Pulse Pattern Generator Research Articles

Optical transmitter for time-bin encoding quantum key distribution

We introduce an electro-optical arrangement that can produce time-bin encoded symbols with the decoy state method over a standard optical fiber in the C-band telecom window. The device consists of a specifically designed pulse pattern generator for pulse production and a field-programmable gate array that controls timing and synchronization. The electrical pulse output drives a sequence of intensity modulators acting on a continuous laser that deliver bursts of weak optical pulse pairs of discrete intensity values. Such a transmitter allows for the generation of all the quantum states needed to implement a discrete variable quantum key distribution (QKD) protocol over a single-mode fiber channel. Symbols are structured in bursts; the minimum relative delay between pulses is 1.25 ns, and the maximum symbol rate within a burst is 200 MHz. We tested the transmitter on simulated optical channels of 7 dB and 14 dB loss, obtaining maximum extractable secure key rates of 3.0 kb/s and 0.57 kb/s, respectively. Time-bin-state parameters such as the symbol rate, pulse separation, and intensity ratio between the signal and decoy states can be easily accessed and changed, allowing the transmitter to adapt to different experimental conditions and contributing to the standardization of QKD implementations.

Development of digitally processed DC reactive sputtering and its application to the synthesis of (Er0.1Y0.9)2SiO5 layered crystalline thin film

We have developed a digitally processed DC reactive sputtering (DPDRS) system that enables synthesis of arbitrarily designed atomically precise deposition of metal oxide compounds. Pulsed-DC sputtering employing a digital pulse pattern generator can perform the temporally alternating process of multiple metal sputtering and oxidation. High-speed switching of the pulsed-DC sputtering process driven by the digital signal processing was confirmed from time-resolved plasma emission spectroscopy. Metal sputtering, which was temporally separated from the oxidation process, resulted in a deposition rate higher than 1 μm/h. It was also found that the temporally separated radical oxidation at the deposited metal surface could control the oxidation process. The DPDRS was applied to layer-by-layer synthesis of (Er0.1Y0.9)2SiO5 (EYSO) films oriented to the ⟨100⟩ direction. The deposition rate for each metal target (Er and Y) was adjusted to 0.86 nm/cycle corresponding to a d-spacing of the (100) plane by changing independently the duty ratio of the base pulse for plasma generation. X-ray diffraction measurements indicated a formation of ⟨100⟩ highly oriented (Er0.1Y0.9)2SiO5 crystalline thin films. Photoluminescence spectra and the decay characteristics also showed synthesis of high crystalline quality EYSO films better than those obtained by pulsed laser deposition.

Driving a low critical current Josephson junction array with a mode-locked laser

We report proof-of-concept experiments on an optically driven Josephson voltage standard based on a mode-locked laser (MLL), a time-division multiplexer, and a cryogenic ultrafast photodiode driving an overdamped Josephson junction array (JJA). Our optical pulse pattern generator (PPG) concept builds on the capability of MLLs to produce trains of picosecond-wide optical pulses with little amplitude and temporal spread. Our present setup enables multiplication of the original 2.3 GHz pulse repetition frequency by a factor of 8. A commercial photodiode converts the optical pulses into about 25 ps wide electrical pulses in liquid helium several cm from the JJA. Using a custom-made MLL, we can drive a JJA with a low critical current of 360 μA at multiple Shapiro steps. We have performed experiments with pulse pairs whose time interval can be set freely without distorting the shapes of individual pulses. Experimental results are in qualitative agreement with theoretical simulations, and they demonstrate, e.g., crossover in the Shapiro step pattern when the time interval between the pulses is approximately equal to the inverse of the characteristic frequency of the JJA. However, there are quantitative discrepancies, which motivate an improved integration of photodiodes and JJAs to improve both the understanding and fidelity of Josephson Arbitrary Waveform Synthesizers. Considering future quantum technologies in a wider perspective, our optical approach is a potential enabler for fast and energy-efficient pulse drive without an expensive high-bandwidth electrical PPG and without high-bandwidth electrical cables that yield too high thermal conductance between cryogenic and room temperatures.

