This work introduces special states for light in multimode fibers featuring strongly enhanced or reduced correlations be-tween output fields in the presence of environmental temperature fluctuations.Using experimental...This work introduces special states for light in multimode fibers featuring strongly enhanced or reduced correlations be-tween output fields in the presence of environmental temperature fluctuations.Using experimentally measured multi-tem-perature transmission matrix,a set of temperature principal modes that exhibit resilience to disturbances caused by tem-perature fluctuations can be generated.Reversing this concept also allows the construction of temperature anti-principal modes,with output profiles more susceptible to temperature influences than the unmodulated wavefront.Despite changes in the length of the multimode fiber within the temperature-fluctuating region,the proposed approach remains capable of robustly controlling the temperature response within the fiber.To illustrate the practicality of the proposed spe-cial state,a learning-empowered fiber specklegram temperature sensor based on temperature anti-principal mode sensi-tization is proposed.This sensor exhibits outstanding superiority over traditional approaches in terms of resolution and accuracy.These novel states are anticipated to have wide-ranging applications in fiber communication,sensing,imaging,and spectroscopy,and serve as a source of inspiration for the discovery of other novel states.展开更多
The detection of the state of polarization(SOP)of light is essential for many optical applications.However,cost-effective SOP measurement is a challenge due to the complexity of conventional methods and the poor trans...The detection of the state of polarization(SOP)of light is essential for many optical applications.However,cost-effective SOP measurement is a challenge due to the complexity of conventional methods and the poor transferability of new methods.We propose a straightforward,low-cost,and portable SOP measurement system based on the multimode fiber speckle.A convolutional neural network is utilized to establish the mapping relationship between speckle and Stokes parameters.The lowest root-mean-square error of the estimated SOP on the Poincarésphere can be 0.0042.This method is distinguished by its low cost,clear structure,and applicability to different wavelengths with high precision.The proposed method is of great value in polarization-related applications.展开更多
Transmission matrix(TM)allows light control through complex media,such as multimode fibers(MMFs),gaining great attention in areas,such as biophotonics,over the past decade.Efforts have been taken to retrieve a complex...Transmission matrix(TM)allows light control through complex media,such as multimode fibers(MMFs),gaining great attention in areas,such as biophotonics,over the past decade.Efforts have been taken to retrieve a complex-valued TM directly from intensity measurements with several representative phase-retrieval algorithms,which still see limitations of slow or suboptimum recovery,especially under noisy environments.Here,we propose a modified nonconvex optimization approach.Through numerical evaluations,it shows that the optimum focusing efficiency is approached with less running time or sampling ratio.The comparative tests under different signal-to-noise levels further indicate its improved robustness.Experimentally,the superior focusing performance of our algorithm is collectively validated by single-and multispot focusing;especially with a sampling ratio of 8,it achieves a 93.6%efficiency of the gold-standard holography method.Based on the recovered TM,image transmission through an MMF is realized with high fidelity.Due to parallel operation and GPU acceleration,our nonconvex approach retrieves a 8685×1024 TM(sampling ratio is 8)with 42.3 s on average on a regular computer.The proposed method provides optimum efficiency and fast execution for TM retrieval that avoids the need for an external reference beam,which will facilitate applications of deep-tissue optical imaging,manipulation,and treatment.展开更多
Imaging through multimode fiber(MMF)provides high-resolution imaging through a fiber with cross section down to tens of micrometers.It requires interferometry to measure the full transmission matrix(TM),leading to the...Imaging through multimode fiber(MMF)provides high-resolution imaging through a fiber with cross section down to tens of micrometers.It requires interferometry to measure the full transmission matrix(TM),leading to the drawbacks of complicated experimental setup and phase instability.Reference-less TM retrieval is a promising robust solution that avoids interferometry,since it recovers the TM from intensity-only measurements.However,the long computational time and failure of 3D focusing still limit its application in MMF imaging.We propose an efficient reference-less TM retrieval method by developing a nonlinear optimization algorithm based on fast Fourier transform(FFT).Furthermore,we develop an algorithm to correct the phase offset error of retrieved TM using defocused intensity images and hence achieve 3D focusing.The proposed method is validated by both simulations and experiments.The FFT-based TM retrieval algorithm achieves orders of magnitude of speedup in computational time and recovers 2286×8192 TM of a 0.22 NA and 50μm diameter MMF with 112.9 s by a computer of 32 CPU cores.With the advantages of efficiency and correction of phase offset,our method paves the way for the application of reference-less TM retrieval in not only MMF imaging but also broader applications requiring TM calibration.展开更多
We propose the trench-assisted multimode fiber(TA-OM4)as a novel sensing fiber in forward Brillouin scattering(FBS)-based temperature sensor,due to its higher temperature sensitivity,better bending resistance and lowe...We propose the trench-assisted multimode fiber(TA-OM4)as a novel sensing fiber in forward Brillouin scattering(FBS)-based temperature sensor,due to its higher temperature sensitivity,better bending resistance and lower propagation loss,compared with the single mode fiber(SMF)and other sensing fibers.The FBS effect and acousto-optic interaction in TA-OM4 are the first time to be demonstrated and characterized at 1550 nm theoretically and experimentally.A 2.0 km long TA-OM4 is put into an oven to measure its temperature sensitivity,which can reach up to 80.3 kHz/℃,exceeding 53%of SMF(52.4 kHz/℃).The simulated and experimental results verify that the TA-OM4 may be a good candidate as the sensing fiber for the FBS-based temperature sensor.展开更多
