Gain and phase dynamics in strained quantum well semiconductor optical amplifiers

Band-gap shrinkage is an important effect in semiconductor lasers and optical amplifiers. In the former it leads to an increase in the lasing wavelength and in the latter an increase in the gain peak wavelength as the bias current is increased. The most common model used for carrier-density dependent band-gap shrinkage is a cube root dependency on carrier density, which is strictly only true for high carrier densities and low temperatures. This simple model, involves a material constant which is treated as a fitting parameter. Strained InGaAsP material is commonly used to fabricate polarization insensitive semiconductor optical amplifiers (SOAs). Most mathematical models for SOAs use the cube root bandgap shrinkage model. However, because SOAs are often operated over a wide range of drive currents and input optical powers leading to large variations in carrier density along the amplifier length, for improved model accuracy it is preferable to use band-gap shrinkage calculated from knowledge of the material bandstructure. In this letter the carrier density dependent band-gap shrinkage for strained InGaAsP is calculated by using detailed non-parabolic conduction and valence band models. The shrinkage dependency on temperature and both tensile and compressive strain is investigated and compared to the cube root model, for which it shows significant deviation. A simple power model, showing an almost square-root dependency, is derived for carrier densities in the range usually encountered in InGaAsP laser diodes and SOAs.

The effects of biaxial compressive and tensile strain on the excitonic resonances and associated changes in refractive index and electro-optic effect in quantum wells have been calculated and measured. Theoretical calculations include the important heavy-hole–light–hole band mixing effects. It is seen that the excitonic contributions dominate near the band edge. With increasing compressive strain the linear electro-optic effect is slightly increased, while the quadratic effect is greatly enhanced. The effects are reversed in quantum wells under tensile strain.

A simple theory for the crosstalk in multichannel wavelength-division multiplexing (WDM) communication systems caused by the cross gain saturation in semiconductor optical amplifier (SOA) is developed. It is shown that increasing the carrier recombination lifetime while reducing the differential gain in the SOA greatly mitigates the crosstalk. An SOA using type-II quantum wells with reduced recombination probability is designed, and its characteristics are numerically modeled for a number of different WDM systems. It is shown that when used as a preamplifier or in local/metro networks with a small number of amplifiers, error-free transmission can be achieved with the type-II SOA.

We proposed a novel extended semiconductor optical amplifier (SOA) model for applications in femtosecond pulse transmission, in which the various ultra-fast nonlinear effects, such as gain dispersion, group velocity dispersion (GVD) were taken into account. We use the extended SOA model to analyze the refractive index in response to variation of the input current and the length of SOA. In addition, the impact of carrier density pulsation and carrier heating on the refractive index dynamics of SOA was discussed respectively. The refraction index dynamics that occur in bulk InGaAsP SOA in response to femtosecond pulse (Full width at half maximum is 200fs) are studied numerically. We use the alpha factors (α-factors) to calculate the phase shift from the gain variations, which are related to the refractive index changes. We have considered the effects of carrier heating (CH), and spectrum hole burning (SHB) to analyze the impact of intra-band carrier dynamics on nonlinear refraction index. We also consider the impact of the length of SOA and operation condition on the refraction dynamics.

Analysis of the broadband gain of a GaInNAs single quantum well (QW) semiconductor optical amplifier (SOA) is developed considering the tuneability of the gain in detail. The SOA is analyzed as a single device multiwavelength channel amplifier in a wavelength-division-multiplexing (WDM) network. The gain model includes the QW material gain derived using a band anti-crossing model and includes quantum dot (QD) fluctuations in the conduction band arising from compositional fluctuations of N within the QW. The material gain is broadened by adding the gain of the QD-like fluctuations and the QW confined level. Simultaneous amplification of two optical signals is analyzed, one at the peak of the QW gain and one at the peak of the QD distribution gain, and the linear and nonlinear regions are established. In addition, multi-channel signal amplification, appropriate for WDM applications, has been modeled across the frequency range of the QW and the QD-like fluctuations and no wavelength degradation between the channels was observed demonstrating the potential of dilute nitride QW as multiwavelength SOAs at optical communications wavelengths.

Modulation of magnetic properties of trilayer MoS2/ZnO/VS2 van der Waals heterostructure via strain engineering for spintronics application

Comparison of structural and optical properties in strained GaInAsP MQW structures grown by MOVPE and MOMBE

We investigate the effect of tensile and compressive strain in Phosphorene FET. Different percentage of tensile and compressive strain are applied on monolayer Phosphorene along the zigzag edge and the corresponding effects on bandgap, electron effective mass and ON current are analyzed. The optimum strain region is observed at 4% tensile strain for Phosphorene for the application in FET device. About 8.5 times improvement in ON current was observed for this strain percentage.

