Four-wavelength DBR laser array with waveguide couplers fabricated using selective MOVPE growth

We have developed an integrated multiwavelength laser with waveguide couplers using a novel selective metal-organic vapor-phase epitaxy (MOVPE) technique. The lasing wavelength was controlled by modulating the effective refractive index of distributed Bragg reflector (DBR) waveguides. Array lasing wavelengths were distributed from 1548.0 to 1553.5 nm with an average spacing of 1.8 nm. The propagation loss of the waveguide coupler was about 16 dB for inner ports and 20 dB for outer ports with a 6 dB splitting loss. Four-wavelength laser outputs were coupled into a single-mode fibre.     

An integrated optical coupler used in a fibre interferometry system for on-line surface measurements

In this paper, an integrated optical (IO) coupler produced using the technique of silica-on-silicon was described. A fibre interferometry system using the IO coupler was then developed and its performance was tested. The environmental noise and disturbances in this system were reduced significantly after combining a reference interferometer and an all fibre polarisation scrambler so as to produce good stability and repeatability. Furthermore, the measurement mirror was mounted on a piezoelectric transducer (PZT) and disturbances were introduced in the system in order to simulate on-line surface measurements. Both a commercial fibre and the IO couplers were compared using this method. Better experimental results were achieved when the system using the IO coupler than using the fibre one.     

The prism-taper coupler for the excitation of single modes in optical transmission fibres

A coupler is described which allows the excitation of pure single guided fibre modes with a single mode laser. The coupler uses a prism and precision taper fibre end to access any of the fibre modes. The conditions for obtaining excitation of single modes are discussed and the technique for producing the tapers is described. In the first tests, an excitation efficiency of approximately ?16 dB has been obtained.     

Polarisation characteristics of a 12 fibre coupler under femtosecond pulsed and continuous wave illumination

We report on the experimental investigation carried out in the polarisation characteristics of femtosecond pulsed and continuous wave beams propagating through a 1×2 fibre coupler. It is demonstrated that the polarisation states of pulsed and continuous wave illumination over the broad wavelength range can be preserved in a conventional fused fibre coupler. Furthermore, the fibre coupler acts as a low-pass spectral filter in the visible wavelength range with a splitting ratio between 99.6/0.4 and 99.7/0.3. The result is of importance for fibre-optic second harmonic generation microscopy which requires the polarisation preservation to extract molecular organization of a sample.     

Switchable and tuneable multi-wavelength Er-doped fibre ring laser using Sagnac filters

We demonstrate experimentally a simple configuration to perform wavelength-tuning and multi-wavelength operation in a fibre ring laser that is composed of an Erbium-doped fibre and includes a fibre-optic Sagnac interferometer as a spectral filter. We consider three different Sagnac filters including a 3 dB coupler, two wave retarders (WRs) and respectively 7 cm, 1 and 7 m of high birefringence fibre. The transmission spectrum of each filter is sinusoidal with a 70, 6, and 0.85 nm period, and its maxima can be shifted over one period by adjusting the angle of the retarders in the loop. By adjusting the WRs included in the filter and in the laser ring, tuneable single wavelength and several two- or three-wavelength lasing regimes were observed. In particular, fine adjustments of the WRs allow observing two- and three- wavelength operation with wavelength separations well below the homogeneous bandwidth of the gain medium. The stability of these modes of operation however strongly depends on environmental conditions at room temperature.     

Tunable asymmetric fibre ring resonator

A fibre ring resonator with coupling via an asymmetric twin-core single-mode coupler with variable mismatch is analysed. It is found that by varying the mismatch in the coupler the resonance conditions of the ring are also changed. Suitable choices of device parameters allow the resonance to be tuned over a range of wavelenths by altering the coupler mismatch.     

A 1 × 7 fibre coupler with Kerr nonlinearity

We study for the first time the evolution of the guided field in a 1×7 fibre coupler with a third-order nonlinearity. An analytical solution of the nonlinear coupled-mode equations is presented in terms of the Weierstrass function. In particular, we found that contrary to the equal power distribution in the linear limit, a cross-state appeared if the coupler was initially excited in the central core and a certain input power was chosen. Finally, we analyse the far-field pattern of the coupler output.     

