JPH1048567A - Optical dispersion compensator and optical pulse generator and optical communication system using the compensator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microminiature, inexpensive and stable optical dispersion compensator capable of dispersing and compensating light pulses of 100 femtosecond order of a wide spectral width by allowing the spread of pulse time width and waveform deterioration to transmit a resonator consisting of multilayered dielectric films. SOLUTION: Spacer layers 2 consisting of AlGaAs layers are grown by an org. metal vapor growth method on an n type GaAs substrate 1. Next, the periodically multilayered dielectric films 5 are formed by laminating GaAs high-refractive index layers 3 and AlAs low-refractive index layers 4 at 9.5 periods thereon. Namely, the multilayered films 5 are formed by alternately laminating n-layers of the low-refractive index layers 4 and (n+1) layers of the high-refractive index layers 3 in the transmitting direction of the light pulses, in such a manner that the high-refractive index layers 3 exist at both ends. The spectral width of the transmission regions adjacent to the high-reflection regions of the resonator structure is made wider to enhance the dispersion effect of the transmission regions by adopting the resonator structure formed of the multilayered dielectric films 5 to the optical dispersion compensator, by which the dispersion compensation of the light pulses from 100 femtoseconds to 10 picoseconds is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a long-distance and large-capacity optical communication system having a time-division multiplex communication system, a hybrid communication system of a time-division multiplex communication and a wavelength-division multiplex communication system, and an ultra-high-speed optical measurement. It relates to an indispensable ultrashort optical pulse generator (optical pulse generator). Also,
The present invention relates to an optical dispersion compensator as an optical waveform shaping device in optical transmission of the communication system.

[0002]

2. Description of the Related Art Light pulses from a short pulse light source, or
An optical pulse propagating in an optical fiber is affected by material and structural dispersion (dispersion: wavelength dependence of the group velocity of light), so that the pulse width is expanded or the waveform is deteriorated on the time axis. In general, in an optical pulse, for a constant C determined by the pulse waveform, its time width Δt and spectrum width Δλ (where λ is a wavelength) are Δt · Δλ ≧ C
The following relationship is shown. In particular, an optical pulse satisfying the relationship of Δt · Δλ = C is a TL pulse (Transform Limit Pulse).
called e). Taking a TL pulse as an example, it is clear that if the pulse width Δt on the time axis becomes Δt + α when the optical pulse passes through the medium, Δλ or C changes correspondingly. The latter change appears as a change in the waveform because C corresponds to the waveform. Desirable transmission of an optical pulse is to preserve the physical quantities Δt, Δλ, and C before and after transmission through the medium. Therefore, a change in these physical quantities can be regarded as deterioration of the optical pulse. Here, the short pulse light source is a light source (optical pulse generator) that generates pulsed light, and particularly generates a pulsed light having a small width Δt and a small spectral width Δλ on the time axis.

The deterioration of the optical pulse is caused by a time-division multiplex communication system using optical pulse transmission or a long-distance large-capacity optical communication system using a time-division multiplex communication and a wavelength-division multiplex communication system as a pillar. In this case, a communication error may occur. That is, the optical signal emitted from the light source (transmitter) as an optical pulse having a physical quantity of Δt ₁ and Δλ ₁ and a waveform corresponding to C ₁ corresponds to the physical quantity of Δt ₂ and Δλ ₂ and C ₂ in the transmission process. Changing to an optical pulse having a waveform causes the information of the optical signal to change in quality. The importance of this problem will be apparent given that the information carried by the optical signal is identified by the Δt, Δλ or waveform of the optical pulse.

[0004] The solution to this problem is to compensate for the effects of dispersion, and an element that does so is called an optical dispersion compensator. A typical example is an optical fiber dispersion compensator 39.
(FIG. 11A), the diffraction grating dispersion compensator 40 (FIG.
(B)), a dielectric multilayer dispersion compensator 41 (FIG. 11C), and a grating optical fiber dispersion compensator 42 (FIG. 11).
(D)), etc. (Reference: "Ultrafast Optoelectronics", Tadashi Sueda, Takeshi Kamiya, Chapter 2, Kawaja et al.,
IEEE Photonics Technology Letter, Volume 7, 158
(1995), JP-A-2-23302).

An optical fiber dispersion compensator propagates a short optical pulse through an optical fiber used for normal transmission,
Perform dispersion compensation using the dispersion of the optical fiber,
This is a transmission type optical dispersion compensator. The diffraction grating dispersion compensator is a transmission-type dispersion compensator that includes two facing diffraction gratings and performs dispersion compensation using the wavelength dependence of a delay time (or propagation distance) generated by two reflections. .
The dielectric multilayer dispersion compensator and the grating optical fiber dispersion compensator are reflection type optical dispersion compensators that perform dispersion compensation using a large dispersion effect in a high reflection region having a wide spectral width caused by multiple reflection of light. It is.

