Incoherent broadband optical pulse generation using an optical gate

In two-dimensional(2D)time-spreading/wavelength-hopping optical code division multiple access (OCDMA)systems,employing less coherent broadband optical pulse sources allows lower electrical oper- ating rate and better system performance.An optical gate based scheme for generating weakly coherent (approximately incoherent)broadband optical pulses was proposed and experimentally demonstrated.In this scheme,the terahertz optical asymmetric demultiplexer,together with a coherent narrowband control pulse source,turns an incoherent broadband continuous-wave(CW)light source into the required pulse source.     

Piezooptical optical bistability

A glass fiber piezooptical optical bistability device is reported.Basing on pho-toelastic and strain effects of single-mode fiber,we have realized piezooptical modulation andperformed experiments of optical bistability.     

An optical method for wavelength fine-selection in optical spectrum analysers

This letter describes a novel optical method for wavelength fine-selection in the optical spectrum analysers (OSAs) for dense wavelength division multiplexing (DWDM) applications. The proposed new method employs a 'refractive optical lever' system consisting of a rotating optical wedge prism. A new OSA system based on Littman-type monochromator is proposed and the wavelength selection accuracy and resolution of OSA that has included such an optical lever system have been improved by a factor of 20 to 100 depending on the wedge angle and offset orientation angle of the optical wedge prism. This proposed 'refractive optical lever' may also simplify the rotation mechanism of the mirror in the commercially available OSAs.     

Separation and insertion of optical bit-serial label in optical packet switching

The bipolar phase-shift-keying (BPSK) optical orthogonal codes (OOCs) are inserted into the optical packet format of bit-serial label. The ultra-fast separation of the label and payload is performed through the auto-correlation pulses indicating the time position at which the optical switch changes the state. The insertion of the new label can also be realized by detecting the auto-correlation pulse at the line rate. Especially, the scheme can be adapted to the asynchronous separation and insertion and realize the variable-length packet switching. The results of simulation verify the feasibility of the scheme.     

Beam-shaping microstructure optical fiber

Microstructure optical fiber with uniform intensity distribution of the fundamental mode is proposed. The design guide line and characteristics of this kind fiber are demonstrated. The relationship between refractive index profile and structure parameters is investigated. The mechanism of forming uniform fundamental mode in these fibers is analyzed.     

Controllable optical delay line using a Brillouin optical fiber ring laser

A controllable optical delay line using a Brillouin optical fiber ring laser is demonstrated and a large time delay is obtained by cascading two optical fiber segments. In experiment, a single-mode Brillouin optical fiber ring laser is used to provide Stokes wave as probe wave. We achieve a maximum tunable time delay of 61 ns using two cascading optical fiber segments, about 1.5 times of the input probe pulse width of 40 ns. In the meantime, a considerable pulse broadening is observed, which agrees well with the theoretical prediction based on linear theory.     

Picosecond optical switching of a 1.5 μm active birefringent optical fiber loop filter using 1.3 μm control optical pulses and a 1.3 μm semiconductor optical amplifier

Less than 100ps, polarization-independent switching operation of an active birefringent optical fiber loop filter using 1.3 μm control optical pulses as well as a 1.3 μm semiconductor optical amplifier (SOA) has been demonstrated. In the proposed SOA-based active birefringent filter operating at 1.55 μm wavelength, 1.3 μm SOA is employed to control the polarization-mode dispersion in the loop part. By injecting 1.3 μm ps gain-switched optical control pulses into the SOA, 1.5 μm input signals can be switched from the transmission port to the reflection port with less than 100 ps rise time.     

Novel MEMS variable optical attenuator

A novel MEMS variable optical attenuator (VOA), which has completely different attenuation mechanism from those in literatures, is proposed and demonstrated in this paper. The basic operation principle is that the optical power coupled between two initially aligned single-mode fibers will be continuously attenuated while the end of one of the fibers is deflected from the initial position. A micromachined solenoid type inductor with a U-shaped permalloy magnetic core is used to attract the deflectable fiber that has a permalloy coat on its end. To fabricate the multi-layer three-dimensional inductive component, a new UV-LIGA process for thick photoresists is developed, combining advantages of both SU-8 and AZ-4000 series photoresists. The inductive component is approximately 1.7 mm×1.3 mm×50μm in size and has a low resistance value (- 2.1Ω). The whole size of the VOA before packaging is 30 mmx2 mmx0.6 mm. The first prototype shows less then 3-dB insertion loss at 0-dB attenuation and nearly 40-dB att     

Nonadiabatic nondegenerate excitation by optical near-field and its application to optical pulse-shape measurement

Using DCM dye grains and light of different wavelengths generated by two CW laser diodes that oscillate in the near-infrared wavelength region, visible light emission from dye grains due to near-infrared excitation based on a nonadiabatic, nondegenerate excitation process was observed for the first time. Unlike sum-frequency generation with nonlinear polarization, the difference in polarization angles of the two beams did not affect the emitted light intensity. Optical sampling based on this nonadiabatic, nondegenerate excitation principle was demonstrated for the first time. The optical pulse shape in the wavelength band of λ=1250–1350 nm, which is close to the wavelength range used for optical fiber communications, was measured with a temporal resolution of 0.8–1.1 ps.     

The study of third harmonic demodulation in phase modulation optical heterodyne technique using optical resonator

With the technique of phase modulation optical heterodyne(PMOH), we detected the beat-frequency signal of the reflected wave from a F-P cavity. The frequency of the beat signal was three times of that of the modulation electric field, when the 3rd harmonic of the modulation electric field was used as the phase reference signal. The line shapes of the signal match those of the theoretical calculations, and the dispersion signal has good frequency-discrimination characteristic.     

