A monolithic passively mode-locked laser is proposed as a compact optical sensor for displacements and vibrations of a reflecting object. The sensing principle relies on the change of the laser repetition frequency that is induced by optical feedback from the object under measurement. It has been previously observed that, when a semiconductor passively mode locked laser receives a sufficient level of optical feedback from an external reflecting surface it exhibits a repetition frequency that is no more determined by the mode-locking rule of the free-running operation but is imposed by the length of the external cavity. Therefore measurement of the resulting laser repetition frequency under self-injection permits the accurate and straightforward determination of the relative position of the reflecting object. The system has an inherent wireless capability since the repetition rate of the laser can be wirelessly detected by means of a simple antenna which captures the microwave signal generated by the saturable absorber and is emitted through the wiring of the laser. The sensor setup is very simple as it requires few optical components besides the laser itself. Furthermore, the deduction of the relative position of the reflecting object is straightforward and does not require any processing of the detected signal. The proposed sensor has a theoretical sub-wavelength resolution and its performance depends on the RF linewidth of the laser and the resolution of the repetition frequency measurement. Other physical parameters that induce phase changes of the external cavity could also be quantified.
The intensity noise properties of injection locked mid-infrared quantum cascade lasers are experimentally investigated. The injection locking is realized below and near the threshold of the free running slave laser, resulting in an efficient technique to achieve low noise operation. It is found that below threshold the locking characteristics (locking range shape and bandwidth) are different in comparison to those above threshold. Furthermore, an alternative injection locking realization is also investigated: injection locking into longitudinal side modes of the slave laser. Here, similar characteristics were observed, however, with the potential to achieve even higher relative intensity noise reduction suppression with respect to the quantum noise limit. The measurements are confirmed by numerical simulations with a travelling-wave model which takes into account the multi-mode spectrum of the slave laser and the spectral profile of the material gain. The experiments give the perspective for the achievement of the relative intensity noise reduction of the slave laser of up to 10 dB (above threshold) and up to 20 dB (below threshold) in comparison to the free running slave laser noise level.
In this study two types of coplanar waveguide (CPW) array antennas are designed and analyzed for use in a 60GHz
Radio over Fiber indoor network. The first one is based on high permittivity Rogers 6010 and Indium Phosphide (InP)
substrates incorporating slots as radiating elements. The second one utilizes stacked geometry based on the above
substrates. Both arrays present more 1 GHz bandwidth and 10dBi gain. Furthermore they can provide beam-forming
operation by properly adjusting the signal’s amplitude and phase. A Least Mean Square (LMS) algorithm is generated
for this purpose and the radiation pattern is steered accordingly. At last, a photodiode is simulated using equivalent
circuit and is adopted with the proposed arrays, and an optical beam forming scenario is discussed.
Semiconductor microring resonators are excellent fundamental building blocks for the development of opto-electronic
integrated circuits (OEICs), due to their large third-order nonlinearities enhanced by the resonance effect and
compactness which leads to monolithic integration capability. A wide range of potential applications is presented and
analyzed and the applicability of microring based devices as low-cost fundamental units in access/metro optical
networks is discussed.
Microring resonators are excellent candidates for very large scale photonic integration due to their compactness, and fabrication simplicity. Moreover a wide range of all-optical signal processing functions can be realized due to the resonance effect. Possible applications include filtering, add/drop of optical beams and power switching, as well as more complex procedures including multiplexing, wavelength conversion, and logic operations. All-active ring components based in InGaAsP/InP are possible candidates for laser sources, lossless filters, wavelength converters, etc. Our work is based on measurement, characterization and proposal of possible exploitation of such devices in a variety of applications. We investigate the spectral characteristics of multi-quantum well InGaAsP(λ=1.55μm)/InP microring structures of various ring diameters and different configurations including racetracks with one or two bus waveguides and MMI couplers. The latter configuration has recently exhibited the possibility to obtain tunable active filters as well as tunable laser sources based on all-active ring-bus-coupler structures. In the case of tunable lasers single mode operation has been achieved by obtaining sufficiently high side mode suppression ratio. The tuning capability is attributed to a coupled cavities effect, resembling the case of multi-section DBR lasers. However, in contrast to the latter, the fabrication of microring resonators is considered an easier task, due to a single step growth procedure,
although further investigation must be carried out in order to achieve wide range tunability. Detailed mappings of achievable wavelengths are produced for a wide range of injection current values.
A novel all-optical regeneration approach based on fiber-optic parametric amplification operating under the strong pump depletion regime is numerically demonstrated. The key point for the regenerator's operation is related to the fact that a high-power intensity modulated signal depletes the continuous wave pump in such a manner that the latter becomes intensity modulated and inverted compared to the signal. Using a cascade of two such devices a non-inverted, either wavelength converted or not, amplitude modulated output, which exhibits regenerative characteristics with respect to the input signal can be provided. Extended numerical simulations have been carried out on one hand to estimate the transfer characteristics of the regenerator and on the other hand to assess the cascadability performance on a typical 40Gb/s transmission system. Through the latter analysis very promising results have been derived proving the potential of the proposed device for all-optical regeneration in cascaded operation for both return to zero and non-return to zero data transmitted along 1Mm of optical fiber at 40Gb/s.
KEYWORDS: Signal processing, Semiconductor optical amplifiers, Semiconductor lasers, Signal to noise ratio, Interference (communication), Four wave mixing, Optical amplifiers, Two wave mixing, Satellites, Nonlinear optics
A detailed numerical and experimental study of the additional RIN induced to the input waves by the FWM process, is presented. The nonlinear medium used in the experiments is a bulk Semiconductor Optical Amplifier (SOA). The measurements are carried out for different operating conditions (pumping level of the SOA, input power, input signals with different intensity noise characteristics, etc.). A complete numerical model is employed to simulate the FWM process, taking into account interaction of four waves in the SOA (two input waves and two product waves). The latter is used in order to obtain realistic behavior of the model, when operation at a wide range of input power is considered. The theoretical interpretation of the above results is based on the static transfer function of the FWM process where all waves interacting in the SOA are continuous waves (CW).
A major advantage of the Four Wave Mixing technique for wavelength conversion is its transparency to modulation format. This advantage becomes important for some IP over WDM network realizations where part of the signaling information is an analog or subcarrier modulation approach. In such applications the phase noise characteristics of the conversion process are very important. In this work, a detailed theoretical and experimental study of the additional phase noise induced by the FWM process is presented. The nonlinear elements used in the experiments are semiconductor optical amplifiers as well as dispersion shifted fibers. Two linewidth measuring techniques have been used, the self-homodyne and the beating with a laser source with already known linewidth. The measurements are carried out for different operating conditions (wavelength, pumping level of the nonlinear elements, input power, input signals with different phase noise characteristics, etc). The theoretical interpretation of the above results is based on a modification (inclusion of the influence of the amplified spontaneous emission noise) of an already presented approach which has focused on the mixing process in a resonant optical cavity.
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