Multichannel spectral mode of the ALOHA up-conversion interferometer

Abstract

In this paper, we propose a multichannel spectral configuration of the Astronomical Light Optical Hybrid Analysis (ALOHA) instrument dedicated to high resolution imaging. A frequency conversion process is implemented in each arm of an interferometer to transfer the astronomical light to a shorter wavelength domain. Exploiting the spectral selectivity of this non-linear optical process, we propose to use a set of independent pump lasers in order to simultaneously study multiple spectral channels. This principle is experimentally demonstrated with a dual-channel configuration as a proof-of-principle.

2023 Astrophotonics Roadmap: pathways to realizing multi-functional integrated astrophotonic instruments

“…For example, the current bandwidth with a single line pump laser at 3.5 µm is only 37 nm for a 2 cm long piece of PPLN. Two possible strategies can be envisioned: (1) injecting several pumps, for example using a comb, in the same crystal and demultiplexing through a multichannel spectral mode [598] or (2) multiplexing different signals on different crystals (with different periodicity to ensure wavelength sampling) which presents the advantage of allowing the conversion of large bandwidth signals with only one monochromatic pump laser. A second important challenge related to sensitivity is to improve the overall efficiency of the conversion chain which requires better mode overlap between the astronomical and pump fields in the nonlinear ridge waveguide, coupling efficiency at the input and output of the waveguide, conversion efficiency and possibly noise-free detection in order to compensate for the losses.…”

Astrophotonics: astronomy and modern optics

“…As the efficient conversion of photons requires long lithium niobate waveguides (2-4 cm), the conversion bandwidth is small and only narrow lines of the MIR spectrum can be explored. A possibility to extend the bandwidth of the the frequency conversion is to use several non-redundant phase-modulated pump sources at slightly different wavelengths which achieve phase-matching at different portions of the MIR spectrum (Lehmann et al 2018a). The phase modulation of the different pump sources allows disentangling the MIR spectral channels by a simple Fouriertransformation of the interferometric signal of both arms of the interferometer.…”

“…The phase modulation of the different pump sources allows disentangling the MIR spectral channels by a simple Fouriertransformation of the interferometric signal of both arms of the interferometer. The initial results of this project are very promising, however the conversion efficiency of the PPLN conversion stage requires improvements (e.g., longer PPLN, higher pump power, reduction of insertion losses), as the achieved overall conversion efficiency is in the order of 0.4% (Lehmann et al 2018a).…”

Towards a mid-infrared L band up-conversion interferometer: first on-sky sensitivity test on a single arm

“…This condition induces a selection on the converted spectral bandwidth denoted the spectral acceptance of the non-linear crystal λ. This selectivity allows spectral multiplexing using a set of independent pump lasers around frequency ν p (Lehmann et al 2018b).…”