All-fiber Acousto-optic Tunable Filter Research Articles

Narrowband all-fiber acousto-optic tunable add-drop filter based on dispersion-compensating fiber

Narrowband all-fiber acousto-optic tunable add-drop filter based on dispersion-compensating fiber

Tuning stability enhancement of all-fiber acousto-optic tunable filter based on multi-piezoelectric transducer

All-fiber acousto-optic tunable filters (AOTFs) have advantages of wide wavelength tuning range, fast tuning speed and low insertion loss. The resonance wavelength of the all-fiber AOTF can be tuned by adjusting the driving frequency of the piezoelectric transducer (PZT). In general, the driving voltage needs to be tuned in wide range in the wavelength tuning process, due to the existence of resonance frequency of the PZT. In this work, we propose and demonstrate a stability-enhanced all-fiber AOTF based on multi-PZT, which can reduce the dependence on the resonant frequency of a single PZT. In the experiment, the acousto-optic coupling efficiency can maintain larger than 80%, when the resonance wavelength of the AOTF is tuned from 1400 nm to 1600 nm, under the condition of a fixed driving voltage. The high tuning stability of the proposed multi-piezoelectric driving configuration can facilitate the practical applications of the all-fiber AOTF, such as the laser wavelength tuning, wavelength-division-multiplexing optical communication, fast optical spectroscopy, and so on.

Dual-wavelength narrowband all-fiber acousto-optic tunable bandpass filter based on dispersion-compensating fiber

A dual-wavelength narrowband all-fiber acousto-optic tunable bandpass filter was proposed and fabricated based on vector mode coupling induced by the acoustic flexural wave in dispersion-compensating fiber with a ring core. In the experiment, the resonant dual wavelengths could be electrically tuned with a range of 1526 nm to 1565 nm and the 3 dB bandwidth was less than 1 nm, which coincides with the calculation results. The structure shows the advantages of fast tuning speed, easy fabrication, and zero frequency shift, which can be applied in fast-tunable dual-wavelength lasers, WDM networks, and microwave and terahertz-wave generation.

Improved All-Fiber Acousto-Optic Tunable Bandpass Filter

An all-fiber acousto-optic tunable bandpass filter based on a 1.185-mm long coreless core mode blocker is reported. Experimental results demonstrate a minimal insertion loss of 1.2 dB at the optical resonant wavelength of 1527.7 nm with 3-dB optical bandwidth of 0.83 nm. The optimization of the device takes into account the attenuation of the acoustic wave and leads to an asymmetric configuration in which the coupling section is shorter than the recoupling part. Under the effect of a standing flexural wave the device can be operated as a bandpass modulator. The device exhibits a maximum modulation depth of 28%, 4 dB of insertion loss and 0.97 nm of optical bandwidth at 4.774 MHz.

All-Fiber Acousto-Optic Tunable Bandpass Filter Based on a Lateral Offset Fiber Splicing Structure

An all-fiber acousto-optic tunable bandpass filter has been proposed and experimentally demonstrated by fabricating a lateral offset fiber splicing structure between the lead-in single-mode fiber and acoustic fiber grating. In the presence of acoustic fiber grating that enables the coupling between the antisymmetric cladding modes and symmetric fundamental core mode, the proposed bandpass filter shows a broadband tunable wavelength range up to 152.9 nm with a wavelength tuning sensitivity of -206.07 nm/MHz through adjusting the acoustic frequency. Further experimental results indicate that by using HF acid to etch part of the fiber cladding, the largest tunable bandpass wavelength range could be expanded to 210.2 nm with an improved wavelength tuning sensitivity of -256.89 nm/MHz. Moreover, by adjusting the applied RF signal voltage, a dynamic peak transmission range in a magnitude of ~10 dB have been experimentally achieved.

Highly Sensitive Axial Strain Fiber Laser Sensor Based on All-Fiber Acousto-Optic Tunable Filter

In this letter, we propose and demonstrate a highly sensitive axial strain fiber laser sensor based on all-fiber acousto-optic tunable filter (AOTF). In the laser sensing system, all-fiber AOTF acts as a band-rejection filter of the fiber laser sensor and the sensing head used for axial strain measurement. When the axial strain is loaded, the optical resonant wavelength of all-fiber AOTF moves to the long wavelength region, resulting in the increasing of the central wavelength of the fiber laser sensor. The proposed fiber laser sensor takes the advantages of high-optical signal-to-noise ratio and narrow bandwidth. Moreover, the fabrication of all-fiber AOTF is also very simple. Experimental results show that a good linearity is obtained between the axial strain and central wavelength of the proposed fiber laser sensor, and a high sensitivity of ~0.148 nm/με with the range of 0-160 με can be successfully achieved.

