By utilizing entanglement property of photons the entangled two-photon absorption (ETPA) effect of an organic
material, porphyrin dendrimer, is demonstrated through the comparison of the property of entangled photons to the
property of quantum-correlated photons. The ETPA showed a cross-section 31 orders of magnitude higher than the
cross-section of the classical two-photon absorption (TPA). This high cross-section is comparable to the cross-section of
the resonant single-photon absorption. The entangled absorption effect is compared to the correlated TPA effect to
determine the degree of correlation between the entangled and quantum correlated photon pairs. The experimental data
describe the different degree of correlation of the non-entangled and entangled photon pairs by demonstrating linear and
nonlinear relationship of the absorbed photon flux to the input photon flux. The linearity of the ETPA is an interesting
quantum effect because the two-photon absorption is an inherently nonlinear process. Virtual state spectroscopy is
also demonstrated as a novel spectroscopic method to investigate the properties of the virtual state from non-monotonic
behavior of the cross-section which is represented by controlling temporal property of the entanglement. These results
from the quantum spectroscopy methods show a unique quantum property which is not feasible to detect using classical
Generating or shaping a light pulse requires complete knowledge of all the parameters of the complex pulse amplitude. But they are not directly available to us. Our gathered data is only proportional to the square modulus of the EM fields as reported to us by various detectors (including non-linear processes). These detector responses are "colored" by their unique quantum "preferences". EM fields are not directly observable to us. They do not operate on (interfere with) each other either. Classical optics recognizes that light beams of different frequencies and of orthogonal polarizations do not "interfere" with each other. The success of Michelson's Fourier Transform spectrometry relies on this non-interference of different frequencies. Yet, beat signal is a result of simultaneous actions of different frequencies on a fast detector. We are promoting the hypothesis of non-interference of light beams as a generalized principle irrespective of the similarities or dissimilarities of their parameters. All superposition effects can become manifest only when the interacting medium is capable of summing all the induced stimulations simultaneously. Accordingly, an array of CW beams with multiple frequencies cannot create temporal pulses as implied by the time-frequency Fourier theorem in free space or in a medium that does not interact with the fields. Dipole undulations induced by the superposed EM fields within appropriate media are always at the root of creating laser pulses, and this brings conceptual congruence between the processes in generating pulses whether they are due to spiking or mode-locking. To illustrate our position, we present a series of experiments: (i) Simple superposition of three coherent frequencies did not generate mode locking. (ii) A series of ordinary CW He-Ne laser beams can produce mode-lock like current pulses by a high speed detector. (iii) A Q-switched ps diode laser shows 100fs train of autocorrelation spikes but it is not mode locked.
High resolution DWDM devices based on the principles of gratings (planar, Bragg, AWG, etc.) and Fabry-Perots (etalon, Lummer-Gehrke plate, etc.) suffer from inherent limitations due to (i) temporal pulse stretching of data, and (ii) broadening of time integrated spectral (demuxed) fringes. While the relation, dν<sub>F</sub>dt >1, can account for these limitations, our analysis imply that dnF does not represent real, physical frequencies. We explain the broader implications of this interpretation in designing DWDM devices based on gratings and Fabry-Perots and illustrate how to use prisms, photonic crystals and non-linear devices for very high data rate per channel.