Superluminescent Diode Light Source Research Articles

Simulation Study on Digital Control Model of Fiber Optic Gyro SLD Light Source

Fiber Optic Gyroscope is an angular velocity sensitive device based on Sagnac effect. Super Luminescent Diode (SLD) is a widely used light source in fiber optic gyroscope, and its characteristics will directly affect the overall performance of gyroscope. In this paper, the working mechanism of SLD light source is studied, and the photoelectric characteristics of SLD light source and the influence of light source temperature and driving current on center wavelength are analyzed. According to the relationship between the central wavelength of the light source and the driving current and die temperature, a three-dimensional model of the central wavelength of the light source is obtained. In order to control the driving current and die temperature quickly and stably, the fuzzy PID control scheme of die temperature and incremental PID control scheme of driving current are studied and designed. Based on the three-dimensional model of the center wavelength of light source, the center wavelength of SLD light source is controlled stably and quickly.

Real-Time Compensation for SLD Light-Power Fluctuation in an Interferometric Fiber-Optic Gyroscope.

An interferometric fiber-optic gyroscope (IFOG) demodulates a rotation signal via interferometric light intensity. However, the working environments of IFOGs typically involve great uncertainty. Fluctuations in temperature, air pressure, electromagnetic field, and the power system all cause the power of the superluminescent diode (SLD) light source to fluctuate as well. In this invited paper, we studied the effects of SLD power fluctuation on the dynamic and static performance characteristics of a gyro system through the use of a light-power feedback loop. Fluctuations of 0.5 mA, 1 mA, and 5 mA in the SLD source entering the IFOG caused zero-bias stability to be 69, 135, and 679 times worse. We established an effective method to monitor power fluctuations of SLD light sources and to compensate for their effects without increasing hardware complexity or system cost. In brief, we established a real-time power-sensing and -compensating system. Experimental results showed that for every 0.1 mA increase in the fluctuation amplitude of the driving current, the zero-bias stability became 4 to 7 times worse, which could be reduced about 95% through the use of SLD power compensation.

Research on light source average wavelength and crystal oscillator frequency for reducing temperature error of the FOG scale factor

Based on the working principle of the digital closed-loop fiber optic gyroscope (FOG), a model for the influence of crystal oscillator frequency on scale factor (SF) temperature error is theoretically derived. Besides, the correlation between the two main light sources average wavelength and the SF temperature error is discussed. The experimental results show that both the crystal oscillator frequency and the light source average wavelength have a greater impact on the FOG SF temperature error. There is a cubic function relationship between crystal oscillator frequency and temperature, the temperature error of the SF is inversely proportional to the crystal oscillator frequency. Using a higher frequency temperature-compensated crystal oscillator, the frequency stability can be improved by two orders of magnitude, from 67.14 ppm to 0.22 ppm, the SF temperature error is also greatly reduced. The SF error is proportional to the relative change in wavelength, and the change caused by the temperature is of the same order of magnitude. Compared with the super luminescent diode (SLD) light source, the Erbium-doped fiber light source has higher average wavelength stability, the SF error caused by it is also smaller. The error can be reduced by 15 ppm and controlled at about 10 ppm after temperature compensation.

The Application of High Efficiency and Low Noise Switching Power Supply in Fiber Optic Gyroscope

For high-precision fiber optic gyro systems, the efficiency and noise in the switching power source limits its application and also affects the system's light source and signal processing circuit, resulting in output errors. The interference mechanism of switching power supply ripple noise on super luminescent diode (SLD) light source and demodulation module in fiber optic gyro system is analyzed. A high-efficiency and low-noise switching power supply based on synchronous rectification is proposed. The power supply uses RC circuit to realize adjustable switching frequency. The push-pull isolation topology, LC filter and LDO regulator circuit are used to achieve constant voltage output with peak-to-peak ripple noise of less than 1mV. The conversion efficiency of the switching power supply is improved by 10%, which provides a high-quality power source for the high-precision fiber optic gyroscope. In the meanwhile, the switching power source for FOG is 541cm in size, which is beneficial to the miniaturization of inertial navigation system.

