Low Facet Reflectivity Research Articles

Influence of a tilted cavity on quantum-dot optoelectronic active devices

Quantum-dot laser diodes (QD-LDs) with a Fabry-Perot cavity and quantum-dot semiconductor optical amplifiers (QD-SOAs) with 7° tilted cavity were fabricated. The influence of a tilted cavity on optoelectronic active devices was also investigated. For the QD-LD, high performance was observed at room temperature. The threshold current was below 30 mA and the slope efficiency was 0.36 W/A. In contrast, the threshold current of the QD-SOA approached 1000 mA, which indicated that low facet reflectivity was obtained due to the tilted cavity design. A much more inverted carrier population was found in the QD-SOA active region at high operating current, thus offering a large optical gain and preserving the advantages of quantum dots in optical amplification and processing applications. Due to the inhomogeneity and excited state transition of quantum dots, the full width at half maximum of the electroluminescence spectrum of the QD-SOA was 81.6 nm at the injection current of 120 mA, which was ideal for broad bandwidth application in a wavelength division multiplexing system. In addition, there was more than one lasing peak in the lasing spectra of both devices and the separation of these peak positions was 6–8 nm, which is approximately equal to the homogeneous broadening of quantum dots.

Design of 1060nm tapered lasers with separate contacts

Numerical simulations have been used to produce advanced designs of high brightness gain guided tapered lasers emitting at 1,060 nm. The simulations predicted high modulation efficiency in devices with separate contacts and low front facet reflectivity. The devices fabricated following these design guidelines demonstrated high internal quantum efficiency in Broad Area lasers, output power of 3 W with good beam quality in tapered lasers with common contacts, and modulation efficiencies up to 20 W/A in tapered lasers with separate contacts, in good agreement with the simulation predictions.

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.

A Simple and Color-Free WDM-Passive Optical Network Using Spectrum-Sliced Fabry–PÉrot Laser Diodes

We propose and demonstrate a simple and color-free wavelength-division-multiplexing passive optical network (WDM-PON) using spectrum-sliced Fabry-Perot laser diodes (F-P LDs). Due to its low front facet reflectivity (~0.1%), the F-P LD shows a broadband lasing spectrum and reduced mode partition noise. By utilizing multiple peaks that are separated by the free-spectral range of the cyclic arrayed waveguide gratings, the 16-channel WDM-PON is successfully demonstrated at 155 Mb/s.

Analysis of Threshold Current and Wall-Plug Efficiency of Diode Lasers with Asymmetric Facet Reflectivity

Threshold current and differential quantum efficiency of broad contact lasers with asymmetric facet reflectivity are discussed with the purpose to reveal factors essential for optimisation of the wall-plug efficiency of such lasers. Lasers with low front facet reflectivity and short cavity often exhibit behaviour difficult to explain with a classical theory. More rigorous calculation performed in this work show that differential quantum efficiency is indeed less affected by a change of the front facet reflectivity or cavity length than predicted by such theory. These findings greatly simplify criteria for optimisation of the wall-plug efficiency of broad contact lasers with coated facets.

Theoretical study on cross-gain modulation wavelength conversion with converted signal feedback

A large signal dynamic theoretical model is presented for wavelength conversion using cross-gain modulation in semiconductor optical amplifiers with converted signal feedback. The resonance effects caused by the device residual facet reflectivity are considered. Theoretical results on the performance of the converter, in terms of extinction ratio, frequency chirping and conversion speed, are discussed and analysed. The converter performance can be enhanced, and restrictions of low facet reflectivity can be relaxed due to the enhancement of the carrier–photon interaction.

