A.A. Jasim

Resonance condition of a microfiber knot resonator immersed in liquids

Effects of immersing a microfiber knot resonator (MKR) in liquid solutions that have refractive indices close to that of silica are experimentally demonstrated and theoretically analyzed. Significant improvement in resonance extinction ratio within 2 to 10 dB was observed. To achieve a better understanding, a qualitative analysis of the coupling ratio and round-trip attenuation of the MKR is performed by using a curve-fitting method. It was observed that the coupling coefficient at the knot region increased when immersed in liquids. However, depending on the initial state of the coupling and the quantity of the increment in the coupling coefficient when immersed in a liquid, it is possible that the MKR may experience a deficit in the coupling parameter due to the sinusoidal relationship with the coupling coefficient.

Dual wavelength erbium-doped fiber laser using a tapered fiber

A tapered fiber is fabricated by heating and stretching a piece of optical fiber after the polymer protective cladding has been removed. An equidistant comb-like transmission spectrum, with a spacing of 1.6 nm and an extinction ratio of more than 5 dB, was obtained by the tapered fiber due to the multibeam interferences of the cladding modes. The tapered fiber was applied in a ring erbium-doped fiber laser (EDFL) to generate dual-wavelength lasing oscillations. The EDFL operates at wavelengths of 1557.0 nm and 1558.6 nm with a stable peak power and a signal-to-noise ratio of more than 40 dB.

Inline Microfiber Mach–Zehnder Interferometer for High Temperature Sensing

A compact inline microfiber Mach-Zehnder interferometer (MMZI) is proposed for high temperature sensing. The MMZI is fabricated using a flame-brushing technique in which both transition parts of a microfiber are tapered to reduce the waist diameter and form an interference region. Since the refractive index of the fiber core exhibits a different temperature coefficient from that of air, the interferometer is sensitive to temperature variation. The temperature sensitivity of the device with a length of 40 mm was measured to be 13.4 pm/°C with an excellent linearity for temperature measurement up to 800°C.

Fabrication of tapered fiber based ring resonator

Tapered fiber based ring resonators are fabricated and its optical characteristic is investigated in detail. The ring resonator is fabricated by coiling the tapered fiber, which is firstly made by heating and stretching a piece of optical fiber, after the polymer protective cladding has been removed The comb filter with a constant free spectral range (FSR) and the maximum extinction ratio of 4.2 dB is achieved by a single-mode fiber based ring resonator. The FSR of ring resonator can be adjusted by controlling the diameter of the ring. The extinction ratio is improved in the polarization maintaining fiber based ring resonator where the maximum extinction ratio of 14 dB is achieved at 1531 nm region.

A Switchable Figure Eight Erbium-Doped Fiber Laser Based on Inter-Modal Beating By Means of Non-Adiabatic Microfiber

A switchable multiwavelength figure eight fiber laser effect of multimode interference is proposed and experimentally demonstrated. A narrow bandpass filter of multiple specific wavelengths was created by incorporating a tapered non-adiabatic microfiber of 70 mm length and 2 μm diameter in a Sagnac loop mirror. Spatial mode beating arose due to the modal interference in the non-adiabatic microfiber, and resulted in a comb filter able to suppress mode competition. The proposed laser generated single longitudinal modes having a 3-dB linewidth of less than 0.16 pm, which represents an upper limit measurement imposed by the restrictions of the optical analyzer resolution, and possessed an optical signal-to-noise ratio of 58 dB at 82 mW pumping power. Moreover, nonlinear polarization rotation and strain switching mechanisms are demonstrated for generating single, dual, and triple wavelength over more than 20 nm span. In addition, a description is provided on a new technique of packaging non-adiabatic microfiber that diminishes issues relating to degradation of the microfiber over time and external perturbation.

Micro-Ball Lensed Fiber-Based Glucose Sensor

The compact micro-ball lens structure fabricated at the cleaved tip of a microfiber coupler (MFC) is proposed and demonstrated for sensing various glucose concentrations in deionized water. The MFC was made by fusing and tapering two optical fibers using a flame brushing technique. It was then cleaved at the center of the minimum waist region to form a ball lens at the tip by an arcing technique using a fusion splicing machine. The proposed glucose sensor uses the micro-ball lensed fiber as a probe and a mirror as a target. The working mechanism of this device is based on the observed reduction in the peak power of the sensor wavelength spectrum as the concentration of glucose is increased. For a concentration change from 0 to 12 volume%, the ouput intensity of the sensor decreases linearly from -57.4 to -60.5 dBm with a sensitivity of 0.26 dB/% and a linearity of more than 99%.

Fabrication and Characterization of Microbent Inline Microfiber Interferometer for Compact Temperature and Current Sensing Applications

A new microbent in-line microfiber interferometer (MI–MI) is proposed and demonstrated as a compact temperature and current sensor. The MI–MI is capable of generating interference fringes with a high extinction ratio of about 12.0 dB and a free spectral range of 1.9 nm at a wavelength of 1545 nm. When employed as a temperature sensor, a copper wire carrying a direct current is placed against the MI–MI sensor, and the interference fringes of the MI–MI sensor shifts toward the longer wavelength as the heat generated by the copper wire increases. As the temperature increase corresponds linearly to the current, thus the measurement of the current can be extrapolated as well. The sensor has a temperature responsivity of 33.0 pm/°C with a linearity of more than 0.97 as well as a current responsitivity of 1.46 °C/A2, and has significant potential for application as a health and warning sensor for electricity generation and distribution grids.

Investigation of spontaneous Brillouin scattering generation based on non-adiabatic microfibres

Brillouin Stokes and anti-Stokes generation is successfully demonstrated in backward direction using a non-adiabatic microfibre as the gain medium. The Stokes light wavelength is up-shifted by 0.088 nm (10 GHz) from the BP wavelength as monitored by using an optical spectrum analyzer. The Brillouin scattering can also be enhanced by employing a microfibre based inline Mach–Zehnder interferometer (IMZI) as the gain medium due to its stronger multimode interference effect. It is shown that the microfibre geometry plays an important role in the spontaneous Brillouin scattering generation and gain bandwidth broadening due to its effect on irritation of the acoustic modes inside the microfibre.

Tapered plastic optical fiber coated with single wall carbon nanotubes polyethylene oxide composite for measurement of uric acid concentration

Purpose – A simple tapered plastic optical fiber (POF) sensor is proposed and demonstrated for measurement of uric acid concentrations in de-ionized water. The paper aims to discuss these issues. Design/methodology/approach – The sensor operates based on intensity modulation technique as the tapered POF probe which was coated by a single walled carbon nonotubes polyethylene oxide (SWCNT-PEO) composite is immersed into the uric acid solution. The probe was fabricated using an etching method and has a waist diameter of 0.46 mm and tapering length of 10 mm. Findings – As the concentration varies from 0 to 500 ppm, the output voltage of the sensor increases linearly from 6.13 to 7.35 mV with a sensitivity of 0.0023 mV/% and a linearity of more than 97.20 percent. The SWCNT-PEO composite coating increases the sensitivity of the proposed sensor due to the effective cladding refractive index, which increases with the coating and thus allows more light to be transmitted from the tapered fiber. Originality/value –...

Fabrication and Characterization of 2 × 2 Microfiber Coupler for Generating Two Output Stable Multiwavelength Fiber Lasers

A compact 2 × 2 microfiber coupler (MC) is proposed and experimentally demonstrated for the generation of stable multiwavelength fiber laser in the C-band region. The 2 × 2 MC is fabricated by twisting and fusing together two lateral dual single mode fibers using the flame-brushing technique. The 2 × 2 MC has a waist diameter of 8 μm with a coupling ratio of 38:62 and 45:55 at ports 1 and 2, respectively. The 2 × 2 MC exploits super mode coupling to produce spatial mode beating and suppress mode competition of the homogeneous gain medium in a fiber ring laser. The channel spacing of the output wavelengths is immune to changes in the external environment and can be extracted from the peaks of the 2 × 2 MCs periodic oscillation. The proposed laser is capable of generating stable single, dual, and triple lasing wavelengths from its two output ports over a range of more than 29 nm, which is further enhanced by the polarization rotation mechanism. The generating lasing wavelengths have a 3 dB line-width of less than ∼30 pm and peak-to-floor ration of about 58 dB at a pump power of 38 mW.