(12) United States Patent
`Raj et al.
`
`USOO6496291B1
`(10) Patent No.:
`US 6,496,291 B1
`(45) Date of Patent:
`Dec. 17, 2002
`
`(54) OPTICAL SERIAL LINK
`(75) Inventors: Kannan Raj, Chandler, AZ (US);
`Werner Metz, Chandler, AZ (US)
`(73) Assignee: Intel Corporation, Santa Clara, CA
`(US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 219 days.
`This patent is Subject to a terminal dis
`claimer.
`
`(*) Notice:
`
`(21) Appl. No.: 09/690,548
`(22) Filed:
`Oct. 17, 2000
`9
`(51) Int. Cl. ................................................ H04B 10/00
`(52) U.S. Cl. ........................ 359/152; 359/173; 359/291
`
`(56)
`
`(58) Field of Search ................................. 359/152, 127,
`359/129, 130, 173,291
`References Cited
`U.S. PATENT DOCUMENTS
`5,594,576 A * 1/1997 Sutherland et al. ......... 359/118
`6,411,424 B1
`6/2002 Raj ............................ 359/291
`sk -
`cited by examiner
`Primary Examiner Kinfe-Michael Negash
`(74) Attorney, Agent, or Firm Trop, Pruner & Hu, P.C.
`(57)
`ABSTRACT
`An optical Serial link may be formed of an optical trans
`ceiver and a reflective wavelength coupler. The coupler may
`reflect light beams of different wavelengths using an ellip
`tical reflector and a dispersive element.
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`25 Claims, 4 Drawing Sheets
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`Electrical Unit
`132
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`138
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`Optical Transceiver
`MOCule
`146
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`144
`Optical Interface
`134
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`Laser Driver
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`Optical TX
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`Data input
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`Data Output
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`Electrica
`interface
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`Reflective
`Wavelength
`Coupler
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`Optical RX
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`Dec. 17, 2002
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`U.S. Patent
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`FIG. 3
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`U.S. Patent
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`1
`OPTICAL SERIAL LINK
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`US 6,496.291 B1
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`2
`Referring to FIG. 2, an optical interface 134 and electrical
`unit 132 may accomplish the functions of the HCA 120,
`links 122, and Switches 124, in one embodiment of the
`present invention. Thus, a fiber cable 136 may be used to
`link the HCA with one or more TCAS 128 that in turn couple
`I/O controllers 130 and I/O devices not shown.
`The optical interface 134 may include a reflective wave
`length coupler 142 that directly couples to a plurality of
`optical fibers contained within the fiber cable 136. The
`reflective wavelength coupler 142 transmits optical signals
`to the fiber 136 and also may receive signals from the fiber
`cable 136. The incoming Signals are transferred to the
`optical receiver 148 and outgoing Signals are received from
`the optical transmitter 146. The optical transmitter 146 may
`for example be a vertical cavity Surface emitting laser
`(VCSEL) or an edge emitting laser diode as two examples.
`The transmitter 146 and receiver 148 may be integrated
`together. In Such case, the optical receiver 148 may include
`an optical detector Such as a reverse biased PN junction
`diode, PIN diode, PNP transistor, or metal-semiconductor
`metal (MSM) detector. Monolithic integration of the
`receiver 148 and transmitter 146 may be accomplished using
`group III-V materials.
`The optical transceiver 144 of the optical interface 134
`communicate with an electrical unit 132. The electrical unit
`132 powers the optical transmitter 146 using a laser driver
`138. The unit 132 also receives optical signals in an elec
`trical interface 140 and converts them into a Suitable elec
`trical Signal format. Data input and output Signals may be
`received at the electrical interface 140 from the HCA120. In
`Some cases, the Signals may be provided directly to the
`memory controller 116 shown in FIG. 1.
`The fiber arrays 28 and 60 may be integrated with or
`integrally connected to a reflector System 142 that includes
`an elliptical reflector 22. Each of the wavelength specific
`light beams received from one of the fiber arrays 28 or 60 is
`reflected by the elliptical reflector 22. The light beams that
`may be received at a foci S1 through S8 of the elliptical
`reflector 22, are reflected toward corresponding or conjugate
`focal points S9 through S16 or vice versa. Of course, the
`number of light beams and the precise orientation of the
`elliptical reflector 22 is subject to considerable variability.
`The present invention is not limited to a specific orientation
`of an elliptical reflector 22 or to the use of a specific number
`of wavelengths.
`In accordance with conventional geometry, any light
`beam issuing from a focus of the elliptical reflector 22 is
`reflected to a conjugate focus of the elliptical reflector 22,
`regardless of the orientation and direction of the light beam.
