Naoyuki Tamura

SUBARU prime focus spectrograph integration and performance at LAM

The Prime Focus Spectrograph (PFS) of the Subaru Measurement of Images and Redshifts (SuMIRe) project for Subaru telescope includes four identical spectrograph modules fed by 600 fibers each. This paper presents the integration, alignment and test procedures for the first spectrograph module composed by an optical entrance unit that creates a collimated beam and distributes the light to three channels, two visible and one near infrared. In particular, we present the performance of the single Red channel module. Firstly, we report on the measured optical performance: optical quality and ghost analysis. We also report on the thermal performance of the visible camera cryostat. Finally, we describe the software used to control and monitor the instrument.

An optimal method for producing low-stress fibre optic cables for astronomy

An increasing number of astronomical spectrographs employ optical fibres to collect and deliver light. For integral-field and high multiplex multi-object survey instruments, fibres offer unique flexibility in instrument design by enabling spectrographs to be located remotely from the telescope focal plane where the fibre inputs are deployed. Photon-starved astronomical observations demand optimum efficiency from the fibre system. In addition to intrinsic absorption loss in optical fibres, another loss mechanism, so-called focal ratio degradation (FRD) must be considered. A fundamental cause of FRD is stress, therefore low stress fibre cables that impart minimum FRD are essential. The FMOS fibre instrument for Subaru Telescope employed a highly effective cable solution developed at Durham University. The method has been applied again for the PFS project, this time in collaboration with a company, PPC Broadband Ltd. The process, planetary stranding, is adapted from the manufacture of large fibre-count, large diameter marine telecommunications cables. Fibre bundles describe helical paths through the cable, incorporating additional fibre per unit length. As a consequence fibre stress from tension and bend-induced ‘race-tracking’ is minimised. In this paper stranding principles are explained, covering the fundamentals of stranded cable design. The authors describe the evolution of the stranding production line and the numerous steps in the manufacture of the PFS prototype cable. The results of optical verification tests are presented for each stage of cable production, confirming that the PFS prototype performs exceptionally well. The paper concludes with an outline of future on-telescope test plans.

Software development of fiber positioning sequencer for prime focus spectrograph of Subaru telescope

The Prime Focus Spectrograph (PFS) is a new optical/near-infrared multi-fiber spectrograph designed for the prime focus of the 8.2m Subaru telescope. PFS will cover a 1.3-degree diameter field with 2394 fibers to complement the imaging capability of Hyper SuprimeCam (HSC). The Fiber Positioning System (FPS) is an automated system that controls the sequences for the operation of the PFS subsystems to achieve accurate positioning of the science fibers for astronomical observations. FPS will be operated continuously for 14 hours a night and accomplish the fiber positioning sequence every 15 minutes. The success rate of each alignment should be 95% or more and FPS should finish the fiber alignment procedure in 105 seconds. A fast centroid algorithm is implemented for measuring 2349 fiber spots within 1 second. In this report, the latest status of the development of FPS system will be given, including the system performance and closed-loop simulations.

Alignment of wide field corrector against the primary mirror optical axis by spot images on auto guide cameras for prime focus spectrograph of Subaru Telescope

Alignment between the primary mirror of the telescope and wide field corrector (WFC) is necessary for Prime Focus Spectrograph (PFS) ,which is the next instrument for Subaru telescope in Hawaii. From 6 defocused star images we can align the optical axis of wide field corrector to primary mirrors optical axis with required accuracy.

FRD characterization in large-scale for FOCCoS of Prime Focus Spectrograph for Subaru telescope

The focal ratio degradation effects on optical fibers, technically referred to as FRD, has been the subject of intense studies since the beginning of the use of optical fibers in the construction of instruments applied in astronomy. A number of studies attempt to relate FRD to light loss in the optical system and other studies attempt to qualify and quantify FRD as a function of the stress induced during assembly of the structures supporting the ends of the optical fibers. In this work, we present a large-scale study to characterize FRD in all the fibers that make up the cables of the FOCCoS, Fiber Optical Cable and Connectors System project. FOCCoS, has the main function of capturing the direct light from the focal plane of Subaru Telescope using 2400 optical fibers, each one with a microlens in its tip, and conducting this light through a route containing connectors to a set of four spectrographs. The optical fiber cable is divided in 3 different segments called Cable A, Cable B and Cable C. Multi-fibers connectors assure precise connection among all optical fibers of the segments, providing flexibility for instrument changes. Our study provides procedures and methods to analyze the effects of FRD on all cable segments for each type of termination involved. Special attention is devoted to the understanding of how angular deviations between the input surface of the fiber and the test beam can significantly influence the calculation of FRD in optical fibers.

Slit device assembly of Prime Focus Spectrograph for Subaru telescope

The Fiber Optic Cable and Connector System, FOCCoS, is a set of optical cables to feed the Prime Focus Spectrograph, PFS, for Subaru telescope [01,02]. The extremity responsible for delivering light to spectrographs is called, FCA, Fiber Cable A. Cable A is the cable installed at the Spectrograph side and consists of the Fiber Slit Assembly, FSA, the routing with its support and the Fiber Input Assembly, FIA. FSA is composed of a set of optical fibers arranged linearly on the Slit device and supported by the Frame, protected by segmented tubes and routed between strain relief boxes and the connection interface. FIA is composed by the Connector Bench (Gang Connector) that allow connection with Cable B, at the Subaru Telescope interface, to receive light from Cable C where the fibers end is coupled with microlens. As four Spectrographs are considered for PFS/Subaru, four units of Cable A are necessary. In this paper, we present in details of a complete FCA to be installed in the spectrograph bench. We discuss about the general design, methods used to manufacture the involved devices.

Permanent optical fiber cable for Prime Focus Spectrograph and Subaru telescope “Cable B”

FOCCoS, Fiber Optical Cable and Connector System, is a part of subsystem of Prime Focus Spectrograph”, for Subaru telescope. FOCCoS are divided in 3 different segments called Cable A, Cable B and Cable C. Multi-fibers connectors assure precise connection among all optical fibers of the segments, providing flexibility for instrument changes. Cable B is permanently installed at Subaru Telescope structure starting in a Connector Bench device and finishing at another different Connector Bench device. By this way, Cable B represent a link between the light entrance, from Cable C, and the light delivery, to Cable A. This cable will be routed to minimize the compression, torsion and bending caused by the cable weight and telescope motion. In this work, we present the current stage of development of Cable B as well as the detailing of its structures. In addition, we present the optical fiber cabling methodology and the test procedures involved in its characterization. A prototype of Cable B was constructed to help us to better understanding the real situation and was tested at Subaru Telescope.