In this thesis, we investigate the design and amplification characteristics of discrete fiber Raman amplifier (FRA), and discuss with amplification characteristics of FRA by employing multi-pumping-wavelength configuration. Recently, because of the invention of high output power of pump laser diodes, so discrete FRA can be practically employed in optical fiber communication system. The fiber Raman amplifier has two merits. One is the low noise characteristic and the other is the arbitrary spectral gain band, so it will play an important role in optical communication system. In this study, we employ backward pumping configurations in the experiment and simulation of discrete FRA. By comparing with results of experiment and simulation, we prove that the simulation results quite agree with the experimental data of four pumping wavelengths configuration, we have successfully designed an L-band gain flattened discrete FRA by using four pumping wavelengths configuration. The experimental results showed that the amplifier, for the input of seven optical channel each with ¡V16 dBm input power level, has an optical gain of >10 dB of each channel with good gain uniformity (<1 dB) in the 1565-1595 nm wavelength region.

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada / In this paper, a small-sized low-noise integrated block downconverter (LNB) used for Ku-band direct reception from broadcasting satellites (DBS) is proposed. The operating frequency of the LNB is from 11.7 to 12.2GHz. The outlook dimension is 41 X 41 X 110mm^3. Measured results show that the average gain of the LNB is 57dB, and noise figures are less than 1.7dB. It has been found that clear TV pictures have been received using the LNB for the experiment of receiving the "BS-2b" (Japanese broadcasting satellite) at Harbin region, Heilongjiang Province, P. R. China.

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The need of the everyday user to transfer large amounts of data is driving the need for larger data transfer capacity. Optical communication networks can satisfy this need. To be economically viable, optical transceivers must be integrated onto chips at low cost, using relatively cheap semiconductor processes. The optical preamplifier (transimpedance amplifier) receives optical information and converts it to a useful electrical form. It must operate at high speed, contribute little distortion to the input signal, and add little electrical noise to the incoming signal. This thesis investigates the design techniques in the literature, and proposes new architectures. Two high performance preamplifiers are designed, one using GaAs HEMTs, and the other using GaAs HBTs, each with different circuit techniques. The HEMT preamplifier has a transimpedance gain of 1.4 kΩ, the highest in the literature for 10 Gb/s operation, along with a low input referred noise current of about 15 pA/Hz1/2 at a bandwidth of 6.3 GHz. The HBT preamplifier also has a transimpedance gain of 1.5 kΩ, with a low input referred noise current of about 7 pA/Hz1/2. Both have clear, open eye-diagrams with a 10 Gb/s bit stream input, and are suitable for integration on a chip. The HEMT preamplifier was implemented as a common-gate, common-source amplifier cascade with a darlington output driver for a 50 Ω load. The HBT preamplifier was implemented as common-emitter darlington amplifier with shunt peaking, and a simple emitter degenerated output driver for a 50 Ω load. Both implementations exceeded the bandwidth, transimpedance gain and noise performance typically expected of the transistor technologies used. It is shown that the transimpedance limit can be circumvented by the use of novel architectures and shunt peaking.

The audio power amplifier is used to amplify low-power audio signals to a level that can be suitable for driving the loudspeakers. Thus the audio power amplifier becomes a kind of essential part in the electronics that could make sounds. In this thesis, a good performance audio power amplifier with tonality control is designed. It consists of three parts: pre-amplifier unit, the tonality control unit and the power amplifier unit. In the pre-amplifier unit, a TL071CP operational amplifier is applied, to amplify the low signal to be suitable for the tonality control unit. For the tonality control unit, a filter is used to achieve bass and treble control, resulting in different frequency response. In the last part, the low voltage power amplifier LM386N-1 is used. The results of simulation in Multisim show a good output waveform and different frequency response with the tonality control. Also the pure sound can be heard by ear clearly. The good simulation result offers the encouragement to build the circuit on the board and do the measurement. The measured results show a good output waveform, the output power 256mW, THD 4.7%, the maximum voltage gain 40 etc. Meanwhile, sound can be heard by ear clearly with the tonality control. Judging from the results, the audio power amplifier is designed successfully.

