Loop Mirror Interferometer Research Articles

Polarization Effect on Dual and Quad Output Fiber Laser Based on Sagnac Loop Mirror Interferometer

ABSTRACT This work investigates the performance of dual and quad laser wavelengths at simultaneous angle adjustment of polarization controller based on a Sagnac loop mirror interferometer. From our observation, 13 m polarization maintaining fibers of PMF length performed better in terms of lasing lines, peak power and extinction ratio of 4, −8 dBm and 38 dB, respectively. When the intensity increases, the flatness and number of channels are improved to prove that significant power setting for the best laser performance. The flatness and number of lasers are changed with the simultaneous adjustment of half-wave plate and quarter-wave plate angles. These dual and quad laser wavelengths have good power stability according to the low fluctuation below 2.25 dB of peak power difference on the laser peaks within 100 minutes.

Vernier Effect in a Compact Strain Sensor Based on Fiber Loop Mirrors Using a 3 × 3 Coupler

In this paper, a new configuration based on two fiber loop mirrors in series using a 3×3 coupler is demonstrated. This configuration is compact and can explore the Vernier effect. The results obtained were a sensitivity of 74.9±0.2 pm/με for the Vernier envelope and 6.41±0.01 pm/με for the Vernier carrier. These results were compared to the sensitivity of the setup using only one fiber loop mirror interferometer, obtaining 14.41±0.01 pm/με. This means a magnification factor of 5.2 for the Vernier envelope. Theoretical treatment of the system was carried out, using Jones matrix calculus, and the subsequent simulation results are also presented, having obtained good agreement with the experimental data.

Measurement of the birefringence variation induced by dihydrogen diffusion into a polarization-maintaining fiber.

We report continuous measurements of the transmission spectrum of a fiber loop mirror interferometer composed of a Panda-type polarization-maintaining (PM) optical fiber during the diffusion of dihydrogen (H2) gas into the fiber. Birefringence variation is measured through the wavelength shift of the interferometer spectrum when the PM fiber is inserted into a gas chamber with H2 concentration from 1.5 to 3.5 vol.% at 75 bar and 70°C. The measurements correlated with simulation results of H2 diffusion into the fiber lead to a birefringence variation of -4.25 × 10-8 per mol m-3 of H2 concentration in the fiber, with a birefringence variation as low as -9.9×10-8 induced by 0.031 μmol m-1 of H2 dissolved in the single-mode silica fiber (for 1.5 vol.%). These results highlight a modification of the strain distribution in the PM fiber, induced by H2 diffusion, leading to a variation of the birefringence that could deteriorate the performances of fiber devices or improve H2 gas sensors.

Nonlinearity Effect on Multiwavelength fiber laser based on Sagnac loop mirror interferometer

This paper demonstrates a multiwavelength fiber laser (MWFL) with erbiumdoped fiber amplifier (EDFA) as gain medium and Sagnac loop mirror interferometer as filter. Stable and flat lasing spectrum was achieved when highly nonlinear fiber (HNLF) was inserted into the laser cavity. The number of lasing lines and extinction ratio (ER) was directly influenced by EDFA gain where at maximum setting, 14 lasing lines with ER of 19 dB were generated. The stable and flat spectrum achieved spanned about 1.6 nm. This is due to the induced intensity dependent loss mechanism in the cavity by adjusting the half-wave plate of the polarization controller in combination with the HNLF. The MWFL output showed peak power variation of about 2.1 dB within 100 minutes of observation time.

Tunable multiwavelength fiber laser based on bidirectional SOA in conjunction with Sagnac loop mirror interferometer

A tunable multiwavelength fiber laser (MWFL) based on bidirectional semiconductor optical amplifier (SOA) in conjunction with a Sagnac loop mirror (SLM) interferometer is proposed. The best multiwavelength spectrum from this setup produces 164 lasing lines within 3 dB uniformity. The main study is to investigate the multiwavelength laser performance by varying the polarization state (PS) at two different locations of polarization controller (PC). Manipulation of a quarter-wave plate (QWP) of PC1 causes PS change before entering polarization-maintaining fiber (PMF) thus affecting the multiwavelength flatness and wavelength bandwidth. Meanwhile, manipulation of QWP of PC2 varied the output power of polarization beam splitter (PBS) and tuned the multiwavelength spectrum with almost similar performance. The multiwavelength tunability, extinction ratio (ER) difference and lasing lines difference is five nm, 2.4 dB and 48 when the QWP angle is adjusted from 0° until 70°, respectively. Lower SOA current reduced the multiwavelength flatness and number of lines. The laser output was found stable at a maximum of 0.31 dB power deviation during the 100 min of stability test.

