JPH0294586A - Optical amplifier - Google Patents

Abstract

PURPOSE:To solve the problem of a gain difference generated between longitudinal and lateral polarized waves and to obtain an optical amplifier having no polarized plane dependency by separately introducing the longitudinal and lateral polarized waves by a polarization beam splitter, and optically amplifying them independently. CONSTITUTION:When a light of an arbitrary polarized wave is injected from a boat X into a polarization beam splitter 1, the lateral polarized component of the light is transmitted through the splitter 1 to an optical amplifier 3 and amplified. The amplified lateral component is rotated at +45 deg. by a Faraday rotor 5, further reflected by a total-reflection mirror 7, the polarizing plane is again rotated further at +45 deg. by the rotor 5, and varied to the longitudinal polarized wave component. The longitudinal component is again amplified reversibly by the amplifier 3, reflected by the splitter 1, and advanced to a boat Y. On the other hand, the longitudinal component of the incident light from the boat X is reflected by the splitter 1, guided to an optical amplifier 2, and amplified. Thus, optical amplifying characteristic having high gain and no polarization plane dependency is obtained as compared with the optical amplification of a normal single optical amplifier.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an optical amplifier for optical transmission.

[Prior Art] Optical amplifiers with bidirectional optical amplification characteristics, such as semiconductor laser injection-locked amplifiers, co-concentrator type or traveling wave type semiconductor laser amplifiers, have been considered as optical amplification devices for optical transmission. There is.

[Problems to be Solved by the Invention] However, in such an optical amplifier, although the active layer thickness of the semiconductor laser constituting the optical amplifier can be sufficiently controlled to 0.2 μl or less, the active layer width is currently limited. It is difficult to process the thickness to 1 μm or less using the above process technology.

Therefore, the cross section of the waveguide is rectangular, and the field distribution of the electric field is different in the thickness direction and the width direction of the active layer. As a result, a difference occurs in the field distribution between the vertically polarized wave in which the electric field is generated in the active layer thickness direction and the horizontally polarized wave in which the electric field is generated in the active layer width direction, resulting in a different signal gain. In other words, in a single optical amplifier, there is a difference in confinement coefficient between vertically polarized waves and horizontally polarized waves, resulting in a difference in signal gain and a drawback that polarization plane dependence occurs in amplification characteristics.

Therefore, an object of the present invention is to separate vertically polarized waves and horizontally polarized waves into separate optical paths using a polarizing beam splitter and perform optical amplification independently of each other. It is an object of the present invention to provide an optical amplifying device that is free from polarization plane dependence by solving the problem of gain differences that occur in the following.

[Means for Solving the Problems] In order to achieve such an object, the present invention receives input light at a first end and extracts a longitudinally polarized component from two mutually orthogonal second and third ends. a polarizing beam splitter that separates and extracts light and horizontally polarized component light; a first optical amplifier that has optical amplification characteristics in both directions and is coupled to a second end to optically amplify input light; A first Faraday rotator coupled to the output end of the first optical amplifier; a first reflection mirror coupled to the first Faraday rotator; , a second optical amplifier that optically amplifies input light, a second Faraday rotator coupled to the output end of the second optical amplifier, and a second reflection mirror coupled to the second Faraday rotator, The present invention is characterized in that an optically amplified output in which the optically amplified outputs from each of the first and second optical amplifiers are combined is taken out from the fourth end of the polarizing beam splitter.

[Function] In the present invention, the vertically polarized wave and the horizontally polarized wave of the input light are separated into separate optical paths using a polarizing beam splitter, and the separated light is used as the vertically polarized wave in each optical path. By passing through optical amplifiers that have optical amplification characteristics in both directions, both once and once as horizontally polarized waves, it is possible to perform optical amplification with high gain and without polarization dependence. Do it like this. This method differs from conventional technology in that high-gain optical amplification is achieved without polarization dependence.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the structure of an embodiment of the present invention.

Here, l is a polarizing beam splitter coupled to boats X and Y, 2 and 3 are traveling wave optical amplifiers coupled to polarizing beam splitter 1 and having optical amplification characteristics in both directions, and 4 and 5 are Faraday rotators 6 and 7 coupled to optical amplifiers 2 and 3 are total reflection mirrors coupled to Faraday rotators 4 and 5, respectively.

