The structural unit of BPLC is not a single liquid crystal molecule, but the double-twist cylinder (DTC) spontaneously formed by them^[17-18]. In a chiral environment, liquid crystal molecules tend to twist relative to each other to reduce the elastic energy of the system^[19]. However, in three-dimensional space, this twisting cannot extend infinitely. To seek the lowest energy state, molecules form a cylinder with a radius of approximately one pitch around a virtual central axis, where molecules in any direction within the cylinder exhibit a helical twisted state; this is the double-twist cylinder structure. These microscopic DTC units act as "structural building blocks," further stacking in space to form a three-dimensional lattice with long-range order on a macroscopic scale. Notably, in regions where DTCs interlace, the ordered arrangement of molecules is disrupted, forming linear topological defects—disclination lines. These disclination lines are not "flaws" in the traditional sense, but rather the skeleton constituting the stable BPLC lattice; they form a network at the center or edges of the lattice, endowing the BPLC with structural stability (Figure 1a). According to different spatial packing modes and symmetries of DTCs, there are mainly two thermodynamically stable blue phases (Figure 1b), namely Blue Phase I (BPI) arranged in a body-centered cubic (BCC) manner (space groupI4₁32) and Blue Phase II (BPII) arranged in a simple cubic (SC) manner (space groupP4₂32)^[20-21]. In addition, there exists Blue Phase III (BPIII), which lacks long-range order; its structure is considered to be an amorphous state similar to "blue fog," composed of a disordered network of DTCs. These special periodic structures create a periodic distribution of dielectric constants, making BPLC a three-dimensional photonic crystal that produces selective reflection of incident white light through Bragg diffraction^[22-23]. By controlling the content of chiral dopants in the material system and the cooling process, BPIII, BPII, and BPI can appear sequentially as the temperature decreases. Researchers have conducted in-depth studies on the layer-by-layer phase transition process of blue phase liquid crystals, revealing the transformation mechanism from the cholesteric phase to the blue phase, which provides an important basis for understanding the formation process of blue phase liquid crystals^[24-25].

The three-dimensional periodic lattice structure of BPLC has a lattice constant typically on the order of hundreds of nanometers, which falls precisely within the visible light wavelength range. This periodic arrangement of dielectric constant (refractive index) essentially makes it a tunable three-dimensional photonic crystal^[26]. When a beam of white light is incident on BPLC, its behavior follows Bragg's law of diffraction. For light waves satisfying specific conditions, reflected light from different lattice planes undergoes constructive interference, causing light of that wavelength to be strongly reflected back, while light of other wavelengths is mostly transmitted^[27]. This forms the iconic, vibrant structural color of BPLC^[28]. The central reflection wavelength (λ₀) of BPLC is described by the Bragg equation (Equation (1)).

where:arepresents the lattice constant;nrepresents the average refractive index (measured via Abbe refractometry, spectroscopy, or ellipsometry);h,kandlare the Miller indices of the crystal plane. For a given BPLC material, its reflection color is primarily determined by the lattice constantaand the crystal plane with the strongest reflection (h,k,l). Due to differences in lattice symmetry, the strongest reflection peak of BPI typically originates from the {110} family of crystal planes, whereas for BPII, it originates from the {100} family.^[29]. Therefore, in systems composed of the same chiral liquid crystal material, since the lattice constant of BPII is typically smaller than that of BPI, its reflection wavelength will be shorter.

A crucial characteristic is that, due to the helical chirality of the internal structure of BPLC, the reflected light is circularly polarized. The polarization handedness of the reflected light aligns with the helical chirality direction of the BPLC. For instance, right-handed BPLC selectively reflects right-handed circularly polarized light while allowing left-handed circularly polarized light to transmit. This property is the fundamental marker distinguishing BPLC from many other reflection-based coloration materials, laying a unique foundation for its applications in fields such as polarization optics and anti-counterfeiting.

The reflection characteristics of BPLC constitute a complex system determined by the combined effects of multi-scale factors^[30-31]. From the microscopic to the macroscopic scale, these factors can be categorized into three levels: intrinsic material parameters, mesoscopic structural integrity, and macroscopic external fields. These levels are interrelated and jointly determine the central wavelength, peak intensity, and bandwidth of the reflection spectrum^[32-33].

