Optical Filter Design and Analysis

This paper reviews the interaction between coherently stimulated acoustic phonons in the form of surface acoustic waves with light beams in semiconductor based photonic structures We address the generation of surface acoustic wave modes in these structures as well as the technological aspects related to control of the propagation and spatial distribution of the acoustic fields The microscopic mechanisms responsible for the interaction between light and surface acoustic modes in different structures are then reviewed Particular emphasis is given to the acousto-optical interaction in semiconductor microcavities and its application in photon control These structures exhibit high optical modulation levels under acoustic excitation and are compatible with integrated light sources and detectors

https://iopscience.iop.org/article/10.1088/0034-4885/68/7/R02/pdf

Modulation of photonic structures by surface acoustic waves

Germania-glass-based core silica glass cladding single-mode fibers (/spl Delta/n up to 0.143) with a minimum loss of 20 dB/km at 1.9 /spl mu/m were fabricated by the modified chemical vapor deposition (MCVD) method. The fibers exhibit strong photorefractivity with the type-IIa-induced refractive-index modulation of 2/spl times/10/sup -3/. The Raman gain of 300 to 59 dB/(km/spl middot/W) was determined at 1.07 to 1.6 /spl mu/m, respectively, in a 75 mol.% GeO/sub 2/ core fiber. Only 3 m of such fibers are enough for the creation of a 10-W Raman laser at 1.12 /spl mu/m with a 13-W pump at 1.07 /spl mu/m. Raman generation in optical fiber at a wavelength of 2.2 /spl mu/m was obtained for the first time.

Germania-based core optical fibers

We report active Q-switching of an all-fiber laser using a Bragg grating based acousto-optic modulator. Q-switching is performed by modulating a fiber Bragg grating with an extensional acoustic wave. The acoustic wave modulates periodically the effective index profile of the FBG and changes its reflection features. This allows controlling the Q-factor of the cavity. Using 1 m of 300 ppm erbium-doped fiber and a maximum pump power of 180 mW, Q-switch pulses of 10 W of peak power and 82 ns wide were generated. The pulse repetition rate of the laser can be continuously varied from few Hz up to 62.5 kHz.

Q-switching of an all-fiber laser by acousto-optic modulation of a fiber Bragg grating

In this topical review, the recent progress on radiation-hardened fiber-based technologies is detailed, focusing on examples for space applications. In the first part of the review, we introduce the operational principles of the various fiber-based technologies considered for use in radiation environments: passive optical fibers for data links, diagnostics, active optical fibers for amplifiers and laser sources as well as the different classes of point and distributed fiber sensors: gyroscopes, Bragg gratings, Rayleigh, Raman or Brillouin-based distributed sensors. Second, we describe the state of the art regarding our knowledge of radiation effects on the performance of these devices, from the microscopic effects observed in the amorphous silica glass used to design fiber cores and cladding, to the macroscopic response of fiber-based devices and systems. Third, we present the recent advances regarding the hardening (improvement of the radiation tolerance) of these technologies acting on the material, device or system levels. From the review, the potential of fiber-based technologies for operation in radiation environments is demonstrated and the future challenges to be overcome in the coming years are presented.

https://iopscience.iop.org/article/10.1088/2040-8986/aad271/pdf

Recent advances in radiation-hardened fiber-based technologies for space applications

Summary form only given. Fiber Bragg gratings (FBGs) written with ultraviolet light are becoming of increasing importance in fiber systems because of their high performance, versatility, and excellent physical characteristics. In this paper, we report a technique that transforms a FBG into a Bragg cell or acousto-optic modulator operating in reflection mode.

/pdf/acousto-optic-superlattice-modulator-using-fiber-bragg-4wwhfbgdwm.pdf

Acousto-optic superlattice modulator using fiber Bragg grating

We have demonstrated fast formation [~1500 pulses at ~1 (J/cm2)/pulse] of fiber gratings with highly negative index modulations (~−3 × 10−4). We have found that the maximum negative index modulations that are achieved do not depend on the pulse intensities, although the inverse of the time taken to reach the negative index-modulation maximum varies linearly with the pulse intensities. This prompts us to use a three-energy-level system to model the photosensitivity in boron-doped germanosilicate fiber. All the necessary parameters of the model can be determined from a single growth measurement of the average index change, and the model’s prediction fits well the measured index-modulation growth.

/pdf/negative-index-gratings-formed-by-a-193-nm-excimer-laser-lrj4jdfa8j.pdf

Negative-index gratings formed by a 193-nm excimer laser.

We have demonstrated fast formation (~1500 pulses at ~1 J/cm). These gratings were found to be far more stable than the gratings with positive index modulations formed at the early stage of the grating growth. We have also found that the maximum negative index modulations achieved do not depend on the pulse intensifies, although the inverse of the time taken to reach the negative index modulation maximum varies linearly with the pulse intensities. This prompts us to use a three energy level system to model the photosensitivity in the boron-doped germanosilicate fibre. All the necessary parameters of the model can be determined from a single growth measurement of the average index change and the model's prediction fits well the measured index modulation growth. A complex grating decay process is also observed at elevated temperatures as predicted by the three energy level model. The thermal stability of both positive and negative index gratings in a Boron-co-doped germanosilicate fibre is characterised at fixed temperatures, so that the stability of such grating can be accessed for any writing fluence

/pdf/experimental-and-theoretical-study-of-stable-negative-index-1voyc3ro2i.pdf

W.F. Liu

Papers

Acousto-optic superlattice modulator using fiber Bragg grating

Negative-index gratings formed by a 193-nm excimer laser.

Experimental and theoretical study of stable negative index gratings formed at 193 nm