We perform shape optimization of anti-resonance fiber (ARF) structures using a particle swarm optimization algorithm, achieving the lowest confinement loss of 2.4347×10−5 dB/m at 1.07 μm based on a single-layer tubing structure. Different from the existing design approaches that focus on size optimization and stacking of tubes, this research employs algorithm-driven point iteration and reconstruction to explore new structures for ARFs. This approach enhances the design flexibility and provides a new perspective for the design of ARFs. Furthermore, it was discovered that adding an additional tubing can effectively control the bending loss. This method enables the optimization of tubing shapes that are difficult to achieve through parameter analysis and supports local optimization of tubing structures. This method is capable of discovering higher-performance ARF structures based on existing classical designs, which is a significant inspiration for the design of non-uniform waveguides.
The photonic generation of high-accuracy triangular waveforms with a tunable duty cycle based on a dual-wavelength in-phase/quadrature-phase (I/Q) modulation is proposed and analyzed. By adjusting the modulation index, the phase shift caused by the electric phase shifter and the bias voltage of the modulator, the optical signals of the upper and lower paths can be superimposed and then passed through the bandwidth limited photodetector to obtain a triangular wave, form with a tunable duty cycle ranging from 0.1≤σ≤0.9. High-order harmonic Fourier series components are used to construct the high-accuracy function waveform. It is found that the waveform rms error can be greatly decreased (around two-time performance improvement with duty cycle 0.1≤σ≤0.9). To evaluate the feasibility of our proposal, the effects of modulation index drift, bias voltage drift, and phase shift drift on the obtained waveform are also discussed.
An asymmetric waveform signal generation scheme based on dual polarization multiplexing-quadrature phase shift keying (PM-QPSK) modulator is proposed and analyzed. The key technique to generate periodic asymmetrical function waveform is how to control the amplitude and phase of the Fourier series of the target waveform simultaneously. In order to achieve this function in this proposal, a continuous-wave laser is modulated by radio-frequency signals with various phases, using a PM-QPSK modulator. The orthogonal sine and cosine harmonic signals are output through a polarization beam combiner. A polarizer is then employed to balance the power of these two orthogonal signals. By properly adjusting the variables, both the amplitude and phase of the Fourier series of the target waveform can be simultaneously set. When the root mean square error is <5%, a half duty cycle ramp wave signal with adjustable slope (20%≤δ≤80%) can be obtained. In addition, the influence of variable drift on the target waveform is analyzed in detail.
The photonic neural processing unit (PNPU) demonstrates ultrahigh inference speed with low energy consumption, and it has become a promising hardware artificial intelligence (AI) accelerator. However, the nonidealities of the photonic device and the peripheral circuit make the practical application much more complex. Rather than optimizing the photonic device, the architecture, and the algorithm individually, a joint device-architecture-algorithm codesign method is proposed to improve the accuracy, efficiency and robustness of the PNPU. First, a full-flow simulator for the PNPU is developed from the back end simulator to the high-level training framework; Second, the full system architecture and the complete photonic chip design enable the simulator to closely model the real system; Third, the nonidealities of the photonic chip are evaluated for the PNPU design. The average test accuracy exceeds 98%, and the computing power exceeds 100TOPS.
A coupled multi-core fiber (CMCF) with selective erbium ions doping is proposed. Due to the small gap between the cores, four signal supermodes are supported. Based on the overlap integral between the signal and pump modes, the concentration proportion of the central core to outer cores is modified. At a concentration ratio of 0.93, the signal gains are higher than 20 dB and at the same time, a small differential modal gain (DMG) of 0.17 dB is obtained.
Polarization beam splitter is an important part of integrated optical system to overcome the strong polarization dependence of silicon nanodevices, and has broad application prospects in optical fiber communication and polarization imaging. In this paper, a polarization beam splitter of metalens based on the fiber end face is designed. Through the planar light field control ability of metalens and the coordinated regulation of the geometric phase and propagation phase, the device adjusts the medium duty cycle in the meta-unit and the rotation angle of the nanoantenna to realize the polarization beam splitting and focusing simultaneously. In order to simplify the manufacturing process and achieve high focusing efficiency even further, Si with high transmittance in the near infrared band is selected as the nanoantenna, and SiO2 is used as the substrate. Since the substrate used the same material with fiber cladding, compared with the traditional polarization beam splitter, the structure can directly etch the nanofins periodically on the fiber end face, which is convenient for optical system integration. Theoretical design and numerical simulation results show that any polarized light in fiber cladding can realize polarization focusing through fiber end face.
A novel square-assisted ring-core fiber characterized by a square region of low refractive index in the core was proposed. This fiber structure allows for spatial mode modulation. When the subscript m of the LPmn modes supported by the fiber is an even number, the spatial modes of the LPmn modes are degenerately separated. This fiber supports 15 modes over the entire C-band. The effective refractive index difference (Δneff) between spatial modes at 1550nm is greater than 1.18×10-4. At the same time, the Δneff between all adjacent modes is in the range of (1.13~13.52)×10-4. The polarization separation level of each mode is below 7.12×10-6, which is two orders of magnitude lower than the level of degenerate separation of spatial modes. Numerical simulations show that the dispersion values range from -16 ps/nm/km to 15 ps/nm/km for 15 modes over the entire C-band. This fiber has a good tolerance for process error, the optical fiber processing requirements can be met by using the existing optical fiber preparation technology.
