Measuring the role of surface chemistry in silicon microphotonics

Borselli, Matthew; Johnson, Thomas J.; Painter, Oskar

doi:10.1063/1.2191475

Cited by 103 publications

(89 citation statements)

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“…Unfortunately, the benefits of tight optical confinement provided by high-index-contrast photonic elements have oftentimes been offset by increased optical losses due to high modal overlap with imperfect surfaces damaged by processing or imperfectly defined by lithography. As advances in the etching and definition of these structures have reduced geometrical nonidealities, absorption has become a significant source of optical loss [5]. Understanding the optical losses of these structures is important for continued progress in developing low-loss microphotonic circuits; as a result, many recent articles [5][6][7][8][9] have detailed methods for inferring the amount of optical loss due to absorption.…”

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Accurate measurement of scattering and absorption loss in microphotonic devices

2007

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We present a simple measurement and analysis technique to determine the fraction of optical loss due to both radiation (scattering) and linear absorption in microphotonic components. The method is generally applicable to optical materials in which both nonlinear and linear absorption are present and requires only limited knowledge of absolute optical power levels, material parameters, and the structure geometry. The technique is applied to high-quality-factor (Q =1ϫ 10 6 to Q =5ϫ 10 6 ) silicon-on-insulator (SOI) microdisk resonators. It is determined that linear absorption can account for more than half of the total optical loss in the high-Q regime of these devices.

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“…Details of the disk resonator fabrication process can be found in [5]. Device characterization was performed by using a tunable external-cavity laser ( 1420-1498 nm, linewidth Ͻ300 KHz for time scales relevant to this work) connected to a computercontrolled fiber taper waveguide probe [6] and two optical attenuators as in Fig.…”

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Accurate measurement of scattering and absorption loss in microphotonic devices

2007

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“…The cavities were then undercut using a 1:1 HF:H 2 O solution to remove the buried oxide layer, and cleaned using a piranha/HF cycle. The silicon surface was hydrogen-terminated with a weak 1:20 HF:H 2 O solution for chemical passivation [16].…”

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Optimized optomechanical crystal cavity with acoustic radiation shield

et al. 2012

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We present the design of an optomechanical crystal nanobeam cavity that combines finite-element simulation with numerical optimization, and considers the optomechanical coupling arising from both moving dielectric boundaries and the photo-elastic effect. Applying this methodology results in a nanobeam with an experimentally realized intrinsic optical Q-factor of 1.2 × 10 6 , a mechanical frequency of 5.1 GHz, a mechanical Q-factor of 6.8 × 10 5 (at T = 10 K), and a zero-point-motion optomechanical coupling rate of g = 1.1 MHz.The use of radiation pressure forces to control and measure the mechanical motion of engineered micro-and nanomechanical objects has recently drawn significant attention in fields as diverse as photonics [1], precision measurement [2], and quantum information science [3]. A milestone of sorts in cavity circuit-and optomechanics is the recent [4,5] cooling of a mechanical resonator to a phonon occupancy n < ∼ 1 using cavity-assisted radiation pressure backaction [6,7]. Backaction cooling involves the use of an electromagnetic cavity with resonance frequency ω o sensitive to the mechanical displacement, x, of the mechanical resonator. The canonical system is a Fabry-Perot cavity of length L with one end mirror fixed and with the other end mirror of mass m eff mounted on a spring with resonance frequency ω m . The coupling between the electromagnetic field and mechanics is quantified by the frequency shift imparted by the zero-point motion of the mechanical resonator, given byOne of many technologies recently developed to make use of radiation pressure effects are optomechanical crystals (OMCs) [8,9]. Optomechanical crystals, in their most general form, are quasi-periodic nanostructures in which the propagation and coupling of optical and acoustic waves can be engineered. In this work we present the comprehensive design, fabrication, and characterization of a quasi-1D OMC cavity formed from the silicon device layer of a silicon-on-insulator (SOI) microchip. Our design incorporates both moving-boundary and photoelastic (electrostriction) radiation pressure contributions, and simultaneously optimizes for optical and acoustic parameters.The nominal unit cell of a nanobeam OMC, geometrically a silicon block with an oval hole in it, is shown schematically in Fig. 1a. The corresponding optical and mechanical bandstructure diagrams are shown in Figs. 1c and d, respectively. As indicated by the gray shaded region in the photonic bandstructure, the continuum of unguided optical modes above the light line precludes the existence of a complete photonic band gap (only a quasibandgap exists for the guided modes of the beam). The physical dimension of the unit cell block (see caption of Fig. 1a) are chosen to yield a photonic quasi-bandgap surrounding a wavelength λ ∼ 1550 nm. The corresponding mechanical bandstructure has a series of acoustic bands in the GHz frequency range (the ratio of the optical frequencies to that of the mechanical frequencies is roughly the ratio of the speed of light to sound in si...

