JP4845145B2 - Broadband multi-wavelength light source - Google Patents

Description

  The present invention relates to a broadband multi-wavelength frequency stabilized light source in which optical phases in optical communication are synchronized with each other.

  In optical fiber communication, wavelength division multiplexing (WDM) technology has been adopted since the late 1990s to increase capacity. The practical system that is adopted is realized by multiplexing and mounting the required number of individual semiconductor lasers having optical frequencies (wavelengths) that match the standardized optical frequency grid.

  In this case, the transmission capability is limited due to the nonlinear phenomenon of the optical fiber that occurs during propagation of the optical fiber. Due to a phenomenon called four-wave mixing, new light is induced at the optical frequency position of the adjacent grid. This induced light affects the signal of the laser light source arranged on the grid as beat noise, and degrades transmission characteristics. The induced light will produce beat noise because it is uncorrelated with the light from the individual semiconductor laser sources. The beat noise intensity has a strong influence on the SNR of the signal light even if the induced light is weak, and is reflected in the error rate when it exceeds −30 dB compared to the signal light intensity.

  In order to suppress the influence of beat noise, many measures have been taken so far to weaken the input light intensity to the optical fiber. Apart from this method, the problem can be solved by correlating the signal light phase states with each other and controlling the interference state of the electric field. Therefore, an optical phase synchronization light source is effective. As such a light source, there is a multi-wavelength light source that generates multi-wavelength light whose phases are synchronized from one CW (continuous-wave) laser (see Patent Document 1).

FIG. 1 shows a configuration example of such a multi-wavelength light source. This multi-wavelength light source 10 is observed as an amplitude modulation component, a CW light source 12 that oscillates continuously, a phase modulator 14 that phase modulates CW light, a group velocity dispersion medium 16 that converts a phase modulation component into an amplitude modulation component, and the like. And a phase modulator 18 for further phase-modulating the optical frequency spectrum sequence to expand the band. The multi-wavelength light source 10 directly drives the phase modulator 14, the signal generator 20 that drives the phase modulator 18 via the phase shifter 22, a circuit 24 that controls the drive current of the CW light source 12, and the CW light source 12. And a circuit 26 for controlling the temperature of the. The signal generator 20 oscillates at a modulation frequency f _m [Hz], and this frequency f _m defines the frequency interval of the optical frequency spectrum sequence.

In this multi-wavelength light source 10, CW light generated from the CW laser light source 12, a phase modulator 14 is incident on, where the modulation index Δθ by a sinusoidal modulation frequency f _m from the signal generator _{1 (= π} / 4 ) Is phase-modulated and chirped. The chirped CW light passes through the group velocity dispersion medium and is given a group velocity dispersion B ₂ (= ± 1 / (4πf _m ² )) [second ² ]. CW light received group velocity dispersion in the phase modulator 18, the sine wave of a frequency f _m, is phase modulated by the modulation index [Delta] [theta] ₂ through the phase shifter. As a result, a flat spectral waveform with excellent SNR can be obtained over a wide frequency range.

  The optical frequency spectrum that can be generated by the multi-wavelength light source 10 has a trapezoidal envelope (envelope) as shown in FIG. This optical frequency spectrum is spread evenly on the short wavelength side and the long wavelength side around the optical frequency of the laser light source 12. The band that can be considered to have a uniform spectrum intensity and that can be applied to long-distance optical communication is the design of multi-wavelength light sources and the development of future technology (for example, reduction of the V-π drive voltage of an LN modulator). Although it depends, it is about 20 nm. Beyond that, the noise characteristics deteriorate and become a limiting factor for long-distance transmission.

JP 2007-94143 A WC Swann and SL Gilbert, “Pressure-induced shift and broadening of 1560-1630nm carbon monoxide wavelength-calibration lines,” J. Opt. Soc. Am. B, Vol. 19, No. 10, October 2002, pp. 2461- 2467

As described above, the multi-wavelength light source 10 can suppress the influence of beat noise and is suitable for the WDM technique, but there is a limit to the number of channels (that is, the band) that can be generated. In order to realize optical fiber transmission for a desired distance, the light source is required to have high quality, that is, low relative intensity noise (RIN). In general, in order to perform signal transmission of several hundred km with an optical fiber, RIN of −140 dB / (Hz) ^1/2 or less is required for the light source. When generating a large number of optical frequency carriers for transmission from one semiconductor laser light source (as shown in FIG. 1), even if a laser light source of −150 dB / (Hz) ^1/2 or less (measurement limit) is used, The transmission optical frequency carrier of −140 dB / (Hz) ^1/2 or less stays on the order of several tens of waves.

