Laura Agazzi

Gain bandwidth of 80 nm and 2 dB/cm peak gain in Al2O3:Er3+ optical amplifiers on silicon

Erbium-doped aluminum oxide integrated optical amplifiers were fabricated on silicon substrates, and their characteristics were investigated for Er concentrations ranging from 0.27 to 4.2×1020 cm−3. Background losses below 0.3 dB/cm at 1320 nm were measured. For optimum Er concentrations in the range of 1 to 2×1020 cm−3, an internal net gain was obtained over a wavelength range of 80 nm(1500-1580 nm), and a peak gain of 2.0 dB/cm was measured at 1533 nm. The broadband and high peak gain are attributed to an optimized fabrication process, improved waveguide design, and pumping at 977 nm as opposed to 1480 nm. In a 5.4-cm-long amplifier, a total internal net gain of up to 9.3 dB was measured. By use of a rate-equation model, an internal net gain of 33 dB at the 1533 nm gain peak and more than 20 dB for all wavelengths within the telecom C-band (1525-1565 nm) are predicted for a launched signal power of 1 μW when launching 100 mW of pump power into a 24-cm-long amplifier. The high optical gain demonstrates that Al2O3:Er3+ is a competitive technology for active integrated optics.

Ultra-narrow-linewidth, single-frequency distributed feedback waveguide laser in Al2O3:Er3+ on silicon.

We report the realization and performance of a distributed feedback channel waveguide laser in erbium-doped aluminum oxide on a standard thermally oxidized silicon substrate. The diode-pumped continuous-wave laser demonstrated a threshold of 2.2 mW absorbed pump power and a maximum output power of more than 3 mW with a slope efficiency of 41.3% versus absorbed pump power. Single-longitudinal-mode and single-polarization operation was achieved with an emission linewidth of 1.70+/-0.58 kHz (corresponding to a Q factor of 1.14 x 10(11)), which was centered at a wavelength of 1545.2 nm.

Monolithic integration of erbium-doped amplifiers with silicon-on-insulator waveguides.

Monolithic integration of Al2O3:Er3+ amplifier technology with passive silicon-on-insulator waveguides is demonstrated. A signal enhancement of >7 dB at 1533 nm wavelength is obtained. The straightforward wafer-scale fabrication process, which includes reactive co-sputtering and subsequent reactive ion etching, allows for parallel integration of multiple amplifier and laser sections with silicon or other photonic circuits on a chip.

Integrated

Integrated Al(2)O(3):Er(3+) channel waveguide ring lasers were realized on thermally oxidized silicon substrates. High pump power coupling into and low laser output power coupling from the ring is achieved in a straightforward design. Output powers of up to 9.5 microW and slope efficiencies of up to 0.11% were measured while lasing was observed for a threshold diode-pump power as low as 6.4 mW for ring lasers with cavity lengths varying from 2.0 to 5.5 cm. Wavelength selection in the range 1530-1557 nm was demonstrated by varying the length of the output coupler from the ring.

Al_2O_3:Er^{3+}

A spectroscopic study of the population mechanisms in erbium-doped amorphous aluminum oxide up to the 2H11/2/4S3/2 levels is performed. Via luminescence decay measurements, absorption and emission spectra, and a Judd-Ofelt analysis we determine luminescence lifetimes, radiative and non-radiative decay-rate constants, and branching ratios of the Er3+ inter-manifold transitions. With a continuous-wave pump-probe technique the excited-state absorption (ESA) spectrum is recorded between 900 and 1800 nm and the cross-sections of the ESA transitions 4I13/2 -> 4I9/2, 4I13/2 -> 4F9/2, and 4I11/2 -> 4F7/2 are determined. The microparameters and efficiencies of resonant and phonon-assisted energy-migration and energy-transfer-upconversion (ETU) processes among Er3+ ions occurring from the first and second excited states are evaluated. From the ratio of the 4S3/2 and 4F9/2 luminescence intensities as a function of Er3+ concentration we prove the existence and quantify the macroscopic ETU coefficient of the two-phonon-assisted ETU process (4I13/2, 4I11/2) -> (4I15/2, 4F9/2).

ring lasers on silicon with wide wavelength selectivity

Measurement of the laser relaxation-oscillation frequency as a function of pump rate allows one to determine parameters of the laser medium or cavity. We show that luminescence quenching of a fraction of the rare-earth ions in a solid-state laser affects the relaxation oscillations, resulting in incorrect values for the parameter deduced from this measurement. In the equations describing the relaxation oscillations, we replace the lifetime of the upper laser level by an effective lifetime that takes the luminescence quenching into account. In an Al2O3:Yb3+ distributed-feedback laser we observe significant quenching, with the effective lifetime being ~18 times shorter than the intrinsic upper-laser-level lifetime.

Spectroscopy of upper energy levels in an Er 3+ -doped amorphous oxide

150 dB/cm gain over 55 nm wavelength range between 977-1032 nm is obtained in a 47.5% Yb-doped potassium double tungstate waveguide amplifier. The dependence of luminescence lifetime and gain on Yb concentration is investigated.

Impact of luminescence quenching on relaxation-oscillation frequency in solid-state lasers

Optical grating cavities in Al2O3 channel waveguides were successfully defined by focused ion beam milling and laser interference lithography. Both methods are shown to be suitable for realizing resonant structures for on-chip waveguide lasers.

150 dB/cm gain over 55 nm wavelength range near 1 μm in an Yb-doped waveguide amplifier

Integrated Al 2 O 3 :Er3+ ring lasers were realized on thermally oxidized silicon substrates. By varying the degree of output coupling from the ring, wavelength selection in the range 1530–1557 nm was demonstrated.

Characterization of Bragg gratings in Al 2 O 3 waveguides fabricated by focused ion beam milling and laser interference lithography

Energy-transfer upconversion (ETU) is a detrimental effect in many rare-earth-ion-doped infrared amplifiers and lasers [1], among them Er³⁺-doped waveguide amplifiers [2]. Er³⁺ concentrations in the order of 10²⁰ cm⁻³ are usually necessary to attain high gain values on the centimeter length scale of an integrated optical device. At such high Er³⁺ doping, electric dipole-dipole interactions between neighboring ions such as energy migration and ETU take place, thereby reducing the population inversion and negatively affecting the gain performance of the amplifier. We investigated these effects by lifetime and gain measurements, see Figs. 1 (a) and (c), respectively, in Al<inf>2</inf>O<inf>3</inf>:Er³⁺ waveguides and analyzed the results in the frame of the microscopic model developed by Zubenko et al. [3]. The luminescent decay from the ⁴I<inf>13/2</inf> first excited level of Er³⁺ can be described by the equation in a given equation is the error function, n(t = 0) = n(0) is the initial excitation density of the ⁴I<inf>13/2</inf> level, τ<inf>D</inf> is its intrinsic lifetime, C<inf>DA</inf> is the microparameter of ETU from the ⁴I<inf>13/2</inf> level, and τ<inf>0</inf> is the mean time of a migration hop. By fitting the experimental decay curves measured in samples with 7 different Er³⁺ concentrations, out of which only 4 are shown in Fig. 1 (a) for simplicity, we find τD = 7.6 ms and C<inf>DA</inf> = (6.1±0.6)×10⁻⁴¹ cm⁶/s, while τ<inf>0</inf> decreases from 65 ms down to 1 ms with increasing Er³⁺ concentration, see Fig. 1(b). This behavior is due to decreasing distance among Er³⁺ ions with increasing concentration, which enhances the probability of the energy-migration process.