A high performance free-space Wavelength Division Multiplexed (WDM) transceiver system is assessed as to its viability for routing collinear entangled photons in place of the classical optical signals for which it was designed. Explicit calculations demonstrate that entanglement in the input state is retained through transit of the system without intrinsic loss. Introducing spatial degrees of freedom changed the entanglement so that it could be manifested at remote locations, as required in non-local Bell test measurements or Quantum Key Distribution (QKD) Protocols. It was also found that by adding proper components, the exit state could be changed from being frequency entangled to polarization entangled, with respect to the (remote) paths of the photons. Finally it was found possible to route a complete entangled state to either of the two remote users by proper selection of the discrete frequencies in the input state. Each entanglement in the photon states was maximal, hence suited for Quantum Information Processing (QIP) applications.
An authorized user receiving bunched photon states from the output of a hyper-entangled photon server can make use on average of one fourth of the total transmitted events to gain situational awareness of the communications channel. Another user receiving bunched states can do the same. Both users then gain greater situational awareness on the confidentiality and integrity of the remaining half of the total transmission events wherein they both perform non-local correlated measurements on anti-bunched photon states. Keyed communication in quantum noise1 (KCQ) is used to enhance confidentiality and efficiency. This depiction forms a baseline for more realistic models; all optical elements are perfect and propagation through channels is noiseless.
Lyot filters have been designed for multi-access high capacity wavelength division multiplexing between a communications hub and spatially separated spokes. Reported here are modifications to a basic classical communications Lyot filter stage , but using a hyper-entangled bipartite input state possessing non-degenerate frequencies for advanced quantum communications. Lyot filters and pre-shared linking knowledge can be used to better ensure efficiency and efficacy in manifesting entanglement correlations between polarization degrees of freedom in non-rotationally invariant measurement bases. Lyot filters also allow entangled photon routing, a function of entanglement between incident frequencies and polarization.
Non-degenerate frequency entanglement has been reported in several recent experiments, since its original observation with Spontaneous Parametric Down-conversion. We report on a configuration based on a Lyot plate, which overcomes shortcomings of prior work by avoiding post-selection and state projection losses. This makes the process suitable, in principle, for use in efficient QKD protocols based on photon pairs entangled in frequency at remote locations.
We propose a quantum key distribution system based on the generation and transmission of random continuous variables in time, energy (frequency), phase, and photon number. The bounds for quantum measurement in our scheme are determined by the uncertainty principle, rather than single quadrature measurements of entangled states, or the no-cloning of (unknown) single quantum states. Correlated measurements are performed in the energy-time, and momentum-displacement frames. As a result the QKD protocols for generation of raw-keys, sifted-keys and privacy amplifications offer a higher level of security against individual or multi-attacks. The network architecture is in a plug-and-play configuration; the QKD protocol; determination of quantum bit error rate, and estimation of system performance in the presence of eavesdropping are presented.
Quantum Key Distribution (QKD) has been shown to be provably secure when certain idealized conditions are
met in a physical realization. All implementations of QKD to date require non-orthogonal basis measurements
to implement it; making it commonly assumed that measurement basis variation is fundamental to making QKD
protocols secure from eavesdropping. We show here that in particular physical conditions this assumption is
incorrect, and that provable security can be achieved without use of multiple bases. Basis setting information
can in fact be shared with all potential eavesdroppers, as they are unable to use it to acquire or influence any
part of the encryption key generation. Furthermore the key generation efficiency is limited to 100 % as
compared with an inherent 50 % limit for alternating bases in BB84 or Entangled Ekert protocols.
