Optical Module Anti-Reflection Film Stabilizes Power Output
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional optical modules experience instability in optical power output due to multiple reflections within the photodiode, which vary with temperature and wavelength, leading to fluctuations in beam intensity and sensitivity.
Innovation Solution
The optical module incorporates an anti-reflection film on the back surface of the semiconductor substrate to eliminate multiple reflections by matching the refractive indices between the semiconductor substrate and the beam splitter, thereby stabilizing the beam intensity and reducing sensitivity variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the photodiode is mounted directly on the beam splitter without an anti-reflection film, then the structure is simpler and manufacturing is easier, but multiple reflections occur within the semiconductor substrate causing instability in optical power output and sensitivity variations
Solution Approach 1:
An anti-reflection film is introduced as an intermediary layer between the beam splitter and the semiconductor substrate of the photodiode. This film has a refractive index that is the geometric mean of the beam splitter and substrate materials, eliminating multiple reflections by matching the optical impedance and preventing interference patterns that cause optical power instability.
Solution Approach 2:
The refractive index parameter of the interface between the beam splitter and semiconductor substrate is modified by introducing the anti-reflection film. This changes the optical properties of the interface to minimize reflection coefficients, thereby stabilizing the transmitted optical power and reducing sensitivity variations with temperature and wavelength changes.
2Reliability
If multiple reflections are eliminated using an anti-reflection film, then optical power stability improves, but the manufacturing process becomes more complex and costly
Solution Approach 1:
The anti-reflection film is designed with specific refractive index and thickness parameters optimized for the operating wavelength range. By carefully selecting these parameters, the film eliminates multiple reflections across a broad spectrum, providing stable beam intensity without requiring complex multi-layer structures or precise thickness control beyond standard manufacturing capabilities.
3Use of energy by moving object
If the semiconductor substrate has high reflectivity surfaces, then light coupling efficiency may improve, but multiple internal reflections cause interference and reduce measurement precision
Solution Approach 1:
The naturally high reflectivity of the semiconductor substrate, which initially causes harmful multiple reflections and interference, is converted into a benefit by introducing the anti-reflection film. The film transforms the problematic reflective interfaces into matched impedance transitions, allowing the substrate's optical properties to be utilized effectively while eliminating the harmful interference effects through proper refractive index matching.
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 anti-reflection film effectively suppresses variations in transmittance, maintaining stable optical power output and reducing the need for temperature control, resulting in a compact and cost-effective optical module.
Implementation Method 1
the PD is mounted on the BS by interposing an anti-reflection film therebetween that eliminates multiple reflections caused between the top and bottom surfaces of the semiconductor substrate for the collimated monitored beam entering through the bottom surface thereof
Implementation Method 2
by matching the refractive indices between the semiconductor substrate and the beam splitter
Implementation Method 3
The first lens is optically coupled with the LD and converts the divergent optical beam into a collimated optical beam
Implementation Method 4
The BS is optical coupled with the first lens and splits the collimated optical beam into a collimated monitored beam and a collimated signal beam
Implementation Method 5
The top surface forms a Fresnel interface against the semiconductor stack provided thereon
Data Source
AI summary
An optical module with a laser diode (LD) without any temperature control and an optical fiber that is coupled with the LD through the two lens system is disclosed. The two lens system first converts laser beam into collimated beam and second concentrates the collimated beam onto the optical fiber. A beam splitter is disposed between the lenses and splits the collimated beam toward a photodiode (PD). The PD, which receives the split collimated beam in a back surface thereof, provides an anti-reflection film in the back surface. The anti-reflection film eliminates multi reflections occurred within the PD.