Signal Beam Research Articles

Experimental Research of the Identification of Topological Charges for Vortex Beams

An optical vortex beam has attracted more and more attention in several fields such as optical communication and quantum information. Generally, the vortex beam carries orbital angular momentum (OAM) and the topological charges (TCs). Measuring and identifying TCs of vortex beams is a key issue in many applications. In this study, the polarization status has been introduced into the interferometric procedure for identifying TCs of vortex beams. The influence of polarization states on the TC identification has been demonstrated experimentally. Furthermore, we demonstrate the satisfactory robustness for the interferometric method during identifying the TCs of vortex beams. When the reference and signal beam do not perfectly overlap in a Mach-Zehnder (M-Z) interferometer, i.e. there is a small tilt angle between two beams, a petal-like interference pattern can still be maintained with good visibility and be used for estimating the magnitude and sign of the TC. Our results might provide reference significance for the long-distance optical communication using vortex beams in the near future.

Cooperative Localization in Hybrid Active and Passive Wireless Sensor Networks With Unknown Tx Power

Hybrid active and passive wireless sensor networks (HWSNs) gain advantages in extending the network lifetime and reducing the overall cost. Because the passive sensors without battery harvest the energy from distributed active sensor signal beam, and only a few active sensors can maintain a large-scale network. Thus, how to track the passive sensor’s location is essential for network management. Since the active sensors are sparsely deployed, cooperative localization which employs passive sensors to locate themselves together is a promising solution. In this paper, we analyze the energy beam generated by the active sensors on the cooperative localization accuracy of the passive sensors. We consider the spatial-temporal cooperative localization based on the received signal strength (RSS) model with unknown Tx power information of each sensor due to the limited processing capabilities, circuit complexity and energy constraints. We formulate the Fisher information matrix (FIM) and the corresponding Cramér-Rao lower bound (CRLB) for the static full connected network and dynamic spatial-temporal recursive network. Accordingly, energy beamforming schemes are proposed to optimize localization accuracy and energy efficiency problems. For the optimal localization problem, we derive the closed-form solution of the optimal energy beamforming wave. For the optimal energy efficiency problem, we propose a semi-definite programming (SDP) solution to achieve optimal energy consumption with a self-calibration method, which can address the over-relax problem. Extensive simulation results indicate that our proposed beamforming schemes have high localization accuracy and lower power consumption compared with the existing power allocation-based schemes.

15-µJ picosecond hollow-core-fiber-feedback optical parametric oscillator.

We report a high-energy, picosecond, mid-infrared (MIR) optical parametric oscillator (OPO), in which a length of hollow-core-fiber (HCF) is employed to enable operation at 1-MHz repetition rate in a compact cavity format. The OPO is synchronously pumped by an ytterbium-doped-fiber (YDF) master-oscillator-power-amplifier (MOPA) system, seeded by a 1040-nm gain-switched laser diode (GSLD). Using periodically poled lithium niobate (PPLN) as the nonlinear crystal, the OPO generates signal and idler beams with tunable wavelengths in the range of 1329-1641 nm and 2841-4790 nm, respectively. The OPO provides 137-ps pulses with a maximum signal energy of 10.05 µJ at 1600 nm and a maximum idler energy of 5.13 µJ at 2967 nm. This, to the best of our knowledge, represents the highest energy MIR pulses, as well as the highest total converted pulse energy (15.18 µJ), ever achieved from a fiber laser pumped picosecond OPO.

Fast, noise-free atomic optical memory with 35-percent end-to-end efficiency

Coherent optical memories will likely play an important role in future quantum communication networks. Among the different platforms, memories based on ladder-type orbital transitions in atomic gasses offer high bandwidth (>100 MHz), continuous (on-demand) readout, and low-noise operation. Here we report on an upgraded setup of our previously-reported fast ladder memory, with improved efficiency and lifetime, and reduced noise. The upgrade employs a stronger control field, wider signal beam, reduced atomic density, higher optical depth, annular optical-pumping beam, and weak dressing of an auxiliary orbital to counteract residual Doppler-broadening. For a 2 ns-long pulse, we demonstrate 53% internal efficiency, 35% end-to-end efficiency, 3 × 10−5 noise photons per pulse, and a 1/e lifetime of 108 ns. This combination of performances is a record for continuous-readout memories.

