Microwave generation with photonic frequency octupling using a DPMZM in a Sagnac loop

A photonic microwave signal generation scheme with frequency octupling is proposed and experimentally demonstrated. The scheme is based on bi-directional use of a dual-parallel Mach–Zehnder modulator (DPMZM) in a Sagnac loop. The two sub-modulators in the DPMZM are driven by two low-frequency signals with a π/2 phase difference, and the dc biases of the modulator are all set at the maximum transmission points. Due to the velocity mismatch of the modulator, only the light wave along the clockwise direction is effectively modulated by the drive signals to generate an optical signal with a carrier and ±4th order sidebands, while the modulation of the light wave along the counterclockwise direction is far less effective and can be ignored. By properly adjusting the polarization of the light wave output from the Sagnac loop, the optical carrier can be significantly suppressed at a polarizer, and then an optical signal with only ±4th order sidebands is generated. In the experiment, a pure 24-GHz microwave signal without additional phase noise from the optical system is generated using a 3-GHz local oscillator signal. As no electrical or optical filter is used, the photonic frequency octupler is of good frequency tunability.     

On the Theory of Stimulated Raman Radiation in an Optical Resonator

Stimulated Raman radiation involving an arbitrary number of Stokes components in an optical resonator is considered for the case when a pumping wave is directly incident on a Raman-active condensed substance at an angle θ to the resonator axis. The expressions are derived for the steady-state radiation intensities of all the Stokes components generated, and the number of the components versus the pumping wave intensity is discussed. The conditions of the effective conversion of the pumping wave into radiation of Stokes components are elucidated. It is shown that in a frequency region close to the point ?² n/? ω² = 0 (n is the effective refractive index of the substance inside the resonator) locking Stokes components is feasible due to a ‘tunnel’ traversal of femtosecond pulses through a dispersive medium, provided the latter occupies a characteristic tunnel length along the resonator axis. For the case of the three components generated, the wave band over which locking occurs is derived and a frequency modulation of the first and the third Stokes components beyond this band is predicted. The possibility of an experimental indication of the band discussed, due to a discontinuous disappearance of the frequency modulation in the band, is noted. For locking four Stokes components the possibility is shown of the change of their stable phase relation on variation of the pumping wave intensity.     

Linear frequency tuning of SAW resonators

Frequency tuning in SAW (surface acoustic wave) resonator-stabilized oscillators is normally accomplished via utilization of a voltage-controlled phase shifter. The design of abrupt junction varactor diode-inductor networks which employ impedance transformation techniques to obtain linear frequency tuning of two-port SAW resonators is reported. The approach is similar to that previously developed for linear tuning of bulk wave, quartz crystal resonators. This technique uses varactor diode parallel inductance to provide a linear reactance versus voltage network, which is effectively connected in series with the resonator motional impedance in order to tune the effective resonator center frequency. Typical tuning ranges are significantly larger than those achievable using the phase shifter approach, and are on the order of 400 ppm for the 320-MHz resonator used.     

Planar ferrite-piezoelectric composite microwave resonator with electric and magnetic frequency tuning

A planar composite microwave resonator based on a bilayer structure comprising a single-crystal yttrium iron garnet (YIG) ferrite film on a lead magnesium niobate-lead titanate (PMN-PT) piezoelectric plate has been studied. The possibility of electric and magnetic tuning of the resonance frequency in this structure is demonstrated. The magnetic tuning in the frequency range of 2–18 GHz is effected by varying the magnetic bias field and the electric tuning within a 20 MHz bandwidth is achieved by applying a dc bias voltage to the piezoelectric layer. An increase in the central frequency of a YIG/PMN-PT composite resonator is accompanied by a growth in the resonator Q from 110 to 990, while the electric tuning bandwidth remains unchanged     

Photonic microwave frequency conversion scheme with flexible phase shift

In this paper, a single, flexible and stable optical frequency conversion scheme with tunable phase shift is proposed. It mainly consists of a dual-parallel binary phase shift keying (DP-BPSK) modulator and a polarization modulator (PolM). Properly setting the values of two DC bias points in the DP-BPSK modulator, the frequency conversion ability can be achieved. Meanwhile, the phase shift can also be realized by controlling the DC voltage that drives the PolM or tuning the polarization controller (PC3). The simulation results show that a 20?GHz RF signal can be converted into a 10?GHz IF signal with the conversion efficiency of ?4.45?dB and a full 0° to 360° phase shift. It should be noted that the system performs well against different non-ideal factors such as extinction ratio, DC drifting or different LO and RF amplitudes. In addition, spurious free dynamic range of 82.14 dB·Hz^2/3 is achieved and it can be greatly improved if a better extinction ratio is available.     

