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Two structures that can realise optical single sideband modulation without generating both second order upper and lower sidebands are presented. They are based on a dual-parallel Mach Zehnder modulator (DP-MZM) with an optical filter and a dual-polarisation dual-parallel Mach Zehnder modulator (DPol-DPMZM) with a 90° hybrid coupler. The former is an all-optical structure and hence it has a very wide bandwidth. The latter uses one DP-MZM to realise single sideband suppressed carrier modulation while the other DP-MZM simply passes the optical carrier. It also suppresses the third order sideband on the same side as the wanted fundamental RF modulation sideband. Hence, in an ideal situation, there is no second order harmonic component generated after photodetection. Experimental results are presented for the novel structures, which demonstrate the realisation of optical single sideband modulation without second order sidebands. The results also show large fundamental to second order harmonic power ratio over a wide input RF signal frequency range even after inserting a long single mode fibre into the system for signal transmission. The new optical single sideband modulators find applications in improving the multioctave spurious free dynamic range in a long-haul fibre optic link and reducing measurement errors in an optical vector analyser.

Based on high efficiency and wide spectral splitter film and Fresnel lens, we have theoretically investigated a full solar-spectrum power-generation system. Designed nano-multilayers are fabricated on Fresnel lens. Then short wavelengths (400 nm ~ 1100 nm) of solar-spectrum can be transmitted 95% to the solar cell, and long wavelengths (1100 nm ~ 2500 nm) of solar-spectrum can be reflected 90% and focused to the thermoelectric cell. This system can combine the efficiency of solar cells and thermoelectric cells to generate electricity across the entire solar spectrum. In theory, the limit for total conversion efficiency is $\eta =56.64$ %.

A photonic radar has recently received considerable interest as a next-generation radar due to its capability to generate wideband signals beyond the technical limitations of the conventional radar. In this paper, we design and implement an ${X}$ -band photonic radar for a low radar cross-section (RCS) target detection and high-resolution image acquisition in real-time. The implemented photonic radar utilizes the photonic frequency quadrupling for the transmitter and detects the dechirped signal by using a delay interferometer and a balanced photo-detector to improve the signal-to-noise ratio. The performance of the photonic radar is verified using a commercial hexacopter having a diagonal wheelbase of 1133 mm as a low-RCS target in the field experiments. We show that the implemented photonic radar can successfully detect the drone on the move even though it is 2.7 km away from the radar. In addition, a high-resolution image of the drone, which is far away 1.1 km from the radar, can be obtained in real-time.

A photonic nanojet (PNJ) is a highly confined light beam that focuses from the shadow side of microparticles. In $46.47\lambda $this work, we propose a PNJ with ultrahigh quality factor formed by dielectric truncated microtoroid. The key properties of PNJ, such as the maximum intensity, the length of PNJ, the full-width at half maximum (FWHM), are studied in detail using finite-difference time-domain (FDTD) analysis. The results show that a PNJ with an enhanced intensity of 55.21 times to the incident light, superlong length of $46.47\lambda $ and subwavelength FWHM of $0.77\lambda $ is formed by semi-microtoroid, thus, an ultrahigh quality factor of 3308.68 is achieved. More importantly, the properties of the PNJ are tunable by changing the truncated proportions of the microtoroid. The structure we proposed has the advantages of compact structure and simple experimental operation, which is expected to apply in many research fields, including optical detection, optical data storage, super-resolution image, nanopattern, nanolithography, and so on.

High-contrast transmitarray (HCTA) metasurfaces, named as metalines in this article, a category of lithographically defined on-chip diffractive elements with minimized scattering loss, enables parallel on-chip optical signal processing. While high-performance devices with different functionalities are reported, most of them are static, and their optical functions are fixed after fabrication. However, dynamically tunable metasurfaces are of essential need in many modern optical systems. Here, we employ an inverse design method, combining FDTD parameter sweep with Fourier-optics simulations, to design thermally-controlled varifocal metalenses. Thermal tunability is accomplished through the thermo-optical effect of silicon. Maximum focal length tunability of 12% and 24% are demonstrated for $400~\mu \text{m}$ and $200~\mu \text{m}$ aperture varifocal metalens doublets at the wavelength of $1.55~\mu \text{m}$ , respectively. The focusing efficiency is more than 74% for the whole temperature range. The $400~\mu \text{m}$ and $200~\mu \text{m}$ aperture metalenses are able to concentrate the input beam to spot sizes less than one wavelength and two wavelengths, respectively. This paves the way for dynamically controlled silicon photonics computational chips.

