Open Access
Add to BibSonomy
Abstract
We demonstrate compact, monolithically integrated thulium-doped tellurium oxide microring lasers on a low-loss silicon nitride platform. We observe lasing in the wavelength range of 1815–1895 nm under 1610 nm resonant pumping at varying waveguide-microring gap sizes and on-chip single-sided output powers up to 4.5 mW. The microlasers exhibit thresholds as low as 18 mW (11 mW) and a single-sided slope efficiency as high as 11% (17%) with respect to the pump power coupled into the TeO2:Tm3+-coated Si3N4 bus waveguide (absorbed pump power). These results are a promising development for integrated tellurite glass devices and light sources for the emerging 2-µm band in silicon nitride photonic integrated circuits.
© 2021 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Laser sources and optical amplifiers operating in the 2 µm window (∼1.7–2.3 µm) are of increasing importance for diverse applications, including free-space and fiber-optic communications, medical diagnostics and surgery, spectroscopy, light detection and ranging (LIDAR), and sensing [1–3]. In particular, the 2-µm band has recently attracted interest for relieving a bandwidth bottleneck in data communications systems, due to the development of low-loss, and low latency hollow-core photonic bandgap fibers, low nonlinearity, broadband thulium fiber amplifiers, and semiconductor optoelectronic lasers, photodetectors, and modulators [4,5]. For applications requiring small form factor, silicon has emerged as an ideal platform for compact, low-loss, and high-speed 2-µm integrated photonic devices and systems [6–8]. In addition, silicon nitride’s (Si3N4’s) low propagation loss (≤ 0.1 dB∕cm) and wide transparency window (∼400 nm to 2.35 µm), high refractive index contrast, nanoscale feature resolution, and mature fabrication methods has made it a versatile complimentary silicon-compatible platform for passive, active, and nonlinear devices [9–14]. However, due to the indirect bandgap and two photon absorption of silicon and large bandgap of silicon nitride, researchers are investigating different materials to integrate 2-µm band laser sources and amplifiers on silicon chips [15–17].
Trivalent thulium ions can be pumped at telecom wavelengths around 1.6 µm and show broad emission on the 3F4 excited state to 3H6 ground state energy transition. Thulium lasers are of interest for 2 µm applications because of their high efficiencies, high output powers, design flexibility and eye-safe emission at wavelengths ranging from 1.7 to 2.2 µm. 2-µm thulium lasers have been developed using glass fibers [18–20], planar and channel waveguides [21–24], and bulk crystals [25], and other integrated hosts materials such as LiNbO3 [26]. Compared to fiber and bulk platforms, integrated waveguide lasers are compact, low cost, and use straightforward fabrication methods, enabling wafer-scale processing and integration with other photonic devices for compact high-performance microsystems [27–29]. Besides continuous wave devices, waveguide lasers have high potential for advanced light sources such as tunable lasers [30,31] and mode-locked lasers for applications such as low-noise frequency synthesis [24]. High performance integrated thulium-doped channel waveguide lasers have been developed in a variety of oxide host materials. Tungstate crystals are particularly promising based on their high rare earth solubility without clustering, resulting in high performance laser demonstrations [32], including devices with a maximum output power of 262 mW and slope efficiency of 82.6% [33]. Recently, thulium lasers have also been demonstrated on silicon and silicon nitride, enabling them to leverage the low-cost, scalable manufacturing and advanced device libraries and microsytems functionalities available on those platforms. Low-threshold Tm-doped microcavity lasers and high-power Tm-doped distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers on silicon have been demonstrated based on micro-trenches and Si3N4 waveguides coated with Tm-doped amorphous Al2O3 gain layers [22,23]. A high gain coefficient and high laser power were also achieved by applying a high Tm concentration and a well-confined waveguide structure for compact integrated devices in a Tm-doped Ta2O5 waveguide on silicon [21].
