1. Introduction

In 1949, Goos and Hänchen showed that an optical beam reflected at an interface under total reflection conditions was laterally shifted from the position expected based on the geometric optics [1]. This displacement is referred to as the Goos-Hänchen (GH) shift and has attracted a great deal of interest in terms of both fundamental physics and practical applications. The GH shift appears at the boundary of absorbing medium [2]. This shift also appears at the Brewster angle, where the phase shift in the reflected beam changes sign [3]. Although the importance of the GH effect increases when the size of the system is reduced to the nanoscale, GH shifts are usually small and comparable to the wavelength of light, and are therefore typically neglected in optics.

Displacement of the GH shift can be enhanced using resonance effects. The GH effect has been investigated in a wide range of systems. Leaky waveguide (WG) mode is a promising system to achieve a giant GH shift [4,5]. A portion of the energy of the incident light beam is transferred into the WG structure, which is leaked back to the reflected beam after propagating a certain distance along the WG structure. Due to the energy flow associated with propagation, the reflected beam exhibits a large lateral displacement. Enhanced GH shifts have also been demonstrated in the surface plasmon polariton (SPP) at the interface between dielectric metals and materials [6], in surface waves at the interface between left- and right-handed materials [7], and in surface waves in a truncated 1-D photonic band gap (PBG) structure [8]. Recently, large GH shifts have also been studied in non-Hermitian systems [9], complex parity-time symmetric photonic crystals with alternating optical loss and gain [10], and defective photonic crystals [11]. These giant GH shifts could be useful in optical applications. Various devices using enhanced GH shifts have been developed, including fiber-to-fiber optical switching [12], narrow band optical filters in cascaded WG structures [13], and sensors [14]. Unfortunately, however, large lateral displacements are not sufficient for practical applications. A major disadvantage of using the resonance effects in conventional passive resonant systems is the significant attenuation of the reflected intensity, which is a major drawback of using the GH shift in practical applications.

Here, we investigate prism-coupled planar dielectric WG mode in a metal-insulator multilayer Fano structure to realize a giant GH shift. The observed GH shift was ${D_{Fano}}$ = 0.176 mm, which corresponded to ${D_{Fano}}/\lambda $ = 493 where $\lambda $ is the incident wavelength. As a unique feature of the dielectric multilayer Fano structure, the giant GH shift appeared without attenuation, i.e., reflectivity ∼1. The origin of this high reflectively lies in the Fano interference [15–18] between the SPP and dielectric WG modes. Fano interference added a $\pi $ rad phase shift to the WG mode resonance and inverted the reflection spectrum. The simultaneously giant and highly reflective GH shift demonstrated here has great potential in applications such as optical switching, optical filters, and sensors, where the reduction of reflected beam intensity is a major disadvantage.

Our strategy is underpinned by the idea that the performance of nanostructured photonic devices can be markedly improved when plasmonic components are replaced with dielectric materials. Recently, dielectric Fano effects have been attracting increasing interest due to the possibility of achieving ultra-high Q resonances in high-index dielectric nanostructures [19–25]. The absorption losses in dielectric materials are much lower than those in their plasmonic counterparts, and therefore dielectric materials are the most suitable materials to achieve ultra-high Q resonances. A variety of structures have been proposed for all dielectric Fano meta-surfaces and all dielectric Fano meta-materials. Using the resultant ultra-high Q resonances, strong photoluminescence enhancement [22] and further enhancement of nonlinear optical effects [23] were demonstrated.

In our previous report, a GH shift in plasmon-induced transparency (PIT) was achieved in a metal-insulator-metal (MIM) structure [26–28]. The SPP yielded a GH shift but the displacement of the GH shift was not large and was severely restricted by the intrinsic loss in the metal. By replacing the plasmonic material with a low-loss dielectric medium, the intrinsic limit in the MIM structure was surmounted and an extremely large GH shift was achieved with high reflectivity ∼1. The Q-factor of the WG mode in the dielectric structure is predominantly determined by the coupling loss between the WG mode and re-emission via the SPP resonance. Hence, we can make the Q-value arbitrarily high by reducing the coupling strength, and achieve an extremely large GH shift without attenuation of the beam intensity. We will also discuss three features of the GH shift in the dielectric multilayer Fano structure: (1) the strength of Fano coupling, i.e., the effect of the thickness of the gap layer; (2) the loss and gain in the WG layer; and (3) two similar but different configurations of the dielectric multilayer Fano structure.

