🔭 astrophysics

PEEPSS: Photonic-Enabled ExoPlanet Spectroscopic Sensor for the Habitable Worlds Observatory

The PEEPSS (Photonic-Enabled ExoPlanet Spectroscopic Sensor) is a proposed system for the Habitable Worlds Observatory that uses photonic lanterns to couple light from a coronagraph's "dark hole" into single-mode fibers, enabling high-precision wavefront sensing and efficient near-infrared spectroscopy to improve the detection of exoplanets at small inner working angles.

Original authors: Genevieve Markees, Stephen S. Eikenberry, Rodrigo Amezcua-Correa, Miguel Bandres, Rebecca Jensen-Clem, Sergio Leon-Saval, Laurent Pueyo, Raphaël Pourcelot

Published 2026-04-28

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Original authors: Genevieve Markees, Stephen S. Eikenberry, Rodrigo Amezcua-Correa, Miguel Bandres, Rebecca Jensen-Clem, Sergio Leon-Saval, Laurent Pueyo, Raphaël Pourcelot

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you are trying to spot a tiny, glowing firefly hovering next to a massive, blindingly bright searchlight from miles away.

In astronomy, that "searchlight" is a distant star, and the "firefly" is a potentially habitable planet. The problem is that the star is so bright it completely washes out the planet. To find these planets, NASA is planning a mission called the Habitable Worlds Observatory (HWO), which will use a device called a coronagraph—essentially a high-tech "sunshade" designed to block the star's light so we can see the planets around it.

However, even with a sunshade, the light from the star is so intense that even a tiny bit of "leakage" can ruin the view. This paper introduces a new invention called PEEPSS to solve this problem.

Here is how PEEPSS works, explained through three simple ideas:

1. The "Smart Funnel" (The Photonic Lantern)

Normally, when light hits a sensor, it’s like dumping a bucket of water onto a floor; it just splashes everywhere, and it's hard to tell exactly where each drop came from.

PEEPSS uses something called a photonic lantern. Imagine instead of a flat floor, you have a collection of hundreds of tiny, specialized funnels. When the light hits these funnels, it sorts the light into specific "lanes" (called modes). This allows scientists to take a messy, chaotic splash of light and organize it into neat, orderly streams that can be studied one by one.

2. The "Double-Duty" Sensor (Wavefront Sensing)

To keep the "sunshade" working perfectly, the telescope needs to constantly adjust itself to make sure no starlight is leaking through. This is called "wavefront sensing."

Think of it like trying to keep a laser pointer beam perfectly steady while you are walking on a bumpy boat. You have to make constant, tiny adjustments.

Usually, telescopes use one tool to check the beam and a different tool to look at the planet. The problem is that the two tools might "see" the light slightly differently (this is called a "non-common-path error").

PEEPSS is a multitasker. It uses the "leaked" starlight in the center of the image to check the telescope's alignment, while simultaneously using the "dark" area around it to look for planets. It’s like a driver who uses the glare on their windshield to judge how much they need to adjust their mirrors, all while keeping their eyes on the road. Because it uses the same path for both tasks, the corrections are much more accurate.

3. The "All-in-One" Camera (Spectroscopy)

Once you actually find a planet, you don't just want to see it; you want to know what it's made of. Does it have oxygen? Water? Methane? To find this out, you need to perform spectroscopy, which is like breaking light into a rainbow to read its "chemical fingerprint."

In traditional telescopes, you might need one instrument to take a picture and another to read the fingerprint. PEEPSS does both at once. Because the "funnels" (the lanterns) have already sorted the light into neat streams, PEEPSS can take a single measurement and give you both a clear picture of the planet and a detailed chemical report of its atmosphere.

Summary: Why does this matter?

If we want to find "Earth 2.0," we need to be incredibly precise. PEEPSS is like giving the telescope a pair of high-tech, smart-glasses that can:

Clean up the glare from the star.
Self-correct its own vision in real-time.
Analyze the chemistry of a planet instantly.

By doing all of this at once, PEEPSS makes it much more likely that we will actually find a world that could support life.

