We propose and demonstrate a tunable multi-wavelength Tm-doped mode-locked fiber laser. The mode-locked operation is enabled by nonlinear polarization evolution technique. The tunable operation and multi-wavelength laser emission is achieved by periodical cavity transmission modulation. The tunable range of dual-wavelength mode-locking is 1864 to 1916 nm and tri-wavelength mode-locking is 1863 to 1912 nm, respectively, which is the widest in multi-wavelength Tm-doped mode-locked fiber laser to the best of our knowledge. The system has compact structure and both the multi-wavelength laser emission and tunable operation can be realized by controlling the polarization in the fiber ring cavity.
Modal properties of disordered optical structures, including a 1D-like multilayer structure and a 2D planar slab, have been numerically simulated in the Mid-IR region. The amount of scattering and the disorder level have been varied. A Finite Element Method solver has been used to show the modal properties of these structures, highlighting the correlation between the spectral behavior and the amount of disorder. The quality factor has also been investigated. A statistical parameter, based on the definition of photons travel distance, has been proposed to give a measure of the disorder according to the modal properties. With the help of a Monte Carlo based software this parameter has been investigated to verify its suitability.
The interaction between surface plasmon polariton (SPP) and acousto-optic tunable filter was studied. Acoustic wave was used to induce core mode to cladding mode coupling and eventually resulted in SPP generation at the fiber cladding surface. The interaction between optical fiber core mode, cladding mode and SPP mode is formulated by using mode coupling theory. The dielectric constant of SPP and light reflection coefficient on fiber surface was calculated using Nlayer model. Experimental studies were also carried out to verify the theory and simulation results. The existence of SPP at fiber surface boosted the acoustic assisted optical energy coupling from fiber core mode to TM and HE cladding mode but not to TE cladding mode, which agrees with the theoretical and simulation results. It provides a motion-free, high speed and full-electronic solution for generation and control of SPP with high flexibility and tunability.
As the most abundant protein in the human body, collagen has a very important role in vast numbers of bio-medical applications. The unique second order nonlinear properties of fibrillar collagen make it a very important index in nonlinear optical imaging based disease diagnosis of the brain, skin, liver, colon, kidney, bone, heart and other organs in the human body. The second-order nonlinear susceptibility of collagen has been explored at the macroscopic level and was explained as a volume-averaged molecular hyperpolarizability. However, details about the origin of optical second harmonic signals from collagen fibrils at the molecular level are still not clear. Such information is necessary for accurate interpolation of bio-information from nonlinear optical imaging techniques. The later has shown great potential in collagen based disease diagnosis methodologies. In this paper, we report our work using an atomic force microscope (AFM), near field (SNOM) and nonlinear laser scanning microscope (NLSM) to study the structure of collagen fibrils and other pro-collagen structures.
Two-photon fluorescence (TPE) and second harmonic generation (SHG) can been used to extract biological information
from tissues at the molecular level, which is blind to traditional microscopes. Through these two image contrast
mechanisms, a nonlinear laser scanning endoscope (NLSE) is able to image tissue cells and the extra cellular matrix
(ECM) through a special fiber and miniaturized scanner without the requirement of poisonous chemical staining.
Therefore, NLSE reserves high potential for in-vivo pathological study and disease diagnosis. However, the high cost
and bulky size of a NLSE system has become one of the major issues preventing this technology from practical clinical
operation. In this paper, we report a fiber laser based multi-modality NLSE system with compact size and low cost, ideal
for in-vivo applications in clinical environments. The demonstration of the developed NLSE nonlinear imaging
capability on different bio-structures in liver, retina and skin are also presented.
A fiber profilometer is developed to measure hard-to-access areas. This system utilizes low coherence light interferometry technique to detect profiles of internal surfaces of samples. A differentiation method is employed to enhance vertical resolutions of imaging results. An auto-focusing scheme is proposed to obtain an optimized lateral resolution. The performance of the profilometer system is demonstrated by experimental studies.
We present a reconstruction method to eliminate the autocorrelation noise (ACN) in optical coherence tomography (OCT). In this method, the optical fields scattered from the sample features are regarded as the response of a sparse finite impulse response (FIR) filter. Then the OCT reconstruction is formulated as one of identifying the parameters of a sparse FIR filter, which are obtained via an ℓ1 optimization with soft thresholding. The experimental results show that the proposed method can obtain OCT reconstruction results with effective attenuation of ACN.
