We present progress on demonstrating a side-channel-free, decoy-state quantum key distribution (QKD) source based on a polarization-modulator and a wavelength-stable attenuated pulsed laser. By modulating the polarization of the quantum state, a three-state QKD protocol is achieved. The polarization-modulator-based QKD source improves security by removing several sources of side-channel attacks that exist when multiple sources are used to generate different QKD states. Here we present our single-source design, as well as an evaluation of critical subsystems characterized by the quantum bit error rate (QBER), quantum state tomography, and achievable key rates. The QKD source is intended to operate using minimal size, weight, and power (SWaP). In our system, we use a custom KTP waveguide modulator designed and fabricated by AdvR. Our QKD source can be operated using both narrow-band and broadband lasers, and we present characterization data using a He-Ne laser, and a diode laser, respectively. The polarization-modulator-based QKD source has applications in future mobile quantum networks incorporating unmanned aerial vehicles (UAV) and autonomous vehicles, as well as fiber-based quantum networks.
We discuss two novel entanglement sources utilizing spontaneous parametric downconversion in periodically poled waveguides. Using quasi-phase matched KTP crystals, we have demonstrated a post-selection-based polarization entangled degenerate source at 810 nm, as well as a post-selection-free non-degenerate collinear source producing entangled photons at 810 nm and 1550 nm. The sources exhibit high brightness and state quality – with the non-degenerate source achieving fidelities and purities up to 99% – with clear paths for further improvement. Furthermore, they are compact, stable, and need little alignment when set, critical for practical quantum communication and network applications. Lastly, their small size, weight, and power (SWaP) makes them an attractive option for mobile platforms, e.g., with drones or satellites.
UV wavelength laser sources are an important area of research due to their use in atmospheric and atomic sensing; however, diode lasers at these wavelengths often have low power, poor spatial mode quality, and broad optical spectra. An alternative approach to a UV laser source is an IR diode laser with frequency conversion. In this work, a dual element ridge waveguide device is presented for third harmonic generation of UV wavelengths. This design has been successfully implemented to generate and sustain 3mW of UV from 200mW of IR pump in the waveguide.
AdvR, through support of the NASA SBIR program, has developed fiber-based components and sub-systems that are routinely used on NASA’s airborne missions, and is now developing an environmentally hardened, diode-based, locked wavelength, seed laser for future space-based high spectral resolution lidar applications. The seed laser source utilizes a fiber-coupled diode laser, a fiber-coupled, calibrated iodine reference module to provide an absolute wavelength reference, and an integrated, dual-element, nonlinear optical waveguide component for second harmonic generation, spectral formatting and wavelength locking. The diode laser operates over a range close to 1064.5 nm, provides for stabilization of the seed to the desired iodine transition and allows for a highly-efficient, fully-integrated seed source that is well-suited for use in airborne and space-based environments. A summary of component level environmental testing and spectral purity measurements with a seeded Nd:YAG laser will be presented. A direct-diode, wavelength-locked seed laser will reduce the overall size weight and power (SWaP) requirements of the laser transmitter, thus directly addressing the need for developing compact, efficient, lidar component technologies for use in airborne and space-based environments.
Jeffrey Wilson, Dalton Chaffee, Nathaniel Wilson, John Lekki, Roger Tokars, John Pouch, Tony Roberts, Philip Battle, Bertram Floyd, Alexander Lind, John Cavin, Spencer Helmick
A high generation rate photon-pair source using a dual element periodically-poled potassium titanyl phosphate (PP KTP) waveguide is described. The fully integrated photon-pair source consists of a 1064-nm pump diode laser, fiber-coupled to a dual element waveguide within which a pair of 1064-nm photons are up-converted to a single 532-nm photon in the first stage. In the second stage, the 532-nm photon is down-converted to an entangled photon-pair at 800 nm and 1600 nm which are fiber-coupled at the waveguide output. The photon-pair source features a high pair generation rate, a compact power-efficient package, and continuous wave (CW) or pulsed operation. This is a significant step towards the long term goal of developing sources for high-rate Quantum Key Distribution (QKD) to enable Earth-space secure communications. Characterization and test results are presented. Details and preliminary results of a laboratory free space QKD experiment with the B92 protocol are also presented.
We have designed and completed initial testing on a laser source suitable for atomic interferometry from compact, robust, integrated components. Our design is enabled by capitalizing on robust, well-commercialized, low-noise telecom components with high reliability and declining costs which will help to drive the widespread deployment of this system. The key innovation is the combination of current telecom-based fiber laser and modulator technology with periodicallypoled waveguide technology to produce tunable laser light at rubidium D1 and D2 wavelengths (and expandable to other alkalis) using second harmonic generation (SHG). Unlike direct-diode sources, this source is immune to feedback at the Rb line eliminating the need for bulky high-power isolators in the system. In addition, the source has GHz-level frequency agility and in our experiments was found to only be limited by the agility of our RF generator. As a proof-of principle, the source was scanned through the Doppler-broadened Rb D2 absorption line. With this technology, multiple channels can be independently tuned to produce the fields needed for addressing atomic states in atom interferometers and clocks. Thus, this technology could be useful in the development cold-atom inertial sensors and gyroscopes.
