JP5522703B2 - All-optical signal processing device - Google Patents

Description

  The present invention relates to an all-optical signal processing device that uses a nonlinear optical effect of a silicon optical waveguide to which input signal light is input to control output signal light output therefrom with control signal light.

  In recent years, research on integrated optical circuits based on silicon has been actively conducted for the purpose of fusion with electrical circuits and optical interconnection. A silicon optical waveguide having silicon as a core [see Patent Document 1] has a very small waveguide cross-sectional area, and the optical power density to be confined is two to three orders of magnitude higher than that of a conventional optical waveguide. Since the non-linearity is similarly strong by 2 to 3 digits, a large non-linear optical effect can be expected.

  The refractive index change due to the non-linear optical effect exhibits a very fast response at the femtosecond level, and ultrafast optical signal processing can be realized. However, in practice, the response time of the change in the refractive index of free carriers generated by the phenomenon of two-photon absorption in the silicon waveguide is on the nanosecond level, limiting the response speed of the optical element. For these reasons, it is said that the response speed of an optical signal processing device using the nonlinear optical effect of a silicon waveguide is limited to 10 Gb / s.

  Also, in future photonics networks, optical signal processing devices with high speed and low power consumption exceeding 160 Gb / s are required, but at present, the technology to perform practical high-speed optical signal processing using silicon waveguides Not developed.

  As an example of the prior art, the technical configuration disclosed in Non-Patent Document 1 is shown in FIG. 1, and FIG. 2 (left) shows a technique for completely relaxing free carriers. In the spatial interferometer shown in FIG. 1, signal light is input to one input port as cw light, and control light is input to the other input port. The signal light is distributed to the upper waveguide and the lower waveguide by the 3 dB coupler. While the distributed input signal light propagates through the lower waveguide as it is, the input signal light that propagates through the upper waveguide is input to the silicon optical waveguide, where it propagates while undergoing cross-phase modulation by the control light. As a result, the signal light undergoes a nonlinear phase shift depending on the optical power of the control light. This spatial interferometer functions as an optical switch using the nonlinear optical effect of a silicon optical waveguide. However, when optical switching is performed by a conventional method, the intensity waveform of an optical signal deteriorates in a manner that causes a tail. This is because two-photon absorption occurs when an optical signal is incident on the silicon optical waveguide, so that the behavior until free carriers generated in the two-photon absorption process are relaxed is seen. The refractive index change in the waveguide depends on the carrier density change (carrier plasma effect). Conventionally, the time domain until the influence of free carriers is completely relieved is the repetition frequency, so as shown in Fig. 2 (left) The repetition frequency of the optical switch was greatly limited.

JP 2004-133446 JP

Ozdal Boyraz, Prakash koonath, Varun Raghunathan, and Bahram Jalali, “All optical switching and continuum generation in silicon waveguides,” Optics Express, Vol. 12, No. 17, pp.4094-4102, 2004 C.R.S.Fludger, V.Handerek, and R.J.Mears, “Pump to Signal RIN Transfer in Raman Fiber Amplifiers,” JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL.19, NO.8, AUGUST 2001 K. Uchiyama et al., "100Gb / s all-optical demultiplexing using nonlinear optical loop mirror with gating-width control", Electron.Lett., 29, pp.1870-1871 (1993)

  If a situation is created in which free carriers are not generated, it is possible to realize an optical signal processing with an ultra-fast response at a femtosecond level based on a refractive index change only by a nonlinear optical effect. FIG. 2 (right) is a diagram for explaining a method of bringing the free carrier proposed by the present invention into a steady state. The present invention focuses on creating a state that suppresses the generation of free carriers by making an optical signal having a repetition frequency faster than the free carrier relaxation time of the silicon optical waveguide as control light and making the free carriers steady state. did. As a result, the process of reducing the refractive index change due to carrier fluctuation as shown in FIG. 2 (right) can be suppressed, and ultrafast optical signal processing can be performed in which the refractive index change due to the nonlinear optical effect is dominant.

