Amplifier Configuration Research Articles

Silicate-based erbium-doped fiber extended to L-band and its amplification performance

With the continuous development of mobile internet, cloud computing, Internet of things, and 5G, the annual growth rate of the existing communication transmission capacity is far from meeting the growing demand. The gain bandwidth of L-band erbium-doped fiber amplification (EDFA) has become the main factor for limiting the bandwidth extension. Owing to its negative effect on the gain and noise figure after 1580 nm, the excited state absorption (ESA) is regarded as a key factor that directly limits the L-band expansion of EDFA. If the ESA coefficient has the same value as the stimulated emission coefficient, the net gain coefficient becomes zero. At the same time, signal amplification cannot be obtained no matter how the pump power and fiber length are adjusted. Improvements from the perspective of erbium-doped fibers, such as changing the host glass and doping components, are extremely beneficial to L-band extension based on simple amplifier configurations. In the present study, an erbium-doped fiber extended to the L-band is fabricated by the modified chemical vapor deposition technology. The saturation curve of the fiber is measured, and then the rate of clustering is obtained. In addition, the absorption coefficient and emission coefficient of the fiber are tested by the truncation method, then the effect of ESA is studied. We demonstrate that modulating the ratio of P to Al in the fiber core has a significant inhibitory effect on the ESA of Er<sup>3+</sup>. To better characterize the amplification performance of the fiber, a single-stage and a multi-stage amplifier system are built respectively. At an input signal injection with a power value of –9 dBm, the fiber exhibits a gain of 10.5 dB with a maximum noise figure of 5.9 dB at 1625.3 nm, based on a single-stage amplifier system under a 980 nm forward-pumping excitation. It indicates that the amplification performance of the fiber in the long-wavelength has improved, which is consistent with the conclusion of the suppression effect on the ESA. By optimizing the fiber length for the first, second and third stage to 19 m, 26 m and 10 m, respectively, a gain of 23.4 dB is obtained at the longest wavelength. The maximum noise figure is 6.3 dB, and the saturation output power is 24.8 dBm. In the meantime, the pump conversion efficiency arrives at 13%. This is the first report on the L-band extended silicate-based erbium-doped fiber that can achieve long-wavelength gain extension to 1625.3 nm.

All-optical phase-preserving amplitude-regeneration technology based on bidirectional orthogonal-pumped semiconductor optical amplifier configuration

The phase-preserving amplitude regeneration scheme based on the bidirectional orthogonal-pumped semiconductor optical amplifier (SOA) is proposed in this work. Experimental investigation into the multiple four-wave mixing (FWM) process from the pump, the signal and their corresponding reflective fields is carried out in detail. The regeneration performance obtained from the product between co-propagating fields is also discussed, including its dependence on the signal launch power and the signal quality, to quantify the amplitude regeneration and the phase preserving behaviors. The amplitude distortion is suppressed by 2.2 dB experimentally, confirming the regeneration capability of the proposed scheme. Moreover, the regeneration performance is further investigated for multiple phase shift keying (MPSK) signals through the simulation. According to the numerical results, the operational parameters of the regenerator are the same for advanced modulation formats, proving the robust operation of the proposed bidirectional orthogonal-pumped SOA configuration.

Planar CMOS and multigate transistors based wide-band OTA buffer amplifiers for heavy resistance load

Analog buffer amplifier configurations capable of driving heavy resistive load using different operational transconductance amplifier (OTA) are presented in this paper. The OTA CMOS buffer configurations are designed using 0.18 ?m SCL technology library in Cadence Virtuoso tool and multigate transistor OTA buffer in TCAD Sentaurus tool. CMOS OTA buffer configuration using simple OTA outperform the OTA buffer circuits using other OTAs in terms of power dissipation and stability. Measured results show that the OTA buffer circuit works well for resistive load below 100 ?. The gain tuning of up to 5 V/V is achieved with RL equal to 50 ?, output swing of 1 V. OTA buffer configuration implemented using multigate transistor with resistive load below 1 k? exhibits a bandwidth around 5 GHz and tunable gain up to 5 V/V.