Performance improvements in XGM‐based wavelength converters with converted signal feedback

AbstractA large‐signal theoretical model is presented for wavelength conversion using cross‐gain modulation (XGM) in semiconductor optical amplifiers with converted signal feedback. Theoretical results on the performance of the converter, in terms of extinction ratio, frequency chirping, and conversion speed, are discussed and analyzed. The converter performance can be enhanced and restrictions of the low‐facet reflectivity can be relaxed due to the enhancement of the carrier–photon interaction. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 18–22, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11274

Fourier-optical transverse mode selection in external-cavity broad-area lasers: experimental and numerical results

Broad-area lasers (BALs) with external Fourier-optical cavities with spatial filter for transverse mode selection have been studied experimentally and theoretically. The transverse mode structure of BALs is modeled using a three mirror cavity approach. The model accounts for gain saturation, carrier diffusion, and anti-guiding effects. Near- and far-field distributions are calculated and compared to experimental results. Transverse mode selection is achieved for BALs with a residual front facet reflectivity of 10% at low pump currents. For BALs having a very low front facet reflectivity of 0.001%, transverse modes can be selectively excited up to pump currents more than 200% above laser threshold. Calculations show that BALs having a 0.001%-antireflection coating with an external Fourier-optical cavity high above threshold can operate in a self-Q-switched-like mode with pulse durations of 2-4 ns and repetition rates of 100-200 MHz. Experimental results obtained with a hybrid integrated-optical external cavity for transverse mode selection are also presented.

Yield estimation of 10-Gb/s electroabsorption modulator-integrated DFB lasers due to chirp

We investigate the yield of 10-Gb/s electroabsorption modulator integrated-distributed feedback (EAMI-DFB) lasers for 40- and 60-km transmissions due to the chirp. The yield has been estimated from the effective positive chirp (EPC) capable to transmit signals over 40 and 60 km within 2-dB dispersion power penalty. The signals with EPC of 0.48 and 0.24 /spl Aring/ can be transmitted over 40 and 60 km with less than 2-dB power penalty, respectively. The chirp is calculated from a large signal dynamic model of EAMI-DFB lasers using the time-dependent transfer matrix method (TMM). The results suggest that the yield is mostly dependent on coupling constant (/spl kappa/L) and should be set around 1.3 for high yield while maintaining low facet reflectivity at modulator.

Angled-facet S-bend semiconductor optical amplifiers for high-gain and 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-/spl mu/m wavelength achieves an extinction ratio up to 70 dB and a fiber-to-fiber gain of 20 dB.

Effect of residual facet reflectivity on the front-rear correlation and nonlinearity of L-I characteristics in quarter-wavelength-shifted DFB lasers

Combined effects of residual facet reflection and spatial hole-burning on the front-rear correlation and nonlinearity in L-I characteristics of quarter-wavelength-shifted DFB lasers have been studied by using an effective index transfer matrix method and rate equations. Changes in front-to-rear power ratio, caused by the spatial hole-burning and asymmetric facet-reflection due to the different grating end phases at the two facets, are shown to be responsible for both the correlation and the linearity problems, while the threshold gain change causes the linearity problem only. The problems are serious even in the cases of low facet reflectivity of 0.3%.

Intensity noise and facet correlation in Fabry–Pérot laser diodes with low facet reflectivities

The intensity noise in Fabry–Pérot lasers with low facet reflectivities is studied. A direct comparison between laser intensity fluctuations under noise suppressed and shot-noise limited current injection is made. Noise levels in excess of the shot-noise level are observed, even when the pump noise is suppressed. Also, an injection current dependent negative correlation between the intensity noise at the output facets of a laser is demonstrated.

Nearly degenerate four-wave mixing in laser diodes with nonuniform longitudinal gain distribution

Nearly degenerate four-wave mixing in above-threshold laser diodes with low or asymmetric facet reflectivities is investigated theoretically. It is shown that the conjugate reflectivity and the four-wave mixing bandwidth are enhanced in lasers with low-reflectivity facets. It is shown, in particular, that the maximum conjugate reflectivity can be obtained in lasers with highly asymmetric facet reflectivities. Longitudinal variations of both the nonlinear interaction and the gain distribution in the laser cavity are taken into account in the model. Such variations are shown to be essential in describing four-wave mixing in laser diodes with low or strongly asymmetric facet reflectivities.

