Showing papers by "Qiwen Zhan published in 2015"
TL;DR: A radially polarized mode-locked fiber laser through the use of a figure-8 cavity in combination with cascade fiber Bragg gratings and a polarization purity as high as 96% for the output transverse mode has been achieved simultaneously.
Abstract: We propose and demonstrate a radially polarized mode-locked fiber laser through the use of a figure-8 cavity in combination with cascade fiber Bragg gratings (FBGs). The mode-locked laser emits rectangular pulses with width tunable from 2.8 to 23 ns under an increasing pump power at 1056.3 nm with 0.2-nm 30-dB linewidth. A polarization purity as high as 96% for the output transverse mode has been achieved simultaneously.
60 citations
TL;DR: In this article, an all fiber passively Q-switching laser was used to generate cylindrical vector beam, a two dimensional material, tungsten disulphide (WS2), was adopted as a saturable absorber inside the laser cavity, while a fewmode fiber Bragg grating was used as a transverse mode-selective output coupler.
Abstract: We proposed and demonstrated an all fiber passively Q-switching laser to generate cylindrical-vector beam, a two dimensional material, tungsten disulphide (WS2), was adopted as a saturable absorber inside the laser cavity, while a few-mode fiber Bragg grating was used as a transverse mode-selective output coupler. The repetition rate of the Q-switching output pulses can be varied from 80 kHz to 120 kHz with a shortest duration of 958 ns. Attributed to the high damage threshold and polarization insensitivity of the WS2 based saturable absorber, the radially polarized beam and azimuthally polarized beam can be easily generated in the Q-switching fiber laser.
49 citations
TL;DR: In this article, an approach for the construction of a uniform three-dimensional (3D) interconnected optical chain with variable length, prescribed spot number and spacing along the optical axis is proposed.
Abstract: An approach is proposed for the construction of a uniform three-dimensional (3D) interconnected optical chain with variable length, prescribed spot number and spacing along the optical axis. This can be achieved in a 4Pi focusing system through reversing the radiation patterns from a uniform magnetic current line source in combination with an electric current line source with a cosine-squared taper. The required pupil plane illumination for generating the desired uniform 3D optical chain near the focus of high NA lens can be found analytically. It is found that the number of dark spots only depends on the parameter N related to magnetic current periodic distribution, while the length of optical chain and the interval between two adjacent spots approximately equal to the length L of line source and L/N, respectively. Numerical results demonstrate that the characteristics of the constructed optical chain can be controlled purposely through proper choices of the parameters N and L. The present work may find valuable applications in optical microscopy as well as multi-particle trapping, delivery, and manipulation.
28 citations
TL;DR: In this paper, the design and alignment strategies of 4f systems used in the vectorial optical field generator are described in detail and blurring due to diffraction effects is minimized when the 4f system is fully aligned.
Abstract: In this paper, the design and alignment strategies of 4f systems used in the vectorial optical field generator are described in detail. Reflection-type 4f systems were adopted due to limited spacing. Alignment patterns are designed and introduced as alignment tools so that the optical property (degree of freedom) controlled by each specific spatial light modulator section can be visualized and alignment of the 4f systems can be performed using the CCD image sharpness as the metric. In particular, blurring due to diffraction effects is minimized when the 4f system is fully aligned.
26 citations
TL;DR: It is demonstrated that the characteristics of the plasmonic vortex are determined by the angular momentum of the light, and the geometrical topological charge of the SBPVL, which is govern by the nonlinear superposition of the pitch and the number of blade element.
Abstract: Optical complex fields have attracted increasing interests because of the novel effects and phenomena arising from the spatially inhomogeneous state of polarizations and optical singularities of the light beam. In this work, we propose a spiral blade plasmonic vortex lens (SBPVL) that offers unique opportunities to manipulate these novel fields. The strong interaction between the SBPVL and the optical complex fields enable the synthesis of highly tunable plasmonic vortex. Through theoretical derivations and numerical simulations we demonstrated that the characteristics of the plasmonic vortex are determined by the angular momentum (AM) of the light, and the geometrical topological charge of the SBPVL, which is govern by the nonlinear superposition of the pitch and the number of blade element. In addition, it is also shown that by adjusting the geometric parameters, SBPVL can be utilized to focus and manipulate optical complex field with fractional AM. This miniature plasmonic device may find potential applications in optical trapping, optical data storage and many other related fields.
25 citations
TL;DR: This work presents a scheme for the construction of coaxially equidistant multiple focal spots with identical intensity profiles for each individual focus and a predetermined number and spacing, which can be easily derived by solving the inverse problem of the antenna radiation field.
