Optical signal processing

Nonlinear optical properties are of interest due to their potential usefulness for unique optical devices. Some of these applications are frequency-doubling devices, optical signal processing, and optical computers. 

Hales JM, Zheng S, Barlow S, Marder SR, Perry JW (2006) Bisdioxaborine polymethines with large third-order nonlinearities for all-optical signal processing. J Am Chem Soc 128 11362-11363... 

D.S. Chemla, D.A.B. Miller, and P.W. Smith, Nonlinear Optical Properties of Multiple Quantum Well Structures for Optical Signal Processing... 

Up to now, many conjugated polymers have been found to possess large and very rapid third-order nonlinear optical response, which originates from the one-dimensionally delocalized ji-conjugation system along the polymer chain. Their application to the all optical signal processing devices has been expected. 

Acousto-Optic Signal Processing Theory and Implementation, edited by Norman J. Berg and John N. Lee... 

M. M. Fejer. Quasi-phasematched for fiequency conversion and all optical signal processing (short course 1260) in Conference on Lasers and Electro-Optics, Baltimore (2001). 

Quantum Well Structures for Optical Signal Processing... 

Acousto-Optic Signal Processing Theory and Implementation, edited by Norman J. Berg and John N. Lee Electro-Optic and Acousto-Optic Scanning and Deflection, Milton Gottlieb, Clive L. M. Ireland, and John Martin Ley Single-Mode Fiber Optics Principles and Applications,... 

Horner, J. L. Optical Signal Processing Academic Press N. Y., 1987. 

The increasing use of optical fibre in the telecommunications network will, ultimately, require all-optical signal processing to exploit the full bandwidth available. This has led to a search for materials with fast, large third order optical nonlinearities. Most of the current materials either respond in the nanosecond regime or the nonlinearity is too small (1-3). Organic materials are attractive because of their ultra-fast, broadband responses and low absorption. However the main problem in the materials studied to date, e.g. polydiacetylenes (4) and aromatic main chain polymers (5), has been the small nonlinear coefficients. 

The maximum %0 2 x 10 11 esu, is the largest ever reported as far as we know for any organic compound doped polymer system. As this cyanine dye-polymer system has a processability and a large %(3), it is expected to be used in optical signal processing experiments. 

For all-optical signal processing (based on pure y nonlinearities) the important quantity is the nonlinear refractive index n2. The resulting refractive index change can be induced either by the beam at the frequency co1 itself (self-phase modulation) or by a beam at another frequency to2 (cross-phase modulation). 

On the route to all-optical signal processing the development of materials with large third-order nonlinear optical effects is of decisive importance. For the material characterization and the assessment of its usefulness for applications the absolute value of the third-order nonlinear optical susceptibility y has to be known. Since most measurements are performed relative to a reference material, the establishment of a well accepted value for a standard material is important. 

In the third-harmonic generation, the third-order susceptibility leads to a nonlinear polarization component which oscillates at the third-harmonic frequency of the incident laser beam. This leads to a light wave at the third-harmonic frequency of the fundamental wave. As optical frequencies are involved and since the output frequency is different from the input frequency only the electronic nonlinearities can participate without any contributions from thermal or orientational effects. Because one needs fast nonlinearities for all-optical signal processing, the main interest is directed towards the fast electronic nonlinearities. Therefore and also due to its simplicity, third-harmonic generation is a very attractive method to characterize newly developed materials. 

The development of highly active third-order nonlinear optical materials is important for all-optical signal processing. In contrast to second-order nonlinear optical molecular systems, there are few rational strategies for optimizing the third-order nonlinear optical response of molecular materials. Unlike second-order materials, there exist no molecular symmetry restrictions for the observation of a third-order nonlinear optical response. It is the instantaneous... 

For any application, resonant contributions to the second-order hyperpolarizability have to be strongly avoided. It is possible to retrieve huge values in the two-photon resonances but they are useless if all-optical signal processing applications are in mind. 

A possible way to become independent of the figures of merit W, T 1 related to absorption is the application of the semiconductors not only as a nonlinear material but also as an amplifier. The depletion of the laser beam is compensated by the active material, which is pumped either optically or electronically. The large nonlinear refractive indices shown in this approach are quite promising for all-optical signal processing (In0 77Ga0 23As in Table 7). 

Measuring An in a spectral region were Ak is much smaller. Such nonlinearities are referred to as non-resonant (associated with virtual states), being excited by photon energies far away from any electronic transition. These nonlinearities can be exploited in photonic devices for full optical signal processing, in which optical losses due to real absorption are kept low [31,45-52,78]. 

Urethane derivatives, (I), of the Step 1 product were prepared by Reuter [ 1 ] and used in optical signal processing. 

---