High-resolution optical backscatter reflectometry (OBR) has become a valuable tool in the design, test and diagnostics of fiber components, photonic integrated circuits (PICs) and short fiber networks. In much the same way that standard OTDRs identify and locate issues and sources of loss in long-range fiber optic systems, high-resolution OBRs can locate and identify issues and defects with sub-millimeter resolution and since they don’t suffer from the “deadzones” associated with OTDR, they are ideal for components and short-run optical networks like those found in modern, high-speed communications networks and data links.

In conjunction with IEEE GlobalSpec, Luna invites you to a free webinar, “Optical Backscatter Reflectometry:  The Key to Accelerating Design Verification and Troubleshooting of Next Generation Optical Network Components.”  This webinar will review how OBR technology works, how it differs from alternative reflectometry techniques, and describe real-world application examples. These application examples include characterizing the optical performance and quality of silicon photonic components such as waveguides and troubleshooting short fiber networks like those found in data centers and on aircraft. These application examples will illustrate how high-resolution OBR delivers an extreme level of detail and sensitivity in identifying sources of loss (bends, breaks, bad splices, defects, interfaces, etc.), as well as making very precise latency measurements. The webinar will include live software demos to illustrate the operation of OBR instruments with real-world optical components and systems.

Date:  July 26, 2018

Time:  2:00 PM EDT / 11:00 AM PDT

Host:  Dr. Brian Soller, VP and GM, Lightwave Division of Luna

Click here to register. 

Figure 1. GAU-8 30mm Gatling gun on the A-10 (top). Typical crack in 30mm barrel wall obtained by destructive analysis (bottom).

Every time a gun is fired, enormous gas pressures are generated inside the barrel to propel a projectile toward its intended target. For perspective, typical pressures can exceed 50,000 pounds of force per square inch:  over three times the water pressure at the deepest ocean depths. The resulting stresses in the barrel’s wall impart fatigue damage each time a round is fired, initiating cracks that propagate radially through the barrel wall (Figure 1). The guns on military weapon systems feature a very high rate of fire. For example, the A-10 “Warthog” has a medium-caliber (30 mm) gun that fires up to ten rounds per second out of each of its seven barrels (Figure 1, top).  At these speeds, fatigue damage can accumulate quickly. 

Currently, maintainers do not have the inspection tools to quantify actual barrel fatigue damage in service. This is why the Air Force Life Cycle Management Center (AFLCMC) has sponsored Luna to invent technologies that will allow maintainers, for the first time, to quantify in-wall barrel fatigue damage as part of their current routine inspections. With improved knowledge of actual damage state, barrels may be retired based on actual condition instead of a highly conservative round-count.

Luna’s in-wall damage inspection system locates cracks using an electromagnetic probe that is scanned inside the full length of the barrel. The probe applies a time-varying (AC) magnetic field to induce small electrical “Eddy” currents in the barrel wall that flow in a closed loop around the barrel’s circumference and around the probe (Figure 2). In regions with no cracks, the currents flow near the barrel bore along the shortest possible path. As the probe scans through cracked regions, the current path is disturbed, requiring a detour around the non-conductive cracks. The resulting change in path length increases the electrical resistance along the path, thereby weakening the Eddy current flow. The probe’s sensing coil output is designed to increase in response to the reduced Eddy current flow, producing a rapid, non-destructive assessment of cracking damage in barrel walls. Critically, this electromagnetic technique is relatively insensitive to the barrel’s rifling grooves. Other NDE methods, particularly ultrasonics, are confused by the complex bore geometry and are not able to reliably identify nearby cracks. Luna’s technique has proven impervious to complex bore geometries and has successfully resolved the depth of cracks in 30mm caliber gun barrels. In this evaluation, Luna’s sensor output correlated very closely with the actual crack depth on a retired gun barrel. Luna is currently developing probes and techniques for 20 and 25mm barrels.

About gun barrel fatigue damage analysis:

Figure 2: Schematic demonstration of eddy current principle for crack detection. Bobbin-type probe shown.

