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Intense multi-peak red fluorescence and effective near-infrared (NIR) ultra-broadband emission have been observed in Pr^3+ doped ion-exchangeable aluminum germanate (NMAG) glasses. The maximum emission cross section for P_03→F_23 red emission is up to 100.58×10^−21  cm^2, and the NIR emission corresponding to D_21→G_41 transition possesses a full-width at half-maximum (FWHM) of 210 nm. Although the obvious cross-relaxation (CR) process at high concentration causes a decrease of the quantum efficiency, the CR broadens the spectral FWHM effectively from another perspective. The admirable red fluorescence trace and the NIR single-mode transmission confirm that Pr^3+ doped NMAG glass planar waveguides can support the generation of visible fluorescence and the amplification of infrared signal. For a waveguide channel ion-exchanged in molten KNO_3 for 2 h, the single-mode field diameters at 1.55 μm are identified to be 10.4 μm in the horizontal direction and 6.5 μm in the vertical direction, implying an acceptable overlap with a standard single-mode fiber. Effective red fluorescence and broad NIR emission demonstrate that Pr^3+ doped NMAG glasses are a promising substrate in developing irradiative luminescence sources and ultra-broadband waveguide amplifiers, especially operating at the entire S-, C-, and L- bands.

Photon conversion is exhibited in a borate (LKZBSB) glass system containing Eu^3+, and the enhanced characteristic emissions of Eu^3+ with the codoping of Ce^3+ have been verified. A large Judd–Ofelt intensity parameter Ω_2 of Eu^3+ indicates a high asymmetrical and strong covalent environment around rare-earth (RE) ions in LKZBSB glasses and spontaneous emission probability and a maximum emission cross section of the dominant D5_0→F_27 transition were derived to be 370  s^−1 and 1.28×10^−21  cm^2, respectively, revealing the potential UV→visible photon-conversion capacity of Eu^3+. Absolutely quantitative evaluation illustrates that Eu^3+ is a favorable photon-conversion center to achieve high photon-conversion efficiency. The addition of Ce^3+ is beneficial to realizing effective red emission of Eu^3+, which possesses commercial value by decreasing the dopant of expensive europium compounds. As an expectation, this photon-conversion LKZBSB glass system can promote the development of a photon downconversion layer for solar cells, which are particularly used in outer space with intense UV radiation.

Ho^3+-doped and Ho^3+/Yb^3+-codoped multicomponent germanium tellurite (MGT) glasses with multifarious emission channels in the near-infrared wavelength region have been fabricated and characterized. Judd–Ofelt intensity parameters of Ho^3+-doped MGT glasses are solved to be Ω_2=5.32×10^−20  cm^2, Ω_4=2.73×10^−20  cm^2, and Ω_6=1.12×10^−20  cm^2, indicating a higher asymmetric and stronger covalent environment around Ho^3+ ions in MGT glasses. Efficient infrared fluorescences have been observed in MGT glasses, and spontaneous emission probabilities are derived to be 230.4, 79.9, and 138.3  s^−1 for the I_65→I_85, (F_45,S5_2)→I_55, and I_75→I_85 radiative transitions, respectively. In Ho^3+/Yb^3+-codoped MGT glasses, the maximum stimulated emission cross-section of 2.0 μm emission is calculated to be 4.93×10^−21  cm^2, and the corresponding gain cross-section is derived to be 3.62×10^−21  cm^2 when the excited state population fraction P reaches 0.8. Multifarious infrared emissions show that Ho^3+ in MGT glasses is a good candidate for optical amplifiers and optoelectronic devices.

K^+-Na^+ ion-exchanged channel waveguide amplifiers have been fabricated in Er^3+/Yb^3+ codoped acid-resistant aluminum germanate (NMAG) glasses. The Judd-Ofelt parameters indicate high asymmetry and strong covalent environment in the glass substrates. The optical gain and the relative gain (the signal enhancement) of a 2.5 cm long waveguide amplifier were measured to be 9.10 and 8.16 dB, respectively, and after compensating both the propagation loss and the absorption loss, a maximum internal gain of ~2.0 dB at 1.534 μm was obtained, which reveals the successful employment of the thermal ion-exchange technology on the low phonon energy glasses. Based on this work, ion-exchanged Pr^3+, Tm^3+, and Ho^3+ doped NMAG glass waveguides will bring surprises in developing O-, S- and U-band waveguide amplifiers, infrared UV-writing grating waveguide lasers, and compact integrated optical devices.

