Advanced Laser Based Measurements in Porous Media Combustion

We present measurements using dual-pump dual-broadband coherent anti-Stokes Raman scattering spectroscopy (DP-DBB-CARS) inside a porous media burner. This work continues our previous measurements in such combustion systems. The existing setup was significantly modified with the aim of providing improved data quality and data rate, reduction of interferences and additional species information. These changes are presented and discussed in detail. The CARS technique was expanded to a dual-pump dual-broadband CARS system which in principle enables acquisition of temperatures together with relative H2/N2- and O2/N2- species concentrations. Experimental complexity was reduced by the use of a modified spectrometer enabling the detection of both signals, vibrational and rotational CARS, with only one detection system

Single-Photon Counting Detector Scalability for High Photon Efficiency Optical Communications Links

For high photon-efficiency deep space or low power optical communications links, such as the Orion Artemis-2 Optical Communications System (O2O) project, the received optical signal is attenuated to the extent that single- photon detectors are required. For direct-detection receivers operating at 1.55 m wavelength, single-photon detectors including Geiger-mode InGaAs avalanche photon diodes (APDs), and in particular superconducting nanowire single-photon detectors (SNSPDs) offer the highest sensitivity and fastest detection speeds. However, these photon detectors exhibit a recovery time between registered input pulses, effectively reducing the detection efficiency over the recovery interval, resulting in missed photon detections, reduced count rate, and ultimately limiting the achievable data rate. A method to overcome this limitation is to divide the received optical signal into multiple detectors in parallel. Here we analyze this approach for a receiver designed to receive a high photon efficiency serially concatenated pulse position modulation (SCPPM) input waveform. From measured count rate and efficiency data using commercial SNSPDs, we apply a model from which we determine the effective detection efficiency, or blocking loss, for different input signal rates. We analyze the scalability of adding detectors in parallel for different modulation orders and background levels to achieve desired data rates. Finally we show tradeoffs between the number of detectors and the required received optical power, useful for real link design considerations

Beam Propagation Through Atmospheric Turbulence Using an Altitude-Dependent Structure Profile with Non-Uniformly Distributed Phase Screens

Modeling the effects of atmospheric turbulence on optical beam propagation is a key element in the design and analysis of free-space optical communication systems. Numerical wave optics simulations provide a particularly useful technique for understanding the degradation of the optical field in the receiver plane when the analytical theory is insufficient for characterizing the atmospheric channel. Motivated by such an application, we use a split-step method modeling the turbulence along the propagation path as a series of thin random phase screens with modified von Karman refractive index statistics using the Hufnagel-Valley turbulence profile to determine the effective structure constant for each screen. In this work, we employ a space-to-ground case study to examine the irradiance and phase statistics for both uniformly and non-uniformly spaced screens along the propagation path and compare to analytical results. We find that better agreement with the analytical theory is obtained using a non-uniform spacing with the effective structure constant for each screen chosen to minimize its contribution to the scintillation in the receiver plane. We evaluate this method as a flexible alternative to other standard layered models used in astronomical imaging applications

Beam Propagation Through Atmospheric Turbulence Using an Altitude-Dependent Structure Profile with Non-Uniformly Distributed Phase Screens

For free-space optical communication systems, numerical wave optics simulations provide a useful technique for modeling turbulence-induced beam degradation when the analytical theory is insufficient for characterizing the atmospheric channel. Motivated by such applications we use a split-step method modeling the turbulence as a series of random phase screens using the Hufnagel-Valley turbulence profile. We employ a space-to-ground case study to examine the irradiance and phase statistics for uniformly and non-uniformly located screens and find better agreement with theory using a non-uniform discretization minimizing the contribution of each screen to the total scintillation. In this poster, we summarize the method and the results of the case study including a comparison to layered models used in astronomical imaging applications

Detector Channel Combining Results from a High Photon Efficiency Optical Communications Link Test Bed

The National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) is developing a low cost, scalable, photon-counting receiver prototype for space-to-ground optical communications links. The receiver is being tested in a test bed that emulates photon-starved space-to-ground optical communication links. The receiver uses an array of single-pixel fiber-coupled superconducting nanowire single-photon detectors. The receiver is designed to receive the high photon efficiency serially concatenated pulse position modulation (SCPPM) waveform specified in the Consultative Committee for Space Data Systems (CCSDS) Optical Communications Coding and Synchronization Blue Book Standard. The optical receiver consists of an array of single-pixel superconducting nanowire detectors, analog phase shifters for channel alignment, digitizers for each detector channel, and digital processing of the received signal. An overview of the test bed and arrayed receiver system is given. Simulation and system characterization results are presented. The data rate increase of using a four-channel arrayed detector system over using one single pixel nanowire detector is characterized. Results indicate that a single-pixel detector is capable of receiving data at a rate of 40 Mbps and a four-channel arrayed detector system is capable of receiving data at a rate of 130 Mbps