Abstract: We present a scheme for the construction of coaxially equidistant multiple focal spots with identical intensity profiles for each individual focus and a predetermined number and spacing. To achieve this, the radiation field from an antenna is reversed and then gathered by high numerical aperture objective lenses. Radiation patterns from three types of line sources, i.e., the electric current, magnetic current and electromagnetic current distributions, with cosine-squared taper are respectively employed to generate predominately longitudinally polarized bright spots, azimuthally polarized doughnuts, and focal spots with a perfect spherically symmetric intensity distribution. The required illuminations at the pupil plane of a 4Pi focusing configuration for the creation of these identical multiple focal spots can be easily derived by solving the inverse problem of the antenna radiation field. These unique focal field distributions may find potential applications in laser direct writing and optical microscopy, as well as multiple-particle trapping, alignment, and acceleration along the optical axis.
25 citations
TL;DR: In this article, a review of complex optical fields with spatially inhomogeneous state of polarizations and optical singularities is presented, and various nano-metallic surface designs that can produce and manipulate complex optical field with tailored characteristics in the optical far field is presented.
Abstract: Abstract Recently there is an increasing interest in complex optical fields with spatially inhomogeneous state of polarizations and optical singularities. Novel effects and phenomena have been predicted and observed for light beams with these unconventional states. Nanostructured metallic thin film offers unique opportunities to generate, manipulate and detect these novel fields. Strong interactions between nano-metallic surfaces and complex optical fields enable the development of highly compact and versatile functional devices and systems. In this review, we first briefly summarize the recent developments in complex optical fields. Various nano-metallic surface designs that can produce and manipulate complex optical fields with tailored characteristics in the optical far field will be presented. Nano-metallic surfaces are also proven to be very effective for receiving and detection of complex optical fields in the near field. Advances made in this nascent field may enable the design of novel photonic devices and systems for a variety of applications such as quantum optical information processing and integrated photonic circuits.
24 citations
TL;DR: A transmission-type metasurface composed of carefully designed rectangular slot antennas for the generation of vectorial optical fields is proposed and demonstrated, and a corresponding π phase modulation is realized as proposed.
Abstract: A transmission-type metasurface composed of carefully designed rectangular slot antennas for the generation of vectorial optical fields is proposed and demonstrated. Acting as local linear polarizers, these slot antennas enable the spatial modulation of optical fields in amplitude, phase, and polarization for the cross-polarized component of the scattered field. As an illustration, a metasurface capable of forming a radially polarized scattered field with specific vectorial beam patterns with appropriate excitation at normal incidence is designed, fabricated, and tested. The radially polarized scattered field is designed to be further tightly focused by a high numerical aperture objective lens in order to obtain a uniform longitudinally polarized optical needle field along the propagation direction. Characterization experiments demonstrate that its overall extinction ratio satisfies the amplitude modulation requirement, and a corresponding π phase modulation is realized as proposed.
20 citations
TL;DR: A simple and flexible method is presented for the generation of optical focal field with prescribed characteristics by reversing the field pattern radiated from a uniform line source to create engineered focal fields with potential applications in particle acceleration, optical microscopy, optical trapping and manipulations.
Abstract: A simple and flexible method is presented for the generation of optical focal field with prescribed characteristics. By reversing the field pattern radiated from a uniform line source, for which the electric current is constant along its extent, situated at the focus of a 4Pi focusing system formed by two confocal high-NA objective lenses, the required illumination distribution at the pupil plane for creating optical focal field with desired properties can be obtained. Numerical example shows that an arbitrary length optical needle with extremely high longitudinal polarization purity and consistent transverse size of ~0.36λ over the entire depth of focus (DOF) can be created with this method. Coaxially double-focus with spot size of ~0.36λ in the transversal direction and ~λ in the axial direction separated by a prescribed spacing is illustrated as another example. The length of optical needle field and the interval between double-focus are determined by the length of uniform line source. These engineered focal fields may found potential applications in particle acceleration, optical microscopy, optical trapping and manipulations.
16 citations
TL;DR: The short effective wavelength of the surface plasmon polaritons (SPPs) mode supported by the metallic waveguide is exploited to dramatically miniaturize the device and improve the sensitivity of the beam steering.
