Cryogenic Optical Transmitter Biasing for Low-Voltage Josephson Drivers
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Solution Overview
Problem
Superconducting circuits are not effectively used to drive or control light-emitting or light-modulating electro-optic devices due to low output voltage swing and modulation frequency limitations, which restrict data transmission rates and efficiency.
Innovation Solution
A superconducting driver circuit with a voltage output connected to an electro-optic device, where one end is coupled to the driver circuit's output and the other end to a separate bias source, allowing for efficient modulation of light emission or absorption by controlling the current through the device, utilizing series-connected Josephson junctions or SQUID stacks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If superconducting Josephson-junction based circuits are used to drive electro-optic devices, then power consumption is reduced, but output voltage swing is limited to below 150 mV which is insufficient for effective modulation
Solution Approach 1:
A semiconductor buffer stage is introduced as an intermediary between the superconducting driver circuit and the electro-optic device. The superconducting circuit generates low-voltage pulses (below 150 mV) that are amplified by the semiconductor buffer to achieve the required voltage swing (0.5-2V) for driving the electro-optic device, thus resolving the voltage swing limitation while preserving the low power consumption of the superconducting circuit.
Solution Approach 2:
The patent changes the operating parameters by using a two-stage architecture where the first stage (superconducting) operates at cryogenic temperature with low voltage, and the second stage (semiconductor) operates at room temperature with higher voltage. This parameter transformation allows the system to benefit from both low power consumption and sufficient voltage swing.
2Device complexity
If the electro-optic device is connected to the same common or ground point as the driver circuit, then the configuration is simplified, but the driver circuit requires output voltage swing comparable to DC bias voltage which superconducting circuits cannot provide
Solution Approach 1:
The semiconductor buffer acts as an intermediary that decouples the driver circuit from the electro-optic device's bias network. The buffer's high input impedance prevents loading effects on the superconducting circuit, while its output stage can drive the electro-optic device with the necessary voltage swing, thus resolving the conflict between circuit simplicity and voltage capability.
3Productivity
If modulation frequency is increased to achieve higher data rates, then productivity is improved, but output voltage swing decreases significantly
Solution Approach 1:
The semiconductor buffer stage provides dynamic voltage amplification that adapts to different modulation frequencies. At higher data rates where the superconducting circuit's voltage swing naturally decreases, the buffer compensates by providing additional gain, thus maintaining sufficient voltage swing across a wide range of operating frequencies and data rates.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables significant modulation of light emission or absorption, overcoming the limitations of prior art by allowing higher data rates and reduced power consumption while maintaining the stability of the superconducting driver circuit.
Implementation Method 1
a superconducting driver circuit comprising at least one Josephson junction
Data Source
AI summary
An optical transmitter includes a superconducting driver circuit including at least one Josephson junction, the superconducting driver circuit having a voltage output and having a connection to a circuit ground, a first bias circuit coupled to the voltage output of the superconducting driver circuit, a second bias circuit, wherein the second bias circuit establishes a positive bias voltage relative to the circuit ground, and an electro-optic device having a first end and a second end, wherein the first end of the electro-optic device is coupled to the voltage output of the superconducting driver circuit, and wherein the second end of the electro-optic device is coupled to the second bias circuit.