High Saturation Power Research Articles

Gallium Nitride and Silicon Transistors on 300 mm Silicon Wafers Enabled by 3-D Monolithic Heterogeneous Integration

We demonstrate industry’s first 300 mm GaN transistor technology and 3-D monolithic heterogeneous integration with Si transistors, enabled by 300 mm GaN metal–organic chemical vapor deposition (MOCVD) epitaxy and 300 mm 3-D layer transfer. The 300 mm GaN technology is a high- ${k}$ dielectric enhancement-mode GaN nMOS transistor technology on Si(111) substrate. It is capable of excellent characteristics and figure-of-merits (FOM) for realizing energy-efficient, compact power-delivery and RF front-end components such as power-amplifiers, low-noise amplifiers, and RF-switches. Our GaN nMOS transistors show e-mode operation with: 1) high ${I}_{\text {D,max}} =1.5$ mA/ $\mu \text{m}$ ; 2) low ${R}_{ \mathrm{\scriptscriptstyle ON}}$ of $610\,\,\Omega -\mu \text{m}$ ( ${L}_{\text {G}} =50$ nm); 3) low ${I}_{ \mathrm{\scriptscriptstyle OFF}}$ of 100 pA/ $\mu \text{m}$ ( ${L}_{\text {G}} \,\,=180$ nm), which are significant improvements over GaN HEMT; 4) excellent RF performance: ${f}_{\text {T}} =190$ GHz, ${f}_{\text {MAX}} =300$ GHz, power-added efficiency (PAE) = 56% ( ${L}_{\text {G}} \,\,=50$ nm) at mmwave frequency 28 GHz, and PAE = 77% at 5 GHz ( ${L}_{\text {G}} =180$ nm), significantly better than industry-standard GaAs and Si RF transistors; 5) good RF-switch FOM, ${R}_{ \mathrm{\scriptscriptstyle ON}}{C}_{ \mathrm{\scriptscriptstyle OFF}} =110$ fs; and 6) low noise figure, NF $_{\text {min}} \,\,=1.36$ dB ( ${f} =28$ GHz) and 0.4 dB ( ${f} =5$ GHz), all at SoC-compatible voltages. We further demonstrate GaN transistor innovations all integrated on 300 mm Si(111) wafer, including depletion-mode GaN nMOS transistor with high ${I}_{\text {D}} =1.8$ mA/ $\mu \text{m}$ ; GaN Schottky gate transistor producing high saturated power of 20 dBm ( $80\mu \text{m}$ width) with peak PAE = 57% at 28 GHz; low leakage compact cascode and multigate GaN transistors; and GaN Schottky diodes with ultralow ${C}_{ \mathrm{\scriptscriptstyle OFF}}$ for electrostatic discharge (ESD) protection. The layer-transferred Si transistors, monolithically stacked on top of the GaN transistors by 300 mm 3-D layer transfer, show high drive current performance: 1.0 mA/ $\mu \text{m}$ (Si nMOS) and 0.5 mA/ $\mu \text{m}$ (Si pMOS). Such a monolithic 3-D Monolithic integration of GaN and Si transistors enables full integration of energy-efficient, truly compact power delivery and RF solutions with CMOS digital signal processing, logic computation and control, memory, and analog circuitries.

The dual-injection Ge-on-Si photodetectors with high saturation power by optimizing light field distribution

In this work, we put forward the length design principle of the dual-injection integrated Ge-on-Si photodetectors based on the characteristics of the light field distribution. When the length of the absorption layer makes the maximum intensity of the incident light from both ends are alternately distributed, the light field distribution is more uniform. Based on this principle, the shorter photodetector could get better saturation performance. Two dual-injection photodetectors with the length of 6μm and 10μm have been investigated, the experimental results show that the saturation current of 6μm length device is 18.33% higher, and the bandwidth is 138.60% higher at 10 mW incident power comparing with the 10μm length device. The 6μm length photodetector realized a responsivity of 1.07 A/W, a bandwidth of 37.3 GHz at 50 μW luminous power @1550 nm.

Photonic-Crystal Josephson Traveling-Wave Parametric Amplifier

An amplifier combining noise performances as close as possible to the quantum limit with large bandwidth and high saturation power is highly desirable for many solid state quantum technologies such as high fidelity qubit readout or high sensitivity electron spin resonance for example. Here we introduce a new Traveling Wave Parametric Amplifier based on Superconducting QUantum Interference Devices. It displays a 3 GHz bandwidth, a -102 dBm 1-dB compression point and added noise near the quantum limit. Compared to previous state-of-the-art, it is an order of magnitude more compact, its characteristic impedance is in-situ tunable and its fabrication process requires only two lithography steps. The key is the engineering of a gap in the dispersion relation of the transmission line. This is obtained using a periodic modulation of the SQUID size, similarly to what is done with photonic crystals. Moreover, we provide a new theoretical treatment to describe the non-trivial interplay between non-linearity and such periodicity. Our approach provides a path to co-integration with other quantum devices such as qubits given the low footprint and easy fabrication of our amplifier.

