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We report a hybrid integrated external cavity laser by butt coupling a quantum dot reflective semi-conductor optical amplifier and a silicon-on-insulator chip. The device lasers at 1302 nm in the O-band, a wave-length regime critical to data communication systems. We measured 18 mW on-chip output power and over 50-dB side-mode suppression ratio. We also demonstrated open eye diagrams at 10 and 40 Gb's. [ABSTRACT FROM AUTHOR]

Single human hairs using a scanning laser terahertz (THz) imaging system are evaluated. The system features near-field THz emission and far-field THz detection. A sample is set in the vicinity of a two-dimensional THz emitter, and an excitation laser beam is scanned over the emitter via a galvanometer. By detecting the transmitted THz wave pulses that are locally generated at the irradiation spots of the excitation laser, we can obtain the THz transmission image and the spectrum of the sample with imaging time of 47 s for 512 x 512 pixels and maximum resolution of ~27 µm. Using the system, we succeeded in observing the specific features of single human hairs in both the THz transmittance spectra and transmission images; it was found that the THz transmittance spectrum of gray hair shows a tendency of increase while that of black hair shows a decrease with increasing frequency above 1.2 THz. We could also observe the change of the moisture retention in the hair, and it is found that cuticles play one of the important roles in keeping moisture inside the hair. Those obtained data indicate that our system can be useful for evaluating single human hairs and those kinds of microscale samples. [ABSTRACT FROM AUTHOR]

High-power fiber lasers and amplifiers have gained tremendous momentum in the last 5 years. Many of the traditional manufacturers of gas and solid-state lasers are now pursuing the fiber-based systems, which are displacing the conventional technology in many areas. High-power fiber laser systems require reliable fibers with large cores, stable mode quality, and good power handling capabilities-requirements that are all met by the airclad fiber technology. In the present paper we go through many of the building blocks needed to build high-power systems and we show an example of a complete airclad laser system. We present the latest advancements within airclad fiber technology including a new 100 μm single-mode polarization-maintaining rod-type fiber capable of amplifying to megawatt power levels. Furthermore, we describe the novel airclad-based pump combiners and their use in a completely monolithic 350 W cw fiber laser system with an M2 of less than 1.1. [ABSTRACT FROM AUTHOR]

We have adapted the point model for the study of an all-fiber laser doped with Nd3+ and Q-switched by a saturable fiber absorber doped with Cr4+. Calculations of the output power of the 1084 nm laser are considered as a function of the pump power supplied by a 790 nm laser diode. The analysis of the simulation results reveals the existence of pulsed, sinusoidal, and dc operating regimes. [ABSTRACT FROM AUTHOR]

A detailed analysis of the efficiency of four-wave mixing (FWM) is performed for a closely spaced energy state quantum dash semiconductor optical amplifier (SOA). The analysis takes into account the effect of all discrete energy states, the gain dispersion of the quantum dash, and the effect of doping on the FWM characteristics. Our analysis reveals that large FWM efficiency can be obtained when the energy of the pump signal is equal to the first excited state. We find that at low-applied current doping the dashes by p-type concentration enhances the FWM efficiency. While at high applied current, we find that doping the SOA with p-type concentration slightly enhances the FWM efficiency of the ground state and the first excited state and lowers the FWM efficiency of the higher excited states. Also we find that doping the dashes by n-type concentration slightly modifies the FWM efficiency spectrum. [ABSTRACT FROM AUTHOR]

It is an effective approach to obtain high-power laser output by spectral beam combining (SBC) technologies. In this paper, a simple SBC system based on the superimposed reflective volume Bragg grating (RVBG) is proposed to reduce the scale of the SBC system. Considering the cross-coupling between the two gratings in a volume, two structure models of the superimposed RVBG-the superimposed RVBG with the same period and the superimposed RVBG with a different period-are analyzed and compared by using the rigorous coupled wave analysis, and their applications for SBC system are discussed. Numerical results show that the superimposed RVBG is easy to be fabricated and has the potential to combine multiple lasers with one volume. Cross-coupling can be neglected for the same period structure when the slant angle divergence is larger than 0.01 rad and for the different period structure when the spectral separation is larger than 1.0 nm. The superimposed RVBG with a different period can achieve high diffraction efficiency simultaneously for each grating with a small slant angle divergence, and is convenient to combine multiple beams with small spectral separation. The effect of wavelength shift on diffraction efficiency can be ignored. [ABSTRACT FROM AUTHOR]