  In order to ensure the stability of the light source, a method of stabilizing the spectrum absorption line of the light absorption gas cell is generally used (Non-Patent Document 1), but the frequency of the absorption line and the standardized optical frequency grid are not matched. Since this was not done, the degree of freedom in designing the frequency band of the multi-wavelength light source was extremely limited.

  The present invention has been made in view of such problems, and can increase the number of optical frequency carriers that can be generated using a multi-wavelength light source, and can improve the degree of freedom in designing the optical frequency band. The object is to provide a multi-wavelength light source.

In order to achieve the above object, the present invention provides a broadband multi-wavelength light source, which is a first multi-wavelength light having a frequency interval fm from the output light of the first laser light source. First multi-wavelength light generating means for generating light, second multi-wavelength light generating means for generating second multi-wavelength light having a frequency interval fm from the output light of the second laser light source , and the first multi-wavelength light generating means. The first multi-wavelength light from the wavelength light generating means is separated into two optical frequency carrier groups having a frequency interval of 2 × fm, one of the separated optical frequency carrier groups is used as the first output light, and the other light A first branching unit that extracts a frequency carrier group as a first control light and the second multiwavelength light from the second multiwavelength light generating unit into two optical frequency carrier groups having a frequency interval of 2 × fm. Separating one of the separated optical frequency carrier groups into the second output light A second branching means for taking out the other optical frequency carrier group as the second control light, a phase detection means for detecting a phase difference between the first and second control lights as an error signal, and the detected error Phase control means for controlling one phase of the first and second laser light sources in accordance with a signal.

The invention according to claim 2 is the broadband multi-wavelength light source according to claim 1, wherein the phase detecting means gives a frequency offset to one of the first and second control lights. A multiplexing means for combining the control light given the frequency offset and the other control light, a light receiving means for receiving the combined light, and applying the frequency offset to a signal from the light receiving means And a phase detecting means for detecting the error signal.

The invention according to claim 3 is the broadband multi-wavelength light source according to claim 1 or 2, wherein the first and second branching units are the first and second multi-wavelength lights, respectively . It is an interleaving means for interleaving wavelengths and extracting them as control light.

The invention according to claim 4 is the broadband multi-wavelength light source according to any one of claims 1 to 3, wherein one of the first and second control lights is subjected to FM modulation. Phase modulation means for phase modulation by a signal, light absorption means for transmitting the phase-modulated control light and absorbing a specific absorption line, and second light receiving means for receiving control light transmitted through the light absorption means When a second phase detecting means for detecting a phase difference between the signal and the microwave signal from the second light receiving means as a second error signal in response to the second error signal the detected, the And a second phase control means for controlling one of the phases of the first and second laser light sources.

  The invention according to claim 5 is the broadband multi-wavelength light source according to claim 4, wherein a part of the frequency of the microwave signal subjected to the FM modulation matches a difference from the ITU-T grid frequency. It is characterized by doing.

The invention according to claim 6 is the broadband multi-wavelength light source according to any one of claims 1 to 3, wherein the third laser light source and laser light from the third laser light source are converted into FM signals. A phase modulation means for phase-modulating the light, a light absorption means for transmitting the phase-modulated laser light and absorbing a specific absorption line, and a third light receiving means for receiving the laser light transmitted through the light absorption means, a third phase detector for detecting a signal from the third light-receiving means as a third error signal, in response to the third error signal the detected, to control the phase of the third laser light source third and phase control means, said third laser beam and a fourth phase detector means for extracting the phase difference between the second microwave signal as a fourth error signal, a fourth error signal out before dangerous In accordance with the first and second lasers. Characterized by comprising a fourth phase control means for controlling one phase of the over light sources.

