Stephen Mihailov

• PhD
• Research Officer at National Research Council Canada

All-fiber visible spectrometers with a sub-nanometer resolution and record-high light outcoupling (70%) are fabricated using violet (400 nm) and near-infrared (800 nm) femtosecond laser pulses and the phase mask technique. The spectrometers are based on highly localized uniform Bragg gratings produced by tightly focusing the femtosecond pulses into...

1000°C-resistant Bragg gratings (i.e., Type-II Bragg gratings) with a 300 nm period are fabricated in non-photosensitized silica-based optical fibers using tightly focused ultraviolet/visible (400 nm) femtosecond pulses and a phase mask. Five millimeter-long Bragg gratings with a -10 dB transmission dip and -0.1 dB off-resonance insertion loss are...

The optical and structural properties of boron nitride nanotube (BNNT) assembly were characterized using optical fiber Bragg grating (FBG) sensors. FBGs were fabricated in tapered fibers with a diameter of less than 30 μm. After tapered fibers were etched in hydrofluoric acid solution for a few minutes, BNNTs were then deposited on the fibers throu...

Durable fiber Bragg grating (FBG) relative humidity (RH) sensors are fabricated in commercially available polyimide (PI) coated 50 μm diameter Ge-doped silica optical fibers using an infrared femtosecond pulse duration laser and a phase mask. FBGs are inscribed directly through the 10 μm thick PI coating which is subsequently thickened with PI usin...

Material modification is produced inside silica-based optical fibers of different diameters using tightly focused near-infrared (central wavelength at 800 nm) femtosecond laser pulses and the phase mask technique which is often employed for laser inscription of fiber Bragg gratings. 1st-, 2nd-, and 3rd-order phase masks designed for the operation a...

We demonstrate the storage and retrieval of heralded single photons in a fiber-based cavity quantum memory. The photons are stored, and retrieved, from the memory using quantum frequency conversion which switches the photon into, and out of, resonance with the cavity. The photons, generated in the telecom O-band with a bandwidth of 81 GHz, are retr...

We demonstrate the generation of photons within a fiber-cavity quantum memory, followed by later on-demand readout. Signal photons are generated by spontaneous four-wave mixing in a fiber cavity comprising a birefringent fiber with dichroic reflective end facets. The detection of the partner herald photon indicates the creation of the stored signal...

Fiber Bragg Grating (FBG) relative humidity (RH) sensors were written in 50 μm diameter fibers through the polyimide coating. Thickening the polyimide resulted in the highest sensitivity reported for polyimide coated FBG RH sensors.

Practical quasi-distributed sensing with Fiber Bragg Gratings (FBGs) depends on the repeatable fabrication of numerous, mechanically robust, low loss FBGs. This work reports an array of 1008 FBGs written with a phase mask through polyimide.

A comparison of Type II Fiber Bragg Grating (FBG) wavelength drift is reported for 600°C, 800°C, 900°C and 1000°C. Significant prolonged redshift was observed at 800°C, transitioning to blueshift more quickly at higher temperatures.

A super-efficient all-fiber visible spectrometer with sub-nanometer resolution is fabricated using one infrared femtosecond laser pulse and a phase mask. The strong light outcoupling from the fiber is due to micropores formed in its core.

Type II Fiber Bragg Grating (FBG) wavelength drift is reported and compared for gratings in single mode fibers, having different diameter and dopant configurations. Some fibers respond with less drift than others.

We demonstrate the storage and on-demand retrieval of single-photon-level telecom pulses in a fiber cavity. The cavity is formed by fiber Bragg gratings at either end of a single-mode fiber. Photons are mapped into and out of the cavity using quantum frequency conversion driven by intense control pulses. In a first spliced-fiber cavity, we demonstr...

The technique of femtosecond laser-induced inscription of fiber Bragg gratings creates a structure in the optical fiber that can be used effectively as a sensor especially when deployed in harsh environments. Depending on the optical fiber chosen and the inscription parameters that are used, devices can be made that are suitable for sensing applica...

Fiber Bragg grating (FBG) relative humidity (RH) sensors are fabricated in commercially available polyimide (PI)-coated optical fibers with diameters of 50 and 125 μm. Infrared (800 nm) femtosecond pulse duration laser pulses and a phase mask are used to inscribe Type-I and Type-II FBGs directly through the protective polyimide coatings of both 50...

The performance of a semiconductor quantum-electronic device ultimately depends on the quality of the semiconductor materials it is made of and on how well the device is isolated from electrostatic fluctuations caused by unavoidable surface charges and other sources of electric noise. Current technology to fabricate quantum semiconductor devices re...

We demonstrate a self-injection locking (SIL) in an Er-doped random fiber laser by a high quality factor (high-Q) random fiber grating ring (RFGR) resonator, which enables a single-mode narrow-linewidth lasing with ultra-low intensity and frequency noise. The RFGR resonator includes a fiber ring with a random fiber grating to provide random feedbac...

We demonstrate the storage and on-demand retrieval of single-photon-level telecom pulses in a fiber cavity. The cavity is formed by fiber Bragg gratings at either end of a single-mode fiber. Photons are mapped into, and out of, the cavity using quantum frequency conversion driven by intense control pulses. In a first, spliced-fiber, cavity we demon...

Fiber Bragg gratings with a very low insertion loss are inscribed using the phase mask technique and a single infrared (800 nm) femtosecond laser pulse. The morphology of the resultant light-induced structural changes in the Ge-doped silica fiber (SMF-28) is analyzed using scanning electron microscopy. The electron microscopy images reveal that eac...

We propose a non-destructive, all-optical technique to imprint embedded lateral superlattices near semiconductor heterostructures by illuminating the samples with a stable interference pattern generated by a phase diffraction grating. We demonstrate the technique on an ultrahigh mobility GaAs/AlGaAs sample with a Si δ-doping by inducing a persisten...

Frequency fluctuation is a major problem in high-precision metrology as real-time optical frequency measurement is not available with commercial photodetectors; alternatively, frequency-stabilized lasers as a reference are also not accessible in most laboratories. In this study, we propose and demonstrate a polarization-maintaining random fiber gra...

Strong scattering random media can localize light and extend photon lifetime through multiple scattering, which offers opportunities for stabilizing random lasers. Here, we demonstrate a frequency stabilized Brillouin random laser with high coherence enabled by photon localization in random fiber grating array (RFGA). Photon trapping is realized du...

We propose a quantum memory protocol based on trapping photons in a fiber-integrated cavity, comprised of a birefringent fiber with dichroic reflective end facets. Photons are switched into resonance with the fiber cavity by intracavity Bragg-scattering frequency translation, driven by ancillary control pulses. After the storage delay, photons are...

We propose a quantum memory protocol based on trapping photons in a fiber-integrated cavity, comprised of a birefringent fiber with dichroic reflective end facets. Photons are switched into resonance with the fiber cavity by intracavity Bragg-scattering frequency translation, driven by ancillary control pulses. After the storage delay, photons are...

Low-loss 1000°C-stable Bragg gratings are inscribed in Ge-doped silica fiber using the phase-mask technique and a single infrared femtosecond laser pulse. The morphology of the light-induced modification is analyzed using scanning electron microscopy.

This paper reports in-pile testing results of radiation-resistant fiber Bragg grating (FBG) sensors at high temperatures, intense neutron irradiation environments, and machine learning methods for radiation-induced sensor drift mitigation and reactor anomaly identification. The in-pile testing of fiber sensors was carried out in an MIT test reactor...

Fiber Bragg gratings (FBG) are extensively used to perform high-temperature measurements in harsh environments, however the drift of the characteristic Bragg wavelength affects their long-term stability resulting in an erroneous temperature measurement. Herein we report the most precise and accurate measurements of wavelength drifts available up to...

A review of recent progress in the use of infrared femtosecond lasers to fabricate optical fiber sensors that incorporate fiber Bragg gratings (FBG) and random fiber gratings (RFG) is presented. The important advancements in femtosecond laser writing based on the phase mask technique now allow through-the-coating (TTC) fabrication of Bragg gratings...

High-temperature-resistant fiber Bragg gratings (FBGs) are the main competitors to thermocouples as sensors in applications for high temperature environments defined as being in the 600–1200°C temperature range. Due to their small size, capacity to be multiplexed into high density distributed sensor arrays and survivability in extreme ambient tempe...