  Therefore, the present invention eliminates the problem of limiting the repetition frequency due to the response time of free carriers in the silicon optical waveguide represented by the prior art, and a new ultra-high speed that does not depend on the response time of free carriers. An object is to provide an all-optical signal processing device.

  The all-optical signal processing device of the present invention uses the nonlinear optical effect of the silicon optical waveguide to which the input signal light is input, and controls the output signal light output therefrom with the control signal light. As this control signal light, an optical signal having a repetition frequency faster than the response time of the free carrier in the silicon optical waveguide is made incident, the free carrier is brought into a steady state, and the nonlinearity depends on the intensity of the optical signal which is not influenced by the carrier response time. For example, optical signal processing of optical switch, optical modulation, optical signal processing reproduction (optical 2R / 3R) is performed using the nonlinearity of the optical effect.

  When an optical signal having a repetition frequency faster than the response time of free carriers in the silicon optical waveguide is incident on the silicon optical waveguide, the free carriers become a steady state after a certain time, and the phenomenon of relaxation of refractive index change due to the response time of the free carriers Thus, the refractive index change due to the nonlinear optical effect depending only on the intensity of the optical signal becomes dominant. By this method, it becomes possible to perform ultrahigh-speed optical signal processing exceeding 160 Gb / s, which has been impossible until now with silicon waveguide optical devices.

ここで、Ｅは入力電界強度、β_TPAは二光子吸収係数、ωは入力光信号の角周波数とする。また、屈折率変化Δｎによる位相変化量Δφは、

と表せる。
ここで、λは入力光信号の波長、Ｌ_effは伝搬中の損失を考慮した実効長である。 When an optical signal is incident on the silicon optical waveguide, a nonlinear optical effect, that is, self-phase modulation accompanied by a refractive index change proportional to the light intensity occurs. In the silicon waveguide, the free carrier density in the silicon optical waveguide increases depending on the intensity of incident light due to the influence of two-photon absorption. This can be described as a function of the input optical electric field by a rate equation relating to the time t of the carrier density N as in the following equation, and the refractive index change amount Δn is related to the carrier density change amount ΔN.

Here, E is the input electric field strength, β _TPA is the two-photon absorption coefficient, and ω is the angular frequency of the input optical signal. The phase change amount Δφ due to the refractive index change Δn is

It can be expressed.
Here, λ is the wavelength of the input optical signal, and L _eff is the effective length considering the loss during propagation.

  FIG. 3 is a diagram showing a change in refractive index and phase after propagation through a silicon waveguide when an optical pulse is incident. When a certain optical pulse enters the silicon optical waveguide, a refractive index change due to self-phase modulation and a refractive index change due to a free carrier density change as shown in FIG. If an optical pulse exceeding 40 Gb / s, which is required in current optical communications, is input, a relaxation phenomenon can be seen due to the long response time of free carriers, so an optical signal processing device using a silicon waveguide It was a bottleneck.

  However, if an optical signal having a repetition frequency faster than the free carrier relaxation time is transmitted to the silicon waveguide, the carrier becomes a steady state after a certain time. For example, since the free carrier relaxation time in the silicon waveguide is on the order of 1 nanosecond, the repetition frequency becomes an optical signal of 10 GHz (100 picoseconds) or higher, which is faster than this. This means that the optical power of the input signal is attenuated due to free carrier absorption and propagation loss of the waveguide itself, and free carrier generation due to two-photon absorption is also attenuated, so that the carrier density becomes steady after a certain time. To do.

  In this state, the free carrier density is in a steady state, and free carriers are not generated even when a new optical signal is input. Therefore, the refractive index change due to only the nonlinear optical effect is dominant. FIG. 4 shows the analysis result of the time characteristic of the phase after propagation of the silicon waveguide when the input optical pulse train is incident. It can be seen that the optical power is in a steady state after a certain time, and the phase change by self-phase modulation proportional to the optical power is dominant. The temporal attenuation of optical power in the output light is due to two-photon absorption and absorption caused by free carriers generated in the process. Therefore, in this steady state region, it is possible to perform ultrafast optical signal processing independent of the carrier response time.

