S. Tseng
Northwestern University
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Featured researches published by S. Tseng.
Optics Express | 2008
H. N. Yum; M. Salit; G. S. Pati; S. Tseng; P. R. Hemmer; M. S. Shahriar
We demonstrate superluminal light propagation using two frequency multiplexed pump beams to produce a gain doublet in a photorefractive crystal of Ce:BaTiO(3). The two gain lines are obtained by two-wave mixing between a probe field and two individual pump fields. The angular frequencies of the pumps are symmetrically tuned from the frequency of the probe. The frequency difference between the pumps corresponds to the separation of the two gain lines; as it increases, the crystal gradually converts from normal dispersion without detuning to an anomalously dispersive medium. The time advance is measured as 0.28 sec for a pulse propagating through a medium with a 2 Hz gain separation, compared to the same pulse propagating through empty space. We also demonstrate directly anomalous dispersion profile using a modified experimental configuration. Finally, we discuss how anomalous dispersion produced this way in a faster photorefractive crystal (such as SPS: Sn(2)P(2)S(6)) could be employed to enhance the sensitivity-bandwidth product of a LIGO type gravitational wave detector augmented by a White Light Cavity.
Journal of Modern Optics | 2014
M. S. Shahriar; Ye Wang; Subramanian Krishnamurthy; Yongming Tu; G. S. Pati; S. Tseng
The Liouville equation governing the evolution of the density matrix for an atomic/molecular system is expressed in terms of a commutator between the density matrix and the Hamiltonian, along with terms that account for decay and redistribution. To find solutions of this equation, it is convenient first to reformulate the Liouville equation by defining a vector corresponding to the elements of the density operator, and determining the corresponding time-evolution matrix. For a system of N energy levels, the size of the evolution matrix is N2 × N2. When N is very large, evaluating the elements of these matrices becomes very cumbersome. We describe a novel algorithm that can produce the evolution matrix in an automated fashion for an arbitrary value of N. As a non-trivial example, we apply this algorithm to a 15-level atomic system used for producing optically controlled polarization rotation. We also point out how such a code can be extended for use in an atomic system with arbitrary number of energy levels.
Journal of The Optical Society of America A-optics Image Science and Vision | 2014
Mehjabin Sultana Monjur; S. Tseng; Renu Tripathi; John Donoghue; M. S. Shahriar
In this paper, we present theoretical details and the underlying architecture of a hybrid optoelectronic correlator (HOC) that correlates images using spatial light modulators (SLMs), detector arrays, and field programmable gate array (FPGA). The proposed architecture bypasses the need for nonlinear materials such as photorefractive polymer films by using detectors instead, and the phase information is yet conserved by the interference of plane waves with the images. However, the output of such an HOC has four terms: two convolution signals and two cross-correlation signals. By implementing a phase stabilization and scanning circuit, the convolution terms can be eliminated, so that the behavior of an HOC becomes essentially identical to that of a conventional holographic correlator (CHC). To achieve the ultimate speed of such a correlator, we also propose an integrated graphic processing unit, which would perform all the electrical processes in a parallel manner. The HOC architecture along with the phase stabilization technique would thus be as good as a CHC, capable of high-speed image recognition in a translation-invariant manner.
Optics Express | 2012
Subramanian Krishnamurthy; Y. Wang; Yongming Tu; S. Tseng; M. S. Shahriar
We demonstrate a high-efficiency optical modulator at ~1323 nm using the quantum Zeno effect in a ladder transition in a Rb vapor cell. The lower leg of the transitions represents the control beam while the upper leg of the transitions represents the signal beam. The cross-modulation of the signal beam transmission is observed as the control beam is intensity modulated, and is explained in terms of the quantum Zeno effect. We observe a modulation depth of near 100% at frequencies up to 1 MHz and demonstrate modulation at speeds up to 75 MHz, with a 3 dB bandwidth of about 5 MHz, limited by the homogeneous linewidth of the intermediate state. We also describe how much higher modulation speeds could be realized by using a buffer gas to broaden the transitions. We identify and explain the special conditions needed for optimizing the modulation efficiency. Numerical simulations of modulation at ~1 GHz are presented. The maximum modulation speed is found to scale with the pressure-broadened linewidth of the intermediate state, so that much higher speeds should be attainable.
Optics Express | 2013
Subramanian Krishnamurthy; Y. Wang; Yongming Tu; S. Tseng; M. S. Shahriar
We demonstrate an optically controlled polarizer at ~1323 nm using a ladder transition in a Rb vapor cell. The lower leg of the 5S(1/2),F = 1->5P(1/2),F = 1,2->6S(1/2),F = 1,2 transitions is excited by a Ti:Sapphire laser locked to a saturated absorption signal, representing the control beam. A tunable fiber laser at ~1323 nm is used to excite the upper leg of the transitions, representing the signal beam. When the control beam is linearly polarized, it produces an excitation of the intermediate level with a particular orientation of the angular momentum. Under ideal conditions, this orientation is transparent to the signal beam if it has the same polarization as the control beam and is absorbed when it is polarized orthogonally. We also present numerical simulations of the system using a comprehensive model which incorporates all the relevant Zeeman sub-levels in the system, and identify means to improve the performance of the polarizer. A novel algorithm to compute the evolution of large scale quantum system enabled us to perform this computation, which may have been considered too cumbersome to carry out previously. We describe how such a polarizer may serve as a key component for high-speed Stokesmetric imaging. We also show how such a polarizer, combined with an optically controlled waveplate, recently demonstrated by us, can be used to realize a high speed optical logic gate by making use of the Quantum Zeno Effect. Finally, we describe how such a logic gate can be realized at an ultra-low power level using a tapered nanofiber embedded in a vapor cell.
