Electrical Phase Shift Research Articles

Atomically thin optical lenses and gratings.

Two-dimensional (2D) materials have emerged as promising candidates for miniaturized optoelectronic devices due to their strong inelastic interactions with light. On the other hand, a miniaturized optical system also requires strong elastic light–matter interactions to control the flow of light. Here we report that a single-layer molybdenum disulfide (MoS2) has a giant optical path length (OPL), around one order of magnitude larger than that from a single-layer of graphene. Using such giant OPL to engineer the phase front of optical beams we have demonstrated, to the best of our knowledge, the world’s thinnest optical lens consisting of a few layers of MoS2 less than 6.3 nm thick. By taking advantage of the giant elastic scattering efficiency in ultra-thin high-index 2D materials, we also demonstrated high-efficiency gratings based on a single- or few-layers of MoS2. The capability of manipulating the flow of light in 2D materials opens an exciting avenue towards unprecedented miniaturization of optical components and the integration of advanced optical functionalities. More importantly, the unique and large tunability of the refractive index by electric field in layered MoS2 will enable various applications in electrically tunable atomically thin optical components, such as micro-lenses with electrically tunable focal lengths, electrical tunable phase shifters with ultra-high accuracy, which cannot be realized by conventional bulk solids.

Generation of Triangular Pulses Based on an Optoelectronic Oscillator

A novel scheme for the generation of full-duty-cycle triangular pulses based on an optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The fundamental tone corresponding to the repetition rate of the pulses is generated by the OEO. Biasing the Mach-Zehnder modulator at the quadratic point, the small-signal gain of the OEO is maximized, while even-order harmonics in the optical intensity are suppressed. By properly setting the gain of the OEO loop, the amplitude of the first-order harmonic is nine times that of the third-order harmonic. After a 90° electrical phase shifter adjusts the phase of the electrical signal at the output of the photodetector, triangular pulses are obtained in the time domain. The oscillating frequency is tuned from 2 to 10 GHz by the yttrium-iron-garnet filter, and the phase noise of generated signal is also investigated. Triangular pulses with repetition rates of 3 and 6 GHz are successfully generated. The root-mean-square errors between the generated and the ideal triangular waveforms are 6.4927e-4 and 9.0932e-4 at 3 and 6 GHz, respectively.

Photonic generation of frequency-quadrupling millimeter-wave signals using polarization property

We propose and analyze a photonic method of generating frequency-quadrupling millimeter-wave signal. This scheme is realized by using a single LiNbO3 intensity modulator (IM) and a Faraday mirror based transverse-electrical and transverse-magnetic mode converter in a Sagnac loop without using an optical filter or an electrical microwave phase shifter. Making use of the intrinsic polarization dependence and the veloc- ity phenomenon of the IM, a special double sideband modulation is implemented, which ensures that the optical carrier can be effectively cancelled employing polarization manipulation. A linear polarizer is used as the polari- zation selection element to choose the second-order sidebands from the modulated light. After beating at the photodiode, a frequency-quadrupled millimeter-wave signal with >30 dB radio frequency spurious suppression ratio is generated. The imperfection of the devices is considered when estimating the system performance.©2015

An optoelectronic oscillator‐based strain sensor with extended measurement range

ABSTRACTAn optoelectronic oscillator (OEO)‐based strain sensor with extended measurement range is proposed and demonstrated. The OEO is embedded with an electrical phase shifter (EPS) to cancel out the strain‐induced phase shift real‐timely via a phase‐locked loop scheme. Theoretically, the control voltage of the EPS is linear to the strain applied on the sensing fiber, leading to a simple and straightforward frequency demodulation. Thanks to the real‐time close‐loop interrogation, the mode‐hopping‐free frequency shift range can exceed one free spectrum range, thus, the measurement range of the sensor is extended. The obtained strain measurement range is up to 2762 με. The achieved strain resolution is 0.86 με. The root‐mean‐square deviation of more than 2‐h test for a fixed strain is 1.1 με. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2336–2339, 2015

A Linearization Analog Photonic Link With High Third-Order Intermodulation Distortion Suppression Based on Dual-Parallel Mach–Zehnder Modulator