In this paper, we propose a longitudinal cascaded few-mode erbium-doped fiber amplifier (FM-EDFA) by particle swarm optimization (PSO). Triple-cascaded few-mode erbium-doped fibers (FM-EDFs) are applied longitudinally, which have the same refractive index distributions and different erbium-ion doping profiles. Each fiber is uniformly doped in different regions. The input power of the pump and signal are settled. The length and order of three pieces of FM-EDFs are optimized by PSO, which helps to minimize the differential modal gain (DMG) and maximize the modal gain at the output port. An ultra-low DMG of 0.007 dB and minimum modal gain (MMG) of about 24.890 dB are obtained at the wavelength of 1550 nm.
Few-mode erbium-doped fiber amplifier (FM-EDFA) is a key element to realize signal gain compensation in a longdistance mode division multiplexing (MDM) system. The differential modal gain (DMG) between modes directly affects the communication quality of the MDM system. In this paper, the particle swarm optimization (PSO) method is applied to design the erbium ion doping profile for high gain and low DMG simultaneously. By adjusting the doping radius and concentration concurrently, both high signal gains and low DMG can be obtained. In the conditions of the core pump and cladding pump respectively, the erbium ion with a multi-layered doping profile is automatically optimized by the PSO for a few-mode erbium-doped fiber (FM-EDF). Results show that as a three-layered ion adjustment, the gain is higher than 20 dB and DMG is lower than 0.15 dB in a four-mode step-index fiber. PSO is easy to implement and simple to operate. Compared with the other intelligent methods, such as the genetic algorithm or gradient descent optimization algorithm, PSO has no "crossover" and "mutation". The optimization time is greatly reduced. The PSO-based fiber design provides new guidance for the improvement of fiber gain equalization.
A novel optical fiber sensor based on weak coupling twin-core fiber (TCF) is proposed and experimentally demonstrated. The sensing structure consists of two single mode fibers (SMF) and fabricated by program controlled tapering the spliced region between the first SMF and a segment of TCF. During this period the light power was gradually transferred from the SMF into the cladding mode near the waist zone, after the waist zone, the optical power was gradually concentrated from the cladding mode into the cores mode, which could affect the extinction ratio of the interference peaks in the transmission spectrum. In order to obtain better interference spectrum, we adjusted the fusion structure of the tail fiber and the TCF, and the cross sections of the optical fibers are dislocated to a certain extent, so that the interference process of the beam changes. In the process of adjusting the structure, we observed the spectral changes in the spectrometer at the same time until the best interference spectrum appeared, and then we completed the fusion. The interference between different modes can be affected by changes in the external environment, like refractive index (RI) and strain, which also dictates the wavelength shift of the transmission spectrum. In the experiment, we have studied the sensing response of the optical fiber sensor to the RI and strain, and the sensing sensitivity is 131.1nm/RIU and 1.26x10-3 dB/με respectively. All sensors fabricated in this paper show good linearity in terms of the spectral wavelength shift.
The three-dimensional refractive index reconstruction (3D-RID) of optical fiber with longitudinal refractive index distribution changing, such as helical fibers and fusion splicing fibers, is necessary for subsequent transmission performance research. However, the longitudinal RID is composed by the superposition of multiple cross-sectional RIDs, which often requires huge amounts of data for calculation. The analytical methods and numerical methods are usually used for the transverse section reconstruction, in which the former needs the complete sinogram and slowly varying approximation for the fiber and the latter is in contrast. Therefore, we present the reconstruction of the 3D-RID of the double-core helical fiber and fusion splicing between single-mode fiber and multi-mode fiber by a numerical method, the total variation (TV) method. The experimental results show that the result of the TV method under the sparse angle (30 rotations) is similar to the result of the refractive index analyzer (IFA) under the complete sinogram (180 rotations). The superiority of TV not only reduces the time spent on mechanical rotation, but also compresses the sinogram for 3D-RID calculation.
In this paper, a polarization splitting square fiber is designed to make up for some defects of Dtype fiber in common fiber devices. Compared with D-type optical fiber, square-type optical fiber can be directly drawn by processing the optical fiber preform. Thereby eliminating the need to process the micron-level optical fiber, while maintain the original core-cladding structure. Most of the optical field energy is still limited to the core, which can greatly reduce the insertion loss of the devices. Using the finite element method, the half-length core distance (30 to 90 microns), radius of arc (1 to 9 microns), numerical aperture (0.18 to 0.24) and isolation thickness (0.1 to 2 microns) of the square fiber are optimized. Theoretical calculation results show that under the optimal parameters, the mode loss of our designed square fiber under X polarization is 0.0179dB/mm. And under Y polarization, the mode loss is 0.0454dB/mm. In addition, the mode mismatch loss is 7.506%. This value will reduce the mode loss by 100 times compared with D-type fiber and make full use of the advantages of good coupling to the allfiber system.
