Narrow linewidth lasers have important applications in optical communication and sensing. To accurately measure the linewidth, we built a laser linewidth measurement system based on 3×3 coupler. It uses the demodulation algorithm of Differential Cross Multiplication to get the phase noise, and then obtains the linewidth value according to the β-separation line method. At the same time, we introduced wavelet denoising in the signal processing in order to reduce the influence of low frequency noise. Two wavelet bases, db4 and sym11, which were more effective for this system were identified through simulation, and experiments were conducted using a 2 μm band laser. The results prove that the frequency noise power spectral density and linewidth values are reduced after using wavelet denoising.
A free space optical communication system at 2 μm band was preliminary demonstrated. The fiber laser source is a homemade continuous wave thulium-doped fiber laser with single-wavelength output. The center wavelength of the fiber laser is 2048.15 nm, and the fluctuation of the wavelength and optical power is less than 0.02 nm and 0.893 dB, respectively. By modulating and demodulating the radio frequency signal, the text and real-time video transmission was realized. The transmission distance in free space is ~1 m, and the transmission rate is less than 66 kbit/s. With further improvement, the system may be well suited in free space optical communication system.
Transverse Mode Instability (TMI) effect has become the biggest obstacle limiting the further improvement of output power and beam quality in high-power fiber lasers. For 2μm-band high-power thulium-doped fiber laser, the simulation is carried out using semi-analytical theoretical model. The results show that the TMI threshold is negatively correlated with the core radius, signal wavelength and positively correlated with the pump wavelength. On the other hand, reducing the relative intensity noise can slightly but not obviously improve the TMI threshold. The relationship curve between them is nearly logarithmic. The simulation provides an effective reference for further improving the TMI threshold.
Optical fiber devices and applications in the 2-μm band have been investigated extensively due to its unique advantages, such as eye safety. A fiber sensor based on tilted fiber Bragg grating with a grating plane angle of 2 deg is fabricated and experimentally tested. To the best of the authors’ knowledge, this is the first tilted fiber Bragg grating sensor to realize simultaneous measurements of temperature, axial strain, and a certain range of surrounding refractive index (SRI) at the 2-μm band. This paper uses the wavelength detection method and selects three independent resonant wavelengths as the investigated parameters. Results show that perturbations of temperature, axial strain, and SRI can shift the wavelengths of the core mode resonance and cladding mode resonance to some degree. The temperature sensitivities of the core mode and cladding mode are nearly the same, but their axial-strain sensitivities are different. Furthermore, the core mode is insensitive to the change in SRI. The sensitivities of SRI, temperature, and strain can thus be obtained by experimentally determining the wavelength shifts of the three independent resonance peaks. A 3 × 3 matrix containing the relationship coefficients between the disturbances of temperature, axial strain, and SRI and wavelength shifts is constructed. By reversely solving the matrix equation, variations in temperature, strain, and SRI can be obtained using the experimental determination of wavelength drifts.
The linewidth performance of all-fiber, linear-cavity Fabry–Perot structures based on fiber Bragg gratings operating at 2-μm band has been investigated numerically. The output linewidth performance of two symmetrical and asymmetrical cavities has been theoretically studied and comprehensively compared. The numerical analysis is based on the transmission matrix method with the simplified parameters. The simulation results show that cavity lengths, cavity lengths ratio, grating lengths, grating lengths ratio, as well as index modulation depths, affect the output linewidth performance. The tolerance ability of the asymmetrical structure is first proposed and investigated under 1 mm accuracy, and single-frequency output can be realized by properly adjusting the properties of the proposed composite linear cavity structure.
A new method of fabricating Panda-type photosensitive polarization-maintaining erbium-doped fiber(PM-EDF) is
proposed and demonstrated. A sample of PM-EDF is fabricated using this method and an exhaustive analysis is made
about the characteristics of PM-EDF, the results shows that this method is practicable. Two fiber Bragg Gratings (FBGs)
are written into PM-EDF directly as the lasers reflectors, a three-states-tuned fiber laser is then obtained using a
polarization controller (PC).
The temperature dependence of fluorescence in erbium-doped silica fiber between ~-30 and ~150°C is discussed.
