光纤光学参量放大器的增益特性研究

介绍了光纤光学参量放大器的理论,基于耦合波方程推导出光纤光学参量放大器的增益表达式.以增益表达式为基础,详细分析了在典型参数下光纤光学参量放大器的性能.在单泵浦情况下,对不同光纤长度、不同泵浦功率及不同泵浦波长的光纤光学参量放大器做了性能分析.在双泵浦情况下,对不同泵浦波长的光纤光学参量放大器做了性能分析.研究结果表明,在典型参数情况下的双泵浦光纤光学参量放大器具有较好的特性.     

Amplification and excited state absorption in longitudinally pumped laser dyes

Direct measurements of optical gain using a probe laser beam for the laser dye cresyl violet perchlorate (CVP) in methanol solution using longitudinal pumping at two different wavelengths are described. An analysis of these longitudinal pumping experiments is developed and analytical expressions relating measured gain to the measured pump laser transmission are presented. This analysis is developed in terms of relevant optical cross sections including the influence of excited state absorption. The results demonstrate the influence of excited state absorption at the pump wavelength on pumping efficiency and on the gain per pass at the probe laser wavelength.     

Analysis of optical gain enhanced erbium-doped fiber amplifiersusing optical filters

Erbium-doped fiber amplifiers (EDFAs) with enhanced optical gain obtained by incorporating narrow-bandpass optical filters into the amplifier length are studied. It is shown in theory that it is possible to increase optical gain by more than 10 dB for optical signals around the wavelength of 1.55 μm, compared with conventional EDFAs without filters. It is also shown that the gain improvement at longer wavelengths away from the amplifier gain peak is much higher than that of the EDFA with an optical isolator within the amplifier length. The optimum filter position is found to be around 42% of the total amplifier length from the input end. The effects of filter insertion loss and pump loss are discussed. This amplifier can be used as an optical preamplifier in a receiver for a wide range of wavelengths     

Temperature dependence of signal gain in Er3+-dopedoptical fiber amplifiers

Temperature-dependent signal gain characteristics at signal wavelengths of 1.536 and 1.552 μm in Er³⁺-doped optical fibers with a temperature range of -40 to 80°C are reported for 0.98 and 1.48 μm pumping. The temperature dependences of signal gain strongly depend on fiber length, pump wavelength, and signal wavelength. The fiber length at which signal gain temperature insensitivity occurs is found for the amplification of a 0.98-μm-pump-1.536-μm-signal, a 0.98-μm-pump-1.552-μm-signal, and a 1.48-μm-pump-1.536-μm-signal. It is confirmed theoretically that the temperature dependences result from linear changes in the fluorescence, and absorption cross sections at the signal and pump wavelengths, and a shift in the effective pump wavelength     

Broadband parametric amplification in photonic crystal fibers with two zero-dispersion wavelengths

In this paper, the fourfold parametric enhancement over Raman gain of the total optical fiber-amplifier gain is analyzed. Such fiber-amplifier gain may be obtained with a relatively flat profile over a bandwidth in excess of 70 nm by using a microstructure or photonic crystal fiber with two zero-dispersion wavelengths. Optimal fiber-amplifier gain enhancement occurs whenever the pump wavelength is slightly shorter than the second zero-dispersion wavelength of a microstructure optical fiber.     

Automatic optical loss compensation with erbium-doped fiberamplifier

The effect of unwanted optical loss varying over 15 dB is automatically offset with an erbium-doped fiber amplifier used in an optical feedback configuration. The loss compensation is possible for signal wavelengths over a 13 nm range centered at about 1550 nm. The system dynamic range for loss fluctuation frequencies is zero to several kilohertz. The proposed loss compensation scheme simultaneously provides an automatic gain control function that stabilizes the gain against slow changes in input signal power or pump power     

Pump-to-signal transfer of low-frequency intensity modulation in fiber optical parametric amplifiers

This paper describes the theoretical and experimental investigation of the transfer of low-frequency intensity modulation (IM) from pump to signal in fiber optical parametric amplifiers (OPAs). It is first established that low-frequency IM of the pump remains unchanged over the length of the amplifier in spite of the presence of parametric gain. The pump-power dependence of the OPA gain is then used to calculate the instantaneous effect of pump IM on the signal and idler output powers. These calculations are performed for both one- and two-pump OPAs. The main predictions are that 1) the ratio /spl rho/ of the signal intensity modulation depth to that of the pump varies across the OPA gain spectrum and 2) for a 20-dB gain, /spl rho/ can exceed 10 at some wavelengths, which indicates that this effect can be detrimental. Experiments have been performed to verify these predictions. Using sinusoidal IM of the pump, the resulting amplified signal IM was measured, and the experimental results were found to be in good agreement with the theoretical predictions.     

