121 results about "Optical fiber amplifiers" patented technology

The invention discloses a signal-to-noise ratio improvement method based on a multi-core optical fiber dual-channel distributed acoustic sensing system, and the method comprises the steps: carrying out the light splitting of light emitted by a narrow linewidth laser through a first coupler C1, enabling one path of light to generate a pulse signal through an acoustic optical modulator (AOM), enabling the other path of light to pass through a second coupler C2, and enabling the other path of light to pass through a second coupler C1; the pulse light is divided into two beams of transmission light, the two beams of transmission light are injected into a connected sensing optical fiber through two groups of erbium-doped optical fiber amplifiers (EDFA), two groups of filters, two groups of circulators and a fan-in coupler Fan-in Coupler, and the pulse light is subjected to backward Rayleigh scattering in the sensing optical fiber; based on a dual-channel DAS system, a multi-core optical fiber is used as a sensing optical fiber, three cores and four cores of the multi-core optical fiber are connected in series to form two sensing channels, seven-core space division signals are multiplexed, the equivalent self-noise pressure suppression effect of the seven-core space division signals is analyzed, after noise correlation is removed through a time domain dislocation-frequency domain phase shift method, the signal-to-noise ratio gain can be increased to 8.65 dB, and the signal-to-noise ratio gain can be increased to 8.65 dB. And the detection capability of the system on low-frequency weak signals can be improved.

The pre-pulse thulium laser lithotripsy system comprises an interaction unit, a control unit, a thulium-doped fiber laser, a thulium-doped fiber amplifier, a laser fiber coupler and a lithotripsy fiber, wherein the interaction unit forwards a user instruction to the control unit; the control unit controls the thulium-doped fiber laser and the thulium-doped fiber amplifier according to a user instruction; the thulium-doped fiber laser outputs laser pulses to the thulium-doped fiber amplifier according to the control instruction; the thulium-doped optical fiber amplifier sets a laser amplification factor according to the control instruction and amplifies the laser pulse; the optical fiber coupler is used for coupling the amplified laser pulse; and the lithotripsy optical fiber acts the coupled laser pulse on the calculus or sticky tissue of the calculus patient. Through the combination of the thulium-doped fiber laser with the MOPA structure and the thulium-doped fiber amplifier, high-peak power nanosecond pulse can be realized, micro-explosion bubbles are instantly generated, the energy loss before laser acts on stones is reduced, the unit energy lithotripsy efficiency is improved, and the lithotripsy effect is improved.

The invention discloses a narrow linewidth optical fiber laser system based on a self-injection locking feedback mechanism, which belongs to the field of optical fiber communication and comprises a main cavity, a self-injection locking feedback module and an erbium-doped optical fiber amplifier. Wherein the main cavity internally comprises a composite ring cavity filter for selecting a longitudinal mode; the composite ring cavity filter is sequentially connected with a polarization controller, a first erbium-doped fiber, a first wavelength division multiplexer, a second erbium-doped fiber and a first uniform fiber bragg grating through a first circulator; the output end of the first uniform fiber bragg grating is connected with the input end of a first optical fiber coupler, one output end of the first optical fiber coupler is sequentially connected with an optical fiber delay line and a Faraday rotating mirror in the self-injection locking feedback module, and the rotating angle of the Faraday rotating mirror is 90 degrees; and the other output end of the first optical fiber coupler is connected with the input end of the erbium-doped optical fiber amplifier. Through the above structure, the stability of the laser system is improved.

The invention discloses a TGD-OFDR / OCC-BOTDR integrated multi-parameter sensing system and a working method thereof, and relates to the technical field of optical fiber sensors. The multi-parameter sensing system comprises a laser, an optical fiber coupler, an electro-optical modulator, an optical fiber circulator, an optical fiber Bragg grating, an acoustic optical modulator, an erbium-doped optical fiber amplifier, a random scrambler, a piezoelectric ceramic tube, a heating vessel, a delay optical fiber, a photoelectric balance detector, a filter and detector, a data acquisition card, a polarization controller, a direct-current power supply and a microwave source. An arbitrary waveform generator and the like. According to the invention, multiple parameters can be represented at the same time, the measuring speed is fast, and the sampling rate of the system can be effectively improved under the condition that sensing parameters are the same; the method has the advantage of high spatial resolution; the sensor has the advantages of high fusion and low cost, can realize simultaneous measurement of vibration and temperature / strain through single sensing, and is high in fusion and effective in cost control.

