High power wavelength linearly swept mode locked fiber laser for OCT imaging

Abstract

We report a long coherence length, high power, and wide tuning range wavelength linearly swept fiber mode-locked laser based on polygon scanning filters. An output power of 52.6 mW with 112 nm wavelength tuning range at 62.6 kHz sweeping rate has been achieved. The coherence length is long enough to enable imaging over 8.1 mm depth when the sensitivity decreases by 8.7 dB (1/e(2)). The Fourier components are still distinguishable when the ranging depth exceeds 15 mm, which corresponds to 30 mm optical path difference in air. The parameters that are critical to OCT imaging quality such as polygon filter linewidth, the laser coherence length, output power, axial resolution and the Fourier sensitivity have been investigated theoretically and experimentally. Since the wavelength is swept linearly with time, an analytical approach has been developed for transforming the interference signal from equidistant spacing in wavelength to equidistant spacing in frequency. Axial resolution of 7.9 microm in air has been achieved experimentally that approaches the theoretical limit.

Doppler optical coherence tomography for interventional cardiovascular guidance: in vivo feasibility and forward-viewing probe flow phantom demonstration

“…The laser employed 15 the Fourier domain mode-locking technique to achieve a ranging depth of 6 mm. For in vivo use, the longer ranging depth may provide a larger field of view, given the relatively small sector scan angles provided by the forward-viewing probe.…”

Hybrid Fourier domain modelocked laser utilizing a fiber optical parametric amplifier and an erbium doped fiber amplifier

“…The cavity is constructed similarly to a traditional ring cavity laser, but with the addition of a spool of ~6km single-mode fiber (SMF) for FDML operation and a polygon-grating filter or a piezo-electric driven TFPI [6].…”

“…Therefore, different wavelengths can be continuously fed through the gain medium without substantial loss due to the rapidly tuning wavelength filter. Common filters used to sweep the optical wavelengths include piezo-electric driven tunable Fabry-Perot interferometer (TFPI) [5] and polygon-grating filters [6]. Compared with traditional SS, FDML can generate equivalent optical output power at a much lower pump power.…”

Optical power transmission in a polygon mirror-based swept source optical coherence tomography system

“…The dispersed spectrum from the grating is captured by a telescope, consisting of two lenses, L1 and L2, (Thorlabs AC254-075-C and AC254-100-C), which focus the beams onto a single facet of the polygon mirror (SA34 Lincoln Laser, radius = 31.75 mm, 72 facets, /facet, 2.77 mm x 6.35 mm facet size). An off-axis design is chosen to double the size of the acceptance angle of the polygon and therefore decrease the laser linewidth by increasing the sweeping range 6,8,9,10 . The offaxis design requires an end reflector mirror to retroreflect the individual linewidths, in sequence, back through the system of components where it is recaptured by the collimator and subsequently circulated through the SOA for amplification before exiting the filter via a fibre coupler and sent to the coherence imaging system.…”