  The invention according to claim 7 is the broadband multi-wavelength light source according to claim 6, wherein the frequency of the second microwave signal matches the difference from the ITU-T grid frequency. To do.

  The invention according to claim 8 is the broadband multi-wavelength light source according to any one of claims 4 to 7, wherein the specific absorption line is in a 1.5 μm band.

The invention of claim 9 is a broadband multi-wavelength light source according to any one of claims 1 to 8, said first output light from said first branching means, said second further comprising a multiplexing means for multiplexing the said second output light from the branching means and said.

The invention according to claim 10 is the broadband multi-wavelength light source according to claim 9, wherein the light adjusts one phase of the first and second output lights input to the multiplexing means. A phase shift means is further provided.

  According to the present invention, it is possible to generate a large number of optical frequency carriers that precisely match the optical frequency grid defined by ITU-T and are optically phase-synchronized with each other while suppressing the overall power consumption. The mechanism by which power consumption is suppressed is as follows. A semiconductor laser light source for long-distance communication generally requires a temperature stabilization circuit. The power consumption in the temperature stabilization circuit cannot be ignored and requires an average of 2 to 3 W. Furthermore, in a 40-channel wavelength multiplexing system, 80 to 120 W is consumed by the temperature stabilization circuit. According to the present invention, a 40-channel carrier can be realized by a single semiconductor laser, so that power consumption can be suppressed to 1/5 even if power consumption necessary for a drive circuit such as a modulator is subtracted.

  In the present invention, the number of optical frequency carriers can be increased by using a plurality of multi-wavelength light sources. Specifically, the optical frequency carrier is expanded by combining the optical phases of a plurality of multi-wavelength light sources in synchronization with each other.

  In the multi-wavelength light source shown in FIG. 1, since a large number of optical frequency carriers are generated from one semiconductor laser light source, the optical phases between these carriers are synchronized. However, when a plurality of multi-wavelength light sources are used, the optical phases are uncorrelated and not synchronized between carriers generated from different multi-wavelength light sources. Therefore, in the present invention, optical frequency carriers are expanded by synchronizing and multiplexing optical phases between carriers generated from these multiple wavelength light sources.

  In addition, the optical frequency spectrum of the multi-wavelength light source has a trapezoidal envelope (envelope) as shown in FIG. That is, since the intensity level of the optical frequency carrier away from the center optical frequency gradually decreases, the spectrum at the end is not suitable as an optical carrier for transmission. In the present invention, when optical carriers from a plurality of multi-wavelength light sources are multiplexed, the optical carriers can be expanded and flat spectral characteristics can be obtained throughout the band by adding the electric fields of the end spectra. . Specifically, the optical phase of the optical carrier of the multi-wavelength light source is phase-shifted by 90 degrees and combined, so that the electric field is added to each other, and the spectral intensity is reduced without degrading the purity of the optical carrier. It can be made uniform.

  Furthermore, the optical carrier frequency of the multi-wavelength light source can be stabilized with respect to the standardized optical frequency grid using the light absorption cell (Non-Patent Document 1). Specifically, a standardized optical frequency is obtained by stabilizing an optical carrier of a multi-wavelength light source by applying an offset to one of atomic or molecular spectral absorption lines whose frequency stability has been accurately evaluated. It can be accurately stabilized against the grid.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 3 shows a configuration example of the broadband multi-wavelength light source according to the first embodiment of the present invention. This broadband multi-wavelength light source 100 is generally composed of two systems. That is, the first system includes a master light source 102 with a stabilized optical frequency, a circuit 104 that generates a multi-wavelength optical carrier, and an interleaver 106 that interleaves the multi-wavelength optical carrier with output light and control light. The second series includes a slave light source 112 having a stabilized optical frequency, a circuit 114 that generates a multi-wavelength optical carrier, and an interleaver 116 that interleaves the multi-wavelength optical carrier into output light and control light. I have. Furthermore, the broadband multi-wavelength light source 100 combines the control light from the second system interleaver 116 with the frequency shift 118, and the frequency-shifted control light and the control light from the first system interleaver 106 are combined. The circuit 120, the light receiver 122 that receives the combined control light, the amplifier 124 that amplifies the received signal, the phase detector 126 that detects the phase of the amplified signal, and the slave light source 112 according to the detected phase And a phase controller 128 for controlling the phase of. Moreover, broadband multi-wavelength light source 100, includes an oscillator 110 which provides a signal of the modulation frequency _{f m} in the multi-wavelength optical carrier generation circuit 104 and 114, an oscillator 130 which provides a signal of the frequency offset Δf to the frequency shifter 118 Yes.