In the optical fiber dispersion compensator, 100 m to several km is required due to the minute dispersion effect of the optical fiber.
Therefore, the length of the optical fiber is required, so that the apparatus becomes large, and disadvantages such as unstable operation and high cost are caused. In the diffraction grating dispersion compensator, it is difficult to set a large-sized diffraction grating such as positioning of two diffraction gratings, which causes unstable operation. On the other hand, the dielectric multilayer film dispersion compensator and the grating optical fiber dispersion compensator are ultra-small and monolithic, so that their operations are stable.

[0007]

In the dielectric multilayer film dispersion compensator and the grating optical fiber dispersion compensator described above, due to multiple reflection of light, a relatively large dispersion compensation effect can be obtained in a wide spectral region in a high reflection region. As a result, a very small optical dispersion compensator can be realized. However, since these are reflection types, it is necessary to change the propagation direction of the optical pulse to be dispersion-compensated, and when a short pulse laser and these optical dispersion compensators are used in combination or integrated, or when an optical repeater is used. However, there is a disadvantage that the system becomes complicated when it is incorporated as a waveform shaper in the system. If one dispersion compensator does not have a sufficient dispersion value for compensation, a plurality of dispersion compensators are required. However, the arrangement is complicated because of the reflection type.

If a conventional periodic dielectric multilayer film dispersion compensator is used in a transmission region adjacent to a high reflection region, it can be used as a transmission type light dispersion compensator. However, the spectral width of the transmission region: δλ _T is not wide enough to perform dispersion compensation of an optical pulse on the order of 100 femtoseconds (FIG. 8, FIG.
FIG. 12 (B)).

[0009] In contrast to the above prior art, the problem to be solved by the present invention is 100 femto-second:
^10-15 seconds to 10 pico-seconds (pico-second: 10)
Compensating for the influence of dispersion occurring in an optical pulse having a time width of ^-12 seconds, that is, for compensating for pulse time width expansion and waveform deterioration (returning the pulse time width and waveform of the optical pulse to a state before being affected by the dispersion) That).

[0010]

In order to solve the above-mentioned problems, the guideline of the present invention is to replace a conventional periodic multilayer structure with a single resonator multilayer structure or a coupled resonator multilayer film. Use the structure. As a result, in the case of the single resonator type multilayer structure or the coupled resonator type multilayer structure, there is a transmission region having a wider spectral width adjacent to the high reflection region as compared with the periodic multilayer structure. Therefore, when the light pulse to be compensated is transmitted through the transmission region, the spectrum width is wide,
Dispersion compensation of an optical pulse having a pulse width of 100 femtoseconds to 10 picoseconds (hereinafter, short optical pulse) can be performed. That is, while the technique disclosed in JP-A-2-23302 reflects light pulses in a multilayer structure, the present invention differs in that dispersion compensation is performed by transmitting light pulses through the multilayer structure. Therefore, the optical dispersion compensator of the present invention has the following structural features.

First, the optical dispersion compensator of the present invention comprises a first dielectric region formed by periodically laminating a first dielectric and a second dielectric having a higher refractive index, a third dielectric and a third dielectric. A second dielectric region formed by periodically laminating a fourth dielectric having a large refractive index, and a third dielectric region formed by a fifth dielectric having a smaller refractive index than the second dielectric and the fourth dielectric. Consisting of 3
There is a resonator configured so that the dielectric region is sandwiched between the first dielectric region and the second dielectric region. In this resonator, the third dielectric region is (1) bonded to the second and fourth dielectrics, or (2) is bonded to the first and third dielectrics. , And connected to the first and second dielectric regions.

The resonator structure thus configured is defined as the single resonator type described above. On the other hand, the above-mentioned coupled resonator type is a single resonator type in which a plurality of single resonator types are coupled in series,
For example, a structure in which the above-described first dielectric region, third dielectric region, second dielectric region, third dielectric region, second dielectric region, third dielectric region, and second dielectric region are stacked in this order. (Here, the use of the second and second dielectric regions means that a slight variation in the composition of the second dielectric region is allowed).

