In this work, chalcogenide all-solid hybrid microstructured optical fibers (Ch-ASHMOF) using As2Se3, As2S5 and AsSe2 glasses are proposed. The polarization-maintaining properties are induced by breaking the symmetry of the rod arrangement and the core shape. The fibers have all-normal chromatic dispersion profiles which are flattened about -10 ps/km/nm over a wavelength range from 5 to 10 m and the birefringence values are up to 4.5x10-4 at 10 μm. By pumping the fiber with a 200-fs-pulse laser source at 5.3 μm, a broad supercontinuum generation from 2 to 10 μm in the mid-infrared window is experimentally demonstrated.
Fiber-based optical parametric amplification (FOPA) has been exploited for various applications due to its broad gain bandwidths and high signal gain in many spectral bands. By extending FOPA gain bandwidth towards the mid-infrared (MIR) region, more novel applications in spectroscopy, sensing, biology and so on are expected to be realized. However, highly efficient and stable FOPA performance is not easy to be obtained. It requires optical fibers with high nonlinearity, suitable control of chromatic dispersion and pump sources to satisfy the phase-matching condition which is the key for FWM process to occur. Among non-silica glasses, chalcogenide glasses have attracted great attention due to their very broad transmission window in MIR region and very high nonlinearity. For these reasons, this work is highly motivated to control and maintain the chromatic dispersion of chalcogenide optical fibers so as to achieve and maintain high-intensity and broad FOPA signal gain bandwidths in the MIR region by using an AsSe2 step-index optical fiber and a pump source near 5.0 μm. It is realized that by adding a chalcogenide buffer layer with appropriate refractive index and diameter to the conventional step-index structure, the performances of chromatic dispersion and FOPA can be improved and their fluctuation due to the change of fiber core can be greatly suppressed. As a result, a broad signal gain bandwidth from 3 to 14 μm at about 15 dB is attainable and can be maintained although the fiber core diameter drastically fluctuated from 2 to 5 μm.
Fiber optical parametric amplifiers (FOPAs) have attracted much attention than conventional optical amplifiers due to their wider operating wavelength ranges. By expanding the FOPA gain bandwidth towards the mid-infrared region, which can only be obtained by using highly nonlinear chalcogenide fibers, more interesting applications in spectroscopy, sensing, biology and metrology can be realized. Chalcogenide hybrid microstructured optical fibers (chalco HMOFs) with buffer layer demonstrated by our group showed good FOPA performance from 3 to 10 μm. However, their tiny and symmetric structures of air holes are difficult to fabricate. To overcome, chalcogenide all solid HMOFs (chalco ASHMOFs) with 6 low-index rods in the cladding were studied in this work using As2Se3, AsSe2 and As2S5 glasses. Moreover, to obtain high birefringence which is necessary to minimize detrimental effects such as, polarization mode dispersion, polarization noise and instability and polarization-maintaining, the symmetry of the fiber was broken by enlarging a pair of solid rods. Numerical analyses show that chalco ASHMOFs can provide near-zero and flattened chromatic dispersion (<10 ps/km.nm) from 5 to about 12 μm and the phase birefringence can be as high as 4.4 x10-3 at 14 μm. When a pump of 5 W at 4890 nm is coupled to a 3-cm-long section of the chalco ASHMOF, 16-dB signal gain can be obtained from about 3 to 12 μm which is equal to 9000-nm FOPA gain bandwidth in the mid-infrared. Compared to the 6500-nm gain bandwidth obtained from the previous chalco HMOF, novel chalco ASHMOFs are very potential candidates of FOPA devices in the mid-infrared region.
