JPH11346023A - Short-pulse light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a short-pulse light source of a structure, wherein the pulse width of an optical pulse train can be set, a phase in each mode is independently controlled to enable a pulse form to design and the optical pulse train in the limit of a transformation can be obtained. SOLUTION: A short-pulse light source is constituted of at least first and second slab waveguides 102 and 104, an array waveguide diffraction grating 100 constituted of a plurality of waveguides linking together these slab waveguides, an optical modulation part 105 and an optical amplification part 106, which are provided on one end of the diffraction grating 100, first and second mirrors 109 and 108 provided in such a way as to hold the diffraction grating 100 between them, a plurality of connection waveguides 107 connecting the waveguide 104 with the mirror 108, a modulation part drive circuit to drive the modulation part 105 and an optical amplification part excitation circuit for forming an inverted population in the amplification part 106.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a short pulse light source that generates a short light pulse train using an arrayed waveguide diffraction grating.

[0002]

2. Description of the Related Art An example of a short light pulse light source of the prior art is as follows.
As shown in FIG. In the figure, reference numeral 201 denotes an optical modulator, 202 denotes a driving circuit thereof, 203 denotes an optical amplifying medium, 204 denotes an excitation circuit thereof, and 205 denotes a mirror. These elements are a mode-locked laser (short optical pulse). Light source). In this short light pulse light source, two mirrors 205
When the optical modulator 201 is driven by a clock having a frequency substantially equal to the resonance mode interval of the optical resonator (or an integer multiple thereof), an optical short pulse train having a clock frequency (or an integer multiple of the clock frequency) is generated. Can occur.

[0003] However, this conventional technique has the following problems.

(1) The oscillation mode envelope spectrum fluctuates greatly depending on operating conditions such as temperature, so that it is difficult to set the center wavelength and pulse width.

(2) Since the phase of each mode cannot be controlled independently, it is difficult to design a pulse shape.

(3) Although a very large number of modes are excited, the correlation between the modes becomes insufficient due to the dispersion and nonlinear effects of the semiconductor medium of the long resonator, so that a pulse train of the transform limit may be generated. Have difficulty.

Another example of the prior art short light pulse light source is shown in FIG. In the figure, 206 is an optical amplification medium, 207 is a high reflection mirror provided at one end of the optical amplification medium 206, 20
8, a low-reflection coating provided on the other end of the optical amplification medium 206; 209, a lens; 210, an optical waveguide;
11 is a slab waveguide, 212 is an array waveguide, 213 is an optical waveguide, and 214 is a high reflection mirror. 215
Is an excitation circuit of the optical amplification medium 206, and 216 is
An array waveguide diffraction grating including the optical waveguide 210, the slab waveguide 211, the array waveguide 212, and the optical waveguide 213 is shown.

In another short pulse light source of this prior art, the optical amplification medium 206 is constantly excited to thereby
Multi-wavelength light can be oscillated simultaneously. However, in this conventional short light pulse light source, the light amplification medium 206
Even if a semiconductor laser is used, modulation can be performed only at a few GHz at most, and a mode-locked short pulse train cannot be generated. In this short light pulse light source, setting and controlling the intensity and phase for each mode is not considered.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and a first object of the present invention is to provide a short light pulse light source capable of setting a pulse width of an optical pulse train. It is in. The second object of the present invention is to
An object of the present invention is to provide a short light pulse light source capable of designing a pulse shape by independently controlling the phase of each mode. Further, a third object of the present invention is to provide a short light pulse light source capable of obtaining an optical pulse train of a transform limit.

[0010]

According to another aspect of the present invention, a short-pulse light source according to the present invention comprises a first and a second slab waveguide and a plurality of waveguides connecting the slab waveguide. An arrayed waveguide diffraction grating composed of a waveguide, a light modulator and an optical amplifier provided at one end of the arrayed waveguide diffraction grating, and first and second optical waveguides provided to sandwich the arrayed waveguide diffraction grating. A second mirror, a plurality of connecting waveguides connecting the second slab waveguide and the second mirror, a modulator driving circuit for driving the optical modulator, and a population inversion in the optical amplifier. An optical amplification unit excitation circuit,
It is characterized by having.

