Abstract:
A common Modular Carrier (MC) unit shares power and control among a plurality of Optical Network Units (ONU) which are plugged into it, thereby increasing the ONU density in an existing equipment shelf. In one embodiment, the MC unit together with its four ONU units is arranged to slide into an existing card slot of the existing equipment shelf and occupy the space of the adjacent slot. The result is a doubling of the capacity over the conventional technique of using a separate slot for each ONU unit.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates to optical communication systems and, more particularly, to a system arrangement for mounting modular optical network units. 
     BACKGROUND OF THE INVENTION 
     Dense Wavelength Division Multiplex (DWDM) optical transmission systems have been typically is employed to increase the capacity of optical fibers as the traffic load on the system increases. Usually, these systems tend to be high capacity, high bit-rate per channel systems such as long haul telephony. Presently many fiber facilities are at or near exhaustion due to increasing traffic, much of which has been generated by new services, but the application of DWDM technology to these systems will increase the fiber capacity many times over. 
     Another DWDM application, in what tends to be of shorter length and have much lower bit-rate per channel applications, is in local optical networking. In this application, the systems evolve from a low first cost (and capacity) and have low incremental cost as the traffic capacity grows or changes. Examples of such systems include local cable television distribution systems and collegiate or corporate campus data networks. In these systems, a cable TV company providing Internet access to customers would add channels, for example, as different neighborhoods start to receive service. Also, at a point in the future, the provider would have to increase the transmission capacity to a given neighborhood as the popularity of the service grew. Such typically non-telephony type networks as these require small, compact size terminals, ease of use, and low cost. 
     In many of the above applications, the space for housing such equipment is limited and existing shelf hardware designs (including all mounting hardware, card guides, and backplanes) can not be easily and economically made to physically accommodate modular capacity growth. As a result, changes in capacity often resulted in expensive shelf redesigns, rearrangements, and unfortunately, in some cases, even service interruptions. 
     SUMMARY OF THE INVENTION 
     The optical communication apparatus of the present invention is directed to solving the prior art problems using a Modular Carrier (MC) unit which shares power and control among a plurality of Optical Network Units (ONU) which are plugged into it, thereby increasing the ONU density in an existing equipment shelf. In one embodiment, the MC unit together with its four ONU units is arranged to slide into an existing card slot of the existing equipment shelf and occupy the space of the adjacent slot. The result is a doubling of the capacity over the conventional technique of using a separate slot for each ONU unit. 
     More particularly, our optical apparatus comprises a common Module Carrier (MC) unit including a power unit, a board controller, and an equipment detector unit for detecting an electrical ONU present signal indicative of the connection of an ONU, the board controller being responsive to the ONU present signal for (1) signaling the power unit to apply power to the connected ONU and (2) for sending control signals to connected ONU. An interface unit includes a connectorized backplane card connected to receive power and control signals from the MC unit, couples a plurality of ONU present signals to the MC unit, and is arranged for mounting each of the plurality of ONU in a separate connector slot of the connectorized backplane card. One or more ONUs may be plugged into the interface unit, each ONU is adapted for mounting into a separate connector slot to connect to the backplane card and arranged to receive the power and control signals from the MC unit, is adapted to generate the ONU present signal, and is adapted to couple optical signals into and out of the ONU. In accordance with the present invention, the ONU may be an Optical Translator Module(OTPM), optical regenerator, optical multiplexer, optical demultiplexer, optical monitor, etc. 
     According to another aspect of the invention, an ONU unit is adapted to mount into a separate connector slot of a MC unit and comprises circuitry for providing an ONU present signals indicative of the mounting of the ONU in a connector slot of the MC unit, circuitry for receiving power and control signals from the MC unit, and a power filter for controlling the rate at which power is applied to the ONU. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the drawing, 
     FIG. 1 shows a block diagram of a prior art multiple slot equipment shelf for housing a plurality of Optical Network Units (ONU); 
     FIG. 2 shows an illustrative system capacity growth versus time diagram; 
     FIG. 3 shows an illustrative multiple slot equipment shelf of FIG. 1 into which three of the optical apparatuses of the present invention are mounted; 
     FIG.  4 . shows an illustrative block diagram of circuitry located in our common Module Carrier (MC); 
     FIG.  5 . shows a illustrative block diagram of circuitry located in our Optical Translator Module (OTPM); and 
     FIGS. 6 and 7 show an illustrative physical housing of an OTPM. 
    
    
     DETAILED DESCRIPTION 
     In the following description, each item or block of each figure has a reference designation associated therewith, the first number of which refers to the figure in which that item is first located (e.g.,  401  is located in FIG.  4 ). 
     While the present invention will be described as using OPTMs, one particular type of ONU, it should be understood that other types of circuits including optical regenerators, optical multiplexers, optical demultiplexers, optical monitors, etc could be incorporated into the ONU design. In such applications the MC unit is adapted to handle the required power and signals appropriate to that ONU unit. The MC unit reads the identity of the ONU being used from a Programmable Read Only Memory (PROM) device on the ONU. 