Dynamic strain sensing over a frequency range from 0.01 to 20 Hz can be used for monitoring earthquakes and volcanoes, charting rock and petroleum formations beneath the earth. However, significant laser frequency drifting (LFD) has limited the detection in this frequency range, especially for distributed frequency detection with phase optical time...

Boron nitride nanotubes (BNNTs) are demonstrated for use in optical fiber sensor applications. A BNNT coated tapered optical fiber sensor has been developed to detect various liquids and gases with enhanced sensitivity and selectivity.

Fiber optic sensor inscribed in radiation-harden fibers can withstand high neutron flux in an operating nuclear reactor. Machine-learning algorithm using temporal convolutional networks was used to mitigate sensor drift and abnormal event prediction.

Pipeline leak detection sensors are created by using fiber Bragg gratings (FBGs) that are inscribed through polyimide coatings of optical fiber with an infrared femtosecond laser and then specially packaged in materials susceptible to hydrocarbons. Depending on the sensor geometry, strain is either applied or released upon exposure to toluene or cr...

A high precision distributed real time measurement for dynamic strain sensing in a chirped pulse phase optical time domain reflectometry (φ-OTDR) system based on random fiber grating array is experimentally demonstrated. The minimum detectable amplitude of dynamic strain is 52 nε with frequency of 1 Hz.

A high-performance distributed sensing system based on a random fiber grating array (RFGA) and multi-frequency database demodulation (MFDD) method for strain induced delay time measurement is demonstrated. It enables a wide measurement range for both static and dynamic strain sensing. The proposed MFDD method can enlarge the strain measurement rang...

Random fiber gratings (RFGs) have shown great potential applications in fiber sensing and random fiber lasers. However, a quantitative relationship between the degree of randomness of the RFG and its spectral response has never been analyzed. In this paper, two RFGs with different degrees of randomness are first characterized experimentally by opti...

Boron nitride nanotubes (BNNTs) are 1-D hollow fibrous nanomaterials. They are thermally stable up to 800 °C in open air and up to 1000 °C in a pure chlorine atmosphere, are electrically insulating, and possess superlative mechanical properties. Since the BNNT assembly is highly porous and easily penetrated by liquids and gases, BNNT thin film coat...

A Bragg grating inscribed into an inorganic optical fiber was tested in proton and neutron fields up to doses of 472 Gy. Observation showed that radiation had no effect on the performance of the Fiber Bragg Grating (FBG) used as a gauge measuring temperature and pressure. The FBG sensor was subsequently employed to measure the temperature and press...

A high-precision distributed time delay measurement in a chirped pulse phase optical time domain reflectometry (CP $\varphi$ φ -OTDR) system based on a random fiber grating array is proposed and demonstrated, in which a temperature-induced refractive index and fiber dimension change associated time delay could be measured for distributed temperatur...

This paper presents a method of reel-to-reel femtosecond laser direct writing that enables the continuous inscription of low-loss and high-temperature stable Rayleigh scattering centers inside the core of single-mode optical fibers for distributed temperature sensing up to 1000°C. By examining the correlation between the Rayleigh backscattering pro...

In this erratum, we correct the mistakes in Eqs. (2) and (2a) in Opt. Lett. 45, 443 (2020).OPLEDP0146-959210.1364/OL.381111

Bragg gratings with ultrastrong cladding modes are inscribed in a standard telecom optical fiber (i.e., SMF-28) using the phase mask technique and an infrared femtosecond laser. 1000°C-resistant fiber Bragg gratings (FBGs) whose cladding modes exceed 30 dB in transmission and spectrally span more than 250 nm can be produced with only a few (i.e., l...

Tilted fiber Bragg gratings are inscribed in non-photosensitized single mode fibers through the polyimide coating using a femtosecond infrared laser and a phase mask. The inscription technique used is based on simultaneously translating the fiber along its axis and the focusing cylindrical lens in the orthogonal direction by means of piezoelectric...

The combined effect of chromatic dispersion and conical diffraction (i.e., off-plane diffraction) in femtosecond laser inscription of fiber Bragg gratings using the phase mask technique is characterized by measuring the light intensity distribution after the phase mask. As the distance from the mask and the observation point grows, chromatic disper...

Thermal and acoustic noises are crucial to the long-term stability of fiber lasers, as it introduces the fluctuation of optical path length on laser cavity, and hence imposing undesirable intensity noise and frequency drift, particularly for a random fiber laser with distributed Rayleigh scattering feedback from a long length fiber. In this Letter,...