Numerical and experimental studies were investigated for the self-Q-switching Nd:LuAG laser which was achieved by the Kerr lens effect. By applying two output couplers of 6% and 1.4%, the shortest pulses of 193.4 ns and 5.1 ns were generated respectively while the corresponding repetition rates were 1.175 MHz and 96.15 MHz respectively. Related to the average powers of 3.34 W and 2.56 W, the system demonstrated the optical to optical efficiency of 21.87% and 21.1% for coupler of 6% and 1.4% respectively. The short pulses with the high repetition rates can be applied in many fields which demonstrate the high value of the research on this self-Q-switching laser.

A novel photonic vector THz-wave signal generation at terahertz-wave (THz-wave) band by Mach Zendell modulator (MZM) -based optical frequency comb and in-phase and quadrature (IQ) modulator for signal modulation scheme is proposed. And we demonstrate 16 quadrature-amplitude-modulation (QAM) vector THz-wave signal generation and transmission by simulation. The IQ modulator is driven by a 2-Gbaud/3-Gbaud 16-QAM-modulated baseband signal.The MZM is driven by a radio frequency signal at the frequency of 30 GHz to generate optical frequency comb. The generated 390 GHz THz-wave radio frequency signal after heterodyne beating in uni-travelling photodiode (UTC-PD) is transmitted over 0 km/10 km single-mode-fiber transmission. The 390-GHz electrical vector THz-wave signal carring 16-QAM modulation can be generated with a bit error ratio (BER) of less than the hard-decision forward-error-correction (HD-FEC) threshold of 3.8e-3. To the best of our knowledge, it's the first time to generate 390 GHz photonic vector THz-wave signal on the basis of simple MZM-based optical frequency comb.

An optical design of a novel structure has been proposed and demonstrated to perform photon recycling in a transmission-type laser-pumping white light. The structure includes a hemisphere reflector and a phosphor plate located at the center of a hemisphere reflector. The hemisphere reflector is not only used for photon recycling to increase the energy efficiency but also to keep the energy efficiency nearly unchanged when the number of the multiplexing laser increases. The experimental measurement shows that the photon recycling with the hemisphere reflector can increase the energy efficiency from 36.2% to 53.3% for on-axis incidence, and 35.2% to 55.7% for off-axis incidence. Besides, the efficiency keeps the same up to three-laser multiplexing in the experiment, and potentially can be extended to more than 10 in the simulation for various hole structures. The result is not only on the efficiency enhancement but also on the enhanced exitance of the laser white light and the unchanged etendue of the light source. This property is an important advantage for lasers rather than LEDs in a solid-state white light source.

A photonics-based channel bandwidth tunable microwave frequency measurement (MFM) is analyzed and verified, which is implemented based on the principle of the frequency-to-phase-slope mapping (FTPSM) in stimulated Brillouin scattering (SBS). The spectrum-controlled Brillouin phase shift curve is created by using an optical frequency comb (OFC) pump instead of a single pump. As a result, the Brillouin phase shift response is superimposed to further realize a flexible and adjustable measurement bandwidth. Meanwhile, thanks to the relationship between the OFC pump and the unknown signal, the frequency measurement can be achieved by the property of monotonous frequency-to-phase-slope mapping. A proof-of-concept experiment is performed to verify the feasibility of the approach. By changing the number of OFC lines, the channel bandwidths of 500, 700, or 900 MHz are demonstrated, with a measurement error lower than 35 MHz. We believe that this FTPSM-based MFM system is a promising solution for radio frequency (RF) channelized receiver.

