Tingting Lang

Cross-order arrayed waveguide grating design for triplexers in fiber access networks

An arrayed waveguide grating (AWG)-based multiplexer has many advantages, including small size, high reliability, and low cost. The commonly used wavelengths for triplexers in fiber access networks are 1310, 1490, and 1550 nm. Because of the wide spectral range and very unequal wavelength spacings, it is difficult to produce satisfactory results with a conventional AWG design. A novel cross-order AWG design particularly suitable for triplexers is presented. The spectral periodicity of the grating is utilized so that the first wavelength works at a different diffraction order and is transposed to a wavelength that is approximately in the middle of the second and third channels. This results in a reduced free-spectral range requirement and more equal distances between the output waveguides. Consequently, the AWG can operate at a higher diffraction order with a smaller overall size, compared to the one designed by conventional methods.

Birefringence compensated AWG demultiplexer with angled star couplers.

A new approach to birefringence compensation in arrayed waveguide gratings (AWG) is proposed. The star couplers are designed according to Rowland circle construction with an oblique incident/diffraction angle, similar to the case of an echelle grating. Such an AWG design is more general and flexible, and the conventional AWG becomes its special case when the grating angle is zero. By appropriately designing the star coupler shape, the birefringence of the arrayed waveguides can be compensated by that of the slab waveguides. The details of the design method and simulation results are presented.

Ultra-Compact Birefringence-Compensated Arrayed Waveguide Grating Triplexer Based on Silicon-On-Insulator

We demonstrate an ultra-compact birefringence- compensated arrayed waveguide grating (AWG) triplexer for application in optical network units (ONUs) based on silicon nanowire waveguides. The cross-order design is employed to cover three operating wavelengths of 1310, 1490 and 1550 nm for the triplexer. The large birefringence of the silicon-on-insulator (SOI) waveguide is compensated by using angled star coupler design in combination with different diffraction orders for TE and TM modes. The device has a small footprint of only 0.18×0.12 mm2. The excess loss for TM polarization for three channels is 3 ~ 4 dB and the crosstalk is better than -18 dB. The polarization dependent wavelength shift (PDλ) is reduced from about 370 nm to less than 2.5 nm for wavelength channels at 1490-1550 nm.

Experimental Demonstration of Birefringence Compensation Using Angled Star Couplers in Silica-Based Arrayed Waveguide Grating

A birefringence compensation technique based on angled star couplers in arrayed waveguide grating (AWG) is experimentally investigated in silica-on-silicon waveguide with B-Ge codoped upper cladding. A 16-channel AWG with 100-GHz channel spacing is designed and fabricated. The star couplers are designed according to Rowland circle construction with an oblique incident/diffraction angle. Five different polarization compensation parameters corresponding to different incident/diffraction angles are employed to investigate the stress-induced birefringence. The experimental results confirm that the polarization-dependent wavelength shift (PDλ) can be tuned by varying the incident/diffraction angle at the star couplers, and a birefringence-free AWG can be achieved without any additional fabrication process.

Uniform Polarization-Dispersion Compensation of All Channels in Highly Birefringent Silicon Nanowire-Based Arrayed Waveguide Grating

A design method for compensating polarization dispersion in arrayed waveguide gratings (AWGs) based on highly birefringent silicon nanowire waveguides is proposed by using angled star couplers in combination with different diffraction orders for TE and TM polarizations. Polarization-dispersion compensation for all output channels is achieved with the maximal polarization-dependent wavelength shift of 0.025 nm in an eight-channel AWG with 200-GHz spacing using 380 nm × 220 nm silicon waveguide with SU-8 upper-cladding.

Birefringence compensated silicon nanowire arrayed waveguide grating for CWDM optical interconnects

We demonstrate an arrayed waveguide grating based on silicon nanowires with birefringence compensation for optical interconnects using coarse wavelength division multiplexing (CWDM). Angled star couplers are employed in combination with different diffraction orders for TM and TE polarizations. This device has a compact footprint of 0.36  mm×0.17  mm. Theoretical and experimental results show that the polarization-dependent wavelength shifts (PDλ) can be reduced from 380-420 to 0.5-3.5 nm, below 25% of the 3 dB bandwidth of channel response. The measured cross talk for TM polarization is better than -18  dB, and that for TE is better than -14  dB.

Design Analysis and Experimental Verification of Cross-Order AWG Triplexer Based on Silica-on-Silicon

A compact arrayed waveguide grating triplexer with silica waveguides on silicon is designed, fabricated, and characterized. Different cross-order designs, which utilize different diffraction orders to cover a large spectral range from 1310 to 1550 nm, are analyzed in detail. B-Ge codoped upper cladding is used to facilitate the gap filling between the waveguides to reduce the loss and the polarization sensitivity. The measured spectra confirmed the operation principle of the cross-order arrayed waveguide grating design, with channel wavelengths and passbands consistent with simulations.

Electromagnetically Induced Transparency in an All-Dielectric Metamaterial-Waveguide With Large Group Index

We investigate numerically an analog of electromagnetically induced transparency (EIT) in an all-dielectric metamaterial-waveguide (ADMW) that consists of a two-dimensional silicon rod array on quartz slab waveguide. The EIT-like response is achieved by the destructive interference between a broad magnetic resonance and a narrow guide mode resonance. By tailoring the guided mode through the thickness of the slab waveguide or the lattice period of the metamaterial, an EIT-like transmission window is achieved with both high Q-factor (>104) and high transmission (>94%). And the group refractive index at the EIT-like resonance of the ADMW can be up to several thousands. These results demonstrate that the proposed ADMW has potential applications in low-loss slow-light based devices, bio-chemical sensing, and optical modulations.

Simultaneous measurement of refractive index and temperature based on all-dielectric metasurface.

In this paper, a novel kind of sensors for simultaneous measurement of refractive index and temperature based on all-dielectric metasurfaces is proposed. The metasurfaces are constructed by an array of silicon nanoblocks on top of the bulk fused silica substrate. We used three-dimensional full wave electromagnetic field simulation by finite integral method to accurately calculate the transmission spectrum of the metasurfaces. Two transmission dips corresponding to the electric and magnetic resonances are observed. Both dips shift as the ambient refractive index or the temperature changes. Simulation results show that the sensing sensitivities of two dips to the refractive index are 243.44 nm/RIU and 159.43 nm/RIU, respectively, while the sensitivities to the temperature are 50.47 pm/°C and 75.20 pm/°C, respectively. After introducing four holes into each silicon nanoblock, the electromagnetic field overlap in the surrounding medium can be further promoted, and the sensitivities to the refractive index increase to 306.71 nm/RIU and 204.27 nm/RIU, respectively. Our proposed sensors have advantages of polarization insensitive, small size, and low loss, which offer them high potential applications in physical, biological and chemical sensing fields.

Loss uniformity improvement for cyclic arrayed waveguide grating based on silicon nanowire waveguides

A cyclic arrayed waveguide grating (AWG) router based on silicon nanowire waveguides with uniform channel insertion loss is designed and experimentally demonstrated. Different from conventional design, the directions of arrayed waveguides are no longer pointed to the central output waveguide, but are adjusted according to a distribution function. The experimental results show that the channel insertion loss non-uniformity is reduced from 2.7 dB to 1.1 dB. This uniform loss design does not change the overall construction of AWGs, and does not increase the device size.