Integrated electro-optic modulators offer huge potential to meet communications and computations' rapidly growing bandwidth requirements. Devices based on silicon allow high-volume, low-cost CMOS fabrication, and co-integration with the CMOS circuits. They are promising candidates for mass-producible Tb/s-scale inter-rack and intra-rack interconnects. This talk will focus on our advancement of silicon-based optical modulators: (1) miniaturized all silicon MOSCAP modulators for co-packaged optics and its integration with low voltage drivers, allowing low optical power consumption of 2 pJ/bit. (2) Novel carrier absorption enhanced electro-optical modulation in MOSCAP ring resonators towards integration with ultra-low voltage (<1V) CMOS drivers; (3) Carrier depletion ring unity device for large scale and high bandwidth density error-free links; (4) Linear DC-Kerr effect dominated silicon modulators towards lidar and quantum applications.
We present the development of Ge-on-Si waveguide-based devices for low-noise mid-infrared absorption spectroscopy of aqueous solutions, targeting wavelengths between 6 and 10 μm, that are able to reduce the relative intensity noise which is a key roadblock when measuring tiny analyte absorptions masked by a large background matrix absorption. The sensor uses a pair of integrated thermo-optic switches to continuously switch light between a reference waveguide and a sensor waveguide, so that common noise components can be cancelled out, even when the light source and photodetector are not integrated on the same chip.
High-speed (upwards of 105 coordinates s-1) and long-range (~10 m) absolute distance measurement applications based on frequency scanning interferometry (FSI) generate very high modulation frequencies (typically >100 GHz) due to the laser frequency sweep rate and the large imbalance between the reference and object arms. Such systems are currently impractical due to the extremely high cost associated with sampling at these signal frequencies. Adaptive delay lines (ADLs) were recently proposed as a solution to balance the interferometer and therefore reduce sampling rate requirements by a factor of 2N, where N is the number of switches in the ADL [1, 2]. The technique has been successfully demonstrated in the lab using bulk optics and optical fiber configurations, and further reduction in size and cost will increase the breadth of metrology applications that can be addressed. Silicon photonics constitute an effective platform to miniaturize ADLs to chip-scale, simplifying instrument manufacture and providing a more robust configuration compared to bulk-optics and fiber-based solutions. We discuss the design and fabrication of chip-scale ADLs on a silicon on insulator (SOI) photonics platform, using optical switches based on heaters, multi-mode interferometer (MMI) couplers and Mach-Zehnder interferometers (MZI). We also establish the heater voltages of 4 switches in series, required to switch the optical path in the reference arm, a necessary step to use the device for FSI range measurements.
A chip-scale solid-state wavelength measuring device based on a silicon photonics platform is presented. It has no moving parts and allows single-shot wavelength measurement with high precision over a nominal bandwidth of 40 nm in the Oband. The wavemeter design is based on multimode interferometer (MMI) couplers and a multi-band Mach–Zehnder interferometer (MZI) structure with exponentially increasing optical path differences and in-phase quadrature detection. The design of the MMI couplers is supported by simulations using the Finite-Difference Time-Domain (FDTD) method. The design, experimental evaluation, and calibration of the device are discussed. Observed performance indicates a spectral support of 38.069 nm (i.e., frequency bandwidth 6.608 THz), with a resolution of 8.3 pm (1σ), corresponding to 1 part in 4,587. This wavelength meter approach has emerged from a need in absolute distance measurements using frequency scanning interferometry, where knowledge of the instantaneous wavelength of a tunable laser is required to relate signal frequency with target range. We also present an adaptive delay line on a chip, demonstrate its use for range measurements, and suggest how the wavelength meter could evolve for real-time applications.
High speed optical modulators are important for a number of applications served by silicon photonics. Here we present our recent work towards high speed free carrier accumulation based optical modulators where a high speed and efficient operation is achieved. Such silicon optical modulators typically need to be built in sub-micrometre sized waveguides which are challenging to couple light to and from. Also presented are experimental results from a buried 3D-taper that is able to couple efficiently between a waveguide of height ~1.5um and a 220nm high waveguide. Losses below 0.6dB are achieved limited by the loss of the material used.
