JP3381941B2 - Group delay optical equalization circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, a group of optical transmission lines.
The present invention relates to a group delay optical equalizer circuit that compensates for delay dispersion.

[0002]

2. Description of the Related Art As is well known, optical transmission systems are required to have higher technology so as to play an important role in the infrastructure of the intelligent information society, and this is due to the demand for more economical optical transmission lines. It is becoming increasingly faster and more multiplexed. Further, in response to the demand for a dramatic increase in the optical transmission distance, which has been conventionally limited by loss, the development of an Er (erbium) -doped optical fiber amplifier that intervenes in the optical transmission line to compensate for the loss is also underway.

By the way, the frequency band of the optical transmission line is restricted by the group delay dispersion characteristic of the material (quartz) used for the optical fiber and the structural group delay dispersion characteristic of the transmission mode. Therefore, the band sufficient for ultra-high speed operation is limited to a narrow optical frequency region near the zero-dispersion frequency of the fiber, resulting in insufficient band.

For example, in a conventional optical transmission system,
The group delay dispersion characteristic of the optical fiber used for the optical transmission line has a zero dispersion point at 1.3 μm, but when changing the used band of this system to the 1.55 μm band where the optical fiber amplifier can be used, Due to the large group delay dispersion, ultra high speed will be restricted.

In order to solve such a problem, it has been conventionally proposed to connect a group delay optical equalization circuit using a Fabry-Perot resonator to an optical fiber. The structure is shown in FIG.

In FIG. 5, the transmitted light is guided to the Fabry-Perot resonator 2 via the optical coupler 1. The light incident on the Fabry-Perot resonator 2 passes through the half mirror 21 made of a dielectric multilayer film, passes through the light transmission medium 22 made of quartz, and is totally reflected by the total reflection mirror 23, so that the light transmission medium 22.
It goes backwards and is partially reflected again by the half mirror 21. The light transmitted through the half mirror 21 is taken out by the optical coupler 1 and led out to an optical fiber (not shown) in the optical transmission line.

That is, the Fabry-Perot resonator 2 has a linear group delay dispersion characteristic with respect to a specific frequency band by appropriately selecting its resonance length. Therefore, in the above optical equalization circuit, the Fabry-Perot resonator 2 is provided with a group delay dispersion characteristic opposite to that of the optical fiber in the used frequency band, thereby expanding the bandwidth in the used frequency band and achieving ultra-high speed operation. We are trying to ease restrictions.

However, in the group delay optical equalization circuit using the Fabry-Perot resonator, the internal loss such as the loss of the dielectric multilayer film cannot be ignored, and there is a drawback that a large loss depending on the frequency is present in the equalization band. Have That is, in the group delay dispersion equalization, the amplitude characteristic is constant without depending on the frequency, and the effect is halved unless the group delay dispersion is compensated. Changes depending on the frequency, which gives distortion to the transmitted light.

Further, the Fabry-Perot resonator has a very narrow bandwidth capable of accurately compensating for linear group delay dispersion (also referred to as first-order dispersion), which significantly limits the design flexibility of the group delay optical equalization circuit.

[0010]

As described above, in the conventional group delay optical equalization circuit, in order to achieve an ultrahigh speed optical transmission line and an increase in communication capacity in the optical transmission system, the amplitude characteristic is changed to the frequency. Accordingly, the bandwidth cannot be maintained constant, and furthermore, the band width with which the linear group delay dispersion can be accurately compensated is extremely narrow, so that the degree of freedom in design is significantly limited.

The present invention has been made to solve the above-mentioned problems, and the amplitude characteristic is constant regardless of the frequency.
Wide bandwidth that can accurately compensate for linear group delay dispersion,
Accordingly, it is an object of the present invention to provide a group delay optical equalization circuit which can increase the degree of freedom in design, can achieve ultra-high speed of an optical transmission line in an optical transmission system, and can increase communication capacity. It
In addition, a suitable optical amplifier is used for this group delay optical equalization circuit.
The purpose is to provide.

