Acousto-optic Tunable Bandpass Filter Research Articles

Experimental study of an in-fiber acousto-optic tunable bandpass filter for single- and dual-wavelength operation in a thulium-doped fiber laser.

A tunable single- and dual-wavelength thulium-doped all-fiber laser is demonstrated based on the implementation of an in-fiber acousto-optic tunable bandpass filter (AOTBF). The AOTBF is fabricated to be operated in the 1.9 µm region, and takes advantage of the intermodal coupling effect produced by traveling flexural acoustic waves in an optical fiber. It exhibits a 3-dB bandwidth of 2.04 nm with an insertion loss of 4.75 dB. The tuning properties of the AO device allows a continuous-wave operation with characteristics of wide tuning range (211.5 nm), narrow linewidth (50 pm) and high signal-to-noise ratio (60 dB). In the dual-wavelength regime, the laser is capable of independent tuning of each of the laser lines, achieving a tunable dual-wavelength emission that extends from 1802.67 to 1932.75 nm. A controllable wavelength spacing with minimum and maximum separations of 1.04 and 130.08 nm is obtained.

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.

Broadband tuning of a long-cavity all-fiber mode-locked thulium-doped fiber laser using an acousto-optic bandpass filter

A long-cavity passively mode-locked thulium-doped all-fiber laser is reported incorporating a tapered acousto-optic tunable bandpass filter (AOTBF). The operation of the AOTBF relies on the intermodal coupling between core and cladding modes when a flexural acoustic wave propagates along an 80μm tapered fiber. The filter works in transmission and exhibits a 3dB bandwidth of 9.02nm with an insertion loss of 3.4dB. The laser supports ultrashort pulse generation at a low repetition rate of 784.93kHz. Optical pulses with 2.43nm of optical bandwidth and 2.1ps pulse duration were obtained in a broad tuning range from 1824.77 to 1905.16nm.

Acousto-optic tunable bandpass filter based on acoustic-flexural-wave-induced fiber birefringence.

An acousto-optic tunable bandpass filter was proposed and fabricated based on acoustic-flexural-wave-induced single-mode fiber birefringence via coupling the core mode to a single-cladding vector mode. In the experiment, the resonant wavelength and insertion loss could be electrically tuned with a span of nearly 100nm and a lowest insertion loss of -1.7 dB. The structure gains advantages of a large tuning range, fast speed, easy fabrication, low insertion loss, and zero frequency shift.

Actively mode-locked all-fiber laser by 5 MHz transmittance modulation of an acousto-optic tunable bandpass filter

Active mode-locking of an all-fiber ring laser by transmittance modulation of an in-fiber acousto-optic tunable bandpass filter (AOTBF) is reported. Cavity loss modulation is achieved by full acousto-optic mode re-coupling cycle induced by standing flexural acoustic waves. The modulator permits the implementation of 28 dB of nonresonant light suppression, 1.4 nm of modulation bandwidth, 74% of modulation depth and 4.11 dB of optical loss in a 72.5 cm-long all-fiber configuration. The effects of the modulated AOTBF on the laser performance are investigated. Transform-limited optical pulses of 8.8 ps temporal width and 6.0 W peak power were obtained at 4.87 MHz repetition rate.

Q-switching of an all-fiber ring laser based on in-fiber acousto-optic bandpass modulator

Active Q-switching of an all-fiber ring laser utilizing a novel in-fiber acousto-optic tunable bandpass filter (AOTBF) is reported. The transmission characteristics of the AOTBF are controlled by amplitude modulation of the acoustic wave; the device exhibits a 3-dB power insertion loss, 0.91-nm optical bandwidth, and 28-dB nonresonant light suppression. Cavity loss modulation is achieved by full acousto-optic mode re-coupling cycle induced by traveling flexural acoustic waves. When the acoustical signal is switched on, cavity losses are reduced, and then, laser emission is generated. In addition, by varying the acoustic wave frequency, a wide wavelength tuning range of 30.7 nm is achieved from 1542 to 1572.7 nm. The best Q-switched pulses were obtained at 1.1-kHz repetition rate, with a pump power of 242 mW, at the optical wavelength of 1569.4 nm. A maximum pulse energy of 8.3 μJ at an average output power of 9.3 mW was achieved, corresponding to optical pulses of 7.8-W peak power and 1-μs temporal width.

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.

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.

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.

Two-mode fiber acoustooptic tunable bandpass filter with zero frequency-shift

We propose and experimentally demonstrate a novel configuration for an acoustooptic tunable bandpass filter based on intermodal coupling in a two-mode fiber. The double-pass scheme provides zero frequency-shift, bandwidth narrowing, and enhanced extinction ratio. A 3-dB bandwidth of 2.0 nm, insertion loss of 5.6 dB, and sidelobe suppression ratio of 14 dB were achieved. The wavelength tuning range was greater than 90 nm for the transmission dynamic range larger than 20 dB. Multiwavelength operation of a single device is achieved by simply applying multifrequency electrical signal. Unwanted intensity modulation of the multiwavelength filter is also investigated.

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.

Double-pass acoustooptic tunable bandpass filter with zero frequency shift and reduced polarization sensitivity

The authors report a zero frequency shift double-pass acoustooptic tunable bandpass filter employing a single acoustic flexural wave to couple light from the core mode to a cladding mode (propagating past a core block) and back again to the core mode. A double pass through the fiber filter yields reduced sidelobe levels and reduced polarization sensitivity. The prototype also exhibited improved dynamic range and a reduction in bandwidth.

Narrow-band light source with acoustooptic tunable filter for optical low-coherence reflectometry

An electrically-tunable narrow-band light source with no moving parts is constructed for jaggedness-free optical low coherence reflectometry. The source incorporates a double-path acoustooptic tunable bandpass filter module whose two passbands automatically agree to within 0.2 nm during wavelength tuning from 1529-1568 nm. The source emits narrow-band light with an FWHM of 1.8/spl plusmn/0.1 nm, a power of >0 dBm and a suppressed background spectrum. The entire wavelength range can be swept electrically within 100 ms by using a variable RF source.