| 摘要: | 薄膜鈮酸鋰 (TFLN) 調製器有望成為實現下一代光通信系統所需的超寬調
製帶寬的理想元件，自從光纖通信出現以來，鈮酸鋰（LN）一直是電光調製器最
好的材料。然而，傳統的 LN 調製器體積龐大、價格昂貴且耗電，無法滿足需求。
製作在晶片上的 TFLN 調製器可以解決這個問題，但在 TFLN 中製造低損耗元
件不是一件簡單的事。在這裡，我們成功製作了 LN 電光調製器，該調製器比傳
統的塊狀 LN 元件小很多且效率更高，同時保留了 LN 的優異材料特性。在量子
領域，我們可以透過鈮酸鋰優異的電光效應，減少製程誤差對量子邏輯閘造成的
影響，甚至可以搭配其他 LN 製程，製造量子光源，並將光源與邏輯閘整合至單
晶片上，實現 System On Chip 的理想。
本實驗根據不同的鈮酸鋰波導備置方法進行系統性測試，並嘗試將其改良成
本實驗室製程設備允許的條件，以利本實驗室自行製作低損耗的 LNOI 波導。在
元件方面，我們以 I-line 曝光機、PECVD、ICP-RIE、離子佈植機、PVD 等半導
體相關技術，製造直波導以及帶有電極的 Mach–Zehnder Modulator (MZM)，製作
不同寬度之直波導，分別對其進行量測，在直波導的製作基礎下，利用鈮酸鋰的
優異電光效應製作電光調製器，並將其應用在 MZM 上。
波導製程方面，分為兩部份，第一部份是利用 ICP-RIE，以 Argon 離子進行
物理性蝕刻的 Ion Etching，第二部份是利用離子佈植的 IBEE(Ion-beam enhanced
etching)。其中，我們以 IBEE 製程成功在鈮酸鋰薄膜上製作出寬度 1~3um，蝕刻
深度 380nm，蝕刻側壁接近 90°，總長 0.5cm 的脊型波導，搭配端面拋光的技術，
並以側邊耦光的方式，測量其模態及損耗，在 TM 偏振下，3、2、1.5um 波導的
傳波損耗分別為 7.16dB/cm、6.76dB/cm、5.65dB/cm；在 TE 偏振下，3、2、1.5um
波導的傳波損耗分別為 3.6dB/cm、7.87dB/cm、3.96dB/cm。
另一方面，我們製作帶有電極的 MZM 結構，並對其單臂進行電光調製，調
製臂長為 1mm 的調製器，測得其 Vπ 為 50V，對應的電壓長度乘積為 5V·cm。
ii
在未來，能夠將傳統的塊狀 LN 調製器以 TFLN 製作的電光調製器取代，能
夠有效縮小元件尺寸，若搭配 CMOS 晶片驅動電壓，可作為光纖通訊裡的重要元
件，因其優於矽基材料的特性，TFLN 具有更多優勢，有機會在 TFLN 上實現光
量子邏輯閘及量子光源。;Electro-optic modulators made of thin-film lithium niobate (TFLN) are expected
to be ideal components for realizing the ultra-wide modulation bandwidth, which are
required by next-generation optical communication systems. Since the invention of
optical fiber communication, lithium niobate (LN) has always been the best material for
electro-optic modulator. However, the traditional LN modulator is bulky, expensive and
power-consuming, and cannot meet the demand. The TFLN modulator can solve this
problem, but it is not easy to fabricate low-loss components on the TFLN substrate.
Here, we have successfully fabricated a LN electro-optic modulator, which is much
smaller and more efficient than the traditional bulk LN components, while preserving
the excellent material properties of LN. In the quantum field, we can reduce the impact
of process errors on quantum logic gates through the excellent electro-optical effect of
lithium niobate, and even use other LN processes to assemble quantum light sources,
integrate the light sources and logic gates on a single chip in order to achieve the ideal
of System On Chip (SOC).
This work carried out a systematic test based on different lithium niobate
waveguide preparation methods and tried to improve it to the conditions allowed by our
laboratory process equipment. Consequently, our laboratory can make low-loss LNOI
waveguides by ourselves. About fabrication method, we use I-line stepper, PECVD,
ICP-RIE, ion implanter, PVD and other semiconductor-related technologies to create
straight waveguides and Mach-Zehnder Modulator (MZM) with electrodes. We
produced different – width straight waveguides and measured them separately. After the
straight – waveguide fabrication, an electro-optic modulator is made because of the
excellent electro-optic effect of lithium niobite. This structure is used to create the MZM.
The waveguide manufacturing process is divided into two parts. The first part is
iv
Ion Etching that uses ICP-RIE by Argon ions, and the second part is IBEE (Ion-beam
enhanced etching) that uses ion implantation. We successfully used I-line stepper to
fabricate ridge waveguides with the minimum width around 1um, etching depth reaches
380nm, sidewall angle close to 90°, and total length of 0.5cm on the lithium niobate
film by the IBEE process. This is more efficient than using e-beam lithography. After
the end face polishing, we use edge coupling to measure the waveguide mode and
propagation loss. Propagation losses of 3.9 dB/cm for TE and 6 dB/cm for TM
polarization were measured at 1550 nm for a 5 mm long and 1.5µm wide waveguide
using the Fabry-Perot method.
In addition, we made an MZM structure with electrodes, and electro-optically
modulate the light of single arm. The modulator with a modulating
length of 1mm measured by the value of VπL ~5V·cm.
In the future, the traditional bulk LN modulator can be replaced with an electrooptic modulator made of TFLN, which can effectively reduce the component size. If it
is matched with the CMOS chip driving voltage, it can be used as an important
component in optical fiber communication. Because of its superiority to silicon-based
materials, TFLN has more advantages and could implement optical quantum logic gates
and quantum light sources on TFLN. |
