Phase instability is a serious problem in swept-source optical coherence tomography (OCT) with polygon tunable lasers; however, these devices have additional issues. We found that polygon tunable lasers also have fluctuations in output power and sweep range: the former creates artifacts that may impair the recognition of sample information, and the latter reduces the interference signal utilization during phase correction. We demonstrate a method that uses the calibration signal to quantify these problems and improve system stability and image quality. The proposed amplitude correction and phase correction methods are used to eliminate vertical artifacts and improve the resolution of OCT flow and intensity images while reducing the phase error.
A multi-wavelength Erbium-doped fiber (EDF) laser based on four-wave-mixing is proposed and experimentally
demonstrated. The 5km single mode fiber in the cavity enhances the four-wave-mixing to suppress the homogenous
broadening of the erbium-doped fiber and get the stable multi-wavelength comb. The lasing stability is investigated.
When the pump power is 300mW, the fiber laser has 5-lasing lines and the maximum fluctuation of the output power is
about 3.18dB. At the same time, a laser with 110m high nonlinear fiber (HNFL) is demonstrated. When the pump power
is 300mW, it has 7-lasing lines (above -30dBm) and the maximum fluctuation is 0.18dB.
A polarization maintaining buffered Fourier domain mode-locked (FDML) swept source at center wavelength of 1310
nm for multiplying the scanning rate of FDML swept source was demonstrated. The scanning rate of the buffered FDML
swept source was doubled without sacrificing the output power of the swept source by combining two orthogonally
polarized outputs with a polarization beam combiner (PBC). The stability of the swept source was improved
significantly because the polarization state of the laser beam inside the cavity is maintained without any polarization
controllers. With the linear polarization states of the output laser beam, the buffered FDML swept source is also ready
to be used in a PSOCT system. The swept source is capable of a tuning range of more than 150 nm at a 102 kHz
sweeping rate. An FDOCT system was developed with the built swept source.
A narrow line-width dual band Fourier domain mode-locked (FDML) swept source at center wavelength of 1310 nm for
long imaging range high speed and high resolution Fourier domain optical coherence tomography was demonstrated. A
fiber Fabry-Perot tunable filter working at multi-spectral band mode is used for wavelength selection in the FDML swept
source. The interference signals in two spectral bands are separated into two channels for detection by use of WDM
couplers with pass-bands matching the spectral bands of the Fabry-Perot tunable filter. The line-width of the output light
from the swept source can be as narrow as 0.04 nm thanks to the small tuning range within each spectral band, while
high axial resolution of the FDOCT system can still be obtained since the total scanning range combining multi bands is
more than 100 nm.
We demonstrate a high-speed and wide-tuning-range swept laser for optical coherence tomography (OCT) imaging.
The repetition rate of the laser is twice the speed of the polygon filter and is achieved by using two delay fibers in
a Fox-Smith cavity. The performance of the laser is the following: a scanning range of 110nm centered at 1310nm,
and the output power of 10mw at a 102.2 kHz sweeping rate.
A novel self-seeded multi-wavelength Brillouin-erbium fiber laser with a
transmissive Sagnac loop filter is proposed. In the laser scheme, the Brillouin pump is
self-excited within the cavity, which doesn't require injection from external cavity. 52 stokes
lines are obtained by adjusting polarization controller (PC) in the Sagnac loop filter. The
experiment also demonstrates that the pump power has an influence on the wavelength
number and power distribution of the generated multi-wavelength comb. The
multi-wavelength comb is tunable in a range of 6.5nm.
We demonstrate a tunable multiwavelength fiber laser in this paper. The multiwavelength comb is produced by a self-seeded Brillouin-erbium fiber laser (BEFL). The self-seeded Brilllouin pump is achieved by incorporation of a transmissive Sagnac loop filter and 2 km single mode fiber. We study the influence of the transmissive Sagnac loop filter on the BEFL in detail, include the tunable characteristics of the BEFL, and the influence of the Sagnac loop bandwidth on the multiwavelength band. A multiwavelength band with 52 lines is achieved when the bandwidth of the Sagnac loop filter is 83.3 nm. At the same time, we observed dual Brillouin bands exciting.
The temperature-dependent insertion-loss of volume phase holographic wavelength-division demultiplexers(WDDM) is analyzed using Bragg diffraction theory in this paper. We demonstrate that most of the temperature-induced insertion-loss results from the diffraction deflection. Finally, we propose a new way to improve the temperature characteristics of volume phase holographic demultiplexers if we have a suitable choice between the thermal expansion coefficients of the gratings and the thermal coefficients of the gratings index. This result is useful to design a self-temperature compensation WDDM.
Proton-exchanged waveguides of Y-cut MgO: LiNbO<SUB>3</SUB> and Z-cut LiNbO<SUB>3</SUB> are fabricated in benzoic acid. The effective refractive indices of guide modes are measured by prism coupling method at 632.8 nm. The refractive index profiles are obtained by the inverse WKB method and the surface refractive index increments are calculated. The results show that the waveguides have the linear-step index profiles and the slope coefficient of the profile for Y-cut MgO: LiNbO<SUB>3</SUB> is much smaller than that of Z-cut LiNbO<SUB>3</SUB> and indicate that the index profile of Y-cut MgO: LiNbO<SUB>3</SUB> waveguides is more like step. The theoretical mode indices are obtained on the basis of the dispersion equations with the simple step and linear- step index profiles respectively. It is found that the linear- step profile is more accurate. The effective diffusion coefficients, diffusion constant and activation energy are achieved with the diffusion law finally.