The silicon optical modulator is a key component in a high speed optical data link. To advance the modulator performance beyond the popular carrier depletion based devices, we have produced a capacitive device which is instead based upon the accumulation of free carriers either side of a thin insulating layer positioned in the middle of the waveguide. Such a device has a superior efficiency compared with the carrier depletion approach allowing compactness and improved power consumption whilst retaining high speed operation and CMOS compatibility.
The interest in developing high-performance optical modulator to meet the growing demands of data processing speed has increased over the last decade. While there have been significant research efforts in developing standalone silicon modulators, works on integrating those with electronics is limited, which is necessary for the practical implementation of short-reach optical interconnects.
In contrast to previous work in the field where electronic–photonic integration was mostly limited to the physical coupling approach, we have introduced a new design philosophy, where photonics and electronics must be considered as a single integrated system in order to tackle the demanding technical challenges of this field.
In this work, I shall present our recent 100Gb/s silicon photonics transmitter, where photonic and electronic devices are co-designed synergistically in terms of device packaging, power efficiency, operation speed, footprint and modulation format.
As the market adoption of silicon photonics technologies continues to rise, and ever more fabless companies enter the market, there is a clear need for a flexible device prototyping foundry service that retains the ability for device level innovation, whilst also offering a clear route to market. The CORNERSTONE platform offers an affordable multi-project-wafer (MPW) service that allows a degree of customisation, which may not be accessible at other foundries. Through the use of DUV projection lithography, fabrication processes can be easily transferred to other foundries for mass production. Additionally, the ability to exploit high resolution e-beam lithography for certain layers mimics more advanced technology nodes, should this be deemed necessary. Several silicon-on-insulator platforms enable a plethora of applications including datacoms, LIDAR and mid-IR sensing.
This talk gives an overview of the present status of the CORNERSTONE platforms, and an outlook for the future.
A CMOS compatible three-dimensional (3D) integrated photonics circuit for multilayer silicon photonics is reported. Slopes with angles between 10o and 15° were created in the oxide layer using single step wet etching to connect the two Si waveguide layers. Amorphous Si (a-Si) deposited using hot wire chemical vapor deposition (HWCVD) at a temperature of 230°C was used to fabricate the device. Losses of 0.5 dB/slope were measured in the slope waveguides at 1310 nm wavelength. As a demonstration, we propose a 4x4 network switch using a-Si based vertical directional coupler.
This work describes the integration of mid-infrared (MIR) silicon photonics with PDMS microfluidics to perform absorption spectroscopy of IPA-water solutions. The MIR spectral region contains strong absorption bands for many molecules, and photonic devices operating in the MIR can be used in many sensing applications. In this work a preliminary demonstration of a silicon-on-insulator (SOI) device is carried out in which the transmission spectra of different concentrations of water-IPA solutions are measured at wavelengths between 3.725 μm and 3.888 μm. A PDMS microfluidic channel is integrated with the waveguides in order to improve the repeatability of sample handing, reduce reagent volumes and prevent evaporation of the analyte. A microfluidic channel with 3000 x 100 μm cross-section and 30 mm length is bonded to a SOI chip comprising 500 nm thick rib waveguides and a 2 μm thick SiO2top cladding isolating the waveguide mode from the analyte. Trenches were patterned into the SiO2 cladding to create sensing windows of varying lengths (10 μm to 3mm) along different waveguides. The devices were used to detect an expected IPA absorption peak at 3.77 μm, and concentration as low as 3% IPA in water (by volume) was detected. Further work will focus on increasing the sensitivity of the measurement by using increased interaction lengths, reduction of noise and instability, and on the detection of drugs using transmission measurements over a broader wavelength range.
The growing demand for fast, reliable and low power interconnect systems requires the development of efficient and scalable CMOS compatible photonic devices, in particular optical modulators. In this paper, we demonstrate an innovative electro absorption modulator (EAM) developed on an 800 nm SOI platform; the device is integrated in a rib waveguide with dimensions of a 1.5 μm x 40 μm, etched on a selectively grown GeSi cavity. High speed measurements at 1566 nm show an eye diagram with dynamic ER of 5.2 dB at 56 Gbps with a power consumption of 44 fJ/bit.
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