JP3470885B2 - Optical frequency sweep light source - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generates many optical frequencies by frequency conversion based on the optical frequency of an incident light source,
The present invention relates to an optical frequency swept light source that outputs a pulse train at equal time intervals.

[0002]

2. Description of the Related Art In a future wavelength division multiplex (WDM) communication system, it is considered that the number of wavelength division multiplexes and the wavelength division multiplex density increase and the wavelength interval of WDM channels becomes narrower in order to meet the demand for an increase in transmission capacity. Further, by using an element having a wavelength selectivity (for example, a wavelength router), the carrier light path (optical path) is switched depending on the wavelength, and an efficient communication system can be constructed. Strict control of the channel optical wavelength (optical frequency) is becoming more and more important in order to realize the channel wavelength interval reduction and the optical path switching using the wavelength, and the strict control of the light source wavelength is indispensable.

To date, research and development for WDM using an optical ring circuit as a highly accurate arbitrary optical frequency generation means (for example, "K. Shimizu et al.," Frequency translati "
on of light waves by propagation around an optical
ring circuit containing afrequency shifter: I.Exp
eriment, "Appl.Opt.32,6718-6726 (1993).") has been conducted. This method is a method to obtain light with many wavelengths (optical frequencies) by repeatedly frequency-converting the light from the light source that is used as a reference, and to return the light whose frequency has been converted by the frequency converter to the frequency converter again. It is called an optical ring circuit because it has a ring-shaped optical circuit (see FIG. 3). Further, since the frequency of the output light changes in proportion to the number of frequency shifts received in the revolving time interval of the optical ring circuit, it is also called an optical frequency sweeper (sweep device). In this method, the frequency accuracy of the output light is determined by the absolute accuracy of the optical frequency of the reference light source and the accuracy of the conversion frequency of the frequency converter. In the reference light source, high accuracy is realized by stabilizing the wavelength by using the absorption line of gas, which is a very highly accurate wavelength reference. On the other hand, the frequency converter can realize very high frequency conversion accuracy by electrical feedback control. By using these,
In the optical ring circuit, it is possible to produce light with extremely high optical frequency accuracy.

The optical ring circuit shown in FIG. 3 comprises an optical multiplexer / demultiplexer 4, an optical delay line 5, an optical frequency shifter 6, a bandpass filter 17, an optical amplifier 18, and an optical fiber 2 for connecting them. The light from the reference light source 1 is cut out by the optical switch 3 and introduced into the optical ring circuit through the optical multiplexer / demultiplexer 4. The light introduced into the optical ring circuit is the optical frequency shifter 6
Undergoes a certain amount of frequency shift. The frequency-shifted light passes through the band-pass filter 17 and the optical amplifier 1
After being amplified by 8, the optical delay line 5 is given a delay time. After that, a part of the light is output to the outside of the optical ring circuit through the optical multiplexer / demultiplexer 4, and the rest goes around the inside of the optical ring again. The light circulating in the optical ring circuit is again frequency-shifted by the optical frequency shifter 6 and circulates in the optical ring circuit.

However, when the optical amplifier 18 such as a fiber amplifier is used for compensating the loss in the optical ring circuit as shown in FIG. 3, amplified spontaneous emission optical noise generated from the optical amplifier accumulates as the light goes around and is output. There is a problem that the signal / noise intensity ratio (S / N ratio) of light deteriorates. As a method for solving the problem of spontaneous emission noise accumulation, a bandpass optical filter 17 has been used as shown in FIG. The bandpass optical filter is required to have characteristics such as narrow bandwidth and high-speed wavelength tunability, and as a filter satisfying these requirements and also having amplification characteristics, Japanese Patent Application No. 11-0
As proposed in No. 43368, an amplification / filter mechanism (hereinafter referred to as an injection locking filter) utilizing the injection locking phenomenon for a wavelength tunable laser can be brought in (see FIG. 4). Synchronous injection means that when a laser oscillating at a certain free-running frequency (fFR) as shown in FIG. 5 (a) is irradiated with light near the free-running frequency (fML) as shown in FIG. 5 (b), This is a phenomenon in which the oscillation frequency of the laser is drawn into and coincides with the incident light frequency fML. In this case, since an oscillating laser is used, the features of narrow band, constant output light intensity, and constant polarization occur.

The optical ring circuit shown in FIG. 4 comprises an optical multiplexer / demultiplexer 4, an optical delay line 5, an optical frequency shifter 6, a lens 7, a semiconductor laser 8 and an optical fiber 2 for coupling them.
The light from the reference light source 1 is cut out by the optical switch 3 and introduced into the optical ring circuit through the optical multiplexer / demultiplexer 4. The light introduced into the optical ring circuit undergoes a certain amount of frequency shift by the optical frequency shifter 6. The frequency-shifted light is
It is incident on the semiconductor laser 8 via the lens 7. The semiconductor laser 8 is frequency-controlled in advance to a frequency near the incident light frequency by the controller 15, and is injection-locked to the incident light. The output light of the semiconductor laser 8 passes through the optical delay line 5 and
Through the optical multiplexer / demultiplexer 4, a part is output to the outside of the optical ring circuit, and the rest goes around the optical ring again. The light circulating in the optical ring circuit is again frequency-shifted by the optical frequency shifter 6 and circulates in the optical ring circuit.

[0007]

However, the difference between the incident optical frequency allowed for injection locking and the optical frequency during free-running oscillation is limited to a narrow range of several GHz. Therefore, it is necessary to control the free-running frequency of the laser receiving the injection locking so as to always keep the range of the allowable frequency error with respect to the signal light frequency circulating in the optical ring circuit while frequency-shifting. As a method of controlling the optical frequency of a semiconductor laser, there are a method of utilizing a change in refractive index due to carrier density fluctuation, a method of utilizing a change in refractive index due to temperature, and the like. Is often changed to control the optical frequency. Generally, a laser having a wide variable wavelength region has many control electrodes, and for example, three electrodes capable of realizing a wavelength change of about 1 THz.
The distributed Bragg reflector (DBR) laser has two optical frequency control electrodes, and the super periodic structure diffraction grating (SSG) DBR laser, which realizes a wider range of wavelength tunable range (up to 4 THz), has three optical frequency control electrodes. Therefore, when the injection locked filter is used for the optical frequency sweeper, it is necessary to change a plurality of control currents at the same time, which causes a problem that control becomes complicated.

The actual use state of the laser is in a transient state in terms of heat because the optical frequency control current changes faster than the temperature control time constant. However, since it is difficult to measure the optical frequency instantaneously exactly, the control current value has been obtained from the measurement in the steady state. Therefore, there is a problem in that the high-speed control of the optical frequency causes a delay in the thermal response, the output optical frequency deviates from the target value, and the continuation of injection locking is hindered.

An object of the present invention is to provide an optical frequency swept light source which enables detuning observation of the free-running frequency of a laser used in an injection locking filter and the injection light frequency and facilitates control of the free-running frequency of the laser. It is in.

[0010]

In order to achieve the above object, the present invention takes the following means.

According to a first aspect of the present invention, a time delay introducing means for introducing a time delay into the light from the reference light source, an optical frequency converting means for converting the frequency of the time delayed light, and a frequency-converted light are provided. Switch means for opening and closing, and when the switch means is in the open state, the frequency-converted light is incident to output light synchronized with the incident light frequency, and when the switch means is in the closed state, light in the free-running state is output. An injection-locked laser for outputting, a means for returning the frequency-synchronized light to the time-delay introducing means, and a means for taking out the light in the free-running state are provided, and the ring-shaped optical circuit is provided. A means for detecting an optical frequency difference between the synchronized light and the light in the free-running state, and an optical frequency in the free-running state of the injection-locked laser so that the detected optical frequency difference becomes a predetermined constant value or less. Equipped with means for controlling An optical frequency swept light source, wherein.

The invention according to claim 2 comprises first means for emitting pulsed light as a frequency reference, second means for introducing a time delay into the pulsed light, and time from the second means. Third means for converting the frequency of the delayed light, fourth means for opening and closing the frequency-converted light, and inputting the frequency-converted light when the fourth means is in an open state Fifth means for outputting light synchronized with the incident light frequency and for outputting light in a free-running state when the fourth means is in a closed state; sixth means for extracting the light in the free-running state; and the frequency a seventh means for introducing a time delay to the synchronous light, and example Bei the ring optical circuit comprising a first means 8 for a time delay light back to the second means from the means of said 7 An optical frequency sweep light source, the optical frequency difference between the frequency-synchronized light and the light in the free-running state. A ninth means for detecting and a tenth means for controlling the optical frequency of the free-running state of the fifth means so that the detected optical frequency difference becomes equal to or less than a predetermined constant value. Is an optical frequency sweep light source.

The invention according to claim 3 is the invention according to claim 1 or 2.
In place of the ring-shaped optical circuit, reciprocating light
It is characterized by using a circuit .

According to a fourth aspect of the present invention, a reflecting mirror, an optical frequency converting unit coupled to the reflecting mirror for converting the frequency of light from the reference light source, and an optical frequency converting unit are coupled to the optical frequency converting unit for applying a time delay to the light. A time delay means to be introduced, a switch means coupled to the time delay means for opening and closing light, and a switch means, which is coupled to the switch means and injects the frequency-converted light when the switch means is in an open state to make the incident light frequency A reciprocating type that is composed of an injection-locked laser that outputs light in synchronization with the injection-locked laser and that outputs light in a free-running state when the switch means is in a closed state, and a means that is coupled to the injection-locked laser and takes out the light in the free-running state. Means for detecting an optical frequency difference between the frequency-synchronized light and the light in the free-running state, and the injection-locked laser so that the detected optical frequency difference is equal to or less than a predetermined constant value. <br/> self-running An optical frequency swept light source, characterized in that a means for controlling the frequency.

The invention according to claim 5 is the invention according to claim 1 or 2.
At the time of orbit of light circulating in the ring-shaped optical circuit
The frequency-synchronized light and the free-running state at half the time interval between
The feature is that the light in the state is switched and time division is performed.

The invention according to claim 6 is the invention according to claim 3 or 4.
In, the round trip time of light traveling back and forth in the reciprocating optical circuit
The frequency-converted light and the free-running at half time intervals of
It is characterized in that the light in the state is switched to perform time division .

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, a portion for producing a standard reference light whose optical frequency changes at equal time intervals, and a standard reference light and a measured light are output in a time-divided manner so that the reference light and the measured light are separated from each other. And a portion for detecting a difference frequency by introducing a time delay into the. Hereinafter, a mechanism for realizing the present invention will be described with reference to specific embodiments. It is to be noted that the same reference numerals are given to the constituent elements in each drawing to indicate the same elements.

In the embodiment of the optical ring circuit type shown in FIG. 1, the optical ring circuit comprises an optical multiplexer / demultiplexer 4 and an optical delay line 5-.
1, an optical frequency shifter 6, an optical switch 3-2, a lens 7,
It is composed of a semiconductor laser 8, an optical demultiplexer 9-1, an optical delay line 5-2, and an optical fiber 2 coupling these.

In FIG. 1, the reference light whose optical frequency changes at equal time intervals is produced by the above-mentioned optical ring circuit, the reference light source 1 and the optical switch 3-1 for controlling the light source 1. The light from the reference light source 1 is cut out by the optical switch 3-1 in a time width that is equal to or less than the time required for one round of the optical ring circuit (hereinafter, rounding time Δt) and introduced into the optical ring circuit through the optical multiplexer / demultiplexer 4. . The light introduced into the optical ring circuit is given a delay time in the optical delay line 5-1 and is then subjected to a certain amount of frequency shift (Δf) by the optical frequency shifter 6. The light subjected to the frequency shift passes through the optical switch 3-2 in the open state and enters the semiconductor laser 8 via the lens 7. The semiconductor laser 8 is frequency-controlled in advance to a frequency near the incident light frequency by the controller 15, and is injection-locked to the incident light. The output light of the semiconductor laser 8 passes through the optical multiplexer 9-1 and the optical delay line 5-2, and a part of the output of the optical multiplexer / demultiplexer 4 is output to the outside of the optical ring circuit through the optical multiplexer / demultiplexer 4. The rest will orbit the optical ring again. The light circulating in the optical ring circuit is again subjected to the frequency shift of Δf by the optical frequency shifter 6 and circulates in the optical ring circuit.

As described above, by repeatedly circulating in the optical ring circuit, standard reference light having equal frequency intervals (Δf) and equal time intervals (Δt) is generated.

Here, by opening the optical switch 3-2, an output as an optical frequency sweeper can be obtained. A time chart at that time is shown in FIG. In FIG. 6, the horizontal axis represents time in units of the circulation time (Δt) of the optical ring circuit, and the vertical axis represents the optical switches 3-1 and 3-.
The open / closed state of No. 2 and the optical frequency of the output from each of the constituent elements 9-1 and 9 are shown. The optical frequency sweeper output is
It is shown as the output of the optical multiplexer / demultiplexer 4. Optical multiplexer / demultiplexer 4
In the output optical frequency diagram of, the light from the reference light source 1 directly output without passing through the optical ring circuit is shown by a broken line. Here, Δt / is provided between the optical multiplexer / demultiplexer 4 and the optical multiplexer / demultiplexer 9-1.
Optical delay lines 5-1 and 5 so that a time delay of 2 is introduced.
A length of -2 is set. With this setting, the injection locking light is output from the optical demultiplexer 9-1 after Δt / 2 when the light from the reference light source 1 reaches the optical multiplexer / demultiplexer 4. Also,
The light from the semiconductor laser 8 output from the optical multiplexer / demultiplexer 4 is further delayed by Δt / 2 with respect to the output of the optical multiplexer / demultiplexer 9-1. The optical frequency in the asynchronous state is observed corresponding to the open time of the optical switch 3-1 being shorter than the circulation time (Δt) of the optical ring circuit. The frequency of the asynchronous state shown here is when the output light of the semiconductor laser 8 is the optical frequency shifter 6
It is a frequency that is synchronized with the light returned by the frequency shift at, and is generally different from the free-running frequency.

The free-running frequency of the semiconductor laser 8 used as the injection locking filter is obtained by blocking the incident light with the optical switch 3-2. Therefore, injection locking is controlled by opening / closing the incident light to the semiconductor laser 8 by the optical switch 3-2 connected to the control device 15, and the reference light (synchronized state) and the measured light (self-propelled state) are generated. Output in time division.
FIG. 7 shows a time chart when the duty ratio of the optical switch 3-2 is 0.5. The horizontal and vertical axes of FIG. 7 are shown in FIG.
Is the same as. The output light of the optical multiplexer / demultiplexer 4 is the optical delay line 5-2.
Is delayed by Δt / 2 from the output of the optical demultiplexer 9-1. The output light from the optical multiplexer / demultiplexer 4 and the optical demultiplexer 9-1
The output light of is incident on the photodetector 11 via the optical demultiplexer 9-2 and the optical multiplexer 10, and the difference frequency between the two output lights is observed as a beat.

FIG. 7 shows the case where the frequency change between the reference light and the measured light is constant, but as shown in FIG. 8, the same result can be obtained when the frequency difference changes.

In the photodetector 11, the same time slot (same revolution, shown by the solid line) and the adjacent time slot (shown by the broken line) appear for each Δt / 2, and the frequency difference between the adjacent slots which is unnecessary at the time of measurement is It is removed by the electric switch 12 which opens and closes in the opposite phase to the optical switch 3-2. Then, the optical frequency difference is observed by the optical spectrum analyzer 13. Further, by using the frequency discriminator 14 and controlling the free-running frequency of the semiconductor laser 8 by the controller 15 so that the frequency discriminated by the frequency discriminator 14 becomes a certain value or less, stable injection is achieved. Achieved synchronization.

Next, FIG. 2 shows an optical sweeper according to a reciprocating embodiment. Elements common to those in FIG. 1 are designated by the same reference numerals. The light reciprocating structure includes a reflecting mirror 16, an optical frequency shifter 6,
It includes an optical multiplexer / demultiplexer 4, an optical delay line 5, an optical switch 3-2, an optical demultiplexer 9-1, a lens 7, a semiconductor laser 8 and an optical fiber 2 coupling these.

In FIG. 2, the initial injection light emitted from the reference light source 1 and cut out by the optical switch 3-1 is introduced into the reciprocating structure via the optical multiplexer / demultiplexer 4. The light introduced into the reciprocating structure is introduced into the optical frequency shifter 6, where it undergoes frequency shift. This light is then reflected by the reflecting mirror 16, enters the optical frequency shifter 6, undergoes frequency shift again here, and then passes through the optical multiplexer / demultiplexer 4 and is introduced into the optical delay line 5. This light, after being given a delay time by the optical delay line 5, enters the semiconductor laser 8 through the open optical switch 3-2. The semiconductor laser 8 is injection-locked with the incident light, and the output light is partly output to the outside of the reciprocating structure via the optical demultiplexer 9-1, but the rest is the optical switch 3.
-2 and the optical delay line 5, a part of which is output to the outside through the optical multiplexer / demultiplexer 4, while the remaining part is reciprocated in the reciprocating structure while undergoing frequency shift by the frequency shifter 6 again. By repeating this, multi-optical frequency light is obtained.

In the example shown in FIG. 2, assuming that the time required for the reciprocating structure to reciprocate is Δt and the unit frequency shift amount received by the optical frequency shifter 6 is Δf / 2, the time chart shown in the embodiment example of FIG. 6 holds. Further, the time charts when the duty ratio of the optical switch 3-2 is 0.5 are shown in FIGS. 9 and 10, and similar to the optical ring circuit type timing charts shown in FIGS. 7 and 8 can be obtained. . However, the reciprocating type is different from the optical ring circuit type,
The output of the optical multiplexer / demultiplexer 4 does not include the free-running frequency of the semiconductor laser 8 that is the measured light. This is because the free-running frequency is cut by the optical switch 3-2.
Therefore, in the illustrated reciprocating type, only beats corresponding to the frequency difference in the same slot are automatically observed. Thus, the optical frequency difference is measured, and the semiconductor laser 8 using the frequency discriminator 14 as in the optical ring type example shown in FIG.
It is possible to control the free-running frequency.

The output light of the optical multiplexer / demultiplexer 4 and the output light of the optical demultiplexer 9-1 are incident on the photodetector 11 via the optical demultiplexer 9-2 and the optical multiplexer 10, and the two output lights are output. The difference frequency between them is observed as a beat. The optical frequency difference is observed by the optical spectrum analyzer 13. Further, by using the frequency discriminator 14 and controlling the free-running frequency of the semiconductor laser 8 by the controller 15 so that the frequency discriminated by the frequency discriminator 14 becomes a certain value or less, stable injection is achieved. Achieved synchronization.

In the embodiment shown in FIG. 2, the output of the optical multiplexer / demultiplexer 4 does not include the free-running frequency of the semiconductor laser 8. However, by arranging the optical switch 3-2 between the optical frequency shifter 6 and the optical multiplexer / demultiplexer 4, and inverting the opening / closing phase of the optical switch 3-2, the output of the optical multiplexer / demultiplexer 4 is changed to the semiconductor laser. It is also possible to extract 8 free-running frequencies. On the contrary, in the embodiment shown in FIG. 1, by arranging the optical switch 3-2 between the optical demultiplexer 9-1 and the optical delay line 5-2, the output of the optical multiplexer / demultiplexer 4 is output. It is possible to avoid mixing of the free-running frequency of the semiconductor laser 8 into the semiconductor laser 8. As a result, a configuration without the electric switch 12 can be realized.

Further, in each of the embodiments, the light incident on the semiconductor laser 8 is controlled by using the optical switch 3-2. However, as the optical frequency shifter 6, an optical frequency shifter having an optical switch function (for example, By controlling the acousto-optical optical frequency shifter, the electro-optical modulator, etc.) by the control device 15, it is possible to serve also as the optical switch 3-2. In addition, in each embodiment, the semiconductor laser 8
In the control of the free-running frequency of the semiconductor laser 8 by combining a high-frequency cutoff filter and a filter that cuts a DC component as the frequency discriminator 14 or using a bandpass filter, the output of the semiconductor laser 8 is always present.
However, it is also possible to use a low frequency cutoff filter as the frequency discriminator 14 and control so that the output signal from the filter disappears.

FIG. 11 shows an example of the optical ring circuit portion. The optical ring circuit shown in FIG.
(Same as reference numeral 4), optical isolator 25, optical circulator 26, wavelength tunable semiconductor laser (distributed reflection laser) 27 via optical circulator 26, optical isolator 2
5, acousto-optical type optical frequency shifter 28 (same as reference numeral 6), optical delay line 29 (same as reference numeral 5), polarization controller 30
And an optical fiber 2 connecting them.

In FIG. 11, the light emitted from the frequency reference light source 1 is cut out by the optical switch 3 in a pulse shape that is equal to or less than the circulation time of the optical ring circuit and is used as reference light pulse light. The reference light pulse is introduced into the optical ring circuit through the fiber coupler 24 and injected into the wavelength tunable semiconductor laser 27 through the optical circulator 26. The wavelength tunable semiconductor laser 27 is controlled by the control circuit 31 (the same as reference numeral 15) so that the difference between the oscillation frequency and the incident light frequency falls within the injection locking range, and is injection locked with respect to the incident light. The output light is output to a port different from that of the incident light by the function of the optical circulator 26. In this output light, the circulating signal light is amplified and the noise level is reduced. The light emitted from the optical circulator 26 is
It is guided to the acousto-optical optical frequency shifter 28. Sound-
After receiving the frequency shift by the optical type optical frequency shifter 28,
A delay time is added by the optical delay line 29, and the polarization controller 30 makes the wavelength tunable semiconductor laser 27 adjusted so that the frequency difference between the self-oscillation light and the circulating light is within the injection locking range, and tunes the wavelength. The semiconductor laser 27 is injection-locked with the frequency-shifted light. In this way, by repeating the circulation of the optical ring circuit and the frequency shift, an optical pulse whose optical frequency changes at equal frequency intervals is obtained as an output.

Further, FIG. 12 shows another example of the optical ring circuit portion. The optical ring circuit shown in FIG. 12 includes a fiber coupler 24, an electro-optical modulator 32, an optical isolator 25,
An optical circulator 26, a wavelength tunable semiconductor laser (distributed reflection laser) 27, an optical delay line 29, a polarization controller 30, and an optical fiber 2 connecting them.

In FIG. 12, the light emitted from the frequency reference light source 1 is cut out by the optical switch 3 in a pulse shape that is shorter than the circulation time of the optical ring circuit. The obtained reference light pulse is
It is introduced into the optical ring circuit through the fiber coupler 24. The light in the optical ring circuit is modulated by the electro-optical modulator 32. The modulator output light includes several-order modulated sidebands and a fundamental wave that has not undergone frequency conversion. The wavelength tunable semiconductor laser 27 is tracking-controlled by the control circuit 31 so as to be injection-locked only to light having a desired frequency shift from the modulator output light. Therefore, from the wavelength tunable semiconductor laser 27, the electro-optical modulator 3
Only the light that has undergone a desired frequency shift with respect to the light incident on 2 is output, and frequency conversion is realized. At this time, at the same time, amplification of the converted light and reduction of noise light other than the converted light can be achieved. A time delay is given by passing the output light from the wavelength tunable semiconductor laser 27 and the optical delay line 29. Then, after the polarization is adjusted by the polarization controller 30 so that the efficiency of the electro-optical modulator 32 and injection locking is maximized, a part of the light is output from the optical ring circuit through the fiber coupler 24, and the rest. Recirculates around the optical ring circuit. By repeating the circulation of the optical ring circuit, a repeated frequency shift is received and a multi-frequency light source is realized. Here, when the wavelength tunable semiconductor laser 27 is controlled by using the control circuit 31, if it is always synchronized with the modulation sideband of the same order, light having an equal frequency interval is obtained as an output. On the other hand, it is also possible to control the injection locking by selecting the order of the modulation sideband for each circulation. In this case, W
Like unequal frequency spacing carrier light in DM communication,
Light is obtained that is spaced at multiples of a certain frequency (corresponding to the modulation frequency). The electro-optical type optical modulator 32 is used as a means for performing optical modulation and generating a modulated sideband.
It is also possible to use an electroabsorption type optical modulator as a means for generating the modulation sideband. Further, by using a means for branching the light into a plurality of optical paths and adding a phase difference between the light and the modulation signal, it becomes possible to easily select the modulation sideband having a desired frequency change amount.

[0035]

As described above, according to the present invention, it is possible to obtain a multi-optical frequency light source capable of adjusting the frequency of the laser used in the injection locking filter.

[Brief description of drawings]

FIG. 1 is a diagram showing an optical ring type optical frequency swept light source as an embodiment of the present invention.

FIG. 2 is a diagram showing a reciprocal optical frequency sweep light source as an embodiment of the present invention.

FIG. 3 is a diagram showing an optical ring circuit type light source.

FIG. 4 is a diagram showing an optical ring circuit to which injection locking is applied.

FIG. 5 is a schematic diagram of injection locking.

FIG. 6 is a time chart of switching and output optical frequency during an optical sweeper.

FIG. 7 is a time chart of switching and output optical frequency when measuring an optical frequency difference in an optical ring type.

FIG. 8 is a time chart when the frequency difference changes.

FIG. 9 is a time chart of switching and output optical frequency when measuring an optical frequency difference in a reciprocating type.

FIG. 10 is a time chart when the frequency difference in the reciprocating type changes.

FIG. 11 is a diagram showing an example of an optical ring circuit portion.

FIG. 12 is a diagram showing another example of the optical ring circuit portion.

[Explanation of symbols]

1 Reference light source 2 optical fiber 3 optical switch 4 Optical multiplexer / demultiplexer 5 Optical delay line 6 Optical frequency shifter 7 lenses 8 Semiconductor laser 9 Optical demultiplexer 10 Optical multiplexer 11 Photodetector 12 electrical switch 13 Spectrum analyzer 14 Frequency discriminator 15 Control device 16 Reflector 17 Band pass filter 18 Optical amplifier 24 Fiber Coupler 25 Optical Isolator 26 Optical circulator 27 Tunable semiconductor laser (distributed reflection laser) 28 Acoustic-Optical Optical Frequency Shifter 29 Optical delay line 30 Polarization controller 31 Control circuit 32 Electro-optical modulator

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP2000-244045 (JP, A) JP55-61082 (JP, A) Mitsuei Ishikawa et al. “Optical ring applying injection locking of tunable laser” Circuit ", Proceedings of the 1999 IEICE General Conference, Electronics 1, March 28, 1999, p. 366 (58) Fields investigated (Int.Cl. ⁷ , DB name) H01S 3/00- 3/30

Claims (6)

(57) [Claims] 1. A time delay introducing means for introducing a time delay into the light from the reference light source, an optical frequency converting means for converting the frequency of the time delayed light, and a switch means for opening and closing the frequency converted light, Note that the switch means is incident the frequency-converted light when in an open state and outputs light that is synchronized with the incident light frequency, said switch means outputs the light of the free-running state when the closed state
An input-locked laser , a means for returning the frequency-synchronized light to the time delay introducing means, and a means for extracting the light in the free-running state are provided in a ring-shaped optical circuit, and the frequency-synchronized light and the A means for detecting an optical frequency difference with respect to the light in the free-running state and a means for controlling the optical frequency in the free-running state of the injection-locked laser so that the detected optical frequency difference is equal to or less than a predetermined constant value. Optical frequency sweep light source characterized by 2. A first means for emitting pulsed light as a frequency reference, a second means for introducing a time delay into the pulsed light, and a frequency of the time-delayed light from the second means. A third means for converting the light, a fourth means for opening and closing the frequency-converted light, and a means for inputting the frequency-converted light when the fourth means is in an open state to synchronize with the incident light frequency. Fifth means for outputting light and outputting light in the free-running state when the fourth means is in the closed state, sixth means for extracting the light in the free-running state, and time for the frequency-synchronized light a seventh means and optical frequency sweep light source example Bei the ring optical circuit comprising a first means 8 for a time delay light back to the second means from the means of said 7 that introduces a delay And detecting an optical frequency difference between the frequency-synchronized light and the free-running light. 10 for controlling the stage and the optical frequency of the free-running state of the fifth means as the detected light frequency difference is equal to or less than a predetermined constant value
And an optical frequency swept light source. 3. The optical frequency swept light source according to claim 1, wherein a reciprocating optical circuit is used instead of the ring-shaped optical circuit. 4. A reflecting mirror, an optical frequency converting unit coupled to the reflecting mirror for converting the frequency of light from a reference light source, and a time delaying unit coupled to the optical frequency converting unit for introducing a time delay into the light. A switch means coupled to the time delay means for opening and closing the light, and coupled to the switch means for injecting the frequency-converted light when the switch means is in an open state and outputting light synchronized with the incident light frequency An injection-locked laser that outputs light in a free-running state when the switch means is closed, and a reciprocal optical circuit that is coupled to the injection-locked laser and that extracts the light in the free-running state. A means for detecting an optical frequency difference between the frequency-synchronized light and the light in the free-running state; and a light in the free-running state of the injection-locked laser so that the detected optical frequency difference becomes a predetermined constant value or less. Hand controlling frequency Optical frequency swept light source, characterized in that it comprises and. 5. The frequency-synchronized light and the light in the free-running state are switched and time-divided at a time interval which is half the circulation time of the light circulating in the ring-shaped optical circuit. Alternatively, the optical frequency sweep light source described in 2. 6. The frequency-converted light and the light in the free-running state are switched and time-divided at a half time interval of a round-trip time of light traveling back and forth in the reciprocating optical circuit. 3. The optical frequency swept light source according to 3 or 4.