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Polarization self‐modulation at frequencies up to 6 GHz is observed in a vertical‐cavity surface‐emitting laser. This self‐oscillation is observed when a portion of the laser output power is injected back into the laser after having rotated its polarization by 90° with respect to the initial laser polarization state. Our experiment demonstrates a simple technique for generating an ultrahigh frequency optical clock. New applications in optical storage are also envisioned.

We report over 130 °C continuous wave operation of unbonded vertical cavity top‐surface emitting lasers emitting more than 1.0 mW at 110 °C. Furthermore, we control threshold currents to within only ±1.35 mA (±12%) over a 150 °C temperature range. We are also able to control the threshold current to within a factor of 2 over a 50 nm wavelength range using the same epidesign.

We report the observation of bistable polarization switching in a vertical‐cavity surface‐emitting laser under optical injection. The wavelength dependence of the switching is measured. It is found that this polarization switching is achieved through injection locking where both the wavelength and the polarization of the vertical‐cavity laser are locked to the injected optical signal.

We demonstrate record high pulsed output power exceeding 530 mW from an electrically pumped phase‐coupled 8×8 vertical cavity surface emitting laser array (SELA) at room temperature. Three array types are compared: an 8×8 pixellated SELA(PSELA), an 8×8 grid contact SELA(CSELA), and a 78 μm×78 μm single broad area SEL(BSEL) emitter. The CSELA operating in a phase‐coupled supermode exhibits the lowest threshold current (100 mA) and voltage (1.6 V), highest damage threshold and a smooth L‐I characteristic with differential quantum efficiency ηd≳27%, the BSEL has the largest output power≳580 mW and a large ηd≳48%, the PSELA exhibited a large voltage with the largest ηd≳80%.

Differential optical switching operation with an optical input of as low as 400 fJ (0.07 fJ/μm2) was realized by using parallel‐connected AlGaAs/GaAs pnpn optical switches. An improvement in the sensitivity of more than two orders of magnitude has been attained by introduction of a new operating concept. The electrical transient time was 10 ns, almost independent of optical input levels.

Single quantum wells were grown on GaAs triangular gratings by molecular beam epitaxy. Cross‐sectional transmission electron microscopy revealed that the quantum wells had a triangular shape above the ridge of the grating. The photoluminescence spectra at 77 K showed strong anisotropy, indicating that the electrons are confined two dimensionally. The calculation confirmed that the electrons tend to be localized at the corner of the bent quantum well wires, and the effective width of the quantum well wire was estimated to be 30 nm.

We report on experimental studies of the nonlinear optical properties of nanocomposites consisting of organic (hyperbranched polymer)-metallic (Au or Pt) nanoparticle complex embedded in polymer films. Open-aperture and closed-aperture z-scan techniques are used to measure the effective third-order nonlinear optical susceptibilities χeff(3) of the composites under picosecond laser radiation at a wavelength of 532 nm. The relative sign of the real and imaginary parts of χeff(3) could be explained qualitatively by the Kramers–Kronig relation. We also determined the third-order nonlinear optical susceptibilities of Au and Pt nanoparticles estimated from the measured values for χeff(3) to be (−5.48+4.76i)×10−8 esu and (4.41−0.65i)×10−6 esu, respectively, at 532 nm with a help of the Maxwell–Garnett model.

GaAs/AlGaAs transverse junction stripe lasers with a distributed feedback structure were fabricated. The cw threshold current was 27 mA at 20 °C. The laser operated in a pure single longitudinal mode at the wavelength of 867 nm.

Room‐temperature cw operation of a GaAs/AlGaAs surface‐emitting grating‐coupled distributed feedback laser is reported. By using a transverse junction stripe scheme which provides a window structure for the surface‐emitted light, cw surface emission having a very narrow beam divergence angle of 0.13° and an output power of more than 3 mW was observed.

The finite element method was used for calculating the wave functions and energy levels of electrons in arbitrarily shaped two‐dimensional quantum‐confined structures. The calculated results indicate the possibility of quasi‐quantum wires by simply growing single quantum wells on corrugated substrates.

