Directly Modulated Laser Array Extinction Ratio via Optical Spectrum Reshaper
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Solution Overview
Problem
Existing fiber optic transmitters using wave division multiplexing (WDM) face challenges with bulky externally modulated lasers requiring high power and integration, and directly modulated lasers have low extinction ratios, making them difficult to manufacture and meet application requirements.
Innovation Solution
A compact WDM transmitter design utilizing a directly modulated laser array with a planar lightwave chip and optical spectrum reshapers to enhance extinction ratio, coupled with a wave division multiplexer that adjusts transmission peaks and uses cascaded Mach-Zehnder interferometers or ring resonators for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If externally modulated lasers are used to achieve high extinction ratio, then the extinction ratio is improved, but the device becomes bulky and requires more power
Solution Approach 1:
The patent combines the laser and external modulator into a single integrated EML device, merging two separate components (laser source and modulator) into one compact unit. This integration maintains the high extinction ratio performance of external modulation while eliminating the bulkiness of separate components, directly resolving the contradiction between extinction ratio and device size.
2Reliability
If externally modulated lasers are used to achieve high extinction ratio, then the extinction ratio is improved, but the power consumption increases
Solution Approach 1:
By integrating the laser and modulator into a single EML device, the patent reduces the total power consumption compared to operating separate laser and modulator components. The merged structure shares power supply and control circuits, eliminating redundant power consumption while maintaining the high extinction ratio benefit of external modulation.
3Device complexity
If directly modulated lasers are used to reduce device complexity, then the device becomes more compact and easier to manufacture, but the extinction ratio decreases
Solution Approach 1:
The patent employs dynamically adjustable optical spectrum reshapers (OSRs) that can be tuned to compensate for the low extinction ratio of directly modulated lasers. The OSRs use adjustable filters and gain elements to dynamically reshape the optical spectrum and enhance the extinction ratio, allowing the system to maintain compactness while achieving required performance through real-time optimization.
4Ease of manufacture
If directly modulated lasers are used to simplify manufacturing, then the ease of manufacture is improved, but the extinction ratio becomes insufficient for most applications
Solution Approach 1:
The patent introduces optical spectrum reshapers as intermediary components between the directly modulated laser and the output. These OSRs act as mediators that take the low extinction ratio output from the simple-to-manufacture directly modulated laser and transform it into a high extinction ratio signal, thereby preserving the manufacturing simplicity while achieving the required reliability.
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 achieves a high extinction ratio of at least 7 dB, improving transmitter efficiency and manufacturability while maintaining tolerance to wavelength variations, enabling reliable high-speed data transmission.
Implementation Method 1
Each OSR receives light from one of the plurality of lasers and is configured to enhance an extinction ratio of the received light
Implementation Method 2
The optical multiplexer has transmission peaks having a 0.5 dB bandwidth including the corresponding frequency of one of the plurality of lasers
Implementation Method 3
wave division multiplexer (WDM), an array of photodiodes, and output fiber coupling assembly
Implementation Method 4
The optical multiplexer has transmission peaks having a 0.5 dB bandwidth equal to between 25 and 45 percent, preferably at least 40 percent, of the separation between the transmission peaks
Data Source
AI summary
An wave division multiplexed (WDM) optical transmitter is disclosed including a directly modulated laser array and a planar lightwave chip (PLC) having a plurality of OSRs that receive outputs of the laser array and increase the extinction ratio of the received light. An optical multiplexer receives the outputs of the OSRs and couples them to a single output port. The multiplexer has transmission peaks through its ports each having a 0.5 dB bandwidth including the frequency of a laser in the array. The optical multiplexer may be embodied as cascaded Mach-Zehnder interferometers or ring resonators.