Real-time wavelength reuse based on Bragg trans-reflection for dynamic reference frequency and data transfer in Datacom

ABSTRACT

We experimentally demonstrate the first VCSEL-based all-optical wavelength reuse technique with reconfigurable fibre Bragg grating add and drop multiplexer. EDFA gain saturation and Bragg trans-reflection effect on a single FBG are respectively, adopted for full-duplex reference frequency and data transfer. A 1550 nm energy-efficient VCSEL is modulated with 1.7?GHz clock signal and transferred downstream over 26.6?km fibre OLT attain a phase noise stability of ?54.01 dBc/Hz at 10?kHz offset frequency. A saturated EDFA is exploited to optically reduce the peak-to-peak voltage of the incoming downstream RF, allowing for wavelength reuse with 10?Gbps upstream data. A 1.57 dB transmission penalty is incurred over the transmission fibre. An all-passive OADM is developed exploiting Bragg trans-reflection at 1549.45?nm. The reflected wavelength is routed over another 24.7?km fibre network attaining an extinction ratio of 6.1?dB and a SNR of 5.8?dB. This work provides an all-optical technique for routing and spectral management in flexible networks.     

Microwave interferometry: application to precision measurements and noise reduction techniques

A concept of interferometric measurements has been applied to the development of ultra-sensitive microwave noise measurement systems. These systems are capable of reaching a noise performance limited only by the thermal fluctuations in their lossy components. The noise floor of a real time microwave measurement system has been measured to be equal to -193 dBc/Hz at Fourier frequencies above 1 kHz. This performance is 40 dB better than that of conventional systems and has allowed the first experimental evidence of the intrinsic phase fluctuations in microwave isolators and circulators. Microwave frequency discriminators with interferometric signal processing have proved to be extremely effective for measuring and cancelling the phase noise in oscillators. This technique has allowed the design of X-band microwave oscillators with a phase noise spectral density of order -150 dBc/Hz at 1 kHz Fourier frequency, without the use of cryogenics. Another possible application of the interferometric noise measurements systems include “flicker noise-free” microwave amplifiers and advanced two oscillator noise measurement systems     

Broad tuning ultra low phase noise dielectric resonator oscillators using SiGe amplifier and ceramic-based resonators

This paper describes the design of very low noise, tunable, X-band dielectric resonator oscillators (DROs) demonstrating phase-noise performance of -135 dBc/Hz at 10 kHz offset. SiGe transistors are used for the oscillator sustaining amplifiers that offer a circulating power of 12 dBm and a gain of 5.4 dB per stage as well as a low flicker noise corner of 40 kHz. A variety of resonator configurations utilising BaTiO₃ resonators are presented demonstrating unloaded Qs from 10 000 to 22 000. These resonators are optimised and coupled to the amplifiers for minimum phase noise where Q_L/Q₀ = 1/2, and hence S₂₁ = -6 dB. To incorporate tuning with low additional phase noise, a phase shifter is also investigated. The theory for the low noise oscillator design is included; experimental results demonstrate close correlation with the theory.     

Application of Bragg grating sensors in the characterization of scaled marine vehicle models

Experiments using two different fiber-optic Bragg grating strain sensor systems to measure dynamic loads, slamming forces, and bending moments on a scaled catamaran model are reported. The system designed to measure slamming forces is based on dynamic locking of the laser diode wavelength to the peak wavelength of a Bragg grating mounted in a force cell. The sensor system has a dynamic range of 27 dB (1-550 N) and a bandwidth in excess of 1 kHz. For the measurement of bending moments, a time-domain multiplexing system, which used a unique pulsed rf modulation technique, of two Bragg grating sensors mounted on a steel beam was designed. The dynamic range of this system was also 27 dB [17 Nm (Newton meter) with a 0.03-Nm resolution]. The bandwidth was limited to approximately 50 Hz.     

All-fiber dynamic gain equalizer based on a twisted long-period grating written by high-frequency CO2 laser pulses

A novel dynamic gain equalizer for flattening Er-doped fiber amplifiers based on a twisted long-period fiber grating (LPFG) induced by high-frequency CO(2) laser pulses is reported for the first time to our knowledge. Experimental results show that its transverse-load sensitivity is up to 0.34 dB/(g.mm(-1)), while the twist ratio of the twisted LPFG is approximately 20 rad/m, which is 7 times higher than that of a torsion-free LPFG. In addition, it is found that the strong orientation dependence of the transverse-load sensitivity of the torsion-free LPFG reported previously has been weakened considerably. Therefore such a dynamic gain equalizer based on the unique transverse-load characteristics of the twisted LPFG provides a much larger adjustable range and makes packaging of the gain equalizer much easier. A demonstration has been carried out to flatten an Er-doped fiber amplifier to +/-0.5 dB over a 32 nm bandwidth.     

