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2-23
Using the Multi-Wavelength Meter
Measuring Modulated Lasers
Measuring Modulated Lasers
Lasers modulated
at low frequencies
A laser that is amplitude modulated at low frequencies (for example, modu-
lated in the audio frequency range) can cause spurious wavelengths to be dis-
played below and above the correct wavelength. The power of these spurious
wavelengths is below that of the correct wavelength. These spurious signals
can be eliminated by decreasing the peak threshold. Refer to “Defining Laser-
Line Peaks” on page 2-16. Even when the laser is amplitude modulated, the
correct wavelength and power is displayed.
The spurious wavelengths caused by low frequency amplitude modulation will
be located above and below the correct wavelength by the following wave-
length spacing:
where F is the modulation frequency in Hz, and
λ
is the correct wavelength
in nm. For example, an amplitude modulation of 10 kHz on a 1550 nm laser
will produce spurious wavelengths spaced by 15 nm from the correct wave-
length, and the spurious wavelengths will be at 1535 and 1565 nm.
Low frequency (10 kHz) AM modulation graph showing rounded sideband spurs.
spacing
6
10
–
×
10
F
λ
2
=