JP3469458B2 - Signal waveform shaping element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical communication, optical switching,
The present invention relates to a signal waveform shaping element which is applied to an optical system for transmitting and processing an optical signal such as optical information processing and is effective for shaping a waveform of an optical signal. [0002] Considering the construction of an optical transmission processing system using light such as optical communication, optical switching, and optical information processing, optical loss in an optical fiber or an optical switch becomes a serious problem, and an attenuated optical signal is generated. Must be compensated by the optical amplifier. However, the following problem arises. First, the use of the optical amplifier degrades the waveform due to noise generated by the optical amplifier. FIG.
7A and 7B schematically show changes in waveform, where FIG. 7A is an example of a waveform that has not deteriorated, and FIG. 7B is an example of a waveform that has changed due to noise. Second, in long-distance optical transmission using an optical fiber, the waveform also deteriorates due to dispersion in the optical fiber.
FIGS. 5A and 5B schematically show changes in the waveform. FIG. 5A shows an example of a waveform that has not deteriorated, and FIG. 5B shows an example of a waveform that has changed due to noise. [0005] For this reason, conventionally, an optical signal is converted into an electric signal by a light receiving element, the waveform is electrically shaped, and then the optical signal is converted again into an optical signal. FIG. 6 shows a configuration example of a system used for such signal conversion. In the figure, reference numeral 61 denotes an optical / electrical conversion element, 62 denotes an electric waveform shaping element, and 63 denotes an electric / optical conversion element. [0006] However, the conventional signal waveform shaping element needs to convert an optical signal into an electric signal.
As the number of lines increases, the ratio of optical / electrical conversion and electrical / optical conversion in the entire system increases, and this has been a major bottleneck in reducing power consumption and cost. Therefore, there has been a demand for a means for waveform shaping of an optical signal as it is. Therefore, the present invention solves the above-mentioned problems,
It is an object of the present invention to provide a signal waveform shaping element for shaping an optical signal as it is. [0008] In order to solve the above problems, a signal waveform shaping element according to the present invention comprises a double layer comprising a clad layer, an active layer, and a clad layer sequentially laminated on a semiconductor substrate. A semiconductor laser type optical amplifying device comprising a hetero structure, a buried structure including an electric insulating layer provided on both sides of an active layer, and antireflection films provided on both end surfaces, wherein the active layer has a thickness of Is less than 0.4 μm and the width is less than 0.4 μm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A signal waveform shaping element according to the present invention is provided on both sides of an active layer, a double hetero structure composed of a clad layer, an active layer, and a clad layer sequentially laminated on a semiconductor substrate. A semiconductor laser type optical amplifying device having a buried structure made of an electrically insulating layer provided on the substrate and antireflection films provided on both end faces, wherein the active layer has a thickness of less than 0.4 μm and a width of 0.4 μm. It is less than 4 μm. Further, the signal waveform shaping element according to the present invention has an electrode structure composed of at least one of an anode and a negative electrode. However, the signal waveform shaping element does not need to have an electrode because it operates essentially without a bias. The operation principle of the signal waveform shaping element according to the present invention is as follows. When a semiconductor laser type optical amplifying element is used with no bias, minute bias or reverse bias, a large loss exceeding 40 dB usually occurs. However, if the thickness of the active layer is smaller than 0.4 μm and the width is smaller than 0.4 μm, -3 dBm (0.5 mW)
It has a large loss for a weak optical input below, but a strong optical input more than that causes loss to be saturated, so-called saturable absorption occurs, and the loss is reduced, resulting in an optical input of 7 dBm (5 mW) or more. On the other hand, there is almost no loss. By utilizing this nonlinear effect, it is possible to shape the optical signal as it is. Hereinafter, a specific example of the signal waveform shaping element according to the present invention will be described. (Embodiment 1) FIG. 1 is a schematic perspective view for explaining an example of a signal waveform shaping element according to the present invention. In the figure, reference numeral 101 denotes an n-InP substrate, 102
