We report a high-speed ring modulator that fits many of the ideal qualities for optical interconnect in future exascale supercomputers. The device was fabricated in a 130nm SOI CMOS process, with 7.5μm ring radius. Its high-speed section, employing PN junction that works at carrier-depletion mode, enables 25Gb/s modulation and an extinction ratio >5dB with only 1V peak-to-peak driving. Its thermal tuning section allows the device to work in broad wavelength range, with a tuning efficiency of 0.19nm/mW. Based on microwave characterization and circuit modeling, the modulation energy is estimated ~7fJ/bit. The whole device fits in a compact 400μm2 footprint.

25Gb/s 1V-driving CMOS ring modulator with integrated thermal tuning

Silicon photonic devices and integrated circuits have undergone rapid and significant progresses during the last decade, transitioning from research topics in universities to product development in corporations. Silicon photonics is anticipated to be a disruptive optical technology for data communications, with applications such as intra-chip interconnects, short-reach communications in datacenters and supercomputers, and long-haul optical transmissions. Bell Labs, as the research organization of Alcatel-Lucent, a network system vendor, has an optimal position to identify the full potential of silicon photonics both in the applications and in its technical merits. Additionally it has demonstrated novel and improved high-performance optical devices, and implemented multi-function photonic integrated circuits to fulfill various communication applications. In this paper, we review our silicon photonic programs and main achievements during recent years. For devices, we review highperformance single-drive push-pull silicon Mach-Zehnder modulators, hybrid silicon/III-V lasers and silicon nitrideassisted polarization rotators. For photonic circuits, we review silicon/silicon nitride integration platforms to implement wavelength-division multiplexing receivers and transmitters. In addition, we show silicon photonic circuits are well suited for dual-polarization optical coherent transmitters and receivers, geared for advanced modulation formats. We also discuss various applications in the field of communication which may benefit from implementation in silicon photonics.

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Silicon photonic devices and integrated circuits

We demonstrate the design, fabrication and measurement of integrated Bragg gratings in a compact single-mode silicon-on-insulator ridge waveguide. The gratings are realized by corrugating the sidewalls of the waveguide, either on the ridge or on the slab. The coupling coefficient is varied by changing the corrugation width which allows precise control of the bandwidth and has a high fabrication tolerance. The grating devices are fabricated using a CMOS-compatible process with 193 nm deep ultraviolet lithography. Spectral measurements show bandwidths as narrow as 0.4 nm, which are promising for on-chip applications that require narrow bandwidths such as WDM channel filters. We also present the die-to-die nonuniformity for the grating devices on the wafer, and our analysis shows that the Bragg wavelength deviation is mainly caused by the wafer thickness variation.

Narrow-band waveguide Bragg gratings on SOI wafers with CMOS-compatible fabrication process.

Integration of electronics and photonics for future applications requires an efficient conversion of electrical to optical signals. The excellent electronic and photonic properties of graphene make it a suitable material for integrated systems with extremely wide operational bandwidth. In this paper, we analyze the novel geometry of modulator based on the rib photonic waveguide configuration with a double-layer graphene placed between a slab and ridge. The theoretical analysis of graphene-based electro-absorption modulator was performed showing that a 3 dB modulation with ~ 600 nm-long waveguide is possible resulting in energy per bit below 1 fJ/bit. The optical bandwidth of such modulators exceeds 12 THz with an operation speed ranging from 160 GHz to 850 GHz and limited only by graphene resistance. The performances of modulators were evaluated based on the figure of merit defined as the ratio between extinction ratio and insertion losses where it was found to exceed 220.

/pdf/theoretical-investigation-of-graphene-based-photonic-3fknyzjx9o.pdf

Theoretical investigation of graphene-based photonic modulators

A fully-integrated, silicon photonic transceiver is demonstrated in a silicon-on-insulator process using photonic microring resonator modulators for low power consumption. The trade-offs between bandwidth and extinction ratio are discussed and motivate the use of transmit pre-emphasis for ring modulators to increase the interconnect data rate. The transmitter and receiver is demonstrated to data rates of 25 Gb/s with a BER of 10 ^-12. The total power consumption of the transceiver is 256 mW and demonstrates a link efficiency of 10.2 pJ/bit excluding laser power. At 25 Gb/s, the driver operates at 7.2 pJ/bit.

A Monolithic 25-Gb/s Transceiver With Photonic Ring Modulators and Ge Detectors in a 130-nm CMOS SOI Process

We demonstrate an add/drop filter based on coupled vertical gratings on silicon. Tailoring of the channel bandwidth and wavelength is experimentally demonstrated. The concept is extended to implement a 1 by 4 wavelength division multiplexer with 6 nm channel separation, 3 nm bandwidth, a flat top response with < 0.8 dB ripple within the 3 dB passband, 1 dB insertion loss and 16 dB crosstalk suppression. The device is ultracompact, having a footprint < 2 X 10(-9)/2.

Wide bandwidth, low loss 1 by 4 wavelength division multiplexer on silicon for optical interconnects

We report a 320fJ/bit transmitter made of a Si microring modulator flip-chip bonded to a CMOS driver. The transmitter consumes only 1.6mW power, and exhibits a wide open eye with extinction ratio >7dB at 5Gb/s.

Ultralow-power high-performance Si photonic transmitter

We demonstrate a hybrid III-V/SOI laser by vertically coupling a III-V RSOA chip with a SOI-CMOS chip containing a tunable wavelength selective reflector We report a waveguide-coupled wall-plug-efficiency of 55% and output power of 10 mW A silicon resistor-based microheater was integrated to thermally tune a ring resonator for precise lasing wavelength control A high tuning efficiency of 22 nm/mW over a range of 18 nm was achieved by locally removing the SOI handler substrate C-band single mode lasing was confirmed with a side mode suppression ratio of 35 dB This grating coupler based vertical integration approach can be scaled up in two dimensions for efficient multi-wavelength sources in silicon photonics

Vertical-coupled high-efficiency tunable III-V- CMOS SOI hybrid external-cavity laser

We demonstrate an add/drop filter based on coupled vertical gratings on silicon. The concept is extended to implement a 1 by 4 wavelength division multiplexer with 3nm bandwidth, 1dB insertion loss and 16dB crosstalk suppression.

A chip package includes an optical integrated circuit (such as a hybrid integrated circuit) and an integrated circuit that are proximate to each other in the chip package. The integrated circuit includes electrical circuits that modulate data, communicate data, and serialize/deserialize data, and the optical integrated circuit communicates optical signals with very high bandwidth. Moreover, a front surface of the integrated circuit is electrically coupled to a top surface of an interposer, and a top surface of the integrated circuit is electrically coupled to a front surface of the optical integrated circuit. Furthermore, a bottom surface of the optical integrated circuit faces the top surface of the interposer, and the front surface of the optical integrated circuit is optically coupled to an optical-fiber receptacle, which in turn is optically coupled to an optical-fiber connector.

Xuezhe Zheng

Papers

Wide bandwidth, low loss 1 by 4 wavelength division multiplexer on silicon for optical interconnects

Ultralow-power high-performance Si photonic transmitter

Vertical-coupled high-efficiency tunable III-V- CMOS SOI hybrid external-cavity laser

Wide bandwidth, low loss 1 by 4 wavelength division multiplexer on silicon for optical interconnects

Packaged opto-electronic module