Gain characteristics of coherent optical amplifiers using aMach-Zehnder interferometer with Kerr media

This paper investigates the gain characteristics of coherent optical amplifiers that amplify only one of two quadrature phase components in an input signal light according to the phase of pump light. It is constructed around a Mach-Zehnder interferometer with Kerr media. To heuristically obtain the design parameters of the coherent optical amplifier, small-signal analysis is adapted to the Mach-Zehnder interferometer with Kerr media. The theoretical results are then compared to experimental results and shown to agree well, which confirms the validity of this design approach. By utilizing low-loss and high-nonlinearity silica fiber as the Kerr medium and optimizing its length, a coherent optical amplifier is constructed that yields high-gain (up to 26 dB) operation     

RZ-DPSK OTDM demultiplexing using fibre optical parametric amplifier with clock-modulated pump

Optical demultiplexing for a 40 Gbit/s RZ-DPSK OTDM signal using a fibre optical parametric amplifier with a sinusoidal-clock-modulated pump is experimentally demonstrated. Less than 1.3 dB power penalty and around 30 dB gain are obtained for all four demultiplexed channels. Superior performance is obtained for the demultiplexed tributaries in RZ-DPSK OTDM systems compared with those in RZOOK OTDM.     

40-GHz mode-locked fiber-ring laser using a Mach-Zehnder interferometer with integrated SOAs

A 40-GHz mode-locked fiber-ring laser based on an optically controlled modulator is presented and analyzed in detail. The modulator is a monolithic InGaAsP-InP Mach-Zehnder interferometer with integrated semiconductor optical amplifiers, which allows optical pulse generation synchronized to an external optical clock pulse stream. The laser generates nearly transform-limited Gaussian pulses of 2.5-ps width and up to 9-mW mean output power with less than 130 fs of timing jitter, and it is wavelength tunable over more than 30 nm. The relationship between key laser parameters and the output pulse characteristics is analyzed experimentally and numerically. An improved cavity design permits the generation of shorter pulses of 1.0-ps width.     

Simultaneous dibit recovery of DQPSK signal using a single Mach-Zehnder interferometer

The dibit recovery of a differential quadrature phase shift keying (DQPSK) signal is demonstrated using a single Mach-Zehnder interferometer, containing a 1-bit delay, and a single balanced receiver. The electrical output levels of the balanced receiver are dependent upon the relative phase delay between the arms of the Mach-Zehnder interferometer. This characteristic is investigated, when the input signal is DQPSK modulated. It is also shown that with a certain amount of phase shift, the DQPSK signal can be converted into four different equally spaced electrical signal levels, with each decoded level representing one of the four possible dibits.     

40 Gbit/s all-optical demultiplexing using a monolithicallyintegrated Mach-Zehnder interferometer with semiconductor laseramplifiers

The authors demonstrate all-optical error-free demultiplexing of 10, 20 and 40 Gbit/s to 5 Gbit/s data signals by using a monolithically integrated Mach-Zehnder interferometer with two semiconductor laser amplifiers     

Experimental demonstration of pattern effect compensation using anasymmetrical Mach-Zehnder interferometer with SOAs

We propose an asymmetrical interferometer to compensate the pattern effect in semiconductor optical amplifier (SOA) as an inline amplifier in dense wavelength-division-multiplexing (DWDM) system. Experiments are demonstrated with a commercial integrated Mach-Zehnder interferometer (MZI)-SOA. The experiments showed that in a 16×10-Gb/s DWDM system, the power penalty induced by the SOA decreased from 6.8 to 0.9 dB by the interference at 1 mW input power, and the input power dynamic range of the SOA was efficiently extended     

Analysis of bulk material sensing using a periodically segmented waveguide Mach-Zehnder interferometer for biosensing

Analysis of a periodically segmented Mach-Zehnder interferometer (MZI), intended for use as a biosensor, was performed using a "modular block" algorithm. The theoretical sensitivity limit increases with the number of cycles but is limited by cumulative attenuation. The periodically segmented MZI was found to exhibit better sensitivity than alternative methods under the same working conditions. However, devices with a high number of cycles (>350) were found to be impractical due to high attenuation losses. A 48-cycle periodically segmented waveguide MZI, with a predicted sensitivity limit of /spl delta/n/sub min//spl sim/3.96*10/sup -5/, requires a shorter sensing length (0.24 mm) than that of alternative devices with similar sensitivity.     