Surface profile measurement of doped silicon using near-infrared low-coherence light.

A scanning interferometry system based on near-infrared low-coherence interferometry by using a superluminescent diode (SLD) as the light source is presented. The system cannot only measure the surface profile of doped double-sided polished silicon but also measure its optical thickness and refractive index. The measurement system uses near-infrared CCD to detect interferometric light in the near infrared, based on the Michelson interference principle. SLD has low temporal and high spatial coherence and high penetration to doped silicon wafers; thus, higher visibility can be obtained when measuring the rear side. Meanwhile, the optical thickness measured by low coherent scanning interference is compared with the optical thickness obtained by spectrally resolved interferometry to verify the accuracy of the system. Due to the periodic characteristics of interference fringes, the coherence length of the narrowband light source is usually greater than the path length difference of the interferometer. It gives the measurement a phase ambiguity of 2π, which may severely limit the application of the measurement. However, the short coherent length SLD light source used in the project can avoid 2π phase ambiguity problems. Besides, this system can perform full scanning in a larger step and achieve rapid on-line measurement of the target surface.

An improved temperature compensation circuit for SLD light source of fiber-optic gyroscope

The super luminescent diode light source is commonly used in Fiber-optic gyroscope. The wavelength temperature stability is one of its key parameters. In this work, simulation model of temperature field of the SLD light source is established, and the temperature distribution of SLD internal structure is simulated and researched. A temperature compensation scheme is designed according to the simulation result and experiment is done to confirm the specific parameter of compensation circuit. Then the designed compensation scheme is used in temperature control circuit of SLD, and the performance of compensated SLD light source is tested. An improvement of 62% is demonstrated compared with uncompensated SLD.

Imaging of spectral-domain optical coherence tomography using a superluminescent diode based on InAs quantum dots emitting broadband spectrum with Gaussian-like shape

We developed a low-coherence light source based on self-assembled InAs quantum dots (QDs) with controlled emission wavelengths and applied it to optical coherence tomography (OCT) imaging. A current-driven superluminescent diode (SLD) light source including four layers of QDs exhibits a broadband (80-nm-bandwidth) emission centered at approximately 1.2 µm with a Gaussian-like spectral shape at room temperature. Spectral-domain OCT (SD-OCT) using the QD-SLD as a light source was developed and imaging with the SD-OCT was demonstrated. The axial resolution was estimated to be approximately 8 µm in air and no apparent side lobes appeared beside the point spread function, indicating the effectiveness of the QD-SLD for high-resolution, noise-reduced OCT imaging.

Technical improvements applied to a double-pass setup for performance and cost optimization

We have studied the possibility of improving the performance, simplifying, and reducing the cost of a double-pass system by the use of alternative technologies. The system for correcting the spherical correction has been based on a focusable electro-optical lens, and a recording device based on CMOS technology and a superluminescent diode (SLED) light source have been evaluated separately. The suitability of the CMOS camera has been demonstrated, while the SLED could not break the speckle by itself. The final experimental setup, consisting of a CMOS camera and a laser diode, has been compared with a commercial double-pass system, proving its usefulness for ocular optical quality and scattering measurements.

Senile retinoschisis versus retinal detachment, the additional value of peripheral retinal OCT scans (SL SCAN‐1, Topcon)

A peripheral senile retinoschisis is sometimes difficult to distinguish from a retinal detachment by biomicroscopy alone. This study evaluated spectral domain OCT (SD-OCT) scans of the far peripheral retina to improve the differentiation between these diseases. Patients were included in whom the distinction between retinal detachment and senile retinoschisis was not clear based on biomicroscopy alone, or who had a presumed clinical diagnosis of senile retinoschisis. OCT scans were made with the SLSCAN-1, through a hand-held lens and a 3-mirror contact lens, while the area of interest was simultaneously observed with the slit lamp. The SLSCAN-1 is a SD-OCT integrated into a slit lamp, superluminescent diode light source with a central wavelength of 830 nm, bandwidth 30 nm, scan resolution 8-9 μm in tissue, scan depth 2 mm, scan speed 5000 A-scans per second. In the 11 patients with an uncertain diagnosis, OCT scans showed a senile retinoschisis in four and a retinal detachment in seven patients. Fifteen of the 18 patients with a presumed diagnosis of retinoschisis showed a retinoschisis on OCT. In five of them, the OCT scans revealed a schisis detachment. Interestingly, three of the 18 patients had a retinal detachment. Senile retinoschisis may mimic a peripheral retinal detachment and vice versa. Differentiation is important with respect to therapeutic decisions. OCT scans of the far peripheral retina, which can be made with the SLSCAN-1 through a 3-mirror contact lens, can contribute significantly to this differentiation. The obtained scans of the far peripheral retina clearly visualize the anatomic differences between both diseases.

