Shigehisa Arai

The Temperature Dependence of the Efficiency and Threshold Current of In1-xGaxAsyP1-y Lasers Related to Intervalence Band Absorption

Measurements are presented of the temperature dependence of the differential quantum efficiency ηd and threshold current density Jth of 1.6 µm In1-xGaxAsyP1-y lasers. The observed sharp decrease in ηd near room temperature is interpreted as due to absorption associated with transitions of electrons from the split-off valence band into holes injected into and thermally generated within the heavy hole valence band. Preliminary calculations using conventional laser theory predict a temperature variation corresponding to T0145 K. This together with the influence of ηd, appears to be sufficient to explain most of the observed temperature variation of Jth.

Dynamic single-mode semiconductor lasers with a distributed reflector

Recent progress in the dynamic single-mode (DSM) semiconductor lasers in the wavelength of 1.5-1.6\mu m are reviewed and the basic principle of DSM operation is given. Study of the DSM laser is originated for application to the wide-band optical-fiber communication in the lowest loss wavelength region of 1.5 to 1.65 μm. A DSM laser consists of a mode-selective resonator and a transverse-mode-controlled waveguide, such as the narrow-striped distributed-Bragg-reflector (DBR) laser, so as to maintain a fixed axial mode under the rapid direct modulation. The technology of monolithic integration for optical circuits is applied to realize some of DSM lasers. Structures, static and dynamic characteristics of lasing wavelength, output power, and reliability of the art DSM lasers are reviewed. The dynamic Spectral width of 0.3 nm, the output power of a few milliwatts, and the reliability over a few thousand hours are reported for experimental DSM lasers.

The temperature dependence of the threshold current of GaInAsP/InP DH lasers

The temperature dependence of the threshold current of GaInAsP/InP lasers was considered in terms of linear gain, loss, and carder lifetime. The linear gain was calculated taking into account electronic intraband relaxation effects. The carrier lifetime, intraband relaxation time, loss in the active region, and dipole moment, all of which determine the threshold condition, were estimated from the experiments. The main loss mechanism which determines the temperature dependence of the differential quantum efficiency appears to be the absorption due to transitions between the split-off and heavy-hole valence bands. The temperature dependence of the theoretical threshold current Ithcalculated in terms of these parameters was compared with the measured results and reasonable agreement was obtained.

High-performance 1.55-/spl mu/m wavelength GaInAsP-InP distributed-feedback lasers with wirelike active regions

High-performance 1.55-/spl mu/m wavelength GaInAsP-InP strongly index-coupled and gain-matched distributed-feedback (DFB) lasers with periodic wirelike active regions mere fabricated by electron beam lithography, CH/sub 4//H/sub 2/-reactive ion etching, and organometallic vapor-phase epitaxial regrowth, whose index-coupling coefficient was more than 300 cm/sup -1/. In order to design lasers for low threshold current operation, threshold current dependences on the number of quantum wells and the wire width mere investigated both theoretically and experimentally. A record low threshold current density of 94 A/cm/sup 2/ among 1.55-/spl mu/m DFB lasers was successfully obtained for a stripe width of 19.5 /spl mu/m and a cavity length of 600 /spl mu/m. Moreover, a record low threshold current of 0.7 mA was also realized at room temperature under CW condition for a 2.3-/spl mu/m-wide buried heterostructure with a 200-/spl mu/m-long cavity. Finally, we confirmed stable single-mode operation due to a gain-matching effect between the standing-wave profile and the wirelike active region.

