45$^{\circ}$-Mirror Terminated Polymer Waveguides on Silicon Substrates

Wet etching of deep trenches on silicon with three-dimensional (3D) controllability

“…Tapering angle of 90 o , 54.7 o and 45 o have been achieved from various combinations of etchant, additives [14] and silicon substrate. The trenches etched by basic wet etching have been widely used for MEMS [15], microfluidic system [16] and optical devices [17,18]. It should be noted that the sidewalls of the tapered trench are not necessary to be flat surfaces.…”

Polymer-Waveguide-Based Optical Circuit With Two Vertical-Transition Output Ports Realized on Silicon Substrate for Optical Interconnects

“…Short-reach optical interconnects have an increasing demand due to the emerging applications in cloud computing, including the board-to-board interconnects [1], [2], the on-board interconnects [3]- [9], the chip-to-chip interconnects [10], [16], and the on-chip interconnects [11]- [15], [17], [18]. The optical waveguides combined with a vertical-transition structure developed on a silicon substrate [15]- [17] or a silicon-on-insulator (SOI) substrate [10]- [14], [18] to form a vertical-coupling configuration have received great attention in the recent years [10]- [18].…”

“…Short-reach optical interconnects have an increasing demand due to the emerging applications in cloud computing, including the board-to-board interconnects [1], [2], the on-board interconnects [3]- [9], the chip-to-chip interconnects [10], [16], and the on-chip interconnects [11]- [15], [17], [18]. The optical waveguides combined with a vertical-transition structure developed on a silicon substrate [15]- [17] or a silicon-on-insulator (SOI) substrate [10]- [14], [18] to form a vertical-coupling configuration have received great attention in the recent years [10]- [18]. Several approaches were proposed to realize the vertical-transition structures, such as the grating coupler [10], the threedimensional (3-D) taper [11], [12], the vertically integrated multimode interferometer (MMI) coupler [13], [14], the through-silicon photonic via (TSPV) combined the grating coupler [15], and the reflective mirrors [16]- [25].…”

“…Considering that the silicon-based 54.7 reflective mirrors apply for the out-of-plane optical coupling, a high coupling loss between waveguide-to-waveguide in the vertical direction (using two 54.7 reflective mirrors) [16] or between vertical-cavity surface-emitting laser (VCSEL)-to-fiber (using one 54.7 reflective mirror) [19] was suffered due to laser beam walk-off at the receiving waveguide [16] or the flat-facet fiber [19]. The 45 reflective mirrors could provide an out-of-plane optical coupling with a reflective angle of minimum deviation [17], [18], [20]- [25]. Several approaches were proposed to realize the 45 reflectors, including a 45 slant end face of waveguide using a liquid-immersion tilt exposure [20], a reactive-ion-etching (RIE) process [21], and a siliconbased rear 45 mirror using an etchant tetramethylammonium hydroxide (TMAH) mixed surfactant NCW-1002 in an anisotropic wet-etching process [22].…”

“…In order to well confine the laser beam in the silicon waveguide, the operating wavelength of 1310 nm was chosen in the demonstrations [18] to avoid material absorption. To extend the wavelength range of the laser sources for the optical interconnects based on the guided-wave optical paths, the silicon-based 45 reflector terminated polymer waveguides developed on silicon substrates were realized for on-chip out-of-plane optical interconnects using the wavelength of 850 nm [17]. In this paper, as shown in Fig.…”