2. Experiments

A schematic illustration of the experimental setup is shown in Fig. 1. The setup was based on attenuated total reflection (ATR) spectroscopy in the Kretschmann configuration [29]. A He-Ne laser with a wavelength of $\lambda $ = 632.8 nm and average power of 10 µW was used as the incident light source. The laser beam was passed through a polarization-maintaining single mode optical fiber. The incident beam diameter (full width at half maximum) was 447 µm, outside the prism. The k domain bandwidth of the incident beam was controlled by adjustment of a beam collimation system and prepared as either a tightly collimated beam or a loosely focusing beam. The polarization of the incident beam was controlled using a half wavelength plate. The beam from the collimator was injected into a 90° SF11 prism (25 mm × 25 mm × 25 mm), which supported multilayer samples at the bottom. We monitored the reflected beam intensity using a Si detector. The GH shift was observed directly using a beam profiler based on a complementary metal-oxide semiconductor (CMOS) camera with a spatial resolution of 2.2 µm. The multilayer structure of the sample is shown in the inset of Fig. 1. The first layer was a coupling layer and consisted of Au. The second layer was a gap layer and consisted of SiO₂. The third layer was a WG layer and consisted of high-index Ta₂O₅ or TiO₂, which supported WG mode between the SiO₂ and air cladding. The Fano interference between the SPP resonance at the interface of the Au layer and WG mode in the Ta₂O₅ layer was achieved through evanescent coupling in the SiO₂ layer. The Fano interference inverted the profile of the reflection spectrum, as well as the phase dispersion, which is relevant to the WG mode. We report the experimental results obtained using two samples, designated as sample 1 with layer thicknesses of ${d_1}$ = 53 nm, ${d_2}$ = 530 nm, and ${d_3}$ = 123 nm (TiO₂), and sample 2 with layer thicknesses of ${d_1}$ = 51 nm, ${d_2}$ = 600 nm, and ${d_3}$ = 149 nm (Ta₂O₅).

 

Fig. 1. Experimental setup. FIS, fiber injection system; F, optical fiber; C, beam collimation system; P, polarizer; 1/2, half wavelength plate; P, prism; S, sample; RT, rotational stage; D, detector (Si photodiode, or complementary metal-oxide semiconductor [CMOS] camera). Inset: Schematic illustration of dielectric multilayer Fano structure.

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Figures 2(a1) and 2(b1) show the experimental observations of reflectivity for samples 1 and 2, respectively, as a function of the incident angle ${\theta _i}$ (ATR spectrum). The collimated beam was used to obtain these spectra. In Fig. 2(a1), where the thickness of the WG layer was not tuned to the SPP mode, the reflection intensity showed two dips. The broad dip at angle ${\theta _{SPP}}$ = 80.2° was attributed to SPP resonance at the interface between the Au and SiO₂ layers [30]. The narrow dip at angle ${\theta _{WG}}$ = 68.4° was attributed to the lowest TM mode in the WG layer. The resonance angle of ${\theta _{WG}}$ changed sensitively depending on the thickness of the WG layer. Figure 2(b1) shows similar results for sample 2, where the thickness of the Ta₂O₅ layer was adjusted so that ${\theta _{WG}}$ moved toward the higher-angle side and coincided with ${\theta _{SPP}}$. Under this condition, the SPP and WG modes couple, causing a Fano interference effect. The relevant energy transfers from one resonance to another and vice versa. In this process, a $\pi $ rad phase shift is added to the WG mode with respect to the incident light [15–18]. Hence, the reflection profile of the WG mode was inverted and appeared as a sharp peak at the center of the broad dip due to SPP resonance. The solid lines in Figs. 2(a2) and 2(b2) denote the calculated reflectivity of samples 1 and 2, respectively. The calculations were performed based on the transfer matrix method [31]. The calculations well reproduced the reflection profile and supported the idea that a sharp peak at the center of the broad dip arose through the Fano interference effect. The solid lines in Figs. 2(a3) and 2(b3) are the reflection phase shift $\phi $, calculated with the same parameters that yielded the data in Figs. 2(a2) and 2(b2). In Fig. 2(a3), the reflection phase of the WG mode exhibited a steep positive dispersion, i.e., $\partial \phi /\partial k > 0$. In contrast, within the peak in Fig. 2(b3), i.e., within the inverted profile of the WG mode, a steep negative dispersion, i.e., $\partial \phi /\partial k < 0$, appeared (red arrow). It should be noted that both the high reflectivity ∼1 and steep phase slope were simultaneously achieved at the resonance angle of the inverted WG mode.

