We describe the fabrication of a Mach-Zehnder optical modulator in LiNbO 3 by femtosecond laser micromachining, which is composed of optical waveguides inscripted by a femtosecond laser and embedded microelectrodes subsequently fabricated using femtosecond laser ablation and selective electroless plating. A half-wave voltage close to 19 V is achieved at a wavelength of 632.8 nm with an interaction length of 2.6 mm. This simple and cost-effective technique opens up new opportunities for fabricating integrated electro-optic devices. © 2008 Optical Society of America OCIS codes: 130.0250, 140.3390, 230.2090 Lithium niobate ͑LiNbO 3 ͒ is one of the most widely used nonlinear optic materials in integrated optics owing to its excellent nonlinear optical and electrooptic (EO) properties. Integrated EO devices based on waveguiding structures such as optical switches [1] and modulators [2,3] have gained significant attention. Conventionally, the waveguide fabrication is based on titanium diffusion or proton exchange, which permits fabrication of channel waveguides only close to the surface [4]. Recently, it has been demonstrated that buried optical waveguides in LiNbO 3 can be fabricated by femtosecond laser inscription [5], which opens the possibility to write 3D optical circuits in the crystal. Various fabrication parameters have been optimized by several groups [6][7][8], such as wavelength, repetition rate, polarization, pulse width, pulse energy, focusing geometry, and scanning speed. To realize integrated EO devices, it is further crucial to design and fabricate microelectrodes, which are usually obtained by use of lithographic methods. However, owing to the inherently planar nature of the lithographic process, this technique is limited in its capability to produce 3D structures. Furthermore, because the optical waveguides fabricated by femtosecond laser inscription usually are deeply buried in the crystal, the conventional surface electrodes give rise to weak EO interaction. As a simple and costeffective technique, laser-induced selective electroless deposition has been widely investigated, because it does not require fabrication steps involved in the traditional lithographic technique, such as deposition of thin layers of metals, pattern etching, and so on [9,10]. Recently, we developed a technique for selective metallization in LiNbO 3 using femtosecond-laser ablation and femtosecond-laser-assisted selective electroless plating, which allows for fabricating microelectrodes deeply embedded in LiNbO 3 [11]. In this Letter, we report the integration of embedded microelectrodes and optical waveguides in LiNbO 3 using a femtosecond laser. Based on this technique, a Mach-Zehnder interferometer (MZI) EO modulator in an x-cut LiNbO 3 crystal is demonstrated.For the fabrication of waveguides and electrodes, a Ti:sapphire laser system (Legend USP, Coherent Inc.) with an operation wavelength of 800 nm, a pulse width of ϳ40 fs, and a repetition rate of 1 KHz was used. Commercially available MgO-doped x-cut LiNbO 3 crystals...
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We report selective metallization on surfaces of insulators (glass slides and lithium niobate crystal) based on femtosecond laser modification combined with electroless plating. The process is mainly composed of four steps: (1) formation of silver nitrate thin films on the surfaces of glass or crystal substrates; (2) generation of silver particles in the irradiated area by femtosecond laser direct writing; (3) removal of unirradiated silver nitrate films; and (4) selective electroless plating in the modified area. We discuss the mechanism of selective metallization on the insulators. Moreover, we investigate the electrical and adhesive properties of the copper microstructures patterned on the insulator surfaces, showing great potential of integrating electrical functions into lab-on-a-chip devices.
An ultra-thin, planar, broadband metalens composed of L-shaped gap antennas on a thin gold film has been designed, which is suitable for both circular and X/Y linear polarizations focusing simultaneously. The phase discontinuity of the cross-polarized transmisson light can be manipulated by the length and width of the L-shaped gap antenna accurately. The designed planar metalens posses a strong focusing ability over a large wavelength range, and the size of the focus spot is in sub-wavelength scale. The focal lengths change from 13 to 7 um with incident wavelength from 750 to 1300 nm, and the cause of dispersion is explained and analyzed in detail. The designed metalens can work very well at a wide incident angles of 0~45°. Most importantly, its unique focusing ability that is independent of the incident polarizations will greatly promotes the practical applications and developments of the metasurfaces.
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