An integrated optical modulator operating at cryogenic temperatures

Abstract

Integrated photonic circuits (PICs) operating at cryogenic temperatures are fundamental building blocks required to achieve scalable quantum computing, and cryogenic computing technologies 1,2. Silicon PICs have matured for room temperature applications, but their cryogenic performance is limited by the absence of efficient low temperature electro-optic (EO) modulation. Here we demonstrate EO switching and modulation from room temperature down to 4 K by using the Pockels effect in integrated barium titanate (BaTiO3)based devices 3. We investigate the temperature-dependence of the nonlinear optical (NLO) properties of BaTiO3, showing an effective Pockels coefficient of 200 pm/V at 4 K. The fabricated devices exhibit an EO bandwidth of 30 GHz, ultra-low-power tuning which is 10 9 times more efficient than thermal tuning, and high-speed data modulation at 20 Gbps. Our results demonstrate a missing component for cryogenic PICs. Our results remove major roadblocks for the realisation of cryogenic-compatible systems in the field of quantum computing, supercomputing and sensing, and for interfacing those systems with instrumentation at room-temperature. Cryogenic technologies are becoming essential for future computing systems, a trend fuelled by the worldwide quest to develop quantum computing systems and future generations of highperformance classical computing systems 4,5. While most computing architectures rely solely on electronic circuits, photonic components are becoming increasingly important (Supplementary Note, SN 1). First, PICs can be used for quantum computing approaches where the quantum nature of photons is exploited as qubits 1,2. Second, optical interconnects can overcome limitations in

Toward Nonvolatile Switching in Silicon Photonic Devices

“…Furthermore, the preservation of the hysteresis has been proved at fast speeds (RF frequencies up to 60 GHz) [ 112 ] and, more recently, even at cryogenic temperatures (4 K), which could find application for quantum photonics. [ 117 ] Nevertheless, the key challenge for enabling a nonvolatile switching is that the best approach to induce the internal electric field to shift the hysteretic response is still unknown and will depend on the ferroelectric material and waveguide structure. For instance, a nonvolatile electro‐optical response was observed in a ring resonator based on a hybrid BTO/Si waveguide (Figure 13d).…”

“…quantum photonics. [117] Nevertheless, the key challenge for enabling a nonvolatile switching is that the best approach to induce the internal electric field to shift the hysteretic response is still unknown and will depend on the ferroelectric material and waveguide structure. For instance, a nonvolatile electrooptical response was observed in a ring resonator based on a hybrid BTO/Si waveguide (Figure 13d).…”

Heterogeneously-Integrated Optical Phase Shifters for Next-Generation Modulators and Switches on a Silicon Photonics Platform: A Review

“…In addition, they can also be epitaxially grown as thin films on an Si substrate. Therefore, BTO emerges as a highly promising material to achieve Pockels electro-optic modulators integrated on a Si photonics platform [74][75][76][77]. First, S. Abel et al demonstrated a large Pockels effect in micro-and nanostructured BTO integrated on Si [74], as shown in Figure 5b.…”

“…The integrated BTO/Si MZ modulator shows excellent V π L of 0.2 Vcm and αV π L of 1.3 VdB (~0.7 VdB when optimized), indicating~5.7 dB/cm (~3.0 dB/cm when optimized) and works at high speed of 25 Gbps, which is expected to reach data rates >50 Gbps by an adapted electrode design. Here, one feature of the optical modulators based on the Pockels effect are that they can be operated at cryogenic temperatures, whereas free-carrier effects-based optical modulators are restricted at low temperatures [76]. This is expected to encourage the use of Si photonics for quantum computing in the future.…”

High-performance integrated graphene electro-optic modulator at cryogenic temperature

“…This may be mitigated with degenerate doping but at the cost of increased insertion loss. Noncarrier-based modulators using Franz-Keldysh or quantum-confined Stark effect [11] or Pockels effect [12] suffer from weak electro-optic strength at low temperature, thus requiring higher drive voltage and increased footprint, which limits the integration density of photonic integrated circuits for cryogenic applications.…”