A Multi-Core Fibre Photonic Lantern Based Spectrograph for Raman Spectroscopy

• Published in: IEEE photonics technology letters Vol. 32; no. 7; p. 1
• Main Authors: Betters, Christopher H., Bland-Hawthorn, Joss, Sukkarieh, Salah, Gris-Sanchez, Itandehui, Leon-Saval, Sergio G.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.04.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: 3D Printed; Apertures; Converters; Detectors; Diffraction; Fibre reformater; Harnesses; Ibuprofen; Multi-core fibre; Optical design; Optical fibers; Optical imaging; Optical sensors; Optical spectroscopy; Photonic lantern; Photonics; Raman spectra; Raman spectroscopy; Robot sensing systems; Spectrum analysis; Three dimensional printing
• ISSN: 1041-1135; 1941-0174
• DOI: 10.1109/LPT.2020.2976599

We report on the development of a compact (volume ≈ 100 cm3), multimode diffraction-limited Raman spectrograph and probe designed to be compact as possible. The spectrograph uses 'off the shelf' optics, a custom 3D-printed two-part housing and harnesses a multi-core fibre (MCF) photonic lantern (multimode to few-mode converter), which slices a large 40 m multimode input into a near-diffraction-limited 6 m aperture. Our unique design utilises the hexagonal geometry of our MCF, permitting high multimode collection efficiency with near-diffraction-limited performance in a compact design. Our approach does not require a complex reformatter or mask and thus preserves spectral information and throughput when forming the entrance slit of the spectrograph. We demonstrate the technology over the interval 800 nm to 940 nm (200 cm-1 to 2000 cm-1) with a resolution of 0.3 nm (4 cm-1), but other spectral regions and resolutions from the UV to the near infrared are also possible. We demonstrate the performance of our system by recording the Raman spectra of several compounds, including the pharmaceuticals paracetamol and ibuprofen.