Variable Optical Attenuator Research Articles

Frequency switched narrow linewidth microwave signal photonic generation based on a double-Brillouin-frequency spaced fiber laser.

A simple photonic approach to generate microwave frequency switched microwave signal is proposed and experimentally demonstrated. In this scheme, a Brillouin fiber laser with double-Brillouin-frequency spacing is used. The Brillouin ring configuration suppresses incoming Brillouin pump and even-order Stokes signals in the cavity. In addition, it also allows propagation of the odd-order Brillouin Stokes signals from configuration to output coupler. A dual-wavelength optical signal is heterodyned at the high-speed photodetector to produce a microwave signal. Frequency switched microwave signals, at 10.75 and 21.39GHz, respectively, can be obtained through adjusting the polarization controller (PC) and loss of the variable optical attenuator (VOA).

A dual-wavelength erbium-doped fiber laser with widely tunable wavelength spacing

A stable dual-wavelength erbium-doped fiber laser (EDFL) with tunable wavelength spacing and equalized output power is proposed and experimentally demonstrated. The fiber laser uses two fiber Fabry-Perot tunable filters (FFPTFs) as the wavelength filter. The main cavity is divided into two sub-cavities with imbalance cavity losses through a 30/70 optical coupler. The tunable wavelength spacing can be achieved by changing the center wavelength of the filters and the equalized dual-wavelength output power can be achieved by properly controlling the variable optical attenuator (VOA) inserted in the lower-loss cavity.

액정을 이용한 반사형 가변 광 감쇠기

본 논문은 광스위치등에 사용되는 가변 광감쇠기를 위해 반사형 액정셀을 채용한 광감쇠기 구조를 제안하고 특성을 검토한다. 본 제안의 가변 광감쇠기는 반사형구조로 소형화가 가능하고 저전압구동이 가능하다. 광통신용 파장에 적합한 액정셀의 설계방법, 주변온도에 따른 동작특성, 광감쇠기의 응답특성 등을 검토하여 본 제안 구조의 유용성을 검증한다. This work studies a variable optical attenuator using a reflective type liquid crystal cell for optical switches. The proposed architecture is capable of comprising a compact and low voltage driving variable optical attenuator. The usefulness of the proposed architecture is demonstrated by showing characterization of the liquid crystal cell, temperature effects, and response characteristics of the architecture.

PDMS-based, magnetically actuated variable optical attenuators obtained by soft lithography and inkjet printing technologies

This paper reports and compares the implementation of magnetic variable optical attenuators (M-VOA) by two fabrication strategies. In the first case, a two-layer structure containing a non-doped polydimethylsiloxane (PDMS) layer on a magnetic PDMS (M-PDMS) layer is fabricated by soft lithography (SLT). M-PDMS is obtained by doping PDMS with different ferrofluid (FF) volumes. The second technology consists of selectively dispense FF microdroplets using the inkjet printing technique (IJP) on a non-doped, non-cured PDMS structure, previously defined by SLT. In this second case, FF volumes are encapsulated inside the polymer matrix. The optical and mechanical properties of structures fabricated using both strategies and containing similar ferrofluid amounts are compared.

Analysis of a Silicon Reconfigurable Feed-Forward Optical Delay Line

We analyze a silicon reconfigurable feed-forward optical delay line (ODL) composed of cascaded Mach-Zehnder interferometer (MZI) switches and waveguide delay pairs. Optical delay is step-tuned by switching among optical routes with an incremental length difference. The crosstalk caused by limited extinction ratios (ERs) of MZI switches and the waveguide loss restricts the ODL buffering capacity. A method to suppress the crosstalk and hence expand the buffering capacity is proposed by inserting variable optical attenuators (VOAs) between successive MZI switches. A design example shows that a seven-stage ODL without VOAs can delay 8-98 bits with a tuning step of 1 bit for a 40 Gbit/s non-return-to-zero (NRZ) 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> - 1 pseudo-random bit sequence (PRBS) optical signal. When VOAs with a 10 dB attenuation ratio are included, the signal-to-crosstalk ratio (SCR) of the output signal is increased by 17 dB on average, making the ODL capable of delaying 8-135 bits at its maximum.

Monolithic InP Receiver Chip With a Variable Optical Attenuator for Colorless WDM Detection

We demonstrate a monolithically integrated quadrature coherent receiver photonic integrated circuit (PIC) on an InP substrate. The PIC comprises a 90° optical hybrid, a variable optical attenuator (VOA), and four RF photodetectors. With a dynamic range of 25 dB, the VOA enables the usage of the receiver PIC for colorless WDM detection.

