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Focusing light through or inside scattering media by the analog optical phase conjugation (AOPC) technique based on photorefractive crystals (PRCs) has been intensively investigated due to its high controlled degrees of freedom and short response time. However, the existing AOPC systems only phase-conjugate the scattered light in one polarization direction, while the polarization state of light scattered through a thick scattering medium is spatially random in general, which means that half of the scattering information is lost. Here, we propose dual-polarization AOPC for focusing light through scattering media to improve the efficiency and fidelity in the phase conjugation. The motivations of the dual-polarization AOPC are illustrated by theoretical analysis and numerical simulation, and then an experimental system is established to realize the dual-polarization AOPC. By separating and rotating the two orthogonal polarization components of the randomly polarized scattered light, light in all polarization states is recorded and phase-conjugated using the same PRC. Experimental results for focusing through a thick biological tissue show that the intensity of the time-reversed focus from the dual-polarization AOPC can be enhanced by a factor of approximate four compared with the existing single-polarization AOPC. [ABSTRACT FROM AUTHOR]

Optical scattering prevents light from being focused through thick biological tissue at depths greater than ~1 mm. To break this optical diffusion limit, digital optical phase conjugation (DOPC) based wavefront shaping techniques are being actively developed. Previous DOPC systems employed spatial light modulators that modulated either the phase or the amplitude of the conjugate light field. Here, we achieve optical focusing through scattering media by using polarization modulation based generalized DOPC. First, we describe an algorithm to extract the polarization map from the measured scattered field. Then, we validate the algorithm through numerical simulations and find that the focusing contrast achieved by polarization modulation is similar to that achieved by phase modulation. Finally, we build a system using an inexpensive twisted nematic liquid crystal based spatial light modulator (SLM) and experimentally demonstrate light focusing through 3-mm thick chicken breast tissue. Since the polarization modulation based SLMs are widely used in displays and are having more and more pixel counts with the prevalence of 4K displays, these SLMs are inexpensive and valuable devices for wavefront shaping. [ABSTRACT FROM AUTHOR]

We demonstrate dynamic recovery of blurred images caused by atmospheric turbulence. In particular, using a phase-conjugate wave generated by a second-order nonlinear crystal or composite, we restore the original quality of the image after the optical radiation forming the image propagates through the turbulent atmosphere. One of the key elements for our experiment is a rotating phase plate being placed in the beam path for simulating turbulent atmosphere. Using the nonlinear composite, we demonstrate that the image recovery is insensitive to the polarization of the optical radiation forming the image. [ABSTRACT FROM AUTHOR]

We demonstrate a method for phase conjugating fluorescence. Our method, called reference free digital optical phase conjugation, can conjugate extremely weak, incoherent optical signals. It was used to phase conjugate fluorescent light originating from a bead covered with 0.5 mm of light-scattering tissue. The phase conjugated beam refocuses onto the bead and causes a local increase of over two orders of magnitude in the light intensity. Potential applications are in imaging, optical trapping, and targeted photochemical activation inside turbid tissue. [ABSTRACT FROM AUTHOR]

We present an imaging modality capable of providing high-speed optical dispersion measurements of live cells. The technique permits wide-field measurement of the optical phase shifts introduced by a sample for multiple discrete wavelengths in a single image capture. Utilizing spatial modulation and the wavelength dependence of the interference-fringe spacing, average refractive index as a function of wavelength is obtained, yielding optical dispersion measurements of the sample under observation. Because of its simple and low-cost design, the technique can be readily integrated into a standard microscope to collect additional diagnostic information about biological cells. [ABSTRACT FROM AUTHOR]

We present an experimental demonstration of an optical phased array implementation on silicon nanomembrane. The integrated on-chip array configuration is non-uniform and avoids grating lobes inside the field of view during beam steering while allowing the waveguide separation to be large enough to prevent optical coupling. A 1 × 12 multimode interference beam splitter uniformly excites the arrayed waveguides. Individually controllable micro-heaters modulate the optical phase in the arrayed waveguides. A beam steering angle of 10.2° in a silicon planar guide equivalent to an effective steering angle of 31.9° in air is demonstrated at 1.55 μm. [ABSTRACT FROM AUTHOR]

