A four-frame phase shift method insensitive to phase shifter nonlinearity

A four-frame phase shift method and an associated algorithm using unequal phase steps are presented. The unique advantage of this method is that it becomes insensitive to phase shifter nonlinearity because of the performance of a special procedure, in which the phase shifts are shared out between the reference beam and the object beam. By this means, any phase shifter can work as long as one phase shift is accurately known. On the basis of the technique, a simple calibration method for the linear phase shifter is suggested. The influences of phase shifter miscalibration, detector nonlinearity and random noise on the algorithm are investigated, and the optimal phase shifts are given.

Influence of the second cladding on the properties of four-layer large flattened mode fibers

A theoretical method to analyze four-layer large flattened mode (LFM) fibers is presented. The influence of the second cladding on the properties of four-layer LFM fiber, including the fundamental and higher-order modal fields, effective area, bending loss, and dispersion, are studied by comparison. At the same time, the reasons for the different characteristics are considered. The obtained results indicate that the effective area of the four-layer LFM fiber is about 1.6 times larger than that of the conventional standard step-index fiber and the fibers have better bend-induced filtering ability than three-layer LFM fibers. (C) 2007 Society of Photo-Optical Instrumentation Engineers.

Influence of the second cladding on the properties of four-layer large flattened mode fibers

A theoretical method to analyze four-layer large flattened mode (LFM) fibers is presented. The influence of the second cladding on the properties of four-layer LFM fiber, including the fundamental and higher-order modal fields, effective area, bending loss, and dispersion, are studied by comparison. At the same time, the reasons for the different characteristics are considered. The obtained results indicate that the effective area of the four-layer LFM fiber is about 1.6 times larger than that of the conventional standard step-index fiber and the fibers have better bend-induced filtering ability than three-layer LFM fibers. (C) 2007 Society of Photo-Optical Instrumentation Engineers.

Design guidelines and characteristics for a kind of four-layer large flattened mode fibers

A theoretical method to analyze a kind of four-layer large flattened mode (LFM) fibers is presented. The properties of the fiber, including the fundamental and higher-order modal fields, effective area and bending loss are discussed by comparison. At the same time, the reasons for the different characteristics are considered. The obtained results indicate that the effective area of the four-layer LFM fiber is about 1.3 times larger than that of the conventional standard step-index fiber and the fiber can suppress the higher-order modes via bending effectively. The four-layer LFM fiber has less efficient bend-induced filtering ability than the conventional step-index fiber; however, it has more efficient filtering ability than the three-layer LFM fiber. (C) 2007 Elsevier GmbH. All rights reserved.

A four-passed ytterbium-doped fiber amplifier

In this paper, a four-passed ytterbium-doped fiber amplifier (YDFA) is discussed. The gain and the pump and the signal light propagation characteristics of the four-passed YDFA are described. It is found that, while using a shorter length of the fiber, a four-passed fiber amplifier can realize the same output power as a single-pass fiber amplifier, and, for the same fiber lengths, a four-passed fiber amplifier offers a significantly higher power than its single-pass counterpart. (C) 2006 Elsevier Ltd. All rights reserved.