Satoshi Tatsuura

Nonlinear optical properties of an organic film formed of dye aggregates with absorption in the telecommunication wavelength range

An organic film formed of newly synthesized dye aggregates with an absorption peak in telecommunication wavelength range exhibited large third-order nonlinear optical susceptibility χ(3) and fast recovery of bleached absorption. A derivative with a di(benzofuranonyl)methanolate structure forms stable aggregates in a spin-coated film and shows an absorption maximum at 1.24 μm. An imaginary part χI(3) of the film assumes a maximum at 1.30 μm, which is −0.83×10−7 esu. The time evolution of differential transmission spectra indicates that the time constant of the recovery of bleached absorption is 80–240 fs for a fast component and 2.2–6.5 ps for a slow one. This organic film has considerable advantages for future planar optical devices.

Ultrafast all-optical switching at 1.55μm using an organic multilayer device

We report ultrafast all-optical switching at optical communication wavelength using a device with a layered structure containing organic films. Spin-coated layers of di(benzofuranonyl)methanolate (BM) derivative are formed alternately with vacuum evaporated layers of germanium (II) oxide. An optical Kerr shutter is constructed using this BM multilayer with 1.55μm signal and 1.63μm gate pulses of 100fs time durations. As a result, optical switching with signal-to-noise ratio over 20dB is attained at gate-pulse intensity above 30pJ∕μm2 and a response time comparable to pulse width is observed. The BM multilayer could be an efficient optical communication device for parallel data processing.

Synthesis of new squaraine dyes for optical switches

This work describes the synthesis of new, highly soluble squaraine dyes, which have absorption maxima over 900 nm in solution. The absorption spectra of their spin-coated films show broad absorption bands, which are caused by aggregation phenomena. The absorption bands in the solid phase are red-shifted compared to those in solution. Because of these characteristics and nonlinear optical data which were obtained by Z-scan measurements, the new substances are principally useful for optical switches.

Cadmium telluride bulk crystal as an ultrafast nonlinear optical switch

A semiconductor bulk crystal has several advantages as a nonlinear optical material, such as low processing cost, long interaction length, and alleviation of the free-carrier absorption caused by two-photon absorption (TPA). We examine optical properties of semiconductor bulk crystals with different orientations at 1.55μm and find that CdTe[111] has favorable capabilities, such as nonlinear refractive index of 5.23×10−17(m2W), TPA coefficient of 18.3(mmGW), and consequent figure of merit of 0.54. Optical three-dimensional measurements of reflective material are carried out using CdTe[111] as ultrafast optical Kerr shutter and clear images corresponding to surface steps are obtained.

Optical gate action of a molecular thin film probed with femtosecond near-field optical microscopy

We have combined a near-field scanning optical microscope with a two-color time-resolved pump–probe measurement system. The sample was a molecular thin film that revealed an excitonic resonance and also had a characteristic domain structure. The measurement system has a noise-equivalent transmittance change as small as 5.0×10−5 for a probe pulse with an intensity of 30 nW, which allows us to detect an optical gate action of a single domain. The results suggest that the film composition is uniform over a distance of several microns while it may vary on a greater scale.

Terabit all-optical logic based on ultrafast two-dimensional transmission gating

Terabit all-optical complementary logic is proposed using two successive time slots to represent a unique logical status. An organic molecular thin film is used as an array of optically controlled optical switches. By utilizing the planar structure of the film and its ultrafast optical response, proof-of-principle fully optical NOT and AND logic operations were demonstrated with 400-fs interval pulses.

Femtosecond timing measurement and control using ultrafast organic thin films

We show a femtosecond timing measurement and control technique using a squarylium dye J-aggregate film, which is an organic thin film that acts as an ultrafast two-dimensional optical switch. Optical pulse timing is directly mapped to space-domain position on the film, and the large area and ultrafast response offer a femtosecond-resolved, large dynamic range, real-time, multichannel timing measurement capability. A timing fluctuation (jitter, wander, and skew) reduction architecture is presented and experimentally demonstrated.

Microstructure of squarylium dye J aggregate films examined on the basis of optical behavior at low temperature

The microstructure of a spin-coated film of squarylium dye J aggregates is examined on the basis of the measurement of the optical properties and the third-order nonlinear optical susceptibility χ(3) at low temperature. The absorption maximum of J aggregates shifted to lower energies as the film temperature decreased, while χ(3) was independent of the temperature. The latter finding indicates that the coherent length of J aggregates is confined by a structural boundary rather than by phonons; consequently, the observed peak energy shift can be due to temperature-dependent conformational change of the aggregates. The small aggregation size may contribute to the ultrahigh-speed optical response of squarylium dye J aggregates.

Enhancement of /spl chi//sup (3)/ of squarylium dye j-aggregates in infrared region by two-photon resonance

Third-order nonlinear optical coefficient (/spl chi//sup (3)/) of organic J-aggregate film was measured in infrared region using Z-scan technique. Enhancement of /spl chi//sup (3)/ due to two-photon resonance was clearly observed, demonstrating the possibility of operation at telecommunication wavelength.

Serial-to-parallel conversion of femtosecond optical pulses using organic optical shutter

Summary form only given. Time-to-space conversion of femtosecond pulses were reported recently. We propose a new concept of serial-to-parallel pulse conversion based on time-to-space conversion, using an organic film as a two-dimensional array of ultrafast optical shutters. As we have already reported, spincoated films of squarylium (SQ) J-aggregates exhibit the bleached absorption at 775 nm and the absorption change relaxes within 200-300 fs. Thus, a SQ film with a large area is used as an array of femtosecond optical shutters. Using this organic optical shutter, we constructed an optical system, which converts serial pulses of 1-THz repetition rate to parallel output pulses by a single femtosecond gate pulse.