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In the present report, requirements and design of a prototype PPM receiver being designed for development over the next year will be elaborated.
We present new codes and modulation formats for the deep space optical channel. By taking maximum avdvantage of inherent physical constraints on the communications link, these codes and modulation formats substantially close the large gap between state of the art systems and the Shannon limit.
Due to its simplicity and robustness against wavefront distortion, pulse position modulation (PPM) with photon counting detector has been seriously considered for long-haul optical wireless systems. This paper evaluates the dual-pulse case and compares it with the conventional single-pulse case. Analytical expressions for symbol error rate and bit error rate are first derived and numerically evaluated, for the strong, negative-exponential turbulent atmosphere; and bandwidth efficiency and throughput are subsequently assessed. It is shown that, under a set of practical constraints including pulse width and pulse repetition frequency (PRF), dual-pulse PPM enables a better channel utilization and hence a higher throughput than it single-pulse counterpart. This result is new and different from the previous idealistic studies that showed multi-pulse PPM provided no essential information-theoretic gains than single-pulse PPM.
A technique which can provide frequency doubling, with high efficiency, while cavity dumping a laser for pulse position M-ary modulation while being used for an optical communication link is discussed. This approach uses a secondary cavity that provides feedback of the undoubled fundamental light, which is normally lost, into the primary cavity to be recirculated and frequency doubled. Specific operations of the electrooptic modulator and frequency-doubling crystal are described along with the overall modulation scheme and experimental setup.
An all-optical micro motor with a rotor driven by a traveling wave of surface deformation of a stator being in contact with the rotor is being studied. Instead of an ultrasonic wave produced by an electrically driven piezoelectric actuator as in ultrasonic motors, the wave is a result of a photo induced surface deformation of a photosensitive material produced by a traveling holographic grating. Two phase modulated coherent optical beams generate the grating. Several types of photosensitive materials are studied such as photorefractive crystals, photosensitive piezoelectric ceramics, and side-chain liquid crystalline polyesters. In order to be considered as a possible candidate for micro motors, the material should exhibit surface deformation produced by moving grating of the order of 10 micron. Deformations produced by static holographic gratings are studied in photorefractive crystals of LiNbO3 using high vertical resolution surface profilometer Dektak 3 and surface interferometer WYKO. An experimental set-up with moving grating has been developed. The set-up uses a two-beam interferometry configuration with one beam being reflected by a thin mirror mounted on a loud speaker. A ramp voltage signal generator drives the speaker. Changing voltage, polarity, and frequency of the signal can easily generate vibrating gratings or moving gratings in both directions. A vibrating grating has been applied to a photorefractive crystal of BSO controlled by an external electric field of the order of 104 V/cm. We have additionally studied effects of moving grating interaction with light absorbing fluids such as solutions of 2,9,16,23-Tetrakis(phenylthio)-29H, 31 Hphthalocyanine in chlorobenzene in capillary tubes. The purpose of using a liquid is to show that the moving gratings can force a liquid to shift. The interaction of a single low power focused laser beam at 633 nm with such fluid produced an intensive circular motion, which also might be applied to all-optical micro motors or actuators.
Here, we report the generation and shaping of ∼20 femtosecond pulses in the deep ultraviolet (DUV). Our approach combines spectral broadening in a stretched hollow-core fiber with compression and shaping via an acousto-optic modulator-based pulse shaper. The pulse shaper allows for automatic compression, useful for in-air delivery of pulses to two-dimensional (2D) spectroscopy and other time-resolved experiments. Unlike previous DUV pulse generation schemes that lack phase stability, our method enables programmable generation of phase-locked pulse-pairs with attosecond-level stability. We demonstrate pulse characterization via self-diffraction frequency-resolved optical gating and dispersion scan methods in the DUV and validate performance through a pump-probe experiment resolving electronic dynamics on attosecond timescales.