According to a second aspect of the present invention, there is provided the short pulse light source according to the first aspect, wherein a phase difference between the plurality of connection waveguides is constituted by first and second mirrors. It is set to compensate for the dispersion of the resonator.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration diagram of an embodiment of a short pulse light source according to the present invention. In the figure, 101 is an InP substrate,
102 is a first slab waveguide, 103 is an array waveguide,
Reference numeral 104 denotes a second slab waveguide. The first slab waveguide 102, the array waveguide 103, and the second slab waveguide constitute an array waveguide diffraction grating 100. Reference numeral 105 denotes an optical modulator, reference numeral 106 denotes an optical amplifier, reference numeral 107 denotes a connection waveguide array, reference numeral 108 denotes a mirror (high reflection film) provided at the end of the connection waveguide array 107, and reference numeral 109 denotes the optical modulation unit 105. Is a mirror (highly reflective film) provided at the front end of the mirror.

FIGS. 2, 3 and 4 show the line II-II 'of FIG.
FIG. 3 is a cross-sectional view taken along lines I-III ′ and IV-IV ′. In these figures, 110 is an AuZnNi electrode layer, 111 is a p ⁺ -1.5Q-InGaAsP contact layer, 112
Is a p-InP cladding layer, 113 is an i-InP etch stop layer, 114 is 0.9Q-InGaAsP / 1.Q
-InGaAsP-5 well strained quantum well layer, 11
5 is an n-InP cladding layer, 116 is an AuGeNi electrode layer, 117 is 0.9Q-InGaAsP / 1.3Q-I
An nGaAsP-2 well strained quantum well layer 118 is a 1.3Q-InGaAsP layer. Further, as shown in FIG. 2, the optical modulator 105 of FIG.
19 is connected to the optical amplification unit 106, and as shown in FIG. 3, an optical amplification unit excitation circuit 120 that forms a population inversion is connected.

The arrayed waveguide diffraction grating (filter) 1
00 is a known element, for example, "Wavelength Multipl
exer Based on SiO ₂ -Ta ₂ O ₅ Arrayed-Waveguide Gratin
g, ”J. of Lightwave Technology, vol. 2, No. 6, p.
See p.989-995 (1994).

In the short-pulse light source having the above-described structure, light incident on the first slab waveguide 102 spreads spatially while propagating through the first slab waveguide 102, so that each light of the array The light enters the wave path at the same phase and is distributed. Each waveguide of the arrayed waveguide 103 has a waveguide length difference of ΔL between adjacent waveguides. Therefore, the light emitted from the array waveguide 103 to the second slab waveguide 104 is located at a specific position satisfying the phase condition within the focal plane at the other end face of the second slab waveguide 104. Form an image. Since the phase condition changes depending on the frequency of light, the second slab waveguide 104 functions as a spectroscope, and forms images at different positions according to the frequency. Second slab waveguide 1
The light split by 04 enters the connection waveguide array 107 and is reflected by the mirror 108. The light incident on the connection waveguide array 107 selects a different frequency depending on the position of each waveguide in the connection waveguide array 107, changes its phase depending on the waveguide length, and is reflected by the mirror 108. .

In the present invention, the arrayed waveguide diffraction grating 100
Since the optical amplifying unit 106 and the mirrors 108 and 109 are attached to the optical amplifier, when the gain in the optical amplifying unit 106 is sufficiently large, laser oscillation occurs in a resonator formed between the mirror 109 and the mirror 108. . Also, the mirror 109
_Assuming that the equivalent optical distance between the optical modulator 105 and the mirror 108 is L _eff , the optical modulator 105 is driven by a sine wave having a frequency f that satisfies the following relationship, which is generated by the optical modulator driver 119, and a sufficiently deep modulation is performed. Is applied, coupling occurs between the oscillation longitudinal modes, and mode-lock oscillation occurs.

[0018]

F = k · c / (2 · L _eff ) = (dx / df) / Δx where k is an integer and c is the speed of light.

In this case, the phase relationship of each longitudinal mode is kept constant, and a short pulse train having a repetition of the frequency f is generated. In a conventional mode-locked laser, it was difficult to set the frequency of each mode. However, according to the present invention, since the frequency of each mode is determined by L _eff , that is, by the position of the mirror provided on the arrayed waveguide grating (filter) 100, the frequency of each mode can be set in detail.

In the conventional mode clock laser, it was difficult to set the pulse width. However, according to the present invention, the number of connection waveguide arrays 107 is controlled,
The pulse width can be set by setting the oscillation spectrum width (the number of modes). This can be understood from the fact that the product of the spectrum frequency width and the pulse width is equal to or less than a certain value.

Further, in the short pulse light source of the present invention, a shape that causes scattering loss in the waveguide, for example, 0.1 to
Providing irregularities of about 0.5 micron on the side wall of the waveguide,
By partially narrowing the waveguide width, it is possible to control the loss of each waveguide. by this,
It is possible to set the spectral intensity and consequently to set the pulse shape. In particular, in the case of the transform limit, since the spectrum intensity and the pulse shape correspond to 1: 1, a complete pulse shape can be set.

