The effects of optical sources with different laser linewidths on Brillouin optical time domain reflectometry （BOTDR） are investigated numerically and experimentally. Simulation results show that the spectral linewi...The effects of optical sources with different laser linewidths on Brillouin optical time domain reflectometry （BOTDR） are investigated numerically and experimentally. Simulation results show that the spectral linewidth of spontaneous Brillouin scattering remains almost constant when the laser linewidth is less than 1 MHz at the same pulse width; otherwise, it increases sharply. A comparison between a fiber laser （FL） with 4-kHz linewidth at 3 dB and a distributed feedback （DFB） laser with 3-MHz linewidth is made experimentally. When a constant laser power is launched into the sensing fiber, the fitting linewidths of the beat signals （backscattered Brillouin light and local oscillator （LO）） is about 5 MHz wider for the DFB laser than for the FL and the intensity of the beat signal is about a half. Furthermore, the frequency fluctuation in the long sensing fiber is lower for the FL source, yielding about 2 MHz less than that of the DFB laser, indicating higher temperature/strain resolution. The experimental results are in good agreement with the numerical simulations.展开更多
By using an external-cavity frequency-doubling master oscillator fiber power amplifier （MOPA）, a 700 mW continuous-wave single-frequency laser source at 780 nm is produced. It is shown that the frequency doubling ef...By using an external-cavity frequency-doubling master oscillator fiber power amplifier （MOPA）, a 700 mW continuous-wave single-frequency laser source at 780 nm is produced. It is shown that the frequency doubling efficiency is improved when the seed diode laser is optically locked to a resonant frequency of a confocal Fabry-Perot （F-P） cavity. This phenomenon can be attributed to the narrowing of the 1.56 μm laser linewidth and explained by our presented theoretical model. The experimental results are found to be in good agreement with the theoretical predictions.展开更多
The ideal behavior of communication system requires a single frequency carrier. In optical communication system, light is used as a carrier. Practical laser source has a finite linewidth due to variations in the frequ...The ideal behavior of communication system requires a single frequency carrier. In optical communication system, light is used as a carrier. Practical laser source has a finite linewidth due to variations in the frequency of operation, hence, resulting in undesired phase perturbations in the signal whereas the ideal requirement is the delta function spectral shape at the carrier frequency. The spectral shape gets broadened due to phase noise and is modeled as lorentzian shape. Linewidth is a measure of stability of laser phase noise with time. Coherent Optical Orthogonal frequency division multiplexing (CO-OFDM) along with the spectrally efficient Quadrature Amplitude Modulation (QAM) formats is emerging as one of the best solutions for future high speed fiber transmission systems. Though the coherent, receivers have advantages in terms of sensitivity and selectivity, laser phase noise is the main limitation of such systems as the laser phase noise further causes common phase rotation of all the subcarriers per symbol and also results in inter carrier interference. QAM formats are also susceptible to laser phase noise. Phase noise in coherent systems is governed by laser linewidth. Hence, it is very important to investigate the impact of laser linewidth in CO-OFDM systems. This paper investigates the tolerable laser linewidths for different QAM formats in a 40 Gbps COOFDM system.展开更多
Two Nd：YAG lasers operating at 1064 nm are separately servo-locked to two vertically mounted ultra-stable cavities. The optical heterodyne beat between two cavity-stabilized lasers shows that the linewidth of each la...Two Nd：YAG lasers operating at 1064 nm are separately servo-locked to two vertically mounted ultra-stable cavities. The optical heterodyne beat between two cavity-stabilized lasers shows that the linewidth of each laser reaches 2 Hz and the average frequency drift reduces to less than 1 Hz/s.展开更多
