Fig. 1. Basic principle of F-P microcavity. (a) General model of F-P microcavity; (b) transmission rate of F-P filter as a function of wavelength, where solid line and dashed line represent transmission rate of all-dielectric F-P microcavity and metal F-P microcavity, respectively. A 50 nm thick silver film is used in metal F-P filter^[28], and a 135 nm thick SiO₂ layer (@550 nm) is used in cavity layer. Multilayer stack expression for all-dielectric F-P filter is Sub|(HL)⁶ H 2L H (LH)⁶, where Sub represents quartz substrate, H represents a 62.5 nm thick Ta₂O₅ layer (@550 nm), and L represents a 94.18 nm thick SiO₂ layer; (c) all-dielectric F-P microcavity; (d) electric field distribution of all-dielectric F-P microcavity

Fig. 2. Schematic diagram of linearly variable F-P filter

Fig. 3. Schematic diagram of integrated F-P filter. (a) Schematic illustration of 3D structure of integrated F-P filter; (b) schematic diagram of transmission spectrum

Fig. 4. All-dielectric integrated F-P filter. (a) Schematic diagram of combinatorial etching technique; (b1) infrared integrated F-P filter with 16 channels^[4]; (b2) transmittance of infrared integrated F-P filter with 16 channels^[4]; (c1) near-infrared integrated F-P filter with 128 channels^[5]; (c2) transmittance of near-infrared integrated F-P filter with 128 channels^[5];(d1)-(d4) realizing in-orbit verification of No. 10 Shijian Satellite^[57]

Fig. 5. Fabrication of integrated metal F-P filter using electron beam grayscale lithography^[60]. (a)-(b) Schematic diagram of integrated metal F-P filter; (c) electron beam grayscale exposure technique

Fig. 6. Fabrication of integrated F-P filter using laser direct-writing grayscale lithography^[10]. (a)-(b) Integrated all-dielectric F-P filter on InGaAs detector; (c) scanning electron microscope (SEM) cross-sectional image of F-P filter; (d)-(e) transmission variation with cavity length; (f) wavelength-dependent response of different pixels in detector

Fig. 7. Metasurface-based F-P filter^[62]. (a)-(b) Schematic diagrams of metasurface-based F-P filter; (c) SEM image of fabricated metasurface-based F-P filter; (d) experimentally measured transmission spectrum of filter

Fig. 8. Schematic diagram of spectral reconstruction algorithm^[21]

Fig. 9. Reconstruction results of shortwave infrared miniature spectrometer^[10]. (a) Reconstructed narrowband spectra from 1000 nm to 1600 nm with 100 nm step; (b) reconstructed narrowband spectra of 1500 nm with 2 nm full width at half maximum (FWHM) by 50 pixel set, and 5 nm FWHM by 20 pixel set. Dashed line is Lorentz fit of spectrum reconstructed by 20 pixel chip-spectrum, and its FWHM is 5 nm

Fig. 10. Structure diagram and characterization and measurement results of CdS laser^[75]. (a) Schematic diagram of CdS laser structure; (b) schematic illustration of interface between CdS nanoribbon and microcavity photon; (c) SEM images of CdS nanoribbon and DBR; (d) photoluminescence spectra of CdS laser at different pump powers; (e) relationship between emission intensity of CdS laser and pump power

Fig. 11. Structure diagram and characterization and measurement results of BP laser^[78]. (a) Schematic diagram of BP nanosheet embedded in a DBR microcavity structure; (b) photoluminescence spectra of BP laser at different pump powers; (c) photoluminescence spectra of BP laser under spontaneous emission states at different pump powers; (d) relationship curve between laser FWHM and pump power; (e) relationship between BP laser radiation intensity and pump power

Fig. 12. Schematic of structure of monolayer WS₂ embedded in a microcavity and it's measurement results^[89]. (a) Structure of monolayer WS₂ embedded in a DBR microcavity; (b) strong coupling effect of monolayer WS₂ in DBR microcavity

Fig. 13. Schematic of structure of WS₂/hBN/WS₂ heterostructure embedded in a microcavity and it's measurement results^[97]. (a) Schematic of structures of WS₂/hBN/WS₂ heterostructure embedded in a microcavity and heterostructure; (b) strong coupling phenomenon between heterostructure excitons and microcavity photons

