Electrical Spectrum Analyzer Research Articles

Mode coherence measurements across a 15 THz spectral bandwidth of a passively mode-locked quantum dash laser

The mode coherence of adjacent and non-adjacent spectral modes of a passively mode locked quantum dash (QDash) semiconductor laser are deduced through radio frequency beat-tone linewidth measurements. A wavelength conversion scheme that uses degenerate four wave mixing in a semiconductor optical amplifier is proposed which considerably extends the mode spacing beyond the limit imposed by conventional fast-photodetection and electrical spectrum analysis of around 100 GHz. Using this scheme, the mode coherence of the QDash laser was measured out to the thirty-first harmonic, or a mode separation of 1.5 THz.

Multipath interference test method using synthesized chirped signal from directly modulated DFB-LD with digital-signal-processing technique

We propose a method of testing transmission fiber lines and distributed amplifiers. Multipath interference (MPI) is detected as a beat spectrum between a multipath signal and a direct signal using a synthesized chirped test signal with lightwave frequencies of f(1) and f(2) periodically emitted from a distributed feedback laser diode (DFB-LD). This chirped test pulse is generated using a directly modulated DFB-LD with a drive signal calculated using a digital signal processing technique (DSP). A receiver consisting of a photodiode and an electrical spectrum analyzer (ESA) detects a baseband power spectrum peak appearing at the frequency of the test signal frequency deviation (f(1)-f(2)) as a beat spectrum of self-heterodyne detection. Multipath interference is converted from the spectrum peak power. This method improved the minimum detectable MPI to as low as -78 dB. We discuss the detailed design and performance of the proposed test method, including a DFB-LD drive signal calculation algorithm with DSP for synthesis of the chirped test signal and experiments on single-mode fibers with discrete reflections.

Enhanced optical single sideband modulation based on fiber nonlinearity

AbstractWe propose an optical single sideband (OSSB) modulation scheme using stimulated Brillouin scattering (SBS) in fiber to achieve OSSB modulation. Drive with 10.87‐GHz radio frequency signal into Mach–Zehnder modulator (MZM). Because of the SBS effect, lower sideband of modulated signal is amplified and upper sideband is attenuated as well. By properly adjust the phase shifter for phase difference between the two paths of electrical signal. Output signal is OSSB format, after 25‐km SMF transmission, we can observe good system performances including sideband power ratio and phase noise using by an optical spectrum analyzer and an electrical spectrum analyzer. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2730–2733, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26388

Fiber Ring Laser Sensor for Temperature Measurement

A novel multi-longitudinal-mode fiber ring laser temperature sensor based on the beat frequency demodulation technology is presented. The beat frequency between any two modes varies linearly with the temperature. It is experimentally demonstrated that the temperature can be measured with a sensitivity of 10.24 kHz/° C @ 1581.7 MHz between 21° C to 50 ° C, 7.42 kHz/° C @ 1175.6 MHz between 22 °C to 240 °C and 8.48 kHz/° C @ 1480.5 MHz between 100 °C to 1000 °C. This method offers a simple scheme for fiber temperature sensing by employing a low-frequency electrical frequency spectrum analyzer.

Semiconductor optical amplifier-based heterodyning detection for resolving optical terahertz beat-tone signals from passively mode-locked semiconductor lasers

An all-optical heterodyne approach based on a room-temperature controlled semiconductor optical amplifier (SOA) for measuring the frequency and linewidth of the terahertz beat-tone signal from a passively mode-locked laser is proposed. Under the injection of two external cavity lasers, the SOA acts as a local oscillator at their detuning frequency and also as an optical frequency mixer whose inputs are the self-modulated spectrum of the device under test and the two laser beams. Frequency and linewidth of the intermediate frequency signal (and therefore, the beat-tone signal) are resolved by using a photodiode and an electrical spectrum analyzer.

