Light-field focusing and modulation through scattering media based on dual-polarization-encoded digital optical phase conjugation.

Digital optical phase conjugation (DOPC) can be applied for light-field focusing and imaging through or within scattering media. Traditional DOPC only recovers the phase but loses the polarization information of the original incident beam. In this Letter, we propose a dual-polarization-encoded DOPC to recover the full information (both phase and polarization) of the incident beam. The phase distributions of two orthogonal polarization components of the speckle field coming from a multimode fiber are first measured by using digital holography. Then, the phase distributions are separately modulated on two beams and their conjugations are superposed to recover the incident beam through the fiber. By changing the phase difference or amplitude ratio between the two conjugate beams, light fields with complex polarization distribution can also be generated. This method will broaden the application scope of DOPC in imaging through scattering media.

Structured light beams created through a multimode fiber via virtual Fourier filtering based on digital optical phase conjugation.

Digital optical phase conjugation (DOPC) is a newly developed technique in wavefront shaping to control light propagation through complex media. Currently, DOPC has been demonstrated for the reconstruction of two- and three-dimensional targets and enabled important applications in many areas. Nevertheless, the reconstruction results are only phase conjugated to the original input targets. Herein, we demonstrate that DOPC could be further developed for creating structured light beams through a multimode fiber (MMF). By applying annular filtering in the virtual Fourier domain of the acquired speckle field, we realize the creation of the quasi-Bessel and donut beams through the MMF. In principle, arbitrary amplitude and/or phase circular symmetry filtering could be performed in the Fourier domain, thus generating the corresponding point spread functions. We expect that the reported technique can be useful for super-resolution endoscopic imaging and optical manipulation through MMFs.

[Analysis of prenatal phenotype and pathogenetic variant in a fetus with Papillorenal syndrome].

OBJECTIVE: To determine the carrier rate of deafness-related genetic variants among 53 873 newborns from Zhengzhou. METHODS: Heel blood samples of the newborns were collected with informed consent from the parents, and 15 loci of 4 genes related to congenital deafness were detected by microarray. RESULTS: In total 2770 newborns were found to carry deafness-related variants, with a carrier rate of 5.142%. 1325 newborns (2.459%) were found to carry heterozygous variants of the GJB2 gene, 1071 (1.988%) were found with SLC26A4 gene variants, 205 were found with GJB3 gene variants (0.381%), and 120 were found with 12S rRNA variants (0.223%). Five newborns have carried homozygous GJB2 variants, two have carried homozygous SLC26A4 variants, five have carried compound heterozygous GJB2 variants, and four have carried compound heterozygous SLC26A4 variants. 33 neonates have carried heterozygous variants of two genes at the same time. CONCLUSION: The carrier rate of deafness-related variants in Zhengzhou, in a declining order, is for GJB2, SLC26A4, GJB3 and 12S rRNA. The common variants included GJB2 235delC and SLC26A4 IVS7-2A>G, which are similar to other regions in China. To carry out genetic screening of neonatal deafness can help to identify congenital, delayed and drug-induced deafness, and initiate treatment and follow-up as early as possible.

Measurement of full polarization states with hybrid holography based on geometric phase.

We propose a method for measuring the full polarization states of a light field by using hybrid polarization-angular multiplexing digital holography based on geometric phase. Through acquiring the geometric phase distribution of the whole light field by only recording a composite hologram, and according to quantitative relationship between the geometric phase and polarization state, the Stokes parameters of a light field can be calculated. Compared with other methods, this method can be used to obtain the complex amplitude information of the light field simultaneously without requiring other complex devices or elements to be adjusted, thus enabling dynamic polarization state measurement. The measurement results of the light fields generated by standard polarized optical elements, vortex half-wave retarder, and liquid crystal depolarizer verified this method's feasibility and validity.

Measurement of ultrafast combustion process of premixed ethylene/oxygen flames in narrow channel with digital holographic interferometry.

