Pei-Hsun Wang

We demonstrate the fabrication of high-quality hydrogenated amorphous silicon (a-Si:H) photonics using the low-temperature high-power impulse magnetron sputtering (HiPIMS) process. The deposited a-Si:H films exhibit a high refractive index ( n ≈ 3.52) and a wide optical bandgap (≈ 1.96 eV), enabling low-loss photonic devices suitable for integrated silicon photonics. By employing an ultra-low-temperature deposition process of 70 °C, a-Si waveguide resonators are investigated, exhibiting quality (Q) factors on the order of 10 ⁵ and high extinction ratios around 20 dB. These results highlight the potential of HiPIMS-deposited a-Si:H film in realizing compact, low-loss photonic devices, while also enabling low-thermal-budget hybrid integration that facilitates heterogeneous photonic integration and serves as a key step toward future co-packaged optics (CPO) implementations.

Nanoimprint lithography (NIL) has emerged as a powerful tool for patterning nanoscale structures with high precision, low-cost, and large-scale manufacturing. In photonics, NIL enables the creation of complex optical structures such as gratings, metamaterials, photonic crystals, and waveguides. These nanoscale features are critical for manipulating light at sub-wavelength scales, offering enhanced control over optical properties such as dispersion, polarization, and transmission. NIL’s high-resolution patterning capability makes it particularly attractive for fabricating large-area photonic devices with high precision and repeatability. A wide range of applications, including integrated photonic circuits, optical sensors, and advanced light management in displays and solar cells, are now the focus of extensive research and discussion. By enabling the precise engineering of refractive index profiles and light–matter interactions, NIL continues to play a crucial role in advancing the performance and functionality of next-generation photonic systems. This review explores the fundamental principles of NIL and its recent developments. In addition, other patterning techniques related to photonics patterning and fabrication are briefly discussed. We will then focus on the applications in photonics and the advantages and challenges associated with this technique.

In this study, we demonstrate photonic resonators by integrating polymeric waveguides using cost-effective ultraviolet (UV) contact lithography on glass substrates. Low-loss waveguides are realized while the quality (Q) factor of waveguide resonators can be up to 10⁵. Employing the glass substrate effectively reduces optical power leakage and lowers the cost of a thick buried SiO₂ layer compared to the conventional silicon substrate. Uniform, high extinction, single-mode resonances are identified within a broad spectrum (1540–1560 nm) in the telecommunication band. In addition, a hybrid waveguide platform integrating both polymers and dielectric Si₃N₄ is introduced on the glass substrates, offering the potential for enhanced optical confinement and a smaller device footprint. A comparable Q factor of approximately 10⁵ is again achieved using etch-free processes and µm-scale UV contact lithography. This demonstration highlights the potential for a simple, fast, low-thermal budget configuration of high-quality glass-based photonics, which is advantageous for future co-packaged photonics on glass interposers.

In this work, we demonstrate the fabrication of high-quality (Q) TiO₂ waveguide resonators by E-gun evaporation. The deposited titanium dioxide (TiO₂) films exhibit superior roughness below 1 nm, demonstrating high-Q TiO₂ integrated photonics. By employing the low-temperature, high-deposition-rate evaporation process, both low-confined and high-confined TiO₂ waveguides are investigated, highlighting their potential for applications in nonlinear and quantum photonics. Meanwhile, the Q factor of waveguide resonators can reach approximately 1.1 × 10⁵. With an optimized pulley coupling design, high extinction ratios (ER) above 27.1 dB for the silicon substrate and 68.7 dB for the glass substrate are achieved, respectively. This work shows the potential in fabricating both high-Q, high-ER waveguide resonators, and highly confined TiO₂ photonic waveguides with E-gun evaporation for applications in co-packaged optics.

We demonstrate integrated TiO₂ photonics by E-gun evaporation. With a superior roughness of 0.69 nm of the deposited TiO₂ film, waveguide resonators with high quality (Q > 6×10⁴) can be realized on the glass substrate.