Interferometric optical testing using computer-generated hologram (CGH) can give highly accurate measurement of aspheric surfaces has been proved. After the system is designed, a phase function is obtained according to the CGH's surface plane. For the requirement of accuracy, an optimization algorithm that transfers the phase function into a certain mask pattern file is presented in this letter, based on the relationship between the pattern error of CGH and the output wavefront accuracy. Then the writing machine is able to fabricate such a mask with this kind of file. With that mask, an improved procedure on fabrication of phase type CGH is also presented. Interferometric test results of an aspheric surface show that the whole test system obtains the demanded accuracy.

The crystalline phase within guiding layers of near-stoichiometric strip and planar Ti:LiNbO3 wave-guides, prepared by the method of simultaneous work of vapour transport equilibration (VTE) treatment and indiffusion of Ti film, was studied by combined confocal microscope Raman scattering and X-ray powder diffraction. The results show that the strip and planar waveguide layers still retain the LiNbO3 phase and no other non-LiNbO3 phases can be identified within the guiding layer. Li/Nb ratios inside and outside the strip and planar waveguide layers were determined from the microscope Raman scattering results and compared to those obtained from the measured optical absorption edge. It is shown that the Li/Nb ratios are homogeneous within the waveguide layer and are close inside and outside the waveguide layer. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A number of X-, Y- and Z-cut Er(/Yb):LiNbO3 crystals with six different doping levels of rare earth ions were annealed at 1110 °C for 120 h using the vapor transport equilibration (VTE) technique. At room temperature, α-polarized or unpolarized absorption spectra of these VTE-treated crystals and corresponding as-grown crystals were recorded in the wavelength range 280–1700 nm. The absorption characteristics of the VTE-treated crystals are summarized and compared with those of the as-grown crystals. The (Li+ + RE3+)/Nb5+(RE3+ = Er3+ or Er3+ + Yb3+) ratios in the VTE-treated Er(/Yb):LiNbO3 crystals were evaluated using the optical absorption edge or Raman linewidth of the 153 cm–1 E(TO) phonon. Based upon the measured spectral data, spectroscopic parameters of Er3+ ions in as-grown and VTE-treated crystals were calculated using the Judd–Ofelt (J–O) theory. The influences of Er3+ doping level, type of crystal cut and VTE treatment on the key spectroscopic parameters, including integrated absorption coefficient, oscillator strength, J–O parameters and radiative lifetimes of three dominant emission manifolds (4I13/2 (∼1530 nm), 4F9/2 (∼660 nm) and 4S3/2 (∼560 nm)), are discussed and summarized and compared with the results for as-grown crystals. The results for as-grown crystals are also compared with those reported previously. The present theoretical result concerning the VTE effect on the 1530 nm lifetime is in rough agreement with the experimental result reported previously. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A Raman scattering study was performed on ErNbO4 powder prepared by thermally calcining the mixture of 50 mol% Er2O3 and 50 mol% Nb2O5 powder at 1100 °C and 1600 °C over different durations. The scattering features are summarized and discussed. In combination with X-ray diffraction results some useful information on the preparation of the ErNbO4 powder was obtained. A simple formation mechanism for ErNbO4 powder phase was suggested on the basis of an elevated-temperature-assisted solid-state chemical reaction: Er2O3 + Nb2O5 ⇔ 2ErNbO4. A Raman study was also performed on some samples powdered from vapor-transport-equilibrated (VTE) Er(2.0 mol%):LiNbO3 crystals, in which nanocrystalline ErNbO4 was induced by the VTE procedure. A comparison of the spectra of the crystal-powdered samples with those of directly calcined powder revealed that Raman peaks observed in the calcined powder cannot be resolved in either the single crystal or the crystal-powdered sample due to the lower content of the ErNbO4 phase in the crystal. Present Raman results on powdered crystal support our earlier work on the assignment of the phonon modes in LiNbO3 crystals. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper reports some of the research work done in the Optoelectronics Research Centre of the City University of Hong Kong. In particular, three areas are discussed: waveguide devices, fibre devices and optical transmission. In the waveguide device area, we report devices such as zero-birefringence polymer waveguides, waveguide Bragg gratings, long period gratings in polymer optical waveguides, X-junction optical waveguide switches, and waveguide optical amplifiers. In the fibre device area, we report devices such as Bragg grating current sensors, long period fibre gratings, Bragg gratings in polymer single mode fibres, segmented cladding polymer optical fibres, and generation of wavelength-tunable short pulses. In optical transmission area, we discuss a communication system based on chaos generated by fibre lasers and soliton trapping within a fibre Bragg grating.

