Direct Light Research Articles

Low-loss and broadband arbitrary ratios 1 × 2 power splitter based on asymmetrically tapered multimode interference

Abstract This work presents a low-loss and broadband 1 × 2 power splitter with arbitrary power splitting ratios (PSRs) based on asymmetrically tapered multimode interference. The asymmetrically input tapered waveguide is employed to gradually alter the direction of light propagating in the multimode region. Experimental results show that the device can maintain low losses (~0.2–0.4 dB) with adjusted PSRs ranging from 50%:50% to 75%:25% at 1550 nm. The adjustable range of PSRs can be extended by increasing the asymmetry of the structure. Additionally, its performance is weakly dependent on wavelength within the range of 1530–1565 nm. In theory, the variations in the PSRs are less than 1.8% for a wavelength range of 100 nm (1500–1600 nm) and less than 4.9% for a wavelength range of 300 nm (1400–1700 nm). Benefiting from the gradual alteration of the direction of light propagation, the device exhibits a low output phase difference of ±8.7°, and the maximum phase deviation is below 6.2° over the wavelength range from 1500 nm to 1600 nm.

Modular Access to Chiral Amines via Imine Reductase-Based Photoenzymatic Catalysis.

The development of catalysts serves as the cornerstone of innovation in synthesis, as exemplified by the recent discovery of photoenzymes. However, the repertoire of naturally occurring enzymes repurposed by direct light excitation to catalyze new-to-nature photobiotransformations is currently limited to flavoproteins and keto-reductases. Herein, we shed light on imine reductases (IREDs) that catalyze the remote C(sp3)-C(sp3) bond formation, providing a previously elusive radical hydroalkylation of enamides for accessing chiral amines (45 examples with up to 99% enantiomeric excess). Beyond their natural function in catalyzing two-electron reductive amination reactions, upon direct visible-light excitation or in synergy with a synthetic photoredox catalyst, IREDs are repurposed to tune the non-natural photoinduced single-electron radical processes. By conducting wet mechanistic experiments and computational simulations, we unravel how engineered IREDs direct radical intermediates toward the productive and enantioselective pathway. This work represents a promising paradigm for harnessing nature's catalysts for new-to-nature asymmetric transformations that remain challenging through traditional chemocatalytic methods.

Illumination matters Part II: advanced comparative analysis of flexible ureteroscopes in a kidney model by PEARLS

PurposeThe aim of the study was to evaluate illumination properties in an in-vitro kidney calyx model in saline.Design and methodsWe evaluated a series of contemporary flexible ureteroscopes including the Storz Flex-Xc and Flex-X2s, Olympus V3 and P7, Pusen 7.5F and 9.2F, as well as OTU WiScope using a 3D-printed closed pink kidney calyx model, submerged in saline. A spectrometer was used for illuminance and color temperature measurements at different openings located at center (direct light), 45° (direct and indirect light) and 90°(indirect light) to the axis of the scope.ResultsMaximum illuminance was at the center opening for all scopes (range: 284 to 12,058 lx at 50% brightness and 454 to 11,871 lx at 100% brightness settings). The scope with the highest center illuminance (Flex-Xc) was 26 times superior to the scope with the lowest illuminance (Pusen 7.5Fr) at 100% brightness setting. For each scope, there was a peripheral illuminance drop ranging from − 43 to − 92% at 50% brightness and − 43% to − 88% at 100% brightness settings, respectively (all p < 0.01). Highest drop was for the P7 and the Pusen 9.2F. All scopes had illuminance skew, except the V3. All scopes had a warm color temperature.ConclusionIllumination properties vary between ureteroscopes in an enclosed cavity in saline, and differs at center vs 45° and 90° positions within scopes. Peripheral illuminance drop can be as high as − 92%, which is undesirable. This may affect the choice of ureteroscope and light brightness settings used in surgery by urologists.