  The master light source 102 outputs laser light having a stabilized frequency, and this laser light is converted into a plurality of optical frequency carriers arranged at regular frequency intervals by the multi-wavelength optical carrier generation circuit 104. Similarly, the slave light source 112 outputs laser light with a stabilized frequency, and this laser light is converted into a plurality of optical frequency carriers arranged at regular frequency intervals by the multi-wavelength optical carrier generation circuit 114. When the configuration shown in FIG. 1 is used as the multi-wavelength optical carrier generation circuit, the spectral characteristic of the optical frequency carrier has a trapezoidal shape as shown in FIG.

Here, the frequency interval of the optical carrier is determined by the clock signal from the oscillator 110 which oscillates at a frequency f _m, the f _m. In the example of FIG. 2, f _m = 25 GHz. The means for realizing the multi-wavelength optical carrier generation circuit is disclosed in, for example, Patent Document 1, and will not be specifically described. Further, many configuration methods are known as the optical frequency stabilization light source used for the master light source 102 and the slave light source 112, and the configuration method using the light absorption cell is disclosed in Non-Patent Document 1, for example. Detailed description will be omitted.

Optical frequency carrier frequency interval f _m generated by the multi-wavelength optical carriers generating circuit 104 is separated into two optical frequency carrier group frequency interval 2 × f _m by interleaver 106. Similarly, the optical frequency carrier frequency interval f _m generated by the multi-wavelength optical carriers generating circuit 114 is separated into two optical frequency carrier group frequency interval 2 × f _m by interleaver 116. Here, one of the two optical frequency carrier groups is output light, and the other is control light.

  FIG. 4 is a diagram schematically showing the spectra of the output light and the control light. 4A and 4B show the output light and the control light in the first system, respectively. FIGS. 4C and 4D show the output and the control light in the second system, respectively. . As seen in FIG. 4, the spectrum of the first system and the spectrum of the second system are arranged and configured so that the center frequencies of the bands are different and the ends of the bands overlap.

  Now, for example, assume that a 60-wave multi-optical carrier generation circuit is designed from a single light source at 25 GHz intervals. Since the output optical frequency of the laser light source is located at the center of the band, the frequency difference between the master and slave laser light sources is roughly extracted so as to be 20 nm and about 2.5 THz. At this time, the laser light source frequency is selected so as to match the optical frequency grid standardized by ITU-T so that it can be applied as a light source for optical fiber communication. The optical frequency grid is defined as 193.1 THz ± 25 × N GHz (N is 0 or a natural number). As a result, the optical frequencies almost coincide and overlap at the ends of the two optical frequency carrier groups. However, even if they are combined at this time, since the optical phases are uncorrelated with each other, the electric field is not added, and beat noise is generated.

  In order to synchronize the optical phase between laser light sources oscillating uncorrelated at 2.5 THz, the following configuration is adopted. In one of the first and second systems of control light, in the example of FIG. 3, the frequency of the second system of control light is slightly shifted by the frequency shifter 118. For example, if the line width of the laser light source 112 is several hundred KHz, it is only necessary to detune 1 MHz or more. The clock frequency Δf output from the offset oscillator 130 gives this detuning frequency.

  The control light detuned by the frequency Δf is combined with the other control light, in the example of FIG. The multiplexer 120 is, for example, an optical Y branch coupler or a directional coupler. Thereafter, a beat signal corresponding to the detuning frequency is generated as an electric signal by a beat signal detector including a light receiver 122 such as a photodiode (PD) and an amplifier circuit 124. Then, phase sensitive detection is performed on the beat signal by the phase detector 126. That is, the phase difference Δθ is detected by multiplying the clock frequency Δf output from the offset oscillator 130 by the beat signal. The laser phase controller 128 controls the oscillation phase of the slave laser light source 112 so that the phase difference Δθ is minimized, that is, cos Δθ is maximized. By this operation, the optical phases of both the master laser light source 102 and the slave laser light source 112 are synchronized.

