Yuhang Wan

Nearly three orders of magnitude enhancement of Goos-Hanchen shift by exciting Bloch surface wave

Goos-Hanchen effect is experimentally studied when the Bloch surface wave is excited in the forbidden band of a one-dimensional photonic band-gap structure. By tuning the refractive index of the cladding covering the truncated photonic crystal structure, either a guided or a surface mode can be excited. In the latter case, strong enhancement of the Goos-Hanchen shift induced by the Bloch-surface-wave results in sub-millimeter shifts of the reflected beam position. Such giant Goos-Hanchen shift, ~750 times of the wavelength, could enable many intriguing applications that had been less than feasible to implement before.

Spectral interferometric measurement of wavelength-dependent phase response for surface plasmon resonance sensors

Here we experimentally demonstrate measurements of the wavelength-dependent phase response of a surface plasmon resonance sensor using a spectral interferometric technique. By using a broadband incoherent fiber light source and a polarimetry configuration with a high-birefringence component, the spectral phase response of a surface plasmon resonance sensor can be retrieved. A combination of wavelength interrogation and phase detection is enabled by our proposed scheme. In contrast to the previously demonstrated heterodyne or spatial fringe detection schemes, this in-line optical configuration is much simpler and can be very compact when implemented with advanced fiber optic and integrated components.

Direct experimental observation of giant Goos–Hänchen shifts from bandgap-enhanced total internal reflection

Giant Goos-Hänchen (GH) shifts are experimentally demonstrated from a prism-coupled multilayer structure incorporating a one-dimensional photonic crystal (PC) through a bandgap-enhanced total internal reflection scheme. By combining the large phase changes near the bandgap of the PC and the low reflection loss of the total internal reflection, 2 orders of magnitude enhancement of the GH shift is realized with rather low extra optical loss, which might help to open the door toward many interesting applications for GH effects.

Fiber-to-Fiber Optical Switching Based on Gigantic Bloch-Surface-Wave-Induced Goos–Hanchen Shifts

Fiber-to-fiber on-off optical switching based on the gigantic Goos-Hanchen (GH) shift on an optical beam induced by the Bloch surface wave is experimentally demonstrated for the first time. Through changing the refractive index of the cladding covering a truncated 1-D photonic crystal, the enhanced GH shift can be toggled dynamically from zero to submillimeter range. By using the finite coupling aperture of the fiber and selecting an optimized pass region of the beam to the output fiber, high extinction ratio can be achieved with reasonable insertion loss. It is also demonstrated that a refractive index change of <; 2*10-3 is sufficient to realize the switching, which opens the way to realize faster and more compact integrated GH switches.

Propagation-dependent beam profile distortion associated with the Goos-Hanchen shift

The propagation-dependent profile distortion of the reflected beam is studied via deriving the theoretical model of the optical field distribution in both the near and far field. It is shown that strong and fast-varying beam distortions can occur along the propagation path, compared to the profile on the reflecting surface. Numerical simulations for the case of a typical SPR configuration with a sharp angular response curve reveal that, when the phase distribution in the angular range covered by the input beam becomes nonlinear, previous theories based on the linear phase approximation fail to predict the Goos-Hanchen shift and its propagation-dependent variations precisely. Our study could shed light on more accurate modeling of the Goos-Hanchen effects impact on the relevant photonic devices and measurement applications.

Experimental observation of the propagation-dependent beam profile distortion and Goos–Hänchen shift under the surface plasmon resonance condition

We accurately measure the profiles of a reflected divergent beam under a very common surface plasmon resonance configuration in both the near- and far-field regions. Through analysis of the normalized beam shapes, significant propagation-dependent distortion is experimentally revealed. The results are in very good agreement with the theoretical estimations, considering the nonlinear phase distribution within the angular range covered by the focused beam. The corresponding minimal positions of the angular reflectance spectrum measured at different locations could shift as much as a few tens of millidegrees. The propagation-dependent Goos–Hanchen shifts are also accurately obtained, and they significantly deviate from the estimates based on the traditional linear phase response but match very well with the simulation results from our model. This verifies our previous theoretical predictions of the propagation-dependent beam distortion, and it could have further implications for various sensing and device applications.

Highly Sensitive, Bloch Surface Wave D-Type Fiber Sensor

A novel sensor based on a D-type optical fiber coated with a specially designed dielectric multilayer forming a one-dimensional photonic bandgap structure is proposed. The characteristics of its propagation modes are numerically analyzed at a wavelength of 785 nm to evaluate the sensors performance. The results show that its sensitivity can drastically exceed that of its metal-coated, surface plasmon resonance counterpart, due to the sharp resonance and low wave-propagation loss of its Bloch surface wave. The novel sensor can also be easily adapted for all kinds of aqueous analytes of different refractive indices by modifying the photonic bandgap structure. This could lead to the development of compact, ultra-sensitive biochemical sensing devices.

Optimizing loss of the dielectric stack for Bloch-surface-wave sensors under different interrogation schemes

Abstract For enhancing the sensitivity of the Bloch surface wave-based sensing applications, the dependency of the Bloch surface wave (BSW) resonance dip and the associated phase change on the loss of a truncated one-dimensional photonic crystal structure is numerically analyzed and studied. Furthermore, through evaluating the sensitivity of a BSW sensor based on the intensity interrogation scheme and the phase detection method, a comparison is carried out to optimize the sensing performance. The results demonstrate that the sensing sensitivity of the BSW sensor is significantly affected by the applied sensing schemes. It is shown that the optimized device loss is not the same for different sensing schemes. Relatively high phase-detection sensing sensitivity can be maintained for low-loss BSW devices, while that of the intensity interrogation scheme may drop sharply. On the other hand, the performance of intensity interrogation scheme is less affected by the higher device loss. Our result could be useful for improving the performance of the BSW sensors and selecting the appropriate sensing scheme for such devices.

Polarimetric-Phase-Enhanced Intensity Interrogation Scheme for Surface Wave Optical Sensors with Low Optical Loss

A polarimetric-phase-enhanced intensity interrogation scheme leveraging the polarization-dependent sharp phase change induced by the surface wave excitation at a low-optical-loss sensor’s surface is proposed and experimentally demonstrated. Based on a simple setup with no moving parts during interrogation, a polarimetric-phase-enhanced intensity can be obtained by subtracting the reflected intensities of two beam polarization states. Our results show a ~4-fold sensitivity increase compared to traditional intensity detection schemes for similar sensors. As novel surface wave optical sensors are designed and engineered with optimized phase responses, this scheme offers a low-complexity solution for such devices instead of traditional phase interrogation schemes.

Experimental characterization of the Bloch-surface-wave device with large loss

The sensing capability and enhanced GH effect of Bloch-surface-wave device with a large loss are experimentally studied. The results demonstrate that the device can show a good performance even with an extinction coefficient of