Due to the air-guiding characteristics of the air-core, hollow-core optical fibers (HCOFs) can give rise to many potential applications including optical data transmission, terahertz propagation, power beam delivery for industrial applications such as cutting, welding, and engraving, medical applications and chemical sensing. In this work, tellurite HCOFs which have 6 air holes in the cladding and a large hollow core in the center are studied. By numerical analysis, it was realized that the confinement loss in the core will be high when the gap between two nearby cladding air -holes is large or when they connect to each other. The light propagation and transmission properties were demonstrated experimentally from 0.4 to 4.0 μm. By carefully controlling the coupling conditions, lights were coupled successfully into the air core by the fundamental mode. The transmission spectrum included high transmission bands and low transmission bands alternately due to the effect of resonant reflection and anti-resonant reflection. Due to the current operating range of the laser source, the transmission spectrum was measured up to 3.9 μm. But, it is expected to extend to the mid-IR range around 6 μm as shown in the calculation. When the input light at 2.1 μm was linearly polarized, the polarization was maintained in the fiber because the fundamental mode was dominant and the coupling efficiency of the 1st order mode was very weak.
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.
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.
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 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.
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.
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.
Neodymium (Nd)-doped fibers are potential candidates for optical fiber amplifiers operating near the 1.3-μm spectral region due to the 4F3/2→4I13/2 transition of Nd3+ ions. But, there is an amplified spontaneous emission at 1.06 μm due to the 4F3/2→4I11/2 transition whose branching ratio is about 5 times larger than that at 1.3 μm. In order to suppress the transmission of the 1.06-μm emission, we propose a new tellurite all-solid photonic bandgap fiber (ASPBF) with a single line of high index rods and double cladding layers. Tellurite glasses of TeO2-Li2O-WO3-MoO3-Nb2O5 (TLWMN), TeO2- ZnO-Na2O-La2O3 (TZNL) and TeO2-ZnO-Li2O-K2O-Al2O3-P2O5 (TZLKAP) are developed. High-index rods of TLWMN and an Nd-doped TZNL rod are arranged symmetrically and horizontally in the x-axis of a hexagonal TZNL cladding. The outer cladding is made of the TZLKAP glass. The finite element method is used to calculate the mode distribution and the bandgap properties. The fiber transmission spectra are numerically investigated with the effects of rod diameter and filling factor variation. When the core diameter is 3.0 μm, rod diameter is 2.3 μm and filling factor is from 0.7 to 0.8, the 1.06-μm emission which is caused by the 4F3/2→4I11/2 transition can be suppressed as compared with the 1.33-μm emission which is caused by the 4F3/2→4I13/2 transition.
We performed numerical analysis of the propagation characteristics of transversely disordered optical fibers with random hexagonal As2Se3 and AsSe2 rods for infrared light in the wavelength of 1-10 μm using beam propagation method and finite element method. Local confinement by random refractive index distribution was observed in both methods. It was revealed that the beam diameter is minimal around a hexagonal rod pitch of 0.8 times of the wavelength.
A tellurite all-solid photonic bandgap fiber (ASPBF) whose cladding consists of 60 high-index rods arranged periodically around a central core was successfully fabricated. The diameter of high-index rod was about 5.0 μm and the distance between the center of two adjacent high-index rods was approximately 8.0 μm. The high-index rod was made of the TeO2-Li2O-WO3-MoO3-Nb2O5 (TLWMN) glass, the cladding was made of the TeO2-ZnO-Na2O-La2O3 (TZNL) glass as the background glass material and the central core was made of TZNL glass doped with 0.5 wt% of Nd2O3. A supercontinuum light from 0.6 to 2.4 μm was coupled into the core of fiber which is 2.2 cm long to measure its transmission spectrum. High transmission bands were obtained in the vicinity of 0.75 and 1.3 μm but the transmission was suppressed in the wavelength range from 1.0 to 1.06 μm. When a titanium∶Sapphire laser source at 0.75 μm was used, the emission spectrum was obtained with two peaks at 1.06 and 1.33 μm which are attributed to the 4F3/2→4I11/2 and 4F3/2→4I13/2 transitions of Nd3+ ion, respectively. The intensities of those emission peaks were compared with those obtained from a bulk glass having the same doping concentration of Nd3+. The results showed that by using tellurite ASPBF, the intensity of the 1.06-μm emission was suppressed by one-twelfth but the intensity of the 1.33-μm emission was maintained. This feature is very advantageous to filter out the 1.06-μm emission of Nd3+ ion in order to realize practical amplifier devices at 1.3 μm.