Surfaces that are recovered by integrating slope estimates are prone to errors caused by discontinuities in the surface. We propose combining laser sectioning and photometric stereo (PS) to estimate surface shape. PS is used to estimate slope; laser lines are used to measure four height profiles. The slopes are integrated along paths that start from the laser height profiles and avoid discontinuities. The scheme is shown to mitigate the bias and surface discontinuity problems associated with PS. [ABSTRACT FROM AUTHOR]

New resonators, namely the hybrid cat-eye resonator (HCER), diffraction-coupled cat-eye resonator (DCCER), and continuously coupled cat-eye resonator (CCCER) are demonstrated for the first time here in a kinetically enhanced copper vapor laser with high optical extraction of 70 to 80, low beam divergence ∼0.15 mrad(approximately five times the diffraction limit), and high misalignment tolerance ∼5 to 6 mradachieved simultaneously from each of these configurations. The laser used in the experiment is a 45- to 47-mmbore, 50-Wkinetically enhanced copper vapor laser. In the case of HCER, the laser beam divergence reduces to about 0.12 mrad(∼30-fold reduction) in an unstable direction and about 0.5 mrad(approximately seven-fold reduction) in a stable direction with average beam power of about 35 W, which is ∼70of 50-Wmaximum set power of the laser. In the DCCER configuration, laser power achieved is about ∼37 W(75 of 50-Wlaser power) with beam divergence of about 0.17 mradand misalignment tolerance of ∼5 mrad. In CCCER, the output power of about 40 W(80 of 50-Wlaser power) is achieved with beam divergence of about 0.1 mrad(approximately three to four times the diffraction limit). [ABSTRACT FROM AUTHOR]

We have investigated the influence of the oscillator beam (the polarization beam) on the small-signal gain and saturation energy of an oscillator-amplifier dye laser transversely pumped by a frequency-doubled Nd:YAG laser. We found that the amplifier relation for this laser agrees with Frantz and Nodvik’s model. [ABSTRACT FROM AUTHOR]

Lasers and laser systems are a mature technology, yet there is a long road ahead for innovation and enthusiasm. We review some of the 40 yearsof R&D and manufacturing of lasers at ELOP–Elbit Systems. Bulk solid state lasers, for designators and range finders, as well as fiber lasers, for directed IR countermeasures and laser radar applications are described. These two technologies provide and will continue to offer a vast number of products for security and defense applications. Current and future generations of laser products will have higher average power together with improved beam quality, better efficiencies, and superior robustness all in a more compact package. [ABSTRACT FROM AUTHOR]

We present a theoretical analysis and a comparison to experimental results on self-mixing interference. From the theoretical analysis and experiment, the error of the velocity measurement, which is caused by a speckle pattern, has been investigated and optimization of the laser diode velocity system by selecting suitable experiment parameters and proper signal processing methods has been reported. The actual measurement error is <3.1over a wide velocity range (5.2–479 mms). [ABSTRACT FROM AUTHOR]

Half a century has passed since Theodore Maiman’s small ruby rod crossed the threshold of laser emission. The breakthrough demonstration earned headlines, but in the early years the laser was called “a solution looking for a problem,” and there was a germ of truth in the joke. Years of development since then have vastly improved laser performance, and tremendously increased their variety, earning lasers important roles in scientific research, consumer products, telecommunications, engineering, medicine, materials working, and a host of other applications. This article reviews the highlights of those developments and puts them into context, showing how laser technology has evolved to meet application requirements. [ABSTRACT FROM AUTHOR]

An optical delay interferometer (ODI) is employed to suppress the pattern effect manifested on a 10 Gbsreturn-to-zero (RZ) data stream when amplified by a semiconductor optical amplifier (SOA) operated in deep gain saturation. The experimental results verify the competence of the scheme to confront the problem for this signal format by achieving a far better performance than that with the SOA alone. [ABSTRACT FROM AUTHOR]

