Compact Optical Isolator Research Articles

Non-reciprocity in a silicon photonic ring resonator with time-modulated regions

Non-reciprocity and breaking of the time-reversal symmetry is conventionally achieved using magneto-optic materials. However, the integration of these materials with complementary metal-oxide semiconductor (CMOS)-compatible platforms is challenging. Temporal modulation is a well-suited approach for achieving non-reciprocity in integrated photonics. However, existing experimental implementations based on this method in silicon uses traveling-wave modulation in the whole structure or tandem ring or waveguide modulators, and they lead to high insertion loss and large footprint. In this work we achieve, to the best of our knowledge, the first experimental demonstration of non-reciprocity in a compact single silicon photonic ring resonator with time-modulated regions, fabricated with a CMOS-compatible commercial foundry. We demonstrate symmetry breaking of counter-rotating modes in an active silicon photonic ring resonator by applying phase-shifted RF signals to only two small p-i-n junctions on the ring, without employing traveling-wave modulation in the whole structure. The non-reciprocity is caused by the cross-coupling between the counter-rotating modes of the ring, which breaks their degeneracy. By reversing the polarity of the RF phase difference (e.g. (45°,−45°) asymmetric phases) opposite resonance wavelengths are obtained, with a 16-dB contrast between the transmissions of the asymmetric phases and a low insertion loss of 0.6 dB under 27 dBm RF power. We achieve the highest ratio of the asymmetric transmission to the insertion loss, among the state-of-the-art silicon non-reciprocal integrated optical structures based on time varying modulation. The non-reciprocal ring can be used as a magnetic-free, low-loss, compact, and CMOS-compatible integrated optical isolator.

Tunable broadband compact optical isolator based on Weyl semimetal

We theoretically set up a 4 × 4 magneto-optical matrix to investigate the transmittances induced by the forward and backward left hand circularly polarized (LCP) waves impinging the 4 μm thickness Weyl semimetal (WSM) material at normal incidence. Because of the different effective permittivity of the two LCP waves in WSM induced by the non-zero off-diagonal term, the two waves experience blocking transmission, bidirectional transmission and unidirectional transmission with the increase of the wavelength, respectively. Based on the wide wavelength of the unidirectional transmission, the broadband optical isolator can be realized. The threshold wavelength of the optical isolator can be regulated by changing the wavelength where the parallel component of the diagonal element is identical to the off-diagonal term. It is also found that the Fermi energy, tilt degree of Weyl cones and Weyl node separation reveal simple and available approaches to achieve the regulation. We believe that the adjustable broadband compact optical isolator can perform a significant role in fiber-optic communication system.

CMOS-compatible compact optical isolator based on space-time modulated coupled resonators.

This work shows how phase-shifted time-modulations applied to two or more near-field coupled resonators can be engineered to achieve magnet-free optical isolation in a compact footprint. Because of the strong light-matter interaction afforded by high quality factor resonant cavities, only modest modulation amplitudes are required. A coupled mode theory model is developed which is subject to simulated annealing to optimize device performance. Then it is shown via finite-difference time-domain simulation how the device may be implemented in a one dimensional photonic crystal geometry etched in a silicon ridge waveguide. These devices can be implemented in native silicon with standard electrical contacts thereby maintaining CMOS-compatible fabrication without the need for additional specialized materials. Isolation ratios of over 40 dB with insertion loss less than 1 dB using modulation frequencies under 25 GHz are achievable in this device platform.

Compact dynamic optical isolator based on tandem phase modulators.

Non-magnetic dynamic optical isolators, constructed from modulators, provide a complementary metal oxide semiconductor (CMOS)-compatible approach to optical isolation in integrated photonics. The size of these isolators is strongly constrained by both the frequency and strength of optical modulation. Recent developments in modulators have indicated that large modulation strength, with a magnitude refractive index modulation up to unity, may be possible at gigahertz modulation frequency. In this Letter, we show that a previously proposed dynamic isolator design, based on tandem modulators, can be modified to take advantage of the possibility of such large modulation strength. Compared with the previously proposed tandem modulator design, our modification can lead to significant reduction of the device length without the need to increase modulation frequency.

Design of a compact waveguide optical isolator based on multimode interferometers using magneto-optical oxide thin films grown on silicon-on-insulator substrates

We report the design of a waveguide optical isolator based on multimode interferometer (MMI) structure using silicon on insulator (SOI) and deposited magneto-optical (MO) thin films. The optical isolator is based on a vertical 1 × 2 SOI MMI utilizing the nonreciprocal phase shift (NRPS) difference of different TM modes of the MO garnet thin film/SOI waveguide. By constructing a silicon/MO thin film/silicon structure, we demonstrate that the NRPS of the fundamental and first order TM modes can show opposite signs for certain device dimensions, therefore significantly reduce the device length. For a 310.42 μm long device, 20 dB isolation bandwidth larger than 1.6 nm with total insertion loss of 0.817 dB is achieved at 1550 nm wavelength. The fabrication tolerances and materials losses are also discussed to satisfy the state-of-the-art fabrication technology and material properties.

