Search Results (28)

Substantial improvements in the performance of optical interconnects based on multi-mode fibers are required to support emerging single-channel data transmission rates of 200 Gb/s and 400 Gb/s. Future optical components must combine very high modulation bandwidths—supporting signaling at 100 Gbaud and 200 Gbaud—with reduced spectral width to mitigate chromatic-dispersion-induced pulse broadening and increased brightness to further restrict flux-confining area in multi-mode fibers and thereby increase the effective modal bandwidth (EMB). A particularly promising route to improved performance within standard oxide-confined VCSEL technology is the introduction of multiple isolated or optically coupled oxide-confined apertures, which we refer to collectively as multi-aperture (MA) VCSEL arrays. We show that properly designed MA VCSELs exhibit narrow emission spectra, narrow far-field profiles and extended intrinsic modulation bandwidths, enabling longer-reach data transmission over both multi-mode (MMF) and single-mode fibers (SMF). One approach uses optically isolated apertures with lateral dimensions of approximately 2–3 µm arranged with a pitch of 10–12 µm or less. Such devices demonstrate relaxation oscillation frequencies of around 30 GHz in continuous-wave operation and intrinsic modulation bandwidths approaching 50 GHz. Compared with a conventional single-aperture VCSELs of equivalent oxide-confined area, MA designs can reduce the spectral width (root mean square values < 0.15 nm), lower series resistance (≈50 Ω) and limit junction overheating through more efficient multi-spot heat dissipation at the same total current. As each aperture lases in a single transverse mode, these devices exhibit narrow far-field patterns. In combination with well-defined spacing between emitting spots, they permit tailored restricted launch conditions in MMFs, enhancing effective modal bandwidth. In another MA approach, the apertures are optically coupled such that self-injection locking (SIL) leads to lasing in a single supermode. One may regard one of the supermodes as acting as a master mode controlling the other one. Streak-camera studies reveal post-pulse oscillations in the SIL regime at frequencies up to 100 GHz. MA VCSELs enable a favorable combination of wavelength chirp and chromatic dispersion, extending transmission distances over MMFs beyond those expected for zero-chirp sources and supporting transfer bandwidths up to 60 GHz over kilometer-length SMF links. Full article

The challenge of water shutoff in carbonate reservoirs is complicated by the presence of fractures, which cannot be effectively blocked using conventional hydrogel screens designed for granular reservoirs. To reliably seal fractures, fibrous and dispersed fillers are added to hydrogels. These fillers must exhibit affinity for the matrix to ensure the composites can effectively isolate water. Given the wide variability in fracture apertures, it is evident that water shutoff composites should incorporate fibers and dispersed fillers of varying geometric sizes. This study presents a range of hydrogel composites reinforced with mono-, bi-, and tri-component fibers, as well as dispersed fillers, designed for water shutoff in fractured carbonate reservoirs with varying fracture apertures. Oscillation test results demonstrated a twofold increase in the elastic modulus (40–45 Pa) for compositions with various fillers compared to the base composition (23 Pa). Filtration studies revealed the effectiveness of the optimized compositions under different fracture apertures. Specifically, even at a fracture aperture of 650 μm, the residual resistance factor (RRF) reached 82.3 and 9.76 at water flow rates of 0.1 cm³/min and 0.5 cm³/min, respectively. The conducted rheological and filtration tests, along with field trials, confirmed the validity of the selected approach. Full article

A polarization-maintaining all-fiber laser source based on a nonlinear amplifying loop mirror with broadband operation (64 nm) around 1920 nm is demonstrated. The oscillator can generate 66 pJ up-chirped dissipative soliton pulses at a repetition rate of 22.8 MHz with a high polarization extinction ratio of 17 dB. By adding a polarization controller to the polarization-maintaining dispersion-compensating fiber, the filter behavior can be adjusted allowing for the tuning of the emission to a center wavelength of 1878 nm, 1907 nm, and 1926 nm. Using an all-polarization-maintaining single-mode fiber amplifier with anomalous dispersion, the pulses are amplified to 0.9 nJ and compressed to a near Fourier-limited pulse duration of 170 fs with a peak power of 4.3 kW. Such all-fiber-based sources are attractive due to their compact size, high beam quality, and good environment stability. Full article

