Saturated Amplifier Research Articles

Realization of the conceptual ideal for x-ray amplification

The Xe(L) system is an amplifier with fundamentally different dynamic characteristics from all previously developed laser amplifiers; it represents the conceptual ideal through full utilization of the Kramers–Kronig relations that fundamentally couple the dispersive and absorptive components. The dispersive response of the system, through optimal governance of the power compression, rules the amplification and establishes a minimum gain for the amplifier. Accordingly, the amplification requires a minimum value of the dispersion to be surpassed; the corresponding gain follows automatically. As a leading consequence, since this minimum gain is sufficiently high, the key experimental observation is the uniform presence of saturated amplification signaled by strong spectral hole burning on all transitions exhibiting amplification, including double-vacancy lines. This cardinal signature demonstrates that the amplification is legislated by the saturated gain gs, not the corresponding small signal value g0. The chief outcome is that explosive dispersion yields perforce explosive amplification and the efficient generation of maximally bright coherent power.

Constellation diagram analysis of DPSK signal regeneration in a saturated parametric amplifier

The regeneration of 10 Gbit/s differential phase shift keying (DPSK) signals in a saturated fiber optic parametric amplifier (FOPA) acting as an optical intensity regenerator is investigated. The regeneration properties are investigated in amplitude and phase separately by means of coherent detection and constellation diagram analysis. A significant reduction of the amplitude fluctuations is observed and the measured signal-to-noise ratio (SNR) after DPSK demodulation is increased up to 10 dB. However, from the constellation analysis it is found that the FOPA introduces phase noise to the signal. The FOPA induced phase noise originates from pump amplitude fluctuations that are transferred to the signal through cross-phase modulation.

Multi-pump discrete Raman amplifier for CWDM system in the O-band

We demonstrate theoretically that discrete Raman amplifiers operating in the O-band region (1260–1360 nm) are more efficient than in any other band if we consider the fiber attenuation. Compared with the C-band (1530–1565 nm), the net gain is 3 dB higher. We present also theoretically two types of discrete Raman amplifiers which can be used in the O-band with a course wavelength division multiplexing system. The first amplifier has a bandwidth of 70 nm that was designed with four pump lasers operating at 12XY nm. The second one has a bandwidth of 100 nm and needed six pump lasers to obtain a flattened gain across the O-band. In addition, we have analyzed the gain saturation in both optical amplifiers.

Gbit-Class Transmission Using SOA Data Rewriter for WDM-PON

We describe the transmission characteristics of a wavelength independent wavelength division multiplexing passive optical network (WDM-PON) based on a wavelength channel data rewriter (WCDR). The WCDR is composed of a linear amplifier (LA) and a saturated semiconductor optical amplifier (SOA), and by using the WCDR in optical network units (ONUs), we can erase the downstream signal and modulate the same wavelength channel with the upstream signal. In this paper, we analyze the data rewriting characteristic, the frequency chirp characteristic and the bit error rate (BER) degradation occasioned by the use of saturated SOAs. Furthermore, we report high-speed transmission with power penalty of less than 1dB at bit rates of 1.25Gbit/s, 2.5Gbit/s and 10Gbit/s for downstream signals and 1.25Gbit/s for upstream signals after transmission through 40km of single-mode fiber.

Analysis of a Fully Matched Saturated Doherty Amplifier With Excellent Efficiency

A saturated Doherty amplifier based on class-F amplifiers is analyzed in terms of its load modulation behavior, efficiency, and linearity. Simulations included the amplitude ratio and phase difference between the fundamental and third harmonic voltages, the current/voltage waveforms, load lines, and the third-order intermodulation amplitudes/phases of the carrier and peaking amplifiers. The saturated doherty power amplifier was implemented using two Eudyna EGN010MK GaN HEMTs with a 10-W peak envelope power. For a 2.14-GHz forward-fink wideband code-division multiple-access signal, the doherty amplifier delivers an excellent efficiency of 52.4% with an acceptable linearity of -28.3 dBc at an average output power of 36 dBm. Moreover, the amplifier can provide the high linearity performance of -50 dBc using the digital feedback predistortion technique.

