Femtosecond laser writing used to create passive and active dual waveguides

01 November 2024

Femtosecond laser writing used to create passive and active dual waveguides

Technology advance could enhance laser performance for compact photonic devices

Researchers have shown that ultrashort laser pulses can be used to produce double waveguides in glasses. When the glass is doped with rare earth ions, the waveguides can be used to achieve laser amplification with low loss for both straight, curved and "Y" geometries. This advance could enable new types of compact, portable photonic devices.

Wagner de Rossi from IPEN in Brazil will present this research at the Latin America Optics and Photonics Congress, held 10 - 14 November 2024 in Puerto Vallarta, Mexico.

Due to their cost efficiency, compactness and simplicity, waveguides are often used to guide light in small photonic devices. In the new work, the researchers developed a way to create both active and passive double waveguides in glasses doped with heavy metals oxides.

"These glasses are relatively inexpensive, with a high nonlinear refractive index and a wide transmission window from visible to infrared," said de Rossi. "The simplicity of production, good optical properties of the material, low cost and its versatility make these guides suitable for use in optical communication amplifiers, beam splitters, optomicrofluidic systems, compact interferometers, etc."

To create the waveguides, the researchers focused femtosecond laser pulses beneath the surface of germanate and tellurite glasses to form tracks of overlapped pulses. Due to spherical aberration and self-focusing effects, these tracks become thin, high walls that have a decreased refractive index, preventing guidance within them. Therefore, a pair of closely spaced walls was used to guide light between them. The researchers created straight and curved guides and varied the energy per pulse and the number of overlapping pulses to optimize the guiding mode and reduce losses. They found that when a repetition rate of 10 kHz was used for laser writing, the best conditions occurred with a line spacing of 10 µm, energy of 30 µJ per pulse, and a scan speed of 1 mm/s.

To achieve laser amplification, they created double waveguides in germanate glass doped with neodymium and erbium/ytterbium. The neodymium-doped glass showed a 3.6 dB/cm gain at 1310 nm with 1.6 mW of pump power at 805 nm. The Er/Yb-doped glass exhibited a 7.5 dB/cm gain at 1550 nm with 105 mW of pump power at 980 nm. They also found that incorporating silver nanoparticles into neodymium-doped germanate glasses significantly increased the gain and guidance performance of the waveguides.

The figure below shows a pair of double guides and the luminescence produced upon amplification in a guide produced in Er/Yb doped GeO2-PbO glass.

Top view microscope images of double line waveguides in GPO:Er/Yb. Image captured by using a 200x magnification and polarized light showing two pairs of guides separated by 40 microns from each other (a). Single double line waveguide pumped at 980 nm, for amplification at 1550 nm (b).

About the Optica Latin America Optics and Photonics Conference (LAOP)

LAOP is the major international conference sponsored by Optica in Latin America with the explicit objective to promote Latin American excellence in optics and photonics research and support the regional community. LAOP is a peer-reviewed, international meeting with content presented in English, which enables maximum international participation. Featuring a comprehensive technical program with recognized experts in fields critical to Latin America, the conference covers all major areas of optics and photonics and features the latest research results that are making an impact in fundamental research and applications.

About Optica

Optica, Advancing Optics and Photonics Worldwide, is the society dedicated to promoting the generation, application, archiving and dissemination of knowledge in the field. Founded in 1916, it is the leading organization for scientists, engineers, business professionals, students and others interested in the science of light. Optica's renowned publications, meetings, online resources and in-person activities fuel discoveries, shape real-life applications and accelerate scientific, technical and educational achievement. Discover more at: Optica.org

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