Experimental characterization of phase tuning using fine wavelength offsets in a tunable complex-coefficient optical tapped-delay-line.

We use fine-detuning of pump wavelengths to adjust the tap phases in a complex-coefficient optical tapped-delay-line that utilizes conversion/dispersion-based delays and nonlinear wave mixing. Full 2π phase tuning is demonstrated by detuning the frequency of laser pumps by <20 GHz, which shows close agreement with theory.

Transcanalicular diode laser assisted dacryocystorhinostomy in primary acquired nasolacrimal duct obstruction: 2-year follow up.

PURPOSE: To evaluate the success rate of 980 nm transcanalicular diode laser-assisted dacryocystorhinostomy (TDL-DCR) in patients with primary acquired nasolacrimal duct obstruction (PANDO) and to consider the time and the reasons of failure. METHODS: Hundred and thirty eyes of 125 patients who underwent of TDL-DCR for the treatment of PANDO are included in this retrospective, noncomparative, nonrandomized, interventional study. The mean follow-up time was 24.29 months (range 8-34 months). Functional success was described as disappearance of epiphora and presence of a patent ostium on lacrimal irrigation. Anatomical success was described as a patent ostium to irrigation but continuing epiphora. Patients with persistent epiphora and a closed ostium were classified as a surgical failure. RESULTS: At third month follow up, 85.4% of cases had complete resolution of their symptoms. The functional success rate decreased to 67.7% at 6 months, to 63.3% at first year, and to 60.3% at second year, while the patency of the lacrimal drainage system was restored in 93.1%, 74.6%, 69.5%, and 68.2% of the cases, respectively. The average total amount of delivered laser energy was 1322.7 J. No correlation could be found between the age of the patient, delivered laser energy, and the surgical success (p = 0.38, p = 0.62). CONCLUSIONS: Transcanalicular diode laser-assisted DCR is a fast and relatively easy alternative surgical method, which avoids a facial skin scar, to treat PANDO. The functional success rate is higher in the first months but decreases to low 60 %'s at the end of first year and remains the same at the second-year follow up.

Coherent correlator and equalizer using a reconfigurable all-optical tapped delay line.

We experimentally demonstrate a reconfigurable optical tapped delay line in conjunction with coherent detection to search multiple patterns among quadrature phase shift keying (QPSK) symbols in 20 Gbaud data channel and also to equalize 20 and 31 Gbaud QPSK, 20 Gbaud 8 phase shift keying (PSK), and 16 QAM signals. Multiple patterns are searched successfully on QPSK signals, and correlation peaks are obtained at the matched patterns. QPSK, 8 PSK, and 16 QAM signals are also successfully recovered after 25 km of SMF-28 with average EVMs of 8.3%, 8.9%, and 7.8%. A penalty of <1 dB optical signal to noise penalty is achieved for a 20 Gbaud QPSK signal distorted by up to 400 ps/nm dispersion.

Reconfigurable optical quadrature amplitude modulation converter/encoder using a tunable complex coefficient optical tapped delay line.

We experimentally demonstrate a reconfigurable optical converter/encoder for quadrature amplitude modulated (QAM) signals. The system utilizes nonlinear wavelength multicasting, conversion-dispersion delays, and simultaneous nonlinear multiplexing and sampling. We show baud rate tunability (31 and 20 Gbaud) and reconfigurable conversions from lower-order QAM signals to higher-order QAM signals (e.g., 64-QAM).

True time delays using conversion/dispersion with flat magnitude response for wideband analog RF signals.

We demonstrate optical true time delays using wavelength conversion coupled with chromatic dispersion. The transfer function of the delay system is investigated, and it is shown that 3-dB bandwidth of the system can be increased over 40 GHz by using offset pumps. A flat magnitude response (<1 dB peak-peak, 0.2 dB RMS deviation) is achieved in the 1-30 GHz band. Calculated matched filter output to LFM pulses shows good performance, maintaining a > 30 dB peak-to-sidelobe-ratio. The effect of pump depletion during wavelength conversion is also investigated.

UWB monocycle pulse generation using two-photon absorption in a silicon waveguide.