An Elegant Method of Analysis for the BJT Amplifiers using Floating Admittance Matrix

The Floating Admittance Matrix (FAM) is an elegant, neat, illustrative, and simplified technique for analyzing all configurations of the BJT amplifiers, starting with the maneuvering of the FAM of the phase-splitter circuit. The conventional analysis method requires a small-signal equivalent circuit, and then conventional tools, either KCL, KVL, or Thevenin, Norton, etc., are used for the analysis. The researcher has to guess which conventional tool suites better than the other for any particular circuit, whether active or passive. The proposed technique is equally ell useful for all circuits. In the FAM method, once the device matrix is known rest of the circuit can be embedded in it by inspection. The sum property of this matrix provides a check to know whether FAM has been written correctly to proceed further.

A Complex Band-Pass Filter for Low-Power and High-Performance Transceivers

In this paper a low-power and high-performance 2nd-order complex band-pass filter in trans-impedance amplifier (TIA) configuration is presented. Thanks to the adopted topology for the passive network and active-components exceeds current solutions exhibiting a gain as high as 121.5 dB $_Ω$ and 1.57 MHz of bandwidth centered around 1.33 MHz. The output noise is only 630 nV/√Hz. Furthermore, a new fully-differential class-AB operational trans-conductance amplifier (OTA) provides the required current to drive heavy ADC loads with very fast signals while an improved common-mode feedback circuit enables ultra low current without introducing stability and avoids start-up problems. The filter has been integrated in a 90-nm complementary metal oxide semiconductor (CMOS) technology. Despite the high performance and accuracy of the transfer function the power consumption is only 400 μA from a 1.2-V power supply.

2.58 kW Narrow Linewidth Fiber Laser Based on a Compact Structure with a Chirped and Tilted Fiber Bragg Grating for Raman Suppression

We report a high power, narrow linewidth fiber laser based on oscillator one-stage power amplification configuration. A fiber oscillator with a center wavelength of 1080 nm is used as the seed, which is based on a high reflection fiber Bragg grating (FBG) and an output coupling FBG of narrow reflection bandwidth. The amplifier stage adopted counter pumping. By optimizing the seed and amplifier properties, an output laser power of 2276 W was obtained with a slope efficiency of 80.3%, a 3 dB linewidth of 0.54 nm and a signal to Raman ratio of 32 dB, however, the transverse mode instability (TMI) began to occur. For further increasing the laser power, a high-power chirped and tilted FBG (CTFBG) was inserted between the backward combiner and the output passive fiber, experimental results showed that both the threshold of Stimulated Raman scattering (SRS) and TMI increased. The maximum laser power was improved to 2576 W with a signal to Raman ratio of 42 dB, a slope efficiency of 77.1%, and a 3 dB linewidth of 0.87 nm. No TMI was observed and the beam quality factor M2 maintained about 1.6. This work could provide a useful reference for obtaining narrow-linewidth high-power fiber lasers with high signal to Raman ratio.

Investigation of multipass Yb-doped fiber amplifiers.

We investigated both numerically and experimentally single-pass, two-pass, and four-pass Yb-doped core-pumped fiber amplifier configurations and compared their performance with respect to achievable pump-to-signal conversion efficiency. Despite numerical calculations predicting the highest efficiency in the four-pass setup, an experimentally highest conversion efficiency of 77% was achieved in the two-pass setup and only 49% in the four-pass setup. Reduced performance of the experimental four-pass fiber amplifier configuration was caused by excess coupling losses, which do not impose a fundamental limitation. At the same time, the four-pass fiber amplifier configuration demonstrated advantageous characteristics of high gain using shorter length of active fiber and lower noise figure compared with other tested configurations.

Novel Dopant Tailored Fibers Using Vapor Phase Chelate Delivery Technique

The vapor phase chelate delivery (VPCD) technique in conjunction with the modified chemical vapor deposition (MCVD) process is adopted to fabricate fibers with customized doping profiles. The three large‐mode area (LMA) step‐index fibers with different rare‐earth doping profiles in the core region, such as uniform doping, centralized doping, and circumferential doping, are fabricated by optimizing the fabrication parameters. The fibers are tested in a cladding‐pumped amplifier configuration and their output beam qualities and signal‐to‐noise ratio (SNR) are characterized. The investigation reveals that the fiber with centralized doping in the core region exhibits lower M 2 compared with the fibers with uniform and circumferential doping, as it has a lower overlap of the higher‐order modes with the doped region. The experimental result is further affirmed through theoretically simulated results. The developed fabrication technique shows potential to fabricate specialty fibers of varied designs, where customized doping profiles are required.