Correction to "Exact Analytical Solution for Raman Fiber Laser"

In the above paper [ibid.,vol. 18, no. 9, pp. 1097–1099, May 1, 2006], the Raman fiber laser was modeled and an analytical solution, verified by numerical simulations and an experimental demonstration, was obtained. In the theoretical analysis of the fiber Raman laser, the pump power evolution was expressed using the known Lambert W function and then the lasing power given by (7) was solved using the Newton–Raphson method, like Dr. Santagiustina had previously done in the case of fiber Raman amplifiers [see Exact integral solution of saturation and depletion in forward and backward optical fiber Raman amplifiers, Opt. Lett., vol. 32, no. 20, pp. 3023–3025, Oct. 2007.]. We sincerely apologize for our negligence to cite the prior work of Dr. Santagiustina in our paper. This correction is provided to give proper credit to Dr. Santagiustina's work, which was originally submitted to Optics Letters in 2005 and published in 2007.

Direct observation of the coherent spectral hole in the noise spectrum of a saturated InAs/InP quantum dash amplifier operating near 1550 nm

We demonstrate a direct observation of the coherent noise spectral hole in a saturated quantum dash amplifier. Its width 500-600 GHz is determined by the response time and is responsible for high speed regeneration properties.

Intrachannel collision of power law optical solitons

The intrachannel collision of optical solitons with power law nonlinearity is studied using the quasiparticle theory. The perturbation terms considered are the nonlinear gain and saturable amplifiers along with filters. The suppression of soliton-soliton interaction, in presence of these perturbation terms, is achieved. The numerical simulations support the quasiparticle theory.

A 20-W Chireix Outphasing Transmitter for WCDMA Base Stations

A Chireix outphasing transmitter for Band I wideband code-division multiple-access base stations was implemented using a nonisolating power combiner and two high-efficiency saturated class-B power amplifiers for 20-W single-carrier power levels. Novel adaptive background calibration algorithms were developed and demonstrated for the mismatch calibration and phase predistortion of the two transmitter chains. The complete demonstrator was able to achieve an average efficiency of 30% for a 3GPP TestModel64 signal, measured at a channel output power of 20 W and an adjacent channel power ratio of -45 dB.

Output Power PDF of a Saturated Semiconductor Optical Amplifier: Second-Order Noise Contributions by Path Integral Method

We have developed a second-order small-signal model for describing the nonlinear redistribution of noise in a saturated semiconductor optical amplifier. In this paper, the details of the model are presented. A numerical example is used to compare the model to statistical simulations. We show that the proper inclusion of second-order noise terms is required for describing the change in the skewness (third-order moment) of the noise distributions. The calculated probability density functions are described far out in the tails and can hence describe signals with very low bit error rate (BER). The work is relevant for describing the noise distribution and BER in, for example, optical regeneration.

Exact integral solution of saturation and depletion in forward and backward optical fiber Raman amplifiers

Exact integral solutions of forward and backward Raman Stokes-pump interaction are presented. They enable one to determine the gain and depletion characteristics of optical Raman amplifiers, as well as a good approximation of the noise figure, without the need of numerically solving the nonlinear boundary value differential equations governing the Raman interaction.

Analytic approach to the small-signal frequency response of saturated semiconductor optical amplifiers using multisection model

An analytic solution derived by multisection model to the small-signal frequency response (SSFR) of wavelength conversion based on cross-gain modulation (XGM) in semiconductor optical amplifiers (SOAs) is presented. The result contains details that can affect the characteristics of SSFR significantly more than previous ones.

Diversity combining with up‐link power control

AbstractWe introduce in this paper a new adaptive power‐controlled diversity combining scheme that reduces the average transmitted power of the mobile units (MUs) while meeting a certain minimum required quality of service. The key idea is (i) to collect and combine all the available diversity paths at the base station (BS) and then (ii) to request the MU to increase or decrease its transmitted power just to track the required target signal‐to‐noise ratio (SNR). Four power control variants accounting for practical implementation constraints including discrete power levels and transmitter gain saturation are proposed and studied. Some selected numerical results show that the proposed scheme offers considerable savings in the transmitted power levels over a wide SNR range but amplifier saturation leads to a violation of the target BER requirement in the low average SNR range. Additional numerical examples show that the power control variants that take into account practical implementation constraints conserve the main features of the ideal continuous power algorithm. Copyright © 2007 John Wiley & Sons, Ltd.

