Pump power changes the Lyot filter’s tuning wavelength

What the study found: The study reports an optically controlled tunable Lyot filter whose wavelength can be adjusted by changing the injected pump power. The authors say the tuning mechanism is mainly due to birefringence changes in the polarization-maintaining ytterbium-doped fiber, with thermal effects as the primary cause.

Why the authors say this matters: The authors conclude that the filter is an effective choice for wavelength tuning in laser systems. They also report that integrating the filter into a laser ring cavity enabled a single-frequency tunable laser with a narrow linewidth.

What the researchers tested: The researchers examined a pump-induced tunable Lyot filter built from spliced polarization-maintaining ytterbium-doped fiber and polarization-maintaining erbium-doped fiber, with a 90° slow-axis offset. They analyzed how pump power in the ytterbium-doped fiber affected wavelength tuning, and they tested the filter inside a laser ring cavity.

What worked and what didn't: Wavelength tuning was achieved by adjusting the pump power. The erbium-doped fiber expanded the filter’s free spectral range, or FSR, and acted as a saturable absorber. The analysis attributes the tuning to birefringence changes from both thermal effects and electronic transitions, but the electronic-transition effect was reported to be one order of magnitude smaller than the thermal effect.

What to keep in mind: The abstract does not describe detailed limitations or failure cases. The stated results come from the specific fiber structure and laser-cavity setup described in the paper.

Key points

• Changing injected pump power tuned the filter’s wavelength.
• The main tuning mechanism was attributed to birefringence changes in the polarization-maintaining ytterbium-doped fiber.
• Thermal effects were reported to be the primary cause of the birefringence change, while electronic transitions were much smaller.
• The polarization-maintaining erbium-doped fiber expanded the free spectral range and served as a saturable absorber.
• In a laser ring cavity, the filter enabled a single-frequency tunable laser from 1554.7 nm to 1561 nm with a 315 Hz linewidth.