Abstract: In this work, we design and study a highly sensitive beam steering device that integrates a spiral plasmonic antenna with a subwavelength metallic waveguide. The short effective wavelength of the surface plasmon polaritons (SPPs) mode supported by the metallic waveguide is exploited to dramatically miniaturize the device and improve the sensitivity of the beam steering. Through introducing a tiny displacement of feed point with respect to the geometrical center of the spiral plasmonic antenna, the direction of the radiation can be steered at considerably high angles. Simulation results show that steering angles of 8°, 17° and 34° are obtainable for a displacement of 50 nm, 100 nm and 200 nm, respectively. Benefiting from the reduced device size and the shorter SPP wavelength, the beam steering sensitivity of the beam steering is improved by 10-fold compared with the case reported previously. This miniature plasmonic beam steering device may find many potential applications in quantum optical information processing and integrated photonic circuits.
14 citations
TL;DR: It is shown that the additional degree of freedom provided by the elliptically polarized vector field allows one to control the spatial structure of polarization, to engineer the focusing field, and to tailor the optical force and torque on a dielectric Rayleigh particle.
Abstract: Generation of vectorial optical fields with arbitrary polarization distribution is of great interest in areas where exotic optical fields are desired. In this work, we experimentally demonstrate the versatile generation of linearly polarized vector fields, elliptically polarized vector fields, and circularly polarized vortex beams through introducing attenuators in a common-path interferometer. By means of Richards-Wolf vectorial diffraction method, the characteristics of the highly focused elliptically polarized vector fields are studied. The optical force and torque on a dielectric Rayleigh particle produced by these tightly focused vector fields are calculated and exploited for the stable trapping of dielectric Rayleigh particles. It is shown that the additional degree of freedom provided by the elliptically polarized vector field allows one to control the spatial structure of polarization, to engineer the focusing field, and to tailor the optical force and torque on a dielectric Rayleigh particle.
Patent•
17 Jun 2015TL;DR: A vectorial optical field generator includes a radiation source, a modulator surface, a first quarter wave plate, a second quarter waveplate, and an output plane as mentioned in this paper, where the output plane is positioned along the path and receives output radiation resulting from modulating the input radiation with the modulator surfaces.
Abstract: A vectorial optical field generator includes a radiation source a modulator surface, a first quarter wave plate, a second quarter wave plate, and an output plane. The radiation source emits an input radiation along a path and the modulator surface is positioned along the path and configured to modulate a phase, an amplitude, a polarization ratio, and a retardation of the input radiation along a fourth area of the modulator surface. The output plane is positioned along the path and receives output radiation resulting from modulating the input radiation with the modulator surface, the first quarter wave plate, and the second quarter wave plate.
TL;DR: In this paper, the authors investigate the interaction between optical vortices and the background field by numerical methods, and find that different combinations of optical Vortices embedded in FP beams lead to different propagation dynamics, even though the polarization maps of electromagnetic fields are identical.
TL;DR: In this article, an integrated photonic electromagnetic field sensor based on a silicon-organic hybrid modulator driven by a bowtie antenna has been developed, with a record-high effective in-device EO modulation efficiency of r33=1230pm/V.
Abstract: The detection and measurement of electromagnetic fields have attracted significant amounts of attention in recent years. Traditional electronic electromagnetic field sensors use large active conductive probes which perturb the field to be measured and also make the devices bulky. In order to address these problems, integrated photonic electromagnetic field sensors have been developed, in which an optical signal is modulated by an RF signal collected by a miniaturized antenna. In this work, we design, fabricate and characterize a compact, broadband and highly sensitive integrated photonic electromagnetic field sensor based on a silicon-organic hybrid modulator driven by a bowtie antenna. The large electro-optic (EO) coefficient of organic polymer, the slow-light effects in the silicon slot photonic crystal waveguide (PCW), and the broadband field enhancement provided by the bowtie antenna, are all combined to enhance the interaction of microwaves and optical waves, enabling a high EO modulation efficiency and thus a high sensitivity. The modulator is experimentally demonstrated with a record-high effective in-device EO modulation efficiency of r33=1230pm/V. Modulation response up to 40GHz is measured, with a 3-dB bandwidth of 11GHz. The slot PCW has an interaction length of 300µm, and the bowtie antenna has an area smaller than 1cm 2 . The bowtie antenna in the device is experimentally demonstrated to have a broadband characteristics with a central resonance frequency of 10GHz, as well as a large beam width which enables the detection of electromagnetic waves from a large range of incident angles. The sensor is experimentally demonstrated with a minimum detectable electromagnetic power density of 8.4mW/m 2 at 8.4GHz, corresponding to a minimum detectable electric field of 2.5V/m and an ultra-high sensitivity of 0.000027V/m Hz -1/2 ever demonstrated. To the best of our knowledge, this is the first silicon-organic hybrid device and also the first PCW device used for the photonic detection of electromagnetic waves. Finally, we propose some future work, including a Teraherz wave sensor based on antenna-coupled electrooptic polymer filled plasmonic slot waveguide, as well as a fully packaged and tailgated device.