We demonstrate potassium bismuth gallate glasses as suitable hosts for rare-earth-ion erbium (Er^3+) operating in the 1.55-μm-wavelength region. The absorption and luminescence spectra along with the luminescence decay time were measured. The emission peak of the ^4I_13/2?^4I_15/2 transition is at the 1.53-μm wavelength, and the spectral bandwidth is 85 nm, which is one of the broadest. The lifetime of the ^4I_13/2 level is ∼2.42 ms, and the quantum efficiency is ∼100%. The emission cross section is estimated to be ∼12.4×10^−21 cm^2, which is one of the highest among different oxide glasses. The gain coefficient is also calculated, and our results show that potassium bismuth gallate glasses are excellent host materials for broadband-amplifier and high-power-laser applications.

Er^3+-doped and Er^3+/Yb^3+-codoped Na_2O ⋅ Ca_3Al_2Ge_3O_12 glasses that are suitable for use in optical waveguide devices have been fabricated and characterized. The density, the refractive indices, the optical absorption, the Judd–Ofelt parameters, and the spontaneous transition probabilities of the glasses have been measured and calculated. Intense 1.533-μm fluorescence was observed in these glass systems under 798- and 973-nm excitation, and the quantum efficiency was ∼100%. Efficient upconversion luminescence at 525, 547, and 659 nm at room temperature was also observed. At a pump intensity of 1220 W/cm^2 at 798 nm, frequency upconversion efficiencies of 0.98×10^−2 and 1.03×10^−2 were obtained for green and red emissions, respectively. The standardized value for green emission is higher than those reported for lead germanate, lead tellurium germanate, silicate, and phosphate glasses. Under 973-nm excitation, the enhancement of 1533-nm emission and visible upconversion fluorescence in Er^3+/Yb^3+-codoped glasses are confirmed, and the sensitizing is due to efficient energy transfer from Yb^3+ to Er^3+.

We propose and demonstrate alkali bismuth gallate glasses as suitable hosts for the rare earth praseodymium (Pr^3+) operating at 1.3-μm wavelength. The structure of the glasses was investigated by Raman spectroscopy. The optical absorption and the photoluminescence properties of Pr^3+ in these glasses were characterized. The Raman spectrum shows two strong peaks, at 134 and 381 cm^−1, and a weak peak at 660 cm^−1. The results indicate that bismuth (Bi^3+) and gallium (Ga^3+) cations do take part in the formation of the glass network. The emission from the Pr^3+:? ^1G_4 ? ^3H_5 transition is at 1.34-μm wavelength, and the spectral bandwidth is 120 nm, which is wider than those of fluoride and chalcogenide glasses. The lifetime of the ^1G_4 level is ~78 μs, and the quantum efficiency is ~17.4%, which is higher than that in fluoride glasses.

