VCSEL Array With Integrated Capacitor for Sharp Optical Pulses
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Solution Overview
Problem
Existing VCSELs face challenges in achieving high power optical pulses with short duration and fast rise and fall times due to parasitic inductance and resistance from external capacitors, which hinder efficient operation and reduce driving efficiency, especially at high currents.
Innovation Solution
Integration of a capacitor within the VCSEL chip, forming a metal-insulator-metal (MIM) or metal-oxide-metal (MOM) structure, reduces parasitic inductance and resistance, enabling sharp and ultra-narrow pulse operation by acting as a charge reservoir or impedance matching circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If an external capacitor is used to enable short duration optical pulses, then pulse duration can be reduced, but parasitic inductance and resistance increase, reducing driving efficiency
Solution Approach 1:
The patent merges the capacitor with the VCSEL structure by integrating it within the chip substrate. The capacitor is formed using the same fabrication processes as the VCSEL, with metal layers and dielectric materials deposited directly on the chip. This integration eliminates the need for external capacitors and their associated parasitic inductance and resistance, thereby maintaining high driving efficiency while enabling short duration optical pulses.
Solution Approach 2:
The integrated capacitor acts as an intermediary charge reservoir between the current source and the VCSEL active region. It provides a local source of charge that can be rapidly discharged to produce high current pulses, enabling short duration optical pulses without requiring external capacitive components that would introduce parasitic losses.
2Power
If high electrical current is applied to achieve high power optical pulses, then optical power increases, but rise time and fall time increase, reducing pulse sharpness
Solution Approach 1:
The integrated capacitor is pre-charged during the low-current phase and then rapidly discharged during the high-current phase. This preliminary charging action allows the system to maintain high optical power while achieving fast rise and fall times, as the capacitor provides the instantaneous current surge needed for sharp pulse edges without requiring continuously high current.
Solution Approach 2:
The system operates in periodic cycles of charging and discharging the integrated capacitor. During the charging phase, current builds up in the capacitor; during the discharging phase, the capacitor releases stored charge to produce the high power optical pulse. This periodic action enables the VCSEL to achieve both high power and fast switching by alternating between these two states.
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
The integrated capacitor enhances operating current, switching speed, and driving efficiency, allowing for faster rise and fall times of optical pulses, supporting higher harmonics and improving the performance of VCSELs in applications requiring sub-nanosecond pulse modes.
Implementation Method 1
a capacitor over at least a portion of an active layer of the VCSEL structure that is outside of an active region
Implementation Method 2
reduces parasitic inductance and resistance, enabling sharp and ultra-narrow pulse operation
Data Source
AI summary
An optical chip may include a vertical-cavity surface-emitting laser (VCSEL) structure. The optical chip may include a capacitor over at least a portion of an active layer of the VCSEL structure that is outside of an active region of the VCSEL structure. The capacitor may include a first metal layer over the portion of the active layer, a dielectric layer on the first metal layer, and a second metal layer on the dielectric layer. The optical chip may include an isolation region between a substrate of the VCSEL and a portion of the capacitor outside of the VCSEL.