JP2014211529A - Optical subcarrier generation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical subcarrier generation device whose configuration is made simpler as compared with conventional one and which stabilizes intensity of an optical subcarrier.SOLUTION: An optical subcarrier generation device 10 includes: a single sinusoidal signal power source 12; a direct voltage source 13; and an optical phase modulator 112 which generates an optical subcarrier in accordance with sinusoidal signals applied from the sinusoidal signal power source 12 and in which the optical subcarrier is adjusted in accordance with a bias voltage from the direct voltage source 13 so that intensity of the optical subcarrier becomes flat.

Description

  The present invention relates to an optical subcarrier generation apparatus that flattens optical subcarriers in optical OFDM (Orthogonal Frequency Division Multiplexing).

  In recent years, in optical fiber communication systems, research and development of wavelength division multiplexing optical transmission systems and devices that enable a total transmission capacity from several terabits / second to several tens of terabits / second have been performed. In the case of the intensity modulation method by binary transmission using the signal of only “0” or “1” used in optical fiber communication and the direct detection method, with the speeding up of 40 gigabit / second or 100 gigabit / second, As a result, the optical spectrum of the transmission signal spreads, and as a result, not only the dispersion tolerance is rapidly deteriorated, but also the frequency utilization efficiency and the flexibility of the network are reduced. This is considered to be due to the fact that it is necessary to ensure a wide wavelength interval in order to avoid crosstalk between channels in wavelength division multiplexing. Therefore, as a method for increasing the bit rate without occupying the frequency band per channel, techniques such as multi-level modulation and multiplexing have become important.

  Orthogonal frequency division multiplexing (OFDM) is promising as a technique for improving dispersion tolerance and increasing frequency utilization efficiency. The OFDM system is a type of multi-carrier transmission system that multiplexes under conditions that each subcarrier has an orthogonal relationship, thereby separating the modulation spectrum between subcarriers at the receiving end. Therefore, it has been put to practical use in wireless transmission such as mobile radio communication. In the orthogonal frequency division multiplexing system, the bit rate per subcarrier can be reduced to 1 / N (N: the number of optical subcarriers) as compared with the case of single carrier transmission. For this reason, by applying orthogonal frequency division multiplexing to optical fiber communications, the spectrum spread of the transmission signal of each subcarrier is suppressed, and restrictions on transmission capacity due to optical fiber chromatic dispersion and polarization mode dispersion are alleviated. can do.

  As a means for applying the orthogonal frequency division multiplexing method to an optical fiber communication system, a method of driving an optical modulator using an OFDM baseband signal generated by electrical processing is known (Non-Patent Document 1).

  Also known is a method of generating optical orthogonal subcarriers in the light region and intensity-modulating or phase-modulating each subcarrier (Patent Documents 1 and 2). Optical subcarriers are modulated using OFDM baseband signals generated by electrical processing, and by using the OFDM method for each optical wavelength band, flexible connection of optical fiber communication and wireless communication is expected. it can. As described above, in the method of actively using an optical subcarrier as a carrier wave, it is not only flexible to determine what modulation is performed for each optical subcarrier, but also necessary for transmitting a necessary amount of information. By ensuring the bandwidth (number of optical subcarriers) and performing appropriate modulation, network flexibility can be improved.

  As the simplest generation method of optical subcarriers, it is possible to control the oscillation frequency (wavelength) of multiple laser light sources with high accuracy. However, for optical OFDM where the frequency interval (wavelength interval) is important, It is difficult to accurately match the frequencies (wavelengths).

  On the other hand, there are methods that use an optical modulator to use a modulation sideband, and methods that use a frequency spectrum as an optical subcarrier by techniques such as using forced mode locking of an optical resonator (Non-Patent Document 2). 3, 4). In these methods, a modulation sideband is generated at the same frequency interval as the modulation frequency by driving the optical modulator with a sinusoidal electric signal. For this reason, it is possible to generate optical subcarriers with a high frequency interval, which is suitable for optical subcarrier generation for optical OFDM as compared with a method using a plurality of laser light sources.

