We propose and experimentally demonstrate a new chemical molecule sensing scheme using multi-wavelength fiber laser based on inter-core interference in twin-core photonic crystal fiber. In our proposed multi-wavelength fiber laser, two separated cores are integrated in a single photonic crystal fiber and surrounded by air channels. The anti-symmetrical super-modes participate in inter-core interference, which leads to the formation of twin-core photonic crystal fiber-based wavelength-selective comb filter. Most of the evanescent waves are localized in the 13 air channels around the two integrated cores, where light-matter interaction takes in place. The presence of chemical molecules in the air channels of TC-PCF leads to perturbation of the inter-core effective index difference between the two propagating core modes and the associated lasing wavelength shift.
This paper presents chemical vapor sensing properties of twin-core photonic crystal fiber-based in-reflection
interferometer. The interferometer is composed of end-cleaved twin-core photonic crystal fiber (TC-PCF) and fiber
circulator. Infiltrating chemical molecules in the air holes of TC-PCF lead to change in inter-core effective index
difference and associated fringe shift in the interferometer. As an example we demonstrate acetone vapor detection and
discuss the potential applications of the proposed device.
An inline Mach-Zehnder interferometer (MZI) is demonstrated using liquid filled twin-core photonic crystal fiber (TCPCF).
The TC-PCF is filled selectively with liquid ethanol, increasing the effective refractive index contrast between
twin cores, resulting in interference fringe spectrum with narrower free spectral range (FSR). Strain induced wavelength
shift of the interference fringes is experimentally monitored. Wavelength shifts to the shorter wavelength side with a
sensitivity of about -1.48 pm/με for applied strain change. Selectively liquid filled TC-PCF based MZI is simple to
fabricate and expected to have wide range of applications in optical sensors, multi-wavelength laser source and tunable
optical devices.
We fabricated asymmetric two-core photonic crystal fiber (AS-TC-PCF) and observed the temperature and strain
responses of the Michelson interferometer based on it. The asymmetric two cores induce optical path length difference
and produce polarization-dependent interference fringes. The temperature and strain sensitivities of the AS-TC-PCF
were measured using the interference fringe shift. With increasing temperature, the interference fringes shifted to longer
wavelengths, and the temperature sensitivities were measured to be 5.06 pm/°C and 11.05 pm/°C, respectively, for
different polarizations. However, with increasing strain, the interference fringes shifted to shorter wavelengths, and the
strain sensitivities were measured to be -0.50 pm/με and -1.87 pm/με, respectively.
Multi-wavelength fiber lasers have attracted a lot of interest, recently, because of their potential applications in
wavelength-division-multiplexing (WDM) systems, optical fiber sensing, and fiber-optics instruments, due to their
numerous advantages such as multiple wavelength operation, low cost, and compatibility with the fiber optic systems.
Semiconductor optical amplifier (SOA)-based multi-wavelength fiber lasers exhibit stable operation because of the SOA
has the property of primarily inhomogeneous broadening and thus can support simultaneous oscillation of multiple lasing
wavelengths. In this letter, we propose and experimentally demonstrate a switchable multi-wavelength fiber laser
employing a semiconductor optical amplifier and twin-core photonic crystal fiber (TC-PCF) based in-line interferometer
comb filter. The fabricated two cores are not symmetric due to the associated fiber fabrication process such as nonuniform
heat gradient in furnace and asymmetric microstructure expansion during the gas pressurization which results in
different silica strut thickness and core size. The induced asymmetry between two cores considerably alters the linear
power transfer, by seriously reducing it. These nominal twin cores form effective two optical paths and associated
effective refractive index difference. The in-fiber comb filter is effectively constructed by splicing a section of TC-PCF
between two single mode fibers (SMFs). The proposed laser can be designed to operate in stable multi-wavelength lasing
states by adjusting the states of the polarization controller (PC). The lasing modes are switched by varying the state of
PC and the change is reversible. In addition, we demonstrate a tunable multi-wavelength fiber laser operation by
applying temperature changes to TC-PCF in the multi-channel filter.
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