Fig. 1. MUTC PDs integrated on TFLN. (a) Structural illustration. (b) Epitaxial structure of the n-down PD. (c) TFLN waveguide cross section. (d) Microscope image of a device under test with a lensed fiber and a radio frequency probe. (e) Microscope image of chip with integrated PDs.

Fig. 2. Device simulations. (a) Calculation of transit time-limited bandwidth versus undepleted absorber thickness with total absorber thickness of 250 nm and a fixed drift layer thickness of 200 nm. Optical simulations of E-field magnitude: (b) yz cross section at x=0  μm (passive waveguide), (c) yz cross section at x=5  μm (PD), and (d) zx cross section at y=0  μm.

Fig. 3. DC measurements of MUTC photodiodes integrated on thin-film LN platform. (a) Dark current characteristics of a 1400-μm2 device. (b) Measurement of photocurrent versus optical power (measured at fiber tip) of a 600-μm2 device.

Fig. 4. AC measurements of MUTC photodiodes integrated on thin-film LN. (a) Frequency responses of a 100-μm2 PD at different photocurrents. (b) Frequency responses of various sized photodiodes at 1-mA photocurrent and 3-V reverse bias. (c) Simulations and measurements of bandwidth for different device areas. (d) Measurement of RF power of a 300-μm2 PD at 48 GHz at different reverse biases.

Fig. 5. Eye diagram measurement. (a) Measurement system setup. (b) Measured eye diagram for a commercial photodiode. (c) Measured eye diagram for an MUTC photodiode on TFLN with 200-μm2 PD area.