`Thus, a one-to-one imaging and coupling may be created
`between the System 142 issuing the light beams through one
`set of foci S1 to S8 and the light directed towards the
`conjugate foci S9 to S16.
`A dispersive element 52, Such as a reflection phase
`grating, a thin film dielectric grating, a prism, or micro
`electromechanical structures (MEMS) contributes to the
`creation of multiple foci S1 through S16. The dispersive
`element 52 may be positioned optically between the reflector
`22 and an fiber array 28.
`Each of the light beams of a different wavelength on a
`fiber in an array 28 or 60 may be reflected by the reflector
`22 from a first plurality of multiple foci S1-S8 towards a
`second plurality of conjugate foci S9-S16 or vice versa.
`However, before reaching the Second Set of conjugate foci,
`the light beams are reflected by the dispersive element 52 to
`a common focal point that corresponds to the end of an
`optical fiber in an array 28 or 60.
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`BACKGROUND
`This invention relates generally to an optical Serial link
`for exchanging data between two or more terminals.
`The Infini-Band Specification includes a link specification
`that describes the behavior of a link and specifies the link
`level operations of devices attached to an Infini-Band fabric.
`See Infini-Band Specification, available from the Infini
`Band Trade Association, 5440 Southwest Westgate Drive,
`Suite 217, Portland, Oreg. 97221 (Rev. 0.9, 2000). The
`Infini-Band architecture interfaces to the external world
`from a host channel adapter (HCA). For example, the HCA
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`may provide communication between the fabric Services and
`one or more central processing units which may, for example
`provide an Internet Server function as one example. The
`HCA may be linked via a Switch to a plurality of input/
`output ports. Generally, the HCA Supports a link with a very
`high data rate.
`An Infini-Band link is bi-directional communication path
`way between two connect points within the Switching fabric.
`Conventionally, the link may be formed of a copper cable.
`A short haul copper interconnect may have a bit rate of 2.5
`gigabits per Second.
`One limitation of a copper link is that its bandwidth does
`not Scale well with additional linkS. Electrical. interconnects
`on copper also face a daunting challenge in electromagnetic
`interference mitigation at very high data rates. This may also
`raise Safety concerns due to increased radiation hazards.
`Thus, there is a need for better techniques for implement
`ing optical Serial links at very high data rates.
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`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic depiction of one embodiment of the
`present invention;
`FIG. 2 is schematic depiction of link/switch fabric in one
`embodiment of the invention;
`FIG. 3 is a schematic depiction of the reflective wave
`length coupler in the embodiment shown in FIG. 2;
`FIG. 4 is a schematic depiction of a portion of the
`embodiment shown in FIG. 3; and
`FIG. 5 is an enlarged cross-sectional view taken generally
`along the line 5–5 of FIG. 3.
`DETAILED DESCRIPTION
`Referring to FIG. 1, a server or other processor-based
`device 100 may include a pair of central processing units 112
`coupled to a hostbus 114. The host bus 114 may in turn be
`coupled to a memory controller 116. The memory controller
`controls read and write accesses to the System memory 118.
`A plurality of input/output devices (not shown) may be
`coupled to input/output controllers 130. The controllers 130
`are coupled to a Switch 124 through fabric services 126. The
`fabric Services 126 may include a target channel adapter
`(TCA) 128 and links 122. Thus, data or commands may be
`shuttled between a host channel adapter (HCA) 120 and a
`variety of input/output devices through the I/O controllers
`130, TCAS 128, links 122 and Switch 124.
`In Some applications, the data rates may be in excess of
`2.5 gigabits per second. The Switch 124, link 122 and HCA
`120 may be implemented using an optical serial link. While
`65
`an Infini-Band Specification embodiment is described, the
`present invention is applicable to optical links in general.
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`3
`A cable 136 including an array 28 or 60 may be made up
`of dispersion shifted fibers (DSF) or dispersion compensated
`fibers (DCF) as two examples. Both the DSF and DCF fibers
`can Support high data rates with low attenuation. Each type
`of fiber may be utilized with a fabric Switch 124 or a passive
`Star network. Data may be transmitted at a first wavelength
`and received at a Second wavelength. To prevent croSS
`coupling of transmitted data due to back reflections from a
`fiber onto the receive channel and into the optical transmitter
`146, an angle polished fiber (APC) may be used. In one
`embodiment of the present invention, a polish angle of 8
`may be Suitable.
`An optical block 25 may include a Substantially transpar
`ent block of material. The elliptical reflector 22 may be
`placed at a predetermined location or locations on the block
`25. The block 25 may, for example, be made of borosilicate.
`The dispersive element 52 may then be patterned on an edge
`of the optical block 25, in accordance with one embodiment
`of the present invention or a MEMS 52 may be used.