Monitoring the Etching Process of Hi-Bi Fiber Through a Fiber Loop Mirror

A method for monitoring the etching process of Hi-Bi fiber is proposed and demonstrated. The birefringence of the etching fiber is accurately calculated by tracking the shift of the interference spectrum in a high-birefringence fiber loop mirror interferometer. Then, the degree of etching can be inferred by the relationship between the etching-fiber birefringence and the fiber structure. A section of PANDA fiber is used as an example to experimentally demonstrate the proposed method. The results show that the calculated birefringence is consistent with the theoretical simulation. Furthermore, four different structural states, which reflected in four different rate of change, are presented in the whole etching process of PANDA fiber. This method has the advantages of easy realization, high precision, and repeatability, and it can be used in the preparation of Hi-Bi microfiber photonic devices.

All-PM Fiber Loop Mirror Interferometer Analysis and Simultaneous Measurement of Temperature and Mechanical Vibration

In this work, a new all-polarization maintaining (PM) fiber loop mirror interferometer is proposed and validated as a temperature and mechanical vibration sensor. The scheme employs the arms of a PM coupler as communication fibers, fused with a relative angle of 45° to the sensing fiber. The length of the arms is equal, so their contribution in canceled, obtaining a total transfer function exclusively defined by the sensing fiber. The capabilities of the system as a sensor are tested, achieving mechanical vibration and temperature sensing without crosstalk between measurands. In this manner, vibration frequencies up to 1.5 kHz have been monitored using a commercial interrogator with a scan rate of 1 Hz and a technique based on the fast Fourier transform. Additionally, the immunity of the setup to external perturbations in the communication fibers is studied and compared to the conventional approach.

Monitoring Multiple Hi-Bi Sensing Fibers in a Single Fiber Loop Mirror

In this paper, multiple high-birefringence (Hi-Bi) sensing fibers have been multiplexed and validated as strain and temperature sensors in a single fiber loop mirror interferometer. The strain and temperature applied to each fiber section have been measured in the spatial frequency domain without crosstalk by means of the fast Fourier transform. The Hi-Bi sensing fibers are fused together with a rotation angle given by the theoretical analysis of the structure, reducing the number of polarization controllers needed in the system and greatly simplifying the operation of the system. Additionally, full-polarization maintaining version of the setup, which does not need any polarization controller, is also presented and validated both theoretically and experimentally.

Add-Drop Filter Based on Microfiber Mach–Zehnder/Sagnac Interferometer

In this paper, we investigate and experimentally demonstrate a Mach-Zehnder/Sagnac loop mirror interferometer (MZ-SI) fabricated from microfiber. We introduce a simple fabrication technique to assemble a miniatured MZ-SI from a single microfiber which can be used as an add-drop filter. The through and drop port transmission spectra of this microfiber structure are analyzed and they are in agreement with the theoretical model. The pattern of interference in the transmission spectra can be controlled by manipulating the parameters of this microfiber structure.

Nonlinear Optical Properties in GaInAsP/InP Waveguides below the Band-gap Wavelength

From picosecond pump-probe and interferometric experiments, we measured the intensity-dependent absorption and refractive index changes of GaInAsP/InP waveguides whose band-gap wavelengths ranged from 1.2 to 1.41 µm. An optical loop mirror interferometer was employed to measure the refractive index change in a time domain. The temporal response of the probe in GaInAsP waveguides was shown to be instantaneous following 4 ps pump pulses. The intensity-dependent refractive index coefficient was measured to be from -0.55 ×10-12 to -3.37 ×10-12 cm2/W. Also, intensity-dependent absorption changes were compared for three types of waveguide.

Measurement of Pump-Induced Absorption and Refractive Index Changes in GaInAsP/InP Waveguides Using an Optical Loop Mirror Interferometer

We investigated the direct measurement of intensity-dependent refractive index changes in GaInAsP/InP ridge waveguides with ps-order pump pulses below the band gap using an optical loop mirror interferometer. The temporal response of the probe in GaInAsP (λg=1410 nm) waveguides was shown to be instantaneous with respect to 4 ps pump pulses. The intensity-dependent refractive index coefficient was measured to be -2.0±0.6×10-12 cm2/W. In addition, pump-induced absorption changes were studied.