[Show abstract][Hide abstract] ABSTRACT: Pulse generation often requires a stabilized cavity and its corresponding
mode structure for initial phase-locking. Contrastingly, modeless cavity-free
random lasers provide new possibilities for high quantum efficiency lasing that
could potentially be widely tunable spectrally and temporally. Pulse generation
in random lasers, however, has remained elusive since the discovery of modeless
gain lasing. Here we report coherent pulse generation with modeless random
lasers based on the unique polarization selectivity and broadband saturable
absorption of monolayer graphene. Simultaneous temporal compression of
cavity-free pulses are observed with such a polarization modulation, along with
a broadly-tunable pulsewidth across two orders of magnitude down to 900 ps, a
broadly-tunable repetition rate across three orders of magnitude up to 3 MHz,
and a singly-polarized pulse train at 41 dB extinction ratio, about an order of
magnitude larger than conventional pulsed fiber lasers. Moreover, our
graphene-based pulse formation also demonstrates robust pulse-to-pulse
stability and wide-wavelength operation due to the cavity-less feature. Such a
graphene-based architecture not only provides a tunable pulsed random laser for
fiber-optic sensing, speckle-free imaging, and laser-material processing, but
also a new way for the non-random CW fiber lasers to generate widely tunable
and singly-polarized pulses.
Full-text · Article · Dec 2015 · Scientific Reports
[Show abstract][Hide abstract] ABSTRACT: Nonlinear optics researches of graphene-based four waves mixing (FWM) effect are important for a new generation of photonic devices. Compared with the ordinary graphene materials, the P-doped graphene based hybrid waveguide structure is more conducive to the simulating of the third-order nonlinear effect in low power due to its smaller transmission loss. In this work, we propose a P-doped graphene coated microfiber hybrid waveguide structure for femto-second laser pumping excited FWM. By the simulations, we analyze the HE11 mode distribution and the effective refractive index of the silica microfiber and P-doped graphene coated microfiber hybrid waveguide with different fiber diameters at a wavelength of ~1550 nm. We also implement the fabrication processing and characterize this P-doped graphene coated microfiber hybrid waveguide. In the experiments, we utilize a femto-second laser as the pump laser with a peak power up to kW. As the graphene material and the microfiber contribute to the nonlinearity, the cascade FWM could be obtained. Experimental results demonstrate that when the peak power of the injection pump is fixed at 1.03 kW, by adjusting the detuning in wavelength to the length less than 10.0nm, there are four sets of frequency components that can be observed. In the present paper, we provide the relationship among the detuning in wavelength, the pump power and the the power of stokes peak. These results indicate that under the condition of a few nanometer detuning wavelength, when the pump power is fixed at 14.1 dBm and the detuning wavelength is 6.7 nm, there are second order stokes light and the second order anti-stokes light, which can be observed, here the obtained conversion efficiency is up to -60 dB, which can be improved by optimizing the waveguide structure and increasing the pump power. Meanwhile, this FWM processing is also fast due to the fast pumping laser. The simulation and experimental results demonstrate that this P-doped graphene coated microfiber hybrid structure has the advantages of highly nonlinearity, compact size and withstanding high power ultrafast laser, showing the important research value and potential applications in fields based on ultrafast optics, such as multi-wavelength laser, phase-sensitive amplification, comb filters and all-optical regeneration.
[Show abstract][Hide abstract] ABSTRACT: An all-optical method to control the lasing modes of Er-doped random fiber lasers (RFLs) is proposed and demonstrated. In the RFL, an Er-doped fiber (EDF) recoded with randomly separated fiber Bragg gratings (FBG) is used as the gain medium and randomly distributed reflectors, as well as the controllable element. By combining random feedback of the FBG array and Fresnel feedback of a cleaved fiber end, multi-mode coherent random lasing is obtained with a threshold of 14 mW and power efficiency of 14.4%. Moreover, a laterally-injected control light is used to induce local gain perturbation, providing additional gain for certain random resonance modes. As a result, active mode selection of the RFL is realized by changing locations of the laser cavity that is exposed to the control light.
[Show abstract][Hide abstract] ABSTRACT: We propose a long range, high precision optical time domain reflectometry (OTDR) based on an all-fiber supercontinuum source. The source simply consists of a CW pump laser with moderate power and a section of fiber, which has a zero dispersion wavelength near the laser's central wavelength. Spectrum and time domain properties of the source are investigated, showing that the source has great capability in nonlinear optics, such as correlation OTDR due to its ultra-wide-band chaotic behavior, and mm-scale spatial resolution is demonstrated. Then we analyze the key factors limiting the operational range of such an OTDR, e. g., integral Rayleigh backscattering and the fiber loss, which degrades the optical signal to noise ratio at the receiver side, and then the guideline for counter-act such signal fading is discussed. Finally, we experimentally demonstrate a correlation OTDR with 100km sensing range and 8.2cm spatial resolution (1.2 million resolved points), as a verification of theoretical analysis.
