We report on a 1550-nm matched filter based on a pair of fiber Bragg gratings (FBGs) that is actively stabilized
over temperature. The filter is constructed of a cascaded pair of athermally-packaged FBGs. The tandem FBG
pair produces an aggregate 3-dB bandwidth of 3.9-GHz that is closely matched to a return-to-zero, 2.880-GHz
differential-phase-shift-keyed optical waveform.
The FBGs comprising the filter are controlled in wavelength using a custom-designed, pulse-width modulation
(PWM) heater controller. The controllers allow tuning of the FBGs over temperature to compensate and cancel
out native temperature dependence of the athermal FBG (AFBG) package. Two heaters are bonded to each
FBG device, one on each end. One heater is a static offset that biases the FBG wavelength positively. The second
heater is a PWM controller that actively moves the FBG wavelength negatively. A temperature sensor measures
the FBGs' temperature, and a feed-forward control loop adjusts the PWM signal to hold the wavelength within
a desired range.
This stabilization technique reduces the device's native temperature dependence from approximately 0.65
pm/°C to 0.06 pm/°C, improving the temperature stability by tenfold, while retaining some control for poten-
tial long-term drifts. The technique demonstrates that the FBGs can be held to ±1.5 pm (±188 MHz) of the
target wavelength over a 0 to +50°C temperature range. The temperature-stabilized FBGs are integrated into
a low-noise, optical pre-amplifier that operates over a wide temperature range for a laser communication system.
Jeffrey M. Roth, Joseph W. Kummer, Jeffrey R. Minch, Bryan G. Malinsky, Vincent Scalesse, and Frederick G. Walther, "Temperature-stabilized, narrowband tunable fiber-Bragg gratings for matched-filter receiver," Proc. SPIE 10096, Free-Space Laser Communication and Atmospheric Propagation XXIX, 100960D (Presented at SPIE LASE: January 30, 2017; Published: 2 March 2017); https://doi.org/10.1117/12.2260667.
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