Anthony Kopa

Process flow innovations for photonic device integration in CMOS

Multilevel thin film processing, global planarization and advanced photolithography enables the ability to integrate complimentary materials and process sequences required for high index contrast photonic components all within a single CMOS process flow. Developing high performance photonic components that can be integrated with electronic circuits at a high level of functionality in silicon CMOS is one of the basic objectives of the EPIC program sponsored by the Microsystems Technology Office (MTO) of DARPA. Our research team consisting of members from: BAE Systems, Alcatel-Lucent, Massachusetts Institute of Technology, Cornell University and Applied Wave Research reports on the latest developments of the technology to fabricate an application specific, electronic-photonic integrated circuit (AS_EPIC). Now in its second phase of the EPIC program, the team has designed, developed and integrated fourth order optical tunable filters, both silicon ring resonator and germanium electro-absorption modulators and germanium pin diode photodetectors using silicon waveguides within a full 150nm CMOS process flow for a broadband RF channelizer application. This presentation will review the latest advances of the passive and active photonic devices developed and the processes used for monolithic integration with CMOS processing. Examples include multilevel waveguides for optical interconnect and germanium epitaxy for active photonic devices such as p-i-n photodiodes and modulators.

Theoretical Analysis and Practical Considerations for the Integrated Time-Stretching System Using Dispersive Delay Line (DDL)

In this paper, we perform the theoretical analysis and experimental demonstration of an on-chip implementation of a Ku-band nanosecond scale time-stretching (TS) system in a 130-nm IBM 8RF CMOS process. The theory of the TS system is applicable to general TS systems. In this study, we explain the impact of the time-bandwidth product (TBP) on practical design considerations and derive the error and distortion of a general TS system based on a dispersive delay line with perfect linear group delay and all pass amplitude characteristic. We also derive the time resolution of a general TS system using both the principle of uncertainty as well as the short time Fourier transform method. This fundamental result enables a designer to understand the qualitative relationship between the TBP and the best possible resolution of the TS system. Finally, we experimentally demonstrate the TS system on chip with nanosecond group-delay variance and 12-16-GHz bandwidth. This demonstration indicates the potential for implementation of more complicated time-scaling signal-processing systems on chip, as well as a quantification of the error and distortion for such systems.

A Novel On-Chip Active Dispersive Delay Line (DDL) for Analog Signal Processing

In this letter, we report the first on-chip design of an active dispersive delay line (DDL) based upon the distributed amplification structure. This distributed amplifier DDL exhibits nanosecond delay variation in the frequency band from 11 to 15 GHz. An on-chip temporal imager is implemented with this active DDL and a linear chirp generator, realized by ramping the control voltage of a voltage controlled oscillator. The experimental data exhibits pulse stretching as well as pulse compression with this system.

Distributed Amplifier With Blue Noise Active Termination

Active terminations can be used to reduce the low frequency noise figure of distributed amplifiers. In this letter we show extension and improvement upon previous active termination techniques. We use a combination of active and passive elements to create a termination with a blue noise spectrum rather than a broadband white noise spectrum. The novel technique is tested in a 180 nm CMOS distributed amplifier and demonstrates a 44% reduction in low frequency noise with no impact on gain, bandwidth or matching when compared to conventional design.

Optical modulation techniques for analog signal processing and CMOS compatible electro-optic modulation

Integrating electronic and photonic functions onto a single silicon-based chip using techniques compatible with mass-production CMOS electronics will enable new design paradigms for existing system architectures and open new opportunities for electro-optic applications with the potential to dramatically change the management, cost, footprint, weight, and power consumption of todays communication systems. While broadband analog system applications represent a smaller volume market than that for digital data transmission, there are significant deployments of analog electro-optic systems for commercial and military applications. Broadband linear modulation is a critical building block in optical analog signal processing and also could have significant applications in digital communication systems. Recently, broadband electro-optic modulators on a silicon platform have been demonstrated based on the plasma dispersion effect. The use of the plasma dispersion effect within a CMOS compatible waveguide creates new challenges and opportunities for analog signal processing since the index and propagation loss change within the waveguide during modulation. We will review the current status of silicon-based electrooptic modulators and also linearization techniques for optical modulation.

Alternative m-derived termination for distributed amplifiers

Use of the bisected-T m-derived filter section at the input and output of distributed amplifiers is a widely known technique to improve matching and gain flatness near the amplifier cutoff frequency. We propose the use of the new bisected-π section to achieve larger gain, lower noise figure, and smaller area for the same bandwidth and matching characteristics. We show the theoretical basis for the improvement and confirm the result by comparing two otherwise identical distributed amplifiers in 130nm CMOS. We measured a gain increase of approximately 1.2dB and a noise figure reduction over the entire bandwidth of the amplifier. Additionally, the new topology uses fewer unique inductor sizes and smaller total inductor area to give reduced design time and cost. The π-based approach should become the new standard for integrated distributed amplifier design.

124dB⋅Hz ⅔ Dynamic range transimpedance amplifier for electronic-photonic channelizer

In this paper, we present a transimpedance amplifier (TIA) based on common-source feedback (CSFB) for use in a hybrid electronic-photonic microwave channelizer. The topology demonstrates improved linearity over conventional techniques, while maintaining comparable gain, bandwidth, and noise. This approach is implemented, fabricated, and tested in 180 nm CMOS. Performance metrics demonstrated include a transimpedance gain of 64 dBOmega, 2GHz bandwidth, input referred noise current of 4.2 pA/Hz1/2 , and 5.8 dBm IP3. The circuit shows 124dBHz2/3 of spurious-free dynamic range.

Common-emitter feedback transimpedance amplifier for analog optical receivers

In this paper, we present a transimpedance amplifier (TIA) for analog optical communication based on common-emitter feedback (CEFB). CEFB is compared to traditional resistive feedback (RFB) in four metrics: gain, bandwidth, noise and linearity. In simulation, CEFB shows a 15% improvement in gain-bandwidth product and a 2dB reduction in noise over RFB. When followed by a common-emitter gain stage, CEFB shows vast improvement in linearity over RFB, 24dB higher IP3 and 57dB higher IP2. This large advantage in linearity makes CEFB especially well suited to analog applications, such as analog optical receivers