Residual phase noise measurements of VHF, UHF, and microwavecomponents

The results of residual phase noise measurements on a number of VHF, UHF, and microwave amplifiers, both silicon (Si) bipolar junction transistor (BJT) and gallium arsenide (GaAs) field effect transistor (FET) based, electronic phase shifters, frequency dividers and multipliers, etc., which are commonly used in a wide variety of frequency source and synthesizer applications are presented. The measurement technique has also been used to evaluate feedback oscillator components, such as the loop and buffer amplifiers, which can play important roles in determining an oscillator's output phase noise spectrum (often in very subtle ways). While some information has previously been published related to component residual phase noise properties, it generally focused on the flicker noise levels of the devices under test, for carrier offset frequencies less than 10 kHz. The work reported herein makes use of an extremely low noise, 500 MHz surface acoustic wave resonator oscillator (SAWRO) test source for residual phase noise measurements, both close-to-and far-from-the-carrier. Using this SAWRO-based test source at 500 MHz, we have been able to achieve a measurement system phase noise floor of -184 dBc/Hz, or better, for carrier offset frequencies greater than 10 kHz, and a system flicker phase noise floor of -150 dBc/Hz, or better, at 1 Hz carrier offset. The paper discusses the results of detailed residual phase noise measurements performed on a number of components using this overall system configuration. Several interesting observations related to the residual phase noise properties of moderate to high power RF amplifiers, i.e., amplifiers with 1 dB gain compression points in the range of +20 to +33 dBm, are highlighted     

Extremely low thermal noise floor, high power oscillators usingsurface transverse wave devices

This paper presents state-of-the-art results on 1-GHz surface transverse wave (STW) oscillators running at extremely high loop power levels. The high-Q single-mode STW resonators used in these designs have an insertion loss of 3.6 dB, an unloaded Q of 8000, a residual PM noise of -142 dBc/Hz at a 1-Hz carrier offset, and operate at an incident power of up to +31 dBm in the loop. Other low-Q STW resonators and coupled resonator filters (CRF), with insertion losses in the 5-9 dB range, can conveniently handle power levels in excess of two Watts. These devices were incorporated into voltage controlled oscillators (VCO's) running from a 9.6-V dc source and provide an RF output power of +23 dBm at an RF/dc efficiency of 28%. Their tuning range was 750 kHz and the PM noise floor was -180 dBc/Hz. The oscillators, stabilized with the high-Q devices and using specially designed AB-class power amplifiers, delivered an output power of +29 dBm and exhibited a PM noise floor of -184 dBc/Hz and a 1-Hz phase noise level of -17 dBc/Hz. The 1-Hz phase noise level was improved to -33 dBc/Hz using a commercially available loop amplifier. In this case, the output power was +22 dBm. In all cases studied, the loop amplifier was found to be the factor limiting the close-to-carrier oscillator phase noise performance     

Interface for MEMS-based rotational accelerometer for HDD applications with 2.5 rad/s/sup 2/ resolution and digital output

A 0.6 /spl mu/m BiCMOS interface for microelectromechanical systems (MEMS) based rotational accelerometers is presented. It is housed in an inexpensive standard SO-24 plastic package with a capacitive rotational accelerometer sensor produced using MEMS technology. This sensitive interface chip includes the analog-to-digital conversion, filtering, and interface functions. The analog-to-digital conversion is realized through a single-bit electromechanical /spl Sigma/-/spl Delta/ loop able to detect capacitive unbalancing as low as 50 aF (50/spl times/10/sup -18/ F). The produced bitstream is then processed by a digital chain and made available through a standard 3.3 V (5 V tolerant) three-wire serial bus. The signal bandwidth is about 800 Hz, the sensitivity is 2.5 rad/s/sup 2/, with a full-scale sinewave of 200 rad/s/sup 2/ and a signal-to-noise ratio peak of 38 dB over 30-800 Hz. Through the serial bus, it is also possible to program device characteristics including gain, offset, filter performance, and phase delay. The complete sensor is used in a feed-forward compensation scheme to cancel external disturbances acting on computer hard-disk drives so as to steadily keep the read-write heads on track: this allows greater track densities and better speed performance.     