Unconscious perceptions and decisions are influenced by gender bias. In this work, we provide an exhaustive data analysis of the Ph.D. theses defended in the field of optics and photonics in Spain by filtering key descriptors and gender. Our results show a severe underrepresentation of women in the Ph.D. stage in the optics community, which becomes even more prominent in technological and theoretical domains. The gender gap is reduced in biomedical and visual optics. This asymmetry is a symptom of gender bias in science associated with traditional stereotypes about health and social care. Further studies and measures are required in specific areas of science to eradicate implicit gender-based associations in scientific disciplines.

In this study, we built a single photon avalanche diode (SPAD) receiver based underwater wireless optical communication (UWOC) system. The bit error rate (BER) and signal-to-noise ratio (SNR) performance of UWOC with different distances and data transmission rates were obtained. Based on the water attenuation coefficient of 0.12 m-1, a series of neutral density (ND) filters were exploited to attenuate the light output power from the blue laser diode (LD) to simulate the long distance UWOC. The maximum estimated distances of 144 m and 117 m with corresponding BERs of 1.89 × 10-3 and 5.31 × 10-4 at data transmission rates of 500 bps and 2 Mbps were acquired in UWOC system using on-off keying (OOK) modulation scheme, respectively. Furthermore, we compared the differences between free-space and underwater channels, and a divergence angle of ~1.02 mrad was measured experimentally at a distance of 50 m in the free space. The long UWOC distances obtained in this study partly benefit from high sensitivity SPAD, the small laser divergence angle and low light attenuation. This study provides an approach to achieve long distance UWOC using SPAD.

Novel imaging techniques utilizing nondegenerate, correlated photon pairs sparked intense interest during the last couple of years among scientists of the quantum optics community and beyond. It is a key property of such "ghost imaging" or "quantum interference" methods that they use those photons of the correlated pairs for imaging that never interacted with the sample, allowing detection in a spectral range different from that of the illumination of the object. Extensive applications of these techniques in spectroscopy and microscopy are envisioned, however, their limited spatial resolution to date has not yet supported real-life microscopic investigations of tiny biological objects. Here we report a modification of the method based on quantum interference by using a seeding laser and confocal scanning, that allows the improvement of the resolution of imaging with undetected photons by more than an order of magnitude, and we also present examples of application in the microscopy of biological samples., Comment: This article has been accepted for publication in IEEE Access, but has not been fully edited

The equivalent filter response in the simultaneous photonic filtering and digitizing system is determined by the temporal precision and duration time of optical pulses. To achieve narrow-bandwidth filter response at high central frequency, a pulse shaping scheme based on the time-frequency mapping and attenuation-delay coupling is presented. The effect introduced by attenuation-delay coupling is derived, and the method to search optimized parameters for target bandwidth, off-band suppression and central frequency is presented. Precise shaping of optical pulses with full width at half-maximum in sub-nanosecond order is realized in experiments, which can generate an equivalent filter with bandwidth of 0.93 GHz and central frequency of 39.9 GHz in the simultaneous photonic filtering and digitizing system.

A polarization lidar with dual Geiger-mode avalanche photodiodes (Gm-APDs) is designed to obtain the high-precision depth image of shallow semitransparent media by using a wide laser pulse. The first surface of the semitransparent media is smooth and can nearly preserve the incident polarization, whereas the second surface is rough and can depolarize the incident polarization. A polarization splitting prism is utilized to separate the two echo signals, which will be detected by dual Gm-APDs. It gives the ability to obtain the extremely shallow depth independent of laser pulse width and dead time of Gm-APD. The theory of laser polarization transmission of dual Gm-APD polarization lidar is analyzed. Signal restoration & center-of-mass algorithm method is used to restrain the range walk error and obtain high range precision. The depth image of shallow semitransparent media with a thickness and distance of 10 cm and 6 m, respectively, is obtained in the experiment with a range precision of 1.1 cm. An experiment of real shallow water layer with different depth features is also performed to verify the result.