[Show abstract][Hide abstract] ABSTRACT: This paper proposes a way of generating polariton solitons (PSs) in a semiconductor microcavity using Stark effect as the trigger mechanism. A Stark pulse performing as the writing beam is used to excite non-resonant fluctuations of polariton, which finally evolves into bright PSs. It is found that a branch of PS solutions versus pump parameters could be found through optimizing parameters of the Stark pulse, and polarization of the generated PS is dependent on the writing beam. (C) 2015 Optical Society of America
[Show abstract][Hide abstract] ABSTRACT: Cascaded four-wave-mixing was effectively demonstrated in a graphene-coatedmicrofiber, by using a pulsed pump at 1550 nm, which may be useful for realization of graphene based fiber-optic nonlinear devices, e.g. lasers, filters, modulators and regenerators.
[Show abstract][Hide abstract] ABSTRACT: A graphene-coated microfiber (GCM)-based hybrid waveguide structure formed by wrapping monolayer graphene around a microfiber with length of several millimeters is pumped by a nanosecond laser at ∼1550 nm, and multi-order cascaded four-wave-mixing (FWM) is effectively generated. By optimizing both the detuning and the pump power, such a GCM device with high nonlinearity and compact size would have potential for a wide range of FWM applications, such as phase-sensitive amplification, multi-wavelength filter, all-optical regeneration and frequency conversion, and so on.
No preview · Article · Apr 2015 · Photonics Research
[Show abstract][Hide abstract] ABSTRACT: A new concept of distributed acoustic communication - sound over fiber (SoF) based on optical fiber distributed acoustic sensing is presented. The concept is validated over an acoustic communication experiment in air, which demonstrates its unique advantages.
[Show abstract][Hide abstract] ABSTRACT: In this letter, the polarization properties of a random fiber laser operating via Raman gain and random distributed feedback owing to Rayleigh scattering are investigated for the first time. Using polarized pump, the partially polarized generation is obtained with a generation spectrum exhibiting discrete narrow spectral features contrary to the smooth spectrum observed for the depolarized pump. The threshold, output power, degree of polarization and the state of polarization (SOP) of the lasing can be significantly influenced by the SOP of the pump. Fine narrow spectral components are also sensitive to the SOP of the pump wave. Furthermore, we found that random lasing's longitudinal power distributions are different in the case of polarized and depolarized pumping that results in considerable reduction of the generation slope efficiency for the polarized radiation. Our results indicate that polarization effects play an important role on the performance of the random fiber laser. This work improves the understanding of the physics of random lasing in fibers and makes a step forward towards the establishment of the vector model of random fiber lasers.
No preview · Article · Jan 2015 · Laser Physics Letters
[Show abstract][Hide abstract] ABSTRACT: We propose a high-resolution optical time domain reflectometry (OTDR) based on an all-fiber supercontinuum source. The source simply consists of a laser with moderate power and a section of fiber which has a zero dispersion wavelength near the laser's central wavelength. Spectrum and time domain properties of the source are investigated, showing that the source has great capability in nonlinear optics, such as correlation OTDR. We analyze one of the key factors limiting the operational range of such an OTDR, i.e., sampling time. Finally, we experimentally demonstrate a correlation OTDR with 25km sensing range and 5.3cm spatial resolution, as a verification of theoretical analysis.
No preview · Article · Jan 2015 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: Random distributed feedback fiber laser (RDF-FL) based on combination of Er-doped fiber (EDF) and single-mode fiber (SMF) is proposed in this paper. Through pumping of both the EDF (i.e., 1480 nm pump) and the SMF (i.e., 1455 nm pump), random lasing is obtained. With increase of pump powers, different transitions between chaotic and stable status of the output spectrum are observed. Especially, single-peak random lasing can be obtained under the stable operation regime.
Full-text · Article · Jan 2015 · IEEE Journal of Selected Topics in Quantum Electronics
[Show abstract][Hide abstract] ABSTRACT: Graphene based new physics phenomena are leading to a variety of stimulating graphene-based photonic devices. In this study, the enhancement of surface evanescent field by graphene cylindrical cladding is observed, for the first time, by using a graphene-coated microfiber multi-mode interferometer (GMMI). It is found theoretically and experimentally that the light transmitting in the fiber core is efficiently dragged by the graphene, hence significantly enhancing the evanescent fields, and subsequently improving the sensitivity of the hybrid waveguide. The experimental results for gas sensing verified the theoretical prediction, and ultra-high sensitivities of ~0.1 ppm for NH<sub>3</sub> gas detection and ~0.2 ppm for H<sub>2</sub>O vapor detection are achieved, which could be used for trace analysis. The enhancement of surface evanescent field induced by graphene may pave a new way for developing novel graphene-based all-fiber devices with compactness, low cost, and temperature immunity.