The properties of RbxK1‐xTiOPO4thin films grown on KTiOPO4substrates are reported. High quality films were obtained using the flux liquid phase epitaxy method, and optical waveguiding was observed in these epitaxial films. X‐ray analysis shows that the epitaxial films are single crystals films. Their cell constants are different from those of the substrates. The epitaxy growth rate and other film properties were compared for films grown on different faces. Two different surface morphologies were observed for films grown on (100) faces. The morphologies on (201) and (201) faces were also different. The quality of films grown on the (201) face was better. The reason for a structure inversion for films grown on the z−face is discussed.

We describe a dual-beam differential phase interferometer that performs direct phase measurement by using a rotating Ronchi grating filter. Two laser beams derived from a single source are focused onto the sample surface. The reflected light will retrace the same path and intersect at the back focus of the objective lens. Interference between the reflected rays will therefore produce intensity fringes with their spatial location governed primarily by the differential optical phase of the probes. When the fringes are projected onto a rotating grating filter with identical periodicity, the transmitted optical signal becomes an oscillating signal from which the optical phase can be measured by standard phase-sensitive techniques. This approach has the advantages of simple system configuration, effective isolation from environmental disturbance, and low-frequency operation, which permit the use of high impedance electronics with shot-noise-limited performance at low laser power.

A simple method is outlined for the calculation of the refractive-index profiles of both multimode and monomode planar optical waveguides. The method is an extension of the well-established IWKB method. The parameters required are the dispersion relation of the surface index changes and the effective indices at different wavelengths. As an example, the refractive-index profile of a monomode z-cut KTiOPO_4 planar waveguide fabricated by Rb^+:K^+ exchange is computed. Close agreement is obtained, indicating the practicality of this method. The method is also applicable to optical waveguides in other materials, such as LiNbO_3, LiTaO_3, and glass.

A simple method is outlined for the calculation of the refractive-index profiles of both multimode and monomode planar optical waveguides. The method is an extension of the well-established IWKB method. The parameters required are the dispersion relation of the surface index changes and the effective indices at different wavelengths. As an example, the refractive-index profile of a monomode z-cut KTiOPO_4 planar waveguide fabricated by Rb^+:K^+ exchange is computed. Close agreement is obtained, indicating the practicality of this method. The method is also applicable to optical waveguides in other materials, such as LiNbO_3, LiTaO_3, and glass.

A cluster model is proposed for study of the effects of the number of ions per cluster on the performance of a heavily erbium-doped fiber laser. The results indicate that both the threshold pump power and the unstable-operation region of the fiber laser increase with increasing numbers of ions per cluster.

A four-channel 400-GHz spacing flat focal field arrayed waveguide grating (AWG) demultiplexer is designed based on polymeric optical waveguide. The waveguide core-layer material is a newly developed negative tone epoxy Novolak resin (ENR) polymer with ultravoilet (UV) cured resin Norland optical adhesive 61 (NOA61) as the cladding layer. The device is fabricated using electron-beam direct writing, which has less processing steps than the reported polymeric AWGs. The experimental result is presented.

Freeform optical surfaces (FOSs) will be the best elements in the design of compact optical systems in the future. However, it is extremely difficult to measure freeform surface with sufficient accuracy, which impedes the development of the freeform surface. The design and fabrication of computer-generated hologram (CGH), which has been successfully applied to the tests for aspheric surfaces, cannot be directly adopted to test FOSs due to their non-rotational asymmetry. A novel ray tracing planning method combined with successively optimizing even and odd power coefficients of phase polynomials in turn is proposed, which can successfully design a non-rotational asymmetry CGH for the tests of FOSs with an F-θ lens. A new eight-step fabrication process is also presented aiming to solve the problem that the linewidth on the same circle of the CGH for testing freeform surface is not uniform. This problem cannot be solved in the original procedure of CGH fabrication. The test results of the step profiler show that the CGH fabricated in the new procedure meets the requirements.

The influence of the imaginary part of nonlinear coefficient on optical bistability in an A-D (Acceptor-Donor) substituted azobenzene-doped poly(methya methacrylate) (PMMA) thin film was studied theoretically and experimentally. The observations of the characteristics of the bistability were essentially consistent with the theoretical predications.