Coupling starlight into single-mode photonic crystal fiber using a field lens

Area of Science:

• Optics and Photonics
• Fiber Optics Engineering

Background:

• Large mode area (LMA) photonic crystal fibers offer high power handling.
• Efficiently coupling light into LMA fibers is crucial for optical system performance.
• Traditional direct coupling methods exhibit wavelength-dependent responses.

Purpose of the Study:

• To characterize the coupling efficiency of LMA photonic crystal fibers using an on-axis field lens.
• To compare the field lens coupling method with direct telescope pupil feeding.
• To evaluate the spectral response of the coupling method in the visible-NIR range.

Main Methods:

• Utilized an on-axis field lens to image the telescope exit pupil onto the LMA fiber input.
• Measured the coupling characteristics and field of view.
• Analyzed the spectral coupling response across the visible to near-infrared (NIR) spectrum.

Main Results:

• The field lens method achieved a maximum field of view comparable to direct PSF feeding.
• A flat, maximized coupling response was achieved across the entire visible-NIR spectrum.
• This contrasts with the wavelength-dependent response of direct coupling to LMA fibers.

Conclusions:

• Field lens coupling provides a superior, broadband coupling solution for LMA photonic crystal fibers.
• This technique overcomes the limitations of wavelength-dependent direct coupling and step-index fibers.
• Optimized coupling is essential for advanced photonic and astronomical applications.