JPH08111561A - Semiconductor wavelength conversion element - Google Patents

Abstract

PURPOSE: To provide a wavelength conversion element formed of semiconductor which is applicable in the field of an optical wave network, optical switching, optical data processing, optical cross connection, and the like. CONSTITUTION: A wave length conversion element of semiconductor laser structure is possessed of an active layer which has an optical gain with an injection of electrical current and three diffraction gratings high in selective reflection factor to light of certain wavelengths both provided in a resonator, wherein the three diffraction gratings are represented by 21 to 23 respectively and different from each other in period, and the reflection center wavelengths of the diffraction gratings determined basing on their periods are so set as to be much different, from the transmission forbidden wavelength width, and light ray of various wavelengths is taken out from a single element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength conversion element formed of a semiconductor used in the fields of lightwave networks, optical switching, optical information processing, optical cross-connects and the like.

[0002]

2. Description of the Related Art Wavelength conversion elements intended for use in the fields of lightwave networks, optical switching, optical information processing, optical cross-connect, etc. include, for example, reports by T. Durhuus (IEEE).
Photonics Technology Letters, Vol. 5, pp.86-88,199
Using a semiconductor laser in the oscillation state according to (3) and, for example, the report by B. Mikkelsen et al. (19th European Con
conference on Optical Communication, Technical Digest
ThP 12.6, 1993).

The principle of wavelength conversion using the semiconductor laser in this oscillating state is to reduce the laser oscillation mode gain due to the input signal light. This will be described with reference to the drawings. As shown in FIG. 8, carriers (electrons, holes) in the laser cavity
As shown in FIG. 9, when the signal light 03 is input to the semiconductor laser that outputs the wavelength-converted light (oscillation light) 02 that is stimulated and emitted by the coupling of 01, the signal light 03
The carrier 01 in the laser resonator is consumed for inductive amplification of, and the intensity of the wavelength-converted light (oscillation light) 02 of the laser decreases.

Therefore, the intensity fluctuation signal, which has been superimposed on the input signal light, can be superimposed on the oscillation wavelength of the laser,
At this time, since the wavelengths of the two are different, wavelength conversion of the signal light is achieved. In this case, since a laser that oscillates in a single mode is used as the semiconductor laser, the signal light wavelength is converted to only one wavelength.

Also, when a multimode laser such as a Fabry-Perot type laser is used as a wavelength conversion element, the mode closest to the input signal light wavelength is the input signal because the mode interval of the laser is narrow and there are many modes. It is drawn into the light and only the oscillation light of that wavelength is output.

The operating principle in wavelength conversion using a semiconductor optical amplifier uses saturation of the element amplification gain due to input light. Input light 1 (probe light) to the extent that the amplification gain is saturated is input to the semiconductor optical amplifier, and signal light having a different wavelength from that is input thereto. The amplification gain in the element is saturated by the signal light, and the intensity of the probe light output from the element also changes depending on the intensity of the signal light. For this reason,
The intensity bias information superimposed on the signal light can be transferred to the probe light of another wavelength and changed, and wavelength conversion is achieved.

[0007]

However, in wavelength conversion using a semiconductor laser in an oscillating state, the input light wavelength is converted into only one wavelength determined by the resonator of the element. In this case, when converting the wavelength of one signal light and sending the signal to the user, it is necessary to switch the converted light wavelength by time division and send the signal to many users. Then, the signal transmission was impossible.

Further, in wavelength conversion using a semiconductor optical amplifier, it is possible to convert the input light wavelength into a signal of a plurality of wavelengths by introducing light of a plurality of wavelengths as probe light, but the probe light is used. Multiple devices are required as a light source, the system becomes large and the power consumption increases, and due to the converted light wavelength,
The problem is that the conversion efficiency changes abruptly.

In order to solve these problems, it has been necessary to realize a wavelength conversion element which is low in power consumption, compact, and capable of converting an input signal light wavelength into a plurality of wavelengths.

The present invention has been made in view of the above prior art, and an object of the present invention is to provide a wavelength conversion element which is low in power consumption, compact, and capable of converting an input signal light wavelength into a plurality of wavelengths.

