Design of a miniature lens for semiconductor laser to single-mode fiber coupling

A design method for a miniature optical lens tipped on a single-mode fiber end to improve power coupling from a semiconductor laser is described. The lens shapes studied are hemispherical, hemicylindrical, and hemiellipsoidal. The optimum coupling conditions and the obtained coupling efficiency are represented in terms of laser beam and fiber parameters. Preferable ranges of hemispherical and hemicylindrical lenses are classified according to the laser and fiber mode spot sizes. Fiber axis offset and tilt effects on coupling efficiency are also studied.     

Characteristics of a hemispherical microlens for coupling between a semiconductor laser and single-mode fiber

A hemispherical microlens is fabricated on the end of a single-mode fiber by an electric arc discharge technique. It improves coupling efficiency between InGaAsP lasers with buried heterostructure geometry and single-mode fiber. The lowest coupling loss of 2.9 dB is achieved with the optimum lens radius of 8.5 μm. This loss is 4.4 dB lower than that with a butt joint. Experimental results of coupling efficiency and alignment tolerances in coupling with different lens radii in the range of3.5-17 mum are discussed in detail. The results are in good agreement with theoretical values derived by Gaussian beam and paraxial ray approximations.     

Spectral beam combining of a single-mode 980-nm laser array for pumping of erbium-doped fiber amplifiers

With a view to improve the power level and brightness of semiconductor pump lasers, we have resorted to a scalable implementation and achieved spectral beam combining through a low-quality-factor external cavity. For that purpose, a high-power single-mode laser array emitting up to 2.1 W at 3.2 A at 980 nm has been realized, which delivers 1.5 W in external cavity. A power of 0.66 W was finally coupled into the single-mode fiber, with a coupling efficiency of 44%. Pumping experiments of an erbium-doped fiber amplifier utilizing this laser have demonstrated efficiency and noise characteristics similar to what is usually obtained with conventional sources, with the noteworthy advantage of a lower gain excursion over the C-band.     

Noise characteristics of semiconductor laser amplifiers

Noise characteristics of Fabry-Perot (FP) cavity type AlGaAs laser amplifiers are studied theoretically and experimentally. Noise power dependencies on pumping rate and input signal level are measured. Multimode rate equations with McCumber's fluctuation operator are solved for the parabolic band and the exponential bandtail models, both with the no k-selection rule. Experimental results are in good agreement with theoretical predictions.     

Packaged double-pass travelling-wave semiconductor laser amplifiers

A novel travelling-wave semiconductor laser amplifier (TW-SLA) proposed previously (1990) was experimentally achieved. The input and output optical signals were transmitted through a single piece of monomode optical fibre which is coupled to the chip of the TW-SLA. An optical circulator was used to separate the two signals.<>     

Recent progress in semiconductor laser amplifiers

Recent progress in semiconductor laser amplifiers (SLAs), mainly GaInAsP traveling-wave semiconductor laser amplifiers (TWAs) for use in optical fiber transmission systems, is discussed. The status of antireflection coating on laser-diode facets which are indispensable for TWAs is discussed. Reported data on small-signal gain, signal-gain saturation, and noise are summarized and discussed in relation to active-layer parameters. Common amplification using SLAs for the amplification of various multiplexed signals, including interchannel crosstalk, is also described. A thick, short active-layer structure for a broadband high-output-power low-noise TWA with polarization-insensitive signal gain is proposed     

Four-wave mixing in traveling-wave semiconductor laser amplifiers

Nondegenerate four-wave mixing (NDFWM) effects on simultaneous amplification of copropagating and counterpropagating waves with a frequency spacing of a few gigahertz in a 1.5-μm nonresonant near traveling-wave semiconductor laser amplifier are discussed. Experimental results are in qualitative agreement with a theoretical model assuming the NDFWM process is mainly due to carrier pulsation produced by the beating of copropagating waves in the amplifier. The amplification of a phase-modulated wave is considered. Time-reversal properties of four-wave mixing are demonstrated     

Time slot interchanging using semiconductor laser amplifiers

A four-channel optical time slot interchange switching experiment operating at 2.5 Gbit/s is reported. The system is based on a parallel switch fabric incorporating semiconductor laser amplifier gates and fibre delay lines. A sensitivity penalty of 0.2 dB for straight through operation, and 0.7 dB for fully interchanged time slots was observed.<>     

用腐蚀熔融法制造单模激光二极管与单模光纤相耦合的半球微透镜

近年来由于单模光纤研究的极大成功，促进了单模光纤通信系统和单模光纤应用技术的迅速发展。单模光纤的实际损耗已降到接近理论值，因此为进一步改善单模光纤传输系统的信噪比，提高激     

Stable single-mode compound-ring erbium-doped fiber laser

In this paper we report the fabrication of a robust, tunable single-longitudinal-mode compound-ring Er³⁺-doped fiber laser. The laser is fundamentally structured on an all-fiber compound-ring resonator in which a dual-coupler fiber ring is inserted into the main cavity. When combined in tandem with a mode-restricting intracavity tunable bandpass filter, the compound-ring resonator ensures single-longitudinal-mode laser oscillation. The laser can provide up to 20 mW output power over much of its 1525 to 1570 nm wavelength tuning range. The short-term linewidth of the laser output measured is less than 5 kHz. The laser frequency is actively stabilized for a long time by exploiting the inherent filter nature of the compound-ring resonator. The reduction of an associated frequency modulation is also discussed in detail     

