Performance of optical heterodyning and external modulation by using an electro-optical modulator technique is evaluated. The first approach is carried out by beating two optical signals with a wavelength spacing corresponding to the desired microwave or millimeter-wave frequency continually tuned. The second technique requires only a single laser source along with a Mach-Zehnder Intensity Modulator (MZ-IM). Due to the available electrical bandwidth of the photodetector used, the experimental results are limited to the frequency range of 13 GHz. All experimental results are validated by a series of simulations using the VPI software. Signal-to-Noise ratio (SNR) and Phase-Noise parameters are measured.
KEYWORDS: Analog electronics, Microwave radiation, Bandpass filters, Microwave photonic filters, Optical filters, Optical fibers, Electronic filtering, Signal to noise ratio, Dispersion, Fiber to the x
A practical application of a bidirectional microwave photonic filter (MPF) to transmit simultaneous analog TV signals coded on microwave carriers is experimentally demonstrated. The frequency response of the bidirectional MPF is obtained by the interaction of an externally modulated multimode laser diode emitting at 1.55 μm associated to the free-spectral range of the optical source, the chromatic dispersion parameter of the optical fiber, as well as the length of the optical link. The filtered microwave bandpass window generated around 2 GHz is used as electrical carrier in order to simultaneously transmit TV signals of 67.25 and 61.25 MHz in both directions. The obtained signal-to-noise ratios for the transmitted signals of 67.25 and 61.25 MHz are 37.62 and 44.77 dB, respectively.
A modulator fundamental part of Mach Zhender interferometer is studied. This interferometer has applications such as a sensor or spectral analyzer. The modulator was designed on a SOI substrate comprising a dual capacitor structure that allows the electro optical modulation through the overlap of the plasma dispersion effect (variations of the free carriers density due to electric field induced carrier depletion) with the guidewave mode that induce the change of the effective refractive index. The modulator is excited by a tension ramp between 0 and 2V yielding performance exceeding 7 GHz.
KEYWORDS: Cadmium sulfide, Thin films, Annealing, Solar cells, Transmittance, Thin film solar cells, Atomic force microscopy, Crystals, Cadmium, Electro optics
In this work we report the fabrication and electro-optical characterization of CdS thin films using glycine as complexing agent with ammonia and ammonia free buffer by the Chemical Bath Deposition (CBD) method. The CdS thin films were grown at different temperatures of 50, 60, 70 and 80 °C in a thermal water bath. The morphology of these films was determined using atomic force microscopy; the resultant films were homogeneous, well adhered to the substrate, and specularly reflecting with a varying color depending on the deposition temperature. Transmittance and reflectance measurements of thermally treated CdS films were carried to study the effect of the ammonia buffer on its optical properties and bandgap. The crystallinity of the CdS thin films was determined by means of X Ray diffraction measurements. Therefore, for this study, an ammonia-free complexing agent has been taken for the deposition of CdS. Among different methods, which are being used for the preparation of CdS films, Chemical Bath Deposition (CBD) is the most attractive due to its low cost, easy to handle and large possibilities regarding doping and deposition on various substrates. In particular it can be used to easily obtain field effect devices by depositing CdS thin films over a SiO2/Si substrate. Heterostructures with interesting physical properties can be imagined, realized and tested in this way.. Structures CdS/PbS also were realized and have shown good solar cell characteristics.
We describe an analog microwave photonic link system, which is used to transmit in a multiplexed way a TV signal over 30 km of standard optical fiber. The experimental setup is composed mainly by two distributed feedback (DFB) laser diodes emitting at 1500 nm. When these DFB lasers are operated in the low laser threshold current region, relaxation oscillation frequencies are obtained. Relaxation oscillations in the laser intensity can be seen as sidebands on both sides of the main laser line. The optical emissions generated in each laser are combined and amplified by using an erbium-doped fiber amplifier. Next, the amplified optical signal is detected by a fast photo-detector using direct detection method, and as result of this photo-detection, microwave signals are generated. Since microwave signals obtained by using this technique are tuned continuously; we can use them as electrical carriers to transmit simultaneously a TV signal at 4 and 5 GHz and over 30 km of standard optical fiber by using a Mach-Zehnder modulator. At the end of the optical link the modulated light is photo-detected in order to recover efficiently and successfully the analog TV signal.
In this paper we describe an analog microwave photonic link system used to transmit simultaneously two TV signals.
The experimental setup is composed mainly by two distributed feedback (DFB) laser diodes emitting at 1500 nm. When
DFB lasers are operated in the low laser threshold current region, relaxation oscillation frequencies are obtained.
Relaxation oscillations in the laser intensity can be seen as sidebands on both sides of the main laser line. The optical
emissions generated in each laser are combined and amplified by using an Erbium-Doped Fiber Amplifier (EDFA).