 

Fig. 2. (a1) and (b1) Experimental observations of reflectivity as a function of the incident angle ${\theta _i}$ in p-polarization (attenuated total reflection [ATR] spectrum). (a1) and (b1) show the results for sample 1 (${d_3}$ = 123 nm) and sample 2 (${d_3}$ = 149 nm), respectively. The upward and downward arrows at 68.4° and 85.3° indicate the waveguide (WG) mode and inverted WG mode, respectively. The notations 1, 2, 3, 4, and 5 in (b1) and 6 in (a1) indicate the angular positions where a Goos-Hänchen (GH) shift was measured. (a2) and (b2) Calculation of the reflectivity (ATR spectrum) for samples 1 and 2, respectively. (a3) and (b3) Calculation of the reflection phase shift for samples 1 and 2, respectively. Inset in (b3) shows an expanded phase shift around the resonance region. The refractive indexes used in the simulation were ${n_{Ag}}$ = 0.165 + i 3.25, ${n_{Si{O_2}}}$ = 1.45, ${n_{Ti{O_2}}}$ = 2.13 and ${n_{T{a_2}{O_5}}}$ = 2.20 .

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We examined the GH shift relevant to the inverted WG mode (i.e., that in the presence of the Fano effect) and the naked WG mode (i.e., that in the absence of the Fano effect) at the incident angle of the laser beam indicated by the number 1 in Fig. 2(b1) and number 6 in Fig. 2(a1), respectively. Figure 3(a1) shows the spatial transverse intensity profile of the reflected beam observed with ${\theta _i}$ = 85.3°, i.e., at the peak angle of the inverted WG mode (number 1 in Fig. 2(b1)). The beam profile was obtained using the beam profiler and the collimated beam. For clear observation of the GH shift, it is necessary to satisfy the condition $\delta k \le \Delta k$, where $\delta k$ and $\Delta k$ are the bandwidths of the incident beam and the resonance, respectively. The bandwidth of the collimated beam was $\delta k$ = 0.99× 10⁴ m⁻¹ and the bandwidth of the Fano peak was $\Delta k$ = 0.90 × 10⁴ m⁻¹, which satisfies the necessary conditions for observation of the GH shift $\delta k \le \Delta k$ ($\delta k\sim \Delta k$). As SPP resonance and TM WG mode appeared only in p-polarization, the beam shift was observed using the beam profile in the s-polarized beam as a reference. As shown in Fig. 3(a1), the Gaussian-shaped beam profile almost retained its shape, and the peak position observed in p-polarization moved toward the positive side (higher-angle side). This shift was attributed to the GH shift relevant to dispersion in the inverted WG mode. The observed beam displacement was ${D_{Fano}}$ = 0.176 mm, which showed good agreement with the theoretically calculated value of 0.202 mm (Fig. 3(a2)). This value of ${D_{Fano}}$ corresponded to ${D_{Fano}}/\lambda $ = 493, where $\lambda $ is the incident wavelength in the prism; hence, the GH shift is extremely large. As a unique feature of the dielectric multilayer Fano structure, this giant GH shift appears without attenuation, i.e., reflectivity ∼1. The horizontal red dotted line in Fig. 3(a1) represents the intensity of the reflected beam ${I_{Fano}}$. It should be noted that the reflected beam intensity was almost the same as that of the incident beam, thus indicating that the GH shift in inverted WG mode was achieved without attenuation. For comparison, we also examined the GH shift caused by the naked WG mode in sample 1 at the resonance, ${\theta _i}$ = 68.4° (indicated by 6 in Fig. 2(a1)). The solid line in Fig. 3(b1) shows the non-normalized data of the observed reflection beam. In contrast to Fig. 3(a1), the beam intensity in Fig. 3(b1) was significantly attenuated. To visualize the displacement of the peak position, we also plotted the normalized reflection beam profile as the dashed line. At the resonance of the naked WG mode, a negative GH shift ${D_{WG}}$=−69.6 µm was observed. Besides the traditional spatial GH shift, there is an angular GH shift, that is, an angular deviation in the light beam when it reflects [32,33]. Specifically, the angular GH shift has been studied in the context of weak measurements [33]. In our experiments the incident beam was tightly collimated, the beam size is large enough to satisfy $\delta k < \Delta k$, and the angular GH shift is negligible [32].