     Shown in FIG. 1 is a block diagram of a prior art multiple connector slot equipment shelf  101  for housing a plurality of Optical Network Units (ONUs)  102 , such as Optical Translator Modules (OTPMs). As shown each ONU occupies a different slot in the equipment shelf  101  and connects via a separate connector to the backplane of the equipment shelf. Once the shelf  101  is filled, an additional shelf must be added to accommodate any additional ONU(s). However, at some locations the additional shelf space may not be available. Thus, there is a continuing need to be able to increase the ONU packing density. 
     FIG. 2 shows an illustrative system capacity growth versus time diagram. If a service provider is being called upon to provide additional transmission (e.g., telephony-related traffic) at a Point 1 capacity, on an existing fiber where traffic is not multiplexed and is close to the capacity of the fiber, it is known that by using digital multiplexed signals, such as an OC-48 (2.488 Gb/s) Time Division Multiplex (TDM) system, the additional needed capacity can be provided. If additional capacity was needed then Dense Wave Division Multiplex (DWDM) techniques could be used to further expand the capacity of this fiber many times over. These techniques are commonly used in the first, telephony-related application previously described. 
     In an illustrative cable TV application, when a cable TV company is making a new offering of cable modem service into an area, a new fiber would be put in service and first service would be offered at Point 2 capacity using, for example, an OC-3 (155.520 Mb/s) channel. At this point in time all of the slots in the equipment shelf  101  may already be occupied. As service demands increase, new channels may be added as depicted, by Points 3 and Point 4. This may be done, for example, when new neighborhoods are added to the service area, as described above. Alternatively, if the first channel installed were at the OC-3 rate, and traffic density increased in the original neighborhood, capacity might be increased to OC-12 (622.08 Mb/s) as at Point 4. In either of these events, if no slots in the equipment shelf  101  are available, it may at best be costly or at worst impossible to add an extra equipment shelf needed to house the additional OTPM(s). Thus what is needed in these local access or optical networking applications are low cost, compact OTPM(s) which can utilize existing shelf space. Additionally, it is a requirement that when a new service is added, or the existing service is upgraded, traffic that is not involved in the service change should not be affected. 
     FIG. 3 shows an illustrative multiple slot equipment shelf  101  of FIG. 1 into which three optical apparatuses  301  (an MC unit with up to four OTPMs) of the present invention are mounted. Since each optical apparatus includes four OTPMs  302  there is an effective doubling of the packing density. A doubling occurs because while each optical apparatus includes four OTPMs  302 , it also occupies the space of two slots  102  (each of which can hold a prior art ONU). 
     With reference to FIG. 4, there is shown a block diagram of a Module Carrier (MC) in accordance with the present invention. As will be discussed, our optical apparatus achieves both the packing density enhancement and uninterruptible service objectives by providing power supply and processor resources on a common plug-in MC circuit pack. The sharing of power supply circuits (battery filter  401 , power converters  402 , power monitor  403  and power filter  404 ), board controller (BC)  405  and equipment detector  406  and alarm/test circuit  407  enables the construction of OTPMs having decreased cost, complexity and power consumption. The power monitor  403 , in a well known manner, detects fuse status and power levels at filters  401  and  404  and converters  402 . The equipment detector  406  detects the present/absence of a ground signal on a predetermined pin of each of the OPTM&#39;s connector indicating the presence/absence of that respective OPTM. The alarm/test circuit  407  provides external alarm indications, test data, and control signals from the MC circuit pack. A control and data bus  409  enables the Board Controller (BC)  405  to communicate with the power monitor  403 , equipment detector  406 , and alarm/test circuit  407 . The BC  405  includes Random Access Memory (RAM),  405   a , to store data identifying the type of OTPMs and operational data specific to the various OTPM units, which data is obtained from PROMs on the installed OTPMs. The MC circuit pack also utilizes the existing shelf hardware designs (including all mounting hardware, card guides, and backplanes  410 ). Thus, with brief references to FIG. 6, the MC unit  602  slides into existing shelf card guides, the connector  605  connects to the existing shelf backplane, and latches  620  engage with the existing shelf housing. 
     Returning to FIG. 4, the sharing of the control and power functions on the MC unit is facilitated by the use of a small backplane  408 , called the mini-backplane  408  , which interfaces the BC  405  to a connector from each of the four OTPMs. Separate power leads are provided to each of the OPTMs. Additionally, BC  405  communicates over separate signal/control bus  410  to each OTPM, e.g., to control the frequency and amplitude of tones used to modulate the laser signal, to monitor laser bias and temperature, and to control status light-emitting-diodes LEDs. 
     As shown in FIGS. 3 and 6, up to four OTPMs can be plugged into a single MC unit. This MC arrangement with plug-in OTPMs, as described above, results in a doubling of the capacity for the shelf. With reference to FIG. 6, there is shown the four OTPMs  603 , three connected  603   a ,  603   b , and  603   c , and one,  603   d , in the process of being connected into support frame  601 . The interface support frame  601  is mounted on the parent board  602  of the MC circuit. The mini-backplane  604  provides the various power and control signal connections between the parent board  602  and the respective connector  606  for each OTPM. As previously noted, the parent board  602  slide into an existing shelf guide and interfaces with the shelf backplane through the connectors  605 . 
