Modal noise in an integrated photonic lantern fed diffraction-limited spectrograph

N. Cvetojevic*, N. Jovanovic, S. Gross, B. Norris, I. Spaleniak, C. Schwab, M. J. Withford, M. Ireland, P. Tuthill, O. Guyon, F. Martinache, J. S. Lawrence

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)


In an attempt to develop a streamlined astrophotonic instrument, we demonstrate the realization of an all-photonic device capable of both multimode to single mode conversion and spectral dispersion on an 8-m class telescope with efficient coupling. The device was a monolithic photonic spectrograph which combined an integrated photonic lantern and an efficient arrayed waveguide grating device. During on-sky testing, we discovered a previously unreported type of noise that made spectral extraction and calibration extremely difficult. The source of the noise was traced to a wavelength-dependent loss mechanism between the feed fiber’s multimode near-field pattern and the modal acceptance profile of the integrated photonic lantern. Extensive modeling of the photonic components replicates the wavelength-dependent loss, and demonstrates an identical effect on the final spectral output. We outline that this could be mitigated by directly injecting into the integrated photonic lantern.

Original languageEnglish
Pages (from-to)25546-25565
Number of pages20
JournalOptics Express
Issue number21
Publication statusPublished - 16 Oct 2017


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