Optical systems and methods based upon temporal stretching, modulation and recompression of ultrashort pulses

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention pulse shaping of picosecond to femtosecond pulses is achieved by temporally dispersing (stretching) optical frequency pulses, modulating the stretched frequencies by means of phase and/or amplitude modulation and then temporally combining (compressing) the modulated frequencies to form the desired shaped pulses which contain information or data to be conveyed.
In our prior invention described in U.
S.
Pat.
No.
4,655,543, we describe the use of diffraction gratings to spatially disperse the frequency components which make up a short, chirped optical pulse and the modulation of the spatially dispersed frequencies by means of amplitude and phase masks.
The modulated frequencies are then spatially recollimated and reassembled to form a shaped pulse corresponding to the Fourier transform of the mask.
In this technique, care is taken to cancel or avoid temporal dispersion of the pulse frequencies.
While high resolution has been demonstrated, present technology does not allow affordable high-speed, real time programmability for applications such as optical communications utilizing this spatial dispersion technique.
In contrast, the present invention which is based upon temporal dispersion of the pulse frequencies overcomes this and other problems.
Some advantages of the present invention are: (1) pulse shapes can be programmed in real time and only a single, serial modulator need be used for such programming; (2) higher resolution shaping, e.
g.
, resolution by at least a factor of six better than that of the Haner and Warren technique, is possible; (3) ultra-short (e.
g.
, in the order of 100 femtoseconds) pulses for greater information density is possible; (4) any output pulse shape may be obtained within limits set by the bandwidth and resolution requirements of the system; and (5) the complication of nonlinear propagation in optical fiber can be avoided.
Temporal dispersion techniques for pulse stretching and pulse compression have recently been reported in the literature