1.5 μm GaInAsP angled-facet flared-waveguide traveling-wavelaser amplifiers

A broadband laser amplifier requires extremely low facet reflectivity (<0.1%). Previously, a low effective facet reflectivity of 0.05% was realized by an angle-facet structure in the 1.3-μm wavelength band. Present work reports an improved structure for the 1.5-μm wavelength band by flaring the waveguide ends near the angled facets. With a conventional antireflection coating of ~1% reflectivity, the measured effective facet reflectivity is less than 0.01% and the resultant devices have a fiber-to-fiber gain of 15 dB centered at 1.49 μm     

Low residual reflectivity of angled-facet semiconductor laseramplifiers

Ridge-waveguide angled-facet semiconductor laser amplifiers for the 1.5 μm band have been fabricated with facet angles of 7° and 10°. Gain measurements performed with a stable, computer-controlled setup have revealed gain ripples as low as 0.025 dB at 22 dB gain for a 10° device. This corresponds to a residual reflectivity of 1×10^-5. Results demonstrate that the residual reflectivity of angled devices with one-layer antireflection coatings can be as low as that for normal facet devices with highly controlled double-layer antireflection coatings     

1.3 μm GaInAsP near-travelling-wave laser amplifiers made bycombination of angled facets and antireflection coatings

1.3 μm GaInAsP near-travelling-wave laser amplifiers have been realised by the combination of angled facets and antireflection coatings. Without in situ monitoring on the device itself during dielectric coatings, one can routinely obtain a low effective modal facet reflectivity of 5-8×10^-4. The devices had an internal gain of 24±1.5 dB for the TE mode and a single-mode fibre coupling loss of 5 dB/facet     

Angled-Facet Spot-Size-Converter Integrated Semiconductor Optical Amplifiers Using Asymmetric Twin Waveguide Technology

The extinction ratio (defined as the difference in the optical power between 0-dB fiber-to-fiber loss and the off state level) is enhanced with the introduction of an S-bend waveguide structure using asymmetric twin waveguide techniques for a spot-size converter integrated semiconductor optical amplifier (SSC-SOA) with a polarization-insensitive offset superlattice. Angled waveguides are introduced in order to obtain low facet reflectivity without the need for antireflection coating. A curved waveguide is introduced to connect the angled and straight waveguide, minimizing their coupling loss while achieving a lateral spatial mode filter. The SSC-SOA, operating at 1.62-mum wavelength, achieves an extinction ratio up to 70 dB and a fiber-to-fiber gain of 10 dB using cleaved, flat end single-mode optical fibers.     

Broadband quantum dot superluminescent LED with angled facet formed by focused ion beam etching

Broadband quantum dot superluminescent light emitting diodes (LEDs) are realised by focused ion beam etching an angled facet in an edge emitting dot-in-well laser diode structure. The device exhibits a large and flat emission spectral width up to 142 nm at 0.3 mW, maximum CW output power as high as 3 mW, and effective facet reflectivity <1times10^-6     

Coupling between angled-facet amplifiers and tapered lens-endedfibers

The coupling between angled facet amplifiers and tapered lens-ended fibers is investigated theoretically and experimentally. The theoretical investigation is based on a three-dimensional plane wave model which accounts for the phase differences introduced by the angled facets. The coupling is investigated with respect to the beam parameters of the amplifier waveguide and the tapered lens-ended fiber, and with respect to the fiber position. The excess coupling losses due to the facet angle and to the variation of the fiber lens radius are investigated theoretically and found to be in good agreement with experimental results. For optimized lens radii, the excess loss for a 10° facet angle is found to be less than 0.5 dB compared to a normal facet amplifier     

Mode coupling in angled facet semiconductor optical amplifiers andsuperluminescent diodes

The modal reflectivity of an angled facet has been calculated for index-guided devices when the fundamental mode excites various higher order modes at the facet. The calculations were carried out for waveguide widths ranging from 2 to 20 μm for various lateral index steps and at wavelengths of 834, 1300, and 1550 nm. Plots from these calculations can be used to determine the appropriate facet angles to obtain a given modal reflectivity and optimize the design of optical amplifiers and superluminescent diodes     

