Fiber Fabry-Perot Tunable Filter |
FFP-TF2
C o p y r i g h t
©
2 0 0 9 M i c r o n O p t i c s , I n c .
F i r s t T i m e U s e r M a n u a l
8
Modes of Operation: Manual vs. Scan vs. Dither
The tunable filter and controller can operate in one of three modes: (1) Manual, (2)
Scan, and (3) Dither (or locked). In
Manual mode
, the amplitude and frequency
knobs are turned completely counter-clockwise. The offset knob adjusts the DC
voltage applied to the filter PZT actuator, thereby adjusting the resonance
wavelength in the Fabry-Perot cavity.
In
Scan mode
, the FFP-C supplies a simple triangular voltage waveform output to
the FFP connection. The triangular wave amplitude can be adjusted from zero to
>50 volts peak to peak. The frequency of the triangular wave can be adjusted from
20 to 100 Hz. The DC offset can be adjusted from less than 5 volts, to over 50
volts. We recommend setting the Offset to 30 volts (the center of the controller
supply voltage range).
Scan mode
is used primarily for sweeping the filter through a
range of wavelengths for applications such as (un-calibrated) optical spectrum
analysis and WDM channel equalization monitoring. Either the internal photo-
detector or an external photo-detector can be used to monitor the filtered optical
signal in Scan mode.
Dither (locked) mode
, on the other hand, requires using the internal FFP-C photo-
detector input for closed loop operation.
Dither mode
is utilized for locking the FFP-
TF or the FFP-SI to a particular narrow line source, and is required to achieve
optimum tuning stability and to compensate for electrical, thermal, and mechanical
variations in the FFP-TF and the input light source. In
Dither mode
, the controller
supplies a low-voltage 2 KHz dither frequency to the FFP device for optimum error
correction within the feedback loop. Note that the feedback circuit was designed
for slowly varying wavelength shifts due to thermal drift in both the source and the
filter.
Note: The controller is not designed to operate in the dither (locked) mode with
high Finesse (> 750) filters.
