JP5509482B2 - Optical loop device and optical signal delay circuit - Google Patents

Description

  The present invention relates to an optical loop device, an optical signal delay circuit, and a laser light pulse that can be converted into a frequency or delayed by making the laser light pulse incident on an optical waveguide loop and rotating the incident laser light pulse a predetermined number of times in the optical waveguide loop. The present invention relates to a frequency conversion method and an optical signal delay method.

  Conventionally, an optical fiber loop device shown in FIG. 17 is known. In the optical fiber loop device 8 of FIG. 17, the laser light emitted from the laser light source 81 is continuously incident on the optical fiber loop 83 via the optical coupler 82. The laser light incident on the optical fiber loop 83 is amplified by the optical amplifier 84 and then frequency-converted by the frequency shifter 85.

  In FIG. 17, the optical fiber loop 83 functions as an optical comb generator, and the generated comb light is incident on an AWG (arrayed waveguide diffraction grating) 86 outside the optical fiber loop 83 via the optical coupler 82, and from the AWG 86. Can obtain a demultiplexed comb light (frequency comb light).

  Further, a spectrum measuring apparatus using an optical comb generator as shown in FIG. 18 is known. In the spectrum measuring apparatus 9, the laser light emitted from the laser light source 91 is incident on the optical comb generator 92. The frequency comb light from the optical comb generator 92 is incident on the sample 98 after being incident on the SSB modulator 94 via the wavelength variable filter (BPF) 93. The response light (frequency comb light) of the sample 98 is detected by the photodetector 95.

  The output of the optical comb generator 92 is measured by the optical frequency meter 96, and the computer 97 can output the spectrum analysis result of the sample 98 from the output of the photodetector 95 and the output of the optical frequency meter 96. it can.

  In the optical fiber loop device 8 of FIG. 17, it is difficult to obtain a single mode frequency, and the output stability is poor due to resonance in the optical fiber loop 83. For this reason, it is necessary to optimize the gain of the optical amplifier 84, but this optimization is actually difficult.

  Further, in the conventional spectrum measuring apparatus 9 of FIG. 18, there is a limit to the performance of the wavelength tunable filter (BPF) 93, the S / N ratio is low, the signal intensity is weak, and the sweepable region is limited. is there.

  An object of the present invention is to make a laser light pulse enter an optical waveguide loop (an optical fiber loop or an optical waveguide loop formed on or in a substrate) and circulate the incident laser light pulse in the optical waveguide loop. An optical loop device and a frequency conversion method capable of generating a laser beam having a desired frequency by generating a frequency-converted laser beam whose frequency is sequentially shifted and emitting the frequency-converted laser beam at a predetermined round timing. There is.

  Another object of the present invention is to provide the above optical loop device that can be used as a spectrum measuring device.

  Still another object of the present invention is to make a laser light pulse enter an optical waveguide loop (an optical fiber loop or an optical waveguide formed on or in a substrate) and circulate the incident laser light pulse in the optical waveguide. Thus, an object of the present invention is to provide an optical signal delay circuit and an optical signal delay method capable of delaying the laser light pulse by a predetermined time.

The gist of the optical loop device of the present invention is (1) to (9).
(1)
An optical path selector for introducing an incident laser light pulse (consisting of a single pulse or a plurality of pulses) into at least one of an optical path circulating around the optical waveguide loop or an optical path bypassing the optical waveguide loop;
The laser light pulse incident on the optical waveguide loop is shifted by a predetermined frequency interval to generate a frequency-converted laser beam. A frequency shifter that sequentially shifts by a predetermined frequency interval to generate a frequency-converted laser beam having a predetermined circulation;
An optical amplifier for amplifying the laser light pulse that circulates around the optical waveguide loop;
An optical loop device comprising an optical waveguide loop having
The optical path selector emits the frequency converted laser light to the outside of the optical waveguide loop at a predetermined timing corresponding to the predetermined rotation.
An optical loop device characterized by that.

(2)
As the optical path selector, an optical loop device using a 2 × 2 optical switch having a bar mode and a cross mode,
When the 2 × 2 optical switch is in a cross mode, the frequency-converted laser light is incident on the optical waveguide loop, and the frequency-converted laser light having the predetermined number of rounds is emitted from the 2 × 2 optical switch.
When the 2 × 2 optical switch is in the bar mode, the laser beam pulse is sent to the optical path through which the frequency-converted laser beam is emitted without entering the optical waveguide loop, and the frequency-converted laser that circulates. Confine light in the optical waveguide loop;
(1) The optical loop device according to (1).

