We report the design and numerical analysis of a composite HfO2-coated-Si3N4 waveguide pumped with femtosecond laser pulses at 1550 nm for mid-infrared wavelength generation at 4.0 µm. The principle of wavelength conversion is based on the degenerate four-wave-mixing in designed HfO2-coated-Si3N4 waveguide. The waveguide design and the dispersion engineering to get the desired phase matching conditions have been discussed. The advantages of composite Si3N4-HfO2 waveguide over Si3N4 strip waveguide include high damage threshold, better electromagnetic interaction and thus strong light confinement, and relatively longer wavelength conversion in the mid-infrared region. Such on-chip composite Si3N4-HfO2 waveguide generating mid-infrared light at 4.0 µm holds considerable potential for the applications in a wide range of the mid-infrared nonlinear optical devices.
Supercontinuum (SC) has been applied in many applications such as optical coherence tomography, high-precision spectroscopy and frequency metrology [1]. SC can be generated in highly nonlinear fibers by launching high intensity laser pulses into these fibers. The dynamics of SC generation (SCG) closely relates to the chromatic dispersion of the fibers [2]. In the normal dispersion regime, the spectrum broadening dynamics is mainly based on self phase modulation and optical wave breaking which are self-seeded processes. Thus, the output SC preserves its high coherence. Highly coherent and broadband mid-infrared SCG in the all-normal dispersion regime was demonstrated by pumping at 8, 10, and 12 μm [3]. However, only few laser sources are able to provide such long wavelengths. Moving the pumping laser wavelengths to around 1.5 or 2 μm will be more attractive because many commercial fiber lasers are available. In this report, we propose a novel tellurite fiber for supercontinuum generation with a pumping laser at 2 μm. The fiber is obtained by adding six solid rods around the core of a step-index fiber. Such fiber is called all-solid hybrid microstructured optical fiber (ASHMOF). The fiber possesses flattened chromatic dispersion from 2 to 4 μm. Successful fabrication of the ASHMOF was done with an in-house drawing tower. Using a laser pumping at 2 μm into the ASHMOF, highly coherent and high spectral flatness supercontinuum spanning a range from 1.4 to 3.0 μm at - 20 dB level was experimentally generated. Such broad and highly coherent SC will be valuable for applications as optical coherence tomography, ultrafast transient absorption spectroscopy, etc.
The mid-IR supercontinuum generation has attracted much attention during the recent years because many unique molecular absorption bands of most of the molecules exist in this domain. Additionally, mid-IR supercontinuum light sources are expected to have potential applications including astro-photonics, bio-photonic diagnostics, nonlinear spectroscopy, infrared imaging and sensing. For high spatial resolution imaging a spatially coherent supercontinuum light source is desirable. The soft-glass optical fiber is the promising medium for the design and development of a high spatially coherent mid-IR light source with the high brightness. Earlier, the broadband mid-IR supercontinuum generation has been reported using the optical fibers in different materials including tellurite, and chalcogenide, but, its coherence property has not been demonstrated extensively. In this work, we experimentally demonstrate the mid-IR supercontinuum spectrum spanning ⁓1.6 μm to 3.7 μm using a 3 cm long tapered chalcogenide step-index optical fiber pumped with femtosecond laser pulses at 2.6 μm. To justify the experimentally obtained results, a numerical simulation also carried out for the same fiber and pulse parameters. The measured supercontinuum spectrum matches well with the simulated spectrum and generated supercontinuum spectrum is highly coherent within the whole spectral range of the supercontinuum generation.
