Remote all-optical nanosecond gain switching of an erbium-doped fiber amplifier

All-optical gain switching of an erbium-doped fiber amplifier located up to 50 km away from the signal and control lasers is demonstrated. The amplifier is deactivated by optical control pulses within the amplifier bandwidth that strongly saturate the gain at the signal Wavelength. Fall times are approximately equal to the control pulse duration of 21 ns. From 25 km, a maximum extinction ratio of 16 dB is demonstrated with the signal at 1527 nm and the control pulse at 1554 nm. The dynamic range for remote switching is limited by a stimulated Raman scattering of the control pulses.     

Space radiation effect on EDFA for inter-satellite optical communication

The erbium-doped fiber (EDF) has been irradiated by electron with a dose of 1000 krad to analyse the space radiation effect on EDF amplifier (EDFA) in inter-satellite optical communication. This is the first work to analyse the effect on actually applied systems. Three critical parameters of EDFA, most important for external module subsystems, have been tested. The output power comes down to −57.21 dBm and the noise figure (NF) climbs up to 18.14 dB at dose 1000 krad, when the input power is −2.00 dBm. Although there is a strong ability to recover after the radiation experiment, EDFA deterioration is really huge. Apart from that, the central wavelength of EDFA never changes. To guarantee the accuracy of analysis of the radiation effect on EDFA, WDM coupler and isolator are also irradiated with the EDF at the same time. According to the results of all the tests, the EDFA could be directly used in the low-radiation dose orbits if doses are less than 20 krad. And the radiation experiment data will also be a good reference for the design of the actual systems in inter-satellite optical communication with different dose orbits.     

宽带碲基掺铒光纤放大器多信道增益竞争的仿真分析

对新型宽带碲基掺铒光纤放大器(EDTFA)多信道间的增益演变关系进行了理论仿真。仿真结果表明:EDTFA多信道间的增益存在着一个竞争过程,竞争的强弱取决于碲基掺铒光纤内的能级粒子数分布;当上能级粒子数处于反转分布态时,具有较大的发射截面与吸收截面差值的波长信道拥有相对较大的竞争优势,可获得相对较高的信号增益;当上能级粒子数处于未反转分布态时,具有较大的发射截面与吸收截面比值的波长信道拥有相对较大的增益竞争优势。     

Placement of hybrid optical amplifier in fiber optical communication systems

In this paper, we investigated the post-, pre- and symmetrical power compensation methods for a different position of hybrid optical amplifier RAMAN–EDFA in fiber link. The effect of increase in signal input power for three power compensation methods is compared in terms of bit error rate, eye closure penalty and output received power. It is found that the post power compensation method is superior to pre- and symmetrical power compensation methods. Further, the effect of variation in length of the standard single mode fiber and dispersion-compensated fiber for three power compensation configurations has also been observed. We observed that RAMAN–EDFA as post power compensation method provides least bit error rate (10^?40) and high output power (12 dBm) at ?15 dBm signal input power at fiber link.     

Placement of optimized semiconductor optical amplifier in fiber optical communication systems

This paper deals with the placement of semiconductor optical amplifier for 10 Gb/s non-return to zero format in single mode and dispersion-compensated fiber link. We investigated post-, pre- and symmetrical power compensation methods for different positions of the SOA in fiber link. The effect of increase in signal input power for the three power compensation methods is compared in terms of eye diagram, bit error rate, eye closure penalty and output received power. It is found that the post-power compensation method is superior to pre- and symmetrical power compensation methods. Further, the effect of variation in length of the standard single mode fiber and dispersion-compensated fiber for three power compensation configurations has also been observed. The impact of eye closure penalty is observed for large transmission distances for different signal input powers.     

Investigation of the irradiation effect on erbium-doped fiber amplifiers composed by different density erbium-doped fibers

Two erbium-doped fibers (EDFs) with different densities, which can make the erbium-doped fiber amplifier (EDFA) achieve the same output power, have been irradiated by ⁶⁰Co at the same rate and same total dose. In addition, the irradiation effect on EDFA composed by different density EDFs is firstly analyzed in this paper. The experimental results indicate that, considering the length of EDF, the high density EDF can make the EDFA deteriorate less than the low that in the irradiation environment. Furthermore, the small change of the central wavelength and the half-wave width also confirm that the irradiation effect on EDFA chiefly introduces the transmission loss, but the physical mechanics of EDFA is not changed by the irradiation. The experimental results and conclusions will be a good reference for EDFA designers who are trying to apply the EDFA in an irradiation environment.     