(3)
The optical loop device according to (1) or (2), wherein the optical waveguide loop has an optical gate switch that is turned off in synchronization with a timing at which the frequency-converted laser light is emitted from the optical waveguide loop.

(4)
An optical path selector for introducing an incident laser light pulse (consisting of a single pulse or a plurality of pulses) into at least one of an optical path circulating around the optical waveguide loop or an optical path bypassing the optical waveguide loop;
The laser light pulse incident on the optical waveguide loop is shifted by a predetermined frequency interval to generate a frequency-converted laser beam. A frequency shifter that sequentially shifts by a predetermined frequency interval to generate a frequency-converted laser beam having a predetermined circulation;
An optical loop device comprising an optical waveguide loop having
The optical path selector has an optical amplifier functioning as a switch in each of an introduction path to an optical path that circulates the optical waveguide loop and an introduction path to an optical path that bypasses the optical waveguide loop, and corresponds to the predetermined circulation. At the predetermined timing, the frequency converted laser light is emitted to the outside of the optical waveguide loop.
An optical loop device characterized by that.

(5)
The optical loop device according to any one of (1) to (4), wherein the laser light pulse is directly intensity modulated or external intensity modulated.
That is, the laser light pulse may be emitted from a laser light source that directly modulates the light intensity. Further, a light intensity modulator may be provided, and the laser light from the laser light source may be output as a laser light pulse by the light intensity modulator.

(6)
The optical loop according to any one of (1) to (5), wherein at least two of the optical path selector, the frequency shifter, the optical amplifier, and the optical waveguide loop are formed on the same substrate. apparatus.

(7)
The optical loop device according to any one of (1) to (6), wherein the optical waveguide loop is formed as an optical fiber loop, or is formed on or in a substrate.

(8)
The optical loop device according to any one of (1) to (7), wherein the laser light pulse is wavelength-locked.
That is, a wavelength locker may be provided, and the reference frequency laser beam may be generated by this wavelength locker.

(9)
The optical loop device according to (8), which is used as a spectrum measurement device,
further,
A frequency shifter that irradiates the sample by sweeping the frequency of the laser light emitted outside the optical waveguide loop;
A photodetector for receiving response light from the sample;
A control processing device that controls a switch constituting the optical path selector, controls a frequency sweep of the frequency shifter, and analyzes a signal detected by the photodetector as a spectrum;
An optical loop device comprising:

The gist of the optical signal delay circuit of the present invention is (10) to (15).
(10)
An optical path selector for introducing an incident laser light pulse (consisting of a single pulse or a plurality of pulses) into at least one of an optical path circulating around the optical waveguide loop or an optical path bypassing the optical waveguide loop;
An optical amplifier for amplifying the laser light pulse that circulates around the optical waveguide loop;
An optical signal delay circuit comprising an optical waveguide loop having
The optical path selector emits the frequency converted laser light to the outside of the optical waveguide loop at a predetermined timing corresponding to the predetermined rotation.
An optical signal delay circuit.

(11)
An optical signal delay circuit using a 2 × 2 optical switch having a bar mode and a cross mode as the optical path selector,
When the 2 × 2 optical switch is in the cross mode, the laser light pulse composed of a single pulse or a plurality of pulses is incident on the optical waveguide loop, and the laser light pulse of the predetermined number of rounds is emitted from the 2 × 2 optical switch. Exit,
When the 2 × 2 optical switch is in the bar mode, the laser light pulse is not incident on the optical waveguide loop, but is sent to the optical path from which the laser light pulse is emitted, and the frequency converted laser light that circulates is transmitted. Confined in the optical waveguide loop;
(10) The optical signal delay circuit according to (10).

(12)
The optical loop device according to (10) or (11), wherein the optical waveguide loop has an optical gate switch that is turned off in synchronization with a timing at which the frequency converted laser light is emitted from the optical waveguide loop.

(13)
An optical waveguide loop having an optical path selector for introducing an incident laser light pulse (consisting of a single pulse or a plurality of pulses) into at least one of an optical path circulating around the optical waveguide loop or an optical path bypassing the optical waveguide loop is provided An optical loop device,
The optical path selector has an optical amplifier functioning as a switch in each of an introduction path to an optical path that circulates the optical waveguide loop and an introduction path to an optical path that bypasses the optical waveguide loop, and corresponds to the predetermined circulation. At the predetermined timing, the frequency converted laser light is emitted to the outside of the optical waveguide loop.
An optical signal delay circuit.