The main task of this paper is to identify a number of physical problems that must be successfully addressed to achieve stabilized laser linewidths well below 1 Hz. After presentation of the basic stability characteristics of available laser sources, it is shown that if any of these lasers were optimally locked to a high-finesse Fabry-Perot cavity it would be theoretically possible to obtain a laser linewidth in the millihertz domain. Problems of optical feedback, modulation waveform errors, mechanical support and isolation of the reference cavity, thermal stabilization of the environment, etc. are considered, and interim solutions are discussed. Experimentally, locking accuracy to successive cavity orders of less than 0.00002 linewidths (+ or - 1.5 Hz) was achieved; mirror birefringence pulled the lock point approximately 10-fold more. Relative phase coherence between two independent lasers locked onto adjacent cavity orders was preserved for 8 sec, corresponding to a linewidth of each optical source of about 50 mHz.
We evaluated the radiation effects of cosmic rays on silicon Mach-Zehnder Modulator loaded on International Space Station. Permanent changes of refractive index (10 -3 ) and carrier lifetime reduction have been observed after 6 months’ radiation.
The MFOX family of standardized fiber-optic communications modules developed for the USAF is described. The MFOX transceivers are designed to operate at wavelength 1.3 microns under severe environmental conditions; their compact subhybrid construction and flexible electronic interfaces permit multiple applications and mountings. The family comprises five performance levels: (1) 1-10,000-kb/s digital and (2) 0.2-50 Mb/s digital using LEDs, (3) up to 10-MHz-bandwidth analog using modulator/demodulators with level (2) transceivers, (4) 0.2-400-Mb/s digital and 70-MHz IF analog using multimode lasers, and (5) 200-1000-Mb/s digital using a single-mode laser; levels (4) and (5) are currently in the experimental stage. Drawings, diagrams, graphs, and tables of physical and optical specifications are provided.
An analysis of directly and externally modulated fiberoptic links is presented. The theoretical analysis is based on the signal flow diagram of the interface circuits to the laser diode, Mach-Zehnder electro-optic modulator, and p-i-n photodiode. System parameters such as gain, noise figure, two-tone intermodulation distortion, and spurious free and compression dynamic range are expressed as a function of frequency and operating point of the laser and external modulator. Two directly and externally modulated fiber-optic links were designed and fabricated to verify the analytical models. The direct modulation FO link was developed at the Ku-band (11.6-12.4 GHz), whereas the external modulation link was at L-band (875-925 MHz). Spurious-free dynamic ranges of 95.8 dB-Hz exp 2/3 and 113 dB-Hz exp 2/3, respectively, were achieved. The predictions based on the analytical models match the measured results.
This presentation presents the testing approach and initial laboratory test results of the Adaptive Optics (AO) Subassembly (AOS) for the Low-Cost Optical Terminal (LCOT), a low-cost and flexible optical communications ground terminal. Leveraging commercial components and subassemblies wherever possible, LCOT is being developed by the NASA Goddard Space Flight Center (GSFC) Advanced Communications Capabilities for Exploration and Science Systems (ACCESS) project. An economical ground terminal allows NASA to create a global optical terminal network and enables the expansion of direct-to-Earth (DTE) optical communications. Located at the Goddard Geophysical and Astronomical Observatory (GGAO), LCOT is in the development phase and will receive first light during initial testing beginning in 2023. This new optical terminal includes a 700 mm Ritchey-Chretien commercial telescope, able to track Low Earth Orbit (LEO) spacecraft, receive instruments specified from 1500 - 1600 nm, and an uplink transmit optical system. Demodulation of optical coherent modulation formats requires downlink signal coupling into single-mode fiber. Due to atmospheric turbulence, signals experience wavefront distortions creating speckle patterns larger than the fiber core and high jitter requiring precise beam steering. AO is necessary to correct atmospheric turbulence effects and allow efficient coupling of received signals. In 2020, GSFC contracted with General Atomics to provide the LCOT AO system. This system has been delivered to GSFC in September 2021 and has been tested in laboratory to evaluate performance. This paper describes the laboratory testing approach, turbulence phase plate design, test results, and the AO field testing plan when installed on the LCOT telescope.
