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.
Highlights
Optical coherence tomography (OCT) [1] is finding widespread applications in biomedical imaging, with micrometer spatial resolution [2, 3] and its Doppler extension can image blood flow with velocity ranging from 0.02 to 100 mm/s [4]
20 mW output power with repetition rates at 115 kHz based on polygon scanner [10] and 370 kHz using scan FabryPerot filters [13, 14] have been achieved experimentally
We report on a long coherence length, high power and wide tuning range wavelength-swept mode-locked fiber laser for OCT imaging
Summary
Optical coherence tomography (OCT) [1] is finding widespread applications in biomedical imaging, with micrometer spatial resolution [2, 3] and its Doppler extension can image blood flow with velocity ranging from 0.02 to 100 mm/s [4]. Photons are required to have sufficient resonant times within the laser cavity for building up the optical power and narrowing the spectral linewidth through mode competition before being coupled out. It is very difficult in practice to build a very short fiber cavity since fiber components are typically tens of millimeters in length and need to be spliced together This significantly limits the performance of high-speed, wavelength-swept fiber lasers, imposing a trade-off between the wavelength sweep rates versus output power, coherence length and wavelength tuning range [11, 12]. We report on a long coherence length, high power and wide tuning range wavelength-swept mode-locked fiber laser for OCT imaging. The laser output power with respect to the driving current, polygon rotation frequency, and axial resolutions have been investigated experimentally
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