Mid-infrared wavelength division (de)multiplexer using an interleaved angled multimode interferometer on the silicon-on-insulator platform

Temperature-insensitive and fabrication-tolerant coarse wavelength division (de)multiplexing on a silica platform using an angled multimode interferometer

Wavelength division (de)multiplexing (WDM) device is a crucial component for optical transmission networks. In this paper, we demonstrate a 4 channel WDM device with a 20 nm wavelength spacing on silica based planar lightwave circuits (PLC) platform. The device is designed using an angled multimode interferometer (AMMI) structure. Since there are fewer bending waveguides than other WDMs, the device footprint is smaller, at 21 mm × 0.4 mm. Owing to the low thermo-optic coefficient (TOC) of silica, a low temperature sensitivity of 10 pm/°C is achieved. The fabricated device exhibits high performance of an insertion loss (IL) lower than 1.6 dB, a polarization dependent loss (PDL) lower than 0.34 dB, and the crosstalk between adjacent channels lower than -19 dB. The 3 dB bandwidth is 12.3∼13.5 nm. Moreover, the device shows a high tolerance with a sensitivity of central wavelength to the width of multimode interferometer < 43.75 pm/nm.

Bidirectional grating based interleaved angled MMI for high-uniformity wavelength division (de)multiplexing and surface-normal fiber packaging

We propose and experimentally demonstrate a vertical fiber interfacing interleaved angled multimode interference (MMI) coupler for wavelength-division multiplexing (WDM) applications. This four-channel WDM device comprises two 1×2 angled MMI couplers and a bidirectional grating-based Mach-Zehnder interferometer (MZI) structure. In the MZI optical interleaver, the uniform bidirectional grating functions as both the perfectly vertical grating coupler and the 3 dB power splitter. Benefitting from the flat-top coupling spectrum of the grating coupler, a high-uniformity wavelength-division (de)multiplexing can be achieved with a simulated insertion loss of 3.15-3.36 dB (the nonuniformity of 0.22 dB). The angled MMIs (AMMIs) are designed and optimized using the eigenmode expansion method. For wavelength matching between the MZI and AMMIs, the circuit simulation model of the interleaved AMMI is built by importing the S-parameter matrices of all the optical components extracted from the physical level simulations. The device was fabricated using standard CMOS technology and all the features were patterned with the 193-nm deep-UV lithography. Experimental results obtained without thermal tuning are in good agreement with the simulation results. The device exhibits an insertion loss of 4.5-4.65 dB (nonuniformity of 0.15 dB), channel spacing of 10 nm, and cross talk of -(21.62-26)dB.

N-rich silicon nitride angled MMI for coarse wavelength division (de)multiplexing in the O-band

We report the design and fabrication of a compact angled multimode interferometer (AMMI) on a 600 nm thick N-rich silicon nitride platform (n=1.92) optimized to match the International Telecommunication Union coarse wavelength division (de)multiplexing standard in the O telecommunication band. The demonstrated device exhibited a good spectral response with Δλ=20  nm, BW_3 dB∼11  nm, IL<1.5  dB, and XT∼20  dB. Additionally, it showed a high tolerance to dimensional errors <120  pm/nm and low sensitivity to temperature variations <20  pm/°C, respectively. This device had a footprint of 0.02  mm×1.7  mm with the advantage of a simple design and a back-end-of-line compatible fabrication process that enables multilayer integration schemes due to its processing temperature <400°C.

Athermal silicon nitride angled MMI wavelength division (de)multiplexers for the near-infrared

WDM components fabricated on the silicon-on-insulator platform have transmission characteristics that are sensitive to dimensional errors and temperature variations due to the high refractive index and thermo-optic coefficient of Si, respectively. We propose the use of NH₃-free SiN_x layers to fabricate athermal (de)multiplexers based on angled multimode interferometers (AMMI) in order to achieve good spectral responses with high tolerance to dimensional errors. With this approach we have shown that stoichiometric and N-rich SiN_x layers can be used to fabricate AMMIs with cross-talk <30dB, insertion loss <2.5dB, sensitivity to dimensional errors <120pm/nm, and wavelength shift <10pm/°C.