A magnetic field sensor based on multilongitudinal mode fiber laser (MMFL) is proposed and demonstrated. The MMFL contains two fiber Bragg gratings (FBGs), one of which is fixed on a magnetostrictive alloy (MA) and works as the sensing FBG. With a magnetic field applied, the MA stretches and transforms the magnetic field into strain due to the magnetostrictive effect of the MA. In this case, the wavelength of sensing FBG and the length of the MMFL cavity both shift with the magnetic field, ultimately resulting in the frequency shift of the longitudinal modes of the MMFL. By sending these longitudinal modes of the MMFL to a photodetector, the longitudinal mode beat signals (LMBSs) are generated, whose frequency would shift with the magnetic field. We experimentally verify that the magnetic field can be demodulated via the LMBS and demonstrate a sensitivity of -47 kHz/mT when selecting an LMBS at 1.608 GHz for demodulation. We also demodulate in optical domain by means of tracking the wavelength of the sensing FBG, a sensitivity of 1.5 pm/mT is achieved. Compared with the conventional fiber optic magnetic field sensors demodulated in the optical domain, radio-frequency demodulation is used in our work, which enhances the sensitivity and resolution. It also provides a potential way for high-speed demodulation. Moreover, the sensing head is a conventional FBG without any elaborate transducer, which enables the features of simple structure, easy fabrication, and compact size.
We experimentally demonstrate an all-fiber Er/Yb co-doped fiber (EYDF) amplifier with a low differential modal gain of 1.6 dB (for LP01, LP11a and LP11b signal modes at 1535 nm, using a 980 nm multi-mode pump). The pump power is coupled into the fiber core by side pumping, which is used a piece of double-clad EYDF and helix-wounded tapering operation. The gain of all three modes is higher than 16 dB. The all-fiber amplifier scheme eliminates the spatial lens in the traditional core-pumping configuration and shows natural ability in integration with the transmission fiber links due to the stable fiber interconnect. Thus, we believe that the all-fiber few-mode amplifier should be probably the highly practical solution in the long-haul mode-division multiplexed transmission.
Optical fiber sensors based on Michelson interferometers (MIs) have potential applications in condition monitoring and measurement systems. We propose an optoelectronic oscillator (OEO)-based interrogation system with MI. The interrogation system has a high interrogation resolution and large measurement scale. The sinusoidal nature of the MI spectrum results in a single-passband microwave photonic filter (MPF), whose central frequency is determined by the dispersion parameters of the employed dispersive element and the free spectral range (FSR) of the MI. When the external environmental or physical factors change, the FSR of the MI varies and leads to the frequency shift o f the MPF, ultimately contributing to the frequency shift of the OEO-generated signal. We verify that the variation of temperature and strain can be demodulated by tracking the frequency of the OEO. We also employ an infinite impulse response (IIR)- MPF based on a fiber ring resonator (FRR) for fine oscillation mode selection and evaluate the interrogation resolution and the measurement accuracy of the interrogation system. Different from conventional interrogation systems tracking the wavelength shift of the MI spectrum, our scheme demodulates the sensing information in the electrical domain utilizing an OEO, providing a potential way to implement high-resolution sensing for conventional optical fiber sensors. Moreover, thanks to the wavelength-to-frequency mapping and the wide frequency tunable range of the OEO, our scheme would support large-scale sensing because it can avoid the overlap of MI periodic spectrum in wavelength demodulation.
In this paper, we develop a novel optical fiber temperature sensor based on Fabry-Perot interferometer (FPI). The structure of the sensor includes a spliced seven-core fiber (SCF) and a piece of quartz glass capillary. During fabrication, we use the fusion splicer to move two SCFs into glass capillaries gradually. The length of the SCF is about 4 cm. In the cavity structure, the end faces of two SCFs are parallel to each other. The light transmitted in the optical fibers will be reflected twice at the two end faces. We can use the relationship between the length of the cavity and the power change of the reflected light to realize the sensing measurement of temperature parameters. We have gradually tested seven groups of reflective spectra as the temperature increases from 20°C to 50°C. The free spectral range (FSR) of the sensor has changed, also the beam propagation in the air cavity will cause loss, and the power of the reflection spectrum will change with the cavity length. The values of FSR and extinction ratio (ER) vary nonlinearly with temperature, and through data analysis, the equation describing the sensor was obtained, like the sensitivity function of FSR is y=107.7exp(-x/12.36)+5.35, the sensitivity function of ER is y=39.6exp(- x/15.75)+3.02, and the correlation coefficients of the two non-linear fitting are 0.991 and 0.998, respectively.