Quadrature-Averaged Homodyne Detection for Estimating Cavity Parameters

Balanced homodyne interferometry is a well-known detection technique that allows for sensitive characterization of light fields. Conventionally a homodyne interferometer is operated by locking the relative phase of a reference beam to the signal beam by means of an active feedback loop. A less often used method is to perform a slow continuous modulation of the reference beam arm length that corresponds to averaging all relative phases during the measurement. Here we show theoretically and experimentally that this quadrature averaging can be advantageous in estimating the parameters of a resonant optical cavity. We demonstrate that the averaging turns the transduction function, from cavity frequency fluctuations into the interferometer signal, into a simple function of the laser detuning that, notably, does not depend on the parameters of possible nonresonant channels present in the system. The method needs no active feedback and gives results that are easy to interpret. Moreover, the phase-averaged measurement allows characterization of the absolute magnitude of a cavity frequency modulation.

Correction to: Generation of amplitude- and phase-modulated signal beam with a phase-only spatial light modulator and its detection by the transport of intensity equation method for holographic data storage

Correction to: Generation of amplitude- and phase-modulated signal beam with a phase-only spatial light modulator and its detection by the transport of intensity equation method for holographic data storage

Generation of amplitude- and phase-modulated signal beam with a phase-only spatial light modulator and its detection by the transport of intensity equation method for holographic data storage

Generation of amplitude- and phase-modulated signal beam with a phase-only spatial light modulator and its detection by the transport of intensity equation method for holographic data storage

Multimode Optical Fiber Beam-By-Beam Cleanup

We introduce and experimentally demonstrate the concept of all-optical beam switching in graded-index multimode optical fibers. Nonlinear coupling between orthogonally polarized seed and signal beams permits to control the spatial beam quality at the fiber output. Remarkably, we show that even a few-mode control beam whose power is about ten times lower than that of the total beam may substantially enhance the quality of an intense, highly multimode signal beam. We propose a simple geometrical representation of the beam switching operation, whose validity is quantitatively confirmed by the experimental mode decomposition of the output beam. All-optical switching of multimode beams may find important applications in high-power beam delivery and fiber lasers.

Reducing the impact of adaptive optics lag on optical and quantum communications rates from rapidly moving sources

Wavefront of light passing through the turbulent atmosphere gets distorted. This causes signal loss in free-space optical communication as the light beam spreads and wanders at the receiving end. Frequency and/or time division multiplexing adaptive optics (AO) techniques have been used to conjugate this kind of wavefront distortion. However, if the signal beam moves relative to the atmosphere, the AO system performance degrades due to high temporal anisoplanatism. Here, we solve this problem by adding a pioneering beacon that is spatially separated from the signal beam with time delay between spatially separated pulses. More importantly, our protocol works irrespective of the signal beam intensity and, hence, is also applicable to secret quantum communication. In particular, using semi-empirical atmospheric turbulence calculation, we show that for low earth orbit satellite-to-ground decoy state quantum key distribution with the satellite at zenith angle <30°, our method increases the key rate by at least 215% and 40% for satellite altitudes of 400 and 800 km, respectively. Finally, we propose a modification of the existing wavelength division multiplexing systems as an effective alternative solution to this problem.

Effect of Wavefront Distortion on the Performance of Coherent Detection Systems: Theoretical Analysis and Experimental Research

Atmospheric turbulence causes signal beam wavefront distortion at the receiving end of a coherent detection system, which decreases the system mixing efficiency. Based on the coherent detection theory, this study establishes a mathematical model of wavefront distortion with mixing efficiency and mixing gain. It also analyzes the improvement limits of wavefront correction on mixing efficiency and mixing gain under different atmospheric turbulence intensities and experimentally measures them. Simulation results show that the mixing efficiency can be improved to 51%, 55%, and 60% after correcting for tilt, defocus, and astigmatism terms, respectively, when turbulence intensity D/r0 is 2. The mixing gain with homodyne detection is 3 dB higher than heterodyne detection. Meanwhile, the wavefront correction orders required for optimal mixing efficiency are higher than the heterodyne correction order. In the experiment, Haso4 NIR + DM 40 was used, and the turbulence intensity D/r0 was 2. After the closed-loop control algorithm corrects the tilt, defocus, and astigmatism terms, the indoor experimental results showed that the mixing efficiency is improved to 36%, 47%, and 62%, respectively. The outdoor experimental results showed that the mixing efficiency improved to 36%, 51%, and 68%, respectively.

