Laser Cavity Pulse Shaping for OTDR
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Solution Overview
Problem
Current OTDRs face limitations in producing short, variable-duration pulses with fast risetimes and tunable wavelengths, making them unsuitable for applications like DWDM systems and PMD measurements, due to the high cost of external optical components like EDFA and AOM, which are necessary to compensate for loss and achieve narrow linewidths.
Innovation Solution
A laser design incorporating a cavity with an active optical gain medium, spectral filter, delay means, and control mechanisms to produce pulses with adjustable duration and wavelength, using a semiconductor optical amplifier and tunable optical bandpass filter to achieve short pulse durations and fast risetimes without the need for expensive external components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external optical components (EDFA, AOM) are used to compensate for loss and achieve narrow linewidths, then pulse quality and wavelength stability are improved, but device cost and complexity increase significantly
Solution Approach 1:
The patent combines the functions of wavelength selection, pulse shaping, and loss compensation into a single integrated laser cavity design. The spectral filter and delay means are incorporated within the cavity to work synergistically with the gain medium, eliminating the need for separate external EDFA and AOM components while achieving the same pulse quality and wavelength stability.
Solution Approach 2:
The laser cavity is designed to perform multiple functions simultaneously: the spectral filter provides both wavelength selection and linewidth narrowing, while the delay means provides both pulse shaping and temporal control. This multi-functional integration reduces overall device complexity while maintaining pulse quality.
2Duration of action of moving object
If external optical modulator and optical amplifier are used to produce fast rise-time short light pulses, then pulse duration and risetime are improved, but device cost increases prohibitively
Solution Approach 1:
The patent integrates pulse shaping and amplification functions directly into the laser cavity through the delay means and gain medium configuration. This eliminates the need for external optical modulators and amplifiers, achieving fast rise-time short light pulses while significantly reducing device complexity and cost.
Solution Approach 2:
The delay means creates a periodic feedback mechanism within the cavity that naturally generates pulsed output with controlled duration and rise time. This periodic action within the integrated cavity replaces the need for external modulation components.
3Device complexity
If directly modulating the gain medium of continuously-tunable OTDR is used to obtain pulsed output, then device simplicity is maintained, but laser linewidth becomes unacceptably wide
Solution Approach 1:
The patent applies local quality by introducing a spectral filter within the laser cavity that selectively filters specific wavelength components. This localized spectral filtering maintains the simplicity of direct gain medium modulation while significantly narrowing the laser linewidth by suppressing unwanted spectral broadening effects.
Solution Approach 2:
The delay means provides optical feedback to the gain medium that stabilizes the laser operation. This feedback mechanism narrows the linewidth by reinforcing specific longitudinal modes while suppressing others, allowing direct modulation to maintain both simplicity and spectral purity.
4Duration of action of moving object
If external optical modulator or switch is used to shape output pulse, then pulse duration control is improved, but device cost and complexity increase
Solution Approach 1:
The patent merges the pulse shaping function into the laser cavity by incorporating delay means that work in conjunction with the gain medium. This integrated approach provides precise pulse duration control without requiring external optical modulators or switches, thereby reducing device complexity while maintaining pulse quality.
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 solution enables the generation of high-power, short-duration pulses with fast risetimes and tunable wavelengths, reducing costs and improving performance for OTDR applications, while maintaining a narrow linewidth, thus addressing the limitations of existing OTDRs.
Implementation Method 1
spectral filter means for limiting the bandwidth of light passing through the gain medium
Implementation Method 2
delay means for delaying light by a predetermined delay time (Δt)
Implementation Method 3
an active optical gain medium... activate the gain medium to produce laser light pulses
Data Source
AI summary
A laser for generating laser light pulses comprises a cavity containing an active optical gain medium (102) and a spectral filtering device (104), a delay device (110) for delaying light by a predetermined delay time (Δt), means (106) for extracting a portion of laser light from the cavity, launching said portion into said delay means (110) and returning the delayed portion to the optical gain medium (102), control means (116) operable to activate the gain medium for a first time period (C1) to produce a first laser light pulse (LP1) having a duration that is less than the delay time (Δt), and activate the gain medium for a second time period (C2) while a said delayed portion of the first light pulse that has been delayed by the delay means (UO) is traversing the gain medium (102), thereby to produce a second laser pulse (LP2) having a shorter duration and faster risetime than the first laser light pulse (LP1), and output means (108) for outputting the second laser light pulse (LP2).