-
文中所设计的双波长电光调制与模分复用集成器件,需要考虑的性能指标主要有消光比、插入损耗、调制速率、调制深度和信道串扰。
消光比定义为:
式中:Imax和Imin分别是调制器在“通”和“断”状态下对应的输出光强。消光比的单位是dB,消光比越大,调制性能越好。
插入损耗定义为:
式中:Iout和Iin分别是调制器的输出光强和输入光强。插入损耗的单位是dB,插入损耗越小,调制性能越好。
调制速率是指调制设备单位时间可调制的码元速率,在电光调制器中能反应“通”、“断”调制的转换速度,其与集成器件的系统总响应时间T成反比,其表达式如下:
式中:
$ {t}_{re} $ 为材料的响应时间;$ {t}_{s} $ 为器件的稳定时间。调制速率的单位为GHz,调制速率越大,调制性能越好。调制深度定义为:
式中:P1和P2分别是调制器在“通”和“断”状态下对应的输出光功率。调制深度越大,表示调制器越有利于长距离、低误码率传输,调制效果越好。
信道串扰定义为:
其中,
${I}_{{\rm{out}}}$ 和${I}'_{{\rm{out}}}$ 分别为集成器件目标输出端口与非目标输出端口的光强。信道串扰的单位是dB,信道串扰越小,调制性能越好。采用Lumerical仿真软件中的时域有限差分法(3D-FDTD)分析了集成器件的消光比、插入损耗、调制电压、调制速率、调制深度和信道串扰值。仿真计算时,光源分别放置在输入端口1和2,探测器放置在输出端口3,图12(a)~(h)分别为波长1552.1 nm和1556.1 nm下TE0和TE1“通”、“断”状态的稳态场分布。
Figure 12. On-off steady-state field distribution diagrams of different wavelengths and modes. (a) 1552.1 nm TE0 "on" state; (b) 1552.1 nm TE0 "off" state; (c) 1552.1 nm TE1 "on" state; (d) 1552.1 nm TE1 "off" state; (e) 1556.1 nm TE0 "on" state; (f) 1556.1 nm TE0 "off" state; (g) 1556.1 nm TE1 "on" state; (h) 1556.1 nm TE1 "off" state
当该集成器件分别处于“通”和“断”状态下时,利用3 D-FDTD进行仿真,得到对应的稳定时间,如图13所示。由于器件的调制响应时间应以“通”状态至“断”状态、“断”状态至“通”状态中的较大值为准[20],因此选取“通”状态下的稳定时间约为27 ps。当电压为0~2 V时,硅在电场控制下的材料响应时间为30 ps[20],所以该集成器件的系统响应时间为57 ps。通过公式(16)和公式(17),得到器件的调制速率为17.54 GHz。通过公式(14)和(18)计算得到该器件的消光比ηER均为20 dB以上,调制深度D均为0.99。通过公式(15)和(19)可得:该集成器件的插入损耗γIL最小为0.47 dB,最大为0.57 dB;信道串扰值C CT最小为−39.50 dB,最大为−34.68 dB。表1对比了参考文献所提出的同类型器件,文中所设计的集成器件可以调制两个波长两个模式四个信道,在保证器件小型化的前提下,扩充了信道数,增加了传输容量。并且从表1中可以看出,该集成器件消光比高,信道串扰低且结构紧凑,易于集成。
Figure 13. Stable time when the integrated device is in the "on" and "off" states. (a) "on" state; (b) "off" state
Reference Extinction ratio/dB Insertion loss/dB Channel crosstalk/dB Footprint [8] - 4-5 - 200 μm [9] 15.1 0.3 - 46 μm×8 μm×0.22 μm [10] 3-4 1 - 200 μm [11] 29.13 1.33 - 9.03 μm [12] - 0.3 <−36 300 μm [13] - 0.3 <−22 >48.8 μm [14] - <1.5 <−30 >100 μm [15] - <3.2 <−21 18 μm [17] 13-16 22 - 0.45 mm2 [18] 19.73 <0.46 <−14.66 54 μm×22 μm This work >21.65 <0.57 <−34.68 65 μm×18 μm Table 1. Performance comparison of photonic crystal electro-optic modulator and two-mode mode division multiplexing integrated device
Integrated device of dual-wavelength electro-optic modulating and mode-division multiplexing based on photonic crystal
doi: 10.3788/IRLA20211107
- Received Date: 2021-12-27
- Rev Recd Date: 2022-02-09
- Available Online: 2022-11-02
- Publish Date: 2022-10-28
-
Key words:
- photonic crystal /
- dual-wavelength modulation /
- finite-difference time-domain method /
- mode-division multiplexing /
- L3 composite resonator
Abstract: In order to realize the miniaturization and multi-function of optoelectronic devices and further improve the capacity and speed of information transmission, an on-chip integrated device based on photonic crystal for dual-wavelength electro-optic modulation and mode division multiplexing (MDM) is proposed. The electro-optical modulation module of the integrated device is composed of a silicon-based photonic crystal waveguide and two L3 composite resonators, and the MDM module consists of silicon-based asymmetric parallel nanowire waveguides. A silicon-based photonic crystal waveguide is used at the junction of the two modules. The L3 composite resonators and PN doping structure are used to achieve the modulation of the two-wavelength TE0 mode, and the asymmetric directional coupling structure is used to convert the TE0 mode of two wavelengths into the TE1 mode. The parameters of the integrated device are calculated using three-dimensional finite-difference time-domain (3D-FDTD) method. The results show that when the voltage is 1.05 V, the integrated device can achieve a center wavelength of 1 552.1 nm and 1 556.1 nm TE0 mode, TE1 mode on-off modulation and two-mode mode division multiplexing function. The extinction ratio of the device is as high as 24.67 dB, and the modulation depths are both 0.99. The insertion loss and the channel crosstalk are less than 0.57 dB and −34.68 dB, respectively. And the minimum modulation speed is 17.54 GHz. The integrated device has compact structure and is expected to be applied to high-speed and large-capacity optical communication systems.