The combination of microstructured fiber designs and improving preform fabrication techniques is allowing rapid progress in the development of new classes of non-silica fibers. Recent progress in the fabrication of soft glass and polymer microstructured preforms and fibers will be described. Emerging soft glass fibers are enabling new fiber operating regimes including efficient supercontinuum generation and extreme nonlinearity, and recent results in will be reviewed.

Optical waveguides have been formed by proton implantation in Nd:YVO₄ crystals using energies from 0.4 to 1 MeV and doses of the order of 1×10¹⁶ ions/cm². Double implants were realized to generate wide optical barriers and a triple implant produced stacked waveguides. Waveguide characterization comprises propagation modes, refractive index profiles, near field imaging and spectroscopic properties. Differences between the waveguides were found in terms of mode confinement which is important for integrated devices.

Er³⁺-Tm³⁺ co-doped tellurite photonic crystal fiber was fabricated via a stack-and-draw procedure and without using extrusion in any stage. The final fiber presents a 187 nm bandwidth of amplified spontaneous emission (ASE) intensity around 1550nm when pumped with 790nm. In this manuscript a soft-glass tube fabrication technique, using the centrifugation method, is also shown.

An ultra-thin optical polarizing film using oblique metal island (OMI) film has been investigated theoretically. The polarizing film consists of a periodic multilayer of the OMI layers and glass layers. The OMI films are composed of prolate metal nanoclusters (I.E., islands) inclining to one side. The MOI films exhibit resonance-type absportion in visible and bear-infrared region and large optical anisotropy as the resonance wavelengths for the polarization along the shorter and longer axes of the prolate metal nanoclusters are different from each other. Therefore, the multilayer using the OMI films can be used as an optical polarizing film at the resonance wavelength. The resonance wavelength depends on the aspect ratio of the prolate islands, distance between the centers of the islands, and choice of the metal. The extinction ratio and insertion loss increase with the number of the OMI layer. In this paper we show the theoretical characteristics of the polarizing films composed of the OMI layers with idea and homogeneous film structure. We have successfully designed the optical polarizing film for the wavelength of 720 nm by choosing silver as metal. The extinction ration and insertion loss of the designed polarizing film are evaluated as 30 dB and 0.03 dB, respectively. The thickness of the polarizing film is calculated as 1800 nm. When aluminum is used as the metal, the polarizing films for the shorter wavelength can be designed.

We report a powerful interferometric measurement technique utilizing Spectral Interferometry using Minimum-phase Based Algorithms (SIMBA) to fully characterize the spectrum (either in reflection or transmission) of any fiber Bragg grating (FBG). This complex spectrum information is crucial to recover several important parameters of an FBG, such as its impulse response or refractive index profile. The core of our approach involves sending an unknown short laser pulse, e.g., ~1-50 ps of temporal width, into the FBG of interest, and using an optical spectrum analyzer (OSA) to record the spectrum of the interference between the reflected pulse from the grating and the time-delayed replicas of the original pulse. This measured spectrum, which yields the square of the Fourier transform (FT) magnitude of the pulse sequence's electric field envelope, is then processed to uniquely recover both the phase and amplitude of the FBG spectrum. The underlying principle of our approach is that by design of the experimental set-up, the pulse sequence sent to the OSA is close to a minimum phase function (MPF). Thus, it is possible to recover its FT phase spectrum using only the knowledge of its FT magnitude spectrum. This is an important result since by merely measuring an FT magnitude, with a rather simple set-up the full complex spectrum of the grating can be recovered. This technique has significant advantages over existing techniques, including a higher resolution, a better noise performance, and the ability to use longer laser pulses. It can also conveniently be used to simultaneously characterize more than one FBG, with a single FT magnitude measurement. We demonstrate the validity of our approach with numerical simulations.