Optical Monitoring of Tumors in BALB/c Nude Mice Using Optical Coherence Tomography

We report a method for optical monitoring of tumors in an animal model using optical coherence tomography (OCT). In a spectral domain OCT system, a superluminescent diode light source with a full width of 66 nm at half maximum and peak wavelength of 950 nm was used to take images having an axial resolution of 6.8 μ m. Cancer cells of PC-3 were cultured and inoculated into the hypodermis of auricle tissues in BALB/c nude mice. We observed tumor formation and growth at the injection region of cancer cells in vivo and obtained the images of tumor mass center and sparse circumferences. On the 5 th day from an inoculation of cancer cells, histological images of the tumor region using cross-sectional slicing and dye staining of specimens were taken in order to confirm the correlation with the high resolution OCT images. The OCT image of tumor mass compared with normal tissues was analyzed using its A-scan data so as to obtain a tissue attenuation rate which increases according to tumor growth.

Ultrahigh resolution spectral-domain optical coherence tomography at 1.3 μm using a broadband superluminescent diode light source

We present an ultrahigh resolution spectral-domain optical coherence tomography imaging system using a broadband superluminescent diode light source emitting at a center wavelength of 1.3μm. The light source consists of two spectrally shifted superluminescent diodes that are coupled together into a single mode fiber. The effective emission power spectrum has a full width at half maximum of 200nm and the source output power is 10mW. The imaging system has an axial resolution of 3.9μm in air (<3.0μm in biological tissue), and a lateral resolution of 6.5μm. The sensitivity and the maximum line rate are 95dB and 46kHz, respectively. Images of an infrared viewing card and a cornea from human eye suffering from glaucoma showing Schlemm's canal are presented to illustrate the performance of the system.

Group-delay-based phase-shifting method for Fourier domain optical coherence tomography

Frequency-domain optical coherence tomography (FD-OCT) has the advantages of an improved sensitivity and a reduced acquisition time since it enables cross-sectional images of the sample of interest to be obtained using a broadband source or a swept source. The phase-shifting method can always be applied to reduce the additional noise within FD-OCT and provide accurate signal processing. We present a phase-shifting method in which a parallel diffraction grating pair is inserted into the reference arm of the OCT system. The gratings separate the spectrum of the illuminating light and stretch the optical pulse in time thereby producing a linear group delay between the adjacent wavelengths in the superluminescent diode light source. The simulation results show that the proposed group-delay-based phase-shifting method improves the precision of the sample parameters extracted using the FD-OCT procedure compared to those obtained using traditional techniques such as the 0/4 phase-shifting method.

Optical coherence tomography (OCT) as a diagnostic tool for the real-time intraoperative assessment of breast cancer surgical margins.