(14)
The optical signal delay circuit according to any one of (10) to (13), wherein at least two of the optical path selector, the optical amplifier, and the optical waveguide loop are formed on the same substrate.

(15)
The optical signal delay circuit according to any one of (10) to (14), wherein the optical waveguide loop is formed as an optical fiber loop, or is formed on or in a substrate.

The gist of the frequency conversion method of the present invention is (16).
(16)
Frequency conversion in which a laser light pulse composed of a single pulse or a plurality of pulses is incident on an optical waveguide loop, and the incident laser light pulse is circulated at least once in the optical waveguide loop and then emitted to the outside of the optical waveguide loop. A method,
The incident laser beam pulse is shifted by a predetermined frequency interval by a frequency shifter provided in the optical waveguide loop to generate a frequency converted laser beam,
After that, each time the circulation is repeated, the frequency converted laser light to be circulated is further sequentially shifted by the frequency shifter by the predetermined frequency interval to generate a frequency converted laser light having a predetermined frequency,
The optical path selector provided in the optical waveguide loop emits the frequency converted laser light to the outside of the optical waveguide loop at a predetermined timing corresponding to the predetermined rotation.
A frequency conversion method characterized by that.

The gist of the optical signal delay method of the present invention is (17).
(17)
An optical signal that enters a laser light pulse composed of a single pulse or a plurality of pulses into the optical waveguide loop, and radiates the incident laser light pulse at least once in the optical waveguide loop, and then emits the laser light pulse to the outside of the optical waveguide loop. A delay method,
The optical path selector provided in the optical waveguide loop emits the frequency converted laser light to the outside of the optical waveguide loop at a predetermined timing corresponding to the predetermined rotation.
An optical signal delay method.

  In the optical loop device and the frequency conversion method of the present invention, since the laser light incident on the optical waveguide loop is not continuous light (because it is a pulse), resonance in the optical waveguide loop is avoided. Thus, the frequency shifter shifts the frequency (single frequency) of the laser light pulse that circulates in the optical waveguide loop, and is excellent in characteristics of a predetermined frequency (discrete frequency) from the optical path selector (S / N ratio is high and stability is high).

  Further, when a 2 × 2 optical switch having a bar mode and a cross mode is used as the optical path selector, efficient control with a reduced number of parts can be performed.

  When the optical loop device of the present invention is used as a spectrum measurement device, spectrum measurement with a high S / N ratio and high stability can be performed.

  In the optical signal delay circuit of the present invention, the laser light pulse (typically an optical packet) is circulated in the optical loop, so that the laser light pulse can be delayed by a predetermined discrete time. The signal delay circuit can be used as an optical memory, for example.

It is explanatory drawing which shows embodiment of the optical loop apparatus and frequency conversion method of this invention. (A) is explanatory drawing which externally modulates the intensity | strength of a laser beam, (B) is explanatory drawing which modulates the intensity | strength of a laser beam directly. It is a figure which shows the example using a 2 * 2 optical switch as an optical path selector, (A) is a cross mode, (B) is a figure which shows a bar mode. It is a figure which shows the example using a coupler and a 1 * 2 optical switch as an optical path selector, (A) is a 1st mode, (B) is a figure which shows a 1st mode. It is a figure which shows the example using 2 * 1 optical switch and 1 * 2 optical switch as an optical path selector, (A) is the 1st mode, (B) is the 2nd mode, (C) Is a diagram showing a third mode, and (D) is a diagram showing a fourth mode. It is explanatory drawing of the optical loop apparatus of this invention which provided the optical gate switch in the optical waveguide loop. It is operation | movement explanatory drawing of the optical loop apparatus of FIG. 6 when a 2 * 2 optical switch is used as an optical path selector. (A) is a figure which shows the optical loop apparatus using the optical path selector with a built-in optical amplifier, (B) is a figure which shows the structure of an optical path selector. It is explanatory drawing of embodiment which used the optical loop apparatus as a spectrum measuring device. It is a figure which shows the optical loop apparatus with which the optical loop apparatus is integrated on the board | substrate. It is a figure which shows the optical loop apparatus with which the optical intensity modulator and the optical loop apparatus are integrated on the board | substrate. It is a figure which shows the optical loop apparatus with which the laser beam pulse source and the optical loop apparatus are integrated on the board | substrate. It is a figure which shows the optical loop apparatus by which the optical path selector with a built-in optical amplifier is integrated on the board | substrate. It is explanatory drawing which shows embodiment of the optical loop apparatus used as an optical signal delay circuit. It is explanatory drawing which shows the optical signal delay circuit which formed the optical waveguide loop into the pattern on the board | substrate, and was formed integrally with the optical path selector, the optical amplifier, and the filter. It is explanatory drawing which shows an optical signal delay circuit using an optical path selector with built-in optical amplifier. It is explanatory drawing which shows the conventional optical fiber loop apparatus. It is explanatory drawing which shows the conventional spectrum measuring device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical loop apparatus 2 Spectral measurement apparatus 3 Optical signal delay circuit 11 Optical waveguide loop 12, 32 Optical path selector 12 ', 32' Amplifier built-in optical path selector 13, 16 Frequency shifter 15 Optical gate switch 14, 33 Optical amplifier 17 Substrate 21 Sample 22 Photodetector 23 Computer 31 Optical fiber loop 34 Filter 36 Communication line 100 Laser light pulse source 101 Laser 102 Light intensity modulator 103 Wavelength locker 110 Optical loop controller 121 3 dB coupler 122, 123 SOA

