Flow chemistry is a continually emerging and ever-growing area of synthetic organic chemistry. It provides an orthogonal approach to traditional batch chemistry, oftentimes allowing for more efficient routes to desired target molecules. It is generally accepted that flow chemistry offers a valuable change to the process landscape. From a process perspective, there are many advantages associated with flow chemistry over traditional batch chemistry, the most prominent of which is an increased safety profile with the use of highly reactive chemical species, such as organolithiums. These reagents are highly valuable species for the efficient synthesis of pharmaceutical intermediates. Disadvantageously, use of these reagents on commercial scale is severely hindered by the highly energetic nature of the reaction intermediates and their concomitant safety risk. Flow chemistry provides a viable platform for use of these reagents, offering a high degree of control over reaction parameters. In this review, we present a comprehensive account of the published literature implementing the use of organolithium reagents as strong bases for deprotonation reactions in flow systems.

We demonstrate how to optimize the performance of PAM-4 transmitters based on lumped Silicon Photonic Mach-Zehnder Modulators (MZMs) for short-reach optical links. Firstly, we analyze the trade-off that occurs between extinction ratio and modulation loss when driving an MZM with a voltage swing less than the MZM's V_π. This is important when driver circuits are realized in deep submicron CMOS process nodes. Next, a driving scheme based upon a switched capacitor approach is proposed to maximize the achievable bandwidth of the combined lumped MZM and CMOS driver chip. This scheme allows the use of lumped MZM for high speed optical links with reduced RF driver power consumption compared to the conventional approach of driving MZMs (with transmission line based electrodes) with a power amplifier. This is critical for upcoming short-reach link standards such as 400Gb/s 802.3 Ethernet. The driver chip was fabricated using a 65nm CMOS technology and flip-chipped on top of the Silicon Photonic chip (fabricated using IMEC's ISIPP25G technology) that contains the MZM. Open eyes with 4dB extinction ratio for a 36Gb/s (18Gbaud) PAM-4 signal are experimentally demonstrated. The electronic driver chip has a core area of only 0.11mm2 and consumes 236mW from 1.2V and 2.4V supply voltages. This corresponds to an energy efficiency of 6.55pJ/bit including Gray encoder and retiming, or 5.37pJ/bit for the driver circuit only.

Two mechanisms that can make frequency conversion based on nonlinear mixing dependent on the phase of the input signal are identified. A novel phase-to-polarization converter that converts the orthogonal phase components of an input signal to two orthogonally polarized outputs is proposed. The operation of this scheme and a previously reported scheme at an increased symbol rate are simulated with semiconductor optical amplifiers (SOAs) as the nonlinear devices. Experimental results demonstrate the effectiveness of SOAs for nonlinear mixing over a wide range of wavelengths and difference frequencies and confirm the accuracy of the numerical model.

A push-pull silicon photonic Mach-Zehnder modulator (MZM) driver is presented which uses a switched capacitor approach to generate a ∼2 V peak-to-peak differential 4-level pulse amplitude modulation (PAM-4) signal. The driver chip includes a Gray encoder and retiming flip-flops. The switched capacitor approach allows driving the lumped silicon photonic MZM with reduced power consumption compared with the conventional approach of driving MZMs (with transmission line based electrodes) with a power amplifier. This is critical for upcoming short-reach link standards such as 400 Gbit/s 802.3 Ethernet. The chip was fabricated using a 65 nm CMOS technology and flipchipped on top of the silicon photonic chip (fabricated using IMEC's ISIPP25G technology) that contains the MZM. Open eyes with 4 dB extinction ratio for a 36 Gbit/s (18 Gbaud) PAM-4 signal are experimentally demonstrated. The electronic driver chip has a core area of 0.11 mm 2 and consumes 236 mW from 1.2 to 2.4 V supply voltages. This corresponds to an energy efficiency of 6.55 pJ/bit including Gray encoder and retiming, or 5.37 pJ/bit for the driver circuit only.

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