Fig. 14. Schematic of structure of monolayer WS₂ embedded in microcavity and it's measurement results^[105]. (a) Structure of monolayer WS₂ embedded in a DBR microcavity; (b) characterization of monolayer WS₂ at room temperature. Blue curve represents absorption spectrum of monolayer WS₂ on PDMS, red curve represents photoluminescence spectrum of monolayer WS₂ on bottom DBR, and dark blue curve represents polariton radiation spectrum; (c) angle-resolved reflectivity spectrum, showing strong coupling phenomenon of structure of monolayer WS₂ embedded in DBR microcavity; (d) angle-resolved photoluminescence spectrum above threshold, showing Bose-Einstein condensation (BEC) phenomenon of monolayer WS₂

Fig. 15. Examples of fiber F-P microcavity used for refractive index and temperature sensing. (a) Basic structure of fiber F-P interferometer (FPI)^[109]; (b) simulation image of temperature-induced sensor deformation^[110]; (c) interference spectra of fiber FPI cantilever at different temperatures (0, 20, and 40 ℃)^[110]; (d) demodulation relationship of F-P microcavity length with temperature change^[110]

Fig. 16. Schematic of acoustic sensing principle of F-P microcavity based on GO (graphene oxide) film^[117]

Fig. 17. Turbulent airflow velocity measurement system^[119]. (a) Schematic diagram of airflow velocity measurement system; peak position change of two sensors at airflow velocity of (b) 93 m/s; (c) 54.5 m/s

Fig. 18. Schematic diagram of principle of cavity resonance-assisted measurement of low-dimensional material refractive index^[123]. (a) Structure diagram of embedding low-dimensional material into n cavities; (b) transmission spectra of corresponding regions with and without embedded low-dimensional material; (c) solid and hollow points represent n and k of monolayer WS₂ material calculated by cavity resonance method, and corresponding lines are from recent work determined by spectroscopic ellipsometry for reference; (d) no polarization, 0° polarization, and 90° polarization microcavity microregion transmission spectra of embedded CdS nanoribbon. Refractive indices of o and e lights of CdS nanoribbon are 2.42 and 2.45 at wavelength of 716.7 nm extracted by cavity resonance method, respectively

Fig. 19. Examples of cell laser. (a) Experimental setup for cell laser^[124]. Cell laser is externally pumped by a laser through a microscope objective. Fluorescence light collected by same objective is separated by a dichroic mirror and sent to a spectrometer and a camera; (b) cells are placed between two high-reflective mirrors and settle onto bottom mirror surface; (c) schematic of generating vector beams through molecular interactions^[126]. Interactions of amyloid-beta (Aβ) with lipid monolayers coated on LC droplets with different assemblies (monomers, oligomers, protofibrils, and fibrils), triggering topological transformation of vector beams

Fig. 20. Example of chiral laser and laser emission imaging. (a) Figure on left: schematic diagram of a chiral laser with chiral molecules as gain media sandwiched in an F-P microcavity. Left-handed (L) and right-handed (R) circularly polarized lasers are alternately used as pump light sources. Figure on right: details of chiral biomolecules^[128]; (b) schematic diagram of experimental setup. Illustration is diagram of detecting different types of biochemical signals in extracellular environment^[129]

Fig. 21. Polarization/spectral control based on F-P microcavity. (a) Schematic cross-section of a nano-cavity based on a metasurface^[14]; (b), (c) experimental results of transmission spectra of structure in (a) under different polarized incident lights^[14]; (d) metainterface spectrum-polarization filter model^[18]; (e) cross-sectional image of metainterface filter captured by SEM^[18]; (f) experimental results of metainterface filter. Solid line and dotted line are transmittances of TM and TE lights of metainterface filter, respectively, while dashed line and dash-dot line are polarization extinction ratios of metainterface filter and bare grating, respectively^[18]

Fig. 22. Example of beam shaping based on F-P microcavity. (a) SEM cross-sectional images of a hemispherical microcavity with a radius of curvature of 5 µm (top) and 3 µm (bottom), respectively. Left graph shows original image, and dots show cracks. Right graph shows dashed image of growth model^[12]; (b) schematic diagram of structure of coupled open microcavity^[13]; (c) schematic diagram of mode splitting and corresponding coupled cavity structure (top panel), and experimental results (dots) and theoretical values (dashed lines) obtained from laser transmission experiments (bottom panel)^[13]

Fig. 23. Beam shaping results of F-P microcavity with introduction of metasurface structure. (a) Structure diagram. Metasurface placed on second DBR surface matches phase evolution of focused Gaussian beam, thus limiting optical field in transverse direction (xy direction) as well; (b) phase evolution calculated by finite-difference time-domain modeling for longitudinal mode index q=5; (c) light intensity distribution of mode in (b) ; (d) design of "H" pattern of metasurface microcavity^[19]

Fig. 24. Multivortex pulsed beam laser^[16]. Spatial encoding is achieved by combining specific components of vortex beam, while temporal encoding is achieved by modulating pulse