A surgical catheter , comprising: a catheter tip assembly (400; 500; 520; 560; 640) coupled to a distal end of a catheter body, wherein the catheter tip assembly (400; 500; 520; 560; 640) comprises a catheter tip (652; 712), a flexing structure (616; 646), and a multi-core fiber (546; 566), wherein the multi-core fiber is configured for force and shape sensing, and wherein the multi-core fiber (546; 566) comprises a plurality of cores (202, 204, 206, 208; 252, 254, 256, 258; 602, 604, 606, 608, 610, 612, 614), and wherein a proximal end of the catheter tip (652; 712) is coupled to a distal end of the flexing structure (616; 646), wherein a distal portion of the multi-core fiber (546; 566) passes through an interior portion of the flexing structure (616; 646), and wherein the flexing structure (616; 646) is configured to bend in response to a force imparted on the catheter tip (652; 712), and wherein the catheter tip assembly further comprises an encasement member surrounding the distal portion of the multi-core fiber (546; 566), the encasement member comprising a first wall at a first axial position of the encasement member and a second wall at a second axial position of the encasement member , characterized in that the first wall is thinner than the second wall , and the multi-core fiber (546; 566) comprises a first set of fiber Bragg gratings for bending and a second set of fiber Bragg gratings for axial compression, wherein the first set of gratings and the second set of gratings are situated in the encasement member at two different axial positions, one with the first wall and the other with the second wall. a catheter tip assembly (400; 500; 520; 560; 640) coupled to a distal end of a catheter body, wherein the catheter tip assembly (400; 500; 520; 560; 640) comprises a catheter tip (652; 712), a flexing structure (616; 646), and a multi-core fiber (546; 566), wherein the multi-core fiber is configured for force and shape sensing, and wherein the multi-core fiber (546; 566) comprises a plurality of cores (202, 204, 206, 208; 252, 254, 256, 258; 602, 604, 606, 608, 610, 612, 614), and wherein a proximal end of the catheter tip (652; 712) is coupled to a distal end of the flexing structure (616; 646), wherein a distal portion of the multi-core fiber (546; 566) passes through an interior portion of the flexing structure (616; 646), and wherein the flexing structure (616; 646) is configured to bend in response to a force imparted on the catheter tip (652; 712), and wherein the catheter tip assembly further comprises an encasement member surrounding the distal portion of the multi-core fiber (546; 566), the encasement member comprising a first wall at a first axial position of the encasement member and a second wall at a second axial position of the encasement member , characterized in that the first wall is thinner than the second wall , and the multi-core fiber (546; 566) comprises a first set of fiber Bragg gratings for bending and a second set of fiber Bragg gratings for axial compression, wherein the first set of gratings and the second set of gratings are situated in the encasement member at two different axial positions, one with the first wall and the other with the second wall. <EOS>