Home Physical Sciences Monolithic temperature-insensitive high-Q Ta2O5 microdisk resonator
Article Open Access

Monolithic temperature-insensitive high-Q Ta2O5 microdisk resonator

  • Zhen Yang , Zheng Zhang , Peng Cheng , Zhe Long , Qi Cheng , Jiaqi Yang , Yu Lin , Bin Fang , Zhongming Zeng , Zhiping Zhou , Ganapathy Senthil Murugan EMAIL logo and Rongping Wang ORCID logo EMAIL logo
Published/Copyright: December 5, 2025
Download Article (PDF)
Nanophotonics
From the journal Nanophotonics Volume 14 Issue 27

Abstract

We demonstrate a temperature-insensitive high-Q tantalum oxide (Ta2O5) microdisk resonator fabricated using electron-beam lithography and inductively coupled plasma reactive-ion etching. The microdisks exhibit a loaded Q-factor of 4.25 × 105 at 1,550 nm, which more than doubles (∼9.3 × 105) following thermal annealing at 600 °C. Remarkably, the temperature-dependent resonant wavelength shift is suppressed to less than 10 pm/°C across a broad 100 nm bandwidth. Furthermore, the resonators maintain high optical stability under elevated input powers, with no observed degradation in optical properties such as extinction ratio or Q-factor. The combination of high Q-factors and exceptional thermal stability positions the Ta2O5 microdisk resonators as a promising platform for integrated photonic device applications, including on-chip narrow-linewidth lasers and precision sensing.

Keywords: tantala waveguide; microdisk resonator; optical cavity

1 Introduction

Optical microresonators with high-quality factors (high-Q) and low optical losses are fundamental building blocks for diverse integrated photonic applications [1], [2], including nonlinear optics [3], precision biochemical sensing [4], and on-chip lasers [5]. These microcavities extend the photon lifetimes and tightly confine lightwaves within small volumes, significantly enhancing the intensity of the optical resonance fields. This enhancement improves device performance and enables novel photonic functionalities [6]. Recent advances have demonstrated high-Q microcavities on numerous material platforms, such as silicon (Si) [7], silicon nitride (Si3N4) [8], tantalum oxide (Ta2O5) [9], lithium niobate/tantalate (LiNbO3/LiTaO3) [3], [10], [11], [12], silicon carbide (SiC) [13], and III-V semiconductors [14]. However, the resonant wavelengths of high-Q microresonators are highly sensitive to environmental temperature fluctuations. This instability poses a critical challenge for applications requiring temperature-independent operation, such as dense wavelength division multiplexing (DWDM) systems and frequency-stabilized microlasers. A key limitation lies in the difficulty of simultaneously achieving both high-Q factors and thermal stability in existing microresonators. In previously reported adiabatic microcavity devices, materials with negative thermo-optic coefficients are used as cladding, and the waveguide size is reduced to expand the effective interaction area between the light field in the waveguide core and the negative thermo-optic coefficient material, enabling adiabatic operation across the entire waveguide. However, these approaches typically yield large mode volumes and Q factors on the order of 104 [15], [16], [17], which significantly degrade performance in practical photonics devices. Especially for on-chip light source applications, achieving thermally stable operation on a single material platform with small mode volume (leading to a stronger interaction between the optical field and the material) without sacrificing the optical performance of the microcavity device is crucial, and further extensive research is still needed.

Among the numerous silicon-compatible materials in photonic research, Ta2O5 stands out as a promising material for integrated photonic devices due to its attractive features, including a wide transparency window spanning the ultraviolet to infrared (0.28–8 µm) [18], a high refractive index (n 0 = 2.05 at 1,550 nm) relative to SiO2 [19], a relatively high nonlinear refractive index (7.2 × 10−19 m2/W) [20] – approximately three times larger than that of silicon nitride – and a low thermo-optic coefficient (5.75 × 10−6/K), which is two orders of magnitude smaller than that of silicon (1.34 × 10−4/K) [21]. In addition, Ta2O5 allows straightforward and high-throughput deposition of high optical quality thin films onto diverse substrates at room temperature. To date, Ta2O5-based photonic devices have been applied in various fields, such as dielectric metasurface optics [22], nonlinear optics [9], and rare-earth ion doped waveguide amplifiers [23]. Although the thermal stability of Ta2O5 microring resonators has been characterized [21], [24], [25], the thermal stability performance of Ta2O5 microdisk cavities has not been reported.

In this paper, we report an athermal, high-Q Ta2O5 microdisk resonator fabricated using electron-beam lithography and inductively coupled plasma reactive ion etching. After annealing, the Q-factor of the Ta2O5 microdisk resonator reaches approximately 9.3 × 105. At the same time, thermal stability across a bandwidth of approximately 100 nm, along with high power-handling stability without degradation in optical performance, is achieved. Synchronized implementation of ultrahigh Q-factor and exceptional thermal stability in Ta2O5 microdisk is key novelty of this work, demonstrating the significant potential of Ta2O5 microdisk resonators for applications in telecommunications, quantum optics, and precision measurement, where the demand for stable, high-Q resonators continues to rise.

2 Device fabrication and measurement

The Ta2O5 microdisk resonator was fabricated as follows. A 400 nm-thick Ta2O5 film was deposited via ion beam sputtering (IBS) onto a 4-inch silicon wafer with a 2 µm-thick thermal oxide layer. The metallic Ta target was sputtered with an oxygen flow of 48 sccm and a sputtering power of 400 W in a home-made IBS system. The refractive index dispersion of the deposited film was characterized using a Woollam V-VASE32 ellipsometer and is plotted in Figure 1(a). The surface roughness of the Ta2O5 film, measured using a Bruker Dimension ICON atomic force microscope (AFM), was determined to be Rq (RMS) = 0.08 nm, as shown in Figure 1(b).

Figure 1: (a) The measured refractive index, and (b) an AFM image of the deposited Ta2O5 film.
Figure 1:

(a) The measured refractive index, and (b) an AFM image of the deposited Ta2O5 film.