The premixed ethylene and oxygen flame that is burning in a narrow channel is investigated with digital holographic interferometry (DHI). Combustion in either a narrow tube or channel is quite different. This is caused by the significant effects of the boundary layer. The flame's acceleration rate will be enhanced as the tube diameter decreases. Usually, flame and shock wave propagation, which occurs during the premixed ethylene/oxygen flame combustion in the measurement area, is less than few milliseconds, so that general camera can rarely capture this fast event. This paper demonstrates that, by introducing the high-speed camera to DHI, the propagation of weak compression wave, flame, and shock wave generated in the narrow channel is successfully measured with a temporal resolution of 10 µs. The ultrafast processes of the flame front changing, as well as the shock wave coupling and separating, are clearly shown from the reconstructed phase distributions of the recorded holograms; corresponding density variations are simultaneously calculated. The results could provide references for the micro-scale propulsion and power devices design and use, and this proposed configuration can also easily adapt to other kinds of ultrafast processes in fluids.

Integrated digital holographic microscopy based on surface plasmon resonance.

We propose a novel digital holographic microscopy (DHM) by integrating surface plasmon holographic microscopy (SPHM) with reflection DHM based on the angular and polarization multiplexing techniques. Taking advantages of the high sensitivity of surface plasmon resonance (SPR) and the high reflectivity of gold film, the tiny variations of specimen's refractive index (RI) can be measured by using SPHM, and meanwhile, the thickness changes of the specimen can be determined by means of reflection DHM. We experimentally monitor the volatilization process of an alcohol-water mixture droplet to verify the validity of the integrated DHM. The proposed microscopy is very promising in the objective-coupling SPR microscopy for multi-information measurements of diverse specimens with low-contrast RI distributions (biomolecules, nanofluids, etc.) in a dynamic and nondestructive way.

Quantitative phase microscopy for cellular dynamics based on transport of intensity equation.

We demonstrate a simple method for quantitative phase imaging of tiny transparent objects such as living cells based on the transport of intensity equation. The experiments are performed using an inverted bright field microscope upgraded with a flipping imaging module, which enables to simultaneously create two laterally separated images with unequal defocus distances. This add-on module does not include any lenses or gratings and is cost-effective and easy-to-alignment. The validity of this method is confirmed by the measurement of microlens array and human osteoblastic cells in culture, indicating its potential in the applications of dynamically measuring living cells and other transparent specimens in a quantitative, non-invasive and label-free manner.

Wavelength-multiplexing surface plasmon holographic microscopy.

Surface plasmon holographic microscopy (SPHM), which combines surface plasmon microscopy with digital holographic microscopy, can be applied for amplitude- and phase-contrast surface plasmon resonance (SPR) imaging. In this paper, we propose an improved SPHM with the wavelength multiplexing technique based on two laser sources and a common-path hologram recording configuration. Through recording and reconstructing the SPR images at two wavelengths simultaneously employing the improved SPHM, tiny variation of dielectric refractive index in near field is quantitatively monitored with an extended measurement range while maintaining the high sensitivity. Moreover, imaging onion tissues is performed to demonstrate that the detection sensitivities of two wavelengths can compensate for each other in SPR imaging. The proposed wavelength-multiplexing SPHM presents simple structure, high temporal stability and inherent capability of phase curvature compensation, as well as shows great potentials for further applications in monitoring diverse dynamic processes related with refractive index variations and imaging biological tissues with low-contrast refractive index distributions in the near field.

Reconstruction of structured laser beams through a multimode fiber based on digital optical phase conjugation.

The digital optical phase conjugation (DOPC) technique is being actively developed for optical focusing and imaging through or inside complex media. Due to its time-reversal nature, DOPC has been exploited to regenerate different intensity targets. However, whether the targets with three-dimensional information through complex media could be recovered has not been experimentally demonstrated, to the best of our knowledge. Here, we present a method to regenerate structured laser beams based on DOPC. Although only the phase of the original scattered wave is time reversed, the reconstruction of a quasi-Bessel beam and vortex beams through a multimode fiber (MMF) is demonstrated. The regenerated quasi-Bessel beam shows the features of sub-diffraction focusing and a longer depth of field with respect to a Gaussian beam. Moreover, the reconstruction of vortex beams shows the fidelity of DOPC both in amplitude and phase, which is demonstrated for the first time, to the best of our knowledge. We also prove that the reconstruction results of DOPC through the MMF are indeed phase conjugate to the original targets. We expect that these results could be useful in super-resolution imaging and optical micromanipulation through complex media, and further pave the way for achieving three-dimensional imaging based on DOPC.