  According to the present invention, by setting the repetition frequency faster than the silicon carrier relaxation time for the control optical signal, the high-speed optical signal exceeding 160 Gbps does not depend on the refractive index change due to free carriers generated in the silicon optical waveguide. Processing operation becomes possible.

1 is a diagram illustrating a technical configuration disclosed in Non-Patent Document 1. FIG. (Left) is a diagram for explaining a method for completely relaxing free carriers, and (right) is a diagram for explaining a method for making free carriers in a steady state proposed by the present invention. It is a figure which shows the refractive index and phase change after a silicon waveguide propagation at the time of optical pulse incidence. It is a figure which shows the analysis result of the time characteristic of the phase after a silicon waveguide propagation when the input optical pulse train is incident. 1 is a diagram illustrating a first embodiment of an all-optical signal processing device embodying the present invention. FIG. 6 is a diagram showing the optical power and phase difference when propagating through the upper waveguide and the lower waveguide with respect to the input signal light. FIG. 7 is a diagram for explaining a phase control method when a random signal is used as the control light. It is a figure which shows 2nd Embodiment of the all-optical signal processing device which embodies this invention. It is a figure explaining the phase component compensation principle by the carrier fluctuation | variation in the case of using a random signal for control light. It is a figure which shows 3rd Embodiment of the all-optical signal processing device which embodies this invention. It is a figure explaining the compensation method of the phase difference component by the relaxation time of the free carrier by a loop type linear waveguide. It is a figure explaining the optical signal processing device by the case where cw light is used for signal light in a silicon optical waveguide.

Hereinafter, the present invention will be described based on examples.
(First embodiment)
FIG. 5 is a diagram showing a first embodiment of an all-optical signal processing device embodying the present invention. The all-optical signal processing device shown in FIG. 5 travels through a silicon optical waveguide and has a Mach-Zehnder interferometer using a change in refractive index due to a nonlinear optical effect depending on optical power. The operation of this all-optical signal processing device will be described. In the all-optical signal processing device of this embodiment, signal light having a wavelength of λ ₁ is input to the input port 1, and control light having a wavelength of λ ₂ is input to the input port 2. The repetition frequency of the control optical signal at this time is required to be faster than the response time of free carriers in the silicon optical waveguide.

  The signal light input from the input port 1 is distributed to the upper waveguide and the lower waveguide by the 3 dB coupler 5. Further, it is divided as follows according to the signal pattern of the control light.

(1) When a regular periodic optical pulse train is used for the control optical signal The control light input from the port 2 is a periodic optical signal. Examples of signals used as periodic signals are “11111111”, “01010101”, and “00010001”. At this time, the time interval from “1” to the next “1” is required to be faster than the response time of free carriers in the silicon optical waveguide. By using this method, it can be used for an optical sampling circuit, NRZ / RZ signal conversion, or an optical signal processing / reproducing circuit (optical 2R / 3R circuit).

  In the lower waveguide, the distributed input signal light propagates as it is (via a phase shifter Δφ described later), whereas the input signal light propagating in the upper waveguide is cross-phased by the control light input from the input port 2. Propagate while undergoing modulation. As a result, the signal light undergoes a nonlinear phase shift depending on the optical power of the control light.

  FIG. 6 is a diagram showing the optical power and phase difference when propagating through the upper waveguide and the lower waveguide with respect to the input signal light. As an example of a periodic signal, when the input optical signal and the control optical signal are a continuous pulse train ('1111111 ...'), it propagates through the upper waveguide and depends on the intensity of the control optical signal by cross-phase modulation with the control optical signal The refractive power change, that is, the optical power and phase difference of the input optical signal that has undergone the phase change take a temporal change as shown in the right of FIG. On the other hand, the input optical signal propagated through the lower waveguide takes a phase difference from the optical power as shown in the left of FIG.