Single-shot digital holography separating the real and imaginary parts of a signal beam in the rhombic region of the Fourier plane

Single-shot digital holography separating the real and imaginary parts of a signal beam in the rhombic region of the Fourier plane

Sixty-Nine-Element Voice Coil Deformable Mirror for Visible Light Communication

To overcome the atmospheric turbulence aberration, and improve the quality of light beam in visible light communication (VLC), a compact 69-element deformable mirror (DM) using micro voice coil actuators was designed based on systematic theoretical analysis. The structural parameters of the micro voice coil actuator were optimized by electromagnetic theory and the finite element method. The DM was optimized from the aspects of thermal deformation, response time, coupling coefficient, and other parameters. Finally, wavefront fitting and residual calculation were completed according to the influence function. The optimized voice coil deformable mirror (VCDM) has a large phase stroke, good thermal stability, a short response time of less than 0.7 ms, and a large first resonance of 2045 Hz. The fitting residuals of the VCDM for the first 10 Zernike modes with a PV value of 8 μm are all below 10 nm (RMS). Compared with a similar DM, the obtained results from our compact VCDM indicate that it has a higher wavefront fitting precision. VCDM corrected complex random aberrations in the VLC scenario and improved the coupling efficiency of the signal beam, proving that the compact VCDM with high performance and low cost has a good application prospect in VLC systems.

Topological charge measurement in a four-level single layer graphene system

In this letter we have proposed a four-level graphene monolayer system for identifying the topological charge of Laguerre–Gaussian light. Here, we have shown that due to the four-wave mixing mechanism in the monolayer graphene system, a weak signal beam can be generated due to quantum coherence and interference effect. We have discussed the spatially dependent linear absorption spectrums of the weak probe and new generated signal beams via quantum mechanical density matrix formalism. We have found that by numbering the spot areas of the probe and signal beams, one can realize the topological charge of the Laguerre–Gaussian beam interacts by monolayer graphene system. Moreover, we have realized that for some topological charge the new generated signal beam can be amplified in the graphene system.

Foreground removal of CO intensity mapping using deep learning

ABSTRACTLine intensity mapping (LIM) is a promising probe to study star formation, the large-scale structure of the Universe, and the epoch of reionization (EoR). Since carbon monoxide (CO) is the second most abundant molecule in the Universe except for molecular hydrogen H2, it is suitable as a tracer for LIM surveys. However, just like other LIM surveys, CO intensity mapping also suffers strong foreground contamination that needs to be eliminated for extracting valuable astrophysical and cosmological information. In this work, we take 12CO($\it J$ = 1-0) emission line as an example to investigate whether deep learning method can effectively recover the signal by removing the foregrounds. The CO(1-0) intensity maps are generated by N-body simulations considering CO luminosity and halo mass relation, and we discuss two cases with median and low CO signals by comparing different relations. We add foregrounds generated from real observations, including thermal dust, spinning dust, free–free, synchrotron emission, and cosmic microwave background anisotropy. The beam with sidelobe effect is also considered. Our deep learning model is built upon ResUNet, which combines image generation algorithm UNet with the state-of-the-art architecture of deep learning, ResNet. The principal component analysis (PCA) method is employed to preprocess data before feeding it to the ResUNet. We find that, in the case of low instrumental noise, our UNet can efficiently reconstruct the CO signal map with correct line power spectrum by removing the foregrounds and recovering PCA signal loss and beam effects. Our method also can be applied to other intensity mappings like neutral hydrogen 21-cm surveys.

Phase-sensitive optical time domain reflectometry based on geometric phase measurement

A phase-sensitive optical time domain reflectometer based on coherent heterodyne detection of geometric phase in the beat signal of light, is reported for the first time to our knowledge. The use of the geometric phase to extract strain makes it immune to polarisation diversity fading. This is because a polarisation mismatch between the interfering beams is not a hindrance to its measurement. The geometric phase is calculated using the amplitude of the beat signal and individual beam intensities without any need for phase unwrapping. It is measured per beat period and can be equated with the traditionally measured dynamic phase with appropriate scaling. The results show that the system based on the geometric phase successfully measures strain, free from polarisation mismatch fading and phase unwrapping errors, providing a completely novel solution to these problems.

Amplification of mid-IR continuum for broadband 2D IR spectroscopy.

We report the generation and characterization of microjoule level, broad bandwidth femtosecond pulses in the mid-infrared (MIR) using optical parametric amplification of continuum MIR seed pulses in GaSe. The signal (3 μm) and idler (6 μm) pulses have energies of 6 μJ and 3 μJ with bandwidths of ∼950 cm-1 and 650 cm-1 FWHM and pulse lengths of 34 fs and 80 fs. Broadband 2D IR spectra of O-H and N-H transitions are acquired with the signal beam demonstrating the capabilities of this source for cross peak and line shape measurements.

