Links at 1 micron offer key advantages over longer wavelength links. Both ultra-stable, low noise Nd:YAG lasers and high power efficiency, temperature-stable GaAs lasers operate at wavelengths around 1 micron. These components are particularly beneficial for quantum optical systems and links which require stability over a wide range of temperatures, such as are required in avionics. However, a key component missing in these 1 micron photonic links is a high-power photodiode receiver with high linearity and high quantum efficiency. Freedom Photonics and the University of Virginia have collaborated to develop photodiodes which fill this need. The photodetectors are based on an optimized vertically illuminated modified uni-traveling carrier (MUTC) photodiode technology. We report devices with quantum efficiencies in excess of 80% at 1064 nm, with a 3-dB bandwidth of 28 GHz, for a 20µm diameter device. The same device size handles very high power, with a 1-dB compression of >16 dBm RF power at a 64-mA photocurrent. These photodiodes have a major impact on peak performance of a photonic link, supporting high link gain and large bandwidths. Additionally, the high linearity of these devices minimizes noise and signal distortion, maximizing spurious-free dynamic range (SFDR). These are the first photodiodes of this type which have been packaged and made commercially available for this target wavelength.
High frequency analog RF photonic links are desirable to reduce the size, weight and power of RF systems by offering the replacement of lossy, bulky coaxial RF cabling for lightweight, low loss and broadband optical fiber, particularly in applications such as avionics and naval RADAR systems, electronic warfare and distribution of low-jitter clocks or local oscillator signals. Freedom Photonics and the University of Virginia have developed high power, wide-bandwidth optical photodetectors operating in the 1550-nm wavelength range. These photodetectors are based on vertically illuminated modified uni-traveling carrier (MUTC) photodiode technology. The devices have been developed into fully packaged, fiber-pigtailed modules with optimization for high powers or high speeds. This paper will present the architecture and experimental results of our range of photodiodes. One family of devices focuses on high power applications. These include high-power photodiodes with 3-dB bandwidths of 25 GHz coupled with output powers in excess of 23 dBm, as well as 35 GHz photodiodes with output powers greater than 19 dBm. Another family of devices focuses on high speed applications, including photodiodes with 3-dB bandwidths of >65 GHz and >100 GHz. These photodiodes, used in a photonic link, have a major impact on peak performance. The high power-handling capability and high speeds of these devices support high link gain and large bandwidths, while the high linearity of these devices minimizes noise and signal distortion, maximizing spurious-free dynamic range (SFDR).
High-performance photodetectors (HPPDs), with high output power and bandwidth, are needed for RF photonics links. Applications for these HPPDs range from high-power remote antennas, low-duty-cycle RF pulse generation, linear photonic links, high dynamic range optical systems, and radio-over-fiber (ROF). Freedom Photonics is a manufacturer of high-power photodetectors (HPPD) for the 1480 to 1620nm wavelength range, now being offered commercially. In 2016, Freedom has developed a HPPD for similar applications extending into the V-band. The basic device structure used for these photodetectors can achieve over 100-GHz bandwidths with slight variations. This work shows data for RF power and bandwidth performance for various size photodiodes, between 10 μm and 28 μm in diameter. Measurement data will be presented, which were collected at both assembly level and for fully packaged detectors. For detector devices with bandwidth performance over 50 GHz, the generated RF power achieved is expected to be over 15 dBm. This performance is exceptional considering the photodiode is fully integrated into a hermetic package designed for 65 GHz. Improvements in the coplanar waveguide (CPW) transmission line and flip-chip bonding design were integral in achieving the higher saturation at the higher bandwidth performance. Further development is required to achieve a >100 GHz packaged photodetector module.