Is an n-InP cladding layer, 103 is InGaAs having a thickness of 0.3 μm, a width of 0.3 μm, and a band gap wavelength of 1.5 μm.
sP active layer, 104 is a p-InP cladding layer, 105 and 106 are Fe-InP insulating layers, 107 is p-InG
aAsP cap layer, 108 is an n-side electrode,
Is a p-side electrode. The signal waveform shaping element has a total length of 300
This is a so-called semiconductor laser type optical amplifying element having an antireflection film (not shown) made of TiO ₂ / SiO _{2 on} both end surfaces. When a semiconductor laser type optical amplifying element is used with no bias, a small bias (usually 5 mA or less) or a reverse bias, a large loss exceeding 40 dB usually occurs. In practice, the active layer has a thickness of 0.4 μm and a width of 0.4 μm.
When it has a size of 4 μm or more, as shown in FIG. 2, there is a large light loss regardless of the light input intensity. However, if the active layer is made smaller than 0.4 μm in thickness and 0.4 μm in width, for example, 0.3 μm in thickness and 0.3 μm in width, a weak light input of -3 dBm (0.5 mW) or less can be obtained. Although there is a large loss, the so-called saturable absorption occurs in which the loss is saturated for a strong optical input and the loss is reduced, and the loss is almost zero for an optical input of 7 dBm (5 mW) or more. become. If this nonlinear effect is used, for example, it is possible to shape a dull optical signal waveform as shown in FIG. 3A as it is, as shown in FIG. 3B. Since the active layer has a substantially square structure, the device basically has polarization-independent characteristics that do not depend on input polarization. (Embodiment 2) A signal waveform shaping element based on this embodiment has substantially the same structure as that of Embodiment 1, but differs from Embodiment 1 in that electrodes 108 and 109 are not provided. That is, since the signal waveform shaping element of the first embodiment scans essentially without bias, reference numeral 108,
The electrode 109 may be omitted. Therefore, the problem of power consumption is fundamentally solved by the biasless operation. In this specification, n-type InP
Although the description has been given by taking the substrate as an example, a similar effect can be obtained in a p-type substrate or another semiconductor crystal. Further, although the example of bulk InGaAsP is given as the active layer, a quantum well structure or a strained quantum well structure (compression strain, extension strain) may be used. InGaAlAs-based, I
Similar effects can be obtained with a material system such as an nAlAs system or an AlGaAs system. Further, regarding the buried structure, Fe-InP
Has been described as an example, but a buried structure by a pn junction does not change the gist of the present invention. As described above, according to the present invention,
It is possible to provide a waveform shaping element for shaping an optical signal as it is.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic perspective view for explaining an example of a signal waveform shaping element according to the present invention. FIG. 2 is a diagram for explaining the relationship between optical loss and input light intensity in the signal waveform shaping element shown in FIG. 3A and 3B are waveform diagrams for explaining signal waveform shaping by the signal waveform shaping element shown in FIG. 1, wherein FIG.
(B) shows the waveform when the waveform is shaped as it is. FIGS. 4A and 4B are waveform diagrams schematically showing waveform changes for explaining signal waveform shaping according to the related art, where FIG. 4A is a waveform that has not deteriorated, and FIG. 4B is a waveform that has changed due to noise. . FIGS. 5A and 5B are waveform diagrams schematically showing waveform changes for explaining signal waveform shaping according to the related art, where FIG. 5A is a waveform that has not deteriorated and FIG. 5B is a waveform that has changed due to noise. . FIG. 6 is a circuit diagram for explaining a conventional signal waveform shaping element. DESCRIPTION OF THE SYMBOLS 101 n-InP substrate 102 n-InP cladding layer 103 InGaAsP active layer 104 p-InP cladding layer 105 Fe-InP insulating layer 106 Fe-InP insulating layer 107 p-InGaAsP cap layer 108 n-side electrode 109 p Side electrode

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-75212 (JP, A) JP-A-2-230221 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/35 JICST file (JOIS)

Claims (1)

(57) [Claim 1] A double hetero structure comprising a clad layer, an active layer, and a clad layer sequentially laminated on a semiconductor substrate, and an electric insulating layer provided on both sides of the active layer. A semiconductor laser type optical amplifying device comprising a buried structure and antireflection films provided on both end surfaces, wherein the active layer has a thickness of less than 0.4 μm and a width of less than 0.4 μm. Characteristic signal waveform shaping element.