The optical amplifier performance of Nd3+-doped polymer and amorphous Al2O3 channel waveguides with single-mode and multi-mode behavior around 880 nm is compared. Internal net gain in the wavelength range 865-930 nm is
investigated under continuous-wave excitation near 800 nm, for Nd3+ dopant concentrations typically in the range of 0.6-
1.0 × 1020 cm-3. A peak gain of 2.8 dB at 873 nm is obtained in a 1.9-cm-long polymer waveguide at a launched pump
power of 25 mW. The small-signal gain measured in a 1-cm-long sample is 2.0 dB/cm. In Al2O3, a peak gain of 1.57
dB/cm in a short and 3.0 dB in a 4.1-cm-long waveguide is obtained at 880 nm. Tapered multi-mode Nd3+-doped
amplifiers are embedded into an optical backplane and a maximum 0.21 dB net gain is demonstrated in a structure
consisting of an Al2O3:Nd3+ amplifier placed between two passive polymer waveguides on an optical backplane. The
gain can be further enhanced by increasing the pump power and improving the waveguide geometry, and the wavelength
of amplification can be adjusted by doping other rare-earth ions.
Erbium-doped aluminum oxide channel waveguides 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, 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. Integrated
Al2O3:Er3+ channel waveguide ring lasers were realized based on such waveguides. Output powers of up to 9.5 μW and
slope efficiencies of up to 0.11 % were measured. Lasing was observed for a threshold diode-pump power as low as 6.4
mW. Wavelength selection in the range 1530 to 1557 nm was demonstrated by varying the length of the output coupler
from the ring.
Amorphous Al2O3 is a promising host material for active integrated optical applications such as tunable rare-earth-ion-doped
laser and amplifier devices. The fabrication of slab and channel waveguides has been investigated and optimized
by exploiting reactive co-sputtering and ICP reactive ion etching, respectively. The Al2O3 layers are grown reliably and
reproducibly on thermally oxidized Si-wafers at deposition rates of 2-4 nm/min. Optical loss of as-deposited planar
waveguides as low as 0.11±0.05 dB/cm at 1.5-μm wavelength has been demonstrated. The channel waveguide
fabrication is based on BCl3/HBr chemistry in combination with standard photoresist and lithography processes. Upon
process optimization channel waveguides with up to 600-nm etch depth, smooth side walls and optical losses as low as
0.21±0.05 dB/cm have been realized. Rare-earth-ion doping has been investigated by co-sputtering from a metallic Er
target during Al2O3 layer growth. At the relevant dopant levels (~1020 cm-3) lifetimes of the 4I13/2 level as high as 7 ms
have been measured. Gain measurements have been carried out over 6.4-cm propagation length in a 700-nm-thick Er-doped
Al2O3 waveguide. Net optical gain has been obtained over a 35-nm-wide wavelength range (1525-1560 nm) with
a maximum of 4.9 dB.
Reactively co-sputtered amorphous Al2O3 waveguide layers with low propagation losses have been deposited. In order to define channel waveguides in such Al2O3 films, the etching behaviour of Al2O3 has been investigated using an inductively coupled reactive ion etch system. The etch rate of Al2O3 and possible mask materials was studied by applying various common process gases and combinations of these gases, including CF4/O2, BCl3, BCl3/HBr and Cl2.
Based on a comparison of the etch rates and patterning feasibility of the different mask materials, a BCl3/HBr plasma and
and standard resist mask were used to fabricate channel waveguide structures. The etched structures exhibit straight
sidewalls with minimal roughness and etch depths of up to 530 nm, sufficient for defining waveguides with strong
optical confinement and low bending losses. Low additional propagation losses were measured in single-mode Al2O3 ridge waveguides defined using the developed etch process. In initial investigations, Al2O3:Er layers fabricated using the same deposition method applied for the undoped layers show typical emission cross-sections, low green upconversion luminescence and lifetimes up to 7 ms.
We report on systematic growth and characterization of low-loss germanosilicate layers for use in optical waveguides. Plasma enhanced chemical vapor deposition (PECVD) technique was used to grow the films using silane, germane and nitrous oxide as precursor gases. Chemical composition was monitored by Fourier transform infrared (FTIR) spectroscopy. N-H bond concentration of the films decreased from 0.43x1022 cm-3 down to below 0.06x1022 cm-3, by a factor of seven as the GeH4 flow rate increased from 0 to 70 sccm. A simultaneous decrease of O-H related bonds was also observed by a factor of 10 in the same germane flow range. The measured TE rate increased from 5 to 50 sccm, respectively. In contrast, the propagation loss values for TE polarization at λ=632.8 nm were found to increase from are 0.20 ± 0.02 to 6.46 ± 0.04 dB/cm as the germane flow rate increased from 5 to 50 sccm, respectively. In contrast, the propagation loss values for TE polarization at λ=1550 nm were found to decrease from 0.32 ± 0.03 down to 0.14 ± 0.06 dB/cm for the same samples leading to the lowest values reported so far in the literature, eliminating the need for high temperature annealing as is usually done for these materials to be used in waveguide devices.