Ultra-narrow linewidth laser with several hundred hertz at room temperature has attracted a great deal of attention in recent years and played a critical role in both optical sensing and communication fields. In this ...Ultra-narrow linewidth laser with several hundred hertz at room temperature has attracted a great deal of attention in recent years and played a critical role in both optical sensing and communication fields. In this paper, a new method based on Rayleigh backscattering to highly compress the laser linewidth was proposed and demonstrated theoretically and experimentally. By theoretical analysis and simulation, Rayleigh backscattering can be collected in any waveguide structure and all wave bands,which could have a revolutionary impact on the field of laser. A single-longitudinal mode fiber ring laser with130-Hz linewidth was achieved with self-injection feedback structure at normal atmospheric temperature. The linewidth compression based on Rayleigh backscattering lies in the fact that laser linewidth after scattering is narrower than that of incident light in high Rayleigh scattering structure. The self-rejection feedback method expanding free spectra range of laser cavity simultaneously was used to further suppress the mode-hopping and stabilizing output. Experimental results showed that the laser linewidth can be easily narrowed to hundreds of hertz with side-mode suppression up to 75 dB. This agrees with the theoretical analysis and simulation results qualitatively.展开更多
Interference filter-stabilized external cavity diode lasers （ECDLs） have properties of simple configurations, high sta- bilities, and narrow linewidths. However, the interference filter used in common ECDL designs r...Interference filter-stabilized external cavity diode lasers （ECDLs） have properties of simple configurations, high sta- bilities, and narrow linewidths. However, the interference filter used in common ECDL designs requires an ultra-narrow bandwidth （about 0.3 nm） to achieve mode selection, that is considerably expensive and not yet available for a wide range of wavelengths. In this paper, a robust ECDL using an available broad bandwidth （about 4 nm） interference filter as the wavelength discriminator is constructed and tested. The ECDL demonstrated a narrow Lorentzian fitted linewidth of 95 kHz and a spectral purity of 2.9 MHz. The long-term frequency stability of the ECDL reaches 5.59 x 10 12.展开更多
We present two cavity-stabilized lasers at 1555 nm, which are built to be the frequency source for a transportable photonic microwave generation system. The frequency instability reaches the thermal noise limit （7 &#...We present two cavity-stabilized lasers at 1555 nm, which are built to be the frequency source for a transportable photonic microwave generation system. The frequency instability reaches the thermal noise limit （7 ×10-16） of the 10-cm ultra-low expansion glass cavity at 1-10s averaging time and the beat signal of the two lasers reveals a remarkable linewidth of 185mHz.展开更多
Theoretical simulation and experiments based on a prism beam expander and an echelle grating are con- ducted to study the dependence of linewidth and pulse energy on incidence angle and slit width. With a larger prism...Theoretical simulation and experiments based on a prism beam expander and an echelle grating are con- ducted to study the dependence of linewidth and pulse energy on incidence angle and slit width. With a larger prism incident angle or narrower slit width, the linewidth becomes narrower while the laser pulse energy becomes lower. However, the pulse energy can be improved by optimally designing the prism beam expander. In addition, a subpicometer linewidth ArF laser is obtained with a double-prism beam expander and an echelle grating.展开更多
We propose and demonstrate a novel single-longitudinal-mode(SLM) erbium-doped fiber laser(EDFL) capable of operating at fixed-wavelength lasing mode with a tunable range more than 54 nm, an ultra-narrow linewidth of 4...We propose and demonstrate a novel single-longitudinal-mode(SLM) erbium-doped fiber laser(EDFL) capable of operating at fixed-wavelength lasing mode with a tunable range more than 54 nm, an ultra-narrow linewidth of 473 Hz and an ultra-high optical signal-to-noise ratio(OSNR) more than 72 dB, or operating at wavelength-swept mode with tunable sweep rate of 10—200 Hz and a sweep range more than 50 nm. The excellent features mainly benefit from a triple-ring subring cavity constructed by three optical couplers nested one another and a fiber Fabry-Pérot tunable filter which can be driven by a constant voltage or a periodic sweep voltage for fixed or wavelength-swept operation, respectively. The proposed EDFL has potential applications in high-resolution spectroscopy and fiber optic sensing.展开更多