The invention discloses a high-power neodymium-doped three-level optical fiber laser. The described laser structurally comprises a signal laser seed source, an auxiliary laser source, a wavelength division multiplexer, an optical isolator, an optical fiber amplifier and an optical fiber collimator. The auxiliary laser is introduced, on one hand, the neodymium-doped optical fiber is used for absorbing the auxiliary laser to reduce the number of particles of the lower energy level, namely the ground state energy level, of the laser, and therefore the influence of the reabsorption effect of the neodymium-doped optical fiber on the signal laser is weakened; on the other hand, after the auxiliary laser is amplified by the neodymium-doped optical fiber, the energy is further transferred to the signal laser in an in-band pumping mode, and high-power and high-conversion-efficiency neodymium-doped three-level laser output is achieved. According to the invention, the conversion efficiency of the existing neodymium-doped three-level fiber laser is improved to a great extent.

The utility model discloses a distributed sound wave sensing system for multi-frequency pulse modulation, and relates to the technical field of distributed sound wave sensing. The system comprises a narrow linewidth laser, an optical fiber coupler, a polarization-maintaining optical isolator, an acousto-optic modulator, a polarization-maintaining delay optical fiber, an erbium-doped optical fiber amplifier, a polarization-maintaining dense wavelength division multiplexer, an optical fiber circulator, an optical fiber Bragg grating, a piezoelectric transducer, a polarization controller, a photoelectric balance detector, a data acquisition card, an arbitrary waveform generator and the like. According to the utility model, the multi-frequency delay ring is utilized to carry out multi-frequency modulation, the frequency number of light waves is increased along with the circulation times of the light waves in the delay ring, and under the condition that the utilization of a large-bandwidth electro-optical modulator is not increased, the flexible modulation of the frequency is realized by utilizing a low-bandwidth acousto-optical modulator without being influenced by carrier frequency and sidebands of each order; the low-bandwidth acousto-optic modulator is used for frequency modulation in the multi-frequency delay ring, and compared with an electro-optical modulation or multi-acousto-optic / multi-light source modulation scheme, the modulation cost is effectively saved.

The invention provides an optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor, which belongs to the technical field of optical fiber sensing and comprises a laser, a 2 * 1 optical fiber combiner, an optical fiber circulator, the Fabry-Perot sensor, a 1 * 2 optical fiber splitter, a photoelectric detector and an erbium-doped optical fiber amplifier. The laser generates a stable light source, and an optical signal enters the Fabry-Perot sensor through the 2 * 1 optical fiber combiner and the optical fiber circulator to generate interference fringes. Then, the 1 * 2 optical fiber beam splitter divides the optical signal into two parts, one part is transmitted to a photoelectric detector for signal detection, and the other part enters an erbium-doped optical fiber amplifier for amplification and is circulated back to the system through a feedback optical path. The optical path structure realizes multi-beam interference by introducing an optical path design of signal amplification and multiple feedback, the fineness of interference fringes is remarkably improved, and the sensitivity of the Fabry-Perot sensor in displacement and phase detection is further improved.

The invention relates to an on-chip integrated phase coding microwave signal generation system and method. The system comprises a laser, a polarization controller, a first chip end face coupler, a thin film lithium niobate optical chip, a second chip end face coupler, a signal generator, an optical fiber amplifier, an optical fiber isolator, a photoelectric detector and a microwave source. According to the invention, a first-order sideband of a phase modulation optical signal generated by the phase modulator is suppressed through filtering of the electrically tunable micro-ring resonator in the thin-film lithium niobate optical chip. The signal generator applies a periodically coded voltage signal to the electrically tunable micro-ring resonator, the position of a micro-ring harmonic peak is periodically controlled, and high and low levels of the voltage control signal correspond to the distance between two adjacent harmonic peaks of the electrically tunable micro-ring resonator and positive and negative first-order sidebands of the phase modulation optical signal. According to the invention, high-frequency and frequency-adjustable phase-coded microwave signals can be generated, and the system has the advantages of small voltage tuning range, flexible coding and simple system structure.

