Yitang Dai

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.

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.

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 Unequalized Phase Shifts

A novel structure for dual-wavelength distributed feedback (DFB) fiber laser is proposed and experimentally demonstrated. This structure is based on a uniform fiber Bragg grating with two unequalized phase shifts, which markedly suppress the mode competition of the two lasing wavelengths; and then a 52-pm-spaced dual-wavelength DFB fiber laser operating at single-longitudinal-mode and single-polarization is achieved at room temperature. A simple method is also implemented to fabricate the phase shifts with high precision

Wideband multichannel dispersion compensation based on a strongly chirped sampled Bragg grating and phase shifts

A novel multichannel dispersion compensator based on a strongly chirped sampled Bragg grating with phase shifts is demonstrated experimentally. With a single phase mask, various channel spacings and dispersion can be achieved by proper control of the sampling period and the phase shifts. A 100 GHz channel-spacing compensator with a dispersion of -1000 ps/nm and another 200 GHz channel-spacing compensator with a dispersion of -500 ps/nm are designed. As an example, a 40 channel, 100 GHz channel-spacing compensator with a dispersion of approximately -560 ps/nm is fabricated. All the designs are based on one phase mask, thus showing the flexibility of our method.

Thermally tunable dispersion compensator in 40-Gb/s system using FBG fabricated with linearly chirped phase mask

An improved design and fabrication method of nonlinearly chirped fiber Bragg gratings is demonstrated. Based on reconstruction-equivalent- chirp method, the nonlinearly chirped fiber Bragg grating is realized with a linearly chirped phase mask instead of a uniform one, which improves the performance of the device. Coated with uniform thin metal film, the obtained grating works as a tunable dispersion compensator with a tuning range ~200ps/nm, peak-to-peak group delay ripple <14ps and 3-dB bandwidth approximately 2nm. Employing this device, the power penalty in a 40- Gb/s X5/10km conventional single mode fiber using carrier suppressed return-to-zero format is less than 0.7dB at a BER=10-10.

511-chip, 500-chip/s OCDMA en/decoders based on equivalent phase-shift method

Novel sampled Bragg gratings without phase shifts are demonstrated for high-quality OCDMA en/decoders with large chip-count. Precise phase control can be realized by only uniform phase mask and fabrication setup with sub-micron precision

Multipolar inserting zeros code and its application in optical code division multiple access systems

We proposed the multipolar inserting zeros MIZ code for direct-sequence optical code division multiple ac- cess OCDMA systems. This code is designed to corre- spond with the judgment based on linear convolution. Simu- lation results showed that it can provide a lower multiuser interference than the conventional Gold sequence. With the same number of users, the bit error rate in the OCDMA sys- tem coded by MIZ can be reduced by several decuples than that coded by Gold, and the source power needed to reach a BER of 110 �9 can also be reduced by several decibels. So the performance of OCDMA can be improved.