Resonant waveguide gratings (RWGs), also known as guided mode resonant (GMR) gratings or waveguide-mode resonant gratings, are dielectric structures where these resonant diffractive elements benefit from lateral leaky guided modes from UV to microwave frequencies in many different configurations. A broad range of optical effects are obtained using RWGs such as waveguide coupling, filtering, focusing, field enhancement and nonlinear effects, magneto-optical Kerr effect, or electromagnetically induced transparency. Thanks to their high degree of optical tunability (wavelength, phase, polarization, intensity) and the variety of fabrication processes and materials available, RWGs have been implemented in a broad scope of applications in research and industry: refractive index and fluorescence biosensors, solar cells and photodetectors, signal processing, polarizers and wave plates, spectrometers, active tunable filters, mirrors for lasers and optical security features. The aim of this review is to discuss the latest developments in the field including numerical modeling, manufacturing, the physics, and applications of RWGs. Scientists and engineers interested in using RWGs for their application will also find links to the standard tools and references in modeling and fabrication according to their needs.

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Recent Advances in Resonant Waveguide Gratings

We propose a design that increases significantly the absorption of a thin layer of absorbing material such as amorphous silicon. This is achieved by patterning a one-dimensional photonic crystal (1DPC) in this layer. Indeed, by coupling the incident light into slow Bloch modes of the 1DPC, we can control the photon lifetime and then, enhance the absorption integrated over the whole solar spectrum. Optimal parameters of the 1DPC maximize the integrated absorption in the wavelength range of interest, up to 45% in both S and P polarization states instead of 33% for the unpatterned, 100 nm thick amorphous silicon layer. Moreover, the absorption is tolerant with respect to fabrication errors, and remains relatively stable if the angle of incidence is changed.

Absorption enhancement using photonic crystals for silicon thin film solar cells

We theoretically investigate the light-trapping properties of one- and two-dimensional periodic patterns etched on the front surface of c-Si and a-Si thin film solar cells with a silver back reflector and an anti-reflection coating. For each active material and configuration, absorbance A and short-circuit current density Jsc are calculated by means of rigorous coupled wave analysis (RCWA), for different active materials thicknesses in the range of interest of thin film solar cells and in a wide range of geometrical parameters. The results are then compared with Lambertian limits to light-trapping for the case of zero absorption and for the general case of finite absorption in the active material. With a proper optimization, patterns can give substantial absorption enhancement, especially for 2D patterns and for thinner cells. The effects of the photonic patterns on light harvesting are investigated from the optical spectra of the optimized configurations. We focus on the main physical effects of patterning, namely a reduction of reflection losses (better impedance matching conditions), diffraction of light in air or inside the cell, and coupling of incident radiation into quasi-guided optical modes of the structure, which is characteristic of photonic light-trapping.

Photonic light-trapping versus Lambertian limits in thin film silicon solar cells with 1D and 2D periodic patterns.

Vertical-cavity surface-emitting lasers (VCSELs) are the ideal optical sources for data communication and sensing. In data communication, large data rates combined with excellent energy efficiency and temperature stability have been achieved based on advanced device design and modulation formats. VCSELs are also promising sources for photonic integrated circuits due to their small footprint and low power consumption. Also, VCSELs are commonly used for a wide variety of applications in the consumer electronics market. These applications range from laser mice to three-dimensional (3D) sensing and imaging, including various 3D movement detections, such as gesture recognition or face recognition. Novel VCSEL types will include metastructures, exhibiting additional unique properties, of largest importance for next-generation data communication, sensing, and photonic integrated circuits.

