1,720,978 research outputs found
Microring resonators for vortex beam emission and their all-optical wavelength tuning
No full textA vortex beam possesses a helical phase front and carries a phase singularity along the propagation axis. The salient properties of vortex beams, including the theoretically unbounded orbital angular momentum (OAM) and spatially variant states of polarization (SOPs), have been utilized for a range of applications, including optical sensing, communications, manipulation and imaging. This thesis reports integrated vortex beam emitters and all-optical wavelength tuning based on microring resonators. The work may be further explored for potential applications such as light detection and ranging (LiDAR) and communication systems. An integrated Terahertz (THz) vortex beam emitter is presented for the first time based on simulation to generate tunable OAM states. The design can convert infrared waveguide modes into a freely propagating THz beam via difference-frequency generation. The output OAM state carries a topological charge that is tunable with input wavelengths. Three devices are evaluated in a test frequency range from 9 THz to 13.5 THz, and the topological charge can change from -2 to 4. A frequency shift accompanies the change in the topological charge, and its magnitude depends on the planar dimensions of the emitter. An on-chip vector vortex beam emitter is demonstrated for the first time via numerical simulation to generate all points on a first-order Poincaré sphere (FOPS). It consists of a wave guide coupled, nanostructured Si microring resonator. The fundamental transverse electric and transverse magnetic input modes produce radial and azimuthal polarization, respectively. These two linear polarization states can form a pair of eigenstates for the FOPS. Consequently, tuning the phase contrast and the intensity ratio of these two coherent inputs can control the SOPs of generated vortex beams. Flexible wavelength modulation of the generated vortex beams is desired to enhance sensing and communication performance. An all-optical wavelength tuning device is experimentally demonstrated based on two coupled microrings, which may combine with the proposed emitters. Pumping the symmetric and antisymmetric resonances of the device can induce attractive and repulsive optical gradient forces, respectively. The optical gradient forces can reconfigure the device and tune its resonant wavelengths. Besides, the wavelength difference between the symmetric and antisymmetric resonances can be significantly increased and decreased by the device's positive and negative pull-back instabilities, respectively
Dataset in support of the paper 'Optical mode localized sensing in on-chip coupled microring resonators'
No full textThis dataset provides the data for plotting Fig. 2b, Fig.3, Fig. 4, Fig. 5 and Fig. 6 in the paper (Title: Optical mode localized sensing in on-chip coupled microring resonators) published in journal Optics Express.</span
Coherent generation of arbitrary first-order Poincaré sphere beams on an Si chip
No full textGeneralized vector vortex light beams possess spatially variant polarization states, and higher-order Poincaré spheres represent a powerful analytical tool for analyzing these intriguing and complicated optical fields. For the generation of these vortex beams, a range of different methods have been explored, with an increasing emphasis placed on compact, integrated devices. Here, we demonstrate via numerical simulation, for the first time, an on-chip light emitter that allows for the controllable generation of all points on a first-order Poincaré sphere (FOPS). The FOPS beam generator consists of a waveguide-coupled, nanostructured Si microring resonator that converts two guided, coherent light waves into freely propagating output light. By matching their whispering gallery modes with the nanostructures, the fundamental TE (transverse electric) and TM (transverse magnetic) input modes produce radial and azimuthal polarizations, respectively. These two linear polarizations can form a pair of eigenstates for the FOPS. Consequently, tuning the phase contrast and the intensity ratio of these two coherent inputs allows for the generation of an arbitrary point on the FOPS. This result indicates a new way for on-chip vector vortex beam generation, which may be applied for integrated optical tweezers and high-capacity optical communications
Nonlinear generation of THz vortex beams with tunable orbital angular momentum in si microdisks
No full textIn this poster presentation, we demonstrate waveguide-coupled microdisks that emit THz light with tunable orbital angular momentum. The topological charge of the THz light can be tuned by changing the driving infrared wavelengths in the difference-frequency generation process
Positive and negative pull-back instabilities in mode splitting optomechanical devices
No full textOptical gradient forces play an essential role in optomechanical systems. The systems based on coupled microresonators are of great importance for applications in signal processing, sensors, and actuators. Here, we theoretically and experimentally studied, for the first time, positive and negative pull-back instabilities originating from attractive and repulsive optical gradient forces, respectively, in an optomechanical device based on coupled microrings. The device consists of two coupled free-standing waveguides in two identical microrings, fabricated in the silicon-on-insulator process. The coupling between the two microrings results in the symmetric and antisymmetric resonances showing in the transmission spectrum of the device. By measuring the wavelength difference between the self-referenced symmetric and antisymmetric resonances, the wavelength tuning due to the optomechanical actuation is decoupled from the tuning due to the thermo-optical effect. It is demonstrated theoretically and experimentally that the positive pull-back instability originates from the attractive optical gradient force and the negative pull-back instability originates from the repulsive optical gradient force when the pump wavelength increases. The positive pull-back instability significantly increases the wavelength difference between the symmetric and antisymmetric resonances. On the contrary, the negative pull-back instability significantly decreases the wavelength difference
On-chip optical pulse train generation through the optomechanical oscillation
