Phosphate Fiber Research Articles

Preparation and characterization of single phase, biphasic and triphasic calcium phosphate whisker-like fibers by homogenous precipitation using urea

Whisker-like calcium phosphate fibers were prepared by a homogenous precipitation method under refluxing conditions in solutions with a Ca/P molar ratio of 1.67 at 90°C and pH 3.0 using urea as additive. The precipitates were characterized by XRD, FTIR, SEM, and FE-SEM. The ICP spectroscopy and elemental analyzer were used to determine Ca/P ratio and carbonate content of products, respectively. The results indicate that the morphology and structural characteristics of the precipitates depend on the urea concentration and reaction time. Whisker-like biphasic monetite/hydroxyapatite (HA) fibers with a mean length of 60µm and a mean width of 1.0µm were obtained with the use of a low concentration of urea. Calcination of the biphasic calcium phosphate at 800°C led to the formation of a triphasic mixture of HA/whitlockite (β-TCP)/calcium pyrophosphate (CPP) with a whisker-like morphology. The use of a higher concentration of urea was caused to form a mixed morphology of spherulites/whisker-like fibers consisting of octacalcium phosphate (OCP) and HA phases. When the reaction time was increased to 10 days, both the above biphasic calcium phosphates transformed to a single phase HA which its morphology and growth pattern were similar to those of a whisker, according to FE-SEM images. The HA whiskers produced by a lower amount of urea had a lower carbonate content compared to those obtained using a higher urea concentration.

Compact frequency-modulation Q-switched single-frequency fiber laser at 1083 nm

A compact frequency-modulation Q-switched single-frequency fiber laser is demonstrated at 1083 nm. The short linear resonant cavity consists of a 12 mm long homemade Yb3+-doped phosphate fiber and a pair of fiber Bragg gratings (FBGs) in which the Q-switching and the frequency excursion is achieved by a tensile-induced period modulation. Over 375 MHz frequency-tuning range is achieved with a modulation frequency varying from tens to hundreds of kilohertz. The highest peak power of the output pulse reaching 6.93 W at the repetition rate of 10 kHz is obtained.

Simultaneously reducing the intensity and frequency noise of single-frequency phosphate fiber laser

We demonstrate an optoelectronic feedback method to simultaneously reduce the intensity and frequency noise of a single-frequency phosphate fiber laser for the first time. Based on the fact that the intensity and frequency noise in this laser mainly originate from the pump power fluctuations, we implement a simple and compact feedback loop and achieve a maximum noise reduction of over 20 dB for the intensity noise at frequencies of 0.3–3 kHz and 10 dB for the frequency noise at around 1 kHz. In addition, the laser instability is improved from ±1.7% to ±0.1%, and the laser line shape is observed to be compressed at the central part.

Heavily Yb-doped phosphate large-mode area all-solid photonic crystal fiber operating at 990 nm

We demonstrate, for the first time to our knowledge, a 16 wt.% Yb-doped phosphate large-mode area all-solid photonic crystal fiber (AS-PCF) laser operating at 990 nm. By carefully tailoring the absorption and emission properties of the active glass and designing the structure of AS-PCF, the excitation of the 990 nm laser and the depression of the laser above 1 µm can be easily realized even without any wavelength-selective optics. The single-mode behavior of PCF with a 35 µm doped core, the largest core diameter of approximately 1 µm in phosphate fiber, is theoretically investigated by finite-difference time-domain method and experimentally confirmed.

Processing and characterization of novel borophosphate glasses and fibers for medical applications

In this paper, we investigate the effect of P2O5 substitution by B2O3 in the (50−x)P2O5·20CaO·20SrO·10Na2O·x B2O3 glass system (x from 0 to 5mol%) on the thermal and structural properties and also on the glass reactivity in simulated body fluid. The goal is to develop new glass candidates for biomedical glass fibers. The addition of B2O3 at the expense of P2O5 increases the refractive index of the glass and also the thermal stability of the glass indicating that these glasses are promising glasses for fiber drawing. Thus, within such glass composition, the core of a core–clad fiber has a larger concentration of B2O3 than the clad of the fiber to enable the light to propagate inside the core. All the investigated glasses form a calcium phosphate layer at their surface when immersed in simulated body fluid. It was found that small addition of B2O3 (1.25mol%) leads to a decrease in the initial dissolution rate and a delayed layer formation. However, with increasing B2O3 content, the chemical durability decreased slightly but was higher than for the B-free glass. In addition, formation of the calcium phosphate layer was further delayed. This suggests that small contents of B2O3 led to formation of P–O–B bonds and only few BO4 units, increasing the chemical durability. At higher B2O3 contents, the amount of BO4 units increases which makes the glass network slightly more prone to be hydrolyzed. Thus, formation of BO4 units induced by the addition of B2O3 at the expense of P2O5 reduces the reactivity of the glass in SBF. Borophosphate fibers were successfully drawn from preform. As expected from the bioresponse of the bulk glasses in simulated body fluid, the reduction in the intensity of the light transmitted is less and slower in a borophosphate fiber than in a phosphate fiber upon immersion.