We propose and experimentally demonstrate ultrawideband monocycle pulse generation using nondegenerate two-photon absorption in a silicon waveguide. The free-carrier absorption induced pulse tail at the rising edge of inverted probe pulse is largely compensated by the overlapped pump pulse and results in a symmetric negative monocycle pulse. A 143 ps Gaussian monocycle pulse is successfully obtained with a 131.7% fractional 10 dB bandwidth using a 68 ps pulsed pump. The 10 dB bandwidth and center frequency of the RF spectrum for the generated monocycle pulse can be largely tuned using an optical delay line. An operational bandwidth of 30 nm is demonstrated experimentally with stable performance, and larger optical bandwidth is expected.

Demonstration of channel-spacing-tunable demultiplexing of optical orthogonal-frequency-division-multiplexed subcarriers utilizing reconfigurable all-optical discrete Fourier transform.

We experimentally demonstrate a tunable and reconfigurable optical discrete Fourier transform (DFT) to demultiplex orthogonal-frequency-division-multiplexed subcarriers with 2/3/4 subcarriers at 20/40 GHz frequency spacing. An average power penalty of ~5 dB (~3.5) at bit error ratio of 10(-9) is achieved for 4×20 Gbit/s (4×10 Gbit/s) OFDM signal with 20 GHz frequency spacing.

Experimental performance of a fully tunable complex-coefficient optical FIR filter using wavelength conversion and chromatic dispersion.

We experimentally characterize the performance of a continuously tunable all-optical complex-coefficient finite-impulse-response (FIR) filter that exploits nonlinear signal processing (multiplexing and multicasting) and conversion-dispersion-based optical delays. Various length (three and four) optical FIR filters with different tap amplitudes (from 0 to -9 dB), tap phases (from 0 to 2π), and tap delays (~37.4 ps and 25 ps) are realized, showing reconfiguration and tuning capabilities of this FIR filter. The measured frequency responses show close agreement with the theoretical filter responses.

Sweep-free distributed Brillouin time-domain analyzer (SF-BOTDA).

A frequency-sweep-free method for distributed Brillouin sensing is proposed, having the potential for fast dynamic strain measurements. In this reported implementation of the method, multiple probe waves with carefully chosen optical frequencies simultaneously propagate in the fiber against an equal number of sequentially-launched, short pump pulses of matching frequencies, where each of pump-probe pair replaces one sweeping step in the classical BOTDA technique. Experimentally, distributed sensing is demonstrated with a spatial resolution of a few meters.

10 Gbit/s tributary channel exchange of 160 Gbit/ssignals using periodically poled lithium niobate.

We propose and demonstrate data exchange in both the wavelength and time domains at a fine granularity, i.e., low-speed tributary channel exchange of wavelength-division multiplexed high-speed optical time-division multiplexed signals. Using the parametric depletion effect of cascaded second-order nonlinear interactions in a periodically poled lithium niobate (PPLN) waveguide, we experimentally implement 10 Gbit/s tributary channel exchange between two 160 Gbit/s signals with a power penalty of less than 4 dB at a bit-error rate of 10(-9). Moreover, taking into account the waveguide propagation loss, we derive analytical solutions to investigate the signal depletion (SD) and extinction ratio (ER) performance of the PPLN-based data exchange. The theoretical analyses indicate that low waveguide propagation loss benefits large achievable SD and ER.

Preconversion phase modulation of input differential phase-shift-keying signals for wavelength conversion and multicasting applications using phase-modulated pumps.

We demonstrate a method to use phase-modulated pumps for multicasting of return-to-zero differential phase-shift keying (RZ-DPSK) signals. The method uses phase modulation of the input signal along with the co-phase-modulated pumps prior to wavelength conversion. Nine copies of a 50 Gbit/s RZ-DPSK data signal are generated via four-wave mixing with an average conversion efficiency of ∼0 dB. An average receiver sensitivity penalty of ∼1.9 dB is observed at a bit-error rate of 10(-9) with a worst case of 2.3 dB. The effects of synchronization errors and phase-modulation frequencies up to 5 GHz are investigated.

Idiopathic and secondary epiretinal membranes: do they differ in terms of morphology? An optical coherence tomography-based study.

