JPH0361928A - Very short optical pulse generator - Google Patents

Abstract

PURPOSE:To stably generate an optical pulse of <=1ps pulse width by generating a pulse by means of a semiconductor laser and using a rate earth element added optical fiber amplifier for power necessary for pulse compression to amplify the optical pulse. CONSTITUTION:An optical pulse generation part 1 using the semiconductor laser comparatively simply generates optical pulses of about 30 to 10ps width. A rare earth element added optical fiber 2 acts as a light direct amplifier and an excited light generation source 3 forms the inverted distribution of inputted optical pulse wavelength by exciting rare earth ions added to the optical fiber to generate the gain of the optical pulses passing the fiber 2. Since the peak power of the optical pulse is increased by the optical fiber amplifier, the pulse can be compressed by the optical fiber. Consequently, the optical pulse of <=1ps can be obtained by the compact device.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrashort optical pulse generator that will be needed in future optical transmission and optical signal processing.

[Prior art and problems to be solved by the invention] Conventional methods for generating ultrashort optical pulses include (1) mode-locking methods using dye lasers, solid-state lasers, etc.; (2) optical pulses generated by (1); There are methods for further compressing (3) a semiconductor laser dein switch method, a Q switch method, etc.

In the mode-locking method (1), a dye laser is used to change the pulse width from several 100 fs (fs: 0-"s) to several tens of fs.
s, Nd: Several ps to several tens of ps (ps:
A light pulse of 10-''s) was obtained. Also, each light pulse had a high output with a peak power of 100 watts or more.

(2) Passes an optical pulse with a high peak power of several watts or more through an optical fiber, and the zero phase modulation that occurs at that time causes wavelength chirping (the center frequency shifts within the optical pulse). This is a method of compressing the pulse width by one to two orders of magnitude by creating a state of !I4) and passing the pulse through a dispersion medium (a medium in which light transit time differs depending on the wavelength) equivalent to a diffraction grating. It is used for mode-locked dye lasers and mode-locked solid-state lasers that can generate short optical pulses with high peak power.

However, dye lasers and solid-state lasers have large resonator configurations and require another laser to generate excitation light, which increases the overall size of the device and reduces reliability.
Lack of longevity and stability.

The semiconductor laser gain switching method and Q-switching method (3) are small and are very superior in terms of convenience, reliability, and stability. Furthermore, since the optical pulses are generated by the injected current, it is very easy to control the repetition frequency of the generated optical pulses by mistake.

However, the shortest pulse width that can be generated is several ps,
Since the peak power of the emitted pulse is several tens of milliwatts at most, it is impossible to compress the output pulse into an optical pulse of 7 microseconds using the pulse compression method (2). Therefore, a method of optically amplifying and compressing an optical pulse having a width of several tens of ps generated by a semiconductor laser may be considered.

However, with the semiconductor laser amplifiers currently in use,
The saturation value of the gain for optical pulses is small, and the ability to amplify an optical pulse of several 10 ps to only several 100+9 W at most makes it impossible to perform pulse compression. Therefore, a highly reliable and stable semiconductor laser is used to generate optical pulses, optical amplification and pulse compression are performed.
A technology for generating optical pulses of less than ps is required.

The present invention has been made in view of the above-mentioned points, and its purpose is to produce a pulse width of 1 by using a semiconductor laser.
The present invention provides an ultrashort optical pulse generator that stably generates pulses of less than ps.

[Means to solve the problem]

According to the invention, the above-mentioned object is distantly related to the above-mentioned object by the means set forth in the above-mentioned feature g'+claims.

That is, the present invention uses a light generation section using a semiconductor laser, an optical amplification means that includes a rare earth element and amplifies an input optical pulse from the light generation section by the amplification effect of the rare earth ions, and an anomalous dispersion medium. The present invention is an ultrashort optical pulse generator provided with an optical pulse compression means for compressing an input pulsed light, and an excitation light source having a wavelength to excite the rare earth element in the optical amplification means.

Below, four examples of the principle configuration of the present invention are shown using figures,
The means used in the present invention will be explained in more detail.

A first example of the basic configuration of an ultrashort optical pulse generator according to the present invention is shown in FIG.

