Principle of a single shot demultiplextion by means of time-to-space conversion was investigated using femtosecond nonlinear optical response of absorption bleaching of squarylium dye (SQ) J-aggregates. Spincoated films of squarylium dye J-aggregates on glass substrates exhibit efficient and ultrafast transmittance change, which recovers 73% of its initial level (0 fs) within 1 ps. A simple method for time-to-space conversion was applied for this film. We took our attention to one of the characteristics of femtosecond pulse, which is the spatial thinness in its propagation direction. Femtosecond pulses of a single pump pulse and train of four probe pulses were illuminated to the same area (diameter of 10 mm) of the surface of the SQ J-aggregates film. Direction of the probe beam was normal to the surface of the film and that of the pump beam was oblique angle in horizontal plane. Caused by spatial delay of a pump pulse due to the illumination in oblique angle to the film, four probe pulses with interval time of 1 ps (1 THz) meet separate places on the film. Because of the fast response of the SQ J-aggregates, the film picked out part of each probe pulse, which has narrower shapes in horizontal direction compared to the initial circular one by transmittance change of the film. The spatially separated four lines were observed by a CCD camera for an image of the transmitted probe pulse train. These results suggest that the response time of SQ J-aggregate film, which determines the horizontal width of each line, to be enough for demultiplexing of 1 THz optical signals.

We fabricated ultrafast nonlinear optical films of squarylium J-aggregates and studied their properties including the absorption spectrum, the refractive index, the third-order nonlinear optical coefficients, the extent of absorption saturation, and the recovery of absorption saturation. The transmittance of the film was increased by 30% due to absorption saturation at a pump energy of several hundreds fJ/µm2/pulse. The half decay time constant of absorption saturation was found to be approximately 100 fs for off-resonant excitation. Two-dimensional demultiplexing was demonstrated using the squarylium film as a switching material. From a train of 8 optical pulses with 100 fs duration and 1 ps interval corresponding to a bit rate of 1 Tbps, 24 spatially resolved spots were obained.