The intrinsic optical parameters of the material are the internal factors and theoretical upper limit determining reflection performance.

(1) Enhancing birefringence (Δn): According to coupled wave theory, both the reflection bandwidth (Δλ) and peak reflectivity (R) are positively correlated with Δn. A high Δn signifies stronger interaction between liquid crystal molecules and the optical field, enabling the formation of wider and deeper photonic bandgaps. Therefore, designing and synthesizing novel liquid crystal monomers with large molecular polarizability anisotropy (such as molecules containing rigid cores like biphenyl or terphenyl) is the most fundamental approach to enhancing reflection performance.^[10,34]. Yang Zhou et al.^[44] proposed a high-throughput blue phase liquid crystal identification method based on convolutional neural networks, providing new insights for optimizing blue phase liquid crystal materials and improving preparation efficiency. Furthermore, breakthrough progress has been made in ferroelectric liquid crystal blue phases in recent years. Ozaki et al.^[76] successfully confined ferroelectric nematic liquid crystals (NFLC) within a three-dimensional blue phase structure using a blue phase polymer templating method, achieving macroscopic polarization cancellation while retaining microscopic ferroelectricity (polarization strength > 2.5 μC/cm²). This composite material exhibits a record-breaking Kerr constant (1.36 nm/V²) and microsecond-level response (50 μs/10 μs), breaking through the bottleneck where high electro-optical activity and fast response are difficult to coexist.

(2) Optimize the chiral doping system: The helical twisting power (HTP) of the chiral agent directly determines the lattice constant and reflection wavelength of BPLC^[45-48]. Selecting a chiral agent with high HTP allows achieving reflection at the target wavelength with lower concentrations, reducing interference with the ordering of liquid crystal mesogens. Meanwhile, optimizing the compatibility between the chiral agent and the host liquid crystal helps form a more stable BPLC phase^[49-52].

(3) Introduction of functional dopants: By doping quantum dots, dye molecules, or nanoparticles into the BPLC system, it is possible not only to achieve a combination of reflection and luminescence (such as circularly polarized luminescence), but also to indirectly enhance reflection efficiency via local field enhancement effects, or to endow the material with entirely new stimulus-responsive properties^[8,11,39].

Even with excellent intrinsic materials, defects such as polycrystalline domains, grain boundaries, and dislocations commonly present in actually prepared BPLC films can induce strong light scattering, significantly weakening the efficiency and color purity of Bragg reflection. Therefore, enhancing lattice perfection is a crucial step toward achieving super-reflection.

Polymer-stabilized blue phase liquid crystals (PS-BPLC) represent the most mainstream and effective strategy currently. By adding a small amount of photosensitive monomers and initiators to the BPLC precursor, followed by photopolymerization after the formation of the BPLC phase, a three-dimensional polymer network penetrating the liquid crystal matrix is formed in situ^[8,11]. This network acts like a "skeleton" that "locks" the ideal BPLC lattice structure. It not only significantly broadens the operating temperature range (from a few K to over 100 K) but, more critically, effectively suppresses the formation of lattice defects, reduces grain size, and lowers light scattering, thereby significantly enhancing reflectivity and contrast^[53-54].

Furthermore, to obtain larger single crystals or lattices with specific orientations, researchers have developed photo-alignment techniques (using linearly polarized UV light to irradiate photosensitive anisotropic films coated on substrates, providing anchoring for the directional alignment of liquid crystal molecules, with pretilt angles precisely controllable via illumination conditions or material chemical structures), rubbing alignment techniques (inducing liquid crystal alignment by rubbing the substrate surface with velvet), and template-assisted growth techniques (using specially treated substrates to induce BPLC growth along specific crystallographic directions (such as [110] or [100]), thereby enhancing reflection from specific crystal planes^[7]), thermal gradient methods (establishing a linear temperature gradient within the blue phase temperature range, where nucleation occurs preferentially at the low-temperature end and grows slowly along the gradient direction), and electric field-assisted crystallization (applying a DC electric field during cooling, where dielectric forces drive preferred orientation of crystal nuclei). In addition, applying shear forces (imposing shear flow within the blue phase temperature range, where shear stress drives DTCs to align directionally along the flow field), electric fields (low-frequency AC electric fields driving double-twist cylinders (DTCs) to reconstruct along the electric field direction via dielectric coupling, forming single-crystal domains), or constructing microstructured confinement can also effectively regulate lattice orientation, reduce defects, and obtain more uniform, higher-quality reflection^[55].