Effect of metal coating in all-fiber acousto-optic tunable filter using torsional wave.

Torsional mode acousto-optic tunable filter (AOTF) is demonstrated using a metal-coated birefringent optical fiber for an improved robustness. The changes in acoustic and optical properties of a metal-coated birefringent optical fiber induced by the thin metal coating were analyzed experimentally and theoretically. The filter wavelength shift is successfully explained as a result of combined effect of acoustic wavelength change and optical birefringence change. We also demonstrated a small form-factor configuration by coiling the fiber with 6 cm diameter without performance degradation. The center wavelength of the filter can be tuned >35 nm by changing the applied frequency, and the coupling efficiency is higher than 92% with <5 nm 3-dB bandwidth.

All-fiber acousto-optic tunable notch filter with a fiber winding driven by a cuneal acoustic transducer

We report a type of all-fiber acousto-optic tunable notch filter consisting of a cuneal acoustic transducer and a fiber winding of four unjacketed single-mode fibers. With -32 dB peak rejection efficiency and 178 nm tunable range of the central wavelength, all of the tunable characteristics of the all-fiber acousto-optic tunable filter are kept. In addition, the structure is versatile and convenient for use in building other complicated filters. As an example, a coarse comblike filter has been built by adjusting the axial strains of the unjacketed fibers.

Sidelobe suppression in all-fiber acousto-optic tunable filter using torsional acoustic wave

We propose two techniques to suppress intrinsic sidelobe spectra in all-fiber acousto-optic tunable filter using torsional acoustic wave. The techniques are based on either double-pass filter configuration or axial tailoring of mode coupling strength along an acousto-optic interaction region in a highly birefringent optical fiber. The sidelobe peak in the filter spectrum is experimentally suppressed from -8.3 dB to -16.4 dB by employing double-pass configuration. Axial modulation of acousto-optic coupling strength is proposed using axial variation of the fiber diameter, and the simulation results show that the maximum side peak of -9.3 dB can be reduced to -22.2dB. We also discuss the possibility of further spectral shaping of the filter based on the axial tailoring of acousto-optic coupling strength.

Fabrication of a highly efficient core-mode blocker using a femtosecond laser ablation technique

We present a method for the fabrication of a highly efficient core-mode blocker based on a laser micromachining technique. The process for the fabrication is as follows. A micron-sized crater is made by irradiation of an ultra-short pulse laser on the end face of a single-mode fiber, and then a defect that acts as a core-mode blocker is formed by splicing the cratered fiber with a normal fiber. The attenuation of the core mode was adjustable up to 25 dB according to the initial crater size and the splicing condition. An all-fiber acousto-optic tunable bandpass filter built with the core-mode blocker is also demonstrated, which exhibits a low insertion loss of 1.8 dB with non-resonance light suppression greater than 23 dB.

Polarization-coupling all-fiber acousto-optic tunable filter insensitive to fiber bend and physical contact

We show that an all-fiber acousto-optic tunable filter based on polarization mode coupling using torsional acoustic wave is immune to the fiber bend and physical contact in the acousto-optic interaction region. We also propose and demonstrate a novel strain-free and size-reduced tunable filter with a 4-m-long fiber acousto-optic interaction region looped into a 5- cm-diameter coil.

Combined effects of optical and acoustic birefringence on acousto-optic mode coupling in photonic crystal fiber

We investigate in detail the origin of multiple resonance peaks experimentally observed in an all-fiber acousto-optic tunable filter built with a photonic crystal fiber having slightly deformed air-hole structure and non-circular outer cladding. A model for the acousto-optic mode coupling in the PCF is formulated taking into account both the acoustic and the optical birefringence. All experimental results are in good agreement with numerical calculations.

1000 nm tunable acousto-optic filter based on photonic crystal fiber

We report an all-fiber acousto-optic tunable filter based on a two-mode photonic crystal fiber. The properties of photonic crystal fiber allow us to demonstrate a notch filter tunable from below 700to1700nm with a single acoustic transducer. The extreme dynamic range coupled with small insertion loss and fast response time (∼100μs) makes this device promising for ultrawideband optical systems.

