Ps Optical Pulses Research Articles

Nonlinear optical properties of lanthanum titanate glasses prepared by levitation melting

Lanthanum titanate glasses (17 La2O3-83 TiO2) are fabricated via aerodynamic levitation melting. Nonlinear refraction and absorption were measured with the Z scan technique using ∼550 ps optical pulses at 532 nm wavelength with peak intensities in the range of 0.25–2.5 GW/cm2. The two-photon absorption coefficient (β) and the effective nonlinear refraction coefficient (n2eff) are found to be, respectively, 2.19 cm/GW and 152 × 10−16 cm2/W (85 × 10−13 esu). The Raman gain is measured to be 106 × 10−11 cm/W. The nonlinearity strength is found to be nearly 60 times larger in lanthanum titanate glasses relative to silica.

Short pulses from a gain-switched quantum cascade laser

The picosecond carrier dynamics observed in quantum cascade lasers (QCLs) poses a fundamental obstacle for the formation of intracavity pulses. On the other hand, the ultrafast gain response makes the QCL ideally suited for high frequency modulation of its pump current. In this work, we leverage this property and use short electrical excitations to generate 33 ps optical pulses with up to Watt level peak power. We ensure lasing on a single resonator mode via optical injection seeding. The resulting pulses are characterized in both time and frequency domains using an optical sampling method in combination with a spectrometer. We interpret the obtained results using laser rate equations. The results presented in this work open new pathways for the generation of highly tunable, high power mid-infrared pulses from a monolithic source.

All-Optical Three-Input “AND” Gate Dependent on a Differential Modulation Architecture

This gazette focuses on simulation and experimental studies for all-optical three-input “AND” gate schemes. The proposed gate exploits the semiconductor optical amplifier Mach-Zehnder Interferometer (SOA-MZI) nonlinearities, particularly the cross-phase modulation (XPM) corollary in addition to the cross-gain modulation (XGM) corollary, which originates from a SOA-MZI differential modulation concept. Further, the system performance is analyzed and examined through actual and simulated results to evaluate the obtained “AND” gate signal. Dependent on the nonlinearity of SOAs, the all-optical “AND” gate can operate with three signals driven by a 2 picoseconds (ps) optical pulse source (OPS). We noticed that our experimental results are perfectly matched to the simulated results. The output “AND” signal is acquired at higher common harmonics up to 200 GHz in the simulation study and the optical “AND”, which can vastly be used in optical networking, is evaluated through many parameters, such as error vector magnitude (EVM), extinction ratio (ER), and gain. As a result, the pinnacle bit rate for the 16-QAM (Quadrature Amplitude Modulation) and 256-QAM “AND” signal reaches 100 and 200 Gbit/s, respectively, at the 100 GHz common harmonic frequency.

Dynamic strain evolution in an optically excited Pt thin film.

The structural evolution of a Pt thin film following photo-thermal excitation by 1 ps optical laser pulses was studied with a time resolution of 100 ps over a total time period of 1 ms. Laser pulse fluences below 50 mJ/cm2 were insufficient to relax the residual stress state of the as-prepared film even after 10 000 pulses. In this fluence regime, a rapid initial lattice expansion and a decrease in the lattice coherence length due to ultrafast photo-thermal heating were observed. The lattice expansion reached a maximum, and the coherence length reached a minimum, 100–200 ps after excitation before monotonically decaying back to their initial values in about 1 µs. Laser pulse fluences greater than 50 mJ/cm2 produced irreversible stress relaxation within the first 10 optical pulses. In this regime, the lattice expansion was qualitatively similar to that in the low fluence regime, except that the initial structural state was not recovered. The evolution in the coherence length, however, was more complex. Following an initial decrease similar to that observed at low fluence, the coherence length then increased to a broad maximum greater than the initial value, before recovery.

A Method of Measuring the Parameters of the Response Speed of Photodetectors

Problems arising in the measurement of the parameters of the response speed of current broadband photodetectors by the method based on measurement results of the rise time of transitional characteristics. A method is proposed for quantitative estimate of response speed, using the results of the determination of impulse response of a photodetector being examined. A pulsed fiber optic laser operating in a condition of self-synchronization of modes, and providing the generation of ultrashort (approximately 3 ps) optical pulses, serves as the source of measurement signals. A measurement installation that makes it possible to implement the proposed method of measurement is provided. Certain results of experimental testing of the method are given.