Figure 2(a) illustrates the fabrication process of the Ta2O5 microdisk resonator. Initially, an 80 nm-thick chromium (Cr) was deposited on the surface of the Ta2O5 film, serving as a hard mask. Subsequently, the devices were patterned with a 150 nm-thick hydrogen silsesquioxane (HSQ) photoresist using electron beam lithography (RAITH e-LINE Plus). The device structure was transferred to the Cr film through etching with a mixture of Cl2 and O2 gases. The underlying Ta2O5 layer was then fully etched using a low-pressure mixture of O2, Ar and CF4 gases in an inductively coupled plasma reactive ion etching (ICP-RIE) system (ULVAC NE-550). After etching, the device surface was treated with 400 W oxygen plasma for 10 min to remove the etching byproducts, and the Cr hard mask was subsequently removed using a chromium etchant (CR7T).

Figure 2: (a) Schematic illustration of the fabrication process flow. (b) SEM image of a Ta2O5 microdisk resonator with a radius of 150 μm and pulley-type coupler. (c) Magnified SEM image of the coupling region highlighted in (b), showing the evanescent coupling gap between the waveguide and microdisk. (d) Cross-sectional SEM image of a fabricated Ta2O5 waveguide, with a width of 1,000 nm and a height of 400 nm.
Figure 2:

(a) Schematic illustration of the fabrication process flow. (b) SEM image of a Ta2O5 microdisk resonator with a radius of 150 μm and pulley-type coupler. (c) Magnified SEM image of the coupling region highlighted in (b), showing the evanescent coupling gap between the waveguide and microdisk. (d) Cross-sectional SEM image of a fabricated Ta2O5 waveguide, with a width of 1,000 nm and a height of 400 nm.

Figure 2(b) shows a scanning electron microscope (SEM) image of the fabricated microdisk resonator with a radius of 150 μm. The resonators are coupled to an access waveguide to enable optical characterization through transmission measurements. The magnified view of the coupling region, highlighted by the red frame in Figure 2(b) is shown in Figure 2(c). Figure 2(d) presents the cross-sectional SEM of a fabricated Ta2O5 waveguide. The waveguide has a width (w) = 1,000 nm, a height (h) = 400 nm, and sidewall angles (θ) = 89°. Evidently, the sidewalls are vertical and smooth, demonstrating the high quality of the fabrication process.

In the experiments, light with a sub-MHz linewidth from a tunable laser (Santac TSL-550) was coupled into the bus waveguide end facet via a lensed fiber (SMF28e). On the output side of the waveguide, the transmitted light was collected and directed into a low-noise power meter (Santec MPM210) using a single-mode fiber (SMF). The coupled optical power was maintained at a low level (∼100 µW) to minimize both nonlinear and thermo-optic effects within the Ta2O5 waveguide. The polarization of the input light was adjusted using a manual fiber polarization controller (Thorlabs FPC526) to excite the fundamental quasi-TE mode of the waveguide. To prevent any thermal drift of the resonator modes, the experimental temperature was fixed at 25 °C using a thermoelectric controller.

3 Results and discussion

Figure 3(a) shows the representative transmission spectrum of the fabricated Ta2O5 microdisk resonator (radius: 150 µm) measured at room temperature (25 °C). The power of the coupled light was maintained at a low level (∼100 µW) to minimize any nonlinear effects. The microdisk resonator operated in an under-coupled region with a 490 nm coupling gap. Since the input laser coupled to microdisk resonator was adjusted to TE polarization, the resonant mode in the transmission spectrum of the microdisk is primarily dominated by TE modes, with no significant TM modes observed. The Ta2O5 microdisk in this study has a radius of 150 μm and led to the excitation of high-order TE modes. By analyzing the transmission spectrum, we identify the most prominent resonant peaks as TE0, TE1, TE2, and TE3 modes, with corresponding free spectral ranges (FSRs) of 1.2 nm, 1.18 nm, 1.17 nm, and 1.1 nm, respectively. These results are shown in Figure 3(a). The representative resonant peak at 1,548.471 nm for the TE0 mode was fitted with a Lorentzian model as shown in Figure 3(b), yielding a full width at half maximum (FWHM, denoted as Δλ) of 3.6 pm. Using the relation Q = λ/Δλ, the loaded Q factor (Q L ) was calculated as ∼ 4.25 × 105 at this wavelength. The intrinsic Q-factor (Q i ) was determined to be 6.78 × 105 by using the equation Q i = 2 Q L / 1 + T 0 [19]for under-coupled devices, where T 0 (=0.065) is the transmission normalized to the minimum value of the fitting curves at the resonant wavelength.

Figure 3: (a) Measured transmission spectrum for the Ta2O5 microdisk resonator with radius = 150 μm and gap = 490 nm. (b) Measured spectrum (black dots) and Lorentzian fitting (red line) around the resonant wavelength at 1,548.471 nm. (c) Extracted Q L (blue dot) at each resonant wavelength. (d) Measured Q factor of microdisk resonance wavelength at 1,548.2 nm after 600 °C annealing.
Figure 3:

(a) Measured transmission spectrum for the Ta2O5 microdisk resonator with radius = 150 μm and gap = 490 nm. (b) Measured spectrum (black dots) and Lorentzian fitting (red line) around the resonant wavelength at 1,548.471 nm. (c) Extracted Q L (blue dot) at each resonant wavelength. (d) Measured Q factor of microdisk resonance wavelength at 1,548.2 nm after 600 °C annealing.

Figure 3(c) shows the Q L extracted from all resonances of the TE fundamental mode between 1,500 nm and 1,600 nm. It was found that Q L -values distribute at around ∼3.5 × 105 in the investigated wavelength range. To the best of our knowledge, this is the first demonstration of high-Q Ta2O5 microdisks with bus waveguide coupling fabricated via electron beam lithography (EBL) and inductively coupled plasma reactive ion etching (ICP-RIE) – in contrast to previously reported high-Q Ta2O5 microdisks fabricated using photolithography-assisted chemical mechanical polishing and coupled via a tapered fibers [19]. To investigate the impact of waveguide sidewall roughness and internal film stress/defects on optical losses, the Ta2O5 microcavities were annealed at 600 °C for 10 h. As shown in Figure 3(d), the Q L increased significantly to ∼ 9.3 × 105 in the annealed devices, and the intrinsic Q was calculated to be 1.8 × 106. With annealing, the microdisk coupling state gradually shifted towards a critical coupling state. Consequently, the extinction ratio (ER) increased after annealing. Further reduction in optical losses may be achieved by optimizing the ICP-RIE etching parameters and improving the coupling conditions between microdisk and the bus waveguide. Alternatively, single-mode operation and enhanced Q-factors could be realized by employing Euler-bent waveguide designs to suppress higher-order modes and scattering losses.