The Focusing Optics X-ray Solar Imager 4 (FOXSI-4) is a heliophysics sounding rocket experiment that is currently in its fourth launch campaign. The payload is comprised of seven x-ray telescopes, which each consist of a 2 m focal length grazing incidence mirror module that focuses x-rays onto an imaging detector. For this fourth flight, Marshall Space Flight Center (MSFC) designed, built, and tested three new high-angular-resolution mirror module assemblies (MMAs). This paper describes the design and assembly of the FOXSI-4 MMAs.
The development of semiconducting conjugated polymers for photoredox catalysis holds great promise for sustainable utilization of solar energy. In this work, a new family of porous methylated triazine‐based linear conjugated polymers is reported that enable efficient photoreduction of carbon dioxide (CO 2 ) with water (H 2 O) vapor, in the absence of any additional photosensitizer, sacrificial agents or cocatalysts. It is demonstrated that the key lies in the generation of methylated triazine linkages through a facile condensation reaction between benzamidine and acetic anhydride, which impedes the formation of conventional triazine‐based frameworks. It is also shown that regulating conjugated linear backbones with different lengths of electron‐donated benzyl units provides a facile means to modulate their optical properties and the exciton dissociation, thereby affording more long‐lived photogenerated charge carriers and boosting charge separation and transfer. A high‐performance carbon monoxide (CO) production rate of 218.9 µmol g −1 h −1 is achieved with ≈ 100% CO selectivity, which is accompanied by exceptional H 2 O oxidation to oxygen (O 2 ). It anticipates this new study will advance synthetic approaches toward polymeric semiconductors and facilitate new possibilities for triazine‐based conjugated polymers with promising potential in artificial photocatalysis.
The contradiction between high transmittance and favorable conductivity poses a great challenge in developing effective cathode interlayer (CIL) materials with sufficient thickness tolerance, which hinders the further advancement of organic solar cells (OSCs). Herein, a completely new class of alcohol processable polyimide-ionene hybrids (PIIHs) is proposed by melding pyromellitic diimide (PMD) subunits into imidazolium-based ionenes backbone covalently. These PIIHs, named PMD-DI and PMD-PD, boast high transparency, suitable energy levels, and decent conductivity. A higher PMD content endows PMD-PD with improved work function tunability, electrical properties, and crystallinity, enabling PMD-PD as CIL material with excellent thickness-insensitive characteristics, while simultaneously improving device stability significantly. Furthermore, PMD-PD also exhibits good compatibility with various electrodes and active layers, offering solar cell efficiencies of up to 19.91% and 19.29% with Ag and Cu cathodes, respectively. More importantly, the application of PMD-PD can improve the performance of semi-transparent OSCs without losing transmittance, thereby drastically enhancing the light utilization efficiency to 4.04% with an ultrathin, low-cost Cu cathode, that competes with leading optical modulation-free semitransparent OSCs with expensive Ag cathodes. This work opens a pathway to realize transparent and conductive interlayers by strategic molecular design, leading to highly efficient, stable, and cost-effective OSCs suitable for diverse applications.
The desorption of conventional ligands from the surface of halide perovskite nanocrystals (NCs) often causes their structural instability and the deterioration of the optoelectronic properties. To address this challenge, we present an approach of using a bidentate Lewis base ligand, namely, 1,4-bis(diphenylphosphino)butane (DBPP), for the synthesis of CsPbBr 3 NCs. The phosphine group of DBPP has a strong interaction with PbBr 2 precursor, forming a highly crystalline intermediate complex during the reaction. In the presence of oleic acid, the uncoordinated phosphine group of DBPP is converted into the phosphonium cation, which strongly binds with the surface bromide of the formed CsPbBr 3 NCs through hydrogen bonding. Density functional theory calculations suggest that DBPP can strongly bind to the undercoordinated lead and surface bromide ions of CsPbBr 3 NCs through its unprotonated and protonated phosphine groups, respectively. The robust binding of DBPP with the surface of perovskite NCs helps to preserve their structural integrity under various environmental stresses. Moreover, the electron density and energy levels are regulated in DBPP-capped CsPbBr 3 NCs via the efficient transfer of electrons from the ligands to the NCs, resulting in their improved photocatalytic CO 2 reduction performance. Furthermore, our study highlights the potential of using bidentate ligands to stabilize the surface of perovskite NCs and modulate their optical and electronic properties.
