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Ultra-compact on-chip spectrometer based on thermally tuned topological miniaturized bound states in the continuum cavity

Xinyi Zhou, Xiaoyu Zhang, Yi Zuo, Zihao Chen, Zhiyuan Qian, Zixuan Zhang, Chao Peng, and Hongbin Li

Open Access Open Access

Abstract

On-chip spectrometers are key components in many spectral sensing applications owing to their unique advantages in size and in situ detection. In this work, we propose and demonstrate a class of thermally tunable spectrometers by utilizing topological miniaturized bound states in the continuum (mini-BIC) cavities in a photonic crystal (PhC) slab combined with a metal micro-ring heater. We achieve a resolution of 0.19 nm in a spectral range of ∼6 nm, while the device’s footprint is only $42\times 42\enspace \mu \mbox {m}^2$. The mini-BIC spectrometer works in nearly vertical incidence and is compatible with array operation. Our work sheds light on the new possibilities of high-performance on-chip spectrometers for applications ranging from bio-sensing to medicine.

© 2023 Optica Publishing Group

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Data availability

Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.

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Figures (4)
Fig. 1.
Fig. 1. Schematic and the principle of the on-chip spectrometer that utilizes a mini-BIC cavity. (a) High-$Q$ resonance of the mini-BIC cavity. (b) High-$Q$ resonance is shifted by applying heating voltages. (c) The input spectrum with unknown and arbitrary spectral features. (d) The solved spectrum obtained by sampling the input spectrum from thermal-optically sweeping the high-$Q$ resonance. (e) Structure of the on-chip spectrometer, in which a mini-BIC cavity is encircled by a micro-ring heater.

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Fig. 2.
Fig. 2. Fabricated samples and experimental setup. (a, b) Scanning electron microscope (SEM) images of the on-chip spectrometer. (c) Schematic of the experimental setup for the calibration and measurement. A narrow linewidth laser is used for the calibration (Scheme A), and a broadband light source combined with a waveshaper is adopted to simulate the spectral features for the measurement (Scheme B). ASE: amplified spontaneous emission, BS: beam splitter, RFP: rear focal plane, PD: photodetector.

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Fig. 3.
Fig. 3. Calibration results of the mini-BIC spectrometer. (a) Measured reflection spectrum from 1530 to 1570 nm of the mini-BIC cavity, showing the cavity supports four modes in such a range. (b) The detailed spectrum of M$_{22}$ mode with $Q=1.3\times 10^4$. (c) The high-$Q$ resonance of M$_{22}$ shifts versus different microheater voltages. (d) The mode wavelengths (black line) and $Q$ (red star) under a series of heater voltage which is adopted as “reference values” to solve the unknown spectrum later.

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Fig. 4.
Fig. 4. Measurement results of the mini-BIC spectrometer. (a) The recorded PD response at heating voltages from 0 to 2.7 V. (b) The solved spectrum calculated by the “reference values” at each voltage value, compared with the spectrum detected by a commercial spectrometer (black solid lines). A minimal spectral feature with FWHM of $0.19$ nm is distinguishable from the solved spectrum. Twenty rounds of repeated measurements are performed to show the statistics.

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Equations (3)

Equations on this page are rendered with MathJax. Learn more.

I r e f ( i ) = ∫ λ 1 λ 2 I r e f _ p d ( λ ) d λ = ∫ λ 1 λ 2 S r e f ( λ ) T ( λ , i ) H ( λ ) d λ ,
I m e a s ( i ) = ∫ λ 1 λ 2 S m e a s ( λ ) T ( λ , i ) H ( λ ) d λ .
S m e a s ( λ , i ) = I m e a s ( i ) I r e f ( i ) S r e f ( λ ) .
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