Search

Abstract We propose highly sensitive trichannel photonic crystal fibre (TCPCF) refractive index (RI) sensor based surface plasmon resonance (SPR). In this design, we have been integrated the sensing layer with thin gold metal deposited over the surface of the TCPCF for fabrication feasible and easy liquid infiltration. Then, Y‐shaped channel is formed through reducing the diametre of air holes for controlling the direction of light through photonic crystal fibre to attain high sensitivity. Also, effective coupling between surface plasmon polariton mode at the metal layer and the core‐guided mode is obtained by numerical simulation of finite element method. The optimized TCPCF sensor exhibits maximum amplitude sensitivity of 1938.5 RIU−1 and wavelength sensitivity of 11,000 nm.RIU−1 within the analyte range from 1.34 to 1.39. Further, we have achieved amplitude resolution of 5.2 × 10−6 RIU and wavelength resolution of 9.1 × 10−6 RIU. It is confirmed high detection accuracy for small changes in RI analyte. Moreover, high figure of merit of 623.9 RIU−1 is obtained for the proposed sensor. Therefore, the proposed TCPCF RI sensor can be utilized in the chemical, bio and gas sensing applications.

Abstract A high sensitivity, simple fabrication all‐fibre strain sensor is proposed and demonstrated experimentally. The sensor consists of a section of Panda‐type polarization maintaining fibre (PMF) built into a Sagnac interferometer. The Panda‐type PMF is intentionally spliced to the single‐mode fibre through enhanced fusion splicing to excite high‐order polarized modes. The enhanced fusion splicing characterizes a large magnitude of overlap. The measured strain sensitivity reaches up to 32 pm/με and the strain resolution of 0.63 με has been achieved. The proposed fibre strain sensor characterizing easy fabrication and high sensitivity can be a good candidate in the field of structural health monitoring.

Transformer oil is widely used in high‐voltage transformers as a cooling and insulation medium. Electrical and thermal stresses expose transformer oil to degradation, which may produce dissolved decay products (DDPs) that are partially adsorbed on the insulation paper and accelerate the degradation of oil and paper. An evanescent field D‐shaped plastic optical fibre (POF) sensor was fabricated using the side‐polishing technique to detect DDPs in transformer oil. A laser light source and power meter were used in the prototype to measure the output power of the POF sensor. The measurement of DDPs was conducted on seven samples of insulating oil collected from the field. The sensor performance was evaluated based on different sensing areas, and the sensor sensitivity was measured. Results show an excellent correlation between the output power and DDPs. A correlation analysis was conducted amongst sensor output power, transformer oil refractive index and area under the absorbance curve. The performance of the sensor demonstrates improved linearity and sensitivity of 97.49% and 26.6779 µW/RIU, respectively. The POF sensor is easily fabricated, low cost and can be used for real‐time monitoring of high‐voltage transformers. [ABSTRACT FROM AUTHOR]

A passively Q‐switched erbium‐doped fibre laser was demonstrated by using tris‐(8‐hydroxyquinoline)aluminium (Alq3) organic material as a passive saturable absorber (SA). The SA was fabricated by a drop casting technique at room temperature and incorporated into a laser cavity by inserting it between two optical fibre ferrules. The Q‐switched fibre laser operates at a centre wavelength of 1559 nm with a full‐width half maximum of 1 nm. The generated pulse train is stable and has a pulse width decreased from 6.65 to 1.2 µs and the pulse repetition rate increased from 31.65 to 144.5 kHz as the pump power increased from 20 to 122 mW. The maximum pulse energy obtained is 63.89 nJ. This work indicates that the Alq3 as SA has a great potential to be utilised for pulsed laser generation. To the best of the authors' knowledge, this is the first time an organic material is utilised as a SA device for generating a stable Q‐switched laser pulse. [ABSTRACT FROM AUTHOR]

This Letter presents the mechanical analysis of polymethyl methacrylate microstructured polymer optical fibres drawn at different pressures. The fibres were drawn at 200, 400 and 600 mmH2 O, where all the samples have a diameter close to 250 µm. Tensile tests were performed in five samples of each drawing pressure and the statistical analysis was applied to Young's modulus, yield stress, strain at breakage and Poisson's ratio of each sample. Results show a statistically significant increase of Young's modulus with the increase in drawing pressure, whereas the strain at breakage presented the opposite behaviour, with its values decreasing as the drawing pressure increases. Furthermore, the Poisson's ratio, as well as, the yield stress do not show a statistically significant variation with the different drawing pressure analysed. [ABSTRACT FROM AUTHOR]