We have studied the possibility to utilize semiconductor quantum dots (QDs) as an optical phase shifter within a vertical geometry for ultrafast information processing. From theoretical analyses, an optical phase nonlinearity in QD structures has been predicted which can be enhanced through the use of an vertical optical cavity. Asymmetric cavity structures with 16/30 periods of GaAs/AlGaAs layers for the front/back mirrors have been fabricated to demonstrate a practical device with significant nonlinear characteristics for optical switching. A phase shift of 18° has been initially observed with a tilted pump scheme. This observation paves the way toward a Mach-Zehnder optical switch using QDs inside a vertical cavity. [ABSTRACT FROM AUTHOR]

Brillouin amplification of strong Stokes seed, which can achieve the output energy of 400 mJ and amplified efficiency of about 85% under the condition that the energy of Stokes beam and pump beam is in the ratio of 39.5/1, is reported. The relationship between output energy of strong signal Brillouin amplification and the energy of Stokes beam as well as pump beam, the interaction length, absorption coefficient is investigated. The design of strong signal Brillouin amplification system with high output energy is also provided. [ABSTRACT FROM AUTHOR]

The nonlinear optical (NLO) and optical limiting (OL) properties of graphene families, including graphene oxide nanosheets, graphene nanosheets (GNSs), graphene oxide nanoribbons (GONRs), and graphene nanoribbons (GNRs), were investigated at 532 and 1064 nm using a nanosecond regime. GNSs, GONRs, and GNRs exhibited broadband NLO and OL properties. Reduced graphene samples exhibited stronger NLO and OL responses than their graphene oxide precursors because of their increased crystallinity and conjugation. Nonlinear scattering and two-photon-absorption were found to have strong effects on the NLO and OL responses of the graphene nanostructures. [ABSTRACT FROM AUTHOR]

We present experiments that study the impact of polarization selection on the phenomenon of turbidity suppression by optical phase conjugation. Counter to intuition, we discovered that the preferential utilization of multiply scattered light field components over their sparsely scattered counterparts via appropriate polarization selection can lead to better image reconstruction quality. This effect was observed with tissue phantoms and biological tissue sections. The physical origin of this effect and its dependence on scatterer properties are discussed. [ABSTRACT FROM AUTHOR]

Catastrophic optical mirror damage (COMD) is analyzed for 808 nm emitting diode lasers in single-pulse operation in order to separate facet degradation from subsequent degradation processes. During each pulse, nearfield and thermal images are monitored. A temporal resolution better than 7 μs is achieved. The thermal runaway process is unambiguously related to the occurrence of a “thermal flash.” A one-by-one correlation between nearfield, thermal flash, thermal runaway, and structural damage is observed. The single-pulse excitation technique allows for controlling the propagation of the structural damage into the cavity. We propose this technique for the analysis of early stages of COMD. [ABSTRACT FROM AUTHOR]

We recognize that the phase control of optical transfer function is profoundly important in realizing nanoimaging beyond the diffraction limit. The difficulty of the optical phase measurement in the near field, required for the conventional adaptive control method, motivates us to achieve active phase control in the superlens imaging system. The visibility and resolving capabilities are significantly enhanced through the index mismatch approach by tuning the wavelength of the incident light. [ABSTRACT FROM AUTHOR]

The optical phase conjugation signal in nearly nondegenerate four wave mixing was studied using a rhodamine 110 doped boric acid glass saturable absorber nonlinear medium. We have demonstrated a narrow band optical filter (2.56±0.15 Hz) using an optical phase conjugation signal in the frequency modulation of a weak probe beam in the presence of two strong counterpropagating pump beams in rhodamine 110 doped boric acid glass thin films (10-4 m). Both the pump beams and the probe beam are at a wavelength of 488 nm (continuous-wave Ar+ laser). The probe beam frequency was detuned with a ramp signal using a piezoelectric transducer mirror. [ABSTRACT FROM AUTHOR]