Damage progression rate can vary widely depending on the type of ammunition fired and the fatigue resistance of the particular barrel material. To avoid catastrophic barrel rupture and secondary damage to the weapons system, the barrels are retired after a specified round count experimentally determined ahead of time to be safe under the most conservative assumptions.  Only after the barrel is removed from service, destructively cross sectioned, and visually inspected is the full extent of its fatigue damage known (Figure 1, bottom). In most cases, the cracks found in retired barrels are well under the allowable length, meaning that they were retired while they still had a significant amount of life remaining. Swapping barrels before they are fully expended effectively reduces weapons system availability and drives up operating and maintenance costs. Because of the high degree of uncertainty in barrel damage prior to cutting them open, this conservative approach is justified for avoiding the risk of a single catastrophic failure, loss of aircraft, and potential loss of life.

Today, maintainers commonly use surface profile inspection tools, such as laser-based scanners, that measure the condition of the barrel bore and rifling grooves that guide and stabilize the projectile. Bore and rifling condition affects the weapon accuracy, but is not the critical safety concern posed by through-wall cracks that are invisible to currently-fielded inspection methods. Luna’s in-wall damage inspection tool will locate cracks inside the full length of the barrel, resulting in enhanced aircraft and weapons system readiness.

Figure 3. Demonstration validating Eddy current predictions. We scanned this 30 mm barrel on site, then the Air Force destructively evaluated it. The barrel breech end is at 0 inches, and the muzzle end at 88 inches.

If you want a chance to see our new multi-channel system for fiber optic strain and temperature measurements, no matter if you’re in Europe or the United States, you’ll have the perfect opportunity at one of our upcoming trade shows next week! 

Sensor + Test

Beginning Tuesday, June 26th, you will find our ODiSI 6100 being demo’d at the Sensor + Test tradeshow in Nürnberg, Germany.  Alongside one of our channel partners, Polytec, Luna will be there to answer any of your questions about our high-definition fiber optic sensing (HD-FOS) system – now with a maximum of 8 channels available, which take hundreds of thousands of measurement points.

Sensor + Test 2018

June 26-28, 2018
The Nürnberg Exhibition Centre | Nürnberg, Germany
Hall 5 Stand 310

JEC Composites in Transportation

Also next week, Luna will be exhibiting at the JEC Composites in Transportation event in Chicago, Illinois, beginning Wednesday, June 27th.   We will have our ODiSI 6100 available for demonstrations.  Our sales representatives are anxious to show off this new product and discuss how it delivers unprecedented visibility into your composite designs, curing and molding processes, and even performance of adhesive bonds. 

JEC Composites in Transportation

June 27-28, 2018
Aon Grand Ballroom at Navy Pier | Chicago, IL
Booth # 111

We hope to see you next week!

Pulsed terahertz imaging can provide a wide array of information about a sample. Whether it is the thickness of particular layers, the presence of an internal void, detection of a specific gas, or the density distribution in a layer of foam, a pulsed terahertz image can provide valuable information.  Although it generates a 3-D dataset, with information on both the surface and the internal structure, one of the drawbacks of pulsed imaging is that it is collected one pixel at a time.

The single point terahertz sensor must be scanned over the object to create an image.  This makes the speed with which each pixel can be acquired particularly important.

For most systems, imaging can be performed with a two-axis scanner.  TeraMetrix offers the T-Image® x-y scanner.  The T-Image is capable of scanning at rates up to 150mm per second, and can provide step resolution down to 25 microns (which is well below the minimum spot size of the terahertz beam).  The imaging speed is still going to be limited by the rate at which a single pixel can be measured.

The TeraMetrix T-Ray® 5000 Terahertz Control Unit (TCU) has the highest speed waveform acquisition rate available.  Even the lower speed versions (TCU5210 and TCU5213) are faster than most systems on the market today, with a waveform acquisition rate of 100 pixels per second.  The high-speed versions (TCU5211 and TCU5212) are unsurpassed, with an acquisition rate of 1000 pixels per second. 

The T-Image can be configured in reflection, as shown here, or in transmission, and can be deployed in any orientation.  This allows scanning of walls or paintings.  The entire system is portable, so it can be taken to where the object is rather than requiring it be brought to the lab.

For larger pixel sizes (greater than 150 microns), the image acquisition rate will be limited by the speed of the T-Image.  To overcome this limitation, the scan axis can be replaced with a deflection scanner.  Imagers of this type can produce cross sectional images in real time.

A handheld version of this scanner, the line scan gauge, or LSG can produce a real time image of subsurface structure.  Here the LSG is shown detecting the support stud under the room’s drywall.