宽带铋基掺铒光纤放大器增益及噪声特性研究

利用Er3 离子四能级结构速率方程组和光功率传输方程组,数值模拟了铋基掺铒光纤放大器(EDFA)的增益及噪声特性,模拟结果与实验报道结果取得了很好的一致。同时,详尽地分析了增益及噪声特性与光纤长度、泵浦功率和输入信号功率的关系,优化了放大器的性能,从理论上得出一个20dB增益带宽达76nm、噪声系数接近4dB的铋基EDFA。研究表明了铋基掺铒光纤放大器适合用作于现代DWDM系统中C L波段的光纤放大器。     

An Active-Filter Device for Extreme Selective Measurements at Low Frequencies

This paper describes the systematic development of an active filter destined for the extreme selective balancing of a low-frequency ac bridge. The power voltage with the frequency of 50 Hz and its higher harmonics were to be suppressed, the measurement voltage with the frequency of 190 Hz was to be amplified. The filter device makes use of the twin-T RC network in connection with operational amplifiers in a manifold way. A theoretical consideration of the stability of an elementary filter circuit is given. The signal (190 Hz) to noise (50 Hz) ratio of the whole filter device is greater than 160 dB.     

Variable-sampling-rate sigma-delta modulator for instrumentationand measurement

We have designed, built, and tested a second-order, variable-sampling-rate, sigma-delta analog-to-digital converter (ADC) which operates over an input frequency range from 1 Hz to 8 kHz. Experimental results show that this circuit performs well and maintains the same signal-to-noise ratio over an input frequency range from 1 Hz to 1 kHz although it was built with individually packaged operational amplifiers and analog switches. For input frequencies above 1 kHz the circuit still performs well, but the signal-to-noise ratio varies with input frequency     

On the flicker noise of ferrite circulators for ultra-stable oscillators

The flicker noise of the ferrite circulator is a critical element in ultra-stable microwave oscillators, in which the signal reflected from the input of the reference cavity is exploited to stabilize the frequency. This paper explains why the circulator noise must be measured in isolation mode, proposes a measurement scheme, and provides experimental results. The observed flicker spans from -162 to -170 dB[rad2]/Hz at 1 Hz off the 9.2 GHz carrier, and at +19 dBm of input power. In the same conditions, the instrument limit is below -180 dB[rad2]/Hz. Experiments also give information on the mechanical stability of the microwave assembly, which is in the range of 10(-11) m. The measurement method can be used as the phase detector of a corrected oscillator; and, in the field of solid-state physics, it can be used for the measurement of random fluctuations in magnetic materials.     

The Direct-Detection Noise-Measuring System and Its Threshold

This paper describes a typical direct-detection noise-measuring system, with particular attention given to the use of Schottky-barrier diodes as envelope detectors. The rise of threshold at low modulation frequencies encountered in these systems has been found to be mainly attributable to FM-to-AM conversion occurring in comparatively narrow-band detectors rather than to diode-flicker noise and thus is largely removable. A sensitivity improvement of 10-20 dB may result at low frequencies, yielding a noise-to-carrier ratio threshold range of about -150 to -155 dB/100 Hz at modulation frequencies from 100 Hz to 50 kHz for measurements of AM noise, and below 0.01 Hz/100 Hz for FM noise, of microwave oscillators at C band.     

Wide-band flat-gain optical amplifier using Hafnia and zirconia erbium co-doped fibres in double-pass parallel configuration

ABSTRACT

A new compact and wide-band erbium-doped fibre amplifier (EDFA) was demonstrated by combining Hafnia-bismuth Erbium co-doped fibre (HB-EDF) and zirconia–yttria–aluminum Erbium co-doped fibre (Zr-EDF) as a hybrid gain medium, in parallel double-pass configuration. The proposed amplifier comprises a 0.5?m long HB-EDF and 4?m long Zr-EDF optimized for C- and L-band operations, respectively. The HB-EDF and Zr-EDF has erbium ion concentration of 12,500?ppm and 2800?ppm, respectively. At -10 dBm input signal, a wide-band flat gain of 15.7?dB is achieved with gain fluctuation of less than 1.5?dB within a wavelength region from 1525 to 1600?nm. Compared to same configuration of HB-EDF and Zr-EDF amplifiers which are using two pieces of HB-EDF and Zr-EDF, respectively with the same total amount of erbium ions, the proposed EDFA with hybrid gain medium provides even better performances in term of flat gain, bandwidth and noise figure.     

A Test Set for the Accurate Measurement of Phase Noise on High-Quality Signal Sources

The test set described here is capable of measuring the spectral density of phase noise on carrier frequencies from 1 to 500 MHz, for offset frequencies from 20 Hz to 50 kHz. Measurements to 50 MHz are described. The test set has a residual single-sideband phase-noise-power-to-signal-power ratio of -142 dB/Hz at 20 Hz offset from the carrier, which decreases to a floor of -172 dB/Hz at offset frequencies greater than 5 kHz. The estimated calibration accuracy achievable is ±0.8 dB, exclusive of random reading errors due to the Gaussian distribution of the phase fluctuations being observed. The estimated 1 ? repeatability of a measurement is 0.7 dB (70 percent of the observations on a given test will fall within ±0.7 dB of the average value). This test set is capable of characterizing the phase-noise performance of existing atomic frequency standards, crystal oscillators, frequency synthesizers, and other high-quality sources more accurately than has previously been possible. The increased accuracy has been achieved by a system design that minimizes readout fluctuations, allows for the accurate measurement of correction factors used to reduce systematic errors, and minimizes the possibility of operator error and bias.     

