Μm In Air Research Articles

Flexible Microdisplacement Sensor for Wearable/ Implantable Biomedical Applications

Wireless monitoring systems are becoming a popular technology in noninvasive diagnosis. Based on current technological trends, low-power consumption, flexibility, small size, disposability, and low cost are the most important parameters to consider when designing sensors for biomedical applications. Echoing this trend, this paper presents a flexible wearable/implantable biocompatible sensor using wireless passive detection scheme, for future studying of the dynamics of an implanted abdominal mesh. Recording information about mechanical behavior of the implanted mesh helps in understanding hernia recurrence, among other post-surgical problems. Microfabricated sliding interdigitated gold plates and a circular coil (parallel inductor–capacitor tank) on a flexible substrate constitute the sensor’s main core. The capacitance and, in consequence, the resonant frequency of the sensor will vary according to the sliding magnitude, because the overlapping area between the interdigitated plates changes on sliding. Thus, the monitored resonant frequency is the sensor response. Different thicknesses cyclo-olefin polymer was used as a dielectric layer. Phantom was used to the ex vivo characterization of tissue behavior. The capacitor was tested in a 0– $600~\mu \text{m}$ displacement’s range. The measured sensitivity was 0.04 and 0.85 pF/ $50~\mu \text{m}$ in simulated conditions, with a resolution of less than $1~\mu \text{m}$ . The maximum sensitivity in the frequency range was 410 kHz/ $50~\mu \text{m}$ . The frequency shift can be detected by an external readout coil up to 20 mm in air and 10 mm in phantom. The experimental results confirm the scalability of the sensor.

Multi-terahertz frequency sweeps for high-resolution, frequency-modulated continuous wave ladar using a distributed feedback laser array.

Swept-wavelength reflectometry is an absolute distance measurement technique with significant sensitivity and detector bandwidth advantages over normal pulsed, time-of-flight methods. Although several tunable laser sources exist, many exhibit short coherence lengths or require mechanical tuning components. Semiconductor distributed feedback laser diodes (DFBs) are advantageous as a swept source because they exhibit a narrow instantaneous linewidth and can be frequency-swept simply via a single injection current. Here, we present a novel bandwidth generation technique that uses a compact, monolithic, 12-element DFB array to create an effectively continuous, gap-free sweep. Each DFB is sequentially swept over 3.5 nm at 1,600 THz/s using a shaped current pulse, ensuring spectral overlap between each element. After combining the self-heterodyned return signatures, the transform-limited resolution of the 43.6 nm sweep is demonstrated to be ~27.4 μm in air with a precision of 0.18 μm at a distance of 1.4 m.

VCSEL-based swept source for low-cost optical coherence tomography.

We present a novel wavelength-swept laser source for optical coherence tomography (OCT) which is based on the conventional laser diode technology of the vertical-cavity surface-emitting laser (VCSEL). In our self-heating sweep VCSEL (SS-VCSEL), a VCSEL device is simply driven by ramped pulses of currents in direct intensity modulation. The intrinsic property of VCSEL produces a frequency-swept output through the self-heating effect. By the injected current, the temperature of the active region is gradually increased in this effect. Consequently, it changes the wavelength of the laser output by itself. In this study, various characteristics of our SS-VCSEL were experimentally investigated for low-cost instrumentation of a swept source OCT system. A low-cost SS-VCSEL-based OCT system was demonstrated in this research that provided an axial resolution of 135 μm in air, sensitivity of -91 dB and a maximum imaging range longer than 10 cm when our source was operated at a sweep repetition rate of 5 kHz with an output power of 0.41 mW. Based on the experimental observations, we believe that our SS-VCSEL swept source can be an economic alternative in some of low-cost or long-range applications of OCT.

Highly sensitive piezoelectric micromachined ultrasonic transducer operated in air

Piezoelectric micromachined ultrasonic transducer (pMUT) is gaining increasing research interest. It overcomes the inherent shortcomings of conventional bulk ultrasonic transducers such as acoustic impedance mismatching and poor sensitivity. In addition, pMUT does not require the extremely large input voltage as capacitive micromachined ultrasonic transducer. Therefore the pMUT is potential to be integrated into portable electronics. A pMUT array operated in air using the lead zirconate titanate (PZT) thin film polled by high voltage pulses is realised and fully investigated. The high voltage pulses are found to be more effective for PZT poling, where the piezoelectric constant d 31 is elevated to 105 pm/V. Benefited from such high performance PZT thin film and optimised structure, the fabricated pMUT (500 × 300 μm) achieves a displacement sensitivity of 807 nm/V at its resonant frequency (482 kHz) without DC offset. Compared with previously reported PZT pMUTs, the sensitivity is superior to them even with a smaller membrane. The in-air transmitting performance is also evaluated. A single pMUT element is able to generate 63.7 dB sound pressure level at 10 mm in air with only 2 V input. The proposed high performance pMUT shows its promise for practical applications in portable electronics.