Nonlinear Second Sound Waves and Acoustic Turbulence in Superfluid 4He

The preliminary results of an investigation of nonlinear second sound waves in a high quality resonator filled with superfluid ⁴He are presented and discussed. It is found that, for a sufficiently strong periodic driving force, a cascade of second sound waves is formed at multiple harmonics of the driving frequency over the extremely wide frequency range 1–100 kHz. It can be described by a power law A _ω =const.×ω ^−m , where the scaling index m≈1. These observation can be attributed to the formation of a Kolmogorov-like turbulent cascade in the system of second sound waves, accompanied by directed energy flux through the frequency scales. It manifests itself as a limiting of the amplitude of a standing wave, a distortion of the shape of the initially harmonic waves, and a reduction of the effective quality factor Q of the resonator.     

Experimental Study of the Nonlinear Second Sound Wave Interaction in Superfluid 4He

We report preliminary results of investigations of the nonlinear second sound wave interaction in a high-quality resonator filled with superfluid ⁴He. The anomalously large nonlinear coefficient of second sound allows us to observe the formation of higher harmonics while pumping the resonator at a resonant frequency and, in this manner, to study wave energy transfer from the low-frequency domain to the high-frequency domain over a wide frequency range. The observed nonequilibrium stationary wave distribution of amplitudes A _f for multiple harmonics over wave frequency f may be described as , where s ≥ 1.5.     

声表面波谐振器型振荡器的研制

本文介绍了金属条射栅双端对声表面波谐振器型的原理和结构特点，给出了一种采用声表面波谐振器稳频的低噪声，高稳定性的振荡器电路设计方案。对影响振荡器频率稳定度的因素进行了分析讨论，并探讨改善声表面波振荡器频率稳定性的方法。该声表面波谐振器的中心频率为１２０ＭＨｚ，无载Ｑｖ，大于２０，０００，插入损耗小于６．０ｄＢ，经测试，秒级频率稳定度为１０＾－１０数量级，在自由室温下的日平均波动为１０＾－６／ｄ数量     

Ringing phenomenon of the fiber ring resonator

A resonator fiber-optic gyro (R-FOG) is a high-accuracy inertial rotation sensor based on the Sagnac effect. A fiber ring resonator is the core sensing element in the R-FOG. When the frequency of the fiber ring resonator input laser is swept linearly with time, ringing of the output resonance curve is observed. The output field of the fiber ring resonator is derived from the superposition of the light transmitted through the directional coupler directly and the multiple light components circulated in the fiber ring resonator when the frequency of the laser is swept. The amplitude and phase of the output field are analyzed, and it is found that the difference in time for different light components in the fiber ring resonator to reach a point of destructive interference causes the ringing phenomenon. Finally the ringing phenomenon is observed in experiments, and the experimental results agree with the theoretical analysis well.     

Optimization of diode-pumped doubly QML laser with neodymium-doped vanadate crystals at 1.34 μm

We present a theoretical model for a diode-pumped, 1.34 μm V³⁺:YAG laser that is equipped with an acoustic-optic modulator. The model includes the loss introduced by the acoustic-optic modulator combined with the physical properties of the laser resonator, the neodymium-doped vanadate crystals and the output coupler. The parameters are adjusted within a reasonable range to optimize the pulse output characteristics. A typical Q-switched and mode-locked Nd:Lu_0.15Y_0.85VO₄ laser at 1.34 μm with acoustic-optic modulator and V³⁺:YAG is set up, and the experimental output characteristics are consistent with the theoretical simulation results.     

Variation of the electroluminescence spectra of ZnZ:Mn thin-film emitters depending on the excitation level

The electroluminescence (EL) spectra of ZnS:Mn thin-film emitters measured in various regions of the luminance wave exhibit, besides the bands characteristic of the intracenter emission from Mn²⁺ ions, additional EL bands peaked at ∼530 and ∼655 nm, which are probably related to the trapping of free electrons on deep centers formed by the sulfur vacancies V _S ²⁺ and V _S ⁺ . These traps may lead to the formation of a negative bulk charge in a near-cathode region, inducing a decrease in the growth rate (or even a drop) of current through the phosphor, as well as a decay of instantaneous luminance.     

Photoacoustic Excitation of the Interior Surface of an Acoustic Resonator for Speed of Sound Measurement

A remote optical technique is proposed as a valid alternative to conventional electroacoustic excitation of sound inside an acoustic resonator. Efficient photoacoustic conversion of an amplitude-modulated light beam, impinging on the interior solid surface of the resonator wall, into a stationary acoustic field is achieved. The reported results were obtained in a cylindrical stainless steel resonator with a volume of about 572 cm³; the radiation source is the 514 nm line of an Ar⁺ laser. The laser beam can be focused on different points of the resonator internal surface. The signal frequency dependence is well interpreted in terms of gas-microphone detection theory. The precision obtained in the measurement of resonance frequency f _N and halfwidth g _N of the cavity modes is on the order of 10^-6 of f _N and is likely to be further improved by minor refinements of the experimental apparatus.     

