Showing papers on "Signal beam published in 2013"

Frequency comb generation by a continuous-wave-pumped optical parametric oscillator based on cascading quadratic nonlinearities

Abstract: We report optical frequency comb generation by a continuous-wave pumped optical parametric oscillator (OPO) without any active modulation. The OPO is configured as singly resonant with an additional nonlinear crystal (periodically poled MgO:LiNbO3) placed inside the OPO for phase mismatched second harmonic generation (SHG) of the resonating signal beam. The phase mismatched SHG causes cascading χ(2) nonlinearities, which can substantially increase the effective χ(3) nonlinearity in MgO:LiNbO3, leading to spectral broadening of the OPO signal beam via self-phase modulation. The OPO generates a stable 4 THz wide (-30 dB) frequency comb centered at 1.56 μm.

Surgical microscopes using optical coherence tomography and related systems and methods

Abstract: Some embodiments of the present inventive concept provide optical coherence tomography (OCT) systems for integration with a microscope. The OCT system includes a sample arm coupled to the imaging path of a microscope. The sample arm includes an input beam zoom assembly including at least two movable lenses configured to provide shape control for an OCT signal beam; a scan assembly including at least one scanning mirror and configured for telecentric scanning of the OCT signal beam; and a beam expander configured to set the OCT signal beam diameter incident on the microscope objective. The shape control includes separable controls for numerical aperture and focal position of the imaged OCT beam.

Quantum-Dot Double Layer Polymer Waveguides by Evanescent Light Coupling

Abstract: In this work we analyze numerically and experimentally new active waveguides based on a bilayer structure composed by a passive polymer and an active poly(mehtyl methacrylate) (PMMA) film doped with CdSe colloidal quantum dots (QDs), namely a nancomposite. In a first bilayer structure a planar PMMA layer is deposited on top of the nanocomposite, where the signal beam intensity is enhanced because this cladding layer is able to collect radiated emission of QDs. Moreover, the pump beam is also propagating through the cladding without limitation by QD absorption. These results are extended to a second bilayer structure, where ridge patterns of a commercially available resist (SU-8) are deposited on the top of the nanocomposite active layer. These SU-8 patterns are also able to guide with low absorption losses both pump and signal beams. The optimum geometrical parameters of the bilayer structures were properly designed to optimize the light waveguiding, previous to their fabrication and optical characterization. For this purpose, a spontaneous emission model has been developed and programmed into an active beam propagation method. This technology can be the base for developing integrated photonics on silicon at visible and telecom wavelengths.

Rapid complex mode decomposition of vector beams by common path interferometry

Abstract: We have used common path interferometry for rapid determination of the electric field and complex modal content of vector beams, which have spatially-varying polarization. We combine a reference beam with a signal beam prior to a polarization beam splitter for stable interferograms that preserve intermodal phase shifts even in noisy environments. Interferometric decomposition into optical modes (IDIOM) provides a direct, sensitive measure of the complete electric field, enabling rapid modal decomposition and is ideally suited to single-frequency laser sources. We apply the technique to beams exiting optical fibers that support up to 10 modes. We also use the technique to characterize the fibers by determining a scattering matrix that transforms an input superposition of modes into an output superposition. Furthermore, because interferograms are linear in the field, this technique is very sensitive and can accurately reconstruct beams with signal-to-noise << 1.

Self-referential holography and its applications to data storage and phase-to-intensity conversion

Abstract: Holographic recording methods require the use of a reference beam that is coherent with the signal beam carrying the information to be recorded. In this paper, we propose self-referential holography (SRH) for holographic recording without the use of a reference beam. SRH can realize purely one-beam holographic recording by considering the signal beam itself as the reference beam. The readout process in SRH is based on energy transfer by inter-pixel interference in holographic diffraction, which depends on the spatial phase difference between the recorded phase and the readout phase. The phase-modulated recorded signal is converted into an intensity-modulated beam that can be easily detected using a conventional image sensor. SRH can be used effectively for holographic data storage and phase-to-intensity conversion.

Lossless polarization attraction of copropagating beams in telecom fibers

Abstract: 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.

Optical measuring apparatus

Abstract: Provided is a compact, low-cost optical measuring apparatus capable of acquiring an image of a target to be measured without moving a mirror or using a wavelength-scanning light source or beam splitter. A laser beam emitted from a light source is split into first and second beams, and the first beam is focused as a signal beam onto the target by a lens for irradiation purposes, while the second beam is reflected as a reference beam by a mirror without irradiating the target. Then, a signal beam reflected by or scattered by the target is multiplexed with the reference beam and then enters interference optics, whereby three or more interference beams with different phases are generated and detected by photodetectors. Then, the detection signals are operated by a signal processing unit. During the measurement, the focus position of the first beam is moved at least in the optical axis direction.