Simultaneously Suppressing Low-Frequency and Relaxation Oscillation Intensity Noise in a DBR Single-Frequency Phosphate Fiber Laser**Supported by the National High-Technology Research and Development Program of China under Grant Nos 2013AA031502 and 2014AA041902, the National Natural Science Foundation of China under Grant Nos 11174085, 51132004, and 51302086, the Guangdong Natural Science Foundation under Grant Nos S2011030001349 and S20120011380, the China National Funds

Effective multiple optoelectronic feedback circuits for simultaneously suppressing low-frequency and relaxation oscillation intensity noise in a single-frequency phosphate fiber laser are demonstrated. The forward transfer function, which relates the laser output intensity to the pump modulations, is measured and analyzed. A custom two-path feedback system operating at different frequency bands is designed to adjust the pump current directly. The relative intensity noise is decreased by 20 dB from 0.2 to 5kHz and over 10 dB from 5 to 10 kHz. The relaxation oscillation peak is suppressed by 22 dB. In addition, a long term (24 h) laser instability of less than 0.05% is achieved.

Nd3+-doped soft glass double-clad fibers with a hexagonal inner cladding

The stack-and-draw technique was used to fabricate Nd3+-doped silicate and phosphate glass double-clad step-index fibers with a non-circular inner cladding. For the silicate fiber, a maximum output power of 7.7 W was obtained from a 94 cm fiber. An output power of 1.25 W was also realized with a short length fiber of 8 cm, confirming the application potential of this fiber in single frequency lasers and pulsed amplifiers where an efficient rare-earth-doped fiber with short length is desirable. For the phosphate fiber, a maximum output power of 2.78 W was obtained from a single-mode fiber with a core diameter of up to 35 μm.

Heavily Yb-doped phosphate fiber with hexagonal inner cladding prepared by the stack-and-draw method

The stack-and-draw method was first used to fabricate a heavily Yb-doped phosphate glass double-clad fiber with non-circular inner cladding. An output power of 11.1 W was extracted with slope efficiency of 51.2% from the fiber with 53 cm length. In addition, we also obtained a ~2.1 W output power from a fiber with the length ~9 cm.

Experimental investigation on linewidth characteristics of a single-frequency phosphate fiber laser at 1.0 μm

We demonstrate an experimental investigation on the linewidth of a single-frequency Yb-doped phosphate fiber laser through a loss-compensated recirculating delayed self-heterodyne (LC-RDSH) method at 1.0 μm. A resolution of 3 kHz is achieved by only using a 6 km fiber delay line in the linewidth measurement system. With optimal parameters of the LC-RDSH system, more than 16 orders of beat note are detected. By analyzing the behaviors of different orders of beat note, a broadening effect on the linewidth is observed with an increasing pump strength of the under-tested fiber laser. Associated with theoretical analysis, the frequency noise incorporated with the linewidth broadening is shown to be the attribution of the Lorentzian noise. Frequency noise of the laser is also measured, to verify the observed linewidth characteristics. To the best of our knowledge, this is the first time that the LC-RDSH has been applied to the 1.0 µm window.

980 nm all-fiber NPR mode-locking Yb-doped phosphate fiber oscillator and its amplifier

We report on a 980nm all-fiber passively mode-locking Yb-doped phosphate fiber oscillator with the nonlinear polarization rotation (NPR) technique and its amplifier. In order to obtaining the stable self-starting mode-locking oscillator at 980nm, a bandpass filter with 30nm transmission bandwidth around 980nm is inserted into the cavity. The oscillator generates the average output power of 26.1mW with the repetition rate of 20.38MHz, corresponding to the single pulse energy of 1.28nJ. The pulse width is 159.48ps. The output spectrum of the pulses is centered at 977nm with a full width half maximum (FWHM) of 10nm and has the characteristic steep spectral edges of dissipative soliton. No undesired ASE and harmful oscillation around 1030nm is observed. Moreover, through two stage all-fiber-integrated amplifier by using the 980nm oscillator as seed source, an amplified output power of 205mW at 980nm and pulse duration of 178.10ps is achieved.

