Output Pulse Width Research Articles

Using pulse width modulation with carrier frequency changing for transmission of two separate signals

Pulse width modulation (PWM) is widely used in different applications. PWM transforms the information in the amplitude of a bounded input signal into the pulse width output signal without suffering from quantization noise. The frequency of the output signal is usually constant. In this paper, the new PWM system with frequency changing (PWMFM) is described. In such PWMFM the pulse width and also the carrier frequency are changed. Therefore, two independent pieces of information can be simultaneously transmitted over one channel; hence PWM and frequency modulation (FM) are simultaneously used. But such system needs 2 demodulators, one for PWM and the second for FM. PWMFM can be used in the following applications: LED light intensity control via PWM and several LED block switching by FM PWMFM is highly useful in motor speed control applications by PWM and direction of rotation with FM. PWMFM can be used also in a class-D audio amplifier for power control, e.g. coarse by means of FM and fine by PWM. PWMFM can be used for the simultaneous transmission of two independent information between all, mutual combinations of analog and digital circuits. The analog and digital circuits for modulation and demodulation of PWMF signal are described and measuring results are presented in this work.

An Ultra-Low Power CMOS Integrated Pulse-Width Modulated Temperature Sensor

In this paper an ultra-low power, integrated pulse width modulated (PWM) temperature sensor is presented. The PWM temperature output is generated by the comparing a temperature dependent voltage with another voltage which is temperature independent. The proposed sensor leverages a 2-transistor voltage reference cell that is corrected using feedback through the bulk terminal to provide steady output across temperature. The feedback allows the reference to operate with supply voltages as low as 450 mV. Owing to the low supply voltage and operation in the sub-threshold region, the sensor has a measured power consumption as low as 47.2 nW (@ 27 °C) and 17.6 nW (@ -20 °C). Because of the low voltage required, it is suitable to be powered by harvested energy sources. To realize a robust temperature measurement, the temperature is measured using a ratio of output pulsewidths. A fabricated prototype in 65 nm CMOS has an area of 305 × 220 μm2. The measured maximum temperature error is +1/-2.5 °C, and requires only a two-point calibration for operation over the temperature range -20-80 °C.

Carboxyl graphene oxide mode-locked femtosecond fiber laser

We report a novel graphene oxide derived nanomaterial, carboxyl graphene oxide (GO-COOH) based saturable absorber (SA) for ultra-short pulse generation. Our GO-COOH based SA demonstrates a large modulation depth of 11.4% and a low saturation intensity of 31.12 MW cm−2. The output pulse width is ∼398 fs with a spectral bandwidth of ∼7.45 nm. Stable bound state solitons are also generated with the GO-COOH based SA. Our results show that the GO-COOH is a promising SA for femtosecond pulse generation.

Analysis of a highly efficient phase-locking stabilization method for electro-optic comb generation.

We theoretically show that a slightly modified Pound-Drever-Hall (PDH) stabilization scheme can lead to the optimum time-domain characteristics for electro-optic comb generators (EOCG). The ideal locking point is located by analyzing the EOCG output pulse width. By summing up the electrical field reflected by the EOCG front mirror, a model of the phase-locking error signal is derived with the Jacobi-Anger identical transformation. The simulation and experiment show that the zero-locking point of the error signal of the modified scheme coincides well with the ideal locking point in contrast with the direct application of the PDH scheme. Finally, a power efficiency of up to 2.9% is achieved with this EOCG stabilization scheme. A relative instability of better than 2.6×10-8 is demonstrated by a dual comb interferometer with fixed paths. The Allan deviations of the comb mode frequencies are smaller than 2.8×10-9 and 1.1×10-10 for average times of 1 and 100 s, respectively.

Highly Efficient Single-Switch-Regulated Resonant Wireless Power Receiver With Hybrid Modulation

In this paper, a highly-efficient single-switch-regulated resonant wireless power receiver with hybrid modulation is proposed. To achieve both high efficiency and good output voltage regulation, phase shift and pulse width hybrid modulation are simultaneously applied. The soft switching operation in this topology is achieved by the cycle-by-cycle phase shift adjustment between the input current and the gate drive signal and also attributed to the reactive components such as the series-compensated secondary coil and the parasitic capacitor of the active switch . The soft switching operation also leads to high efficiency and low EMI. By adjusting the duty ratio of the switch, tight regulation of the output voltage can be attained. The steady-state and dynamic models of the resonant receiver with hybrid modulation are analytically derived in order to properly design the feedback controller. An experimental setup of a two-coil wireless power transfer system, including the hardware prototype of the proposed receiver, is constructed for experimental verification. The experimental results show the effectiveness of the soft-switching operation in the receiver with high efficiency while maintaining good regulation of the output voltage, regardless of line and load variations.

