J. Shimizu

THz optical-frequency conversion of 1 Gb/s-signals using highly nondegenerate four-wave mixing in an InGaAsP semiconductor laser

The authors report the application of the highly nondegenerate four-wave mixing (HNDFWM) process to a 1.5- mu m InGaAsP semiconductor laser in optical-frequency conversion experiments on 1-Gb/s intensity-modulated signals in a 1-THz conversion range. This conversion is based on a subpicosecond ultrafast nonlinear gain process in the laser. The HNDFWM was generated through the use of an injection-locking technique. The possibility of applying this phenomenon to an optical fiber dispersion compensator is also discussed.<<ETX>>

Analysis of differential gain in InGaAs-InGaAsP compressive and tensile strained quantum-well lasers and its application for estimation of high-speed modulation limit

A simplified model that furnishes an intuitive insight for the change in quantum-well (QW) laser gain due to QW strain and quantum confinement is presented. Differential gain for InGaAs-InGaAsP compressive and tensile strained multi-quantum-well (MQW) lasers is studied using the model. The comparison between the calculated and experimental results for lattice-matched and compressive strained MQW lasers shows that this model also gives quantitatively reasonable results. It is found that the variance-band barrier height strongly affects the differential gain, especially for compressively strained MQW lasers. The tensile strained MQW lasers are found to have quite high differential gain, due to the large dipole matrix element for the electron-light-hole transition, in spite of the large valence-band state density. Furthermore, a great improvement in the differential gain is expected by modulation p doping in the tensile strained MQW lasers. The ultimate modulation bandwidth for such lasers is studied using the above results. >

Optical-confinement-factor dependencies of the K factor, differential gain, and nonlinear gain coefficient for 1.55 mu m InGaAs/InGaAsP MQW and strained-MQW lasers

Optical-confinement-factor Gamma dependencies of the K factor, differential gain, dg/dN, and nonlinear gain coefficient epsilon , for 1.55 mu m InGaAs/InGaAsP multiple-quantum-well (MQW) and compressively strained MQW lasers, were investigated experimentally. For both MQW and strained-MQW lasers, when Gamma is increased, the K factor is reduced, dg/dN is increased, but epsilon is almost constant. These results indicate that the Gamma dependence of the K factor mainly results from a change in dg/dN, and does not result from a change in epsilon . For the strained MQW lasers, the K factor, dg/dN, and epsilon are, respectively, half as large, twice as large, and the same as those for the MQW lasers, when both types of lasers have the same Gamma (=0.05). This suggests that the strained MQW lasers with a large Gamma have a small K factor and thus are preferable for achieving large modulation bandwidths.<<ETX>>

Observation of highly nondegenerate four‐wave mixing (≳1 THz) in an InGaAsP multiple quantum well laser

Highly nondegenerate four‐wave mixing (NDFWM) in the pump‐probe detuning region of more than 1 THz has been observed in an InGaAsP multiple quantum well laser for the first time. Each of the probe and signal frequencies is closed to cavity resonance modes for the pump laser and those outputs are enhanced. The highly NDFWM process is based on a mechanism whose response time is less than 0.2 ps.

Measurements of the polarization dependence of field‐induced refractive index changes in GaAs/AlAs multiple quantum well structures

The measurements of the polarization dependence of field‐induced refractive index changes in GaAs/AlAs multiple quantum wells, which are directly measured by using the modulation spectroscopy method for the TE and TM modes, are described. Clear polarization dependences, such as differences in the spectra shape and the peak wavelength, were observed. The polarization dependences originate from the different excitonic transitions: the n=1 heavy‐hole and light‐hole exciton for the TE mode and the n=1 light‐hole exciton for the TM mode. The experimental results show qualitatively good agreement with the theoretical calculation.

Strain dependence of the linewidth enhancement factor in long-wavelength tensile- and compressive-strained quantum-well lasers

Values of the linewidth enhancement factor alpha in InGaAs/InGaAsP tensile- and compressive-strained quantum-well (QW) Fabry-Perot lasers are measured and compared to calculated values. The strain dependence of the measured values agrees with that of the calculated values: Values of alpha are smaller for tensile-strained QW lasers than for compressive-strained QW lasers, and alpha decreases with the increase of tensile or compressive strain. According to the model used in the calculation, short-wavelength-composition barriers reduce alpha in compressive-strained QW lasers, and alpha for such lasers is expected to be as low as that for the tensile-strained QW lasers.<<ETX>>

A new technique for fabrication of OEICs-the etched back planar process-and its application to the fabrication of planar embedded InP-InGaAs p-i-n photodiodes

The etched back planar process utilizes a nonselective reactive ion beam etching (RIBE) technique both for semiconductor layers and for photoresist. Application of the technique to the fabrication of a planar InP-InGaAs embedded p-i-n photodiode is discussed. The groove depth on the wafer was reduced from 5.3 mu to 0.6 mu m, and the wafer was nearly planarized. Estimates based on photoluminescence intensity variation and the characteristics of the fabricated p-i-n photodiode indicate that little damage was incurred during the process. These results indicate that fabrication of planar OEICs by means of this process is feasible.<<ETX>>

Optical Confinement Factor Dependence of K-factor, Differential Gain and Nonlinear Gain in 1.55/spl mu/m Mqw and Strained Mqw Lasers

Summary form only given. Systematic studies on the optical confinement factor dependence of the K-factor, differential gain, and nonlinear gain coefficient in 1.55- mu m MQW and strained MQW lasers are reported. The most important conclusion of these studies is that the K-factors in the MQW and strained MQW lasers are reduced as the optical confinement factor is increased. This mainly results from the increase in the differential gain. Strained MQW lasers with large optical confinement factors are expected to achieve small K-factors and large modulation bandwidths. >