Ultra-wide bandwidth wavelength selective couplers based on the all solid multi-core Ge-doped fibre

A novel wavelength selective coupler based on the all solid nine-core Ge-doped fibre has been proposed. The wavelength selective coupler is based on the phenomenon of a multi-core coupling. All the cores are made of Ge-doped silica and the index of central core is larger than the outer core. At the fixed fibre length, the different wavelength can be selected. The performances of coupling and propagation characteristics have been numerically investigated by using a full beam propagation method (BPM). Simulation results show that the all solid nine-core Ge-doped fibre can achieve simultaneous shorter coupler length and wideband filtering characteristics. The 0.763 mm and 0.745 mm wavelength selective coupler are proposed to achieve different wavelength division and the bandwidth is up to the 400 nm, and 300 nm, respectively.     

A high performance backscattering set-up using multimode light channels

The utilization of multimode ion-exchanged waveguides to form an optical directional coupler for multimode fibre backscattering measurements is discussed. The optical properties of the integrated branching element are described in detail. A very high directivity of 70 dB was obtained with this new device. The dynamic range in the backscattering measurement was 23 dB fibre one-way loss.     

On the radiation mode effects in integrated optical directional couplers

In this work we study the effect of radiation modes generated at the input of a directional coupler on its performance. We focus on the splitting ratio and the coupling length of the coupler. The Beam Propagation Method (BPM) is used for numerical simulation. Numerical results are compared to analytical expectations of the coupled mode theory (CMT). We show that, when the coupler is excited by a single mode fibre, ideal 3 dB couplers could be obtained by a simple adjustment of the exciting fibre. On the other hand, when the coupler has input and output bend structures, its coupling length as well as its splitting ratio are affected by the geometry of this bend.     

Mechanism and elimination of spectrum filtering in a high power mode-locked fibre laser witha free output coupler

The filtering mechanism of a free output coupler mode-locked laser based on large-mode-area photonic-crystal fibre is analysed. A filtering-soliton mode-locked laser with 495~fs pulse width and 21 nJ pulse energy is achieved. Another novel cavity configuration is established to eliminate the filtering effect. Pulses, each 457~fs in width and 16.5 nJ in energy, are obtained in a soliton-like regime. Pulses, each 387~fs in width and 15.8 nJ in energy, are also generated in a stretched pulse regime and could be dechirped to 119~fs externally to the cavity.     

Large core, multimode, chalcogenide glass fibre coupler by side-polishing

A novel method for obtaining a multimode optical coupler in chalcogenide glass fibre is described. The fibres used had a large $\text{ Ge }_{17}\text{ As }_{18}\text{ Se }_{65}$ Ge 17 As 18 Se 65 core comprising about 74 % of the total cross-sectional area with an optical cladding of $\text{ Ge }_{17}\text{ As }_{18}\text{ Se }_{62}\text{ S }_{3}$ Ge 17 As 18 Se 62 S 3 . A single arc-shaped U-groove was formed in each of two silicate glass blocks. A length of fibre was embedded into each groove and glued in place. The centre of each fibre length was subsequently side-polished. Finally two such embedded fibres were glued together in close contact to form the coupler, whilst monitoring the coupling ratio at the output.     

A Novel Design of Grating Couplers for Efficient Broadband Coupling between Silicon-on-Insulator Nanophotonic Waveguides and Fibres

A novel design of out-of-plane grating couplers is proposed for coupling between silicon-on-insulator nanophotonic waveguides and single-mode fibres. The coupler with the first-order diffraction coupling to the optical fibre is actually a second-order reflected grating with two times of period of the first-order grating. To enhance outcoupled power, a back hole is designed to form in the silicon substrate and a kind of metals is placed on the top acting as a reflection layer. The coupler is optimized using coupled-mode-based simulations, showing that the coupling efficiency to and from tapered optical fibre can be as high as 85% with 1dB bandwidth about 23 nm.     

