Low-noise Pulse Research Articles

Artificial neural network on-chip and in-pixel implementation towards pulse amplitude measurement

We present the design of an in-pixel artificial intelligence (AI) for extraction of an amplitude of a pulse generated in semiconductor detector. The AI is design with traditional multi-level perceptron scheme having 6 layers and the total number of 420 parameters. The implementation shows 0.34% measurement accuracy. The AI block is fed by the 6-bit ADC at 5 MHz sampling rate. Standard front-end is optimized for low-noise pulses carrying 1000–3000 electrons. The methodology was tested using FPGA and results are promising. The design is intended to be fabricated and verified in the prototype solution.

Investigation of locked operation in a system of two passively mode-locked semiconductor lasers under weak lateral coupling

We study theoretically the operation of two semiconductor passively mode-locked lasers laterally coupled through evanescent fields. The investigation is carried out using a time domain traveling wave numerical model for two-section lasers (gain and absorption) enhanced to include weak mutual coupling. The study of the coupled system shows that although the operation is dominated mostly by instabilities and amplitude modulated pulse trains, under specific conditions, stable mode locking with low intensity noise and time-synchronized pulses emerges. The influence of operational and geometrical parameters on the coupled dynamics is identified and discussed.

The development of low-noise pulse traveling wave tube amplifier for radar scatterometer

The development of low-noise pulse traveling wave tube amplifier for radar scatterometer

High-Fidelity Control of Superconducting Qubits Using Direct Microwave Synthesis in Higher Nyquist Zones

Control electronics for superconducting quantum processors have strict requirements for accurate command of the sensitive quantum states of their qubits. Hinging on the purity of ultra-phase-stable oscillators to upconvert very-low-noise baseband pulses, conventional control systems can become prohibitively complex and expensive when scaling to larger quantum devices, especially as high sampling rates become desirable for fine-grained pulse shaping. Few-GHz radio-frequency digital-to-analog converters (RF DACs) present a more economical avenue for high-fidelity control while simultaneously providing greater command over the spectrum of the synthesized signal. Modern RF DACs with extra-wide bandwidths are able to directly synthesize tones above their sampling rates, thereby keeping the system clock rate at a level compatible with modern digital logic systems while still being able to generate high-frequency pulses with arbitrary profiles. We have incorporated custom superconducting qubit control logic into off-the-shelf hardware capable of low-noise pulse synthesis up to 7.5 GHz using an RF DAC clocked at 5 GHz. Our approach enables highly linear and stable microwave synthesis over a wide bandwidth, giving rise to high-resolution control and a reduced number of required signal sources per qubit. We characterize the performance of the hardware using a five-transmon superconducting device and demonstrate consistently reduced two-qubit gate error (as low as 1.8%) which we show results from superior control chain linearity compared to traditional configurations. The exceptional flexibility and stability further establish a foundation for scalable quantum control beyond intermediate-scale devices.

Femtosecond Mode-locked Fiber Laser at 1 \u03bcm Via Optical Microfiber Dispersion Management

Mode-locked Yb-doped fiber lasers around 1 μm are attractive for high power applications and low noise pulse train generation. Mode-locked fiber lasers working in soliton and stretched-pulse regime outperform others in terms of the laser noise characteristics, mechanical stability and easy maintenance. However, conventional optical fibers always show a normal group velocity dispersion around 1 μm, leading to the inconvenience for necessary dispersion management. Here we show that optical microfibers having a large anomalous dispersion around 1 μm can be integrated into mode-locked Yb-doped fiber lasers with ultralow insertion loss down to −0.06 dB, enabling convenient dispersion management of the laser cavity. Besides, optical microfibers could also be adopted to spectrally broaden and to dechirp the ultrashort pulses outside the laser cavity, giving rise to a pulse duration of about 110 fs. We believe that this demonstration may facilitate all-fiber format high-performance ultrashort pulse generation at 1 μm and may find applications in precision measurements, large-scale facility synchronization and evanescent-field-based optical sensing.