A Comparison Study Between Spot Scanning Intensity Modulated Proton and Photon Grid Therapy

The purpose of this research was to compare grid therapy using photons to grid therapy using a novel, collimator-free, intensity modulated proton therapy (IMgPT) method. IMgPT plans were developed using robust optimization and compared to grid therapy plans developed using photons. Plans were evaluated and compared by spot size and separation distance, number of beams, peak-to-valley ratios (PVRs), dose to organs at risk, integral, and distal edge dose. The relative biological effectiveness (RBE) of the valley regions was simulated with the Monte Carlo Damage Simulation (MCDS) model of DSB damage implemented in the FLUKA Monte Carlo radiation transport code. A pediatric sarcoma case, located on the patient’s right hip, was selected as a basis for evaluating the IMgPT approach because of the size (13 cm) and location of the tumor (15-cm depth); according to the published literature for photon grid therapy, bulky tumors more than 7.6 cm across are usually considered to be good candidates for grid therapy. The full width at half-maximum (FHWM) of the proton beam spot size varied from 2 to 15 mm in air at 220 MeV. The calculated RBE values were increased by a maximum of 30% in the valley regions. Applying IMgPT with robustness revealed no dependence on beam direction. A constant spot separation of 1 cm produced similar PVR values (of approximately 3) to those reported for 3D photon grid therapy. The plan prescription was a single fraction of 2000 cGy, following the reported dose for photon grid therapy. The doses delivered to 95% (D95) of the clinical target volume and gross tumor volumes were 1399 and 1436 cGy, respectively. The dose to 1% (D1) was 3650 and 3505 cGy, for the respective volumes. The maximum dose to the bladder and ovaries was 1587 and 797 cGy, respectively. Planning with multiple beams resulted in a high dose to the overlapping beam areas, an approach that may improve skin sparing. The average integral dose was calculated to be 425 cGy for photon plans, 141 cGy for a single beam IMgPT plan, and 152 cGy for 2-beam IMgPT plans. The distal dose was 1543 cGy for photons and 388 cGy for a single proton beam, compared to 645 cGy for a 2-beam IMgPT plan and 952 cGy for an IMPT plan with robust optimization. IMgPT improves distal and integral dose compared to grid therapy using photons. An increased RBE was noted for valley regions. This finding supports bystander effects noted from prior reports and might be harnessed to increase local tumor control.

Enhanced Evaporation of Microscale Droplets With an Infrared Laser

Enhancement of water droplet evaporation by added infrared radiation was modeled and studied experimentally in a vertical laminar flow channel. Experiments were conducted on droplets with nominal initial diameters of 50 μm in air with relative humidities ranging from 0% to 90% RH. A 2800 nm laser was used with radiant flux densities as high as 4 × 105 W/m2. Droplet size as a function of time was measured by a shadowgraph technique. The model assumed quasi-steady behavior, a low Biot number liquid phase, and constant gas–vapor phase material properties, while the experimental results were required for model validation and calibration. For radiant flux densities less than 104 W/m2, droplet evaporation rates remained essentially constant over their full evaporation, but at rates up to 10% higher than for the no radiation case. At higher radiant flux density, the surface-area change with time became progressively more nonlinear, indicating that the radiation had diminished effects on evaporation as the size of the droplets decreased. The drying time for a 50 μm water droplet was an order of magnitude faster when comparing the 106 W/m2 case to the no radiation case. The model was used to estimate the droplet temperature. Between 104 and 5 × 105 W/m2, the droplet temperature changed from being below to above the environment temperature. Thus, the direction of conduction between the droplet and the environment also changed. The proposed model was able to predict the changing evaporation rates for droplets exposed to radiation for ambient conditions varying from dry air to 90% relative humidity.

High-resolution, dual-depth spectral-domain optical coherence tomography with interlaced detection for whole-eye imaging.

