In-fiber Gratings Research Articles

A Compact and Highly Efficient Compressive Sensing Imaging System Using In-Fiber Grating

Serial time-encoded amplified microscopy can achieve ultrafast imaging speed within varied dynamic regimes. However, it has two challenges: the high-throughput data issue and low-efficiency diffraction issue. Here, we report a compact and highly efficient ultrafast optical imaging system based on compressive sensing and in-fiber grating. Our proposal is confirmed by the proof-of-principle experiment and obtains a minimum data compression ratio of 5% with a continuous ultrafast imaging speed of 10 Mfps at a field of view of 0.5 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${}^{\ast} 1.6$ </tex-math></inline-formula> mm. A barcode with a moving speed of 4m/s is also demonstrated for imaging and an imaging speed of 1.25 Mfps is obtained. The proposed optical imaging system overcomes the big data issue, increases energy efficiency, and paves the way for compact and highly efficient ultrafast optical imaging within dynamic scenarios.

An Undersampling Communication System Based on Compressive Sensing and In-Fiber Grating

An undersampling free-space optical (FSO) communication system based on compressive sensing (CS) and in-fiber grating is proposed. Our proposal drastically mitigates the data scale unfavorable issue and reduces the great amount of required data. Also, our proposal employs low-bandwidth and low-cost photodetectors (PDs) and analog-to-digital converters (ADCs) and decreases the cost of data detection. Besides, the data transmitted in the free space is encrypted, which enhances the security of the system. The in-fiber grating, which has the advantage of highly efficient thanks to its inherent compatibility with optical fiber links, plays the roles of light emitter, in-fiber polarizer, and light diffraction device, simultaneously. A sinusoidal radio frequency (RF) signal with a frequency of 1 GHz is utilized for a 2.4 m data transmission. And each PD with a bandwidth of 300 MHz is employed for detecting the transmitted signal on each channel. The proposal obtains data compression ratios of 25%, 15%, and 5% both in the temporal domain and frequency domain. Besides, a two-tone signal and a random RF signal are applied in the proposed FSO transmission for data transmission. Our proposal not only has the merits of secure, compact, stable, and highly efficient, but also has great potential in extremely secure situations, such as secured indoor and under water data communication.

Self-heating tilted fiber Bragg grating device for melt curve analysis of solid-phase DNA hybridization and thermal cycling

We demonstrate a DNA-based optical fiber device that uses an in-fiber grating, a light absorbing coating with surface anchored DNA, and a built-in optical thermometer. This device is used for precisely thermal cycling surface DNA spots bound by a simple UV cross-linking technique. Near-infrared light of wavelengths near 1550 nm and guided power near 300 mW is coupled out of the fiber core by a tilted fiber Bragg grating inscribed in the fiber and absorbed by the coating to increase its temperature to more than 95 °C. A co-propagating broadband light signal (also in the near-infrared region) is used to measure the reflection spectrum of the grating and thus the temperature from the wavelength shifts of the reflection peaks. The device is capable of sensitive DNA melt analysis and can be used for DNA amplification. Graphical abstract.

In-fiber Long-Period Grating and Fiber Bragg Grating-Based Sensor for Simultaneously Monitoring Remote Temperature and Stress

In-fiber Long-Period Grating and Fiber Bragg Grating-Based Sensor for Simultaneously Monitoring Remote Temperature and Stress

In-Fiber Grating Fabricated by Femtosecond Laser Direct Writing for Strain Sensing

In this letter, we reported long period fiber gratings (LPFGs) fabricated by femtosecond laser pulses direct writing in grapefruit microstructured fiber. The mode field distribution and dispersion property of this fiber was analyzed by finite-element method. Two LPFGs were fabricated with different periods of 230 and 250 μm, the resonant dips appeared at the wavelengths of 1325.8 and 1449.4 nm, respectively. In addition, sensing characteristics of the LPFG with the period of 250 μm were investigated in theory and experiment. The experimental results show that the strain and temperature sensitivities are 1.88 pm/με and 0.267 pm/°C, respectively. It indicates that the temperature cross sensitivity is as low as 0.142 με/°C.

In-Fiber Gratings for Simultaneous Monitoring Temperature and Strain in Ultrahigh Temperature

In this letter, a pair of regenerated gratings with Bragg wavelengths of 1547 and 1304 nm in a single piece of single-mode fiber has been fabricated for simultaneous monitoring of temperature and strain in ultrahigh temperature environment. A $3\times 3$ matrix is used to characterize the cross sensitivity of the proposed sensor in which the strain sensitivity varies with temperature change. The proposed structure exhibits the deviation of 28.3 $\mu \varepsilon $ and 4.1 °C at the ranges of 0–1000 $\mu \varepsilon $ and 25 °C–900 °C, respectively.

Effective Permittivity of Ultrathin Chemical Vapor Deposited Gold Films on Optical Fibers at Infrared Wavelengths

The geometry- and size-dependent effective medium properties of ultrathin gold films deposited on the bare cladding of single mode optical fibers by chemical vapor deposition are characterized by measuring the polarized transmission spectra of in-fiber gratings at wavelengths near 1550 nm. The real part of the complex refractive indices of films with average thicknesses ranging from 6 to 65 nm are about 10 times higher than that of bulk gold at these wavelengths, while the imaginary part values are 2 orders of magnitude lower. The films are essentially isotropic, apart from a small increasing dichroism between the in-plane and out-of-plane component of the imaginary part of the refractive index at thicknesses larger than 25 nm. Unlike gold films prepared by other means, the optical properties of the coatings do not converge rapidly toward bulk values at thicknesses larger than 10 nm but remain characteristic of gold films prepared by very slow physical deposition processes. The modified Clausius–Mossotti ...