That is, the configuration includes a light pulse generation unit 1 using a semiconductor laser, a rare earth-doped light 7 eyeper 2, an excitation light source 3 that generates light having a wavelength that excites the rare earth ions, and the light pulse generating unit 1 that uses a semiconductor laser. a coupling point Pi4 for inputting the optical pulse generated from the optical pulse generator 1 and the excitation light generated from the excitation light source 3 into the rare earth doped light 7T fiber 2; and a wavelength of the optical pulse generated from the optical pulse generator 1. The present invention is characterized in that it includes a single mode optical fiber 5 having anomalous dispersion, and means for making the optical pulses emitted from the rare earth doped optical fiber 2 enter the single mode optical fiber 5.

Part 2: 1. In the second principle configuration example, the rare earth-doped optical fiber in the first principle Wlt example and the single mode 77 IPA having anomalous dispersion are constructed of the same optical fiber. It has become a vI precept. This is shown in FIG.

That is, the configuration includes an optical pulse generating section 1 using a semiconductor laser, a single mode optical fiber 6 doped with a rare earth element and having anomalous dispersion at the wavelength of the optical pulse generated from the optical pulse generating section, and An excitation light source 3 that generates light having a wavelength that excites ions, and a light pulse generated from the light pulse generator 1 and excitation light generated from the excitation light source 3 are connected to the rare earth doped anomalous dispersion single mode optical fiber. It is characterized in that it includes a coupling means 4 for inputting data to 6.

In a third principle configuration example, instead of the rare earth-doped anomalous dispersion single mode optical fiber 7 fiber 6 having anomalous dispersion in the second principle example, a single mode optical fiber 7 having ordinary dispersion is used. The anomalous dispersion medium 8 is used. This is shown in FIG.

That is, the configuration includes an optical pulse generator 1 using a semiconductor laser, an optical fiber 2 doped with rare earth elements, an excitation light source 3 that generates light having a wavelength that excites the ions of the above-mentioned species. a coupling means 4 for inputting the optical pulse generated by the optical pulse generator 1 and the excitation light generated from the excitation light source 3 into the rare earth doped optical fiber 2; and a coupling means 4 for inputting the light emitted from the rare earth doped optical fiber 2. a single mode optical fiber 7 which is arranged as shown in FIG.
It is characterized in that it includes an anomalous dispersion medium 8 which is disposed so as to input the light emitted from the optical fiber 7 and has an anomalous dispersion property at the wavelength of the optical pulse generated from the optical pulse generator 1.

Grave 1! In the fourth principle configuration example, the rare earth doped optical fiber and the ordinary dispersion optical fiber in the third principle configuration example are integrated.

This is shown in FIG.

That is, the configuration includes an optical pulse generating section 1 using a semiconductor laser, a single mode optical fiber 9 doped with rare earth elements and having normal dispersion at the wavelength of the optical pulse generated from the optical pulse generating section 1, and the above-mentioned optical pulse generating section 1. An excitation light source 3 that generates light having a wavelength that excites rare earth ions, and a light pulse generated from the optical pulse generator 1 and excitation light generated from the excitation light source 3 are combined into the rare earth-doped ordinary dispersion single mode light. a coupling means 4 for inputting into the fiber 9;
It is characterized in that it includes an anomalous dispersion medium 8 which is disposed so as to input the light emitted from the single mode light 7 fiber 9 and has an anomalous dispersion property at the wavelength of the light pulse generated by the light pulse generator 1.

[For production]

In the present invention, pulses are generated using a gain switch method using a highly reliable and stable semiconductor laser without using a large dye laser or solid-state laser, and a rare earth-doped optical fiber amplifier is used to generate the power necessary for pulse compression. It is amplified using

For this reason, it is possible to achieve miniaturization, which was not possible using dye lasers, etc., and at the same time, to obtain high stability and reliability.Furthermore, by using a semiconductor laser in the pulse generation section, which can be controlled by injection current, Because of this, the repetition frequency can be easily controlled electrically, making it difficult to generate conventional ultrashort optical pulses.
It has features that other devices do not have.

Hereinafter, the operation of the present invention will be explained in more detail based on the first to fourth theoretical configuration examples described above.

Optical pulse generation methods using a semiconductor laser include a mode locking method, a gain switch method, a Q-switch method, and the like, each of which relatively easily generates an optical pulse with a width of about 30 ps to 10 ps. The rare earth doped optical fiber acts as a direct optical amplifier. First, the light emission source excites rare earth ions added to the optical fiber to form a population inversion with respect to the input optical pulse wavelength, thereby producing a gain for the optical pulse passing through the rare earth doped optical fiber. The average optical output power of a rare earth-doped optical fiber amplifier also has a limit in principle, similar to that of a semiconductor laser amplifier, and at present it is possible to output an average output power of about 1 mW.