Dual-depth spectral-domain optical coherence tomography (SD-OCT) enables high-resolution in vivo whole-eye imaging. Two orthogonally polarized beams from a source are focused simultaneously on two axial positions of the anterior segment and the retina. For the detector arm, a 1×2 ultrafast optical switch sequentially delivers two spectral interference signals to a single spectrometer, which extends the in-air axial depth range up to 9.44 mm. An off-pivot complex conjugate removal technique doubles the depth range for all anterior segment imaging. The graphics-processing-unit-based parallel signal processing algorithm supports fast two- and three-dimensional image displays. The obtained high-resolution anterior and retinal images are measured biometrically. The dual-depth SD-OCT system has an axial resolution of ∼6.4 μm in air, and the sensitivity is 91.79 dB at 150 μm from the zero-delay line.

Astigmatism corrected common path probe for optical coherence tomography.

Optical coherence tomography (OCT) catheters for intraluminal imaging are subject to various artifacts due to reference-sample arm dispersion imbalances and sample arm beam astigmatism. The goal of this work was to develop a probe that minimizes such artifacts. Our probe was fabricated using a single mode fiber at the tip of which a glass spacer and graded index objective lens were spliced to achieve the desired focal distance. The signal was reflected using a curved reflector to correct for astigmatism caused by the thin, protective, transparent sheath that surrounds the optics. The probe design was optimized using Zemax, a commercially available optical design software. Common path interferometric operation was achieved using Fresnel reflection from the tip of the focusing graded index objective lens. The performance of the probe was tested using a custom designed spectrometer-based OCT system. The probe achieved an axial resolution of 15.6 μm in air, a lateral resolution 33 μm, and a sensitivity of 103 dB. A scattering tissue phantom was imaged to test the performance of the probe for astigmatism correction. Images of the phantom confirmed that this common-path, astigmatism-corrected OCT imaging probe had minimal artifacts in the axial, and lateral dimensions. In this work, we developed an astigmatism-corrected, common path probe that minimizes artifacts associated with standard OCT probes. This design may be useful for OCT applications that require high axial and lateral resolutions. Lasers Surg. Med. 49:312-318, 2017. © 2016 Wiley Periodicals, Inc.

High-resolution and nondestructive profile measurement by spectral-domain optical coherence tomography with a visible broadband light source for optical-device fabrication

We developed a spectral-domain optical coherence tomography (OCT) using a visible broadband light source (vis-OCT) for application to high-resolution and nondestructive profile measurement and imaging in semiconductor optical-device fabrication. By using visible broadband light centered at 625 nm and with spectral bandwidth of 260 nm, an axial resolution of 0.69 µm in air was obtained. This was effective for inspection of a transparent photoresist film with thickness of 1–2 µm coated on a semiconductor wafer; the interface between the photoresist film and its substrate and the interface between the photoresist and air were resolved, and the film thickness was measured. In addition, the interface between an opaque epitaxially grown semiconductor layer (Al0.35Ga0.65As) and a GaAs substrate was also detected by vis-OCT. Here we propose a thickness-measurement technique that combines finite-difference time-domain simulation with vis-OCT. This method enables us to determine the thickness of even an optically absorbent epitaxial layer and offers a profile-measurement method that is particularly suitable for the fabrication of semiconductor optical devices.

ACCURACY ASSESSMENT OF UNDERWATER PHOTOGRAMMETRIC THREE DIMENSIONAL MODELLING FOR CORAL REEFS

Abstract. Recent advances in automation of photogrammetric 3D modelling software packages have stimulated interest in reconstructing highly accurate 3D object geometry in unconventional environments such as underwater utilizing simple and low-cost camera systems. The accuracy of underwater 3D modelling is affected by more parameters than in single media cases. This study is part of a larger project on 3D measurements of temporal change of coral cover in tropical waters. It compares the accuracies of 3D point clouds generated by using images acquired from a system camera mounted in an underwater housing and the popular GoPro cameras respectively. A precisely measured calibration frame was placed in the target scene in order to provide accurate control information and also quantify the errors of the modelling procedure. In addition, several objects (cinder blocks) with various shapes were arranged in the air and underwater and 3D point clouds were generated by automated image matching. These were further used to examine the relative accuracy of the point cloud generation by comparing the point clouds of the individual objects with the objects measured by the system camera in air (the best possible values). Given a working distance of about 1.5 m, the GoPro camera can achieve a relative accuracy of 1.3 mm in air and 2.0 mm in water. The system camera achieved an accuracy of 1.8 mm in water, which meets our requirements for coral measurement in this system.

