KEYWORDS: Laser communications, Receivers, Telecommunications, Acquisition tracking and pointing, Single mode fibers, Signal to noise ratio, Optical amplifiers, Mirrors, Free space optics, Free space
This work highlights 10G uncoded OOK communications signals in a lab-based over-the-air demonstration through one of Fibertek’s terminals designed for 1G LEO direct to earth links. Our demonstration not only proves that the 1G terminals are capable of higher data rates without penalty but also validate the pointing stability of the system. The bit error rate tests resulted in a less than 3-dB power penalty compared to back-to-back measurements at 1e-9 which is in line with the theoretical half-angle divergence-to-jitter ratio (w0/σ) of around 7. This ratio meets the design goals for the terminal. We show that the jitter performance of the terminal meets the design goals of providing optimal performance for error free requirements of 1e-9 and demonstrate that through both direct measurement of the jitter on a PSD and the performance impact on a communications signal.
Fibertek has developed a space qualifiable 50W 8Ch. WDM Amplifier prototype that is designed to meet all the environmental and optical requirements of a DSOC mission. The deliverd amplifier is optimized for efficiency and athermal performance achieving 22% e-o efficiency. The high TRL 1.5-μm high TL fiber amplifier supports up to 6W/channel, with >128-ary pulse-position-modulation (PPM) format, and with 25-nm gain-flat bandwidth. Output electro-optic characteristics, the System Reliability Analysis, Mechanical Thermal analysis and Mechanical Structural and Vibration analysis of the high TRL delivered laser prototype are presented. A power efficient TDM based FWM mitigation technique that improves PEV performance of Tx, is demonstrated.
51W average power, 7 Channel WDM Fiber Laser Transmitter with 25nm flat gain has been demonstrated for optical space communication applications. Power Amplifier supports >10kW/channel SBS limited peak power and achieves o-o efficiency 44%. Pulse energy variation (PEV) due to gain dynamics and four wave mixing of the PPM tx output is characterized. Significant improvement in PEV with wavelength dependent pre-pulse shaping is demonstrated. A high reliability 50W 8 WDM channel amplifier design is described. The amplifier will be housed in a high TRL small SWAP space laser package with dimensions 10.6x13.8x 5.3” and weighs 28.7 lbs
This paper describes progress toward a space -based 51 W average power amplifier for deep space PPM and Earth GEO links. We demonstrated a broadband WDM amplification at 50W with flat gain across a 25 nm bandwidth. Similarly, for 5 W amplifier we demonstrated a flat gain across a 32 nm bandwidth. These amplifiers demonstrate the feasibility for multi-channel space optical communications links. To increase the bandwidth GEO links to multi-Tbps and deep space links to > Gbps. The laser supports kW/channel SBS limited peak power for PPM and achieves an optical-to-optical efficiency of > 40%. In a separate but related effort for a deep space uplink beacon, we achieved 500 W average power, 2.6 kW peak power PPM (2,2) for a 1 μm uplink transmitter. Reliable SBS free operation is achieved with phase modulation resulting in 26 GHz transmitter linewidth. Uplink transmitter is optimized for 65 usec (pulsewidth) slot size—achieving fastest possible rise/fall times (<10 usec) and pulse uniformity.
We describe Fibertek’s progress toward commercializing space laser communications and new features of our secondgeneration compact laser communication terminal (LCT). The LCT design is modular, flexible and can accommodate a variety of waveforms and data formats. Fibertek has a unit deployed in space for initial testing followed by additional units for more broad-based market applications. Our first-generation optical telescope assembly was originally designed for NASA Deep Space CubeSat laser communications. It was customized as a complete commercial LEO LCT system which is 2U in size, 2 kg in mass, and provides Gbps data rates. The optical transceiver has a shared transmit/receive optical path that uses a laser beacon to ensure high pointing accuracy, active control of the pointing stability, and ensures a strong optical signal-to-noise ratio (SNR) during link operation. The terminal has been manufactured and tested, providing high accuracy pointing and low jitter. Our second generation LCT system features bidirectional operation and support for an eyesafe beacon for uplink applications. Bi-directional operation is attractive for inter-satellite links (ISL), uplinks of data, pointing acquisition and tracking (PAT), position, navigation and timing (PNT), and for telemetry, tracking, and command (TTandC). The eyesafe uplink beacon makes it easier to get FCC authorization for operation. The LCT includes a 64 mm telescope and a 1.5-μm fiber-amplifier with >2 W optical power that enables future updates to allow operation up to GEO orbit with the addition of SCPPM and 10-100 Gbit/sec.
