[Paper Review] Integrated optics for astronomical interferometry. I. Concept and astronomical applications

F. Malbet, P. Kern+3 more|ArXiv.org|Jul 2, 1999

Adaptive optics and wavefront sensing16 references60 citations

TL;DR

This paper proposes using integrated optics—miniaturized, stable, and low-cost optical circuits on a chip—for high-precision optical and infrared interferometry in astronomy. By replacing bulk optical components with waveguide-based systems, it enables compact, alignment-free beam combination with intrinsic polarization control, particularly suited for multi-aperture interferometers and space-based missions.

ABSTRACT

We propose a new instrumental concept for long-baseline optical single-mode interferometry using integrated optics which were developed for telecommunication. Visible and infrared multi-aperture interferometry requires many optical functions (spatial filtering, beam combination, photometric calibration, polarization control) to detect astronomical signals at very high angular resolution. Since the 80's, integrated optics on planar substrate have become available for telecommunication applications with multiple optical functions like power dividing, coupling, multiplexing, etc. We present the concept of an optical / infrared interferometric instrument based on this new technology. The main advantage is to provide an interferometric combination unit on a single optical chip. Integrated optics are compact, provide stability, low sensitivity to external constrains like temperature, pressure or mechanical stresses, no optical alignment except for coupling, simplicity and intrinsic polarization control. The integrated optics devices are inexpensive compared to devices that have the same functionalities in bulk optics. We think integrated optics will fundamentally change single-mode interferometry. Integrated optics devices are in particular well-suited for interferometric combination of numerous beams to achieve aperture synthesis imaging or for space-based interferometers where stability and a minimum of optical alignments are wished.

Motivation & Objective

• Address the challenges of stability, alignment, and complexity in long-baseline optical interferometers.
• Overcome limitations of bulk optics in multi-beam combination and space-based applications.
• Leverage mature telecom-integrated optics technology for astronomical interferometry to reduce cost and improve reliability.
• Enable high-precision interferometric measurements with intrinsic polarization control and thermal stability.
• Pave the way for compact, scalable instruments for future ground-based and space-based interferometric missions.

Proposed method

• Adapt integrated optics technology—originally developed for telecommunications—for astronomical interferometry.
• Use planar substrates with ion-exchanged or silicon-etched waveguides to confine and guide light in a single chip.
• Implement beam combiners, photometric calibration channels, and polarization-maintaining components on a single integrated chip.
• Minimize external optical components by eliminating relay optics and reducing alignment requirements through monolithic integration.
• Utilize waveguides to directly feed spectrographs, replacing cylindrical optics for fringe compression.
• Integrate components into a dewar to reduce thermal background and improve detector efficiency.

Experimental results

Research questions

• RQ1 Can integrated optics provide a stable, low-cost alternative to bulk optics for beam combination in astronomical interferometers?
• RQ2 To what extent can integrated optics reduce alignment complexity and improve thermal and mechanical stability in interferometric instruments?
• RQ3 How well can integrated optics maintain polarization across multiple beams, a critical requirement for high-precision interferometry?
• RQ4 Can integrated optics enable efficient, compact multi-beam combination suitable for aperture synthesis imaging with many apertures?
• RQ5 What are the feasibility and performance limits of integrated optics in space-based interferometric missions?

Key findings

• Integrated optics components can be fabricated on a single chip measuring approximately 5 mm × 20 mm, enabling full instrument integration in a compact form factor.
• The technology exhibits high stability due to monolithic integration, with low sensitivity to temperature, pressure, and mechanical stress.
• Only one optical alignment is required—coupling light into the waveguides—dramatically reducing mechanical complexity compared to bulk optics.
• The components provide intrinsic polarization control, with no differential phase shift introduced when the design is symmetrical.
• Thermal background is reduced by integrating the waveguide directly into the dewar, eliminating relay optics and minimizing photon loss.
• Laboratory experiments successfully demonstrated fringes using a white light source, validating the feasibility of the approach (confirmed in Paper II).