JP2001004860A - Optical equalizer and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust wavelength characteristic with stable properties, low insertion loss, and without polarization dependent loss. SOLUTION: This optical equalizer, is provided with a center core 2 and a ring core 3 at the center of an optical fiber 1 and around the periphery of the center core 2, respectively, and an inner clad 4 and an outer clad 5 between the center core 2 and the ring core 3 and around the periphery of the ring core 3, respectively, and thereby its insertion loss is varied with wavelength. This insertion loss varies in a sine wave form and has positive and/or negative gradient in the 1,500-1,650 nm region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical equalizer,
In particular, the present invention relates to an optical equalizer having stable characteristics, small insertion loss, no polarization dependent loss, and capable of adjusting wavelength characteristics, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, Dense-WDM (Wavelength Division Multiplex) (Dense Wavelength Division Multiplexing) has been actively used in optical signal transmission of optical fibers.
It has become necessary to transmit using a 50 nm band, that is, a wavelength band in a wide band (wavelength range) from 1530 nm to 1610 nm.

For this reason, in this wavelength range, it is important to flatten the insertion loss (gain) of the optical device at each wavelength. At present, flattening the gain of an optical amplifier has been attracting attention, and flattening the wavelength dependence of the insertion loss of an optical device used in the vicinity has been actively performed. I have. That is,
The flattening of the wavelength-dependent characteristics of the optical components in the repeater has been promoted.

[0004] On the other hand, the wavelength loss itself of an optical fiber used in a transmission line has also become a problem. The wavelength loss of the optical fiber is caused by the wavelength characteristic of the loss of the line itself and the bending loss generated by the distortion generated when the cable is formed. That is, the wavelength characteristic of the optical fiber transmission line changes each time depending on the length of the optical fiber, the state of the cable, and the state of installation.

The following is a recent conventional technique for flattening the insertion loss of the optical device and the loss of the line itself. Long Period Fiber Grating
Grating) (1997 IEICE General Conference, C-3-150, PP335, “Temperature-dependent long-period fiber grating”) In the case of an equalizer using a long-period fiber grating,
If the temperature changes, the loss value will change.
Special packages are required. For this reason, there are disadvantages that the characteristics are not stable and that the cost is increased.

[0006] Equalizer using dielectric multilayer film and etalon (IEICE Technical Report, EMD96-42, CPM96-65, OPE9
6-64, LQE96-66 (1996-08), PP19-24, "Wavelength multiplexing transmission optical fiber amplifier and gain equalizer") When using dielectric multilayer film or etalon, bulk type between optical fibers In order to insert the above components, the optical fiber must be once out of the fiber, and the light needs to be incident on the optical fiber. For this reason, there are disadvantages that the insertion loss increases and the cost increases.

An equalizer using a fiber coupler type (The Institute of Electronics, Information and Communication Engineers, 1993, C-246, PP4-282) A fiber coupler generally has a sinusoidal wavelength characteristic of insertion loss. The disadvantage is that the polarization dependent loss is large. Equalizer using twin-core type (1999 IEICE General Conference, B-13-3, PP584, "Optical fiber filter using twin-core fiber") A fiber coupler is manufactured by using two optical fibers. However, in the case of the twin core fiber type, the optical fiber has two cores. However, as in the case of the fiber coupler type, it is difficult to increase the polarization dependent loss.

[0008]

As described above, in order to flatten the insertion loss of the optical device and the loss of the line itself, in the prior art, the characteristics are not stable, the insertion loss is large, There were difficulties such as an increase in wave-dependent loss. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and the present invention provides an optical equalizer having stable characteristics, small insertion loss, no polarization dependent loss, and capable of adjusting wavelength characteristics, and a method of manufacturing the same. It is intended to provide.

[0009]

In order to achieve this object, an optical equalizer according to the present invention is provided with a center core at the center of an optical fiber and a ring core at the periphery, and a center between the center core and the ring core. By providing an inner clad and an outer clad on the outer periphery of the ring core, the insertion loss is changed according to the wavelength.

In the optical equalizer of the present invention, the insertion loss changes depending on the wavelength, and the manner of the change is sinusoidal. The optical equalizer of the present invention has a positive and / or negative slope with an insertion loss of 1500 to 1650 nm. The optical equalizer of the present invention has a structure in which an optical fiber is reinforced with a reinforcing member such as glass or a ferrule.

