Santec TSL-210 - 8. Functions of This Unit; 8-1. Wide-band Wavelength Tuning TSL-210; 8-2. Coherence Control

TUNABLE LD LIGHT SOURCE TSL-210
8-1
8-1. Wide-band Wavelength Tuning TSL-210
The use of a diffraction grating as external mirror in the design controls the loss to wavelength
within the external cavity by controlling the angle of diffraction grating in a high-precision
manner, and also allows for the tuning of an oscillated wavelength over a wide range. TSL-210
wavelength setting is not only accomplished by diffraction grating, but also by changing the
length of the cavity. The combined manipulation of external cavity length and diffraction grating
angle realizes high-precision wavelength tuning. The operating table allows for the diffraction
grating to be adjusted for cavity length and for grating angle via microcomputer control.
8-2. Coherence Control
The oscillated spectrum linewidth of the TSL-210 is fairly narrow in comparison with normal
semiconductor lasers. Spectrum linewidth is one of the factors that determines light coherence,
and the narrower the spectrum linewidth, the more improved the coherence. Considering the
length of fiber used or the complexity of some test set-ups, there is the possibility that within the
length of fiber in the test set-up there is a reflection point in the optical fiber transmission system,
optical output power changes within the fiber due to interference. To combat this, the TSL-210 is
equipped with a Coherence Control.
The measurement example of optical output power stability and spectrum linewidth in the case
where optical fiber type coupler is connected at the output end of the TSL-210 is shown below:
TSL-210 has the spectrum linewidth 2-step control so as to configure a stable measurement
system even in such a case.
The optical output power stability at control and the measurement example of spectrum line-
width are shown below :
8
Functions of This Unit
0.3dB (p-p)
326.0
306.0
286.0
326.0
306.0
286.0
100sec.
600sec.
without
Coherence
Control
85kHz
FREQUENCY [Hz]
When optical fiber type coupler is connected
with
Coherence
Control
46.5MHz
FREQUENCY [Hz]
0.03dB (p-p)
326.0
306.0
286.0
326.0
306.0
286.0
100sec.
600sec.
When optical fiber type coupler is connected
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