JPH05315682A - Ring laser type device for generating short light pulse - Google Patents

Abstract

PURPOSE:To provide a simple, high-speed device for emitting perfect transform- limit, short light pulses. CONSTITUTION:A ring resonator comprises a polarization-preserving fiber through which are connected a polarizer 12, optical isolator 13, Er-doped fiber 15 and a light-intensity modulator 16. The ring resonator is connected with a pumping source 17 through an optical multiplexor/demultiplexor 14 to form a ring laser, which operates a repetition rate equal to an integer multiple of the repetition rate defined by the ring resonator. This ring laser is supplied with light pulses through a polarization-preserving fiber coupler 18 from a mode-locked semiconductor laser 20 that operates at the same frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ring laser type short light pulse generator for generating a short light pulse with a transform limit.

[0002]

2. Description of the Related Art A mode-locking method and a gain switching method have been conventionally used as a technology for generating a short optical pulse at a high speed from a semiconductor laser. However, it was difficult for both of them to generate a perfect transform-limited short light pulse.

Recently, a collision-mode-locked multiple quantum well distributed feedback semiconductor laser was prototyped by making full use of optical integration technology.
Successful generation of sub-picosecond transform limit pulse by repetition over 00GHz (CLEO;
YK Chen et al, “Monolithic Colliding Pulse Mod
o-Locked Quantum Well Lasers ”CWK3, p.304, 199
1).

Further, due to recent progress in optical amplification technology, a ring laser is constructed by using an optical fiber amplifier excited by a semiconductor laser, and an intensity modulator is inserted into the ring resonator to perform mode locking. A technique for generating an optical pulse has received attention.

[0005]

However, since a sophisticated optical integration technique is required to manufacture the collision mode-locked multiple quantum well distributed feedback semiconductor laser, it cannot be said to be a simple pulse generation technique. In addition, the resonator length of the ring laser is generally as long as several meters, and the basic repetition frequency f at the time of mode locking is determined by the resonator length.
It becomes about 100MHz. Therefore, in order to generate a short optical pulse from a ring laser at an ultrahigh speed, an RF (high frequency) oscillator having an integral multiple of f is used to forcibly perform mode locking. Since it is larger than the mode interval f, its operation becomes unstable.

As described above, conventionally, it has been difficult to easily generate a complete transform limit short optical pulse at an ultrahigh speed by using a semiconductor laser. In view of such circumstances, it is an object of the present invention to provide a ring laser type short optical pulse generator that easily generates a complete transform limit short optical pulse at a high speed using a semiconductor laser.

[0007]

A ring laser type short optical pulse generator according to the present invention which achieves the above object is provided with a rare earth-doped optical waveguide, an optical isolator, and an optical intensity modulator, and absolutely. It is configured by connecting the excitation light source of the rare earth-doped optical waveguide to a ring resonator that holds a single polarization, and has a repetition frequency of 2 determined by the ring resonator length.
A mode-locked optical fiber ring laser that operates at an integer multiple of the above, and a mode-locked optical fiber ring laser that operates at the same repetition frequency as this repetition frequency and is connected to the ring resonator via a polarization maintaining optical coupler. A mode-locked semiconductor laser for injecting an optical pulse is provided, and a rare earth-doped optical waveguide, an optical isolator, and an optical intensity modulator are interposed, and absolutely single polarization is maintained. A mode-locked optical fiber ring laser configured by connecting a pumping light source of the rare earth-doped optical waveguide to a ring resonator and operating at an integer multiple of 2 or more of a repetition frequency determined by the ring resonator length, and the same repetition frequency The mode-locked light that operates at a repetition frequency and is connected to the ring resonator through a polarization maintaining optical coupler Characterized by including in § Iba ring laser and a gain-switched semiconductor laser to inject light pulses.

[0008]

In a mode-locked optical fiber ring laser which operates in a mode-locked manner, an integral multiple n of the fundamental repetition frequency f
When a short optical pulse generated from a mode-locked semiconductor laser or a gain switch semiconductor laser with a repetition frequency nf of (n> 1) is forcibly injected with a repetition frequency nf, the optical fiber ring laser itself becomes independent. The unstable operation when operating at the repetition frequency nf is eliminated.

[0009]

EXAMPLES The present invention will be described below based on examples.

FIG. 1 shows a ring laser type short optical pulse generator according to an embodiment. As shown in the figure, a mode-locked Er ring laser 11 comprises a polarizer 12, an optical isolator 13, an optical multiplexer / demultiplexer 14, an Er-doped optical fiber 15, and an optical intensity modulator 16 which are sequentially polarized in a ring-shaped optical fiber. Optical multiplexer / demultiplexer 1
A pumping light source 17 for pumping the Er-doped optical fiber 15 is connected to 4. Further, polarization-maintaining optical fiber couplers 18 and 19 are provided between the optical intensity modulator 16 and the polarizer 12, and between the optical isolator 13 and the optical multiplexer / demultiplexer 14 in the ring resonator, respectively. The mode-locked semiconductor laser 20 is connected to the input end 18a of one polarization-maintaining optical fiber coupler 18.

