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7 / 192018-08-16 | Document No.: AN097
temperature dependent wavelength drift (typ. 0.25 nm/K). Figure 5 and 6 present
the typical wavelength behavior (λ
centroid
and FWHM) vs. ambient temperature
and drive current.
Using short pulses minimizes temperature dependent wavelength shift as well as
spectral broadening due to internal heating of the LED (e.g. pulse width < 300 μs
and repetition rate > 2 ms).
Figure 5: Dependence of the centroid wavelength on ambient temperature and drive
current. Operating condition is a single 1 μs pulse
Figure 6: Dependence of the FWHM on ambient temperature and drive current.
Operating condition is a single 1 μs pulse. The “harder” the IR-LED is driven the
broader the spectrum becomes
Although technically no longer state-of-the-art, some iris-recognition
requirements have interest in the percentage of total optical power within any
given 100 nm bandwidth (e.g. NIST mobileID “best practices report” (SP 500-
280)). Figure 7 illustrates this data for a centroid wavelength of 810 nm. At least
35 % of the total power per 100 nm wide subband are within 707 nm / 807 nm
up to 820 nm / 920 nm range.
1
Ambient temperature [°C]
Centroid wavelengtgh [nm]
840
830
820
810
800
790
-40 -20 0 20 40 60 80 100 120
Ambient temperature [°C]
FWHM [nm]
42
36
30
24
21
15
-40 -20 0 20 40 60 80 100 120
39
33
27
18