The Fiber Optical Cable and Connector System, ”FOCCoS”, subsystem of the Prime Focus Spectrograph,
“PFS”, for Subaru telescope, is responsible to feed four spectrographs with a set of optical fibers cables. The light
injection for each spectrograph is assured by a convex curved slit with a linear array of 616 optical fibers. In this paper
we present a design of a slit that ensures the right direction of the fibers by using masks of micro holes. This kind of
mask is made by a technique called electroforming, which is able to produce a nickel plate with holes in a linear
sequence. The precision error is around 1-μm in the diameter and 1-μm in the positions of the holes. This nickel plate
may be produced with a thickness between 50 and 200 microns, so it may be very flexible. This flexibility allows the
mask to be bent into the shape necessary for a curved slit. The concept requires two masks, which we call Front Mask,
and Rear Mask, separated by a gap that defines the thickness of the slit. The pitch and the diameter of the holes define
the linear geometry of the slit; the curvature of each mask defines the angular geometry of the slit. Obviously, this
assembly must be mounted inside a structure rigid and strong enough to be supported inside the spectrograph. This
structure must have a CTE optimized to avoid displacement of the fibers or increased FRD of the fibers when the device
is submitted to temperatures around 3 degrees Celsius, the temperature of operation of the spectrograph. We have
produced two models. Both are mounted inside a very compact Invar case, and both have their front surfaces covered by
a dark composite, to reduce stray light. Furthermore, we have conducted experiments with two different internal
structures to minimize effects caused by temperature gradients.
This concept has several advantages relative to a design based on Vgrooves, which is the classical option. It is
much easier and quicker to assemble, much cheaper, more accurate, easier to adjust; and it also offers the possibility of
making a device much more strong, robust and completely miniaturized.
Extremely low temperatures may damage the optical components assembled inside of an astronomical instrument due to the crack in the resin or glue used to attach lenses and mirrors. The environment, very cold and dry, in most of the astronomical observatories contributes to this problem.
This paper describes the solution implemented at SOAR for remotely monitoring and controlling temperatures inside of a spectrograph, in order to prevent a possible damage of the optical parts. The system automatically switches on and off some heat dissipation elements, located near the optics, as the measured temperature reaches a trigger value. This value is set to a temperature at which the instrument is not operational to prevent malfunction and only to protect the optics. The software was developed with LabVIEWTM and based on an object-oriented design that offers flexibility and ease of maintenance.
As result, the system is able to keep the internal temperature of the instrument above a chosen limit, except perhaps during the response time, due to inertia of the temperature. This inertia can be controlled and even avoided by choosing the correct amount of heat dissipation and location of the thermal elements. A log file records the measured temperature values by the system for operation analysis.
Focal Ration Degradation (FRD) is a change in light’s angular distribution caused by fiber optics. FRD is important to
fiber-fed, spectroscopic astronomical systems because it can cause loss of signal, degradation in spectral resolution, or
increased complexity in spectrograph design. Laboratório Nacional de Astrofísica (LNA) has developed a system that
can accurately and precisely measures FRD, using an absolute method that can also measure fiber throughput. This
paper describes the metrology system and shows measurements of Polymicro’s fiber FBP129168190, FBP127165190
and Fujikura fiber 128170190. Although the FRD of the two fibers are low and similar to one another, it is very
important to know the exact characteristics of these fibers since both will be used in the construction of FOCCoS (Fiber
Optical Cable and Connectors System) for PFS (Prime Focus Spectrograph) to be installed at the Subaru telescope.
The SOAR Integral Field Unit Spectrograph (SIFS) is fed by an integral field unit composed of a bi-dimensional
arrangement of 1300 optical fibers. It has been developed in Brazil by a team of scientists and engineers led by the
National Laboratory of Astrophysics (MCT/LNA) and the Department of Astronomy of the Institute of Astronomy,
Geophysics and Atmospheric Sciences of the University of São Paulo (IAG/USP). It comprises three major subsystems;
a fore-optics installed on the Nasmyth port of the telescope or the SOAR Adaptive Optics Module, a 14-m optical fiber
IFU, and a bench-mounted spectrograph installed on the telescope fork. SIFS is successfully assembled and tested on the
SOAR Telescope in Chile and has now moved to the commissioning phase. This paper reports on technical
characteristics of the mechanical design and the assembly, integration and technical activities.
The use of Volume Phase Holographic (VPH) gratings in astronomy is increasing worldwide due to its high efficiency,
flexibility in manufacturing and lower costs. For example 3 of 4 SOAR Telescope spectrographs are based on VPH
gratings. Following the growth in this technology use, tools are needed to characterize these gratings for their physical
and diffraction efficiency properties. We developed, at Laboratorio Nacional de Astrofisica / MCT (LNA), Brazil, an
assembly for characterization of VPH gratings. The relative efficiency of the gratings can be measured for specific
angles or scanned through the grating operation angles. Furthermore surface flatness and mounting stress effects are
measured using interferometric techniques. We present the experiment design and characteristics, describe the
measurement procedures and show the characterization results for some gratings of the SOAR Telescope spectrograph