A novel technique to achieve real-time and high-precision interrogation of a linearly chirped fiber Bragg (LCFBG) grating sensor array based on dispersive time delay and optical pulse compression is proposed and experimentally demonstrated. In the proposed system, an ultra-short optical pulse is launched into an LCFBG sensor array consisting of N i...

By using the plane-by-plane grating inscription method with a fs-IR laser, random fiber gratings with low laser-induced loss were fabricated in SMF-28 fiber for distributed temperature sensing. Compared to conventional random gratings having broadband backscattering enhancement, the demonstrated random fiber grating has a well-defined narrower band...

Narrowband high-temperature stable fiber Bragg gratings (FBGs) can be made by introducing a π-phase shift in the middle of a Type II periodic grating structure. This creates a passband inside the wavelength rejection band. During the inscription of Type II Bragg gratings broadband, optical loss is induced in the fiber core as a result of interactio...

A real-time random grating sensor array for quasi-distributed sensing based on spectral-shaping and wavelength-to-time (SS-WTT) mapping and time-division multiplexing is proposed and experimentally demonstrated. The sensor array consists of multiple random gratings written in a single-mode fiber (SMF) at different physical locations. When the tempe...

Birefringent π-phase-shifted Bragg gratings for multi-parameter sensing at temperatures ~1000 °C are written inside a standard single mode silica optical fiber (SMF-28) with infrared femtosecond pulses and a special phase mask one half of which is shifted with respect to the other by 5/4 of the mask period. The birefringence is caused by the presen...

High-speed and high-resolution interrogation of a random fiber grating sensor based on spectral shaping and wavelength-to-time (SS-WTT) mapping, and pulse compression for simultaneous measurement of strain and temperature is proposed and demonstrated. In the proposed system, an ultra-short pulse is spectrum shaped by a high-birefringence (Hi-Bi) ra...

Type II π-phase-shifted Bragg gratings stable up to ~1000°C are written inside a standard single mode silica optical fiber (SMF-28) with infrared femtosecond pulses and a special phase mask. Inscription through the protective polyimide fiber coating is also demonstrated. The birefringence of the Bragg gratings and, as a result, the polarization dep...

This review paper presents recent developments on the fabrication of novel thermally stable Type II fiber Bragg grating structures using femtosecond lasers and the phase mask technique. By manipulating the inscription beam and phase mask designs, exotic grating structures, such as ultrashort gratings < 100 μm in length, Fabry-Perot structures or π-...

Multi-wavelength (MW) laser sources with high optical signal-to-noise ratios (OSNR) are of great interest for optical communications with ultrahigh data capacity as well as microwave and terahertz photonics. In this paper, we report the first demonstration of MW Brillouin random fiber laser in the telecom spectral window around 1.5 μm based on a un...

This paper reports the testing results of radiation resistant fiber Bragg grating (FBG) in random air-line (RAL) fibers in comparison with FBGs in other radiation-hardened fibers. FBGs in RAL fibers were fabricated by 80 fs ultrafast laser pulse using a phase mask approach. The fiber Bragg gratings tests were carried out in the core region of a 6 M...

Plane-by-plane fabrication of fiber Bragg gratings in optical fibers using a short-pulse femtosecond IR laser is proposed and demonstrated. By incorporating a cylindrical lens in the fabrication setup, a plane of index modification can be directly inscribed in fiber core by a single laser pulse. The planes of index modification are produced in the...

This chapter presents the state of the art of femtosecond laser-induced fiber Bragg gratings for sensing applications. It summarizes the laser-material processing mechanisms for dielectric modification with femtosecond pulse duration sources, techniques for grating inscription with said sources, and applications of femtosecond laser-induced grating...

A photonic approach to pseudo-random waveform generation based on a random fiber grating is proposed and demonstrated. A pseudo-random waveform with a temporal duration of 10 ns and a time-bandwidth product of 322.4 is demonstrated.

Femtosecond laser written fiber Bragg gratings are useful for extreme sensing, including combustor applications for energy and aerospace. This paper reviews our fabrication and deployment of such sensors, for monitoring temperature gradients within such environments.

