Ultrashort mid-infrared (mid-IR) laser pulses are essential for applications such as molecular spectroscopy, nonlinear microscopy, and biomedical imaging, but their generation often relies on complex and power-intensive systems that are difficult to implement outside of specialized laboratories. These systems usually require high pump powers, elaborate optical setups, and precise alignment, which can limit their widespread adoption and practical use in everyday research and clinical settings.
In a paper made available online on 28 November 2025 and published in Volume 62, Issue 1 of the IEEE Journal of Quantum Electronics on 01 February 2026, a team of researchers from SASTRA Deemed University, Thanjavur, report a compact, fiber-based method for generating clean ultrashort mid-IR pulses at significantly reduced input power. The study demonstrates that high-quality pulse compression can be achieved using a holmium-doped ZBLAN photonic crystal fiber integrated into a nonlinear optical loop mirror (NOLM), offering a simpler and more energy-efficient alternative to conventional systems.
A carefully engineered tapered fiber geometry enables self-similar pulse evolution, ensuring that the pulse maintains its shape as it propagates along the fiber. This is crucial for achieving efficient compression and preserving pulse fidelity during propagation. Holmium doping provides optical gain near 2.86 μm, which amplifies the signal and compensates for losses that can occur during propagation. Together, these features enable efficient pulse compression, suppress unwanted temporal pedestals that can reduce pulse quality, and prevent fiber damage even under high-intensity operation. The integration of these components within a single fiber-based architecture allows for a compact and robust system design that minimizes alignment complexity and enhances overall operational stability, making it more suitable for real-world deployment.
"By combining rare-earth enabled gain and nonlinear pulse shaping mechanism of nonlinear optical loop mirror configuration, we reduced the required input power from the kilowatt range to just 80 watts," said G. Sornambigai, the lead author. This dramatic reduction in power not only improves energy efficiency but also reduces the thermal load on the fiber, lowering the risk of damage and extending the operational lifetime of the system significantly.
At the optimized fiber length, the system compressed 5-picosecond pulses to 187 femtoseconds, achieving a compression factor of 26.7 with pedestal energy as low as 0.63%. "This architecture delivers clean, high-contrast pulses that are well suited for mid-IR spectroscopy and nonlinear imaging," added co-author R. Vasantha Jayakantha Raja.
Self-similar pulse modelling and system-level analysis played a key role in optimizing performance and ensuring reliable pulse compression. The researchers note that this is the first demonstration of a Ho:ZBLAN-based NOLM system producing sub-200 femtosecond pulses in the mid-infrared, marking an important milestone in the development of compact, low-power, and highly efficient ultrafast mid-IR sources.
By providing a robust, alignment-free, and energy-efficient route to ultrashort mid-IR pulse generation, this fiber-based approach has the potential to accelerate advances in spectroscopy, nonlinear imaging, and other emerging photonic applications, bringing ultrafast mid-infrared technologies closer to practical real-world deployment.
