Coherent detection has been found increasing applications in fiber sensing as well as in conventional RF and optical communications. In the past several years, coherent technology has been advanced dramatically in high-speed optical communications. With this, key parts and components (such as narrow linewidth lasers, optical hybrid, balanced photo-receivers and DSP, etc.) are commercially available and cost-effective for many applications beyond telecommunications. Optoplex has developed a series of products for coherent applications.   

Optoplex has developed a series of products for coherent applications:   

• 90deg optical hybrid
• 2x8 coherent mixer
• Integrated 40G coherent receiver (40G ICR)
• Integrated 100G coherent receiver (100G ICR)
• 90deg optical hybrid integrated with balanced receiver
• 2x8 coherent mixer with photodiode outputs
• Balanced Photoreceivers

Optoplex’s balanced photoreceiver is designed for optical coherent detection for non-telecom applications. It features a pair of photodiodes that are well matched and balanced in responsivity, bandwidth and noise, etc. The outputs of the photodiodes are amplified by low-noise TIA to produce a single RF output that is proportional to the difference between the photo-currents from the two photodiodes.   

Functional Block Diagram of the Ballanced Photoreceiver   

The photoreceiver has a 3dB bandwidth of about 100MHz. The RF output swing is +/-3.6V for high impedance load (±1.8 V into 50 Ω). The CMRR is better than 20dB (with a typical value of 30dB).   

The balanced photoreceivers are used with a 90deg optical hybrid or a polarization-diversified coherent mixer for coherent detection in Coherent Doppler Lidar, DAS (distributed acoustic sensing system), OCT (optical coherent tomorgraphy) in biomedical optics, Coherent OTDR (Optical Time-Domain Reflectometry), Coherent OSA (optical spectrum analyzer) etc.   

Two typical examples of coherent detection are shown in following Figures.   

Functional Block Diagram of a 90deg Optical Hybrid Integrated with 2 Ballanced Photoreceivers   

Functional Block Diagram of a polarization-diversified 90deg Optical Hybrid (also called 2x8 Coherent Mixer) integrated with 4 Balanced Photoreceivers   

Optoplex provides the 90deg optical hybrid integrated with balanced receivers as well as the 2x8 coherent mixer integrated with balanced receivers as shown in Figures above.   

ABSOLUTE MAXIMUM RATINGS   

OPERATING CONDITIONS   

Optical-Electrical Characteristics (100MHZ BW)