Multimode Light Research Articles

The efficiency of parallel quantum memory for light in a cavity configuration

We present a new scheme of quantum memory for optical images (spatially multimode light fields) that allows mapping the quantum state of the signal onto the long-lived coherence of the ground state of an ensemble of stationary atoms or impurity centers. The memory medium is embedded in an optical cavity with degenerate transverse modes, which increases the effective optical thickness of the medium and allows one, in principle, to store information in optically thin atomic layers. Since, in reality, storage and retrieval of limited-duration signals, including signals shorter than the lifetime of the field in the cavity, is of interest, we do not use the low-Q cavity approximation. The influence of losses due to partial reflection of the nonstationary signal field incident on a coupling mirror on the storage efficiency is considered. We used the method of approximate impedance matching, wherein losses due to reflection can be minimized by controlling the coupling parameter of the light field with memory medium in time, thus creating conditions for destructive interference of the signal and local fields on the coupling mirror. The influence of diffraction on the transverse resolution of memory at the writing and readout stages is investigated, and the number of effectively stored transverse spatial modes of the signal is estimated.

Multiband processing of multimode light: combining 3D photonic lanterns with waveguide Bragg gratings

The first demonstration of narrowband spectral filtering of multimode light on a 3D integrated photonic chip using photonic lanterns and waveguide Bragg gratings is reported. The photonic lanterns with multi-notch waveguide Bragg gratings were fabricated using the femtosecond direct-write technique in boro-aluminosilicate glass (Corning, Eagle 2000). Transmission dips of up to 5 dB were measured in both photonic lanterns and reference single-mode waveguides with 10.4-mm-long gratings. The result demonstrates efficient and symmetrical performance of each of the gratings in the photonic lantern. Such devices will be beneficial to space-division multiplexed communication systems as well as for units for astronomical instrumentation for suppression of the atmospheric telluric emission from OH lines.

Asymmetric double-clad fiber couplers for endoscopy

We present an asymmetric double-clad fiber coupler (A-DCFC) exploiting a disparity in fiber etendues to exceed the equipartition limit (≤50% extraction of inner cladding multi-mode light). The A-DCFC is fabricated using two commercially available fibers and a custom fusion-tapering setup to achieve >70% extraction of multi-mode inner cladding light without affecting (>95% transmission) single-mode light propagation in the core. Imaging with the A-DCFC is demonstrated in a spectrally encoded imaging setup using a weakly backscattering biological sample. Other applications include the combination of optical coherence tomography with weak fluorescent or Raman scattering signals.

Coherent storage of temporally multimode light using a spin-wave atomic frequency comb memory

We report on the coherent and multi-temporal mode storage of light using the full atomic frequency comb memory scheme. The scheme involves the transfer of optical atomic excitations in Pr3+:Y2SiO5 to spin waves in hyperfine levels using strong single-frequency transfer pulses. Using this scheme, a total of five temporal modes are stored and recalled on-demand from the memory. The coherence of the storage and retrieval is characterized using a time-bin interference measurement resulting in visibilities higher than 80%, independent of the storage time. This coherent and multimode spin-wave memory is promising as a quantum memory for light.

Solving the Maxwell–Bloch equations for resonant nonlinear optics using GPUs

We solve the Maxwell–Bloch equations of resonant nonlinear optics using GPUs and compare the computation times with traditional single- and multithreaded programs. A detailed benchmarking of programs as a function of various parameters shows how the massive parallelism built into GPUs becomes more and more advantageous as the physical problem becomes more and more demanding. For the case of multimode light propagating through an inhomogeneously broadened medium of many-level quantum systems, the program executing on GPUs can be over 20 times faster than that executing on all cores of a modern CPU. The methods presented can be applied in a wide area of atomic physics where the time evolution of atomic ensembles is to be computed.

Generation and delayed retrieval of spatially multimode Raman scattering in warm rubidium vapors

We apply collective Raman scattering to create, store and retrieve spatially multimode light in warm rubidium-87 vapors. The light is created in a spontaneous Stokes scattering process. This is accompanied by the creation of counterpart collective excitations in the atomic ensemble - the spin waves. After a certain storage time we coherently convert the spin waves into the light in deterministic anti-Stokes scattering. The whole process can be regarded as a delayed four-wave mixing which produces pairs of correlated, delayed random images. Storage of higher order spatial modes up to microseconds is possible owing to usage of a buffer gas. We study the performance of the Raman scattering, storage and retrieval of collective excitations focusing on spatial effects and the influence of decoherence caused by diffusion of rubidium atoms in different buffer gases. We quantify the number of modes created and retrieved by analyzing statistical correlations of intensity fluctuations between portions of the light scattered in the far field.