The high degree of freedom and novel nonlinear phenomena of multimode fiber are attracting attention. In this work,we demonstrate a spatiotemporal mode-locked multimode fiber laser, which relies on microfiber knot res...The high degree of freedom and novel nonlinear phenomena of multimode fiber are attracting attention. In this work,we demonstrate a spatiotemporal mode-locked multimode fiber laser, which relies on microfiber knot resonance(MKR) via dissipative four-wave-mixing(DFMW) to achieve high-repetition-rate pulses. Apart from that, DFMW mode locking with switchable central wavelengths can also be obtained. It was further found that high pulse energy induced nonlinear effect of the dominant mode-locking mechanism transforming from DFMW to nonlinear Kerr beam cleaning effect(NL-KBC). The experimental results are valuable for further comprehending the dynamic characteristics of spatiotemporal mode-locked multimode fiber lasers, facilitating them much more accessible for applications.展开更多
A refractive index （RI） sensor based on hybrid long-period fiber grating （LPFG） with multimode fiber core （MMFC） is proposed and demonstrated. The surrounding RI can be determined by monitoring the separation be...A refractive index （RI） sensor based on hybrid long-period fiber grating （LPFG） with multimode fiber core （MMFC） is proposed and demonstrated. The surrounding RI can be determined by monitoring the separation between the resonant wavelengths of the LPFG and MMFC since the resonant wavelengths of the LPFG and MMFC will shift in opposite directions when the surrounding RI changes. Experimental results show that the sensor possesses an enhanced sensitivity of 526.92nm/RIU in the RI range of 1.387-1.394 RIU. The response to the temperature is also discussed.展开更多
Mode division multiplexing(MDM)using multimode fibers(MMFs)is key to meeting the demand for higher data rates and advancing internet technologies.However,optical transmission within MMFs presents challenges,particular...Mode division multiplexing(MDM)using multimode fibers(MMFs)is key to meeting the demand for higher data rates and advancing internet technologies.However,optical transmission within MMFs presents challenges,particularly due to mode crosstalk,which complicates the use of MMFs to increase system capacity.Quantitatively analyzing the output of MMFs is essential not only for telecommunications but also for applications like fiber sensors,fiber lasers,and endoscopy.With the success of deep neural networks(DNNs),AI-driven mode decomposition(MD)has emerged as a leading solution for MMFs.However,almost all implementations rely on Graphics Processing Units(GPUs),which have high computational and system integration demands.Additionally,achieving the critical latency for real-time data transfer in closed-loop systems remains a challenge.In this work,we propose using field-programmable gate arrays(FPGAs)to perform neural network inference for MD,marking the first use of FPGAs for this application,which is important,since the latency of closed-loop control could be significantly lower than at GPUs.A convolutional neural network(CNN)is trained on synthetic data to predict mode weights(amplitude and phase)from intensity images.After quantizing the model’s parameters,the CNN is executed on an FPGA using fixed-point arithmetic.The results demonstrate that the FPGA-based neural network can accurately decompose up to six modes.The FPGA’s customization and high efficiency provide substantial advantages,with low power consumption(2.4 Watts)and rapid inference(over 100 Hz),offering practical solutions for real-time applications.The proposed FPGA-based MD solution,coupled with closed-loop control,shows promise for applications in fiber characterization,communications,and beyond.展开更多
In vivo microscopic imaging inside a biological lumen such as the gastrointestinal tract,respiratory airways,or within blood vessels has faced significant technological challenges for decades.A promising candidate tec...In vivo microscopic imaging inside a biological lumen such as the gastrointestinal tract,respiratory airways,or within blood vessels has faced significant technological challenges for decades.A promising candidate technology is the multimode fiber(MMF)endoscope,which enables minimally invasive diagnostics at a resolution reaching the cellular level.However,for in vivo imaging applications deep inside a biological lumen,sample-induced aberrations and the dynamic dispersion in the MMF make the MMF endoscope a chaotic system with many unknowns,where multiple minor fluctuations can couple and compound into intractable problems.We introduce a dynamically encoding,cascaded,optical,and ultrathin polychromatic light-field endoscopy(DECOUPLE)to tackle this challenge.DECOUPLE includes an adaptive aberration correction that can accurately track and control MMF behavior in the spatial-frequency domain to compensate for chaos introduced during complex dynamic imaging processes.We demonstrate the flexibility and practicality of DECOUPLE for noninvasive volumetric imaging in two colors for light passing through various highly aberrating samples including 120-μm-thick onion epidermal slices and 80-μm-thick layers of fat emulsions.To summarize,we represent a significant step toward practical in vivo imaging deep within biological tissue.展开更多
We propose and validate a novel optical semantic transmission scheme using multimode fiber(MMF).By leveraging the frequency sensitivity of intermodal dispersion in MMFs,we achieve high-dimensional semantic encoding an...We propose and validate a novel optical semantic transmission scheme using multimode fiber(MMF).By leveraging the frequency sensitivity of intermodal dispersion in MMFs,we achieve high-dimensional semantic encoding and decoding in the frequency domain.Our system maps symbols to 128 distinct frequencies spaced at 600 kHz intervals,demonstrating a seven-fold increase in capacity compared to conventional communication encoding.We further enhance spectral efficiency by implementing 4-level pulse amplitude modulation(PAM-4),achieving 9.12 bits/s/Hz without decoding errors.Additionally,we explore the application of this system for sentiment analysis using the IMDb movie review dataset.By encoding semantically similar symbols to adjacent frequencies,the system's noise tolerance is effectively improved,facilitating accurate sentiment analysis.This work highlights the potential of MMF-based semantic communication to enhance both capacity and robustness in optical communication systems,offering promising applications in bandwidth-constrained and noisy environments.展开更多
