Phase Modulation Technology Research Articles

Continuous phase modulation technology based on grating period interval for high grating coupling coefficient and precise wavelength control.

A novel, to the best of our knowledge, grating modulation technique for distributed feedback laser arrays is proposed and demonstrated. This method modifies the initial phase within each grating period, applying a total phase shift that increments in an arithmetic progression, realizing laser arrays with channel spacings of 0.493 nm, 0.949 nm, and 1.956 nm. This method maintains a coupling coefficient comparable to traditional uniform grating structures. Furthermore, the continuous phase modulation enhances the stability of the lasing wavelength of the primary mode, reducing sensitivity to fabrication errors. This improved tolerance to manufacturing inaccuracies represents a significant technological advancement, making this approach highly promising for applications requiring precise and stable wavelength control.

Dynamic geometric phase holography based on in-plane switching liquid crystal

ABSTRACT Liquid crystal geometric phase modulation technology is expected to achieve thin, small and achromatic spatial light modulation, which in turn has the potential to achieve holographic displays with large field angles and high clarity. This article presents a continuous dynamic geometric phase liquid crystal spatial light modulation method based on in-plane switching (IPS) mode. The relationship between geometric phase modulation and driving voltage is calibrated by using interferometry. Two hundred fifty-six phase orders within the phase modulation range of 0~π/2 is achieved. Subsequently, a phase hologram with a modulation range of 0~π/2 was designed by combining the GS (Gerchberg-Saxton) algorithm and single Fourier transform, demonstrating the holographic display capability. This article provides a low-cost approach for dynamic geometric phase holographic display.

Manipulating dispersive wave emission via temporal sinusoidal phase modulation.

We report the dispersive wave (DW) emission from the Gaussian pulse with temporal sinusoidal phase (TSP) modulation. The TSP-induced chirp can enhance or cancel the chirp generated by self-phase modulation by properly selecting the modulation parameters of TSP, which can influence the nonlinear propagation of the TSP-modulated pulse. It is shown that the TSP can effectively control the resonant frequency and energy conversion efficiency of the DW emission. We give a modified phase-matching condition to predict the resonant frequencies, which agree with the simulation results obtained by numerically solving the nonlinear Schrödinger equation. The enhanced conversion efficiency of the DWs can be increased up to 28% with only TSP modulation. Our results can extend the application of temporal phase modulation technology for wavelength conversion, and broadband supercontinuum generation.

Development of the CO2 dispersion interferometer on HL-2M Tokamak

To meet the requirement of electron density measurement on HL-2M, a single channel CO2 dispersion interferometer based on second harmonic generation technology has been developed and commissioned on HL-2M Tokamak. The short wavelength system can avoid fringe jump and refraction and has a large measuring range to meet the designed density parameter on HL-2M. The dispersion system is compact and insensitive to mechanical vibration. A data acquisition/ analyze/uploading system based on phase-modulation technology is developed for the dispersion system. Density curve measured by CO2 dispersion interferometer was agree with the curve measured by microwave interferometer. Density resolution of the system is about 2 × 1017/m3, and the measuring range is up to 1021/m3.

Specific Phase Modulation with Dynamic Variable Spectral Width of Nanosecond Optical Pulse in High-Power Lasers

High-power laser pulse transmitted by phase modulation with certain spectrum distribution can suppress the buildup of transverse stimulated Brillouin scattering (TSBS) in large aperture laser optics and smooth the speckle pattern illuminating the target by spectral smoothing dispersion (SSD). In this paper, based on the requirements of the double-cone ignition scheme including simultaneously realizing that the focal spot is variable at different times in size and the spatial intensity distribution is uniform, we propose a novel phase modulation technology with a rapid variable modulation index in the nanosecond scale instead of utilizing conventional constant amplitude sinusoidal curve. The relevant simulation results indicate that the proposed technology can realize the dynamic nanosecond spectral distribution and the trend correlates with the variety of modulation index. Particularly, we indirectly measure this rapid changeable spectral distribution based on the mapping relationship between frequency and time domain. We believe that the new technology is expected to meet the requirements of SSD and the dynamic focus simultaneously.