Mid-infrared cascaded Stimulated Raman scattering (SRS) is experimentally investigated in an AsS optical fiber which fabricated based on As38S62 and As36S64 glasses and whose fiber loss was ∼0.09 dB/m at ∼2000 nm. Using a nanosecond laser operated at ∼1545 nm as the pump source, mid-infrared cascaded SRS up to eight orders is obtained in a 16 m AsS fiber. To the best of our knowledge, this is the first demonstration of eighth-order cascaded SRS in non-silica optical fibers, and it may contribute to developing tunable Raman fiber lasers in the mid-infrared region based on the C-band pump sources. When the pump wavelength switches to ∼2000 nm, only mid-infrared cascaded SRS up to five orders is obtained.
The mid-infrared (MIR) range is of great interest because fundamental molecular vibrational absorption bands exist in the MIR range. In the MIR range, typically, lasing can be generated using quantum cascade lasers, cascaded Raman lasers, and optical parametric oscillators (OPOs). Recently, fiber OPOs (FOPOs) in the MIR range have received attention because of their flexibility of the parametric gain curve designing the chromatic dispersion. Chalcogenide glass is the promising candidate for MIR FOPO because of their wide transmission window and high nonlinear coefficient. In the present paper, we design the chromatic dispersion of four-hole As2S5 chalcogenide suspended core fiber (SCF), and demonstrate a far-detuned four-wave mixing (FWM) for MIR FOPO. We design the four-hole As2S5 chalcogenide SCF for far-detuned FWM using a ∼2 μm pump source. A four-hole As2S5 chalcogenide SCF which has a core diameter of 3.25 μm is fabricated using a homemade draw tower. We experimentally observed far-detuned FWM in the four-hole As2S5 chalcogenide SCF. A detuning frequency of over 80 THz is measured in 21 cm long fiber using a 2.7 ps pulse laser at 1.96 μm. The experimental observation was confirmed by numerical demonstration.
All-solid tellurite-glass optical rod and fiber with transversely-disordered refractive index profile were successfully fabricated to study the transport of infrared images by using transverse localization of light. The fabrication was carried out by using stack-and-draw and rod-in-tube techniques. The fabricated tellurite optical rod and fiber were composed of high-index and low-index units which were arranged randomly in the transverse plane but were invariant in the longitudinal direction. The diameter of each unit was approximately 1.0 μm. The high-index and low-index materials were TeO2-Li2O-WO3-MoO3-Nb2O5 (TLWMN) glass and TeO2-ZnO-Na2O-La2O3 (TZNL) glass, respectively. At 1550 nm, their refractive index difference ∆n is 0.096. To investigate the optical image transport capability, A CW laser light at 1550 nm was used as an input probe beam and the 1951 U.S. Air Force test target was installed in front of 10-cm-long segments of the fabricated rod and fiber in the experimental setup. The output signal was recorded by a beam profiler. As a result, clear transported images of numbers and lines on the test target were obtained.
We experimentally investigate mid-infrared (MIR) supercontinuum (SC) generation in chalcogenide step-index optical fibers. The pump source is generated by the difference frequency generation with a pulse width of ~170 fs, a repetition rate of ~1000 Hz, and a wavelength range tunable from 2.5 to 11 μm. The wide MIR SC will be applied in sensing, medical and biological imaging areas.
We experimentally demonstrate mid-infrared supercontinuum (SC) generation in chalcogenide multi-step index fibers (MSIF) pumped by a femtosecond laser. The fabricated chalcogenide MSIF is composed of a high refractive index core (C1) in the center, which is enclosed by a lower refractive index core layer (C2) and an outer cladding. This fiber structure is advantageous to tailor the chromatic dispersion with higher freedom and to keep the effective mode area small at long wavelengths. The high refractive index core, low refractive index core, and the outer cladding materials are As2Se3, AsSe2 and As2S5, respectively. When the diameter of C1 and C2 are 7.8 and 30 μm, respectively, the zerodispersion wavelength (ZDW) of the fiber is 12.5 μm. The chromatic dispersion profile is near-zero and flattened within the range of ±20 ps/km/nm in the wavelength range from 4 to 17 μm and a broad normal dispersion region is obtained in the wavelength range shorter than the ZDW. In practice, a 2.8 cm long fiber is pumped at 10 μm by using a femtosecond laser whose pulse width is ~200 fs. The SC generation extending from 2 to 14 μm is obtained. Most of its spectrum is in the normal dispersion region of the fiber. These results are promising for the highly coherent mid-infrared SC generation.
