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.
Starting with a waveguide amplifier as a crucial building block among many others, we demonstrate a library of optical elements that can be seamlessly integrated on a single silica-on-silicon chip and produce complex integrated optical circuits. This new level of planar waveguide integration is made possible by recent advances in our waveguide manufacturing technology capable of combining up to three different core materials on the same wafer. We discuss in details the performance and applications of these elements as well as new circuits, such as an amplified reconfigurable add-drop module.
From its foundation Inplane Photonics focused on developing integrated solutions based on Planar Lightwave Circuit(PLC) technology. It is universally agreed that the path to lower cost-per-function in Photonics, as in Electronics, leads to integration. The timing of introduction of a new technological solution and the rate at which it will penetrate the market very much depends on the interplay between the size of the market, advantages the new technology offers, and the investment needed to achieve the level of performance that is envisioned. In telecom applications, where the main drivers for technology selection are cost and performance, such large-scale investment did not materialized yet for the PLC technology mostly due to a limited market size.
Planar waveguide technology has long been touted as the major platform for optical integration, which could dramatically lower component/module size and cost in optical networks. This technology has finally come to maturity with such waveguide-based optical products as wavelength multiplexers, switches, splitters and couplers, which are common nowadays. However, its potential as a complete solution for integration of a subsystem on a chip has so far been limited by the lack of integrated active elements providing gain to deteriorating optical signals. As the signal propagates through the fiber-optic network, it dissipates its energy and requires amplification in the network subsystems to maintain a required signal to noise ratio. Discrete fiber amplifiers are designed into systems and maintain required signal levels. However, if new components are introduced or the current ones are changed, current amplifiers have a limited ability to compensate for changes. Inplane's solution to the signal degradation problem is an optical amplifier that can be integrated onto the same planar waveguide platform as the other passive elements of the subsystem. Subsystems on such a platform will be able to automatically and internally adjust signal optical power, and enable simple interfacing between optical modules, module replacement and upgrades in the network. Inplane Photonics has developed Er-doped waveguide amplifier (EDWA) technology, which is fully compatible with the glass-on-silicon waveguide platform. In this paper we will present recent EDWA performance that approaches that of a fiber amplifier. Furthermore, we will demonstrate several examples of practical integration between passive and active building blocks on a single optical chip.
Local access fiber optic systems and distributed gain fiber amplifier systems require low-cost and highly stable laser diode packages with high coupling efficiencies. These systems may use uncooled packaged lasers from the central office to the subscriber units in discrete or integrated transceiver packages. Low cost and high volume manufacturing technologies must be developed in order to produce these laser packages. A simple alternative to existing technologies is described in this paper. AT&T Bell Laboratories has been developing silicon optical bench (SiOB) technology for use as an integrated packaging platform for lasers, photodetectors and passive optical components. In this paper we describe an integrated optical sub-assembly for use in high volume and low cost laser packaging. The assembly integrates bond sites for a laser, a backface monitor photodetector and a metallized lensed fiber onto a single silicon optical sub-assembly. The approach allows for low cost batch processing, assembly and testing of components using the silicon wafer as a carrier and the use of automated pick and place machines for assembly.
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