A filter-free, image-reject, sub-harmonic downconverted RoF link is proposed based on a dual-polarization quadrature phase-shift keying (DP–QPSK) modulator. At the remote antenna unit, the receiving radio frequency signal is applied to the upper QPSK modulator to achieve carrier-suppressed single-sideband (CS–SSB) modulation. The local oscillator (LO) is applied to the lower QPSK modulator, achieving sub-harmonic single-sideband (SH–SSB) modulation. The I/Q mixing is realized by exploiting a two-channel photonic microwave phase shifter, which mainly consists of a modulator, two polarization controllers, and two polarizers. The image interference signal can be rejected when combing the I and Q IF signals through a 90° electrical hybrid. Because the scheme is simple and filter-free, it has a good image-reject capability over a large frequency tunable range. Moreover, due to the special SH-SSB modulation, the modulated signals are immune to the chromatic dispersion-introduced power fading effect. Last, the sub-harmonic downconverter can decrease the frequency requirement of the LO signal. Experimental results show that an image rejection ratio (IRR) greater than 50 dB can be achieved when transmitted through a 25 km single-mode fiber (SMF). Simultaneously, under different RF signals and IF signals, the IRR has no periodic power fading, only small fluctuations. Image rejection capability of the scheme for the 50-MBaud 16-QAM wideband vector signal is also verified and the demodulation of the desired IF signal with a good EVM of less than 5% is realized. Full article

An all-fiber low-repetition-rate SESAM mode-locked fiber oscillator combined with a dispersion-managed active fiber loop produces a flexible GHz burst-mode laser source. The high-power output is then produced by amplifying the GHz burst-mode laser source using an all-fiber chirped-pulse amplification system. Then, the laser is compressed using a grating pair compressor; a maximum amplified power of 97 W is obtained. This results in a compressed high power of 82.07 W with a power stability RMS of 0.09% and beam quality better than 1.2. Accurate dispersion control allows for the production of a high-quality pulse duration of 265 fs. Full article

Fiber optic parametric and phase sensitive amplifiers (PSA) are interesting for modern day communication technologies due to their low noise and high gain amplification properties with a potential for all optical signal processing and wide band operation. PSAs are typically employed in either a single pump or dual pump configuration. In this article we explore the utilities of both configurations, however considering a fiber with a longitudinally varying dispersion profile. For the single pump case, PSA operation at large pump-signal detunings, that arise due to the longitudinal dispersion variation, were studied numerically, and recipes of using the system as a wide band wavelength selective filter were laid out. For the dual-pump case, emphasis was laid on achieving a larger signal gain, by reducing stimulated Brillouin scattering (SBS) that prevents large pump power transport through the nonlinear fiber. First, the effects of dispersion variation on the gain of a dual pump PSA were studied analytically and numerically in order to optimize the dispersion variation profile, neglecting SBS processes. Then we independently studied the SBS dynamics of the system numerically. A sinusoidally dispersion oscillating fiber (DOF) was found to be an optimal candidate with respect to its PSA and SBS performances. To establish this claim, we also experimentally compared the performance of an available DOF over a standard highly nonlinear fiber (HNLF) that has a constant dispersion profile and established its utility for designing a high gain PSA system, thanks to the SBS mitigation due to the longitudinal dispersion variation of the fiber. Full article

We propose and experimentally demonstrate a tunable frequency-doubling optoelectronic oscillator (FD-OEO) based on a single-bandpass dispersion-induced microwave photonic filter (MPF) consisting of a Mach–Zehnder modulator (MZM), a linearly chirped fiber Bragg grating and polarization-multiplexed dual-loop. Thanks to the polarization dependence of the MZM, a special double sideband modulation is implemented where the optical carrier (OC) and subcarriers are orthogonally polarized. By simply tuning the PC in the OEO loop, the phase difference between the orthogonal polarization carrier and two sidebands can be controlled, and thus the center frequency of the fundamental OEO can be tuned. Furthermore, a PC and a polarizer are placed outside the OEO to achieve optical carrier suppression (OCS) modulation, which ensures that a frequency-tunable microwave signal at the second-harmonic frequency is generated. In the experiment, a fundamental frequency signal with tunable frequency from 3.6 to 6.85 GHz and FD-OEO with a tunable frequency range from 7.2 to 13.7 GHz are generated. Full article