Hybrid lighting approach to improve interior workspace environments: a case study in the UAE

PurposeInterior workspace environments use exclusively artificial light, resulting in a loss of biological connection and natural light quality, as well as greater energy consumption. The purpose of the study is to identify a suitable system that can provide natural light to such interior spaces throughout the day while supplementing it with artificial light when necessary. The fundamental aim is to provide insights into the most effective solutions for energy-efficient lighting design in the UAE's environment, with the potential to lower energy consumption related to interior lighting.Design/methodology/approachThe study adopted an empirical approach to gather and analyze primary data based on field measurements to understand and assess existing lighting conditions, as well as DIALux lighting simulation software to test the efficacy of the proposed HLS in terms of natural light delivery, illumination quality and energy consumption. A branch of a local bank in the United Arab Emirates, situated inside one of the shopping malls where there is no natural light penetration, has been chosen as a case study.FindingsThe findings of comparing the base case to four probable scenarios that used HLS revealed that the third scenario, which uses 100% pure sunshine and 35% artificial LED light during daylight operations and 100% LED light during night duty, is considered to be optimal in terms of illumination quality and energy efficiency.Originality/valueThe study demonstrated the potential of innovative lighting to improve the visual working environment in interior spaces with limited access to direct natural lighting, especially in arid regions, where sunlight is plentiful throughout the year. The study contributes new insights into the establishment of lighting-related recommendations and standards for the UAE context. This may include advice for sustainable construction practices, lighting guidelines or incentives to encourage the use of hybrid lighting technology in commercial and institutional buildings.

Optical switching with high-Q Fano resonance of all-dielectric metasurface governed by bound states in the continuum

The discovery of bound states in the continuum (BIC) of optical nanostructures has garnered significant research interest and found widespread application in the field of optics, leading to an attractive approach to achieve high-Q (Quality factor) Fano resonance. Herein, an all-dielectric metasurface consisting of four gallium phosphide (Gap) cylinders on the MgF2 substrate is designed and analyzed by the finite element method (FEM). By breaking the symmetry of the plane, specifically by moving the two cylinders to one side, it is possible to achieve a transition from the symmetry-protected BIC to quasi-BIC. This transition enables the excitation of sharp dual-band Fano resonance at wavelengths of 1,045.4 nm and 1,139.6 nm, with the maximum Q factors reaching 1.47 × 104 and 1.28 × 104, respectively. The multipole decomposition and near-field distributions show that these two QBICs are dominated by the electric quadrupole (EQ) and magnetic quadrupole (MQ). Furthermore, bidirectional optical switching can be accomplished by changing the polarization direction of the incident light. As a result, the maximum sensitivity and figure of merit (FOM) are 488.9 nm/RIU and 2.51 × 105 RIU−1, respectively. The results enrich our knowledge about BIC and reveal a platform for the development of high-performance photonics devices such as optical switches and sensors.

Electrodynamic Interference and Induced Polarization in Nanoparticle-Based Optical Matter Arrays.

Optical matter (OM) arrays are self-organizing, ordered arrangements of nanometer- to micrometer-size particles, where interparticle forces are mediated by incident and scattered coherent light. The structures that form and their dynamics depend on the properties (e.g., material, size) of the constituent particles, as well as the incident and scattered light. While significant progress has been made toward understanding how the OM arrays are affected by the phase, polarization, and intensity profile of the incident light, the polarization induced in the particles and the light scattered by OM arrays have received less attention. In this paper, we establish the roles of electrodynamic interference, many-body coupling, and induced-polarization concomitant with the coherent light scattered by OM arrays. Experiments and simulations together demonstrate that the spatial profile and directionality of coherent light scattered by OM arrays in the far field are primarily influenced by interference, while electrodynamic coupling (interactions) and the associated polarization induced in the nanoparticle constituents have a quantitative wavelength-dependent effect on the total amount of light scattered by the arrays. Furthermore, the electrodynamic coupling in silver nanoparticle OM arrays is significantly enhanced by constructive interference and increases superextensively with the number of particles in the array. Particle size, and hence polarizability, also has a significant effect on the strength of the coupling. Finally, we simulate larger hexagonal OM arrays of Ag nanoparticles to demonstrate that the electrodynamic coupling and scattering enhancement observed in small OM arrays develop into surface lattice resonances observed in the infinite array limit. Our work provides insights for designing OM arrays to tune many-body forces and the coherent light that they scatter.

Numerical Simulations of Thermoacoustic Binary Gas Mixture Batch Separation

In this paper, 2D simulations were carried out to prove the potential of thermoacoustic technology in separating a binary gas mixture. A 2D model of a gas mixture separator was developed, including a loudspeaker responsible for producing acoustic waves in the separation pipe. As a result of the imposed sound waves propagating inside the separator, main parameters including pressure, temperature, and density undergo oscillations, which in turn drive the light and heavy gas components in opposite directions. Through time, one end of the separator is enriched with the light component while the other end is enriched with the heavy one. Simulations were all performed using ANSYS Fluent. The aim was to separate an ideal gas mixture of Helium–Argon and study the impact of different parameters on the separation process.

