JPS63273828A - Optical isolator - Google Patents

Abstract

PURPOSE:To prevent isolation from decreasing according to temperature variation by using two kinds of magneto-optical materials which vary in Faraday rotation coefficient differently with temperature for one optical isolator. CONSTITUTION:A 1st magneto-optical material 11 and 2nd magneto-optical material 12 are arranged between a polarizer 3 and an analyzer 4 respectively, and permanent magnets 13 and 14 are arranged at their outer peripheries correspondingly. The two kinds of the magneto-optical material 12 and 13 which differ in variation in Faraday rotation coefficient with temperature are used in combination for one optical isolator and then a parameter of a composition ratio (weight component ratio) free from temperature variation in Faraday rotation coefficient is converted into a thickness parameter of the magneto- opticals. Consequently, the isolation is easily prevented from decreasing with temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical isolator used in optical communications and optical information processing.

[Conventional technology]

An optical isolake is an optical element that uses magneto-optical materials, and has the function of blocking reflected light from the light that passes through it.By placing it in the light emitting part of a laser oscillator, it enables stable laser oscillation. ing. A conventional optical isolator 1 includes a polarizer 3 and an analyzer 4 placed on both sides of a magneto-optic material 2, and a permanent magnet 5 placed around the outer periphery of the magneto-optic material 2, as shown in FIG. There is.

The operating principle of the optical isolake will now be described in the case where the laser oscillator is placed on the left side of the optical isolake 1, and the optical fiber coupling end (all paths shown in the figure) are placed on the right side.

Light 6 emitted from the laser diode (path shown) enters the polarizer 3 of the optical isolator 1. The light 6 is separated into two components, ordinary light 7 and extraordinary light 8, by the analyzer 4. The emission position of the extraordinary light 8 after passing through the polarizer 3 is separated from the emission position of the ordinary light 7 by a certain distance. Ordinary light 7 after passing through polarizer 3
, extraordinary light 8 is incident on the magneto-optic material 2.

The magneto-optical material 2 is polished to a thickness that rotates the polarization direction of the incident light 45 degrees counterclockwise when viewed from the center direction of the light 6 when sufficient saturation magnetization is achieved by a permanent magnet 5 or the like. Therefore, the polarization directions of the ordinary light 7 and extraordinary light 8 that have passed through the magneto-optic material 2 are counterclockwise when viewed from the light incident direction with respect to the polarization directions of the ordinary light 7 and extraordinary light 8 before passing through the magneto-optic material 2. It rotates 45 degrees and enters the analyzer 4.

The analyzer 4 transmits ordinary light 7 and extraordinary light 8 that have passed through the magneto-optical material 2 to the analyzer 4 as ordinary light 7 and extraordinary light 8.
It is arranged so that. Therefore, the emission position of the extraordinary light 8 after passing through the analyzer 4 is a certain distance further away from the emission position of the ordinary light 7 after passing through the analyzer 4 than before passing through the analyzer 4. The optical isolake 1 is arranged so that the ordinary light 7 after passing through the analyzer 4 is coupled to the optical fiber at the optical fiber coupling end.

Next, in the optical isolator 1 arranged in this manner, the reason why the reflected return light from the right optical fiber end does not return to the laser oscillator will be explained. The light reflected from the fiber end is separated into ordinary light 7 and extraordinary light 8 by an analyzer 4.

The emission position of the extraordinary light 8 after passing through the analyzer 4 is a certain distance apart from the emission position of the ordinary light 7 after passing through the analyzer 4. The ordinary light 7 and the extraordinary light 8 separated by the analyzer 4 are transmitted through the magneto-optical material 2 so that their respective polarization directions are 45 degrees clockwise relative to the polarization direction before transmission, as viewed from the direction of incidence of the light. Rotate.

In the magneto-optical material 2, the rotating direction of the polarization direction is opposite to the direction of the light incidence when the direction of the applied magnetic field and the direction of the light incidence are the same direction and when they are opposite. . Therefore, while the polarization direction rotates counterclockwise in the forward direction, it rotates clockwise in the reverse direction. The ordinary light 7 and extraordinary light 8 after passing through the magneto-optical material 2 become extraordinary light 8 and ordinary light 7 with respect to the polarizer 3. Therefore, the ordinary light 7 after passing through the polarizer 3
The position is a certain distance away from the position of the ordinary light 7 before passing through the polarizer 3, and the light from the end of the optical fiber is the ordinary light 7.
, and the abnormal light 8 do not return to the laser oscillator. This is the principle of the optical isolake 1.

