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1.INTRODUCTION1.1The ProblemAs a longtime industry engineer in USA and a professor in India, Mexico and USA, I have sensed that our advanced educational system effectively (not directly) discourages asking difficult and deeper enquiry driven questions in classes. Therefore, students get used to and become accustomed to accept the prevailing working theories as the final theories without further deliberations, and/or understanding the subtleties behind the relevant phenomena they are studying. We know that all 1 to 2-year olds, all over the world, irrespective of economic classes or religious persuasions of their parents; barrage the adults around them with simple, as well as deeply enquiring, questions persistently. However, our educational systems, almost all over the world, eventually succeed in seriously dampening out these genetically inherited enquiring minds of the majority of our children world-wide. Therefore, nationwide school systems in many countries, at the lower levels, are now active in implementing enquiry driven education. ‘ How do we re-inculcate enquiring trend among those who have already graduated while indirectly trained not to ask difficult questions? These young professionals are already in the pipeline to lead our academic and industrial institutions. Should we not try to develop a forum to encourage them to re-develop their enquiring mindset so they naturally become more creative again? 1.2Objective and ApproachThe key objective is to create forums (conference workshops, papers and continue through web discussions) where our young scientists are encouraged and enticed to present their enquiring questions designed for deeper understanding of optics/physics phenomena that they have studied, or are studying. We can easily start with the members of all the international Student Chapters as question generators. Then we need to solicit experienced volunteers, out of industry scientists and professors, to help generate detailed responses to these questions. Selected enquiries that have deeper pedagogical values and/or connect/challenge some of the foundational postulates should be presented as conference papers and published as Educational Papers. The ETOP publication forum (run by ICO, SPIE & OSA) can become the generic platform for publication of these papers. However, to engage the maximum number of international students, we need to organize separate “Enquiry Sessions” during all major conferences organized by OSA, SPIE, IEEE-Photonics, etc. We can also solicit donations for yearly awards to students and scientists generating the best “Enquiring Question” and the best “Scientific Response”. This could be a long-term enticement to make the initiative, “Re-energizing Enquiry”, successful and long lasting. 1.3.The specific content of this articleMethodology of thinking behind scientific explorations and research is many million years old, which started with the human evolution as an enquiring species. For a deep history of the evolution of modern scientific thinking, the readers are encouraged to consult these references [1-8]. The phrase “evidence based science” has recently become popular in the press while some segments of our society are challenging the conclusions of the scientific observations; even biological evolution is being denied. In Section 2, I will briefly underscore the logical reason behind perpetual Scientific Revolutions [8]. Evidence is measured data. However, no amount of data can ever reveal all the details behind interactions that give rise to the data in our instruments, as has been discussed in section 2. This is why our knowledge perpetually remains incomplete. In other words, we must not declare any working theory as our final theory and the final knowledge of nature. We still really do not know what the electrons and photons are made of in spite of highly successful and advanced theory of quantum physics. This is the reason why we need to promote perpetual enquiring mindset among our young scientists. section 3 provides the core content of the article. I present a number of specific enquiring questions related to different optical phenomena, simply as examples to inspire enquiry. The purpose is to elucidate existing contradictions and logical in-congruencies within the working theories that we gloss over without underscoring. I hope that these examples will encourage our students to identify newer contradictions and logical in-congruencies, and hence, generate newer enquiring questions. This would lead to the development of the next generation better theories. 2.WHAT IS MEASUREMENT? “EVIDENCE BASED SCIENCE” DOES NOT REPRESENT OUR FINAL KNOWLEDGE ABOUT NATURE!We have developed the assumption that we all think objectively while interpreting scientific observations and experimentally gathered data, as if no further discussions about the interpretations are necessary. In reality, we all have slightly different templates for logical thinking to create self-consistent meaning out of the same set of observations. Lack of explicit discussions in classes about this inherent divergences in our thinking have slowed down the continuous enhancement and evolution of our “correct” theories. I illustrate this point in the next two sub-sections. 