Pulsed Optical Power Research Articles

Unusual fault detection and loss analysis in optical fiber connections with refractive index matching material

We investigated and analyzed an unusual fault that occurs in optical access fiber networks, which is caused by a defective fiber connection. We developed a fault-detection system to locate such a fault by using both optical power level and optical pulse measurement methods. We investigated a defective mechanical splice in three laboratory tests: outward appearance, non-destructive, and dismantled. As a result, we confirmed that the defective mechanical splice had large gaps of more than 10μm. We also analyzed the unusual fault that occurs from such a defective mechanical splice in mechanically transferrable (MT) connector experiments. The experimental results revealed that the optical performance of fiber connections with a mixture of refractive index matching material and air-filled gaps was extremely unstable and varied widely. In the worst case, the insertion loss worsened to more than 30dB. The case of the fault caused by a mixture of refractive index matching material and air-filled gaps between the ends of optical fibers is thought to occur independently of the sorts or structures of optical fiber connectors and could be a characteristic peculiar to optical fiber connections using refractive index matching material. These findings can be applied to optical fiber connections that use refractive index matching material, such as MT connectors in outside underground facilities, mechanical splices, or field assembly connectors at aerial and home sites in optical access networks. These findings also support the practical construction and operation of optical network systems.

Portable Methane Sensor Demonstrator based on LTCC Differential Photo Acoustic Cell and Silicon Cantilever

Abstract A novel portable methane sensor demonstrator based on Low Temperature Co-fired Ceramic (LTCC) differential Photo Acoustic (PA) cell, silicon cantilever and spatial interferometer was demonstrated. Silicon Micro-Electro-Mechanical-System (MEMS) cantilever-based PA technology allows sensing of extremely low gas concentrations with wide dynamic measuring range. The sensitivity enhancement is achieved with a cantilever microphone system in which the cantilever displacement was probed with an optical interferometer providing a pico-meter resolution. In the demonstrated gas sensor structure, the silicon cantilever microphone was placed in a two-chamber differential gas cell so that the achieved differential pressure signal was proportional to gas concentration in the open measurement path for gas flow. The pulsed optical power was produced by two Mid Infra-Red (MIR) Light Emitting Diodes (LEDs). The differential PA gas cell structure included two 8 mm cylindrical cells, diameter 2.4 mm, for reference and measurement detection portions coated with a silver paste. A transparent sapphire window was hermetically sealed on top of the differential gas cell structure in order to probe the displacement of the silicon cantilever inside the sealed differential cell. The sealed methane gas produced selectivity against other possible gases in the measurement path. The first sensor prototype sensitivity was 300 ppm with 1 s response time for the methane gas. Sensitivity is increased to be 30 ppm, when response time of 100 s is used. The selectivity in the demonstrated sensor is possible to tune simply by filling the differential cell with specific gas in focus and selecting corresponding LED with proper emission spectrum. Sensor concept provides possibility to measure extremely low gas concentrations of a wide range of gases having fundamental absorption bands at 3 - 7 μm wavelength range including CO, CO2 and CH4.

High-power 745-nm Laser Diode Utilizing InP/InGaP Quantum Structures Grown by Using Migration Enhanced Epitaxy

We report the performance of 745-nm laser diodes (LDs) utilizing InP/InGaP quantum structures (quantum dots + quantum dashes) grown by using migration-enhanced epitaxy method. The photoluminescence of the LD structures before the fabrication of the LDs shows two peaks, around 800 nm and 750 nm, attributed to quantum dots and dashes, respectively. The lasing wavelength is thought to the result from quantum dashes instead of ground states of QDs. The pulse optical power of the LD is above 600 mW at room temperature.

Numerical modeling of quasitransient backward Raman amplification of laser pulses in moderately undercritical plasmas with multicharged ions

It was proposed recently that powerful optical laser pulses could be efficiently compressed through backward Raman amplification in ionized low density solids, in spite of strong damping of the resonant Langmuir wave. It was argued that, even for nonsaturated Landau damping of the Langmuir wave, the energy transfer from the pump laser pulse to the amplified seed laser pulse can nevertheless be highly efficient. This work numerically examines such regimes of strong damping, called quasitransient regimes, within the simplest model that takes into account the major effects. The simulations indicate that compression of powerful optical laser pulses in ionized low density solids indeed can be highly efficient.