The invention relates to the technical field of optical fiber lasers, and provides an ultra-wideband tunable optical fiber communication light source based on gas stimulated Raman scattering. Comprising a 1 [mu] m wave band seed source, an electro-optical modulator, a signal generator, an optical fiber amplifier, a solid core-hollow core compact coupling device, an optical fiber end cap, a hollow core optical fiber, a miniature gas cavity, a lens and a dichroic mirror, and the tuning range of the methane gas 1 [mu] m wave band tunable pumping source at least covers 1024-1126 nm. The laser can be converted into communication wave band laser covering the whole S + C + L + U wave band, and benefited from the Raman characteristic of methane molecules, the output laser under single wavelength pumping has a corresponding narrow-linewidth single spectral line, no accompanying ASE noise amplification and the like, and secondary filtering is not needed for selection; and meanwhile, the use of the hollow-core optical fiber ensures that the output laser is only a single mode, and high beam quality can be ensured without other operations.

The invention discloses a cylindrical vector optical fiber amplifier based on a rotary conical optical fiber. The cylindrical vector optical fiber amplifier comprises a cylindrical vector optical seed source; an isolator, a beam combiner, a rotary conical optical fiber and a cladding light pumping stripper are sequentially arranged in the column vector light transmission direction of the column vector light seed source, and a first pumping source is further welded to the input end of the beam combiner. The rotary conical optical fiber is adopted as the gain optical fiber, the stability of light polarization can be effectively kept in the cylindrical vector light amplification process, the sensitivity to temperature is reduced, and meanwhile the mode purity is improved.

The invention provides an optical time domain reflection system and demodulation method based on reference optical fiber phase compensation, and the system comprises a signal generator, a distributed feedback laser, a semiconductor optical fiber amplifier, a first amplifier, a circulator, a second amplifier, a wave filter, a detector, a reference optical fiber, and an optical fiber to be measured. A continuous laser signal of the distributed feedback laser is converted into a pulse optical signal through the semiconductor optical fiber amplifier and is amplified through the first amplifier; the amplified pulse optical signal enters a second port of the circulator through a first port of the circulator and sequentially enters a reference optical fiber and an optical fiber to be detected, and an optical fiber Rayleigh scattering signal enters a third port of the circulator through the second port and sequentially passes through a second amplifier and a filter to be detected; and the detector obtains Rayleigh interference spectrums of the reference optical fiber and the optical fiber to be detected according to the filtered scattering signals. According to the invention, the technical problem of insufficient measurement precision caused by the influence of light source phase drift on the traditional phase-OTDR system can be solved.

The invention belongs to the technical field of microwave photons and optical communication, particularly relates to a tunable narrow-linewidth microwave photonic oscillator based on forward Brillouin scattering, and solves the technical problems that an existing microwave photon generation method is complex in structure and poor in tunability, and linewidth cannot meet requirements. The erbium-doped optical fiber amplifier is connected to a first optical fiber coupler through a filter, two output ends of the first optical fiber coupler are respectively connected to a third optical fiber coupler and a second optical fiber coupler, and two output ends of the second optical fiber coupler are respectively connected to a spectrograph and are sequentially connected with a photoelectric detector and a spectrum analyzer; two output ends of the third optical fiber coupler are respectively connected to an input end c of a fourth optical fiber coupler through a first polarization controller and a first single-mode optical fiber and connected to an input end b of the fourth optical fiber coupler through a second polarization controller and a second single-mode optical fiber in sequence; and the fourth optical fiber coupler is connected to an erbium-doped optical fiber amplifier through a third polarization controller.

