Silicon microspheres for electronic and photonic integration

Accepted Manuscript

Title: Silicon Microspheres for Electronic and PhotonicIntegration

Authors: Ali Serpenguzel, Adnan Kurt, Ulas Kemal Ayaz

PII: S1569-4410(08)00020-5DOI: doi:10.1016/j.photonics.2008.08.005Reference: PNFA 133

To appear in: Photonics and Nanostructures – Fundamentals and Applications

Received date: 4-12-2007Revised date: 8-8-2008Accepted date: 8-8-2008

Please cite this article as: A. Serpenguzel, A. Kurt, U.K. Ayaz, Silicon Microspheresfor Electronic and Photonic Integration, Photonics and Nanostructures - Fundamentalsand Applications (2007), doi:10.1016/j.photonics.2008.08.005

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*Corresponding author: Telephone: + 90 (212) 338 1312 Fax: + 90 (212) 338 1547, E-mail:

[email protected] (Ali Serpengüzel)

Silicon Microspheres for Electronic and Photonic Integration

Ali Serpengüzel,* Adnan Kurt**, and Ulaş Kemal Ayaz****Koç University, Physics Department, Microphotonics Research Laboratory,

Rumelifeneri Yolu, Sariyer, Istanbul 34450 Turkey**Teknolfil Ltd., 3. Cadde No 8,

Zekeriyaköy, Sarıyer, Istanbul 34450 Turkey***Polytechnic University, Department of Aerospace and Mechanical Engineering,

Six MetroTech Center, Brooklyn, New York 11201, USA

Abstract

Silicon microspheres are transparent in the near infrared telecommunication bands and can be used for

electrophotonic interation. We have experimentally observed blue shifts in resonance wavelengths of an electrically

driven silicon microsphere of 500 microns in radius, in the near-infrared. We have used a DFB laser operating at

1475nm, and applied electical potential differences up to 9V to the silicon microsphere. We have observed blue

shifts in the resonance wavelengths up to 0.05 nm, which corresponds to a change in in the refractive index of 10-4.

Keywords: channel dropping, coupling, microcavity, microdisk, microresonator, microring, microsphere,

microtoroid, morphology dependent resonance, photonics, photonic atom, planar lightwave circuit, resonance,

silicon, volumetric lightwave circuit, wavelength division multiplexing, waveguide, whispering gallery mode.

Manuscript

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Introduction

Silicon photonics is experiencing a rapid growth, [1] which is driven by the need for low cost photonic devices [2,3]

and the need for high speed intrachip communication [4, 5]. Although silicon photonics is less well developed as

compared to the III-V photonics; silicon is poised to make a serious impact on the optical communications [6].

Silicon, with a bandgap of 1.1 eV is transparent in the near-infrared (IR), and is a suitable high refractive index

group IV material. The high refractive index (m = 3.48) of silicon increases the optical pathwidth and makes the use

of smaller devices possible, which is an additional miniaturisation advantage over the devices made from dielectrics.

Recent progress in silicon photonics is being heralded by the observation of Raman amplification [7,8,9], stimulated

Raman scattering (SRS) oscillation in pulse [10,11] modulated [12] and in CW [13] silicon “Raman” lasers, and

finally the hybrid silicon “Raman” laser [14]. Additionally, silicon modulators [15, 16] have been developed using

metal-oxide-semiconductor (MOS) capacitor [17], Mach-Zehnder [18], SRS [19], and microring [20] configurations.

Recently, a silicon microring based wavelength converter has been realized [21]. With well established CMOS

processing techniques, it will be possible to integrate lasers, waveguides, modulators, switches, wavelength

converters, and photodetectors into silicon motherboards [22] for WDM [23] as well as intrachip communication.

