In-band Group Delay Research Articles

Efficient Technique for Increasing the Channel Density in Multiwavelength Sampled Fiber Bragg Grating Filters

We introduce a new class of high channel count multiwavelength comb filters based on sampled fiber Bragg gratings (FBGs). Our approach exploits the spectral fractional Talbot effect in sampled chirped FBGs (S-CFBGs). For specific conditions between the grating chirp and sampling period, the channel spacing can be reduced compared to the value obtained using conventional sampling techniques. In this way, the channel density can be multiplied without needing to increase the sampling period. Moreover, despite the fact that the grating is chirped, operating under the spectral Talbot regime ensures that the resultant in-band group delay characteristics are similar to those of a sampled uniform period FBG.

Large-band periodic filters for DWDM using multiple-superimposed fiber Bragg gratings

The tight specifications of dense wavelength division multiplexing (DWDM) filters are challenging for any available technologies. In this letter, periodic transmission filters based on superimposed chirped fiber Bragg gratings are designed to have flat amplitude response and nearly constant in-band group delay. These filters should prove to be useful as interleavers and mux/demux filters in DWDM systems.

Tailoring Chirped MoirÉ Fiber Bragg Gratings for Wavelength-Division-Multiplexing and Optical Code-Division Multiple-Access Applications

The design and fabrication of chirped Moiré fiber Bragg gratings (CMGs) are presented, which can be used in either (1) transmission as passband filters for providing wavelength selectivity in wavelength-division-multiplexed (WDM) systems or (2) reflection as encoding/decoding elements to decompose short broadband pulses in both wavelength and time in order to implement an optical code-division multiple-access (OCDMA) system. In transmission, the fabricated CMGs have single or multiple flattened passbands (< 0.5 dB ripple) and exhibit > 12 dB isolation and near constant in-band group delay. It is shown that these filters do not produce any measurable dispersion-induced power penalties when used to provide wavelength selectivity in 2.5 Gbit/s systems. It is also demonstrated how CMGs can be used in reflection to encode/decode short pulses from a wavelength-tunable mode-locked Er-doped fiber laser.

Fabrication of transmission filters with single or multiple flattened passbands based on chirped Moiré gratings

The fabrication of transmission filters with single or multiple flattened passbands based on chirped Moiré gratings is reported. The gratings are fabricated by the dual-exposure of a single chirped phase mask in conjunction with an amplitude mask. The filters have a ripple &lt; 0.5 dB in the passband, exhibit an isolation of &gt; 12 dB, and have near-constant in-band group delay.

Fibre Bragg grating transmission filters with near-ideal filter response

The authors demonstrate that transmission filters based on chirped moire gratings can be designed to have flattened passbands, steep slopes, and nearly constant in-band group delay. These filters should prove to be very useful for add/drop operations in wavelength division multiplexed systems.

A low-distortion BiCMOS seventh-order Bessel filter operating at 2.5 V supply

This paper presents the design of a seventh-order continuous-time Bessel filter using a new low-voltage and highly linear BiCMOS transconductor. A high-gain and parasitic-insensitive integrator is obtained by using an active capacitor scheme. The filter has been designed to operate at a 2.5 V supply with a nominal -3 dB cutoff frequency of 600 kHz. It has been fabricated in 1 /spl mu/m, double-poly 6-GHz BiCMOS process. The inband group delay variation is less than 10 ns. The total harmonic distortion (THD) measured with a 100 kHz input signal is less than -49 dB for a 2 V/sub pp/ amplitude and the dynamic range is 77 dB. The filter can be frequency tuned over almost one decade with a gain variation less than 0.2 dB in the passband. A common-mode rejection ratio (CMRR) of 53 dB in the passband is observed, thanks to a careful common-mode control strategy.

Equiripple group delay digital filter sets for use in FSK modems

Frequency shift keyed data signals may be demodulated by splitting the message signals into two spectral bands and comparing the received signal energy in the two bands. The band splitting filters in this type of demodulator are required to have both constant in-band group delay and matched group delay between the two bands. The problem considered in this paper is that of designing recursive digital filters which approximate this group delay requirement in an equiripple sense, and which can perform the required band splitting function.