A novel low‐loss photonic crystal fibre (PCF) has been suggested for THz spectral applications. The proposed PCF contains five layers cladding with three layers core. The cladding and core region of the fibre are arranged in the octagonal and porous manner, respectively, where both the core and cladding vicinity are constituted by circular air cavities. The optical properties of the PCF are investigated by utilising the full vectorial finite‐element method along with the perfect match layers boundary condition. All numerical outcomes show the ultra‐low effective material loss of 0.049 cm−1 and large effective area of 3 × 10−7 m2 at 1 THz operating frequency. The power fraction is also considered as another significant parameter to design a low loss fibre. The almost more than half of the useful power (about 53.78% at f = 1 THz) goes through the core over the wider operating frequency. In addition this, the proposed single‐mode PCF can be fabricated using the sol–gel method and is useful not only for high data traffic transmission applications but also for THz waveguide applications. [ABSTRACT FROM AUTHOR]

The thermal response of packaged biconic taper filter with a free spectral range of 1.7 nm is investigated over a temperature range of 0–70°C. The filter length dependence with temperature is estimated from the spectral offset. This device presented thermal stability of 3 × 10−3 nm/°C, measured at λ0 = 1550 nm. [ABSTRACT FROM AUTHOR]

Fibre Bragg grating inscription in the crystalline silicon (Si)‐core fibre is described using visible light femtosecond laser pulses. The femtosecond pulses at 517 nm propagate through the transparent silica glass cladding and are fully absorbed by the Si core generating locally high temperatures and stress fields in forming the grating periods. The Si FBGs were characterised in reflection, calibrated for a first time as strain and temperature sensors and compared with that of FBGs inscribed in standard silica fibres. [ABSTRACT FROM AUTHOR]

This study reports on the demonstration and characterisation of a short cavity fibre Fabry‐Perot resonator (FPR) for the detection of ultrasonic waves propagating through a solid medium over a frequency range of 1 kHz–10 MHz. The proposed sensing device has some outstanding features in terms of simple fabrication technique, frequency response and high sensitivity over a wide frequency range. The response of the surface‐mounted FPR sensor showed good agreement with that of a commercially available piezoelectric transducer during ultrasonic excitation. [ABSTRACT FROM AUTHOR]

Earlier reported micro-Mach-Zehnder interferometer (MMZI) sensors, fabricated by concatenation of tapered fibers, considered the interference between LP01 and LP02 modes only for generating the fringe pattern. However, the experimental studies evidenced aperiodic and nonsinusoidal spectral response, which may be attributed to the occurrence of interference among higher order cladding and LP01 and LP02 modes enroute the interference region. In order to accommodate the effect of interference among the higher order cladding modes, a perturbation term has been inserted in the expression for free spectral range and formula for shift in the fringes, due to rise in temperature of the fiber, in this paper. Furthermore, three samples of in-house fabricated MMZIs, placed over a direct current carrying power resistor, senses the temperature produced due to emanation of Joule's heat and resulted into shift in the output fringe pattern. The effect of change in temperature/current is displayed as shift in the output spectrum, recorded on an optical spectrum analyzer, in accordance with the amended equations. The fabricated sample demonstrates the higher current sensitivity 1.76 nm/A2 with the regression/correlation coefficient (R2) value 0.99. [ABSTRACT FROM PUBLISHER]

