Implantable device for measuring the glucose concentration of a body fluid when implanted, the implantable device comprising: a housing containing: a glucose measurement unit comprising: a first linearly polarized light source configured to emit linearly polarized light to outside of the housing of the device; and a linearly polarized light sensor configured to detect linearly polarized light returned from the linearly polarized light source via the outside of the housing, and output a first electrical signal based on the detected linearly polarized light; and a wireless communication module configured to wirelessly communicate with an external wireless communication device; wherein the linearly polarized light sensor comprises a linearly polarized light filter and a first optical sensor, wherein the linearly polarized light filter is configured to linearly polarize the light returned through the light transmissive part from the first linearly polarized light source, and wherein the first optical sensor is configured to output the first electrical signal based on the detected light linearly polarized by the linearly polarized light filter, wherein the linearly polarized light filter comprises a Kerr cell arranged such that the linearly polarized light returned from the linearly polarized light source via the outside of the housing passes through the Kerr cell before being detected by the first optical sensor, wherein the glucose measurement unit further comprises a second optical sensor and a linear polarizer, wherein the linear polarizer is arranged to linearly polarize light returned from the linearly polarized light source via the outside of the housing, wherein the second optical sensor is arranged to detect the light linearly polarized by the linear polarizer and output a second electrical signal based on the detected light linearly polarized by the linear polarizer, wherein a control unit of the implantable device is configured to process the first electrical signal and the second electrical signal based on a ratio of the first electrical signal and the second electrical signal to reduce or remove the effects of interference or background noise, and wherein the wireless communication module is configured to wirelessly transmit a signal based on the processed first electrical signal and processed second electrical signal to the external wireless communication device. a housing containing: a glucose measurement unit comprising: a first linearly polarized light source configured to emit linearly polarized light to outside of the housing of the device; and a linearly polarized light sensor configured to detect linearly polarized light returned from the linearly polarized light source via the outside of the housing, and output a first electrical signal based on the detected linearly polarized light; and a wireless communication module configured to wirelessly communicate with an external wireless communication device; a glucose measurement unit comprising: a first linearly polarized light source configured to emit linearly polarized light to outside of the housing of the device; and a linearly polarized light sensor configured to detect linearly polarized light returned from the linearly polarized light source via the outside of the housing, and output a first electrical signal based on the detected linearly polarized light; and a first linearly polarized light source configured to emit linearly polarized light to outside of the housing of the device; and a linearly polarized light sensor configured to detect linearly polarized light returned from the linearly polarized light source via the outside of the housing, and output a first electrical signal based on the detected linearly polarized light; and a wireless communication module configured to wirelessly communicate with an external wireless communication device; wherein the linearly polarized light sensor comprises a linearly polarized light filter and a first optical sensor, wherein the linearly polarized light filter is configured to linearly polarize the light returned through the light transmissive part from the first linearly polarized light source, and wherein the first optical sensor is configured to output the first electrical signal based on the detected light linearly polarized by the linearly polarized light filter, wherein the linearly polarized light filter comprises a Kerr cell arranged such that the linearly polarized light returned from the linearly polarized light source via the outside of the housing passes through the Kerr cell before being detected by the first optical sensor, wherein the glucose measurement unit further comprises a second optical sensor and a linear polarizer, wherein the linear polarizer is arranged to linearly polarize light returned from the linearly polarized light source via the outside of the housing, wherein the second optical sensor is arranged to detect the light linearly polarized by the linear polarizer and output a second electrical signal based on the detected light linearly polarized by the linear polarizer, wherein a control unit of the implantable device is configured to process the first electrical signal and the second electrical signal based on a ratio of the first electrical signal and the second electrical signal to reduce or remove the effects of interference or background noise, and wherein the wireless communication module is configured to wirelessly transmit a signal based on the processed first electrical signal and processed second electrical signal to the external wireless communication device.