Toyokazu Sakamoto

Kerr-effect-induced S-R flip-flop operation in an optical fiber loop resonator with double couplers.

We carry out a theoretical analysis of Kerr bistability in a double-coupler optical fiber loop resonator in a case of two coexisting input optical fields, and we propose a set-reset (S-R) flip-flop operation that uses two input ports. We found that in the optimum case set and reset operation can be achieved at relatively low optical input powers.

Chaos in coupled semiconductor lasers with an electronic delayed feedback caused by injection locking

We proposed and demonstrated a novel hybrid chaotic system using injection locking in coupled laser diodes. This system consists of double laser diodes, a Fabry-Perot etalon, and an electronic delay feedback. The bifurcation diagram route to chaos and variation of the temporal waveform of the output light intensity were observed relative to the feedback gain. Some peculiar bifurcation properties, which were caused by a strong nonlinear effect due to injection locking, were observed. We also analyzed the experimental results using Van der Pole equations coupled with rate equations. The results of theoretical analysis showed good agreement with the experimental results.

Ray trace evaluation method of a multimode optical fibre grating demultiplexer using a GRIN-rod lens

Abstract An evaluation method based on a ray trace analysis is reported for a multimode optical fibre demultiplexer using a GRIN-rod lens and a blazed reflection grating. The validity of this evaluation method is assessed by reference to an existing demultiplexer and a fairly good agreement is obtained between the calculated performance and the experimental results for the previously reported device. An extensive tolerance analysis is also reported, to establish a basis for the fabrication of this device. The results of this analysis are given as a map of the 3 dB contour of the transmission loss.

Analytic Solutions of the Eikonal Equation for a GRIN-rod Lens

Abstract A systematic method based on the perturbation method is proposed for analytically solving the eikonal equation for a meridional ray in a GRIN-rod lens. Using this method, the perturbation solutions up to third order are derived together with those of the ray equation. The computational accuracy of the derived perturbation solutions is examined against the exact one for the sech index profile. At the typical numerical aperture 0·45 of a compact disc pickup objective, the accuracy of the second-order perturbation solution is found to be as high as 1/100 waves.

Optical Signal Inverter Using Injection Locking of Coupled Semiconductor Lasers

We propose and demonstrate a unique optical signal inverter using injection locking in coupled semiconductor lasers with a narrow-band Fabry-Perot (F-P) etalon. In this method, one laser diode is operated as a master laser to control the injection locking and the other is operated as a slave laser. By setting of the F-P etalon inside the coupled cavity, the locking and unlocking states can be allocated to the low and high levels for the output power, respectively. Under direct modulation of the master laser, the inverted light signal is available from the output port. This optical inverter can be operated at an output power of ~7 mW.

Optical Signal Inverter Based on Injection Locking of Laser Diode for Directly Modulated Optical Pulses

We constructed an optical signal inverter based on the injection locking of a laser diode and observed signal inversion for the pulse train emitted from a directly modulated laser diode. The inverter consists of two laser diodes and narrow-band Fabry-Perot etalons. The optical pulse train emitted from the master laser was injected into the slave laser whose free-running wavelength was about 3 nm away from the master laser oscillating wavelength. The free-running component of the slave laser output shows the inverted waveform of the injected pulse train. The optical signal inverter is suitable for high output power operation.

A 7/spl times/6 optical fiber grating demultiplexer-multiposition switch for 0.64-0.88 /spl mu/m band

An optical fiber grating demultiplexer-multiposition switch having seven demultiplexing channels and six position-switching channels is demonstrated. This device consists of a unique fiber array in which 42 output fibers are aligned radially around an input fiber, a single gradient-index (GRIN)-rod lens and a rotatable blazed reflection grating. In this device, seven demultiplexing channels can be switched to six different directions by rotating blazed reflection grating. Therefore, this device can realize total transmission channels of 42. The device had a working band of 0.64-0.88 /spl mu/m, a channel separation of 35-42 nm and a 3 dB band width of 18-22 nm. The deviations of center wavelengths among the switching channels were suppressed less than 3 nm.

Optical Fibre Grating Demultiplexer-multiposition Switch Using a Single Gradient-index-rod Lens

Abstract An optical fibre device using a single gradient-index (GRIN)-rod lens and a rotatable blazed reflection grating is proposed for simultaneously realizing the functions of both demultiplexing and multiposition switching. An example of design using the commercially available GRIN-rod lens is shown for the 0·8 μm band multimode fibre use. An extensive tolerance analysis is also done as a basis for fabricating this device. In addition, the potential of a GRIN-rod lens is clarified in terms of the channel separation and the transmission loss.

Nonlinear Dynamics in Directly Modulated Self-Pulsating Laser Diodes with a Highly Doped Saturable Absorption Layer.

Nonlinear dynamics in directly modulated self-pulsating laser diodes with a highly doped saturable absorption layer was experimentally and theoretically investigated. Commercially available 660 nm laser diodes developed for digital versatile disk (DVD) systems were used in the experiment. Not only stable pulsations locked to the modulation frequency or its subharmonics, but also unstable pulsations and unique frequency-locked pulsations in which multiple spikes appear within some modulation periods were observed. The numerical calculations based on the rate equations explain well the observed nonlinear dynamics.

Analytic Solutions of the Eikonal Equation for a GRIN-rod Lens 2. Skew Rays

Abstract Analytic solutions of the eikonal equation for a skew ray in a GRIN-rod lens are derived together with those of the ray equation by the perturbation method. It is algebraically shown that the derived solutions agree with the exact ones for a meridional ray in the sech profile and for a helical ray in the helical exact profile. The numerical accuracy is also examined by the Runge-Kutta-Gill method for the sech profile.