Instituto de Óptica “Daza de Valdés”

An Integrated Pump-Controlled Variable Coupler Fabricated by Ultrafast Laser Writing


Madrid / November 17, 2023

Advances in photonics technology continue to drive innovation in on-chip optical signal processing and communication systems, surpassing the capabilities of electronic technologies. In this context, a team of researchers from the University of Zaragoza and the Laser Processing Group of the IO-CSIC have designed and manufactured a symmetrical directional coupler integrated on a chip that changes the output signal with the pump power and operates at a wavelength of 1534 nm.
The results of this work have been published in the journal Micromachines

What is a directional coupler?

Power dividers and directional couplers are devices used in the field of optical communications. These devices couple some of the power transmitted through one transmission line to another optical guide, often using two transmission lines arranged close enough so that the power flowing through one of the lines is coupled to the other.
The coupler presented in this article, developed with funding from the Spanish Ministry of Science and Innovation and the Government of Aragon, is based on a dual-core waveguide that has been etched into a phosphate glass base co-doped with Er3+ /Yb3+ using the femtosecond pulsed laser direct writing technique. This method allows for precise manufacturing in three dimensions, giving devices greater flexibility and functionality.
This ultrafast laser writing technique works by focusing a narrow femtosecond laser pulse into a transparent material, causing a permanent modification of the refractive index through nonlinear processes.
What distinguishes this coupler is its ability to modulate the power ratio that comes out of each line through the changes induced in the refractive index of the material thanks to the variations in optical pumping power. The experiments carried out showed that the coupling ratio can be gradually adjusted from 100/0 to 50/50 by increasing the power of the control beam from 0 to 350 mW.

4 pairs of three yellow dots on a blue background, in some cases one of the dots looks much brighter than its partner, in other cases they look the same
Output signal intensity distribution for the coupler under different input pump power levels. / Micromachines magazine
This adjustment feature makes it an active device compared to other passive couplers in which its characteristics do not change, and thus allows it to adapt to different configurations of integrated circuits, in fields ranging from telecommunications to data processing.
This work is just the beginning of this line of research, as future research is expected to explore the potential of this coupler and its ability to operate at even higher power levels, which could lead to greater variability in the coupling ratio. and to even more innovative applications in the field of photonics.

IO-CSIC Communication

Related news