Recent research by Li Quan's team has outlined several specific implementation schemes: (1) Surface orientation control: Utilizing surface orientation control, patterned alignment is preset on the substrate via photo-alignment techniques (such as digital photo-alignment or laser direct writing) to guide BP into single-crystal domains or ordered arrangements. For instance, by alternating ordered and disordered regions, dynamic Bragg reflection and diffraction modulation can be achieved, with optical responses adjusted via electric fields. (2) Electric field-induced lattice modulation: Electric fields can induce three-dimensional deformation of the BP lattice, with responses depending on dielectric anisotropy and lattice orientation. By controlling the direction and strength of the electric field, precise control over lattice orientation can be achieved, reducing defects and improving optical uniformity. (3) Preparation of polymer-stabilized blue phase liquid crystals: Introducing a polymer network into blue phase liquid crystals forms a polymer-stabilized blue phase, significantly enhancing thermal and mechanical stability while suppressing defect generation. Furthermore, the polymer network can adjust the helical pitch under an electric field through a charge trapping mechanism, enabling dynamic modulation of the reflection bandwidth.^[55,74].

In summary, achieving high-performance blue phase liquid crystal reflectors requires synergistic optimization across three levels: materials, structure, and devices. However, the extreme pursuit of a single strategy often accompanies new technical bottlenecks. For example, regarding the synergy between materials and structure: introducing high Δnliquid crystals with three-dimensional polymer networks can significantly enhance reflectivity and stability, but high Δnmaterials and polymer networks may induce new lattice distortions or interface defects due to mismatches in interfacial tension and polymerization shrinkage stress, thereby exacerbating light scattering^[1,35]. Similarly, regarding the synergy between structure and devices: achieving perfect lattice matching in multilayer films or microcavity structures is highly challenging; orientation conflicts and stress accumulation at interlayer interfaces will become severe performance limiting factors^[55].

Therefore, future research priorities should shift from optimizing single parameters to multi-level collaborative design. This includes developing network monomers with higher Δnthat exhibit better compatibility with liquid crystals to reduce internal stress, designing smart alignment layers to achieve cross-scale lattice control, and advancing interfacial engineering methods to eliminate interlayer mismatch. Only by systematically addressing these cross-level technical challenges can the immense application potential of blue phase liquid crystals in frontier fields such as metasurfaces and photonic chips be fully unleashed^[12].

Building upon material and structural optimization, ingenious device design can further break through the performance ceiling of single-layer BPLC. Theoretically, a single chiral BPLC layer can reflect at most 50% of unpolarized incident light (as it reflects only circularly polarized light of one handedness). To overcome this limitation, left-handed and right-handed BPLC films can be stacked. In this way, one circular polarization component of the incident light is reflected by the first layer, while the transmitted component of the opposite handedness is reflected by the second layer, theoretically driving the total reflectivity close to 100%.^[12,56]. Similarly, stacking BPLC layers with different reflection wavelengths can achieve broadband reflection or white light reflection. Furthermore, placing BPLC between two mirrors constitutes a Fabry-Pérot (F-P) optical resonant cavity. When the cavity length satisfies the resonance condition, light of specific wavelengths undergoes multiple reflections and interference within the cavity; its reflection intensity is drastically amplified, while the spectral linewidth becomes extremely narrow.^[55]. This method can achieve peak reflectivity close to 100% and an extremely high quality factor (Q-value), albeit at the cost of some bandwidth, making it highly suitable for applications such as lasers, narrowband filtering, and high-sensitivity sensing. Luo Dan et al.^[38,57]designed and fabricated multilayer blue phase liquid crystal films. As shown in Figure 3a, they stacked left-handed (LH) and right-handed (RH) blue phase templates, filling the intermediate space with non-chiral liquid crystals. By electrically controlling the alignment of the liquid crystal molecules in the middle layer to reduce scattering, ultra-high reflectivity was achieved: Red (89%), Green (82%), and Blue (68%), representing a 2.7 to 3.6-fold improvement over traditional single-layer films. Under electric field switching, the reflectivity reached new highs: Red (94%), Green (86%), and Blue (72%), requiring only a low voltage of 1 V/μm. With sub-millisecond response speeds (0.36 ms on / 0.53 ms off), these films are suitable for high-speed displays and photonic devices. By introducing a resonant cavity structure and utilizing BPLC as part of the cavity or mirror, reflection at specific wavelengths is enhanced; additionally, anti-reflection coatings or refractive index matching layers are used to reduce interfacial reflection losses. Device-level design is a crucial pathway to achieving "super" reflection. As shown in Figure 3b, Wang Jingxia et al.^[1]first employed an in-situ secondary growth method to prepare single-helix (left-handed) polymer-templated blue phase films (LH-PTBP), washing away unpolymerized components to create a porous structure. Using the LH-PTBP as a bottom layer, they assembled a liquid crystal precursor containing the opposite handedness (right-handed) on top. Precise temperature-controlled cooling induced the formation of a right-handed blue phase (RH-BP) in the upper layer, which was then cured by UV light to form a tightly bonded bilayer structure (DH-BP). Subsequently, unpolymerized components were washed away to obtain an open double-helix polymer-templated blue phase film (DH-PTBP). Furthermore, through interface modification, thinning of the bottom layer, and increasing the proportion of non-polymerized components in the upper liquid crystal precursor, they significantly improved the formation of large-area single-domain blue phases, color uniformity, and reflectivity (reaching up to 93%), while simultaneously resolving issues of color/structural inhomogeneity arising during the fabrication process.

The above impacts are summarized inTable 1As shown, through precise regulation of these factors, the design and optimization of reflection characteristics can be achieved, providing a theoretical foundation for developing high-performance optical devices and offering directions for exploring novel applications.

Traditional reflective display technologies (such as electrophoretic electronic paper) offer low power consumption advantages but are limited by low color saturation and slow response speeds. Super-reflective BPLC technology addresses the key defect of insufficient reflectivity in traditional BPLC, achieving color performance comparable to emissive displays while fully retaining the zero static power advantage of reflective displays and the trait of enhanced visibility under stronger ambient light. Its sub-millisecond response speed further supports smooth video playback, providing an ideal solution for developing "paper-like" color video e-books and billboards. The physical basis of blue phase liquid crystal reflective devices stems from their unique photonic crystal structure's dynamic response mechanism to external electric fields. Fundamentally different from the principle of traditional liquid crystals relying on polarized light modulation, this technology utilizes Bragg reflection generated by a three-dimensional periodic cubic lattice to achieve color control, eliminating the need for polarizers and alignment layers required by traditional liquid crystals, thereby greatly simplifying the device structure to a three-layer basic construction (blue phase liquid crystal layer/transparent electrode/glass substrate) (Figure 5a). In the zero electric field state, the self-assembled [110] lattice planes selectively reflect the visible spectrum with precise lattice constants (200~400 nm); when an external electric field is applied, directional Coulomb forces induce the rearrangement of liquid crystal molecules, achieving continuous tunability of the reflection wavelength across the visible light band through the synergistic effect of lattice constant modulation and birefringence changes.

The introduction of Polymer-Stabilized Blue Phase (PSBP) technology marks a major breakthrough in broadband electric field tuning devices. The White team^[60]utilized a three-dimensional polymer network to precisely replicate the BP lattice skeleton, effectively suppressing lattice collapse induced by electric fields, and achieved a red-shift tuning range of 160 nm under DC electric field drive for the first time (Fig. 5b). However, this system is limited by a low polymer content with a mass fraction of 5%, maintaining phase stability only within a narrow temperature window (ΔT=6 °C). In 2015, Lin et al.^[61]achieved a key breakthrough: by applying a specific threshold electric field (3.5 V/μm) to Blue Phase I (BP I) to induce the formation of a novel Blue Phase X (BP X), and combining this with UV curing to construct a cross-linking density gradient network, they expanded the operating temperature range to over 60 °C. In the optimized system, the red shift under DC field jumped to 200 nm, and a symmetric broadening of the reflection band half-peak width from 50 nm to 120 nm was observed in a 27 μm thick device (Fig. 5c), significantly improving the smoothness of color gradients. In 2017, the Wang Meng team^[62]further broke through the barriers of asymmetric modulation technology: by programmatically controlling the polarity and amplitude of the bias voltage, they enabled a device originally reflecting 517 nm green light to achieve full color gamut coverage. Mechanism studies indicate that directional electrostatic forces drive the displacement of the charged polymer network, triggering electromechanical deformation of the cubic lattice, with its non-uniform density distribution being key to the bias polarity-dependent response. Subsequent research achieved precise spatial control of photonic properties through molecular design and process innovation. By employing chiral dopants to construct a helical polymer network, a shift of the photonic bandgap across the entire visible spectrum from 450 to 750 nm was realized under a unidirectional DC field (5 V/μm). By regulating polymerization kinetics via thiol-ene click chemistry and combining it with spatially selective UV mask curing, patterned devices with regional electrochromic characteristics were fabricated (Fig. 5d): under electric field drive, the exposed regions exhibited a dynamic spectral migration from green (550 nm) through yellow-orange (600 nm) to red (650 nm), while the masked regions, due to differences in polymer network cross-linking density, had their bandgap stably locked in the blue wavelength range (480 nm). This strong correlation between "electric field response" and "spatial position" lays the material foundation for pixelated reflective displays. Comprehensive studies indicate that by regulating key experimental parameters, the morphology and microstructure of the polymer network within the three-dimensional periodic structure of blue phases can be directionally optimized, thereby designing BPLC reflective devices with diversified electric field response characteristics.