     With joint reference to FIGS. 6 and 7, a spring clip  701  mounted on the OPTM  603  is used to contact the interface support frame  601  to provide a building ground to the OTPM as that unit is being inserted to the interface support frame  601 . This grounding arrangement discharges any electro-static between the human installer, OTPM card and equipment bay before the OTPM card  603  is connected to the interface support frame  601 . Additionally, signal grounding is obtained using a longer ground pin  607  on MC connector  606  which mates with the OTPM connector  702  ground pin prior to the mating of other pins on connectors  606  and  702 . While MC connector is shown having the longer ground pin, obviously if desired, the connector  702  can be arranged with the longer pin. 
     FIG.  5 . shows a block diagram of circuitry located in the Optical Translator Module (OTPM). All optical and electrical circuitry for one direction of transmission resides on each OTPM. The OTPM plug-in units, include an optical receiver  501  and optical transmitter  502  which are used to carry optical signal channels. As shown in FIG. 6, the optical signals are received via connector  610  and outputted via connector  611 . In one optional arrangement, receiver  501  includes clock and data recovery and the OTPMs performs regeneration and performance monitoring functions. Optical signal data entering the receiver  501  may be received at any wavelength, λ 1 , illustratively, at 1310 nm, and converted in the transmitter  502  to any one of, for example, sixteen, possible wavelength channels, e.g., λ 2 , in the 1540 nm to 1560 nm DWDM band. Any combination of wavelengths or bit rates can be equipped in any OTPM. 
     Each OPTM communicates power and control signals  503  over a connector ( 606  of FIG.  6 ). Power filter unit  504  distributes power to the various circuits of the OTPM. Power filter unit  504  includes analog power filter circuits which control the rate at which power is applied to the OTPM. Performance monitor  506  monitors signals such as loss of signal, clock, and signal parity errors. Control and data signals are communicated to control logic  505 . Control logic  505  receives signals from performance monitor  506  and also monitors signals such as laser bias, laser temperature, and modulation tone amplitude and frequency. Control logic  505  also compares many of the received status signals to predetermined status signals stored in a PROM device  505   a . The PROM  505   a  also stores information that identifies the type of OTPM that is plugged in. In response to control signals from BC  405  the control logic  505  sends laser on/off signals to control the transmit laser in optical transmitter  502 , sets the frequency and amplitude of laser modulation tone from tone generator  507 , and controls OTPM status LEDs  508  to indicate failure and in-service conditions. 
     With joint reference to FIGS. 4,  5 ,  6  and  7  we describe an illustrative sequence of events when an OTPM is inserted or removed from the MC unit. 
     The installation sequence is: 
     1. When an OTPM is partially inserted in to the shelf, with no connector  606  mated, physical contact between the human installer, the OTPM framework, and the equipment bay is made, discharging any electrostatic charge into the bay framework and to building ground. This is accomplished using metal spring clip  701  on OTPM which contacts the MC framework. 
     2. Additionally, signal ground is provided first using a longer ground pin  607  on MC connector  606  which mates with the ground pin of OTPM connector  702  prior to the mating of other pins on connectors  606  and  702 . 
     3. Then BC  405  determines which OTPM has been inserted by testing for a ground potential on the equipment leads  411 . 
     4. Then BC  405  verifies when an OTPM is inserted and issues a command to power monitor  403  to turn-on the power to the particular OTPM. The power is turned-on at a prescribed rate. Additionally, circuits on the newly inserted OTPM slowly ramp up the power to reduce the in-rush current in order to prevent disturbances to other previously installed OTPMs. 
     5. Then BC  405  turns on signals to the newly installed OTPM. After an OTPM is installed, firmware at BC  405  reads it&#39;s code (to know it&#39;s bit rate)and other data from PROM  505   a  on the OTPM. Circuits on the newly inserted OTPM slowly ramp up to power to reduce the in-rush current in order to prevent disturbances to other previously installed OTPMs. With power established, transmission can be initiated from the newly installed OTPM. 
     The OTPM removal sequence is: 
     1. Removal is detected by BC  405  when it detects an “open” condition, e.g., lack of ground signal, on pin  607  from an OTPM, indicating that it has been removed. 
     2. Then BC  405  determines which specific OTPM is being removed. 
     3. Then BC  405  turns-off signals to the connector  606  associated with the removed OTPM (control signals only; no transmission signals are turned off). 
     4. Then BC  405  turns-off power to the connector  606  of the removed OTPM. 
     5. Lastly, the long ground pin  606  and then the spring clip  701  ground connections are broken as the OTPM is slid out of the interface support frame  601 . 
     What has been described is merely illustrative of the application of the principles of the present invention. Other arrangements and methods can be implemented by those skilled in the art without departing from the spirit and scope of the present invention.