2.1Two convergent views from two dramatically different ancient civilizations, West and EastSome 6-thousand years old eastern allegorical story tells us that: We are all “blind” as far as our perfect objectivity is concerned (Fig.2.1, 1st image). Therefore, we must collaborate to discover the deeper truth. We know today that sustainable evolution in nature derives from collaboration between intra-species members and inter-species. The individual model of the Cosmic Elephant derived by individual sensorial inputs from five blind men (Fig.2.1, 1st image) is quite limited. They perceived the elephant as a snake, or a pair of spears, or a pair of fans, etc. (Fig.2.1, 2nd image). However, once they trusted each other to collaborate and try to synthesize a living animal, their model converged to a reasonably close model of an elephant, albeit not the complete and perfect reality. Our working knowledge of science has also been evolving in a similar way with the contributions from innumerable scientists working through millennia. Separate individual theories, validated by experimental data, are somewhat similar to modeling the Cosmic Elephant! However, collaborative synthesis will always bring out continuously enhanced reality[5]. Figure 2.1Left Two Elephant Images: The allegorical story tells us that five blind men, individually, perceived the elephant as a snake, a pair of spears, or a pair of fans, etc. However, once they trusted each other to collaborate and try to synthesize a living animal, their model came reasonably close to the reality, albeit not the complete reality. Extreme Right Image: Plato (~ 424 - 348 BCE) warned people that our observations are only “shadows” of interactions that goes on between interactants in our instruments. He gave the analogy of the limitations of drawing conclusions about the outside world based on the shadows of the outside objects cast on a cave-wall, by people who were imprisoned inside the cave permanently. [Figures have been collected from Google Images]  2.2Philosophers’ “Measurement Problem” is, in reality, the “Information Retrieval Problem”Let us dissect the key and essential steps behind any data gathering measurement [Ch. 12 in ref.9]
We want to underscore the following point. The evidence-based science is the best approach, which we have been following for millennia; and yet these data-validated-theories cannot give us the complete objective picture behind the interaction processes modeled by the theory. Hence, we should not consider data-validated-theories to represent our final knowledge about nature. We need to inculcate this mode of thinking among our young scientists so their enquiring minds always remain vigilant against accepting any working theory as our final knowledge of nature. The following two quotations from two major physicists of modern human history will further strengthen my points. Newton supposed to have said, “If I have seen further than other men, it is by standing on the shoulders of giants”. Since Newton’s time we have now accumulated thousands of more accomplished scientists. We must respectfully learn to stand on the top of the pyramid built out of the great minds of these scientists to increase our knowledge horizon. We must not bow down our heads out of our cultural “messiah complex” to these scientists and, thereby, reduce the growth of our knowledge horizon. Einstein, a short time before his death, was supposed to have said, “…. After 50 years’ of brooding over the question of what are light quanta; I still do not understand it!” This is the sign of a truly honest enquiring mind of a scientist. Einstein’s “indivisible light quanta” (“photon”) has got him the Nobel Prize and has been the prevailing mode of thinking by physicists until today; and yet, Einstein was questioning his “successful” postulate because of many built-in contradictions he was recognizing. In fact, it is this enquiring view of Einstein that has inspired the author to continue to challenge the postulate of “indivisible light quanta”! 3.EXAMPLES OF ENQUIRING QUESTIONS IN OPTICAL SCIENCESFraming the questions determine the answers. Therefore, framing new questions will lead us to explore and discover new knowledge. That has been the history of evolution of human knowledge. History also tells us that all working theories eventually yield to newer and better postulates [8]. Therefore, research students should be encouraged to seek out proactively the prevailing contradictions and logical incongruences that are hiding in current working theories and their foundational postulates. Because, all earlier postulates, however rational they appeared to be during their earlier times, were formulated based upon insufficient knowledge of the deeply interconnected universe. There is always room for new research, develop new knowledge in every field. 3.1Diffraction Phenomenon. [Non-Interaction of Waves (NIW) built into it.]
Figure 3.1.1Diagrams sketched by Christian Huygens in his book [10] explaining the intrinsic properties required by waves to keep on propagating perpetually energized by cosmic ether as a tension field. Each point on every wave front functions as a source for a secondary wavelet. He also explicitly stated that his secondary wavelets keep on expanding through each other without influencing (interacting with) each other. This is Non-Interaction of Waves (NIW).  Figure 3.1.2Proposed pictorial model to compute diffractive pulse broadening using Huygens Principle, both for free space (left diagram) and for dispersive materials (right diagram), when the pulse physically contains multiple optical frequencies. Each light pulse should be propagated taking its carrier frequency as the real physical frequency [see Fig 4.6 in 9].  3.2Spectrometry Theory (see Ch.5 in ref.9)In classical spectrometry, we derive the spectrometer response function using the non-causal continuous wave (CW) that does not exist in nature. At least, we recognize that this CW response function of finite width does not represent the existence of real physical frequencies. Therefore, we de-convolve this CW response function from the data for “CW” light to derive the actual physical spectrum.