In the case of the optical isolator 1 with such a configuration, the condition that the light does not return to the laser oscillator in the opposite direction is that the separation direction of the extraordinary light 8 is relatively shifted by 45 degrees between the polarizer 3 and the analyzer 4. The point is that a magneto-optical material 2 that rotates the polarizer 3 by 45 degrees must be inserted into the polarizer.

However, in the currently used magneto-optical materials 2, the angle at which the polarization direction is rotated, that is, the Faraday rotation coefficient, changes with temperature. This results in a large deviation, and the isolation of the optical isolator 1 deteriorates. In such a situation, the distributed feedback laser module will suffer from unstable laser oscillation due to reflected return light.
When the optical isolator 1 is mounted, laser oscillation becomes unstable in areas where the environmental temperature changes, making it impossible to use it for communication.

Therefore, the development of magneto-optical materials 2 with less change in Faraday rotation coefficient with respect to temperature is underway, and in bulk crystal type optical isolators, C, YIG (yttrium, iron, garnet) is used instead of YIG (yttrium, iron, garnet). dYIG (gadolinium, yttrium, iron, garnet) and a thick film crystal grown by LPE (liquid phase epitaxial) method are (G d B
1) Instead of 3 I G (bismuth substitution, iron, garnet), TbB1 IC (terbium/bismuth substitution/
Garnet) and YbTbIG (yttrium bismuth substituted garnet) have been produced, and the development of temperature characteristics is progressing using these materials (P,
P1941-1945 June1986/Vo125
, No. 12/APPLIBD 0PTIC3, Institute of Electronics and Communication Engineers Technical Report CPM86-36).

On the other hand, there is a way to avoid a decrease in isolation due to temperature changes by increasing the absolute value of isolation by making the conventional optical isolator two stages (preliminary paper of the 1986 IEICE National Conference of Optical and Radio Division) Collection 2-109).

[Problem that the invention seeks to solve]

The above-mentioned improvement in the temperature characteristics of conventional optical isolators is achieved by adjusting the composition ratio of the magneto-optical material, but it is actually possible to reduce the temperature change in the Faraday rotation coefficient, but it cannot be reduced to zero. This is the current situation. Further, even when high isolation is achieved by using two stages of optical isolators, temperature dependence still exists. Therefore, it has the disadvantage that high isolation cannot be ensured over a wide temperature range.

An object of the present invention is to provide an optical isolator with significantly improved temperature characteristics by improving magneto-optic materials.

[Means for solving problems]

The optical isolator of the present invention uses a combination of two types of magneto-optical materials whose Faraday rotation coefficients change with respect to temperature in one optical isolator, and the composition ratio (weight component ratio) that does not change the Faraday rotation coefficient with temperature. By being able to convert the parameter to the thickness parameter of each magneto-optical material, it is possible to easily prevent a decrease in isolation against temperature changes.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a longitudinal sectional front view of an optical isolake showing the principle of the present invention, and the principle will be explained based on this figure.

Between the polarizer 3 and analyzer 4 of the optical isolake, there is a first
A magneto-optical material 11 and a second magneto-optic material 1112 are arranged respectively, and permanent magnets 13 and 14 are arranged on the outer periphery of these materials.
are arranged accordingly.

Now, the Faraday rotation coefficients of the magneto-optic material 11 and the magneto-optic material 12 at a certain temperature To are expressed as θFOI, θ
,. 2. Let the thickness of each material be tl and t2. At this time, if the increase and decrease of the Faraday rotation coefficient at an arbitrary temperature T are respectively △θFl(a) and △θP2(a), the Faraday rotation angle at this temperature is as shown in the following equation (where a −ΔT).

θF1−(θ, .1+ΔθPI(a’l)) Xt.

θF2−(θpo2+Δθp2(a)) X j2 At this time, by satisfying the following condition, the Faraday rotation angle becomes independent of temperature.

Iθ,. 1]-1θ,. 21Xt2=45...
(1) 1△θPI(al l l△θp2(a) l X
t2=0 (2) Therefore, these formulas (1) and (2) are satisfied.

The first
When the optical isolator shown in the figure is configured, it is possible to prevent a decrease in isolation caused by the temperature dependence of each Faraday rotation angle by combining two magneto-optical materials.

