JP3249732B2 - Optical pulse generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pulse generator used for observing an optical signal and evaluating an optical device, and more particularly to an optical pulse generator in which a generated optical pulse signal has a small time width.

[0002]

2. Description of the Related Art There are various methods for generating a short optical pulse signal having a small time width as shown in Table 1. A ring laser using a forced mode locking method has a pulse width of about 5 ps. This is a promising method for observing optical signals and evaluating optical devices.

[0003]

[Table 1] FIG. 9 is a block diagram showing a configuration of a conventional ring laser. In FIG. 9, 1 is an electric signal driver that generates a drive electric signal for an optical modulator for each repetition cycle of a short optical pulse output, 2 is an optical modulator that modulates an optical signal with the drive electric signal for an optical modulator, and 3 is the optical modulator. An optical amplifier that receives the output of the optical modulator 2 and amplifies it. 4 is a variable optical delay device that adjusts the length of the entire ring so as to perform mode synchronization. 5 is an optical pulse that receives the output of the variable optical delay device 4. 9 is a variable wavelength filter (BPF) for receiving the output of the optical amplifier 3 and cutting wavelengths other than the output wavelength. Next, the operation of the ring laser shown in FIG. This will be described with reference to FIG.

The oscillation threshold value in FIG. 10 is about 0.9 when the peak value determined by the configuration of the ring laser is normalized to 1. Figure 10 shows the pulse width of the ring laser.
Is determined by the width a. Therefore, a high frequency having a high repetition frequency may be input to the optical modulator 2 to obtain a narrow pulse width.

However, the frequency band of the optical modulator 2 is limited to about 70 GHz at present. When a sine wave of 70 GHz is input, the pulse width is obtained by equation (1).

[0006]

(Equation 1) Therefore, the pulse output has a half value width of 2.5 ps according to the equation (1). In the current ring laser, this is the limit of the output pulse width.

[0007]

In the above-mentioned conventional ring laser, the output pulse width of the output short optical pulse signal depends on the repetition frequency and waveform of the electric signal for driving the optical modulator, and can be modulated by the electric signal. It was impossible to make the output pulse width smaller than 2.5 ps at 70 GHz.

An object of the present invention is to obtain a thinner short optical pulse signal by inputting the optical signal as it is to the optical coupler of another ring laser using the short optical pulse signal. An object of the present invention is to provide an optical pulse generator for obtaining a short optical pulse signal having a pulse width shorter than an output pulse width.

[0009]

An optical pulse generator according to the present invention comprises two ring lasers, and outputs a short optical pulse signal obtained from a first ring laser using an electric signal for driving an optical modulator. Is input to the second ring laser as an optical signal.

Further, the output of the short optical pulse signal obtained from the first ring laser is converted from a rectangular wave into a triangular wave by an optical triangular wave generator and inputted to the second ring laser.

The main feature of these arrangements is to obtain a narrower short optical pulse signal as compared with a conventional ring laser.

[0012]

In the present invention, the short optical pulse signal obtained from the first ring laser is input to the second ring laser in the form of an optical signal, so that the short optical pulse signal exceeding the limit of the electric signal is obtained. Is obtained.

[0013] thereon, since the input after converting the short optical pulse signal of rectangular wave into a triangular wave in the optical triangular wave generator in the second ring laser, a short optical pulse signal is obtained more narrow.

[0014]

FIG. 1 shows the principle of an optical pulse generator according to the present invention.
FIG. 2 is a block diagram showing a configuration. In the figure, reference numeral 7 denotes a first ring laser based on the forced mode locking method, which comprises the following components. That is, 1 is an electric signal driver that outputs an electric signal for driving an optical modulator, and 2 is an optical modulator that modulates the amplitude of the orbiting optical signal of the first ring laser 7 with the electric signal.
Made of iNbO _{3 and} other materials, currently 70MHz
Degree of modulation. 3 is an optical amplifier having a gain necessary for the oscillation of the first ring laser 7, 4 is a variable optical delay device for adjusting the ring length of the first ring laser 7 to a value appropriate for oscillation, Reference numeral 5 denotes an optical coupler that branches the signal of the first ring laser 7 into an output signal and a ring signal. Reference numeral 6 denotes a variable wavelength filter that narrows the oscillation spectrum of the first ring laser 7. An optical isolator 8 receives the output of the first ring laser 7 and eliminates the influence of reflection of a device or the like connected thereafter, and 9 an optical isolator.
The optical attenuator (ATT) 10 for setting the output having a high peak value of the ring laser 7 (approximately +40 dB Max depending on the amplifier gain) as an input level of the second ring laser 17 described below is 10. This is a BPF that cuts wavelengths other than the output wavelength of the ring laser 7.