This paper investigates the influences of a semiconductor laser with narrow linewidth on a fibre-optic distributed disturbance sensor based on Mach-Zehnder interferometer. It establishes an effective numerical model t...This paper investigates the influences of a semiconductor laser with narrow linewidth on a fibre-optic distributed disturbance sensor based on Mach-Zehnder interferometer. It establishes an effective numerical model to describe the noises and linewidth of a semiconductor laser, taking into account their correlations. Simulation shows that frequency noise has great influences on location errors and their relationship is numerically investigated. Accordingly, there is need to determine the linewidth of the laser less than a threshold and obtain the least location errors. Furthermore, experiments are performed by a sensor prototype using three semiconductor lasers with different linewidths, respectively, with polarization maintaining optical fibres and couplers to eliminate the polarization induced noises and fading. The agreement of simulation with experimental results means that the proposed numerical model can make a comprehensive description of the noise behaviour of a semiconductor laser. The conclusion is useful for choosing a laser source for fibre-optic distributed disturbance sensor to achieve optimized location accuracy. What is more, the proposed numerical model can be widely used for analysing influences of semiconductor lasers on other sensing, communication and optical signal processing systems.展开更多
The design of 1.3μm He-Ne single frequency laser for optical fiber communication is in-troduced.The scheme for obtaining steady single-mode oscillation by raising gas pressureand the method of getting linear-polariza...The design of 1.3μm He-Ne single frequency laser for optical fiber communication is in-troduced.The scheme for obtaining steady single-mode oscillation by raising gas pressureand the method of getting linear-polarization single frequency output by longitudinal Zeemaneffect are present.The relations of linewidth to some factors are discussed.展开更多
Mode gain spectrum is measured by the Fourier series expansion method for InAs/GaAs quantum-dot （QD） lasers with seven stacks of QDs at different injection currents. Gain spectra with distinctive peaks are observed ...Mode gain spectrum is measured by the Fourier series expansion method for InAs/GaAs quantum-dot （QD） lasers with seven stacks of QDs at different injection currents. Gain spectra with distinctive peaks are observed at the short and long wavelengths of about 1210nm and 1300nm. For a QD laser with the cavity length of 1060μm, the peak gain of the long wavelength first increases slowly or even decreases with the injection current as the peak gain of the short wavelength increases quickly, and finally increases quickly before approaching the saturated values as the injection current further increases.展开更多
We propose a theoretical model to describe external-cavity distributed feedback semiconductor lasers and investigate the impact of the number of external feedback points on linewidth and side-mode suppression ratio th...We propose a theoretical model to describe external-cavity distributed feedback semiconductor lasers and investigate the impact of the number of external feedback points on linewidth and side-mode suppression ratio through numerical simulation. The simulation results demonstrate that the linewidth of external-cavity semiconductor lasers can be reduced by increasing the external cavity length and feedback ratio, and adding more external feedback points can further narrow the linewidth and enhance the side mode suppression ratio. This research provides insight into the external cavity distributed feedback mechanism and can guide the design of high-performance external cavity semiconductor lasers. .展开更多
Quantum cascade lasers(QCLs) have broad application potentials in infrared countermeasure system,free-space optical communication and trace gas detection.Compared with traditional Fabry-Pérot(FP) cavity and exter...Quantum cascade lasers(QCLs) have broad application potentials in infrared countermeasure system,free-space optical communication and trace gas detection.Compared with traditional Fabry-Pérot(FP) cavity and external cavity,distributed feedback quantum cascade lasers(DFB-QCLs) can obtain narrower laser linewidth and higher integration.In this paper,the structure design,numerical simulation and optimization of the Bragg grating of DFB-QCLs are carried out to obtain the transmission spectrum with central wavelength at 4.6 μm.We analyze the relationship among the structure parameters,the central wavelength shift and transmission efficiency using coupled-wave theory and finite-difference time-domain(FDTD) method.It is shown that the increase in the number of grating periods enhances the capabilities of mode selectivity,while the grating length of a single period adjustment directly determines the Bragg wavelength.Additionally,variations in etching depth and duty cycle lead to blue and red shifts in the central wavelength,respectively.Based on the numerical simulation results,the optimized design parameters for the upper buffer layer and the upper cladding grating are proposed,which gives an optional scheme for component fabrication and performance improvement in the future.展开更多