We report here the design of a new chalcogenide hybrid microstructured optical fiber (HMOF) with a buffer layer around the core and its potential performance of tailoring chromatic dispersion and supercontinuum (SC) generation. The new chalcogenide HMOF has an AsSe2 core. The refractive index difference Δn between the AsSe2 core and cladding material is supposed to be 0.3. The fiber microstructure and the Δn between the core and buffer materials are designed in order to obtain broad anomalous dispersion regimes with near-zero and flattened chromatic dispersion profiles for broadband SC generation. Moreover, the suppression of chromatic dispersion fluctuation caused by fiber transverse geometry variation is investigated. By using the proposed chalcogenide buffer-embed HMOFs, the calculation shows that near-zero and flattened anomalous chromatic dispersion regimes from 4.5 μm can be obtained. When the variation of fiber structure occurs for ±1, ±5 and ±10 %, the chromatic dispersion fluctuation can be greatly suppressed. In addition, the calculation shows that a broad SC spectrum from 2.5 to more than 16.0 μm can be obtained when a 0.9-cmlong section of the new chalcogenide buffer-embed HMOF is pumped at 5.0 μm by a femtosecond laser with 1-kW peak power.
We report the coherent mid-infrared supercontinuum generation in an all-solid chalcogenide microstructured fiber with all-normal dispersion. The chalcogenide microstructured fiber is four-hole structure with core material of AsSe2 and air holes are replaced by As2S5 glass rods. Coherent mid-infrared supercontinuum light is generated in a 2-cm-long chalcogenide microstructured fiber pumped by a 2.7 μm laser. The simulated and experimental results have a good match and the coherence property of supercontinuum light in the chalcogenide microstructured fiber has been studied by using the complex degree of coherence theory. Coherent mid-infrared supercontinuum generation is extended to 3.3 μm in this work.
We report here the potential of fiber optical parametric amplification (FOPA) by using highly nonlinear chalcogenide double-cladding fibers. The fibers are designed with an AsSe2-based core layer surrounded by two cladding layers. The size and the refractive index differences (dn) between the core and cladding are investigated to obtain flattened chromatic dispersion spectra over a wide wavelength range up to the mid-infrared window. The inner cladding with dn2 is added to suppress the variation of the chromatic dispersion caused by the fluctuation of the core diameter. Our numerical calculations shows that very broad anomalous dispersion ranges from 5.0 μm up to 11.0 μm where the chromatic dispersion is less than 10 ps/km-nm can be obtained when the core diameter varies from 2.0 to 9.0 μm and the inner cladding diameter is kept at 9.0 μm. The dn1 and dn2 are 0.30 and 0.02, respectively. The FOPA calculation is carried out using a 3-cm-long fiber whose core diameter is 3 μm. When the pump power is 3 W at 5320 nm, a very broad gain bandwidth is obtained from 3.3 up to 11 μm. Moreover, the gain spectrum is flattened (about 32 ± 1 dB) in the ranges from 3.3 to 4.1 μm and from 7.5 up to 11.0 μm. When the core diameter fluctuates from 2.0 to 5.0 μm, the FOPA gain spectra can be maintained.
Based on a suspended core birefringent tellurite microstructured optical fiber (BTMOF), the supercontinuum (SC) spectra are generated by pumping near the zero dispersion wavelengths (ZDWs) in the telecommunication band with a tunable picosecond fiber laser. The ZDWs of the suspended core BTMOF are calculated to be 1560 nm and 1532 nm for the X-axis and Y-axis, respectively. When the pump is polarized along the X-axis, the SC broadening is governed by the nonlinear effects of four-wave mixing (FWM), cross-phase modulation (XPM) and stimulated Raman scattering (SRS). When the pump is polarized along the Y-axis, the SC generation is governed by the nonlinear effects of SRS.
