Approach For Power Scaling Research Articles

High output power, single mode, and TEM00 operation of a multiple gain chip VECSEL using a twisted-mode configuration.

A vertical external cavity surface emitting laser (VECSEL) has been developed for a sodium guide star application. Stable single frequency operation with 21 W of output power near 1178 nm with multiple gain elements while lasing in the TEM00 mode has been achieved. Higher output power results in multimode lasing. For the sodium guide star application, the 1178 nm can be frequency doubled to 589 nm. The power scaling approach used involves using multiple gain mirrors in a folded standing wave cavity. This is the first demonstration of a high power single frequency VECSEL using a twisted-mode configuration and multiple gain mirrors located at the cavity folds.

Coherent control of transverse modes in semiconductor laser frequency combs via radio-frequency injection

Increasing the output power of semiconductor laser frequency combs, while maintaining a single-lobe far-field characteristic is of great interest for mid-infrared sensing applications. Broadening of the ridge waveguide represents the most common approach for power scaling, however, the excitement of higher-order transverse modes often limits general applicability. Here, we demonstrate that the coherent control of the longitudinal laser modes enables control over the transverse modes of a quantum cascade laser. Modulating the laser in a frequency range 60 ± 3 MHz above the free-running laser beatnote and applying modulation powers above 25 dBm provides reliable fundamental transverse mode operation, observable as single-lobe, Gaussian-like characteristic in the recorded far-field. Furthermore, coherent comb operation for both fundamental and higher-order transverse mode states is demonstrated.

Full-duplex decode-and-forward relaying with joint relay-antenna selection

This paper is concerned with wireless relay networks that employ K full-duplex (FD) decode-and-forward relays to help a source to communicate with a destination. Each FD relay is equipped with multiple antennas, some for receiving and some for transmitting. The paper considers joint relay-antenna selection schemes that are based on the instantaneous channel conditions for two cases of antenna configurations, namely fixed antenna configuration (FAC) and adaptive antenna configuration (AAC). Under FAC, the transmit and receive antennas at each relay are fixed, whereas in the case of AAC an antenna at a relay can be configured to be either a transmit or a receive antenna.In addition to equal power allocation between the source and selected relay, a power scaling approach to counteract the effect of residual self-interference is also examined. Closed-form expressions of the outage probability and average capacity are obtained and provide important insights on the system performance. The accuracy of the obtained expressions are corroborated by simulation results. In particular, it is shown that under FAC and without power scaling, the diversity order approaches K as the self-interference (SI) level gets smaller, while it approaches zero whenever the SI level is nonzero and the SNR increases without bound. Under FAC and with power scaling, the diversity order approaches K for any SI level. For the case of AAC and without power scaling, the diversity order approaches 2K for small SI level. When power scaling is applied in AAC, the diversity order approaches 2K at any SI level.

Beam quality analysis and optimization for 10 kW-level spectral beam combination system

Filter-based spectral beam combining provides a promising approach for power scaling and brightness enhancement, especially for broad-linewidth fiber lasers. In this paper, we have demonstrated the beam combining experiments of two high power broad-linewidth fiber lasers using an edge filter as the combining element and achieved 10.25 kW combined power with an efficiency of 97%. Due to the thermal lens effect, the combined beam quality shows obvious signs of deterioration, which occurs in all cases of high power spectral beam combination system, including grating-based and prism-based schemes. The surface deformation and the thermal behavior are monitored in real-time so as to research the mechanism of the combined beam quality deterioration during the combining process. The primary reason for the decline of beam quality could be attributed to the thermal induced change in the refractive index, which not only results in an inhomogeneous wave-front aberration but causes the different focal waists of the incident channels. To counterbalance these aberrations, an air-cooling device and a passively thermally compensated optical system based on CaF2 windows are integrated into the system. In this case, the thermal lensing effect is minimized and the beam quality deterioration factor (BQD) of the combined output beam has been improved 52% in horizontal direction and 101% in vertical direction, showing the great potential of the filter-based approach to achieve a combined beam with high power and excellent beam quality.