基金the National High Technology Research and Development Program of China(Grant No.2012AA041203)the Science and Technology Commission of Shanghai Municipality,China(Grant No.13XD1425400)the Pudong New Area Science and Technology Development Fund,China(Grant No.PKJ2012-D04)
文摘The effects of optical sources with different laser linewidths on Brillouin optical time domain reflectometry （BOTDR） are investigated numerically and experimentally. Simulation results show that the spectral linewidth of spontaneous Brillouin scattering remains almost constant when the laser linewidth is less than 1 MHz at the same pulse width; otherwise, it increases sharply. A comparison between a fiber laser （FL） with 4-kHz linewidth at 3 dB and a distributed feedback （DFB） laser with 3-MHz linewidth is made experimentally. When a constant laser power is launched into the sensing fiber, the fitting linewidths of the beat signals （backscattered Brillouin light and local oscillator （LO）） is about 5 MHz wider for the DFB laser than for the FL and the intensity of the beat signal is about a half. Furthermore, the frequency fluctuation in the long sensing fiber is lower for the FL source, yielding about 2 MHz less than that of the DFB laser, indicating higher temperature/strain resolution. The experimental results are in good agreement with the numerical simulations.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 60527003,60608011 and 60878003)the State Key Program for Basic Research of China (Grant No 2007CB316501)
文摘By using an external-cavity frequency-doubling master oscillator fiber power amplifier （MOPA）, a 700 mW continuous-wave single-frequency laser source at 780 nm is produced. It is shown that the frequency doubling efficiency is improved when the seed diode laser is optically locked to a resonant frequency of a confocal Fabry-Perot （F-P） cavity. This phenomenon can be attributed to the narrowing of the 1.56 μm laser linewidth and explained by our presented theoretical model. The experimental results are found to be in good agreement with the theoretical predictions.
文摘The ideal behavior of communication system requires a single frequency carrier. In optical communication system, light is used as a carrier. Practical laser source has a finite linewidth due to variations in the frequency of operation, hence, resulting in undesired phase perturbations in the signal whereas the ideal requirement is the delta function spectral shape at the carrier frequency. The spectral shape gets broadened due to phase noise and is modeled as lorentzian shape. Linewidth is a measure of stability of laser phase noise with time. Coherent Optical Orthogonal frequency division multiplexing (CO-OFDM) along with the spectrally efficient Quadrature Amplitude Modulation (QAM) formats is emerging as one of the best solutions for future high speed fiber transmission systems. Though the coherent, receivers have advantages in terms of sensitivity and selectivity, laser phase noise is the main limitation of such systems as the laser phase noise further causes common phase rotation of all the subcarriers per symbol and also results in inter carrier interference. QAM formats are also susceptible to laser phase noise. Phase noise in coherent systems is governed by laser linewidth. Hence, it is very important to investigate the impact of laser linewidth in CO-OFDM systems. This paper investigates the tolerable laser linewidths for different QAM formats in a 40 Gbps COOFDM system.
基金Project supported by the National Natural Science Foundation of China (Grant No 60490280)the State Key Development for Basic Research Program of China (Grant Nos 2006CB806005 and 2006CB921104)+2 种基金the Science and Technology Commission of Shanghai Municipality, China (Grant Nos 06JC14026 and 07JC14019)Shanghai Pujiang Talent Program, China (Grant No 07PJ14038)the Program for Changjiang Scholars and Innovative Research Teams, China
文摘Two Nd：YAG lasers operating at 1064 nm are separately servo-locked to two vertically mounted ultra-stable cavities. The optical heterodyne beat between two cavity-stabilized lasers shows that the linewidth of each laser reaches 2 Hz and the average frequency drift reduces to less than 1 Hz/s.
