VCSEL Miniarray Aperture Coupling for 70 GHz Bandwidth
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Solution Overview
Problem
Existing VCSELs face a challenge in meeting the requirements of high modulation bandwidth and efficient coupling to multimode fibers due to the contradiction between needing a large aperture for high output power and a narrow spectrum, which is not achievable with traditional array designs.
Innovation Solution
A miniarray of optically-coupled oxide-confined apertures is created by etching holes in the chip surface, allowing for different aperture sizes and coatings to stabilize lasing in a single coherent mode, extending the modulation bandwidth through photon-photon interaction effects and enhancing coupling efficiency to multimode fibers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a large aperture is used to increase output power for high modulation bandwidth, then the modulation bandwidth is improved, but the spectrum becomes broader which reduces coupling efficiency to multimode fibers
Solution Approach 1:
The patent divides a single large aperture into multiple smaller sub-apertures arranged in an array. Each sub-aperture has a small size that supports only the fundamental transverse mode, ensuring narrow spectrum. The collective array structure provides sufficient total aperture area for high output power and extended modulation bandwidth, thus resolving the contradiction between aperture size and spectrum narrowness.
Solution Approach 2:
The patent combines multiple small sub-apertures into a unified array structure that functions as a single optical source. The sub-apertures are optically coupled through their proximity, merging their individual fundamental modes into a coherent array mode that couples efficiently to multimode fibers while maintaining narrow spectrum and high output power.
2Manufacturing precision
If traditional array designs are used to achieve narrow spectrum, then the spectrum is narrowed, but the device complexity and lateral size increase reducing coupling efficiency
Solution Approach 1:
The patent applies local quality by making each sub-aperture identical in size and shape, with each locally optimized to support only the fundamental mode. The uniform local structure across all sub-apertures simplifies fabrication compared to traditional arrays requiring precise individual element positioning, while the collective arrangement achieves the desired narrow spectrum.
3Reliability
If oxide confinement is used to define current path, then the current confinement is improved, but the aperture size is reduced limiting output power
Solution Approach 1:
The patent segments the current path into multiple independent oxide-confined channels, one for each sub-aperture. Each channel provides strong current confinement for reliable operation, while the parallel arrangement of multiple channels collectively delivers high total output power, resolving the contradiction between current confinement and output power.
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 miniarray of VCSELs achieves a modulation bandwidth increase of up to 70 GHz and efficient coupling to multimode fibers with an efficiency of at least 70%, addressing the limitations of traditional VCSEL designs.
Implementation Method 1
the selective oxidation is possible, where one or several layers of AlAs or Ga(1−x)Al(x)As with a high Al content (preferably above 95%) is oxidized forming amorphous dielectric material AlO(y) or Ga(1−x)Al(x)O(y) (120)
Implementation Method 2
the cavity is sandwiched between a bottom distributed Bragg reflector, DBR, (102) and a top DBR (106), each DBR being composed of alternating layers having a high and a low refractive index
Implementation Method 3
effective interaction of the neighboring optical modes in the related aperture regions through optical field coupling effect causing the interaction-induced splitting of the wavelengths of the optical modes confined by different neighboring apertures
Implementation Method 4
Splitting of the cavity modes in a frequency domain 3-100 GHz extends the modulation bandwidth of the device due to photon-photon interaction effects
Data Source
AI summary
An on-chip miniarray of optically-coupled oxide-confined apertures of vertical cavity surface emitting lasers (VCSELs) is realized by etching holes from the chip surface down to at least one aperture layer. Oxidation of the aperture layer results in electrically-isolated apertures suitable for current injection. The lateral distance between the aperture centers and the shape of the aperture is chosen to result in effective interaction of the neighboring optical modes in the related aperture regions through optical field coupling effect causing the interaction-induced splitting of the wavelengths of the optical modes. At least one aperture has a different surface area due to different spacing of the etched holes. Different aperture sizes result in different wavelengths of the coupled modes. Splitting of the cavity modes in a frequency domain 3-100 GHz extends the modulation bandwidth of the device due to photon-photon interaction effects.Selective deposition of highly reflective coating and/or anti-reflecting coating over apertures of different VCSELs foiining a miniarray allows stabilizing lasing in a single coherent mode of the array. Most preferably, highly reflective coating covers the largest aperture and stabilizes the fundamental mode of the coherent array. Anti-reflecting coatings can be deposited on at least one other aperture to reduce the photon lifetime and increase the homogeneous broadening of the related resonant wavelength. Consequently broadening of the photon-photon interaction resonances between the cavity modes can be controlled. Such resonance broadening allows control over the shape of the current modulation curve of the miniarray of VCSELs with the frequency maximum defined by the splitting of the cavity modes and the broadening defined by the broadening of the photon resonances. An increase in −3dB modulation bandwidth of the VCSEL miniarray up to at least 70 GHz is possible.Such miniarray of VCSELs enables efficient coupling of the emitted light to a multimode optical fiber with the efficiency of at least 70%.