Applications of Integrated Photonic Spectrographs in astronomy

One of the problems of producing instruments for Extremely Large Telescopes is that their size (and hence cost) scales rapidly with telescope aperture. To try to break this relation alternative new technologies have been proposed, such as the use of the Integrated Photonic Spectrograph (IPS). Due to their diffraction-limited nature the IPS is claimed to defeat the harsh scaling law applying to conventional instruments. In contrast to photonic applications, devices for astronomy are not usually used at the diffraction limit. Therefore to retain throughput and spatial information, the IPS requires a photonic lantern (PL) to decompose the input multimode light into single modes. This is then fed into either numerous Arrayed Waveguide Gratings (AWGs) or a conventional spectrograph. We investigate the potential advantage of using an IPS instead of conventional monolithic optics for a variety of capabilities represented by existing instruments and others planned for Extremely Large Telescopes. We show that a full IPS instrument is equivalent to an image-slicer. However, the requirement to decompose the input light into individual modes imposes a redundancy in terms of the numbers of components and detector pixels in many cases which acts to cancel out the advantage of the small size of the photonic components. However, there are specific applications where an IPS gives a potential advantage which we describe. Furthermore, the IPS approach has the potential advantage of minimising or eliminating bulk optics. We show that AWGs fed with multiple single-mode inputs from a PL require relatively bulky auxiliary optics and a 2-D detector array. A more attractive option is to combine the outputs of many AWGs so that a 1-D detector can be used to greatly reduce the number of detector pixels required and provide efficient adaptation to the curved output focal surface.

Generating function approach for creation of coherent multimode beams by diffractive optics

Tailored compositions of transverse modes provided by mathematical generating functions are exploited for the synthesis of multimode laser beams in free space. We show that analytical equations which are available for the generating functions provide physical insight into modal phase and power balance in multimode coherent light beams. Multimode coherent beams were created by methods of diffractive optics implementing the generating functions. Experimental and computer simulated results demonstrate a good match.

相干和多模热光场的光子统计实验

On the basis of the properties of two beams in heterodyne detection,the photon statistical models for the coherent light and multi-mode thermal light fields were analyzed.The second and third order statistical characters of the two kinds of optical fields were discussed,in which the second order statistics was corresponding to the Fano factor,while the third order one was to the symmetry parameter.The Fano factor and the symmetry parameter for the two kinds of light fields were measured experimentally.The results indicate that Fano factor and symmetry parameter do not change with the variance of incident photons for the coherent light field.Combined with the theoretical model and experimental data,it shows that the cross-talk probability is 0.032 1 and the gain coefficient is 1.0460 ph.However,the Fano factor of multi-mode thermal light field increases with the incident photons and gives a linear ascending trend.The factor reduces with the increase of the target velocity,which means the fluctuation of the echo photons decreases because of the averaging effect caused by increasing the number of thermal modes.Moreover,the symmetry parameter of multi-mode thermal light field is parabolic curve distribution.The research of coherent and multi-mode thermal light statistics provides a foundation for the laser heterodyne detection based on photon counting.

High-speed spatially multimode atomic memory

We study the coherent storage and retrieval of a very short multimode light pulse in an atomic ensemble. We consider a quantum memory process based on the conversion of a signal pulse into a long-lived spin coherence via light matter interaction in an on-resonant $\ensuremath{\Lambda}$ -type system. In order to study the writing and reading processes we analytically solve the partial differential equations describing the evolution of the field and of the atomic coherence in time as well as in space. We show how to optimize the process for writing as well as for reading. If the medium length is fixed, for each length, there is an optimal value of the pulse duration. We discuss the information capacity of this memory scheme and we estimate the number of transverse modes that can be stored as a quantum hologram.

Quantum holography upon resonant adiabatic interaction of fields with an atomic medium in a Λ-configuration

We study the quantum memory protocol for spatially multimode light based on an atomic ensemble in the Λ-configuration. We analytically solve a system of partial differential equations that describe the evolution of the medium and field for the case where the interaction time considerably exceeds the lifetime of the excited state. This time ratio makes it possible to apply the adiabatic approximation. Unlike problems aimed at storage the time profile of the signal field, we propose optimizing the relation between the writing and reading times and the optical density of the medium, which ensures a high retrieval efficiency of the quantum image.

Encircled Flux-based optimized simple launch condition for standardization of multimode polymer optical waveguide evaluations

Multimode polymer optical waveguide evaluations by using a combination of multimode optical fibers (MMF) and Light Emitting Diode (LED) give very often inconsistent experimental result. It is due to the over-filled properties of the launch light created by this configuration. We propose an optimized simple launch configuration to overcome the problems by using similar configuration. The optimized launch configuration creates an optimal-filled launch light where its encircled flux (EF) profile satisfies the EF template provided by the International Electrotechnical Commission (IEC). We have used the standard optical fibers and optical fiber adaptors to create the optimized simple launch configuration with high stability. Therefore, our proposed launch configuration is suitable for realizing a cost effective optimized launch configuration for standardization of multimode polymer optical waveguide evaluations. We demonstrated reliability of the proposed launch configuration by examining the reproducibility of the insertion loss (IL) measurements. We have used two waveguide samples that have different characteristics for this purpose. It was found that the insertion loss (IL) measurements of the two samples are consistent with the largest variation of less than 5%. This variation is better than the proposed value given by the IEC that is 10%.