In this paper, a novel optical fiber pressure sensor based on duralumin grooved plate was experimentally demonstrated. The sensing structure consists of two duralumin plates, and uniform grooves were carved on the plates. The fiber was vertically placed between the plate grooves. Under different pressure conditions, there will be different micro-bending of the optical fiber, which will result in the modes conversion of the fiber. Some fiber modes become radiative modes, which will lead to the loss of transmission power in the fiber. We can make use of this special effect to fabricate optical fiber pressure sensor. We first tested the single mode fiber (SMF). By repeat applied cyclic pressure on the sensing structure, we recorded the changes of light power and obtained the sensitivity of 1.11 mW/kgf and 1.4 mW/kgf at 1550 nm and 1310 nm, respectively. In addition, we analyzed the spectral changes in the fiber and experimentally analyzed the temperature characteristics of the sensing structure, found that the sensor has good temperature stability. Moreover, because of its simple fabrication and highly adjustable property, this sensor is suitable for engineering application. We also use this duralumin grooved plate to test the few mode fiber (FMF), and found that due to a variety of core modes coupling in the fiber, the pressure sensing characteristics are not good. However, by analyzing its spectrum, we found that this device can achieve some special mode conversion and has a good application prospect.
A side-hole fiber surface plasmon resonance (SPR) sensor is proposed and numerically analyzed to solve the cross-sensitivity problem of temperature and magnetic field. In the side-hole fiber SPR sensor, the side-holes I and II are filled with magnetic fluid and a mixture of ethanol–glycerin, respectively, resulting in a loss spectrum with two channels. Each channel has different sensing characteristics. When the external magnetic field intensity increases, the magnetic field sensitivities of channels I and II are 1.098 and −0.018 nm / Oe, respectively. Moreover, with the increasing temperature, the temperature sensitivities of channels I and II are −5.909 and −4.211 nm / ° C, respectively. Therefore, the variations of magnetic field intensity and temperature can be simultaneously measured by detecting resonant wavelengths of channels I and II of side-hole fiber SPR effects, resulting in the influence of temperature in a side-hole fiber SPR magnetic field sensor being eliminated. The side-hole fiber SPR sensor has obvious advantages of compact structure and high sensitivity, and it also has solved the problem of liquid storage glassware to compact the structure of the fiber SPR sensor further.
KEYWORDS: Extremely high frequency, Modulation, Radio optics, Single mode fibers, Eye, Fiber Bragg gratings, Modulators, Radio over Fiber, Tunable lasers, Light sources
We propose and demonstrate a radio-over-fiber system to generate an optical millimeter wave (MMW) and realize wavelength reuse for an uplink connection. A tunable optical comb generated by a single Fabry–Perot laser serves as the optical source. The central carrier is separated by an optical circulator cascaded with a fiber Bragg grating. For the downlink, the unmodulated central carrier is coupled with one subcarrier, which has been modulated with 2.5-Gb/s data. Then, different MMWs can be generated by choosing different subcarriers. While for the uplink, the same central carrier is reused for an uplink connection with 1.25-Gb/s data. In the scheme, a 60-GHz MMW is obtained and the bidirectional data are simultaneously transmitted over 60-km transmission with <0.5-dB power penalty. This system shows a simple cost-efficient configuration and good performance over long-distance delivery.
We propose and analyze a frequency 32-tupling scheme which is capable of generating millimeter and terahertz waves without being affected by the phase noise difference between two incoherent sources. In our work, the process of the optical sidebands’ phase noise change is theoretically analyzed and confirmed by simulations. In addition, the system performance in terms of linewidth, tunability, and stability is also investigated.
KEYWORDS: Terahertz radiation, Phase modulation, Radio optics, Modulators, Frequency combs, Radio over Fiber, Modulation, Lithium, Continuous wave operation, Signal generators
We propose a prototype for frequency-reconfigurable terahertz (THz) wireless transmission using an optical comb based on radio-over-fiber technology. In the proposal, an electro-absorption modulator (EAM) followed by a phase modulator and an intensity modulator are used to generate a flat optical comb with a tunable frequency spacing. Then, a different THz signal can be generated by photo-mixing of optical two-tone signals from the comb lines. In the scheme, we obtain 46 comb lines within a 1-dB power deviation with an interval of about 10 GHz, and a THz up to 440 GHz is obtained. Moreover, a much higher bandwidth can be easily reached by adjusting the driving signal of the EAM. The feasibility and tunability of the proposed scheme are confirmed by the simulations. This method shows a simple cost-efficient configuration and good performance over long-distance delivery.
KEYWORDS: Modulation, Fiber Bragg gratings, Phase shift keying, Radio optics, Radio over Fiber, Phase shifts, Single sideband modulation, Photodiodes, Optical amplifiers, Single mode fibers
We propose a prototype for single-sideband (SSB) transmission based radio-over-fiber system by employing a phase-shifted fiber Bragg grating. The grating has different transmission spectrum characteristics with different phase-shift magnitudes. Then, it is used in a millimeter-wave (mm-wave) SSB modulation scheme. In the scheme, only one PS-FBG is used to realize the following functions: first, the conversion from optical dual-sideband to optical single-sideband with carrier reduction modulation can be easily achieved and second, the optical carrier-to-sideband ratio (OCSR) can be eliminated completely. In our work, the OCSR can be reduced from 33.95 dB to the optimum 0 dB and a 60 GHz mm-wave can be detected after photodiode.
