Rachid Hamdi | University 8 May 1945 Guelma (original) (raw)

Papers by Rachid Hamdi

In this paper, we present a novel procedure for the synthesis of a filter having an arbitrarily s... more In this paper, we present a novel procedure for the synthesis of a filter having an arbitrarily specified amplitude transmittance. The filter configuration consists of N birefringent stages placed between a polarizer and an analyzer, with each stage containing an identical section and a variable section. An additional variable section is placed in front of the analyzer. The synthesis procedure is based on the resolution of a generalized nonlinear equation system directly deducted from the Jones matrix formalism to determine the angles of each stage, the angle of the analyzer and the phase shifts of the variable sections. A typical example of a 6-stage birefringent filter having an arbitrarily non-symmetric amplitude transmittance is shown and the opto-geometrical parameters are given to demonstrate the efficiency of the proposed synthesis procedure. The results obtained show an excellent agreement with those developed in the literature.

We demonstrate that the birefringence of the liquid-crystal cell (LCC) can be varied by applying ... more We demonstrate that the birefringence of the liquid-crystal cell (LCC) can be varied by applying different frequency values of a single applied ac square voltage. For the experimental evaluation of the birefringence, associated with a certain wavelength λ, as a function of the frequency F LCC of the electrical signal applied to the LCC, we use, for the first time to our knowledge, what we call here a frequency-dependent transmission technique. It consists in measuring the transmission responses between crossed and parallel polarizers as a function of the frequency F LCC. Experimental tests were carried out using a 7 μm-thick E63 nematic LCC and a laser source emitting at λ=1.55 μm with a launch power of −3 dBm. The tuning voltage V LCC applied to the LCC is an alternative square wave electrical signal whose frequency ranges from 0.5 to 15 kHz. The peak to peak amplitude of the electrical signal is 5 V. The curve of the measured variations of the optical path difference of the LCC versus the frequency F LCC has a positive slope. Application to the tuning of the center wavelength of the transmission response of a one stage hybrid birefringent filter is shown as a proof-of-principle test.

Optics Communications, 2007

We demonstrate that in addition to their role in tuning the wavelength of an N-stage hybrid liqui... more We demonstrate that in addition to their role in tuning the wavelength of an N-stage hybrid liquid-crystal Š olc filter, liquid-crystal cells can also be used to vary the transmission bandwidth of such filter around any of the tuned wavelength. This bandwidth tuning is based on the variation of the number of stages by what we call here an ''optical cancelling technique''. This is achieved by varying the birefringence of the liquid-crystal cells whose optical path difference switches between two particular values. We show that for a 10-stage filter and at k i = 1.532 lm, the calculated 3-dB bandwidth varies from 2.6 to 11.8 nm when the number of ''optically-cancelled'' hybrid plates increases from 0 to 8. During the tuning process, the contrast ratio remains equal to that of the equivalent classical Š olc filter.

Photonic Materials, Devices, and Applications, 2005

An electro-optically tunable erbium-doped fiber ring laser with a side mode suppression ratio of ... more An electro-optically tunable erbium-doped fiber ring laser with a side mode suppression ratio of ~ 51.2 dB and a 0.062 nm linewidth is demonstrated. Wavelength tuning is achieved with a hybrid liquid crystal Solc structure used as an intracavity tunable filter. The laser wavelength is tuned over 28.6 nm with a tuning rate of 2.38 nm/V.

2012 19th International Conference on Telecommunications (ICT), 2012

We experimentally demonstrate the feasibility of the bandwidth tuning of a liquid-crystal based b... more We experimentally demonstrate the feasibility of the bandwidth tuning of a liquid-crystal based bandpass Lyot filter. This bandwidth tuning is achieved by applying a voltage to vary the birefringence of the liquid-crystal cells whose optical path difference takes predefined discrete values. We show that for a 2-stage liquid-crystal Lyot filter and at λ i = 1.543 μm, the measured 3-dB bandwidth varies from 17nm to 60 nm when the applied voltage increases from 0V to 5.24V. The shape of the transmission response remains unchanged during the bandwidth tuning process.

2009 International Conference on Advances in Computational Tools for Engineering Applications, 2009

This paper discusses the design of a wavelength blocker/channel equalizer (WB/CE) based on stacke... more This paper discusses the design of a wavelength blocker/channel equalizer (WB/CE) based on stacked liquid-crystal birefringent blocks. Each block, which is optimized to control a predefined channel wavelength, consists of three components. The wavelength blocking/transmitting and the equalizing actions are provided by the liquid-crystal cell (LCC) whose optical path difference varies between two particular values when its birefringence is electrically

2006 International Conference on Photonics in Switching, 2006

A novel 1×2 wavelength routing switch is introduced and analyzed. It is based on a tunable hybrid... more A novel 1×2 wavelength routing switch is introduced and analyzed. It is based on a tunable hybrid liquid-crystal Solc filter and a polarization beamsplitter. The device can be set into the bar state for an arbitrary subset of WDM channels while remaining in the cross state for the rest of channels. This is achieved via a tuning voltage applied to