Recording of self-induced waveguides in lithium niobate at 405 nm wavelength by photorefractive–pyroelectric effect

Abstract: We characterize the process of soliton waveguides (SWGs) recording at 405 nm wavelength using pyroelectric effect in lithium niobate (LN) crystals. We experimentally study and discuss the influence of the input irradiance, the polarization of the signal beam, and the crystal temperature change on the waveguide writing time and mode-profile. These characteristics significantly change when changing the recording wavelength. The advantages of recording SWGs in LN by using blue-violet light and pyroelectric field are emphasised. The generation of radiation at 405 nm wavelength by inexpensive laser diodes, the fast recording at this wavelength, and the convenient way to produce a static electric field inside the crystal by heating it with few degrees leads to a next step in the soliton waveguides recording process with applications in 3D integrated optical circuits.

Generation of 2- $\mu{\rm m}$ Light Based on a Noncritical Phase Matching OPO Technique

Abstract: We propose an experimental technique for efficient 2- μm light generation based on the intracavity noncritical phase matching optical parametric oscillator (OPO). Intra-cavity pumped by a diode pumped actively Q-switched Nd:YVO4 laser operating at 1.3 μm, we have achieved efficient 2093-nm signal beam emission making full use of noncritical phase matching KTA-OPO. At a diode pump power of 9.8 W and a Q-switching repetition rate of 30 kHz, a signal beam with a spectral linewidth of ~ 1 nm and an average power of 1.01 W have been obtained, giving a diode pump power to signal power conversion efficiency of 10.3%. The short pulse width of ~ 3.4 ns is achieved, which is much shorter than other approaches with Q-switched operation to generate 2-μm laser beams.

System and method for a self-referencing interferometer

Abstract: Systems and methods are described herein for a self-referencing interferometer. The interferometer can comprise an improved spatial phase shifter that reduces the number of components, size and complexity of the spatial phase shifter and maintains a common path for a combined reference beam and signal beam. The self-referencing interferometer further comprises a single mode fiber shunt for filtering the reference beam and further reducing the size of the interferometer. The angle of the reference beam can be tilted before being recombined with the single beam which further simplifies the spatial phase shifting component of the interferometer.

Microresonator-based all-optical transistor

Abstract: We present theoretical estimates for a low-loss, all-optical transistor using a microresonator device whose fields interact evanescently with rubidium vapor. We use a four-level, electromagnetically induced absorption scheme to couple the light fields of the transistor. We show results indicating that a weak control beam with less than single-photon intensities can switch a much stronger signal beam with switching contrast of greater than 25 dB and loss less than 0.5 dB.

Optically controlled polarizer using a ladder transition for high speed Stokesmetric Imaging and Quantum Zeno Effect based optical logic.

Abstract: We demonstrate an optically controlled polarizer at ~1323 nm using a ladder transition in a Rb vapor cell. The lower leg of the 5S1/2,F = 1->5P1/2,F = 1,2->6S1/2,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.

Slow light via four-wave mixing in a hot rubidium vapour

Abstract: In this work, we report on an off-resonant four-wave mixing experiment via a ladder-type configuration in a hot rubidium atomic vapour. We find for the first time, to the best of our knowledge, that the generated light is delayed compared with the reference. At the same time, the seeded signal beam is also delayed, though the delay time is not as so large as the one that the generated light has. Both delayed times can be adjusted experimentally by controlling the two-photon detuning. The experimental results are in good agreement with our theoretical predictions. Our results may be important for storing telecom-band photons.

High speed hologram recording apparatus

Abstract: A hologram recording apparatus is provided, including: a coherent light source; a beam splitter which splits a beam emitted from the coherent light source into a signal beam and a reference beam; a signal beam forming unit including a first optical element which splits the signal beam into a plurality of sub signal beams and deflects the plurality of sub signal beams in different directions. The signal beam forming unit further directs the plurality of sub signal beams onto a hologram recording medium. The recording apparatus also includes a reference beam forming unit which directs the reference onto a location on the hologram recording medium which overlaps with locations on the hologram recording medium on which the plurality of sub signal beams are incident.

Broadband THz-wave generation by satisfying the noncollinear phase-matching condition with a reflected signal beam.