Analysis of a narrowband terahertz signal generated by a unitravelling carrier photodiode coupled with a dual-mode semiconductor Fabry–Pérot laser

A narrowband terahertz signal generated by a unitravelling carrier photodiode (UTC-PD) interfaced with a dual-mode Fabry–Pérot laser diode is demonstrated. A beat tone corresponding to the free spectral range is generated on the UTC-PD, and radiated by a transverse-electromagnetic-horn antenna. A terahertz signal at a frequency of 372 GHz, featuring a linewidth of 17 MHz is recorded by a subharmonic mixer coupled to an electrical spectrum analyzer. All components involved in this experiment operate at room temperature. The linewidth and the frequency of the emitted terahertz wave are analyzed, along with their dependency on dc-bias conditions applied to laser diode.

Aerosol electrical mobility spectrum analyzer

An aerosol electrical mobility spectrum analyzer (AEMSA) that consists of saturator, mobility analyzer, condenser, and position detector is newly devised. This device can detect charged particle electrical mobility spectrum regardless of its polarity without electrical scanning procedure in nanometer size range. The performance of AEMSA is tested with equilibrium charging state particles using soft X-ray neutralizer and Am 241 radioactive source and compared with the approximated Fuchs model ( Wiedensohler, 1988) and Boltzmann prediction. The result shows the approximated Fuchs model predicts better for neutralized nano-particles.

Quantitative Study of Optical Frequency Noise to Intensity Noise Conversion in Line-by-Line Pulse Shaping

We report the first quantitative study of intensity noise induced in line-by-line pulse shaping in response to time-varying changes in the comb frequency offset. Controllable comb linewidth broadening is synthesized through frequency dithering of a continuous-wave laser that is fed to a phase modulator. An electrical spectrum analyzer is used to examine the current power spectra of shaped time-domain intensity waveforms subject to comb frequency noise. A theoretical model predicting a 20 dB/decade scaling relation between the dither-induced noise and the frequency dither amplitude is presented. A numerical simulation method capable of predicting the precise form of the RF power spectrum in the presence of optical frequency dithering is explained. Two line-by-line shaping cases are considered in detail. Experimental data are in excellent agreement with the simulated results down to frequency dithers of a few tenths of a percent of the comb spacing. Tolerances to laser frequency fluctuations are given for several simple pulse shaping examples. The effect of pulse shaper parameters is also discussed.

Experimental study of a semiconductor laser diode having a Mach–Zehnder interferometer in the cavity

The performance of a semiconductor laser diode that has an asymmetric Mach–Zehnder interferometer all-optical switch in the cavity has been studied experimentally. This novel device was designed to be free from clock pulse insertion, since mode-locked optical pulses are generated internally and change the balance of the interferometer periodically. The device was fabricated using a InGaAsP/InP buried heterostructure and the primary optical properties of the device were investigated. Lasing characteristics that were peculiar to the twin-cavity structure were observed, i.e., continuous-wave lasing power oscillation in relation to the injection current balance between the two arms, and cyclic changes in the single/multiple emission peaks as a function of bias voltage at the saturable absorber. Electrical spectrum analysis indicated 40 GHz modulation of lasing output from the twin-cavity laser.

Measurement and System Impact of Multipath Interference From Dispersion Compensating Fiber Modules

Dispersion compensating modules (DCM) are key components in long distance and high-speed fiber-optic transmission systems. However, many types of DCMs exhibit multipath interference (MPI) that acts as noise in transmission and degrades the bit error rate of the system. Further, MPI generated in DCMs is mostly due to forward scattering and mostly of the coherent type. This type of MPI cannot be correctly measured using conventional measurement techniques that use electrical spectrum analysis to measure post-detection noise. We demonstrate an accurate and simple method of MPI measurement using a swept wavelength system apparatus. We discuss the strengths and limitations of this measurement method and show system results of Q penalty due to MPI from concatenated DCMs.

A novel chromatic dispersion measurement method in frequency domain using a multi-wavelength optical pulse train generated by Fabry–Perot laser diode

We propose and demonstrate a simple and robust measurement method for the chromatic dispersion of single mode fibers. Multi-wavelength picosecond optical pulse train from a gain-switched Fabry–Perot laser diode in conjunction with the highly dispersive fiber is used for multi-wavelength light source. The frequency of the separated pulse train may suffer a frequency change in dispersive optical fiber, which can be measured very accurately by an electrical spectrum analyzer. This method was applied to measure the chromatic dispersion of the standard single mode fiber for various lengths. The measured chromatic dispersion of a standard single mode fiber was 17.60 ps/nm/km at 1561 nm with an experimental standard deviation of 0.20 ps/nm/km and time resolution was less than 0.18 ps. The measurement setup is compact and economical compared to conventional methods. This technique can be applied in both long and short lengths (∼50 m) of fibers with very high accuracy.

