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Showing papers in "Optics Letters in 2014"


Journal ArticleDOI
TL;DR: This work demonstrates the multiplexing/demultiplexing of 1008 data channels carried on 12 OAM beams, 2 polarizations, and 42 wavelengths, providing an aggregate capacity of 100.8 Tbit/s.
Abstract: We investigate the orthogonality of orbital angular momentum (OAM) with other multiplexing domains and present a free-space data link that uniquely combines OAM-, polarization-, and wavelength-division multiplexing. Specifically, we demonstrate the multiplexing/demultiplexing of 1008 data channels carried on 12 OAM beams, 2 polarizations, and 42 wavelengths. Each channel is encoded with 100 Gbit/s quadrature phase-shift keying data, providing an aggregate capacity of 100.8 Tbit/s (12×2×42×100 Gbit/s).

450 citations


Journal ArticleDOI
TL;DR: The generation of a femtosecond pulse in a fiber ring laser by using a polyvinyl alcohol (PVA)-based molybdenum disulfide (MoS(2) SA) saturable absorber indicates that the filmy PVA-based MoS( 2) SA is indeed a good candidate for an ultrafast saturable absorption device.
Abstract: We report on the generation of a femtosecond pulse in a fiber ring laser by using a polyvinyl alcohol (PVA)-based molybdenum disulfide (MoS2) saturable absorber (SA). With a saturable optical intensity of 34 MW/cm2 and a modulation depth of ∼4.3%, the PVA-based MoS2 SA had been employed with an erbium-doped fiber ring laser as a mode locker. The mode-locking operation could be achieved at a low pump threshold of 22 mW. A ∼710 fs pulse centered at 1569.5 nm wavelength with a repetition rate of 12.09 MHz had been achieved with proper cavity dispersion. With the variation of net cavity dispersion, output pulses with durations from 0.71 to 1.46 ps were obtained. The achievement of a femtosecond pulse at 1.55 μm waveband demonstrates the broadband saturable absorption of MoS2, and also indicates that the filmy PVA-based MoS2 SA is indeed a good candidate for an ultrafast saturable absorption device.

351 citations


Journal ArticleDOI
TL;DR: High-field terahertz transients with 0.9-mJ pulse energy produced in a 400 mm² partitioned organic crystal by optical rectification of a 30-m J laser pulse centered at 1.25 μm wavelength are reported on.
Abstract: We report on high-field terahertz transients with 0.9-mJ pulse energy produced in a 400 mm² partitioned organic crystal by optical rectification of a 30-mJ laser pulse centered at 1.25 μm wavelength. The phase-locked single-cycle terahertz pulses cover the hard-to-access low-frequency range between 0.1 and 5 THz and carry peak fields of more than 42 MV/cm and 14 Tesla with the potential to reach over 80 MV/cm by choosing appropriate focusing optics. The scheme based on a Cr:Mg₂SiO₄ laser offers a high conversion efficiency of 3% using uncooled organic crystal. The collimated pump laser configuration provides excellent terahertz focusing conditions.

260 citations


Journal ArticleDOI
TL;DR: This work demonstrates the first time that distributed vibration sensing is realized over such a long distance without inserting repeaters, and the novel hybrid amplification scheme in this work can also be incorporated in other fiber-optic sensing systems for extension of sensing distance.
Abstract: A phase-sensitive optical time-domain reflectometry (Φ-OTDR) with 175 km sensing range and 25 m spatial resolution is demonstrated, using the combination of co-pumping second-order Raman amplification based on random fiber lasing, counter-pumping first-order Raman amplification, and counter-pumping Brillouin amplification. With elaborate arrangements, each pumping scheme is responsible for the signal amplification in one particular segment of all three. To the best of our knowledge, this is the first time that distributed vibration sensing is realized over such a long distance without inserting repeaters. The novel hybrid amplification scheme in this work can also be incorporated in other fiber-optic sensing systems for extension of sensing distance.

231 citations


Journal ArticleDOI
TL;DR: An ultrahigh coupling efficiency (CE) fully etched apodized grating coupler on the silicon-on-insulator (SOI) platform using subwavelength photonic crystals and bonded aluminum mirror is designed and fabricated.
Abstract: We design and fabricate an ultrahigh coupling efficiency (CE) fully etched apodized grating coupler on the silicon-on-insulator (SOI) platform using subwavelength photonic crystals and bonded aluminum mirror. Fabrication error sensitivity and coupling angle dependence are experimentally investigated. A record ultrahigh CE of −0.58 dB with a 3 dB bandwidth of 71 nm and low back reflection are demonstrated.