Fabrication and characterization of a highly sensitive surface plasmon resonance-based fiber optic sensor for the detection of low concentrations of ammonia gas have been reported. The sensor probe is fabricated by coating an unclad core of the optical fiber with successive layers of indium tin oxide (ITO) and bromocresol purple (BCP). Increase in the concentration of ammonia gas around the sensing probe increases the resonance wavelength linearly implying that the absorption of ammonia gas by BCP layer increases its refractive index. In addition, ITO layer also contributes to the increase in the resonance wavelength because it is porous and has grains, which allow the reaction products to enter the pores of the ITO layer causing swelling of the layer resulting in mechanical stress and hence increase in the refractive index. To achieve maximum sensitivity of the sensor, the thickness of the BCP layer is optimized and is found to be 70 nm. The sensitivity of the sensor with optimized thickness of BCP layer is 1.891 nm/ppm and is larger than the sensitivity values obtained in the cases of Ag/BCP and Cu/BCP-coated probes for the concentration range 1-10 ppm of the ammonia gas. The selectivity of the probe is checked by carrying out experiments on the probe with different gases and it is observed that the probe is highly selective for ammonia gas. The sensor has many advantages, such as low cost, online monitoring, and remote sensing, due to the fabrication of the surface plasmon resonance probe on an optical fiber. [ABSTRACT FROM PUBLISHER]

In this letter, a pair of regenerated gratings with Bragg wavelengths of 1547 and 1304 nm in a single piece of singlemode fiber has been fabricated for simultaneous monitoring of temperature and strain in ultrahigh temperature environment. A 3 × 3 matrix is used to characterize the cross sensitivity of the proposed sensor in which the strain sensitivity varies with temperature change. The proposed structure exhibits the deviation of 28.3 με and 4.1 °C at the ranges of 0-1000 με and 25 °C- 900 °C, respectively. [ABSTRACT FROM PUBLISHER]

We proposed and demonstrated an innovative magnetic field optical fiber sensor utilizing magnetic ferrofluid and a thin-core fiber (TCF)-based modal interferometer. The modal interferometer was fabricated by splicing a TCF between two single mode fibers. Two TCF interferometers with different dip wavelength were connected in a fiber to demonstrate the sensors multiplexing capability. The transmission dip wavelength of interferometer is shifting with a maximum sensitivity of 11.8 pm/Oe. [ABSTRACT FROM PUBLISHER]

In this paper, a bilayer metallic grating with pitch of 1 μm on the flank of a cylindrical plastic optical fiber was proposed as a novel optical sensor. Surface plasmon resonance excited by this structure for refractive index sensing is investigated by finite difference time domain methods. A theoretical sensitivity of 643.75 nm/RIU is obtained, where the wavelength of the resonant sharp dip is obviously shifted from 1.398 μm to 1.501 μm for surrounding refractive index increased from 1.33 to 1.49. Several factors which affect the accuracy of the device, such as the polarization state of the incident light, grating pitch, and refractive index of the sensing medium, are discussed. The successful fabrication of the grating indicates the feasibility of the devices. The sensor is expected to have potential applications in the chemical, biomedical, environmental safety, and food safety industries as well as in many other aspects. [ABSTRACT FROM PUBLISHER]

A point-by-point dip coating method has been proposed and demonstrated for fabricating long-period gratings (LPGs) in microfibers. Using a high precision 3D translation stage, the grating structure is formed by periodically immersing the microfiber into a miniature polydimethylsiloxane droplet suspended at the end-tip of the single mode fiber. A 10-period LPG with a grating period of about 143 μm fabricated in the 7.6 μm diameter microfiber demonstrates a resonant dip of 19 dB. Investigations of the strain and temperature response characteristics of the fabricated devices show that the devices have great potential for tunable filter and sensor applications with the merits of flexibility and compactness. [ABSTRACT FROM PUBLISHER]

In this letter, we propose and demonstrate a highly sensitive axial strain fiber laser sensor based on all-fiber acousto-optic tunable filter (AOTF). In the laser sensing system, all-fiber AOTF acts as a band-rejection filter of the fiber laser sensor and the sensing head used for axial strain measurement. When the axial strain is loaded, the optical resonant wavelength of all-fiber AOTF moves to the long wavelength region, resulting in the increasing of the central wavelength of the fiber laser sensor. The proposed fiber laser sensor takes the advantages of high-optical signal-to-noise ratio and narrow bandwidth. Moreover, the fabrication of all-fiber AOTF is also very simple. Experimental results show that a good linearity is obtained between the axial strain and central wavelength of the proposed fiber laser sensor, and a high sensitivity of ~0.148 nm/με with the range of 0-160 με can be successfully achieved. [ABSTRACT FROM PUBLISHER]