The immediate priorities for high-power delivery employing solid-core fibers are balancing the nonlinear effect and beam deterioration.Here,the scheme of tapered multimode fiber is experimentally realized.The tapered ...The immediate priorities for high-power delivery employing solid-core fibers are balancing the nonlinear effect and beam deterioration.Here,the scheme of tapered multimode fiber is experimentally realized.The tapered multimode fiber,featuring a 15 m(24/200μm)–10 m(tapered region)–80 m(48/400μm)profile,guides the laser with a weakly coupled condition.With the input power of 1035 W,the maximum output power over the 105 m delivery is 962 W,corresponding to a high efficiency of over 93%and a nonlinear suppression ratio of over 50 dB.Mode resolving results show high-order-mode contents of less than–30 dB in the whole delivery path,resulting in a high-fidelity delivery with M2 factors of 1.20 and 1.23 for the input and output lasers,respectively.Furthermore,the ultimate limits of delivery lengths for solid-core weakly coupled fibers are discussed.This work provides a valuable reference to reconsider the future boom of high-power laser delivery based on solid-core fibers.展开更多
We investigated 1-μm multimode fiber laser based on carbon nanotubes,where multiple typical pulse states were observed,including Q-switched,Q-switched mode-locked,and spatiotemporal mode-locked pulses.Particularly,st...We investigated 1-μm multimode fiber laser based on carbon nanotubes,where multiple typical pulse states were observed,including Q-switched,Q-switched mode-locked,and spatiotemporal mode-locked pulses.Particularly,stable spatiotemporal mode-locking was realized with a low threshold,where the pulse duration was 37 ps and the wavelength was centred at 1060.5 nm.Moreover,both the high signal to noise and long-term operation stability proved the reliability of the mode-locked laser.Furthermore,the evolution of the spatiotemporal mode-locked pulses in the cavity was also simulated and discussed.This work exhibits the flexible outputs of spatiotemporal phenomena in multimode lasers based on nanomaterials,providing more possibilities for the development of high-dimensional nonlinear dynamics.展开更多
Optical endoscopy has become an essential diagnostic and therapeutic approach in modern biomedicine for directly observing organs and tissues deep inside the human body,enabling non-invasive,rapid diagnosis and treatm...Optical endoscopy has become an essential diagnostic and therapeutic approach in modern biomedicine for directly observing organs and tissues deep inside the human body,enabling non-invasive,rapid diagnosis and treatment.Optical fiber endoscopy is highly competitive among various endoscopic imaging techniques due to its high flexibility,compact structure,excellent resolution,and resistance to electromagnetic interference.Over the past decade,endoscopes based on a single multimode optical fiber(MMF)have attracted widespread research interest due to their potential to significantly reduce the footprint of optical fiber endoscopes and enhance imaging capabilities.In comparison with other imaging principles of MMF endoscopes,the scanning imaging method based on the wavefront shaping technique is highly developed and provides benefits including excellent imaging contrast,broad applicability to complex imaging scenarios,and good compatibility with various well-established scanning imaging modalities.In this review,various technical routes to achieve light focusing through MMF and procedures to conduct the scanning imaging of MMF endoscopes are introduced.The advancements in imaging performance enhancements,integrations of various imaging modalities with MMF scanning endoscopes,and applications are summarized.Challenges specific to this endoscopic imaging technology are analyzed,and potential remedies and avenues for future developments are discussed.展开更多
Coiling technique is used to control the transverse mode of a large-mode-area （LMA） multimode fiber laser. By winding the fiber to a coil with different radius, high-order modes of a multimode fiber laser are suppre...Coiling technique is used to control the transverse mode of a large-mode-area （LMA） multimode fiber laser. By winding the fiber to a coil with different radius, high-order modes of a multimode fiber laser are suppressed one by one and finally 15.4-W single-transverse-mode output is achieved when the coil radius is 20 mm. It is found that as the coil radius decreases, the beam quality of a multimode fiber laser gets better but the slope efficiency drops for higher-order modes are discriminated. During the experiment, as the coil radius of multimode fiber changes, output characteristic of the laser has been measured. Meanwhile, the mode loss of different modes is calculated theoretically. It is proved that the experimental measured results fit well with the theoretically calculated results.展开更多
We report Q-switched mode-locked(QML)pulses generation in an Yb-doped multimode fiber(MMF)laser by using a graphene-deposited multimode microfiber(GMM)for the first time,to the best of our knowledge.The single-wavelen...We report Q-switched mode-locked(QML)pulses generation in an Yb-doped multimode fiber(MMF)laser by using a graphene-deposited multimode microfiber(GMM)for the first time,to the best of our knowledge.The single-wavelength QML operation with the central wavelength tunable from 1028.81 nm to 1039.20 nm and the dual-wavelength QML operation with the wavelength spacing tunable from 0.93 nm to 5.79 nm are achieved due to the multimode interference filtering effect induced by the few-mode fiber and MMF structure and the GMM in the cavity.Particularly,in the single-wavelength QML operation,the fifth harmonic is also realized owing to the high nonlinear effect of the GMM.The obtained results indicate that the QML pulses can be generated in the MMF laser,and such a flexible tunable laser has promising applications in optical sensing,measuring,and laser processing.展开更多