We present an application of fiber Bragg gratings as tunable optical delays in transmission for use as true-time-delay line in a RF-Photonic phased array antenna. Most delay line applications using fiber gratings require that they be used in reflection mode and they can provide only discrete variation of time delay. It also requires the use of bulky and expensive optical circulators. We have designed an optical true time delay array generator using fiber gratings in cascading transmission mode for such applications which significantly simplified the system and lowered the cost. A wavelength tunable laser is used as the light source. The laser light is modulated by an RF-microwave input signal, then enters into the optical true time delay array generator to provide a sequence of time delays Δt, 2Δt,...nΔt. The goal is to obtain large group delay Δt with low loss and with the capability of tuning Δt continuously by varying the wavelength of the laser. We combined an apodized grating profile, large index step and increased grating length to achieve our goal. We fabricated and tested the grating with about 100mm length which showed at least Δt=60 ps tunable time delay range. We have demonstrated the applicability of the transmission-mode fiber Bragg gratings in an optical true-time-delay type of phased array antenna.

Er-doped waveguide amplifiers (EDWA) require high doping levels due to their length limit of a few to tens of cm, making the host selection of great importance to avoid deleterious high concentration effects. The wet thermal oxides of InAlP (lattice matched to GaAs) are phosphate rich, making them an attractive rare earth host for EDWAs where monolithic integration of pump lasers may be possible. InAlP epilayers are partially oxidized in water vapor (4 h, 500°C). Er-implantation (300 keV, 10¹⁵ cm^-2 total dose) performed either before or after growth of the 300 nm thick oxide results in a peak Er concentration of ~10²⁰ cm^-3. Room temperature photoluminescence (PL) characterization shows broad (61 nm FWHM) emission with a long 8 ms lifetime. We present a comparison of PL characteristics of Er-doped InAlP and AlGaAs native oxides, and results of rapid thermal processor (RTP) annealing studies for host optimization. At 683°C, the 3 sec optimal annealing time for post-oxidation-implanted samples is notably shorter than that of the preoxidation-implanted samples (20 sec), indicating less thermal energy is required for Er. A spectral line shape change is also observed for the post-oxidation-implanted samples when over-annealed, indicating a host phase change and local environment change for Er ions. For both post- and pre-oxidation-implanted samples, PL lifetimes remain near 8 ms after RTP annealing over the entire temperature range of 500°C to 800°C, indicating minimal Er clustering and suggesting that even higher Er concentrations, desirable for increased EDWA gain, are possible.

In this paper, we present results concerning the fabrication and characterization of glass-ceramics based on chalcohalide for application as laser host materials. The objective is to develop a highly efficient host material for rare-earth doping. The studied system is Ga-Ge-S-CsCl with Er³⁺ ions as doping elements. Glass-ceramics have been prepared by thermal treatment of the base glass. The evolution of the optical transmission versus annealing time and temperature has been investigated. Preliminary up-conversion measurement of Er³⁺ were performed. Glass ceramics show higher luminescence efficiency as compared to the base glass. Nano-crystalline phases have been generated in well-controlled experimental conditions, so that crystals with reproducible size smaller than 50 nm could be achieved.

The radiative transition in Tm³⁺-doped fibre at 1.47 μm (³H₄ → ³F₄) remains a potential route for designing efficient fibre and waveguide amplifiers for the S-band (1420-1520 nm). The transition however suffers from a long metastable lifetime (5 times longer) than the ³H₄ level, which means that the ³F₄ level must be depopulated rapidly for efficient inversion for laser and amplifiers applications. One of the known means so far for depopulation of the lower ³F₄ level is via co-doping with other rare-earth ions, essential for modest gain. For the Tm³⁺ - Ho³⁺ and Tm³⁺ - Tb³⁺ doped tellurite glasses, the IR static and time-resolve fluorescence spectra and the lifetimes of the upper ³H₄ and lower ³F₄ lasing levels for 1.47 μm of Tm³⁺ were measured. The energy transfer rate and non-radiative transfer efficiency between donors and acceptors are compared. The quenching mechanism has been explained. Both the Ho³⁺and Tb³⁺ ions reduce the lifetimes of the upper and lower lasing levels, with Tb³⁺ ions proving more effective than the effects observed for Ho³⁺ ions.

