Abstract:
A modular optical data communication network operational as a computer backplane includes interconnectable bus modules providing both optical data transmission and electrical data transmission. Each bus module comprises and optical link interface having one input receiving data from an optical/electrical converter and a second terminal connected to receive electrical data from an electrical/optical converter. The bus modules are interconnectable by coupling an electrical/optical converter of one module to an optical/electrical converter of an adjacent module through a free-space connection. Each optical link interface includes a row by column VCSEL/photodetector array for dedicated path transmission of data over an optical network from a circuit card coupled to one bus module transmitting data to a circuit card of an adjacent or remote bus module.

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. provisional application Serial No. 60/159,618 filed Oct. 14, 1999, entitled Optical High Speed Bus and High Speed Modular Computer Backplane. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention is related in general to light beam routing in a computer system, and more particularly, the invention is related to a high speed bus and high speed modular light beam routing for a computer. 
     BACKGROUND OF THE INVENTION 
     Most people familiar with computer-based systems know that the primary mechanism to transfer data from one circuit card to another and for interconnecting the circuit cards is the backplane. Also known as a motherboard, the backplane is typically a printed circuit board with a limited number of sockets into which circuit boards may be inserted. Typically, an interrupt-based bus protocol is used to arbitrate between contending circuit cards requiring access to the bus. 
     Such backplane-based system bus architectures suffer from several disadvantages. The bandwidth or speed of the system is limited. For example, conventional small PCI (peripheral component interconnect) bus systems run at a maximum aggregate bandwidth of 133 megabytes per second. The number of circuit cards that may be part of the system is also restricted to the number of available sockets on the backplane. The backplane itself also adds weight and size to the system. Many backplanes are also custom designed, thereby adding cost and time to the development cycle. 
     In order to fully interconnect all circuit cards in the system, a large full access switch is required. Current networking topologies that guarantee data delivery in real time, such as asynchronous transfer mode (ATM) switches, require large switching hubs. Further, in order to achieve large bandwidths, conventional systems use single coax or fiber optic cables to carry the data traffic. Each link also requires a dedicated network adaptor card. 
     A unique system application is for those systems that require a separation of secured or encrypted and unsecured or decrypted data. Conventional systems use complex networks of discrete filters to isolate the secured or encrypted data from the unsecured data. These discrete filters take up extra space and require elaborate tests to verify the isolation of the secured data. Further, the speed of the backplane is adversely impacted. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention there is provided a bus module providing mechanical, electrical, optical, and power interface for individual circuit cards and for network adaptability. Each bus module provides low latency interconnectivity between modules for data packet transfer, such as 32-bit word read and write. Interconnectability of the bus module provides near unrestricted expansion of a computer backplane. 
     Each bus module includes an optical interface—left and optical interface—right. Each interface comprises a two-dimensional N by N, for example 16×16, bi-directional array of VCSEL (vertical cavity surface emitting laser)/photodetector elements. Each bi-directional VCSEL/photodetector element functions to provide high speed data communication through interconnected adjacent bus modules from one module in the interconnection to any other module by means of a pre-programmed transfer path through VCSEL/photodetector elements arranged in a row by column matrix. This provides the advantage of a high-speed data transfer without the need for a header for each data packet. The interconnection of one circuit card to other circuit cards through the interconnected bus modules is along a fixed path known to both the transmitting circuit card and the receiving circuit card. 
     In accordance with the present invention VCSEL/photodetector element arrays pass data to each other over free space. Bus alignment is an important aspect of this interconnect technology that allows programmed interconnect schemes by establishing dedicated channels from bus module “m” to bus module “n”, where “m” and “n” are within the range of 2 to N. By establishing such dedicated data links switching data transfer is simplified. The number of modules “C” that can be interconnected is valid for all positive values of “C” and “m” satisfying the equation C(C−1)&lt;2 m. 