Further, by adjusting the thickness of each dielectric layer, the spectral width of the light pulse incident on the resonator can be made first and second.
It is made to exist in the transmission region adjacent to the high reflection region including the resonance point of the resonator composed of the second and third dielectric regions.
These thicknesses are based on the resonance wavelength λ _r (this wavelength is a value in a vacuum), and the thickness of each dielectric layer is the resonance wavelength λ _r / n (where n
Is the refractive index of the dielectric), and the first to fourth dielectric layers: (λ
_r / n) / 4 and the fifth dielectric layer: (λ _r / n) / 2. The definition of the resonance wavelength will be described later in Examples 1 to 3.

In the above-described coupled resonator structure, the thickness of the fifth dielectric layer forming the third dielectric region is further set to the fifth dielectric layer, and the thickness of the third dielectric layer forming the second dielectric region is changed. The thicknesses of the body and fourth dielectric layers are set according to the third dielectric layer and the fourth dielectric layer, respectively (the same applies to the third and second dielectric regions). Thus, the spectral width of the light pulse incident on the coupled resonator structure exists in the transmission region adjacent to the high reflection region including the plurality of resonance points of the coupled resonator structure. Next, referring to FIG. 8, FIG. 9, FIG. 10, and FIG. 12, the difference in the behavior of the light pulse between the conventional periodic multilayer structure and the single resonator multilayer structure or the coupled resonator multilayer structure will be described. Will be described. FIGS. 8 and 9 show examples of calculation of reflection spectra of a conventional periodic multilayer structure, a single resonator multilayer structure of the present invention, and a coupled resonator multilayer structure in which two resonators are coupled. (A) and FIG. 10 (A).
Adjacent to the high-reflection area where the reflectance is almost 1, including the resonance point (a sharp concave where the reflectance is almost zero), there is a transmission area where the reflectance is almost zero. However, in the case of the periodic multilayer structure, there is no resonance point in the high reflection region. Also, the number of resonance points is equal to the number of resonators. For example, there is one in the case of a single resonator structure, and two in the case of a coupled resonator in which two resonators are coupled. Hereinafter, the spectrum width of this transmission region is referred to as dlT.

A conventional short optical pulse dispersion compensator having a periodic multilayer structure uses a high reflection region having a wide spectral width to cover a wide spectral width of a short optical pulse. For this reason, it becomes a reflection type (FIG. 12A). That is, FIG.
In the optical dispersion compensator having a periodic multilayer structure having the following spectrum, the dispersion of the dispersion of the light pulse incident thereon is compensated in a wide wavelength range from λ = 1.40 to 1.61 μm corresponding to the high reflection region. You. However, when this conventional short optical pulse dispersion compensator having a periodic multilayer structure is made a transmission type and dispersion compensation of an optical pulse is performed in a transmission region adjacent to a high reflection region, FIG. As shown, the correction (compensation) of the light pulse is not sufficiently performed. The reason is,
This is because, because δλ _{T of the} transmission region is smaller than the spectral width of the optical pulse (see near λ = 1.39 and 1.62 μm in FIG. 8), only a part of the spectral component of the optical pulse is subjected to dispersion compensation. Δλ _{T in} this case is 100
It is less than one tenth of the spectral width of a femtosecond order light pulse.

On the other hand, the δλ _T of the single-cavity multilayer structure or the coupled-cavity multilayer structure of the present invention is much larger than that of the periodic multilayer structure (FIGS. 8 and 9A). 10A), which is almost equal to the spectrum width of the optical pulse on the order of 100 femtoseconds.
Light pulse correction (compensation) by dispersion compensation of femtosecond-order light pulses is possible in transmission. That is, in the present invention, by employing the resonator structure formed by the dielectric multilayer film for the optical dispersion compensator, the spectral width of the transmission region adjacent to the high reflection region of the resonator structure is reduced by the dispersion effect of the transmission region. , Thereby enabling dispersion compensation of light pulses of 100 femtoseconds to 10 picoseconds. In FIG. 12, the optical dispersion compensator 47 of the present invention is shown in the same pattern as the conventional optical dispersion compensators 45 and 46, but the structural difference will be apparent from the embodiment described later. .

In practicing the present invention, in a single-cavity structure or a coupled-type resonator structure composed of a dielectric multilayer structure, the spectrum of an incident light pulse has a transmission region adjacent to a high reflection region of the resonator structure. Set to exist in. In this structure, in the transmission region adjacent to the high reflection region, a dispersion effect of a magnitude necessary for dispersion compensation can be obtained in a wide spectral region of an optical pulse on the order of 100 femtoseconds (see FIGS. 9 and 10). Therefore, it is possible to realize a transmission type optical dispersion compensator which is ultra-small, stable, inexpensive, and easy to couple with other devices.

