If I can rephrase that it it, the diode needs to see the difference signal of the mixer? -----Original Message----- From: Bruce Griffiths <[email protected]> Sender: [email protected] Date: Sun, 31 Mar 2013 11:43:48 To: Discussion of precise time and frequency measurement<[email protected]> Reply-To: Discussion of precise time and frequency measurement <[email protected]> Subject: Re: [time-nuts] Photodiodes for high frequency OPLL
The detectors don't have to be fast enough to keep up with optical carrier frequency as long as the incident optical power has a component at a much lower frequency. Bruce ed breya wrote: > Ooops - never mind. I wrote before my memory was updated. My > experience in E-O stuff was years ago using AM at relatively low > frequency, and nowhere near the lasers and microwave/gigabit/sec stuff > - I didn't think the detectors were fast enough to actually keep up > with the optical carrier frequency. I was also picturing > wavelength/spatial separation with interference in order to allow > relatively slow detectors to see it, or mixing in nonlinear optical > materials. > > Ed > > Bruce Griffiths wrote: > > A photodiode is in fact a nonlinear device for optical fields as it is > essentially a linear optical power detector. > The output is proportional to the incident optical power not the field > amplitude. > Photomixers are routinely used in wide range of diverse application such > as translating the frequency fluctuations of the (Mie) scattered light > due to Brownian motion of the colloidal particle sizes to baseband. The > size of the scattering particles can be inferred from the shape of the > resultant frequency spectrum. > > An interferometer of itself (without a detector) is a linear device that > merely superimposes optical fields and will of itself produce no > difference frequency output. > > Bruce > > ed breya wrote: > > I don't think that you can effectively directly mix two laser > > wavelengths in a semiconductor light detector and get a useable IF - > > it's hard enough just to get the tens of GHz modulation signals out > > above the noise floor, let alone a tiny difference signal between > > hundreds of THz. You need an optical interference or nonlinear device > > up front to do the "mixing" and get the wavelength discrimination, > > while the optical detector(s) serve as the first IF O-E transducer. > > > > My knowledge of this stuff isn't up to date - maybe nowadays there are > > detector devices and methods that take care of this directly, but I > > don't think so. > > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