Anomalous dispersion in a solid, silica-based fiber

We demonstrate an all-solid (nonholey), silica-based fiber with anomalous dispersion at wavelengths where silica material dispersion is negative. This is achieved by exploiting the enhanced dispersion engineering capabilities of higher-order modes in a fiber, yielding + 60 ps/nm km dispersion at 1080 nm. By coupling to the desired higher-order mode with low-loss in-fiber gratings, we realize a 5 m long fiber module with a 300 fs/nm dispersion that yields a 1 dB bandwidth of 51 nm with an insertion loss of approximately 0.1 dB at the center wavelength of 1080 nm. We demonstrate its functionality as a critical enabler for an all-fiber, Yb-based, mode-locked femtosecond ring laser.

Dynamic tuning of optical waveguides with electrowetting pumps and recirculating fluid channels

We have developed an approach for using electrowetting actuation in recirculating fluidic channels to achieve dynamic tuning of optical fiber structures. The electrically controlled and fully reversible motion of the fluids and lubricants in these channels alters the refractive index profile experienced by the optical waveguide modes of the fiber. When combined with in-fiber gratings and etched fibers, this fluidic system yields dynamically adjustable narrow and broadband fiber filters, respectively. The nonmechanical operation of these systems, their ability to support switching speeds on the order of milliseconds, and their excellent optical characteristics indicate a promising potential for electrowetting-actuated fluidic tuning in optical fiber devices and other photonic components.

Analysis of heat flow in optical fiber devices that use microfabricated thin film heaters

This paper describes finite element analysis of heat flow in a new class of tunable optical fiber devices that uses thin film resistive heaters microfabricated on the surface of the fiber. The high rate of heat loss from these cylindrical microstructures and the relatively low thermal diffusivity of the glass yield thermal properties (e.g. short axial thermal diffusion lengths, small radial temperature gradients and good power efficiency) that can be exploited for tuning the optical properties of in-fiber gratings. The modeling captures important thermal characteristics of these devices and anticipates their suitability for dynamic dispersion compensation and other applications in high bit rate lightwave communication systems.

Demonstration of incoherent wavelength-encoding/time-spreading optical CDMA using chirped moire gratings

We demonstrate a wavelength-encoding/time-spreading optical code-division multiple-access system that uses in-fiber chirped moire gratings for encoding/decoding. We present results for a system comprising four users, one desired and three interfering, and operating at the OC-12 transmission speed (622.08 Mbit/s). Our measurements verify the principle of encoding/decoding and the rejection of multiuser interference.

In-fiber grating sensors

The period of in-fiber grating can be changed due to the change of pressure or temperature that the in-fiber grating bears. The reflecting wavelength of in-fiber grating will shift as its period changes. This characteristic trait of in-fiber grating can render it to be used as a sensor element to detect pressure or temperature. The key issue is how to interrogate the reflecting wavelength shift accurately. The techniques of in-fiber grating sensors are reviewed with an emphasis on interrogation approaches to reflecting wavelength shift induced by measurement quantities. Some suggestions are also made in this paper.

Using microcontact printing to generate amplitude photomasks on the surfaces of optical fibers: A method for producing in-fiber gratings

This letter describes a method for producing in-fiber gratings that reduces the effects of mechanical and optical instabilities limiting other methods. In this technique, opaque lines formed on the outside of the fiber using a procedure known as microcontact printing, serve as an amplitude photomask for exposure to ultraviolet light. Long-period fiber optic attenuators formed by ths technique demonstrate its advantages.

Inline quantum-well waveguide photodetectors for the measurement of wavelength shifts

A two-segment GaAs-InGaP-InGaAs p-i-n quantum-well waveguide photodiode has been fabricated and demonstrated to function as a sensitive wavelength monitor. The ratio of the two segments' photocurrents varies linearly with wavelength in a region near the absorption band edge. A wavelength sensitivity on the order of 1 pm was measured for input optical power levels above 30 /spl mu/W and signal averaging times of 0.2 s. An operating range from 980 to 1020 nm was achieved using electroabsorption tuning of the band edge. The intended application for this detector is wavelength demodulation of Bragg grating fiber optic strain sensors. A strain sensor with resolution of /spl plusmn/6 /spl mu//spl epsiv/ was demonstrated using a superluminescent diode and the inline detectors to monitor strain-induced changes in the reflection wavelength of an in-fiber grating.

Simultaneous strain and temperature sensing with photogenerated in-fiber gratings

A new technique for simultaneous strain and temperature sensing is demonstrated. The approach employs two different types of photogenerated fiber grating, namely, a fiber Bragg grating and a fiber polarization-rocking filter. The method relies on the different dependencies of the fiber refractive index and birefringence on strain and temperature. Both of these measurands can be determined from the effect that they have on the resonant wavelength of each grating. The information is provided in the frequency domain, avoiding the problem of limited unambiguous signal range associated with the use of competing optical fiber interferometers.

Elasto-optically induced modulation of in-fiber grating

Strong effects due to uniaxial stress applied to an in-fiber grating reflection peak splits because of the elastooptically induced birefringence. The separation between the two peaks increases with the stress, and they broaden and shift. By modulating the pressure using a PZT disk at frequencies up to 1 MHz, modulation of the reflectivity, which varies with the wavelength within the grating reflection band, was obtained. >