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.

Commercial Opportunities

  • Spectroscopy
  • Sensors
  • MHz-OCT

Development Status

Prototype working

Figure: each burst represents a full back-forth sweep between 1270 and 1370nm. This light source can used measuring tomographs in real time with MHz-OCT (insert)


(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

Reference Number: