Showing papers by "Harith Ahmad published in 2012"

A Q-Switched Erbium-Doped Fiber Laser with a Carbon Nanotube Based Saturable Absorber

Abstract: We demonstrate a simple, compact and low cost Q-switched erbium-doped fiber laser (EDFL) using single-wall carbon nanotubes (CNTs) as a saturable absorber for possible applications in metrology, sensing, and medical diagnostics. The EDFL operates at around 1560 nm with repetition rates of 16.1 kHz and 6.4 kHz with saturable absorbers SA1 and SA2 at a pump power of 120 mW. The absorbers are constructed by optically driven deposition and normal deposition techniques. It is observed that the optical deposition method produces a Q-switched EDFL with a lower threshold of 70 mW and better Q-switching performance compared to that of the normal deposition method. The EDFL also has pulse energy of 90.3 nJ and pulse width of 11.6 μs at 120 mW pump power.

Integrated Microfibre Device for Refractive Index and Temperature Sensing

Abstract: A microfibre device integrating a microfibre knot resonator in a Sagnac loop reflector is proposed for refractive index and temperature sensing. The reflective configuration of this optical structure offers the advantages of simple fabrication and ease of sensing. To achieve a balance between responsiveness and robustness, the entire microfibre structure is embedded in low index Teflon, except for the 0.5–2 mm diameter microfibre knot resonator sensing region. The proposed sensor has exhibited a linear spectral response with temperature and refractive index. A small change in free spectral range is observed when the microfibre device experiences a large refractive index change in the surrounding medium. The change is found to be in agreement with calculated results based on dispersion relationships.

Nanosecond soliton pulse generation by mode-locked erbium-doped fiber laser using single-walled carbon-nanotube-based saturable absorber

Abstract: We demonstrate a simple and low cost mode-locked erbium-doped fiber laser (EDFL) operating in the nanosecond region using a single-walled carbon nanotube (SWCNT)-based saturable absorber (SA). A droplet of SWCNT solution is applied on the end of a fiber ferrule, which is then mated to another clean connector ferrule to construct an SA. Then the SA is integrated into a ring EDFL cavity for nanosecond pulse generation. The EDFL operates at around 1570.4 nm, with a soliton-like spectrum with small Kelly sidebands, which confirms the attainment of the anomalous dispersion. It produces a soliton pulse train with a 332 ns width, repetition rate of 909.1 kHz, an average output power of 0.31 mW, and energy of 0.34 nJ at the maximum pump power of 130.8 mW.

Fiber-Optic Salinity Sensor Using Fiber-Optic Displacement Measurement With Flat and Concave Mirror

Abstract: A simple intensity modulated displacement sensor is proposed for sensing salinity based on different concentration of sodium chloride (NaCl) in deionized water. The proposed sensor uses a 594-nm He-Ne laser as light source due to the high absorbance of NaCl within that wavelength. The peak voltage and its position of the displacement from both flat and concave mirror are studied. For a concentration change from 0% to 12%, the peak voltage decreases linearly from 2.46 to 1.48 mV, while its corresponding position from the flat mirror increases linearly from 1.00 to 1.35 mm with a linearity of more than 96% and 99%, respectively. Similarly, the peak voltage corresponding to the displacement with concave mirror decreases linearly from 3.67 to 3.57 mV, while its position increases linearly from 1.20 to 1.45 mm with a linearity of more than 98% and 95%, respectively. From the experimental results, it is concluded that as the concentration or density of NaCl increases, the peak voltage decreases proportionately. The stability, high sensitivity, simplicity of design, and low fabrication cost make this sensor suitable for chemical, pharmaceutical, biomedical, and process-control application.

