Proof of concept of heterodyne interferometry at 10.6 um using photonic correlation

The task of imaging complex dust environments such as the inner astronomical units of a planet-forming disks requires dedicated mid-infrared (MIR) interferometric facilities with kilometric baselines and a large number of telescopes.

Extrapolating technologies from current facilities is not straightforward.

We aim to demonstrate the feasibility of using MIR heterodyne interferometry with a photonic correlation approach to recombine MIR signals from distant telescopes.

We want to determine the current technological limits of such systems are.

We developed a laboratory demonstration bench that can correlate MIR signals at 10 um with a photonic correlator.

The photonic correlator uses commercially available telecom components at 1.5 um to transport and correlate heterodyne signals that could go up to 10 GHz in bandwidth, directly extendable to 40 GHz.

We used the demonstration bench to study the noise levels and detection limits of a heterodyne interferometer with a photonic correlation.

We confirm the correlation exhibited by wideband MIR signals with the photonic correlator, along with a characterization of the performance of the system and analyzed the noise levels.

We show that the photonic correlator does not limit the detection and that it can be used to compensate for free-space delays at 10 um with a fiber delay at 1.5 um.

With our current sub-optimal commercial infrared (IR) detectors, we have derived a detection limit of 130 Jy that is coherent flux for 8 m class telescopes with 1 h of incoherent integration.

We discuss the possibility of lowering the detection limit down to typical T-Tauri stars (approximately 1 Jy) using new detectors and coherent integration based upon local oscillator synchronization with telecom fiber links.