dB Uniformity Research Articles

Effect of hybrid optical amplifier in multiwavelength fiber laser utilizing Sagnac loop mirror interferometer

This paper presents a multiwavelength fiber laser (MWFL) utilizing a Sagnac loop mirror (SLM) interferometer with a hybrid optical amplifier comprising a semiconductor optical amplifier (SOA) and an erbium-doped fiber amplifier (EDFA). Previously, no research reported MWFL based on SOA and EDFA combination utilizing SLM interferometer. The combination of a polarizer and SOA induces intensity-dependent loss mechanism at a certain polarization state. It is utilized to flatten and stabilize the multiwavelength spectrum. The laser produces maximum lasing lines of 65 channels within 5 dB uniformity and with 10 dB of extinction ratio. The removal of EDFA from the cavity reduces the peak power by 11 dB with the output spectrum shifted to shorter wavelength by 6 nm. Furthermore, the laser shows a significantly stable output with peak power fluctuation lower than 0.8 dB within 100 min of observation time.

Investigation on factors influencing flatness of a bidirectional SOA-based multiwavelength fiber laser

We investigate the flatness of the output spectrum in two multiwavelength fiber lasers (MWFLs) using two different configurations, unidirectional and bidirectional semiconductor optical amplifiers (SOAs). The most significant finding is the large variance in flatness values between the configurations where the unidirectional SOA is at 6.54 dB and the bidirectional SOA is at 1.45 dB. This is due to the lower total power and incomplete counter propagation in the cavity. The best SOA-based MWFL using a bidirectional SOA can generate 215 spectral lines within 5 dB uniformity. The multiwavelength spectrum is flat with a broad range, about 20 nm, owing to the property of spectral reshaping by the bidirectional amplification process in the SOA as well as complete counter propagation. Apart from the bidirectional SOA, the intensity-dependent loss (IDL) mechanism also contributes to the multiwavelength spectrum flatness. The adjustment of the half-wave plate (HWP) in the polarization controller (PC) affects the wavelength range and optical signal-to-noise ratio (OSNR). The MWFL shows excellent power stability, with the highest power deviation being only 0.95 dB.

Tunable multiwavelength fiber laser based on bidirectional SOA in conjunction with Sagnac loop mirror interferometer

A tunable multiwavelength fiber laser (MWFL) based on bidirectional semiconductor optical amplifier (SOA) in conjunction with a Sagnac loop mirror (SLM) interferometer is proposed. The best multiwavelength spectrum from this setup produces 164 lasing lines within 3 dB uniformity. The main study is to investigate the multiwavelength laser performance by varying the polarization state (PS) at two different locations of polarization controller (PC). Manipulation of a quarter-wave plate (QWP) of PC1 causes PS change before entering polarization-maintaining fiber (PMF) thus affecting the multiwavelength flatness and wavelength bandwidth. Meanwhile, manipulation of QWP of PC2 varied the output power of polarization beam splitter (PBS) and tuned the multiwavelength spectrum with almost similar performance. The multiwavelength tunability, extinction ratio (ER) difference and lasing lines difference is five nm, 2.4 dB and 48 when the QWP angle is adjusted from 0° until 70°, respectively. Lower SOA current reduced the multiwavelength flatness and number of lines. The laser output was found stable at a maximum of 0.31 dB power deviation during the 100 min of stability test.

Stable and Broad Multiwavelength Generation with the Assistance of Intensity Dependent Loss Mechanism based on Bidirectional SOA

Multiwavelength fiber laser is based on bidirectional semiconductor optical amplifier (SOA) is demonstrated. The multiwavelength spectrum from this setup produces 143 lasing lines within 5 dB uniformity. This bidirectional setup can maintain a flat multiwavelength lines with high peak power since both lights from SOA are fully utilized. The combination of polarization controllers (PCs), SOA and polarization beam combiner (PBC) induces an intensity dependent loss (IDL) mechanism which acts as the flatness element. The multiwavelength performance is investigated at different SOA current and PCs setting. Lower SOA current and different PC adjustment deteriorate multiwavelength performance. The laser is greatly stable since no laser fluctuation is found within 100 minutes of stability test.

Broad bandwidth SOA-based multiwavelength laser incorporating a bidirectional Lyot filter

We demonstrate a broad bandwidth multiwavelength laser based on a bidirectional Lyot filter and a semiconductor optical amplifier with a mechanism of intensity-dependent loss as the flatness agent. A wide bandwidth of a multiwavelength spectrum of 32.9 nm within a 5 dB uniformity is obtained under optimized polarization parameters. For this case, the number of generated lasing lines is 329 with a fixed wavelength separation of 0.1 nm. The power stability of this multiwavelength laser is less than 1.35 dB within 200 min time frame. This shows that the bidirectional Lyot filter provides an alternative option for multiwavelength generation in laser systems.

Optimized design of six-wave fiber optical parametric amplifiers by using a genetic algorithm.

A governing equation of the six-wave fiber optical parametric amplifier (FOPA) for the power and phase difference evolution of the six interacting waves is deduced. To optimize the gain of the six-wave FOPA, a multivariate stochastic optimization algorithm, i.e., the genetic algorithm (GA), is applied. The effect of pump depletion on the gain characteristic of the six-wave FOPA is emphasized and the effect of the fiber length, the wavelength, and the power of two pumps on bandwidth, flatness, and magnitude of the gain spectrum has also been studied. A broader and flatter six-wave FOPA gain is obtained by adopting optimum design parameters, which theoretically provide a uniform gain of 65dB with 0.3dB uniformity over a 110nm bandwidth for the six-wave FOPA.