Numerical study of structural optimization for improving gas-liquid flow and microalgae carbon fixation rate in air-lift photobioreactors

In this paper, the gas-liquid flow pattern and CO2 dissolution transport process of microalgae solution in an air-lift photobioreactor (PBR) are investigated by numerical simulations. In order to promote the gas-liquid mass transfer efficiency to enhance the carbon fixation, we propose different optimization schemes for the structure. Firstly, a two-phase flow model and a mass transfer model are employed to investigate the fluid flow characteristics. The flow state is evaluated by velocity in light direction, turbulent kinetic energy (TKE), gas hold-up and CO2 mass transfer coefficient. The results show that the gas flow rate of 0.2 V/V/min is the optimum value for the inlet. Secondly, CO2 mass transfer and carbon fixation rates are analyzed for different inlet CO2 volume fractions. With the increase of CO2 volume fraction, the carbon fixation rate first increases and then decreases, the highest fixation rate reaching 2.21 × 10−4 mol m−3 s−1 at 6 %. Finally, based on numerical simulations, three optimized structures with different spacing of baffles are proposed and evaluated the performance in comparison with the original. The results show that the gas distribution and CO2 mass transfer are significantly improved, with the one-sided baffle structure is the best. In summary, this study provides a new and useful reference to evaluate the gas-liquid mixing and improve the microalgae carbon fixation rate.

Broadband and highly efficient asymmetric optical transmission through periodic Si cylinder arrays on the dielectric substrates

Asymmetric optical transmission is widely used in various fields due to the manipulation of light direction. This work theoretically investigates highly efficient and polarization-independent asymmetric optical transmission in the broadband wavelength through the periodic Si cylinder arrays on the dielectric substrates. The simulated results show that the maximum asymmetric optical transmission can reach 0.894, with high forward transmission of 0.898 and nearly zero backward transmission of 0.004 at the wavelength of 540 nm. The structure also exhibits excellent light-trapping characteristics with low energy loss and anti-reflection. The formation of asymmetric optical transmission comes from the diffraction which contributes differently to the transmission under forward and backward illuminations. Furthermore, asymmetric optical transmission in the structure is insensitive to the refractive index of the dielectric substrate and the height of the Si cylinder, and the wavelength position of the maximum asymmetric optical transmission is only sensitive to the height of the Si cylinder. This work proposes a multifunctional nanostructure and provides guidelines for designing practical devices that utilize asymmetric optical transmission.

Measuring the profile of aircraft engine blades using spectral confocal sensors

The geometric parameters of aircraft engine blades need to be precisely measured to ensure the quality of the blades for the normal operation of aircraft engines. This study aims to address the challenges of existing measurement systems in balancing efficiency, accuracy, and completeness. Additionally, it aims to enhance the accuracy and robustness of the algorithm for extracting blade profile characteristic parameters. In this paper, a spectral confocal sensor is employed to establish a blade profile measurement system. The design includes a probe sampling strategy, and a standard ball is used to calibrate the sensor probe’s light emission direction and the precise rotation center of the turntable. The paper proposes the use of methods such as partition search algorithm, binary search, and curvature segmentation to process point cloud data of blade body and tenon. We have conducted experimental measurements on the blades of an aircraft engine. The acquired three-dimensional point cloud data of multiple sets of blade cross-sections and dovetail sections were processed. After calculation, the maximum measurement errors for chord length, maximum blade thickness, tenon width, bottom height, top angle, and bottom angle are −0.0036 mm, −0.00721 mm, −0.0102 mm, −0.00928 mm, 0.0086°, and −0.0058°, respectively. This process validates the effectiveness of the proposed method and has high measurement accuracy. Compared with the CMM method, this method is more accurate in measuring small pits and large curvature micro surfaces, with higher measurement integrity and higher measurement efficiency.

Do attenuation coefficients based on luminescence bleaching fronts reflect true light attenuation in rocks?