While both of these imagers are impressive, they are only possible due to the high acquisition speed of the TeraMetrix T-Ray 5000.

For more information contact

The June 2018 issue of CompositesWorld highlights Luna’s ODiSI measurement system and its value in the design and testing of composite materials and components.  The design and validation of composite components and systems is significantly more complex than for traditional materials, and the article describes how high-definition fiber optic sensing (HD-FOS) is uniquely suited for composite test and measurement.  Specifically, HD-FOS can be used to:

  • More accurately and completely validate composite models and simulations
  • Assess and characterize performance of adhesive bonds and multi-material joints
  • Create smart parts using embedded sensors

Read the complete article in CompositesWorld here.

Learn more about the ODiSI measurement system for HD-FOS here.

The following is a re-post of a popular past blog post that explains the basics of return loss, why it’s an important measurement, and technologies for measuring return loss.

Fiber optic networks span a wide range of lengths. Intercity and transoceanic fiber optic telecommunications networks span thousands of kilometers. In aircrafts and ships, telecommunications systems have link lengths up to 500m. Data center networks have lengths on the order of meters. Finally fiber optic components have very short lengths on the centimeter and smaller scale.

Across all these applications, data needs to be sent with great fidelity from the source to the receiver. Any loss or reflection events along the way will contribute to a degradation of the signal. This blog post is intended to give an overview of potential sources of optical return loss (RL) and the importance of measuring it.

Definition of Return Loss

In technical terms, RL is the ratio of the light reflected back from a device under test, Pout, to the light launched into that device, Pin, usually expressed as a negative number in dB. 

            RL = 10 log10(Pout/Pin)

Sources of loss include reflections and scattering along the fiber network. A typical RL value for an Angled Physical Contact (APC) connector is about -55dB, while the RL from an open flat polish to air is typically about -14dB. High RL is a large concern in high bitrate digital or analog single mode systems and is also an indication of a potential failure point, or compromise, in any optical network.

What Does High Return Loss Indicate?

Dirty Connector

There are some very simple faults within an optical network that can cause high RL. A dirty connector is one such source. Even a tiny dust particle on a 5 micron single-mode core can end up blocking the optical signal, resulting in signal loss.

Broken Optical Fiber

A break in the optical fiber can also cause high RL. In some instances, it is possible for the optical fiber to have a break in it, but still be able to guide light through. In this case, a measurement of insertion loss (IL) across this fiber will result in a low IL. This disguises the extent of the problem where a direct RL measurement would immediately highlight it. In addition, a crack in a fiber can have both low IL and low RL and easily be missed as a problem in the system.  However, a sensitive RL measurement will show a reflection peak where there should be none, indicating a crack in the fiber that will likely lead to failure. 

Poorly Mated Connector

If a connector is not fully seated, the resulting air gap between connector end faces would result in high RL from that point. In this case, the IL may be low and the signal fidelity could still be good. However, this would be a source of concern as this loose connection is now a possible source of failure, as it could become misaligned or completely disconnected while in service.

Creates Multipath Interference and Degrades Signal

Multiple high reflection points within a network can lead to the optical effect known as multipath interference. This interference can easily lead to signal degradation, especially in high speed networks. In addition, many fiber optic transmission systems use lasers to transmit signals over optical fiber. High RL can cause undesirable feedback into the laser cavity which can also lead to signal degradation.

Methods for Measuring Return Loss

There are three established reflectometry techniques used for measuring RL as a function of location along an optical fiber assembly or network: optical time domain reflectometry (OTDR), optical low coherence reflectometry (OLCR) and optical frequency domain reflectometry (OFDR). The different methods have tradeoffs in range, resolution, speed, sensitivity and accuracy. Typically, the low coherence technique is used for sub-millimeter resolution measurements over a limited range (< 5 m). OTDR is typically used for long range (several kilometers) measurements with low spatial resolution.

OFDR by Luna

OFDR, the technology used in our OBR product line, is ideal for measurements from the component level to short networks (up to 2 km). OFDR produces measurements with spatial resolutions as fine as 10 microns over 30 m or a few mm over 2 km. This high spatial resolution measurement over intermediate lengths can provide significant advantages.  For example, when an OBR is used to troubleshoot a network on an aircraft it is able to very precisely pinpoint the location of a fault, so that a technician knows which panel to open or on which side of a connector the fault was located.  The sensitivity of OFDR also makes it possible to detect small RL events such as cracks that would be difficult to detect with other methods, but could lead to in-service failures.

