Biomedical Engineering Reference
In-Depth Information
Beam expander
Focusing lens
Single mode
VCSEL array
Microlens array
FIGURE 2.56
This figure shows the architecture of collimating the individual beams from the VCSELs and
further reducing their divergence by using a beam expander and a focusing lens. A divergence
of 0.5 mR can be achieved from the entire array with this approach. (Courtesy of Princeton
Optronics [PO] and Dr. Chuni Ghosh. With permission.)
VCSEL 2D arrays on
submounts
Anode
Micro-channel coolers
Cathode
Closed cycle coolant in/out
(to radiator/fan system)
FIGURE 2.57
The diagram of the 400 W illuminator module. The dimensions of the module is 2.5 × 1.5 × 5.5″.
(Courtesy of Princeton Optronics [PO] and Dr. Chuni Ghosh. With permission.)
and therefore a junction-down, bottom-emitting structure is preferred to
improve current injection uniformity in the active region and to reduce the
thermal impedance between the active region and the heat spreader. A sche-
matic of the structure without the heat spreader is shown in Figure 2.61.
For current and optical confinement, the selective oxidation process is
used to create an aperture near the active region to improve performance.
A low-doped GaAs N-type substrate is used to minimize absorption of
the output light while providing electrical conductivity for the substrate-
side N-contact. The growth is performed in a MOCVD or MBE reactor and
starts with an AlGaAs N-type partially reflecting DBR. The active region
consists of InGaAs quantum wells designed for 1064 nm emission and
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