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A tomographic waveguide-based augmented reality display technique is proposed for near-eye three-dimensional (3D) display with accurate depth reconstructions. A pair of tunable lenses with complementary focuses is utilized to project tomographic virtual 3D images while maintaining the correct perception of the real scene. This approach reconstructs virtual 3D images with physical depth cues, thereby addressing the vergence-accommodation conflict inherent in waveguide augmented reality systems. A prototype has been constructed and optical experiments have been conducted, demonstrating the system's capability in delivering high-quality 3D scenes for waveguide-based augmented reality display.

Laser-induced plasma micromachining (LIPMM) is an advanced technology that utilizes the plasma generated from laser breakdown to remove material, thereby facilitating the fabrication of microstructures. This paper explores the use of LIPMM on 304 stainless steel surfaces parallel to the laser beam in different solutions, focusing on the impact of the liquid environment on the machining process. It presents a theoretical analysis of the material removal mechanisms unique to this orientation and experimentally investigates how water, a salt solution, and ethanol affect plasma shockwave characteristics. Notably, the plasma shockwave in the salt solution demonstrates the most significant peak pressure and energy, enhancing the micromachining efficiency. These findings suggest that varying the liquid environment can significantly influence LIPMM's effectiveness, offering potential improvements in precision and control. This study broadens the understanding of LIPMM applications, especially in orientations not commonly explored, and opens new possibilities for advanced micromachining techniques in various industrial applications.

The purpose of this study is to present a physical layer security scheme for key concealment and distribution based on carrier scrambling. The three-dimensional (3D) Lorenz system is used to generate independent chaotic sequences that encrypt the information with bit, constellation and subcarrier. In order to realize the flexible distribution of the key and ensure its security, the key information is loaded into a specific subcarrier. While key subcarrier and the ciphertext subcarrier are scrambled simultaneously. The encrypted key position information is processed and transmitted in conjunction with the training sequence (TS) to facilitate demodulation by the legitimate receiver. The processed TS can accommodate up to 10 key position information, thereby demonstrating the scheme's exceptional scalability. Experimental results show that the proposed scheme can safely transmit 131.80 Gb/s Orthogonal frequency division multiplexing (OFDM) signals across 2 km 7-core fiber. Meanwhile, the scheme enables simultaneous flexible distribution and concealment of the key, thereby offering a promising solution for physical layer security.

We propose a simple dynamical method to realize fast enantio-specific state transfer (ESST) of chiral molecules. Driven by three external electromagenetic fields, the chiral molecules are modeled as cyclic three-level systems, where the overall phase differs by π for the left- and right-handed chiral molecules. We unveil that the ESST is allowed when the amplitudes of three Rabi frequencies in the cyclic three-level systems are equal. Our method is robust and highly efficient in the sense that the external fields can have arbitrary waveforms. This thus provides the opportunity of simplifying the experimental implementations of ESST through pulse design.

We report, for the first time to the best of our knowledge, a spatiotemporal mode-locked (STML) multimode fiber laser based on nonlinear amplifying loop mirror (NALM), generating dissipative soliton resonance (DSR) pulses. Due to the complex filtering characteristics caused by the inherent multimode interference filtering structure and NALM in the cavity, the STML DSR pulse has wavelength tunable function. What's more, kinds of DSR pulses are also achieved, including multiple DSR pulses, and the period doubling bifurcations of single DSR pulse and multiple DSR pulses. These results contribute to further understand the nonlinear properties of STML lasers and may shed some light on improving the performance of the multimode fiber lasers.

The rapid development of laser technologies promises a significant growth of peak laser intensity from 10 22 W/cm 2 to >10 23 W/cm 2 , allowing the experimental studies of strong field quantum-electrodynamics physics and laser nuclear physics. Here, we propose a method to realize the ultra-intense laser field amplification of petawatt-class laser pulse in moderate density plasma via relativistic self-focusing and tapered-channel focusing. Three-dimensional particle-in-cell simulations demonstrate that almost an order of magnitude enhancement of laser intensity is possible even though the γ-ray radiation results in massive laser energy loss. In particular, with a seed laser intensity of ∼10 23 W/cm 2 , duration of 82.5 fs and power of 31 petawatt, one can obtain ∼10 24 W/cm 2 intensity and up to ∼60% energy conversion efficiency from the initial seed laser to the focused laser in plasma with density of 3.3 × 10 22 /cm 3 . This may pave the way to the new research field of ultra-intense laser plasma interaction in the upcoming laser facilities.