PURPOSE: The purpose of this study was to define the morphologic differences in idiopathic and secondary epiretinal membranes (ERMs) using a time domain optical coherence tomography. METHODS: The medical records and optical coherence tomography images of 293 eyes of 236 consecutive patients diagnosed to have ERM were evaluated retrospectively. Demographic features, best-corrected visual acuities, central macular thickness, membrane attachment patterns, macular changes, and the presence of posterior retinal detachment at the time of diagnosis were compared between the groups (idiopathic group, n = 125 eyes; secondary group, n = 168 eyes). RESULTS: The mean age was higher among idiopathic ERMs (67 ± 9 vs. 62 ± 10 years, P = 0.001). In the secondary group, best-corrected visual acuity was estimated to be worse (P < 0.001) and central macular thickness higher (P = 0.02) than the idiopathic group. In both groups, ERMs were mostly diagnosed at Grade 1 level. Diffuse attachment was more common in both of the groups. Among macular changes, only cystoid macular degeneration differed significantly between the groups (P = 0.0001). CONCLUSION: Idiopathic and secondary ERMs were estimated to differ significantly at the time of diagnosis in terms of age, visual acuities, macular thickness, presence of cystoid macular degeneration, and posterior vitreous detachment. These parameters may assist the retinal surgeon in the treatment process of ERM.

Orthogonal tributary channel exchange of 160-Gbit/s pol-muxed DPSK signal.

We report the orthogonal tributary channel exchange of a polarization-multiplexed (pol-muxed) differential phase-shift keying (DPSK) optical time-division multiplexed (OTDM) signal by exploiting the Kerr effect-induced nonlinear birefringence in a highly nonlinear fiber (HNLF). We first implement Kerr effect-based 40-to-10, 80-to-10, and 160-to-10 Gbit/s demultiplexing of DPSK OTDM signals with power penalties of less than 0.5, 1.5, and 2.6 dB, respectively, at a bit-error rate (BER) of 10(-9). We further demonstrate 10-Gbit/s tributary channel exchange between two orthogonal polarizations of a 160-Gbit/s pol-muxed DPSK OTDM signal with a power penalty of less than 4 dB at a BER of 10(-9). Moreover, Jones matrix analyses are applied to the orthogonal polarization exchange, indicating the exchange condition of orthogonal polarization exchange with the characteristic of transparency to the modulation format. The exchange performance is analyzed in terms of the extinction ratio (ER) of the newly converted signal to the original residual signal. The dynamic range of the product of nonlinear coefficient, pump power, and effective fiber length, the dynamic range of pump power, the impact and tolerance of pump polarization offset are discussed to characterize and optimize the performance of orthogonal polarization exchange.

Eightfold 40-320 Gbit/s phase-coherent multiplexing and 320-40 Gbit/s demultiplexing using highly nonlinear fibers.

We experimentally demonstrate 40-320Gbit/s phase-coherent multiplexing based on cross-phase modulation and subsequent 320-40Gbit/s demultiplexing using cross-phase-modulation-induced frequency shift in highly nonlinear fibers. An average penalty of approximately 7dB at a 10(-9) bit-error rate is observed after the nonlinear processes. We also show the generation of a phase-coherent 320GHz optical pulse train. A delay-line interferometer based on differential group delay is used to verify the phase coherence characteristic of the multiplexed 320Gbit/s signal and the generated 320GHz pulses.

40 Gbit/s optical data exchange between wavelength-division-multiplexed channels using a periodically poled lithium niobate waveguide.

We propose a time- and channel-selective optical data exchange between wavelength-division-multiplexed (WDM) channels by exploiting the cascaded second-order parametric nonlinear interactions in a periodically poled lithium niobate (PPLN) waveguide. It is observed that the PPLN-based optical data exchange provides nearly symmetric performance with signals located in the short- and long-wavelength ranges. Optical data exchange between two WDM channels is realized with a power penalty of less than 1.5 dB at 10 Gbit/s and 3 dB at 40 Gbit/s at a bit-error rate of 10(-9). We demonstrate the 40 Gbit/s channel-selective optical data exchange between four WDM channels with a power penalty of approximately 4 dB.

Bit-rate-variable and order-switchable optical multiplexing of high-speed pseudorandom bit sequence using optical delays.

We experimentally demonstrate high-speed optical pseudorandom bit sequence (PRBS) multiplexing with coarse and fine bit-rate tuning capability and a switchable order using optical delays. Data multiplexing of 80 Gbit/s and 160 Gbit/s is shown, each with a tunable rate using a conversion/dispersion-based continuously tunable optical delay and tunable PRBS order with large switchable fiber delays. A 7% bit-rate tunability, i.e., 80-85.6 Gbit/s and 160-171.2 Gbit/s, is shown for both 2(7)-1 and 2(15)-1 PRBS. The rf spectra before and after multiplexing are measured in each case and show a suppression ratio of >30 dB, exhibiting the expected PRBS spectral characteristics.

