JPH04161929A - Light amplifier and optical transmission - Google Patents

Abstract

PURPOSE:To enable optical transmission by furnishing a semiconductor laser element and an input and an output optical fiber, specifying the gain center wavelength of this semiconductor laser element, and thereby keeping the signal level constant over a wide wavelength range. CONSTITUTION:Arrangement according to the present invention comprises a semiconductor laser element 3 and an input and an output optical fiber 1. wherein the gain communication wavelength of the laser element 3 lies either on the side longer than 1.55mum or on the shorter side. Dislocation of the gain center wavelength of light amplifier off 1.55mum provides a flat wavelength amplification characteristic on the longer or shorter side off 1.55mum. Thereby the signal light level can be kept constant over a specific wavelength range, which enables optical transmission.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to optical amplifiers and optical transmission devices used in optical communications.

BACKGROUND OF THE INVENTION In recent years, wavelength division multiplexing optical communication and optical amplification technologies have been actively researched as optical transmission systems have become faster and larger in capacity. Wavelength multiplexing optical communication is a method of transmitting multiple signals through a single optical fiber using signal lights with different wavelengths, and optical amplification is a method of amplifying optical signals that are attenuated during fiber transmission while still being optical. . In optical amplification, wavelength-multiplexed optical signals can be amplified all at once. The configuration of the optical amplifier is shown in FIG.

Signal light incident from the input fiber 11 is coupled to the semiconductor laser element 14 via the lens 12.

Both end faces of the semiconductor laser element 14 are coated with an antireflection film or a window structure S.
As a result, the end face reflectance is suppressed, and it is more excited than the Pi lightning current. When light is incident on this semiconductor laser element 14, the amplified light is emitted from the other end (for example, Institute of Electronics and Communication Engineers Technical Research Report 0QE-114, page 23, Saito et al., 1986).

Problems to be Solved by the Invention Currently, the wavelength band for optical communication is 1.3μ, where dispersion is 0.
The m band and the 1,5511 m band with the lowest transmission loss are used. The relationship between wavelength, optical fiber transmission loss, and wavelength is shown in No. 140. Loss in the fiber is caused by Lehle scattering on the short wavelength side and infrared absorption on the long wavelength side. 1.5
The minimum value is reached at 5 μm. On the other hand, the gain of a semiconductor laser element used in an optical amplifier draws a parabolic curve around a certain wavelength, as shown in FIG. If the wavelength of the transmission signal light is a single wavelength, the gain center wavelength of the semiconductor laser element 14 is set to 1.55μ, which minimizes the fiber loss.
If it is set to m, the optical amplification effect can be utilized to the maximum, and the relay distance can be increased. However, when wavelength-multiplexed signal light is amplified, the gain characteristic of the semiconductor laser element 14 has a large wavelength dependence, so if it deviates from the gain center wavelength, the amplification degree decreases. The signal level will vary, and the possible transmission distance will vary, placing constraints on system design. Furthermore, since the transmission loss of an optical fiber is also wavelength dependent, the signal level difference is emphasized as shown in FIGS. 16 and 17. Therefore, if such optical amplifiers are connected in multiple stages, the difference in signal strength for each wavelength at the receiving section will be greatly expanded.

In view of the above problems, the present invention provides an optical amplifier and an optical transmission device that maintain a constant signal level over a wide wavelength range and transmit light.

Means for Solving the Problems In order to solve the above problems, the optical amplifier of the present invention is such that the gain center wavelength of the semiconductor laser element is shifted to the longer or shorter wavelength side than the wavelength of 1.55 μm.

Even if the gain center wavelength of the semiconductor laser device increases by 1.3 μm, it does not shift toward the shorter wavelength side.

= Two semiconductor laser elements, gain center wavelength is wavelength 1.5
It is composed of a combination of lengths longer than 5 μm and lengths shorter than 5 μm.

The laser element has a quantum well structure and the gain curve has two peaks relative to the center wavelength.

A device that provides chromatic aberration through the wavelength dispersion of the coupling lens and maximizes coupling efficiency at wavelengths longer or shorter than the gain center wavelength of the semiconductor laser element.

Chromatic aberration is imparted to the pattern of the coupling hologram lens, and the coupling efficiency is maximized on the long and short wavelength sides of the gain center wavelength of the semiconductor laser element, and the coupling efficiency is reduced at the gain center wavelength.

The gain center wavelength is attenuated by an optical filter.

Also, in optical transmission equipment, the gain of the optical amplifier is reduced in the minimum loss wavelength region of the optical fiber.

Operation The present invention provides an optical amplifier and an optical transmission device that maintain a constant level of signal light over a specific wavelength range and transmit light using the above-described configuration.

Embodiment Hereinafter, an embodiment of the optical amplifier and optical transmission device of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of an optical amplifier in one embodiment of the present invention.