We experimentally demonstrate a sensitivity-enhanced fiber-optic pressure sensor using a simplified hollow-core photonic crystal fiber (SHC-PCF). The sensing head is fabricated by splicing a single mode fiber to a section of SHC-PCF, while the air claddings at the end of the PCF are selectively blocked by glue sealing and femtosecond laser machining. By immersing the end into water, a compressible Fabry-Pérot cavity can be formed in the fiber core of the PCF. Since the air core is opened up to the air claddings at the splicing joint, changing of environmental pressure will cost a large change of the cavity length to balance the pressure, which greatly enhances the pressure sensitivity of the sensor. A pressure sensitivity of 18.15 μm/kPa is experimentally demonstrated in the pressure range from 110 to 130 kPa. This sensor has potential applications in the area of highly sensitive pressure measurement. [ABSTRACT FROM PUBLISHER]

We investigated a nonadiabatically tapered microfiber refractive index sensor with an ultrashort waist length. Free spectral range (FSR) is one common issue in the interferometry-based sensors. Such sensors will not work properly once the resonant wavelengths shift over one cycle. It was found that the temperature and pulling speed are the crucial parameters to achieve a desired tapering profile. By setting a cooler tapering temperature and fast pulling speed, we successfully fabricated ultrashort microfibers with a waist length of only 2.4 mm and total length of 5.5 mm. The resulting FSR is ~80 nm and the maximum sensitivity achieved for such short microfiber is 25 667 nm/RIU. [ABSTRACT FROM PUBLISHER]

Nanoantennas have been used in a wide range of applications in sensing, spectroscopy, and imaging-in general, the antennas can enhance physical phenomena such as the local electric field or concentrate light in a certain direction. We have fabricated an array of 80 plasmonic Yagi-Uda nanoantennas on the cladding of an optical fiber and, by doing this, we show that the signal reaching the fast detector can be increased by a factor of 5 dB. The experiment demonstrates that plasmonic directive nanoantennas can indeed collect and concentrate electromagnetic radiation along a certain direction and eventually could be used to enhance weak signals. [ABSTRACT FROM PUBLISHER]

Higher-order solitons are formed by coupling femtosecond pulses into the fundamental mode of a highly nonlinear silica photonic crystal fiber (HNL-SPCF) fabricated in our laboratory. It is experimentally observed that the higher-order solitons break up into a series of stable and broadband discrete fundamental solitons at the mid-infrared wavelength longer than 2000 nm through the process of soliton self-frequency shift due to the perturbations induced by the higher-order dispersive and nonlinear effects. The maximum soliton red-shift and the tunable wavelength range can be up to 1600 nm and over 400 nm, respectively. The nonlinear dynamic processes of femtosecond pulse breakup are consistent with the solution of the generalized nonlinear Schrödinger equation. This multiple stable and broadband mid-infrared wavelengths generated in such an HNL-SPCF can be used as all-fiber multiwavelength ultrashort pulse sources for multiphoton microscopy and ultrafast photonics. [ABSTRACT FROM PUBLISHER]

The polarization characteristics of the multifunctional integrated optic chip (MFIOC) are fully evaluated with high accuracy by using optical coherence domain polarimetry based on white light interferometer. Two polarization maintaining (PM) fibers, serving as extended fibers, are spliced to the PM pigtails of the MFIOC with polarization axes aligned. By launching light at 45° to the birefringence axes of the lead-in extended PM fiber, the beams along the fast and slow axes of the birefringent waveguides interfere after a 45° polarization analyzer and an optical path correlator. The polarization extinction ratio (PER) and birefringence of the LiNbO3 Y-waveguide, the birefringence of the PM pigtails, and the crosstalks at the connection points between the Y-waveguide and the PM pigtails can be simultaneously obtained from the amplitudes and positions of the corresponding interference peaks. The characteristic peak of the Y-waveguide's PER is shifted out of the interference peak of the light source ripple by selecting proper length of the extended fibers. The extended fibers also brings in two additional cross-coupling points at the ends of the PM pigtails, which are used for calculating the birefringence of the PM pigtails. In addition, the alignment type between the PM pigtails and the birefringent Y-waveguide is identified according to the position of the characteristic peak of the Y-waveguide's PER. Theoretical model based on Jones matrix is built to describe the characteristic peaks of the MFIOC. Two MFIOCs with different alignment angle between the PM pigtails and the Y-waveguide are experimentally tested. Results show that the PER resolution of the proposed method can achieve nearly -90 dB and the dynamic range of the test system is about 90 dB. [ABSTRACT FROM PUBLISHER]

