Dan Botez

Recent advances in antiguided diode laser arrays

Antiguided arrays have been optimized for single-spatial-mode operation to high output power. Diffraction-limited beam operation to cw power levels of 0.5 W have been reproducibly obtained. The high efficiency operation (wall plug efficiency = 20%) and demonstrated reliability make these practical devices, and useful for many applications requiring a high output power spatially coherent beam. Two-dimensional optical waveguide calculations demonstrate the mechanisms responsible for the high mode selectivity of these structures. It is also made clear why coupled-mode theory failed to predict how to obtain single-lobe phase-locked array operation, and what are the conditions to obtain stable, in-phase mode behavior.

6.1 W cw power, Al-free active region diode lasers at 0.805 /spl mu/m

100 /spl mu/m-wide, 1 mm-long, 0.805 /spl mu/m-emitting, Al-free active region diode lasers with 10%/90% AR/HR facet coatings provide 6.1 W cw power at a heat sink temperature of T=10/spl deg/C. The corresponding internal power density at COMD, P~/sub COMD/, is /spl sim/15 MW/cm/sup 2/; almost twice the P~/sub COMD/ value, /spl sim/8 MW/cm/sup 2/, for similarly designed AlGaAs based devices.

Modulation characteristics of high-power phase-locked arrays of antiguides

The small signal modulation characteristics, large signal modulation characteristics and dc noise spectra on 70 micron-wide 20-element high-power phase-locked arrays of antiguides are reported. The relaxation resonance frequency at 1.5 times threshold is found to be 1.65 GHz. Large-signal pulse modulation produced no distortion to the far-field characteristics. The dc noise spectra showed a damped shot noise resonance at 1.32 GHz for a dc bias level of 1.18 times threshold.

Monolithic two-dimensional surface-emitting laser diode arrays with 45 degree micromirrors

Development and performance of large area (0.5 cm2) junction-down monolithic two- dimensional surface-emitting arrays is reported. This involves fabrication of 45 degree(s) and vertical micromirrors with +/- 2 degree(s) tolerances and < 0.2 RMS smoothness, lapping and polishing of 2 in. diameter wafers with < 10 micrometers thickness tolerances, integration of 100 micrometers thick current spreading electrodes which minimize ohmic losses, large area packaging, and mounting to heat exchangers for long pulse operation and minimum chirp. Single monolithic surface emitter diodes exhibit superior performance (slope efficiencies of (eta) d > 50%, threshold currents of Ith equals 220 mA, and output powers in excess of 720 mW). This projects to power densities > 860 W/cm2 and > 50% differential slope efficiencies for arrays of devices. Large area array operation (scaling) was demonstrated. Uniform lasing was achieved from 0.2 cm X 0.5 cm and 0.5 cm X 1.0 cm active area junction-down monolithic arrays (120 and 600 emitters respectively) using 100 microsecond(s) ec long pulses at a 1% duty cycle. Differential slope efficiencies of > 40% were achieved for rows of 12 emitters, and 8% for the large area arrays. The drop in efficiency was due to current leakage, which limited the output power densities to 150 W/cm2. Chirp in these devices was measured to be < 4 nm at twice the threshold current.

High CW power 0.8 /spl mu/m-band Al-free active-region diode lasers

100 /spl mu/m-wide stripe, Al-free, uncoated, 0.83 /spl mu/m diode lasers provide 4.7 W CW maximum output power and 45% maximum CW wallplug efficiency at T=20/spl deg/C. The active region consists of a 150 /spl Aring/ In/sub 0.09/Ga/sub 0.91/As/sub 0.8/Pb/sub 0.2/ quantum well surrounded by 0.4 /spl mu/m In/sub 0.5/Ga/sub 0.5/P confining layers and 1.5 /spl mu/m In/sub 0.5/(Ga/sub 0.5/Al/sub 0.5/)P cladding layers. For 1 mm-long devices, we obtain threshold-current densities as low as 220 A/cm/sup 2/ and threshold-current characteristic temperature, T/sub 0/, as high as 160 K.

High power lasers based on antiguided structures

The Antiresonant Reflecting Optical Waveguide (ARROW)-type antiguided lasers have demonstrated stable, single-spatial mode operation up to 500 mW at 980nm and 450 mW at 850 nm. These devices are desirable as pump sources for rare-earth-doped fiber amplifiers and/or fiber-based frequency upconversion. An understanding of the above-threshold mode behaviour in these structures is necessary for an optimal device design. To study these structures, an above-threshold model has been developed including gain spatial hole burning (GSHB) and carrier diffusion, as previously described for antiguided arrays. The study reveals the importance of preferential pumping to the low-index core region, and projects stable, single-mode operation to high powers for 6-10 /spl mu/m-wide ARROW lasers. The fundamental-mode far-field beamwidth is found to remain virtually constant to 10x threshold ( i.e. no self-focusing).

Injection locking of antiguided resonant optical waveguide arrays

Twenty element resonant optical waveguide (ROW) antiguided arrays were locked to 2.6 times above the threshold level (2.6 x Ith) by injecting light from a master oscillator in a direction normal to the diode facet and only in one element of the array. The spectra and far-field output pattern of the SL were found to be independent of the MO beam position on the SL facet, and the far-field pattern was stable with wavelength detuning (i.e. no steering) . Single frequency tuning was achieved over a < 30 A spectral range, and the beam pattern was found to be stable and diffraction-limited for nearly resonant devices. Two and four coupled ROW arrays on a bar were also injection—locked by injecting an external MO into one element of one of the arrays. Two locked arrays were wavelength tuned over a 12 A spectral range.

High-power CW operation of laser diodes with etched micromirrors

Monolithic in—plane surface emitting laser diode arrays with 45° micromirrors offer great promise for both coherent and incoherent applications. This paper describes several such laser diode structures in both the junction-up and junction-down configurations, and summarizes their design, fabrication and performance characteristics.

Development of efficient monolithic surface-emitting laser diode arrays (Invited Paper)

Monolithic surface—emitting laser diodes (SELDs) and laser diode arrayswith 45° micromirrors offer great promise for both coherent and incoherent(solid state laser pumping) applications. Four basic types of SELDs havebeen developed to date, and are illustrated in Figure 1. Figure 1 (a) and(b) devices are of the junction-down configuration, while Figure 1 (c) and(d) shows SELDs in the junction-up configuration. The former two types ofdevices have the heat-generating active region in close proximity to theheat sink, while the latter two have a thick (100 .Lm) GaAs substratebetween the active region and the device heat sink. Since GaAs is a poor

High-power coherent diode lasers

Diffraction-limited beam operation at high output power levels (0.5 W cw and 1.5 W pulsed) has been demonstrated from resonant-optical-waveguide (ROW) array structures. Uniphase mode operation is achieved without the need for active phase control. As a result, a reliable monolithic device capable of watt-range coherent output power is obtained.