Abstract: We demonstrated broadband terahertz (THz) wave generation by satisfying the noncollinear phase-matching condition with a reflected signal beam. We constructed a dual-wavelength optical parametric oscillator with two potassium titanium oxide phosphate crystals pumped by a frequency-doubled Nd:YAG laser. The collinear pump and signal waves were irradiated into a lithium niobate crystal. The pump and the signal waves were reflected at the crystal surface. Because the pump and the signal waves have a finite beam diameter, when the reflected signal wave and unreflected pump wave were irradiated at the correct angle, the noncollinear phase-matching condition was satisfied. By changing the incident angle to the crystal, broadband THz-wave generation with a range of over 0.2–7.2 THz was achieved.

Dynamic aperture holographic multiplexing

Abstract: Systems and methods for dynamic aperture holographic multiplexing are disclosed. One example process may include recording a set of holograms in a recording medium by varying both the reference beam angular aperture and the signal beam angular aperture. The angular aperture of the signal beam may be dynamically changed such that the closest edge of each signal beam angular aperture is selected to be a threshold angle different than the angular aperture of the reference beam used to record it. In some examples, the dynamic aperture holographic multiplexing process may include dynamic aperture equalization to reduce cross-talk, to improve error correction parity distribution for improved recovery transfer rate, to provide multiple locus aperture sharing for increased recording density, and to provide polarization multiplexed shared aperture multiplexing for increased transfer rate in both recording and recovery.

Polarization-sensitive optical measurement instrument

Abstract: A beam emitted from a light source is split into a probe beam that irradiates a measurement object and a reference beam that does not irradiate the measurement object. A signal beam obtained by the reflection of the probe beam is split into first and second split signal beams, which are mutually orthogonal polarized components. The first split signal beam and the reference beam are inputted to a first coherence optical system to cause the beams to interfere with each other to generate at least three coherence beams differing in phasic relationship. The second split signal beam and the reference beam are inputted to a second coherence optical system to cause the beams to interfere with each other to generate at least three coherence beams differing in phasic relationship. The coherence beams are then detected.

A 5 μm wavelength laser for dielectric laser acceleration

Abstract: A high-energy 5 μm laser source which will be used to pump a dielectric photonic structure for GV-per-meter electron acceleration has been designed and modeled. The source utilizes two-step ultrafast optical parametric amplification and can be pumped by a Ti:sapphire laser. The experimental implementation and system integration are in progress. We describe 5-μm seed pulse generation using optical parametric generation in AgGaS2 and ZnGeP2 crystals and the commissioning of a 2-μm pump source, including supercontinuum generation and the preliminary results on the amplification of the signal beam at 1.3 μm.

Optimization of gain in traveling-wave optical parametric amplifiers by tuning the offset between pump- and signal-waist locations.

Abstract: We present experimental demonstration and modeling of the optimization of a phase-sensitive optical parametric amplifier by tuning the relative position between the pump and signal beam waists along the propagation direction. At the optimum position, the pump beam focuses after the signal beam, and this departure from colocated waists increases with increasing pump power. Such optimization leads to more than 3 dB improvement in the measured deamplification response of the amplifier.

Long wavelength infrared detection and imaging with long wavelength infrared source

Abstract: An infrared detection system comprises the following elements. A laser source provides radiation for illuminating a target (5). This radiation is tuned to at least one wavelength in the fingerprint region of the infrared spectrum. A detector (32) detects radiation backscattered from the target (5). An analyser determines from at least the presence or absence of detected signal in said at least one wavelength whether a predetermined volatile compound is present. An associated detection method is also provided. In embodiments, the laser source is tunable over a plurality of wavelengths, and the detector comprises a hyperspectral imaging system. The laser source may be an optical parametric device has a laser gain medium for generating a pump beam in a pump laser cavity, a pump laser source and a nonlinear medium comprising a ZnGeP2 (ZGP) crystal. On stimulation by the pump beam, the ZnGeP2 (ZGP) crystal is adapted to generate a signal beam having a wavelength in a fingerprint region of the spectrum and an idler beam having a wavelength in the mid- infrared region of the spectrum. The laser gain medium and the ZnGeP2 (ZGP) crystal are located in the pump wave cavity.

System and method for the calibration and verification of wireless networks with control network

Abstract: In a system and method computerized devices are connected to each other over a wireless network and to a controller over an additional network. The devices perform antenna beam angle testing of the wireless network. The controller receives, over the additional network, transmitted and received test signal data acquired during such testing. Based on the test signal data, the controller calculates calibration data, which indicates, for each pair of devices, different path loss amounts associated with different transmitted test signal beam angles and a single transmitted test signal power level. The controller generates calibration matrices corresponding to each pair of devices using the calibration data; analyzes the matrices to determine, for each pair, an optimal antenna beam angle that results in the least amount of path loss; determines an optimal power level for the pair based on the path loss; and communicates the optimal specifications to the pair.