In this letter, an optic fiber high-temperature sensor with a low-fineness Fabry-Pérot cavity formed by dielectric films at the end of multimode fiber is proposed and demonstrated. The sensor is proved to be simple in configuration and low cost for component and easy for batch fabrication. Experimental investigation shows that the sensor exhibits a sensitivity of 5.4 × 10-3nm/°C when the ambient temperature changes from 250 °C to 750 °C. [ABSTRACT FROM PUBLISHER]

We report on a low-loss fusion splice between a hollow-core photonic bandgap fiber (NKT's HC-1550-02) and a conventional single mode fiber (Corning's SMF28) using a high V-number intermediate fiber. Compared to the commonly used fiber postprocessing techniques, the intermediate fiber method offers a new adjusting degree of freedom of V-numbers, enabling the reduction of coupling loss to 0.35 dB. Experimentally, a low fusion splice loss of 0.63 dB has been achieved between Nufern's SM1950 (V =2.836) and HC-1550-02 fiber, resulting in an overall insertion loss of 0.73 dB from SMF28 to HC-1550-02 fiber. We believe this is the lowest splice loss value reported for HC-1550-02 fiber using an arc splicer, on the aspect of both using a step-index solid-core fiber (0.63 dB) and a SMF28 fiber (0.73 dB). [ABSTRACT FROM PUBLISHER]

We demonstrated a simple and batch-producible fiber-optic sensor based on hybrid Fabry-Pérot (FP) configuration for simultaneous pressure and temperature sensing. The proposed sensor head chips are batch fabricated by double-sided anodic bonding of a through-holes-array-structured glass wafer and two silicon wafers. The silicon-glass-silicon sandwich bonding structure constructs two serially connected low-finesse FP cavities naturally. The first cavity (FP1) is a silicon cavity and utilizes the refractive indices temperature dependence of silicon to achieve temperature sensing. The second cavity (FP2) is a vacuum cavity and employs a thin silicon diaphragm as a pressure sensing element. The reflection spectra exhibit hybrid interference fringes with different frequencies produced by silicon and vacuum cavity, and the temperature and pressure are simultaneously measured. Experiment results demonstrate that the pressure sensitivity of FP2 is 12.82 nm/kPa with a high linear pressure response over the range of 10-250 kPa, and the temperature sensitivity of FP1 is 142.02 nm/°C under the range of -20 °C-70 °C. [ABSTRACT FROM PUBLISHER]

A silica/electro-optic (EO) polymer phase modulator is proposed for microwave radiation receiver with the use of a bowtie antenna. Waveguide design optimization is presented for a waveguide with an EO polymer core and silica/sol-gel cladding. Electrode effects on the insertion loss and poling efficiency are also analyzed and conditions for low-loss and high poling efficiency established. The bowtie antenna is simulated and shows a broadband response with a maximum at 5 GHz and a 3 dB-bandwidth of approximately 12 GHz. A fiber splicing technique is presented that reduces coupling loss between SMF-28 and the waveguide. Experimental results for a fabricated device with microwave-response between 10-14 GHz are shown with carrier to first sideband intensity difference of up to -36 dB. [ABSTRACT FROM PUBLISHER]

We present a temperature and strain fiber sensor utilizing fiber Bragg grating (FBG) inscribed in silica-germanate few-mode fiber. The temperature and strain sensitivities of resonant wavelength formed by mode LP01 self-coupling and mode LP01-LP11 cross-coupling are investigated theoretically and characterized experimentally. Two resonant wavelengths demonstrate different temperature sensitivities of 11.5 pm/°C 10.6 pm/°C, respectively, due to different mode profile, while the strain sensitivities are quite similar with a value of 0.9 pm/με. By using FBG character matrix, the proposed fiber sensor can measure those two parameters simultaneously within a compact and cost-effective setup. [ABSTRACT FROM PUBLISHER]

