Dual-control technique for temperature stabilization and tunability of narrowband fiber Bragg gratings

Abstract

We present a dual-heater control approach for narrowband, fiber Bragg gratings (FBGs) that allows both dynamic wavelength stabilization of the devices over a wide temperature range and flexible tunability of the setpoint. The control technique is applied to athermally-packaged FBGs operating in the 1.55-µm band with 3-dB bandwidths of approximately 5 GHz. The devices are actively stabilized within approximately ±7 pm (±0.9 GHz) of wavelength accuracy over a wide temperature range of 0 • C to +50 • C, and the setpoint is tunable over approximately 280 pm (35 GHz).A custom-designed, pulse-width modulation (PWM) heater controller is applied in two locations to the FBGs to compensate and reduce the native temperature dependence of the athermal FBG package, as well as to provide tunability of the setpoint. A temperature sensor bonded to each FBG measures the local temperature, and a feed-forward control loop adjusts the PWM signal based on the ambient case temperature, to hold the wavelength at the desired setpoint.Two different resistive heaters are bonded to opposite ends of the FBG devices, to evaluate different stabilization and tuning responses. One heater approach provides expanded thermal tunability, while the other provides improved temperature stability. An embedded processor is used to generate two different PWM, heater-control signals, which are applied to the different resistive heaters to achieve this dual-control technique. Calibration polynomials for the temperature stabilization are derived for different tuning setpoint offsets and verified with testing.