Optics Communications, 2007

We demonstrate that in addition to their role in tuning the wavelength of an N-stage hybrid liqui... more We demonstrate that in addition to their role in tuning the wavelength of an N-stage hybrid liquid-crystal Š olc filter, liquid-crystal cells can also be used to vary the transmission bandwidth of such filter around any of the tuned wavelength. This bandwidth tuning is based on the variation of the number of stages by what we call here an ''optical cancelling technique''. This is achieved by varying the birefringence of the liquid-crystal cells whose optical path difference switches between two particular values. We show that for a 10-stage filter and at k i = 1.532 lm, the calculated 3-dB bandwidth varies from 2.6 to 11.8 nm when the number of ''optically-cancelled'' hybrid plates increases from 0 to 8. During the tuning process, the contrast ratio remains equal to that of the equivalent classical Š olc filter.

Journal of Lightwave Technology, 2000

We propose and demonstrate a new modified Lyot filter to independently ensure the channel amplitu... more We propose and demonstrate a new modified Lyot filter to independently ensure the channel amplitude equalization and the bandwidth tuning functions. The device consists of hybrid liquid crystal interferometers. We show numerically and experimentally that for a modified four-stage Lyot filter, the two first interferometers ensure equalization function with a maximum extinction ratio, while the last interferometer allows full-width at

IEEE Photonics Technology Letters, 2000

We propose and demonstrate a novel optical imple- mentation to simultaneously improve the contras... more We propose and demonstrate a novel optical imple- mentation to simultaneously improve the contrast and increase the finesse of a classical -stage Lyot filter. The new device based on the multiple-passage concept uses two mirrors placed at the ex- tremities of the filter. The light beam passes through the structure back and forth and each passage has a significant influence

Journal of Optics A: Pure and Applied Optics, 2009

We propose the design of a multi-channel amplitude-equalizing polarization interference filter ba... more We propose the design of a multi-channel amplitude-equalizing polarization interference filter based on stacked liquid crystal birefringent blocks. Each block, which is optimized to control a predefined wavelength channel, consists of three components. The wavelength blocking/ transmitting and the equalizing actions are provided by the liquid crystal component whose optical path difference varies between two particular values when its birefringence is electrically controlled. For a typical three-channel equalizing filter, the three liquid crystal cells provide all eight possible combinations to block/transmit channels and also allow us to independently equalize their corresponding levels. The benefit of such a polarization-based filter is that it operates without free-space demultiplexing optics and with no moving parts. It can be used as a key element in the present reconfigurable optical networks.

In this paper, we present a novel procedure for the synthesis of a filter having an arbitrarily s... more In this paper, we present a novel procedure for the synthesis of a filter having an arbitrarily specified amplitude transmittance. The filter configuration consists of N birefringent stages placed between a polarizer and an analyzer, with each stage containing an identical section and a variable section. An additional variable section is placed in front of the analyzer. The synthesis procedure is based on the resolution of a generalized nonlinear equation system directly deducted from the Jones matrix formalism to determine the angles of each stage, the angle of the analyzer and the phase shifts of the variable sections. A typical example of a 6-stage birefringent filter having an arbitrarily non-symmetric amplitude transmittance is shown and the opto-geometrical parameters are given to demonstrate the efficiency of the proposed synthesis procedure. The results obtained show an excellent agreement with those developed in the literature.

We demonstrate that the birefringence of the liquid-crystal cell (LCC) can be varied by applying ... more We demonstrate that the birefringence of the liquid-crystal cell (LCC) can be varied by applying different frequency values of a single applied ac square voltage. For the experimental evaluation of the birefringence, associated with a certain wavelength λ, as a function of the frequency F LCC of the electrical signal applied to the LCC, we use, for the first time to our knowledge, what we call here a frequency-dependent transmission technique. It consists in measuring the transmission responses between crossed and parallel polarizers as a function of the frequency F LCC. Experimental tests were carried out using a 7 μm-thick E63 nematic LCC and a laser source emitting at λ=1.55 μm with a launch power of −3 dBm. The tuning voltage V LCC applied to the LCC is an alternative square wave electrical signal whose frequency ranges from 0.5 to 15 kHz. The peak to peak amplitude of the electrical signal is 5 V. The curve of the measured variations of the optical path difference of the LCC versus the frequency F LCC has a positive slope. Application to the tuning of the center wavelength of the transmission response of a one stage hybrid birefringent filter is shown as a proof-of-principle test.

Optics Communications, 2007

We demonstrate that in addition to their role in tuning the wavelength of an N-stage hybrid liqui... more We demonstrate that in addition to their role in tuning the wavelength of an N-stage hybrid liquid-crystal Š olc filter, liquid-crystal cells can also be used to vary the transmission bandwidth of such filter around any of the tuned wavelength. This bandwidth tuning is based on the variation of the number of stages by what we call here an ''optical cancelling technique''. This is achieved by varying the birefringence of the liquid-crystal cells whose optical path difference switches between two particular values. We show that for a 10-stage filter and at k i = 1.532 lm, the calculated 3-dB bandwidth varies from 2.6 to 11.8 nm when the number of ''optically-cancelled'' hybrid plates increases from 0 to 8. During the tuning process, the contrast ratio remains equal to that of the equivalent classical Š olc filter.