Next, the amplified optical signal is detected by a fast photo-detector using direct detection method and as result of this
photo-detection microwave signals are generated. Microwave signals obtained by this technique are used as electrical
carriers to transmit analog TV signals over 30 km of standard optical fiber by using a Mach-Zehnder modulator (MZM).
At the end of the optical link the modulated light is photo-detected in order to recover efficiently and successfully the
analog TV signals.
Relaxation oscillation frequency is produced when a laser is operated in the low laser threshold current region. In this
operation region, a semiconductor laser shows a smooth curve, where we can observe uncertainty into defining the onset
of laser oscillation. Relaxation oscillations in the laser intensity can be seen as sidebands on both sides of the main laser
line. In this context, a communication system by using a relaxation oscillation frequency as an information carrier is
proposed in this paper. The experimental setup is based on operation principle of direct detection, where the obtained
microwave signal at the output of a fast photodetector is located on C band and it is modulated with an analog NTSC TV
signal.
Optical microspectrometers have huge potential for application in industry, science, medicine, agriculture and biology.
The actuallity is towards fully integrated optical microsystems. Complete silicon IC compatible MEMS-based optoelectrical
microsystems on a single chip. This systems however, impose limitations. The required process compatibility
and limited choice of acceptable materials does not necessarily give high optimal optical performance. This work study
the best characteristics of micromirrors fabricated with anisotropic etching and used in spectrophotometers and endedended
systems. The trends, the potential, the limitations and approaches to obtain a sufficient optical performance, in
terms of spectral resolution and throughput, for serving the majority of applications.
The generation, distribution and processing of microwave signals in the optical domain is a topic of research
due to many advantages such as low loss, light weight, broadband width, and immunity to electromagnetic
interference. In this sense, a novel all-optical microwave photonic filter scheme is proposed and experimentally
demonstrated in the frequency range of 0.01-15.0 GHz. A microwave signal generated by optical mixing drives the
microwave photonic filter. Basically, photonic filter is composed by a multimode laser diode, an integrated Mach-
Zehnder intensity modulator, and 28.3-Km of single-mode standard fiber. Frequency response of the microwave
photonic filter depends of the emission spectral characteristics of the multimode laser diode, the physical length
of the single-mode standard fiber, and the chromatic dispersion factor associated to this type of fiber. Frequency
response of the photonic filter is composed of a low-pass band centered at zero frequency, and several band-pass
lobes located periodically on the microwave frequency range. Experimental results are compared by means of
numerical simulations in Matlab exhibiting a small deviation in the frequency range of 0.01-5.0 GHz. However,
this deviation is more evident when higher frequencies are reached. In this paper, we evaluate the causes of
this deviation in the range of 5.0-15.0 GHz analyzing the parameters involved in the frequency response. This
analysis permits to improve the performance of the photonic microwave filter to higher frequencies.
In this work we report the photonic generation of microwave signals for distributing point to point analog TV signals by
using microstrip antennas. The experimental setup is based on optical heterodyne technique where two optical waves at
different wavelengths are mixed and applied to a photodetector. The microwave signal obtained by using this technique
is used in a wireless communication system for transmitting and receiving analog TV signals.
KEYWORDS: Microwave radiation, Signal generators, Signal detection, Radio optics, Optical filters, Telecommunications, Signal processing, Electronic filtering, Sensors, Heterodyning
In this work we report the generation of microwave signals using photo-mixing of two laser beams. In this case, one laser beam is single mode and the other one shows a multimode spectrum. Due to spectral separation between the two lasers, microwave signals can be generated and tuned between 1 and 25 GHz, the bandwidth of the generated signal is approximately 2.5 GHz; however, using narrow-band microwave filters, the photo generated signal can provide microwave information carriers for high-speed telecommunication systems.
In this work we report the generation of microwave signals using photomixing of two diodes lasers. With this technique we can mix two optical signals that come from two different lasers. One laser is a single mode and the other laser is a multimode. Due to spectral separation between two lasers, microwave signals can be generated and tuned between 1 and 25 GHz. The bandwidth of the generated signal is approximately 2.5 GHz, however with the design and realization of microwave filters we can filter the photo generated signal and in this way, it is possible to obtain a radio frequency signal that can be used as a high frequency information carrier.
A theoretical design and experimental realization of multi-layer mirrors for Fabry-Perot interferometry and optical telecommunications is described in this work. The mirrors were designed and fabricated by 13 successive thin layers to achieve very high reflectance at optical wavelengths around 1300 nm. Thin layers are ZnS y MgF2 presenting high and low refractive index respectively. Layer thickness are of λo/2 at λo = 656 nm. Experimental results include the characterization of the transmittance of mirrors around 1300 nm. Additionally the mirrors were integrated in a Fabry-Perot interferometer to characterize optical sources emitting at 1300 nm. Finally to show a practical application, optical phase modulation was analyzed, using the fabricated mirrors.
In this work we study the generation of radio frequency signals using optical mixing. This is a recent technique for generating rf carriers which can be used in telecommunication systems for multiple purposes.
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