Thermo-optic properties play a critical role in stabilizing on-chip light sources, particularly in applications such as microcavity-based soliton frequency combs [26] and rare-earth-doped laser systems [27]. To evaluate the thermo-optic response of Ta2O5 waveguides in the telecommunications band, temperature-dependent TE mode spectral measurements were performed on a Ta2O5 microdisk resonator. The substrate temperature was varied from 35 °C to 60 °C in 5 °C increments, covering multiple resonant wavelengths. Figure 4(a)-(c) display the linear dependence of the resonant wavelength on temperature at 1,505 nm, 1,550 nm, and 1,595 nm, yielding the resonance wavelength shifts (dλ/dT) of 8.99 pm/°C, 9 pm/°C, and 8.93 pm/°C, respectively. Figure 4(d) shows the resonant wavelength shift per °C across the entire telecom band, revealing a temperature-dependent shift of less than 10 pm/°C over a ∼100 nm spectral bandwidth.

Figure 4: (a)–(c) Fitting of resonance wavelength with increasing temperature at various wavelength ranges around (a) 1,505 nm, (b) 1,550 nm, and (c) 1,595 nm. (d) Resonant wavelength shifts per °C across the entire telecom band.
Figure 4:

(a)–(c) Fitting of resonance wavelength with increasing temperature at various wavelength ranges around (a) 1,505 nm, (b) 1,550 nm, and (c) 1,595 nm. (d) Resonant wavelength shifts per °C across the entire telecom band.

Table 1 compares the thermal stability of reported athermal microcavities across different material platforms. Microcavities based on materials with high thermo-optic coefficients, such as silicon and lithium niobate, typically require precise geometric engineering and the use of cladding layers with negative thermo-optic coefficients to achieve athermal behaviour. However, these compensatory approaches often compromise optical performance, particularly the achievable Q-factors. In contrast, Ta2O5 offers intrinsic thermal stability due to its naturally low thermo-optic coefficient, enabling broadband athermal behaviour in microdisk resonators while preserving high quality (Q) factors (>105). This eliminates the need for complex structural modifications or performance trade-offs.

Table 1:

Comparison of reported parameters of athermal microcavities based on different material platforms.

Material Cladding Structure dλ/dT (pm/K) λ(nm) Q L Athermal bandwidth (nm) FOMa ( Q L / Δ λ ) Ref.
Si PSQ-LN Ring 5 1,525 – – – [28]
Si LFR-372 Ring 0.2 1,550 1.8 × 104 – 9 × 104 [29]
Si TiO2 Ring 6.0 1,310 – 70 – [30]
Si TiO2 Ring −1.6 1,548 1.65 × 104 – 1.03 × 104 [15]
Si EP Ring 0.5 1,524 – 65 – [31]
Si Electro-optic polymer Ring 2.1 1,550 1.25 × 104 – 0.6 × 104 [32]
Si As20S80 Ring 13.95 1,610 2.6 × 105 80 1.86 × 104 [33]
Ta2O5 Air Ring 7.8 1,543 5.5 × 104 – 0.71 × 104 [34]
Ta2O5 SiO2 Ring 10.96 1,550 2.29 × 105 – 2.65 × 104 [25]
Ta2O5 Air Ring ∼9 1,549 1.84 × 106 – 20.4 × 104 [24]
Ta2O5 Air Disk 9 1,550 9.3 × 105 100 10.3 × 104 This work
Ta2O5 SU-8 Disk 3 1,550 3.2 × 105 – 10.7 × 104 This work

  1. aHigher is better.

The temperature dependent wavelength shift (Δλ) of Ta2O5 microdisk resonator arises from both the thermal expansion effects and the thermo-optic effects according to Eq. (1) [35]

(1) Δ λ = d λ d T = λ 1 n eff d n eff d T + 1 R d R d T

where d n eff d T is the effective thermo-optic coefficient, 1 R d R d T is the effective thermal expansion coefficient. However, due to silica’s low thermal expansion coefficient and the thin Ta2O5 layer in our resonator geometry, material thermal expansion contributions are negligible [17]. From the measured wavelength shift of ∼9 pm/°C at 1,550 nm, we calculated a thermo-optic coefficient (TOC) of ∼ 4.8 × 10−6/K for the Ta2O5 microdisk resonator, which is two orders of magnitude smaller than that of silicon, in excellent agreement with the published values [34], [35].

Since the focus of this study is to simultaneously achieve a high Q-factor and low thermal drift, we define a figure of merit (FOM) to compare the performance of our Ta2O5 resonator with other on-chip cavities. For a fair comparison, we define the FOM given as F O M = Q L / Δ λ , which represents the ratio of the microcavity’s load quality factor to the temperature-dependent wavelength shift. In the equation, Q L represents the microcavity’s load quality factor, and Δλ represents the temperature-dependent wavelength shift. This FOM does not consider the resonator design and only compares the microcavity’s quality factor and thermo-optical properties across different waveguides. A higher FOM is preferred, implying a higher quality factor and thermal stability of the microcavity. Table 1 summarizes a few representative designs with respect to this FOM.

To further enhance the thermal stability of the Ta2O5 microdisk, a 1 μm-thick SU-8 polymer layer was spin-coated onto the device to serve as an upper cladding. The SU-8 polymer, which possesses a negative thermo-optic coefficient (−2.9 × 10−4/K) [35], was employed to partially compensate for the positive thermo-optic effect of the Ta2O5 microdisk. The resonance shift of the microdisk was characterized over a temperature range from 35 °C to 60 °C. As shown in Figure 5(a), the resonance peak at 1,549.8622 nm wavelength was red-shifted to 1,549.9394 nm. Figure 5(b) shows the linear relationship between resonant wavelength and temperature, with a fitted temperature sensitivity of approximately 3 pm/ oC, in contrast to the previous 9 pm/ oC, confirming that SU-8 upper cladding layer significantly improves thermal stability of the device. However, the improvement is limited. Due to the fixed geometry of the microdisk, the majority of the optical mode remains confined within the Ta2O5 core, and only a small portion interacts with the SU-8 cladding. As a result, the influence of SU-8’s negative thermo-optic coefficient on the overall device stability is modest. The measured Q-factor of the SU-8–coated microdisk is approximately 3.2 × 105, lower than that of the air-clad counterpart. This reduction is likely due to unoptimized structural parameters, including cladding thickness, coupling coefficient, and microdisk radius. Here, we mainly characterize the thermal stability of the microdisk working in TE mode, and the thermal stability performance of the microdisk working in TM mode can be further tested later. The TE mode has a higher light field confinement capability than the TM mode, resulting in more light being confined to the Ta2O5 waveguide core and less light leaking into the SU-8 cladding. Conversely, for the TM mode, more light leaks into the SU-8 cladding. Therefore, under the same external temperature and input power, Ta2O5 microdisks operating in the TM mode will exhibit superior thermal stability. Future work should focus on engineering the mode confinement to balance the optical field overlap between materials with positive and negative thermo-optic coefficients through carefully designing the SU-8 cladding thickness and the microdisk’s radius and height. By integrating careful microcavity design with optimized fabrication processes, it will be possible to realize high-Q microresonators operating in the athermal regime, thereby enhancing their suitability for applications such as on-chip optical frequency comb generation.

