Cleaved Single-mode Fiber Research Articles

The Low-Loss Spot Size Converter for Alignment with Cleaved Single Mode Fiber

Integrating the graded index (GRIN) waveguide with the 2-D inversely-tapered waveguide, a new design of spot size converter (SSC) has been proposed to couple the light beam between the cleaved single-mode fiber (SMF) and the silicon (Si) wire waveguide on the silicon-on-insulator (SOI) platform. The device demonstrates a low coupling loss of 0.27 dB when it is coupled to a cleaved SMF. The polarization-dependent loss (PDL) is less than 0.25 dB, and the 1-dB alignment tolerance is about −2.0~2.0 µm for both vertical and horizontal directions. At the same time, the starting tip width of the tapered waveguide is kept at the level of the lithography limitation at the current commercial silicon photonics fab. This integrated SSC could be an improved design for reducing the coupling loss between the cleaved SMF and the Si waveguide.

An air-pressure and acoustic fiber sensor based on graphene-oxide Fabry-Perot interferometer

A fibre optic sensor for both air-pressure and acoustic signal detection based on graphene-oxide Fabry-Perot interferometer (GO-FPI) is proposed and demonstrated. The GO-FPI consists of a cleaved single-mode fibre (SMF) and GO film with good uniformity and high surface evenness. As for air-pressure detection, the highest sensitivity is 3.81 nm/kPa. As for acoustic sensing, the frequency response ranges from 4 Hz to 20 kHz with good fidelity and extremely high linearity of ∼ 1, with capability of single-frequency and multi-frequency signal detection. Moreover, the GO-FPI can detect the acoustic signal both in air and underwater with high stability. The noise-limited minimum detectable pressure levels are 28.74 µPa/Hz1/2@20 kHz in air and 14.44 µPa/Hz1/2@13 kHz underwater. The proposed multi-parameter sensor with high compactness and stability has potential applications in structure health and vibration monitoring.

Low-cost and high-efficiency single-mode-fiber interfaces to silicon photonic circuits

A high-efficiency and large-alignment-tolerance fiber interface to silicon-on-insulator wire waveguides is introduced. A spot-size converter is built through a full three-dimensional polymer waveguide and a silicon inverse taper is employed to expand the optical mode field from a silicon sub-micro waveguide to a normal cleaved single-mode fiber with a mode size of about 10μm. The fabrication for the three-dimensional structure relies on simple spin-coating processes. The coupling loss from the fiber to the silicon waveguide through the proposed structure reaches -1.0dB for both transverse electrical and transverse magnetic modes, respectively. The polarization-dependent loss for the best coupling case is kept within -0.6dB in the whole measured wavelength range. The coupling facet of the proposed fiber interface structure is polishable and facilitates an easy package procedure with standard fiber arrays.

Demonstration of a microelectromechanical tunable Fabry-Pérot cavity based on graphene-bonded fiber devices.

Taking advantage of the high thermal conductivity of graphene, this Letter demonstrates a microelectromechanical (MEM) tunable Fabry-Pérot (F-P) cavity, based on a graphene-bonded fiber device (GFD), which acts as a microheater. By increasing the electric current from 0 to 8mA in the heater, the temperature of the GFD can rise and approach a value of 760K theoretically. This high temperature will cause a deformation of the fiber, allowing the graphene-bonded fiber end to form a gap-adjustable F-P cavity with a cleaved single-mode fiber. The gap in the cavity can be reduced by increasing the current applied, leading the transmittance of the cavity to change. In this work, a highly sensitive current sensor (5.9×105 nm/A2) and a tunable mode-locked fiber laser (1.2×104 nm/A2) are created based on the MEM tunable F-P cavity.