The invention discloses an optical time domain reflectometer based on ring structure modulation and a working method thereof, and relates to the technical field of optics. The optical time domain reflectometer comprises a laser, an optical fiber coupler, a semiconductor optical amplifier, an acoustic optical modulator, an optical isolator, a delay optical fiber, an erbium-doped optical fiber amplifier, a dense wavelength division multiplexer, a circulator, a Raman laser, piezoelectric ceramics, an arbitrary function generator, an arbitrary waveform generator, a polarization controller, a photoelectric balance detector, a data acquisition card, a computer and the like. Multi-frequency modulation is carried out based on an annular structure, the multi-frequency modulation range is only limited by the bandwidth of a detector and the sampling rate of an acquisition card, a pulse sequence is generated through modulation of the optical annular structure, dependence on the bandwidth performance of a microwave signal source and a modulator is reduced, and the bandwidth is improved; and by injecting the Raman light, the sensing distance is also increased, the equipment cost is effectively controlled, and meanwhile, a new scheme is provided for time sequence pulse sequence modulation.

The invention is suitable for the field of optical fiber sensing technology and power equipment detection, and provides an RC algorithm-assisted optical fiber partial discharge detection system and a high-speed signal inquiry method. The system comprises a mode-locked laser, a dispersion compensation optical fiber, an erbium-doped optical fiber amplifier, a first optical fiber coupler, a single-mode optical fiber, an adjustable optical fiber delay line, a second optical fiber coupler, a sensing unit, a photoelectric detector, an oscilloscope and a PC terminal, and the sensing unit is a micro-nano optical fiber coupler and comprises an input end, an output end and a ZnO composite graphene coating area. The PC terminal inquires a signal through an RC algorithm, the RC algorithm is composed of an input layer, a storage layer and an output layer, the sensing method is that the wavelength of an ultra-short optical pulse is mapped to time, a non-equilibrium dispersion MZI structure carries out chirp frequency coding on the broadened optical pulse, the RC algorithm optimizes a data processing method, and the inquiry speed is further improved by five times. In addition, through combination of mapping from wavelength to time, chirp frequency coding and an RC algorithm, high sensing system stability and high demodulation speed are realized.

The invention relates to the technical field of optical fiber communication and sensing, in particular to an indoor positioning system based on distributed ultrasonic sensing, which is characterized in that a detection pulse is modulated to light for emission, the detection pulse is amplified by an erbium-doped optical fiber amplifier and then is sent to a to-be-detected optical fiber through an optical circulator; and the received Rayleigh backscattering signal is coupled with the local oscillator after being amplified, and finally demodulation processing is carried out. According to the invention, limitation of sensing distance and sensing frequency can be broken through in a traditional DAS system, effective sampling and recovery of high-frequency signals are realized, a distributed ultrasonic sensing technology is applied to indoor positioning, and a new application direction is developed for the field of real-time detection.

The invention provides a digital heterodyne interference demodulation technology based on a chaotic signal enhancement array. An all-optical random code optical path module, a heterodyne interference optical path module, a sensing array module and a data processing module are included. The all-optical random code optical path module is composed of a polarization controller (PC), an electro-optical modulator (EOM), an erbium-doped optical fiber amplifier (EDFA), a highly nonlinear optical fiber (HNLF), a band-pass filter (BPF) and a first optical fiber coupler which are sequentially connected through optical fibers, wherein EOM electric control signals are connected through a chaotic entropy source. The heterodyne interference light path module is composed of a single-frequency laser, a second optical fiber coupler, an upper interference arm, a lower interference arm, an optical fiber circulator, an acoustic optical modulator (AOM) and a third optical fiber coupler; the sensor array module is composed of a plurality of optical fiber weak reflection points (FWR) and optical fiber sensors connected between the FWR and the FWR. The data processing module is composed of a photoelectric detector (PD), a plurality of delay units, a plurality of multipliers, a phase demodulator and a computer. The method has the advantages that on the basis of a traditional digital heterodyne interference demodulation method, a chaotic entropy source all-optical true random code is introduced to serve as a digital modulation signal, and the spatial resolution of a demodulation system can be improved to the magnitude of cm as high as 10 Gb / s; the infinite code length effect of the all-optical random code in the chaotic signal enhanced heterodyne interference breaks through the signal-to-noise ratio limit of the traditional digital enhanced heterodyne interference method.

