Abstract:
An integrated optoelectronic module and optical fiber for coupling a pair of information system devices having an electrical input/output interface using optical signal communication including an optical fiber; a housing on at least one end of the optical fiber including an electrical connector for coupling with one of said information system devices; an electro-optic subassembly disposed in the housing for coupling to the information system device integrally coupled and attached to the optical fiber for transmitting an optical signal over the fiber; a circuit disposed in the housing for detecting the power of the received optical signal; and a communications interface for communicating the received power level to allow setting of the remove optics transmitter.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation in part of U.S. patent application Ser. No. 10/965,984 filed Oct. 15, 2004, and U.S. patent application Ser. No. 11/732,996 filed Apr. 5, 2007, both assigned to the common assignee. This application is also related to U.S. patent application Ser. No. 11/854,319, filed Sep. 12, 2007, now issued as U.S. Pat. No. 7,494,287. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to optical communications systems, and parallel optic transceivers used in high throughput fiber optic communications links in local and wide area networks and storage networks, and in particular to fiber optic cables with integral transceivers mounted at each end for coupling to an electrical connector on an information system unit. 
     2. Description of the Related Art 
     Communications networks have experienced dramatic growth in data transmission traffic in recent years due to worldwide Internet access, e-mail, and e-commerce. As Internet usage grows to include transmission of larger data files, including content such as full motion video on-demand (including HDTV), multi-channel high quality audio, online video conferencing, image transfer, and other broadband applications, the delivery of such data will place a greater demand on available bandwidth. The bulk of this traffic is already routed through the optical networking infrastructure used by local and long distance carriers, as well as Internet service providers. Since optical fiber offers substantially greater bandwidth capacity, is less error prone, and is easier to administer than conventional copper wire technologies, it is not surprising to see increased deployment of optical fiber in data centers, storage area networks, and enterprise computer networks for short range network unit to network unit interconnection. 
     Such increased deployment has created a demand for electrical and optical transceiver modules that enable data system units such as computers, storage units, routers, and similar devices to be optionally coupled by either an electrical cable or an optical fiber to provide a high speed, short reach (less than 100 meters) data link within the data center. 
     A variety of optical transceiver modules are known in the art to provide such interconnection that include an optical transmit portion that converts an electrical signal into a modulated light beam that is coupled to a first optical fiber, and a receive portion that receives a optical signal from a second optical fiber and converts it into an electrical signal, and similar implementations employ one fiber for both optical signals, traveling in opposite directions. The electrical signals are transferred in both directions over an electrical connectors that interface with the network unit using a standard electrical data link protocol, such as Infiniband. 
     The optical transmitter section of such transceiver modules includes one or more semiconductor lasers and an optical assembly to focus or direct the light from the lasers into an optical fiber or fibers, which in turn, is connected to a receptacle or connector on the transceiver to allow an external optical fiber to be connected thereto using a standard connector, such as SC, FC, LC, or ribbon fiber type MPO. The optical receive section includes an optical assembly to focus or direct the light from the optical fiber or fibers onto a photodetector or array, which in turn, is connected to an IC circuit on a circuit board. 
     Optical transceiver modules are therefore packaged in a number of standard form factors which are “hot pluggable” into a rack mounted line card network unit or the chassis of the data system unit. Standard form factors set forth in Multiple Source Agreements (MSAs) provide standardized dimensions and input/output interfaces that allow devices from different manufacturers to be used interchangeably. Some of the most popular MSAs include XENPAK (see www.xenpak.org), X2 (see www.X2 msa.org), SFF (“small form factor”), SFP (“small form factor pluggable”), XFP (“10 Gigabit Small Form Factor Pluggable”, see www.XFPMSA.org), and the QSFP (“Quad Small Form-factor Pluggable,” see www.QSFPMSA.org). 
     In addition to such pluggable modules, customers and users of such systems are increasingly interested in fiber optic cables which incorporate integral transceivers fixedly mounted on the ends of such cables such as described in U.S. patent application Ser. No. 10/965,984. In order to increase the number of interconnections or port density associated with the network unit, such as, for example in rack mounted line cards, switch boxes, cabling patch panels, wiring closets, and computer I/O interfaces, such transceivers should be able to couple to multiple parallel optical fibers, or ribbons, and utilize parallel electro-optical converters in the transceivers. 