FIG. 1 is an explanatory diagram showing a first embodiment of an optical loop device and a frequency conversion method according to the present invention. In FIG. 1, an optical loop device 1 includes an optical waveguide loop (optical fiber loop in FIG. 1) 11 and an optical path selector 12, and the optical waveguide loop 11 includes a frequency shifter 13 and an optical amplifier 14. .
The laser light pulse incident on the optical loop device 1 is generated by the laser light source pulse source 100. The laser light from the laser light pulse source 100 can be modulated (externally modulated) by the light intensity modulator 102 as shown in FIG. That is, the light intensity modulator 102 receives laser light (seed light) from the laser 101, modulates the light intensity of the incident laser light, and outputs it as a laser light pulse LP (consisting of a single pulse or a plurality of pulses). . Further, instead of using the light intensity modulator 102, the laser light generated by the laser light pulse source 100 may be directly intensity modulated as shown in FIG.

Further, as shown in FIGS. 2A and 2B, a wavelength locker 103 can be attached to the laser 101, and the wavelength of the laser beam emitted from the laser 101 can be locked.
The optical loop control unit 110 sends a control signal to the optical path selector 12 and the frequency shifter 13, introduces a laser light pulse to the optical waveguide loop 11, sends a laser light pulse to an optical path that bypasses the optical waveguide loop 11, The confinement of the frequency converted laser light that circulates in the optical waveguide loop 11 into the optical waveguide loop 11 and the transmission of the frequency converted laser light that circulates in the optical waveguide loop 11 to the outside of the loop (to the bypass optical path described above). Take control. In FIG. 1, FIG. 2 (A), (B), and FIG. 3 and after, the control signal from an optical loop control part is shown with a broken line. In FIG. 1, the optical loop control unit 110 sends a synchronization control signal for intensity modulation to the laser light source pulse source 100. 1, FIG. 2 (A), (B), and FIG. 3 and subsequent figures, this synchronization signal is also indicated by a broken-line arrow.
Note that there is a relationship of T _LP <T _FL between the time width T _LP of the laser light pulse LP and the time T _FL during which the laser light pulse LP makes one round of the optical waveguide loop 11.

The optical path selector 12 can select at least one of an optical path for introducing the laser light pulse LP into the optical waveguide loop 11 and an optical path for bypassing the optical waveguide loop 11. When the laser light pulse LP is introduced into the optical waveguide loop 11, the incident laser light pulse LP is rotated N times (N is a positive integer) in the optical waveguide loop 11, and the optical waveguide loop 11 is at a predetermined frequency. It is external to exit as a frequency to be converted laser beam LM _N. Emission frequency to be converted laser beam LM _N also performed by the optical path selector 12.
More specifically, the optical path selector 12 is described later with reference to FIGS. 3A, 3B, 4A, 4B, 5A, 5B, 5C, 5D. As shown in FIG. 8, it can be constituted by an LN switch or a nonlinear optical effect switch, or it can be constituted by including an SOA (semiconductor optical amplifier) as shown in FIGS. 8A and 8B described later.