A novel AlGaAs/GaAs distributed Bragg reflector laser utilizing a multiquantum well structure both as an active waveguide and as a low loss passive waveguide was fabricated. The threshold current was 102 mA at room temperature, and the differential quantum efficiency for the edge‐ and surface‐emitted light was 16% and 3.7%, respectively. No mode hopping was observed in a temperature range of 35 K. A 0.17°×17° far‐field pattern was obtained for the surface‐emitted light.

The first cw operation of an AlGaAs/GaAs distributed Bragg reflector laser was achieved at room temperature with a threshold current as low as 38 mA. Surface emission exceeding 4 mW was obtained with an external differential quantum efficiency of 9% and a beam divergence of 0.17°×10°. A two‐dimensional laser array with 3×4 gratings was also fabricated and an output power exceeding 500 mW was obtained under pulsed condition.

We demonstrate the reduction of the spectral linewidth in AlGaAs/GaAs distributed feedback lasers by a multiple quantum well structure for the first time. The spectral linewidth‐output power product was 54 MHz mW and was eight times smaller than that of conventional double heterostructure distributed feedback lasers. The narrowest spectral linewidth was 10.5 MHz at 5 mW.

A semiconductor optical‐fiber ring laser was constructed using an AlGaAs/GaAs multiple quantum well laser diode as a gain medium. The single‐mode oscillation was demonstrated and the measured spectral linewidth was less than 45 kHz. This is consistent with a theoretical calculation of its linewidth.

AlGaAs/GaAs distributed feedback lasers with oxide‐stripe structure were fabricated by two‐step molecular beam epitaxy (MBE) growth for the first time. The large coupling coefficient of 90 cm−1 was obtained by controlling precisely the thickness of each layer. As a result, the threshold current of 165 mA, which is the lowest ever reported, was obtained at room temperature. The characteristic temperature T0 was as high as 210 K. Single longitudinal mode oscillation over the temperature range of 50 K was observed without mode hopping. Due to the uniformity of the thickness and composition of the layers grown by MBE, uniform oscillation wavelengths were observed.

A surface‐emitting distributed Bragg reflector (DBR) laser with a mode control section was fabricated. By increasing the injection current into the control section, the lasing wavelength switches from the DBR mode to the Fabry–Perot mode. The lasing wavelength difference was about 13 nm, and the output beam was deflected by 3° while the beam width was kept less than 0.3°. The time required for the switching was as short as 60 ps. The maximum output power exceeded 8 mW under a cw condition at room temperature.

Monolithically integrated surface‐emitting device consisting of an AlGaAs/GaAs multiple quantum well distributed feedback laser and a grating coupler is demonstrated for the first time. The grating coupler was made by utilizing the properties of low loss and easily saturable absorption in the multiple quantum well structure. No additional crystal growths or complicated fabrication processes were required for the integration. An output power of 2 mW and a narrow beam divergence of 0.22° were obtained under continuous wave operation.

Ridge waveguide AlGaAs/GaAs distributed feedback lasers with the cavity length of 820 μm were fabricated. The differential quantum efficiency was as high as 28%, and the power‐dependent linewidth was more than an order of magnitude smaller than that of the 290 μm laser, which agrees with theory. The narrowest linewidth was 12 MHz at 6.2 mW.

Ridge waveguide AlGaAs/GaAs distributed feedback lasers were fabricated by a two‐step molecular beam epitaxial growth technique. A threshold current as low as 42 mA, which is the lowest ever reported, was obtained under a continuous wave condition at room temperature. Stable single longitudinal mode oscillation was observed in the temperature range from −20 to 30 °C without any suppression of the Fabry–Perot mode.

Ridge waveguide AlGaAs/GaAs distributed feedback lasers with multiple quantum well structure were fabricated for the first time. The threshold current of 28 mA, which is the lowest ever reported among AlGaAs/GaAs distributed feedback lasers, was obtained at room temperature. Stable single longitudinal and transverse mode oscillation was observed over the wide temperature range. The dynamic linewidth was also measured and it was five to six times smaller than that of a double heterostructure distributed feedback laser.