Noise of Negative Resistance Oscillators at High Modulation Frequencies

The theory of AM and FM noise in oscillators of the negative resistance type is extended to higher modulation frequencies, i.e., to modulation frequencies beyond the bandwidth of the stabilizing cavity. The results are expressed in terms of the input impedance of the stabilizing cavity and are found to agree well with measurements.     

6 GHz direct frequency modulation of cleaved-coupled-cavity channeled-substrate buried-heterostructure lasers

The measured intensity modulation (IM) and frequency modulation (FM) characteristics of single-cavity channeled-substrate buried-heterostructure (CSBH) lasers and cleaved-coupled-cavity (C³) CSBH lasers are described. If the bias is well above threshold, the lasers have -3 dB IM bandwidths of approximately 800 MHz. In contrast, the FM response rolls off less rapidly, and efficient FM operation up to 6 GHz is possible. The IM and FM responses of C³CSBH lasers are similar to single-cavity CSBH lasers provided the modulated cavity is above threshold. If the modulated cavity is below threshold, the FM response of the C³laser is larger but rolls off rapidly for modulation frequencies above 200 MHz.     

Attainment of a low-noise high-power and highly stable Gunn oscillator by coupling to a superconducting cavity

A 100-mW Gunn-diode oscillator has been coupled to a 5 × 10⁸Q factor superconducting Nb cavity. The frequency stability is then improved up to 1.8 × 10^-11over a measuring time of 10s. The long-term frequency shift is removed by placing the cavity in a constant pressure vessel cooled by the He bath. The FM noise has been measured at modulating frequencies as close to the carrier as 0.1 Hz.     

The Measurement of Noise in Microwave Transmitters

A tutorial review of the basis for transmitter noise measurements shows that noise is best described and measured as AM and FM noise. The determination of RF spectrum is done by calculation after the AM and FM noise are known. The contribution of AM noise to RF spectrum shape is determined by the power spectral density shape of the AM noise. The contribution of FM noise to RF spectrum is to make the shape that of an RLC circuit resonant response rather than a delta function with a sideband structure. The measurement of AM noise is done with a direct detector diode. The measurement of FM noise for frequencies above 5 GHz is done with a discriminator based on a one-port cavity resonator. The measurement of FM noise below 5 GHz is done with an improved transmission line discriminator which is described in detail. Measurement of low-power low-noise signal sources is made posbible with an injection-locked oscillator for a preamplifier to the discriminator. The most widely used baseband analyzer is the constant bandwidth superhetdrodyne wave or spectrum analyzer. Most differences in measurement results are resolved by understanding the baseband analyzers. At least the baseband spectrum analysis of transmitter noise measurements can be automated with worthwhile savings in time and improvement of documentation.     

Coupled-cavity effects in FM semiconductor lasers

Numerical simulations of frequency modulated (FM) external cavity semiconductor lasers have been performed and a range of dynamic and spectral phenomena observed. It is shown that FM lasing action can be suppressed due to changes in the FM modulation frequency. Coupled cavity effects are seen to be significant in the development of a broad spectral emission associated with experimentally observed coherence collapse in such a configuration     

Monolithically integrated InGaAsP/InP composite-cavity distributedfeedback lasers

Linewidth reduction to 1 MHz for monolithically integrated extended-cavity DFB lasers that are designed to achieve high optical coupling to a low-loss extended cavity is described. Since a high-efficiency extended cavity at the same time degrades the frequency-modulation (FM) response, an active gain section is integrated at the end of the extended cavity, and its use as a modulator section that maintains a flat FM response at 0.7 GHz/mA is shown. The linewidth and FM characteristics of this DFB extended-passive/active-cavity laser are compared to those of the conventional DFB extended-passive-cavity laser and a two-section DFB laser     

Transition to pulsed operation in short external-cavity FMsemiconductor lasers

Conditions are established for the occurrence of a transition from FM operation to pulsed output in short external-cavity FM semiconductor lasers. It is shown that there are dual operating points around which FM operation is possible. The position of the modulation frequency in relation to these two FM operating frequencies determines the type of behavior exhibited by the configuration. In particular, pulsed and mixed pulsed-FM behavior is observed when the modulation frequency is between the two possible FM operating frequencies     