Technical Summary: PEEPSS (Photonic-Enabled ExoPlanet Spectroscopic Sensor)

1. Problem Statement

The proposed Habitable Worlds Observatory (HWO) aims to directly image and characterize approximately 25 Earth-like exoplanets. To achieve this, the telescope must reach extreme contrasts of one part in ten billion ( $10^{-10}$ ). The primary technical challenge is the requirement for extreme wavefront stability and precision. Even minute misalignments or aberrations in the telescope's optics can cause starlight to leak into the "dark hole" (the region in the coronagraph focal plane where the planet is expected to be), masking the dim signal of an exoplanet.

Furthermore, performing high-contrast imaging in the Near-Infrared (NIR) is difficult because the Inner Working Angle (IWA) of a coronagraph scales with wavelength, often exceeding the orbital radius of the target planets. There is also a need for efficient, simultaneous methods to perform wavefront sensing, imaging, and spectroscopy without introducing "non-common-path errors" (errors caused by light traveling through different optical paths for sensing vs. science).

2. Methodology

The authors propose PEEPSS, a sensor module placed after the coronagraph pupil that utilizes astrophotonics, specifically photonic lanterns.

Photonic Lantern Technology: The system uses two types of lanterns to decompose a multi-mode light field into discrete single-mode outputs:
- Standard Photonic Lanterns: Couple to linearly-polarized (LP) modes.
- Ring Photonic Lanterns: Designed with an annular cross-section to couple to Orbital Angular Momentum (OAM) modes.
System Architecture: The module splits light using a polarizing beamsplitter into four channels (two sets of paired ring and standard lanterns).
- The Ring Lantern captures the "dark hole" region (the annulus where the planet resides).
- The Standard Lantern captures the central "core" region (dominated by residual starlight).
- A mirror coating on the face of the ring lantern redirects the central starlight to the standard lantern.
Wavefront Reconstruction: By measuring the amplitude and phase of the discrete modes exiting the lanterns, the system uses a Gerchberg-Saxton-style algorithm to reconstruct the full complex electric field of the incoming light.
Core-Annulus Mapping: To enhance sensing, the researchers use a matrix factorization technique (Single Value Decomposition) to create a "core-annulus matrix." This allows the system to use the bright residual starlight in the core to predict and reconstruct the aberrations present in the dark hole annulus.

3. Key Contributions

Common-Path Wavefront Sensing: By placing the sensor at the spectroscopic focal plane, PEEPSS eliminates non-common-path errors, as the sensing and science light follow the same path.
Simultaneous Multi-functionality: The design enables simultaneous wavefront sensing, direct imaging, and spectroscopy.
NIR Optimization: The use of photonic lanterns allows for smaller IWAs in the NIR, expanding the observational parameter space for HWO.
Modal Decomposition: The use of OAM modes via ring lanterns provides a novel way to capture the spatial information of the dark hole.

4. Results

Wavefront Fidelity: Simulations using a 6-meter aperture and a $V=1$ mag reference star demonstrated that PEEPSS can reconstruct the true modal composition of the dark hole with high fidelity. A single 100-second observation provided enough information to enable a ten-fold improvement in contrast.
Effective Aberration Tracking: The "core-annulus" mapping approach successfully reproduced dark hole aberrations using only information from the central starlight, proving that HWO could track wavefront errors in real-time during science observations.
Spectroscopic Performance: Simulations compared PEEPSS to traditional Integral Field Units (IFUs). The results showed that in shot-noise-limited scenarios (typical for faint targets), the Signal-to-Noise Ratio (SNR) of PEEPSS is comparable to an IFU. While PEEPSS may have a slightly lower SNR in detector-noise-limited scenarios due to light being spread across more modes, it remains a highly viable spectroscopic tool.

5. Significance

PEEPSS represents a significant technological leap for the HWO mission. By integrating wavefront sensing directly into the science channel, it maximizes observational productivity—reducing the time needed to characterize targets. Its ability to provide high-fidelity wavefront control while simultaneously performing spectroscopy makes it a lightweight, efficient, and powerful solution for the search for life on Earth-like exoplanets.