Impact of 1530 nm-ASE filtering on the S-band gain using erbium-doped silica fiber amplifier

Experimental and numerical investigations are realized to show the impact of the number of ASE-filters on the S-band gain of an erbium doped fiber. Gain as a function of (number of filters, filter ASE-isolation) is studied to optimize the S-band amplifier by using ASE-isolation tunable all-fiber filters.     

Numerical study on adiabatic compression of ultrashort fundamental solitons in an erbium-doped fiber amplifier

In this paper, the compression and amplification of fundamental solitons in an erbium-doped fiber amplifier (EDFA) are investigated by using the numerical method. The results show that the unchirped fundamental solitons can be compressed and amplified by selecting an appropriate length of the EDFA when the peak gain of the EDFA is fixed, and the compression and amplification satisfy the adiabatic condition. Furthermore, the fundamental solitons with appropriate positive chirp parameters can be compressed and amplified effectively by selecting an appropriate length of the EDFA, but the pulse compression cannot satisfy the adiabatic condition. Moreover, the compression of the fundamental solitons with negative chirp also cannot satisfy the adiabatic condition, and the compression effects are very poor. Thus, the chirp should be reduced before adiabatic compression using the EDFA.     

Signal wavelength dependence of gain saturation in a fiber optical parametric amplifier

Signal gain-saturation characteristics in a fiber optical parametric amplifier are described. Experiments and calculations for the high-gain-saturation region are presented in which the direction of optical power transfer, which is from the pump to the signal and the idler in the unsaturated region, becomes reversed at high-signal-input powers. It is shown that the signal gain soon saturates for signal wavelengths far from the pump. This wavelength dependence is explained by the power-dependent phase mismatch and its behavior in the high-signal-input region.     

A novel method for measuring optical fiber delay lines based on the optical fiber low-coherence Young's interferometer

According to the principle of double-beam interference imaging using an infrared broadband light source, a novel method based on the optical fiber low-coherence Young's interferometer for the measurement of programmable optical fiber delay line is proposed. By measuring the small length increments of delay fiber through the evaluation of the central positions of zero-order interference fringes, we successfully construct a system with a variety of important functions, such as real-time controlling, measurement and displaying. This system offers the benefit that it can be regulated precisely to generate interference stripes once again after the length of fiber segment changes. When the locations of central stripes are moved to coincide with the original markers, the determination of the corresponding fiber optical delay time becomes really simplified, as just by reading out the tinny displacement of the reference arm. Multiple groups of experimental results demonstrate the outstanding performance of the proposed system since it bears a measuring accuracy of μm and a measuring range from 1 mm to 20 cm.     

A theoretical analysis of the effects of erbium ion pair on the dynamics of an optical gain stabilized fiber amplifier

In this paper, the effects of ion-pair formation on the gain dynamics of multi cavity optical automatic gain control erbium doped fiber amplifier is modelled. The inhomogeneous Cabezas simple model is used to write the rate and propagation equations for the active medium. The solution of the governing equations shows that in high concentration of the erbium ions, depending on the pumping rate, the relaxation oscillations are converted to nT-Periodic or even to chaotic behavior. Although the high concentration erbium ion in the optical amplifiers decreases the conversion efficiency and increases the threshold pump power, amplitude of the transient effects is reduced in the multi feedback-loop WDM amplifiers relative to the low concentration erbium ions multi feedback-loop optical amplifiers and ion-pairs, which act as a saturable absorber to compensate the gain tilt caused by the OAGC laser spectral hole burning. The theoretical results are in complete agreement with the previous published experimental results.     

A full-field method for measuring residual stresses in optical fiber

A method for measuring the axial residual stress profile in axisymmetric optical fibers is presented. The procedure is based on integrated photoelasticity and a fringe shifting technique is used to measure the optical retardation. The radial distribution of the axial residual stress is reconstructed using the inverse Abel transform. The paper describes the operating principle, the experimental setup and the results obtained on a multimode fiber are also reported. The influence of the measurement errors is finally discussed.     