Compared to other metal oxides, tellurium dioxide (TeO2), is a highly promising material for active monolithically integrated optical devices and host for rare-earth ions due to its high rare-earth solubility, low quenching, and low phonon energy of around 600–800 cm−1 [34]. TeO2 has a high refractive index and is transparent throughout the visible and near-infrared and into the mid-infrared with low dispersion. It also has higher nonlinearity and higher Raman gain than Si3N4 [34–36]. Thus, TeO2 is an ideal medium for active (light-emitting), passive, and nonlinear devices on a single platform. Its low temperature and straightforward wafer-scale deposition via sputtering also make TeO2 a versatile and inexpensive material for hybrid integration on silicon and silicon nitride platforms [37–39]. In [40], an erbium-doped tellurium oxide waveguide amplifier pumped at 980 nm was demonstrated with high internal gain exceeding 14 dB and lasing was observed from the end facets, showing the potential for high-performance active on-chip devices in the material. Prior to this work, we have also reported a hybrid TeO2:Tm3+-Si3N4 waveguide amplifier with 7.6 dB internal net gain [41] and an erbium-doped tellurium oxide (TeO2:Er3+)-Si3N4 amplifier with up to 5 dB gain. We have also demonstrated low-loss waveguides and resonators [39,42] and the prospect for efficient nonlinear devices on the TeO2-Si3N4 platform [12,43]. However, to the best of our knowledge, an integrated tellurite-based laser on a silicon nitride platform had not previously been demonstrated. Here, we report on integrated TeO2:Tm3+-Si3N4 microring resonator lasers. We describe the film and waveguide fabrication, design and characterization of the waveguide lasers and show up 4.5 mW single-sided output power at 1828 nm and lasing from 1815–1895 nm for different microring-bus gaps. Such integrated thulium-doped lasers are promising for emerging silicon-nitride-based photonic microsystems operating around 2 µm.
2. Design and fabrication
We fabricated the thulium-doped tellurium oxide waveguide lasers on a silicon nitride platform using a wafer-scale foundry process and a monolithic, reactive co-sputtering post-processing step outlined in [39]. We first deposited a 0.2-µm-thick Si3N4 film on a 100-mm silicon wafer with an 8-µm-thick thermal SiO2 layer using low pressure chemical vapor deposition (LPCVD). The Si3N4 layer thickness was chosen as a standard nitride thickness to achieve low-loss, single-mode, and moderate confinement strip waveguides for compact bends in ring resonator structures. Stepper lithography and reactive ion etching were applied to pattern 1.0-µm-wide microring resonators with 300-µm radii, and gaps varying from 0.9 to 1.8 µm between the outer walls of the Si3N4 ring and bus waveguide. The wafers were then annealed at high temperature (> 1100 °C) for several hours in N2 to remove hydrogen from the Si3N4 layer and reduce absorption around 1.5 µm wavelength. The silicon nitride wafer was then diced into chips for post-processing.
We deposited a 0.39-µm-thick TeO2:Tm3+ coating layer onto the passive silicon nitride chips using a radio frequency (RF) reactive co-sputtering process. Three-inch metallic tellurium and thulium targets with 99.999 and 99.9% purity, respectively, were sputtered in an argon/oxygen atmosphere at ambient temperature. We set the Te and Tm RF sputtering powers to 120 and 85 W, and the Ar and O2 flow rates to 12 and 7.4 sccm, respectively, at 20°C. The deposition rate for the TeO2:Tm3+ film was 11 nm/min and its refractive index was 2.03 at 638 nm and 1.98 at 1550 nm wavelengths measured by spectroscopic ellipsometry. Thin film propagation losses of ≤ 1.0 dB/cm at 847 nm and ≤ 0.75 dB/cm at 1510 nm were determined using the prism coupling method and a witness sample deposited on a thermally oxidized wafer. We measured a thulium ion dopant concentration of 4.1 × 1020 cm−3 using Rutherford backscattering spectrometry (RBS). The thulium concentration was selected to be high enough to achieve greater gain than microring roundtrip losses, including propagation and ring-waveguide coupling losses. We prepared smooth waveguide end facets using focused-ion-beam (FIB) milling. In Fig. 1, we display the microring laser structure. Figures 1(a) and 1(b) show a 3D drawing of the TeO2:Tm3+-coated Si3N4 ring resonator and a cross section diagram of the hybrid waveguide structure, respectively. A scanning electron microscope (SEM) image of the top view of ring resonator and its bus waveguide is shown in Fig. 1(c). The calculated electric field profile of the transverse-electric- (TE-) polarized fundamental mode for the laser wavelength using a finite-element method mode solver is displayed in Fig. 1(d).