     In accordance with the present invention, there is provided an optical data transfer network comprising at least one network backplane bus module having a global electrical bus, a local electrical bus, and an optical bus. A plurality of bi-directional optical/electrical converters coupled to the optical bus converts optical signals to electrical signals and vice versa. An optical link interface coupled between the local electrical bus and the bi-directional optical electrical converters routes data between the local electrical bus and the optical bus. A controller coupled to an optical link interface provides signals for controlling data routing between the local electrical bus, the global electrical bus and the optical bus. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, reference may be made to the accompanying drawings, where: 
     FIG. 1 is a block diagram of an embodiment of an interface module coupled between a secured bus module and an unsecured bus module according to the teachings of the present invention; 
     FIG. 2 is a block diagram of an embodiment of a portion of the bus module according to the teachings of the present invention; 
     FIG. 3 is a more detailed block diagram of an embodiment a portion of the bus module according to the teachings of the present invention; 
     FIG. 4 is a block diagram showing a representative layout of VCSEL/photodetector pairs according to the teachings of the present invention; 
     FIG. 5 is a diagram illustrating an exemplary network channel interconnection scheme using the VCSEL/photodetector matrix; 
     FIG. 6 is a block diagram of an embodiment of switch fabric according to the teachings of the present invention; 
     FIG. 7 is a block diagram of an embodiment of a full access switch of the switch fabric according to the teachings of the present invention; 
     FIG. 8 is a block diagram of an embodiment of a bus interface according to the teachings of the present invention; 
     FIG. 9 is a block diagram of an embodiment of a receive/transmit circuit according to the teachings of the present invention; 
     FIG. 10 is a perspective view of an embodiment of a high speed electrical and optical bus module according to the teachings of the present invention; and 
     FIG. 11 is a perspective view of an embodiment of a series of interconnected high speed electrical and optical bus modules according to the teachings of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a block diagram of an embodiment of a high speed modular backplane system  10  having at least one secured bus module  12  (system X) coupled to an interface module  14  (X/Y Interface), in turn coupled to at least one unsecured bus module  16  (system Y). Each module  12 ,  14  and  16  is constructed according to the teachings of the present invention. The secured bus module  12  and the unsecured bus module  16  have separate and independent global electrical buses  18  and  20 , respectively, to isolate the sensitive confidential (secured) data from unsecured data. The interface bus module  14  does not have a global electrical bus. Each bus module  12 ,  14  and  16  has a local electrical bus  22  coupled to a circuit card (not shown) plugged into the bus modules by means of a conventional circuit card connector. An optical bus  24  links the bus modules together. Secure data is transmitted and received on the optical bus  24  utilizing a different optical wavelength from the optical wavelength utilized for unsecured data to maintain data isolation. An optical link interface  26 , an electrical/optical converter  28  and optical/electrical converter  30 , in each module  12 ,  14  and  16  serve as the interface between the local electrical bus  22  and the optical bus  24  in each bus module under the control of a controller central processing unit (CPU)  32 . A bus bridge  34  in the modules  12  and  16  is an optional bus data buffer. A bus module with a bus bridge  34  is used when there is more than a predetermined number of bus modules interconnected. 
     FIG. 2 is a block diagram of an embodiment of an optical link interface  26  in a bus module according to the teachings of the present invention. The optical link interface  26  includes a switch fabric slice  36  that performs signal routing between the optical bus  24  and the local electrical bus  22 . A data bus interface  38  is coupled to the switch fabric slice  36  as an interface between the optical bus  24  and the local electrical bus  22 . 
     Referring to FIG. 3 there is shown a more detailed block diagram of the switch fabric slice  36  and optical bus buffers of a bus module according to the teachings of the present invention. The switch fabric slice  36  includes a receive/transmit circuit  40  coupled to a switch fabric  42 . The electrical/optical converter  28  and optical/electrical converter  30  each connects to buffer  46  having a predetermined wavelength VCSEL/photodetector diode  44  outputting a light signal and a predetermined wavelength photodetector  48  receiving light for conversion to an electrical signal. To insure optical isolation for security, the module  14  of FIG. 1 includes two different predetermined wavelength VCSEL/photodetector diodes  44  for secure and unsecure outputting of light signals and two different predetermined wavelength photodetectors  48  receiving light for conversion to an electrical signal. 