Stable L-band multi-wavelength SOA fiber laser based on polarization rotation.

We propose and experimentally demonstrate a stable multi-wavelength fiber ring laser operating in the L-band with wavelength spacing of 25 GHz. The mechanism is induced by a polarization rotation intensity equalizer consisting of a semiconductor optical amplifier and polarization devices. A Fabry-Perot filter is inserted into the cavity to serve as a multi-wavelength selection device. Stable L-band multi-wavelength lasing with 3 dB uniformity of 21.2 nm, and simultaneous oscillation of 101 lines with wavelength spacing of 25 GHz, is obtained.

Design and fabrication of polymer-based multimode interference optical splitters

A polymer-based multimode interference optical splitter chip has been designed and fabricated. Fiber-waveguide coupling loss as well as the structure of the multimode waveguide are optimized in the design to achieve higher performance. A simple UV-based soft nanoimprint lithography (Soft UV-NIL) technique is adopted in the fabrication. Fluorinated acrylate resins, LFR, with different refractive indices are used in this work. Both the residual layer and waveguide deformation are improved by controlling the fabrication processes. An average of 12.98 dB insertion loss is obtained from 1×4 splitters with 1.08 dB uniformity and 0.05 dB polarization-dependent loss. The validity of the polymer optical splitters fabricated through Soft UV-NIL technique is demonstrated by software simulation as well as experimental works.

Design and fabrication of polymer-based 1 × 4 Y-branch splitters

A polymer-based Y-branch splitter chip has been designed and fabricated in this work. Fiber-waveguide coupling loss, propagation loss as well as bending loss are considered in the design to optimize the overall performance. A simple UV-based soft nanoimprint lithography (Soft UV-NIL) technique is adopted in the fabrication. Fluorinated acrylate resins produced by ChemOptics with different refractive indices are used. Residual layer and waveguide deformation are improved via controlling fabrication processes. An average 11.28dB insertion loss is obtained for 1×4 splitters with a 1.73dB uniformity, 0.06dB polarization dependent loss (PDL). The validity of the polymer optical splitters fabricated through Soft UV-NIL technique is demonstrated by software simulation as well as experimental works.

Multi-wavelength fiber laser based on self-seed light amplification and wavelength-dependent gain

In this paper, a multi-wavelength fiber laser based on self-seed light amplification and wavelength-dependent gain is proposed and demonstrated. A pumped erbium-doped fiber (EDF) in the linear cavity acts as the seed light source, which is also conducive to the gain equalization. A high power erbium-doped fiber amplifier (EDFA) is deployed for self-seed amplification, and a highly nonlinear fiber (HNLF) is incorporated in the ring cavity to alleviate the mode competition induced by the homogeneous gain broadening of EDF. In the experiments, 25-wavelength operation within 0.5dB uniformity is achieved with the extinction ratio of ~42dB using 500m HNLF, and 38-wavelength operation within 3dB uniformity is obtained with the extinction ratio of ~35dB using 1000m HNLF. Our proposed laser has more lasing wavelengths with a better uniformity and stability.

Broadly Tunable Fiber Laser Based on Merged Sagnac and Intermodal Interferences in Few-Mode High-Birefringence Fiber Loop Mirror

A broadly tunable fiber ring laser including a few-mode high-birefringence fiber (FM-HBF) loop mirror is proposed and demonstrated. The operation mechanism is based on simultaneous occurrence of Sagnac and intermodal interferences in the FM-HBF loop mirror and polarization dependence of the modal excitation in the FM-HBF. While adjusting only a polarization controller next to the FM-HBF in the loop arm, the lasing wavelength can be tuned at a discrete step defined by the intermodal interference. The tunable range exceeding 40 nm with sidemode suppression ratio over 40 dB and power uniformity better than 1 dB at a discrete step of about 2.2 nm has been successfully demonstrated for the proposed fiber ring laser.

1×2 Multimode interference couplers based on semiconductor hollow waveguides formed from omnidirectional reflectors

A 1x2 hollow multimode interference (MMI) coupler based on semiconductor hollow waveguides formed from omnidirectional reflectors (SHOW-ODR) is demonstrated. The device has a shorter coupling length than a conventional silicon-on-insulator MMI coupler. A 2 dB uniformity was achieved at operating wavelengths between 1520 and 1562 nm. The device exhibited a weak polarization dependence in the TE and TM modes.

Sol-gel multimode interference power splitters

We report on the design and fabrication of 1/spl times/32 MMI power splitters through the sol-gel process. The MMI splitter is designed for 1.55-/spl mu/m wavelength and characterized in terms of tolerance, wavelength response, and polarization sensitivity. The splitter is then UV-imprinted in aluminosilicate material coated on SiO/sub 2/. It is found that the responses of fabricated and designed splitter are in good agreement, with an excess loss of /spl sim/0.75 dB and power uniformity of /spl sim/0.95 dB.

Computer-generated waveguide holograms by double-ion exchange process in glass

A double-ion exchange process (potassium ion exchange with a subsequent silver ion exchange) is proposed for the fabrication of synthetic diffractive optical elements in glass waveguides. A computer-generated holographic guided-wave beam splitter with fanout to eight and 0.9 dB uniformity error is demonstrated.