Mizuki Shirao

Lateral current injection GaInAsP/InP laser on semi-insulating substrate for membrane-based photonic circuits

A room-temperature pulsed operation was demonstrated using lateral current injection-type lasers composed of a 400-nm-thick GaInAsP core layer with compressively strained 5 quantum wells. A threshold current of 105 mA and corresponding density of 1.3 kA/cm(2) (260 A/cm(2) per well) were obtained with the stripe width of 5.4 microm and the cavity length of 1.47 mm. A fundamental transverse mode operation was obtained with the narrower stripe device of 2.0 microm and the cavity length of 805 microm, while the threshold current and corresponding density were 49 mA and 3.0 kA/cm(2), respectively.

Large-Signal Analysis of a Transistor Laser

Small- and large-signal analyses of transistor lasers (TLs) are demonstrated for 0.98-μm wavelength GaInAs/GaAs and 1.3-μm AlGaInAs/InP systems. The modulation bandwidth of the TL was larger than that of a laser diode due to the lower damping effect in the former. Comparisons between TLs with different numbers of quantum wells indicated that a large signal response and high modulation bandwidth could be realized simultaneously. However, in the case of large-signal analysis, the calculated eye diagrams were degraded by a resonance oscillation peak. By changing structural parameters such as the facet reflectivity and by controlling the damping effect, the resonance frequency peak was suppressed and clear eye diagrams of >;40 Gb/s were obtained.

Improved Regrowth Interface of AlGaInAs/InP-Buried-Heterostructure Lasers by In-Situ Thermal Cleaning

The influence of in-situ thermal cleaning on the regrowth interface quality of 1.3-μm wavelength AlGaInAs/InP-buried-heterostructure (BH) lasers grown by organo-metallic vapor-phase epitaxy was investigated. The surface recombination velocity estimated from below threshold electroluminescence measurements was used to quantitatively study regrowth interface quality. The relationship between surface recombination velocity and lasing properties was supported by theory. In this way, we could validate the use of surface recombination velocity as a measure of interface quality. In-situ thermal cleaning at 650°C for 45 min under PH3 atmosphere resulted in operational BH lasers (1.6 μm stripe width) with a differential quantum efficiency of 66% and an internal quantum efficiency of approximately 76%.

Design and Characterization of AlGaInAs/InP Buried Heterostructure Transistor Lasers Emitting at 1.3-μm Wavelength

We discuss the wafer design and fabrication process for the 1.3-μm-wavelength AlGaInAs/InP transistor lasers, and the structural dependence of lasing and the electrical characteristics are shown. We particularly focus on the base structure, and the thickness and width dependence are numerically and experimentally analyzed. A thicker base layer resulted in lower optical confinement factor in the quantum wells (QWs), higher optical loss, and lower current gain. In addition, a wider base width caused leak current recombination outside the QWs. By modifying the structure of an n-p-n TL, it was possible to simultaneously realize room-temperature continuous-wave lasing and transistor operation.

Room-temperature operation of npn- AlGaInAs/InP multiple quantum well transistor laser emitting at 1.3-µm wavelength.

Room-temperature pulsed operation of a 1.3-µm wavelength transistor laser (TL), consisting of a buried heterostructure (BH) with an npn configuration and an AlGaInAs/InP multiple-quantum-well (MQW) active region, was successfully attained. A threshold base current of 18 mA (threshold emitter current of 150 mA) was obtained with a stripe width of 1.3 µm and a cavity length of 500 µm. The transistor activity as well as the lasing operation were achieved at the same time, which is essential for the high-speed operation of TLs.

Theoretical analysis of the damping effect on a transistor laser

The impact of carrier pulling on the modulation characteristics of a transistor laser is discussed. The results of a theoretical analysis of modulation bandwidth and damping effect show that the carrier transport effect obtained by using a transistor laser allows for a gain compression factor of about one-tenth that of a conventional laser (0.7×1017 cm3), as well as for a maximum modulation bandwidth of 45 GHz.

Room-Temperature Continuous-Wave Operation of 1.3-µm Transistor Laser with AlGaInAs/InP Quantum Wells

The room-temperature continuous-wave operation of a 1.3-µm AlGaInAs/InP transistor laser (TL) with a pnp configuration was achieved for the first time. A threshold emitter current density of 1.9 kA/cm2 was obtained for a stripe width of 1.8 µm and a cavity length of 500 µm, and it was controlled by the collector–base bias. Despite a current gain of 0.01, three terminal operation of the laser, i.e., the control of the output power by the collector–base voltage as well as the emitter current was demonstrated.

Preliminary Experiment on Direct Media Conversion from a 1.55 µm Optical Signal to a Sub-Terahertz Wave Signal Using Photon-Generated Free Carriers

A novel method of direct media conversion from an optical signal to a terahertz (THz) signal using free carriers generated by photons and the skin effect is proposed. A semiconductor modulator absorbs modulated optical signals and generates free carriers. These free carriers inside the modulator absorb THz waves owing to the skin effect, thereby creating an inverted pattern signal of the THz wave with respect to the optical signal. In preliminary experiments using 192 GHz continuous waves and a 1.55 µm optical signal, a modulation depth of 45% and a modulation speed of up to 1 MHz were demonstrated.

Room-Temperature Continuous-Wave Operation of npn-AlGaInAs Transistor Laser Emitting at 1.3-

Room-temperature continuous-wave operation of a 1.3-μm npn-AlGaInAs/InP transistor laser is successfully achieved for the first time. A threshold current of 39 mA and an external differential quantum efficiency of 13% are obtained under common base operation, while simultaneous transistor action is achieved with a current gain β of 0.02.

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High-speed direct modulation capability was investigated in 1.55-μm GaInAsP/InP distributed reflector (DR) lasers with wirelike active regions in terms of carrier transport from GaInAsP optical confinement layers (OCLs) to the active regions. Theoretical analysis revealed strong dependence of the modulation bandwidth on the thickness of the OCLs and width of the wirelike active regions. To confirm this prediction, two DR lasers with OCLs of different thicknesses (120 and 40 nm) were fabricated and their 3-dB bandwidths (f3 dB) under small-signal modulation were compared. The device with the narrower OCL exhibited f3 dB exceeding 15 GHz and clear eye opening under 25 Gb/s modulation, whereas that with the thicker OCL had f3 dB of only 2 GHz. These results were in good agreement with the theoretical predictions.