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Get PDF Abstract Several inorganic and organic materials have been suggested for utilization as nonlinear optical material performing light-controlled active functions in integrated optical circuits, however, none of them is considered to be the optimal solution.

The results may serve as a basis for the future realization of protein-based integrated optical devices that can eventually lead to a conceptual revolution in the development of telecommunications technologies.

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Introduction The continuous growth of internet traffic is expected to last for the foreseeable future. All-optical photonic data processing is generally considered to be the most promising approach to achieve these goals.

Contrary to the electronic conductors and transistors, their optical counterparts, miniature light guides and optical switches, respectively, serve as passive and active elements to process optically coded information.

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To this end, the basic problem is to find proper nonlinear optical materials that are able to actively control optical circuits. Several materials have been considered for this special application requiring high speed and sensitivity, however, so far none of them is regarded as the optimal solution. Singles witten to the most recent view, the more versatile and cost-effective organic materials represent a promising alternative of the currently used inorganic semiconductor materials [ 1 ].

Specifically designed organic, Pi-conjugated molecular materials have attracted so far the most attention [ 23 ]. They show singles witten high third-order optical singles witten, without two-photon absorption losses.

These dye molecular structures, however, should be further optimized, embedded and tested in solid films before they can singles witten applied in high-performance all-optical devices. Hence, in view of the urgency of the technical requirements, it seems to be desirable to explore other approaches, too. Nature readily provides us with Pi-conjugated materials optimized for sensing light during myriads of years of evolution [ 4 ].

Although biological materials in general are disregarded in technical applications because of their fragile nature, there are some proteins that are extraordinarily robust, so their biological origin does not represent a practical disadvantage in any respect, on the contrary, they offer special advantages singles witten can be exploited in bioelectronic applications [ 5 ].

Among biological molecules under consideration for technical use, the chromoprotein bacteriorhodopsin bR has generated the most interest due to its striking robustness and other favourable physical properties [ 6 — 8 ]. Isolated from the cell membrane of the microorganism Halobacterium salinarum, bR is the simplest ion pump, and one of the best-characterized membrane proteins [ 4 ].

It has a Pi-conjugated chromophore, the retinal molecule, as a light-sensing prosthetic group that is stabilized by polar aromatic residues of the protein. The optical properties spectra and kinetics of bR are fine-tuned by point charges on amino acid side chains adjacent to the retinal molecule, and can be easily modified by genetic engineering techniques site-directed mutagenesisor by specific physical and chemical treatment of the chromoprotein [ 9 ].

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All singles witten are also light sensitive [ 1011 ], i. Thin films of optical quality prepared from bR are used in most of the bioelectronic applications, like holography. In these dried bR samples, the photocycle lacks all the intermediates after M, that directly decays back to BR.

The photocycle reactions are accompanied by change of absorption, hence the refractive index also changes corresponding to the Kramers-Kronig relations [ 814 ]. The first experiments concerning the integrated optical application of bR proved that under continuous singles witten of the ground-state bR, the refractive index of a dried bR film at nm changes while the M state develops [ 15 ]. Consequently, if a probe laser light at a wavelength outside of the excitation range of bR is coupled into an integrated optical device e.

On these grounds, we demonstrated high-quality all-optical switching based on the M intermediate [ 16 ].

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Experimental setup In order to reveal ultrafast integrated optical switching based on the nonlinear optical properties of bR, pump-probe experiments were performed with the use of picosecond and femtosecond light pulses Fig.

The concept of the measurement was the following: A short pump pulse at a wavelength in the absorption band of bR nm initiated the photocycle of the protein. The induced change of refractive index was then probed by a subsequent laser pulse at singles witten central wavelength around nm, which lies outside the absorption bands of all intermediates this way the photocycle is not affected by the probe pulse.

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The probed transition was then characterized by changing the time delay between the pump and probe pulses, as well as their duration. The traces were detected by a spectrophotometer or a photodiode, and recorded by a multichannel analyzer. The Fabry-Perot interferometer was used only in the sub-picosecond measurements.

A bR adlayer purple was deposited above a 1D photonic crystal coupler grating, rainbow onto a thin- film optical waveguide blue carried by singles witten glass substrate gray. Probe light: red, pump light: green.

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  • OSA | Protein-based ultrafast photonic switching

The broadband pulses of nm pulse energy 80μJ were generated from the more intense part of the fundamental beam with the unique combination of non-collinear optical parametric chirped pulse amplification and chirp-assisted sum-frequency generation [ 20 ].

The less intense part of the beam 1 μJ, nm was used to probe the sample excited by the pump pulses.

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The outcoupled spectrum and intensity were monitored by a spectrograph OceanOptics, HR and a fast photodiode. In the first series of experiments the generated pump pulses singles witten left stretched to 45 ps. Note that these pulses were not transform-limited, as their duration was lengthened by spatial and temporal chirp introduced by the grating. In the second series sub-picosecond experiments the pump pulse was compressed to fs by a transmission grating compressor.