212 citations


Journal ArticleDOI
TL;DR: A noncontact low-coherence optical phase-based imaging method, termed shear wave imaging optical coherence tomography (SWI-OCT), which enables 2D depth-resolved visualization of the low-amplitude elastic wave propagation in tissue with ultrahigh frame rate and has the potential to be further developed as a major technique for depth-resolution high-resolution tissue elastography in vivo.
Abstract: We report on a noncontact low-coherence optical phase-based imaging method, termed shear wave imaging optical coherence tomography (SWI-OCT), which enables 2D depth-resolved visualization of the low-amplitude elastic wave propagation in tissue with ultrahigh frame rate. SWI-OCT is based on 1D transverse scanning of the M-mode OCT imaging that is precisely synchronized with a low-pressure short-duration air-puff loading system. This approach of scanning and data recording allows visualization of the induced tissue deformation at high frame rate. The applied phase-resolved interferometric technique, with sensitivity on the nanometer scale, makes the low-amplitude tissue displacement detectable. For the demonstration of this method, and to study its application for tissue biomechanics, we performed pilot experiments on agar phantoms and ex vivo rabbit corneas. Samples with different elastic properties can be differentiated based on the velocity of the elastic wave propagation that is directly visualized with a 25 kHz frame rate. Our results indicate that SWI-OCT has the potential to be further developed as a major technique for depth-resolved high-resolution tissue elastography in vivo.

186 citations


Journal ArticleDOI
TL;DR: Experimental results indicate that the GMFBG-based NH3 gas sensor has fast response due to its highly compact structure and such a miniature fiber-optic element may find applications in high sensitivity gas sensing and trace analysis.
Abstract: A graphene coated microfiber Bragg grating (GMFBG) for gas sensing is reported in this Letter. Taking advantage of the surface field enhancement and gas absorption of a GMFBG, we demonstrate an ultrasensitive approach to detect the concentration of chemical gas. The obtained sensitivities are 0.2 and 0.5 ppm for NH3 and xylene gas, respectively, which are tens of times higher than that of a GMFBG without graphene for tiny gas concentration change detection. Experimental results indicate that the GMFBG-based NH3 gas sensor has fast response due to its highly compact structure. Such a miniature fiber-optic element may find applications in high sensitivity gas sensing and trace analysis.

176 citations


Journal ArticleDOI
TL;DR: With this new milestone result, this work has successfully scaled the pulse energy of ultrafast laser oscillators to a new performance regime and can predict that pulse energies of several hundreds of microjoules will become possible in the near future.
Abstract: We present a semiconductor saturable absorber mirror (SESAM) mode-locked thin-disk laser generating 80 μJ of pulse energy without additional amplification. This laser oscillator operates at a repetition rate of 3.03 MHz and delivers up to 242 W of average output power with a pulse duration of 1.07 ps, resulting in an output peak power of 66 MW. In order to minimize the parasitic nonlinearity of the air inside the laser cavity, the oscillator was operated in a vacuum environment. To start and stabilize soliton mode locking, we used an optimized high-damage threshold, low-loss SESAM. With this new milestone result, we have successfully scaled the pulse energy of ultrafast laser oscillators to a new performance regime and can predict that pulse energies of several hundreds of microjoules will become possible in the near future. Such lasers are interesting for both industrial and scientific applications, for example for precise micromachining and attosecond science.

176 citations


Journal ArticleDOI
TL;DR: A sub-micron silica diaphragm-based fiber-tip Fabry-Perot interferometer for pressure sensing applications is demonstrated, with a high pressure sensitivity and low temperature cross-sensitivity, suitable for high sensitivity pressure sensing in harsh environments.
Abstract: We demonstrate a sub-micron silica diaphragm-based fiber-tip Fabry–Perot interferometer for pressure sensing applications. The thinnest silica diaphragm, with a thickness of ∼320 nm, has been achieved by use of an improved electrical arc discharge technique. Such a sub-micron silica diaphragm breaks the sensitivity limitation imposed by traditional all-silica Fabry–Perot interferometric pressure sensors and, as a result, a high pressure sensitivity of ∼1036 pm/MPa at 1550 nm and a low temperature cross-sensitivity of ∼960 Pa/°C are achieved when a silica diaphragm of ∼500 nm in thickness is used. Moreover, the all-silica spherical structure enhanced the mechanical strength of the micro-cavity sensor, making it suitable for high sensitivity pressure sensing in harsh environments.

