Patent Publication Number: US-10320487-B2

Title: Power management implementation in an optical link

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 14/993,028, filed on Jan. 11, 2016, and entitled “POWER MANAGEMENT IMPLEMENTATION IN AN OPTICAL LINK”, which is a continuation of U.S. patent application Ser. No. 14/182,492, filed on Feb. 18, 2014, and entitled “POWER MANAGEMENT IMPLEMENTATION IN AN OPTICAL LINK” and now U.S. Pat. No. 9,236,948, issued Jan. 12, 2016, which is a divisional of U.S. patent application Ser. No. 12/974,654, filed on Dec. 21, 2010, and entitled “POWER MANAGEMENT IMPLEMENTATION IN AN OPTICAL LINK” and now U.S. Pat. No. 8,712,236 issued Apr. 29, 2014, the entire disclosures of which are hereby incorporated by reference and for all purposes. 
    
    
     FIELD OF THE INVENTION 
     Embodiments of the present invention are directed to optical links and, more particularly, to optical links which may save power when the optical link is unplugged and maintain eye safety standards. 
     BACKGROUND INFORMATION 
     Most optical links to date are used in the telecom and datacom industries, where optical modules tend to be connected during installation, and stay connected for the life of the equipment. These connections stay active as long as the link is connected, never switching off once started. 
     Optical links to be used in a consumer application may have different requirements, as the links are used dynamically, with devices being plugged and unplugged from the systems. In this case, it is desirable to save power when a port is not being used, insure that the port meets eye safety standards when the fiber is not connected, and that the port is able to robustly and reliably detect connections as they occur. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and a better understanding of the present invention may become apparent from the following detailed description of arrangements and example embodiments and the claims when read in connection with the accompanying drawings, all forming a part of the disclosure of this invention. While the foregoing and following written and illustrated disclosure focuses on disclosing arrangements and example embodiments of the invention, it should be clearly understood that the same is by way of illustration and example only and the invention is not limited thereto. 
         FIG. 1  is a plan view of a universal serial bus (USB) device with optical capabilities, such as a light-peak (LPK) device; 
         FIG. 2  a dual simplex optical link according to one embodiment of the present invention; and 
         FIG. 3  timing diagram illustrating low speed optical pulses (LSOPs) for power management of an optical link according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Meeting the simultaneous requirements of low power during idle times, eye safety, and robust connection detection requires the implementation of a power management scheme for the optical link. 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
     Referring now to  FIG. 1  there is shown an example of a universal serial bus (USB) device with additional optical capabilities for achieving even greater bandwidths. The USB device  100  has been referred to as the so-called Light Peak (LPK) optical USB. As shown, a cable  102  may join with a plastic housing  104 . A plug head  106  may include openings  108  in the head  106  used to lock the connector in place when plugged into a corresponding female connector. Optical ports  110  and  112  may be housed in the head  106  to provide optical capabilities. Optical port  110  may for example be to connect to an optical transmitter (Tx) module and optical port  112  may connect to an optical receiver (Rx) module. 
     Referring to  FIG. 2 , there is shown a dual simplex optical link according to one embodiment of the present invention. In the Light Peak implementation, the components involved comprise a Light Peak Switch Port (LPK-SP)  200  and a Light Peak Optical Module (LPK-OM)  202 . The LPK-OM  202  may comprise an optical transmit (Tx) module  204  and an optical receiver (Rx) module  206 . Control and data signals  208  and  210  between the LPK-SP  200  and the LPK-OM  202  select the various power states of the module  202  and directly control the on/off conditions of the laser transmitter  204 . 
     The optical receiver  206  may also be placed in the various power states, and then uses the received optical signals to indicate link states to the receiving portion of the LPK-SP  200 . A complete optical link may comprise a LPK-SP  200  and LPK-OM  202  on one side, an optical fiber connection  212 , and another LPK-OM  302  and LPK-SP  300  on the other side. Each link is dual-simplex, with each side having a transmit channel connected to the opposite side receive channel. A separate fiber may be used for each direction, with both fibers  212  contained in the same optical cable. 
     Future implementations may combine the LPK-SP  200  and LPK-OM  202  into a more integrated unit, where the control and data Signals  208  become internal to the design. However, the power management functionality and states being used to control the optics would still exist. 
     Another option may be the integration of the LPK-OM  202  into a mechanical connector eliminating the fiber jumper from the LPK-OM  202  to the LPK Port Connection  215 , and building the system side of the port connection directly into the mechanical connector. This scheme also would not alter the power management functionality between the LPK-SP  200  and the LPK-OM  202 ; it only changes the physical connection of the LPK-OM optical interface. 
     When an optical port has no connection, it is desirable to save as much power as possible, and it is desired to meet eye safety standards. This is achieved by placing the optical module into a very low power Standby state, where the transmit laser  204  is disabled most of the time. The transmit stage  204  consumes almost no power while the laser is disabled. At the same time, the receive stage  206  has minimal functionality, where it only needs to detect the presence of low speed optical pulses (LSOP) and signal these pulses to the LPK-SP  200 . 