Investigation of Broadband Wilkinson Power Dividers for Pulse-Driven Josephson Voltage Standards

This paper describes recent developments for increasing the output voltage of the Josephson Arbitrary Waveform Synthesizer (JAWS) at PTB. For this purpose, we developed modified broadband Wilkinson power dividers, which enable the operation of two or four Josephson junction series arrays per RF channel of the pulse pattern generator and thus the generation of increased output voltages. In detail, we designed and investigated two different Wilkinson power dividers: the one-stage three-section Wilkinson power divider with extended bandwidth and the two-stage single-section Wilkinson divider with more outputs to combine four parallel series arrays. They were both integrated with triple-stacked Josephson junction series arrays. Additionally, a new modulator pulse amplifier was introduced into the JAWS set-up to provide sufficient power for all the junction arrays. Our measurement results show that spectrally pure sinusoidal waveforms were successfully generated with both types of power dividers. With the one-stage three-section Wilkinson power divider, we obtained RMS voltages of nearly 53 mV at a clock-frequency of 15 GHz combined with a test array of 3000 Josephson junctions. As for the two-stage single-section Wilkinson power divider combined with a test array of 6000 Josephson junctions, we synthesized RMS output voltages of about 105 mV. These test results show a promising prospect for quantum voltage standard applications.

Development of RF Power Dividers for the Josephson Arbitrary Waveform Synthesizer

To make the experimental setup of the Josephson arbitrary waveform synthesizer less complex by reducing the number of RF cables between room and cryogenic temperature, we developed on-chip RF power dividers. By integration of these components, we can eventually increase the number of Josephson junctions operated by one single pulse-pattern generator channel, and thus reduce the costs of the setup. At Physikalisch-Technische Bundesanstalt, we designed, fabricated, and investigated the performance of two different RF power dividers types: the serial–parallel and the Wilkinson power divider. Spectrally pure sinusoidal waveforms were successfully synthesized with both types of power dividers. With the Wilkinson power divider, we obtained 17.55 mV (rms) at a clock frequency of 15 GHz combined with a test array of 1000 Josephson junctions. As for the serial–parallel power divider combined with a test array of 2000 Josephson junctions, we synthesized rms output voltages of 19.0 mV.

Electrical Quantum Metrology Standard for the Synthesis of Ac Voltages

A prototype Josephson quantum standard for synthesizing sine waves characterised by low-level harmonics and high accuracy was developed, opening up new possibilities for metrological support in the area of ac voltage. The standard includes a cryogenic probe with Josephson chips, a delta-sigma modulator, a pulse pattern generator, a compensation circuit, a spectrum analyzer, a video control unit, as well as special software. A capability of sine wave synthesis with an output voltage up to 130 mV RMS over a wide frequency range from 1 kHz to 100 kHz is demonstrated. Higher harmonics are suppressed below the noise floor up to 100 dBc.

Optical frequency comb generation via pulsed gain-switching in externally-injected semiconductor lasers using step-recovery diodes

We report on the experimental generation of high-quality Optical Frequency Combs (OFCs) at low repetition rates in an externally-injected gain-switched semiconductor laser using a Step-Recovery Diode (SRD) as the pulsing source. The use of an SRD as the electrical pulse generator allows us to produce high-quality OFCs with over 900 comb tones spaced by 100 MHz. Through experimental measurements, supported by simulations, the timing jitter of the electrical source has been demonstrated to impact the quality of the generated OFCs giving rise to a non-uniform Carrier-to-Noise Ratio which is higher around the injection and reduces with decreasing frequency. Nevertheless, comparing the OFC quality obtained using an SRD with those obtained with a costly pulse pattern generator, we conclude, that despite the slightly degraded OFC quality, the use of SRDs could reduce the cost, size and footprint of the equipment required for low repetition rate OFC generation.

Quantum Standard for Synthesis AC Voltage

Prototype of quantum standard based on the Josephson effect for synthesis sine wave with low level harmonics and high accuracy was developed at VNIIM, which opens up new possibilities for metrological support in the field of АС voltage. The standard includes cryogenic probe with Josephson chips, delta-sigma modulator, pulse pattern generator, compensation circuit, spectrum analyzer, video control unit and software. The capability of synthesis sine wave with an output voltage up to 130 mV RMS over a wide frequency range from about 1 kHz to 100 kHz is shown. Higher harmonics are suppressed bellow the noise floor up to 100 dBc.