[0012]

In order to achieve the above object, a group delay light equalization circuit according to the present invention uses a semiconductor laser having first and second control electrodes, and uses one of the semiconductor lasers. A low reflection film is applied to the input / output end and a high reflection film is applied to the other light input / output end, and incident light from the light input / output end on the low reflection film side is reciprocated between the low reflection film and the high reflection film, A control current for mainly controlling the gain of the input / output light is applied to the first control electrode, and a control current for mainly shifting the phase of the input / output light is applied to the second control electrode of the semiconductor laser. An optical amplifier that amplifies the incident light from the light input / output end on the low reflection film side and gives a predetermined group delay dispersion characteristic and radiates from the light input / output end on the low reflection film side, and the low reflection film side of this optical amplifier. The transmitted light is guided from the optical fiber of the optical transmission line to the optical input / output end of And a transmission optical path control means for guiding the light emitted from the width device to the optical fiber, wherein the group delay dispersion characteristic of the optical amplifier is opposite to the linear group delay dispersion characteristic of the optical fiber of the optical transmission line. It is characterized in that the characteristic is set.

[0013]

In the group delay optical equalization circuit having the above structure, the optical amplifier having the optical amplification function is provided with the function of compensating the linear delay dispersion characteristic of the optical fiber similar to that of the Fabry-Perot resonator, whereby the amplitude characteristic is improved. Constant regardless of frequency,
The compensation band width of the linear group delay dispersion is widened, thereby increasing the degree of freedom in design, ultra-high speed of the optical transmission line in the optical transmission system, and increasing the communication capacity.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows the configuration of a group delay optical equalizer circuit according to the present invention. In FIG. 1, 11 is an optical fiber. The end of this optical fiber 11 is coupled to the light emitting end of an optical transmitter (not shown). The transmitted light incident on the optical fiber 11 is sent to the optical circulator 12,
The optical circulator 12 guides the optical fiber 13. The transmitted light incident on the optical fiber 13 is irradiated onto the aspherical lens 14 from its end, and is condensed on the half mirror mounting surface of the optical amplifier 15 by the aspherical lens 14.

In this optical amplifier 15, a half mirror 152 is attached to one laser emission surface of a pn junction type semiconductor laser 151, and a total reflection mirror 153 is attached to the other laser emission surface. The incident light from the aspherical lens 14 is applied to one laser emitting portion of the laser 151 via the half mirror 152.

A conductor layer is formed on the n-channel side of the semiconductor laser 151 and is grounded as a ground electrode a.
First and second control electrodes b and c are formed on the p-channel side. A gain control current Ig is applied to the first control electrode b, and a phase shift control current Ip is applied to the second control electrode c.

The semiconductor laser 151 is of InGaAsP type having a gain at the wavelength of transmitted light of 1.55 μm.
It is maintained immediately before oscillation, and is excited when light is applied to the n- and p-channel junctions and emits laser light proportional to the incident light from the pn junctions on both end faces thereof. However, since the total reflection mirror 153 is mounted on the side opposite to the light incident surface, the laser light is emitted only from the light incident surface side.

The light emitted from the semiconductor laser 151 travels backward through the aspherical lens 14 and the optical fiber 13 via the half mirror 152, is guided to the optical fiber 16 by the optical circulator 12, and from the end thereof the optical fiber of the optical transmission line. (Not shown).

That is, this group delay light equalization circuit is used by coupling the light emitting end of the optical fiber 16 to the optical fiber light incident end of the optical transmission line, and transmits the transmitted light from the optical transmitter by the optical circulator 12. It leads to the amplifier 15. A semiconductor laser type is used as the optical amplifier 15, and laser light is generated by using the transmitted light as excitation light.

Here, the gain and the phase shift are controlled by the control currents Ig and Ip for the semiconductor laser 151, and the optical resonance frequency is matched with the incident light. As a result, laser light obtained by amplifying incident light is emitted from the semiconductor laser 151. However, the half mirror 152 is provided on the light incident surface.
Is mounted, and the total reflection mirror 153 is mounted on the surface on the opposite side. Therefore, the characteristics opposite to the group delay dispersion characteristics of the optical fiber of the optical transmission line are realized just like the Fabry-Perot resonator described above. can do.

The relationship between the optical frequency and the group delay dispersion amount of the optical amplifier 15 is shown in FIG. 2 (a), and the relationship with the optical frequency vs. amplitude square characteristic is shown in FIG. 2 (b). As is clear from the figure, the optical amplifier 15 has a function of amplifying the incident light and a function of compensating for the group delay dispersion of the transmission line. The emitted light travels backward in the incident system path and is guided to the optical transmission path by the optical circulator 12.

Therefore, it is possible to widen the bandwidth for accurately compensating the linear group delay dispersion while keeping the amplitude characteristic constant regardless of the frequency. As a result, the degree of freedom in design can be increased, and the optical transmission line in the optical transmission system can be made ultra-high-speed and the communication capacity can be increased.