1 is an input fiber, 2 is a coupling lens, 3 is a semiconductor laser element, and 4 is a coupling lens. Semiconductor laser element 3
has a gain center wavelength on the longer or shorter wavelength side than 1.55 μm. The wavelength characteristic considering both the gain of the optical amplifier and the loss due to optical fiber transmission is shown in FIG. The gain center wavelength of the optical amplifier is set to 1.55 μm.
By shifting from 1.55 μm, a flat wavelength amplification characteristic can be obtained on the long wavelength or short wavelength side.

In the second embodiment, the gain center wavelength of the semiconductor laser device 3 shown in FIG. 1 is set to a wavelength shorter than 1.3 μm. The wavelength characteristics at this time are flattened as shown in FIG.

FIG. 4 shows a third embodiment. The incident light is amplified in two stages by semiconductor laser elements 31 and 32. The wavelength gain characteristics of semiconductor laser elements 31 and 32 have a deviation of 1.55 μm.
on the long wavelength and short wavelength sides.

Therefore, the wavelength characteristic is 1.55μ as shown in Figure 5.
It is flattened around m.

In the fourth embodiment, the semiconductor element 3 has a quantum well structure. A semiconductor laser element having a quantum well structure has a bimodal gain characteristic as shown in FIG. 6, so when this is combined with fiber transmission loss, the wavelength characteristic is flattened around 155 μm.

A fifth embodiment is shown in FIG.
chromatic aberration is generated due to the wavelength dispersion property of the glass material, and the focus is focused at the long or short wavelength of the gain center wavelength of the semiconductor laser element 3, and the output of the semiconductor laser element 3 is maximally coupled to the output fiber 5, and the gain center At wavelengths, chromatic aberration causes blurring and coupling loss.

Therefore, as shown in FIG. 7, the wavelength characteristics can be flattened by the combination of the coupling loss of the lens 4 or 2 and the gain characteristics of the semiconductor laser element 3.

A sixth embodiment is shown in FIG. Reference numeral 41 denotes a coupling hologram lens, which focuses on the long and short wavelengths of the gain center wavelength of the semiconductor laser element 43 and
The output of No. 3 is maximally coupled to the output fiber 45, and at the gain center wavelength, blurring occurs due to aberrations and coupling loss occurs. Therefore, as shown in FIG. 9, the wavelength characteristics can be flattened by the combination of the coupling loss of the lens 41 and the gain characteristics of the semiconductor laser element 43.

A seventh embodiment is shown in FIG. An optical filter 58 is given a predetermined transmittance at the gain center wavelength of the semiconductor laser element 53, and absorbs or reflects a part of the light at the maximum gain wavelength of the semiconductor laser element 53 to reduce the maximum gain. FIG. 11 shows the gain of the semiconductor laser element 53, the wavelength characteristics of the optical filter 58, and the combined wavelength characteristics.

Furthermore, a coating may be applied to the coupling lens 52Q instead of the optical filter.

No. 121 shows an optical transmission device of the present invention. It is composed of a signal light source 21 with different wavelengths, an optical fiber 22, an optical amplifier 23, and an optical receiver 24, and the light of each wavelength emitted from the signal light source 21 is combined into one fiber 22 by a multiplexer or optical coupler 25. be combined. When signal light is transmitted through a fiber, its intensity is attenuated according to the transmission characteristics of the fiber. The attenuated wavelength multiplexed signal light is amplified by the optical amplifier 23. Since the optical amplifier has amplification gain characteristics that are flattened in the wavelength range by the above means,
As shown in Part 18, the amplified output light has approximately the same intensity at each wavelength. Therefore, after connecting optical amplifiers in multiple stages, the signal light intensity at each wavelength of the signal received by the optical receiver 24 has small variations.

Effects of the Invention As described above, the present invention provides an optical amplifier with improved wavelength characteristics at wavelengths longer or shorter than 1.55 μm by shifting the gain center wavelength of the semiconductor laser element toward longer or shorter wavelengths than 155 μm. is flattened.

The wavelength characteristics are flattened by shifting the gain center wavelength of the semiconductor laser element to the shorter wavelength side than the wavelength of 1.3 μm.

Two semiconductor laser elements have a gain center wavelength of 1.55.
The wavelength characteristics are flattened by configuring a combination of lengths longer than μm and lengths shorter than μm.

The laser element has a quantum well structure and the gain curve is bimodal with respect to the center wavelength, thereby flattening the wavelength characteristics.

A device that gives chromatic aberration through the wavelength dispersion of the coupling lens, maximizes the coupling efficiency on the longer or shorter wavelength side than the gain center wavelength of the semiconductor laser element, and flattens the wavelength characteristics on the longer or shorter wavelength side than the gain center wavelength. It is.

