Diagonal Waveguide Optical Semiconductor Device Suppresses Spectral Linewidth
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Solution Overview
Problem
The digital coherent method in optical communications faces challenges due to phase noise from light sources, specifically increased spectral linewidth caused by rearward output light reflection in wavelength-variable light sources, which affects the quality of optical communication signals.
Innovation Solution
An optical semiconductor device is designed with semiconductor lasers, light detectors, and waveguides on a semiconductor substrate, where light detectors are positioned to receive reflected light from the rear-end side, guiding it diagonally away from the semiconductor lasers to minimize return light reflection, thereby reducing spectral linewidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If rearward output light is outputted perpendicularly from the rear-end face of semiconductor lasers, then the light can be monitored by an external wavelength monitor, but the reflected light returns to the semiconductor laser causing increase in spectral linewidth
Solution Approach 1:
The patent changes the output direction of rearward light from perpendicular (0 degrees) to a diagonal angle (e.g., 45 degrees) relative to the rear-end face. This angular dimensionality change causes reflected light to diverge from the original propagation path, preventing it from returning to the semiconductor laser while still allowing external monitoring through the diagonally oriented waveguide and detector.
Solution Approach 2:
The patent extracts the wavelength monitoring function from the main optical path by using a separate waveguide that couples diagonally to the rear-end face. This separate monitoring path is physically decoupled from the forward output path, allowing independent optimization of each function without mutual interference.
2Device complexity
If light detectors are integrated close to semiconductor lasers on the same substrate, then the device complexity is reduced, but return light from reflection may still affect the semiconductor laser
Solution Approach 1:
The patent introduces asymmetric angular orientation between the rearward light output direction and the waveguide input direction. The waveguide is positioned at a diagonal angle (e.g., 45 degrees) relative to the semiconductor laser rear-end face, creating an asymmetric geometric relationship that allows the light detector to receive rearward light while reflected light follows a different path that does not return to the laser.
Solution Approach 2:
The patent introduces a diagonal waveguide as an intermediary component between the semiconductor laser rear-end face and the light detector. This waveguide mediates the light transmission by capturing rearward output light at a diagonal angle and guiding it to the detector, while its angular orientation acts as a spatial filter that blocks reflected light from reaching the laser.
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 configuration effectively suppresses the increase in spectral linewidth of the output light, enhancing the accuracy and stability of digital coherent optical communication by reducing return light reflection, leading to a narrower spectral linewidth and improved communication performance.
Implementation Method 1
said plural waveguides serving to guide respective rays of the second light toward one end face of the optical semiconductor device
Implementation Method 2
said plural light detectors serving to receive respective rays of reflected light
Data Source
AI summary
An optical device includes: lasers output first light from a front-end side and output second light from a rear-end side; an optical multiplexer circuit multiplex respective rays of the first light, to thereby send out output light; waveguides guide respective rays of the second light toward one end face of the optical device; and light detectors receive respective rays of reflected light that are due to reflection of the respective rays of the second light after being guided by the waveguides, on the one end face or on respective inclined end faces in concave portions formed on that one end face. The light detector is located between the rear-end side of the laser and the one end face or the inclined end face, and the second light is outputted diagonally relative to a perpendicular line with respect to the one end face or the inclined end face.