The feasibility of operating the semiconductor optical amplifier (SOA)–based ultrafast nonlinear interferometer (UNI) in nontrivial switching mode is methodically investigated and demonstrated. For this purpose, a comprehensive model that simulates the dynamical behavior of an SOA subject to an ultra-high-speed pseudorandom binary sequence is appropriately adapted to the case of the specific configuration. By undertaking a detailed theoretical treatment, the impact of the most important SOA parameters on the fully loaded Q-factor is thoroughly analyzed and assessed, enabling us to extract useful design rules for their proper selection so as to ensure enhanced error-free performance at the desired output port of the considered interferometric arrangement. The outcome of this effort may assist the study and implementation of all-optical circuits and subsystems of nontrivial functionality, in particular with feedback, in which the UNI employing a SOA as the nonlinear element is the core logical module. [ABSTRACT FROM AUTHOR]

Currently, no infrared scene projector technology has the ability to simulate the real-world, high-dynamic-range temperatures encountered by modern infrared imagers. This paper presents the application of type II W-quantum-well diode lasers used in a high-radiance mid-infrared-emitting object plane in an effort to develop the first truly high-dynamic-range infrared scene projector. The observed dynamic-range capability simulates 250 K apparent background temperature to 1100 K maximum apparent temperature for inband mid-wave 3 to 5 μm radiance. In the presented research a linear array of high-power continuous-wave mid-infrared diode lasers and a high-speed optical polygon scanner were used to produce two-dimensional projected images. The ability to simulate high apparent temperatures was the direct result of luminescent infrared radiance emitted by the diode lasers. The simulation of the low background apparent temperatures was obtained by enclosing the entire projector system in an environmental chamber operating at 232 K. The apparent temperature of the infrared scene projector was calculated analytically and compared with the measured results. Sample imagery from the high-dynamic-range infrared scene projector is also given. [ABSTRACT FROM AUTHOR]

Relatively inexpensive laser-guided weapons were identified as an important threat to naval platforms operating in littoral environments. Countermeasures (CM) developed against laser-assisted threats in air and land environments are all based on accurate threat detection. Due to the limited performance of current laser detecting capabilities applied to large maritime platforms, there are no known CMs that can be used to protect them. We present a new far off-axis laser detection approach for minimizing the number of laser sensors required to protect a ship. A model predicting the detection of aerosol scattering in the spectral band used by laser threats, exploiting the high humidity conditions present in maritime environments, is described, as well as its limitations and some preliminary results regarding its validation. [ABSTRACT FROM AUTHOR]

Pollution is known to play an important role in optical performances of high power laser components. In this study, we propose a method to characterize the particulate pollution and to evaluate its impact on the optical component lifetime. We applied it at the Ligne d’Inte´gration Laser (LIL), which is a prototype installation of the future Laser Mega Joule facility. By systematic examination of each particle, we obtain, in number, size, and chemical composition, an overview of pollution deposited on optical surfaces. Then we deduce the origin of the principal pollutions. After irradiation of the polluted samples, with conditions close to the maximum of the LIL operation, no laser-induced damage is observed. In contrast, irradiation induces an important cleaning. [ABSTRACT FROM AUTHOR]

TiCN/Ti reinforced layers were fabricated on titanium alloy by the laser cladding method, aiming at improving its surface properties. Ti and TiCN powders of size 60 and 3 μm, respectively, were mixed in a certain ratio, prepasted on a Ti-6Al-4V substrate, and irradiated with a pulsed YAG laser in nitrogen atmosphere. The temperature field was calculated with a semi-infinite model. The calculated results show that the laser scanning velocity should be in the range of 1.0 to 3.0 mm/s; the best value for metting the substrate and realizing the cladding process is about 1.4 mm/s. The cladded samples were analyzed with x-ray diffraction, optical microscope observation, and a microhardness test. The results indicate that the composition of the cladding layer changes with the ratio of Ti to TiCN. The optimum Ti:TiCN mass ratio is about 15:85. The optical micrograph revealed a TiCN film thickness about 100 μm. The hardness was increased from 330 HV in the substrate to nearly 1500 HV in the modified layers, due to the presence of the hard TiCN phase. It is found that the proper laser scanning velocity to obtain high cladding quality is about 1.5 mm/s, which agrees with the calculated result of 1.4 mm/s. [ABSTRACT FROM AUTHOR]