で表される。Δφ_NL＝が180度となる時に出力光波形は最大となる。 By adjusting the optical power of the control light, it is possible to manipulate the phase difference at the point where the optical power of the signal light after propagation through the upper waveguide is maximized and at the point where it is minimized. Further, by setting the waveguide length of the upper and lower waveguides, a combined signal in which the optical signal interferes due to the phase difference between the upper waveguide and the lower waveguide is output from the 3 dB coupler 7 and obtained from the input port 3 as the output optical signal. It is done.
At this time, when the nonlinear phase shift [Delta] [phi _NL, the light power P _out of the output optical signal after interference loss of the waveguide is assumed to not at all, with respect to the input power P _in,

It is represented by When Δφ _NL = is 180 degrees, the output light waveform is maximum.

  In the upper waveguide, the carrier density of free carriers is in a steady state by the control light input. This means that the density of free carriers is different between the upper waveguide and the lower waveguide. As a result, the reference phase of the optical signal after propagating through the lower waveguide and the reference phase of the optical signal propagating through the upper waveguide are shifted by Δφ as shown in the lower right of FIG. Can not. Therefore, it is assumed that the reference phase is matched with this phase difference by using a phase shifter, and the maximum interference condition, that is, the optimum output power is obtained.

(2) When a random transmission signal is used for the control optical signal The operation of the all-optical signal processing device when a random transmission signal is propagated in the control optical signal input from the port 2 in FIG. 5 will be described. FIG. 7 is a diagram for explaining a phase control method when a random signal is used as the control light. By using this method, for example, it can be used as a wavelength conversion element.

While the distributed input signal light propagates as it is in the lower waveguide, the input signal light that propagates in the upper waveguide propagates while undergoing cross-phase modulation by the control light input from the input port 2. The control light is a random signal. In the case where the control light is a random signal, the free carrier density continues to decrease when the optical signal “0” continues as shown in the center diagram of FIG. 7, so that the refractive index change, that is, the fluctuation of the phase change after propagation occurs. Although not constant, the phase change changed by adaptively controlling the phase shifter of FIG. 6 is compensated. For example, the phase shifter uses a principle such as a thermo-optic effect to adaptively control the current flowing through the heater portion of the phase shifter. When the response time of the phase shifter control is τ _p and the response time of the free carriers in the silicon waveguide is τ _c , τ _p <τ _c is set. By controlling the phase shifter, even when the control light is a random signal as shown in FIG. 7, the fluctuation of the refractive index due to free carriers is canceled.

で表される。Δφ_NLが180度となる時に出力光波形は最大となる。 By adjusting the optical power of the control optical signal, the phase difference at the point where the optical power of the signal light after propagation through the upper waveguide is maximized and the phase difference at the point where it is minimized can be manipulated. Further, by setting the waveguide length of the upper and lower waveguides, a combined signal in which the optical signal interferes due to the phase difference between the upper waveguide and the lower waveguide is output from the 3 dB coupler 7 and obtained from the input port 3 as the output optical signal. It is done. At this time, when the nonlinear phase shift [Delta] [phi _NL, the light power P _out of the output optical signal after interference loss of the waveguide is assumed to not at all, with respect to the input power P _in,

It is represented by When Δφ _NL is 180 degrees, the output light waveform is maximized.

  In the lower waveguide, the optical power of the input optical signal. In the upper waveguide, the free carrier degree is in a steady state due to the control light input, so the density of free carriers is different between the upper waveguide and the lower waveguide. Therefore, since the reference phase of the optical signal after propagating through the lower waveguide and the reference phase of the optical signal propagating through the upper waveguide are shifted by Δφ as shown below, complete interference cannot be caused. For this phase difference, phase compensation is performed by temporally controlling the phase shifter so as to follow the temporal phase change caused by the free carrier density change. Thus, by controlling the refractive index change due to the mutual phase modulation, it is possible to realize an ultrahigh-speed optical signal processing device that does not depend on the relaxation time of free carriers in the silicon optical waveguide.