We experimentally demonstrate the simultaneous generation of tunable multi-wavelength picosecond laser pulses using a self-seeding configuration that consists of a gain-switched Fabry-Perot laser diode （FPLD） with a...We experimentally demonstrate the simultaneous generation of tunable multi-wavelength picosecond laser pulses using a self-seeding configuration that consists of a gain-switched Fabry-Perot laser diode （FPLD） with an external cavity formed by a tilted multimode fiber Bragg grating. Dual- and triple-wavelength pulses are obtained and tuned in a flexible manner by changing the temperature of the FPLD. The side mode suppression ratio larger than 25 dB is achieved at different dual- and triple-wavelengths and the typical pulsewidth of the output pulses is ,-70 ps. In the experiment, the wavelength separation can be narrowed to 0.57 nm.展开更多
A monolithic visible supercontinuum(SC)source with a record average output power of 204 W and a spectrum ranging from580 nm to beyond 2400 nm is achieved in a piece of standard telecom graded-index multimode fiber(GRI...A monolithic visible supercontinuum(SC)source with a record average output power of 204 W and a spectrum ranging from580 nm to beyond 2400 nm is achieved in a piece of standard telecom graded-index multimode fiber(GRIN MMF)by designing the pumping system.The influence of the GRIN MMF length on the geometrical parameter instability(GPI)effect is analyzed for the first time,to the best of our knowledge,by comparing the SC spectral region dominated by the GPI effect under different fiber lengths.Our work could pave the way for robust,cost-effective,and high-power visible SC sources.展开更多
We propose an adaptive parallel coordinate （APC） algorithm for quickly forming a series of focused spots at a multimode fiber （MMF） output by controlling the MMF input field with a spatial light modulator （SLM）....We propose an adaptive parallel coordinate （APC） algorithm for quickly forming a series of focused spots at a multimode fiber （MMF） output by controlling the MMF input field with a spatial light modulator （SLM）. Only passing over the SLM once, we can obtain SLM reflectance to form focused spots on different positions. Com- pared with the transmission matrix method, our APC does not. require iterations and massive calculations. The APC does not require as much access device time as the adaptive sequential coordinate ascent （SCA） algorithm. The experiment results demonstrate that the time taken to form 100 spots with our APC is 1/54th the time with the SCA.展开更多
We propose and demonstrate single fiber dual-functionality optical tweezers based on a graded-index multimode fiber. By using the multi-angle fiber grinding and polishing technology, we fabricate the multimode fiber t...We propose and demonstrate single fiber dual-functionality optical tweezers based on a graded-index multimode fiber. By using the multi-angle fiber grinding and polishing technology, we fabricate the multimode fiber tip to be a special tapered shape, contributing to focus the outgoing beam with a large intensity gradient for the first functionality--three-dimensional contactless trapping of a microparticle. By adjusting the radial direction offset between the lead-in single mode fiber and the graded-index multimode fiber, we perform the second functionality--axial shift of the trapped microparticle with respect to the fiber tip without need of moving the fiber probe itself. It is convenient for practical applications, The theoretical and experimental results about the relationship between the radial offset and the equilibrium positions of the microparticle have the good consistency. Tailoring the trap and axial shift of the microparticle based on the graded-index multimode fiber provides convenient avenues for fiber optical tweezers a~）Dlied in practical researches.展开更多
By using a graded-index multimode fiber （GI-MMF） with a relatively flat index profile and high refractive index of the fiber core, a microextrinsic fiber-optic Fabry Prot interferometric （MEFPI） strain sensor is f...By using a graded-index multimode fiber （GI-MMF） with a relatively flat index profile and high refractive index of the fiber core, a microextrinsic fiber-optic Fabry Prot interferometric （MEFPI） strain sensor is fabricated through chemical etching and fusion splicing. Higher reflectance of the microcavity is obtained due to the less-curved inner wall in the center of the fiber core after etching and higher index contrast between the GI-MMF core and air. The maximum reflection of the sensor is enhanced 12 dB than that obtained by etching of the Er- or B-doped fibers. High fringe contrast of 22 dB is obtained. The strain and temperature responses of the MEFPI sensors are investigated in this experiment. Good linearity and high sensitivity are achieved, with wavelength-strain and wavelength-temperature sensitivities of 7.82 pm/με and 5.01 pm/°C, respectively.展开更多
基金financial supports from the National Natural Science Foundation of China (62075132 and 92050202)Natural Science Foundation of Shanghai (22ZR1443100)
文摘This work introduces special states for light in multimode fibers featuring strongly enhanced or reduced correlations be-tween output fields in the presence of environmental temperature fluctuations.Using experimentally measured multi-tem-perature transmission matrix,a set of temperature principal modes that exhibit resilience to disturbances caused by tem-perature fluctuations can be generated.Reversing this concept also allows the construction of temperature anti-principal modes,with output profiles more susceptible to temperature influences than the unmodulated wavefront.Despite changes in the length of the multimode fiber within the temperature-fluctuating region,the proposed approach remains capable of robustly controlling the temperature response within the fiber.To illustrate the practicality of the proposed spe-cial state,a learning-empowered fiber specklegram temperature sensor based on temperature anti-principal mode sensi-tization is proposed.This sensor exhibits outstanding superiority over traditional approaches in terms of resolution and accuracy.These novel states are anticipated to have wide-ranging applications in fiber communication,sensing,imaging,and spectroscopy,and serve as a source of inspiration for the discovery of other novel states.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFB2800902)the National Natural Science Foundation of China(Grant No.62225110)+1 种基金the Key Research and Development Program of Hubei Province(No.2022BAA001)the Innovation Fund of WNLO.
