A fibre optic cable structure comprising: an optical fibre; and a bend inducer responsive to an environmental parameter to control bending of the optical fibre; wherein the bend inducer is configured to adopt a first configuration at a first value of said environmental parameter that induces a first curvature of the optical fibre and to adopt a second configuration at a second, different, value of the environmental parameter that induces a second, different, curvature of the optical fibre such that a change in value of the environmental parameter imparts a bending force on the optical fibre; wherein the bend inducer comprises: a first component with a longitudinal dimension along a longitudinal length of the fibre optic cable structure that varies with the environmental parameter; and a second component with a longitudinal dimension along a longitudinal length of the fibre optic cable structure that varies with the environmental parameter; wherein the amount of variation in said dimension of said first component to a given change in the environmental parameter is different to that of the second component and wherein the first component and second component are configured such that a given change in the environmental parameter results in a positive change in dimension for one of the first and second components and a negative change in dimension for the other of the first and second components. an optical fibre; and a bend inducer responsive to an environmental parameter to control bending of the optical fibre; wherein the bend inducer is configured to adopt a first configuration at a first value of said environmental parameter that induces a first curvature of the optical fibre and to adopt a second configuration at a second, different, value of the environmental parameter that induces a second, different, curvature of the optical fibre such that a change in value of the environmental parameter imparts a bending force on the optical fibre; wherein the bend inducer comprises: a first component with a longitudinal dimension along a longitudinal length of the fibre optic cable structure that varies with the environmental parameter; and a second component with a longitudinal dimension along a longitudinal length of the fibre optic cable structure that varies with the environmental parameter; wherein the amount of variation in said dimension of said first component to a given change in the environmental parameter is different to that of the second component and wherein the first component and second component are configured such that a given change in the environmental parameter results in a positive change in dimension for one of the first and second components and a negative change in dimension for the other of the first and second components. a first component with a longitudinal dimension along a longitudinal length of the fibre optic cable structure that varies with the environmental parameter; and a second component with a longitudinal dimension along a longitudinal length of the fibre optic cable structure that varies with the environmental parameter; wherein the amount of variation in said dimension of said first component to a given change in the environmental parameter is different to that of the second component and wherein the first component and second component are configured such that a given change in the environmental parameter results in a positive change in dimension for one of the first and second components and a negative change in dimension for the other of the first and second components.