Width-Increased Dual-Pump Enhanced Coherent Anti-Stokes Raman Spectroscopy (WIDECARS)

WIDECARS is a dual-pump coherent anti-Stokes Raman Spectroscopy technique that is capable of simultaneously measuring temperature and species mole fractions of N2, O2, H2, C2H4, CO, and CO2. WIDECARS is designed for measurements of all the major species (except water) in supersonic combustion flows fueled with hydrogen and hydrogen/ethylene mixtures. The two lowest rotational energy levels of hydrogen detectable by WIDECARS are H2 S(3) and H2 S(4). The detection of these lines gives the system the capability to measure temperature and species concentrations in regions of the flow containing pure hydrogen fuel at room temperature

Real Time Photon-Counting Receiver for High Photon Efficiency Optical Communications

We present a scalable design for a photon-counting ground receiver based on superconducting nanowire single photon detectors (SNSPDs) and field programmable gate array (FPGA) real-time processing for applications to space-to-ground photon starved links, such as the Orion EM-2 Optical Communication Demonstration (O2O), and future deep space or low transmitter power missions. The receiver is designed to receive a serially concatenated pulse position modulation (SCPPM) waveform, which follows the Consultative Committee for Space Data Systems (CCSDS) Optical Communications Coding and Synchronization Red Book standard. The receiver design uses multiple individually fiber coupled, 80% detection efficiency commercial SNSPDs in parallel to scale to a required data rate, and is capable of achieving data rates up to 528 Mbps. For efficient fiber coupling from the telescope to the array of parallel detectors that can be scaled both to telescope aperture size and the number of detectors, we use either a single mode fiber (SMF) photonic lantern or a few-mode fiber (FMF) photonic lantern. In this paper we give an overview of the receiver system design, the characteristics of the photonic lanterns, the performance of the SNSPDs, and system level tests. We show that 40 Mbps can be received using a single SNSPD, and discuss aspects for scaling to higher data rates

Performance and Characterization of a Modular Superconducting Nanowire Single Photon Detector System for Space-to-Earth Optical Communications Links

Space-to-ground photon-counting optical communication links supporting high data rates over large distances require enhanced ground receiver sensitivity in order to reduce the mass and power burden on the spacecraft transmitter. Superconducting nanowire single-photon detectors (SNSPDs) have been demonstrated to offer superior performance in detection efficiency, timing resolution, and count rates over semiconductor photodetectors, and are a suitable technology for high photon efficiency links. Recently photon detectors based on superconducting nanowires have become commercially available, and we have assessed the characteristics and performance of one such commercial system as a candidate for potential utilization in ground receiver designs. The SNSPD system features independent channels which can be added modularly, and we analyze the scalability of the system to support different data rates, as well as consider coupling concepts and issues as the number of channels increases

Real Time Optical Receiver Project

The goals for the Real Time Optical Receiver project are to Infuse Consultative Committee for Space Data Systems High Photon Efficiency standard into missions, such as Artemis and to provide a real time ground receiver solution (fiber device, detector, real time FPGA-based receiver) that is: (1) Scalable: data rate, atmosphere conditions, telescope aperture, etc., and (2) Uses COTS components when available and work with companies to move custom parts to COTS

Characteristics of a Broadband Dye Laser Using Pyrromethene and Rhodamine Dyes

A broadband dye laser pumped by a frequency-doubled Nd:YAG laser with a full-width half-maximum (FWHM) from 592 to 610 nm was created for the use in a dual-pump broadband CARS system called WIDECARS. The desired broadband dye laser was generated with a mixture of Pyrromethene dyes as an oscillator gain medium and a spectral selective optic in the oscillator cavity. A mixture of Rhodamine dyes were used in the amplifier dye cell. To create this laser a study was performed to characterize the spectral behavior of broadband dye lasers created with Rhodamine dyes 590, 610, and 640, Pyrromethene dyes 597 and 650 as well as mixture of these dyes