Hereinafter, description will be made using mathematical expressions. The electric field components of the control light of the first system and the control light of the second system are E ₁₁ and E ₂₁ , respectively.

E ₁₁ = A ₁₁ cos (2πf ₁₁ + φ ₁₁ )
E ₂₁ = A ₂₁ cos {2π (f ₂₁ + Δf) + φ ₂₁ }
The amplitude of each A _11, A ₂₁ is E _11, E _21, the frequencies of f _11, f ₂₁ is _{E 11, E 21, φ 11} , respectively phi ₂₁ represents the phase of E _11, E _21. When E ₁₁ and E ₂₁ are multiplexed by the multiplexing circuit 120, the light intensity I is expressed by the following equation.

I = <| E ₁₁ + E ₂₁ | ² >
_{= (A 11 + A 21)} 2/2 + 2A 11 A 21 cos {2π (f 11 -f 21 -Δf) + (φ 11 -φ 21)}
Since the direct current component is omitted and f ₁₁ ≈f ₂₁ , it can be expressed by the following equation.

I = 2A ₁₁ A ₂₁ cos {2πΔf + (φ ₁₁ −φ ₂₁ )}
By multiplying this by Δf, 2A ₁₁ A ₂₁ cos {(φ ₁₁ −φ ₂₁ )} is obtained. Therefore, optical synchronization is achieved by controlling the slave laser light source 112 with the laser phase controller 128 so that cos {(φ ₁₁ −φ ₂₁ )} = 0, that is, the phase difference (φ ₁₁ −φ ₂₁ ) is 90 degrees. realizable.

  As described above, high-precision synchronization is established between the master laser light source and slave laser light source, and the optical frequency carrier (optical comb) generated from each laser is also kept in sync. Can be realized. If necessary, an optical filter may be inserted in front of the light receiver 112 in order to remove unnecessary spectral components.

FIG. 5 shows a configuration example for combining the output light from the first system and the output light from the second system to synthesize a broadband spectrum with uniform intensity. When these two output lights are synchronized in optical phase, the relative phase relationship is shifted by 90 degrees and input to a multiplexer 152 such as a Y branch circuit or a 3 dB directional coupler. Can be combined without any loss of strength. In the case of the configuration shown in FIG. 3, the phase difference (φ ₁₁ −φ ₂₁ ) between the first system and the second system is controlled to be 90 degrees. Can wave.

  In addition, in the optical frequency region where the light intensity at the end of the spectrum as shown in FIG. 2 gradually decreases, if both spectra are complementarily added, the optical phase is synchronized, so that the electric fields are added to each other. The optical frequency spectrum at each end is made uniform. FIG. 6 schematically shows how the end portions of the spectrum are added to each other by an electric field, and the optical frequency spectrum is made uniform. FIG. 6 shows a state in which the two output lights in FIGS. 4A and 4B are added.

  Since the phase fluctuation may occur before the two output lights are combined, the use of the optical phase shifter 154 capable of finely adjusting the relative phase with respect to 90 degrees enables the electric field addition to be performed more stably. Specifically, the maximum phase can be adjusted while monitoring the output power.

  Thus, by synchronizing the optical phase between the optical frequency carriers at the base of the multi-optical frequency carrier, it is possible to achieve a wide band by combining a plurality of multi-wavelength light sources. This technique can be implemented not only for two carrier groups but also for a plurality of optical frequency carrier groups. Therefore, a broadband light source having a desired band or a desired number of optical frequency carriers can be realized as necessary by such a chaining technique. Note that the ability to generate a spectrum sequence in which optical phases are synchronized in a wide band means that it is also effective for generating an ultrashort pulse light source. That is, an ultrashort pulse can be generated by synthesizing synchronized spectrum sequences. Further, when the output light of the broadband multi-wavelength light source of FIG. 3 is used after being demultiplexed into each wavelength, the two output lights do not have to be combined as shown in FIG.

(Second Embodiment)
FIG. 7 shows a configuration example for increasing the degree of freedom in selecting the oscillation light frequency of the master and slave light sources. Functional blocks similar to those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted. The broadband multi-wavelength light source 200 includes, in addition to the components of the broadband multi-wavelength light source 100, a phase modulator 202 that modulates the phase of the control light of the first system, a Ga light absorption cell 204 having a specific absorption line, The light receiver 206 that receives the control light transmitted through the light absorption cell, the amplifier 208 that amplifies the received signal, the phase detector 210 that detects the phase of the amplified signal, and the master light source 102 according to the detected phase. And a phase controller 212 for controlling the phase. In the second embodiment, unlike the first embodiment, the frequency shifter 118 is installed toward the control light of the first system.

  In the first embodiment, as an example, a configuration method using a light absorption cell as a master laser light source has been shown (Non-Patent Document 1). In the first embodiment, laser light is transmitted from the master laser light source 102 through the gas of the light absorption cell, and the oscillation frequency of the laser light is stabilized to the spectral absorption line of the gas. In this embodiment, independent of the oscillation frequency of the light source 102, an absorption line having a large spectral absorption or an absorption line capable of reducing the frequency shift amount with respect to a standardized grid is selected, and the stabilization is inexpensive with a high SN. A configuration example capable of implementing

In the present embodiment, any optical frequency of control light from the multi-wavelength optical carrier generation circuit can be used for stabilization to the absorption line. The light absorption cell generally uses an atomic or molecular absorption line whose frequency stability has been accurately evaluated by a laser spectroscopy technique or the like. Some of them are certified as reference materials in metrological standards. Examples of the light absorption cell 204 include molecules such as acetylene (C ₂ H ₂ ), hydrogen cyanide (HCN), carbon monoxide ( ¹² C ¹⁶ O, ¹³ C ¹⁶ O), and water vapor (H ₂ O) in the optical communication band. One or a plurality of these are encapsulated. In the present embodiment, carbon monoxide ( ¹² C ¹⁶ O) will be described as an example.

FIG. 8 shows an example of an absorption spectrum when an absorption cell in which carbon monoxide ( ¹² C ¹⁶ O) is enclosed is used as the light absorption cell 204. ¹² C ¹⁶ O has a total of 40 or more absorption lines in the L band, and the wavelength of these absorption lines is known to be stable with an uncertainty of sub pm (on the order of 10 MHz) ( Non-patent document 1).

Table 1 shows the difference ν _offset between the optical frequency corresponding to the absorption peak of FIG. 8 and the ITU grid frequencies at 100 GHz intervals and 50 GHz intervals. This ν _offset is shown in the columns of 100 G Grid and 50 G Grid in Table 1, and the unit is GHz. As can be seen from the table, this ν _offset is about several GHz to several tens of GHz.

When the frequency of the output light of the interleaver 106 is ν _out (i), the following equation is established.
ν _out (i) = ν _cell (i) + ν _offset (i)
Here, ν _cell (i) represents the optical frequency of the i-th absorption line. The minimum frequency offset value ν _offset (i) for obtaining the ITU grid frequency ν _out (i) near the i-th absorption line of interest can be obtained from the table. Since the frequency ν _out (i) of the output light of the interleaver 106 extends to a range of about 20 nm, it is possible to select an absorption line that has a large spectral absorption and can be designed to have a large SN of the control circuit.