Fig. 1. (a) 3D drawing of the TeO2:Tm3+-Si3N4 ring laser. (b) Cross-section profile of the hybrid waveguide structure. (c) Top-view SEM image of a TeO2:Tm3+-Si3N4 ring laser. (d) Calculated electric field profile of the fundamental TE-polarized mode at 1610 nm pump and 1828nm laser wavelengths for a silicon nitride strip width and height of 1.0 and 0.2 µm, respectively, and TeO2:Tm3+ film height of 390 nm.
The theoretical properties of the TeO2:Tm3+-coated Si3N4 ring resonators were investigated using a finite element method (FEM) mode solver. The waveguides were designed to be single mode at > 1500 nm wavelength. Due to the asymmetry of the waveguide structure, simulations show that it only supports the TE-polarized mode. According to the simulation results, approximately 66.7% of the optical power at 1610 nm is confined in the TeO2:Tm3+ coating, with 18.1% confined to the nitride layer with the calculated mode area is 1.2 µm2, and the rest of the optical power in the SiO2 and air. At the laser wavelength, 63.3% of the optical power is in the TeO2:Tm3+ coating, with 17.3% confined to the nitride layer, and the rest of the optical power in the SiO2 and air with a similar mode area of 1.4 µm2. The hybrid waveguide design was selected to provide good optical confinement in the TeO2:Tm3+ layer while also minimizing both the mode size to enhance intensity and the bend radius for compact rings. The calculated radiation loss and equivalent Q factor for the TeO2:Tm3+-coated silicon nitride microring structure using a finite element bent eigenmode solver, shows that radiation loss is negligible at the selected bend radius of 300 µm [42]. These results show the potential for the fabrication of more compact devices without introducing significant radiation losses.
3. Experimental setup
We characterized the microring lasers using the experimental setup shown in Fig. 2. We coupled pump light from a tunable 1510–1640 nm laser set around 1610 nm and high-power L-band erbium-ytterbium-co-doped fiber amplifier (L-band EYDFA) to the chip via a polarization controller, a 1600/1900 nm fiber wavelength division multiplexor (WDM), and 2-µm spot size tapered optical fiber at 1550-nm wavelength mounted on an xyz stage. The laser output was also coupled from the chip using a lensed fiber with a 2-µm spot size tapered fiber at 1550-nm wavelength, filtered from the pump light with a 1600/1900 nm WDM and coupled to an optical spectrum analyzer (OSA) to observe the output spectrum and power. The transmitted pump light was also measured using a power detector.
During measurements, the polarization paddles and xyz stages were adjusted to select TE polarization and maximize the transmitted pump/signal intensity. Passive transmission measurements were carried out on the same setup without the L-band EYDFA and the OSA replaced with a photodetector to determine the background waveguide propagation loss. Passive characterization was carried out over the full range of the tunable laser to include wavelengths around 1510 nm, where we observe negligible thulium absorption loss, and the fitted Q factor can be assumed to represent the passive waveguide loss of the structure.
4. Results
We measured the transmission properties of the TeO2:Tm3+ coated Si3N4 waveguides and ring resonators around the pump wavelength from 1510 nm to 1610 nm. The transmitted pump power for a device with waveguide-resonator gap of 1.1 µm and TE polarization is shown in Fig. 3. We observe decreasing Q factor and lower extinction ratios corresponding to increasing Tm3+ ion absorption at wavelengths > ∼1550 nm as observed in other host materials [44] (we note that the measurement upper limit was determined by the maximum wavelength of the tunable laser – 1620 nm and the Tm3+ absorption peak is around 1650 nm). As displayed in the inset, we observe narrow resonances associated with the fundamental TE mode in the resonator. We performed a best fit of the resonance, assuming a Lorentzian shape of the transmission dip. The quality factor is intrinsically limited by thulium absorption and waveguide propagation loss. As shown in the inset of Fig. 3, the background propagation loss is 0.75 dB/cm at 1519 nm wavelength linked to an internal quality factor of 4.8×105 fitted to the resonance spectrum obtained in the under-coupled ring resonator [42]. The fiber-chip coupling loss was determined to be 5.0 dB, influenced by mode mismatch, Fresnel reflections and scattering due to the conformal TeO2:Tm3+ coating on the facet.