Abstract Abstract #802 Background: The decrease in the number of breast cancer deaths has largely been attributed to increased awareness, earlier detection, and improved treatment options. However, as the number of breast-conserving surgeries rose over the years, the need for negative margins and little or no residual disease has become critical to help reduce the chances of local recurrence. OCT is a high resolution imaging modality that has been used to image tumor margins in an NMU-carcinogen-induced rat mammary tumor model. Due to the location of breast lesions, the use of needle-based imaging probes may be used to further extend the reach of the OCT imaging beam by incorporating an optical fiber into biopsy needle tips, providing real-time information to guide biopsies or to place localization wires.&amp;#x2028; Material &amp; Methods: A clinical spectral domain OCT system was developed with a super luminescent diode light source centered at 1310 nm with a bandwidth of 92 nm yielding an axial resolution of 8.3 µm. The beam delivery sample arm uses a 60 mm achromatic lens to focus 4.75 mW of light to a 35.0 µm spot size (transverse resolution) with a confocal parameter of 1.47 mm. The patients included in this study had primary breast tumors diagnosed by needle-biopsy and were in need of surgical resection, as determined by their physicians. At Carle Foundation Hospital, the OCT system was placed inside the operating room during breast conserving surgical procedures to image the tissue specimens. The OCT images were evaluated by a single operator allowing for consistent classification based on the level of scattering intensity and heterogeneity, scattering profile, and physical extent of the highly scattering area.&amp;#x2028; Results: An initial training data set of OCT images from 17 patients was used to establish standard imaging protocols and standard evaluation criteria of the surgical margins. Of the 20 additional tissue specimen imaged for the feasibility study, 11 were identified as having a positive or close surgical margin and nine as a negative margin under OCT. In comparing to the H&amp;E histology, there were 9 true positives, 9 true negatives, 2 false positives, and 0 false negatives yielding a sensitivity of 82% and specificity of 100%.&amp;#x2028; Discussion: With an imaging penetration depth of 2-3 mm, equivalent to that used for histological assessment, OCT provides unique real-time cellular-level imaging to identify positive and close margins. In these studies, areas of higher scattering tissue with an irregular or heterogeneous pattern were identified, differentiating them from the abundant adipose tissue found in normal breast tissue. The small nucleus to cytoplasm (N/C) ratio is observed with low-scattering adipocytes compared with the larger N/C ratio found from highly-scattering tumor cells. These intraoperative imaging studies have demonstrated the ability for OCT to identify positive surgical margins. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 802.

Noninvasive Volumetric Imaging and Morphometry of the Rodent Retina with High-Speed, Ultrahigh-Resolution Optical Coherence Tomography

To demonstrate high-speed, ultrahigh-resolution optical coherence tomography (OCT) for noninvasive, in vivo, three-dimensional imaging of the retina in rat and mouse models. A high-speed, ultrahigh-resolution OCT system using spectral, or Fourier domain, detection has been developed for small animal retinal imaging. Imaging is performed with a contact lens and postobjective scanning. An axial image resolution of 2.8 mum is achieved with a spectrally broadband superluminescent diode light source with a bandwidth of approximately 150 nm at approximately 900-nm center wavelength. Imaging can be performed at 24,000 axial scans per second, which is approximately 100 times faster than previous ultrahigh-resolution OCT systems. High-definition and three-dimensional retinal imaging is performed in vivo in mouse and rat models. High-speed, ultrahigh-resolution OCT enabled high-definition, high transverse pixel density imaging of the murine retina and visualization of all major intraretinal layers. Raster scan protocols enabled three-dimensional volumetric imagingand comprehensive retinal segmentation algorithms allowed measurement of retinal layers. An OCT fundus image, akin to a fundus photograph was generated by axial summation of three-dimensional OCT data, thus enabling precise registration of OCT measurements to retinal fundus features. High-speed, ultrahigh-resolution OCT enables imaging of retinal architectural morphology in small animal models. OCT fundus images allow precise registration of OCT images and repeated measurements with respect to retinal fundus features. Three-dimensional OCT imaging enables visualization and quantification of retinal structure, which promises to allow repeated, noninvasive measurements to track disease progression, thereby reducing the need for killing the animal for histology. This capability can accelerate basic research studies in rats and mice and their translation into clinical patient care.

