To meet the stringent requirements of a submarine cable system, our 1.3-μϊα laser prequalification program has two objectives-first, to define the testing methodology that will accurately evaluate the potential reliability of the laser; and second, to obtain a preliminary indication of laser reliability on which the system configuration can be designed. Our testing methodology involves a combination of step-temperature, step-power, and isothermal test ing over the temperature interval between 10 and 80°C and power levels of 1 to 5 mW per facet. Our results show that the long-term degradation process is thermally accelerated, with a median activation energy of 1 eV and a standard deviation of 0.13 eV. By using these activation energies, in conjunc tion with our measurements of degradation rates, we can project laser perform ance to 10°C, i.e., system operating temperature. It is estimated that the median time to failure for "light bulb" operation at 10°C is over 2 X 10 7 hours; and with 98-percent probability it is greater than 5 X 10 6 hours. Hence, when viewed strictly in terms of light bulb sources of stimulated power, these 1.3-μιη lasers have adequate life. In addition, other potential operational malfunc tions are being investigated, and they do not seem to change our basic conclusion about the usefulness of these 1.3-μνα lasers for submarine cable application.

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We present the results of the cw electro-optical characteristics of 5-μm shallow proton-bombarded strip laser fabricated from molecular beam epitaxy (MBE)-grown double-heterostructure (DH) wafers that have Al0.08Ga0.92As active layers at elevated temperatures (55–70 °C), and compare them with those obtained from similar lasers fabricated from liquid phase expitaxy (LPE)-grown DH wafers. It is shown that the MBE lasers maintain their excellent cw device characteristics even at elevated temperatures. The temperature dependence of the cw Ith of MBE lasers is significantly less than that of the LPE lasers. Furthermore, the cw Ith’s of these MBE lasers are at least as good as good LPE lasers. Owing to the very uniform layer thicknesses generated by the MBE process, the resultant slice quality is highly uniform. This results in a significantly increased yield of good lasers per MBE wafer.

The cw accelerated aging behavior of proton-bombarded stripe geometry lasers fabricated from MBE grown DH wafers have been studied. The laser diodes were formed into a 5-μm-wide shallow proton-irradiated stripe geometry and operated without mirror coatings in dry nitrogen 70 °C ambients at constant power outputs of 2.5 mW and 3.0 mW/mirror. A feasibility demonstration of long lifetimes was obtained for lasers from three selected MBE wafers; where a median lasing lifetime of 8800 h with a standard deviation of 1.5 was found at 70 °C, which projects to a mean laser lifetime ≳106 h at room temperature. After initial aging, long-term degradation rates as low as 0.7 mA/kh for the operating current at 70 °C have been measured. The present results also show that the rate of change of the operating current with aging for MBE diodes is more uniform than for typical LPE diodes fabricated with the same technology. Data are presented for lasers from one of the wafers that show that after 1500 h of 70 °C cw aging, many of the electrooptical characteristics are relatively unchanged.

A statistical study of the self-induced pulsation behavior of cw (AlGa)As double-heterostructure (DH) (having Al0.08Ga0.92 As active layers) proton-bombarded stripe lasers grown by molecular beam epitaxy (MBE) during accelerated aging at elevated (55 or 70 °C) temperatures is made and compared with that of similar lasers grown by liquid-phase epitaxy (LPE). For the 5-μm-stripe, shallow proton-bombarded (proton damage does not reach the active layer) stripe lasers, those fabricated from an MBE DH wafer studied show a significantly higher oscillation frequency (Fosc) of the self-pulsation than those fabricated from LPE DH wafers. It is also shown that by going from 10-μm-stripe and deep proton-bombarded (proton damage penetrates the active layer) to 5-μm-stripe and shallow proton-bombarded stripe lasers, the Fosc are significantly higher even after an initial burn-in at elevated temperatures (55 or 70 °C) for 100 h.