Hybrid Grating Surface-Emitting Laser for Low-Loss Feedback

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Solution Overview

Problem

Conventional surface emitting distributed feedback (SE-DFB) lasers with second-order grating structures suffer from lower efficiency and require larger areas and higher threshold currents due to additional first-order diffracted light output coupling loss.

Innovation Solution

A surface emitting laser with a hybrid grating structure is designed, integrating first-order and second-order grating structures in the same grating layer. The first-order grating structure acts as a high-efficiency reflection feedback area, while the second-order grating structure is limited to the laser emitting surface, achieving a balance between slope efficiency and critical current value.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Shape

If second-order grating structure is used in SE-DFB laser, then laser emitting angle is reduced and on-wafer test capability is improved, but slope efficiency decreases and threshold current increases due to additional first-order diffraction loss

Engineering Contradiction:

Improvelaser emitting angleVSAvoidslope efficiency

Core Design Contradiction:

ShapeVSLoss of energy

Solution Approach 1:

The grating layer is divided into two distinct regions: a first grating region with first-order grating structures and a second grating region with second-order grating structures. This segmentation allows each region to perform its specialized function - the first-order region provides high-efficiency feedback while the second-order region enables surface emission with controlled diffraction patterns, thereby resolving the contradiction between efficiency and emission characteristics

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the grating layer are assigned different grating structures with specific local properties. The first grating region uses first-order structures optimized for feedback efficiency, while the second grating region uses second-order structures optimized for surface emission. This local differentiation allows the system to simultaneously achieve high slope efficiency in the first-order region and proper emission characteristics in the second-order region

Inventive Principle:

Principle #3Local quality

2Reliability

If second-order grating structure is used in SE-DFB laser, then in-plane cavity formation is improved, but device area and threshold current increase

Engineering Contradiction:

Improvein-plane cavity formationVSAvoiddevice area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of using second-order grating structures across the entire device area, the invention applies them only in a specific second grating region. This partial application provides sufficient in-plane cavity formation capability where needed, while minimizing the overall device area and threshold current by limiting the second-order structure coverage

Inventive Principle:

Principle #16Partial or excessive action

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 hybrid grating structure achieves a balance between high slope efficiency and low critical current value, improving optical coupling efficiency and stabilizing the laser light field modal, which is difficult to achieve with conventional SE-DFB lasers.

Implementation Method 1

the first-order grating structure acts as a high-efficiency reflection feedback area

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

there will be first-order and second-order diffractions, respectively corresponding to the coupling constant κ1 (related to the efficiency of surface light emission) and κ2 (related to the efficiency of formation of in-plane cavity)

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 3

the second-order diffraction of the micro-grating structure is used in-plane for coupling the forward and backward modes in the waveguide to form a cavity to emit laser light

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentUS12294198B2Surface emitting laser with hybrid grating structure

Publication Date: 2025.05.06 TRUE LIGHT

AI summary

The grating layer of a surface emitting laser is divided into a first grating region and a second grating region along a horizontal direction. The second grating region is located at a middle area of the grating layer, while the first grating region is located in an outer peripheral area of the grating layer. Each of the first and second grating regions comprises a plurality of micro-grating structures. The grating period of the micro-grating structures in the first grating region is in accordance with the following mathematical formula:⋀=m⁢λ2*neff;in addition, the grating period of the micro-grating structures in the second grating region is in accordance with the following mathematical formula:⋀=o⁢λ2*neff.Wherein, ∧ is the length of grating period, λ is the wavelength of the laser light, neff is the equivalent refractive index of semiconductor waveguide, m=1, and o=2. The first grating region is a first-order grating region, and the second grating region is a second-order grating region, so as to form a hybrid grating structure in the grating layer. The surface emitting laser emits laser light perpendicularly from a light-emitting surface defined by the second grating region.