"Anti" up the aperture [antiguided VCSEL structures]

Coupled vertical cavity surface-emitting laser (VCSEL) arrays are an attractive means to increase the coherent output power of VCSELs. Single-mode VCSELs, with output powers greater than 10 mW, would be useful as telecommunication transmitters /spl lambda/=1.3-1.55 /spl mu/m) or sources for optical interconnects. Commercially available single-mode VCSELs, even at shorter wavelengths /spl lambda/=0.85 /spl mu/m), are generally limited to a few milliwatts of output power. The conventional VCSEL structure incorporates a built-in positive-index waveguide, designed to support a single fundamental mode. Promising results in the 3-5 mW range (/spl lambda/=0.85 /spl mu/m) have been obtained from wet-oxidized, positive-index-guided VCSELs with small emission apertures (less than 3.5 /spl mu/m-dia). The small aperture size leads to a high electrical resistance and high current density, which can impact device reliability. By contrast, antiguided VCSEL structures have shown promise for achieving larger aperture single-mode operation. To obtain high single-mode powers with a larger emitting aperture, the use of a negative-index guide (antiguide) is beneficial. This paper discusses antiguided structures and some of their advantages when incorporated in 2-D VCSEL array structures.     

Vertical cavity surface emitting lasers with 21% efficiency bymetalorganic vapor phase epitaxy

Proton implanted, vertical cavity top-surface emitting lasers exhibit the highest single-mode and multi-mode output powers, highest power conversion efficiency, and lowest threshold voltage for such devices reported to date. These lasers use new mirror grading designs that are enabled by metalorganic vapor phase epitaxy's capabilities of alloy grading and carbon doping. The results validate this growth technology by exceeding the previous best results which were based on molecular beam epitaxy     

Laterally coupled DBR laser emitting at 1.55 /spl mu/m fabricated by focused ion beam lithography

By using focused ion beam lithography high performance 1.55-/spl mu/m emitting distributed Bragg reflector lasers were realized suitable for high-speed optical telecommunication. Threshold currents of 8 mA and continuous-wave efficiencies of 0.37 W/A for 600-/spl mu/m-long devices were achieved. Stable single-mode emission with sidemode suppression ratios of > 40 dB were observed for the entire operation range. By relative intensity noise measurements an intrinsic 3-dB modulation frequency of > 10 GHz was estimated for a single-mode output power of 23 mW.     

High-Power Coherent Beam Combining of Two Photonic Crystal Fiber Lasers

Coherent beam combining of two large mode area photonic crystal fiber (LMA PCF) lasers is studied experimentally by using a self-imaging technique. Steady interference strips with high visibility of 35% are observed in high-power operation, which demonstrates the obvious advantages of the LMA PCF over the conventional double-clad fiber in coherent beam combining. Experiments also show that the reflectivity of coupling output mirror affects the coherent output power. The maximum coherent output power of 80 W with approximate 90% combining efficiency is achieved when the pump power is 130 W and the reflectivity of coupling output mirror is 5%.     

Tuned front-end design for heterodyne optical receivers

A theoretical analysis of the noise performance of optical receivers with front-end tuning, suitable for wideband coherent systems, is presented. An algorithm for choosing the values of the tuning components in the front end so as to minimize the thermal noise output power has been developed. This theory is applied to the well-known simple parallel and serial tuning configurations and also to three more advanced designs. It is shown that any tuning is better than none in the wide-bandwidth designs considered and that the more advanced designs yield up to 12-dB reduction in thermal noise power. Two of the designs can be implemented with discrete components and should yield shot-noise-limited detection with 50-100 μW of local oscillator power in receivers with 5-GHz bandwidth. The practical problem of equalizing the front-end response is considered, and it is shown that good performance can be expected using realizable components     

Powerful single-mode radiation by injection locking of a CW dyelaser amplifier

The generation of high-power tunable single-mode continuous-wave (CW) radiation using a dye ring laser amplifier is demonstrated. Weak radiation of a single-mode master oscillator is amplified in an injection-locked slave oscillator. The way in which the output power depends on injected power, pump power, and frequency is investigated. The theoretical equations for the output power are discussed. A maximum output power of 6.2 W was achieved at 20 W pump power and 0.8 W injected power     

Two cross-coupled-mode operation of a twin-stripe laser:bistability for wide ranges of output power level and current ratio

A theoretical approach is reported which models cases where the twin-stripe laser generates either one resonant mode alone or two resonant modes simultaneously. The model determines the ratio of output powers of the light emitted from the two stripes as a function of the ratio of currents to the two stripes. The model simulates the laser operation in regions for which an earlier single-mode approach does not provide solutions. Bistability is predicted to occur over much wider ranges of output power level and current ratio than the previous single-mode case     