Considerations of non-locality and correlation measures provide insights to Quantum Mechanics. Nonphysical
states are shown to exceed limits of QM in both respects and yet conform to relativity’s ‘nosignaling’
constraint. Recent work has shown that the Uncertainty Principle limits non-locality to
distinguish models that exceed those of QM. Accordingly, the Uncertainty Principle is shown to limit
correlation strength independently of non-locality, extending interpretation of the prior work, and to
underlie the security of Quantum Key Distribution. The established Ekert protocol is compared with
more secure variations, in particular H. Yuen's Keyed Communication in Quantum Noise (KCQ)  and
a new Time-Gating protocol which minimizes authentication and susceptibility to active eavesdropping.
Experimental measurements of entangled photons have enabled effective probing of foundational principles of physical
law, Quantum Mechanics (QM) in particular. When it was noted that QM is non-local and precludes certain real
properties, change in the description of basic phenomena was required. Bell's Inequality work clarified this conflict with
Local-Realistic descriptions but left open whether locality, realism, or both should be abandoned. More recent
investigations consider models that maintain forms of non-local realism as alternatives to QM. Problems with those are
illustrated here, and support a non-local QM description of entangled photons having non-determinate properties.
This paper expands upon prior work on an entangled photon source generating six pairs of photons via spontaneous
parametric down-conversion in a single pass configuration. Experimental results measuring entangled photons at 810 nm
are shown and other wavelength regimes will be discussed. The design and fabrication considerations for a group
velocity matched (GVM) superlattice photon source are discussed. An application of this source enables various multiqubit
cluster states to be generated in a compact unidirectional configuration. This configuration simplifies the
interferometric stability for any associated feed-forward methods required in photon-based quantum logic circuitry.
In this work, we discuss a novel compact source that generates six pairs of entangled photons via spontaneous parametric
down-conversion from a single pass of a pump beam through a crystal assembly. The experimental demonstrations
reported are at 810 nm so as to utilize high quantum efficiency Si-APD detectors, but the design can be readily
implemented in other wavelength regimes including the telecom bands near 1550 nm. An immediate application of this
source enables particular multi-qubit cluster states to be generated in a highly compact unidirectional configuration. This
can significantly simplify the interferometric stability, as well as feed-forward methods required in photon-based
quantum logic circuitry.
Bell's theorem, and inequalities that stem from it, address the conflict between the explanation of key experimental
observations by quantum mechanics (QM) and by models expressing Locally Realistic (LR) properties, regardless of
their inclusion or exclusion of hidden variables. To demonstrate the conflict between experimental results described by
QM and LR models, a physical realization of the quantum state must be chosen. Entangled photons or electrons provide
the most viable choices. In this work we consider a simplified version of a Bell inequality (BI) that focuses entirely on
the physical state properties of photons in order to demonstrate the difference between QM and LR correlations. While
the experiment we propose is in principle similar in intent to prior Bell inequality experiments, our version requires
fewer measurements, and is more advantageous in its conceptual clarity.
Spontaneous downconversion yields photons for Quantum-Optical-Gate development though their generation is
probabilistic. Optimized efficiency requires control over the spectral wavefunction, generally achieved via spectral
filtering which sacrifices most downconverted photons. Selecting crystal parameters to address the issue has been
demonstrated, but no natural media enable this for 800 nm applications with optimal detection. Synthesizing parameters
with super-lattices of known crystals was also analyzed but two-crystal experiments were insufficient to exploit it.
Prototype twelve-crystal-assemblies have now been fabricated and the first results are reported here. We review
implications for further work and discuss how methods described here enhance efficiency in applications of entangled
photons requiring multi-crystal sources, such as cluster states, entanglement swapping, and teleportation.
An electroabsorption modulator (EAM) is designed to optimize dynamic range performance over 20
GHz bandwidth. The single stripe waveguide enables an extremely compact and integrated package to
be fabricated with single mode fiber pigtails. The transfer function's shape permits suppression of
higher order intermodulation products, yielding a spur-free dynamic range exceeding that of Mach-
Zehnder designs. A dilute optical core diverts energy flow from absorbing layers into low loss
waveguide; the 20 dBm optical power tolerance is significantly higher than that of commercially
available electroabsorption devices. The tunable performance over 20 GHz is characterized and
applications are discussed. New approaches to the broadband impedance matching requirements are
calculated and the impact on system performance is assessed.