Six-wavelength Raman fibre laser for C- and L-band Ramanamplification and dynamic gain flattening

A novel six-wavelength Raman fibre laser exhibiting a dynamic gain flattening capability in the C + L optical telecommunications band is demonstrated. The power distribution in the six lasing wavelengths is adjusted with voltage-controlled Bragg-grating output couplers. The fibre laser was used as a pump source for distributed Raman amplification in several transmission span lengths. For example, the multiwavelength laser provides an on/off gain of 19 dB over a 100 km span of True-Wave RS optical fibre. The measured gain flatness is 1.7 dB peak-peak and the effective noise figure ranges from 1.6 to -5.2 dB in the 1530 to 1600 nm bandwidth     

多波长小功率泵浦拉曼光纤放大器的优化设计

提出用多个小功率激光器作为拉曼放大器泵浦光源,以获得较为理想的增益谱和降低成本。结合模拟退火法的优点,对遗传算法进行了改进,能很好地用于该类型拉曼光纤放大器泵浦的优化配置。仿真结果表明,这种改进的遗传算法收敛速度大大加快,并且精度与改进前一致。优化结果同时表明,这种配置方案的效果非常理想。获得的增益谱平坦且有陡峭的边沿,可有效节省总的功率。     

Phase-Regenerative Wavelength Conversion for BPSK and DPSK Signals

Phase-regenerative wavelength conversion is demonstrated experimentally. The simultaneous combination of two nonlinear optical processes, phase conjugation and frequency conversion (Bragg scattering), produces phase-sensitive gain at two new idler wavelengths in addition to the original signal wavelength. This single-stage approach does not require phase-locking of the tunable pump. At maximum pump depletion, amplitude and phase regeneration occur simultaneously.     

Erbium-doped optical fiber amplifiers pumped in the 660- and 820-nmbands

State-of-the-art erbium (Er)-doped optical fiber amplifiers (EDFA's) pumped in the 660- and 820-nm bands are described. We have demonstrated highly efficient EDFA's incorporating optimized 664- and 827-nm pump wavelengths and an Er-doped high numerical aperture (NA) fiber with thermally diffused expanded core (TEC) fiber ends. Gain coefficients of 3.8 and 1.3 dB/mW at respective wavelengths of 664 and 827 nm were achieved at a signal wavelength of 1535 nm. Noise figures of 3.1 and 4.1 dB at respective pump wavelengths of 670 and 827 nm were obtained at a signal wavelength of 1535 nm. A highly efficient Er-doped fiber amplifier module, in which an AlGaInP visible laser diode (LD) was used as the pump source, was successfully developed as a practical application of this technology. A maximum overall gain coefficient of 3.0 dB/mW was achieved at a signal wavelength of 1535 nm. The EDFA module realized a maximum overall signal gain of 33 dB at 1535 nm with a saturated output power of -1 dBm. A maximum saturated output power of 3.9 dBm was obtained at a signal wavelength of 1552 nm. The present EDFA design using a low-cost laser diode for optical disk memory use and a high NA Er-doped fiber has great potential for providing inexpensive, high-performance EDFA's     

Tunable wavelength conversion in a semiconductor-fiber ring laser

A tunable wavelength converter is demonstrated using highly nondegenerate four-wave mixing in a semiconductor-fiber ring cavity with no external pump light and low input signal power requirements. This device allows continuous tuning of both pump and converted wavelengths over the semiconductor optical amplifier gain bandwidth. Results for 11.8-nm down- and 6.9-nm up-wavelength conversion with input signal power as low as -10 dBm have been obtained at 1 Gb/s with less than 1.6-dB power penalty     

Influence of Raman effect on the noise characteristics in a dual pump FOPA

Influence induced by Raman effect on the noise characteristics of a depleted and lossy dual pump fiber optical parametric amplifier (FOPA) is investigated. Taking the Raman effect into account, the modified coupled amplitude equations are firstly built, then the influences of Raman effect on the stokes and anti-stokes wavelengths with different initial signal powers are further analyzed. Besides, the effect on the FOPA gain is also shown with the same initial signal power and constant noise figure (NF).     

