||Laser therapy has a great attraction in past decades because of healing faster, less pain and less swelling. The different wavelength of laser sources is used for different treatment. However, the tuning range of laser wavelength in laser therapy is narrow so far. So, we propose the “cholesteric liquid crystal based tunable fiber laser" device to achieve compact size, low cost and tunable laser.|
Cholesteric liquid crystal is a 2D periodic strcucture so it is a photonic crystal and there is photonic bandgap in it. When the frequency of incident light locates at the photonic band edges of cholesteric liquid crystal, the velocity of incident light comes to zero. Then, by adding some laser dye into the CLC material and applying external force, there would lase in the mixture of CLC and laser dye. In this thesis, we formulate the CLC fiber laser device and measure the optical property and tunability of laser wavelength.
The CLC fiber laser is formulated by CLC (nematic E48 and S811) with adding some laser dye DCM, two pieces of multi-mode fiber and hollow core fiber. However, It’s hard to do a good alignment film at the fiber ends, so the multi-domain of CLC planar texture results in multi-peak lasing output. The multi-mode fiber at incident way uses single-mode fiber to instead. The pumping spot size of SMF is small enough to see the single domain so the output lasing signal would be single mode. Additionally, The temperature controlled tunability of cholesteric liquid crystal fiber laser(SMF in, MMF out) is 22 nm.