980nm pumping configuration is used in our experiment. 1450nm and 1531nm wavelengths are chosen to calculate the
FIR (fluorescence intensity ratio) at the first time instead of the mostly used wavelengths 525nm and 550nm. It shows
that as the temperature increases, the fluorescence intensity increases obviously at short wavelengths but changes a little
at long wavelengths. The temperature coefficient can achieve ~0.023dB/°C, and its resolution is improved as the
temperature decreases. Because there are many effects in our experiments, so it shows a deviation from the behavior of
simulation.
The effect of non-ideal dispersion and reflection characteristics of chirped fiber Bragg gratings (CFBG)
on the 40-Gb/s and 10-Gb/s transmission is investigated. The effect of group delay ripple (GDR) on
eye-opening penalty (EOP) of carrier-suppressed return-to-zero (CSRZ) and return-to-zero (RZ)
formats is analyzed and compared. The system penalty for different amplitude and period ripples are
quantified.
A high concentration silica host Erbium Doped Fiber with Bismuth-Gallium-Aluminum co-doped was fabricated. The
absorption coefficient of this fiber was up to 19dB/m at the wavelength of 980nm and 42dB/m at 1530nm. Ring structure
lasers with different fiber lengths were presented. Their output characteristics were measured and analyzed.
Influence of stress area mismatched Panda erbium-doped polarization-maintaining fibre on the birefringence is analyzed
and compared by finite element method and approximate analytical expression educed by the complex variable method
of elasticity with superposition techniques.
A new near-elliptic cladding Polarization-maintaining photonic crystal fibre (PM-PCF) with four different hole diameters was proposed. Since the refractive index decreases gradually from x-axis to y-axis, less polarization coupling and high extinction ratio were obtained compared to the conventional PM-PCFs. Secondly, every hole diameter of near-elliptic cladding was optimized to get good performance, considering proper mode field diameter of x-axis and y-axis for better coupling to SLD and smaller confinement loss of the new PCF, high birefringence and high extinction ratio, especially the effects of disturbance on extinction ratio stability. According to series of comparison on different hole diameters and correlation between different holes, the optimum parameters of this new PCF of Λ=2.2μm, d1=2μm, d2=1.1μm, d3=1.7μm and d4=1.2μm were derived. The optimized near-elliptic cladding PCF can obtain both high extinction ratio (>29dB) and good extinction ratio stability (<2dB with ±10% transverse disturbance of d3) which is useful for practical use.
Some kinds of high birefringence photonic crystal fibers (PCFs) with elliptical inner cladding are analyzed by Galerkin
finite element method with transparent boundary conditions (TBC). Several properties of them, such as the birefringence,
confinement loss and dispersion are deduced and compared .It is shown that PCFs with different elliptical inner cladding
formed by enlarging or diminishing air holes have different properties. High birefringence can be obtained through
intruding the difference of air holes size along orthogonal direction. Enlarged air holes reduce the CL, and increase the
dispersion and dispersion slope; but diminished air holes is reversed.
A new near-elliptic inner cladding (NEIC) structure of polarization-stable highly birefringent photonic crystal fiber (HB-PCF)
is proposed and analyzed by using a full-vector finite element method (FEM) with anisotropic perfectly matched
layers. From the numerical results it is confirmed that, with the diameter of air hole A varied by ~10%, the modal
birefringence degradations of the three proposed NEIC-PCFs are less than 4.2 × 10-5, 6 × 10-5 and 1.17 × 10-4,
respectively, while the average birefringence is of the order of 2 × 10-3 at 1.55μm, which strongly proves that the
proposed structure is highly polarization-stable. Especially, the MFDs in x-direction and y-direction of NEIC-PCF with
three holes diminished in the center are measured as 5.8 μm and 2.6 μm, respectively, which are very attractive in the
application field of fiber optic sensor, e.g. fiber optic gyros.
Four types of YDFs with different Al3+ concentration and mole content of GeO2 were manufactured and the refractive
index and absorption spectra of these fibers were explored. With the comparison of four YDFs and detailed analyze, it
was found that higher Al3+ concentration leads to more GeO2 volatilization, which results in the refractive index decrease.
Therefore, mole content of GeO2 should be increased when co-doping Al3+ in YDF to maintain numerical aperture.