Figure 3.2The output response of a spectrometer shows fringes of finite width (dashed vertical curves on the right diagram) even when the input signal is infinitely narrow thee CW laser modes (shown on the left). We correctly recognize this width as the CW instrumental response function. The output response would be wider (solid vertical curves) if we allow a simple screen to chop out a single pulse from the 3-mode CW laser. We should recognize this widening as the pulse response function of the spectrometer, rather assuming that the width is due to existence of Fourier frequencies in the chopped pulse [see Fig. 1.1 in ref.9].  3.3.Coherence TheoryDegradation of fringe visibility steadily increases in both the cases for white light and pulsed light interferometry as the relative path delay is increased. However, the physical reasons behind these two phenomena are distinctly different.
Figure 3.3.Left Diagram (see Fig.1.2 in ref.9): Some of the most precise measurements using optical interferometry is done by using broadband or white light. Highly “incoherent ” white light can produce quantifiable fringes for measurements for small path differences (see the very bottom sketch above). The fringes wash out for increasing relative path differences. This can be appreciated from the bottom of the left figure. The red, green, and blue fringes have different spatial frequencies. When they all are present simultaneously, the fringes show increasing wash-out effect as one move further from the“ zero-path-delay” position. Right Diagram [see Fig.6.1 and 6.2 in ref.9]: In pulse autocorrelation experiments, a single pulse is replicated and superposed with different relative delays. Replicated pulses are phase steady; not incoherent. Fringe visibility degrades because unequal amplitudes are superpose, not due to physical presence ofFourier frequencies.  3.4.Mode Lock TheoryBasic texts on laser mode-lock theory simple sums, as per Fourier theorem, the periodic set of longitudinal modes allowed by a laser cavity under the mutually steady phase condition. It obtains (sin/sin) amplitude envelope with mean central carrier frequency as in Eq. 1 (see also the right sketch in Fig.3.4). In reality, mode locked lasers clearly show the existence of the independent “comb frequencies”; which have been finding wide variety of engineering applications, including the most precise atomic clocks. Figure 3.4Mode lock theory in basic textbooks sums the amplitudes of a periodic array of phase-steady frequencies (left diagram) to obtain a continuous train “mode locked” pulses. Clear implication is that wave amplitudes are interacting and re-grouping their energies, which violates the NIW property of light, as explained earlier. In reality, it is the time-periodic intensity response function of the intra-cavity mode-locking device, which functions as a time gating device, enforcing the intra-cavity gain of a train of reverberating light pulses. [see Fig. 7.1 in ref.9] 
3.5.Dispersion Phenomenon (frequency dependent light velocity)
Figure 3.5Left Diagram: Two phase steady continuous waves. Right Diagram: Mathematical summation of two phase-steady continuous cosine waves for two different carrier frequencies will give a mathematical wave with a new carrier frequency of value equaling the mean of the sum frequencies modulated by an envelope wave, which is the mean of the difference frequency. Since materials impose frequency dependent velocities, one mathematically finds that the envelope wave travels with a group velocity that is different from the phase velocity of the resultant carrier wave. This is the standard textbook theory. However, it violates the NIW property of waves, underscored earlier. The two component waves will co-propagate unperturbed by each other, as long as the medium supporting the waves remain liner and non-interacting with the waves [see Fig.8.4 in ref.9].  3.6.Polarization PhenomenonWe are taught that orthogonally polarized light beams, even if they are phase-steady, do not interfere with each other. In light of NIW property, this is correct; no light beams interfere in the absence of interacting materials. Therefore, the above statement is superfluous. However, when we insert a Polaroid in front of the detector array (see Fig3.6.1) precisely bisecting the 90° orientation of the two polarized beams; we could register perfect visibility fringes (the right photograph in Fig.3.6.1). Obviously, the interaction physics is in the detector. Figure 3.6.1Left Diagram: Two orthogonally polarized beams were generated in the two arms of a Mach-Zehnder interferometer (MZI) and were superposed non-collinearly on the beam-combiner (BC). (The MZI is in fringe mode when only a detector array can register spatial fringe intensity variation.) However, with orthogonally polarized beams, it does not produce any fringes until a polarizer is inserted bisecting the two orthogonal direction of polarizations. Right Diagram: The recorded fringes visible only within the boundary of the Polaroid. No fringes were visible outside boundary of the Polaroid (see Fig.1.3 in ref.9). 