Characterization of dental caries using Optical Coherence Tomography

BackgroundOptical Coherence Tomography (OCT) is a noninvasive imaging technique that compiles successive interferometric signals into a tomographic image. Although the capacity of OCT to image dental structures has been verified, the anisotropic nature of teeth and gingival tissue may limit the resolution of conventional OCT.ObjectiveThe objective of this study was to compare the imaging characteristics of dental caries using polarization-sensitive (ps-OCT) and conventional OCT.Study designFive teeth with no evidence of caries and 4 teeth with dentinal caries were imaged using 2 prototype OCT systems. The conventional OCT system consisted of an autocorrelator scanning interferometer using a 1310-nm (60 nm spectral bandwidth) 14-mW superluminescent diode (SLD) light source. The second system was a prototype ps-OCT using a 2-mW, 1300-nm SLD with a spectral bandwidth of 40 nm. Light from the SLD first passed a vertical polarizer and was then separated by a beamsplitter. In the sample arm, light was circularly polarized with a quarter waveplate in which the fast axis was oriented at 45 degrees with respect to the vertical direction. Light returning from both the sample and the reference arms was again separated by a polarizing beamsplitter. The vertically and horizontally polarized signals were then detected in 2 channels and images were reconstructed by combining the signals.ResultsConclusionsOur ps-OCT dental prototype provides higher-resolution images and should introduce a precision of measurement that is not possible with current methods. Ps-OCT is relatively inexpensive, is noninvasive, and can produce 3-dimensional images of dental caries. BackgroundOptical Coherence Tomography (OCT) is a noninvasive imaging technique that compiles successive interferometric signals into a tomographic image. Although the capacity of OCT to image dental structures has been verified, the anisotropic nature of teeth and gingival tissue may limit the resolution of conventional OCT. Optical Coherence Tomography (OCT) is a noninvasive imaging technique that compiles successive interferometric signals into a tomographic image. Although the capacity of OCT to image dental structures has been verified, the anisotropic nature of teeth and gingival tissue may limit the resolution of conventional OCT. ObjectiveThe objective of this study was to compare the imaging characteristics of dental caries using polarization-sensitive (ps-OCT) and conventional OCT. The objective of this study was to compare the imaging characteristics of dental caries using polarization-sensitive (ps-OCT) and conventional OCT. Study designFive teeth with no evidence of caries and 4 teeth with dentinal caries were imaged using 2 prototype OCT systems. The conventional OCT system consisted of an autocorrelator scanning interferometer using a 1310-nm (60 nm spectral bandwidth) 14-mW superluminescent diode (SLD) light source. The second system was a prototype ps-OCT using a 2-mW, 1300-nm SLD with a spectral bandwidth of 40 nm. Light from the SLD first passed a vertical polarizer and was then separated by a beamsplitter. In the sample arm, light was circularly polarized with a quarter waveplate in which the fast axis was oriented at 45 degrees with respect to the vertical direction. Light returning from both the sample and the reference arms was again separated by a polarizing beamsplitter. The vertically and horizontally polarized signals were then detected in 2 channels and images were reconstructed by combining the signals. Five teeth with no evidence of caries and 4 teeth with dentinal caries were imaged using 2 prototype OCT systems. The conventional OCT system consisted of an autocorrelator scanning interferometer using a 1310-nm (60 nm spectral bandwidth) 14-mW superluminescent diode (SLD) light source. The second system was a prototype ps-OCT using a 2-mW, 1300-nm SLD with a spectral bandwidth of 40 nm. Light from the SLD first passed a vertical polarizer and was then separated by a beamsplitter. In the sample arm, light was circularly polarized with a quarter waveplate in which the fast axis was oriented at 45 degrees with respect to the vertical direction. Light returning from both the sample and the reference arms was again separated by a polarizing beamsplitter. The vertically and horizontally polarized signals were then detected in 2 channels and images were reconstructed by combining the signals. Results ConclusionsOur ps-OCT dental prototype provides higher-resolution images and should introduce a precision of measurement that is not possible with current methods. Ps-OCT is relatively inexpensive, is noninvasive, and can produce 3-dimensional images of dental caries. Our ps-OCT dental prototype provides higher-resolution images and should introduce a precision of measurement that is not possible with current methods. Ps-OCT is relatively inexpensive, is noninvasive, and can produce 3-dimensional images of dental caries.