Reference numeral 17 denotes a second ring laser comprising the following components. That is, 11 is the second ring laser 17.
, An optical coupler that receives and multiplexes the output of the BPF 10, an optical amplifier 12 having a gain necessary for the oscillation of the second ring laser 17, and a ring length 13 of the second ring laser 17. A variable optical delay device for adjusting the value to an appropriate value for oscillation; 14 is an optical coupler for splitting the circulating optical signal of the second ring laser 17 for output and ring;
Is a variable wavelength filter for narrowing the oscillation spectrum of the second ring laser 17, and 16 is a polarization plane controller for adjusting the polarization plane to stably oscillate the second ring laser 17.

The output pulse width of the short optical pulse signal obtained in this basic configuration is as follows.

First, as shown in FIG. 2, a short optical pulse signal having a pulse width of 5 ps is obtained from the first ring laser 7 based on the operation principle described with reference to FIGS. The output pulse width at the time of inputting to 17 is estimated. When a short optical pulse signal having a pulse width of 5 ps is input to the second ring laser 17, the frequency is converted to a sine wave repetition frequency to be 40 GHz by the following estimation method.

That is, for convenience, for a sine wave of 100 GHz, the pulse width at the oscillation threshold is estimated to be 2 ps as shown in FIG. From these results, other pulse widths were estimated as shown in [Table 2] as being inversely proportional to the frequency.

[0019]

[Table 2] The output when 40 GHz is input to the first ring laser 7 has a pulse width of 5 ps from Table 2, but is actually 3.3 ps from equation (1).

3.3 ps is 70 when estimated from [Table 2].
GHz, and when this is input to the second ring laser 17, the output of the second ring laser 17 is 2.5 ps from the equation (1).

By the way, assuming that the short optical pulse signal output from the first ring laser 7 has a waveform like the bold line inside FIG. 2, the output pulse width at the oscillation threshold of the first ring laser 7 is as shown in FIG. If it can be estimated to be 2 ps or less from Equation (2), it can be estimated to be 100 GHz from [Table 2] when converted into a sine wave, and from Equation (1), actually 2 ps or less can be expected.

FIG. 4 shows an embodiment of the optical pulse generator according to the present invention. The optical pulse generator is provided with an optical triangular wave generator in the principle configuration of FIG. In FIG. 4, the same reference numerals as those in FIG. 1 denote the same parts, and reference numeral 18 denotes an optical triangular wave generator which converts a rectangular optical pulse into a triangular optical pulse. The details of the optical triangular wave generator 18 will be described later.

Now, as shown by the dotted line in FIG. 2, if a triangular wave can be obtained from the output of the first ring laser 7,
The output of the second ring laser 17 is further reduced to about 1 /
About 2, that is, 1 ps or less can be expected.

FIG. 5 is a diagram showing an example of the configuration of the optical triangular wave generator 18. As shown in FIG. In FIG. 5, 18A is an optical amplifier, 1
Reference numeral 8B denotes a single-mode optical fiber that causes down-chirp or up-chirp due to nonlinearity, and 18C denotes a band-pass filter (BPF) having a center wavelength within the chirp range of the optical fiber 18B.

The principle of operation will be described with reference to FIGS. The input optical pulse signal is sufficiently amplified in the optical amplifier 18A and then applied to the optical fiber 18B. Since the optical fiber 18B is a material having nonlinearity, when a high-intensity optical pulse signal is input thereto, a chirp phenomenon occurs due to the nonlinear optical effect, and the wavelength changes with time, as shown in FIG. When this is applied to the BPF 18C, portions other than the center wavelength are attenuated, and as shown in FIG.
A triangular wave having a peak at the center wavelength of the PF18C is obtained.

Although the above optical fiber 18B exceeds the up-chirp, an inverse dispersion optical fiber having the opposite dispersion characteristic at the working wavelength can be used as the one exceeding the down-chirp.