Lateral shearing common-path digital holographic microscopy based on a slightly trapezoid Sagnac interferometer.

We propose a compact and easy-to-align lateral shearing common-path digital holographic microscopy, which is based on a slightly trapezoid Sagnac interferometer to create two laterally sheared beams and form off-axis geometry. In this interferometer, the two beams pass through a set of identical optical elements in opposite directions and have nearly the same optical path difference. Without any vibration isolation, the temporal stability of the setup is found to be around 0.011 rad. Compared with highly simple lateral shearing interferometer, the off-axis angle of the setup can be easily adjusted and quantitatively controlled, meanwhile the image quality is not degraded. The experiments for measuring the static and dynamic specimens are performed to demonstrate the capability and applicability.

Compact surface plasmon holographic microscopy for near-field film mapping.

We develop a compact objective-coupling surface plasmon holographic microscopy with a common-path configuration by introducing a Wollaston prism. Through off-axis hologram recording and numerical reconstruction, amplitude- and phase-contrast surface plasmon resonance (SPR) images can be obtained simultaneously. Based on the four-layer SPR model, the thin film thickness distribution in near field can be mapped unambiguously using a novel demodulation method without a priori knowledge. The technique demonstrates nondestructive and full-field measurement capabilities with sub-nanometer resolution theoretically. Furthermore, owing to the high temporal stability, the recommended system shows great potential for dynamic measurement of near-field tiny refractive index or thickness variation in fields such as chemistry and biomedicine, etc.

Common-path digital holographic microscopy for near-field phase imaging based on surface plasmon resonance.

We develop a common-path digital holographic microscopy based on prism-coupling surface plasmon resonance (SPR) for near-field phase imaging. A single beam splitter with specific configuration is introduced in an SPR imaging system to realize off-axis holographic recording. By measuring the phase shift difference of the reflected light at SPR exploiting the proposed holographic microscopy with high temporal stability, near-field characteristic measurement can be realized. With its simplicity, vibration isolation, and inherent capability of phase curvature compensation, the recommended system shows advanced performance in monitoring tiny refractive index variations and imaging biological tissues.

Efficient generation of vector beams by calibrating the phase response of a spatial light modulator.

The spatial light modulator (SLM) is considered as an effective device to create beams with inhomogeneous phases and polarizations, such as vortex beams and vector beams. However, the nonlinear responses of SLM severely reduce the generation efficiency of these beams. In this paper, by calibrating the SLM to present a linear phase response in the scope of 0-2π, we propose a convenient and efficient method of creating vector beams with arbitrary polarizations based on phase encoding. Compared with the common methods of generating vector beams, our approach can distinctly enhance the generation efficiency.

Phase-shifting infrared digital holographic microscopy based on an all-fiber variable phase shifter.

Phase-shifting infrared digital holographic microscopy based on a homemade all-fiber variable phase shifter is presented to quantitatively obtain the phase distribution of an object wave carrying the information of a transparent specimen in the infrared band. The all-fiber variable phase shifter, which consists of a tubular piezoelectric transducer (PZT) and a single-mode fiber, can accurately produce any phase shift between 0 and 2π by modulating the driving voltage of the tubular PZT. Taking measurements of different staircase structures on a silicon wafer as samples, two configurations are presented based on different phase-shifting implementations: one is a slight off-axis two-step phase shift and the other is an in-line four-step phase shift. The reconstructed results prove the validity of this method.

Generation of perfect vectorial vortex beams.

We propose the concept of perfect vectorial vortex beams (VVBs), which not merely have intensity profile independent of the polarization order and the topological charge of spiral phase, but also have stable intensity profile and state of polarization (SoP) upon propagation. Utilizing a Sagnac interferometer, we approximately generate perfect VVBs with locally linear and elliptical polarizations, and demonstrate that such beams can keep their intensity profile and SoP at a certain propagation distance. These proposed VVBs can be expanded to encode information and quantum cryptography, as well as to enrich the conversion of spin and orbital angular momenta.

Transmission and total internal reflection integrated digital holographic microscopy.

