A low cost and highly reliable fiber coupled laser diode is demonstrated with up to 1.0 W output power in 0.14 NA out of a 60 micrometer core fiber. Package reliability with extended operation at 600 mW is shown for over 600 hours at 85 degrees Celsius, and with stringent environmental tests, including thermal cycling, high temperature storage, and two sec. on two sec. off power cycling.
Low threshold operation of the 550 nm holmium laser is reported in a Ho<SUP>3+</SUP>:ZBLAN fiber pumped near 650 nm. The 550 nm transition has been pumped by an InGaAlP diode laser producing approximately 30 mW at 643 nm. Over 1.2 mW of green laser output and an optical conversion efficiency of 12% has been obtained. The threshold diode laser pump power was 3.5 mW launched.
The various components for red MOPAs (Master Oscillator Power Amplifier) have been demonstrated and exhibit excellent performance. A major impediment has been the regrowth over material with high aluminum concentration, necessary for short wavelength operation. Nevertheless, amplifiers, DFB, and DBR lasers have been demonstrated in discrete form. Single frequency DBR and DFB lasers using a buried diffraction grating emit over 20 mW with efficiencies of up to 0.4 W/A. The DBR can be tuned over 3 nm using current injection in the grating, and preliminary lifetests indicate good reliability. Discrete flared amplifiers exhibited nearly 1.6 W pulsed, and 500 mW CW output power. The performance of the individual devices and integration issues in developing the MOPA will be discussed.
High-power semiconductor sources capable of high-speed modulation are very desirable for free-space digital telecommunications such as satellite optical communication links. Moreover, a diffraction limited beam quality is necessary for most applications. We describe advances in the development of high-power, diffraction-limited semiconductor lasers based on the master oscillator/power amplifier (MOPA) architecture and capable of high-speed modulation. Devices containing monolithically integrated electro-absorption or phase modulators demonstrate 5 GHz small signal modulation bandwidth at 1 W output power.
A monolithically integrated array of InGaAs/AlGaAs flared amplifiers driven by a single DBR laser through a power splitter network and individually addressed phase modulators is described. Phase adjustment of > 2(pi) per element by free-carrier effects is verified by monitoring the interference pattern of 4 emitters, and typically requires < 15 mA of current to obtain a 2(pi) phase shift. Phase matching is achieved among all four diffraction-limited emitters at a pulsed output power of > 5 W, and, combined with the proper external lensing, could therefore result in an ultra-narrow, single-lobed far-field pattern whose width is determined by the extended aperture of the array. This architecture is capable of providing single-mode, diffraction-limited performance from each emitter and is scalable to unprecedented power levels. Over 20 W of pulsed, spectrally coherent emission is generated at 955 nm from a 4-element array, and 39 W is obtained from an 8-element array.
Physical parameters contributing to the threshold current and its temperature characteristics of 1.5 micrometers semiconductor lasers have been separately measured in lattice matched and compressively strained lasers. It is found that the reduction of threshold current density in strained devices is attributed to the reduction of Auger recombination, intervalence band absorption and transparency carrier density brought about by the introduction of strain. It is also found that the temperature sensitivity of both lattice matched and strained devices is dominated by the strong differential gain change with temperature, instead of Auger recombination.