System and method for removing far field limitations in microwave photonic arbitrary waveform generators

Abstract

A photonic waveform generator and a method of generating an electrical waveform based on a photonic signal are disclosed. The generator includes an input port for receiving an optical signal, a pulse shaper coupled to the input port and configured to Fourier transform the optical signal and apply a pre-distort waveform onto optical spectrum of the optical signal, a dispersive pulse stretcher coupled to the pulse shaper, an optical-to-electrical converter coupled to the dispersive pulse stretcher, and an output port coupled to the optical-to-electrical converter, the pre-distortion removes distortion of the electrical signal that exists in the absence of the pre-distortion caused by violation of far field limitation between the optical signal and the electrical signal.

1 . A photonic waveform generator, comprising:
 an input port for receiving an optical signal;   a pulse shaper coupled to the input port and configured to Fourier transform the optical signal and apply a pre-distortion waveform onto optical spectrum of the optical signal resulting in a shaped optical signal having both optical amplitude and optical phase spectral shaping;   a dispersive pulse stretcher coupled to the pulse shaper and configured to provide a frequency dependent delay which disperses the shaped optical signal;   an optical-to-electrical converter coupled to the dispersive pulse stretcher and configured to convert an optical input corresponding to the dispersed shaped optical signal to an electrical output; and   an output port coupled to the optical-to-electrical converter and configured to output an electrical signal corresponding to the electrical output,   the pre-distortion waveform of the transformed optical signal removes distortion of the electrical signal that exists in the absence of the pre-distortion waveform caused by violation of far field limitation between the optical signal and the electrical signal.   
     
     
         2 . The photonic waveform generator of  claim 1 , wherein the optical-to-electrical converter is a photodetector. 
     
     
         3 . The photonic waveform generator of  claim 2 , wherein the photodetector is a photodiode. 
     
     
         4 . The photonic waveform generator of  claim 1 , wherein the dispersive pulse stretcher comprises an optical element having a non-zero dispersion characteristic. 
     
     
         5 . The photonic waveform generator of  claim 1 , wherein the pulse shaper comprises:
 a spatial modulator;   an optical grating; and   a reflective surface,   wherein the spatial modulator is a liquid crystal module, disposed between the optical grating and the reflective surface,   wherein the reflective surface is a mirror, and   where the spatial modulator is a transmissive film resulting in one of a spatial pattern of polarization change, transmission loss, transmission phase shift, or a combination thereof.   
     
     
         6 . The photonic waveform generator of  claim 1 , wherein an input and an output of the pulse shaper are co-linear. 
     
     
         7 . The photonic waveform generator of  claim 1 , where time bandwidth product of the electrical signal is capable of being about 50% to about 100% the maximum time bandwidth product available from the pulse shaper. 
     
     
         8 . A method for generating an electrical pulse with controlled spectral characteristics, the method comprising:
 receiving an optical signal;   Fourier transforming the optical signal using a pulse shaper to generate a transformed optical signal;   pre-distorting the transformed optical signal to generate a pre-distorted transformed optical signal; and   stretching the pre-distorted transformed optical signal through a dispersive pulse stretcher; and   converting the stretched pre-distorted transformed optical signal to an electrical signal by an optical-to-electrical converter,   wherein the pre-distortion of the transformed optical signal removes distortion of the electrical signal that exists in the absence of the pre-distortion caused by violation of far field limitation between the optical signal and the electrical signal.   
     
     
         9 . The method of  claim 8 , wherein the optical-to-electrical converter is a photodetector. 
     
     
         10 . The method of  claim 9 , wherein the photodetector is a photodiode. 
     
     
         11 . The method of  claim 10 , photonic waveform generator of  claim 1 , wherein the dispersive pulse stretcher comprises an optical element having a non-zero dispersion characteristic. 
     
     
         12 . The method of  claim 8 , wherein the pulse shaper comprises:
 a spatial modulator;   an optical grating; and   a reflective surface,   wherein the spatial modulator is a liquid crystal module, disposed between the optical grating and the reflective surface,   wherein the reflective surface is a mirror, and   where the spatial modulator is a transmissive film resulting in one of a spatial pattern of polarization change, transmission loss, transmission phase shift, or a combination thereof.   
     
     
         13 . The method of  claim 8 , wherein an input and an output of the pulse shaper are co-linear. 
     
     
         14 . The method of  claim 13 , where time bandwidth product of the electrical signal is capable of being about 50% to about 100% the maximum time bandwidth product available from the pulse shaper.