A simple and general approach for implementing all-fiber high-order optical temporal differentiator based on twin-core fiber (TCF) is presented and demonstrated. Specifically, the core 2 (or core 1) of the TCF should be cut in N sections with the same length for achieving N ’th-order optical temporal differentiator, which can be considered to consist of N cascaded first-order optical temporal differentiators based on TCF. Our simulations show that the proposed approach can provide optical operation bandwidths in the several THz regime, which is capable of accurately processing time features as short as subpicoseconds. Performance analysis results show a good accuracy calculating the high-order time differentiation of the optical signal launched at core 2 (or core 1).
A prototype of a 160 GHz millimeter-wave (mm-wave) generator is proposed and analyzed. In the scheme, two lasers with 100 GHz frequency interval serve as sources. Then, a frequency 16-tupling feed-forward modulation technique is employed to generate two-phase correlated sidebands with a 160 GHz interval. The desired sidebands can be selected by using optical interleavers. A 160 GHz mm-wave signal free of phase noise can be achieved.
Twin-core fiber (TCF) can provide the required spectral response for implementing an optical temporal differentiator. It is shown that the output temporal waveform from one core of the TCF providing full energy coupling is proportional to the first derivative of the optical temporal signal launched at the input. Moreover, TCF can also be used as the first order optical temporal differentiator for multiwavelength optical signals, in which the position and the number of central wavelength can be tunable simply by changing the fiber length. Our numerical results confirmed that the TCF has a good accuracy by calculating the first time derivatives of the input optical signals with temporal features in the picosecond and subpicosecond ranges.
This study analyzes a photonic ultrawideband pulse generator by using a dual-parallel Mach-Zehnder modulator. A simple configuration capable of generating two popular types of ultrawideband pulse shape, Gaussian monocycle and doublet, is proposed. The generated ultrawideband pulses have very high quality, and the exact waveform is tunable with respect to parameter settings. By changing the time delay between two-path driving pulses applied to the upper and lower sub-Mach-Zehnder modulator of the dual-parallel Mach-Zehnder modulator, the generated ultrawideband pulses can be switched from Gaussian monocycle to doublet. The proposal is first analyzed and then validated by simulations. Results of the study demonstrate that it can offer a realistic solution to photonic ultrawideband pulse generation.
We present a prototype for optical single sideband (SSB) modulation with carrier (OSSB+C) by employing an overwritten fiber Bragg grating (FBG) is proposed and demonstrated. The grating is written using two different uniform phase masks of slight variation in the period. Then it is used in millimeter-wave SSB modulation scheme. Its operation principle can be concluded as the following two steps: (i) first, an intensity modulator double sideband (DSB) modulates the lightwave with millimeter-wave driving signals; (ii) then, the generated DSB modulation signals are reflected by the overwritten FBG. The overwritten FBG can reflect the carrier and the sideband simultaneously, resulting in two coherent subcarriers. Thus the conversion from DSB to OSSB+C can be easily achieved by using only one grating. Also, carrier-to-sideband ratio (CSR) can be optimized by using grating with different reflection depth. We demonstrate this scheme via simulation and successfully reduce signals' CSR from 14.44 to 1.25 dB.
A new method which makes use of the variable accelerated motion of servo motor is presented to fabricate the triangular
fiber Bragg grating. Considering the exponential relationship between the changes of grating refractive index and the
exposure of UV laser, this method only requires one exposure, the variable accelerated motion of servo motor is
controlled by computer program to control the increment of UV laser exposure and the linear change of grating refractive
index on the fiber axial, then the edge of triangular fiber Bragg grating can be gained. The experiment result shows that
the edge of triangular fiber Bragg grating has a good linearity, the bandwidth is 1.6nm, the linear bandwidth which can
be used is 1nm, and the maximum reflectivity is 90%. As a fiber Bragg grating sensor demodulation device, triangular
fiber Bragg grating will be more widely used in sensing fields.
A CCD fiber Bragg grating sensor demodulation system based on FPGA is proposed. The system is divided into three
units: spectral imaging unit, signal detection unit and signal acquisition and processing unit. The spectral imaging unit
uses reflective imaging system, which has few aberration, small size, simple structure and low cost. In the signal
detection unit, information of spectrum are accessed by CCD detector, the measurement of spectral line is converted into
the measurement of the pixel position of spot, multi point can be simultaneously measured, so the system's reusability,
stability and reliability are improved. In the signal acquisition and processing unit, drive circuit and signal acquisition
and processing circuit are designed by programmable logic device FPGA, fully use of programmable and high real-time
features, simplified system design, improved the system's real-time monitoring capabilities and demodulation speed.