The invention relates to the technical field of optical fiber lasers, and proposes an ultra-wideband tunable optical fiber communication light source based on gas stimulated Raman scattering, comprising a 1μm band seed source, an electro-optic modulator, a signal generator, an optical fiber amplifier, a solid-hollow compact coupling device, an optical fiber end cap, a hollow-core optical fiber, a micro gas cavity, a lens, a dichroic mirror, and a methane gas 1μm band tunable pump source. The tuning range covers at least 1024nm-1126nm. Based on the stimulated Raman scattering effect of methane gas, it can be converted into a communication band laser covering the entire S+C+L+U band. Thanks to the Raman characteristics of methane molecules, the output laser has a corresponding narrow line width single spectral line under single wavelength pumping, without accompanying ASE noise amplification, etc., and does not need to be selected through secondary filtering. At the same time, the use of the hollow-core optical fiber ensures that the output laser is only single-mode, and high beam quality can be guaranteed without other operations.

The application relates to a method of an electric field sensor based on an optoelectronic oscillator, belonging to the field of optical devices and optical fiber sensing. The device comprises a laser source, a polarization controller, a phase modulator, a fiber Bragg grating with an acrylate glue cavity, a stacked piezoelectric ceramic, an electric field generator, an erbium-doped fiber amplifier, a photodetector, a power divider and an electric amplifier. The stacked piezoelectric ceramic is combined with the fiber Bragg grating with the acrylate glue cavity as a sensing head, the wavelength change of the fiber Bragg grating with the acrylate glue cavity caused by the piezoelectric effect is mapped to the frequency change of the microwave signal generated by the optoelectronic oscillator, and the electric field change value can be obtained by monitoring the microwave signal of the optoelectronic oscillator. In the loop of the optoelectronic oscillator, the electric spectrum analysis technology is used for demodulation, and high-speed and high-resolution electric field measurement can be obtained. The method has the advantages of simple structure, high measurement sensitivity and easy practicability.

A device comprises a quantum random number generator, and further comprises following device parts: a first SPAD diode, a second SPAD diode, an optical fiber which optically couples the first SPAD diode and the second SPAD diode to one another, an amplifier and / or filter, an analog-to-digital converter, a comparator, a time-to-digital converter, and an entropy extraction device converting output values of the time-to-digital converter into first and second values and generates random bits therefrom.

The present invention is applicable to the field of pulsed laser technology and provides a pulsed laser modulation system. The system includes: a laser seed source for emitting a laser signal; a polarization-maintaining circulator having an incident end, a first emission end, and a second emission end, with the laser seed source and the incident end of the polarization-maintaining circulator being located on the same optical path; a fiber preamplifier and a laser pulse stretcher, with the first emission end, the fiber preamplifier, and the laser pulse stretcher being sequentially arranged on the same optical path; and an acousto-optic modulator and a fiber amplifier, with the second emission end, the acousto-optic modulator, and the fiber amplifier being sequentially arranged on the same optical path. The present invention proposes a design scheme for a pulsed laser modulation device that integrates stretching, preamplification, and frequency selection. By using this scheme, a low-repetition-rate pulsed laser output with a compact structure, good stability, and a high signal-to-noise ratio can be achieved.

The invention provides a coherent optical time domain reflection sensing device and a method thereof, and relates to the technical field of distributed optical fiber acoustic wave detection. The device comprises a light source, a 1 * 2 coupler, a control and signal processing unit, an arbitrary waveform generator, a double-path parallel Mach-Zehnder electro-optical modulator, a reference arm optical fiber, an erbium-doped optical fiber amplifier, an optical filter, a circulator, a sensing optical fiber, a 90-degree optical mixer, a photoelectric detector and a data acquisition card. A detection light sequence containing positive and negative frequency shift light pulse sequences is injected into a sensing optical fiber, returned signal light which carries light phase information of each detection point and has superposed frequencies is mixed with local reference light, signal separation is achieved after the signal light is multiplied by complex factors corresponding to each frequency shift pulse and integration of a periodic integral multiple window is carried out, and the detection point light phase information is obtained. And optical phase information demodulation is carried out, and then fusion of detection results of optical signals of various frequencies is carried out, so that high-sampling-rate sensing of acoustic vibration is realized.