基金supported by the National Natural Science Foundation of China(61377066)the Fundamental Research Funds for the Central Universities(CDJZR12125502,106112013CDJZR120002,and 106112013CDJZR160006)
文摘Ultra-narrow linewidth laser with several hundred hertz at room temperature has attracted a great deal of attention in recent years and played a critical role in both optical sensing and communication fields. In this paper, a new method based on Rayleigh backscattering to highly compress the laser linewidth was proposed and demonstrated theoretically and experimentally. By theoretical analysis and simulation, Rayleigh backscattering can be collected in any waveguide structure and all wave bands,which could have a revolutionary impact on the field of laser. A single-longitudinal mode fiber ring laser with130-Hz linewidth was achieved with self-injection feedback structure at normal atmospheric temperature. The linewidth compression based on Rayleigh backscattering lies in the fact that laser linewidth after scattering is narrower than that of incident light in high Rayleigh scattering structure. The self-rejection feedback method expanding free spectra range of laser cavity simultaneously was used to further suppress the mode-hopping and stabilizing output. Experimental results showed that the laser linewidth can be easily narrowed to hundreds of hertz with side-mode suppression up to 75 dB. This agrees with the theoretical analysis and simulation results qualitatively.
基金Project supported by the Foundation of Based Technology of China(Grant No.YXBGD20151JL01)the National Natural Science Foundation of China(Grant Nos.61376049,61604007,11674016,61378058,61575008,and 61574011)+1 种基金the Natural Science Foundation of Beijing City,China(Grant Nos.4172009 and4152003)the Beijing Municipal Commission of Education of China(Grant Nos.PXM2017 014204 500034 and PXM2016 014204 500018)
文摘Interference filter-stabilized external cavity diode lasers （ECDLs） have properties of simple configurations, high sta- bilities, and narrow linewidths. However, the interference filter used in common ECDL designs requires an ultra-narrow bandwidth （about 0.3 nm） to achieve mode selection, that is considerably expensive and not yet available for a wide range of wavelengths. In this paper, a robust ECDL using an available broad bandwidth （about 4 nm） interference filter as the wavelength discriminator is constructed and tested. The ECDL demonstrated a narrow Lorentzian fitted linewidth of 95 kHz and a spectral purity of 2.9 MHz. The long-term frequency stability of the ECDL reaches 5.59 x 10 12.
基金Supported by the National Natural Science Foundation of China under Grant No 91536217the West Light Foundation of the Chinese Academy of Sciences under Grant No 2013ZD02the Youth Innovation Promotion Association of the Chinese Academy of Sciences under Grant No 2015334
文摘We present two cavity-stabilized lasers at 1555 nm, which are built to be the frequency source for a transportable photonic microwave generation system. The frequency instability reaches the thermal noise limit （7 ×10-16） of the 10-cm ultra-low expansion glass cavity at 1-10s averaging time and the beat signal of the two lasers reveals a remarkable linewidth of 185mHz.
基金supported by the National Science and Technology Major Project and the Natural Science Foundation of Shanghai,China(No.11ZR1441400)
文摘Theoretical simulation and experiments based on a prism beam expander and an echelle grating are con- ducted to study the dependence of linewidth and pulse energy on incidence angle and slit width. With a larger prism incident angle or narrower slit width, the linewidth becomes narrower while the laser pulse energy becomes lower. However, the pulse energy can be improved by optimally designing the prism beam expander. In addition, a subpicometer linewidth ArF laser is obtained with a double-prism beam expander and an echelle grating.
基金supported by the Natural Science Foundation of Hebei Province(No.F2016201023)the Technology Foundation for Selected Overseas Chinese Scholar of Ministry of Human Resources and Social Security of China(No.CG2015003006)the Advanced Talents Program of Hebei Educational Committee(No.GCC2014020)
文摘We propose and demonstrate a novel single-longitudinal-mode(SLM) erbium-doped fiber laser(EDFL) capable of operating at fixed-wavelength lasing mode with a tunable range more than 54 nm, an ultra-narrow linewidth of 473 Hz and an ultra-high optical signal-to-noise ratio(OSNR) more than 72 dB, or operating at wavelength-swept mode with tunable sweep rate of 10—200 Hz and a sweep range more than 50 nm. The excellent features mainly benefit from a triple-ring subring cavity constructed by three optical couplers nested one another and a fiber Fabry-Pérot tunable filter which can be driven by a constant voltage or a periodic sweep voltage for fixed or wavelength-swept operation, respectively. The proposed EDFL has potential applications in high-resolution spectroscopy and fiber optic sensing.
