P.J. Fiddyment

Spectral properties of strongly coupled 1.5 µm DFB laser diodes

Spectral measurements of strongly coupled DFB lasers operating at 1.5 μm are presented. The magnitude of the coupling coefficient k in these devices was determined to be 80 cm-1for lasers with \lambda = 1.12 \mu m cladding layers and 160 cm-1for devices with \lambda = 1.3 \mu m cladding layers. These values for k are believed to be the largest reported for 1.5 μm DFB lasers. CW spectral linewidths as low as 10 MHz at 15 mW output power were obtained, and the linewidth was observed to vary approximately as the inverse of the device length cubed. Spectral measurements performed under 2 Gbit/s direct modulation exhibited a side mode suppression ratio of >38 dB. The effects of transient wavelength chirping were also investigated in detail and the maximum wavelength deviation was found to be ≃1.5 A.

CW operation of GaInAsP stripe lasers

A quantitative investigation of the constraints on dc operation of GaInAsP stripe-geometry lasers at room temperature and above has been made. Laser pulse threshold current, its temperature sensitivity, electrical series resistance, and the thermal resistance of the bonded device are critical parameters in this respect. Sets of theoretical curves have been generated that allow expected de thresholds to be determined from the value of the pulsed threshold. Experimental results confirm the accuracy of the expressions. For GaInAsP lasers, the low values of T 0 reported in the literature (47-80 K) imply that both electrical series resistance and thermal resistance must be minimized in order to obtain stable dc operation over a reasonable temperature range in conventional oxide or proton isolated stripe structures. Both parameters are calculated theoretically for a range of structures. The calculations show that thermal runaway is sensitive to electrical resistance in the range 1-10 \Omega this suggests an area where improvements are possible. To this end, the use of tunneling Schottky contacts to a ternary InGaAs p-capping layer has been developed to minimize contact resistance.

Tapered active layer laser device performance and its impact on low cost optoelectronics

75% coupling to cleaved single mode fibre has been obtained for a 1.55 /spl mu/m tapered active strained MQW layer device. A fully packaged component using precision laser die cleaving and a silicon micro machined substrate has produced a record 55% passive coupling.