Splitting-on-demand optical power splitters using multimode interference (MMI) waveguide with programmed modulations

Reconfigurable multi-channel optical power splitter is proposed and its optical properties are calculated. The device can dynamically reconfigure the number of splitting channels by providing programmed refractive index modulations on a multimode interference (MMI) waveguide. A reconfigurable 3-channel optical power splitter is designed to work as 1 × 1, 1 × 2 or 1 × 3 optical power splitter depending on the state of the heat electrodes using thermo-optic modulation, and the input light can be distributed to three output channels with sequential orders. The device can work in the whole C-band (1530-1565 nm) with extinction ratio better than −29.0 dB, excess loss better than −0.45 dB, imbalance better than 0.08 dB and polarization dependent loss (PDL) better than 0.14 dB. The design conception is scalable to a multi-channel splitting-on-demand optical power splitter which can divide input light to 1, 2, …, N output channels equally by using the 3-channel reconfigurable optical power splitter as a building block.     

All-optical NRZ-OOK-to-RZ-OOK format conversions with tunable duty cycles using nonlinear polarization rotation of a semiconductor optical amplifier

We experimentally demonstrate an all-optical 10 Gb/s format conversion from non-return-to-zero (NRZ) on-off-keying (OOK) to return-to-zero (RZ)-OOK with tunable duty cycle in the whole C-band using nonlinear polarization rotation (NPR) arising in an semiconductor optical amplifier (SOA). The experimental results show that, by tuning the polarizer at the SOA output, an RZ signal with tunable duty cycle from 33% to 66% could be obtained with an extinction ratio(ER) over 10 dB. In addition, we show that the NRZ-to-RZ conversion with duty cycle of 33-66% can be obtained with less than 1 dB power penalty at the bit error ratio (BER) of 10⁻⁹. The device can facilitate the cross-connection between optical transmission networks employing different modulation formats.     

All optical SR and D flip-flop employing XGM effect in semiconductor optical amplifiers

This paper presents a simple and novel scheme for all-optical SR and D flip-flop employing cross gain modulation (XGM) effect in two wideband semiconductor optical amplifiers. The proposed flip-flop has a fast response, with less than 20 ps transition times for both rising and falling edges. The FF speed-limit is mainly determined by the SOA recovery time and the intra-FF coupling length. The simulation results exhibit a contrast ratio of 13 dB between two states with an AM of less than 2.5 dB.The distinctive simplicity of the flip-flop implies reduced footprint and low power consumption which makes it ideal for photonic integration.     

Switchable dual-wavelength erbium-doped fiber-ring laser based on one polarization maintaining fiber Bragg grating in a Sagnac loop interferometer

A switchable erbium-doped fiber-ring laser providing dual-wavelength outputs with orthogonal polarizations when operating at room temperature is proposed. One polarization-maintaining fiber Bragg grating (PMFBG) in a Sagnac loop interferometer is used as the wavelength-selective filter. Due to the enhancement of the polarization hole burning (PHB) by the PMFBG, the laser can be designed to operate in stable dual-wavelength or wavelength-switching modes with a wavelength spacing of 0.336 nm at room temperature by adjusting a polarization controller (PC). The optical signal-to-noise ratio (OSNR) is over 42 dB. The amplitude variation over 90 min is less than 0.6 dB for both wavelengths.     

Frequency modulated and polarization maintaining fiber laser with narrow linewidth

A novel configuration of fiber laser with frequency modulation is presented. Frequency modulation, stable polarization state and narrow linewidth are realized by using the waveguide phase modulator, polarization maintaining devices and saturable absorber. It is shown that the laser output reaches 23 mW, linewidth is less than 1 kHz, polarization extinction ratio is higher than 20 dB and maximum value of frequency deviation can reach 7.5 MHz.     

Reconfigurable all-optical logic gate using four-wave mixing (FWM) in HNLF for NRZ-PolSK signal

We demonstrate a reconfigurable all-optical logic gate for NRZ-PolSK signal based on FWM in a highly nonlinear fiber at 10 Gb/s. Half subtracter, XOR, AB?, āB or XNOR, AND, and NOR logic gates can be implemented simultaneously. The input power for the HNLF is optimized to be as low as about 15.2 dBm and the high Q factors above 8 dB for eye diagrams are achieved. Experimental results show Q factors of AB?, āB, AND, and NOR were higher than those of XOR, and XNOR. Error-free operation is achieved experimentally for 10 Gb/s 2⁷-1 pseudorandom bit sequence (PRBS) data. Power penalties for the logic gate are less than 3 dB. Simulation analysis about the wavelength characteristic for all logic gates is given and it predicts that the reconfigurable logic gate can realize error-free operation when the wavelength separation is less than 5 nm.     

Experimental demonstration of polarization multiplexing for simultaneously providing broadband wireless and wired access

A fiber-based wavelength-division-multiplexing (WDM) network utilizing polarization multiplexing (PolMUX) is proposed to simultaneously provide broadband wireless and wired services. In such a dual-service access network, the wireless and wired services are separately delivered in two orthogonal states of polarization with well independence in a single WDM channel. The impact of several polarization-dependent interferences becomes insignificant due to the relatively short transmission distance in access networks. The feasibility of PolMUX is experimentally demonstrated with a power penalty at BER = 10^-9 of about 0.5 dB and 1 dB for 2.5 Gb/s wired and wireless downstream services, respectively. The proposed system is compatible with the current reported techniques in either WDM passive optical networks (WDM-PON) or radio-over-fiber (ROF) systems.     

Polarization beam splitter with wide bandwidth in air-hole-based periodic dielectric waveguides

A polarization beam splitter with wide bandwidth and simple structure in air-hole-based periodic dielectric waveguides has been proposed and designed. Operation principle of the device is based on different directional coupling properties of beams in TE and TM polarizations in parallel periodic dielectric waveguides. Performances have been evaluated by a finite-difference time-domain simulation. Results show that the polarization beam splitter provides a wide bandwidth of 113 nm with both a high extinction ratio (higher than 21 dB) and a low insertion loss (less than 1.5 dB) for optical communication wavelengths at ∼1.55 μm. Moreover, the performances of the polarization beam splitter are insensitive to longitudinal alignment errors in the coupling region, which is desirable for device fabrication and practical application.     

Switchable single-longitudinal-mode dual-wavelength erbium-doped fiber ring laser based on one polarization-maintaining fiber Bragg grating incorporating saturable absorber and feedback fiber loop

Switchable single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber ring laser based on one polarization-maintaining fiber Bragg grating (PMFBG) is demonstrated. Due to the enhancement of the polarization hole burning (PHB) by the PMFBG, the laser can be designed to operate in stable dual-wavelength or wavelength-switching modes with a wavelength spacing of 0.336 nm at room temperature by adjusting a polarization controller (PC). The stable SLM operation is guaranteed by a compound-ring cavity and a saturable absorber (SA). The optical signal-to-noise ratio (OSNR) is over 45 dB. The amplitude variation in nearly one and half an hour is less than 0.2 dB.     

Optical alignment tolerances in double-side irradiated self-written waveguide-induced fiber arrays packages

In this paper, we present our experimental study on the optical alignment tolerance between the couplings of single-mode fibers (SMFs) connected with a double-side irradiation-induced self-written waveguide (SWW). The study firstly focuses on the coupling of two SMFs and then on the two fiber arrays (FAs) for parallel optical communication. The SWW was formed in dye-dispersed epoxy materials by the photopolymerization technique. Rhodamine 6G dye was dispersed in epoxy, which is commonly used in the photonic packaging industry as a bonding adhesive. Using double-side irradiated SWW, we found the alignment tolerance for such optical interconnect to relax significantly. All the formed SWWs were evaluated in terms of optical loss. In our study, up to 4 µm misalignment tolerance was allowed for only 1 dB loss penalty. In addition, the optical interconnect formed by this technique was also able to tolerate up to ± 10 µm lateral shift with only 1 dB extra loss. The wavelength-dependent loss (from 1520 to 1610 nm) and polarization-dependent loss were less than 0.4 dB. The double-side irradiated SWW-induced couplings between two FAs also provided low optical loss. They were found to be less sensitive to temperature changes, and no significant distortion in the digital signal transmission test was observed. We believe that the findings are useful and applicable to other dye-dispersed epoxy material systems for relaxing the alignment tolerance of the optical interconnects in various photonic packaging situations.     

