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200Gbps Per Lambda, 800G Four Lane CWDM PAM4 Transmitter…,, The Dawn of the Nanophotonics Age ... Mark Stansberry ...  Dec 27 2023

The diagram below illustrates a next generation 200Gbps Lambda 800G Course Wave Division Multiplexer (CWDM) Four Level Pulse Amplitude Modulated  (PAM4) optical transmitter design. The concept design includes POET Technologies’ optoelectronic interposer embedded multiplexer,  four 200 Gbps compatible Electro-Absorption  Modulation Lasers (EML) with light wavelengths of 1271 nm, 1291 nm, 1311 nm and 1331 nm.  The EML laser  modulates the four streams of 200 Gbps PAM4 analog electronic data with the four individual laser light wavelengths. 

Waveguides route light in  photonic integrated circuits. The waveguide constrains the path for the light to travel from its source to its destination. The arrayed waveguide grating  funnels (multiplexes) the four200 Gbps  modulated  light wavelengths in the four individual waveguides into one output waveguide, which could be called a polyinfrared output waveguide, resulting in a 800 Gbps data rate. A light coupler, grating coupler, or tapered waveguide then couples the polyinfrared light to another waveguide, one fiber optic cable or an optoelectronic device. 

Besides through physical waveguides, light can travel in free space to reach a destination. However, such an approach leads to light energy loss that may not be tolerable. In the free space case, dielectric materials that the light waves pass through will change the direction of the light.  Light that passes through the dielectric material will change direction according to the associated refraction angle the dielectric imposes on the specific wavelength. The refraction angle will be different for different wavelengths of light that pass through the dielectric. Based on a similar dielectric-refractive principle, optical objects such as prisms and water molecules  separate the components of sunlight into their component color wavelengths, helping explain rainbows and the basis for wavelength based light beam steering. 

The illustration also alludes to the photon up conversion of light. In such an arrangement, a photonic up converter converts the infrared light waves from the lasers to visible spectrum light waves.  Photon up conversion techniques are often based on Lithium Niobate. POET Technologies has an agreement with Liobate Technologies, a company that offers lithium niobate based optoelectronic modulators.