Eye safety mechanism for use in optical cable with electrical interfaces
View Patent ↗An eye safety mechanism for use with a bi-directional data cable having an electrical interface at at least one (but potentially both) ends, despite the fact that the cable communicates over much of its length using a bi-directional optical channel. Upon power-up, the eye safety mechanism determines whether or not a loss of signal condition is present on an optical receive channel of the bi-directional data cable. If the loss of signal is present, the mechanism intermittently disables the optical transmit channel of the bi-directional data cable. On the other hand, if the loss of signal is not present, the mechanism enables the optical transmit channel of the bi-directional data cable without intermittently disabling transmission at least for most of the time until the next time a loss of signal is detected on the optical receive channel.
1. A method for performing eye safety in a bi-directional optical communication cable, the bi-directional optical communication cable including a first optical fiber for transmitting optical signals in a first direction from a first end of the cable to a second end of the cable; a second optical fiber for transmitting optical signals in a second direction from the second end of the cable to the first end of the cable; a transmit optical sub-assembly having an optical transmitter that is optically coupled to the first optical fiber such that when an electrical data signal is received at an electrical interface at the first end of the cable, a corresponding optical data signal is transmitted by the optical transmitter onto the first optical fiber during normal operation; and a receive optical sub-assembly having an optical receiver that is optically coupled to the second optical fiber such that when an optical data signal is received at the optical receiver, a corresponding electrical data signal is produced at the electrical interface at the first end of the cable during normal operation, the method comprising:
an act of determining whether or not the receive optical sub-assembly is detecting a loss of signal on the second optical fiber;
when the loss of signal is detected on the second optical fiber, an act of intermittently disabling the optical transmitter transmitting the optical data signal onto the first optical fiber; and
when the loss of signal is not detected on the second optical fiber, an act of enabling the optical transmitter to transmit the optical data signal onto the first optical fiber until the next time a loss of signal is detected on the second optical fiber.
2. A method according to claim 1 , wherein by intermittently disabling the optical transmitter in the case of a loss of signal on the receive channel an average optical power emitted by the optical transmitter is reduced.
3. A method according to claim 1 , wherein when the loss of signal is detected on the second optical fiber, the optical transmitter is only intermittently disabled and intermittently enabled.
4. A method according to claim 3 , wherein the disabled optical transmitter is not capable of transmitting data that is represented by optical high signals.
5. A method according to claim 3 , wherein a duty cycle of the optical transmitter is less than fifty percent when intermittently disabled.
6. A method according to claim 3 , wherein a duty cycle of the optical transmitter is less than twenty percent when intermittently disabled.
7. A method according to claim 3 , wherein a duty cycle of the optical transmitter is less than ten percent when intermittently disabled.
8. A method according to claim 1 , wherein the intermittency is achieved using a counter, that causes the state of the optical transmitter to periodically transition between the transmitter disabled state and the transmitter enabled state.
9. A method according to claim 8 , wherein, when in the transmitter disabled state and a count by the counter does not reach a specific count threshold, then the transmitter disabled state is maintained.
10. A method according to claim 9 , wherein when in the transmitter disabled state and the count by the counter reaches the specific count threshold, then the state transitions from the transmitter disabled state to the transmitter enabled state.
11. A method according to claim 1 , wherein the method is entirely performed in the bi-direction optical communication cable.
12. A method according to claim 1 , wherein the method is performed entirely within the transmit optical sub-assembly of the bi-direction optical communication cable.
13. A method according to claim 1 , wherein the method is performed at least partially within a host connected to the bi-directional optical communication cable.
14. A method according to claim 1 , wherein the bi-directional optical communication cable is an integrated cable with electrical connections at both ends.
15. A method according to claim 1 , wherein the bi-directional optical communication cable is an integrated cable an electrical connector at a first end and an optical connector at a second end of the bidirectional optical communication cable.
16. A method according to claim 1 , wherein the method is performed upon power-up of the bi-directional optical communication cable.
17. A bi-directional optical communication cable comprising means for performing the method of claim 1 .
18. A host comprising means for performing the method of claim 1 in connection with the bi-directional optical communication cable.