Photonic integrated circuit with sampled grating lasers fabricated on a generic foundry platform for broadband terahertz generation.

We demonstrate a monolithically integrated photonic integrated circuit (PIC) for terahertz spectroscopy with wide spectral bandwidth. The PIC includes two widely tunable sampled grating DBR (SG DBR) lasers, semiconductor optical amplifiers (SOAs), and passive components to combine signals. The SG DBR lasers cover 22 nm and 24 nm tuning range, respectively, with 4 nm overlap in the C band. The side mode suppression ratio (SMSR) exceeds 37 dB with a linewidth below 4.3 MHz. We used the PIC to generate THz radiation with a state-of-the-art photodiode emitter. The measured THz power spectrum between 0.03 and 1 THz compares well with the spectrum generated with commercial tunable laser sources. This demonstrates the suitability of our PIC for future miniaturized continuous wave (cw) THz systems.

High-extinction-ratio directional-coupler-type polarization beam splitter with a bridged silicon wire waveguide.

We demonstrate an integrated polarization beam splitter (PBS) of a simple and compact device geometry with high polarization extinction ratios (PERs). A silicon PBS based on a three-waveguide directional coupler is numerically simulated for optimum device parameters, and fabricated experimentally. The measured PER values of the fabricated PBSs are 40.74 dB and 39.01 dB for transverse electric and transverse magnetic modes, respectively, and their corresponding insertion losses are 0.35 dB on average for a coupler length of about 29.4 µm.

Ultracompact transverse magnetic mode-pass filter based on one-dimensional photonic crystals with subwavelength structures.

We propose and experimentally demonstrate an ultracompact transverse magnetic (TM) mode pass filter based on a rectangularly-shaped one-dimensional (1-D) photonic crystal silicon waveguide with an extremely high polarization extinction ratio (PER) of >30 dB and a low insertion loss (IL) of ~1 dB. The device structure of the TM mode-pass filter is numerically simulated using a three-dimensional (3-D) finite difference time domain (FDTD) method. The proposed device supports its fundamental TM mode only, whereas the transverse electric (TE) mode is reflected by the 1-D photonic crystals (PhCs). The measured PER of the fabricated TM mode-pass filter is ~34 dB, and the IL is about 1 dB. The entire device length is about 4 µm. Our simulation results predict that the device bandwidth of 30 dB PER is about 200 nm.

Planar-type polarization beam splitter based on a bridged silicon waveguide coupler.

We demonstrate a compactly integrated polarization beam splitter (PBS) with high polarization extinction ratios greater than 20 dB over the full C-band wavelength range based on a simple bridged silicon nanowaveguide directional coupler. The PBS device is designed via three dimensional finite-difference time-domain (3D-FDTD) simulation, and fabricated experimentally. The optimum dimension of the bridge waveguide is determined to be 7.5-µm-long and 500 nm-wide for 250-nm thick silicon core. At the 1,550-nm wavelength, the measured polarization extinction ratios (PERs) of the PBS device are 22.5 dB and 22.9 dB for TE and TM polarization modes, respectively, and its corresponding insertion losses (ILs) are about 2.1 dB and 1.8 dB, both PERs and ILs within the maximum error range of ± 2.0 dB.