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“…13 A 250 nm thick semiconductor disk with index n disk = 3.4 and radius R d = 0.65 m is simulated with a centered metal contact of varying radius ͑R m ͒. A schematic of the microdisk device is shown in Fig.…”

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Surface-plasmon mode hybridization in subwavelength microdisk lasers

Perahia

Alegre

Safavi-Naeini

et al. 2009

Applied Physics Letters

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Hybridization of surface-plasmon and dielectric waveguide whispering-gallery modes are demonstrated in a semiconductor microdisk laser cavity of subwavelength proportions. A metal layer is deposited on top of the semiconductor microdisk, the radius of which is systematically varied to enable mode hybridization between surface-plasmon and dielectric modes. The anticrossing behavior of the two cavity mode types is experimentally observed via photoluminescence spectroscopy and optically pumped lasing action at a wavelength of ϳ 1.3 m is achieved at room temperature. © 2009 American Institute of Physics. ͓doi:10.1063/1.3266843͔In wavelength-scale lasers, the very small number of optical modes and small volume of gain material allows one to probe the subtle and often interesting properties of lasing action. 1 Semiconductor microdisk lasers, in particular, have been actively studied due to their simple geometry and amenability to planar chip-scale integration with microelectronics. [2][3][4] More recently there has been great interest in using surface-plasmon ͑SP͒ modes at a semiconductormetal interface for guiding as well as high intensity and subwavelength optical confinement. 5 There has been significant work on the incorporation of SP waveguides that also act as electrical contacts in mid-infrared quantum cascade lasers, 6 in increasing SP propagation lengths using SP-dielectric waveguide mode hybridization, 7 as well as in creating ultrasmall laser cavities. 8,9 In miniaturizing semiconductor lasers to the nanoscale one encounters several design challenges that must be addressed, such as thermal management, 10,11 proximity of metal contacts to the optical cavity, surface states, 12 and demanding tolerance levels in fabrication. In this letter, we investigate the purposeful integration of a metal contact into a subwavelength whispering-gallery microdisk laser. We show that whispering-gallery SP and dielectric modes hybridize into low loss modes. We predict and map out this hybridization using finite-element-method ͑FEM͒ simulations, and experimentally measure the properties of fabricated microdisk laser cavities with varying levels of mode hybridization.Simulation of the hybrid laser cavities is performed using fully-three-dimensional FEM simulations with azimuthal symmetry. 13 A 250 nm thick semiconductor disk with index n disk = 3.4 and radius R d = 0.65 m is simulated with a centered metal contact of varying radius ͑R m ͒. A schematic of the microdisk device is shown in Fig. 1͑a͒. Silver with a complex refractive index of n Ag = 0.11− i9.5 at = 1.3 m is chosen for the metal layer due to its low optical loss. 14 For this disk size in the 1300 nm wavelength band there occurs a near degeneracy of the transverse-electric-like ͑TE-like͒ whispering-gallery mode ͑WGM͒ with dominant electric field polarization in the plane of the disk and the transversemagnetic-like ͑TM-like͒ mode with dominant electric field normal to the disk plane. A plot of the wavelength and Q-factor of these two resonances is shown in Fig. 2͑a͒ a...

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Measuring the role of surface chemistry in silicon microphotonics

Cited by 103 publications

References 32 publications

Accurate measurement of scattering and absorption loss in microphotonic devices

Accurate measurement of scattering and absorption loss in microphotonic devices

Optimized optomechanical crystal cavity with acoustic radiation shield

Surface-plasmon mode hybridization in subwavelength microdisk lasers

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