Tunable Optical Bandpass Filter Research Articles

Switchable microwave photonic filter between high Q bandpass filter and notch filter with flat passband based on phase modulation

We propose and demonstrate a novel switchable microwave photonic filter based on phase modulation. Both a microwave high Q bandpass filter and a microwave notch filter with flat passband are achieved respectively. And the switchability between them by tuning the two tunable optical bandpass filters is demonstrated. We also present a theoretical model and analytical expression for the proposed scheme. A frequency response of a high Q bandpass filter with a Q factor of 327 and a rejection ratio of exceeding 42 dB, and a frequency response of a notch filter with flat passband with a rejection ratio exceeding 34 dB are experimentally obtained. The operation frequency of microwave photonic filter is around 20 GHz.

Wavelength swept amplified spontaneous emission source for high speed retinal optical coherence tomography at 1060 nm

The wavelength swept amplified spontaneous emission (ASE) source presented in this paper is an alternative approach to realize a light source for high speed swept source optical coherence tomography (OCT). ASE alternately passes a cascade of different optical gain elements and tunable optical bandpass filters. In this work we show for the first time a wavelength swept ASE source in the 1060 nm wavelength range, enabling high speed retinal OCT imaging. We demonstrate ultra-rapid retinal OCT at a line rate of 170 kHz, a record sweep rate at 1060 nm of 340 kHz with 70 nm full sweep width, enabling an axial resolution of 11 μm. Two different implementations of the source are characterized and compared to each other. The last gain element is either a semiconductor optical amplifier or an Ytterbium-doped fibre amplifier enabling high average output power of >40 mW. Various biophotonic imaging examples provide a wide range of quality benchmarks achievable with such sources.

Bidirectional hybrid CATV/radio-over-fiber WDM transport system

A bidirectional hybrid cable antenna television (CATV)/radio-over-fiber (ROF) wavelength-division-multiplexing (WDM) transport system using injection locking technique to suppress the rf power degradation, tunable optical bandpass filter to generate optical single-sideband format for the CATV signal or only one optical sideband format for the ROF one, and photonic crystal fiber to reduce the net dispersion is proposed and demonstrated. Impressive performances of the carrier-to-noise ratio, the composite second-order, the composite triple beat, and the bit error rate were obtained in our proposed systems.

Patterning characteristics and its alleviation in high bit-rate amplification of bulk semiconductor optical amplifier

An investigation is carried out on high bit-rate pulse propagation through bulk semiconductor optical amplifier (SOA) and a tunable optical bandpass filter (OBPF) placed at the output of the SOA for the alleviation of patterning of the amplified signal due to gain saturation in SOA. The effect of the OBPF in terms of its central wavelength detuning and bandwidth on the quality of peak power equalization of the output signal is investigated for signal pulsewidth smaller and larger than the critical pulsewidth of the amplifier at bit-rates of 20 and 40 Gb/s, respectively. It is observed that the scheme is highly useful for the signal pulses with width greater than the critical width.

Magneto-optical effect of DPS-DNG layered structure

The influence of an applied static magnetic field on a periodic structure composed of alternating layers of double positive index of refraction (DPS) uniaxial and double negative index of refraction (DNG) has been studied. We present theoretical and numerical results of our investigation of the reflection spectra of the visible waves on this structure. This structure works as a bandpass filter, and our evaluation indicates this structure functions as a tunable optical bandpass filter. The bandgap effect varies with the periodic parameters of the DPS-DNG structure, applied magnetic field, incidence angle, and frequency.

Wavelength swept amplified spontaneous emission source

We present a new, alternative approach to realize a wavelength swept light source with no fundamental limit to sweep speed. Amplified spontaneous emission (ASE) light alternately passes a cascade of optical gain elements and tunable optical bandpass filters. We show that for high sweep speeds, the control signal for the different filters has to be applied with a defined, precise phase delay on the order of nanoseconds, to compensate for the light propagation time between the filters and ensure optimum operation. At a center wavelength of 1300 nm sweep rates of 10 kHz, 100 kHz and 340 kHz over a sweep range of 100 nm full width and an average power of 50 mW are demonstrated. For application in optical coherence tomography (OCT), an axial resolution of 12 microm (air), a sensitivity of 120 dB (50 mW) and a dynamic range of 50 dB are achieved and OCT imaging is demonstrated. Performance parameters like coherence properties and relative intensity noise (RIN) are quantified, discussed and compared to the performance of Fourier Domain Mode Locked (FDML) lasers. Physical models for the observed difference in performance are provided.