Spectral and temporal breathing self-similar evolution in a fiber amplifier for low-noise transform-limited pulse generation

We demonstrate a simple scheme for high-power low-noise high-contrast ultrashort pulse generation. It is enabled by the spectral and temporal breathing self-similar pulse evolution with an optimized negative pre-chirp. Experiments and simulations indicate the enhanced tolerances of this scheme to the gain-shaping distortions and pump fluctuations. It can lead to ∼16% increase in the compressed pulse quality with more than a two times wider spectrum and ∼31% reduction in the root-mean-square (rms) relative intensity noise (RIN). Transform-limited pulses as short as 36 fs are generated with the rms RIN of 0.029% (1 kHz-5 MHz) from a 2 m Yb-fiber amplifier.

A low-power CMOS ASIC for X-ray Silicon Drift Detectors low-noise pulse processing

We present an Application Specific Integrated Circuit (ASIC), named VEGA-1, designed and manufactured for low-power analog pulse processing of signals from Silicon Drift Detectors (SDDs). The VEGA-1 ASIC consists of an analog and a digital/mixed-signal section to achieve all the functionalities and specifications required for high-resolution X-ray spectroscopy in the energy range from 500 eV to 60 keV with low power consumption. The VEGA-1 ASIC has been designed and manufactured in 0.35-μm CMOS mixed-signal technology in single and 32-channel version with dimensions of 200 μm × 500 μm per channel. A minimum intrinsic ENC of 12 electrons r.m.s. at 3.6 μs shaping time and room temperature is measured for the ASIC without detector. The VEGA-1 has been tested with Q10-SDD designed in Trieste and fabricated at FBK, with an active area of 10 mm2 and a thickness of 450 μm. The aforementioned detector has an anode current of about 180 pA at +22°C. A minimum Equivalent Noise Charge (ENC) of 16 electrons r.m.s. at 3.0 μs shaping time and −30°C has been demonstrated with a total measured power consumption of 482 μW.

High-Power Versatile Picosecond Pulse Generation from Mode-Locked Quantum-Dot Laser Diodes

This paper presents the current status of our research in mode-locked quantum-dot edge-emitting laser diodes, particularly highlighting the recent progress in spectral and temporal versatility of both monolithic and external-cavity laser configurations. Spectral versatility is demonstrated through broadband tunability and novel mode-locking regimes that involve distinct spectral bands, such as dual-wavelength mode-locking, and robust high-power wavelength bistability. Broad tunability of the pulse repetition rate is also demonstrated for an external-cavity mode-locked quantum-dot laser, revealing a nearly constant pulse peak power at different pulse repetition rates. High-energy and low-noise pulse generations are demonstrated for low-pulse repetition rates. These recent advances confirm the potential of quantum-dot lasers as versatile, compact, and low-cost sources of ultrashort pulses.

Operation of a high-Tc DC-SQUID-gradiometer on a non-metallic pulse tube refrigerator

A planar high-Tc DC-SQUID gradiometer has been operated with a specially developed low noise pulse tube refrigerator. The cold finger of the refrigerator consists only of non-metallic and non-magnetic materials. The high sensitive SQUID-gradiometer with a base length of 4 mm has a field gradient resolution of about 3 pT/(cm Hz1/2) at 1 Hz and 0.7 pT/(cm Hz1/2) in the white noise region in magnetically shielded environment. During the operation of both, the sensor and the refrigerator, the noise generated by the cryocooler is below the noise level of the SQUID-gradiometer. We demonstrate the potential of this non-metallic pulse tube refrigerator by measuring the magnetic field originating from a human heart (magnetocardiogram), without additional suppression of the intrinsic refrigerator noise.

Compact low-noise pulse generating lasers with repetition rates of 10 to 50 GHz

We review the main results obtained with our recently introduced passively fundamental mode-locked Er : Yb :glass lasers mainly in the context of telecom applications, and we discuss their key enablers. Specifically, we focus on the aspects of the lasers for application in the time-domain for optical time-division multiplexing and in the wavelength domain for dense wavelength-division-multiplexing.