The light source of the mode-locked semiconductor laser 20 comprises a semiconductor laser 21 having an AR (anti-reflection) coating on one end 21a and a grating 23 coupled to this one end 21a through an optical system 22. Laser 2
The other end 21b of 1 is coupled to the input end 18a of the polarization maintaining optical fiber coupler 18 via the optical system 24. Also,
An RF (high frequency) oscillator 25 that performs mode locking by modulating the semiconductor laser 21 is provided.

Here, the RF oscillator 25 is a mode-locked E
A sine wave electric signal is sent to the light intensity modulator 16 of the r-ring laser 11. Therefore, the mode-locked Er ring laser 11 generates an optical pulse synchronized with the signal.
However, in order to synchronize the phase of this electric signal with the optical pulse guided from the mode-locked semiconductor laser 20 to the mode-locked Er ring laser 11, the phase adjuster 26 is provided between the RF oscillator 25 and the light intensity modulator 16. Is provided.

The ring laser type short optical pulse generator having the above-mentioned structure is configured to inject the highly repetitive 1.5 μm band short optical pulse generated from the mode-locked semiconductor laser 20 into the mode-locked Er ring laser 11 to generate light. It stabilizes the pulse. That is, the mode-locked Er ring laser 11 is operated at an integer n times (n> 1) of the repetition frequency f determined by the ring resonator length, and the mode-locked semiconductor laser 20 is also operated at the repetition frequency nf. The short optical pulse generated from the semiconductor laser 20 is injected into the mode-locked Er ring laser 11 via the polarization maintaining optical fiber coupler 18. At this time, both pulses are synchronized by the adjustment by the phase adjuster 26. In this way, the mode-locked Er ring laser 1 that also operates at the repetition frequency nf for the optical pulse having the repetition frequency nf from the mode-locked semiconductor laser 20.
Injecting into 1 stabilizes the operation as compared with the case where the optical pulse is not injected. Then, from the emitting end 19a, it is possible to obtain a complete transform limit short optical pulse at an ultra high speed.

In the above embodiment, the short optical pulse to be injected into the mode-locked Er ring laser 11 is generated by using the semiconductor active mode-locking method, but it is also possible to use a passive mode-locked semiconductor laser. Further, a gain switch semiconductor laser can be used as shown in Examples described later.

Further, in the above embodiment, the grating 23 is provided on the side of the one end 21a of the semiconductor laser 21 in the mode-locked semiconductor laser 20, but the invention is not limited to this, and a normal reflector may be used. The use of the grating 23 has the effects of facilitating mode locking and making the wavelength tunable.

FIG. 2 shows a ring laser type short optical pulse generator according to another embodiment. The members having the same functions as those in FIG. In this embodiment, a gain-switched semiconductor laser 20A is used in place of the synchronous mode semiconductor laser, and a highly repetitive 1.5 μm band short optical pulse generated from this laser is used to perform mode-locked E.
The optical pulse generated from the r-ring laser 11 is stabilized.

In FIG. 2, a gain switch semiconductor laser 20A is for gain-switching a semiconductor laser 21 using an RF oscillator 25, and is coupled to an input end 18a of a polarization maintaining optical fiber coupler 18 via an optical system 24. ing. Since the optical frequency of the optical pulse generated from the gain switch semiconductor laser 20A is generally red-shift chirping, a polarization maintaining optical fiber 27 having normal dispersion is provided to compensate for this.

If the ring laser type short optical pulse generator of this embodiment is used, a stable transform-limit optical pulse can be generated from the emitting end 19a of the polarization-maintaining optical fiber coupler 19 in the same manner as in the above embodiment. Obtainable.

FIG. 3 shows a ring laser type short optical pulse generator according to still another embodiment. Note that FIG. 1 or FIG.
The same reference numerals are given to members having the same function as, and duplicate description will be omitted. The present embodiment uses a gain switch semiconductor laser 20A and stabilizes the optical pulse generated from the mode-locked Er ring laser 11 by using a highly repetitive 1.5 μm band short optical pulse generated from this laser. Is the same as in the above embodiment.

As described above, when the gain switch semiconductor laser 20A is used, the optical frequency of the optical pulse is generally red-shift chirping, and in order to compensate for this, normal dispersion is achieved also in this embodiment. A polarization maintaining optical fiber 27 having the same is provided. However, there may be a nonlinear chirp that cannot be completely compensated by the polarization maintaining optical fiber 27, and therefore the optical spectrum filter 28 is further used to compensate for this.

