Broadband MIR Source Facilitates Fiber Optic Sensors

A collaborative research project has demonstrated a broadband mid-infrared (MIR) source designed to facilitate a simplified environmental monitoring system with potential value in industrial and medical applications. The source generates a highly stable broadband beam in the MIR wavelength range between 2.5 and 3.7 μm that, in testing, maintained its full brightness due to a very high beam quality. The light source features a simple configuration and is a necessary component of a MIR fiber optic sensor.

A research team of the National Institutes of Natural Sciences, the National Institute for Fusion Science, and Akita Prefectural University, all in Japan, demonstrated the light source and sensor technology.

In the MIR wavelength region, there are many strong absorption lines of molecules due to the change of their rotational and vibrational states. MIR sources therefore show promise in sensitive remote monitoring systems. This is especially true of fiber-optic sensor systems for MIR absorption spectroscopy, which show potential as next-generation detection devices targeting exhaust gases in industrial plants or breath analysis in a medical setting.

To optimize that kind of a system, however, such a device would require an MIR light source capable of exhibiting broadband spectrum and high beam quality.

The new work demonstrates an ultrabroadband amplified spontaneous emission (ASE) source in the MIR, meeting those requirements.

Diode-pumped configuration showing the enabling of a compact/low-cost device construction. Courtesy of the National Institute for Fusion Science.

The researchers first custom-developed an optical fiber using fluoride glass co-doped with trivalent ions of erbium (Er) and dysprosium (Dy). The completed fiber enabled a simple, low-cost ASE light source configuration with diode-pumping stemming from an energy transfer between the two trivalent ions. The researchers were able to then investigate a broadband and moderate power ASE light source (2.5 to 3.7 μm) experimentally for the optimal design of fluoride fiber, considering factors of fiber length, ion concentration, pumping configuration, and pumping power.

The light source’s excellent beam quality also enabled high coupling efficiency using an external optical fiber, the researchers reported.

In addition to industrial and life sciences applications, research team member Hiyori Uehara said the light source can facilitate the inspection of fiber optic devices.

Uehara said that the team plans further research aimed at demonstrating highly sensitive multiple-gas detection using a MIR fiber sensor and that work in that area is currently ongoing.

The research was published in Scientific Reports (www.doi.org/10.1038/s41598-021-84950-y).

*This article has been updated for accuracy