The authors show by experiment and theory that thick electro-optic crystals are suitable media for sampling electromagnetic radiation from 0.3 to 50 THz with 10 fs visible laser pulses. For example, the detection of frequencies above 10 THz with a 250 μm thick, <110>-oriented ZnTe crystal is as efficient as that with a 10 μm thin crystal. This surprising behavior and a much flatter detector response arise because phase-matching oscillations are greatly smeared out by the broad spectrum of the sampling pulse and the crystal dispersion. [ABSTRACT FROM AUTHOR]

The authors report on a scheme for the generation of few-optical-cycle pulses broadly tunable in the visible with passively stabilized carrier-envelope phase (CEP). The system starts with an infrared optical parametric amplifier in which both pump and seed are derived from an amplified, non-CEP-stabilized Ti:sapphire laser. The passively stabilized idler beam is then spectrally broadened through white-light generation and seeds a blue-pumped noncollinear optical parametric amplifier. The system produces few-optical-cycle pulses tunable from 500 to 800 nm, with energy up to 5 μJ and 0.23 rad rms CEP fluctuations. [ABSTRACT FROM AUTHOR]

The authors report room-temperature measurements of the third order nonlinear susceptibility modulus |χ(3)| of thick (∼600 nm) InN layers. Transmission measurements provide a room-temperature value for the optical band gap of the samples slightly above 1500 nm. Third order nonlinear optical susceptibility has been measured using degenerate four wave mixing experiments at wavelengths near and above band gap. |χ(3)| values of (4.2–10)×10-10 esu were measured at this wavelength range. The associated relaxation time of the generated population grating at 1500 nm was measured. The obtained value of 4.8 ps is consistent with a nonradiative recombination mechanism. [ABSTRACT FROM AUTHOR]

The spatial coherence and the optical phase distribution across a two-dimensional (2D) photonic crystal implemented with coupled arrays of vertical cavity surface emitting lasers (VCSELs) are experimentally characterized. This is achieved by performing Young’s interference experiments between pairs of array elements using a spatial light modulator arrangement. In contrast to far-field measurements that provide information only on the global spatial coherence, this approach can yield full mapping of the complex degree of spatial coherence. Examples of such analysis are presented for nominally uniform one-dimensional and 2D arrays of coupled VCSELs and possible mechanisms of the observed coherence degradation are discussed. [ABSTRACT FROM AUTHOR]

A recent theory of supercritical phase conjugation gives explicitly the paraxial analytical solution for a completely active conjugator in contact with arbitrary media. This letter extends the theory to the more realistic case of a limited active zone inside a conjugator in contact with arbitrary media. This configuration describes more accurately the experimental situations in ultrasonic parametric phase conjugation. The main practical result is the possibility of adjustable artificial impedance. [ABSTRACT FROM AUTHOR]

This letter reports on the observation of resonant enhancement by intersubband transitions of the second-harmonic generation of ∼1 μm radiation in GaN/AlN quantum wells grown on AlN/c-sapphire templates. Quantum wells with a nominal well thickness of 10 ML have been investigated in terms of intersubband linear and nonlinear optical properties. A strong increase of the second-harmonic conversion is observed at a pump wavelength of ∼2 μm, which is attributed to double-resonance enhancement of the nonlinear susceptibility by intersubband transitions. The second-order susceptibility at resonance is of the order of 114 pm/V, in good agreement with calculations. [ABSTRACT FROM AUTHOR]