Pulse Characteristics of Cavityless Solid-State Laser * *Supported by the National Natural Science Foundation of China under Grant No. 62875100

We propose a theoretical model (cavityless pulsed solid-state-laser theory) to analyze the pulse characteristics of cavity-less solid-state lasers. A high gain Nd:YVO 4 end-pumped cavityless laser system is adopted to verify the theoretical model. It shows that the performance of output energy and pulse width achieved in cavityless configuration is better than that in resonator configuration when the small-signal gain reaches the saturated level. The simulation results calculated by our theoretical model agree very well with the experimental results. This agreement proves the validity of our theoretical model, which has great importance for theoretical analyses of high gain pulsed laser.

A compact, highly stable spectral shearing interferometer to accurately reconstruct ultrafast laser fields

This paper presents a compact design for spectral shearing interferometry to reconstruct an ultrafast electric-field (SPIDER) with a high signal-to-noise ratio (SNR) and stability. Compared experimentally with the traditional SPIDER based on a Michelson interferometer (MI), this design can improve the SNR by a factor of 3.7 in a 25 dB BW region. Using the material dispersions of 6 mm BK7 plates as a target, the phase errors between the measured and theoretical values are less than 2.6 mrad, which is improved by a factor of ~4 from 10.3 mrad measured with the MI-based version. Even for a 1 mm fused silica plate, the measured phase errors are less than 2.1 mrad from the calculated values. Using this design for a 3-day test of our ultrashort pulse laser system, the variation in the output pulse width from the first to the third day is only 1.5%. We attribute this excellent performance to the common-path and all-transmission design of the test pulse pair, giving the design superior capacity against external disturbances. Our design can also work with the two-step phase-shift (TSPS) method to improve its measurement of the plulses with complex temporal/spectral structures.

Tellurene-based saturable absorber to demonstrate large-energy dissipative soliton and noise-like pulse generations

Abstract Two-dimensional layered monoelemental materials (Xenes) with excellent optoelectronic properties have various property-related applications, such as energy, biomedicine, and optoelectronic devices. Xenes also show excellent performance in acting as saturable absorbers (SAs) for obtaining ultrafast laser operations. Few-layer tellurene as a typical Xenens exhibits distinct optoelectronic properties and promising practical application potential, and its nonlinear optical absorption characteristics and related ultrafast modulation applications have been investigated preliminarily. However, tellurene-based SAs to demonstrate large-energy mode-locked operations, which have special applications in industrial and scientific research areas, are seldom studied. In this work, we focus on the preparation of tellurene-based SAs and explore its applications in demonstrating large-energy mode-locked operations [dissipative soliton (DS) and noise-like pulses (NLP)]. For DS operation, the maximum average output power, pulse width, and largest pulse energy are 23.61 mW, 5.87 ps, and 1.94 nJ, respectively. NLP operation with a recorded average output power of 106.6 mW and a pulse energy of 8.76 nJ is also generated, which shows significant enhancement in comparison to previously reported Xenes-based works. Our contribution reveals the great potential and capacity of tellurene-based SAs in obtaining large-energy pulse operations and further promotes the explorative investigation of Xenes-based optoelectronic devices.

Passively Q-switched Tm:YAlO3 laser based on WS2/MoS2 two-dimensional nanosheets at 2 μm

A comparison of the pulsed laser performances of 2 μm passively Q-switched Tm:YAlO3 (YAP) lasers based on the use of tungsten disulfide (WS2) and molybdenum disulfide (MoS2) two-dimensional (2D) nanosheets as saturable absorbers is reported. The novel nanosheets were prepared by chemical vapor deposition (CVD) technology. The microstructure and optical characteristics of the nanosheets were investigated experimentally. In a continuous-wave (CW) operation, the maximum output power of 2.8 W was obtained at an absorbed pump power of 6.9 W, with a corresponding slope efficiency of 46.4%. In a passively Q-switched operation at a pump power of 1.45 W, the average output power, pulse width, repetition rate, pulse energy, and peak power for the Tm:YAP/WS2 laser were 0.11 W, 2.65 μs, 34.7 kHz, 2.9 μJ, and 1.23 W, respectively. As for the Tm:YAP/MoS2 laser, the corresponding values were 0.10 W, 2.5 μs, 24.0 kHz, 3.8 μJ, and 1.55 W.