The invention relates to the technical field of optical functional materials, in particular to transparent biphase glass ceramics for rare earth induction associated crystallization, a preparation method and application. According to the preparation method, SiO2, ZnF2 and KF are taken as matrix glass raw materials, rare earth and transition metal ions are taken as optical activity doping ions, precursor glass is prepared through melting, and the transparent biphase glass ceramic is obtained through annealing, heat treatment and associated devitrification. The transparent dual-phase glass ceramic prepared by the invention contains KYb3F10 nanocrystals and KZnF3 nanocrystals, and compared with glass ceramic containing K2SiF6 and ZnF2 nanocrystals, the bandwidth luminous efficiency of the transparent dual-phase glass ceramic is improved by more than 100 times; the method provides good reference for preparation of two-phase glass ceramics of more different systems, and has important application prospects in the fields of broadband optical fiber amplifiers and tunable optical fiber lasers.

The invention provides a method for generating high-peak-power intermediate infrared ultrafast laser based on pulse / continuous wave system parametric conversion. Comprising a pumping source 1 which is used for providing mu J-level energy and 10ps-level pulse width near-infrared pulse laser. Pump light is focused and subjected to path adjustment through the high reflectors 2, 3 and 5 and the lens 4, the pump light and signal light are combined through the dichroscope 15, and optical parametric conversion is carried out through the nonlinear crystal 16. Comprising a signal source 6 which is used for providing near-infrared continuous waves, signal light power and polarization direction are accurately regulated and controlled through an erbium-doped optical fiber amplifier 7, an attenuator 8, a polarization maintaining optical fiber circulator 9, a collimator 10 and a half-wave plate 11, and focusing and path adjustment are carried out through a lens 12 and high reflectors 13 and 14. Comprising a dichroscope 17 and long-pass filters 18 and 19 and is used for filtering out mid-infrared laser.

The invention discloses an optical fiber collimator, isolator and circulator in an orbital angular momentum mode, and belongs to the field of optoelectronic communication devices. Based on a special optical fiber collimator design scheme, the OAM optical fiber collimator which is simple in structure and excellent in performance is realized. On the basis of an OAM optical fiber collimator, an isolation core and an annular core are combined, and an OAM optical fiber isolator and an OAM optical fiber circulator which are low in cost, low in processing complexity, small in occupied size and excellent in performance are respectively realized through a special packaging process. The isolator and the circulator have the characteristics of low insertion loss, high isolation degree, high quality of a transmitted OAM mode and the like. The OAM optical fiber collimator, isolator and circulator realized by the invention can replace free space optical devices with consistent functions in systems such as an OAM mode optical fiber communication system, an OAM optical fiber amplifier and the like. The cost of the mode division multiplexing optical fiber communication system based on the OAM mode is reduced, the flexibility of the system is improved, and the method has important significance for promoting the practicability and miniaturization of the optical fiber communication system.

The invention provides a pure solid-state scanning type absolute ranging system and a target detection method thereof. The pure solid-state scanning type absolute ranging system comprises a light source, an optical fiber amplifier, a spatial light polarization controller, a pure solid-state light beam scanning and interference module, a spectrum acquisition module and a control and calculation module, the pure solid-state light beam scanning and interference module is based on the wavefront regulation and control principle, dynamic modulation of incident light wavefront is achieved by loading a two-dimensional programmable grating phase on a spatial light modulator, and therefore light beams are controlled to complete pure solid-state scanning in space according to a set path. When a scanning light beam irradiates a target pyramid, a strong return light signal is generated, the spectrum acquisition module captures two-dimensional spectrum resolution and two-dimensional spectrum image imaging of an interference signal, and the control and calculation module performs high-precision distance calculation of a target absolute distance through phase extraction and interference fringe analysis based on a dispersion interference principle.