However, its spontaneous emission lifetime is more than five orders of magnitude longer than that of a semiconductor laser amplifier, so by lowering the repetition frequency and reducing the duty ratio, it is possible to increase the lifetime by several tens of orders of magnitude.
A light pulse of 0 kW can be obtained.

Therefore, for example, if erbium ions are used as rare earth ions, the repetition frequency IMH21 pulse [2
For 0ps Hals train, output peak power 50W
of light pulses can be obtained. Optical fiber amplifiers have increased the peak power of optical pulses, making it possible to compress pulses using optical fibers. When an optical pulse with a peak power of about IW or higher propagates through an optical fiber, the optical power -
The effect induces self-phase modulation, which shifts the center wavelength of the optical pulse from the longer wavelength side to the shorter wavelength side (wavelength chirping).

When this optical pulse passes through an anomalous dispersion medium characterized by a high propagation speed for short-wavelength light, the pulse width is narrowed because the rear part of the pulse catches up with the pulse storage area.

Therefore, if the optical fiber that causes self-phase modulation is an anomalous dispersion medium with an appropriate dispersion value, wavelength chirping and pulse compression due to self-phase modulation will occur simultaneously, so the fiber-emitted pulse will be a compressed optical pulse. . The peak power of the input pulse is 1W or more, and the pulse width is 1
If it is approximately 0 ps, the pulse width will be compressed to one-tenth or less, so that an optical pulse of 1 ps or less can be obtained as an output pulse.

In the second fundamental configuration example, the optical pulse amplification function and the pulse compression function are realized by the same optical fiber.

In other words, light 7 doped with rare earth elements for optical amplification.
It has anomalous dispersion so that AIPA can perform pulse compression at the same time. By doing so, the incident optical pulse is simultaneously amplified and compressed, so that an optical pulse of 1 ps or less can be obtained with a simpler configuration.

In the third principle configuration example of the precepts, the induction of wavelength chirping by self-phase modulation and pulse compression by anomalous dispersion, which were explained in the operation of the first principle configuration example, are realized using separate elements. are doing.

That is, a light pulse amplified using an erbium-doped optical fiber is first guided into a light 7γ ipa having ordinary dispersion, and wavelength chirping is caused by self-phase modulation. The reason for using the optical 7-eyeper with ordinary dispersion here is to cause linear wavelength chirping with respect to time.

Next, this optical pulse is introduced into an anomalous dispersion medium, and pulse compression is caused by the above-described compression principle in the dispersion medium of optical pulses having wavelength chirping.

In the fourth principle configuration example of the fourth principle, the optical pulse amplification function and the wavelength chirping inducing function by self-phase modulation in the third principle configuration example are realized in the same fiber.

That is, an optical fiber doped with rare earth elements for optical amplification is also an optical fiber for causing wavelength chirping.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

The tISS diagram shows the first embodiment of the present invention.

11 is a distributed feedback semiconductor laser (DFB-LD) with an oscillation wavelength of 1.535 μm, and 12 is a pulse width of 200 μm.
ps, is a transistor circuit (short current pulse generator) that generates short current pulses with a peak width of 10 V, and has a variable width of repetition frequency of 100 Hz to IM Hz. By superimposing this short current pulse on a bias current using a bias tee and applying it to the DFB-LDI 1, an optical pulse with a pulse width of 30 ps and a peak power of about 20 mW can be generated.

Typically, the optical pulse generated by this method has wavelength chirping in which the center wavelength of the optical pulse shifts from a shorter wavelength to a longer wavelength. Here, in order to perform pulse compression using this wavelength chirping, the zero dispersion wavelength is set to 1,535 μm so that it has normal dispersion at 1,535 μm.
A dispersion-shifted single mode optical fiber 13 that is shifted to the longer wavelength side than the optical fiber is disposed.

The optical pulse generated by the semiconductor laser is compressed to a pulse width of about 10 ps by passing through the optical fiber 13.

14 is a rare earth M (erbium) doped optical fiber, and 15 is a semiconductor laser excitation light source with an optical output of 100 mW and a wavelength of 1.48 μm. Rare earths include erbium, neodymium, etc., and erbium is used here. When using neodymium, the wavelength of DFB-LDI 1 is 1.31.
9 .mu.m, the excitation light source 15 may be a 0.8 .mu.m semiconductor laser.

Reference numeral 16 denotes a gicchroic mirror for combining the optical pulse and the excitation light source and guiding them to the erbium-doped optical fiber. By setting the erbium doping concentration to 30 ppm and the length to about 100 a+, a gain of about 30 dB can be obtained.

