Osamu Mikami

Polarization insensitive traveling wave type amplifier using strained multiple quantum well structure

Signal gain agreement between TE and TM modes is realized under a specific operation condition in a traveling wave type amplifier using a strained multiple quantum well structure for the first time. The signal gain of the TM mode completely agrees with that of the TE mode at an amplifier driving current of 70 mA. The identical signal gain is 7.5 dB at present. However, the signal gain could be easily improved by using a device with a longer active region. In order to achieve polarization insensitive TWAs, the design parameter is the only confinement factor for the conventional bulk type.<<ETX>>

Impact ionization rates in an InGaAs/InAlAs superlattice

An In0.53Ga0.47As/In0.52Al0.48As superlattice avalanche photodiode is fabricated by molecular beam epitaxy, and ionization rates are measured. The electron ionization rate is enhanced by a factor of 20 over hole ionization rate. This is the first time that such a remarkable increase has been observed for a superlattice. The increase is attributed to the large conduction‐band offset.

LiNbO3 coupled‐waveguided TE/TM mode splitter

A novel optical TE/TM mode splitter was fabricated using Ti‐diffused LiNbO3 coupled waveguides. This splitter can spatially separate the TE and TM mode components and is compatible with single‐mode fiber systems. Crosstalk less than −20 dB was realized at 1.15‐μm wavelength. Optical insertion loss was 1.7 dB.

Polarization-insensitive optical amplifier with tensile-strained-barrier MQW structure

A new approach to achieving a polarization-insensitive semiconductor optical amplifier is presented. The active layer consists of a tensile-strained-barrier MQW structure that enhances TM mode gain. Polarization sensitivity below 0.5 dB is realized at a wavelength of 1.56 /spl mu/m. A signal gain of 27.5 dB is obtained along with a saturation output power of 14 dBm. Deriving the refractive indices of well and barrier layers from both experiment and theory, we succeed in separation of the effect of the confinement factor and the gain coefficient. It is determined that TM mode gain enhancement in this structure is primarily due to the increase in the confinement factor. >

Dependence of the GaAs/AlGaAs superlattice ionization rate on Al content

Al content dependence of GaAs/Alx Ga1−xAs superlattice ionization rates was studied. The electron ionization rate is enhanced when the AlGaAs of the barrier is a direct transition type. It is drastically reduced at the Γ‐X band crossover in the AlGaAs layer. The ionization rate ratio (hole to electron) as determined by excess multiplication noise measurement is reduced from a value of 0.5 at x=0.3 to 0.14 at x=0.45. At higher values of x, corresponding to the onset of indirect electron transitions, the noise is increased.

Broader spectral width InGaAsP stacked active layer superluminescent diodes

Fabrication and characteristics of broader spectral width 1.3 μm and 1.5 μm InGaAsP superluminescent diodes having a novel stacked active layer (STAC‐SLDs) structure are reported. The emission spectral width is successfully broadened as much as twice that of conventional SLDs, yielding spectral widths of 80 and 140 nm for the 1.3 μm and the 1.5 μm SLD, respectively.

DESIGN CALCULATIONS FOR DIRECTIONAL COUPLERS FABRICATED BY Ti-DIFFUSED LiNbO//3 WAVEGUIDES.

Coupling characteristics for designing a LiNbO(3) directional coupler fabricated by Ti diffusion have been investigated with a modified WKB method. The present analysis is verified by comparing the refractive-index change in the Ti-diffused LiNbO(3) waveguide derived from direct measurement and coupling length calculation. Coupling length variations due to refractive-index change, diffusion length waveguide spacing, and wavelength are described. Tolerances in coupling length mismatch and propagation constant differences affecting cross talk of the directional coupler are discussed.

Self-written waveguide on a VCSEL-emitting window using a photomask transfer method

This study is focused on a self-written waveguide (SWW) fabricated using a new photomask transfer method. With the proposed photomask transfer method, an SWW array was successfully fabricated on vertical-cavity surface-emitting laser (VCSEL) diode-emitting windows. It was found that the output power of a VCSEL having the SWW increased as compared to that of VCSEL without the SWW. We have confirmed that the optical output is independent of the placement of the emitting window inside the SWW. Optical coupling between an SWW and a graded-index multimode fiber was also demonstrated

TE/TM mode selective channel waveguides in GaAs/AlAs superlattice fabricated by SiO2 cap disordering

Novel structure TE/TM mode selective optical channel waveguides are proposed and fabricated in GaAs/AlAs superlattices (SLs) using impurity‐free disordering induced by SiO2 cap annealing. The disordered SL regions are found to be useful as low‐loss waveguides even at a wavelength close to the absorption edge of the as‐grown SL. By observing the near‐field patterns, it is confirmed that these channel waveguides could selectively confine TE or TM polarized light.

Single-mode optical-waveguide fiber coupler

A single-mode fiber coupler to the Ti diffused LiNbO(3) strip waveguide has been devised. The influences of three axial displacements and two angular misalignments on the coupling efficiency have been investigated at 6328-A wavelength. The coupler has a special feature wherein coupling degradation caused by fiber displacement after connection can be recovered to the initial state. The total optical insertion loss is 3 dB after fixing the fiber to the LiNbO(3) strip waveguide, which is 4 microm wide and 8 mm long.