Meanwhile, the temperature of making porous layer should be controlled exactly to obtain good repetition of Al3+-
codoped YDF as the little change of temperature has little effect on mole content of GeO2 and SiO2 but has great effect
on compactness of porous layer. By drawing the fiber and testing the related parameters, the results show that the
optimum temperature range for making soot layer should between 1440°C and 1480°C where the absorption coefficients
were as high as 620dB/m with better repeatability. Finally, the ratio of GeO2 to SiO2 should be controlled to obtain long
fluorescence lifetime for fabricating highly ytterbium-doped fiber with required numerical aperture.
A novel technique for dispersion compensation is presented. Based on the theoretical analysis, an ideal instance of
characteristics of linear chirped fiber Bragg grating (CFBG) with 11 thermal heads and a laboratory instance of
characteristics of the CFBG with 5 thermal heads varies with different temperature is shown. They are analyzed at room
temperature with variation of the decrease from 3°C to -3°C and the increase from -2°C to 2°C. According to the results
of the simulations based on theoretical analysis, the change of micro-heaters temperature will induce the change of
grating temperature, and then change the Bragg wavelength, delay and delay slope of the CFBG. Further more, a
material experiment is presented. These results show that if the temperature controller is good enough, we will be able to
limit the temperature from 0°C to 4°C and we will receive some random dispersion values from -2608.2ps/nm to -
2835.6ps/nm. Therefore, this dispersion compensator can compensate the survival dispersion completely and can be
applied to the long-distance transmission and the optical communication system.
The amplification mechanism of ultra-wide-band telluride-based fiber Raman amplifier (T-FRA) is analyzed by
comparing the stimulated Raman scattering (SRS) characteristics of the telluride-based fiber with silica-based fibers.
Then a multi-pumping scheme to get a gain-flattened FRA is presented. We calculate the pump power in designing
multi-wavelength pumped Raman amplifiers by using some optimal searching method such as genic algorithm and an
effective linear multi-steps method based on average power called Adams-Bashforth method is proposed which not
only utilizes former multi-steps known information to get higher accuracy but also avoids iterative scatting by using
forecasting-correcting policy The search time of genic algorithm is about 8 minutes and the calculation time is 2 to 3
minutes. The optimizing process of six pumps can be completed within 20minutes and the time may increase if we use
'shot' method. Furthermore, a complete computing model is established to optimize the pump wavelength and power
allocation with flat net gain and broad bandwidth. As a result, using telluride-based fiber Raman amplifier, the gain
over 10dB from 1500nm to 1620nm (C and L band) is obtained and the gain spectra is more flat especially in C band.
The design criteria of the Panda-type erbium-doped polarization-maintaining fiber (EDPMF) are presented, which take into account the cutoff wavelength, mode field diameter, modal birefringence and background loss. The structural parameters are optimized in terms of the design criteria. A Panda-type EDPMF has been manufactured. The fabrication process and the parameter control of the Panda-type EDPMF are in detail described. Its refractive index profile, birefringence and absorption spectra are experimentally investigated.
The modal characteristics of dual-core photonic crystal fibers are analyzed by a full vector supercell method. The fundamental and second order modes of dual-core PCF consist of a pair of even and odd modes with different polarization, the parity properties of the modal electric field are illuminated. Based on the analysis of parity of modal electric fields, we investigated the vector modal interference in dual-core PCF. The power transfer induced by interference of different mode pair is investigated. It is the interference between two same polarized modes that contribute to the inter-core coupling of power. It is shown that the optical power will oscillate from one core to the other. The dependence of the coupling coefficients on wavelength and structural parameter for different polarization is discussed.
The optical properties of near elliptical core polarization maintaining photonic crystal fiber are analyzed by using a full vector model. We classify guided modes in the near elliptical core photonic crystal fibers (PCFs) according to the minimum waveguide sectors and its appropriate boundary conditions. Because the field patterns of the near elliptical core PCF is similar to that of rectangular waveguide, the guided modes are labeled in this PCF in the same way as in rectangular waveguide. The numerical results exhibit that the modal birefringence of elliptical core PCF is at least one order of magnitude higher than the conventional elliptical polarization-maintaining fibers (PMF). Zero walkoff point occur at the longer wavelength than that of convention elliptical PMF. This can restrain the first order polarization mode dispersion. This fiber has a number of potential applications in polarization control and management.