Figure 5: (a) Measured transmission spectra of the Ta2O5 microdisk resonator at various temperatures with SU-8 cladding, (b) the microdisk resonance wavelength shift with SU-8 cladding as a function of temperature.
Figure 5:

(a) Measured transmission spectra of the Ta2O5 microdisk resonator at various temperatures with SU-8 cladding, (b) the microdisk resonance wavelength shift with SU-8 cladding as a function of temperature.

In addition to the previously discussed characteristics, we further investigated the impact of high optical power on the stability of the Ta2O5 microcavity. Specifically, when the microcavity operates at its resonance wavelength, constructive interference leads to a buildup of intracavity power. In such cases, any linear or nonlinear absorption within the resonator can induce localized heating, which in turn may affect the optical properties of the device. Certain material platforms, such as Si [16] and SiC [36], are known to exhibit significant linear and nonlinear absorption under high-power operation, potentially degrading device performance. To evaluate whether similar effects occur in the Ta2O5 microdisk resonator, we used a tunable laser source to perform wavelength scans while monitoring the corresponding transmission spectra.

Figure 6(a) presents the power-dependent transmission spectra of the Ta2O5 microdisk resonator for coupled input powers ranging from 0.1 mW to 25.1 mW, the latter being limited by the maximum output power of the laser. Notably, the transmission spectra appear nearly identical across all input power levels. The corresponding resonant wavelengths under varying power conditions, extracted from Figure 6(a), are plotted and fitted in Figure 6(b). The results show that the resonance peak position remains virtually unchanged as input power increases. In addition, the Q factors and extinction ratios (ER) associated with each resonance peak were extracted and are shown in Figure 6(c). The analysis indicates that neither the Q-factor nor the ER is significantly affected by increasing optical power. The Q-factors are consistently maintained around ∼4 × 105, and the ER remains approximately 13 dB. The energy buildup in the Ta2O5 microdisk cavity primarily results from the field enhancement factor (FE). The field enhancement factor describes the ability of the cavity to amplify the local electric field amplitude. The power enhancement factor (M) describes the enhancement factor of the optical power stored or circulating within the cavity relative to the incident optical power. Because optical power is proportional to the square of the electric field intensity, the power enhancement factor is numerically equal to the square of the field enhancement factor [37]. At the resonance wavelength, the buildup factor can be estimated by [37], [38]:

(2) F E = κ 1 − τ ⁡ exp α L / 2 + j κ L

where a is the round-trip amplitude transmission, κ and τ are coupling coefficient and transmission coefficient, respectively. They are assumed to satisfy κ 2 + τ 2 = 1, and can be calculated using equation T 0 = a − τ 2 / 1 − a τ 2 , here T 0 is the fraction of transmitted optical power at the resonance wavelength. L is physical length of the microdisk resonator. Based on this, the field enhancement factor in the Ta2O5 microdisk cavity is estimated to be approximately 22, indicating that the intracavity power at resonance is amplified by a factor of 484 compared to the input power. This observed stability confirms that Ta2O5 microcavities exhibit exceptional thermal insensitivity and negligible nonlinear absorption, even under conditions of high intracavity energy. These properties make Ta2O5 a highly promising material platform for developing thermally stable, high-performance on-chip integrated light sources.

Figure 6: (a) Power-dependent transmission spectra of Ta2O5 microdisk resonator. (b) Extraction of the resonance peak position at different input power in (a). (c) Changes in the extinction ratio (ER) and loaded Q (Q L ) of the resonance peak at ∼ 1,549.09 nm in (a) at various input powers.
Figure 6:

(a) Power-dependent transmission spectra of Ta2O5 microdisk resonator. (b) Extraction of the resonance peak position at different input power in (a). (c) Changes in the extinction ratio (ER) and loaded Q (Q L ) of the resonance peak at ∼ 1,549.09 nm in (a) at various input powers.

4 Conclusions

In summary, we have demonstrated a high-Q, athermal Ta2O5 microdisk resonator fabricated using e-beam lithography and inductively coupled plasma reactive ion etching. The fabricated microdisk resonator with a radius of 150 µm exhibits a loaded Q-factor of 4.25 × 105 for the TE fundamental mode at 1,550 nm. After thermal annealing, the loaded Q-factor more than doubles, reaching approximately 9.3 × 105, with an intrinsic Q-factor as high as 1.8 × 106. Notably, the temperature-dependent resonant wavelength shift of the Ta2O5 microdisk remains below 10 pm/oC across the entire telecom band, spanning a ∼100 nm bandwidth. Furthermore, power-dependent transmission measurements reveal no observable shift or distortion in resonant wavelengths, Q-factors (4 × 105), or extinction ratios (∼13 dB), even at input powers up to 25.1 mW. These results confirm the exceptional thermal insensitivity and low nonlinear absorption of Ta2O5 microdisks under high intracavity power conditions. The combination of ultrahigh Q-factors and superior thermal stability establishes Ta2O5 as a highly promising material platform for integrated, narrow-linewidth on-chip lasers [35]. Future work will focus on optimizing thermal compensation techniques, refining fabrication processes, and integrating these microresonators into scalable photonic circuits. This study represents a significant step forward realizing thermally robust, high-Q photonic devices, enabling new opportunities in precision metrology, quantum optics and integrated photonic systems.

