Abstract: Provided is a clamp of elastic box of stiff true-triaxial testing system and a displacement monitoring method for cuboid specimens. The clamp includes six pressing plates and eight plate springs, which form an elastic pressure box. One surface of the elastic pressure box can be disassembled, which simplifies the steps of rock sample mounting, and saving the mounting time. The springs connected with the pressing plates ensures the stability of the clamp but cannot affect the stress state of other surfaces of the rock sample during the test of the rock sample, thereby ensuring test accuracy. The invention further provides a displacement monitoring method for the rock sample by using the elastic box clamp. Six displacement sensors are mounted on the elastic box clamp, and the displacement of the rock sample can be monitored in real time.

Abstract: Techniques for designing efficient gratings with multiple frequency response channels based on sampled patterns based predominantly on phase modulation of the underlying grating structure. Each period of the phase sampled patterns may include contiguous, discrete phase segments with different phase values, or alternatively, a continuous spatial phase pattern that changes the phase of the underlying grating structure. Moderate amplitude modulation of the underlying grating structure by the sampling structure may also be used together with phase modulation. The grating period or the sampling period may be chirped.

Abstract: The present invention is directed to a system and method for designing efficient multi-channel FBG gratings using a pre-compensated phase mask for diffracting light for side-writing the grating on an optical fiber core. A desired phase function of the FBG is generated, specifically tailored to an effective spacing between the phase mask and the optical fiber core. From the phase function a phase mask is pre-compensated to offset diffraction effects associated with each longitudinal position of the FBG receiving light from two corresponding longitudinal positions of the phase mask substantially symmetrically spaced longitudinally relative to each particular longitudinal position of the FBG. The two corresponding longitudinal positions of the phase mask are spaced longitudinally from each other by a spacing determined by the effective spacing between the phase mask and fiber core and by the first order diffraction angle of light through the phase mask.

Abstract: The present invention is directed to a system and method for designing efficient multi-channel FBG gratings using a pre-compensated phase mask for diffracting light for side-writing the grating on an optical fiber core. A desired phase function of the FBG is generated, specifically tailored to an effective spacing between the phase mask and the optical fiber core. From the phase function a phase mask is pre-compensated to offset diffraction effects associated with each longitudinal position of the FBG receiving light from two corresponding longitudinal positions of the phase mask substantially symmetrically spaced longitudinally relative to each particular longitudinal position of the FBG. The two corresponding longitudinal positions of the phase mask are spaced longitudinally from each other by a spacing determined by the effective spacing between the phase mask and fiber core and by the first order diffraction angle of light through the phase mask.

Abstract: Techniques for designing efficient gratings with multiple frequency response channels based on sampled patterns based predominantly on phase modulation of the underlying grating structure. Each period of the phase sampled patterns may include contiguous, discrete phase segments with different phase values, or alternatively, a continuous spatial phase pattern that changes the phase of the underlying grating structure. Moderate amplitude modulation of the underlying grating structure by the sampling structure may also be used together with phase modulation. The grating period or the sampling period may be chirped.

Abstract: Techniques for optically evaluating phase masks for fabricating waveguide Bragg gratings by measuring diffraction orders.