Widely wavelength tunable soliton self-frequency shift (SSFS) from 1.58 μm to 2.07 μm was experimentally demonstrated in a highly nonlinear fiber pumped with a mode-locked sub-100 fs Er-doped fiber laser. The maximum output spectrum (full width at half maximum, FWHM) around 2 μm is 143 nm. Although the pulse width of SSFS was measured to be a few picoseconds, the large FWHM bandwidth of SSFS spectrum shows that soliton with sub-50 fs could be achieved if the giant chirped pulse is efficiently re-compressed to be transforms limited. Dispersive wave with a minimum pulse width of 50 fs was also observed.
We present the broad and ultra-flat optical parametric gain in the highly nonlinear tellurite fibers with tailored chromatic dispersion. The effect of pump wavelengths and powers on dual-pump configuration of four-wave mixing (FWM) are investigated. It is clarified that an ultra-flat gain bandwidth with 658 nm and ±0.01 dB fluctuation can be achieved at the dual-pumping power of 1.25 W. Moreover, a gain bandwidth with 1524 nm and 60 dB signal gain with gain ripples can be obtained at the dual-pumping power of 3.0 W in 25 cm-long hybrid tellurite microstructured optical fiber.
We report here flattened supercontinuum (SC) generated in tellurite-phosphate and chalcogenide-tellurite hybrid microstructured optical fibers (HMOFs) whose chromatic dispersion spectra are tailored with high freedom due to large refractive index difference (∆n) between the core and cladding glasses. It is shown in the simulation that the tellurite-phosphate HMOF whose chromatic dispersion spectrum is near-zero and flattened with three zero-dispersion wavelengths (ZDWs) over a wide wavelength range from 1000 to 4000 nm is beneficial to obtain broad and flattened SC spectra. By using a large ∆n of 0.49, the tellurite-phosphate HMOF which has flattened chromatic dispersion and three ZDWs is successfully fabricated. When a 20-cm-long tellurite-phosphate HMOF is pumped at 1550 nm with a 1560-W peak power, an SC extended from ~800 to 2400 nm where ~5-dB spectral flatness in the wavelength ranges from 890 to 1425 nm and from 1875 to 2400 nm (~1060-nm bandwidth in total) is observed. In addition, a flattened SC spectrum with ~6-dB spectral flatness over a broad wavelength range from 950 to 3350 nm (2400-nm bandwidth in total) is generated by pumping a 1-cm-long chalcogenide-tellurite HMOF at 2300 nm with a 40-MW peak power.
We present here, the extensive study of broadband and high parametric gain in highly nonlinear tellurite optical fiber.
The chromatic dispersion has been designed to achieve broad gain bandwidth and phase-matching over broad spectral
range. The optical parametric gain under pulse repetition rate dependence and with no influence of group velocity gain
spectrum has been calculated for different fiber lengths. When the parametric gain was calculated, with dependence on
group velocity and repetition rate of pulse, the gain bandwidth was found to be shrinking abruptly due to lessening of
pump power. The pulse repetition rate was assumed to be 20 GHz, with fiber core diameter of 0.895 μm and calculated
nonlinearity coefficient γ was 6642 W-1km-1. The study has been extended to realize the impact of pump power variation over supercontinuum generation with fiber length of 75 cm.
Fiber-optical parametric amplification (FOPA) has been intensively studied and exploited for various interesting
applications such as wavelength conversion, wavelength division multiplexing, optical signal processing and so on.
However, its efficiency is governed by the fiber nonlinearity and chromatic dispersion. By employing tellurite glass we
propose novel highly nonlinear tellurite hybrid microstructured optical fibers (HMOFs) which have nonlinearity of 6642
W-1km-1 and near-zero flattened dispersion profiles from 1.3 to 2.3 μm with four zero dispersion wavelengths for FOPA applications. The linear phase-mismatch, optical signal gain and gain bandwidth are precisely calculated by using a full propagation constant which includes the contribution of all high-order dispersion parameters. In contrast with silica fibers, the signal gain is shown to be generated in the wavelength regions where Δβ<-4ΥP and the parametric gain coefficient g is imaginary. It is shown that the proposed tellurite HMOFs with short fiber length L<90 cm have the gain bandwidth as broad as 760 nm when it is pumped at 1550 nm. The increase in pump power from 1 to 4 W not only increases the signal gain but also broadens the FOPA gain bandwidth. At 1700-nm pump wavelength, the signal gain
larger than 14 dB is obtained over a very broad gain bandwidth of 1200 nm (from 1290 to 2490 nm). To our best
knowledge, it is the first time that highly nonlinear tellurite HMOFs are demonstrated as attractive candidates for high
performance of FOPA.