Externally coupled electroabsorption modulators (EAM) are commonly used in order to transmit RF signals on
optical fibers. Recently an alternative device design with diluted waveguide structures has been developed.  Bench
tests show benefits of lower propagation loss, higher power handling (100 mW), and higher normalized slope efficiency.
This paper addresses the specific issues involved in packaging the diluted waveguide EAM devices. An evaluation
of the device requirements was done relative to the standard processes. Bench tests were performed in order to
characterize the optical coupling of the EAM. The photo current maximum was offset from the optical power output
maximum. The transmissions vs. bias voltage curves were measured, and an XY scanner was used to record the mode
field of the light exiting from the EAM waveguide in each position. The Beam Propagation Method was used to simulate
the mode field and the coupling efficiency. Based on the bench tests and simulation results, a design including
mechanical, optical and RF elements was developed. A Newport Laser Welding system was utilized for fiber placement
and fixation. The laser welding techniques were customized in order to meet the needs of the EAM package design.
Herein is described a novel approach of performing adaptive photonic beam forming of an array of optical fibers with the
expressed purpose of performing laser ranging. The beam forming technique leverages the concepts of time reversal,
previously implemented in the sonar community, and wherein photonic implementation has recently been described for
use by beamforming of ultra-wideband radar arrays. Photonic beam forming is also capable of combining the optical
output of several fiber lasers into a coherent source, exactly phase matched on a pre-determined target. By implementing
electro-optically modulated pulses from frequency chirped
femtosecond-scale laser pulses, ladar waveforms can be
generated with arbitrary spectral and temporal characteristics within the limitations of the wide-band system. Also
described is a means of generating angle/angle/range measurements of illuminated targets.
Generation of stable pulses and a frequency stabilized optical comb are two key requirements for Fourier Based
Arbitrary Waveform Generation (AWG) techniques. The longitudinal mode spacing of the laser must remain as stable
as possible to permit effective isolation and processing of the modes for waveform synthesis. The short and long term
temporal stability ultimately limits the system's precision as well as its operability in fielded systems. A packaged
erbium-doped waveguide provided a highly compact gain medium for the harmonically mode-locked laser design.
Stability was achieved by use of an intracavity etalon for frequency stabilization of the optical comb, a Pound-Drever-
Hall (PDH) method, and an active bias feedback loop for low frequency noise suppression. The temperature was
controlled to limit cavity length variation, and the contribution to stability of each method is quantitatively assessed.
The system's stable operating time was increased from hours to greater than a day, and the timing jitter is demonstrated
to be lower than that of commercially available erbium-doped fiber laser (EDFL) systems. Applications to optical signal
synthesis and Laser Radar are briefly discussed.
Progress in the last decade has enabled the generation and detection of both single and entangled photons for use in new applications of quantum cryptography, secure key distribution in particular, Nevertheless, fundamental and practical restrictions restrict the implementation to protoype systems. Methods of circumvent certain of those are presented in configurations that retain the features essential to single photon and photon pair signal processing.
Precise control of the dispersion within mode-locked laser cavities can lead to optical pulse compression and reduced timing jitter of mode-locked lasers. Two simple measurement techniques are used to provide a complete picture of the dispersion within an erbium doped mode-locked fiber laser cavity. We measured the optical dispersion of erbium-doped fiber, standard single mode fiber, and chirped Bragg gratings. We built a Michelson interferometer with a wideband LED source to measure the dispersion of fiber lengths of less than 1 meter. Next, we measured the dispersion of chirped Bragg gratings using a network analyzer and a tunable laser in a differential phase measurement technique.