Facet reflectivity of a spot-size-converter integratedsemiconductor optical amplifier

Traveling-wave type semiconductor optical amplifiers (SOAs) integrated with a spot-size-converter (SSC) are extensively studied for improvement of coupling efficiency with single-mode fibers and for cost reduction in packaging. In this paper, the structural dependence of the SSC on effective facet reflectivity R_eff is investigated theoretically and experimentally. It is shown that, not only sufficient mode-conversion in the SSC region, but also the introduction of angled facets, are essential for reducing R_eff. A small gain ripple (less than 0.1 dB) in an amplified spontaneous emission (ASE) spectrum, fiber-to-fiber gain of 26 dB, and saturation output power of 7 dBm are observed for the fabricated SOA, which consists of a window length of 20 μm, facet angle of 7°, and anti-reflection coated facet of less than 1% reflectivity     

Improved selectivity and decreased spontaneous emission from anAR-HR coated SL-MQW DFB semiconductor laser amplifier

It is shown that the performance of a DFB filter/amplifier can be improved considerably with respect to selectivity and amplified spontaneous emission by applying a high reflective coating to the output facet. To illustrate this a strained-layer multiple quantum well DFB filter/amplifier with an output facet reflectivity of 97% is compared with a conventional, AR-coated phase adjusted DFB filter/amplifier. Peak fiber-to-fiber gains for these devices are 21 and 18 dB, respectively, when biased at 98% of their threshold current. The transmission gain of these DFB filter/amplifiers has been measured over a wavelength span of 30 nm. For the AR-HR coated SL-MQW DFB filter/amplifier the selectivity is improved with 11 dB resulting in an extinction ratio for interfering channels of better than 35 dB and the amplified spontaneous emission is reduced by 16 dB down to -37 dBm compared to the conventional DFB filter/amplifier     

Analysis of antireflection coatings on angled facet semiconductor laser amplifiers

An analysis of the modal reflectivity of antireflection coated semiconductor laser amplifiers is presented. The effect of an angle between the facet normal and the amplifier axis is shown to lead to less stringent tolerances on coating index and thickness, and reflectivities of less than 10/sup -4/ can be achieved with a 7 degrees facet angle for TE and TM modes simultaneously.<>     

Real-time in situ monitoring of antireflection coatings forsemiconductor laser amplifiers by ellipsometry

Very strict requirements need to be met for producing a high-quality single-layer antireflection coating on a traveling-wave laser amplifier facet. In order to obtain a facet reflectivity of 10^-4 or less, the index of refraction and the layer thickness of single-layer coatings have to be controlled to better than 0.03 and 30 Å, respectively. An innovative approach to highly controlled antireflection layer deposition based on in situ real-time ellipsometry is presented. Index control within ±0.01 and a facet reflectivity on the order of 10^-4 are reproducibly obtained     

Amplified spontaneous emission effects in semiconductor laseramplifiers

The analysis presented provides a quantitative method for predicting semiconductor laser amplifier performance in the presence of ASE (amplified spontaneous emission). It indicates that in order to increase the fraction of pump power that contributes to the amplification of the input laser field relative to that spent in overcoming internal losses, an amplifier should operate at as high an excitation level as possible. This may mean operating an amplifier above its free-running oscillation threshold. A limitation to the maximum pump power is the increase in ASE. With too high an excitation, ASE dominates over the amplified input laser field, resulting in a quenching of the amplifier gain, efficiency and coherence. ASE effects may be mitigated by increasing the input laser intensity, decreasing the amplifier facet reflectivities, or, in some cases, tuning the master oscillator so that it is resonant with the amplifier. The analysis indicates that minimizing the facet reflectivity is the most effective way to circumvent ASE limitations to power scaling semiconductor laser amplifiers     

Semiconductor optical amplifier for wavelength conversion in subcarrier multiplexed systems

The fabrication and performance of a InGaAsP-InP semiconductor optical amplifier for wavelength conversion in subcarrier multiplexed system is described. The amplifier is of the buried facet design and has polarization and reflectivity gain ripple of less than 1 dB. Using subcarrier multiplexing, multiple 50-Mb/s data streams at a wavelength of 1.553 /spl mu/m are infected into the amplifier. The gain nonlinearity of the amplifier transfers the data to a different wavelength of light simultaneously injected into the amplifier. Error free retrieval of subcarrier multiplexed data has been demonstrated for the wavelength converted output. The small signal bandwidth of the wavelength conversion process is 5 GHz. Calculation suggests that higher bandwidth is feasible at higher input powers at the expense of lower modulation transfer during wavelength conversion.     