Multi parameter optimization of Raman Fiber Amplifier using genetic algorithm for S band dense wavelength division multiplexed system

A simple genetic algorithm is implemented to perform multi parameter optimization of Raman Fiber Amplifier for 100 channel S band dense wavelength division multiplexed system at 25 GHz interval. A cost effective system using single Raman pump is investigated aiming at maximum average gain. The single counter propagating pump is optimized to frequency of 211.528 THz and 652.93 mW power level with optimum Raman fiber length of 44.064 Km. There is evidence to show that the optimum solution presents a small gain variation (less than 3 dB) over an effective bandwidth covering 197–199.475 THz. The optimized configuration enabled an adequate system performance in terms of acceptable Q-factor (19.52 dB) and BER (1.46 × 10⁻²¹).     

Tunable double-clad ytterbium-doped fiber laser based on a double-pass Mach-Zehnder interferometer

We have demonstrated an adjustable double-clad Yb³⁺-doped fiber laser using a double-pass Mach-Zehnder interferometer. The laser is adjustable over a range of 40 nm from 1064 nm to 1104 nm. By adjusting the state of the polarization controller, which is placed in the double-pass Mach-Zehnder interferometer, we obtained central lasing wavelengths that can be accurately tuned with controllable spacing between different tunable wavelengths. The laser has a side mode suppression ratio of 42 dB, the 3 dB spectral width is less than 0.2 nm, and the slope efficiencies at 1068 nm, 1082 nm and 1098 nm are 23%, 32% and 26%, respectively. In addition, we have experimentally observed tunable multi-wavelengths lasing output.     

Incorporate, switchable dual-wavelength fiber laser with Bragg gratings written in a polarization-maintaining erbium-doped fiber

A stable, incorporate and switchable dual-wavelength fiber laser with two fiber Bragg gratings written in a photosensitive and polarization-maintaining erbium-doped fiber directly, that is, without splices in the laser cavity, is proposed and demonstrated. Simultaneous dual-wavelength oscillation is achieved at room temperature with a wavelength spacing of 0.343 nm. The power fluctuation and wavelength shift of single-wavelength oscillations are measured to be less than 0.24 dB and 0.013 nm over 2 h. The wavelength switchability between single- and dual-wavelength oscillations is realized by altering the voltage upon the electrostrictive ceramic actuator.     

Tunable and switchable multi-wavelength Erbium-doped photonic crystal fiber ring laser incorporating a length of highly nonlinear photonic crystal fiber

A tunable and switchable multi-wavelength Erbium-doped photonic crystal fiber ring laser incorporating a length of single-mode highly nonlinear photonic crystal fiber is proposed and demonstrated experimentally. Stable dual-wavelength and triple-wavelength operations at room temperature are achieved by employing the highly nonlinear photonic crystal fiber to induce four-wave mixing effect and a polarization controller to vary the polarization states of propagation lights in the laser cavity. The laser cavity is free from any wavelength selection components. The laser obtains maximal 30 dB signal-to-noise ratio and the peak power fluctuations of lasing lines are less than 1.39 dB.     

Switchable triple-wavelength erbium-doped fiber laser using a single fiber Bragg grating in polarization-maintaining fiber

A stable and narrow wavelength spacing multiwavelength erbium-doped fiber laser is proposed and demonstrated. The laser can produce simultaneous dual- and triple-wavelength lasing oscillations with a narrow wavelength spacing of less than 0.1 nm via using a single fiber Bragg gratings written in polarization-maintaining (PM) fiber. By adjusting polarization controller, the wavelength spacing of dual-wavelength lasing oscillations can be tuned to as small as 0.032 nm. The maximum amplitude variation for every lasing wavelength is less than 0.5 dB. The room-temperature operation principle is based on the polarization hole burning and deeply saturated effect in an ordinary erbium-doped fiber ring laser (EDFRL). The laser has the advantages of simple all-fiber configuration, low cost, high stability and operating at room temperature.     

