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Ultra-Low Noise Laser Chapter 3: Description
Rev B, October 23, 2020 Page 11
Figure 9
3.3. Frequency Noise Characteristics
The frequency noise spectral density of each ULN laser is measured before shipment. Typical performance is
shown in Figure 10. As shown in the figure, the noise changes with current within a single-frequency zone. The
frequency noise is always minimized at the high-current end of the zone; all lasers meet or exceed the specified
linewidth under these conditions when combined with proper control electronics and minimal optical feedback
(see Chapter 4).
Figure 10 Frequency noise of a ULN at various currents within a single mode region. The peak in
noise at 43 Hz is due to HVAC systems present in the testing facility.
The Lorentzian / instantaneous linewidth may be estimated from the high-frequency white noise level of the noise
plot, according to:
Lorentzian linewidth
= 𝜋 × (
white noise level)
2
,
where the white noise level is measured in hertz/sqrt(hertz). The linewidth at longer integration times may be
estimated using the method described in:
Gianni Di Domenico, Stéphane Schilt, and Pierre Thomann, “Simple approach to the relation between laser
frequency and laser line shape”,
Applied Optics , vol. 49, no. 25, pp. 4801 - 4807, 2010.
10
1
10
2
10
3
10
4
10
5
10
6
10
7
10
0
10
1
10
2
10
3
10
4
10
5
458 mA
496 mA
532 mA
Frequency Noise Spectral Density
Frequen
cy
Noise
Amp
litu
de
(Hz
/

Hz
)
Frequency (Hz)