Lasing characteristics of 1.5 mu m GaInAsP-InP SCH-BIG-DR lasers

Higher differential quantum efficiency eta /sub df/, smaller chirp Delta lambda , narrower linewidth Delta nu , and high coupling efficiency C/sub out/ between active and passive regions of 1.5 mu m GaInAsP-InP SCH-BIG-DR lasers with a thin active layer and asymmetric gratings were experimentally demonstrated by a comparison of those properties of distributed feedback (DFB) lasers from the same wafer. A submode suppression ratio (SMSR) of more than 39 dB at 1.7 times the threshold current and a C/sub out/ of almost 100% in the SCH-BIG-DR lasers indicated that a separate-confinement-heterostructure (SCH) with a thin active layer and a bundle-integrated-guide (BIG) structure are quite adequate to realize high-performance distributed reflector (DR)-type lasers. >

Optically pumped membrane BH-DFB lasers for low-threshold and single-mode operation

High optical confinement and high index coupling in 1.55 /spl mu/m-wavelength GaInAsP-InP membrane buried heterostructure distributed feedback (BH-DFB) lasers consisting of deeply etched single-quantum-well wire-like active regions were demonstrated under room-temperature (RT) continuous-wave (CW) optical pumping. A threshold pump power of 1.5 mW and a submode suppression ratio (SMSR) of 42 dB were obtained for a 142-nm-thick membrane with a cavity length of 120 /spl mu/m and a stripe width of 2 /spl mu/m. We have also realized membrane BH-DFB laser arrays by arranging the laser cavities (10 /spl mu/m spaced 15 elements with five different grating periods). A total wavelength span of 72 nm was achieved with a small lasing wavelength fluctuation up to 1.2 nm at RT-CW condition under optical pumping. From this value, membrane thickness fluctuation was estimated to be 0.4 nm. Threshold pump power of 3.4 mW and SMSR of 45 dB were achieved in a typical device.

Light Emission from Quantum-Box Structure by Current Injection

Light emitting from quantum-box structure by current injection was observed for the first time. GaInAsP/InP quantum-box structures were fabricated from one-dimensional quantum-well (quantum-film) structures grown by OMVPE. Holographic lithography, wet etching, and LPE regrowth techniques were employed. Three-dimensional quantum size effect was suggested by the wavelength shift of the light emission.

Fabrication of Vertical and Uniform-Size Porous InP Structure by Electrochemical Anodization

A vertical porous InP structure with an aspect ratio larger than 100 was obtained by electrochemical anodization of a A-oriented n-InP substrate with HCl etchant. The photoluminescence spectrum of this porous InP showed less surface recombination as well as a slight blue shift attributed to the quantum-size effect. By initiating the etching through SiO2-defined mask windows, which were prepared by electron-beam direct writing along 3 crystalline directions, a uniformly sized (around 72% within the permissible fluctuation error of about 4 nm against 100-nm-sized triangles), high-density (around 50%) structure was fabricated for the first time. These results reveal that this process is very attractive for the fabrication of high-density and low-size-fluctuation quantum-wire and -box structures.

Strongly Index-Coupled Membrane BH-DFB Lasers With Surface Corrugation Grating

We realized strongly index-coupled membrane buried-heterostructure (BH) distributed-feedback (DFB) lasers fabricated by electron-beam lithography, CH4/H2 reactive-ion etching, and regrowth by organometallic vapor-phase epitaxy, using surface corrugation DFB. First, we fabricated narrow stripe membrane BH-DFB lasers with surface corrugation for stable single-mode operation. Under optically pumped room-temperature continuous-wave (RT-CW) operation, a wide stopband width of 68 nm was observed in spite of the narrow stripe width of 0.6 mum. The corresponding index-coupling coefficient of 2950 cm-1 is over two times larger than that of a flat-surface (conventional) membrane BH-DFB laser with a stripe width of 2.0 mum. In addition, we fabricated a short-cavity membrane DFB laser with a surface corrugation structure. A threshold optical pump power of as low as 0.34 mW was realized for a 2.0-mum-wide and 80-mum-long device under RT-CW conditions.

Reduction of effective linewidth enhancement factor alpha /sub eff/ of DFB lasers with complex coupling coefficients

The effective linewidth enhancement factor alpha /sub eff/ of DFB lasers which have both gain and index coupling coefficients is theoretically analyzed. The unique reduction mechanism of alpha /sub eff/ due to the optical negative feedback of modal phase and modal gain in gain coupled DFB lasers was found for the first time. The numerical result showed that alpha /sub eff/ can be reduced to almost one half of the material defined linewidth enhancement factor alpha when there exists an index coupling coefficient comparable to the gain coupling coefficient.<<ETX>>