Fiber Optic Displacement Sensor for Temperature Measurement

Abstract: A simple design of a temperature sensor is proposed and demonstrated using a fiber optic displacement sensor based on an intensity modulation technique. The proposed sensor uses a plastic optical fiber (POF)-based coupler as a probe in conjunction with a flat surface aluminum rod as a target. The aluminum rod is placed within the linear range of the sensor's displacement curve, which is from 0 to 1400 μm. The sensor is capable of measuring the temperature of an aluminum rod ranging from 42°C to 90°C with a measured sensitivity of 0.0044 mV/°C, with a linearity of more than 98% and a resolution of 2.4°C. The proposed sensor also shows a high degree of stability and good repeatability. The simplicity of design, accuracy, flexible dynamic range, and the low cost of fabrication are favorable attributes of the sensor and beneficial for real-field applications.

Graphene-based Q-switched pulsed fiber laser in a linear configuration

Abstract: A pulsed laser system is realized with graphene employed as a Q-switch. The graphene is exfoliated from its solution using an optical deposition and the optical tweezer effect. A fiber ferrule that already has the graphene deposited on it is inserted into an erbium-ytterbium laser (EYL) system with linear cavity configuration. We successfully demonstrate a pulsed EYL with a pulse duration of approximately 5.9 \mu s and a repetition rate of 20.0 kHz.

Graphene-Based Saturable Absorber for Single-Longitudinal-Mode Operation of Highly Doped Erbium-Doped Fiber Laser

Abstract: In this paper, a conventional wavelength band (C-band) fiber laser with a tunable single-longitudinal-mode (SLM) output using multilayer graphene as a saturable absorber is demonstrated. The proposed fiber laser uses a short length of highly doped erbium-doped fiber (EDF) as the gain medium and a fiber ferrule with graphene flakes adhered to it by index matching gel (IMG) that acts as the saturable absorber. The fiber laser is able to generate an adjustable wavelength output between 1547.88 and 1559.88 nm with an average peak power of -6.48 dBm with a measured signal-to-noise ratio between 66.0 and 68.3 dB. The SLM output is verified by the absence of frequency beating in the radio frequency (RF) spectrum output and by a measured linewidth of 206.25 kHz using the self-heterodyne technique. The deposition of graphene flakes on the fiber ferrule using the IMG is a new and effective technique to generate SLM operation in the fiber laser.

S-band multiwavelength ring Brillouin/Raman fiber laser with 20 GHz channel spacing.

Abstract: We propose and demonstrate a tunable S-band multiwavelength Brillouin/Raman fiber laser (MBRFL) with a tuning range of between 1490 to 1530 nm. The proposed MBRFL is designed around a 7.7 km long dispersion compensating fiber in a simple ring configuration, acting as a nonlinear medium for the generation of multiple wavelengths from stimulated Brillouin scattering (SBS) and also as a nonlinear gain medium for stimulated Raman scattering (SRS) amplification. A laser source with a maximum power of 12 dBm acts as the Brillouin pump (BP), while two 1420 nm laser diodes with a total power of 26 dBm act as the Raman pumps (RPs). The MBRFL can generate a multiwavelength comb consisting of even and odd Stokes at an average power of -12 dBm and -14 dBm respectively, and by separating the even and odd Stokes outputs, a 20 GHz channel spacing is obtained between two consecutive wavelengths. Due to the four-wave mixing (FWM) effect, anti-Stokes lines are also observed. The multiwavelength comb generated is not dependent on the BP, thus providing high stability and repeatability and making it a highly potential source for many real-world applications. This is the first time, to the knowledge of the authors, that a tunable MBRFL has been developed using SRS to obtain gain in the S-band region.