Power amplifiers are an indispensible part of the wireless communication systems. Conventional PAs provide peak efficiency at peak output power which is obtained at a certain fixed optimum resistance. These kind of amplifiers are normally called switched-mode power amplifiers (SMPAs) and are used for constant envelope signals. However, there is low efficiency at low output power which is the linear operation of a PA and is used for the amplification of non-constant envelope signals. For an optimum PA design, linearity and efficiency are the requirements. There are efficiency  enhancement techniques and Doherty architecture is one such approach. Classical Doherty (symmetric) approach entertains the signals that have peak to average power ratio (PAPR) of 6 dB. Applications like Long Term Evolution (LTE) having high PAPR of nearly 9 dB demand efficiency throughout the back-off range. Therefore the challenge is to design and implement an asymmetric Doherty power amplifier that ensures high efficiency in the back-off range greater than 6 dB. This work presents the design and implementation of an Asymmetric Doherty Power Amplifier (ADPA) for 12 dB back-off at 2.65 GHz in Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs) technology. The carrier and peaking amplifiers are biased in class-B and C mode of operations, respectively. A branchline coupler is used to divide the input signal equally to amplifiers input. A 10 W GaN HEMT transistor is used as an active device for both amplifiers. The design has been implemented with ideal transmission lines and then shifted to microstrip lines using 508 um substrate. The measurement results of the ADPA prototype, when drain of carrier and peaking devices are biased at 24 V and 28 V  respectively, showed an input power back of (IPBO) of 9.68 dB with almost same power added efficiency (PAE) of 44% throughout the entire back-off range. The simulations are done with Agilent ADS and Momentum is used for Electromagnetic (EM) simulation.

Due to the fast growing communication need, the required capacity of the optical fiber network has been more than doubled every year. The technology breakthrough in dry fiber fabrication opens the possibility for fiber bandwidth from 1.3 £gm to 1.6 £gm. The fast increasing demand of communication capacity results in the emergence of wavelength division multiplexing (WDM) technology, enabling tens or even hundreds of channels with different wavelengths transmitted simultaneously on an optical fiber, which results in the need for ultra-broadband optical amplifier. Cr4+:YAG has a strong spontaneous emission spectrum covers from 1.3 £gm to 1.6 £gm. In addition, its absorption spectrum is between 0.9 £gm to 1.2 £gm, which matches the pumping wavelength of current erbium doped optical amplifier. Such fiber is, therefore, eminently suitable for optical amplifier applications. In this thesis, we introduce the development of ultra-broadband optical amplifier using the Cr4+:YAG double-clad crystal fiber, which is grown by the laser-heated pedestal growth (LHPG) technique. Try to use passive tence theoretical models and numerical simulations to know we can get more than 2 dB gross gain when signal propagations two times in Cr4+:YAG double-clad crystal fiber. With the butt-coupling method, a net gain of 0.0 dB is demonstrated at 1.3W bi-directional pump power and signal double pass in Cr4+:YAG double-clad crystal fiber at present. In the future, in order to reduce pump excited-state-absorption. We attempt to use clad-pump or side-pump scheme instead of core-pump scheme, to choose pumping wavelength at 925 nm instead of 1064 nm and to use side deposition of Yb2O3 and CuO . At the same time, we will continue to fabricate small-core-diameter Cr4+:YAG DCF to achieve a single-mode fiber and to extend its length to improve gain performance.

Abstract Spread spectrum technique modifies the signal spectrum to spread it out and increase its bandwidth. There are two major methods in spread spectrum technique: direct sequence and frequency hopping. The resistance capability of jamming signal for frequency hopping system is better than that for direct sequence system. Two types of frequency hopping techniques can be distinguished. In ¡§fast frequency hopping¡¨ the period of a frequency-hop is smaller than a data symbol-period while in ¡§slow frequency hopping¡¨ the period of a frequency-hop is larger than a data symbol-period. Fast frequency hopping systems have the advantages that the error correction codes are not needed and diversity can be applied. The disadvantage of fast frequency hopping system is that coherent data detection is not possible because of phase discontinuities. Traveling wave tube amplifier is often used in satellite communications. It has nonlinear characteristics which can be classified as nonlinear amplitude and phase distortions toward the output signals. Certain backoff input power makes the amplifier work within the linear region. However, in order to have more output power, the amplifier usually operates in the saturation region and in consequence serious nonlinear signal distortion would be introduced. In this thesis, the effect of nonlinear amplifier on a frequency hopping multiple access (FHMA) system with binary frequency shift keying is discussed. In the simulation, two types of nonlinear amplifiers, traveling wave tube amplifier and solid state power amplifier, are applied to the FHMA system. Tradeoff between power efficiency and performance degradation is determined by the index of total performance degradation, which is obtained from simulation. With known single carrier output power, third-order intermodulation, and same input power, the bit error rate performance is also analyzed.

In this thesis, We have fabricated 1.55