Modeling temperature effects and spatial hole burning to optimizevertical-cavity surface-emitting laser performance

Two-dimensional physical models for single-mode index guided vertical cavity surface emitting lasers (VCSELs) are developed and compared with experimental measurements on state-of-the-art devices. Starting with the steady-state electron and photon rate equations, the model calculates the above threshold light-current (LI) characteristics. Included are temperature effects, spatial hole burning effects, carrier diffusion, surface recombination, and an estimation of optical losses. The model shows that the saturation of output power in the experimental devices is due to carrier leakage over the heterojunction and not simply the shifting of the gain peak relative to the cavity mode. Using the verified model new designs are analyzed, showing that output powers greater than 15 mW and power efficiencies above 20% should be achievable with existing processing technology     

All-fiber phase-modulated master oscillator power amplifier forcoherent communication

An all-fiber phase-modulated master oscillator power amplifier for free-space coherent communication is presented. A distributed-feedback fiber laser at 1.06 μm is used as master oscillator. A novel phase modulator based on a ZnO-coated single-mode fiber modulates the single frequency communication signal. The modulated signal is then amplified in a double-clad doped fiber power amplifier. Up to 1 W cw single-frequency output power, phase modulated at 196 MHz, has been obtained     

Comprehensive above-threshold analysis of antiresonant reflecting optical waveguide edge-emitting diode laser

A three-dimensional (3-D) above-threshold analysis has been performed for laterally antiguided laser structures of the antiresonant-reflecting-optical-waveguide type, of relatively large core width (/spl sim/ 10 /spl mu/m), for high-power, single-spatial-mode operation. A 3-D numerical code has been developed, which takes into account carrier diffusion in the quantum well as well as edge radiation losses. The laser characteristics are calculated as functions of the above-threshold drive level. Within the simulation, 3-5 higher order optical modes on a "frozen background" are computed by the Arnoldi algorithm. Because of the nonuniform gain saturation of the lasing mode, the modal gains for higher order modes increase with the drive current due to increasing overlap of their fields with the two-dimensional gain distribution. The onset of threshold for higher order modes puts an upper limit on the range for stable single-mode operation. The above-threshold analysis is done for various values of the width of the reflector region, below and above the lateral-antiresonance condition. It is found that the maximum intermodal discrimination, which in turn provides the maximum single-mode power, is obtained when the reflector-region width is /spl sim/25 % larger that its value at antiresonance. Then, for 10-/spl mu/m-core devices, stable, single-mode operation is found to occur to drive levels as high as 41 /spl times/ threshold, with single-mode output powers as high as 1.45 W.     

一种基于三芯光纤的模式复用器/解复用器的设计

提出了一种基于三芯光纤的模式复用器/解复用器,三个纤芯包括两个相同的单模纤芯和一个少模纤芯,在少模纤芯中写入长周期光纤光栅以实现单模纤芯中LP01模与少模纤芯中LP11模间的转换。同时从两个单模纤芯输入LP01模,能激发少模纤芯中两个简并的LP11,a模和LP11,b模。采用光束传播法分析了该模式复用器/解复用器的耦合特性及串扰。数值模拟结果显示,若以少模纤芯中LP11模输出能量大于-1dB的波长范围作为该模式复用器/解复用器的工作带宽,则能够达到23nm,并且少模纤芯中生成的其他模式的输出能量皆比LP11模的输出能量小-21dB以上。该模式复用器/解复用器能够实现对少模光纤的模式复用与解复用,并具有极低的串扰。     

High-power high-efficiency operation of read-type IMPATT-diode oscillators

C.W. operation of GaAs Schottky-barrier Read-type IMPATT-diode oscillators is reported. These devices exhibited efficiences from 20 to 24% with output powers of 2 ~ 3 W c.w. in the Ku-band. The best efficiency was 24%, with an output power of 1.8 W c.w., while the maximum output power was 3.2 W c.w., with an efficiency of 20.7% at frequencies near 14 GHz.     

Focusing properties of high brightness gain tailored broad-areasemiconductor lasers

In this letter, we present a simple broad-area semiconductor laser using a current spreading layer to modify the transverse gain profile. The device exhibits excellent spatial coherence to total output powers of 2.5 W under pulsed operation. Devices have been focused down to a spot size of approximately 5 μm full-width at half-maximum at 2.5 W, with the beam profile and position remaining stable over the entire range of operation. Under continuous-wave operation, thermal effects reduce spatial coherence, leading to a significantly increased spot size and loss of beam stability. This work demonstrates the advantages of modifying the transverse gain profile, and how it can be used to produce high brightness devices required for single-mode fiber coupling     

100 W C-band single-chip GaN FET power amplifier

A single-chip GaN-FET amplifier exhibits record output powers of C-band solid-state amplifiers under continuous-wave (CW) and pulsed operation conditions. At 5.0 GHz, the developed GaN-FET amplifier with 24 mm gate periphery delivered a CW 100 W output power with 12.9 dB linear gain and 31% power-added efficiency and a pulsed 155 W output power with 13.0 dB linear gain.     