Low-noise amplification under the 3 dB noise figurein high-gain phase-sensitive fibre amplifier

A noise figure which is less than the standard quantum limit of 3 dB has been observed for the first time in a high gain phase-sensitive fibre parametric amplifier. A noise figure of 1.8 dB with a 16 dB signal gain was measured by a precisely calibrated electrical spectrum analyser.

Characterization of Pacemaker Electrode Surfaces Utilizing Scanning Electron Microscopy (SEM) and In-Vitro Electrochemical Analysis

The efficiency of implantable electrodes for cardiac pacing depends on the ratio of the conductive surface area to the geometric area of the interface with excitable tissue. New models of heart pacers require reduction of post-pulse polarization, i.e. the potential left on the electrode / tissue interface after a pacemaker pulse. Increasing the conductive surface area is an effective method to this end. Microscopy provides an important tool in elucidating the role of surface structure in electrode performance.Three different surface textures were characterized on a 90% platinum(Pt)/10% iridium (Ir) polished electrode substrate of roughly 5 mm2 geometric surface area. These consisted of the polished substrate itself, a thin film of textured platinum in the 1-3 micron size range, and a sub-micron platinum black coating. Sample surface effects were characterized via scanning electron microscopy (SEM), in-vitro electrical impedance spectrum analysis, and polarization after-potential measurements.

Experimental demonstration of noise figure reduction caused by nonlinear photon statistics of saturated EDFA's

For the first time, experimental evidence is presented for the prediction that the noise figure for an EDFA in the nonlinear or saturated regime, calculated by measuring the ASE power, can lead to an overestimation when compared to a direct measurement of the noise variance with an electrical spectrum analyzer. These results are in line with theories based on the quantum mechanical photon master equation describing an optical amplifier with saturated upper and lower ion inversion levels.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Chirping characteristic and frequency response of MQW optical intensity modulator

The spectral linewidth enhancement factor and frequency responses of electro-absorption-type optical-intensity modulators, especially InGaAs/InAlAs MQW modulators, are described. A method of exactly estimating the value of the alpha factor is presented under the nonlinearity of extinction-ratio characteristics. For measuring the frequency response of modulators, the sideband strength of the modulated output light with an optical spectrum analyzer, is analytically compared with the microwave power of photodiode direct detection with an electrical spectrum analyzer. >

Wavelength dependences of Brillouin frequency shifts of optical fibres in 1.55 μm wavelength region

The Brillouin frequency shifts of three types of optical fibres are measured by the heterodyne method using an electrical spectrum analyser. Owing to its excellent resolution, a change of 10 MHz in the Brillouin frequency shift, which corresponds to a change of the order of 1 nm in pump wavelength, can be easily measured. The longitudinal acoustic velocities of different fibre types can be deduced. The results also confirm that the frequency shift (10 GHz) varies inversely to the wavelength and decreases with an increase of GeO2 doping concentration.

Bovine serum albumin adsorption on a water/nitrobenzene interface

The electrochemical properties of an interface between two immiscible solutions of electrolytes are investigated as the interface is altered by adsorption of the water soluble protein bovine serum albumin. Cyclic voltammetry and electrical impedance spectrum analysis are employed as the tools of this study. The impedance behavior in the presence of bovine serum albumin shows that the protein macromolecule is adsorbed at the interface. The imaginary impedance of the interface increases with increasing concentration of bovine serum albumin to about 10 ppm, suggesting that the adsorbed monolayer forms gradually, which causes the interfacial capacitance to decrease. The impedance behavior has been analyzed as a function of applied interfacial potential. The potential of zero charge of the interface was obtained for different concentrations of bovine serum albumin. The impedance behavior is further discussed as a function of pH and temperature.