Structural-color nanoprinting, which can generate vivid colors with spatial resolution at subwavelength level, possesses potential market in optical anticounterfeiting and information encryption. Herein, we propose an ultracompact metasurface with a single-cell design strategy to establish three independent information channels for simultaneous watermarked structural-color nanoprinting and holographic imaging. Dual-channel spectrum manipulation and single-channel phase manipulation are combined together by elaborately introducing the orientation degeneracy into the design of variable dielectric nanobricks. Hence, a structural-color nanoprinting image covered with polarization-dependent watermarks and a holographic image can be respectively generated under different decoded environments. The proposed metasurface shows a flexible method for tri-channel image display with high information capacity, and exhibits dual-mode anticounterfeiting with double safeguards, i.e., polarization-controlled watermarks and a far-field holographic image. This study provides a feasible route to develop multifunctional metasurfaces for applications including optical anticounterfeiting, information encryption and security, information multiplexing, etc.

Laguerre-Gaussian (LG) modes can be converted from fundamental Gaussian mode by using phase optical elements such as spiral phase plates (SPP), but the conversion efficiency is strongly reduced in high charge plates because of the transverse intensity deviation. In this paper, a three-step scheme is proposed to dramatically improve the conversion efficiency. First, a fundamental Gaussian beam is converted to a 1st-order LG beam via a 1st-order SPP and a spatial filtering system. Then, by using a periscopic axicon mirror (PAM), the lst-order LG beam is transformed into an annular beam with larger beam radius. Finally, by using a second high-order SPP, this intensity-matched ring beam can be effectively converted to a high-charge LG0l beam. Through optimization of the PAM's parameter, the total conversion efficiency from fundamental Gaussian beam to LG0l mode as high as 91.85% is obtained, which is much higher than the case without PAM. Numerical simulations are carried out by the particle-in-cell (PIC) code EPOCH to verify the effectiveness of the scheme.

As a high-precision fiber optic sensor, a single optical fiber Fabry Pérot interferometer (FFPI) sensor is often used to measure parameters such as temperature or strain. However, the use of combined FFPIs to measure multiple parameters simultaneously has rarely been reported. In this paper, a compact Tri-FFPI sensor consisting of three series-connected FFPIs is proposed to measure high temperature, high acceleration, and large strain. The total length and diameter of the sensing part are only 2558.9 µm and 250 µm, respectively. One of the FFPIs, FFPI-1, contains a cantilever beam structure to measure vibration acceleration. FFPI-2 is used to measure temperature and the temperature compensation of the strain measurement. FFPI-3 is used to measure strain. To ensure that the sensor has high measurement sensitivity, two demodulation methods are used: the light intensity demodulation method for vibration acceleration and the wavelength demodulation method for temperature and strain. The sensor is capable of withstanding ultrahigh temperatures up to 1000°C.

The whole ecosystem is suffering from serious plastic pollution. Automatic and accurate classification is an essential process in plastic effective recycle. In this work, we proposed an accurate approach for plastics classification using a residual network based on laser-induced breakdown spectroscopy (LIBS). To increasing efficiency, the LIBS spectral data were compressed by peak searching algorithm based on continuous wavelet, then were transformed to characteristic images for training and validation of the residual network. Acrylonitrile butadiene styrene (ABS), polyamide (PA), polymethyl methacrylate (PMMA), and polyvinyl chloride (PVC) from 13 manufacturers were used. The accuracy of the proposed method in few-shot learning was evaluated. The results show that when the number of training image data was 1, the verification accuracy of classification by plastic type under residual network still kept 100%, which was much higher than conventional classification algorithms (BP, kNN and SVM). Furthermore, the training and testing data were separated from different manufacturers to evaluate the anti-interference properties of the proposed method from various additives in plastics, where 73.34% accuracy was obtained. To demonstrate the superiority of classification accuracy in the proposed method, all the evaluations were also implemented by using conventional classification algorithm (kNN, BP, SVM algorithm). The results confirmed that the residual network has a significantly higher accuracy in plastics classification and shows great potential in plastic recycle industries for pollution mitigation.