Recent reports of the release of large numbers of respirable and critically long fiber-shaped fragments from mesophase pitch-based carbon fiber polymer composites during machining and tensile testing have raised inhalation toxicological concerns. As carbon fibers and their fragments are to be considered as inherently biodurable, the fiber pathogenicity paradigm motivated the development of a laboratory test method to assess the propensity of different types of carbon fibers to form such fragments. It uses spallation testing of carbon fibers by impact grinding in an oscillating ball mill. The resulting fragments were dispersed on track-etched membrane filters and morphologically analyzed by scanning electron microscopy. The method was applied to nine different carbon fiber types synthesized from polyacrylonitrile, mesophase or isotropic pitch, covering a broad range of material properties. Significant differences in the morphology of formed fragments were observed between the materials studied. These were statistically analyzed to relate disintegration characteristics to material properties and to rank the carbon fiber types according to their propensity to form respirable fiber fragments. This tendency was found to be lower for polyacrylonitrile-based and isotropic pitch-based carbon fibers than for mesophase pitch-based carbon fibers, but still significant. Although there are currently only few reports in the literature of increased respirable fiber dust concentrations during the machining of polyacrylonitrile-based carbon fiber composites, we conclude that such materials have the potential to form critical fiber morphologies of WHO dimensions. For safe-and-sustainable carbon fiber-reinforced composites, a better understanding of the material properties that control the carbon fiber fragmentation is imperative. Full article

In this work, we present the generation of two distinct types of soliton pulses using a Bismuth Selenide (Bi₂Se₃) saturable absorber (SA) synthesized in our laboratory. The soliton pulses were generated in two different laser cavity configurations, resulting in two types of solitons: a soliton pulse with Kelly sidebands and a bunched soliton pulse with peak-dip sidebands. Both solitons operated at the fundamental repetition rate—23.3 MHz (for the soliton with Kelly sidebands) and 13 MHz (for the bunched soliton with peak-dip sidebands). We observed that the accumulation of nonlinear phase shift from the added single mode fiber (SMF) split the single soliton pulse into 44 pulses in a bunched oscillation envelope. At the same time, peak-dip sidebands were imposed on the bunched soliton spectrum due to constructive and destructive interferences between soliton pulse and dispersive waves. The measured pulse width for both solitons were 0.63 ps (for the soliton with Kelly sidebands) and 1.52 ps (for the bunched soliton with peak-dip sidebands), respectively. Our results demonstrate the potential of Bi₂Se₃ SAs in generating different types of soliton pulses, which could have potential applications in various areas of optical communication and spectroscopy. Full article

A broadband microwave photonic mixer with tunable phase shift and supporting dispersion-induced power-fading-free fiber transmission is proposed and demonstrated based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM). In this scheme, the intermediate-frequency (IF)/radiofrequency (RF) signal and the local oscillation (LO) signal are applied to the four sub-MZMs biased at their minimum transmission points via a power splitter and a 90° hybrid coupler, respectively. Through mutual beating between the IF/RF and the LO modulation sidebands in a high-speed photodetector at the remote site, high-efficiency frequency conversion is achieved. The dispersion-induced power fading over long-distance fiber transmission is eliminated through setting the biased-induced phase difference between the parent-MZMs in the two sub-DPMZMs of the DP-DPMZM to be π/2. In addition, the phase shift of the frequency-converted signal can be continuously tuned over 360° through synchronously adjusting the bias voltages of the parent-MZMs in the two sub-DPMZMs. The proposed scheme is experimentally demonstrated, where a microwave photonic mixer with a 6-dB operation bandwidth of 40 GHz and supporting dispersion-induced power-fading-free transmission over 20 km SMF is realized. Meanwhile, a continuously tunable phase shift over 360° in the frequency range of 0.1 GHz to 29.9 GHz is achieved, where the power variation during phase tuning is smaller than 4 dB. Full article

A photonic approach to the cancellation of self-interference in the optical domain with fiber dispersion immunity and harmonic frequency down-conversion function is proposed based on an integrated, dual-parallel, dual-drive Mach–Zehnder modulator (DP-DMZM). A dual-drive Mach–Zehnder modulator (DMZM) is used as an optical interference canceller, which cancels the self-interference from the impaired signal before fiber transmission to avoid the effect of fiber transmission on the cancellation performance. Another DMZM is used to provide carrier-suppressed, local-oscillation (LO)-modulated, high-order double optical sidebands for harmonic frequency down-conversion to release the strict demand for high-frequency LO sources. By regulating the DC bias of the main modulator, the signal of interest (SOI) can be down-converted to the intermediated frequency (IF) band after photoelectric conversion with improved frequency-conversion efficiency, immunity to the fiber-dispersion-induced power-fading (DIPF) effect, and effective signal recovery. Theoretical analyses and simulation results show that the desired SOI in the X and K bands with a bandwidth of 500 MHz and different modulation formats can be down-converted to the IF frequency. The self-interference noise with the 2 GHz bandwidth is canceled, and successful signal recovery is achieved after a 10 km fiber transmission. The recovery performance of down-converted signals and the self-interference cancellation depth under different interference-to-signal ratios (ISRs) is also investigated. In addition, the compensation performance of DIPF is verified, and a 6 dB improvement in frequency conversion gain is obtained compared with previous work. The proposed scheme is compact, cost-effective, and thus superior in wideband self-interference cancellation, long-range signal transmission, and effective recovery of weak desired signals. Full article