Fig. 3. Transmission measurement in a thulium-doped microring with microring-waveguide gap of 1.1 µm from 1510 to 1620 nm and for TE polarization. The inset picture shows a zoomed-in view of the resonance at 1519 nm wavelength and fitted Lorentzian function giving an internal Q factor of 4.8×105. This corresponds to 0.75 dB/cm waveguide propagation loss at 1519 nm wavelength, which is outside the Tm absorption range, and can be taken as the pump background loss.
We resonantly pumped the TeO2:Tm3+-coated Si3N4 ring resonators to investigate their lasing potential, with up to 60 mW power launched into the bus waveguide. We determined the launched pump power by measuring the incident power from the input fiber using an integrating sphere photodiode power monitor and accounting for 5.0 dB fiber-chip coupling loss. As shown in Fig. 4, we observe multimode lasing around 1828 nm for thulium doped laser with a gap of 1.1 µm at 1610 nm pump wavelength. The laser output is bidirectional and the similar output power was observed at the pump input side of the chip. Single mode laser emission was also observed in the resonator with up to 3.6 mW single-sided on-chip power and 7.2 mW double-sided output power, when the pump wavelength was shifted to 1600 nm, as shown in the inset of Fig. 4. We observed single mode laser emission for pump wavelengths from 1590 to 1604 nm where the thulium absorption is not as high as the thulium absorption around the peak. When pumping at wavelengths from 1604 to 1620 nm, where the thulium absorption is high, we observed multimode lasing with higher output powers in the device.
Fig. 4. Multimode laser emission spectrum of a TeO2:Tm3+-coated Si3N4 ring resonator under 1610-nm pumping at a microring-waveguide gap of 1.1 µm obtained with ∼60 mW on-chip pump power. The inset picture shows single mode laser emission of the same TeO2:Tm3+-coated Si3N4 ring resonator pumped at 1600 nm.
We observed the highest output power and laser efficiency for the device with gap of 1.1 µm and for a pump wavelength of 1610 nm. Figure 5 shows the single-sided laser output power of up to 4.5 mW measured as a function of on-chip and absorbed pump power. The on-chip power is the power coupled into the silicon nitride bus waveguide, taking into account the fiber-chip coupling loss of ∼5.0 dB per facet, and the absorbed power is the power coupled into the resonator. We note that the laser output power also includes a small amount of amplification in the TeO2:Tm3+-coated bus waveguide (we measured a peak internal net gain of up to 1.4 dB in the 0.6 cm long straight waveguide at 1870 nm for 60 mW launched power [41]). We observe the lowest device threshold of 18 mW versus on-chip launched pump power at a gap of 1.1 µm to the bus waveguide and 11 mW as the threshold pump power in the ring resonator. We observe slope efficiencies of 11% and 17% in the ring laser, respectively. Considering bidirectional emission, we observe 9 mW total on-chip output power and a slope efficiency versus absorbed pump power of 34%.
Fig. 5. Tm3+ laser curves for a microring resonator with a gap of 1.1 µm, showing a maximum on-chip output power of up to 4.5 mW and slope efficiencies of 11% and 17% versus launched and absorbed pump power.