(Second Embodiment)
FIG. 8 is a diagram showing a second embodiment of the all-optical signal processing device embodying the present invention. The all-optical signal processing device shown in FIG. 5 utilizes the form of a Mach-Zehnder interferometer configured with a silicon optical waveguide that utilizes a change in refractive index that depends on the light intensity that travels in the waveguide. The operation of this all-optical signal processing device will be described. In the all-optical signal processing device of this embodiment, signal light having a wavelength of λ ₁ is input to the input port 1 in FIG. 8, and control light having a wavelength of λ ₂ is input to the input port 2. The signal light input from the input port 1 is equally distributed to the upper waveguide and the lower waveguide by the 3 dB coupler 5. Hereinafter, it is assumed that the pattern is divided into the following two patterns according to the control light signal.

(1) When a regular periodic optical pulse train is used for the control light signal The input signal light propagating through the upper waveguide propagates while undergoing cross-phase modulation by the control light input from the port 2 in FIG. The control light input from port 2 is a periodic optical signal. Examples of signals used as periodic signals are “11111111”, “01010101”, and “00010001”. At this time, the time interval from “1” to the next “1” is required to be faster than the response time of free carriers in the silicon optical waveguide. By using this method, it can be used for an optical sampling circuit, NRZ / RZ signal conversion, or an optical signal processing / reproducing circuit (optical 2R / 3R circuit).

で表される。つまり、Δφ_NL＝180度となる時に出力光波形は最大となる。 By adjusting the optical power of the control light, it is possible to manipulate the phase difference (non-linear phase shift) between the peak portion and the bottom portion of the optical power caused by the phase change received by the signal light by the mutual phase modulation. Further, by setting the waveguide length of the upper and lower waveguides, a combined signal in which the optical signal interferes due to the phase difference between the upper waveguide and the lower waveguide is output from the 3 dB coupler 7 and obtained from the input port 3 as the output optical signal. It is done. At this time, when the nonlinear phase shift [Delta] [phi _NL, the light power P _out of the output optical signal after interference loss of the waveguide is assumed to not at all, with respect to the input power P _in,

It is represented by That is, the output optical waveform becomes maximum when Δφ _NL = 180 degrees.

  In the upper waveguide, the free carrier density is in a steady state due to the input of the control light. However, since the refractive index of the upper waveguide changes due to the presence of the carrier, complete interference cannot be caused. Therefore, in order to match this refractive index change amount with the lower waveguide, the same control light as the control light incident from the input port 2 is input from the input port 4, thereby aligning the carrier density of the upper waveguide and the lower waveguide, The maximum interference condition, that is, the maximum output power is obtained. In this case, in the lower waveguide, the input optical signal from the port 5 to the port 8 and the control light from the port 8 to the port 5 pass each other, and thus are not subjected to cross phase modulation. Due to the interference at the port 7, only the input optical signal of the portion overlapping in time with the control optical signal that does not depend on the response time of the free carrier is output to the port 9.

ここにおいて、Ｌはシリコン光導波路の導波路作用長であり、図８ではポート１からポート５、８を経由したポート４までの距離である。ｖ_gは導波路を伝搬する光の群速度である。この下部導波路でのすれ違いの時定数を制御する事によって上部導波路で起きる自由キャリア密度のゆらぎ(図９中央)を相殺し、相互位相変調による位相変調効果を支配的にする事を特徴とする。例えば、シリコンの屈折率を3.4、光導波路長を1cmとすると、すれ違いの時定数τ_sが230psとなる。キャリアの緩和時間τ_cはナノ秒オーダーなので、これよりも短くなるように導波路長を設定する。ポート７での干渉により、自由キャリアの応答時間に依存しない制御光信号と時間的に重なり合った部分の入力光信号だけがポート９に出力される。 (2) When a random transmission signal is used as the control optical signal The operation of the all-optical signal processing device when a random transmission signal is propagated in the control optical signal input from the port 2 in FIG. 8 will be described. FIG. 9 is a diagram for explaining the principle of phase component compensation due to carrier fluctuation when a random signal is used as the control light. By using this method, for example, it can be used as a wavelength conversion element. When a random transmission signal is used as the control light signal, a difference between input signal light traveling from port 5 to port 8 and control light traveling from port 8 to port 5 is considered. The time constant of this passing is τ _s , the free carrier relaxation time in the silicon optical waveguide is τ _c, and τ _s <τ _c . In general, it is known that the passing time constant can be approximated as follows [see Non-Patent Document 2].

