Abstract

Second-harmonic generation has been observed in glass optical fibers¹ prepared by an intense light at 1064 nm with a simultaneous seeding light at double frequency, although the centrosymmetric structure of silica forbids any second-order optical nonlinearity. It can be interpreted in terms of nonclassical holographic processes with coherent multifrequency fields.² Indeed the interference between a light wave and its second harmonic leads to a nonzero average cube of the optical field resulting of the coherent superposition of the two fields at ω and 2ω frequencies. In glass, however, the magnitudes of the induced nonlinearities remain quite weak. In view of these limitations a new breakthrough has emerged after recent demonstration of photoinduced bulk transient χ⁽²⁾-grating in organic solutions. Indeed large benefit can be derived from highly nonlinear molecules and the potentiality of molecular engineering in organics is enormous.

© 1994 IEEE