Squeezed states of the electromagnetic field have been generated by nondegenerate four-wave mixing due to Na atoms in an optical cavity. The optical noise in the cavity, comprised of primarily vacuum fluctuations and a small component of spontaneous emission from the pumped Na atoms, is amplified in one quadrature of the optical field and deamplified in the other quadrature. These quadrature components are measured with a balanced homodyne detector. The total noise level in the deamplified quadrature drops below the vacuum noise level.

Observation of squeezed states generated by four-wave mixing in an optical cavity

The density-matrix theory of semiconductor lasers with relaxation broadening model is finally established by introducing theoretical dipole moment into previously developed treatments. The dipole moment is given theoretically by the k . p method and is calculated for various semiconductor materials. As a result, gain and gain-suppression for a variety of crystals covering wide wavelength region are calculated. It is found that the linear gain is larger for longer wavelength lasers and that the gain-suppression is much larger for longer wavelength lasers, which results in that single-mode operation is more stable in long-wavelength lasers than in shorter-wavelength lasers, in good agreement with the experiments.

Density-matrix theory of semiconductor lasers with relaxation broadening model - Gain and gain-suppression in semiconductor lasers

A device for emitting radiation at a predetermined wavelength is presented. This device has a cavity with an active layer in which said radiation is generated by charge carrier recombination. The edges of the device define the region or space for radiation and/or charge carrier confinement. At least one of the edges of this cavity has a substantially random grating structure. The edge of the device has substantially random grating structure and can extend as at least one edge of a waveguide forming part of this radiation emitting device. The radiation emitting device of the present invention can have a cavity comprising a radiation confinement space that includes confinement features for the charge carriers confining the charge carriers to a subspace being smaller than the radiation confinement space within the cavity. The emitting device can comprise at least two edges forming, in cross-section, a substantially triangular shape. The angle between these two edges is smaller than 45°. At least one of the two edges has a transparent portion. the devices according to the present invention can be arranged in arrays.

Method of manufacturing surface textured high-efficiency radiating devices and devices obtained therefrom

We have studied experimentally and theoretically the spontaneous emission from 1.3- and 1.5-/spl mu/m compressively strained InGaAsP multiple-quantum-well lasers in the temperature range 90-400 K to determine the variation of carrier density n with current I up to threshold. We find that the current contributing to spontaneous emission at threshold I/sub Rad/ is always well behaved and has a characteristic temperature T/sub 0/ (I/sub Rad/)/spl ap/T, as predicted by simple theory. This implies that the carrier density at threshold is also proportional to temperature. Below a breakpoint temperature T/sub B/, we find I /spl alpha/ n/sup Z/, where Z=2. And the total current at threshold I/sub th/ also has a characteristic temperature T/sub 0/ (I/sub th/)/spl ap/T, showing that the current is dominated by radiative transitions right up to threshold. Above T/sub B/, Z increases steadily to Z/spl ap/3 and T/sub 0/ (I/sub th/) decreases to a value less than T/3. This behavior is explained in terms of the onset of Auger recombination above T/sub B/; a conclusion supported by measurements of the pressure dependence of I/sub th/. From our results, we estimate that, at 300 K, Auger recombination accounts for 50% of I/sub th/ in the 1.3-/spl mu/m laser and 80% of I/sub th/ in the 1.5-/spl mu/m laser. Measurements of the spontaneous emission and differential efficiency indicate that a combination of increased optical losses and carrier overflow into the barrier and separate confinement heterostructure regions may further degrade T/sub 0/ (I/sub th/) above room temperature.

The temperature dependence of 1.3- and 1.5-/spl mu/m compressively strained InGaAs(P) MQW semiconductor lasers

Planar, gain-guided vertical-cavity surface-emitting lasers (VCSELs) with a modulation bandwidth of 14 GHz are described. This bandwidth is reached at a drive current of only 8 mA. The intrinsic bandwidth of these devices is estimated to be greater than 50 GHz. Nonlinear light-current characteristics of these lasers may lead to a high level of nonlinear harmonic distortion of the high-frequency output. It is shown that the relative intensity of the second-harmonic response decreases rapidly at higher drive currents, in agreement with a phenomenological model based on the DC characteristics of the laser. >