In Fig. 6 we show the laser spectra obtained under 1610-nm pumping and at different gaps of 0.9, 1.1, 1.4, 1.6 and 1.8 µm. We observe multi-mode lasing and laser modes spanning from 1815 to 1895 nm. For smaller gap sizes (and longer wavelengths), the ring resonator modes incur greater coupling losses, favoring lasing closer to the thulium gain peak around 1800 nm, while, for larger gap sizes, the laser output shifts to longer wavelengths where the Tm3+ absorption is lower, and population inversion is more easily achieved. Therefore, by pumping different gaps, different lasing wavelengths can be achieved. The laser performance can be enhanced and emission wavelength can be controlled by engineering the pump and signal coupling using, for example, Mach-Zehnder couplers [45]. Furthermore, by building on this demonstration of a TeO2:Tm3+ integrated laser and silicon nitride’s versatile and high-resolution wafer-scale fabrication, various laser cavity designs of interest can be explored, including DBR, DFB and tunable lasers. In addition to thulium devices, different rare earth dopants can be investigated for lasing at a wide variety of wavelengths on the hybrid tellurite glass-silicon nitride platform.
Fig. 6. Laser emission spectra of TeO2:Tm3+-Si3N4 ring resonators under 1610-nm pumping and for microring-waveguide gaps of a) 0.9 µm b) 1.1 µm, c) 1.4 µm, d) 1.6 µm and e) 1.8 µm. The laser emission shifts from ∼1815 to 1895 nm by increasing the gap size.
5. Conclusion
In summary, we have demonstrated thulium-doped tellurium oxide microring resonator lasers emitting at wavelengths from 1815–1895 nm on a silicon nitride chip. We measure a minimum threshold of 18 (11) mW and maximum slope efficiency of 11% (17%) with respect to on-chip (absorbed) pump power. In the future, optimizing the coupler and cavity designs and waveguide cross-section can lead to efficient and low threshold laser emission over a wider wavelength range across thulium’s broad gain spectrum (∼1.7 − 2.1 µm). Such devices are promising for ultra-compact light sources for silicon-based photonic microsystems in the emerging 2-µm optical communications and sensing band.
Funding
Natural Sciences and Engineering Research Council of Canada (RGPIN-2017-06423, RTI-2017-00474, STPGP 494306); Canada Foundation for Innovation (35548); Ontario Ministry of Research and Innovation (ER17-13-077).
Acknowledgments
We acknowledge the Centre for Emerging Device Technologies (CEDT) at McMaster University for support with the reactive sputtering system.
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. K. Scholle, S. Lamrini, P. Koopmann, and P. Fuhrberg, “2 µm laser sources and their possible applications,” Frontiers in Guided Wave Optics and Optoelectronics (InTech, 2010).
2. Q. Wang, J. Geng, and S. Jiang, “2-µm fiber laser sources for sensing,” Opt. Eng. 53(6), 061609 (2014). [CrossRef]
3. M. Ebrahim-Zadeh, G. Leo, and I. Sorokina, “Mid-Infrared coherent sources and applications: introduction,” J. Opt. Soc. Am. B 35(12), MIC1 (2018). [CrossRef]
4. R. Soref, “Enabling 2 µm communications,” Nat. Photonics 9(6), 358–359 (2015). [CrossRef]
