Northern Telecom Limited

Kiu-Chi D Chik

John C Dyment

Christopher M Look

Tibor F Devenyi

Double heterostructure lasers which use a narrow stripe contact exhibit linear characteristics with a low lasing threshold current making them very suitable for fiber optic communication systems. Linearity and low threshold currents are achieved if the carrier current injected into the device is confined to a narrow region of the active layer. To further confine the current a p-type diffusion is performed to produce a relatively low conductivity path between the contact stripe and the lasing region of the active layer. Ideally the diffusion front extends to within 0.5 microns of the active layer. In order to achieve this, a p-type double heterostructure second confining layer of 0.5 microns or less is grown immediately adjacent to the active layer and an n-type blocking layer is grown on the second confining layer. By diffusing the p-type dopant through the n-type blocking layer the diffusion front can be accurately monitored using a scanning electron microscope. As soon as the diffusion front merges with the p-type second confining layer then it can be concluded that it is within 0.5 microns of the active layer. Moreover the pn junction between the second confining layer and the blocking layer is reverse biased in use and so provides further charge carrier confinement in comparison with the conventional wholly p-type second confining layer which is usually of the order of 1.5 .mu.m thick.

Planar narrow-stripe laser with improved charge carrier confinement

A method for screening double heterostructure laser diodes before mounting and packaging is disclosed. At a normal laser diode operating temperature, a range of pulsed current is passed through the laser diode and the lasing threshold current and slope efficiency of the laser diode are monitored. The laser diode is then subjected to a burn-in process in which it is driven at a high junction temperature for an extended time period. Subsequently the lasing threshold current and slope efficiency are again monitored by applying the same range of pulsed current at the normal operating temperature. If either the threshold current or the slope efficiency have changed by more than a predetermined amount, the laser diode is rejected. Otherwise, the laser diode is gauged as likely to have a lifetime greater than a predetermined value at normal operating conditions so warranting further testing prior to installation into a laser package.

Method for screening laser diodes

Semiconductor lasers exhibit transient relaxation oscillation on start-up and specific lasers often exhibit sustained spontaneous pulsations caused probably by crystalline defects. These fluctuations are suppressed in a laser having an integrally formed light emitting diode (LED) which generates spontaneous light which is coupled into the laser by virtue of the close proximity of the laser and the light emitting diode.

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Nepean, Canada

Kiu-Chi D Chik