Stability Analysis of Mode Locked Figure-Eight Fiber Laser

Mode locked fiber laser, as a source of short pulse generation finds applications in telecommunications and optical signal processing where low noise and stable pulse train is the main requirement. It is therefore important to analyze its shot to shot pulse amplitude stability and timing jitter. By introducing a gradual twist in fiber and using a length of normal dispersion EDF to stretch and amplify the pulse, high energy and stable pulse train generated from a figure eight laser has been analyzed. Fluctuations in pulse repetition time and in pulse energy as well as jitter in pulse width occur simultaneously. All these types of noise have been characterized quantitatively by examining the higher harmonics of the RF spectrum. By optimizing the total dispersion and cavity length of the laser, it was found by measurement that a peak to peak stability of 99.2% and a timing jitter of 5.59 psec for 2.31 MHz pulse train was obtained. This is quite remarkable. However, it is observed that the variation of cavity parameters results in increased timing jitter and peak pulse instability.

A novel detection system consisting of a large-area sensor and a multicell Si-pad array operated in spectroscopic mode for X-ray breast imaging

The ability of coherent X-ray scatter to provide the molecular structure of breast tissues could add a new dimension in X-ray breast imaging capable of tracking the molecular structural changes during disease progression and of improving the sensitivity to low-contrast lesions without increasing the radiation dose. Work is under way to build a laboratory prototype dual-sensor breast-imaging scanning system, which combines the diagnostic information from both the transmitted primary and the forward scattered X-rays. This required the design and development of a coherent X-ray scatter detection system based on a high-resistivity multielement two-dimensional (2-D) Si-pad array, a multichannel low-noise pulse processing front-end electronics chip, the XA1.3, and a new DAQ system. X-rays in the energy range of 17-45 keV can be detected with a FWHM energy resolution of 1-3 keV. Results on the characterization and optimization of the detector-readout electronics-DAQ system and its performance to measure diffraction signatures of most commonly used breast-equivalent materials of interest are presented.

Frequency stabilization of mode-locked Erbium fiber lasers using pump power control

Mode-locked erbium fiber lasers can serve as frequency comb generators in the 1.5 μm telecommunication band or as frequency dividers generating low noise pulse trains at microwave repetition rates from a visible or near infrared frequency standard. Such applications require suitable stabilization methods both for the laser’s carrier frequency and the pulse repetition frequency. While control of the optical resonator length with the help of a piezo actuator is an obvious method, we investigate in this paper frequency stabilization of the fiber laser via pump power control. Using this method, we stabilize the pulse repetition rate of the Er:fiber-laser with respect to a hydrogen-maser with residual averaged timing errors of a few femtoseconds (for averaging times between one and one hundred seconds), an order of magnitude below the timing noise of the maser itself.

Josephson voltage standard circuit operation with a pulse tube cooler

For a more wide-spread use of Josephson voltage standards, cryogen-free operation, by means of an appropriate closed-cycle refrigerator, is highly desirable. In this work we present a low-noise pulse tube cooler (PTC) that is capable to cool the voltage standard circuits to temperatures below 4 K. As a low loss dielectric waveguide with a very small thermal conductivity a Teflon strip was used for the microwave transmission. The matched transition from the WR12 rectangular waveguide to the Teflon strip and vice versa was made using special exponential tapers. Programmable 1 Volt 14 bit SINIS and 10 Volt SIS arrays assembled in the PTC operated well, i.e., demonstrated a similar performance to that measured in liquid helium. The Josephson junction arrays were integrated in coplanar strips instead of the commonly used microstriplines for the microwave transmission lines. The 1 Volt SINIS array contained 8192 Josephson junctions (JJs). It generated an inherently stable Josephson voltage step of 1.19 V at a driving microwave frequency of 70 GHz. The step width was 150 /spl mu/A and the critical current of the junctions was 550 /spl mu/A. Similar results were obtained under liquid helium cooling conditions. In another experiment a 10 Volt voltage standard chip with 19700 SIS JJs was installed. It was possible to generate stable Shapiro steps at the 10 V level.

Theory of SiGe waveguide avalanche detectors operating at λ=1.3 μm

The potential performance of SiGe waveguide avalanche photodiodes is analyzed for operation at a wavelength of 1.3 /spl mu/m. It is found that response speeds in excess of 5 Gbit/s with gains of /spl sim/40 should be readily achievable in the absence of carrier trapping effects. Analysis of the electron initiated avalanche current shows an initial low-noise fast pulse due to primary ionization. This is followed by a noisy tail involving hole initiated processes. Structures for future experimental study are proposed.