[Show abstract][Hide abstract] ABSTRACT: A phase-sensitive optical time-domain reflectometry (Φ-OTDR) with 175 km sensing range and 25 m spatial resolution is demonstrated, using the combination of co-pumping second-order Raman amplification based on random fiber lasing, counter-pumping first-order Raman amplification, and counter-pumping Brillouin amplification. With elaborate arrangements, each pumping scheme is responsible for the signal amplification in one particular segment of all three. To the best of our knowledge, this is the first time that distributed vibration sensing is realized over such a long distance without inserting repeaters. The novel hybrid amplification scheme in this work can also be incorporated in other fiber-optic sensing systems for extension of sensing distance.
[Show abstract][Hide abstract] ABSTRACT: In this Letter, a graphene-coated D-shaped fiber (GDF) chemical gas sensor is proposed and demonstrated. Taking advantage of both the graphene-induced evanescent field enhancement and the in-fiber multimode interferometer, the GDF shows very high sensitivity for polar gas molecule adsorptions. An extinction ratio of up to 28 dB within the free spectrum range of ∼30 nm in the transmission spectrum is achieved. The maximum sensitivities for NH<sub>3</sub> and H<sub>2</sub>O gas detections are ∼0.04 and ∼0.1 ppm, respectively. A hybrid sensing scheme with such compactness, high sensitivity, and online monitoring capabilities may pave the way for others to explore a series of graphene-based lab-on-fiber devices for biochemical sensing.
[Show abstract][Hide abstract] ABSTRACT: Graphene Bragg gratings (GBGs) on microfiber are proposed and investigated in this paper. Numerical analysis and simulated results show that the mode distribution, transmission loss, and central wavelength of the GBG are controllable by changing the diameter of the microfiber or the refractive index of graphene. Such type of GBGs with tunability may find important applications in optical fiber communication and sensing as all-fiber in-line devices.
[Show abstract][Hide abstract] ABSTRACT: An inline fiber-optic micro Fabry–Perot (MFP) cavity and a short fiber Bragg grating (SFBG) is overlapped to form an integrated MFP/SFBG sensor for simultaneous measurement of temperature and strain under high temperature (300°C). The FP cavity is fabricated on a GeO2 doped photon sensitive fiber by using the 157nm laser micro-machining technique and the SFBG is written at the same position of the MFP cavity by using the standard 248nm laser method. As the MFP cavity and the SFBG have different sensitivity coefficients to temperature and strain, they can be utilized for realization of simultaneous measurement of dual parameters.
[Show abstract][Hide abstract] ABSTRACT: Random lasing (RL) characteristics through different combinations of single-mode fiber (SMF) and dispersion compensated fiber (DCF) with a Raman pump (i.e., DCF is mounted at the front or at the end of the SMF; the length of the SMF and DCF is also changeable) are studied in this paper. The results indicate that the position and length ratio of DCF and SMF influence the output of the random distributed feedback fiber laser (RDF-FL) greatly (e.g., lasing threshold, spectrum stability, and shape). When the DCF is located at a position where higher laser power is distributed, RL can be enhanced remarkably. In addition, second-order RDF-FL is realized in an SMF/DCF mixed cavity pumped bidirectionally from the fiber center, indicating that the pump method is also an important factor that influences the performance of the RDF-FL. These results are useful for revealing the role of DCF in RL and light amplification, and also for providing theoretical support for flexible design and optimization of the RDF-FL.
Full-text · Article · Aug 2014 · Journal of the Optical Society of America B
[Show abstract][Hide abstract] ABSTRACT: We propose a phase-sensitive optical time-domain reflectometry (Φ-OTDR) scheme with counterpumping fiber Brillouin amplification (FBA). High-sensitivity perturbation detection over 100 km is experimentally demonstrated as an example. FBA significantly enhances the probe pulse signal, especially at the second half of the sensing fiber, with only 6.4 dBm pump power. It is confirmed that its amplification efficiency is much higher than 28.0 dBm counterpumping fiber Raman amplification. The FBA Φ-OTDR scheme demonstrated in this work can also be incorporated into other distributed fiber-optic sensing systems for extension of sensing distance or enhancement of sensing signal level.
[Show abstract][Hide abstract] ABSTRACT: This paper proposes a novel concept of refractive index sensing taking advantage of a high-refractive-index-contrast optical Tamm plasmon (OTP) structure, i.e., an air/dielectric alternate-layered distributed Bragg reflector (DBR) coated with metal. In the reflection spectrum of the structure, a dip related to the formation of OTP appears. The wavelength and reflectivity of this dip are sensitive to variation of ambient refractive index, which provides a potential way to realize refractive index sensing with a large measuring range and high sensitivity.
[Show abstract][Hide abstract] ABSTRACT: Ultra-long-distance distributed fiber-optic sensing based on Brillouin optical time-domain analysis (BOTDA) is achieved by using a proposed configuration of hybrid distributed Raman amplification (H-DRA), that is realized by incorporating random fiber laser (RFL) based 2nd-order pump and low-noise laser-diode (LD) based 1st-order pump. A repeater-less sensing distance of up to 154.4km with 5m spatial resolution and ∼±1.4°C temperature uncertainty is successfully demonstrated, which is the longest repeater-less BOTDA reported to date.
No preview · Article · Jun 2014 · Proceedings of SPIE - The International Society for Optical Engineering