Laser Diode Priming Current to Reduce Accumulation Latency
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Solution Overview
Problem
Laser diodes in scanned-beam displays experience a significant accumulation period before stimulated emission, which shortens the available time window for pixel illumination, leading to potential pixel compression and offset, especially in high-resolution displays where the time window is already constrained.
Innovation Solution
A drive circuit is used to draw a priming current through the laser diode over a priming period, insufficient to cause lasing, but sufficient to shorten the accumulation period, followed by an above-threshold current to trigger emission, allowing for synchronized and efficient light emission within the limited time window.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a laser diode is operated in pulsed mode with above-threshold current, then stimulated emission of light is achieved, but a significant accumulation period is required before emission occurs
Solution Approach 1:
The patent applies preliminary action by applying a priming current before the above-threshold current to pre-accumulate charge carriers in the quantum well. This preliminary carrier accumulation reduces the time required for the subsequent above-threshold current to reach the emission threshold, effectively shortening the accumulation period while maintaining light emission efficiency
2Reliability
If the accumulation period is long, then sufficient charge carriers accumulate for stimulated emission, but the available time window for pixel illumination is reduced
Solution Approach 1:
By applying a priming current pulse before the main above-threshold current, the system pre-accumulates charge carriers in the quantum well during the priming period. This preliminary action ensures that when the above-threshold current is applied, the emission occurs more rapidly within the available pixel illumination time window, maintaining emission reliability while fitting within the constrained display timing
3Duration of action of moving object
If the accumulation period is shortened without priming current, then pixel illumination time window is improved, but charge carrier accumulation is insufficient for reliable stimulated emission
Solution Approach 1:
The priming current serves as a preliminary action that accumulates charge carriers before the main emission current is applied. This two-stage approach allows the system to achieve sufficient carrier accumulation for reliable stimulated emission while keeping the actual emission pulse duration short enough to fit within the pixel illumination time window without causing compression or offset
Solution Approach 2:
The patent employs periodic action through a two-stage current pulse sequence: a priming current pulse followed by an above-threshold current pulse. This periodic structure allows charge carrier accumulation during the priming phase and rapid emission during the second phase, achieving both reliability and timing precision
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 approach effectively shortens the accumulation period, enabling precise and timely emission of light for high-resolution scanned-beam displays, improving display resolution and maintaining pixel illumination without compression or offset.
Implementation Method 1
When electrical current is injected into the diode laser, inverted population of electrons and holes accumulate within the quantum well of the laser diode. Some of the accumulated charge carriers may recombine by stimulated photon emission, causing a coherent, collimated beam to emerge from the laser cavity.
Implementation Method 2
A laser diode is an electro-optical device in which an intrinsically-doped, direct-bandgap semiconductor zone separates opposing p- and n-doped zones. Under forward bias, the p- and n-doped zones inject charge carriers into the intrinsically-doped zone, which is configured as a laser cavity.
Data Source
AI summary
A modulated light source comprises a laser diode and a drive circuit coupled operatively to the laser diode. The laser diode is configured to lase upon passing an above-threshold current for an accumulation period. The drive circuit is configured to draw a priming current through the laser diode over a priming period, the priming current being insufficient to cause the laser diode to lase during the priming period, but sufficient to shorten the accumulation period. The drive circuit is further configured to draw the above-threshold current through the laser diode after the priming period, thereby triggering emission from the laser diode following a shortened accumulation period.