文摘The detection of the state of polarization(SOP)of light is essential for many optical applications.However,cost-effective SOP measurement is a challenge due to the complexity of conventional methods and the poor transferability of new methods.We propose a straightforward,low-cost,and portable SOP measurement system based on the multimode fiber speckle.A convolutional neural network is utilized to establish the mapping relationship between speckle and Stokes parameters.The lowest root-mean-square error of the estimated SOP on the Poincarésphere can be 0.0042.This method is distinguished by its low cost,clear structure,and applicability to different wavelengths with high precision.The proposed method is of great value in polarization-related applications.
基金supported by the National Natural Science Foundation of China(NSFC)(Grant No.81930048)the Hong Kong Innovation and Technology Commission(Grant Nos.GHP/043/19SZ and GHP/044/19GD)+3 种基金the Hong Kong Research Grant Council(Grant Nos.15217721,R5029-19 and C7074-21GF)the Guangdong Science and Technology Commission(Grant No.2019BT02X105)the Shenzhen Science and Technology Innovation Commission(Grant No.JCYJ20220818100202005)the Hong Kong Polytechnic University(Grant Nos.P0038180,P0039517,P0043485 and P0045762).
文摘Transmission matrix(TM)allows light control through complex media,such as multimode fibers(MMFs),gaining great attention in areas,such as biophotonics,over the past decade.Efforts have been taken to retrieve a complex-valued TM directly from intensity measurements with several representative phase-retrieval algorithms,which still see limitations of slow or suboptimum recovery,especially under noisy environments.Here,we propose a modified nonconvex optimization approach.Through numerical evaluations,it shows that the optimum focusing efficiency is approached with less running time or sampling ratio.The comparative tests under different signal-to-noise levels further indicate its improved robustness.Experimentally,the superior focusing performance of our algorithm is collectively validated by single-and multispot focusing;especially with a sampling ratio of 8,it achieves a 93.6%efficiency of the gold-standard holography method.Based on the recovered TM,image transmission through an MMF is realized with high fidelity.Due to parallel operation and GPU acceleration,our nonconvex approach retrieves a 8685×1024 TM(sampling ratio is 8)with 42.3 s on average on a regular computer.The proposed method provides optimum efficiency and fast execution for TM retrieval that avoids the need for an external reference beam,which will facilitate applications of deep-tissue optical imaging,manipulation,and treatment.
基金supported by the National Natural Science Foundation of China(Grant Nos.T2293751,T2293752,61735017,62020106002,and 62005250)the National Key Basic Research Program of China(Grant No.2021YFC2401403)the Major Scientific Research Project of Zhejiang Lab(Grant No.2019MC0AD02).
文摘Imaging through multimode fiber(MMF)provides high-resolution imaging through a fiber with cross section down to tens of micrometers.It requires interferometry to measure the full transmission matrix(TM),leading to the drawbacks of complicated experimental setup and phase instability.Reference-less TM retrieval is a promising robust solution that avoids interferometry,since it recovers the TM from intensity-only measurements.However,the long computational time and failure of 3D focusing still limit its application in MMF imaging.We propose an efficient reference-less TM retrieval method by developing a nonlinear optimization algorithm based on fast Fourier transform(FFT).Furthermore,we develop an algorithm to correct the phase offset error of retrieved TM using defocused intensity images and hence achieve 3D focusing.The proposed method is validated by both simulations and experiments.The FFT-based TM retrieval algorithm achieves orders of magnitude of speedup in computational time and recovers 2286×8192 TM of a 0.22 NA and 50μm diameter MMF with 112.9 s by a computer of 32 CPU cores.With the advantages of efficiency and correction of phase offset,our method paves the way for the application of reference-less TM retrieval in not only MMF imaging but also broader applications requiring TM calibration.