https://depositonce.tu-berlin.de/bitstream/11303/13913/1/Liu_etal_2021.pdf

Vertical-cavity surface-emitting lasers for data communication and sensing

Colloidal self-assembly concepts for light management in photovoltaics

An approach of enhanced light-trapping in a thin-film silicon solar cell by adding a two-filling-factor asymmetric binary grating on it is proposed for the wavelength of near-infrared. Such a grating-on-thin-film structure forms a guided-mode resonance notch filter to couple energy diffracted from an incident wave to a leakage mode of the guided layer in the solar cell. The resonance wave coupled between two-filling-factor gratings would laterally extend the optical power and induce multiple bounces within the active layer. The resonance effect traps light in the cell enhancing its absorption probability. A dynamic light-trapping behaviour in solar cells is observed. A photon dwelling time is proposed for the first time to quantify the light-trapping effect. Moreover, the light absorption probability is also quantified. As compared the grating-on-thin-film structure with the one of planar silicon thin film, simulation results reveal that it is 3-fold enhancement in the light absorption within a spectral range of 920-1040 nm. Moreover, such an enhancement can be maintained even the incident angle of near-IR broadband light wave varies up to +/-40 degrees.

Enhanced light trapping based on guided mode resonance effect for thin-film silicon solar cells with two filling-factor gratings

In this letter, we demonstrate a chip-level high-speed optical interconnect, where the optical transmitter/receiver, the polymer waveguides, and the silicon-trench 45° microreflectors are integrated on a single silicon platform. The silicon platform with a silicon trench can provide independent photonic and electrical layers, respectively, for high-speed and low-speed (except high-frequency transmission lines) data transmissions. In order to demonstrate the technical capability of chip-level optical interconnects, the vertical-cavity surface-emitting laser (VCSEL)/photodetector (PD) and the driver/amplifier IC as well as the polymer waveguides combined with the 45° microreflectors are integrated on the electrical and photonic layers of the silicon platform, respectively. The total optical transmission (VCSEL-to-waveguide-to-PD via two 45° microreflectors) is −4.7 dB. The high-speed transmission experiment shows the clear eye opening up to 20-Gbit/s data rate. The bit error rate better than $10^{\mathrm {\mathbf {-12}}}$ for the proposed architecture is also successfully demonstrated. It reveals such chip-level optical interconnects based on the proposed silicon platform with the polymer waveguides is suitable for high-speed data transmission.

Chip-Level Optical Interconnects Using Polymer Waveguide Integrated With Laser/PD on Silicon

A guided mode resonance solar cell includes a solar cell body and a guided mode resonance unit. The solar cell body is used for converting optical energy into electrical energy. The guided mode resonance unit is formed on the solar cell body, and includes a grating structure and a waveguide structure. The grating structure includes multiple sub-wavelength light pillars. When a light emitted from a light source is incident onto the grating structure, a resonant of the light occurs in the grating structure to facilitate trapping the light in the waveguide structure and elongating an optical path length.

Guided mode resonance solar cell

An optical coupler module includes a semiconductor substrate disposed on the print circuit board; a reflecting trench structure formed on the semiconductor substrate; a reflector formed on a slant surface of the reflecting trench structure; a strip trench structure formed on the semiconductor substrate and connecting with the reflecting trench structure; a thin film disposed on the above-mentioned structure. The optical coupler module further includes a signal conversion unit disposed on the semiconductor substrate and the position of the signal conversion unit corresponds to the reflector; and an optical waveguide structure formed in the trench structures. The optical signal from the signal conversion unit is reflected by the reflector and then transmitted in the optical waveguide structure, or in a reverse direction to reach the signal conversion unit.

Optical coupler module having optical waveguide structure

An optical transmission module includes a semiconductor substrate, a first film layer, an electronic component layer and a waveguide structure. The electronic component layer is used for converting a first electrical signal into an optical signal. The waveguide structure is formed on the first film layer, and includes a first reflective surface, a waveguide body and a second reflective surface. After the optical signal is transmitted through the semiconductor substrate and the first film layer and enters the waveguide structure, the optical signal is reflected by the first reflective surface, transmitted within the waveguide body and reflected by the second reflective surface. After the optical signal reflected by the second reflective surface is transmitted through the first film layer and the semiconductor substrate and received by the electronic component layer, the optical signal is converted into a second electrical signal by the electronic component layer.

Yun-Chih Lee

Papers

Enhanced light trapping based on guided mode resonance effect for thin-film silicon solar cells with two filling-factor gratings

Chip-Level Optical Interconnects Using Polymer Waveguide Integrated With Laser/PD on Silicon

Guided mode resonance solar cell

Optical coupler module having optical waveguide structure

Optical transmission module