This paper summaries our effort to develop new Nd3+, Er3+ and Yb3+ doped phosphate laser glasses, which exhibit high strength and low thermal expansion coefficient as well as acceptable optical athermal behavior. Ion-exchange chemical strengthening processes and laser performances of these glasses are presented.
The optical properties and characteristics of rare earth- doped polymers have been studied to evaluate their viability for use in amplifier and laser applications. Rare earth ions are encapsulated in organic, covalent bonded chromophores. The optical properties of various rare earth chromophores doped into polymers are measured and calculated and are then used in numerical simulations of amplifiers and lasers. The result provide an estimate of their potential device performance and establish the fundamental bases for these applications in photonics. Owing to their distinct and important advantages, such as chromophore energy transfer effects, high rare earth ion concentrations, shielding of the ion from high energy vibrations of the host, enhanced optical transition moments, and controllable decay rates and branching ratios, rare earth-doped polymers are found to be promising candidates for various device applications. Numerical simulations for samarium chromophore, for example, indicate that gains about 10 dB and greater are achievable in relatively short polymer optical fiber amplifiers operating at 650 nm.
Optical transition properties of Er3+ ions in ZnCl2-KCl-BaCl2 glass were studied and were discussed on the comparison with those in the other glass systems, i.e., ZrF4-based and Ga2S3-based glasses. Judd-Ofelt analysis was performed using eight absorption bands of Er3+ in the ZnCl2-based glass. Among the Judd- Ofelt intensity parameters, the (Omega) 2 was larger than that of the ZrF4-based glass. This is probably due to the covalency of the bonds of the rare-earth and ligand ions in comparison with those of the ZrF4-based glass. Decay curves of the emission from the 4F5/2, 4F7/2, 4S3/2, and 4F9/2 levels were measured. From the lifetime data and the radiative transition probabilities calculated using the Judd-Ofelt intensity parameters, multiphonon relaxation rates are estimated for the four excited levels. The multiphonon relaxation rates of the 4F5/2, 4F7/2, and 4F9/2 were much smaller than those in the ZrF4- based and Ga2S3-based glasses. This is the consequence of the extremely low-phonon-energy property of the ZnCl2-based glass. The multiphonon relaxation rates were inversely proportional to the exponential of the energy gap between the emission and the next-lower levels (a so- called `energy-gap low') as well as the other glass systems.
Sulfide glasses based on GeGaS are stabilized by the addition of a fourth element: antimony. They show very weak crystallization upon heating as compared to standard GeGaS glass. Because of the low phonon energy inherent in sulfide glasses, the 1.3 micrometers emission of Dy3+ ions can be observed. This transition is characterized in terms of emission cross-section and quantum efficiency. Refractive indices are measured for various concentrations of cesium halides in standard GeGaS glass.
A new Er3+ doped phosphate glass exhibiting an excellent durability in both boiling water and NaNO3 molten salt was developed. Ion-exchange process of this glass was investigated by treating glass samples in a variety of salt bathes with various exposure times. Planar waveguide with one mode at 1.54 micrometers and three modes at 632.8 nm was demonstrated. Spectral properties of Er3+ in this glass were characterized by measuring absorption and emission spectra, and fluorescence lifetimes. Emission cross section of Er3+ in this glass was calculated to be 0.76 X 10-20 cm2 using McCumber theory. Our preliminary experimental results indicate this new Er3+ doped glass is an excellent material for ion-exchanged waveguide lasers and amplifiers.
The absorption spectra and fluorescence spectra of a novel Er:Yb:phosphate glass were measured, and some emission parameters including the intensity parameters, integrated cross-section, emission cross-section, spontaneous emission probability were calculated by J-O theory. Green and red upconversion luminescence were obtained when excited with 966 nm LD, the mechanism of upconversion were analyzed in detail. Laser around 1.54 micrometers were obtained with the glass, the power is 5.2 mW.
Planar devices made by ion-exchange provide efficient active or active/passive functions. Compact amplifiers with 24 dB single pass gain for a single 980 nm laser diode pumping are presented, as well as 1535 nm lasers with 27% slope efficiency.
Sol-gel-based photonic components' technology is gaining an increasing interest. This is due in part to the overall properties of the sol-gel process, and in part to the specific characteristics which concern the inclusion into a glass matrix of nonlinear and/or active compounds, thus paving the way to the development of all-optical devices. Here a brief review is presented of the progress under way in the design and development of different sol-gel glass matrices where neodymium and erbium ions have been dispersed. So far, at our knowledge, a measurement of optical gain in this class of materials is still lacking; however, optical propagation and spectroscopic properties of the newly developed materials are quite satisfactory and perspectives of realizing lasers and amplifiers before too long are good.
Characteristics of potassium ion exchanged channel waveguide amplifiers fabricated in a commercial phosphate glass with 1.65 wt% Er2O3 and 22 wt% Yb2O3 are reported. Comparison of measured small signal gain with theoretical results shows that the upconversion coefficient n the waveguides made in this glass is approximately 1.4 X 10-23 m3s-1. Theoretical investigations reveal that at 1.530 micrometers signal wavelength, 4.2 dB can be achieved in 1.0 cm long potassium ion exchanged channel waveguides when 120 mW pump power at 974 nm wavelength is used. Theoretical studies predict 42% slope efficiency with 45.5 mW threshold pump power in a 1.0 cm long potassium ion-exchanged waveguide lasers in this glass.