A facile hydrothermal method for synthesis of submillimeter-long octacalcium phosphate and hydroxyapatite as drug carriers with sustained release behaviors

A facile hydrothermal method was employed to synthesize submillimeter-long octacalcium phosphate (OCP) and hydroxyapatite (HAp) crystals as drug carriers. After hydrolysis reaction of urea, calcium phosphate fibers grew preferentially along c-axis due to modulation of crystallization by glutamic acid. With increasing addition of urea, OCP and HAp precipitated with decreased values of crystallite size and aspect ratio. It was found that the conversion of OCP to HAp was completed after hydrothermal treatment at 160°C for 6h. The formation of fibrous crystals and adsorption of water-insoluble drugs were accomplished in one-step synthesis process with presence of ibuprofen molecules. The sustained-release behavior of ibuprofen could be described by a Higuchi model. HAp and OCP fibers might be simultaneously used for high-performance reinforcements to improve mechanical properties of composite materials and sustained-release drug carriers to cure postoperative infection of bone replacement.

Short monolithic dual-wavelength single-longitudinal-mode DBR phosphate fiber laser.

We propose and demonstrate a 5-cm-long monolithic dual-wavelength single-longitudinal mode distributed Bragg reflector (DBR) all-phosphate fiber laser. Strong UV-induced fiber Bragg gratings are directly written in highly Er/Yb codoped phosphate fiber. The separation between gratings is selected as 1cm to only excite two longitudinal modes in the DBR cavity. By exploiting the spatial hole burning effect and the polarization hole burning effect, stable narrow-linewidth dual-wavelength lasing emission with 38pm wavelength spacing and a total emitted power of 2.8mW is obtained from this DBR fiber laser. A microwave signal at 4.58GHz is generated by the heterodyne detection of the dual-wavelength laser.

Phosphate Yb3+ photonic crystal fiber single-mode laser with enormous high pump absorption

We demonstrate a single-mode 6 cm long, phosphate fiber laser with maximum power of 9.0 W. Laser action output power per fiber length of 150 W m−1 was achieved and this is the highest value ever reported in a single-mode fiber laser using a phosphate glass fiber. The slope efficiency of the laser was 36.2% and lasing wavelength was 1028 nm. We used a 6% mol ytterbium-doped, air-clad photonic crystal fiber with the core of 30 µm in diameter. Estimated pump absorption in the fiber exceeded 400 dB m−1.

High-efficiency watt-level 1014 nm single-frequency laser based on short Yb-doped phosphate fiber amplifiers

High-efficiency single-frequency compact master-oscillator power amplifiers (MOPAs) based on core-pumped highly Yb-doped phosphate fibers (YPFs), several centimeters long, are investigated theoretically and experimentally. By using numerical modeling and testing different YPF lengths to optimize the amplifier configuration, a stable output of more than 1.06 W, at 1014 nm, was measured experimentally from a MOPA laser, with a 4.0 cm long YPF. An optical-to-optical conversion efficiency of 81.4%, a typical net gain of more than 20.5 dB, and an output power per unit length of up to 265 mW/cm were obtained with this laser system. The measured optical signal-to-noise ratio of the MOPA laser is higher than 62 dB and the estimated laser linewidth is less than 20 kHz, without obvious broadening or degradation after amplification. There is excellent agreement between the results of the simulations and the experiments.

Suppression of the low frequency intensity noise of a single-frequency Yb3+-doped phosphate fiber laser at 1083 nm

The suppression of the low frequency intensity noise of a 1083 nm single-frequency Yb3+-doped phosphate fiber laser is reported. The noise suppression scheme is to use a liquid crystal device as a variable attenuator to modulate the laser power to close to the desired level. The achieved long term (12 h) laser instability is less than 0.2%, while the relative intensity noise (RIN) has been decreased to lower than −140 dB Hz−1 at frequencies from 250 Hz to 1 kHz. Moreover, the laser linewidth value remains the same as before suppression, while the degree of polarization (DOP) declined slightly.