Results are presented on the influence of acoustic waves on the performance of high-repetition-rate TEA CO2 lasers. It is shown that acoustic waves generated inside the laser cavity lead to nonuniform discharges, resulting in a deterioration of the laser beam quality, decreased output energy, and an increase in pulse-to-pulse energy variation. The effect of the gas mix on the acoustic behavior is investigated, and experimental results on laser performance across a range of gas mixtures are presented. Methods to reduce the effects of acoustic waves are presented together with experimental results. The influence of acoustic damping measures on laser gain are demonstrated, showing a significant improvement in gain and output power at high pulse repetition rates. [ABSTRACT FROM AUTHOR]

A fiber laser with two different polarization-dependent output states is demonstrated. On the one hand, intensity-dependent loss in a nonlinear optical loop mirror, induced by nonlinear polarization rotation, can balance mode competition of a homogeneous broadening gain medium, and thus allows for stable room-temperature multiwavelength generation. On the other hand, intensity-dependent transmission can act as an equivalent saturable absorber, which results in passive mode locking of the fiber laser. It may thus serve two functions: passive mode locking and multiwavelength emission. [ABSTRACT FROM AUTHOR]

A novel scheme of photonic frequency conversion based on two-pump four-wave mixing in a semiconductor optical amplifier is proposed. Characterized by its wide conversion range, the proposed scheme has the potential to generate millimeter waves at much higher frequency and convert several signal channels simultaneously. The system performance is analyzed through a numerical model, and the effect of the pump-signal pulse parameters on the conversion efficiency is discussed. [ABSTRACT FROM AUTHOR]

Using the ABCD matrix theory that takes into account the thermal lens effect of the gain medium and rate equations that consider the Gaussian spatial distributions of the intracavity photon density and pump beam, the pulse duration of a passively Q-switched laser is optimized by choosing the appropriate oscillating beam radius on the Q-switch wafer and pump beam radius in the gain medium, which provides a simple way to optimize the pulse duration. By changing the positions of the GaAs in the cavity or the pump beam focal plane in the gain medium in a diode-pumped passively Q-switched Nd:YVO4 laser with a GaAs saturable absorber, the optimization of pulse duration is easily realized, which is in good agreement with the theoretical calculations. [ABSTRACT FROM AUTHOR]

Semiconductor optical amplifiers (SOAs) as nonlinear devices always work in the gain saturation region. Therefore, the saturation gain is an important parameter of SOAs. However, the existing theoretical gain formula greatly deviates from the experimental measurements. We find experimentally that the effect of the absorption loss on the SOA gain cannot be neglected, especially when the SOA is biased into the saturation region. In this paper, considering the influence of the absorption loss, we propose a modification to the SOA gain formula in common use. We are able to validate the revised formula against the experimental measurements. Thus the theoretical formula after modification can be accurately applied to evaluate the SOA gain in practice. [ABSTRACT FROM AUTHOR]

All-optical NOR and OR gates using the same setup, based on cross-polarization modulation in a single semiconductor optical amplifier, have been demonstrated experimentally at 10 Gbit/s with two and three input signals. The results show good dynamic extinction ratios of 13.2 and 11.0 dB for NOR and OR outputs, respectively. The logic output performance of this logic configuration versus input signal and probe power have been investigated experimentally. [ABSTRACT FROM AUTHOR]

Taking into account ultrafast carrier dynamics, we model 640 Gbit/s wavelength conversion based on nonlinear polarization rotation (NPR) assisted with sideband filtering in a single semiconductor optical amplifier (SOA) and investigate the performance of two types of wavelength conversion schemes: one based only on NPR and the other based on NPR assisted by red-shifted filtering. Simulated results show that the two types of wavelength conversion schemes are achieved with clear open-eye diagrams and have signal regeneration capability at 640 Gbits/s. Simulated analyses also show that the wavelength conversion based on NPR assisted by red-shifted filtering scheme exhibits better performance in terms of wavelength conversion and signal regeneration. [ABSTRACT FROM AUTHOR]

We report the two-stage single-pump configuration of an erbium-doped fiber amplifier, in which a Sagnac interferometer is introduced to reduce the most important contribution of amplified spontaneous emission (ASE) noise, providing significant improvement on the amplifier performance. A Sagnac interferometer, made from a high-birefringence fiber loop, is included between the first and second stages. It is designed to provide transmittance with a period of 46 nm that allows us to adjust the minimum transmission around 1530 nm (peak of ASE noise) and maximum transmission at 1550 nm (signal wavelength). For optimizing the configuration, we measure the erbium-doped fiber parameters and simulate the amplification of the signal along the fiber. In the experiment, a significant absorption coefficient for pump and signal is found. The absorption looks to be too strong for the background absorption, and we suppose that it may be caused at least partly by excited-state absorption (ESA). Including the absorption coefficient allows very good correspondence between simulation and experiment. Experimental results show that with a simple configuration, we obtain up to 53-dB amplification with only 73 mW of pump power. [ABSTRACT FROM AUTHOR]