For more information on how OBR reflectometers use OFDR technology to deliver ultra-high resolution of loss, as well as polarization, dispersion, and other optical measurements, explore the OBR here.

Learn more about OFDR technology.

Learn more about OBR high-resolution reflectometers.

by Judy M. Obliosca, Dimpal Patel, Yang Xu, Christopher Tison

Rapid and Sensitive Detection of Organ Injuries Could Save Lives

Major organ injuries such as those to the liver, lung, kidney and brain can lead to high mortality in critically ill patients. Since these injuries are internal and frequently do not present for easy identification, their misdiagnosis can be deadly. Advanced noninvasive testing with low level detection (high sensitivity) and the ability to identify the exact problem (high specificity) is therefore needed to enhance detection, particularly at early stages. Biomarkers may have predictive values before tissue injury for specific organs becomes irreversible. Identification of such biomarkers in clinical samples would improve the early detection of organ injury, help identify appropriate preventive or curative strategies, prevent organ injury from proceeding to organ failure, and improve quality of life. So far, detection of these biomarkers relies on expensive and time consuming methods such as polymerase chain reaction, mass spectrometry, bead- and absorption-based assays and enzyme-linked immunosorbent assay (ELISA). Even with their drawbacks, they still don’t have the specificity and sensitivity desired, and are limited to looking for one biomarker at a time.

The nanoSPRi Technology Fills a Critical Market Need

Luna has developed a sensing chip that monitors biomolecular interactions on its surface.  Technically, it’s an in vitro diagnostic assay based on a nano-enhanced surface plasmon resonance imaging (nanoSPRi) technique. Luna’s assay immobilizes diverse capture points of antibodies and aptamers onto designated regions of the chip.  When the sample of human serum is flowed across the chip, specific proteins and nucleic acids (DNA/RNA) are simultaneously trapped by their respective capture agents on the chip.  This binding enables a portable, benchtop SPRi instrument equipped with a highly sensitive CCD camera to capture changes in the reflectivity on the chip in real-time. The results from the detection are displayed as a “sensorgram” (binding response on the y-axis plotted against time on the x-axis). From studying the shape of the produced sensorgram, capabilities of the technique such as binding, specificity, affinity, kinetics, active binding concentration and limit of detection were determined.

Luna’s nanoSPRi-based assay is designed for rapid, highly sensitive and specific detection of protein and nucleic acid (DNA/RNA) organ injury biomarkers in human serum in less than an hour of assay analysis time. Activated sensing chip is both functionalized and blocked using Luna’s blocking system.


Luna’s nanoSPRi-based assay is designed for rapid, highly sensitive, and simultaneous detection of protein, DNA, and microRNA biomarkers in human serum in less than an hour of analysis. Luna’s assay consists of 3 major features: (1) The novel sensing chip surface functionalization and blocking system that can almost eliminate (>95%) non-specific binding events from human serum. (2) The array technology that enables multiplexed detection of a panel of biomarkers (both protein- and nucleic acid-based) for diverse types of organ (lung, liver, brain) injuries. (3) The nanoenhancer quantum dots (QD) that enable ultrasensitive biomarker detection at very low concentration (pg/mL). Combined, these features result in a highly sensitive, rapid, and multiplexed.

Successful detection of human interleukin 4 (IL4) biomarker in human serum using Luna’s nanoSPRi platform. (A) 10 ng/mL IL4 in 10% and (B) 100% human serum. (C) Detection of IL4 in 10% serum shows very high sensitivity with limit of detection at 0.1 pg/mL. (D) Simultaneous detection of 3 biomarkers (MIP3, IL4 and MIP1b, 5 ng/mL each) in 10% human serum.