5. F. C. Garcia Gunning, N. Kavanagh, E. Russell, R. Sheehan, J. O’Callaghan, and B. Corbett, “Key enabling technologies for optical communications at 2000 nm,” Appl. Opt. 57(22), E64–E70 (2018). [CrossRef]
6. D. J. Thomson, L. Shen, J. J. Ackert, E. Huante-Ceron, A. P. Knights, M. Nedeljkovic, A. C. Peacock, and G. Z. Mashanovich, “Optical detection and modulation at 2µm-2.5 µm in silicon,” Opt. Express 22(9), 10825–10830 (2014). [CrossRef]
7. J. J. Ackert, D. J. Thomson, L. Shen, A. C. Peacock, P. E. Jessop, G. T. Reed, G. Z. Mashanovich, and A. P. Knights, “High-speed detection at two micrometres with monolithic silicon photodiodes,” Nat. Photonics 9(6), 393–396 (2015). [CrossRef]
8. W. Cao, D. Hagan, D. J. Thomson, M. Nedeljkovic, C. G. Littlejohns, A. Knights, S. Alam, J. Wang, F. Gardes, W. Zhang, S. Liu, K. Li, M. Said Rouifed, G. Xin, W. Wang, H. Wang, G. T. Reed, and G. Z. Mashanovich, “High-speed silicon modulators for the 2 µm wavelength band,” Optica 5(9), 1055–1062 (2018). [CrossRef]
9. D. J. Blumenthal, R. Heideman, D. Geuzebroek, A. Leinse, and C. Roeloffzen, “Silicon nitride in silicon photonics,” Proc. IEEE 106(12), 2209–2231 (2018). [CrossRef]
10. J. Mu, M. Dijkstra, J. Korterik, H. Offerhaus, and S. M. García-Blanco, “High-gain waveguide amplifiers in Si3N4 technology via double-layer monolithic integration,” Photonics Res. 8(10), 1634–1641 (2020). [CrossRef]
11. L. Gaeta, M. Lipson, and T. J. Kippenberg, “Photonic-chip-based frequency combs,” Nat. Photonics 13(3), 158–169 (2019). [CrossRef]
12. K. Miarabbas Kiani, H. M. Mbonde, H. C. Frankis, R. Mateman, A. Leinse, A. P. Knights, and J. D. B. Bradley, “Four-wave mixing in high-Q tellurium-oxide-coated silicon nitride microring resonators,” OSA Continuum 3(12), 3497–3507 (2020). [CrossRef]
13. J. F. Bauters, M. J. R. Heck, D. D. John, J. S. Barton, C. M. Bruinink, A. Leinse, R. G. Heideman, D. J. Blumenthal, and J. E. Bowers, “Planar waveguides with less than 0.1 dB/m propagation loss fabricated with wafer bonding,” Opt. Express 19(24), 24090–24101 (2011). [CrossRef]
14. J. P. Epping, M. Hoekman, R. Mateman, A. Leinse, R. G. Heideman, A. van Rees, P. J. M. van der Slot, C. J. Lee, and K.-J. Boller, “High confinement, high yield Si3N4 waveguides for nonlinear optical applications,” Opt. Express 23(2), 642–648 (2015). [CrossRef]
15. E. Kasper, M. Kittler, M. Oehme, and T. Arguirov, “Germanium tin: silicon photonics toward the mid-infrared [Invited],” Photonics Res. 1(2), 69–76 (2013). [CrossRef]
16. G. Roelkens, U. D. Dave, A. Gassenq, N. Hattasan, C. Hu, B. Kuyken, F. Leo, A. Malik, M. Muneeb, E. Ryckeboer, D. Sanchez, S. Uvin, R. Wang, Z. Hens, R. Baets, Y. Shimura, F. Gencarelli, B. Vincent, R. Loo, J. Van Campenhout, L. Cerutti, J.-B. Rodriguez, E. Tourníe, X. Chen, M. Nedeljkovic, G. Mashanovich, L. Shen, N. Healy, A. C. Peacock, X. Liu, and R. Osgood, “Silicon-based photonic integration beyond the telecommunication wavelength range,” IEEE J. Sel. Top. Quantum Electron. 20(4), 394–404 (2014). [CrossRef]
17. A. Elbaz, D. Buca, N. Driesch, K. Pantzas, G. Patriarche, N. Zerounian, E. Herth, X. Checoury, S. Sauvage, I. Sagnes, A. Foti, R. Ossikovski, J.-M. Hartmann, F. Boeuf, Z. Ikonic, P. Boucaud, D. Grützmacher, and M. El Kurdi, “Ultra-low-threshold continuous-wave and pulsed lasing in tensile-strained GeSn alloys,” Nat. Photonics 14(6), 375–382 (2020). [CrossRef]