[Other Embodiments] Even if the order of each device in the first and second ring lasers 7 and 17 is changed, the same operation and effect can be obtained. Also,
The polarization plane controller 16 in the configuration shown in FIGS. 1 and 4 may not be provided if the second ring laser 17 is in the polarization maintaining state. The optical amplifiers 3 and 12 use either an EDFA (fiber amplifier) or an LD amplifier. Also,
If the gain is insufficient, the number of stages may be added.

FIG. 8 shows an application example of the optical pulse generator according to the present invention, wherein 100 is an optical pulse generator according to the present invention, 200 is a sampling element, and 300 is a display. In this way, if the short optical pulse signal according to the present invention is used as a light source for sampling and used for observing an optical signal to be observed, a shorter sampling time than before can be realized.
It is possible to observe the light waveform in a time of 1 ps or less.

Further, it can be used for evaluation of ultra-high-speed operation of an element used as a sampling element or the like.

[0030]

As described above, the principle configuration of the present invention is an electric signal driver for generating an electric signal for driving an optical modulator, and an optical pulse signal driven by the optical modulator driving signal from the electric signal driver. A first ring laser by a forced mode-locking method, and a pulse of an optical pulse signal of the first ring laser which is multiplexed with a circular optical signal of the second ring laser upon receiving the output of the first ring laser. Since the second ring laser outputs a short optical pulse signal having a pulse width shorter than the width, it is possible to obtain a short optical pulse signal having a short output pulse width exceeding the limit of driving by an electric signal.

According to the present invention, since the output of the first ring laser is input to the second ring laser as a triangular wave by the optical triangular wave generator, a short optical pulse signal having a shorter output pulse width can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of an optical pulse generator according to the present invention.

FIG. 2 is a waveform chart for explaining the operation of the configuration of FIG. 1;

FIG. 3 is a waveform chart for explaining the operation of the configuration of FIG. 1;

4 is a block diagram showing the configuration of a real施例optical pulse generator of the present invention.

FIG. 5 is a block diagram showing a configuration of an optical triangular wave generator in the embodiment of FIG.

FIG. 6 is a waveform diagram for explaining the operation of the triangular wave generator of FIG.

FIG. 7 is a waveform diagram for explaining the operation of the optical triangular wave generator of FIG.

8 is a block diagram showing an example of the use of the optical pulse generator of the present invention.

FIG. 9 is a block diagram illustrating a configuration example of a conventional ring laser.

FIG. 10 is a waveform diagram for explaining the operation of the conventional ring laser of FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 electric signal driver 2 optical modulator 3 optical amplifier 4 variable optical delay device 5 optical coupler 6 variable wavelength filter 7 first ring laser 8 optical isolator 9 optical ATT 10 BPF 11 optical coupler 12 optical amplifier 13 variable optical delay device 14 light Coupler 15 Variable wavelength filter 16 Polarization plane controller 17 Second ring laser 18 Optical triangular wave generator

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-6-120602 (JP, A) JP-A-7-15062 (JP, A) JP-A-5-102582 (JP, A) JP-A-5-102 63258 (JP, A) JP-A-8-76070 (JP, A) JP-A-7-263786 (JP, A) JP-A-6-125124 (JP, A) JP-A-2-310982 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H01S 3/10 H01S 3/098 H01S 3/06-3/07 H01S 3/083 H01S 5/00-5/50

Claims (1)

(57) [Claims] An electric signal driver for generating an electric signal for driving an optical modulator, and a first ring laser.
When, a second ring laser (17), said first ring
Between the laser (7) and the second ring laser (17)
The optical pulse signal output from the first ring laser
Triangular wave generator (1)
8) , wherein the first ring laser modulates the circulating light signal of the first ring laser by the electric signal for driving the light modulator, and an output of the light modulator. An optical amplifier for amplification (3), a variable optical delay unit (4) for adjusting the length of a ring for mode synchronization, an optical coupler (5) for branching into an optical pulse signal output and a ring output, and the output of the optical amplifier A variable wavelength filter (6 ) for cutting wavelengths other than the output wavelength of the above is connected in a ring shape to output a short optical pulse signal , and the second ring laser receives an output of the optical triangular wave generator , An optical coupler (11) for multiplexing with the circulating optical signal of the second ring laser, an optical amplifier (12) for amplifying the output of the optical coupler, and a variable optical delay unit for adjusting the length of the ring for mode synchronization (13) Optical pulse generator, wherein the variable wavelength filter for cutting a wavelength other than the optical coupler (14) and the output wavelength for branching an optical signal output (15) is configured to output a short optical pulse signal is connected to the ring apparatus.