FiberPol
Measuring More Than Light
Astronomy has traditionally advanced by building bigger telescopes. The next wave of discoveries will also come from extracting more information from every photon that reaches our telescopes.
FiberPol is a fibre-fed spectropolarimetric front-end developed for the SpUpNIC spectrograph on the South African Astronomical Observatory (SAAO) 1.9 m telescope. The project was conceived to show that high-precision spectropolarimetry can be achieved with a compact, modular, and relatively low-cost design, while remaining compatible with existing telescope infrastructure.
As Principal Investigator of the project, I led the scientific conception, optical design, optomechanical development, commissioning, and early science exploitation of FiberPol. The broader goal is to develop precision spectropolarimetric capability that can reveal astrophysical information inaccessible to imaging and spectroscopy alone.
Project Overview
| Role | Principal Investigator |
| Institution | South African Astronomical Observatory |
| Status | Operational (2025–present) |
| Host Telescope | SAAO 1.9 m |
| Instrument Type | Fibre-fed spectropolarimeter |
| Primary Science | Interstellar dust, magnetic fields, transient astronomy |
Why FiberPol?
Polarization carries information about magnetic fields, scattering geometries, dust grains, and three-dimensional structures that are often hidden from ordinary imaging and spectroscopy. Yet these signals are typically faint, often at the level of one percent or less, and require exceptional calibration and instrumental stability.
FiberPol was designed to make such measurements practical. By feeding telescope light through optical fibres into a stable bench-mounted spectrograph, the system improves environmental stability and enables higher polarimetric precision. It also serves as a technology demonstrator for future fibre-fed spectropolarimetric instruments.
From Idea to Instrument
FiberPol has involved every stage of instrument development:
- scientific motivation
- optical design
- optomechanical design
- laboratory characterisation
- calibration
- commissioning
- pipeline development
- scientific exploitation
The project combines classical dual-beam polarimetry with fibre-fed spectroscopy. A rotating half-wave plate and Wollaston prism separate the orthogonal polarization states, which are then injected into fibres and reformatted for the spectrograph.
Key features include:
- rotating super-achromatic half-wave plate
- Wollaston prism beam splitter
- dual fibre feed to the spectrograph
- compact modular optical design
- compatibility with existing telescope infrastructure
Commissioning
FiberPol achieved first light in 2025 and has since undergone commissioning observations at the SAAO 1.9 m telescope. Early observations demonstrated stable fibre injection, successful polarization modulation and demodulation, and repeatable calibration.
The commissioning campaign established the observing procedures and reduction pipeline used for routine science observations. Early reductions show promising spectropolarimetric performance approaching the design goals.
Science Enabled
FiberPol is being used to study:
- interstellar dust
- Galactic magnetic fields
- dust grain alignment
- circumstellar environments
- spectropolarimetry of stellar and Galactic sources
- optical transient phenomena
The broader message is simple: FiberPol is not only a new instrument, but a step toward a new observing capability. It shows how precision spectropolarimetry can be added to existing facilities and used to extract new physical information from astronomical sources.
Looking Ahead
FiberPol is part of a longer-term programme to develop increasingly capable spectropolarimetric instruments. Future directions include:
- improved calibration strategies
- higher polarimetric precision
- integral-field spectropolarimetry
- optical and near-infrared extension
- a northern counterpart on an Indian telescope
- ultra-stable bench-mounted spectropolarimeters
The long-term goal is to build a scalable instrumentation pathway that can support future surveys and precision follow-up observations.
Publications
- Maharana, S., Dennison-Farrar, K. C. J., Chattopadhyay, S., et al. (2026), Commissioning and On-sky Performance of FiberPol: A Fibre-fed Spectropolarimeter for the SAAO 1.9 m Telescope, SPIE Astronomical Telescopes + Instrumentation.
- Maharana, S., Chattopadhyay, S., Bershady, M. (2024), FiberPol-6D: Spectropolarimetric Integral-Field Mode for the SAAO 1.9 m Telescope using Fibres, SPIE Astronomical Telescopes + Instrumentation.
Gallery
Additional photographs from laboratory integration, commissioning, observing runs, and instrument development will be added here.