Picosecond pulse-width ultra-low repetition rate passive mode-locked fibre ring laser

The authors experimentally demonstrate an ultra-low repetition rate passive mode-locked fibre ring laser with a semiconductor optical amplifier works like as a gain medium and non-linear polarisation rotation. A unidirectional erbium-doped fibre amplifier provides additional gain to increase cavity power. By exploiting non-linear polarisation rotation combined with dispersion management stable 5.18 ps optical pulses with 67.2 kHz repetition rate and energy of 1.75 nJ were generated with an extinction ratio >35 dB. The central wavelength is 1557.89 nm and the optical 3-dB bandwidth 1.82 nm very appropriate for optical applications that often require high-peak-power, low repetition rate and picosecond pulses.

Method for measuring the speed parameters of photodetectors

The article discusses the difficulties that arise when measuring the speed parameters of modern broadband photodetector devices by a method based on the measurement results of the rise time of the transition characteristic are considered. As a solution of the described problems a method is proposed for quantitatively evaluating of speed parameters using the results of determining the impulse response of the studied photodetector. The source of the test signals is a pulsed fiber laser operating in the self-mode locking mode and generating ultrashort (about 3 ps) optical pulses. The article describes in detail the method itself, the measuring setup that allows it to be implemented, and presents some results of experimental testing of the method

Soliton-effect optical pulse compression in CMOS-compatible ultra-silicon-rich nitride waveguides

The formation of optical solitons arises from the simultaneous presence of dispersive and nonlinear properties within a propagation medium. Chip-scale devices that support optical solitons harness high field confinement and flexibility in dispersion engineering for significantly smaller footprints and lower operating powers compared to fiber-based equivalents. High-order solitons evolve periodically as they propagate and experience a temporal narrowing at the start of each soliton period. This phenomenon allows strong temporal compression of optical pulses to be achieved. In this paper, soliton-effect temporal compression of optical pulses is demonstrated on a CMOS-compatible ultra-silicon-rich nitride (USRN) waveguide. We achieve 8.7× compression of 2 ps optical pulses using a low pulse energy of ∼16 pJ, representing the largest demonstrated compression on an integrated photonic waveguide to date. The strong temporal compression is confirmed by numerical calculations of the nonlinear Schrödinger equation to be attributed to the USRN waveguide’s large nonlinearity and negligible two-photon absorption at 1550 nm.

Single-channel 7.68 Tbit/s, 64 QAM coherent Nyquist pulse transmission over 150 km with a spectral efficiency of 9.7 bit/s/Hz.

We achieved a record capacity of 7.68 Tbit/s in a single-channel OTDM transmission with a 9.7 bit/s/Hz spectral efficiency, where a polarization-multiplexed 640 Gbaud, 64 QAM coherent Nyquist pulse has been transmitted over 150 km. In this scheme, a 1.39 ps optical Nyquist pulse with an OSNR of 53 dB at a 0.1 nm resolution was generated by combining a mode-locked laser and a highly nonlinear fiber and used at both the transmitter and receiver. Phase synchronization was achieved between these pulse sources with an advanced optical phase-locked loop based on the higher harmonics of the mode-locked laser mode. In addition, we suppressed a nonlinear phase rotation at an EDFA in the transmitter by broadening the pulse width with second-order dispersion and recompressed it to the original pulse width before a 150 km transmission link. We succeeded in a bit error rate below 2 x 10-2 for all tributaries.

Nonvolatile All‐Optical 1 × 2 Switch for Chipscale Photonic Networks

Integrated chip‐level photonics has the potential to revolutionize future computer systems by eliminating the “von‐Neumann information bottleneck” and the power losses resulting from the use of electrical interconnects. Yet, the need for optical‐to‐electrical conversion has so far hindered the implementation of chip‐level all‐optical routing schemes, which remain operational without continuous power consumption. Here, a crucial component to successful implementation of such all‐photonic networks is demonstrated – an effective, practicable all‐optical nonvolatile switch. Current integrated all‐optical switches require constant bias power to operate, and lose their state when it is removed. By contrast, our switch is entirely nonvolatile, with the direction of light flow altered by switching the phase state of an embedded phase‐change cell using 1 ps optical pulses. High on/off switching contrast devices are achieved that are fully integrated and compatible with existing photonic circuits. It is shown that individual switching events occur with transition times below 200 ps and thus hold promise for ultrafast light routing on chip. The approach offers a reliable and simple route toward hybrid reconfigurable photonic devices without the need for electrical contacting.