A four-wave mixing assisted multiwavelength semiconductor optical amplifier laser is experimentally demonstrated in a fiber ring cavity. A sampled linearly chirped fiber Bragg grating is used as the wavelength-selective component. Four-wave mixing enhances the number of peak-power-equalized lasing wavelengths and operation stability of the ring laser. The extinction ratio of the 20 multiwavelengths output is greater than 40 dB, and the peak-power difference is less than 3 dB. [ABSTRACT FROM AUTHOR]

A simple scheme for an all-optical AND logic gate is proposed based on a sagnac interferometric structure. The operations of this scheme with a 40-Gbit/s return-to-zero (RZ) pseudorandom bit stream (PRBS) are simulated correctly with an output extinction ratio (ER) of about 14.7 dB. Through numerical analyses and discussions, it can be seen that the output ER of the AND operation is improved more than 6 dB, and the output pattern effect is decreased by about 0.4, compared to terahertz optical asymmetric demultiplexer schemes under the same condition. Furthermore, the carrier recovery time of a semiconductor optical amplifier (SOA) is no longer a crucial parameter to restrict the operation speed of this scheme. This scheme is potentially capable of AND operation rates to 100 Gbit/s. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a novel high-gain-efficiency long-wavelength band (L-band) erbium-doped fiber amplifier with a double-pass backward-pump configuration, in which the strong backward C-band amplified spontaneous emission is effectively utilized. The L-band gain is greatly enhanced in comparison with the copumped configuration. Without using any excessive components, the new configuration can provide the same gain as the conventional configuration, but only using 40% pump power. Meanwhile, the noise figure is also effectively improved under the low pump power. [ABSTRACT FROM AUTHOR]

We present experiments of line and parallel configurations of hybrid erbium-doped fiber amplifiers/fiber Raman amplifiers (EDFAs/FRAs). For the line structure, a gain flatness of ±1.15 dB over a range of 47 nm (1483 to 1530 nm) is obtained. In the parallel configuration, the gain flatness is below ±2 dB for 1487 to 1507 nm and 1520 to 1550 nm. Using a high-birefringence fiber loop mirror as a signal reflector, a noise figure is less than 6 dB in the gain bandwidth. Then performances of different hybrid configurations are compared. [ABSTRACT FROM AUTHOR]

Semiconductor-based optical amplifiers (SOAs) offer solutions to a variety of amplification needs covering wavelengths ranging from of 0.6 to 1.6 μm. Gain adjustment, through the bias current, enables automatic power control to be implemented. However, this requires knowledge of the signal strength. The amplified spontaneous emission power, particularly in high gain SOAs, can be significant with respect to the signal strength, and therefore additional components may be required to derive an accurate measure of the signal strength. This increases both the complexity and cost of implementing automatic power control (APC). We report on a method for estimating the signal strength based on measurement of the total output power and the SOA drive current. The method is extendable to other methods of optical amplification, e.g., erbium-doped fiber amplifiers. [ABSTRACT FROM AUTHOR]

We investigate and demonstrate experimentally a two-stage erbium-based amplifier with a larger amplified-spontaneous-emission light source for a long-distance fiber sensor by using strain-induced fiber Bragg gratings in the fiber systems. In a 20-km-long fiber sensor system, the sensor has a maximal ≈2.28-nm wavelength shift under a 1500-μm/m strain. [ABSTRACT FROM AUTHOR]

A loadable and erasable fiber loop optical buffer based on a semiconductor optical amplifier (SOA) is presented. Two SOAs in our configuration not only provide nonlinear phase shift to implement buffer function, but also compensate for the propagation attenuation during long time storage. In particular, we present a simplified model to investigate the influence of background noise to the optical buffer performance. Both theoretical and experimental results reveal that the background noise can be suppressed by intentionally increasing the fiber loop loss. We also demonstrate that the packet pattern is well maintained after a storage time of 145 μs without self-oscillation. [ABSTRACT FROM AUTHOR]