Linear and Nonlinear Noise Characterisation of Dual Stage Broadband Discrete Raman Amplifiers

We characterise the linear and nonlinear noise of dual stage broadband discrete Raman amplifiers (DRAs) based on conventional Raman gain fibres. Also, we propose an optimised dual stage DRA setup that lowers the impact of nonlinear noise (generated in the amplifier) on the performance of a transmission link (with 100-km amplifier spacing). We numerically analyse the design of a backward pumped cascaded dual stage 100-nm DRA with high gain (∼20 dB) and high saturated output power (>23 dBm). We show that the noise figure (NF) of the dual stage DRA is mainly dominated by the first stage irrespective of the type of gain fibre chosen in the second stage, and we also demonstrate that optimising the length and the type of Raman gain fibre can have significant impact on the size of inter/intrasignal nonlinearities generated. Here, we report a theoretical model to calculate the nonlinear noise power generated in transmission spans with dual stage DRAs considering piecewise signal power evolution through the Raman gain fibres. The predicted signal-to-noise ratio (SNR) performances are calculated from the combined contributions from NF and nonlinear product power obtained using the proposed analytical model for transmission systems deployed with 100-km transmission span compensated by different dual stage DRAs. Finally, an optimised IDF 6 km–SMF 10 km dual stage configuration has been identified using the theoretical model, which allows maximum SNR of 14.6 dB at 1000 km for 1 THz Nyquist wavelength division multiplexed signal and maximum transmission reach of 3400 km at optimum launch power assuming 8.5 dB HD-FEC limit of the Nyquist PM-QPSK signal.

Scaling Capacity Growth of Fiber-Optic Transmission Systems Using 100+nm Ultra-Wideband Semiconductor Optical Amplifiers

We report on the use of semiconductor optical amplifiers (SOAs) to extend the optical bandwidth of next generation optical systems. After discussing the technological progress and the motivation for rekindling the interest in SOAs for line amplification, we point out that the nonlinear gain dynamics of SOA is not a limiting factor for employing SOA as line amplifier. We show that the passage to high wavelength division multiplexed (WDM) channel count tends to substantially reduce nonlinear impairments, both through numerical analysis and experimental investigations based on standard off the shelf SOA devices. We then present the characteristics of our novel ultrawideband SOA-based packaged devices exhibiting high gain over 100+nm optical bandwidth, high output saturation power and low noise figure. We finally review the recent demonstration of the first >100+Tb/s transmission based on such novel 100+ nm wide semiconductor optical amplifiers over 100 km distance.

Mapping Exchangeable Protons to Monitor Protein Alterations in the Brain of an Alzheimer's Disease Mouse Model by Using MRI.

The study aimed to investigate exchangeable proton signals of Aβ proteins of the brains of Alzheimer's disease (AD) model mice by using a chemical exchange-sensitive spin-lock (CESL) MR imaging technique. Eight non-transgenic (Tg) mice (5 young and 3 old) and twelve Tg-APPswe/PSdE9 mice (5 young and 7 old) were used in this study. CESL Z-spectra were obtained by using two saturation powers, which were ω1 = 25 Hz with TSL = 3.0 s and ω1 = 500 Hz with TSL = 150 ms, at 71 offsets with uneven intervals between the offset frequencies at Ω = ±7.0 ppm at a 9.4-T animal MRI system. For Zspectrum analyses, regions of interest (ROIs) were drawn in the cortex, hippocampus, and thalamus of both hemispheres. Magnetization transfer ratio asymmetry (MTRasym) curves were obtained from the Zspectra. The Mann-Whitney test was used to compare the MTRasym values between the Tg and non-Tg mice for each offset frequency and for each ROI. The water saturation width of the full Z-spectrum was narrow with the 25-Hz saturation power, but relatively broad with the 500-Hz saturation power. With the 25-Hz CESL saturation power, most of the MTRasym values were negative for 3.5-, 3.0-, 2.0-, and 0.9-ppm offset frequencies and the MTRasym values were significantly different between the control and Tg groups only in the left thalamus region at 3.5 ppm offset (p=0.0487). The MTRasym values were -6% to -7% for both 3.5 and 3.0 ppm, but less than -2% for both 2.0 and 0.9 ppm. With 500-Hz CESL saturation power, all the MTRasym values were positive for the 3.5-, 3.0-, 2.0-, and 0.9-ppm offset frequencies and the MTRasym values were not significantly different between the control and Tg groups at all ROIs and at all offset frequencies. However, a trend towards a significant difference was observed between the control and Tg groups in the right cortex at 3.5 ppm (p=0.0578). The MTRasym values were 6% to 9% for 3.5, 3.0, and 2.0 ppm, but less than 2% for 0.9 ppm. In an in-vivo AD model experiment, MTRasym values increased with the high saturation power than with the low saturation power. The MTRasym values were not significantly different, except in the left thalamus region at 3.5 ppm offset. The CESL technique should be further developed to enable its application in the brain of patients with neurodegenerative diseases.