We present here the broadband and parametric gain for tellurite/phospho-tellurite optical fiber by carefully engineering the chromatic dispersion for optical parametric amplifier. This optical parametric amplification with broad bandwidth promises significant solutions for wavelength division multiplexing (WDM) and advanced ultrafast optical telecommunication systems. The parametric gain has been obtained with inclusion of higher and even order dispersion parameters in phase-mismatching factor (Δβ). The results have been obtained for step index fiber (SI) and hybrid microstructured optical fiber (HMOF) with engineered chromatic dispersion, having one zero dispersion wavelength (ZDW) and two ZDWs. The HMOF with a core diameter of 1.1 μm and chromatic dispersions having two ZDWs at 1262 and 1559 nm provides broadest parametric gain bandwidth (280 nm). This broad bandwidth advents due to the high nonlinear coefficient of tellurite/phospho-tellurite hybrid microstructured optical fiber. The paper explores variation in dispersion parameters, supercontinuum spectra and bandwidth of the parametric gains for these fibers.
The dependence of chromatic dispersion of tellurite microstructured optical fiber on composition and structure was investigated. The material dispersion is mainly dependent on material composition of core glass. And the waveguide dispersion of fiber mainly depends on refractive index distribution in cross-section. The radial step of refractive index produces a peak in waveguide dispersion curve whose value and position are related to both contrast of refractive index and its position. Based on this guidance, some particular dispersion profiles were designed in tellurite fibers.
The hybrid microstructured optical fibers (HMOFs) are emerging due to their capability of tailoring the dispersion. The chromatic dispersion and other related optical properties, such as optical mode confinement and effective index, have been calculated using the finite element method. We have realized four zero dispersion wavelengths (ZDWs) of 1566, 1605, 1726 and 1790 nm. The signal and idler wavelength dependent on pump wavelength is calculated. The gain bandwidth is 134 nm for the pump wavelength of 1761 nm between third and fourth ZDW. The supercontinuum generation is studied for the pump wavelength 1761 nm.
The compositional dependences of glass formation, thermal properties and optical properties are investigated for TeO2-ZnO-Na2O-P2O5 system for hybrid microstructured optical fibers. The refractive indexes at 1.55 μm and glass transition temperature vary in a wide range from 1.513 to 2.036 and from 265°C to 376°C by controlling of the TeO2/P2O5 and ZnO/Na2O content, respectively. These properties endow tellurite-phosphate glasses with large freedom in the hybrid microstructured optical fiber design. The structures of glasses are investigated by Raman spectra to understand the structural dependence on composition. Using the present glasses, some microstructured optical hybrid fibers with particular dispersion profiles are designed and demonstrated.
We present an all-solid tellurite-phosphate photonic bandgap fiber (PBGF) with high-index rods in the cladding. The
low-index background material is phosphate glass (PZNK) and the high-index rods are made of tellurite glass (TZLB).
The all-solid tellurite-phosphate PBGF has three bandgaps and the first one is wide in frequency. It is easier to draw than
the silicon PBGF due to the phosphate glass has lower fiber-drawing temperature. It can be widely used in the
photoelectron field, compact nonlinear devices and devices which work in the mid-infrared range, such as wavelength
filter, phase-locked high-power lasers, fiber sensors in the mid-infrared for gases detecting, etc.
The microstructured optical fibers have been considered in this paper due to their unique nonlinear properties.
