Evanescent-wave imaging is demonstrated using solid-immersion Lloyd's mirror interference lithography at λ = 325 nm to produce 44-nm half-pitch structures (numerical aperture, NA = 1.85). At such an ultrahigh NA the image depth is severely compromised due to the evanescent nature of the exposure, and the use of reflections from plasmonic underlayers is discussed as a possible solution. Simulations and modeling show that image depths in excess of 100 nm should be possible with such a system, using silver as the plasmonic material. The concept is scalable to 193 nm illumination using aluminium as the plasmonic reflector, and simulation results are shown for 26-nm half-pitch imaging into a 37-nm thick resist layer using this scheme.
Evanescent-wave imaging is demonstrated using solid-immersion Lloyd's-mirror interference lithography (SILMIL) at
λ = 325 nm to produce 44-nm half-pitch structures (numerical aperture, NA = 1.85). At such an ultra-high NA the image
depth is severely compromised due to the evanescent nature of the exposure, and the use of reflections from plasmonic
under-layers is discussed as a possible solution. Simulations and modelling show that image depths in excess of 100 nm
should be possible with such a system, using silver as the plasmonic material. The concept is scalable to 193 nm
illumination using aluminium as the plasmonic reflector, and simulation results are shown for 26-nm half-pitch imaging
into a 37-nm thick resist layer using this scheme.
Sampling rates of high-performance electronic analog-to-digital converters (ADC) are fundamentally limited by the timing jitter of the electronic clock. This limit is overcome in photonic ADC's by taking advantage of the ultra-low timing jitter of femtosecond lasers. We have developed designs and strategies for a photonic ADC that is capable of 40 GSa/s at a resolution of 8 bits. This system requires a femtosecond laser with a repetition rate of 2 GHz and timing jitter less than 20 fs. In addition to a femtosecond laser this system calls for the integration of a number of photonic components including: a broadband modulator, optical filter banks, and photodetectors. Using silicon-on-insulator (SOI) as the platform we have fabricated these individual components. The silicon optical modulator is based on a Mach-Zehnder interferometer architecture and achieves a VπL of 2 Vcm. The filter banks comprise 40 second-order microring-resonator filters with a channel spacing of 80 GHz. For the photodetectors we are exploring ion-bombarded silicon waveguide detectors and germanium films epitaxially grown on silicon utilizing a process that minimizes the defect density.
Microphotonic devices employing strong confinement of light are of growing importance for key applications such as
telecommunication and optical interconnects. They have unique and desirable characteristics but their extreme
sensitivity to dimensional variations makes them difficult to successfully implement. Here, we discuss strategies towards
the successful realization of strong confinement devices. We leverage what planar fabrication technology does best:
replicating structures. Although the absolute dimensional control required for successful fabrication of many strong
confinement devices is all but impossible to achieve, we show that surprisingly-high relative dimensional accuracy can
be obtained on structures in proximity of one another on a wafer. This provides an advantage to schemes that are based
on multiple copies of low-complexity structures. These copies can be made nearly identical or with precise relative-dimensional
offsets to achieve the desired function. We quantify the achievable relative dimensional control and discuss
the first demonstration of multistage filters, integrated polarization diversity, and high-order microring-filter banks.
Photonic Analog-to-Digital Conversion (ADC) has a long history. The premise is that the superior noise performance of
femtosecond lasers working at optical frequencies enables us to overcome the bottleneck set by jitter and bandwidth of
electronic systems and components. We discuss and demonstrate strategies and devices that enable the implementation
of photonic ADC systems with emerging electronic-photonic integrated circuits based on silicon photonics. Devices
include 2-GHz repetition rate low noise femtosecond fiber lasers, Si-Modulators with up to 20 GHz modulation speed,
20 channel SiN-filter banks, and Ge-photodetectors. Results towards a 40GSa/sec sampling system with 8bits resolution
Photonic circuits based on silicon wire waveguides have attracted significant interest in recent years. They allow strong
confinement of light with moderately low propagation losses. Moreover, the high thermo-optical coefficient of silicon
and the small device size in silicon photonics allow for micro-heaters induced trimming, tuning, and switching with
relatively low power. In this paper, we review our recent progress towards telecom-grade reconfigurable optical add-drop
multiplexers (ROADMs) based on silicon microring resonators. We discuss waveguide and micro-heater design
and fabrication as well as the first demonstration of telecom-grade silicon-microring filters and the first demonstration of
transparent wavelength switching. The reported devices can be employed in numerous optical interconnect schemes.
Advances in femtosecond lasers and laser stabilization have led to the development of sources of ultrafast optical pulse
trains that show jitter on the level of a few femtoseconds over tens of milliseconds and over seconds if referenced to
atomic frequency standards. These low jitter sources can be used to perform opto-electronic analog to digital conversion
that overcomes the bottleneck set by electronic jitter when using purely electronic sampling circuits and techniques.
Electronic Photonic Integrated Circuits (EPICs) may enable in the near future to integrate such an opto-electronic
analog-to-digital converters (ADCs) completely. This presentation will give an overview of integrated optical devices
such as low jitter lasers, electro-optical modulators, Si-based filter banks, and high-speed Si-photodetectors that are
compatible with standard CMOS processing and which are necessary for the implementation of EPIC-chips for advanced
Progress in developing high speed ADC's occurs rather slowly - at a resolution increase of 1.8 bits per decade. This slow progress is mostly caused by the inherent jitter in electronic sampling - currently on the order of 250 femtoseconds in the most advanced CMOS circuitry. Advances in femtosecond lasers and laser stabilization have led to the development of sources of ultrafast optical pulse trains that show jitter on the level of a few femtoseconds over the time spans of typical sampling windows and can be made even smaller. The MIT-GHOST (GigaHertz High Resolution Optical Sampling Technology) Project funded under DARPA's Electronic Photonic Integrated Circuit (EPIC) Program is trying to harness the low noise properties of femtosecond laser sources to overcome the electronic bottleneck inherently present in pure electronic sampling systems. Within this program researchers from MIT Lincoln Laboratory and MIT Campus develop integrated optical components and optically enhanced electronic sampling circuits that enable the fabrication of an electronic-photonic A/D converter chip that surpasses currently available technology in speed and resolution and opens up a technology development roadmap for ADC's. This talk will give an overview on the planned activities within this program and the current status on some key devices such as wavelength-tunable filter banks, high-speed modulators, Ge photodetectors, miniature femtosecond-pulse lasers and advanced sampling techniques that are compatible with standard CMOS processing.