In this study, we demonstrate high-extinction stop-band photonic filters based on Mach–Zehnder interferometer (MZI)-coupled silicon nitride (Si₃N₄) resonators fabricated using I-line lithography technology. Leveraging the low-loss silicon nitride waveguide, our approach enables the creation of stable, high-performance filters suitable for applications in quantum and nonlinear photonics. With destructive interference at the feedback loop, photonic filters with an extinction ratio of 35 dB are demonstrated with four cascaded MZI-coupled resonators. This cascading design not only enhances the filter’s extinction but also improves its spectral sharpness, providing a more selective stop-band profile. Experimental results agree well with the theoretical results, showing linear scaling of extinction ratios with the number of cascaded MZI-coupled resonators. The scalability of this architecture opens the possibility for further integration and optimization in complex photonic circuits, where high extinction ratios and precise wavelength selectivity are critical for advanced signal processing and quantum information applications.

In this study, we demonstrate the fabrication of waveguide resonators using nanoimprint technology. Without relying on traditionally costly lithography methods, such as electron-beam lithography or stepper lithography, silicon nitride (Si3N4) resonators with high-quality factors up to the order of 105 can be realized at C-band by nanoimprint lithography. In addition, by properly designing the waveguide geometry, a low-dispersive waveguide can be achieved with waveguide dispersion at around −35 ps/nm/km in the normal dispersion regime, and the waveguide dispersion can be further tuned to be 29 ps/nm/km in the anomalous dispersion regime with the polymer cladding. The tunability of nanoimprinted devices is demonstrated by the aid of microheaters, realizing on-chip optical functionalities. This work offers the potential to fabricate low-dispersive waveguide resonators for integrated modulators and filters in a significantly cost-effective and process-friendly scheme.

A FMCW LiDAR system of both the distributed feedback laser and external cavity laser is established in baseband beat notes, rather than up-conversion to an intermediate frequency to exclude flicker noise. Meanwhile, utilizing fast-scanning MEMS mirrors, high-quality real-time (1 fps) 4-D images of the slow-moving object (10 mm/s) can be directly constructed at the baseband with a central frequency as low as 100 kHz and a small Doppler shift. The proposed LiDAR architecture based on such a low-frequency baseband significantly improves the optical power budget on the transmitter side and eliminates the costly high-speed sampling circuits on the receiver side.

In this work, we demonstrate photonic fabrication by integrating waveguide resonators and groove structures using cost-effective i-line stepper lithography on a 6-inch full wafer. Low-loss silicon nitride (SiN) waveguide can be realized with the quality (Q) factor of waveguide resonators up to 10⁵. In addition, groove structures are also integrated by the full-wafer process, providing long-term stability of coupling and package solutions. The uniformity of different die locations is verified within the full wafer, showing the good quality of the fabricated photonic devices. This process integration of photonic devices provides the potential for mass-productive, high-yield, and high-uniformity manufacturing.

In this work, we demonstrate gallium nitride (GaN) waveguide resonators by sputtering amorphous GaN films on the silicon-based substrate. With the aid of high-power impulse magnetron sputtering (HiPIMS), high-quality, high-deposition-rate, and high-flatness GaN films can be deposited directly onto the silicon substrate with a 4 μm buried oxide layer at room temperature. Waveguide resonators with a quality factor of up to 4 × 104 are demonstrated, and closely critical coupling is achieved at a 0.2 μm gap by optimizing the gap sizes, showing a high extinction ratio of waveguide resonators at ≈24 dB. The fabrication process of HiPIMS-GaN waveguide resonators utilizes CMOS-compatible techniques and operates at a low thermal budget. Compared to conventional GaN films fabricated using metal-organic chemical vapor deposition, this study offers the potential to produce low-cost GaN waveguides on amorphous substrates and realize integrated GaN photonics in optical communication, nonlinear photonics, and quantum photonics by high-quality HiPIMS films.