Fibertek has designed and is building a spaceflight (TRL 5-6) high-efficiency, high reliability (97.2% for 5-year mission) 100 W average, 1940 nm thulium doped fiber laser (TDFL) meeting all requirements for a NASA Earth Science spaceflight 2 μm Ho:YLF pump laser. These include polarization extinction ratio <16dB, diffraction limited beam quality, narrow linewidth (0.35nm) and >50% optical to optical efficiency. High reliability laser package, optimized for space environment and SWAP has size 10.6”x13.8”x4.4”and weight 30lbs. A summary of laser package design is presented, including structural and thermal analysis. Preliminary environmental testing results of the space laser are also presented. A spaceflight 100 W PM Tm laser provides a path to space for a pulsed, Q-switched 2 μm Ho:YLF laser with ~80 mJ/pulse at 100-200 Hz.
A cladding-pumped, LMA ErYb fiber-based, amplifier is presented for use in a LIDAR transmitter for remote sensing of atmospheric CO2 from space. The amplifier is optimized for high peak power, high efficiency, and narrow linewidth operation at 1572.3nm. Using highly reliable COTS components, the amplifier achieves 0.5kW peak power (440uJ pulse energy), 3.3W average power with transform limited (TL) linewidth and M2<1.3. The power amplifier supports a 30% increase in pulse energy when linewidth is increased to 100MHz. A preliminary conductively cooled laser optical module (LOM) concept has size 9x10x1.25 in (113 in3) and estimated weight of 7.2lb (3.2 kg). Energy scaling with pulse width up to 645uJ, 1.5usec is demonstrated. A novel doubleclad ErYb LMA fiber (30/250um) with high pump absorption (6 dB/m at 915nm) was designed, fabricated, and characterized for power scaling. The upgraded power amplifier achieves 0.8kW peak power (720uJ pulse energy) 5.4W average power with TL linewidth and M2<1.5.
We demonstrate highly efficient, 1.5um-fiber-amplifier, optimized for athermal and reliable operation. High efficient operation is sustained for a wide range of pulse-position-modulation (16 to 128-ary PPM) formats with pulse widths varying from 8nsec to 0.5nsec. System achieves 6W average and ~1kW peak power with 8nsec pulses and 3Ghz linewidth. Stimulated Brillion scattering is managed by use of LMA fiber in final stage and precise linewidth control while maintaining the required diffraction limited, and (PER>20dB) polarized output. System maintains performance for ambient temperatures 10-50°C.
In the management of caverned fuel oil inventory, a strict rule of fire control has always been the first priority due to the special conditions. It is always a challenge to perform automatic measurement by means of conventional electrical devices for inspecting oil tank level there. Introduced in this paper is a fiber optic gauging technique with millimeter precision for automatic measurement in caverned tanks. Instead of using any electrical device, it uses optical encoders and optical fibers for converting and transmitting signals. Its principle, specifications, installation and applications are discussed in detail. Theoretical analysis of the factors affecting its accuracy, stability, and special procedures adopted in the installation of the fiber optic gauge are also discussed.
