Microresonators have been extensively studied in integrated photonics over the past two decades. However, the thermal frequency drift of a resonator limits its applications in practice. Athermal microresonators, as a passive solution, have become highly attractive. We propose two types of broadband athermal waveguides, with three zero-thermal-drift wavelengths achieved through mode anti-crossing effect, for the first time. For the polymer-coated waveguide, the effective thermo-optical coefficient (TOC) has a variation of ±1.5×10−6/K from 1350 to 1790 nm. For the TiO2-coated waveguide, the effective TOC has a variation of ±1.5×10−6/K from 1510 to 2090 nm. Over such a wide band of 440 or 580 nm, both the athermal microring resonators show excellent athermal property of <1 pm/K. The broadband athermal characteristics of the resonators would enable a wide variety of applications, e.g., wavelength-division multiplexing filters, modulators, lasers, sensors, and nonlinear optical sources.
In the rapidly evolving fields of silicon photonics, microresonator-based devices have promising applications due to a small footprint, high performance, and low power consumption. However, the frequency of the optical resonator could drift due to the change in the optothermal refractive index. Here, we propose two types of broadband athermal waveguides which are achieved through the mode anti-crossing effect. These waveguides have three zero-thermal-drift wavelengths (ZTDWs), while the previously published structures have no more than two ZTDWs. A polycarbonate (PC)-coated waveguide shows a small effective thermo-optical coefficient (TOC) variation of ±1.5×10-6 /K from 1350 to 1790 nm. For the TiO2-coated waveguide, the effective TOC has a variation of ±1.5×10-6 /K from 1510 to 2090 nm. The temperature depended wavelength shift (TDWS) of both microring resonators with a radius of 100 μm has a variation of ±1 pm/K. Both athermal microring resonators show a low bending loss and stable broadband athermal property at longer wavelengths. The highly stable broadband athermal performance of microring resonators will greatly expand the applications in optical communications and sensing systems.
The formation and manipulation of ultrashort pulses on chip would be of great interest to ultrafast optics and integrated photonics. One of the important issues is dispersion-assisted nonlinear interactions of broadband frequency components. In this paper, we show for the first time that a bilayer waveguide for quasi-TE mode produces a quite flat and saddleshaped dispersion profile. Different from previously reported TE-mode waveguides with flattened dispersion, the proposed waveguide exhibits a greatly simplified structure with no need for a high-aspect-ratio slot and has quite small group delay difference in a wide spectral range with four zero-dispersion wavelengths (ZDWs). For the first time we study supercontinuum generation in hybrid dispersion regime, in which the broadened spectrum covers a bandwidth with all ZDWs. It is found that one can obtain greatly improved spectral flatness in supercontinuum generation, with a power variation as small as 3 dB over a bandwidth of <500 nm. Moreover, the proposed waveguides are particularly suitable for low-distortion pulse propagation over a long distance, which is important for on-chip ultrashort pulse delivery.
Dispersion engineering in integrated waveguides and microresonators has been intensely studied in recent years. The main focus is to achieve desirable adjustment of dispersion value, slope, bandwidth and flatness, which is important for broadband nonlinear applications. Dispersion has been viewed as a control knob to leverage the parameter space provided by high-index-contrast on-chip devices, enabling strong interactions of far apart frequency components over an octavespanning bandwidth. Here, we review recent advances in dispersion engineering in integrated waveguides and microresonators based on various material platforms, with an emphasis on their applications in mid-infrared (IR) photonics.
Photonic integrated circuits suffer from a thermal drift of device performance, which is a key obstacle to the development of commercial optoelectronic products. Temperature-insensitive integrated waveguides and resonators have been demonstrated at a single wavelength, using materials with a negative TOC, which are not suitable for WDM devices and wideband nonlinear devices. Here, we propose two waveguides to realize the generation of broadband athermal features. For one of them, the temperature-insensitivity over a bandwidth of 780 nm (1280 to 2060 nm) with an ultra-small effective-TOC within is ±1×10-6/K. Uniquely, the waveguide has small anomalous dispersion (from 66 to 329 ps/nm/km) over the same band and is suitable for frequency comb generation without being affected by intra-cavity thermal dynamics. We also show another waveguide design with an effective-TOC variation of ±1×10-6/K over a bandwidth of 1060 nm, from 1220 to 2280 nm. The obtained dispersion varies from -232 to -502 ps/nm/km over the same band, which can be used in nonlinear devices.
Group-velocity dispersion (GVD) engineering is vital to many nonlinear optical phenomena and has been widely used for nonlinear optics. Aiming at different applications, one need to control and engineer the sign, value, slope of dispersion and the number of zero-dispersion wavelengths (ZDWs). In this work, we demonstrate generation of 5 ZDWs in a new type of bilayer waveguides. Outer layer of this waveguide can be formed by depositing without etching. Material combinations are Ge23Sb7S70 (n≈2.2) and Ge28Sb12Se60 (n≈2.6). In this waveguide, an extremely wideband-low and flat dispersion can be obtained from 2.6 to 15.5 μm (2.6 octaves).
Microresonator-based frequency combs have attracted a great deal of attention in recent years. Traditional generation scheme could be slow due to the operation of tunable lasers and thermal effects. In some spectral ranges, it is also difficult to find a tunable laser with a certain tuning range. In this paper, we propose a fast and simple method for Kerr comb generation without laser detuning and local cooling. In this way, the generation time can be reduced to tens of nanoseconds, three orders of magnitude faster.
Photonic circuits suffer from thermal drift of device performance, which is a key obstacle to the development of commercial optoelectronic products. Temperature-insensitive integrated waveguides and resonators have been demonstrated by using materials with a negative TOC at a single wavelength, which are not suitable for WDM devices and wideband nonlinear devices. Here, we propose a waveguide structure with temperature-insensitivity over a bandwidth of 780 nm (1280 to 2060 nm) with an ultra-small effective TOC within ±1×10-6/K. Uniquely, the waveguide has small anomalous dispersion (from 66 to 329 ps/nm/km) over the same band and is suitable for frequency comb generation without being affected by intra-cavity thermal dynamics.
A strip/slot hybrid horizontal silicon nitride slot waveguide is designed to provide an ultraflat and low dispersion. By optimizing the height and width of the structure, an ultraflat and low dispersion of ∼0±7 ps/nm/km over 812 nm wavelength range (from 1137 to 1949 nm) can be achieved. The waveguide with a 20-nm conformal overlayer has chromatic dispersion within ±1 ps/nm/km over 682-nm bandwidth. So the flatness is 0.0015, which is the lowest flatness in near-infrared regime of this kind of waveguide to our knowledge. The influence of the waveguide sidewall to dispersion is also discussed.
To study the relationship between Aerosol Optical Depth (AOD) and concentration of PM2.5(Particulate Matter) basing on CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) data, 51 samples among the CALIPSO Level 2 aerosol profile data of local region from January to April 2014 are selected. After screening these 51 samples under the decided conditions, such as system stability and the type of the materials, the AODs of the samples are calculated. Then a linear regression model is constructed through Matlab software, in which AOD is independent variable and PM2.5 is dependent variable. All the data are fit by the selected five functions: linear, logarithmic, exponential, power, and quadratic. Experimental results show that the value of correlation coefficient of the quadratic equation model is the best one among the functions. So it is feasible to monitor the concentration of PM2.5 using the AOD calculated from CALIPSO Level 2 data.
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