Q-switching an all-fiber laser using acousto-optic null coupler

A new method for Q-switching an all-fiber laser is presented. It is based on induced acoustic long period grating operating on a null coupler, which acts as acoustically controlled tunable output coupler. Q-switching is achieved by switching on and off the acoustic wave in a burst mode, thereby generating laser pulses that are ~400 times shorter than the acoustically controlled coupler’s rise time. Output pulse energy of 22 μJ and temporal width of ~100 ns were measured at a wavelength of 1.54 μm.     

Modes and power splitting in a 5×5 coupler with application to coherent detection

The 5×5 coupler is of interest because of its application to coherent detection. The supermodes of the entire structure are determined by analysing the coupling of the component fibre modes through coupled-mode theory. The beating of the supermodes along the coupler determines the output power in each of the cores. Equal power splitting is a requirement for coherent detection. We show that this condition is not easily satisfied.     

Self-polarized ytterbium-doped fiber laser

We demonstrate a linearly-polarized, ytterbium-doped fiber laser that uses an uncoated, undoped ceramic YAG plate as the output coupler, and the corresponding polarization extinction ratio of laser beam increases with incident pump power and then saturates at larger pump power. For comparison, the output coupler of the fiber laser is replaced by 10% reflectivity plane mirror, while the feature of the polarization of laser output is kept unchanged. The results show that the origin of the pump-dependent and self-started polarization is associated with the intensity-dependent nonlinear birefringence in the gain fiber.     

Tapered fused fiber bundle coupler capable of 1 kW laser combining and 300 W laser splitting

A high efficiency 7 × 1 multimode fiber coupler using the method of fusion and tapering is reported. This coupler can be applied to combine laser power, ad it can be used as a 1 × 7 splitter with reversible simultaneously. In the experiment, for combiner, coupling output power of 1032 W is obtained with the input power of 1066 W. The total coupling efficiency is 96.8%. The average insertion loss of each input fiber is 0.14 dB at ∼150 W input power. To splitter, the sum of 7 output ports power is 294 W with the input power of 341 W, and the insertion loss is about 13.8%. This fiber coupler can be applied in pumping all-fiber double clad fiber laser, as well as power combination and splitting of fiber lasers.     

Output-coupling-dependent polarization state of a continuous-wave Yb:YCa4O(BO3)3 laser

High-power continuous-wave laser operation was demonstrated with a y-cut Yb:YCa(4)O(BO(3))(3) crystal, showing critical dependence on the output coupler used. Polarized laser oscillation with E||x was obtained at 1085.6 nm by using a coupler of 0.5% transmission, yielding an output power of 7.3 W with an optical-to-optical efficiency of 63%. Higher output couplings (>/=2%) led to polarized oscillation with E||z at laser wavelengths 相似文献   

Er-doped twin-core fibre coupler as a saturable-absorber-based narrow-band filter for fibre lasers

We have proposed and demonstrated experimentally that an Er-doped twin-core fibre (ErTCF) can be employed as a tracking narrow-band filter in fibre ring lasers for line narrowing and enhancement of the spectral stability. The device mimics a saturable absorber with inhomogeneous broadening. The slow erbium ion saturation dynamics in the ErTCF prevents wavelength hopping whilst it enables the filter to track the operation wavelength on its tuning. We have improved the device operation by utilizing the inherent filtering effect of a twin-core fibre coupler. Presented at the 1st Czech-Chinesse Workshop “Advanced Materials for Optoelectronics”, Prague, Czech Republic, June 13–17, 1998 This research has been in part supported by the Commission of the European Union in the frame of Copernicus programme, Project # 7882 and by the Ministry of Education of the Czech Republic under Contract OC 241.10/1998.     

An injection-locked erbium-doped fibre ring laser

The effects of injection-locked on an erbium-doped fibre laser based on a ring configuration have been demonstrated. A comparison between experimental results and theoretical prediction in the locking range is made with consistent results in a small wavelength range of about 15 nm. Frequency stabilisation was obtained by applying this approach, ensuring stable output power of the fibre laser system.