Two-wave mixing in an erbium-doped fiber amplifier for modulation depth enhancement of optically carried microwave signals

We experimentally and theoretically analyze an original method based on two-wave mixing in an erbium-doped fiber amplifier for optical carrier reduction of microwave signals. 75% optical carrier attenuation has been observed, and a 10 dB modulation depth increase of the microwave signal is experimentally demonstrated. Moreover, calculated results are in good agreement with measurements and predict that up to 80% carrier attenuation is easily possible.     

A moment method for analysis the gain spectrum in fiber Raman amplifier with broadband pumps

The governing equations of optical fiber Raman amplifier with broadband pumps in the steady state are systems of uncountable nonlinear ordinary differential equations (NODE). In this paper, the Moment method is used to reduce the uncountable system of NODE to a system of finite number of NODE. This system of equations is solved numerically. The results are compared with that of the full numerical method. It was shown that the Moment method is a precise and efficient technique for analysis of optical fiber Raman amplifier with broadband pumps.     

All-fiber phase actuator based on an erbium-doped fiber amplifier for coherent beam combining at 1064 nm

Active phase control in fiber amplifiers is of considerable interest for low-noise single-frequency amplifiers and for coherent beam combining. We demonstrate phase control at 1064 nm by use of an erbium-doped fiber. We investigated the phase shift by guiding the beam through an erbium-doped fiber amplifier in a Mach-Zehnder configuration and applied the results to stabilize the relative phase of two ytterbium-doped fiber amplifiers. To the best of our knowledge, this is the first demonstration of an all-fiber coherent beam combining at 1064 nm employing an erbium-doped fiber as a phase actuator.     

The effect of phase mismatch on two-pump fiber optical parametrical amplifier

In the paper, the effect of phase mismatch on two-pump fiber optical parametric amplifier is investigate based on analytic solutions of parametric gain. The phase mismatch is mainly induced by the fiber losses, the fourth-order dispersion and zero-dispersion wavelength fluctuations. The fiber losses reduce the pump powers resulting in a fall of the parametric gain, and make the phase mismatch vary with propagation distance leading to an obvious gain ripple. When the fiber losses are taken into account, the fourth-order dispersion produces a deeper ripple on the parametric gain and deteriorates the gain flatness. Zero-dispersion wavelength fluctuations result in variations of gain spectrum, and the long-scale fluctuations are more devastating than the short-scale ones.     

Investigations of optical coherence properties in an erbium-doped silicate fiber for quantum state storage

We studied optical coherence properties of the 1.53 μm telecommunication transition in an Er³⁺-doped silicate optical fiber through spectral holeburning and photon echoes. We find decoherence times of up to 3.8 μs at a magnetic field of 2.2 T and a temperature of 150 mK. A strong magnetic-field dependent optical dephasing was observed and is believed to arise from an interaction between the electronic Er³⁺ spin and the magnetic moment of tunneling systems in the glass. Furthermore, we observed fine-structure in the Erbium holeburning spectrum originating from superhyperfine interaction with ²⁷Al host nuclei. Our results show that Er³⁺-doped silicate fibers are promising material candidates for quantum state storage.     

Character analysis of slow light with communication waveband in fiber optical parametric amplifier

The comprehensive characters of delay time and delay bandwidth with distortion, signal wavelength dependence and delay bandwidth product in fiber optical parametric amplifier are investigated theoretically when the pump locates at anomalous dispersion region. The delay character of single pulse, data stream with certain bit pattern and pseudo random data stream are analyzed comprehensively. In this category of fiber optical parametric amplifier, the delay time and delay bandwidth product vary from signal wavelengths and bit rates. For the same nonlinear coefficient, pump power and fiber length, the diverse dependences of bit pattern in different signal wavelengths are found by numerical simulation. The impacts of pump power and fiber length on the delay character and distortion are also discussed. These relations are conductive to the design of slow light based on fiber optical parametric amplifier in telecommunication waveband.     

光纤通信中有色散影响的受激喇曼散射信道特性研究

提出了在波分复用光纤通信系统中，考虑光纤色散“走离”时受激喇曼散射(SRS)信道的新模型,给出了计算中距离步长的选取公式。根据该模型，数值计算了各信道在随机数字序列调制下和在受激喇曼散射(SRS)非线性效应作用下经过有色散“走离”的波分复用光纤系统的传输功率。得出光纤色散会降低SRS效应引起的输出功率波动的结论,画出了在SRS效应作用下输出功率标准差随色散系数变化的曲线，并对产生该现象的机理进行了定性分析。该模型适合于任意光纤色散、任意输入功率和任意信道数目。