[0011]

In order to achieve the above object, the semiconductor wavelength conversion device of the present invention has at least an active layer having a gain for light by injecting a current and a wavelength for the light. In a wavelength conversion element having a semiconductor laser structure having a diffraction grating having a selectively high reflectance in a resonator, it has at least two diffraction gratings having different periods, and the diffraction gratings having a plurality of periods are It is characterized in that the reflection center wavelength (Bragg wavelength) determined by the period of each diffraction grating is significantly different from the transmission prohibited wavelength width (stop band width) of the diffraction grating.

In the semiconductor wavelength conversion device having the above structure,
The plurality of diffraction gratings formed in the resonator are characterized in that each diffraction grating region has a portion in which a phase of the diffraction grating is shifted by a half cycle in a central portion with respect to a traveling direction of light.

In the semiconductor wavelength conversion device having the above structure,
One of the electrodes that applies a bias current to the device has a split electrode structure.

That is, in the present invention, a diffraction grating having a plurality of periods is formed in the resonator of the element, and the element itself can oscillate at a plurality of wavelengths determined by the periods of the plurality of diffraction gratings. By injecting the signal light into the element, the signal superimposed on the signal light can be converted into a plurality of oscillation wavelengths of the element.

[0015]

In the above structure, the Bragg wavelength λ _B of the diffraction grating formed in the optical waveguide is expressed as 2Λ · n _eq . Here, Λ represents the period of the diffraction grating, and n _eq represents the equivalent refractive index of the light in the optical waveguide. Also, because of the diffraction grating,
Light that can propagate through the optical waveguide has wavelength dependence, and light in a specific wavelength region cannot propagate through the optical waveguide.
This wavelength region is called "stop band". By providing a diffraction grating with different period Λ'in the optical waveguide and setting the Bragg wavelength difference between them to be equal to or larger than the stop band width of the diffraction grating, both Bragg gratings can be used when the optical waveguide is made to wait for gain to light. Simultaneous oscillation near the wavelength can be obtained. By forming a plurality of diffraction gratings having different periods in the optical waveguide, it is possible to obtain oscillated light with a corresponding plurality of wavelengths. In this way, by changing the period of the diffraction grating formed in the element resonator, the Bragg wavelength of the diffraction grating is changed, and the oscillation is performed at the wavelength corresponding to that wavelength. Light of multiple wavelengths can be extracted from the device.

[0016]

The present invention will be described in detail below with reference to a preferred embodiment of the present invention.

[Embodiment 1] FIG. 1 schematically shows a first embodiment of a semiconductor wavelength conversion device of the present invention.

As shown in the figure, the active region 12 formed on the n-InP substrate 11 has a band edge wavelength of 1.55 μm.
m InGaAsP semiconductor mixed crystal. InGa having a band edge wavelength of 1.3 μm formed on the active region 12
An AsP layer 13 is formed, and each diffraction grating 21, 2 is formed thereon.
2 and 23 were formed respectively. Then, p-InP14 was formed, and the p-side electrode 15 and the n-side electrode 16 were respectively formed.

In this embodiment, the number of periodic changes in the diffraction grating is 3
And The length L of the three regions of this diffraction grating 21-23
Was 300 μm (total device length 900 μm).

The coupling constant of the diffraction grating is 100 cm ^-1.
And a phase-inverted region (λ / 4 shift region) 24 was formed in each central portion. The periods Λ ₁ , Λ ₂ and Λ ₃ of the diffraction gratings 21 to 23 in the regions I, II and III are 240
6A, 2422A and 2438A. FIG. 2 shows the oscillation spectrum of this device when a bias current is applied above the threshold value. 1.54 μm (λ ₁ ), 1.55 μm
_Three oscillation modes were observed at (λ ₂ ) and 1.56 μm (λ ₃ ) corresponding to the period of each diffraction grating. This wavelength interval is the stop band width of each diffraction grating (~
3 nm) was sufficiently large.

As shown in FIG. 3, the time dependence of the output light (wavelength-converted light) from the device when the signal light having the wavelength of 1.555 μm (λ ₀ ) emphasized by the 10 Gb / s NRZ signal is injected. As shown in FIG. It was found that the signal superposed on the input signal light of the wavelength (λ ₀ ) can be simultaneously converted into the signal light of the wavelengths λ ₁ , λ ₂ and λ ₃ .

