Date: Mar 01, 2007 Source: DARPA Success Stories (
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Technical Challenge Addressed:
The DARPA SBIR project was initiated to reduce manufacturing costs and overcome performance limitations in lasers used in photonic transport of analog radio frequency (RF) signals in communication, radar, and other RF signal-processing systems operating at high modulation speeds. New technology was required to develop and tightly integrate semiconductor lasers with advanced modulation methods to produce low cost, robust, high performance optical transmitters. Production called for new manufacturing methods. Essential performance measures for the optical transmitters included high modulation bandwidth, low relative intensity noise (RIN), and miniaturizing the integrated laser and modulator to 300 x 500 micrometers with low weight and power consumption. Meeting these challenges resulted in a foundry for manufacturing the new optical devices, technology for additional applications, advanced waveguide techniques for avionics, and a business based on the family of resulting laser products.
Technology Description:
Under the DARPA Phase II work, modulation doped multi-quantum well (MQW) distributed feedback (DFB) lasers were fabricated and their performance characteristics measured. These tests showed low threshold current; high slope efficiency; and high output power. The measured RIN decreased with increasing current, yielding an improvement of approximately 20 dB and resulting in lower values than those for regular MQW lasers. The DFB laser was monolithically integrated with an electro-absorption modulator (EAM) on a single InGaAsP/InP chip, with the resulting package being much smaller than a hybrid packaged laser with an external modulator. An innovative selective area growth (SAG) metalorganic chemical vapor deposition (MOCVD) method was used for monolithic integration of the laser and EAM. The SAG method is a band-gap engineering technique that was developed for the epitaxial growth of the MQW laser and the EAM in the same MOCVD run.
This method grows the epitaxial layers by chemical reaction rather than physical deposition. It simplifies single-chip photonic integration and has become the dominant process for manufacture of laser diodes, solar cells, and light-emitting diodes (LEDs). Low device yield of EAM lasers (EML), an issue at that time, was overcome using this technique. The DFB laser, the integrated DFB laser with modulator, and later a tunable distributed Bragg Reflector (DBR) laser with integrated modulator all met design goals in RF photonic transmission experiments and 10 Gb/s optical fiber transmission systems. Subsequently, Multiplex, Inc. developed methods to monolithically integrate an injection locked laser with an electro-absorption modulator under an Air Force SBIR project. The company also has successfully developed a custom compound semiconductor foundry service that produces a family of company products based on EAM and MOCVD technologies.
Lessons Learned & Best Practices:
- Identify realistic market opportunities and ªªtechnologies or products based on company capabilities and resources.
- Seek SBIR funding to develop promising high-risk and ªªhigh-reward technology.
- Establish and manage clear, realistic program goals, ªªapproaches, schedules, and resources; and use effective risk mitigation techniques.
- Identify commercialization paths in Phase I, and ªªpursue them early and aggressively in Phase II.
Economic Impact:
The DARPA SBIR work helped spawn the use of EML optical transmitters for telecommunication systems and opened up growth opportunities for Multiplex, Inc. The company's staff grew from fewer than 40 to more than 200, and achieved significant growth in revenue from sales of optical components and products. The company also received funding for related Air Force SBIR work, from DoD prime companies, such as Lockheed Martin, and secured funding from several commercial investment firms. These successful initiatives have given Multiplex, Inc. a prominent position in the optoelectronics industry.
Applications:
EML transmitters are now used for many applications in telecommunication networks because of their superior performance over directly modulated lasers. Products include high-speed EML-based lasers operating at 10 Gb/s, high-sensitivity photo receivers, tunable EMLs, and transponders that integrate both tunable EMLs and photo receivers with multiplexing devices. The latter integration, for example, enables wavelength routing and conversion for reconfigurable networks in a more compact package than other devices.
Partnering & Collaboration:
This DARPA SBIR program was conducted in collaboration with the University of Connecticut. University personnel performed testing to measure the performance characteristics of the modulation doped laser devices developed during the project. The Air Force Research Lab funded a subsequent SBIR project to integrate EA modulation with a DFB laser by MOCVD methods for an ultra-high speed monolithic injection-locked analog transmitter array (MILATA) used for laser detection and ranging (LADAR) sensors and scene generation. The LADAR scans large areas, processes a 3D image of the scene, and compares the image with 3D target files to identify targets and select the best attack position. The Air Force MILATA work demonstrated the LADAR device concept, but packaging the devices requires extensive funding, which thus far has not materialized.
Multiplex, Inc. is collaborating with Lockheed Martin in the development of tunable EML transmitters for avionics in a program funded by the U.S. Air Force. Several venture capital investments were received, and along with product sales, allowed Multiplex, Inc. to develop a semiconductor foundry and a family of products for military and commercial use. Multiplex, Inc. also has relationships with a number of equipment