Based on a non-sequential raytrace simulation, a previously developed tubular optical waveguide probe for magnetic- focusing immunosensors has been redesigned and tested. The design features a tubular waveguide tapered at both ends with a tapered magnet embedded inside of the waveguide. For reducing background, the excitation light is directly projected into the sample solution via a fiber against the cuvette wall adjacent to the waveguide. The fluorescent signal is collected by the probe and is coupled into a transmission fiber at the distal end of probe. Simulated antigen samples (paramagnetic microspheres of 5-micron diameter with immobilized antibodies that are labeled with Cy5 dye) have been prepared for testing magnetic signal enhancement and fluorescent signal collection. Typical results show that the sensitivity of the tubular probe is one order of magnitude higher than that of a similar dual- fiber probe. With the improved excitation and transmission scheme, the new tubular probe reduces background noise to one-third that of a previously reported tubular probe and is less sensitive to the interference of ambient light.
A tubular optical probe for fluorescent immunosensors based on magnetic focusing of paramagnetic microspheres has been developed. The optical probe features a tubular optical waveguide tapered at both ends with a tapered magnet embedded inside the waveguide. Laser light is delivered to a dye-labeled spot in the inner surface of a cuvette and the fluorescent signal is guided to an optical detection system. A 3D computer model of this system has been created and its optical properties evaluated with a commercially available non-sequential ray-trace program. Up to 10,000 rays are traced from the laser to the cuvette and again from the fluorescent source to the detector. Results lead to the optimization of the component properties.
A novel fluorescence immunosensor using a tapered tubular optical waveguide probe for analyte detection has been developed based on magnetic focusing of paramagnetic microspheres. The new design features a tubular optical waveguide tapered at both ends with a tapered magnet embedded inside of the waveguide. The excitation light is injected from the middle part of the tubular waveguide and is guided to the front end where it illuminates paramagnetic particles attracted by the magnet. The associated fluorescent signal is collected by the optical probe and is guided to the distal end, where it is connected to the optical detection system. The waveguide thus serves multiple purposes: the front end of the waveguide serves as the optical probe while the rear end serves as the connector to the signal transmission fiber; the waveguide body serves as a holder for the magnet, a directional coupler for the excitation and a high split-ratio coupler for the fluorescent signal.
From 1988 through 1992 Salmonellosis accounted for 27% of the total reported foodborne disease outbreaks and 57% of the outbreaks in which the pathogen was identified. The prevalence of Salmonellosis and the new requirements to monitor the organism as a marker in pathogen reduction programs will drive the need for rapid, on-site testing. A compact fiber optic fluorometer using a red diode laser as an excitation source and fiber probes for analyte detection has been constructed and used to measure Salmonella. The organisms were isolated with anti-Salmonella magnetic beads and were labeled with a secondary antibody conjugated to a red fluorescent dye. The response of the system was proportional to the concentration of Salmonella typhimurium from 3.2 X 105 colony forming units (CFU)/ml to 1.6 X 107 CFU/ml. The system was developed to utilize a fiber-optic magnetic focusing problem that attracted the magnetic microspheres to the surface of a sample chamber directly in front of the excitation and emission fibers. The signal obtained from a homogenous suspension of fluorescent magnetic microspheres was 9 to 10 picowatts. After focusing, the signal from the fluorescent labeled magnetic microspheres increased to 200 picowatts, approximately 20 times greater than the homogeneous suspension. The magnetic focusing assay detected 1.59 X 105 colony forming units/ml of Salmonella typhimurium cultured in growth media. The process of magnetic focusing in front of the fibers has the potential to reduce the background fluorescence from unbound secondary antibodies, eliminating several rinsing steps, resulting in a simple rapid assay.
A fiber optic monitoring technique for the thickness of furnace wall is demonstrated where conventional monitoring techniques failed because of harsh environments. Based upon OTDR technique, its working principle, structure, and installing manner are introduced. This technique can monitor the thickness wall continuously with an accuracy of 5mm which is enough for the management of operating the furnace.
Introduced in this paper is a fiber optic gauging technique with millimeter accuracy for river level measurement. It plays an important part in flood-control season. The principle of operation and structure are illustrated. In order to ensure the reliability and to keep the millimeter accuracy in 16-meter range of fluctuation, some key techniques in optic, mechanism and electronics of this gauge are discussed in detail in this paper.
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