硅基宽带高分辨率免制程傅里叶变换光谱仪

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本文报道了一种先进的硅基傅里叶变换光谱仪（FTS），与之前在Nature Communications上发表的研究显著改进，实现了更宽的光谱覆盖范围和更高的分辨率。相比于2018年的一项成果[Nature Communications 9, 665(2018)]，新设计的FTS在193 THz附近能获取7 THz宽的频谱，分辨率高达0.11 THz或sub-nm级别，这是先前记录的三倍以上。这一突破性的进步解决了硅光子学中普遍存在的波导宽度制造公差问题，这是该领域的一大挑战。该光谱仪采用了平衡马赫-泽德勒干涉仪（balanced Mach-Zehnder interferometer,MZI）结构。在传统的硅光子器件中，由于微纳尺度的加工误差，波导宽度的一致性对性能有很大影响。然而，通过创新的设计和优化，研究人员能够使新FTS对制造过程中的这种不一致性具有一定的容忍度，确保了在实际生产中的稳定性和准确性。该研究的关键在于利用硅材料的优良光学特性以及对干涉效应的精细控制。马赫-泽德勒干涉仪的工作原理是利用光信号在两个分支路径上的相位差来测量光谱信息，当这两个分支的长度不同或受到微小变化时，会导致光的干涉模式发生相应变化，从而反映输入光的频率或波长。通过精确控制和分析这些干涉图案，科学家们能够解析出光的频谱特征。在实现高分辨率的同时，该FTS还具备了小型化和集成的优势，这使得硅基FTS有潜力在诸如光纤通信、环境监测、化学分析甚至量子计算等应用领域发挥重要作用。整体来看，这项工作不仅提升了硅光子技术的性能极限，也为未来的光谱学研究和实际应用提供了新的可能性，标志着硅基光谱仪技术迈入了一个全新的发展阶段。

Fabrication-tolerant Fourier transform

spectrometer on silicon with broad bandwidth

and high resolution

ANG LI,

*JORDAN DAVIS,

ANDREW GRIECO,

NAIF ALSHAMRANI,

1,2

AND YESHAIAHU FAINMAN

1,3

Department of Electrical and Computer Engineering, University of California, San Diego, California 92093, USA

King Abdulaziz City for Science and Technology (KACST), Riyadh 11442, Saudi Arabia

e-mail: fainman@ece.ucsd.edu

*Corresponding author: angli@ucsd.edu

Received 2 October 2019; revised 9 December 2019; accepted 16 December 2019; posted 18 December 2019 (Doc. ID 379184);

published 31 January 2020

We report an advanced Fourier tran sform spectrometer (FTS) on silicon with significant improvement compared

with our previous demonstration in [Nat. Commun. 9, 665 (2018)]. We retrieve a broad band spectrum (7 THz

around 193 THz) with 0.11 THz or sub nm resolution, more than 3 times higher than previously demonstrated

[Nat. Commun. 9, 665 (2018)]. Moreover, it effectively solves the issue of fabrication variation in waveguide

width, which is a common issue in silicon photonics. The structure is a balanced Mach–Zehnder interferomet er

with 10 cm long serpentine waveguides. Quasi-continuous optical path difference between the two arms is in-

duced by changing the effective index of one arm using an integrated heater. The serpentine arms utilize wide

multi-mode waveguides at the straight sections to reduce propagation loss and narrow single-mode waveguides at

the bending sections to keep the footprint compact and avoid modal crosstalk. The reduction of propagation loss

leads to higher spectral efficiency, larger dynamic range, and better signal-to-noise ratio. Also, for the first time to

our knowledge, we perform a thorough systematic analysis on how the fabrication variation on the waveguide

widths can affect its performance. Additionally, we demonstrate that using wide waveguides efficiently leads to a

fabrication-tolerant device. This work could further pave the way towards a mature silicon-based FTS operating

with both broad bandwidth (over 60 nm) and high resolution suitable for integration with various mobile

platforms.

https://doi.org/10.1364/PRJ.379184

1. INTRODUCTION

Fourier transform spectrometers (FTSs) recovering an un-

known spectrum are powerful tools in various fields including

chemical sensing, bio-medical applications, and autonomous

vehicles, etc. [1–4]. Compared to other direct-detection-based

spectrometers, such as monochromators or grating-based spec-

trum analyzers, one of the key advantages of FTSs is Fellgett’s

advantage, namely, higher signal-to-noise ratio and dynamic

range [5]. The FTS employs an interferogram (i.e., autocorre-

lation function) generated from the input signal with unknown

spectra using an interferometer, where the input signal is di-

vided into two paths with variable optical path difference

(OPD). At the output of the interferometer, the optical signals

from these two optical paths are recombined on a photodetec-

tor, which is used to generate a photocurrent as a function

of OPD, thereby generating the desired interferogram. The

Fourier transform of the detected interferogram (i.e., autocor-

relation function) produces the power spectral density of the

input signal. The larger the maximum OPD, the higher the

spectral resolution. A classical FTS typically uses a moving

element (such as a mirror) to introduce quasi-continuous

tunable OPD between two paths and generates a temporal in-

terferogram (i.e., autocorrelation function). Thus, FTSs are

usually realized as bulky free-space interferometric systems

and suffer from slow scanning speeds, resulting in long mea-

surement times.

Use of silicon photonics as a platform for FTS realization has

attracted widespread attention as a candidate to meet the rap-

idly growing demand for low-cost, portable devices [6]. In con-

trast to free-space FTSs, most FTSs demonstrated on silicon

platforms are spatial heterodyne spectrometers (SHSs) that em-

ploy a large array of unbalanced Mach–Zehnder interferome-

ters (MZIs) with varying length differences, each of which

introduces a fixed amount of OPD to the spectrum [3,7–9].

In order to achieve high resolution (i.e., large OPD), the inci-

dent spectral signal is typically required to be split into over

Research Article

Vol. 8, No. 2 / February 2020 / Photonics Research 219

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