Next, an embodiment of an optical isolator to which the principle of the present invention is applied will be described based on FIG. The wavelength of the light used is
1.31 μm, and YI as the first magneto-optical material 11.
G, Gd2.G as the second magneto-optical material 12; l BIQ, 9 (FeAAGag) 50
12 (Gadolinium/Bismuth substitution/Iron/Garnet)
I decided to use . These materials rotate the polarization direction of the light counterclockwise and clockwise, respectively, when the direction of the light incident edge matches the direction of the magnetic field. Now, assume that the direction of clockwise rotation is positive. T'C
'IMC used in.

and G d2. + B 10.9 (F e A j
! G as)s 0+2 (7) The Faraday rotation coefficients are as shown in the following equation within the range that can be approximated by a straight line.

θ,,=220-0. 176 (T-25) (dig
/cm) θF2=-1500+2.63 (T-25) (dig
/cm) These magneto-optical materials 11.12 are expressed by formulas (1) and (2).
) The respective thicknesses that do not satisfy the formula are t+ = 3.
76 mm, t2 = 0.251 mm, and the Faraday rotation angle at 25°C is 82.
7 degrees, which is 37.7 degrees in the negative direction.

The optical isolator shown in FIG. 2 was constructed using these magneto-optical materials 11 and 12, a polarizer 3 made of a Rochon prism, and an analyzer 4. Figure 3 shows the isolation obtained using this optical isolake in the temperature range from 0°C to 60'''C.The two permanent magnets 13, 14 in Figure 1 are YIG and G d2., B. io,,,(F e A RG
When the direction of the magnetic field of ashs ○1□ and the direction of incidence of light are the same, the directions of rotating the polarization direction of light are opposite, so it is necessary to apply magnetic fields in opposite directions to each magneto-optical material 11.12. is lost, so one permanent magnet I5
I made it.

Also, Gd2. + 810.9 (F eAβGa9>50,
2, and T b2. o B it, o F e5
012 Optical isolake with improved temperature characteristics by making the magneto-optical material (telephram, bismuth substitution, garnet) to a thickness that satisfies the conditions of equations (1) and (2), and applying magnetic fields in opposite directions. It is possible to configure As the polarizer 3 and analyzer 4, a calcite plate, rutile plate, PBS (
It is also possible to use polarized beam blocks).

In this example, the Faraday rotation coefficient of the magneto-optical material used was linearly approximated, but it is presumed that high isolation can be achieved over a wider temperature range by performing curve approximation and optimally selecting the composition ratio of the material. Ru.

In the examples described above, YIG was also used as the magneto-optical material used in the examples.

G d2g B io, 9(F e A I G a
s) s 0+2 was used, but this magneto-optical material has an established crystal growth technology, and it is possible to secure a stable material for use in the optical isolator and to ensure that the two magneto-optic materials have different polarization rotation directions. , there is an advantage that one permanent magnet can be used.

〔Effect of the invention〕

As explained above, according to the present invention, by using two types of magneto-optical materials with different Faraday rotation coefficient changes with respect to temperature in one optical isolake, it is possible to prevent a decrease in isolation due to temperature changes. This makes it possible to significantly improve the temperature characteristics of the optical isolake.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional front view of an optical isolator showing the principle of the present invention, FIG. 2 is a longitudinal sectional front view of an optical isolator showing an embodiment of the invention to which the principle of FIG. 1 is applied, and FIG. A diagram showing insertion loss and isolation with respect to temperature of the optical isolator of the invention, and FIG. 4 is a longitudinal sectional front view showing an example of a conventional optical isolator. 3...Polarizer (lotion prism), 4...
...Analyzer (lotion prism), 7...
・Ordinary light, 8...Abnormal light, 11...1st
magneto-optical material (YIG), 12... Second magneto-optic material (G d2.+B 1o, 9 (F e A 12 G
as) so+2), 13.14.15...Permanent magnet. Applicant: NEC Corporation Agent
Patent Attorney Umeo Yamauchi Figure 1

Claims (1)

[Claims] In an optical isolator in which a magneto-optical material is disposed between a polarizer and an analyzer, and a permanent magnet is provided on the outer periphery of the magneto-optic material, the polarization rotation direction of the magneto-optic material,
An optical isolator characterized in that two types of magneto-optical materials different in at least one of composition and thickness are disposed between the polarizer and the analyzer, respectively.