The emerging technique of rock surface luminescence dating employs a double-exponential fitting dating model based on the Bouguer-Lambert law. The accuracy of exposure age determination is sensitive to the light attenuation coefficient, μ, which is usually derived from fitting the luminescence profile as a function of depth into the rock. Alternatively, μ might be determined by direct measurement using a spectrophotometer. However, their directly measured values of μ were significantly larger than those estimated from field luminescence bleaching data. Here, we aim to confirm these previous results by measuring the luminescence-depth profiles of both IRSL and IRPL signals from granite rock exposed to different light sources, including sunlight, SOL2 and IR LEDs under controlled conditions. We also measured monochromatic light (blue LED: (470 ± 30) nm, green LED: (520 ± 30) nm, and infrared LED: (850 ± 30) nm) attenuation in granite rock slices of varying thickness (0.62–2.60 mm) using a high-sensitivity photodiode. Finally, we use a camera-based measurement system and a Risø Luminescence Imager to investigate spatial variation in transmitted light as a function of slice thickness. The spatial correlation between direct light transmission and luminescence emission is then investigated, to investigate the underlying reasons for the difference between direct measurement and luminescence-based estimates of μ. We find that light attenuation through a granite rock slice is very heterogeneous; most light penetrates through localized low attenuation light paths corresponding to transmission through the most transparent grains, presumably quartz. The light penetration and escape into the surrounding matrix are assumed to be influenced by the surface area of quartz grains. As a result, transmissive light paths result in a significant area of feldspar grains at depth in the slice being exposed to more light than might be expected from average attenuation measurement. When the incident light predominantly travels through feldspar minerals, simultaneously stimulating luminescence from within any potassium feldspar (K-feldspar), the attenuation coefficients derived from the luminescence-depth profiles tend to be smaller than the average of 1.18 ± 0.07 (n = 79) irrespective of the kinetic model used for fitting. Thus, luminescence-based attenuation coefficient estimates appear to be affected by the distribution of light attenuation across and within the rock slice, making such estimates preferable to directly measured (average) estimates of light attenuation coefficients. These insights are important for our understanding of the significance of light attenuation coefficients in rock samples; they contribute to the reassessment of parameters and measurement methods in dating models and so to improvements in accuracy of rock surface luminescence dating techniques.

Reciprocally tailored transparent artificial media for frequency and direction dependent light trapping

We propose a quasiperiodic leveled-wave structure whose reciprocal space is represented by spherical belt sections, designed to achieve scattering only for the defined wavelength and direction of incident light. At the same time light is scattered only towards directions of k-vectors for which the waves are trapped by total internal reflection in the structured slab. The trapped light is only weakly scattered and thus spends a long time inside the slab and is attenuated by weak absorption in the slab. The incident light of other direction and/or wavelength is transmitted through the slab almost undisturbed. We quantitatively estimated the scattering mean free paths for incident and trapped light from the first-order Born approximation and develop an analytical model which predicts the absorption for a given slab thickness, refractive index contrast and spherical belt parameters. Reducing the refractive index contrast and thickness of the belt, the selectivity can be increased and the absorption contrast for incident light of different wavelengths can reach 70%. We present numerical simulations with absorption contrast of 63% for refractive index contrast of 0.1, which is in good agreement with our analytical model.

Image dehazing using non-local haze-lines and multi-exposure fusion

Images captured under haze conditions suffer from color distortion and low saturation due to the light propagates through scattering particles, causing light intensity attenuation and direction deflection, which affects the imaging quality of the visual system. To deal with these issues, we propose an image dehazing method based on non-local haze-line and multi-exposure fusion, called NHMF. Specifically, we first equalize the brightness and color of the input image according to a multi-scale fusion strategy. Meanwhile, we use the dark channel prior based on a local window to solve the atmospheric light value. Afterward, we employ the preprocessed image to obtain fog lines with better generalization performance that enhances the estimation of the transmission rate. Furthermore, we introduce weighted least-squares filtering to refine transmittance estimation accuracy further and ultimately employ an atmospheric scattering model to reverse process the haze-free image. Our extensive experiments on three image enhancement datasets demonstrate the effectiveness of our approach in quantitative and qualitative dehazing of images with haze. Moreover, our method exhibits excellent generalization performance in dehazing remote sensing images and enhancing underwater images.