173 citations


Journal ArticleDOI
TL;DR: 3D differential phase-contrast microscopy is demonstrated, based on computational illumination with a programmable LED array, which achieves 3D DPC with simple, inexpensive optics and no moving parts.
Abstract: We demonstrate 3D differential phase-contrast (DPC) microscopy, based on computational illumination with a programmable LED array By capturing intensity images with various illumination angles generated by sequentially patterning an LED array source, we digitally refocus images through various depths via light field processing The intensity differences from images taken at complementary illumination angles are then used to generate DPC images, which are related to the gradient of phase The proposed method achieves 3D DPC with simple, inexpensive optics and no moving parts We experimentally demonstrate our method by imaging a camel hair sample in 3D

173 citations


Journal ArticleDOI
TL;DR: A high-sensitivity strain sensor based on an in-fiber Fabry-Perot interferometer (FPI) with an air cavity, which was created by splicing together two sections of standard single-mode fibers, is demonstrated.
Abstract: We demonstrated a high-sensitivity strain sensor based on an in-fiber Fabry–Perot interferometer (FPI) with an air cavity, which was created by splicing together two sections of standard single-mode fibers. The sensitivity of this strain sensor was enhanced to 6.0 pm/μe by improving the cavity length of the FPI by means of repeating arc discharges for reshaping the air cavity. Moreover, such a strain sensor has a very low temperature sensitivity of 1.1 pm/°C, which reduces the cross sensitivity between tensile strain and temperature.

Journal ArticleDOI
TL;DR: A 16-element optical phased array integrated on chip is presented for achieving two-dimensional (2D) optical beam steering, which enables narrow far field beam widths while mitigating the precise etching needed for conventional shallow etch gratings.
Abstract: A 16-element optical phased array integrated on chip is presented for achieving two-dimensional (2D) optical beam steering. The device is fabricated on the silicon-on-insulator platform with a 250 nm silicon device layer. Steering is achieved via a combination of wavelength tuning and thermo-optic phase shifting with a switching power of Pπ=20 mW per channel. Using a silicon waveguide grating with a polycrystalline silicon overlay enables narrow far field beam widths while mitigating the precise etching needed for conventional shallow etch gratings. Using this system, 2D steering across a 20°×15° field of view is achieved with a sidelobe level better than 10 dB and with beam widths of 1.2°×0.5°.

Journal ArticleDOI
TL;DR: An on-chip optical phased array fabricated in a CMOS compatible process with continuous, fast (100 kHz), wide-angle (51°) beam-steering suitable for applications such as low-cost LIDAR systems is demonstrated.
Abstract: We demonstrate an on-chip optical phased array fabricated in a CMOS compatible process with continuous, fast (100 kHz), wide-angle (51°) beam-steering suitable for applications such as low-cost LIDAR systems. The device demonstrates the largest (51°) beam-steering and beam-spacing to date while providing the ability to steer continuously over the entire range. Continuous steering is enabled by a cascaded phase shifting architecture utilizing, low power and small footprint, thermo-optic phase shifters. We demonstrate these results in the telecom C-band, but the same design can easily be adjusted for any wavelength between 1.2 and 3.5 μm.

Journal ArticleDOI
Feng Xu1, Jinhui Shi1, Gong Kui1, Li Hefei1, Rongqing Hui2, Benli Yu1 
TL;DR: A fiber-optic acoustic pressure sensor based on a large-area nanolayer silver diaphragm is demonstrated with a high dynamic pressure sensitivity and simple fabrication process, making it an attractive tool for acoustic sensing and photo-acoustic spectroscopy.
Abstract: A fiber-optic acoustic pressure sensor based on a large-area nanolayer silver diaphragm is demonstrated with a high dynamic pressure sensitivity of 160 nm/Pa at 4 kHz frequency. The sensor exhibits a noise limited detectable pressure level of 14.5 μPa/Hz(1/2). Its high dynamic pressure sensitivity and simple fabrication process make it an attractive tool for acoustic sensing and photo-acoustic spectroscopy.

Journal ArticleDOI
TL;DR: It is shown that realizable fiber structures can provide greatly improved performance in terms of leakage and bending losses compared to previously reported antiresonant fibers.
Abstract: An improved design for hollow antiresonant fibers (HAFs) is presented. It consists of adding extra antiresonant glass elements within the air cladding region of an antiresonant hollow-core fiber. We use numerical simulations to compare fiber structures with and without the additional cladding elements in the near- and mid-IR regimes. We show that realizable fiber structures can provide greatly improved performance in terms of leakage and bending losses compared to previously reported antiresonant fibers. At mid-IR wavelengths, the adoption of this novel fiber design will lead to HAFs with reduced bending losses. In the near-IR, this design could lead to the fabrication of HAFs with very low attenuation.