230W C-band GaN-FET power amplifier

A C-band high-power amplifier with two GaN-based FET chips exhibits record output powers under continuous-wave (CW) and pulsed operation conditions. At 5.0 GHz, the developed GaN-FET amplifier delivers a CW 208 W output power with 11.9 dB linear gain and 34% power-added efficiency. It also shows a pulsed 232 W output power with 8.3 dB linear gain.     

Diode-pumped semiconductor disk laser with intracavity frequencydoubling using lithium triborate (LBO)

Diode-pumped semiconductor disk lasers, also referred to as vertical external cavity surface-emitting lasers show excellent beam characteristics in combination with high output powers. In this letter, we present a diode-pumped semiconductor disk laser based on the InAlGaAs material system without any additional phosphorus containing layers for strain compensation. We have achieved a near-infrared λ~972-nm laser output power of 0.25 W in the fundamental transverse mode. The disk laser beam has been coupled into a single-mode fiber with a coupling efficiency of >70%. Moreover, we have shown 490-nm blue-green light generation by intracavity frequency doubling using lithium triborate (LBO)     

Laser power at 600W

Southampton Photonics Inc (SPI) and the Optoelectronics Research Centre (ORC), University of Southampton, UK, have demonstrated over 600W from a single fibre laser. The team believes this to be the highest power reported to date with a single fibre gain module, demonstrating that cladding pumped fibre lasers can produce the high powers needed to compete with more traditional laser technology, in applications such as remote welding, by offering high powers which preserve beam quality. Led by Dr Johan Nilsson researchers produced over 600W output power at 1090μ from an Ytterbium Doped Fibre Laser, one of the most efficient lasers available. According to SPI’s roadmap, single fibre, single-mode output powers well in excess of 1kW will be achievable. These lasers can then be combined to produce multi-kW solutions with excellent beam quality, efficiency and reliability. The work was funded by DARPA under its High Power Fibre Laser programme.This is a short news story only. Visit www.three-fives.com for the latest advanced semiconductor industry news.     

High-power double-clad fiber lasers

Rare-earth doped, laser-diode-pumped, single-mode, double-clad fiber lasers are studied in detail, experimentally and theoretically, with particular attention to properties of scaling to higher output powers. Gain saturation, spontaneous emission, fiber propagation loss, and the optimum output coupler are considered for oscillator design and laser performance. Thermal properties are investigated, including the thermal fracture limit, the decrease of quantum efficiency with increasing pump power through the temperature dependence of multiphonon decay and ion-ion energy transfer, and thermal lensing. Self-focusing and Raman effects are briefly considered. It is shown that output powers in the tens of watts range are readily feasible with available double-clad fiber lasers     

大模场掺铥光纤增益特性研究

为了进一步提升光纤激光器的输出功率,采用大模场面积掺铥光纤来抑制非线性效应,利用非均匀布喇格掺铥光纤结构,通过优化参量,在满足单模传输条件下获得模场面积为719μm2的大模场面积光纤。基于此光纤建立了793nm波长抽运下大模场掺铥光纤放大器理论模型。由于大模场面积光纤能降低光功率密度,抑制Stokes光功率,因此该种光纤放大器在高抽运功率下相比普通单模光纤放大器能够得到更大的输出功率。结果表明,当抽运光功率为100W时,所设计大模场面积光纤与普通单模光纤相比,转换效率提高5%,达到40%,输出功率达到41.01W。以上研究对于实际掺铥光纤放大器的设计有重要应用价值。     

Compact hybrid master oscillator power amplifier with 3.1-W CW output power at wavelengths around 1061 nm

A hybrid master oscillator power amplifier (MOPA) laser source has been realized by coupling a single-mode three-section distributed Bragg reflector (DBR) laser as master oscillator and a tapered power amplifier with a single lens only. A maximum continuous-wave optical output power of 3.1 W was achieved. The emission spectrum was completely determined by the DBR laser. Single longitudinal mode operation at a wavelength of /spl lambda/=1061 nm was maintained over the whole power range. Up to an output power of 1.8 W, the beam propagation factor M/sup 2/was less than 1.6.