Multiplexed fiber optic Fabry-Perot interferometer (FPI) sensors are well known for their precision, simple construction, simpler wiring, and high sensing qualities. However, the limitations on existing demodulation methods degrade the measurement accuracy of multiplexed FPI sensors and necessitate large cavity length differences. In this paper, we propose an adaptive high-precision demodulation method based on vector matching and cluster-competitive particle swarm optimization (CCPSO), which transforms cavity length demodulation into searching for the global extreme. The proposed CCPSO, which uses agglomeration within clusters and competition between clusters simultaneously, enables the improvement of the global extreme search capabilities. The theoretical analysis and experimental results show that the proposed demodulation method decreases the lower limit of the needed cavity length differences to 22 μm, which is reduced by 76.9% compared with the fast Fourier transform-based method. An accuracy of 1.05 nm is achieved with a cavity length difference of 27.5 μm and a signal-to-noise ratio of 36.0 dB for the noise.

We propose a helically twisted pig-nose-shaped core microstructured optical fiber (HPC-MOF) for orbital angular momentum (OAM) mode generation. It comprises seven air-hole rings hexagonally arranged with two air holes and one air-hole ring replaced, forming two cores in a line 3 µm from the fiber center and one ring-shaped core. The fiber is helically twisted along the rotation axis. In this fiber, supermodes in inner dual-core can be coupled to high-order modes in outer ring-core, yielding OAM ring-shaped modes at different certain wavelengths, and various OAM modes at different twist rates were investigated in this paper. We demonstrate the distinct coupling differences of symmetric and antisymmetric supermodes in inner dual-core when the supermode coupled to ring-core mode. A modal matching rule is presented to characterize the coupling differences, which is suitable for describing supermode coupling characteristics in HPC-MOFs. Compared to conventional methods, these properties indicate that the fiber can generate higher-order OAM modes and more easily integrate into all-fiber optical communication systems, with potential in OAM generators, light-controlling devices, and integrated optics applications.

A few-mode fiber Bragg grating (FM-FBG) inscribed in a few-mode fiber (FMF) can maintain multiple reflection peaks due to the stable multiple modes in FMF. This paper studies the sensing characteristics of multiple reflection peaks for a four-mode FBG (4M-FBG) and innovatively proposes a joint-peak demodulation method based on one FM-FBG to reduce measurement error in temperature or strain sensing. This joint-peak demodulation method, theoretically explained and experimentally verified, provides the possibility of generating miniature sensors with high measurement accuracy and stable measurement performance. The potential of 4M-FBG for simultaneous measurement of strain and temperature is studied in this paper. By measuring the changes of wavelength and intensity of the reflection peaks, temperature and strain can be measured effectively.

Q-switching operation based on stimulated Brillouin scattering (SBS) has been developed for decades due to its inexpensive configuration, high pulse energy output, and the potential to be free from wavelength and material limitations. However, unstable and uncontrollable pulse output affected by SBS's stochastic nature hinders its development. In this work, we demonstrated a unique robust SBS-based Q-switched all-fiber laser. Firstly, a numerical model is developed and a general analysis about the robust Q-switching mechanism is presented. Simulation results show that the spectrum modulation effect such as FP interference is efficient for system to realize steady and controllable output. Secondly, we incorporated a Fabry-Perot (FP) interferometer made of two un-contact end faces of fiber connectors into a SBS-based Q-switched system and demonstrated passively robust Q-switching with simpler and cheaper configuration than most reported ones. Under 600 mW pump power, the SNR was measured to be as high as 62.96 dB, which is the highest SNR obtained from SBS-based Q-switched lasers. To our best knowledge, this is the first demonstration of robust SBS-based Q-switching without any external measures.

Broadcast and multi-cast communications are two important applications in quantum information science. Such applications guarantee the implementation of quantum information theory. In this paper, we propose two general schemes for the quantum broadcast and multi-cast communications to ensure that the central party (sender) can broadcast arbitrary single-qubit state to multiple receivers synchronously. Moreover, it is guaranteed that the information among the multiple receivers is different to satisfy the requirement in multi-cast communications. In particular, the proposed schemes indicate the probabilities, of which the multiple receivers obtain the quantum states successfully, could reach 1. We expect this works will shed some light for the prospective research on multi-party quantum communications and quantum cryptography.

We show that iterative solution of Maxwell's equations using the finite-difference frequency-domain method can be significantly accelerated by using a Schur complement domain decomposition method. We account for the improvement by analyzing the spectral properties of the linear systems resulting from the use of the domain decomposition method.

