10 Gbps DPSK transmission over free-space link in the mid-infrared.

We experimentally demonstrate the implementation of 10 Gbps high-speed mid-infrared (MIR) free-space optical (FSO) communication, by means of our developed robust high-speed MIR transmitter and receiver modules. Such modules can enable frequency down- and up-conversion between 1550 nm and 3594 nm based on difference frequency generation (DFG) in MgO-doped periodically poled LiNbO3 (MgO: PPLN). The MIR transmitter generates 5.34 dBm power at 3594 nm for input powers of 33 dBm at 1550 nm and 37 dBm at 1083 nm. The MIR receiver regenerates -24.5 dBm power at 1550 nm for input powers of -1.2 dBm at 3594 nm and 36.7 dBm at 1083 nm. The eye diagram of regenerated 1550 nm signal is clear, and both for the on-off keying (OOK) and differential phase shift keying (DPSK) modulation, the power penalties compared with back to back (BTB) signals are lower than 3.5 dB measured at bit error ratio (BER) of 1E-6. According to our analyses, the system supports variable data rate, wavelength, and modulation format. Furthermore, the optical and electrical components are well integrated and fixed in MIR transmitter and receiver modules, which exhibit long-term stability and can be applied to field experiments.

Mid-infrared transmitter and receiver modules for free-space optical communication.

We report on the experimental implementation of single-frequency fiber-laser pumped mid-infrared (mid-IR) transmitter and receiver modules for free-space communications. These modules enable frequency upconversion and downconversion between the 1550-nm telecom wavelength and the mid-IR, thus providing essential free-space transmission links with mid-IR single-frequency lasers in the 3.6 µm region. Specifically, based on difference frequency generation (DFG) in MgO-doped periodically poled LiNbO3 (MgO:PPLN), the mid-IR transmitter produces 9.3-mW power at 3594 nm with 5-W pump power at 1083 nm (<10 kHz linewidth) and 3-W signal power at 1550 nm (<10 kHz linewidth), and the mid-IR receiver reproduces 12-µW power at 1550 nm with 4.7-W pump power at 1083 nm and 5-mW laser at 3594 nm. The whole modules are integrated into portable and compact devices by incorporating single-frequency fiber lasers, fiber amplifiers, DFG units, and related electronic circuits. In addition, the uses of all polarization-maintaining fiber configuration and well-controlled heat dissipation make the mid-IR transmitter and receiver exhibit a long-term stability.