 

Fig. 3. (a1), (b1), (c), (d), (e), and (f) Experimental observations of the spatial profiles in the reflected beam. (a1), (c), (d), (e), and (f) Beam profiles obtained with incident angles of ${\theta _i}$ = 85.3° (center), 72°, 83.5°, 85.8 °, and 98° in sample 2 (as indicated by notations 1, 2, 3, 4, and 5 in Fig. 2(b1), respectively). (b1) Incident angle of ${\theta _i}$ = 68.4° in sample 1 (as indicated by notation 6 in Fig. 2(a1)). The solid black lines correspond to the reference beam profile (s-polarization). The solid red [(a1), (a2)], blue [(b1), (b2), (d), and (e)], and green [(c), (f)] lines represent the non-normalized spatial profiles of the reflected beam. The dashed lines [(b1), (b2), (d), and (e)] show the spatial profile normalized with respect to the reference beam. The scales of the horizontal axes are recalibrated by taking refraction at the prism into account. The horizontal red and blue dotted lines in (a1) and (b1), respectively, represent the intensity of the reflected beam for the eye guide. (a2) and (b2) Spatial beam profiles calculated using the dispersion curves in Fig. 2(b3) and 2(a3), respectively.

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Figures 3(d) and 3(e) show the spatial profiles of the reflected beams observed at ${\theta _i}$ = 83.5° and ${\theta _i}$ = 85.8° at the lower and higher sides of the inverted WG mode (arrows 3 and 4 in Fig. 2(b1), respectively). For these measurements, we used a loosely focused laser beam as the incident beam to enhance the spatial resolution [26]. The bandwidth of the focused laser beam was $\delta k$ = 8.39 × 10⁴ m⁻¹ and the bandwidth of the broad SPP dip was $\Delta k$ = 1.04× 10⁵ m⁻¹, which still satisfied the condition $\delta k < < \Delta k$. At these angles, negative GH shifts were observed. The sign of the GH shifts reflects the positive k-domain dispersions at both sides of the inverted WG mode, as shown in Fig. 2(b3), which is attributed predominantly to the SPP resonance. Figures 3(c) and 3(f) show the spatial profiles of the reflected beams observed at the off-resonance angle of the WG mode (arrows 2 and 5 in Fig. 2(b1), respectively). In these measurements, the beam did not show the GH shift.

3. Discussion

3.1 The dependence of GH shift on the gap layerSiO₂ thickness

A giant GH shift of ${D_{Fano}}/\lambda $ = 493 was demonstrated using the present dielectric Fano system. We can further enhance the GH shift by controlling the coupling strength. The WG mode, which is responsible for the giant GH shift, was sustained in the Ta₂O₅ layer. The intrinsic absorption of Ta₂O₅ is extremely low; therefore, the Q-value of the WG mode sustained in the dielectric structure was predominantly determined by leakage loss arising from the coupling between the WG mode and re-emission via the SPP resonance. Further, we can control the evanescent coupling between the WG mode and the SPP resonance by changing the thickness of the gap layer (SiO₂), i.e., ${d_2}$. To observe the enhancement of the GH shift, we simulated the dependence of the GH shift on the gap layer thickness. The left, middle, and right columns in Fig. 4(a)–4(d) show the calculated reflectivity (ATR spectrum), reflection phase shift, and GH shift, respectively, for different SiO₂ layer thicknesses. When the SiO₂ layer is thin (${d_2}$ = 300 nm), the coupling between SPP and WG becomes very strong (Fig. 4(a1)). The mixed modes are good eigenstates, but the SPP and WG are not. The coupled modes were split into two new modes at lower (74.8°) and higher (92.4°) angle regions. As the thickness of the SiO₂ layer increases, the coupling becomes weak. The reflection spectrum transforms into an electromagnetically induced transparency (EIT)-type shape [15–18], where the inverted WG mode is a good eigenstate (Fig. 4(b), 4(c), and 4(d)). The slope of the resultant reflection phase shift also becomes steep and the GH shift increases markedly as the thickness of the SiO₂ layer increases. The black solid and dashed lines in Fig. 5(a) represent the GH shift and refractivity of the inverted WG mode as a function of the SiO₂ layer thickness, respectively. The GH shift increases exponentially with a constant of 6.10 × 10⁻³ µm/nm, which is consistent with the penetration depth of the SPP and WG modes. As an example, based on the simulation in Fig. 5, the GH shift of ${D_{Fano}}$∼0.18 mm at an SiO₂ thickness of 600 nm is expected to increase as ${D_{Fano}}$∼12.6 mm at an SiO₂ thickness of 900 nm. The performance of nanostructured photonic devices can be markedly improved when plasmonic components are replaced with low-loss dielectric material [19–23]. The refractivity was ∼1.0, and was independent of SiO₂ layer thickness, where absorption in the WG mode was negligible.