Corresponding authors: Rongping Wang, Laboratory of Infrared Materia and Devices, Advanced Technology Research Institute, Ningbo University, Ningbo, Zhejiang, 315211, China, E-mail: ; and Ganapathy Senthil Murugan, Optoelectronics Research Centre, University of Southampton, Southampton, SO17 1BJ, United Kingdom, E-mail: 

Funding source: The Royal Society International Exchanges Grant

Award Identifier / Grant number: IEC\NSFC\201068

Funding source: jiang su funding program for excellent postdoctoral talent

Funding source: National Natural Science Foundation of China

Award Identifier / Grant number: 62405354

Award Identifier / Grant number: 62475126

  1. Research funding: National Natural Science Foundation of China (62405354, 62475126); Jiang su Funding Program for Excellent Postdoctoral Talent. The Royal Society International Exchanges Grant (IEC\NSFC\201068).

  2. Author contribution: ZY: data curation (lead); investigation (lead); writing – original draft (equal). ZheZ: data curation (supporting); investigation (supporting). PC: data curation (equal); investigation (supporting). ZL: data curation (supporting); investigation (supporting). QC: formal analysis (equal); supervision (equal); validation (equal). JY: investigation (supporting). YL: formal analysis (equal); supervision (equal); validation (equal). BF: formal analysis (equal); supervision (equal); validation (equal). ZhoZ: formal analysis (equal); supervision (equal); validation (equal). ZhiZ: formal analysis (equal); supervision (equal); validation (equal). GSM: conceptualization (lead); funding acquisition (lead); writing – review & editing (lead). RW: conceptualization (lead); formal analysis (equal); funding acquisition (lead); investigation (equal); project administration (lead); supervision (lead); validation (lead); writing – original draft (equal); writing – review & editing (lead). All authors have accepted responsibility for the entire content of this manuscript and consented to its submission to the journal, reviewed all the results and approved the final version of the manuscript.

  3. Conflict of interest: Authors state no conflicts of interest.

  4. 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. J. Vahala, “Optical microcavities,” Nature, vol. 424, no. 6950, pp. 839–846, 2003. https://doi.org/10.1038/nature01939.Search in Google Scholar PubMed

[2] T. M. Benson et al.., “Micro-optical resonators for microlasers and integrated optoelectronics,” in Frontiers in Planar Lightwave Circuit Technology: Design, Simulation, and Fabrication, Berlin, Germany, Springer, 2006, pp. 39–70.10.1007/1-4020-4167-5_02Search in Google Scholar

[3] C. Wang et al.., “Lithium tantalate photonic integrated circuits for volume manufacturing,” Nature, vols. 1–7, no. 8013, pp. 784–790, 2024.10.1038/s41586-024-07369-1Search in Google Scholar PubMed PubMed Central

[4] L. Zhang and D. Dai, “Silicon subwavelength-grating microdisks for optical sensing,” IEEE Photon. Technol. Lett., vol. 31, no. 15, pp. 1209–1212, 2019. https://doi.org/10.1109/lpt.2019.2922230.Search in Google Scholar

[5] W. Jin et al.., “Hertz-linewidth semiconductor lasers using CMOS-ready ultra-high-Q microresonators,” Nat. Photonics, vol. 15, no. 5, pp. 346–353, 2021. https://doi.org/10.1038/s41566-021-00761-7.Search in Google Scholar

[6] A. Matsko et al.., “Review of applications of whispering-gallery mode resonators in photonics and nonlinear optics,” IPN Prog. Rep., vol. 42, no. 162, pp. 1–51, 2005.Search in Google Scholar

[7] L. Zhang et al.., “Ultrahigh-Q silicon racetrack resonators,” Photon. Res., vol. 8, no. 5, pp. 684–689, 2020. https://doi.org/10.1364/prj.387816.Search in Google Scholar

[8] M. W. Puckett et al.., “422 million intrinsic quality factor planar integrated all-waveguide resonator with sub-MHz linewidth,” Nat. Commun., vol. 12, no. 1, p. 934, 2021. https://doi.org/10.1038/s41467-021-21205-4.Search in Google Scholar PubMed PubMed Central

[9] H. Jung, S.-P. Yu, D. R. Carlson, T. E. Drake, T. C. Briles, and S. B. Papp, “Tantala Kerr nonlinear integrated photonics,” Optica, vol. 8, no. 6, pp. 811–817, 2021. https://doi.org/10.1364/optica.411968.Search in Google Scholar

[10] R. Gao et al.., “Lithium niobate microring with ultra-high Q factor above 10^ 8,” Chin. Opt. Lett., vol. 20, no. 1, p. 011902, 2022. https://doi.org/10.3788/col202220.011902.Search in Google Scholar

[11] C. Li et al.., “Ultra-high Q lithium niobate microring monolithically fabricated by photolithography assisted chemo-mechanical etching,” Opt. Express, vol. 31, no. 19, pp. 31556–31562, 2023. https://doi.org/10.1364/oe.498086.Search in Google Scholar

[12] M. Zhang, C. Wang, R. Cheng, A. Shams-Ansari, and M. Lončar, “Monolithic ultra-high-Q lithium niobate microring resonator,” Optica, vol. 4, no. 12, pp. 1536–1537, 2017. https://doi.org/10.1364/optica.4.001536.Search in Google Scholar

[13] C. Wang et al.., “High-Q microresonators on 4H-silicon-carbide-on-insulator platform for nonlinear photonics,” Light Sci. Appl., vol. 10, no. 1, p. 139, 2021. https://doi.org/10.1038/s41377-021-00584-9.Search in Google Scholar PubMed PubMed Central

[14] W. Xie et al.., “Ultrahigh-Q AlGaAs-on-insulator microresonators for integrated nonlinear photonics,” Opt. Express, vol. 28, no. 22, pp. 32894–32906, 2020. https://doi.org/10.1364/oe.405343.Search in Google Scholar

[15] S. S. Djordjevic et al.., “CMOS-compatible, athermal silicon ring modulators clad with titanium dioxide,” Opt. Express, vol. 21, no. 12, pp. 13958–13968, 2013. https://doi.org/10.1364/oe.21.013958.Search in Google Scholar PubMed

[16] S. Grillanda et al.., “Post-fabrication trimming of athermal silicon waveguides,” Opt. Lett., vol. 38, no. 24, pp. 5450–5453, 2013. https://doi.org/10.1364/ol.38.005450.Search in Google Scholar

[17] G. Kang et al.., “High quality chalcogenide-silica hybrid wedge resonator,” Opt. Express, vol. 25, no. 13, pp. 15581–15589, 2017. https://doi.org/10.1364/oe.25.015581.Search in Google Scholar PubMed