In this study, we present a novel optical fiber magnetic sensor based on electroforming long-period optical fiber grating (ELPFG) with a periodic polymer-metal (SU-8 photoresist and nickel) structure that is fabricated via a LIGA-like process. We measure the magnetic field through the nickel grating on the optical fiber, and an ELPFG magnetic sensor calibration experiment is also described. The coil produces a magnetic field to modulate the ELPFG, and we use an optical spectrum analyzer to analyze the resonant wavelength and changes in transmission loss. It is discovered from the experimental results that the optimal sensitivity of the ELPFG is -0.465 dB/mT, the linearity is 0.965, and the transmission loss will gradually increase following magnetic field enhancement. We infer that this phenomenon is due to the magnetostriction materials of nickel, which cause the nickel structure to impose a slight stretching strain on the ELPFG with the applied magnetic field. [ABSTRACT FROM PUBLISHER]

We have developed a 1.55-μm 40 Gbps electro-absorption modulator laser (EML)-based transmitter optical subassembly (TOSA) using a novel flexible printed circuit (FPC). The return loss at the junctions of the printed circuit board and the FPC, and of the FPC and the ceramic feedthrough connection was held better than 20 dB at up to 40 GHz by a newly developed three-layer FPC. The TOSA was fabricated and demonstrated a mask margin of >16% and a path penalty of <;0.63 dB for a 43 Gbps signal after 2.4-km SMF transmission over the entire case temperature range from -5° to 80 °C, demonstrating compliance with ITU-T G.693. These results are comparable to coaxial connector type EML modules. This TOSA is expected to be a strong candidate for 40 Gbps EML modules with excellent operating characteristics, economy, and a small footprint. [ABSTRACT FROM PUBLISHER]

We demonstrate an integrated waveguide platform and optomechanical transduction circuit for chip-scale displacement sensing. The waveguide consists of a thin silicon nitride core layer, a thick silicon oxide bottom cladding, and a top air cladding with a large evanescent field at the waveguide surface. Although the structures feature subwavelength (<;λ/4ncore) vertical confinement, they are fabrication tolerant with micrometer-scale lateral features. We demonstrate via simulations and measurements that the waveguides exhibit a low confinement with a maximized evanescent field as well as an effective index only slightly larger than the SiO2 bottom cladding index. Despite the low confinement, the waveguide platform enables complex photonic circuits. As a demonstration of this technology, we fabricate and characterize an unbalanced Mach-Zehnder interferometer for chip-scale displacement sensing. A micrometer-scale fiber taper interacts with the waveguide's evanescent field and induces a phase shift proportional to displacement, thereby acting as an optomechanical transducer. We analyze the responsivity, displacement limit of detection, and strength of optomechanical coupling for high-resolution sensing. An outlook toward other applications is also given. [ABSTRACT FROM PUBLISHER]

A method based on fiber-optic surface plasmon resonance (FO-SPR) to detect mixed petrol is proposed to realize real-time, rapid monitoring of the mixed petrol interface in transportation pipelines. When the sensing region of the FO-SPR sensor was immersed in the petrol sample, the mixed petrol could be detected by measuring the refractive index of the petrol, which responds to the resonance wavelength in the SPR curve. Numerical simulation was performed according to the optical fiber theory and the SPR principle to optimize the structural parameters of the sensor. The optimized sensor can reflect small changes of the refractive index for mixed petrol detection. Next, the end-reflection FO-SPR sensor was designed and fabricated. The fiber was rotated in addition to the revolution of the coating disc to realize a uniform coating of the circumferential surface of the fiber core during vacuum coating. A wavelength modulation optical measurement system with the FO-SPR sensor was constructed. Petrol 90#, Petrol 93#, Petrol 97#, and their mixtures were measured. The experimental results indicated that this method could detect different mixing ratios of petrol with good repeatability, which lays the technical foundation for fast and accurate online detection of the mixed petrol interface in transportation pipelines. [ABSTRACT FROM PUBLISHER]

A modified chelate precursor doping technique using high‐purity materials and accurate gas flow control system is proposed to fabricate an efficient ytterbium‐doped large‐mode‐area silica fibre for laser development. This technique enables to make homogeneous large‐core preform with symmetrical shape, relatively low numerical aperture of ∼0.06 and large‐core size of over 4 mm. Homemade preform was drawn into standard fibre for testing and fully characterised by electron probe microanalysis and time‐of‐flight secondary ion mass spectrometry. On the basis of two‐stage master oscillator power amplifier system, 1 kW laser output with slope efficiency of 81.0% was realised at ∼1064 nm. [ABSTRACT FROM AUTHOR]