The optical dispersion compensator of the present invention described above has
One optical dispersion compensator may be configured by combining multiple stages (see Embodiment 7). Also, an optical pulse generator may be configured in combination with a short pulse laser (see Examples 4 and 5). When a surface-emitting type semiconductor laser device is used as a light source for generating a short-pulse laser and an optical dispersion compensator is formed in a stacked manner on the semiconductor laser device, there is an advantage that the optical pulse generator can be downsized. This is an advantage that cannot be obtained by the conventional reflection type optical dispersion compensator. When an optical communication system is configured by using such an optical pulse generator as a light source, an increase in the distance and capacity of optical signal transmission is promoted. On the other hand, the optical dispersion compensator of the present invention may be used as an optical pulse waveform shaping element in an optical repeater circuit of an optical communication system (Embodiment 6).
reference).

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the optical dispersion compensator according to the present invention will be described below in detail with reference to the accompanying drawings.

<Embodiment 1> In this embodiment, an example of the structure of a single-cavity type optical dispersion compensator and its operating principle will be described with reference to FIG.
This will be described with reference to FIG. FIG. 1 is a sectional view of one embodiment of the optical dispersion compensator according to the present invention.

An n-type GaAs (donor concentration: N _D = 2 × 10 ¹⁸ cm ⁻³ ) substrate having a crystal orientation (001) plane is formed on a substrate 1 by MOVPE (Metal Organic Vapor Phase Epitaxy). A spacer layer 2 composed of a layer (Al molar ratio: x = 0.2, refractive index: 3.2) is grown to a thickness of 10 mm. Next, the GaAs high refractive index layer 3 (refractive index: 3.4) and the AlAs low refractive index layer 4 (refractive index:
2.9) are laminated for 9.5 periods to form a periodic dielectric multilayer film 5. That is, the dielectric multilayer film 5 includes n low refractive index layers and (n + 1) high refractive index layers (where n
Is a natural number. In this case, n = 9) is formed by alternately stacking high refractive index layers at both ends.

The thickness of each layer of the high refractive index layer 3 low refractive index layer 4, the resonance wavelength in a vacuum that has been set: the 1/4 of the effective wavelength inside the respective layers to the λ _r (λ _r settings Will be described later). Then laminating the half-wave low index layer 6 made of AlAs layer, resonant wavelength in vacuum, which is set the thickness: lambda and 1/2 of the effective wavelength inside the half-wave low index layer with respect to _r .

Further, the GaAs high refractive index layer 3 (refractive index: 3.
4) and an AlAs low refractive index layer 4 (refractive index: 2.9) are laminated for 9.5 periods to form a periodic dielectric multilayer film 5, and an AlGaAs layer (Al molar ratio: x = 0.2, refractive index: 3.2) A spacer layer 2 of 10 mm is grown. Next, a part of the n-type GaAs substrate 1 is removed by chemical etching to form an optical window 8. Finally, an anti-reflection coating film (AR coating film) 7 is formed on the upper and lower spacer layers 2 to prevent reflection at the interface with air. When the refractive index of the layer in contact with the air before attaching the AR coating film and n _1, the refractive index of the AR coat film, n _AR =
n ₁ ^1/2 and its thickness is (λ _r / 4) / n _AR .

[0024] In the following, the resonator length: describes the λ _r of the setting method. The optical dispersion compensator according to this embodiment, the spectrum 37 of the incident light pulses, as present in the transmissive region adjacent to the high-reflection region of the resonator structure, sets the lambda _r (FIG. 9 (A) see ). When compensating for down-chirp, λ _r is set so that the spectrum of the incident light pulse exists in the transmission region adjacent to the long wavelength side of the high reflection region (λ _r =
Around 1.70 μm). When compensating for up-chirp, λ _r is set so that the spectrum of the incident light pulse exists in the transmission region adjacent to the short wavelength side of the high reflection region (λ _r = around 1.34 μm). In addition, chirp (chirp)
Means the spread of the waveform in the direction of the wavelength axis or the time axis.
FIG. 9B shows the calculation result of the second-order phase dispersion in the transmission region adjacent to the long wavelength side of the high reflection region according to the present embodiment.

This embodiment can be applied not only to AlGaAs-based materials but also to other material systems, for example, materials such as SiO ₂ / TiO ₂ .

<Embodiment 2> In this embodiment, an example of the structure of a coupled resonator type optical dispersion compensator and its operating principle will be described with reference to FIGS. 2, 10 and 13. FIG. FIG. 2 is a sectional view of one embodiment of the optical dispersion compensator according to the present invention.

