Electro-Optics - Applied Optics Fundamentals and Device Applications - page 77

Single mode
VCSEL array

Focusing lens

Fiber

Microlens array

FIGURE 2.51
This figure shows a 100 W CW single-mode VCSEL array mounted on a microcooler (top left).
On top right, it shows the single-mode array coupling scheme to couple the array with the
fiber. At bottom left, it shows the package that has a dimension of (2 × 1.5 × 0.5″), which is water
cooled. (Courtesy of Princeton Optronics [PO] and Dr. Chuni Ghosh. With permission.)

480 nm is single-mode and highly monochromatic with a beam divergence
(half angle) of 8 mR. The VCSEL devices and arrays are capable of delivering
very high power in a 2-D array and hence frequency doubled arrays are able
to deliver very high levels of power. PO developed 6 W of peak power from
a single-VCSEL device that was frequency doubled and is working toward a
10 mJ pulse, 1 kHz rep rate blue laser in a small form factor. Figure 2.52 shows
the schematic of the approach and Figure 2.53 shows the experimental setup
for the blue laser using VCSELs.
For UV lasers, an external frequency doubler material BGO doubles the
frequency of the laser. PO is developing several millijoules of UV energy per
pulse from these devices with kilohertz repetition rate. Figure 2.54 shows
the schematics of the approach obtaining 1 mJ pulse energy, with a 100 Hz
repetition rate.

2.12.10 Narrow Divergence Arrays

VCSEL arrays with microlens collimation become very narrow divergence
light sources. A single-mode array (Figure 2.55) shows the collimation of
the beams from individual VCSELs. Using a microlens aligned with the
VCSEL array and held in position by laser-welding the holding frames pro-
duces divergence of 60 mrad (full angle) for self-lasing arrays and 8 mrad
(full angle) for external cavity arrays. Figure 2.56 shows schematically the