Fig. 1. Parallel modal interferometer. (a) Schematic representation of the parallel combined modal interferometer system with sensing arm (SA) and reference arm (RA). (b) FEM analysis (using COMSOL Multiphysics) of light beam propagation through each modal interferometer with single-mode fiber (SMF) and solid core photonic crystal fiber (SCPCF). (c) Transmission spectra of the identical interferometers (SA/RA) and their resultant transmission spectrum when combined parallel (Comb). (Inset) FFT of the transmission spectra of SA, RA, and their combination has 0.03  nm−1 as the prominent spatial frequency.

Fig. 2. Optical signal modulation. (a) Signal amplification: characteristic plot for amplification of the resultant signal with change in field amplitude about RA at three different frequencies. (Inset) Real-time resultant transmission signal of the parallel interferometers at 100 Hz for operating only SA and subsequently both SA & RA at 7 V. (b) Signal attenuation: characteristic plot for attenuation of the resultant signal with change in the initial phase of the field about RA at three different frequencies. (Inset) Real-time resultant transmission signal of the parallel interferometers at 100 Hz and constant amplitudes, for operating only SA and subsequently both SA & RA with an initial phase of field about RA as 180°. (c) Signal filtering: computed SNR values for the resultant signals obtained by varying the amplitude of the dynamic field about RA at 100 Hz. (Inset) Corresponding real-time signals of SA (fixed amplitude 7 V) and combined signal of SA & RA, with field amplitude about RA at 1 V. (d) Variation of only SA signal SNR (green triangles) with frequency and variation of filtered signal SNR (blue circles) with frequency when RA is active keeping at field amplitude of 0.5 V.

Fig. 3. Signal modulation of optical flowmeter. (a) Schematic diagram of in-house optical flowmeter (SA) integrated with reference interferometer (RA) for modulating the former’s optical signal. SLED, superluminescent light emitting diode; AFG, arbitrary function generator; PZC, piezo controller; PZT, piezo transducer; 1×2 and 2×1, 3 dB fiber couplers; BB, bluff body; and WI, wavelength interrogator. (b) Real-time signal of SA before and after being modulated by RA signal. The signal amplitude increases as the RA is operated, and is designated with mode wavelength shifts marked in the plots. (c) Characteristic plot for amplification of the resultant signal with change in field amplitude about RA at definite fluid velocity and vortex frequency. (Top inset) Real time signal before (green) and after (red) operating the RA at definite frequency and amplitude. (Bottom inset) Variation in resultant signal SNR with RA field amplitude. (d) FFT of the SA response with noise field (green curve) and resultant signal of SA and RA (red curve) without the noise signal is shown for fixed fluid velocity. (Inset) Real-time signal before (green) and after (red) operating RA depicting suppression of noise frequency.

Fig. 4. (a) Schematic representation of the modal interferometer (MI). SMF, single-mode fiber; CR, collapse region; SCPCF, solid core photonic crystal fiber; I/P, input; and O/P, output. (b) and (c) Transmission spectra and corresponding FFT of the spectra for interferometers of varied SCPCF lengths.

Fig. 5. Schematic representation of the experimental setup used for system characterization. PZT, piezo transducer; SLED, superluminescent light-emitting diode; SMF, single-mode fiber; PCF, photonic crystal fiber; SA, sensing arm; and RA, reference arm.

Fig. 6. Schematic diagram of experimental setup for signal modulation of optical flowmeter response.