An n-type GaAs (donor concentration: N _D = 2 × 10 ¹⁸ cm ⁻³ ) substrate having a crystal orientation (001) plane is formed on a substrate 1 by MOVPE (Metal Organic Vapor Phase Epitaxy). A spacer layer 2 composed of a layer (Al molar ratio: x = 0.2, refractive index: 3.2) is grown to a thickness of 10 mm. Next, the GaAs high refractive index layer 3 (refractive index: 3.4) and the AlAs low refractive index layer 4 (refractive index:
2.9) are laminated for 9.5 periods to form a periodic dielectric multilayer film 5.

The thickness of each layer of the high refractive index layer 3 low refractive index layer 4, the resonance wavelength in a vacuum that has been set: the 1/4 of the effective wavelength inside the respective layers to the lambda _r. Next, a half-wave low index layer 6 made of AlAs layers are laminated, the resonance wavelength in vacuum, which is set the thickness: for lambda _r, and 1/2 of the effective wavelength inside this layer.

Further, the GaAs high refractive index layer 3 (refractive index: 3.
4) and an AlAs low refractive index layer 4 (refractive index: 2.9) are laminated for 9.5 periods to form a periodic dielectric multilayer film 5, and a half-wavelength low refractive index layer 6 composed of an AlAs layer is laminated. The thickness is set to の of the effective wavelength inside this layer with respect to the resonance wavelength: λ _r in a vacuum set. Next, the GaAs high refractive index layer 3 (refractive index: 3.4) and the AlAs low refractive index layer 4 (refractive index: 2.9)
The periodic dielectric multilayer film 5 is formed by laminating five periods. The thickness of each layer of the high refractive index layer 3 low refractive index layer 4, the resonance wavelength in a vacuum that has been set: for lambda _r, and 1/4 of the effective wavelength inside the layers. Further, an AlGaAs layer (Al molar ratio:
x = 0.2, Refractive index: 3.2) Spacer layer 2 consisting of 10 mm
After growing, a part of the n-type GaAs substrate 1 is removed by chemical etching to form an optical window 8. Finally, an AR coat film 7 is formed on the upper and lower spacer layers 2 to prevent reflection at the interface with air. When the refractive index of the layer in contact with the air before attaching the AR coating film and n _1, the refractive index of the AR coating film n _AR
= N ₁ ^1/2 and its thickness is (λ _r / 4) / n _AR .

[0030] In the following, the resonator length: describes the λ _r of the setting method. In the optical dispersion compensator of the present embodiment, λ _r is set so that the spectrum 38 of the incident light pulse exists in the transmission region adjacent to the high reflection region of the resonator structure (see FIG. 10A). ). When compensating for down chirp, λ _r is set so that the spectrum of the incident light pulse exists in the transmission region adjacent to the long wavelength side of the high reflection region. When compensating for up-chirp, λ _r is set so that the spectrum of the incident light pulse exists in the transmission region adjacent to the short wavelength side of the high reflection region. FIG. 10B shows a calculation result of the second-order phase dispersion in the transmission region adjacent to the long wavelength side of the high reflection region according to the present embodiment.

The present embodiment is not limited to AlGaAs-based materials, but can be applied to other material systems, for example, materials such as SiO ₂ / TiO ₂ .

The characteristics of the coupled resonator type multilayer optical dispersion compensator of the present invention were evaluated by computer simulation.
The result is shown in FIG. The result is plotted in spatial coordinates: z / λ ₀ normalized by the center wavelength of the incident pulse. In the structure used for the calculation, the periods of the three periodic dielectric multilayer films 5 are 6.5, 5.5, and 6, respectively. As for the refractive index, the refractive index of the low refractive index layer was set to 1 and the refractive index of the high refractive index layer was set to 1.2 so as not to deteriorate the calculation accuracy.
Also, it was assumed that there was no influence of reflection at the boundary between the optical dispersion compensator and the outside. The time width of the incident light pulse was 125 femtoseconds, and the center wavelength: λ ₀ was 1.5 μm.

Referring to FIG. 13, the optical dispersion compensator 49 of the present invention of the optical pulse 48 affected by the frequency chirp (or the spectrum width is expanded by the influence of the third-order optical nonlinearity).
, The characteristics of the optical dispersion compensator of the present invention are evaluated. It can be seen that the incident light pulse 48 is almost transmitted, and the transmitted pulse 50 is about half the time width due to dispersion compensation (see inset, dashed line indicates incoming light pulse, solid line indicates transmitted pulse). Thus, it has been shown that, by using the structure of the present invention, dispersion compensation of an optical pulse on the order of 100 femtoseconds can be performed in transmission.

