PHOTON SCIENCES, INCORPORATED — Department of Defense SBIR Phase II: N212-D04

Description

Wavelength Division Multiplexed (WDM) solutions are readily available from the commercial sector in both single mode and multimode formats. However, these solutions are not readily adaptable to use in the harsh environmental conditions required by the Military and Aerospace segment, nor are they capable of the high passive loss requirements. For example, the commercially available solutions in the 850 to 940nm band (so called SWDM band) are typically rated from 0 to 70C and are manufactured using complex chip on board die placement and utilize molded plastic optics. Operation over extended temperature ranges and other environmental factors such as mechanical shock and vibration are not possible. Additionally, the receiver sensitivity is generally at -11dBm (OMA). Transceivers in the traditional telecom wavelength range of 1310 to 1550nm operate on single mode optical fiber, which has shown to not be robust in the Navy operating environment. Here we propose a wavelength multiplexed digital receiver that is capable in the extreme military environment that is built using traditional TO packaged receivers and a hermetic optical path. The design uses either a fiber pigtail or connectorized input, and the optical output is collimated through the assembly. A series of filters is used to separate the individual wavelengths and direct them to the individual photodetectors and TIAs. The TO can package includes a lens and will be actively aligned to the input laser beams. The TO can will be laser welded in place and back filled with epoxy to complete the hermetic assembly. An avalanche photodiode will be used in the receiver to improve the receiver sensitivity at 850nm to approximately -14dBm (OMA). Sensitivity in the 1310nm to 1550nm will also be improved due to improved responsivity of the APD by approximately 6dB.The overall assembly is readily customizable to any wavelength from 850nm to 1550nm with appropriate choice of filters and APDs. Additionally, the signaling speed of each channel can be readily customized to any rate up to 28Gbps, possibly even 28GBd, making the total data throughput 200Gbps.  Additional link margin can be obtained by increasing the launch power of the transmitter. PSI has also developed high speed lasers with dual lasing cavities to increase the average launch power by ~2.5dB, or a minimum power level of +2dBm. Taken together with the receiver sensitivity, this gives a total link budget of 16dB, and allows for 13dB of passive loss.  Similar link margins are expected for a 1310 to 1550nm solution on single mode fiber. Traditional multimode fiber has limited bandwidth at 1310nm and imparts significantly more bandwidth penalty to the link. One method of reducing the link penalty would be to manufacture multimode optical fiber optimized for operation at 1310nm, providing bandwidth on par with the OM5 solution at 850nm. This would give TDP near 3dB, and provide passive link margin in excess of 14dB.