18. N. J. Ramírez-Martínez, M. Núñez-Velázquez, A. A. Umnikov, and J. K. Sahu, “Highly efficient thulium-doped high-power laser fibers fabricated by MCVD,” Opt. Express 27(1), 196–201 (2019). [CrossRef]
19. S. V. Muravyev, E. A. Anashkina, A. V. Andrianov, V. V. Dorofeev, S. E. Motorin, M. Y. Koptev, and A. V. Kim, “Dual-band Tm3+-doped tellurite fiber amplifier and laser at 1.9 µm and 2.3 µm,” Sci. Rep. 8(1), 16164 (2018). [CrossRef]
20. S. D. Jackson, “Towards high-power mid-infrared emission from a fibre laser,” Nat. Photonics 6(7), 423–431 (2012). [CrossRef]
21. A. S. K. Tong, C. J. Mitchell, A. Aghajani, N. Sessions, G. S. Murugan, J. I. Mackenzie, and J. S. Wilkinson, “Spectroscopy of thulium-doped tantalum pentoxide waveguides on silicon,” Opt. Mater. Express 10(9), 2201–2211 (2020). [CrossRef]
22. Z. Su, N. Li, E. Salih Magden, M. Byrd, T. N. Purnawirman, G. Adam, D. Leake, J. D. B. Coolbaugh, M. R. Bradley, and Watts, “Ultra-compact and low-threshold thulium microcavity laser monolithically integrated on silicon,” Opt. Lett. 41(24), 5708–5711 (2016). [CrossRef]
23. N. Li, Z. Purnawirman, E. S. Su, P. T. Magden, K. Callahan, M. Shtyrkova, A. Xin, C. Ruocco, E. P. Baiocco, F. X. Ippen, J. D. B. Kärtner, D. Bradley, M. R. Vermeulen, and Watts, “High-power thulium lasers on a silicon photonics platform,” Opt. Lett. 42(6), 1181–1184 (2017). [CrossRef]
24. K. Shtyrkova, P. T. Callahan, N. Li, E. S. Magden, A. Ruocco, D. Vermeulen, F. X. Kärtner, M. R. Watts, and E. P. Ippen, “Integrated CMOS-compatible Q-switched mode-locked lasers at 1900nm with an on-chip artificial saturable absorber,” Opt. Express 27(3), 3542–3556 (2019). [CrossRef]
25. F. D. Trapani, X. Mateos, V. Petrov, A. Agnesi, U. Griebner, H. Zhang, J. Wang, and H. Yu, “Continuous-wave laser performance of Tm: LuVO4 under Ti:sapphire laser pumping,” Laser Phys. 24(3), 035806 (2014). [CrossRef]
26. M. George, “Ti: Tm: LiNbO3 waveguide amplifiers and lasers,” Ph.D. Thesis (University of Paderborn, 2012).
27. M. Pollnau and J. D. B. Bradley, “Optically pumped rare-earth-doped Al2O3 distributed-feedback lasers on silicon [Invited],” Opt. Express 26(18), 24164–24189 (2018). [CrossRef]
28. S. Li, D. Zhang, J. Zhao, Q. Yang, X. Xiao, S. Hu, L. Wang, M. Li, X. Tang, Y. Qiu, M. Luo, and S. Yu, “Silicon micro-ring tunable laser for coherent optical communication,” Opt. Express 24(6), 6341–6349 (2016). [CrossRef]
29. F. Kish, V. Lal, P. Evans, S. W. Corzine, M. Ziari, T. Butrie, M. Reffle, H. S. Tsai, A. Dentai, J. Pleumeekers, M. Missey, M. Fisher, S. Murthy, R. Salvatore, P. Samra, S. Demars, N. Kim, A. James, A. Hosseini, P. Studenkov, M. Lauermann, R. Going, M. Lu, J. Zhang, J. Tang, J. Bostak, T. Vallaitis, M. Kuntz, D. Pavinski, A. Karanicolas, B. Behnia, D. Engel, O. Khayam, N. Modi, M. R. Chitgarha, P. Mertz, W. Ko, R. Maher, J. Osenbach, J. T. Rahn, H. Sun, K. T. Wu, M. Mitchell, and D. Welch, “System-on-chip photonic integrated circuits,” IEEE J. Sel. Top. Quantum Electron. 24(1), 1–20 (2018). [CrossRef]
30. M. Ahmadi, W. Shi, and S. LaRochelle, “Widely tunable silicon Raman laser,” Optica 8(6), 804–810 (2021). [CrossRef]