Real-time digital holographic beam-shaping system with a genetic feedback tuning loop

A novel implementation of a real-time digital holographic system with a genetic feedback tuning loop is proposed. The proposed genetic feedback tuning loop is effective in encoding optimal phase holograms on a liquid-crystal spatial light modulator in the system. Optimal calibration of the liquid-crystal spatial light modulator can be achieved via the genetic feedback tuning loop, and the optimal phase hologram can then overcome the aberration of the internal optics of the system.     

用于原子重力仪的扫频频率源系统

原子重力测量实验中,需要通过扫频频率源来实现主从Raman激光的线性啁啾,进而补偿原子在自由下落过程中产生的多普勒频移,实现当地重力加速度g的测量。针对传统扫频频率源体积大、发热量大的问题,通过AD9959数字芯片设计了一款扫频频率源,可用作原子喷泉扫频控制和Raman光锁相环鉴频鉴相本振参考。最终通过实验测得：该扫频信号源的相位噪声为-112 dB@1 kHz,频率稳定度为1.38×10^-11@1 s,对原子重力仪灵敏度影响为2.81×10^-9 g/Hz^1/2,600 s积分时间对原子重力仪实验影响为1.15×10^-10 g。该系统具有低噪声、高稳定度的特点,可满足搬运式原子重力仪分辨力10^-10 g需求。研究结果为原子重力仪从原理样机向工程化可搬运实验测试仪器发展提供了一定参考。     

Resonance ring interferometry with incoherent light

A new method of measuring the phase nonreciprocity in a passive ring resonator using a light source of low coherence is described. The method provides effective suppression of noise from the backscattering of light in the ring resonator and insensitivity of the interferometer to excursions of the resonance frequencies of the resonator due to reciprocal effects (e.g., thermal expansion) and also permits modulation and compensation of the phase nonreciprocity by using a device outside the resonator to shift the frequency of the light. One version of a low-coherent resonance ring interferometer is examined, viz., a two-transit asymmetric interferometer with a rotating mirror. Pis’ma Zh. Tekh. Fiz. 24, 24–29 (September 12, 1998)     

Laser with rapid tuning of the spectrum shape

We have studied a laser system with quick electronic tuning of the spectrum shape and continuous distribution. The proposed method is based on separate control of phase and amplitude spatial distributions of resonator transmittance. Evolution of the spectral function of the diffractively coupled dispersive resonators and the model for the formation of the resonator with the spectral function given by its moments are studied theoretically. The synthesis of continuous spectra is investigated experimentally in the laser with a novel control element including a spatial acousto-optic modulator and a tunable lens telescope.     

铌酸锂光纤型行波调制器研究

以LiNbO3光纤作为通光部分,Si2N2O为衬底分别取代了传统波导电光调制器的中Ti:LiNbO3波导和铌酸锂衬底设计了带宽为95.49 GHz铌酸锂光纤型调制器.今利用有限元法分析SCPS电极结构下该铌酸锂光纤调制器的性能.研究结果表明,该新型调制器可以在很宽的频带内实现调制速度的匹配和阻抗匹配,半波驱动电压为2.56 V,特性阻抗为55.3Ω.     

Transient response of a resonator fiber optic gyro with triangular wave phase modulation

We present an in-depth analysis of the transient response of a resonator fiber optic gyro based on triangular wave phase modulation. Unusual effects have been observed in the process of tracking the resonant frequency of an optical fiber ring resonator (OFRR). There is a distortion phenomenon, unlike the ideally square wave or a pure DC output of the OFRR, but signal overshoot or undershoot occurs. A deep analysis of the influence of the nonideal square wave or pure DC output on gyro performance is fully developed for the first time, to the best of our knowledge. Further analysis shows that this is the transient response process after modulation by the triangular wave, and the process is related both to the parameters of the OFRR and the modulation frequency of the triangular wave. By sampling the steady-state signal of the distortion square wave, or by oversampling the distortion signal to get a number of data, and then accumulating and averaging these data to be demodulated, the distortion's effect can be considerably decreased.     

Phase modulation spectroscopy using an all-fiber piezoelectric transducer modulator for a resonator fiber-optic gyroscope

The theoretical analysis and experimental demonstration of phase modulation spectroscopy employing an all-fiber piezoelectric transducer modulator for a fiber ring resonator fiber-optic gyroscope is presented for the first time as far as we know. The results support the feasibility of such a technique as a rotation detection scheme for a resonator fiber-optic gyroscope.