Strain-induced work function in h-BN and BCN monolayers

Strain-tuned structural, optoelectronic and dielectric properties of cubic MAPbI3 perovskite driven by SOC using first-principles theory

The thermal conductivities of single-layer BC3 (SLBC) sheets and their responses to environmental temperature, vacancy defects and external strain have been studied and compared with those of single-layer C3N (SLCN) sheets by molecular dynamics (MD) simulations. We found that SLBC and SLCN are isotropic in the basal plane and that their predicted thermal conductivities for infinite length sheets are 488.54 W m-1 K-1 and 799.87 W m-1 K-1, respectively. Despite many similar features in the structures of these materials, SLBC exhibits a lower thermal conductivity than SLCN due to stronger flexural acoustic phonon-defect scattering rates and weaker interatomic bonding stiffnesses. The vibrational density of states (VDOS) are calculated in both structures to elucidate their thermal conductivity differences. SLBC exhibits a more substantial redshift phenomenon in the high- and low-frequency domains than SLCN. In addition, the thermal conductivities of these materials exhibit decreasing trends in response to increases in temperature and defect ratio, and the temperature effect in SLBC is more substantial than that in SLCN, while the defect effect in SLBC is less substantial than that in SLCN. The influences of uniaxial compressive and tensile strains on the thermal conductivities of these materials are analysed separately. These two deformation modes cause different effects on the thermal transport behaviours of SLBC and SLCN: the effect of uniaxial compressive strain is slightly negative, while the effect of uniaxial tensile strain is initially positive and then negative. Moreover, the biaxial strains result in a more severe reduction in thermal conductivity than the uniaxial strains. Remarkably, the impact of uniaxial and biaxial tensile strains on thermal transport was stronger in SLBC than in SLCN. We propose that SLBC nanomembranes are promising candidates for various thermal applications.

Summary form only given. An overview is presented of the progress in design and characteristics of semiconductor optical amplifiers (SOA) for 1310, 1400 and 1550 nm operation in fiber optical transmission systems. The technology and performance of SOAs will be discussed with respect to optical gain, noise figure, saturation output power and polarization (in-) dependent behavior. The use of both strained quantum wells and bulk tensile material will be discussed in view of obtaining polarization independent behavior. Gain clamping in SOAs has been shown to improve the linearity performance especially for analogue signal transmission. The SOA technology has been demonstrated for optical pre-amplification, in-line application and optical booster applications. DWDM experiments using SOAs in up to 20 Gbit/s systems in short- and medium-distance transmission will be highlighted. Also, SOAs have been used in optical demultiplexing from 40 Gbit/s down to 10 Gbit/s RZ signals using its phase properties and in integrated photonic devices like multiwavelength lasers.

First principle study of strain tunable electronic and optical properties of half-Heusler alloys XCoGe (X=V, Nb, Ta)

Vibrations of single- and double-walled carbon nanotubes with layerwise boundary conditions: A molecular dynamics study

Al2O3 atomic layer deposition (ALD) is a model ALD system and Al2O3 ALD films are excellent gas diffusion barrier on polymers. However, little is known about the response of Al2O3 ALD films to strain and the potential film cracking that would restrict the utility of gas diffusion barrier films. To understand the mechanical limitations of Al2O3 ALD films, the critical strains at which the Al2O3 ALD films will crack were determined for both tensile and compressive strains. The tensile strain measurements were obtained using a fluorescent tagging technique to image the cracks. The results showed that the critical tensile strain is higher for thinner thicknesses of the Al2O3 ALD film on heat-stabilized polyethylene naphthalate (HSPEN) substrates. A low critical tensile strain of 0.52% was measured for a film thickness of 80 nm. The critical tensile strain increased to 2.4% at a film thickness of 5 nm. In accordance with fracture mechanics modeling, the critical tensile strains and the saturation crack densities scaled as (1/h)1/2 where h is the Al2O3 ALD film thickness. The fracture toughness for cracking, KIC, of the Al2O3 ALD film was also determined to be KIC = 2.30 MPa m1/2. Thinner Al2O3 ALD film thicknesses also had higher critical strains for cracking from compressive strains. Field-emission scanning electron microscopy (FE-SEM) images revealed that Al2O3 ALD films with thicknesses of 30–50 nm on Teflon fluorinated ethylene propylene (FEP) substrates cracked at a critical compressive strain of ∼1.0%. The critical compressive strain increased to ∼2.0% at a film thickness of ∼20 nm. A comparison of the critical tensile strains on HSPEN substrates and critical compressive strains on Teflon FEP substrates revealed some similarities. The critical strain was ∼1.0% for film thicknesses of 30–50 nm for both tensile and compressive strains. The critical compressive strain then increased more rapidly than the critical tensile strain for thinner films with thicknesses < 30 nm. The high critical tensile and compressive strains for thin Al2O3 ALD films should be very useful for flexible gas diffusion barriers on polymers.