ACCURACY ASSESSMENT OF UNDERWATER PHOTOGRAMMETRIC THREE DIMENSIONAL MODELLING FOR CORAL REEFS

Recent advances in automation of photogrammetric 3D modelling software packages have stimulated interest in reconstructing highly accurate 3D object geometry in unconventional environments such as underwater utilizing simple and low-cost camera systems. The accuracy of underwater 3D modelling is affected by more parameters than in single media cases. This study is part of a larger project on 3D measurements of temporal change of coral cover in tropical waters. It compares the accuracies of 3D point clouds generated by using images acquired from a system camera mounted in an underwater housing and the popular GoPro cameras respectively. A precisely measured calibration frame was placed in the target scene in order to provide accurate control information and also quantify the errors of the modelling procedure. In addition, several objects (cinder blocks) with various shapes were arranged in the air and underwater and 3D point clouds were generated by automated image matching. These were further used to examine the relative accuracy of the point cloud generation by comparing the point clouds of the individual objects with the objects measured by the system camera in air (the best possible values). Given a working distance of about 1.5 m, the GoPro camera can achieve a relative accuracy of 1.3 mm in air and 2.0 mm in water. The system camera achieved an accuracy of 1.8 mm in water, which meets our requirements for coral measurement in this system.

Dual-band optical coherence tomography using a single supercontinuum laser source.

We developed a simultaneous visible-light (Vis) and near-infrared (NIR) dual-band optical coherence tomography (OCT) system using a single supercontinuum laser source. The goal was to benchmark our newly developed Vis-OCT against the well-developed NIR-OCT. The Vis-OCT subsystem operated at 91 nm full-width-at-half-maximum (FWHM) bandwidth centered at 566 nm; the NIR-OCT subsystem operated at 93 nm FWHM bandwidth centered at 841 nm. The axial resolutions were 1.8 and 4.4 μm in air for the Vis- and NIR-OCT subsystems, respectively. We compared the respective performances, including anatomical imaging, angiography, absolute retinal blood flow measurements, and spectroscopic analysis for retinal blood oxygen saturation (sO2), between the two subsystems in rodents in vivo. While demonstrating minor discrepancies related to operation wavelengths, both subsystems showed comparable performances in the first three tests. However, we were only able to retrieve sO2 using the Vis-OCT subsystem.

High resolution corneal and single pulse imaging with line field spectral domain optical coherence tomography.

We report the development of a Spectral Domain Line Field Optical Coherence Tomography (LF-OCT) system, using a broad bandwidth and spatial coherent Super-Continuum (SC) source. With conventional quasi-Continuous Wave (CW) setup we achieve axial resolutions up to 2.1 μm in air and 3D volume imaging speeds up to 213 kA-Scan/s. Furthermore, we report the use of a single SC pulse, of 2 ns duration, to temporally gate an OCT B-Scan image of 70 A-Scans. This is the equivalent of 35 GA-Scans/s. We apply the CW setup for high resolution imaging of the fine structures of a human cornea sample ex-vivo. The single pulse setup is applied to imaging of a coated pharmaceutical tablet. The fixed pattern noise due to spectral noise is removed by subtracting the median magnitude A-Scan. We also demonstrate that the Fourier phase can be used to remove aberration caused artefacts.

