Niloy K. Dutta

Performance of gain-guided surface emitting lasers with semiconductor distributed Bragg reflectors

The performance limitations of gain-guided vertical cavity surface emitting lasers (VCSELs) which use epitaxially grown semiconductor distributed Bragg reflectors (DBRs) are discussed. The light-current (L-I) characteristics and emission wavelength of such lasers are examined as a function of temperature and time under continuous wave (CW) and pulsed operation. The authors observed a sharp roll-over in the CW L-I characteristics which limits the maximum output power. The threshold current under CW operation is found to be lower than that obtained under pulsed conditions. Several microseconds long delay in lasing turn-on is also observed. It is shown quantitatively that these anomalies are a consequence of severe heating effects. It is shown that reduction of the series resistance and threshold current density can lead to significant improvements in the power performance of VCSELs. >

The case for Auger recombination in In1−xGaxAsyP1−y

The possible Auger recombination mechanisms in direct‐gap semiconductors are investigated. These include band‐to‐band processes, phonon‐assisted processes, and Auger recombination via shallow traps. The band‐to‐band Auger rates are calculated including Fermi statistics, nonparabolic bands, and screening effects both for n‐type and p‐type semiconductors. The nonparabolicity is calculated using the Kane‐band model. The band‐to‐band Auger processes are characterized by a strong temperature dependence, the Auger rate decreasing rapidly with decreasing temperature. The phonon‐assisted and the trap processes do not exhibit such a strong temperature dependence. This is because the additional momentum conservation for the four‐particle states in band‐to‐band processes gives rise to a ’’threshold energy’’ for the process. For the same reason, the band‐to‐band Auger rate decreases rapidly with increasing band gap. In large‐band‐gap semiconductors the weakly temperature‐dependent phonon‐assisted processes are expect...

Study of all-optical XOR using Mach-Zehnder Interferometer and differential scheme

All-optical XOR functionality has been demonstrated experimentally using an integrated SOA-based Mach-Zehnder interferometer (SOA-MZI) at 20 and 40 Gb/s. The performance of the XOR results has been analyzed by solving the rate equation of the SOA numerically. The high-speed operation is limited by the carrier lifetime in the SOA. In order to solve the limitations imposed by carrier lifetime, a differential scheme for XOR operation has been experimentally investigated. This scheme is potentially capable of XOR operation to >100 Gb/s.

Temperature dependence of threshold of InGaAsP/InP double‐heterostructure lasers and Auger recombination

We have calculated the nonradiative Auger recombination rate as a function of temperature in InGaAsP. Inclusion of this process can explain the observed temperature dependence of threshold and carrier lifetime of both the 1.3‐ and 1.55‐mm InGaAsP double‐heterostructure lasers. The threshold calculations are carried out using the Halperin‐Lax‐Kane band model, Stern’s matrix element, and Beattie‐Landsberg theory of Auger recombination. Evidence of the Auger recombination is provided by a sublinearity of the spontaneous emission as a function of injection current.

Excellent uniformity and very low (<50 A/cm2) threshold current density strained InGaAs quantum well diode lasers on GaAs substrate

We report the growth and fabrication of InGaAs/GaAs strained quantum well (QW) lasers with a very low threshold current density, Jth, of <50 A cm−2 emitting at 0.98 μm. The lasers, 1350 μm long, had two InGaAs 80 A quantum wells in the active region and Al0.6Ga0.4As in cladding layers, and were grown on 3° off (100) towards 〈111〉A GaAs substrate. Misorienting the substrate towards 〈111〉A improves the material quality and device performance substantially for x≊0.6 in the cladding layer, but degrades it somewhat for x≊0.35. The Jth increased about 25% with decreasing x from 0.6 to 0.35 due to decreased optical confinement. Single QW stripe lasers with x=0.35 tested on a 3.0 cm×1016 μm size bar, representative of the whole 5‐cm‐diam substrate, exhibited a yield of ≳90% and an excellent spatial uniformity of Jth and emission wavelengths which were 212±4 A cm−2 and 989±1 nm, respectively.

Semiconductor optical amplifiers

# Basic Concepts # Recombination Mechanisms and Gain # Epitaxial Growth and Amplifier Designs # Low Reflectivity Facet Designs # Amplifier Rate Equations and Operating Characteristics # Photonic Integrated Circuit Using Amplifiers # Functional Properties and Applications # Optical Logic Operations # Optical Logic Circuits

Calculation of Auger rates in a quantum well structure and its application to InGaAsP quantum well lasers

We discuss the possible intrinsic limitation on the temperature dependence of threshold current of long wavelength InGaAsP quantum well lasers caused by Auger recombination and intervalence band absorption. A model calculation of the various band‐to‐band Auger rates are presented. We find that the Auger rates increase with decreasing band gap and also with increasing temperature as in the case of bulk semiconductors. The temperature dependence and the band‐gap dependence arises from the energy and momentum conservation (in the direction normal to the well) that the four particle states involved must satisfy. The estimated Auger coefficient is large enough to be important in single quantum well lasers. However, the Auger effect should be much smaller in a multiquantum well laser than for a single quantum well laser. This is because the carrier density at threshold is smaller (by a factor of 3 to 4) for multiquantum well lasers than for single quantum well lasers. The increased intervalence band absorption ...

Calculated threshold current of GaAs quantum well lasers

A model calculation of the threshold current of a laser in a quantum well structure is presented. The band‐to‐band radiative recombination rate is calculated using a constant density of states and the k‐selection rule. This calculation shows that the threshold current of a GaAs single quantum well laser has low‐temperature sensitivity (T0∼330 K for T>300 K). The calculated threshold current of a 200‐A‐wide GaAs single quantum well laser is ∼550 A/cm2. The results of the calculation are compared with experimental results.

Characterization of erbium-doped fibers and application to modeling 980-nm and 1480-nm pumped amplifiers

Erbium-doped fibers are characterized using loss and gain coefficients, and one amplifier saturation parameter. With a large-signal amplifier model that resolves the amplified spontaneous emission spectrum, these easily measured parameters allow the fiber performance in 980-nm or 1480-nm pumped optical amplifiers to be assessed rapidly. In tests at 980-nm pump wavelength, good agreement between the theoretical and experimentally measured gains was obtained with amplifiers having either germano-silicate or germano-alumino-silicate core fibers.<<ETX>>

InGaAs/InP quantum well lasers with sub‐mA threshold current

We evaluate the effect of high‐reflectivity facet coatings on the threshold current of lattice matched and compressively strained InGaAs/InP quantum well lasers. A large decrease in the threshold current is observed in structures with low internal losses. Coated lasers exhibit threshold currents as low as 1.1 mA at 20 °C and 0.9 mA at 10 °C, down from ∼15 mA in as‐cleaved devices with cavity length of 200 μm. These changes are carefully modeled and the prospects for further reduction of the threshold current discussed.