Passive and active silicon racetrack resonators, [24] microring resonators, [25] and silicon waveguides with feedback

[26, 27] are some of the geometries pursued for 2D silicon planar lightwave circuits (PLC's). Silicon microspheres

are the natural extensions of 2D silicon microresonators and can be integrated in 3D to fabricate volumetric

lightwave circuits (VLC’s). Microspheres have been used to construct 1D chains [28], 2D arrays [29], and 3D

lattices [30]. Dielectric microspheres have found ample applications in photonics [31] such as microlasers [32],

switches [33], molecular sensors [34], displacement sensors [35], and rotation sensors [36]. The microsphere [37] is

the only 3D microresonator with a high quality factor. Additionally, microsphere resonators are uniquely applicable

for electro-optical integration [38]. Fiber optic add-drop filters based on a silica microsphere system on a taper-

resonator-taper coupler [39] and channel-dropping filter using a microsphere and integrated waveguides have been

developed [40]. Recently, optical resonances from silicon microspheres at 1.3 μm have been observed [41]. In this

paper, we are investigating the electro-optical response of a silicon microsphere in the near-IR resonant wavelengths.

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1. Electronic Properties of Silicon Microspheres

The electrical contacts are made by placing two electrical probes to the poles of the silicon microsphere. Figure 1

shows the I-V curve of the silicon microsphere, which has a radius a = 500 m. The I-V characteristics exhibits the

response of two Schottky MSM contacts back to back. The graph is not fully symmetric, due to the non-symmetric

geometry of the contact.

2. Electro-optical properties of the silicon microsphere

Figure 2 shows the schematic of the experimental setup for the silicon microsphere electro-optic measurements.

Light is coupled to the silicon microsphere by using an optical fiber half coupler (OFHC). The OFHC is

manufactured by polishing the optical fiber that is glued in a silica substrate. OFHC is fabricated from 1500 nm

standard single mode fiber (SMF). The silicon microsphere is placed on the interaction region of the OFHC. The

microsphere was held in position by the electrical probes from the poles, which were also used for electrical input.

The output of a distributed feedback (DFB) laser is coupled to the optical fiber. Wavelength tuning is achieved by

tuning the temperature of the DFB laser with a laser diode controller (LDC). The DFB laser light is coupled into the

-8.9

-6.9

-4.9

-2.9

-.9

1.1

3.1

5.1

7.1

-80 -60 -40 -20 0 20 40 60 80

Applied Potential (V)

Current (mA)

Fig. 1. IV curve of the silicon microsphere.

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OFHC using the pigtail output of the laser. The transmitted light is observed using an InGaAs optical power/wave

head connected to an optical multimeter (OMM). The elastically scattered light from the microsphere at 90 is

collected by a microscope lens through a Glen polarizer and detected by an InGaAs photodiode (PD). The InGaAs

photodiode signal is sent to the digital storage oscilloscope (DSO) for signal monitoring and data acquisition. A

near-IR viewer is used to observe the elastically scattered light from the microsphere. Data acquisition and control

are performed with IEEE-488 GPIB interface.

Both the refractive index and the absorption of silicon can be changed using carrier injection or depletion. The

refractive index change (∆m) due to free carrier concentration (∆N) is given by the Kramers-Kronig analysis [42],

DFB source laser

DSO

OMM Computer LDCLDC

InGaAsPDPD

Microscope

Near-IR Viewer

GPIB

Function Generator

InGaAsPWH OFHC

Glen Polarizer

Red probe laser

USB

InGaAs PD

Polarization ControllerElectrical

input

Fig. 2. The schematic of the experimental setup for the silicon microsphere electro-optic measurements.

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∆me= -8.8x 10-22∆Ne and ∆mh= -8.5x 10-18(∆Nh)0.8, where ∆me and ∆mh are the refractive index changes resulting

from the changes in the free electron concentration (∆Ne) and free hole concentration (∆Nh), respectively.