Bovine serum albumin adsorption on a water / nitrobenzene interface

The electrochemical properties of an interface between two immiscible solutions of electrolytes are investigated as the interface is altered by adsorption of the water soluble protein bovine serum albumin. Cyclic voltammetry and electrical impedance spectrum analysis are employed as the tools of this study. The impedance behavior in the presence of bovine serum albumin shows that the protein macromolecule is adsorbed at the interface. The imaginary impedance of the interface increases with increasing concentration of bovine serum albumin to about 10 ppm, suggesting that the adsorbed monolayer forms gradually, which causes the interfacial capacitance to decrease. The impedance behavior has been analyzed as a function of applied interfacial potential. The potential of zero charge of the interface was obtained for different concentrations of bovine serum albumin. The impedance behavior is further discussed as a function of pH and temperature.

INSTABILITIES IN THE POWER SPECTRUM OF MODE-LOCKED SEMICONDUCTOR LASERS

Sideband instabilities in the intensity spectrum of synchronously mode-locked external cavity semiconductor lasers are investigated as a function of the cavity length and frequency detuning. A sideband spectrum with distinct narmw lines is observed in the optical power spectrum for modulation frequencies smaller than the inverse photon round trip time and is attributed to fr&quency and phase modulation of the modelocked pulse train. 1.INTRODUCTION: Mode-locking of semiconductor lasers has been widely used for the generation of coherent short light pulses on the picosecond and subpiposecond timescale applying either active, passive or hybrid mode-locking techniques. With purely active mode-locking coherent pulses with 5ps duration have been obtained /I/. Apart from its use as a source for very short light pulses the mode-locked laser may serve as a model system for the investigations on nonlinear dynamics and instabilities. We have performed systematic studies of the power spectrum of an actively modelocked semiconductor laser as a function of the detuning between the modulation frequency f and the inverse photon round trip time f . mod res 2.EXPERIMENTAL: We use an external cavity configuration (cavity length 1.87~1) with an one facet antireflection coated GaAs / (GaA1)As CSP laser (Hitachi HLP1400) in the experiments. The residual reflectivity of the coated facet 4 is smaller than 10 . An intracavity etalon (bandwidth 10nm) is employed for spectral bandwidth con(''present address : Research Institute for Technical Physics of the Hungarian Academy of Sciences. H-1325 Budapest. Hungary Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1988296 C2-406 JOURNAL DE PHYSIQUE trol and tuning. The cw threshold in the external cavity configuration is about the same as for the solitary laser (1~~=54.5mA) without antireflection coating. Mode-locking is achieved by modulating the prebiased diode ( I ~ ~ * I ~ ~ ) with the current pulses from a comb generator (HP33002A), which have a duration of 130ps and an amplitude of typically 15V at an impedance of 50 Ohms. The optical output was analyzed by a fast photodiode (risetime loops) and an electrical spectrum analyzer (DC-2GHz). HR Etalon MO ARcoated Laser APD ca.8OMHz 0.5 -1 W HP33002A HP33150A HLPUM) TEK4514 MSGllA Fig.l:Experimental setup. 3.RESULTS: Under optimum mode-locking conditions, fmod=fres=80MHz, the power spectrum consists of a series of equally spaced narrow lines of width 150kHz and signal to noise ratio 50dB at multiples of the modulation frequency fmodt indicating proper mode-locking. The power spectrum shows an unstructured noise band of width 13MHz for positive detuning (fmod-f >O). This broad noise band res is symmetric with respect to the inverse resonator round trip time fres9 independent on detuning. Its height and width are a measure for the amplitude and phase fluctuations in qualitative agreement with the results of mode-locked dye lasers /2/. Opposite, the power spectrum shows a characteristic structure of narrow sidebands (Fig.21, if the laser is detuned a few 10kHz to the negative side. This sideband structure is symmetric with respect to the modulation frequency fmod

Optical heterodyne (coherent) detection

The optical heterodyne principle is described and its history traced. Early hopes for optical communication by this technique were frustrated by problems of wavefront degradation and laser frequency instability. However, fiber optics has recently revitalized this as an attractive possibility. In the interim, many other successful applications have been found that exploit different advantages of the heterodyne principle. Several examples are described. A number of simple optical heterodyne experiments utilizing a HeNe laser and electrical spectrum analyzer are presented. Details are furnished concerning experimental requirements and special considerations for optical heterodyne detection.