High peak power mode locked fiber lasers are effective tools for many applications like optical metrology, biomedical imaging, micromachining and so on. All-fiber architecture and high pulse energy mode locked fiber lasers are very attractive to these applications due to their compactness and robustness. In recent years, an attractive mode-locking scheme based on Mamyshev regenerator was demonstrated to realize high pulse energy mode locked pulse output leading to breakthroughs in the mode locked fiber laser performance. We experimentally demonstrate an all-fiber linear Mamyshev regenerator operating at 1550 nm. Self-phase modulation and off-set spectral filtering provide high peak power pulse pick-up effect in the laser cavity and impel the laser to operate in the mode locking regime. With properly setting of the parameters, the all-fiber Mamyshev regenerator can achieve self-starting of the mode locking easily. No external pulse seeds or auxiliary starting arms are needed for the self-starting of the mode locking, which makes the laser very convenient to operate. Pulses with maximum energy of ~18 nJ and pulse width of 230 fs were achieved. The pulse width almost keeps unchanged with increasing in the pump power and the output power increases almost linearly with the pump power. The spectra from the two outputs with different pump powers were experimentally investigated as well. This high pulse energy Mamyshev regenerator can be used as a high quality and cost-effective laser source for many applications.
A rectangular photonic crystal fiber in GeSe2-As2Se3-PbSe chalcogenide system has been numerically modeled for coherent mid-infrared supercontinuum generation.. The proposed design offers zero dispersion wavelength at 4100 nm for the optimized geometrical parameters. The nonlinear coefficient is found as high (206 W-1.km-1) corresponding to the effective mode area of 8.5 μm2 against pump wavelength at 4.1 μm. The proposed fiber is expected to be a good candidate for the generation of coherent supercontinuum mid-infrared lasers sources.
A linear mode-locked fiber laser based on the semiconductor saturable absorption mirror was demonstrated to realize mode locking in group velocity locked vector soliton regime and polarization rotation vector soliton regime. The highly fixed birefringence was introduced into the linear fiber laser cavity by using a piece of polarization maintaining Erdoped fiber. The vector nature of pulse of the mode-locked fiber laser was experimentally studied. It turned out that, this birefringence enhanced mode-locked fiber laser can generate both group velocity locked vector soliton and polarization rotation vector soliton though slightly changing the birefringence of the laser cavity. The experimental results reveal the fundamental physics of group-velocity locked vector soliton and polarization rotation vector soliton generation and demonstrate that the linear birefringence enhanced fiber laser is a good platform for investigating the vector soliton.
A W-type co-axial chalcogenide optical fiber structure is designed and numerically analysed for the broadband and highly coherent supercontinuum sources in the mid-IR region. The structural parameters of the designed W-type optical fiber are optimized to obtain small absolute group velocity dispersion in broad spectral range in the mid-IR region. The proposed W-type fiber structure possesses a flat dispersion profile with the flatness of the dispersion of ±2.45 ps/nm/km in the spectral range of 4.9 – 12.6 μm. The broadband and coherent mid-IR supercontinuum spectrum extending from 2.28 μm to 15.52 μm at -40 dB level is obtained using a 4 cm long chalcogenide W-type fiber pumped by 200 fs laser pulse of peak power of 10 kW at 7 μm. The average coherence property of the supercontinuum spectrum is almost unity in the full spectral range for the chalcogenide W-type fiber. Such broad and highly coherent mid-IR supercontinuum spectrum is very important because most of the biological tissue possesses their molecular fingerprints within this spectral range. Therefore, this region of electromagnetic spectrum is extremely useful to determine a tissue spectral map which provides very important information concerning the existence of the critical diseases such as cancer. The W-type chalcogenide fiber structure reported in this paper is a promising candidate for the development of the coherent broadband mid-IR supercontinuum sources which have potential applications in early cancer diagnostic, food quality control, gas sensing, and imaging.
The mid-infrared (mid-IR) spectral region is very important topic of research because the molecular fingerprint of most of the molecules find in this region. Therefore, the mid-IR supercontinuum has been of great interest for the application of spectroscopic chemical sensing, metrology, and hyper-spectral imaging. Presently available mid-IR light sources such as optical parametric oscillators, quantum cascade lasers, thermal emitters and synchrotron radiation are not suitable for such mid-IR applications where we require broadband, spatial coherence, portable and high brightness of laser sources. Supercontinuum generation using the optical fibers has been one of the prominent approaches to obtain broadband mid- IR light sources. In this work, we have numerically investigated an all-normal dispersion engineered tapered tellurite step-index fiber structure for the generation of coherent supercontinuum spectrum in the mid-IR region. Supercontinuum spectrum spanning 1.04 – 4.34 μm is obtained by 200 fs laser pulse pumping of coupled peak power of 44 kW at 2.0 μm. Broadband and coherent mid-IR supercontinuum light is generated in a 4 cm long tapered step-index tellurite fiber. Coherent mid-IR supercontinuum spectrum reported in this work is expected to have potential applications for a variety of important applications in various fields including imaging, early cancer detection, sensing, and precision spectroscopy.
