Cost-effective coherent ONU transceiver based on single directly modulated laser

Area of Science:

• Optical Communications
• Photonics
• Telecommunications Engineering

Background:

• Ultra-dense wavelength division multiplexing passive optical networks (UDWDM-PONs) require cost-effective transceiver solutions.
• Coherent detection in PONs typically necessitates separate lasers for transmission and local oscillation.
• Directly modulated lasers (DMLs) offer a potential path to cost reduction but face challenges in coherent applications.

Purpose of the Study:

• To propose and validate a novel, cost-effective transceiver structure for UDWDM-PONs.
• To demonstrate the feasibility of using a single DML as both transmitter and local oscillator.
• To investigate and optimize key parameters affecting performance, such as extinction ratio and frequency offset.

Main Methods:

• A single directly modulated laser (DML) was employed for both upstream transmission and downstream local oscillator (LO) in the optical network unit (ONU) transceiver.
• The extinction ratio (ER) of the DML signal was optimized by adjusting driving amplitude and bias.
• Heterodyne detection was utilized to mitigate Rayleigh backscattering (RB) in bidirectional transmission.
• The impact of frequency offset (FO) between upstream and downstream signals was analyzed.

Main Results:

• A cost-effective ONU transceiver structure based on a single DML was successfully proposed.
• The study demonstrated the first use of a DML as both an optical transmitter and a local oscillator for coherent detection in UDWDM-PONs.
• The impact of DML extinction ratio and frequency offset was investigated and managed.
• 2.5-Gb/s bidirectional On-Off Keying (OOK) transmission over 60-km standard single-mode fiber (SSMF) was achieved within a 12.5-GHz grid.
• Receiver sensitivities of approximately -43 dBm (downstream) and -45.5 dBm (upstream) were obtained.

Conclusions:

• The proposed single-DML transceiver structure offers a cost-effective solution for coherent UDWDM-PONs.
• The successful demonstration validates the use of DMLs in advanced coherent optical network architectures.
• This approach significantly reduces component count and complexity, paving the way for more economical PON deployments.