Series-Connected VCSEL Array for Driver Impedance Matching
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Solution Overview
Problem
Conventional VCSEL arrays have fixed, low input impedance due to parallel connection of emitters, leading to impedance mismatch with pulsed laser driver circuits, limiting their applications and increasing production costs.
Innovation Solution
A series-connected VCSEL array design with semi-insulating layers and common anode/cathode contacts, allowing for adjustable impedance matching through sub-array configurations and multiple input impedance options.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If VCSEL emitters are parallelly connected with common cathode contact and shorted anode contacts, then the electrical input impedance is very low, but this causes impedance mismatch with pulsed laser driver circuits and requires additional energy-consuming resistors
Solution Approach 1:
The patent inverts the conventional parallel connection topology to a series connection topology. In the series configuration, the anode of one VCSEL is connected to the cathode of the next VCSEL, creating a chain where current flows sequentially through all emitters. This inversion fundamentally changes the impedance characteristics from low (parallel) to high (series), achieving natural impedance matching with pulsed laser driver circuits without requiring additional resistive elements that consume energy.
Solution Approach 2:
The patent changes the electrical connection parameter from parallel to series configuration. This parameter change transforms the overall input impedance of the VCSEL array, making it compatible with the output impedance of pulsed laser driver circuits. The series connection enables the array to present a higher input impedance that matches the driver circuit requirements, eliminating the need for impedance-matching resistors and reducing energy loss.
2Ease of manufacture
If VCSEL array chip is made with fixed impedance characteristic, then the impedance cannot be changed after fabrication, but this limits applications of the VCSEL chips and increases production cost
Solution Approach 1:
The patent introduces dynamic configurability to the VCSEL array by incorporating switching elements (such as MOS transistors) that can dynamically control the connection topology. After fabrication, the array can be reconfigured between series and parallel connection modes by activating or deactivating these switches. This dynamic capability allows the same chip to adapt to different application requirements with varying impedance demands, significantly enhancing versatility without requiring multiple fixed-impedance chip variants.
Solution Approach 2:
The patent designs the VCSEL array with multi-functional capability by integrating reconfigurable connection structures. A single VCSEL array chip can serve multiple applications by switching between series connection mode (for high-impedance applications like pulsed LIDAR) and parallel connection mode (for low-impedance applications). This universal design eliminates the need for separate fixed-impedance chips for different applications, reducing production costs and inventory complexity while maximizing adaptability.
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
Enhances impedance matching with laser driver circuits, increases slope efficiency, and provides flexibility in impedance selection, reducing energy consumption and production costs.
Implementation Method 1
materials of the semi-insulating layer are selected such that its bandgap energy level is higher than the photon energy of the output beam. Thus, the semi-insulating layer is transparent to the output wavelengths of the VCSEL array. Photon-induced carrier generation and resultant leaky currents between sub-arrays are reduced.
Data Source
AI summary
A VCSEL array comprises series-connected VCSEL sub-arrays formed on a single chip. The VCSEL sub-arrays each comprises VCSEL emitters fabricated on a semi-insulating layer. A common cathode contact of a VCSEL sub-array is electrically connected to a common anode contact of a neighboring VCSEL sub-array. To reduce leakage, the bandgap energy level of the semi-insulating layer is higher than the photon energy of the output beam. In one embodiment, the semi-insulating layer is grown on a conductive layer. A common cathode contact of the last VCSEL sub-array in a series is electrically connected to the conductive layer. In another embodiment, multiple wire-bonding areas are electrically connected to common anode contacts of multiple VCSEL sub-arrays respectively. The wire-bonding areas provide different input impedance options for a VCSEL array.