Chromatic dispersion controlling is crucial in designing practical optical communication systems, and nonlinear systems. Ultra-flattened chromatic dispersion has been numerically performed in silica photonic crystal fibers (PCFs) whose chromatic dispersion variation can be as small as ±0.5 ps/km/nm. However, keeping arrays of air holes at precise sizes and shapes is highly required to realize the targeted dispersion. Consequently, this requires much effort in controlling air pressure during fiber fabrication and is considered as a disadvantage of PCFs. In this report, we propose a novel fiber structure for flexible controlling of chromatic dispersion. The fiber structure is obtained by adding six solid rods around the core of a step-index fiber. Ultra-flattened and close-to-zero chromatic dispersion can be realized by using this fiber structure. The variation of chromatic dispersion from 2.5 to 3.7 μm is as small as 0 ± 0.2 ps/km/nm. Using a laser pumping at 2 μm into a 5-cm-long fiber, highly coherent supercontinuum (1.2 – 3.3 μm at -20 dB level) is experimentally generated.
Experimental realization of a fiber Bragg grating-based compact, high-sensitive, and fully packaged single-axis accelerometer has been demonstrated. To verify experimentally observed results, simulation has been carried out for the performance comparison of packaged single-axis accelerometer with the cantilever of various materials. The experimental demonstrations have been conducted at unknown seismic vibrations of random frequencies as well as the vibrations of known frequencies. The experimental results for the reported seismic events (i.e., footprint and hammering) demonstrate that the developed fully packaged accelerometer possesses good response to the signals with random vibrations. The developed accelerometer holds a high sensitivity up to 88 pm/g in the broad bandwidth. Such a compact fully packaged accelerometer with improved sensitivity can be deployed at any civil engineering structures, such as highways, bridges, dams, tunnels, pipelines, and aeronautical platforms for broadband dynamic monitoring of the random vibrations ranging from 5 to 100 Hz.
We numerically report a design of a highly nonlinear spiral-shaped photonic crystal fiber (PCF) in Ga8Sb32S60 chalcogenide glass for nonlinear applications in mid-infrared region. We have tailored the structural parameters to obtain all-normal and nearly zero flat-top dispersion profile. A flat-top dispersion curve is obtained with a negative dispersion value of -98.63 ps.nm-1 km-1 . This structure possesses a very high nonlinear coefficient of 49190 W-1 km -1 with effective mode area of the propagating fundamental mode as 0.833 μm2 at a pump wavelength of 1.9 μm. This highly nonlinear spiral-shaped PCF is suitable for the generation of an ultra-broadband supercontinuum spectrum in mid-IR domain. Various nonlinear applications of supercontinuum generation are pump-probe spectroscopy, nonlinear microscopy, metrology, frequency combs generation and optical coherence tomography.
We have designed and analysed a rib waveguide structure in recently reported Ga-Sb-S based highly nonlinear
chalcogenide glass for nonlinear applications. The proposed waveguide structure possesses a very high nonlinear
coefficient and can be used to generate broadband supercontinuum in mid-infrared domain. The reported design of the
chalcogenide waveguide offers two zero dispersion values at 1800 nm and 2900 nm. Such rib waveguide structure is
suitable to generate efficient supercontinuum generation ranging from 500 – 7400 μm. The reported waveguide can be
used for the realization of the compact on-chip supercontinuum sources which are highly applicable in optical imaging,
optical coherence tomography, food quality control, security and sensing.