The authors report on the implementation of phase sensitivity into Brillouin light scattering spectroscopy from propagating spin-wave packets. In order to access phase information, interference between the light inelastically scattered by the spin-wave and a frequency shifted coherent reference beam is used. This approach allows for access to quantities such as the space- and time-resolved phase profile and the wave front of spin-wave packets and beams. The authors apply the developed method to investigations of the phase profiles of linear and nonlinear (soliton) spin-wave pulses. In particular, the constant phase profile characteristics for an envelope spin-wave soliton are demonstrated. [ABSTRACT FROM AUTHOR]

We propose tunnel junctions with type-II heterostructures to reduce the electrical resistance of vertical-cavity surface-emitting lasers. We fabricated the type-II tunnel junctions on GaAs substrates, which consist of highly C-doped GaAsSb on the p side and highly Si-doped InGaAs on the n side. We achieved an extremely low specific resistance of 4×10-6 Ω cm2, which corresponded to a resistance of 20 Ω for an aperture 5 μm in diameter. The specific resistance of the type-II tunnel junction was about 40% smaller than that of the type-I tunnel junction. [ABSTRACT FROM AUTHOR]

The optical phase characteristics of an indium phosphide (InP) vertically coupled microdisk were experimentally demonstrated. Overcoming the material losses by injecting current into the active quantum well microdisk layer has allowed us to observe the phase behavior in all three coupling regimes. The ability to tune the resonant wavelength of this device makes it suitable for use as a phase modulator or tunable optical delay element. [ABSTRACT FROM AUTHOR]

Peculiar light emission properties have been observed in cylindrical microcavity hosting dye-doped helixed liquid crystals, which behaves as a fiber-like multidirectional distributed feedback laser. Experimental studies performed for this level of confinement show that laser action is exhibited both axially and radially, indicating a self-organized three-dimensional blue phase-like configuration. Thermal wavelength tunability was observed for both orientations emphasizing two different linear behaviors. The distributed feedback mechanism and the Q factor of the mirrorless resonant cavity result enhanced for axial stimulated emission because of the significant increase in the number of helical periods. In addition, long-lived spectrally narrow defect modes appear within the photonic band gap owing to optical phase jumps which take place in local structural defects. [ABSTRACT FROM AUTHOR]

For developing a beam combination laser with the stimulated Brillouin scattering-phase conjugate mirrors (SBS-PCMs), the phase control of the backward SBS waves is essentially required. We proposed a new effective and practical technique in previous works, in which entirely independent SBS-PCMs are used, so that there is no limit of the number of the beams for the beam combination laser. In this letter, we show that in the proposed technique, the phase of the SBS wave significantly depends on the pump energy and it can be stabilized—although the independently separate SBS-PCMs are used—provided that the pump energies are balanced under the density modulation. In this experimental work, the standard deviation of the relative phase difference between the SBS waves has been reduced less than λ/30 by the amplitude dividing method to provide the pump beams with the nearly same energies. [ABSTRACT FROM AUTHOR]

We report that the phase of a backward wave by stimulated Brillouin scattering (SBS) can be controlled by a self-generated density modulation without any backward Stokes seed beam, which is generated due to electrostriction induced by electromagnetic standing wave through the interferences between the main beam and the low intensity counter-propagating beam. The density modulation ignites the position of the Brillouin grating so that the phase of the backward SBS can be controlled. We obtained 96% success with the phase error less than a quarter wave under a proper scheme of the self-seeding methods. This phase control technique is so simple, scalable, and very efficient that it can be applied to many beam combination systems for a high power laser system with a high repetition rate over 10 Hz. [ABSTRACT FROM AUTHOR]