Pulsation of InGaAs Photodiodes in Liquid Helium for Driving Josephson Arrays in AC Voltage Realization

A commercially available InGaAs p-i-n photodiode chip has been custom packaged and high-speed operated in liquid helium. The photodiode was driven by light pulses using a dc-biased 1310-nm laser, a Mach-Zehnder modulator, and a return-to-zero pulse pattern generator up to 15 GHz clock frequencies, which produced pulse widths down to 77 ps and maximum peak current heights above 10 mA. With the prospect of using this photodiode assembly to operate pulse-driven Josephson junction arrays for ac voltage realization, pulsation modes with constant pulse width and varying pulse density were applied to the diode, which resulted in consistent pulse shapes for bit rates as high as 7.5 Gb/s. This could yield realizable peak voltages as high as 15.525 μV per Josephson junction. Time-lapse pulse measurements were performed over the span of 90 min, which demonstrated good waveform stability. Using the measured current waveforms, the behavior of a typical Josephson junction was simulated according to the Stewart-McCumber model, which resulted in an operational margin of 2 mA for the first Shapiro step.

Sub-Kelvin (100 mK) time resolved electron paramagnetic resonance spectroscopy for studies of quantum dynamics of low-dimensional spin systems at low frequencies and magnetic fields.

This article presents a time-resolved electron paramagnetic resonance spectrometry setup designed to work at frequencies below 20 GHz and temperatures down to 50 mK. The setup consists of an on-chip microstrip resonator (Q < 100) placed in a dilution cryostat located within a superconducting 3D vector magnet. A housemade spin echo circuitry controlled by a microwave network analyzer, a pulse pattern generator, and an oscilloscope connects to the microstrip through a series of copper, stainless steel, and superconducting semirigid coaxial lines which are thermally anchored to the different cooling stages of the fridge by means of power attenuators, circulators, and a cryogenic amplifier. Spin echo experiments were performed at a 0.5-T magnetic field on a spin 1 2 paramagnetic coal marker sample mounted on a 15 GHz microstrip resonator at temperatures ranging from 100 to 800 mK. The results show an increase in echo signal intensity as temperature is decreased until saturation as theoretically expected in reaching 99% spin polarization at 100 mK. Our technique allows tuning of the spin system in the pure-state regime and minimizing dipolar fluctuations, which are the main contribution to decoherence in solid-state samples of single-molecule magnets (SMMs) - molecular spin systems that are currently being tested for applications in quantum computation. The achievement of full spin polarization at 100 mK will allow for coherent control over the time evolution of spin systems without the need for large magnetic fields (commonly used to polarize the dipolar bath at higher temperatures) and high frequencies.

Optical Pulse-Drive for the Pulse-Driven AC Josephson Voltage Standard

We developed an optical pulse-drive for the operation of the Josephson Arbitrary Waveform Synthesizer (JAWS) using a fast photodiode (PD) operated at 4 K, close to the JAWS chip. The optical pulses are transmitted to the PD by an easily removable optical fiber attached to it. A bare-lensed PD is mounted by flip-chip technique to a custom-made silicon-carrier chip. This carrier chip is equipped with coplanar waveguides to transmit the electrical pulses from the PD to the JAWS chip mounted on a separate printed circtuit board (PCB). The main components of this optical setup are a laser source, a high-speed Mach–Zehnder modulator, and the modulator driver. The waveform pattern is supplied by a commercial pulse pattern generator providing up to 15 GHz electrical return-to-zero (RTZ)-pulses. Unipolar sinusoidal waveforms were synthesized. Using a JAWS array with 3000 junctions, an effective output voltage of 6.6 mV root mean square (RMS) at the maximum available clock-frequency of 15 GHz was achieved. Higher harmonics were suppressed by more than 90 dBc at laser-bias operation margins of more than 1 mA.

All-PM wavelength-tunable and harmonically mode-locking Yb-doped fiber laser.

We report a wavelength-tunable harmonically mode-locking dissipative soliton fiber laser based on a high-speed intensity modulator with a simple all-polarization-maintaining (all-PM) cavity. The center wavelength can be precisely tuned from 1029.35 to 1079.25nm by tuning only the frequency of the pulse pattern generator (PPG), and the linear tuning accuracy of the wavelength can reach 0.0093nm/kHz. The degree of polarization can reach 98.969%. The FWHM of the pulse is measured to be 30.1ps, and the intracavity pulse energy after the gain fiber can reach 5.41nJ. All orders of the harmonic mode-locking repetition rate are tuned from ∼33.346 to ∼366.806 MHz through adjustment of the data length and frequency of PPG.

