Singly generated quasivarieties and residuated structures

A quasivariety K of algebras has the joint embedding property (JEP) iff it is generated by a single algebra A. It is structurally complete iff the free countably generated algebra in K can serve as A. A consequence of this demand, called "passive structural completeness" (PSC), is that the nontrivial members of K all satisfy the same existential positive sentences. We prove that if K is PSC then it still has the JEP, and if it has the JEP and its nontrivial members lack trivial subalgebras, then its relatively simple members all belong to the universal class generated by one of them. Under these conditions, if K is relatively semisimple then it is generated by one K-simple algebra. It is a minimal quasivariety if, moreover, it is PSC but fails to unify some finite set of equations. We also prove that a quasivariety of finite type, with a finite nontrivial member, is PSC iff its nontrivial members have a common retract. The theory is then applied to the variety of De Morgan monoids, where we isolate the sub(quasi)varieties that are PSC and those that have the JEP, while throwing fresh light on those that are structurally complete. The results illuminate the extension lattices of intuitionistic and relevance logics

Multiple Conclusion Rules in Logics with the Disjunction Property

We prove that for the intermediate logics with the disjunction property any basis of admissible rules can be reduced to a basis of admissible m-rules (multiple-conclusion rules), and every basis of admissible m-rules can be reduced to a basis of admissible rules. These results can be generalized to a broad class of logics including positive logic and its extensions, Johansson logic, normal extensions of S4, n-transitive logics and intuitionistic modal logics

Demonstration of pulse frequency division multiplexing using terahertz optical asymmetric demultiplexer

A new method of pulse frequency division multiplexing (PFDM) to increase the capacity of local fiber-optic communications networks heavily relies on optical signal processing using an all-optical AND gate. In this letter, we report a conceptual demonstration of the PFDM method using a terahertz optical asymmetric demultiplexer as a fast (picosecond switching time), low switching energy (as low as 125 fJ) optical AND gate for the optical signal processing. This creates a real possibility for the practical realization of the PFDM method

Comparison of Sagnac and Mach-Zehnder ultrafast all-optical interferometric switches based on a semiconductor resonant optical nonlinearity

We present a theoretical analysis of recently demonstrated ultrafast all-optical interferometric switching devices (based on Sagnac and Mach-Zehnder interferometers) that use a large optical nonlinearity in a resonant regime. These devices achieve ∼10-ps switching windows and do not require high-energy optical control pulses. We theoretically analyze and compare one Sagnac and two Mach-Zehnder switching configurations

Demonstration of digital phase-sensitive boosting to extend signal reach for long-haul WDM systems using optical phase-conjugated copy

We demonstrate a hybrid optical/digital phase-sensitive boosting (PSB) technique for long-haul wavelength division multiplexing (WDM) transmission systems. The approach uses four-wave mixing (FWM) to generate a phase-conjugated idler alongside the original signal. At the receiver, the signal and idler are jointly detected, and the phases of the idler symbols are conjugated and summed with the signal symbols to suppress noise and nonlinear phase distortion. The proposed hybrid PSB scheme is independent of modulation format and does not require an optical phase-locked loop to achieve phase matching required by conventional phase-sensitive amplifiers. Our simulation and experimental results of 112-Gb/s dual-polarization quadrature phase-shift-keying (DP-QPSK) transmission confirmed the principle of the PSB scheme, attaining a Q-factor improvement of 2.4 dB over conventional single-channel transmission after 4,800 km of dispersion-managed fiber (DMF) link at the expense of 50% reduction in spectral efficiency and extending the system reach by 60% to 7,680 km

Solar Cell Emitters Fabricated by Flash Lamp Millisecond Annealing

Phosphorus ion implantation was used for the emitter formation in mono- and multicrystalline silicon solar cells. After ion implantation the silicon is strongly disordered or amorphous within the ion range. Therefore subsequent annealing is required to remove the implantation damage and activate the doping element. Flash-lamp annealing offers here an alternative route for the emitter formation at overall low thermal budget. During flash-lamp annealing, only the wafer surface is heated homogeneously to very high temperatures at ms time scales, resulting in annealing of the implantation damage and electrical activation of phosphorus. However, variation of the pulse time also allows to modify the degree of annealing of the bulk region to some extent as well, which can have an influence on the gettering behaviour of metallic bulk impurities. The μ-Raman spectroscopy showed that the silicon surface is amorphous after ion implantation. It could be demonstrated that flash-lamp annealing at 800°C for 20 ms even without preheating is sufficient to recrystallize implanted silicon. The highest carrier concentration and efficiency as well as the lowest resistivity were obtained after annealing at 1200°C for 20 ms both for mono- and multicrystalline silicon wafers. Photoluminescence results point towards P-cluster formation at high annealing temperatures which affects metal impurity gettering within the emitter

Demonstration of ultrafast, all-optical, low control energy, single wavelength, polarization independent, cascadable, and integratable switch

A new type of ultrafast all optical switch based on a Mach-Zehnder interferometer is demonstrated with a 10 ps switching window which requires only 0.65 pJ of control pulse energy. The optical nonlinearity which is utilized is associated with the gain compression of semiconductor optical amplifiers, and the switching turnoff transition does not depend on the slow amplifier recovery time. Both data and control pulses are at the same wavelength of 1.313 μm, and are not polarized orthogonal to each other. The device configuration and the semiconductor amplifiers allow for small scale integration and data output cascadability