One Micrometer Integrated Transmitter for Balanced Radio-Frequency-Over- Fiber Photonic Links

We propose to develop a heterogeneously integrated optical transmitter for balanced radio-frequency (RF) photonic link applications on air platforms that incorporates a high-power Nd:Glass laser source operating near 1054nm. During Phase I, we will develop a Nd:Glass prototype laser using a design that has already been  used to demonstrate hundreds of mW of single-longitudinal mode (ultra-narrowband) and multiple-longitudinal-mode CW output power at 1535nm from Yb,Er:Glass lasers. The laser will operate in single transverse and longitudinal modes. Due to the fact that the Nd:Glass kinetics system is four-level, and the stimulated-emission cross-section is much greater than in Er:Glass, obtained power output powers of > 1 W can be obtained from very small packages. To operate the laser uncooled, the broad absorption bandwidth of Nd:Glass is preferred to the much narrower bandwidths found in crystalline lasers. For this STTR program, we have teamed with Clemson University to develop a diffusion-bonding process that will allow us to bond low thermal conductivity Nd:Glass plates to high thermal conductivity substrates such as SiC to eliminate thermal-expansion induced surface bulging and to allow more efficient thermal removal from the laser package. In addition to the laser development discussed in the aforementioned, we propose to design and minimize the footprint of an integrated transmitter using techniques already demonstrated in a related program. These techniques include detailed discussions with modulator vendors that utilize a thin-film LiNbO3 approach that minimizes modulator volume, integration of minimum coil radius fibers, and miniature bias and laser control printed circuit boards. An additional technique is the use of a 3-D design package (SolidWorks) to model the individual components in the transmitter design and optimally arrange them in configurations that minimize package size. We anticipate that the bench-top demonstration of a new high-power Nd:Glass narrow-band laser will be the major achievement of the Phase I program. While we will complete a detailed design of a transmitter that reduces the package size to < 150 cm3, only limited laboratory demonstrations can be completed because of the long lead time and cost associated with thin-film optical modulators. Nevertheless, we will complete a transmitter design that can be built and demonstrated during a Phase II program, based on input from a number of modulator vendors. The work performed during the Phase I program will enhance and lower the risk for demonstrating optimized devices and packages that can be further tested during Phase II, including under airborne environmental conditions.