The resulting temporal and spectral widths of the transform-limited probe pulse were 3 ps and 0. In each case the duration of the pump and probe pulses were carefully measured with an autocorrelator singles witten a cross correlator, respectively, at the sample position. Under proper conditions the first-order diffracted probe lily társkereső was coupled into the guiding layer: The waveguide operates in single mode for wavelengths in the visible range, that is only one transverse electric TE and one transverse magnetic TM polarized guided modes exist [ 2122 ].

Besides the wavelength of the measuring light, the propagation constants of these single modes are fully determined by the thickness and refractive index of the film and the refractive indices of the materials surrounding the guiding layer substrate and bR adlayer.

The TE and TM modes can be induced by a resonance incoupling of the measuring light at well-defined angles of incidence [ 1521 ].

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The angle of incidence was considered to be positive singles witten turning the sample from its initial position i. During the measurements part of the guiding layer above the grating was covered with a dry patch of bR [ 15 ]. Once the angle of incidence was fixed to a proper value, so that one of the guided modes TE or TM, depending on the polarization of the probe beam could propagate in the layer, the conditions of coupling could be altered by varying the refractive index of the bR layer, that functioned this way as a nonlinear optical NLO element of the optical switch.

Measurements For practical reasons, in all of the measurements, the TM resonance peak was used to demonstrate optical switching, corresponding to singles witten angle of incidence of ca. Due to the change of the refractive index of bR following excitation, the coupling wavelength is expected to be shifted by 0.

The effects can be detected by a spectrophotometer or by a photodiode, respectively.

In order to detect the wavelength shift of the coupled light due to fast excitation of bR, the full-width-at-half-maximum bandwidth FWHM of the linearly polarized probe pulses of 12 ps was chosen to be 3 nm. The spectrum selected by the waveguide was then measured by a spectrophotometer. The bR photocycle was initiated by a pump pulse with duration of 45 ps, hitting the sample ps before the probe pulse. Under these conditions, the only intermediate present in the photocycle singles witten the K form, with a singles witten absorption spectrum relative to the ground state BR.

Such a spectral shift should result in a refractive index increase in the adlayer at wavelengths longer than that of the absorption peak [ 14 ].

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This, in turn, should change the coupling conditions such that the wavelength of the incoupled light, selected by the grating coupler, is shifted to the red, provided that the angle of incidence is unchanged Fig. In fact, the traces in Fig.

As a consequence, a red-shifted narrow band is selected from the broad spectrum indicated by the red-orange Gaussian. Download Full Size PPT Slide PDF According to our calculations singles witten on the wave equations of grating-coupled single-mode waveguides [ 152122 ], the amount of the shift is consistent with a refractive index change of ca.

The intensity of the singles witten light was monitored by a low noise nanosecond photodiode. Note that the actual time resolution of the switch is determined not by the photodiode, but by the time delay and duration of the pump and probe singles witten.

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In order to maximize the effect, the angle of the incident pulse was slightly singles witten by turning the sample counterclockwise CCWoff the resonance peak, until the output intensity reached the half-maximum [ 15 ]. When the switch is turned on by the green pump pulse, under such conditions the refractive index change is expected to shift the resonance peak so that the intensity of singles witten incoupled light increases Fig.

From the measured intensities of the incoupled pulses one can see that when both the exciting and measuring lights hit the singles witten, the incoupled intensity Meas.

Note that a small amount of stray light also reached the detector when the exciting pulse was on Pump. Correcting to this Corr. The red férfi találkozó albertville indicates the expected intensity change at the counterclockwise half maximum of the original resonance peak. Note that the time course of the signal represents the response of the photodiode only, not that of the actual light pulse.

Figure 4 b shows the relative intensities of the output probe pulses krisma társkereső at the half-maximum on CCW side of the resonance peak, both without excitation of the bR adlayer and with a pump pulse arriving at zero time delay to the sample i.

The calculated unweighted contributions of the intermediates to the measured signal are listed. This singles witten be interpreted as a shift of the coupling peak in the direction opposite to that for the K intermediate described above, meaning that the refractive index of the adlayer decreases upon excitation Fig.

Discussion To check this hypothesis, we performed a kinetic analysis of the fast reactions of the bR photocycle. At very short times for the duration of the applied pump and probe pulses, a mixture of the I, J and K intermediates will coexist during singles witten pump pulse that was chosen to have a duration of 3 ps to yield narrow spectral bandwidth.

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Using the published rate constant values of these intermediates [ 1223 — 25 ], their relative contribution to the light-induced change singles witten the probe signal was determined [ Fig.

In order to estimate these contributions to the optical signals detected by our ultrafast measurements, we simulated the development and decay of H, I, J and K during the time course of the probe pulse, based on the experimental conditions and the data available in the literature.

Several experimental and theoretical studies have been performed to reveal the fast intramolecular events after photoexcitation of bacteriorhodopsin bR [ 1226 — 29 ]. According to a consensus view, a quasistationary electronic excited state I of bR is formed from the Franck-Condon excited state Hand followed by an electronic transition to J A subsequent vibrational relaxation process leads to the Kstate containing a cis isomerized retinal chromophore.

The 3 ps probe pulse was used to monitor the refractive index change of the dried bR sample after the excitation. On the time scale of the probe pulse, singles witten the early intermediates were concurrently present in the sample, hence the recorded signal contained contributions from all these intermediate states.