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IntroductionAmong the planar actuators, the SPMPM has the advantages such as no heating problem, high power conversion ratio, and so on. However, conventional moving-coil type SPMPMs are shown to have the limits to expend their working range since they have power cables in the mover. In addition, x-and ydirection motions are coupled each other [1]. In this paper, we propose a novel Maglev moving-magnet-type SPMPM that has a simple and thin stator composed of several PCBs. In order to study the feasibility of the proposed SPMPM, the magnetic flux density and thrust force equations are estimated analytically and verified using the finite-element method (FEM) and experimental works Design and Analysis Fig. 1(a) and 1(b) show the side view of analytical model and the upper view of the stator respectively. The three-phase PWM method is used to supply the power source into the prototype motor fed by an IGBT inverter, using the standard vector control for normal brushless PM DC servo-motors. Distribution equations of the electromagnetic systems can be expressed using Maxwell's equations and Ohm's law, and governing equation of the electromagnetic systems is expressed as the partial differential equations for the magnetic vector potential A. From the boundary conditions of the system, the z-direction flux density distribution in the air gap is calculated. The intensity of propulsion planar force depends on the values of the current density of the stator windings and the flux density established by PMs. Experimental Validations Fig. 2 shows the structure of the proposed SPMPM, which has the dimensions and parameters given in Table I. Fig. 3(a) and 3(b) show the analytical and 3-D FEM results of the z-direction flux density distribution respectively. Fig. 4 shows the comparison results between the analytical and experimental values for the propulsion force. Table II presents the values of the x-direction thrust force corresponding to the phase currents by means of the analytical, FEM, and experimental method. The measured values of thrust force are smaller than the analytical results because some parameters are neglected to simplify the modeling

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Multi-mode cw blue-violet diode-lasers exhibit interference revival when the interferometric path-length-difference is much greater than the self-coherence time. Using the equally-spaced and recurring interference envelopes, high-resolution mode-spacing measurement is possible without using high-resolution spectrometers. OCIS codes: (030.1670) Coherent optical effects, (120.3180) InterferometryIn recent years, high-power blue-violet diode lasers are becomming more and more common in many areas of optics. Since these lasers tend to operate in the multi-mode (longitudinal modes) regime, it is of interest to have the accurate knowledge of mode spacing: the mode spacing information is important for interferometry experiments, laser diode characterization [1,2], and understanding the optical gain mechanism in InGaN laser diodes [3,4].Due to the small cavity length of the blue-violet diode laser, however, mode spacing measurement would require a costly high-resolution spectrometer with the resolution of the order of 10 −3 nm [1, 2]. Another approach would be to indirectly determine the mode spacing Δλ by using the relation derived from the resonant condition of the FabryPerot modes [3],where λ 0 is the wavelength of the peak of the lasing spectrum, L is the laser cavity length, and the effective refractive index, n eff , of the waveguide at λ 0 is given as n eff = n − λ 0 dn/dλ 0 [1, 2, 3, 4]. Although λ 0 could be measured accurately using a low cost spectrometer, the information on L and/or n eff is not available in general, causing the mode spacing anomaly [2,3,4].In this paper, we first report on the observation of interference revival when the interfrometric path length difference is much greater than the coherence length of the multi-mode blue-violet cw diode laser. We then show that this unusual interference phenomenon can be used for high-resolution mode spacing measurement of the laser.Let us first briefly discuss the physics behind revival of the interference when the interferometric path length difference is much greater than the coherence length. Consider the multi-mode field E i (t) at any given point inside the diode laser cavity as the incoherent sum of multiple longitudinal modes,where the subscript m is the mode number, E m is the amplitude of a particular field mode, ν 0 is the frequency of the peak mode, Δν is the frequency difference between the adjacent modes, and θ m is the random phase of each longitudinal mode. The individual modes have random phases so the multi-mode field outside the cavity, E o (t), has a chaotic waveform. The chaotic waveform, however, should repeat itself at every time interval 1/Δν because of the fact that the mode spacing Δν is constant. Since 1/Δν is equivalent to the time it takes for the cavity field to make one roundtrip inside the laser cavity of the length L (with the effective refractive index n eff ), the chaotic multi-mode cw field outside the cavity should repeat itself at every T p which is given as,where c is the speed of light in vacuum (air). Therefore, by u...