Optical image measurement device, image display device, and image display method

Abstract: An objective of the present invention is to carry out a circulatory measurement with a high degree of reliability. An optical image measurement device of an embodiment comprises an optical assembly, a scanning unit, an image forming unit, a blood vessel region identification unit, and a circulatory information generation unit. The optical assembly segments light from a light source into a signal beam and a reference beam, and detects a coherent light of scattered light of the signal beam from a lifeform and the reference beam which is routed via a reference beam path. The scanning unit carries out a first scan in which a first cross-section which intersects with a blood vessel of interest of the lifeform is repeatedly scanned with the signal beam. On the basis of the result of the detection of the coherent light which is obtained in the first scan by the optical assembly, the image forming unit forms a first tomographic image which represents a time series change of a form in the first cross-section and a phase image which represents a time series change of a phase difference. The blood vessel region identification unit identifies a blood vessel region corresponding to the blood vessel of interest for both the first tomographic image and the phase image. The circulatory information generation unit generates circulatory information relating to the blood vessel of interest on the basis of the blood vessel region of the first tomographic image and the time series change of the phase difference in the blood vessel region of the phase image.

Conversion of broadband incoherent pump to narrowband signal in an optical parametric amplifier

Abstract: The parametric amplification of the signal beam with a narrow angular spectrum in the field of an incoherent broadband pump is investigated theoretically as well as experimentally. It is demonstrated that in the absence of beam walk-off a significant enhancement of the parametric gain takes place, and the power of the incoherent pump can be effectively transferred into the signal beam. The background of the signal spectrum appearing in the process of amplification due to pump amplitude fluctuations can be removed by filtering, and the coherence of the input signal can be recovered.

Localization algorithm for conferencing

Abstract: A conferencing device and method of talker localization for steering a plurality of sensors arranged in sectors around a housing to a current active direction beam. A beamformer is implemented for determining a loudest sector based on signals from the sensors. In the event the loudest sector persists for a first duration then forming signal beams from sensor signals in the loudest sector and a plurality of adjacent sectors over a further duration to create respective signal beam envelopes. Then selecting a highest energy of the beam envelopes to be a loudest non-active beam and comparing the loudest non-active beam to the current active direction beam. If the highest energy one of the beams is greater than the energy of the current active direction beam by a threshold, then selecting the highest energy one of the beams to be the current active direction beam and directing the sensors thereto.

Phase-sensitive amplifier and method of designing same, bpsk signal phase noise suppressor using phase-sensitive amplifier, bpsk signal regenerator, qpsk signal demultiplexer, and qpsk signal regenerator

Abstract: [Problem] To obtain a large gain-extinction ratio with a small nonlinear effect. [Solution] This phase-sensitive amplifier comprises: a pump beam emission means; a multiplexed beam emission means for multiplexing an inputted signal beam with the pump beam and emitting a multiplexed beam; a phase difference adjustment means for adjusting a relative phase difference between the signal beam and the pump beam; and a nonlinear medium which receives the relatively phase difference adjusted multiplexed beam and causes a parametric process. When a circle is drawn in a complex plane with the origin in the center, said circle having a radius which is a complex amplitude of an output signal beam of the phase-sensitive amplifier in which a target gain-extinction ratio is established to be 20dB or more, the intensity of the pump beam, and a nonlinear constant, a propagation length, and a distribution value of the nonlinear medium, are set such that the complex amplitude of the output signal beam when the phase of the input signal matches a quadrature component is contained in the circle, and the product of the nonlinear constant, the propagation length, and the intensity of the pump beam is less than 1.7rad.

Phase mask and holographic recording apparatus employing the same

Abstract: A phase mask includes a phase modulation layer that modulates a phase of different portions of incident light, differently, such that a different optical phase delay, in a range between 0 and 2π is imparted to different portions of the incident light. A hologram recording apparatus includes a light source; a signal beam optical system that divides a beam emitted from the light source into a reference beam and a signal beam, modulates the signal beam according to hologram pixel information, and radiates the signal beam onto a hologram recording medium. The signal beam optical system includes the phase mask. The hologram recording apparatus also includes a reference beam optical system that radiates the reference beam onto the hologram recording medium.