The frequency shifter 13 frequency-converts the light circulating in the optical waveguide loop 11 to generate a frequency-converted laser beam. That is, first, the incident laser light pulse LP is frequency-converted to generate the first round frequency-converted laser light LM ₁ .
Next, the frequency conversion laser light LM ₁ of the first round is frequency converted (shifted by a predetermined interval) to generate the frequency converted laser light LM ₂ of the second round.
Further, the second round frequency converted laser beam LM ₂ is frequency converted (shifted by a predetermined interval) to generate the third round frequency converted laser beam LM ₃ .

Hereinafter, similarly to the frequency to be converted laser beam LM _N is generated, performs frequency conversion of the orbiting frequency to be converted laser light (predetermined interval shift).
That is, after the second round, the frequency-converted laser light LM _k of the k-th round is frequency-converted (shifted by a predetermined interval), and the frequency-converted laser light LM _{k + 1} (k = 2,. .., N-1) is generated. As the frequency shifter 13, for example, a single sideband (SSB) optical modulator, an acousto-optic (AO) modulator, or the like can be used.

  The optical amplifier 14 amplifies the laser light so as to compensate for the loss when the laser light circulates in the optical waveguide loop 11. As shown in FIG. 1, the optical amplifier 14 may be in the subsequent stage of the frequency shifter 13 or in the previous stage of the frequency shifter 13. It is desirable from the viewpoint of stable operation that the optical amplifier 14 is operated in a constant gain control mode so that the optical output level after leaving the amplifier is always constant.

Optical path selector 12 at a predetermined timing corresponding to the number of turns (number of passes through the frequency shifter), at a predetermined timing corresponding to the number of turns N, and emits a frequency to be converted laser beam LM _N outside the optical waveguide loop 11 .

Examples in which a mechanical optical switch, an interference optical switch, and a polarization control optical switch are used as the optical path selector 12 are shown in FIGS. 3 (A), 3 (B), 4 (A), 4 (B), and 5 (A). , (B), (C), (D).
3A and 3B show an example in which a 2 × 2 optical switch having a bar mode and a cross mode is used as the optical path selector 12. As shown in FIG. 3A, when the 2 × 2 optical switch SW _{2 × 2} is in the cross mode (the input terminal a1 is connected to the output terminal b2 and the input terminal a2 is connected to the output terminal b1). make incidence laser light pulse LP to the optical waveguide loop 11, to the 2 × 2 optical switch SW 2 _{× 2} emits a first N orbiting frequency to be converted laser beam LM _N. As shown in FIG. 3B, the 2 × 2 optical switch SW _{2 × 2} is in the bar mode (the input terminal a1 is connected to the output terminal b1 and the input terminal a2 is connected to the output terminal b2). when a laser beam pulse LP, and transmitted to the optical path of the frequency to be converted laser beam LM _N is emitted without incident on the optical waveguide loop 11, and confine the orbiting frequency be converted laser beam into the optical waveguide loop 11 .

It is desirable that the switching time (switching cycle) of the 2 × 2 optical switch SW _{2 × 2} is sufficiently shorter than the time (for example, 100 μsec) for the laser light to make one round of the optical waveguide loop 11. That, 2 × 2 optical switch SW 2 _{× 2} switching time T _SW, between the time T _FL of the optical waveguide loop 11 is laser light pulse LP to one rotation, that there is a relation of T _SW << T _FL Is desirable.

4A and 4B show an example in which a coupler CP and a 1 × 2 optical switch are used as the optical path selector 12. As shown in FIG. 4A, the laser light pulse LP is incident on the 1 × 2 optical switch SW _{1 × 2} via the coupler CPL. When the 1 × 2 optical switch SW _{1 × 2} is in one mode (the input terminal a is connected to the output terminal b2), the laser light pulse LP operates so as to enter the optical waveguide loop. The frequency converted laser light to be confined in the optical waveguide loop 11. As shown in FIG. 4B, when the 1 × 2 optical switch SW _{1 × 2} is in the other mode (the input terminal a is connected to the output terminal b1), the 2 × 1 optical switch The frequency-converted laser beam LM _N of the Nth round is emitted from SW _{2 × 1} .

It is desirable that the switching time (switching cycle) of the 2 × 1 optical switch SW _{2 × 1} is sufficiently shorter than the time for the laser light to make one round of the optical waveguide loop 11. That is, a relation between the 2 × 1 optical switch SW 2 _× with ₁ switching time T _SW, the time T _FL of the optical waveguide loop 11 is laser light pulse LP to one rotation, that there is a relation of T _SW << T _FL Is desirable.