16.3 W Peak-Power Pulsed All-Diode Laser Based Multi-Wavelength Master-Oscillator Power-Amplifier System at 964 nm

An all-diode laser-based master oscillator power amplifier (MOPA) configuration for the generation of ns-pulses with high peak power, stable wavelength and small spectral line width is presented. The MOPA emits alternating at two wavelengths in the spectral range between 964 nm and 968 nm, suitable for the detection of water vapor by absorption spectroscopy. The monolithic master oscillator (MO) consists of two slightly detuned distributed feedback laser branches, whose emission is combined in a Y-coupler. The two emission wavelengths can be adjusted by varying the current or temperature to an absorption line and to a non-absorbing region. The power amplifier (PA) consists of a ridge-waveguide (RW) section and a tapered section, monolithically integrated within one chip. The RW section of the PA acts as an optical gate and converts the continuous wave input beam emitted by the MO into a sequence of short optical pulses, which are subsequently amplified by the tapered section to boost the output power. For a pulse width of 8 ns, a peak power of 16.3 W and a side mode suppression ratio of more than 37 dB are achieved at a repetition rate of 25 kHz. The measured spectral width of 10 pm, i.e., 0.1 cm−1, is limited by the resolution of the optical spectrum analyzer. The generated pulses emitting alternating at two wavelengths can be utilized in a differential absorption light detection and ranging system.

Analysing a common-source amplifier implemented with floating-gate transistors and coupled feedback loop

ABSTRACT The input stage of an operational or transconductance amplifier could be a common-source amplifier and it should be designed carefully, since it contributes in a significant way to the performance of the entire cell. In this document, we show the results of analysing a basic transconduction cell based on the multiple-input ffioating-gate transistor in a common-source amplifier configuration. A particular feature of the cell that we analyse is that it contains a feedback loop towards one of the coupled gates that serves to improve the linearity. This simple cell could be a input stage in more complex circuits. We present studies of linearity, gain, output resistance and distortion to be compared with an entirely MOS common-source amplifier. Experimental tests were conducted based on an implemented integrated circuit. In our comparison, we note that the cell based on the ffioating-gate transistor has a remarkable linearity in conditions in which the MOS version would not operate properly. In addition, we experimentally observe the phenomena predicted by the theory, such as gain and operation point manipulation, according to the values of the voltages at the other control gates. Thus, it is possible to improve the design of operational amplifiers, and other similar circuits, because they provide greater linearity and less distortion; however, we observed lower transconductance and an increase in the output resistance.

Architectural configuration of a magnetic flux density amplifier composed of second-generation high-temperature superconducting (2G HTS) 8-shaped rare earth-Ba–Cu–O (REBCO) loops

Superconducting devices composed of the second-generation high-temperature superconducting (2 G HTS) RE-Ba-Cu-O (REBCO, RE is rare earth) tapes have extensive applications in high magnetic flux density measurements. Here an architectural configuration for a magnetic flux density amplifier is designed and an experimental setup is established to characterize the amplification of the magnetic flux density. The system is composed of REBCO HTS tapes with one central slit excited by field cooling. The HTS tape has a longitudinally cut slit with a width of 12 mm that is transversally pulled apart and mechanically twisted to form an 8-shaped loop with two different sized closed-loops. The large closed-loop includes an excitation coil composed of copper wire wound on an iron core so that there is more dense flux density generated in the smaller closed-loop. The amplified magnetic flux densities in the small closed-loops have been verified experimentally and by simulation at 77 K. The results demonstrate that the REBCO loops amplify the magnetic flux density.

SKKL PERFORMANCE ANALYSIS OF SUBMARINE CABLE COMMUNICATION SYSTEM (SKKL) EDFA - SOA AMPLIFIER LINK JAVA – BALI USING OPTISYSTEM

The Submarine Cable Communication System (SKKL) is a communication backbone that is deployed under the sea that used to connect networks between islands and between countries. DWDM (Dense Wavelength Division Multiplexing) technology can support long distance communication. Repeater used to reduce the impact of loss, on the detector side the signal can be detected properly. EDFA (Erbium Doped Fiber Amplifier) and Semiconductor Optical Amplifier (SOA) amplifiers can minimize the impact of loss and increasing the gain of each amplifier. The EDFA (Erbium Doped Fiber Amplifier) is an optical amplifier that can work at a wavelength of 1550 nm which provides amplification for the input signal that passes through it which is doped with the element erbium (Er). SOA amplifier is an optical amplifier that utilizes cavity or room cavity to strengthen light. By using branching unit configuration and repeaterless, repeatered, and parallel in-line amplifier configuration and optical system software 7.0 with system reliability parameters such as Q-factor, Bit Error Rate, Power Receiver, and Signal to Noise Ratio with power variations (0 dBm, 2 dBm, 4 dBm, 6 dBm, 8 dBm) at a frequency of 100 GHz for 10 channels. The best result on the Q-Factor parameter is 15,928, the BER parameter is 5.87 x 10-057, the receiver power parameter is -10,319 dBm, and the SNR is 42,713 dB. In this research the best value obtained in the Parallel in-line configuration. So as the best average is in the Repeatered EDFA configuration.