An Improved Electronic Image Motion Compensation (IMC) Method of Aerial Full-Frame-Type Area Array CCD Camera Based on the CCD Multiphase Structure and Hardware Implementation.

In this paper, the performance of the electronic conventional image motion compensation (IMC) method based on the time delay integration (TDI) mode was analyzed using the optical injection formula of charge coupled devices (CCDs). The result shows that the non-synchronous effect of charge packet transfer caused by line-by-line transfer during exposure makes the compensated image dissatisfying. Then an improved electronic IMC method based on the CCD multiphase structure was proposed. In this method, a series of proper driving clocks were applied to drive the charge packet to move electrode-by-electrode during the exposure time, which results in a minimum non-synchronous effect of charge packet transfer. The mismatch of velocity between charge packet transfer and image motion was decreased. The performance of the improved electronic IMC method was also analyzed using the optical injection formula. The modulation degrees of the two methods were compared. The average value of the modulation degree of the improved electronic IMC method was 47/96, greater than the conventional electronic IMC method, which was 1/3. To achieve the improved electronic IMC, the driver timing diagram of the improved electronic IMC method was proposed. This paper presented an improved hardware implementation method for the improved electronic IMC method. Based on the basic FTF4052M drive circuit system, an IMC pulse pattern generator that worked together with the main pulse pattern generator (SAA8103) was added to achieve the improved electronic IMC. Then, the internal structure of the IMC pulse pattern generator was given. A dual pulse pattern generator drive circuit system was proposed. After computer simulation and indoor real shot verification, the compensation effect of the improved electronic IMC method was better than the compensation effect of the conventional electronic IMC method.

Experimental demonstration of message transmission over an optical fiber link modulated by an ultra-wideband carrier generated by a chaotic laser diode

In this paper, we experimentally demonstrate message transmission over a commercial optical fiber link modulated by an ultra-wideband (UWB) carrier generated by a chaotic laser diode subject to optical feedback. The laser diode subject to the optical loop feedback is adopted to generate the chaotic UWB carrier. The message, which is generated by a pulse pattern generator, is modulated by the optical intensity modulator. After being transmitted over a 2 km standard single-mode fiber (SSMF), the waveform is recorded by a real-time oscilloscope, in front of which is a photodetector. A message with a bit rate of 2 Gb/s is successfully transmitted over the 2 km SSMF using the chaotic UWB-over-fiber system. In addition, the influences of the amplitude, the bit rate of the message, and the optical power in the SSMF on the transmission quality are separately analyzed in detail. The results presented in this paper are of great importance for UWB communications.

Ultrafast, high repetition rate, ultraviolet, fiber-laser-based source: application towards Yb+ fast quantum-logic.

Trapped ions are one of the most promising approaches for the realization of a universal quantum computer. Faster quantum logic gates could dramatically improve the performance of trapped-ion quantum computers, and require the development of suitable high repetition rate pulsed lasers. Here we report on a robust frequency upconverted fiber laser based source, able to deliver 2.5 ps ultraviolet (UV) pulses at a stabilized repetition rate of 300.00000 MHz with an average power of 190 mW. The laser wavelength is resonant with the strong transition in Ytterbium (Yb+) at 369.53 nm and its repetition rate can be scaled up using high harmonic mode locking. We show that our source can produce arbitrary pulse patterns using a programmable pulse pattern generator and fast modulating components. Finally, simulations demonstrate that our laser is capable of performing resonant, temperature-insensitive, two-qubit quantum logic gates on trapped Yb+ ions faster than the trap period and with fidelity above 99%.

Advanced Pulse Pattern Generation and Fine Tuning for STED Microscopy

Stimulated Emission Depletion (STED) microscopy has evolved into an established imaging method offering super-resolution well beyond 50 nm. Whereas STED is now available in many laboratories, it is still in the focus of research to push the boundaries of its capabilities and applications. Time-resolved STED microscopy using time correlated single photon counting (TCSPC), is advantageous for many applications and promises further development for increased resolution and less photo-damage.Here, we show the application of established methods (e.g. gSTED) as well as emerging applications of time-resolved STED. We employ pulsed interleaved excitation (PIE), where the STED laser is pulsed at half the frequency of the excitation laser, such that STED and confocal data is taken practically at the same time. By using this approach, single molecule STED experiments can be carried out while the confocal control-experiment is performed simultaneously, allowing to account for measurement artifacts due to the high power of the STED laser. We will show examples from single molecule imaging, where blinking and bleaching are monitored using the confocal data. Furthermore, we will present STED-FCS data, where the confocal data allows insight into changes of the sample due to the STED laser. Since the control experiment for the influence of the STED laser is performed at the same time as the STED measurement, experimental parameters can be adjusted online to give highest resolution while ascertaining that the relevant information drawn from the experiment is not affected.Furthermore, we will present how electronically delaying the STED laser with respect to the excitation laser can increase resolution with no increase in photo-bleaching. By setting the arrival of the STED laser with an accuracy of about 20 ps, experimental conditions for fluorophores with different fluorescence lifetimes can be adjusted.