Graphene-Oxide-Based Saturable Absorber for All-Fiber Q-Switching With a Simple Optical Deposition Technique

Abstract: A Q-switched erbium-doped fiber laser (EDFL) incorporating a graphene-oxide-based saturable absorber (SA) is proposed and demonstrated. The SA is fabricated by first dissolving graphene oxide nanopowder in water and subsequently using the thermophoresis effect to deposit it onto the fiber ferrule. The SA is integrated into a ring cavity EDFL, which uses a 3-m-long MetroGain Type-12 erbium-doped fiber (EDF) as the gain medium. The EDFL has a continuous-wave (CW) lasing threshold at a pump power of ~9 mW, with Q-switching behavior observed at pump powers ~18 mW and above. At the maximum pump power of ~100 mW, the Q-switched pulses generated by the EDFL have a repetition rate and pulsewidth of 61 kHz and 6.6 μs, respectively, along with an average output power of about 3.7 mW. Additionally, at the maximum power, the energy per pulse and peak power of the generated pulses are 61.3 nJ and 9.3 mW, respectively.

Spacing-Switchable Multiwavelength Fiber Laser Based on Nonlinear Polarization Rotation and Brillouin Scattering in Photonic Crystal Fiber

Abstract: A new spacing-switchable multiwavelength erbium-doped fiber laser (EDFL) is demonstrated using switchable nonlinear polarization rotation (NPR) and stimulated Brillouin scattering (SBS) effects. The laser employs a 100-m-long photonic crystal fiber in conjunction with a four-port circulator in a figure-of-eight arrangement to provide the intensity-dependent transmission effect, as well as to discriminate the even-order and odd-order Brillouin Stokes to have a double-frequency Brillouin Stokes output. Without the Brillouin pump (BP), the laser operates in an NPR mode to produce at least 22 lasing wavelengths with a side mode suppression ratio of more than 10 dB and a wavelength spacing of 0.27 nm. In the Brillouin erbium fiber laser mode, at least 30 Brillouin lines with a spacing of 0.16 nm are obtained at BP power of 3 dBm and 980-nm pump power of 120 mW.

Electrically Tunable Microfiber Knot Resonator Based Erbium-Doped Fiber Laser

Abstract: A compact and tunable fiber laser is demonstrated using a microfiber knot resonator structure made by a highly doped Erbium fiber. A stable laser output is achieved at the 1533-nm region with a signal to noise ratio of 15 dB using a 63-mW 980-nm pump power. With the assistance of a copper wire touching the circumference of the ring, operating wavelength of the proposed laser can be tuned by injecting electric current into the copper wire. The peak wavelength of the laser can be tuned from 1533.3 to 1533.9 nm as the loading current is increased from 0 to 1.0 A. This is due to the thermally induced optical phase shift attributable to the heat produced by the flow of the current. It is also shown experimentally that the wavelength shift is linearly proportional to the square of the amount of current with a tuning slope of 700 pm/A2.

Performance Comparison of Mode-Locked Erbium-Doped Fiber Laser with Nonlinear Polarization Rotation and Saturable Absorber Approaches

Abstract: A mode-locked erbium-doped fiber laser (EDFL) is demonstrated using a highly concentrated erbium-doped fiber (EDF) as the gain medium in a ring configuration with and without a saturable absorber (SA) Without the SA, the proposed laser generates soliton pulses with a repetition rate of 12 MHz, pulse width of 111 ps and energy pulse of 16 pJ By incorporating SA in the ring cavity, the optical output of the laser changes from soliton to stretched pulses due to the slight change in the group velocity dispersion With the SA, a cleaner pulse is obtained with a repetition rate of 113 MHz, a pulse width of 058 ps and a pulse energy of 23 pJ

Temperature Sensing Using Frequency Beating Technique From Single-Longitudinal Mode Fiber Laser

Abstract: In this paper, a high-resolution fiber temperature sensor is proposed and demonstrated using the frequency beating technique. The sensor uses a constant wavelength (CW) at 1539.96 nm as the reference signal for the frequency beating technique. The sensor signal is provided by a fiber Bragg grating (FBG) tuned single-longitudinal mode (SLM) fiber laser, which consists of a 0.5-m long highly doped Zirconium-Erbium doped with an erbium concentration of 3000 ppm as the gain medium. The signal of the SLM, which is generated by the FBG in response to external temperature changes, is mixed with the CW signal using a 3-dB fused coupler into a 6-GHz photodetector to generate frequency beating. The typical response of the system is about 1.3 GHz/°C, with nominal temperature measurement resolutions of 0.0023°C being achieved, taking into account the resolution bandwidth of 3 MHz of the radio frequency spectrum analyzer.