  The spectrum intensity of each optical subcarrier must be constant to generate a transmission signal suitable for the receiving system from the viewpoint of equalization amplification and reception sensitivity of the optical signal when constructing the transmission system It becomes. In the method disclosed in Non-Patent Document 2, an optical phase modulator and an optical intensity modulator are used together, and each is driven by a synchronization signal having the same modulation frequency. Then, the modulation sideband generated by the optical phase modulator at the first stage is intensity-modulated by the optical intensity modulator connected at the subsequent stage, and the light spectrum is made constant by interfering the frequency spectrum with each other. ing. Although it is possible to generate optical subcarriers with good flatness by this method, since synchronous driving in which the optical phase modulator and the optical intensity modulator are directly connected is indispensable, the configuration of the apparatus becomes complicated.

  In the method disclosed in Non-Patent Document 4, a single Mach-Zehnder type optical modulator is used to drive an optical phase modulator formed on each Mach-Zehnder arm with sinusoidal signals having different amplitude voltages. To do. As a result, the modulation spectra are combined in a vector-like manner at the output multiplexing end of the Mach-Zehnder, thereby making the light intensity constant. In this method, two optical modulators as described in Non-Patent Document 2 are unnecessary, and synchronous driving is also unnecessary. However, since each phase modulator is driven with an amplitude voltage having a different magnitude, two devices for adjusting the voltage, such as an electric amplifier and an attenuator, are required. Becomes larger.

  FIG. 1 shows the configuration of an apparatus disclosed in Non-Patent Document 5. The apparatus 100 includes a CW light source 101, a polarization controller 102, an optical phase modulator 103, a sine wave signal source 104, an electric multiplexer 105, a phase shifter 106, and a sine wave signal source 107. The sine wave signal sources 104 and 107 supply sine wave signals having different amplitudes and modulation frequencies. In this apparatus 100, the intensity of the output spectrum is made constant by a single optical phase modulator 103 being driven synchronously based on two sine wave signals having different amplitudes and modulation frequencies. In this case, since the single optical modulator 103 is used, the configuration of the modulator 103 can be simplified as compared with those shown in Non-Patent Documents 2 and 4. On the other hand, the configuration for driving the modulator is complicated as in the case of Patent Documents 2 and 4.

  As a problem common to Non-Patent Documents 2 to 5, it is necessary to prepare a light source for generating CW light outside the modulator. For this reason, not only an external light source but also a polarization controller for connecting the light source and the optical modulator in an optimal polarization state is required, and as a result, the overall configuration of the optical subcarrier generator is complicated.

JP 2009-17320 A JP 2009-124700 A

SLJansen, I. Morita, N. Takeda, and H. Tanaka, “20-Gb / s OFDM Transmission over 4,160-km SSMF Enabled by RF-Pilot Tone Phase Noise Compensation,” Proc. Of OFC / NFOEC2007, paper PDP15, 2007. M. Fujiwara, J. Kani, et al. "Flattened optical multicarrier generation of 12.5 GHz spaced 256 channels based on sinusoidal amplitude and phase hybrid modulation." Electronics Letters 37 (15): 967-968 (2001). M. Kourogi, K. Nakagawa, et al. "Wide-span optical frequency comb generator for accurate optical frequency difference measurement." Quantum Electronics, IEEE Journal of 29 (10): 2693-2701 (1993). T. Sakamoto, T. Kawanishi, et al. "Asymptotic formalism for ultraflat optical frequency comb generation using a Mach-Zehnder modulator." Opt. Lett. 32 (11): 1515-1517 (2007). S. Ozharar, F. Quinlan, I. Ozdur, S. Gee, and PJ Delfyett, "Ultraflat Optical Comb Generation by Phase-Only Modulation of Continuous-Wave Light", Photon. Tecnol. Lett. 20 (1): 36- 38 (2008).