Single crystals and polycrystalline powders of rare earth mixed chalcogenide iodides La 3 Si 2 Se 1.21 S 6.79 I, Ce 3 Si 2 Se 1.39 S 6.61 I, Pr 3 Si 2 Se 1.22 S 6.78 I, and Nd 3 Si 2 Se 1.18 S 6.82 I were prepared using the reactive flux-assisted boron–chalcogen mixture (BCM) method at 850 °C. All compounds crystallized in the monoclinic crystal system, space group C2/c (space group number 15). The series adopts the La 3 Si 2 O 8 Cl structure type, containing isolated SiQ 4 tetrahedra connected by REQ 8 (RE = La, Ce, Pr and Nd) polyhedra; this arrangement creates tunnels that are filled by I atoms. The partial substitution of S by Se was carried out to modulate the optical properties. Phase pure samples and uniform solid solutions were obtained for all compositions as determined using powder X-ray diffraction patterns. Polycrystalline powders were used for physical property measurements, including magnetic susceptibility and UV-Vis diffuse reflectance. The solid-state UV-Vis data for the polycrystalline La 3 Si 2 Se 1.21 S 6.79 I, Ce 3 Si 2 Se 1.39 S 6.61 I, and Pr 3 Si 2 Se 1.22 S 6.78 I samples revealed band gaps of E g = 2.5(1), 2.2(1), and 2.3(1) eV, typical of semiconductors. Magnetic measurements indicated that Ce 3 Si 2 Se 1.39 S 6.61 I and Nd 3 Si 2 Se 1.18 S 6.82 I exhibit paramagnetic behavior with slightly negative Weiss constants θ = −25 and −38. The photoluminescence spectrum of Ce 3 Si 2 Se 1.39 S 6.61 I exhibits a broad emission band around ∼493 nm.
Electrochemical intercalation of cations within two-dimensional transition metal dichalcogenides presents a promising route for tailoring their optoelectronic properties. We have now succeeded in modulating the optical properties of MoS2 thin films through electrochemical intercalation of quaternary ammonium cations. The spectroelectrochemical experiments conducted with varying sizes of the intercalant revealed the size-dependent stability of the intercalated MoS2 nanosheets. The observed absorption change of the exciton bands is reversible and arises from the storage of electrons in MoS2 nanosheets and the subsequent weakening of interlayer van der Waals interactions following cation intercalation. This structural change is evidenced by the emergence of A*1g out-of-plane Raman mode. Additionally, the photoelectron spectroscopy reveals the emergence of a lower binding energy component of Mo 3d and the shift in Fermi level to higher energies, confirming the presence of stored electrons in cation intercalated-MoS2. The underlying mechanism of intercalation-induced property modifications in MoS2 discussed in the present study is useful in developing strategies for energy conversion devices.
Frequency-bin encoding is massively parallelizable and robust for optical fiber transmission. When coupled with an additional degree of freedom (DoF), the expansion of the Hilbert space allows for deterministic controlled operations between two DoFs within a single photon. Such capabilities, when combined with photonic hyperentanglement, are of great value for quantum communication protocols, including dense coding and single-copy entanglement distillation. In this talk, we present an all-fiber-coupled, ultrabroadband polarization–frequency hyperentangled source and conduct comprehensive quantum state tomography across multiple dense wavelength division multiplexing channels spanning the optical C+L-band (1530–1625 nm). In addition, we design and implement a high-fidelity controlled-NOT (cnot) operation between polarization and frequency DoFs by exploiting electro-optic phase modulation within a fiber Sagnac loop. Collectively, our hyperentangled source and two-qubit gate should unlock new opportunities for harnessing polarization–frequency resources in established telecommunication fiber networks for future quantum applications.