In the optical equalizer according to the present invention, optical fibers for transmission lines are connected to both ends of the optical fiber. The method for manufacturing an optical equalizer of the present invention is to prepare a preform in which a center core, an inner clad, a ring core, and an outer clad are sequentially laminated from the center toward the outer periphery, and the preform is melt-drawn. It consists of reducing the diameter to a predetermined diameter. This preform may be an optical fiber.

In the method for manufacturing an optical equalizer according to the present invention, the melt drawing is performed by applying a laser beam from one end of the optical fiber and monitoring the received light power at the other end to give a predetermined insertion loss wavelength characteristic. In this optical equalizer, the characteristics are stable, the insertion loss is small, and the wavelength characteristics can be adjusted without any polarization-dependent loss.

According to the method of manufacturing the optical equalizer,
An optical equalizer having the above characteristics can be easily manufactured.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an optical equalizer and a method for manufacturing the same according to the present invention will be described below with reference to the drawings. In FIG. 1A, the optical equalizer of the present invention is provided with a center core 2 at the center of an optical fiber 1 and a ring core 3 at a periphery thereof.
An inner clad 4 is provided between the ring core 3 and an outer clad 5 on the outer periphery of the ring core 3. FIG. 1B shows a profile in which the horizontal axis represents the radius of the optical equalizer and the vertical axis represents the refractive index difference. With this refractive index profile, the insertion loss changes depending on the wavelength, as described later.

In the optical equalizer of the present invention, as shown in FIG. 4, the insertion loss changes depending on the wavelength, and the manner of the change is sinusoidal. The optical equalizer of the present invention has a positive slope p and / or a negative slope n at an insertion loss of 1500 to 1650 nm as shown in FIG. 4 and 5 in the optical equalizer of the present invention.
It can be seen that there is a loss variation at a period of about 80 nm as shown in FIG.

As described above, in the optical equalizer of the present invention, the insertion loss changes depending on the wavelength. In the optical equalizer of the present invention, the optical fiber 1 is made of glass (quartz) as shown in FIG.
It has a structure in which it is fixed on a substrate with a UV adhesive and packaged, or reinforced with a reinforcing member 8 such as a ferrule 7. The optical equalizer is used by connecting an optical fiber for a transmission line to both ends of an optical fiber 1.

In order to provide a desired wavelength characteristic of insertion loss in the optical equalizer of the present invention, the lengths of the center core 2, the ring core 3 and the optical fiber 1 of the optical fiber 1 must be designed. When fine adjustment of the wavelength range of the wavelength characteristic or the amount of insertion loss is required, the adjustment is performed by melt stretching described later. In order to obtain a desired refractive index profile of the optical fiber 1 (FIG. 1 (a)), CVD, MCVD, and O which are generally used for manufacturing a preform (base material) of the optical fiber are used.
This can be achieved by using the VD method or the like.

That is, as shown in FIG. 2, the manufacturing method of the optical equalizer is such that the center core 2 is moved from the center to the outer periphery.
, An inner clad 4, a ring core 3, and an outer clad 5 are sequentially laminated to prepare a preform 10, and the preform 1 is heated using a burner 11.
0 is spun to a predetermined diameter, which is melt-drawn and reduced to an optical fiber 1 having a predetermined diameter. In addition, the preform 10 may be an optical fiber in which the center core 2, the inner clad 4, the ring core 3, and the outer clad 5 are sequentially stacked from the center to the outer periphery.

In this melt drawing, a laser beam is incident from one end of the optical fiber by a wavelength-tunable Fabry-Perot laser diode FP-LD, and the received light power is monitored by a photodiode PD at the other end to obtain the required length and diameter. The adjustment is performed by giving a predetermined insertion loss wavelength characteristic. FIG. 3 shows a profile in which the abscissa represents the radius after the melt stretching and the ordinate represents the difference in refractive index. As shown in FIG. 3, the refractive index between the center core 2 and the ring core 3 is different between the state of the preform (FIG. 1B) and the state of the optical fiber after spinning and melt drawing (FIG. 3).

According to the method for manufacturing an optical equalizer of the present invention, an optical equalizer having the above characteristics can be easily manufactured. In this optical equalizer, the structure of the center core 2 is similar to that of a normal SMF (single mode fiber) or the like. In particular, the MFD (mode field diameter)
Transmission fiber (not shown) attached to both ends of this optical equalizer
Will be similar to MFD. The ring core 3 is designed to have the LP02 mode. The feature of this optical equalizer is that there are two modes, a mode LP01 dominated by the center core 2 and a mode LP11 dominated by the ring core 3, and the mutual mode coupling causes the wavelength dependence of the insertion loss. Changes into a sine shape (FIGS. 4 and 5). This is because the propagation constants of the two modes LP01 and LP11 are different,
This is because the two modes interfere.