Widely Continuous Tunable ps Pulse Train Generation Based on SOA Nonlinear Dynamics

We propose a simple setup based on nonlinear dynamics in a semiconductor optical amplifier (SOA) and solitonic compression for the generation of stable and tunable repetition rate picosecond (ps) optical pulses. A quantum-well SOA is used to amplify electrical-optic-modulated rectangular optical signal, during which the nonlinear amplification process induces front-edge distortion. Due to the non-zero linewidth enhancement factor, the front-edge distortion can be isolated by the optical filtration of the chirped frequency component, which eventually becomes Gaussian-like pulse train of tens of ps FWHM pulsewidth. Following a stage of solitonic compression and a stage of pedestal suppression, we are able to obtain a train of 1-ps high-quality pulses for which the root mean square timing jitter is $C$ -band.

Spot event detection along a large-scale sensor based on ultra-weak fiber Bragg gratings using time-frequency analysis.

A simple scheme for interrogating a 5 m long photonics device and its potential applications to quasi-distributed fiber sensing is proposed. The sensor consists of an array of 500 identical, very weak fiber Bragg gratings (FBGs). The gratings are 9 mm long and have been serially written in cascade along a single optical fiber. The measurement system is based on a combination of optical time domain reflectometry and frequency scanning of the interrogating pulse. The time-frequency analysis is performed by launching an optical pulse into the sensor and retrieving and analyzing the back-reflected signal. The measurement of the temperature, length, and position of spot events along the sensors is demonstrated with good accuracy. As both spatial and temperature resolution of the method depend on the input pulse duration, the system performance can be controlled and optimized by properly choosing the temporal duration of the interrogating pulse. A spatial resolution of 9 mm (ultimately dictated by one grating length) has been obtained with an 80 ps optical pulse, while a temperature resolution of less than 0.42 K has been demonstrated using a 500 ps incident pulse. The sensor proposed proves to be simple, robust, and polarization insensitive and alleviates the instrumentation complexity for distributed sensing applications.

Periodic modulation-based spectral and temporal superresolution with a single measurement.

In a superresolution technique, based on periodic modulation of the signal to be tested, high resolution is obtained for a large number of modulation harmonics. However, the number of measurements, required for measuring one quantity, is equal to the number of harmonics. Two techniques of spectral and temporal superresolution with a single measurement, based on replication of the signal, are proposed and numerically demonstrated. In the first one, replication and modulation lead to sampling and compression in the Fourier transform domain. It is shown that an optical spectrum analyzer with a resolution of 0.01 nm (1.25 GHz) is capable of measuring 1 MHz spectral lines with a resolution of 60 kHz, using the superresolution technique proposed. The spectrum is magnified by a factor of 10,000. Similarly, the measurement of 1.7 ps optical pulses with a resolution of 44 fs can be performed with a 30 GHz real-time oscilloscope. The magnification factor is 160. In the second proposed method, the parts of the signal Fourier transform for each replica are shifted into the system passband. This method is useful for measurement of very long single-shot ultrafast temporal waveforms.

Supercontinuum generation at 1.55 μm in an all-normal dispersion photonic crystal fiber with high-repetition-rate picosecond pulses

We demonstrate the generation of supercontinuum (SC) spectrum covering S+C+L band of optical communication by injecting 1.4 ps optical pulses with center wavelength of 1 552 nm and repetition rate of 10 GHz into an all-normal dispersion photonic crystal fiber (PCF) with length of 80 m. The experimental results are in good agreement with the numerical simulations, which are used to illustrate the SC generation dynamics by self-phase modulation and optical wave breaking (WB).

Pulse capture without carrier absorption in dynamic Q photonic crystal nanocavities.