High-contrast organic light-emitting diodes (OLEDs) with low-reflection cathode structures were constructed. The cathode structure consisted of a semitransparent cathode layer, a transparent phase-changing layer, and a highly reflective metal overlayer. When samarium (Sm), tris (8-quinolinolato) aluminum (Alq[sub 3]), and Al were used as the cathode layer, phase-changing layer, and reflective layer, respectively, luminous reflectance of the resulting OLED was reduced from 81% to 2.7% as compared to a conventional OLED with a LiF/Al cathode. A further reduction to 0.9% was realized by replacing a multilayer of Alq[sub 3]/Sm/Alq[sub 3] for the single phase-change layer of Alq[sub 3]. In such a structure, the spectral reflectance was below 0.03 in the entire visible region and showed a weak dependence on incident angles of light. A contrast ratio of 250:1 can be achieved at a brightness of 100 cd/m2 under 140 lx of ambient-lighting. Device efficiencies of the high-contrast OLEDs were reduced, while their electrical characteristics were almost identical to that of the control device. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on the observation of phase conjugation (PC) using low-power, continuous-wave degenerate four-wave mixing in nonlinear polymer multimode fibers. The fibers are made of poly(methyl methacrylate) doped with Disperse Red 1 as the photosensitive chromophore. With a power less than 2.5 mW at wavelength 633 nm for each beam inside the fiber, a maximum PC reflectivity of 1% is obtained. Phase conjugation is observed for both parallel and orthogonally polarized probe and pump beams. Experimental results show that polarization and intensity profile are preserved in the PC wave. The predominant phase conjugation wave is attributed to the formation of sub-refractive-index gratings inside the fibers. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We demonstrate the enhancement and reduction of the specular reflection from the surface of a photorefractive crystal in the presence of a "pump" beam. The pump beam could be the phase conjugate beam of the input beam or another laser beam. The contribution of the reflection grating is also demonstrated in a 45°-cut crystal. The change of the specular reflection with respect to the intensity ratio of the input beam to the pump beam is measured. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We found that the formation of self-pumped phase-conjugate mirrors (SPPCM) in photorefractive Bi[sub 12]TiO[sub 20] crystals under external alternating electric field is accompanied by strong enhancement of spatial subharmonics. This combined formation of the fundamental grating and its spatial subharmonics results in an expansion of the spatial-frequency band allowed for SPPCM recording. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This letter presents the experimental results of self-pumped phase conjugation (SPPC) in barium titanate (BaTiO[sub 3]) crystals doped with Rh or Ce. It has been shown that the main parameters of SPPC depend very strongly on the concentration of dopants, the incident angles, and the cut type of the crystals. Some qualitative explanation of the experimental results are also given. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the time resolved characteristics of phase conjugation in metal-semiconductor phase transition in VO[sub 2]. Change in the reflection behavior; Nonlinearity caused by photoinduced transition.

Focuses on the generation and characterization of self-pumped phase conjugation of 450 nanometer femtosecond pulses in BaTiO[sub 3]. Pump beam; Group velocity dispersion; Angular dispersion caused by the air crystal interface; Concepts and techniques utilizing nonlinear optical methods to characterize femtosecond laser pulses.

Examines experimental lasing in a broad area twin-contact semiconductor laser operating as a phase conjugation (PC) mirror in an external cavity configuration. Sensitivity of external cavity laser system to tilt misalignments; Importance of angular separation between the pump and probe beams for PC; Effect of PC feedbacks and external mirrors on semiconductor lasers.

Fabricates an optomechanical media consisting of three dimensional arrays of elongated metal coated dielectric beams suspended by torsional springs. Use of microelectromechanical system technology; Detection of spatial grating formation; Feasibility of using optomechanical media for phase conjugation.

Investigates the fast mutually pumped phase-conjugation (MPPC) in Bi[sub 12]TiO[sub 20] crystal using transient photorefractive beam coupling under a direct current electric field. Effect of external electric field on the photorefractive crystal; Features of transient fanning effect on crystals; Reliance of MPPC on beam fanning.

