Zero-dispersion Wavelength Research Articles

Single-mode silica microsphere Raman laser tunable in the U-band and beyond

We demonstrate experimentally a silica microresonator-based single-mode Raman laser tunable in the U-band and beyond. The Stokes wavelength is tuned in the 1631–1685 nm range when tuning a C-band pump laser in the 1520–1570 nm range. We also demonstrate switching between Raman lasing modes which corresponds to “jumps” by 2 or 3 whispering gallery modes (WGMs) while sweeping the pump laser near a certain WGM (without pump “jumps” between WGMs). In addition, four-wave mixing (FWM) leading to single mode anti-Stokes wave generation in the E-band near 1450 nm is obtained when the pump wavelength is near the microresonator zero dispersion wavelength (ZDW) and the phase matching condition for the pump, Stokes, and anti-Stokes waves is satisfied.

Design and Analysis of a Dispersion-engineered and Highly Nonlinear Rib Waveguide for Generation of Broadband Supercontinuum Spectra

AbstractIn this paper, a waveguide consisting of a core of As2Se3 chalcogenide glass and the upper and lower claddings of MgF2 with two zero-dispersion wavelengths (ZDW) has been proposed. By optimization of the dimensions of the core and the claddings, their effects on the dispersion curve have been investigated and a suitable structure with a flat dispersion curve, an effective mode area of ​​1.6 μm2 in a pump wavelength of 2.8 μm, and hence, a nonlinear coefficient greater than 34 w−1 m−1 has been obtained. A broadband supercontinuum in a wavelength range of 1.5 μm to 15 μm has been generated by applying an input pulse with duration of 100 fs and a maximum power of 2 kw to this waveguide. Due to the large width of the supercontinuum generated (SCG), the short length of the waveguide (maximum 5 mm), and a low input power, this structure is suitable for use in optical integrated circuits and its various applications.

Investigation of continuum generation in the non-zero dispersion-shifted fiber pumped by femtosecond nanojoule pulses in 1450–1800 nm spectral range

A synchronously pumped optical parametric oscillator based on periodically poled potassium titanyl phosphate (PPKTP) crystal delivering femtosecond nanojoule energy pulses in the 1.45 μm–1.8 μm spectral range is used as pump source for continuum generation in conventional non-zero dispersion shifted optical fiber. Detailed numerical simulations and experiments employing cross-correlation frequency-resolved optical gating (XFROG) reveal soliton and dispersive wave generation dynamics and can help to estimate limits of how far the pump wavelength can be shifted from zero-dispersion wavelength (ZDW) to still obtain sufficient spectrum broadening. We also demonstrate the applicability of recently introduced fiber dispersion measurement technique based on XFROG trace analysis to conventional optical fibers. Combination of this efficient parametric device with standard non-zero dispersion shifted low cost and low loss optical fiber results in efficient continuum generation with output/input average power ratio greater than 50%.

Dispersion-tunable chalcogenide tri-cladding fiber based on novel continuous two-stage extrusion

A novel robust tri-cladding stepped fiber structure has been proposed for the dispersion tuning, and a systematic simulation has been given for the fibers with different sizes of claddings and cores. The results show that double zero-dispersion wavelength (ZDW) points can be obtained, and the first ZDW is shorter at 3.3 µm and the second ZDW at 9.9 µm. Based on the simulation of the structural optimization, we have prepared a well-structured tri-cladding fiber with a minimum loss of 1.55 dB/m at 6.77 µm by a novel continuous two-stage extrusion method. Moreover, a flattened supercontinuum extending from 1.3 to 12.9 µm pumping at anomalous dispersion wavelength of 5 µm between the two ZDWs can be achieved, which fits well with the simulated results. After all, the optimized fiber consisting of As2Se3, Ge10As22Se68, As2S3 exhibits excellent properties that demonstrate the potential for a simple way to prepare high quality fiber with a tri-cladding structure.

Temperature-assisted broadly tunable supercontinuum generation in chalcogenide-glass-based capillary optical fiber

We propose an alternative technique for generating a tunable supercontinuum in a liquid-filled chalcogenide capillary optical fiber exhibiting three zero-dispersion wavelengths. To investigate the tunable supercontinuum, a nonlinear Schrödinger equation is solved to understand the soliton pulse dynamics. Utilizing temperature-assisted dispersion tailoring, the generation of dispersive waves that are tunable within a broad wavelength range of 3630–4650 nm and 2230–2560 nm is reported, with detailed investigations of various spectrograms confirming the predictions of dispersive waves through phase-matching characteristics. Also, temperature-controlled soliton spectral tunneling is numerically predicted in the same fiber and depends on the spectral width of the normal dispersion region between two anomalous regions.