In addition, semiconductor waveguides generally have strong dispersion characteristics. However, in the short pulse light source of the present invention, the dispersion in the resonator is compensated by adjusting the length of each waveguide of the connection waveguide array 107, the leading value of the pulse is increased, the mode coupling is deepened, and the pulse Transform limit is possible. Further, the connection waveguide array 10
Since the waveguide length of No. 7 can be increased or decreased by an integral multiple of 1/2 wavelength without changing the set phase difference, the length up to the mirror 108 can be adjusted.

A short-pulse light source that is stabilized and has a pulse width set as described above is particularly useful for an ultra-high-speed transmission device. The reason is described below.

(1) In a high-speed transmission device using an ultrashort pulse as a light source, a waveform is inevitably deteriorated due to dispersion in a transmission line. Therefore, a dispersion compensator is indispensable. If there is a fluctuation, the dispersion compensator does not operate sufficiently. In addition, since a dispersion compensator generally has a strong wavelength dependence, the wavelength of the light source must be designed in accordance with the dispersion compensator. For this reason, a wavelength-stabilized short-pulse light source whose wavelength is stabilized is useful.

(2) The cause of difficulty in high-speed transmission is waveform distortion due to nonlinear effects in an optical fiber.
The system is designed in advance by taking this waveform distortion into account, and the magnitude of the nonlinear effect is determined by the pulse height.
Since the average intensity of the incident pulse can be controlled by an AGC (automatic gain control circuit) or the like, if the pulse width can be set, the pulse height can be determined. If the pulse height cannot be set, it is necessary to set the system margin excessively, and it becomes difficult to design a high-speed transmission device. For this reason, a short pulse light source whose pulse width can be set is useful.

[0026]

As described above, the short pulse light source of the present invention can generate a short light pulse train having a desired light waveform (pulse width). For example, the center wavelength and pulse width of an optical pulse train can be set. Further, it is possible to independently control the phase of each mode to design a pulse shape.
Further, an optical pulse train close to the transform limit can be obtained. Further, since the module can be made small and modular, there is an advantage that handling is easy and that it can be incorporated into other devices. Therefore, the short pulse light source of the present invention can be used for a high-speed optical signal processing device, a transmission device, and the like.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of one embodiment of a short pulse light source according to the present invention.

FIG. 2 is a cross-sectional view taken along the line II-II ′ of FIG.

FIG. 3 is a cross-sectional view taken along the line III-III ′ of FIG.

FIG. 4 is a sectional view taken along the line IV-IV ′ of FIG. 1;

FIG. 5 is a block diagram of a mode-locked laser which is an example of a conventional short pulse light source.

FIG. 6 is a configuration diagram of a multi-wavelength light source, which is another example of a conventional short pulse light source, that simultaneously emits light of many wavelengths.

[Explanation of symbols]

REFERENCE SIGNS LIST 100 Array waveguide diffraction grating 101 InP substrate 102 Slab waveguide 103 Array waveguide 104 Slab waveguide 105 Optical modulator 106 Optical amplifier 107 Connecting waveguide array 108 Mirror (high reflection film) 109 Mirror (high reflection film) 110 AuZnNi Electrode layer 111 p ⁺ -1.5Q-InGaAsP contact layer 112 p-InP cladding layer 113 i-InP etch stop layer 114 0.9Q-InGaAsP / 1.1Q-InG
aAsP-5 well strained quantum well layer 115 n-InP cladding layer 116 AuGeNi electrode layer 117 0.9Q-InGaAsP / 1.3Q-InG
aAsP-2 well strained quantum well layer 118 1.3 Q-InGaAsP layer 119 optical modulation section drive circuit 120 optical amplification section excitation circuit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masaki Shintoku Nippon Telegraph and Telephone Corporation 3-19-2, Nishishinjuku, Shinjuku-ku, Tokyo

Claims (2)

[Claims] 1. An arrayed waveguide diffraction grating comprising first and second slab waveguides, a plurality of waveguides connecting the slab waveguides, and light provided at one end of the arrayed waveguide diffraction grating A modulator and an optical amplifier; first and second mirrors provided so as to sandwich the arrayed waveguide diffraction grating; and a plurality of connections for connecting the second slab waveguide and the second mirror. A short pulse light source comprising: a waveguide; a modulator driving circuit that drives the optical modulator; and an optical amplifier excitation circuit that forms a population inversion in the optical amplifier. 2. The apparatus according to claim 1, wherein a phase difference between the plurality of connection waveguides is set so as to compensate for dispersion of a resonator constituted by first and second mirrors.
2. The short pulse light source according to 1.