Analysis and Optimization of Acoustic Sensor Based on Fiber Fabry-Pérot Etalon

Fiber optic sensors have been extensively studied in recent years. Due to the advantages of high sensitivity, compact structure, and anti-electromagnetic interference, the sensors based on the Fabry-Pérot (FP) cavity have become a research hotspot. The Fabry-Pérot etalon (FPE) acoustic sensor consists of two Plano-Concave Lenses coated with a highly reflective film, the Graded Index Lenses (GRIN) lenses, the optical fibers and a glass tube. Acoustic detection is realized by detecting the small change in the refractive index of the cavity medium caused by sound pressure, and the phase modulation technology realizes the modulation and demodulation of the acoustic signal. Matlab is used to analyze the influence of refractive index changes on the resonance spectrum and sensitivity curve, so the cavity mirrors with the reflectivity of 99% are selected. The structure of the FPE sensor is optimized using Zemax software. The optimal length of the sensor is 29.973 mm and the diameter is 6 mm. The high quality factor values of experiment and simulation are both 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> . At the same time, the experimental results show that the sensor has a response in the range of 50 Hz-20 kHz, with a high Signal-to-Noise Ratio (SNR) of 61.97 dB when the sound pressure is 19.795 Pa, and the sensitivity response is linear, reaching 0.19013 V/Pa. The research results provide useful guidance for the optimal design of the sensor, and the correctness of the theory is verified by the performance test of the optical acoustic sensor.

An Optical Acoustic Detection System Based on Fabry Pérot Etalon Stability Structure.

The optical acoustic detection system based on the Fabry Pérot Etalon (FPE) with high quality–factor (High Q) and stability structure is described and tested. The FPE contains two high–reflectivity Plano–Concave lenses, achieving high fineness and stability. The protective structure of the confocal stabilized FPE is composed of an invar tube, copper sheath, Bakelite sheath and aluminum housing to protect the sensor from the effects of ambient temperature and vibration. The audio signal is injected into the cavity through the sound hole located in the center of the cavity. Acoustic waves induce the vibration of the medium in the cavity, which leads to a simultaneous change in the FPE optical path and a shift of the interference spectrum. The acoustic detection system is built, and the frequency of the laser is locked on the resonant frequency points of the FPE by using phase modulation technology, so as to detect acoustic signals of different frequencies and amplitudes. In addition, the sensitivity of the proposed sensor exceeds 34.49 mV/Pa in the range of 20 Hz–20 kHz. A Signal-to-Noise Ratio (SNR) of 37 dB can be achieved at 20 Hz. Acoustic signal detection technology based on the FPE stability model is used to test the theoretical feasibility of the future high sensitivity Fabry Pérot Interferometric (FPI) acoustic sensors.

Optically tuned dielectric characteristics of SrTiO3/Si thin film in the terahertz range* *Project supported by the National Natural Science Foundation of China (Grant No. 62075248), the National Key R&D Program of China (Grant Nos. 2017YFB0405400 and 2020YFB2009300), and the Program for the Innovation Team of Science and Technology in University of Henan, China (Grant No. 20IRTSTHN014).

Active control of the optical parameters in strontium titanate (SrTiO3, STO) thin films is highly desirable for tunable terahertz (THz) integrated devices such as filters, phase modulators, and electro-optical devices. In this work, optically tuned dielectric parameters of a STO thin film epitaxially grown on a silicon wafer were characterized in the THz region with an 800 nm laser pump-THz detection system. The refractive index, extinction coefficient, and complex dielectric constant of the STO thin film were calculated using thin-film parameter extraction. Owing to carrier transportation and soft-mode oscillation, the above optical parameters changed notably with the pump power of the external laser. This study is of great significance for rapid and non-contact THz phase-modulation technology and may serve as a powerful tool to tune the dielectric properties of the STO thin films.

Hybrid Method to Identify Second-trip Echoes Using Phase Modulation and Polarimetric Technology

For pulse Doppler radars, the widely used method for identifying second-trip echoes (STs) in the signal processing level yields significant misidentification in regions of high turbulence and severe wind shear. In the data processing level, although the novel algorithm for ST identification does not yield significant misidentification in specific regions, its overall identification performance is not ideal. Therefore, this paper proposes a hybrid method for the identification of STs using phase modulation (signal processing) and polarimetric technology (data processing). Through this approach, most of the STs are removed, whereas most of the first-trip echoes (FTs) remain untouched. Compared with the existing method using a signal quality index filter with an optimized threshold, the hybrid method exhibits superior performance (Heidke skill scores of 0.98 versus 0.88) on independent test datasets, especially in high-turbulence and severe-wind-shear regions, for which misidentification is significantly reduced.

