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.
This paper presents a double-pass low-noise bismuth-doped fiber amplifier based on a Sagnac comb filter. The amplifier utilizes a Sagnac loop to filter out spontaneous emission light outside the signal wavelength, effectively decreasing the noise figure. Experimental results show that the amplifier achieves a minimum noise figure of only around 3.7 dB. Moreover, its gain bandwidth can cover a significant portion of the O-band. Under a forward pump power of 0.538 W, with an input signal power of -30 dBm, the amplifier can reach a gain of 29.6 dB, while the noise figure is only approximately 4 dB. Under backward pump, the gain difference for different input signal powers is larger compared to forward pump. We also studied the variation of gain with input signal power at a pump power of 0.5 W, using both forward and backward pump methods. The results indicate that the pump direction has a minor impact on the gain but significantly affects the noise figure, with the noise figure under forward pump being 1-2 dB lower than that under backward pump. Additionally, the amplifier exhibits a maximum saturation output power of approximately 9.5 dBm. In conclusion, this amplifier has great potential for application in WDM communication systems.
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 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.
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 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.
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.
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.
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.
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.
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.
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.
Modulation bandwidth and frequency chirping of the optical injection-locked (OIL) microring laser (MRL) in the cascaded configuration are investigated. The unidirectional operation of the MRL under strong injection allows simple and cost-saving monolithic integration of the OIL system on one chip as it does not need the use of isolators between the master and slave lasers. Two cascading schemes are discussed in detail by focusing on the tailorable modulation response. The chip-to-power ratio of the cascaded optical injection-locked configuration has decreased by up to two orders of magnitude, compared with the single optical injection-locked configuration.
A simple fiber-optic sensor based on a fiber Bragg grating (FBG) embedded in a fiber modal interferometer (MI) for simultaneous measurements of temperature and strain is proposed and experimentally demonstrated. The fiber MI is constructed by splicing two sections of the no-core fiber (NCF) between the single-mode fibers. Due to the different responses of the NCF-based MI and the FBG to the same temperature and strain, the discrimination between temperature and strain can be easily achieved. For a 0.01-nm wavelength resolution, the resolution of the sensor is 0.216°C and 6.75 με in temperature and strain, respectively.
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.
An optical single sideband (OSSB) modulation radio over a fiber system, by using an acousto-optic filter (AOF), is proposed and demonstrated. In the AOF, a uniform fiber Bragg grating is etched and modulated by an axially propagating acoustic wave. Due to the acousto-optic superlattice modulation, two secondary reflection peaks, centered on the primary reflection peak, are generated. In the scheme, an optical double-sideband signal passes though the AOF to realize OSSB modulation. Because the reflect depth of the primary peak is much deeper than those of the secondary peaks, the carrier experiences higher attenuation than the upper sideband, which means the carrier-to-sideband ratio (CSR) can be optimized at the same time. We demonstrate this scheme via simulations, and successfully reduce the CSR from 9.73 to 2.9 dB. As a result, the receiving sensitivity improved from −23.43 to −31.18 dBm at BER of 10 −9 with 30 km long SMF.
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.
The spectrum shift of FBG to ultrasonic wave is caused by the refractive index profile changing along the FBG, which
can be attributed to nonuniform perturbation caused by strain-optic and geometric effects of ultrasonic wave. Response
of FBG to the above two effects was analyzed by V-I transmission matrix model, showing high computing efficiency.
Spectra response of FBG under changing ultrasonic frequencies was simulated and discussed. In experiment, the system
was sensitive enough to detect ultrasonic wave from 15 kHz to 1380 kHz. These results would provide a guideline for
FBG-based acoustic detection system design in a specific ultrasonic frequency.
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.
Nowadays, researches on microwave photonics become more and more important due to the needs for wideband
and wireless multimedia. The typical utility system is the radio over/on fiber (ROF ) system. In the past few years, fiber
Bragg grating (FBG) has been widely used due to its unique characteristic of wavelength selectivity. Hence, a variety of
ROF devices based on FBG have become one of the best programs. In this paper, two kinds of microwave photonic filter
are studied, the frequency responses are simulated and the perfect results are gotten. Besides, a method is proposed to
realize millimeter-wave sub-carrier generation at central station by using a double-uniform FBG filter scheme. The
advantages are analyzed by designing a ROF downlink system, and the eye diagrams in different transmission distance
are also analyzed.