An optical amplifier having 5 cm long silica-clad erbium doped phosphate glass fiber fabricated by “core-suction” technique

We have fabricated an erbium-doped phosphate glass fiber with a silica cladding and used 5cm length of it to form an optical amplifier. A bulk erbium phosphate glass called MM2 was used as a core glass in a silica cladding tube to prepare a preform using “core-suction” technique. This MM2 glass preform was drawn to a fiber and the resultant fiber was of good optical quality, free from air bubbles and major defects. The fiber was mechanically strong enough to allow for ease of handling and could be spliced to conventional silica fiber using commercial fusion splicer. This fiber was then used to setup an EDFA. Our work demonstrates the potential to form silica clad optical fibers with phosphate cores doped with very high levels of rare-earth ions. It is demonstrated that the core suction technique can be used to make a high-gain erbium phosphate fiber amplifier that is compatible with conventional silica fibers.

All-fiber fundamentally mode-locked 12 GHz laser oscillator based on an Er/Yb-doped phosphate glass fiber

We have developed a compact and stable all-fiber fundamentally mode-locked 12GHz laser system. The passively mode-locked laser centered at 1535nm has temporal pulse width of ∼2 ps and average power of 5mW. The timing jitter, which is cumulative from pulse-to-pulse, has been measured using an optical cross-correlation method and found to be 44 fs/pulse. The self-starting, mode-locked laser consists of a semiconductor-based saturable absorber with high modulation depth and a high gain per unit length, polarization-maintaining 0.8cm long Er/Yb phosphate fiber as a gain medium.

Fracture resistance of endodontically restored, weakened incisors

To test the fracture strength of weakened bovine incisors endodontically treated with mineral trioxide aggregate (MTA), calcium phosphate bone cement (CPBC) or fibre reinforced composite (FRC) posts, and to evaluate the fracture mode. Weakened bovine incisors (n = 75), standardized according to the dentinal wall thickness at the cervical area, were randomly assigned to one control group and three experimental groups. Unfilled teeth were assigned to group 1 (n = 20) and served as control group. Group 2 (n = 17) consisted of teeth filled with MTA. In group 3 (n = 18), the incisors were filled with CPBC and in group 4 (n = 20) with FRC posts. All specimens were subjected to load at a cross-head speed of 60 mm min(-1) until fracture occurred. The initial (IL) and final fracture (FL) loads (N) were recorded, and the failure mode among the different groups was evaluated. anova showed a statistically significant difference in fracture load among the groups. Tukey's test revealed a significant difference for the IL between the control group and the experimental groups with exception of the MTA group. The FL was not significantly different among the experimental groups. A high percentage of favourable fractures was seen in the FRC and CPBC groups. FRC posts and CPBC could be promising materials to strengthen non-vital structurally compromised teeth.

High OSNR watt-level single-frequency one-stage PM-MOPA fiber laser at 1083 nm

A 1.03 W optical signal-to-noise ratio (OSNR) of > 70 dB single-frequency polarization-maintained master-oscillator power amplifier (PM-MOPA) laser at 1083 nm was demonstrated. The seed laser of this laser system was a distributed Bragg reflector short cavity Yb-doped phosphate fiber oscillator. A one-stage core-pumped amplification configuration was employed, in which the typical gain is 9.7 dB and the optical-to-optical conversion efficiency is 68.7%. The estimated laser linewidth is less than 3.5 kHz, the measured polarization-extinction ratio is greater than 25 dB, and the obtained relative intensity noise of fiber laser for frequencies of over 2 MHz is less than -130 dB/Hz.

The ASE noise of a Yb3+-doped phosphate fiber single-frequency laser at 1083 nm

A thorough investigation of the effect of amplified spontaneous emission (ASE) on the noise characteristics of a heavily Yb-doped phosphate fiber single-frequency laser at 1083 nm was made. Both the intensity noise and the frequency noise were measured and analyzed by introducing a band pass filter (BPF) into the fiber laser. For the intensity noise, it was found that the ASE noise is present at frequencies beyond the resonant relaxation oscillation (RRO) and until 6 MHz at low pump intensity, while it is diminished in the high power regime. Under a pump power of 42 mW, a maximum reduction of over 3 dB of the relative intensity noise (RIN) was observed with the help of the BPF. As for the frequency noise, a transition of the dominating noise sources from ASE noise in the low pump intensity condition to pump noise in the high pump intensity condition was observed. In the low power condition, more than 7 dB of the ASE noise was found to add to the frequency noise spectrum. It is believed that the obtained results will be helpful in understanding and optimizing the noise characteristics of this type of fiber laser.