In this work we present a detailed analysis of the room temperature infrared to visible upconversion in Nd³⁺-doped KPb₂Br₅ crystal by using both steady-state and time-resolved luminescence spectroscopy. The study includes one photon absorption and emission spectroscopy and lifetime measurements for the visible and infrared fluorescence, and infrared to, blue, green, orange, and red upconversion processes. The possible upconversion mechanisms are discussed in terms of excitation spectra, excitation power dependence, and lifetimes of the upconversion emissions.

Poly(vinylidenefluoride) film (PVDF) doped with Eu(III)(NO₃)₃(o-Phenanthroline)₂ complex (complex A) was manufactured using an extrusion technique. Emission spectrum of the film was compared to spectra of the dopant and polyethylene based film. Stretching the film resulted in a sharp growth of intensity and reshaping of the luminescence spectrum. The impact of the PVDF matrix on the photoluminescence spectra of complex A is attributed to the Stark effect. Reasons for the increase of luminescence intensity are discussed. Quantum chemical calculations revealed a marked longwave shift of the lowest triplet and singlet energy levels of complex A compared to free phenanthroline. The amplification and frequency shifting of the luminescent spectrum of europium-complex-doped PVDF may lead to promising applications.

Fiber lasers offer substantial advantages compared to conventional solid-state lasers due to their high efficiency, compact size, diffraction-limited beam quality, tunability, and facile thermal management. A number of important applications require high peak powers and pulse energies, which has generated great interest in Yb-doped, large-modearea (LMA) fibers. Liekki has pioneered a new manufacturing technology for rare-earth-doped fibers, Direct Nanoparticle Deposition (DND), that is capable of producing fibers uniquely well suited to power scaling. Conventional fiber fabrication methods are characterized by poor process accuracy and flexibility due to the large particle sizes and relatively small number of deposition layers (2-10). In contrast, DND provides independent control of the composition of hundreds of layers that make up the core, thereby allowing previously unattainable precision, accuracy, and uniformity in the index and rare-earth-dopant profiles. DND allows the simultaneous use of both gasphase and liquid precursors, providing unprecedented flexibility in the glass composition. Furthermore, DND enables fabrication of fibers with extremely high rare-earth concentrations, which minimizes the required fiber length and correspondingly raises the threshold power for nonlinear processes. Finally, the single-step, direct-deposition process makes manufacturing of fibers rapid and cost-effective, even for fibers with large core diameters or sophisticated geometries and dopant distributions. DND fibers have shown high conversion efficiency (low clustering), low photodarkening, and high damage threshold. DND thus promises to revolutionize the use of fiber lasers in applications previously restricted to bulk, solid-state lasers and to enable new applications of high-power lasers.

A novel all-optical regeneration approach based on fiber-optic parametric amplification operating under the strong pump depletion regime is numerically demonstrated. The key point for the regenerator's operation is related to the fact that a high-power intensity modulated signal depletes the continuous wave pump in such a manner that the latter becomes intensity modulated and inverted compared to the signal. Using a cascade of two such devices a non-inverted, either wavelength converted or not, amplitude modulated output, which exhibits regenerative characteristics with respect to the input signal can be provided. Extended numerical simulations have been carried out on one hand to estimate the transfer characteristics of the regenerator and on the other hand to assess the cascadability performance on a typical 40Gb/s transmission system. Through the latter analysis very promising results have been derived proving the potential of the proposed device for all-optical regeneration in cascaded operation for both return to zero and non-return to zero data transmitted along 1Mm of optical fiber at 40Gb/s.