We develop a transmission and total internal reflection (TIR) integrated digital holographic microscopy (DHM) by introducing a home-made Dove prism with a polished short side. With the help of angular and polarization multiplexing techniques, the 2D refractive index distribution of a specimen adhered on the prism surface is determined using TIR-DHM. Meanwhile, the thickness profile is unambiguously calculated from the phase information using transmission DHM. This integrated microscopy is nondestructive and dynamic and can be used to simultaneously measure the index distribution and thickness profile of transparent or semi-transparent liquid or solid samples.

Dual-wavelength common-path digital holographic microscopy for quantitative phase imaging based on lateral shearing interferometry.

A dual-wavelength common-path digital holographic microscopy based on a single parallel glass plate is presented to achieve quantitative phase imaging, which combines the dual-wavelength technique with lateral shearing interferometry. Two illumination laser beams with different wavelengths (λ1=532 nm and λ2=632.8 nm) are reflected by the front and back surfaces of the parallel glass plate to create the lateral shear and form the digital hologram, and then the hologram is reconstructed to obtain the phase distribution with a synthetic wavelength Λ=3339.8 nm. The experimental configuration is very compact, with the advantages of vibration resistance and measurement range extension. The experimental results of the laser-ablated pit, groove, and staircase specimens show the feasibility of the proposed configuration.

Simultaneous measurement of refractive index distribution and topography by integrated transmission and reflection digital holographic microscopy.

We propose a method for simultaneously measuring dynamic changes of the refractive index distribution and surface topography, which integrates the transmission and reflection digital holographic microscopy based on polarization and angular multiplexing techniques. The complex amplitudes of the transmitted and reflected object waves can be simultaneously retrieved. The phase information of the reflected object wave is directly used to determine the topography of the specimen which corresponds to its physical thickness. Assuming that the refractive index distribution is uniform in the direction of the specimen thickness, the refractive index distribution can be deduced from the phase distributions of the transmitted and reflected object waves without any approximation. The refractive index distribution and dynamic changes of the topography of a tiny deionized water droplet have been measured for the availability of the proposed method.

Harmonic mode locking of bound-state solitons fiber laser based on MoS(2) saturable absorber.

We present a kind of harmonic mode locking of bound-state solitons in a fiber laser based on molybdenum disulfide (MoS(2)) saturable absorber (SA). The mode locker is fabricated by depositing MoS(2) nanosheets on a D-shaped fiber (DF). In the fiber laser, two solitons form the bound-state pulses with a temporal separation of 3.4 ps, and the bound-state pulses are equally distributed at a repetition rate of 125 MHz, corresponding to 14th harmonics of fundamental cavity repetition rate (8.968 MHz). Single- and multiple-pulses emissions are also observed by changing the pump power and optimizing the DF based MoS(2) SA. Our experiment demonstrates an interesting operation regime of mode-locked fiber laser, and shows that DF based MoS(2) SA can work as a promising high-power mode locker in ultrafast lasers.

Stacking-Controlled Growth of rBN Crystalline Films with High Nonlinear Optical Conversion Efficiency up to 1.

Nonlinear optical crystals lie at the core of ultrafast laser science and quantum communication technology. The emergence of 2D materials provides a revolutionary potential for nonlinear optical crystals due to their exceptionally high nonlinear coefficients. However, uncontrolled stacking orders generally induce the destructive nonlinear response due to the optical phase deviation in different 2D layers. Therefore, conversion efficiency of 2D nonlinear crystals is typically limited to less than 0.01% (far below the practical criterion of >1%). Here, crystalline films of rhombohedral boron nitride (rBN) with parallel stacked layers are controllably synthesized. This success is realized by the utilization of vicinal FeNi (111) single crystal, where both the unidirectional arrangement of BN grains into a single-crystal monolayer and the continuous precipitation of (B,N) source for thick layers are guaranteed. The preserved in-plane inversion asymmetry in rBN films keeps the in-phase second-harmonic generation field in every layer and leads to a record-high conversion efficiency of 1% in the whole family of 2D materials within the coherence thickness of only 1.6 µm. The work provides a route for designing ultrathin nonlinear optical crystals from 2D materials, and will promote the on-demand fabrication of integrated photonic and compact quantum optical devices.