  As described above, the conventional apparatus is configured to make the intensity of the optical subcarrier constant. However, since a plurality of light sources are required, the configuration is complicated.

  The present invention has been made under such circumstances, and it is an object of the present invention to provide an optical subcarrier generation apparatus that has a simpler configuration than that of the prior art and has a constant optical subcarrier intensity.

  In order to solve the above-described problem, the present invention provides an optical subcarrier generation apparatus, which includes a single sine wave signal power source, a bias voltage source, and a sine wave signal applied from the single sine wave signal power source. And at least one optical phase modulator that generates an optical subcarrier in response to a bias voltage from the bias voltage source so that the intensity of the subcarrier is flat. And an optical phase modulator.

  Here, the optical phase modulator may be configured such that a phase modulation amount changes nonlinearly with respect to the applied sine wave signal.

  As the operating condition of the optical phase modulator, the fundamental wave component of the phase changing in the optical phase modulator is given by 0.45π to 0.55π, and the nonlinear component of the phase is given by 1.5π or more. As described above, the value of the bias voltage may be set.

  The optical subcarrier generation apparatus further includes a light source and an optical amplifier that amplifies an optical signal from the light source and outputs the amplified optical signal to the optical phase modulator, and the light source, the optical amplifier, and the optical phase modulator May be configured on the same semiconductor substrate.

  The light source may be a continuous light source or a wavelength tunable light source.

The optical subcarrier generation apparatus further includes a plurality of light sources, a multiplexer that multiplexes optical signals from the plurality of light sources,
An optical amplifier that amplifies the output of the multiplexer and outputs it to the phase modulator, and the plurality of light sources, the multiplexer, the optical amplifier, and the optical phase modulator are on the same semiconductor substrate You may make it comprise above.

  The optical subcarrier generation apparatus further includes a plurality of light sources, a plurality of optical amplifiers that amplify optical signals from each of the plurality of light sources and output to each optical phase modulator, and an output of each optical phase modulator The plurality of light sources, the plurality of optical amplifiers, the optical phase modulators, and the multiplexer may be configured on the same semiconductor substrate. .

  According to the present invention, the intensity of the optical subcarrier can be made constant with a simpler configuration.

It is the figure which showed the structure of the conventional light generator. It is a figure which shows the structural example of the optical subcarrier generation apparatus which concerns on 1st Embodiment. It is a figure for demonstrating the relationship between the applied voltage and phase in an optical phase modulator. It is a figure for demonstrating the spectrum distribution of an optical subcarrier. It is a figure for demonstrating the relationship between the nonlinear component of a phase modulation amplitude, and a basic component. It is the figure which expanded the relationship of FIG. It is a figure which shows the structural example of the optical subcarrier generation apparatus which concerns on 2nd Embodiment. It is a figure which shows the structural example of the optical subcarrier generator which concerns on 3rd Embodiment. It is a figure which shows the structural example of the optical subcarrier generation apparatus which concerns on 4th Embodiment. It is a figure which shows the structural example of the optical subcarrier generation apparatus which concerns on 5th Embodiment.

<First Embodiment>
Hereinafter, a first embodiment of the optical subcarrier generating apparatus of the present invention will be described. FIG. 2 is a diagram illustrating a configuration example of the subcarrier generation apparatus 10 of the present embodiment.

  The optical subcarrier generation apparatus 10 generates an OFDM signal composed of optical subcarriers having flat intensity characteristics. As shown in FIG. 2, the optical subcarrier generation device 10 includes a CW light source 111 that generates, for example, CW (Continuous Wave) light as laser light, a phase modulator 112 that performs phase modulation on the CW light, A sine wave signal light source 12 that generates a sine wave signal having a frequency and applies the sine wave signal to the phase modulator, and a DC voltage source (bias voltage source) 13 that generates a DC voltage as a bias signal and applies the same to the phase modulator 112. Prepare. In this optical subcarrier generation device 10, the modulation of the phase modulator 112 is not performed only by the CW light source 111 but can be adjusted by the DC voltage source 13 so that the intensity of the optical subcarrier becomes constant. .