We report the results of emission and amplification in Tm³⁺- and Er³⁺-fibres for signal gain in the 1420 nm to 1600 nm wavelength range, which covers S-, C- and L-bands of silica fibre optical communication networks. The paper explains the mechanism for alleviating the pump excited state absorption (ESA) in Er-doped tellurite fibres for maximizing the pump inversion efficiency at 980 nm using the Ce-ions as a co-dopant and via the structural modification of TeO₂ glass using B₂O₃. The spectroscopic data and gain bandwidth of Er-doped fibres are reported in the C- and L-bands. Methods for enhancing gain in the S-band using the co-dopants (Tb³⁺, Yb³⁺) with 800 nm and 980 nm pumping schemes are also explained. The measured maximum relative gain in short fibres of 5 to 10 cm in length in C- and L-bands are: 30 dB and 15 dB, respectively. By comparison the internal gain in a 20 cm long Tm/Yb ion co-doped fibre pumped with a 980 nm source was 7 dB.

We report on the design, fabrication and performance of high-power and high-modulation-speed 1060-nm DBR lasers for green-light emission by second harmonic generation. Single-spatial-mode and single-wavelength power more than 450 mW of 1060-nm wavelength was achieved with a 3-section DBR laser with non-absorbing DBR and phase sections created by an impurity-free quantum-well intermixing technique. A thermally-induced wavelength tuning of 2.4 nm and a carrier-induced wavelength tuning of -0.85 nm were obtained by injecting current into the DBR section. The green power as high as 104.6 mW was demonstrated by coupling the DBR laser output to a second-harmonic-generation waveguide. Measured rise/fall times of 0.2 ns for direct intensity modulation and 0.6 ns for wavelength modulation make the DBR lasers suitable for >=50-MHz green-light-modulation applications. The detrimental thermally-induced patterning effect and a differential-phase modulation scheme as a solution are discussed.

Optical switches based on the electro-optic effect in III-Vs such as GaAs have fast optical switching times, typically shorter than 1 ns, and thus are promising candidates for a wide variety of optical network applications ranging from fault restoration and network configuration to optical packet switching. A Mach-Zehnder interferometer (MZI) is often used to implement a 2x2 electo-optic switch in which two identical multi-mode interference (MMI) couplers connected by two identical parallel single mode waveguides (two MZI arms) with electrodes allowing to vary the phase difference between the two MZI arms based on the electro-optic effect. In this paper, we report the design, fabrication, and test of MMI couplers and 2x2 MZI-MMI optical switches based on these couplers. The waveguide structure has 5 undoped GaAs-GaAlAs layers with a 1.7um-thick core layer. In both simulation and fabrication, various values of MMI width, MMI length, and waveguide width have been considered. Both simulation and experimental results have indicated that the device performance is most sensitive to the MMI width and is less sensitive to the MMI length. From simulation and experimental results, optimized structures have been obtained for 2x2 MZI-MMI optical switches. Devices based on the optimized structure have been fabricated without electrodes. The fabricated MZI-MMI optical switches have shown very promising switching properties such as low insertion loss and low cross-talk. The propagation loss of straight waveguides is typically around 0.3 dB/cm. There is almost no measurable additional loss due to the MMI couplers. A cross-talk of - 22 dB has been achieved.

Wavelength conversion with high contrast ratio and low OSNR penalty has been achieved by using a resonant vertical-cavity all-optical switch based on saturable absorption in multiple-quantum-wells. The device was grown by MBE on InP substrate. It comprised a 19.5 pairs n⁺-Ga_0.47In_0.53As/InP bottom DBR, 28 Ga_0.47In_0.53As QWs, and a 50% reflective top dielectric mirror. We carried out conversion experiments between a wavelength-tunable modulated pump signal and a CW beam with a wavelength matching the Fabry-Perot resonance of the switch. Using a 622 Mb/s modulated pump with an average power of only 6-dBm we have demonstrated a 15 dB extinction ratio for the converted signal. The wavelength conversion process exhibited a weak dependence on the pump signal wavelength; we have achieved wavelength conversion in a range of 20 nm. BER/OSNR measurements on the wavelength converted data signal indicated a maximum OSNR penalty (at a BER=10^-9) of about 2.5 dB, with respect to the input pump data, over the entire conversion range. Error free operation was observed up to 2 Gb/s when device performance degraded due to its long absorption recovery time. However, with further optimization, the device recovery time could be reduced to the picosecond range, extending its application to much higher date rates.