Figure 3 and 4 show the elastic scattering spectrum at a scattering angle of 90 from the silicon microsphere, when a

positive or a negative potential difference is applied to the poles of the microsphere, respectively. In both figures,

there is a background due to OFHC surface imperfections. The temperature of the DFB laser is tuned from 19C to

25C at a constant current of 26.3 mA. The temperature range corresponds to 1474.6 to 1476.8 nm. The width and

magnitude of the MDR peaks are highly sensitive functions of the size parameter (2πa/λ) and refractive index (m) of

the microsphere. The mode spacing (), i.e., the wavelength difference between morphology dependent resonances

(MDR’s) with consecutive mode numbers (n) with the same mode order (l), is measured to be 0.28 nm, which

correlates well with the optical size of the microsphere. In figures 3 and 4, electric potential differences of 3, 6, 9

Volts and -3, -6, -9 Volts were applied to the microsphere by a DC power supply, and the elastic scattering spectrum

has been measured. In both the positive and the negative electric potential differences, the elastic scattering spectrum

0.032

0.034

0.036

0.038

0.04

0.042

1474.7 1475.2 1475.7 1476.2

Wavelength (nm)

Sc

att

ere

d S

ign

al

(arb

. u

nit

s)

0V9V6V3V

a

m Silicon spherea = 500 micrometersm = 3.48

Fig. 3. The elastic scattering spectra of the silicon microsphere with positive potential difference.

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exhibited a blue shift, which was proportional to the applied electric potential difference. For an applied electric

potential difference of ±9V, the MDR’s blue shift by 0.05 nm, which corresponds to a refractive index decrease of

∆m = 10-4.

3. Conclusions

We have experimentally observed the elastic scattering spectra from a silicon microsphere in the near-IR at 1475 nm.

The mode spacing () of the MDR’s 0.27 nm correlates well with the optical size of the silicon microsphere.

Moreover, we have observed a blue of shift of the MDR’s on the order of 0.005 nm/V, which correlate well with the

electro-optical properties of silicon. This electro-optical observation heralds the silicon microsphere as a potential

building block for electrophotonic integration. Possible active optoelectronic device applications include high quality

factor resonant filters, detectors, modulators, switches, light sources, wavelength converters, and variable

attenuators.

0.0335

0.0345

0.0355

0.0365

0.0375

0.0385

0.0395

0.0405

0.0415

0.0425

1474.7 1475.2 1475.7 1476.2

Wavelength (nm)

Sca

tter

ed S

ign

al (

arb

. un

its)

0V

-9V

-6V

-3V

a

m

Silicon spherea = 500 micrometersm = 3.48

Fig. 4. The elastic scattering spectra of the silicon microsphere with negative potential difference.

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Acknowledgments

We would like to acknowledge the partial support of this research by the EC Grants No: FP6-IST-003887 NEMO,

FP6-IST-511616 PHOREMOST and TUBITAK Grant No: EEEAG-106E215.

References

[1] R. Soref, “The past, present, and future of silicon photonics,” IEEE Journal of Selected Topics in Quantum Electronics, 2006. 12(6): p. 1678-1687.

[2] M. Paniccia, M. Morse, and M. Salib, “Integrated Photonics,” in “Silicon Photonics,” L. Pavesi and D. J. Lockwood, Eds. Springer Verlag, Berlin, 2004, p. 51-85.

[3] L. Pavesi and D. J. Lockwood, “Silicon Photonics,” New York: Springer-Verlag, 2004.[4] G. T. Reed, G. Z. Mashanovich, W. R. Headley, S. P. Chan, B. D. Timotijevic and F. Y. Gardes, “Silicon Photonics: Are Smaller Devices

Always Better?,” Japanese J. of Appl. Phys. 45, 2006, p. 6609-6615.[5] Kimerling, L. C., Dal Negro, L., Saini, S., Yi, Y., Ahn, D., Akiyama, S., Cannon, D., Liu, J., Sandland, J. G., Sparacin, D., Michel, J.,

Wada, K., and Watts, M. R., “Monolithic Silicon Microphotonics,” in “Silicon Photonics,” L. Pavesi and D. J. Lockwood, Eds. Springer Verlag, Berlin, 2004. 94: p. 89-119.

