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Conventional tunable semiconductor lasers tuned by the carrier induced effect suffer from intrinsically nonuniform optical frequency modulation (FM) response due to the associated thermal effect. Electric field effect tuned lasers involving no current injection, offer intrinsically uniform FM response. We report here the first quantum-confined Star...
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... a twin guide structure laser using QCSE tuning [14] (FM response uniform within 15 dB from 300 kHz to 4 GHz), a butt-jointed DBR structure laser tuned by the related Wan- nier-Stark effect [15] (no uniformity data, cutoff frequency less than 4 GHz) and bulk and quantum well electroabsorption tuned lasers [10], [11] (no uniformity data) have been reported. These lasers require regrowth and very complicated fabrication steps. Using a simple two-section integrated ridge waveguide laser structure, we have demonstrated the highly uniform FM response capability of a QCSE tuned laser ( 0.7 dB from 10 kHz to 100 MHz), free from thermal effect [16]. We now report results on QCSE tuned lasers fabricated on a SI GaAs substrate with postgrowth bandgap detuning and low parasitic capacitance air-bridged contacts, offering simple fabrication requirements, highly uniform FM response, high cut-off frequency, independent control of output power, and suitable for application where an uniform FM response over a limited tuning range is required. Fig. 1 shows the schematic cross section of the device. The GaAs-AlGaAs multiquantum-well (MQW) active layer is grown on a (100) SI GaAs substrate by MOVPE in a single epitaxy step and contains five quantum wells, the number being chosen to optimize the relationship between modal gain and threshold current of the gain section and refractive index change in the tuning section. The undoped MQW layer and two 0.15-m-thick AlGaAs guiding layers are sandwiched between silicon doped lower cladding and carbon-doped upper cladding layers, each of thickness 1.5 m. Carbon is chosen rather than zinc as the acceptor dopant for the upper cladding layer to avoid the problem of zinc diffusion into the active layers during the high temperature annealing required for postgrowth bandgap detuning. Gain and tuning sections share a single cavity optically, but are isolated from each other electrically by a 30-m-wide etched isolation gap in the contact and cladding layers between them, giving an intersection resistance of 5 k ...
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... In this perspective, the theoretical investigation of the electric field effect on the conduction intraband structure and implicitly on the radiative transitions in QWs and QWWs acquires a special relevance. It becomes of wide interest the significant modification of the energies and wave functions (WFs) of the charge carriers in biased quantum structures, that is, the Stark Effect [19][20][21][22][23][24]. In the last 30 years, the improvement of the techniques for growing QWWs has allowed obtaining novel one-dimensional structures of various compositions and shapes [25][26][27][28][29][30][31][32]. ...
We investigate the tunnel effect influence on the intersubband optical absorption and refraction in a gallium arsenide quantum well wire in transverse electric field. The quasi-stationary energy levels and escape times are obtained using the complex eigenvalue study in a two-dimensional finite element method. The linear absorption coefficient and the relative change of the refractive index are calculated according to the Fermi's golden rule and by involving the intersubband relaxation time. Our work shows that the electronic linewidth broadening related to the carrier tunneling has a major effect on the optical absorption lines, especially for intense electric fields. Absorption peaks are blue-shifted by the increasing electric field and, at the same time, they are enlarged and decreased in amplitude. A field-invariable relaxation rate, as is assumed by many previous theoretical studies, could not be justified, even for moderate electric fields.
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... Complex-coupled DFB lasers have been shown to have flat FM responses without phase inversion between 10 kHz and over 20 GHz [22]. The requirement for precise control of the lasers' bias current and the fact that the FM-response uniformity and sensitivity depend on the output power level are disadvantageous for OPLL applications [19]. Multi-section tunable semiconductor lasers have been very popular in the past in OPLLs [2], [17], [19], [23], [25]. ...
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... For frequency tuning by injection current, the available bandwidth of an OPLL is also limited by the inversion in sign of the FM response, usually observed for semiconductor lasers at typically a few megahertz. Special lasers, frequency tuned by the quantum confined Stark effect (QCSE) [18] can be used to overcome this limit [19]. One heterodyning method offering the possibility to use standard wide linewidth lasers with the long term stability offered by the OPLL, without the requirement for very short loop delay time, is the optical injection phase-lock loop (OIPLL) [20], [21]. ...
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This paper provides a comprehensive understanding of a novel photonic
high-speed analog-to-digital converter (ADC) approach and its
anticipated performance. Compelling analytic models, experimental dat,
and simulation results will convince the reader that the system will
achieve the goal of developing an ADC with a resolution on the order of
12-bits and with conversion speeds in excess of 10 Gsps.
This paper provides a comprehensive understanding of a tunable
wavelength-based photonic high-speed analog-to- digital converter (ADC)
approach and its anticipated performance. Analytic models, experimental
data, and simulation results will provide the fundamental limits on the
expected conversion speed and bit resolution.
This paper provides a comprehensive understanding of a tunable
wavelength-based photonic high-speed analog-to- digital converter (ADC)
approach and its anticipated performance. Analytic models, experimental
data, and simulation results will provide the fundamental limits on the
expected conversion speed and bit resolution. A thorough in situ study
of the photonic signal conversion system under simulated space radiation
conditions is required to precisely determine its performance in either
a natural or man-made space environment. Although this study has not yet
been performed on the entire system, preliminary performance predictions
will be made based on previously published studies on the individual
components within the system. The photonic components of particular
interest that will be discussed in the context of radiation hardness
includes the edge emitting laser diode with a MQW tuning element, the
processor filters, the delay equalizers and the photodetectors.
Using a tunable semiconductor laser diode and an array of diffractive optical elements (DOEs), a time-continuous, free-space optical analog to digital converter (ADC) with five bits of resolution was experimentally evaluated. The signal to be A/D-converted was fed to the tuning sections of a grating coupled twin-guide sampled reflector (GCSR) laser diode, giving a quasi-continuous tuning range of 10 nm that spanned 40 longitudinal modes. The 32 central modes were mapped to specific digital output values by first converting wavelength to deflection angle using a diffraction grating and then focusing on an array of beam splitting DOEs. Each DOE element generated a five-spot digital code word in the detector plane. Using Gray code, only one code bit changed value at a time. Thus, the beam could straddle two adjacent DOE elements without large read out errors. Furthermore, the grating components of the elements in the DOE array were all in-phase to keep the spot focused when such straddling occurs. The SNR of a converted 10 MHz sine signal covering 23 modes was 21 dB, mainly limited by tuning hysteresis. This SNR corresponds to 3.2 effective bits. The laser's analog tuning bandwidth was found to be 45 MHz, probably limited by the carrier lifetime in the passive tuning sections, but we also measured the ADC performance at 100 MHz. As the studied ADC system is time-continuous, the sampling was done in the digital domain.