  In FIG. 2, the CW light source 111 and the phase modulator 112 are configured to be monolithically integrated on the semiconductor substrate 11.

  The phase modulator 112 has a low-dimensional semiconductor structure such as a quantum well, for example, and performs phase modulation of CW light from the CW light source 111 in accordance with voltage application from the sine wave signal light source 12. The phase modulator 112 of the present embodiment has a non-linear characteristic of voltage and phase using light absorption-induced refractive index change in addition to the electro-optic effect.

  FIG. 3 is a diagram for explaining the relationship between the applied voltage and the phase in the phase modulator 112, where (a) is the relationship between the applied voltage and the phase shift, (b) is the relationship between time and the voltage, (C) shows the relationship between time and phase shift.

  As shown in FIG. 3A, the phase shift changes when the value of the applied voltage is greater than zero. In this case, the phase shift increases nonlinearly with respect to the value of the applied voltage. On the other hand, when the applied voltage is 0 or less, the phase does not change and is 0 regardless of the voltage value.

  In FIG. 3B and FIG. 3C, no phase change occurs in the region where the voltage polarity is reversed.

In general, the phase characteristic as shown in FIG. 3 has a light absorption-induced refractive index caused by a change in the light absorption coefficient of the phase modulator 112 in addition to the electro-optic effect caused by voltage application from the external sine wave signal voltage 12. It is known to be obtained by change. The phase φ (t) shown in FIG. 2C is expressed by the following formula (1).
φ (t) = C ₁ V (t) + C ₂ V ² (t) (1)

  In equation (1), C1: arbitrary coefficient, C2: arbitrary coefficient, and V: applied voltage (V> 0) are shown.

  As shown in FIG. 3A, the phase φ (t) when V <0 is 0 regardless of the value of V itself.

  In equation (1), the phase change occurs only in one direction with respect to the applied voltage. As shown in FIGS. 3B and 3C, this causes a phase change for a voltage in a specific bias direction, but prevents a phase change in the inversion direction. It means to become.

Here, in the formula (1), voltage V (t) and the bias voltage _{V b,} the amplitude voltage _{V m,} given modulation angular frequency omega _m is represented by the following formula (2).

  The phase change in the phase modulator 112 when V (t) is given is expressed by the following equation (3).

As can be seen from the above equation (3), by the driving of the sinusoidal signal, omega in addition to _m, the nonlinear phase shift due to the effect of the second harmonic component 2 [omega _m occurs at the same time.

In the above equation (3), the first to third terms on the right side are divided into a bias component φ _dc1 , a fundamental wave component φ _m as a phase modulation amplitude component, and a nonlinear component φ _nl , and the following equation (4) Represented by

From this point of view, the phase modulator 112 of the present embodiment adjusts the phase modulation amplitude by the bias voltage from the DC voltage source 13, and further adjusts the phase modulation amplitude of the nonlinear component by the amplitude voltage. Yes. Specifically, as described in the above equation (1), since no phase change occurs in the region where the voltage polarity is reversed, the time waveform of the phase change is changed by varying the time waveform of the phase change with the bias voltage _Vb. By controlling, the intensity is adjusted to be constant on the optical spectrum.

In the phase modulator 112, the relationship between the input E _in and the output E _OUT is expressed by the following equation (5).

  Here, when the above equations (3) and (4) are substituted into the above equation (5) and rearranged using the first-type Bessel function, the following equation (6) is obtained.

  In the above equation (6), the k-th spectral intensity, that is, the optical subcarrier intensity Ik is expressed by the following equation (7).

In the phase modulator 112, when the amplitude voltage V _m shown in the above formula (4) is given, by adjusting the bias voltage V _b, optionally a phase modulation amplitude phi _m is controlled. In this case, the value taken by the bias voltage _Vb is expressed by the following equation (8).