The Dosimetric Impact of Air in Vaginal Vault Brachytherapy

Vaginal vault brachytherapy is an adjuvant treatment option to reduce risk of local recurrence for intermediate and high risk endometrial cancer. The aim of this planning study is to examine the dosimetric effect of air gaps between the surface of a cylindrical vaginal stump applicator and mucosal wall with dose prescribed to a depth of 5mm from the mucosal surface. The applicability of the TG 43 formalism in the presence of air was also assessed. The planning CT scans for a retrospective sample of 82 patients treated between January 2014 and October 2015 were examined for the presence of air gaps. These were quantified in terms of the radial and longitudinal aspect with reference to the applicator, frequency per patient and location along the applicator. The effect of the geometric displacement of the target tissue was calculated on the planning system. Ionisation chamber measurements were also made in a phantom to estimate the uncertainty of the TG43 algorithm resulting from the impact of air on the dosimetry. 75 of the 82 patients that were analysed had at least one air gap. The overall incidence of air gaps was 91.4%. Of the total gaps observed, 23.7% were located above the tip of the applicator. The most common radial size was between 2 and 3mm (43.0%) which resulted in an average dose reduction using the TG43 formalism of 14.8%. Only 4.3% of the gaps were above 5mm in radial size. There is a strong correlation between radial dimension and TG43 calculated dose reduction, showing a Pearson’s correlation coefficient of 0.92. Phantom measurements indicated that the inhomogeneity introduced by air resulted in a maximum of 2.3% deviation from doses calculated using TG43 (Figure 1). It has been established that the TG43 formalism is not significantly compromised by the presence of air. The error in dose calculation using TG43 will shift the prescription isodose by at most 0.5 mm towards the mucosal surface with an air gap diameter of 10mm. However the presence of the air does produce a displacement of the mucosal surface away from the applicator and this causes a clinically significant dose reduction of 33.7% for 5mm of air. An approximately linear relationship is seen between increasing radial diameter of air and percentage dose reduction caused by the displacement by air of the tissue at the prescription point.

Polarization properties of single layers in the posterior eyes of mice and rats investigated using high resolution polarization sensitive optical coherence tomography.

We present a high resolution polarization sensitive optical coherence tomography (PS-OCT) system for ocular imaging in rodents. The system operates at 840 nm and uses a broadband superluminescent diode providing an axial resolution of 5.1 µm in air. PS-OCT data was acquired at 83 kHz A-scan rate by two identical custom-made spectrometers for orthogonal polarization states. Pigmented (Brown Norway, Long Evans) and non-pigmented (Sprague Dawley) rats as well as pigmented mice (C57BL/6) were imaged. Melanin pigment related depolarization was analyzed in the retinal pigment epithelium (RPE) and choroid of these animals using the degree of polarization uniformity (DOPU). For all rat strains, significant differences between RPE and choroidal depolarization were observed. In contrast, DOPU characteristics of RPE and choroid were similar for C57BL/6 mice. Moreover, the depolarization within the same tissue type varied significantly between different rodent strains. Retinal nerve fiber layer thickness, phase retardation, and birefringence were mapped and quantitatively measured in Long Evans rats in vivo for the first time. In a circumpapillary annulus, retinal nerve fiber layer birefringence amounted to 0.16°/µm ± 0.02°/µm and 0.17°/µm ± 0.01°/µm for the left and right eyes, respectively.

Superluminescent diode with a broadband gain based on self-assembled InAs quantum dots and segmented contacts for an optical coherence tomography light source

We report a broadband-gain superluminescent diode (SLD) based on self-assembled InAs quantum dots (QDs) for application in a high-resolution optical coherence tomography (OCT) light source. Four InAs QD layers, with sequentially shifted emission wavelengths achieved by varying the thickness of the In0.2Ga0.8As strain-reducing capping layers, were embedded in a conventional p-n heterojunction comprising GaAs and AlGaAs layers. A ridge-type waveguide with segmented contacts was formed on the grown wafer, and an as-cleaved 4-mm-long chip (QD-SLD) was prepared. The segmented contacts were effective in applying a high injection current density to the QDs and obtaining emission from excited states of the QDs, resulting in an extension of the bandwidth of the electroluminescence spectrum. In addition, gain spectra deduced with the segmented contacts indicated a broadband smooth positive gain region spanning 160 nm. Furthermore, OCT imaging with the fabricated QD-SLD was performed, and OCT images with an axial resolution of ∼4 μm in air were obtained. These results demonstrate the effectiveness of the QD-SLD with segmented contacts as a high-resolution OCT light source.

Supercontinuum generation in optimized photonic crystal fiber at 1.3 μm for optical coherence tomography

In this paper, we have designed a high nonlinear photonic crystal fiber (HN-PCF) based on square-lattice geometry with the zero dispersion wavelength (ZDW) around 1300 nm. The exploitation of different nonlinear mechanisms in the pulse propagation allows supercontinuum generation, which is used to enhance the axial resolution of the optical coherence tomography (OCT) systems. First mechanism demonstrated is the soliton self-compression, we came up to realize pulse compression of 28.4 fs around 1300 nm by the generation of solitons of different orders to obtain ultrashort pulses of about 4 fs pulses in a PCF length of 66cm, then, we improved the pulse compression until 1.2 fs in a PCF length of 26 cm.The exploitation of the interplay between many nonlinear effects as self-phase modulation, intrapulse Raman scattering and self-steepening as second mechanism allows a generation of supercontinuum with a spectral bandwith of SBW=260 nm. The obtained spectral bandwidth could contribute to enhance the OCwith OCT imaging axial resolution which can be evaluated to 2.8 μm in air, working at 1.3 μm center wavelength which is widely used in several fields.

