity is 81.25% of the maximum capacity.
An embodiment macromodule for a center stage switching card includes two 32×32 crosspoint chips, 32 polarization splitters and rotators, 32 polarization rotators and combiners, and 64 SOAs. With core chip size is 13 mm×13 mm for a crosspoint chip, plus 3 mm for output coupling to the substrate, there are two 16 mm×16 mm chips for an area of 256 square mm each, or 512 square mm total. The 32 polarization rotators and splitters are about 1.3 mm×0.3 mm or less, for an overall area of around 0.4 square mm to around 0.5 square mm per device, or about 16 square mm for the 32 devices. The polarization rotators and combiners have areas similar to the polarization splitters and rotators. Hence, the overall polarization processing functions may be about 32 square mm, or about 32 square mm to about 50 square mm with a margin. The 64 SOAS may be about 1-2 square mm each as discrete chips, for a total of about 64 square mm to about 128 square mm. The total area budget is about 608 square mm to about 690 square mm, which may be rounded up to about 700 square mm. The dense optical interconnect to link the functions together is conservatively about 2100 square mm, for a total of 2800 square mm.
The area of the active functions plus the interconnect is around 50 mm to about 70 mm squared, which is much smaller than the size for the connector field for the aperture. There may be a high density optical design of the active macromodule area in the center of a less optically dens larger overall area, so the optical waveguides are tracked out to V-groove mounted expanded beam connectors. Alternatively, the macromodule size is limited to that of the photonic functions and the compliant waveguide array is used to extend in a controlled path length environment out to the expanded beam lens carriers at the overall module edge.
An embodiment packaging approach exploits the use of macromodules at the system level for low skew and delay photonic switch. The low skew facilitates a high bit rate of photonic packet and/or container switching in a fast synchronous space switch. The overall fabric timing and skew behavior is compatible with a 100 Gb/s packet or encapsulated packet stream switching individual long containerized packets. A frame format mapping one long packet or padded long packet into a nominally 120 ns frame with a 3-5% clock acceleration yields a commutation platform with a clock rate of about 120%.
An embodiment packaging approach facilitates a three stage photonic switch, for example using a CLOS configuration, where the first stage is implemented by a macromodule-based solution. The first stage may provide 1:2 dilation for a non-blocking CLOS switch fabric. In one example, the center stage has a slide in mounting to be physically orthogonal to the first stage, for example using a macromodules. The third stage may be implemented in a similar manner to the first stage. This configuration yields a three stage CLOS switch which, due to the lithographic control in the macromodules and the low inter-stage skew from the direct stage to stage optical connections and orthogonal physical packaging, may have low skew. This facilitates a low intrinsic switched path-to-switched path skew. This facilitates the operation of the switch at 100 Gb/s with standard IPGs or ICGs.
An embodiment photonic structure includes a plurality of input stage cards including a first input stage card and a second input stage card, where the first input stage card is parallel to the second input stage card, where a first plane is at an edge of the plurality of input stage cards, and where the first plane is orthogonal to the plurality of input stage cards. The photonic structure also includes a plurality of center stage cards optically coupled to the plurality of input stage cards, where the plurality of center stage cards includes a first center stage card and a second center stage card, where the first center stage card is orthogonal to the first input stage card and the second input stage card, where the second center stage card is orthogonal to the first input stage card and the second input stage card, where the first plane is at a first edge of the plurality of center stage cards and orthogonal to the plurality of center stage cards, where a second plane is at a second edge of the plurality of center stage cards, where the second plane is parallel to the first plane, where the first center stage card is directly optically coupled to the first input stage card and the second input stage card, and where the second center stage card is directly optically coupled to the first input stage card and the second input stage card. Additionally, the photonic structure includes a plurality of output stage cards optically coupled to the plurality of center stage cards, where the plurality of output stage cards includes a first output stage card and a second output stage card, where the first output stage card is orthogonal to the first center stage card and the second center stage card, where the second output stage card is orthogonal to the first center stage card and the second center stage card, where the second plane is at an edge of the plurality of output stage cards, where the second plane is orthogonal to the plurality of output cards, where the first output stage card is directly optically coupled to the first center stage card and the second center stage card, and where the second output stage card is directly optically coupled to the first center stage card and the second center stage card.
In one example, a first optical path length is through the first input stage card, from the first input stage card to the first center stage card, through the first center stage card, from the first center stage card to the first output stage card, and through the first output stage cards, where a second optical path length is through the second input stage card, from the second input stage card to the second center stage card, through the second center stage card, from the second center stage card to the second output stage card, and through the second output stage cards, and where a difference between a length the first optical path and a length the second optical path length is less than one ns.