In this embodiment, the normalized transfer characteristic is 0.84 (absorption is 16%) as shown in FIG. 7, and the absorption is the largest in the R branch, and the frequency offset value with respect to the 100/50 GHz grid interval is relatively small from Table 1. The sixth absorption line 15687.7756 nm (= 191.09964 THz) is optimal. FIG. 9 is an enlarged view of this absorption line. In this case, when 191.1 THz is selected as the optical frequency grid of ITU-T, the frequency offset is −360 MHz as shown in Table 1. Then, the signal for driving the phase modulator 202 can be composed of an FM modulation signal having an offset frequency f _offset (i) = 360 MHz, a maximum frequency deviation f _{FM ≈10} MHz, and a modulation frequency f _mpsd = 1-10 KHz. The phase modulator 202 modulates the control light from the interleaver 106 with this FM modulation signal, passes through the light absorption cell 204 and is received by the light receiver 206, thereby converting the frequency shift amount into intensity modulation. This intensity modulation component can be amplified by the amplifier 208 and detected as an error signal by the phase detector 210. By controlling the oscillation frequency of the master light source 102 by the laser phase controller 212 according to the detected error signal, the oscillation frequency can be stabilized to the center frequency of the selected absorption line. This error signal is extracted as follows. The f _mpsd component of the modulated f _offset is set to match the cell. After electrical conversion by the light receiver, only the AC component remains and f _mpsd is input from the amplifier 208 to the phase detector 210. On the other hand, the output from the modulation frequency generator f _mpsd is also input to the phase detector, and the phase detector 210 extracts the phase difference between the two f _mpsd signals.

(Third embodiment)
FIG. 10 shows a configuration example of a broadband multi-wavelength light source according to the third embodiment of the present invention. The broadband light source 300 uses a third laser light source 304 in addition to the master light source 102 and the slave light source 112. In the second embodiment, the control light on the master light source side is stabilized by using the light absorption cell. However, in this embodiment, the third laser light source is stabilized by using the light absorption cell, and further, the laser. The light source is used to stabilize the master light source.

The output light from the laser light source 304 is input to the phase modulator 202 and undergoes phase modulation at f _mpsd . Further, after passing through the light absorption cell 204, it is electrically converted by the light receiver 206 and amplified by the amplifier 208. Thereafter, the phase detector 210 detects the phase of f _mpsd . The laser light source 304 is locked to the absorption line of the light absorption cell 204 by the laser phase modulator 302 controlling the laser light source 304 in accordance with the phase detection amount. The other output of the optical splitter 306 is combined with a part of the control light from the interleaver 106 by an optical coupler, electrically converted by a light receiver 312, amplified by an amplifier 314, and then a phase detector 316. _Is phase-compared with f _ref . In response to the output of the phase detector 316, the laser phase controller 318 controls the optical frequency stabilized master light source 102. Here, by making f _ref equal to the difference between the wavelength locked by the laser light source 304 and the wavelength generated by the optical frequency stabilization master light source, the optical frequency stabilization master light source can be locked to an arbitrary wavelength. it can. For example, if the laser light source 304 is locked to the absorption line of the CO absorption cell P-branch # 4 (Table 1-2), if f _ref is 1.22 GHz, the optical frequency stabilized master light source is an ITU-T grid. Can be synchronized to the frequency. Note that the principle of synchronizing the slave light source 112 with the master light source 102 is the same as in the second embodiment, and is therefore omitted.

  While the present invention has been described with respect to several specific embodiments, the embodiments described herein are merely illustrative in view of the many possible embodiments to which the principles of the present invention can be applied. It is not intended to limit the scope of the invention. The configuration and details of the embodiment exemplified here can be changed without departing from the spirit of the present invention. Further, the illustrative components and procedures may be changed, supplemented, or changed in order without departing from the spirit of the invention.

It is a functional block diagram which shows the structural example of the conventional multiwavelength light source. It is a figure which shows an example of the optical frequency spectrum produced | generated with the multiwavelength light source of FIG. It is a functional block diagram which shows the structural example of the broadband multiwavelength light source which concerns on the 1st Embodiment of this invention. It is the figure which represented typically the spectrum of the output light of FIG. 3, and control light. FIG. 4 is a functional block diagram illustrating a configuration example for multiplexing two output lights in FIG. 3. It is a figure which shows typically a mode that two output lights of FIG. 3 are combined, and an optical frequency spectrum is equalized. It is a functional block diagram which shows the structural example of the broadband multiwavelength light source which concerns on the 2nd Embodiment of this invention. It is a diagram illustrating an example of the absorption spectrum of carbon monoxide ⁽¹² C ¹⁶ O) encapsulated absorption cell. It is the figure which expanded the 6th absorption line (1566.8756nm) of FIG. It is a functional block diagram which shows the structural example of the broadband multiwavelength light source which concerns on the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Multiwavelength light source 20 Signal generator 100 Broadband multiwavelength light source 110 Oscillator 130 Oscillator 200 Broadband multiwavelength light source 300 Broadband multiwavelength light source