Experimental Research on HLS-II Performance by Means of the RF Phase Modulation Technique

In this article, radio frequency (RF) phase modulation (PM) technology is introduced to effectively improve the beam lifetime and study the longitudinal beam dynamics at Hefei Light Source-II (HLS-II) storage ring. In the experiment, an optical streak camera is employed for real-time observation of the longitudinal distribution and the bunch lengthening under the single-bunch operation mode. Simultaneously, the mechanism of island formation and annihilation caused by PM is deeply investigated based on theoretical analysis and preliminary online experimental measurements. The measured results are in good agreement with the theoretical simulation results. The applicable bunch lengthening factor and the optimal beam lifetime improvement factor are obtained as 2.01 and 1.87, respectively, over the range 20.2-20.7 kHz, which is in the vicinity of the synchrotron frequency. In addition, we further analyze and discuss the corresponding relationship between the modulation frequency and other characteristic parameters of HLS-II, such as the beam size, emittance, and energy spread, under PM.

Analysis and Optimization of Dynamic Performance for Resonant Integrated Optical Gyroscope

In this article, a closed-loop signal detection method is proposed to improve the dynamic performance of the resonant integrated optical gyroscope. We firstly establish a closed-loop error model of the angular velocity tracking system with optical nonlinearity and parameter uncertainty based on triangular phase modulation technology. Then, we optimize the loop gains of the signal processing to improve the signal-to-noise ratio of the closed-loop error signal about angular velocity tracking. Secondly, we design a timing sequence control method to effectively eliminate the time-delay of signal processing for optimizing the dynamic performance of the angular velocity tracking system. Finally, a control algorithm is designed to suppress the influence of the optical nonlinearity and parameter uncertainty for improving the dynamic tracking performance of resonant integrated optical gyroscopes. The experimental results demonstrate that the resonant integrated optical gyroscope has a rise time less than 36 μs, a high frequency response with the bandwidth 13.1 kHz, and a low scale factor nonlinearity less than 269.2 ppm, which verifies the effectiveness of the proposed closed-loop signal detection method for the resonant integrated optical gyroscope.

Study on the Influence of Intermittent Phase Modulation on the Spectrum Shift Characteristics of Radar Signals

Intermittent sampling and forwarding interference is a new type of radar interference. It captures and transmits intercepted signals to enemy radars to form multiple false targets. The essence is an amplitude modulation. The phase modulation technique alternates the phase of the electromagnetic wave by adjusting the instantaneous phase of the electromagnetic wave. Phase modulation technology is currently widely used in the field of communication and radar signal design, such as binary phase shift keying and phase encoding signals. In this paper, the spectral shift characteristics of intermittent phase modulation on radar signals are studied, and the influence of modulation parameters on the moving results is analyzed. Finally, the simulation results verify the effectiveness of the method.

Collinear holographic data storage technologies

In the era of information explosion, the demand of data storage is increased dramatically. Holographic data storage technology is one of the most promising next-generation data storage technologies due to its high storage density, fast data transfer rate, long data life time and less energy consumption. Collinear holographic data storage technology is the typical solution of the holographic data storage technology which owns a more compact, compatible and practical system. This paper gives a brief review of holographic data storage, introduces collinear holographic data storage technology and discusses phase modulation technology being used in the holographic data storage system to achieve higher storage density and higher data transfer rate.

谐振式集成光学陀螺系统中用于抑制背散射噪声的相位调制技术

Phase modulation technology is widely used in detecting the rotational signal of gyro in resonator integrated optic gyroscopes in order to improve the sensitivity and suppress noises. This paper we review various phase modulation techniques that have been proposed by many researchers in recent years. The influences of backscattering noises on the performance of RIOG are introduced firstly. Various improved phase modulation techniques are proposed by different research groups. The advantages and limitations of these modulation techniques are investigated. The modulation techniques include two broad categories:namely, single-phase modulation technique (SPMT) and double phase modulation technique (DPMT). Compared with SPMT, DPMT can further improve accuracy and system robustness of RIOGs. High precision sideband locking technology is the latest emerging modulation method that is expected to fulfill performance requirements in the fields of aerospace and defense.

