Instrument: Fiber Subsystems
MEGARA has two different modes that correspond to
the two fiber bundles available: the Large Compact Bundle IFU (LCB)
and the Multi-Object Spectrograph (MOS) mode.
The Folded Cassegrain subsystems are as follows:
- A mechanical interface plate (attached to the Folded
Cassegrain rotator) shall provide support to the Field Lens, the
IFU and MOS.
- A Field lens corrects the lack of telecenticity of the GTC
focal station. The opto-mechanical axes of all the fiber bundles
will be parallel among them.
- The 2D refractive microlens arrays shall couple the light
at the focal plane of the telescope, defining the FOV to be
introduced in the fiber, adapting F# from f/17 to f/3 to minimize
FRD and providing a telescope pupil image on the 100 μm fiber
core. The refractive microlenses have been manufactured by AMUS
using standard semiconductor technologies, which allows very
accurate shaping of the lens profile and precise positioning of the
lenslets in the array.
- The fibers, organized in bundles, transport the light
coupled via the microlenses to the pseudo slit at the entrance of
the spectrographs. The selected fibers are FBP 100/140/170 from
Polymicro. These provide a wide broadband spectral response, a good
FRD and have a numerical aperture of 0.2 ± 0.02. SEDI is in
charge of fiber bundles manufacturing.
- The fibers are placed in front of each spectrograph at the
pseudo-slit position, where the focal plane is smoothly curved with
a ROC of 1075 mm and a size of 119 mm. Two different pseudo-slits
are being manufactured for the two MEGARA modes: the LCB
pseudo-slit (which shall contain the fibers from the LCB and 8
positioners, marked in orange in the figure, that shall be used for
sky substraction) and the MOS pseudo-slit (which shall contain the
fibers from the other 92 positioners).