Wavelength swept amplified spontaneous emission source

Abstract

We present a new, alternative approach to realize a wavelength swept light source with no fundamental limit to sweep speed. Amplified spontaneous emission (ASE) light alternately passes a cascade of optical gain elements and tunable optical bandpass filters. We show that for high sweep speeds, the control signal for the different filters has to be applied with a defined, precise phase delay on the order of nanoseconds, to compensate for the light propagation time between the filters and ensure optimum operation. At a center wavelength of 1300 nm sweep rates of 10 kHz, 100 kHz and 340 kHz over a sweep range of 100 nm full width and an average power of 50 mW are demonstrated. For application in optical coherence tomography (OCT), an axial resolution of 12 microm (air), a sensitivity of 120 dB (50 mW) and a dynamic range of 50 dB are achieved and OCT imaging is demonstrated. Performance parameters like coherence properties and relative intensity noise (RIN) are quantified, discussed and compared to the performance of Fourier Domain Mode Locked (FDML) lasers. Physical models for the observed difference in performance are provided.

Picosecond pulses from wavelength-swept continuous-wave Fourier domain mode-locked lasers

“…4a (dark green curve, 1 Â pass; dark blue curve, 4 Â pass). Temporal compression of a per se incoherent wavelength-swept ASE 36,37 with adjustable instantaneous linewidth 36 (see Methods) demonstrates very good agreement with this model (see crosses in Fig. 4a).…”

Wavelength swept amplified spontaneous emission source for high speed retinal optical coherence tomography at 1060 nm

“…Since for ASE swept light sources both sweep directions have almost identical properties [20], the bidirectional operation of the filter leads to 2 Â higher effective sweep rate without any additional optical setup. So unlike standard wavelength swept lasers which often require external buffering to achieve ultra-high sweep rates [13,14,23], with wavelength swept ASE sources both sweep directions of the bidirectional sweep can directly be used.…”

“…Another approach, which also overcomes the physical limitations set by the build-up time for lasing from fluorescence, is the wavelength swept amplified spontaneous emission (ASE) source, also exhibiting no fundamental sweep speed limit and additionally providing operation over a continuous range of sweep frequencies [20]. However, up to now, the wavelength swept amplified spontaneous emission (ASE) source has only been demonstrated at 1300 nm, a wavelength range that cannot be used for imaging the human retina due to high water absorption.…”

“…In order to prevent subsequent amplification of unfiltered ASE, light has to be filtered again by the second FFP-TF 2 (Lambda Quest, LLC). Two precisely set, sinusoidal voltage signals U1(t) and U2(t) are applied to both filters to ensure optimal operation [20]. Due to thermal drifts in the filter slight corrections of the filter drive parameters can be necessary to maintain optimal operation over a time scale larger than $30 min.…”

A rapid, dispersion-based wavelength-stepped and wavelength-swept laser for optical coherence tomography

“…Many technologies have been used to build high-speed swept-wavelength sources for optical coherence tomography (OCT) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. In 2003, Yun et al presented a wavelength-swept semiconductor laser utilizing a polygonal scanner-based wavelength filter with a sweep repetition rate of ~16 kHz [1].…”