Demonstrating the integration of a photonic lantern with an all-fiber-based nulling interferometer

Introduction to the show: ident: Astrophysics. The day in astrophysics: observations, models and what the data forces.

Vera: We're looking at the paper: "Demonstrating the integration of a photonic lantern with an all-fiber-based nulling interferometer".

Jocelyn: Here's the gist of the paper. High-contrast imaging of Solar System scale exoplanets and protoplanets demands advancements in instrumentation to access deeper starlight suppression at smaller angular separations than today’s state-of-the-art.

Vera: The multi-mode to single-mode conversion capabilities of photonic lanterns (PLs) provide new avenues to implement techniques such as nulling interferometry due to the inherent spatial filtering of single-mode waveguides.

Jocelyn: This work presents laboratory results on an all-fiber-based focal plane nulling interferometer using off-the-shelf components operating at 1550 nm.

Vera: Instrument Design and Components The IR version of the nulling interferometer, hereafter the “nuller,” builds on the design used in Diaz et al.

Title and authors: Vera: Let's talk about the title and the authors of this paper, "Demonstrating the integration of a photonic lantern with an all-fiber-based nulling interferometer." It immediately tells us that they are showing a way to combine two specific pieces of technology for high contrast imaging.

Jocelyn: And it’s interesting because they’re focusing on using these photonic lanterns to feed light into an all-fiber setup, which is a specific engineering challenge in this kind of work.

Subrahmanyan: From a theoretical side, combining the spatial filtering of single-mode fibers with the redistribution capability of photonic lanterns suggests a potential pathway for achieving deeper starlight suppression at those smaller separations you mentioned.

Vera: They are essentially showing that these PLs can be used to redistribute light to different ports based on where an object is in the sky, which helps suppress the contaminating starlight when we look for a companion.

Jocelyn: And they’re using visible laser light for their proof-of-concept demonstration in this infrared version of the instrument.

Subrahmanyan: The fact that they moved to infrared and demonstrated this integration is a step toward making these concepts more relevant to real astronomical observations, where we deal with much longer wavelengths.

Vera: They also discuss a specific application for this instrument, which is the identification of accreting protoplanets, which is something we’ve been thinking about.

The paper's summary: Jocelyn: So, what they summarize in this paper is that they built an infrared version of their nulling interferometer called the "nuller," and they used a photonic lantern to feed light into it for the first time in this setup.

Vera: They built this nuller on top of the design from a previous work by Diaz et al. two thousand twenty-four and they’re using something called a Mach-Zehnder interferometer structure that benefits from the spatial filtering properties of single-mode fibers <ref:2607.24737#pg2>.

Subrahmanyan: The core mechanism they are demonstrating is how the photonic lantern can be used to feed light into the instrument in a way that exploits those inherent spatial filtering properties of the SM fibers to improve the nulling performance.

Jocelyn: They also stabilized this nuller with active phase and intensity modulation components, which is important for keeping it stable against noise during measurement.

Vera: They show two ways they fed light into the instrument: one using a directional coupler directly connected to the laser, and another configuration that uses the photonic lantern.

Subrahmanyan: The comparison between these two light-feeding configurations shows how much better the performance is when you use the photonic lantern compared to just using a directional coupler.

The paper's improvements: Vera: One of the main improvements they suggest is that using the photonic lantern helps with nulling, because it leads to a flatter envelope of null depth over a wider range of pupil diameters.

Jocelyn: They show that the shape of this envelope is flatter and exhibits a deeper null level compared to the non-photonic case, especially when you look at extended ranges of PLDs.

Subrahmanyan: That means for detecting objects at different separations, this setup gives you a better null depth over more of those separations than the previous methods they tested.

Vera: They also point out that the preliminary models they made didn't match their experimental data perfectly because they didn't have all the details on how well the laser emitted light.

Jocelyn: So, they hypothesize that this difference might be due to an error in light injection when using a directional coupler instead of the photonic lantern, especially at that interface between the laser and the fiber patch cable.

Subrahmanyan: That suggests that controlling exactly how light gets from the source into the system is a really critical factor for getting accurate nulling measurements.

Conclusion: Vera: To wrap up, they demonstrated using a seven-port photonic lantern to feed this all-fiber nulling interferometer with monochromatic infrared light at a wavelength of one thousand five hundred fifty nm.

Jocelyn: And the key result is that nulling with the PL outperformed the case when using just a directional coupler, maintaining deeper levels of light rejection over extended pupil diameter ranges and reaching a maximum null depth about three times deeper, which they put as two to the k with the PL versus six to the k with just a directional coupler.

Subrahmanyan: That improvement in null depth is significant for our goal of accessing those smaller angular separations where we need that high contrast suppression.

Vera: This work is noted by the authors as being among the first to validate using a photonic lantern for nulling interferometry with active phase and intensity control components.

Jocelyn: And they say this will contribute to the advancement of photonic-based systems working in synergy with photonic integrated circuits for future ground- and space-based telescopes.

Subrahmanyan: The next step toward using this nuller as an instrument for detecting accreting protoplanets involves feeding it with broadband light and doing the nulling with Pa beta light, which is a specific hydrogen recombination line.

Vera: So, to finish up on the "Demonstrating the integration of a photonic lantern with an all-fiber-based nulling interferometer," we see that this setup provides a path forward for better starlight suppression in high-contrast imaging.