 

Fig. 4. The left [(a1)–(f1)], middle [(a2)–(f2)], and right [(a3)–(f3)] columns show the calculated reflectivity (ATR spectrum), reflection phase shift, and GH shift, respectively, as a function of the incident angle ${\theta _i}$. I) Dependence on the gap layer thickness ${d_2}$ in the absence of attenuation or gain. The layer thicknesses ${d_2}$ were (a) 300, (b) 500, (c) 600, and (d) 700 nm. The deep blue lines in (a2)–(d2) represent the slope of the dispersion curve at the resonance of the inverted WG mode. Note that the vertical scales in the right column are different from each other. II) Similar calculations in the presence of attenuation in the WG layer (Ta₂O₅). The refractive index assumed in the WG layer was (e) ${n_2}$ = 2.20 + i1.0 × 10⁻⁴. III) Similar calculations when the gain was introduced as (f) ${n_2}$ = 2.20−i1.0 × 10⁻⁵. The layer thickness ${d_2}$ was 850 nm in (e) and (f). The thicknesses were ${d_1}$ = 51 nm and ${d_3}$ = 147 nm in all calculations. The horizontal red dotted lines in (b1)–(f1) represent the intensity of the reflected beam ${I_{Fano}}$.

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Fig. 5. Solid and dashed lines show the calculated GH shift, ${D_{Fano}}$ (left axis) and the intensity of the reflected beam ${I_{Fano}}$ (right axis) respectively, as a function of the thickness of the gap layer (SiO₂). (a) The black line shows the results without attenuation or gain. Colored lines show the results in the presence of attenuation in the WG layer (Ta₂O₅). The refractive indexes used were ${n_2}$ = 2.20 (black), 2.20 + i1.0 × 10⁻⁵ (yellow), 2.20 + i5.0 × 10⁻⁵ (green), and 2.20 + i1.0 × 10⁻⁴ (blue). The closed and open circles represent experimental results of ${D_{Fano}}$ and ${I_{Fano}}$ respectively, shown in Fig. 3. (b) The black line shows the results without attenuation or gain (same plot as in (a)). The red line is a similar plot in the presence of gain in the WG layer (Ta₂O₅) layer. The refractive index used was ${n_2}$ = 2.20 − i1.0 × 10⁻⁵.

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In ideal lossless systems, one may expect that the GH shift becomes infinite when the thickness of the gap layer increases to infinity. In real systems, however, the bandwidth of the Fano peak $\Delta k$ is restricted by the finite sample size as $\Delta k \approx 1/L$, where $L$ is the transverse sample size. When the thickness of the gap layer increases beyond this limit, the Fano peak becomes weak and disappears.

3.2 Attenuation and gain in the WG layer (Ta₂O₅)

Although the intrinsic loss in the Ta₂O₅ layer is negligibly small, absorption and scattering by impurities or imperfections in the fabrication processes cannot be neglected in real samples. Attenuations could dissipate the lateral energy flow along the WG structure and reduce the GH shift. To evaluate real systems, we simulated the effects of absorption on the GH shift. Figure 4(e) shows the calculations of reflectivity, reflection phase shift, and GH shift, where the attenuation is artificially introduced through the imaginary part of the refractive index in the WG layer (Ta₂O₅). The colored solid and dashed lines in Fig. 5(a) summarize the GH shift ${D_{Fano}}$ and the intensity of the reflected beam ${I_{Fano}}$ as a function of the SiO₂ layer thickness, respectively. In the presence of attenuation, the GH shift ${D_{Fano}}$ shows saturation in the thick SiO₂ region (${d_2}$ > 850 nm) and approaches a constant value, as determined by the absorption; simultaneously, ${I_{Fano}}$ decreases. The reduction in refractivity counteracts the advantage of the dielectric multilayer Fano structure, where the giant GH shift occurred without attenuation.