Therefore, if the repetition frequency is IMHz, the peak power of the output pulse will be 50W.

The anomalous dispersion optical fiber 17 for pulse compression has a zero dispersion wavelength of 1.56μ, a dispersion value of 3 at 1,535μ,
Ops/nm/ka+, a single mode optical fiber with a core diameter of 6 μm is used. The erbium-doped optical fiber 14 and the anomalous dispersion optical fiber 17 are coupled by fiber fusion. When the length of the anomalous dispersion 7 fiber 17 is 600 ta, a compression ratio of 0.03, that is, an output pulse width of 0°6 ρS is obtained.

42 difference I4 FIG. 6 shows a second embodiment of the invention.

Erbium-doped fiber 14 in the first embodiment,
This embodiment has the same configuration as the first embodiment except that the pulse compression anomalous dispersion optical fiber 17 is the same fiber.

In this case, the wave if, anomalous variance value 3 at 535 μ horse mackerel
ps/nm/k-, single mode with a core diameter of 6μ, erbium in the 7-iper approx. 1i, concentration 3p9-
Erbium-doped anomalous dispersion optical fiber 18
At this time, as in the first embodiment, an optical pulse with a pulse width of 0.6 ps or less can be obtained.

Figure 7 shows a third embodiment of the present invention. The configuration is the same as that of the first embodiment except that pulse compression in the anomalous dispersion optical fiber in the first embodiment is realized using a normal dispersion optical fiber 19 and an anomalous dispersion medium 20.

In this case, the ordinary dispersion optical fiber 19 is a single mode optical fiber having a length of 30 rings and a core diameter of 6μ-1 dispersion value of about -15ps/n+e/1m.

Examples of anomalous dispersion media include ordinary single-mode optical fibers with a zero dispersion wavelength of 1.3 μm, grating bare fibers, etc.
Ialln grating pair 20 is used.

At this time, a light pulse of 1110.5 ps or less is obtained.

Figure 8 shows a fourth embodiment of the present invention. The structure is the same as that of the third embodiment except that the erbium-doped optical fiber 14 and the compression ordinary dispersion optical fiber 19 in the third embodiment are the same fiber.

In this case, the normal dispersion value -1 at wave f: 1,535μ-
0ps/nm/km, length 60+*, :) diameter 6
Erbium concentration 5 to μ-single mode optical fiber
An erbium-doped normally dispersive optical fiber 21 doped with about 0 ppm may be used. At this time, as in the third embodiment, a light pulse with a pulse width of 0.5 ps or less is obtained.

〔Effect of the invention〕

As described above, according to the present invention, optical pulses of 1 ps or less can be stably and small-sized by a semiconductor laser without using a large laser such as a dye laser.

Therefore, this technology can be expected to be applied to ultra-high-speed optical signal processing such as optical sampling and optical dating.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a first principle configuration example of the present invention, FIG. 2 is a diagram showing a second principle configuration example of the present invention, and tIS3 diagram is a diagram showing a third principle configuration example of the present invention. 4 is a diagram showing a fourth example of the basic configuration of the present invention, FIG. 5 is a diagram showing a first embodiment of the present invention, and FIG. 6 is a diagram showing a second embodiment of the present invention. FIG. 7 is a diagram showing a third embodiment of the present invention, and FIG. 8 is a diagram showing a fourth embodiment of the present invention. 1... Optical pulse generator using semiconductor laser, 2... Rare earth doped optical fiber, 3
...Excitation light emission source, 4...Coupling means, 5...Single mode optical fiber having anomalous dispersion, 6...Doping with rare earth to produce anomalous dispersion. Single mode optical fiber with 7.
...Single mode optical fiber with normal dispersion,
8...Anomalous dispersion medium, 9.
...Rare-earth doped chamber dispersion single mode optical fiber, 11 ...Distributed feedback semiconductor laser (DFB-LD), 12...
...Short current pulse generator, 13...
...Dispersion shifted single mode optical fiber, 14
...Erbium-doped optical fiber, 1
5... Semiconductor laser excitation light source (LD light source),

Claims (1)

[Scope of Claims] A light generation section using a semiconductor laser; an optical amplification means that includes a rare earth element and amplifies an input optical pulse from the light generation section by an amplification effect of the rare earth ions; and an anomalous dispersion medium. An ultrashort optical pulse generator comprising: optical pulse compression means for compressing input pulsed light; and an excitation light source having a wavelength that excites rare earth elements in the optical amplification means.