Fiber-Loop Pulse Burst Generation for Stable GHz Repetition Rates
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Solution Overview
Problem
Existing methods for generating high repetition rate bursts of short or ultrashort laser pulses are unstable, sensitive to cavity parameters, require complex and inflexible setups, and are unsuitable for controlling pulse characteristics such as amplitude and duration, making them inadequate for industrial applications.
Innovation Solution
A method using an active fiber loop with a fiber-optic delay line and optical switches to synthesize bursts of laser pulses, allowing control over pulse repetition rate, amplitude, and duration, capable of producing bursts with a flexible number of pulses and consistent intra-burst separation, suitable for generating GHz range pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If mode-locked fiber laser oscillators are used to generate GHz pulse repetition rate bursts, then pulse repetition rate is improved, but stability deteriorates because bursts are highly unstable and unsuitable for industrial applications
Solution Approach 1:
The invention segments the pulse train generation into two independent stages: a mode-locked oscillator generates a stable base pulse train at MHz repetition rate, and a separate pulse picker selectively transmits pulses at GHz repetition rate. This segmentation allows each stage to be optimized independently, maintaining stability while achieving high repetition rate.
Solution Approach 2:
The invention introduces a pulse picker as an intermediary device between the oscillator and the output. This pulse picker acts as a mediator that selectively transmits pulses based on timing, enabling conversion from MHz to GHz repetition rates while maintaining the stability of the original oscillator.
2Speed
If fiber laser resonators are made longer to achieve fundamental mode locking, then pulse repetition rate is reduced, but if harmonic mode locking is used to increase repetition rate, then reliability deteriorates because operation becomes unreliable
Solution Approach 1:
The invention separates the pulse generation function (performed by a compact, reliable oscillator) from the pulse selection function (performed by an external pulse picker). This allows the oscillator to operate reliably at its natural repetition rate while the pulse picker independently controls the output repetition rate.
Solution Approach 2:
Instead of trying to make the resonator shorter to achieve GHz rates directly (which causes instability), the invention inverts the approach: use a longer, more stable resonator operating at MHz rates, and then use external pulse picking to achieve the desired GHz output rate.
3Speed
If cavity parameters are adjusted to control pulse repetition rate in cavity-induced modulation instability, then pulse repetition rate is improved, but adaptability deteriorates because repetition rate cannot be controlled independently from other output pulse characteristics
Solution Approach 1:
The invention separates pulse generation from pulse selection, allowing independent control of different pulse characteristics. The oscillator generates pulses with stable characteristics, while the pulse picker independently controls the repetition rate by selectively transmitting pulses based on timing.
Solution Approach 2:
The pulse picker introduces dynamic control capability, allowing the repetition rate to be adjusted independently from other pulse characteristics by changing the picking frequency and phase, while the oscillator maintains stable pulse generation.
4Speed
If complex setups with multiple fiber arms of different lengths are used to generate GHz pulses, then device complexity is increased, but ease of operation deteriorates because the system is sensitive to temperature changes and requires active stabilization
Solution Approach 1:
The invention uses a simple single-arm oscillator design segmented from a separate pulse picking stage. This eliminates the need for complex multi-arm interferometric arrangements and their associated temperature sensitivity and stabilization requirements.
Solution Approach 2:
The invention extracts the pulse picking function from the oscillator cavity itself and places it externally. This removes the complex length-matching requirements and temperature sensitivity from the oscillator design, simplifying both the device and its operation.
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 method enables stable, cost-effective generation of bursts of short or ultrashort laser pulses with controlled characteristics, suitable for industrial applications, achieving pulse repetition rates from hundreds of MHz to THz and providing consistent pulse duration and amplitude.
Implementation Method 1
delaying a part of an input pulse with respect to another part of the input pulse
Implementation Method 2
an optical switch which is controlled by a drive signal D2, wherein the optical switch is used to block or attenuate parts of pulses propagating in said fiber loop
Implementation Method 3
a segment of a doped optical fiber, wherein the segment of the doped optical fiber is used for pulse amplification
Implementation Method 4
at least one dispersion compensation element designed to compensate a chromatic dispersion of the active fiber loop
Implementation Method 5
a fiber-optic coupler with two input and two output ports, wherein a first output port of the fiber-optic coupler is connected with a first input port of the fiber-optic coupler via said fiber loop
Data Source
AI summary
A method for generating gigahertz bursts of laser pulses is provided, where: 1) time delay T2 of the delayed part with respect to the undelayed part of the input pulse is longer than a time period T1 between said input pulse and the next input pulse; 2) the bursts of output pulses have an incrementally increasing number of pulses; 3) intra-burst pulse separation inside the formed bursts is equal to T3=T2−T1 and corresponds to an ultra-high pulse repetition rate higher than 100 MHz. In another embodiment: 1) T2 is longer than M*T1, where M=2, 3, etc.; 2) output train of bursts is composed of bursts of pulses wherein M adjacent bursts have identical number of pulses; 3) T3 is equal to T3=T2−M*T1. The laser apparatus for implementing the method is provided.