Page 156 - High Power Laser Handbook

124 Diode Lasers Semiconductor Laser Diodes 125

when passivated by dielectric coatings. Moisture may be generated
internally (e.g., from inadequate bakes prior to lid sealing) or from
leaks created (e.g., via the fiber-snout or lid-housing interfaces, or
electrical feed throughs). A getter can be sized to accommodate inter-
nal moisture accumulated over the device’s lifetime, depending on
environmental conditions and corresponding leak rates. 44–45 All the
aforementioned sealing methods are capable of attaining internal
moisture levels much less than 5000 ppm over the device lifetime via
standard helium fine-leak screens with getters.
Catastrophic optical damage (COD) of the laser facet may also
result from a photochemical phenomenon known as package-induced
failure (PIF). In the presence of organics, near-infrared photons pro-
46
duce carbon-rich hydrocarbons at the facet that absorb light until a
thermal runaway melts the facet. Accordingly, organics (e.g., adhe-
sives or epoxies) are frowned upon by the telecom industry. How-
ever, organics can be introduced safely in the presence of oxygen
(since O reacts with carbon-rich deposits to form harmless CO and
2
2
volatile hydrocarbons, thereby cleaning the facets and restoring their
reliability). In fact, nearly-transparent epoxies reduce cladding-light
absorption, which is an increasing benefit for higher-power and
lower-NA fiber.

5.13 Performance Attributes
Customers seek high electro-optic performance, high coupling and
thermal efficiency, and high power and linearity in a compact space
and at low price. For a single-emitter fiber-coupled package with
100-mm core diameter output fiber (Fig. 5.21), output powers up to
~11 W and 50 percent PCE are commercially available.

Figure 5.21 Photograph of a fiber-coupled, single-emitter laser diode
package. 18