Needless to say, the simultaneous signal conversion wavelength can be increased by increasing the regions of the diffraction grating having different periods.

[Second Embodiment] FIG. 5 schematically shows a second embodiment of the semiconductor wavelength conversion device of the present invention.

As shown in the figure, the element according to the present embodiment is the n-side electrode 1 in the element according to the first embodiment shown in FIG.
6 denotes three regions I, I having different periods of the diffraction gratings 21-23.
Three divisions by I and III, that is, the n-side electrode 16 in the region I
A, the n-side electrode 16B in the region II, and the n-side electrode 16C in the region III are each divided. As a result, it is possible to independently control the current value biasing each of the regions I, II, and III.

When the above three regions were biased at the same time and the signal light having the wavelength (λ ₀ ) shown in FIG. 3 was injected, the same result as shown in Example 1 could be obtained as shown in FIG.

Further, in the device according to the present embodiment, the current value biased to the region II is biased just below the value at which the region reaches oscillation, so that FIG. 6 (converted light spectrum) and FIG. 7 (time corresponding spectrum). As shown in
The converted light of wavelength λ ₂ could be removed.

This mechanism can also be realized with converted light of other wavelengths, and the signal light converted into multiple wavelengths can be easily deleted.
Moreover, it was found that each wavelength can be independently performed.

[0028]

As described above in detail with reference to the embodiments, according to the semiconductor wavelength conversion element of the present invention, one compact semiconductor element can change the wavelength of one input signal light to another. It is now possible to convert the signal light of multiple wavelengths at once to the same time.

Further, the signal light converted into a plurality of wavelengths can be controlled by independently controlling the bias current to the element.

[Brief description of drawings]

FIG. 1 is a schematic view of a semiconductor wavelength conversion device as a first embodiment of the present invention.

FIG. 2 is a converted light spectrum of the device of FIG.

FIG. 3 is a time-corresponding spectrum of input signal light (wavelength λ ₀ = 1.555 μm).

FIG. 4 is a time response spectrum of converted light from the semiconductor wavelength conversion device according to the first embodiment.

FIG. 5 is a schematic view of a semiconductor wavelength conversion device as a second embodiment of the present invention.

FIG. 6 is a converted light spectrum in the case where only the bias current to the region II of the semiconductor wavelength conversion device according to Example 2 is set just below the threshold value.

FIG. 7 is a time-corresponding spectrum of the converted light when only the bias current to the region II of the semiconductor wavelength conversion device according to the second embodiment is set just below the threshold value.

FIG. 8 is a diagram for explaining the operating principle of the wavelength conversion element.

FIG. 9 is a diagram for explaining the operation principle of the wavelength conversion element.

[Explanation of symbols]

11 n-InP Substrate 12 Active Region 13 InGaAsP Layer 14 p-InP 15 p-side Electrode 16 n-side Electrode 16A Region I n-side Electrode 16B Region II n-side Electrode 16C Region III n-side Electrode 21 Region I Period Λ ₁ Diffraction grating 22 Diffraction grating with period Λ ₂ of region II 23 Diffraction grating with period Λ ₃ of region III 24 region (λ / 4 shift region)

Claims (3)

[Claims] 1. A semiconductor laser structure having at least an active layer having a gain for light by injecting a current and a diffraction grating having a high reflectance selectively with respect to a wavelength of light in a resonator. In the wavelength conversion element, at least two diffraction gratings having different periods are provided, and the diffraction gratings having a plurality of periods have reflection center wavelengths (Bragg wavelengths) that are mutually determined by the periods of the respective diffraction gratings.
A semiconductor wavelength conversion device characterized in that the wavelength is significantly different from the transmission-prohibited wavelength width (stop band width) of the diffraction grating. 2. The semiconductor wavelength conversion device according to claim 1, wherein the plurality of diffraction gratings formed in the resonator have diffraction gratings in a central portion with respect to the traveling direction of light in each diffraction grating region. A semiconductor wavelength conversion device having a portion with a phase shifted by a half cycle. 3. The semiconductor wavelength conversion element according to claim 1, wherein the electrode on one side for applying a bias current to the element has a split electrode structure.