Optoelectronic Design of a Closed-Loop Depolarized IFOG with Sinusoidal Phase Modulation for Intermediate Grade Applications

Abstract

A depolarized fiber optic gyroscope (DFOG) prototype with closed-loop configuration, sinusoidal-bias, and serrodyne-feedback electrooptic phase modulations was designed. A complete optoelectronic design is realized by using computational simulation tools (optical subsystem: Synopsys ® -Optsim™ software and electronic subsystem: National Instruments ® -MultiSim™ software). The design presented here includes both optical and electronic circuits, being the main innovation, is the use of an analogical integrator provided with reset and placed in the feedback of the electrooptic phase-modulation chain that produces a serrodyne-shaped voltage ramp signal for obtaining the interferometric signal phase cancellation. The performance obtained for this model (threshold sensitivity ≤0.052 /h; dynamic range = AE 78.19 /s) does reach the IFOG intermediate grade (tactical and industrial applications) and does demonstrate the suitability and reliability of simulation-based software tools for this kind of optoelectronic design.

Optical Phase-Modulation Techniques

“…Figure 8 represents the block-diagram of a closed-loop IFOG configuration with sinusoidal BIAS and serrodyne FEED-BACK phase modulations, see Ref. [30]. The main novelty of this design is the structure of phase modulation feedback chain.…”

“…The corresponding voltage signal at its Closed-loop IFOG scheme with sinusoidal BIAS and serrodyne FEEDBACK phase modulations, see Ref. [30] (below, in the inset, the block-diagram definition). output (V S ) scales as sine-function of ϕ S .…”

“…[18,25,26]) or closed-loop (Refs. [27][28][29][30]) IFOG configurations. In both cases, the PSD block (phase-sensitive-demodulation) must contain two selectively adjusted filtering circuits.…”

“…Second one is a selective band-passfilter to filter the component of first harmonic of interference signal, see also Ref. [30].…”

“…This way, by adjusting appropriately the period T (or the frequency) of serrodyne-wave, the resulting value of phase-difference can be exactly matched with the ϕ S Sagnac phase shift to achieve the phase cancelation by means of a specific feed-back circuit located on the way of feed-back signal, see for example Refs. [30][31][32][33].…”