Reduced transposed flicker noise in microwave oscillators using gaas-based feedforward amplifiers

Transposed flicker noise reduction and removal is demonstrated in 7.6 GHz microwave oscillators for offsets greater than 10 kHz. This is achieved by using a GaAs-based feedforward power amplifier as the oscillation-sustaining stage and incorporating a limiter and resonator elsewhere in the loop. 20 dB noise suppression is demonstrated at 12.5 kHz offset when the error correcting amplifier is switched on. Three oscillator pairs have been built. A transmission line feedback oscillator with a Qo of 180 and two sapphire-based, dielectric resonator oscillators (DROs) with a Qo of 44,500. The difference between the two DROs is a change in the limiter threshold power level of 10 dB. The phase noise rolls-off at (1/f)(2) for offsets greater than 10 kHz for the transmission line oscillator and is set by the thermal noise to within 0-1 dB of the theoretical minimum. The noise performance of the DROs is within 6-12 dB of the theory. Possible reasons for this discrepancy are presented.     

1/f frequency noise of 2-GHZ high-Q thin-film sapphire resonators

We present experimental results on intrinsic 1/f frequency modulation (FM) noise in high-overtone thin-film sapphire resonators that operate at 2 GHz. The resonators exhibit several high-Q resonant modes approximately 100 kHz apart, which repeat every 13 MHz. A loaded Q of approximately 20000 was estimated from the phase response. The results show that the FM noise of the resonators varied between S_y (10 Hz)=-202 dB relative (rel) to 1/Hz and -210 dB rel to 1/Hz. The equivalent phase modulation (PM) noise of an oscillator using these resonators (assuming a noiseless amplifier) would range from L(10 Hz)=-39 to -47 dBc/Hz     

A Frequency Synthesizer for 10/2? kHz

A sinusoidal voltage source of frequency nominally 10/2? kHz (? = 104 rad/s) is derived from a 5-MHz standard. Digital counters are used to generate the required frequency, which differs from 10/2? kHz by less than 2 parts in 108, and is as stable as the standard. Using a crystal filter and low-distortion amplifiers, an output of 10 V rms with total harmonic distortion less than 1 part in 103 is obtained.     

A piezoelectric, flexural-disk, neutrally buoyant, underwater accelerometer

A piezoelectric, flexural-disk accelerometer for underwater use is composed of two PZT-5A lead zirconate-titanate disks that are bonded to an aluminum substrate. The substrate is edge-supported inside an aluminum housing. The housing is enclosed in syntactic foam so that the sensor is neutrally buoyant. The overall height is 1.0 in. (26 mm), the overall diameter is 1.9 in. (49 mm), and the total mass is 0.054 kg. With 25 ft (7.6 m) of (230 pF/m) cable attached, the sensitivity is -42 dB re 1 V-s(2)/m (-22 dB re 1 V/g), the capacitance is 5.0 nF, and the resonance frequency is 11 kHz. When used in conjuction with a Micro Networks MN3210 preamplifier, the spectral noise-equivalent acceleration floor is approximately -171 dB re 1 m/s(2)- radicalHz (-151 dB re 1 g/ radicalHz) at 5 kHz.     

Spectroelectrochemical sensing based on multimode selectivity simultaneously achievable in a single device. 16. Sensing by fluorescence

A fluorescence spectroelectrochemical sensor capable of detecting very low concentrations of metal complexes is described. The sensor is based on a novel spectroelectrochemical sensor that incorporates multiple internal reflection spectroscopy at an optically transparent electrode (OTE) coated with a selective film to enhance detection limits by preconcentrating the analyte at the OTE surface. Nafion was used as the selective cation exchange film for detecting Ru(bpy)(3)(2+), the model analyte, which fluoresces at 605 nm when excited with a 441.6-nm HeCd laser. The unoptimized linear dynamic range of the sensor for Ru(bpy)(3)(2+) is between 1 x 10(-)(11) and 1 x 10(-)(7) M with a calculated 2 x 10(-)(13) M detection limit. The sensor employs extremely thin films ( approximately 12 nm) without significantly sacrificing its sensitivity. The sensor response is demonstrated with varying film thicknesses. A state-of-the-art flow cell design allows variable cell volumes as low as approximately 4 microL. Fluorescence of the sample can be controlled by electromodulation between 0.7 and 1.3 V. Sensor operation is not reversible for the chosen model film (Nafion) and sample (Ru(bpy)(3)(2+)) but it can be regenerated with ethanol for multiple uses.