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.
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.
An electronic system based on a novel high-speed massive video memory array using an optical fiber clock distribution network has been investigated for the generation of random patterns for testing high-resolution color video monitors with screen sizes in the realm of 4096 by 4096 pixels. For frame rates in the range of 30 to 100 per second with 256 (28) to 4096 (212) intensity levels for each primary color the speed requirement amounts to 1.21x1010 to 6.04x1010 bits per second. The massive memory makes use of high-speed MSM photodetectors, optical receiver amplifiers and gallium arsenide charged coupled devices which are integrated on GaAs chips. These chips are assembled into 16 planes of multi-chip modules with 32 GaAs chips per plane. Only GaAs CCDs have been found to provide the short access times required to achieve the above data rates that exceed the capabilities of current silicon-based DRAMs. For proper operation clock skew must be eliminated, therefore, a 2-phase laser driven optical fiber distribution network has been considered. In addition, the photodetectors and amplifiers driving the CCDs must have speeds that do not compromise the access times of the CCD registers. To meet all requirements the design was implemented with optical fiber v-groove coupling to the MSM monolithic detectors and high-speed preamplifiers that are fabricated with the same technology as used for the fabrication of the CCDs.
The semiconductors gallium arsenide and polycrystalline diamond can both be obtained in a high resistivity form suitable for the fabrication of photosensors and detector arrays for the ultraviolet region of the electromagnetic spectrum. These materials have different energy bandgaps and chemical properties which make them complementary partners in providing photodetectors for coverage of the spectral range from near 100 nm in the vacuum ultraviolet to the near infrared at 870 nm. The readily available forms of these two semiconductors are different. GaAs is available in the form of single crystal wafers with uniform properties while polycrystalline diamond in a tight packing of crystallites with varying orientations providing only an average uniformity on the micron scale determined by the size of the crystallites. The GaAs MSM detectors were studied for use in monolithic GaAs-based charge-coupled device scanners for the ultraviolet spectroscopy. The polycrystalline diamond MSM devices are being investigated for hybrid scanners on silicon for the vacuum ultraviolet.