Showing papers on "Extinction ratio published in 1998"

Free-space micromachined optical switches with submillisecond switching time for large-scale optical crossconnects

Abstract: Optical crossconnects with large port counts are fast becoming critical components for high-capacity optical transport networks. The free-space micromachined optical switches (FS-MOS) demonstrated in this letter represent a means of filling this network need by combining the advantages of free-space interconnection with the virtues of integrated optics. Featuring free-rotating hinged micromirrors, the switch overcomes the common drawback of mechanical-type switches, namely long switching time. Measurements have revealed switching times less than 700 /spl mu/s, crosstalk less than -60 dB, extinction ratio greater than 60 dB, negligible polarization-dependent loss, and excellent bit-error-rate (BER) performance.

Performance analysis of wavelength converters based on cross-gain modulation in semiconductor-optical amplifiers

Abstract: An analytical theory describing all-optical wavelength converters based on cross-gain modulation (XGM) in semiconductor-optical amplifiers is derived. Our theory consists of two parts: a large-signal analysis yielding the transmission function for the signal, and a small-signal analysis in order to describe the transformation of the signal and probe intensity noise. Both the large-signal as well as the small-signal theory reveal similar performance for the co- and the counterpropagating injection scheme for bit rates up to 2.5 Gb/s. This is confirmed by computer simulations. Consequently, the counterpropagating configuration is preferable because the implementation is simpler and conversion to the same wavelength is possible. In order to increase the conversion efficiency it is better to reduce the average signal power than to increase the probe power, which additionally reduces the output power range. However, there is a tradeoff between conversion efficiency and output extinction ratio. According to the small-signal analysis, the relative-intensity noise (RIN) due to the probe and due to the amplified spontaneous emission is negligible. Moreover, the converted signal has a lower RIN than the input signal.

Low-loss and high-extinction-ratio silica-based strictly nonblocking 16/spl times/16 thermooptic matrix switch

Abstract: A low-loss and high-extinction-ratio silica-based 16/spl times/16 thermooptic matrix switch is demonstrated. The switch, which employs a double Mach-Zehnder interferometer switching unit and a matrix arrangement which reduces the total waveguide length, is fabricated with 0.75% refractive index difference waveguides on a 6-in silicon wafer. The average insertion loss and the average extinction ratio are 6.6 and 55 dB, respectively. The total power consumption is 17 W.

All-optical space switches with gain and principally ideal extinction ratios

Abstract: Asymmetric Mach-Zehnder interferometer (MZI) configurations are proposed to build all-optical space switches with gain and principally ideal extinction ratios. Actually, three asymmetries in MZI configurations with semiconductor optical amplifiers (SOA's) on their arms are discussed. The asymmetries in the all-optical switches are necessary to overcome the extinction ratio limitations that are due to the disturbing gain changes that arise when control signals are introduced into the SOA's to induce the necessary refractive index change for switching. Starting from a generic MZI configuration with SOA's on the arms, a description in terms of transmission matrices is used and applied to identify 1/spl times/2 and 2/spl times/2 all-optical switch configurations with high on-state transmissions and close to ideally large extinction ratios. The theoretical predictions are verified and found to be in excellent agreement with experiments for a switch with symmetric MZI splitters in a monolithically integrated InP waveguide version that allows operation with equally or unequally biased SOA's.

Fiberoptic transmitter using thermistor to maintain stable operating conditions over a range of temperature

Abstract: Techniques for controlling the operation of a laser diode to maintain optimum operating characteristics (i.e., fairly constant output power and extinction ratio) despite the fact that the threshold current and slope efficiency vary greatly over a the desired range of operating temperature. A laser driving circuit includes a bias current generator, a temperature-dependent modulation current generator, and a switching element for switching the modulation current on and off in accordance with a desired input pattern. The modulation current is caused to vary with temperature in a manner that compensates for the fact that the laser diode's slope efficiency varies with temperature.

Stacked thermo-optic switch, switch matrix and add-drop multiplexer having the stacked thermo-optic switch

Abstract: Cores of an optical waveguide forming a Y-branch structured thermo-optic switch are stacked in a direction perpendicular to a substrate, and a heater is disposed on a clad right above an area where the cores overlap, thereby utilizing a large temperature gradient by the heater in the direction perpendicular to the substrate. The resulting stacked thermo-optic switch is low in power consumption and signal loss and high in extinction ratio.