Design and analysis of dispersion-compensating chalcogenide photonic crystal fiber with high birefringence

The photonic crystal fiber (PCF) with a bunch of air holes enclosing the silica core field has momentous and compelling attributes when compared with the ordinary single-mode fibers. In this work, both the birefringence and dispersion properties of a polarization-maintaining chalcogenide (ChG) photonic crystal fiber are numerically investigated by means of the finite element method. Through simulation, it is found that the birefringence of the proposed $${\mathrm{G}\mathrm{e}}_{11.5}{\mathrm{A}\mathrm{s}}_{24}{\mathrm{S}\mathrm{e}}_{64.5}$$ PCF can reach as high as $$0.03$$ when compared with the conventional fiber that has merely $$5\times {10}^{-4}$$ for wavelengths in the 2–10 $$\upmu \mathrm{m}$$ range. The PCF is designed with zero-dispersion wavelengths for x- and y-polarized modes in the 2–10 $$\upmu \mathrm{m}$$ range. It is also observed that over the entire MIR wavelength range, the GVD remains positive and has a maximum value of 30,000 ps2/nm-km. Hence, the proposed $${\mathrm{G}\mathrm{e}}_{11.5}{\mathrm{A}\mathrm{s}}_{24}{\mathrm{S}\mathrm{e}}_{64.5}$$ PCF plays the dual role of acting as a very good polarization-maintaining fiber due to its very high birefringence and an excellent dispersion-compensating fiber due to its large positive GVD. This $${\mathrm{G}\mathrm{e}}_{11.5}{\mathrm{A}\mathrm{s}}_{24}{\mathrm{S}\mathrm{e}}_{64.5}$$ PCF serves as a very good candidate for ultra-broadband high bit-rate transmission. Supercontinuum generation is another important application of PCF. Supercontinuum generation is a generation of coherent and broadband light. SC generation in PCFs has several applications in optical coherence tomography (OCT), optical frequency metrology (OFM), pulse compression, and design of ultrafast femtosecond laser pulses.

High-order dispersion mapping of an optical fiber.

We report on measurements of high-order dispersion maps of an optical fiber, showing how the ratio between the third and fourth-order dispersion (β3/β4) and the zero-dispersion wavelength (λ0) vary along the length of the fiber. Our method is based on Four-Wave Mixing between short pulses derived from an incoherent pump and a weak laser. We find that the variations in the ratio β3/β4 are correlated to those in λ0. We present also numerical calculations to illustrate the limits on the spatial resolution of the method. Due to the good accuracy in measuring λ0 and β3/β4 (10 -3% and 5% relative error, respectively), and its simplicity, the method can be used to identify fiber segments of good uniformity, suitable to build nonlinear optical devices such as parametric amplifiers and frequency comb generators.

High Coherence at f and 2f of Mid-Infrared Supercontinuum Generation in Silicon Germanium Waveguides

Absorption spectroscopy based on supercontinuum generation in the mid-infrared is a powerful technique to analyze the chemical composition of samples. Furthermore, phase-coherent supercontinuum sources can enable fast data acquisition with coherent, stable pulses that allow single-shot measurements. We report here a numerical study of the coherence of an octave-spanning mid-infrared supercontinuum source that was experimentally obtained in an air-clad SiGe/Si waveguide. We show that engineering two closely spaced zero-dispersion wavelengths that enclose an anomalous dispersion band centered around a fixed pump wavelength can produce supercontinuum pulses with high spectral density and full coherence at the extreme ends of the spectrum. This work is important for absorption spectroscopy, on-chip optical frequency metrology, and f -to-2 f interferometry applications.