31. N. Li, D. Vermeulen, Z. Su, E. Salih Magden, M. Xin, N. Singh, A. Ruocco, J. Notaros, C. V. Poulton, E. Timurdogan, C. Baiocco, and M. R. Watts, “Monolithically integrated erbium-doped tunable laser on a CMOS-compatible silicon photonics platform,” Opt. Express 26(13), 16200–16211 (2018). [CrossRef]
32. K. van Dalfsen, S. Aravazhi, C. Grivas, S. M. García-Blanco, and M. Pollnau, “Thulium channel waveguide laser in a monoclinic double tungstate with 70% slope efficiency,” Opt. Lett. 37(5), 887–889 (2012). [CrossRef]
33. E. Kifle, P. Loiko, U. Griebner, V. Petrov, P. Camy, A. Braud, M. Aguiló, F. Díaz, and X. Mateos, “Diamond saw dicing of thulium channel waveguide lasers in monoclinic crystalline films,” Opt. Lett. 44(7), 1596–1599 (2019). [CrossRef]
34. A. Jha, B. D. O. Richards, G. Jose, T. T. Fernandez, C. J. Hill, J. Lousteau, and P. Joshi, “Review on structural, thermal, optical and spectroscopic properties of tellurium oxide-based glasses for fibre optic and waveguide applications,” Int. Mater. Rev. 57(6), 357–382 (2012). [CrossRef]
35. S. Shen, A. Jha, X. Liu, M. Naftaly, K. Bindra, H. J. Bookey, and A. K. Kar, “Tellurite glasses for broadband amplifiers and integrated optics,” J. Am. Ceram. Soc. 85(6), 1391–1395 (2002). [CrossRef]
36. K. Vu and S. Madden, “Tellurium dioxide erbium doped planar rib waveguide amplifiers with net gain and 2.8 dB/cm internal gain,” Opt. Express 18(18), 19192–19200 (2010). [CrossRef]
37. R. Nayak, V. Gupta, A. L. Dawar, and K. Sreenivas, “Optical waveguiding in amorphous tellurium oxide thin films,” Thin Solid Films 445(1), 118–126 (2003). [CrossRef]
38. S. J. Madden and K. T. Vu, “Very low loss reactively ion etched tellurium dioxide planar rib waveguides for linear and non-linear optics,” Opt. Express 17(20), 17645–17651 (2009). [CrossRef]
39. H. C. Frankis, K. Miarabbas Kiani, D. B. Bonneville, C. Zhang, S. Norris, R. Mateman, A. Leinse, N. D. Bassim, A. P. Knights, and J. D. B. Bradley, “Low-loss TeO2-coated Si3N4 waveguides for application in photonic integrated circuits,” Opt. Express 27(9), 12529–12540 (2019). [CrossRef]
40. K. Vu, S. Farahani, and S. Madden, “980 nm pumped erbium doped tellurium oxide planar rib waveguide laser and amplifier with gain in S, C and L band,” Opt. Express 23(2), 747–755 (2015). [CrossRef]
41. K. Miarabbas Kiani, H. C. Frankis, H. M. Mbonde, R. Mateman, A. Leinse, A. P. Knights, and J. D. B. Bradley, “Thulium-doped tellurium oxide waveguide amplifier with 7.6 dB net gain on a silicon nitride chip,” Opt. Lett. 44(23), 5788–5791 (2019). [CrossRef]
42. H. C. Frankis, K. Miarabbas Kiani, D. Su, R. Mateman, A. Leinse, and J. D. B. Bradley, “High-Q tellurium-oxide-coated silicon nitride microring resonators,” Opt. Lett. 44(1), 118–121 (2019). [CrossRef]
43. N. Singh, H. M. Mbonde, H. C. Frankis, E. Ippen, J. D. B. Bradley, and F. X. Kärtner, “Nonlinear silicon photonics on CMOS-compatible tellurium oxide,” Photonics Res. 8(12), 1904–1909 (2020). [CrossRef]
44. G. Huber, C. Kränkel, and K. Petermann, “Solid-state lasers: status and future,” J. Opt. Soc. Am. B 27(11), B93–B105 (2010). [CrossRef]
45. L. Chang, M. de Goede, M. Dijkstra, C. I. van Emmerik, and S. M. García-Blanco, “Modular microring laser cavity sensor,” Opt. Express 29(2), 1371–1383 (2021). [CrossRef]