Cadmium telluride small probes for gamma-ray spectrometry

Cadmium telluride (CdTe), having a rather high atomic number Z and large bandgap E g, is well adapted for manufacturing small gamma ray spectrometers operating at room temperature. Recent progress in materials performance, combined with new approaches in detector structures as well as progress in small sized hybrid low noise electronics and pulse handling systems, have made possible the manufacturing of very small efficient probes. This paper considers different aspects of these new probes, including their spectroscopic performance.

An analog front-end bipolar-transistor integrated circuit for the SDC silicon tracker

A low-noise, low-power, high-bandwidth, radiation hard, silicon bipolar-transistor full-custom integrated circuit (IC) containing 64 channels of analog signal processing has been developed for the SDC silicon tracker The IC was designed and tested at LBL and was fabricated using AT&T's CBIC-U2, 4 GHz f/sub /spl tau// complementary bipolar technology. Each channel contains the following functions: low-noise preamplification, pulse shaping and threshold discrimination. This is the first iteration of the production analog IC for the SDC silicon tracker. The IC is laid out to directly match the 50 /spl mu/m pitch double-sided silicon strip detector. The chip measures 6.8 mm/spl times/3.1 mm and contains 3,600 transistors. Three stages of amplification provide 180 mV/fC of gain with a 35 nsec peaking time at the comparator input. For a 14 pF detector capacitance, the equivalent noise charge is 1300 el. RMS at a power consumption of 1 mW/channel from a single 3.5 V supply. With the discriminator threshold set to 4 times the noise level, a 16 nsec time-walk for 1.25 to 10 fC signals is achieved using a time-walk compensation network. Irradiation tests at TRIUMF to a /spl Phi/=10/sup 14/ protons/cm/sup 2/ have been performed on the IC, demonstrating the radiation hardness of the complementary bipolar process. >

Recent advances in partial discharge measurement capabilities at NIST

Three techniques for measuring the properties of partial discharges (PDs) are described. The first is concerned with an advanced, real-time PD measurement system that allows a complete characterization of the stochastic properties of PD. With this system it is possible to measure a set of conditional PD pulse-amplitude and pulse-time separation distributions from which memory effects characteristic of the discharge phenomena can be quantified and interpreted. Results for pulsating negative corona discharges in gases are shown. The second technique allows PD location in cables using time-domain reflectometry with appropriate statistical analysis. With the third technique, simultaneous measurements are made of the optical and electrical characteristics of PD in liquid dielectrics using fast photography combined with broadband. low-noise pulse current measurements. >

Superconducting strip detector in zero bias current mode: First results on the real-time detection of flux penetration

The real-time detection of flux penetration in superconducting strips placed in a perpendicular magnetic field and no bias current is observed by low-noise pulse implifier. In contrast to the usual resistive technique using bias current we get signals even when a fraction of the width of the strip is transiting.

MICROCALORIMETERS FOR X-RAY SPECTROSCOPY

The merits of microcalorimetry below 1 ° K for high resolution spectroscopy has become widely recognized on theoretical grounds. By combining the high efficiency, broadband spectral sensitivity of traditional photoelectric detectors with the high resolution capabilities characteristic of dispersive spectrometers, the microcalorimeter could potentially revolutionize spectroscopic measurements of astrophysical and laboratory plasmas. In actuality, however, the performance of prototype instruments has fallen short of theoretical predictions and practical detectors are still unavailable for use as laboratory and space-based instruments. These issues are currently being addressed by the new collaborative initiative between LLNL, LBL, U.C.I., U.C.B., and U.C.D.. Microcalorimeters of various types are being developed and tested at temperatures of 1.4, 0.3, and 0.l°K. These include monolithic devices made from NTD Germanium and composite configurations using sapphire substrates with temperature sensors fabricated from NTD Germanium, evaporative films of Germanium-Gold alloy, or material with superconducting transition edges. A new approache to low noise pulse counting electronics has been developed that allows the ultimate speed of the device to be determined solely by the detector thermal response and geometry. Our laboratory studies of the thermal and resistive properties of these and other candidate materials should enable us to characterize the pulse shape and subsequently predict the ultimate performance. We are building a compact adiabatic demagnetization refrigerator for conveniently reaching 0.1°K in the laboratory and for use in future satellite-borne missions. A description of this instrument together with results from our most recent experiments will be presented.