Gain Equalization for Few-Mode Erbium-Doped Fiber Amplifiers via Strong Mode Coupling

Few-mode erbium-doped fiber amplifiers (FM-EDFAs) are one of the most important optical subsystems for successful space division multiplexed transmission systems. In this paper, we propose a new FM-EDFA designed to achieve significantly reduced differential modal gain (DMG) via strong mode coupling. Using a new numerical model based on a fiber transfer matrix, the DMGs of FM-EDFAs are systematically investigated and two different types of six-mode fiber amplifiers are analyzed, as exemplar demonstrations. In a uniformly doped step-index fiber, the DMG can be reduced from 9.3 to 1.1 dB (i.e., 8.2 dB reduction) and further reduced to 0.5 dB in a dual-layer doping structure.

Modal Gain Characteristics of A Two-section InGaAs/GaAs Double Quantum Well Passively Mode-locked Laser with Asymmetric Waveguide

Monolithic two-section InGaAs/GaAs double quantum well (DQW) passively mode-locked lasers (MLLs) with asymmetric waveguide, concluding the layers of P-doped AlGaAs waveguide and no-doped InGaAsP waveguide, emitting at ∼1.06µm, with a fundamental repetition rate at ∼19.56GHz have been demonstrated. Modal gain characteristics, such as a gain bandwidth and a gain peak wavelength of the MLL, as a function of the saturable absorber (SA) bias voltage (Va) as well as the injection current of gain section (Ig), were investigated by the Hakki-Paoli method. With the increase of Va, the lasing wavelength and net modal gain peak of the MLL both exhibited red-shifts to longer wavelength significantly, while the modal gain bandwidth was compressed. Both the net modal gain bandwidth and gain peak of the MLL followed a polynomial distribution versus the reverse bias at the absorber section. In addition, for the first time, it was found that Va had an obvious effect on the differential gain of the MLL.

Experimental Measurement of Absorption Coefficients for Effective Erbium-Doping Concentration to Optimize Few-Mode Erbium-Doped Fiber Amplifiers with Low Differential Mode Gain

According to the analytical expression for modal gain of few-mode erbium-doped fiber amplifiers (FM-EDFAs), we propose a method of measuring the absorption loss coefficients of few-mode signals in few-mode erbium-doped fibers (FM-EDFs) by extrapolating the mode–gain curve dependent on the average population inversion. The absorption loss coefficient of an FM-EDF was measured in our experimental platform and used to estimate the effective erbium-ion doping concentration. The feasibility of the extrapolation method was verified by simulation and comparison with the transmission method. Furthermore, the FM-EDFAs with high modal gain and low differential mode gain (DMG) could be optimized by adjusting the FM-EDF’s length and pump power. The analysis process presented here is very useful for the efficient design of FM-EDFAs from a practical point of view.

Study of the spectral and power characteristics of In0.2Ga0.8N/GaN superluminescent light emitting diodes by taking into account the piezoelectric polarization fields

In this study, the effects of the piezoelectric polarization field have been investigated on the spectral and power characteristics of In0.2Ga0.8N/GaN superluminescent light emitting diodes. The Schrödinger and Poisson equations, the rate equations in the multiple quantum well active region and separate confinement heterostructure layers, and the optical propagating equations have been solved in the presence of the piezoelectric field. The results have been compared with results of the case of without piezoelectric field. According to the results, in the presence of piezoelectric field, the red-shift occurs in the spectra, and the width of spectrum increases. Also, the piezoelectric field decreases the peak intensity of spectrum and modal gain of the device.

Numerical Design and Frequency Response of all group-IV alloys based MQW Transistor Laser

In this work, a theoretical model is developed for n-p-n mid-infrared transistor laser (TL) with strain-balanced Ge0.85Sn0.15 multiple quantum well (MQW) structure in the base. Variation of optical confinement factor, modal gain and threshold current density have been rigorously investigated for different number of QWs (N) in MQW structure. The result shows that overall optical confinement factor and modal gain increase with N. The frequency response of MQWTL for common base (CB) configuration is estimated from small signal relationship between the photon density and emitter current density by solving laser rate equation and continuity equation considering the virtual states as a conversion mechanism. Increment of N causes modulation bandwidth to initially increase and then decreases with N, which reveals a shifting of device nature for higher values of N. The results also suggest that on judicious selection of N, the proposed device can become a viable monolithic light source.