A method to enhance the reflectivity of acoustic phase conjugate mirrors by nonlinear piezoelectricity is discussed. Static electric or static stress fields were applied together with the pump electric field. In highly nonlinear piezoelectric ceramics, the phase conjugate reflectivity was enhanced by the factor of 50 using this method. The maximum reflectivity reached 10-2. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines mutually pumped phase conjugator (MPPC) with high coupling efficiency in copper-doped potassium sodium strontium barium niobate (KNSBN) crystal. Growth of KNSBN crystal by Czochralski method; Occurrence of four-wave mixing (FWN) in transition grating; Existence of FWN interaction in MPPC.

Investigates optical phase conjugation using spatially nondegenerate four-wave mixing in a broad-area laser diode. Dependence of phase conjugate reflectivities on the bias current of the laser diode; Result of operating laser diode above the lasing threshold; Advantages of four-wave mixing-based optical phase conjugation.

Examines the enhancement of the response rate of internal reflection self-pumped phase conjugators (SPPC) with cerium and manganese-doped crystals using intermittent laser beam. Migration of charge carriers driven by photoinduced electric field; Formation of SPPC; Impact of migration on energy coupling.

Demonstrates the innovative type of self-pumped phase conjugation (SPPC). Measurement of the phase conjugate reflectivity; Use of a helium-neon laser; Reduction of the need for special crystal qualities in obtaining SPPC.

Examines the green and violet light generation through quasiphase matching based on lithium niobate optical superlattice. Prediction of simultaneous generation of green and violet light; Calculation of the conversion efficiency percentage; Creation of compact two outputting wavelength light source.

Examines the retracting behavior of phase matching in infrared radiation by difference frequency mixing of Nd:YAG laser and tunable dye laser in lithium triborate. Observation of large spectral acceptance at spectral phase-matching point; Presence of angular acceptance at angular phase matching point.

Presents self-pumped phase conjugator (SSPC) based on backward stimulated photorefractive scattering in barium titanate/cerium crystals. Details on reflectivities and image fidelity of phase-conjugate beam; Development of SSPC through high-gain photorefractive grating; Correlation between reflectivities and incident laser beam.

Investigates the photorefractive phase conjugator by optical low-coherence reflectometry. Characterization the photorefractive devices; Importance of crystal geometry for obtaining self-pumped phase conjugation; Presence of several distinct gratings in the crystal.

Examines the effect of thermal self-defocusing on phase conjugate wave produced by degenerate wave mixing in absorbing media. Impact of refractive index changes on the phase conjugate wave; Occurrence of phase mismatch prior to the beam intensity distribution distortion.

Proposes a model to explain the origin of the self-pumped phase conjugation in photorefractive crystals. Characteristics of the self-pump phase conjugator; Use of Faraday isolator to prevent feedback of the related beam; Advantage of the phase conjugator used.

Observes the phase conjugation in indium gallium arsenide/gallium arsenide multiple quantum wells at 1.06 micrometer wavelength. Measurement of nonlinearity of the medium; Induction of nonlinearity by saturation absorption; Examination of band filling and exciton filling.

Coupling of temporal information between two beams is demonstrated using a combination of a multimode fiber and a photorefractive passive phase conjugation mirror. It is shown that the polarization and spatial properties are fully recovered but temporal information is exchanged. The theoretical explanation for these phenomena and possible applications are discussed. [ABSTRACT FROM AUTHOR]

A double pass phase conjugate master oscillator-power amplifier has been demonstrated at 820 nm using AlGaAs gain elements and BaTiO3 in a self-pumped ring configuration. Single frequency operation with diffraction-limited output beam quality was achieved at output powers in excess of 50 mW cw. [ABSTRACT FROM AUTHOR]

We measure the spectral characteristics of an external cavity semiconductor laser which uses a phase conjugate mirror for its external reflection. This device has significant advantages over the conventional external cavity system owing to the self-aligning nature of the phase conjugate mirror. The fiber delay line self-heterodyne technique is used to measure the fundamental linewidth for single mode operation of this device. It shows the linewidth to be at least as narrow as the instrumental resolution of 100 kHz. [ABSTRACT FROM AUTHOR]