As described above, according to the phase modulator 112, by adjusting the bias voltage _Vb , the phase modulation amplitude is controlled under a single amplitude voltage as shown in the above equation (4). Thereby, in the phase modulator 112, the optical spectrum is flattened so that the intensity of the optical spectrum becomes constant by adjusting only the bias voltage.

  The frequency interval of the optical subcarrier is determined by the frequency of the sine wave signal provided by the sine wave signal source 12.

  Depending on the configuration of the optical subcarrier generation apparatus 10, the optical subcarrier generated by the phase modulator 112 has a spectrum distribution as shown in FIG.

Figure 4 is a view for explaining the spectral distribution of the optical subcarrier, (a) shows the optical subcarrier when flattening is performed by adjusting the bias voltage V _b, (b) the bias voltage V _b changing the by indicating the optical subcarriers in the case of changing the phase modulation amplitude phi _m.

  In FIG. 4A, for example, when the number of subcarriers is 10, when the flatness of the optical subcarrier is defined from the difference between the maximum value and the minimum value, the flatness in this case is 0.1 dB. It becomes.

On the other hand, the flatness in the case of varying the bias voltage V _b by changing the phase modulation amplitude phi _m is the value shown in FIG. 4 (b), a value of more than 10 dB. In this case, the intensity fluctuation increases.

Here, when the number of optical subcarriers is 10, the basic component phase modulation amplitude φ _m and nonlinear component (also referred to as nonlinear term) φ _nl are given as parameters to define the flatness of 2 dB or less. In this case, from the above equation (8), φ _nl when the amplitude voltage V _m is given is determined, and furthermore, the bias voltage V _b is given to determine φ _m . In this way, the parameters φ _m and φ _nl are given, and these parameters take values as shown in FIGS.

FIG. 5 is a diagram for explaining the relationship between the phase modulation amplitude φ _m and the nonlinear term φ _nl . FIG. 6 is an enlarged view of a part of the relationship shown in FIG.

In FIG. 5 and FIG. 6, the portion where the flatness is larger than 2 dB is represented in white. 5 and 6, the flatness of 2 dB or less is, for example, the case of φ _m = 0.45π to 0.55π and φ _nl = 1.5π. In other words, as the operating condition of the phase modulator 112 in this case, the bias voltage V _b is set so that φ _m = 0.45π to 0.55π and φ _nl = 1.5π.

  As described above, according to the optical subcarrier generation device 10 of the present embodiment, the sine wave signal applied from the single sine wave signal power supply 12 and the bias voltage applied from the DC voltage source 13 are used. The optical subcarrier is generated by the operation of the phase modulator 112. That is, the phase modulator 112 adjusts the subcarrier intensity according to the bias voltage from the bias voltage source to flatten the subcarrier so that the subcarrier intensity becomes constant. Therefore, the bias voltage can be adjusted by applying an amplitude voltage having a single frequency from the sine wave signal source 12 to the phase modulator 112, so that the optical subcarrier generator 10 itself can be simplified. It can be configured.

Second Embodiment
The optical subcarrier generating apparatus of the second embodiment is configured to include an optical amplifier in order to compensate for a loss caused by propagation of an optical signal.

  FIG. 7 is a diagram illustrating a configuration example of the optical subcarrier generation device 20 according to the second embodiment. The optical subcarrier generation device 20 includes a CW light source 211, an optical amplifier 212, a phase modulator 213, a sine wave signal light source 22, and a DC voltage source 23. Note that the CW light source 211, the phase modulator 213, the sine wave signal light source 22 and the DC voltage source 23 are respectively the CW light source 111, the phase modulator 112, the sine wave signal light source 12 and the DC voltage source 13 shown in FIG. The configuration is the same.