High-speed vertical-cavity surface emitting laser

The dependencies of the main lasing characteristics on the facet reflectivity for GaAs and AlGaAs single-quantum-well (SQW) separate-confinement heterostructure (SCH) broad-area laser diodes (LDs) are analyzed. Conditions for the facet reflectivity to achieve optimum values are identified. Under these conditions, the authors obtained respective maximum output powers of 2.9 and 2.6 W for GaAs-SQW and AlGaAs-SQW single-stripe LDs for 150 mu m stripe width, lasing at about 808 nm under a continuous-wave (CW) condition. These LDs were stably operated for over 2000 h under the condition of 1 W constant output power with automatic power control circuits at 45 degrees C in CW operation. >

High-power operation of broad-area laser diodes with GaAs and AlGaAs single quantum wells for Nd:YAG laser pumping

The coupling constant that determines the characteristics of distributed feedback laser diodes (DFB LDs) is controlled by employing the metalorganic chemical vapor deposition (MOCVD) technique and inserting a barrier layer between the active layer and the guiding layer. It is shown that the measured coupling constant is in good agreement with the designed coupling constant. Lasers with a small coupling constant have a large slope efficiency. Lasers with the above structure are expected to have a long life, comparable to that of conventional DFB LDs. >

1.3- mu m distributed feedback laser diode with a grating accurately controlled by a new fabrication technique

Harmonic distortion of distributed feedback laser diodes (DFB-LDs) for analog transmission systems is investigated. It is shown that, under a modulation frequency of less than 1 GHz, the harmonic distortion depends on the nonlinearity of the light output power-current (P-I) curve under the continuous wave (CW) condition, which is determined by the coupling constant kappa L, and that the distortion can be minimized at kappa L approximately 1. A 1.3 mu m wavelength InGaAsP DFB-PPIBH (p-substrate partially inverted buried heterostructure) LD and its module, with low distortion by the control of a coupling constant, have been developed. >

Distributed feedback laser diode and module for CATV systems

A modal reflector, which consists of a high-reflectivity region surrounded by low-reflectivity regions, is added to the front facet of two types of broad-area laser diodes (LD's) to control the lateral modes. One type of LD is the self-aligned laser with a bent active layer (SBA LD) that has a real index-guiding mechanism. The other is a planar-stripe LD that consists of a Zn-diffused region to confine the current flow and has a gain-guiding mechanism. For the SBA LD's with a modal reflector, stable single-lobed far-field patterns (FFP's) are obtained at up to 0.3 and 0.4 W output powers in continuous wave (CW) operation and pulsed operation, respectively. In addition, for planar-stripe LD's with a modal reflector, stable single-lobed FFP's are obtained at up to 0.4 W in CW operation. The lateral modes inside the cavity are analyzed by utilizing a slit model and FFP's are calculated. Good agreement is found between experimental and calculated FFP's for a large Fresnel number. >

Achieving broad-area laser diodes with high output power and single-lobed far-field patterns in the lateral direction by loading a modal reflector

Laser diodes with the p-substrate buried-crescent structure have been fabricated for the 1.2-1.55- mu m wavelength region. The dependence of laser characteristics on wavelength has been measured. Up to 70 degrees C, the increasing rates of the threshold current with temperature are similar, while, above 70 degrees C, a shorter-wavelength laser shows a larger increasing rate. At the same full width at half maximum of the far-field pattern perpendicular to the junction plane, the external differential quantum efficiency of the 1.55- mu m laser diode is only 10% smaller than that of the 1.3- mu m laser. The absorption loss coefficients in the active layer of the 1.2-, 1.3-, and 1.55- mu m laser are estimated to be 26, 34, and 73 cm/sup -1/, respectively. >

S. Kakimoto

Papers

High-power operation of broad-area laser diodes with GaAs and AlGaAs single quantum wells for Nd:YAG laser pumping

1.3- mu m distributed feedback laser diode with a grating accurately controlled by a new fabrication technique

Distributed feedback laser diode and module for CATV systems

Achieving broad-area laser diodes with high output power and single-lobed far-field patterns in the lateral direction by loading a modal reflector

Wavelength dependence of characteristics of 1.2-1.55 mu m InGaAsP/InP p-substrate buried crescent laser diodes