Here, L is the waveguide action length of the silicon optical waveguide, and is the distance from port 1 to port 4 via ports 5 and 8 in FIG. v _g is the group velocity of the light propagating in the waveguide. Controlling the time constant of passing in the lower waveguide cancels out the fluctuation of free carrier density (center in FIG. 9) that occurs in the upper waveguide and makes the phase modulation effect due to cross-phase modulation dominant. To do. For example, if the refractive index of silicon is 3.4 and the optical waveguide length is 1 cm, the passing time constant τ _s is 230 ps. Since the carrier relaxation time τ _c is on the order of nanoseconds, the waveguide length is set to be shorter than this. Due to the interference at the port 7, only the input optical signal of the portion overlapping in time with the control optical signal that does not depend on the response time of the free carrier is output to the port 9.

(Third embodiment)
FIG. 10 is a diagram showing a third embodiment of an all-optical signal processing device embodying the present invention. The all-optical signal processing device shown in FIG. 10 uses a loop-type linear waveguide [see Non-Patent Document 3] and a silicon optical waveguide. The signal input from the port 1 is distributed by the 3 dB coupler 2 into the signal light 3 propagating counterclockwise and the signal light 4 propagating clockwise. Assuming that the optical distance from the 3 dB coupler 2 via the counterclockwise 3 to the silicon optical waveguide end face 7 is L ₁ and the optical distance from the 3 dB coupler 2 via the clockwise 4 to the silicon optical waveguide end face 8 is L ₂ , L ₁ = L _{It is} configured to satisfy ₂ .

(1) When a regular periodic optical pulse train is used for the control optical signal The control light input from the port 5 is a periodic optical signal. Examples of signals used as periodic signals are “11111111”, “01010101”, and “00010001”. At this time, the time interval from “1” to the next “1” is required to be faster than the response time of free carriers in the silicon optical waveguide.

  Since the control signal light always receives a periodic optical pulse from the port 5 and propagates through the silicon optical waveguide, the free carrier density in the silicon optical waveguide is in a steady state. Since the signal light 4 that is branched by the 3 dB coupler 2 and propagates clockwise is propagated in the same direction as the control light input from the port 5 by the 3 dB coupler 6, it undergoes cross-phase modulation. On the other hand, since the signal light 3 that is branched by the 3 dB coupler 2 and propagates counterclockwise propagates in a direction different from that of the control light input from the port 5 by the 3 dB coupler 6, the signal light is not subjected to cross-phase modulation. Not modulated.

  The control light signal is controlled so that the phase difference between these two signals is 180 degrees. The light that has propagated through the silicon optical waveguide causes interference again at the 3 dB coupler 2, and only the input optical signal that is temporally overlapped with the control optical signal that does not depend on the relaxation time of the free carrier is output to the port 9.

ここにおいて、Ｌはシリコン光導波路の導波路長である。 (2) When a random optical signal is used as the control optical signal The operation of the all-optical signal processing device when a random transmission signal is propagated in the control optical signal input from the port 5 in FIG. 9 will be described. FIG. 11 is a diagram for explaining a compensation method for a phase difference component based on a free carrier relaxation time by a loop type linear waveguide. When a random transmission signal is used for the control light, a difference between the light 3 propagating counterclockwise and the control light is considered. The time constant of this passing is τ _s , the free carrier relaxation time in the silicon optical waveguide is τ _c, and τ _s <τ _c . In general, it is known that the passing time constant can be approximated as follows [see Non-Patent Document 2].

Here, L is the waveguide length of the silicon optical waveguide.