5A, 5 </ b> B, _{5 </ b} > C, and 4 </ b> D, an example in which 2 × 1 optical switch SW _{2 × 1} and 1 × 2 optical switch SW _{1 × 2} are used as the optical path selector 12. Show. As shown in FIG. 5A, the 2 × 1 optical switch SW _{2 × 1} and the 1 × 2 optical switch SW _{1 × 2} are in the first mode (the input terminal a1 of SW _{2 × 1} is connected to the output terminal b). When the SW _{1 × 2} input terminal c is connected to the output terminal d 2), the laser light pulse LP enters the optical waveguide loop 11.

As shown in FIG. 5B, the 2 × 1 optical switch SW _{2 × 1} and the 1 × 2 optical switch SW _{1 × 2} are in the second mode (the input terminal a2 of SW _{2 × 1} is connected to the output terminal b). When the SW _{1 × 2} input terminal c is connected to the output terminal d 2), the frequency-converted laser light that circulates in the optical waveguide loop 11 is confined in the optical waveguide loop 11.

As shown in FIG. 5C, the 2 × 1 optical switch SW _{2 × 1} and the 1 × 2 optical switch SW _{1 × 2} are in the third mode (the input terminal a2 of SW _{2 × 1} is connected to the output terminal b). When the SW _{1 × 2} input terminal c is connected to the output terminal d 1), the frequency-converted laser light that circulates in the optical waveguide loop 11 passes through the 1 × 2 optical switch SW _{1 × 2} It is emitted as a frequency to be converted laser beam LM _N of N orbiting.

As shown in FIG. 5D, the 2 × 1 optical switch SW _{2 × 1} and the 1 × 2 optical switch SW _{1 × 2} are in the fourth mode (the input terminal a1 of SW _{2 × 1} is connected to the output terminal b). When the SW _{1 × 2} input terminal c is connected to the output terminal d 1), the laser light pulse LP passes through without being incident on the optical waveguide loop 11.

It is desirable that the time for shifting from the first mode to the second mode is sufficiently shorter than the time for the laser beam to make one round of the optical waveguide loop 11. That is, the time T _M1-M2 of the first and second modes, between the time T _FL of the optical waveguide loop 11 is laser light pulses LP for one rotation, T _M1-M2 «T _FL relationship It is desirable that there is.

Incidentally, the switches shown in FIGS. 3 to 5 are interference type optical switches and polarization control type optical switches capable of high-speed operation. However, these switches have a problem that the extinction ratio is insufficient and the S / N ratio at which light remaining in the optical waveguide loop 11 becomes noise is deteriorated.
In order to eliminate this inconvenience, an optical gate switch 15 can be provided in the optical waveguide loop 11 as shown in FIG. In FIG. 6, the optical gate switch 15 is provided before the frequency shifter 13 and the optical amplifier 14. The frequency to be converted laser beam LM _N is synchronized with the timing of output from the optical waveguide loop 11, by quenching the off to light components to be loop again optical gate switch 15 to compensate for the extinction ratio of the optical path selector 12 be able to. Also in the laser light pulse source 100 of FIG. 6, the light intensity of the laser light LP can be externally modulated or directly modulated.

FIG. 7 shows a time chart of the optical loop device 1 of FIG. 6 when the 2 × 2 optical switch SW _{2 × 2} is used as the optical path selector. S1, S2, and S3 in FIG. 7 indicate states of control signals that the optical loop control unit 110 illustrated in FIG. 6 sends to the laser light pulse source 100, the optical path selector 12, and the optical gate switch 15. In the first round, S1 is turned ON (H level) and the laser light pulse LP is generated, and at the same time, SW _{2 × 2} is in the cross mode (S2 is CROSS). As a result, the laser light pulse LP is introduced into the optical waveguide loop 11. At this time, the optical gate switch 15 is turned off (S3 is turned off). Thereafter, SW _{2 × 2} immediately becomes the bar mode (S2 is BAR), the optical gate switch 15 is turned ON (S3 is ON), and the laser light pulse LP circulates in the optical waveguide loop 11. During the circulation, the laser light pulse is frequency-converted. When the circulating laser beam (frequency-converted laser beam) rotates N times, SW _{2 × 2} enters the cross mode (S2 is CROSS) and the optical gate switch 15 is OFF (S3 is OFF), so that the frequency-converted laser light LM _N is emitted. In FIG. 6, a signal S4 sent from the optical loop control unit 110 to the frequency shifter 13 is a preset signal that determines the amount of frequency shift.

