S. O'Brien

High-brightness flared lasers

A variety of applications continue to demand semiconductor lasers with higher brightness. These applications include printing, marking, frequency-doubling, sensing, and free-space communication, as well as pumps for fiber-amplifiers and solid-state laser crystals. The traditional narrow-stripe single-mode laser is limited in power to 200 - 400 mW due to the small mode volume and high optical intensity at the mirrors. The traditional broad-area laser can deliver higher power but with a significantly larger aperture-divergence product. The key to very high-brightness lasers is to increase the output power without increasing the aperture-divergence product. Numerous concepts have been proposed, of which several have been demonstrated. As of today, only two types of broad-area single-spatial-mode lasers are commercially available; flared-amplifier lasers and angled-grating distributed-feedback ((alpha) -DFB) lasers. Near-diffraction- limited powers of 5 W and 1.6 W have been reported for these lasers, respectively. This paper will review properties of flared-amplifier lasers in several different configurations.

Monolithically integrated high-speed high-power diffraction-limited semiconductor sources for space telecommunications

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.

High power GaInAs lasers with distributed Bragg reflectors

Single-mode strained-layer lasers have been fabricated which use buried second-order gratings for distributed Bragg reflectors. The lasers contain a strained GaInAs quantum well in the active region and operate in an edge emitting fashion with CW powers in excess of 110 mW. Single longitudinal and transverse mode operation is maintained at about 971.9 nm up to 42 mW. Total power conversion efficiencies as high as 28 percent have been observed. The longitudinal and transverse mode behavior is stable under 90 percent amplitude modulation with 50 percent duty cycle pulses at 10 kHz and 10 MHz. Preliminary life-test data at 40 C also indicate room temperature lifetimes in excess of 45,000 hours.

Advances in high-power fiber-coupled laser diodes

We describe advances in the development of high-power diffraction-limited lasers for single- mode fiber-coupled sources. The development of the tapered amplifier has led to the realization of a monolithic MOPA diode laser, which provides up to 3 W cw of single-spatial- mode output power. We further describe the implementation of the MOPA in fiber-coupled architectures that provide up to 1.2 W cw coupled into a single-mode optical fiber and some of the optical considerations unique to devices based on tapered amplifiers.

1.3-W cw diffraction-limited monolithically integrated master oscillator flared amplifier at 860 nm

A high-power monolithically integrated master oscillator flared power amplifier is demonstrated which operates at approximately 860 nm to an output power greater than 1.3 cw with a far field pattern consisting of a single, diffraction-limited lobe.

Improved wavelength stability of GaAs laser diodes under amplitude modulation

Spectral properties of commercially available Fabry-Perot and distributed Bragg reflector (DBR) GaAlAs and InGaAs laser diodes operating under deep current modulation are presented. At kHz modulation frequencies spectral widths of commercial diodes are 2.5 nm 15 dB down from the maximum intensity. Structural modifications can narrow this value to 0.4 nm. Prototype DBR devices with maximum output power of 110 mW exhibit extremely narrow CW linewidths of 4 MHz, and are suitable for coherent communication as well as direct detection communication formats.