Superconducting series nanowire single-photon detectors (SNDs) have been used for resolving photon numbers. But it can also exhibit a higher counting rate than a single superconducting nanowire single-photon detector (SNSPD), because the serial architecture allows multiple detectors working in parallel and the inductance of each pixel is reduced. In this paper, we found each pixel of the SND could reset fast although the whole detector took a much longer time for recovering. Therefore, the speed of an SND with a large kinetic inductance of 1.25 μH was characterized and compared to a standard SNSPD with the same total inductance. By measuring the detected photon rate over the input photon rate, we obtained a photon counting rate enhancement by 7.5 times. Meanwhile, the timing jitter of the SND was 63 ps at single photon detection regime. Our results show that the series structure and the readout scheme are quite practical in realizing high speed single-photon detectors besides resolving photon numbers.

Reflection spectra based on guided-mode resonance (GMR) are simulated and discussed with transformation between one-dimensional (1-D) and two-dimensional (2-D) photonic lattices by introducing intermediate structures consisting of vertically-stacked 1-D and 2-D gratings. Dependences of reflection spectra on a 2-D fractional ratio are investigated for two examples of narrowband and broadband resonance elements. Observed complicated spectrum transformations for the narrowband example are successfully explained by combining simple models with guided-mode indices and multilayer reflection. The understanding of the fundamental transformation dynamics will aid in the reflection band engineering for development of new optical components.

The photonics integrated interference imaging technique has attracted intensive attention because of its superior imaging performance and structural compactness. Traditional architecture designs of the photonics integrated interference imaging systems are of radial patterns and rectangular patterns. Due to their large lens intervals, the resulting frequency distributions are insufficient to satisfy the Nyquist sampling conditions. In this article, a new structural type of hexagonal arrays is designed, which has a dense lens distribution. Two paring methods are developed for the radial baselines and lateral baselines, and they can be selected according to the actual frequency bands of interest. The imaging performance of different arrays is analyzed, and the hexagonal array is proved superior over the radial pattern and rectangular pattern in terms of point spread functions. A reconstruction algorithm based on the compressed sensing theory is proposed to restore salient features from insufficiently sampled signals. A measurement matrix is set in accordance with the structural design to avoid data regridding. Experimental results demonstrate that the imaging resolution is improved remarkably with respect to the original images.

Recently, two special photonic jets, photonic hooks and twin photonic jets, have been proposed to deal with complex conditions in nanoscale manipulation. Photonic hooks are generated by a single light plane wave and an asymmetric microparticle, while the twin photonic jets are produced by two incident light beams. In this letter, we presented and demonstrated a method to combine photonic hooks and twin photonic jets. A single light plane wave and a symmetric microparticle, twin-ellipse microcylinder, are used in this research. The curvature degree, length and maximum E2 field enhancement of twin photonic hooks are varied significantly, with the change of refractive indices and shape of twin-ellipse microcylinder. And a liquid-immersed core-shell is built to achieve a flexible tunability.

We establish a novel kind of microdisk cavities that utilize transmission at Brewster's angle. Thus, we design a microstar cavity where light is trapped without any kind of reflection. The ray and the wave dynamics is discussed as well as the unification with whispering-gallery cavities.

We discuss a novel technique for the simultaneous recovery of quantitative phase and amplitude information of a complex-valued object in ghost imaging by adopting the concepts of holography in combination with the ghost diffraction scheme. The applicability of the approach is experimentally demonstrated with quantitative imaging for various pure phase objects, planar transparencies, etc.

Stable single mode operation with output more than 4W is realized for first order surface grating loaded VCSELs with a cavity length of 2mm. A nearly-diffraction-limited narrow divergence of 0.05° is obtained under CW operation.

We have developed a pulse compressor with low input power and a high compression ratio of 90 or more. Finally, we succeeded in producing a broadband LFC from 950 to 1750 nm with 12.5-GHz spacing and high contrast across the whole spectrum.

we discuss state-of-the-art techniques to generate on-demand structured light and their application to quantum light-matter interactions, especially in the generation and control of charged-particle beams and X-ray light sources.

In this study, we simulate and analyze a CMOS compatible angle-sensitive pixel in the near-infrared spectral range. A set of diffractive gratings can achieve the angle sensitivity where the gratings can be integrated into the CMOS image sensor by utilizing metal interconnect layers.

We propose multiple-frequency-spaced optical comb generation by superposing deeply phase-modulated lights. A multiple-parallel modulator with pure phase-modulator arms flexibly generates optical combs with any multiplication orders of frequency spacing, powered by interferometric blocking technique.

