In this work, a racetrack ring resonator (RTRR) integrated with a multimode interferometer (MMI) structure based on a silica–titania (SiO₂:TiO₂) platform is projected for refractive index sensing application. The typical ring resonator structure requires a gap of ~100 nm to 200 nm between the bus waveguide (WG) and the ring structure which makes it challenging to fabricate a precise device. Thus, the device proposed in this paper can be considered a “gapless” ring resonator structure in which the coupling of light between the ring and bus WG can be achieved via an MMI coupler. A minor change in the refractive index in the vicinity of the MMI structure can trigger a shift in the resonance wavelength of the device. Thus, this simple and fascinating structure can be employed as a refractive index sensor. The device’s sensitivity is ~142.5 nm/RIU in the refractive index range of 1.33 to 1.36 with a figure of merit (FOM) of 78.3. This simple device structure can potentially be fabricated via a low-cost and highly efficient sol–gel process and dip-coating method combined with the nanoimprint lithography (NIL) method.

Photonic sensing devices have become increasingly important in various fields such as agriculture, medicine, biochemical sensing, and manufacturing. They are highly sensitive and can classify minor changes in the physical and chemical properties of the ambient medium with high precision. This makes them practical in applications where accurate measurements are critical, such as medical diagnostics and environmental monitoring. In this review paper, recent advances in different types of photonic sensors are discussed, which include photonic crystal-based sensors, surface plasmon resonance-based sensors, optical fiber-based sensors, optical waveguide-based sensors, and wearable sensors. These highly fascinating sensing devices play a crucial role in countless applications and have several advantages over traditional sensors. As technology continues to advance, we can expect photonic sensors to become even more precise, versatile, and reliable.

Silicon photonics has been an area of active research and development. Researchers have been working on enhancing the integration density and intricacy of silicon photonic circuits. This involves the development of advanced fabrication techniques and novel designs to enable more functionalities on a single chip, leading to higher performance and more efficient systems. In this review, we aim to provide a brief overview of the recent advancements in silicon photonic devices employed for telecommunication and sensing (biosensing and gas sensing) applications.

Herein, a numerical analysis of a 1 × 2 demultiplexer based on a silica-titania integrated photonics platform is conducted via the finite element method. The structure is composed of two coupled racetrack microrings (RTMRs) and a subwavelength grating (SWG) structure for the demultiplexing of 1310 nm and 1550 nm telecommunication wavelengths. The material platform selected for this design is highly attractive due to its refined optical, physical, and chemical properties. Moreover, silica-titania sol-gel thin-films can be deposited on glass substrates with the dip-coating method. The proposed device has a small footprint of 84 × 125 μm² and offers crosstalk as low as ~−6.6 dB and ~−9.04 dB for 1550 nm and 1310 nm, respectively. We are convinced that this study promotes the use of the silica-titania platform for the development of low-cost on-chip optical communication devices for signal multiplexing and demultiplexing.