Few-mode erbium-doped fiber amplifier based on a multi-inclusions core optical fiber.

In this work, we demonstrate and evaluate a new design of micro-structured core erbium-doped few-mode fiber to be used as optical amplifier in the context of mode-division multiplexing. This concept is proposed so as to better control the distribution of the Er3+ ions in the core area, thus permitting to adjust the overall differential modal gains between the different signal modes. The design presented here consists of 19 erbium-doped inclusions embedded in a pedestal geometry guiding 10 modes in the C-band. It has been optimized numerically so as to reach the equalized amplification of all the signal modes. The fiber has been realized and combined with custom-made dual-wavelength mode multiplexers based on multi-plane light conversion to shape the signal and pump beams. Amplification properties have finally been evaluated experimentally.

Structured light signal transmission through clouds

Dynamic media such as atmospheric clouds and fog form a formidable barrier to light propagation for free-space optical communication (FSO). To overcome such an obstacle, we propose to make use of the acoustic properties of a laser filament coupled together with a donut-shaped signal beam. A filament generated by an ultrafast laser is accompanied by an acoustic wave that clears a cylindrical chamber around the filament’s plasma column that can mimic a transmission channel. We present a method to couple a Laguerre–Gauss beam through the obstacle-free channel. We image and measure the transmitted signal carried by the structured beam to demonstrate an efficient method for FSO through cloudy conditions, which requires low energy, is resilient to noise, and is unaffected by the filament.

Design Build a 4x4 Mimo Microstrip Antenna with Artificial Dielectric Muse Array Technique to increase Antenna Gain pexisting Application 5G

The development of fifth-generation cellular technology, commonly referred to as "5G" networks, is believed to be able to maximize data speed access needs. In order to maximize the utilization of the existing 5G network in Indonesia, Telkomsel providers are using a frequency of 2.3 GHz with a bandwidth of 50 MHz. So we need an antenna amplifier that is easy to fabricate and place anywhere to maximize the signal capture range. A microstrip antenna is a suitable antenna for this amplifier. The advantage of this antenna is that it has a light mass and is easy to fabricate. while the drawbacks come in the form of narrow bandwidth and small gains. Therefore, an antenna design with an artificial substrate and array technique was made to overcome this. The design of this microstrip antenna was made in the CST Studio Suite 2019. The design was carried out by entering the antenna dimension values to be simulated and seeing the parameters; if they are not suitable, then they need to be optimized again, and when they are appropriate, the design results are fabricated and printed. In testing the signal capture power using the Xirrus WiFi Inspector, this antenna was able to capture the signal beam, which was 105 meters or 40 meters further than not using the antenna. In addition, from testing, it is known that this antenna has a gain of 16.15 dBi. While in the simulation, it is also known that this antenna has the following characteristics: return loss: -32,353 dB (S11), -32,737 dB (S22), -33,974 dB (S33), -34,423 dB (S44), VSWR: 1,049 (VSWR 1), 1,047 (VSWR 2), 1.040 (VSWR 3), 1.038 (VSWR 4), impedance: 50.7 -111 MHz.

Dispersive FSO Performance Estimation with Gaussian Pulses and Laplace Modeled Time Jitter

FSO communications tend to be one of most convenient, wireless, high-data-rate communications technologies of global telecom networking, and they are implemented and operated with low-cost resources. Despite their advantages, FSO systems’ performance is delimited by several physical phenomena, which act on propagating signal beams through the atmospheric path. Among other effects, chromatic dispersion and time jitter affect the shape and the detection instant of the incoming optical pulse, respectively. This results in signal fading and probable misdetections, and the signal fades along the propagation path due to power losses. Particularly, chromatic dispersion affects the width of the longitudinal information pulse, while the stochastic nature of the time jitter effect is treated with the use of a statistical model for the instantly received irradiance of the detecting pulse at the corresponding time slot. In this study, the symmetrical Laplace distribution was chosen for weak time jitter effect emulation because of its symmetry in pulse detection before or after the center of the specific timeslot. Thus, the joint influence of all three effects could considered, including all the parameters involved. Moreover, new-closed-form mathematical expressions were derived in order to accurately estimate the availability and the reliability of the FSO links under consideration. Next, using the derived mathematical forms, performance outcomes were presented for typical parameter values for realistic FSO links.