We demonstrate a master oscillator power amplifier (MOPA) architecture based on Yb:YAG amplifiers and adaptive optics (AO) systems with a high power and high beam quality laser output. With two conduction cooled, dual-end-pumped Yb:YAG zigzag-slab amplifiers at room temperature, the fiber laser of 300 W was scaled to 11.9 kW. Moreover, AO system positioned downstream was utilized to correct wavefront of amplified laser. The beam quality β at maximum output power was 2.8 times diffraction limited with closed-loop AO system.

Nodal aberration theory (NAT) describes the aberration properties of optical systems without symmetry. NAT was fully described mathematically and investigated through real-ray tracing software, but an experimental investigation is yet to be realized. In this study, a two-mirror Ritchey-Chrétien telescope was designed and built, including testing of the mirrors in null configurations, for experimental investigation of NAT. A feature of this custom telescope is a high-precision hexapod that controls the secondary mirror of the telescope to purposely introduce system misalignments and quantify the introduced aberrations interferometrically. A method was developed to capture interferograms for multiple points across the field of view without moving the interferometer. A simulation result of Fringe Zernike coma was generated and analyzed to provide a direct comparison with the experimental results. A statistical analysis of the measurements was conducted to assess residual differences between simulations and experimental results. The interferograms were consistent with the simulations, thus experimentally validating NAT for third-order coma.

The photosynthetic process of phytoplankton is the basis of the material circulation and energy flow of the ecosystem. The rapid and accurate measurement of phytoplankton photosynthesis rate is of great significance to water ecological environment monitoring, marine resource assessment and global climate change prediction. On the basis of "Bio-Optical" model, a photosynthetic rate measurement method based on tunable pulsed light induced fluorescence kinetics was put forward in this paper. The chlorophyll fluorescence was used as the probe of photosynthesis process, and the phytoplankton photosynthetic rate was evaluated by the photosynthetic electron transport rate. Comparative experiment results showed that the photosynthetic electron transport rate measured by fluorescence kinetic method under different conditions of DCMU, culture light and nutrients (nitrogen) were consistent with the photosynthetic oxygen evolution rate measured by oxygen evolution method, and the correlation coefficient R 2 were 0.934, 0.957 and 0.955 respectively.

In view of the problem of the on-line measurement of algae classification, a method of algae classification and concentration determination based on the discrete three-dimensional fluorescence spectra was studied in this work. The discrete three-dimensional fluorescence spectra of twelve common species of algae belonging to five categories were analyzed, the discrete three-dimensional standard spectra of five categories were built, and the recognition, classification and concentration prediction of algae categories were realized by the discrete three-dimensional fluorescence spectra coupled with non-negative weighted least squares linear regression analysis. The results show that similarities between discrete three-dimensional standard spectra of different categories were reduced and the accuracies of recognition, classification and concentration prediction of the algae categories were significantly improved. By comparing with that of the chlorophyll a fluorescence excitation spectra method, the recognition accuracy rate in pure samples by discrete three-dimensional fluorescence spectra is improved 1.38%, and the recovery rate and classification accuracy in pure diatom samples 34.1% and 46.8%, respectively; the recognition accuracy rate of mixed samples by discrete-three dimensional fluorescence spectra is enhanced by 26.1%, the recovery rate of mixed samples with Chlorophyta 37.8%, and the classification accuracy of mixed samples with diatoms 54.6%.

We report a novel center-sunken and cladding-trenched Yb-doped fiber, which was fabricated by a modified chemical vapor deposition process with a solution-doping technique. The simulation results showed that the fiber with a core diameter of 40 µm and a numerical aperture of 0.043 has a 1217 µm 2 effective mode area at 1080 nm. It is also disclosed that the leakage loss can be reduced lower than 0.01 dB/m for the LP 01 mode, while over 80 dB/m for the LP 11 mode by optimizing the bending radius as 14 cm. A 456 W laser output was observed in a MOPA structure. The laser slope efficiency was measured to be 79% and the M 2 was less than 1.1, which confirmed the single mode operation of the large mode area center-sunken cladding-trenched Yb-doped fiber.