A novel solid-state Lidar is designed using two TE polarized beams counter-propagating towards each other. Two corresponding output beams can be seamlessly combined, doubling beam steering angle. A 28-degree beam steering range is achieved with a 100-nm wavelength tuning.

We are investigating Two Photon Excited Fluorescence (TPEF) as a non-invasive imaging technique for retinal imaging due to its axial sectioning ability. We combined TPEF with Optical Coherence Tomography (OCT) and Sensorless Adaptive Optics (SAO) to obtain co-registered multi-volume averaged images. © 2021 The Authors.

A new type of anisotropic nested hollow-core anti-resonant fiber is proposed which has propagation loss of

Optical wireless power transmission (OWPT) systems are attractive photonic systems. However, OWPT has safety problems such as unexpected and unnecessary light irradiation. In this report, an improved safety system based on a depth camera is constructed, and response time of less than 60 ms and detection range limit are confirmed.

We verify signal-modulation based on the frequency response of direct-modulation utilizing photon-photon resonance on simulation. It was confirmed that extinction ratio (ER) was improved, not degraded, from 0.8 dB to 3.2 dB when the peak height shifted from 5 dB to 15 dB, however, the phase fluctuation degraded ER.

Molding light scattering through artificially engineered materials has been the subject of intensive research so far. However, the majority of these studies have focused on the engineering of scattering in the spatial or wavevector domain, where, for instance, the scatterer has been designed to eliminate wave scattering in certain spatial directions. Different from these approaches, here we show that a complex time-periodic medium, namely a non-Hermitian photonic time crystal, offers a new degree of control over the scattering response in the frequency direction. Specifically, we show that the phase difference between real and imaginary parts of the temporal modulation can be controlled to induce spectral scattering predominantly in a specified frequency-direction. Such a unidirectional spectral scattering feature might find important applications, such as for optical isolation and cloaking of electrically large objects.

In this work, we will review our recent progress in development of active optical metasurfaces in the quasi-static and time-modulated operation regimes. We will first present methodologies to achieve widely tunable phase responses with high amplitude efficiencies by exploiting high-Q resonant modes supported by all-dielectric metasurfaces. We will then discuss unique opportunities for light manipulation with extended degree of freedom enabled by active time-modulated metasurfaces. In particular, we will introduce a tunable geometric phase shift in time-modulated metasurfaces which allows for dispersionless dynamic wavefront engineering of higher-order sidebands. It will be emphasized that this feature can be used to overcome several limitation of quasi-static metasurfaces and yields several distinctive capabilities for time-modulated platforms including wideband all-angle beam scanning and topological space-time photonic transitions. Various implementations of time-modulated metasurfaces at optical frequencies will be presented and their applicability as optical phased arrays with flexible pattern synthesis will be highlighted. Moreover, design approaches for achieving higher efficiency in sideband generation and broadband performance will be proposed.

Multiband data signal transmission using intermediate frequency over fiber (IFoF) is proposed and demonstrated with local photonic millimetre wave (mmW) generation. The proposed scheme is based on a low cost directly-modulated laser (DML) and Mach-Zehnder modulator (MZM) biased at a null point for optical carrier suppression to realize optical frequency multiplication (OFM). Transmission of 4- and 64-quadrature amplitude modulation (QAM) signals providing data rates of 3 and 1.5 Gbps, respectively, over 25 km standard single mode fiber (SSMF) are demonstrated and signals are delivered at 40 GHz to be radiated by the remote radio heads (RRHs). As a proof of concept, also multiband signal of various modulation formats and bandwidths have been transmitted successfully along 25 km fiber link and delivered in the mm W band. Quality signal assessment by error vector magnitude (EVM) measurement at mmW bands is demonstrated and an estimation of the optical sensitivity of the system is provided.

The dark photon, one of the candidates of dark matter, can be generated from high-power millimeter waves. This paper points out possible emission of dark photons from waveguide structures in high-power microwave infrastructure and suggests potential detection of such dark photon signal with a coherent circuit scheme.

