optical circulator as a bidirectional one fiber solution

Jameson, Daniel Daniel.Jameson at tdstelecom.com
Mon Aug 13 22:19:58 UTC 2018

You would still need to frequency shift TX and RX.  They are travelling opposite directions on the same piece of glass;  as the traffic rate increases the likelihood of collisions increases and you’ll start to get errors.  The collision would either cancel the ‘bit’ or act like OBI and get erroneous bits and checksum errors or missing chunks from the constellation.  There are BIDI 100G transceivers for Multi-mode available today based on the Foxconn optics, I’d imagine we’ll see BIDI for the O and C bands in the next 18 months.

From: NANOG [mailto:nanog-bounces at nanog.org] On Behalf Of Eric Kuhnke
Sent: Monday, August 13, 2018 3:56 PM
To: ben at 6by7.net; nanog at nanog.org list
Subject: Re: optical circulator as a bidirectional one fiber solution

For 1 and 10Gbps OOK modulation yes, but not for something like a ITU DWDM grid channelized or tunable coherent optic. In which the (QPSK, 8PSK, 16QAM) signal has a specific THz width and frequency not unlike a radio operating in a very, very narrow waveguide.

On Mon, Aug 13, 2018 at 1:57 PM Ben Cannon <ben at 6by7.net<mailto:ben at 6by7.net>> wrote:
Good news about almost all optics, their Rx window is pretty wide. Meaning a 1550nm optic will activate the receiver on a 1560nm optic just fine (and probably anything in the 1500nm band).  Careful use of specialized single strand DWDM muxes (FS.com<http://FS.com>) can yield great bidi-like results with increased channel count.

On Aug 13, 2018, at 10:49 AM, Eric Kuhnke <eric.kuhnke at gmail.com<mailto:eric.kuhnke at gmail.com>> wrote:
Something that is broadly the same as a coherent 100G QPSK single wavelength optical module, but in two different frequencies, and a passive CWDM mux/demux prism at each end might work. The limitation would be availability of optics for a modern 100G MSA that are both coherent and Tx/Rx at two different THz frequencies.

Or with some box and vendor equipment in between, such as:


On Tue, Aug 7, 2018 at 1:00 PM Daniel Corbe <dcorbe at hammerfiber.com<mailto:dcorbe at hammerfiber.com>> wrote:
On 8/7/2018 15:46:03, "Baldur Norddahl" <baldur.norddahl at gmail.com<mailto:baldur.norddahl at gmail.com>>

>There is a lack of bidirectional one fiber (BIDI) options for 40G and
>100G optics. Usually BIDI is implemented using two CWDM wavelengths,
>one for tx and one for rx. However there is also a lack of CWDM and
>DWDM options for 40G and 100G.
>Would it be possible to use an optical circulator like this one
>(customized to 1310 nm)?
>Combined with a traditional two fiber 1310 nm 10 km 40G QSFP module
>like this: https://www.fs.com/de/en/products/24422.html
>The link distance would be 5 km.
>The optical circulator separates tx and rx by the direction the light
>travels in. It would work even though both directions use the same
>wavelength. There will likely be some reflection but hopefully
>attenuated enough that it is regarded as background noise.
>Has anyone done this? Any reason it would not work?

The main issue you're going to run into (especially trying to plug
anything into a DWDM shelf) is 40G and 100G transceivers usually emit 4
lanes of traffic instead of a single lane like 10 and 1G optics do.

I'd imagine that's why there are so few solutions that don't involve
things like OTN.
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