By controlling the passing time constant, the light propagating clockwise is offset in the free carrier density fluctuation (center of FIG. 11) generated when propagating in the same direction as the control light in the silicon optical waveguide. It is characterized by making the phase modulation effect by modulation dominant. For example, if the refractive index of silicon is 3.4 and the optical waveguide length is 1 cm, the passing time constant τ _s is 230 ps. Since the carrier relaxation time τ _c is on the order of nanoseconds, the waveguide length is set to be shorter than this. As a result, only the input optical signal of the portion overlapping in time with the control optical signal that does not depend on the response time of the free carrier is output to the port 9.

(Fourth embodiment)
FIG. 12 is a diagram showing a fourth embodiment of an all-optical signal processing device embodying the present invention. The all-optical signal processing device shown in FIG. 12 travels through a silicon optical waveguide and utilizes a change in refractive index due to a nonlinear optical effect depending on optical power. This all-optical signal processing device will be described. In the all-optical signal processing device of this embodiment, signal light having a wavelength of λ ₁ is input to the input port 1 as cw light, and control light having a wavelength of λ ₂ is input to the input port 2. The repetition frequency of the control optical signal at this time is required to be faster than the response time of free carriers in the silicon optical waveguide. In this case, it can be used as an optical phase modulation element.

  The signal light input from the input port 1 and the control light from the input port 2 propagate through the silicon optical waveguide by the 3 dB coupler 3 while undergoing mutual phase modulation. By adjusting the optical power of the control light, it is possible to manipulate the phase difference (non-linear phase shift) between the peak portion and the bottom portion of the optical power caused by the phase change received by the signal light due to the mutual phase modulation.

ここにおいて、Ｌはシリコン光導波路の導波路作用長である。これによって、自由キャリアに密度のゆらぎを相殺し、相互位相変調による位相変調効果を支配的にする事を特徴とする。例えば、シリコンの屈折率を3.4、光導波路長を1cmとすると、すれ違いの時定数τ_sが230psとなる。キャリアの緩和時間τ_cはナノ秒オーダーなので、これよりも短くなるように導波路長を設定する。 Also, consider the difference between input signal light traveling from port 3 to port 4 and control light traveling from port 4 to port 3. The time constant of this passing is τ _s , the free carrier relaxation time in the silicon optical waveguide is τ _c, and τ _s <τ _c . In general, it is known that the passing time constant can be approximated as follows [see Non-Patent Document 2].

Here, L is the waveguide action length of the silicon optical waveguide. This is characterized in that density fluctuations are canceled by free carriers, and the phase modulation effect by cross phase modulation becomes dominant. For example, if the refractive index of silicon is 3.4 and the optical waveguide length is 1 cm, the passing time constant τ _s is 230 ps. Since the carrier relaxation time τ _c is on the order of nanoseconds, the waveguide length is set to be shorter than this.

  The signal light subjected to the mutual phase modulation is distributed by the 3 dB coupler 4, and is subjected to phase modulation depending on the optical power of the input control optical signal and output from the port 6.

Claims (4)

