Tilted Nano-Grating Based Ultra-Compact Broadband Polarizing Beam Splitter for Silicon Photonics

An ultra-compact broadband silicon polarizing beam splitter is proposed based on a tilted nano-grating structure. A light cross coupling can be realized for transverse-magnetic mode, while the transverse-electric light can almost completely output from the through port. The length of the coupling region is only 6.8 μm, while an extinction ratio of 23.76 dB can be realized at a wavelength of 1550 nm. As a proof of concept, the device was fabricated by a commercial silicon photonic foundry. It can realize a 19.84 dB extinction ratio and an 80 nm working bandwidth with an extinction ratio of larger than 10 dB. The presented device also shows a good fabrication tolerance to the structure deviations, which is favorable for its practical applications in silicon photonics.

Continuously Wavelength-Tunable First-Order Narrowband Fiber Comb Filter Using Composite Combination of Wave Retarders

Here, by harnessing a composite combination of wave retarders, we propose and experimentally demonstrate a first-order narrowband fiber comb filter capable of continuously tuning its wavelength, of which the filter structure is on the fundamental basis of a polarization–diversity loop structure. The demonstrated comb filter consists of a polarizing beam splitter (PBS), two high birefringence fiber (HBF) segments of the same length, an ordered wave retarder combination (WRC) of a quarter-wave retarder (QWR) and a half-wave retarder (HWR) before the first HBF segment, and an ordered WRC of an HWR and a QWR before the second HBF segment. The second HBF segment is butt-coupled to one port of the PBS so that its principal axis should be 22.5° away from the horizontal axis of the PBS. Taking the filter transmittance obtained by Jones calculus into consideration, we found the azimuth orientation angle (AOA) sets of the four wave retarders, which could allow extra phase shifts (ψ’s) ranging from 0° to 360° to be induced in the narrowband transmittance function. From filter transmission spectra calculated according to the AOA sets found above, it is confirmed that the first-order narrowband comb spectrum can be continuously tuned by properly controlling the AOA’s, clearly indicating the continuous wavelength tunability based on a composite combination of ordered wave retarders. This theoretical prediction was verified by actually constructing the proposed filter. Then, it is concluded that our filter employing the composite combination of wave retarders can be continuously frequency-tuned by properly controlling the AOA’s of the wave retarders.