基金supported in part by the National Natural Foundation of China(Nos. 61875086, 61377086)the Aerospace Science Foundation of China (No.2016ZD52042)Nanjing University of Aeronautics and Astronautics Ph. D. short-term visiting scholar project (No.190901DF08)
文摘We propose the trench-assisted multimode fiber(TA-OM4)as a novel sensing fiber in forward Brillouin scattering(FBS)-based temperature sensor,due to its higher temperature sensitivity,better bending resistance and lower propagation loss,compared with the single mode fiber(SMF)and other sensing fibers.The FBS effect and acousto-optic interaction in TA-OM4 are the first time to be demonstrated and characterized at 1550 nm theoretically and experimentally.A 2.0 km long TA-OM4 is put into an oven to measure its temperature sensitivity,which can reach up to 80.3 kHz/℃,exceeding 53%of SMF(52.4 kHz/℃).The simulated and experimental results verify that the TA-OM4 may be a good candidate as the sensing fiber for the FBS-based temperature sensor.
基金Project partially supported by the National Natural Science Foundation of China (Grant Nos. 91950105 and 62175116)the 1311 Talent Plan of Nanjing University of Posts and Telecommunications。
文摘The high degree of freedom and novel nonlinear phenomena of multimode fiber are attracting attention. In this work,we demonstrate a spatiotemporal mode-locked multimode fiber laser, which relies on microfiber knot resonance(MKR) via dissipative four-wave-mixing(DFMW) to achieve high-repetition-rate pulses. Apart from that, DFMW mode locking with switchable central wavelengths can also be obtained. It was further found that high pulse energy induced nonlinear effect of the dominant mode-locking mechanism transforming from DFMW to nonlinear Kerr beam cleaning effect(NL-KBC). The experimental results are valuable for further comprehending the dynamic characteristics of spatiotemporal mode-locked multimode fiber lasers, facilitating them much more accessible for applications.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61327012 and 61505160the Natural Science Foundation of Shaanxi Province under Grant No 2016JQ6021the Shaanxi Key Laboratory of Optical Information Technology under Grant No OIT201601
文摘A refractive index （RI） sensor based on hybrid long-period fiber grating （LPFG） with multimode fiber core （MMFC） is proposed and demonstrated. The surrounding RI can be determined by monitoring the separation between the resonant wavelengths of the LPFG and MMFC since the resonant wavelengths of the LPFG and MMFC will shift in opposite directions when the surrounding RI changes. Experimental results show that the sensor possesses an enhanced sensitivity of 526.92nm/RIU in the RI range of 1.387-1.394 RIU. The response to the temperature is also discussed.
基金funded by the Federal Ministry of Education and Research of Germany with the project 6G-life(grant identification number:16KISK001K)QUIET(project identification number:16KISQ092)supported by the German Research Foundation for funding(grant number:CZ 55/42-2).
文摘Mode division multiplexing(MDM)using multimode fibers(MMFs)is key to meeting the demand for higher data rates and advancing internet technologies.However,optical transmission within MMFs presents challenges,particularly due to mode crosstalk,which complicates the use of MMFs to increase system capacity.Quantitatively analyzing the output of MMFs is essential not only for telecommunications but also for applications like fiber sensors,fiber lasers,and endoscopy.With the success of deep neural networks(DNNs),AI-driven mode decomposition(MD)has emerged as a leading solution for MMFs.However,almost all implementations rely on Graphics Processing Units(GPUs),which have high computational and system integration demands.Additionally,achieving the critical latency for real-time data transfer in closed-loop systems remains a challenge.In this work,we propose using field-programmable gate arrays(FPGAs)to perform neural network inference for MD,marking the first use of FPGAs for this application,which is important,since the latency of closed-loop control could be significantly lower than at GPUs.A convolutional neural network(CNN)is trained on synthetic data to predict mode weights(amplitude and phase)from intensity images.After quantizing the model’s parameters,the CNN is executed on an FPGA using fixed-point arithmetic.The results demonstrate that the FPGA-based neural network can accurately decompose up to six modes.The FPGA’s customization and high efficiency provide substantial advantages,with low power consumption(2.4 Watts)and rapid inference(over 100 Hz),offering practical solutions for real-time applications.The proposed FPGA-based MD solution,coupled with closed-loop control,shows promise for applications in fiber characterization,communications,and beyond.
基金Financial support was provided by the National Natural Science Foundation of China(Grant Nos.T2293751,T2293750,62405278,6240030458,62020106002,61735017,and 92250304)National Key Basic Research Program of China(Grant No.2021YFC2401403)+2 种基金National Key Research and Development Program of China(Grant Nos.2024YFF1206700 and 2024YFF1206705)Major Scientific Research Project of Zhejiang Laboratory(Grant No.2019MC0AD02)the Zhejiang University Education Foundation Global Partnership Fund.
文摘In vivo microscopic imaging inside a biological lumen such as the gastrointestinal tract,respiratory airways,or within blood vessels has faced significant technological challenges for decades.A promising candidate technology is the multimode fiber(MMF)endoscope,which enables minimally invasive diagnostics at a resolution reaching the cellular level.However,for in vivo imaging applications deep inside a biological lumen,sample-induced aberrations and the dynamic dispersion in the MMF make the MMF endoscope a chaotic system with many unknowns,where multiple minor fluctuations can couple and compound into intractable problems.We introduce a dynamically encoding,cascaded,optical,and ultrathin polychromatic light-field endoscopy(DECOUPLE)to tackle this challenge.DECOUPLE includes an adaptive aberration correction that can accurately track and control MMF behavior in the spatial-frequency domain to compensate for chaos introduced during complex dynamic imaging processes.We demonstrate the flexibility and practicality of DECOUPLE for noninvasive volumetric imaging in two colors for light passing through various highly aberrating samples including 120-μm-thick onion epidermal slices and 80-μm-thick layers of fat emulsions.To summarize,we represent a significant step toward practical in vivo imaging deep within biological tissue.
