Abstract
Next-generation wireless communication will require increasingly faster data links. To achieve those higher data rates, the shift towards mmWave frequencies and smaller cell sizes will play a major role. Radio-over-Fiber has been proposed as a possible architecture to allow for this shift but is nowadays typically implemented digitally, as CPRI (Common Public Radio Interface). Centralization will be important to keep next-generation architectures cost-effective and therefore shared optical amplification at the central office could be preferable. Unfortunately, limited power handling capabilities of photodetectors still hinder the shift towards centralized optical amplification. Traveling wave photodetectors (TWPDs) have been devised to allow for high-linearity, high-speed opto-electronic conversion. In this paper, an architecture is discussed consisting of such a TWPD implemented on the iSiPP25G silicon photonics platform. A monolithically integrated star coupler is added in the design to provide compact power distribution while preserving the high linearity of the TWPD. The traveling wave structure (using 16 photodetectors) has a measured 3 dB bandwidth of 27.5 GHz and a fairly flat S21 up to 50 GHz (less than 1 dB extra loss). Furthermore, the output referred third-order intercept point at 28 GHz, is improved from -1.79 dBm for a single Ge photodiode to 20.98 dBm by adopting the traveling wave design.
Highlights
Future wireless communication links will require increasingly higher data rates to accommodate generation applications [1]
The aforementioned architecture can be altered to a more centralized topology by moving the amplifiers to the optical domain, where the amplification can be done for multiple remote antenna unit (RAU) at once, resulting in a significant decrease in RAU complexity
To push towards an increase in centralization and a drop in cost and power consumption, amplification can be done for multiple RAUs simultaneously
Summary
Future wireless communication links will require increasingly higher data rates to accommodate generation applications [1]. Improving the power handling capabilities of the photodetectors eventually allows for the omission of electrical amplification in the DL-RAU (downlink RAU, i.e. from central office to mobile end user), paving the road for passive DL-RAUs [6]. Implementing such high-power-handling photodiodes on a silicon photonics platform enables the low-cost manufacturing of such devices in high volume. To improve the power handling capabilities of an integrated high-speed p-i-n photodetector one can opt to use different materials and detector principles (e.g. III-V uni-travelling carrier photodetectors integrated on silicon [7,8,9,10,11,12,13]) or more complex photodetector configurations. The output referred IP3 linearity at 28 GHz is improved from −1.79 dBm for a single Ge photodiode to 20.98 dBm by adopting a traveling wave design with dual-fed photodetectors
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