Phase-transparent optical data exchange of 40 Gbit/s differential phase-shift keying signals.

We report the phase-transparent optical data exchange of differential phase-shift keying (DPSK) signals by exploiting the parametric depletion of nondegenerate four-wave mixing (FWM) in a highly nonlinear fiber. Theoretical analyses of nondegenerate FWM involving two signals and two pumps are presented. Analytical solutions are derived, indicating the exchange condition and the feasibility of phase-transparent data exchange. Optical data exchange between 10.7 Gbit/s non-return-to-zero DPSK (NRZ-DPSK) and return-to-zero DPSK signals is implemented with a power penalty of approximately 1.5 dB at a bit-error rate (BER) of 10(-9). Moreover, we demonstrate phase-transparent optical data exchange between two 40 Gbit/s NRZ-DPSK signals with a power penalty of approximately 4.5 dB at a BER of 10(-9).

Pneumatic displacement of acute submacular hemorrhage with and without the use of tissue plasminogen activator.

PURPOSE: To evaluate the efficacy of C(3)F(8) gas-assisted pneumatic displacement in the treatment of massive submacular hemorrhage, with and without the use of tissue plasminogen activator (tPA). METHODS: Twenty-one eyes of 21 patients with recently developed (up to 10 days) dense submacular hemorrhage underwent intravitreal injection of pure C(3)F(8) gas (0.4-0.5 mL) followed by face-down positioning for pneumatic displacement. Seven of them received additional intravitreal injection of 25-50 microg tPA. The primary etiology of submacular hemorrhage was age-related macular degeneration (n=16), myopic choroidal neovascularization (n=2), retinal arterial macroaneurysm (n=2), and trauma (n=1). Visual acuity and displacement of hemorrhage were the main outcome measures. RESULTS: Follow-up period was 6-12 months. Effective displacement of hemorrhage was obtained in 20 of 21 patients within 7 days. Final median Snellen visual acuity (0.18) was found significantly improved compared to baseline (0.03) (p<0.001). Visual acuity improvement was similar in both groups (p=0.72). CONCLUSIONS: Intravitreal injection of C(3)F(8) effectively displaced thick submacular hemorrhage and improved visual acuity independently from primary cause. Additional tPA use in this study had no impact on the final outcomes.

Pars plana vitrectomy results of exogenous endophthalmitis in children.

PURPOSE: To identify the etiology, culture results, pars plana vitrectomy results, complications, and visual outcome of exogenous endophthalmitis in children. METHODS: Seven eyes of 7 consecutive pediatric patients who were treated and followed up for exogenous endophthalmitis between February 2006 and June 2008 were included in this study. The etiology of endophthalmos was penetrating eye injuries in 4 eyes and intraocular surgery in 3 eyes. Combined pars plana vitrectomy and intravitreal vancomycin plus ceftazidime injection were performed on all 7 eyes. Anterior chamber fluid and vitreous cultures were taken from all eyes. The patient files were inspected retrospectively. RESULTS: Mean follow-up time was 10.3 months (4-16 months). Mean age of the patients was 8.5 years (3-14 years). At baseline, visual acuity values of the patients were light perception (n=2), hand movements (n=4), and counting fingers from 1 meter (n=1). At final examination, visual acuity improved in 5 eyes, stayed the same in 1 eye, and decreased in 1 eye. Positive culture results were obtained in 3 eyes: alpha hemolytic Streptococcus (n=2) and coagulase-negative Staphylococcus (n=1). Complications seen after vitreoretinal surgery were transient ocular hypertension, emulsification of silicone oil, phthisis bulbi, and secondary retinal detachment. CONCLUSIONS: Early pars plana vitrectomy and intravitreal vancomycin plus ceftazidime injection improved anatomic and functional success in pediatric eyes with exogenous endophthalmitis.

Controllable optical demultiplexing using continuously tunable optical parametric delay at 160 Gbit/s with <0.1 ps resolution.

We experimentally demonstrate the use of continuously tunable optical parametric delay at 160 Gbit/s, based on conversion/dispersion for demultiplexing a 160 Gbit/s signal to 40 Gbit/s. A 15.2 ns delay is shown for a 160 Gbit/s signal, with <0.1 ps resolution, achieved by inserting cascaded acousto-optic modulators after the pump laser for delay fine tuning.