Focus on materials, semiconductors, vacuum, and cryogenics

Focus on materials, semiconductors, vacuum, and cryogenics

A phase-locked laser system based on double direct modulation technique for atom interferometry

We demonstrate a laser system based on phase modulation technology and phase feedback control. The two laser beams with frequency difference of 6.835 GHz are modulated using electro-optic and acousto-optic modulators, respectively. Parasitic frequency components produced by the electro-optic modulator are filtered using a Fabry–Perot Etalon. A straightforward phase feedback system restrains the phase noise induced by environmental perturbations. The phase noise of the laser system stays below −125 rad2/Hz at frequency offset higher than 500 kHz. Overall phase noise of the laser system is evaluated by calculating the contribution of the phase noise to the sensitivity limit of a gravimeter. The results reveal that the sensitivity limited by the phase noise of our laser system is lower than that of a state-of-the-art optical phase-lock loop scheme when a gravimeter operates at short pulse duration, which makes the laser system a promising option for our future application of atom interferometer.

Reduction of backscattering noise in a resonator integrated optic gyro by double triangular phase modulation.

A high carrier suppression level is required to reduce the backscattering noise of a resonator integrated optic gyro (RIOG). This paper proposes a double triangular phase modulation (DTPM) technology for backscattering noise reduction. The principle of the DTPM is described and the carrier suppression of the DTPM is theoretically analyzed and simulated. Based on the numerical simulations, the modulation parameters of the DTPM are optimized. Compared with single triangular phase modulation technology, the DTPM can not only achieve higher carrier suppression but also relax the requirements of modulation amplitude accuracy and temperature stability. The advantage of the DTPM for carrier suppression is validated by experiments, demonstrating that the DTPM is helpful in backscattering noise reduction. As a result, the experimental setup of the RIOG based on the DTPM is established: a bias stability of 0.22 deg/s (10s integrated time) is achieved for 1h. To our knowledge, this is the best long-term bias stability of an RIOG reported to date.

Feedback Network Applied in Frequency Locking of Resonator Gyro

Frequency locking of resonator gyro (R-FOG) is a key technology in gyro signal detection, the frequency locking stability determines the performance of the gyro. Based on transmission theory of ring resonator, this paper analyzes the resonant characteristics, builds the R-FOG system, realizes the output of resonance spectral line first harmonic by using sine wave phase modulation and demodulation technology. According to the source of circuit drift error in the traditional analogue proportion integral (PI), the T-type feedback network which can effectively inhibit the drift error was proposed and applied to the frequency locking of resonator gyro, which obtained better effect. By Allan variance analysis, the locking stability of resonant frequency for 4000s is better than 9×10-12.

Development of 2-Chlorophenol Sensor Based on a Fiber Optic Oxygen Transducer via Oxidation Reaction Catalyzed by Tetranitro Iron (II) Phthalocyanine

This paper develops a 2-chlorophenol sensor based on the improvement of a fiber optic oxygen transducer. The measurement of a sensor depends on the principle of stoichiometric relationship between dissolved oxygen and 2-chlorophenol in catalytic oxidation reaction. Specifically, oxygen was consumed fast in oxidation of 2-chlorophenol catalyzed by tetranitro iron (II) phthalocyanine (TNFe(II)Pc), and the concentration changes of dissolved oxygen could be measured by a fiber optic oxygen transducer. The phase-modulation technology was employed to record the signals of phase delay responding to the aerobic oxidation process catalyzed by TNFe(II)Pc. In addition, the sensing performance of this sensor could be demonstrated by a modified Stern-Volmer equation, φ = 0.12 + 3710[2 - CP] (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.9949), where φ and [2-CP] represent the phase delay and concentration of 2-chlorophenol, respectively. The detection limit of this sensor is 8.0 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> M. In addition, this sensor shows the satisfactory results compared with that of HPLC method for detection of the samples from Changjiang river.

780 W narrow linewidth all fiber laser

High-power narrow linewidth fiber lasers are extensively applied in coherent detection and power-spectrum beam combination etc. The suppressing method of stimulated Brillouin scattering is analyzed. And the theory of sinusoidal phase modulation is analyzed also. A single frequency laser is broadened to become a 2.9 GHz linewidth seed by sinusoidal phase modulation technology. The power of the seed is then boosted from 50 mW to 780 W through a three-stage power amplifiber configuration. Central wavelength and linewidth of the laser are 1064.34 nm and 2.9 GHz respectively, with an optical-optical efficiency being 79%. And the beam quality is Mx2 =1.44 and My2 =1.43. The output powers before and after phase modulation are compared with each other. And the reason why output power increases is analyzed. The stimulated Brillouin scattering threshold is promoted by added longitudinal mode. Finally, the output power is promoted after phase modulation, so that the output power of this laser is only limited by the pump power. If the pump power is increased, the higher output power of narrow linewidth fiber laser will be achieved.