TUNABLE FDML LASER
Tunable lasers are used in a wide range of applications like profilometry, laser spectroscopy, optical sensors for measuring pressure and temperature and optical coherence tomography (OCT). In many applications, a very rapid tuning, i.e. shifting from one wavelength to another is desired. A powerful concept enabling ultra-high tuning rates is e.g. Fourier Domain Locking (FDML).
The next generation of OCT-systems entered the market in 2015. They are FDML driven and outperform their predecessors by a factor of 20 in speed and therefore they allow MHz-OCT with its opportunities for ultra-widefield retinal MHz-OCT or 4-D Real-Time OCT. This close relative to FDML uses subharmonic spectral mode coupling to overcome several restrictions shown by FDML. Instead of using a kilometre long glass fibre, the subharmonic mode-coupling uses a shorter optical resonator, thus reducing the production costs of the laser-system. The specific setup also allows for a much faster tuning and tuning with different repetition rates. Several hundred thousand wavelength sweeps per second over a sweep range >100nm at 0.1nm linewidth in the region of 1050 to 1600 nm have been realized with the available prototype.
(1) Eigenwillig, C. M., Wieser, W., Biedermann, B. R., und Huber, R.: Subharmonic Fourier domain mode locking. Optics Letters, vol. 34, no. 6, pp. 725 - 727, mar, 2009