文摘This paper investigates the influences of a semiconductor laser with narrow linewidth on a fibre-optic distributed disturbance sensor based on Mach-Zehnder interferometer. It establishes an effective numerical model to describe the noises and linewidth of a semiconductor laser, taking into account their correlations. Simulation shows that frequency noise has great influences on location errors and their relationship is numerically investigated. Accordingly, there is need to determine the linewidth of the laser less than a threshold and obtain the least location errors. Furthermore, experiments are performed by a sensor prototype using three semiconductor lasers with different linewidths, respectively, with polarization maintaining optical fibres and couplers to eliminate the polarization induced noises and fading. The agreement of simulation with experimental results means that the proposed numerical model can make a comprehensive description of the noise behaviour of a semiconductor laser. The conclusion is useful for choosing a laser source for fibre-optic distributed disturbance sensor to achieve optimized location accuracy. What is more, the proposed numerical model can be widely used for analysing influences of semiconductor lasers on other sensing, communication and optical signal processing systems.
文摘The design of 1.3μm He-Ne single frequency laser for optical fiber communication is in-troduced.The scheme for obtaining steady single-mode oscillation by raising gas pressureand the method of getting linear-polarization single frequency output by longitudinal Zeemaneffect are present.The relations of linewidth to some factors are discussed.
基金Supported by the National High Technology Development Program of China under Grant No 2003AA311070, and the National Natural Science Foundation of China under Grants Nos 60225011 and 60625405.
文摘Mode gain spectrum is measured by the Fourier series expansion method for InAs/GaAs quantum-dot （QD） lasers with seven stacks of QDs at different injection currents. Gain spectra with distinctive peaks are observed at the short and long wavelengths of about 1210nm and 1300nm. For a QD laser with the cavity length of 1060μm, the peak gain of the long wavelength first increases slowly or even decreases with the injection current as the peak gain of the short wavelength increases quickly, and finally increases quickly before approaching the saturated values as the injection current further increases.
文摘We propose a theoretical model to describe external-cavity distributed feedback semiconductor lasers and investigate the impact of the number of external feedback points on linewidth and side-mode suppression ratio through numerical simulation. The simulation results demonstrate that the linewidth of external-cavity semiconductor lasers can be reduced by increasing the external cavity length and feedback ratio, and adding more external feedback points can further narrow the linewidth and enhance the side mode suppression ratio. This research provides insight into the external cavity distributed feedback mechanism and can guide the design of high-performance external cavity semiconductor lasers. .
基金supported by the Scientific Research Project of Beijing Municipal Education Commission (No.KM202411232020)the Young Backbone Teacher Support Plan (No.YBT202408)the Scientific Researchof Beijing Information Science and Technology University (No.2023XJJ08)。
文摘Quantum cascade lasers(QCLs) have broad application potentials in infrared countermeasure system,free-space optical communication and trace gas detection.Compared with traditional Fabry-Pérot(FP) cavity and external cavity,distributed feedback quantum cascade lasers(DFB-QCLs) can obtain narrower laser linewidth and higher integration.In this paper,the structure design,numerical simulation and optimization of the Bragg grating of DFB-QCLs are carried out to obtain the transmission spectrum with central wavelength at 4.6 μm.We analyze the relationship among the structure parameters,the central wavelength shift and transmission efficiency using coupled-wave theory and finite-difference time-domain(FDTD) method.It is shown that the increase in the number of grating periods enhances the capabilities of mode selectivity,while the grating length of a single period adjustment directly determines the Bragg wavelength.Additionally,variations in etching depth and duty cycle lead to blue and red shifts in the central wavelength,respectively.Based on the numerical simulation results,the optimized design parameters for the upper buffer layer and the upper cladding grating are proposed,which gives an optional scheme for component fabrication and performance improvement in the future.