효율이 특화된 전력 증폭기와 개선된 바이어스 모듈레이터로 구성되는 진보된 WCDMA용 하이브리드 포락선 제거 및 복원 전력 송신기

We have proposed a new “hybrid” envelope elimination and restoration(EER) transmitter architecture using an efficiency optimized power amplifier(PA) and modified bias modulator. The efficiency of the PA at the average drain voltage is very important for the overall transmitter efficiency because the PA operates mostly at the average power region of the modulation signal. Accordingly, the efficiency of the PA has been optimized at the region. Besides, the bias modulator has been accompanied with the emitter follower for the minimization of memory effect. A saturation amplifier, class F?¹ is built using a 5-W PEP LDMOSFET for forward-link single-carrier wideband code-division multiple-access(WCDMA) at 1-㎓. For the interlock experiment, the bias modulator has been built with the efficiency of 64.16 % and peak output voltage of 31.8 V. The transmitter with the proposed PA and bias modulator has been achieved an efficiency of 44.19 %, an improvement of 8.11 %. Besides, the output power is enhanced to 32.33 ㏈m due to the class F operation and the PAE is 38.28 % with ACLRs of －35.9 ㏈c at 5-㎒ offset. These results show that the proposed architecture is a very good candidate for the linear and efficient high power transmitter.

A Bidirectional WDM/TDM-PON Using DPSK Downstream Signals and a Narrowband AWG

We present an innovative architecture to realize a single feeder bidirectional amplified wavelength-division-multiplexing/time-division-multiplexing passive optical network based on modified nonreturn-to-zero differential phase-shift keying (DPSK) downstream signals at 20 Gb/s and a narrowband arrayed waveguide grating (AWG). The AWG plays at the same time the role of channel distributor, simultaneous demodulator for all DPSK channels, and eliminates the need for chromatic dispersion compensation. A saturated semiconductor optical amplifier (SOA) provides bidirectional amplification to compensate the splitter losses. The remodulated upstream signals are obtained at 1 Gb/s by means of a reflective SOA. Experimental results show error-free operation on both downstream and upstream signal.

High gain amplifiers: Power oscillations and harmonic generation

We discuss the power oscillations in saturated high gain free electron laser amplifiers and show that the relevant period can be written in terms of the gain length. We use simple arguments following from the solution of the pendulum equation in terms of Jacobi elliptic functions. Nontrivial effects due to nonlinear harmonic generation and inhomogeneous broadening are discussed too, as well as the saturated dynamics of short pulses.

High-power Ti:Sapphire lasers: Temporal contrast and spectral narrowing

New extensions of the chirped pulse amplification (CPA) scheme designed specially for petawatt Ti:Sapphire lasers are considered. The two new schemes support a spectral bandwidth sufficient for 20 fs pulses and a temporal contrast of 1012. The Double CPA scheme consists of two CPA stages with an intermediate temporal pulse filtering for temporal contrast improvement. The scheme of Negative–Positive CPA amplification takes advantage of consecutive saturated amplification of down chirped and up chirped pulses. This allows a suppress imprint of gain narrowing, which usually limits the spectral bandwidth at the multi-terawatt power level, and reach the bandwidth in excess of 50 nm without using any direct spectral shaping of the pulse.

Development of a chirped pulse amplification laser with zigzag slab Nd:glass amplifiers dedicated to x-ray laser research

A chirped pulse amplification laser with zigzag slab Nd:glass amplifiers dedicated to x-ray laser research is described. The laser provides a 1.6 ps duration pulse with approximately 7 J energy at a repetition rate of 0.1 Hz. In the power amplifier system, laser light is amplified in a two-step manner: The first step is image-relayed multipass amplification up to approximately 1 J with a 10 mm x 10 mm beam. The second step is double-pass amplification up to >10 J with a 10 mm x 90 mm beam. By using this laser system, the saturated amplification of the Ni-like Ag laser at a wavelength of 13.9 nm has been successfully demonstrated.

Feasibility Study of SOA-Based Noise Suppression for Spectral Amplitude Coded OCDMA

We investigate the benefits of employing a saturated semiconductor optical amplifier (SOA) to reduce the optical noise in an incoherent light optical code division multiple access (OCDMA) system. In the context of spectrum slicing, SOA-based noise suppression has shown significant potential in enhancing the signal quality of noisy light. In this paper, we evaluate the viability of the technique for spectral amplitude coded OCDMA and show that the benefits of SOA-based noise suppression do not extend readily to this application due to post-SOA optical-filtering effects at the receiver. However, appreciable performance improvements can in principle be realized through optimized system and decoder design

A simple and low-power optical limiter for multi-GHz pulse trains

We study the limiting-amplification capability of a saturated Semiconductor Optical Amplifier (SOA) followed by an optical band-pass filter. We experimentally demonstrate that this simple optical circuit can be effectively exploited to realize a low-power optical limiter for amplitude-modulated pulse trains at multi-GHz repetition rate. We report very large amplitude-modulation-reduction factors for the case of 20 and 40 GHz pulse trains that are super-imposed with modulating frequencies ranging from 100kHz to several GHz.