Re: Fast sampler

On 2025-03-09 19:22, Tom Del Rosso wrote:

Phil Hobbs wrote:

Hi, All,
>
Late last year we did a fast sampler/TDR with nice clean 60 ps edges.
>
We're gearing up to actually sell them, so I did a short technical
writeup on the design, which may be of interest.
>
<https://electrooptical.net/News/a-high-performance-time-domain-reflectometer>
>
Cheers
>
Phil Hobbs

 Why is a LASER ruler that can measure distances in air with 2mm accuracy
$16,
 and an OTDR for measuring fiber $600?
 

Well, the OTDR needs a fiber-coupled laser, for one thing, and a decent TIA.  Also as John says, it's a time-domain instrument.  A laser ruler can just be a diode laser with a monitor photodiode, a collimating lens, a simple TIA and a micro with built-in ADC.
You put a small (1-3 mA) current ramp on the laser, and look at the beat signal coming out of the monitor photodiode.  The frequency gives you the round-trip delay.  This sort of laser feedback measurement can be pretty good if the diode stays reasonably single-mode.
I have no idea how the $16 ones do it, but if I were building one, that's the first thing I'd try.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com