Takahiro Numai

SURFACE-EMITTING LASER OPERATION IN VERTICAL-TO-SURFACE TRANSMISSION ELECTROPHOTONIC DEVICES WITH A VERTICAL CAVITY

We demonstrate the first surface‐emitting laser operation in a vertical‐to‐surface transmission electrophotonic device with a vertical cavity. The thyristor‐like current‐voltage characteristics, which are required for optical and electrical switching, are achieved. Threshold current during the on state is as low as 1.2 mA. All 100 devices, which were randomly extracted from a grown wafer, emit laser light.

Analysis of repeated unequally spaced channels for FDM lightwave systems

In long-haul optical frequency-division-multiplexing (FDM) systems, transmission characteristics are degraded by four-wave mixing (FWM). To overcome this problem, repeated unequally spaced (RUS) channels have been recently proposed as a new frequency allocation. In this paper, frequency distribution and intensity of generated FWM lights, and a total bandwidth of signal lights of RUS channels are compared with those of already known equally spaced (ES) and unequally spaced (US) channels. It is found that intensities of generated FWM lights of RUS are less than those of ES when the number of channels and a total bandwidth of signals are common in both channels. It is also revealed that RUS has a narrower total bandwidth than US when the number of channels and the minimum channel spacing are common in both channels. Since RUS simultaneously satisfies a low FWM light intensity and a narrow signal bandwidth, it is considered that RUS is suitable for FDM lightwave transmission systems.

1.5 μm tunable wavelength filter using a phase-shift-controlled distributed feedback laser diode with a wide tuning range and a high constant gain

We demonstrate a 1.5 μm tunable wavelength filter which uses a newly developed phase‐shift‐controlled distributed feedback laser diode. A tuning range as wide as 120 GHz (9.5 A) with 24.5 dB constant gain has been achieved. An 18‐channel wavelength selection with less than −10 dB crosstalk is expected with this filter.

Reduction in the series resistance of the distributed Bragg reflector in vertical cavities by using quasi‐graded superlattices at the heterointerfaces

Surface emitting optical devices with a vertical cavity have been investigated for applications in optical interconnections. To integrate these devices into a two‐dimensional array, it is necessary to improve the conversion efficiency from electrical power to optical power. To meet this requirement, the series resistance of the distributed Bragg reflectors that form the vertical cavity must be reduced. This article demonstrates the reduction in the series resistance of the distributed Bragg reflector by introducing quasi‐graded superlattices at the heterointerfaces. By using this structure, we obtain a low series resistance distributed Bragg reflector without compromising the high reflectivity. The mechanism of the reduction in the series resistance is studied and it is found that an increase in tunneling current leads to a decrease in the resistance. The dependence of tunneling current on doping concentration of the distributed Bragg reflector and the superlattice structure is also discussed.

Current versus Light-Output Characteristics with No Definite Threshold in pnpn Vertical to Surface Transmission Electro-Photonic Devices with a Vertical Cavity

We demonstrate surface-emitting laser operation in pnpn structure vertical to surface transmission electro-photonic devices (VSTEPs) with a vertical cavity, i.e., VC-VSTEPs. Continuous-wave (cw) laser operation at room temperature is achieved with a VC-VSTEP mounted directly on a glass sheet with no heat sink. The threshold current is 3 mA for a 10 µm square device. In pulsed operation, this device shows current vs light-output characteristics with no definite threshold. The light output spectrum shows single mode operation in which the spectral width is the same value as the resolution of a spectrometer.

Record Low Threshold Current in Microcavity Surface-Emitting Laser

We demonstrate a record low threshold current of 190 µA in a microcavity surface-emitting laser with a 5-µm-diameter airpost, in pulsed operation at room temperature with no heat sink. This low threshold current is attributed to high-quality epitaxial layers and a dry-etched smooth sidewall.

Tunable wavelength filters using λ/4-shifted waveguide grating resonators

We report on wide tuning range 1.5 μm wavelength filters using λ/4‐shifted waveguide grating resonators. A tuning range of a transmission resonance wavelength as wide as 42 A by carrier injection and two‐channel wavelength signal switching was achieved.

Self-Organized CdSe Quantum Dots on (100)ZnSe/GaAs Surfaces Grown by Metalorganic Molecular Beam Epitaxy

II–VI semiconductor low-dimensional structures, quantum dots, have been grown on GaAs substrates by metalorganic molecular beam epitaxy (MOMBE). Before the heteroepitaxial growth, atomically flat, As-stabilized GaAs surfaces were prepared by high-temperature As cleaning using tris-dimethylamino-arsenic (TDMAAs). CdSe thin films deposited on (100)ZnSe/GaAs surfaces have been investigated with atomic force microscopy (AFM) and were found to form three-dimensional islands with rather uniform size distribution. A large mismatch (~7%) of lattice constants between CdSe and ZnSe pseudomorphically grown on GaAs possibly results in the Stranski-Krastanov growth mode. CdSe quantum dots with a diameter of 97±11 nm were successfully formed at 350°C.

1.5 μm tunable wavelength filter with wide tuning range and high constant gain using a phase‐controlled distributed feedback laser diode

We demonstrate a 1.5 μm tunable wavelength filter which uses a phase‐controlled distributed feedback laser diode. Tuning range as wide as 43 GHz (3.4 A) with 27 dB constant gain has been achieved. A five‐channel wavelength selection with less than −10 dB crosstalk is expected with this filter.

1.5 mu m phase-shift-controlled distributed feedback wavelength tunable optical filter

A 1.5- mu m phase-controlled distributed feedback wavelength-tunable optical filter is studied. This is the first optical filter which controls the transmissivity (gain) and the transmission wavelength independently. Wavelength tuning range as wide as 43 GHz (3.4 AA) with high constant gain of 27 dB has been achieved. A five-channel wavelength selection with less than -10 dB crosstalk is expected with this filter. This device also operates as a wavelength tunable laser, and the wavelength tuning range as a laser is larger than as a filter. The reason is studied, and it is shown that suppression of the submodes is important to expand the wavelength tuning range. >