Kushant Uppal

Noncollinear four-wave mixing in a broad area semiconductor optical amplifier

A high-efficiency noncollinear four-wave mixing in a broad area traveling-wave semiconductor optical amplifier is demonstrated. A key feature of the demonstrated configuration is the ability to isolate generated sidebands from the inputs. A wave-mixing efficiency of +8.2 dB with 22.6 dB of sideband isolation at 6° separation between the two pump beams was obtained. The dependence of the efficiency on pump detuning, separation angle, and probe wavelength was also investigated. Use of a high quality traveling-wave amplifier enabled us to achieve ripple-free broadband operation over 37 nm. The demonstrated configuration is a key to practical implementations of four-wave mixing based devices.

AMBIPOLAR DIFFUSION COEFFICIENT AND CARRIER LIFETIME IN A COMPRESSIVELY STRAINED INGAASP MULTIPLE QUANTUM WELL DEVICE

By using the technique of noncollinear nearly-degenerate four-wave mixing, ambipolar diffusion coefficients and carrier lifetimes were directly determined for a compressively-strained InGaAsP multiple quantum well semiconductor optical amplifier operating at 1.3 μm. A diffusion coefficient of 8.0 cm2/s and a carrier lifetime of 1.33 ns, were obtained at the amplifier current density of 1.88 kA/cm2. The current-density dependent measurements show that the diffusion coefficient will drop with increasing amplifier pumping current, which is consistent with the prediction of the conventional semiconductor theory.

Strain effects on InGaP-InGaAsP-GaAsP tensile strained quantum-well lasers

Tensile strained InGaP-InGaAsP-GaAsP single quantum well broad area lasers have been grown by metalorganic chemical vapor deposition and the effects of strain on the device parameters have been studied. The lasing mode is found to be TE for a strain of -0.46% and TM for a strain of -0.71%. The role of barrier height in controlling gain and temperature dependence in this system is measured. A low threshold current density of 221 A/cm/sup 2/ has been obtained for a cavity length of 2.34 mm with -0.46% strain.<<ETX>>

Composition control of InGaAsP in metalorganic chemical vapor deposition using tertiarybutylphosphine and tertiarybutylarsine

Abstract The incorporation of source elements in the low-pressure metalorganic chemical vapor deposition of InGaAsP quaternary compounds using tertiarybutylphosphine (TBP) and tertiarybutylarsine (TBA) has been investigated. Measurement of the specific heat of TBP and TBA allows the absolute delivery rates of reactants to be controlled accurately to achieve a wide range of V/III ratios. The analysis of the quaternary composition shows that the incorporation of group III elements is determined solely by their delivery rate, independent of the group V composition. Meanwhile, the group V sublattice composition at typical growth temperatures is determined by a single parameter – the TBP/III ratio. The incorporation efficiency of TBA relative to TBP increases and then saturates as the TBP/III ratio increases. A model is proposed based on the balance between enhancement of the decomposition of TBA in the presence of t-butyl or PHn (n=1 or 2) radicals and its suppression by the presence of group III radicals.

A novel all-optical switch: the wavelength recognizing switch

A new class of an all-optical switch-the wavelength recognizing switch is proposed and experimentally demonstrated. The device uses a control signal to sense the wavelength of the input packet and taps a portion of the data packet to the appropriate output port. The device is based on noncollinear four-wave mixing in a broad-area traveling-wave semiconductor optical amplifier. Measured switching efficiency is +8.2 dB with -28.8 dB of crosstalk. The recognition bandwidth is as narrow as 0.03 /spl Aring/ and the 3-dB switching bandwidth is 42 nm.

Characterization of mixed strain quantum well structures

Polarization resolved photoluminescence from a cleaved sample edge (edge photoluminescence) is shown to be a useful tool for characterization of complex multiple quantum well InP based structures with wells of different strains. The polarization resolved luminescence resulting from the heavy- and light-hole transitions of In0.51Ga0.49As0.78P0.22 tensile and In0.9Ga0.1As0.52P0.48 compressive wells are found to match closely with theoretical values, validating assignments applied to the peaks obtained from photoluminescence. Strain distribution is shown to be an important effect when quantum wells of opposite strain are mixed together in the growth structure. The overlap of the transverse-electric (TE) and transverse-magnetic (TM) emissions found from edge photoluminescence on a mixed strain quantum well structure is shown to have an excellent match with the overlap of the TE and TM modes of a laser which uses the same structure in its active region.

Growth and doping properties of AlGaAs/GaAs/InGaAs structures on nonplanar substrates for applications to low threshold lasers

Abstract The growth behavior of AlGaAs/GaAs/InGaAs structures on non-planar (100) GaAs substrates has been studied. The structures were grown by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) on substrates which have mesa stipes aligned along the ( 1 10) direction with (100) mesa tops and (111)A sidewalls. The growth rates and the doping of the AlGaAs/GaAs/InGaAs layers are shown to have a strong dependence on the crystallographic orientation as the sidewall approaches the (111)A plane. Growth temperature and III–V ratio also affect the relative growth rate and the doping of the layers. Using the above properties, we have grown and fabricated low threshold InGaAs/GaAs QW lasers by a single step MOCVD growth. Threshold current as low as 0.5 mA for uncoated DQW lasers has been achieved.

Sub-milliampere threshold InGaAs/GaAs/AlGaAs laser array elements by single step growth on nonplanar substrates

Ultra-low-threshold current InGaAs/GaAs lasers are made by single-step MOCVD growth on nonplanar substrates. Active region widths ranging from 1.6 to 0.2 /spl mu/m have been studied. Uncoated laser threshold currents as low as 0.5 mA has been obtained.

An optical filter based on carrier nonlinearities for optical RF channelizing and spectrum analysis

We experimentally demonstrate filtering based on the finite time response of the interband carrier nonlinearities in a direct bandgap semiconductor. The filter is implemented in a mixed strain polarization insensitive multiple-quantum-well, broad-area semiconductor amplifier. The key to the filter implementation is the separation of a four-wave mixing generated sideband from the linearly amplified inputs based on spatial filtering. Both spectrum analysis and channelizing of RF modulated optical carriers are demonstrated.

A tunable optical domain microwave filter suitable for wideband channelizing

We present the experimental demonstration of a novel narrowband optical domain RF filter based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). With the advent of high bandwidth, low V, electro-optical modulators, it has become feasible to modulate a very broad band RF signal (100 GHz) onto an optical carrier and distribute it by fiber with a respectable link gain.