     FIG. 4 is a matrix illustration showing a representative layout of VCSEL/photodetector according to the teachings of the present invention. The exemplary layout is in a row and column configuration where each rectangle represents a VCSEL/photodetector and detector pair. Although the illustration shows an eight-by-eight array, the typical application utilizes an M by M array of laser/detector pairs, where “M” is a positive number. 
     FIG. 5 is a diagram illustrating an exemplary network channel interconnection for four circuit cards using the VCSEL/photodetector matrix as illustrated in FIG.  4 . In this example, the VCSEL/photodetector diode and photodetector pair in column  1 , row  4  of card  1  is used to transmit data from circuit card  1  to circuit card  4 . Therefore, the switch matrices for circuit cards  1  through  4  are configured to receive data from the local electrical bus in circuit card  1 , transmit the data onto the optical bus in bus module  1 , repeat the received data to pass through bus modules  2  and  3 , and route the received data to the local electrical bus in circuit card  4  and then to circuit card  4  plugged into bus module  4 . 
     FIG. 6 is a block diagram of an embodiment of switch fabric  36  according to the teachings of the present invention. By way of example, the switch fabric  36  comprises 256 (m) electrical signal switches  50  each having a left input output connection to one of the optical/electrical converters  30 . The general relationship between “C” and “m” is given by the expression C(C−1)&lt;2m, as stated earlier. Each of the electrical signal switches  50  also includes a right input output connection to one of the electrical/optical converters  28  as illustrated in FIGS. 2 and 3. Each of the switches  50  is programmable to pass an electrical signal received at a left connection through the switch and applied to a right connection or in the alternative, depending on the program, the receive signal is directed to a multiplexer  52 . The multiplexer  52  is configured to receive a signal from any one of the 256 switches  50  for multiplexing to 1 of 24 possible serial links connected to a circuit card coupled to one of the bus modules containing a fabric switch  36 . 
     As illustrated in FIG. 6, the switch fabric  36  is configured to receive an electrical input signal on any one of 256 input lines and to transmit the received electrical signal to one of 256 output lines, where both the input lines and output lines are individually connected to one of the 256 switches  50 . Each of the 256 switches  50  are coupled to an address decoder  54  through one of 256 address registers  56 . The address decoder  54  receives a slot number code from the controller CPU  32  to either pass the input signals to an output terminal or to pass an input signal to the multiplexer  52 . This pass-through function is illustrated in FIG.  5  and previously discussed. 
     Although the description of FIG. 6 to this point only discussed transmission of signals from the multiplexer  52 , the multiplexer is bi-directional and also receives signals from a circuit card, thus making the switch fabric slice  36  also bi-directional. A signal received at one of the 24 inputs to the multiplexer  52  is applied to each of the 256 switches  50  that are individually programmed to transmit a received signal either to the left or to the right, that is, to an adjacent switch fabric slice  36  or to terminate the received signal within the switch  50 . This operation enables transmission of a received signal to an adjacent circuit card coupled to an adjacent bus module in a manner as described with reference to FIG. 5, cards  2  and  3 . 
     FIG. 7 is a block diagram of an embodiment of an access switch  50  of the switch fabric  36  according to the teachings of the present invention. The blocks labeled A through F are two-position switches which are opened or closed under the control of a signal from switch register  56  on one of the lines A-F. Data to be passed through the switch fabric slice  36  on an optical bus is transmitted via closed switches E and F. Data to be sent to or received from the local electrical bus  22  are transmitted via switches A through D. 
