Irina A. Kostko

Dynamics of ultimate spectral narrowing in a semiconductor fiber-grating laser with an intra-cavity saturable absorber

The ultimate spectrum-narrowing and side-mode suppression due to the presence of a saturable absorber in an external cavity of a fiber Bragg grating semiconductor laser is numerically simulated. The proposed algorithm describes an effect of absorption bleaching in a saturable absorber using earlier measurements and shows the evolution of a dynamic grating in the laser cavity. The simulations confirm for the first time an empirical theory of spectral line narrowing in a laser with an intra-cavity saturable absorber.

Tunable Lattice-Form Mach–Zehnder Interferometer for Arbitrary Binary Code Generation at 40 GHz

We use the direct temporal domain approach to design spectrally periodic optical filters for pulse repetition rate multiplication (PRRM) with envelope shaping. In particular, we demonstrate a tunable lattice-form Mach-Zehnder interferometer using Silica-based planar lightwave circuit (PLC) for arbitrary 4-bit binary amplitude code generation at 40 GHz and to increase the repetition rate of a 10 GHz input pulse train to 20 GHz or 40 GHz. In addition to PRRM and envelope shaping, the device also has the capability of arbitrary phase coding.

Generating 4

We demonstrate a tunable pulse repetition rate multiplier using a silica-based planar lightwave circuit (PLC). The PLC is a six-stage lattice-form Mach-Zehnder interferometer which can be tuned thermally to generate 20- and 40-GHz output pulse trains from a 10-GHz input. We use a nonlinear optical loop mirror as a wavelength converter to perform intensity-to-field conversion to eliminate pulse-to-pulse phase fluctuations in the higher-rate output pulse trains. Moreover, we use wavelength multicasting (simultaneous wavelength conversion) to generate multiple pulse trains (4 × 20 GHz and 4 × 40 GHz in the example shown here) from a single 10-GHz input.

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We study the feasibility of a radio-over-fiber (ROF) link with external modulation and an unamplified photodetector; we show high-quality (EVM -38 dB, RF power -1 dBm) 64-QAM- OFDM transmission when optimizing the photodiode impedance matching and the modulator bias point.

20 GHz and 4

We report on the spectral analysis of the first 1490 nm external cavity laser with an intra-cavity erbium-doped fiber. Self-mode beating and heterodyne beating methods are employed to measure the side mode suppression ratios and to study the effect of the rare-earth doped fiber on the spectrum of the external-cavity laser. Experimental and simulated results show a substantial decrease in the number of the external-cavity modes and a side-mode suppression ratio of >15 dB.

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We demonstrate a tunable planar lightwave circuit for arbitrary 4-bit binary code generation at 40 GHz. The device is a 6-stage lattice-form Mach-Zehnder interferometer fabricated in silica-on-silicon technology.

40 GHz Pulse Trains From a Single 10-GHz Mode-Locked Laser Using a Tunable Planar Lightwave Circuit

We present an experimental study of tuning characteristics and wavelength stability of a 1490 nm doped fiber external cavity laser. The standing wave in the erbium-doped fiber in an external-cavity laser causes spatial hole burning and absorption modulation and forms a dynamic grating. The dynamic grating can effectively suppress side modes and eliminate wavelength fluctuations in the laser. The operating wavelength of this hybrid laser is shown for the first time to our knowledge to be smoothly tunable by changing the semiconductor laser drive current or temperature.

A radio-over-fiber link for OFDM transmission without RF amplification

Measurements and analysis of electrical and temperature tuning characteristics of a 1490 nm erbium doped fiber external cavity semiconductor laser (DFECL) are presented. The laser has a long piece of doped fiber in the external cavity. The standing wave in the external cavity causes spatial hole-burning and absorption modulation in the saturable absorber, and forms a long dynamic grating. In this paper, we show that the wavelength of DFECL can be tuned within the bandwidth of the FBG (~100 pm), by tuning the semiconductor laser temperature. The wavelength of the laser can also be tuned smoothly and continuously over 60 pm by controlling the current over 160 mA; the equivalent optical frequency tuning rate is ~50MHz/mA. The results indicate that the peak wavelength of the dynamic grating can be tuned with the dominant mode within the bandwidth of the fiber Bragg grating. This fine tuning characteristic is very attractive for microwave optical generation in Radio over Fiber applications.

Side mode suppression using a doped fiber in a long external-cavity semiconductor laser operating at 1490 nm.

Using the direct time domain approach and thermo-optic properties of silica, we show that a single spectrally periodic filter can generate any 4-bit binary amplitude and phase code pattern. We design and analyze a tunable 6-stage lattice-form Mach-Zehnder interferometer using silica-on- silicon planar lightwave circuit technology for generating 40 GHz pulse trains with arbitrary binary amplitude and phase code profiles from a uniform 10 GHz input pulse train.

Tunable 6-stage lattice-form Mach-Zehnder interferometer for arbitrary binary code generation at 40 GHz

We demonstrate reconfigurable demultiplexing of arbitrary single or multiple 10 Gb/s tributary channels from a higher rate 40 Gb/s data signal using a programmable planar lightwave circuit (PLC) and four-wave mixing (FWM). The PLC is a thermally tunable six-stage lattice-form Mach-Zehnder interferometer fabricated in silica-on-silicon. We present results for optical time-division-multiplexing (OTDM) demultiplexing of both return-to-zero on-off keying (RZ-OOK) and differential phase-shift-keying (RZ-DPSK) data.