     A typical parallel optical transceiver consists of a vertical cavity surface emitter laser (VCSEL) array, and a PIN diode array. A parallel optical ribbon can be inserted into the optical transceiver, coupling to the VCSEL array or the PIN diode array, and individual lane transmitter and receiver properties can be measured. In these measurements the light source, a VCSEL array is adjusted or programmed over temperature to maintain good operating characteristics. The purpose of such receiver side measurements is that the driving conditions (e.g. bias voltage and current) of the VCSELs (or any other lasers) need to be adjusted and set at the factory since their threshold and efficiency varies from device to device and also changes as a function of temperature. 
     In an integrated module/optical cable, the parallel ribbon fiber may be permanently attached to electrical-optical converters at both ends. Since the optical interface is not accessible on either end, the VCSEL performance can not be measured or characterized directly. An alternative method must be found to properly characterize the performance of VCSEL over temperature to ensure the performance of the communications link. 
     SUMMARY OF THE INVENTION 
     Briefly, and in general terms, the present invention provides, an integrated optical fiber and optoelectronic module for optically coupling a pair of information system devices having an electrical input/output interface using optical signal communication including an optical fiber; a first term housing including (i) an electrical connector for coupling with one of the information system devices and for transmitting or receiving information-containing electrical signals over the connector; (ii) an electro-optic subassembly disposed in the housing for coupling to the information system device for converting the electrical signal to a modulated optical signal corresponding to the electrical signals at a predetermined wavelength, the subassembly being integrally coupled and attached to the optical fiber for transmitting or receiving an optical signal; a power detector circuit disposed in the housing for detecting the power level of the optical signal received over the optical fiber; and a communications interface disposed in the housing for communicating the power level to allow setting of the operational parameters in the remote device. 
     In another aspect, the invention provides an electro-optical connector module integral with an optical fiber cable having a plurality of parallel optical transmit lanes and a plurality of parallel optical receiver lanes, the module comprising optical receiver lane signal detection circuitry to detect the signal power on one or more of the receive lanes, and optical transmit lane control circuitry to transmit a control mode optical signal indicating the received signal power on the corresponding receive lane. 
     In another aspect, the invention provides a communications cable for providing a short range, high speed optical data communications link between information system units including a group of 2N optical fibers, where N is a positive integer; a first terminal housing integral with and disposed at a first end of said 2N optical fibers, including (i) an multi-channel electro-optical converter including a VCSEL array abutting and coupled to a first set of N of said optical fibers, and a photodiode array abutting and coupled to a second set of N of said optical fibers; (ii) signal detection means coupled to said photodiode array for determining the power of a optical signal on at least one of said optical fibers; (iii) power adjustment means coupled to said VCSEL array for adjusting the power output of at least one of said VCSELs in response to the level of received power of said one VCSEL in said second terminal housing; and (iv) an electrical connector extending from the housing and adapted to mate with a corresponding electrical connector on a first external information system unit for transferring information signals between the unit and the communications link; and a second terminal housing integral with and disposed at a second end of said 2N optical fibers, including (i) an multi-channel electro-optical converter including a VCSEL array abutting and coupled to the second set of N of said optical fibers, and a photodiode array abutting and coupled to the first set of N of said optical fibers; (ii) signal detection means coupled to said photodiode array for determining the power of a optical signal on at least one of said optical fibers; (iii) power adjustment means coupled to said VCSEL array for adjusting the power output of at least one of said VCSELs in response to the level of received power of said one VCSEL in said first terminal housing; and (iv) an electrical connector extending from the housing and adapted to mate with a corresponding electrical connector on a second external information system unit for transferring information signals between the unit and the communications link. 