<Embodiment 3> In this embodiment, a structural example of an optical dispersion compensator according to the present invention using an optical fiber will be described. FIG. 3 shows an embodiment of a resonator type optical dispersion compensator according to the present invention using an optical fiber. A Bragg grating layer 9 shown in FIG. 3 is formed with a half-wavelength low refractive index 6 interposed therebetween. This structure can be produced by exposing the photo-sensitive optical fiber 10 to interfering ultraviolet light (UV light) (Reference for production: Hill et al., Applied Physics Letter, Vol. 62, 103).
5 (1993)). Finally, AR coating films 7 are formed on both ends to prevent reflection at the interface with air. When the refractive index of the layer in contact with the air before attaching the AR coating film and n _1,
The refractive index of the AR coating film is n _AR = n ₁ ^1/2 , and its thickness is (λ
_r / 4) / _nAR .

The resonator length of the resonator type optical dispersion compensator is as follows:
A method for setting λ _r will be described. In the optical dispersion compensator of the present embodiment, the spectrum of the incident light pulse is located in the transmission region adjacent to the high reflection region of the resonator structure.
Setting the λ _r. When compensating for down chirp, λ _r is set so that the spectrum of the incident light pulse exists in the transmission region adjacent to the long wavelength side of the high reflection region. When compensating for up-chirp, λ _r is set so that the spectrum of the incident light pulse exists in the transmission region adjacent to the short wavelength side of the high reflection region.

In this embodiment, the optical dispersion compensator having the single resonator structure has been described. However, the optical dispersion compensator having the coupled resonator structure described in the second embodiment can also be manufactured.

Embodiment 4 In this embodiment, a semiconductor short pulse light source in which the optical dispersion compensator of the present invention is integrated will be described. FIG. 4 is a sectional view of an embodiment of a semiconductor short pulse light source in which an optical dispersion compensator according to the present invention is integrated.

First, the fabrication of the laser section will be described.
N-InP substrate 1 with (111) or (110) crystal orientation
MOVPE: Metal Organic Vapor
Phase Epitaxy) method using n-InGaAsP (bandwidth 1.4
High refractive index layer 1 having a thickness of 5 mm and a donor concentration of N _D = 2 × 10 ¹⁸ cm ⁻³ )
2 and n-InP (forbidden bandwidth wavelength 0.92 μm, N _D = 2 × 10 ¹⁸ cm
³ ) The low refractive index layer 13 is laminated for 30 periods to form an n-type dielectric multilayer film reflector 14. However, the thickness of each layer is １ ／ of the wavelength λ inside each layer. Next, undoped In
GaAsP (forbidden bandwidth wavelength 1 μm, thickness 0.4 μm) spacer layer 2, InGaAs quantum well layer (forbidden bandwidth wavelength 1.55 μm)
m, thickness 3.5 nm) and InGaAsP (bandwidth 1.15μ)
A 10-period compression-strained multiple quantum well layer 15 composed of a barrier layer (m, thickness 15 nm) and a resonator 16 composed of an undoped InGaAsP (bandwidth 1 μm, 0.4 μm thick) spacer layer 2 are provided. However, the barrier layer of the multiple quantum well layer has a P-type modulation dope (acceptor concentration: N _A = 5 × 10 ¹⁸ cm).
^-3 ) is performed. Subsequently, a low refractive index layer 17 of p-InP (thickness λ _r / 4, forbidden bandwidth wavelength 0.92 μm, N _A = 2 × 10 ¹⁸ cm ⁻³ ).
And p-InGaAsP (bandwidth 1.45 μm, N _A = 2 × 10
A high refractive index layer 18 of ¹⁸ cm ^-3 ) is stacked for 30 periods to form a p-type dielectric multilayer film reflector 19. Next, an Au / Zu / Au / Ti / Au p-side electrode 20 having an optical window is formed on the p-type dielectric multilayer reflector 19 by vapor deposition. Further, the n-side electrode 2
1 is formed by evaporating AuGe on an n-InP substrate. Lastly, for example, the single-cavity type optical dispersion compensator 22 described in the first embodiment is separately manufactured, directly adhered to the optical window, and integrated in the laser unit.