Optimization-Based Cell Selection Method for Grid-Connected Modular Multilevel Converters

Modular multilevel converters (MMCs) are widely used in different applications. Due to low-loss operation, compactness, and high modularity, MMC is extremely attractive for high-voltage direct-current (HVDC) transmission systems. The HVDC station loss is highly related to the converter switching pulse pattern, which is generated by modulation algorithm and cell selection methods. This paper formulates the switching pulse pattern generation, as a versatile optimization problem. The problem constraints and objectives are formulated for HVDC applications and compared with similar problems in the field of computer science. To overcome the computational complexity in solving the introduced optimization problem, a heuristic method is proposed for cell selection algorithm. The method utilizes the current level in order to obtain lossless switching at zero-current crossings. The study of the proposed method, in a time-domain simulation platform, shows that the method can reduce the switching converter losses by 60% compared to carrier-based modulation, maintaining the same capacitor voltage ripple. Eventually, the practical functionality of the proposed method is verified in a real-time digital simulator, RTDS, for a 512-level converter in a point to point HVDC link. Although this paper focuses on HVDC, the mathematical model is applicable for any MMC application.

Towards a 1 V Josephson Arbitrary Waveform Synthesizer

The establishment at PTB of an AC Josephson voltage standard (Josephson Arbitrary Waveform Synthesizer- JAWS) based on pulse-driven Josephson arrays is focused on achieving an output voltage of at least 1 Vrms which is required for many metrology applications. In this paper, we approached this goal by increasing the number of active junctions in two ways. Firstly, we fabricated arrays containing triple-stacked SNS-type Josephson junctions with Nb x Si 1-x as barrier material. We obtained current operation margins of about 0.2 mA with arrays of up to 9000 Josephson junctions at an rms voltage of 355 mV. Secondly, we used a new 8-channel ternary pulse pattern generator (PPG) to bias up to 8 arrays connected in series. An output voltage of V RMS = 1006 mV(V PP = 2.845 V) was achieved by using 8 arrays (arranged on 4 separate chips) with 63000 junctions in total. Higher harmonics are suppressed by at least -116 dBc. The fabrication process and the experimental setup will be described, as well as experimental results that are leading towards our 1 V goal.

Pulse Information Detection Based on Image Senor

In order to simulate the diagnosis by feeling the pulse with Traditional Chinese Medicine，the pulse image acquisition system was developed. A CMOS camera attached to a magnifying lens is used to solve the problem that industrial cameras can not carry out the image acquisition in microspur. The improved system could avoid the influence from environment light. The cantilever beam structure was adopted to obtain the pulse-taking pressure value directly and accurately. The thin film is made of the liquid membrane silica gel, which can overcome some shortages of the previous film. The typical pulse images were collected from the MM-3 pulse pattern generator by using the improved system. The results show that the improved system provides reliable conditions for analyzing the pulse information.

Low-jitter single flux quantum signal readout from superconducting single photon detector

We developed a single-flux-quantum (SFQ) readout technology for superconducting single-photon detectors (SSPDs) to achieve low-jitter signal readout. By optimizing circuit parameters of the SFQ readout circuit, the input current sensitivity was improved below 10 μA, which is smaller than a typical critical current of SSPD. The experiment using a pulse-pattern generator as an input pulse source revealed that the measured jitter of the SFQ readout circuit is well below the system jitter of our measurement setup for the input current level above 15 μA. The measured jitter of the SSPD connected to the SFQ readout circuit was 37 ps full width at half maximum (FWHM) for an SSPD bias current of around 18 μA, which is a significant improvement on 67 ps FWHM jitter observed in conventional readout without an SFQ readout circuit.