Researchers have developed a innovative hybrid fiber pump combiner that overcomes a critical challenge in the development of mid-infrared (mid-IR) fiber laser systems. This breakthrough solution leverages the evanescent field to efficiently couple light from silica pump fibers to soft glass signal fibers, enabling more sophisticated all-fiber mid-IR laser configurations. The design offers significant advantages over existing techniques and has the potential to drive further advancements in this important field of photonics.
Mid-IR Fiber Lasers: Releasing the Power
With the emergence of various applications such as environmental monitoring, medical diagnostics and global positioning systems, significant attention is also being given towards generation of novel mid-IR light sources, with high levels of efficiency and power handling capabilities. Among these, fiber-based mid-IR lasers, which operate above 2.5 μm wavelength, are of considerable interest as high-brightness sources.
Despite its successful lawfulness, scaling up laser generation to the mid-IR regime has remained largely an unrealizable dream principally due to devastating absorbance in silica fibers. Glass is one material matrix whose matrices have high phonon energy. In order to address this, scientists have begun investigating the use of alternative materials such as soft glass fibres. However, this transition necessitate a re-visitation of the design and development process for fiber lasers because soft glasses are not only high in thermal expansion (meaning they expand faster than conventional fused silica type glasses) but are also low melting point materials that can flow easily at typical cladding-preshapes temperatures; it is difficult to get them into large diameters whilst maintaining short lengths without collapsing due to their lack of mechanical rigidity.
Solving the Silica VS Soft Glass Fibers Problem
One of the most severe problems associated with pump source into mid-IR fiber laser systems is that Silica fibers do not match to soft glass fibers (Fluoride glass type). Considering that their melting temperature is half of silica and the expansion factor with temperature change is 30 times as high, these soft-glass fibers are virtually impossible to splice with mechanical methods known from standard splicing devices.
To overcome this problem, a research team led by Dr Maria Chernysheva from the Leibniz Institute of Photonic Technology has developed a new approach to combine an ytterbium-doped pump fiber and the Raman combiner in a single hybrid fiber pump combiner. Using the evanescent field, they demonstrated a coupling efficiency higher than 80 % without splicing fiber to the groove. This side-coupling allows the heat load to be uniformly spread over the extended polished fiber area, enabling a high-power, long-term stable operation with <0.09% RMS stability.
The Universal Workhorse Enabling Mid-IR Fiber Laser Systems
The small signal loss of the hybrid fiber pump combiner is lower than 0.getActiveSheet (Worksheet2)The demonstrated excess losses of the hybrid fiber pump combiner are less than 0.9 dB, which is at least as good as commercially available WDMs based on silica fibers and operating in neighbouring wavelength ranges for longer signal wavelengths. However, the design is flexible to accommodate a variety of fiber type used in combiner (whether active or passive) and can be tailored for different glass materials or polymer-based optical fibers.
This established novel scheme for the first time, provide new way to develop mid-IR all-fiber laser sources with obvious advantages over other butt-coupling ways. The design provides a new route to realise more complex laser configurations with enhanced performance and operation regimens, and it can be adaptable to other components such as material saturable absorbers or sensors.