Journal ArticleDOI
TL;DR: A novel high temperature sensor based on customized multicore fiber (MCF) spliced between two standard single-mode fibers is proposed and experimentally demonstrated, enabling temperature measurements with high sensitivity and accuracy.
Abstract: A novel high temperature sensor based on customized multicore fiber (MCF) is proposed and experimentally demonstrated. The sensor consists of a short, few-centimeter-long segment of MCF spliced between two standard single-mode fibers. Due to interference effects, the transmission spectrum through this fiber chain features sharp and deep notches. Exposing the MCF segment to increasing temperatures of up to 1000°C results in a shift of the transmission notches toward longer wavelengths with a slope of approximately 29 pm/°C at lower temperatures and 52 pm/°C at higher temperatures, enabling temperature measurements with high sensitivity and accuracy. Due to its compact size and mechanical rigidity, the MCF sensor can be subjected to harsh environments. The fabrication of the MCF sensor is straightforward and reproducible, making it an inexpensive fiber device.

Journal ArticleDOI
Lijun Meng1, Ding Zhao1, Zhichao Ruan1, Qiang Li1, Yuanqing Yang1, Min Qiu1 
TL;DR: The large sensitivity and simultaneous small FWHM result in a huge figure-of-merit of 2300/RIU, which enables the structure to have great potential in plasmonic sensing and to be used as a highly directional thermal emitter according to Kirchhoff's law.
Abstract: Lamellar gratings are investigated via temporal coupled-mode theory and numerical simulations. Total absorption can be achieved by an optimized grating with shallow grooves under normal incidence and the full width at half-maximum (FWHM) is only 0.4 nm. For certain wavelengths, the structure shows high absorption only within an ultra-narrow angle, which suggests that it can be used as a highly directional thermal emitter according to Kirchhoff’s law. Besides, the resonant wavelength is sensitive to the refractive index of the environmental dielectric. The large sensitivity (1400 nm/RIU) and simultaneous small FWHM result in a huge figure-of-merit of 2300/RIU, which enables the structure to have great potential in plasmonic sensing.

Journal ArticleDOI
TL;DR: Dual-drive Mach-Zehnder modulators were utilized to produce power-leveled optical frequency combs (OFCs) from a continuous-wave laser, which allows for robust measurements of trace gas species and alleviates much of the cost and complexity associated with the use of femtosecond OFCs produced with mode-locked pulsed lasers.
Abstract: Dual-drive Mach–Zehnder modulators were utilized to produce power-leveled optical frequency combs (OFCs) from a continuous-wave laser. The resulting OFCs contained up to 50 unique frequency components and spanned more than 200 GHz. Simple changes to the modulation frequency allowed for agile control of the comb spacing. These OFCs were then utilized for broadband, multiheterodyne measurements of CO2 using both a multipass cell and an optical cavity. This technique allows for robust measurements of trace gas species and alleviates much of the cost and complexity associated with the use of femtosecond OFCs produced with mode-locked pulsed lasers.

Journal ArticleDOI
TL;DR: It is shown that the amplitude and phase information from a two-dimensional complex field can be synthesized from a phase-only optical element with micrometric resolution from a 4-f optical system.
Abstract: We show that the amplitude and phase information from a two-dimensional complex field can be synthesized from a phase-only optical element with micrometric resolution. The principle of the method is based on the combination of two spatially sampled phase elements by using a low-pass filter at the Fourier plane of a 4-f optical system. The proposed encoding technique was theoretically demonstrated, as well as experimentally validated with the help of a phase-only spatial light modulator for phase encoding, a conventional CMOS camera to measure the amplitude of the complex field, and a Shack-Hartmann wavefront sensor to determine its phase.

Journal ArticleDOI
TL;DR: This source is used to demonstrate table-top x-ray near-edge fine-structure spectroscopy at the carbon K-edge of a polyimide foil and retrieve the specific absorption features corresponding to the binding orbitals of the carbon atoms in the foil.
Abstract: We report on the first table-top high-flux source of coherent soft x-ray radiation up to 400 eV, operating at 1 kHz. This source covers the carbon K-edge with a beam brilliance of (4.3±1.2)×10(15) photons/s/mm(2)/strad/10% bandwidth and a photon flux of (1.85±0.12)×10(7) photons/s/1% bandwidth. We use this source to demonstrate table-top x-ray near-edge fine-structure spectroscopy at the carbon K-edge of a polyimide foil and retrieve the specific absorption features corresponding to the binding orbitals of the carbon atoms in the foil.

