| dc.description.abstract | Wavelength-division multiplexer (WDM) is one of the most important technologies in the lightwave network systems, such as Fiber-to-the-home (FTTH) application [2-5]. Thin film filter (TFF) has been widely used in the passive optical network (PON) architecture, and its optical sub-assembly (OSA) is generally adopted as the TO-CAN [2-3] and planar lightwave circuits (PLC) type [4-5]. TFF based on TO-CAN OSA is the con-ventional type. However, it suffers from hard packaging tasks, whose alignment tolerance between LD, TFF, SMF, or ball lens should be achieved micro-scaled precision within such macro-sized device [2-3]. PLC-typed OSA can be further miniaturized and straightly become a platform of assembling drive IC, opto-electronic devices [4-5]. Suntae Jung et al. have developed hybrid integration technology via inserting a TFF in the trench with an adhesive . However, for reducing coupling efficiency between waveguide facets, the width of trench is only 20 μm. It is still a big task to insert such tiny film within this small trench.
In this paper, a monolithic integrated-WDM via sub-wavelength si grating filter, which is replaced the hybrid-integrated TFF, is proposed on SOI-based PLCs. As shown in Fig. 1-7, this Si-grating filter structure can be monolithically fabricated on the integrated PLC, and the separated length between waveguide facets can also be narrowed to sub-wavelength scaled by e-beam lithography process, which maintains the waveguide coupling efficiency.
In design consideration, this sub-wavelength si grating is formed as a guided-mode resonance (GMR) filter [16]. As satisfying the phase-matched condition, lightwave of the resonant wavelength would be extremely reflective, and the others would be trans-mitted. This sub-wavelength Si grating is very different from conventional free-space GMR filter because the incident lightwave emitted from rib waveguide is of finite-size and Gaussian-like profile, which is away from the free-space condition [16]. Fortunately,not only the sub-wavelength-scaled distance between waveguide facets maintains a finite-sized, however, planar wave-front of the waveguide field, but also the large dielectric constants of silicon, both of which make the resonant mode indeed locally exist in this si grating.
In this work, the 1310/1550 nm WDM filter via this monolithically integrated device is demonstrated numerically and experimentally. The stop- and pass-band of 1310 and 1550 nm, respectively, are broad of 60 and 40 nm within 0.5 dB variations. The fabrication process is also dis-cussed. | en_US |