`The block 25 thickness, the dispersive element 52 grating
`parameters and the ellipticity of the elliptical reflector 22
`may be determined by the wavelengths and wavelength
`spacing. Ray tracing and known grating equation formula
`tions may be used to position these elements. Aligning the
`optical block 25 to the arrays 28 and 60 and may be
`facilitated by the use of fiducial marks on the arrays 28 and
`60, the optical block 25, and the Support 30 for the optical
`fibers in the arrays 28 or 60.
`The optical block 25 may hold the elliptical reflector 22
`and a Securement System 26 for the optical fibers in the
`arrays 28 or 60. As shown in FIG. 5, the securement system
`26 includes a top plate 30 clamped to a support 36 by a pair
`of Securement devices 32 that may be clamps as one
`example. Each Securement device 32 engages the top plate
`30 and pulls it downwardly causing an optical fiber 28 or 60
`to be sandwiched between the top plate 30 and the support
`36, in a V-shaped groove 34.
`The V-shaped groove 34 may be etched into the surface of
`the Support 36. The support 36 may be made of silicon or
`thermo-plastic material as examples. The X and y alignment
`of each fiber in the array 28 or 60 is controlled by placing
`each fiber 28 on a V-shaped groove 34. The V-shaped groove
`34 is centered in alignment with the conjugate foci S1-S16
`relative to the dispersive element 24. The height of the
`V-shaped groove 34 is compatible with the diameter of the
`optical fiber in each array 28 or 60 to be coupled.
`The optical block 25 provides for accurate location of the
`fibers in each array 28 and 60. Additionally, the reflector 22
`is held by the optical block 25 so that the major axis of the
`reflector 22 is coincident with the laser light input and the
`minor axis is perpendicular to the midpoint of the foci. The
`optical block 25 may include a pair of mating halves in Some
`embodiments. The optical block 25 may also provide a stop
`or end point for accurately positioning the end of the optical
`fiber.
`The elliptical reflector 22 may be a reflective ellipsoid or
`conic section placed on one side of the optical block 25. The
`reflector 22 may be secured with adhesive to the optical
`block 25. The elliptical reflector 22 may be made by
`replication of a diamond turned master or by injection
`molding to manufacture in high Volumes. Aluminum, Silver,
`or gold coating, as examples, may be applied to the reflector
`22 to create a highly reflecting Surface. While fixed posi
`tioning of the elliptical reflector 22 is illustrated in FIG. 1,
`the reflector 22 may be adjustable for precise alignment of
`the reflector 22 with the dispersive element 52 and the fiber
`arrays 28 and 60.
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`4
`The coupler 142 may include a plurality of micro
`electromechanical structures (MEMS) acting as the element
`52. Each of the structures forming the element 52 pivots
`around at least one (if not more) axes. In the illustrated
`embodiment, each MEMS element 52 may be tilted out
`wardly at the top, outwardly at the bottom or be maintained
`relatively untilted to vary the angle of reflection of light
`beams reflected by the reflector 22. The element 52 may be
`arranged in a one or two dimensional array.
`Referring to FIG. 4, each MEMS element 52, such as the
`mirror 52a, includes a pivot 54 that mounts the MEMS
`element 52 for pivotal rotation under control of two contacts
`58a and 58b. Mating contacts 56 are provided on the
`backside of each MEMS element 52. Thus, by placing
`appropriate charges on a contact 58a or 58b, the contacts 56a
`or 56b may be attracted or repelled to adjust the angular
`orientation of the MEMS element 52. The signals provided
`to the contacts 58a and 58b may be provided from an
`integrated circuit 59 that generates Signals of appropriate
`timing to implement user Selected combinations of output
`signals for particular fibers in an array 28 or 60.
`Each of the fibers in an array 28 or 60 may be mounted
`on V-shaped grooves and held between a top plate 30a and
`support 36 by clamps 32. Thus, a plurality of grooves 34
`hold a plurality of output fibers 28, 60 clamped between a
`top plate 30 and a support 36. In this way, the focal point of
`any given fiber 28 or 60 may be the target of a particular
`MEMS element 52 whose position is controlled by the
`integrated circuit 59.
`Each of the free ends of the fibers in the array 60 (eight
`of which are shown in FIG. 3) define a focus of a elliptical
`reflector 22 also secured to the optical block 25. The
`reflector 22 reflects light from each and every one of the
`fibers in the array 60 towards a MEMS element 52 including
`a plurality of mirrors 52a in a number equal to the number
`of fibers. In other words, each fiber in the array 60 has a
`corresponding mirror 52a through 52h assigned to it. Thus,
`each fiber controls or routes each output Signal from a given
`fiber to a given output fiber 28a through 28h in one embodi
`ment. The output fiberS28 also include a Securement System
`including the clamps 32, the V-shaped grooves 34 and the
`top plate 30, which together collectively secure a plurality of
`output fibers 28 with their free ends abutted against the
`optical block 25.