     In another aspect, the invention provides a communications cable for providing a short range, high speed optical data communications link between information system units including: a group of 2N optical fibers, where N is a positive integer; a first terminal housing integral with and disposed at a first end of said 2N optical fibers, including (i) an multi-channel electro-optical converter including a VCSEL array abutting and coupled to a first set of N of said optical fibers, and a photodiode array abutting and coupled to a second set of N of said optical fibers; and (ii) an electrical connector extending from the housing and adapted to mate with a corresponding electrical connector on a first external information system unit for transferring information signals between the unit and the communications link; and a second terminal housing integral with and disposed at a second end of said 2N optical fibers, including (i) an multi-channel electro-optical converter including a VCSEL array abutting and coupled to the second set of N of said optical fibers, and a photodiode array abutting and coupled to the first set of N of said optical fibers; and (ii) an electrical connector extending from the housing and adapted to mate with a corresponding electrical connector on a second external information system unit for transferring information signals between the unit and the communications link. 
     In a preferred embodiment, the module also includes optical receiver lane signal detection circuitry for detecting the transmitted control mode optical signal, and to controlling the laser bias of the corresponding laser to the receive lane on which the optical signal was received. 
     Some implementations of the present invention may incorporate or implement fewer of the aspects and features noted in the foregoing summaries. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of this invention will be better understood and more fully appreciated by reference to the following detailed description when considered in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an exploded perspective view of a pluggable parallel optoelectronic module as known in the prior art coupled to a ribbon fibers; 
         FIG. 2  is a perspective view of a pluggable module being inserted into a receptacle or cage in a host unit; 
         FIG. 3  is a highly simplified perspective view of an integral transceiver/optical fiber cable at one end of a fiber according to the present invention; and 
         FIG. 4  is a highly simplified block diagram of a transceiver module according to the present invention. 
     
    
    
     Additional objects, advantages, and novel features of the present invention will become apparent to those skilled in the art from this disclosure, including the following detailed description as well as by practice of the invention. While the invention is described below with reference to preferred embodiments, it should be understood that the invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional applications, modifications and embodiments in other fields, which are within the scope of the invention as disclosed and claimed herein and with respect to which the invention could be of utility. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Details of the present invention will now be described including exemplary aspects and embodiments thereof. Referring to the drawings and the following description, like reference numbers are used to identify like or functionally similar elements, and are intended to illustrate major features of exemplary embodiments in a highly simplified diagrammatic manner. Moreover, the drawings are not intended to depict every feature of the actual embodiment nor the relative dimensions of the depicted elements, and are not drawn to scale. 
     The present invention relates generally to the adjustment of laser transmitter parameters, such as electrical bias and operating temperature in optical communications transceiver modules used in fiber optic communications systems. 
     Referring now to  FIG. 1 , there is shown an exploded view of an exemplary pluggable optical transceiver module  100  as known in the prior art. In this particular example, the module  100  is compliant with the QSFP MSA. In this particular case the optical transceiver has four transmit channels and four receiving channels. Each transmit channel can transmit optical signal at 850 nm or its vicinity, at up to 10 Gbps data rate. Each receiving channel can receive the 850 nm signal and convert it into an electrical signal at the same data rate. 
     The transceiver module  100  includes a two-piece housing including a base  102  and a cover  101 . The housing  101  and  102  are constructed of die-case or milled metal, preferably die-cast zinc, although other materials also may be used, such as specialty plastics and the like. Preferably, the particular material used in the housing construction assists in reducing EMI. 
     The front end of the housing  102  includes a port  115  for securing a MPO insert  114 . The insert is configured to receive an MPO fiber optic connectors (not shown) which mate with optical lens  112  An EMI blocker  113  is inserted in between the lens and the MPO insert to block EMI from emitting into open space in the front. 
     In the illustrated example, the housing holds one subassembly or circuit boards, including a rigid circuit board  103 , a flexible board  105 , a microprocessor  104  which is used to control the laser driver IC  109  and receiver IC  111 . Both ICs sit on a thermally conductive substrate  106 , and are connected to the flexible circuit board  105  through wirebond. A VCSEL array  108  and photodiode array  110  are also located on the substrate  106 , and are wirebonded to  109  and  111  respectively. The optical lens array  112  is aligned to both the VCSEL array  108  and photodiode array  110  to provide best coupling from the VCSEL array to the fiber ribbon, and from fiber ribbon to the photodiode array. 