Swept-source optical coherence tomography powered by a 1.3 - μ m vertical cavity surface emitting laser enables 2.3-mm-deep brain imaging in micein vivo

We report noninvasive, in vivo optical imaging deep within a mouse brain by swept-source optical coherence tomography (SS-OCT), enabled by a 1.3-μm vertical cavity surface emitting laser (VCSEL). VCSEL SS-OCT offers a constant signal sensitivity of 105 dB throughout an entire depth of 4.25 mm in air, ensuring an extended usable imaging depth range of more than 2 mm in turbid biological tissue. Using this approach, we show deep brain imaging in mice with an open-skull cranial window preparation, revealing intact mouse brain anatomy from the superficial cerebral cortex to the deep hippocampus. VCSEL SS-OCT would be applicable to small animal studies for the investigation of deep tissue compartments in living brains where diseases such as dementia and tumor can take their toll.

High-resolution extended source optical coherence tomography.

High resolution optical coherence tomography (OCT) is capable of providing detailed tissue microstructures that are critical for disease diagnosis, yet its sensitivity is usually degraded since the system key components are typically not working at their respective center wavelengths. We developed a novel imaging system that achieves enhanced sensitivity without axial resolution degradation by the use of a spectrally encoded extended source (SEES) technique; it allows larger sample power without exceeding the maximum permissible exposure (MPE). In this study, we demonstrate a high-resolution extended source (HRES) OCT system, which is capable of providing a transverse resolution of 4.4 µm and an axial resolution of 2.1 µm in air with the SEES technique. We first theoretically show a sensitivity advantage of 6-dB of the HRES-OCT over that of its point source counterpart using numerical simulations, and then experimentally validate the applicability of the SEES technique to high-resolution OCT (HR-OCT) by comparing the HRES-OCT with an equivalent point-source system. In the HRES-OCT system, a dispersive prism was placed in the infinity space of the sample arm optics to spectrally extend the visual angle (angular subtense) of the light source to 10.3 mrad. This extended source allowed ~4 times larger MPE than its point source counterpart, which results in an enhancement of ~6 dB in sensitivity. Specifically, to solve the unbalanced dispersion between the sample and the reference arm optics, we proposed easy and efficient methods for system calibration and dispersion correction, respectively. With a maximum scanning speed reaching up to 60K A-lines/s, we further conducted imaging experiments with HRES-OCT using the human fingertip in vivo and the swine eye tissues ex vivo. Results demonstrate that the HRES-OCT is able to achieve significantly larger penetration depth than its conventional point source OCT counterpart.

Design of high-performance adaptive objective lens with large optical depth scanning range for ultrabroad near infrared microscopic imaging.

We report on the theory and design of adaptive objective lens for ultra broadband near infrared light imaging with large dynamic optical depth scanning range by using an embedded tunable lens, which can find wide applications in deep tissue biomedical imaging systems, such as confocal microscope, optical coherence tomography (OCT), two-photon microscopy, etc., both in vivo and ex vivo. This design is based on, but not limited to, a home-made prototype of liquid-filled membrane lens with a clear aperture of 8mm and the thickness of 2.55mm ~3.18mm. It is beneficial to have an adaptive objective lens which allows an extended depth scanning range larger than the focal length zoom range, since this will keep the magnification of the whole system, numerical aperture (NA), field of view (FOV), and resolution more consistent. To achieve this goal, a systematic theory is presented, for the first time to our acknowledgment, by inserting the varifocal lens in between a front and a back solid lens group. The designed objective has a compact size (10mm-diameter and 15mm-length), ultrabroad working bandwidth (760nm - 920nm), a large depth scanning range (7.36mm in air) - 1.533 times of focal length zoom range (4.8mm in air), and a FOV around 1mm × 1mm. Diffraction-limited performance can be achieved within this ultrabroad bandwidth through all the scanning depth (the resolution is 2.22 μm - 2.81 μm, calculated at the wavelength of 800nm with the NA of 0.214 - 0.171). The chromatic focal shift value is within the depth of focus (field). The chromatic difference in distortion is nearly zero and the maximum distortion is less than 0.05%.