BPLC demonstrates significant application potential in the field of optical anti-counterfeiting due to its unique photonic crystal structure and the resulting structural color properties. Its periodic three-dimensional helical structure endows the material with a physical basis that is difficult to replicate. Unlike traditional technologies relying on chemical pigments, the structural color of BPLC exhibits distinct angle dependence and unique circular polarization selectivity; these two intrinsic optical characteristics constitute its core advantages for anti-counterfeiting applications.

BPLC anti-counterfeiting technology is primarily achieved through two approaches: static encoding and dynamic response. In terms of static encoding, its selective reflection can generate highly saturated structural colors at specific wavelengths. More ingeniously, the irreproducibility of its microstructure can be utilized for high-density information storage. For example, Wang Jingxia et al.^[10]'s research indicates (as shown in Figure 6a), the random multi-domain structure of BPLC can be directly imaged under a polarized optical microscope and converted into a binary QR code with a resolution as high as 37×37 pixels. Since each pixel corresponds to a unique liquid crystal domain arrangement, this "Physical Unclonable Function (PUF)" characteristic significantly enhances the security of anti-counterfeiting labels. Furthermore, researchers have developed ternary encoding based on green-blue-black tri-color responses by leveraging the multiphase coexistence characteristics of its core-shell structure and temperature-driven diffusion behavior without phase transitions, significantly increasing information storage density.

In terms of dynamic response, the introduction of external fields (such as electric fields, thermal fields, and mechanical stress) as stimuli enables reversible switching of anti-counterfeiting information, thereby increasing the complexity and security of verification. Asshown in Figure 6b, Zhao Dongyu et al.^[58]designed a dual-mode anti-counterfeiting label that achieves synergistic regulation of BPLC temperature-sensitive structural color (reflection state) and photoluminescence from doped luminescent molecules (AIEgens) (fluorescence state). This system allows the label to present and independently encrypt different information under visible light (reflection) and ultraviolet light (fluorescence), constituting a high-security multimodal and dynamic anti-counterfeiting mechanism. Chen Quanming et al.^[63]investigated the phenomenon of asymmetric domain growth in blue phase liquid crystals and the corresponding changes in blue phase liquid crystals in response to both temperature and electricity. Asshown in Figure 6c, they discovered that structural asymmetry can be utilized for information hiding and display; the figure shows that the displayed portion has higher reflectivity compared to the hidden portion. Therefore, it can be concluded that structure is the key factor determining reflection quality. To promote the practical application of BPLC anti-counterfeiting technology, patterning processes and polymer stabilization are key enabling technologies. The former is used to manufacture macroscopically visible anti-counterfeiting marks, while the latter ensures excellent environmental stability of the labels across a wide temperature range. Furthermore, the discovery of new physical phenomena, such as asymmetric domain growth, provides new mechanisms for information hiding and dynamic display. Meanwhile, intelligent responsiveness, flexibility, and stretchability are important development directions for BPLC anti-counterfeiting labels to adapt to diverse application scenarios. For example, the team led by Guo Jinbao^[42], based on the unique mechanical/thermal CPL tuning performance of quantum dot-doped blue phase liquid crystal elastomers (Figure 6d), explored their applications in anti-counterfeiting and information encryption. First, multi-layer anti-counterfeiting authentication was achieved through pattern design. Second, information writing was realized by partially stretching QD-BPLCE, and information storage was achieved via thermal programming. Finally, by combining different types of QD-BPLCE, multi-level information encryption was accomplished, leveraging their optical behaviors in different states to effectively prevent information leakage.