[0039] Hereinafter, the resonator length of a single cavity optical dispersion compensators 22: describes lambda _r setting method. In the optical dispersion compensator of the present embodiment, λ _r is set so that the spectrum of the light pulse from the so-called surface-emitting type laser unit exists in the transmission region adjacent to the high reflection region of the resonator structure. . When compensating for down chirp, λ _r is set so that the spectrum of the incident light pulse exists in the transmission region adjacent to the long wavelength side of the high reflection region. When compensating for up-chirp, λ _r is set so that the spectrum of the incident light pulse exists in the transmission region adjacent to the short wavelength side of the high reflection region.

In this embodiment, the laser portion is made of InGaAsP.
The present invention can be applied not only to the system material but also to other material systems, for example, an AlGaAs material. In the optical dispersion compensator, it can be applied to other material systems, for example, a material such as SiO ₂ / TiO _2. is there.

<Embodiment 5> In this embodiment, an example will be described in which the optical dispersion compensator according to the present invention is used as a dispersion compensator for an external cavity mode-locked laser. FIG. 5 is a configuration diagram of an external cavity mode-locked laser having an optical dispersion compensator according to the present invention. The laser device includes mirrors 23, 2
4, a saturable absorbing dye 25 sandwiched by 4, a laser dye 28 as an amplification medium sandwiched by mirrors 26 and 27, a mirror 29 necessary to form a resonator with the mirror 24, and a light pulse extraction. Necessary output mirror 30, optical dispersion compensator 31, half-wave plate 32, excitation light source
It comprises an Ar ion laser 33.

Embodiment 6 In this embodiment, an example in which the optical dispersion compensator according to the present invention is used as an optical pulse waveform shaper in an optical communication system using an optical fiber will be described with reference to FIG. The optical pulse 35 is applied to the optical fiber 34
When propagating inside, the optical pulse 35 spreads due to the dispersion of the optical fiber. Therefore, the dispersion compensation is performed using the optical dispersion compensator 31 according to the present invention, and the optical pulse waveform is shaped (FIG. 6A). Alternatively,
In the optical fiber used for optical communication, the interference ultraviolet rays (UV
Exposure to light (light) produces an optical dispersion compensator according to the present invention (FIG. 6B).

<Embodiment 7> In this embodiment, an example of an optical dispersion compensator 36 constituted by combining optical dispersion compensators according to the present invention in multiple stages will be described with reference to FIG. To increase the amount of dispersion without changing the spectral width of the dispersion, FIG.
As shown in (A) and (B), a plurality of optical dispersion compensators 31 according to the present invention are arranged in series to compensate for a larger amount of dispersion and to shape an optical pulse waveform.

[0044]

According to the present invention, in a single resonator structure or a coupled resonator structure comprising a dielectric multilayer structure,
Since a large dispersion effect is obtained in the transmission region having a wide spectral width adjacent to the high reflection region of the resonator structure, an ultra-compact, low-cost, dispersion-compensating optical pulse on the order of 100 femtoseconds having a wide spectral width can be obtained. Thus, a stable transmission type optical dispersion compensator can be realized. The above optical dispersion compensator is used for long-distance, large-capacity optical communication systems that are based on time-division multiplex communication systems or hybrid communication systems of time-division multiplex communication and wavelength division multiplex communication, or for ultra-high-speed optical measurement. It is suitable for an ultrashort light pulse generator indispensable for the above.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment according to the present invention.

FIG. 2 is a diagram showing a second embodiment according to the present invention.

FIG. 3 is a diagram showing a third embodiment according to the present invention.

FIG. 4 is a diagram showing a fourth embodiment according to the present invention.

FIG. 5 is a diagram showing a fifth embodiment according to the present invention.

FIG. 6 is a diagram showing a sixth embodiment according to the present invention.

FIG. 7 is a diagram showing a seventh embodiment according to the present invention.

FIG. 8 is a diagram showing a reflection spectrum of a conventional optical dispersion compensator having a periodic dielectric multilayer structure.

FIG. 9 is a diagram showing calculation results regarding the reflection spectrum and the second-order phase dispersion of the optical dispersion compensator (the first embodiment) having a single resonator structure according to the present invention.

FIG. 10 is a diagram showing calculation results regarding a reflection spectrum and a second-order phase dispersion of an optical dispersion compensator (Example 2) having a coupled resonator structure according to the present invention.

FIG. 11 is a configuration diagram of a conventional optical dispersion compensator.

FIG. 12 is an explanatory diagram showing a difference in behavior of an optical pulse between a conventional periodic multilayer film structure and a single resonator multilayer film structure or a coupled resonator multilayer film structure.

FIG. 13 is a diagram showing a calculation result of a transient response characteristic of an optical pulse for a coupled resonator type multilayer optical dispersion compensator in which two resonators are coupled.