Brain investigations of rodent disease models by chemical exchange saturation transfer at 21.1 T.

This study explores opportunities opened up by ultrahigh fields for in vivo saturation transfer brain magnetic resonance imaging experiments. Fast spin-echo images weighted by chemical exchange saturation transfer (CEST) effects were collected on Sprague-Dawley rats at 21.1T, focusing on two neurological models. One involved a middle cerebral artery occlusion emulating ischemic stroke; the other involved xenografted glioma cells that were followed over the course of several days as they developed into brain tumors. A remarkably strong saturation-derived contrast was observed for the growing tumors when calculating magnetization transfer ratios at c. 3.8ppm. This large contrast originated partially from an increase in the contribution of the amide CEST effect, but mostly from strong decreases in the Overhauser and magnetization transfer contributions to the upfield region, whose differential attenuations could be clearly discerned thanks to the ultrahigh field. The high spectral separation arising at 21.1T also revealed numerous CEST signals usually overlapping at lower fields. Ischemic lesions were also investigated but, remarkably, magnetization and saturation transfer contrasts were nearly absent when computing transfer asymmetries using either high or low saturation power schemes. These behaviors were consistently observed at 24hours post-occlusion, regardless of the data processing approach assayed. Considerations related to how various parameters defining these experiments depend on the magnetic field, primarily chemical shifts and T1 values, are discussed.

Experimental performance of semiconductor optical amplifiers and praseodymium-doped fiber amplifiers in 1310-nm dense wavelength division multiplexing system

One of the key optical transmission components is optical amplifiers. Studies on the amplification properties of the 1310-nm optical amplifiers are presented. The evaluated optical amplifiers are semiconductor optical amplifier (SOA) and praseodymium-doped fiber amplifier (PDFA). The study is aimed at the dynamic operation in single- and multiwavelength domains with high rate signals. The maximum obtained gain was 25.0 dB for SOA and 20.9 dB for PDFA. For the SOAs, the minimum achieved value of the receiver sensitivity was −11.5 dBm for a single channel and −11.5 dBm for a dense wavelength division multiplexing case while for PDFA those values were −11.0 dBm and −10.9, respectively. The main advantage of the PDFA in comparison to the measured SOAs is its higher saturation power. The SOAs proved to be viable candidates for high-speed amplification in the 1310-nm wavelength domain.

Mode-evolution-based coupler for high saturation power Ge-on-Si photodetectors.

We propose a mode-evolution-based coupler for high saturation power germanium-on-silicon photodetectors. This coupler uniformly illuminates the intrinsic germanium region of the detector, decreasing saturation effects, such as carrier screening, observed at high input powers. We demonstrate 70% more photocurrent generation (9.1-15.5mA) and more than 40 times higher opto-electrical bandwidth (0.7-31GHz) than conventional butt-coupled detectors under high-power illumination. The high-power and high-speed performance of the device, combined with the compactness of the coupling method, will enable new applications for integrated silicon photonics systems.

Determining the chemical exchange saturation transfer (CEST) behavior of citrate and spermine under in vivo conditions.

