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New Member

connection OC-3 SMI to OC3- SML

hello,

I would like to connect two ATM OC-3 modules:

-3360, OC3 single mode, intermediate

-cat 8500, OC3 single mode, long reach

what should I put between both interfaces to make it working?

best regards

1 ACCEPTED SOLUTION

Accepted Solutions
Gold

Re: connection OC-3 SMI to OC3- SML

To answer your last question, no, you don't need an attenuator for the TX with that length; you do need it for the RX, but only the one that Don identified earlier, the IR one. (See below for further explanation.)

Based on the optical power specifications Don provided, you will need at least 8dB attenuation between the TX port on the SM-LR interface and the RX port of the SM-IR interface, to avoid "burning out" the RX optics at the SM-IR end. That comes from assuming that there's no effective attenuation in the fiber due to the 3m length. (Actually, there is a minimal amount, due to connector loss, probably less than 1.0dB.) 10dB to 15dB gives you a little extra cushion; at most, you want no more than 23dB attenuation, because any more than that increases the chances that the signal may not be received at all.

To elaborate further:

At the high end of the power range, 0.0dBm TXmax out of the LR into -8.0dBm RXmax of the IR means the optical power out is 8dBm higher than what the IR interface can take in. You've got to bleed off at least 8dBm to be sure you're not overdriving the optics. Whether you do it at the TX end of the LR, or the RX end of the IR, doesn't really matter in your scenario, as long as it gets done. In practice, however, since what you're trying to protect is the RX port on any interface, the best way to guarantee that the RX optics are protected is to put the attenuator there. (Think of looking at the sun: where do you want your sunglasses to be? Over your eyes, so you don't go blind. ALWAYS PROTECT THE RECEIVE OPTICS!) This is your "Minimum Attenuation" required.

Attenuation required in the other direction: -8.0dBm TXmax out of the IR into -8.0dBm RXmax of the LR means the optical power out is equal to what the LR interface can take in. No minimum attenuation is required.

At the low end of the power range, -5.0dBm TXmin out of the LR into -28.0dBm RXmin of the IR means the minimum optical power out is 23dBm higher than the least that the IR interface can work with. As long as you bleed off no more than 23dBm, you're 100% guaranteed not to underdrive the optics. This is your link loss budget in this direction.

Best practice is to leave yourself some cushion here, too; in your example, introduce no more than say 20dB attenuation at the RX end.

Link loss budget in the other direction: -15.0dBm TXmin out of the IR into -28.0dBm RXmin of the LR means the minimum optical power out is 13dBm higher than the least that the LR interface can work with. Since in your example we're not introducing any physical attenuators on this strand of the connection, as long as you bleed off no more than 13dBm with your 3m patch, you're 100% guaranteed not to underdrive the optics.

If you were to take this installation out of the 3-meter "lab" environment and into km's of the "real-world", the 13.0dBm link budget above, as the smaller of the two, would be the limiting factor as to how far you could go. (Without amplification.)

Hope this helps.

3 REPLIES
Silver

Re: connection OC-3 SMI to OC3- SML

You will need an attenuator for the RX side of the Intermediate reach (atleast 10Db and probably 15Db depending on the length of your fiber) so you do not overdrive the intermeidiate reach optics with the LR transmit side.

Optical Power information for these interfaces:

Fiber Interface Output Power Input Power Input Sensitivity Wavelength

SM-IR -15.0 dBm -8.0 dBm -8.0 dBm -28.0 dBm 1261 nm 1360 nm

SM-LR -5.0 dBm 0.0 dBm -8.0 dBm -28.0 dBm 1285 nm 1335 nm

Hope this helps you,

Don

New Member

Re: connection OC-3 SMI to OC3- SML

it will be 3m max - don't I need an attenuator for the TX with that length?

best regards

Gold

Re: connection OC-3 SMI to OC3- SML

To answer your last question, no, you don't need an attenuator for the TX with that length; you do need it for the RX, but only the one that Don identified earlier, the IR one. (See below for further explanation.)

Based on the optical power specifications Don provided, you will need at least 8dB attenuation between the TX port on the SM-LR interface and the RX port of the SM-IR interface, to avoid "burning out" the RX optics at the SM-IR end. That comes from assuming that there's no effective attenuation in the fiber due to the 3m length. (Actually, there is a minimal amount, due to connector loss, probably less than 1.0dB.) 10dB to 15dB gives you a little extra cushion; at most, you want no more than 23dB attenuation, because any more than that increases the chances that the signal may not be received at all.

To elaborate further:

At the high end of the power range, 0.0dBm TXmax out of the LR into -8.0dBm RXmax of the IR means the optical power out is 8dBm higher than what the IR interface can take in. You've got to bleed off at least 8dBm to be sure you're not overdriving the optics. Whether you do it at the TX end of the LR, or the RX end of the IR, doesn't really matter in your scenario, as long as it gets done. In practice, however, since what you're trying to protect is the RX port on any interface, the best way to guarantee that the RX optics are protected is to put the attenuator there. (Think of looking at the sun: where do you want your sunglasses to be? Over your eyes, so you don't go blind. ALWAYS PROTECT THE RECEIVE OPTICS!) This is your "Minimum Attenuation" required.

Attenuation required in the other direction: -8.0dBm TXmax out of the IR into -8.0dBm RXmax of the LR means the optical power out is equal to what the LR interface can take in. No minimum attenuation is required.

At the low end of the power range, -5.0dBm TXmin out of the LR into -28.0dBm RXmin of the IR means the minimum optical power out is 23dBm higher than the least that the IR interface can work with. As long as you bleed off no more than 23dBm, you're 100% guaranteed not to underdrive the optics. This is your link loss budget in this direction.

Best practice is to leave yourself some cushion here, too; in your example, introduce no more than say 20dB attenuation at the RX end.

Link loss budget in the other direction: -15.0dBm TXmin out of the IR into -28.0dBm RXmin of the LR means the minimum optical power out is 13dBm higher than the least that the LR interface can work with. Since in your example we're not introducing any physical attenuators on this strand of the connection, as long as you bleed off no more than 13dBm with your 3m patch, you're 100% guaranteed not to underdrive the optics.

If you were to take this installation out of the 3-meter "lab" environment and into km's of the "real-world", the 13.0dBm link budget above, as the smaller of the two, would be the limiting factor as to how far you could go. (Without amplification.)

Hope this helps.

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