Laser modulation control method and apparatus

Abstract: Laser modulation control apparatus and methods which provide direct control of the transmitted optical extinction ratio of a semiconductor laser. A relatively low frequency and low amplitude pilot tone is superimposed on the signal used to drive the laser. Setting the amplitude of the pilot tone to a fixed fraction of the laser modulation current causes the transmitted optical power to vary a fixed fraction of the optical data amplitude at the pilot tone frequency. By using feedback to control the laser modulation current, the amplitude of the variation can be maintained at a desired value, which in turn maintains the transmitted optical data amplitude at a constant value, regardless of variations due to operating temperature or laser aging. A separate control loop is employed to maintain the average optical power at a fixed value. Since the optical data amplitude and the average optical power remain constant, the optical extinction ratio is also constant. Alternate embodiments are disclosed.

Tunable dual-wavelength-switching fiber grating laser

Abstract: We report a tunable dual-wavelength-switching fiber grating laser by exploiting the large homogeneous gain broadening in erbium (Er)-doped fiber to suppress simultaneous lasing. Wavelength switching was accomplished through a novel design which has two overlapping cavities sharing a single-gain medium. The loss corresponding to one of the lasing wavelengths can be modulated via an optical chopper. Output power of about 6 mW and extinction ratio up to 50 dB were observed. The lasing wavelengths were tunable and switching was demonstrated for wavelength separations ranging from 0.35 to 23.5 nm.

Proposed WDM cross connect using a planar arrangement of waveguide grating routers and phase shifters

Abstract: We propose a reconfigurable wavelength-division-multiplexing (WDM) cross connect consisting of two "interleave-chirped" waveguide grating routers connected by waveguides with phase shifters. For the 2 line/spl times/2 line case, any wavelength channel in one line can be exchanged with the same wavelength channel in the other line. For the P line/spl times/P line case, the channels can be switched in a cyclical fashion between lines. The device is compact with no waveguide crossings; is predicted to have relatively low and even losses for all channels; can theoretically achieve very high, fabrication-tolerant, switching extinction ratios; and can theoretically achieve a nearly excess-loss-free rectangular spectral response.

Wavelength-division multiplexing cross connect in InP

Abstract: We demonstrate a 2 line/spl times/2 line, 6 channel/spl times/200 GHz spacing, wavelength-division multiplexing (WDM) cross connect in InP consisting of two interleave chirped waveguide grating routers connected by a series of waveguides with current-controlled phase shifters. Employing a simple fabrication process, we achieved >21-dB extinction ratio, 10-12-dB on-chip loss, and switching currents <17 mA. The present device is, however, polarization sensitive.

Integrated optical waveguide polarizer on glass with a birefringent polymer overlay

Abstract: An integrated optical waveguide polarizer on glass is described. It is based on a filtering zone propagating only TE mode whereas the TM mode leaks out into a birefringent polymer simply deposited on the glass. The polymer is poled by a corona process. The measured polarization extinction ratio between TE and TM modes is better than 39 dB and the excess loss due to the filtering zone is less than 4 dB. The total loss is in the order of 7 dB.

Efficient Q-switched Ti:Er:LiNbO3 waveguide laser

Abstract: Diode-pumped Q-switched Ti:Er:LiNbO/sub 3/ waveguide lasers have been developed with a monolithically integrated folded Mach-Zehnder type modulator of high extinction ratio as the Q-switch. The lasers are operated at 1562 nm wavelength, emitting pulses of 4.3 ns halfwidth with up to 1.44 kW peak power at 1 kHz repetition frequency. Good agreement between experimental and theoretical results has been obtained.

High-extinction ratio and low-loss silica-based 8/spl times/8 thermooptic matrix switch

Abstract: A high-extinction ratio and low-loss silica-based 8/spl times/8 thermooptic matrix switch is demonstrated. The 8/spl times/8 matrix switch is realized by using a double Mach-Zehnder interferometer switching unit and a matrix arrangement which reduces the total waveguide length. The average extinction ratio and the average insertion loss are 60.3 and 5.2 dB, respectively.

Integrated optical intensity modulator and method for fabricating the same

Abstract: An integrated optical intensity modulator and a method for fabricating the same are provided. The integrated optical intensity modulator includes a substrate having spontaneous polarization, cut in a predetermined direction, an optical waveguide formed on the substrate, a plurality of domain-inversion areas having domains in the reverse direction of the spontaneous polarization, arranged in a staggered pattern around the optical waveguide, and a first electrode formed on the optical waveguide and second and third electordes formed on the substrates on the right and left of the optical waveguide, wherein if a predetermined voltage is applied to the electrode, a light wave is deflected and scattered in a domain-inversion area in accordance with a change of the refractive index of thedomain-inversion area in the optical waveguide and the refractive index of the spontaneous polarization area. According to the optical intensity modulator of the present invention, the domain-inversion structure of a ferroelectric material isformed in a staggered pattern around the optical waveguide, and an optical guided mode is deflected by an applied voltage, to thereby half driving voltage of the optical waveguide, and an area for deflecting the optical guided mode to the right and left can be formed in multiple stages, to thereby increase the extinction ratio.