In this paper, we have demonstrated a dispersion-managed, high-power, Tm-Ho co-doped ultrashort pulse fiber laser using a single walled carbon nanotube (SWNT) dispersed in polyimide film. An in-line type spectral filter was developed to control the output pulse spectra. Two SWNT films with different modulation depths were examined as a mode-locker. Normal dispersion fiber was used in the fiber laser oscillator, and dependence on net cavity dispersion was investigated. Passive mode-locking was achieved in a wide dispersion range, from −0.319 to +0.101 ps². Stable soliton mode-locking operation and dissipative soliton mode-locking operations were observed. The pumping efficiency was ~3 times higher than that in a Tm-doped fiber laser with a similar configuration. The developed fiber laser showed self-start and stable operations, and this laser is useful for practical applications. Full article

In the present experimental study, the transverse oscillating laser beam technique was applied for the post-melting of metal matrix composite coatings, thermally sprayed with nickel-based self-fluxing NiCrCoFeCBSi alloy and 40 wt.% WC, to improve their hardness and wear resistance. The study was conducted using the single module optical fiber laser at 300 W power, >9554 W/cm² power density, 250–1000 mm/min laser speed, 1 mm and 2 mm transverse oscillation amplitude. Scanning electron microscopy, energy dispersive spectroscopy, Knop hardness measurements, and “Ball-on-disc” dry sliding tests were conducted to study the effect of the processing parameters on the molten pool geometry and microstructure, hardness, and tribology of the processed layers. Oscillating laser processing with an amplitude of 1 mm, 250–750 mm/min laser operating speed, and sample preheating to 400 °C gave a satisfactory result: wide and shallow molten pools of ~200–350 μm in depth, hardness between ~1100 and 1200 HV0.2 and minimum cracks obtained. The coatings obtained with laser beam oscillation and preheating, and ~1150 HV0.2 hardness showed an improvement in the wear resistance and friction coefficient (~0.33) of ~2.9 times and ~20%, respectively, compared with the respective values of the coatings remelted in furnace. Full article

We reported on the generation of 99.8 fs, 25 kW peak-power, dispersion-managed pulses directly from a passively mode-locked Yb-fiber laser oscillator with a figure-of-9 configuration. The introduction of strongly injected pump power and optical components with a high damage threshold enables high-power operation, while the polarization-maintaining (PM) fiber supports environmentally stable self-started mode-locking. Mode-locking in the soliton-like and negative-dispersion regime is characterized by the dispersion management via tuning the separation distances between a pair of gratings inside the cavity. The oscillator generates stable pulses with up to 40.10 mW average power at a 16.03 MHz repetition rate, corresponding to a pulse energy of 2.5 nJ. To the best of our knowledge, it is the highest peak-power directly obtained by a laser oscillator with a figure-of-9 configuration. Full article

Photonics-based microwave generation brings the advantages of photonic oscillators, such as high stability, wide bandwidth, and low loss, to the microwave domain. In this paper, the generation of tunable microwave signals was investigated both theoretically and experimentally based on an all-polarization-maintaining 1-GHz mode-locked fiber laser. Based on beating between two highly chirped optical pulse trains with a relative time delay at the photodetector, tunable microwave signals could be obtained. The numerical simulations show that 40 GHz or higher microwave signals could be obtained by tuning the time delay and dispersion. To experimentally validate the theoretical model, the generation of tunable microwave signals from 2–4 GHz was demonstrated. Due to the utilization of polarization-maintaining devices, the optical output has a high degree of linear polarization of more than 99%, which verifies the enhanced system stability. These demonstrations are imperative for solidifying the advancements of recent years and could promote the utilization of photonics-based microwave generation in microwave photonics. Full article