No full textThis paper proposes a novel on-chip optical pulse train generator (OPTG) based on optomechanical oscillation (OMO). The OPTG consists of an optical cavity and mechanical resonator, in which OMO periodically modulates the optical cavity field and consequently generates optical pulse trains. The dimensionless method are introduced to simulate the OMObased OPTG with reduced analysis complexity. We investigate the optomechanical coupling and the dynamic back-action processes, by which we found a dead zone that forbids the OMO, and derived the optimal laser detuning and the minimum threshold power. We analysed the OMO-based OPTG in terms of the pulse shape distortion, extinction ratio (ER) and duty-cycle (DC). Increasing input power, mechanical and optical Q-factors will increase ER, reduce DC and produce sharper and shorter optical pulses. We also discuss the design guidance of OMO-based OPTG and explore its application in distributed fibre optical sensor (DFOS)
Optical mode localization sensing based on fiber-coupled ring resonators
No full textMode localization is widely used in coupled micro-electro-mechanical system (MEMS) resonators for ultra-sensitive sensing. Here, for the first time to the best of our knowledge, we experimentally demonstrate the phenomenon of optical mode localization in fiber-coupled ring resonators. For an optical system, resonant mode splitting happens when multiple resonators are coupled. Localized external perturbation applied to the system will cause uneven energy distributions of the split modes to the coupled rings, this phenomenon is called the optical mode localization. In this paper, two fiber-ring resonators are coupled. The perturbation is generated by two thermoelectric heaters. We define the normalized amplitude difference between the two split modes as: (T
M1 − T
M
2)/T
M
1 × 100%. It is found that this value can be varied from 2.5% to 22.5% when the temperature are changed by the value from 0K to 8.5K. This brings a ∼ 2.4%/K variation rate, which is three orders of magnitude greater than the variation rate of the frequency over temperature changes of the resonator due to thermal perturbation. The measured data reach good agreement with theoretical results, which demonstrates the feasibility of optical mode localization as a new sensing mechanism for ultra-sensitive fiber temperature sensing.
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Geometric representation of vector vortex beams: the total angular momentum-conserving Poincaré sphere and its braid clusters
No full textThis paper presents the total angular momentum-conserving Poincaré sphere (TAM-C PS), which offers a novel framework for efficiently characterizing a wide range of vector vortex beams. Unlike other types of Poincaré spheres, the TAM-C PS achieves a better balance between generality and validity, while also providing clearer physical interpretation. By linking the poles of different spheres, the study also introduces two distinct categories of TAM-C PS braid clusters, enabling the representation of various Poincaré spheres within a unified framework. The Poincaré spheres include classical, higher-order, hybrid-order, Poincaré sphere with orbital angular momentum, and TAM-C PS. This is the first clear and unified approach to express multiple Poincaré spheres within a single framework. The TAM-C PS and its braid cluster can be employed to guide the creation of targeted vector vortex light beams, offer a geometric description of optical field evolution, and calculate the geometric phase of optical cyclic evolution
Manipulation of higher-order Poincaré sphere beams beyond the diffraction limit using single-layer metasurface
No full textControl and generation of arbitrary higher-order Poincaré sphere (HOPS) beams have attracted intensive interest because of the potential of extreme optical manipulation using HOPS beams. Here, we experimentally demonstrate the control of focused HOPS beams with multi-foci of 22% smaller than the diffraction limit via a single-layer metasurface. Since the optical tweezer based on a highly focused laser beam was invented in 1970 and awarded the Nobel Prize in 2018, it has been explored for manipulating microscale and nanoscale particles in both over-damped and under-damped regimes, which makes it possible to move biological and chemical molecules via a contactless way, to study light-matter interaction, and to realize a macro quantum system. The on-chip generation and manipulation of HOPS beams would effectively extend the dimension (2D to 3D) and complexity (single particle to multiple particles) of optical manipulation. Here, we show that a single-layer dielectric metasurface can be used for simultaneously manipulating and highly focusing the HOPS beam via manipulating the incident laser beam’s polarization. A metasurface with a diameter of 1.2mm and a numerical aperture of 0.9 is fabricated following a CMOS-compatible process. Then, it is measured in a custom-built microscope system with a camera working at 1550nm
Electrogyration in metamaterials: chirality and polarization rotatory power that depend on applied electric field
No full textOne of the most fascinating properties of chiral molecules is their ability to rotate the polarization of light. Since Faraday’s experiments in 1845 it has been known that non-reciprocal polarization rotatory power can be induced by a magnetic field. But can reciprocal polarization rotation in chiral molecules be influenced by an electric field? In the 1960s Aizu and Zheludev introduced the phenomenon of electrogyration. While the linear (Pockels) and quadratic (Kerr) electro-optical effects describe how an external electric field changes linear birefringence and dichroism, electrogyration describes how a field changes the circular birefringence and dichroism of a medium. Electrogyration has been observed in dielectrics, semiconductors and ferroelectrics, but the effect is small. This work demonstrates a nanostructured photonic metamaterial that exhibits quadratic electrogyration – proportional to the square of the applied electric field – six orders of magnitude stronger than in any natural medium. Giant quadratic electrogyration emerges as electrostatic forces acting against forces of elasticity change the chiral configuration of the metamaterial’s nanoscale building blocks and consequently its polarization rotatory power. This observation of giant electrogyration alters the perception of the effect from that of an esoteric phenomenon into a functional part of the electro-optic toolkit with application potential
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