Analytical model of a semiconductor optical amplifier

The spatial dependence of the material gain is introduced in the model of a semiconductor optical amplifier. Analytical expressions of the profiles of the carrier density, spontaneous emission, and amplified fields are obtained for amplifiers with arbitrary facet reflectivities. The nonuniformity of the carrier density is demonstrated in the case of low facet reflectivities. The model predicts the output saturation power and gain ripple, with good agreement with experimental results in resonant and traveling-wave amplifiers. Very low-gain ripple measured in low facet reflectivities amplifiers is explained by the model. A comparison with the uniform gain model shows that important deviations can occur in the case of low facet reflectivities. It is also shown that with the currently achievable low facet reflectivities, the maximum available gain is limited by spontaneous emission.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Large-scale longitudinal spatial-hole burning contribution to laser gain compression

The impact of large-scale longitudinal optical power nonuniformities on the dynamics of a Fabry-Perot semiconductor laser is analyzed. New rate equations which incorporate this effect are derived. The effects of optical power nonuniformity are shown to be small compared to those of phenomenological gain compression at low frequencies, and insignificant at the relaxation oscillation frequency, except in the limit of low facet reflectivity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Curved and tapered waveguide mode-locked InGaAs/AlGaAs semiconductor lasers fabricated by impurity induced disordering

Summary form only given. Modelocking using curved waveguide devices for low facet reflectivity and using tapered waveguide devices for high output power has been demonstrated. Strong suppression of reflection-seeded secondary pulses was observed for curved waveguides, and increased output power for tapered waveguides. InGaAs/AlGaAs quantum-well semiconductor diode lasers were fabricated using impurity induced disordering. The waveguide has a linear taper from 2.5 mu m to 7.5 mu m width over a 150 mu m distance. The modelocked output pulse energy was increased to 4.1 pJ, compared to 1.8 pJ for a similar 2.5 mu m waveguide untapered device. >

A reassessment of standard rate equations for low facet reflectivity semiconductor lasers using traveling wave rate equations

A set of traveling wave equations, which are a simple extension of the common rate equations, is used to study the effect of longitudinal gain saturation in Fabry-Perot semiconductor lasers. Analytical solutions are derived which are valid for both low and high Q cavities. A comparison is made to a theory with no spatial dependence. The maximum longitudinal carrier density deviation from the threshold value under lasing conditions is calculated for arbitrary facet reflectivities. It is shown that this deviation leads to linear equations for the emitted output power when compared to a standard rate equation theory. Improved designs for semiconductor lasers are suggested from this analysis. >

1.5 μm InGaAsP/InP vertically coupled semiconductor optical pre-amplifier

Vertical coupling of light output from a stripe InGaAsP/InP laser amplifier to the bottom of the substrate for detection by means of a 45° mirror has been demonstrated. The composite-cavity amplifier structure is shown to have an inherent low facet reflectivity and unidirectional amplification property. With a fiber-to-detector gain of 15.4 dB and a nearly diffraction-limited output spot size, the device is suitable for compact integration with a photodetector as an optical pre-amplifier in a high bit-rate direct detection system.

Gain-coupled DFB lasers versus index-coupled and phase shifted DFB lasers: a comparison based on spatial hole burning corrected yield

A statistical yield analysis is presented for gain- and index-coupled distributed feedback (DFB) laser structures, allowing a comparison of their single longitudinal mode (SLM) yield capabilities. For the yield calculations, the threshold gain difference and the longitudinal spatial hole burning (SHB) are taken into account. By comparing the experimental and theoretical yield of index-coupled DFB lasers, the significance of SHB for correct yield predictions is illustrated. For the purpose of comparison, yield calculations for various lambda /4-shifted DFB lasers (with low facet reflectivities) are presented. The most emphasis, however, is on partly gain-coupled DFB lasers. Estimations of practical gain coupling coefficient values for gain and for loss gratings are discussed. >

1.5 mu m GaInAsP angled-facet flared-waveguide traveling-wave laser 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- mu m wavelength band. Present work reports an improved structure for the 1.5- mu m wavelength band by flaring the waveguide ends near the angled facets. With a conventional antireflection coating of approximately 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 mu m.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>