In this brief-article the effect of the number of taps on the quality (Q) for infinite- and finite-impulse-response microwave photonic filters (IIRMPFs and FIRMPFs) is analyzed. For FIRMPFs, an increas of Q with the number of taps from 2 to 10 is deduced by analyzing the free spectrum ranges with 3-dB bandwidths. For IIRMPFs, a pretty high Q can be realized when the product of the coefficient and the gain in the feedback loop equals 1. Our analytical results are verified by a typical IIRMPF structure based on a fiber Bragg grating (FBG), and the Q value can be increased up to 804 by using two FBGs with reflectivities of 50% and 99.5%, respectively.
The growth of long period fiber grating written in H2-loaded fiber within one hour immediately after fabrication was
measured and analyzed. Fast deepen on difference of refraction index was obviously observed in all the experiments,
but the peak wavelength to time and cross-coupling coefficient to time curves are fitted better in exponential decay
function than power function, and suggest a same variation pattern in difference of refraction index.
Switchable dual-wavelength fiber lasers with orthogonal polarizations, based on the semiconductor optical amplifier at room temperature, are proposed. One polarization-maintaining fiber Bragg grating (PMFBG) is used as the wavelength-selective filter in three different laser configurations. Owing to the polarization-dependent loss of the PMFBG, the laser can be designed to operate in stable dual-wavelength or wavelength-switching modes with a wavelength spacing of 0.336 nm at room temperature by adjusting a polarization controller in each laser configuration. The amplitude variation over nearly half an hour is less than 0.1 dB for both wavelengths in each laser configuration, which is more stable than that of erbium-doped fiber lasers with similar configuration.
Dual-wavelength with orthogonal polarizations erbium-doped fiber ring laser at room temperature is proposed. One
polarization-maintaining fiber Bragg grating (PMFBG) in a Sagnac loop interferometer is used as the wavelength-selective
filter. Due to the polarization hole burning (PHB) enhanced by the PMFBG, the laser can operate in stable dual-wavelength
operation with wavelength spacing of 0.336 nm at room temperature by adjusting a polarization controller
(PC). The optical signal-to-noise ratio (OSNR) is over 52 dB. The amplitude variation in nearly one and half an hour is
less than 0.6 dB for both wavelengths.
A novel design of M-Profile Ytterbium doped Fibers (YDFs) for high power fiber Lasers was given. The output power
was two times higher than that in standard double-cladding fiber under the same threshold of damage.
The relationship between the gain flatness performances with the pump wavelength spacing in single-stage backward-pumped
distributed fiber Raman amplifiers (B-DFRAs) were demonstrated theoretically. It was shown that the gain
spectrum of B-DFRA which pump wavelengths were arranged in a geometric proportion interval sequence were flatter
than one which pump wavelengths were arranged in an equal interval sequence in the same conditions.
A linear cavity photonics crystal fiber (PCF) laser has been fabricated. The
home-made polarization-maintaining PCF is acted as active material, and
polarization-maintaining fiber Bragg grating (PMF-FBG) is used as filter. The stabile
two-wavelength laser, which has high degree of polarization (DOP), has been exported. The
output power is 0.3mW, and DOP is about 98%. In this paper, we discuss the characteristics
of PCF laser and PMF-FBG. in detail.
The impact of cascaded CFBGs delay ripple for dispersion compensation has been analyzed. The experimental results show that the overall penalty was proportional either to the number or to the square root of the number of CFBGs employed along the link. The delay ripple of the overall CFBGs fluctuates, and the overall CFBGs reflectivity was not simply additive but was related to the placement of the CFBG and line amplifier gain. For the first time, the experimental results of dispersion compensation for a 2-×10-Gb/s, 1000-km WDM system using self-made CFBGs with less than 1-dB power penalty for each channel have been achieved.
Time independent rate equations for fiber laser are solved accurately with numerical method under multipoint boundary conditions. A novel method based on genetic algorithm is firstly proposed to optimize distributed pump powers and fiber segment lengths of kilowatt YDDC fiber laser. The uniformity of temperature distribution is improved by using optimized method. The calculated results show that the lower operating temperature and better uniformity can be obtained through increasing the number of segments at the cost of decreased output signal power.
System performance degradation caused by group delay ripples of chirped fiber Bragg grating dispersion compensators is analyzed in detail with considerations for the ripple period, amplitude and phase offset. And the induced different kinds of signal distortions are also shown and explained.
The dispersion of 8×10Gb/s wavelength division multiplex (WDM) system has been compensated by the cascaded chirped fiber Bragg gratings(CFBGs), with ITU-T standard wavelengths and wavelength grid. The ASE of the EDFA could be reduced, the OSNR of the transmitted signal could be increased and the fluctuation of the EDFA gain could be controlled in the certain scope by the dispersion compensated CFBGs' WDM system. Impact of cascaded CFBGs' delay ripple on dispersion compensation has been analyzed. Experiment of error-free 8×10Gb/s 2015km transmission without forward error correction (FEC) and electronic repeaters were demonstrated. In the transmission, simplex CFBGs compensators were used and no other form of dispersion compensators were adopted. The experiment result showed that the consistency of the dispersion compensating in each channel is perfect over 2015km optical fiber transmission. The experiment result does agree with the theoretic analysis.