It is assumed that the polarizing beam splitter 1 is configured to transmit only horizontally polarized waves and reflect vertically polarized waves. It is assumed that optical amplifiers 2 and 3 have the same amplification characteristics.

Now, suppose that light of arbitrary polarization is injected from boat Ru. The horizontally polarized wave component amplified in this way is rotated +45° by the Faraday rotator 5, further reflected by the total reflection mirror 7, and then its polarization plane is further rotated +45° by the Faraday rotator 5 again. Therefore, it changes to a vertically polarized component. This longitudinally polarized wave component is again amplified in the opposite direction by the optical amplifier 3, reflected by the polarizing beam splitter 1, and proceeds to the boat Y. That is, the horizontally polarized input light is amplified once each by the horizontally polarized wave and the vertically polarized wave in the optical amplifier 3, so that the plane of polarization is 90°.
It is rotated and output.

On the other hand, the vertically polarized wave component of the input light from boat X is reflected by polarization beam splitter 1 and guided to optical amplifier 2.
It is amplified here. The vertically polarized wave component amplified in this way is guided to the Faraday rotator 4, where the plane of polarization of the vertically polarized wave component is rotated by +45°, and further reflected by the total reflection mirror 6, after which the plane of polarization is It is further rotated by +45° by Faraday rotator 4. Therefore, when the light passes through the optical amplifier 2 from the opposite direction again, it becomes a horizontally polarized wave component, passes through the polarization beam splitter 1, and proceeds to the boat Y. That is, the input light of the vertically polarized component is also amplified once in both the vertical and horizontal polarizations in the optical amplifier 2, and is output with the plane of polarization rotated by 90 degrees.

In this way, in this embodiment, the horizontal polarization, 1ij Has independent amplification properties. Also, for any polarized wave component, optical amplification is performed twice: amplification as a vertically polarized wave and amplification as a horizontally polarized wave, so as usual,
Compared to using a single optical amplifier, a large gain can be obtained.

FIG. 2 shows the configuration of another embodiment of the present invention, in which:
In the arrangement shown in FIG. 1, a 172 wavelength plate 8 is additionally arranged between the polarizing beam splitter 1 and the boat Y. Here, the same parts as in FIG. 1 are given the same reference numerals. By using the I72 wavelength plate 8, it is possible to maintain the polarization plane of input light while providing optical amplification characteristics that are independent of the polarization plane. In this embodiment as well, both of the two output lights from the polarizing beam splitter 1 are 412 (
Since the light is amplified by passing through optical amplifiers 2 and 3 twice, once as an m-wave and once as a horizontally polarized wave, it is much larger than when using a single optical amplifier as usual. Gain is obtained.

[Effects of the Invention] As explained above, according to the present invention, input light is separated into vertically polarized waves and horizontally polarized waves by a polarizing beam splitter and introduced into separate optical paths, and the separated lights are In each optical path, the vertically polarized wave and the horizontally polarized wave pass through the optical amplifier once each and are bidirectionally amplified, so compared to normal optical amplification using a single optical amplifier, the gain is higher and the polarization plane is higher. The advantage is that optical amplification characteristics without dependence can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of an optical amplification device according to the present invention, and FIG. 2 is a block diagram showing another embodiment of the present invention. 1... Polarizing beam splitter, 2.3... Optical amplifier, 4.5... Faraday rotator, 6.7... Total reflection mirror

Claims (1)

[Claims] 1) A polarized beam that receives input light at a first end and separates and extracts vertically polarized light and horizontally polarized light from two mutually orthogonal second and third ends. a splitter; a first optical amplifier having bidirectional optical amplification characteristics and coupled to the second end to optically amplify input light; a first optical amplifier coupled to the output end of the first optical amplifier; a Faraday rotator; a first reflecting mirror coupled to the first Faraday rotator; and a second reflecting mirror coupled to the third end and having optical amplification characteristics in both directions, and coupled to the third end to optically amplify input light. an optical amplifier; a second Faraday rotator coupled to an output end of the second optical amplifier; and a second reflective mirror coupled to the second Faraday rotator, the polarizing beam splitter having a second polarizing beam splitter. , an optical amplification device characterized in that an optical amplification output obtained by combining optical amplification outputs from each of the first and second optical amplifiers is extracted.