A 90-GHz InP-HEMT lossy match amplifier with a 20-dB gain using a broadband matching technique

We demonstrated a 90-GHz InP-HEMT lossy match amplifier (LMA) with a 20-dB gain for the first time. The power consumption was 220 mW, which is the smallest ever reported for a broadband amplifier with a bandwidth of over 80 GHz. The amplifier acts as a C-R coupled amplifier in the low to medium frequency range and as an L-C match amplifier at high frequencies. This configuration provides both high gain and wide bandwidth. The key to achieving a bandwidth of over 80 GHz is broadband matching in the L-C match amplifier. In this paper, we propose a broadband matching technique with a low-Q network and describe the design guideline we used to get excellent performance.     

Theoretical and experimental investigation of a thin-film waveguide laser amplifier with a lossy cladding

In laser amplifiers using high gain materials such as dyes or semiconductors, the inherent broad-band amplified spontaneous emission (ASE) may strongly saturate the amplifier gain: this yields a severe limitation on the amplification of small signals. We show that this difficulty can be appreciably overcome in an optical waveguide amplifier with a lossy cladding. A theoretical analysis of gain saturation by the ASE noise in a lossy cladding waveguide amplifier is given, and the small-signal gain improvement is stressed. An experiment involving a metal-clad thin-film dye laser amplifier is reported, the results of which are in agreement with the theoretical predictions.     

Noise modeling in MESFET and HEMT mixers using a uniform noisy linemodel

The aim of this paper is to present a noise model which predicts the noise performance of MESFET and HEMT mixers. The conversion and noise correlation matrices of a FET mixer are calculated using a uniform nonlinear noisy active line concept to describe the FET. This calculation is based on a perturbation analysis of the large-signal noiseless steady state, making it a “microscopic nonlinear noise model”. This method is applied to the case of a hot HEMT gate mixer and we show that the theoretical results are in agreement with experimental data     

Continuous-wave fiber optical parametric amplifier with 60-dB gain using a novel two-segment design

We have obtained 60 dB of internal (ON-OFF) gain with a continuous-wave fiber optical parametric amplifier by using an isolator between two fiber segments to increase the pump stimulated Brillouin scattering threshold. Subdecibel penalties were measured for transmission of 10-Gb/s signals, with 35 dB of gain.     

Simultaneous all-optical inverted and noninverted wavelength conversion using a single-stage fiber-optical parametric amplifier

We have demonstrated, for the first time to our knowledge, simultaneous all-optical inverted and noninverted wavelength conversion by using a single-stage two-pump fiber-optical parametric amplifier with an extinction ratio between 7 and 14 dB over 24 nm.     

Noise analysis of a photoreceiver using a P-I-N and GaAs HBT distributed amplifier combination

A noise analysis for a common-collector-cascode traveling wave HBT preamplifier is developed. The photoreceiver, consisting of a P-I-N and GaAs HBT MMIC distributed amplifier, was implemented using Nortel's f/sub T/=70 GHz GaAs HBT process, is the first to have a P-I-N mounted on the MMIC chip. The P-I-N preamplifier, having a measured bandwidth of 22 GHz, displayed a measured average equivalent input noise current density of 24 pA//spl radic/Hz. Good agreement was obtained between the predicted and measured noise performance.     

Gain characteristics of a dual-pump fiber optical parametric amplifier with Raman effect

We investigate the pump-depleted model of a dual-pump fiber optical parametric amplifier(FOPA) with Raman effect.As bandwidth increases,the gain profile of the distorted FOPA would be impacted seriously.Under the widebands,especially when the pump separation is large,zero dispersion wavelength(ZDW) fluctuation is another factor which can not be neglected.Numerical simulations with these comprehensive factors are mainly analyzed to obtain their influence on gain characteristics.Saturated gain spectrum is also discussed in detail.     

