Traveling Wave Amplifier Pre-Emphasis for Sharper Optical Edges
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Solution Overview
Problem
Traveling wave amplifiers (TWAs) used to drive optical modulators or semiconductor laser diodes experience signal degradation, particularly at high frequencies above 10 Gbps, resulting in dull leading and falling edges of optical output.
Innovation Solution
A TWA configuration comprising non-inverting and inverting amplifiers connected in parallel, with specific delays between input and output, and differential amplifier architecture, including transmission lines with varying lengths to achieve phase reversal and delay differences, enhancing signal edges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional TWA configuration is used to drive optical modulators at high frequencies, then the amplifier can operate at high speeds, but the leading and falling edges of the optical output become dull
Solution Approach 1:
The TWA is divided into multiple amplifier sections (first through fourth amplifiers) with different configurations. Non-inverting amplifiers and inverting amplifiers are segmented into separate groups, each handling specific delay components. This segmentation allows independent optimization of each section's delay characteristics to achieve overall edge sharpening while maintaining high-speed operation.
Solution Approach 2:
Different amplifier sections are assigned different local qualities: non-inverting amplifiers provide signals with specific delay characteristics, while inverting amplifiers provide signals with different delay characteristics. Transmission lines connected to each amplifier are designed with specific lengths to provide localized delay adjustments. This local quality differentiation enables precise control over the composite signal's edge characteristics.
2Manufacturing precision
If transmission lines with different lengths are used to create delay differences, then rising and falling edges can be strengthened, but the device complexity increases
Solution Approach 1:
The TWA employs an asymmetric configuration where non-inverting amplifiers and inverting amplifiers are treated differently. Non-inverting amplifiers are connected through transmission lines of one length, while inverting amplifiers are connected through transmission lines of a different length. This asymmetric design creates the necessary delay differences for edge sharpening while maintaining a systematic approach that limits complexity growth.
Solution Approach 2:
The invention changes the delay parameter of different amplifier paths by using transmission lines of different lengths. Specifically, the sum of delays through non-inverting amplifiers and their transmission lines is made different from the sum of delays through inverting amplifiers and their transmission lines. This parameter change enables edge sharpening without requiring complex active delay elements in each path.
Data Source
AI summary
A traveling wave amplifier (TWA) primarily for driving a semiconductor optical device is disclosed. The TWA of an embodiment provides a plurality of differential amplifiers of the first type and an additional differential amplifier of the second type, where are they are connected between the input and the output of the TWA. The differential amplifiers of the first type provide a first delay from the input to the output, while, the differential amplifier of the second type provide a second delay longer than the first delay between the input and the output of the TWA.