We develop a gallium arsenide (GaAs) photonic crystal nanocavity device capable of capturing and releasing a pulse of light by dynamic control of the Q factor through free carrier photoexcitation. Unlike silicon-based devices where the performance of this dynamic optical control is limited by absorption from free carriers with nanosecond-order lifetimes, the short carrier lifetime (∼ 7 ps) of our equivalent GaAs devices enables dynamic control with negligible absorption losses. We capture a 4 ps optical pulse by briefly cycling the Q factor from 40,000 to 7900 and back just as the light couples to the nanocavity and confirm that the captured energy can be subsequently released on demand by a second injection of free carriers. Demonstrating dynamic control with negligible loss in a GaAs nanophotonic device also opens the door to dynamic control of cavity quantum electrodynamics with potential application towards quantum information processing.

Generation of mode-locked optical pulses at 1035 nm from a fiber Bragg grating stabilized semiconductor laser diode

We report the generation of transform-limited, ~18 ps optical pulses from a fiber Bragg grating (FBG) stabilized semiconductor laser diode. Up to 7.2 pJ of pulse energy and a peak power of 400mW were achieved when operating at a repetition frequency of 832.6 MHz, a multiple of the cavity (diode + FBG) free spectral range (FSR). A small detuning in the repetition frequency resulted in broader optical pulses. We have shown experimentally the transition from a gain-switched regime of operation to mode-locked operation once the injection current modulation frequency is set to match a harmonic of the cavity FSR. The transition also results in a reduction in the timing jitter of the optical pulses.

All optical quantum control of a spin-quantum state and ultrafast transduction into an electric current

The ability to control and exploit quantum coherence and entanglement drives research across many fields ranging from ultra-cold quantum gases to spin systems in condensed matter. Transcending different physical systems, optical approaches have proven themselves to be particularly powerful, since they profit from the established toolbox of quantum optical techniques, are state-selective, contact-less and can be extremely fast. Here, we demonstrate how a precisely timed sequence of monochromatic ultrafast (~ 2–5 ps) optical pulses, with a well defined polarisation can be used to prepare arbitrary superpositions of exciton spin states in a semiconductor quantum dot, achieve ultrafast control of the spin-wavefunction without an applied magnetic field and make high fidelity read-out the quantum state in an arbitrary basis simply by detecting a strong (~ 2–10 pA) electric current flowing in an external circuit. The results obtained show that the combined quantum state preparation, control and read-out can be performed with a near-unity (≥97%) fidelity.

Demonstration of ultrafast phase recovery in semiconductor optical amplifiers

Presented is an experimental investigation on phase recovery time in semiconductor optical amplifiers (SOAs). The experiment is carried out using an integrated SOA-based Mach-Zehnder interferometer switch, under the injection of 2 ps optical pump pulses at 10 GHz. The phase recovery is derived from the measured output of the interferometer. An ultrafast component in the phase recovery is observed, and a delay between phase and gain recovery is also found.

Optical Bistability in an Acousto-Optic Tunable Filter (AOTF) Operating with Short Optical Pulses

In this paper we report for the first time the presence of bistability in an acoustic-optic tunable filter (AOTF) operating with ultrashort (2 ps) optical light pulses. The results for the study of bistability has shown the dependence of the hysteresis curve with the product of the coupling constant (κ) by the length of the device (ξL) and the conversion power-coupling constant factor (G). The range of bistability varies significantly with both G and with κξL parameters. The variation of κξL directly increases the size of the range of bistability hysteresis while the increase in G causes the bistability to occur at low powers. The phenomenon of optical bistability (OB) is the object of increasing interest due to its possibilities for important device applications. A bistable device is a device with a capability to generate two different outputs for a given input and the physical requirements for this are an intensity-dependence refractive index and an optical feedback mechanism.

10 GHz, 11 ps optical pulse generation from a regeneratively mode-locked Yb fiber laser in the 11 μm band

We report a 10 GHz harmonically and regeneratively mode-locked Yb fiber laser with a phase-locked loop (PLL) technique at 1.1 μm. Stable mode locking was achieved by optimizing the average dispersion of the fiber cavity to an anomalous dispersion to operate as a soliton laser. As a result, a 1.1 ps optical pulse with a timing jitter of 140 fs was successfully generated.