[Starlink] mems optical switching

[Christian von der Ropp]

All-optical switching could greatly reduce complexity and power 
consumption on the satellites at the cost of flexibility. Up to 44 
satellites in an orbital plane would use individual wavelengths which 
would be passed on transparently down the daisy chain and only 
satellites in range of gateways would convert the optical signals back 
into electrical ones, and send them down to earth while they pass a 
gateway. This would result in relatively short duty cycles, hence less 
power draw per orbit and less heat dissipation issues.

Actually I've been suspecting that the SDA targets all-optical switching 
for the Transport Layer constellation as I don't seen any other 
immediate reason for the requirement of their OISL standard to require 
wavelength switching within the ITU channel grid for LCTs (see p. 18 of 
the OISL 3.0: 
https://www.sda.mil/wp-content/uploads/2022/04/SDA-OCT-Standard-v3.0.pdf)

As a matter of fact tuneable wavelenghts were already required in the 
draft version of the OISL standard published in April 2020:
https://twitter.com/Megaconstellati/status/1310336728595562499

-Christian

Am 19.03.2023 um 16:16 schrieb Brandon Butterworth via Starlink:
> On Sat Mar 18, 2023 at 03:19:49PM -0700, Dave Taht via Starlink wrote:
>> Today, this about google's mems switching tech hit,
> They've been talking about it since last year, seems to have got
> a hype bump recently.
>
> Who expected circuit switching to make a comeback?
>
>> I keep wondering where else it could be applied.
> They've been used for a long time, eg almost 20 years ago -
> https://archive.nanog.org/meetings/nanog32/presentations/zwart.pdf
>
> There is a goal of optical packet switching, until then you're
> limited to where there are limited flows of long enough duration
> to make the change from packet to circuit switching viable. So mostly
> automated testing.
>
> I've dabbled with the idea in an archive use case where very few of
> a large set of storage nodes need to connect to a moderate number
> of servers. For some cases we could have zero switches. The goal was
> a mostly dark infrastructure and many 1000s of storage nodes,
> removing the switches saves a lot of power.
>
> Commercial optical switches are expensive so I was looking at
> making an optical strowger as I wanted a high fan out not
> large n^2.
>
> In the mobile world they are looking at doing flexible bandwidth
> per node with coherent optics over gpon fibre plant, allocating
> variable amounts of spectrum to each, which could be adapted to a
> similar circuit model. It'd be no use to google as they want the
> full bandwidth between each node but as dwdm coherent optic costs
> come down you could imagine doing the same with a full channel
> between each pair, so like a conventional WSS but cheaper. If it
> wasn't for the optics cost I suspect they'd have done that reducing
> switching time to a channel change.
>
> brandon
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