Photonic Materials, Devices, and Applications, 2005

An electro-optically tunable erbium-doped fiber ring laser with a side mode suppression ratio of ... more An electro-optically tunable erbium-doped fiber ring laser with a side mode suppression ratio of ~ 51.2 dB and a 0.062 nm linewidth is demonstrated. Wavelength tuning is achieved with a hybrid liquid crystal Solc structure used as an intracavity tunable filter. The laser wavelength is tuned over 28.6 nm with a tuning rate of 2.38 nm/V.

2012 19th International Conference on Telecommunications (ICT), 2012

We experimentally demonstrate the feasibility of the bandwidth tuning of a liquid-crystal based b... more We experimentally demonstrate the feasibility of the bandwidth tuning of a liquid-crystal based bandpass Lyot filter. This bandwidth tuning is achieved by applying a voltage to vary the birefringence of the liquid-crystal cells whose optical path difference takes predefined discrete values. We show that for a 2-stage liquid-crystal Lyot filter and at λ i = 1.543 μm, the measured 3-dB bandwidth varies from 17nm to 60 nm when the applied voltage increases from 0V to 5.24V. The shape of the transmission response remains unchanged during the bandwidth tuning process.

2009 International Conference on Advances in Computational Tools for Engineering Applications, 2009

This paper discusses the design of a wavelength blocker/channel equalizer (WB/CE) based on stacke... more This paper discusses the design of a wavelength blocker/channel equalizer (WB/CE) based on stacked liquid-crystal birefringent blocks. Each block, which is optimized to control a predefined channel wavelength, consists of three components. The wavelength blocking/transmitting and the equalizing actions are provided by the liquid-crystal cell (LCC) whose optical path difference varies between two particular values when its birefringence is electrically

2006 International Conference on Photonics in Switching, 2006

A novel 1×2 wavelength routing switch is introduced and analyzed. It is based on a tunable hybrid... more A novel 1×2 wavelength routing switch is introduced and analyzed. It is based on a tunable hybrid liquid-crystal Solc filter and a polarization beamsplitter. The device can be set into the bar state for an arbitrary subset of WDM channels while remaining in the cross state for the rest of channels. This is achieved via a tuning voltage applied to

Optics Communications, 2007

We demonstrate that in addition to their role in tuning the wavelength of an N-stage hybrid liqui... more We demonstrate that in addition to their role in tuning the wavelength of an N-stage hybrid liquid-crystal Š olc filter, liquid-crystal cells can also be used to vary the transmission bandwidth of such filter around any of the tuned wavelength. This bandwidth tuning is based on the variation of the number of stages by what we call here an ''optical cancelling technique''. This is achieved by varying the birefringence of the liquid-crystal cells whose optical path difference switches between two particular values. We show that for a 10-stage filter and at k i = 1.532 lm, the calculated 3-dB bandwidth varies from 2.6 to 11.8 nm when the number of ''optically-cancelled'' hybrid plates increases from 0 to 8. During the tuning process, the contrast ratio remains equal to that of the equivalent classical Š olc filter.

Journal of Lightwave Technology, 2000

We propose and demonstrate a new modified Lyot filter to independently ensure the channel amplitu... more We propose and demonstrate a new modified Lyot filter to independently ensure the channel amplitude equalization and the bandwidth tuning functions. The device consists of hybrid liquid crystal interferometers. We show numerically and experimentally that for a modified four-stage Lyot filter, the two first interferometers ensure equalization function with a maximum extinction ratio, while the last interferometer allows full-width at

IEEE Photonics Technology Letters, 2000

We propose and demonstrate a novel optical imple- mentation to simultaneously improve the contras... more We propose and demonstrate a novel optical imple- mentation to simultaneously improve the contrast and increase the finesse of a classical -stage Lyot filter. The new device based on the multiple-passage concept uses two mirrors placed at the ex- tremities of the filter. The light beam passes through the structure back and forth and each passage has a significant influence

Journal of Optics A: Pure and Applied Optics, 2009

We propose the design of a multi-channel amplitude-equalizing polarization interference filter ba... more We propose the design of a multi-channel amplitude-equalizing polarization interference filter based on stacked liquid crystal birefringent blocks. Each block, which is optimized to control a predefined wavelength channel, consists of three components. The wavelength blocking/ transmitting and the equalizing actions are provided by the liquid crystal component whose optical path difference varies between two particular values when its birefringence is electrically controlled. For a typical three-channel equalizing filter, the three liquid crystal cells provide all eight possible combinations to block/transmit channels and also allow us to independently equalize their corresponding levels. The benefit of such a polarization-based filter is that it operates without free-space demultiplexing optics and with no moving parts. It can be used as a key element in the present reconfigurable optical networks.