PurposeTo estimate the exchange rates of labile 1H in citrate and spermine, metabolites present in prostatic secretions, to predict the size of the citrate and spermine CEST effects in vivo.MethodsCEST z‐spectra were acquired at high‐field [11.7 Tesla (T)] from citrate and spermine solutions at physiological pH (6.5) using saturation power 6 μT. CEST was performed at different temperatures to determine exchange regimes (slow, intermediate or fast). For low pH solutions of spermine, exchange rates were estimated from resonance line width, fitting z‐spectra using the Bloch equations incorporating exchange, and using quantifying exchange using saturation time experiments (QUEST). These rates were extrapolated to physiological pH.ResultsCitrate showed little CEST effect at pH 6.5 and temperature (T) = 310 K (maximum 0.001% mM‐1), indicating fast exchange, whereas spermine showed greater CEST effects (maximum 0.2% mM‐1) indicating intermediate‐to‐fast exchange. Extrapolating data acquired from low pH spermine solutions predicts exchange rates at pH 6.5 and T of 310 K of at least 2 × 104s‐1.ConclusionCitrate and spermine show minimal CEST effects at 11.7T even using high saturation power. These effects would be much less than 2% at clinical field‐strengths due to relatively faster exchange and would be masked by CEST from proteins. Magn Reson Med 76:742–746, 2016. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Bandwidth improvement of high power uni-traveling-carrier photodiodes by reducing the series resistance and capacitance**Project supported by the National Basic Research Program of China (Grant Nos. 2012CB315605 and 2014CB340002), the National Natural Science Foundation of China (Grant Nos. 61176015, 61176059, 61210014, 61321004, and 61307024), and the Open Fund of State Key Laboratory on Integrated Optoelectronics, China (Grant Nos. IOSKL2012KF08 and IOSKL2014KF09).

A backside illuminated mesa-structure InGaAs/InP modified uni-traveling-carrier photodiode (MUTC-PD) with wide bandwidth and high saturation power is fabricated and investigated. The device structure is optimized to reduce the capacitance and resistance. For the 22-μm-diameter device, the maximum responsivity at 1.55 μm is 0.5 A/W, and the 3-dB cutoff frequency reaches up to 28 GHz. The output photocurrent at the 1-dB compression point is measured to be 54 mA at 25 GHz, with a corresponding output radio frequency (RF) power of up to 15.5 dBm. The saturation characteristics of the MUTC-PD are also verified by the electric field simulation, and electric field collapse is found to be the cause of the saturation phenomenon.

Noise Suppression in Quantum-Dot Semiconductor Optical Amplifiers: A Bit Rate-SNR Analysis

Based on high output saturation power of quantum dot semiconductor optical amplifiers, it has been shown that exploiting a saturating holding beam (HB) can effectively suppress amplitude noise with HB power as a tunability degree of freedom. A simultaneous study of amplitude noise and pattern effect induced at high data rates on the quality factor of output signal reveals that desirable $Q$ -factor level can be obtained through modifying the bias current density and HB power. An upper data rate limit for $Q$ -factor penalty-free operation at various input signals to noise ratios is also predicted. A wide power range for the applied HB is promising for developing a tunable noise suppression scheme.

Analysis of electron dynamics and two mechanisms in a coaxial magnetic wiggler

The electron dynamics in a coaxial magnetic wiggler are analyzed numerically and studied in particle-in-cell (PIC) simulation. Electrons wiggle in angular direction to coherently generate a TE01 mode, and the results are consistent with each other. The trajectory of the electron in 3-D space and the effects on the trajectories of the initial phases of wiggler magnetic fields are researched, which helps to choose appropriate initial phases to control the trajectory of the electron. An oscillator of FEL with a coaxial magnetic wiggler based on a quasi cavity is designed for efficiently generating the TE01 mode with the high saturation power and high efficiency. The advantages of the quasi cavity structure are analyzed and the parameter-selection rules are investigated. Based on the electron dynamics, the process of electron bunching in the self amplified spontaneous emission (SASE) and the Seeded mechanisms are studied. The Seeded mechanism could accelerate electron bunching greatly and reduce the saturation time than the SASE by half.

Silicon-based traveling-wave photodetector array (Si-TWPDA) with parallel optical feeding.

We demonstrate silicon-based traveling-wave photodetector arrays (Si-TWPDAs) with parallel optical feeding by integrating multiple Germanium photodetectors. Such Si-TWPDAs feature the merit of high optical saturation power with remaining the large operation bandwidth. The impedance-matched traveling-wave electrode design takes into account the individual Ge photodetector loading effect. Optical waveguide delay lines are designed in order to balance the electrical phase delay of the traveling-wave electrode. The maximum linear photocurrent at -4V biased voltage are respectively 16 mA, 38 mA, and 65 mA with integrating 1, 2, and 4 photodetectors, upon the saturation power of 40 mW, 100 mW, and 160 mW. This corresponds to a normalized photocurrent generation of >0.32 mA/µm3 and a normalized saturation power of 0.8 mW/µm3. The extracted fiber access responsivity is ~0.42 A/W and the intrinsic responsivity of ~0.82 A/W. The measured 3-dB bandwidth for 4-channel TWPDA is ~20 GHz.