Coherent Light with Tunable Polarization from Single-Pass Free-Electron Lasers

Tunable polarization over a wide spectral range is a required feature of light sources employed to investigate the properties of local symmetry in matter. In this Letter, we provide the first experimental characterization of the polarization of the harmonic light produced by a free-electron laser and demonstrate a method to obtain free-electron laser harmonics with tunable polarization. Experimental results are successfully compared with theory. Our findings can be expected to have a deep impact on the design and realization of experiments requiring full control of light polarization.

Investigation of InGaAsP Quantum-Well EAM Based Pump-Probe Configuration for Ultrafast Optical Signal Processing

A comprehensive theoretical model for analyzing both static and dynamic properties of arbitrary composition <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm In}_{1-x}{\rm Ga}_{x}{\rm As}_{y}{\rm P}_{1-y}$</tex></formula> quantum-well (QW) electro-absorption modulator (EAM) is proposed. Optical absorption spectra of the QW-EAM considering both excitonic transitions and continuum conduction-band to valence-band transitions are included to evaluate the QW-EAM static performance. The dynamic absorption recovery of EAM is calculated as a function of electric field and pump power. Then, based on the theory of the carrier and absorption dynamics, a 40 Gb/s pump-probe configuration for optical signal processing using <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm In}_{0.53}{\rm Ga}_{0.47}$</tex></formula> As/InP QW-EAM as nonlinear element is thoroughly investigated. Influence of various parameters including pulse width, optical wavelength, optical power, and QW structure on the intensity and phase variation of the output probe signal through nonlinear interactions between pump and probe signals are investigated. The presented model and investigation are suitable for optimizing the device design and describing the properties of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm In}_{1-x}{\rm Ga}_{x}{\rm As}_{y}{\rm P}_{1-y}$</tex></formula> QW-EAM used in ultrafast optical signal processing applications.

High-power edge-emitting laser diode with narrow vertical beam divergence

10.5 W pulsed optical power with ultra-narrow vertical beam divergence (full width at full maximum ∼1.1°) is achieved at 20 A pulsed current in a 1060 nm laser diode with as-cleaved facets (100 µm-wide and 3500 µm-long cavity). The lasing occurs through the tilted wave mode excited in the GaAs substrate. Temperature-stable operation at low threshold current densities is demonstrated.

Nonlinear gain dynamics of quantum dot optical amplifiers

In this work, the ultrafast gain dynamics of a quantum dot (QD)-based semiconductor optical amplifier (SOA) is modeled on the basis of semiconductor Bloch equations that include microscopically calculated nonlinear scattering rates between QD carriers and the surrounding carrier reservoir. This enables us to separately study the dynamics of electrons and holes inside the device as well as the coherent effects related to the fast polarization dynamics. We show that the optical pulse power and the dephasing time of the polarization mainly affect the gain depletion inside the active region, while the electric injection current density and thus the internal carrier dynamics influence the gain recovery. We observe that carrier–carrier scattering is the source of desynchronized behavior of electrons and holes in the recovery dynamics of QD-based SOAs. The amplification of pulse trains in the SOA predicted by our model agrees well with experimental data.

All-optical pulse repetition frequency divider utilizing an injection-unlocked Fabry-Perot laser diode

We propose and demonstrate an all-optical pulse repetition frequency divider based on the nonlinear period-one oscillation of a Fabry-Perot laser diode (FP-LD).By adjusting the injection power of input optical pulses and detuning the wavelength of the FP-LD, frequency-divided optical pulses including divide-by-two and divide-by-three output can be readily achieved with suppressed phase noise over wide frequency range. For an 18-GHz pulse train, we experimentally obtain 9-GHz optical pulses train with phase noise of −105.6 dBc/Hz and 6-GHz optical pulses train with phase noise of −105.5 dBc/Hz, separately. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2641–2643, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25565