Towards a fully functional integrated photonic-electronic platform via a single SiGe growth step

Silicon-germanium (Si(1-x)Ge(x)) has become a material of great interest to the photonics and electronics industries due to its numerous interesting properties including higher carrier mobilities than Si, a tuneable lattice constant, and a tuneable bandgap. In previous work, we have demonstrated the ability to form localised areas of single crystal, uniform composition SiGe-on-insulator. Here we present a method of simultaneously growing several areas of SiGe-on-insulator on a single wafer, with the ability to tune the composition of each localised SiGe area, whilst retaining a uniform composition in that area. We use a rapid melt growth technique that comprises of only a single Ge growth step and a single anneal step. This innovative method is key in working towards a fully integrated photonic-electronic platform, enabling the simultaneous growth of multiple compositions of device grade SiGe for electro-absorption optical modulators operating at a range of wavelengths, photodetectors, and bipolar transistors, on the same wafer. This is achieved by modifying the structural design of the SiGe strips, without the need to modify the growth conditions, and by using low cost, low thermal-budget methods.

Mid-infrared wavelength multiplexer in InGaAs/InP waveguides using a Rowland circle grating

We report the monolithic integration of a 15-channel multiplexer on indium phosphide. It covers the 7.1-to-8.5 µm wavelength range suitable for combining the outputs of several individual lasers. The fabrication is compatible with the growth of active layers, therefore enabling a fully integrate broadband laser source in the mid-infrared spectral range. Channels are accurately spaced in wavelength (97 nm) in good agreement with design.

A silicon-on-insulator polarization diversity scheme in the mid-infrared

We propose a silicon-on-insulator (SOI) polarization diversity scheme in the mid-infrared wavelength range. In consideration of absorption loss in silicon dioxide (SiO₂), the polarization splitter-rotator (PSR) is designed and optimized with silicon nitride (SiN) upper-cladding and SiO₂ lower-cladding. This asymmetry allows the PSR, which consists of mode-conversion tapers and subsequent mode-sorting asymmetric Y-junctions, to be fabricated with a simple one-step etching process. Simulation shows that our PSR has good performance with low mode conversion loss (< 0.25 dB) and low crosstalk (< -18 dB) in a very large wavelength range from 4.0 μm to 4.4 μm. The PSR also exhibits large fabrication tolerance with respect to the size deviations in waveguide width, height and refractive index of the upper-cladding. Additionally, PSR devices based on Y-junctions with SiO₂ upper-cladding, and SiN upper- and lower-claddings are designed for potential applications at shorter and longer wavelengths, respectively. These PSR devices could facilitate the development of silicon photonic devices in the mid-infrared.

Next generation device grade silicon-germanium on insulator

High quality single crystal silicon-germanium-on-insulator has the potential to facilitate the next generation of photonic and electronic devices. Using a rapid melt growth technique we engineer tailored single crystal silicon-germanium-on-insulator structures with near constant composition over large areas. The proposed structures avoid the problem of laterally graded SiGe compositions, caused by preferential Si rich solid formation, encountered in straight SiGe wires by providing radiating elements distributed along the structures. This method enables the fabrication of multiple single crystal silicon-germanium-on-insulator layers of different compositions, on the same Si wafer, using only a single deposition process and a single anneal process, simply by modifying the structural design and/or the anneal temperature. This facilitates a host of device designs, within a relatively simple growth environment, as compared to the complexities of other methods, and also offers flexibility in device designs within that growth environment.

Cascade-coupled racetrack resonators based on the Vernier effect in the mid-infrared

In this paper we report the experimental demonstration of racetrack resonators in silicon-on-insulator technology platform operating in the mid-infrared wavelength range of 3.7-3.8 μm. Insertion loss lower than 1 dB and extinction ratio up to 30 dB were measured for single resonators. The experimental characterization of directional couplers and bending losses in silicon rib waveguides are also reported. Furthermore, we present the design and fabrication of cascade-coupled racetrack resonators based on the Vernier effect. Experimental spectra of Vernier architectures were demonstrated for the first time in the mid-infrared with insertion loss lower than 1 dB and maximum interstitial peak suppression of 10 dB.

Optical detection and modulation at 2µm-2.5µm in silicon

Recently the 2μm wavelength region has emerged as an exciting prospect for the next generation of telecommunications. In this paper we experimentally characterise silicon based plasma dispersion effect optical modulation and defect based photodetection in the 2-2.5μm wavelength range. It is shown that the effectiveness of the plasma dispersion effect is dramatically increased in this wavelength window as compared to the traditional telecommunications wavelengths of 1.3μm and 1.55μm. Experimental results from the defect based photodetectors show that detection is achieved in the 2-2.5μm wavelength range, however the responsivity is reduced as the wavelength is increased away from 1.55μm.