We demonstrate a 10.7Gb/s-line-rate L-band WDM loop transmission over 1890km standard single-mode fiber (SSMF) with 100km amplifier spacing as well as non-return-to-zero (NRZ) format. For the first time, dispersion compensating fiber (DCF) plus chirped fiber Bragg grating (CFBG) is employed for hybrid inline dispersion compensation. The power penalty of each channel is less than 3dB after three loop transmission. The experimental results show that high-performance-CFBGs can be successfully used in ultra-long haul (>1000km) WDM systems. We also point out that all-CFBG compensation scheme is not suitable for re-circulating loop transmissions.
The effect of source wavelength instability on the performance of a system using chirped fiber Bragg gratings as dispersion compensators is numerically investigated, by which it's shown that source wavelength instability will surely induce an additional penalty for the system. And quantified relations of the EOP induced by group delay ripples and reflection ripples with the extent of wavelength instability is given.
The successful fabrication of multi-wavelength FBG by using the high precision exposure clamp of scanning stage that made by ourselves are introduced. Only a single phase mask is used, and the wavelengths of FBGs fit the wavelength standard of the ITU-T. FBGs with four different wavelengths are fabricated by using one phase mask, and they have been used in a 4×10Gb/s, 1000 km conventional single mode optical fiber(G.652) transmission system. In each channel, 6 FBGs are used for the dispersion compensation and the power penalty in each channel is less than 1.8dB.
The random deviation of the periodicity of the gratings will affect the performance of the fiber gratings. The random errors would not accumulate when the gratings were cascaded. But we found a kind of fabricating system errors induced by the method for the side writing of fiber gratings, which would accumulate when cascaded. So laser with the less pulse energy should be used to write the gratings to developing the system's performance.
In this paper, we present and design a new type of tunable filter. The polymer with high electro-optic (EO) coefficient is fabricated as the outer layer of the long period fiber grating (LPG), since the resonant wavelength of LPG is extremely sensitive to the refractive index change outside the cladding, it is possible to achieve very fast speed broad tuning of wavelength by slightly tuning the refractive index of the surround area through the fast speed EO effect.
A temperature-compensated material of fiber Bragg grating (FBG), which has negative thermal-expansion coefficients, has been presented. The temperature coefficient of FBG's center wavelength is less than 0.0005nm/°C after three-layers-structure package under tension. For the first time, PMD of temperature-compensated FBG have been detailedly studied. The PMD of temperature-compensated FBG has been measured from -20°C to 60°C. The measured result shows that the PMD has little changed at different temperature.
Polarization-related impairments have become a critical issue for high-data-rate optical systems, particularly when considering polarization-mode dispersion (PMD). Consequently, compensation of PMD, especially for the first-order PMD is necessary to maintain adequate performance in long-haul systems at a high bit rate of 10 Gb/s or beyond. In this paper, we successfully demonstrated automatic and tunable compensation for first-order polarization-mode dispersion. Furthermore, we reported the statistical assessment of this tunable compensator at 10 Gbit/s. Experimental results, including bit error rate measurements, are successfully compared with theory, therefore demonstrating the compensator efficiency at 10 Gbit/s. The first-order PMD was max 274 ps before PMD compensation, and it was lower than 7ps after PMD compensation.
A novel widely tunable fiber laser which can rapidly select the desired ITU-T wavelength has been proposed. This multiwavelength source, based on vernier caliper component(two sampled fiber Bragg gratings with a slight different in channel separation) appears very promising for wavelength division multiplexing since which has many advantages such as a widely tuning range of selective wavelength, easily lock to the wavelength separation, cheap costly, stable performance and so on.
Based on the theory of Jones Matrix, a model for the analysis of non-PM fiber ring lasers polarization
characteristics was developed. The model was further tested by experiments. From the numerically and
experimentally analysis results, it was found that lasers composed by non-PM fiber can achieve stable output but
its polarization varied with external perturbation. If a polarizer was inserted into the laser cavity, though the
polarization state was more stable, the instability of output was even more serious. So special polarization control
must be performed to obtain single polarization laser output using non-PM fiber.
In this paper, we focus on the improvement of accuracy of phase-shift methods to measure the fiber dispersion. By the analysis of experiment results and possible error sources, the more suitable measurement conditions are provided to decrease the measurement error to a great extent. Except keeping a constant temperature and isolating the device from mechanical vibrations when measurement is carried out, as large as 1nm measurement wavelength step and large wavelength span at several tens nm level are preferred to obtain more
accurate and repeatable measurement.
For the first time, we study the transmission performance of 10Gbps PRBS data stream over ultra-high polarization mode dispersion (PMD) dispersion compensating fiber (DCF), which PMD coefficient is 237.95ps/km1/2. The simulation has been done by coupled nonlinear Schrodinger equations. Also transmitted experiment has been done by DCF with a PMD coefficient of 237.95ps/km1/2. The result of the simulation is consistent with that of the experiment.
