The demand for ever-increasing system performance- channel count, bit rate and span length- is driving the development of higher-performance erbium doped fiber amplifiers (EDFAs) and the deployment of distributed Raman amplification. This in turn has driven requirements for increasing output power from the highly reliable 1420nm to 1510nm laser diodes used in the power amplifier stage(s) of EDFAs and as the basis for C- and L-band Raman amplification. Wavelength division multiplexing (WDM) of pump lasers for higher-power EDFAs and control of the gain spectrum in Raman amplification have also driven the increased need for wavelength stabilization of these devices. At the same time, tight system space constraints have driven the need for improved efficiency and thermal management as the operating currents of these devices have increased. This paper reports progress at Agere Systems in the development and manufacture of extremely high-reliability, high-power laser diode pump sources, including >300mW Fiber Bragg Grating (FBG) -stabilized and Distributed FeedBack (DFB) -based wavelength stabilized modules, for current and future-generation telecommunications systems.
Quantum well intersubband photodetectors (QWIPs) are potentially important devices for mid- and long-IR wavelengths, especially for focal plane arrays and two-color applications. State-of-the-art QWIPs for detecting light in the mid-IR wavelength range consist of multiple InGaAs quantum wells separated by AlGaAs barriers. The multiple strained InGaAs wells necessary for detection in this wavelength range inevitably lead to lattice relaxation in the epitaxial structure. We have previously demonstrated that the dark current of InGaAs/GaAs QWIPs for detection near 14 microns could be reduced significantly by using strain-compensation to reduce the lattice relaxation in the structure. Here we apply strain-compensation to reduce the relaxation of InGaAs/AlGaAs QWIPs designed for mid- wavelength IR response. We demonstrate the growth of 20 periods of 30A In0.35Ga0.65As quantum wells separated by 330A barriers which shows no lattice relaxation as measured by asymmetric x-ray diffraction rocking curves. A strain-compensated QWIP with peak response near 5.5 microns is demonstrated with responsivity of 0.07A/W and 105K background limited operation at 5V bias.
A very high performance two-stack, two-color, high strain (HS- ) quantum well infrared photodetector (QWIP) has been demonstrated. The sample was grown on a semi-insulating (100) GaAs by molecular beam epitaxy (MBE). It consists of two stacks of MWIR and LWIR QWIPs as the active region with a 100 nm thick highly doped contact layer grown between the two stacks. Each stack is designed to have detection in one of the two atmospheric windows, 3 - 5 micrometer (MWIR) and 8 - 12 micrometer (LWIR), respectively. The MWIR stack consists of 20 periods of 300 angstrom Al0.38Ga0.62As barrier and 24 angstrom doped In0.35Ga0.65As well sandwiched between two 5 angstrom GaAs, and the LWIR stack is composed of 20 periods of 500 angstrom Al0.27Ga0.73As barrier and 55 angstrom GaAs well. In this work, a 35% of indium has been employed in the MWIR-stack which not only shifts the peak wavelength to 4.3 micrometer, but also enhances the responsivity greatly in this wavelength band. This is due to the fact that higher indium concentration in the InGaAs QW reduces the electron effective mass and increases the intersubband absorption. Despite of the large strain induced by the high indium concentration, the device is highly uniform with very low dark current. For the MWIR stack, a peak responsivity of Rp equals 0.65 A/W and D* equals 1.9 by 1011 cm-Hz1/2/W at 4.3 micrometer, 3 V bias, and 77 K were obtained, while for the LWIR stack, Rp equals 0.55 A/W and D* equals 2.7 by 1010 cm-Hz1/2/W at 9.4 micrometer, 2 V bias, and 77 K were obtained using 45 degree light coupling. Normal incidence without grating coupling also has high responsivity with about 50% for the MWIR stack and 40% for the LWIR stack respectively, compared with the 45 degree incidence coupling. The BLIP temperature was found to be 125 K for the MWIR stack with cutoff wavelength of lambdac equals 4.6 micrometer and 70 K for the LWIR stack with (lambda) c equals 10 micrometer.
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