Laser Diode Bipolar Pulse Control for Emission Tail Suppression
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Solution Overview
Problem
Existing high peak power ultrafast semiconductor lasers suffer from secondary emission tails due to residual carriers in the active gain region after the primary optical pulse, which are undesirable in applications requiring sub-nanosecond high peak power pulses.
Innovation Solution
A bipolar current pulse is applied to the gain-switched semiconductor laser diode, comprising a direct current pulse for the main optical output and a reverse current pulse to eliminate secondary peaks, with a transient region between the pulses controlled to prevent carriers from reaching the lasing threshold, thereby suppressing emission tails.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a direct current pulse is applied to generate high peak power optical pulses, then the optical output power is improved, but emission tails with secondary oscillations occur due to residual carriers
Solution Approach 1:
A reverse current pulse is applied immediately after the direct current pulse to actively remove residual carriers from the active gain region before they can generate secondary oscillations. This preliminary anti-action prevents the formation of emission tails by neutralizing the harmful residual carriers that would otherwise cause unwanted secondary optical emissions.
Solution Approach 2:
The invention changes the electrical pumping parameters from a simple unipolar pulse to a bipolar pulse sequence consisting of a direct current pulse followed by a reverse current pulse. This parameter change allows precise control over carrier population dynamics, enabling the suppression of emission tails while maintaining high peak power output during the direct pulse phase.
2Object-generated harmful factors
If the current pulse duration is extended to ensure complete carrier depletion, then emission tails are suppressed, but the pulse width increases beyond sub-nanosecond range
Solution Approach 1:
The invention employs a periodic bipolar pulse sequence with a direct current pulse followed by a reverse current pulse at a precisely controlled interval. This periodic action structure allows the system to achieve complete carrier depletion and emission tail suppression during the reverse pulse phase, while the overall pulse width remains within the sub-nanosecond range by optimizing the timing and duration of each phase.
3Object-generated harmful factors
If a bipolar current pulse with reverse pulse is applied, then emission tails are eliminated, but the device complexity increases
Solution Approach 1:
The laser diode structure itself is designed to support bipolar current operation, with the active gain region and carrier dynamics naturally responding to both direct and reverse current phases. This self-service approach allows the device to achieve emission tail suppression through its inherent physical response to the bipolar pulse, minimizing the need for additional external control circuitry or complex modulation schemes.
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 generates intense, ultra-short optical pulses with substantially suppressed or completely eliminated emission tails, ensuring high peak power without secondary oscillations.
Implementation Method 1
The stimulated emission is the process by which, when perturbed by a photon, matter may lose energy resulting in the creation of another photon with the substantially same phase, frequency, polarization, and direction of travel as the original photon. In a semiconductor laser, the injected carriers—electrons—are absorbed by the laser medium, placing some of its particles into high-energy ('excited') quantum states.
Implementation Method 2
At the threshold, the number of particles in one excited state starts exceeding the number of particles in some lower-energy state—the phenomenon known as population inversion. Further pumping leads to a generation of additional exited particles.
Implementation Method 3
the reverse (negative) pulse will substantially eliminate one or more secondary peaks. The transient part is applied during period shorter than time which would be sufficient for carriers, remaining in the active gain region after the first pulse, to reach threshold n.
Data Source
AI summary
A method of controlling an optical output of a laser diode includes applying a bipolar current pulse to the laser diode, thereby substantially suppressing the emission tail of the optical output of the laser diode. A device for generating sub-nanosecond intense optical pulses includes a driver unit operative to generate a plurality of bipolar current pulses, and a semiconductor laser diode driven by the bipolar current pulses and operative to emit the intense optical pulses each of which has a substantially suppressed or completely eliminated emission tail.