A novel reflection-type filter composed of microring resonator array and MZI is presented and analyzed. Simulation
results show that the devices can be used as reflection-type filters for DWDM system or wavelength-selective reflectors
for fixed or tunable lasers by properly choosing the values of coupling ratios.
By decreasing the arc power and choosing the optimal arc time, we use the FSM-20PM ARC Fusion Splicer for joining
fluoride(ZBLAN) and silica fibers. The best results of the splice loss is 1.58dB, and the results can be improved if the
Fusion Splicer with more stable arc power. Then glue connection is used to fix the splicing point, and the minimal loss
we measured is 0.14dB. The above results show that it is possible to connect the fluoride and silica fibers by using
Fusion Splicer with appropriate arc power and arc time, which will make the fabrication of these splices simpler and
easier to be handled.
The coupled-mode equations corresponding to a novel complex long-period-grating-assisted coupler (LPGAC), which consists of both the periodic refractive index modulation and gain/loss perturbation, is introduced and the close-form analytical solution is obtained, for the first time to our knowledge. And a unique unidirectional and
nonreversible filtering characteristic is achieved by adjusting the gain/loss to match with the refractive index modulation. In addition, the impact of deviations in the grating profile is also evaluated, and the results show that the required device performance can be realized by controlling the amplitude and phase deviation <5%.
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.
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.
Combined the characteristics of Mach-Zehnder interferometer (MZI) with the advantages of microring resonator, a new and simple method for improving the performance of MZI electro-optic modulators (EOMs) is proposed. Using the coupled-mode theory and transfer matrix method, the transfer function of the device is analyzed and parameters are optimized. Numerical results demonstrate that Q-factor exceeding 1x104 and modulator bandwidth above 40Gbit/s is achieved by choosing the proper microring radius. And the 3rd-order nonlinear harmonic distortion of the modulator curve is cancelled and linear range higher than 90% is obtained by setting biasing point and choosing coupling coefficients. Compare with the single ring structure, performances of the designed device can be improved further by integrating multiple microring resonators.
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.
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.
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.
The transfer functions of the vertically coupled microring resonator are derived. The effects of parameters such as: the coupling coefficients, the internal propagation loss and the microring’s radius on the characteristics of the resonator are analyzed theoretically. And the optimum parameters are chosen. The higher order microring resonator is compared with the single ring resonator. At last, a wide wavelength range tunable filter based on microring resonator is proposed and its structure is shown in details.
LPG's sensitivities in the spectral shift and the strength change of the attenuation band to the surrounding medium are analyzed and the results are in close agreement with our experiments. According to the characteristics of LPG, we will introduce, for the first time to our knowledge, a novel all-fiber electro-optic (EO) polymer modulator that is based on the LPG. The materials used in the modulator are chosen and the processing is also given. The purpose of this analysis is to provide design insight and the feasibility of making such a device. Using the theory of multi-claddings optical wave-guide, we achieved the relationship between LPG’s resonant wavelength and the drive voltage.
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.
In this paper, we present the design of a new type of high speed electro-optic (EO) modulator based on long period fiber grating (LPG). The outer layer of the LPG is fabricated by material with high EO coefficient, and a special material with ultra-negative temperature coefficient is used for the temperature compensation. This
modulator can work steadily with low power microwave driver, its speed is very high and its cost is low. To our knowledge, this is the first time for a modulator designed with such a simple and effective structure.
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.
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.
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.
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.
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.
Principle of biconically fused fiber polarization beainsplitters (FPBS) has been introduced in this paper, and a new method for fabricating FPBS has been presented. Compared with the conventional methods in which the first polarization modulation waist point (PMWP) arrived after drawing through many power transfer cycles, the power transfer variation versus the drawn length became fast and the stop point in the drawing process was difficult to control, our method has the advantages of easy fabrication. We use a low temperature heater to fuse and taper the fiber coupler, so the coupling region of the coupler is extremely weakly fused such that the fibers are barely touching. Consequently, the number of power transfer cycles before arriving the first PMWP is greatly reduced, and the first PMWP can be determined easily. In our experiment, the first PMWP in the power transfer curve monitored with unpolarized 1312-nm laser light is taken as the stop point in the coupler drawing process, the experimental results show that, an average extinction ratio of -14.06dB at the throughput port and -14.11dB at the coupled port have been achieved at 1312-nm wavelength. Experimental results show that, this method is simple and convenient.
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