Injection seeding of a passively mode-locked fiber laser by an actively mode-locked fiber laser source is described. The passively mode-locked laser employs a multiple quantum well saturable absorber to establish pulsed operation. Mode-locked synchronized operation was maintained with average injection powers as low as 1.3 mW. Stable synchronized pulses were observed with pulse widths as narrow as 10 ps.
We describe a simple efficient erbium fiber laser mode locked with a multiple quantum well saturable absorber whose reflectivity can be controlled with an applied electric field. The laser produces 30 ps, duration pulses at a repetition rate of 3.25 MHz.
The construction and operating characteristics of a compact self starting mode locked erbium fiber laser are described in this paper. The laser employs a Fabry-Perot cavity with a fiber grating as one reflector and a nonlinear mirror based on a saturable absorber as the other. It operates at a pump power of less than 50 mW and produces mode locked pulses of 16.5 ps duration at a frequency of 3.25 MHz and a peak power of about 20 W.
A microwave variable delay line has been demonstrated based on the dispersive properties of optical fibers. This processor offers high bandwidth and tunability with the stability that fiber optics offers. A two-tap processor has been demonstrated with a 1.3 ns spacing.
We have constructed a harmonically modelocked laser that includes an electronically driven modulator and an intracavity Fabry-Perot etalon. We use experimentally observed performance of this laser, and number simulations based on the operating parameters of this laser, to examine strategies for generating stable synchronized trains of ultrashort duration solitons at multi-GHz repetition rates. Introduction of a saturable absorber based on a mechanism that both saturates and recovers promptly is examined. This strategy provides means of generating stable trains of solitons, where the soliton durations are of the order of a few ps or less, as well as synchronizing those trains with optical pulsewidth precision. We identify a rapidly saturating and rapidly recovering saturable absorber with a shorter pathlength as a potentially useful improvement on the nonlinear loop mirror. Significant work remains, but generation and distribution of these synchronized ultrashort duration soliton trains over networks on a scale of km or more appear feasible.
The Brillouin threshold in PM fiber is measured and compared with calculated values as well as previous cited results on standard SM fiber. Factors affecting it are identified, and methods of working around the limitations posed to fiber signal levels are briefly discussed.
The operating characteristics of a simple self-starting mode-locked erbium fiber ring laser based on a commercial optical fiber gain module are described. The laser produces pulses of the order of 50 mW. In contrast to earlier lasers of the same type, no polarizing element was needed in the ring to initiate mode locking. the implications of this fact relative to possible mechanisms for mode locking are discussed.
We report the development of a simple self starting passively mode locked diode pumped laser oscillator utilizing erbium doped fiber and a minimum number of readily available components. With pump powers as low as 8.0 mw, the oscillator generates stable pulses of 1.2 ns width and rates of 5.0 MHz at wavelengths around 1.55 micrometers . Evidence exists for substructure as short as 35 ps within the 1.2 ns pulses. A mechanism for the observed characteristics of the oscillator based on the all optical Kerr effect is proposed.
A semi-conductor TWLA provides the gain medium for an external cavity laser source at 1.32 microns for compatibility with single mode fiber optic systems. The active layer of the waveguide is InGaAsP in an angle stripe geometry. Parameters for CW lasing are established. Pulsed operation is then achieved by two methods: direct RF modulation of the bias current, and regenerative feedback of the converted optical output signal. Both methods yield short pulses of different frequency noise characteristics. The mode-locked rate can be adjusted over a wide range for different applications by varying the cavity length. Wavelength tuning is achieved by replacing the cavity end mirror with a grating the use of an all fiber cavity is examined.
A tunable erbium doped fiber ring laser, pumped with a 980 nm InGaAs diode laser was constructed. Output power as a function of pump power and output wavelength for a given fiber length was measured. Spectral and temporal analysis of the signal showed mode-locked pulses of short duration and broad frequency content, as well as a CW component confined to a relatively narrow optical frequency range. The mechanisms for this type of mode-locking are discussed as well as the limitations placed on the lasing line width and spectral tunability.