Claims (10)

A broadband multi-wavelength light source,
First multi-wavelength light generating means for generating first multi-wavelength light having a frequency interval of fm from output light of the first laser light source;
Second multi-wavelength light generating means for generating second multi-wavelength light having a frequency interval of fm from the output light of the second laser light source;
Separating said first multi-wavelength light from the first multiple-wavelength light generating means into two light frequency carrier group frequency interval 2 × fm, the separated one of the optical frequency carrier group first output light And first branching means for taking out the other optical frequency carrier group as the first control light,
Separating the second multiple wavelength light from said second multiple wavelength light generating means into two light frequency carrier group frequency interval 2 × fm, the separated one of the optical frequency carrier group a second output light And second branching means for taking out the other optical frequency carrier group as second control light,
Phase detection means for detecting a phase difference between the first and second control lights as an error signal ;
A broadband multi-wavelength light source comprising: phase control means for controlling one phase of the first and second laser light sources in accordance with the detected error signal. The broadband multi-wavelength light source according to claim 1,
The phase detection means includes
Frequency shifting means for providing a frequency offset to one of the first and second control lights;
A multiplexing means for multiplexing the control light given the frequency offset and the other control light;
A light receiving means for receiving the combined light;
A broadband multi-wavelength light source further comprising: phase detection means for detecting the error signal by applying the frequency offset to a signal from the light receiving means. The broadband multi-wavelength light source according to claim 1 or 2,
The broadband multi-wavelength light source characterized in that the first and second branching means are interleaving means for interleaving the wavelengths of the first and second multi-wavelength lights as control lights, respectively . The broadband multi-wavelength light source according to any one of claims 1 to 3,
Phase modulation means for phase-modulating one of the first and second control lights with an FM-modulated microwave signal;
A light absorbing means for transmitting the phase-modulated control light and absorbing a specific absorption line ;
A second light receiving means for receiving control light transmitted through the light absorbing means;
Second phase detection means for detecting a phase difference between the signal from the second light receiving means and the microwave signal as a second error signal;
A broadband multi-wavelength light source, further comprising: second phase control means for controlling one of the phases of the first and second laser light sources in accordance with the detected second error signal. The broadband multi-wavelength light source according to claim 4,
A broadband multi-wavelength light source, wherein a frequency of a part of the microwave signal subjected to the FM modulation matches a difference with an ITU-T grid frequency. The broadband multi-wavelength light source according to any one of claims 1 to 3,
A third laser light source;
Phase modulation means for phase-modulating the laser light from the third laser light source with an FM signal;
A light absorbing means for transmitting the phase-modulated laser light and absorbing a specific absorption line;
Third light receiving means for receiving the laser light transmitted through the light absorbing means;
Third phase detecting means for detecting a signal from the third light receiving means as a third error signal;
Third phase control means for controlling the phase of the third laser light source in accordance with the detected third error signal;
A fourth phase detecting means for extracting a phase difference between the third laser light and the second microwave signal as a fourth error signal;
Depending on the fourth error signal out before dangerous, the first and second fourth broadband multi-wavelength light source, characterized in that a phase control means for controlling one phase of the laser light source. The broadband multi-wavelength light source according to claim 6,
A broadband multi-wavelength light source characterized in that the frequency of the second microwave signal matches the difference from the ITU-T grid frequency. The broadband multi-wavelength light source according to any one of claims 4 to 7,
The specific absorption line is in a 1.5 μm band. The broadband multi-wavelength light source according to any one of claims 1 to 8,
Wherein the first output light, said second wideband multiple-wavelength to the second, further comprising a multiplexing means for multiplexing the output light from the branching means from said first branching means light source. The broadband multi-wavelength light source according to claim 9,
A broadband multi-wavelength light source further comprising optical phase shift means for adjusting one phase of the first and second output lights input to the multiplexing means .

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