Compensating unflattened WDM chips spectra using dynamic backward-pumped fiber Raman amplifiers technology

Fiber Raman amplifiers (FRAs) with multiple pumps are proposed to realize dynamic gain equalization for a spectral chips signal with a non-flattened broadband light source (BLS) in a spectrum-sliced wavelength-division multiplexing (WDM) network. In FRAs with multiple pumps, the gain profile can be adjusted via appropriate specification of the relative position of the pump wavelengths and the power of the pump waves. This paper combines a pump-power control algorithm and a genetic algorithm (GA) to establish the optimal pump spectrum for any specified gain spectrum in the WDM system. The method flattens the power spectra of WDM chips by identifying the optimal pump wavelengths and pump power of backward-pumped FRAs. It avoids the conventional requirement for time-consuming trial-and-error adjustments or intensive numerical simulations. Simulation results show that the scheme is simple, effective, and applicable for various BLSs in a spectrum-sliced WDM transmitter.     

Flat-gain fiber Raman amplifiers using equally spaced pumps

This paper analyzes the gain flatness of multiwavelength pumped fiber Raman amplifiers using equally spaced pumps with both a fixed and an optimized central pump wavelength. The signal gain ripple using equally spaced pumps is compared with the case in which the pump wavelengths are allowed to vary for two, four, and eight pumps with 20-, 40-, and 80-nm signal bandwidths. The paper shows that using an optimized central pump wavelength with equal pump spacing simplifies system design, while the gain ripple is no more than 0.4 dB larger than the ripple obtained when the pump wavelengths are optimized for the cases considered.     

Phase-matched four-wave mixing between pumps and signals in a copumped Raman amplifier

We observe four-wave mixing (FWM) between copropagating pumps and signals in a Raman amplifier when the zero-dispersion wavelength of the transmission fiber lies symmetrically between the pump and the signal wavelengths. The resultant FWM products, which grow as they experience Raman gain along the fiber, can degrade the signal's optical signal-to-noise ratio by as much as 10 dB for a Raman ON-OFF gain of 15 dB.     

Parameters for Quantitative Comparison of Two-, Three-, and Four-Level Laser Media, Operating Wavelengths, and Temperatures

Several parameters are proposed for describing the statistical thermodynamic component of the exchange of photons between a pump and a laser beam. They are based on the occupation probability of absorbing and emitting, pump and laser levels, and are complementary to the optical cross sections. The ldquooccupation factor,rdquo f ₀ , is appropriate for describing an optical amplifier in the small signal regime. f ₁ is appropriate for describing an amplifier in the large signal regime, e.g., a laser. They serve to facilitate a quantitative comparison of laser gain media, operating temperatures, and choice of pump and laser wavelengths. After a simple scaling, both occupation factors have a numerical value that coincides well, in most cases, with conventional usage of the terms two-, three-, and four-level laser. They can thus serve as an unambiguous, quantitative alternative to the quasi-two-, quasi-three-, and quasi-four-level terminology. The proposed definitions are general enough to apply to many types of gain media, but are particularly useful for comparing systems with discrete levels, pumped with a narrowband source, in near-resonance with the laser wavelength. Several low-quantum-defect combinations of pump and laser wavelengths are analyzed for Er³⁺ , Nd³⁺ , Yb³⁺ , and Ho³⁺ in YAG, as a function of temperature.     

Comparison of distributed gain in two dual-wavelength pumping schemes for thulium-doped fibre amplifiers

Using the coherent optical frequency domain reflectometry technique, a non-invasive study has been made of the distributed gain in two pumping schemes for thulium-doped fibre amplifiers. The compared schemes employed 800+1050 nm or 800+1400 nm pump wavelengths, and it was concluded that the former is advantageous over the latter primarily due to the ground-state absorption and pumping mechanism.     

Numerical calculation of the small signal gain in Er:Ti:LiNbO/sub 3/ channel waveguides

The overlap integral describing the small signal gain coefficient in Er:Ti:LiNbO/sub 3/ channel waveguides is numerically evaluated, and the results are used to discuss the polarization dependence and the influence of the erbium ion distribution. It is shown that bleaching is obtained at a substantially lower pump power for an extraordinarily polarized mode. A study of the influence of the overlap and the mode confinement at different pump bands indicates that the poorer overlap between the pump and signal mode at shorter pump wavelengths can be compensated for by an improved overlap with the erbium ions.<>     

Semianalytical approach to the gain ripple minimization in multiple pump fiber Raman amplifiers

A simplified approach to the search of Raman pump powers and wavelengths minimizing the gain ripple in a Raman multiple-pump amplifier is presented. The first step is to evaluate the pump path average powers and the wavelengths through a minimization algorithm. Then, an approximated analytical derivation of the initial pump powers, that yields an approximated path average power, is given. The results of the algorithm are in excellent agreement with the full numerical calculations.