Soichi Kobayashi

Nonlinear optical materials derived from biopolymer (DNA)-surfactant azo dye complex

This paper reports on optical and optoelectronic properties of DNA-surfactant complex films which were intercalated with a NLO dye, Disperse Red 13(DR-13). Circular dichroism (CD) analysis indicated that the orientation of the azo dye, DR-13 doped in DNA-surfactant complex film was achieved by inserting the dye molecules into the nano-size space between base pairs of DNA. The Disperse Red 13-doped DNA thin film displayed higher THG than that of CS2 about two orders. On the other hand, SHG signal could not be observed even in the presence of anisotropic ordering of the molecular chromospheres on template of the double helix of DNA, perhaps because of absorption of the dye for SHG light.

Narrow Tunable Polysilane Optical Waveguide Bragg Grating Filters

A new Bragg grating filter (BGF) in a polysilane waveguide has been fabricated by a two-beam interferometric photobleaching method using a He-Cd laser. A narrow reflected bandwidth of 0.4 nm was measured using a 1.55-mum light-emitting diode. The temperature dependence of the BGF was measured as 0.096 nm/degC with temperature control over a range between 30 degC and 70 degC and exhibited a good coincidence with the theoretical values

Spectral-Phase Characterization and Adapted Compensation of Strongly Chirped Pulses from a Tapered Fiber

A computer-controlled feedback system that combined a modified spectral-phase interferometer as a direct electric-field reconstruction apparatus and a 4-f pulse shaper with a spatial phase modulator as a programmable chirp compensator was developed. The system enabled us to successfully characterize the complex spectral phase and temporal intensity profile of a weak peak-intensity pulse from a tapered fiber with a high sensitivity comparable to that of the conventional interferometric autocorrelator. In addition, we were able to compress for the first time 185 fs fiber input pulses to 16 fs with subpulses originating from the beat between two splitting-spectral components of the fiber output.

Improvement in Intensity Fluctuation Noise of a 1 Gbit/s-Modulated InGaAsP Laser by a Light Injection Technique

The effect of laser light injection on the mode spectrum and intensity fluctuation noise of an InGaAsP semiconductor laser modulated at 1 Gbit/s was studied. The power ratio of the injected mode to the total emitting mode was improved to 0.9, in comparison with 0.3 without injection. The intensity fluctuation noise in one longitudinal mode, caused by mode competition, was also reduced by 8 dB at 10 MHz, compared with systems without injection.

Automatic frequency control in a semiconductor laser and an optical amplifier

Automatic frequency control (AFC) in an injection locked or resonant type amplifier in an AlGaAs semiconductor laser was achieved through using the terminal voltage change induced by light injection. Signal-to-noise ratio in the control signal of 10 dB was obtained when the input optical power was -47 dBm and the optical gain Was 51 dB. The AFC was maintained for 3 h with an 0.3-percent output power fluctuation for 2°C ambient temperature change and 65-MHz frequency stability. Step response showed that the system response time was 1.5 s. Sensitivity to input optical power deteriorates at -49 dBm, with a 53-dB locking gain, because of frequency deviation caused by temperature modulation. The second derivative of the induced voltage and its relation to the optical frequency is constant at 5 \times 10^{-10} [V/(MHz)2] for all input power levels in a buried-heterostructure (BH)-AlGaAs laser. Terminal voltage change induced by light injection is calculated by simple rate equations with a Gaussian-Halperin-Lax (GHL) bandtail model. Good agreement with experimental results was seen.

Optically controlled photonic switches based on spiropyran-doped marine-biopolymer DNA-lipid complex films

Optical switching properties based on the photochromism of spiropyran-doped DNA-lipid complex films have been studied. On-off switching of the incident light under the alternate excitation of UV- and visible light showed strong dependence of the intensity of the excitation light. We have obtained the switching times of around 200-300ms, but much faster response could be expected since the proportional tendency has not been saturated yet.

Optical and photochromic properties of spiropyran-doped marine-biopolymer DNA-surfactant complex films

Optical and photochromic properties of spiropyran-doped DNA-surfactant complex films have been studied. They strongly depended on the type of spiropyran as well as the type of surfactant. Spiropyrans containing the oxazine ring and intercalated into DNA showed very rapid photochromic response. It is also shown that photochromic response times are expected much faster by increasing the intensity of the excitation light.

Optical properties of photochromic-compound-doped marine-biopolymer DNA-surfactant complex films for switching applications

Optical properties of spiropyran-doped DNA-CTMA films have been studied. They strongly depended on molar ratio of DNA/spiropyran. Switching experiments was performed for 1.55-μm signal light. Measured slow transition times indicate much precise adjustment and optimization.

Polysilane Optical Waveguide Devices using Photo-bleaching Effect

The polysilane optical waveguide fabrications by using photo-bleaching technology with the UV lamp and the UV laser direct drawing technologies are reported. The characteristics of the 1xN optical waveguide splitters and the semiconductor tunable lasers (STLs) with polymer tunable external resonators are presented. An average propagation loss of the straight waveguide was less than 0.7dB/cm at 1550 nm. PDL was measured less than 0.5 dB in the case of 1×8 splitter. The insertion loss of 1×4 splitter patterned by laser drawing method was measured less than 7.5 dB/cm. In the STLs the external resonator consists of a singlemode polysilane waveguide and a Bragg grating filter. The power ratio between main and side modes was over 30 dB. Laser power was measured as 5.6 mW at 70% reflective index of the Bragg grating.

Phase and amplitude comparison between experiment and calculation of ultrabroad-band pulses generated in a taper fiber

Using a cross-correlation frequency-resolved optical gating apparatus, the phases and amplitudes of ultrabroad-band optical pulses from a taper fiber have been measured for various input pulse peak powers. The measured waveforms have been compared with calculated waveforms using a finite-difference in the frequency domain method, in which no envelope approximations were used and the variation of the taper shape was taken into account. Excellent agreement between the measured and the calculated waveforms was obtained when the additional dispersion of a normal fiber and an objective was considered.