Although the above embodiment has a single-stage configuration, as shown in FIG. 3, a plurality of stages (three stages A to C in the figure) are connected in series, and the gain wavelength band of the semiconductor laser is provided at each stage. If they are shifted, the compensation range of the linear dispersion characteristic can be further expanded.

In the above embodiment, the case where the semiconductor laser is used as the optical amplifier 15 has been described, but it is also possible to use the ring resonator. The structure is shown in FIG. In FIG. 4, 31 is an Er-doped ring optical fiber, 32 is an excitation light source, 33 is an optical coupler, and optical isolators 34 and 35 are coupled to the light input / output ends thereof.

That is, this optical amplifier optically amplifies the transmission light on the ring optical fiber 31 by the excitation light emitted from the excitation light source 32. Here, by selecting the ring resonance wavelength band of the ring optical fiber 31 as the used wavelength band, it is possible to realize linear dispersion compensation similar to that of the Fabry-Perot resonator. Needless to say, various modifications can be made in the same manner without departing from the scope of the present invention.

[0027]

As described above, according to the present invention, the amplitude characteristic is constant irrespective of the frequency, and the wide band width with which the linear group delay dispersion can be accurately compensated is widened, thereby increasing the degree of freedom in design and optical transmission. A group delay optical equalization circuit that can achieve ultra-high speed optical transmission lines in systems and increase communication capacity
A path can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a group delay light equalization circuit according to the present invention.

2 is a characteristic diagram showing an optical frequency characteristic of the optical amplifier of the embodiment of FIG.

FIG. 3 is a configuration diagram showing a state in which the group delay optical equalization circuits of the embodiment of FIG. 1 are connected in multiple stages.

FIG. 4 is a configuration diagram showing a configuration when a ring resonator is used in an optical amplifier as another embodiment according to the present invention.

FIG. 5 is a configuration diagram showing a configuration of a conventional group delay optical equalization circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical coupler, 2 ... Fabry-Perot resonator, 21 ... Half mirror, 22 ... Optical transmission medium, 23 ... Total reflection mirror, 1
DESCRIPTION OF SYMBOLS 1 ... Optical fiber, 12 ... Optical circulator, 13 ... Optical fiber, 14 ... Aspherical lens, 15 ... Optical amplifier, 151
... Semiconductor laser, 152 ... Half mirror, 153 ... Total reflection mirror, 16 ... Optical fiber, 31 ... Ring optical fiber, 32 ... Excitation light source, 33 ... Optical coupler, 34, 35 ... Optical isolator, Ig ... Gain control current, Ip ... Phase shift control current.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-2-120830 (JP, A) JP-A-62-29188 (JP, A) JP-A-3-169131 (JP, A) JP-A 64-- 50016 (JP, A) JP-A-3-71118 (JP, A) JP-A-58-52890 (JP, A) JP-A-3-192222 (JP, A) Yafumi Y. Paul, et al. Optical phase compensation 2 Area Semiconductor Amplifier, 1990 IEICE Autumn National Conference Proceedings, October 1, 1990, Volume 4, pp. 4-168 (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02F 1/35-1/365 H01S 5/50 JISST file (JOIS)

Claims (2)

(57) [Claims] 1. A semiconductor laser having first and second control electrodes is used, wherein one of the semiconductor lasers has a low reflection film on one light input / output end and the other has a high reflection film on the other light input / output end. Incident light from the light input / output end on the reflection film side is reciprocated between the low reflection film and the high reflection film, and a control current for mainly controlling the gain of the input / output light is given to the first control electrode. A predetermined group delay dispersion characteristic is provided while applying a control current mainly for shifting the phase of input / output light to the second control electrode to amplify the incident light from the light input / output end of the semiconductor laser on the low reflection film side. And an optical amplifier that emits light from the optical input / output end on the low reflection film side, and guides the transmitted light from the optical fiber of the optical transmission line to the optical input / output end on the low reflection film side of this optical amplifier. A transmission optical path control means for guiding the emitted light to the optical fiber, Group delay optical equalizer being characterized in that so as to set the reverse characteristics to the linear group delay dispersion characteristic having a group delay dispersion characteristics optical fiber of the optical transmission line of the optical amplifier. 2. The group delay optical equalizer circuit according to claim 1, wherein the group delay optical equalizer circuits are connected in multiple stages and are responsible for different wavelength bands.