Analysis of Self-Oscillations in Three-Level Hysteresis Current Controlled H-Bridge

Abstract In direct-current control scheme, self-oscillations or limit cycles occur due to the hysteresis controller. In this contribution, the different types of self-oscillations in a three-level hysteresis current controlled H-bridge are analyzed. The investigations are based on Tsypkin’s method for self-oscillations in relay control systems. So, the conditions for the different types of self-oscillations are given and the frequency of the oscillation and the on-to-off-ratio or pulse width of the switching hysteresis output are calculated exactly. The values correspond to the switching frequency and the duty cycle of the H-bridge. Furthermore, some analyses about the transfer characteristic of the control loop are made.

High-Resolution All-Digital Transmit Beamformer for High-Frequency and Wearable Ultrasound Imaging Systems

In this article, we present a high delay resolution and all-digital transmit-beamforming circuit for use in high-frequency and wearable ultrasound imaging systems. The proposed transmit beamformer comprises an all-digital delay-locked loop (ADDLL), a cycle-based beamforming delay line (CBDL), and a pulse controller. ADDLL can provide specific digital control code for the CBDL to generate stable and suitable delays to excite array transducer elements without variations in process, voltage, and temperature. CBDL not only provides a finer delay resolution for high-frequency ultrasound imaging systems but also requires a few delay cells to maintain the duty cycle of long prorogation signals, thereby significantly reducing hardware costs. The pulse controller can adjust the number and width of output pulses to meet the requirements of different ultrasonic transducers and Doppler ultrasound color imaging. The proposed transmit beamformer uses a 0.18- $\mu \text{m}$ CMOS technology for a 30-MHz high-frequency linear array with 256 elements, and the focusing depth is from 3.5 to 8.1 mm. The measurement results indicate that the proposed transmit-beamforming design can achieve a maximum time delay of 562.6 ns with an average time resolution of 535 ps. The proposed design offers a smaller volume and finer delay resolution, and it is highly suitable for wearable ultrasound imaging systems.

Theoretical and experimental investigation of injection seeded Nd:YAG zigzag slab ring lasers

A comprehensive theoretical and experimental investigation of injection seeded Nd:YAG zigzag slab ring lasers is presented. The effects of injected intensity and detuning frequency on the dynamic process of mode competition are analyzed. A stable single frequency injection seeded Nd:YAG zigzag slab ring oscillator has been built by using the ramp-fire technique with a RbTiOPO4 phase modulator. A linear ramp voltage is used and the detuning frequency is precisely controlled by firing the Q-switch with an adjustable delay time after the resonance condition. Both the simulation and the experiments carried out at various injection conditions have demonstrated that the spectral purity of the output pulse increases with the increase of injected intensity and with the decrease of detuning frequency, and that the frequency locking range increases for both high injected intensity and high gain. The experimental measurements of output pulse energy and pulse width are also in good agreement with the theoretical results.

Graphdiyne for Ultrashort Pulse Generation in an Erbium-Doped Hybrid Mode-Locked Fiber Laser

An erbium-doped hybrid passively mode-locked fiber laser based on few-layer graphdiyne (GDY) saturable absorber (SA) has been investigated for the first time. Hybrid mode-locked fiber laser is composed of nonlinear polarization rotation (NPR) technology and GDY-SA. The central wavelength, pulse width and repetition rate of the output pulse are 1530.7 nm, 690.2 fs and 14.7 MHz, respectively. Compared with the passively mode-locked pulse laser with GDY-SA or NPR technology alone, the output pulse width of hybrid passively mode-locked fiber laser is reduced more than 50 fs. It is demonstrated that the performance of GDY can be potentially applied in ultrafast laser.

A 2.41-pJ/bit 5.4-Gb/s Dual-Loop Reference-Less CDR With Fully Digital Quarter-Rate Linear Phase Detector for Embedded DisplayPort

This paper describes a low-power reference-less 5.4-Gb/s clock and data recovery (CDR) circuit with a fully digital quarter-rate linear phase detector (QLPD) having an extended pulse width output. By using a fully digital circuit and merging XOR function with charge pump, the power efficiency and linearity of the phase detector are improved. The proposed QLPD responds correctly up to 0.75 UI of phase difference at 5.4 Gb/s. The CDR was designed to conform to Embedded DisplayPort (eDP) standard of the Video Electronics Standards Association (VESA). The proposed CDR circuit has been fabricated using a 40-nm CMOS technology. The jitter tolerance (JTOL) margin was measured at 0.75 UI, which is 20% higher than the eDP specification of 0.624 UI at the 20-MHz jitter frequency. BER was measured as less than 10−12 with a 27−1 pseudo random bit sequence (PRBS) pattern. The CDR consumes 12.99 mW, including a bandgap reference circuit and power efficiency achieving 2.41 pJ/bit at 5.4 Gb/s. The area of the proposed CDR is 0.13 mm2.