Fabrication and Applications of Microfiber

Abstract: Microfibers have attracted growing interest recently especially in their fabrication methods and applications. This is due to a number of interesting optical properties of these devices, which can be used to develop low-cost, miniaturized and all-fiber based optical devices for various applications (Bilodeau et al., 1988; Birks and Li, 1992 ). For instance, many research efforts have focused on the development of microfiber based optical resonators that can serve as optical filters, which have many potential applications in optical communication and sensors. Of late, many microfiber structures have been reported such as microfiber loop resonator (MLR), microfiber coil resonator (MCR), microfiber knot resonator (MKR), reef knot microfiber resonator as an add/drop filter and etc. These devices are very sensitive to a change in the surrounding refractive index due to the large evanescent field that propagates outside the microfiber and thus they can find many applications in various optical sensors. The nonlinear properties of the micro/nanostructure inside the fiber can also be applied in fiber laser applications. This chapter thoroughly describes on the fabrication of microfibers and its structures such as MLR, MCR and MKR. A variety of applications of these structures will also be presented in this chapter.

Wideband Spectrum-Sliced ASE Source Operating at 1900-nm Region Based on a Double-Clad Ytterbium-Sensitized Thulium-Doped Fiber

Abstract: A wideband spectrum-sliced amplified spontaneous emission (ASE) source operating in 1900-nm region is demonstrated using a newly developed double-clad ytterbium-sensitized thulium-doped fiber (YTF) and a Sagnac loop mirror. The YTF used was drawn from a D-shape preform, which was fabricated using the modified chemical vapor deposition (MCVD) and solution doping technique. The YTF was pumped by a 980-nm multimode laser to generate an ASE at 1900 nm through the transition of thulium ion from 3F4 to 3H6 with the assistance of ytterbium to thulium ion energy transfer. The broadband ASE was spectral sliced by the loop mirror, which was constructed using a 3-dB coupler and a piece of polarization maintaining fiber (PMF). A wideband comb with channel spacing of 3.3 nm and an extinction ratio of 9 dB was achieved with a multimode pump power of 1 W within a wavelength range of more than 300 nm. The center of the comb spectrum was at 1888 nm with peak power of around -53 dBm.

Microfiber Mach-Zehnder interferometer embedded in low index polymer

Abstract: Microfiber Mach Zehnder Interferometer (MMZI) is demonstrated by micromanipulating an optical microfiber drawn from a single mode fiber (SMF) using a flame brushing technique. The MMZI shows good interference fringes with an extinction ratio of 13 dB and a free spectral range (FSR) of 0.52 nm at 1530 nm. The MMZI is then embedded in a polymer with the refractive index of 1.36 to increase the stability and robustnes of the device. It is found that the transmission spectrum of the packaged MMZI is changed by the polymer, which increases the FSR to 0.83 nm. The degradation in transmission loss and extinction ratio are attributed to the disturbance at the coupling area during the packaging. Compared with waveguide based mach zehnder interferometer, the proposed MMZI is favoured due to easy fabrication, compact size, and easy integration with the fiber system.