A photonic crystal fiber (PCF) structure in Ga–Sb–S-based chalcogenide glass has been designed for nonlinear applications. The propagation characteristics of the designed structure have been investigated by employing COMSOL multiphysics software based on a full-vectorial finite element method. The proposed PCF structure possesses a nonlinear coefficient as high as 14.92 W−1 m−1 with the effective mode area of 3.37 μm2 at the operating wavelength of 1.55 μm. The proposed structure exhibits a flat and low dispersion value between spectral spanning 2.4 and 2.7 μm with a maximum dispersion variation of 20 ps/nm km. To the best of our knowledge, the PCF design is investigated for first time in Ga–Sb–S-based chalcogenide glass. The structure possesses a zero dispersion wavelength value at 2.6 μm. The structure is a promising candidate for nonlinear applications, such as midinfrared supercontinuum generation, slow-light generation, and midinfrared fiber lasers.
The terahertz and mid-infrared region of the electromagnetic spectrum is relatively new area of interest and incorporates a wide range of applications from image sensing to spectroscopy and many more yet to be discovered. In the area of metamaterials many new designs have been discovered, but “chevrons” shaped split ring resonators (ch-SRRs) in the mid-infrared region has not been studied to the best of our knowledge. This paper presents the analysis and simulation of ch-SRRs in the mid infrared region. Tunability of SRRs is important for various industrial and scientific applications and hence this paper analyzes the tunability of the ch-SRRs by variation of angle. The device is simulated in two configurations i.e., one with two chevrons shaped SRRs on the same plane of the dielectric substrate and the other with each of the two chevron shaped SRRs on the opposite plane of the substrate. Gold SRRs is used, since we are working in the terahertz region Lorentz-Drude model is employed to incorporate the losses. The ch-SRRs have been embedded upon the silicon substrate. The models are designed and simulated in COMSOL and result is shown in MATLAB. The results obtained for reflectance are of particular interest. The effective medium parameters viz. Impendence, permittivity, permeability and refractive index obtained for the split ring resonator are also evaluated. This design shows sharp results for reflectance which can be used in sensors application.
Recently, photonic crystal fibers have attracted significant attention for their applications in optical fiber communication systems. In some polarization sensitive applications photonic crystal fibers with single-mode and single-polarization are desirable. In this paper, a rectangular-core single-mode single-polarization large-mode-area photonic crystal fiber structure has been designed based on higher order mode filtering. The single-polarization is obtained with asymmetric design and introducing different loss for x-polarization and y-polarization of fundamental mode. Single-polarization single-mode operation of a highly bi-refringent photonic crystal fiber is investigated in detail by using a full-vector finite-element- method with anisotropic perfectly-matched-layer. At optimized parameters, the confinement loss and effective-mode-area is obtained as 0.9 dB/m and 927 μm2 for x-polarization as well as 12.53 dB/m and 921 μm2 for y-polarization of fundamental mode respectively at 1.55 μm. Therefore, 1.6 m length of fiber will be sufficient to get x-polarized fundamental mode with effective-mode-area as large as 927 μm2.
A rectangular core photonic crystal fiber design in As2Se3 chalcogenide glass has been reported for mid-infrared supercontinuum generation. The structural parameters have been tailored for all normal dispersion profile. The proposed structure possesses nonlinearity (Υ) as large as 20956 W-1 km-1 at 2800 nm wavelength with very low and flat dispersion of -2.38 ps/(nm×km). We have generated supercontinuum spectra spanning 1480 – 9990 nm using only 4 mm length of proposed photonic crystal fiber pumped with femtosecond optical pulses of peak power of 500 W at 2800 nm.
Stimulated Brillouin scattering (SBS) performances of small core tellurite photonic crystal fibers (PCF) are rigorously studied. We propose a design of tellurite PCF that is used for slow-light-based applications. We developed a two-dimensional finite element mode solver to numerically study the acoustic and optical properties of complex refractive index profiles including tellurite PCF. Our results include the calculation of Brillouin gain spectrum, Brillouin gain coefficient (gB) and Brillouin frequency shift by taking into account the contribution of the higher-order acoustic modes. Several simulations were run by varying the air-filling ratio of various PCF structures to enhance the SBS. The real scanning electron microscope image of a small core of highly nonlinear tellurite fiber is considered. Optimized results show a frequency shift of 8.43 GHz and a Brillouin gain of 9.48×10−11 m/W with a time delay between 21 and 140 ns. Such fibers have drawn much interest because of their capacity for increasing and tailoring the SBS gain.