FIG. 6 shows wavelength on the horizontal axis and PDL (polarization dependent loss) on the vertical axis. As shown in FIG.
L (polarization dependent loss) is 0.035dB over the whole range of 1450-1580nm
Because it is below, it can be almost ignored. In the equalizer configured as described above, the characteristics are stable, the insertion loss is small, and the wavelength characteristics can be adjusted without the polarization-dependent loss. According to this equalizer, it is possible to equalize the loss of the optical fiber line depending on the wavelength by placing the equalizer in an optical repeater or the like.

The optical equalizer of the present invention is used as a repeater in an optical fiber transmission line, an optical component in an optical amplifier, or an optical fiber type device, and has a wavelength dependency on insertion loss and loss of the line itself. It is possible to eliminate.

[0023]

As is clear from the above description, according to the optical equalizer of the present invention, the characteristics are stable, the insertion loss is small, and the wavelength characteristics can be adjusted without the polarization-dependent loss. . According to the method for manufacturing an optical equalizer of the present invention,
An optical equalizer having such characteristics can be easily manufactured.

[Brief description of the drawings]

1A is a cross-sectional view illustrating an optical equalizer according to an embodiment of the present invention, and FIG. 1B is a diagram illustrating a refractive index profile according to an embodiment of the optical equalizer according to the present invention.

FIG. 2 is a diagram showing a method for manufacturing an optical equalizer according to the present invention.

FIG. 3 is a view showing a refractive index profile after melt stretching of an embodiment of the optical equalizer according to the present invention.

FIG. 4 is a diagram showing wavelength and insertion loss in one embodiment of the optical equalizer according to the present invention.

FIG. 5 is a partially enlarged view showing wavelength and insertion loss in one embodiment of the optical equalizer according to the present invention.

FIG. 6 is a diagram showing wavelength / PDL characteristics in an embodiment of the optical equalizer according to the present invention.

FIG. 7 is a diagram showing a structure in which an embodiment of the optical equalizer according to the present invention is reinforced with a reinforcing member.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical fiber 2 ... Center core 3 ... Ring core 4 ... Inner clad 5 ... Outer clad p ... Positive inclination n ... Negative inclination 6 ... Glass substrate 7 ... Ferrule 8 ... Reinforcement 10 ... Preform

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuichi Murakami 2-1-1, Oda Sakae, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Inside Showa Electric Wire & Cable Co., Ltd. (72) Inventor Shiro Katsuki Sakae Oda, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture 2-1-1, Showa Electric Wire & Cable Co., Ltd. F-term (reference) 2H050 AA04 AB03Z AC28 AD16 5K002 AA07 BA02 CA01 DA02 FA01

Claims (8)

[Claims] An optical fiber has a center core at a central portion thereof, a ring core at a peripheral portion thereof, an inner cladding between the center core and the ring core, and an outer cladding at an outer peripheral portion of the ring core. An optical equalizer characterized in that the insertion loss is changed according to the wavelength. 2. The optical equalizer according to claim 1, wherein said insertion loss changes according to the wavelength, and the manner of the change is sinusoidal. 3. The optical equalizer according to claim 1, wherein said insertion loss has a positive and / or negative slope between 1500 and 1650 nm. 4. The optical equalizer according to claim 1, wherein said optical fiber has a structure in which said optical fiber is reinforced by a reinforcing member such as glass or ferrule. 5. The optical equalizer according to claim 1, wherein optical fibers for a transmission line are connected to both ends of said optical fiber. 6. A preform in which a center core, an inner clad, a ring core, and an outer clad are sequentially laminated from a central portion to an outer peripheral portion is prepared, and the preform is melt-drawn and reduced to a predetermined diameter. A method for manufacturing an optical equalizer, comprising: 7. The method according to claim 6, wherein said preform is an optical fiber. 8. The optical fiber according to claim 6, wherein the melt drawing is performed by applying a laser beam from one end of the optical fiber and monitoring the received light power at the other end to give a predetermined insertion loss wavelength characteristic. A manufacturing method of the optical equalizer described in the above.