Polarization-independent optical fiber modulator by use of polymer-dispersed liquid crystals

Abstract: Ultrasmall light modulators have been made by sandwiching a polymer-dispersed liquid crystal (PDLC) between two ferrules with optical fibers. The device can modulate light independent of the state of polarization, because the PDLC becomes transparent or opaque when either sufficient or no voltage is applied to the film. The PDLC was prepared by mixing and annealing a prepolymer and nematic liquid crystal with large anisotropy. An optical fiber modulator with a 30-μm thick PDLC film had an extinction ratio of 8:1–33:1, an insertion loss of 1.3 dB, and rise and decay times of 4 ms at a wavelength of 1.3 μm.

Wide-band polarization-independent tensile-strained InGaAs MQW-SOA gate

Abstract: A high-performance tensile-strained InGaAs multi-quantum-well semiconductor optical amplifier (MQW-SOA) gate developed for wavelength-division-multiplexing (WDM) applications is reported. The -0.47% InGaAs-strained SOA gate has a very low polarization dependence of 0.3 dB over a driving current between 30 and 60 mA and a wide-input signal wavelength range from 1530 to 1580 nm. The fabrication tolerance of the mesa stripe width is very large, ranging from 1.0 to 1.75 /spl mu/m. The MQW-SOA gate has an extinction ratio of more than 40 dB. The fiber-to-fiber lossless operation current is less than 50 mA over the fiber-amplifier gain band. The gating speed is less than 1 ns.

Integrated multistack waveguide polarizer

Abstract: Waveguide polarizers based on embedded thin metallic stacks are proposed. Highly efficient TM polarization is obtained for metal thicknesses smaller than the optical skin depth. The optimal single-metal-layer waveguide is found to yield an extinction ratio better than 12.2 dB/mm and a linear loss below 0.075 dB/mm. Experimental confirmation for this structure is also obtained in polymeric waveguides. Polarization efficiencies better than 100 dB/mm with linear losses below 2 dB/mm are calculated for multi-stack waveguides. This high performance is found to hold even if oxidation at metal-core boundaries is considered.

Record low-power all-optical semiconductor switch operation at ultrafast repetition rates above the carrier cutoff frequency.

Abstract: The switch repetition-rate limit of all-optical semiconductor switches, for which the dynamic extinction ratio decreases with increasing repetition rate, is examined and overcome. The extinction ratio is improved by optimization of the interferometer phase bias, which has previously been set to ?. The extinction-ratio increase accompanies a drastic change in the output pulse spectrum. Both the output pulse profiles and the spectra, before and after optimization, are successfully reproduced by simulation. As a result, switch repetition of 42 GHz (2.5 times higher than the semiconductor-carrier cutoff frequency) is achieved by use of 5-ps, 1548-nm pump pulses. What are believed to be record low input pump-pulse energies of 750 aJ (peak power, 140 µW) at 10 GHz and 6 fJ (1.1 mW) at 42 GHz are used.

All-optical wavelength conversion system comprising an optical discriminator

Abstract: The optical signal produced by a semiconductor-optical-amplifier based wavelength converter is passed through an optical discriminator. The resulting signal has improved extinction ratio for return-to-zero data and improved high-frequency response for both non-return-to-zero and return-to-zero data.

Direct-detection optical asynchronous CDMA systems with double optical hard-limiters: APD noise and thermal noise

Abstract: Performance of optical asynchronous code-division multiple-access (CDMA) systems with double optical hard-limiters is analyzed in the presence of avalanche photodiode (APD) noise and thermal noise. The following effects on the optimal thresholds of double optical hard-limiters and on-off keying (OOK) decoder are clarified: sequence codes, the number of users, the received laser power, and the modulation extinction ratio. The results show that the optical asynchronous CDMA systems with double optical hard-limiters have good performance in the presence of the APD noise and the thermal noise even when the number of simultaneous users is large. Moreover the optical asynchronous CDMA systems with double optical hard-limiters are shown to be practical in the respect of setting optimal thresholds.

Wavelength stabilizing apparatus of laser light source

Abstract: The light emitted by the laser diode 1 is put into an interference optical filter 5. The light passing through the interference optical filter 5 and the reflected light are respectively received in photo diodes PD1, PD2. Their output ratio is calculated by an adder 13, a subtracter 14, and a divider 15, and a wavelength signal is obtained. The difference of the output ratio and reference value is detected as error signal by an error detector 16, and the emission wavelength of the laser diode 1 is controlled so that the error signal may be zero.