Single-fiber single-vibration kilowatt magnitude all-fiber laser

Abstract: The utility model discloses a single-fiber single-vibration kilowatt magnitude all-fiber laser which comprises pump lasers, pump beam combiners, a high power pump signal beam combiner used for a positive pump, a high reflective fiber grating, a ytterbium doped large mode-field double-clad fiber, a low reflective fiber grating, a high power pump signal beam combiner used for a negative pump, a cladding-layer power filter, an output fiber, and a fiber end cap. The single-fiber single-vibration kilowatt magnitude all-fiber laser has the advantages that through a primary fiber oscillator, the kilowatt magnitude laser power output is realized, compared with a kilowatt magnitude all-fiber laser based on main shock power amplification technology, the technological content is higher, the structure is simpler, a power amplifier is not needed, a lot of expensive fiber devices are saved, the size is smaller, the cost is lower, the industrialization is facilitated, at the same time, in the aspect of the laser performance, the spontaneous emission signal to noise ratio of a laser signal outputted by the single fiber oscillator is larger, the spectrum is more clean, and the application of the laser in the field of industrial processing is facilitated.

Broadly-tunable near- and mid-IR source by direct pumping of an OPA with a 42 MHz femtosecond multi-Watt Yb:KGW oscillator

Abstract: Laser sources delivering high repetition rate broadband mid-IR radiation enable a number of key applications [1], for example in near-field and FTIR spectroscopy [2]. Here, we present an OPA that is directly pumped by a diode-pumped solid-state oscillator without the need for any amplifier or cavity dumping, generating tunable radiation in the near- and mid-IR spectral region.We employ a passively mode-locked dual-crystal Yb:KGW oscillator delivering up to 7.4 W average power with 425 fs pulse duration and 41.7 MHz repetition rate at 1040 nm as pump source [3]. A fraction of the light is used to generate the supercontinuum seed in an 8 cm long tapered fiber with 4 μm waist diameter, whereas the remaining light is used to pump the parametric amplifier. Pump and signal beam are combined with a dichroic mirror and focused separately into the crystal with a collinear interaction geometry. Using a 5 mm long PPLN crystal for frequency conversion, the OPA signal wavelength is continuously tunable between 1380 and 1830 nm, which corresponds to idler wavelengths from 2.41 to 4.22 μm, by changing the poling period of the crystal (28.0 to 31.0 μm in 0.5 μm steps) and by changing the crystal temperature between 20 and 200 °C. The signal and idler spectra measured at room temperature are shown in Fig. 1(a) and 2(b), respectively. We exceed 325 mW over the whole signal range with a maximum power of 540 mW at 1400 nm and we exceed 140 mW over the whole idler range with a maximum power of 220 mW at 3.06 μm. The pump power was set to 2 W in order to remain well below the damage threshold of the PPLN crystal. Using the maximum available pump power of 4 W, signal powers up to 800 mW were achieved. To generate mid-JR radiation at longer wavelengths we used a 2 mm long GaSe crystal instead of the PPLN crystal. We performed type J phase matching (e - o → o). The pump power was set to 4 W. Broadband mid-JR pulses tunable from 4.85 to 9.33 μm were generated with up to 830 μW average power at 6.46 μm, see Fig. 1(c).Power and spectra are temporally stable with power fluctuation of 0.9 % rms in the NJR and 3.3 % rms in the MJR region. We numerically model the parametric process using a χ(2) Nonlinear Envelope Equation [4] and show good agreement between simulations and experiments. Our source is compact and cost efficient and has the potential to replace more complex Ti:sapphire/OPO systems for ultrafast spectroscopy and mid-JR applications.

Apparatus for recording and reproducing hologram

Abstract: A hologram recording and reproducing apparatus including: a coherent light source; a beam splitter which splits a beam emitted from the coherent light source into a signal beam and a reference beam; a signal beam forming unit which modulates the signal beam split and directs the modulated signal beam onto a hologram recording medium; and a reference beam forming unit which directs the reference beam to be irradiated onto a location on the hologram recording medium which overlaps with a location on the hologram recording medium on which the signal beam is incident, wherein the signal beam forming unit includes: a first light guide member which transmits the signal beam split by the beam splitter; a spatial light modulator (SLM) which modulates the signal beam transmitted through the first light guide member; and a holographic Fourier transformation optical device which focuses the modulated signal beam onto the hologram recording medium.

Method and apparatus for holographic recording

Abstract: Provided is a holographic recording method in which an interference fringe between a reference beam and a signal beam, modulated according to information regarding a plurality of hologram pixels, is recorded on a holographic recording medium, the holographic recording method including multiplexing-recording the interference fringe of the plurality of hologram pixels such that at least a part of the interference fringe recorded of neighboring hologram pixels of the plurality of hologram pixels is overlapped.