Yoshiaki Nakano

Facet reflection independent, single longitudinal mode oscillation in a GaAlAs/GaAs distributed feedback laser equipped with a gain‐coupling mechanism

By loading periodic loss perturbation into a GaAlAs/GaAs distributed feedback laser, we have realized complete single longitudinal mode oscillation which is hardly disturbed by cleaved facet reflection. Our coupled‐mode analysis explains this empirical result well.

Demonstration of an optical isolator with a semiconductor guiding layer that was obtained by use of a nonreciprocal phase shift

We present the experimental study of an optical isolator with a semiconductor guiding layer that was obtained by use of a nonreciprocal phase shift. The isolator is equipped with an optical interferometer composed of tapered couplers, nonreciprocal phase shifters, and a reciprocal phase shifter. The nonreciprocal phase shifter was constructed by wafer direct bonding between the semiconductor guiding layer and the magneto-optic cladding layer. The isolator, designed for the 1.55-mum wavelength, was fabricated to investigate the characteristics of each component. By applying an external magnetic field to the nonreciprocal phase shifter, we achieved an isolation ratio of approximately 4.9 dB in the interferometric isolator.

All-optical flip-flop multimode interference bistable laser diode

All-optical flip-flop operation of multimode interference bistable laser diodes (MMI-BLDs) was experimentally demonstrated for the first time. The MMI-BLD was prepared with a conventional ridge waveguide laser diode fabrication procedure, suitable for photonic integrated circuits. Bistable switching via two-mode bistability was obtained with approximately 0-dBm input powers due to cross-gain saturation and the saturable absorbers. Bit-length conversion was successfully obtained with noninverted and inverted outputs. This device will be useful in future photonic systems requiring all-optical latching functions such as optical memory, self-routing, and further optical signal processing.

Talbot interferometry for measuring the focal length of a lens

A method for measuring the focal length of lenses using the Talbot effect and the moire technique is described. The test lens is placed in front of a set of two gratings. The first grating illuminated by the light passing through the test lens produces the magnified Talbot image. The moire fringe is generated by superimposing this Talbot image on the second grating. The tilt angle of the moire fringe is a measure of the focal length of the lens. In the experiments, the focal lengths of positive, negative, and power-distributed lenses are measured.

Fabrication and characterization of an InGaAsP/InP active waveguide optical isolator with 14.7 dB/mm TE mode nonreciprocal attenuation

The authors have fabricated transverse electric (TE) mode InGaAsP/InP active waveguide optical isolators based on the nonreciprocal loss shift and demonstrated improved TE mode isolation ratio of 14.7 dB/mm with reduced insertion loss at a wavelength of 1550 nm for monolithically integrable optical isolators. The wavelength dependence of the isolation ratio and the propagation loss were also measured. An isolation ratio greater than 10 dB/mm was realized over the entire wavelength range of 1530-1560 nm. These results lead to the monolithic integration of semiconductor waveguide optical isolators with edge-emitting semiconductor lasers and highly functional photonic integrated circuits with many cascaded optical devices.

Purely gain‐coupled distributed feedback semiconductor lasers

We propose a new distributed feedback (DFB) laser structure in which almost pure gain coupling can be embodied in principle, without sacrificing low threshold operation. An analysis of coupling coefficients has revealed the condition for canceling index‐coupling component. Utilizing organometallic vapor phase epitaxy, we have fabricated GaAlAs/GaAs ridge waveguide distributed feedback lasers having this structure. Excellent single longitudinal mode oscillation independent of facet reflection has been obtained along with low threshold current. The single‐mode spectrum has exhibited distinctive characters of purely gain‐coupled DFB lasers.

Thin Body III--V-Semiconductor-on-Insulator Metal--Oxide--Semiconductor Field-Effect Transistors on Si Fabricated Using Direct Wafer Bonding

We have demonstrated thin body III–V-semiconductor-on-insulator (III-V-OI) n-channel metal–oxide–semiconductor field-effect transistors (nMOSFETs) on a Si wafer fabricated using a novel direct wafer bonding (DWB) process. A 100-nm-thick InGaAs channel was successfully transferred by the low damage and low temperature DWB process using low energy electron cyclotron resonance (ECR) plasma. The transferred InGaAs-OI nMOSFET on the Si wafer exhibited a high electron channel mobility of 1200 cm2V-1s-1, indicating that the present DWB process allows us to form thin III-V-OI channels without serious plasma and bonding damage. This technology is expected to open up the possibility of integrating the ultrathin body III-V-OI MOSFETs on Si platform.

Measurements of phase objects using the Talbot effect and moiré techniques

In this paper, we describe deflection mapping of phase objects using a Talbot interferometer. To examine the deflection of light by the phase objects, the moire fringes are generated by superimposing the Fourier image of the first grating on the second one in the interferometer. The phase object is placed in front of the first grating. The light passing through the objects and impinging on the first grating produces the shifted Fourier image, and the resultant moire fringes give the deflection mapping, which depends on the distribution of the refractive index of the phase object. The experiments show deflection mapping of a piece of plastic plate and a candle flame. This technique is used for measuring the focal length of a lens.

III-V-semiconductor-on-insulator n-channel metal-insulator-semiconductor field-effect transistors with buried Al2O3 layers and sulfur passivation: Reduction in carrier scattering at the bottom interface

We have developed III-V-semiconductor-on-insulator (III-V-OI) structures on Si wafers with excellent bottom interfaces between In0.53Ga0.47As-OI channel layers and atomic-layer-deposited Al2O3 (ALD-Al2O3) buried oxides (BOXs). A surface activated bonding process and the sulfur passivation pretreatment have realized the excellent In0.53Ga0.47As-OI/ALD-Al2O3 BOX bottom interface properties. As a result, the III-V-OI n-channel metal-insulator-semiconductor field-effect transistors under the back-gate configuration showed the peak mobility of 1800 cm2/V s and the higher electron mobility than the Si universal one even in the high effective electric field range because of the reduction in the surface roughness and fixed charges.

Multimode interference bistable laser diode

We propose a novel bistable laser diode (BLD) with active multimode interference (MMI) cavity. Bistable switching can be realized between two cross-coupled modes by means of gain saturation. Static characteristics of the multimode interference (MMI)-BLD are analyzed using a finite-difference beam propagation method. The photon-carrier interactions are calculated using the carrier-rate equation. This model gives accurate distributions of photon and carrier densities, optical gain, and refractive index inside the cavity. We predict that the MMI-BLD shows bistable switching between the two cross-coupled modes by light injection, therefore allowing it to be used as all-optical flip-flop or optical memory.