In the all-optical signal processing device that controls the output signal light output from the nonlinear optical effect of the silicon optical waveguide to which the input signal light is input, by the control signal light,
The input signal light is distributed to the first waveguide and the second waveguide,
An optical signal of a random optical pulse train having a repetition frequency faster than the response time of free carriers in the silicon optical waveguide is incident on the silicon waveguide connected to the first waveguide as control signal light,
The input signal light propagating through the first waveguide propagates while being subjected to cross-phase modulation by the control signal light comprising the random optical pulse train, and the input signal light is a nonlinear phase shift depending on the optical power of the control signal light. Receive
The second waveguide propagates the distributed input signal light through the phase shifter,
The phase shifter temporally compensates for a phase difference Δφ between the reference phase of the optical signal after propagating through the second waveguide and the reference phase of the optical signal propagated through the first waveguide. The fluctuation of the phase change due to the change in the refractive index due to the change in the free carrier density of the optical signal after propagating through the first waveguide and subjected to the nonlinear shift is adaptively controlled earlier than the response time of the free carrier. Than cancel
By adjusting the optical power of the control optical signal, the phase difference at the point where the optical power of the signal light after propagation through the first waveguide becomes the maximum and the phase difference at the minimum point is manipulated, and the first And by setting the waveguide length of the second waveguide, by the phase difference in both waveguides,
The input signal light that has undergone the nonlinear phase shift in the first waveguide and the input signal light propagated through the phase shifter to the second waveguide are interfered by a coupler and combined, and the combined signal is An all-optical signal processing device that outputs an output optical signal. In the all-optical signal processing device that controls the output signal light output from the nonlinear optical effect of the silicon optical waveguide to which the input signal light is input, by the control signal light,
The input signal light is distributed to the first waveguide and the second waveguide,
An optical signal of a random optical pulse train having a repetition frequency faster than the response time of free carriers in the silicon optical waveguide is incident on the silicon waveguide connected to the first waveguide as control signal light,
The input signal light propagating through the first waveguide propagates while being subjected to cross-phase modulation by the control signal light comprising the random optical pulse train, and the input signal light undergoes a nonlinear phase shift depending on the optical power of the control signal light. received,
The second waveguide propagates the distributed input signal light,
In order to match the amount of change in the refractive index of the first waveguide with that of the second waveguide, the same control signal light as that of the control signal light is incident on the second waveguide in the opposite direction. Align the carrier density of the second waveguide,
By controlling the time constant of the passing in the second waveguide, the fluctuation of the free carrier density that occurs in the first waveguide is offset,
By adjusting the optical power of the control optical signal, the phase difference at the point where the optical power of the signal light after propagation through the first waveguide becomes the maximum and the phase difference at the minimum point is manipulated, and the first And by setting the waveguide length of the second waveguide, by the phase difference in both waveguides,
The input signal light that has undergone the nonlinear phase shift in the first waveguide and the optical signal of the input signal light that has been propagated to the second waveguide and has the same carrier density are combined by interfering with a coupler, An all-optical signal processing device that outputs a combined signal as an output optical signal. In the all-optical signal processing device that controls the output signal light output from the nonlinear optical effect of the silicon optical waveguide to which the input signal light is input, by the control signal light,
The input signal light is distributed by a coupler and input to both sides of the silicon optical waveguide via a first loop-type linear waveguide and a second loop-type linear waveguide,
An optical signal of a random optical pulse train having a repetition frequency faster than the response time of free carriers in the silicon optical waveguide is incident on the waveguide connected to the first loop type linear waveguide as control signal light,
The input signal light propagating through the first loop-type linear waveguide propagates while undergoing cross-phase modulation by propagating in the same direction as the control signal light consisting of a random optical pulse train,
The second loop-type linear waveguide propagates the distributed input signal light, propagates in the opposite direction to the input control optical signal,
The first loop type linearity is controlled by controlling the time constant of the difference between the control signal light and the input signal light distributed to the second loop type linear waveguide between the first and second loop type linear waveguides. Canceling fluctuations in free carrier density that occurs when the input signal light propagating through the waveguide propagates in the same direction as the control signal light,
The optical signal after propagation through the silicon optical waveguide is caused to interfere with the coupler again and is not affected by fluctuations in the number of free carriers, and only the input optical signal in the portion overlapping with the control optical signal in time is output. An all-optical signal processing device. In the all-optical signal processing device that controls the output signal light output from the nonlinear optical effect of the silicon optical waveguide to which the input signal light is input, by the control signal light,
As a control signal light, an optical signal of a random optical pulse train having a repetition frequency faster than the response time of free carriers in the silicon optical waveguide is incident,
The input signal light and the control signal light composed of a random optical pulse train are combined by a coupler, and then the input signal light which is cw light propagating through the silicon optical waveguide is mutually transmitted by the control signal light composed of the random optical pulse train. Propagating while undergoing phase modulation, the input signal light undergoes a nonlinear phase shift depending on the optical power of the control signal light,
Furthermore, by making the same control signal light as the control signal light enter the silicon optical waveguide in the opposite direction, the phase modulation effect depending on the optical power of the control light signal is made unaffected by fluctuations in the number of carriers. The all-optical signal processing device, wherein the input optical signal is received and output as output signal light.

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