Planar Lightwave Circuit Multiplexer for Non-Sequential Wavelength Channels
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Solution Overview
Problem
Current laser-based transmission systems face challenges in wavelength registration and tolerance, leading to high discard rates and reduced yield in hybrid integration of laser arrays and optical multiplexers, particularly due to fabrication limitations and the need for precise wavelength spacing according to industry standards like the ITU grid.
Innovation Solution
The use of multiple laser arrays with double the channel spacing between adjacent diodes, allowing for re-grouping of wavelengths and re-ordering of non-sequential signals using waveguide cross-connect sections or Mach-Zehnder couplers to achieve the required monotonic sequence for multiplexing, thereby relaxing fabrication tolerances and improving integration yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a monolithic array of laser diodes is used to provide multiplexer input, then wavelength division multiplexing can be achieved, but the monotonic wavelength sequence limitation requires each laser diode to operate within tight tolerance levels, resulting in high discard rates when fabrication variations occur
Solution Approach 1:
The invention divides the monolithic laser array into multiple separate sub-arrays, each handling a subset of wavelength channels. This segmentation allows each sub-array to have relaxed wavelength tolerance requirements, as long as the combined output of all sub-arrays covers the full wavelength range in monotonic sequence, thereby reducing discard rates due to fabrication variations
Solution Approach 2:
The invention changes the wavelength spacing parameter within each sub-array to be a multiple of the standard channel spacing (e.g., 200 GHz instead of 100 GHz). This parameter change allows each sub-array to operate with relaxed tolerance while still achieving the required overall wavelength coverage when sub-arrays are combined at the multiplexer input
2Measurement precision
If temperature tuning is used to modify center wavelength values of laser diodes, then wavelength registration to the ITU grid can be improved, but device performance and power consumption are limited
Solution Approach 1:
By segmenting the laser array into multiple sub-arrays with relaxed individual wavelength requirements, the invention reduces the need for aggressive temperature tuning to achieve wavelength registration, thereby lowering power consumption while still achieving acceptable overall wavelength alignment through the combined output
3Productivity
If multiple separate laser arrays are used with multiple-channel spacing, then relaxed tolerances and improved yield are achieved, but additional components such as waveguide cross-connect sections or Mach-Zehnder couplers are required to re-order non-sequential signals
Solution Approach 1:
The invention introduces waveguide cross-connect sections or Mach-Zehnder couplers as intermediary components between the multiple sub-arrays and the multiplexer input. These intermediaries perform the necessary signal re-ordering to convert non-sequential wavelength outputs from sub-arrays into the monotonic sequence required by the multiplexer, enabling relaxed tolerance operation while maintaining system functionality
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 enables the use of laser arrays with relaxed tolerances, reduces the need for temperature tuning, and increases the yield of usable laser arrays, while maintaining the desired wavelength spacing and multiplexing performance, thus enhancing the integration and efficiency of laser arrays with optical multiplexers.
Implementation Method 1
An AWG is a planar structure comprising an array of waveguides that are positioned in a side-by-side configuration, with the array disposed between input and output couplers. These components then act together as a diffraction grating in a spectrometer.
Implementation Method 2
Each of the waveguides differs in length with respect to its nearest neighbor by a predetermined amount. In operation as a multiplexer, a plurality of separate and distinct wavelengths is applied to separate and distinct input ports of the device. These wavelengths are combined as they pass through the structure, exiting at a single output port.
Data Source
AI summary
A wavelength division multiplexer utilizes an optical source in the form of at least two separate laser array components, each laser array component including a group of laser diodes operating at wavelengths that are spaced by a multiple of the pre-defined channel spacing of the multiplexer. This optical source thus generates a plurality of non-sequential optical signals that need to be re-ordered at some point along the signal path so that all of the signals are multiplexed onto a single output signal path. The multiplexer utilizes an arrayed waveguide grating (AWG) to combine the various optical signals, with a specialized apparatus for re-ordering the non-sequential wavelengths of the propagating plurality of N optical signals disposed either at the input or output of the AWG.