Theory of carrier depletion and light amplification in active slow light photonic crystal waveguides

Using a perturbative approach, we perform a quantitative three-dimensional analysis of slow-light enhanced traveling wave amplification in an active semiconductor photonic crystal waveguide. The impact of slow-light propagation on the carrier-depletion-induced nonlinear gain saturation of the device is investigated. An effective rate-equation-based model is presented. It is shown that it well accounts for the three-dimensional simulation results. Simulations indicate that a slow-light-enhanced photonic crystal traveling-wave amplifier has a high small-signal modal gain and low saturation power.

Integrated Guided-Wave Photodiode Using Through-Absorber Quantum-Well-Intermixing

A high-speed, high-saturation power photodiode compatible with a relatively simple monolithic integration process is described. The detector is comprised of an intrinsic bulk absorption layer, an electron drift region, and a field termination layer, and is grown above a main waveguide core comprised of a number of quantum wells, which are used as the active region of a phase modulator. Through-absorber quantum-well-intermixing is used to blue-shift the bandedge of the underlying quantum wells, reducing the optical losses of that material. The detectors demonstrate quantum efficiency, input saturation power, and 3-dB bandwidth of 50 GHz.

Swept-Source OCT System Based on a Polarization-Dependent Semiconductor Optical Amplifier-Enabled Fourier Domain Mode Locked Laser

We demonstrate a swept-source OCT system based on a polorization-dependent semiconductor optical amplifier (SOA)-enabled Fourier Domain Mode Locked laser (FDML). The broad bandwidth and high saturation power of the semiconductor optical amplifier enables single semiconductor optical amplifier operation with enough bandwidth and output power. The FDML generates ~32mW output power at 45kHz sweep rates, with a tuning range of 115 nm centered at 1326 nm. Using the SOA-enabled FDML laser, ~12.9μm axial resolution,9μm transverse spot size and 105dB sensitivity are achieved. OCT imaging of biological sample is also demonstrated.

Back-to-Back UTC-PDs With High Responsivity, High Saturation Current and Wide Bandwidth

A novel back-illuminated mesa-structure back-to-back uni-traveling-carrier photodiode (UTC-PD) is proposed and realized. By stacking two UTC-PDs to form a PINIP structure, high responsivity, high output saturation power, and wide bandwidth are achieved simultaneously. The responsivity of a 24-μm -diameter device is as high as 0.86 A/W, and a 3-dB bandwidth up to 28.3 GHz is attained. The saturation current up to 62 mA at 1-dB compression point is demonstrated at the frequency of 24 GHz.

Ultralow Noise, Etalon Stabilized, 10-GHz Optical Frequency Comb Based on an SCOW Amplifier

A slab-coupled optical waveguide amplifier (SCOWA) is used to construct a 10-GHz harmonically modelocked laser with an intra-cavity etalon that serves as a high-finesse spectral filter. The laser output is a frequency comb that is actively stabilized to the transmission peaks of the etalon through a Pound-Drever-Hall scheme. The linewidth of the individual comb-lines is ~1 kHz and the frequency instability <;300 kHz over 60 s. The output power exceeds 20 mW due to the high saturation power of the SCOWA. The residual timing jitter of the pulse-train is ~1.9 fs (1 Hz to 100 MHz). A much broader comb (~10 nm) is generated after dispersion compensation of the cavity and the output pulses are compressible to <;1 ps. A comparison of the timing jitter of the all-anomalous dispersion and dispersion compensated cavities is presented along with a previous result with a similar architecture.

Spurious-Free Dynamic Range in Photonic Integrated Circuit Filters With Semiconductor Optical Amplifiers

Among other advantages, radio-frequency (RF) signal processing in the optical domain using photonic integrated circuits (PICs) offers unprecedented bandwidth and tunability. However, modern RF-photonic link applications demand PICs with high spurious-free dynamic range (SFDR). The SFDR of active PICs integrating semiconductor optical amplifiers (SOAs) is limited by amplified spontaneous emission noise and distortion caused by four-wave mixing. Here, we derive an analytical model for the SFDR of SOAs, and extend it to PICs with arbitrary transfer functions integrating many SOAs. The model is general and applicable to any photonic signal-processing circuit operating in the linear amplification regime below saturation. We show analytically the importance of SFDR-driven photonic design over noise-figure-driven design. Using this model, we explore the SFDR of coupled-ring bandpass filters integrated on a high saturation power integration platform and show SFDR as high as 117.0 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm dB}\cdot{\rm Hz}^{2/3}$</tex></formula> for filters with bandwidths in the 1–2 GHz range. We show how the material parameters and PIC design determine the SFDR. Tradeoffs between SFDR and filter bandwidth, extinction, and stopband roll-off are investigated.