Optical Phase Lock Loop Using External Cavity Lasers
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Solution Overview
Problem
Existing Optical Phase Locked Loop (OPLL) systems using diode-pumped Nd: YAG and fiber lasers face limitations such as slow frequency tuning, high sensitivity to environmental changes, and instability due to phase reversal frequencies, requiring complex electronics and frequent calibration.
Innovation Solution
A high-performance OPLL system utilizing a pair of narrow-linewidth semiconductor-based External Cavity Lasers (ECLs) with precision controller-modulators and associated opto-electronic components, including a microwave heterodyne receiver, direct digital synthesizer, and loop filter, to achieve stable and identical phase performance within a small form-factor package.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diode-pumped Nd: YAG lasers or fiber lasers are used in OPLL systems, then long-term stable operation is achieved, but frequency tuning speed becomes slow (tens of milliseconds) due to PZT limitations
Solution Approach 1:
The patent replaces the mechanical PZT-based cavity length tuning system with an electric current-controlled injection laser system. The laser frequency is tuned by adjusting the injection current, eliminating the need for mechanical PZT movement and achieving fast tuning response in the microsecond range while maintaining long-term stability.
Solution Approach 2:
The patent changes the control parameter from mechanical PZT voltage to electrical injection current. By controlling the laser frequency through current modulation rather than mechanical cavity length adjustment, the system achieves both fast tuning speed and stable operation without the limitations of PZT response time.
2Volume of moving object
If DFB lasers are used in OPLL systems, then smaller size and lower power consumption are achieved, but very large bandwidth is required due to large linewidth (more than a few hundred kHz)
Solution Approach 1:
The patent changes the laser type from DFB to external cavity laser (ECL), which fundamentally alters the linewidth parameter. The ECL achieves a linewidth of less than 100 kHz compared to DFB's several hundred kHz, thereby reducing the required OPLL bandwidth while maintaining the compact size and low power consumption of semiconductor-based devices.
3Adaptability or versatility
If DFB-based OPLL operates with large bandwidth, then frequency coverage is improved, but phase reversal frequency (1-10 MHz) falls within the bandwidth causing instability
Solution Approach 1:
The patent changes the laser linewidth parameter by using external cavity lasers instead of DFB lasers. This reduction in linewidth allows the OPLL to operate with a narrower bandwidth that excludes the phase reversal frequency region, thereby eliminating instability while maintaining adequate frequency coverage for applications.
4Ease of manufacture
If DFB lasers are used in OPLL systems, then manufacturing cost is reduced, but very high sensitivity to environmental changes causes frequent loss of lock requiring ramping
Solution Approach 1:
The patent changes the laser structure from DFB to external cavity configuration, which fundamentally improves wavelength stability against environmental changes. The ECL's external cavity design provides better thermal and mechanical stability, reducing sensitivity to temperature and vibration while maintaining semiconductor-based manufacturing advantages.
5Adaptability or versatility
If semiconductor-based ECLs with very narrow linewidth are used, then bandwidth requirement is reduced and phase reversal frequency is avoided, but device complexity increases due to precision control requirements
Solution Approach 1:
The patent replaces complex mechanical stabilization systems with simple electrical current control. The external cavity laser's frequency is controlled through injection current modulation, which is electronically simple and does not require complex mechanical adjustment mechanisms or additional stabilization components.
Solution Approach 2:
The external cavity laser design inherently provides frequency stability and narrow linewidth without requiring additional active stabilization systems. The laser structure itself self-regulates to maintain stable operation, reducing the need for external control complexity while achieving the desired bandwidth efficiency.
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 system provides long-term stable operation with reduced bandwidth requirements, low power consumption, and lower manufacturing costs, avoiding phase reversal frequencies and environmental sensitivity issues, enabling reliable and easily controllable performance across various applications.
Implementation Method 1
a laser select logic (LSL) module that switches between feeding the error signal to a master or a slave controller-modulator
Implementation Method 2
a loop filter that provides gain in a bandwidth of a frequency response of the controller-modulators
Implementation Method 3
a microwave heterodyne receiver that receives a coherent heterodyne optical beat signal from the master and the slave ECLs
Implementation Method 4
a direct digital synthesizer (DDS) that supplies a control frequency to an electronic phase lock loop (PLL) circuit
Implementation Method 5
controller-modulators being precision modules with low frequency-noise temperature and current control circuitry
Data Source
AI summary
An optical phase lock loop (OPLL) system is disclosed that includes a master external cavity laser (ECL), and a substantially identical slave ECL. The master and slave ECLs are fabricated using a planar semiconductor device with waveguide-integrated planar Bragg gratings (PBG). Both the master and slave ECLs have a narrow linewidth and a low frequency-noise. Each of the ECLs has their own controller-modulator circuits for thermal tuning or electrical tuning via direct modulation. A laser-select-logic (LSL) module receives and processes a filtered phase error signal from a loop filter coupled to an electronic PLL device, and directs the processed phase error signal to one or both of the master and slave controller-modulators according to a logical determination of a required mode of operation of the OPLL system in order to achieve a stable and identical phase performance of the master and the slave ECLs. The required mode of operation is chosen from a locking mode, a prediction mode, a tracking mode, and a searching mode.