An Electrically Tunable Liquid Crystal Lens for Fiber Coupling and Variable Optical Attenuation

An electrically tunable Liquid Crystal (LC) lens for both of fiber coupling and variable optical attenuation is demonstrated. The LC lens modulates the beam waist coupling to the fiber by electrically changing the lens power. When the modulated beam waist is close to the core size of the fiber, the LC lens is operated as a lens coupler. When the beam waist increases by reducing the lens power, the LC lens is operated as a Variable Optical Attenuator (VOA) as a result of the corresponding coupling coefficient variation of the transformed beam into a multimode fiber. The study provides a way to design an optical device for fiber coupling and variable optical attenuation based on electrically tunable focusing optical component.

基于Polymer/SiO2的快速低功耗可变光衰减器的研制

基于Polymer/SiO2的快速低功耗可变光衰减器的研制

Variable Optical Attenuator Based on Long‐Range Surface Plasmon Polariton Multimode Interference Coupler

The fabrication and characterization of a thermal variable optical attenuator based on long‐range surface plasmon polariton (LRSPP) waveguide with multimode interference architecture were investigated. The surface morphology and waveguide configuration of Au stripe were studied by atomic force microscopy. The fluctuation of refractive index of poly(methyl‐methacrylate‐glycidyl‐methacrylate) polymer cladding was confirmed to be less than 3 × 10−4 within 8 h curing at 120°C. The end‐fire excitation of LRSPP mode guiding at 1550 nm along Au stripe indicated that the extinction ratio of attenuator was about 12 dB at a driving power of 69 mW. The measured optical rise time and fall time are 0.57 and 0.87 ms, respectively. These favorable properties promise potentials of this plasmonic device in the application of optical interconnection.

A switchable single- and dual-wavelength erbium fiber ring laser in single-longitudinal-mode operation

A simple stable single-longitudinal-mode (SLM) single- and dual-wavelength erbium-doped fiber ring laser using an arrayed waveguide grating as the wavelength filter is proposed and demonstrated. SLM operation is guaranteed by a saturable-absorber-based auto-tracking filter. A 40/60 optical coupler is used to form two imbalanced loss cavities in the fiber laser initially, and single- and dual-wavelength operation can be changed by properly modifying the variable optical attenuator. The side mode suppression ratios of the laser outputs are higher than 60 dB. Through switching the two fiber optical switches, the dual-wavelength spacing is tuned from the narrowest 0.82 nm to the widest 12.05 nm, which offers potential uses in the generation of terahertz (THz) radiation.

Effect of Dy substitution on ferroelectric, optical and electro-optic properties of transparent Pb0.90La0.10(Zr0.65Ti0.35)O3 ceramics

Highly transparent Dy-codoped lead lanthanum zirconate titanate (PLZT) ceramics were sintered from oxide powders by the hot pressing method. The ceramics exhibited a transparency as high as 67% at 632.8nm (close to the theoretical value). The effects of substituting Lanthanum by Dysprosium on the phase structure, microstructure, dielectric, ferroelectric, optical and electro-optic properties of PLZT were examined. The results showed that Dy substitution decreased the coercive field, improved the optical transmittance and electro-optic properties of PLZT ceramics. Moreover, the high half-wave voltage (affecting the working voltage of devices) of PLZT was reduced from 850V to 510V by Dy substitution. Modified PLDZT transparent ceramics are competitive candidate materials for modern optical communication, and the variable optical attenuator (VOA) based on PLDZT exhibited excellent performances.

340 nm Bandwidth Automatic Dynamic Optical Equalizer for CWDM Networks

This paper presents an automatic optical equalizer based on a pair of in-house developed high efficiency, acousto-optic variable optical attenuators (AO-VOAs). The system is polarization insensitive and presents a wide bandwidth compatible with coarse wavelength division multiplexing (CWDM) requirements: 340 nm. The system operation is automatic and bidirectional and equalization is obtained in one single iteration of algorithm loop.

Fast-response liquid crystal variable optical retarder and multilevel attenuator

We propose and demonstrate a fast-response liquid crystal (LC) variable optical retarder or attenuator with several transmission levels. The fast-response LC optical device consists of dual π -cells. The device is designed so that the transition between any two states is controlled by the application of an increased voltage level rather than by applying a lower level. This design offers transition times in the range of tens of microseconds between any transmission states. A limitation of the device is that the time between transitions cannot be arbitrarily short and is typically milliseconds.