FM noise in a Gunn-effect oscillator

FM noise in a cavity-controlled Gunn oscillator is investigated both theoretically and experimentally. The susceptance of a GaAs Gunn diode fluctuates following velocity fluctuations of high field domains. This results in FM noise. The fluctuations of the velocity are considered to be due mainly to those of carrier concentration fluctuations. Measured FM noise is in good agreement with the model, verifying that fluctuations of carrier concentration result in FM noise in the oscillator. When the quality factor Qexof the resonant cavity used becomes large, the FM noise characteristic deviates from the theoretical one based on the fluctuations of carrier concentration. The fluctuations of the voltage across the diode in the resonant cavity also influence the domain dynamics and hence the diode susceptance. These seem to be causes of the deviation.     

Cavity Stabilized X-Band Gunn Oscillator

The design and resultant experimental investigation of a pulling mechanism for a highly stable X-band Gunn oscillator, stabilized by a high Q TE/sub 011/-mode reflection cavity, are described. The oscillator shows a temperature coefficient of less than -7 x 10/sup -7/ / /spl deg/C,a low FM noise of 8 Hz per 1-kHz BW at 100 kHz from the carrier, and a wide-band mechanical-tuning capability of several hundred megahertz. In addition, experimental results concerning the hysteresis phenomena of oscillating frequencies, power, FM-noise versus cavity-pulling frequencies, and bias voltages are described.     

A new LMS-based Fourier analyzer in the presence of frequency mismatch and applications

The performance of the conventional least mean square (LMS) Fourier analyzer may degenerate significantly, if the signal frequencies given to the analyzer are different from the true signal frequencies. This difference is referred to as frequency mismatch (FM). We first analyze the performance of the conventional LMS Fourier analyzer for a single sinusoid in the presence of FM. We derive the dynamics and steady-state properties of this analyzer as well as the optimum step size parameter which minimizes the influence of the FM. Extensive simulations reveal the validity of the analytical results. Next, a new LMS-based Fourier analyzer is proposed which simultaneously estimates the discrete Fourier coefficients (DFCs) and accommodates the FM. This new analyzer can very well compensate for the performance degeneration due to the FM. Applications to estimation/detection of dual-tone multiple frequencies (DTMF) signals and analysis of real-life noise signals generated by a large-scale factory cutting machine are provided to demonstrate the excellent performance of our new Fourier analyzer.     

The high-speed limit of FM response in semiconductor lasers

The high-speed frequency modulation (FM) response has been investigated through rate equation analysis. The intrinsic limit of FM response has been found to be given by the product of FM efficiency, η_FM, and the FM bandwidth, B. This relation shows that a wide FM bandwidth means a small FM efficiency. Although the FM efficiency changes with the differential gain or the nonlinear gain coefficient, η_FMB is almost constant. The value of η _FMB was about 5 GHz²/mA for 1.5-μm InGaAsP/InP lasers with 300-μm cavity length. This limit has been confirmed experimentally     

Performance of P-type epitaxial silicon millimeter-wave IMPATT diodes

A series of p-type IMPATT diodes (p⁺pn⁺) have been fabricated from epitaxially grown silicon for operation as oscillators at Ka-band frequencies. A maximum CW output power level of 700 mW at 29.6 GHz, a maximum conversion efficiency of 10.9 percent, and a minimum FM noise parameter, M, of 25 dB have been measured on this series of p-type diodes. A diode oscillating in a variable height radial disk cavity was frequency tuned from 27.5 to 40 GHz, covering the entire Ka-band, with a 1.4 dB power variation over the tuning range. The minimum CW output power of this tunable oscillator was 360 mW at 6.5 percent efficiency.     