In this report we investigate the optical properties and energy-transfer upconversion luminescence of Ho³⁺- and Tb³⁺/Yb³⁺-codoped PbGeO₃-PbF₂-CdF₂ glass-ceramic under infrared excitation. In Ho³⁺/Yb³⁺-codoped sample, green (545 nm), red(652 nm), and near-infrared(754 nm) upconversion luminescence corresponding to the ⁴S₂(⁵F₄) → ⁵I₈, ⁵F₅ → ⁵I₈, and ⁴S2(⁵F₄) → ⁵I₇, respectively, was readly observed. Blue (490 nm) signals assigned to the ⁵F_2,3 → ⁵I₈ transition was also detected. In the Tb³⁺/Yb³⁺ system, bright UV-visible emission around 384, 415, 438, 473-490, 545, 587, and 623 nm, identified as due to the ⁵D₃(⁵G₆) → ⁷F_J(J=6,5,4) and ⁵D₄→⁷F_J(J=6,5,4,3) transitions, was measured. The comparison of the upconversion process in glass ceramic and its glassy precursor revealed that the former samples present much higher upconversion efficiencies. The dependence of the upconversion emission upon pump power, and doping contents was also examined. The results indicate that successive energy-transfer between ytterbium and holmium ions and cooperative energy-transfer between ytterbium and terbium ions followed by excited-state absorption are the dominant upconversion excitation mechanisms herein involved. The viability of using the samples for three-dimensional solid-state color displays is also discussed.

Few years ago, the inverse linear polarizing method (ILPM) has been suggested as an effective measurement method for the residual stress of optical fibers by Y. Park et al. and it has been used as an important tool to study photoelastic and birefringent characteristics of optical fibers. Non-elastic frozen-in residual stress was only recently found to be an important draw-induced inelastic strain that can significantly perturb the refractive index profile and hence the waveguiding properties of optical fibers. We have investigated residual stress distributions of optical fibers drawn at various draw tensions along the distance from the cleaved fiber end by using the ILPM. From the measurement of residual stress distributions and the definition of the mean axial stress, we calculated non-elastic frozen-in residual stress of optical fibers drawn at various draw tension. By the calculation of non-elastic frozen-in residual stress distributions of optical fibers, we have found that non-elastic frozen-in residual stress in the optical fiber can be released near the cleaved fiber end and release degree of non-elastic frozen-in residual stress near the cleaved fiber end is proportional to draw tension applied on the optical fiber fabrication. We have also found that non-elastic frozen-in residual stress along the cleaved fiber end becomes restored and restoration tendency of non-elastic frozen-in residual stress from the cleaved fiber end is dependent on draw tension applied on the optical fiber fabrication.

Optical fibers are composed of the core and the cladding that are covered by the polymer coating to protect them from subsequent handling damage. Sometimes, this polymer coating, however, should be removed to fabricate optical devices involving the optical fiber such as Bragg gratings, optical couplers, optical sensors and optical connectors. In general, the mechanical stripper is used to remove this polymer coating. In this case, the mechanical stripper may cause mechanical defects on the surface of the optical fiber and also, mechanical defects make the optical fiber weak. We have researched relationship between these mechanical defects and the residual stress gradient in the optical fiber. We have made a mechanical defect on the surface of a single mode fiber with a mechanical blade and measured the residual stress distribution along the axial direction of the optical fiber. From this research, we have observed that at the position with the mechanical defect, the residual stress in the core was converted to the compressive residual stress (about 15MPa) and the residual stress in the cladding was converted to the tensile residual stress (about 7MPa). We have demonstrated that the mechanical defect on the fiber surface can cause the gradient of the residual stress distributions in the optical fiber and also, measurement of the residual stress distribution in the optical fiber can be used as a tool to find out the mechanical defects on the optical fiber.