TL;DR: In this paper, an integrated photonic electromagnetic field sensor based on a silicon-organic hybrid modulator driven by a bowtie antenna was designed, with a record-high effective in-device EO modulation efficiency of r33=1230pm/V.
Abstract: In this work, we design, fabricate and characterize a compact, broadband and highly sensitive integrated photonic electromagnetic field sensor based on a silicon-organic hybrid modulator driven by a bowtie antenna. The large electro-optic (EO) coefficient of organic polymer, the slow-light effects in the silicon slot photonic crystal waveguide (PCW), and the broadband field enhancement provided by the bowtie antenna, are all combined to enhance the interaction of microwaves and optical waves, enabling a high EO modulation efficiency and thus a high sensitivity. The modulator is experimentally demonstrated with a record-high effective in-device EO modulation efficiency of r33=1230pm/V. Modulation response up to 40GHz is measured, with a 3-dB bandwidth of 11GHz. The slot PCW has an interaction length of 300um, and the bowtie antenna has an area smaller than 1cm2. The bowtie antenna in the device is experimentally demonstrated to have a broadband characteristics with a central resonance frequency of 10GHz, as well as a large beam width which enables the detection of electromagnetic waves from a large range of incident angles. The sensor is experimentally demonstrated with a minimum detectable electromagnetic power density of 8.4mW/m2 at 8.4GHz, corresponding to a minimum detectable electric field of 2.5V/m and an ultra-high sensitivity of 0.000027V/m Hz^-1/2 ever demonstrated. To the best of our knowledge, this is the first silicon-organic hybrid device and also the first PCW device used for the photonic detection of electromagnetic waves. Finally, we propose some future work, including a Teraherz wave sensor based on antenna-coupled electro-optic polymer filled plasmonic slot waveguide, as well as a fully packaged and tailgated device.
TL;DR: In this paper, a modified gold bowtie antenna integrated on a transparent glass substrate is numerically investigated, specifically its resonant frequency and enhancement factor, and it shows dipole-like characteristics with large beam width.
Abstract: The bowtie antenna is a topic of growing interest in recent years. In this paper, we design, fabricate, and characterize a modified gold bowtie antenna integrated on a transparent glass substrate. We numerically investigate the antenna characteristics, specifically its resonant frequency and enhancement factor. We simulate the dependence of resonance frequency on bowtie geometry, and verify the simulation results through experimental investigation, by fabricating different sets of bowtie antennas on glass substrates utilizing CMOS compatible processes and measuring their resonance frequencies. Our designed bowtie antenna provides a strong broadband electric field enhancement in its feed gap. The far-field radiation pattern of the bowtie antenna is measured, and it shows dipole-like characteristics with large beam width. Such a broadband antenna will be useful for a myriad of applications, ranging from wireless communications to electromagnetic wave detection.
TL;DR: In this article, a reflection type metal-insulator-metal (MIM) metasurface composed of hybrid optical antennas is proposed for comprehensive spatial engineering the properties of optical fields.
Abstract: We propose a reflection type metal-insulator-metal (MIM) metasurface composed of hybrid optical antennas for comprehensive spatial engineering the properties of optical fields. Its capability is illustrated with an example to create a radially polarized vectorial beam for optical needle field generation. Functioning as local quarter-wave-plates (QWP), the MIM metasurface is designed to convert circularly polarized incident into local linear polarization to create an overall radial polarization with corresponding binary phases and desired normalized amplitude modulation ranged from 0.07 to 1. To obtain enough degrees of freedom, the optical-antenna layer comprises periodic arrangements of double metallic nano-bars with perpendicular placement and single nano-bars respectively for different amplitude modulation requirements. Both of the antennas enable to introduce π/2 retardation while reaching the desired modulation range both for phase and amplitude. Through adjusting the antennas’ geometry and array carefully, we shift the gap-surface plasmon resonances facilitated by optical antennas to realize the manipulation of vectorial properties. Designed at 1064 nm wavelength, the particularly generated vectorial light output can be further tightly focused by a high numerical aperture objective to obtain longitudinally polarized flat-top focal field. The so-called optical needle field is a promising candidate for novel applications that transcend disciplinary boundaries. The proposed metasurface establishes a new class of compact optical components based on nano-scale structures, leading to compound functions for vectorial light generation.