In summary, blue phase liquid crystal super-reflective anti-counterfeiting technology has evolved from a single color-changing mark into an integrated anti-counterfeiting system combining static high-resolution encoding with dynamic multi-modal response. This technology integrates topological phase transitions and optical properties, breaking through the technical bottlenecks of traditional static anti-counterfeiting. With its continuously improving security levels and functional diversity, BPLC is becoming a highly promising core technological route in the field of optical anti-counterfeiting.

The super-reflective properties of BPLC originate from its self-assembled three-dimensional photonic crystal structure, which is extremely sensitive to external environmental changes, laying the physical foundation for its applications in optical sensing and advanced imaging. Its core working mechanism manifests as a chain response of "external stimulus → change in lattice constant → change in reflection wavelength/intensity," achieving the efficient conversion of physical or chemical signals into optical signals.

In terms of optical sensors, such asFigure 7shows, BPLC optical sensors, with their high sensitivity, fast response, label-free operation, and miniaturization capabilities, provide a highly competitive technical platform for cutting-edge fields such as environmental monitoring, biomedicine, and smart wearable devices. The sensing applications of BPLC can be categorized based on the type of stimulus:

(1) Physical sensing (temperature and pressure): Temperature is the most fundamental sensing object for BPLC. Its lattice is highly sensitive to temperature; minute temperature fluctuations can cause significant shifts in the Bragg reflection peak, manifesting as color changes visible to the naked eye, making it suitable for creating simple and efficient temperature indicators. In terms of pressure sensing, external stress directly causes reversible deformation of the photonic crystal structure, thereby altering the structural color according to the magnitude and distribution of the pressure (Figure 7a)^[64]. For example, Nie Zhenzhou et al.^[7]developed a BPLC-elastomer composite material. Through integrated structural-functional design, it achieved micro-Newton-level mechanical sensitivity and millisecond-level fast response, showing broad prospects in fields such as wearable electronics, biomedical monitoring, and structural health monitoring.

(2) Chemical and Biosensing: By introducing functional molecules sensitive to specific analytes into the BPLC system, its sensing capabilities can be extended from the physical domain to the chemical and biological domains. This functionalized design enables the development of specialized sensors with specific optical responses to humidity, pH, specific gases, or biomolecules. For example,Figure 7illustrates the design of humidity-responsive BPLCs and the development of multiple applications, such as rewritable BPLCs (Figure 7b), color-changing BPLC pattern printing via humidity response (Figure 7c), and fruit-based colorimetric humidity sensors (Figure 7d)^[65]indicate that blue phase liquid crystals can be used to prepare humidity-responsive colored photonic polymer coatings. Such coatings can dynamically change color in response to environmental humidity variations, achieving visualized humidity sensing. The mechanism is as follows: the periodic three-dimensional cubic structure of blue phase liquid crystals gives them a photonic bandgap, enabling selective reflection of light at specific wavelengths. Under humidity stimulation, the material structure expands or contracts, causing a shift in the photonic bandgap, which results in a color change.^[75]. Furthermore, asFigure 7eshows, by introducing toluene into the liquid crystal matrix, intermolecular forces are disrupted, molecular alignment is altered, and the free energy of the helical columnar structures and line defects within the polymer-stabilized blue phase (PSBP) structure is affected. These microscopic changes manifest macroscopically as a Bragg diffraction shift, leading to a redshift or blueshift in the spectrum, thereby enabling the detection of toluene vapor.^[66].

In the future, integrating multiple response mechanisms is an important development direction for BPLC sensing technology. Through ingenious molecular functionalization and material composite strategies, intelligent sensing systems capable of simultaneously detecting multiple parameters such as temperature, humidity, and specific chemical substances can be constructed. Furthermore, these studies lay a solid foundation for the application of super-reflective BPLC materials in the field of optics.