A new device for improving the free-space optical monitoring and coupling into a single mode fiber is proposed. It consists of a fiber taper, which can easily be drawn from a suitable fiber with large core radius. The taper acts as a mode filter discarding higher order modes. A first device is fabricated. Measurements show that lateral tolerances increase linearly with the taper input core radius and longitudinal tolerances increase with the square of the input core radius. [ABSTRACT FROM PUBLISHER]

An evanescent field-based microfiber knot resonator (MKR) refractive index sensor with long-term stability was proposed in this letter. To protect the microfiber from the mechanical and optical degradation and at the same time preserve the large evanescent waves, a dip-coating technique was presented to coat the MKR and a thin coating in the submicrometer thickness range was experimentally fabricated. The temporal stability of the coated MKR and its sensing properties in refractive index were, respectively, investigated. The results indicated that the coated MKR did not degrade over a long time, and the minimal detectable refractive index of \(2 \times 10 ^-4\) was successfully achieved. [ABSTRACT FROM PUBLISHER]

We demonstrate a highly efficient grating coupler with center wavelength near 1310 nm fabricated on a silicon-on-insulator (SoI) wafer by 248-nm deep ultraviolet lithography. One of the lowest reported losses of 2 dB is achieved using feature sizes of 200 nm and without other process enhancements, such as polysilicon. The higher efficiency is obtained through improved mode-matching based on a novel genetic algorithm, which utilizes two different etch depths. The 3-dB bandwidth is 50 nm, and the back-reflection to the waveguide is better than 20 dB. The result shows low-loss coupling between waveguides and single-mode fibers for 1310~nm applications suitable for mass production on the commonly used 220-nm SoI platform. [ABSTRACT FROM PUBLISHER]

The fabrication of Ce-doped fibers (CeDFs) is demonstrated by drawing-tower method employing rod-in-tube technique. The fluorescence spectrum of CeDFs with a 16-μm core exhibited a 160-nm broadband emission with 1.45-μm axial resolution. This CeDF may be functioned as a high-resolution light source for optical coherence tomography applications. [ABSTRACT FROM PUBLISHER]

A novel polarization splitter based on dual-core silica glass photonic crystal fiber with a liquid crystal modulation core is studied by the finite-element method. The mode birefringence is enlarged greatly with the infilling of nematic liquid crystal of E7. The simulation results demonstrate that the polarization splitter has an ultrabroad bandwidth of 250 nm, covering the E S C L optical communication bands, with the extinction ratio better than -20 dB. The separate length is 0.175 mm, and the extinction ratio is -80.7 dB at the communication wavelength of 1550 nm. The polarization splitter exhibits satisfactory splitter performance as the fabrication deviation reaches to 1%. The extinction ratio maintains better than -20 dB, at the C L optical communication bands, as the temperature increases from 15 °C to 50 °C. [ABSTRACT FROM PUBLISHER]

The high cost and low scalability of interfacing standard optical fibers to nanophotonic waveguides hinder the deployment of silicon photonics. We propose a mechanically compliant low-cost interface with integrated polymer waveguides. Our concept promises better mechanical reliability than a direct fiber-to-chip coupling and a dramatically larger bandwidth than diffractive couplers. Our computations show a 0.1-dB penalty over a 200-nm bandwidth, whereas typical two-polarization vertical couplers show a ~1-dB penalty over a 30-nm bandwidth. In this paper, we present a comprehensive analysis of the design space using optimization routines to achieve a fabrication- and assembly-tolerant design. We demonstrate the concept feasibility through extensive tolerance analysis with parameter control assumptions derived from low-cost manufacturing. [ABSTRACT FROM PUBLISHER]

miniature fiber-optic Fabry-Pérot cavity interferometerA miniature fiber-optic Fabry-Pérot cavity interferometer is presented. The interferometer is fabricated at the fiber tip by wet chemical etching using hydrofluoric acid. A concave well is created on the fiber end face. Interference happens between the reflections from the fiber core and the end of the cladding. We demonstrate applications of the interferometric sensor for temperature and gas refractive index sensing. [ABSTRACT FROM PUBLISHER]