Nonlinear Spectrum Compression of Negatively Chirped Picosecond Pulses in Dispersion-Shifted Telecom Fiber

We investigated both experimentally and numerically self-phase modulation-induced spectrum compression dynamics of negatively chirped picosecond Gaussian pulses in the low-loss dispersion-shifted telecom fiber near its zero dispersion wavelength (ZDW). It was experimentally observed linearly interpolated monotonous increase in spectrum compression ratio (SCR) with negative chirp growth of the incident pulse in the range from −5.9 to −91.9. According to numerical simulations, despite its small values in the vicinity of ZDW, fiber dispersion limits both SCR growth and spectrum compression quality expressed in terms of time-bandwidth product value and energy confinement ratio at larger chirp values (|C| > 100), in a combined action with self-phase modulation (SPM). Having optimized fiber length and pulse energy, we achieved record 49.2-fold spectrum compression of 38.3-ps, 2.08 nJ negatively chirped Gaussian pulses with compressed spectrum FWHM of 0.23 nm and a50% energy confinement at 1560 nm wavelength, leading to a13.3-times spectral brightness magnification. We believe that results obtained can be promising for ultra-short pulse laser systems development with enhanced spectral brightness.

Elliptical-spiral elliptical-hole photonic crystal fiber with high birefringence, large nonlinearity, and two zero dispersion.

This paper presents a soft-glass (SF-57) elliptical-spiral photonic crystal fiber with elliptical air holes for achieving high birefringence, large nonlinearity, and tailoring two zero-dispersion wavelengths (ZDWs) in the near-infrared region. A full-vector finite-element method with perfectly matched boundary layer is used to characterize the properties of the photonic crystal fiber for different ellipticity ratios. The designed fiber has a birefringence 4 times higher than the circular-spiral structure. There are two ZDWs at around 1.2 µm and 2.8 µm which can be finely tuned depending on the ellipticity ratios along with a large nonlinearity. Due to the superior guiding properties, the proposed structure can be used for polarization control and broadband supercontinuum generation.

10-GHz broadband optical frequency comb generation at 1550/1310 nm

The generation of high-repetition rate (frep ≥ 10 GHz) ultra-broadband optical frequency combs (OFCs) at 1550 nm and 1310 nm is investigated by seeding two types of highly nonlinear fibers (HNLFs) with 10 GHz picosecond pulses at the pump wavelength of 1550 nm. When pumped near the zero dispersion wavelength (ZDW) in the normal dispersion region of a HNLF, 10 GHz flat-topped OFC with 43 nm bandwidth within 5 dB power variation is generated by self-phase modulation (SPM)-based OFC spectral broadening at 26.5 dBm pump power, and 291 fs pulse trains with 10 GHz repetition rate are obtained at 18 dBm pump power without complicated pulse shaping methods. Furthermore, when pumped in the abnormal dispersion region of a HNLF, OFCs with dispersive waves around 1310 nm are studied using a common HNLF and fluorotellurite fibers, which maintain the good coherence of the pump light at 1550 nm. At the same time, sufficient tunability of the generated dispersive waves is achieved when tuning the pump power or ZDW.

A modified large mode-field area fiber with managing chromatic dispersion

We present a new scheme of large mode-field area fiber with chromatic dispersion management. The large core fiber is modified with two rod-arrays, which are able to manage chromatic dispersion. The rod-arrays are composed of high Ge-doped rods and located symmetrically on the both sides of the large core. Moreover the high-order modes can be removed efficiently by the rod-arrays. Characteristics of the proposed fiber are studied numerically in detail, including modes characteristics, bending loss, and chromatic dispersion. Through optimizing the key parameters of rod-arrays, the zero-dispersion wavelength is controllable, a large mode-field area and the single mode operation can be achieved. We hope that the modified large mode-field area fiber can be further applied to high power fiber lasers and amplifiers.

Supercontinuum Generation in Highly Nonlinear PQF with Two Zero Dispersion Wavelength

An optical input pulse with a duration of nanosecond to femtosecond propagates through a dispersive nonlinear medium, it is subject to an extreme spectral broadening termed as white light supercontinuum (SC). In PCF, dispersion characteristics can be modified by the waveguide geometric parameters and thereby the nonlinear dynamics can be altered. In this article, the fiber parameters like core diameter, doping percentage, and pitch are varied and analyzed to achieve a conclusive zero-dispersion wavelength (ZDW) and a high nonlinearity. The numerical study presents different designs of solid-core photonic quasi-crystal fiber (PQF) and selection of highly nonlinear fiber with an effective area of 1.14 mm2 and nonlinearity of 196 W-1-km-1 at 780 nm exhibiting two-zero dispersion wavelength for supercontinuum generation in different regimes. The results exhibit a significant pulse broadening effect when the pump pulse (FWHM) was varied from 25 fs to 100 fs. Similarly, the influences of the pulse energy and peak average power on the bandwidth of the generated SC are studied

1.2-15.2 μm supercontinuum generation in a low-loss chalcohalide fiber pumped at a deep anomalous-dispersion region.