Widely tunable ring-cavity tellurite fiber Raman laser

We report a widely tunable ring-cavity tellurite fiber Raman laser covering the S+C+L+U band. A tunable range (1495-1600 nm, limited by the tunable optical bandpass filter) over 100 nm is obtained by using a single-mode tellurite fiber with high Raman gain coefficients (55 W(-1)km(-1)) and large Raman shift (approximately 22.3 THz) as the gain medium. Furthermore, the free-running 1665 nm Raman fiber laser is achieved from the ring cavity by removing the tunable optical bandpass filter, which shows that such a tellurite fiber has potential for constructing a widely tunable fiber Raman laser covering the S+C+L+U band. A high optical signal-to-noise ratio of over 60 dB for almost all of the tunable range is also demonstrated.

Tunable and programmable optical bandpass filter

We demonstrate a novel tunable and programmable optical bandpass filter with a transmission peak less than 5 pm wide that is tunable over 18.5 nm. The number of transmission windows within the stop band, as well as each window's position and strength, is set by applying a heat profile to a chirped fibre Bragg grating with the aid of a thermal printer head comprising a 640 pixel array. It is shown that the width of a transmission peak formed by local heating is mainly determined by the refractive index modulation depth and chirp rate and not by the width of the heated region.

A 1-D Photonic Band Gap Tunable Optical Filter in (110) Silicon

In this paper, we describe an electrostatically tunable optical bandpass filter that is fabricated in (110) silicon. Deep reactive-ion etching is the main process that is used to fabricate the overall device structure. To create the highly parallel surfaces that are needed for the photonic band gap elements, electrochemical (KOH) etching of the vertical (111) planes is then used. Back etching is used to release the moving parts. Fiber pigtails are attached in etched alignment grooves, and fiber-fiber insertion loss below 11 dB was obtained. The measured passband width was 3 nm with a tuning range of 8 nm.

Tunable Optical Bandpass Filter With Variable-Aperture MEMS Reflector

We report on a tunable optical bandpass filter with precise and independent control of its optical bandwidth and center wavelength. The optical filter is based on a double-pass monochromator configuration and a variable-aperture microelectromechanical systems (MEMS) reflector with two blocking micromirrors that manipulate the optical passband. The MEMS reflector is fabricated on the sidewalls of (110) silicon-on-insulator material by a combination of wet etching and deep reactive ion etching. The 1-dB optical bandwidth is continuously tunable from 3.65 to 6.35 nm by changing the position of the blocking micromirrors with lateral combdrive actuators. The center wavelength can be accurately controlled within a 30-nm spectral range by rotating the diffraction grating and/or changing the center location of the variable aperture with the combdrive actuators. The measured group delay variation across the passband was negligible

Widely tunable optical bandpass filter by use of polymer long-period waveguide gratings

We report the design and fabrication of a widely tunable optical bandpass filter based on using two identical long-period gratings formed along a polymer channel waveguide with a section of the waveguide core removed. The peak transmission of the passband of the fabricated filter is approximately 60% and the bandwidth of the passband is approximately 6 nm. The filter is thermally tunable over the C + L band (1520-1610 nm) for both TE and TM polarizations with a temperature control of approximately 30 degrees C.

Broad-band tunable wavelength conversion using Raman-assisted parametric four-wave mixing in highly nonlinear fibers with double-pass geometry

Efficient wavelength conversion using distributed Raman gain and the Raman-assisted parametric four-wave mixing in 1 km of highly nonlinear fibers (HNLFs) is demonstrated in this letter. We present the theoretical analysis of the Raman-assisted parametric process and investigate the mechanism of wavelength conversion between parametric Stokes and anti-Stokes light. The system is implemented in a double-pass Raman amplifier where a tunable optical bandpass filter and a wide-band reflector are used to form a laser oscillation in the normal dispersion region of HNLF. The lasing light acts as the parametric pump to enable the wide-band wavelength conversion about the pump wavelength. Conversion efficiency greater than 0 dB over 50 nm is obtained and the converted idler wavelength can be adjusted more than 10 nm continuously by tuning the tunable optical filter. Hence, an arbitrary new wavelength can be converted within the tunable range of optical filter with high efficiency.

Tunable and switchable optical bandpass filters using a single linearly chirped fiber Bragg grating

We propose a new method for the development of tunable optical bandpass filters (TOBFs) by thermal tuning of a single linearly chirped fiber Bragg grating (LCFBG). Two resistance wires are placed across the grating section as thermal heads to introduce local temperature changes into the LCFBG. A passband peak is thus generated within the stopband of the LCFBG due to the local Bragg wavelength shift and thermally induced temporary phase shifts. The passband peak can be tuned by scanning the resistance wires along the LCFBG. The developed TOBF has a bandwidth of ∼0.2 nm, an out-of-band rejection range of ∼20 nm, a continuously tuning range of ∼15 nm, a minimum insertion loss of ∼4 dB, and a maximum rejection ratio of ∼25 dB.