A scheme to realize a high linear analog photonic link based on a dual-parallel Mach–Zehnder modulator (DPMZM) is proposed and demonstrated in this paper. By using only two electrical phase shifters with $\pi$ phase shift and optimizing the biases of the DPMZM, the third-order intermodulation distortion (IMD3) is completely eliminated by taking all the sidebands in the optical spectrum that produce IMD3 into consideration in theory. Without digital linearization, other optical processers, and symmetrical single-sideband modulation, optical carrier suppression (OCS) is achieved in one of the submodulators of DPMZM, which guarantees the effectiveness of information transmission. Quadrature modulation is achieved in the other submodulator of DPMZM, and the electrical signals on the two electrodes are the same, which result in a simple operation. The simulated results show that IMD3 is completely suppressed when the sinusoidal electrical signals have two tones, such as 11.9 and 12 GHz, and IMD3 is lower than the noise floor at the $-$ 120 dBm level. The simulated results show that IMD3 is lower than the noise floor with $-$ 120 dBm level, and the simulated results agree well with the theoretical prediction. In addition, IMD3 suppression of approximately 45 dB is experimentally demonstrated in this paper, and the spurious-free dynamic range is improved by $11.2 \hbox{dB}\cdot\hbox{Hz}^{2/3} $ . The scheme could simplify the design of a high linearized analog photonic link and make it stable.

Cylindrical Liquid Crystal Microlens Array With Rotary Optical Power and Tunable Focal Length

A novel cylindrical liquid crystal microlens array with rotary power and tunable capability is proposed and experimentally demonstrated. This structure is capable of generating tunable cylindrical microlenses in two different axis by low voltage control. For this, complex electrical signals are required (electrical phase shift of 180°). A control over the maximum phase shift from $4\pi $ to $34\pi $ radians has been demonstrated. This effect modifies the effective focal length (from 0.2 to 1.2 mm). Moreover, an OFF-state is also possible (behaving like a transparent medium). The structure is simple and does not require a complex fabrication process. The proposed device has several advantages over the existing microlens arrays and is simple and low cost. The device could contribute to developing new applications and to reducing the fabrication costs of current devices. For example, this device can be used in the next generation of mobile displays with autostereoscopic capability.

Revisiting the Marton, Simpson, and Suddeth experimental confirmation of the Aharonov–Bohm effect

We perform an “archeological” study of one of the original experiments used as evidence for the static, time-independent Aharonov–Bohm effect. Since the experiment in question [1] involved a time varying magnetic field we show that there are problems with the explanation of this experiment as a confirmation of the static Aharonov–Bohm effect – specifically the previous analysis ignored the electric field which arises in conjunction with a time-varying magnetic flux. We further argue that the results of this experiment do in fact conform exactly to the recent prediction [2,3] of a cancellation between the magnetic and electric phase shifts for the time-dependent Aharonov–Bohm effect. To resolve this issue a new time-dependent Aharonov–Bohm experiment is called for.

Effect of magnetic spins flipping process on the dielectric properties of α-Fe1.6Ga0.4O3 system

The α-Fe1.6Ga0.4O3 (Ga doped α-Fe2O3) sample has been stabilized in rhombohedral structure. The sample is a canted ferromagnet at 300 K and above. The spins structure starts flipping from in-plane direction to out of plane direction of the rhombohedral structure to exhibit an antiferromagnetic order below a typical temperature ∼ 215 K, known as Morin transition. The magnetic and dielectric properties of α-Fe1.6Ga0.4O3 system have been discussed in the temperature range 123 K to 350 K to examine the effect of magnetic spins flipping process on dielectric properties. The dielectric constant has shown an anomalous peak at ∼ 310 K, followed by a rapidly decrease of dielectric constant with temperature and becomes weakly temperature dependent below Morin transition. The temperature dependent dielectric constant is accompanied with the changes in electrical conductivity, dielectric loss and phase shift of the current with respect to applied ac voltage across the material. The magnetization and dielectric constant showed a linear relation over a wide range of temperature across the Morin transition. The dielectric constant at room temperature decreases under magnetic field, which indicates magneto-dielectric effect in the system. The signature of magneto-dielectric effect reveals a coupling between spins degrees of freedom (magnetic order) and charge degrees of freedom (electric polarization) in corundum structured non-traditional ferroelectric systems.

Ultraprecise Resonance Wavelength Determination for Optofluidic Sensing Applications

We propose an ultraprecise resonance wavelength determination algorithm for optofluidic sensing applications, which can be expected to overcome the defect that the quality factor of the capillary resonator is deteriorated by the severe absorption in water. A parameter proportional to sinusoidal value of electrical field phase shift before and after the interaction with the capillary is constructed to determine the resonance wavelength of the optofluidic capillary. It is numerically demonstrated that this algorithm can narrow the full-width at half-maximum (FWHM) of resonance peak down to ~5% of the FWHM of transmission spectrum, which makes an ultraprecise peak determination feasible. Besides, this algorithm can reduce the FWHM of resonance peak to at least one quarter of FWHM of transmission spectrum in a rather wide region spans from undercoupling to overcoupling, and can be widely used in whisper-gallery mode-based sensor to improve the sensing precision conveniently.