In the above embodiment, an example in which the optical path selector 12 and the optical amplifier 14 are configured separately has been described. However, as shown in FIGS. An optical amplifier built-in optical path selector 12 ′ having a function as one member is provided.
As shown in FIG. 8B, the optical path built-in optical path selector 12 ′ includes a coupler (3 dB coupler) 121 and semiconductor optical amplifiers (SOA) 122 and 123. The coupler (3 dB coupler) 121 can demultiplex the incident laser light pulse LP to the SOAs 122 and 123.
The SOA 122 can function as a switch when activated or inactive, and can emit the laser light pulse LP to the optical waveguide loop 11 only when activated. The SOA 123 amplifies and outputs the laser light pulse LP demultiplexed from the 3 dB coupler 121.
The SOA 123 may be operated as a switch in the same manner as the SOA 122 (by making it active or inactive). In FIG. 8B, the SOA 123 is always active.

An embodiment in which the optical loop device 1 is used as a spectrum measuring device will be described with reference to FIG. In the spectrum measuring apparatus 2 of FIG. 9, the laser light pulse source 100 and the optical loop apparatus 1 have the same configuration as described above. In the optical loop device 1, an optical waveguide loop 11, an optical path selector 12, a frequency shifter 13, an optical amplifier 14, an optical gate switch 15, and a fine shift frequency shifter 13 are formed.
Spectrum measuring apparatus 2, the irradiation output of the optical loop device which is the output of the first frequency to be converted laser beam LM _N in FIG. 1, further converts the finer optical frequency through the frequency shifter 16 for fine adjustment, the sample 21 is swept Then, the intensity of the light transmitted (or reflected) through the sample 21 is detected by the photodetector 22.

  In the present embodiment, the detection signal output from the photodetector 22 is sent to the computer 23, and the computer 23 performs spectrum analysis based on this signal. The computer 23 is a control processing device according to the present invention, and controls the sweep of the frequency shifter 16. In FIG. 9 as well, the optical gate switch 15 is provided before the frequency shifter 13 and the optical amplifier 14. The optical amplifier 14 may be in the subsequent stage of the frequency shifter 13 or in the previous stage. Further, instead of the optical path selector 12 and the optical amplifier 14, an optical path selector 12 ′ with a built-in optical amplifier shown in FIGS. 8A and 8B may be used.

An embodiment of the optical loop device of the present invention that is hybrid integrated will be described with reference to FIGS.
In FIG. 10, the optical loop device 1 (optical waveguide loop 11, optical path selector 12, frequency shifter 13, optical amplifier 14) is integrated on a substrate 17. In FIG. 11, the light intensity modulator 102 and the optical loop device 1 (the optical waveguide loop 11, the optical path selector 12, the frequency shifter 13, and the optical amplifier 14) are integrated on the substrate 17. In FIG. 12, the laser light pulse source 100 and the optical loop device 1 (the optical waveguide loop 11, the optical path selector 12, the frequency shifter 13, and the optical amplifier 14) are integrated on the substrate 17.
In FIGS. 10, 11, and 12, the optical waveguide loop 11 is formed in a spiral pattern on the substrate 17. The optical waveguide loop 11 is formed on or in the glass substrate. Although not shown, for example, only the optical waveguide loop 11 is formed on the substrate 17, and the substrate 17, the optical path selector 12, the frequency shifter 13, the optical amplifier 14, and the light intensity modulator 102 are provided. Can be configured to combine. Further, the optical waveguide loop 11 and at least one of the optical path selector 12, the frequency shifter 13, the optical amplifier 14, and the optical intensity modulator 102 can be integrated on the substrate 17. Of course, the fine shift frequency shifter 16 described in FIG. 9 may be integrated on the substrate 17.
In FIG. 13, the optical loop device 1 is configured using an optical path selector 12 ′ with built-in optical amplifier (see FIGS. 8A and 8B).

FIG. 14 is an explanatory diagram showing an embodiment of the optical loop device of the present invention used as an optical signal delay circuit. In FIG. 14, the optical signal delay circuit (optical loop device) 3 is connected to a communication line 36. The optical signal delay circuit 3 includes an optical waveguide loop 31, and the optical waveguide loop 31 includes an optical path selector 32, an optical amplifier 33, a filter 34, and an optical gate switch 35.
The optical path selector 32 receives a laser light pulse (optical packet LP) and causes the incident optical packet LP to circulate at least once in the optical waveguide loop 31. The optical amplifier 33 amplifies the optical packet LP that circulates in the optical waveguide loop 31, and prevents attenuation in the loop. The optical amplifier 33 may be located anywhere within the optical waveguide loop 31.

