Xiangfei Chen

Dual-wavelength erbium-doped fiber laser with a simple linear cavity and its application in microwave generation

A single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber (EDF) laser based on a simple linear cavity is proposed and demonstrated. The SLM operation is achieved by incorporating a dual-phase-shift fiber grating with two ultranarrow transmission bands. Due to the gain grating produced by spatial hole-burning in the EDF, the proposed linear cavity supports dual-wavelength oscillation at room temperature with a wavelength interval of 27 pm. The laser output is heterodyned on a photodetector and the generated microwave signal has a linewidth <20 kHz without any feedback.

Stable Dual-Wavelength DFB Fiber Laser With Separate Resonant Cavities and Its Application in Tunable Microwave Generation

A single-longitudinal-mode dual-wavelength distributed feedback fiber laser with a wavelength spacing of 0.312 nm is proposed and demonstrated. Based on two spatially separated resonant cavities in a single fiber Bragg grating made by a simple method, stable dual-wavelength lasing is established. Then, a 38.67-GHz microwave signal generated by beating the two lasing wavelengths is obtained with a 3-dB bandwidth of ~6 kHz and a frequency drift <5 MHz without any feedback mechanism. As a potential application of this device, a tunable microwave source ranging from 18.67 to 58.67 GHz (with a small discontinuity) is proposed and partially demonstrated

High channel-count comb filter based on chirped sampled fiber Bragg grating and phase shift

Based on strongly chirped sampled fiber Bragg grating and phase shifts, a novel approach to obtain high channel-count comb filters is proposed in this letter. Various channel spacing can be achieved by a single strongly chirped phase mask where the required phase shifts can be gained by a precise translation stage. Comb filters with channel spacing of 50, 100, and 200 GHz are then designed with the same phase mask. Experimentally, a 35-channel 100-GHz channel-spacing comb filter is fabricated, from which one can expect that high-performance comb filter with various channel spacing can be fabricated by conventional technology.

Equivalent phase shift in a fiber Bragg grating achieved by changing the sampling period

It is proposed and demonstrated experimentally for the first time to achieve the desired phase shifts within one channel of a sampled Bragg grating by changing the sampling period. Only ordinary phase masks and submicrometer precision are needed, leading to improved flexibility, repeatability, and cost-effectiveness in fiber Bragg grating design and fabrication especially when multiple and mutable phase shifts are required. Based on this method, a /spl pi/-shift and two bipolar encoders for direct-sequence optical code-division multiple-access systems are obtained experimentally, which are in good agreement with simulation.

Novel flat multichannel filter based on strongly chirped sampled fiber Bragg grating

A novel optical fiber filter based on a strongly chirped sampled Bragg grating is proposed for wavelength-division-multiplexing (WDM) system applications. It features in multiple equalized passbands with flat-top steep-edge nearly linear phase response and high transmittance. Refractive index modulation amplitude with Gaussian spatial profile is used within the samples, which contributes to the marked improvement of the filter performance. Furthermore, there are also multiple flat and equalized stopbands to be used as multichannel optical add/drop filters in a WDM system.

Sampled Bragg grating with desired response in one channel by use of a reconstruction algorithm and equivalent chirp

The reconstruction algorithm is first applied to a sampled Bragg grating (SBG) with chirp in the sampling period. This method is demonstrated to achieve various profiles of both reflection and group delay within one channel of the SBG. This method has the advantage that the phase mask does not need any chirp, and only submicrometer precision is needed in the fabrication process. Based on this method, a tunable dispersion compensator is fabricated with a tuning range of 300 ps/nm in a flat band of 1 nm.

Correction to "Analytical expression of sampled Bragg gratings with chirp in the sampling period and its application on dispersion management design in a WDM system"

An analytical expression for a sampled Bragg grating (SBG) with chirp in the sampling period (CSP) is derived for the first time. It is shown that such a grating can be equivalent to a special SBG with a chirp in the grating period (CGP) which is varied in the stopbands. The corresponding equivalent chirp coefficients are determined, and the design procedure of a SBG with both CSP and CGP is outlined aiming at dispersion management in WDM system device.

A novel distributed feedback fiber laser based on equivalent phase shift

A distributed feedback fiber laser employing an equivalent phase shift (EPS) of /spl pi/ is studied theoretically and experimentally for the first time. The EPS is formed through extending one sampling period by 50% in the center of a sampled Bragg grating. An output power of 0.20 mW with sidemode suppression of 67 dB is experimentally observed.

Dual-Wavelength DFB Fiber Laser Based on a Chirped Structure and the Equivalent Phase Shift Method

A chirped phase-shifted structure is demonstrated for compact multiwavelength distributed feedback (DFB) fiber laser at room temperature for the first time. The chirped structure provides separated resonance cavities and then the stable multiwavelength operation. The equivalent phase shift method is demonstrated to realize the desired chirp and phase shifts simply and flexibly. A 44-pm-spaced dual-wavelength DFB fiber laser is then achieved experimentally, which is the narrowest spacing ever reported for a compact multiwavelength fiber laser

High-performance, high-chip-count optical code division multiple access encoders-decoders based on a reconstruction equivalent-chirp technique

Fiber Bragg grating-based, 511 chip, 500 Gchip/s encoders-decoders are experimentally demonstrated by the reconstruction equivalent-chirp (REC) method. Encoding-decoding efficiency close to the theoretical value is achieved. Without any real phase shifts, the encoders-decoders are fabricated by use of the traditional setup. Highly precise phase control requires only submicrometer precision. The encoding-decoding performance can be further improved by REC-based correction.