Grating Element Wavelength Stability in External Resonator Lasers
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Solution Overview
Problem
Existing semiconductor lasers, particularly those with Fabry-Perot resonators, suffer from wavelength instability and mode hopping due to temperature changes, leading to fluctuations in optical power, which is problematic in applications like optical communication and gas sensing, and often require temperature control using Peltier devices, increasing complexity and cost.
Innovation Solution
An external resonator type light emitting system is developed with a grating device having a refractive index of 1.8 or more, a short grating length of 300 µm or less, and a full width at half maximum of the Bragg reflectance adjusted to 0.8 nm or more, which increases the temperature coefficient and reduces mode hopping by widening the wavelength spacing, allowing operation without a Peltier device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a Fabry-Perot resonator configuration is used in semiconductor lasers, then the laser can be manufactured with simple structure, but the wavelength stability deteriorates and mode hopping occurs due to temperature changes
Solution Approach 1:
A grating element is introduced as an intermediary component between the laser diode and the external resonator. This grating element acts as a wavelength-selective mirror that reflects only the desired wavelength back into the laser diode, thereby stabilizing the output wavelength and preventing mode hopping while maintaining the simple FP resonator structure
Solution Approach 2:
The invention changes the physical parameters of the grating element, specifically setting the refractive index to 1.8 or more and the grating length to 300 µm or less. These parameter changes optimize the grating's wavelength selectivity and reflection characteristics, enabling stable single-mode operation without compromising the simple structural design
2Reliability
If temperature control components (Peltier devices) are added to stabilize wavelength, then the wavelength stability improves, but the device complexity increases
Solution Approach 1:
The grating element serves as a passive intermediary that provides wavelength stabilization without requiring active temperature control. By using the grating's inherent wavelength-selective reflection property, the system achieves wavelength stability through optical design rather than thermal management, thereby avoiding additional control components
Solution Approach 2:
The invention replaces the mechanical/thermal control system (Peltier device) with an optical system (grating element). Instead of controlling wavelength stability through active temperature management, the system uses passive optical wavelength selection, substituting a complex thermal control mechanism with a simpler optical component
3Reliability
If the grating length is increased to improve wavelength selectivity, then the wavelength stability improves, but the full width at half maximum of Bragg reflectance decreases causing mode hopping
Solution Approach 1:
The invention optimizes the grating parameters by setting the grating length to 300 µm or less while maintaining a refractive index of 1.8 or more. This parameter combination achieves the right balance: the sufficient grating length provides wavelength selectivity, while the high refractive index broadens the Bragg reflectance width to prevent mode hopping, resolving the contradiction between selectivity and reflectance width
4Reliability
If the refractive index of the grating element is increased to broaden Bragg reflectance width, then the temperature stability improves, but the manufacturing precision requirements increase
Solution Approach 1:
The invention selects a refractive index of 1.8 or more for the grating element, which broadens the Bragg reflectance width and improves temperature stability. This parameter choice is optimized to achieve sufficient temperature insensitivity while remaining compatible with conventional fabrication techniques, balancing performance improvement with manufacturing feasibility
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 enhances wavelength stability and reduces optical power variations, preventing mode hops and maintaining stable operation over a broader temperature range without the need for additional temperature control components.
Implementation Method 1
mirrors that uses Bragg reflection for realizing a resonator
Data Source
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AI summary
A grating device includes a support substrate, an optical material layer 11 disposed on the support substrate and having a thickness of 0.5 µm or more and 3.0 µm or less, a ridge optical waveguide formed by a pair of ridge grooves in the optical material layer and having a light-receiving surface for receiving a semiconductor laser light and a light-emitting surface for emitting light having a desired wavelength, a Bragg grating 12 comprising convexes and concaves formed in the ridge optical waveguide, and a propagating portion 13 disposed between the light-receiving surface and the Bragg grating. The relationships represented by the following Formulas (1) to (4) are satisfied: 0.8 nm ≤ΔλG≤ 6.0 nm ··· (1); 10 µm ≤Lb ≤ 300 µm ··· (2); 20 nm ≤ td ≤ 250 nm ··· (3); and nb ≥ 1.8 ··· (4).