Thermal Lens (TL) and spectroscopic characterizations were performed in 70TeO₂-19WO₃-7Na₂O-4Nb₂O₅ (mol%) tellurite glasses. TL measurements were accomplished in Er³⁺ /Tm³⁺ co-doped tellurite glasses in function of the Tm₂O₃ concentration (0.4-1.6 x10²⁰ ions/cm³). Fluorescence spectra at 488 nm showed that Er³⁺ /Tm³⁺ co-doped tellurite glasses present several emission bands between (500-1800) nm. However, the more intense emission bands correspond to the Tm³⁺ and Tm³⁺ transitions (⁴I_13/2 → ⁴I_15/2 and ³F₄ → ³H₆), respectively. The absolute nonradiative quantum efficiency (φ) was determined by TL method. Higher values of φ were obtained with the increase of Tm₂O₃ concentration inside of the Er³⁺/Tm³⁺ co-doped tellurite glasses. These results are corroborated by the Judd-Ofelt calculations.

Temperature dependences of optical path length (dS/dT; calculated using the equation, dS/dT = dn/dT + na, where a is coefficient of thermal expansion, n is refractive index and dn/dT is temperature coefficient of refractive index) in various oxide glasses were investigated. The dS/dT is generally difficult to adjust by change of glass composition because dn/dT and a are interrelated. However, low dS/dT materials are desired for optical applications such as athermal devices, and high dS/dT materials can be used for thermo-optic devices. Pure silica glass is well-known as a typical low dS/dT material but still not sufficient. Fluorine-doped silica glass showed a lower dS/dT than that of pure silica glass. By fluorine-doping in silica glass, refractive index and dn/dT decreased but a near room temperature stayed at the same level. As a result, the dS/dT decreased with increasing fluorine concentration. On the other hand, bismuthate glass showed the highest dS/dT in this study. Most glasses having high a such as tellurite glass showed negative dn/dT. However, bismuthate glasses showed positive dn/dT in spite of high a. As a result, bismuthate glasses showed quite high dS/dT. These results indicate that dS/dT of the glass can be controllable and that fluorine doped silica glass and bismuthate glass are appropriate candidate materials for optical applications.

This work reports the fabrication of planar and channel waveguides by Ag⁺ → Na⁺ ion exchange in an Er³⁺ doped tellurite glass with a composition of 75TeO₂-2GeO₂-10Na₂O-12ZnO-1Er₂O₃ (mol %). The glass was chemically stable during the ion-exchange process. We have been able to produce single and multi-mode planar waveguides controlling the depths of the waveguides by varying ion-exchange temperatures, from 250 to 280 °C, and times, from 3 to 12 h. We also show preliminary results of channel waveguide fabrication with the same technique. The waveguide effective refractive index curves and attenuation (11 dB/cm) at 1536 nm were measured with a Metricom prism coupler. The Amplified Spontaneous Emission (ASE) spectra showed a 152 nm bandwidth when pumped with 120 mW laser pump at 980 nm.

In this work we used a Thermal Mechanic Analysis equipment to produce the channel FOG waveguides by pressing an Er³⁺ doped tellurite glass optical fiber against one Er³⁺ ion doped tellurite glass substrate kept under T_c ± 30 ^oC (T_c = soft point). The luminescence and waveguide refractive index were measured. Scanning electron microscopy was used to observe the obtained structure. The objective is to produce a new concept in components of integrated optical circuits. Then this work report the production of Er³⁺-doped tellurite glass channel waveguides using the novel concept of Benson et al^[1] of fiber on glass (FOG). To succeed with this technique it is important to correlate the main thermo-physical characteristics of the substrate and the fiber, which are the transition temperature T_g, the temperature of the onset of crystallization T_x, the maximum crystallization temperature T_c and the thermal expansion coefficient. The T_g, T_x and T_c values were determined by Differential Thermal Analysis (DTA), while the thermal expansion coefficient was determined by Thermal Mechanical Analysis (TMA). For the FOG purpose the thermal stability range, T_x - T_g, is an important temperature region which defines if the glass will have enough viscosity to shape in the FOG concept.