Nonreciprocalμ-near-zero mode inPT-symmetric magnetic domains

We find that a new type of non-reciprocal modes exist at an interface between two \emph{parity-time} ($\mathcal{PT}$) symmetric magnetic domains (MDs) near the frequency of zero effective permeability. The new mode is non-propagating and purely magnetic when the two MDs are semi-infinite while it becomes propagating in the finite case. In particular, two pronounced nonreciprocal responses could be observed via the excitation of this mode: one-way optical tunneling for oblique incidence and unidirectional beam shift at normal incidence. When the two MDs system becomes finite in size, it is found that perfect-transmission mode could be achieved if $\mathcal{PT}$-symmetry is maintained. The unique properties of such an unusual mode are investigated by analytical modal calculation as well as numerical simulations. The results suggest a new approach to the design of compact optical isolator.

Optical isolator using an atomic vapor in the hyperfine Paschen–Back regime

A light, compact optical isolator using an atomic vapor in the hyperfine Paschen-Back regime is presented. Absolute transmission spectra for experiment and theory through an isotopically pure 87Rb vapor cell show excellent agreement for fields of 0.6 T. We show π/4 rotation for a linearly polarized beam in the vicinity of the D2 line and achieve an isolation of 30 dB with a transmission >95%.

High efficiency continuous-wave single-frequency Nd:YVO4 ring laser under diode pumping at 880 nm

An efficient single-frequency continuous-wave Nd:YVO4 ring laser pumped at 880 nm is presented. With compact four-mirror ring cavity and optical isolator, we obtained an output power of 14.56 W at 1064 nm, corresponding to a slope efficiency of 61.7% and an optical-to-optical efficiency of 58.4% with respect to the absorbed pump power. The stability of the output power was better than ±0.5% over two hours. At the same time, a beam quality factor of M 2≈1.2 was measured and the line width of the longitudinal mode was about 25 MHz. To the best of our knowledge, this is the highest slope efficiency and optical-to-optical efficiency in single-frequency Nd:YVO4 ring laser.

Light fare

This serving of laser equipment will have to sustain readers until next year, offering a variety of lasers, software for laser measurement, a compact optical isolator for diode lasers, as well as mirror, filter and optics accessories.

A 10-Gb/s optical transmitter module with a monolithically integrated electroabsorption modulator with a DFB laser

A compact 10-Gb/s optical transmitter module with small-chirp output was developed by using a monolithically integrated electroabsorption modulator with a distributed-feedback laser. This module can be operated at a bit rate of more than 10 Gb/s at 1.55 mu m, and shows a high modulated output power of approximately 1 dBm with a low optical coupling loss of 3.2 dB between chip and fiber. A multifunctional and compact optical isolator with a monitor photodiode was also developed to decrease noise.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ultraviolet optical isolators utilizing KDP-isomorphs

The KDP isomorphs have both large Verdet constants and excellent optical properties in the ultraviolet. With these combined features it is possible to construct a compact optical isolator using these materials with rare earth permanent magnets. This paper describes the construction of an optical isolator using the KDP-isomorph ADA, and its operation at 351 and 308 nm. The potential use of the other isomorphs in the ultraviolet will also be discussed.

Optical isolators using Bi-substituted rare-earth iron garnet films

Using Bi-substituted rare-earth iron garnet film, (GdBi)3 (FeAlGa)5O12 or (YbTbBi)3 Fe5O12, grown by liquid phase epitaxy technique, we have fabricated a compact, low cost and high performance optical isolator for near-infrared wavelength region, in comparison with conventional isolator using yttrium iron garnet (YIG) single crystal as Faraday rotator. Typical insertion loss and isolation of developed isolators are 0.6 dB and 35 dB respectively at λ=1.31 μm and the size is 6ϕ×6 mm. The isolators, which could be used in the wavelength range of 1.31 to 1.55 μm, are also fabricated with insertion loss of less than 1.1 dB and isolation of more than 35 dB.

Waveguide magneto-optic isolator fabricated by laser annealing

A compact waveguide optical isolator whose input and output light are TE or TM mode has been realized by making adjacent nonreciprocal and reciprocal TE-TM mode converters in a (BiGdLu)3(FeGa)5O12 film. Designed configurations of the magnetization directions were produced by making use of local laser annealing of the film grown on a Gd3Ga5O12 substrate of which the face normal is tilted from the [111] axis. The laser-annealed and nonannealed regions worked as the nonreciprocal and reciprocal mode converters, respectively. The observed isolation agreed with theoretical calculation. An isolation ratio of 12.5 dB was achieved at a wavelength λ=1.15 μm.