基金supported by the National Key Research and Development Program of China(2023YFB2906300)National Natural Science Foundation of China(61931010,62225110)JD project of Hubei province(2023BAA013).
文摘We propose and validate a novel optical semantic transmission scheme using multimode fiber(MMF).By leveraging the frequency sensitivity of intermodal dispersion in MMFs,we achieve high-dimensional semantic encoding and decoding in the frequency domain.Our system maps symbols to 128 distinct frequencies spaced at 600 kHz intervals,demonstrating a seven-fold increase in capacity compared to conventional communication encoding.We further enhance spectral efficiency by implementing 4-level pulse amplitude modulation(PAM-4),achieving 9.12 bits/s/Hz without decoding errors.Additionally,we explore the application of this system for sentiment analysis using the IMDb movie review dataset.By encoding semantically similar symbols to adjacent frequencies,the system's noise tolerance is effectively improved,facilitating accurate sentiment analysis.This work highlights the potential of MMF-based semantic communication to enhance both capacity and robustness in optical communication systems,offering promising applications in bandwidth-constrained and noisy environments.
基金supported by the National Key R&D Program of China(No.2022YFB3606000)the Graduate Innovation Project of Hunan Province(No.QL20220004).
文摘The immediate priorities for high-power delivery employing solid-core fibers are balancing the nonlinear effect and beam deterioration.Here,the scheme of tapered multimode fiber is experimentally realized.The tapered multimode fiber,featuring a 15 m(24/200μm)–10 m(tapered region)–80 m(48/400μm)profile,guides the laser with a weakly coupled condition.With the input power of 1035 W,the maximum output power over the 105 m delivery is 962 W,corresponding to a high efficiency of over 93%and a nonlinear suppression ratio of over 50 dB.Mode resolving results show high-order-mode contents of less than–30 dB in the whole delivery path,resulting in a high-fidelity delivery with M2 factors of 1.20 and 1.23 for the input and output lasers,respectively.Furthermore,the ultimate limits of delivery lengths for solid-core weakly coupled fibers are discussed.This work provides a valuable reference to reconsider the future boom of high-power laser delivery based on solid-core fibers.
基金supported by the National Natural Science Foundation of China(Grant No.62071016)the State Key Laboratory of Advanced Optical Communication Systems Networks,Chinathe Academic Excellence Foundation of BUAA for PhD Students.
文摘We investigated 1-μm multimode fiber laser based on carbon nanotubes,where multiple typical pulse states were observed,including Q-switched,Q-switched mode-locked,and spatiotemporal mode-locked pulses.Particularly,stable spatiotemporal mode-locking was realized with a low threshold,where the pulse duration was 37 ps and the wavelength was centred at 1060.5 nm.Moreover,both the high signal to noise and long-term operation stability proved the reliability of the mode-locked laser.Furthermore,the evolution of the spatiotemporal mode-locked pulses in the cavity was also simulated and discussed.This work exhibits the flexible outputs of spatiotemporal phenomena in multimode lasers based on nanomaterials,providing more possibilities for the development of high-dimensional nonlinear dynamics.
基金supported by National Natural Science Foundation of China(62135007 and 61925502).
文摘Optical endoscopy has become an essential diagnostic and therapeutic approach in modern biomedicine for directly observing organs and tissues deep inside the human body,enabling non-invasive,rapid diagnosis and treatment.Optical fiber endoscopy is highly competitive among various endoscopic imaging techniques due to its high flexibility,compact structure,excellent resolution,and resistance to electromagnetic interference.Over the past decade,endoscopes based on a single multimode optical fiber(MMF)have attracted widespread research interest due to their potential to significantly reduce the footprint of optical fiber endoscopes and enhance imaging capabilities.In comparison with other imaging principles of MMF endoscopes,the scanning imaging method based on the wavefront shaping technique is highly developed and provides benefits including excellent imaging contrast,broad applicability to complex imaging scenarios,and good compatibility with various well-established scanning imaging modalities.In this review,various technical routes to achieve light focusing through MMF and procedures to conduct the scanning imaging of MMF endoscopes are introduced.The advancements in imaging performance enhancements,integrations of various imaging modalities with MMF scanning endoscopes,and applications are summarized.Challenges specific to this endoscopic imaging technology are analyzed,and potential remedies and avenues for future developments are discussed.
基金National Key Basic Research Project of China,the Shanghai Science & Technology Foundation(No.04DZ05120,05DZ22001)the Knowledge Innovation Project of Chinese Academy of Sciences.
文摘Coiling technique is used to control the transverse mode of a large-mode-area （LMA） multimode fiber laser. By winding the fiber to a coil with different radius, high-order modes of a multimode fiber laser are suppressed one by one and finally 15.4-W single-transverse-mode output is achieved when the coil radius is 20 mm. It is found that as the coil radius decreases, the beam quality of a multimode fiber laser gets better but the slope efficiency drops for higher-order modes are discriminated. During the experiment, as the coil radius of multimode fiber changes, output characteristic of the laser has been measured. Meanwhile, the mode loss of different modes is calculated theoretically. It is proved that the experimental measured results fit well with the theoretically calculated results.