CO$_{2}$ Gas Sensing Using Optical Fiber Fabry–Perot Interferometer Based on Polyethyleneimine/Poly(Vinyl Alcohol) Coating

An optical fiber Fabry–Perot interferometer (FPI) based on poly (ethyleneimine) (PEI)/ poly (vinyl alcohol) (PVA) blend membrane is proposed and realized experimentally as a sensor for the pressure of CO $_{2}$ in the atmosphere. The functional material layer based on PEI/PVA blend polymer exhibits reversible optical path difference change because of absorption and release of CO $_{2}$ gas molecules. The cavity of the FPI is fabricated by coating a 15- $\mu$ m PEI/PVA blend film on the end-face of a cleaved single-mode fiber. An interference spectrum with fringe contrast of 19.5 dB and free spectra range of 33.15 nm is obtained. The proposed FPI sensor is sensitive to the changes of concentration of CO $_{2}$ , as well as a sensitivity of 0.281 nm/ $\%$ within an interval which ranges from 7.6 $\%$ to 86.9 $\%$ .

Microfluidic Flow Rate Detection With a Large Dynamic Range by Optical Manipulation

Sensitive flow rate detection with a large dynamic range is highly desirable for the lab-on-a-chip applications. We demonstrate an optofluidic flow rate detection method based on the optical manipulation of a single microparticle by a cleaved single-mode fiber (SMF). The microbalance between the optical force and the flow force on the single polystyrene microparticle was used as a new strategy for the detection. Due to the inverse sensitivity, the limit of detection is pushed down to 20 nL/min by detecting the manipulation length as a function of the flow rate. The measurement range of about three orders of magnitude is achieved. The experimental results indicate that the method produces a good repeatability for the flow rate measurement. The cleaved SMF for the optofluidic manipulation also enables low cost, repeatable, and mass production of the sensing device.

240 GHz pedestal-free colliding-pulse mode-locked laser with a wide operation range

A 240 GHz, sixth-harmonic monolithic ~1.55 μm colliding-pulse mode-locked laser is reported using a three-quantum-well active layer design and a passive far-field reduction layer. The device emits 0.88 ps pulses with a peak power of 65 mW and intermediate longitudinal modes suppressed by >30 dB. The device demonstrates a wide operation range compared to the conventional five-quantum-well design as well as having a low divergence angle (12.7° × 26.3°), granting a twofold improvement in butt-coupling efficiency into a flat cleaved single-mode fibre.

UV-Curable Polymer Microhemisphere-Based Fiber-Optic Fabry–Perot Interferometer for Simultaneous Measurement of Refractive Index and Temperature

A fiber-optic Fabry-Perot interferometer based on UV-curable polymer micro- hemisphere is proposed and demonstrated. The polymer microhemisphere is formed by adhering and solidifying a liquid microdroplet of UV-curable adhesive to the end face of a cleaved single-mode fiber. The height of polymer microhemisphere could be flexibly con- trolled by adjusting the diameter of a single-mode fiber. The theoretical and experimental results demonstrate that the refractive index (RI) and the temperature of external environ- ment can be simultaneously measured by the fringe contrast variation and the wave- length shift of reflection spectra separately, alleviating the cross sensitivity effectively. The obtained temperature and RI sensitivities are about 0.19 nm= � C and 260 dB/RIU in the RI range of 1.38-1.42.

160-GHz 1.55-$\mu{\rm m}$ Colliding-Pulse Mode-Locked AlGaInAs/InP Laser With High Power and Low Divergence Angle

A monolithic ~1.55-μm colliding-pulse mode-locked AlGaInAs/InP laser with a three-quantum-well active layer incorporating a passive far-held reduction layer has been demonstrated. The device emits pulses at 162 GHz, with a pulsewidth of 0.98 ps, a pulse energy of 0.13 pJ, and a time-bandwidth product of 0.52, while demonstrating a low divergence angle (12.7° × 26.3°) with a twofold improvement in butt coupling efficiency to a flat cleaved single-mode fiber, compared to the conventional mode-locked lasers.

