A high-speed receiver optical subassembly (ROSA) based on silica hybrid-integrated technology for 400 G Ethernet applications is designed and manufactured. It consists of an eight-channel-arrayed waveguide grating (AWG) with a 2% refractive index difference, two 4-channel InP-based waveguide photodetector (PD) array chips, eight lenses for enhancing the coupling between AWG and PDs, two 4-channel trans-impedance amplifier array chips, and an eight-channel high-frequency flexible printed circuit. All the channels of the ROSA have achieved 3 dB bandwidths of above 27.05 GHz, and receiver sensitivities of below −8.5 dBm, supporting a receiving rate of 8×53 Gbps.
A silica-based 90 deg optical hybrid based on a 4 × 4 multimode interference coupler with a refractive index contrast of 0.36% is designed and fabricated for coherent receiver. The measured results of this device show that the common mode rejection ratios are better than 23 dB and excess loss including a coupling loss of −0.3 dB is less than −0.9 dB in C band (1530 to 1565 nm). The phase error is less than ±4 deg. The designed low-cost 90 deg optical hybrid is promising for further improving the sensitivity of quadrature phase shift keying coherent receivers.
Quantum key distribution can realize unconditional security of communication. Here, a quantum decoding chip based on silica-on-silicon planar lightwave circuit (PLC) platform, which is compatible for multiprotocol has been demonstrated. PLC technology provides stability, high integration, and practicality for the chip, whereas silica-on-silicon material makes it low loss and low cost. The chip is integrated with three variable optical splitters, two asymmetric Mach–Zehnder interferometers, and four variable directional couplers. The interference visibility is investigated by self-interfering method, and the results showed it is high to 98.2% under temperature control. The extinction ratio for the phase states is kept between 23 and 25 dB for 6 h without active phase correction.
Silica-based planar lightwave circuit (PLC) devices can offer great potential for quantum key distribution (QKD) with the benefits of low-loss, low-cost, large-scale integration, miniaturization, stability and mass production. A quantum decoding integrated chip for QKD based on silica PLC technology was demonstrated, which consists of a variable optical splitter (VOS), an asymmetric Mach–Zehnder interferometer (AMZI) with a thermo-optic phase modulator (TOPM) and a delay line (DL) whose delay time is 400ps, and a variable directional coupler (VDC). The balanced pulsepairs of double channels with measured delay times of 396ps and 398ps respectively were obtained in the conditions of both classical optics and single-photon transmissions. The chip has advantageous to achieve high interference visibilities of double channels simultaneously for BB84 phase and time-bin protocols.
A receiver optical subassembly (ROSA) based on hybrid integrated technology is designed and fabricated. It consists of an 8-channel arrayed waveguide grating (AWG) with 2% refractive index difference, two 4-channel positive intrinsic-negative photodetector arrays, and two 4-channel transimpedance amplifier arrays. A flat-top optical spectrum was observed because the output waveguides have a multimode structure, and the average 1-dB bandwidth of AWG channels is 2.8 nm. The insertion loss of all channels is between −1.8 and −2.9 dB, and the cross talk between adjacent channel is less than −20 dB. The ROSA shows a maximum responsivity of 0.4 A / W and 3-dB bandwidth of more than 22 GHz for four channels, which can meet the data transmission rate of 25 Gb / s. In the future, we will improve the fabrication process to achieve a transmission rate of 8 × 25 Gb / s.
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