Construction and characterization of a fiber coupled laser diode module emitting 15 W CW in the green spectral range
Rantaniemi, Antti (2023)
Rantaniemi, Antti
2023
Teknis-luonnontieteellinen DI-ohjelma - Master's Programme in Science and Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.
Hyväksymispäivämäärä
2023-05-22
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202305105540
https://urn.fi/URN:NBN:fi:tuni-202305105540
Tiivistelmä
In 2013, Nichia published the 1 W output power, 525 nm wavelength green laser diode (LD) filling the green gap in high power directly emitting semiconductor laser devices. The green gap of 520-530 nm had been in high demand due to the potential for full-color displays and projectors utilizing high power laser light sources. The new laser diodes also paved way for more affordable green light optical pumping sources of certain solid state and semiconductor lasers. One advantage of semiconductor membrane external cavity surface emitting lasers (MECSELs) is that they do not require high beam quality or wavelength accuracy from the used pumping laser source providing energy to the MECSEL. In high power MECSELs, the more flat top output of a multimode optical fiber output can even have thermal benefits over a high quality fundamental mode beam from a typically more expensive laser source.
At Tampere University’s Optoelectronics Research Centre (ORC), there was interest for two high power green fiber coupled laser diode modules for double-side pumping of a MECSEL. Such devices were not yet commercially available, but a suitable 12 W setup was published in 2018 in Applied Optics Vol. 57 by Zhao et al., which was used as the initial reference for the design and construction of a similar laser diode module described in this thesis. The goal was to achieve the same output power from a similar 200 µm core diameter optical fiber, and make the setup into a device like module with a housing and standalone user interface with its own control electronics.
The final design of the LD module was achieved after some characterizations of the used Nichia 1 W 525 nm laser diodes, and design iterations at the university’s laser laboratory. The design consists of commercial optomechanical parts some of which were modified, custom machined parts, mirrors and lenses, and custom printed circuit boards (PCBs) utilizing commercial ATLS2A212D current drivers from Analog Technologies, an Arduino nano microcontroller platform with an ATmega328p microcontroller, and some user interface elements for setting and controlling the device parameters. The design and construction of the module is explained in detail and all relevant design documents are shared in the appendix.
The final design consists of two separate submodules using ten laser diodes each. These are spatially combined to form a 2 x 10 laser beam array to be coupled into the 200 µm core diameter optical fiber with two cylindrical lenses with focal lengths of 29.99 mm and 50.99 mm. The combined fiber output beam profile shape was satisfactory, and the maximum achieved output power was 14.8 W when overdriving the diodes at a 2.0 A operating current. The nominal maximum output power with the achieved alignment and fiber coupling efficiencies was 12.1 W, meaning a total optical efficiency of 60.4 %. However, not all of the beams could be efficiently fiber coupled, and suggestions for different module designs are presented based on the application’s power requirements. The similar 12.1 W nominal maximum output power should be achieved by using only a 2 x 8 beam array in an identical design leading to a total optical efficiency of 75.7 %. A single fiber coupled submodule using nine LDs would suffice for at least 7 W of fiber output power, as a fiber coupling efficiency of 85.0 % was achieved. By replacing the 29.99 mm cylindrical lens with a focal length closer to 8.9 mm and by improving the mirror and lens alignment methods, one should be able to improve the coupling efficiency so that a 2 x 9 beam array version would provide essentially more output power than the results presented in this thesis.
At Tampere University’s Optoelectronics Research Centre (ORC), there was interest for two high power green fiber coupled laser diode modules for double-side pumping of a MECSEL. Such devices were not yet commercially available, but a suitable 12 W setup was published in 2018 in Applied Optics Vol. 57 by Zhao et al., which was used as the initial reference for the design and construction of a similar laser diode module described in this thesis. The goal was to achieve the same output power from a similar 200 µm core diameter optical fiber, and make the setup into a device like module with a housing and standalone user interface with its own control electronics.
The final design of the LD module was achieved after some characterizations of the used Nichia 1 W 525 nm laser diodes, and design iterations at the university’s laser laboratory. The design consists of commercial optomechanical parts some of which were modified, custom machined parts, mirrors and lenses, and custom printed circuit boards (PCBs) utilizing commercial ATLS2A212D current drivers from Analog Technologies, an Arduino nano microcontroller platform with an ATmega328p microcontroller, and some user interface elements for setting and controlling the device parameters. The design and construction of the module is explained in detail and all relevant design documents are shared in the appendix.
The final design consists of two separate submodules using ten laser diodes each. These are spatially combined to form a 2 x 10 laser beam array to be coupled into the 200 µm core diameter optical fiber with two cylindrical lenses with focal lengths of 29.99 mm and 50.99 mm. The combined fiber output beam profile shape was satisfactory, and the maximum achieved output power was 14.8 W when overdriving the diodes at a 2.0 A operating current. The nominal maximum output power with the achieved alignment and fiber coupling efficiencies was 12.1 W, meaning a total optical efficiency of 60.4 %. However, not all of the beams could be efficiently fiber coupled, and suggestions for different module designs are presented based on the application’s power requirements. The similar 12.1 W nominal maximum output power should be achieved by using only a 2 x 8 beam array in an identical design leading to a total optical efficiency of 75.7 %. A single fiber coupled submodule using nine LDs would suffice for at least 7 W of fiber output power, as a fiber coupling efficiency of 85.0 % was achieved. By replacing the 29.99 mm cylindrical lens with a focal length closer to 8.9 mm and by improving the mirror and lens alignment methods, one should be able to improve the coupling efficiency so that a 2 x 9 beam array version would provide essentially more output power than the results presented in this thesis.