九州大学学術情報リポジトリ
Kyushu University Institutional Repository
High Direct Modulation Speed with Space Mode Selectivity by Using Active Multimode
Interferometer Laser Diode
洪, 秉宙
http://hdl.handle.net/2324/2236274
出版情報：九州大学, 2018, 博士（学術）, 課程博士 バージョン：
権利関係：
（様式３）Form 3
氏 名 ：
Bingzhou Hong
論 文 名 ：
High Direct Modulation Speed with Space Mode Selectivity by Using Active Multimode Interferometer Laser Diode
（アクティブ
MMI
レーザによる超高速直接変調空間モード選択光源）区 分 ：甲
論 文 内 容 の 要 旨 Thesis Summary
This thesis discussed the research on high speed mode selective light source. With the huge development of mobile technology, and super computer technology, the inner connection link bandwidth requirements have reached new level. In the near future, it is predicted that the 1 Tb/s level speed is necessary for such links. In general, only optical communication links can provide such huge bandwidth.
Thus, the high speed direct modulated laser diodes that can be used in such optical links is the best candidate to be integrated within compact size mobile devices. Although wavelength length division (WDM) technology could be used to enhance the capacity, the relative complex WDM system is not suitable for integrated device system. Especially when considering the fact that mobile devices are extremely sensitive to the power consumption, a single chip that can operate on Tb/s level with low energy consumption is desired. On the other hand, similar to wavelength, optical mode has also been researched intensively to carry information. By utilizing spatial mode division multiplexing (SDM) technology, the transmission capacity is also largely enhanced. In such case, SDM can also be used for such inner connection optical links. In terms of SDM technology, considering single mode carries 100 Gb/s level signal, integration of 10 modes can bring 1 Tb/s level in total. In this thesis, the high speed mode selective light source is discussed.
The first issue is to design the mode selective light source. As the first trial, two lateral mode selective light source has been demonstrated. The core principle to design the mode selectivity is to separate propagation path within the device for each single mode. After separation, the current injection electrodes into each mode section are also separated electrically. By setting so, the current injected into each mode propagation path is controlled. Thus, the gain of each mode is controlled through current injection.
Consequently, the output mode is controlled by such arrangement. As the active multimode interferometer laser diode (active-MMI LD) has an MMI section at central part of the device, multiple optical modes are introduced and separated inside the device. As a result, active-MMI LD is the best candidates for mode selective light source.
Another issue is to achieve the high direct modulation bandwidth on laser diode. Traditional laser diode bandwidth is limited by the carrier photon resonance, which is the intrinsic physical bottleneck. On the other hand, photon photon resonance phenomenon (PPR) has been researched to extend the modulation bandwidth. Although PPR largely extend the bandwidth to more than 60 GHz on two section DBR lasers, the damping at high frequency still limits the furthermore bandwidth enhancement. To solve such problem and to extend the bandwidth to extremely high frequency range such as more than 100 GHz level, multiple PPRs ideals are proposed. By setting multiple PPRs that are placed not far from each other, the damping between each PPR can be compensated. Actually, ideal of multiple PPR is able to extend the modulation bandwidth to infinite level in principle. To achieve multiple PPRs, the basic requirement is to introduce multiple oscillating cavities inside the laser diodes. The active-MMI LD is able to integrate multiple access waveguides that acts as oscillating cavities, which exactly satisfied such requirements.
Furthermore, by utilizing high-mesa waveguide, the MMI edge forms an inner reflection mirror, which further introduces much more inner reflection mirrors. Based on the ideal described above, 1 by 3 active-MMI LD with 34 GHz direct modulation bandwidth is fabricated. With the combination of the two ideals described above, mode selectivity and high speed scheme are combined within single device. As a
result, a 1 by 3 active MMI LD with selective output mode are demonstrated. Because of the existence of multiple PPRs, over 40 GHz bandwidth for each single mode has been confirmed. Such high speed mode selective light source is the proof of design and fabricate a single laser chip with over 1 Tb/s level capacity.