[6] H. Zimmermann, “Integrated Silicon Optoelectronics,” Springer Verlag, Berlin (2000).[7] A. Liu, H. Rong, M. Paniccia, O. Cohen, and D. Hak, "Net Optical Gain in a Low Loss Silicon-on-Insulator Waveguide by Stimulated

Raman Scattering," Opt. Express 12, 4261-4268 (2004).[8] H. Rong, A. Liu, R. Nicolaescu, M. Paniccia, "Raman Gain and Nonlinear Optical Absorption Measurements in a Low-Loss Silicon

Waveguide," Appl. Phys. Lett. 85, 2196-2198 (2004).[9] R. Jones, H. Rong, A. Liu, A. Fang, and M. Paniccia, "Net Continuous Wave Optical Gain in a Low Loss Silicon-on-Insulator Waveguide

by Stimulated Raman Scattering," Opt. Express 13, 519-525 (2005).[10] O. Boyraz and B. Jalali, “Demonstration of a silicon Raman laser,” Opt. Express 12, 5269-5273 (2004).[11] H. Rong, A. Liu, R. Jones, O. Cohen, D. Hak, R. Nicolaescu, A. Fang and M. Paniccia, "An All-Silicon Raman Laser," Nature 433, 292-

294 (2005).[12] O. Boyraz and B. Jalali, “Demonstration of directly modulated silicon Raman laser,” Opt. Express 13, 796-800 (2005).[13] H. Rong, R. Jones, A. Liu, O. Cohen, D. Hak, A. Fang, and M. Paniccia, "A Continuous-Wave Raman Silicon Laser," Nature 433, 725-

728 (2005).[14] A. W. Fang, H. Park, O. Cohen, R. Jones, M. J. Paniccia, and J. E. Bowers, “Electrically pumped hybrid AlGaInAs-silicon evanescent

laser,” Opt. Express, 14, 9203-9210 (2006). [15] A. Liu, D. Samara-Rubio, L. Liao, and M. Paniccia, "Scaling the Modulation Bandwidth and Phase Efficiency of a Silicon Optical

Modulator," IEEE J. Sel. Top. Quantum Electron. 11, 367-372 (2005). [16] L. Liao, A. Liu, R. Jones, D. Rubin, D. Samara-Rubio, O. Cohen, M. Salib and M. Paniccia, "Phase Modulation Efficiency and

Transmission Loss of Silicon Optical Phase Shifters," IEEE J. Quantum Electron. 41, 250-257 (2005).[17] A. Liu, R. Jones, L. Liao, D. Samara-Rubio, D. Rubin, O. Cohen, R. Nicolaescu, M. Paniccia, "A High-Speed Silicon Optical Modulator

based on a Metal-Oxide-Semiconductor Capacitor," Nature 427, 615-618 (2004). [18] L. Liao, D. Samara-Rubio, M. Morse, A. Liu, D. Hodge, D. Rubin, U. D. Keil, and T. Franck, "High Speed Silicon Mach-Zehnder

Modulator," Opt. Express 13, 3129-3135 (2005).[19] R. Jones, A. Liu, H. Rong, M. Paniccia, O. Cohen, and D. Hak, "Lossless Optical Modulation in a Silicon Waveguide using Stimulated

Raman Scattering," Opt. Express 13, 1716-1723 (2005).[20] Q. Xu, S. Manipatruni, B. Schmidt, J. Shakya, and M. Lipson, “12.5 Gbit/s carrier-injection-based silicon microring silicon modulators,”

Opt. Express 15, 431-436 (2007).[21] S. F. Preble, Q. Xu, and M. Lipson, “Changing the colour of light in a silicon resonator,” Nature Photon. 1, 293-296 (2007).[22] B. Jalali, S. Yegnanarayanan, T. Yoon, T. Yoshimoto, I. Rendina, and F. Coppinger, “Advances in Silicon on insulator Optoelectronics,”

