[time-nuts] Photodiodes for high frequency OPLL

[lists at lazygranch.com]

I forgot to mention if you use the bootstrap technique, you can keep a negative bias on the photodiode, which improves bandwidth by reducing capacitance. That is, you drive the AC signal across the diode to zero, but not the DC bias. If you use the fully differential amplifer, then the bias voltage is zero, hence more capacitance. 
I've looked into transformer coupling for photodiodes as a way to go fully differential and still apply a bias. A few years ago, the idea would be silly, but RF applications have created a supply of really high frequency transformers. 

The UDT diodes with the BNC attached are pretty common on ebay. I think the company was bought out. 


-----Original Message-----
From: "jmfranke" <jmfranke at cox.net>
Sender: time-nuts-bounces at febo.com
Date: Sat, 30 Mar 2013 13:46:51 
To: <time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] Photodiodes for high frequency OPLL

I used UDT PIN10 photodiodes to observe the mode spacings in HeNe lasers. 
The typical mode spacings were around 600 MHz.

John  WA4WDL

--------------------------------------------------
From: "ed breya" <eb at telight.com>
Sent: Friday, March 29, 2013 8:20 PM
To: <time-nuts at febo.com>
Subject: Re: [time-nuts] Photodiodes for high frequency OPLL

> 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.
>
> Most really high speed diodes are optimized for the 1550 nm region where 
> EDFAs work, but maybe they have usable response at other ranges. It 
> depends on your particular application and wavelength. I think detectors 
> are usually specified over the entire IR region, so datasheets may tell 
> enough.
>
> Here's link to some good info, but not current state of the art:
>
> http://e-collection.library.ethz.ch/eserv/eth:28429/eth-28429-02.pdf
>
> There are various methods that use lower frequency modulation techniques 
> so that regular detectors can be used directly. If you study up on related 
> patents, you may find some ideas and leads to appropriate actual devices.
>
> Ed
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to 
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
> 

_______________________________________________
time-nuts mailing list -- time-nuts at febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.