Characterization of wavelength-swept active mode locking fiber laser based on reflective semiconductor optical amplifier

Abstract

The static and dynamic characteristics of a wavelength-swept active mode locking (AML) fiber laser are presented in both the time-region and wavelength-region. This paper shows experimentally that the linewidth of a laser spectrum and the bandwidth of the sweeping wavelength are dependent directly on the length and dispersion of the fiber cavity as well as the modulation frequency and sweeping rate under the mode-locking condition. To achieve a narrower linewidth, a longer length and higher dispersion of the fiber cavity as well as a higher order mode locking condition are required simultaneously. For a broader bandwidth, a lower order of the mode locking condition is required using a lower modulation frequency. The dynamic sweeping performance is also analyzed experimentally to determine its applicability to optical coherence tomography imaging. It is shown that the maximum sweeping rate can be improved by the increased free spectral range from the shorter length of the fiber cavity. A reflective semiconductor optical amplifier (RSOA) was used to enhance the modulation and dispersion efficiency. Overall a triangular electrical signal can be used instead of the sinusoidal signal to sweep the lasing wavelength at a high sweeping rate due to the lack of mechanical restrictions in the wavelength sweeping mechanism.

Phase stable swept-source optical coherence tomography with active mode-locking laser for contrast enhancements of retinal angiography

“…An active mode-locking (AML) laser, which is a type of akinetic light source, has also been developed 11 , 12 . The AML laser sweeps the wavelengths through dispersion variation using the dispersive material in the AML laser cavity.…”

“…In addition, electric modulation enables programmable wavelength sweeping (linear sweeping in time) so that the axial resolution does not change with depth without a k-linearization procedure. Despite these advantages, there are disadvantages such as shortening of the coherence length owing to the large cavity length in the laser system and deteriorating sensitivity roll-off characteristic of OCT 11 – 13 . To overcome these limitations, Shirahata et al .…”

Akinetic swept-source optical coherence tomography based on a pulse-modulated active mode locking fiber laser for human retinal imaging

“…Another type of akinetic wavelength-swept laser is based on the active mode locking (AML) method with dispersive fiber cavity 11,23–33 . Its feasibility for use with fiber Bragg grating sensor systems 25 and SS-OCT systems 11,23,26–33 with AML wavelength-swept sources has been reported.…”

“…Its feasibility for use with fiber Bragg grating sensor systems 25 and SS-OCT systems 11,23,26–33 with AML wavelength-swept sources has been reported. The SS-OCT images showed various samples, such as cover glasses, adhesive tape, and an in-vivo human finger, at a sweep rate of 1 kHz.…”

“…Therefore, in a previous study, a frequency shifter was inserted into the interferometer to extend the imaging depth range, but the whole corneal structure still could not be shown simultaneously 11 . In addition, the center wavelengths of all studies were 1300 nm and 1550 nm, which are unsuitable for in-vivo human retinal OCT imaging 11,23,26 .…”