The Future Prospects for SiPM-Based Receivers for Visible Light Communications

A silicon photomultiplier (SiPM) could be used to create visible light communications receivers whose sensitivity is determined by shot-noise. However, its finite output pulse width will limit its bandwidth and its recovery time, and dark count rate could limit its sensitivity. In this paper, a method of accurately determining the signal levels needed to transmit data in a shot-noise limited system using pulse-amplitude modulation is described. In addition, a method of estimating the additional power needed to use equalisation to overcome inter-symbol interference caused by the finite output pulse width of SiPMs is described. The best way to achieve more than 1 Gb/s with this type of receiver and how to select the best available SiPM as a receiver are then discussed.

Energy scale-up and mode-quality enhancement of the LED-pumped Nd:YAG Q-switched laser achieving a millijoule green pulse.

An efficient LED pumping module is explored for the demonstration of energy scaling of passively Q-switched output to millijoule high-pulse-energy level. For the free-running operation at fundamental wavelength, the highest optical conversion efficiency of 23.7% is reached. By using a Cr4+:YAG crystal as the saturable absorber, the passively Q-switched output energy is up to 14.5mJ in a compact setup. The laser resonator is further optimized to shorten the output pulse width and to obtain better mode quality. The pulse width of the Q-switched emission is as short as 25ns, and the peak power is up to 0.7MW. With such a highly efficient configuration, the extracavity second-harmonic generation at 532nm can be achieved with 4.5mJ pulse energy.

Soliton mode-locking in thulium-doped fibre laser by evanescent field interaction with reduced graphene oxide-titanium dioxide saturable absorber

Soliton mode locking pulse generation in a thulium-doped fibre laser (TDFL) by evanescent wave interaction from a D-shaped fiber coated with rGO-TiO2 nanoparticles is proposed and demonstrated. The rGO-TiO2 nanoparticle coating serves as a saturable absorber (SA), and generates a mode locked pulse with a repetition rate, average output power and pulse width of 9.28 MHz, 11.17 nW and 1.49 ps respectively. The proposed laser has a central lasing wavelength of 1939.4 nm, which is the longest as of yet generated by evanescent wave interaction in a TDFL. An average signal-to-noise ratio of around 50 dB is obtained from the generation pulse, with minimal power and wavelength fluctuations indicating high stability. The proposed laser would have significant applications in various fields, particularly medicine for its operation in the eye-safe region of 2 µm.

Mode-locked ytterbium-doped fiber laser based on offset-spliced graded index multimode fibers

We developed a passively mode-locked ytterbium-doped fiber laser based on offset-spliced graded index multimode fibers (OS-GIMFs), where OS-GIMFs play the role of saturable absorbers. The modulation depth of the saturable absorber is 15.28%, which significantly improves the performance of saturable absorber by adopting offset-spliced method. A stable mode-locked pulse train at 1040 nm with a 27.32 MHz repetition rate is generated when pump power reaches the threshold. The output pulse-width is a ∼11 ps and can be compressed to 980 fs by using a pair of gratings. The fiber laser is superior in terms of low cost, high damage threshold, and easy fabrication; thus, it has potential for application in ultrafast photonics and industrial processing.

Pulse delay-controlled passive Q-switched laser with tunable pulse width

We present a method for obtaining a passive Q-switched Nd : YAG / Cr4 + : YAG laser with tunable pulse width. The output pulse width is tuned based on the delay time between the pumping pulse and trigger pulse. An auxiliary laser with a narrow pulse is used to trigger the laser pulse generation at different delay times during the pumping pulse duration. It is found that the output pulse width can be continuously adjusted from 1415 to 562 ps with an output peak power ranging from 44 to 240 kW at a fixed pumping power. The beam quality factor M2 is kept <1.5 with changing of the pulse width.

PMMA Sandwiched Bi2Te3 Layer as a Saturable Absorber in Mode-Locked Fiber Laser

In this paper, we fabricated a PMMA sandwiched Bi2Te3 self-assembly layer as a saturable absorber device, which was used as a passive mode locker for ultrafast pulse generation at the telecommunication band. Nanosheets of Bi2Te3 as a bulk topological insulator were successfully synthesized through a solvothermal treatment and self-assemble method to form a thin film at a water-air interface. In order to transfer the Bi2Te3 self-assembly layer to the optical fiber end, we design a construction of two PMMA layers sandwiched self-assembly layer. By incorporating this saturable absorber into an erbium-doped fiber laser, femtosecond mode-locking operation was experimentally demonstrated. The output pulse width is about 505 fs. Our results indicate that PMMA sandwiched topological insulator layer structure could be an improvement technology in traditional PMMA transfer method and could be used as a long-term stable saturable absorber for the passively mode locking lasers.