Theory of signal degradation in semiconductor laser amplifiers withfinite facet reflectivities

An analytic expression is derived for the output signal spectrum from a semiconductor laser amplifier (SCLA) using an approach analogous to the Langevin equations of laser noise analysis. The authors present an analysis of the line broadening effects of SCLAs taking into account the effect of facet reflectivities. The signal linewidth is shown to increase with input linewidth and amplifier gain. There is an optimum facet reflectivity which gives the smallest linewidth increase. The results have significant implications in weakly coherent systems utilizing cascades of optical amplifiers     

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.     

Angled-facet S-bend semiconductor optical amplifiers for high-gainand large-extinction ratio

The extinction ratio of an optical gate with a spot-size-converter-integrated semiconductor optical amplifier (SSC-SOA) is deteriorated following the direct coupling of unguided light between the input and output fibers. In this letter, an S-bend waveguide structure is introduced into an active waveguide to suppress such direct coupling. Angled facet structures are also introduced for obtaining low facet reflectivity. The fabricated SSC-SOA operating at 1.55-μm wavelength achieves an extinction ratio up to 70 dB and a fiber-to-fiber gain of 20 dB     

High-speed photodetection characteristics of a Fabry-Perot laser amplifier under AM and FM formats

A comparison between the photodetection characteristics of an FP laser amplifier under AM and FM formats is reported. A 450 MHz photodetection bandwidth is obtained under the AM format using a Fabry-Perot laser amplifier, with two antireflection coated facets with 10/sup -5/ reflectivity. Using an FP laser amplifier with 10/sup -3/ reflectivity as an FM discriminator/photodetector, a photodetection bandwidth of up to 2.6 GHz was measured.<>     

AlGaInAs-InP材料系1550nm偏振无关半导体光放大器

采用低压金属有机气相外延设备生长并制作了1550nm AlGaInAs-InP偏振无关半导体光放大器,有源区为3周期的张应变量子阱结构,应变量为-0.40%.器件制作成脊型波导结构,并采用7°斜腔结构以有效抑制腔面反射.经蒸镀减反膜后,半导体光放大器的自发辐射功率的波动小于0.3dB,3dB带宽为56nm.半导体光放大器小信号增益近20dB,带宽大于55nm.在1500～1590nm波长范围内偏振灵敏度小于0.8dB,峰值增益波长的饱和输出功率达7.2dBm.     

SOA反射率对谐波锁模光纤激光器的影响

基于半导体光放大器(SOA)的锁模光纤环行激光器因其能得到高质量、高重复率的光脉冲而受到人们的广泛关注。计及SOA端面剩余反射率,建立了基于SOA的谐波锁模光纤环行激光器的理论模型。利用该模型研究了SOA的端面剩余反射率对输出脉冲的波形、峰值功率及其脉冲宽度的影响。结果表明,SOA的端面剩余反射率对锁模脉冲影响较大;随着端面剩余反射率的增大,峰值功率逐渐增加,脉冲宽度逐渐变宽。     

Superluminescent diodes with bent waveguide

Superluminescent diodes are fabricated with a bent waveguide to prevent optical feedback. The bent ridge waveguide is formed with one end normal to the cleaved facet and the other angled at 7/spl deg/ from the facet normal. The spectral ripple of these devices is around 10% at 6 mW output power. The farfield pattern emitted from the angled facet is crescent-shaped. As the device is set up in an external-cavity configuration, lasing operation is observed regardless of the additional 10.8 dB bending loss introduced by the bent waveguide.