     Referring to FIG. 8, there is shown a block diagram of an embodiment of a global electrical bus interface  34  according to the teachings of the present invention. The bus interface  34  includes a bus arbiter  60 , a field programmable gate array core  62 , and an interface circuit  64 . The bus arbiter  60  responds to data on the global electrical bus  18  or  20  (FIG. 1) to control the transfer of electrical data signals to adjacent bus modules. Electrical data signals on the global electrical bus  18  or  20  are also input to the field programmable gate array core  62  that functions to selectively format electrical data signals for transmission from a bus module. The bus arbiter  60  in combination with the gate array core  62  identifies when electrical data transmitted on the global electrical bus  18  or  20  is intended for the circuit card coupled to the bus module. 
     An output from the gate array core  62  is applied to the 24 by 1 interface  64  in accordance with the identified circuit card coupled to a particular bus module. Typically, the interface  64  is a multiplexer. Data output from the interface  64  is applied to the local electrical bus  22 , and if identified with the circuit card coupled to a particular bus module, then the data is transferred to the circuit card. If the electrical data on the local electrical bus  22  is to be transmitted on the optical bus  24  then the output of the interface  64  is routed through the optical link interface  26 . 
     The above description of the bus interface  34  is based on the assumption that data is received by the bus interface on the global electrical bus  18  or  20 . The bus interface  34  is bi-directional and is configured to also receive electrical data from a circuit card or electrical data from the optical link interface  26 , in either case for further transmission on the global electrical bus. 
     FIG. 9 is a block diagram of an embodiment of a receive/transmit circuit  40  according to the teachings of the present invention. The receive/transmit circuit  40  includes memory circuits  66 T or  66 R such as a FIFO (first-in-first-out) registers, a controller  68 , and an array of multiplexers  70  (MUXs). Each of the multiplexers  70  is connected to the full access switch  52  (see FIG. 6) and multiplexes the received inputs to the respective memory  66 T or  66 R. Each of the memories  66  in response to control signals from the controller  68  selects the input from the multiplexers coupled thereto for transmission to a circuit card connected to the bus module. The selected electrical data signal may also be coupled through the global electrical bus interface  34  to the global electrical bus  18  or  20 . The electrical bus  20  is also configured to receive electrical data from a circuit card or the global electrical bus  18  or  20  through the memory  66 R. 
     When receiving data, the receive/transmit circuit  40  distributes a signal from a memory  66 R to the multiplexers connected thereto for further transmission and processing by full access switch  52 . The memory  66 T receives electrical data from the full access switch  52  for transmission to a circuit card or for transmission over the global electrical bus  18  or  20  while the memory  66 R functions to receive electrical data from a circuit card by means of the global electrical bus  18  or  20 . Operation of the memory  66 T and the memory  66 R is in accordance with signals from the controller  68 . 
     FIG. 10 is a perspective view of an embodiment of a high speed electrical and optical bus module  72  according to the teachings of the present invention. The bus module  72  configured to enable interconnection of a plurality of bus modules to form a computer backplane. The bus module  72  includes slot  74  containing an electrical connector to provide coupling to a circuit card (not shown). Optical ports or windows  76  are provided to receive and transmit optical signals when assembled together with adjacent bus modules. Electrical connectors  78  are provided to interconnect the bus modules  72  to form a global electrical bus  20 . The bus modules also include alignment buttons  80  or other mechanical connectors to provide secure physical connections with an adjacent bus module. Thus each module is also provided with mating elements to receive the alignment buttons. 
     Referring to FIG. 11 there is shown a perspective view of a plurality of interconnected high speed electrical and optical bus modules  12 ,  14 ,  16  according to the teachings of the present invention. Also shown are circuit cards  82  plugged into the card slots  74  of the bus modules. The interface bus module  14  is shown disposed between secured bus modules  12  and unsecured bus modules  16  to maintain separation and confidentiality of secured data. 
     The invention is a modular computer backplane and a full access switched network. In particular, secured data is separated and isolated from unsecured data to ensure confidentiality. The invention is fully scalable due to its modularity. 
     Although several embodiments of the present invention and its advantages have been described in detail, it should be understood that changes, substitutions, modifications, variations, and alterations can be made without departing from the teachings of the present invention as set forth by the appended claims.