Transmission, optical limiters

The transmissivity decreases with the input intensity (Fig. 3.107) and dopant concentration (Fig. 3.108) [529]. The good agreement between experimental data and the theoretical predictions given by Eqs. (86) and (87) demonstrates the dominant role of TPA in causing the observed optical limiting properties of compound 94a [529]. 

Figure 3 compiles selected results obtained for optical limiting properties of materials containing gold or silver nanoparticles. Note that the ordinate axis shows the normalized transmission - that is, the transmission normalized to unity at low input fluence - and not the absolute one. All kinds of materials roughly present the... 

For the second harmonic generation, we find that above a certain input intensity a dynamics reminiscent of a competitive, multi-wave mixing process occurs the pump field is mostly reflected, revealing a novel type of optical limiting behavior, while forward a nd b ackward g eneration i s g enerally b alanced. W e a Iso s tudy t he case of parametric down-conversion, where an intense second harmonic signal is injected in order to control a much weaker fundamental beam. Our results reveal the onset of a new process that has no counterpart in bulk materials both transmission and reflection display an unexpected, unusual, resonance-like effect as functions of input second harmonic power. 

A new type of nonlinear nano-layered polymeric optical material is described. The material comprises alternating polymer layers with thousands of layers and a layer thickness down to 30 nm or less. A nonlinear response is introduced by including an appropriate dye in alternate polymer layers. Such materials have several uses, including optical limiting. Several nano-layered materials using optical limiter dyes in alternate layers were fabricated. Some of the linear optical properties and a verification of nonlinear transmission and reflectivity at high intensity for example materials are reported. 

Optical limiters are devices with a transmission that decreases as the light intensity increases. Ideally, the transmission is high at normal light intensities, and it instantaneously decreases to minimal levels when intense beams are present. The intensity dependent transmission limits the output intensity so that it is always below some maximum value. All-optical, passive optical limiters... 

The results are presented of an investigation of the optical infrared transmission and reflection spectra of the alloy 0.7 InSb-0.3 InAs, doped with tellurium to obtain different electron densities (n). The optical width of the forbidden band (AE) and the optical effective mass of the electrons (mn) were determined from the spectra and their dependence on n studied. It was established that the conduction bands of InSb-InAs solid solutions are nonparabolic. Attempts were made by extrapolation to obtain an estimate of the limiting values of AE and mg in the region of low values of n, and an estimate of the matrix element P was made. It is concluded that there is general agreement between the structure of the energy bands of the semiconductor alloys considered and the Kane model. 

Semiconductor lasers have a tremendous potential for use in optical communication systems due to their high efficiency, small size, and direct modulation capability. Because of their small size, they become the ideal source for optical radiation to be utilized in an optical fiber transmission system. The reason for developing an optical communications system is that these systems can take advantage of the large bandwidth that optics has to offer. For example, in a conventional copper wire communication system, the bandwidth of the transmission channel, i.e., the coaxial cable, is limited to approximately 300 MHz. In a normal telephone conversation, fi equency components up to 3 kHz are required for the listener to understand the conversation. By multiplexing many telephone conversations on different carrier fi equencies, approximately 100,000 conversations can be sent through a single... 

A medium with saturable absorption can also be used for the nonlinear medium. In this case, the resonance condition is always met as far as the wavelength is concerned, but the feedback from the second mirror, which is required for resonant transmission, is not obtained until sufficient light is present inside the cavity to bleach the nonlinear medium. Devices of this type can show differential gain and optical bistability but not optical limiting. 

The end user s receiver then receives the transmitted signal through a bandwidth-limited transmission channel, which consists of any one or combination of coaxial cable, microwave, satellite, fiber optic, or broadcast transmitter. In the television receiver, the modulated RF carrier is amplified and detected to restructure the video signal and synchronizing pulses. These signals are then used to drive the display device, usually a cathode-ray tube (CRT) or other display device, which reproduces an image of the original scene. 

The bandwidth of a fiber determines the maximum transmission data rate or maximum transmission distance. Most common POF (plastic optical fiber) transmission systems adopt on-off keying by direct modulation of the optical source (laser or light-emitting diode). If an input pulse waveform can be detected without distortion at the other end of the fiber, the maximum link length is limited by the fiber attenuation. However, in addition to the optical power attenuation, the output pulse is generally broader in time than the input pulse. This pulse broadening limits the transmission capacity, namely, the bandwidth of the fiber. The bandwidth is determined by the impulse response as follows [1] Optical fibers are usually considered quasi-linear systems thus, the output pulse is described by... 

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