Abstract: An optical device 10 comprises an objective lens 11 defining a focal plane FP and an eyepiece 12 spaced apart therefrom, defining an optical axis OA therethrough. The optical device 10 comprises an optical member 13 having a first planar face 14, arranged on the optical axis OA proximal the focal plane FP, wherein the first planar face 14 is arranged to oppose the objective lens 11. The optical device 10 comprises a filter assembly 100 comprising a first notch filter 101 arranged to attenuate transmission of electromagnetic radiation having a first wavelength ?1, wherein the first notch filter 101 is arranged in front of the optical member 13. The first notch filter 101 is arranged at a first oblique angle ?1 to the optical axis OA whereby, in use, incident electromagnetic radiation having a predetermined wavelength ?i propagating along the optical axis is reflected by the first notch filter 101 away therefrom, wherein the first wavelength ?1 and the predetermined wavelength ?i are different.

Abstract: A vehicle surface includes a set of retroreflectors configured to reflect, at least in part, incident hostile light towards a source of the incident hostile light.

Abstract: A network, or part thereof for example a link, 1 is described. The network 1 is for data communication through a medium, preferably wherein the medium comprises and/or is, at least in part, a liquid medium LM. The network 1 comprises a set of transmitters 11, including a first transmitter 11A comprising a controller 110A, wherein the first transmitter 11A is configured to transmit a set of polarised optical signals S, including a first polarised optical signal S1 comprising first data D1 of set of data D. The network 1 comprises a set of receivers 12, including a first receiver 12A comprising a controller 120A, wherein the first receiver 12A is configured to receive the first polarised optical signal S1.

Abstract: An optical filter includes a first layer including a first notch filter arranged to attenuate electromagnetic radiation having a first wavelength ?1 incident normally thereupon. The optical filter includes a second layer including a second notch filter arranged to attenuate electromagnetic radiation having a second wavelength ?2 incident normally thereupon. The first wavelength ?1 and the second wavelength ?2 are different. The second layer is stacked upon the first layer. In use, the first notch filter attenuates the electromagnetic radiation having a predetermined wavelength ? incident thereupon at a first angle of incidence ?1 and the second notch filter attenuates the electromagnetic radiation having the predetermined wavelength ? incident thereupon at a second angle of incidence ?2, wherein the first angle of incidence ?1 and the second angle of incidence ?2 are different.

Abstract: A vehicle surface 30, preferably wherein the vehicle is an aircraft, is described. The vehicle surface 30 comprises thereon and/or therein a set of retroreflectors 300, including a first retroreflector 300A, configured to reflect, at least in part, incident hostile light towards a source thereof.

Abstract: Methods and apparatus for detecting a modulating element of an object are described in which signal values are obtained from one or more optical detectors. A determination is made if there is a time dependent variation in the obtained signal values at the one or more optical detector and a modulating element is detected based on the determination.

Abstract: Methods and apparatus for detecting a modulating element of an object in a scene are described in which an element in a scene is illuminated with a modulated light source. A signal is obtained from an optical detector based on light received from the illuminated element. An intermediate frequency signal is detected from the signal obtained from the optical detector, the intermediate frequency signal being related to a frequency of the modulated light source and a frequency of modulation of the element within the scene. The modulating element is detected based on the intermediate frequency signal.

Abstract: A coating material (10) for coating an article is described. The coating material (10) comprises a surface (100) having an optical interference coating (110) thereon. The coating material (10) improves protection of the article from incident electromagnetic radiation having a predetermined wavelength. The coating material (10) may retroreflect at least some of the incident electromagnetic radiation, for example towards a source (e.g. a laser) thereof. An article having a coating provided by such a coating material and methods of providing such coating materials are also described.

Abstract: An optical device 10 comprises an objective lens 11 defining a focal plane FP and an eyepiece 12 spaced apart therefrom, defining an optical axis OA therethrough. The optical device 10 comprises an optical member 13 having a first planar face 14, arranged on the optical axis OA proximal the focal plane FP, wherein the first planar face 14 is arranged to oppose the objective lens 11. The optical device 10 comprises a filter assembly 100 comprising a first notch filter 101 arranged to attenuate transmission of electromagnetic radiation having a first wavelength ?1, wherein the first notch filter 101 is arranged in front of the optical member 13. The first notch filter 101 is arranged at a first oblique angle ?1 to the optical axis OA whereby, in use, incident electromagnetic radiation having a predetermined wavelength ?i propagating along the optical axis is reflected by the first notch filter 101 away therefrom, wherein the first wavelength ?1 and the predetermined wavelength ?i are different.

Abstract: An optical filter 100 for a visor is described. The optical filter 100 comprises a first layer 101 comprising a first notch filter 102 arranged to attenuate electromagnetic radiation having a first wavelength ?1 incident normally thereupon. The optical filter 100 comprises a second layer 103 comprising a second notch filter 104 arranged to attenuate electromagnetic radiation having a second wavelength ?2 incident normally thereupon. The first wavelength ?1 and the second wavelength ?2 are different. The second layer 103 is stacked upon the first layer 101. In use, the first notch filter 102 attenuates the electromagnetic radiation having a predetermined wavelength ? incident thereupon at a first angle of incidence ?1 and the second notch filter attenuates the electromagnetic radiation having the predetermined wavelength ? incident thereupon at a second angle of incidence ?2, wherein the first angle of incidence ?1 and the second angle of incidence ?2 are different.

Abstract: A protective housing for a camera system mounted on a platform is described. The housing is formed in a domed shape and covers sensitive optical systems. The housing is mounted on or forms part of the external housing of the seeker system. The housing is optically transparent whilst also being conductive. In this way, the housing allows transmission of multiple wavelengths of radiation through the housing whilst also acting so as to reduce radar cross section of the platform and preventing transmission of electromagnetic rf pulse in to the sensitive optical systems of the seeker system.

Abstract: A target detection apparatus is described that is capable of improved detection of targets in urban environments or hidden in cluttered environments. The apparatus emits radiation in a modulated fashion, of a known wavelength, wavelengths or range of wavelengths and detects radiation returned by the targets in the environment.