Bidirectional single-mode Er-doped fiber ring laser

Rare Er-doped fiber lasers have been studied for fibe sensor applications with the advantage of frequency readou [1,2]. Due to this advantage, gyroscope application for a bidi rectional Er-doped fiber-ring laser was also demonstrated They also have high s…     

1.5 µm GaInAsP traveling-wave semiconductor laser amplifier

This paper presents a theoretical and experimental study in terms of small-signal gain, signal gain saturation, and noise characteristics of a 1.5 μm GaInAsP traveling-wave amplifier (TWA), realized through the application of SiOxfilm antireflection coatings. This TWA, having a residual facet reflectivity of 0.04 percent, exhibits a wide, flat signal gain spectrum and a saturation output power of +7 dBm at a 20 dB signal gain. The TWA also has a noise figure of 5.2 dB, which is the smallest value reported for semiconductor laser amplifiers. The experimental results are confirmed to be in good agreement with the theoretical predictions based on the multimode traveling-wave rate equations in conjunction with the photon statistic master equation analysis, which takes into account the amplifier material and device structural parameters. Signal gain undulation, saturation output power, and noise figure are also theoretically evaluated as functions of the facet reflectivity. The superior performance of the TWA demonstrates that the device is favorable for use in linear optical repeaters in fiber transmission systems.     

Saturation characteristics ofGa0.68In0.32As/GaInAsP/InP tensile-strainedquantum-well semiconductor laser amplifiers with tapered-waveguidestructures

With an aim toward a high-saturation power operation, a tapered-waveguide traveling-wave semiconductor laser amplifier (SLA) with a Ga_0.68In_0.32As/GaInAsP/InP tensile-strained quantum-well (QW) structure was investigated and realized for the first time. In spite of the high differential gain in the tensile-strained QW active layer, a high-saturation-output power of 18.5 dB (1 mW) (71 mW) and a high-maximum-output power of 20.4 dB(1 mW) (110 mW) were obtained with a narrow single-lobed beam-divergence property. These results indicate that the saturation performances of SLA's with tensile-strained active layers can be improved by the tapered-waveguide structures     

5 Gbit/s, 233 km optical fiber transmission experiment employingfive semiconductor laser amplifiers

A directly modulated 1.519-μm distributed-feedback laser signal was transmitted over 233 km of single-mode fiber consisting of dispersion shifted fiber and conventional step-index fiber to minimize the dispersion penalty. The power penalty after the transmission was 0.25 dB. The results show the effectiveness of an optical amplifier repeater system for high-speed long-haul fiber optic transmission     

半导体激光放大器的理论与实验研究

从理论与实验上研究了1.3μm的法布里-珀罗放大器(FP-SLA)与行波放大器(TW-SLA).分析了半导体激光器的增益特性,指出了“准”行波放大器的优越性.     

四能级系统光纤激光放大器的理论分析

本文从理论上分析了属于四能级系统的光纤激光放大器的增益特性,得到了信号增益与光纤长度、掺杂离子浓度、泵浦光和信号光功率等参数之间的关系式,并进行了数值计算。对四能级系统的激光放大器的设计有一定的指导作用。     

Analysis of fiber Brillouin ring laser composed ofsingle-polarization single-mode fiber

A fiber Brillouin ring laser made of SPSM fiber is analyzed. The eigenstate of polarization (ESOP) is strictly considered both for the pump and the Stokes light. It is clarified that the laser intensity fluctuation caused by the interaction between two kinds of ESOP is highly suppressed in this structure. The numerical computations using the typical values show that the fluctuation within 7.5% can be realized for the output Stokes light. While this ring-resonator does not offer high-grade performance when applied to the passive resonator fiber optic gyro, it could realize the high-grade performance when applied to the Brillouin fiber optic gyro     

A broad-band superfluorescent fiber laser using single-mode dopedsilica fiber combinations

We demonstrate the possibility of broadening the emissions spectra of superfluorescent fiber lasers by combinations of different kinds of single-mode doped silica fibers. We obtained an optical bandwidth of more than 70 nm (FWHM) between 1030 and 1100 nm using Nd:Cs, Nd:Ge, and Yb-doped fibers. The total output power measured from the single-mode fibers was more than 100 μW in a single pass configuration     

Noise in semiconductor laser amplifiers with quantum box structure

The low-noise properties of a quantum-box traveling-wave semiconductor laser amplifier (QB-TW-SLA) are discussed. The gain and population-inversion parameter of a quantum-box structure are precisely expressed using density matrix theory. Due to sharp gain characteristics as well as a small population inversion parameter, dominant two-beat noise is significantly reduced, even in a solitary device without a narrow bandpass filter. The noise figure can be reduced to 3.5 dB