Fabrication of miniaturized and compact photonic devices utilising femtosecond laser pulses at high repetition rates
Zusammenfassung der Projektergebnisse
This research fellowship addresses the fabrication and investigation of new waveguide lasers (WGL) towards a compact and integrated photonic laser device. The WGL is based on a waveguide structure that is directly written into a laser-active glass material. A high energy femtosecond laser is utilized to generate the permanent modification of refractive index change in the glass chip. One main goal was to utilize a femtosecond fabrication laser with faster repetition rates (MHz) than previous systems (kHz) to create long-term stable waveguide structures. Although it was not possible to realize a waveguide laser with Yb:borosilicate, as described in the initial fellowship proposal, the main project objectives were achieved with other Yb-doped glass materials. Therefore the following three materials have been studied: Yb:IOG1, Yb:IOG10, and Yb:ZBLAN. With MHz-repetition rates the refractive index change is negative for most glass materials (as it was for the latter). It is not possible to guide directly light in such structures. Thus the core task was to find appropriate modification parameters and modification geometries to obtain a depressed cladding that offers the capabilities for single mode wave-guiding. Although Yb:IOG1 was not qualified for WGL fabrication it was possible to demonstrate a long-term stable WGL with both Yb:IOG10 and Yb:ZBLAN. With both media we also demonstrated higher slope efficiencies and lower laser thresholds than previously investigated lasers (Yb:phosphate glass). Indeed the slope efficiency of the investigated Yb:ZBLAN belongs to the highest ever reported for a direct-written Yb-WGL (> 80 %). Hence all the main fellowship objectives were achieved. However modification size reduction and homogeneity could not be improved enough to simultaneously write Bragg-gratings into the waveguide structures for the emission wavelength of 1030 nm. Instead the photonic chip lasers had to be operated with external cavity mirrors. The remaining fellowship work concentrated on the secondary goals to add further photonic circuitry and functionality to the WGL-chips. WGL of only a few millimeters length yield GHz-repetition rates when being mode-locked. Such a pulsed WGL is therefore highly relevant for scientific and industrial applications. The report includes mode-locking experiments with Yb:ZBLAN and Tm:ZBLAN WGL-samples where either graphene or carbon-nanotube coatings were tested as a saturable absorber component. The most encouraging results were obtained with a graphene coated Yb:ZBLAN WGL. Instead of mode-locked operation the WGL worked in q-switch mode with 830 kHz repetition rate and pulse durations ranging from 160 to 200 ns. My other research efforts aimed at the simultaneous integration of a polarizer structure and combination of an un-doped (passive) with a doped (active) glass sample as it was described in the fellowship proposal. However first tests and measurements were not successful at the end of the fellowship but will be analyzed and investigated in future projects.
Projektbezogene Publikationen (Auswahl)
- “Ultrafast Laser Inscription in Soft Glasses: A Comparative Study of Athermal and Thermal Processing Regimes for Guided Wave Optics,” (invited) Int. J. Appl. Glass Sci. 3 (4), 332– 348 (2012)
S. Gross, M. Ams, G. Palmer, C. T. Miese, R. J. Williams, G. D. Marshall, A. Fuerbach, D. G. Lancaster, H. Ebendorff-Heidepriem, and M. J. Withford
(Siehe online unter https://doi.org/10.1111/ijag.12005) - "High slope efficiency and high refractive index change in direct-written Yb-doped waveguide lasers with depressed claddings," Opt. Express 21, 17413-17420 (2013)
G. Palmer, S. Gross, A. Fuerbach, D. G. Lancaster, and M. J. Withford
(Siehe online unter https://doi.org/10.1364/OE.21.017413) - “Efficient direct-laser written Yb:ZBLAN Waveguide Laser,” The European Conference on Lasers and Electro-Optics (CLEO), Munich, Germany, CJ-12.6, (1433), 2013
G. Palmer, S. Gross, A. Fuerbach, D. Lancaster, T. Monroe, and M. Withford
- “Ultrafast laser inscribed 3D integrated photonics,” Proc. SPIE 8876, Nanophotonics and Macrophotonics for Space Environments VII, 887604 (September 24, 2013)
S. Gross ; A. Arriola ; G. Palmer ; N. Jovanovic ; I. Spaleniak ; T. D. Meany ; Y. Duan ; Q. Liu ; P. Dekker ; D. G. Lancaster ; H. Ebendorff-Heidepriem ; P. G. Tuthill ; B. Norris ; A. Fuerbach ; M. Ireland ; M. J. Steel ; M. J. Withford
(Siehe online unter https://doi.org/10.1117/12.2025535)