Magneto-Optical Properties of (GdBi)3(FeAl)5O12 Bulk Single Crystals and Their Application to a 1.3 ¿m Optical Isolator

A compact optical isolator has been developed for use at a wavelength of 1.3 μm, using a Bi-substituted gadolinium iron garnet (Gd3-xBixFe5O12) single crystal as a Faraday rotator. The optical isolator features a 0.35 dB insertion loss, 34 dB backward loss, and approximately 33.6 dB isolation ratio at 1.3 μm. The insertion loss and the magneto-optical figure of merit in Gd1·8Bi1·2Fe5O12 at 1.3 μ are about 0.025 dB and 3000 deg/dB, respectively. The temperature and magnetic field dependences of the Faraday rotation and the optical absorption have been measured for Gd3-xBixFe5-yAlyO12 single crystals, grown by an improved flux method in which Bi2O3 is used as a flux. The saturation field of the Faraday rotation decreases with Al substitution. The magneto-optical figure of merit of the Fe3+ absorption region at about 0.9 μm was approximately independent of the Al content for y ≪ 0.5. The Faraday rotation in Gd3-xBixFe5O12 (0.85 ≪ x ≪ 1.2) changes by about 7.5%/50°C as the temperature rises above 25°C.

Compact bulk optical isolator with monomode fibre pigtails for use at 1.3 μm

A compact optical isolator has been designed, with monomode optical fibre pigtails, for use at a wavelength of 1.3 μm. The device has an isolation of greater than 26 dB and a fibre-to-fibre insertion loss of 3.5 dB, and the return loss is better than 26 dB.

（ＧｄＢｉ）３（ＦｅＡｌ）５Ｏ１２バルク単結晶の磁気光学特性と１．３μｍ用光アイソレータへの応用

A compact optical isolator has been developed for a wavelength of 1.3 μm using Bi-substituted gadolinium iron garnet (Gd3-xBixFe5O12) single crystal as a Faraday rotator. The optical isolator features 0.35dB insertion loss, 34dB backward loss and about 33.6dB isolation ratio at a wavelength of 1.3 μm. The insertion loss and the magneto-optical figure of merit are about 0.025dB and 3,000 deg/dB, respectively, at a wavelength of 1.3 μm in Gd1.8Bi1.2Fe5O12.Temperature and the magnetic field dependence of the Faraday rotation and the optical absorption have been measured for the single crystals Gd3-xBixFe5-yAlyO12 grown by an improved flux method in which Bi2O3 is used as a flux.The saturation field of the Faraday rotation decreases with an amount of AI-substitution. The magneto-optical figure of merit of Fe3+ absorption region at a wavelength of about 0.9 μm was approximately independent of Al content for y<0.5. The Faraday rotation of Gd3-xBixFe5O12(0.85<x<1.2) changes about 7.5%/50°C as the temperature rises above 25°C.

Waveguide mode conversion by magnetic linear birefringence of Bi-substituted iron garnet films tilted from (111)

TE-TM mode conversion caused by magnetic linear birefringence (MLB) has been studied in liquid-phase-epitaxially grown (BiGdLu)3 (FeGa)5O12 films. The films were grown on Gd3Ga5O12 substrates of which the face normal is tilted from the (111) axis by the angle θc. The LPE growth on the substrate with θc ≠0 made the magnetization of the film tilt from the film normal, and this enabled the mode converter to work without any applied external field. The theory developed to describe the function of the mode converter agreed well with the experimental results. The MLB coefficient is about −9 rad/cm at a wavelength λ=1.15 μm. The Bi substitution is effective to enhance the MLB effect. A role of the MLB mode converter to realize a simple and compact waveguide optical isolator is discussed.

ビスマス多量置換ガドリニウム鉄ガーネットの結晶育成と０．８μｍ光アイソレータへの応用

Single crystals of highly Bi-substituted gadolinium iron garnets have been grown by an improved flux method in which Bi2O3, is used as a flux. Faraday rotation and optical absorption are measured in the near-infrared region at room temperature. The magnetooptical figure of merit is 44deg/dB at 0.78μm in Gd1.8Bi1.2Fe5O12. A very compact optical isolator has been developed for 0.8μm wavelength by using this crystal as a Faraday rotator. The optical isolator features 1.5dB insertion loss and 32 dB backward loss at wavelength of 0.78μm.

ビスマス多量置換ガドリニウム鉄ガーネットの結晶育成と光アイソレータへの応用

Single crystals of highly Bi-substituted gadolinium iron garnets have been grown by an improved flux method using Bi2O3 as a flux. Faraday rotation and optical absorption were measured in the near-infrared region at room temperature. The Faraday rotation of Gd3-xBixFe5O12 increased linearly with x up to 1.15 and the magneto-optical figure of merit reached 180 deg./dB at 1.0μm in Gd1.85Bi1.15Fe5O12. By using this crystal as a Faraday rotator, a compact optical isolator has been developed for near-infrared light. The optical isolator featured <1 dB insertion loss and 36dB isolation at a wavelength of 1.15μm.

A compact optical isolator

This report describes the design and performance of a compact optical isolator for use in the visible region of the spectrum. The device is simple and cheap to manufacture, providing a figure of merit of 37.6 dB with a typical 1 dB insertion loss.