Fabrication and application of zirconia-erbium doped fibers

Abstract: In this work, the fabrication of a Zirconia-Erbium co-Doped Fiber (Zr-EDF) and its application in the generation of non-linear effects as well as use in a compact pulsed fiber laser system is described. The Zr-EDF is fabricated by the Modified Chemical Vapor Deposition (MCVD) technique in combination with solution doping to incorporate the glass modifiers and nucleating agent. The resulting preforms are annealed and drawn into fiber strands with a 125.0 ± 0.5 µm diameter. Two Zr-EDFs, ZEr-A and ZEr-B, are fabricated with erbium ion concentrations of 2800 and 3888 ppm/wt and absorption rates of 14.5 and 18.3 dB/m at 980 nm respectively. Due to its higher erbium dopant concentration, a 4 m long ZEr-B is used to demonstrate the generation of the Four-Wave-Mixing (FWM) effect in the Zr-EDF. The measured FWM power levels agree well with theoretical predictions, giving a maximum FWM power - 45 dBm between 1558 nm to 1565 nm, and the generated sidebands are as predicted. The non-linear coefficient of ZEr-B is measured to be 14 W−1km−1, with chromatic and slope dispersion values of 28.45 ps/nm.km and 3.63 ps/nm2.km respectively. The ZEr-B is also used together with a graphene based saturable absorber to create a compact, passively Q-switched fiber laser. Short pulses with a pulse width of 8.8 µs and repetition rate of 9.15 kHz are generated at a pump power of 121.8 mW, with a maximum average output power of 161.35 µW and maximum pulse energy value of 17.64 nJ. The fabricated Zr-EDF has many potential applications in multi-wavelength generation as well as in the development of compact, pulsed laser sources.

Regenerated fibre Bragg grating fabricated on high germanium concentration photosensitive fibre for sensing at high temperature

Abstract: A Regenerated Fibre Bragg Grating (RFBG), with repeatable high temperature response between 400 °C–1200 °C, has been demonstrated using a hydrogen-loaded, highly germanium-doped, photosensitive fibre. A wavelength shifts of as much as 20 nm is attained during temperature calibration up to 1300 °C. A large temperature response of 17 pm/°C is obtained from the RFBG, with very good repeatability.

Analytical Model for Broadband Thulium-Bismuth-Doped Fiber Amplifier

Abstract: Due to the tremendous growth in applications for fiber laser in medical science, sensor solution, and light detection and ranging system at 1.8 to 2-μm region, more research efforts have been directed toward developing highly efficient broadband fiber amplifiers in this range. In order to amplify this region, Thulium-Bismuth-doped fiber amplifier (TBDFA) is proposed in conjunction with 800-nm pumping. Optimal Thulium ion concentration of 4.17 × 1026 ion/m3 and Bismuth ion concentration of 2.08 × 1026 ion/m3 together with low phonon energy of germanate glass lead to the highest energy transfer rates. Effective energy transfer mechanism from Bismuth to Thulium in addition to the cross relaxation process between Thulium ions results in higher amplification, efficiency, and super broadband amplification in TBDFA. We analytically solve the rate equations of TBDFA including the effect of energy transfer in order to calculate the broadband amplifier gain.

Tunable laser generation with erbium-doped microfiber knot resonator

Abstract: A tunable laser is demonstrated using a microfiber knot resonator structure made by erbiumdoped fiber (EDF). The laser is made of a 2 m long EDF where 30 mm of its end section is tapered to construct a microfiber knot resonator (MKR). The combination of the EDF and MKR generates a stable single wavelength laser at 1555 nm wavelength with a signal to noise ratio (SNR) of 33.7 dB using a 63 mW of 980 nm pump power. The peak wavelength of the laser can be tuned by 340 pm as the MKR diameter reduces from 5.0 to 0.5 mm with an acceptable penalty in output power.