Possible designs for a new type of mode converters based on microstructuring the refractive-index profile of an optical fiber with ultrashort laser pulses are proposed and characterized numerically. Both LP01-LP02 and LP01-LP11 converters exhibit in excess of 20-dB extinction ratio over more than 200-nm bandwidth with moderate losses. The length of the converters is only a few hundred micrometers, making them some of the shortest mode converters available. [ABSTRACT FROM PUBLISHER]

We demonstrate a miniaturized fiber device based on fiber inner air-cavity with periodical microstructures and platinum (Pt)-doped WO3 coating for hydrogen concentration sensing. The fiber inner air-cavity is formed by use of femtosecond laser micromachining together with fusion splicing technique and the line shape microstructures are inscribed by femtosecond laser beam scanning. The Pt-doped WO3 coating on the fiber surface near the cavity leads to the device sensitivity to hydrogen concentration, and the maximum wavelength shift obtained is ~2.64 nm when the hydrogen concentration is increased from 0% to 4% in volume percentage. The system is highly sensitive and miniature and exhibits a low temperature cross-sensitivity. [ABSTRACT FROM PUBLISHER]

A low loss broadband terahertz (THz) polarization splitter with a compact and simple structure has been proposed, which is based on the mode coupling between two porous fibers with orthogonally oriented cross section microstructures. The dispersion curves of the porous fibers are adjusted by the index converse matching coupling method. An interlacing stacking technique using polymer tubes and rods is presented for the fabrication of the proposed high-birefringence porous fiber. The characteristics of single porous fibers have been analyzed in detail. In addition, the dual-porous fiber-based polarization splitter has such desirable merits as ultrashort splitting length, low loss, and broad operation band. Compared with other dual-core PCF polarization splitters, this scheme possesses simpler structure, ease of fabrication, and better practical feasibility. This letter would be also of significance for the design of related broadband operation THz devices. [ABSTRACT FROM PUBLISHER]

We describe a new technology for the fabrication of polydimethylsiloxane (PDMS) optical fibers and PDMS fiber structures, based on fiber drawing from partially cured PDMS. This technology allows the fabrication of PDMS fibers in a wide range of diameters and different lengths. We demonstrate the potential of such prepared PDMS optical fibers on a variety of typical and unconventional fiber structures such as multimode optical fibers, looped and twisted fibers, and optical fiber couplers. [ABSTRACT FROM PUBLISHER]

Rubidium vapor is loaded into hypocycloidal core shaped Kagome hollow-core photonic crystal fiber (HC-PCF) with the wall of its inner core coated with aluminosilicate ceramic (sol-gel). We show that the presence of Rb vapor is maintained for a longer duration when compared to uncoated Kagome HC-PCF. Rb vapor within the hollow-core of a sol-gel coated Kagome HC-PCF is preserved for over 500 h after the source of Rb is halted. And Rb vapor is detected in the sol-gel coated HC-PCF for more than 80 h after the background Rb vapor signal is no longer observed. [ABSTRACT FROM PUBLISHER]

In this letter, an optical fiber refractometer fabricated by etched-stress applying parts (SAPs) PANDA fiber is proposed and experimentally demonstrated. The proposed structure depends on an in-fiber Mach-Zehnder interferometer (MZI), which is induced by the two orthogonal polarization modes of the fiber and the dip wavelength shifts as a function of the surrounding medium refractive index. In the sensor area, one of the axes is quickly etched to near the fiber core modifying the evanescent field, which results in increasing birefringence variation by the surrounding medium. The fiber has been chemically etched with the etched length of 5 cm. High sensitivity of 151 nm/RIU (refractive index unit) within the linear sensing range from 1.3401 to 1.3997 and a resolution of 1.32 × 10-4 RIU are obtained for the proposed liquid refractive index sensor. [ABSTRACT FROM PUBLISHER]

Different types of fibers were compared for construction of reflection-based surface-enhanced Raman-scattering (SERS) fiber probes. The probes were made by direct femtosecond (fs) laser micromachining of nanometer structures on the fiber endface and subsequent chemical plating of a thin layer of silver. Rhodamine 6G solutions were used to evaluate the performance of the SERS probes. In comparison with the silica fibers, the single-crystal sapphire fiber has much lower background Raman scattering. The fs laser is found effective to fabricate high-quality sapphire fiber SERS probes for detection of weak Raman signals in a reflection configuration. [ABSTRACT FROM PUBLISHER]