The filter 34 shapes the waveform of the circulating laser packet LP to the original shape. Then, the optical packet LP that circulates in the optical waveguide loop 31 is emitted to the outside of the optical waveguide loop 31 by the optical path selector 32 at a predetermined timing corresponding to the number of circulations N.
The optical gate switch 35 is provided in front of the optical amplifier 33, and in synchronization with the timing when the circulating optical packet LP is emitted from the optical waveguide loop 31, the optical gate switch 35 is turned off and the optical component to be looped again is quenched. By doing so, the extinction ratio of the optical path selector 32 can be supplemented.

As described above, the optical signal delay circuit 3 can delay the optical packet LP composed of the laser light pulse group by a predetermined discrete time.
For example, in a future photonic network, it is expected that the packet is routed as an optical signal. In this case, the optical signal delay shown in FIG. 14 is used as an optical memory for delaying the optical signal by a variable time. Circuit 3 can be used. In the optical signal delay circuit 3 of FIG. 14 as well, the optical path selector 32 can be configured by the optical switch described in FIG. 3, FIG. 4, and FIG.
Further, the optical path selector can be configured in the same manner as the optical path selector 12 ′ with a built-in optical amplifier shown in FIGS. 8A and 8B, and in this case, the optical amplifier 33 can be omitted.

  Further, as shown in FIG. 15, the optical waveguide loop 31 can be formed on the substrate in a pattern and formed integrally with the optical path selector 32, the optical amplifier 33, and the filter 34. When the optical amplifier built-in optical path selector 32 ′ having the same configuration as the optical amplifier built-in optical path selector 12 ′ shown in FIG. 8B is used, the optical amplifier 33 is omitted as shown in FIG. be able to. Although not shown, the optical signal delay circuit 3 shown in FIGS. 14, 15, and 16 may be provided with other optical elements (couplers and the like).

Claims (8)

An optical path selector for introducing an incident laser light pulse into at least one of an optical path that circulates in the optical waveguide loop or an optical path that bypasses the optical waveguide loop;
The laser light pulse incident on the optical waveguide loop is shifted by a predetermined frequency interval to generate a frequency-converted laser beam. A frequency shifter that sequentially shifts by a predetermined frequency interval to generate a frequency-converted laser beam having a predetermined circulation;
An optical loop device comprising an optical waveguide loop having
The optical path selector has an optical amplifier functioning as a switch in each of an introduction path to an optical path that circulates the optical waveguide loop and an introduction path to an optical path that bypasses the optical waveguide loop, and corresponds to the predetermined circulation. At the predetermined timing, the frequency converted laser light is emitted to the outside of the optical waveguide loop.
An optical loop device characterized by that.   2. The optical loop device according to claim 1, wherein the laser light pulse is directly intensity-modulated or externally intensity-modulated.   The optical loop device according to claim 1, wherein at least two of the optical path selector, the frequency shifter, the optical amplifier, and the optical waveguide loop are formed on the same substrate.   4. The optical loop device according to claim 1, wherein the optical waveguide loop is formed as an optical fiber loop, or is formed on or in the substrate.   The optical loop device according to any one of claims 1 to 4, wherein the laser light pulse is wavelength-locked. An optical signal delay circuit comprising an optical waveguide loop having an optical path selector for introducing an incident laser light pulse into at least one of an optical path that circulates through the optical waveguide loop or an optical path that bypasses the optical waveguide loop,
The optical path selector has an optical amplifier functioning as a switch in each of an introduction path to an optical path that circulates through the optical waveguide loop and an introduction path to an optical path that bypasses the optical waveguide loop, and corresponds to the predetermined circulation. Emitting the frequency-converted laser light to the outside of the optical waveguide loop at the predetermined timing.
An optical signal delay circuit.   The optical signal delay circuit according to claim 6, wherein at least two of the optical path selector, the optical amplifier, and the optical waveguide loop are formed on the same substrate.   8. The optical signal delay circuit according to claim 6, wherein the optical waveguide loop is formed as an optical fiber loop, or formed on or in a substrate.