Supercontinuum from Zr-EDF using Zr-EDF mode-locked fiber laser

Abstract: We propose and demonstrate the generation of a supercontinuum (SC) spectrum from a 10 m long silica fiber co-doped with zirconia-yttria-alumino and erbium (Zr-EDF) as a non-linear medium. The proposed system utilizes a 2 m long Zr-EDF in a ring laser configuration to generate mode-locked pulses at 1560 nm based on the non-polarization rotation (NPR) technique. The fiber laser generates a mode-locking spectrum from 1526 to 1640 nm with a peak power of –10 dBm at approximately 1565 nm as well as a 6.1 nm bandwidth at the 3 dB level. The generated mode-locked pulses have average and peak powers of 15 mW and 1 kW respectively with a repetition rate of 23.2 MHz. These pulses are subsequently used to generate the SC spectrum from the 10 m Zr-EDF, with the SC spectrum obtained having a 200 nm bandwidth from 1500 nm as well as a large 3-dB bandwidth of 68.2 nm. The SC pulse width is 0.59 ps with a symmetrical shape at about 1600 nm and a 3-dB bandwidth of approximately 0.12 ps. This is the first report of a zirconia host employed as a non-linear medium for SC generation.

Fiber laser at 2 micron region using double-clad thulium/ytterbium co-doped yttria-alumino-silicate fiber

Abstract: A lasing action from a newly developed double-clad Tm3+/Yb3+ co-doped yttria-alumino-silicate fiber (TYDF) is demonstrated based on cladding pumping technique. The TYDF used was drawn from D-shape preform, which was fabricated using a modified chemical vapor deposition (MCVD) process in conjunction with a solution doping technique. The Tm3+ and Yb3+ ions concentrations in this fiber are 5.55×1019 and 15.52×1019 ions/cc, respectively. The fiber laser operates at wavelength of 1948.4 and 1947.2 nm with pump power thresholds of 0.6 and 1.0 W for 915 and 940 nm pumping, respectively. The maximum output power of 10.5 mW was achieved with the 915 nm pumping at the maximum pump power of 1.5 W. It is found that the laser is more efficient with 915 nm pumping compared to 940 nm pumping.

Tunable single longitudinal mode S-band fiber laser using a 3 m length of erbium-doped fiber

Abstract: In this paper a tunable single-longitudinal mode (SLM), short-wavelength band (S-band) fiber laser using a conventional erbium-doped fiber (EDF) with a length of 3 m and a step index erbium dopant profile as opposed to the commonly used depressed cladding erbium-doped fiber (DC-EDF) is proposed and demonstrated. The proposed SLM fiber laser has a tuning range of 1496 to 1507 nm in a ring configuration using two 0.15 m of EDF which acts as saturable absorbers (SAs). The highest peak power measured is about −0.6 dBm at a wavelength range of 1502 to 1507 nm. The measured signal-to-noise ratio (SNR) is approximately 74 dB for the same wavelength range. The line-width of the SLM output is measured to be 140 kHz.

New Design of a Thulium–Aluminum-Doped Fiber Amplifier Based on Macro-Bending Approach

Abstract: A new method for gain enhancement in a S-band thulium-doped fiber amplifier (TDFA) co-doped with aluminum is demonstrated using a macro-bending approach. The macrobending of the doped fiber in a small radius suppresses both amplified spontaneous emissions (ASEs) at 800 and 1800 nm band and thus increases the population inversion in the S-band region. The numerical aperture and core radius of the doped fiber are optimized so that 800 nm ASE propagates with higher order modes to achieve a significant suppression while the loss is minimum in the S-band region. Meanwhile, the 1050 nm pump wavelength should propagate in the fundamental mode to maximize the overlap factor and thulium ion absorption so that the ASE loss is maximum at the 1800 nm region. Gain enhancements of about 5-8 dB are obtained with macrobending at the wavelength region between 1420 and 1470 nm.

Effect of transverse distribution profile of thulium on the performance of thulium-doped fibre amplifiers

Abstract: We study numerical models for different transverse thulium distribution profiles (TTDPs) characterising the fibres used in thulium-doped fibre amplifiers (TDFAs). Our models consider the overlap factor and the absorption/emission dynamics. Basing on the radial TTDP function of the form nT (r) = nT,max exp[-(| r-δ |/θ) β], we show that the TDFA gain increases with increasing β parameter and decreases as the θ parameter increases from 1 up to 3 μm, due to the overlap factor which affects the absorption and emission dynamics of the TDFA. The overlap factor increases with increasing β and decreases with increasing θ value. Finally, the noise figure increases as θ does so, due to suppression of the amplified spontaneous emission.