Closed-Loop Optical Tracking of a Micro-Conveyor over a Smart Surface

In this work, a closed loop control system is developed to optically localize and track micro-robots with high precision. These micro-robots (i.e., micro-conveyors) are in motion simultaneously across a smart surface.The developed method’s primary objectives are to optimize their trajectories, avoid collisions between them, and control their position with micrometric resolution. This article presents and characterizes the tracking of a single micro-conveyor, and the method works similarly when multiple micro-robots move over the surface. Our tracking method starts with a scanning phase, where a 2D steering mirror, placed above the smart surface, reflects a laser beam toward the conveying surface seeking for the target. Localization occurs when this light beam reaches the micro-conveyor. By adding a retro-reflective element, that reflects the light in the same direction of the the incident light, onto the surface of the micro-conveyor, the light will be reflected towards a photodetector. Depending on the feedback from the photodetector, the steering mirror rotates to track the trajectory of the micro-conveyor. The tip-tilt angular values of the steering mirror allows the micro-conveyor position to be obtained via calibrated localization system. The aim of this work is to regulate the micro-conveyor, within a closed-loop control system, to reduce the positional error between the actual and desired position. The actual position value is measured in real-time application using our developed optical sensor. Results for tracking in the x-and y-axis have validated the proposed method, with an average tracking error less than 30 µm within a range 150 mm × 150 mm.

Comparison between Two Adaptive Optics Methods for Imaging of Individual Retinal Pigmented Epithelial Cells.

The Retinal Pigment Epithelium (RPE) plays a prominent role in diseases such as age-related macular degeneration, but imaging individual RPE cells is challenging due to their high absorption and low autofluorescence emission. The RPE lies beneath the highly reflective photoreceptor layer (PR) and contains absorptive pigments, preventing direct backscattered light detection when the PR layer is intact. Here, we used near-infrared autofluorescence adaptive optics scanning laser ophthalmoscopy (NIRAF AOSLO) and transscleral flood imaging (TFI) in the same healthy eyes to cross-validate these approaches. Both methods revealed a consistent RPE mosaic pattern and appeared to reflect a distribution of fluorophores consistent with findings from histological studies. Interestingly, even in apparently healthy RPE, we observed dynamic changes over months, suggesting ongoing cellular activity or alterations in fluorophore distribution. These findings emphasize the value of NIRAF AOSLO and TFI in understanding RPE morphology and dynamics.

A photoelectrochemical biosensor based on self-calibration platform of carbon-rich plasmonic probe with near-infrared driving signal amplification

Exploring the photochemical (PEC) method induced by low-energy light source makes great significance to achieve high stability and accurate analysis. A sensing platform driven by near-infrared (NIR) light was designed by making the biochemically encoded carbon rich plasmonic hybrid (CPH) probe, the peptide@C–Mo2C. The inherent plasmonic effect of C–Mo2C CPH can directly absorb NIR light, thus starting effective electronic-hole pairs separation. Moreover, the photothermal effect of C–Mo2C CPH also promoted the reaction yield of photothermal catalyst reaction on sensing interface to assist the PEC signal amplification. In the presence of target trypsin, it cleaves the peptides, resulting in the release of peptide@C–Mo2C probe from interface, which leads to a relative decrease in PEC signal. More importantly, a self-calibration system consisting of two independent PEC test channels attempted to eliminate the influence of background signal and baseline drift. The test channel was used to specify the recognition target, while the blank channel was used as a reference. Therefore, the signal difference between two channels was recorded, so as to obtain results with less error and higher stability. In this NIR driven PEC sensor, the carbon rich probe with direct and efficient NIR light conversion promoted the sensitivity and a self-calibration system guaranteed the stability which provided innovative thoughts for developing ingenious PEC sensor.

Optically-modulated edge states and resonant tunneling based on valley-Zeeman spin–orbit coupling

The valley-Zeeman spin–orbit coupling (VZSOC) in graphene provides a platform to discover novel edge states and enrich the quantum transport phenomena. In this work, based on the VZSOC induced helical edge states regarded as two copies of chiral edge states, we investigate the modulation of the edge state and corresponding resonant tunneling with the well-defined transmission peaks under off-resonant circularly polarized (ORCP) light. It shows that the spin-up or spin-down chiral edge state can be transformed into two types of antichiral edge state where the edge states propagate in the same direction at two parallel boundaries and the bulk states propagate in opposite direction, and reversed chiral edge states by the intensity and polarized direction of the ORCP light, finally leading to fascinated edge states. These edge-state transitions are attributed to regulating the Dirac gaps by the ORCP light. Particularly, some novel resonant tunneling in junctions consisting of different edge states are discovered, most of which can be intuitively understood as different types of the loop currents that the current flows in a loop. Interestingly, the combined effect of the backscattering and loop current also plays an important role in generating resonant tunneling. These results provide a new view to manipulate helical edge state induced by the VZSOC and understand rich physics of the resonant tunneling by the loop current.