  The optical amplifier 212 is configured to amplify the CW light and output it to the phase modulator 213. In FIG. 7, the CW light source 211, the optical amplifier 212, and the phase modulator 213 are monolithically integrated on the semiconductor substrate 21. Since the optical power input to the phase modulator 213 can be increased by the optical amplifier 212, the phase modulator 213 can increase the output intensity of the optical subcarrier. In this embodiment, since the input light to the optical amplifier 212 is, for example, CW light, there is no effect on the optical modulation spectrum generated by passing through the optical amplifier 212. Flattening is realized.

<Third Embodiment>
The optical subcarrier generating apparatus of the third embodiment is configured to use a wavelength tunable laser instead of using a CW laser.

  FIG. 8 is a diagram illustrating a configuration example of the optical subcarrier generation device 30 according to the third embodiment. The optical subcarrier generating apparatus 30 includes a wavelength tunable light source 311, an optical amplifier 312, a phase modulator 313, a sine wave signal light source 32, and a DC voltage source 33. The optical amplifier 312, the phase modulator 313, the sine wave signal light source 32, and the DC voltage source 33 are respectively the optical amplifier 212, the phase modulator 212, the sine wave signal light source 22, and the DC voltage source 23 shown in FIG. The configuration is the same.

  The wavelength variable light source 311 is configured to generate a wavelength variable laser. In FIG. 8, the variable wavelength light source 311, the optical amplifier 312, and the phase modulator 313 are configured to be monolithically integrated on the semiconductor substrate 31. Thereby, miniaturization of the optical subcarrier generation device 30 is realized.

  In the optical subcarrier generation device 30, the center frequency of the optical subcarrier can be varied by using a wavelength tunable laser. Thereby, for example, in wavelength division multiplexing (WDM) transmission, the subcarrier interval can be set in a specific frequency band so as to be accommodated in the WDM grid.

<Fourth embodiment>
The optical subcarrier generation device according to the fourth embodiment is configured to generate optical subcarriers having a wide optical frequency band.

  FIG. 9 is a diagram illustrating a configuration example of the optical subcarrier generation device 40 of the fourth embodiment. This optical subcarrier generation device 40 includes a plurality of light sources 411a, 411b, 411c,..., 411n that generate optical signals having different center wavelengths, and a multiplexer that combines the optical signals from the light sources 411a to 411n. 412, an optical amplifier 413 that amplifies the output of the multiplexer 412, a phase modulator 414, a sine wave signal light source 42, and a DC voltage source 43. The optical amplifier 413, the phase modulator 414, the sine wave signal light source 42, and the DC voltage source 43 are respectively the optical amplifier 212, the phase modulator 213, the sine wave signal light source 22 and the DC voltage source 23 shown in FIG. The configuration is the same.

  In FIG. 9, the light sources 411 a to 411 n, the multiplexer 412, the optical amplifier 413, and the phase modulator 414 are configured to be monolithically integrated on the semiconductor substrate 41. Thereby, miniaturization of the optical subcarrier generation device 40 is realized.

  The light sources 411a to 411n generate optical signals having different central wavelengths, and the multiplexer 412 collectively supplies the optical signals of multiple wavelengths to the phase modulator 414 via the optical amplifier 413. With the configuration of the phase modulator 414, a broadband flattened optical subcarrier can be generated in a wavelength-dependent range.

<Fifth Embodiment>
The optical subcarrier generation device of the fifth embodiment is configured to generate an optical subcarrier by further expanding the optical subcarrier band.

  FIG. 10 is a diagram illustrating a configuration example of the optical subcarrier generating apparatus 50 according to the fifth embodiment. The optical subcarrier generation device 50 includes phase modulation devices 51 </ b> A to 51 </ b> D, a sine wave signal light source 52, and a multiplexer 53 arranged in parallel. The configurations of the phase modulators 51A to 51D have the functions of the wavelength variable light source 311, the optical amplifier 312 and the phase modulator 313 shown in FIG. That is, the phase modulation devices 51A to 51D include wavelength variable light sources 511a to 511d, optical amplifiers 512a to 512d, and phase modulators 513a to 513d, as shown in FIG.