Single-Longitudinal-Mode Fiber Ring Laser Stabilized by Tandem All-Fiber Fabry–Pérot Micro-Cavities

We demonstrate a stabilized single-longitudinal-mode fiber ring laser using tandem-Fabry-Pérot-microcavities (T-FP-MCs) as the all-fiber intracavity filter. The T-FP-MCs are formed with short adjustable air gaps between pairs of vertical cleaved single-mode fiber ends without mirror-coating deposition. The T-FP-MCs' spectral filtering effect is analyzed with the Rouard's method. Mode-hopping-free continuous-wave operation with 19-dBm power, 0.06-nm bandwidth and sidemode suppression ratio of 28 dB at 1565-nm wavelength is achieved using two T-FP-MCs. Q-switching pulsed operation of this fiber laser with 10-W peak power is also investigated and analyzed.

Photophoretic assembly of two-dimensional crystals from microparticle suspensions

We report a photophoretic assembly of two-dimensional (2D) crystals from microparticle suspensions. The assembly of microparticles is based on the negative photophoresis induced by a 1550 nm laser beam from a cleaved single-mode fiber. The influence of particle size and laser power on the assembly was experimentally investigated and the photophoresis behavior was analyzed by using a finite-difference time-domain simulation. The results indicate that larger particle diameter or higher laser power will lead to higher assembly speed. Moreover, the diffraction property of the assembled 2D crystals was tested with the assistance of 632.8 nm red light and 532 nm green light, which confirmed that the assembled 2D crystals exhibit hexagonal-close-packed lattice orientation.

10-GHz AlGaInAs/InP 1.55-$\mu$m Passively Mode-Locked Laser With Low Divergence Angle and Timing Jitter

We present a 10-GHz 1.55-μm passively mode-locked laser based on a novel AlGalnAs/InP epitaxial structure with a three-quantum-well active layer incorporating a passive far-field reduction layer. The device generated 1.06 ps pulses with a state-of-art timing jitter value of 194 fs (4-80 MHz), and a radio-frequency linewidth of 2 kHz, while demonstrating a low divergence angle (14.7° × 27.3°) with a twofold butt coupling efficiency to a flat cleaved single-mode fiber, compared to conventional five-quantum-well mode-locked lasers.

Dual-wavelength 925 GHz self-mode-locked InP-based quantum dot laser

We report on the generation of dual-wavelength self-mode-locking pulses from an InP-based quantum dot laser. The demonstrated device operates simultaneously at both 1543.7 and 1571.7 nm and has a repetition rate of 92.5 GHz. The pulse width is below 960 fs, and the average power coupled to a cleaved single-mode fiber is nearly 9 mW at a current bias of 60 mA.

Self-starting mode locking by multi-spatial-mode active waveguiding

We demonstrate a novel principle of self-starting mode locking in a compact semiconductor laser diode, where the needed saturable loss is provided by spatial effects resulting from multi-spatial-mode active waveguiding. The demonstrated device operates over a 1.54 microm wavelength range and has a repetition rate of 47 GHz. The pulse width is below 5 ps, and the average power coupled to the cleaved single-mode fiber is nearly 0 dBm.

Linear MEMS variable optical attenuator using reflective elliptical mirror

We propose an improved design of variable optical attenuator (VOA) using a micromachined elliptical mirror, which offers the advantages of both the shutter-type VOAs and the flat-mirror reflection-type VOAs while overcoming their problems. This design positions the input and output fibers at the two focal centers of the reflective elliptical mirror. Since the ellipse can focus the light from one center to the other, the VOA enjoys low insertion loss while using the normally cleaved single-mode fibers. As the mirror is displaced, the input beam is rapidly defocused, producing a large attenuation range without requiring a large mirror displacement. This VOA also has low polarization dependence loss (PDL), low wavelength dependence loss (WDL), and low back reflection. It is fabricated by the deep reactive ion etching process and achieves 44-dB attenuation at 10.7-V driving voltage. The PDL is 0.8 dB at the 40-dB attenuation level and the WDL is 1.2 dB at the 20-dB level for 100-nm wavelength change. More importantly, the measurement shows that attenuation has a nearly linear relationship with the mirror displacement over a 30-dB attenuation range.

