Low Cost NIR Camera Technology
Spiricon’s 1550 series, phosphor coated CCD cameras, provide a new low cost alternative for measuring and viewing the output of NIR telecom devices and NIR lasers. The thin phosphor film coating is an anti-Stokes material that up-converts NIR radiation in the 1440nm to 1605nm range to visible light measurable by the CCD.
Phosphor Coating Technology
The up-conversion from NIR to visible light in the 1550 series cameras is nonlinear. The anti-Stokes phosphor coating produces visible photons at a rate roughly the square of the input signal. This is shown dramatically in Figure 1, where the camera total output increases dramatically faster than a linear output shown in the bottom line.
The anti-Stokes up-conversion efficiency is very wavelength dependent. Figure 3 shows the typical spectral response curve of a new, high response coating. As seen, we have calibrated the response from 1527nm to 1605nm. We have extrapolated the shorter wavelength region by comparing our measured response to data published over the entire range. Phosphor Coated NIR Cameras
|Application||NIR wavelengths, 1/2" format|
|Spectral Response||1440 - 1605nm|
|Maximum beam size||4.7mm x 5.4mm|
|Pixel spacing(1)||8.4µm x 9.8µm|
|Number of effective pixels||640 x 480 pixels|
|Minimum system dynamic range(2)||~ 30 dB|
|Linearity with Power||±5%|
|Accuracy of beam width||±5% for beams larger than 0.6 mm|
|Frame rates(3) In 12 bit mode||30 Hz|
|Shutter duration||1/60 to 1/100,000 sec, 9 steps|
|Gain control||Manual adjustment|
|Saturation intensity||7mW/cm2 at 1550 nm|
|Lowest measurable signal||~ 50µW/cm2|
|Damage threshold||70 mW/cm2 at 1550 nm|
|Dimensions and CCD recess||37mm x 34mm x 56mm CCD recess from surface 12.5mm, Adjustable|
|Operation mode||Interline Transfer interlaced CCD|
|Software supported||LBA-PC only (no longer available)|
|PC interface||RS-170 Framegrabber (no longer available, see USB version for PC control)
Despite the small pixel size, the spatial resolution will not exceed 50µm due to diffusion of the light by the phosphor coating.Signal to noise ratio is degraded due to the gamma of the phosphor's response. Averaging or summing of up to 256 frames improves dynamic range by up to 16x = +24dB. In normal (non-shuttered) camera operation, the frame rate is the fastest rate at which the laser may pulse and the camera can still separate one pulse from the next. With electronic shutter operation, higher rate laser pulses can be split out by matching the laser repetition to the shutter speed. This is the damage threshold of the filter glass of the filters. Assuming all filters mounted with ND1 (red housing) filter in the front. Distortion of the beam may occur with average power densities as low as 5W/cm2.