Controllable optical bistability of Bose-Einstein condensate in an optical cavity with a Kerr medium

We study the optical bistability for a Bose-Einstein condensate of atoms in a driven optical cavity with a Kerr medium. We find that both the threshold point of optical bistability transition and the width of optical bistability hysteresis can be controlled by appropriately adjusting the Kerr interaction between the photons. In particular, we show that the optical bistability will disappear when the Kerr interaction exceeds a critical value.     

The role of the interactive Kerr effect in two-photon optical multistability

We show that bistable behaviour in a two-photon resonant system within a cavity may be attributed to interactive mode-pulling via the two-photon optical Kerr effect and also to absorptive bleaching (atomic saturation). The interactive Kerr process may be regarded as giving rise to a new category of optical bistability. Moreover, a mechanism for the recently-predicted tristability can be found in terms of simultaneous competition between the interactive Kerr effect and bleaching.     

Dissipative discrete spatial optical solitons in a system of coupled optical fibers with the Kerr and resonance nonlinearities

The propagation of monochromatic radiation in a system of weakly coupled single-mode optical fibers with saturable amplification and absorption and Kerr nonlinearity of the refractive index is analyzed. Conditions of stability and bistability of plane-wave regimes are determined. Discrete dissipative optical solitons are found and their stability is studied. The hysteresis dependences of the peak intensity of the discrete solitons on the value of the Kerr nonlinearity and the input beam intensity are demonstrated. The numerical estimates of the parameters of the spatial dissipative discrete solitons are presented.     

Optical bistability in nonlinear subwavelength metal hole array involving Kerr materials

We investigate an optical bistability phenomenon in a structure consisting of a silver film with a hole array filling with Kerr medium with single wavelength. We explore the mechanism of optical bistability in our structures and find that the excitation condition of surface plasmon at this moment is related with that at last moment. The contrast of optical bistability can reach to the maximum at the wavelength of the transmission peak. Our structure can realize the function of the beam splitter.     

Optical bistability of subwavelength metallic film coated by Kerr dielectric gratings

We studied the optical bistability of subwavelength metallic film coated by Kerr dielectric gratings numerically. It is found that the effect of optical bistability in the structure is explained by the excitations of the coupled surface plasmon polaritons at the coated metallic films. The effect of thickness of the metallic films on bistability loop is analyzed in detail, and the authors attribute the change of the bistability loop to the lifetime of the coupled surface plasmon polaritons.     

Nonlinear polarisation effects in optical microcoil resonators with fibre twist and birefringence

We study the nonlinear response of optical microcoil resonators (OMRs) based on twisted birefringent microfibres by incorporating Kerr nonlinearity into the underlying coupled mode equations. The resulting hysteresis characteristics were found to be highly polarisation dependent, with both the switching powers and contrast levels strongly influenced by the twist-induced cross-polarisation coupling. In addition, the existence of multiple bistability in OMRs is explored when the two orthogonal polarisations' resonances are spectrally close enough to influence the propagation of a monochromatic pump. Both the bistability and nonlinear switching may potentially be utilised for implementing polarisation-sensitive devices, especially for signal processing purposes, and benefit from the low threshold powers needed to observe nonlinear effects in OMRs.     

Surface plasmon-assisted optical switching/bistability at telecommunication wavelengths in nonlinear dielectric gratings

In this paper, we numerically investigate nonlinear optical responses in dielectric gratings coated by flat metallic surface, where the structural parameters are chosen for wavelengths of operation at the telecom regime. The presented designs show the output light reflection with respect to the incident intensity of increasing, decreasing, and non-monotonic belt-shape functions. Nonlinear optical responses including switching and bistability appeared in the telecom region owing to assistance of surface plasmon resonance excited at the metal/dielectric interface, which enhances the diffraction efficiency and induces the momentum matching for the leaky modes of the dielectric grating. This results in electric intensity-effective refractive index dependence enhancement in the Kerr nonlinear media. Our design and investigation of the linear and nonlinear optical responses will provide a general guideline for a hybrid metallic-dielectric structure-based optical switching/bistability device design.     

Controlling the optical bistability via interacting dark-state resonances

We analyze the behavior of optical bistability in a four-level mercury atomic system driven by a cavity and two external coherent fields by means of a unidirectional ring cavity. We find that without interacting dark resonances and for large intensity of coupling field, the optical bistability disappears. So, the double dark resonances could significantly establish the optical bistability. Moreover, we demonstrate that the double dark resonances can dramatically reduce the threshold of optical bistability.     

Cavity nonlinear optics at low photon numbers from collective atomic motion

We report on Kerr nonlinearity and dispersive optical bistability of a Fabry-Perot optical resonator due to the displacement of ultracold atoms trapped within. In the driven resonator, such collective motion is induced by optical forces acting upon up to 10(5) 87Rb atoms prepared in the lowest band of a one-dimensional intracavity optical lattice. The longevity of atomic motional coherence allows for strongly nonlinear optics at extremely low cavity photon numbers, as demonstrated by the observation of both branches of optical bistability at photon numbers below unity.     

Optical bistability and differential amplification in a tapered fiber coupler — microsphere resonator with nonlinear medium

We propose and study a coupling system composed of the tapered fiber and the microsphere with nonlinear medium. The optical bistability and differential amplification caused by optical Kerr effect is demonstrated using a geometrical method. We show that their operation characteristics can be controlled by parameters: linear phase detuning, attenuation coefficient and real amplitude coupling coefficient.