We report on the design, development, and testing of the high-power Laser Transmitter Assembly (LTA) supporting the Deep Space Optical Communications (DSOC) demonstration hosted on the Psyche Discovery class mission, due to launch in 2022. The DSOC project, under development by NASA’s Jet Propulsion Laboratory, will test space-to-ground high-bandwidth laser communications while en route to the Psyche-16 asteroid in the main asteroid belt, in what will be the longest range high rate optical communications link in history. The LTA is based on a master-oscillator power-amplifier optical architecture, using highly-efficient cladding-pumped amplification. The transmitter is designed to deliver average optical output powers <4 W at 1550 nm for low power consumption data links at <100 Mbps. The output signal operates across multiple pulse-position modulation (PPM) orders and pulse-widths to optimize the space-to-ground link. The architecture is designed for high-reliability and radiation hardness, and features hardware interlocks and secondary signal/pumping paths to reduce single points of failure. We also detail the effective management of optical nonlinearities which could damage the LTA or impact the communications link. These include the suppression of stimulated Brillouin scattering, self-phase modulation, and pulseto- pulse energy variation (PEV), which arises from the gain dynamics of the power amplifier, and will manifest when the LTA is configured for large pulse energies and long inter-pulse delays. The LTA also incorporates hardware and software controls to enable autonomous operation, including closed-loop control of intra-stage and output power levels, modulator bias control, and detailed reporting of LTA status through telemetry.
The use of optical frequency combs (OFCs) for multi-heterodyne spectroscopy has enabled unprecedented measurement capabilities for spectroscopic sensing, including rapid acquisition speed, high resolution and high sensitivity<sup>1,2</sup>. Development of field deployable OFC sources that are widely tunable in the important chemical fingerprint region in the long-wavelength infrared (LWIR) is a major research challenge. In this paper, we report our recent efforts towards developing LWIR comb source for SILMARILS (Standoff ILluminator for Measuring Absorbance and Reflectance Infrared Light Signatures) program by IARPA. LGS has developed fiber optic sources producing spectral combs in the SWIR (1.52 to 1.56 μm and 1.7 to 2.0 μm) and in the LWIR (7.7 to 12.1 μm) regions. The spectral combs in the LWIR are generated by difference-frequency mixing one OFC centered around 1.54 μm with another OFC, whose center wavelength is tunable between 1.7 and 2.0 μm, in a nonlinear optical crystal. Average power of the generated LWIR is 1.2-12 mW and its instantaneous spectral breadth of the combs is > 80 cm<sup>-1</sup>, sufficiently broad to cover multiple molecular absorption peaks. We demonstrate standoff sensing of chemical targets having concentration as low as 12 μg/cm<sup>2</sup> by measuring LWIR transflectance spectra using the comb source.
Semiconductor optical amplifiers are important for wide range of applications in optical networks, optical tomography
and optical logic systems. For many of these applications particularly for optical networks and optical logic, high speed
performance of the SOA is important. All optical Boolean operations such as XOR, OR, AND and NOR has been
demonstrated using SOA based Mach-Zhender interferometers (SOA-MZI). A rate equation model for SOA-MZI has
been developed. The model has been used to analyze the Set-Reset (S-R) latch, the gated S-R latch and the D-Flip-Flop
devices. The modeling results suggest that the Flip-Flop circuits should work at high speeds.
All optical XOR, AND, OR, and, NOR functionality has been demonstrated experimentally using
semiconductor optical amplifier (SOA) based devices at 40 Gb/s, 80 Gb/s. The performance of
the optical logic operations has been analyzed by solving the rate equation of the SOA
numerically. The high-speed operation is limited by the gain and phase recovery times in the
SOA. In order to solve these limitations, a differential scheme for XOR operation has been
experimentally investigated. This scheme is potentially capable of XOR operation to > 100 Gb/s.
All-optical XOR operation has been demonstrated using a semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI) and delayed interferometer (DI) at 80 Gb/s. The DI is based on a polarization maintaining loop mirror (PML). The results show using the PML-DI to perform differential scheme can improve the pulse quality of the XOR result.
All optical Boolean logic functionality has been demonstrated experimentally using integrated semiconductor optical amplifier (SOA) based interferometry at 40 Gb/s. The demonstrated functions are XOR, AND, and OR. The performance of the operations has been analyzed by solving the rate equation of the SOA numerically. The high-speed operation is limited by the carrier lifetime in the SOA. In order to solve the limitations imposed by carrier lifetime, a differential scheme for the XOR operation has been experimentally investigated.
All optical XOR, AND, and, OR functionality has been demonstrated experimentally using semiconductor optical amplifier (SOA) based devices at 40 Gb/s, 80 Gb/s. The performance of the optical logic operations has been analyzed by solving the rate equation of the SOA numerically. The high-speed operation is limited by the gain and phase recovery times in the SOA. In order to solve these limitations, a differential scheme for XOR operation has been experimentally investigated. This scheme is potentially capable of XOR operation to > 100 Gb/s.
All-optical OR operation has been demonstrated using a semiconductor optical amplifier (SOA) and delayed interferometer (DI) at 20 Gb/s and 40 Gb/s. The DI is based on a polarization maintaining loop mirror. Q-factor of the operation is discussed through the numerical simulations. The results show the OR gate operation rate is limited by the carrier lifetime and the input pulse energy.
All optical XOR functionality has been demonstrated experimentally using an integrated SOA-based Mach-Zehnder interferometer (SOA-MZI) at 20 Gb/s. The performance of the XOR results has been analyzed by solving the rate equation of the SOA numerically. The high-speed operation is limited by the carrier lifetime in the SOA. In order to solve the limitations imposed by carrier lifetime, a differential scheme for XOR operation has been experimentally investigated. This scheme is potentially capable of XOR operation to > 100 Gb/s.
Fiber optic based analog and/or digital CATV systems experience composite second order distortion (CSO) caused by the interaction between the gain tilt of the doped fiber amplifier and the laser chirp due to modulation. The gain tilt for an analog/digital transmission system using a high power Er-Yb co-doped fiber amplifier has been experimentally measured and its contribution to the CSO of the transmission system is evaluated. The results are in good agreement when compared with the direct measurement of the CSO of the system with and without the amplifier. The dependence of the gain tilt on the input light modulation frequency and the input light wavelength is also investigated.
In this paper, we present the results of a preliminary investigation on the reliability of high power optical diodes. Commercially available 970 nm optical diodes were subjected to various levels of stress, including: operating current, optical power and operating temperature. Optical diodes that failed during testing were subsequently analyzed using a variety of techniques, including: optical microscopy, scanning electron microscopy, eletroluminescence, and near-field profiling. It has been observed that the major cause of optical failure can be attributed to damage on the emitting facet of the optical diodes. Preliminary evidence suggests that facet damage is a result of catastrophic optical damage.
The effects of gamma radiation on rare-earth doped optical fibers have been investigated over the range of 0.01 to 145 kilorads(Si) per hour to total doses exceeding 100 kilorads(Si). The effects of 3 to 4 MeV protons have also been investigated. The level of radiation induced damage has been found to be strongly dependent on radiation dose rate and fiber composition. The existence of dose rate dependence is explained by the process of simultaneous creation of color center defects and annihilation via thermal annealing. Through the use of a suitable kinetic analysis technique, we have determined appropriate rate constants for this process and have developed an empirical model based on our experimental results. In addition to these results, we present the effects of gamma radiation on the performance of operational high power erbium-ytterbium optical amplifiers.