[18] M. Belt, M. L. Davenport, J. E. Bowers, and D. J. Blumenthal, “Ultra-low-loss Ta2O5-core/SiO2-clad planar waveguides on Si substrates,” Optica, vol. 4, no. 5, pp. 532–536, 2017. https://doi.org/10.1364/optica.4.000532.Search in Google Scholar

[19] M. Li et al.., “Fabrication of ultra-high-Q Ta2O5 microdisks by photolithography-assisted chemo-mechanical etching,” Opt. Express, vol. 32, no. 17, pp. 29566–29572, 2024. https://doi.org/10.1364/oe.529379.Search in Google Scholar PubMed

[20] C.-Y. Tai et al.., “Determination of nonlinear refractive index in a Ta2O5 rib waveguide using self-phase modulation,” Opt. Express, vol. 12, no. 21, pp. 5110–5116, 2004. https://doi.org/10.1364/opex.12.005110.Search in Google Scholar PubMed

[21] C.-L. Wu et al.., “Tantalum pentoxide (Ta2O5) based athermal micro-ring resonator,” OSA Continuum, vol. 2, no. 4, pp. 1198–1206, 2019. https://doi.org/10.1364/osac.2.001198.Search in Google Scholar

[22] C. Zhang et al.., “Tantalum pentoxide: A new material platform for high-performance dielectric metasurface optics in the ultraviolet and visible region,” Light Sci. Appl., vol. 13, no. 1, p. 23, 2024. https://doi.org/10.1038/s41377-023-01330-z.Search in Google Scholar PubMed PubMed Central

[23] Z. Zhang et al.., “On-chip Er-doped Ta2O5 waveguide amplifiers with a high internal net gain,” Opt. Lett., vol. 48, no. 21, pp. 5799–5802, 2023. https://doi.org/10.1364/ol.499779.Search in Google Scholar

[24] J. Rasmus Bankwitz et al.., “High-quality factor Ta2O5-on-insulator resonators with ultimate thermal stability,” Opt. Lett., vol. 48, no. 21, pp. 5783–5786, 2023. https://doi.org/10.1364/ol.499726.Search in Google Scholar

[25] Q. Zhao et al.., “Low-loss low thermo-optic coefficient Ta2O5 on crystal quartz planar optical waveguides,” APL Photonics, vol. 5, no. 11, p. 116103, 2020. https://doi.org/10.1063/5.0024743.Search in Google Scholar

[26] D. Xia et al.., “Integrated chalcogenide photonics for microresonator soliton combs,” Laser Photon. Rev., vol. 17, no. 3, p. 2370013, 2023. https://doi.org/10.1002/lpor.202200219.Search in Google Scholar

[27] K. Miarabbas Kiani, H. C. Frankis, C. M. Naraine, D. B. Bonneville, A. P. Knights, and J. D. B. Bradley, “Lasing in a hybrid rare‐earth silicon microdisk,” Laser Photon. Rev., vol. 16, no. 1, p. 2100348, 2022. https://doi.org/10.1002/lpor.202100348.Search in Google Scholar

[28] J. Teng et al.., “Athermal Silicon-on-insulator ring resonators by overlaying a polymer cladding on narrowed waveguides,” Opt. Express, vol. 17, no. 17, pp. 14627–14633, 2009. https://doi.org/10.1364/oe.17.014627.Search in Google Scholar PubMed

[29] M. M. Milošević, N. G. Emerson, F. Y. Gardes, X. Chen, A. A. D. T. Adikaari, and G. Z. Mashanovich, “Athermal waveguides for optical communication wavelengths,” Opt. Lett., vol. 36, no. 23, pp. 4659–4661, 2011. https://doi.org/10.1364/ol.36.004659.Search in Google Scholar PubMed

[30] S. Feng et al.., “Athermal silicon ring resonators clad with titanium dioxide for 1.3 µm wavelength operation,” Opt. Express, vol. 23, no. 20, pp. 25653–25660, 2015. https://doi.org/10.1364/oe.23.025653.Search in Google Scholar

[31] V. Raghunathan, N. Y. Winnie, J. Hu, T. Izuhara, J. Michel, and L. Kimerling, “Athermal operation of silicon waveguides: Spectral, second order and footprint dependencies,” Opt. Express, vol. 18, no. 17, pp. 17631–17639, 2010. https://doi.org/10.1364/oe.18.017631.Search in Google Scholar PubMed

[32] F. Qiu et al.., “Athermal hybrid silicon/polymer ring resonator electro-optic modulator,” Acs Photonics, vol. 3, no. 5, pp. 780–783, 2016. https://doi.org/10.1021/acsphotonics.5b00695.Search in Google Scholar

[33] P. Jean, A. Douaud, T. Thibault, S. LaRochelle, Y. Messaddeq, and W. Shi, “Sulfur-rich chalcogenide claddings for athermal and high-q silicon microring resonators,” Opt. Mater. Express, vol. 11, no. 3, pp. 913–925, 2021. https://doi.org/10.1364/ome.421814.Search in Google Scholar

[34] J. Ling, Y. He, R. Luo, H. Liang, and Q. Lin, “Athermal lithium niobate microresonator,” Opt. Express, vol. 28, no. 15, pp. 21682–21691, 2020. https://doi.org/10.1364/oe.398363.Search in Google Scholar

[35] Z. Geng et al.., “Low-loss tantalum pentoxide photonics with a CMOS-compatible process,” Opt. Express, vol. 32, no. 7, pp. 12291–12302, 2024. https://doi.org/10.1364/oe.518545.Search in Google Scholar PubMed

[36] P. Xing, D. Ma, L. C. Kimerling, A. M. Agarwal, and D. T. H. Tan, “High efficiency four wave mixing and optical bistability in amorphous silicon carbide ring resonators,” APL Photonics, vol. 5, no. 7, p. 076110, 2020. https://doi.org/10.1063/5.0009692.Search in Google Scholar

[37] Y. Zheng, M. Pu, A. Yi, X. Ou, and H. Ou, “4H-SiC microring resonators for nonlinear integrated photonics,” Opt. Lett., vol. 44, no. 23, pp. 5784–5787, 2019. https://doi.org/10.1364/ol.44.005784.Search in Google Scholar PubMed

[38] W. Bogaerts et al.., “Silicon microring resonators,” Laser Photon. Rev., vol. 6, no. 1, pp. 47–73, 2012. https://doi.org/10.1002/lpor.201100017.Search in Google Scholar
Received: 2025-09-18
Accepted: 2025-11-22
Published Online: 2025-12-05

© 2025 the author(s), published by De Gruyter, Berlin/Boston

This work is licensed under the Creative Commons Attribution 4.0 International License.

