Fibre-optic sensor for measuring a physical quantity

A fibre-optic sensor for measuring a physical quantity, such as a pressure, force, acceleration or tilt, comprising:

• a housing member;
• an optical fibre comprising at least a first measurement section for measuring a strain in said optical fibre;
• a first structural member and a second structural member, wherein said optical fibre is connected to a first fibre connection section of the first structural member and is connected to a second fibre connection section of the second structural member, wherein said first and second fibre connection sections are arranged on opposite sides of the first measurement section, such that at least said first measurement section is suspended between said first and second fibre connection sections;
• wherein at least one of the first and second structural members is movable relative to the other of the first and second structural members in at least a first direction that is substantially parallel to the optical fibre that is suspended between said first and second fibre connection sections for measuring the relative movement between the first and a second structural members, wherein the one of the first and second structural members is arranged to move in dependence of the physical quantity that is measured;
• wherein said first structural member is made from a first material having a first coefficient of thermal expansion and said second structural member is made from a second material having a second coefficient of thermal expansion that is different from said first coefficient of thermal expansion, such that a temperature induced strain in said optical fibre due to a temperature change is reduced;
• wherein the other of the first and second structural members is connected to the housing member by means of a thermal-stress-reduced coupling, wherein said thermal stress-reduced coupling is arranged to fixedly interconnect the housing member and the other of the first and second structural members while accommodating a relative thermal expansion between the housing member and the other of the first and second structural members in at least the first direction;
• and
• wherein:
• the thermal-stress-reduced coupling comprises a hinge coupling for fixedly interconnecting the other of the first and second structural members to the housing member in three translational directions that are substantially perpendicular to each other;
• and/or
• the thermal-stress-reduced coupling comprises a slidable hinge coupling for interconnecting the other of the first and second structural members to the housing member in one translational direction.