Honggen Li

Free-space coupling of a light beam into a symmetrical metal-cladding optical waveguide

We report on a coupling method, which transfers energy of a light beam from free space into a symmetrical metal-cladding optical waveguide from the top surface without employing the prism, grating, tapered film, and other coupling components. In the experiment, a glass flat with a thickness about 100 μm, sandwiched between two gold films is used as a guiding layer. A top gold film of 46 nm thick serves as a coupling layer as well as the cladding and a base gold film of 200 nm serves as the substrate of the waveguide. Up to 50% of the incident light energy fed into the waveguide has been demonstrated.

Observation of large positive and negative lateral shifts of a reflected beam from symmetrical metal-cladding waveguides.

Both large positive and negative lateral shifts were observed for the reflected light beam on a symmetrical metal-cladding waveguide. The positive and negative shifts approach about 480 and 180 microm, respectively, which to our knowledge are the largest experimental results ever reported. The experiment also proves that the positive or the negative shift depends on sign of the difference between the intrinsic and radiative damping.

Study of ultrahigh-order modes in a symmetrical metal-cladding optical waveguide

We report theory and experiment on ultrahigh-order modes in a symmetrical metal-cladding thick optical waveguide. The waveguide consists of a LiNbO3 slab or a glass slab with a thickness greater than 0.1mm, two gold films deposited on the upper and bottom sides of the slab serving as the cladding of the waveguide. By using the free-space coupling technique, ultrahigh-order modes (m>2000) are excited, and its high sensitivity to both refractive index and thickness of the guide, as well as the polarization independence are demonstrated.

Oscillating wave sensor based on the Goos–Hänchen effect

Instead of the evanescent field sensors, an oscillating wave sensor based on the Goos–Hanchen effect is proposed in this letter. It is demonstrated that as the intrinsic damping is well-matched with the radiative damping of the ultrahigh-order modes in a symmetrical metal-cladding waveguide with submillimeter scale, the enormously enhanced lateral beam shift results in a very high sensitivity of the sensor.

Oscillating wave displacement sensor using the enhanced Goos–Hänchen effect in a symmetrical metal-cladding optical waveguide

An oscillating wave displacement sensor based on the enhanced Goos-Hänchen (G-H) effect in a symmetrical metal-cladding optical waveguide is proposed. Since the detected signal is irrelevant to the power fluctuation of the incident light and the magnitude of the G-H shift is enhanced to hundreds of micrometers, a 40 pm resolution is demonstrated in our experiment without employing any complicated optical equipment and servo techniques.

High-sensitivity temperature sensor using the ultrahigh order mode-enhanced Goos-Hänchen effect

A high-sensitivity temperature sensor based on the enhanced Goos-Hänchen effect in a symmetrical metal-cladding waveguide is theoretically proposed and experimentally demonstrated. Owing to the high sensitivity of the ultrahigh-order modes, any minute variation of the refractive index and thickness in the guiding layer induced by the thermo-optic and thermal expansion effects will easily give rise to a dramatic change in the position of the reflected light. In our experiment, a series of Goos-Hänchen shifts are measured at temperatures varying from 50.0 °C to 51.2 °C with a step of 0.2 °C. The sensor exhibits a good linearity and a high resolution of approximately 5×10(-3) °C. Moreover, there is no need to employ any complicated optical equipment and servo techniques, since our transduction scheme is irrelevant to the light source fluctuation.

Electric control of spatial beam position based on the Goos–Hänchen effect

A structure of symmetrical metal-cladding waveguide, which contains optically nonlinear material in the guiding layer, is proposed to control the lateral shift of the reflected beam via an external electric field. Owing to the high sensitivity of ultrahigh-order modes, any minute index change of the waveguide will lead to a dramatic variation of the resonance condition, which gives rise to a change of the lateral beam displacement. Experimental result shows that the electric control of the lateral beam shift is realized in a range of 720μm.

An electro-optic polymer modulator based on the free-space coupling technique

An electro-optic (EO) polymer modulator employing a symmetrical metal-cladding waveguide structure is presented. Based on the free-space coupling technique, the energy of incident light on the metal-cladding is coupled directly from free space into the waveguide without using a prism, grating and other coupling components. An externally applied voltage modulates the reflected light intensity by changing the energy coupling efficiency of the incident light into the waveguide through the refractive index of the EO polymer. The fabricated modulator achieves an 8.2% modulation depth with 10 Vp−p driving voltage at 1 MHz. The device also provides the benefits of simple fabrication and compact size owing to the use of the free-space coupling technique.

Optical transduction of E. Coli O157:H7 concentration by using the enhanced Goos-Hanchen shift

Within the symmetrical metal-cladding waveguide structure, the optical transduction of the E. coli O157:H7 concentration by using the enhanced Goos-Hanchen (GH) shift is demonstrated to be an advantageous alternative over those evanescent wave-based biosensors. The experimental results indicate that the interaction between the analyte and the excited ultrahigh order modes (in the form of the oscillating wave) is the dominant reason leading to ultrahigh sensitivity. On the condition that the intrinsic damping is well-matched with the radiative damping, the giant GH shift (hundreds of micrometers) offers a higher sensitivity than the regular measurement of reflected light intensity. The transduction limit of E. Coli O157:H7 concentration about 100 cfu ml−1 is achieved.

1.5 mm light beam shift arising from 14 pm variation of wavelength

We investigate the dependence of the Goos–Hanchen shift on the penetration depth of light beam. Experiments reveal that the deeper the penetration depth, the larger the Goos–Hanchen shift becomes. Through a tuning of 14 pm in wavelength, a lateral displacement as large as 1.5 mm is observed on the surface of symmetric metal-cladding optical waveguides with different thicknesses of the guiding layer experimentally. It is proved that the lateral shift is not only closely dependent on the well excitation condition of the guided modes, but also on the penetration depth of the light beam.