Wafer-fused optoelectronics for switching

Abstract: Wafer fusion technique for realization of compact waveguide switches and three-dimensional (3-D) photonic integrated circuits is investigated theoretically and experimentally. Calculations based on beam propagation method show that very short vertical directional couplers with coupling lengths from 40 to 220 /spl mu/m and high extinction ratios from 20 to 32 dB can be realized. These extinction ratios can be further improved using a slight asymmetry in waveguide structure. The optical loss at the fused interface is investigated. Comparison of the transmission loss in InGaAsP-based ridge-loaded waveguide structures with and without a fused layer near the core region, reveals an excess loss of 1.1 dB/cm at 1.55 /spl mu/m wavelength. Fused straight vertical directional couplers have been fabricated and characterized. Waveguides separated by 0.6 /spl mu/m gap layer exhibit a coupling length of 62 /spl mu/m and a switching voltage of about 2.2 V. Implications for GaAs-based fused couplers for 850 nm applications will also be discussed.

High performance non-interferometric semiconductor-optical-amplifier/fibre-Bragg-grating wavelength converter

Abstract: The authors have demonstrated a high performance, non-interferometric, semiconductor-optical-amplifier/fibre-Bragg-grating wavelength converter requiring a record low switching power of < –12 dBm for return-to-zero data at 10 Gbit/s. The converted output is a non-inverting signal with an extinction ratio of 30. The transmission properties of the converted output in non-dispersion-shifted fibre are also investigated.

Wavelength converter for binary optical signals

Abstract: The invention relates to a wavelength converter including an interferometer structure for delivering an output optical signal, in which converter a first branch contains a first semiconductor optical amplifier and a second branch contains a second semiconductor optical amplifier, the amplifiers being coupled to a common probe laser, and said first amplifier being organized to receive a modulating input signal, said converter including regulator means for acting on the total optical power delivered to said amplifier in response to a negative feedback signal representative of the extinction ratio of the output signal. The invention is applicable to making routing systems using wavelength-division multiplexing.

Precise measurement of the extinction ratio of a polarization analyser

Abstract: We determined the extinction ratio of a polarization analyser on the basis of Malus' law by relating the transmitted light intensity to the analyser azimuth measured at only a small range of analyser azimuth angles around the minimum position, thus avoiding the requirement for an optical detector with a high dynamic range. To adjust the orientation of the analyser azimuth we manufactured a precise rotation stage which had an angular resolution of less than rad. The minimum value of the extinction ratio was , obtained for a polarization analyser of the Glan - Taylor type. To calibrate the apparatus we measured the Faraday rotation of a glass plate placed in a magnetic field in the optical path.

Design of finite-length metal-clad optical waveguide polarizer

Abstract: The performance of optical metal-clad waveguide polarizers is analyzed in this paper with a view to optimizing the extinction ratio, a condition for which power of the TM mode is completely attenuated is identified here. In general, such a condition corresponding to an infinitely high extinction ratio can be met for a wide range of buffer layer thicknesses by selection of metal film thickness and polarizer length. When a very thick (e.g., semi-infinitely thick) metal film is used, the aforementioned condition can be met with a properly chosen buffer layer thickness and polarizer length. The numerical results show that all the polarizers designed here for realization of infinitely high extinction ratios have either quite low or reasonably acceptable attenuations for the TE mode.

High-input-power saturation properties of a polarization-insensitive semiconductor Mach-Zehnder interferometer gate switch for WDM applications

Abstract: We propose that a polarization-insensitive Mach-Zehnder interferometer (MZI) switch is useful for optical gate elements, especially if multiwavelength signals are input. This device has high-input-power saturation properties, which shows that both the operating voltage and the extinction ratio do not change when the optical input power reaches at least +18 dBm. A high extinction ratio of 30 dB was achieved in the wide-wavelength range of 20 nm. Moreover, the extinction ratio can be improved by up to 45 dB by using a cascaded configuration to decrease crosstalk. These results indicate the MZI gate switch is well suited to wavelength-division multiplexing (WDM) network components.

Irradiation device for an alignment layer of a liquid crystal cell element

Abstract: Uniform irradiation of an entire region to be irradiated with polarized light for optical alignment of a liquid crystal cell element using a small polarization element is achieved by light, which contains UV radiation emitted from a lamp, being focused by an oval focusing mirror, and being incident via a first planar mirror and a polarization element using a multilayer film on an integrator lens which makes a uniform distribution of the portion of unpolarized light or the distribution of the illuminance of the polarized light in a certain direction and the distribution of the polarization direction. The extinction ratio of the polarized light emerging from the integrator lens is therefore made uniform over the entire region to be irradiated even if scattered light is incident on the polarization element. The light emerging from the integrator lens is incident on a bandpass filter via a shutter. The polarized light in a predetermined wavelength range is incident, via a second planar mirror, on a workpiece, such as a liquid crystal cell element or the like. Furthermore, a polarization element using the Brewster angle or the like can also be used.