     In order to actually detect a connection, the transmit stage  204  is pulsed on periodically, with a very low duty cycle, low speed pulse. The pulse represents below a 0.25% duty in one embodiment. This saves a significant amount of power for transmit stage  204  and easily meets the eye safety standards for an open port. When a physical connection is made, by connecting optical fiber between the two sides of the link, the link partner receiver  302  would detect the low speed optical pulse (LSOP), and signal the reception to the LPK-SP  300 . At this point, the LPK-SP  200  can begin the detection process. 
     For robust connection detection, including the avoidance of false connection detection, the LPK-SP  200  may use a number of LSOPs to be received before deciding that a connection exists. For example, three pulses in a row, with no missing pulses, may be used to indicate that a fiber is connected. Once the pulses have been detected, the LPK-SP  200  commands the LPK-OM  202  to transition to a higher power Idle state, where more functionality is enabled and where higher speed responses are possible. The connection uses a modified LSOP, with a somewhat higher duty cycle of about 1% to signal to the link partner that the Idle state has been activated. The LPK-SP  200  and LPK-OM  202  continue this signaling until both sides of the link are in the same state. That is, the LPK-SP  200  is both sending and receiving the modified LSOP. 
     Once both sides of the link are signaling the modified LSOP, the link is transitioned to the Active state, using a different LSOP signal called RESUME. While in the Active state, the optical link is fully functional, sending high speed data from each transmit stage to the link partner receive stage. This involves higher power consumption, as all high speed data circuits are operational, and the optical signal is being modulated with the high speed data. Since the optical fibers are now connected in the link, the eye safety standards allow a higher power optical signal to be transmitted, as the signal will not be exposed to an open port while the fiber is connected. 
     The above described connection signaling scheme is illustrated in  FIG. 3 . When the optical link is not connected  400  the optical link is in a standby state and disabled most of the time as shown pulsing at a duty cycle below 0.25% using very little power and easily meeting eye safety standards. Once connected the link goes into a connected standby state  402  and the transmitter pulses a number of pulses, for example three low speed optical pulses, in a row signaling the receiver on the other side that a connection has been made. The optical link then transitions to a higher power Connected Idle state  404 , for example a 1% duty cycle pulses, where more functionality is enabled and where higher speed responses are possible. This enables detection of a shorter duration RESUME pulse  406  to transition to an Active state  408  wherein the optical link is fully functional, sending high speed data from each transmit stage to the link partner receive stage. 
     Once in the Active state  408 , the link can transition back and forth between Active and Idle without the fiber being disconnected. This represents another opportunity to save power in cases where there is a pause in the data flow. Since the fibers stay connected, it is possible to quickly transition back and forth between the Active and Idle states, as needed. During extended Idle states, the transmit stages send another LSOP signal, call CONNECT, to indicate that the fibers are still connected and that the link is still enabled. Note that the transition between Active and Idle can be independent in each fiber direction, so one link partner could be sending high speed data to the corresponding receive stage, while that transmit stage is signaling only the CONNECT pulses in the opposite direction. 
     If the fibers are disconnected from an enabled link, either on purpose, or due to a fault, the receive stage will no longer be receiving any optical signal, and the LPK-OM  202  will signal this case to the LPK-SP  200 . If the receive stage was in the Idle state, receiving only the CONNECT LSOP signals, these signals will also no longer be detected. This would be the indication that the link has been disconnected. At this point, the LPK-SP  200  will disable the transmit stage, to again comply with the eye safety standards, then the LPK-OM  204  back to the Standby state, where it will wait for another connection. 
     The LPK-OM  204  should maintain the eye safety limits even when faults occur that would cause the optical signals to exceed these limits. Circuitry exists to shut down the laser in any fault situation; open, hardware short, or software issue, that would cause a violation to the eye safety limits. 
     This power management scheme takes the best advantage of a dynamic connection environment, where ports may be connected and disconnected at any time, and where data flows may start and stop as needed by the applications using the high speed data links. Power consumption is optimized, eye safety standards are met, and robust connection detection is preserved. 
     As a side benefit, running the transmit lasers in a higher power mode after the fibers are connected allows a larger range of laser transmit power to be used than has been the case in traditional telecom or datacom connections. This enables higher production yields for the lasers, larger link margins with similar eye safety classifications, and lower costs for the optical modules. This benefit would not be possible without the power management scheme to keep laser power very low while the fibers are disconnected. 
     The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. 
     These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.