Observation of naturally canalized phonon polaritons in LiV2O5 thin layers

Polariton canalization is characterized by intrinsic collimation of energy flow along a single crystalline axis. This optical phenomenon has been experimentally demonstrated at the nanoscale by stacking and twisting van der Waals (vdW) layers of α-MoO3, by combining α-MoO3 and graphene, or by fabricating an h-BN metasurface. However, these material platforms have significant drawbacks, such as complex fabrication and high optical losses in the case of metasurfaces. Ideally, it would be possible to canalize polaritons “naturally” in a single pristine layer. Here, we theoretically predict and experimentally demonstrate naturally canalized phonon polaritons (PhPs) in a single thin layer of the vdW crystal LiV2O5. In addition to canalization, PhPs in LiV2O5 exhibit strong field confinement (λp~λ027\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{{{\\boldsymbol{\\lambda }}}}}}}_{{{{{{\\bf{p}}}}}}} \\sim \\frac{{{{{{{\\boldsymbol{\\lambda }}}}}}}_{{{{{{\\bf{0}}}}}}}}{{{{{{\\bf{27}}}}}}}$$\\end{document}), slow group velocity (0.0015c), and ultra-low losses (lifetimes of 2 ps). Our findings are promising for the implementation of low-loss optical nanodevices where strongly directional light propagation is needed, such as waveguides or optical routers.

The Dark Energy Survey Supernova Program: Cosmological Biases from Host Galaxy Mismatch of Type Ia Supernovae

Redshift measurements, primarily obtained from host galaxies, are essential for inferring cosmological parameters from type Ia supernovae (SNe Ia). Matching SNe to host galaxies using images is nontrivial, resulting in a subset of SNe with mismatched hosts and thus incorrect redshifts. We evaluate the host galaxy mismatch rate and resulting biases on cosmological parameters from simulations modeled after the Dark Energy Survey 5 Yr (DES-SN5YR) photometric sample. For both DES-SN5YR data and simulations, we employ the directional light radius method for host galaxy matching. In our SN Ia simulations, we find that 1.7% of SNe are matched to the wrong host galaxy, with redshift differences between the true and matched hosts of up to 0.6. Using our analysis pipeline, we determine the shift in the dark energy equation of state parameter (Δw) due to including SNe with incorrect host galaxy matches. For SN Ia–only simulations, we find Δw = 0.0013 ± 0.0026 with constraints from the cosmic microwave background. Including core-collapse SNe and peculiar SNe Ia in the simulation, we find that Δw ranges from 0.0009 to 0.0032, depending on the photometric classifier used. This bias is an order of magnitude smaller than the expected total uncertainty on w from the DES-SN5YR sample of ∼0.03. We conclude that the bias on w from host galaxy mismatch is much smaller than the uncertainties expected from the DES-SN5YR sample, but we encourage further studies to reduce this bias through better host-matching algorithms or selection cuts.

In-plane photoelectric effect in phosphorene nanoribbons

Recently, a new photoelectric phenomenon dubbed in-plane photoelectric (IPPE) effect has been demonstrated experimentally. In this work, we investigate the IPPE effect in a zigzag-edged or armchair-edged phosphorene nanoribbons (ZPNRs or APNRs) that is modulated by a step barrier. Based on the Floquet theory, we calculate the directed photocurrent Ī|| (Ī⊥) generated by a non-resonant linearly-polarized light with polarization vector in parallel with (perpendicular to) the nanoribbon direction. We find that such a photocurrent depends on the edge type of the nanoribbon and the polarization direction of light. At high Fermi energies, the IPPE current Ī|| in APNRs is significantly stronger than that in ZPNRs under the same conditions. In APNRs, both Ī|| and Ī⊥ always have the same direction and |Ī||:Ī⊥|>10. In contrast, in ZPNRs Ī⊥ can reverse its direction (becoming negative) and is comparable to Ī|| in amplitude. The negative photocurrent arises from both the photon-emission and photon-absorption process related to the quasi-flat-band in ZPNRs. This indicates that the mid-gap states can be detected by the IPPE effect. The energy scope and amplitude of negative photocurrent can be tuned by adjusting the height of the step barrier, the light frequency, and the light intensity.