By imparting chromatic aberration to the pattern of the coupling hologram lens, the coupling efficiency is maximized on the long and short wavelength sides of the gain center wavelength of the semiconductor laser element, and the coupling efficiency is decreased at the gain center wavelength 52, and the coupling efficiency is maximized on the long and short wavelength sides of the gain center wavelength of the semiconductor laser element. Or on the short wavelength side; the wavelength characteristics are flattened here.

The optical filter S lowers the gain at the gain center wavelength of the semiconductor element and flattens the wavelength characteristics.

Furthermore, by reducing the gain of the optical amplifier in the minimum loss wavelength region of the optical fiber in the optical transmission device, it is possible to suppress variations in the signal light intensity of each wavelength even if the fibers are connected in multiple stages.

[Brief explanation of drawings]

1, 4, 8, and 10 are block diagrams of optical amplifiers in one embodiment of the present invention, and FIGS. 2, 3, 5,
6, 7, 9, and 11 are overall gain curve diagrams of the optical amplifier according to the present invention, FIG. 12 is a configuration diagram of an optical transmission device according to an embodiment of the present invention, and FIG. 13 is a conventional FIG. 14 is a transmission loss characteristic diagram of an optical fiber, FIG. 15 is a gain characteristic diagram of a semiconductor laser element, and FIG. 161 is a general f in a conventional embodiment.
111 circuit diagram, FIG. 17 is a signal transmission characteristic diagram in a conventional actual example, and FIG. 18 is a signal transmission characteristic diagram of an optical transmission device according to the present invention. 1, Il, 33.40.51... Input fiber, 5.36.45, 55.16... Output fiber, 2.4.12.15.34.35°42 .5
2.54... Combined lens, 3.14°31.3
2.43.53... Semiconductor laser element, 41...
... Combined hologram lens, 58 ... Optical filter. Name of agent: Patent attorney Haruaki Koba 2nd person: To Tomonaga [Nn-1] 3rd figure: To the Deputy Director (prnl): 32-1-↓Hikiri-Zakami ; 33--manpower 774+ 3, 3f--one sister Lucis °" 3C-11 fat fiber 3'T---", skin 1 ~ meeting) mokimaru 3a---4 middle nine Is 5 figure self skin long entry] Fig. 6 5 zacho entry (, 11 hat 7 figure skin input (ρm1 3°53-1 ↑ 9th figure ten moxibustion Fig. 14 To Jikinaga (Unit) Fig. 15 To Jikinaga Fig. 16 To Mirai [7J Tsuyoshi Fig. 17 Shoulder λ table □ λ]-1 -N IΣL IL Jyu T Talented woman-
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Claims (8)

[Claims] (1) A semiconductor laser device and an input and output optical fiber are provided, and the gain center wavelength of the semiconductor laser device is wavelength 1.
．． An optical amplifier characterized in that the wavelength is shifted to the longer or shorter wavelength side than 55 μm. (2) A semiconductor laser element and an input and output optical fiber are provided, and the gain center wavelength of the semiconductor laser element is a wavelength of 1.
．． An optical amplifier characterized by shifting the wavelength to shorter than 3 μm. (3) An optical amplifier comprising two semiconductor laser elements and input and output optical fibers, the semiconductor laser elements having a gain center wavelength longer than 1.55 μm and one shorter than the wavelength of 1.55 μm. (4) An optical amplifier comprising a semiconductor laser element and input and output optical fibers, wherein the semiconductor laser element has a quantum well structure and a gain curve is bimodal with respect to a center wavelength. (5) A semiconductor laser element, input and output optical fibers, and a coupling lens are provided, and chromatic aberration is imparted by the wavelength dispersion of the coupling lens, and the coupling efficiency is maximized at a wavelength longer or shorter than the gain center wavelength of the semiconductor laser element. An optical amplifier characterized by: (6) A semiconductor laser element, input and output optical fibers, and a coupling hologram lens are provided, and a chromatic aberration is imparted to the pattern of the coupling hologram lens, and the coupling efficiency is maximized on the long wavelength and short wavelength sides of the gain center wavelength of the semiconductor laser element. An optical amplifier characterized in that the coupling efficiency is reduced at the gain center wavelength of the semiconductor laser element. (7) Light comprising a semiconductor laser element, input and output optical fibers, a coupling lens, and an optical filter, and the coupling efficiency is maximized at a wavelength longer or shorter than the gain center wavelength of the semiconductor laser element. amplifier. (8) A plurality of signal light sources with different wavelengths, an optical fiber, an optical amplifier, and an optical receiver are provided, and the gain of the optical amplifier is reduced in the minimum loss wavelength region of the optical fiber to increase the optical intensity of the signal light at the optical receiver. An optical transmission device that maintains a constant value.