Molecular and Supramolecular Information Processing: From Molecular Switches to Logic Systems
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The efficient transmission of data relies on the integration of optoelectronic devices and optical fibers.
Molecular and Supramolecular Information Processing: From Molecular Switches - Google Книги
They are responsible for the generation, amplification, conduction, routing, and detection of optical signals. At each step, the continuous interplay between optical and electrical stimulations controls data processing. In particular, electronically controlled switches guide the traveling optical signals along programmed routes across the communication networks.
Signal routing requires multiple optoelectronic and electroopitc conversion steps. From input fibers, the propagating optical signals reach the routing devices, where they are converted into electrical signals, processed in this form, reconverted into optical signals and, finally, directed to specific output fibers. Besides the obvious loss in signal intensity associated with each conversion step, these switching devices are relatively slow and can process only few signals simultaneously. Only a tiny fraction of the potential transmission capacity of optical fibers is used in present communication networks.
These limitations are stimulating considerable research efforts to develop innovative operating principles for optical switching 5 — 8. A variety of clever and efficient strategies to completely eliminate undesired optoelectronic and electroopitc conversion steps have already been identified 5 — 8. It is now possible to maintain the propagating signals exclusively at the optical level. However, these methods rely heavily on electronics and, presumably, they will not be able to support the terabit-per-second capacities that will be needed in the near future.
Their major limitation is that the switching operations are still controlled by electrical stimulations. The traveling optical signals are routed in response to electrical signals, which cannot handle the immense parallelism offered by optical fibers. Strategies to control optical signals in response to optical signals are potentially much more attractive. However, the identification of reliable operating principles for all-optical switches is a challenging goal.
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Molecular switches 9 — 12 are emerging as alternative materials for digital processing 13 — Simple logic functions 16 have been implemented at the molecular level, operating individual molecular switches 17—32 or ensembles of communicating molecules 33 — In this article, we demonstrate that arrays of independent photoactive molecular switches can execute NAND, NOR, and NOT operations 16 that rely exclusively on optical inputs and optical outputs.
The spiropyran derivative SP see Fig. The optical networks shown in Figs. The output intensity was measured immediately after, rather than during, the application of the optical inputs. The intensity of the optical output O switches between low and high values as the optical input I is turned on and off. This signal transduction behavior is equivalent to a NOT operation. The intensity of the optical output O switches between low and high values as the three optical inputs I 1, I 2 , and I 3 are turned on and off. This signal transduction behavior is equivalent to a three-input NOR operation.
Recently, we have developed a three-state molecular switch Fig.
All-optical processing with molecular switches
Similarly, ME reisomerizes to SP when stored in the dark. The direct interconversion between the two states SP and ME relies on the photoisomerization of a spiropyran chromophore 36 — This switching process is controlled solely by optical inputs, and the two isomers have distinct absorption properties in the visible region The colorless state SP , instead, does not absorb at nm b in Fig. The photoinduced transformation of SP into ME is extremely fast and involves the formation of colored intermediates Time-resolved laser spectroscopy has demonstrated that, in the case of the parent 6-nitrospiropyran, colored species can be detected within 10 ps from irradiation.
Thus, an optical input addressing SP can be transduced, at least in principle, into an optical output on a picosecond time scale. It follows that this ultrafast all-optical molecular switch is particularly attractive for digital processing at the molecular level. In the optical network illustrated in Fig.
The wavelength of this signal is nm and corresponds to the absorption maximum of the purple-state ME a in Fig. Thus, the optical output O switches between low and high values as the optical input I is turned on and off lower left table in Fig. It is worth noting the analogy between this all-optical switch and conventional field-effect transistors In a basic complementary metal oxide semiconductor CMOS field effect transistor inverter, for example, a voltage output switches between low and high values as a voltage input is turned on and off.
Of course, the switch in Fig. The optical network illustrated in Fig. In this instance, the traveling optical signal yellow arrows has to pass through two quartz cells before reaching the detector. Thus, the optical output O is high only when both optical inputs I 1 and I 2 are turned off in Fig. The intensity of the optical output O switches between low and high values as the two optical inputs I 1 and I 2 are turned on and off. This signal transduction behavior is equivalent to a two-input NOR operation.
Following a similar approach, all-optical networks with n input terminals can be realized introducing n independent switching elements between the visible light source and the detector. The resulting array of switches transduces 2 n strings of n optical inputs I 1 — In into a single optical output O.
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However, it is sufficient to address only one of the n switches to block the traveling optical signal. The intensity of the optical output O is high only when all of the input stimulations I 1 — In are turned off. As an example, a simple array with three switching elements is shown in Fig.
Molecular and Supramolecular Information Processing: From Molecular Switches to Logic Systems. Editor(s). Prof. Dr. Evgeny Katz. Molecular and Supramolecular Information Processing: From Molecular Switches to Logic Systems. Molecular and Supramolecular Information Processing.
Thus, the optical output O is high only when all of the optical inputs I 1 , I 2 , and I 3 are turned off Fig. The tables at the bottom left of Figs.
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In all instances, the input signals can be either off or on. The values above and below can be defined high and low, respectively. Following these assumptions and conventions, the signal transduction of the all-optical switch in Fig. The output O is 1 when the input I is 0 and vice versa.
The signal transductions of the all-optical networks in Figs. The output O is 1 only when all of the inputs are 0. All of the other combinations of two- and three-input strings are converted into a 0. Comparison of the combinational logic circuits illustrated in Figs. In fact, the transition form the one-cell system Fig. Similarly, the transition from the two-cell system Fig.
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