Photon-counting 155 μm optical communications with pulse-position modulation and a multimode upconversion single-photon receiver

We report single-photon frequency upconversion of multimode light from 1.55 to 0.532microm and demonstrate an end-to-end optical link that emulates photon-starved communications and atmospheric propagation. Using 64-ary pulse-position modulation and a half-rate serially concatenated turbo code we achieve a decoded efficiency of 0.3 detected photons/bit.

Generation of hollow beams by spiral rays in multimode light guides

The generation of hollow beams by a multimode light guiding device is analyzed. The light propagation through the light guide is simulated by ray tracing. It is shown that hollow beams are generated by light rays that propagate along a spiral path through the light guide. The properties of the hollow beam depend on the tilt angle and location of the input beam on the front surface of the light guide. The properties of the output beam are investigated experimentally.

电磁诱导下Y型四能级原子系统的左手效应

The quantum system with an interaction between a closed Y-type four-level atom and multi-mode light fields is adopted to possess left handedness by means of the technique of quantum coherence. In the representation of interaction, the density matrix method is utilized in view of the rotating-wave approximation and the di-pole approximation.The conclusion of the numerical simulation shows that under the appropriate parameter conditions, the medium can achieve negative permittivity and negative permeability simultaneously (i.e. the left handedness effect happens and the left-handed material is realized.) In the condition of the weak probe field, when the Rabi frequency of probe light increases, the frequency range of the medium to achieve its left-handed effect decreases and the refractive index and absorption coefficient will also changed correspondingly. The medium to affect light absorption and gain in the conditions of the establishment of left -handed effect are also discussed. The paper can be concluded that, in the conditions of weak probe field, the electro-magnetic induction can be used to achieve the left-handed effect of the medium, which extends the implementation of left-handed materials in the experiment, and extends the application field of electro-magnetic induction.

Fabrication of channel waveguides in Er 3+-doped tellurite glass via N + ion implantation

Er 3+-doped tellurite glasses are of great interest for the fabrication of active integrated optical circuits because of their unique properties in terms of bandwidth and rare-earth solubility. Multimode channel waveguides in a glass of this family, namely, a sodium–tungsten–tellurite glass, have been realized with high-energy ion irradiation, where the ion beam size in one dimension was reduced to a few tens of micrometers by a silicon mask. This approach makes possible the fast fabrication of waveguides with high aspect ratio (∼10 3). The 24 μm wide and 10 mm long waveguide stripes achieved by 1.5 MeV N + irradiation with fluences between 5 × 10 15 and 4.0 × 10 16 ions/cm 2 were studied using interference phase contrast microscopy and surface profilometry. The waveguiding effect was investigated by the end-fire coupling technique. Multimode light propagation has indeed been observed in these channels, confirming the effectiveness of this method. Dark-line spectroscopy revealed that light propagated in the channel via the optical barrier formed by the N + implantation.

Nanowire Waveguides and Ultraviolet Lasers Based on Small Organic Molecules

Single crystalline nanowires of 2,4,5-triphenylimidazole, a small organic functional compound, are prepared by adsorbent-assisted physical vapor deposition. As-prepared nanowires are shown to propagate multimode UV light and serve as single wire active optical waveguides and optically driven ultraviolet lasers (see figure).

Control of optical dynamic memory capacity of an atomic Bose-Einstein condensate

Light storage in an atomic Bose-Einstein condensate is one of the most practical usage of these coherent atom-optical systems. In order to make them even more practical, it is necessary to enhance our ability to inject multiple pulses into the condensate. In this paper, we report that dispersion of pulses injected into the condensate can be compensated by optical nonlinearity. In addition, we will present a brief review of our earlier results in which enhancement of light storage capacity is accomplished by utilizing multi-mode light propagation or choosing an optimal set of experimental parameters.

Multilayer Optical Head Using Butted-grating for Hybrid Recording

We developed a multilayer optical head with a planar structure that was designed using the finite-difference time domain (FDTD) method for hybrid recording. This optical head has a butted-grating structure, including its central and side parts. We initially discuss the advantages of the method of end-fire coupling for using the planar optical head. Second, we briefly explain our optical head and demonstrate how it can project a single-peak spot, even if multimode light is supplied by end-fire coupling that can be used. Finally, we present details on the asymmetric butted-grating optical head to position the output beam close to the magnetic writer pole in practical use.

Electromagnetically induced left handedness in inverted Y-type four level atomic system

The system of inverted Y-type four-level atoms interacting with multi-mode light fields is discussed. Through the mechanism of quantum interference, the relative dielectric permittivity and the relative magnetic permeability will changed remarkably. Using appropriately chosen parameters, the real parts of both the relative dielectric permittivity and the relative magnetic permeability will be negative, and then the left handedness effect happens and the left-handed material is realized. The properties of left-handed materials such as the range of frequencies of the negative refractive index can be manipulated via changing certain parameters of the system.