A novel low-loss selenium-based chalcohalide fiber, with a low zero-dispersion wavelength, was prepared by an innovative preparation process. The composition optimized fiber has a wide transmission range of up to 11.5μm, a lowest fundamental mode zero-dispersion wavelength of 4.03μm, and a minimum optical loss of 1.12dB/m at 6.4μm, which provides a possibility to replace As2S3 and As2Se3 in a cascade of ZrF4-BaF2-LaF3-AlF3-NaF(ZBLAN)-As2S3-As2Se3 fiber in the practical all-fiberized supercontinuum (SC) source. Meanwhile, the broadest SC spectrum, ∼1.2 to 15.2μm, was achieved by pumping a 12-cm-long fiber with a femtosecond laser at a deep anomalous-dispersion region. Furthermore, simulations are adopted to interpret the results as well as to demonstrate spectral evolution along the fiber. To the best of our knowledge, this is the broadest SC spectrum reported in any selenium-based chalcogenide fiber.

Trajectory manipulation of an Airy pulse near zero-dispersion wavelength under a free-carrier-generated linear potential

We investigate the dynamics of an Airy pulse that experiences free carrier generated optical linear potential in the vicinity of zero group velocity dispersion (GVD) wavelength inside a Si based waveguide. The optically induced potential can be realized by an inhomogeneous medium which possesses a time dependent refractive index. We propose a pump-probe scheme in Si-based waveguide where a strong continuous wave (CW) pump excites free carriers that leads to a linear potential through a time dependent refractive index change which is experienced by the finite energy Airy pulse (FEAP) (probe). The linear potential significantly manipulate the dynamics of a FEAP and leads to a monotonous spectral shift. We mathematically model the dynamics of the Airy pulse using linear dispersion equation containing an optical potential term and establish the general solution of the pulse for non-vanishing third order dispersion (TOD). We derive the expression of the trajectory of FEAP which deviates significantly from its usual ballistic nature and can be tailored with the strength of the linear potential. For positive TOD, the propagating Airy pulse experiences a singularity and flips in time domain. We theoretically derive that for a specific potential strength the flipping region is squeezed to a point and revives thereafter. We propose an exact analytical solution beyond flipping region for this specific case. Our theoretical analysis corroborates well with the numerical results. The present study may be useful in applications related to pulse reshaping and trajectory manipulation

Design of all-solid W-type index fluorotellurite fibers with near-zero-flattened chromatic dispersion for optical frequency comb generation.

All-solid W-type index fluorotellurite fibers (AWFTFs) with near-zero-flattened dispersion profiles are designed for optical frequency comb (OFC) generation. The fiber core and cladding materials are ${{\rm TeO}_2} {\text - } {{\rm BaF}_2} {\text - } {{\rm Y}_2}{{\rm O}_3}$TeO2-BaF2-Y2O3 (TBY) and fluoroaluminate glasses. Those two glasses have large refractive index contrast as well as similar thermal expansion coefficients and softening temperatures. The zero-dispersion wavelength of the TBY glass is about 2517 nm. By introducing fluoroaluminate glasses with relatively low refractive index as the cladding material and controlling the core diameter, the zero-dispersion wavelength of the fiber is shifted from 2517 nm to the wavelength region of 1500-1600 nm. Furthermore, two layers of thin annular glasses including a fluoroaluminate-glass-based inter-layer and a TBY-glass-based outer layer are added around the fiber core, which makes the fiber have a flat dispersion profile in the wavelength range of 1500-1600 nm. By optimizing the parameters (the core diameter, the thickness of the thin annular glass, etc.) of AWFTFs, the fiber with the chromatic dispersion value between $ - {0.2}$-0.2 and 0.35 ps/nm/km in the wavelength range of 1500-1600 nm is achieved. To investigate the application of the AWFTFs for OFC generation via cascaded four-wave mixing, we perform numerical simulations. The simulated results show that flat-top OFC spectrum expanding from 1450 to 1700 nm with tunable mode spacing from 25 to 100 GHz can be generated in 2 m long fiber by using a 1550 nm laser with a pulse width of 0.825 ps and a peak power of 60 W as the pump source.