       FIG. 2  is a perspective view of a prior art pluggable modules ( 202  and  203 ) inserted into a receptacle or cage in a host unit. An optical cable connector  205  is employed to connect module  202  to the host optical cable plant  206  by mating with the pluggable fiber port  204  within module  202 . 
       FIG. 3  is a perspective view of an integrated transceiver/optical fiber according to the present invention. The transceiver module  400  at one end of the cable includes a two-piece housing  300  including a base  301  and a cover  302 . In addition, contact strips (not shown) may be provided to ground the module to an external chassis ground as well. The housing  300  is constructed of die-case or milled metal, preferably die-cast zinc, although other materials also may be used, such as specialty plastics and the like. Preferably, the particular material used in the housing construction assists in reducing EMI. A similar configuration is shown in U.S. Pat. No. 7,137,744 of the present assignee, which is hereby incorporated by reference. 
     The front end of the housing  303  includes a faceplate  304  that secures the optical fiber ribbon  420  (as shown in  FIG. 4 ). 
     In the illustrated example, the housing  300  holds a simple printed circuit board  305  including a transmit driver IC  401 , a receive controller  405 , and a microprocessor or module controller. An electrical connector  421  is formed by electrical contacts on both sides of the module, to provide an electrical interface to the mating receptacle connector on the external computer or communications unit (not shown). The VCSEL transmit subassembly  402  includes a VCSEL array of N semiconductor lasers, which may be mounted in a single plastic enclosure  306 , which interfaces to N fibers of a fiber ribbon ferrule  307 . 
     Adjacent to the VCSEL array  402  is a photodiode array  404  which interfaces to the ribbon ferrule  307 , and thereby to N fibers of the 2N fiber ribbon cable  420 . The enclosure  306  is electrical coupled to the printed circuit board  305  by means of the flex cable  307  and mechanical supports  308 ,  309  which sandwich the printed circuit board (PCB)  305  there between, and allow the cable  307  to make electrical contact with appropriate traces on board  305 . 
     Other electrical components  310 ,  311 ,  403  for driving the VCSEL transmitters  402 , and amplifying and processing the signals from the photodiode array  404  are also shown mounted on the PCB  305 , and will be described in greater detail in connection with  FIG. 4 . 
     On the right hand side of the Figure is depicted the ribbon ferrule  307  which secures the ribbon cable  420  to the housing  400 . The ribbon ferrule  307  allows the individual fibers in the cable  420  to be aligned with the N VCSELs and N photodiodes as disposed on the enclosure  306 . Suitable alignment pins and mating receptacles are provided on the enclosure  306  and the ferrule  307  so that the optical coupling between the VCSEL/photodiode array and the fiber ribbon may be achieved in the most expeditious manner from a manufacturing perspective, the details of which go beyond the scope of the present invention. Suffice it to say that once aligned, the ferrule is glued or otherwise fixedly secured to the enclosure  306  so that the ribbon cable  420  is fixedly secured to the transceiver module  400 . 
       FIG. 4  is a block diagram illustrating an integrated optoelectronic module/fiber optic cable with an electro-optical module at each end according to an embodiment of the invention. Here, a first electro-optical module  400  at end A of the cable is provided, which is connected, via a parallel optical ribbon  420  comprising 2N fibers, where N is an integer, to a second electro-optical module  409 , provided at end B of the cable. The first electro-optical module  400  comprises a VCSEL array  402 , comprising N VCSELs arranged in parallel. Also provided is a photodiode array  404 , comprising N photodiodes arranged in parallel. A module controller  403  is further provided, as well as a receiver controller  405 , arranged to receive signals from the photodiode array. A transmitter driver  401 , which controls the VCSEL array, is also included. 
     The transmitter driver  401  is arranged to receive data from a coupled information system device, in the form of an electrical signal over electrical connector  421 , and to control the VCSEL, which converts the electrical signal into an optical signal, which is transmitted via the parallel optical fiber  420 . Similarly, the parallel optical signal received at the photodiode array  404  is converted into an electrical signal and passed to the receiver controller  405 , and then output as an electrical data output signal over connector  421 . The overall operation of the electro-optical module  400  to convert between the optical and electrical domains is controlled by the module controller  403 , in a conventional manner. 