Ook modulator using photoconductive feedback oscillator

AbstractDesign approach and characterization of an integrated oscillator switched by an optical power are discussed. The oscillator is driven into oscillation at a frequency of 4.9 GHz under a light excitation power upper than a threshold value of 40 mW at a wavelength of 800 nm. On‐off Keying modulation of the oscillator is performed with a digital optical power modulation allowing thus direct data transfer from optical to microwave carrier by photoconductivity. Illumination of the oscillator with optical pulses reveals the generation of short oscillations. The number of the generated signal periods depends on the optical power level and optical pulses width. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 2010–2016, 2010; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/mop.25371

Approach to Spectral Measurements of a Millimeter-Wave-Band Relativistic Magnetron

Rigorous 3-D finite-difference time-domain computer simulations are used to investigate the electromagnetic characteristics of the diffraction output of a millimeter (mm)-wave-band relativistic magnetron. In the simulations, the diffraction output is outfitted with a dielectric grating that can be tuned in either reflection or transmission mode at definite operation wavelengths. This grating acts as a tunable filter of high-power oscillations generated by the magnetron and is similar to gratings widely used in optics to control ultrashort power optical pulses. Specifically, computer simulations establish a relation between the generation wavelength of the magnetron and the configuration of the grating, as well as predict that the grating provides the field reduction of up to -40 dB. The application of the grating suggests an approach to spectral measurements of mm-wave-band relativistic magnetrons with a measurement accuracy of better than 0.3 mm. The implementation of the approach solves a series of engineering and metrological problems arising during spectral measurements of a variety of high-power vacuum microwave devices.

Multifilamentation of powerful optical pulses in silica

The multiple filamentation of powerful light pulses in fused silica is numerically investigated for central wavelengths at $355$ nm and $1550$ nm. We consider different values for beam waist and pulse duration and compare the numerical results with behaviors expected from the plane-wave modulational instability theory. Before the nonlinear focus, the spatiotemporal intensity patterns can be explained in the framework of this theory. Once the clamping intensity is reached, for long input pulse durations ($~1$ ps), the ionization front defocuses all trailing components within a collective dynamic, and a spatial replenishment scenario takes place upon further propagation. Short pulses ($~50$ fs) undergo similar ionization fronts, before an optically turbulent regime sets in. We observe moderate changes in the total temporal extent of ultraviolet pulses and in the corresponding spectra. In contrast, infrared pulses may undergo strong temporal compression and important spectral broadening. For short input pulses, anomalous dispersion and self-steepening push all pulse components to the trailing edge, where many small-scaled filaments are nucleated. In the leading part of the pulse, different spatial landscapes, e.g., broad ring patterns, may survive and follow their own propagation dynamics.

Photoconductive switch design for microwave applications

A procedure for choosing the dimensions of a photoconductive semiconductor switch (PCSS) for operation at microwave switching frequencies, and particularly at 10.0 GHZ, is described. The critical dimension is the switch length (electrode separation), which must be small enough to force photoinduced charge removal during switch turn-off via sweep out rather than recombination. The switch depth in the direction of turn-on optical pulse absorption must be several optical absorption depths long to ensure absorption of all the incident light, which optimizes optical to electrical signal gain. The switch width is determined in conjunction with the peak intensity of the optical pulse because the switch width-optical intensity product, which represents optical power, determines the turn-on time, the on-state switch resistance and the turn-off delay time. Simulations show that a switch with a 0.5 ¿m length, 5.0 ¿m depth, and 20 ¿m width, illuminated with 1.0 W peak power optical pulses at 10 GHz, will have a 4.8 ps turn-on time, a 0.23 ¿ on-state resistance, and a 46 ps turn-off time.

80 kHz repetition rate high power fiber amplifier flat-top pulse pumped OPCPA based on BIB_3O_6

We present a high peak power optical parametric chirped pulse amplifier (OPCPA) seeded by a cavity dumped Ti:Sapphire oscillator. A frequency doubled high power Ytterbium-doped fiber amplifier is pumping the device. Temporal synchronization of the pump pulses is done via soliton generation in a highly nonlinear photonic crystal fiber. This soliton is fiber amplified and spectrally filtered in several fiber amplifiers. A simple birefringent pulse shaper generates a flat-top temporal pump pulse profile. Direct amplification of these pulses in large mode area fibers without using a stretcher and compressor provides significantly reduced complexity. For the first time to our knowledge broadband amplification around 800 nm central wavelength is demonstrated in BIB(3)O(6) (BIBO) crystals. The stretched Ti:Sapphire oscillator pulses are amplified up to a pulse energy of 25 microJ. Recompression with a grating compressor yields 50.7 fs pulses with 16.2 microJ pulse energy.