Optics Express | 2016
J. Yablon; Zifan Zhou; Minchuan Zhou; Ye Wang; S. Tseng; M. S. Shahriar
We have demonstrated experimentally a Diode-Pumped Alkali Laser (DPAL) with a Raman resonance induced dip in the center of the gain profile, in order to produce an anomalous dispersion, necessary for making the laser superluminal. Numerical calculations match closely with experimental results, and indicate that the laser is operating superluminally, with the group index far below unity (~0.00526) at the center of the dip. The estimated factor of enhancement in the sensitivity to cavity length perturbation is ~190, approximately equaling the inverse of the group index. This enhancement factor can be made much higher via optimal tuning of parameters. Such a laser has the potential to advance significantly the field of high-precision metrology, with applications such as vibrometry, accelerometry, and rotation sensing.
Optics Express | 2015
Subramanian Krishnamurthy; Y. Wang; Yongming Tu; S. Tseng; M. S. Shahriar
Modulators using atomic systems are often limited in speed by the rate of spontaneous emission. One approach for overcoming this limit is to make use of a buffer gas such as Ethane, which causes rapid fine structure mixing of the P(1/2) and P(3/2) states, and broadens the absorption spectra of the D1 and D2 lines in alkali atoms. Employing this effect, we show that one can achieve high speed modulation using ladder transitions in Rubidium. We demonstrate a 100-fold increase, due to the addition of the buffer gas, in the modulation bandwidth using the 5S-5P-5D cascade system. The observed bandwidth of ~200 MHz is within a factor of 2.5 of the upper bound of ~0.51 GHz for the system used, and is limited by various practical constraints in our experiment. We also present numerical simulations for the system and predict that a much higher modulation speed should be achievable under suitable conditions. In combination with a tapered nano fiber or a SiN waveguide, it has the potential to be used for high-speed, low-power all-optical modulation.
Journal of The Optical Society of America A-optics Image Science and Vision | 2014
Mehjabin Sultana Monjur; S. Tseng; Renu Tripathi; M. S. Shahriar
In this paper, we show that our proposed hybrid optoelectronic correlator (HOC), which correlates images using spatial light modulators (SLMs), detectors, and field-programmable gate arrays (FPGAs), is capable of detecting objects in a scale and rotation invariant manner, along with the shift invariance feature, by incorporating polar Mellin transform (PMT). For realistic images, we cut out a small circle at the center of the Fourier transform domain, as required for PMT, and illustrate how this process corresponds to correlating images with real and imaginary parts. Furthermore, we show how to carry out shift, rotation, and scale invariant detection of multiple matching objects simultaneously, a process previously thought to be incompatible with PMT-based correlators. We present results of numerical simulations to validate the concepts.
Optics Express | 2014
Subramanian Krishnamurthy; Yongming Tu; Y. Wang; S. Tseng; M. S. Shahriar
We demonstrate an optically controlled waveplate at ~1323 nm using the 5S(1/2)-5P(1/2)-6S(1/2) ladder transition in a Rb vapor cell. The lower leg of the transitions represents the control beam, while the upper leg represents the signal beam. We show that we can place the signal beam in any arbitrary polarization state with a suitable choice of polarization of the control beam. Specifically, we demonstrate a differential phase retardance of ~180 degrees between the two circularly polarized components of a linearly polarized signal beam. We also demonstrate that the system can act as a Quarter Wave plate. The optical activity responsible for the phase retardation process is explained in terms of selection rules involving the Zeeman sublevels. As such, the system can be used to realize a fast Stokesmetric imaging system with a speed of ~3 MHz. When implemented using a tapered nano fiber embedded in a vapor cell, this system can be used to realize an ultra-low power all-optical switch as well as a Quantum Zeno Effect based all-optical logic gate by combining it with an optically controlled polarizer, previously demonstrated by us. We present numerical simulations of the system using a comprehensive model which incorporates all the relevant Zeeman sub-levels in the system, using a novel algorithm recently developed by us for efficient computation of the evolution of an arbitrary large scale quantum system.
conference on lasers and electro optics | 2013
Y. Wang; Tony Y. Abi-Salloum; J. Yablon; S. Tseng; Yongming Tu; M. S. Shahriar
We show how a dual-peak gain produced via optical pumping and non-degenerate Raman pumps in a single vapor cell can be used to realize a superluminal ring laser with enhanced sensitivity for gyroscopy and accelerometry.