Highly efficient active Integrated Optical waveguides are currently deeply investigated both theoretically and experimentally in view of their optimal design and characterization. A Finite Difference approach based on the Alternate Direction Implicit technique to calculate the propagation constant and the transversal components of the modes in optical waveguides with complex refractive index is presented. Preliminary results of experimental characterization of such waveguides are reported as well.
This paper presents an overview of rare earth-doped waveguide lasers in both glass and lithium niobate (LiNbO3). The historical development of these devices together with the most recent advances in the field are described.
A soda lime silicate glass, designed for waveguide fabrication by ion-exchange, was produced by melting. Two additional glasses were prepared by doping the base glass with different percentages of Er2O3 (2% and 3% weight, respectively). Spectroscopic analysis of the glass with higher Er concentration is reported, together with preliminary results of the characterization of the waveguides produced in the base glass as well as in the doped ones by ion exchange.
An erbium-doped fiber ring laser, with a single- longitudinal-mode, operating at 1548.5 nm, has achieved traveling wave operation without the use of an optical isolator. The unidirectional operation is guaranteed by a combination of an output coupler and an external fiber Bragg grating. The laser can provide up to 19.6 mW output power. The linewidth of the laser was measured to be < 24 kHz.
Optical fiber-to-thin film optical waveguide couplers have been studied experimentally as the base for in-line fiber- optic active components. Laser active crystals have been used in a planar structure as active substrate or active core for fiber-optic active components design.
Integrated optic planar waveguides fabricated by sol-gel method by doping Neodymium (Nd3+) in glass were studied for gain properties. To our knowledge, this is the first time that a theoretical model based on atomic susceptibility (χas) is applied to the study of sol- gel based Nd-glass waveguide amplifier. Single pass amplification through these waveguides using this theory correlates well with the experimental results. As we see a strong dependence of χas in the observed gain coefficient, it is also possible to extend this theory to the case of inhomogeneously distributed Nd-atomic clusters in the gain medium. Studies on the absorption spectra of the samples showed a strong peak at λ equals 585 nm, which was used as the wavelength for pumping the waveguide. We note that a net gain of over 15 dB is achievable over a few cm's of the waveguide, assuming a homogeneous dispersion of the dopant ions in the medium. The precursors for the sol were TEOS (Tetraethyl orthosilicate) and TPOT (Titanium(IV) isopropoxide) in the ratio of 4:1 and Nd2O3 was used as the dopant. The concentration of the Nd3+ in the waveguide was 2.5 at. %. On a clean glass substrate, with typical dimensions of 2 cm x 1 cm, spincoated films comprising of multi-layers, produced a thickness of approximately 4 micrometers and a refractive index change of 0.0476 as revealed by the m-line measurements using the prism coupling technique. The samples supported two modes at λ=633 nm.
The upconversion fluophosphor codoped erbium-ytterbium was powdered into a grain diameter of near 1 micrometers . The upconversion powder was mixed with glue and addition agent. The colloid was printed on a sheet of paper forming a pattern shaped by a mask. The upconversion powder is white and the glue is transparent. As-printed pattern is too thin to see by human eyes. An intense visible pattern in green with wavelength of 542 nm has been observed at room temperature on the sheet of the paper using a GaAs infrared light emission diode as a pump source with a main wavelength of 900 nm. The fabrication process of the invisible pattern on the paper has been described in detail. The upconversion mechanism has been discussed.
New rare-earth-rich fluoroarsenate glasses are synthesized in the M2O, As2O5, BaF2, YF3 system, with M equals Na or K. The glass-forming region is remarkably large in the Na4As2O7, BaF2, YF3 system. Stable compositions with rare-earth fluoride concentration as high as 40 mol% can be synthesized. Thermal and optical properties are given for these new glasses. The behavior of neodymium ions in this new host is investigated in terms of Judd-Ofelt calculations, emission and excitation spectroscopy, and lifetime measurements as a function of temperature and concentration.
We report the fabrication, characterization and comparison of waveguides in Z-cut Erbium-doped LiNbO3, obtained by Proton Exchange, Anneal Proton Exchange and Reverse Proton Exchange (RPE). We found that even in the very low proton concentration (α-phase) waveguides, the radiative lifetime reduction, hence the fluorescence quenching, of the 4I13/2 yields 4I15/2 laser transition due to OH phonons is dramatic. At the contrary, in the RPE waveguides we measured a nearly unaffected lifetime as the ordinary polarized modes are supported by a surface layer nearly free of proton. As it is known that the ordinary polarization is largely advantageous in terms of pump absorption efficiency and relative signal amplification, such waveguides appear to be a workable solution for amplification/lasing around 1.5 μm, provided that the losses due to leakage through the index barrier can be sufficiently reduced.
Transparent oxyfluoride glass-ceramics can provide a low- phonon energy fluoride environment for active rare earth ions while maintaining the durability, formability, and mechanical strength of an oxide glass. Fluorescence from RE doped samples indicate substantial partitioning into the fluoride crystals. Eu3+ doped glasses emit only red luminescence from the 5D0, but after treatment emit blue, green, and red luminescence, indicative of a low phonon energy rare earth environment. Er3+ doped samples show broadening and flattening of the 1530 emission band upon heat treatment, making them attractive for broad band amplifiers. Cerammed Pr3+ doped samples exhibit 240 microsecond(s) 1G4 fluorescent lifetimes, which indicates a 1310 nm quantum efficiency of 8%. It was determined that active rare earth partitioning into the LaF3 nanocrystallites that form upon heat treatment are responsible for the novel optical properties of these hybrid materials.