Journal ArticleDOI
TL;DR: The successful performance of a beam-tilting array and a large-scale lens functioning at 195 THz demonstrates the ability of the dielectric metasurface that is thin and has also high efficiency of more than 80%.
Abstract: The concept of an ultra-thin metasurface made of single layer of only-dielectric disks for successful phase control over a full range is demonstrated. Conduction loss is avoided compared to its plasmonic counterpart. The interaction of the Mie resonances of the first two modes of the dielectric particles, magnetic and electric dipoles, is tailored by the dimensions of the disks, providing required phase shift for the transmitted beam from 0° to 360°, together with high transmission efficiency. The successful performance of a beam-tilting array and a large-scale lens functioning at 195 THz demonstrates the ability of the dielectric metasurface that is thin and has also high efficiency of more than 80%. Such configurations can serve as outstanding alternatives for plasmonic metasurfaces especially that it can be a scalable design.

Journal ArticleDOI
TL;DR: The first erbium-doped zirconium-fluoride-based glass fiber laser operating well beyond 3 μm with significant power and efficiency is reported, and it exhibited the longest wavelength of operation obtained to date for a room temperature, nonsupercontinuum fiber laser.
Abstract: We report the first, to the best of our knowledge, erbium-doped zirconium-fluoride-based glass fiber laser operating well beyond 3 μm with significant power. This fiber laser achieved 260 mW in CW at room temperature. The use of two different wavelength pump sources allows us to take advantage of the long-lived excited states that would normally cause a bottleneck, and this enables maximum incident optical-to-optical efficiency of 16% with respect to the total incident pump power. Both output power and efficiency are an order of magnitude improvement over similar lasers demonstrated previously. The fiber laser operating at 3.604 μm also exhibited the longest wavelength of operation obtained to date for a room temperature, nonsupercontinuum fiber laser.

Journal ArticleDOI
TL;DR: Dispersive Fourier transformation is used to measure single-shot spectra of Raman-induced noise-like pulses, demonstrating that for low cavity gain values Raman emission is sporadic and follows rogue-wave-like probability distributions, while a saturated regime with Gaussian statistics is obtained for high pump powers.
Abstract: We report on an experimental study of spectral fluctuations induced by intracavity Raman conversion in a passively partially mode-locked, all-normal dispersion fiber laser. Specifically, we use dispersive Fourier transformation to measure single-shot spectra of Raman-induced noise-like pulses, demonstrating that for low cavity gain values Raman emission is sporadic and follows rogue-wave-like probability distributions, while a saturated regime with Gaussian statistics is obtained for high pump powers. Our experiments further reveal intracavity rogue waves originating from cascaded Raman dynamics.

Journal ArticleDOI
TL;DR: The experimental results confirm that the suggested full-color lens-array HOE can provide the full- color 3D virtual images in the optical see-through AR system.
Abstract: A novel system of optical see-through augmented reality (AR) is proposed by making use of a holographic optical element (HOE) with full-color and lens-array functions. The full-color lens-array HOE provides see-through property with three-dimensional (3D) virtual images, for it functions as a conventional lens array only for Bragg-matched lights. An HOE recording setup was built, and it recorded a 30 mm × 60 mm sized full-color lens-array HOE by using the techniques of spatial multiplexing for large-area recording and wavelength multiplexing for full-color imaging. The experimental results confirm that the suggested full-color lens-array HOE can provide the full-color 3D virtual images in the optical see-through AR system.

Journal ArticleDOI
TL;DR: It is shown that local Fabry-Perot modes residing in the grating ridges and reflecting off a high-contrast interface are not the root cause of wideband reflection, and it is demonstrated that zero-cont contrast grating reflectors outperform comparable high-Contrast gratingreflectors.
Abstract: We present wideband resonant reflectors designed with gratings in which the grating ridges are matched to an identical material, thereby eliminating local reflections and phase changes. This critical interface thus possesses zero refractive-index contrast; hence “zero-contrast gratings.” We design reflectors with zero-contrast gratings and high-contrast gratings and compare the results. For simple gratings with two-part periods, we show that zero-contrast grating reflectors outperform comparable high-contrast grating reflectors. An example silicon-on-glass reflector exhibits a 99% reflectance bandwidth of ∼700 nm for zero refractive-index contrast Δn=0, whereas a high-contrast device with Δn=2 yields a bandwidth of ∼600 nm. It follows that local Fabry–Perot modes residing in the grating ridges and reflecting off a high-contrast interface are not the root cause of wideband reflection.

