An all-fiber flat-top orbital angular momentum (OAM) mode convertor with ultra-wideband is numerically demonstrated, which is based on a helical long period fiber grating (HLPG) with phase modulation. The proposed phase-modulated HLPG is formed in a single mode fiber (SMF) and works at dispersion turning point. A flat-top OAM mode convertor with a bandwidth of ∼371 nm and a conversion efficiency of ∼100% has been successfully obtained. The temperature and strain effects on the proposed OAM mode convertor have been also theoretically investigated, respectively. The results show that the proposed phase-modulated HLPG based flat-top OAM mode convertor has a certain resistance to external temperature and strain changes, which will be beneficial to reduce its packaging cost and difficulty. The proposed device may find potential applications in the OAM mode division multiplexing (MDM) system combined with the wavelength division multiplexing (WDM) technique.
A novel power-interrogated sensor that allows for the simultaneous measurement of temperature and strain is proposed and experimentally demonstrated. The sensor is based on the use of a linearly chirped fiber Bragg grating (FBG) with a broad (~10 nm) as well as slant reflection spectrum. Unlike most of the previous FBG-based sensors, the FBG proposed here is simultaneously used as both the sensing and the interrogating element. The measurement accuracies for the temperature and the strain are estimated to be ±2 °C in the range of 12-197 °C and ±24in με the range of 0-1270 με, respectively.
A novel all-optical simultaneous pulse multiplication and shaping approach is proposed, which is based on a triply sampled spectral filter utilizing fiber Bragg grating. This proposed method enables one to create a pulse train efficiently with both a high multiplication factor and arbitrary pulse profile. As an example, pulse train with a repetition rate of 225-GHz and flat-top intensity profile is numerically demonstrated, which is generated from 1-GHz transform-limited Gaussian pulse train with pulse width of 0.4 ps.
A novel approach to calibrate a phase-shift formed in a long-period fiber grating (LPG) is proposed and successfully demonstrated, which is based on the use of either a power- or a wavelength-interrogation technique to the loss-peak existed in the transmission spectrum of the phase-shifted LPG. Moreover, in this study, by tapering a LPG with CO2 laser, phase-shift is successfully created at central part of the LPG. Finally, base on the use of this kind of phase-shifted LPG, a simultaneous measurement for the temperature and the surrounding refractive index has been proposed and experimentally demonstrated.
Slow light is theoretically and experimentally demonstrated in a phase-shifted multichannel fiber Bragg grating (FBG)
which has the ability not only to produce the slow-lights in multiple channels simultaneously but also to make the delay
time tunable by changing the magnitude of the inserted phase shift. Phase shift is introduced into a phase-only sampled
51-channel FBG by utilization of a small piezoelectric transducer (PZT). On the other hand, the group delay of each
channel can be further enhanced by incorporating stimulated Brillouin scattering (SBS).
As one of the fiber-based wide-band promising components, high channel-count fiber Bragg grating has recently
attracted great interests. In this paper, we introduce our recent developments in the design techniques for the ultra-high
channel-count fiber Bragg gratings (FBG). The key technique is based on the utilization of a continuous phase-only
sampling, which is the same as the one for the optimization of a phase-only grating in the diffractive optics. With the
proposed sampling method, we have theoretically demonstrated a novel doubly sampled FBG with channels up to 405,
which could be used as either the dispersion compensator or the comb filter in broad-band wavelength-division
multiplexing (WDM) system.
In this paper, we introduce our recent developments in the design techniques for high channel-count fiber Bragg gratings
(FBG). Based on a double sampling method, we theoretically demonstrate a linearly chirped FBG with channels up to
153, which could be used as the dispersion compensator. Moreover, we propose a novel technique for the realization of a
multi-channel notch filter by using a thermally-induced phase-shift of this kind of FBG. As an example, a multi-channel
narrow band-pass filter is realized and successfully used to implement a multi-wavelength fiber laser.
We introduce our recent progresses in the design and fabrication of the high channel-count fiber Bragg grating (FBG).
We theoretically and experimentally demonstrated the phase-only sampled FBG with channels up to 81, which could be
used as the dispersion compensator, the simultaneous dispersion and dispersion-slope compensator, respectively.