In this paper, the amplification mechanism of ultra-wide-band telluride-based fiber Raman amplifier (T-FRA) is described, and the Raman gain coefficient spectra of telluride-based fiber are studied thoroughly by compare the stimulated Raman scattering (SRS) characteristics of the telluride-based fiber with silica-based fibers. First, the cooperation of phonons and photons in telluride-based fibers is analyzed. Then the reason why Raman scattering of the telluride-based fibers can lead to a large gain coefficient and Stokes shift is discussed. The physical basis is analyzed in this paper and the energy of molecular vibration is taken into account. A multi-pumping scheme is provided at the end of the paper to apply gain-flattened T-FRA to WDM system.
This paper presents a novel technique for dispersion compensation, employing a linear chirped fiber Bragg grating (CFBG) with a thermal head consisting of several micro-heaters. The micro-heaters temperature are controlled by computer, and the change of micro-heaters temperature will induce the change of grating temperature, and the change of Bragg wavelength, and the change of delay and dispersion of the grating. Thereby, the goal of tunable dispersion compensation to different systems dispersion and the survival dispersion has been achieved.
An experimental setup was established by using a high stability, narrow line bandwidth fiber laser with a fiber optic amplifier, polarization maintaining fiber coupler with split ratio of 50:50 and 95:5 respectively, a fiber optic sensing coil with high birefringence large nonlinear polarization maintaining fiber, and uniform fiber Bragg grating that was used at output port for filtering the excess pumping component. Based on this experimental setup, the threshold power of the pumping laser was deduced, and the relationship of the spectra and intensity between pumping laser component and stokes component with frequency downshift was obtained experimentally.
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.
In this paper, the characteristic of thermal induced non-reciprocal phase noise was analyzed theoretically, and the temperature distribution model was derived for the fiber sensing coil. The zero point drift of the fiber optic gyros(FOG) induced by outside temperature fluctuation was simulated numerically and compared for the four type fiber sensing coil manufacture methods (ZYL, SYM, DIP, QUA). The related zero point drift compensated method was proposed.
The formulas concerning degree of the polarization for a Lyot optical fiber depolarizer with respect to the corresponding parameters have been derived by considering splice misalignment for the first time. Experimental results verify the theoretical predictions.
The experiment conducted between Beijing and Taiyuan City, Shanxi province has ben done to verify the feasibility of utilizing the fiber gyro in railway system in order to enhance the transportation capacity, and safety. This report presents the experimental results of two inertial systems with one using ring laser gyros, and the other using fiber optical gyro. The former is going to be intended for track inspection, and the later for train positioning application.
In this paper, a new type of depolarized fiber optic gyroscope is described. Sensing coil is constructed by single-mode optical fiber with 200 meters length and 70 mm wounding diameter. A superluminescent diode source is used to reduce both the coherent scattering effect and Kerr effect. Two depolarizers with 1.0 percent degree of polarization and one polarizer with 40dB extinction ratio were used to reduce the output bias drift and improve the scale factor stability. A specially designed PZT phase modulator is used to suppress the AM noise. Under laboratory environment, the zero point error of 1.5 degrees/hr over seven hours with one second time constant and 700 ppm scale factor with +/- 100 degrees/sec maximum rotating rate were achieved for this depolarized I-FOG.
The polarization effect of the all PM FOG is studied by using the Jones matrix theory on the first time. Above this study, the expression of the output noise is derived, which include the polarization degree (or extinction ratio) of the every element in the gyro system. The influence of each parameter on the detected polarization noise is theoretically analyzed, and an effective theory to reduce the detected noise is established.
In this paper, the stress induced birefringence of the all fiber PZT phase modulator was analyzed in detail, a method of `align axis' in manufacturing all polarization maintaining fiber PZT phase modulator was put forward and realized on the first time. Demonstrated by experiment, it can effectively depress the polarization noise on the output caused by the stress induced birefringence in the all PZT phase modulator.
The Kerr -induced rotation-rate error in fiber-optic gyroscopes was described theoretically, and an effective method was proposed to reduce this rotation-rate error.
In this paper, a new type depolarized fiber optic gyroscope is described. Sensing coil is constructed by single-mode optical fiber. A superluminescent diode source is used to reduce both the coherent scattering effect and Kerr effect. Two depolarizers with 1.0% degree of polarization were used to reduce the output bias drift and improve the scale factor. Long-term bais stability better than 2.0° /hr is obtained during ten hours observed time.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.