IEEE J. Select. Top. Quantum Electron. 4, 938-947 (1998).[23] B. J. Offrein, R. Germann, F. Horst, H. W. M. Salemink, R. Beyerl, and G. L. Bona, “Resonant coupler-based tuneable add-after-drop filter

in silicon–oxynitride technology for WDM networks,” IEEE J. Select. Top. Quantum Electron. 5, 1400-1406 (1999). [24] Timotijevic, B.D., Gardes, F. Y., Headley, W. R., Reed, G. T., Paniccia, M. J., Cohen, O., Hak, D., Masanovic, G. Z. et al., Multi-stage

racetrack resonator filters in silicon-on-insulator. Journal of Optics a-Pure and Applied Optics, 2006. 8(7): p. S473-S476.[25] Xu, Q.F. and M. Lipson, All-optical logic based on silicon micro-ring resonators. Optics Express, 2007. 15(3): p. 924-929.[26] Jalali, B., Teaching silicon new tricks. Nature Photonics, 2007. 1(4): p. 193-195.[27] Alduino, A. and M. Paniccia, Interconnects - Wiring electronics with light. Nature Photonics, 2007. 1(3): p. 153-155.[28] BM Möller et al, Band Formation in Coupled-Resonator Slow-Wave Structures, Opt. Express, 15, 17362 (2007).[29] VN Astratov et al, Optical coupling and transport phenomena in chains of spherical dielectric microresonators with size disorder, Appl.

Phys. Lett. 85, 5508 (2004).

Page 8 of 8

Accep

ted

Man

uscr

ipt

[30] VN Astratov, Percolation of light through whispering gallery modes in 3D lattices of coupled microspheres, Opt. Express 15, 17351 (2007).

[31] R. K. Chang, A. J. Campillo, Eds., Optical Processes in Microcavities, World Scientific, Singapore, 1996.[32] M. Cai, O. Painter, and K. J. Vahala, “Fiber-coupled microsphere laser,” Opt. Lett., vol. 25, pp. 1430-1432, 2000.[33] H.C. Tapalian, J.P. Laine, and P.A. Lane, “Thermooptical switches using coated microsphere resonators,” IEEE Photon. Techn. Lett., vol.

14, pp. 1118-1120, Aug. 2002.[34] I. Teraoka, S. Arnold, F. Vollmer, “Perturbation approach to resonance shifts of whispering-gallery modes in a dielectric microsphere as a

probe of a surrounding medium,” J. Opt. Soc. Am. B, vol. 20, pp. 1937-1946, 2003.[35] J. P. Laine, H. C. Tapalian, B. E. Little, and H. A. Haus, “Acceleration sensor based on high-Q optical microsphere resonator and pedestal

antiresonant reflecting waveguide coupler,” Sensors and Actuators A, vol. 93, pp. 1-7, 2001.[36] A.B. Matsko, A.A. Savchenkov, V.S. Ilchenko, and L. Maleki, “Optical gyroscope with whispering gallery mode optical cavities,” Optics

Communications, vol. 233, pp. 107–112, 2004.[37] ML Gorodetsky at al , “Rayleigh scattering in high-Q microspheres,” JOSA B, Vol. 17, 1051 (2000).[38] A. Serpengüzel, S. Arnold, G. Griffel, and J. A. Lock, “Enhanced coupling to microsphere resonances with optical fibers,” J. Opt. Soc. Am.

B., vol. 14, no. 4, pp. 790-795, Apr. 1997.[39] M. Cai, G. Hunziker, and K. Vahala, “Fibre optic add-drop device based on a silica microsphere-whispering gallery mode system,” IEEE

Photon. Technol. Lett., vol. 11, pp. 686-687, June1999.[40] T. Bilici, S. Isçi, A. Kurt, and A. Serpengüzel, “Microsphere Based Channel Dropping Filter with Integrated Photodetector,” IEEE Photon.

Technol. Lett. 16, 476-478, (2004)[41] Y.O. Yilmaz, A. Demir, A. Kurt, and A. Serpengüzel, “Optical Channel Dropping with a Silicon Microsphere,” IEEE Photon. Technol.

Lett., 17, 1662-1664 (2005).[42] Reed T. Graham and Knights P. Andrew: “Silicon Photonics; An Introduction” John Wiley and Sons Ltd. West Sussex, (2004).