Power optimization of LTE-800 and coexistence with DVB-T services

The emergence of cognitive radio technologies and the reallocation of the upper Ultra High Frequency (UHF) band (790−862 MHz) for broadband services has led to interference concerns for the DVB-T (Digital Video Broadcasting-Terrestrial) services. The DVB-T receivers need to be protected from aggregate interference coming from in-band and out-of-band transmissions, especially from the LTE-800 (Long-Term Evolution at 800 MHz) networks due to the operation in near spectral and location proximity. Although operating in different, but neighboring bands, the LTE-800 networks can be a serious threat to the DVB-T services due to excessive aggregate out-of-band interference caused to the DVB-T receivers. The regulators have assessed and defined the protection criteria for these cases. The power optimization of the LTE cellular networks, operating in near one spectral reuse factor, also remains an open issue due to the non-convex optimization problems. This paper proposes a novel algorithm for LTE-800 power allocation algorithm for capacity maximization of an LTE-800 network under DVB-T protection criteria. The algorithm uses k-means clustering to find the most critical geographical areas based on the DVB-T receivers protection ratios. It also adapts a local D.C. (Difference of two Convex functions/sets) programming approach to make the power optimization problem convex and perform the LTE-800 coverage and capacity optimization. The simulation analysis of the algorithm include realistic data for DVB-T modeling and Poisson Point Process for LTE-800 base stations (BS) spatial modeling. The proposed algorithm is compared to two extreme approaches, i.e. the max LTE BS power approach totally ignoring the DVB-T protection and the uniform power scaling approach that certainly protects the DVB-T service. The results prove the performance increase introduced by the proposed algorithm in terms of spatial capacity and coverage and DVB-T service protection.

Securing Massive MIMO Via Power Scaling

In this work, we study how fast we are able to scale down the power for both training and data transmission while guaranteeing security in a massive MIMO network without the help of artificial noise. We consider a multicell network with a large number of base station (BS) and eavesdropper antennas, but limited number of cells and mobile users. By offering an achievable lower bound on secrecy rate for both uplink and downlink, we observe that we can always find a power scaling approach for security as long as the ratio of the number of eavesdropper antennas to the number of BS antennas is smaller than a threshold. In particular, we find that when the eavesdropper and its targeting receiver share the same distance to the information source, the threshold is exactly the total pilot power received at the BS for uplink training.

Photosynthesis and growth in macroalgae: linking functional-form and power-scaling approaches

Grouping species into functional-form groups and measuring directly their surface area to volume ratio are 2 common approaches to forecast primary production of marine macroalgae. A link between the functional-form model (FFM) and the power-scaling approach (PSA) for a wide vari- ety of marine macroalgae has been attempted for the first time in the present work. To test both approaches, thalli of 44 species of marine benthic macroalgae were collected from intertidal zones adjacent to Cadiz Bay. Metabolic rates, tissue nutrient content, surface area to biomass ratio (SA/B) and specific growth rates were measured for these species. PSA slopes were close to 2/3 power for growth rate, while metabolic rates scaled very close to, or matched, 3/4 power. The FFM descriptive model provided similar results to the PSA when it was transformed to a numerical model through the SA/B ratio. Even though both models appear to be valid, the problems derived from species alloca- tion into morphological groups, and other previous criticisms, make the direct use of SA/B ratios more suitable for representing primary production in macroalgal functional groups in numerical models of coastal ecosystems.

Power Scaling of End-Pumped Solid-State Rod Lasers by Longitudinal Dopant Concentration Gradients

The power scalability of solid-state rod lasers in general is limited by the thermally induced mechanical stress approaching the fracture stress of the laser material. In conventional end-pumped lasers, the spatial heat-generation density profiles follow a nearly exponential law, resulting in a reduction of the maximum possible pump power when compared with a transversally pumped rod of the same length. In this paper, an approach for power scaling of end-pumped solid-state lasers by employing crystals with longitudinally varying dopant concentration profiles is presented. The optimum continuously varying dopant concentration profiles for a pump-light single and double pass are derived. Multisegmented crystals approximate these continuous doping profiles. An algorithm for optimizing the segment lengths and dopant concentrations in these crystals is described, the resulting optimum segment data are tabulated, and the relative power capability of these crystals is given.

A review of phase-conjugate solid-state lasers

Phase conjugation by stimulated Brillouin scattering represents a fundamentally promising approach for achieving power scaling of solid-state lasers. Following a summary of the power scaling problem and an overview of phase conjugation concepts, a review is presented of the application of phase conjugation to solid-state lasers. The author describes power scaling using demonstrated techniques for compensating static and thermally induced aberrations and depolarizations, as well as energy scaling by coherent coupling of multiple-gain media. Applications to diode-pumped lasers are discussed, as is a novel approach for power scaling of diode lasers themselves. Future research directions are indicated regarding conjugation fidelity at increasingly higher energies or with short-pulse and/or broadband lasers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>