`In this way, the ultimate disposition of each channel on
`each fiber 60 may be controlled by the MEMS element 52
`to Specifically direct or route each input channel to a
`particular output fiber 28. This arrangement allows shifting
`of a group of wavelengths on one set of channels to another
`Set of channels while adding or dropping one or more
`channels in a Selective manner. A relatively high precision,
`compact arrangement is possible in Some embodiments.
`While the mirrors 52a-h are shown in a one dimensional
`arrangement, two dimensional arrays of MEMS may also be
`utilized in Some embodiments. By integrating the System
`142 with the other components, relatively compact and
`potentially low loSS arrangements are possible.
`While the present invention has been described with
`respect to a limited number of embodiments, those skilled in
`the art will appreciate numerous modifications and varia
`tions therefrom. It is intended that the appended claims
`cover all Such modifications and variations as fall within the
`true Spirit and Scope of this present invention.
`What is claimed is:
`1. An optical Serial link comprising:
`a first and a Second optical fiber array,
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`S
`an elliptical reflector optically aligned with Said arrays,
`a dispersive element aligned with Said elliptical reflector
`to reflect a light beam from the first to the second
`optical fiber array; and
`an optical transceiver optically coupled to one of Said
`arrayS.
`2. The link claim 1 including a Support that Supports Said
`elliptical reflector and dispersive element as a unit.
`3. The link of claim 2 wherein said support includes an
`optical block that optically couples Said elliptical reflector
`and Said dispersive element.
`4. The link of claim 3 wherein said optical block is a
`transparent Solid block of material.
`5. The link of claim 4 including a securement system for
`Securing an output fiber in Said Second array to Said Support.
`6. The link of claim 5 wherein said securement system is
`arranged to align an end of an optical fiber with Said focal
`point.
`7. The link of claim 1 wherein said dispersive element is
`aligned to deflect a plurality of beams of different wave
`lengths onto a single fiber.
`8. The link of claim 1 wherein said dispersive element is
`a micro-electromechanical Structure including a plurality of
`mirrors.
`9. The link of claim 8 wherein said beams are directed to
`at least two different focal points by Said micro
`electromechanical Structure.
`10. The link of claim 9 wherein said micro
`electromechanical Structure includes a plurality of mirrors
`whose angle of tilt is selectively controllable.
`11. A method comprising:
`receiving an electrical Signal;
`converting Said electrical signal into a light beam;
`reflecting Said light beam from an elliptical reflector; and
`reflecting Said light beam from Said elliptical reflector
`towards an optical fiber.
`12. The method of claim 11 including reflecting said light
`beams from said elliptical reflector to at least two focal
`points.
`13. The method of claim 11 further including securing an
`optical fiber having an end and Securing Said end at Said
`focal point.
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`14. The method of claim 13 including securing said
`optical fiber in a V-shaped groove and clamping Said fiber in
`Said V-shaped groove.
`15. The method of claim 11 wherein reflecting said beams
`from Said elliptical reflector includes reflecting Said beams
`using a micro-electromechanical Structure including a plu
`rality of mirrors.
`16. The method of claim 15 including reflecting said
`beams from said elliptical reflector to a plurality of focal
`points.
`17. The method of claim 16 including aligning an optical
`fiber at each of Said focal points.
`18. An optical System comprising:
`a host channel adapter;
`a target channel adapter; and
`a Serial link coupling Said adapters, Said link including a
`reflective wavelength coupler.
`19. The system of claim 18 wherein said coupler includes
`an elliptical reflector that receives a light beam from one of
`Said adapters at a first focus of Said reflector and reflects Said
`beam to a Second focus on Said reflector.
`20. The system of claim 18 wherein said coupler includes
`a micro-electromechanical Structure that Selectively focuses
`Said beams onto one or more of a plurality of output
`channels.
`21. The system of claim 20 including a controller and said
`Structure includes a plurality of mirrors, Said controller
`controls the orientation of Said mirrors in Said micro
`electromechanical Structure to Select the output channel for
`each of Said beams.
`22. The system of claim 18 wherein said serial link
`includes an optical transmitter and an optical receiver
`coupled to Said reflective wavelength coupler.
`23. The system of claim 22 wherein said transmitter and
`Said receiver are integrated into the same module.
`24. The system of claim 23 wherein said optical receiver
`is coupled to an electrical interface that converts optical
`Signals to electrical Signals.
`25. The system of claim 24 wherein said electrical inter
`face is coupled to a processor-based System.
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