Femtosecond laser-inscribed optical waveguides in dielectric crystals: a concise review and recent advances

Li, Lingqi; Kong, Weijin; Chen, Feng

doi:10.1117/1.ap.4.2.024002

Cited by 66 publications

(21 citation statements)

References 197 publications

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“…As can be seen from figure 1(c), TPP-based methods are advantageous in terms of truly 3D fabrication of complex and largescale 3D photonic circuits, in parts due to enabling fast fabrication speeds [8,9]. However, efforts are needed to advance photo-induced fabrication methods in order to approach the low propagation losses achievable with DLW into bulk materials [10][11][12][13] or standard silicon photonics platforms [14][15][16][17], to increase the refractive index contrast and to reduce the minimal feature size.…”

Section: Introductionmentioning

confidence: 99%

Additive 3D photonic integration that is CMOS compatible

et al. 2023

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Today, continued miniaturization in electronic integrated circuits (ICs) appears to have reached its fundamental limit at ∼2 nm feature-sizes, from originally ∼1 cm. At the same time, energy consumption due by communication becomes the dominant limitation in high performance electronic ICs for computing, and modern computing concepts such a neural networks further amplify the challenge. Communication based on co-integrated photonic circuits is a promising strategy to address the second. As feature size has leveled out, adding a third dimension to the predominantly two dimensional integrated circuits appears the most promising future strategy for further IC architecture improvement. Crucial for efficient electronic-photonic co-integration is CMOS compatibility of the associated photonic integration fabrication process. Here, we review our latest results obtained in the FEMTO-ST RENATECH facilities on using additive photo-induced polymerization of a standard photo-resin for truly 3D photonic integration according to these principles. Based on one- and two-photon polymerization and combined with direct-laser writing, we 3D-printed air and polymercladded photonic waveguides. An important application of such circuits are the interconnects of optical neural networks, where 3D integration enables scalability in terms of network size versus its geometric dimensions. In particular via flashTPP, a fabrication process combining blanket one- and high-resolution two-photon polymerization, we demonstrated polymer-cladded step-index waveguides with up to 6 mmlength, low insertion (∼0.26 dB) and propagation (∼1.3 dB/mm) losses, realized broadband and low loss (∼0.06 dB splitting losses) adiabatic 1 to M couplers as well as tightly confining air-cladded waveguides for denser integration. By stably printing such integrated photonic circuits on standard semiconductor samples, we show the concept’s CMOS compatibility. With this, we lay out a promising, future avenue for scalable integration of hybrid photonic and electronic components.

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Section: Introductionmentioning

confidence: 99%

Additive 3D photonic integration that is CMOS compatible

et al. 2023

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“…One of the fabrication tools that is appealing for micro-manufacturing of optical devices in glass or transparent materials, is the femtosecond-laser direct writing technique (FLDW). This technique relies on the RI modification of the material in a fixed point 1 . However, a 3D-modification can be generated when the material is moved in the X, Y, Z directions, while the beam is held fixed 2 .…”

Section: Introductionmentioning

confidence: 99%

“…The waveguide's refractive index, as well as that of the surrounding environment, is an important parameter to know since they determine the confinement and propagation of light 7 . It can be found that the quantitative phase microscopy (QPM), a transmission method that quantifies the phase shift from the images acquired when the light passes through the transparent material, provides the sensitivity and accuracy required in the RI measurement of waveguides 1 . It is achieved since the phase is proportional to OPL 8 , and it is well-known that 𝑂𝑃𝐿 = 𝑛𝐿 (where n is the refractive index and L is the material length).…”

Section: Introductionmentioning

confidence: 99%

Extrinsic fiber Fabry-Perot interferometer for measuring the refractive index of waveguides inscribed in glass

Alonso Murias,

Saldaña Sánchez,

Vázquez

et al. 2023

European Workshop on Optical Fibre Sensors (EWOFS 2023)

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An extrinsic fiber Fabry-Perot interferometer (EFFPI) is proposed and implemented for the characterization of waveguides inscribed by the femtosecond-laser direct writing technique. Various waveguides of 7.08 mm in length were inscribed in a soda-lime glass substrate by varying the laser scanning velocity in order to induce different refractive index (RI) changes. The measurement of the RI of the waveguide was carried out by means of an EFFPI formed between the end face of a multicore fiber (MCF) with seven coupled cores and the two polished surfaces of the inscribed waveguide. The end face of the MCF tip provided a broad beam and a wide effective area to ensure a large collection of the reflected light. The optical spectrum obtained by the interference of the multiple reflected beams was transformed to the Fourier domain and visualized in real-time. In the Fourier domain, the waveguides’ optical path length (OPL) was obtained and used to calculate its refractive index since its physical length was fixed and known. To obtain the value of the RI of the medium surrounding the waveguide, the fiber tip was displaced parallel to the polished surface, about 40 μm far from the center of the waveguide. The relative refractive index difference (Δn), which defines the light propagation and the insertion loss in a waveguide, was calculated for each waveguide inscribed at different velocities.

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“…Recently, femtosecond laser direct writing has been proven as a powerful 3D micro/nanofabrication method for high accuracy and flexible fabrication of planar or 3D microstructures, including optical waveguides, [ 42 ] microfluidics masks, [ 43 ] microfluidic chips, [ 44 ] microchannels [ 45 ] and polymer‐based microcavities. [ 46 ] Compared to traditional fabrication technology, FsLDW offers several distinct advantages: it is a facile, rapid, non‐contact and maskless approach that can realize arbitrary, designable and complicated architectures with a nanometric resolution.…”

Section: Introductionmentioning

confidence: 99%

Femtosecond‐Laser‐Direct‐Writing Micro‐Scale Soft Actuators with Controllable Shape Morphing

Wang,

Li,

Geng

et al. 2023

Adv Materials Technologies

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Micro‐scale soft actuators with controllable shape‐morphing are the focus of advanced technological fields, ranging from advancing sensing, industrial robotics, and digital manufacturing to medical devices. Particularly, there is a growing interest in the scientific community to leverage liquid crystal polymers (LCPs) to fabricate such soft actuators, because LCPs can offer reversible, programmable deformations under external stimuli. However, pattern micromachining of LCPs into micro‐scale remains a daunting challenge. Herein, a femtosecond laser direct writing (FsLDW) method for cross‐linked LCP (CLCP) microstructure construction is reported that enables arbitrary pattern machining with a minimum size of 40 µm and average heat‐affected zone (HAZ) below 8 µm through optimization of processing parameters. Light‐driven behaviors of CLCP microstructures are systematically characterized through analyzing the effects of film thickness, length‐width ratio, light irradiation time, incident angle, light intensity, and cutting direction on bending and twisting behaviors. Finally, a light‐driven micromirror system is demonstrated, which can achieve not only a controllable swing but also a rotation of the mirror surface with a maximum scanning frequency of ≈2 Hz.

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Femtosecond laser-inscribed optical waveguides in dielectric crystals: a concise review and recent advances

Cited by 66 publications

References 197 publications

Additive 3D photonic integration that is CMOS compatible

Additive 3D photonic integration that is CMOS compatible

Extrinsic fiber Fabry-Perot interferometer for measuring the refractive index of waveguides inscribed in glass

Femtosecond‐Laser‐Direct‐Writing Micro‐Scale Soft Actuators with Controllable Shape Morphing

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