We present a theoretical study on an index-asymmetric double-electrode waveguide structure and identify a
long-range surface plasmon polariton (LRSPP) super-mode for index-sensing. We propose to operate the
LRSPP by monitoring its cut-off wavelength which promises ultra-sensitivity. The sensitivity is calculated to be
6.5×104 nm per refractive index unit (RIU), which is one order magnitude higher than most plasmonic sensors
based on spectral interrogation. Additionally, based on computations from the transfer matrix theory, we present
the properties of this LRSPP supermode.
Photonic crystal fibers (PCFs), although a highly effective platform for sensing, encounter difficulties with coupling as
well as infiltration and evacuation. A PCF integrated microfluidic chip has therefore been fabricated to demonstrate
improved coupling for real-time chemical sensing. Furthermore, an extremely sensitive dip-shifting analysis was
employed for the detection regime. Results eventually demonstrated its notable sensitivity and a refractive index
resolution of 10-7 RIU, rendering it suitable for utilization in highly sensitive sensing applications.
We present an all-fiber linear-phase equalizer for equalizing Gaussian-like spectra. The equalizer uses an optical lattice filter in a symmetric folded structure. Compared to existing solutions to linear phase equalization, the proposed equalizer has guaranteed linear phase responses and lower power attenuation. As an illustrative example, the effectiveness of the proposed equalizer is demonstrated with the flattening of the output spectrum of a superluminescent light emitting diode.
We present an all-fiber spectrum equalization filter that uses a Mach-Zehnder interferometer terminated with a loop. Compared with existing results, the proposed filter has a simpler and a more efficient all-fiber structure for equalizing Gaussian-like spectra with desired specifications.
In this paper, we present a design and a design scheme for the phase locked-in loops satisfying given specifications. The proposed design suggests imposing an additional control signal on the normal input to the variable controlled oscillator (VCO) of the phase locked-in loop (PLL). Based on this design, a scheme of using the second method of Lyapunov is developed to choose the additional control signal and the loop filter parameters of the PLL. The proposed design and design scheme have improved the conventional PLL design results by obtaining a phase locked-in loop with pre-specified performance. The design scheme is based on nonlinear model of the PLL and it is applicable to the design of high order PLLs. Simulations results are reported to demonstrate the effectiveness of the proposed scheme.
In this paper, a linearity index is proposed to assess the performance of the position measurement of using position sensitive devices (PSDs). Using the index, a set of position measurement formulae is proposed for PSD with tetra-lateral structures. Compared to the conventional results, the proposed measurement formulae have improved the area with distortion less than 1% from the currently best result of 13% to 25%. Simulation results are reported to verify the theoretical analysis.
This paper presents an IIR (infinite impulse response) structure for an optical interleaver to deliver simultaneously three channels of 2π/3 shifted passband transmissions. Using the proposed structure, the phase responses and the spectral response of the IIR interleaver can be designed separately. Therefore, the design of an IIR interleaver is simplified, and the obtained interleaver can achieve a better performance than that of an FIR (finite impulse response) interleaver in terms of wider passband bandwidth, higher channel isolation, and lower insertion loss. A numerical design example is given to demonstrate the effectiveness of the proposed IIR interleaver design scheme.
We present an all-fiber filter with symmetric forward and feedback lattice structures. Using the proposed filter, Gaussian-like spectra can be equalized in the maximally flat sense while the output power is maximized. As an illustrative example, the proposed filter is designed to flatten the output spectrum of a superluminescence light-emitting Diode (SLED). Compared to existing filters, the proposed filter achieved better performance in experiments.
A dual optical detection scheme is proposed for optical code division multiple-access systems utilizing on-off-keying modulation technique. The proposed detector is developed by combining a correlation detector and a chip-level detector with the logical OR operation. In this way, the merits of two detectors can be fully exploited. Thus the dual detector can achieve the enhanced bit error rate performance in the presence of both multi-user interference and noise.
In this paper, a novel all-fiber Acousto-optical tunable filter (AOTF) is proposed, which employs a mode feedback mechanism. It is shown that the proposed AOTF has superior performance with high isolation and narrow linewidth. Simulation studies are done to verify the effectiveness of the proposed filter.
This paper presents a new three-wavelength ring laser using one erbium-doped fiber amplifier. The simultaneous output of three lasing wavelengths is achieved by controlling the gains of different filters through utilizing a cascaded fiber Mach-Zender interferometer (MZI) with the triangular-shaped interference transmission spectrum. The key advantage of the proposed system over existing technologies is that the output is channel-wavelength selectable. Each channel can be tuned individually from one channel wavelength to the other. The channel wavelengths are selectable over the range of 1522-1665nm.