基金supported by the National Natural Science Foundation of China(Nos.92050101,61875058,11874018,11974006,and 61378036)the Natural Science Foundation of Guangdong Province(No.2021A1515011608)。
文摘We report Q-switched mode-locked(QML)pulses generation in an Yb-doped multimode fiber(MMF)laser by using a graphene-deposited multimode microfiber(GMM)for the first time,to the best of our knowledge.The single-wavelength QML operation with the central wavelength tunable from 1028.81 nm to 1039.20 nm and the dual-wavelength QML operation with the wavelength spacing tunable from 0.93 nm to 5.79 nm are achieved due to the multimode interference filtering effect induced by the few-mode fiber and MMF structure and the GMM in the cavity.Particularly,in the single-wavelength QML operation,the fifth harmonic is also realized owing to the high nonlinear effect of the GMM.The obtained results indicate that the QML pulses can be generated in the MMF laser,and such a flexible tunable laser has promising applications in optical sensing,measuring,and laser processing.
基金supported by the Project of Shanghai Science & Technology Committee (Nos. 09530500600 and 09PJ1404600)the Key Project of Shanghai Education Committee (No. 09ZZ92)+1 种基金partly supported by the Shanghai Leading Academic Discipline Project under Grant No. S30108.the support provided by the Program for Professors of Special Appointment (Eastern Scholar) at the Shanghai Institutions of Higher Learning, China
文摘We experimentally demonstrate the simultaneous generation of tunable multi-wavelength picosecond laser pulses using a self-seeding configuration that consists of a gain-switched Fabry-Perot laser diode （FPLD） with an external cavity formed by a tilted multimode fiber Bragg grating. Dual- and triple-wavelength pulses are obtained and tuned in a flexible manner by changing the temperature of the FPLD. The side mode suppression ratio larger than 25 dB is achieved at different dual- and triple-wavelengths and the typical pulsewidth of the output pulses is ,-70 ps. In the experiment, the wavelength separation can be narrowed to 0.57 nm.
基金supported by the Natural Science Foundation of Hunan Province(No.2022JJ30653)。
文摘A monolithic visible supercontinuum(SC)source with a record average output power of 204 W and a spectrum ranging from580 nm to beyond 2400 nm is achieved in a piece of standard telecom graded-index multimode fiber(GRIN MMF)by designing the pumping system.The influence of the GRIN MMF length on the geometrical parameter instability(GPI)effect is analyzed for the first time,to the best of our knowledge,by comparing the SC spectral region dominated by the GPI effect under different fiber lengths.Our work could pave the way for robust,cost-effective,and high-power visible SC sources.
基金supported by the National Natural Science Foundation of China under Grant No.51275120
文摘We propose an adaptive parallel coordinate （APC） algorithm for quickly forming a series of focused spots at a multimode fiber （MMF） output by controlling the MMF input field with a spatial light modulator （SLM）. Only passing over the SLM once, we can obtain SLM reflectance to form focused spots on different positions. Com- pared with the transmission matrix method, our APC does not. require iterations and massive calculations. The APC does not require as much access device time as the adaptive sequential coordinate ascent （SCA） algorithm. The experiment results demonstrate that the time taken to form 100 spots with our APC is 1/54th the time with the SCA.
基金supported by the National Natural Science Foundation of China(Nos.11574061,61405043,and 61675053)the 111 Project(No.B13015)the Fundamental Research Funds for Harbin Engineering University of China
文摘We propose and demonstrate single fiber dual-functionality optical tweezers based on a graded-index multimode fiber. By using the multi-angle fiber grinding and polishing technology, we fabricate the multimode fiber tip to be a special tapered shape, contributing to focus the outgoing beam with a large intensity gradient for the first functionality--three-dimensional contactless trapping of a microparticle. By adjusting the radial direction offset between the lead-in single mode fiber and the graded-index multimode fiber, we perform the second functionality--axial shift of the trapped microparticle with respect to the fiber tip without need of moving the fiber probe itself. It is convenient for practical applications, The theoretical and experimental results about the relationship between the radial offset and the equilibrium positions of the microparticle have the good consistency. Tailoring the trap and axial shift of the microparticle based on the graded-index multimode fiber provides convenient avenues for fiber optical tweezers a~）Dlied in practical researches.
基金supported by the State Key Laboratory of Advanced Optical Communication Systems and Networks,China
文摘By using a graded-index multimode fiber （GI-MMF） with a relatively flat index profile and high refractive index of the fiber core, a microextrinsic fiber-optic Fabry Prot interferometric （MEFPI） strain sensor is fabricated through chemical etching and fusion splicing. Higher reflectance of the microcavity is obtained due to the less-curved inner wall in the center of the fiber core after etching and higher index contrast between the GI-MMF core and air. The maximum reflection of the sensor is enhanced 12 dB than that obtained by etching of the Er- or B-doped fibers. High fringe contrast of 22 dB is obtained. The strain and temperature responses of the MEFPI sensors are investigated in this experiment. Good linearity and high sensitivity are achieved, with wavelength-strain and wavelength-temperature sensitivities of 7.82 pm/με and 5.01 pm/°C, respectively.