A high finesse cavity operating around 620 GHz has been constructed to improve the sensitivity limit for the measurement of weakly absorbing gases. An effective path length of 1 km is achieved significantly improving the available sensitivity. The measurement of the cavity decay time allows the quantification of the absorption coefficient.

A scheme for generating Barker-code phase-coded terahertz signals is proposed and experimentally demonstrated based on optical frequency combs (OFC) and optical heterodyne. A dual-parallel Mach-Zehnder modulator (DPMZM) is employed for modulation implementation, where a radio frequency is applied to one arm, and the Barker-code is used to drive the other. In the experiment, we successfully generate a 10 Gbit/s Barkercode phase-coded THz signal at 357 GHz with a π phase shift, which can be potentially used in the THz pulse compression radar and communication systems.

A high-speed frequency modulated continuous wave (FMCW) radar system is proposed for three-dimensional (3D) terahertz imaging. In order to obtain a high range resolution of mm-order together with fast data acquisition speed, the photonics-based approach is adopted. Thanks to the high-speed frequency sweep of a tunable laser device, the wide bandwidth ranged from 200 GHz to 420 GHz, which corresponds to a range resolution of ~1.3 mm, can be achieved within 35 msec. Furthermore, the 3D imaging of a multi-layer model was demonstrated with quasioptical imaging system, both range and spatial resolution can achieve to ~1.3 mm without using complicated signal processing.

We study, using the integral-equation-based in-house guaranteed-convergence numerical code, the effect of a circular air hole on the frequency, threshold gain and directionality of emission of the whispering-gallery modes of a two-dimensional model of circular-disk microcavity laser. We show that a small hole can enhance the directionality greatly and leave the threshold gain intact, if disk's refractive index is large enough and hole's location is chosen properly. This location should be close to the area where the same uniform disk, if illuminated with a plane wave, displays a broadband focusing in the form of hot spot called photonic jet.

The NA is a basic parameter of a lens, which can determine its focusing spot size in the far field. High NA(close to 0.9 or above) metalens with a deep sub-wavelength focusing spot is an important metadevice in the modern optics and photonics. In this paper, a four-layer microwave metalens and its applications in the high-gain and low-profile antenna are studied and demonstrated. A high NA=0.88 (FWHM is 0.57λ) metalens based on high transmission phase gradient metasurface is firstly designed and is also verified by experimental result. Besides, a feeding source is placed at the focal spot of the proposed metalens, and a quasi-spherical wave is emitted and then transformed to a plane wave. Thus, a high gain antenna is obtained and the beam-width of the bare antenna is also significantly decreased. The simulated results show that the gain of the high NA metalens is largely enhanced by 10.47dB compared to bare antenna at the frequency of optimized 9GHz. More importantly, the relation between the focusing efficiency of high NA metalens and the enhanced gain of lens antenna is discussed and highlighted. The work opens new avenues to design high-gain lens antenna based on high NA plasmonic metalens in the microwave band.

Forster resonance energy transfer (FRET) is a near-field interaction between pairs of quantum emitters. FRET plays a key role in many applications, from the photosynthetic apparatus of plants and bacteria [1] to manipulating, storing, and transferring quantum information [2] . Although FRET depends on the donor and emitter itself, it is also modified by the electromagnetic environment [3] , [4] and studied with the Green function. This dependence led to a potentially efficient near-field control method, through engineering the environment of a given simple source. In photonics, FRET can be controlled by structuring the materials surrounding the emitter on scales much smaller than the operating wavelengths [5] . The control of the FRET by engineering the environment and its relationship with local density of states (LDOS) has been studied before analytically and experimentally [6] , [7] in the optic range. But experiments in optics are challenging due to the weak signals involved and the low spatial resolution, also highly specialized equipment is required. The resonance energy transfer effect is an analog of the effect on the power transferred between two classical dipoles [3] . One of the most effective ways to investigate this effect is to analyze the antenna impedance in the microwave, this is a direct measurement of the energy transfer unlike optics where measurements are indirect.

Inverse design of silicon-on-insulator metasurfaces for aberration correction purpose is demonstrated numerically. Here, image quality of a bulk midwave infrared lens is improved by combining it with two metasurfaces designed by the adjoint gradient method to form a hybrid imaging system.