In another example, a plurality of optical path lengths through input states of the plurality of input stages, center stages of the plurality of center stages, and output stages of the plurality of output stages is within one ns.
In an additional example, an optical path through the first input stage card, from the first input stage card to the first center stage card, through the first center stage card, from the first center stage card to the first output stage card, and through the first output stage card has a propagation delay of less than 5 ns.
In a further example, the first center stage card includes a first photonic module and a first electrical module on a first surface, where the second center stage card includes a second photonic module and a second electrical module on a second surface, where the first surface is parallel to the second surface, where the first photonic module is directly over the second photonic module, and where the first electrical module is not directly over the second electrical module.
In an example, the first input stage card includes a first photonic module and a first electrical module on a first surface, where the second input stage card includes a second photonic module and a second electrical module on a second surface, where the first surface is parallel to the second surface, where the first photonic module is directly over the second photonic module, and where the first electrical module is not directly over the second electrical module.
In another example, the first output stage card includes a first photonic module and a first electrical module on a first surface, where the second output stage card includes a second photonic module and a second electrical module on a second surface, where the first surface is parallel to the second surface, where the first photonic module is directly over the second photonic module, and where the first electrical module is not directly over the second electrical module.
In a further example, the first center stage card of the plurality of center stage cards includes a first non-contact optical connector directly coupled to the first input stage card and a second non-contact optical connector directly coupled to the first output stage card.
In an additional example, the first center stage card includes a strength plate, a photonic module disposed on the strength plate, and an optical module disposed on the strength plate.
An example further includes an orthogonal mapper card directly optically coupled to the plurality of input cards and the plurality of output cards.
An example also includes a first mid-plane electrically coupled to the plurality of input stage cards and the plurality of center stage cards and a second mid-plane electrically coupled to the plurality of output stage cards and the plurality of center stage cards. This example may also include a mid-plane interconnect coupled between the first mid-plane and the second mid-plane. Additionally, the first mid-plan includes a plurality of retractable multi-pin electrical connectors coupled to the plurality of center stage cards. The first mid-plane also includes an aperture, where a plurality of non-contact optical connections is between the plurality of input stage cards and the plurality of center stage cards are in the aperture. In an example, the plurality of input stage cards include a first switching stage, where the plurality of center stage cards include a second switching stage, and where the plurality of output stage cards include a third switching stage.
In an example, the plurality of center stage cards are optically coupled to the plurality of input stage cards by a first plurality of two part non-contact expanded beam optical connectors, and where the plurality of center stage cards are optically coupled to the plurality of output stage cards by a second plurality of two part expanded beam non-contact optical connectors, and where first center stage card includes a retractable electrical connector.
An example also includes a first registration plate mechanically coupled between the plurality of input stage cards and the plurality of center stage cards and a second registration plate mechanically coupled between the plurality of center stage cards and the plurality of output stage cards.
An embodiment optical connection includes a first array of holes on a first side of a registration plate and an array of grooves having a plurality of end stops on a second side of the registration plate. The optical connection also includes a first plurality of graded refractive index (GRIN) lenses inserted into the first array of holes, where the first plurality of GRIN lenses includes a first GRIN lens in a first hole of the first array of holes and a second plurality of GRIN lenses inserted in grooves of the array of grooves, where the first side of the registration plate is opposite the second side of the registration plate, where the second plurality of GRIN lenses includes a second GRIN lens in a first groove of the array of grooves opposite the first GRIN lens, and where the first GRIN lens is optically coupled to the second GRIN lens by an air gap in the first hole.
In one example, the first GRIN lens has a first diameter, where the second GRIN lens has a second diameter, and where the first diameter is smaller than the second diameter, and where the first lens is configured to propagate light to the second lens.
In another example, the second plurality of GRIN lenses is configured to slide in along the array of grooves.
An embodiment registration plate includes a row of holes and a groove configured to receive a card along the row of holes, where the card includes a row of non-contact optical connectors, and where the groove is configured to align the row of non-contact optical connectors with the row of holes. The registration plate also includes an end stop at an end of the groove, where the end stop is configured to align the row of non-contact optical connectors with the row of holes.
An example also includes a plurality of registration details above the row of holes.
An embodiment device includes an optical macromodule and a plurality of flexible waveguide extensions having a surface. The device also includes a plurality of graded refractive index (GRIN) lenses, where the plurality of flexible waveguide extensions are optically coupled between the optical macromodule and the plurality of GRIN lenses.
An embodiment also includes an electrical module electrically coupled to the optical macromodule and a retractable electrical connector electrically coupled to the electrical module.
In an additional example, the plurality of flexible waveguide includes optical connectors, where the plurality of flexible waveguides is bowed in orthogonal to the surface and parallel to the optical connector.
While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented.
In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.