Pre-compensation of thermally induced refractive index changes in a depressed core fully aperiodic large-pitch fiber for high average power operation.

To prevent the thermally induced spatial beam degradation occurring in high-power fiber lasers and amplifiers, index-depressed core "fully aperiodic large-pitch fibers" (FA-LPFs) have been designed and fabricated. In contrast to previous experimental works performed on FA-LPFs, in which the active core and the surrounding cladding material are quasi-index-matched, the core refractive index is in slight depression compared to the surrounding material (Δn≈-3×10-5). Thus, the index-depressed fiber core tends first to behave as an anti-guide, preventing light from being properly guided into it. However, by increasing the absorbed pump power, the thermal load induces a parabolic refractive index change sufficient to compensate for the -3×10-5 index depression in the core, enabling a robust single-mode amplification at high average power. As a proof of concept, using a 110 µm depressed core FA-LPF, M2 values of 1.3 were demonstrated in amplifier configuration from 60 W to a maximal value of 170 W of emitted average power only limited by the available pump power.

Peak-Current-Ratio-Enhanced Compact Symmetrical Doherty Amplifier Design by Using Active Harmonic Control

This article proposes a new and compact symmetrical Doherty power amplifier (DPA) configuration that provides extended output-back-off (OBO) and enhanced load modulation. The concept of active harmonic control (AHC) is introduced to remedy the reduced-conduction-angle operation of the class-C auxiliary device, providing enhanced auxiliary current and power capability. Semianalytical study based on generalized load-modulation theory and large-signal simulation reveal that an optimal AHC can offer increased peak current ratio, improved load modulation, boosted output power, and power utilization factor (PUF). Besides, a new output combiner, with the inclusion of parasitic effect, is devised for ultracompactness and simplicity. For verification, a 11-dB-OBO 2-GHz symmetrical DPA based on GaN HEMT transistors is designed, fabricated, and measured. Excellent performance with drain efficiency of 74% (52%) is obtained at saturation (back-off of 11 dB). Moreover, a saturation power of 42.98 dBm is achieved, corresponding to an uplifted PUF of 1.25 (compared with conventional symmetrical DPA design). Under 20-MHz modulated signal (peak-to-average power ratio of 11 dB) excitation, the prototype exhibits average efficiency of 53.2% at an average output power of 32 dBm. The adjacent channel leakage power ratio (ACLR) is found to be −27.5 and −50.9 dBc before and after digital predistortion, respectively.

Watt-level superfluorescent fiber source near 3 µm.

We report a watt-level mid-infrared (mid-IR) superfluorescent fiber source from ${{\rm Er}^{3 +}}$-doped ZBLAN fiber near 3 µm spectral range. With the power amplifier configuration, the mid-IR superfluorescent fiber source with power up to 1.85 W has been delivered successfully with slope efficiency about 18.6%. The experimental results may pave an avenue toward a high-power, high-temporal-stability superfluorescent source for versatile mid-IR applications.

Spacially resolved coupled mode analysis for TMI threshold powers in quantum and Rayleigh scattering limits.

A 3D spatially resolved coupled mode and perturbation analysis for the transverse mode instability (TMI) threshold powers in Yb-doped fiber amplifiers is presented in this paper. Threshold powers are computed in the quantum and thermal Rayleigh scattering limits and are compared with those calculated by other coupled mode analyses. Quantum-limited threshold powers are found to be more than three times greater than those calculated with coupled-mode analyses that use uniform and/or average gain approximations. The analysis presented here includes pump depletion, gain saturation, and transverse hole burning. Simulations are applied to co-, cnt-, and bidirectionally pump amplifier configurations. The appearance of TMI is attributed to the formation of a dynamic thermal grating, which enables the exchange of optical power between the fundamental mode (FM) and higher-order mode (HOM). The sole approximation made is that the power in the HOM is much less than that in the FM. A distributed thermal Rayleigh scattering model is introduced that includes a ray-optic representation of the fiber mode structure that relates the Rayleigh power captured by the HOM to the waveguide structure. The location and strength of the thermal gratings are identified to assist in the application of mitigation techniques.