The application of BPLC in the field of optical imaging is mainly reflected in its potential as a functional optical component. Leveraging its narrowband reflection characteristics, BPLC can serve as a high-performance tunable filter for applications such as hyperspectral imaging to enhance image contrast and signal-to-noise ratio. Meanwhile, its inherent circular polarization selectivity provides a new pathway for polarization imaging; by constructing BPLC micro-arrays with different chiralities, spatially resolved detection of light field polarization information can be achieved, showing broad application prospects in biological tissue analysis and non-destructive material testing. Based on the electric field modulation characteristics of BPLC (such as the Kerr effect), a series of active optical devices can be developed, including tunable focal length lenses, beam scanners, and dynamic diffraction gratings. These components can introduce real-time reconfigurability and flexibility into optical systems, breaking through the performance bottlenecks of traditional static optical systems and promoting the development of adaptive optics and computational imaging technologies. Wang Jingxia's team^[67]Through PTBP material innovation, diffusion kinetics analysis, and double helix structure design, a theoretical and technical system for spatiotemporal programming of blue phase liquid crystals was established. First, by removing non-polymerized components from polymer-stabilized blue phase (PSBP), PTBP films with a microporous structure were developed. By infiltrating liquid crystal ink (such as 5CB) to induce lattice swelling, adaptive color switching was achieved, resulting in inkjet-printed multicolor patterns, such asFigure 8ashown in the BP polymer coating printed with the "LC-Ink" pattern. Furthermore, through FAS hydrophobic modification to suppress diffusion combined with diffusion kinetics control, high-resolution "live" pattern dynamic color changing was obtained, with resolution improved from approximately 100 μm to 33.7 μm, creating a Mona Lisa pattern and an anti-counterfeiting QR code (Figure 8b)^[29]. Recently, the team introduced machine learning parameter optimization and multi-dimensional encryption strategies. By combining double helix networks (RH/LH) with machine learning optimization, they produced vaccine monitoring labels integrating spatiotemporal programmed chiral units with double helix encryption, as well as dynamic encryption of "Girl with a Pearl Earring" (Figure 8c), further advancing the application of dynamic optical modulation in fields such as information security and intelligent sensing^[68]. Their work highlights the strong potential of biomimetic material design in solving challenges related to dynamic optical modulation, laying the foundation for the next generation of smart responsive devices.

Furthermore, BPLC demonstrates transformative potential in tunable lasers and intelligent laser protection due to the dynamic tunability of its three-dimensional periodic photonic crystals. Its core advantages lie in the high selectivity and real-time reconfigurability of the photonic bandgap—through molecular engineering, the central wavelength and bandwidth of the reflection band can be precisely customized to achieve directional suppression of specific laser threats while maintaining high transmittance in non-threat bands, thereby completely overcoming the inherent limitation of traditional absorptive materials where "broad-spectrum shielding leads to transmittance loss."

In laser protection applications, the Wang Jingxia team^[70-71]replaced traditional liquid crystals with a fully polymerized network architecture, combined with DCM dye optimization and a vacuum low-temperature testing apparatus, to achieve stable lasing for the first time across an ultra-wide temperature range of -180 to 240 °C (threshold <0.220 μJ/pulse, linewidth 0.0516 nm), covering extreme environments from liquid nitrogen cooling to high temperatures^[56,69]. Additionally, they developed a stretchable blue phase liquid crystal laser based on nonlinear three-dimensional asymmetric deformation, achieving optical stability under deformation conditions^[55]. The cross-linked network topological engineering of this system enables the device to maintain its body-centered cubic structure under tensile strain (ε<40%), outputting single-mode tunable laser light (wavelength shift of 44.43 nm) and fully recovering after strain release; its intrinsic chiral structure can further emit right-handed circularly polarized (RCP) laser light, exhibiting gain characteristics in thex/y/zdirections, paving a new path for three-dimensional stress sensing. These breakthrough advances, synergized with patterned polymerization technology (spatial resolution of 10 μm), are driving BPLC from the laboratory toward high-end applications such as battlefield protection and laser medical equipment. In the future, through integration with metasurfaces and machine learning-optimized molecular design, it is expected to realize a new generation of intelligent laser devices with wide-angle anti-interference capabilities^[29,72-73].

Table 2summarizes the applications of super-reflective BPLC in various fields through its excellent performance.