     The electro-optical module  409  has a corresponding structure to the first electro-optical module  400 . In this respect, the second electro-optical module  409  comprises a photodiode array  410 , having N photodiodes arranged in parallel. The photodiode array  410  feeds a signal to the receiver controller at  411 , which then outputs an electrical data out signal. Also provided is a VCSEL array  415 , comprising N VCSEL lasers arranged in parallel. A transmitter driver circuit  414  is arranged to receive an electrical data input signal, and to drive VCSEL array  415  so to produce a parallel optical signal, which is then output over the N fibers  416 . The overall operation of the electro-optical module  409  to convert between the electrical and optical domains is controlled by the module controller  413 , in a conventional manner. It should be noted that the photodiode array  410  of the second electro-optical module  409  is coupled by N fibers  408  to the VCSEL array  402  of the first electro-optical module  400 , while the VCSEL array  415  of the second electro-optical module  409  is coupled to the photodiode array  404  of the first electro-optical module  400 . The coupling is performed by a parallel optical ribbon, in this case having 2N optical fibers, with N fibers  408  carrying the signal from  402  to  410 , and N fibers  416  carrying the signals from  415  to  404 . 
     Thus, according to the embodiment, where an electro-optical module according to the embodiment detects the power level of a received signal on one of its receive lanes, it converts the data into an electrical control signal which is transmitted preferably in a predetermined format to the remote transmitting module. 
     The control signal  406  is applied to the module controller  403  to set power level of each VCSEL in the array  402  in response to the respective received power in the photodiode array  410  in module  409 . A similar operation would be performed in module  400  to set the power level of VCSEL array  415 . Such an adjustment in bias and operating current is done by conventional techniques known in the art, and allows both the modules  400  and  409  to be adjusted and tuned at the factory, so that the entire integral transceiver/fiber cable assembly  400 ,  420 ,  409  is ready for use when received by the customer or end user. 
     Within the above described first embodiment there is a corresponding number of transmit and receive lanes at both transceivers, providing a one to one correspondence. However, while this is preferred to give the greatest open fiber signaling resolution, in other embodiments there can be a different number of transmit and receive lanes, provided that each transmit lane is “paired” with a receive lane, even if more than one transmit lane/receive lane is paired with the same receive lane/transmit lane. 
     In summary, therefore, the embodiments of the invention allow the VCSELs driving parallel optical links to be adjusted and controlled substantially on a per lane basis, by pairing transmit and receive lanes. 
     Further modifications, substitutions, additions and/or rearrangements to the above described embodiments and falling within the spirit and/or scope of the underlying inventive concept will be apparent to the person skilled in the art to provide further embodiments of the invention, any and all of which are intended to be encompassed by the appended claims. 
     Various aspects of the techniques and apparatus of the present invention may be implemented in digital circuitry, or in computer hardware, firmware, software, or in combinations of them. Circuits of the invention may be implemented in computer products tangibly embodied in a machine-readable storage device for execution by a programmable processor, or on software located at a network node or web site which may be downloaded to the computer product automatically or on demand. The foregoing techniques may be performed by, for example, a single central processor, a multiprocessor, one or more digital signal processors, gate arrays of logic gates, or hardwired logic circuits for executing a sequence of signals or program of instructions to perform functions of the invention by operating on input data and generating output. The methods may advantageously be implemented in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one in/out device, and at least one output device. Each computer program may be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired; and in any case, the language may be compiled or interpreted language. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, a processor will receive instructions and data from read-only memory and/or random access memory. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example, semiconductor devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. Any of the foregoing may be supplemented by or incorporated in, specially designed application-specific integrated circuits (ASICS). 
     It will be understood that each of the elements described above, or two or more together, also may find a useful application in other types of constructions differing from the types described above. 
     While the invention has been illustrated and described as embodied in an optical transmission system, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.