Shibnath Pathak

Germanium-on-Silicon Mid-Infrared Arrayed Waveguide Grating Multiplexers

In this letter, we describe the use of a germanium-on-silicon waveguide platform to realize an arrayed waveguide grating (AWG) operating in the 5 μm wavelength range, which can be used as a wavelength multiplexer for mid-infrared (midIR) light engines or as the core element of a midIR spectrometer. Ge-on-Si waveguide losses in the range 2.5-3.5 dB/cm for TE polarized light and 3-4 dB/cm for TM polarized light in the 5.15-5.4 μm wavelength range are reported. A 200 GHz channel spacing 5-channel AWG with an insertion loss/crosstalk of 2.5/3.1 dB and 20/16 dB for TE and TM polarization, respectively, is demonstrated.

Demonstration of silicon-on-insulator mid-infrared spectrometers operating at 3.8 um

The design and characterization of silicon-on-insulator mid-infrared spectrometers operating at 3.8 μm is reported. The devices are fabricated on 200 mm SOI wafers in a CMOS pilot line. Both arrayed waveguide grating structures and planar concave grating structures were designed and tested. Low insertion loss (1.5-2.5 dB) and good crosstalk characteristics (15-20 dB) are demonstrated, together with waveguide propagation losses in the range of 3 to 6 dB/cm.

Optimized Silicon AWG With Flattened Spectral Response Using an MMI Aperture

We demonstrate compact 12-channel 400 GHz arrayed waveguide grating wavelength demultiplexers (AWG) in silicon with a flattened spectral response. Insertion loss, crosstalk and non-uniformity are -3.29 dB, 17.0 dB and 1.55 dB, respectively. The flattened spectral response is obtained by using an optimized mode shaper consisting of a multi-mode interference coupler as the input aperture of the AWG. The ratio of the 1 dB bandwidth to the 10 dB bandwidth is improved by 50%, from 0.33 to 0.49 compared to a conventional AWG. The device size is only 560×350 μm2 .

Design trade-offs for silicon-on-insulator-based AWGs for (de)multiplexer applications.

We demonstrate compact silicon-on-insulator-based arrayed waveguide gratings (AWGs) for (de)multiplexing applications with a large free spectral range (FSR). The large FSR is obtained by reducing the arm aperture pitch without changing the device footprint. We demonstrate 4 × 100 GHz, 8 × 250 GHz, and 12 × 400 GHz AWGs with FSRs of 6.9, 24.8, and 69.8, respectively. We measured an insertion loss from -2.45 dB for high to -0.53 dB for low-resolution AWGs. The crosstalk varies between 17.12 and 21.37 dB. The bandwidth remains nearly constant, and the nonuniformity between the center wavelength channel and the outer wavelength channel improves with larger FSR values.

Silicon-on-insulator spectrometers with integrated GaInAsSb photodiodes for wide-band spectroscopy from 1510 to 2300 nm

We present a silicon-on-insulator (SOI) based spectrometer platform for a wide operational wavelength range. Both planar concave grating (PCG, also known as echelle grating) and arrayed waveguide grating (AWG) spectrometer designs are explored for operation in the short-wave infrared. In addition, a total of four planar concave gratings are designed to cover parts of the wavelength range from 1510 to 2300 nm. These passive wavelength demultiplexers are combined with GaInAsSb photodiodes. These photodiodes are heterogeneously integrated on SOI with benzocyclobutene (DVS-BCB) as an adhesive bonding layer. The uniformity of the photodiode characteristics and high processing yield, indicate a robust fabrication process. We demonstrate good performance of the miniature spectrometers over all operational wavelengths which paves the way to on-chip absorption spectroscopy in this wavelength range.

Silicon and silicon nitride photonic circuits for spectroscopic sensing on-a-chip [Invited]

There is a rapidly growing demand to use silicon and silicon nitride (Si3N4) integrated photonics for sensing applications, ranging from refractive index to spectroscopic sensing. By making use of advanced CMOS technology, complex miniaturized circuits can be easily realized on a large scale and at a low cost covering visible to mid-IR wavelengths. In this paper we present our recent work on the development of silicon and Si3N4-based photonic integrated circuits for various spectroscopic sensing applications. We report our findings on waveguide-based absorption, and Raman and surface enhanced Raman spectroscopy. Finally we report on-chip spectrometers and on-chip broadband light sources covering very near-IR to mid-IR wavelengths to realize fully integrated spectroscopic systems on a chip.

Compact Silicon Nitride Arrayed Waveguide Gratings for Very Near-Infrared Wavelengths

In this letter, we report a novel high-index-contrast silicon nitride arrayed waveguide grating (AWG) for very near-infrared wavelengths. This device is fabricated through a process compatible with a complementary metal-oxide-semiconductor fabrication line and is therefore suitable for mass fabrication. The large phase errors that usually accompany high-index-platform AWGs are partly mitigated through design and fabrication adaptions, in particular the implementation of a two-level etch scheme. Multiple devices are reported, among which a 0.3-mm2 device which, after the subtraction of waveguides loss, has a -1.2 dB on-chip insertion loss at the peak of the central channel and 20-dB crosstalk for operation

Comparison of AWGs and Echelle Gratings for Wavelength Division Multiplexing on Silicon-on-Insulator

\sim 900

Compact SOI-based polarization diversity wavelength de-multiplexer circuit using two symmetric AWGs

nm with a channel spacing of 2 nm. These AWGs pave the way for numerous large-scale on-chip applications pertaining to spectroscopy and sensing.

Effect of Mask Discretization on Performance of Silicon Arrayed Waveguide Gratings

We compare the performance (insertion loss and crosstalk) of silicon-based arrayed waveguide gratings (AWGs) and echelle gratings for different channel spacings. For high-resolution de/multiplexer (DWDM) applications, AWGs are the better choice, whereas echelle gratings perform well for low-resolution de/multiplexer (CWDM) applications. Alternatively, for low-resolution de/multiplexer applications, the conventional box-shaped silicon AWG can be modified by an S-shaped AWG. We report crosstalk as low as -27 dB for regular AWGs, whereas in the S-shaped AWGs, the crosstalk is better than -19 dB, with an insertion loss below -2 dB. The crosstalk of the echelle gratings varies between -19 and -23 dB, with insertion loss below -2 dB.