G. Sorbello

Performance of high-concentration Er/sup 3+/-Yb/sup 3+/-codoped phosphate fiber amplifiers

Performance of high-concentration Er/sup 3+/-Yb/sup 3+/-codoped phosphate fiber amplifiers in a copumping configuration is presented. Gain, noise figure, and output signal saturation power of fiber amplifiers with different lengths are reported. From a 3.6-cm-long fiber, 18-dB internal gain, i.e., 5 dB/cm, for small signal input at 1535 nm, was achieved. To the best of our knowledge, this is the highest gain per unit length for erbium-doped fiber amplifiers ever reported.

Measurement of the energy transfer and upconversion constants in Er–Yb-doped phosphate glass

A simple method to measure the ytterbium-to-erbium energy transfer and the co-operative upconversion constants in a phosphate laser glass is proposed. The technique is based on the experimental acquisition of the luminescence decay from the Er3+ 4I13/2 metastable level at 1.5μm as a function of time and on a suitable fit of the experimental data. The fitting procedure relies on a simplified model of the Er–Yb system and makes use of a numerical solution of the rate equations to describe the dynamics of the populations, showing considerable sensitivity to the fitting parameters. The results obtained are in fairly good agreement with previous data reported in the literature.

230-mW diode-pumped single-frequency Er:Yb laser at 1.5 μm

We report on a diode-pumped Er:Yb laser able to generate a single-frequency output power in excess of 200 mW at both 1.53 /spl mu/m and 1.56 /spl mu/m and over 300 mW in multimode operation. The tuning characteristics of the source are reported and discussed. The relative intensity noise presents in all configurations a peak value lower than -92 dB/Hz and its level decreases below -160 dB/Hz for frequencies higher than 8 MHz.

Comparative study of Ag-Na thermal and field-assisted ion exchange on Er-doped phosphate glass

Abstract Silver–sodium ion-exchanged waveguides on a new erbium-doped phosphate glass have been fabricated and characterized. Thermal diffusion and field-assisted ion exchanges have been investigated and compared. A simple yet effective method to reconstruct the refractive index profile from the measured effective indexes, obtained by the m -lines spectroscopy with prism-coupling technique, has been successfully adopted. The optical parameters describing the waveguide properties, namely the refractive index variation, the diffusion coefficient and, for the field-assisted ion exchanges, the drift velocity, have been calculated and correlated with the fabrication parameters. Thermal diffusion is more reproducible while the field-assisted process provides a step-like index and better confinement by an appropriate control. Straightforward guidelines have been outlined for choosing appropriate diffusion time, temperature and melt composition to fabricate active waveguides compatible with optical fibers.

New Er-doped phosphate glass for ion-exchange active waveguides: accurate determination of the refractive index

The optical properties of a new Er-doped glass for ion-exchange active waveguides have been characterized, including fluorescence lifetime, Ag–Na diffusion coefficient, and refractive index. In particular, the Sellmeier curve was determined from the visible to the near infrared by means of a non-conventional method based on the measurement of the output angle of radiation modes propagating within the substrate. An accuracy of about 1×10−4 for the determination of the refractive index is obtained.

Cooperative upconversion in a new high Er-doped tellurite glass

A model for population dynamics of Er3+ in tellurite glasses with high erbium concentrations is proposed. Luminescence decay curves from transitions of 4I13/2 yields 4I15/2 and 4S3/2 yields 4I15/2 were measured experimentally. Cooperative upconversion coefficients were obtained by numerically solving the rate equations of the model to fit the population dynamics of the 4I13/2 and 4S3/2 levels. The cooperative upconversion coefficient for 4I13/2 + 4I9/2 yields 4I15/2 + 4I15/2 is found to be 2.74 X 10-18 cm3/s and for 4I11/2 + 4I11/2 yields 4I15/2 + 2F7/2 is 1.09 X 10-18 cm3/s. The model provides a god basis for explaining the experiment data as it shows a high sensitivity to the input fitting parameters. This model can be used to analyze spectroscopic properties of Er3+ ions in glass hosts where various energy levels of Er3+ and transitions between them cannot be neglected.

Laser action in ion-exchanged waveguides fabricated on Er-Yb-doped phosphate glasses using planar technology

Waveguide laser arrays operating at 1.5 micrometers have been fabricated on Er:Yb-doped glass substrates by a two-step silver-sodium ion-exchange process based on thermal diffusion followed by a field-assisted burial step. The fabrication parameters have been optimized to achieve low propagation losses and good mode matching between waveguide channels and standard single-mode output fibers. Each laser cavity is formed by two Bragg gratings butt-coupled to the two ends of the channel waveguide. Fiber-coupled output power in excess of 10 mW is readily available from a single channel, when pumped from both sides by two 980-nm laser diodes providing a maximum power of ~300 mW. Single-longitudinal mode operation with output power of the order of 1 mW has been achieved using narrow reflectivity band (<30 GHz) Bragg gratings with different laser configurations. The laser operating wavelength can be selected across the whole C-band of optical communications (1530-1565 nm) by changing the Bragg grating peak reflectivity wavelength. A relative intensity noise lower than -150 dB/Hz has been measured for frequencies larger than 2 MHz. Stability of single-frequency operation, low intensity noise and flexibility in the choice of the operating wavelength make this laser array particularly attractive for wavelength division multiplexing optical transmissions.

Intensity-noise suppression in a diode-pumped Tm,Ho:YAG laser

Summary form only given. Laser source amplitude stability is of great interest to improve detection sensitivity in many applications such as metrology, sensor, and optical communications. We experimentally investigate, for the first time to our knowledge, the noise characteristics of a diode-pumped single-frequency Tm,Ho:YAG laser and we report complete suppression of the relative-intensity noise (RIN) peak by means of a suitable electronic feedback circuit acting on the drive current of the pump diode.

Buried-channel active waveguide array on Er,Yb:phosphate glass by field-assisted ion-exchange technique

Summary form only given. Active waveguide arrays are of particular interest for optical network applications as laser sources and integrated amplifiers. In this paper we report on fabrication procedure and optical characterisation of an active buried-channel waveguide array fabricated on a special erbium-ytterbium-doped phosphate glass by the ion-exchange technique.

Erbium-ytterbium miniaturized laser devices for optical communications

In this work we review the most recent results obtained by our group on miniaturized diode-pumped Er-Yb:glass lasers of potential interest for optical communication applications. In single frequency operation we achieved output powers larger than 25 mW using a 200-micrometers length microchip laser and in excess of 100 mW, with a large tunability over the wavelength range between 1528 nm and 1564 nm, using a 5-mm length resonator containing an intracavity 50-micrometers thick Polarcor etalon. The Er-Yb microlaser has been locked and frequency stabilized at a level better than 1 X 10-9 to C2H2 and 13C2H2 absorption lines in the wavelength range from 1530 nm to 1550 nm, to built a narrow-linewidth absolute frequency reference in this spectral region suitable for WDM applications. A 30-dB suppression of the intensity noise peak at the relaxation oscillation frequency has been obtained and a relative intensity noise level of less than -160 dB/Hz at frequencies higher than 20 MHz is expected. In pulsed operation regime, picosecond pulse trains with repetition rate up to 10 GHz have been generated by either the FM mode-locking and a novel technique based on frequency modulation operation of the laser followed by external spectral filtering of the optical field, able to produce transform-limited single and dual-wavelength pulse trains particularly suitable for soliton transmission.