Comparison of Optical Self-Phase Locked Loop Techniques for Frequency Stabilization of Oscillators

Self-phase locked loop (SPLL) through long optical delay lines is investigated for improving the phase noise of the optoelectronic oscillator (OEO) and the voltage-controlled oscillator (VCO). This paper features analytical modeling of close-in to carrier phase noise of oscillators employing SPLL technique using single and multiple delay loops. Experimental results are also provided to verify the analytical modeling and explore critical circuit design parameters to achieve substantial phase noise reduction. Performance comparison is presented for SPLL using electrical phase shifter, Mach-Zehnder modulator (MZM)-based phase shifting, and electrical VCO. Phase noise reduction of 65 dB at 1-kHz offset is achieved for an electrical VCO employing a dual-loop SPLL with 3- and 5-km optical fiber delay lines, whereas the phase locking based on MZM and electrical phase shifter provided 20- and 38-dB reductions at 1-kHz offset for an OEO, respectively.

Selective harmonic elimination in multi‐level inverter with zig‐zag connection transformers

This study applies the selective harmonic elimination (SHE) technique to determine the switching angles for a multi-level inverter that cooperated with specially connected transformers. With the ability of directly controlling harmonics, the SHE technique has the adaptability to associate with apparatus which are congenitally immune to specific harmonics, such as the zig-zag connection transformers. In this study, the two sets of primary windings of the transformers are supplied by two six-switch full-bridge inverters with 30 electrical degrees phase shift. Harmonics with orders other than 12h ± 1 (h is positive integral) will not appear in the output voltages in the secondary side of the transformer because they are prohibited by the transformers. Then, the SHE technique with half-wave symmetry is employed to eliminate some selected harmonics with orders equal to 12h ± 1, and adjusts the amplitude of the fundamental. This study obtains a set of precise switching angles through offline calculation over a wide range of modulation indices. A digital signal processor is used to implement online calculation of the switching angles by an approximate method derived from the precise solutions. Some selected analysis and experimental results are demonstrated in this paper. A 4 kW prototype is built to verify the validity of the proposed system.

A Modified Phaseless Inverse Scattering Setup Based on Indirect Holography Implemented at Submillimeter-Wave Band

The aim of this communication is to present an enhanced phaseless inverse scattering setup and its implementation at the submillimeter-wave band. This setup is based on a modified indirect holography with synthesized reference signal so that a phase shifter is not required. Thus, a phaseless scanner can be built using a simple power detector resulting in a simplified measurement scheme very suitable to work in the millimeter-wave band and beyond. Mechanical phase shifting is used to bypass the use of electrical phase shifters. In addition, the reference signal is injected by coupling the transmitter and receiver antennas so that directional couplers and power combiners are avoided. New errors introduced by these techniques are analyzed and quantified. The method is validated with simulations as well as measurements at 300 GHz.

Photonic generation of frequency quadrupling signal for millimeter-wave communication

We propose and demonstrate a photonic method of generating frequency quadrupling signal for millimeter-wave (mm-wave) wireless communication system. The frequency quadrupling scheme is based on carriers cancellation within an integrated dual-parallel Mach–Zehnder modulator (DPMZM), thus avoiding the use of an optical filter or an electrical phase shifter. The effects of modulation-depth on the power level of generated mm-wave signal as well as on the system performance of wireless transmission are analyzed theoretically and measured experimentally. In the experiment, transmission of 155Mbps OOK baseband data on a photonic-generated 40GHz mm-wave over a length of 25km standard single-mode fiber (SMF) and 20m wireless distance with error free is successfully demonstrated.

A Novel Two-Phase Permanent Magnet Synchronous Motor Modeling for Torque Ripple Minimization

This paper proposes a novel two-phase, two-pole, permanent magnet synchronous motor (PMSM) with dual U-core stator structure for torque ripple minimization. The proposed motor is modeled based on the conventional single-phase U-core PMSM with approximate output power and core dimension. Torque ripple in the novel motor can be reduced significantly due to 90 $^{\circ}$ electrical angle phase shift in two sets of magnet pairs and 90 $^{\circ}$ shift in two-phase excitation currents. Characteristics of both PMSMs such as back-EMF, cogging torque and electromagnetic torque are analyzed and compared by using the 3-D finite element analysis (FEA). As shown in the result, the cogging torque and torque ripple in the novel two-phase PMSM are efficiently reduced with sinusoidal back-EMF waveform and reasonable current density value. The validity of both PMSM models is also verified by the comparison between simulated and experimental measured results.