During the inscription of Type II Bragg gratings a certain amount of optical loss is induced in the fiber. For Type II phase-shifted gratings, this broadband loss imposes strong restrictions on the grating passband.

An intensity-modulated fiber laser sensor incorporating distributed feedback from a random fiber grating is experimentally investigated for the detection of multiple sub-MHz ultrasonic continuous waves with minimum frequency spacing of 3 Hz.

By using the plane-by-plane grating inscription method with a fs-IR laser, random fiber gratings were fabricated in SMF-28 fiber with different phase shifts between different planes for temperature sensing. With the well-defined bandwidth of the enhanced backscattering, the random grating based distributed temperature sensing system shows high accu...

The femtosecond laser-induced fiber Bragg grating is an effective sensor technology that can be deployed in harsh environments. Depending on the optical fiber chosen and the inscription parameters that are used, devices suitable for high temperature, pressure, ionizing radiation and strain sensor applications are possible. Such devices are appropri...

Fiber Bragg gratings (FBGs) are written using an infrared (IR) femtosecond laser and a phase mask into pure silica microstructured optical fiber having a cladding region comprised of random air-lines (RAL). Scanning electron microscopy measurements of the IR irradiated RAL fiber samples shows the presence of subwavelength nanograting structures ass...

We demonstrate for the first time, to the best of our knowledge, a high-speed physical random bit generator at gigabits/second without the time-delay signature based on chaotic power fluctuations of a random fiber laser. The random fiber laser is configured using a ring structure with semiconductor optical amplifiers as the optical gain and a fiber...

We demonstrate that a semiconductor laser perturbed by distributed feedback with random time delays from a large number of scattering centers along a fiber random grating can emit light chaotically without the time-delay signature (TDS). A theoretical model is developed based on the modified Lang–Kobayashi model to numerically explore the chaotic d...

Very short Type I and Type II Bragg gratings, on the order of 100 µm in length, are written through the protective polyimide coating of high NA and standard single mode silica optical fibers with infrared femtosecond pulses and a phase mask. By exploiting the transverse walk-off of apertured diffracted beams produced by the phase mask and a slit pl...

Type II-IR fiber Bragg gratings (FBGs) were written directly through the protective polyimide coatings of off-the-shelf pure silica core and telecom standard Ge-doped silica core single mode fibers using ultrafast IR radiation and the phase mask FBG writing method. Using a short focal length acylindrical lens and nonlinear photoluminescent imaging,...

Gas turbine engines produce thrust or power by expanding hot gases generated by burning fuel. Therefore, it is very important to measure and monitor temperature accurately in order to control and protect the engine. In particular, for advanced gas turbine engines, accurate temperature measurement in hot sections such as the combustor and turbine be...

Nonlinear photoluminescence imaging is used to visualize the intensity distribution of femtosecond laser pulses inside the optical fiber during Bragg grating inscription based on side illumination through a phase mask. This technique, which results in direct imaging of the inscription laser field inside the optical fiber, facilitates i) the charact...

A novel highly sensitive ultrasound sensor based on a random fiber laser is proposed and demonstrated for the first time, to the best of our knowledge. The random fiber laser is constructed with the erbium-doped fiber gain. A fiber random grating provides random-distributed feedback for the random laser and acts as an ultrasound sensing head. The r...

We demonstrate that a semiconductor laser perturbed by the distributed feedback from a fiber random grating can emit light chaotically without the time delay signature. A theoretical model is developed based on the Lang-Kobayashi model in order to numerically explore the chaotic dynamics of the laser diode subjected to the random distributed feedba...

Periodic planar nanostructures are found in Type II-IR Bragg gratings produced in SMF-28 fiber by side-illuminating it with infrared femtosecond-laser pulses through a phase mask. The planar nanostructures are aligned perpendicular to the laser polarization, as demonstrated using scanning electron microscopy analysis of cleaved fiber samples. Dark...

A semiconductor laser with distributed feedbacks from a novel fiber random grating is perturbed to emit chaotically. The time delay signature of the chaotic output is suppressed with the largest extent to date.

A novel type of fiber Bragg grating is produced by annealing a type I-like grating that is written with multiple infrared femtosecond laser pulses through a phase mask under conditions that are typically used to fabricate thermally stable type II gratings. This new grating is created through a process similar to a regenerative one and displays low...