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

Abstract: 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.

Upconversion luminescence in Tm3+/Yb3+ co-doped double-clad silica fibers under 980 nm cladding pumping

Abstract: An investigation is reported of the visible and near-infrared upconversions in Tm3+/Yb3+ co-doped double-clad silica fibers (TYDFs) under excitation at 980 nm. The TYDFs used were fabricated using the modified chemical vapor deposition (MCVD) and solution doping techniques. Three distinct upconversion luminescences were observed at wavelengths of 482, 649 and 816 nm and their intensities found to increase with Yb3+ concentration. The intensity of blue and red fluorescence bands at 482 and 649 nm were found to be the highest with LTY-8 fiber, which had Tm3+ and Yb3+ concentrations of 5.6 × 1019 and 15.5 × 1019 ions/cc, respectively. The upconversion luminescence intensity was also observed to decrease with an increase in temperature. The main emission switched from 482 nm to 816 nm as the temperature increased above 200°C.

Fiber Optic Temperature Sensors

Abstract: S. W. Harun1,2, M. Yasin1,3, H. A. Rahman1,2,4, H. Arof2 and H. Ahmad1 1Photonic Research Center, University of Malaya, Kuala Lumpur 2Department of Electrical Engineering, University of Malaya, Kuala Lumpur 3Department of Physics, Faculty of Science and Technology, Airlangga University, Surabaya 4Faculty of Electrical Engineering, Universiti Teknologi MARA (UiTM), Shah Alam 1,2,4Malaysia 3Indonesia

Compact and Tunable Erbium-Doped Fiber Laser With Microfiber Mach–Zehnder Interferometer

Abstract: A compact and tunable Erbium-doped fiber laser is demonstrated using a highly concentrated Erbium-doped fiber in conjunction with a microfiber Mach-Zehnder interferometer (MMZI) structure for the first time. A stable laser output is achieved at 1531.7 nm region with a peak power of -19 dBm and an optical signal to noise ratio of 30.1 dB using a 980-nm pump at 100 mW power. The operating wavelength of the laser can be tuned from 1530.2 to 1532.7 nm by changing the path length difference (PLD) inside the MMZI from 1.6 to 2.7 mm at room temperature. It is also observed that the operating wavelength linearly shifts to a longer wavelength as the PLD increases with a tuning slope efficiency of 0.17 nm/mm. The tuning ability is due to the alteration of the induced optical phase shift inside the MMZI which affects the optical interference and the dominant peak which is responsible for the lasing action.

Fiber Optic Displacement Sensors and Their Applications

Abstract: Optical fiber-based sensor technology offers the possibility of developing a variety of physical sensors for a wide range of physical parameters (Nalwa, 2004). Compared to conventional transducers, optical fiber sensors show very high performances in their response to many physical parameters such as displacement, pressure, temperature and electric field. Recently, high precision fiber displacement sensors have received significant attention for applications ranging from industrial to medical fields that include reverse engineering and micro-assembly (Laurence et al., 1998; Shimamoto & Tanaka, 2001); Spooncer et al., 1992; Murphy et al., 1991). This is attributed to their inherent advantages such as simplicity, small size, mobility, wide frequency capability, extremely low detection limit and non-contact properties. One of the interesting and important methods of displacement measurement is based on interferometer technique (Bergamin et al., 1993). However, this technique is quite complicated although it can provide very good sensitivity. Alternatively, an intensity modulation technique can be used in conjunction with a multimode fiber as the probe. The multimode fiber probes are preferred because of their coupling ability, large core radius and high numerical aperture, which allow the probe to receive a significant amount of the reflected or transmitted light from a target (Yasin et al., 2009; Yasin et al., 2010; Murphy et al., 1994). For future applications, there is a need for better resolution, longer range, better linearity, simple construction and low cost unit.