Tunable continuous wave (CW) green light generation between 517 nm and 538 nm at room-temperature has been
demonstrated from a frequency-doubled broadly tunable quantum well (QW) external-cavity fiber-coupled diode laser
by use of an uncoated periodically poled potassium titanyl phosphate (PPKTP) crystal waveguide crystal. Green light at
530 nm with maximum conversion efficiency of 14.8% and output power of 12.88 mW has been generated using a
PPKTP crystal waveguide with the cross-sectional area of 3x5μm2. The possibility of tunable second harmonic
generation in the PPKTP crystal waveguides with the cross-sectional areas of 4x4μm2 and 2x6μm2 was also investigated.
Orange light with maximum conversion efficiency exceeding 10% and CW output power of 12.04 mW, 10.45 mW and 6.24 mW has been generated at 606, 608, and 611 nm, respectively, from a frequency-doubled InAs/GaAs quantum-dot external-cavity diode laser by use of a periodically-poled KTP waveguides with different cross-sectional areas. The wider waveguide with the cross-sectional area of 4×4 μm2 demonstrated better results in comparison with the narrower waveguides (3×5 μm2 and 2×6 μm2) which corresponded to lower coupling efficiency. Additional tuning of second harmonic light (between 606 and 614 nm) with similar conversion efficiency was possible by changing the crystal temperature.
We demonstrate a compact all-room-temperature picosecond laser source broadly tunable in the visible spectral region between 600 nm and 627 nm. The tunable radiation is obtained by frequency-doubling of a tunable quantum-dot external-cavity mode-locked laser in a periodically-poled KTP multimode waveguide. In this case, utilization of a significant difference in the effective refractive indices of the high- and low-order modes enables to match the period of poling in a very broad wavelength range. The maximum achieved second harmonic output peak power is 3.25 mW at 613 nm for 71.43 mW of launched pump peak power at 1226 nm, resulting in conversion efficiency of 4.55%.
Quasi-phase matched (QPM) frequency conversion in ion exchanged potassium titanyl phosphate (KTP) waveguides can
be used for highly efficient single pass conversion of low power cw and quasi-cw lasers. Applications include frequency
doubling diode lasers for display and biomedical, pulsed sources for fluorescence and remote sensing, and recently KTP
waveguides have been used to generate photon pairs using both Type I and II down conversion for quantum information
science and technology (QUIST) applications.
In this paper, we will describe a nondestructive, all optical technique that can be used to assess the quality and modal
index of the ion exchanged waveguide before periodic poling. The structure of the waveguide is interrogated utilizing
Type II sum frequency generation (SFG) and is enabled by the fact that the ion exchange process results in waveguides
that can support both TE and TM optical modes. The results of this technique can be used to determine the uniformity of
the created waveguide and are used to determine the necessary period for a desired poling result. Furthermore, this
technique can be utilized to provide an in situ assessment of the poling for any QPM period without needing the laser
sources for the particular frequency conversion interaction. Experimental results will be reviewed.
We describe a robust heralded single photon source based on parametric down conversion
of CW 532-nm light in a periodically polled KTP waveguide. Low required pump power (sub-mW),
reasonable operational temperature (43oC), high heralding efficiency (60%), and narrow spectral
width of the heralded photons (sub-nm) make it an ideal light source for long-distance quantum
communications.
Gain-guiding in an optical amplifier can have a significant effect on the quantum noise properties of the amplified signal. It has been demonstrated, both theoretically and experimentally, that gain-guiding in a steady state Raman amplifier can lead to excess noise in the output signal. Experiments using a Raman amplifier operating in the extreme transient regime also indicate that gain-guiding can have a significant effect on the output Stokes field. In this paper, a theoretical description of transient stimulated Raman scattering in a focused gain geometry is developed. The theory accounts for diffraction, gain-guiding, and quantum initiation.
KEYWORDS: Scattering, Diffusion, Light scattering, Imaging systems, Point spread functions, Raman scattering, Anisotropy, Sensors, Optical resolution, Signal to noise ratio
We measured the time-dependent optical point-spread-function of light which has traversed a turbid, multiply scattering medium. We used a coherently amplified raman polarization (CARP)-gate system which had 250 femtosecond temporal and submillimeter spatial resolution. We find that resolutions better than the theoretically predicted diffusion limited value are achievable for samples longer than 90 scattering lengths when the anisotropy parameter g is greater than 0.995. Experimental results can be fit adequately with a model based on the isotropic-scattering solution to the transport equation in an infinite, turbid solid, characterized by a rescaled scattering length lr.
We describe a class of nonlinear optical field cross-correlation processes capable of producing a high contrast subpicosecond optical gate with long broadband laser pulses. Two of the techniques, coherent anti-Stokes Raman scattering and coherently amplified Raman polarization gating, were used to produce an image of an object hidden behind a strong scattering media. We also demonstrate the capability of three-dimensional imaging using optical gating with the reflected light. The temporal resolution of these techniques is on the order of the inverse bandwidth of the laser.
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