Compact Robust Integrated PPM Laser Transceiver Chip Set with High Sensitivity, Efficiency, and Re-Configurability

Abstract The realization of a monolithically integrated pulse-position-modulated (PPM) laser transmitter and receiver chips with high functionalities based on silicon photonics for space optical communications is of great interest to increase the robustness, security, data rate, and cost for high-bandwidth space communications. The proposed work will realize a laser transmitter chip and a laser receiver chip using electronic-photonic integration technology. The integrated PPM laser transmitter chip will be capable of generating pulses at variable time interval with pulse width of 1 nanosecond or shorter. It will be capable of pulse output power of over 20mW, up to 50mW. In emergency situation, the laser power can be increased by 10 folds to help in increasing the signal to noise ratio and beam locking. Furthermore, the laser can emit 10 or more different wavelength channels into a single beam with DWDM wavelength channel resolution. Each wavelength channel can be individually modulated at 1Gbps or faster. The rate will be user variable from 10Mbps to 1Gbps. The multi-wavelength channel capability will enable more secure communication and will increase the data rate by 10 times or more. A PPM data rate of 10 Gbps, up to 100Gbps will be possible. The integrated PPM laser receiver chip will be capable of receiving the laser beam with high efficiency and relatively low pointing requirements through a careful design of chip coupling method, which is a challenge for planar integration that we will address. The reception will be beam polarization independent. The receiver will be capable of de-multiplexing a multi-wavelength-channel beam with 10 or more wavelength channel at DWDM wavelength channel resolution. The bit rate for each channel can be at the high-bit-rate of 1Gbps, up to 10Gbps. The receiver chip will have high photodetection efficiency and will provide on-chip optical pre-amplification of the incoming beam with spectral noise filtering to reduce the spontaneous emission beat noise from the optical amplifier. This will result in a higher detection sensitivity of over 10 times higher than with PIN diode detector and will be comparable to that with avalanche photodetector (APD) or better but without the high voltage requirement of APD. In addition to the above capabilities, we will develop an integrated PPM receiver chip capable of coherent detection. An integrated laser will provide the local oscillator beam. In order to make the coherent detection in sensitive to incoming beam alignment, the receiver will involve the use of photodetector array. It has been shown that coherent detection with use of photodetector array can reduce the effect of air turbulence to almost the quantum limit (without the air turbulence). In the long term, coherent detection will give an ideal detection scheme that will be shot-noise and quantum limited with significantly higher detection sensitivity than direct photodetection. All these capabilities will be delivered in the proposed 3-year research program. By the end of the program, various PPM laser and receiver chips will be realized that will push the capability of integrated PPM transceiver to a higher level than currently possible.