Teunis van Dongen

Dependence of polarization, gain, linewidth enhancement factor, and K factor on the sign of the strain of InGaAs/InP strained‐layer multiquantum well lasers

The sign of the strain in a multiquantum well (MQW) active layer of an InGaAs/InP laser determines whether lasing occurs from the electron–heavy hole transition or from the electron‐light hole transition. Lasing from the electron‐light hole transition is reported to provide a much better performance than predicted by theory. It is concluded that this gives the best device performance, providing a higher differential gain, a lower threshold current, a record low linewidth enhancement factor of 1.5, and a K factor of 0.22 ns, potentially allowing a 3 dB modulation bandwidth of 40 GHz.The sign of the strain in a multiquantum well (MQW) active layer of an InGaAs/InP laser determines whether lasing occurs from the electron–heavy hole transition or from the electron‐light hole transition. Lasing from the electron‐light hole transition is reported to provide a much better performance than predicted by theory. It is concluded that this gives the best device performance, providing a higher differential gain, a lower threshold current, a record low linewidth enhancement factor of 1.5, and a K factor of 0.22 ns, potentially allowing a 3 dB modulation bandwidth of 40 GHz.

Effect of free carriers on the linewidth enhancement factor of InGaAs/InP (strained-layer) multiple quantum well lasers

In this letter the linewidth enhancement factor measured from a tensile strained, a compressively strained, and a lattice matched InGaAs/InP multiple quantum well laser is analyzed taking free‐ carrier effects into account. We find that the free carriers in the wells of compressively strained and lattice matched structures degrade the linewidth enhancement factor by about 40% due to the plasma effect. In tensile strained TM polarized lasers however, carrier movement parallel to the E vector is inhibited due to the quantum confinement, allowing a linewidth enhancement factor as low as 1.6 at the peak wavelength. Heterobarrier carrier leakage must be prevented using sufficiently large band‐gap barrier and separate confinement layers, otherwise the free carriers in these layers result in an additional degradation of the linewidth enhancement factor.

27-dB gain unidirectional 1300-nm polarization-insensitive multiple quantum well laser amplifier module

An unidirectional polarization-insensitive multiple quantum well laser amplifier module for the 1300-nm window with a record high gain of 27 dB and a 3-dB saturation output power of 13 dBm is demonstrated. The module gain has a 3-dB width exceeding 60 nm and shows a typical polarization sensitivity and gain ripple as low as 0.3 dB. To provide immunity for backscattered or reflected light, polarization independent optical isolators were inserted in the input and output coupling optics of the package. A practical optical amplifier module for the 1300-nm window is very desirable, because most of the presently installed fiber has its zero dispersion wavelength around 1310 mm, while much of the older fiber often only can be operated around this wavelength.<<ETX>>

Direct measurement of the transparency current and valence band effective masses in tensile and compressively strained InGaAs/InP multiple quantum‐well laser amplifiers

Transparency current densities of 250 and 160 A/cm2 per well at the bandgap wavelength are reported for compressively and tensile strained multi quantum‐well laser amplifiers. A strong wavelength dependence of the transparency current is found, due to level broadening, which shows that the threshold current of a quantum‐well laser is inherently loss limited, rather than transparency limited. The spectral and polarizational dependence of the gain is measured and analyzed. From this it is concluded that the compressively (1.8%) and tensile (1.6%) strained quantum‐well laser amplifiers exhibit valence band effective masses of 0.07 m0 and 0.1 m0, respectively, which shows that they both have a nearly symmetric band structure.

Temperature dependence of a 1300 nm polarization-insensitive multiple quantum well laser amplifier and its implications for the ultimate capacity of cascaded amplifier systems

The temperature characteristics of a 1300 nm polarization-insensitive multiple quantum well laser amplifer are investigated at a constant level of the amplified spontaneous emission. Upon increasing the amplifier temperature from O/spl deg/C to 40/spl deg/C, a 20% increase in the gain bandwidth and a twofold increase in the saturation output power, due to an increase in Auger recombination, are observed. The implications of these results on the ultimate capacity of cascaded amplifier systems is evaluated using the concept of the maximum length amplifier cascade. When operated at 40/spl deg/C, this length extends to 6000 km, which is of great relevance for the design of 1300 mm soliton systems, because these short pulses are considered to be able to traverse these large lengths of optical fiber without distortion.<<ETX>>

Direct electronic compensation of the amplification nonlinearity in semiconductor laser amplifiers

Direct electronic compensation of the inherent amplification nonlinearity of semiconductor laser amplifiers is investigated. It is found that operating the active layer junction from a voltage source, which in theory would hold the carrier density at a constant value, does not remove the amplification nonlinearity because of the intraband carrier dynamics. However, compensation of the nonlinearity is shown to be possible by driving the laser amplifier from a negative output impedance source. Using this at 80 mA drive current compensation of the amplification nonlinearity is demonstrated for a 1310 nm polarization insensitive multiple quantum well laser amplifier showing 18 dB gain (13 dB fiber to fiber) and a nonlinearity of 0.36 dB/mW. It is further shown that the intraband carrier dynamics, mainly the carrier heating, cause limitations to both the driving conditions for which the nonlinearity can be compensated, and to the use of laser amplifiers as an amplifying detector.