Effects of few optical cycles approximation to spectral broadening generated in two-zero dispersion wavelengths fibers

It is both experimentally and numerically confirmed that Supercontinuum can be generated by pumping a few-tens-femtoseconds short pulse in anomalous dispersion region of a two zero-dispersion wavelengths (ZDW) fiber, such as, photonic crystal fiber. In numerical method, a well-known slowly varying envelope approximation (SVEA) has always been used to illustrate how the short pulse expands to a broadband spectrum in two-ZDWs fiber. But, the limit of SVEA is that it can only be applied for the short pulse, which its temporal envelope changes slowly comparing with its optical cycle. However, a few optical cycles short pulse is not fit with the condition of the SVEA approximation. In this report, another model, namely slowly evolving wave approximation (SEWA), is applied for numerical demonstration of supercontinuum generated by pumping the few optical cycles short pulse in two-ZDWs fiber. According to our simulation, under SEWA the final spectral width of the very short input pulse in the two-ZDWs fiber is between about 500 - 2000 nm, even the center wavelength of input pulse is near second-ZDW of fiber. Moreover, other effects of these two approximations since the center wavelength of the very short input pulse is close to both upper and lower ZDWs of the fiber in the same fiber’s length are also compared in our presentation.

Ultra-flat dispersion in an integrated waveguide with five and six zero-dispersion wavelengths for mid-infrared photonics

We propose a new type of dispersion flattening technology, which can generate an ultra-flat group velocity dispersion profile with five and six zero-dispersion wavelengths (ZDWs). The dispersion value varies from −0.15 to 0.35 ps/(nm·km) from 4 to 8 μm, which to the best of our knowledge is the flattest one reported so far, and the dispersion flatness is improved by more than an order of magnitude. We explain the principle of producing six ZDWs. Mode distribution in this waveguide is made stable over a wide bandwidth. General guidelines to systematically control the dispersion value, sign, and slope are provided, and one can achieve the desired dispersion by properly adjusting the structural parameters. Fabrication tolerance of this waveguide is also examined.

Multi-octave mid-infrared supercontinuum and frequency comb generation in a suspended As2Se3 ridge waveguide.

In this paper, we numerically investigate the mid-infrared supercontinuum (SC) generation in a suspended ${{\rm As}_2}{{\rm Se}_3}$As2Se3 ridge waveguide, which is designed with the two zero-dispersion wavelengths. Simulation results show that when the pump pulses at wavelength 3.3 µm with width of 100 fs and peak power of 900 W are launched into the anomalous dispersion region of the designed waveguide with a length of 0.87 mm, the SC can be generated in the wavelength range from 1.76 to 14.42 µm (more than three octaves), extending deep into the "fingerprint" region. The stability of the generated SC is confirmed by the first-order coherence. Moreover, we demonstrate the performance of the SC-based frequency comb by assuming a 50 pulse pump source at a repetition rate of 100 MHz.

Chalcogenide–Tellurite Composite Photonic Crystal Fiber: Extreme Non-Linearity Meets Large Birefringence

In this paper, we propose a novel design of a photonic crystal fiber (PCF) with tellurite-cladding, three rings of air-holes and elliptical concentration of As2S3 in the fiber core. The combined effect of tight mode confinement (an effective mode area of nearly 0.6 µm2), large non-linear refractive index of As2S3 and significant variation between the effective modal index values of the two orthogonal states of the fundamental guided mode leads to extreme non-linear coefficient and birefringence values, all achieved at the zero dispersion wavelength (ZDW) of 1550 nm. The corresponding birefringence and non-linear coefficient (7 × 10−3 and 28 W−1 m−1, respectively) are more than three orders of magnitude larger than that of the regular silica-based highly non-linear PCFs. In addition, we numerically demonstrate that by modifying the core and air-hole dimensions one can easily control the dispersion curve and tune the ZDW of the proposed fiber to any excitation wavelength ranging from near-infrared to short-wave-infrared, including optical telecommunication windows close to 1550 nm. The superior characteristics of the proposed elliptical-core composite PCF including extreme non-linearity, nearly-zero confinement loss (2.47 × 10−12 dB/cm), the ability to maintain polarization of light, and tunable ZDW can open the door to new possibilities in non-linear optics, optical telecommunications, optical signal processing, and sensing devices.