Proprietary Modifications to the Sensor Have Resulted in Significant Advances in Biomarker Analysis

Luna has successfully developed a novel functionalization and blocking system on the sensing chip surface for use with human serum-based samples, and eliminated >95% of non-specific binding of unwanted constituents. By using the activated sensing chip, the inflammatory biomarker human interleukin 4 (IL-4) was successfully detected in less than an hour for both dilute (10%) and whole (100%) human serum samples. The assay achieved a 0.1 pg/mL IL4 limit of detection, which is 2 orders of magnitude better than that obtained using a typical ELISA. Luna also successfully achieved simultaneous detection of 6 inflammatory and acute lung injury biomarkers (IL4, MIP3, MIP1b, TNF-α, IL1β and IL8), 2 nucleic acid-based liver injury biomarkers (the DNA counterpart of miR122 and the human angiopoietin-like 3) and 1 traumatic brain injury biomarker (eotaxin CCL11) in 10% human serum with great sensitivity, selectivity and high S/N ratio. Moreover, Luna successfully integrated protein and DNA/RNA biomarker detections in serum on a single sensing chip with minimal cross-reactivity issue.

Luna’s nanoSPRi Assay is Posed to Revolutionize Advanced Biomarker Detection in Multiple Fields

Overall, Luna’s superior results demonstrate that the assay is a promising platform for accurate early diagnosis of multiple organ injuries. To date, this has been demonstrated with high sensitivity detection of biomarkers indicated in lung, liver, and kidney injuries. Further, our recently successful detection of the brain injury biomarker eotaxin CCL11 demonstrates capability for use in military and sports head trauma injury analysis. For example, CCL11 was recently shown to be predictive of chronic traumatic encephalopathy, or CTE, and has become a critical focus in brain injuries to professional athletes. This diagnostic capability being developed by Luna is a platform technology, and upon successful implementation for organ injuries, could be reconfigured for the study of a wide variety of diseases in various body fluids.

This work was supported by the US Army Medical Research Acquisition Activity (USAMRAA) under Contract No. W81XWH-14-C-0146. The views, opinions, and findings contained are those of the author(s) and should not be construed as official USAMRAA position, policy, or decision unless designated by other documentation.

The TeraMetrix division of Luna will be announcing two new products for the non-destructive testing (NDT) market at ECNDT in Gothenburg, Sweden (  The products will be displayed in the booth of Baugh and Weedon NDE, (Booth #:  C04:01).

Both the pulsed terahertz SPG (Single Point Gauge) and the LSG (Line Scan Gauge) will be available for demonstration.  These handheld terahertz sensors are easy to use, and can make multiple measurements.

The SPG is a tool for analyzing the waveform return (A-scan) from an object, and displaying on the handheld screen a variety of measurements, including multi-layer thickness, delamination, water ingress and more.  The SPG is connected to the T-Ray 5000 TCU (Terahertz Control Unit).

The LSG uses the same control unit, but provides a cross-sectional image of the sample under test (B-scan).  The LSG provides a real time image useful for identifying defects, or sub-surface structure of an object.

The SPG and the LSG were both originally developed for use in manufacture and testing of the F-35 Joint Strike Fighter.  For more information contact

During the time before deployment and usage, armaments (missiles, rockets, bombs) are placed in storage for long durations and exposed to a variety of environmental conditions during transportation.  Training missions, in which armaments are loaded and unloaded from active aircraft, can expose them to the severe flight environment, stressing the systems’ electronics, structures, and payload.  Throughout their lifecycles, missile systems may experience a multitude of environmental and physical effects that can induce degradation.  Tracking individual missiles is a challenge, but knowing their history of environmental exposure and operational use is next to impossible.  Two missiles of the same age could have very different use profiles and very different maintenance and sustainment needs. 

Sensors exist that monitor some environmental effects on armaments, but due to power limitations none are currently able to remain operational for a full armament lifetime.  Any system must be battery operated as there are no power supplies available in missile storage locations, so no sensors have been able to identify and log time spent in various states such as in storage or installed on aircraft.  As long term exposure to harsh environments during storage and transportation can have significant negative effects on missiles, bombs, and other armaments, it has become critical to understand the full life-cycle exposure of in-service weapon systems.  Rudimentary efforts at better understanding storage and handling conditions using small MEMS accelerometers have been attempted, but up to now there is no sensor system available that is able to track and identify the full profile of environments – in storage, on the flightline, on aircraft, or in the air – that would lead to more efficient sustainment through condition based maintenance. 

