hello forum, I know that is it is possible to downconvert high frequencies to lower frequencies.... what is the highest frequency we can downconvert and why? How is it done? ( I don't think the issue exists in the reverse direction: we can convert any low frequency signal to a high frequency one) thanks fisico32
downconverting optical frequencies...
Started by ●July 18, 2010
Reply by ●July 18, 20102010-07-18
On 07/18/2010 06:41 AM, fisico32 wrote:> hello forum, > > I know that is it is possible to downconvert high frequencies to lower > frequencies.... > > what is the highest frequency we can downconvert and why? How is it done? > > ( I don't think the issue exists in the reverse direction: we can convert > any low frequency signal to a high frequency one)To respond to your title, yes, there are nonlinear optical materials that will mix two laser beams to a longer wavelength signal. I don't know how far above the visible this sort of thing works -- it is, AFAIK, a chemical bond thing, which would stop responding to light somewhere between far infrared and X-ray. But -- AFAIK -- the phase noise in even a really good laser beam is huge, so you'd have to have exceptionally high data rates to maintain enough phase correlation over a bit interval to make such a technique worthwhile. I think it's still in the experimental stage, and will be for quite a while. (The reason for all the "AFAIK" qualifications above is because I have friends to chat with who've done work on this, but no direct experience, or even articles read) -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
Reply by ●July 18, 20102010-07-18
Tim Wescott <tim@seemywebsite.com> wrote: (snip)> To respond to your title, yes, there are nonlinear optical materials > that will mix two laser beams to a longer wavelength signal.> I don't know how far above the visible this sort of thing works -- it > is, AFAIK, a chemical bond thing, which would stop responding to light > somewhere between far infrared and X-ray.I would expect the limit to be somewhere before vacuum UV, which is the frequency where all dielectrics start absorbing. Otherwise, you need a crystal with the appropriate non-linearities. It is techniques like this that allow for optical frequency counting, and the reason for defining the speed of light. Until that point, time measurments and distance measurements had about the same relative uncertainty, around 1e-8. Optical frequency counting moved the relative uncertainty of time measurements down to 1e-15 or so. Defining the speed of light allows for the same uncertainty for distance (defined in terms of speed and time.)> But -- AFAIK -- the phase noise in even a really good laser beam is > huge, so you'd have to have exceptionally high data rates to maintain > enough phase correlation over a bit interval to make such a technique > worthwhile. I think it's still in the experimental stage, and will be > for quite a while.-- glen
Reply by ●July 18, 20102010-07-18
On Jul 19, 1:41�am, "fisico32" <marcoscipioni1@n_o_s_p_a_m.gmail.com> wrote:> hello forum, > > I know that is it is possible to downconvert high frequencies to lower > frequencies.... > > what is the highest frequency we can downconvert and why? How is it done? > > �( I don't think the issue exists in the reverse direction: �we can convert > any low frequency signal to a high frequency one) > > thanks > fisico32Yep and people have even worked on optical PLLs. In theory if you pass a laser through a special crystal that doubles the frequency you should be able to get X-rays off it but I don't believe you do as the freq response is seldom high enough in the material. Hardy
Reply by ●July 18, 20102010-07-18
>hello forum, > >I know that is it is possible to downconvert high frequencies to lower >frequencies.... > >what is the highest frequency we can downconvert and why? How is it done? > > ( I don't think the issue exists in the reverse direction: we canconvert>any low frequency signal to a high frequency one)One crude downconvert with real world applications is to shine two lasers on a silicon photosensor. I think most types of silicon sensor work OK for this. The modes of a laser are typically hundreds of megahertz apart. If you use gratings to pick out a single mode from each of the lasers, you will see the difference frequency in the output of the sensor. Steve
Reply by ●July 18, 20102010-07-18
steveu <steveu@n_o_s_p_a_m.coppice.org> wrote: (snip)> One crude downconvert with real world applications is to shine two lasers > on a silicon photosensor. I think most types of silicon sensor work OK for > this. The modes of a laser are typically hundreds of megahertz apart. If > you use gratings to pick out a single mode from each of the lasers, you > will see the difference frequency in the output of the sensor.I thought they used microwave mixer diodes, but maybe you don't need that to get 300MHz by now. There are diodes that go much faster than that, though. -- glen
Reply by ●July 19, 20102010-07-19
On Jul 18, 9:41�am, "fisico32" <marcoscipioni1@n_o_s_p_a_m.gmail.com> wrote:> hello forum, > > I know that is it is possible to downconvert high frequencies to lower > frequencies.... > > what is the highest frequency we can downconvert and why? How is it done? > > �( I don't think the issue exists in the reverse direction: �we can convert > any low frequency signal to a high frequency one) > > thanks > fisico32How high do you want to go? Check out both the Compton and Inverse Compton scattering. http://en.wikipedia.org/wiki/Compton_scattering You can upconvert E-M radiation to make x-ray or gamma beams by upconverting uv light by ramming them head on into a electron stream (inverse compton effect). Optically heteodyning is done in the lab via nonlinear mixing. Just mix two high power laser beams in a crystal such as ammonium dihydron phospate. Clay
Reply by ●July 19, 20102010-07-19
fisico32 wrote:> hello forum, > > I know that is it is possible to downconvert high frequencies to lower > frequencies.... > > what is the highest frequency we can downconvert and why?~1e35 Hz. Nothing higher then that had been discovered so far.> How is it done?All processes are nonlinear; they only seem to be linear because of the law of big numbers.> ( I don't think the issue exists in the reverse direction: we can convert > any low frequency signal to a high frequency one) > thanks > fisico32I think you are Radium the Troll. VLV
Reply by ●July 19, 20102010-07-19
On 7/19/2010 11:50 AM, Vladimir Vassilevsky wrote: ...> I think you are Radium the Troll.Radium >> Green Xenon Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●July 19, 20102010-07-19
On 07/19/2010 07:08 AM, Clay wrote:> On Jul 18, 9:41 am, "fisico32"<marcoscipioni1@n_o_s_p_a_m.gmail.com> > wrote: >> hello forum, >> >> I know that is it is possible to downconvert high frequencies to lower >> frequencies.... >> >> what is the highest frequency we can downconvert and why? How is it done? >> >> ( I don't think the issue exists in the reverse direction: we can convert >> any low frequency signal to a high frequency one) >> >> thanks >> fisico32 > > How high do you want to go? Check out both the Compton and Inverse > Compton scattering. http://en.wikipedia.org/wiki/Compton_scattering > > > You can upconvert E-M radiation to make x-ray or gamma beams by > upconverting uv light by ramming them head on into a electron stream > (inverse compton effect).Does that result in light that is coherent to the source? I.e. is the amplitude of the light wave multiplied by some power function, or is the mechanism more like cyclotron radiation? -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