Ultrahigh resolution optical coherence tomography imaging with a broadband superluminescent diode light source

Ultrahigh resolution optical coherence tomography imaging is performed with a compact broadband superluminescent diode light source. The source consists of two multiplexed broadband superluminescent diodes and has a power output of 4 mW with a spectral bandwidth of 155 nm, centered at a wavelength of 890 nm. In vivo imaging was performed with approximately 2.3 microm axial resolution in scattering tissue and approximately 3.2 microm axial resolution in the retina. These results demonstrate that it is possible to perform in vivo ultrahigh resolution optical coherence tomography imaging using a superluminescent diode light source that is inexpensive, compact, and easy to operate.

Fiber-optic polarimetric strain sensor with three-wavelength digital phase demodulation

A fiber-optic polarimetric strain sensor of l(S)=10-cm sensing length with three-wavelength passive quadrature digital phase demodulation is investigated. The demodulation unit uses a superluminescent diode light source with narrow-band interference filters in front of the photodiodes and real-time processing of the interference intensities by an arctan-phase-stepping algorithm. Quasi-static strain sensing is performed during slow periodic compression of a composite reinforced plastic rod with a sensor glued to its surface. The measured displacement sensitivity of delta?/deltal=125 mrad/mum, with a resistive strain gauge as a reference, agrees well with the value of 119 mrad/mum previously determined by fringe-distance measurement [Bock et al., Pure Appl. Opt. 5, 125 (1996)]. Despite a coherence-limited fringe contrast of only a few percent, a linearity of the phase-strain characteristic of the order of 1% and a strain resolution of 2.5muepsilon are demonstrated.

Pockels high-voltage measurement system

The practical use of optical sensors to measure direct high voltages can be limited by their high sensitivity. A new optical high voltage measurement technique for applying to high voltage levels up to 400 kV in a wide bandwidth between DC to 30 MHz is developed. A prototype of the optical voltage transformer is assembled using Pockels crystals in a multisegmented arrangement, a super luminescent diode (SLD) light source and a special optical fiber link. A good performance of linearity and accuracy is obtained for DC, AC, lightning impulse and step voltage measurements, In addition, an excellent agreement is observed between the measured and predicted values.

Fiber-optic extrinsic Fabry–Perot interferometer sensors with three-wavelength digital phase demodulation

A three-wavelength-based passive quadrature digital phase-demodulation scheme has been developed for readout of fiber-optic extrinsic Fabry-Perot interferometer vibration, acoustic, and strain sensors. This scheme uses a superluminescent diode light source with interference filters in front of the photodiodes and real-time arctan calculation. Quasi-static strain and dynamic vibration sensing with up to an 80-kHz sampling rate is demonstrated. Periodic nonlinearities owing to dephasing with increasing fringe number are corrected for with a suitable algorithm, resulting in significant improvement of the linearity of the sensor characteristics.

Optical Coherence Tomography for Optical Biopsy

Optical coherence tomography (OCT) is an recently developed medical diagnostic technology that uses back-reflected infrared light to perform in situ micron scale tomographic imaging. In this work, we investigate the ability of OCT to perform micron scale tomographic imaging of the internal microstructure of in vitro atherosclerotic plaques. Aorta and relevant nonvascular tissue were obtained at autopsy. Two-dimensional cross-sectional imaging of the exposed surface of the arterial segments was performed in vitro with OCT. A 1300-nm wavelength, superluminescent diode light source was used that allows an axial spatial resolution of 20 microns. The signal-to-noise ratio was 109 dB. Images were displayed in gray scale or false color, Imaging was performed over 1.5 mm into heavily calcified tissue, and a high contrast was noted between lipid- and water-based constituents, making OCT attractive for intracoronary imaging. The 20-microns axial resolution of OCT allowed small structural details such as the width of intimal caps and the presence of fissures to be determined. The extent of lipid collections, which had a low backscattering intensity, also were well documented. OCT represents a promising new technology for imaging vascular microstructure with a level of resolution not previously achieved with the use of other imaging modalities. It does not required direct contact with the vessel wall and can be performed with a catheter integrated with a relatively inexpensive optical fiber. The high contrast among tissue constituents, high resolution, and ability to penetrate heavily calcified tissue make OCT an attractive new imaging technology for intracoronary diagnostics.