Articles in the same Issue

  1. Frontmatter
  2. Reviews
  3. Light-driven micro/nanobots
  4. Tunable BIC metamaterials with Dirac semimetals
  5. Large-scale silicon photonics switches for AI/ML interconnections based on a 300-mm CMOS pilot line
  6. Perspective
  7. Density-functional tight binding meets Maxwell: unraveling the mysteries of (strong) light–matter coupling efficiently
  8. Letters
  9. Broadband on-chip spectral sensing via directly integrated narrowband plasmonic filters for computational multispectral imaging
  10. Sub-100 nm manipulation of blue light over a large field of view using Si nanolens array
  11. Tunable bound states in the continuum through hybridization of 1D and 2D metasurfaces
  12. Integrated array of coupled exciton–polariton condensates
  13. Disentangling the absorption lineshape of methylene blue for nanocavity strong coupling
  14. Research Articles
  15. Demonstration of multiple-wavelength-band photonic integrated circuits using a silicon and silicon nitride 2.5D integration method
  16. Inverse-designed gyrotropic scatterers for non-reciprocal analog computing
  17. Highly sensitive broadband photodetector based on PtSe2 photothermal effect and fiber harmonic Vernier effect
  18. Online training and pruning of multi-wavelength photonic neural networks
  19. Robust transport of high-speed data in a topological valley Hall insulator
  20. Engineering super- and sub-radiant hybrid plasmons in a tunable graphene frame-heptamer metasurface
  21. Near-unity fueling light into a single plasmonic nanocavity
  22. Polarization-dependent gain characterization in x-cut LNOI erbium-doped waveguide amplifiers
  23. Intramodal stimulated Brillouin scattering in suspended AlN waveguides
  24. Single-shot Stokes polarimetry of plasmon-coupled single-molecule fluorescence
  25. Metastructure-enabled scalable multiple mode-order converters: conceptual design and demonstration in direct-access add/drop multiplexing systems
  26. High-sensitivity U-shaped biosensor for rabbit IgG detection based on PDA/AuNPs/PDA sandwich structure
  27. Deep-learning-based polarization-dependent switching metasurface in dual-band for optical communication
  28. A nonlocal metasurface for optical edge detection in the far-field
  29. Coexistence of weak and strong coupling in a photonic molecule through dissipative coupling to a quantum dot
  30. Mitigate the variation of energy band gap with electric field induced by quantum confinement Stark effect via a gradient quantum system for frequency-stable laser diodes
  31. Orthogonal canalized polaritons via coupling graphene plasmon and phonon polaritons of hBN metasurface
  32. Dual-polarization electromagnetic window simultaneously with extreme in-band angle-stability and out-of-band RCS reduction empowered by flip-coding metasurface
  33. Record-level, exceptionally broadband borophene-based absorber with near-perfect absorption: design and comparison with a graphene-based counterpart
  34. Generalized non-Hermitian Hamiltonian for guided resonances in photonic crystal slabs
  35. A 10× continuously zoomable metalens system with super-wide field of view and near-diffraction–limited resolution
  36. Continuously tunable broadband adiabatic coupler for programmable photonic processors
  37. Diffraction order-engineered polarization-dependent silicon nano-antennas metagrating for compact subtissue Mueller microscopy
  38. Lithography-free subwavelength metacoatings for high thermal radiation background camouflage empowered by deep neural network
  39. Multicolor nanoring arrays with uniform and decoupled scattering for augmented reality displays
  40. Permittivity-asymmetric qBIC metasurfaces for refractive index sensing
  41. Theory of dynamical superradiance in organic materials
  42. Second-harmonic generation in NbOI2-integrated silicon nitride microdisk resonators
  43. A comprehensive study of plasmonic mode hybridization in gold nanoparticle-over-mirror (NPoM) arrays
  44. Foundry-enabled wafer-scale characterization and modeling of silicon photonic DWDM links
  45. Rough Fabry–Perot cavity: a vastly multi-scale numerical problem
  46. Classification of quantum-spin-hall topological phase in 2D photonic continuous media using electromagnetic parameters
  47. Light-guided spectral sculpting in chiral azobenzene-doped cholesteric liquid crystals for reconfigurable narrowband unpolarized light sources
  48. Modelling Purcell enhancement of metasurfaces supporting quasi-bound states in the continuum
  49. Ultranarrow polaritonic cavities formed by one-dimensional junctions of two-dimensional in-plane heterostructures
  50. Bridging the scalability gap in van der Waals light guiding with high refractive index MoTe2
  51. Ultrafast optical modulation of vibrational strong coupling in ReCl(CO)3(2,2-bipyridine)
  52. Chirality-driven all-optical image differentiation
  53. Wafer-scale CMOS foundry silicon-on-insulator devices for integrated temporal pulse compression
  54. Monolithic temperature-insensitive high-Q Ta2O5 microdisk resonator
  55. Nanogap-enhanced terahertz suppression of superconductivity
  56. Large-gap cascaded Moiré metasurfaces enabling switchable bright-field and phase-contrast imaging compatible with coherent and incoherent light
  57. Synergistic enhancement of magneto-optical response in cobalt-based metasurfaces via plasmonic, lattice, and cavity modes
  58. Scalable unitary computing using time-parallelized photonic lattices
  59. Diffusion model-based inverse design of photonic crystals for customized refraction
  60. Wafer-scale integration of photonic integrated circuits and atomic vapor cells
  61. Optical see-through augmented reality via inverse-designed waveguide couplers
  62. One-dimensional dielectric grating structure for plasmonic coupling and routing
  63. MCP-enabled LLM for meta-optics inverse design: leveraging differentiable solver without LLM expertise
  64. Broadband variable beamsplitter made of a subwavelength-thick metamaterial
  65. Scaling-dependent tunability of spin-driven photocurrents in magnetic metamaterials
  66. AI-based analysis algorithm incorporating nanoscale structural variations and measurement-angle misalignment in spectroscopic ellipsometry
https://doi.org/10.1515/nanoph-2025-0485
Keywords for this article
tantala waveguide; microdisk resonator; optical cavity
Creative Commons
BY 4.0