These optical fibers have enormous potential and they are also unrestraint to tailor the design for obtaining promising
dispersion properties. It has been observed that conversion efficiency significantly increases when nonlinear contribution
to propagation constant is considered for phase matching. The phase matching have been obtained for even and higher
order dispersion with the optical pump pulse conditions. The coupled mode theory along with nonlinear Schrödinger
equation has been used to reveal the optical properties of telluride/phospho-tellurite hybrid microstructured optical fiber.
The paper has been focused to investigate the effective index, pulse propagation intensity and quasi phase matching.
We report the fabrication of tellurite composite microstructured optical fiber (CMOF) with ultra-flattened zero dispersion
(±3 ps/nm/Km) over 200nm band. To obtain this dispersion profile together with high nonlinearity, one ring of air holes
and two layers of glass cladding are employed in the tellurite CMOF. The core of fiber is made of TeO2-Li2O-WO3
-MoO3-Nb2O5 (TLWMN) tellurite glass which possesses high linear and nonlinear refractive indices. The refractive
index (n) at 1544nm and nonlinear refractive index (n2) of TLWMN glass is 2.08 and 3.78×10-11 esu, respectively.
TeO2-ZnO-Na2O-La2O3 (TZNL) glass with n of 1.96 at 1544 nm and TeO2-ZnO-Li2O-Na2O-P2O5 (TZLNP) glass with
low refractive index n of 1.63 at 1544 nm are used as the first cladding and the second cladding, respectively. Six small
air holes are located between the core and the first glass cladding. Such kind of fiber with ~1.7 μm core and ~0.6 μm air
holes are fabricated by a rod-in-tube method. The chromatic dispersion of the fiber is calculated by the fully vectorial
finite difference method (FV-FDM) and becomes (±3 ps/nm/Km) in the wide range from 1.53 μm to 1.72 μm. And the
nonlinear coefficient of present fiber is about 3.47 m-1W-1 which is much higher than that of silica MOFs. Furthermore,
broad and flattened supercontinuum generation is demonstrated in 30-cm-long fiber with femtosecond laser pumping at
1557 nm. This kind of fiber has promising potential in nonlinear applications owing to the high nonlinearity and
flattened dispersion profile.
Four wave mixing and supercontinuum from tellurite photonic crystal fibers have been widely researched. Their
efficiencies depend largely on fiber nonlinearity and chromatic dispersion. We have shown that the composite
microstructured optical fibers (CMOFs) can have high flexibility on chromatic dispersion control when refractive index
difference between core and cladding becomes larger. Cladding materials with much lower refractive index than tellurite
glass are required. We report here a novel tellurite core-phosphate cladding CMOF. Phosphate glasses which thermal
expansion coefficient, viscosity, glass transition temperature, deformation and crystallization temperature are close to
those of tellurite 78TeO2 - 5ZnO - 12Li2O - 5Bi2O3 (mol%) (TZLB) glass are systematically investigated. The
phosphate glass we developed has high transparency and a broad transmission region up to 3 μm as well as a notably low
refractive index. Using the phosphate glass doped with mixed alkali oxides obtained in this work, the refractive index
difference between core and cladding becomes as high as 0.5 which is sufficiently high to control the chromatic
dispersion with high freedom. Our work shows that tellurite-phosphate CMOFs are promising candidates as highly
nonlinear fibers with freely controlled chromatic dispersion for nonlinear applications.
We propose a tellurite core phosphate cladding composite microstructured optical fiber (MOF) with high nonlinearity
and flattened dispersion for parametric amplification. To realize flattened dispersion, the structure parameters such as the
tellurite core diameter, the air hole diameter and the distance between the centers of the two neighboring air holes are
optimized. The ultraflat dispersion curve is obtained for tellurite core of 1.1μm, pitch of 1.2 μm and air hole diameter of
0.5 μm. In this case, the flattened dispersion with value between -4 and 0.5 ps/nm/km is obtained ranging from 1400 to
1600 nm. The nonlinear coefficient γ is as high as 2.5 m-1W-1 at 1.5 μm. The optical parametric gain bandwidth of
nearly 200 nm can be achieved in composite tellurite/phosphate MOF with the length of 2.5 m and the pump power of
0.4 W.
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