Dispersion-compensating chirped fiber gratings provide a compact low-loss means of compensating fiber dispersion.
They are potential candidates for per-channel tunable dispersion compensation devices [2]. Group delay ripple (GDR) is
the principle reason restraining the practical implementation of chirped fiber Bragg gratings and many papers indicate
how the GDR impairs the systems performance [1, 3, 4]. S.Jamal has indicated that the period of the group delay ripple
has much important influence on the systems performance [1]. But the ripple period of the chirped fiber grating was not
consistent along side the grating, and Michael Sumetsky has explained the cutoff phenomenon of the high frequency in
[2]. Because the period of the chirped fiber grating changed with the wavelength and the components of different
frequency overlapped with each other, the time-frequency analysis was needed to descript the time-frequency distribution
of the GDR of the grating. [5]
Delay ripples of chirped fiber Bragg gratings (CFBGs), which a CFBG can compensate 200 km long optic fiber's dispersion, have been analyzed in detail. A numerical simulation of cascaded grating delay ripples has been done by Schroedinger equation and compared with experiment of 1,000 km transmission over G652 fiber by 5 groups of CFBGs dispersion compensation. The research shows that the system degradation depends on the delay ripple period, which is 0.01~0.1nm through a lot of experiments, and amplitude of delay ripple. We had experimentally studied fluctate of power penalty depend on ripple perod of CFBGs when source wavelength changed +/-20GHz around CFBGs center wavelength, the results of theory agree well with these of experiment.
We have succeeded in transmitting the signal as long as 1400km with G.652 fiber using chirped fiber gratings. Asymmetrical apodization was adopted to reduce the grating’s GDR (group delay ripple). Power and dispersion management was adopted here to suppress the nonlinear effects.
We used UV laser to write Bragg gratings on the polarization maintaining fiber (PMF). Because of the high-birefringence of the fiber, the Bragg wavelength of the grating on the two polarization axes was different. So that it could introduce great polarization mode dispersion (PMD). When the input was adapted to the axis of the grating, it can serve as the polarization compensation. We measured the polarization of the grating at the end of the article.
It is first time to study on Gauss pulse transmission over ultra-high PMD fiber. Gauss pulse is broken into a series of deformed pulse when it transmits over ultra-high PMD fiber. He has explained that the walk-off deformed pulses cause by ultra-high PMD. Transmitted experiment has been done using fiber with PMD coefficient 237.95ps/km1/2. The simulated result is consistent with experiment.
In this paper, the dispersion compensation of 4 X 10Gb/s 800km G.652 fiber by chirped optical fiber Bragg grating(FBG) was originally implemented. The ripple coefficient of reflectivity and time delay of FBGs are less than 0.9dB and 3Ops. When BER is 10-10 and the bit error is zero, the power penalty ofeach channel is less than 1.67dB.
With a new apodisation method and special package material, we have made high-quality chirped fiber Bragg gratings (CFBGs) with the fluctuating error of reflectivity less than 1dB, the delay ripple less than +/-15ps and the temperature coefficient being as low as 0.5‰onm/°C. Using such self-made high-quality CFBGs, we present, for the first time, the experiment results of dispersion compensation of 2x10Gb/s 1000km WDM system with less than 1 dB power penalty for each channel.
For the first time, the polarization mode dispersion(PMD) of fiber Bragg grating(FBG) was measured and compensated. And the FBGs are used for dispersion compensation of 4 X 10Gb/s 400km G.652 fiber. When BER is 10-10 and the bit error is zero, the best power penalty of transmission channel is negative.
In this article, we introduce the fabrication of apodized chirp FBG by scanning method, which monitored by computer. The FBGs are 13.5 cm long with 3 dB bandwidth 0.851 nm and 0.423 nm, respectively. The reflectivity are flatness with ripple coefficient less than 0.7 dB and the ripple coefficient of time delay are less than 20 ps. The dispersion of 10 Gb/s 100 km and 200 km G.652 optical fiber is compensated by the grating respectively, and more than 98% dispersion is compensated. (The original pulse width is 36.78 ps; after compensation the pulse width is 37.23 ps and 37.19 ps). With 10-10 BER, the power penalty of the system is 0 dB.
It is very important to get optical fiber Bragg grating (FBG) with stabilize property, this article briefly describes the anneal characteristics of H2-loaded FBG, the experiments show that after annealing the wavelength ((lambda) ), 3 dB bandwidth ((Delta) (lambda) ) and reflectivity (R) of the FBG all changed, these changes are relative to many parameters, such as the lay time of the H2-loaded optical fiber, the lay time of the FBG, the channel numbers of the FBG, the reflectivity of the FBG, and the bandwidth of the FBG and so on.
Accompany with the changed outside pressure, the Bragg center reflective wavelength of OFG changed correspondingly. According to the characteristic, a new kind of optical fiber grating pressure sensor combined with computer monitor is designed. The measure time of it is 1ms/point, it can be widely used for train real-time tracing, the parameters of train can be given, such as position, length, velocity, acceleration, disjoint and so on.
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