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Comment by ragix | Hacker News Reader

We have been swapping out duplex sfp's for single fibre working duplex sfp's for a few years on our backhaul links here. It is a great way to increase capacity. We have also rolled out a photonic switching fibre network for customers to lease 100gbit circuits across the country. Photonic switching (basically routing at the optical level) is impressive technology 1 rack can push terabits of data.

However the equipment is in the $1,000,000 range. But that is peanuts for a large carrier.

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I've seen photonic switching refer to a lot of different ideas. Sometimes it's just a remotely-controllable add-drop multiplexer.

Does this type of photonic switching differ from CWDM/DWDM?

Are routers putting the signal onto different wavelengths depending on where they want packet to go?

A lot of the equipment I've seen is largely described in broad marketing-friendly terms which makes it hard to understand why the equipment is actually more useful than existing approaches.

No it doesn't differ, its all modulating wavelengths of light through a piece of glass, CWDM using LEDs and DWDM using actual lasers. Routers put packets onto an interface queue at layer 2. Layer 1 what is what handles which wavelength(lambdas)those bits modulate.

CWDM doee actually use with lasers in some contexts. The big difference is that CWDM uses frequencies that are all far apart, with just a few frequencies. DWDM uses frequency channels that are very close. DWDM performs better because it focuses the energy in the band's that have the best properties in terms of absorption, distortion and group delay.

Yes the "C" is for course and the "D" is for dense. All of the CWDM gear I have been exposed to was LEDs, generally actual lasers are much more expensive and you dont need that sensitivity for such loose banding. In what implementations is CWDM using lasers instead of LEDs?

CWDM uses lasers too, the reduced wavelength tolerance simply means that the lasers can be uncooled (reducing the power draw) and that chirp (frequency shift during modulation) does not cause interference with neighbouring channels, making them easier to modulate directly. The 'loose' CWDM banding is actually smaller than the bandwidth of typical LEDs.

Photonic switching is basically a lot of servo motor controlled mirrors in a box, you can accomplish the thing with a human and a lot of SC/UPC to SC/UPC patch panels and cables. It's an OSI layer 1 thing and agnostic of servers, switches. The "box" lets you reconfigure crossconnects in software. It does introduce a degree of loss.

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