Journal ArticleDOI

# Ultra-Broadband Add-Drop Filter/Switch Circuit Using Subwavelength Grating Waveguides

01 May 2019--Vol. 25, Iss: 3, pp 1-11

AbstractAn ultrabroadband add-drop filter/switch circuit is designed and demonstrated by integrating a pair of subwavelength grating waveguides in a $2\times 2$ Mach–Zehnder interferometer configuration using silicon photonics technology. The subwavelength grating is designed such that its stopband and passband are distinguished by a band-edge wavelength $\lambda _{\text{edge}} \sim$ 1565 nm, separating C and L bands. The stopband ( $\lambda ) is filtered at the drop port of the device, whereas the passband ($\lambda >\lambda _{\text{edge}}$) is extracted either in cross port or in bar port. The device is designed to operate only in TE polarization. Experimental results exhibit a nearly flat-top band exceeding 40 nm for both stopband and passband. The stopband extinction at cross- and bar ports are measured to be$>$35 dB with a band-edge roll-off exceeding 70 dB/nm. Wavelength independent directional coupler design and integrated optical microheaters at different locations of the Mach–Zehnder arms for thermo-optic phase detuning are the key for stopband filtering at the drop port and switching of passband between cross- and bar ports with flat top response. Though the insertion loss of fabricated subwavelength grating waveguides are negligibly small, the observed passband insertion loss is$\sim$2 dB, which is mainly due to the combined excess loss of two directional couplers. Experimental results also reveal that the passband switching between cross- and bar ports of the device has been possible with an extinction of$>$15 dB by an electrical power consumption of$P_\pi \sim$54 mW. A switching time of 5$\mu\$ s is estimated by analyzing the transient response of the device. The passband edge could also be detuned thermo-optically at a rate of 22 pm/mW.

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##### References
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Journal ArticleDOI
, Chen Sun2, Sen Lin1
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Abstract: An electronic–photonic microprocessor chip manufactured using a conventional microelectronics foundry process is demonstrated; the chip contains 70 million transistors and 850 photonic components and directly uses light to communicate to other chips. The rapid transfer of data between chips in computer systems and data centres has become one of the bottlenecks in modern information processing. One way of increasing speeds is to use optical connections rather than electrical wires and the past decade has seen significant efforts to develop silicon-based nanophotonic approaches to integrate such links within silicon chips, but incompatibility between the manufacturing processes used in electronics and photonics has proved a hindrance. Now Chen Sun et al. describe a 'system on a chip' microprocessor that successfully integrates electronics and photonics yet is produced using standard microelectronic chip fabrication techniques. The resulting microprocessor combines 70 million transistors and 850 photonic components and can communicate optically with the outside world. This result promises a way forward for new fast, low-power computing systems architectures. Data transport across short electrical wires is limited by both bandwidth and power density, which creates a performance bottleneck for semiconductor microchips in modern computer systems—from mobile phones to large-scale data centres. These limitations can be overcome1,2,3 by using optical communications based on chip-scale electronic–photonic systems4,5,6,7 enabled by silicon-based nanophotonic devices8. However, combining electronics and photonics on the same chip has proved challenging, owing to microchip manufacturing conflicts between electronics and photonics. Consequently, current electronic–photonic chips9,10,11 are limited to niche manufacturing processes and include only a few optical devices alongside simple circuits. Here we report an electronic–photonic system on a single chip integrating over 70 million transistors and 850 photonic components that work together to provide logic, memory, and interconnect functions. This system is a realization of a microprocessor that uses on-chip photonic devices to directly communicate with other chips using light. To integrate electronics and photonics at the scale of a microprocessor chip, we adopt a ‘zero-change’ approach to the integration of photonics. Instead of developing a custom process to enable the fabrication of photonics12, which would complicate or eliminate the possibility of integration with state-of-the-art transistors at large scale and at high yield, we design optical devices using a standard microelectronics foundry process that is used for modern microprocessors13,14,15,16. This demonstration could represent the beginning of an era of chip-scale electronic–photonic systems with the potential to transform computing system architectures, enabling more powerful computers, from network infrastructure to data centres and supercomputers.

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### "Ultra-Broadband Add-Drop Filter/Swi..." refers background in this paper

• ...photonics, most of the optical filters demonstrated till date are based on microring resonators [9], [27], arrayed waveguide gratings [28], photonic crystal cavities [29], DBR [30] etc....

[...]

• ...configurable optical filters [8], silicon photonics has ingrained its benchmark not only in on-chip optical communications [9], but for futuristic quantum computation [10], lab-on-chip sens-...

[...]

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TL;DR: This review provides an extended overview of the state-of-the-art in integrated photonic biosensors technology including interferometers, grating couplers, microring resonators, photonic crystals and other novel nanophotonic transducers.
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### Additional excerpts

• ...ing [11] and numerous other applications [12]....

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Journal ArticleDOI

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### "Ultra-Broadband Add-Drop Filter/Swi..." refers background in this paper

• ...fective index and dispersion characteristics of the guided mode [19]–[21]....

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