Building on our extensive experience with low power sensing and wireless communication, Luna is currently developing a solution to track the environmental and physical parameters experienced by missile armaments in a form factor that is readily applicable to existing platforms.  Luna’s system, known as ArmaLife™, will collect key environmental parameters and use this data to classify the missile as being in one of four states: indoor storage, ground transportation/handling, active/open storage, and flight.

ArmaLife: Lifecycle Monitoring for Improved Reliability, Maintainability, and Availability

The ArmaLife sensor will be small and low power with an integrated battery.  It will be designed so it can be retrofit to the outside of an existing missile casing for rapid upgrading of current weapons.  The sensor system will be used to monitor environmental factors experienced by the armament over its entire lifetime (at least 20 years) such as vibration, temperature, relative humidity, ultraviolet intensity, lux (ambient light) intensity, and barometric pressure.  By combining these parameters using sensor fusion algorithms, the ArmaLife system will quantify the amount of time an armament has spent in indoor/outdoor storage, in transport, on a flightline, installed on a plane, or in flight (Figure 1).  The system will be developed with extremely low power consumption components to ensure extended sensor lifetimes with limited power sources.  The ArmaLife hardware will use small, reliable, inexpensive sensor designs to enable ease of integration into legacy and future armament systems. 

Figure 1. ArmaLife sensor system architecture and representative data collected from handling a 4” steel test pipe.

In addition to recording armament status information and environmental exposure, the sensing system will categorize vibration events into low, intermediate, and high levels.  To provide additional information for determining armament reliability, maintainability, and availability (RM&A), the sensing system will record min/max values and duration of environmental factors experienced by the missile.  To make collected data easily accessible, the ArmaLife sensor system will use a radio frequency identification (RFID) transponder chip to monitor for a wake-up command from a maintainer, in turn initiating the transfer of collected data through wireless communications.  The ArmaLife system is currently being engineered to be ultra-low profile for external armament integration, while not interfering with mechanical, electrical, or aerodynamic operation of the weapon.

ArmaLife Hardware and Targeted Data Analysis Will Lead to Better Condition Based Maintenance

The ability to monitor critical parameters and use them to classify armament status throughout the weapon system’s life-cycle will allow the Air Force to perform high efficiency condition based maintenance.  The Air Force will be able to observe how long the armaments resides in each lifecycle stage, such as handling and transportation (Figure 2).  Engineers and operators can then review exposure conditions and analyze what status and exposure effects have contributed to the current condition of their assets.  The ArmaLife system will give the Air Force another data point in assessing missile reliability, maintainability, and availability for optimization of current maintenance schedules to effectively execute condition based maintenance.  

Figure 2. Handling of AIM-9X missile. (U.S. Air Force photo/Levin Gaddie,

This week at Space Tech Expo in Pasadena, CA, we are showcasing our industry leading ODiSI 6100 measurement sensor for high-definition fiber optic sensing (HD-FOS).  We are highlighting the unique capabilities of the ODiSI 6100 by demonstrating the real-time acquisition of strain across the entire surface of a carbon fiber composite sample.  The composite sample was instrumented with a Luna HD strain sensor, a polyimide coated optical fiber calibrated for accurate strain measurements.  The 5m long HD fiber optic sensor was attached with epoxy to the interior surface of the composite sample, traversing the entire surface back and forth in order to get a full picture of strain across the entire component.  The surface has some tight curves which would be very difficult or impossible to instrument with traditional foil strain gages.

The screenshot below from the ODiSI 6100 software shows real-time strain from the attached sensor versus length.  The large periodic positive and negative peaks occur on sections of the sensor that are in line with the applied strain, while sections of the sensor running transverse to the applied strain show very low or zero strain.  This plot, taken with the ODiSI configured for a 1.3 mm gage pitch, is literally displaying nearly 4000 unique strain measurements along the length of the sensor.  This resolution can even be increased further by simply reconfiguring the ODiSI for a 0.65 mm gage pitch.

With dense data like this, alternative visualization of the data can be very useful. For example, the following visualization shows the measured strain data mapped to a 3D model of the composite component, indicating the intensity of the strain with color.

While you could have seen all this live and in person in Pasadena this week, there are plenty of other opportunities to see and learn how HD-FOS sensing and the ODiSI can deliver unprecedented resolution and visibility into your designs or processes.  You can learn more about the ODiSI 6100 measurement system here, or contact us to arrange a consultation with one of our engineers and see the ODiSI in action yourself.