Vescent Photonics
D2 Series Product Manual
Beam Conditioning
The collimation of the output beam is set at the factory and should not be adjusted unless
absolutely necessary. Remove the isolator subassembly from the baseplate with the 4 screws
accessible from the bottom. The locking set screw on the right side of the DBR subassembly can
then be loosened and the lens repositioned with a 9 mm spanner wrench (Thorlabs, SPW301).
Tighten the locking screw and reattach the isolator subassembly.
Laser diodes all have astigmatism, which means the horizontal and vertical axis have different
foci. Vescent uses a powerful asphere with a short focal length and an anamorphic prism pair to
create a small diameter circular beam. This reduces the costs of the isolator and other downstream
modules by reducing the clear aperture requirements. While the aspheres and anamorphic prisms
produce a circular beam, astigmatism dictates that a single lens will not simultaneously collimate
both orthogonal axes of the beam with the result that in the far field the beam is again elliptical.
The far-field pattern is the most important for ascertaining the quality of the diode output. The
near-field pattern often shows stray light from the diode waveguide and ASE that doesn’t
propagate as part of the primary beam. However, aberrations and beam clipping due to an
insufficient lens NA will show up as fringes-on the far field pattern. Vescent has taken care in
the design of the DBR laser module to keep aberrations and clipping to a minimum, resulting in a
clean beam in the far field.
8
Figure 3: Lock screws and beam pointing controls.
Lock Screws
Horizontal adj.
Vertical adj.
Lock Screws
Horizontal adj.
Vertical adj.
