Anujit Shastri

Ultra-Low-Power Single-Polarization QAM-16 Generation Without DAC Using a CMOS Photonics Based Segmented Modulator

Long-haul communication systems are requiring more and more spectral efficiency as data rates increase. QAM-16 is a promising candidate for each wavelength in a Wavelength-Division Multiplexed (WDM) system, providing double the spectral efficiency of Quadrature Phase-Shift Keying (QPSK) and four times the spectral efficiency of traditional On-Off Keying (OOK). However, generation of QAM-16 signals can be complex, expensive, and power-hungry when electrical Digital-to-Analog Converters (DACs) are required. We have developed a QAM-16 modulator that precludes the use of an electrical DAC while simultaneously keeping the optical architectural complexity similar to that of a traditional In-phase/Quadrature (IQ) modulator. Using this modulator, we experimentally demonstrate single-polarization, back-to-back transmission, and homodyne detection of QAM-16 signals at rates up to 28.125 Gsymbols/s, resulting in single-polarization system per-wavelength bit rates up to 112.5 Gb/s. This would translate to dual-polarization system per-wavelength bit rates up to 225 Gb/s. This is done using a segmented modulator built on an ultra-low-power CMOS Photonics platform, allowing the modulator and drivers to consume less than 1 W of power.

Silicon high speed modulator for advanced modulation: device structures and exemplary modulator performance

Fiber optics is well established today due to the high capacity and speed, unrivaled flexibility and quality of service. However, state of the art optical elements and components are hardly scalable in terms of cost and size required to achieve competitive port density and cost per bit. Next-generation high-speed coherent optical communication systems targeting a data rate of 100-Gb/s and beyond goes along with innovations in component and subsystem areas. Consequently, by leveraging the advanced silicon micro and nano-fabrication technologies, significant progress in developing CMOS platform-based silicon photonic devices has been made all over the world. These achievements include the demonstration of high-speed IQ modulators, which are important building blocks in coherent optical communication systems. In this paper, we demonstrate silicon photonic QPSK modulator based on a metal-oxide-semiconductor (MOS) capacitor structure, address different modulator configuration structures and report our progress and research associated with highspeed advanced optical modulation in silicon photonics

Experimental demonstration of ultra-low-power single polarization 56 Gb/s QAM-16 generation without DAC using CMOS photonics

We experimentally demonstrate back-to-back transmission of QAM-16 at 56 Gb/s over a single polarization, representing a dual polarization system link of 112 Gb/s, without using an electrical DAC, on a CMOS Photonics platform.

Design of Low-Power DSP-Free Coherent Receivers for Data Center Links

Coherent detection offers high spectral efficiency and receiver sensitivity, but digital signal processing (DSP)-based coherent receivers may be prohibitively power hungry for data centers even when optimized for short-reach applications, where fiber propagation impairments are less severe. We propose and evaluate low-power DSP-free homodyne coherent receiver architectures for dual-polarization quadrature phase shift keying (DP-QPSK) for inter- and intradata center links. We propose a novel optical polarization demultiplexing technique, for DP-QPSK and higher-order modulation formats, with three cascaded phase shifters driven by marker tone detection circuitry. We consider carrier recovery based on either optical or electrical phase-locked loops (PLLs). We propose a novel multiplier-free phase detector based on XOR gates, which exhibits less than 0.5 dB power penalty relative to a conventional Costas loop phase detector. We also study the relative performance of homodyne DP-differential QPSK, for which carrier phase recovery is unnecessary. Our proposed DSP-free architectures exhibit ∼1 dB power penalty at small chromatic dispersion compared to their DSP-based counterparts. We estimate conservatively that the high-speed analog electronics of an electrical PLL-based coherent receiver consume nearly 4 W for 200 Gbit/s DP-QPSK, assuming a 90-nm complementary metal-oxide semiconductor process.

Integrated optical-wireless broadband access networks

Optical and wireless technologies have complementary characteristics in capacity and mobility. This talk describes our research toward the convergence of both optical and wireless technologies to address the needs of future access networks.