Modeling of InGaAsP–InP 1.55 μm lasers with integrated mode expanders using fiber-matched leaky waveguides

A new concept for InGaAsP–InP 1.55 μm lasers integrated with spot size converters using leaky waveguides is presented. The large fundamental mode size and the high discrimination of the higher order modes make ARROWs (Antiresonant Reflecting Optical Waveguides) and antiguided waveguides useful for fiber coupling functions. Three-dimensional (3-D) beam propagation method (BPM) results show that the devices have transformation losses lower than 0.22 dB. Fiber-coupling efficiencies of 60% are possible with standard cleaved single-mode fibers (SMF). The horizontal and vertical FWHM can be efficiently reduced to 9.70° (horizontal) and 17.80° (vertical). The fabrication of such devices avoids the growth of thick layers of quaternary material with a low Ga and As fraction, and simplifies the fabrication to one planar epitaxial growth step and one non-critical conventional etch.

Passive active resonant coupler (PARC) platform with mode expander

We have developed a monolithic integration platform where three waveguides of different characteristics are using a single epitaxial growth. This is achieved by having three waveguides in the growth direction and by coupling the mode between them by resonance over compact tapers. The top waveguide is an active waveguide optimized for gain at 1.55 μm. The middle waveguide is a confined passive waveguide optimized for passive devices such as splitters and filters, etc. The bottom waveguide is a large loosely confined passive waveguide optimized for a high coupling efficiency to a single-mode fiber. The mode is coupled from the active waveguide to the confined passive waveguide over a 120-μm-long taper with less than 0.1-dB coupling loss. To couple the mode from the confined passive waveguide to the large-mode passive waveguide, a 270-μm-long taper is used with less than 0.25-dB coupling loss. Lasers have been fabricated to test the platform and have a butt-coupling loss of 3.5 dB to a standard cleaved single-mode fiber.

Compact mode expanded lasers using resonant coupling between a 1.55-μm InGaAsP tapered active region and an underlying coupling waveguide

We demonstrate a novel expanded mode laser for enhanced laser-fiber coupling based on resonant coupling between a tapered active waveguide and an underlying coupling waveguide. This device was grown in a single standard epitaxial growth and was processed using conventional fabrication techniques, thus making it attractive for low-cost manufacturing. The total taper length required for mode transformation was 200 /spl mu/m and the excess transformation loss was 0.6 dB indicating the compact, low-loss mode transformation. Far-field divergence angles (13/spl deg//spl times/24/spl deg/) and improved coupling to cleaved single-mode fibers (3.8-dB coupling loss), were achieved.

1.55-μm InGaAsP-InP spot-size-converted (SSC) laser with simple technological process

In this letter, we report the realization of a 1.55-/spl mu/m spot-size-converted (SSC) laser using conventional SCH-MQW active layers and conventional photolithography. The laser consists of a 300-/spl mu/m-long rectangular gain section, with compensated multiple-quantum-well (MQW) structure, and a 300-/spl mu/m-long tapered passive waveguide, fabricated on lower SCH layer. The device exhibits a beam divergence of 13/spl deg//spl times/18/spl deg/ and 3.5-dB coupling loss with a cleaved single-mode fiber (SMF). The 1-dB alignment tolerance is /spl plusmn/2.3 /spl mu/m in the vertical direction and /spl plusmn/1.9 /spl mu/m in the lateral direction, respectively.

Compact mode expanders using resonant coupling between a tapered active region and an underlying coupling waveguide

A novel technique for enhanced laser-fiber coupling, based on resonant power coupling between a tapered active waveguide and an underlying coupling waveguide, is presented. Spot-sizes are transformed from 2.0×1.1 μm in the active region to 6.0×3.1 μm in the coupling waveguide, over a length of 200 μm, with a mode transformation loss of only 0.36 dB. Butt-coupling efficiencies of 55% (2.6 dB loss) are estimated to standard cleaved single-mode fibers at 1.55 μm. The proposed device requires a single epitaxial growth and conventional processing techniques, making it amenable for low-cost manufacturing.