Effect of time-dependent ionization on properties of the ultrashort pulse propagation and optical power limiting in a two-photon absorption molecular medium

By taking the strong two-photon absorption 4,4′-bis （dimethylamino） stilbene molecules as medium, the propagation of femosecond laser pulses in this medium is simulated by numerically solving the Maxwell-Bloch equations using an iterative predictor-corrector and finite-difference time-domain method. The influences of time-dependent ionization on two-photon absorption and optical power limiting behavior are emphatically investigated. The numerical results show that the nonlinear interactions between the pulses and the medium and the corresponding spontaneous emission become weaker when the time-dependent photoionization is considered. The effects of photonionization on the main pulse become more evident as the amplitude of input electric field is increased. When the photonionization cross section is larger, the dynamic optical limiting range becomes broader, which demonstrates that the limited photonionization ability is favorable for the optical power limiting. Furthermore, the propagating-distance dependence of the dynamical behavior of the ultrashort laser pulse in the medium is observed.

TIMING SHIFT OF OPTICAL PULSES DUE TO INTER-CHANNEL CROSS-TALK

This paper considers the influence of interchannel crosstalk on pulse timing shift and optical power due to the propagation of optical pulse through a nonlinear dispersive fiber. The numerical results are shown. An influencing parameter of the pulse distortion through the fiber is the eye opening penalty.

High-Power Picosecond Pulse Generation Due to Mode-Locking With a Monolithic 10-mm-Long Four-Section DBR Laser at 920 nm

A 10-mm-long four-section distributed Bragg reflector laser with a double-quantum-well heterostructure at 920 nm was realized. A maximum optical pulse power of 3.6 W with a repetition rate of 4.1 GHz corresponding to the laser length was reached. The full-width at half-maximum of the pulses was 7 ps measured with an autocorrelator. A maximum pulse energy of 25 pJ was reached.

Initial stochastic modulation and break up of soliton bound states in optical fibers

We analyzed the influence of the initial phase stochastic modulations of high power optical pulses on their propagation in optical fiber. Our numerical results are compared with those of Cavalcanti S.B., Agrawal G.P.: Phys. Rev. A 51, 4086–4092 (1995), Fattakhov A.M., Chirkin A.S.: Kvantovaya Elektronka 11, 1989 (1983), Kvantovaya Elektronka 11, 2349 (1984), Maimistov A.I., Manykin B.A., Skliyarov Y.M.: Kvantovaya Elektronka 13, 2243–2248 (1986). Break up of soliton bound states due to initial phase stochastic modulations is observed.

Bias level dependence of turn-off oscillations in vertical-cavity surface-emitting lasers

Turn-off oscillations are dynamical phenomena that appear when modulating the current applied to vertical-cavity surface-emitting lasers (VCSELs). These phenomena consist of the generation of significant pulsed optical power, while the laser current remains at the lowest (bias) value during the modulation. We study the dependence of turn-off oscillations on the bias current for both single-mode and multitransverse-mode VCSELs. We show that as the bias current increases, the maximum power of these oscillations obtained with multimode lasers becomes similar to the one obtained with single-mode lasers. A criterion for obtaining the bias current above which turn-off oscillations are no longer dominated by spatial effects is given. We also show that the transverse spatial profile of the light emitted in multimode VCSELs during turn-off oscillations depends on the value of the bias current.

超高速ペタワットレーザーシステム

I review progress in the generation of ultrahigh peak power optical pulses in the femtosecond range. A design, performance and characterization of a Ti: sapphire laser system based on chirped-pulse amplification, which has produced a peak power of 0.85-PW with 33-fs pulse durations are described. Extension of laser systems to the multi-petawatt power level is also discussed.