In this work, Na + ions doping into the Yb-doped fiber is proposed to improve the photo-darkening resistance. The results show that the photo-darkening induced excess loss at equilibrium state at 633nm, 702 nm, 810 nm, and 1041 nm is 115.54dB/m, 86.87dB/m, 25.51 dB/m, 2.92 dB/m, respectively, when co-doping with Na + ions. More than 30% excess loss is reduced comparing to the Yb-doped fiber without Na + ions. The mechanism of Na + ions doping to mitigate the PD excess loss is discussed. Besides, we measured the laser efficiency of Yb/Al/Na co-doped fiber to be 76.1%. This result remains almost the same with Yb-doped fiber and proves that the addition of Na + ions do not deteriorate the fiber slope efficiency. The background loss of the two fibers also stays close. The results indicate this method is promising in high power fiber laser development.

Spatially selective excitation was proposed to improve excitation efficiency in laser-induced breakdown spectroscopy combined with laser-induced fluorescence (LIBS-LIF). Taking chromium (Cr) and nickel (Ni) elements in steels as examples, it was discovered that the optimal excitation locations were the center of the plasmas for the matrix of the iron (Fe) element but the periphery for Cr and Ni elements. By focusing an excitation laser at the optimal locations, not only excitation efficiency but also the analytical accuracy and sensitivity of quantitative LIBS-LIF were better than those with excitation at the plasma center in conventional LIBS-LIF. This study provides an effective way to improve LIBS-LIF analytical performance.

We demonstrate a high-efficiency, high-average-power, CW master oscillator power amplifier based on a conduction-cooled, end-pumped Yb:YAG slab architecture at room temperature (RT). Firstly, the CW amplification property is theoretically analyzed based on the kinetics model for Yb:YAG. To realize high-efficiency laser amplification extraction for RT Yb:YAG, not only intense pump but also a high-power seed laser is of great importance. Experimentally, a composite Yb:YAG crystal slab with three doped and two un-doped segments symmetrically is employed as the gain medium, which is end-pumped by two high-power, 940-nm diode lasers. A high-power, narrow-spectral-width, 1030-nm fiber seed laser then double passes the composite slab to realize efficient power amplification. For 0.8-kW seed input, maximum output power of 3.54 kW is obtained at 6.7 kW of pump power, with the optical conversion efficiency of 41% and the highest slope efficiency of 59%. To the best of our knowledge, this is the highest power and efficiency reported for Yb:YAG lasing at RT except thin-disk lasers.

It is still difficult to determine the concentrations of polycyclic aromatic hydrocarbons accurately in natural water by fluorescence technique because of their low solubility, different fluorescent intensity, and the complex interferents from water environments. In this work, three-way fluorescence spectra combined with three methods including three-way parallel factor analysis, multi-way partial least square with residual bilinearization and unfolded partial least square with residual bilinearization were used to predict the concentrations of polycyclic aromatic hydrocarbons at the μg L -1 level in reservoir and river water, respectively. The prediction abilities of these methods on different analytes were evaluated by validation sets. The results demonstrate that unfolded partial least square with residual bilinearization yields the optimal results with relative error less than or equal to 6% for phenanthrene, pyrene, anthracene and fluorene, and 35% for acenaphthene and fluoranthene in different water backgrounds.

We report on the strong photo-bleaching of the photo-darkening (PD) induced loss under the cladding pump of a 793 nm laser diode (LD) in double clad Yb-doped fibers. Up to 68% PD loss at 810 nm was bleached. The bleaching rates under different powers show that the higher pump power corresponds to the more bleached loss within the same time. Moreover, repeatable processes of PD and photo-bleaching were observed when alternately pumped with 915 and 793 nm LDs. Furthermore, it was found that simultaneously pumping the fiber with 915 and 793 nm LDs can suppress about 80% PD loss, compared with pumping the fiber only with 915 nm LD. The mechanism of photo-bleaching under 793 nm pump was also discussed.

Tm-doped fiber laser or amplifier can be applied in varied adverse environments. In this work, we demonstrate the pump bleaching of Tm-doped silica fiber with 793nm pump source under gamma-ray irradiation in the range 50Gy-675Gy. The recovery time, the fiber slope efficiency and the fiber cladding absorption spectra after irradiation and bleaching have been measured. It is found that the recovery time and radiation induce absorption are positively associated with doses, however, the fiber slope efficiency of irradiated TDF and bleached TDF are both negatively correlated with doses. Based on the simulation of the fiber core temperature, the probable mechanism of pump bleaching is also discussed.