An equiangular spiral (ES) photonic crystal fiber (PCF) design in tellurite glass has been presented. The structure
parameters have been tailored for zero dispersion wavelength (ZDW) at λZDW=1570 nm. The fiber structure has high
nonlinearity (γ = 2000 w-1 Km-1) at 1550 nm wavelength with very low and flat dispersion -0.152 [ps/(nm×km)]. We have generated supercontinuum using only 2 mm length of tellurite ES PCF with low input pulse energy of 200 pJ by
pumping at 1550 nm. The proposed fiber may be a suitable candidate for nonlinear applications.
A single mode microstructured polymer optical fiber has been designed and analysed based on finite element method
(FEM). The design parameters of proposed microstructured polymer optical fiber structure have been optimized to obtain
single mode operation along with mode area of 895 μm2. The differential loss between fundamental and higher order
modes of structure have been obtained very large (~103) with negligible loss of fundamental mode. The proposed
structure is effectively single mode at 632.8 nm wavelength after the short distance 1.65 m with very low loss of guiding
mode. The proposed structure is applicable for high power delivery devices.
A new design of the As2Se3 microfiber has been presented. With the optimized geometric parameters: pitch Λ= 0.8 μm
and five different air filling ratios varying from 0.4 to 0.95, the structure exhibits an all normal dispersion with a flat top
equal to -2.3 [ps/(nm.km)], a confinement loss less than 10-2 dB/km, and a large nonlinear coefficient equal to 7250 (w.
km)-1. Using the generalized nonlinear Schrödinger equation, we generate a very broadband supercontinuum (SC) in the
mid-infrared region. By pumping the fiber at λp=5.24 μm with a femtosecond laser having 50 fs as a width with a
relatively low energy of E=80 pJ, we generate a large spectrum extending from 2 μm to 10 μm in only 2 mm fiber
length. The generated SC demonstrates perfect coherence property over the entire bandwidth. SC generation extended
into the mid-infrared (IR) spectral region have potential usefulness in a variety of applications requiring a broad mid-IR
spectrum such as fiber sensing, IR spectroscopy, fiber laser, optical tomography coherence.
A novel design of single polarization single mode (SPSM) photonic nanowire is proposed. Using a cladding structure
with circular air holes, a new design of a photonic nanowire with ultra-wideband range of 740 nm for SPSM operation is
obtained. The numerical results show that the SPSM-nanowire is low-loss within the wavelengths ranging from 1.17 μm
to 1.91 μm, the confinement loss of the slow-axis mode is less than 0.15 dB/km and the fast-axis mode is unguided. This
fiber has greater advantages in polarization sensitive applications, such as fiber optic gyroscopes, fiber optic current
sensors, high-power fiber lasers, and coherent optical communications.
We present a multi-trench channel waveguide design that supports a single-guided mode with large-mode area. Geometrically shaped waveguide with suitable design parameters ensure effective single-mode operation by introducing high leakage loss to higher-order modes while a nominal loss to the fundamental mode. A waveguide of ~ 2.2 mm length is able to ensure single-mode operation with the core area of 100 μm2. Such a large confinement area for mode propagation can effectively suppress nonlinear optical effects. The proposed channel waveguide structure is expected to find applications in high power devices and components such as high power waveguide lasers, amplifiers and sensors.
A large-mode-area (LMA) single-mode (SM) photonic crystal fiber (PCF) structure for applications in high power fiber lasers, amplifiers and sensors is proposed. In the proposed structure the center air hole has been removed to form the core and the six elliptical air holes of inner ring around the center core have been selectively filled with high refractive index material. Effects of design parameters on SM operation and mode area are numerically investigated by using the full vectorial finite-element method. Structure offers large-mode-area exceeding 835 μm2 at 1.064 μm wavelength. A PCF with such a large-mode-area would significantly reduce the nonlinear effects and would be useful for high power applications.
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