Victor V. Kozlov

A universal optical all-fiber omnipolarizer

Wherever the polarization properties of a light beam are of concern, polarizers and polarizing beamsplitters (PBS) are indispensable devices in linear-, nonlinear- and quantum-optical schemes. By the very nature of their operation principle, transformation of incoming unpolarized or partially polarized beams through these devices introduces large intensity variations in the fully polarized outcoming beam(s). Such intensity fluctuations are often detrimental, particularly when light is post-processed by nonlinear crystals or other polarization-sensitive optic elements. Here we demonstrate the unexpected capability of light to self-organize its own state-of-polarization, upon propagation in optical fibers, into universal and environmentally robust states, namely right and left circular polarizations. We experimentally validate a novel polarizing device - the Omnipolarizer, which is understood as a nonlinear dual-mode polarizing optical element capable of operating in two modes - as a digital PBS and as an ideal polarizer. Switching between the two modes of operation requires changing beams intensity.

Theory of fiber optic Raman polarizers

We propose and apply a theoretical description of a Raman amplifier based on the vector model of randomly birefringent fibers to the characterization of Raman polarizers. The Raman polarizer is a special type of Raman amplifier with the property of producing a highly repolarized beam when fed by relatively weak and unpolarized light.

Theoretical Study of Optical Fiber Raman Polarizers With Counterpropagating Beams

The theory of two counter-propagating polarized beams interacting in a randomly birefringent fiber via the Kerr and Raman effects is developed and applied to the quantitative description of Raman polarizers in the undepleted regime. Here Raman polarizers, first reported by Martinelli, are understood as Raman amplifiers operating in the regime in which an initially weak unpolarized beam is converted into an amplified fully polarized beam towards the fiber output. Three parameters are selected for the characterization of a Raman polarizer: the degree of polarization of the outcoming beam, its state of polarization, and its gain. All of these parameters represent quantities that are averaged over all random polarization states of the initially unpolarized signal beam. The presented theory is computer friendly and applicable to virtually all practically relevant situations, including the case of co-propagating beams, and in particular to the undepleted as well as the depleted regimes of the Raman polarizer.

Theoretical study of polarization attraction in high-birefringence and spun fibers

Lossless polarizers are conservative nonlinear optical devices that transform unpolarized light into highly polarized light without polarization-dependent losses. The device proposed here consists of an up to 100-m-long segment of nonlinear highly birefringent or unidirectionally spun fiber pumped from the output end by an intense backward-propagating beam. An initially unpolarized (scrambled) signal beam acquires a degree of polarization close to 100% toward the fiber output.

Theory of polarization attraction in parametric amplifiers based on telecommunication fibers

We develop from first principles the coupled wave equations that describe polarization-sensitive parametric amplification based on four-wave mixing (FWM) in standard (randomly birefringent) optical fibers. We show that in the small-signal case these equations can be solved analytically, and permit us to predict the gain experienced by the signal beam as well as its state of polarization (SOP) at the fiber output. We find that, independently of its initial value, the output SOP of a signal within the parametric gain bandwidth is solely determined by the pump SOP. We call this effect of pulling the polarization of the signal towards a reference SOP the polarization attraction, and we call the parametric amplifier the FWM polarizer (which can equivalently be called the fiber-optic parametric amplifier polarizer). Our theory is valid beyond the zero polarization mode dispersion (PMD) limit, and it takes into account moderate deviations of the PMD from zero. In particular, our theory is capable of analytically predicting the rate of degradation of the efficiency of the parametric amplifier, which is caused by the detrimental PMD effect.

Nonlinear repolarization in optical fibers: polarization attraction with copropagating beams

We propose a type of lossless nonlinear polarizer, novel to our knowledge, a device that transforms any input state of polarization (SOP) of a signal beam into one and the same well-defined SOP toward the output, and perform this without any polarization-dependent losses. At the polarizer output end, the signal SOP appears to be locked to the input pump SOP. The polarizer is based on the nonlinear Kerr interaction of copropagating signal and pump beams in a telecom or randomly birefringent optical fiber.

Maxwell-Drude-Bloch dissipative few-cycle optical solitons

We study the propagation of few-cycle pulses in a two-component medium consisting of nonlinear amplifying and absorbing two-level centers embedded into a linear and conductive host material. First we present a linear theory of propagation of short pulses in a purely conductive material and demonstrate the diffusive behavior for the evolution of the low-frequency components of the magnetic field in the case of relatively strong conductivity. Then, numerical simulations carried out in the frame of the full nonlinear theory involving the Maxwell-Drude-Bloch model reveal the stable creation and propagation of few-cycle dissipative solitons under excitation by incident femtosecond optical pulses of relatively high energies. The broadband losses that are introduced by the medium conductivity represent the main stabilization mechanism for the dissipative few-cycle solitons.

Lossless polarization attraction of copropagating beams in telecom fibers

We study the performance of a nonlinear lossless polarizer (NLP), the device that transforms an input arbitrary state of polarization (SOP) of a signal beam into one and the same SOP toward the output and, unlike conventional passive polarizers, performs this transformation without polarization-dependent losses. The operation principle of this device is based on the nonlinear rotation of the SOP of the strong signal beam under the interaction with a copropagating strong pump beam in a Kerr medium, which in our case is a telecom fiber. We quantify the performance of this NLP by introducing the notion of instantaneous degree of polarization, which is a natural extension of the conventional notion of the degree of polarization appropriate for CW beams to the case of pulses whose SOP is not constant across the pulse. We pay particular attention to the regime when signal and pump beams experience a walk-off in the dispersive medium. In particular, we demonstrate that a signal pulse experiences much stronger repolarization when the walk-off effect is present as compared with the case of no walk-off. We also study the degradation of the efficiency of the NLP in the presence of polarization mode dispersion.

Harmonic and supercontinuum generation in quadratic and cubic nonlinear optical media

We present numerical simulations by means of the generalized nonlinear envelope equation of harmonic and supercontinuum generation induced by femtosecond pump pulses in optical media with both quadratic and third-order nonlinearities. Application examples to higher harmonic generation in periodically poled lithium niobate and optical parametric generation of a mid-infrared continuum in gallium arsenide are discussed.

Suppression of Relative Intensity Noise in Fiber-Optic Raman Polarizers

We propose a method for the suppression of relative intensity noise (RIN) at the output of a Raman polarizer, a special type of Raman amplifier that transforms an input weak beam of unpolarized light into an highly polarized amplified beam towards its output. We show that the RIN which is induced by polarization-dependent gain is suppressed whenever the Raman polarizer works in the depleted pump regime.