调频信号的数字合成方法

调频信号作为一种常见信号在电子技术的各个领域，特别是通信领域有着广泛的应用。因此调频信号的合成就成为了其中关键性的一项技术。传统的调频信号通常是通过模拟方法合成的。但是模拟合成有频率不稳定、参数设置不可量化等缺点，而用数字合成的方法就可以解决这些问题。数字频率合成通常采用DDS技术，调频信号的数字合成也基于这项技术。本文首先介绍了DDS的基本原理。然后提出用双DDS结构实现调频信号数字合成的方法。由于把调制波形的幅度量化成了频率字，构成了一个输出频率字的DDS。因此只要改变这个DDS波形RAM中的数据。就可以产生任意以周期信号为调制波形的调频信号，并且调制频率和深度都精确可调。     

Determination of Equivalent Circuit Parameters Describing Noise from a Gunn Oscillator

The AM and FM fluctuations in an oscillator output are originated from impedance fluctuation in low frequencies (baseband noise) and voltage or current fluctuation in the vicinity of the carrier frequency (RF noise). In this paper, from newly defined "complex correlation coefficient between AM and FM noises," contributions of baseband and RF noises to the AM and FM noises are determined. Examples of data for X-band Gunn oscillators show that both the AM and FM noises are mainly caused by the baseband noise in the vicinity of the carrier frequency (within 1-kHz band), whereas they are mainly due to the RF noise at frequencies further than 10 kHz from the carrier frequency.     

Enhanced AM and FM modulation response of complex coupled DFBlasers

Significant improvements in the small AM bandwidth and FM efficiency of a DFB laser are obtained by introducing a carrier dependent complex coupling coefficient. A simulation using a large-signal dynamic model shows that the 3-dB cutoff frequencies for AM can be increased by factors of three by having the index and gain coefficients in antiphase. In contrast, the efficiency of FM, at low frequencies, can be similarly improved if the index and gain coupling are in phase     

A method for calculating distortion of an FM signal by a passivenetwork

Linear passive networks cannot manufacture RF signals but they can accord a different treatment to signals of different frequencies, and it is this property which enables some of them to modify an FM signal in a way which results in apparent addition of harmonics and crossmodulation products of the baseband frequencies. The author attempts to show how this comes about and to provide ways of calculating the magnitudes of the various modulation byproducts which can be added to an FM signal by a given passive network     

FM response of narrow-linewidth, multielectrode λ/4 shiftDFB laser

Flat FM response from 100 kHz to 15 GHz was achieved in a multielectrode distributed-feedback (DFB) laser. A λ/4-shifted corrugation and a 1200-μm-long cavity were very effective not only in reducing the linewidth to less than 1 MHz, but also in making FM response flat by selective current injection     

AM and FM Noise of BARITT Oscillators

AM, FM, and baseband noise of a BARITT diode oscillator in the range 100 Hz-50 kHz off the carrier has been measured under various operating conditions. A simple calculation has been made, relating the baseband noise to the oscillator AM and FM noise via measured amplitude and frequency modulation sensitivities and the results have been compared with the noise measured. It is shown that, depending on the bias current applied, both AM and FM noise performance can be degraded by up-conversion. Complete removal of up-converted noise requires a high-impedance low-noise bias supply since both the diode noise and bias supply noise at baseband frequencies may be significant when up-converted. Even with all modulation suppressed, the AM and FM noise has a flicker component almost completely correlated with the diode flicker noise at baseband frequencies. The RF power dependence of the AM and FM noise has also been investigated. It is shown that the BARITT oscillator noise compares very favorably with that of IMPATT's and TEO's. Values of -142 dB/100 Hz (AM noise) and 3.5 Hz/(100 Hz)/sup 1/2/ for Q/sub ext/ = 200 (FM noise) have been measured at 30 kHz off the carrier.     

基于FP-LD实现副载波信号产生

采用一种基于法布里-珀罗腔激光二极管(FP-LD)的副载波信号的产生方案,此方案主要包括一个FP-LD和一个电光相位调制器(PM)。首先利用可调谐激光器、电光PM及微波源产生光正弦相位调制信号,将该信号注入到FP-LD中,通过FP-LD的注入锁定将该信号转换为副载波信号。在实验中,分别以2、3、4和5 GHz的调制频率注入到FP-LD中,相应得到22、21、24和25 GHz的副载波信号。     

一种合成孔径激光雷达激光器带宽测量新方法

提出一种合成孔径激光雷达(SAL)调频激光器带宽测量的新方法。使用法布里-珀罗(F-P)扫描共焦腔,对调频He-Ne激光器的带宽进行测量,结果表明,在测量激光器的调频带宽时不受调频速率的限制,可以实现对SAL系统调频激光器的带宽测量。