Performance tests of quasi-CW laser diode pump arrays conducted or sponsored by NASA Goddard Space Flight Center

Abstract

We present tests of 100 Whar quasi-CW laser diode arrays conducted, at SDL Inc. (at various deratings with constant junction temperature) and NASAsGoddard, to assist in designing lasers for use in space.Several performance tests of quasi-CW laser diode pump arrays have been conducted1 and documented. Space flight missions2 are being considered which require diode lifetimes in excess of 2 billion shots with little available (greater than one billion shot) reliability data.For the vendor conducted test (denoted Test l), one SDL-3257-H6 device was started at 100 W quasi-CW power, one SDL-3257-H6 device at 80 W quasi-CW power, and one SDL-3257-H6 device at 60 W quasi-CW power. Before the test began, the shot repetition rate was adjusted such that the device junction temperature was 30 C for every device. These devices were kept at the these optical powers throughout the test (i.e., constant optical power). The pump diode laser pulse width was chosen as 200 microseconds for all devices. The 100 Whar device operated with a 450 Hz repetition rate (9% duty factor), the 80 Whar device operated with a 533 Hz repetition rate (1 1.2% duty factor), and the two 60 Whar devices operated with a 750 Hz repetition rate (15 % duty factor). The Test 1 data is shown in Figure 1. The Test 1 constant peak optical power lifetest shows a 5 to 7 times increase in the expected lifetime for the SDL Inc. laser diode pump arrays (rated at 100 W peak optical power per bar) when they are derated to 80 W and 60 W respectively. All of the bars operated with less than 20% degradation for over 2 billion shots. Predicted lifetimes exceed 20 billion shots for the bars that were derated to 60 W.The lifetime of the laser diodes varies inversely to the power loading at the facet and follows the power law:The data was normalized relative one of the devices and the ratio of life time was plotted as a function of the ratio of operating peak optical power. It was found that the lifetime does vary inversely with optical power as in equation (1) with n E 3.5.

A unified multiple stress reliability model for microelectronic devices — Application to 1.55 μm DFB laser diode module for space validation

“…If J is defined as the current density, the lifetime of the device is defined as t, and the empirical value parameter is defined as n, then there exists a relationship such that t ≈ I −m . Similarly, the lifetime of laser diode varies inversely proportional to the power loading at the facet [30] and follows the power law t ≈ P …”