Narrowband, polarization insensitive all-fiber acousto-optic tunable bandpass filter

We demonstrate an all-fiber acousto-optic tunable bandpass filter exhibiting narrow optical bandwidth and negligible polarization dependence by employing a novel ultraviolet (UV)-induced core-mode blocker written in a high numerical aperture (NA) fiber. It was demonstrated that the device had the measured 3-dB optical bandwidth of 0.65 nm, the polarization-dependent center-wavelength splitting of 0.05 nm and the extinction ratio of -22dB at the wavelength around 1550 nm. The details of the transmission characteristics and the loss mechanism of the core-mode blocking element inscribed in the high NA fiber are discussed.

Design of tunable composite spectrums using all-fiber acoustooptical filters subject to strain control

This paper addresses the tunability issue of the all-fiber acoustooptic tunable filter (AF-AOTF) when it is used to design optical filters that are capable of producing tunable complex spectrums. A strain control scheme implemented on a loop-structure AF-AOTF is proposed for the filter design. In this paper, the mathematical model of the proposed scheme is first derived. Based on this model, the tunability of the composite spectrum obtained via the proposed scheme is analyzed and compared with existing AF-AOTF schemes. It is shown in theory that, when compared to existing schemes, the strain control scheme implemented on a loop-structure AF-ATOF has a better capability of maintaining a composite spectrum while the spectrum is being tuned. The theoretical analysis is verified by simulations and experiments.

Characterization of wavelength-tunable single-frequency fiber laser employing acoustooptic tunable filter

This paper demonstrates and characterizes a novel wavelength-tunable single-frequency erbium-doped fiber ring laser incorporating an all-fiber acoustooptic tunable bandpass filter and a self-constructed saturable absorption grating (SAG). Stable single-longitudinal-mode operation was achieved over the wavelength range of 48 nm with a sidemode suppression ratio higher than 50 dB. The wavelength tuning characteristics, and the laser dynamics in wavelength switching and sweeping are analyzed in detail. A theoretical analysis on the effect of the SAG is also described.

Performance characteristics of a WDM channel monitor based on an all-fiber AOTF with an on-fiber photodetector

We demonstrated an all-fiber wavelength-division-multiplexing channel monitor based on a narrow-band acoustooptic tunable filter (AOTF) with a built-in on-fiber photodetector. By employing a frequency-shift keying (FSK) modulation scheme, intrinsic wavelength accuracy of 0.02 nm is obtained for single-channel detection and 0.05 nm for multiple-channel detection. The minimum resolvable channel spacing is 1.0 nm. The measured channel power accuracy is <1 dB. The demonstrated channel monitor showed a polarization-dependent wavelength shift of /spl sim/0.15 nm, which is limited by the polarization mode splitting of the AOTF itself. The influence of FSK frequency spacing and the effect of channel crosstalk are also discussed.

All-fiber acousto-optic tunable notch filter with electronically controllable spectral profile

We demonstrate a novel all-fiber acousto-optic tunable notch filter based on coupling to cladding modes in a single-mode fiber. The device has the advantage of low loss (<0.1 dB) and low polarization dependence. By coupling input light to multiple cladding modes by use of multiple acoustic waves, we achieved an electronically controllable variable spectral profile without a significant coherent cross-talk problem.

Low-loss all-fiber acousto-optic tunable filter

We report significant advances in the development of simple all-fiber, tunable acousto-optic spectral filters based on null couplers. The performance agrees well with theoretical predictions and is attributed to improved control of the coupler uniformity. Furthermore, using a double-pass arrangement, we demonstrate filter bandwidth reduction and improved sidelobe suppression of -20 dB . The double-pass configuration is also shown to double the frequency shifts that are obtainable from such devices.

An electronically wavelength-tunable mode-locked fiber laser using an all-fiber acoustooptic tunable filter

We have demonstrated a novel scheme of a continuously wavelength-tunable and passively mode-locked fiber laser by using the sliding frequency effect of an all-fiber acoustooptic tunable filter. Stable and nearly transform-limited pulses of 800-fs pulsewidth were produced with this laser scheme for a wavelength tuning range of 17 nm at around 1550 nm.