Chaos synchronization and communication in unidirectionally coupled VCSELs with fiber channel

Lin-Fu Li

Supervisor: Min Xu

    Chaos synchronization is an interesting phenomenon that occurs in many nonlinear dynamic systems. It originates from the nonlinear interactions of the system and exists widely in physics, chemistry, biology, social science, and many other fields. Especially, chaos synchronization was put forward firstly by Pecora and Carroll in 1990 , chaos and chaos synchronization have received a great deal of interest due to its potential applications in various research fields.

In this work, a chaos synchronization system based on two unidirectional coupled VCSELs subject to polarization-preserved optical feedback at the T-VCSEL port and polarization-preserved optical injection at the R-VCSEL port is presented. This system is constructed on the basis of unidirectionally coupled VCSELs and signal transmission in fiber. The transmitter VCSEL is subject to an isotropic optical feedback, the receiver VCSEL is subject to an orthogonal optical injection from the transmitter VCSEL, the chaotic signal transmission in fiber channel is adopted, also message encoding and decoding of the chaotic system have been investigated. The results show that, during to the fiber nonlinear and chromatic dispersion, the amplitude characteristics of chaotic signal are distorted partially and the system synchronization quality will be impaired, but message can be hidden efficiently in the chaotic signal during the fiber transmission with additive chaos modulation (ACM). Better decoding performance is achieved by choosing appropriate matched parameters.  

参考文献:

[1]   Pecora, L. M. and Carroll, T.  L., "Synchronization in chaotic systems", Phys. Rev. Lett. 64(8), 821-824(1990).

[2]   Wang, X. F., Xia, G. Q., Wu, Z. M., "Chaotic synchronization performances of two unidirectionally coupled VCSELs subject to negative optoelectronic feedback," Acta Phys. Sin. 58(7), 4669-4674 (2009).

[3]   Schires, K., Hurtado, A., Henning, I.D., and Adams, M.J., "Polarization and Time-Resolved Dynamics of a 1550-nm VCSEL Subject to Orthogonally Polarized Optical Injection," IEEE Photonics Journal. 3(3), 555-563(2011).

[4]   Castro, J. M., Pimpinella, R., Kose, B. and Lane, B., "Investigation of the Interaction of Modal and Chromatic Dispersion in VCSEL–MMF Channels," J. Lightwave Technol. 30(15), 2531-2541(2012).

[5]   Lin, H., Zhang, Y., Pierce, D. W., Quirce, A., and Valle, A., "Polarization dynamics of a multimode vertical-cavity surface-emitting laser subject to orthogonal optical injection," J. Opt. Soc. Am. B 29(4), 867-873(2012)

Whispering gallery mode(WGM) microcavity lasers

Zhenmin Chen

Supervisor: Lei Xu

Whispering gallery mode(WGM) microcavities play an important role in modern optical for their high quality factor and small volume of the resonant mode. Up to now, WGM microcavities have at least four applications as follows: strong-coupling cavity quantum electrodynamics(CQED), enhancement and suppression of spontaneous emission, novel sources, and dynamic filters in optical communication and achieved remarkable results.

Lasing from WGM microresonants always attract much attention since liquid droplet WGM microcavity lasers several decades ago. Due to Purcell enhancement of spontaneous emission of WGM microresonants, WGM microcavity lasers has been achieved ultralow threshold for the large value of Q/V. Furthermore, the Raman and Brillouin laser can be easily obtained at low threshold.

There are at least two methods for obtain laser from WGM resonant by either introducing active materials to the resonator or using intrinsic nonlinearities of the resonator material. Combination of high Q resonators and different gain materials, e. g. rare-earth metal ions(Yb3+,Er3+,Nd3+), organic dyes and QDs, leads to a variety of laser configurations covering a wide lasing spectral range from ultraviolet to infrared.

 Microlasers are achieved great interests as ultra-sensitive sensors (such as biological and chemical sensors) due to their narrow linewidths capable of reporting slight changes in resonance. Using microcavity lasers can detect single nanoparticles as small as 10nm in radius for gold nanoparticles.

参考文献:

[1] Kerry J. Vahala, Nature, 424,839-846(2003).

[2] Lina He, Sahin Kaya Özdemir and Lan Yang, Laser Photonics Rev. 7, No. 1, 60–82 (2013) / DOI 10.1002/lpor.201100032.

[3] Tao Lu, Lan Yang, Tal Carmon, and Bumki Min, IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 47, NO. 3, MARCH 2011

[4] Ivan S. Grudinin, Andrey B. Matsko,and Lute Maleki, PRL 102, 043902 (2009)

[5] V. Sandoghdar et al. PHYSICAL REVIEW A. VOLUME 54 (1996)

[6] Lina He, Sahin Kaya Özdemir, Jiangang Zhu, Woosung Kim and Lan Yang, NATURE NANOTECHNOLOGY, DOI: 10.1038/NNANO.2011.99

Study of Titanium oxide thin films by

Variable Temperature Spectroscopic Ellipsometry

Shangdong Yang

Supervisor: Yuxiang Zheng

Titanium oxide (TiO2) is one of the most commonly used materials for antireflective films, planar waveguides, photo catalysts, and high-refractive-index components of multilayer optical filter due to its good durability, high transmittance in the visible spectral region, wide band gap of around 3.2eV, and high refractive index of over 2.0 at a wavelength of 550nm. TiO2 also has a very high melting point of 1840℃, and is established as an optical coating material for optical temperature sensing applications.

Nowadays, knowledge of the temperature dependence of optical constants and band gap of TiO2 thin films is of fundamental importance in many fields, such as optical fibers, optoelectronic switches, and laser techniques. Spectroscopic ellipsometry as one of the most widely used optical detection technologies in the semiconductor, data storage, optical coating, and display industries has the advantage of high sensitivity in the detection of the temperature-induced variation in film optical constants and thickness.

Here we studied the temperature-dependent optical properties of TiO2 thin films synthesized by the electron-beam evaporation technique and followed by thermal annealing. A variable-angle spectroscopic ellipsometry measurement combined with a data processing method was also performed to accurately obtain the refractive index spectra, extinction coefficient spectra, physical thickness, and band gap of materials at different temperatures in the spectral range from 300nm to 800 nm at incident angles of 65°, 70°, and 75° respectively.

The variation of the optical constants and band gap with temperature is based on the thermal expansion and thermo optic effect in which the interaction between the phonons and electrons affect the optical properties of the TiO2 thin films at different temperatures.

参考文献：

[1] Z. G. Hu and P. Hess: Appl. Phys. Lett. 89 (2006) 081906.

[2] N. Cherroret, A. Chakravarty, and A. Kar: J. Mater. Sci. 43 (2008) 1795.

[3] S. Wiechmann and J. Muller: Thin Solid Films 517 (2009) 6847.

[4] G. Gulsen and M. Naci Inci: Opt. Mater. 18 (2002) 373.

[5] A. R. Forouhi and I. Bloomer: Phys. Rev. B 38 (1988) 1865.

[6] L. Prod’homme: Phys. Chem. Glasses 1 (1960) 119.

[7] T. Izumitani and H. Toratani: J. Non-Cryst. Solids 40 (1980) 611.