Engineering topics

Ortiz, Gerardo G.

Publications and source records attributed to Ortiz, Gerardo G..

10 records

NASA NTRS2011

Two-Photon-Absorption Scheme for Optical Beam Tracking

A new optical beam tracking approach for free-space optical communication links using two-photon absorption (TPA) in a high-bandgap detector material was demonstrated. This tracking scheme is part of the canonical architecture described in the preceding article. TPA is used to track a long-wavelength transmit laser while direct absorption on the same sensor simultaneously tracks a shorter-wavelength beacon. The TPA responsivity was measured for silicon using a PIN photodiode at a laser beacon wavelength of 1,550 nm. As expected, the responsivity shows a linear dependence with incident power level. The responsivity slope is 4.5 x 10(exp -7) A/W2. Also, optical beam spots from the 1,550-nm laser beacon were characterized on commercial charge coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) imagers with as little as 13.7 microWatts of optical power (see figure). This new tracker technology offers an innovative solution to reduce system complexity, improve transmit/receive isolation, improve optical efficiency, improve signal-to-noise ratio (SNR), and reduce cost for free-space optical communications transceivers.

Ortiz, Gerardo G.↗

NASA NTRS2006

Exo-atmospheric telescopes for deep space optical communications

For deep space optical communications, optical telescopes located above the Earth's atmosphere would have significant performance advantages over telescopes mounted on the Earth's surface. Link outages due to could cover would be eliminated, atmospheric attenuation would be eliminated, and signal degradation due to stray light would be reduced.

orbiting optical terminal↗

NASA NTRS2006

Exo-atmospheric telescopes for Deep Space Optical Communications

For deep space optical communications, optical telescopes located above the Earth's atmosphere would have significant performance advantages over telescopes mounted on the Earth's surface. Link outages due to cloud cover would be eliminated, atmospheric attenuation would be eliminated, and signal degradation due to stray light would be reduced. A study has been conducted to compare various exo-atmospheric platforms for the Earth end of the optical link.

orbiting optical terminal↗

NASA NTRS2003

Design of an Event-Driven Random-Access-Windowing CCD-Based Camera

Commercially available cameras are not design for the combination of single frame and high-speed streaming digital video with real-time control of size and location of multiple regions-of-interest (ROI). A new control paradigm is defined to eliminate the tight coupling between the camera logic and the host controller. This functionality is achieved by defining the indivisible pixel read out operation on a per ROI basis with in-camera time keeping capability. This methodology provides a Random Access, Real-Time, Event-driven (RARE) camera for adaptive camera control and is will suited for target tracking applications requiring autonomous control of multiple ROI's. This methodology additionally provides for reduced ROI read out time and higher frame rates compared to the original architecture by avoiding external control intervention during the ROI read out process.

event driven↗

NASA NTRS2003

Design of an event-driven random-access-windowing CCD-based camera

Commercially available cameras are not designed for the combination of single frame and high-speed streaming digital video with real-time control of size and location of multiple regions-of-interest (ROI). A new control paradigm is defined to eliminate the tight coupling between the camera logic and the host controller. This functionality is achieved by defining the indivisible pixel read out operation on a per ROI basis with in-camera time keeping capability. This methodology provides a Random Access, Real-time, Event-driven (RARE) camera for adaptive camera control and is well suited for target tracking applications requiring autonomous control of multiple ROIs. This methodology additionally provides for reduced ROI read out time and higher frame rates compared to the original architecture by avoiding external control intervention during the ROI read out process.

Ortiz, Gerardo G.↗

NASA NTRS1999

Design of a 2.5 Gbps Optical Transmitter for the International Space Station

A high data rate laser transmitter assembly (LTA) has been designed as the source for an optical free-space communication link between the International Space Station and the 1-meter Optical Communication Telescope Laboratory (OCTL) to be built at the Table Mountain Facility (IMF, Wrightwood, CA). The transmitter design concept uses a fiber-based master oscillator power amplifier (MOPA) configuration with an average output power of 200 made at a 1550 nm transmit wavelength. This transmitter source is also designed to provide a signal at 980 nm to the Silicon-based focal plane array for the point-ahead beam control function. This novel integration of a 980 nm boresight signal allows the use of Silicon based imagers for the acquisition/tracking and point-ahead functions, yet permits the transmit signal to be at any wavelength outside the Silicon sensitivity. The LTA, a sub-system of the Flight Terminal, has been designed to have a selectable data rate from 155 - 2500 Mbps in discrete steps. It also incorporates a 2.5 Gbps pseudo-random bit sequence (PRBS) generator for complete link testing and diagnostics. The design emphasizes using commercial off the shelf components (COTS).

Ortiz, Gerardo G.↗

NASA NTRS1992

Cooled Low-Noise HEMT Microwave Amplifiers

Prototype cooled low-noise microwave amplifiers based on high-electron-mobility transistors (HEMT's) considered as replacements for cooled ruby masers used as low-noise receiver-front-end amplifiers in communications, radio science, radar systems, radio astronomy, and telemetry. HEMT amplifier operates at 12 K, requires less cooling power and operates at lower cost with simpler, more-reliable cooling system.

Bautista, J. Javier↗

NASA NTRS1991

Performance of a high T(sub c) superconducting ultra-low loss microwave stripline filter

Discussed here is the successful fabrication of a five-pole interdigital stripline filter made of the 93-K superconductor (Y1Ba2Cu3O(y)) coated on a silver substrate, with center frequency of 8.5 GHz and an extremely high rejection ratio of 80 dB. The lowest insertion loss measured was 0.1 dB at 12 K, with a return loss of better than 16 dB, representing a significant improvement over a similar copper filter; it is comparable to low critical temperature filters. The insertion loss appears to be limited by extrinsic factors, such as tuning mismatch and joint losses, and not by the superconducting material losses.

Bautista, J. J.↗

NASA NTRS1991

A cooled 1-2 GHz balanced HEMT amplifier

The design details and measurement results for a cooled 1-GHz-bandwidth L-band HEMT amplifier are presented. The HEMT noise parameters were measured at a physical temperature of 12 K, and a balanced configuration was adopted. This has the advantage of providing a good input match even though the amplifiers in the two arms of the balanced circuit are poorly matched. However, there are disadvantages. The loss of the input hybrid degrades the noise temperature and coupling errors in the hybrids, and differences between the amplifiers reduce the gain and result in a noise contribution from the input load. In the amplifier described, these effects degrade the noise temperature by less than 1 K. The amplifier uses commercially available packaged HEMT devices. At a physical temperature of 12 K the amplifier achieves noise temperatures between 3 and 6 K over the 1-2-GHz band. The associated gain is about 20 dB.

Padin, Stephen↗

NASA NTRS1989

32-GHz cryogenically cooled HEMT low-noise amplifiers

The cryogenic noise temperature performance of a two-stage and a three-stage 32 GHz high electron mobility transistor (HEMT) amplifier was evaluated. The amplifiers employ 0.25 micrometer conventional AlGaAs/GaAs HEMT devices, hybrid matching input and output microstrip circuits, and a cryogenically stable dc biasing network. The noise temperature measurements were performed in the frequency range of 31 to 33 GHz over a physical temperature range of 300 K down to 12 K. Across the measurement band, the amplifiers displayed a broadband response, and the noise temperature was observed to decrease by a factor of 10 in cooling from 300 to 15 K. The lowest noise temperature measured for the two-stage amplifier at 32 GHz was 35 K with an associated gain of 16.5 dB, while the three-stage amplifier measured 39 K with an associated gain of 26 dB. It was further observed that both amplifiers were insensitive to light.

Duh, K. H. George↗