Moreover, we have presented a novel method for multi-channel FBG design, which enables us to design any kind of
multi-channel FBGs where the amplitude or the spectral response of each channel could be either identical or non-identical.
As an example, a novel design for a multi-channel FBG with asymmetrical triangular reflection spectrum has
been demonstrated.
Effect of the cladding-mode coupling losses on the spectrum of multi-channel fiber Bragg grating (FBG) has been numerically investigated on the basis of the extended coupled-mode equations. It has been shown that there exists a reflection slope in the spectrum of both the intra- and inter-channels due to the existences of the cladding-modes. This slope could be larger than 1 dB when the induced index change is about 3x10-3, which makes the channels especially the one at the shortest wavelength considerably asymmetric. For comparison, a 39-channel linearly chirped FBG with a channel spacing of 0.8 nm and a chromatic dispersion of -850 ps/nm has been designed and fabricated. The experimental results show good agreement with the numerical ones.
The fiber Bragg grating (FBG) with a very high count, up to N=80, identical channels for dispersion compensators has been commercialized. The design utilizes the phase-only sampling, which requires η / N time higher refractive index modulation than the N times required by the amplitude sampling design. The phase sampling is implemented by inserting phase shifts in the FBG. Hence, the positive valued coupling coefficients of the FBG become complex-valued, which greatly increase the functionality and spectral performance of the FBG. In the fabrication of the phase-shifted FBG we find that the phase shifts in the phase mask for writing the FBG are not replicated into the FBG, as believed by many people, but are split into two half-magnitude phase-shifts due to the near field diffraction. We show the split of the phase shift by using the Finite Difference in Time Domain (FDTD) analysis and we show that this split of the phase shifts results in the FBG spectral asymmetry by a physical model of the phase-only sampling function distortion and by the FBG experiments. The new pre-compensating phase mask technique is introduced to remove the errors and therefore ensure the success of the high count multiple channel FBGs.
A phase shift in phase mask is split into two half-magnitude phase-shifts in near field, resulting in FBG spectral asymmetry. The errors are removed using new pre-compensating phase mask for binary-phase Dammann sampled multi-channel FBGs.
We have applied the diffractive optics and digital holography technologies to the design and fabrication of fiber Bragg gratings (FBG). We studied the phase mask near field diffraction using the numerical simulation. Our new understanding on the phase mask has critical importance for fabrication of complex FBGs, such as the sampled grating DBR laser, multi-channel dispersion compensator, and phase-shift band-pass filters. In the design of the FBGs we introduced the phase-only sampling multi-channel FBGs using the Dammann diffractive grating, such that the maximum reflective index modulation required for N channels is only √N times of that for the single channel. We apply the discrete layer-peeling algorithm directly design the multi-channel FBGs, whose seed grating contains abrupt phase jumps in order to correct the channel distortions in the sampled multi-channel complex gratings. In addition, we introduced the iterative layer-peeling algorithm as a generic approach for the design of the FBGs. Our research provided a foundation of the advanced multichannel complex FBGs technology, which produces FBGs of very high channel count (45 channels and higher).
Self-electrooptic effect devices (SEEDs) and GaAs field- effect transistors (FETs) are used to form smart pixels. A 8 X 4 array of simple field-effect transistor-self- electrooptic effect device (FET-SEED) smart pixels has been fabricated by interconnecting a SEED chip and a GaAs FET chip on a printed circuit board. The smart pixel consists of a detector SEED, a modulator SEED, and a simple GaAs FET amplifier. An optical system have been designed and constructed to demonstrate the smart pixels. The operational principle of the smart pixels is also described.
The design theory of fresnel microlens is described and the errors introduced by fabricating process are analyzed. The fresnel microlens arrays of four-level phase with diffractive efficiency larger than 60% are obtained. Crossover optical interconnect module is constructed by using fresnel microlens arrays.
This paper presents a new optoelectronic hybrid numerical system for the parallel processing of algebra polynomial evaluation. Free-space optical perfect shuffle interconnection network is adopted in our systems. Optical interconnection networks can make the operating time the minimum, which is proportional to log2N.
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