2.4 kW 1045 nm narrow-spectral-width monolithic single-mode CW fiber laser by using an FBG-based MOPA configuration.

A 24 kW narrow-spectral-width near-diffraction-limited monolithic fiber laser system at ${\sim}{1045.2}\;{\rm{nm}}$ in a fiber Bragg grating (FBG)-based master oscillator power amplifier (MOPA) configuration is demonstrated in this paper. The near-diffraction-limited beam quality (${{\rm{M}}^2}\sim{1.2}$) and a spectral width of 0.35 nm (${\sim}{{96}}\;{\rm{GHz}}$) are achieved. The stimulated Raman scattering (SRS) is theoretically and experimentally investigated. The SRS has been suppressed by carefully optimizing the length of the Yb-doped fiber and the pumping scheme, and a signal-to-noise ratio of ${\sim}{{33}}\;{\rm{dB}}$ between the laser signal and the Raman Stokes component is achieved. The stimulate Brillouin scattering and the transverse mode instability are not observed. To our best knowledge, this is the highest-output power for ${{104}} \times {\rm{nm}}$ single-mode fiber laser with ${\sim}{{96}}\;{\rm{GHz}}$ spectral width by using an FBG-based MOPA configuration.

Estimation of four wave mixing effect in pre-, post- and in-line configuration of EDFA using advanced modulation formats for 1.28 Tbps WDM system

This paper reported the effect of different EDFA configurations on the four wave mixing (FWM) effect in wavelength division multiplexed (WDM) system which is operating at 1.28 Tbps data speed. Also, the comparative analysis of pre-, post (booster) and inline configuration of EDFA using both forward pumping and backward pumping techniques at variable input signal power and pump signal power levels. Further, the effect of various modulation formats on the signal quality of WDM system is analyzed in presence of dispersion compensated fiber. The original contribution of this investigation is to check the effect of EDFA amplification on FWM for future high-speed optical access networks and it can be observed that in line EDFA amplification configuration gives the best amplification performance among other configurations.

5 kW monolithic fiber amplifier employing homemade spindle-shaped ytterbium-doped fiber.

We have demonstrated a 5 kW high-power monolithic fiber amplifier employing a homemade spindle-shaped ytterbium-doped fiber (YDF) based on the main oscillator power amplifier configuration. The YDF consists of a spindle-shaped core and cladding along the fiber length, with a core/cladding diameter of 27/410 µm at both ends and 39.5/600 µm in the middle. An output power of over 5 kW and beam quality of about 1.9 and an optical-to-optical conversion efficiency of 66.6% were achieved in the amplifier under a bidirectional pump scheme. While operating at the maximum power, the laser performance was evaluated, and the transverse mode instability and stimulated Raman scattering effects were well mitigated. To the best of our knowledge, this is the highest power demonstration in a continuous-wave fiber laser employing a tapered fiber. Further power scaling is promising by optimizing the structure of the YDF.

Power scalability of a continuous-wave high-power Er-Yb co-doped fiber amplifier pumped by Yb-doped fiber lasers.

The power scaling of Er-Yb co-doped fiber lasers and amplifiers has been limited by the bottleneck effect of energy-transfer saturation between Yb ions and Er ions. The emerging method of Er-Yb co-doped fiber amplifiers pumped by Yb-doped fiber lasers is considered as an approach to enhance the threshold of the bottleneck effect. In this paper, we quantitatively characterize the threshold of the bottleneck effect via the method of extreme value analysis of the second-order derivative. The method facilitates the optimization of the amplifier configuration. Afterward, we numerically investigate the bottleneck effect of various Er-Yb co-doped fiber amplifiers off-peak cladding-pumped by 10××nm Yb-doped fiber lasers for what we believe, to the best of our knowledge, is the first time. The result shows that the most optimal configuration is long gain fiber over 20 m pumped by a 1020-1025 nm fiber laser, with more than two times the output limit of a conventional laser diode pumping scheme. The essential factors of an amplifier are discussed afterward, including the pump-launching direction, the optimization of large-mode-area fiber, the core-cladding ratio, the concentration of doping ions, the nonlinearity limit, and the distribution of the heat load.