TL;DR: In this paper, the authors theoretically and experimentally investigate the focusing properties of asymmetric sector-shaped vector beams with localized linear polarization, and they show that shape-only modulation of the vector beam allows one to simultaneously change the intensity, phase, polarization, as well as spin angular momentum distributions of the focused field.
Abstract: We theoretically and experimentally investigate the focusing properties of asymmetric-sector-shaped vector beams with localized linear polarization. Simulation results show that the shape-only modulation of the vector beam allows one to simultaneously change the intensity, phase, polarization, as well as spin angular momentum distributions of the focused field. Experimentally, we generate asymmetric-sector-shaped vector beams and study its intensity distributions and the polarization characteristics at the focal plane, which are in good agreements with the numerical simulations. The presented approach enriches the methods for focus engineering and inspires the manipulation of the angular momentum of light, which would be useful for optical manipulation.
TL;DR: In this paper, a method of generating spherical focal spot is demonstrated through reversely propagating and tightly focusing the electric field at the pupil plane radiated from an infinite biconical antenna centered at the foci of two confocal high numerical aperture aplanatic objective lenses.
TL;DR: In this paper, a modified gold bowtie antenna integrated on a transparent glass substrate is numerically investigated, specifically its resonant frequency and enhancement factor, and it shows dipole-like characteristics with large beam width.
Abstract: The bowtie antenna is a topic of growing interest in recent years. In this paper, we design, fabricate, and characterize a modified gold bowtie antenna integrated on a transparent glass substrate. We numerically investigate the antenna characteristics, specifically its resonant frequency and enhancement factor. We simulate the dependence of resonance frequency on bowtie geometry, and verify the simulation results through experimental investigation, by fabricating different sets of bowtie antennas on glass substrates utilizing CMOS compatible processes and measuring their resonance frequencies. Our designed bowtie antenna provides a strong broadband electric field enhancement in its feed gap. The far-field radiation pattern of the bowtie antenna is measured, and it shows dipole-like characteristics with large beam width. Such a broadband antenna will be useful for a myriad of applications, ranging from wireless communications to electromagnetic wave detection.
TL;DR: In this paper, an all-fiber actively mode-locked laser emitting cylindrical vector beam was demonstrated. Butler et al. used an offset splicing of single-mode fiber with fourmode fiber as a mode coupler in the laser cavity.
Abstract: We demonstrated an all fiber actively mode-locked laser emitting cylindrical vector beam. A few-mode fiber Bragg grating is adopted to achieve mode selecting and spectrum filtering. An offset splicing of single-mode fiber with fourmode fiber is utilized as a mode coupler in the laser cavity. A LiNbO3 Mach-Zehnder modulator is used to achieve active mode locking in the laser. The laser operates at 1547nm with 30 dB spectrum width of 0.3nm. The emitted modelocked pulses have a duration of 1ns and repetition of 12.06MHz. Both radially and azimuthally polarized beams have been obtained with very good modal symmetry by adjusting the polarization in the laser cavity.
06 Nov 2015
TL;DR: In this paper, a wavefront sensor based on the smartphone platform has been implemented for thin-films and bio-related sensing areas, where distorted micro-gratings are designed and introduced into the system in the dual role of both beam splitter and defocuser.
Abstract: Smartphone camera system has the capability of being integrated into powerful field-sensing tools, capturing data and sharing these data with computing servers or cloud experts. The purpose of this work is to implement a wavefront sensor based on the smartphone platform, which has many potential applications in thin-films and bio-related sensing areas. To overcome problems caused by traditional wavefront curvature sensing setups, distorted micro-gratings are designed and introduced into the system in the dual role of both beam splitter and defocuser. The new design is capable of capturing two images of different levels of defocus in a single shot, which are then used as the input data to reconstruct the wavefront. Through testing with generated known spherical wavefronts, the smartphone based wavefront sensor has demonstrated decent system resolution and wavefront sensing accuracy.
TL;DR: In this article, the authors show that the generation of spatially variable polarization states can be easily realized by using the light scattered from a thin metallic cylinder, which can be described as closed paths on the Poincare sphere that connect antipodal polarizations.
06 Nov 2015
TL;DR: In this paper, the authors demonstrate the design, fabrication and testing of miniature steerable optical sources that are capable of beaming photons with spin and orbital angular momentum through coupling nanoscale emitters to plasmonic waveguide and antenna structures.
Abstract: We demonstrate the design, fabrication and testing of miniature steerable optical sources that are capable of beaming photons with spin and orbital angular momentum through coupling nanoscale emitters to plasmonic waveguide and antenna structures.