In contrast to attenuation, the gain in the WG mode could enhance the GH shift, compensating for energy leakage during propagation. We simulated the GH shift under conditions where the WG layer was doped with gain material and externally pumped to achieve the gain. Figure 4(f) shows the calculated reflectivity, reflection phase shift, and GH shift, where the gain is introduced through the imaginary part of the refractive index in the WG layer. In this case, the reflectivity exceeds 1.0, reflecting the gain in the WG mode. The reflectivity and GH shift ${D_{Fano}}$ are summarized in Fig. 5(b). When the gain does not exceed total loss in the WG mode, it enhances the GH shift. When the gain exceeds the total loss, the laser action occurs in WG mode and the system becomes unstable. Here, we used a simple loss and gain system. Large GH shift could also be achieved in a complex multilayer system with alternating optical loss and gain [10].

3.3 Two types of configuration: Under- and over-coupling conditions in the coupling layer (Au)

Finally, we briefly comment on two types of possible configuration of a multilayer Fano structure. In our sample, we prepared the coupling layer (Au) to be 51-nm-thick, so that the light field component in the re-radiation process occurring via the SPP would be weaker than the directly reflected light component (under-coupling condition). We denote this configuration of the multilayer structure type I. For the type I case, we already showed the reflectivity, reflection phase shift, and GH shift in Fig. 4(c1)–4(c3). Another possible configuration is the case in which the Au layer is thin, so that the re-radiation component via SPP is stronger than the directly reflected light component (over-coupling condition). We denote this configuration as type II. The boundary thickness of the Au layer between types I and II, i.e., the critical coupling condition, is 49 nm in our configuration. In Fig. 6(a), the reflectivity, reflection phase shift, and GH shift are calculated for the type II case. The reflectivity appeared the same as in type I, as shown in Fig. 4(c1) and Fig. 6(a1); however, the resultant dispersions were different. In the type I configuration, the steep negative dispersion relevant to the inverted WG mode was superimposed on the broad positive dispersion produced by SPP substractively (Fig. 4(c2)). On the other hand, in the type II configuration, the dispersion relevant to the inverted WG mode overlapped the broad negative dispersion produced by SPP additively (Fig. 6(a2)). To make this difference clear, we plotted the optical admittance in Fig. 6(b) and  6(c), i.e., the reflected field was plotted on the complex plain, where the vertical and horizontal axes represent the imaginary and real parts of the reflected electric field, respectively. In the type II configuration (Fig. 6(c)), the trajectory passed through the origin twice, and hence the reflected phase changed by 2 × 2π rad when the incident frequency increased across the resonance. We prepared our samples in the type I configuration, as this exactly corresponds to the traditional EIT configuration [15–18]. Experimentally, we can distinguish between type I and type II samples by observing the sign of the GH shift at the angular positions below and above the WG mode resonance (notations 3 and 4, respectively, in Fig. 2(b1)). In the experiments shown in Fig. 3(d) and 3(e), the GH shifts occurred in the negative direction, in good agreement with the sample preparation in the type I configuration.

 

Fig. 6. (Upper figures) (a1), (a2), and (a3) The reflectivity, reflection phase shift, and GH shift in the type II configuration, respectively. The layer thicknesses were (a) ${d_1}$ = 46 nm, ${d_2}$ = 600 nm, and ${d_3}$ = 147 nm. (Lower figures) (b) and (c) Optical admittance of the reflected field for the type I and type II configurations, respectively. Notations A–E in (c) represent the corresponding angles shown in (a1).

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Note that the giant GH shift in the Fano system is the counterpart of slow light in the induced transparency window in the frequency domain [26]. Discussion of the dispersion in the type I and II configurations also apply to the frequency domain dispersions.

4. Summary

In summary, we experimentally demonstrated a giant GH shift, with reflectivity ∼1, in a dielectric multilayer Fano structure. The observed GH shift was ${D_{Fano}}$ = 0.176 mm, which corresponded to ${D_{Fano}}/\lambda $ = 493. The Q-value of the WG mode in the dielectric structure is predominantly determined by the coupling loss. Hence, we can achieve an extremely large GH shift without attenuation of the beam intensity by reducing the coupling strength. The unique feature of the giant GH shift appearing without attenuation has great potential for a number of applications, such as optical switching, optical filters, and sensors, where the reduction of reflected beam intensity is currently a major disadvantage. The strategy to enhance the performance of nanostructured photonic devices by replacing the plasmonic components with low-loss dielectric Fano materials could also be successfully implemented in the dielectric multilayer Fano structure.