Experimental study of SOA-based NRZ-to-PRZ conversion and distortion elimination of amplified NRZ signal using spectral filtering

We experimentally study both reshaping of nonreturn-to-zero (NRZ) signal and NRZ to pseudoreturn-to-zero (PRZ) format conversion based on self-phase modulation of a semiconductor optical amplifier (SOA) and detuning an optical bandpass filter (OBF). When an OBF with 1 nm bandwidth is blue shifted by 0.8 nm, the distortion of the amplified NRZ signal at 10 Gbit/s is shown to be eliminated completely. When an OBF with 0.32 nm bandwidth is red shifted by 0.42 nm from the carrier frequency, NRZ-to-PRZ conversion at 10 Gbit/s is obtained. A holding beam is used to suppress the SOA noise and improve the output extinction ratio (ER). The output ER of both the reshaped NRZ and the converted PRZ is larger than 10 dB when the signal wavelength is longer than 1540 nm, and an input power dynamic range from −7 dBm to 2 dBm is obtained at a signal wavelength of 1563.6 nm. The average power of the reshaped NRZ signal is about 3 dBm at an input power dynamic range of 13 dB. The amplitude fluctuation of the converted PRZ signal is around 1.6 dB.     

Switchable quadruple-wavelength erbium-doped fiber ring laser based on two-segment Lyot-Sagnac filter

We propose and demonstrate a novel switchable quadruple-wavelength erbium-doped fiber ring laser (EDFL) based on two-segment Lyot-Sagnac filter which is used as the wavelength-selective filter. Due to the deeply saturated spectral hole-burning (SHB) effect in an ordinary erbium-doped fiber, the laser realizes stable single-wavelength, dual-wavelength, triple-wavelength, and quadruple-wavelength output by controlling two polarization controllers (PCs) appropriately. The optical signal-to-noise ratio (OSNR) is over 30 dB. The peak fluctuation is less than ~2 dB over 1.5 h at room temperature.     

A multi-channel full-duplex 60-GHz-band radio-over-fiber system

We propose and simulate a novel full-duplex radio-over-fiber system using a single light source at central station (CS). The scheme is employed to generate 60-GHz optical millimeter wave at CS for down-link transmission while the same optical carrier is reused at base station for up-link connection. There is no additional laser source for the upstream data generation in the base station. The bidirectional full-duplex 2.5 Gb/s data are successfully transmitted over 40 km standard single-mode fiber (SMF). The power penalty for the down-link data after transmission over 40 km SMF is less than 0.6 dB, while for the up-link data, the power penalty after transmission over 40 km SMF is neglected. This system shows good performance over long-distance delivery and has important applicable value in high radio frequency (RF) sector and multi-channel full-duplex system.     

Experimental and theoretical studies on a double-pass C-band bismuth-based erbium-doped fiber amplifier

Performance of a Bismuth-based Erbium-doped fiber amplifier is experimentally and theoretically investigated using 1480 nm pumping with double-pass scheme. In the theoretical analysis, the rate and power propagation equations are solved to examine the optimum length for the C-band operation as well as the gain and noise figure characteristics. The calculated small signal gain is 38 dB with gain variation of less than 3 dB. The measured gain is 4 dB lower due to spurious reflections which were ignored in the theoretical analysis. At input signal power of 0 dBm, a gain of 14.5 dB is obtained experimentally with gain variation of less than 1 dB within the wavelength region from 1530 to 1565 nm. The noise figure is less than 12 dB within this region.     

Fabrication of low OH loss holey fibers with varying air hole sizes and their optical properties

We experimentally investigate a flexible fabrication technique for low OH and transmission losses holey fibers with a Ge-doped core and air holes in a silica cladding region. Versatile holey fibers of different size, pitch, and shape of air holes were achieved by controlling the temperature and heating time of the holey fiber preform. In addition, we suppress the OH loss of less than ∼0.323 dB/km at 1383 nm. After fabricating holey fibers, we measure their optical properties including cut-off wavelength, mode field diameter, splicing loss, dispersion, bending loss, and polarization dependent loss based on the size of air holes. The total transmission loss was measured to be ∼0.226 dB/km at 1550 nm by improving the fabrication process. After fabricating optical patch cord based on holey fibers, we measured the long-term stability of the fabricated holey fiber by using the temperature cycling technique for 24 and obtained low power fluctuation of 0.2 dB. We achieve the high quality holey fiber with a low bending loss of ∼0.04 dB/turn under a bending radius of 2.5 mm at 1550 nm. We also obtain a tunable band rejection filter with a number of bending turns.