Analysis of a microstrip crossover embedded in a multilayeredanisotropic and lossy media

The equivalent circuit and the scattering parameters of the orthogonal microstrip crossover discontinuity are determined by assuming that the conducting strips are embedded in a multilayered substrate which may contain both anisotropic dielectrics and materials with a nonnegligible conductivity. The equivalent circuit of the crossover is obtained in terms of the complex excess charge densities on the strips. These excess charge densities are computed by means of the Galerkin method in the spectral domain. Comparison is carried out with previously existing results for microstrip crossovers on lossless isotropic substrates and original results are presented for crossovers on anisotropic and lossy substrates     

Simultaneous measurement of temperature and refractive index based on a core-offset Mach-Zehnder interferometer cascaded with a long-period fiber grating

An all-fiber sensor based on a cascaded optical fiber device is proposed and demonstrated, and its sensor head is composed of a core-offset Mach-Zehnder interferometer(MZI) and a long-period fiber grating(LPFG). In the experiment, two dips shaped by the intermodulation between the interference fringe of MZI and the resonant wavelength of LPFG are monitored. Experimental results show that temperature sensitivities of two dips are 0.060 7 nm/°C and 0.056 3 pm/°C, and the refractive index(RI) sensitivities are –18.025 nm/RIU and –55.06 nm/RIU, respectively. The simultaneous measurement of the temperature and external RI is demonstrated based on the sensitive matrix. Its low fabrication cost, simple configuration and high sensitivity make this sensor have potential applications in chemical and biological sensing.     

Hot spots in parametric fluorescence with a pump beam of finitecross section

The parametric fluorescence from a nonlinear crystal driven by a pump beam of finite cross section displays a hot spot in the angular and spectral distribution of the signal radiation. The hot spot in the signal radiation occurs where the pump and idler Poynting vectors are collinear. Similarly, a hot spot in the idler radiation is predicted when the pump and signal Poynting vectors are collinear. Signal photons entering the signal hotspot are generally not correlated in direction or frequency with idler photons entering the idler hot spot. We report experimental observation of the signal hot spot in a AgGaS₂ crystal pumped by a Nd:YAG laser and describe a theory developed to understand the phenomenon. Qualitative and quantitative comparisons of the theory and data show good agreement     

Noise figure of UHF transistors as a function of frequency and bias conditions

It is shown that the observed values of the minimum noise figureF_{min}of UHF transistors in common base connection can be explained in terms of the device parameter(1-alpha_{dc}) r_{b'b}/R_{e0}and fαfor frequencies up to 1000 MHz. An interesting collector saturation effect is observed that gives a strong increase in UHF noise figure at high currents. Many features of the dependance ofF_{min}on operating conditions can be explained by this effect. The current dependence ofF_{min}for large values of |VCB| and high currents suggests a distribution in diffusion times through the base region. At intermediate frequencies, the noise figure increases with increasing collector bias |VCB| due to an increase inr_{b'b}, which in turn is caused by the dependence of the base width on |VCB|.     

Noise reduction, smoothing and time interval segmentation of noisy signals using an energy optimisation method

Noise reduction and time interval segmentation of a noise-contaminated piecewise continuous signal is considered by the authors as a non-linear optimisation problem. The mathematical framework of this method is presented both in continuous-time and discrete-time domains. The smoothed signal and segmented time intervals of the original noisy signal are calculated as an optimised solution for an energy functional. An algorithm similar to the level set method is developed to find the optimised solution. In this algorithm, the discontinuity points separating consecutive continuous signals are preserved while the noise is reduced. Therefore this method fundamentally exhibits a better performance compared with a traditional low-pass filter suppressing high frequency components, including discontinuity points. The results also demonstrate a better quality in noise reduction in comparison to the median and Gaussian filters.