Journal ArticleDOI
TL;DR: The efficiency of ring microresonator-based mode-locked frequency combs under different dispersion conditions is investigated and it is found that the efficiency degrades with growth of the comb spectral width and is inversely proportional to the number of comb lines.
Abstract: We analytically and numerically investigate the nonlinear conversion efficiency in ring microresonator-based mode-locked frequency combs under different dispersion conditions. Efficiency is defined as the ratio of the average round trip energy values for the generated pulse(s) to the input pump light. We find that the efficiency degrades with growth of the comb spectral width and is inversely proportional to the number of comb lines. It depends on the cold-cavity properties of a microresonator only and can be improved by increasing the coupling coefficient. Also, it can be increased in the multi-soliton state.

Journal ArticleDOI
TL;DR: It is shown that by subwavelength patterning of silicon-wire waveguides the field delocalization can be engineered to increase the sensitivity, achieving sensitivities of 0.83 RIU/RIU and 1.5·10(-3)‬ RIU/nm for bulk and surface sensing.
Abstract: We explore, to the best of our knowledge, the potential of diffractionless subwavelength grating waveguides for sensing applications. We show that by subwavelength patterning of silicon-wire waveguides the field delocalization can be engineered to increase the sensitivity. Fully vectorial 3D-FDTD simulations confirm the sensitivity enhancement, achieving sensitivities of 0.83 RIU/RIU and 1.5·10−3 RIU/nm for bulk and surface sensing, respectively, which compare favorably to state-of-the-art sensing waveguides.

Journal ArticleDOI
TL;DR: Geometric scaling of a Kerr-lens mode-locked Yb:YAG thin-disk oscillator yields femtosecond pulses with an average output power of 270 W and peak power of 38 MW, which surpass the performance of any previously reported femTosecond laser oscillator operated in atmospheric air.
Abstract: Geometric scaling of a Kerr-lens mode-locked Yb:YAG thin-disk oscillator yields femtosecond pulses with an average output power of 270 W. The scaled system delivers femtosecond (210-330 fs) pulses with a peak power of 38 MW. These values of average and peak power surpass the performance of any previously reported femtosecond laser oscillator operated in atmospheric air.

Journal ArticleDOI
Xiaowei Guan1, Pengxin Chen1, Sitao Chen1, Peipeng Xu1, Yaocheng Shi1, Daoxin Dai1 
TL;DR: An ultracompact and low-loss TM-pass polarizer on silicon is proposed and demonstrated experimentally with a subwavelength-grating (SWG) waveguide to support Bloch mode for TM polarization.
Abstract: An ultracompact and low-loss TM-pass polarizer on silicon is proposed and demonstrated experimentally with a subwavelength-grating (SWG) waveguide The SWG waveguide is designed to support Bloch mode for TM polarization so that the incident TM-polarized light goes through the SWG waveguide with very low excess loss On the other hand, for TE polarization, the SWG waveguide works as a Bragg reflector, and consequently the incident TE-polarized light is reflected For a fabricated ∼9 μm long polarizer (with the period number N=20), the measured extinction ratio is ∼27 dB and the excess loss is ∼05 dB at the central wavelength 1550 nm The bandwidth to achieve an extinction ratio of 20 dB is about 60 nm (from 1520 to 1580 nm) When increasing the period number to N=40, the measured extinction ratio is up to 40 dB (which is not as high as the expected theoretical value 65 dB due to the limit of the measurement system)

Journal ArticleDOI
TL;DR: A sparsity-regularized solution is reported that separates K interfering components using multiple modulation frequency measurements and has applications in improving depth profiles and exploiting multiple scattering.
Abstract: Time-of-flight (ToF) cameras calculate depth maps by reconstructing phase shifts of amplitude-modulated signals. For broad illumination of transparent objects, reflections from multiple scene points can illuminate a given pixel, giving rise to an erroneous depth map. We report here a sparsity-regularized solution that separates K interfering components using multiple modulation frequency measurements. The method maps ToF imaging to the general framework of spectral estimation theory and has applications in improving depth profiles and exploiting multiple scattering.