Night Vision Devices (NVDs) work by collecting tiny amounts of light, imperceptible to the human eye, and amplifying it to a point we can easily see an image. NVDs gather ambient reflected light which emanates when starlight or moonlight falls on to an object. The front lens receives the reflected light made up of photons and sends it into an Image Intensifier Tube (II Tube). The light first falls on the Photocathode tube that changes the photons into electrons. The electrons are then passed on through a Micro Channel Plate (MCP), wherein their numbers are amplified through an electrical and chemical process. The electrons are then impinged against a phosphorus screen that changes the amplified electrons back into visible light (image), which is seen through the eyepiece. The image will be seen as a clear, green-hued, amplified, recreation of the scene being observed.
II Tube Generations
Night VisionandElectronicSensors Directorate of the US Army has classified image intensifiers as Gen I, Gen II, Gen III, etc, based on the changes happening in manufacturing technologies. Generation I had a low gain and no MCP. Image intensifiers with MCP were subsequently developed and called Generation II. Both these had the Photo Cathode made of multi alkali material. Next came the image intensifiers which used GaAs as cathode material and a filmy layer coating on MCP, termed as Generation III. The definition of Generation IV would be an unfilmed MCP in the image intensifier. These are all technical issues, they tell how image intensifiers are produced, but not how they perform.
Innovations in photocathode technology significantly reduced the tube’s noise and increased the signal to noise ratio which is the undisputed characteristic to describe the low light level performance of an Image Intensifier Tube. The US government has recognised the fact that technology employed by different manufacturers varies, and itself makes little difference as long as an operator can see clearly at night.
Performance criterion of II Tubes
The generation number tells only how an image intensifier is manufactured. It does not tell anything about the performance of a tube. By 2001, the United States federal government concluded that a tube’s ‘generation’ was not a determining factor of a tube’s global performance, and therefore the term was eliminated as a basis of export regulations. Consequently, the United States has based its export regulations not on the generation, but on a calculated factor calledfigure of merit(FOM). FOM is an abstract measure of image intensifier performance, derived from the number of line pairs per millimetre (resolution) multiplied by the tube’s signal-to-noise ratio.
In India, there is still fascination about the generation of an Image Intensifier Tube. But one should realise that a reference to generation is nothing more than a marketing tool. Generation is not an assurance of performance or quality, says Mr M V Raja Sekhar, CTO (Electro Optics & Lasers), BEL.
Photonis, a world leader in night vision technologies, classifies its image intensifiers as Super Gen, Hyper Gen, XD-4, XR-5, etc, based on FOM. Night vision products of Photonis are in use at various NATO affiliates and are largely deployed worldwide.
The Indian Army has understood the importance of FOM and all its recently released Request for Information (RFI)/Request for Proposals (RFP) for Night Vision Devices specifically mention the required FOM.
BEL Optronic Devices Ltd (BELOP)
II Tube manufacturing facility BEL Optronic Devices Ltd (BELOP)— formerly BEL DELFT—a fully owned subsidiary of BEL started manufacturing of 2nd Generation Image Intensifiers in collaboration with and as a Joint Venture with BV DELFT Netherlands in the year 1994, as directed by the Ministry of Defence. This was aimed at having indigenous capability in India for such critical technologies. Subsequently, the technology was upgraded to Super Generation and Hyper Generation grade with in-house developments.
In 2012, the plant was upgraded to produce XD-4 II Tubes with technical know-how from Photonis, France, and about 40,000 tubes were supplied. The plant is presently being upgraded to XR- 5 grade with a capacity to produce more than 30,000 Image Intensifier Tubes per year. BEL also has plans to produce MCP indigenously with ToT from Photonis once the XR-5 is fully established.
The typical values of FOM for various grades of image intensifiers that are produced at BELOP are given below:-
The plant set up by BELOP is a stateof- the-art facility with a huge investment exceeding Rs 500 crores built on a total area of 13,608 sq mt and the built-up area of 8,650 sq mt. It has a workforce of about 130 permanent employees besides contract staff. There are more than 200 processes involved in the manufacture of XR-5 Image Intensifier Tubes and are controlled and monitored by highly qualified and competent engineers. BELOP has also established advanced test facilities to ensure quality and reliability of the II Tubes. BELOP is ISO 9001:2008 certified. India is today one of the few countries in the world possessing this highly guarded technology.
This facility is an asset worth mentioning among the top OEMs of II Tubes in the world and thus, provides the following strategic advantages to India:
• National asset for indigenous manufacture of II Tube
• Prompt and quick supplies
• Effective product support of Passive Night Vision Devices with indigenous supplier of spares for II Tubes
• No necessity of End User Import and Monitoring License for II Tubes procurement by OEMs of PNVDs.
|Type of Image Typical FOM||Intensifier|
|XR-5||1600 to 2100|