External Cavity Laser Array for WDM Optical Systems
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Solution Overview
Problem
Wavelength division multiplexed (WDM) passive optical networks face challenges in efficiently utilizing the capacity of trunk fibers due to the inefficiencies of time domain multiplexing, which limits data rates and bandwidth utilization, and require tunable lasers that are costly and sensitive to external conditions, making them unsuitable for lower-cost, lower-performance applications.
Innovation Solution
An external cavity laser array system with distributed Bragg reflectors and arrayed waveguide gratings that emit a range of wavelengths, allowing for narrow mode spacing and high-speed optical modulation, enabling universal transmitters that can operate across multiple channel wavelengths without the need for continuous tuning or external wavelength locking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If time domain multiplexing is used to transmit data on the trunk fiber, then the fiber count is reduced, but the bandwidth utilization and data rates are limited
Solution Approach 1:
The patent employs dynamically tunable laser sources that can adjust their wavelength of operation. This dynamic capability allows the same physical transmitter to be assigned to different wavelength channels as needed, enabling the system to transition from static TDM wavelength assignment to flexible WDM wavelength assignment, thereby improving bandwidth utilization without increasing fiber count
Solution Approach 2:
The system changes the operating parameter of the laser source from fixed wavelength to tunable wavelength. By varying the wavelength parameter, the transmitter can operate on multiple wavelength channels, effectively converting a single-wavelength TDM system into a multi-wavelength WDM system that utilizes the full bandwidth capacity of the trunk fiber
2Productivity
If tunable lasers are used to provide multiple wavelengths in WDM systems, then bandwidth utilization improves, but the cost and sensitivity to external conditions increase
Solution Approach 1:
The patent segments the wavelength selection function from the laser source itself by introducing external wavelength selection mechanisms (such as tunable filters or wavelength multiplexers). This allows the use of simpler, less expensive laser sources while achieving wavelength diversity through external components, thereby reducing overall system cost
Solution Approach 2:
The system uses a single physical transmitter design that can be configured to operate at different wavelengths through software control and external wavelength selection components. This 'copying' approach allows the same hardware platform to serve multiple wavelength channels, reducing the need for multiple specialized transmitters and lowering costs
3Adaptability or versatility
If continuously tunable lasers are used to achieve wavelength selection, then wavelength flexibility improves, but manufacturing complexity and sensitivity to external conditions worsen
Solution Approach 1:
The patent introduces intermediary components such as tunable optical filters, wavelength multiplexers, or external cavity elements that mediate between a simple laser source and the wavelength selection requirement. These intermediaries provide the wavelength flexibility needed for WDM operation while keeping the core laser source simple and robust against external conditions
4Object-affected harmful factors
If TDM burst mode transmission is used to prevent noise, then noise is reduced, but data rates and stabilization time are limited
Solution Approach 1:
The patent employs dynamically tunable wavelength capability that allows transmitters to operate continuously on their assigned wavelength channel without needing to turn off and on rapidly between transmissions. This dynamic wavelength assignment eliminates the need for burst mode operation, allowing continuous data transmission at high rates without cumulative noise issues
Solution Approach 2:
The system enables continuous transmission by assigning dedicated wavelength channels to different transmitters. Each transmitter can maintain continuous operation on its assigned wavelength without interruption, eliminating the start-stop burst mode operation and associated stabilization delays while preventing noise through wavelength separation rather than time separation
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 solution enhances bandwidth utilization, allows for higher data rates, and reduces the complexity and cost of transmitters by enabling interchangeable devices that can operate across different wavelengths, improving the efficiency and maintainability of WDM-PON systems.
Implementation Method 1
distributed Bragg reflectors and arrayed waveguide gratings that emit a range of wavelengths
Implementation Method 2
arrayed waveguide gratings that emit a range of wavelengths
Implementation Method 3
extended lasing cavities that narrow the mode spacing while maintaining a relatively small gain region in the laser emitter capable of higher speed optical modulation
Data Source
AI summary
An external cavity laser array system may be used in a WDM optical system, such as a WDM-PON, for transmitting optical signals at multiple channel wavelengths. The system generally includes a plurality of laser emitters (e.g., gain chips) optically coupled to and separated from respective exit reflectors (e.g., tunable narrow-band reflectors), thereby forming an array of external cavity lasers with extended lasing cavities. The exit reflectors may be distributed Bragg reflectors (DBRs) located in the waveguides in an arrayed waveguide grating (AWG). The laser emitters emit a range of wavelengths including multiple channel wavelengths and the DBRs reflect a subset of channel wavelengths including at least a channel wavelength associated with the laser emitter such that lasing occurs at the subset of channel wavelengths. The AWG then filters the emitted laser light at the associated channel wavelengths.