Microwave-to-optical conversion (A Nature paper)

[shpongle]

Hello everyone

I recently read a publication (attached) in Nature which talks about microwave-to-optical conversion. The setup consists of resonator depicted by a circle. It is mentioned that this resonator has non-linear electromagnetic response. Up-conversion takes place by three-wave mixing in resonator. The resonator is excited by microwaves (say 100 GHz) channeled through the rectangular waveguide. The resonator is also excited by an optical signal (say 500 THz) through the input optical fiber placed on the opposite side.

Some questions:

1. In which port of the device, do we get the output or the up-converted signal, is it not the output optical fiber? If it is the output optical fiber as shown in the paper, will it not have the same signal? I assumed this because only the original input optical signal can couple back into the optical fiber waveguide.
2. What is the use of the input optical signal? Don't we want an optical signal at the end?
3. What is meant by non-linear response in the resonator and what is three wave mixing in the resonator?

 

[tech99]

Some questions:

1. In which port of the device, do we get the output or the up-converted signal, is it not the output optical fiber? If it is the output optical fiber as shown in the paper, will it not have the same signal? I assumed this because only the original input optical signal can couple back into the optical fiber waveguide.
2. What is the use of the input optical signal? Don't we want an optical signal at the end?
3. What is meant by non-linear response in the resonator and what is three wave mixing in the resonator?

[/QUOTE]
1. The output is on the output optical fibre. The prism is to give isolation between the optical input and the output.
2. The optical input signal is the local oscillator for mixing purposes. The optical output signal is a replica of the microwave signal, upconverted to the optical range.
3, The non linear response means that output is not proportional to input, so that mixing occurs.

 

[sophiecentaur]

• What is the use of the input optical signal? Don't we want an optical signal at the end?

The modulated microwave input carries the 'wanted signal'. Presumably, the input optical signal is the 'Local Oscillator' for the mixing process. (It's just a very posh Super-het.) The 'I.F' optical output signal will be a sideband of the optical input. Presumably, there would be some filtering to eliminate the Local Oscillator - or maybe the form of modulation that goes on in the resonator would suppress the L.O, naturally by virtue of the optical resonance. The article mentions photonic processing. I don't know why that would be an advantage but the 'circuit' makes sense if that is what's needed. It is not uncommon to use an IF frequency that's higher than the input signal frequency. Perhaps that's an advantage as it can eliminate unwanted Image frequencies. The article quotes from the previous article and that may be worth reading.
The resonator had the function of the Mixer and it must have a non linear response (as in a normal mixer diode). From the article, it seems that the coupling of the input microwave signal doesn't involve any resistive contact so it will be low loss and, presumably, a good noise figure.