Photonic Integrated Circuit (PIC) technology is becoming more and more mature and the three main platforms that offer Multi Project Wafer runs (Indium Phosphide (InP), Silicon on Insulator (SOI) and the silicon nitride based TriPleX platform) each have their own unique selling points. New disruptive PIC based modules are enabled by combinations of the different platforms complementing each other in performance. In particular the InP-TriPleX combination are two very complementary technologies. Combining them together yields for instance tunable ultra-narrow linewidth lasers extremely suitable for telecom and sensing applications. Also microwave photonics modules for Optical Beam Forming Networks and 5G communication can, and have been realized with this combination. Important part of this combination is the integration of the different platforms in modules via cost effective assembly techniques. This talk will present the combination of both technologies, the interconnection issues faced in the assembly process and latest measurement results on these hybrid integrated devices.
The spectral response of a distributed-feedback resonator with a thermal chirp is investigated. An Al<sub>2</sub>O<sub>3</sub> channel waveguide with a surface Bragg grating inscribed into its SiO<sub>2</sub> top cladding is studied. A linear temperature gradient along the resonator leads to a corresponding variation of the grating period. We characterize its spectral response with respect to wavelength and linewidth changes of the resonance peak. Simulated results show good agreement with the experimental data, indicating that the resonance wavelength is determined by the total accumulated phase shift. The calculated grating reflectivities at the resonance wavelength largely explain the observed changes of the resonance linewidth. This agreement demonstrates that the linewidth increase is caused by the increase of resonator outcoupling losses.
We thoroughly investigate the Fabry-Pérot resonator, avoid approximations, and derive its generic Airy distribution, equaling the internal resonance enhancement, and all related Airy distributions, such as the commonly known transmission. We verify that the sum of the mode profiles of all longitudinal modes is the fundamental physical function characterizing the Fabry-Pérot resonator and generating the Airy distributions. We investigate the influence of frequency-dependent mirror reflectivities on the mode profiles and the resulting Airy distributions. The mode profiles then deviate from simple Lorentzian lines and exhibit peaks that are not located at resonant frequencies. Our simple, yet accurate analysis greatly facilitates the characterization of Fabry-Pérot resonators with strongly frequency-dependent mirror reflectivities.
Distributed-feedback (DFB) laser resonators are widely recognized for their advantage of generating laser emission with extremely narrow linewidth. Our investigation concerns ytterbium-doped amorphous Al<sub>2</sub>O<sub>3</sub> channel waveguides with a corrugated homogeneous Bragg grating inscribed into its SiO<sub>2</sub> top cladding, in which a λ/4 phase-shift provides a resonance and allows for laser emission with a linewidth as narrow as a few kHz. Pump absorption imposes a thermal chirp of the grating period, which has implications for the spectral characteristics of the resonator. Thermal effects on the spectral response of a DFB passive resonator were investigated via simulations using Coupled Mode Theory by considering (i) a constant deviation of the grating period or (ii) a chirp with a linear profile. We report an increase of the resonance linewidth up to 15%. This result is due to two factors, namely changes of the grating reflectivity at the resonance frequency up to 2.4% and of the shift of resonance frequency up to 61 pm due to an accumulated phase shift imposed on the grating by the chirp profile. The linewidth decrease due to gain is on the order of 10<sup>6</sup>, which is a much larger value. Nevertheless, according to the Schawlow-Townes equation the linewidth increase of the passive resonator due to a thermal chirp quadratically increases the laser linewidth.
Here we report on the generation of ten deep blue to cyan laser emission lines using an intracavity frequency converted
Raman laser. The fundamental laser field of the intracavity Raman laser is based on the 3 level transition of a Nd:YLF
laser crystal, providing a short wavelength at 903 or 908 nm. When combined with generation of a Stokes shifted field
via intracavity stimulated Raman scattering (SRS) by a KGW Raman crystal, enables generation of laser emission in the
deep blue to cyan wavelength regime via additional nonlinear frequency conversion. Output at several blue-green
wavelengths was achieved, with quasi continuous wave (qcw) output powers of up to 1W. A detailed study of the
spectral behavior of the underlying Raman laser processes revealed strong spectral broadening of the fundamental laser
line at 908 nm to a width of up to 4 nm. The effect of the spectral broadening on the overall laser efficiency is analyzed.
In this work we demonstrate for the first time, to the best of our knowledge, quasi-continuous wave (qcw) laser operation of a diode-side-pumped Nd:YVO<sub>4</sub> self-Raman laser operating at 1176 nm. The double beam mode controlling (DBMC) technique used in this work allows fundamental mode laser oscillation, resulting in a beam quality M<sup>2</sup> of 2.42 and 2.18 in the horizontal and vertical directions, respectively. More than 3.5 W of peak output power at 1176 nm was achieved with TEM<sub>00</sub> laser mode, corresponding to an optical conversion efficiency of 5.4%.With multimode operation, more than 8W of peak output power was achieved, corresponding to 11.7% optical conversion efficiency.
Amorphous Al<sub>2</sub>O<sub>3</sub> 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 Al<sub>2</sub>O<sub>3</sub> 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 BCl<sub>3</sub>/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 Al<sub>2</sub>O<sub>3</sub> layer growth. At the relevant dopant levels (~10<sup>20</sup> cm<sup>-3</sup>) lifetimes of the <sup>4</sup>I<sub>13/2</sub> 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
Al<sub>2</sub>O<sub>3</sub> waveguide. Net optical gain has been obtained over a 35-nm-wide wavelength range (1525-1560 nm) with
a maximum of 4.9 dB.