According to the laser detection system for detecting the health condition of the underground comprehensive pipe gallery provided by the invention, the narrow-linewidth high-stable-frequency laser is combined with a balance detection technology, so that the capability of detecting weak ultrasonic signals of a pipe wall is remarkably improved, and environmental common-mode noise is effectively inhibited; the attenuation problem of laser in long-distance transmission is overcome by using an erbium-doped optical fiber amplifier light amplification technology, and continuous health monitoring of a several-kilometer-level pipe gallery is realized; through cooperative work of the 180-degree mixer and the signal acquisition system, high-precision analysis of phase change of reflected light is realized, and the position of a damage or disturbance source can be accurately positioned without contact with a pipe wall; furthermore, through feature analysis of the ultrasonic frequency spectrum, the system can sensitively capture early hidden defects such as internal cracks and corrosion of the pipe gallery structure and threats such as external construction excavation, and reliable data support is provided for health assessment and risk early warning of the pipe gallery structure.

A photonic crystal fiber (10) comprises: a core region (11) having a rare earth element added thereto; and a cladding region (12) including a plurality of refractive index reduction parts (13) provided around the core region (11). Each of the refractive index reduction parts (13) is formed of a glass rod having a refractive index lower than that of the cladding region (11) or a hole. The mode field diameter of the basic mode at a wavelength of 1.55 µm is not less than 16.4 µm.

The invention belongs to the technical field of optical communication, and discloses a few-mode erbium-doped optical fiber amplifier, an optical signal amplification method and an optical communication system. The few-mode erbium-doped optical fiber amplifier comprises a multi-channel adjustable light source, a first mode multiplexer, a first few-mode wavelength division multiplexer, a first pumping source, a first few-mode circulator, a few-mode erbium-doped optical fiber, a second few-mode circulator, a second few-mode wavelength division multiplexer, a pumping mode selector, a second pumping source and a second mode multiplexer. According to the invention, multi-mode high-gain and low-gain differences can be obtained at the same time. Besides, the refractive indexes of multiple layers of fiber core structures contained in the few-mode erbium-doped optical fiber in the few-mode erbium-doped optical fiber amplifier are different, the doping concentrations of front and rear sections for light amplification are also different, low-mode noise can be realized, and the few-mode erbium-doped optical fiber amplifier also supports simultaneous amplification of multiple mode signals.

The invention provides a gain flattening filter, an optical fiber amplifier and a wavelength division multiplexing communication system, relates to the technical field of optical communication, and is used for realizing gain flattening filtering. The gain flattening filter comprises N first optical fibers in a first fiber core mode, N second optical fibers in the first fiber core mode, M second optical fibers in the second fiber core mode and N third optical fibers in the first fiber core mode, the second optical fiber comprises a plurality of cascaded fiber bragg gratings, and the plurality of cascaded fiber bragg gratings are used for coupling at least one first fiber core mode in the N first fiber core modes to at least one second fiber core mode in the M second fiber core modes, the mode order of at least one second fiber core mode in the M second fiber core modes is higher than the mode order of at least one first fiber core mode in the N first fiber core modes; the first optical fiber, the second optical fiber and the third optical fiber are sequentially connected. According to the scheme, the gain flattening of the optical signal can be realized through the gain flattening filter with a simple structure.

This invention discloses a high-efficiency nonlinear optical frequency converter based on high-power continuous optical transmission using quartz micro / nano fiber, comprising a wavelength-tunable laser, an optical fiber amplifier, a quartz micro / nano fiber, a sealed cavity, and an optical fiber low-pass filter; the quartz micro / nano fiber includes a first untapered portion, a second untapered portion, a first tapered transition region, a second tapered transition region, and a waist region, transmitting an optical field TE. 01 The mode cutoff method precisely controls the waist diameter of micro / nano fiber and accurately tunes the input light wavelength. The nonlinear light frequency conversion process excited by high-power continuous light transmitted in quartz micro / nano fiber satisfies perfect phase matching. The fundamental mode of the input light and the higher-order mode fields of the harmonic signal light have high overlap in the waveguide mode, which can efficiently generate continuous second and third harmonic signal light. The device has high stability, high efficiency, and low cost, and can be applied in fiber lasers, all-optical signal processing, fiber optic sensing and other fields.