Patent
1988-12-07
1991-05-14
Gonzalez, Frank
350 9611, 350 9613, 350 9614, G02B 610
Patent
active
050150510
DESCRIPTION:
BRIEF SUMMARY
The invention concerns an integrated single-mode isolator and, particularly, a guiding device enabling a laser diode to be coupled with optical circuits, while at the same time efficiently preventing the return of light energy towards the laser diode.
As an example, to illustrate the state of the art, FIG. 1 shows a drawing of an isolator and its working. This device consists of a non-reciprocal section I and two accurately oriented polarizers P1, P2. In the non-reciprocal section I, formed by a YIG section, the incident light polarizing plane rotates by 45.degree. by Faraday effect. Any reflected light will have, after a second passage through this section, a polarization crossed with the input polarizer. The isolation effect is then obtained.
In integrated optics, light is propagated in a thin layer of yttrium-iron-garnet doped, for example, with gadolinium and gallium ions, in the form of type TE and TM (plane guide) or E and H (two-dimensional guide) inherent modes. The Faraday effect couples the TE and TM or E and H modes. Thus for a single-mode plane guide, assuming that the incident wave at the input of the guide has a polarization parallel to the mode TEo, the intensity R, converted non-reciprocally into TMo at a point located at a distance Lx from the input of the guide, will have the following expression: ##EQU1##
Where K is the Faraday constant: ##EQU2## being respectively the effective indices of the TEo and TMo modes. FIG. 2 represents the variation of R as a function of L. The relationship (1) shows that, for K constant, the conversion is complete (R=1) only if .DELTA..beta.=0. In this case, the modes are degenerated and a total conversion is obtained for a distance of propagation Z.sub.o such that ##EQU3## For .DELTA..beta..noteq.0, the maximum conversion rate R.sub.M is given by (1) satisfies: ##EQU4##
Thus, for a layer of yttrium-iron-garnet (YIG) substituted by gadolinium and gallium ions, of a thickness of 3 .mu.m, the refractive index n.perspectiveto. to 2.15 and the Faraday rotation K=206.degree./cm at .lambda.=1.15 .mu.m, .DELTA..beta.=1633.degree./cm, giving RM.perspectiveto.1.6%.
By analogy with non-guided optics, an integrated optical isolator uses a non-reciprocal section with a length corresponding to a conversion of 50% in the OUTGOING direction and 50% in the RETURN direction. This section is completed by a polarizer at the input and a polarizer at the output. A single polarizer may suffice. This is the case, for example, with semiconductor lasers which it is desired to shield from stray reflections. For, it has been shown that these sources are practically insensitive to stray reflections having polarization which is perpendicular to their own polarization. In this case, an integrated version of the isolator, formed by a metallic layer which is separated from the garnet by a dielectric, may be envisaged. The drawback in this case comes from the non-coincidence between the planes of the laser and of the garnet.
But in all cases, the isolator, in integrated optics, necessitates a total conversion between the two coupled modes after a to-and-fro movement in the non-reciprocal section. It is therefore imperative to cancel .DELTA..beta., therefore .DELTA.N.
Different solutions have been envisaged to resolve this problem. The article, Effets magnetooptiques dans les grenats et leur application a la realisation d'un isolator et d'un circulator optique (Magneto-optical Effects in Garnets and their Application to the Making of an Isolator and an Optic Circulator", by J. P. CASTERA et al. published in the "Revue Technique THOMSON CSF", Vol. 18, No. 2., June 1986, pp. 255 to 300, describes these different solutions. Two types of solutions were envisaged:
A modulation of the magneto-optical interaction, hence of the coupling constant of the transmission modes as described, for example, in: Letters", Vol. 21, 1972, page 394; Vol. 26, 1975, page 408;
An equalization of the constants of propagation of the two coupled modes, as described in: 13, 1974, page 2007. 14, 1975, page 1479.
However,
REFERENCES:
patent: 4575179 (1986-03-01), Lee et al.
patent: 4671721 (1987-06-01), Dillon, Jr. et al.
patent: 4859014 (1989-08-01), Schmitt et al.
Revue Techniques Thomson-CSF, vol. 18, No. 2, Jun. 1986, Gauthier-Villars J.-P. Castera et al, pp. 255-300.
Applied Optics, vol. 25, No. 12, Jun. 15, 1986, S. Matsumoto et al, pp. 1940-1945.
Optical and Quantum Electronics, vol. 10, No. 5, Sep. 5, 1978, Chapman and Hall Ltd. (GB), pp. 393-398.
Conference Europeenne sur les Communications Optiques, Sep. 21-24, 1982, R. C. Booth et al, pp. 238-243.
Journal of Lightwave Technology, vol. LT-2, No. 2, Apr. 1984, IEEE (New York, U.S.), S. Hava et al, pp. 175-180.
Electronics Letters, vol. 20, No. 25/26, Dec. 6, 1984, (Stevenage, Herts, GB), R. C. Booth et al, pp. 1045-1047.
Carenco Alain
Castera Jean-Paul
Dupont Jean-Marie
Friez Pierre
Meunier Paul-Louis
"Thomson-CSF"
Gonzalez Frank
L'Etat Francais
LandOfFree
Integrated single-mode isolator waveguide and application to a s does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Integrated single-mode isolator waveguide and application to a s, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Integrated single-mode isolator waveguide and application to a s will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1643587