Ultrafast fiber lasers play a significant role in our society with many aspects ranging from fundamental physics to industrial purposes. Searching for high-performance saturable absorbers (SAs) is vital to the developments of ultrafast fiber lasers. Gold nanorods (GNRs) have been discovered to possess saturable absorption effect. However, a major obstacle to make the GNRs as high-performance and practical SA is the low optical damage threshold. To overcome this drawback, herein we proposed the nanocomposites with gold nanorods/silica core-shell structure (GNRs@SiO(2)) as a high-performance SA for ultrashort pulse generation in a fiber laser. The GNRs@SiO(2) SA presents a modulation depth of 4.2% and nonsaturable loss of 45.6%. With the proposed GNRs@SiO(2) SA, 379 fs pulse was directly obtained from the fiber laser. The achieved results demonstrated that the GNR@SiO(2) could be indeed a good candidate of high-performance SA towards practical applications in the field of ultrafast photonics.

We report on the trapping of noise-like pulse in a figure-eight fiber laser mode locked by nonlinear amplifier loop mirror (NALM). After achievement of noise-like vector pulse, it was found that the wavelength shift of the two resolved polarization components responsible for the pulse trapping was very sensitive to the cavity birefringence. By properly rotating the polarization controllers (PCs), the wavelength shift could be up to 4.8 nm, which is much larger than that of conventional soliton trapping. The observed results would shed some light on the fundamental physics of noise-like pulse as well as its vector features in fiber lasers.

We demonstrate the first few-mode-fiber based passive optical network, effectively utilizing mode multiplexing to eliminate combining loss for upstream traffic. Error-free performance has been achieved for 20-km low-crosstalk 3-mode transmission in a commercial GPON system carrying live Ethernet traffic. The alternative approach of low modal group delay is also analyzed with simulation results over 10 modes.

We reported on the generation of versatile soliton molecules in a fiber laser mode-locked by a microfiber-based graphene saturable absorber (GSA). By virtue of the highly nonlinear effect of the microfiber-based GSA, the soliton molecules could be easily observed. In addition to regular soliton molecules, it is found that the "soliton atoms" in molecules could exhibit different characteristics and show ultra-narrow pulse separations, which was termed as 'structural soliton molecule'. The pulse profiles of 'structural soliton molecules' were further reconstructed theoretically. The obtained results would give further insight towards understanding the dynamics of soliton molecules in fiber lasers.

We reported on the generation of dual-wavelength rectangular pulses in a Yb-doped fiber laser (YDFL) by using a microfiber-based graphene saturable absorber (GSA). The duration of dual-wavelength rectangular pulse could be varied from 1.41 ns to 4.23 ns with the increasing pump power. With a tunable bandpass filter, it was found that the characteristics of the rectangular pulses centered at 1061.8 nm and 1068.8 nm are similar to each other. Moreover, the dual-wavelength switchable operation was also realized by properly rotating the polarization controllers (PCs). The demonstration of the dual-wavelength rectangular pulses from a YDFL would open some applications for fields such as spectroscopy, biomedicine and sensing research.

We reported on the generation of femtosecond pulse in a fiber ring laser by using a polyvinyl alcohol (PVA)-based topological insulator (TI), Bi2Se3 saturable absorber (SA). The PVA-TI composite has a low saturable optical intensity of 12 MW/cm2 and a modulation depth of ~3.9%. By incorporating the fabricated PVA-TISA into a fiber laser, mode-locking operation could be achieved at a low pump threshold of 25 mW. After an optimization of the cavity parameters, optical pulse with ~660 fs centered at 1557.5 nm wavelength had been generated. The experimental results demonstrate that the PVA could be an excellent host material for fabricating high-performance TISA, and also indicate that the filmy PVA-TISA is indeed a good candidate for ultrafast saturable absorption device.

Using a Sagnac fiber loop functions as a deterministic splitter of photon pairs produced by the frequency degenerate four wave mixing, we show that the background noise of the degenerate photon pairs is contributed by both Raman scattering and frequency non-degenerate four wave mixing. To improve the purity of photon pairs in the high gain regime, in addition to suppressing the noise photons by cooling the nonlinear fiber and by optimizing the detuning between the frequencies of the pump and photon pairs, the walk-off effect of the two pulsed pump fields should be mitigated by managing the dispersion of the fiber. Our investigation is not only the first step towards the generation of multi-mode squeezed vacuum in fiber optical parametric amplifiers pumped with pulsed lights, but also contributes to improving the purity of the fiber sources of degenerate photon pairs.