  Although not shown in FIG. 10, the phase modulators 513a to 513d are supplied with a bias voltage from the DC voltage source shown in FIG. The number of phase modulation devices 51A to 51D shown in FIG. 10 may be changed.

  In FIG. 10, the phase modulation devices 51 </ b> A to 51 </ b> D and the multiplexer 53 are configured to be monolithically integrated on the semiconductor substrate 51. Thereby, miniaturization of the optical subcarrier generation device 50 is realized.

  The sine wave signal light source 52 supplies a sine wave signal having a single amplitude to each of the phase modulators 513a to 513d. In the optical subcarrier generation device 50 of the present embodiment, the wavelength variable light sources 511a to 511d and the phase modulators 513a to 513d are individually arranged for each of the phase modulation devices 51A to 51D. Therefore, by configuring the phase modulators 513a to 513d suitable for the wavelengths of the wavelength tunable light sources 511a to 511d, optical subcarriers are generated without being limited by wavelength dependency.

  Even when the phase modulators 513a to 513d are arranged in parallel, the phase modulators 513a to 513d can be driven in accordance with a single amplitude signal from the single sine wave voltage signal source 52. As in the first embodiment, by adjusting only the bias voltage applied to the phase modulators 513a to 513d, the subcarrier can be flattened so that the intensity of the subcarrier becomes constant.

  As mentioned above, although each said embodiment was explained in full detail, a specific structure is not restricted to each said embodiment.

10, 20, 30, 40, 50 Optical subcarrier generator 12, 22, 32, 42, 52 Sinusoidal signal source 13, 23, 33, 43 DC voltage source 111, 211 CW light source 112, 213, 313, 414 Phase Modulator 212, 312, 413 Optical amplifier 311 Wavelength variable light source 411a to 411n Light source

Claims (7)

An optical subcarrier generator,
A single sinusoidal signal power supply,
A bias voltage source;
At least one optical phase modulator that generates an optical subcarrier according to a sine wave signal applied from the single sine wave signal power supply, and the optical subcarrier has a flat intensity of the subcarrier. And an optical phase modulator that is adjusted according to a bias voltage from the bias voltage source.   The optical subcarrier generation apparatus according to claim 1, wherein the optical phase modulator is configured such that a phase modulation amount changes nonlinearly with respect to the applied sine wave signal.   As the operating condition of the optical phase modulator, the fundamental wave component of the phase changing in the optical phase modulator is given by 0.45π to 0.55π, and the nonlinear component of the phase is given by 1.5π or more. The optical subcarrier generation apparatus according to claim 1, wherein the value of the bias voltage is set as described above. A light source;
An optical amplifier that amplifies an optical signal from the light source and outputs the amplified optical signal to the optical phase modulator;
Further including
4. The optical subcarrier generation device according to claim 1, wherein the light source, the optical amplifier, and the optical phase modulator are configured on the same semiconductor substrate. 5.   The optical subcarrier generation apparatus according to claim 4, wherein the light source is a continuous light source or a wavelength tunable light source. Multiple light sources;
A multiplexer that multiplexes optical signals from the plurality of light sources;
An optical amplifier that amplifies the output of the multiplexer and outputs the amplified output to the phase modulator;
Further including
4. The device according to claim 1, wherein the plurality of light sources, the multiplexer, the optical amplifier, and the optical phase modulator are configured on the same semiconductor substrate. 5. Optical subcarrier generator. Multiple light sources;
A plurality of optical amplifiers for amplifying an optical signal from each of the plurality of light sources and outputting the amplified signal to each optical phase modulator;
A multiplexer for multiplexing the outputs of the optical phase modulators;
Further including
4. The device according to claim 1, wherein the plurality of light sources, the plurality of optical amplifiers, the optical phase modulators, and the multiplexer are configured on the same semiconductor substrate. The optical subcarrier generation device according to 1.