Figure 3.6.2An MZI in collinear superposition mode for a pair of phase-steady orthogonally polarized light beams. The detector can observe the superposition effect only when one of the mirrors is scanned to introduce relative phase delay between the two beams along with a polarizer before the detector. The two superposed beams on the detector are now parallel, dictated by the polarizer. The detectors now can respond to the superposition effect. The beam combiner (BC) remains passive to the orthogonally polarized beams as in the case for non-collinear superposition above (Fig.3.6.1).  3.7.Can “indivisible single photon” generate interference effect?See the paper in this volume #ETP100-83, “Demonstration and implications when 50% beam combiners can behave as 0 or 100% reflector/transmitter inside some interferometers” [12]. In these set of experiments, we demonstrate that a classical MZI in scanning mode, as shown in the above Fig.3.6.2, the beam combiner can re-direct all the energy of both the incident beams into one or the other direction, depending upon the relative phase delay between the two incident beams from the opposite directions. This is a classically predicted result. The aggregate molecules of the dielectric boundary layer of the beam combiner are actively participating in determining how much energy from which beam goes in which direction. No photo-active quantum material is necessary. However, the key point to recognize is that both the light beams from the opposite directions must be present simultaneously to generate this simple classical superposition effect. Then, the question is this:
4.EXTENDING HUYGENS’ ETHER CONCEPT TO MODERN PHYSICSPeople realized from old times that it is the surface tension field of water surface that facilitate perpetual propagation of water waves from the point of generation (say, where one gently and vertically drops a stone) to far distances until it dies out due to various dissipative forces. The same is also true for sound waves; it is the three dimensional pressure tension field of air. Therefore, ancient physicists were aware of the necessity of a complex tension field that fills the entire cosmic volume, which facilitates the propagation of light with a constant velocity across the entire galaxy. The field of experimental and theoretical optical physics and the precision optical measurement tools have been at the foundation of promoting the evolution of most of the branches of sciences. This is true from ancient to modern times. Therefore, for the sake of inspiring all optical physics students, we are adding more enquiring questions by extending the concept that space is a stationary complex tension field [Ch.10 & 11 in ref.9]. Therefore, for the sake of completeness, some more enquiring questions are presented here very briefly without extended explanations. These are more challenging enquiring questions. Some relevant papers can be down loaded from the author’s website [14]. 4.1Quantum and Relativity PhysicsI have already mentioned a number of the quantum optics related enquiring questions in the last section 3.7. Here are a few more questions beyond “photons”.
We measure the 3D space with physical measuring “stick”. We can “dilate” or “contract” such physical scales by changing the temperature or some other relevant physical parameters around the “stick”. In contrast, we have no physical object that can directly measure the running time t. In the real world, we can only measure (count) the frequency of oscillations of diverse oscillators like household pendulum clock, or the laser light frequency for atomic clock, etc. We invert the frequency to derive a secondary parameter, the period or the time interval. Then by counting larger and larger number of oscillations, we derive the human concept of running time. We can also “dilate” or “contract” the frequency of oscillators using suitable change in the physical environment around them. Key primary mathematical parameters should be directly measurable as a physical property of something real in nature to keep our theories connected to nature’s objective reality. 5.CONCLUSIONSWe have proposed a good number of enquiring questions for the beginning and advanced research students along with brief rationales and some references. We hope that this will generate serious participation by research student and scientists to develop a sustained environment that will keep on encouraging our students to keep on questioning the foundational postulates behind all working theories. This is the only way that we can avoid waiting for accidental appearance of another Newton, or another Einstein. We should not allow such uncertainty to continue! We should be proactive to encourage persistent enquiry and create the necessary secure environment. In the current scientific enterprise, such a culture does not exist now. We will have to create it. But, how? REFERENCESWikipedia,
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