Optoelectronic $K$-Band Oscillator With Gigahertz Tuning Range and Low Phase Noise

We propose and demonstrate a K -band optoelectronic oscillator with ultralow phase noise performance and a frequency tuning range exceeding 1 GHz. The operation principle is based upon using two parallel optoelectronic loops with similar but not equal length and an electrical phase shifter for frequency tuning. We experimentally demonstrate tunable microwave signal generation within 20.7-21.8 GHz with a coarse frequency resolution of ~100 MHz. Fine tuning of the generated signal within a range of ±5 MHz is also achieved. The linewidth and phase noise of the generated microwave signal are <;3 Hz and -105 dBc/Hz at 10-kHz offset, respectively. Within the full gigahertz tuning range, the phase noise and output power of the generated microwave signal varies by only ±1.5 and <;1 dB, respectively.

Precompensated Optical Double-Sideband Subcarrier Modulation Immune to Fiber Chromatic-Dispersion-Induced Radio Frequency Power Fading

We propose and demonstrate a new optical double-sideband modulation technique that is immune to fiber chromatic dispersion and thus free of dispersion-induced RF power fading. The proposed modulation technique also provides a 3 dB improvement of RF power compared with optical single-sideband modulation. The proposed modulation technique is analyzed in theory and simulation. It is shown that for a given fiber length an optimum electrical phase shift exists to completely cancel the dispersion-induced RF power fading. We verify this proposed modulation technique experimentally for a single-tone RF signal and for a multiband orthogonal frequency division multiplexing ultrawideband signal.

Dispersion compensation in atom interferometry by a Sagnac phase

We reanalyzed our atom interferometer measurement of the electric polarizability of lithium now accounting for the Sagnac effect due to Earth rotation. The resulting correction to the polarizability is very small but the visibility as a function of the applied phase shift is now better explained. The fact that the Sagnac and polarizability phase shifts are both proportional to $v^{-1}$, where $v$ is the atom velocity, suggests that a phase shift of the Sagnac type could be used as a counterphase to compensate the electric polarizability phase shift. This exact compensation opens the way to higher accuracy measurements of atomic polarizabilities and we discuss how this can be practically done and the final limitations of the proposed technique.

Photonic generation of a millimeter-wave signal based on sextuple-frequency multiplication

A millimeter-wave signal with sextuple-frequency multiplication of a microwave source is obtained with two cascaded optical modulators, which are driven by the same microwave source with phase deviation of pi/2 introduced by an electrical phase shifter. Without any optical filter, a wideband continuously tunable millimeter-wave signal is easily generated.

Dual Semiconductor Laser System With Rapid Time-Delay for Ultrafast Measurements

We present a dual semiconductor laser system at 1.55 mum with femtosecond pulse widths and very low timing jitter for rapid pump-probe measurements. Synchronizing the two lasers to the same low-noise radio frequency-oscillator allows the use of an electrical phase shifter for the relative time delay between the lasers. This leads to a large scanning window that nearly matches the pulse period of 2.5 ns, as well as achieving a discrete time step of below 100 fs. The timing jitter of the complete dual laser system including all electronics is only 540 fs across the whole time delay. The nonlinear pulse compression using especially designed comb-like dispersion profiled fiber leads to autocorrelation widths of 310 fs. The system performance, i.e., the high time resolution is demonstrated by optical cross correlation of the pump and probe pulse, showing a very low full-width at half maximum of 1.3 ps

Finite element modeling (FEM) simulation of interactions between wood and microwaves

The aim of this study was to use finite element modeling (FEM) as a tool to analyze microwave scattering in wood and to verify the model by measurements with a microwave scanner. A medical computed tomography scanner was used to measure distribution of density and moisture content in a piece of Scots pine (Pinus sylvestris). Dielectric properties were calculated from measured values for cross sections from the piece and used in the model. Images describing the distribution of the electric field and phase shift were obtained from the FEM simulation. The model was verified by measurements with a scanner based on a microwave sensor. The results show that simulated values correspond well to measured values. Furthermore, discontinuities in the material caused scattering in both the measured and the simulated values. The greater the discontinuity in the material, the greater was the need for computational power in the simulation.