Thermally tunable narrow-bandpass filter based on a linearly chirped fiber Bragg grating.

We propose a new method for the development of a tunable optical bandpass filter (TOBF) based on a linearly chirped fiber Bragg grating (LCFBG). A NiCr wire heater is used to heat the LCFBG at a small point to introduce a narrow passband within the stop band of the LCFBG. The central wavelength of the passband is tuned by scanning the wire heater along the LCFBG. As an example demonstrating the effectiveness of the proposed method, we demonstrate a TOBF with a very small 3-dB bandwidth of approximately 7 pm, a tuning range of 16.4 nm, and a rejection ratio of more than 25 dB. Compared with previously reported tunable-fiber-based bandpass filters, this method provides the advantages of a large tuning range, continuous tunability, a switchable passband, a simple tuning mechanism, low cost, and narrow bandwidth.

Tunable Optical Band-Pass Filter for Video-Routing Networks Using Dense Wavelength Division Multiplexing

A tunable optical band-pass filter with a narrow bandwidth and a fast tuning speed is essential for large-scale video-routing networks using dense wavelength division multiplexing. We have developed a Ti-diffused lithium niobate optical waveguide-type filter that attains both a narrow bandwidth and fast tuning. It uses two cascaded Fabry-Perot filters to extend the wavelength tuning range. This filter will enable the development of large-scale video-routing networks for distributing uncompressed high-definition television signals.

Dual-wavelength 10-GHz actively mode-locked erbium fiber laser

We present the first 10 GHz dual-wavelength actively mode-locked erbium fiber laser (ML-EFL). Dual-wavelength operation is achieved by introducing two intracavity branches, each containing a tunable optical bandpass filter. A variable output coupler combining the filter branches also equalizes the effective cavity gain for the two wavelengths, By adjusting the filters and the coupler, dual-wavelength ML-EFL operation is achieved at different wavelengths. Nearly transform-limited, 4- and 6.2-ps-wide 10-GHz soliton pulses are e.g., simultaneously generated at 1542.3 and 1563.8 nm, respectively. The experimental results agree very well with analytical calculations.

Transmission characteristics of multilayer films composed of electro-optic and dielectric materials

We describe the theoretical evaluation for the transmission characteristics of multilayer films composed of periodic electro-optic and dielectric materials in a variable electric field. The films are assumed to have cavity-type layer stacking structures, which work as a narrow bandpass filter, and their electro-optic material is uni-axial BaTiO 3, whose electro-optic coefficient r 51 is larger than 1300 pm/V. The evaluation indicates that films composed of BaTiO 3 and SiO 2 or MgO function as tunable optical bandpass filters, with a tunable range larger than 6 nm for an electric field of less than 4 V/μm.

Repeated Bidirectional Transmission Using Two 4-Port Optical Circulators and a Bidirectional EDFA without Isolators

By using a newly designed bidirectional erbium-doped fiber amplifier, we demonstrated a 2×2.5 Gb/s repeated bidirectional transmission over a 100-km single-mode fiber. Two tunable optical bandpass filters were used to suppress the Rayleigh backscattering and amplified spontaneous emission in the bidirectional transmission system. The bit error rate performances were measured for both directions. A negligible power penalty of 0.2 dB for the 2×2.5 Gb/s transmission due to backreflections was observed when comparing the bidirectional transmission with single-channel, unidirectional transmission.

Experimental demonstration of an ultraselectiveand tunable optical bandpass filter using a fibre grating and a Fabry-Perot

The authors report on the use of a structure composed of a fibre Fabry-Perot and a fibre grating as an ultraselective and tunable optical bandpass filter. The first experimental demonstration of the filter operation is presented and a range of tuning of several hundreds of gigahertz can be achieved by using the presented techniques.

Three wave mixing using a fiber ring resonator

Three wave mixing using a fiber ring resonator scheme is discussed, and experimental results are presented. In this scheme, an optical nonlinear medium is placed into the fiber ring laser cavity, and a semiconductor optical amplifier and a tunable optical band pass filter (TOBPF) are used as the gain medium and lasing wavelength selector. The phase-matching condition, which is necessary for efficient wave mixing, can easily be satisfied by tuning the TOBPF. Second-harmonic generation (SHG) and sum-frequency generation (SFG) were demonstrated using a LiNbO3 waveguide with a periodically domain inverted structure. Enhancements of SHG and SFG were achieved.