Modeling and Characterization of a Vernier Latching MEMS Variable Optical Attenuator

We report on the modeling and testing of a Vernier latched MEMS variable optical attenuator (VOA) which uses chevron electrothermal microactuators to control fiber-to-fiber optical power coupling. The use of microlatches has the advantage of holding the mechanical position of the fiber, and therefore the level of attenuation, with no electrical energy supplied except only to change the attenuation. Results of analytical electro-thermo-mechanical models of the device are obtained and compared with experimental test results, showing a good agreement. A step resolution of 0.5 μm for this multi-state latched device is achieved using a Vernier latch approach. This incremental step size is smaller than previously reported latched microactuators. The VOA demonstrated an attenuation range of over 47 dB and an insertion loss of 1 dB. The wavelength dependent loss across the optical communications C-band is 1.4 dB at 40 dB attenuation and the 10-90% transition time of the unlatched VOA is measured to be 1.7 ms.

Broadband Watt-Level Mid-Infrared Fiber-Coupled Variable Optical Attenuator

Direct intensity modulation of laser systems in the mid-infrared is marred by instabilities in power output, emission wavelength, and mode profile. In particular, emission characteristics of current implementations of quantum cascade lasers are especially susceptible to modulations in the driving current. We present a broadband mid-infrared variable optical attenuator with large dynamic range and sub-millisecond response time. The modulator has demonstrated 52 dB dynamic range (limited by the detector noise) and frequency response, and has been tested at various wavelength covering 3.5-4.8 μm. The system is composed of a piezoelectric controlled tilt-mirror that images the laser beam into a mid-infrared transmitting optical fiber. The use of broadband anti-reflection optics in the system maintains a high throughput of . Power handling of the system has been confirmed up to 4 W (limited by the laser output power).

Near-infrared absorption detection in picolitre liquid volumes using amplified fibre loop ring-down detection

Cavity ring-down spectroscopy is performed using a single-mode fibre loop as an optical cavity. The loop contains absorption cells for either liquids or gases, as well as an erbium-doped fibre amplifier. The fibre amplifier is gain-clamped using a second fibre-loop. Ring-down times can be tuned to permit several hundred roundtrips by adjusting the loss ratio between the two nested loops using a variable optical attenuator. Ring-down measurements were performed either in the time domain or using phase shift measurements.Acetylene gas was detected through a ro-vibrational absorption line of the ν1–ν3 combination band at 1532nm at a limit of detection of 50ppm. Liquid 1-octyne and 1-dodecyne were detected in a 1pL volume at detection limits of ∼20% dilution in dodecane through their C–H stretch vibrational overtone transition.

Variable optical attenuator based on photonic crystal waveguide with low-group-index tapers

We demonstrate a compact thermo-optic variable optical attenuator (VOA) based on the cutoff effect of W1 photonic crystal waveguide (PCW). In experiment, a variable attenuation range of 29 dB is achieved with a device length of only 16.8 μm. The coupling loss is also reduced by 7.5±2.5 dB through introducing low-group-index tapers between the W1 PCW and strip waveguide. This VOA provides the largest variable attenuation range in the reported tunable PCW device to our knowledge.

On-chip optical phase locking of single growth monolithically integrated slotted fabry perot lasers

This work investigates the optical phase locking performance of Slotted Fabry Perot (SFP) lasers and develops an integrated variable phase locked system on chip for the first time to our knowledge using these lasers. Stable phase locking is demonstrated between two SFP lasers coupled on chip via a variable gain waveguide section. The two lasers are biased differently, one just above the threshold current of the device with the other at three times this value. The coupling between the lasers can be controlled using the variable gain section which can act as a variable optical attenuator or amplifier depending on bias. Using this, the width of the stable phase locking region on chip is shown to be variable.

Tunable plasmonic filter and variable optical attenuator based on ring metal–insulator–metal waveguide

A tunable nanoscale plasmonic filter and variable optical attenuator structure based on a rectangular ring metal–insulator–metal waveguide cavity containing electro-optic (EO) material is proposed and numerically demonstrated by using the finite-difference time-domain technique. The simulation results show that the output of the device can be electrically controlled by tuning the refractive index of the EO material and the structure can be used as tunable filter and variable optical attenuator alternatively under very low voltage.

Fast Response MEMS VOA with Grid-Type Shutter

In this paper, a microelectromechanical variable optical attenuator (VOA) with grid-type shutter is described. The device is used to control the power in the all optical nelworks. Besides the advantage of good switching performance and the relatively low driving voltage, its fabrication is simple and reliable. In our laboratory, a MEMS VOA with grid-type shutter has been fabricated and setup for investigation. Experimental results have shown that the proposed approaches improve the VOA performance.