[Explanation of symbols]

1 ... n-type GaAs substrate, 2 ... spacer layer, 3 ... high refractive index layer,
4 Low refractive index layer 5 Periodic dielectric multilayer film 6 Half wavelength low refractive index layer 7 AR coating film 8 Optical window 9 Bragg grating layer 10 Photosensitive optical fiber , 11 ... n-type InP substrate, 12 ... n-type high refractive index layer, 1
3 ... n-type low refractive index layer, 14 ... n-type dielectric multilayer film, 15 ... p
-Type modulation-doped compression-strained quantum well layer, 16 ... resonator, 17
... p-type low refractive index layer, 18 ... p-type high refractive index layer, 19 ... p-type dielectric multilayer film, 20 ... p-side electrode, 21 ... n-side electrode, 22 ... single-cavity optical dispersion compensator, 23 mirror, 24 mirror, 25 saturable absorbing dye, 26 mirror, 27 mirror, 28 laser dye, 29 mirror, 30 output mirror, 31 optical dispersion compensator, 32 half-wave plate, 33: Ar ion laser, 34: Optical fiber, 35: Optical pulse, 3
6 ... multistage type optical dispersion compensator, 37 ... incident light spectrum, 3
8: Incident light spectrum, 39: Optical fiber dispersion compensator, 40: Diffraction grating dispersion compensator, 41: Dielectric multilayer film dispersion compensator, 42: Grating optical fiber dispersion compensator, 43: Incident light spread due to the influence of dispersion Pulse, 44 ...
Transmitted light pulse, 45: reflected light pulse, 46: periodic multilayer optical dispersion compensator, 47: single-cavity or coupled-cavity multilayer optical dispersion compensator, 48: incident optical pulse subjected to frequency chirp, 49: coupled resonator type multilayer optical dispersion compensator in which two resonators are coupled; 50: transmitted light pulse; 51: reflected light pulse.

Claims (8)

[Claims] 1. An optical pulse having a time width of 100 femtoseconds to 10 picoseconds, which is formed of a dielectric multi-layer film. An optical dispersion compensator characterized in that compensation is performed by transmitting the light through a resonator. 2. The resonator according to claim 1, wherein the resonator includes a first dielectric region formed by periodically stacking a first dielectric and a second dielectric having a higher refractive index than the first dielectric, and a third dielectric. A second dielectric material having a fourth dielectric material having a refractive index larger than that of the third dielectric material and being periodically laminated;
A dielectric region, a third dielectric region made of a fifth dielectric having a lower refractive index than the second dielectric and the fourth dielectric, and the third dielectric region is made up of the first dielectric region and the third dielectric region. The second dielectric and the fourth dielectric are sandwiched between the second dielectric regions, and the second dielectric and the fourth dielectric are configured to contact the third dielectric region. The above first and second
2. The optical dispersion compensator according to claim 1, wherein the optical dispersion compensator exists in a transmission region adjacent to a high reflection region including a resonance point of the resonator formed of the third dielectric region. 3. The resonator according to claim 1, wherein the resonator includes a first dielectric region formed by periodically laminating a first dielectric and a second dielectric having a higher refractive index than the first dielectric; And a second dielectric region formed by periodically laminating a fourth dielectric having a higher refractive index than the third dielectric, and a fifth dielectric having a higher refractive index than the second dielectric and the fourth dielectric. A third dielectric region comprising a body,
The third dielectric region is sandwiched between the first dielectric region and the second dielectric region, and the first dielectric and the third dielectric are in contact with the third dielectric region. Wherein the spectral width of the light pulse incident on the resonator exists in a transmission region adjacent to a high reflection region including a resonance point of the resonator composed of the first, second, and third dielectric regions. The optical dispersion compensator according to claim 1, wherein 4. A coupled resonator structure in which a plurality of resonators according to claim 2 or 3 are coupled in series, and the spectral width of the light pulse incident on the coupled resonator structure is equal to 2. The optical dispersion compensator according to claim 1, wherein the optical dispersion compensator exists in a transmission region adjacent to a high reflection region including a plurality of resonance points of the coupled resonator structure. 5. An optical dispersion compensator comprising a plurality of optical dispersion compensators according to claim 1 coupled in multiple stages. 6. An optical pulse generator comprising a short pulse laser and the optical dispersion compensator according to claim 1. 7. An optical communication system using the optical pulse generator according to claim 6 as a light source. 8. An optical communication system having an optical repeater circuit using the optical dispersion compensator according to claim 1 as an optical pulse waveform shaping element.