When the ring laser type short optical pulse generator of this embodiment is used, a stable transform-limit optical pulse can be generated from the emitting end 19a of the polarization-maintaining optical fiber coupler 19 in the same manner as in the above embodiment. Obtainable.

In each of the embodiments described above, it is possible to control the oscillation wavelength by inserting an optical bandpass filter in the mode-locked Er ring laser 11. However, in this case, it is necessary to match the center wavelength of the injected short optical pulse with the oscillation wavelength of the ring laser.

In each of the above embodiments, the Er-doped optical fiber 15 is used as the gain medium of the ring laser.
It is also possible to use an optical fiber doped with another rare earth element such as Nd or Pr. Further, instead of the optical fiber, it is possible to use a planar waveguide (PLC) to which rare earth is added. However, when the doped rare earths are different, it is necessary to match the center wavelength of the injected optical pulse with the oscillation wavelength of the ring laser. For example, when using a gain medium doped with Nd or Pr, an optical pulse of 1.06 μm band is injected.

Further, in each of the above embodiments, in order to suppress the mode competition between the polarized waves at the time of oscillation, the ring resonator is composed of a polarization maintaining optical fiber and the polarizer 12 is inserted in the ring resonator. Although the ring laser is made to operate with a single polarized wave in the above, the present invention is not limited to this. For example, the entire ring resonator can be composed of an absolute single polarized optical fiber.

Further, the gain switch semiconductor laser 20A
In the embodiment using, the polarization maintaining optical fiber 27 having normal dispersion is used to compensate for the red shift chirping, but a polarization state controller may be used instead.

[0026]

As described above, the ring laser type short optical pulse generator according to the present invention is a method of injecting a highly repetitive short optical pulse from a semiconductor laser into a ring laser to generate an optical pulse generated from the ring laser. Since it stabilizes, it is possible to easily generate the transform limit short optical pulse with high repetition. The obtained optical pulse is suitable for use in ultrahigh-speed long-distance optical transmission, particularly optical soliton transmission.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a ring laser type short optical pulse generator according to an embodiment.

FIG. 2 is a configuration diagram showing a ring laser type short optical pulse generator according to another embodiment.

FIG. 3 is a configuration diagram showing a ring laser type short optical pulse generator according to another embodiment.

[Explanation of symbols]

 11 Mode-locked Er ring laser 12 Polarizer 13 Optical isolator 14 Optical multiplexer / demultiplexer 15 Er-doped optical fiber 16 Optical intensity modulator 17 Pumping light source 18, 19 Polarization-maintaining optical fiber coupler 20 Mode-locked semiconductor laser 20A Gain switch semiconductor laser 21 Semiconductor laser 22, 24 Optical system 23 Grating 25 RF oscillator 26 Phase adjuster 27 Polarization maintaining optical fiber 28 Optical spectrum filter

Claims (4)

[Claims] 1. A pumping light source of the rare earth-doped optical waveguide is connected to a ring resonator in which a rare earth-doped optical waveguide, an optical isolator, and a light intensity modulator are interposed, and an absolute single polarization is maintained. And a mode-locked optical fiber ring laser that operates at an integer multiple of 2 or more of the repetition frequency determined by the ring resonator length, and that operates at the same repetition frequency as this repetition frequency and via a polarization maintaining optical coupler. And a mode-locking semiconductor laser which is connected to a ring resonator and injects a light pulse into the mode-locking optical fiber ring laser. 2. A pumping light source of the rare earth-doped optical waveguide is connected to a ring resonator in which a rare earth-doped optical waveguide, an optical isolator, and a light intensity modulator are interposed, and an absolute single polarization is maintained. And a mode-locked optical fiber ring laser that operates at an integer multiple of 2 or more of the repetition frequency determined by the ring resonator length, and that operates at the same repetition frequency as this repetition frequency and via a polarization maintaining optical coupler. A ring laser type short optical pulse generator comprising: a gain switch semiconductor laser connected to a ring resonator to inject an optical pulse into the mode-locked optical fiber ring laser. 3. The ring laser type short optical pulse generator according to claim 2, wherein an optical spectrum filter is interposed between the gain switch semiconductor laser and the mode-locked optical fiber ring. 4. The optical bandpass filter according to claim 1, wherein an optical bandpass filter is provided in a ring resonator of the mode-locked optical fiber ring laser, and an optical pulse injected into the mode-locked optical fiber ring is A ring laser short optical pulse generator characterized in that the center wavelength of the optical bandpass filter is matched.