Articles in the same Issue

  1. Frontmatter
  2. Reviews
  3. Light-driven micro/nanobots
  4. Tunable BIC metamaterials with Dirac semimetals
  5. Large-scale silicon photonics switches for AI/ML interconnections based on a 300-mm CMOS pilot line
  6. Perspective
  7. Density-functional tight binding meets Maxwell: unraveling the mysteries of (strong) light–matter coupling efficiently
  8. Letters
  9. Broadband on-chip spectral sensing via directly integrated narrowband plasmonic filters for computational multispectral imaging
  10. Sub-100 nm manipulation of blue light over a large field of view using Si nanolens array
  11. Tunable bound states in the continuum through hybridization of 1D and 2D metasurfaces
  12. Integrated array of coupled exciton–polariton condensates
  13. Disentangling the absorption lineshape of methylene blue for nanocavity strong coupling
  14. Research Articles
  15. Demonstration of multiple-wavelength-band photonic integrated circuits using a silicon and silicon nitride 2.5D integration method
  16. Inverse-designed gyrotropic scatterers for non-reciprocal analog computing
  17. Highly sensitive broadband photodetector based on PtSe2 photothermal effect and fiber harmonic Vernier effect
  18. Online training and pruning of multi-wavelength photonic neural networks
  19. Robust transport of high-speed data in a topological valley Hall insulator
  20. Engineering super- and sub-radiant hybrid plasmons in a tunable graphene frame-heptamer metasurface
  21. Near-unity fueling light into a single plasmonic nanocavity
  22. Polarization-dependent gain characterization in x-cut LNOI erbium-doped waveguide amplifiers
  23. Intramodal stimulated Brillouin scattering in suspended AlN waveguides
  24. Single-shot Stokes polarimetry of plasmon-coupled single-molecule fluorescence
  25. Metastructure-enabled scalable multiple mode-order converters: conceptual design and demonstration in direct-access add/drop multiplexing systems
  26. High-sensitivity U-shaped biosensor for rabbit IgG detection based on PDA/AuNPs/PDA sandwich structure
  27. Deep-learning-based polarization-dependent switching metasurface in dual-band for optical communication
  28. A nonlocal metasurface for optical edge detection in the far-field
  29. Coexistence of weak and strong coupling in a photonic molecule through dissipative coupling to a quantum dot
  30. Mitigate the variation of energy band gap with electric field induced by quantum confinement Stark effect via a gradient quantum system for frequency-stable laser diodes
  31. Orthogonal canalized polaritons via coupling graphene plasmon and phonon polaritons of hBN metasurface
  32. Dual-polarization electromagnetic window simultaneously with extreme in-band angle-stability and out-of-band RCS reduction empowered by flip-coding metasurface
  33. Record-level, exceptionally broadband borophene-based absorber with near-perfect absorption: design and comparison with a graphene-based counterpart
  34. Generalized non-Hermitian Hamiltonian for guided resonances in photonic crystal slabs
  35. A 10× continuously zoomable metalens system with super-wide field of view and near-diffraction–limited resolution
  36. Continuously tunable broadband adiabatic coupler for programmable photonic processors
  37. Diffraction order-engineered polarization-dependent silicon nano-antennas metagrating for compact subtissue Mueller microscopy
  38. Lithography-free subwavelength metacoatings for high thermal radiation background camouflage empowered by deep neural network
  39. Multicolor nanoring arrays with uniform and decoupled scattering for augmented reality displays
  40. Permittivity-asymmetric qBIC metasurfaces for refractive index sensing
  41. Theory of dynamical superradiance in organic materials
  42. Second-harmonic generation in NbOI2-integrated silicon nitride microdisk resonators
  43. A comprehensive study of plasmonic mode hybridization in gold nanoparticle-over-mirror (NPoM) arrays
  44. Foundry-enabled wafer-scale characterization and modeling of silicon photonic DWDM links
  45. Rough Fabry–Perot cavity: a vastly multi-scale numerical problem
  46. Classification of quantum-spin-hall topological phase in 2D photonic continuous media using electromagnetic parameters
  47. Light-guided spectral sculpting in chiral azobenzene-doped cholesteric liquid crystals for reconfigurable narrowband unpolarized light sources
  48. Modelling Purcell enhancement of metasurfaces supporting quasi-bound states in the continuum
  49. Ultranarrow polaritonic cavities formed by one-dimensional junctions of two-dimensional in-plane heterostructures
  50. Bridging the scalability gap in van der Waals light guiding with high refractive index MoTe2
  51. Ultrafast optical modulation of vibrational strong coupling in ReCl(CO)3(2,2-bipyridine)
  52. Chirality-driven all-optical image differentiation
  53. Wafer-scale CMOS foundry silicon-on-insulator devices for integrated temporal pulse compression
  54. Monolithic temperature-insensitive high-Q Ta2O5 microdisk resonator
  55. Nanogap-enhanced terahertz suppression of superconductivity
  56. Large-gap cascaded Moiré metasurfaces enabling switchable bright-field and phase-contrast imaging compatible with coherent and incoherent light
  57. Synergistic enhancement of magneto-optical response in cobalt-based metasurfaces via plasmonic, lattice, and cavity modes
  58. Scalable unitary computing using time-parallelized photonic lattices
  59. Diffusion model-based inverse design of photonic crystals for customized refraction
  60. Wafer-scale integration of photonic integrated circuits and atomic vapor cells
  61. Optical see-through augmented reality via inverse-designed waveguide couplers
  62. One-dimensional dielectric grating structure for plasmonic coupling and routing
  63. MCP-enabled LLM for meta-optics inverse design: leveraging differentiable solver without LLM expertise
  64. Broadband variable beamsplitter made of a subwavelength-thick metamaterial
  65. Scaling-dependent tunability of spin-driven photocurrents in magnetic metamaterials
  66. AI-based analysis algorithm incorporating nanoscale structural variations and measurement-angle misalignment in spectroscopic ellipsometry
Sign up now to receive a 20% welcome discount
Institutional Access
How does access work?
Have an idea on how to improve our website?
Please write us.
© 2026 De Gruyter Brill
Downloaded on 22.1.2026 from https://www.degruyterbrill.com/document/doi/10.1515/nanoph-2025-0485/html
Scroll to top button